We have known for some time that certain conditions like obesity, cancer and some autoimmune disorders like lupus may cause changes in the composition of our gut microbiota. We did not know, however, which conditions caused more modifications than others, what the effects were and whether these alterations could be used to identify those different illnesses.
Two studies led by Spanish scientists from the Spanish National Research Council (CSIC) and published in the Nature group journals Scientific Report and ISME Journal, respectively, have, for the first time, quantified and classified the effects of some disorders on our gut microbiota based on studies of the substances produced by bacteria when decomposing food molecules, the metabolites. In these studies, the researchers focused on three disorders – one metabolic (obesity), one immune (lupus erythematosus) and one infectious (diarrhoea caused by the Clostridium difficile bacteria).
“In the two articles published we study what the changes related to different conditions are, not so much whether these alterations lead to a specific illness, but rather the opposite – which modifications take place in the microbiota as a result of specific illnesses,” said to our blog Manuel Ferrer, CSIC researcher at the Institute of Catalysis and Petrochemistry (ICP) and co-author of both articles.
To do this, the researchers carried out a study of the metabolites produced by gut bacteria – an important differential fact and a key factor in both research projects. Previously, scientists had directly studied stool samples without finding a correlation between the microbiota’s composition and the conditions. The problem was that the stools also contained dietary waste, which masked the real effects of the illnesses under study. “Analysing just the molecules produced by the microbiota allowed us to link the diversity and composition of the metabolites to specific conditions,” says Ferrer.
They worked with three groups of patients who suffered from these conditions (obesity, lupus, CD diarrhea) and one group of healthy individuals as the control group. The CSIC scientists analysed the composition and diversity of the metabolites produced by the gut bacteria, or metabolome, of every subject participating in the study and they identified a catalogue of specific markers for each of the conditions under study.
With regards to the effect of obesity, the researchers found that healthy people with normal weight – the control group – and obese individuals show a very different composition and diversity of bacterial metabolites and they suggest that body mass index is the regulating factor for this difference, regardless of age or any other environmental factor.
With lupus, they also found that individuals suffering from the condition had a different metabolic profile to those in the control group. Nevertheless, in this autoimmune disorder, body mass index had no influence – both normal-weight and obese people suffering from lupus had a similar gut metabolic capacity.
“Autoimmune disorders like lupus, but also others like arthritis or Crohn’s disease, affect the microbiota much more than a metabolic illness, such as obesity. This disorder causes such changes in the microbiota that factors like age, weight, antibiotic use, diet or smoking become secondary,” said CSIC researcher Ferrer.
With regards to infectious diseases, the researchers analysed the effect of a range of pathogens that cause severe diarrhoea, including the Clostridium difficile bacteria, which has the ability to produce two toxins that heighten the effect of acute diarrhoea and reduce the effectiveness of antibiotic treatment. They saw that when a person has C. diff and generates these toxins, an avalanche of reactions takes place that make the gut microbiota work less intensely.
In spite of the interesting results of these two articles, it should be mentioned that they only focus on one side of the coin, in particular, on how the illness affects the metabolic activity of the gut microbiota. We still need to define the mechanisms through which these changes take place and the point to which these changes modulate the development of different disorders and the host’s response.