Effect of an AGE-modified type I collagen matrix on the ALP activity of UMR106 and MC3T3E1 cells. Osteoblastic cells were cultured on control or AGE-modified type I collagen at 37°C either for 24 hours (UMR106 cells), or for one and three weeks (MC3T3E1 cells). At the end of all incubations, the cell monolayer was lysated in 0.1 % Triton X-100. Alkaline phosphatase activity was determined in the lysates using p-nitro-phenyl-phosphate as a substrate, and was normalized for cellular protein content. Results are given as a percentage of the corresponding basal condition (unmodified collagen), and are expressed as the mean ± SEM. Differences between collagen vs. AGE-collagen are as follows: * p<0.01. Basal ALP activity was 168 ± 8 nmol pNP / min x mg protein for UMR106 cells; 2.77 ± 0.33 nmol pNP / min x mg protein for a one-week culture of MC3T3E1 cells; and 3.05 ± 0.23 nmol pNP / min x mg protein for a three-week culture of MC3T3E1 cells.