Brain derived neurotrophic factor-BDNF- and Autism-I

BDNF or brain derived neurotrophic factor was the second neurotrophic to be characterized. The other two are nerve growth factor or NGF and neurotrophin 3 (NT-3). The Gene for BDNF is located in the chromosome 11p13 (an interesting location I must say, thinking in autism and keeping in mind recent findings). There is a fourth one called neurotrophin-4/5 ( NT 4/5).
A very graphic and simple presentation of the function (please see figure in color)
Neurotrophic factors

BDNF binds at least two receptors on the cells
1-TRkB (pronounced TRACK B). This is a receptor tyrosine kinase. Kinase is a kind of enzyme that transfers phosphate groups (PO4 with 3 negative charges) from ATP (Adenosin TriPhosphate) to substrates. This is named phosphorylation. The tyrosine kinase (TK) adds phosphate to a tyrosine of an enzyme.

And here a simple explanation of what is the function and how the process is in terms of how TK begins a cascade of signals
Link
You can find here
Link
some images on neurotrophins- and this is the only reason I posted-nothing to do with promotion of nothing, but the demonstration of the status of the science in terms of testing
2- LN GFR or low affinity nerve growth factor receptor, also known as p75-NTR, whose role is less clear. It seems a sink for neurofactors. This factor can signal a cell to die by apoptosis. The p75NTR belongs to the tumor necrosis factor (TNF) receptor family and was the first identified neurotrophin receptor

Low levels of BDNF have been linked to depression, OCD, Alzheimer, Rett, Huntigton and dementia. BDNF modulates excitatory and inhibitory synaptic transmission by inhibition of GABA (gama amino butyric acid)-A receptors.

Here you can find more information on neurotrophic factors- if you want.
Review
You can find in figure 2 that NGF activates TrkA receptor, BDNF activates TrkB receptors such as NT4/5 and NT-3 activates TrkC, all the Trk are tyrosine kinase receptors.

The Trk-independent pathway of p75NTR increases intracellular ceramide levels and further activates Nuclear Factor k B (NFkB) transcription factor and Jun N- terminal K kinase.

BDNF is a neurotrophin, such as Nerve growth factor or NGF, neurotrophin 3- NT3 and neurotrophin 4/-NT4/5. There are also neuropoietins, Insulin-like Growth Factors 1 and 2, transforming growth factors, fibroblast growth factors and finally other factors.
There is a theory, the Target Field theory. In this theory the axons of neurons growth towards the higher concentration of tropic factors in the target tissue. Neurons that succeed are maintained; if they do not succeed they die. In is interesting that they act like dimmers and they all share six cysteine residues (an aminoacid with SH bond).
From here thereafter, I will link a certain study, will transcribe some interesting conclusion from the authors in italics and I will add my own ideas about in normal.

Studies on knockout mice on neurotrophin have been unsuccessful because it is considered that probably a system of compensation is acting in the CNS in the development, a back up system that allows the differentiation of the neurotrophins to compensate for the loss of some. Even more , the knockout mice lacks the gene; probably this situation is totally different to a decrease/increase of the amount of a neurotrophin ( or its receptor) in cells.
As you know, neurexin/neuroligin have been very much mentioned about autism lately.
From Columbia Health Sciences
Link
Here there is an explanation of what the neuroligin/neuroxin couple do in terms of concerted mechanism of synaptogenesis.

Development and Regulation of Dendritic Spine Synapses
Link
Let´s go to focus on neurotrophin and neuroligin/neurexin. Please go to the figure 1. The “Connections” between the dendritic spine and the presynaptic terminal are N cadherin with B catenin in blue; neuroligin and neurexin in light brown and ephrin with EphR.

From here, not only neurotrophin but also neuroligin/neurexin are extremely important to generate dendritic spine synapses. It seems that neuroligin/neurexin are active mainly in the first step of synapse formation

What is the role of a neurotrophic factor?
Here
Link
In figure 1 you can find a map of the cascade of reactions that the BDNF tyrosine kinase domain produces.
Basically the tyrosin kinase receptor or TrkB- through the BDNF- activates
A-the phospholipase C pathway (PLC), that produces Ca and diacylglicerol and affects the protein kinase C (PKC) and CAM (Ca+2/calmodulindependent protein kinase) kinases
B-the phosphatidylinositol 3-OH (PI-3-K)- PI-3-K activates AKT ( a serine/threonine kinase or Protein Kinase B) and p-70 s6 that act on Caspaces and Bad proteins (proapoptotic therefore these are signals to the cell to die). The PI3K dependent AKT activation could be regulated through the PTEN (remember the last news about a role in autism), which work as the opposite of PI3K. AKT regulates the cellular survival by binding and regulating several receptors, such as nuclear factor kB or NFkB.
About PTEN, the link has been considered to neurodegenerative disease, not autism per se.
c-The RAS (a protein G that switches in activated and deactivated forms RAS GDP and RAS GTP; the diference is from di (D) to tri (T) Phosphate) activation the change is related to one group phosphate more added. RAS activates a number of pathways but an especially important one seems to be, the mitogen-activated protein (MAP) kinases, which themselves transmit signals downstream to other protein kinases and gene regulatory proteins. MAP is a Serine/threonine-specific protein kinase that respond to extracellular stimuli (mitogens). MAP regulates mitosis differentiation and apoptosis of cells.
To date, four distinct groups of MAPKs have been characterized in mammals:
I-extracellular signal-regulated kinases (ERKs). The ERKs (also known as classical MAP kinases) signaling pathway is preferentially activated in response to growth factors and a tumor promoter, and regulates cell proliferation and cell differentiation.
II-Jun N-terminal kinases (JNKs), also known as stress-activated protein kinases (SAPKs).
III-p38 isoforms. Both JNK and p38 signaling pathways are responsive to stress stimuli, such as cytokines, ultraviolet irradiation, heat shock, and osmotic shock, and are involved in cell differentiation and apoptosis.
IV-ERK5. ERK5, which has been found recently, is activated both by growth factors and by stress stimuli, and it participates in cell proliferation.
Yes, it is extremely difficult. To have a picture of how difficult, I have found these very illustrative:
1- MAPK
Link
2-Apoptosis
link
3-Protein Kinases
Link
4-Protein Kinase C-PKC
link
5-NFkB
link
Localize AKT
6-Protein Kinase B or AKT
link
Please localize the PTEN, to the left.
I am very enthusiastic on all this but I have also a headache if I try to understand everything. I have found useful to use these graphs to follow the explanation of the manuscripts, that are per se very complicated.Indeed. Please do not look for the commercial aspect- the pathways have been posted by a company of testing-, I considered the pathways clear- and colourful. I think is a good picture of the complexity we are talking about, don´t you think?
About BDNF roles
1-Exposure to stress and corticoesterone has been shown to decrease the expression of BDNF in rats and lead to eventual atrophy of hippocampus
2-Glutamate, voluntary exercise, caloric restriction, intellectual stimulation increase expression of BDNF.
3-Targeted disruption of the BDNF gene pertubs brain and sensory neuron development, but not motor neuron development.
Each kind of neurotrophin could be linked to an specific disease or susceptibility.
Neurotrophin can also play a role in immune modulation.
4- Brain-Derived Neurotrophic Factor Stimulates Energy Metabolism in Developing Cortical Neurons
link
Some comments particularly interesting
“The increased Na+-dependent amino acid uptake by BDNF is followed by an enhancement of overall protein synthesis associated with the differentiation of cortical neurons. Together, these data demonstrate the ability of BDNF to stimulate glucose utilization in response to an enhanced energy demand resulting from increases in amino acid uptake and protein synthesis associated with the promotion of neuronal differentiation by BDNF. Results revealed that BDNF increases glucose utilization and the expression of the neuronal glucose transporter GLUT3.
Thus BDNF knock-out mice exhibit substantially reduced numbers of cranial and spinal sensory neurons as well as marked decreases in the expression of neuropeptide Y (NPY) and calcium-binding proteins in specific brain regions, including cerebral cortex and hippocampus. It is also well established that BDNF increases peptidergic differentiation of GABA-containing neurons as it stimulates the expression of specific neuropeptides such as somatostatin, substance P, NPY, and cholecystokinin both in vitro and in vivo In the CNS BDNF promotes structural changes in axonal and dendritic arborisation.Thus BDNF increases the length and complexity of dendrites of cortical pyramidal neurons.
Our in vitro observations provide evidence that BDNF plays a determinant role as a stimulator of glucose utilization and GLUT3 expression in response to the increased energy demand resulting from the enhanced amino acid uptake and protein synthesis associated with the promotion of neuronal development by this neurotrophic factor”

And I thought in Ian´s post (from A shade of Grey) on increased demands of nutrients and minicolumns posts ; if there is a higher brain growth the first 2 years of life when I read this. Also in the transport system of aminoacids, carboxylic acids and glucose through the BBB in children.

5- BDNF part of a serie of genes involved in ASD?
It is important to remember that c- MET gene polymorphisms has been reported in families with MORE than one child with autism. cMET is also a receptor tyrosine kinase.
I only want to mention
Link
How c-met ( in magenta) is related to our PI3K ( in red) activated by BDNF. cMET affects PI3K and AKT.
How can we think that only one or two genes can affect the overall function of for example this pathway? How someone on the earth can present something for sure with the level of complexity that this has is something out of my understanding (what about interactions between genes?)
I want to focus on BDNF and autism
About role and function of BDNF
Link
The main conclusions from this manuscript
a-There are several theories about the neuronal release of neurotrophins.. They seem contradictory depending of the kind of neuron used (cortical or from the hippocampus)
b-NT-3 and BDNF- but not NGF-modulate the efficiency of synaptic transmission.
c-Neurotrophins induce the presynaptic release of glutamate(excitatory), GABA (inhibitory), and acethylcholine.
d-There are clues about the direct interaction of BDNF/TRkB with synapsin, a protein required for the release of vesicles.
e-Neurotrophins mediates the activation of ion channels (Na+, Ca+2) and interact with NMDA-N methyl D aspartate- receptors.
f-Neurotrophins participate in neuronal plasticity.BDNF is directly involved in hippocampal Long Term Potentiation or LPT ( involved in learning and memory).
g-The interplay between slow and fast events must be considered. The key question is how spatial and temporal availability of acutely secreted neurotrophins contribute to multiple pathways that regulate neuronal function in the CNS:

How Visual Stimulation Turns Up Bdnf Genes to Shape the Brain
"This suggests that sensory experience regulates different genes in your brain depending on your age and past experience. Thus, nurture, our experience of the world via our senses, acts through nature, sets of genes, to alter brain circuits."
Link
The sensory integration and how the sensorial information is analyzed impact the neurotrophins and modulates their activity.

BDNF and Huntigton´s disease
Link
Huntingtin protein is the transcription factor that allows the expression of BDNF.In Huntigton´s BDNF is very low.

In Autism
Genetic analyses of the brain-derived neurotrophic factor (BDNF) gene in autism.
Link
“BDNF expression in the drug-naive autistic group was found to be significantly higher than in the control group. We suggest that BDNF has a possible role in the pathogenesis of autism through its neurotrophic effects on the serotonergic system”
It is clear that autism is well different than Huntigton´s disease from the BDNF point of view. BDNF is overexpressed in autism, not underexpressed. BDNF is higher in autism.

Brain-derived neurotrophic factor and autoantibodies to neural antigens in sera of children with autistic spectrum disorders, Landau-Kleffner syndrome, and epilepsy.
Link
“BDNF levels and IgG/IgM autoantibodies to BDNF, ECs, MBP, and histones were measured in children with autism, childhood disintegrative disorder (CDD), pervasive developmental delay-not otherwise specified (PDD-nos), acquired epilepsy, Landau-Kleffner syndrome (LKS); healthy children (HC), and children with non-neurological illnesses (NNI).
Children with developmental disorders and epilepsy have higher autoantibodes (AAs) to several neural antigens compared to controls. The presence of both BDNF AAs and elevated BDNF levels in some children with autism and CDD suggests a previously unrecognized interaction between the immune system and BDNF.”

Impaired cerebellar development and function in mice lacking CAPS2, a protein involved in neurotrophin release.
Link
CAPS2 mediated BDNF release may be involved in synaptic plasticity even in the fully developed cerebellar circuit, because BDNF is regulatory of Purkinje cells synapses. CAPS2 is specifically associated with the cerebellar postnatal development during which tens of millions of neurons undergo vigorous differentiation events.
From Link

Therefore we have autoantibodies to BDNF, high levels of BDNF in autism and the reported impact of BDNF in cerebellar postnatal development, mainly Purkinje cells synapsis.

High levels of Alzheimer beta-amyloid precursor protein (APP) in children with severely autistic behavior and aggression.
“Although no neuropathologic substrate underlying autism has been found, the findings of brain overgrowth via neuroimaging studies and increased levels of brain-derived neurotrophic factor (BDNF) in neuropathologic and blood studies favor an anabolic state”
There are beta amyloid precursor protein and BDNF high levels in autism.

Reduced serum levels of brain-derived neurotrophic factor in adult male patients with autism.
Link

Now, it seems that at birth BDNF is overexpressed and in adult autistic male is lower than controls.
Two questions
a-Is this a common finding in non-autistic with development or this is an isolated case?
b-Why/how/when BDNF changes with age?

Neurotrophic factors in the pathogenesis of Rett syndrome.
Link
“Impairment in dendritic development in Rett syndrome could be the consequence of cholinergic deficiency and of neurotrophic factor/glutamate imbalance. Cholinergic gene expression might be influenced by the Rett syndrome gene directly or via the neurotrophic factor system.”

The implicancies of impact in cholinergic, glutamate systems are clear from this report.

Neuropeptides and neurotrophins in neonatal blood of children with autism or mental retardation
Link
"Neonatal concentrations of VIP (vasoactive intestinal peptide), CGRP (calcitonin gene-related peptide) , BDNF, and NT4/5 (neurotrophin 4/5) were higher (ANOVA, all p values < 0.0001 by Scheffe test for pairwise differences) in children in the autistic spectrum and in those with mental retardation without autism than in control children"


Localization of neurotrophins and their high-affinity receptors during human enteric nervous system development.
Link
From infancy through adulthood, TrkA and TrkB immunoreactivities were localized to both enteric ganglion cells and glia, whereas TrkC was localized exclusively to enteric ganglion cells. In postnatal intestine, BDNF immunoreactivity was primarily localized to enteric ganglion cells, with NT-3 localized to enteric plexuses, intermuscular basal lamina, and along or between circular and longitudinal smooth muscle cells. CONCLUSIONS: These data indicate that neurotrophic influences may be involved in ENS development and survival, with potential importance in functional differentiation disorders of the intestinal ENS.

Nutr Rev. 2006 Sep;64(9):428-32. Links
Regulation of the NMDA receptor: implications for neuropsychological development.Levenson CW.

Recent work has shown that zinc is involved in the developmental regulation of neurotrophins and N-methyl-D-aspartate (NMDA) receptors, controlling use of glutamate as a neurotransmitter in the central nervous system (CNS). This is particularly important in the hippocampus, a region of the brain involved in learning and memory, and is an intriguing link to the role of zinc in neuropsychological development.
It is supposed that this is kind of a feedback.
NMDA receptor stimulation induces the influx of extracelular Ca+2 that may evoke the release of BDNF and the activation of TRkB. TrkA is the receptor of NGF and TrkB is the receptor of BDNF. Interferon gamma increased NFG expression, down regulate BDNF expression The chronic blocking of NMDA receptors has a secondary effect the inhibition of BDNF synthesis in the hippocampus and may impair neuronal development. Brain specific phosphorylation of MECP2 regulates BDNF transcription, dendritic growth and spine maturity

Critical Periods of Vulnerability for the Developing Nervous System: Evidence from Humans and Animal Models
Link
In addition, a number of environmental chemicals and pharmaceutical agents alter the expression and/or signal transduction of these trophic molecules, including ethanol (146-152), methyl mercury (153,154), aluminum (155), and cholinesterase inhibitors (138,139,156). Although neurotrophic factors are perturbed in experimental animals after exposure to environmental agents, the involvement of these factors in developmental disorders has only recently been suggested in humans (157).

Dietary restriction (DR) increases the lifespan of rodents and increases their resistance to several different age-related diseases including cancer and diabetes. Beneficial effects of DR on brain plasticity and neuronal vulnerability to injury have recently been reported, but the underlying mechanisms are unknown. We report that levels of brain-derived neurotrophic factor (BDNF) are significantly increased in the hippocampus, cerebral cortex, and striatum of rats maintained on a DR regimen compared to animals fed ad libitum (AL). Seizure-induced damage to hippocampal neurons was significantly reduced in rats maintained on DR, and this beneficial effect was attenuated by intraventricular administration of a BDNF-blocking antibody. These findings provide the first evidence that diet can effect expression of a neurotrophic factor, demonstrate that BDNF signaling plays a central role in the neuroprotective effect of DR, and proffer DR as an approach for reducing neuronal damage in neurodegenerative disorders.
Link


Well. The effect/nature/role of BDNF and its importance from here is clear. Now, how can the environment modulate this neurotrophin and the signals of TrkB? There are a lot of reported clues about. I will let the analysis of them for a forthcoming post.

From Dr Julie Grether Epidemiology of Autism: Current Controversies and Research Directions “We don’t yet know if BDNF and other identified neurotrophins and neuropeptides actually contribute to the pathogenesis of autism or may only represent markers of the disorder. Available evidence regarding their role in early brain development and abnormal levels present in newborns, if confirmed, strongly suggest, however, that these proteins may have etiologic significance”.

The other side of BDNF
a-Neurotrophin-mediated potentiation of neuronal injury.
Link
a more specific manuscript
Link

The p75 receptor is related to the Janus K Pathway and these are signals to the cells to die. It seems that VIP (vasoactive intestinal peptide) can prevent partially neuronal death. It seems that, depending on conditions, BDNF can be toxic to cortical grey matter. An enzyme NADPH oxidase seems to be involved,

b-The role of NADPH oxidase, neuronal nitric oxide synthase and poly(ADP ribose) polymerase in oxidative neuronal death induced in cortical cultures by brain-derived neurotrophic factor and neurotrophin-4/5.
Link
Three distinct mechanisms generate oxygen free radicals in neurons and contribute to cell death during anoxia and reoxygenation.
Link

“We found that three distinct mechanisms contribute to neuronal injury by generating ROS and oxidative stress, each operating at a different stage of ischemia and reperfusion. In response to hypoxia, mitochondria generate an initial burst of ROS, which is curtailed once mitochondria depolarize or prevented by previous depolarization with uncoupler. A second phase of ROS generation that followed after a delay was blocked by the xanthine oxidase (XO) inhibitor oxypurinol. This phase correlated with a rise in [Mg2+]c, suggesting XO activation by accumulating products of ATP consumption. A third phase of ROS generation appeared at reoxygenation. This was blocked by NADPH oxidase inhibitors and was absent in cells from gp91(phox-/-) knock-out mice. It was Ca2+ dependent, suggesting activation by increased [Ca2+]c during anoxia, itself partly attributable to glutamate release. Inhibition of either the NADPH oxidase or XO was significantly neuroprotective. Thus, oxidative stress contributes to cell death over and above the injury attributable to energy deprivation”

Potentiated necrosis of cultured cortical neurons by neurotrophins
Link
c-
Characterization of the toxic mechanism triggered by Alzheimer's amyloid-beta peptides via p75 neurotrophin receptor in neuronal hybrid cells.
Link
Remember please the high levels of beta amyloid protein found in some autistics.

Considering these reports, BDNF can activate the p75 receptor and include the activation of NADPH oxidase, pro stress oxidative.

What is the balance between the pro-oxidative stress vs the protective effect when BDNF levels are high, such as in autism?

Gene-Gene interactions, polygenia and epigenetics

Experimental gene interaction studies with SERT mutant mice as models for human polygenic and epistatic traits and disorders.
Link

“When diseases or disorders or traits are due to genetic factors, there are several mechanisms by which they can inherited. Such conditions can essentially be divided into single gene disorders and polygenic disorders. Single gene disorders include hemophilia, cystic fibrosis, neurofibromatosis and Huntington disease. In single gene disorders a rare mutation results in the complete disruption of the function of a gene. Some of the greatest advances in genetics during the past 100 years have come from the elucidation of the genes for virtually every single gene disorder. Their DNA has been cloned, sequenced and the gene localized to a specific chromosomal region.

Polygenic disorders, by contrast, are due to the interactive or epistatic effects of many different genes on different chromosomes, each gene contributing to only a small part of the picture (variance). These genes interact with environmental factors. Except for a few rare families [12], all behavioral disorders such as manic-depressive disorder, schizophrenia, major depression, panic disorder, autism and ADHD [3] are likely to be polygenic. While we do not yet know the total number of genes involved, it is likely to range from 50 to several hundred. In contrast to the gene defects for single gene disorders (mutations), the defects for polygenic disorders are much less severe, otherwise they would be single gene disorders. Thus, we call them gene variants instead of gene mutations, and individuals have to inherit a number of them if they are to cause a clinical effect [13]. A second distinction is that mutations that severely affect gene function are very rare. Since they are often present in less than 1 in 100,000 individuals the diseases they cause are also very rare. In fact, all single gene disorders combined affect less than 1.5% of the population. By contrast, the gene variants involved in polygenic disorders are common and polygenic disorders themselves are common. This "common gene, common disorder" theory of polygenic disorders has gained wide acceptance. An alternative theory, of "rare gene, common disorder," postulates a large number of rare mutations of different genes [14].In association studies of a wide range of behavioral disorders, even when the association is significant the percent of the variance attributable to that gene is usually in the 0.5 to 3% range and averages less than 1.5%. This suggests that even if genes only account for 72 to 95% of the total variance, 50 or more different genes would be involved […]. This does not mean that every affected individual has inherited 50 or more of these variants. It is likely that only a subset of the total potential set of gene variants is required in a given individual. Because of this, polygenic disorders show a great deal of genetic heterogeneity […]. That is, different individuals with ADHD are likely to have inherited somewhat different sets of genes. However, each affected ADHD individual must have inherited enough gene variants to pass a liability threshold, allowing them to develop ADHD.
From Link

Now, more and more I think on autism as a polygenic disorder.

The Genetics of Autism
Link

Some of the genes that have been reported to be linked or associated to autism are:
1-Chromatin remodelling and gene expression:MeCp2 (importance in Rett syndrome); FMRP (important in fragile X mental retardation),EN2, HOXA2 and WNT (the last three transcription factors dysregulated).
2-Actin cytoskeleton dynamics- look please for the MET pathway and you will find the actin to the left.TSC1/TSC2 (important in tuberous sclerosis) ; NF1 ( important in neurofibromatosis);cAMPGEF. These produce inactivation of GTPase (inactivation of an enzyme).
3-Synaptic scaffolding proteins: Schank Dendrite induction, binding partner of neuroligin
4-Receptors and transporters.GRIN2A (A NMDA receptor subunit), GriK2 (kainite receptor subunit), GABAr (GABA receptor), SLOSA4 (serotonine trasnporter¡), SLC 25 A (aspartate-glutamate); OXTR (oxytocin receptor) and AVPR1 (vasopressin receptor). 5 HTT is the serotonin transporter.
5-Second messenger problems:PRKCB1 (protein kinase C); CaCNA (Ca+2 Channel), NBEA (PKA(Protein Kinase A) anchor protein.
6-Cell adhesión molecules NLGN-3; NLGN-4 (NLGN seems important in autism) ; NrCAM
7-Secreted proteins: RELN, LAMB (laminin).

If you can get the manuscript
Searching for way outs of the autism maze:…” from Persico and Burgeroun from Trends in Neuroscience please go to the figure 1 and you will have a graph in colors about the proteins that can be altered in autism related to synapsis.
BDNF would be related to second messenger problems and cell adhesion molecules because of the signals that these receptors produce.

Some clues of correlations
1-Wang H, Chan SA, Ogier M, Hellard D, Wang Q, Smith C, Katz DM. Related Articles,Dysregulation of brain-derived neurotrophic factor expression and neurosecretory function in Mecp2 null mice.J Neurosci. 2006 Oct 18;26(42):10911-5.
2- Neurobiol Dis. 2002 Oct;11(1):221-9.BDNF regulates the expression of fragile X mental retardation protein mRNA in the hippocampus.Castren M, Lampinen KE, Miettinen R, Koponen E, Sipola I, Bakker CE, Oostra BA, Castren E.
3-BDNF induced the phosphorylation of tuberin / There are results that are consistent with a model wherein neurofibromin acts as a negative regulator of neurotrophin-mediated signaling for survival of embryonic peripheral neurons.
4-Caldeira MV, Melo CV, Pereira DB, Carvalho R, Correia SS, Backos DS, Carvalho AL, Esteban JA, Duarte CB.BDNF regulates the expression and the synaptic delivery of AMPA receptor subunits in hippocampal neurons.J Biol Chem. 2007 Mar 2;
5-Chen Q, He S, Hu XL, Yu J, Zhou Y, Zheng J, Zhang S, Zhang C, Duan WH, Xiong ZQ.Differential roles of NR2A- and NR2B-containing NMDA receptors in activity-dependent brain-derived neurotrophic factor gene regulation and limbic epileptogenesis.J Neurosci. 2007 Jan 17;27(3):542-52.
6-Carrasco MA, Castro P, Sepulveda FJ, Tapia JC, Gatica K, Davis MI, Aguayo LG.
Regulation of glycinergic and GABAergic synaptogenesis by brain-derived neurotrophic factor in developing spinal neurons.Neuroscience. 2007 Mar 16;145(2):484-94. Epub 2007 Feb 15.
7-Neurotrophins modulate neuron-glia interactions at a vertebrate synapse.
Link

“Our results indicate that acute application of both NT-3 and BDNF, but not NGF, increased PSC (perisynaptic Schwann cells) Ca2+ responses. BDNF increased PSC responsiveness through potentiation of ATP (adenosine triphosphate) responses while NT-3 modulated muscarinic acetylcholine receptor signalling.”

8-Taniguchi N, Shinoda Y, Takei N, Nawa H, Ogura A, Tominaga-Yoshino K. Possible involvement of BDNF release in long-lasting synapse formation induced by repetitive PKA activation. Neurosci Lett. 2006 Oct 2;406(1-2):38-42. 2006 Aug 9.

With this very partial picture, it seems to me that the picture is extremely complex to discard nothing. With such a number of interactions, retrograde signals and feeback, multiple changes depending on the development. What if BDNF roles are very much wide and complete and interelated with other systems ( immune system, gastrointestinal system)?

What do you think?
María Luján-Argentina

Some comments in Gastrointestinal issues in ASD

You know, I have prepared a long – and I say LONG- post about published science in gastrointestinal issues in autism as concomitant medical problem (CMP), including all the topics on my previous post. But somehow, I was not convinced about. I feel I was lacking the key questions to answer, trying to present a very much wide picture- and therefore what I wanted to say would be diluted with much information not so important.
Therefore I focused on the questions I presented in my previous post.

The no written sentence in all cases is: “We need more high quality, high level research done by high level and commited scientists to confirm anecdotical evidence and previous clues in autism“. If you are interested, I can send the expanded version- much longer with all the proper citations in which I based these analysis (Or please let a comment therefore I include the link). Thanks

No cause/cures implications. For now, they are CMP that SHOULD be screened, tested, diagnosed and treated SUCH as in the case of non-autistics, IMHO. For me, another aspect of the advocate for my son I am, and yes he had several of the gut conditions I mention-now properly screened, tested, diagnosed and treated.
In bold, remarks and (partial) conclussions- or better opinions about potential conclussions-, in normal the manuscript´s findings and in italics my comments.

1-In general, autistic children/teens/adults have gastrointestinal issues more than non-autistic children/teen/adults?
One of the most recent published manuscripts form the Dr Horvath group (2002) reported for 36 children with ASD symptoms like chronic diarrhea, abdominal discomfort and distension. The histological examination revealed grade I or II reflux esophagitis in 69.4 % (25/36), chronic gastritis in near 40 %(15/36) and chronic duodenitis in near 66.6 % (24/36). Twenty two of the 25 children with reflux (88%) had night awakenings, signs of abdominal disconfort and pushing on the abdomen. None of the patients had H. Pylori.
Low intestinal carbohydrate digestive enzyme activity was reported in 21 children of 36 (58.3 %), even when no abnormality was found in pancreatic function. 27 of 36 children had an increased pancreatico billiar fluid output after intravenous secretin administration. 21 of 36 children had diarrhea (near 60 %). Low lactase was found in 14 patients. One kind of cells, the Paneth cells, showed similar results to studies done to Chron´s patients.
Kushak R and Buie T reported lactase deficiency in 58-65 %, isomaltase/palatinase deficiency in 30 to 40 % in ASD. Children with intestinal inflamation are 77 % deficient in lactase and 64 % in isomaltase.
Same author studied the possibility of GER (Gastroesophageal reflux) with GI complaints and aggression or self-injurious behavior GER was identified in 5 of 5 patients tested by wireless pH testing. Esophagitis was seen in 3 of 6 patients biopsied.
* pH testing data are reported in a scale called de Meester score. Normal is less than 14.72. Autistic Children showed from 19.7 to 75.1.
* Author concludes that aggressive or self injury behavior may be a manifestation of pain from GERD
And in adults the problem is generally underdiagnosed
Link

Data show quite distinct patterns of O-glycosylation within the glycocalix in children with autism, not simply due to inflammation.This may contribute to alterations in the colonic mucosal flora. As clinical improvement has been reported in autistic children when enteric dysbiosis is treated, these changes warrant further study if confirmed in larger series.
*The glycocalix is the polysaccharide-containing material (that is a covering of polymers of monosugars) lying outside the cells of the gut.
*Glycosylation is a process by which the glycocalix is modified by other sugars ( involving other enzymes for example). Abnormalities associated with disease states are major contributors to diversity in glycan expression
* It seems that not only inflammation, but altered glycosilation pathways of glycocalix can be found in gut in ASD.

…findings demonstrate a focal CD8-dominated gastritis in autistic children, with novel features. The lesion is distinct from the recently recognized focal gastritis of Crohn's disease, which is not CD8-dominated. As in the small intestine, there is epithelial deposition of IgG.

*CD8 is a glycoprotein- that is a protein with a sugar attached- When the cytotoxic T-Cells have a CD8 attached they are called CD8+Tcells. A cytotoxic T cell is a cell that can kill cells infected by viruses or other pathogens after activation.
*The epitelial deposition of IgG is suggestive of gut autoimmunity following Torrente et al.
*There are 7 medical conditions that can be related to milk/gluten/food allergies, not only Celiac disease, mediated by IgE or not. Food allergy is not the same as food intolerance.
*Suspected hypoacidity and gastroesophageal reflux can be present, specially if asthma is present
*There are acid and non-acid reflux and can be gastroesophageal or duodenogastric .

The development of non-IgE-mediated food allergies is associated with relatively subtle immunological abnormalities, including maturational delay in IgA, IgG subclass, CD8, and NK cell responses (Simon Murch Comment)- this is the topic of another post.

*Pancreatic deficiency affects more lipid digestion than protein digestion.
*There are published clues of carbohydrate, lipids and protein degradation problems in ASD (lack of enzymes, several organs of the digestive system malfunction).
*There are published clues of inflammation/immune activation in gut in ASD (Paul Ashwood recent work). These inflammation conditions includes: ileal lymphoid nodular hyperplasia-LNH- (and related), ileitis, colitis and colonic LNH, upper and lower gastrointestinal tract inflammation
*In almost all patients with heartburn, there is identifiable esophageal mucosal pathology, though only about 40% have endoscopically detectable erosions. The remaining 60% of patients with heartburn but no erosions have nonerosive GERD.
*Gastritis can be of different kinds. Although gastropathies may be mediated by inflammatory mechanisms, mucosal infiltration by polymorphonuclear or mononuclear cells is not necessary. The modern classification of gastritis incorporates etiology and morphologic and topographic mucosal changes
*Duodenitis is basically inflammation and irritation of the wall of the first part of the small intestine.
It is true that it has been published that the percentage of autistic children with GI issues was EXACTLY (9%) the same than non-autistic children with GI issues (BMJ. 2002 Aug 24;325(7361):419-21.
Relation of childhood gastrointestinal disorders to autism: nested case-control study using data from the UK General Practice Research Database.Black C, Kaye JA, Jick H. )BUT the authors considered ONLY 2 first years of age. My celiac son was diagnosed at 3y 2 months and he never had diarrhea or GI issues during his 2 first years of life. Horvath manuscript presents data on children with 5.7 + or – 2 years.

* It seems that near 10-20 % of the general population has IBS.
Considering all the gastrointestinal problems, children with autism- (age range 0-8 years) has 38 to 60 % maximum diarrhea and near 36 % constipation problems.

A recent manuscript on the issue confirm a high percentage
Biol Psychiatry. 2007 Feb 15;61(4):492-497. Epub 2007 Jan 3.
Relationship of Dietary Intake to Gastrointestinal Symptoms in Children with Autistic Spectrum Disorders.Levy SE, Souders MC, Ittenbach RF, Giarelli E, Mulberg AE, Pinto-Martin JA.
“Reported frequency of GI abnormalities, including abnormal stool consistency (e.g., bulky or loose), was increased (54%)”
These data say that autistic children have near 3 times more GI issues than non- autistic children- for now (20 vs 60 %).

2-Autistic children/teens/adults with gastrointestinal problems have the same symptoms and severity of non-ASD children with the same medical problem-considering other factors such as stress ALSO?
This work compares autistic individuals and non-autistic individuals with different Gastrointestinal issues
Disaccharidase activities in 308 autistic (AI) and 206 non-autistic individuals (NAI) with different GIP (gastrointestinal problems).
The frequency of GIP among AI and NAI was: diarrhea, 38 vs 18 %; abdominal pain, 36 vs 59 %; food sensitivity, 14 vs 11%; constipation, 4 vs. 0.5%; GER (reflux), 3 vs. 11%; FTT (failure to thrive), 2 vs. 6%; diarrhea with abdominal pain, 6 vs 5%; diarrhea with food sensitivity, 6 vs 3%; and abdominal pain with food sensitivity, 4 vs 3%. AI with diarrhea (n = 206) demonstrated significantly lower maltase (P < 0.05) activity than NAI with diarrhea. Frequency of lactase deficiency in AI with FTT (n = 5) was significantly higher (80% vs 25%; P < 0.05) than in NAI with FTT and frequency of palatinase deficiency in AI with diarrhea was significantly higher than in NAI (28% vs 11%; P < 0.05) with the same GIP. AI and NAI with other GIP had similar frequency of disaccharidase deficiencies.
This study presents results on constipation
Although constipation occurs in 2% to 5% of healthy children, its clinical diagnosis is often difficult in children with behavioral disorders. Despite this, moderate or severe constipation was more frequent in the autistic group than in the control subjects (36% vs 10%). 54.4% of autistic children had moderate/severe loading or acquired megarectum compared with 24.1% of control subjects. Milk was the strongest predictor of constipation in the autistic group, whereas stool frequency, gluten consumption, soiling, and abdominal pain were not predictive of constipation (Dr Heuschkel / Dr Afzal publication).

*Diarrhea was present in 38 vs 18%; Lactase deficiency in Autistics with failure to thrive was VERY much higher 80% vs 25 % and palatinase deficiency 28 vs 11 %.
*It seems from these results that milk intolerance ( through lactose, casein intolerance) was related with constipation and enzyme deficiencies –lactase, maltase and palatinase- with diarrhea
The prevalence of IBS in North America is 10-15 % equally divided among IBS with constipation, IBS with diarrhea and IBS alternating between diarrhea and constipation (that is near 3.33 to 5 % of the general population for each). There are 9 population studies and the prevalence varied between 3 to 20 % but most estimates were concentrated between 10 and 15 %. However, these studies´s quality and quantity are limited.

Patients with IBS symptoms have been studied by different tests. In general Colitis IBD, Colorectal cancer, celiac disease, gastrointestinal infection, thyroid malfunction and lactose malabsorption are found. The main difference bewteen the general population and IBS patients is celiac disease (4.67 % vs 0.25 – 0.5 %), being the others in the same range. IBS patients exhibit visceral hypersensivity. Finally behavioral therapy seems to be more effective than placebo at relieving individual IBS symptoms, however no trial has provided unequivocal evidence that psychological treatment is efficacious in IBS.
Then,let´s go to see celiac disease as a form of gluten intolerance. A modern view would focus on gluten intolerance, a very much wider spectrum of problems with gluten
Increasing numbers of atypical or asymptomatic cases of celiac disease are being diagnosed. Celiac disease and cow's milk protein allergy are key examples of chronic enteropathy.

The dietary approach to allergy has evolved to include active stimulation of the immature immune system in order to support the establishment of tolerance.

Nestle Nutr Workshop Ser Pediatr Program. 2007;(59):115-31. Links
Chronic enteropathy and feeding.Salvatore S, Hauser B, Vandenplas Y.
Curr Opin Gastroenterol. 2007 Mar;23(2):142-8.
Advances in celiac disease.Craig D, Robins G, Howdle PD.
Academic Medical Unit, Leeds Institute of Molecular Medicine, Leeds, UK.

Although celiac disease is predicted by screening studies to affect approximately 1% of the population of the United States and is seen both in children and in adults, 10%-15% or fewer of these individuals have been diagnosed and treated.

J Clin Invest. 2007 Jan;117(1):41-9. Links
Celiac disease: pathogenesis of a model immunogenetic disease.
Kagnoff MF.
Celiac disease: pathogenesis of a model immunogenetic disease
And Gluten sensitivity as a neurological illness Hadjivassiliou M, Grunewald RA, Davies-Jones G in Journal of Neurology Neurosurgery and Psychiatry 2002;72:560-563
Where the authors say
“Gluten sensitivity can be primarily and at times exclusively a neurological disease. The absence of an enteropathy should not preclude patients from treatment with a gluten-free diet… Antigliadin antibodies are also found in the CSF… This inflammation was primarily seen in the white matter of the cerebellum. There was also marked but patchy Purkinje cell loss. We have also found antibodies against Purkinje cells in patients with gluten ataxia. Our research suggests that IgG antigliadin antibodies cross react with epitopes on Purkinje cells from human cerebellum… Characterisation of the anti-Purkinje cell antibodies by immunoblotting may provide a useful marker for the diagnosis of gluten ataxia in a manner analogous to the use of antiendomysium antibodies as a marker for coeliac disease or the anti-Yo antibody in paraneoplastic cerebellar degeneration.”
Other authors include conclusions like this
“Celiac disease should be considered in patients with idiopathic neuropathy even when gastrointestinal symptoms are absent”.(Muscle Nerve. 2007 Jan 16; Celiac disease presenting with motor neuropathy: Effect of gluten free-diet.Rigamonti A, Magi S, Venturini E, Morandi L, Ciano C, Lauria G).
Well, now, let´s go to see gut flora differences and other published clues about
* Presence of Clostridia hystoliticum was one of the main findings in FS of autistic chidlren
*Children with autism had 9 species of Clostridium not found in controls, whereas controls yielded only 3 species not found in children with autism.
*Analysis of the real-time PCR data indicated that the cell count differences between autistic and control children for C. bolteae and the following Clostridium groups were statistically significant: mean counts of C. bolteae and clusters I and XI in autistic children were 46-fold (P = 0.01), 9.0-fold (P = 0.014), and 3.5-fold (P = 0.004) greater than those in control children, respectively,
*There is a profile of composition of the intestinal flora that changes with age and development in non-autistic children:
*Healthy children can have chlostridia infections present but they are solved with development –after the year of age-and controlled with the maturation of the immune system. It seems that this change in the immune system has no place in some autistic children, that maintain unhealthy levels of abnormal bacteria in gut and who are affected differently by them.
* Positive presence of fungus of Candida strain in stool in some autistic children is related- many times- to IgA deficiency. Only immunedepressed people present this kind of fungal infections out of control
* Other bacterial infections (Giardasis Escherichia coli ,Blastocytis hominis, staphylococcus aureus amebiasis, parasites) are present under testing-anecdotal evidence [Blastocystis hominis and bowel diseases.]
In vitro growth control of selected pathogens by Lactobacillus acidophilus- and Lactobacillus casei-fermented milk
Bacterial infections of the gut (excluding enteric fever)
Luminal host-defense mechanisms against invasive amebiasis
The bacterial weaponry: lessons from Shigella


This is a free chapter of an immunology book-from the web. It explains very graphically what happens with gut pathogen infections and mucosa gut integrity- with other explanations about adaptive immunity.

Chapter 10


Apparently, very specific kinds of food allergies or intolerances- different things- (non- necessarily IgE mediated or presented as celiac disease as such in the case of gluten), inflammatory gastrointestinal conditions- of several kinds-,alterations of gut flora and overgrowth of certain fungal/bacterian infections would be present in some subgroups of autistic children- generally in combination. This kind of situation in combination are found only in immunedepressed people and in some IBS complicated patients (or transplanted).

3-How does the treatment of GI issues changes the IQ and child´s adaptative behavior with certain recorded changes in biochemistry-metabolism? Anecdotical and published evidence.
There are plenty of anecdotes about the GFCF diet- without clinical correlates. Also, there are plenty of anecdotes with important changes in behaviors upon the treatment of GI issues that provoke disconfort, pain, malabsorption and nutritional imbalances. There are also anecdotes of no effect of a diet GFCF ALONE, especially if there is not concomitant search for potential concomitant medical problems to –if present- gastrointestinal issues ( from reflux to nutritional imbalances). And There are also anecdotes of no effect of the GFCF diet, even with a lot of treatments concomitant to these diagnosis. In some other cases, disaccharidases can be imbalanced and the SCDiet has shown to produce some help. Otherwise, when oxalates are high the oxalate-free diet also has provided some help. And in other cases ketogenic diet has produced positive effects. There is probably no field as changing and challenging as the individual detections of GI issues and the concomitant tretament of TROUGH dietary changes.
Because the problems are presented in combination (Gut flora alterations, presence of abnormal bacteria, food intolerances and nutritional imbalances-related to immune alterations, lack of several enzymes, high level of certain compounds related to malabsorption or biochemical alterations) the research of the treatment should be integral, considering all the aspects TOGETHER. I know that this is a nightmare for controls, but it is the problem many parents must face- and very few researchers consider as such (recent work of Elder et al is a demonstration of my point). The needed incorporation of ambiguety and individuality is not easy from the scientific point of view. However, in my anecdotical experience, it has been important to consider.
Why the GFCF diet is going to produce some change if a child has not a food intolerance to gluten and/or casein? You need testing for this- and there are many test available in current labs.
Why the GFCF diet is going to be tested WITHOUT gut support in the form of probiotics and fungal/bacterian/other testing, diagnosis and treatment? In my anecdotical experience, diet is a tiny part of the overall problem- although it helps.
Why the GFCF diet is going to have some kind of effect in celiac, lactose defficient, enzyme defficient children if the enzymes are not tested, the lactose defficiency is not tested, the nutritional imbalances are not balanced (vitamins, essential elements, minerals, fatty acids- recently present in the news- probably related to lipase defficiencies) and the OTHER gut problems are not treated?
Why almost no researchers take all this into consideration, rendering useless in many cases their findings?
An autistic or non-autistic child with celiac disease, milk intolerance, fungal /bacterian infections in gut, enzyme and nutritional defficiencies, Why avoidance of ONLY gluten and casein si going to show improvement if there are many other problems ALSO that remain undetected/untreated?

O no! again I begun in the basement (gastrointestinal problems) and ended in the living room (the immune system). Well there is an excellent recently published paper- beyond the one on the MET signaling in autism- relating the gut with the immune system that I think it will be interesting to analyze together with the NK, CD8, IgG and IgA…Next time :)