Relationship of ghrelin with appetite and aging

Ghrelin, a 28-amino acid peptide, is mainly secreted by the stomach. Ghrelin is functionally unique, as it is the only identified peripheral signal of insufficient energy intake that promotes feeding behavior involved mechanisms inthe central nervous system (CNS). Ghrelin has been shown to have neuroprotective effects. In humans, plasma ghrelin levels rise shortly before and fall shortly after every meal, a pattern that is consistent with a role in the urge to begin eating. If circulating ghrelin participates in long-term regulation of body weight, its level should increase with weight loss as part of the compensatory response to an energy deficit. On the other hand, aging is commonly accompanied by increased fat mass and chronic low-grade inflammation, thus the concurrences of obesity and insulin resistance are significantly greater in aging. In addition, obesity is accompanied by numerous metabolic abnormalities including insulin resistance, dyslipidemia, subclinical inflammation, and endocrine dysregulations that could contribute to its etiopathogenesis and the development of complications. Currently, ghrelin is the only known circulating acylated orexigenic peptide with potential for hunger/body weight regulation. Additionally, it is a neuropeptide (endogenous ligand for the GH secretagogue) recently isolated from the oxyntic mucosa and synthesized mainly in the stomach. Ghrelin blood concentration is reduced in obesity, nonalcoholic steatohepatitis, polycystic ovary syndrome, acromegaly, hypogonadism, and aging. In this review, a better understanding of the role of ghrelin signaling has been described in the regulation of age-associated adipose tissue inflammation.