Some other neuroinflammatory neuroendocrine and neurotrophic

Some other neuroinflammatory, neuroendocrine, and neurotrophic pathway but not the ghrelin/GHSR pathway may mediate the CUMS-induced depression- and anxiety-like behaivors. The endogeous ghrelin/GHSR pathway activated by chronic mild stress may plays a role in homeostasis. With respect to the mechanism involved in the reversal of the depression-like behaviors induced by ghrelin, it is well demonstrated that imbalanced neurotransmitters and/or decreased synaptic plasticity participated in the psychopathology of depression [51], [52]. As described in previous section, ghrelin may indirectly affect the functions of glutamatergic neurons or integrate with dopamine receptors, to regulate the synaptic plasticity through binding with GHSR. The relationship of ghrelin with these functional neurons may be one potential area of depression research. On the other hand, some researches indicated that ghrelin played a neuroprotective role to hippocampal neurons [53] and had anti-apoptotic effects on animal models of either ischemia [54], PD [55], spinal cord injury [56] or epilepsy [57]. Several studies suggested that ghrelin treatment could defend against Niflumic acid injury induced by sepsis [58] or pilocarpine-induced seizures [59] via PI3K/Akt signaling activation. Ghrelin exert its neuroprotective effects maybe by activating some intracellular signaling pathway in a GHSR1a-dependent manner.
Acknowledgments The project was funded by the National Key Basic Research Program of China (2013CB531906), and the National Natural Science Fund of China (81071103, 81271500 and 31371083). Special acknowledgement to Prof. Yanqing Wang, and Technician Jianwei Jiang, for their selfless technical support, encouragement, and guidance during this work. Another grateful acknowledgement is devoted to Qiang Xiao, for his unselfish help and careful revisions to eliminate possible grammatical or spelling errors, and to conform to correct scientific English for this manuscript.
The Growth Hormone Secretagogue receptor (GHSR) has been implicated in a number of important biological functions, including the regulation of growth, metabolism, and food intake. Small molecule agonists of GHSR have been studied in the clinic for the treatment of growth hormone disorders, frailty, and cachexia. GHSR is a member of the G-protein-coupled receptor (GPCR) protein superfamily, and as part of an in-house effort to identify novel GHSR agonists we screened a series of GPCR-targeted libraries, including one based on a secondary amine chemotype. This library afforded a number of low micromolar GHSR agonist hits, and the identification and optimization of these hits is described herein. The secondary amine GPCR-targeted library was synthesized on solid support and comprised three reagent sets: R, consisting of cyclic and acyclic secondary amino alcohols; R, consisting of primary amines and anilines; and R, consisting of carboxylic acids. The overall dimensions of the library were 11 R×31 R×42 R, which in theory would afford 14,322 discrete products. However, each library sample underwent a rigorous quality control (QC) process: each sample was analyzed by HPLC (with UV and ELS detection) and mass spectrometry. Samples which did not afford ⩾70% purity by HPLC and a mass ion corresponding to the desired product were discarded. Upon completion of the QC process, 11,520 samples were submitted for screening against a variety of GPCR targets and resulted in the identification of a series of prolinol-derived GHSR agonists as described in . Given that 11,520 library members were screened in the GHSR assay, the high degree of structural homology for the active samples described in was compelling. Indeed, a modest amount of SAR could be elucidated from the HTS data, with the caveat that the original library samples were submitted as crude (but ⩾70% pure by HPLC) samples. Moreover, the 31 primary amines (30 anilines and 1 benzylamine) used in the library spanned a wide range of chemical property space and thus the R substituents listed in Entries 1–6 of do not constitute a focused library by any stretch of the imagination. The -AcNH substituent (Entry 2) was the most active R substituent in the aniline series (=0), and it appeared that a methyl group was the optimal R substituent, although the R SAR was confounded by a significant number of missing samples—these samples were not screened because they failed our QC process and were discarded. In addition to the aniline series exemplified by Entries 1–6, a benzylamine analog (=1) afforded sub-micromolar GHSR agonist activity (Entry 7, R=Et). Because only a single benzylamine reagent was present in the library, the absence of the R=Me sample (which was anticipated to be more potent than the R=Et sample) served to heighten our interest in the benzylamine series.