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