Targeting Nrf2/Keap1 signaling pathway by bioactive natural agents: Possible therapeutic strategy to combat liver disease

BACKGROUND

Nuclear factor erythroid 2-related factor (Nrf2), a stress-activated transcription factor, has been documented to induce a defense mechanism against oxidative stress damage, and growing evidence considers this signaling pathway a key pharmacological target for the treatment of liver diseases.

PURPOSE

The present review highlights the role of phytochemical compounds in activating Nrf2 and mitigate toxicant-induced stress on liver injury.

METHODS

A comprehensive search of published articles was carried out to focus on original publications related to Nrf2 activators against liver disease using various literature databases, including the scientific Databases of Science Direct, Web of Science, Pubmed, Google, EMBASE, and Scientific Information (SID).

RESULTS

Nrf2 activators exhibited promising effects in resisting a variety of liver diseases induced by different toxicants in preclinical experiments and in vitro studies by regulating cell proliferation and apoptosis as well as an antioxidant defense mechanism. We found that the phytochemical compounds, such as curcumin, naringenin, sulforaphane, diallyl disulfide, mangiferin, oleanolic acid, umbelliferone, daphnetin, quercetin, isorhamnetin-3-O-galactoside, hesperidin, diammonium glycyrrhizinate, corilagin, shikonin, farrerol, and chenpi, had the potential to improve the Nrf2-ARE signaling thereby combat hepatotoxicity.

CONCLUSION

Nrf2 activators may offer a novel potential strategy for the prevention and treatment of liver diseases. More extensive studies are essential to identify the underlying mechanisms and establish future therapeutic potentials of these signaling modulators. Further clinical trials are warranted to determine the safety and effectiveness of Nrf2 activators for hepatopathy.

Analysis of the Exonic Single Nucleotide Polymorphism rs182428269 of the NRF2 Gene in Patients with Diabetic Foot Ulcer

BACKGROUND

The pivotal role of Nuclear factor erythroid-2-related factor 2 (NRF2) in redox homeostasis and wound healing has been well documented. However, the genetic mechanisms that regulate NRF2 in type 2 diabetes and diabetic foot ulcers remain unexplored. The present study investigated the association of single nucleotide polymorphism rs182428269 (-127 C/T) in subjects with type 2 diabetes and diabetic foot ulcers.

METHODS

This cross-sectional study comprised 400 participants that included group I: normal glucose tolerant subjects (NGT, n = 150), group II: type 2 diabetes mellitus subjects (T2DM, n = 150) and group III: infected diabetic foot ulcer subjects (DFU, n = 100). The non-synonymous SNP rs182428269 was selected based on in silico analysis and genotyped by PCR-restriction fragment length polymorphism (RFLP) followed by bidirectional Sanger sequencing. In addition, the gene expression of NRF2 in patients with polymorphism was analyzed by qPCR to evaluate the functional impact of the SNP.

RESULTS

NRF2 expression was significantly decreased among the T2DM and DFU subjects when compared to the NGT subjects. Of particular interest, the homozygous mutant (TT) genotype of rs182428269 polymorphism was significantly associated with an increased risk for the development of T2DM (OR = 1.95 (1.02-3.72), p = 0.04) and DFU (OR = 5.66 (2.98-10.76), p = 0.0001). Furthermore, a progressive decline in NRF2 expression was observed among the T2DM and DFU subjects with "TT" genotype compared to the "CC" and "CT" genotypes.

CONCLUSION

NRF2 polymorphism rs182428269 is associated with the pathogenesis of T2DM and DFU.

Role of Nrf2 in MALAT1/ HIF-1α loop on the regulation of angiogenesis in diabetic foot ulcer

Diabetic non healing wounds often result in significant morbidity and mortality. The number of effective targets to detect these wounds are meagre. Slow lymphangiogenesis is one of the complex processes involved in impaired healing of wounds. Long non coding RNAs (lncRNAs) have been importantly recognized for their role in pathological conditions. Multiple studies highlighting the role of lncRNAs in the regulation of several biological processes and complex diseases. Herein, we investigated the role of lncRNA Metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) in the progression of diabetic foot ulcer (DFU). We report a significant reduction in the expression of lncRNA MALAT1 in the infected DFU subjects which was positively correlated with the expression of angiogenic factors such as Nrf2, HIF-1α and VEGF. Further, expression of pro-inflammatory markers TNF-α and IL-6 were found to be increased while, the expression of anti-inflammatory marker IL-10 was decreased in infected DFU tissues. Involvement of lncRNA MALAT1 in angiogenesis in EA.hy926 cells was demonstrated by silencing the expression of Nrf2, HIF-1α, and VEGF through interference mediated by MALAT1. In addition, its inflammatory role was demonstrated by decreased expression of TNF-α, IL-6 and not affecting the expression of IL-10. Further, CRISPR-Cas9 knock out of Nrf2 decreased the expression of lncRNA MALAT1, HIF-1α and VEGF which revealed the association of Nrf2 in regulating MALAT1/HIF-1α loop through positive feedback mechanism. Collectively, our results suggested the role of Nrf2 on MALAT1/HIF-1α loop in the regulation of angiogenesis, which could act as a novel target in the treatment of diabetic wounds.

Tissue-specific role of Nrf2 in the treatment of diabetic foot ulcers during hyperbaric oxygen therapy

Hyperbaric oxygen (HBO) therapy is proven to be very successful for diabetic foot ulcer (DFU) treatment due to its antimicrobial effect, increased angiogenesis and enhanced collagen synthesis. The molecular mechanism underlying HBO therapy particularly the involvement of Nrf2 in the wound healing process was investigated in the present study. In addition, we have studied the levels of angiogenic markers in ulcer tissues and their correlation with Nrf2 during HBO therapy compared with standard therapy (Non-HBO) for DFU. A total of 32 Patients were recruited and randomized to standard wound care procedure alone (n = 17) or HBO therapy in combination with standard wound care procedure (n = 15) for 20 days. Our results showed that the tissue levels of Nrf2 along with its downstream targets were significantly increased in patients who underwent HBO therapy when compared to Non-HBO therapy. Further, HBO therapy induced angiogenesis as assessed by increased levels of angiogenesis markers such as EGF, VEGF, PDGF, FGF-2 and CXCL10 in the tissue samples. The expressions of eNOS and nitrite concentrations were also significantly increased in HBO therapy when compared to Non-HBO therapy subjects. Moreover, HBO therapy sensitises the macrophages to release FGF-2 and EGF thereby promotes angiogenesis. Further, it increased the levels of neutrophil attractant CXCL-8 thereby promotes the release of chemokine CCL2, a well-known mediator of neovascularization. The Pearson correlation showed that Nrf2 has a positive correlation with EGF, VEGF and PDGF. In conclusion, the findings of the present study suggest that HBO therapy promotes wound healing by increasing oxygen supply and distribution to damaged tissues, stimulating angiogenesis, decreasing inflammation, and increasing the nitrite levels. Increased levels of Nrf2 transiently regulate the expression of angiogenic genes in wound biopsies, which may result in accelerated healing of chronic wounds.

Circulatory levels of B-cell activating factor of the TNF family in patients with diabetic foot ulcer: Association with disease progression

Enhanced and prolonged expression of tumor necrosis factor alpha (TNF-α), a potent pro-inflammatory cytokine is evidenced during the chronic wound healing process of infected diabetic foot ulcer (IDFU). B-cell activating factor (BAFF) is the member of TNF-α family, which implicit in B-cell dysfunction. This study was aimed to evaluate the role of BAFF in diabetic foot ulcer (DFU) patients and to correlate its association with other family of inflammatory cytokines. Circulating levels of BAFF and other cytokines were measured in IDFU (n = 44) and non-IDFU patients (n = 40) using multiplexed bead-based cytokine immunoassay. A stepwise significant increase was observed in both circulatory BAFF and C-reactive protein (CRP) during the disease progression. The area under the receiver operating characteristic curve (AUC_ROC ) for BAFF was found to be high (0.89; [95% CI: 0.73-1.0]), when compared to CRP (0.68; [95% CI: 0.61-0.76]). Optimum diagnostic cutoff level for BAFF was found to be ≥2.35 pg/mL with 62.0% sensitivity and 85.7% specificity. Further, BAFF levels showed a significant positive correlation with CRP among IDFU patients. With respect to other family cytokines, BAFF levels were positively correlated with TNF-α, interferon family cytokines such as IFN-α2, IL-28A/IFN-λ2, IFN-γ, and IL-10 family cytokines such as IL-19, IL-22, and IL-26 and negatively correlated with IL-6 receptor family such as gp130/sIL-6Rβ. Hence, our data suggest that devising therapeutic strategies to reduce the levels of BAFF may contribute in amelioration of IDFU.

Serum levels of chemokines IP-10, IL-8 and SDF-1 serve as good biomarkers for diabetes-tuberculosis nexus

BACKGROUND

Inflammation has long been identified as an essential component of both Type-2 diabetes and tuberculosis. Chemokines are low molecular weight proteins which play an important role in both inflammation (diabetes) and immunity (tuberculosis).

METHODS

In this study, we measured the serum levels of IP-10, IL-8 and SDF-1 in subjects with Normal Glucose Tolerance (NGT-TB^- = 108; NGT-TB⁺ = 200), Pre-Diabetes (PDM-TB^- = 118; PDM-TB⁺ = 105), Newly Diagnosed Diabetes (NDM-TB^- = 105; NDM-TB⁺ = 63) and Known Diabetes (KDM-TB^- = 131; KDM-TB⁺ = 108), by ELISA. Along with chemokines pro-inflammatory cytokines TNF-ɑ and IL-6 were also measured in these groups.

RESULTS

While IP-10 levels were significantly reduced in TB⁺ subjects in all the sub-groups, IL-8 levels were significantly reduced in NDM-TB⁺ and increased in KDM-TB⁺ subjects. SDF-1 levels were significantly elevated in TB⁺ subjects in all the subgroups, except for KDM-TB⁺.

CONCLUSION

Altered serum chemokine levels can alter anti-TB immunity in diabetes patients and can fuel DM-TB nexus.

Single nucleotide polymorphisms in cytokine/chemokine genes are associated with severe infection, ulcer grade and amputation in diabetic foot ulcer

Compared to other complications the genetics of diabetic foot ulcer is poorly studied. The Interleukin (IL)-6 (-174G > C/rs1800795), Tumor Necrosis Factor (TNF)-α (-308G > A/rs1800629) and (-238G > A/rs361525) and Stromal cell Derived Factor (SDF)-1 (+801G > A/rs1801157) are well characterized single nucleotide polymorphisms (SNPs) which were previously shown to be associated with Diabetic Foot Ulcer (DFU). In the present study, we looked at the association of these SNPs with foot microbial infection, Wagner's ulcer grade and treatment procedure, along with serum levels of these cytokines (intermediate phenotype) and other serum biomarkers (adiponectin, leptin, CRP and HOMA-IR) in subjects with DFU. Subjects with DFU (n = 270) were genotyped by PCR-RFLP and the serum levels of IL-6, TNF-α and SDF-1 were determined by ELISA. Microbial infections were determined by standard microbiological methods. Ulcer grade and treatment procedures were recorded. IL-6 (-174G > C), TNF-α (-308G > A) and SDF-1 (+801G > A) SNPs were associated with severe microbial infections. TNF-α (-308G > A) and (-238G > A) SNPs were associated with severe ulcer grades. SDF-1 (+801G > A) SNP was associated with major amputation even after adjusting for confounding variables. Identification of these SNPs in DFU subjects would help in identifying high risk individuals who need better treatment care.

BSMI single nucleotide polymorphism in vitamin D receptor gene is associated with decreased circulatory levels of serum 25-hydroxyvitamin D among micro and macrovascular complications of type 2 diabetes mellitus

Vitamin D Receptor (VDR) gene single nucleotide polymorphism (SNP) in the intron 8 is a well characterized SNP which has previously been linked to various diseases including Type 2 Diabetes Mellitus (T2DM). However, the association of this SNP with micro and macrovascular complications of T2DM remains poorly studied. Hence, the present study was designed to investigate the association of VDR gene SNP with complications of T2DM (disease phenotype) and correlated it with the serum levels of (25[OH]D) (intermediate phenotype) along with other clinical risk factors of T2DM. Genotyping was carried out in a total of 866 subjects, in which Group-I had Control subjects (n = 252), Group-II with T2DM without complications (n = 200); Group-III and Group-IV had subjects with micro (n = 216) and macrovascular (n = 198) complications respectively by PCR -RFLP. The 'G' allele of the VDR gene SNP is associated with a significant risk for T2DM, Diabetic Neuropathy (DN) and Coronary Artery Disease (CAD). In addition, subjects with mutant GG genotype had lower levels of (25[OH]D) in both T2DM and micro-macrovascular complications than AA genotype. Thus, VDR (rs1544410) SNP was found to be associated with decreased serum (25[OH]D) levels in both micro-macrovascular complications of T2DM among South Indian Population.