Effects Of Sodium Butyrate Intervention On Obesity Prone And Obesity Resistance Of Bone Metabolism In Rats Induced By High-fat Diet

Obesity caused by a high-fat diet（HFD）is closely related to osteoporosis.Mitochondria are the main sites for the production of energy metabolism and reactive oxygen species（ROS）,which regulates calcium absorption and bone metabolism by maintaining the redox homeostasis.Butyrate,a volatile short chain fatty acids,is the byproduct of microbial fermentation of dietary fiber in the gastrointestinal tract and easily combines with sodium to form sodium butyrate（NaB）.Previous studies show that NaB modulates several antioxidant enzymes activity,improves mitochondrial redox homeostasis and reduces bone loss.However,the specific mechanism is still undefined.In the present study,we induced different obese phenotype rats by HFD and explored the regulation and differences of duodenal calcium absorption and femoral metabolism by 4%NaB intervention.Meanwhile,the oxidative damage model of osteoblasts was established in MC3T3-E1 cells to verify the molecular mechanism of mitochondrial energy metabolism and redox homeostasis in vitro by NaB incubation,so as to provide a valuable theoretical basis for the nutritional intervention strategy of osteoporosis caused by HFD.SD rats were fed HFD for 8 weeks,and then divided into obesity prone（OP）and obesity resistance（OR）group according to the upper 1/3 and lower 1/3 of body weight.Sample analysis was performed after the addition of 4%NaB to the HFD for 12 weeks.We detected body weight gain,food intake,energy intake and other apparent indicators,and analyzed blood lipids,calcium levels,calcium homeostasis,and bone mechanics parameters.At the same time we investigated duodenum and femur mitochondrial antioxidant enzyme activity,mitochondrial energy metabolism,oxidative pathway（Nrf2/GSK-3β）related gene expression levels and other related indicators.After the pretreatment of 0.1⁰.75 mM NaB for 72 h,the oxidative injury model was established by incubating MC3T3-E1 osteoblasts with H₂O₂ for 1h.Cell viability,ROS levels,and redox status were measured.Mitochondrial membrane potential was detected by flow cytometry.Mitochondrial antioxidant enzyme activity,mineralization of bone matrix,alkaline phosphatase activity and ATP content were also analyzed respectively.The study found that long-term HFD caused lipid metabolism disorder in OP rats,decreased the serum and bone calcium content,and led to body calcium deficiency,which reduced bone mineral density,bone volume fraction and trabecular thickness significantly,and damaged bone microstructure.NaB intervention improved the oxidative stress of the duodenum in OP rats,maintained mitochondrial redox homeostasis,and promoted intestinal calcium absorption.At the same time,by promoting the phosphorylation of GSK-3βSer9 and inhibiting the activity of GSK-3β,NaB promoted the the expression and the nucleus to cytoplasm ratio of Nrf2 and up-regulated the expression of its downstream antioxidant genes.NaB also maintained the mitochondrial redox homeostasis and energy metabolism,and restored the balance of bone metabolism by the improvement of PGC-1αand TFAM.In addition,OR rats resisted the disorder of blood lipid metabolism,imbalance of calcium homeostasis and the destruction of bone microstructure caused by HFD to a certain extent,so NaB intervention had no significant regulatory effect on OR rats.Vitro studies showed that0.3 mM NaB incubation prevented H₂O₂-induced oxidative damage in cells effectively,improved cell osteoblasts mineralization and differentiation significantly,and maintained the balance of bone metabolism by enhancing intracellular antioxidant enzyme activity,reducing ROS levels,and increasing mitochondrial membrane potential and ATP production.In conclusion,NaB intervention improves the intestinal calcium absorption and bone microstructure in OP rats induced by HFD,and enhances the mineralization of bone matrix,osteoblast differentiation and bone metabolism by maintaining mitochondria redox homeostasis and energy metabolism,which may be partly through a regulation of GSK-3β/Nrf2 signaling pathway,an increase of nuclear translocation of Nrf2 and the expression of PGC-1αand TFAM.