Xianglu Rong

Inhibition of TRPC6 Channel Activity Contributes to the Antihypertrophic Effects of Natriuretic Peptides-Guanylyl Cyclase-A Signaling in the Heart

Rationale: Atrial and brain natriuretic peptides (ANP and BNP, respectively) exert antihypertrophic effects in the heart via their common receptor, guanylyl cyclase (GC)-A, which catalyzes the synthesis of cGMP, leading to activation of protein kinase (PK)G. Still, much of the network of molecular mediators via which ANP/BNP-GC-A signaling inhibit cardiac hypertrophy remains to be characterized. Objective: We investigated the effect of ANP-GC-A signaling on transient receptor potential subfamily C (TRPC)6, a receptor-operated Ca2+ channel known to positively regulate prohypertrophic calcineurin–nuclear factor of activated T cells (NFAT) signaling. Methods and Results: In cardiac myocytes, ANP induced phosphorylation of TRPC6 at threonine 69, the PKG phosphorylation site, and significantly inhibited agonist-evoked NFAT activation and Ca2+ influx, whereas in HEK293 cells, it dramatically inhibited agonist-evoked TRPC6 channel activity. These inhibitory effects of ANP were abolished in the presence of specific PKG inhibitors or by substituting an alanine for threonine 69 in TRPC6. In model mice lacking GC-A, the calcineurin-NFAT pathway is constitutively activated, and BTP2, a selective TRPC channel blocker, significantly attenuated the cardiac hypertrophy otherwise seen. Conversely, overexpression of TRPC6 in mice lacking GC-A exacerbated cardiac hypertrophy. BTP2 also significantly inhibited angiotensin II–induced cardiac hypertrophy in mice. Conclusions: Collectively, these findings suggest that TRPC6 is a critical target of antihypertrophic effects elicited via the cardiac ANP/BNP-GC-A pathway and suggest TRPC6 blockade could be an effective therapeutic strategy for preventing pathological cardiac remodeling.

A 35-day gavage safety assessment of ginger in rats

Ginger (Zingiber officinale Roscoe, Zingiberacae) is one of the most commonly used spices around the world and a traditional medicinal plant that has been widely used in Chinese, Ayurvedic and Unani-Tibb medicines for several thousand years. However, there was still lack of systemic safety evaluation. We conducted a 35-day toxicity study on ginger in rats. Both male and female rats were daily treated with ginger powder at the dosages of 500, 1000 and 2000 mg/kg body weight by a gavage method for 35 days. The results demonstrated that this chronic administration of ginger was not associated with any mortalities and abnormalities in general conditions, behavior, growth, and food and water consumption. Except for dose-related decrease in serum lactate dehydrogenase activity in males, ginger treatment induced similar hematological and blood biochemical parameters to those of controlled animals. In general, ginger treatment caused no overt organ abnormality. Only at a very high dose (2000 mg/kg), ginger led to slightly reduced absolute and relative weights of testes (by 14.4% and 11.5%, respectively). This study provides a new understanding of the toxicological properties of ginger.

Amelioration of anti-cancer agent adriamycin-induced nephrotic syndrome in rats by Wulingsan (Gorei-San), a blended traditional Chinese herbal medicine

Anti-cancer agent adriamycin (ADR) has demonstrated high anti-tumor efficacy. However, its use in chemotherapy has been limited largely due to its diverse toxicities, including renal toxicity, such as nephrotic syndrome with proteinuria. Podocyte injury leads to glomeruli proteinuria. Wulingsan (WLS) is a blended traditional Chinese herbal medicine specifically used for various kidney diseases. In the present study, we found that a water extract of WLS (480 mg/kg, p.o., x 28 days) reduced ADR-induced increase in urine protein excretion, plasma total cholesterol and triglyceride, and decrease in plasma total protein and albumin in rats. Furthermore, the results of electron microscopy demonstrated suppression by WLS of ADR-induced increase in width of foot process, increase in surface density and decrease in volume density. These results suggest that WLS ameliorates ADR-induced proteinuria and podocyte injury. Gene analysis results demonstrated a suppression of renal overexpression of nephrin mRNA and protein by WLS. Radioimmunoassay showed that WLS suppressed ADR-induced increased renal angiotensin II content in rats. Thus our results demonstrate that WLS ameliorates ADR-induced nephrotic syndrome in rats possibly by suppressing ADR-induced hyperactivity of renal renin-angiotensin system to modulate renal nephrin gene expression, thereby protecting podocyte from injury.

Rhodiola crenulata root ameliorates derangements of glucose and lipid metabolism in a rat model of the metabolic syndrome and type 2 diabetes

ETHNOPHARMACOLOGICAL RELEVANCE Rhodiola species are traditionally used as tonics and stimulants to treat asthenia, suggesting their possible regulatory effect on energy metabolism. Clinical trials have demonstrated their glucose-lowering effect in type 2 diabetes. AIM OF THE STUDY To examine the effects of Rhodiola on glucose and lipid metabolism in the metabolic syndrome and type 2 diabetes. MATERIALS AND METHODS Zucker diabetic fatty (ZDF) rats were treated with Rhodiola crenulata root (RCR) powder (100 and 500 mg/kg, by gavage, once daily for 4 weeks). In addition, the effects of RCR on sucrose-induced acute hyperglycemia in mice and olive oil-induced hypertriglyceridemia in rats were also examined. Biochemical variables were determined enzymatically or by ELISA. RESULTS In ZDF rats, RCR treatment decreased the increased plasma insulin and triglyceride concentrations at baseline, the index of the homeostasis model assessment of insulin resistance (HOMA-IR) and excessive hepatic triglyceride accumulation. This treatment also inhibited abnormal increases in plasma glucose and insulin concentrations during oral glucose tolerance test. Furthermore, RCR reversed the increased adipose insulin resistance index, and accelerated the decline of plasma concentrations of non-esterified fatty acids after exogenous glucose stimulation. However, RCR minimally affected sucrose-induced acute hyperglycemia in mice and olive oil-induced acute hypertriglyceridemia in rats. CONCLUSIONS The present results demonstrate that RCR treatment improves metabolic derangements in animal model of the metabolic syndrome and type 2 diabetes. Our findings may provide new pharmacological basis of therapeutics for the adaptogenic plants to treat metabolic derangements-associated disorders, such as asthenia.

Azilsartan treatment improves insulin sensitivity in obese spontaneously hypertensive Koletsky rats

Aim: Hypertension often coexists with insulin resistance. However, most metabolic effects of the antihypertensive agents have been investigated in nomotensive animals, in which different conclusions may arise. We investigated the metabolic effects of the new angiotensin II type 1 receptor blocker azilsartan using the obese Koletsky rats superimposed on the background of the spontaneously hypertensive rats.

Irbesartan treatment up-regulates hepatic expression of PPARα and its target genes in obese Koletsky (fak/fak) rats: a link to amelioration of hypertriglyceridaemia

Hypertriglyceridaemia is associated with an increased risk of cardiovascular disease. Irbesartan, a well‐established angiotensin II type 1 receptor (AT1) blocker, improves hypertriglyceridaemia in rodents and humans but the underlying mechanism of action is unclear.

An aqueous extract of Salacia oblonga root, a herb-derived peroxisome proliferator-activated receptor-alpha activator, by oral gavage over 28 days induces gender-dependent hepatic hypertrophy in rats

Activation of peroxisome proliferator-activated receptor (PPAR)-alpha by natural and synthetic chemicals induces hepatic hypertrophy. An aqueous extract of Salacia oblonga root (SOW) is an Ayurvedic medicine with anti-diabetic and anti-obesity properties. In the present study, it was found that SOW (100, 300 and 900mg/kg, once daily by oral gavage over a 28 day period) elicited dose-related increases in liver weight (LW) by 1.6%, 13.4% and 42.5%, respectively, and in the ratio of LW to body weight by 8.8%, 16.7% and 40.2%, respectively, in male rats. These effects were less pronounced in females. SOW selectively increased liver mass in male rats but Sudan red staining was not different, which indicates that hepatic lipid accumulation was similar in both genders. However, SOW even at the highest dosage did not influence serum ALT and AST activities in male or female rats. Moreover, SOW was found to activate PPAR-alpha in human hepatoma-derived HepG2 cells, as evidenced by the upregulation of PPAR-alpha and acyl-CoA oxidase mRNA expression. Thus, SOW-dependent PPAR-alpha activation may precede the development of the gender difference in hepatic hypertrophy; this process may be influenced by sex hormone status.

An Adipose Tissue-Independent Insulin-Sensitizing Action of Telmisartan: a Study in Lipodystrophic Mice

Adipose tissue plays an important role in energy balance and metabolism and is the major target for insulin-sensitizing peroxisome proliferator-activated receptor (PPAR) γ agonists. The angiotensin II type 1 receptor blocker telmisartan, a partial agonist of PPAR-γ, has been demonstrated to improve insulin sensitivity. However, there is uncertainty about the sites of its action. Here, we demonstrate that treatment with telmisartan (3 mg/kg p.o.) for 7 weeks decreased plasma glucose levels in oral glucose and insulin tolerance tests and the index of the homeostasis model assessment of insulin resistance in A-ZIP/F-1 transgenic mice, an animal model of lipodystrophy. These effects were accompanied by decreases in circulating triglyceride and fatty acid levels. However, this treatment did not affect body weight and plasma adiponectin, leptin, and corticosterone levels. In A-ZIP/F-1 mouse liver the transcripts encoding PPAR-γ and its downstream lipogenic genes were highly up-regulated, consistent with increased hepatic triglyceride content and lipid droplet accumulation. Telmisartan reversed these effects and also down-regulated mRNAs encoding gluconeogenic genes. Thus, the present findings are consistent with a novel mode of insulin-sensitizing action of telmisartan, involving an adipose tissue-independent pathway. Telmisartan-elicited down-regulation of hepatic expression of PPAR-γ-regulated lipogenic genes is associated with amelioration of fatty liver.

Increased renal collagen cross‐linking and lipid accumulation in nephropathy of Zucker diabetic fatty rats

Zucker diabetic fatty (ZDF) rat is a genetic model of type 2 diabetes and obesity. The mechanism underlying nephropathy in ZDF rats, however, remains unclear.

Guanylyl Cyclase-A Inhibits Angiotensin II Type 2 Receptor-Mediated Pro-Hypertrophic Signaling in the Heart

Angiotensin II plays a key role in the development of cardiac hypertrophy. The contribution of the angiotensin II type 1 receptor (AT1) in angiotensin II-induced cardiac hypertrophy is well established, but the role of AT2 signaling remains controversial. Previously, we have shown that natriuretic peptide receptor/guanylyl cyclase-A (GCA) signaling protects the heart from hypertrophy at least in part by inhibiting AT1-mediated pro-hypertrophic signaling. Here, we investigated the role of AT2 in cardiac hypertrophy observed in mice lacking GCA. Real-time RT-PCR and immunoblotting approaches indicated that the cardiac AT2 gene was overexpressed in GCA-deficient mice. Mice lacking AT2 alone did not exhibit an abnormal cardiac phenotype. In contrast, GCA-deficiency-induced increases in heart to body weight ratio, cardiomyocyte cross-sectional area, and collagen accumulation as evidenced by van Gieson staining were attenuated when AT2 was absent. Furthermore, the up-regulated cardiac expression of hypertrophy-related genes in GCA-null animals was also suppressed. Pharmacological blockade of AT2 with PD123319 similarly attenuated cardiac hypertrophy in GCA-deficient mice. In addition, whereas the AT1 antagonist olmesartan attenuated cardiac hypertrophy in GCA-deficient mice, this treatment was without effect on cardiac hypertrophy in GCA/AT2-double null mice, notwithstanding its potent antihypertensive effect in these animals. These results suggest that the interplay of AT2 and AT1 may be important in the development of cardiac hypertrophy. Collectively, our findings support the assertion that GCA inhibits AT2-mediated pro-hypertrophic signaling in heart and offer new insights into endogenous cardioprotective mechanisms during disease pathogenesis.