Evidence for apoptosis, MMP-1, MMP-3 and TIMP-2 expression and their effect on the mechanical and biochemical properties of fresh viable knee medial meniscal allografts and autografts in the rabbit

INTRODUCTION: The study sought evidence for apoptosis, the expression of MMP-1, MMP-3 and TIMP-2 and their effect on the mechanical and biochemical properties of rabbit fresh knee medial meniscal grafts in a 6-month follow-up. MATERIAL AND METHODS: Forty white male New Zealand rabbits were chosen for the study. The medial meniscus was excised from 28 animals and stored under tissue culture conditions for 2 weeks, following which 14 of them were implanted as autografts and 14 as allografts. When the animals were euthanized, 20 menisci were used for immunohistochemical examinations. Apoptosis (TUNEL method) and MMP-1, MMP-3 and TIMP-2 immunoexpression were estimated semiquantitatively. The other 20 menisci were subjected to biochemical analysis and their degree of elasticity was evaluated. RESULTS: An increased level of apoptosis (p <0.05) was observed both in allografts (1.57 ±0.98) and autografts (0.86 ±0.69); no statistical differences existed between them. An increased level of metalloproteinases and TIMP-2 expression was observed only in the allografts (p < 0.05). The highest decrease of degree of elasticity and the most significant changes in biochemical composition were observed in allografts (p < 0.05). CONCLUSIONS: The studies confirmed the existence of excessive apoptosis in both kinds of fresh viable medial meniscal implants: auto- and allografts. Our results suggest that apoptosis and increased MMP-1 and MMP-3 expression have an adverse effect on the biological properties of implants. The results of experimental studies on humans indicate the need to devise a method of apoptosis inhibition in transplanted menisci to improve long-term results.