Bardoxolone Methyl Displays Detrimental Effects on Endothelial Bioenergetics, Suppresses Endothelial ET-1 Release, and Increases Endothelial Permeability in Human Microvascular Endothelium

Abstract

Nrf2 is a master regulator of antioxidant cellular defence, and agents activating the Nrf2 pathway have been tested in various diseases. However, unexpected side effects of cardiovascular nature reported for bardoxolone methyl in patients with type 2 diabetes mellitus and stage 4 chronic kidney disease (the BEACON trial) still have not been fully explained. Here, we aimed to characterize the effects of bardoxolone methyl compared with other Nrf2 activators—dimethyl fumarate and L-sulforaphane—on human microvascular endothelium. Endothelial toxicity, bioenergetics, mitochondrial membrane potential, endothelin-1 (ET-1) release, endothelial permeability, Nrf2 expression, and ROS production were assessed in human microvascular endothelial cells (HMEC-1) incubated for 3 and 24 hours with 100 nM–5 μM of either bardoxolone methyl, dimethyl fumarate, or L-sulforaphane. Three-hour incubation with bardoxolone methyl (100 nM–5 μM), although not toxic to endothelial cells, significantly affected endothelial bioenergetics by decreasing mitochondrial membrane potential ( concentrations ≥ 3 μ M ), decreasing spare respiratory capacity ( concentrations ≥ 1 μ M ), and increasing proton leak ( concentrations ≥ 500 nM ), while dimethyl fumarate and L-sulforaphane did not exert such actions. Bardoxolone methyl at concentrations ≥ 3 μ M also decreased cellular viability and induced necrosis and apoptosis in the endothelium upon 24-hour incubation. In turn, endothelin-1 decreased permeability in endothelial cells in picomolar range, while bardoxolone methyl decreased ET-1 release and increased endothelial permeability even after short-term (3 hours) incubation. In conclusion, despite that all three Nrf2 activators exerted some beneficial effects on the endothelium, as evidenced by a decrease in ROS production, bardoxolone methyl, the most potent Nrf2 activator among the tested compounds, displayed a distinct endothelial profile of activity comprising detrimental effects on mitochondria and cellular viability and suppression of endothelial ET-1 release possibly interfering with ET-1–dependent local regulation of endothelial permeability.

The Good and Bad of Nrf2: An Update in Cancer and New Perspectives in COVID-19

“…It is currently in clinical trials against hyperglycaemia and has been recently suggested against COVID-19, being able to inhibit SARS-CoV-2 replication [ 163 ]. However, its detrimental effects on microvascular endothelium represent a limitation of its employment [ 164 ].…”

Eat Your Broccoli: Oxidative Stress, NRF2, and Sulforaphane in Chronic Kidney Disease

“…A recent study evaluated the effects of bardoxolone and SFN on human dermal microvascular endothelial cell function [ 141 ]. Both agents augmented NRF2 expression, but bardoxolone was 2–5 times more potent in NRF2 activation than SFN at equal concentration [ 141 ]. Both agents decreased ROS production; however, bardoxolone was found to have more cytotoxicity.…”

“…Both agents decreased ROS production; however, bardoxolone was found to have more cytotoxicity. Endothelial cells incubated with 3, 5, or 10 µM bardoxolone showed a decrease in cell viability due to an increase in both apoptosis and necrosis, whereas endothelial cells treated with similar SFN concentrations did not display cytotoxicity [ 141 ]. Bardoxolone, but not SFN, also had detrimental effects on mitochondria as evidenced by a significant increase in proton leakage, and decrease in spare respiratory capacity and mitochondrial membrane potential [ 141 ].…”

“…Endothelial cells incubated with 3, 5, or 10 µM bardoxolone showed a decrease in cell viability due to an increase in both apoptosis and necrosis, whereas endothelial cells treated with similar SFN concentrations did not display cytotoxicity [ 141 ]. Bardoxolone, but not SFN, also had detrimental effects on mitochondria as evidenced by a significant increase in proton leakage, and decrease in spare respiratory capacity and mitochondrial membrane potential [ 141 ]. It should be noted that, compared to control, SFN at “low dose” or 0.5 µM concentration, ex vivo, is able to induce expression of the genes in human peripheral blood mononuclear cells (PBMCs) that encode the enzymes Aldo-Keto Reductase Family 1 Member C1 (AKR1C1) and NQO1 that play a role in reducing radical species [ 142 ].…”

“…Cell culture data suggest differential action of bardoxolone and SFN. A recent study evaluated the effects of bardoxolone and SFN on human dermal microvascular endothelial cell function [141]. Both agents augmented NRF2 expression, but bardoxolone was 2-5 times more potent in NRF2 activation than SFN at equal concentration [141].…”