Wednesday, 7 May 2014

Oxidative stress inducing mitochondrial dysfunction in autism?

Consider this post a sort of accompaniment to my recent chatter about the paper by Suzanne Goh and colleagues on brain lactate levels and mitochondrial dysfunction as a neurobiological subtype of autism (see here). Read on...

I've probably mentioned it before but outside of some light reading around the topic, mitochondria (plural) and mitochondrial dysfunction still remains a source of bafflement to me. Yes, I think I know the basics as per my learner post (see here) but it's the kinda of topic where I need to keep reading and re-reading sentences before any sense comes of it.
Bord de mer II @ Wikipedia 

It is therefore with a degree of trepidation that I approach the paper by Shannon Rose and colleagues [1] (open-access here) and their conclusion: "a significant subgroup of AD [autistic disorder] children may have alterations in mitochondrial function, which could render them more vulnerable to a pro-oxidant microenvironment as well as intrinsic and extrinsic sources of ROS [reactive oxygen species] such as immune activation and pro-oxidant environmental toxins". I might add that reports of mitochondrial dysfunction in cases of autism are seemingly increasing in the peer-reviewed literature [2].

OK, in very small steps, a few things to talk about here outside of my previous links to describing mitochondria shown above. ROS - reactive oxygen species - describes as the name suggests, molecules which contain oxygen (the important stuff that most creatures including us humans rely on for living). ROS are both a by-product of living (endogenous production) and can produced via other external sources (exogenous ROS). Endogenous production of ROS involves mitochondria, the so-called power plants in cells. Oxygen and various simple sugars are used to create ATP (adenosine triphosphate) as part of the process of oxidative phosphorylation. ROS are a by-product of this reaction which under certain circumstances can result in cell damage.

I'll also draw your attention to the concept of oxidative stress and it's relevance to this story. Basically, the body has ways to ensure that ROS production doesn't get out of hand via various cellular antioxidants. Regular readers of this blog might have already comes across some discussions on one of those antioxidants - glutathione - and the various findings in relation to autism (see here). As long as a happy balance is struck between appropriate levels of ROS and the scavenging availability of antioxidants, everything should tick along just fine. If however, ROS start to get the upper hand as described by the term oxidative stress, all sorts of effects can occur such as lipid peroxidation and oxidative damage to DNA. Ergo, balance is an important concept.

Back to the Rose paper then, which relied on something called lymphoblastoid cell lines (LCLs) as a means of measuring something called reserve capacity: "a measure of the ability of the mitochondria to respond to physiological stress" in cases of autism. LCLs came from the AGRE or the NIMH and researchers looked at mitochondrial reserve capacity "before and after exposure to reactive oxygen species (ROS)". Actually that wasn't the only research done on these LCLs, as the effect of N-acetylcysteine (NAC), "a glutathione precursor", pretreatment was also reported in the paper. The agent of choice for representing ROS in the study was something called DMNQ by the way.

Results, bearing in that I'm not going to go into the details of all the results because it's all there in open-access form for your interpretation:

  • First and foremost: "LCLs derived from children with AD exhibit significant abnormalities in mitochondrial respiration after exposure to increasing levels of ROS". I temper those words with the authors suggestion that getting on for about half of the LCLs looked at (44%) seemed to drive the results obtained for the autism group. This might imply that in amongst all the talk about plural autisms, a sizeable subgroup of people on the autism spectrum may demonstrate such issues.
  • "NAC rescues the atypical mitochondrial respiratory response". So, that pretreatment of the LCLs with NAC, specifically those 44% (10/22) who showed an abnormal adaptive response to ROS, seemed to improve mitochondrial respiration. This effect was not significantly present in the remaining LCLs from participants with autism.
  • Glutathione (GSH) levels were also checked in cells (intracellular free GSH and also reduced glutathione - GSSG). As probably would be expected based on the other research literature in this area [3] lower glutathione levels were reported in the LCLs from participants with autism and a higher GSSG compared with controls. Perhaps not unexpectedly: "Pretreatment with NAC increased intracellular GSH and the GSH/GSSG ratio and reduced GSSG" in the LCLs from participants with autism.
  • There are various other findings reported but the authors summarise by saying: "we demonstrate a new type of mitochondrial disorder that may affect a significant subgroup of AD children and provide insight into the interactions between systems that have been independently demonstrated to be abnormal in ASD [autism spectrum disorder]".

I know that I have gone on a little bit in this post because of the often quite technical jargon which is included in a study like this, so for that I apologise. My amateur status when it comes to talking about mitochondria and autism has probably not helped matters but I hope you can seem some glimmers of what the important results were derived from this relatively small-scale study. And yes, replication - independent replication - is an absolute must for this area of research bearing in mind facets of these results overlap with previous research by some of the same authors [4] and also here [5]. I might also add that other groups have started to talk about similar processes being involved in some autism too [6].

That all being said, I think you can see how important this work might eventually turn out to be when it comes to the area of mitochondrial dysfunction and autism, and indeed the possibility of links with other important areas of work such as the glutathione and NAC stories. Once again, I'm waiting attentively to see other published results in this area... including further replication of even more results from Napoli and colleagues [7] further discussed here.

And just in case my explanation of this area of work still leaves you baffled, I'll hand over to the experts and their recent review paper [8] ...

[Update: 16 March 2015: a clarification has been published over the paper from Rose and colleagues. Overlapping results had been mentioned...]

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[1] Rose S. et al. Oxidative stress induces mitochondrial dysfunction in a subset of autistic lymphoblastoid cell lines. Transl Psychiatry. 2014 Apr 1;4:e377.

[2] Giulivi C. et al. Mitochondrial Dysfunction in Autism. JAMA. 2010; 304(21): 2389–2396.

[3] Main PAE. et al. The potential role of the antioxidant and detoxification properties of glutathione in autism spectrum disorders: a systematic review and meta-analysis. Nutr Metab (Lond). 2012; 9: 35.

[4] James SJ. et al. Cellular and mitochondrial glutathione redox imbalance in lymphoblastoid cells derived from children with autism. FASEB J. 2009 Aug;23(8):2374-83.

[5] Rose S. et al. Oxidative stress induces mitochondrial dysfunction in a subset of autism lymphoblastoid cell lines in a well-matched case control cohort. PLoS One. 2014 Jan 8;9(1):e85436.

[6] Napoli E. et al. Evidence of reactive oxygen species-mediated damage to mitochondrial DNA in children with typical autism. Mol Autism. 2013 Jan 25;4(1):2.

[7] Napoli E. et al. Deficits in Bioenergetics and Impaired Immune Response in Granulocytes From Children With Autism. Pediatrics. 2014. April 21.

[8] Rossignol DA. & Frye RE. Evidence linking oxidative stress, mitochondrial dysfunction, and inflammation in the brain of individuals with autism. Front. Physiol. 2014. April 22.

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ResearchBlogging.org Rose, S., Frye, R., Slattery, J., Wynne, R., Tippett, M., Melnyk, S., & James, S. (2014). Oxidative stress induces mitochondrial dysfunction in a subset of autistic lymphoblastoid cell lines Translational Psychiatry, 4 (4) DOI: 10.1038/tp.2014.15