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Abstract
Activity and half-life play key roles in the application of GHRH analogues. The GHRH monomers produced in a solid synthesizer were incubated, respectively, in NH4OH solution and lyophilized to obtain their dimers. The activities, specificities, and receptor affinities of the GHRH dimers were evaluated in rGH release/inhibition, rACTH/LH/PRL release, pituitary homogenate binding, and fluorescent staining. Compared to hGHRH(1-44)NH2 (S), PP-hGHRH(1-44)-GGC-CGG-hGHRH(44-1)-PP (2D), P-hGHRH(1-44)-GGC-CGG-hGHRH(44-1)-P (2E), 1P-hGHRH(2-44)-GGC-CGG-hGHRH(44-2)-1P (2F), or hGHRH(1-44)-GGC-CGG-hGHRH(44-1) (2Y) had potency of 104 ± 16.7%, 94 ± 32.6%, 114 ± 16.6%, or 122 ± 14.5% and similar specificities. The inhibition effect of GHIH on rGH stimulated by GHRH dimer was in dose-/time-dependent manner. The staining of FITC-labeled dimer showed cytomembrane distribution and the binding ranking was 2F>2D>2Y>2E>S. 2F presents the strongest activity and the highest affinity to pituitary cells. The dimer with 1Pro-GHRH stimulates stronger rGH release than that with 1Tyr-GHRH and the N-terminal single cyclic amino acid is required for the stimulation.
Acknowledgements
We appreciate Dr. Xiao-Dong Wang's donation for GHIH reagent. We thank Mr. Wen-Feng Wu for his hard work during his graduate program.
Declaration of interest
The authors report that they have no conflicts of interest. This research work was supported by the National Natural Science Fund (81001391), Sin Education Ministry Grant (SRF for ROCS 44143012), Guangdong Provincial Natural Grant (S2012010009953 and 2014A030313589), and Guangdong Provincial Medical Grant (A2011456).