Research article

Lens epithelial cell apoptosis and intracellular Ca²⁺ increase in the presence of xanthurenic acid

Halina Malina^1,2 , Christoph Richter² , Beatrice Frueh³ and Otto M Hess¹

¹Swiss Cardiovascular Research Center, Inselspital, CH-3010 Bern, Switzerland

²Institute of Biochemistry, Swiss Federal Institute of Technology (ETH), Universitaetstrasse 16, CH-8092 Zuerich, Switzerland

³Department of Ophthalmology, Inselspital, CH-3010 Bern, Switzerland

author email corresponding author email

BMC Ophthalmology 2002, 2:1doi:10.1186/1471-2415-2-1

Published:	5 April 2002

Abstract

Background

Xanthurenic acid is an endogenous product of tryptophan degradation by indoleamine 2,3-dioxygenase (IDO). We have previously reported that IDO is present in mammalian lenses, and xanthurenic acid is accumulated in the lenses with aging. Here, we studied the involvement of xanthurenic acid in the human lens epithelial cell physiology.

Methods

Human lens epithelial cells primary cultures were used. Control cells, and cells in the presence of xanthurenic acid grow in the dark. Western blot analysis and immunofluorescence studies were performed.

Results

In the presence of xanthurenic acid human lens epithelial cells undergo apoptosis-like cell death. In the control cells gelsolin stained the perinuclear region, whereas in the presence of 10 μM xanthurenic acid gelsolin is translocated to the cytoskeleton, but does not lead to cytoskeleton breakdown. In the same condition caspase-3 activation, and DNA fragmentation was observed. At low (5 to 10 μM) of xanthurenic acid concentration, the elongation of the cytoskeleton was associated with migration of mitochondria and cytochrome c release. At higher concentrations xanthurenic acid (20 μM and 40 μM) damaged mitochondria were observed in the perinuclear region, and nuclear DNA cleavage was observed. We observed an induction of calpain Lp 82 and an increase of free Ca²⁺ in the cells in a xanthurenic acid concentration-dependent manner.

Conclusions

The results show that xanthurenic acid accumulation in human lens epithelial cells disturbs the normal cell physiology and leads to a cascade of pathological events. Xanthurenic acid induces calpain Lp82 and caspases in the cells growing in the dark and can be involved in senile cataract development.