A number of brain and gut peptides regulate food intake. An important aspect of gut peptides is their co-release depending on the metabolic status. We were the first to identify a physiological synergistic interaction between cholecystokinin (CCK) and leptin to induce postprandial satiety in rodents. Such interaction is exerted at the levels of capsaicin-sensitive vagal afferents, resulting in the activation of specific brain nuclei. Likewise, CCK acts synergistically with the stress peptide urocortin 1 to suppress food intake through activation of gastric vagal afferents.
Rodents fed a Western diet containing 40% fat lost the synergistic interactions between CCK and other peptides. Dr. Lixin Wang showed that rats fed a Western diet developed increased visceral fat mass and an inflammatory response in the hypothalamus and the brain stem. Switching to a high protein diet curtailed the increase in fat mass induced by the Western diet, normalized blood glucose and restored the satiety signaling of CCK while not influencing the brain inflammation. Of importance, the study showed a correlated expansion of cecal Akkermansia muciniphila, along with a loss of fat mass induced by switching rats from a Western diet to a high-protein diet, pointing to a beneficial effect of the bacterium.
New insight into the regulation of the gastric orexigenic hormone ghrelin was gained by our initial reports that endotoxin, the cytokine interleukin-1ß and abdominal surgery suppressed circulating ghrelin levels and food intake through distinct underlying mechanisms. Of relevance, the restoration of circulation ghrelin prevented the associated decreased gastric emptying induced by endotoxin, abdominal surgery and levodopa administration in rodents. These data may have translational applications for the use of ghrelin agonists under conditions of surgery and as an anti-Parkinsonian drug treatment associated with slow gastric transit and response fluctuations.