Chronic administration of ghrelin regulates plasma glucose and normalizes insulin levels following fasting hyperglycemia and hyperinsulinemia

The Potential Roles of Ghrelin in Metabolic Syndrome and Secondary Symptoms of Alzheimer's Disease

Although the major causative factors of Alzheimer's disease (AD) are the accumulation of amyloid β and hyperphosphorylated tau, AD can also be caused by metabolic dysfunction. The major clinical symptom of AD is cognitive dysfunction. However, AD is also accompanied by various secondary symptoms such as depression, sleep-wake disturbances, and abnormal eating behaviors. Interestingly, the orexigenic hormone ghrelin has been suggested to have beneficial effects on AD-related metabolic syndrome and secondary symptoms. Ghrelin improves lipid distribution and alters insulin sensitivity, effects that are hypothesized to delay the progression of AD. Furthermore, ghrelin can relieve depression by enhancing the secretion of hormones such as serotonin, noradrenaline, and orexin. Moreover, ghrelin can upregulate the expression of neurotrophic factors such as brain-derived neurotrophic factor and modulate the release of proinflammatory cytokines such as tumor necrosis factor α and interleukin 1β. Ghrelin alleviates sleep-wake disturbances by increasing the levels of melatonin, melanin-concentrating hormone. Ghrelin reduces the risk of abnormal eating behaviors by increasing neuropeptide Y and γ-aminobutyric acid. In addition, ghrelin increases food intake by inhibiting fatty acid biosynthesis. However, despite the numerous studies on the role of ghrelin in the AD-related pathology and metabolic disorders, there are only a few studies that investigate the effects of ghrelin on secondary symptoms associated with AD. In this mini review, our purpose is to provide the insights of future study by organizing the previous studies for the role of ghrelin in AD-related pathology and metabolic disorders.

Overall safety of relamorelin in adults with diabetic gastroparesis: Analysis of phase 2a and 2b trial data

BACKGROUND

Relamorelin, a pentapeptide ghrelin receptor agonist, accelerated gastric emptying significantly and improved symptoms in adults with diabetic gastroparesis in phase 2 trials.

AIM

To assess the safety and tolerability of relamorelin across phase 2 trials.

METHODS

Safety assessments in patients aged 18-75 years (weight, adverse events [AEs] and laboratory tests) from two randomised, double-blind phase 2 trials (NCT01571297, NCT02357420; results published previously) were reviewed descriptively. Analysis of covariance assessed treatment effect on glycated haemoglobin (HbA1c) and blood glucose post hoc. Phase 2a and 2b trial durations were, respectively, 4 weeks (relamorelin 10 µg once or twice daily [b.d.] or placebo b.d.) and 12 weeks (relamorelin 10, 30 or 100 µg or placebo b.d.) with 1- and 2-week, single-blind placebo run-ins.

RESULTS

Among 204 phase 2a and 393 phase 2b patients, respectively, 67% and 62% were female, and 88% and 89% had type 2 diabetes. Proportions of patients reporting serious AEs were similar across treatment groups, as were those with ≥1 treatment-emergent AE (TEAE). TEAE-related discontinuations were proportionally higher in relamorelin groups than placebo. Of 12 serious TEAEs in phase 2a, none occurred in >1 patient. In phase 2b, five serious TEAEs were reported in >1 patient, and one (100 µg) died (urosepsis), all unrelated to relamorelin. In phase 2b, increased HbA1c and fasting blood glucose levels were dose-related (P < 0.0001 and P = 0.0043, respectively).

CONCLUSIONS

Relamorelin showed acceptable safety and tolerability in phase 2 trials. Relamorelin may elevate blood glucose: this should be managed proactively in relamorelin-treated patients.

Chronic ghrelin administration restores hippocampal long-term potentiation and ameliorates memory impairment in rat model of Alzheimer's disease

Alzheimer's disease (AD), as a common age-related dementia, is a progressive manifestation of cognitive decline following synaptic failure resulted majorly by senile plaques composed of deposits of amyloid beta (Aβ). Ghrelin is a multifunctional peptide hormone with receptors present in various brain tissues including hippocampus and has been associated with neuroprotection, neuromodulation, and memory processing. Here, we investigated the neuroprotective and therapeutic effects of intracerebroventricular (icv) ghrelin infusion for 2 weeks on passive avoidance learning (PAL), memory retention, and synaptic plasticity in the hippocampal dentate gyrus (DG) and CA1 of both normal rats and Aβ1-42-induced neurotoxicity in AD model. Male Wistar rats were evaluated for their passive memory performance using a shuttle box while some groups had already received Aβ1-42 and/or chronic ghrelin. Using field potential recording, the induction of short- and long-term potentiation (STP and LTP) was studied in DG granule cells along with the LTP changes in CA1 pyramidal neurons through stimulation of the medial perforant path (mPP) and Schaffer collaterals (SCs), respectively. Our results demonstrated that chronic ghrelin treatment not only improved memory processing and retrieval in normal rats during the PAL task, but also promoted memory retention and alleviated memory loss by amelioration of Aβ1-42-induced synaptic plasticity impairment in AD subjects through augmentation of field excitatory postsynaptic potential (fEPSP) slope that led to LTP restitution in both the mPP-DG and the CA3-CA1 synapses. Meanwhile, STP was not significantly changed, meaning that although ghrelin enhanced postsynaptic excitability in DG, it did not change presynaptic transmitter release significantly. This suggests the involvement of postsynaptic mechanisms in long-term ghrelin-enhanced memory. In conclusion, it can be inferred that chronic ghrelin administration has an auspicious therapeutic value for impaired cognitive performance and memory deficits in AD-like neuropathology.

Decreased Serum Levels of Ghrelin and Brain-Derived Neurotrophic Factor in Premenopausal Women With Metabolic Syndrome

Objective

We aimed to investigate the association between serum levels of ghrelin and brain-derived neurotrophic factor (BDNF) with MetS and its components in premenopausal women.

Methods

43 patients with MetS and 43 healthy controls participated in this study. Participants' body mass index (BMI), waist circumference (WC), systolic and diastolic blood pressure (SBP and DBP) were measured. Serum levels of total cholesterol (TC), triglyceride (TG), low and high density lipoprotein cholesterol (LDL-C and HDL-C), fasting blood sugar (FBS), insulin, BDNF and ghrelin determined. Homeostasis model assessment insulin resistance index (HOMA-IR) was also calculated.

Results

Participants in MetS group had higher waist-to-hip ratios, elevated SBP and DBP, and higher serum levels of TG, FBS and insulin when compared with the control group. Serum ghrelin and BDNF levels were significantly lower in participants with MetS than in the healthier control subjects. There was a strong, positive correlation between serum ghrelin and BDNF levels. Both proteins negatively correlated with TG, FBS, HOMA-IR and positively with HDL-C. Furthermore, serum BDNF levels negatively associated with insulin levels.

Conclusions

The findings indicate that variations occur in the circulating level of ghrelin and BDNF proteins in MetS patients. A strong correlation between serum ghrelin and BDNF suggests that production, release or practice of these 2 proteins might be related mechanically.