Leptin receptor gene deficiency minimally affects osseointegration in rats.

Metabolic syndrome represents a cluster of conditions such as obesity, hyperglycaemia, dyslipidaemia, and hypertension that can lead to type 2 diabetes mellitus and/or cardiovascular disease. Here, we investigated the influence of obesity and hyperglycaemia on osseointegration using a novel, leptin receptor-deficient animal model, the Lund MetS rat. Machined titanium implants were installed in the tibias of animals with normal leptin receptor (LepR) and those harbouring congenic leptin receptor deficiency (LepR) and were left to heal for 28 days. Extensive evaluation of osseointegration was performed using removal torque measurements, X-ray micro-computed tomography, quantitative backscattered electron imaging, Raman spectroscopy, gene expression analysis, qualitative histology, and histomorphometry. Here, we found comparable osseointegration potential at 28 days following implant placement in LepR and LepR rats. However, the low bone volume within the implant threads, higher bone-to-implant contact, and comparable biomechanical stability of the implants point towards changed bone formation and/or remodelling in LepR rats. These findings are corroborated by differences in the carbonate-to-phosphate ratio of native bone measured using Raman spectroscopy. Observations of hypermineralised cartilage islands and increased mineralisation heterogeneity in native bone confirm the delayed skeletal development of LepR rats. Gene expression analyses reveal comparable patterns between LepR and LepR animals, suggesting that peri-implant bone has reached equilibrium in healing and/or remodelling between the animal groups.