Orexins A and B are hypothalamic neuropeptides, in the regulation of food intake, metabolic rate, cardiovascular function, body temperature, locomotor activity, sleep-wake cycle and stress response. These peptides derive from the prepro-orexin (preprohypocretin) gene, which encodes a precursor that is cleaved into orexin-A and orexin-B
Orexins A and B, also known as hypocretin 1 and 2, are neuropeptides derived from a common 130-amino acid precursor peptide, prepro-orexin (PPO), by proteolytic cleavage. Orexin A is a 33-amino acid residue peptide with two intramolecular disulphide bonds in the N-terminal region, whereas orexin B is a linear 28-amino acid residue peptide. The discussed peptides have a 46% sequence identity. Both orexins act via two closely related G-protein coupled receptors, orexin type 1 receptor (OX1R) and orexin type 2 receptor (OX2R). OX1R appears to be selective for orexin A, while OX2R binds both orexin A and orexin B[1].
Orexin-A controls glucose production and utilization in the peripheral tissues via the autonomic nervous system. In addition it has been shown that orexins A and B differentially regulate glucagon release from pancreas. In addition, the presence of orexin receptors in other cerebral areas suggests that orexin-A plays additional functions. It has been demonstrated that the orexins play a role in sleep regulation[2]
Some reports show that Orexin B (ORXB) modulates the function of peritoneal macrophages through activation of calcium-dependent potassium channels and induces enhancement of phagocytosis in mouse peritoneal macrophages. it is plausible that ORXB may function as an anti-infective molecule. However, it has not been reported whether ORXB has antimicrobial properties[3].
[1]Maleszka A, Smolinska N, Nitkiewicz A, et al. Expression of orexin A and B in the porcine hypothalamus during the oestrous cycle. J Physiol Pharmacol. 2013,64(1):55-63. [2]Giovanni Messina, Carmine Dalia,Domenico Tafuri,ea al.Orexin-A controls sympathetic activity and eating behavior. Front Psychol. 2014, 5: 997. [3]Kouji Ohta, Mikihiko Kajiya,Tongbo Zhu, et al.Additive effects of Orexin B and vasoactive intestinal polypeptide on LL-37-mediated antimicrobial activities. J Neuroimmunol. 2011,233(1-2): 37–45.
