|Sprouts, sprouts, sprouts @ Wikipedia|
Up until this point, the collected research looking at glutathione in relation to autism had however tended to be focused on circulating levels of glutathione in its various forms alongside the enzymes supporting its important tasks. Enter then a paper published by Rose and colleagues* (full-text) on glutathione, the brain and autism previously described at IMFAR 2012 (here). You may have spotted a few familiar names on the authorship panel of this paper including Jill James (hypomethylation and autism) and Richard Frye (folate receptor autoantibodies).
Aside from a couple of forays into the world of brain research and the autism spectrum (see here for example), I have tended to keep away from discussing such investigations in too much detail on this blog. My reasoning: adhering to the phrase 'a cobbler should stick to his last', coupled with a view that the various research focused on the brain and autism just seemed so darned complicated. Suffice to say that it all brings back blurred memories of my undergraduate days where I admit to being more than a little confused about what brain region was supposed to do what.
In this post I am going to include some discussion on the findings reported by Rose et al albeit with the caveat that my brain may not be up to exploring all the avenues of potential interest related to these findings and what they mean.
Since I am discussing glutathione, I also want to bring to your attention some slightly more 'preliminary' findings reported in this poster by Cruikshank and Wood** on urinary glutathione in relation to autism. The caveat here being that this is not a peer-reviewed piece of research and hence still requires quite a lot more work before being taken as Gospel (despite the recent media interest).
Back to Dr Rose's paper:
- This was a study of post-mortem brain specimens. In light of the recent news of a freezer malfunction linked to the destruction of a number of stored brain tissue samples from people with autism, there is a degree of poignancy to this study reiterating how valuable these types of tissue are to furthering autism research.
- Samples from two areas of the brain - the cerebellum and Brodmann area 22 (BA22) (part of the superior temporal gyrus) - were studied, comparing samples from people with autism (n=15 & n=12 for the two areas) with control specimens. These brain areas have been talked about before with autism in mind (here and here) as the name Eric Courchesne drifts into my consciousness.
- Levels of various compounds were examined in samples including: reduced glutathione (GSH), oxidised glutathione disulfide (GSSG), 3-nitrotyrosine (3-NT) and 3-chlorotyrosine (3-CT); calculating glutathione redox/antioxidant capacity (GSH/GSSG), oxidative protein damage and oxidative DNA damage (8-oxo-deoxyguanosine; 8-oxo-dG). Aconitase activity was also measured.
- The results: in both brain regions, all studied compounds were altered at a group level in cases of autism compared to controls. So, levels of glutathione (GSH) were decreased in both brain areas compared to control samples (43% and 32% reductions in cerebellum and BA22 respectively). Levels of oxidised glutathione disulfide (GSSG) were elevated in autism vs. controls in both brain areas (18% vs. 19% elevations respectively) and overall glutathione redox/antioxidant capacity (GSH/GSSG) was significantly different in autism vs. controls. These findings are roughly in line with what has been reported in studies of other tissues in cases of autism.
- Oxidative stress and oxidative protein damage markers were also significantly elevated in the autism group vs. controls in both brain areas. Aconitase activity was significantly lower in the autism group in the cerebellum but escaped significance in relation to BA22.
- The authors note: "decreased glutathione-mediated redox/antioxidant capacity previously observed in plasma and immune cells from children with autism is also significantly decreased in two brain regions previously shown to be affected in autism, the cerebellum and BA22".
There is quite a bit of information to take in from this study and as a result, several important things which will require some external replication with suitable age and sex matched controls. Oxidative stress / damage is something that tends to get banded around quite a lot in these days of the free radical. Rose and colleagues have now provided some very important preliminary flesh on the bones to this story, suggesting "functional consequences" on specific brain areas previously linked to autism following their results. Their findings also pretty much confirm what quite a few others have been saying about glutathione in relation to cases of autism: whether causative or epiphenomenal, there's something amiss with the whole oxidative stress / antioxidant balance in at least a proportion of cases of autism and it may well extend beyond just a casual relationship.
I note also their findings with regards to glutathione redox/antioxidant capacity (GSH/GSSG) and 8-oxo-dG in the cerebellum. Combining autism cases and control data, the authors report on an important relationship between how well the GSH/GSSH capacity performs and the amount of oxidative DNA damage potentially present. Similar things have been reported in other studies so no real surprises there.
I'm not going to get too far into the findings with regards to decreased aconitase activity in the autism cases and its link to mitochondrial oxidative stress. If you really want some reading on the subject, this paper by Cantu and colleagues**** (full-text) should keep you going for a while. Suffice to say that mitochondrial aconitase inactivation might have some pretty negative implications as per this article by Vasquez-Vivar and colleagues***** (full-text).
Just a couple of more things to add then I'm done. The suggestion of "a chronic neuroinflammatory state" at the brain sites under investigation has to be included in any synopsis. Neuroinflammation in autism is a topic that has cropped up quite a few times in the research literature. To pick out one study that springs to mind, the findings from Vargas and colleagues****** and their introduction of microglia into the mix is a case in point. Microglia is another area not readily touched upon this blog so in this case I will perhaps refer you to a nice blog post by Paul Patterson on the topic of hungry microglia potentially eating synapses in autism. I'm not necessarily saying that this is an essential part of the Rose findings but it could be a potentially important tie-in.
The link between elevated levels of 3-NT and elevated nitric oxide (NO) production described in the Rose paper is a final point. The mechanism for this relationship is explained pretty well here. I've covered some of the work on elevated NO metabolites and autism in a previous post. The net results seeming to indicate that levels of NO metabolites are elevated quite consistently in cases of autism. And then there is the inflammation link which has been covered quite a bit before.
OK that's enough for now. You might have realised that I am fairly interested in this paper by Rose and colleagues despite the preliminary nature of their study and the limitations of my knowledge in the area of the brain in autism. Yet another good reason why glutathione in relation to autism deserves a lot more research interest alongside tentative suggestions on whether we might actually be able to do something about it (see previous post).
To finish, how very dare they make this song which implies a world without Brussels sprouts. You will eat your phenylthiocarbamide and like it...
* Nijhoff WA. et al. Effects of consumption of Brussels sprouts on intestinal and lymphocytic glutathione S-transferases in humans. Carcinogenesis. 1995; 16: 2125-2128.
** Rose S. et al. Evidence of oxidative damage and inflammation associated with low glutathione redox status in the autism brain. Translational Psychiatry. July 2012.
*** Cruikshank C. & Wood T. Quantitation of glutathione as a urinary autism biomarker (poster).
**** Cantu D. et al. Oxidative inactivation of mitochondrial aconitase results in iron and H2O2-mediated neurotoxicity in rat primary mesencephalic cultures. PLoS ONE. 2009; 4: e7095.
***** Vasquez-Vivar J. et al. Mitochondrial aconitase is a source of hydroxyl radical. The Journal of Biological Chemistry. 2000; 275: 14046-14069.
****** Vargas DL. et al. Neuroglial activation and neuroinflammation in the brain of patients with autism. Annals of Neurology. 2005; 57: 67-81.
Rose S, Melnyk S, Pavliv O, Bai S, Nick TG, Frye RE, & James SJ (2012). Evidence of oxidative damage and inflammation associated with low glutathione redox status in the autism brain. Translational Psychiatry, 2 PMID: 22781167