Hydroxynonenal-activated 5-lipoxygenase promoter in human osteoarthritis chondrocytes. Cells were transfected with human 5-lipoxygenase (5-LOX) promoter. The next day, they were incubated with single addition of 10 μM 4-hydroxynonenal for increasing incubation time periods. Luciferase activity was measured in cell extracts and normalized to β-galactosidase activity. Data are means ± standard errors of the mean, n = 4, expressed as percentages of untreated cells. Student's unpaired t test: *P < 0.05. VDRE: vitamin D responsive element.