Diabetic kidney disease (DKD) is the leading cause of end-stage renal disease and a main contributing factor for cardiovascular morbidity and mortality in patients with diabetes mellitus. Strategies employed to delay the progression of this pathology focus on the control of traditional risk factors, such as hyperglycemia, and elevated blood pressure. Although the intimate mechanisms involved in the onset and progression of DKD remain incompletely understood, inflammation is currently recognized as one of the main underlying processes. Untangling the mechanisms involved in the appearing of a harmful inflammatory response in the diabetic patient is crucial for the development of new therapeutic strategies. In this review, we focus on the inflammation-related pathogenic mechanisms involved in DKD and in the therapeutic utility of new anti-inflammatory strategies.

Background and Aims Klotho (KL) is a transmembrane protein that is expressed the highest in the tubular cells of the kidneys. In addition to membrane KL, a secreted form of this protein that is present in blood and urine is generated by ectodomain shedding of membrane KL from the cell surface or from the KL gene through alternative splicing. Preserved KL expression has been related to physiological protection in the human kidneys. Sodium-glucose cotransporter 2 inhibitors (SGLT2i) are a new class of antidiabetic drugs with important renal benefits. The aim of the present proof-of-concept study was to analyze if treatment with SGLT2i is associated with changes in soluble KL concentrations as well as with modifications in mRNA expression levels of the KL gene in renal tubular cells. Method Thirty-four patients (18 males and 16 males; mean age 61±5 years) with type 2 diabetes (mean diabetes time higher than 10 years) and CKD G2-A2, all treated with metformin and blockers of the renin-angiotensin system during more than one year, were included in the study. Twenty-four of them received SGLT2i during 6 months (8 empagliflozin, 8 canagliflozin, 8 dapagliflozin), and their data and evolution were compared with a group of 10 patients matched by age, sex and stage of CKD who received sulfonylureas or DPP4 inhibitors. Serum and urine levels of soluble KL and tumor necrosis factor-alpha (TNFa) were determined by ELISA. In addition, the effect of SGLT2i on mRNA expression levels of KL was assessed in vitro in renal tubular cells cultures. Results Baseline median values of serum and urinary KL and TNFa were similar in both groups. Urinary KL was inversely correlated with albuminuria and TNFa excretion (r = -0.39 and r = -0.37, respectively, P<0.05). There were no relationship between the serum and urinary levels of these molecules, suggesting their renal origin. At the end of the study, there was a similar improvement in metabolic control, with a reduction in blood pressure significantly higher in patients treated with SGLT2i. Estimated glomerular filtration rate and albuminuria decreased by 5.8% and 17%, respectively, in subjects receiving SGLT2i (P<0.0001), without changes in the control group. In patients under SGLT2i therapy there was a 21% significant reduction in urinary TNFa with a concomitant 41% increase in urinary KL (P<0.001); there was also a small but significant rise in serum KL (P<0.01 vs baseline). Partial correlation analysis showed that the changes in the urinary excretion of albumin and TNFa were associated with the variation in urinary KL after controlling for other variables (r = -0.50, P<0.01, and r = -0.41, P<0.05, respectively). Finally, renal tubular cells cultured with dapagliflozin showed a significant and dose-dependent increase of mRNA expression levels of KL. Conclusion Treatment with SGLT2i induces a reduction in albuminuria and modulates inflammation (as reflected by a decrease in the urinary excretion of TNFa), which is associated with a significant increase in soluble KL concentrations as well as mRNA expression levels of the KL gene. The preservation of KL by SGLT2i may be an important mechanism of renal protection in type 2 diabetes.