Inflammation Leading to Cognitive Dysfunction

Today’s post highlights a paper with some very concise insights into how microglial cells become “activated” resulting in the “exaggerated inflammatory response” that many people with autism experience on a daily basis.  

This is very relevant to treatment, which is not usually the objective of much autism research.

I recall reading a comment from John’s Hopkins about neuroinflammation/activated microglia in autism; they commented that no known therapy currently exists and that, of course, common NSAIDs like ibuprofen will not be effective.  But NSAIDs are effective.

As we see in today’s paper, there a least 4 indirect cytokine-dependent pathways leading to the microglia, plus one direct one.

NSAIDs most definitely can reduce cytokine signaling and thus, indirectly, reduce microglial activation.

The ideal therapy would act directly at the microglia, and as Johns Hopkins pointed out, that does not yet exist with today's drugs.  If you read the research on various natural flavonoids you will see that “in vitro” there are known substances with anti-neuroinflammatory effects on microglial activation.  The recurring “problem” with such substances is low bioavailability and inability to cross the blood brain barrier.

Back to Today’s Paper

It was a conference paper at the 114th Abbott Nutrition Research Conference - Cognition and Nutrition

The full conference proceedings can be downloaded

The paper is not about autism, it is about more general cognitive dysfunction.  It is from mainstream science (I checked).

It explains how inflammation anywhere in the body can be translated across the BBB (Blood Brain Barrier) to activate the microglia.  This of course allows you to think of ways to counter these mechanisms.

It also raises the issue of whether or not anti-inflammatory agents really need to cross the BBB.  While you might think that ability to cross the BBB is a perquisite to mitigate the activated microglia, this may not be the case.  Much can be achieved outside the BBB, and we should not rule out substances that cannot cross the BBB.

Very many known anti-inflammatory substances do not cross the BBB.   

  

From Inflammation to Sickness and Cognitive Dysfunction: When the Immune System Subjugates the Brain

extracts from the above paper ...

Example – Influenza and Cognition

Neurological and cognitive effects associated with influenza infection have been reported throughout history.

The simplest explanation for these neurocognitive effects is that influenza virus makes its way to the brain, where it is detected by neurons.

However, most influenza strains, including those responsible for pandemics, are considered non-neurotropic, neurological symptoms associated with influenza infection are not a result of direct viral invasion into the CNS.

Moreover, neurons do not have receptors to detect viruses (or other pathogens) directly.

Cells of the immune system do, however, as the immune system’s primary responsibility is to recognize infectious pathogens and contend with them. For example, sentinel immune cells such as monocytes and macrophages are equipped with toll-like receptors (TLR) that recognize unique molecules associated with groups of pathogens (i.e., pathogen-associated molecular patterns). Stimulation of TLRs that recognize viruses (TLR3 and TLR7) and bacteria (TLR4) on immune sentinel cells can have profound neurological and cognitive effects, suggesting the immune system conveys a message to the brain after detecting an infectious agent. This message is cytokine based.

Macrophages and monocytes produce inflammatory cytokines (e.g., interleukin [IL]-1β, IL-6, and tumor necrosis factor-α [TNF-α]) that facilitate communication between the periphery and brain.

Cytokine-dependent Pathways to the Brain

Several cytokine-dependent pathways that enable the peripheral immune system to transcend the blood-brain barrier have been dissected.

Inflammatory cytokines present in blood can be actively transported into the brain.

But there are also four indirect pathways:-

1.     Cytokines produced in the periphery need not enter the brain to elicit neurocognitive changes. This is because inflammatory stimuli in the periphery can induce microglial cells to produce a similar repertoire of inflammatory cytokines. Thus, brain microglia recapitulates the message from the peripheral immune system.

2.     in a second pathway, inflammatory cytokines in the periphery can bind receptors on blood-brain barrier endothelial cells and induce perivascular microglia or macrophages to express cytokines that are released into the brain

3.     In a third pathway, cytokines in the periphery convey a message to the brain via the vagus nerve. After immune challenge, dendritic cells and macrophages that are closely associated with the abdominal vagus have been shown to express IL-1β protein; IL-1 binding sites have been identified in several regions of the vagus as well. When activated by cytokines, the vagus can activate specific neural pathways that are involved in neurocognitive behavior. However, activation of the vagus also stimulates microglia in the brain to produce cytokines via the central adrenergic system 

4.     A fourth pathway provides a slower immune-to-brain signaling mechanism based on volume transmission.  In this method of immune-to-brain communication, production of IL-1β by the brain first occurs in the choroid plexus and circumventricular organs—brain areas devoid of an intact blood-brain barrier. The cytokines then slowly diffuse throughout the brain by volume transmission, along the way activating microglia, neurons, and neural pathways that induce sickness behavior and inhibit cognition.

Can Flavonoids Reduce Neuroinflammation and Inhibit Cognitive Aging?

Flavonoids are naturally occurring polyphenolic compounds present in plants. The major sources of flavonoids in the human diet include fruits, vegetables, tea, wine, and cocoa.  Significant evidence has emerged to indicate that consuming a diet rich in flavonoids may inhibit or reverse cognitive aging

Flavonoids may improve cognition in the aged through a number of physiological mechanisms, including scavenging of reactive oxygen and nitrogen species and interactions with intracellular signaling pathways. Through these physiological mechanisms, flavonoids also impart an anti-inflammatory effect that may improve cognition. This seems likely for the flavone luteolin, which is most prominent in parsley, celery, and green peppers.

Whereas luteolin inhibits several transcription factors that mediate inflammatory genes (e.g., nuclear factor kappa B [NF-κB]and activator protein 1 [AP-1]), it is a potent activator of nuclear factor erythroid 2-related factor 2 (Nrf2), which induces the expression of genes encoding antioxidant enzymes. A recent study of old healthy mice found improved learning and memory and reduced expression of inflammatory genes in the hippocampus when luteolin was included in the diet. Thus, dietary luteolin may improve cognitive function in the aged by reducing brain microglial cell activity.

Hence, the flavonoid luteolin is a naturally occurring immune modulator that may be effective in reducing inflammatory microglia in the senescent brain.

Conclusion

In light of the recent evidence suggesting microglial cells become dysregulated due to aging and cause neuroinflammation, which can disrupt neural structure and function, it is an interesting prospect to think dietary flavonoids and other bioactives can be used to constrain microglia. But how can flavonoids impart this anti-inflammatory effect? Although in vitro studies clearly indicate that several flavonoids can act directly on microglial cells to restrict the inflammatory response, results from in vivo studies thus far do not prove that dietary flavonoids access the brain to interact with microglia in a meaningful way. This is a complicated question to dissect because flavonoids reduce inflammation in the periphery and microglia seem to act like an “immunostat,” detecting and responding to signals emerging from immune-to-brain signaling pathways. Thus, whether dietary flavonoids enter the brain and impart an anti-inflammatory effect on microglia is an interesting question but one that is more theoretical than practical because what is most important is how the immunostat is adjusted, whether that is via a direct or indirect route. However, because flavonoids are detectable in the brain they most likely affect microglia both directly and by dampening immune-to-brain signaling.

Interesting Natural Substances

In no particular order, these are several very interesting flavonoids/carotenoids.  In the lab, they all do some remarkable things.

In humans, they also do some interesting things; how helpful they might be in autism remains to be seen.

Being “natural” does not mean they are good for you and have no side-effects.

Some of the following are very widely used and so you can establish if there are issues with long term use.  It also makes them accessible.

Quercetin (found in many fruits, numerous interesting effects)

and two Quercetin-related flavonoids:-

Kaempferol (widely used in traditional medicine)

Myricetin (has good and bad effects)

Lycopene  (from tomatoes, potent anti-cancer, does not cross the BBB)

  

Luteolin(in many vegetables, like broccoli) 

Apigenin (from chamomile, stimulates neurogenesis, PAM of GABA_A, block NDMA receptors, antagonist of opioid receptors …)

Tangeretin (from tangerines, does cross the BBB, has potent effects in vitro)

Nobiletin (from tangerines)

Hesperidin (from tangerines)

Naringin (from Grapefruit, contraindicated with many prescription drugs)

Epicatechin/Catechin  (the chocolate/cocoa flavonoids, do cross the BBB, well researched)

Cytokines from the Eruption of Permanent Teeth causing Flare-ups in Autism

A recent post looked again at inflammation in autism and some possible therapies to try.  Over Christmas and New Year, Monty, aged 11 with ASD, had occasional outbursts, more typical of his summertime raging, which was later solved using allergy /mast cell therapies.

At least it did let me establish whether Verapamil was a universal “cure” for SIB.  It is not.  It works great for allergy-driven aggressive behaviors, but had no effect on these ones.

Christmas is often a stressful period for many people with, or without, autism; but Monty likes presents and he loves food.

Having pulled out a wobbly tooth on Boxing Day and noticed an apparent behavior change, I thought that perhaps the loss of milk teeth and development of permanent teeth might cause an effect similar to that of his mild pollen allergy.  Monty, in common with many people with autism, has a high pain threshold.  While teething causes well known problems in babies, most children have minimal problems when their milk teeth are replaced by their permanent ones.

I just wondered if perhaps the underlying biological mechanism might provide an inflammatory insult to the highly inflammation-sensitive autistic brain.

Just as histamine provokes a release of inflammatory cytokines like IL-6, perhaps losing your milk teeth does something similar.

Ibuprofen experiment

I decided that I would buy some Ibuprofen, the least problematic NSAID.   A day or two later, Monty declared that another tooth was wobbly and needed to be pulled out.  This tooth was, and remains, well and truly attached.

So I decided that in advance of another, potentially stressful, Christmas event, I would give 10 ml of Ibuprofen.  I did not give it in response to any comment about pain.

It did indeed seem to work.

Skiing

A few days later we were in the Alps for skiing.

Monty can ski, but we always give him a 1:1 instructor.  On the first day, without Ibuprofen, he got agitated during the queuing at the bottom of the beginners’ ski lift.  The instructor thought it was the loud booming music.  It was clear that by the end of the lesson, it was no fun at all.

The following days, I gave 10 ml of Ibuprofen, 20 minutes before the lesson started.  He had a great time, going up by cable car to the top of the mountain and skiing along the blue/red slopes and coming down in a neighboring resort a couple of hours later.  Even a change of instructor on one day, passed without issue.

It might not be scientific proof of the effectiveness of Ibuprofen, but it was enough for me.

The Science

Since this is a scientific blog, arriving home I did some checking on the biology of what happens when you lose your milk teeth.

There is more written about “teething” when you first get your milk teeth, but there is information about “root resorption” of milk teeth and “eruption” of the permanent teeth.  The process is indeed modulated by inflammatory cytokines and transcription factors.

These cytokines will then circulate around the body and cross the blood brain barrier.

Cytokine levels in gingival crevicular fluid of erupting primary teeth correlated with systemic disturbances accompanying teething.

Abstract

PURPOSE:

The aim of this study was to investigate whether there are increased levels of the inflammatory cytokines IL-1beta, IL-8, and TNF alpha in the gingival crevicular fluid (GCF) of erupting primary teeth. This increase could explain such clinical manifestations as fever, diarrhea, increased crying, and sleeping and eating disturbances that occur at this time.

METHODS:

Sixteen healthy children aged 5 to 14 months (mean=9.8 months) were examined twice a week over 5 months. Gingival crevicular fluid samples were taken from erupting teeth. As a control, GCF was collected from the same teeth 1 month later. Cytokine production was measured by ELISA. Signs and clinical symptoms were listed. Pearson correlation coefficients were used in the comparisons described below. A paired t test was used to analyze the same variable at different times.

RESULTS:

Fifty teeth of the 16 children were studied. GCF samples were collected from 21 of these teeth. Statistically significant differences (P<.05) were found with regard to the occurrence of fever, behavioral problems, and coughing during the teething period and the control period. During the control period, 72% of the children did not exhibit any clinical manifestations, whereas during the teething period only 22% of the children did not exhibit any clinical manifestations. The study revealed high levels of inflammatory cytokines during the teething period, with a statistically significant difference in TNF alpha levels (P<.05) between the teething period and the control period. Correlations were found between cytokine levels and some of the clinical symptoms of teething: IL-1beta and TNF alpha were correlated with fever and sleep disturbances; IL-beta and IL-8 were correlated with gastrointestinal disturbances; IL-1beta was correlated with appetite disturbances.

CONCLUSIONS:

Cytokines appear in the GCF of erupting primary teeth. The cytokine levels are correlated to some symptoms of teething.

Mechanism of Human Tooth Eruption: Review Article Including a New Theory for Future Studies on the Eruption Process

Physiologic root resorption in primary teeth: molecular and histological events

Root resorption is a physiologic event for the primary teeth. It is still unclear whether odontoclasts, the cells which resorb the dental hard tissue, are different from the osteoclasts, the cells that resorb bone. Root resorption seems to be initiated and regulated by the stellate reticulum and the dental follicle of the underlying permanent tooth via the secretion of stimulatory molecules, i.e. cytokines and transcription factors. The primary root resorption process is regulated in a manner similar to bone remodeling, involving the same receptor ligand system known as RANK/RANKL (receptor activator of nuclear factor-kappa B/ RANK Ligand). Primary teeth without a permanent successor eventually exfoliate as well, but our current understanding on the underlying mechanism is slim. The literature is also vague on how resorption of the pulp and periodontal ligament of the primary teeth occurs. Knowledge on the mechanisms involved in the physiologic root resorption process may enable us to delay or even inhibit exfoliation of primary teeth in those cases that the permanent successor teeth are not present and thus preservation of the primary teeth is desirable. (J. Oral Sci. 49, 1-12, 2007)

Nonsteroidal anti-inflammatory drugs (NSAIDS), such as ibuprofen, work by inhibiting the enzyme COX which converts arachidonic acid to prostaglandin H₂ (PGH₂). PGH₂, in turn, is converted by other enzymes to several other prostaglandins ,which are mediators of pain, inflammation, and fever.

Prostaglandin E synthase

Prostaglandin E₂ (PGE₂) is generated from the action of prostaglandin E synthases on prostaglandin H₂ (PGH₂).

PGE₂ has various known effects, but one known effect is to increase the pro-inflammatory cytokine IL-6.  The same one that is increased by histamine released from mast cells during allergic reactions.

Elevated interleukin 6 is induced by prostaglandin E2 in a murine model of inflammation: possible role of cyclooxygenase-2.

Abstract

Injection of mineral oils such as pristane into the peritoneal cavities of BALB/c mice results in a chronic peritonitis associated with high tissue levels of interleukin 6 (IL-6). Here we show that increased prostaglandin E2 (PGE2) synthesis causes induction of IL-6 and that expression of an inducible cyclooxygenase, Cox-2, may mediate this process. Levels of both PGE2 and IL-6 are elevated in inflammatory exudates from pristane-treated mice compared with lavage samples from untreated mice. The Cox-2 gene is induced in the peritoneal macrophage fraction isolated from the mice. A cause and effect relationship between increased macrophage PGE2 and IL-6 production is shown in vitro. When peritoneal macrophages are activated with an inflammatory stimulus (polymerized albumin), the Cox-2 gene is induced and secretion of PGE2 and IL-6 increases, with elevated PGE2 appearing before IL-6. Cotreatment with 1 microM indomethacin inhibits PGE2 production by the cells and reduces the induction of IL-6 mRNA but has no effect on Cox-2 mRNA, consistent with the fact that the drug inhibits catalytic activity of the cyclooxygenase but does not affect expression of the gene. Addition of exogenous PGE2 to macrophages induces IL-6 protein and mRNA synthesis, indicating that the eicosanoid stimulates IL-6 production at the level of gene expression. PGE2-stimulated IL-6 production is unaffected by addition of indomethacin. Taken together with the earlier finding that indomethacin diminishes the elevation of IL-6 in pristane-treated mice, the results show that PGE2 can induce IL-6 production in vivo and implicate expression of the Cox-2 gene in the regulation of this cytokine

Indomethacin is another NSAID, like Ibuprofen.

Implications

If, as seems likely, many incidents of anxiety, aggression, explosive behavior, or "meltdowns" are made possible by elevated levels of the pro-inflammatory cytokine IL-6, then the occasional use of drugs known to inhibit IL-6 makes a lot of sense.

Ibuprofen is an NSAID and it is known that some people respond much better to certain NSAIDs and suffer side effects from others.   NSAID drugs work by affecting both COX-1 and COX-2.  It appears that desired effect of NSAIDs comes from their effect on COX-2, while the side effects come from changes made to COX-1.  So it is logical that some NSAIDs are better tolerated than others and for some people a different NSAID may be more appropriate.

Other common drugs also lower IL-6;  leukotriene receptor antagonists like Montelukast (Singulair)  being an example.  This drug is used in autism, but a known side-effect in typical people is to worsen behavior, sometimes severely.  There are plenty of reports of Singulair in autism, some good and some bad.  Since almost all drugs have multiple effects, this is not surprising.

Interestingly, one of the drugs in my Polypill, NAC, is also known to reduce IL-6; but it also reduces the “good” anti-inflammatory cytokines like IL-10.  Perhaps this is why NAC is not beneficial to some people with autism?

Occasional use of Ibuprofen at times anticipated to be stressful makes a lot of sense. 

Conclusion

While it is well known that Ibuprofen relieves pain from teething, low level pain is often completely ignored by people with ASD.  The cytokine release associated with the resorption of the milk teeth and the eruption of the permanent tooth appears to be much more problematic.

Ibuprofen, available OTC, limits the production of pain mediators, called prostaglandins, which in turn stimulate production of the inflammatory cytokine IL-6.

Ibuprofen will reduce both pain and the level of cytokines like IL-6.

In earlier extensive posts on mast cell degranulation in autism, I concluded that the resulting elevated levels of IL-6 likely produced behaviors ranging from anxiety, through aggression, all the way to self-injury.