Effects of intermittent UVA exposure on cultured lens epithelial cells

Abstract

Purpose. This paper addresses the question of whether a single non-lethal dose of UVA radiation or the same dose divided three daily one-third doses have like or unlike effects on the growth and the catalase activity of cultured rabbit epithelial (RLE) and immortalized human epithelial (HLE) cells. Methods. Non-confluent cultured RLE and HLE cells were used to study the effects of UVA radiation on their growth. The effects of three doses of 3 J/cm 2 given one day apart on cell growth (i.e. live cell number) over a three day period were compared with those of a single 9 J/cm 2 exposure. Estimation 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 radiation 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 H 2 O 2 measured spectro-photometrically 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 exposures 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 controls 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, over three days, RLE catalase activity was reduced to 75% of the controls. There appeared to be no recovery within two additional days. Conclusions. While single below lethal doses of UVA allow no recovery of RLE or HLE cell growth, partial recovery does occur after several daily intermittent exposures. Recovery of the catalase activity by RLE cells does occur after single sub lethal exposures, but intermittent exposures allow no recovery. The recovery of lens epithelial cell growth and catalase activity from UVA damage varies with the exposure regimen.