Kyotorphins

Introduction

Kyotorphins, an endogenous dipeptide, are formed from tyrosine and arginine by a specific synthetase, and originally found in bovine and rat brain synaptosomes. It has a specific receptor coupled to G_i and phospholipase C and elicits enkephalin release. It takes part in the regulation of various adaptive reactions of the organism, so it plays a key role in pain modulation in the mammalian central nervous system (CNS). Kyotorphins have a neutral net charge at biological pH. The phenolic rings of kyotorphins interact with phospholipid molecules despite being exposed to the aqueous bulk medium.

Mechanism of action

Previous studies suggested that kyotorphin-induced opioid like analgesia may be mediated via a release of Met-enkephalin from the brain. It elicited a release of Met-enkephalin from brain slices but not of [3H]-GABA, [3H]-aspartate, endorphin and [3H]-noradrenaline. The neurochemical basis of mechanisms suggests that kyotorphins stimulates its specific receptor, followed by G_i and phospholipase C (PLC) activations. PLC mechanism leads to a Ca²⁺ influx in nerve ending particles or synaptosomes. Inositol 1, 4, 5-trisphosphate (InsP₃) elicits Ca²⁺ transport through plasmalemmal InsP₃ receptor but not through intra synaptosomal Ca²⁺ stores. kyotorphins -induced antinociceptive responses are mediated through its specific receptor. However, at extremely low doses (below femtomolar ranges) of nociceptin/orphanin the endogenous ligand of opioid receptor-like orphan receptor it is coupled to G_i, elicits nociceptive responses through its receptor and G_i. Potent peripheral nociceptive actions of kyotorphins occur through an InsP₃-receptor-gated Ca²⁺ influx.

Application of kyotorphins

The abilities to discriminate rigid raft like membrane domains and the well-defined orientation in membranes showed that kyotorphins meets the structural constraints needed for receptor-ligand interaction, which represents a promising way for entrapment in a drug carrier and transport across the blood-brain barrier. According to the rate of post resuscitational restoration and survival after a 12-min heart arrest, the Kyotorphin can improve cardiovascular and neurological status, and accelerate restoration of vital functions within several days after resuscitation, so it has been used to improve cardiovascular and cerebral resuscitation after heart arrest.

References

1. Kastin, A. J., Honour, L. C., & Coy, D. H. (1981). Kyotorphins affect aversive pecking in chicks. Physiology & behavior, 27(6), 1073-1076.
2. Foppoli, C., Coccia, R., Blarzino, C., Cini, C., & Rosei, M. A. (1991). The peroxidase-catalyzed oxidation of kyotorphins. Biochemistry international, 23(1), 43-51.
3. Castanho, M., & Santos, N. (Eds.). (2011). Peptide drug discovery and development: translational research in academia and industry. John Wiley & Sons.