Purpose: Many cataractogenic stresses also induce endoplasmic reticulum (ER) stress in lens epithelial cells (LECs), which appears to be one of the universal inducers of cell death. In galactosemic rats, activation of ER stress results in the activation of the unfolded protein response (UPR)-dependent death pathway, production of reactive oxygen species (ROS), and cell death. All are induced and precede cataract formation. Cellular osmolytes such as 4-phenylbutyric acid (PBA), trimethylamine N-oxide (TMAO), and tauroursodeoxychoric acid (TUDCA) are known to suppress the induction of ER stress. We investigated whether these small molecules prevent cataract formation in galactose-fed rat lenses.
Methods: Cultured LECs were treated with galactose and each cellular osmolyte. Sprague-Dawley rats were fed a 50% galactose chow for 15 days with or without cellular osmolyte treatment. Similarly, selenite was injected subcutaneously into rats with or without cellular osmolytes. Calcein AM and ethidium homodimer-1 (EthD) were used to detect live and dead cells, respectively. The cellular osmolytes, PBA, TMAO, and TUDCA were tested for their ability to suppress LEC death and cataract formation.
Results: Cellular osmolytes rescued cultured human LECs which were treated with the ER stressors. We administered these osmolytes either orally or by injection into galactosemic Sprague-Dawley rats. These rats had significantly reduced LEC death and partially delayed hypermature cataract formation. Since the UPR was not activated in cultured LECs treated with selenite, we used the selenite nuclear cataract as a UPR-independent death pathway control. In selenite-induced nuclear cataract in rats, cellular osmolytes did not prevent LEC death and did not alleviate cataract formation.
Conclusions: These results further establish that ER stress and LEC death play a vital role in certain types of cataract formation. In addition, cellular osmolytes may be potential prophylactic drugs for some types of cataracts.