TOXICOLOGICAL HIGHLIGHT |
Variation in Gut Microbiota Strongly Influences Individual Rodent Phenotypes
Biological Chemistry, Biomedical Sciences Division, Faculty of Medicine, Imperial College, London, SW7 2AZ, UK
1 To whom correspondence should be addressed. E-mail: elaine.holmes{at}imperial.ac.uk.
Received July 4, 2005; accepted July 13, 2005
Key Words: gut microbiota rodent phenotypes; metabolic profiling.
Understanding genetic and phenotypic differences between experimental animals (both within a single population and between populations held at different sites) is potentially important in explaining variability in responses to drugs and other stressors. Population changes in endogenous and exogenous metabolism in laboratory animal colonies have often been ascribed to genetic drift in the experimental animals themselves. This undoubtedly occurs in laboratory rodents; however, phenotypic drift in animal colonies can have an immediate and potentially greater short term impact on normal physiological variation and mammalian metabolism, as exemplified by Robosky et al. in this issue of Toxicological Sciences. They describe clear and stable metabolic differentiation of two groups of rats of identical strain obtained from the same supplier, but housed in separate rooms within the supplier's barrier unit. These observations were based on urinary metabolite signatures defined by 1H NMR spectroscopy and mass spectrometry (MS), which comprise thousands of low-molecular-weight molecules in a range of concentrations that can be profiled and interpreted using computer-based pattern recognition methods.
The two distinct room-dependent phenotypes were predominantly distinguished by their major gut microbial mammalian co-metabolites, hippurate and 3-hydroxyphenylpropionic acid, indicating that animals in different locations were exposed to different microflora. Further minor metabolite differences between the two phenotypes were identified, giving a robust characterization of each phenotype. It is not known which of the two phenotypes described in this study are more representative of the strain, although most research articles showing NMR urinary profiles report hippurate (benzoyl glycine) as the dominant aromatic gut microbial-mammalian co-metabolite profile of both Sprague Dawley and Han Wistar rats (Gavaghan et al., 2000
; Phipps et al., 1998). Moreover, the direct effects of different microbial communities on drug metabolism are unknown. The metabolite profiles for each phenotype were shown to be stable for at least 1 year, indicating the effectiveness of the animal husbandry procedures. Robosky et al. go on to show that, on transferring animals from one room to the other, the urinary metabolite profile rapidly accommodated to match the dominant profile of the animals already resident there, such that animals originally excreting a greater ratio of chlorogenic acid metabolites to hippurate predominantly excreted hippurate after changing their location. On isolation of the transferred animals, the animals retained the newly acquired metabolite profile rather than reverting to their original metabolite excretion pattern, indicating that the change in microbial composition or activity resulted in the production of an ecologically stable population. Conflicting reports have been published regarding the perseverance of nutritionally or drug-modified microflora in humans, with some evidence for longer-term stability of the newly acquired microflora after altering the urinary microbial excretion product profile (Wang et al., 2005). Other studies have shown a reversal of the intervention-induced microflora changes (Tannock et al., 2000). This is of potentially great significance, as the two different co-metabolic phenotypes of the same animal strain are likely to have different drug metabolizing capabilities and may show different toxicological susceptibilities. The potential for such gut microbial variations to have an influence on drug metabolism and toxicity in man and animals has recently been reviewed (Nicholson et al., 2004, 2005), and therefore, this experimental study is particularly timely as it indicates that significant microbial variation in laboratory rodents is probably very common. Intestinal microflora have variously been associated both with the production of toxic or genotoxic metabolites from drugs and food components (Kassie et al., 2001; Upreti et al., 2004) and also with the detoxification of other chemicals, such as chromium complexes (Kuroda et al., 2004).
The role of changing symbiotic mammalian–microbial relationships in toxicology studies is poorly understood, and its impact little appreciated. However, the importance has been well documented in other areas, and a renewal of interest in the impact of symbiont microbes on mammalian health has lead to recent publications showing the association of particular strains of microbe with insulin resistance, autism, Crohn's disease, and other disorders of the GI tract, food allergies, cardiovascular disease, insulin resistance, and certain cancers (Dunne, 2001).
The gut microbes act in many ways that could impact on drug toxicity and carcinogenicity. First, many have a significant capability for metabolism of numerous endogenous and drug-related compounds; for example, the large intestine contains a complex and diverse microbial population demonstrating a level of metabolic activity comparable to that of the liver (Dunne, 2001). However, the capacity of the intestine for metabolism of drug candidates and other xenobiotics, and the importance of the gut microbiota in influencing the disposition, fate, and toxicity of drugs in the host are often overlooked. Numerous studies conducted in 1970s and 1980s highlighted the influence of intestinal microbiota on drug metabolism (Rowland, 1986). The microbiota represent a significant route for metabolism of drugs and other xenobiotics and can significantly increase the half-life of xenobiotics in the body by hydrolysis and consequent reabsorption. Second, the gut microbes constantly dose the host with many drug-like substances that are co-metabolised by the host (Nicholson et al., 2003, 2005). It is easy to see how inducible enzyme systems could be modulated by these substances, resulting in changes in the disposition, metabolism, and fate of genuine drugs introduced into the system. Furthermore the gut microbes have major effects on the immune system, introducing possible modulations of drug interactions that may result in idiosyncratic toxicity.
Direct correlation of specific microbial species with urinary metabolites is challenging, since many of the active microbes are anaerobic and rely on other microorganisms for their survival, thereby making single bacterial colonies impractical to culture. However, metabolic profiling using NMR or MS provides an indirect means of characterizing global changes in gut microbial populations and enables the investigation of mammalian–microbial metabolic interactions. The study by Robosky et al. (2005) demonstrates the presence of subgroups or colonies of animal models with characteristic microbial communities that influence the urinary metabolite signature and discusses the potential impact of microfloral composition on the metabolic profile of the mammalian host. Given the integral nature of the mammalian–microbe symbiotic relationship, these differences in microbial communities could result in differences in metabolism of exogenous compounds and may account for abnormal findings commonly encountered in toxicology or drug metabolism studies. Considering the vastly increased number of environmental and genetic factors influencing variation in human metabolism, it becomes apparent that intestinal microbial composition may impact profoundly upon patient stratification and, ultimately, personalized healthcare.
ACKNOWLEDGMENTS
Conflict of interest: none declared.
REFERENCES
Dunne, C. (2001). Adaptation of bacteria to the intestinal niche: Probiotics and gut disorder. Inflamm. Bowel Dis. 7, 136–145.[CrossRef][Medline]
Gavaghan, C. L., Holmes, E., Lenz, E., Wilson, I. D., and Nicholson, J. K. (2000). An NMR-based metabonomic approach to investigate the biochemical consequences of genetic strain differences: Application to the C57BL10J and Alpk:ApfCD mouse. FEBS Lett. 484, 169–174.[CrossRef][Web of Science][Medline]
Kassie, F., Rabot, S., Kundi, M., Chabicovsky, M., Qin, H. M., and Knasmuller, S. (2001). Intestinal microflora plays a crucial role in the genotoxicity of the cooked food mutagen 2-amino-3-methylimidazo [4,5-f]quinoline. Carcinogenesis 22, 1721–1725.
Kuroda, K., Yoshida, K., Yoshimura, M., Endo, Y., Wanibuchi, H., Fukushima, S., and Endo, G. (2004). Microbial metabolite of dimethylarsinic acid is highly toxic and genotoxic. Toxicol. Appl. Pharmacol. 198, 345–353.[Medline]
Nicholson, J. K., and Wilson, I. D. (2003). Understanding ‘global’ systems biology: metabonomics and the continuum of metabolism. Nat. Rev. Drug. Disrov. 2, 668–676.
Nicholson, J. K., Holmes, E., Lindon, J. C., and Wilson, I. D. (2004). The Challenges of Modelling Mammalian Biocomplexity. Nat. Biotechnol. 10, 1268–1274.
Nicholson, J. K., Holmes, E., and Wilson, I. D. (2005). Gut microorganisms, mammalian metabolism and personalized health care. Nat. Rev. Microbiol. 3, 431–438.[CrossRef][Web of Science][Medline]
Phipps, A. N., Stewart, J., Wright, B., and Wilson, I. D. (1998). Effect of diet on the urinary excretion of hippuric acid and other dietary-derived aromatics in rat. A complex interaction between diet, gut microflora and substrate specificity. Xenobiotica 28, 527–537.[Medline]
Robosky, L. C., Wells, D. F., Egnash, L. A., Manning, M. L., Reily, M. D., and Robertson, D. G. (2005). Metabonomic Identification of Two Distinct Phenotypes in Sprague-Dawley (Crl:CD(SD)) Rats. ToxSci Advance Access published on June 2, 2005. doi:10.1093/toxsci/kfi214.
Rowland, I. R. (1986). Reduction by the gut microflora of animals and man. Dev. Biochem. Pharmacol. 35, 27–32.
Tannock, G. W., Munro, K., Harmsen, H. J., Welling, G. W., Smart, J., and Gopal, P. K. (2000). Analysis of the fecal microflora of human subjects consuming a probiotic product containing Lactobacillus rhamnosus DR20. Appl. Environ. Microbiol. 66, 2578–2588.
Upreti, R. K., Shrivastava, R., and Chaturvedi, U. C. (2004). Gut microflora and toxic metals: Chromium as a model. Indian J. Med. Res. 119, 49–59.[Web of Science][Medline]
Wang, Y., Tang, H., Nicholson, J. K., Hylands, P. J., Sampson, J., and Holmes, E. (2005). Metabonomic strategy for the detection of the effects of chamomile (Matricaria recutita L) ingestion. J. Agric. Food Chem. 53, 191–196.[Medline]
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