Short-Term Effects of Poly-L-Lactic Acid-b-Polyethylene Glycol Microsphere Injection on Different Adipose Tissue Types in Rats.

[BACKGROUND] Wrinkles and sagging, characteristics of aging, are associated with reductions in collagen and fat. Poly-L-lactic acid (PLLA) is widely used clinically as a tissue filler owing to its good biocompatibility and ability to improve wrinkles and signs of aging. Despite extensive studies of the mechanism of action of PLLA when used as a dermal filler, few studies have examined its effects on adipose tissue.

[OBJECTIVES] The short-term effects of PLLA-b-polyethylene glycol (PEG) microspheres implanted in subcutaneous back adipose tissue (BAT) and visceral epididymal adipose tissue (EAT) of rats were examined.

[METHODS] The authors divided 15 male Sprague-Dawley rats into 5 groups based on implantation time, and PLLA-b-PEG microspheres were implanted into the BAT (3 groups were sampled at 6, 8, and 12 weeks) and EAT (2 groups were sampled at 6 and 12 weeks) of rats. Tissue samples were collected at different time points postimplantation and subjected to histological analyses using hematoxylin and eosin, Masson's trichrome, and immunofluorescence staining.

[RESULTS] Implantation of PLLA-b-PEG microspheres into different adipose tissues resulted in a mild and persistent inflammatory reaction, increased fibrous connective tissue, and noticeable collagen regeneration. Immunofluorescence showed the upregulation of uncoupling protein (UCP) 1 and UCP2 in the visceral adipose tissue surrounding the implant.

[CONCLUSIONS] PLLA-b-PEG microspheres exhibited good tissue compatibility and induced an increase in fibrous connective tissue postimplantation, potentially mitigating oxidative damage and improving adipose tissue quality.