Experimental Study Of Botulinum Toxin Type A Assisting Muscle-related Fat Grafting

Background and Objection:Fat grafting is an ideal method for soft tissue filling and reconstruction in the field of plastic surgery.But the unpredictable retention rate greatly limits its application.In the clinic,soft tissue filling such as breast augmentation and facial rejuvenation often involves muscle-related fat grafting.In studies of fat grafting in different recipient areas,it was found that the intramuscular graft fat retention rate was less than ideal in subcutaneous and fat.Therefore,it is necessary to study a method that can be used clinically to improve the retention rate of muscle-related fat grafts.It is currently believed that the poor retention rate of muscle-related fat grafts is due to the movement of muscles.Botulinum toxin type A(BoNTA)is a neurotoxin that acts on the distal end of cholinergic motor nerves,antagonizes the action of calcium ions,interferes with the release of acetylcholine,prevents muscle fibers from contracting,causes muscle relaxation and atrophy,and is widely used by plastic surgery.Improve areas such as facial wrinkles and reduced muscle volume.Therefore,we believe that the use of BoNTA as the braking condition of muscles in this experiment is reversible,safe and clinically feasible.The purpose of this study was to apply the BoNTA to the muscle-related fat grafting model,observe its effect on retention rate and analyze the possible causes,and explore a new clinical application to improve the retention rate of muscle-related fat grafting method.Materials&MethodsThe experiment divided the muscle-related fat graft into two parts:supramuscular and intramuscularfat grafting.Pre-BTX+nude mice were injected BoNTA onright quadriceps femoris 1 week before the supramuscular(intramuscular)fat graft.BTX+nude mice simultaneously underwent BoNTA injection and transplantation.Control nude mice underwent transplantation without BoNTA.Graftswere determined volumeand underwent histological and immunostaining.CatWalk XT gait analysis was conducted on BTX+mice.Using biomechanical methods to detect the changes of BoNTA in the microenvironment of transplanted areas,explore the role of BoNTA in intramuscular fat grafting model;use immunofluorescence technique and western-blot method to explore the changes of graft region stiffness to fat regeneration.The effects of simultaneous reduction of dynamic mechanical forces on the adipogenic differentiation of ASCs were further elucidated in a way that further clarified the results.ResultsFor supramuscularfat grafting,the retention rate of the grafts in the experimental groups were significantly better than that in the control group,and both histological staining and immunofluorescence suggested that the experimental groups had more CD34-positive neovascularization and more obvious adipogenesis.The results of CatWalk XT gait analysis showed that BoNTA caused the quadriceps muscle to be in a defined and suspended resting position,and the muscle movement was significantly reduced.This braking effect was most obvious at 4 weeks and then recovered.For intramuscular fat grafting,the retention rate of the control group was much lower than that of supramuscularfat grafting,but histology and generally indicated that the intramuscular graft had better vascularization than the supramuscularfat graft.After the application of BoNTA,the retention rate of the experimental groups were improved,and the degree of vascularization was further improved.Histological and immunofluorescence showed that a large number of newborn adipose precursor cells appeared in grafts of experimental groups,and the expression of peroxisome proliferator-activatedreceptor?(PPAR?)was also increased.However,these adipose precursor cells did not grow into mature adipose cells in the later stage.The determination of muscle tissue stiffness revealed a significant decrease in the stiffness of the quadriceps muscle after application of BoNTA.ConclusionsThe main factors affecting the final outcome of fat transplantation are vascularization and microenvironment.These two seemingly similar receiving areas on the muscle surface and in the muscles face different dilemmas.For supramuscularfat grafting,it is difficult forvessels to grow into the grafts.The BoNTA temporarily brakes the muscle,so that the graft is in a relatively stable state,promotes vascularization,and can improve long-term retention.For intramuscular fat grafting,the grafts can establish sufficient blood supply,but the microenvironment is not suitable for adipogenesis.The BoNTA can reduce muscle mechanical strength and muscle stiffness,makethe microenvironment more conducive,and promote adipogenesis for better retention.