Unacylated Ghrelin Improves Vascular Dysfunction and Attenuates Atherosclerosis during High-Fat Diet Consumption in Rodents

Abstract

Unacylated ghrelin (UnGhr) exerts several beneficial actions on vascular function. The aim of this study was to assess the effects of UnGhr on high-fat induced endothelial dysfunction and its underlying mechanisms. Thoracic aortas from transgenic mice, which were overexpressing UnGhr and being control fed either a standard control diet (CD) or a high-fat diet (HFD) for 16 weeks, were harvested and used for the assessment of vascular reactivity, endothelial nitric oxide synthase (eNOS) expression and activity, thiobarbituric acid reactive substances (TBARS) and glutathione levels, and aortic lipid accumulation by Oil Red O staining. Relaxations due to acetylcholine and to DEA-NONOate were reduced (p < 0.05) in the HFD control aortas compared to vessels from the CD animals. Overexpression of UnGhr prevented HFD-induced vascular dysfunction, while eNOS expression and activity were similar in all vessels. HFD-induced vascular oxidative stress was demonstrated by increased (p < 0.05) aortic TBARS and glutathione in wild type (Wt) mice; however, this was not seen in UnGhr mice. Moreover, increased (p < 0.05) HFD-induced lipid accumulation in vessels from Wt mice was prevented by UnGhr overexpression. In conclusion, chronic UnGhr overexpression results in improved vascular function and reduced plaque formation through decreased vascular oxidative stress, without affecting the eNOS pathway. This research may provide new insight into the mechanisms underlying the beneficial effects of UnGhr on the vascular dysfunction associated with obesity and the metabolic syndrome.

A Decade’s Progress in the Development of Molecular Imaging Agents Targeting the Growth Hormone Secretagogue Receptor

“…The resulting peptide analogue, [Dpr 3 (octanoyl), Lys 19 (triazole-ADIBO-F)]ghrelin(1-19) (13), was found to have an IC 50 value of 9.7 nM and was labeled with fluoride-18 to produce [ 18 F]13 in radiochemical yields of 64-66% and molar activities of 0.6-0.9 GBq/mmol. 82 Charron et al continued with this theme and reported a probe containing a 1,4,7,10-tetraazacyclododecane-1,4,7,10tetraacetic acid (DOTA) chelator off the C-terminal lysine residue (Figure 8), [Dpr 3 (octanoyl), Lys 19 (Ga-DOTA)]ghrelin (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19) (14), which possessed an IC 50 value of 5.9 nM, comparable to natural ghrelin (IC 50 ¼ 3.1 nM). 58 The probe was labeled with gallium-68 in radiochemical yields of 54%-83% and molar activities of 10.2-22.8 GBq/mmol.…”

“…However, DAG does participate in physiological pathways independent of the GHSR including binding to the corticotropin releasing factor receptor type 2a (CRF2a), exerting beneficial actions on vascular function, and cardiac protection. [17][18][19] Additionally, a cyclic analogue of DAG, known as Livoletide, is currently in phase III clinical trials for the treatment of Prader-Willi syndrome. 20 The GHSR-1b isoform does not bind ghrelin or growth hormone secretagogues and, therefore, does not share the same signaling profile as the GHSR-1a.…”

“…Fowkes et al sought to develop a growth hormone secretagogue-based probe for PET imaging of the GHSR. 86 The authors studied an extensive number of growth hormone secretagogues including GHRP-1, GHRP-2, GHRP-6, ipamorelin, and G-7039 as potential 18 in an average, overall radiochemical yield of 48% (n ¼ 3) and molar activity >34 GBq/mmol. This probe was further analyzed through in vivo PET imaging of cardiac GHSR.…”

“…However, no significant correlation between tracer uptake and GHSR expression in the heart was observed and there was significant uptake in off The recent identification of LEAP2 as a second endogenous ligand for the GHSR prompted a desire to develop a fluorescent analogue of LEAP2 suitable for studying the pharmacological behavior of GHSR: LEAP2 complexes compared to those of GHSR: ghrelin. 25,27,28 Barrile et al recently reported the resulting fluorescent ligand, LEAP2(1-17)-DY-647P1 (18), also referred to as F-LEAP2, which is based on the first 17 amino acids of the mature peptide sequence (Figure 10). 89 By taking advantage of Cys 17 , which traditionally forms an intramolecular disulfide bridge with Cys 28 in the endogenous sequence, the authors were able to conjugate a DY-647P1 fluorophore to the C-terminus of the ligand.…”

“…Structures of small molecule GHSR antagonists for18 F-PET and 11 C-PET imaging reported by Kawamura et al92 …”