Oxidative stress plays an important role in systemic lupus erythematosus (SLE) and especially in lupus nephritis (LN). The aim of this study was to compare redox-related biomarkers between patients with active LN, quiescent SLE (Q-SLE) and healthy controls (HC) and to explore their association with clinical characteristics such as disease activity in patients. We investigated levels of plasma free thiols (R-SH, sulfhydryl groups), levels of soluble receptor for advanced glycation end products (sRAGE) and levels of malondialdehyde (MDA) in SLE patients with active LN (n = 23), patients with quiescent SLE (n = 47) and HC (n = 23). Data of LN patients who previously participated in Dutch lupus nephritis studies and longitudinal samples up to 36 months were analyzed. Thiol levels were lower in active LN at baseline and Q-SLE patients compared to HC. In generalized estimating equation (GEE) modelling, free thiol levels were negatively correlated with the Systemic Lupus Erythematosus Disease Activity Index (SLEDAI) over time (p < 0.001). sRAGE and MDA were positively correlated with the SLEDAI over time (p = 0.035 and p = 0.016, respectively). These results indicate that oxidative stress levels in LN patients are increased compared to HC and associated with SLE disease activity. Therefore, interventional therapy to restore redox homeostasis may be useful as an adjunctive therapy in the treatment of oxidative damage in SLE.

Systemic lupus erythematosus (SLE) is a complex autoimmune disease in which kidney involvement, so-called lupus nephritis (LN), is common and one of the most severe manifestations. Oxidative stress (OS) may play a role in the pathogenesis of LN through the exacerbation of inflammation and immune cell dysfunction/dysregulation. Nuclear factor erythroid 2-related factor 2 (Nrf2), also known as nuclear factor erythroid-derived 2-like 2, is a transcription factor that in humans is encoded by the NFE2L2 gene and is regarded as a central regulator of the antioxidative response. Nrf2-activating compounds have been shown to alleviate oxidative stress in cells and tissues of lupus-prone mice. Although the precise mechanisms of Nrf2 activation on the immune system in SLE remain to be elucidated, Nrf2-activating compounds are considered novel therapeutical options to suppress OS and thereby might alleviate disease activity in SLE, especially in LN. This review therefore summarizes the role of the Nrf2 signaling pathway in the pathogenesis of SLE with LN and describes compounds modulating this pathway as potential additional clinical interventions.

Oxidative stress plays an important role in systemic lupus erythematosus (SLE). To elucidate whether it is already present in early phases, we investigate oxidative stress-related genes in incomplete SLE (iSLE) and quiescent SLE (qSLE, inactive disease), as well as the effect of nuclear factor erythroid-derived 2-like 2 (NRF2) activators on NRF2-related genes in peripheral blood mononuclear cells (PBMCs) and HaCaT keratinocytes. In total, 28 qSLE patients, 29 iSLE patients and 21 age- and sex-matched healthy controls (HCs) were included. Serum free thiols, reactive oxygen species (ROS) levels and NRF2-related antioxidant gene expression were measured. Furthermore, PBMCs and HaCaT keratinocytes were treated with the NRF2 activators sulforaphane (SFN) and dimethyl fumarate (DMF) in vitro to assess expression of antioxidant genes. Finally, NRF2 and Heme oxygenase-1 (HMOX1) proteins in non-sun-exposed skin sections were assessed. Thiols were significantly lower in qSLE patients compared to HCs. In whole blood, Kelch-like ECH-associating protein 1 (KEAP1) and catalase (CAT) mRNA levels were significantly reduced in iSLE and qSLE. Treatment with SFN or DMF in PBMCs upregulated HMOX1 and NAD(P)H quinone dehydrogenase-1 (NQO1) mRNA expression and downregulated CAT expression. In HaCaT cells, mRNA expression of HMOX1, NQO1 and thioredoxin was upregulated. There were no differences in protein expression of NRF2 and HMOX1 in skin tissues. In conclusion, in qSLE patients, oxidative stress is elevated, while antioxidant capacity is decreased. A similar trend, although not significant, is seen in iSLE patients, which indicates that redox imbalances are already present in early phases, but not as obvious as in established SLE. NRF2 activators upregulate antioxidant gene expression in PBMCs and HaCaT cells, highlighting their potential role to modulate oxidative stress pathways in SLE.