Comparison of the effect of HNE on normal (N) and osteoarthtitic (OA) osteoblast metabolism. Cells were incubated in the absence or presence of 20 μM HNE for 48 hours. ALPase activity (a) was determined in cellular extract as described in Materials and methods. OC (b), IL-6 (c), and PGE2 (d) levels were measured in culture media using specific kits. Data are means ± standard error of the mean of n = 3 and expressed as a percentage of untreated cells. Statistics: Student unpaired t test; *p < 0.05, **p < 0.01, ***p < 0.001. ALPase, alkaline phosphatase; HNE, 4-hydroxynonenal; IL-6, interleukin-6; OC, osteocalcin; PGE2, prostaglandin E2.