In Vivo Models for the Study of Hyaluronic Acid Fillers: A Review.

BACKGROUND: Hyaluronic acid (HA) filler application is one of the most frequent minimally invasive aesthetic procedures used worldwide. Its properties and characterization, performance, effects in other tissues, and response to complication treatments have been studied in several animal models. This review aims to categorize animal models considering the advantages and disadvantages regarding the purpose of the study. METHODS: Literature research was made using MEDLINE via PubMed by two reviewers using keywords "hyaluronic acid" "filler" and "animal model". Full-text articles published in English and with an in vivo animal model were included for data extraction. RESULTS: The rat model was the most common animal used to evaluate properties or characteristics and degradation of HA fillers. Rabbits were preferred for evaluating HA embolism treatments; however, anatomical names of the arteries differ in some studies. Mice and rats used as vascular occlusion model are challenging due to the size of the vessels and viscosity of the filler. CONCLUSION: There is a wide variability of options of in vivo animal models to evaluate HA fillers. The animal characteristics, laboratory resources, and HA properties should be considered in accordance with the objective of the study, when choosing the ideal model. LEVEL OF EVIDENCE III: This journal requires that authors assign a level of evidence to each submission to which Evidence-Based Medicine rankings are applicable. This excludes Review Articles, Book Reviews, and manuscripts that concern Basic Science, Animal Studies, Cadaver Studies, and Experimental Studies. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Hyaluronic Acid Embolism Treated with Subcutaneous High and Low Hyaluronidase Doses: Efficacy and Surrounding Tissue Effect.

BACKGROUND: The use of hyaluronidase in hyaluronic acid vascular occlusion has been evaluated; however, the models used do not accurately assimilate the facial morphologic characteristics or study the effects on adjacent tissues. The purpose of this study was to determine an effective concentration of subcutaneous hyaluronidase to dissolve a hyaluronic acid embolism and its effect on surrounding tissue. METHODS: Fifteen rabbits were divided into six groups. An inguinal incision was performed on the femoral artery to create a hyaluronic acid embolism in the control and treatment groups (low-, medium-, and high-hyaluronidase groups). Hyaluronidase was injected subcutaneously. Photographic follow-up, histologic analysis, and quantification of hyaluronic acid were performed. Kruskal-Wallis test and post hoc with Bonferroni correction (p < 0.05) was used to compare the presence of hyaluronic acid in the arterial lumen between groups. RESULTS: Despite the persistence of intravascular hyaluronic acid, macroscopic and microscopic differences were found between the embolism control group and embolism hyaluronidase high-dose group. Histologic analysis demonstrated thrombosis throughout groups. Skeletal muscle was least affected in the embolism hyaluronidase 500 IU group with less lysis and inflammatory infiltrate. CONCLUSIONS: A 500 IU hyaluronidase dose partially prevents the damage caused by the embolism, and does not affect the surrounding tissue. The use of thrombolytic therapy combined with higher doses of hyaluronidase subcutaneously in this model is proposed.