The use of nutraceuticals and development of functional foods

Ageing is a complex natural process characterised by a progressive decline in physiological function that increases susceptibility to disease and the risk of mortality. Domestic dogs have extended their lifespan and are increasingly recognised as a suitable translational model for human ageing, as they have co-evolved and are exposed to the same environmental conditions such as housing, diet and lifestyle. By modelling the human condition, complex issues such as the contribution of the environment during ageing can be investigated with long-term treatment protocols in dogs. Skeletal muscle tissue is subject to a premature and general ageing process characterised by a loss of muscle mass, function and strength. It is responsible for frailty and disability, which drastically reduces the independence and quality of life of humans and dogs. Finally, the gut microbiota is also subject to significant changes at different ages, which can contribute to age-related diseases. Premature senescence can be triggered by the accumulation of reactive oxygen species (ROS) and oxidative stress damage. In senescent cells, oxidative stress increases due to an imbalance in the redox system as well as an impairment of mitochondrial dynamics and a loss of efficiency of the autophagic process, which leads to an acceleration of the senescence process. Antioxidant bioactive compounds and physical activity are considered natural strategies for the prevention of age-related diseases as they promote antioxidant and autophagic pathways and stimulate mitochondrial biogenesis. The aim of the present study is to test the efficacy of natural bioactive molecules and their mechanisms of action, especially in terms of antioxidant activity and autophagy promoters, as preventive anti-ageing properties prior to an induced senescence stimulus in human AB1079 and canine Myok9 skeletal muscle cell lines. The main focus was on the dietary supplements oleuropein aglycone (OLE), allicin (ALLI) and the hormone-like myokine irisin. The first molecule is a polyphenol found in extra virgin olive oil and is responsible for the benefits of the Mediterranean diet, while ALLI is an extract from garlic with antioxidant and anti-ageing properties. Irisin is secreted by skeletal muscle in response to contraction and may simulate the beneficial effects of exercise at systemic level. Finally, the third-generation MinION sequencing of the 16S rRNA gene was optimised to compare the gut microbiota of young and old dogs. The results discussed confirm the preventive anti-ageing properties of the three molecules in canine skeletal muscle cells. In particular, OLE also showed its effect in human cells by inducing transcription factors and genes involved in antioxidant mechanisms, such as FOXO3a and SOD2, activating AMPK and leading to mTORC1 inhibition and promotion of the autophagic process, overexpressing the sestrin family, in particular SESN3, and attenuating mitochondrial fission induced by the senescence stimulus. However, the results also show that the molecular mechanisms may differ between species such as the timing of AMPK phosphorylation by OLE. Potential prototypes of antioxidant supplements containing molecules with promising results in vitro could be developed to prevent muscle ageing in domestic dogs following dose-switching considerations in vivo. A comparison of the gut microbiota of young and old dogs linked ageing to dysbiosis and an increase in Fusobacteriota. The higher taxonomic resolution of the Oxford Nanopore technology enables a better understanding of the gut microbiota and even the detection of the effects of dietary supplement.