A cyclic neuropeptide and metabolite of TRH
Cyclo(L-His-L-Pro) is an endogenous cyclic neuropeptide and a metabolite of thyrotropin-releasing hormone (TRH).1 It is formed in the hypothalamus via the hydrolytic removal of pyroglutamic acid from TRH followed by non-enzymatic cyclization but is also synthesized de novo.2 It is ubiquitously expressed in the CNS, but is also found in the gastrointestinal tract and blood. Cyclo(L-His-L-Pro) (50 ?M) reduces LPS-induced production of reactive oxygen species (ROS) and nitric oxide (NO), as well translocation of NF-κB in BV-2 microglia. Levels of cyclo(L-His-L-Pro) are increased in rat brain after six weeks of continuous ethanol consumption and cyclo(L-His-L-Pro) reduces ethanol-induced sleep time in rats when administered at a dose of 1 ?mol/kg.1,3 Cyclo(L-His-L-Pro) induces analgesia in the hot-plate test and reduces acetic acid-induced writhing in mice, effects that can be partially reversed by the opioid antagonist naloxone.1
1.Prasad, C.Neurobiology of cyclo(His-Pro)Ann. N. Y. Acad. Sci.553(1)232-251(1989) 2.Grottelli, S., Ferrari, I., Pietrini, G., et al.The role of cyclo(His-Pro) in neurodegenerationInt. J. Mol. Sci.17(8)1332(2016) 3.Prasad, C., Matsui, T., and Peterkofsky, A.Antagonism of ethanol narcosis by histidyl-proline diketopiperazineNature268(5616)142-144(1977)
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