[In vitro experimental study on influences of final degradation products of polyactic acid on proliferation and osteoblastic phenotype of osteoblast-like cells].

OBJECTIVE: To investigate the influences of lactic acid (LA), the final degradation product of polylactic acid (PLA) on the proliferation and osteoblastic phenotype of osteoblast-like cells so as to provide theoretical basis for bone tissue engineering. METHODS: Ros17/2.8 osteoblast-like cells were harvested and divided into 3 groups. In groups A and B, the cells were cultured with the medium containing 4, 8, 16, 22, and 27 mmol/L L-LA and D, L-LA, respectively. In group C, the cells were cultured with normal medium (pH7.4). The cell proliferation was determined with MTT method after 1, 3, and 5 days. The relative growth ratio (RGR) was calculated, and the cytotoxicity was evaluated according to national standard of China. In addition, the alkaline phosphatase (ALP) activity of cells cultured with medium containing 4 mmol/L L-LA (group A), 4 mmol/L D, L-LA (group B), and normal medium (group C) after 1 and 5 days were detected with ALP kits, and the relative ALP ratio (RAR) was calculated; after 21 days, the calcium nodules were tested with von Kossa staining method, and were quantitatively analyzed. RESULTS: When LA concentration was 4 mmol/L, the mean RGR of both groups A and B were all above 80%, and the cytotoxic grades were grade 0 or 1, which meant non-cytotoxicity. When LA concentration was 8 mmol/L and 16 mmol/L, groups A and B showed cytotoxicity after 5 days and 3 days, respectively. When LA concentration was above 22 mmol/L, cell proliferations of groups A and B were inhibited evidently after 1-day culture. At each LA concentration, RGR of group A was significantly higher than that of group B at the same culture time (P < 0.05) except those at 4 mmol/L after 1-day and 3-day culture. After 1 day, the RAR of group A was significantly higher than that of group B on 1 day (144.1% ± 3.2% vs. 115.2% ± 9.8%, P < 0.05) and on 5 days (129.6% ± 9.8% vs. 78.2% ± 6.9%, P < 0.05). The results of von Kossa staining showed that the black gobbets in group A were obviously more than those of groups B and C. The staining area of group A (91.2% ± 8.2%) was significantly higher than that of groups B (50.3% ± 7.9%) and C (54.2% ± 8.6%) (P < 0.05). CONCLUSION: The concentration and composition of LA have significant effects on the cell proliferation and osteoblastic phenotype of osteoblast-like cells.