Enzymes involved in osmolyte synthesis: how does oxidative stress affect osmoregulation in renal cells?

Kidney medulla cells are exposed to a wide range of changes in the ionic and osmotic composition of their environment as a consequence of the urine concentrating mechanism. During antidiuresis NaCl and urea concentrations increase and an efficient urinary concentrating mechanism is accompanied by medullar hypoxia. Medullar hypotonicity increases reactive oxygen species, a byproduct of mitochondria during ATP production. High intracellular ionic strength, hypoxia and elevated ROS concentration would have deleterious effects on medulla cell function. Medulla cells respond to hypertonicity by accumulating organic osmolytes, such as glycine betaine, glycerophosphorylcholine, sorbitol, inositol, and taurine, the main functions of which are osmoregulation and osmoprotection. The accumulation of compatible osmolytes is thus crucial for the viability of renal medulla cells. Studies about the effects of reactive oxygen species (ROS) on the enzymes involved in the synthesis of osmolytes are scarce. In this review we summarize the information available on the effects of ROS on the enzymes involved in osmolyte synthesis in kidney.