Abstract
Leptin has a central role in the maintenance of energy homeostasis, and its sensitivity is influenced by both the photoperiod and dietary polyphenols. The aim of this study was to investigate the effect of seasonal consumption of polyphenol-rich fruits on the hypothalamic leptin signaling system in non-obese and obese animals placed under different photoperiods. Non-obese and diet-induced obese male Fischer 344 rats were placed under either a short-day (SD) or long-day (LD) photoperiod and were supplemented with either 100 mg/kg of lyophilized red grapes or cherries. In non-obese animals, both fruits reduced energy balance independent of the photoperiod to which they were placed. However, the hypothalamic gene expression of Pomc was significantly up-regulated only in the SD photoperiod. In contrast, in obese animals only cherry significantly decreased the energy balance, although both fruits were able to counteract the diet-induced increase in hypothalamic AgRP mRNA levels when consumed during the SD photoperiod. In conclusion, the consumption of rich-polyphenol fruits may increase leptin sensitivity through the modulation of the hypothalamic leptin signal pathway mainly when consumed in the SD photoperiod. Therefore, fruit seasonality should be considered, as it can influence energy homeostasis and obesity.
Highlights
Leptin is a hormone produced by adipose tissue that has a key role in the central regulation of energy homeostasis[1]
Polyphenols are an important group of compounds present in fruits[10], and some studies have recently demonstrated that specific polyphenols increase leptin sensitivity in obese animals[11,12,13]
Control animals placed in the SD photoperiod showed significantly lower fat mass percentage than those placed in the LD photoperiod, and grape consumption completely abolished this photoperiod-dependent effect
Summary
Leptin is a hormone produced by adipose tissue that has a key role in the central regulation of energy homeostasis[1]. Various studies with mammals sensitive to photoperiods have shown that animals develop adaptive leptin resistance in long-day periods to overcome periods of food scarcity[8]. This means that, despite presenting high leptin levels in blood, leptin is unable to produce anorexigenic effects, providing animals with sufficient energy stores for future short-day seasons. This peculiar metabolic behavior described in mammals has been recently considered an evolutionary mechanism for survival[9]. Numerous studies report the metabolic protective effects of grapes, grape by-products, cherries or their pure compounds[14,15,16,17,18,19], and we chose red grape and cherry as representative polyphenol-rich fruits for autumn and spring, respectively
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