Archive for March 2010
Neat Study: “Increased serum levels of high mobility group box 1 protein in patients with autistic disorder”
Posted March 27, 2010on:
Hello friends – The other day a pretty neat abstract hit my inbox: Increased serum levels of high mobility group box 1 protein in patients with autistic disorder
BACKGROUND: High mobility group box 1 (HMGB1) is a highly conserved, ubiquitous protein that functions as an activator for inducing the immune response and can be released from neurons after glutamate excitotoxicity. The objective of the present study was to measure serum levels of HMGB1 in patients with autistic disorder and to study their relationship with clinical characteristics. METHODS: We enrolled 22 adult patients with autistic disorder (mean age: 28.1+/-7.7years) and 28 age- and gender-matched healthy controls (mean age: 28.7+/-8.1years). Serum levels of HMGB1 were measured by enzyme-linked immunosorbent assay (ELISA). RESULTS: Compared with healthy subjects, serum levels of HMGB1 were significantly higher in patients with autistic disorder (10.8+/-2.6ng/mL versus 5.6+/-2.5ng/mL, respectively, P<0.001). After adjustment for potential confounders, serum HMGB1 levels were independently associated with their domain A scores in the Autism Diagnostic Interview-Revised, which reflects their impairments in social interaction. CONCLUSIONS: These results suggest that HMGB1 levels may be affected in autistic disorder. Increased HMGB1 may be a biological correlate of the impaired reciprocal social interactions in this neurodevelopmental disorder.
I had not heard of “high mobility group box 1” before, but as being described as an ‘activator for inducing the immune response’, my interest was definitely piqued! The author, Emanuele Enzo, was extremely gracious in providing me a copy of his manuscript. Below are the juicy parts: From the introduction:
In recent years, many different mechanisms have been suggested to play a role in the pathophysiology of ASD, including impaired neurotransmission, genetic mutations, viral infections, gastrointestinal factors, and excitotoxicity (Levy et al., 2009; Rapin and Tuchman, 2008). Growing evidence has also suggested that inflammation (Cohly and Panja, 2005), neuroinflammation (Pardo et al., 2005), and oxidative stress (McGinnis, 2004) may be involved in the pathogenesis of ASD. High mobility group box 1 (HMGB1) is a highly conserved, ubiquitous protein released from inflammatory cells that functions as a signal for inducing inflammation and as an activator for inducing the immune response (Klune et al., 2008; Bianchi and Manfredi, 2007). The action of extracellular HMGB1 appears to be dependent on interaction with several cell surface receptors, including toll-like receptors 2/4 (TLRs-2/4) (Yu et al., 2006) and the receptor for advanced glycation endproducts (RAGE) (Rauvala and Rouhiainen, 2007). RAGE is a member of the immunoglobulin superfamily of cell surface receptors that is activated by HMGB1 but also by advanced glycation end products and S100 proteins (Yan et al., 2009), all of which have been shown to be altered in autism (Boso et al., 2006; Junaid et al., 2004). In addition, HMGB1 seems to be released from neurons after glutamate excitotoxicity (Kim et al., 2006; Kim et al., 2008). [emphasis and links are mine]
Some familiar players here , namely, neuroinflammation [Vargas, Li, Garbett], and TLR2 and TLR4 [Engstrom, Jyounouci]. I read Klune this afternoon and it is a very good review paper regarding HMGB1, which essentially illuminates on its description as ‘a signal for inducing inflammation’ involved with TLR2 and TLR4. In it, HMGB1 is termed an ‘alarmin’, an endogenous immune adjuvant, or more plainly, a homegrown danger signal. There is mention of synergistic effects in promoting an inflammatory response in conjunction with tnf-alpha, a presence in autoimmunity, cancer and other nasty conditions, as well as potential restorative effects. Anyone who has been paying attention to the ‘abnormal immune response’ findings in autism is going to see a lot of crosstalk here. [Interested by the semantics, I would encourage readers to take a look at paperwork on resolvins as potential mediators of inflammation]. The RAGE stuff is another paper when Enzo is an author that I haven’t read yet, but mean to. From the results section:
After allowance for age, BMI, and Raven’s Progressive Matrices scores, we found a positive independent association between HMGB1 levels and the ADI-R Social Scores (HMGB1, the worse the social interaction β=0.39, t=2.81, P < 0.01, Fig. 2); the higher the serum level of HMBG1, the worse the social interaction.
Now, this is pretty interesting, because it is another instance where we observe a correlation between immunomodulators and autism severity; Grigorenko found that MIF, a known upregulator of the innate immune response, was positively associated with autism severity, and Ashwood found an inverse relationship between the immune regulating cytokine, TGF-Beta1 and autism severity. It would seem that by several measurements, a propensity towards an inflammatory state seems to be able to affect the degree of impairment.
From the very lightweight discussion section:
HMGB1 has been shown to function as a proinflammatory cytokine-like involved in both excitotoxicity (Kim et al., 2006) and glial activation (Pedrazzi et al., 2007) . Of note, growing evidence has suggested a pathophysiological role for excitotoxicity (Blaylock and Strunecka, 2009) and glutamatergic dysregulation (Blaylock, 09; Shinohe et al., 2006) in ASD. In addition, neuroinflammation may be an important feature in some patients with autistic disorder (Pardo et al., 2005; Vargas et al., 2005). Recently, Pedrazzi et al. (2007) have shown that HMGB1 promotes a specific proinflammatory program in primary astrocytes. Increased oxidative stress and immune dysregulation are other important feature in ASD (McGinnis, 2004; Cohly and Panja, 2005; Blaylock, 2009), and HMGB1 protein plays important roles in both processes (Bianchi and Manfredi, 2007; Klune et al., 2008). Interestingly, HMGB1 may induce a prooxidative state through interaction with its cell-surface receptor RAGE (Rauvala and Rouhiainen, 2007), a molecule previously implicated in the pathogenesis of ASD (Boso et al., 2006). An interesting observation in this study is that raised HMGB1 levels in our patient group were correlated with disturbances in social function as assessed with ADI–R, suggesting that this molecule may be a biological correlate of the impaired reciprocal social interactions in this neurodevelopmental disorder. This finding is intriguing, but needs to be confirmed with further studies.
You don’t see Blaylock get referenced too often, I need to read those papers, he does seem to have an online credibility problem that I can’t figure out. Anyways, the statement that HMGB1 and astrocytes is particularly interesting, because we can see from the seminal Vargas paper, Neuroglial Activation and Neuroinflammation in the Brain of Patients with Autism that astrocytes were the primary producer of the increased cytokine IL-6 and chemokine MCP-1 in the brains of autistics. A link to increased oxidative stress doesn’t surprise me too much, though again, I haven’t read anything about RAGE, so seeing another pathway towards increased oxidative stress is a nice touch. There is a section on the weaknesses of the study including smaller study sizes and uncertainty towards the source of HMGB1. As always, there is a call for additional study.
Brain inflammation is a major factor in epilepsy, but the impact of specific inflammatory mediators on neuronal excitability is incompletely understood. Using models of acute and chronic seizures in C57BL/6 mice, we discovered a proconvulsant pathway involving high-mobility group box-1 (HMGB1) release from neurons and glia and its interaction with Toll-like receptor 4 (TLR4), a key receptor of innate immunity. Antagonists of HMGB1 and TLR4 retard seizure precipitation and decrease acute and chronic seizure recurrence. TLR4-defective C3H/HeJ mice are resistant to kainate-induced seizures. The proconvulsant effects of HMGB1, like those of interleukin-1b (IL-1b), are partly mediated by ifenprodil-sensitive N-methyl-d-aspartate (NMDA) receptors. Increased expression of HMGB1 and TLR4 in human epileptogenic tissue, like that observed in the mouse model of chronic seizures, suggests a role for the HMGB1-TLR4 axis in human epilepsy.
Unequal distributions of scary chemicals and (possible) implications for autism clusters, a static rate of autism, and why some of us may be more doomed than others
Posted March 12, 2010on:
Hello friends –
Recently there have been a few studies that tackled the issue of apparent autism clusters in California, The spatial structure of autism in California, 1993-2001, and Geographic distribution of autism in California: A retrospective birth cohort analysis. A nice overview and some discussion of these papers can be found at LBRB, here, and here. One of the arguments we see made there is that the rates of autism diagnosis are, in fact, a reflection of the available services in an area, as opposed to an actual difference in the number of children with autism; essentially that an undiagnosed child with autism who lives far from a center of autism services will not get a diagnosis, but a child born relatively close to such services, will be appropriately diagnosed. We are measuring diagnosis, as opposed to autism. I have no doubt that there is some validity to this, but have many doubts that we can, or should, assign all of our observed increases in autism as consequences of this type of artifact.
There have been several other studies that looked at things like mercury emissions, or airborne pollutants, or Superfund sites and autism rates at larger scales. However, on a macro level, these types of studies have, so far, been unable to design around a feature of reality; the likelihood that things like Superfund sites or airborne pollution are situated in relative proximity to an urban center, and as such, autism diagnosis services. In effect, the argument that these observations are diagnostic only is the same; without a controlling factor for diagnostic availability, we can not assume that other parameters are actually responsible. And again, I have no doubt that this is a force that contributes to the findings of these studies.
At the end of the day, I’m just not satisfied with a God of the Gaps explanation; what we seem to be seeing is just too goddamned important to explain away with the spongy soft and ultimately unmeasurable forces of greater awareness et all. (The Fairytale, 20##).
Anyways, the other day pubmed alerted me to the publication of this interesting study:
BACKGROUND: Levels of brominated flame retardants are increasing in US populations, yet little data are available on body burdens of these and other persistent hormonally active agents (HAAs) in school-aged children. Exposures to such chemicals may affect a number of health outcomes related to development and reproductive function. OBJECTIVE: Determine the distribution of biomarkers of polybrominated diphenyl ethers (PBDEs), polychlorinated biphenyls (PCBs), and organo-chlorinated pesticides (OCPs), such as DDT/DDE, in children, and their variation by key descriptor variables. METHODS: Ethnically diverse cohorts of girls 6-8y old at baseline are being followed for growth and pubertal development in a multi-site, longitudinal study. Nearly 600 serum samples from the California and Ohio sites were analyzed for lipids, 36 PCB congeners, 11 PBDE congeners, and 9 OCPs. The biomarker distributions were examined and geometric means compared for selected analytes across categories of age, race, site, body mass index (BMI), parental education, maternal age at delivery, and breast feeding in adjusted models. RESULTS: Six PBDE congeners were detected among greater than 70% of samples, with BDE-47 having the highest concentration (median 42.2, range 4.9-855ng/g lipid). Girls in California had adjusted geometric mean (GM) PBDE levels significantly higher than girls in Ohio. Furthermore, Blacks had significantly higher adjusted GMs of all six PBDE congeners than Whites, and Hispanics had intermediate values. GMs tended to be lower among more obese girls, while other variables were not strongly associated. In contrast, GMs of the six PCB congeners most frequently detected were significantly lower among Blacks and Hispanics than Whites. PCBs and the three pesticides most frequently detected were also consistently lower among girls with high BMI, who were not breast-fed, whose mothers were younger, or whose care-givers (usually parents) were less educated. Girls in California had higher GMs than in Ohio for the pesticides and most PCB congeners, but the opposite for CB-99 and -118. CONCLUSIONS: Several of these potential HAAs were detected in nearly all of these young girls, some at relatively high levels, with variation by geographic location and other demographic factors that may reflect exposure pathways. The higher PBDE levels in California likely reflect differences in fire regulation and safety codes, with potential policy implications.
The environmental impact argument usually focuses on vaccines, or in some instances, similarly widespread environmental pollutants (i.e., mercury emissions); external forces which tend to operate more or less evenly across large geographic swaths, and also largely independent of things like culture or race. But with this paper we can observe the counter-intuitive opposite, chemicals that have achieved widespread distribution in society and the environment, seem to be bioaccumulating differentially according to factors such as geography, race, body type, and education levels. The paper here mentions fire regulation as a possible factor in state by state differences, but taking things a bit further, it can quickly be seen how socio-economic factors might play a role in why we might observe different levels of chemicals. It takes a lot of crazy chemistry to make a baby onesie not catch on fire, but at a high level, it involves dousing the material with a bunch of exotic chemicals. Politically correct or not the facts on the ground are that the well to do white woman has baby showers where she gets a bewildering array of freshly minted, ‘extra safe’ baby clothes more often than, say, the not so well to do Latina woman. We have already established a connection between having older parents and a diagnosis of autism, it would seem, there is also a correlation between having older parents and your bodies burden of these molecular mimics; and again, white women tend to have babies at later stages in life than their Black or Latina counterparts; especially the ones that happen to be residing near the trendy autism diagnosis hubs (i.e., the wealthier white women). The ability for these types of chemicals to cause a variety of difficult to predict developmental trajectories is too long, and terrifying to go into detail in this post; for purposes of this discussion, it is sufficient to understand that we have a growing body of evidence that endocrine disrupting compounds can have wide ranging effects; including epigenetic changes, changes in immune profiles, altered behaviors and neuroanatomical structures known to be abnormal in autism.
I found the finding of BDE-47 particularly intriguing, considering it was used as a primer for immunological response measurement by Ashwood, who found in vitro differences in immune responses in the autism population (an exaggerated innate immune response was observed).
Of course, this study does not present sufficient evidence for us to draw conclusions about the geographic distribution of autism rates in the two California studies above; but it should give us enough to pause before we take the comforting road out and assume that our observation are the result of diagnostic artifact alone; such assumptions feel good (except for the guilt), but ultimately require that we ignore our growing knowledge of how unpredictable endocrine disruptors affect the body, and how much more we have to learn.