Beneficial association of serum ghrelin and peptide YY with bone mineral density in the Newfoundland population

Role and molecular mechanism of ghrelin in degenerative musculoskeletal disorders

Ghrelin is a brain-gut peptide, and the first 28-peptide that was found in the gastric mucosa. It has a growth hormone (GH)-releasing hormone-like effect and can potently promote the release of GH from pituitary GH cells; however, it is unable to stimulate GH synthesis. Therefore, ghrelin is believed to play a role in promoting bone growth and development. The correlation between ghrelin and some degenerative diseases of the musculoskeletal system has been reported recently, and ghrelin may be one of the factors influencing degenerative pathologies, such as osteoporosis, osteoarthritis, sarcopenia and intervertebral disc degeneration. With population ageing, the risk of health problems caused by degenerative diseases of the musculoskeletal system gradually increases. In this article, the roles of ghrelin in musculoskeletal disorders are summarized to reveal the potential effects of ghrelin as a key target in the treatment of related bone and muscle diseases and the need for further research.

Effect of adipokine and ghrelin levels on BMD and fracture risk: an updated systematic review and meta-analysis

Context

Circulating adipokines and ghrelin affect bone remodeling by regulating the activation and differentiation of osteoblasts and osteoclasts. Although the correlation between adipokines, ghrelin, and bone mineral density (BMD) has been studied over the decades, its correlations are still controversial. Accordingly, an updated meta-analysis with new findings is needed.

Objective

This study aimed to explore the impact of serum adipokine and ghrelin levels on BMD and osteoporotic fractures through a meta-analysis.

Data sources

Studies published till October 2020 in Medline, Embase, and the Cochrane Library were reviewed.

Study selection

We included studies that measured at least one serum adipokine level and BMD or fracture risk in healthy individuals. We excluded studies with one or more of the following: patients less than 18 years old, patients with comorbidities, who had undergone metabolic treatment, obese patients, patients with high physical activities, and a study that did not distinguish sex or menopausal status.

Data extraction

We extracted the data that include the correlation coefficient between adipokines (leptin, adiponectin, and resistin) and ghrelin and BMD, fracture risk by osteoporotic status from eligible studies.

Data synthesis

A meta-analysis of the pooled correlations between adipokines and BMD was performed, demonstrating that the correlation between leptin and BMD was prominent in postmenopausal women. In most cases, adiponectin levels were inversely correlated with BMD. A meta-analysis was conducted by pooling the mean differences in adipokine levels according to the osteoporotic status. In postmenopausal women, significantly lower leptin (SMD = -0.88) and higher adiponectin (SMD = 0.94) levels were seen in the osteoporosis group than in the control group. By predicting fracture risk, higher leptin levels were associated with lower fracture risk (HR = 0.68), whereas higher adiponectin levels were associated with an increased fracture risk in men (HR = 1.94) and incident vertebral fracture in postmenopausal women (HR = 1.18).

Conclusions

Serum adipokines levels can utilize to predict osteoporotic status and fracture risk of patients.

Systematic review registration

https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42021224855, identifier CRD42021224855.

Zhuang-Gu-Fang Treats Osteoporosis in Ovariectomized Rats by Increasing the Osteogenesis-Related Factors Leptin, Ghrelin, and PYY

Zhuang-Gu-Fang is a Chinese medicinal compound mixture, which is mainly composed of traditional remedies like the Epimedium Herb, Astragalus, and Eucommia among many others. The study is aimed at investigating the therapeutic effect of Zhuang-Gu-Fang in ovariectomized rats. Fifty six-month-old Wistar rats were randomly selected and divided into 5 groups (n = 10), namely, model group, positive group, low-dose Chinese medicine group, medium-dose group, and high-dose group. Another 10 sham operation Wistar rats were taken as a negative control group. After 3 months of intervention, the bone mineral density (BMD), procollagen type I N-peptide (PINP), beta C-terminal cross-linked telopeptides of type I collagen carboxyl-terminal peptide (β-CTX), Leptin, Ghrelin, and Peptide YY (PYY) of each group were measured. Besides, the ultrastructure of bone structure and osteoblasts was also observed by transmission electron microscopy. Western blot method was used to detect the expression levels of Leptin and Ghrelin in bone tissue, and RT-PCR detected the mRNA expression levels of Leptin and Ghrelin. BMD test indicated that Zhuang-Gu-Fang could effectively prevent the loss of tibia bone in ovariectomized rats. Histomorphology analysis showed that Zhuang-Gu-Fang could preserve trabecular bone structure integrity and improve osteoblast ultrastructure. Notably, the study found out that Zhuang-Gu-Fang worked through balancing the bone metabolism via increasing bone formation/resorption ratio. Additionally, Zhuang-Gu-Fang highlighted the recovery effects in multiple levels of osteogenesis- and osteanagenesis-related factors Leptin, Ghrelin, and PYY. Conclusively, the study proved the therapeutic potential of the Zhuang-Gu-Fang for postmenopausal osteoporosis (PMOP) and further revealed that its therapeutic effect was related to the balance of bone metabolism and the recovery effects of bone-related factors Leptin, Ghrelin, and PYY.

Dysregulation of the ghrelin/RANKL/OPG pathway in bone mass is related to AIS osteopenia

BACKGROUND

Osteopenia has been well documented in adolescent idiopathic scoliosis (AIS), and ghrelin has been shown to have a positive effect on bone metabolism. However, the circulating level of ghrelin is increased in AIS osteopenia, and the relationship between ghrelin and low bone mass in AIS osteopenia remains unclear.

METHOD

A total of 563 AIS and 281 age-matched controls were recruited for this study. Anthropometry and bone mass were measured in all participants. Plasma ghrelin levels were determined by enzyme-linked immunosorbent assay (ELISA) in both AIS and control groups. An improved multiplex ligation detection reaction was performed to analyze single-nucleotide polymorphisms (SNPs). Facet joints were collected and subjected to immunohistochemistry; osteogenic gene and protein expression was also measured. Furthermore, primary cells were extracted from facet joints and bone marrow to observe the response to ghrelin stimulation.

RESULTS

The body mass index was lower and circulating ghrelin was markedly higher in the AIS osteopenia group than in the control group. No significant difference was observed in four ghrelin level-related SNPs between the AIS osteopenia and control groups. RNA and protein analyses revealed higher RANKL/OPG and lower runx2 levels in AIS cancellous bone. Compared with normal primary osteoblasts and BMSCs, AIS osteopenia primary cells were insensitive to the same ghrelin concentration gradient and showed lower osteogenic ability, increases in OPG and decreases in RANKL.

CONCLUSION

Our results indicate that high circulating ghrelin levels may not result from gene variations in AIS osteopenia. Dysregulation of the ghrelin/RANKL/OPG pathway may lead to decreased osteogenic ability of osteoblasts and BMSCs, which may be related to lower bone mass in AIS osteopenia.

Increases in PYY and uncoupling of bone turnover are associated with loss of bone mass after gastric bypass surgery

CONTEXT

The gut hormones peptide YY (PYY) and ghrelin mediate in part the metabolic benefits of Roux-en-Y gastric bypass (RYGB) surgery. However, preclinical data suggest these hormones also affect the skeleton and could contribute to postoperative bone loss.

OBJECTIVE

We investigated whether changes in fasting serum total PYY and ghrelin were associated with bone turnover marker levels and loss of bone mineral density (BMD) after RYGB.

DESIGN, SETTING, PARTICIPANTS

Prospective cohort of adults undergoing RYGB (n=44) at San Francisco academic hospitals.

MAIN OUTCOME MEASURES

We analyzed 6-month changes in PYY, ghrelin, bone turnover markers, and BMD by dual-energy x-ray absorptiometry (DXA) and quantitative computed tomography (QCT). We calculated the uncoupling index (UI), reflecting the relative balance of bone resorption and formation.

RESULTS

Postoperatively, there was a trend for an increase in PYY (+25pg/mL, p=0.07) and a significant increase in ghrelin (+192pg/mL, p<0.01). PYY changes negatively correlated with changes in spine BMD by QCT (r=-0.36, p=0.02) and bone formation marker P1NP (r=-0.30, p=0.05). Relationships were significant after adjustments for age, sex, and weight loss. No consistent relationships were found between ghrelin and skeletal outcomes. Mean 6-month UI was -3.3; UI correlated with spine BMD loss by QCT (r=0.40, p=0.01).

CONCLUSIONS

Postoperative PYY increases were associated with attenuated increases in P1NP and greater declines in spine BMD by QCT. Uncoupling of bone turnover correlated with BMD loss. These findings suggest a role for PYY in loss of bone mass after RYGB and highlight the relationship between intestinal and skeletal metabolism.

CHANGES IN BONE MINERAL PARAMETERS AFTER SLEEVE GASTRECTOMY: RELATIONSHIP WITH GHRELIN AND PLASMA ADIPOKINE LEVELS

CONTEXT

Metabolic surgery is currently the most efficient treatment for obesity, but concern is raised about the possible long-term nutritional side effects. Bone metabolism is often adversely affected after surgery, but literature data are contradictory.

OBJECTIVE

The aim of this study was to evaluate the evolution of bone mass parameters in the first year after laparoscopic sleeve gastrectomy in relation to anthropometric and body composition parameters and specific hormones of obesity.

DESIGN

We conducted a prospective study on 75 patients with obesity that underwent metabolic surgery over a course of 18 months at our center, with a follow-up period of 12 months.

SUBJECTS AND METHODS

All patients underwent a complex preoperative assessment and were required to return for medical follow-up at 6 and 12 months after surgery. Each visit included anthropometric parameters, DEXA and determination of specific hormonal parameters.

RESULTS

We noticed a significant improvement in anthropometric and body composition parameters after surgery. The value of adiponectin presented a significant increase after surgery and leptin showed a significant decrease at 6 and 12 months postoperative; ghrelin level decreased postoperative compared to preoperative, but without statistical significance. We observed no reduction in BMD after surgery, but a significant improvement in BMC at 12 months after surgery compared to preoperative. Ghrelin negatively correlated to BMD preoperative.

CONCLUSIONS

Despite the significant alterations in anthropometric, body composition and hormonal parameters, we found no negative effect on BMD and BMC in our study population.

Associations of serum leptin, ghrelin and peptide YY levels with physical activity and cardiorespiratory fitness in adolescent boys with different BMI values

The aim of this study was to investigate the differences in associations of serum acylated and des-acylated ghrelin, peptide YY (PYY) and leptin levels with physical activity (PA) and cardiorespiratory fitness (CReF) in adolescent boys (mean age of 14.0 years) with overweight (OWB; n=55) and with normal weight (NWB; n=154).

METHODS

Total PA was measured by 7-day accelerometry (counts/min) and CReF by peak oxygen consumption (VO²peak/kg).

RESULTS

No differences were found in serum PYY, acylated ghrelin or des-acyl ghrelin levels, whereas mean leptin (11.6±10.6 vs. 2.0±2.7 ng/ml; p<0.05) and insulin (18.1±8.7 vs. 11.0±6.2 mU/l; p<0.05) levels were significantly higher in OWB compared to NWB. Mean CReF was significantly lower in OWB compared to NWB (39.7±8.7 vs. 50.5±6.8 ml/min/kg; p<0.05). Leptin was negatively correlated with CReF in both groups (r=-0.43; p<0.05), des-acylated ghrelin with CReF only in OWB (r =-0.36; p<0.05). In OWB leptin was negatively correlated with total PA (r=-0.32; p<0.05) and positively with sedentary time of PA (r=0.35; p<0.05). In NWB 28.1% of the variability of CReF was determined by leptin and insulin resistance index (HOMA-IR), whereas in OWB 71.9% was determined by trunk FM and BMI.

CONCLUSIONS

Leptin concentration was inversely associated with CReF in adolescent boys independently of BMI in both groups, while des-acylated ghrelin was associated with CReF only in OWB. Low PA in OWB was associated with high serum leptin level.

Boning up on DPP4, DPP4 substrates, and DPP4-adipokine interactions: Logical reasoning and known facts about bone related effects of DPP4 inhibitors

Dipeptidyl peptidase 4 (DPP4) is a conserved exopeptidase with an important function in protein regulation. The activity of DPP4, an enzyme which can either be anchored to the plasma membrane or circulate free in the extracellular compartment, affects the glucose metabolism, cellular signaling, migration and differentiation, oxidative stress and the immune system. DPP4 is also expressed on the surface of osteoblasts, osteoclasts and osteocytes, and was found to play a role in collagen metabolism. Many substrates of DPP4 have an established role in bone metabolism, among which are incretins, gastrointestinal peptides and neuropeptides. In general, their effects favor bone formation, but some effects are complex and have not been completely elucidated. DPP4 and some of its substrates are known to interact with adipokines, playing an essential role in the energy metabolism. The prolongation of the half-life of incretins through DPP4 inhibition led to the development of these inhibitors to improve glucose tolerance in diabetes. Current literature indicates that the inhibition of DPP4 activity might also result in a beneficial effect on the bone metabolism, but the long-term effect of DPP4 inhibition on fracture outcome has not been entirely established. Diabetic as well as postmenopausal osteoporosis is associated with an increased activity of DPP4, as well as a shift in the expression levels of DPP4 substrates, their receptors, and adipokines. The interactions between these factors and their relationship in bone metabolism are therefore an interesting field of study.

Associations between Bone Mineral Characteristics and Serum Levels of Ghrelin and Peptide YY in Overweight Adolescent Boys

BACKGROUND/AIMS

The role of ghrelin and peptide YY (PYY) in bone mineralization is not fully known. The aim of this study was to determine whether acylated and des-acyl ghrelin and PYY in addition to leptin are related to bone mineral density (BMD) in adolescent overweight boys (OWB) and normal-weight boys (NWB).

PARTICIPANTS AND METHODS

Fifty- five OWB (BMI >85th percentile) and 154 NWB (BMI <85th percentile) aged 12-16 years participated in this study. Fasting serum acylated and des-acyl ghrelin, PYY, leptin, testosterone levels, total body (TB) and lumbar spine (LS) bone mineral content (BMC), and BMD were measured. TB BMC for height and TB and LS bone mineral apparent density (BMAD) were calculated.

RESULTS

No differences were seen in acylated and des-acyl ghrelin or PYY levels, while the leptin levels were significantly higher in the OWB compared to the NWB. In the OWB, TB BMAD was positively correlated with acylated ghrelin and leptin, and TB BMC for height was positively correlated with PYY. In the OWB, the variability of TB BMD was determined by TB fat-free mass and des-acyl ghrelin, whereas the variability of TB BMAD was determined by leptin.

CONCLUSIONS

Des-acyl ghrelin and PYY are involved in the bone mineralization process in puberty, and the impact can vary between normal and overweight subjects.

The neuropeptide Y-ergic system: potential therapeutic target against bone loss with obesity treatments

Obesity is no longer considered to provide protection against osteoporosis. Moreover, treatments for obesity are now suspected of reducing bone mass. With the escalating incidence of obesity, combined with increases in the frequency, duration and intensity of interventions used to combat it, we face a potential increase in health burden due to osteoporotic fractures. The neuropeptide Y-ergic system offers a potential target for the prevention and anabolic treatment of bone loss in obesity, due to its dual role in the regulation of energy homeostasis and bone mass. Although the strongest stimulation of bone mass by this system appears to occur via indirect hypothalamic pathways involving Y2 receptors (one of the five types of receptors for neuropeptide Y), Y1 receptors on osteoblasts (bone-forming cells) induce direct effects to enhance bone mass. This latter pathway may offer a suitable target for anti-osteoporotic treatment while also minimizing the risk of adverse side effects.

Ghrelin Increases Beta-Catenin Level through Protein Kinase A Activation and Regulates OPG Expression in Rat Primary Osteoblasts

Ghrelin, by binding growth hormone secretagogue receptor (GHS-R), promotes osteoblast proliferation but the signaling mechanism of GHS-R on these cells remains unclear. Since canonical Wnt/β-catenin pathway is critically associated with bone homeostasis, we investigated its involvement in mediating ghrelin effects in osteoblasts and in osteoblast-osteoclast cross talk. Ghrelin (10(-10)M) significantly increased β-catenin levels in rat osteoblasts (rOB). This stimulatory action on β-catenin involves a specific interaction with GHS-R1a, as it is prevented by the selective GHS-R1a antagonist, D-Lys(3)-GHRP-6 (10(-7)M). The effect of ghrelin on β-catenin involves the phosphorylation and inactivation of GSK-3β via protein kinase A (PKA). Inhibition of PKA activity reduces the facilitatory action of ghrelin on β-catenin stabilization. Ghrelin treatment of rOB significantly increases the expression of osteoprotegerin (OPG), which plays an important role in the regulation of osteoclastogenesis, and this effect is blocked by D-Lys(3)-GHRP-6. Furthermore, ghrelin reduced RANKL/OPG ratio thus contrasting osteoclastogenesis. Accordingly, conditioned media from rOB treated with ghrelin decreased the number of multinucleated TRAcP+ cells as compared with the conditioned media from untreated-control rOB. Our data suggest new roles for ghrelin in modulating bone homeostasis via a specific interaction with GHSR-1a in osteoblasts with subsequent enhancement of both β-catenin levels and OPG expression.

The hunger games of skeletal metabolism

Gastrointestinal peptides and adipokines are critical signalling molecules involved in controlling whole-body energy homeostasis. These circulating hormones regulate a variety of biological responses such as hunger, satiety and glucose uptake. In vivo experiments have established that these hormones also regulate bone metabolism, while associations between these hormones and bone mass have been observed in human clinical studies. With a focus on recent research, this review aims to describe the roles that gastrointestinal peptides (ghrelin, peptide YY, glucose-dependent insulinotropic polypeptide, glucagon-like peptide 1 and glucagon-like peptide 2) and adipokines (leptin and adiponectin) have in bone metabolism and to examine their effects on bone in situations of altered metabolism, such as obesity. As the prevalence of obesity continues to increase, there is a growing interest in understanding the interactions between nutritional regulators from the gut and adipose tissue and their influence on bone mass.

The bone and fat connection in inflammatory bowel diseases

Osteopenia and osteoporosis are common manifestations in inflammatory bowel diseases (IBD) but the pathogenetic mechanism of bone loss in IBD is only partially understood. There is evidence that fat mass is an important determinant of the bone mineral density and adipose-derived factors seem to play an important role for the association between fat mass and bone mass. The association between adiposity and low bone density is rather poorly studied in IBD, but emerging data on adipokines in IBD in relation to osteoporosis provide a novel pathophysiological concept that may shed light on the etiology of bone loss in IBD. It could be suggested that adipokines interfere in bone metabolism by altering the sensitive balance between osteoblasts and osteoclasts although further studies in this setting are needed.

Impairment of ghrelin synthesis in Helicobacter pylori-colonized stomach: New clues for the pathogenesis of H. pylori-related gastric inflammation

Ghrelin, the ligand of growth hormone secretagogue receptor 1a, takes part in several functions of the digestive system, including regulation of appetite, energy homeostasis, gastric acid secretion and motility. Ghrelin has also immunoregulatory properties and is supposed to inhibit some inflammatory pathways that can mediate gastric damage. Interestingly, ghrelin synthesis is reduced in the gastric mucosa of patients with Helicobacter pylori (H. pylori) infection, a worldwide condition inducing a T helper (Th)1/Th17 cell response-driven gastritis, which may evolve towards gastric atrophy and cancer. In this article, we review the available data on the expression of ghrelin in H. pylori infection and discuss how the defective ghrelin synthesis may contribute to sustain the ongoing inflammatory response in this disease.