Reversal of galactosemic-induced inhibition of PGH synthase activity in cultured lens epithelial cells

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Abstract
Inhibition of prostaglandin synthesis as determined by prostaglandin endoperoxide synthetase (PGH synthase) activity is associated with polyol accumulation in cultured bovine lens epithelial cells (BLECs) incubated six days in minimal essential medium (MEM) containing 40 mM galactose (Gal). In order to better understand the nature of the correlation between hypergalactosemic exposure polyol accumulation and inhibition of prostaglandin synthesis, a series of culture media reversal and sorbinil (an aldose reductase inhibitor) addition studies were carried out. BLECs were incubated in Gal for six days, then changed to galactose-free MEM + sorbinil for a three day recovery period. PGH synthase activity reduced to 66% of control after six days of exposure to Gal. The simultaneous administration of sorbinil during a nine day Gal incubation significantly protected the enzymatic activity. while the activity of PGH synthase further declined to 41% of control under the same conditions in the absence of sorbinil. Within 72 hours of media reversal, PGH synthase activity equaled or exceeded control values in BLECs switched to either MEM or MEM + sorbinil. Indeed, an enhanced prostaglandin biosynthetic capacity as demonstrated by radioimmunoassay was exhibited with microsomes prepared from cells switched from Gal into Gal-free MEM + sorbinil, corroborating the beneficial effect of media reversal. Furthermore, following 72 hours of reversal, the cellular dulcitol level was 93 nmol/μg PO4 for BLECs switched to MEM alone; no detectable level of polyol was observed in BLECs changed to MEM + sorbinil. In contrast, the polyol content in BLECs after six days of exposure to Gal was 185 nmol/μg Po4 and increased to 334 nmop/μg Po4 after nine days of continuous incubation. Moreover, the co-addition of sorbinil during the nine day exposure period prevented any detectable accumulation of dulcitol. These results show that although sorbinil facilitates the reversal of dulcitol accumulation and can completely block polyol accumulation when co-administered, halting the exposure of BLECs to Gal is of itself sufficient stimulus to reduce the cellular polyol level and to normalize PGH synthase activity.