Andrographolide suppresses high glucose-induced fibronectin expression in mesangial cells via inhibiting the AP-1 pathway

Andrographolide Promotes Uptake of Glucose and GLUT4 Transport through the PKC Pathway in L6 Cells

Glucose transporter 4 (GLUT4) is a membrane protein that regulates blood glucose balance and is closely related to type 2 diabetes. Andrographolide (AND) is a diterpene lactone extracted from herbal medicine Andrographis paniculata, which has a variety of biological activities. In this study, the antidiabetic effect of AND in L6 cells and its mechanism were investigated. The uptake of glucose of L6 cells was detected by a glucose assay kit. The expression of GLUT4 and phosphorylation of protein kinase B (PKB/Akt), AMP-dependent protein kinase (AMPK), and protein kinase C (PKC) were detected by Western blot. At the same time, the intracellular Ca2+ levels and GLUT4 translocation in myc-GLUT4-mOrange-L6 cells were detected by confocal laser scanning microscopy. The results showed that AND enhanced the uptake of glucose, GLUT4 expression and fusion with plasma membrane in L6 cells. Meanwhile, AND also significantly activated the phosphorylation of AMPK and PKC and increased the concentration of intracellular Ca2+. AND-induced GLUT4 expression was significantly inhibited by a PKC inhibitor (Gö6983). In addition, in the case of 0 mM extracellular Ca2+ and 0 mM extracellular Ca2+ + 10 μM BAPTA-AM (intracellular Ca2+ chelator), AND induced the translocation of GLUT4, and the uptake of glucose was significantly inhibited. Therefore, we concluded that AND promoted the expression of GLUT4 and its fusion with plasma membrane in L6 cells through PKC pathways in a Ca2+—dependent manner, thereby increasing the uptake of glucose.

Effects of andrographolide on renal tubulointersticial injury and fibrosis. Evidence of its mechanism of action

BACKGROUND

Diabetic nephropathy (DN) is associated with renal interstitial injury and fibrosis. Our previous study showed that andrographolide protected against the progression of DN and high glucose (HG)-induced mesangial dysfunction. However, the protective effects of andrographolide on renal tubular epithelial cells have not been fully elucidated.

PURPOSE

To determine the protective effects of andrographolide on renal tubular damage and explore the underlying mechanism.

STUDY DESIGN

Human tubular epithelial cells (HK-2 cells) were treated with andrographolide (5 and 10 μM) under HG conditions. Diabetic mice were treated with andrographolide (i.p. 2 and 4 mg/kg, twice per week).

METHODS

Western blotting, reverse transcription-polymerase chain reaction (RT-PCR), immunofluorescence and flow cytometry were used to analyze the effects of andrographolide on renal tubular injury and fibrotic mechanisms in HK-2 cells. The protective effects of andrographolide against renal tubulointerstitial injury and fibrosis were investigated in diabetic mice fed a high-fat diet (HFD). Renal interstitial tissue was collected at sacrifice for immunohistochemistry, immunofluorescence analysis, RT-PCR and Western blotting to analyze the effects of andrographolide on renal tubular injury and fibrosis.

RESULTS

In vitro assay results indicated that andrographolide (5 and 10 μM) effectively inhibited HG-induced apoptosis, epithelial-mesenchymal transition (EMT) and collagen deposition in HK-2 cells. Mechanistically, HG stimulated mitochondrial reactive oxygen species (mtROS)-mediated NOD-like receptor family and pyrin domain-containing protein 3 (NLRP3) inflammasome activation and EMT in tubular epithelial cells, and andrographolide (5 and 10 μM) inhibited these effects by ameliorating mitochondrial dysfunction. In vivo, treatment with andrographolide (2 and 4 mg/kg) inhibited renal tubular cell apoptosis, EMT and tubulointerstitial fibrosis, mitochondrial dysfunction and NLRP3 inflammasome activation in diabetic mice.

CONCLUSION

Andrographolide (5 and 10 μM) prevents HG-induced renal tubular cell damage, and andrographolide (2 and 4 mg/kg) protects against the progression of diabetic tubular injury and fibrosis in mice by suppressing mitochondrial dysfunction and NLRP3 inflammasome activation.

Andrographolide Protects against HG-Induced Inflammation, Apoptosis, Migration, and Impairment of Angiogenesis via PI3K/AKT-eNOS Signalling in HUVECs

Andrographolide (Andr) is a major component isolated from the plant Andrographis paniculata. Inflammation, apoptosis, and impaired angiogenesis are implicated in the pathogenesis of high glucose (HG)-induced injury of vascular endotheliocytes. Our study is aimed at evaluating the effect of Andr on HG-induced HUVEC injury and the underlying mechanism. HUVECs were exposed to HG levels (33 mM) and treated with Andr (0, 12.5, 25, and 50 μM). Western blot analysis, real-time PCR, immunofluorescence staining, the scratch test, and the tube formation assay were performed to assess the effects of Andr. We discovered that Andr inhibited the inflammatory response (IL-1β, IL-6, and TNFα), decreased the apoptosis ratio and cell migration, and promoted tube formation in response to HG stimulation. Andr ameliorated the levels of phosphorylated PI3K (p-PI3K), phosphorylated AKT (p-AKT), and phosphorylated eNOS (p-eNOS). The expression of vascular endothelial growth factor (VEGF) protein, a vital factor in angiogenesis, was improved by Andr treatment under HG stimulation. LY294002 is a blocker of PI3K, MK-2206 2HCI (MK-2206) is a highly selective AKT inhibitor, and L-NAME is a suppressor of eNOS, all of which significantly reduce Andr-mediated protective effects in vitro. Hence, Andr may be involved in regulating HG-induced injury by activating PI3K/AKT-eNOS signalling in HUVECs.

Hyperglycemia-Induced Aberrant Cell Proliferation; A Metabolic Challenge Mediated by Protein O-GlcNAc Modification

Chronic hyperglycemia has been associated with an increased prevalence of pathological conditions including cardiovascular disease, cancer, or various disorders of the immune system. In some cases, these associations may be traced back to a common underlying cause, but more often, hyperglycemia and the disturbance in metabolic balance directly facilitate pathological changes in the regular cellular functions. One such cellular function crucial for every living organism is cell cycle regulation/mitotic activity. Although metabolic challenges have long been recognized to influence cell proliferation, the direct impact of diabetes on cell cycle regulatory elements is a relatively uncharted territory. Among other "nutrient sensing" mechanisms, protein O-linked β-N-acetylglucosamine (O-GlcNAc) modification emerged in recent years as a major contributor to the deleterious effects of hyperglycemia. An increasing amount of evidence suggest that O-GlcNAc may significantly influence the cell cycle and cellular proliferation. In our present review, we summarize the current data available on the direct impact of metabolic changes caused by hyperglycemia in pathological conditions associated with cell cycle disorders. We also review published experimental evidence supporting the hypothesis that O-GlcNAc modification may be one of the missing links between metabolic regulation and cellular proliferation.

Andrographolide Ameliorates Diabetic Cardiomyopathy in Mice by Blockage of Oxidative Damage and NF-κB-Mediated Inflammation

Andrographolide (Andro), a major bioactive component obtained from Andrographis paniculata Nees, has exerted wide antioxidant as well as cytoprotective properties. However, whether Andro treatment could retard the progress of diabetic cardiomyopathy (DCM) remains unknown. In this study, we evaluated the effects of Andro against diabetes-induced myocardial dysfunction and explored the underlying mechanism in STZ-induced diabetic mice. As a result, treatment with Andro dose dependently suppressed cardiac inflammation and oxidative stress, accompanied by decreasing cardiac apoptosis, which subsequently ameliorated cardiac fibrosis and cardiac hypertrophy. Further, Andro blocked hyperglycemia-triggered reactive oxygen species (ROS) generation by suppressing NADPH oxidase (NOX) activation and augmenting nuclear factor erythroid 2-related factor 2 (Nrf2) expression both in vitro and in vivo. Our results suggest that the cardioprotective effects afforded by Andro treatment involve the modulation of NOX/Nrf2-mediated oxidative stress and NF-κB-mediated inflammation. The present study unravels the therapeutic potential of Andro in the treatment of DCM by attenuating oxidative stress, inflammation, and apoptosis.

SP600125 suppresses Keap1 expression and results in NRF2-mediated prevention of diabetic nephropathy

c-Jun N-terminal kinase (JNK) contributes to the pathogenesis of diabetic nephropathy (DN). The JNK inhibitor SP600125 was reported to ameliorate DN. However, the mechanism remained unclear. We previously reported that SP600125 activated nuclear factor erythroid 2-related factor 2 (NRF2), a governor of the cellular antioxidant defense system, in the aortas of the diabetic mice. Given the critical role of NRF2 in preventing DN, the present study aimed to test whether or not NRF2 is required for SP600125's protection against DN. To test the role of NRF2 in SP600125's effect, streptozotocin-induced C57BL/6 wild-type (WT) and Nrf2-knockout (KO) diabetic mice were treated in the presence or absence of SP600125, for 24 weeks. To explore the mechanism by which SP600125 activates NRF2, mouse mesangial cells (MMCs) were treated with high glucose (HG), in the presence or absence of either SP600125 or JNK siRNA. SP600125 significantly attenuated the diabetes-induced renal oxidative stress, inflammation, fibrosis, pathological change and dysfunction in the WT, but not the Nrf2 KO mice. SP600125 inactivated JNK, inhibited kelch-like ECH-associated protein 1 expression, preserved NRF2 protein and facilitated its nuclear translocation in the kidneys of the WT mice, the effects of which were similarly produced by either SP600125 or JNK siRNA in HG-treated MMCs. Further, both SP600125 and JNK siRNA alleviated HG-induced mesangial oxidative stress and expression of inflammatory and fibrotic genes. The present study demonstrates that NRF2 is required for SP600125's protection against DN. SP600125 activates NRF2 possibly via inhibition of JNK-induced Keap1 expression.

Andrographolide ameliorates diabetic nephropathy by attenuating hyperglycemia-mediated renal oxidative stress and inflammation via Akt/NF-κB pathway

Diabetic nephropathy (DN) is characterized by proliferation of mesangial cells, mesangial hypertrophy and extracellular matrix (ECM) accumulation. Our recent study found that andrographolide inhibited high glucose-induced mesangial cell proliferation and fibronectin expression through inhibition of AP-1 pathway. However, whether andrographolide has reno-protective roles in DN has not been fully elucidated. Here, we studied the pharmacological effects of andrographolide against the progression of DN and high glucose-induced mesangial dysfunction. Diabetes was induced in C57BL/6 mice by intraperitoneal injection of streptozotocin (STZ). After 1 weeks after STZ injection, normal diet was substituted with a high-fat diet (HFD). Diabetic mice were intraperitoneal injected with andrographolide (2 mg/kg, twice a week). After 8 weeks, functional and histological analyses were carried out. Parallel experiments uncovering the molecular mechanism by which andrographolide prevents from DN was performed in mesangial cells. Andrographolide inhibited the increases in fasting blood glucose, triglyceride, kidney/body weight ratio, blood urea nitrogen, serum creatinine and 24-h albuminuria in diabetic mice. Andrographolide also prevented renal hypertrophy and ECM accumulation. Furthermore, andrographolide markedly attenuated NOX1 expression, ROS production and pro-inflammatory cytokines as well. Additionally, andrographolide inhibited Akt/NF-κB signaling pathway. These results demonstrate that andrographolide is protective against the progression of experimental DN by inhibiting renal oxidative stress, inflammation and fibrosis.

Emodin suppresses hyperglycemia-induced proliferation and fibronectin expression in mesangial cells via inhibiting cFLIP

As one of the most serious microvascular complications of diabetes and a major cause of end stage renal disease, diabetic nephropathy (DN) is calling for effective treatment strategies. Here, we provide evidence that hyperglycemia can induce proliferation and decreasing apoptosis of mesangial cells (MCs) and subsequent renal dysfunction by up-regulating cellular FLICE-inhibitory protein (cFLIP). Treatment with emodin significantly turns down the accelerated cell cycle and proliferation of MCs cultured in high glucose (HG) via inhibiting cFLIP. In vitro, knockdown of cFLIP can arrest cell cycle and accelerate cell death by activating caspase-8, caspase-3 and caspase-9, and down-regulate proliferating cell nuclear antigen (PCNA). Our results also suggest that emodin regulates cFLIP expression in transcriptional level. Importantly, emodin lessens proteinuria and fibronectin expression in early-stage of streptozotocin (STZ)-induced diabetic rats. These findings demonstrate that emodin represent a promising strategy to prevent renal dysfunction in early-stage of diabetes mellitus.