Psychiatric use of lithium has been associated with hypoglycemic effects, but its effect on type 1 diabetes mellitus (T1D) is unknown. In streptozotocin (STZ) induced murine models of T1D, microdose lithium therapy improved hyperglycemia, attenuated body weight loss and prevented early signs of diabetic kidney injury. This beneficial effect was associated with preservation of pancreatic islet histology and β-cell production of insulin as well as mitigated oxidative damage of islets. Mechanistically, lithium in islets cells induced inhibitory phosphorylation of glycogen synthase kinase 3β (GSK3β), the major molecular target of lithium that has been recently implicated in non-canonical regulation of Nrf2 activity. In turn, Nrf2 antioxidant response was potentiated in islets, marked by nuclear translocation of Nrf2 and augmented expression of its target antioxidant enzyme heme oxygenase 1 (HO-1). Conversely, cotreatment with trigonelline, a selective blockade of Nrf2, offset the lithium enhanced Nrf2 antioxidant response in islets, blunted the protective effect of lithium on pancreatic islets and β-cells, and abolished the hypoglycemic activity of lithium in STZ-injured mice. Collectively, our findings suggest that microdose lithium confers a protective effect on islet β-cells via targeting the GSK3β-regulated Nrf2 antioxidant response and thereby ameliorates T1D and its related kidney impairment.
One of the major complications of diabetes mellitus is diabetic nephropathy (DN), the pathogenesis of which is primarily driven by oxidative stress. As a major regulator of antioxidant responses, the transcription factor nuclear factor erythroid 2-related factor 2 (NRF2) has recently attracted much interest. NRF2 is a primary defense mechanism against the cytotoxic effects of oxidative stress, involving heterogeneous detoxification, the production of antioxidants and anti-inflammatory molecules, DNA repair, nuclear chaperones, and proteasome systems. A myriad of studies in pre-clinical models of DN have consistently demonstrated a beneficial effect of NRF2 activation, suggesting that NRF2 is likely a promising target for treating DN. This has been further supported by findings from clinical trials of bardoxolone methyl, an activator of NRF2, despite the unexpected adverse cardiovascular effects. This review summarizes the support for therapeutic targeting of NRF2 in DN and emphasizes the need for the optimization of NRF2-based treatment with the minimization of potential adverse effects.
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