Urinary histidine as a marker of 'dioxin-induced' neurodevelopmental issues?

The paper by Muneko Nishijo and colleagues [1] (open-access) caught my eye recently and their continuing investigations into the potential effects of perinatal dioxin exposure on offspring neurodevelopmental outcomes. For a bit of background on this initiative based in Vietnam, I would refer readers to a previous post on this blog (see here).

Your weakness is copper? Y-you're kidding right?

In case you can't be bothered to follow that previous link, the idea was that exposure to TCDD [2,3,7,8-tetrachlorodibenzo-p-dioxin], a particularly hazardous chemical which contaminated the compound known as Agent Orange quite extensively used in Vietnam a few years back, might have some important links to infants exposed to said compound, particularly in relation to the expression of autistic traits. As an aside, I note that dioxin and Agent Orange continues to generate headlines and debate as per news items such as this one suggesting that the legacy of the Vietnam war continues even today.

The latest paper from Nishijo et al sought to look at urinary amino acid profiles of groups (N=26) exposed or not to various combinations of "high total dioxin toxic equivalent (TEQ-PCDDs/Fs)" and/or TCDD. The analytical weapon of choice was gas chromatography-mass spectrometry (GC-MS), and alongside the examination of urine samples, researchers also took into account breast milk concentrations of "PCDD and PCDF congeners (PCDDs/Fs)" as well as variables such as body size, food intake and neurodevelopmental measures based on scores from the "Bayley Scales of Infant and Toddler Development, Ver. 3 (Bayley III)."

Results: "The present study demonstrated that perinatal dioxin exposure to TCDD and TEQ-PCDDs/Fs, as indicated by levels in breast milk, significantly decreased urinary excretion of histidine and tryptophan in 3-year-old Vietnamese children with lower neurodevelopmental scores in dioxin contamination hot spots." As per the title of this post: "urinary levels of histidine were decreased in 3-year-old Vietnamese children who had been exposed to high dioxin levels." Histidine also features quite a bit in the discussion of the study results as per one section labelled: Histidine and brain function.

There is obviously a lot more work to do in this area to further enlighten the research path about the hows, whys and wherefores of dioxin exposure affecting both psychological and biological functions in children. Not least is the need for further prospective study methods to get around the use of breast milk levels of these compounds as a marker of perinatal dioxin exposure. I might also add that decreased levels of urinary histidine have been reported previously with autism in mind [2] (see here for some discussion) so suggesting that dioxin levels might be the only correlate of the group in question might be a step too far at the moment.

With my autism research blogging hat on, I continue to be interested in the chemical exposure link postulated with the expression of 'some' autism and the roads where this might lead autism research. The paper from Peter Stein and colleagues [3] who just featured in that that other paper on urinary histidine among other things [2], suggesting that there may be more to see with regards to Bisphenol-A (BPA) and autism (which I will be blogging about soon) adds to interest in this area, albeit with again the need for further independent verification and more data on the hows and whys.

Music. In memory of Demis... and with the hopes and dreams of Greece and the Greek nation in mind.

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[1] Nishijo M. et al. Urinary Amino Acid Alterations in 3-Year-Old Children with Neurodevelopmental Effects due to Perinatal Dioxin Exposure in Vietnam: A Nested Case-Control Study for Neurobiomarker Discovery. PLoS ONE. 2015; 10(1): e0116778.

[2] Ming X. et al. Metabolic perturbance in autism spectrum disorders: a metabolomics study. J Proteome Res. 2012 Dec 7;11(12):5856-62.

[3] Stein TP. et al. Bisphenol A Exposure in Children With Autism Spectrum Disorders. Autism Research. 2015. Jan 13.

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Nishijo M, Tai PT, Anh NT, Nghi TN, Nakagawa H, Van Luong H, Anh TH, Morikawa Y, Waseda T, Kido T, & Nishijo H (2015). Urinary Amino Acid Alterations in 3-Year-Old Children with Neurodevelopmental Effects due to Perinatal Dioxin Exposure in Vietnam: A Nested Case-Control Study for Neurobiomarker Discovery. PloS one, 10 (1) PMID: 25584822

You heard me right... autism prevalence and meat consumption

"The paper presents some exploratory analyses demonstrating the correlation between particular aspects of meat consumption and autism prevalence". The paper by Wojciech & Ewa Pisula [1] (open-access) does indeed suggest that there may "a correlation between increasing meat consumption and autism prevalence".

"Goonies never say die!"

Readers are invited to draw their own conclusions on such a correlation. Personally, I'm not yet convinced that meat consumption is the primary driving force behind the increase in cases of autism being diagnosed worldwide outside of any mention of the word 'correlation'.

I am however open to further study on aspects of food or food production potentially being linked to autism in some roundabout way as per areas talking about dioxin exposure through food consumption (see here) or even animal antibiotic use being linked into changing gut microbiota [2] (open-access) (see here too) bearing in mind my not over-selling the whole gut bacteria bit (see here).

I might also draw your attention to some "fundamental limitations" that the authors include about their hypothesis:

"1. None of the authors is an epidemiologist. Our experience is in different fields, namely comparative psychology (first author) and clinical child psychology (second author).

2. The data presented here do not cover sufficient ground to facilitate the proposal of a precise hypotheses.

3. We did not have enough data to run confirmatory analyses, therefore we have limited ourselves to purely correlational statistics, while providing raw numbers retrieved from the cited sources.

4. It is very likely that the real variable that may definitively explain the observed correlations remains invisible, and what we see is just a surface aspect of the phenomenon."

'Nuff said.

And speaking of meat, I'll also draw your attention to the recent BBC Horizon programme looking at meat and health by Dr Michael Mosley (see here). Although not the best of Dr Mosley's TV efforts (particularly the 'making sense of the statistics' section and the N=1 experiment) the message seems to be that meat - real meat not the processed stuff - in moderation is probably not going to be particularly harmful to health for those that choose an omnivorous diet. Oh, and fat isn't necessarily the bad guy but those trillions of beasties which inhabit our gut might need some further inspection [3]. If however you want an alternative form of animal protein which has a more environmentally friendly footprint, how about mussels a few times a week?

Some music then and having finally taken the plunge into the wonder that is Spotify, I discovered a bit of a blast from the past: A.M. 180 from Grandaddy. Be prepared for more nuggets in future posts...

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[1] Pisula W. & Pisula E. Autism prevalence and meat consumption - a hypothesis that needs to be tested. Medical Hypotheses. 2014. August 14.

[2] Forslund K. et al. Country-specific antibiotic use practices impact the human gut resistome. Genome Res. 2013. 23: 1163-1169

[3] Koeth RA. et al. Intestinal microbiota metabolism of L-carnitine, a nutrient in red meat, promotes atherosclerosis. Nature Medicine. 2013; 19: 576–585.

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Wojciech Pisula, & Ewa Pisula (2014). Autism prevalence and meat consumption - a hypothesis that needs to be tested Medical Hypotheses : 10.1016/j.mehy.2014.08.007

Dioxin exposure and autistic traits?

As promised in a previous post, today I'm turning my attention to the paper by Muneko Nishijo and colleagues [1] and their conclusion of "a specific impact of perinatal TCDD [2,3,7,8-tetrachlorodibenzo-p-dioxin] on autistic traits in childhood, which is different from the neurotoxicity of total dioxins (PCDDs/Fs) [polychlorinated dibenzo-p-dioxins/furans]".

TCDD @ Wikipedia 

With all the recent chatter about [surrogate] environmental markers and the numbers of cases of autism spectrum disorders and environmental toxicants and autism risk it is indeed timely that the Nishijo paper comes to publication now. Environmental factors, however you wish to define this, are certainly no stranger to autism research, and are fast finding a place in the autism research psyche, perhaps in part due to the rise and rise of the science of epigenetics (see here) as a bridge between genetics and environment. Genes, or rather the blueprint that is your genome, might not necessarily be your destiny and all that jazz...

The Nishijo paper in a little more detail:

• Set in Vietnam, which it has to be said, has seen more than its fair share of chemical exposures in recent history, the authors looked at the possibility of perinatal dioxin exposure being linked to the presence of autistic traits based on a sample of 153 infants. This follows other work by this group looking at dioxin exposure and more generalised infant neurodevelopment [2] as part of a wider research agenda. Dioxins for those who might not know, are categorised as environmental pollutants, and because of their biological persistence, are deemed pretty hazardous to human and other animal health (see the WHO fact sheet here). It's accurate that I mentioned Agent Orange in reference to the chemical load witnessed in Vietnam because Agent Orange was contaminated with TCDD - the chemical name for dioxin -  and there are some very scary quotes about TCDD being for example "perhaps the most toxic molecule ever synthesized by man". The US IOM report 'Veterans and Agent Orange' provides some sober reading on the topic.
• Scare tactics aside, the authors assessed the levels of TCDD in breast milk as part of a larger analysis of various other dioxins (PCDDs, PCDFs) based on analysis of samples via GC-MS. Actually quite a good overview of their methods can be found in another paper by this group [3] (open-access). Data from these analyses were transformed to form something called the TEQ (Toxic Equivalent) which basically gives you some idea of the toxicity of these classes of compounds relative to TCDD. TCDD has a value of 1 so setting the gold standard of toxicity. 
• Offspring were followed-up based on the use of the Bayley Scales of Infant and Toddler Development, Third Edition (Bayley-III) and specifically with autism in mind, the Autism Spectrum Rating Scales (ASRS).  
• Results: exposure groups (mild and high) were determined according to a cut-off level of 3.5 pg/g fat of TCDD being detected and results were reported according to gender. So: "The high-2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposed groups... showed significantly higher Autism Spectrum Rating Scale (ASRS) scores for both boys and girls than the mild-TCDD exposed groups, without differences in neurodevelopmental scores". This indicates some kind of dose-dependent relationship between TCDD exposure and autistic traits in study participants. When it came to looking at any connection between other PCDDs/Fs and autistic traits, nothing significant was picked up. Ergo, TCDD exposure seemed to have specifically impacted on infant autistic traits.

These are interesting results, of that there is no doubt. I could start to go on about correlation not being the same as causation, or how the ASRS might not necessarily have been the best instrument to use in this particular instance given it being standardised on American children and not officially translated into Vietnamese. That also it is not a professionally-administered instrument is another potential gap. But I'm not going to let all that get too far in the way of the Nishijo findings.

I see from some of the additional data from this paper that there were some other differences noted across the high and mild TCDD exposure groups which may be relevant to the results. When comparing boys and girls in the high and mild exposure groups, I note that mean birth weight was lower in the high exposed group compared to the mild exposed group (average 2920g vs. 3298g respectively) for boys. Realising that low birth weight is not an exclusively autism-correlated phenomena (see here) one might however consider this to be something which could potentially have affected the results obtained.

As per the discussions about the geographical location of this study [4], one of the question which then needs to be asked is whether the possibility of a TCDD exposure link is something applicable to other areas and other cases of autism/autistic traits. I'm no expert on TCDD so cannot readily answer this question aside from directing you to some data from the US Environmental Protection Agency on sources of TCDD. It does appear that there are quite a few potential sources of TCDD; although food seems to be the most widely cited source of exposure in modern times. By saying that I'm not trying to panic anyone, given that many countries do monitor foods for dioxin levels (see here) and act accordingly when high levels are detected.

Still, if we assume that there may be many roads towards a diagnosis of autism or the presentation of autistic traits, and that those roads may not be the same in every part of the world, the Nishijo results make for an interesting addition to the research landscape. As to mechanisms of effect, well take your pick; TCDD is categorised an endocrine disruptor so potentially falling into the same type of effect as that discussed by Rzhetsky and colleagues [5]. I also note some research chatter about TCDD and GABA [6] with specific mention of GAD (see here for some description of what this is). Jumping on the epigenetics bandwagon however, one might also suggest some further inquiry in that area if results like those by Manikkam and colleagues [7] are anything to go by, bearing in mind the continued focus on sperm and eggs and autism risk. That all being said, I don't doubt that it's going to be a complicated effect from TCDD with various factors involved.

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[1] Nishijo M. et al. 2,3,7,8-Tetrachlorodibenzo-p-dioxin in breast milk increases autistic traits of 3-year-old children in Vietnam. Mol Psychiatry. 2014 Mar 18.

[2] Tai PT. et al. Dioxin exposure in breast milk and infant neurodevelopment in Vietnam. Occup Environ Med. 2013 Sep;70(9):656-62.

[3] Nishijo M. et al. Impact of perinatal dioxin exposure on infant growth: a cross-sectional and longitudinal studies in dioxin-contaminated areas in Vietnam. PLoS One. 2012;7(7):e40273.

[4] Banout J. et al. Agent orange footprint still visible in rural areas of central Vietnam. J Environ Public Health. 2014;2014:528965.

[5] Rzhetsky A. et al. Environmental and state-level regulatory factors affect the incidence of autism and intellectual disability. PLoS Comput Biol. 2014 Mar 13;10(3):e1003518.

[6] Hays LE. et al. Evidence that GABAergic neurons in the preoptic area of the rat brain are targets of 2,3,7,8-tetrachlorodibenzo-p-dioxin during development. Environ Health Perspect. 2002 Jun;110 Suppl 3:369-76.

[7] Manikkam M. et al. Dioxin (TCDD) Induces Epigenetic Transgenerational Inheritance of Adult Onset Disease and Sperm Epimutations. PLoS ONE. 2012; 7(9): e46249.

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Nishijo M, Pham TT, Nguyen AT, Tran NN, Nakagawa H, Hoang LV, Tran AH, Morikawa Y, Ho MD, Kido T, Nguyen MN, Nguyen HM, & Nishijo H (2014). 2,3,7,8-Tetrachlorodibenzo-p-dioxin in breast milk increases autistic traits of 3-year-old children in Vietnam. Molecular psychiatry PMID: 24637425