Effects of Curcumin on High Glucose-Induced Epithelial-to-Mesenchymal Transition in Renal Tubular Epithelial Cells Through the TLR4-NF-κB Signaling Pathway

Modulation of renal fibrosis-related signaling pathways by traditional Chinese medicine: molecular mechanisms and experimental evidence

Renal fibrosis (RF), characterized by excessive deposition of extracellular matrix leading to tissue damage and scar formation, represents a refractory disease and a pivotal pathological basis for the progression to end-stage renal disease. The pathogenesis of RF is intricate, prominently implicating multiple key signaling pathways, including adenosine monophosphate-activated protein kinase/mammalian target of rapamycin (AMPK/mTOR), phosphoinositide 3-kinase/protein kinase B (PI3K/Akt), transforming growth factor-β1/small mother against decapentaplegic (TGF-β1/Smad), toll-like receptor 4/nuclear factor kappa B (TLR4/NF-κB), wingless integrated/β-catenin (Wnt/β-catenin), hypoxia-inducible factor-1α (HIF-1α), Hedgehog, and mitogen-activated protein kinase (MAPK). The current Western medical practices primarily rely on supportive and replacement therapies, which are often costly and suboptimal in efficacy. In contrast, traditional Chinese medicine (TCM), with its inherent advantages of multi-target, multi-pathway, and multi-effect modulation, emerges as a promising new strategy for RF treatment. However, a systematic, comprehensive, and detailed summary of these advancements remains absent. Therefore, this review consolidates the recent research progress on TCM modulation of RF-related signaling pathways, aiming to provide a theoretical foundation for further investigations into RF and the development of TCM interventions.

FSTL1 aggravates high glucose-induced oxidative stress and transdifferentiation in HK-2 cells

Chronic hyperglycemia, a hallmark of diabetes, can trigger inflammatory responses in the kidney, leading to diabetic nephropathy (DN). Follistatin-like protein 1 (FSTL1) has emerged as a potential therapeutic target in various kidney diseases. This study investigated the effect of high glucose on FSTL1 expression and its role in oxidative stress and cellular transdifferentiation injury in HK-2 human proximal tubule epithelial cells, a model of DN. We investigated FSTL1's level in HK-2 cells exposed to high glucose using Western blotting and quantitative real-time polymerase chain reaction (qRT-PCR). FSTL1 was manipulated using recombinant human FSTL1 (rhFSTL1) or lentiviral shFSTL1. We then analyzed proliferation, oxidative stress, transdifferentiation, cell migration, and the nuclear factor kappa-B (NF-κB) signaling pathway potentially involved in FSTL1 effects. Finally, we blocked the NF-κB pathway to see its influence on these cellular processes. High glucose exposure significantly increased FSTL1 in HK-2 cells, with longer/higher glucose further amplifying this effect. Silencing of FSTL1 ameliorates cellular damage by promoting proliferation, enhancing superoxide dismutase (SOD) and glutathione (GSH) activity, and reducing malondialdehyde (MDA) production, inhibiting cell migration. Furthermore, it prevented the harmful conversion of HK-2 cells from epithelial to myofibroblast-like phenotypes, evidenced by decreased fibronectin (FN) and α-smooth muscle actin (α-SMA) and preserved E-cadherin. Notably, silencing FSTL1 also inhibited the NF-κB signaling pathway. Conversely, rhFSTL1 exhibited opposite effects. Importantly, blocking NF-κB reversed the detrimental effects of FSTL1. These findings suggest that FSTL1 contributes to high glucose-induced kidney injury by promoting oxidative stress and cellular transdifferentiation potentially via the NF-κB pathway. Targeting FSTL1 may represent a novel therapeutic strategy for preventing or mitigating DN progression.

Nesfatin-1 peptide protects rat renal epithelial cells against high glucose and H2O2 induced injury via inhibition of oxidative stress, apoptosis, and fibrosis

Nesfatin-1 is a potent polypeptide and plays a crucial role in many physiological functions. Nesfatin-1 levels are reported in both the central nervous system and peripheral organs. However, the expression of nesfatin-1 in the renal system under chronic oxidative stress-induced conditions and the direct effect of nesfatin-1 treatment on stress-induced pathological damage are not reported. Thus, the present study aimed to explore the role of nesfatin-1 in vitro in oxidative stress-induced renal epithelial cells. High glucose (HG) and H2O2 combination were used to induce oxidative stress (OS). MTT, crystal violet, and H and E staining were used to measure cell viability, cytotoxicity, and morphology. FACS analysis and confocal microscopy were used to measure OS and apoptosis. RT-PCR was done for gene expression analysis. Decreased nesfatin-1 expression was observed in renal epithelial cells induced with HG and H2O2 compared to an untreated control (0.16; p < 0.0001). Nesfatin-1 co-treatment with HG and H2O2 attenuated ROS, apoptosis, and fibrosis. SOD, Catalase, and Bcl-2 expression decreased (p < 0.0001) and Caspase-3 and TGF-β1 expression increased in HG and H2O2-induced cells compared to control cells (p < 0.0001). Nesfatin-1 co-treatment attenuated these changes induced by HG and H2O2 (p < 0.0001). Nesfatin-1 expression was decreased in renal epithelial cells under stress-induced conditions. Moreover, nesfatin-1 co-treatment under stress-induced conditions protects the renal epithelial cells via inhibition of oxidative stress, apoptotic, and fibrotic signaling pathways.

Oxidative stress as a culprit in diabetic kidney disease

Diabetic kidney disease (DKD) has become the leading cause of end-stage renal disease (ESRD), and the prevalence of DKD has increased worldwide during recent years. DKD is associated with poor therapeutic outcomes in most patients, but there is limited understanding of its pathogenesis. This review suggests that oxidative stress interacts with many other factors in causing DKD. Highly active mitochondria and NAD(P)H oxidase are major sources of oxidants, and they significantly affect the risk for DKD. Oxidative stress and inflammation may be considered reciprocal causes of DKD, in that each is a cause and an effect of DKD. Reactive oxygen species (ROS) can act as second messengers in various signaling pathways and as regulators of metabolism, activation, proliferation, differentiation, and apoptosis of immune cells. Epigenetic modifications, such as DNA methylation, histone modifications, and non-coding RNAs can modulate oxidative stress. The development of new technologies and identification of new epigenetic mechanisms may provide novel opportunities for the diagnosis and treatment of DKD. Clinical trials demonstrated that novel therapies which reduce oxidative stress can slow the progression of DKD. These therapies include the NRF2 activator bardoxolone methyl, new blood glucose-lowering drugs such as sodium-glucose cotransporter 2 inhibitors, and glucagon-like peptide-1 receptor agonists. Future studies should focus on improving early diagnosis and the development of more effective combination treatments for this multifactorial disease.

Counteracting Action of Curcumin on High Glucose-Induced Chemoresistance in Hepatic Carcinoma Cells

Along with direct anticancer activity, curcumin hinders the onset of chemoresistance. Among many, high glucose condition is a key driving factor for chemoresistance. However, the ability of curcumin remains unexplored against high glucose-induced chemoresistance. Moreover, chemoresistance is major hindrance in effective clinical management of liver cancer. Using hepatic carcinoma HepG2 cells, the present investigation demonstrates that high glucose induces chemoresistance, which is averted by the simultaneous presence of curcumin. Curcumin obviated the hyperglycemia-induced modulations like elevated glucose consumption, lactate production, and extracellular acidification, and diminished nitric oxide and reactive oxygen species (ROS) production. Modulated molecular regulators are suggested to play a crucial role as curcumin pretreatment also prevented the onset of chemoresistance by high glucose. High glucose instigated suppression in the intracellular accumulation of anticancer drug doxorubicin and drug-induced chromatin compactness along with declined expression of drug efflux pump MDR-1 and transcription factors and signal transducers governing the survival, aggressiveness, and apoptotic cell death (p53, HIF-1α, mTOR, MYC, STAT3). Curcumin alleviated the suppression of drug retention and nuclear condensation along with hindering the high glucose-induced alterations in transcription factors and signal transducers. High glucose-driven resistance in cancer cells was associated with elevated expression of metabolic enzymes HKII, PFK1, GAPDH, PKM2, LDH-A, IDH3A, and FASN. Metabolite transporters and receptors (GLUT-1, MCT-1, MCT-4, and HCAR-1) were also found upregulated in high glucose exposed HepG2 cells. Curcumin inhibited the elevated expression of these enzymes, transporters, and receptors in cancer cells. Curcumin also uplifted the SDH expression, which was inhibited in high glucose condition. Taken together, the findings of the present investigation first time demonstrate the ability of curcumin against high glucose-induced chemoresistance, along with its molecular mechanism. This will have implication in therapeutic management of malignancies in diabetic conditions.