I analysed stool samples from 100 young (< 30 years) and aged (> 65 years) Danish individuals at the Center for Basic Metabolic Research (University of Copenhagen, UCPH). I selected the samples based on metabolic measures to include individuals that were as healthy as possible. Both groups included slightly more women than men (55-60%). I set up a protocol to detect IgA-coating levels of gut microbes by flow cytometry and separate the microbes based on their coating levels by magnetic-activated cell sorting. I determined the microbiota compositions by next-generation sequencing (NGS). Specifically, the essential 16S marker gene was sequenced from the purified microbial DNA on a NGS machine. Since it is essential, the 16S gene is present in all microbes, but its DNA is sufficiently divergent to allow taxonomic characterisation of the microbiota composition. I wrote R code to streamline the analysis of the sequencing reads based on state-of-the-art analysis pipelines. The code is publicly available (www.arumugamlab.org/projects/GutInflammAge).
I found no signs of increased intestinal inflammation in the samples from aged individuals. The proportions of highly IgA coated microbes in the old group were within the range of proportions found in the young group. Similarly, the microbiota compositions of the aged individuals fitted into the range of compositions of the young individuals. These results are well in line with recent studies, done on different ethnicities, all indicating that the gut microbiota of healthy old people is comparable to that of healthy young people.
The fasting experiment was done in collaboration with the Department of Biology (UCPH). The mice underwent periodic fasting from 8.5 to 14.5 months of age (comparable to ~35 to 50 years in humans). The scheme included two fasting periods à 3 days per month. To avoid no-food stress, the mice could always eat as much as they want, but they got food of low caloric content during the fasting periods. In practice, their calorie intake was ~50% reduced in the fasting periods, but 30% increased in the first 4 days of the re-feed periods. The overall calorie intake in the 6 months was ~5% lower in the fasted mice than in control mice. All mice stayed metabolically healthy (normal glucose and insulin tolerance). But, interestingly, the fasted mice accumulated more body fat than the control mice. On the plus side, we observed a mild re-juvenation of the blood profile in the fasted mice.
I determined the microbiota compositions of young, middle-aged, and old mice as references for the fasting experiment, and found clear differences between the age groups. Due to the controlled environment, the microbiota of lab mice is less variable than of humans. The analysis of how the gut microbiota of the mice changed during the fasting scheme is still ongoing. It is likely that microbiota changes were linked to the fat accumulation, considering that gut microbes are responsible for up to 10% of the energy uptake of the host. I presented my work at conferences and workshops, and we are working on final analyses to publish the results in scientific journals.
