Glyoxalase 1 inducer therapy for the treatment of experimental diabetic kidney disease

Abstract

Diabetic kidney disease (DKD), one of the most common diabetic complications, is identified as a progressive kidney disease in patients with diabetes resulting from angiopathy of the capillaries in renal glomeruli. DKD affects nearly 40% of patients with diabetes and is characterised by increased albuminuria and decreased glomerular filtration rate (GFR). Hyperglycaemia and inflammation enhance DKD through increased glycation formation. Current treatments address only ca. 15% of the risk of DKD development. Development of DKD and other microvascular complications of diabetes is linked to glycemic control. In hyperglycaemia, dysregulation of glucose metabolism drives the activation of multiple metabolic pathways potentially damaging to the kidney, for example mitochondrial dysfunction with NADPH oxidase-driven increased formation of reactive oxygen species, the polyol pathway, the hexosamine pathway, and increased formation advanced glycation endproducts (AGEs). Driving the latter process leads to increased formation and decreased metabolism of the reactive dicarbonyl metabolite, methylglyoxal (MG), leading to increased concentrations of MG – an abnormal metabolic state called dicarbonyl stress. MG is the precursor of the major quantitative and damaging AGE in physiological systems, arginine residue derived hydroimidazolone, MG-H1. Most MG, ca. 99%, formed in the body is metabolised by glyoxalase 1 (Glo1) of the glyoxalase system. Glo1 activity decreased in the kidney in diabetes. The host research team have recently developed a new strategy for treatment of DKD: induction of Glo1 expression by small molecule activators of transcription factor Nrf2; Nrf2 binds a functional antioxidant response element in the GLO1 gene and increase expression. The optimised Glo1 inducer is a combination of trans-resveratrol and hesperetin (tRSV-HESP) this coformulation increases Glo1 expression and might drive improvements in microvascular complications of diabetes linked to hyperglycemia. The aim of this project is to evaluate the effect of Glo1 inducer treatment on human renal cell dysfunction in high glucose concentration primary cultures in vitro. Thesis work set out to characterise the glyoxalase system in primary human renal cells (Tubular epithelial cells and Mesangial cells) in models of hyperglycaemia in vitro and investigate the effects of the Glo1 inducer treatment, tRSV-HESP, on human renal cell function and protein expression in high glucose cultures in vitro. Data indicated that Glo1 inducer treatment had a significant impact on MG metabolism, as determined by measuring D-lactate flux, in both primary proximal tubular epithelial cells and primary mesangial cells, with evidence of treatment-induced increases in Glo1 levels shown via Western blot. Also, data showed significant, quantitative changes in proteomic profiles between treatment groups in mesangial cells, but much less so in proximal tubular epithelial cells. Where detected, tRSV-HESP affected expression of key functional clusters involved in energy metabolism. Paradoxically, changes in Glo1 levels did not reach statistical significance between experimental groups. A striking discovery was that the impact of tRSV-HESP on proteomic profile for both sets of cells was greatly diminished by the presence of high glucose (25 mM) in the cultures. Taken together, these findings suggest that tRSV-HESP has potential to modulate therapeutically the Glo1 system and reduce dicarbonyl stress, but that any potential pharmacological effects would require greater glucose control prior to starting treatment.