Monday, 27 July 2015

Many things influence hydrogen sulfide metabolism

Some time ago hydrogen sulphide (H2S) was suggested to play a role in ME/CFS 1,2. Since then the general research literature has continued to forge ever more intricate and compelling links between H2S, health and disease. Gone are the days of H2S being exclusively viewed as an environmental toxicant; H2S is now widely recognised as a major biological mediator (even in mitochondria! 3). Recently H2S was even found to mediate the beneficial effects of dietary restriction on stress resistance and lifespan 4.

There are several sources of H2S in the body. H2S is produced by the transsulfuration enzymes (i.e. CBS and CSE), mitochondrial 3-MST, and can also be released from redox or pH-liable sulfur stores 5. H2S biochemistry is complex with many derivatives being formed which may mediate its biological effects 5,6. But generally H2S (or its derivatives) is active in the body as a redox signaling molecule, antioxidant and mitochondrial electron donor 3,5. Through these mechanisms H2S regulates many cellular processes and body systems (e.g. immune, neurological and cardiovascular systems).

So what things might influence the H2S system in health and disease? Apparently lots of things, as shown in my table below, some of which relate to specific tissues, cells or subcellular compartments.

As can be seen, many things can influence H2S. I wonder if this may create some dichotomies in ME/CFS, and other chronic conditions. For instance immune activation decreases H2S in the brain, but increases H2S in the periphery. Also autonomic dysfunction (parasympathetic dominance) might serve to augment vascular H2S. However nutritional deficiencies and elevated homocysteine could blunt H2S production everywhere. Also at a subcellular level, perhaps oxidative stress might inhibit 3-MST and lower H2S in mitochondria, hindering its pro-bioenergetic effects 3?

1.         Lemle, M. D. Hypothesis: chronic fatigue syndrome is caused by dysregulation of hydrogen sulfide metabolism. Med. Hypotheses 72, 108–9 (2009).
2.         De Meirleir, K., Roelant, C. & Fremont, M. Unravelling the Origin of Myalgic Encephalomyelitis: Gastrointesinal Dysfunction, Production of Neurotoxins and Environmental Exposure. in (2009). at
3.         Szabo, C. et al. Regulation of Mitochondrial Bioenergetic Function by Hydrogen Sulfide. Part I. Biochemical and Physiological Mechanisms. Br. J. Pharmacol. (2013). doi:10.1111/bph.12369
4.         Mitchell, J. R., Hine, C. M., Ph, D. & Mair, W. B. Endogenous Hydrogen Sulfide Production Is Essential for Dietary Restriction Benefits. Cell 160, 132–144 (2015).
5.         Kimura, H. Hydrogen sulfide and polysulfides as signaling molecules. Proc. Jpn. Acad. Ser. B. Phys. Biol. Sci. 91, 131–59 (2015).
6.         Mishanina, T. V, Libiad, M. & Banerjee, R. Biogenesis of reactive sulfur species for signaling by hydrogen sulfide oxidation pathways. Nat. Chem. Biol. 11, 457–464 (2015).
7.         Benavides, G. A. et al. Hydrogen sulfide mediates the vasoactivity of garlic. Proc. Natl. Acad. Sci. U. S. A. 104, 17977–82 (2007).
8.         Flannigan, K. L. et al. Impaired hydrogen sulfide synthesis and IL-10 signaling underlie hyperhomocysteinemia-associated exacerbation of colitis. Proc. Natl. Acad. Sci. U. S. A. 111, 13559–64 (2014).
9.         Li, J.-J. et al. Homocysteine Triggers Inflammatory Responses in Macrophages through Inhibiting CSE-H2S Signaling via DNA Hypermethylation of CSE Promoter. Int. J. Mol. Sci. 16, 12560–12577 (2015).
10.       Sen, U., Mishra, P. K., Tyagi, N. & Tyagi, S. C. Homocysteine to hydrogen sulfide or hypertension. Cell Biochem. Biophys. 57, 49–58 (2010).
11.       Mitsuhashi, H. et al. Oxidative stress-dependent conversion of hydrogen sulfide to sulfite by activated neutrophils. Shock 24, 529–34 (2005).
12.       Kolluru, G. K., Shen, X. & Kevil, C. G. A tale of two gases: NO and H2S, foes or friends for life? Redox Biol. 1, 313–318 (2013).
13.       Módis, K., Asimakopoulou, A., Coletta, C., Papapetropoulos, A. & Szabo, C. Oxidative stress suppresses the cellular bioenergetic effect of the 3-mercaptopyruvate sulfurtransferase/hydrogen sulfide pathway. Biochem. Biophys. Res. Commun. 433, 401–7 (2013).
14.       Niu, W.-N., Yadav, P. K., Adamec, J. & Banerjee, R. S-glutathionylation enhances human cystathionine β-synthase activity under oxidative stress conditions. Antioxid. Redox Signal. 22, 350–61 (2015).
15.       Paul, B. D. & Snyder, S. H. H2S signalling through protein sulfhydration and beyond. Nature Reviews Molecular Cell Biology 13, 499–507 (2012).
16.       Carbonero, F., Benefiel, A. C., Alizadeh-Ghamsari, A. H. & Gaskins, H. R. Microbial pathways in colonic sulfur metabolism and links with health and disease. Front. Physiol. 3, 448 (2012).
17.       Shen, X. et al. Microbial regulation of host hydrogen sulfide bioavailability and metabolism. Free Radic. Biol. Med. 60, 195–200 (2013).
18.       Sen, N. et al. Hydrogen sulfide-linked sulfhydration of NF-κB mediates its antiapoptotic actions. Mol. Cell 45, 13–24 (2012).
19.       Zheng, Y. et al. Lipopolysaccharide regulates biosynthesis of cystathionine γ-lyase and hydrogen sulfide through Toll-like receptor-4/p38 and Toll-like receptor-4/NF-κB pathways in macrophages. In Vitro Cell. Dev. Biol. Anim. 49, 679–88 (2013).
20.       Miller, T. W. et al. Hydrogen sulfide is an endogenous potentiator of T cell activation. J. Biol. Chem. 287, 4211–21 (2012).
21.       Wallace, J. L., Ferraz, J. G. P. & Muscara, M. N. Hydrogen sulfide: an endogenous mediator of resolution of inflammation and injury. Antioxid. Redox Signal. 17, 58–67 (2012).
22.       Dufton, N., Natividad, J., Verdu, E. F. & Wallace, J. L. Hydrogen sulfide and resolution of acute inflammation: A comparative study utilizing a novel fluorescent probe. Sci. Rep. 2, 499 (2012).
23.       Lee, M., Schwab, C., Yu, S., McGeer, E. & McGeer, P. L. Astrocytes produce the antiinflammatory and neuroprotective agent hydrogen sulfide. Neurobiol. Aging 30, 1523–34 (2009).
24.       Gong, Q.-H. et al. Hydrogen sulfide attenuates lipopolysaccharide-induced cognitive impairment: a pro-inflammatory pathway in rats. Pharmacol. Biochem. Behav. 96, 52–8 (2010).
25.       Gong, Q.-H. et al. S-propargyl-cysteine, a novel hydrogen sulfide-modulated agent, attenuates lipopolysaccharide-induced spatial learning and memory impairment: involvement of TNF signaling and NF-κB pathway in rats. Brain. Behav. Immun. 25, 110–9 (2011).
26.       Manna, P. & Jain, S. K. Vitamin D up-regulates glucose transporter 4 (GLUT4) translocation and glucose utilization mediated by cystathionine-γ-lyase (CSE) activation and H2S formation in 3T3L1 adipocytes. J. Biol. Chem. 287, 42324–32 (2012).
27.       Wiliński, B., Wiliński, J., Somogyi, E., Piotrowska, J. & Opoka, W. Vitamin D3 (cholecalciferol) boosts hydrogen sulfide tissue concentrations in heart and other mouse organs. Folia Biol. (Praha). 60, 243–7 (2012).

Monday, 13 July 2015

Why does gut dysbiosis always involve Enterobacteriaceae?

Several studies by Maes et al. have implicated Enterobacteriaceae in CFS. Specifically there are elevated antibody responses to the LPS of commensal Enterobacteriaceae which correlates immune markers and abdominal symptoms 1,2. This suggests Enterobacteriaceae or their components (LPS) have translocated from the gut into the body (i.e. leaky gut) and stimulated an immune response. This post compiles some factors found to influence Enterobacteriaceae growth and translocation in other diseases, which may also be of some relevance in ME/CFS.

Enterobacteriaceae and disease
Enterobacteriaceae are a large family of gram-negative facultative bacteria, which belong to the class Gammaproteobacteria and phylum Proteobacteria. The Enterobacteriaceae family contains gut symbionts but also many familiar pathogens (e.g. Klebsiella, E. coli, Salmonella, Citrobacter, Enterobacter, etc). Proteobacteria and Enterobacteriaceae are normally present in the gut at relatively low levels, and exist in close proximity to the mucosa, since as facultative bacteria they can tolerate oxygen diffusing from the epithelium 3. However they are amongst the most frequently overgrown gut bacteria in many conditions, including gut infections, IBD, IBS, constipation, celiac disease, AIDS, SIRS, obesity, Parkinson’s disease and major depression.

Enterobacteriaceae promote disease via immune activation; largely because they are a major source of potent inflammatory PAMPs such as lipopolysaccharide (LPS) 4. For instance in the gut Enterobacteriaceae/LPS can increase inflammatory tone 5, slow intestinal motility 6, exacerbate NSAID-induced intestinal injury 7, increase intestinal permeability in celiac disease 8, promote intestinal hypersensitivity in IBS 9 and exacerbate inflammation in IBD, amongst other things. Translocation of LPS into blood is associated with systemic immune activation, neuroinflammation 10, insulin resistance 11, etc.

So elevated levels of Enterobacteriaceae is bad! But how does it occur in the first place? Below are some mechanisms which could be important.

Dietary factors
Diets high in sugar, fat and protein, but low in plants and indigestible carbohydrate (e.g. western or weight-loss diets), favour the growth of Proteobacteria and Enterobacteriaceae 12,13. This could be for several reasons. Diets high in protein promote a putrefactive microbial metabolism which generates harmful metabolites 14, while diets high in indigestible carbohydrate (resistant starch and fibre) promote a saccharolytic metabolism which generates beneficial short-chain fatty acids (SCFAs) 12. SCFAs acidify the colon and inhibit Enterobacteriaceae 12. Diets high in fat, saturated fat and omega-6 promote Enterobacteriaceae growth and LPS translocation, while omega-3 does the opposite 15–18. The beneficial effects of omega-3 on the gut microbiota are due to regulation of intestinal alkaline phosphatase (IAP) 18.

Low stomach acid
Suppression of gastric acid secretion by proton pump inhibitor (PPI) administration was found to induce jejunum dysbiosis, consisting of an overgrowth of aerobic bacteria and Enterobacteriaceae, and a decrease in Bifidobacteria 7. Many other studies have found an association between PPI use and small intestinal bacterial overgrowth (SIBO) in humans 19 (note that Enterobacteriaceae can be hydrogen-producers 20). This may involve several mechanisms: gastric acid can inhibit the growth of many bacteria, promote protein digestion and trigger other intestinal secretions/processes.

The gut barrier regulates levels of mucosal bacteria by releasing antimicrobial peptides and IgA 21,22. Innate immune functions are impaired in inflammatory bowel disease (IBD), especially Crohn’s disease, which allows for increased growth of bacteria such as invasive E. coli  23,24. Also genetic variations which impair function of the NOD2 gene (encodes an intracellular immune receptor) is associated with increased abundance of Enterobacteriaceae in IBD 25. In both HIV/AIDS and ICL there is major disruption of the intestinal immune system, resulting in barrier disruption and translocation of LPS 26,27.

Inflammation & oxidative stress
Gut inflammation has been shown to induce blooms in Proteobacteria and Enterobacteriaceae. This is due to the increased formation of oxidation products (e.g. nitrate) which can serve as electron acceptors in the anaerobic respiration of some facultative bacteria 28,29. In fact nitrate reductase activity is most prevalent in the genomes of Enterobacteriaceae 30. Moreover some Enterobacteriaceae pathogens (e.g. Salmonella) may actually induce inflammation as part of an evolutionary survival strategy 29. Notably antibiotic treatment can induce low-grade gut inflammation which enhances the growth of Enterobacteriaceae 28–30. Inflammation can also increase intestinal permeability and may therefore allow bacterial translocation, perhaps especially in the ileum 31.

1.         Maes, M. et al. Increased IgA responses to the LPS of commensal bacteria is associated with inflammation and activation of cell-mediated immunity in chronic fatigue syndrome. J. Affect. Disord. 136, 909–17 (2012).
2.         Maes, M., Leunis, J.-C., Geffard, M. & Berk, M. Evidence for the existence of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) with and without abdominal discomfort (irritable bowel) syndrome. Neuro Endocrinol. Lett. 35, 445–453 (2014).
3.         Albenberg, L. et al. Correlation Between Intraluminal Oxygen Gradient and Radial Partitioning of Intestinal Microbiota in Humans and Mice. Gastroenterology (2014). doi:10.1053/j.gastro.2014.07.020
4.         Hakansson, A. & Molin, G. Gut Microbiota and Inflammation. Nutrients 3, 637–682 (2011).
5.         Rodes, L. et al. Effect of probiotics Lactobacillus and Bifidobacterium on gut-derived lipopolysaccharides and inflammatory cytokines: an in vitro study using a human colonic microbiota model. J. Microbiol. Biotechnol. 23, 518–26 (2013).
6.         Pasqualetti, V. et al. Antioxidant activity of inulin and its role in the prevention of human colonic muscle cell impairment induced by lipopolysaccharide mucosal exposure. PLoS One 9, e98031 (2014).
7.         Wallace, J. L. et al. Proton pump inhibitors exacerbate NSAID-induced small intestinal injury by inducing dysbiosis. Gastroenterology 141, 1314–22, 1322.e1–5 (2011).
8.         Cinova, J. et al. Role of intestinal bacteria in gliadin-induced changes in intestinal mucosa: study in germ-free rats. PLoS One 6, e16169 (2011).
9.         Crouzet, L. et al. The hypersensitivity to colonic distension of IBS patients can be transferred to rats through their fecal microbiota. Neurogastroenterol. Motil. 25, (2013).
10.       Gárate, I. et al. Stress-induced neuroinflammation: role of the Toll-like receptor-4 pathway. Biol. Psychiatry 73, 32–43 (2013).
11.       Fei, N. & Zhao, L. An opportunistic pathogen isolated from the gut of an obese human causes obesity in germfree mice. ISME J. 7, 880–4 (2013).
12.       Simpson, H. L. & Campbell, B. J. Review article: dietary fibre-microbiota interactions. Aliment. Pharmacol. Ther. 42, 158–179 (2015).
13.       Brown, K., DeCoffe, D., Molcan, E. & Gibson, D. L. Diet-induced dysbiosis of the intestinal microbiota and the effects on immunity and disease. Nutrients 4, 1095–119 (2012).
14.       Windey, K., De Preter, V. & Verbeke, K. Relevance of protein fermentation to gut health. Mol. Nutr. Food Res. 56, 184–96 (2012).
15.       Kim, K.-A., Gu, W., Lee, I.-A., Joh, E.-H. & Kim, D.-H. High fat diet-induced gut microbiota exacerbates inflammation and obesity in mice via the TLR4 signaling pathway. PLoS One 7, e47713 (2012).
16.       Ghosh, S. et al. Fish oil attenuates omega-6 polyunsaturated fatty acid-induced dysbiosis and infectious colitis but impairs LPS dephosphorylation activity causing sepsis. PLoS One 8, e55468 (2013).
17.       Mani, V., Hollis, J. H. & Gabler, N. K. Dietary oil composition differentially modulates intestinal endotoxin transport and postprandial endotoxemia. Nutr. Metab. (Lond). 10, 6 (2013).
18.       Kaliannan, K., Wang, B., Li, X.-Y., Kim, K.-J. & Kang, J. X. A host-microbiome interaction mediates the opposing effects of omega-6 and omega-3 fatty acids on metabolic endotoxemia. Sci. Rep. 5, 11276 (2015).
19.       Fujimori, S. What are the effects of proton pump inhibitors on the small intestine? World J. Gastroenterol. 21, 6817–9 (2015).
20.       Bures, J. et al. Small intestinal bacterial overgrowth syndrome. World J. Gastroenterol. 16, 2978–90 (2010).
21.       Wang, G. Human antimicrobial peptides and proteins. Pharmaceuticals (Basel). 7, 545–94 (2014).
22.       Kubinak, J. L. et al. MyD88 Signaling in T Cells Directs IgA-Mediated Control of the Microbiota to Promote Health. Cell Host Microbe 17, 153–163 (2015).
23.       Gersemann, M., Wehkamp, J. & Stange, E. F. Innate immune dysfunction in inflammatory bowel disease. J. Intern. Med. 271, 421–8 (2012).
24.       Glocker, E. & Grimbacher, B. Inflammatory bowel disease: is it a primary immunodeficiency? Cell. Mol. Life Sci. 69, 41–8 (2012).
25.       Knights, D. et al. Complex host genetics influence the microbiome in inflammatory bowel disease. Genome Med. 6, 107 (2014).
26.       Lee, P. I. et al. Evidence for translocation of microbial products in patients with idiopathic CD4 lymphocytopenia. J. Infect. Dis. 199, 1664–70 (2009).
27.       Klatt, N. R., Funderburg, N. T. & Brenchley, J. M. Microbial translocation, immune activation, and HIV disease. Trends Microbiol. 21, 6–13 (2013).
28.       Winter, S. E. & Bäumler, A. J. Why related bacterial species bloom simultaneously in the gut: Principles underlying the ‘like will to like’ concept. Cell. Microbiol. 16, 179–184 (2014).
29.       Winter, S. E., Lopez, C. a & Bäumler, A. J. The dynamics of gut-associated microbial communities during inflammation. EMBO Rep. 14, 319–27 (2013).
30.       Winter, S. E. & Bäumler, A. J. Dysbiosis in the inflamed intestine: chance favors the prepared microbe. Gut Microbes 5, 71–3 (2014).
31.       Yue, C., Ma, B., Zhao, Y., Li, Q. & Li, J. Lipopolysaccharide-induced bacterial translocation is intestine site-specific and associates with intestinal mucosal inflammation. Inflammation 35, 1880–8 (2012).