Synthesis of CNS active thyrotropin-releasing hormone (TRH)-like peptides: Biological evaluation and effect on cognitive impairment induced by cerebral ischemia in mice

Abstract

Thyrotropin-releasing hormone (TRH)-like peptides were synthesized by replacing critical histidine and pGlu residues in the native peptide. The peptides were evaluated in vitro for receptor binding activity assay and in the cell functional assay; the peptides exhibit selective basal signaling agonist behavior toward TRH-R2. For example, peptides 8a, 8b, 8c, 8f, 8h, 8l and 12d activated TRH-R2 with potency (EC50) of 0.53μM, 0.048μM, 0.05μM, 0.006μM, 0.31μM, 0.034μM and 0.004μM, respectively. In contrast for signaling activation of TRH-R1, the same peptide required higher concentration of 19.35μM, 3.98μM, 2.54μM, 0.287μM, 11.28μM, 0.986μM and 0.944μM, respectively. The results showed that peptides were 36.5, 82.9, 50.8, 47.8, 36.3, 32.6 and 235-fold selective to TRH-R2 receptor subtype. The peptides were investigated for CNS activity at 10μmol/kg in pentobarbital-induced sleep assay study. Peptides 8c (16.5±1.4min) and 8l (16.5±2.1min) displayed excellent CNS activity. In an in vivo study, peptide 8c did not cause significant change in the rat plasma TSH levels. The peptide 8c was further investigated for neuroprotective potential, and significantly reduced infracts volume and neurological score in the focal cerebral ischemia model in mice. Peptide 8c also significantly lowered MDA levels, indicating reduction of oxidative and enhanced percentage cell survival in CA1 region, when compared to ischemic brain.