Stabilization of endogenous Nrf2 by minocycline protects against Nlrp3-inflammasome induced diabetic nephropathy

Abstract

While a plethora of studies support a therapeutic benefit of Nrf2 activation and ROS inhibition in diabetic nephropathy (dNP), the Nrf2 activator bardoxolone failed in clinical studies in type 2 diabetic patients due to cardiovascular side effects. Hence, alternative approaches to target Nrf2 are required. Intriguingly, the tetracycline antibiotic minocycline, which has been in clinical use for decades, has been shown to convey anti-inflammatory effects in diabetic patients and nephroprotection in rodent models of dNP. However, the mechanism underlying the nephroprotection remains unknown. Here we show that minocycline protects against dNP in mouse models of type 1 and type 2 diabetes, while caspase -3,-6,-7,-8 and -10 inhibition is insufficient, indicating a function of minocycline independent of apoptosis inhibition. Minocycline stabilizes endogenous Nrf2 in kidneys of db/db mice, thus dampening ROS-induced inflammasome activation in the kidney. Indeed, minocycline exerts antioxidant effects in vitro and in vivo, reducing glomerular markers of oxidative stress. Minocycline reduces ubiquitination of the redox-sensitive transcription factor Nrf2 and increases its protein levels. Accordingly, minocycline mediated Nlrp3 inflammasome inhibition and amelioration of dNP are abolished in diabetic Nrf2−/− mice. Taken together, we uncover a new function of minocycline, which stabilizes the redox-sensitive transcription factor Nrf2, thus protecting from dNP.

NLRP3 expression and urinary HSP72 in relation to biomarkers of inflammation and oxidative stress in diabetic nephropathy patients

“…The findings of this study supported the role of NLRP3 inflammasome in the development of DN. Two signals are required for full NLRP3 activation; the first is a TLR‐dependent activation of NF‐κB, which may be induced by extracellular HSP72, resulting in the upregulation of NLRP3 and pro‐IL‐1β expression (“priming”), and the second signal is NLRP3 activating signal which has been mechanistically linked with hyperglycemia and oxidative stress .…”

“…The findings of this study supported the role of NLRP3 inflammasome in the development of DN. Two signals are required for full NLRP3 activation; the first is a TLR-dependent activation of NF-jB, which may be induced by extracellular HSP72, resulting in the upregulation of NLRP3 and pro-IL-1b IUBMB LIFE expression ("priming"), and the second signal is NLRP3 activating signal which has been mechanistically linked with hyperglycemia and oxidative stress (15,51,52). Recently, Elmonem et al suggested that NLRP3 inflammasome system may play an important role in the activation of CHIT1 expression, as IL-1b can directly or indirectly stimulate NF-jB signaling pathway and induce the production of tumor necrosis factor-a (TNF-a) thus stimulating the expression of CHIT1 (44).…”

“…NLRP3 plays an important role in different inflammatory diseases such as atherosclerosis, gout, type I and type 2 diabetes (6)(7)(8)(9). Some studies have reported the role of NLRP3 in DN in cultured cell and animal models (5,(10)(11)(12)(13)(14)(15)(16); however, data from human is rare.…”

Recent novel approaches to limit oxidative stress and inflammation in diabetic complications

“…Completion of the Phase 2 study has shown early positive results, with a statistically significant increase in kidney function from baseline at the 12‐week endpoint. A more recent study by Shahzad et al 77. using the antibiotic minocycline has exhibited antioxidative effects in the kidneys of db/db mice.…”

The role of caloric load and mitochondrial homeostasis in the regulation of the NLRP3 inflammasome

“…Other antioxidant compounds that blunt ROS production have been found to be inhibitors of the inflammasome in vivo, such as the mitochondrial ROS scavenger MitoQ, which suppresses activation of the NLRP3 inflammasome in a model of dextran sulfate-induced colitis [132], or natural compounds such as Aloe vera extract, emodin, ginseng or curcumin [133]. The broad-spectrum tetracycline antibiotic Minocycline also inhibits the NLRP3 inflammasome in several disease models by a mechanism that involves the dampening of ROS generation [134–136]. …”