3.4. Agomelatine treatment restores the gut dysbiosis in obese mice.
This study explores for the first time the effect of agomelatine on gut microbiota. Only the highest dose (50mg/kg) was evaluated since it was the one that showed a greater effect in the macroscopic and biochemical parameters.
Several ecological features were determined, including Chao1 richness (diversity estimation), Observed OTUs (count of unique OTUs in each sample) and Shannon diversity (a richness and evenness estimator). Microbial richness, evenness and diversity were significantly decreased in the HFD group compared to non-obese mice. Although all treatments were able to increase these ecological parameters, only agomelatine significantly restored all of them (Figure 7). The principal coordinates analysis (PCoA) showed evident differences between control diet- and HFD-fed groups, indicative of extremely different gut environments (Figure 7B). Interestingly, the treatments displayed marked shifts in the obese gut microbiome (Figure 7B). Further analysis at phylum level (Figure 7C) revealed that HFD induced a dramatic change in the two most abundant phyla when compared to non-obese mice, significantly increasingFirmicutes and reducing Bacteroidetes (Figure 7C). Agomelatine significantly restored to baseline F/B ratio (Figure 7C).Verrucomicrobia phylum was also reduced in the HFD-fed group but agomelatine restored it (Figure 7C).
At order level, untreated HFD mice presented a reduced proportion in the sequences of Bacteroidales, Verrucomicrobiales andLactobacillus whilst Erysipelotrichales ,Clostridiales and Lachnospirales abundance were significantly increased (Figure 8). Agomelatine treatment showed a similar profile than non-obese mice while metformin only counteracted some of the altered orders (Figure 8). When the functional-gene profile was assessed, our results showed a clear difference between non-obese mice and un-treated HFD ones (Figure 9A). Interestingly, the treatments also produced an important change in this profile, which was more accentuated in the case of agomelatine and metformin (Figure 9A). Thus, while metformin increased the bacterial genes associated with tryptophan, fructose and mannose metabolism and with glycosaminoglycan degradation, agomelatine up-regulated the genes involved in glycolysis, gluconeogenesis and lipid metabolism (Figure 9A), and decreased genes involved in the transport (including ABC transporter), bacterial secretion, PPAR signalling, fatty acid biosynthesis, motility and sugars assimilation, along with others, which appeared increased in HFD-mice (Figure 9A).
Agomelatine also had a clear effect on short chain fatty acids (SCFA)-producing bacteria. Non-treated HFD-fed mice showed a decrease in butyrate-producing bacteria abundance in comparison with non-obese mice (Figure 9B), but oral administration of agomelatine and metformin significantly increased the relative abundance of butyrate-producing bacteria (Figure 9B). Propionate-producing bacteria were also reduced by HFD intake (Figure 9B) although all treatments increased the abundance of these bacteria, being agomelatine the most relevant (Figure 9B). Interestingly, agomelatine also augmented the abundance of A. muciniphila (Figure 9C), a propionate producing bacteria(Louis & Flint, 2017).