Exogenous pancreatic kininogenase protects against tacrolimus-induced renal injury by inhibiting PI3K/AKT signaling: The role of bradykinin receptors

Background: Tissue kallikrein offers a wide spectrum of biological activity in the protection against various types of injury. However, information on its role in tacrolimus (TAC)-induced renal injury is limited. Objectives: This study aimed to assess the beneficial effects of pancreatic kininogenase (PK) in a rat model of chronic TAC nephrotoxicity and in vitro. Methods: Sprague Dawley rats were treated daily with either TAC or PK or a combination of the two for four weeks. The influence of PK on renal injury was examined in terms of renal function, histopathology, cytokine expression, oxidative stress, intracellular organelles, programmed cell death, and PI3K/AKT signaling. Human kidney proximal tubular (HK-2) cells and mouse mesangial (SV40 MES13) cells treated with TAC and PK were also studied. Results: PK treatment improved renal function and histopathology. This effect was paralleled by downregulation of proinflammatory and profibrotic cytokine expression. TAC-induced oxidative stress was closely associated with endoplasmic reticulum stress and mitochondrial dysfunction, resulting in excessive programmed cell death (apoptosis and autophagy) that was significantly abrogated by concurrent PK interference with PI3K/AKT signaling. PK also stimulated bradykinin receptor 1 (B1R) and B2R mRNA synthesis and increased bioactive nitric oxide (NO) and cAMP concentrations in TAC-treated kidneys. Blockade of either B1R or B2R eliminated the renoprotective effects of PK. In HK-2 and SV40 MES13 cells, PK decreased TAC-induced overproduction of intracellular reactive oxygen species and inhibited apoptotic cells, whereas cell viability was improved. Moreover, activated PI3K/AKT signaling in HK-2 cells was inhibited by PK and the PI3K inhibitor, LY294002. Conclusions: These findings indicate that PK treatment protects against chronic TAC nephrotoxicity via inhibition of PI3K/AKT signaling.