An interesting article published in Nature by Rimal and Patterson looks at this issue. 

As we age, we are more likely to develop aging related illnesses such as cardiovascular  disease, cancer and type 2 diabetes. Yet centenarians, those who are over the age of 100, are less susceptible to such conditions than those aging individuals who do not live as long.  For some of those, the answer to this conundrum might lie in the gut. Sato and others have  identified a previously unknown connection between healthy aging in humans over the age of  100 and gut bacteria and bile acids.  

The study of bile acids began in earnest in the early 1900s with the characterisation of primary  bile acids: Cholic acid and Chenodeoxycholic acid. Bile acids have long been recognised for  their detergent properties, such as their ability to dissolve fat and fat soluble vitamins. It has  also emerged that they can act as potent hormones that control metabolic processes in the  intestine, liver, pancreas and brain.  

Sato and others explored the possibility that gut bacteria such as the gut microbiome – the  major component along with microorganisms and viruses might hold clues to how Japanese  centenarians age in a healthy way.  

The authors recruited Japanese study participants of varying ages: 47 young people average  age 31. 

112 older people average age 86 and 160 centenarians average age 107.  

Sato and colleagues characterised stool samples from the participants to gain insight into the  bacteria present and performed mass spectrometry based filing to assess for molecules in  samples. Sato and others reported that the microbiome profiles of centenarians showed differences from those of the other two cohorts. A hallmark was the presence of some genes  encoding enzymes that metabolise bile acids. Analysis of the bile acids in the participants’ stool samples confirmed the predictions based on the sequencing results, showing an  increase in the level of secondary bile acids in centenarians compared with the other age  cohorts. 

They carefully identified the microorganisms responsible for generating these bile acids using  bacteria obtained from a sample stool from one of the participating centenarians. 

The authors suggested that isoallo-LCA producing bacteria might help to promote or maintain  intestinal homeostasis through the antimicrobial effects of isoallo-LCA on harmful bacteria and  that this mechanism could contribute to the healthy aging of centenarians. This study is  important because it lays the foundation for asking more questions about the role of the  microbiome, and particularly bile acids, in human health.

It provides an impressive interdisciplinary example of how classical microbiological analysis  together with sequencing based approaches, metabolite profiling and computational analysis  can be used to uncover new biosynthetic pathways in bacteria that are normally resident in the  gut. This study will undoubtedly drive further research aimed at uncovering the potential health  promoting effects of gut bacteria and microbiome associated molecules. 

Dr Paul Ettlinger 
BM, DRCOG, MRCGP, FRIPH, DOccMed

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