The influence of ghrelin, adiponectin, and leptin on bone mineral density in healthy postmenopausal women

The association of body fat mass (FM) with bone mineral mass (BMC) and bone mineral density (BMD) has been attributed to a mechanical load exerted on the skeleton by FM and by the effect of different hormones. The aim of the present study was to determine whether there is a relationship between ghrelin, adiponectin, and leptin with BMC and BMD in healthy postmenopausal women (n = 88; age, 68.9 ± 6.8 years; body mass index, 27.4 ± 3.6 kg/m²). Body composition, BMC, and BMD were derived by dualenergy X-ray absorptiometry. Waist-to-hip (WHR) and waist-to-thigh (WTR) ratios were also obtained. Ghrelin was associated with total BMC (β = −0.945; P = 0.0001), total BMD (β = −0.959; P = 0.0001), lumbar spine BMD (β = −0.945; P = 0.0001), and femoral neck BMD (β = −0.957; P = 0.0001), and remained associated (P < 0.041) in different analyses that controlled for measured body composition and hormonal and insulin resistance values. However, the associations between ghrelin and measured bone mineral values were no longer significant (P > 0.149) when adjusted for body fat distribution values (WHR, WTR). Adiponectin was significantly related to total BMC (β = −0.931; P = 0.0001), total BMD (β = −0.940; P = 0.0001), lumbar spine BMD (β = −0.937; P = 0.0001), and femoral neck BMD (β = −0.940; P = 0.0001) values, and these relationships remained significant (P < 0.019) after adjusting for measured body fat, hormonal, and insulin resistance values but not when adjusted for fat-free mass (FFM; P > 0.106). In addition, significant associations of leptin with total BMC (β = 0.912; P = 0.0001), total BMD (β = 0.907; P = 0.0001), lumbar spine BMD (β = 0.899; P = 0.0001), and femoral neck BMD (β = 0.906; P = 0.0001) were found. These associations remained significant (P < 0.010) in different analyses that controlled for hormonal and insulin resistance values, but the associations between leptin and bone mineral values were no longer significant (P > 0.145) when adjusted for specific body composition values (WHR, WTR, FM, and FFM). In conclusion, it appears that the influence of plasma ghrelin, adiponectin, and leptin levels on BMC and BMD values is mediated or confounded by the specific body composition parameters in healthy postmenopausal women.     

Ghrelin stimulates milk intake by affecting adult type feeding behaviour in postnatal rats

The influence of ghrelin on feeding behaviour during infancy is unknown. To determine whether ghrelin influences milk intake in rat pups, newborn rats received a single i.p. injection of either rat ghrelin (100 μg/kg) or rabbit anti-ghrelin immunoglobulin G (100 μg/kg) every 5 days from postpartum day 5 to day 30 (P5–P30). Milk intake was then assessed by body weight gain following a 2-h suckling period. Ghrelin significantly increased weight gain relative to vehicle-injected controls in P20, P25 and P30 pups, but not in younger animals. Similarly, after 8 h of milk restriction, anti-ghrelin injections significantly decreased weight gain in P25 and P30, but not in younger pups. Interestingly, however, ghrelin did increase independent feeding in P10 and P15 pups using a paradigm in which pups consumed milk from a milk-soaked paper towel. We therefore conclude that ghrelin stimulates milk intake at an early postnatal stage, primarily by affecting adult-type feeding behaviour.     

胃饥饿素对高糖下人视网膜血管内皮细胞的保护作用及机制

目的：探讨胃饥饿素(ghrelin)对高糖下的人视网膜血管内皮细胞的保护作用及机制。

方法：以人视网膜血管内皮细胞为研究对象,建立高糖损伤模型。胃饥饿素处理细胞后,采用CCK-8试剂盒检测不同浓度胃饥饿素对高糖下细胞增殖的影响,以筛选最佳浓度。将细胞分为正常对照组(NC)、胃饥饿素组(ghrelin)、高糖组(HG)和胃饥饿素+高糖组(ghrelin+HG)。采用CCK-8试剂盒检测细胞增殖,Annexin-APC/7-AAD试剂盒检测细胞凋亡,蛋白质印迹法检测细胞NLRP3、Caspase-1、IL-1β及IL-18的表达。

结果：与NC组(100.00%±0.00%)相比,HG组细胞增殖率(69.87%±0.68%,P<0.05)明显下降。与HG组相比,ghrelin+HG组细胞增殖率(92.31%±3.62%,P<0.05)明显升高。与NC组(4.94%±0.15%)相比,HG组细胞凋亡率(28.33%±1.37%,P<0.05)明显升高。与HG组相比,ghrelin+HG组细胞凋亡率(14.24%±0.32%,P<0.05)明显降低。与NC组相比,HG组细胞表达NLRP3、Caspase-1、IL-1β及IL-18蛋白均明显升高(均P<0.05)。与HG组相比,ghrelin+HG组细胞表达NLRP3、Caspase-1、IL-1β及IL-18蛋白均明显下降(均P<0.05)。

结论：胃饥饿素能对高糖损伤的视网膜血管内皮细胞起到保护作用,可能是通过抑制NLRP3炎症小体信号通路发挥其功能。     

Growth hormone secretagogue receptor antagonists

The patent claims peptidic/nonpeptidic inhibitors of the ghrelin receptor, the growth hormone secretagogue receptor (GHSR) 1A. Among these compounds, it was disclosed that the addition in some compounds of a GlyMetAla tripeptide at the N-terminus of the ghrelin peptide agonists converts them into ghrelin receptor antagonists. One of these peptides, among the few that have been studied in vivo, was shown to be able to reduce food intake and body weight gain in rats.     

Ghrelin Increases GABAergic Transmission and Interacts with Ethanol Actions in the Rat Central Nucleus of the Amygdala

The neural circuitry that processes natural rewards converges with that engaged by addictive drugs. Because of this common neurocircuitry, drugs of abuse have been able to engage the hedonic mechanisms normally associated with the processing of natural rewards. Ghrelin is an orexigenic peptide that stimulates food intake by activating GHS-R1A receptors in the hypothalamus. However, ghrelin also activates GHS-R1A receptors on extrahypothalamic targets that mediate alcohol reward. The central nucleus of the amygdala (CeA) has a critical role in regulating ethanol consumption and the response to ethanol withdrawal. We previously demonstrated that rat CeA GABAergic transmission is enhanced by acute and chronic ethanol treatment. Here, we used quantitative RT-PCR (qRT-PCR) to detect Ghsr mRNA in the CeA and performed electrophysiological recordings to measure ghrelin effects on GABA transmission in this brain region. Furthermore, we examined whether acute or chronic ethanol treatment would alter these electrophysiological effects. Our qRT-PCR studies show the presence of Ghsr mRNA in the CeA. In naive animals, superfusion of ghrelin increased the amplitude of evoked inhibitory postsynaptic potentials (IPSPs) and the frequency of miniature inhibitory postsynaptic currents (mIPSCs). Coapplication of ethanol further increased the ghrelin-induced enhancement of IPSP amplitude, but to a lesser extent than ethanol alone. When applied alone, ethanol significantly increased IPSP amplitude, but this effect was attenuated by the application of ghrelin. In neurons from chronic ethanol-treated (CET) animals, the magnitude of ghrelin-induced increases in IPSP amplitude was not significantly different from that in naive animals, but the ethanol-induced increase in amplitude was abolished. Superfusion of the GHS-R1A antagonists 𝒟-Lys3-GHRP-6 and JMV 3002 decreased evoked IPSP and mIPSC frequency, revealing tonic ghrelin activity in the CeA. 𝒟-Lys3-GHRP-6 and JMV 3002 also blocked ghrelin-induced increases in GABAergic responses. Furthermore, 𝒟-Lys3-GHRP-6 did not affect ethanol-induced increases in IPSP amplitude. These studies implicate a potential role for the ghrelin system in regulating GABAergic transmission and a complex interaction with ethanol at CeA GABAergic synapses.     

Ghrelin receptor activity amplifies hippocampal N‐methyl‐d‐aspartate receptor‐mediated postsynaptic currents and increases phosphorylation of the GluN1 subunit at Ser896 and Ser897

Although ghrelin and its cognate receptor growth hormone secretagogue receptor (GHSR1a) are highly localized in the hypothalamic nuclei for the regulation of metabolic states and feeding, GHSR1a is also highly localized in the hippocampus, suggesting its involvement in extra‐hypothalamic functions. Indeed, exogenous application of ghrelin has been reported to improve hippocampal learning and memory. However, the underlying mechanism of ghrelin regulation of hippocampal functions is poorly understood. Here, we report ghrelin‐promoted phosphorylation of GluN1 and amplified N‐methyl‐d ‐aspartate receptor (NMDAR)‐mediated excitatory postsynaptic currents in the CA1 pyramidal cells of the hippocampus in slice preparations. The ghrelin‐induced responses were sensitive to a GHSR1a antagonist and inverse agonist, and were absent in GHSR1a homozygous knock‐out mice. These results indicated that activation of GHSR1a was critical in the ghrelin‐induced enhancement of the NMDAR function. Interestingly, heterozygous mouse hippocampi were also insensitive to ghrelin treatment, suggesting that a slight reduction in the availability of GHSR1a may be sufficient to negate the effect of ghrelin on GluN1 phosphorylation and NMDAR channel activities. In addition, NMDAR‐mediated spike currents, which are of dendritic origin, were blocked by the GHSR1a antagonist, suggesting the presence of GHSR1a on the pyramidal cell dendrites in physical proximity to NMDAR. Together with our findings on the localization of GHSR1a in the CA1 region of the hippocampus, which was shown by fluorescent ghrelin binding, immunoreactivity, and enhanced green fluorescent protein reporter gene expression, we conclude that the activation of GHSR1a favours rapid modulation of the NMDAR‐mediated glutamatergic synaptic transmission by phosphorylating GluN1 in the hippocampus.     

Effect of Deletion of Ghrelin‐O‐Acyltransferase on the Pulsatile Release of Growth Hormone in Mice

Ghrelin, a gut hormone originating from the post‐translational cleavage of preproghrelin, is the endogenous ligand of growth hormone secretagogue receptor 1a (GHS‐R1a). Within the growth hormone (GH) axis, the biological activity of ghrelin requires octanoylation by ghrelin‐O‐acyltransferase (GOAT), conferring selective binding to the GHS‐R1a receptor via acylated ghrelin. Complete loss of preproghrelin‐derived signalling (through deletion of the Ghrl gene) contributes to a decline in peak GH release; however, the selective contribution of endogenous acyl‐ghrelin to pulsatile GH release remains to be established. We assessed the pulsatile release of GH in ad lib. fed male germline goat^?/? mice, extending measures to include mRNA for key hypothalamic regulators of GH release, and peripheral factors that are modulated relative to GH release. The amount of GH released was reduced in young goat^?/? mice compared to age‐matched wild‐type mice, whereas pulse frequency and irregularity increased. Altered GH release did not coincide with alterations in hypothalamic Ghrh, Srif, Npy or Ghsr mRNA expression, or pituitary GH content, suggesting that loss of Goat does not compromise canonical mechanisms that contribute to pituitary GH production and release. Although loss of Goat resulted in an irregular pattern of GH release (characterised by an increase in the number of GH pulses observed during extended secretory events), this did not contribute to a change in the expression of sexually dimorphic GH‐dependent liver genes. Of interest, circulating levels of insulin‐like growth factor (IGF)‐1 were elevated in goat^?/? mice. This rise in circulating levels of IGF‐1 was correlated with an increase in GH pulse frequency, suggesting that sustained or increased IGF‐1 release in goat^?/? mice may occur in response to altered GH release patterning. Our observations demonstrate that germline loss of Goat alters GH release and patterning. Although the biological relevance of altered GH secretory patterning remains unclear, we propose that this may contribute to sustained IGF‐1 release and growth in goat^?/? mice.     

Ghrelin receptors as targets for novel motility drugs

Constipation arises from a multitude of causes, including aging, spinal cord injury (SCI), and dietary issues. The heterogeneity of inciting factors has made the treatment of constipation particularly challenging. Agonists of ghrelin receptors have beneficial effects on delayed gastric emptying, but less is known about their ability to improve colorectal motility. Recent publications indicate that the activation of the ghrelin receptors in the spinal cord can alleviate constipation due to dietary causes, Parkinsonism, and SCI in rodents. Ghrelin‐responsive neurons in the intermediolateral cell column of the lumbosacral spinal cord can activate enteric microcircuits that coordinate propulsive colorectal contractions, leading to defecation. Learning more about the properties of neurons in the spinal defecation center and the roles of ghrelin receptors in the defecation reflex will accelerate the development of improved treatments of constipation.     

Immunomodulatory effect of ghrelin in the intestinal mucosa

The gastrointestinal tract is the largest endocrine organ in the body and it produces a wide array of hormones and neuropeptides. Ghrelin, a 28‐amino acid hormone produced mainly by the X/A‐like endocrine cells in the gastric mucosa, has widespread tissue distribution and diverse physiological functions such as hormonal, orexigenic, metabolic, cardiovascular, neurological and immunological activities. Recent research has implicated ghrelin in gastrointestinal pathological conditions and immune system regulation, but its contribution is controversial. Although ghrelin levels are elevated in clinical active inflammatory bowel diseases, confirmation of its exact role using experimental models remains unclear. This review discusses the conflicting effects of ghrelin on intestinal inflammation, through the different possible immune and intracellular mechanisms and highlights new findings.