Investigation of the effect of ghrelin on bone fracture healing in rats

Ghrelin alleviated TiO2 NPs-induced inhibition of endochondral osteogenesis and promoted longitudinal growth of long bones in juvenile rats via Wnt/β-catenin signaling pathway

Titanium dioxide nanoparticles (TiO2 NPs) are widely used in children's daily necessities and foods, and their health hazards to children have attracted particular attention. Childhood is a critical time for accelerated bone growth and development. Current studies revealed that TiO2 NPs exposure causes bone damage in juvenile rats; however, the underlying mechanism is unknown. Ghrelin is a polypeptide hormone that is considered to be a candidate factor for regulating bone growth and development. In this research, 3-week-old juvenile male rats were administered 0, 100 or 200 mg/kg TiO2 NPs and 50 μg/kg ghrelin for 4 weeks to explore the underlying mechanism of TiO2 NPs-induced bone damage, and the protective effect of ghrelin. Our results revealed that TiO2 NPs resulted in decreased synthesis of bone growth-related hormones, disturbed bone metabolism, and destruction of bone structure. Further mechanism studies showed that TiO2 NPs inhibited Wnt/β-catenin pathway, reduced collagen synthesis, inhibited chondrocyte proliferation and differentiation, promoted chondrocyte apoptosis, and inhibited endochondral osteogenesis, ultimately leading to long bone longitudinal growth retardation and osteoporosis. Ghrelin alleviated the negative effects of TiO2 NPs-induced bone growth in juvenile rats by upregulating the Wnt/β-catenin signaling pathway. This study provided a reference for the clinical treatment of growth retardation and idiopathic short stature in juvenile children caused by environmental pollutants.

Sinusoidal alternating electromagnetic field accelerates fracture healing in rats

OBJECTIVES

To investigate the effect of sinusoidal alternating electromagnetic field (SEMF) on fracture healing and its mechanism.

METHODS

Femoral fracture model was established using specific pathogen free male Wistar rats. Thirty rats were randomly divided into the control and SEMF groups with 15 rats in each group. The SEMF group was given 50 Hz 1.8 mT for 90 min every day, while the control group was not treated. X-ray examinations were performed every two weeks to determine the formation of bone scabs. Three rats from both groups were sacrificed after 2 and 4 weeks of treatment. Protein was extracted from the fractured femurs, and the expression of type Ⅰ collagen (COL-1), osterix (OSX), Runt-related transcription factor 2 (RUNX2), and vascular endothelial growth factor (VEGF) was detected by Western blotting. After 8 weeks, the femur on the operated side was taken for micro-CT scanning to observe fracture healing, angiography to observe blood vessel growth, and organs such as hearts, livers, spleens, lungs, and kidneys were taken for safety evaluation by hematoxylin-eosin staining (HE staining).

RESULTS

The bone scab scores of the SEMF group were significantly higher than those of the control group after 2, 4, 6, and 8 weeks of treatment (all P<0.01). The fracture healing of the SEMF group was better than that of the control group after 8 weeks, and the bone volume scores of the two groups were 0.243±0.012 and 0.186±0.008, respectively (P<0.01); the number of blood vessels in the SEMF group was also more than that of the control group after 8 weeks. Western blotting results showed that the expressions of COL-1, OSX, RUNX2, and VEGF were higher in the SEMF group than those in the control group after 2 and 4 weeks of treatment (all P<0.05). HE staining showed that histopathological results of the examined organs were normal in both groups.

CONCLUSIONS

SEMF can accelerate fracture healing by promoting the expression of osteogenic factors and vascular proliferation without significant adverse effects.

Cellular and Molecular Mechanisms Associating Obesity to Bone Loss

Obesity is an alarming disease that favors the upset of other illnesses and enhances mortality. It is spreading fast worldwide may affect more than 1 billion people by 2030. The imbalance between excessive food ingestion and less energy expenditure leads to pathological adipose tissue expansion, characterized by increased production of proinflammatory mediators with harmful interferences in the whole organism. Bone tissue is one of those target tissues in obesity. Bone is a mineralized connective tissue that is constantly renewed to maintain its mechanical properties. Osteoblasts are responsible for extracellular matrix synthesis, while osteoclasts resorb damaged bone, and the osteocytes have a regulatory role in this process, releasing growth factors and other proteins. A balanced activity among these actors is necessary for healthy bone remodeling. In obesity, several mechanisms may trigger incorrect remodeling, increasing bone resorption to the detriment of bone formation rates. Thus, excessive weight gain may represent higher bone fragility and fracture risk. This review highlights recent insights on the central mechanisms related to obesity-associated abnormal bone. Publications from the last ten years have shown that the main molecular mechanisms associated with obesity and bone loss involve: proinflammatory adipokines and osteokines production, oxidative stress, non-coding RNA interference, insulin resistance, and changes in gut microbiota. The data collection unveils new targets for prevention and putative therapeutic tools against unbalancing bone metabolism during obesity.

Circadian clock genes as promising therapeutic targets for bone loss

The circadian clock regulates many key physiological processes such as the sleep-wake cycle, hormone release, cardiovascular health, glucose metabolism and body temperature. Recent evidence has suggested a critical role of the circadian system in controlling bone metabolism. Here we review the connection between bone metabolism and the biological clock, and the roles of these mechanisms in bone loss. We also analyze the regulatory effects of clock-related genes on signaling pathways and transcription factors in osteoblasts and osteoclasts. Additionally, osteocytes and endothelial cells (ECs) regulated by the circadian clock are also discussed in our review. Furthermore, we also summarize the regulation of circadian clock genes by some novel modulators, which provides us with a new insight into a potential strategy to prevent and treat bone diseases such as osteoporosis by targeting circadian genes.