The Role of Dietary Antioxidants against Oxidant-Induced Acute Kidney Injury

Abstract

Acute kidney injury (AKI) is defined by a sudden loss of kidney function, within hoursto days. The Initiation and propagation of AKI corresponds to oxidative stress (OS) inthe proximal convoluted tubule. AKI has increasing morbidity and mortality rates overthe past decade, predominantly in patients admitted to intensive care. Treatments forAKI remain inadequate and reside in supportive care, increasing the requirement ofrenal replacement therapies (RRT). Dietary antioxidants, hydroxycinnamates (HXCs)small phenylpropanoid plant metabolites and resveratrol (RESV) a stilbene, have wellestablishedantioxidant properties and may provide prophylaxis against AKI.The effects of HXCs: para-coumaric acid (p-CA), meta-coumaric acid (m-CA), orthocoumaricacid (o-CA), caffeic acid (CFA), ferulic acid (FRA), sinapic acid (SAA) andchlorogenic acid (CGA) and stilbenoid, resveratrol were investigated in vitro inproximal convoluted tubular cells (NRK-52E cells). The effects of potent oxidants:Paraquat (PQ), hydrogen peroxide (H2O2), peroxynitrite (ONOO-) and 3-morpholinosydnonimine (SIN-1) in NRK-52E cells. Cell viability (MTT), cellmembrane integrity (LDH), superoxide generation (NBT), antioxidant capacity (ABTS•+) and the initiation of apoptosis or necrosis in vitro for the protection againstOS in NRK-52E cells model of AKI. Attenuation of AKI by antioxidants (m-CA, FRAand RESV) was studied in vivo using a rat model of PQ-mediated AKI usingbiomarkers for kidney function (serum creatinine) and injury (β-NAG and KIM-1).HXCs and RESV demonstrated concentration-dependant antioxidant/ pro-oxidantactivity in NRK-52E cells in OS states. OS inducers (PQ, H2O2, ONOOandSIN-1) reduced cell viability and membrane integrity against differing concentrations (10µ10mM)and time-dependent (0-24 hours) manner. HXCs and RESV attenuated internally generated ROS (e.g. by PQ). Pre-treatment of HXCs and RESV demonstratedimproved protection before exposure to OS-inducers. Protection from PQ-induced OSby treatment of HXCs and RESV was (in descending order): m-CA ≥ FRA > p-CA>RESV > CGA, CFA, o-CA > SAA. Protection has been attributed to scavenging of OSinducers(to generated ROS or binding to PQ) or boosting of the endogenousantioxidant defence before oxidant exposure. PQ-treatment had a concentrationdependentreduction in the antioxidant capacity of the NRK-52E cells. Pre-treatment ofHXC and RESV protected against this loss. Pre-treatment of m-CA, FRA and RESVincreased apoptosis in NRK-52E cells during PQ exposure. The pre-treatment of HXCsand RESV against externally active oxidants (H2O2, SIN-1 and ONOO-) provided limited or no protection to NRK-52E cells. PQ-induced injury and loss to kidneyfunction in vivo. Treatment of m-CA, FRA and RESV protected against loss to kidneyfunction. However, Kidney injury in m-CA and FRA interventions were present,although RESV treatment reduced kidney injury. The demonstrated effects of HXCsand RESV against oxidant-AKI implies additional roles in antioxidant defence, redoxand cell survival signalling in the pathophysiology of the proximal convoluted tubulesduring AKI.In Summary, dietary antioxidants demonstrated protection to proximal tubular cells andthe function of the kidney against oxidant-induced AKI. Principally, they attenuated invitro and in vivo PQ-induced AKI. In lieu of antioxidant action, results suggest, HXCsand RESV have alternative esoteric effects in proximal tubule cells. The thesis mayprovide insights and understanding of the cellular mechanisms and pathophysiology ofAKI and role of dietary antioxidants.

Date of Award	2018
Original language	English
Awarding Institution	University of Brighton
Supervisor	Charley Chatterjee (Supervisor)