Systemic leptin administration alters callus VEGF levels and enhances bone fracture healing in wildtype and ob/ob mice

Emerging roles of nerve-bone axis in modulating skeletal system

Over the past decades, emerging evidence in the literature has demonstrated that the innervation of bone is a crucial modulator for skeletal physiology and pathophysiology. The nerve-bone axis sparked extensive preclinical and clinical investigations aimed at elucidating the contribution of nerve-bone crosstalks to skeleton metabolism, homeostasis, and injury repair through the perspective of skeletal neurobiology. To date, peripheral nerves have been widely reported to mediate bone growth and development and fracture healing via the secretion of neurotransmitters, neuropeptides, axon guidance factors, and neurotrophins. Relevant studies have further identified several critical neural pathways that stimulate profound alterations in bone cell biology, revealing a complex interplay between the skeleton and nerve systems. In addition, inspired by nerve-bone crosstalk, novel drug delivery systems and bioactive materials have been developed to emulate and facilitate the process of natural bone repair through neuromodulation, eventually boosting osteogenesis for ideal skeletal tissue regeneration. Overall, this work aims to review the novel research findings that contribute to deepening the current understanding of the nerve-bone axis, bringing forth some schemas that can be translated into the clinical scenario to highlight the critical roles of neuromodulation in the skeletal system.

Alterations of ocular surface parameters in patients with obstructive sleep apnea syndrome

Purpose

This study aimed to evaluate changes in ocular surface parameters among obstructive sleep apnea syndrome (OSAS) patients.

Methods

44 healthy volunteers (88 eyes) and 27 OSAS patients (54 eyes) were recruited in our cross-sectional study. 14 patients were classified as mild&moderate OSAS, and 13 patients were classified as severe OSAS. For evaluating the ocular surface, the following tests were conducted: the height of tear meniscus (TMH), first non-invasive tear break-up time (FNITBUT), mean non-invasive tear break-up time (MNITBUT), the score of Meibomian gland dropout area (Meiboscore), the tear test of anesthesia-free Schirmer I (SIT), corneal fluorescein staining (CFS), partial blinks rate (PBR), the lipid layer thickness (LLT), ocular surface disease index (OSDI). The results obtained from the study were analyzed and compared among the groups.

Results

FNITBUT, MNITBUT, and TMH were lower. OSDI, CFS, Meiboscore and PBR were higher in the OSAS group than those in the control group. The mild&moderate as well as the severe OSAS subgroups had statistically significantly lower TMH, and higher OSDI and PBR than the control group. Meanwhile, we found there were no significant differences between two OSAS subgroups. CFS was higher in the severe OSAS group than the mild&moderate OSAS group. Significantly lower FNITBUT, MNITBUT and higher Meiboscore were observed in the severe OSAS subgroup than in the control group, and MNITBUT was higher in severe OSAS objects than in the mild&moderate OSAS objects. LLT and SIT did not exhibit significant differences among control and OSAS subgroups. FNITBUT and MNITBUT showed significantly negative correlations with BMI, while Meiboscore showed a significant positive correlation with AHI.

Conclusion

Patients with OSAS have a tendence of dry eyes, whereas control subjects do not. This indicates us that the OSAS patients should pay more attention to ocular surface care.

Interoceptive regulation of skeletal tissue homeostasis and repair

Recent studies have determined that the nervous system can sense and respond to signals from skeletal tissue, a process known as skeletal interoception, which is crucial for maintaining bone homeostasis. The hypothalamus, located in the central nervous system (CNS), plays a key role in processing interoceptive signals and regulating bone homeostasis through the autonomic nervous system, neuropeptide release, and neuroendocrine mechanisms. These mechanisms control the differentiation of mesenchymal stem cells into osteoblasts (OBs), the activation of osteoclasts (OCs), and the functional activities of bone cells. Sensory nerves extensively innervate skeletal tissues, facilitating the transmission of interoceptive signals to the CNS. This review provides a comprehensive overview of current research on the generation and coordination of skeletal interoceptive signals by the CNS to maintain bone homeostasis and their potential role in pathological conditions. The findings expand our understanding of intersystem communication in bone biology and may have implications for developing novel therapeutic strategies for bone diseases.

Leptin-VEGF crosstalk in excess body mass and related disorders: A systematic review

By 2030, it is expected that a billion people will have suffer from obesity. Adipose tissue synthesizes leptin, an adipokine that affects cardiovascular risk. Leptin intensifies the synthesis of vascular endothelial growth factor (VEGF). Our study reviews recent reports on leptin-VEGF crosstalk in obesity and related disorders. PubMed, Web of Science, Scopus, and Google Scholar were searched. One hundred and one articles involving human, animal, and in vitro research were included. In vitro studies show the crucial role of interaction between endothelial cells and adipocytes and hypoxia as a factor that intensifies leptin's effects on VEGF. Leptin-VEGF crosstalk promotes the progression of cancer. The animal research reveal that a high-fat diet enhances leptin and VEGF crosstalk. Genetic and epigenetic mechanisms and procreator-offspring programming may be involved in leptin-VEGF crosstalk. Some female-specific characteristics of leptin-VEGF relation in obesity were observed. The human studies have shown that increased leptin and VEGF synthesis and leptin-VEGF crosstalk are factors linking obesity with elevated cardiovascular risk. The studies of the last 10 years documented a range of significant aspects of leptin-VEGF crosstalk specific for obesity and related disorders, shedding new light on the link between obesity and increased cardiovascular risk.

Leptin-deficient ob/ob mice exhibit periodontitis phenotype and altered oral microbiome

BACKGROUND AND OBJECTIVE

Leptin-deficient obesity is associated with various systemic diseases including diabetes and low bone mass phenotype. However, the periodontal status of leptin-deficient obese individuals is still unclear. In this study, we aimed to analyze the periodontal status, alveolar bone phenotype, and oral microbiome status in leptin-deficient obese mice (ob/ob mice).

METHODS

This study used 12-week-old wild-type and ob/ob male mice. The alveolar bone phenotype and periodontal status in the maxilla were analyzed by micro-CT and histological analysis. Osteoclasts in alveolar bone were visualized by TRAP staining. Expressions of inflammatory markers (MMP-9, IL-1β, and TGF-β1) and osteoclastogenic markers (RANKL and OPG) in periodontium were analyzed by immunohistochemistry and RT-qPCR. The oral microbiome was analyzed by 16 S rDNA sequencing.

RESULTS

CEJ-ABC distance in maxillary molars (M1-M3) of ob/ob mice was significantly higher compared with that of wild-type. The alveolar bone BV/TV ratio was reduced in ob/ob mice compared with wild-type. Higher numbers of osteoclasts were observed in ob/ob mice alveolar bone adjacent to the molar root. Epithelial hyperplasia in gingiva and disordered periodontal ligaments was observed in ob/ob mice. RANKL/OPG expression ratio was increased in ob/ob mice compared with wild-type. Expressions of inflammatory markers MMP-9, IL-1β, and TGF-β1 were increased in ob/ob mice compared with wild-type. Oral microbiome analysis showed that beneficial bacteria Akkermansia and Ruminococcaceae_UCG_014 were more abundant in the wild-type mice while the inflammation-related Flavobacterium was more abundant in ob/ob mice.

CONCLUSION

In conclusion, ob/ob mice showed higher expressions of inflammatory factors, increased alveolar bone loss, lower abundance of the beneficial bacteria, and higher abundance of inflammatory bacteria in the oral cavity, suggesting leptin-deficient obesity as a risk factor for periodontitis development in ob/ob mice.

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.

Local administration of low doses of exogenous BMP2 and leptin promotes ectopic bone regeneration in leptin-deficient mice

BACKGROUND

Obesity and leptin deficiency are associated with compromised bone regeneration.

OBJECTIVE

This study aims to investigate the role of locally administrated low-dose BMP2+leptin on bone regeneration in leptin-deficient obese (ob/ob) mice.

METHODS

Wildtype (WT) and ob/ob mice were divided into 3 groups (4 mice/group): BMP2 (5 μg) group, BMP2+low-dose leptin (1 μg) group, and BMP2+high-dose leptin (2.5 μg) group. WT mice were used as control mice. An equal size absorbable collagen sponge was prepared by loading the BMP2 or/and leptin and implanted subcutaneously. After 19 days, samples were collected and analyzed by micro-CT and H&E staining.

RESULTS

No significant difference in bone regeneration among the three groups in WT mice. Quantification of newly formed bone parameters from micro-CT and H&E staining showed that low-dose BMP2 treatment formed less new bone in ob/ob mice compared to WT. BMP2+low-dose leptin treatment substantially rescued the compromised bone regeneration in ob/ob mice up to the level in WT mice. However, the BMP2 and high dose of leptin failed to rescue the compromised bone regeneration in ob/ob mice.

CONCLUSION

Our findings suggest that a combination of the low-dose BMP2 and leptin could be a strategy to promote osteogenesis in obese populations with leptin deficiency.

Leptin's concentration in tears and dry eye: a clinical observational study

AIM

To investigate the concentration of leptin in tears and its correlation with dry eye symptoms and signs.

METHODS

The study enrolled individuals (n=39) responding to an advertising or dry eye patients (n=58) from the Ophthalmology Department. Tear samples were collected for leptin concentration measuring. Ocular Surface Disease Index (OSDI), tear meniscus height (TMH), tear break up time (TBUT), cornea fluorescein staining, Schirmer test (ST) and impression cytology (IC) were assessed. Leptin concentration in tears of dry eye patients and healthy controls, and its correlation with clinical features of dry eye disease (DED) were analyzed.

RESULTS

Age, body mass index (BMI), OSDI scores and cornea fluorescein staining scores showed a negative correlation with leptin concentration in tears (r=-0.340, P=0.001; r=-0.332, P=0.001; r=-0.258, P=0.011; r=-0.424, P<0.001, respectively). ST showed positive correlation with leptin concentration in tears (r=0.206, P=0.045). No significant difference was observed in leptin concentration between dry eye patients and controls (P=0.682). Multivariate linear regression analysis revealed that dry eye, OSDI, corneal fluorescein staining scores and ST correlated with leptin concentration in tears.

CONCLUSION

This is the first study measuring leptin concentration in tears. The correlation between leptin concentration and DED symptoms and signs reveal that leptin level correlated with the dry eye, potentially contributing to repair of ocular damage and dry eye improvement.

Effect of adiponectin secreted from adipose-derived stem cells on bone-fat balance and bone defect healing

The efficacy of adiponectin (APN) in regulating bone metabolism remains controversial. This study aimed to investigate the role of APN secreted from adipose-derived stem cells on adipogenesis and osteogenesis. Human APN gene was transfected via recombinant adenovirus into adipose derived stem cells (ASCs) in vitro and were cocultured with bone marrow mesenchymal stem cells (BMSCs) in using a transwell chamber. Adipogenesis was inhibited in APN-transfected ASCs; in BMSCs, adipogenesis was inhibited, but osteogenesis was promoted in coculture with APN-transfected ASCs. Next, the same adenovirus construct was transfected into the abdominal adipose tissue of a Sprague Dawley rat in vivo, and then a tibia defect was established in the same rat. We confirmed there was higher gene and protein expression of APN in ASCs and the abdominal adipose tissue of these rat models. Development of adipocytes in abdominal adipose tissue was suppressed, and less new bone was formed in the bone defect area. In conclusion, APN secreted from ASCs could directly inhibit adipogenesis in ASCs and BMSCs and promote osteogenesis in the latter. However, APN overexpression in adipose tissue was inversely associated with bone formation in tibia defects potentially due to decreased levels of circulating bone-activating hormones.

Triple-threat activity of PEDF in bone tumors: Tumor inhibition, tissue preservation and cardioprotection against doxorubicin

Pigment epithelium-derived factor (PEDF) is known for its osteogenic properties, but its effects against primary and secondary bone tumors have not comprehensively been demonstrated. We show the ubiquitous expression of PEDF in murine embryonic tissue. Continuous administration of PEDF in pregnant mice for five days did not adversely affect foetal health, despite PEDF's known potent antiangiogenic properties. In the case of the devastating childhood bone cancer osteosarcoma, PEDF has direct anticancer activity per se, and protects against the toxicity of doxorubicin in the heart, small intestine and testes. PEDF demonstrated anti-proliferative and pro-apoptotic effects against human prostate and breast cancer cells, tumors which are known to metastasize to bone as the preferred secondary site. Caspase-2 was activated in both tumor cell types by PEDF. In models of prostate and breast cancer in bone, PEDF significantly reduced tumor volumes. When combined with zoledronic acid, continuously-administered PEDF significantly reduced breast tumor volume at the bone, and was able to preserve the quality of bone better than the combination therapy. These multiple positive findings make PEDF an ideal endogenous and safe biological for possible future clinical testing.

Do Systemic Factors Influence the Fate of Nonunions to Become Atrophic? A Retrospective Analysis of 162 Cases

INTRODUCTION

Nonunions are a challenge for orthopedic surgeons. In hypertrophic nonunions, improvement of mechanical stability usually is the satisfactory treatment, whereas in atrophic nonunions improvement of the biological environment is most important. However, scientific evidence revealed that "avital" nonunions are not avascular and fibrous tissue contains cells with osteogenic potential. To find out if systemic factors suppress this intrinsic potential in atrophic nonunions, this study compares characteristics of hypertrophic with atrophic nonunion patients.

METHODS

We analyzed medical records of 162 surgically treated patients suffering from aseptic long bone nonunions. Atrophic and hypertrophic nonunions were distinguished by absence or presence of callus and calcification in the fracture gap. Mechanical implant loosening and patient characteristics such as age, gender, and body mass index were assessed. Fracture classification according to AO/OTA, open and closed fractures, and osteosynthesis were recorded. In addition, comorbidities and allergies between both groups were compared.

RESULTS

A higher number of hypertrophic nonunion patients were male with often allergies. Hypertrophic nonunion occurred more often after intramedullary nailing compared to atrophic nonunions. Atrophic nonunion patients being nonallergic were significantly older than nonallergic patients suffering from hypertrophic nonunions. In both atrophic and hypertrophic nonunion patients, age was lower in patients with accompanying injuries compared with age of patients with isolated fractures.

CONCLUSION

Systemic factors influence development of nonunion types. In nonallergic patients, atrophic nonunions occur more often in the elderly. This manuscript is a first step to identify different factors which might influence the nature of nonunion. To enable nonunion treatment which is tailored to individual patient characteristics, further prospective studies with more sophisticated research methods are necessary.