- Praque, Czech Republic
- Theoretical Neurosciences Research, LLC, Ridgeland, Mississippi, USA
- Faculty of Health and Social Studies, Institute of Radiology, Toxicology and Civil Protection, University of South Bohemia Ceske Budejovice, Branisovska, Czech Republic
- Laboratory of Applied Hydrobiology, University of South Bohemia, Husova tř. 458/102, 370 05 České Budějovice, Czech Republic
Correspondence Address:
Russell L. Blaylock
Laboratory of Applied Hydrobiology, University of South Bohemia, Husova tř. 458/102, 370 05 České Budějovice, Czech Republic
DOI:10.4103/sni.sni_407_17
Copyright: © 2018 Surgical Neurology International This is an open access journal, and articles are distributed under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 License, which allows others to remix, tweak, and build upon the work non-commercially, as long as appropriate credit is given and the new creations are licensed under the identical terms.How to cite this article: Anna Strunecka, Russell L. Blaylock, Jiri Patocka, Otakar Strunecky. Immunoexcitotoxicity as the central mechanism of etiopathology and treatment of autism spectrum disorders: A possible role of fluoride and aluminum. 09-Apr-2018;9:74
How to cite this URL: Anna Strunecka, Russell L. Blaylock, Jiri Patocka, Otakar Strunecky. Immunoexcitotoxicity as the central mechanism of etiopathology and treatment of autism spectrum disorders: A possible role of fluoride and aluminum. 09-Apr-2018;9:74. Available from: http://surgicalneurologyint.com/?post_type=surgicalint_articles&p=8838
Abstract
Our review suggests that most autism spectrum disorder (ASD) risk factors are connected, either directly or indirectly, to immunoexcitotoxicity. Chronic brain inflammation is known to enhance the sensitivity of glutamate receptors and interfere with glutamate removal from the extraneuronal space, where it can trigger excitotoxicity over a prolonged period. Neuroscience studies have clearly shown that sequential systemic immune stimulation can activate the brain's immune system, microglia, and astrocytes, and that with initial immune stimulation, there occurs CNS microglial priming. Children are exposed to such sequential immune stimulation via a growing number of environmental excitotoxins, vaccines, and persistent viral infections. We demonstrate that fluoride and aluminum (Al3+) can exacerbate the pathological problems by worsening excitotoxicity and inflammation. While Al3+ appears among the key suspicious factors of ASD, fluoride is rarely recognized as a causative culprit. A long-term burden of these ubiquitous toxins has several health effects with a striking resemblance to the symptoms of ASD. In addition, their synergistic action in molecules of aluminofluoride complexes can affect cell signaling, neurodevelopment, and CNS functions at several times lower concentrations than either Al3+ or fluoride acting alone. Our review opens the door to a number of new treatment modes that naturally reduce excitotoxicity and microglial priming.
Keywords: Aluminofluoride complexes, aluminum, autism spectrum disorders, cytokines, fluoride, glutamatergic neurotransmission, immunoexcitotoxicity, microglial activation, neurodevelopment
INTRODUCTION
The mechanisms involved in autism spectrum disorder (ASD) etiopathology are many, but central to these disorders appears to be prolonged and repeated systemic immune activation and excitotoxicity. It has been generally accepted that chronic inflammation is the hallmark of many neurological and neurodegenerative diseases.[
The initial reaction to systemic inflammation may be microglial priming or full neurotoxic activation, depending on the intensity of the activating stimulus. It is known that a great number of conditions can lead to the priming/activation of microglia, such as stress, obesity, trauma, infections, sequential vaccination, hypoxia-ischemia, and exposure to certain neurotoxic metals, such as mercury, lead, and aluminum.
Microglia are involved in every aspect of neurodevelopment.[
There is growing evidence that glutamate and glutamate receptors (GluRs) are involved in neurodevelopment.[
In 1969, Olney demonstrated that exposure of specific types of neurons to high levels of glutamate caused a delayed death process that involved intense excitation of neuronal activity (excitotoxicity).[
In a previous article, we presented evidence that most heterogeneous symptoms of ASD have a common set of events closely connected with dysregulation of glutamatergic neurotransmission in the brain.[
In areas with fluoridated drinking water, we observe some symptoms of ASD, such as IQ deficits, sleep-pattern disturbance, inflammation, impaired ability of cognition, and learning and behavioral problems in some individuals. Prolonged exposure to fluoride in the prenatal and postnatal stages of development might have toxic effects on the development and metabolism of brain. Moreover, both fluoride and Al3+ interfere with a number of enzymes, resulting in a significant suppression of cellular energy production and oxidative stress.[
MICROGLIAL ACTIVATION IN BRAIN DEVELOPMENT AND AUTISM SPECTRUM DISORDER
Microglia and astrocytes are involved in every aspect of brain development, including synaptogenesis and refinement, synaptic pruning, neuron elimination, angiogenesis, as well as for maintenance, proliferation, differentiation, and migration of progenitor cells.[
Disturbance of microglial activation by immune stimulation during a critical stage can adversely affect synaptogenesis.[
NEURODEVELOPMENT AND MICROGLIA
Early in brain development a special glial scaffolding network derived from astrocytic cells, is formed called radial glial cells.[
Development and distribution of microglia in central nervous system
Microglia are derived from yolk sac progenitors that seed the brain around 4.5 weeks of gestation in the human brain and appear only when blood circulation develops.[
While amoeboid microglia migrate along radial glial cells and white matter in most mammals, in humans, microglia also invade and attach to blood vessels within the cortical parenchyma.[
Development of six-layered cortex, germinal zones, migration of progenitors to pial surface, and emergence of astrocytes and oligodendroglialcytes
The major germinal zones in the brain during embryogenesis include the ventricular zone (VZ) and the subventricular zone (SVZ) [
Figure 1
Microglia and Neurodevelopment. This illustration demonstrates how microglia plays a major role in all stages of neurodevelopment, by a programed release of cytokines and chemokines, a programmed release of glutamate and by active phagocytosis of excessive synaptic units, neurites and even whole cells. Acting at each of the germinal zones, VZ, IZ and CP, microglia controls cell proliferation, migration, angiogenesis, synaptogenesis, and dendritic and axonal development
Normal microglial “pruning” of neuropil, differences in microglial distribution by sex, and reason for early appearance in males of autism spectrum disorder
Cunningham et al. demonstrated that the size of the neuronal precursor pool was regulated by microglia, principally by phagocytosis.[
Females were shown to have a greater number of microglia than males, but this appeared later in development (P30–60). Interestingly, they also found that most microglia in the P4 males were of an activated (amoeboid) morphology, whereas the females at P30–60 were more often ramified [
Figure 2
Microglial Priming and Full Activation by Sequential Immune Stimulation. Demonstrating the transition from a resting (ramified) microglial phenotype to a primed phenotype by an initial immune stimulus. Primed microglia have enhancement of cytokine generation, but no release of cytokines or excitotoxins. The second stimulus fully activates the microglia, resulting in a hyperintense immunoexcitotoxic reaction
Microglial population of different brain areas
Microglia colonizes different areas of the brain at significantly different rates.[
The neuroepithelial cells are the most primitive neural precursors, which give rise to all neurons, astrocytes, and microglia in the CNS. It is from the neural plate that we see the appearance of radial glia, which share properties with astrocytes. Importantly, these cells have specific glutamate transporters.[
New microglia are not derived from entering macrophages/monocytes, but rather are produced within the brain itself.[
Microglia concentration in cerebellum and autism spectrum disorder
Several studies have shown the cerebellum to be the most involved area of the brain in ASDs.[
Normal microglial pruning of synaptic connections; Abnormal microglia activation directed by compliment tags on synapses leads to abnormal neural development, and miswiring of brain in autism spectrum disorder; positron emission tomography scanning shows areas of microglia activation in autism spectrum disorder patients
Pruning is essential because during early neurodevelopment more synaptic connections are constructed than are ultimately needed by the mature brain. It has been shown that synaptic pruning is activity dependent, during which time large numbers of synapses are eliminated and the remaining ones are strengthened.[
Abnormal activation of microglia and/or the complement system leads to abnormal neural development, as seen in ASD.[
Suzuki et al. examined twenty men, aged 18–31 with confirmed autism versus matched controls using microglial activation PET scanning techniques utilizing the [11C]R-PK11195 tracer.[
What activates the microglia?
Microglia can be activated by peripheral autoantibodies, as are frequently seen in autistic patients.[
Reelen (a glycoprotein in brain development for neurla migration)
Reelin is a critical glycoprotein in brain development. Secreted from Cajal–Retzius cell in the marginal zone reelin plays an important role in neuronal migration in the prenatal and early postnatal brain.[
Maternal infections can lead to abnormal neural development as in autism spectrum disorder; Is the RELN gene a factor?
Human studies have shown that maternal infections can lead to several abnormalities of neurodevelopment, such as aberrant neural migration, decreased dendritic arborization, and abnormal cytoarchitecture in the adult, possibly related to abnormal reelin levels. Some authors suggested that reelin and RELN gene were significantly related with psychiatric disorders including ASD.[
CYTOKINES AND CHEMOKINES IN AUTISM SPECTRUM DISORDER AND NEURODEVELOPMENT; AUTISM SPECTRUM DISORDER AND IMMUNE DYSFUNCTIONS AND THE ROLE OF EXCITOTOXICITY IN AUTISM SPECTRUM DISORDER
It becomes evident that several cytokines and chemokines play essential roles in brain development regarding migration of progenitors, differentiation, maturation, dendrite arborization, and synaptogenesis. Significant alterations of these immune mediators during critical periods of brain development can also cause varying degrees of functional brain disruptions as well, resulting in abnormal connectivity and cytoarchitecture. Disturbances of these microglial-derived signaling molecules, such as systemic immune activation, would be expected to alter numerous brain pathways and functional systems.
Studies of autistic patients have confirmed the presence of a number of immune dysfunctions, such as neuroinflammation, brain directed autoantibodies, increased T-cell, NK cells, and macrophage responses.[
Figure 3
TNF-Alpha and Immunoexcitotoxicity This chart demonstrates how TNF-α, through one of its receptors (TNFR1) and via oxidative injury, is linked to enhanced excitotoxicity. This involves suppression of GS, trafficking GluA2-lacking AMPARs, upregulation of glutaminase, impaired glutamate transport and endocytosis of GABA receptors.
Using cerebellar granules cell cultures of individual populations of neurons, Oldeive and Doherty found that TNF-α had highly specific developmental effects on these neurons, depending on the embryonic stage of development.[
Together, these observations make a compelling case for a link between sequential systemic immune stimulation and neurobehavioral disorders such as the ASDs. Unfortunately, many studies and discussions have omitted or severely downplayed the role of other microglial components linked to immune destruction, such as excitotoxicity.
GLUTAMATE'S ROLE IN EXCITOTOXICITY AND AUTISM SPECTRUM DISORDER
In 1957, Lucas and Newhouse observed that mice exposed to high-dose monosodium glutamate (MSG) demonstrated extensive neuronal lesions in the inner layer of retinal neurons.[
Figure 4
Aluminum and Aluminofluoride link to excitotoxicity. This diagram demonstrates stimulation of systemic immune activation and microglial activation within the brain by aluminum and fluoride as well as aluminofluoride. Al3+, F- and AlF4- all suppresses mitochondrial energy production and trigger ROS/RNS and LPP generation both directly and indirectly via microglial generated inflammatory cytokines, ROS/RNS, LPP and excitotoxicity. This can produce all the core features of ASD
THE GLUTAMATERGIC RECEPTOR SYSTEM – ITS LINK TO AUTISM SPECTRUM DISORDER AND ROLE IN EXCITOTOXICITY: AN OVERVIEW
Subsequent studies confirmed the status of glutamate as a neurotransmitter system and that it involved a number of specific types of receptors. Over 50% of the brain's neurotransmission is via glutamatergic neurotransmission and 90% of cortical neurons utilize glutamate as a neurotransmitter.[
The ionotropic GluRs are the N-methyl-D-aspartate receptors (NMDARs), amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptors (AMPAR), and kainate type receptors (KAR). NMDARs are linked to sodium, potassium, and Ca2+ channels. It is thought that the entry of excessive Ca2+ into the neuron plays a major role in the excitotoxic process by triggering cascades of destructive cellular signaling. Glutamate affinity is greater with NMDARs than AMPAR/KARs but AMPARs are faster conducting [
Glutamate receptor: NMDAR
Each of these receptor types is composed of a variable arrangement of subunits, which determines their biophysical and physiological properties. The NMDARs are composed of a tetrad arrangement of subtype receptor units–GluN1, GluN2A-D, and GluN3A and B (NR1, NR2A-D, and NR3A-B by the older classification system). Distribution of these variously composed NMDARs varies with their location in the brain. During development, there are significant changes in the composition of these subunits. In the mammalian brain, functional NMDARs require a GluN1 (NR1) subunit associated with one or more GluN2 (NR2) subunits. Magnesium (Mg2+) sites within NMDAR channels regulate receptor function, with Mg2+ playing a major role as a voltage-dependent channel blocker. With depolarization, the Mg2+ block is relieved, allowing the action potential to proceed. Sensitivity to Mg2+ blockade also varies with subunit composition.
Glutamate receptor: AMPAR
AMPARs are composed of GluA1-4 subunits (GluR1-4 by older nomenclature). The presence of the GluA2 (GluR2) subunit in the compositional structure of the AMPA receptor blocks Ca2+ entry into the neuron [
Figure 5
Synaptic Subunit Trafficking. Illustration of the pre- and post-synaptic units, demonstrating modulation of synaptic strength by trafficking of AMPA and NMDA subunits to the synaptic density. Trafficking of GluA2 (Glu2B)-lacking AMPARs, converts the AMPAR into a calcium permeable receptor, greatly increasing its excitatory strength. Presence of the GluA2 receptor within the AMPAR blocks calcium permeability. Inflammation converts AMPARs to the calcium permeable form
Glutamate receptors: Metabotropic receptors (mGluRs)
In addition to the ionotropic GluRs, researchers have identified three major classes of mGluRs with eight subunit types. These receptors operate through G-protein-coupled receptors (GPCRs) via seven transmembrane domains, with an extracellular N-terminal and intracellular COOH terminal domain. Group I mGluRs contain two subtype receptors, mGluR1 and mGluR5, which activate phospholipase C (PLC), producing inositol 1,4,5-trisphosphate, and diacylglycerol (DAG) as second messengers [
The mGluRs also vary in location, which affects their physiological effect. Some are close to the postsynaptic density and others occur on the presynaptic axon.[
GLUTAMATE AND GLUTAMATE RECEPTORS IN NEURODEVELOPMENT
Glutamate receptors (GluRs) are expressed very early in development and play a vital role in most aspects of neurodevelopment, including brain wiring, synaptogenesis, progenitor migration, differentiation, and maturation of cells.[
Within the intermediate germinal zone, a site of precursor cell proliferation, and the cortical plate, where neuronal differentiation occurs following radial migration of the precursors, we see further changes with developmental progression [
Furuta and Martin examined sheep neocortex during cortical lamination, specifically for expression of AMPARs (GluR1, GluR2/3 and GluR4), KARs (GluR6/GluR7), and mGluR5.[
Smith and Thompson, examining the visual cortex of ferrets, found that NMDARs and non-NMDARs follow quite distinct developmental patterns.[
Similar patterns of expression for the various subunits have been confirmed in the developing human brain as well.[
Sodium-dependent glutamate transporters have also been shown to play a major role in neurodevelopment, primarily by controlling glutamate levels, and hence, GluR activation during developmental stages. In humans, there have been five identified glutamate transporters, EAAT1-5. In animal species, GLAST represents EAAT1 and GLT-1, EAAT2. EAAT1 and EAAT2 are present on the cell membranes of microglia, astrocytes, and oligodendrocytes. EAAT1 (GLAST) is the major glutamate transporter in the cerebellum, being mostly expressed in astrocytes.[
Furuta et al. found that in the rat, GLAST levels were low prenatally in the forebrain, but were high in Bergmann glia in the cerebellum early postnatally.[
GROWTH CONES, GLUTAMATE RECEPTORS, AND CALCIUM GUIDANCE
Growth cones are specialized structures located at the tip of developing axons that act as guidance mechanisms for successful union with synaptic partners. Located at the leading edge of the growth cone are special structures called filopodia and lamellipodia, which guide the axon to its destination among an enormously complex array of possibilities. A number of studies have identified GluRs, in particular NMDARs, within the membrane of growth cones.[
Activation of the growth cone NMDARs produce calcium (Ca2+) oscillations that act as guidance signals for axon movement, which includes neuron migration, neurite outgrowth, motility, axon turning, and activation of intracellular signaling pathways involving Rho GTPases, all of which lead to brain architectural construction.[
Disruption of cortical column cytoarchitecture and connectivity is characteristic of ASDs. For example, Damarla et al. examined high functional autistics using a combination of behavioral testing, functional MRIs, functional connectivity, and corpus callosum morphometric methological tools, and found that autistics had lower functional connectivity between higher order working memory/executive areas and visuospatial regions (between frontal and parietal-occipital regions).[
Underconnectivity, with severe changes in many brain structures, has also been shown for the cerebellum, an area of the brain most affected in autism.[
Synaptogenesis and synaptic pruning within the brain follows a programmed timeline that is specific for individual areas of the brain. A recent study found that synaptic density begins to decline at puberty and is completed during adolescence, within the prefrontal cortex. Substantial elimination of synaptic spines continues beyond adolescence, well into the third decade.[
Glutamate receptors and the cerebellum in autism spectrum disorder
Within the cerebellum, it has been shown that GluA2 receptors, an AMPAR subunit that reduces Ca2+ influx, is required for normal development of Purkinje cell dendrites.[
Glutamate receptors and synapse formation
Presynaptic NMDARs also play a major role in synapse formation, and stabilization. GluN2B (NR2B) is essential for neural pathway construction and is widely expressed in the brain during neurodevelopment.[
Glutamate receptors: Metabotropic GluRs and neurodevelopment
Metabotropic GluRs have also been shown to play a major role in neurodevelopment.[
Glutamate receptors and autism spectrum disorder; A short neurobiochemical summary
Together, these studies strongly suggest that glutamate and its receptors are playing a major role in the progressive elaboration of the architecture of the developing brain and that a number of internal and external environmental conditions can alter both glutamate levels and GluR physiology, resulting in varying degrees of abnormal brain development.
IMMUNOEXCITOTOXICITY IN BRAIN DEVELOPMENT AND AUTISM SPECTRUM DISORDER
A growing number of studies are defining an interrelationship between the immune system and excitatory neurotransmission. This includes alteration of glutamate transporters as well as direction of glutamate transport, trafficking of Ca2+-permeable AMPARs and NMDARs, elevation of glutaminase activity, and suppression of mitochondrial function with alteration of mitochondrial energy generation, thus enhancing excitotoxicity [
FROM ALTERATION OF THE IMMUNE RESPONSE TO GLUTAMATE RECEPTORS TO EXCITOTOXICITY WITH EXCESS GLUTAMATE AS A NEUROTRANSMITTER
One of the principle control systems of extraneuronal levels of glutamate is accomplished by a series of five glutamate transport proteins (EAAT1-5) discussed above. Both inflammatory cytokines and excitotoxins, alter the redox status of EAATs, making them dysfunctional, thus allowing the accumulation of extracellular glutamate and possible excitotoxicity. Extraneuronal glutamate can also be altered by another system called the cystine/glutamate antiporter Xc-. Under normal conditions, this system exchanges extracellular cystine for intracellular glutamate, thus raising extracellular glutamate levels, which are then quickly lowered by EAATs [
Figure 6
A simplified scheme of the phosphoinositide signaling system. Phosphatidylinositol 4,5-bisphosphate (PIP2) in the plasma membrane is hydrolyzed by phospholipase C (PLC) after GPCR activation and yields inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) and diacylglycerol (DAG). Both products of this hydrolysis have a second messenger role. Ins(1,4,5)P3 binds to a receptor in membranes of endoplasmic reticulum, which results in a release of Ca2+ into the cytosol. DAG activates protein kinase C (PKC). The coupling between the GPCR and PLC is mediated by G proteins. PA – phosphatidic acid, PI – phosphatidylinositol.
REPEATED IMMUNE ACTIVATION LEADS TO MICROGLIAL ACTIVATION, EXCESS GLUTAMATE, AND NEUROPATHOLOGICAL CHANGES IN THE NEUROPIL THAT CAN BE BLOCKED BY GLUTAMATE RECEPTOR BLOCKERS
Prolonged and repeated systemic immune activation appears to be central to ASD etiopathology. With subsequent, especially closely spaced immune stimulation, full activation of the overactive primed microglia occurs, leading to progressive pathological changes in the developing brain. This is especially so if the episodes of systemic immune stimulation are closely spaced together.[
INTEGRATION OF IMMUNE DYSFUNCTION, GLUTAMATE RECEPTOR CHANGES, MICROGLIAL ACTIVATION, AND DISRUPTION OF NEURODEVELOPMENTAL MILESTONES LEADING TO PATHOLOGIC CHANGES IN AUTISM SPECTRUM DISORDER
In most studies, the target was neurodegeneration, yet the effects of elevation of glutamate brain levels during neurodevelopment can occur at concentrations lower than needed to cause neurodegeneration. This means that microglial activation alone, as long as it is associated with an elevation of glutamate levels, holds the possibility of disrupting neurodevelopmental milestones, particularly if occurring at periods when glutamate levels should fall. This would especially be of concern should inflammation be prolonged and associated glutamate levels were constantly elevated as well, as we see in ASDs.[
Of particular interest is the inflammation-induced enhanced trafficking of GluRs and alteration of glutamate subunits, as well as inflammatory cytokine-stimulated endocytosis of GABA receptors, which would shift the balance in the brain toward excitotoxicity. The interaction between immune mediators and GluRs triggers a neurotoxic reaction, which involves the generation of high levels of ROS and RNS, along with LPP. These neurotoxic compounds have been shown to inhibit glutamate transport proteins (EAATs), inhibit metabolic glutamate-clearing enzymes, such as glutamine synthetase (GS), glutamate dehydrogenase (GDH) and glutamic acid dehydrogenase (GAD), as well as interfere with mitochondrial energy generation [
Interestingly, maternal inflammation has also been associated with a significant increase in glutaminase, an increase in NMDAR subunit GluN2 (NR2) expression and impairment of GLT-1 function, all things that trigger excitotoxicity.[
The ability of immune cytokines and other immune mediators of inflammation, to enhance microglial priming/activation and to magnify the excitotoxic potential of GluRs, indicate that the two processes operate together, both physiologically and pathologically.
THE ROLE OF FLUORIDE AND ALUMINUM IN ETIOPATHOLOGY OF AUTISM SPECTRUM DISORDER
A considerable amount of scientific evidence demonstrates that fluoride and Al3+ can harm a great number of physiological functions, including critical regulatory enzymes, mitochondrial energy production, neurotransmitter and endocrine signaling, brain development, higher CNS functions, and immune system dysfunctions.[
FLUORIDE AS A NEUROTOXIN IS IN ENVIRONMENTAL EXCESS IN GROWING YOUNG CHILDREN
Fluoride is a ubiquitous compound found in drinking water (both naturally and added) in many soils, incorporated within edible plant components, and is considered a natural compound. Millions of people live in endemic areas with high concentrations of fluoride in groundwater and in the biosphere. Fluoride exposure is common in fetuses, newborns, and small children. The United States Environmental Protection Agency (EPA) has done both a dose-response analysis and a relative source contribution analysis.[
EXCESS FLUORIDE AND NEURODEVELOPMENTAL DEFECTS
Fluoride is not an essential element for human growth and development. Prolonged exposure to fluoride in the prenatal and postnatal stages of development might have toxic effects on the development and metabolism of brain. In fluoridated areas, we observe some core symptoms of ASD in some individuals. These include IQ deficits, hypocalcemia, hypomagnesemia, hypothyroidism, sleep-pattern disturbance, inflammation, impaired ability of cognition, learning, and behavioral problems. Blaylock was the first to suggest that excitotoxicity may be a central mechanism of fluoride toxicity.[
ALUMINUM AS A NERUOTOXIN
There are a number of Al3+ sources, such as the drinking water, dietary substances, cosmetics, and the widespread use of Al3+ in medicine, namely in vaccines. Many investigations show that Al3+ can elicit impairment of development and immunity; that it acts as a hormonal disruptor, a neurotoxin, and elicits intense and prolonged activation of brain inflammation. Al3+ toxicity in humans, especially as regards the CNS, has been studied and discussed by several authors [e.g. 23,171,256,271. It is not surprising that Al3+ appears among the environmental toxins, which can participate in the etio-pathology of ASD.[
INCREASE IN EXPOSURE TO ALUMINUM; RELATIONSHIP BETWEEN ALUMINUM EXPOSURE AND INCREASE IN AUTISM SPECTRUM DISORDER
Among the suspected environmental toxins surveyed, Al3+ and Al3+-adjuvants have increasingly correlated positively to the rise in ASD.[
Widespread mobilization of Al3+ into our biosphere may place all of humankind at a heightened inflammatory status thereby increasing general risk for the development of ASD and other progressive neurodegenerative disorders associated with an inflammatory component.[
ALUMINUM AND FLUORIDE EXPOSURE INDUCES MICROGLIA ACTIVATION, INCREASES GLUTAMATE BLOOD AND BRAIN LEVELS AND ABNORMALITY IN THE DEVELOPING BRAIN AND NEURODEGENERATION
Recent studies have also shown that both fluoride and Al3+, as well as AlFx can induced microglial, astrocyte and B-cell activation, with resulting increases in blood and brain ROS, RNS, and LPP.[
METABOLIC AND DEVELOPMENTAL EFFECTS OF FLUORIDE
The highly electronegative fluoride ion with the same size and the same valence orbital as oxygen became a useful laboratory tool in our understanding of the biochemical and biophysical mechanisms of enzyme catalysis underlying biological processes such as metabolism and signal transduction.[
Almost 50% of children with ASD may display peripheral markers of disturbances of mitochondrial energy metabolism.[
Several researchers have reported evidence of mitochondrial dysfunction in ASD brain samples compared to controls.[
Recently, Delhey et al. measured mitochondrial enzyme activity on the one of the largest cohorts of individuals with ASD studied to date with concurrent measurement of symptoms in a subset and found that children with ASD demonstrated significantly greater variation in mitochondrial activity compared to controls.[
It has also been demonstrated that suppression of energy generation significantly increases sensitivity to excitotoxicity.[
One of the best documented biochemical changes in ASD is a decrease in cellular glutathione (GSH), a major intracellular antioxidant, and an increase in oxidized glutathione (GSSG), resulting in a reduction in the ratio of reduced (active) GSH to inactive GSSG [
Figure 9
The GSH redox system. Hydrogen peroxide (H2O2), the immediate precursor of hydroxyl radical, is metabolized via the action of catalase and glutathione peroxidase (GPx). GPx also metabolizes reactive hydroperoxides (ROOH) and oxidizes reduced glutathione (GSH) to its disulfide form (GSSH), which is recycled back to GSH by the action of glutathione reductase (GR). A cofactor for GR is NADPH, which is supplied by the action of glucose-6-phosphate dehydrogenase
GSH, a radical scavenger, is converted to GSSG through glutathione peroxidase (GPx), and converted back to GSH by glutathione reductase (GR). GSH can detoxify hydrogen peroxide (H2O2), preventing the formation of hydroxyl radicals [
The reduced/oxidized GSH-redox equilibrium regulates a pleiotropic range of functions that includes ROS/RNS scavenging, detoxification, maintaining cell membrane integrity, signal transduction, and apoptosis. Under normal physiologic conditions, glutathione reductase activity is sufficient to maintain the high GSH/GSSG ratio. Excessive intracellular oxidative stress could result in GSSG export to the plasma. Therefore, an increase in plasma GSSH is a strong indicator of intracellular oxidative stress, which may have functional consequences such as increased mitochondrial superoxide production and a chronic inflammatory response.[
GSH and GSSG levels are significantly changed in autistic individuals, mainly as the consequence of disturbances in processes of transmethylation/transsulfuration. Plasma concentrations of methionine, S-adenosylmethionine (SAM), S-adenosylhomocysteine (SAH), adenosine, homocysteine, cystathionine, cysteine, GSH and GSSG have been repeatedly measured in children with autism and found to be disturbed[
Highly significant (P ≤ 0.001) decrease of SAM and SAH was also observed in subjects with ASD.[
Fluoride can contribute to disturbances in GSH homeostasis because it enters the cascade and attaches to the SAH. Fluoride has been identified as an inhibitor of SAH hydrolase.[
Oxidative stress, which can stimulate microglial activation and immunoexcitotoxicity, may lead to neurodevelopmental abnormalities in children by affecting numerous cellular processes, especially via cell signaling and mitochondrial dysfunction.
THE EFFECTS OF FLUORIDE ON THE BRAIN AND NEURODEVELOPMENT
Numerous animal studies have been published, which have raised a level of concern about the impact of increasing fluoride exposure on the brain of individuals with autism.[
Human studies validating animal observations of fluoride toxicity
Two studies provided evidence that peripheral markers of oxidative stress observed in plasma and immune cells of subjects with ASD are similarly changed in several brain regions. Chauhan et al. found that GSH levels were significantly decreased by 34.2 and 44.6%, with a concomitant increase in the levels of GSSG by 38.2 and 45.5%, respectively, in the cerebellum and temporal cortex from patients with autism compared to the control group.[
Rose et al. examined frozen samples from the cerebellum (n = 15) and Brodmann area 22 (BA-22) of the temporal cortex (n = 12) from individuals with autism and unaffected controls. GSH and GSH/GSSG were significantly decreased in both the autistic cerebellum and BA-22.[
However, unlike systemic cells, brain neurons depend on the transfer of astrocytic generated GSH, which is produced by the glutamate/cystine antiporter Xc-. The glutamate/cystine antiporter Xc- is an exchange system involving an exchange of intracellular glutamate for extracellular cystine. Intracellular cystine is broken down into cysteine, which is metabolized to GSH. Cysteine is the rate-limiting substrate for GSH and, along with cystine, it also forms a key redox couple on its own. That is, they act to reduce oxidative stress. High levels of extraneuronal glutamate inhibit the exchange and can lower brain GSH.[
Human studies on impaired neural development found in brains of aborted fetuses in an endemic flourosis area of China by a pathological study and by a IQ assessment study
Based on the research from China, the fetal brain is highly susceptible to fluoride poisoning.[
Meta-analyses studies of intelligence in children with high fluoride exposure
Tang et al. published a meta-analysis of 16 studies carried out in China between 1998 and 2008 evaluating the influence of fluoride levels on the IQ of children.[
Findings from meta-analyses of 27 studies published over 22 years suggest an inverse association between high fluoride exposure and children's intelligence.[
More human studies on the inverse association of fluoride exposure and IQ
The team of Fluoride Action Network summarized 57 human studies; 50 of which found that elevated fluoride exposure is associated with reduced IQ and only 7 studies found no such association (
The results from several geographic regions support the view that fluoride may be a developmental neurotoxicant that affects brain development at exposures much below those that can cause toxicity in adults. Serum fluoride concentrations associated with high intakes from drinking water may exceed 1 mg/L (50 μmol/L) – more than 1,000 times the levels of some other neurotoxicants that cause neurodevelopmental damage.[
FLUORIDE AND ENDOCRINE DISRUPTIONS
Fluoride and thyroid dysfunction
Disturbance of thyroid hormone production has been found in correlation with lowered IQ in children. The investigations from India demonstrated that the thyroid gland appears to be very sensitive tissue in the body in relation to fluoride burden. Susheela et al. compared the production of free thyroid hormones (FT3/FT4) and thyroid-stimulating hormone (TSH) of 90 children living in fluoride endemic, non-iodine deficient areas of Delhi, India, along with 21 children from non-endemic areas.[
Thyroid deficiency leads to brain damage in autism spectrum disorder
Thyroid hormones are essential for brain maturation and for brain function throughout life. Thyroid hormone deficiencies even for short periods, may lead to irreversible brain damage, the consequences of which depend on the specific timing of onset and duration of thyroid hormone deficiency.
Thyroid dysfunction is frequently found in children with ASD.[
FLUORIDE ACCUMULATION IN THE PINEAL GLAND; MELATONIN DEFICIENCY AND AUTISM SPECTRUM DISORDER
Some symptoms of ASD, such as the sleep problems and the early onset of puberty, suggest abnormalities in melatonin physiology and dysfunctions of the pineal gland.[
Decreased levels of melatonin in blood or urine have been reported as very frequent features in individuals with ASD compared to typically developing controls.[
FLUORIDE AND NEUROINFLAMMATION: EVIDENCE FROM ANIMAL STUDIES
Few have examined the possibility of direct microglial activation by fluoride, despite that Shivarajashankara with colleagues reported in 2003 increased levels of ROS, RNS, and LPP in the blood of experimental animals treated with fluoride.[
In astrocytes, fluoride activates phospholipase C (PLC) and increases intracellular Ca2+ level. Once activated by fluoride, microglia secrete large concentrations of IL-1ß and TNF-α, which can then recruit more microglial activation in a vicious cycle that ultimately leads to neurodegeneration. Likewise, excitotoxins can activate microglia and stimulate release of inflammatory cytokines and additional glutamate.[
The abovementioned experiments suggest that the toxic effects of fluoride on the CNS may be attributed to the release of inflammatory cytokines and ROS, but fluoride concentration used in animal trials is very high. In humans, stimulation of the immune system with fluoride is not generally discussed among fluoride's adverse effects.
ALUMINUM AS ENVIRONMENTAL TOXIC SUBSTANCE
Al3+ has, until relatively recently, existed in forms not generally available to living organisms, and was therefore regarded as nontoxic. We underscore the remarkable and ongoing liberation of Al3+ into the biosphere, resulting in its increased bioavailability to biological systems. The most significant factor driving complacency about the potential dangers of Al3+ is its omnipresence in modern life. It is likely that Al3+ is present in every physical and chemical compartment in the human body.[
However, Al3+ is a non-essential element and it has no biological function in humans.
Sources of aluminum; entry into body
There are a number of ways in which humans are exposed to Al3+, such as through the skin, the lung, the nose, gastrointestinal system and of course, via intramuscular vaccination. Other major contributors include Al3+ used in medicines: dialysis solutions, parental and intravenous nutrition solutions used in pediatrics. Vaccines, allergy skin tests, human serum albumin, baby skin creams, baby diaper wipes and antacids, which are frequently given to infants, are extremely high in Al3+.
The primary natural source of Al3+ is food, which provides approximately 16–100 fold more Al3+ to systemic circulation than drinking water. While Al3+ content of breast milk is very small (about 20 μg/L), a recent review of 30 infant formulas found that all contained Al3+ and a number had concentrations far in excess of safety standards for oral consumption.[
Aluminum as an activation agent of microglial-induced immunoexcitotoxicity
As a powerful immune activating element, Al3+ can act both as the priming agent and the activation agent of microglial-induced immunoexcitotoxicity. This can occur with environmental exposure to excess Al3+, as well as injection by vaccination. The major difference is that ingested Al3+ is very poorly absorbed, whereas injected Al3+ nanoaggregates with antibodies is completely absorbed and distributed throughout the body, including the brain.[
Aluminum-induced neurodegeneration
With the demonstrated widespread accumulation of Al3+ in the brain and CSF following Al3+ exposure, all the conditions for an intense and prolonged activation of brain inflammation are present. Al3+ can activate microglia leading to secretion of TNF-α, IL-6 and cytokine-inducible NO synthase, and the development of neuroinflammatory ROS/RNS.[
In animal models, aluminum leads to increased glutamate, potentiates damaging redox activity, displaces metal ions with strong binding capacity in cellular reactions, alters enzymes of oxidative metabolism in mitochondria, enters the brain, is active in developing brains, which could contribute to neurodegeneration.
Al3+ also induces significant alterations of glutamate/glutamine recycling within astrocytes leading to increased glutamine to glutamate conversion coupled with increased uptake of glutamate (see section 3).[
Al3+ alters the activity of several enzymes of oxidative metabolism in mitochondria, such as a significant decrease in the activity of cytochrome C oxidase, NADH and succinate dehydrogenase.[
In a study of the fate of injected Al3+-adjuvants into muscle, researchers found that the Al3+ particles were taken up mostly by microglia.[
Al3+ has no known beneficial physiological action in the human body. Al3+ induced events likewise include oxidative stress, disruptions of energy metabolism, inflammation, glutamate excitotoxicity and effects on Ca2+ homeostasis, and therefore might participate in etio-pathology of ASD.
THE ROLE OF ALUMINOFLUORIDE COMPLEXES IN ETIOPATHOLOGY OF AUTISM SPECTRUM DISORDER
Binding of aluminum to fluoride
The synergistic action of fluoride and Al3+ has an important implication for pathological injury. Fluorine is the most chemically reactive nonmetal and the most electronegative element. Al3+ binds fluoride anion more strongly than 60 other metal ions tested by Martin.[
Aluminofluoride as an analogue of phosphate groups in biochemical reactions
Under physiological conditions and even with micromolar concentrations of Al3+, these two atoms react to form AlF4−, a molecule whose shape and physical properties closely resemble those of the phosphate anion, PO43-. AlF4− has been widely used as an analogue of phosphate groups to study phosphoryl transfer reactions and heterotrimeric G proteins involvement. Phosphoryl-transfer reactions are involved in processes such as regulation of cell metabolism, energy transduction, cytoskeletal protein assembly, regulation of cell differentiation and growth, aging, and apoptosis. Numerous laboratory studies demonstrated that AlF4− interacts with all known G proteins and this feature has been exploited to help researchers understand phosphate-dependent reactions in signaling cascades.[
Aluminofluoride binding to ADP and GDP b-phosphate and effects on protein conformation, interference in other signaling cascades
AlF4− binds ionically to the terminal oxygen of ADP or GDP β-phosphate. ADP or GDP could therefore form a complex with AlF4− that imitates ATP or GTP in its effect on protein conformation. This effect causes a structural change that locks the site and prevents the release of the γ-phosphate. Several authors have presented evidence that AlF4− interferes with regulatory GTP hydrolases, which play an initiating role in regulation of effector enzymes.[
Aluminofluoride and its influence on the immune system
Fluoride in the presence of micromolar Al3+ affects the function of lymphocytes and cells of the immune system, ion transport, Ca2+ influx and mobilization, protein phosphorylation, processes of neurotransmission, growth and differentiation, cytoskeletal proteins, and many other processes. These effects are not surprising when considering the extensive role of G proteins and GPCRs in the cell physiology. Approximately 800 GPCRs are encoded in the human genome. Physiological agonists include neurotransmitters and hormones, such as glutamate, dopamine, serotonin, melatonin, acetylcholine, TSH, neuropeptides, and excitatory amino acids.
Gs proteins stimulate adenylyl cyclase (AC) to produce intracellular cyclic adenosine monophosphate (cAMP), whereas Gi proteins inhibit the same process. Members of the cAMP-dependent second-messenger pathways participate in the regulation of cellular growth and differentiation and are also implicated in a variety of embryonic stages including brain development. cAMP is one of the key factors for neuronal outgrowth, plasticity, and regeneration.
Animal studies on aluminum leading to autism spectrum disorder; suppression of melatonim
Notably, the autistic-like behaviors were observed in an animal model of adenylyl cyclase type 5 (AC5) knockout (KO) mice. Kim et al., reported that loss of AC5 in the dorsal striatum produces increased repetitive behaviors and sociability deficits.[
In animal models aluminofluoride effects metabolic processes governing Ca2+ regulation that can affect excitotoxicity, can lead to neurodegeneration; low dose fluoride enhances uptake of aluminum, fluoride in tap water likely fed to infants; Aluminofluoride complex can lead to neurodegeneration
Many of metabolic and physiological processes are affected by alterations in intracellular Ca2+ levels. Gαq mediate phospholipase C (PLC)-dependent phosphoinositide hydrolysis, yielding inositol-1,4,5-trisphosphate and diacylglycerol (DAG) as second messengers to trigger both the increase of intracellular Ca2+ level as well as PKC activation [
It has been, for example, observed that Al3+-induced neural degeneration in rats is greatly enhanced when the animals were fed low doses of fluoride. The presence of fluoride caused more Al3+ to cross the BBB and be deposited in the brain of rats. The formation of AlF4−, according to experimental evidence, in quantities as little as 1 ppm of fluoride contamination of water supplied to rats led to a greater uptake of Al3+ into the brain along with the formation of amyloid deposits like those in Alzheimer's disease.[
Amplification of false message of AlF4− in signaling cascades
The effects of AlF4− are amplified by processes of signal transduction [
Figure 12
AlF4- acts as the messenger of false information. Its message is greatly amplified during the conversion into the functional response of a cell. Effector enzymes are adenylyl cyclase or phospholipase C, the second messenger molecule could be cAMP, inositol 1,4,5-trisphosphate and diacylglycerol
Basically, by mimicking the mechanism that activates G-protein signaling, aluminofluoride can activate several reactions utilizing G-protein signaling, such as metabotropic glutamate receptors. Protein kinases are essential for GPCRs-mediated signal transduction. AlF4− mimics the transition state of protein phosphorylation. Protein phosphorylation is also important in posttranslational modification of GluRs. The studies of mGluRs show that like many GPCRs they can activate more than a single G protein, can produce various second messengers, and interact with several common protein kinases. The effects of AlF4− might thus result in numerous pathophysiological consequences at several times lower concentrations than either Al3+ or fluoride acting alone. Several common protein kinases, including protein kinase A (PKA), PKC, and mitogen-activated protein kinases (MAPKs), directly interact with mGluR1/5, phosphorylate specific serine or threonine sites, and thereby regulate trafficking, distribution, and function of mGluR1/5 receptors.[
Ji et al., examined alterations in the activity of cAMP-dependent PKA (Protein Kinase A) and PKC (Protein Kinase C) in postmortem brain tissue samples from the frontal, temporal, parietal, and occipital cortices, and the cerebellum of individuals with regressive autism as compared to age-matched control subjects and autistic subjects without clinical history of regression.[
In another trial, Akinrinade et al., treated male adult Wistar rats with low and high doses of fluoride, Al3+ or a combination of both elements for 30 days and compared their effects on brain homogenates.[
In recent years, our understanding of function of G-protein coupled receptors (GPCRs) has changed from a picture of simple signal relays, transmitting only a particular signal to a particular G protein, to versatile machines, capable of various responses to different stimuli and being modulated by various factors. Malfunction of myriads of GPCRs functions is prevalent in human diseases, so that approximately half (estimates vary between 30 and 60%) of marketed drugs target GPCRs.[
The synergistic action of fluoride and micromolar Al3+ can thus evoke a whole network of pathological events. Simultaneously, the heterogeneity of their mutual dynamic interactions can explain the clinically heterogeneous symptoms of ASD and contribute to an understanding of the various responses in any given child to the identical environmental neurotoxins, since we know that each case of autism is unique.
PREVENTION AND AMELIORATION OF AUTISM SPECTRUM DISORDER SYMPTOMS
Recently, Lyra et al. published a review called What do Cochrane systematic reviews say about interventions for autism spectrum disorders?[
HYPOTHESIS FOR THE DEVELOPMENT OF AUTISM SPECTRUM DISORDER FROM AVAILABLE EVIDENCE AND POSSIBLE METHODS OF REVERSAL OF THE SYMPTOMATIC EXPRESSION OF AUTISM SPECTRUM DISORDER AFFECTED NERVOUS SYSTEM SUPPORTED BY OBSERVATIONS FROM THE LITERATURE
Based on our hypothesis of immunoexcitotoxicity we suggest that it is reasonable to conclude that infants and children are exposed to a number of environmental and food-based excitotoxin additives, or conditions that can worsen intrinsic brain inflammation and excitotoxicity. What has emerged is the insight by most investigators that ASD is a complex, multisystem disorder. Disruptions in energy metabolism resulting in mitochondrial dysfunction, impairment in critical regulation of oxidative stress with disturbances of transmethylation/transsulfuration system and decreased GSH level, produce a systemic disorder that affects brain development and function. Basic to this hypothesis is the finding that one sees extensive and prolonged microglial and astrocytic activation and resulting inflammation/excitotoxicity in most cases of ASD. In this review, we show that processes of immunoexcitotoxocity are both triggered and amplified by the environmental toxin fluoride and Al3+.
Reversal of fluoride induced cell injury and fluorosis through the elimination of fluoride and consumption of a diet containing essential nutrients and antioxidants, have been shown by studies in India to be beneficial to brain function, where millions of people suffer with fluorosis.[
Role of nutrition in brain development and the role of Vitamins C, E, and D3, as antioxidants, in reversing the metabolic changes found in fluoride intoxication
Early nutrition has been shown to play a major role in the brain development, mental and immune function. Children and adolescents with poor nutritional status are exposed to alterations of mental and behavioral functions that can be corrected to a certain extent by dietary measures.[
Role of vitamin B6 and vitamin B12, in treating immunoexcitotoxicity
Vitamin B6 can dramatically lower blood and tissue glutamate levels and raise seizure thresholds. High dose of vitamin B6's ability to powerfully inhibit excitotoxicity at least partially explains the often dramatic results reported by Rimland in treating autistic children.[
Role of vitamin D3 in treating autism spectrum disorder
Vitamin D3 deficiency is accounted among the potential environmental risk factors for ASD.[
Saad et al. published a controlled RTC study on 122 ASD children and found that 57% of the patients had vitamin D deficiency, and 30% had vitamin D insufficiency.[
Role of diets in autism spectrum disorder
Many of the diets now being proposed for autistic children emphasize elimination of foods known to be exceedingly high in excitotoxin additives. They are also low in sugar. Jones et al. demonstrated that children respond to glucose challenges with a hypoglycemic response at higher levels of blood glucose than adults.[
Other neutraceuticals that may be of benefit in treating autism spectrum disorder
A number of nutraceuticals have been shown to improve mitochondrial function, including thiamine, riboflavin-5 phosphate, pyridoxal-5 phosphate, ascorbate, acetyl-L-carnitine, pyruvate, malate, CoQ10, curcumin, niacinamide, ketones, DHA, vitamins K, folate and methylcobalamin.[
Taurine may play a crucial role in the protection of antioxidant system and ATPases against Al3+-induced toxicity in brain and blood of rats. Deficiency of taurine in a cat leads to immune activation in the CNS with Purkinje cell loss, microglial activation and astrocytosis, similar to that observed in the ASD brain.[
Many parents of children with ASD report that their child has stool with a sand-like appearance. One of the most common causes comes from a lack of bile acid formation in the liver. Taurine conjugates with bile acids and increases their pool size. Some autism intervention specialist therefore recommend supplementation with taurine.
There is a need for a non-invasive method to both reduce the absorption of Al3+ in the gastrointestinal system and facilitate the excretion of systemic Al3+ in the urine, especially in children, pregnant mothers and women of childbearing age who may become pregnant. Based on the knowledge that silicon is the natural antagonist to Al3+, some researchers have shown that silicon-rich mineral waters can be used to reduce the body burden of Al3+ in individuals with Alzheimer's disease, macrophagic myofasciitis, and chronic fatigue syndrome.[
Pogue and Lukiw[
Mg2+ and zinc also powerfully inhibit excitotoxicity as well as act as co-factors in numerous enzyme systems. Low Mg2+ is associated with dramatic increases in free radical generation as well as GSH depletion. In addition, low Mg2+ enhances NMDA sensitivity, making excitotoxicity more likely even in the presence of physiological levels of extracellular glutamate. High glutamate levels have also been shown to deplete cellular GSH.
Of great interest is the use of selected flavonoids as antioxidants, anti-inflammatories, GluR blockers, and antimicrobials. The flavonoids are more powerful and versatile as antioxidants than are the vitamins.[
Supplementation with the amino acid tryptophan is considered in the treatment of depression and sleep disorders, mainly due to its relationship with the synthesis of serotonin and melatonin. It is also used in helping to resolve cognitive disorders, anxiety, or neurodegenerative diseases.[
In August 2017, Li with co-workers[
Value of melatonin in the treatment of autism spectrum disorder
Rossignol and Frye evaluated twenty clinical studies, which have reported improvements in sleep parameters with exogenous melatonin supplementation in ASD, including longer sleep duration, less nighttime awakenings and quicker sleep onset.[
CONCLUSIONS
The etiology and pathogeneis of ASD are not well understood. Autism Spectrum Disorders comprise a complex of clinical syndromes found predominantly in infants and younger people consisting of disturbances in cognition and comprehension, communication disorders, epilepsy, and behavior that have an underlying common pathology of neurodegeneration of the cerebellar Purkinje cells and other areas of the brain. Other studies in humans have shown chronic inflammatory changes in the brain, particularly in the cerebellum, and involvement of the microglia in this pathology.
Our review presents evidence suggesting a hypothesis unifying the syndromes in ASD. The clinical as well as pathological findings of the ASD have a set of pathological events with the common denominator being immunoexcitotoxicity leading to neurodegeneration and abnormalities in the connectome, particularly in developing brains in the neonate and young with evidence that explains the clinical presentation of ASD.
Our hypothesis is supported by experimental evidence from animal models and by some clinical testing and pathology studies that give credibility to the concept of immunoexcitotoxicity as the underlying cause of ASD. A great number of conditions can trigger both the inflammatory and the excitotoxic cascade, including sequential vaccination, infections, hypomagnesemia, ROS, RNS and LPP, fluoride and Al3+ as well as a number of other neurotoxic metals and industrial chemicals. Chronic activation of the brain's immune system increases extracellular glutamate levels sufficiently to trigger the excitotoxic cascade, which in conjunction with inflammatory cytokines and prostaglandins, magnifies the damaging effects of both. This mechanism explains most of the features of the ASD, including the behavioral difficulties, language problems, repetitive behaviors, intellectual delay, and episodic dyscontrol of anger. In addition, these mechanisms explain the pathological findings as well, including the changes in the cerebellum, abnormalities in connectivity and the widespread activation of microglia and astrocytes. It also explains why ASD has not disappeared despite the removal of mercury from most childhood vaccines, since excessive immune activation is the initiating and sustaining event in ASD. Evidence is presented that the abundance of fluoride added to the water worldwide and the widespread availability of aluminum particularly to infants and young children through aluminum containing vaccinations, singly or together as aluminofluoride can be potent factors in producing the condition of immunoexcitotoxicity that leads to the pathological changes seen in ASD. The vaccination program should be evaluated to reduce the excessive stimulation of immature immune system and to replace Al3+-adjuvants.
We have also reviewed studies that indicate that fluoride and Al3+, as ubiquitous environmental and food-derived toxins, can exacerbate the pathological and clinical problems of ASD. In synergistic action as AlF4− these elements induce numerous chronic pathophysiological consequences at several times lower concentrations than either Al3+ or fluoride acting alone. AlF4− may evoke several signaling disorders and act as an endocrine disruptor. Moreover, most of the excitotoxic events may enhance the subclinical pathological alterations and/or the genetic susceptibility seen in ASD. The full genetic potential of the child for brain and mental development may be also compromised due to deficiency of micronutrients.
Our immunoexcitotoxic hypothesis opens the door to a number of new modes of prevention and amelioration of ASD. Elimination of various sources of fluoride and Al3+ in early development and consumption of a diet containing essential nutrients and antioxidants have been shown to be beneficial to brain function. As a multifaceted disorder, ASD requires a multifaceted approach, one that should include the protection against excitotoxicity, as well as the protection against microglial activation.
There are several experimental studies that can be constructed to test the immunoexcitotoxic hypothesis, especially as regards vaccines. Such a study would require the use of non-human primates at various stages of development, from intrauterine life to early post-natal development corresponding to human neurodevelopment during vulnerable neurodevelopmental milestones. The study would follow the vaccine schedules used with human newborns and pre-schoolers. One would need to use the exact vaccines used in the human vaccine schedules but of comparable doses based on weight.
To measure microglial activation in response to the vaccines, it would be necessary to use microglial activation PET scanning techniques at various time schedules before and following the vaccines. Newer microglial activation PET scanning techniques are being developed that hold the possibility of differentiating between M1 and M2 microglial activation phenotypes. Long-term follow-up scanning would be necessary to delineate prolonged microglial activation as has been observed in cases of autism. Measure of glutamate levels in the affected areas of the brain should also be conducted, perhaps in a separate set of monkeys to prevent inadvertent activation of local microglia. More extensive studies could be envisioned, such as measures of EAATs, glutaminase, and NADPH oxidase within affected brain areas in response to vaccination.
In addition, studies should be conducted measuring the aluminum, fluoride and aluminofluoride complex concentration in the affected areas of the brain in autopsied cases of autism. This should include the various cell types as well as cellular compartments. This could also be done experimentally in the non-human primate studies using human vaccines described above. Controls could establish the levels of these toxicants to establish the baseline levels in non-vaccinated animals.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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