Mechanism For Tyrosol In Inducing Neovascularization Of Hind-limb Ischemia In Diabetic Mice

Diabetes mellitus is a chronic metabolic disease which severely threatens human health.As the global standard of living keeps increasing,the prevalence of diabetes mellitus rises steadily as well and affects young-aged population in a greater extent.The disease is often accompanied by a series of complications,making it a major problem threatening public health in China.Among the complications,diabetic foot caused by critical limb ischemia(CLI)severely impairs the quality of life of diabetic patients.Wounds and blood vessels damage in diabetic CLI patients are difficult to heal and easy to deteriorate.It leads to poor peripheral blood circulation,in severe cases,it would lead to ulceration of the lower limb,necrosis of surrounding tissues,and even mortality.However,the aberrant molecular mechanism underlying diabetic CLI has not been clearly elucidated,and effective clinical treatments are still on demand.In clinical practice,it is necessary to recover,the blood circulation in the necrotic tissue of the lower limb to prevent the worsening of the disease.While by-pass surgery is effective for patients with mild diabetic CLI,for patients with more severe ischemic state,amputation has to be done to prevent further deterioration.However,the acute mortality rate caused by the amputation itself is about 30% and the 5-year survival rate is less than 30%,which causes a serious burden on patients with diabetic CLI.Therefore,developing a new strategy for effectively preventing further deterioration of diabetic foot disease and for avoiding amputation in order to improve the quality of life of patients is urgently needed.Rhodiola rosea,known as “ginseng on the plateau”,could effectively prevent altitude sickness caused by ischemia and hypoxia,with salidroside and tyrosol as the main active compounds.In general,rhodiola is administered orally,and 30 minutes following the uptake,salidroside in the extract of Rhodiola rosea is metabolized into tyrosol,its glycosides form.Tyrosol is a phenolic compound that plays important roles in anti-oxidative stress,anti-inflammation,and cell protection.In a previou study by our group,we have investigated the effect and regulatory mechanism of salidroside,one of the active components in Rhodiola,on vascular repair in hind limb ischemia mice.However,the effect and regulatory mechanism of tyrosol,the metabolite of salidroside,on vascular regeneration and repair remain unclear.This study is the first to investigate the effect and mechanism of tyrosol on vascular remodeling in diabetic hind limb ischemia(HLI)mouse model.Our studies showned tyrosol could improve the survival rate and the secretory functions of skeletal muscle cells under hyperglycemia.And skeletal muscle cells,through its secreted factors,play important roles in mediating intercellular communication and subsequently,promoting the proliferation and migration potentials of vascular endothelial cells and vascular smooth muscle cells.Finally,in vivo experiments also showed that tyrosol could promote the blood perfusion recovery in diabetic HLI mice,improve the vascular structure in the gastrocnemius muscle of the hind limbs,and thus provide a therapeutic effect in promoting angiogenesis and vessel repair in diabetic HLI.In this study,we found that tyrosol significantly promotes the production of HO-1 and inhibites the apoptosis induced by ROS accumulation caused hyperglycemia in skeletal muscle cells,thus playing an critical role in protecting skeletal muscle cells.At the same time,tyrosol could improve the paracrine functions of skeletal muscle cells by secreting angiogenic factors,such as VEGF-A and PDGF-BB.These factors will in ture improve blood vessels repair.This regulatory process appears to be mediated through HIF indepentent pathways.Based on the above results,our in vitro and in vivo experiments indicate that the active ingredient of Rhodiola rosea,tyrosol,could be a potential natural compound for diabetic CLI therapy,and this study provides important evidences for the basis of clinical treatment of diabetic CLI using tyrosol.