Research ArticleImpact of oral vancomycin on gut microbiota, bile acid metabolism, and insulin sensitivity
Graphical abstract
Introduction
The intestinal microbiota consists of several thousands of species, which collectively maintain gut physiology and homeostasis [1], including metabolic energy balance and immune responses [2], [3]. Recent studies in both mice and humans revealed a novel concept in which, depending on genotype and lifestyle, the changes in intestinal microbiota are thought to actively contribute to the development of obesity and systemic insulin resistance [4], [5], [6], [7]. In line, obesity has been found to be associated with significant alterations in the composition of the intestinal microbiota [7], [8], [9], [10]. Landmark experiments by Gordon and colleagues elegantly provided evidence for a regulating function of the gut microbiota in energy homeostasis [7], [9]. Germ-free mice were shown to be protected from obesity and insulin resistance when consuming a high fat diet [11], [12], whereas colonization led to increased body fat content with concomitant insulin resistance [13]. The fact that colonization of germ-free mice with microbiota obtained from obese mice induced an even greater increase in (visceral) adipose tissue lends further support to a causal relation between gut microbiota, systemic fat and insulin homeostasis [9], [14]. Recently, we have extrapolated these experimental findings towards human pathophysiology as we demonstrated that transfer of lean donor fecal microbiota to obese subjects with the metabolic syndrome significantly altered the composition of the intestinal microbiota, which was associated with an improvement of peripheral insulin sensitivity [15].
Oral antibiotic treatment results in short- and long-term changes of the intestinal microbiota in both mice and humans [16], [17], [18], [19]. Long-term intravenous vancomycin administration was also reported to correlate with the development of obesity in a retrospective study [20]. Recently, animal and human studies implicated that prolonged antibiotic treatment early after birth is associated with an increased risk of overweight [21], [22]. In line, it has been long recognized that antibiotic treatment can induce profound changes in bile acid metabolism [23]. Primary bile acids (i.e., cholate and chenodeoxycholate) are produced in the liver from cholesterol by the enzyme cholesterol 7α-hydroxylase (CYP7A1). Prior to their secretion into the small intestine, bile acids are conjugated with either taurine or glycine. Subsequently, intestinal microbiota further modify the bile acids within the intestine [24]. Several gram-positive bacterial species, such as Lactobacilli deconjugate primary bile acids [24], which is in contrast to most gram-negative intestinal bacteria, with the exception of two strains of Bacteroides [25]. After deconjugation, additional microbial modifications occur, including oxidation and dehydroxylation, giving rise to the formation of secondary bile acids [26], which is only carried out by a minor population of gram-positive anaerobic Clostridium species [27], [28], [29], [30]. Interestingly, bile acids have recently emerged as potential regulators of systemic energy homeostasis. For example, binding of particularly secondary bile acids (i.e., deoxycholate and lithocholate) to the G protein-coupled receptor TGR5 in the intestine strongly induces secretion of the incretin GLP-1, thereby affecting glucose homeostasis [31], [32], [33].
To date, it is poorly understood whether and to what extent intestinal bacteria are involved in the regulation of human bile acid and energy homeostasis. In view of the different role of gram-positive and -negative bacteria in intestinal bile acid metabolism, modification of either of these bacteria may have distinct effects on bile acid homeostasis. We thus hypothesize that the intestinal microbiota composition can affect bile acid composition with subsequently altered FGF-19 signaling thereby affecting glucose metabolism. In the present study, we thus set out to evaluate the impact of two different antibiotic regimens known to affect murine bile acid metabolism (amoxicillin and vancomycin orally administered) on intestinal microbiota composition, bile acid homeostasis and systemic insulin sensitivity in humans. We show that reduction of the gram-positive intestinal microbiota by vancomycin is associated with a decrease in peripheral insulin sensitivity in obese subjects and that modulation of the bile acid pool may be instrumental in mediating this effect.
Section snippets
Subjects
Male Caucasian obese subjects were recruited via local advertisements and screened for characteristics of the metabolic syndrome, including waist circumference >102 cm and fasting plasma glucose >5.6 mmol/L [34]. Subjects with a history of cholecystectomy, as well as subjects who used any medication (including probiotics and/or antibiotics in the past 3 months) were excluded. All subjects had a stable weight for 3 months prior to inclusion. Written informed consent was obtained from all subjects.
Baseline characteristics
Twenty male subjects fulfilling the criteria of the metabolic syndrome were randomized to either amoxicillin (500 mg t.i.d.) or vancomycin (500 mg t.i.d.) (Supplementary Fig. 1). Table 1 shows the baseline characteristics for both groups. Almost half of the volunteers in each treatment group reported diarrhea during antibiotic treatment, and no difference was found in the reported stool frequency or compliance between the two treatment groups. No other side effects were noted and there was no
Discussion
We show that following 7 days of oral vancomycin administration in male subjects with metabolic syndrome, both peripheral insulin sensitivity and bile acid dehydroxylation were significantly impaired with a concomitantly marked change in intestinal microbiota composition. In contrast, treatment with amoxicillin did not have any effect on these parameters. Gram-positive bacteria (mostly affected by vancomycin) are thought to be more important in maintaining intestinal microbiota stability than
Financial support
M. Nieuwdorp: NWO-VENI Grant 2008 (016.096.044), E. van Nood: NWO-ZONMW VEMI Grant (170881001), M.R. Soeters: DFN Ruby Grant 2011, W.M. de Vos: NWO-Spinoza Grant 2008, R.S. Kootte and D. Reijnders (TIFN G003 Grant 2011).
Conflict of interest
The authors who have taken part in this study declared that they do not have anything to disclose regarding funding or conflict of interest with respect to this manuscript.
Authors’ contribution
M.N., F.H., J.B.L.H., A.K.G., J.A.R., E.S, E.E.B., E.G.Z, E.vanN., and W.M.deV. designed the study. A.V., C.O, L.J., I.R, R.S.K, M.R.S., and E.R. performed the research. M.K., M.T.A., M.J.S., F.K.K., G.M.D.T., E.K.S. J.J.H, C.vd.L., and I.P.K. provided analytic tools. S.F. performed the statistical analysis. M.N., A.V., C.O, W.M.deV., and A.K.G. drafted the paper; all authors critically reviewed the manuscript.
Acknowledgments
We are grateful to Ineke Heikamp-de Jong, Philippe Puylaert and Wilma Akkermans-van Vliet (Wageningen University) for their excellent laboratory assistance.
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