Aldose reductase inhibition ameliorates the detrimental effect of estrogen replacement therapy on neuropathology in diabetic rats subjected to transient forebrain ischemia

Estrogen replacement therapy (ERT) elicits a deleterious, instead of protective, effect on neuropathology in diabetic ovariectomized (OVX) rats subjected to cerebral ischemia. This transformation may be linked to an estrogen-associated increase in function of the receptor for advanced glycation end-products (RAGE). Moreover, under diabetic conditions, advanced glycation end-products (AGEs) are excessively generated through the aldose reductase (AR)-polyol pathway. As such, in diabetic rats given ERT, a RAGE-related exacerbation of post-ischemic brain injury can occur. Thus, in the present study, we evaluated the contribution of AR in estrogen's detrimental effect on diabetic animals subjected to transient forebrain ischemia (TFI). Streptozotocin- and 17-β estradiol-treated OVX female rats were divided into two groups, where AR activity was blocked using epalrestat; or AGEs production was restricted, via administrating the protein glycation crosslink breaker, ALT-711. In all animals, ERT was initiated ∼ 10 days before TFI. Pial venular leukocyte adhesion was evaluated over 10 h post-TFI using a cranial window/intravital microscopy technique. In vehicle-treated control groups, a significant increase in leukocyte adhesion was observed post-TFI. Leukocyte extravasation, starting at ∼ 6 h post-TFI, was detected in most of the control animals. Chronic administration of either epalrestat or ALT-711 was associated with a marked decrease in post-TFI leukocyte adhesion, and the complete prevention of leukocyte extravasation. Animals receiving either epalrestat or ALT-711 exhibited a significant improvement in neurologic function, at 72 h post-ischemia, compared to vehicle-treated controls. Post-ischemic (72 h) histopathology was significantly reduced by epalrestat. Compared to the non-diabetic (ND) controls, diabetic OVX rats in the absence or presence of ERT showed a significant 2-fold or 3-fold increase in cortical AR mRNA levels, respectively. In contrast, only a modest increase in AR protein expression, relative to ND control, was detected in the two diabetic groups. The present findings suggest that AR participates in estrogen's deleterious action on post-ischemic neuropathology in diabetics by promoting inflammation. Targeting the AR-controlled polyol pathway may be a clinically promising strategy to restore the neuroprotection of ERT in diabetic females.