Effects of intermittent UVA exposure on cultured lens epithelial cells

Purpose. This paper addresses the question of whether a single non-lethal d ose of UVA radiation or the same dose divided three daily one-third doses h ave like or unlike effects on the growth and the catalase activity of cultu red rabbit epithelial (RLE) and immortalized human epithelial (HLE) cells. Methods. Non-confluent cultured RLE and HLE cells were used to study the ef fects of UVA radiation on their growth. The effects of three doses of 3 J/c m(2) given one day apart on cell growth (i.e. live cell number) over a thre e day period were compared with those of a single 9 J/cm(2) exposure. Estim ation of live cell numbers was done 24 hrs after each exposure by counting trypan blue exclusive cells using a hemocytometer. Confluent cultures of RLE cells were used to study the effects of UVA radia tion on their catalase activity. The effects of three doses of 1.25 J/cm(2) each given one day apart on catalase activity (breakdown of H2O2 measured spectrophotometrically at 240 nm) were compared with that of a single 3.75 J/cm(2) exposure. Results. A single 9 J/cm(2) dose of UVA reduced the cell growth to only 10% of controls after 24 hrs. By three days after a single 9 J/cm(2) exposure, the number of live cells was only 70% of controls. Three intermittent expo sures of 3 J/cm(2) each for three consecutive days reduced the cell number to 76% of controls. Similar results were obtained for HLE cells. Little if any recovery of cell numbers occurred after three intermittent exposures. A single dose of 3.7 J/cm(2) reduced RLE catalase activity to 20% of contro ls by one day. By three days after exposure, catalase activity returned to 90% of controls. After three intermittent exposures to 1.25 J/cm(2) each, o ver three days, RLE catalase activity was reduced to 75% of the controls. T here appeared to be no recovery within two additional days. Conclusions. While single below lethal doses of UVA allow no recovery of RL E or HLE cell growth, partial recovery does occur after several daily inter mittent exposures. Recovery of the catalase activity by RLE cells does occu r after single sub lethal exposures, but intermittent exposures allow no re covery. The recovery of lens epithelial cell growth and catalase activity f rom UVA damage varies with the exposure regimen.