Activation of AQP4, p66Shc and endoplasmic reticulum stress is involved in inflammation by carrageenan and is suppressed by argirein, a derivative of rhein

Argirein alleviates vascular endothelial insulin resistance through suppressing the activation of Nox4-dependent O2- production in diabetic rats

BACKGROUND

Insulin resistance in endothelial cells contributes to the development of cardiovascular disease in type 2 diabetes mellitus (T2DM). Therefore, there are great potential clinical implications in developing pharmacological interventions targeting endothelial insulin resistance. Our previous studies indicated that argirein which was developed by combining rhein with L-arginine by a hydrogen bond, could substantially relieved stress related exacerbation of cardiac failure and alleviated cardiac dysfunction in T2DM, which was associated with suppressing NADPH oxidase activity. However, it is unclear whether argirein treatment attenuates the vascular lesion and dysfunction in T2DM and its underlying mechanisms.

METHODS AND RESULTS

The rat aortic endothelial cells (RAECs) were used to treat with palmitic acid (PA), a most common saturated free fatty acid, which could induce insulin resistance. It was showed that argirein increased glucose uptake and glucose transporter-4 (Glut4) expression and reversed the phosphorylation of IRS-1-ser307 and AKT-ser473, consequently resulting in the increase of the production of eNOS and NO in PA-induced RAECs. We further found that argirein blocked the Nox4-dependent superoxide (O₂^-.) generation, which regulated glucose metabolism in RAECs during PA stimulation. In vitro, argirein increased the release of endothelial NO to relieve the vasodilatory response to acetylcholine and insulin, and restored the expression of Nox4 and pIRS-1-ser307 in the aorta endothelium of high-fat diet (HFD)-fed rats following an injection of streptozocin (STZ).

CONCLUSION

These results suggested that argirein could improve endothelial insulin resistance which was attributed to inhibiting Nox4-dependent redox signaling in RAECs. These studies thus revealed the novel effect of argirein to prevent the vascular complication in T2DM.

Renal aquaporin-4 associated pathology in TG-26 mice

Human immunodeficiency virus-associated nephropathy (HIVAN) is a leading cause of end-stage renal disease in HIV patients, which is characterized by glomerulosclerosis and renal tubular dysfunction. Aquaporin-4 (AQP-4) is a membrane bound water channel protein that plays a distinct role in water reabsorption from renal tubular fluid. It has been proven that failure of AQP-4 insertion into the renal tubular membrane leads to renal dysfunction. However, the role of AQP-4 in HIVAN is unclear. We hypothesize that impaired water reabsorption leads to renal injury in HIVAN, where AQP-4 plays a crucial role. Renal function is assessed by urinary protein and serum blood urea nitrogen (BUN). Kidneys from HIV Transgenic (TG26) mice (HIVAN animal model) were compared to wild type mice by immunostaining, immunoblotting and quantitative RT-PCR. TG26 mice had increased proteinuria and BUN. We found decreased AQP-4 levels in the renal medulla, increased endothelin-1, endothelin receptor A and reduced Sirtuin1 (SIRT-1) levels in TG26 mice. Also, oxidative and endoplasmic reticulum stress was enhanced in kidneys of TG26 mice. We provide the first evidence that AQP-4 is inhibited due to induction of HIV associated stress in the kidneys of TG26 mice which limits water reabsorption in the kidney which may be one of the cause associated with HIVAN, impairing kidney physiology. AQP-4 dysregulation in TG26 mice suggests that similar changes may occur in HIVAN patients. This work may identify new therapeutic targets to be evaluated in HIVAN.

A Comprehensive and System Review for the Pharmacological Mechanism of Action of Rhein, an Active Anthraquinone Ingredient

Rhein is a major medicinal ingredient isolated from several traditional Chinese medicines, including Rheum palmatum L., Aloe barbadensis Miller, Cassia angustifolia Vahl., and Polygonum multiflorum Thunb. Rhein has various pharmacological activities, such as anti-inflammatory, antitumor, antioxidant, antifibrosis, hepatoprotective, and nephroprotective activities. Although more than 100 articles in PubMed are involved in the pharmacological mechanism of action of rhein, only a few focus on the relationship of crosstalk among multiple pharmacological mechanisms. The mechanism of rhein involves multiple pathways which contain close interactions. From the overall perspective, the pathways which are related to the targets of rhein, are initiated by the membrane receptor. Then, MAPK and PI3K-AKT parallel signaling pathways are activated, and several downstream pathways are affected, thereby eventually regulating cell cycle and apoptosis. The therapeutic effect of rhein, as a multitarget molecule, is the synergistic and comprehensive result of the involvement of multiple pathways rather than the blocking or activation of a single signaling pathway. We review the pharmacological mechanisms of action of rhein by consulting literature published in the last 100 years in PubMed. We then summarize these pharmacological mechanisms from a comprehensive, interactive, and crosstalk perspective. In general, the molecular mechanism of action of drug must be understood from a systematic and holistic perspective, which can provide a theoretical basis for precise treatment and rational drug use.

AMPK activator-mediated inhibition of endoplasmic reticulum stress ameliorates carrageenan-induced insulin resistance through the suppression of selenoprotein P in HepG2 hepatocytes

Carrageenan (CGN) has been shown to cause inflammation through toll-like receptor 4, which may play an important role in insulin resistance and type 2 diabetes mellitus. Selenoprotein P (SeP) has recently been identified as a novel hepatokine that causes insulin resistance. Here, we report that treatment of HepG2 cells with CGN increased both CCAAT enhancer binding protein homologous protein (CHOP) and SeP expression. Pretreatment with 4-phenylbutyrate (4-PBA), an endoplasmic reticulum stress inhibitor, and PD98059, a c-Jun N-terminal kinase (JNK) inhibitor, reversed CGN-induced SeP expression. Moreover, both 4-PBA and knock-down of SeP improved CGN-induced insulin resistance. In addition, we found that adenosine monophosphate-activated protein kinase (AMPK) activators ameliorated CGN-induced insulin resistance in addition to suppressing CHOP and SeP expression. In conclusion, CGN-induced ER stress increased the expression of SeP through the JNK pathway, while AMPK activators ameliorated CGN-induced insulin resistance via SeP inhibition through the AMPK-mediated alleviation of ER stress in hepatocytes.

Fourier transform near-infrared spectroscopy used for purity determination of rhein-L-arginine cocrystal (argirein)

A method is described using rapid and sensitive Fourier transform near-infrared spectroscopy (FT-NIRS) for the determination of rhein-L-arginine cocrystal (argirein). By mixing different values of argirein into different proportions with rhein and arginine, we obtained 41 batches of samples to deatermine. Partial least squares (PLS) regression was selected as the analysis type and standard normal variate (SNV) and original spectra were adopted for the spectral pretreatment. The correlation coefficient (R) of the calibration model was above 0.99 and the root mean square error of predictions (RMSEP) was under 0.012. The developed model was applied to 10 batches of known samples with satisfactory results. The established method is validated and can be applied to the intrinsic quality control of synthetic products and other cocrystals.

AQP4 KO exacerbating renal dysfunction is mediated by endoplasmic reticulum stress and p66Shc and is attenuated by apocynin and endothelin antagonist CPU0213

Aquaporin 4 (AQP4) is essential in normal kidney. We hypothesized that AQP4 knockout (KO) may exacerbate pro-inflammatory factors in the stress induced renal insufficiency. Mechanisms underlying are likely due to activating renal oxidative stress adaptor p66Shc and endoplasmic reticulum (ER) stress that could be mediated by endothelin (ET)-NADPH oxidase (NOX) pathway. AQP4 KO and wild type (WT) mice were randomly divided into 4 groups: control, isoproterenol (1mg/kg, s.c., 5d), and interventions in the last 3 days with either apocynin (NADPH oxidase inhibitor, 100mg/kg, p.o.) or CPU0213 (a dual endothelin receptor antagonist 200mg/kg, p.o.). In addition, HK2 cells were cultured in 4 groups: control, isoproterenol (10(-6)M), intervened with apocynin (10(-6)M) or CPU0213 (10(-6)M). In AQP4 KO mice elevated creatinine levels were further increased by isoproterenol compared to AQP4 KO alone. In RT-PCR, western blot and immunohistochemical assay p66Shc and PERK were significantly increased in the kidney of AQP4 KO mice, associated with pro-inflammatory factors CX40, CX43, MMP-9 and ETA compared to the WT mice. Expression of AQP4 was escalated in isoproterenol incubated HK2 cells, and the enhanced protein of PERK and p-PERK/PERK, and p66shc in vivo and in vitro were significantly attenuated by either apocynin or CPU0213. In conclusion, AQP4 KO deteriorates renal dysfunction due to exacerbating ER stress and p66Shc in the kidney. Either endothelin antagonism or NADPH oxidase blockade partly relieves renal dysfunction through suppressing abnormal biomarkers by APQ4 KO and isoproterenol in the kidney.

Hypoxia alters pharmacokinetics of argirein because of mitochondrial dysfunction that is alleviated by apocynin

OBJECTIVES

Pharmacokinetics (PK) of argirein might be changed in response to mitochondrial (MITO) dysfunction and activated nicotinamide adenine dinucleotide phosphate oxidase (NOX) on hypoxia. We hypothesized that hypoxic changes in MITO and NOX could alter PK and tissue distribution of argirein. We tested if these changes in PK of argirein by hypoxia could be relieved by apocynin (APO), a blocker of NOX, through normalizing MITO and NOX.

METHODS

Male Sprague-Dawley rats were exposed to hypoxia (O2 10% ± 5% 8 h per day) for 7 days and treated with APO (80 mg/kg, i.g.) in the last 4 days. The PK and tissue distribution of argirein were monitored by measuring its main metabolite rhein using HPLC analysis. Manganese superoxide dismutase (MnSOD) and NOX were assayed.

KEY FINDINGS

The PK parameters and concentrations of rhein in the kidney, liver, heart and testes were significantly altered under hypoxia, accompanied with a reduced MnSOD and upregulated NOX compared with the normal. Altered argirein PK and distribution in these organs were relieved following APO administration.

CONCLUSION

Abnormal PK and distribution of argirein by assaying its metabolite rhein are significant, consequent to hypoxic injury that is significantly ameliorated by APO through normalizing MITO and NOX.

Hepatosteatosis and hepatic insulin resistance are blunted by argirein, an anti-inflammatory agent, through normalizing endoplasmic reticulum stress and apoptosis in diabetic liver

OBJECTIVES

Insulin resistance represents a mechanism underlying defect metabolism of carbohydrate and lipid linked to inflammatory reactions in diabetic liver. We hypothesized that the changes may be secondary to endoplasmic reticulum (ER) stress, which could be alleviated by either argirein or valsartan.

METHODS

Hepatosteatosis in diabetic liver was induced in rats fed with a high-fat diet (HFD) for 12 weeks combined with a single low dose of streptozotocin (STZ 35 mg/kg, ip). Interventions (mg/kg/d, po)with either argirein (50, 100 and 200) or valsartan (12) were conducted in the last 4 weeks.

KEY FINDINGS

In diabetic liver fat was significantly accumulated in association with elevated hepatic glucose, serum insulin and homeostasis model assessment of insulin resistance value. Downregulated glucose transporter 4, insulin receptor substrate-1 and leptin receptor (P < 0.01) were found relative to normal, where DNA ladder, downregulated B cell lymphoma/leukemia-2, upregulated B cell lymphoma/leukemia-2 Associated X protein and upregulated ER stress chaperones such as Bip/GRP78 (also known as Binding Protein, BiP), PKR-like ER kinase (PERK), p-PERK/PERK and C/EBP homologous protein were significant. These abnormalities were significantly ameliorated by argirein and valsartan.

CONCLUSIONS

Hepatosteatosis induced by HFD/low STZ manifests insulin resistance and apoptosis, linked to an entity of low-grade inflammation due to activated ER stress sensors. With anti-inflammatory activity either argirein or valsartan blunts hepatosteatosis through normalizing ER stress and apoptosis in the diabetic liver.

Depressed calcium-handling proteins due to endoplasmic reticulum stress and apoptosis in the diabetic heart are attenuated by argirein

Diabetic cardiomyopathy (DC) is a unique disease frequently complicated to diabetes mellitus, manifesting endoplasmic reticulum (ER) stress and depressed calcium-handling proteins. We hypothesized that the abnormal FKBP12.6, SERCA2a, and CASQ2 are consequent to ER stress and apoptosis that are likely due to an entity of inflammation. These abnormalities may be attributed to reactive oxygen species genesis from activated NADPH oxidase which could respond to argirein (AR) through its anti-inflammatory activity. Sprague Dawley rats were randomly divided into six groups. Except the normal group, rats were injected with streptozotocin (STZ; 60 mg/kg, i.p.) once. During weeks 5 to 8 following STZ injection, rats were treated (in milligrams per kilogram per day, i.g.) with aminoguanidine (AMG, 100; an inducible nitric oxide synthase and AGEs inhibitor) or three doses of AR (50, 100, and 200). FKBP12.6, SERCA2a, and CASQ2 and ER stress chaperones Bip and PERK and apoptotic molecules were monitored in vivo and in vitro. Impaired cardiac performance and downregulated FKBP12.6, SERCA2a, and CASQ2 were significant in DC in vivo, and abnormal calcium-handling proteins were also found in high-glucose-incubated myocytes in vitro. ER stress manifested by upregulated Bip and PERK was predominant in association with DNA ladder and upregulated Bax and downregulated BCL-2 in vivo and in vitro. AR is effective to attenuate these abnormalities compared to AMG. Diabetic myocardium has inflammatory entity expressed as ER stress contributing to downregulated calcium-handling proteins. AR has potential in managing DC through attenuating depressed calcium-handling proteins, activated ER stress, and apoptosis in the myocardium.