Studies on the effect of Time-Restricted Feeding on ageing and carcinogenesis

Ageing is a major risk factor for neoplastic disease. Moreover, what is less appreciated is the fact that some of the most relevant risk factors for humans cancer, such as smoking or UV light, are also associated with accelerated ageing in their target organ. Yet, biological and molecular mechanisms underlying this link are far from being fully elucidated. Studies presented in this thesis stem from the working hypothesis that ageing entails the emergence of a more favorable tissue soil for the clonal expansion of normal or altered cells, including putative pre-neoplastic cells. Caloric restricted feeding (CRF) represents one of the most effective strategies to delay ageing and age-related pathologies, including cancer. It is almost axiomatically implied that the beneficial effects of CRF are linked to the lower amount of delivered daily calories. However, CRF is often associated with a time-restricted feeding (TRF) schedule and this becomes important to consider in light of the increasing evidence documenting that TRF per se, without reduced caloric intake, can afford several positive effects on the development of age-associated phenotypes. Given the better translational potential of TRF as opposed to CRF, the aim of the present studies was twofold. Taking advantage of a unique experimental model developed by our research group, we tested the effect of TRF on the emergence of the neoplastic-prone tissue microenvironment associated with ageing. Moreover, we determined the impact of TRF on both local (liver) and systemic age-related alterations. In order to investigate whether TRF is able to exert any putative effect on either the tissue microenvironment and/or directly on the pre-neoplastic cell population, we set up a simple experimental protocol based on syngeneic hepatocyte transplantation. Hepatocytes isolated from chemically-induced liver nodules were injected in recipient rats following long-term exposure to TRF regimen. Animals were then continued on ad libitum feeding (ALF) and the growth of transplanted cells was evaluated. A significant increase in the frequency of larger size clusters of pre-hepatocytes was seen in TRF-exposed group compared to controls given ALF throughout the experiment, indicating that this dietary regimen was able to delay the emergence of the neoplastic-prone/clonogenic tissue landscape typical of ageing. To our knowledge, this is the first investigation to describe a direct beneficial effect of TRF on carcinogenesis. While longer follow-up studies are certainly warranted in our experimental setup, it is important to note that the present results parallel very closely those reported by our research group on CRF-treated rats. It was shown that the retarding effect CRF on neoplastic development was attributable, to a significant extent, to a lower clonogenic potential of the tissue microenvironment in caloric-restricted animals. Parameters related to both liver and systemic ageing were found to be modulated by TRF towards the persistence of a younger phenotype, including a decrease in liver cell senescence, lower incidence of cholangiofibrosis, diminished fat accumulation and up-regulation of Sirt1 in the liver, down-regulation of plasma insulin like growth factor (IGF) 1, up-regulation of hippocampal brain derived neurotrophic factor (BDNF), decreased levels of plasma lipoproteins. Of note, the beneficial effect of TRF on the above parameters was still detectable after 3 months of ALF diet, suggesting that it is based on stable biological changes as opposed to transient metabolic alterations. As mentioned above, these results have important mechanistic implications. If in fact several effects of CRF can be reproduced by TRF with no decrease in caloric intake, the implication is that the beneficial effects of the former are mediated, at least in a relevant part, by biochemical/molecular mechanisms set in motion by the latter.