Enhanced pressor response to acute Ang II infusion in mice lacking membrane-associated prostaglandin E2 synthase-1.

AIM: To examine the contribution of vascular membrane-associated prostaglandin E2 synthase-1 (mPGES-1) to acute blood pressure homeostasis. METHODS: Angiotensin II (AngII, 75 pmol·kg⁻¹·min⁻¹) was continuously infused via the jugular vein into wild-type and mPGES-1(-/-) mice for 30 min, and blood pressure was measured by carotid arterial catheterization. RT-PCR and immunohistochemistry were performed to detect the expression and localization of mPGES-1 in the mouse arterial vessels. Mesenteric arteries were dissected from mice of both genotypes to study vessel tension and measure vascular PGE2 levels. RESULTS: Wild-type and mPGES-1(-/-) mice showed similar blood pressure levels at baseline, and the acute intravenous infusion of AngII caused a greater increase in mean arterial pressure in the mPGES-1(-/-) group, with a similar diuretic and natriuretic response in both groups. mPGES-1 was constitutively expressed in the aortic and mesenteric arteries and vascular smooth muscle cells of wild-type mice. Strong staining was detected in the smooth muscle layer of arterial vessels. Ex vivo treatment of mesenteric arteries with AngII produced more vasodilatory PGE2 in wild-type than in mPGES-1(-/-) mice. In vitro tension assays further revealed that the mesenteric arteries of mPGES-1(-/-) mice exhibited a greater vasopressor response to AngII than those arteries of wild-type mice. CONCLUSION: Vascular mPGES-1 acts as an important tonic vasodilator, contributing to acute blood pressure regulation.

Level Of Natriuretic Peptide Determines Outcome In Atrial Fibrillation.

Background: Natriuretic peptide (NP) is high in atrial fibrillation (AF) and may decrease after cardioversion to sinus rhythm and the levels of atrial NP (ANP) and brain NP (BNP) in different types of AF and whether ANP and BNP have predictive values for relapsed AF have not been determined. Purpose: We aimed to examine the levels of ANP and BNP in AF to determine their roles in different types of AF, including a predictive value in relapsed AF. Methods and Results: ANP and BNP were measured in 100 consecutive patients with AF and without heart dysfunction at baseline and in 20 controls. All patients had higher levels than controls (p<0.01). After cardioversion treatment with antiarrhythmic therapy, 40 patients failed to cardioversion successfully and still showed AF, whereas 60 patients were successful. ANP and BNP levels decreased significantly after cardioversion (163.55±54.27pg/ml vs. 200.20±55.63 pg/ml; 124.15±43.00 pg/ml vs. 161.99±48.04 pg/ml, for ANP and BNP respectively, both p<0.0001). 18 of the 60 successfully cardioverted patients had AF recurred within 24 hours, who were then excluded from 500-day follow-up and the remaining 42 patients were enrolled. During 500-day follow-up period, AF relapsed in 16 patients. Comparing with the 42 patients, the 16 patients showed higher concentrations of ANP (187.72±32.79 pg/ml vs. 138.42±30.65 pg/ml, p<0.0001). Besides, both ANP and BNP were significantly higher in the relapsed patients than those remained SR during follow-up (153.38±29.61pg/ml vs. 129.21±27.98pg/ml for ANP, p=0.01 and 147.41±25.95pg/ml vs. 121.87±20.53pg/ml for BNP, p=0.001). The area under the receiver-operating characteristic curve was 0.799 for BNP and 0.706 for ANP in predicting a relapse of AF. Using the BNP optimized cut-off level of 138 pg/ml, relapsed AF can be predicted with relatively acceptable accuracy. CONCLUSIONS: ANP and BNP decrease significantly after cardioversion in patients with AF, and both can be useful predictors of relapsed AF.

[Activation of liver X receptor regulates fatty acid synthase expression in diabetic liver].

OBJECTIVE: To investigate the effects of liver X receptor (LXR) on the expression of fatty acid synthase (FAS) in diabetic liver. METHODS: Sixteen-week-old male db/db mice with C57BL/6 background were administered via gavaging of T0901317 (TO), a LXR synthetic agonist, at the dose of 3 mg x kg(-1) x d(-1) or dimethyl sulfide (DMSO), a vehicle alone for 7 days. Then the mice were killed with their livers taken out to undergo immunohistochemistry to observe the distribution of FAS protein. Human hepatocellular liver carcinoma cell of the line HepG2 were cultured with TO (10 micromol/L) or DMSO for 24 hours. Another HepG2 cells were transfected with mouse FAS promoter-luciferase reporter recombinants with or without pcDNA3.1, LXR expression vector, or an active sterol regulatory element binding protein-1c (SREBP-1c) expression vector for 12 hours. Real-time PCR and Western blotting were used to detect the levels of mRNA and protein of FAS and SREBP-1c respectively. Luciferase reporter assay was utilized to examine the activity of mouse FAS promoter. RESULTS: FAS was abundantly expressed in the mouse livers, especially in the cytoplasm of liver cells. The FAS mRNA levels of the livers of the db/db mice was about 5.5 times as high as that of the db/m mice (P < 0.01). The FAS protein levels in the livers of db/db and db/m mice treated with TO were 1.7 and 3.5 times higher than those of the control mice (both P < 0.05). The SREBP-1 mRNA levels in the liver of the db/m and db/db mice treated with TO were 2.4 and 2.1 times higher compared with the control mice (P < 0.05, P < 0.01). Luciferase test showed that the FAS promoter activity of the HepG2 cells treated with TO was 1.5 times that of the control cells (P < 0.01). The FAS promoter activities of the HepG2 cells transfected with LXR and SREBP-1c were 1.9 and 1.6 times those of the control cells (botn P < 0.01). CONCLUSION: LXRE directly or indirect (via SREBP-lc) upregulates the expression of FAS gene in the diabetic liver. LXR may mediate the lipid accumulation in liver of diabetes.

[Liver X receptors mediate cholesterol efflux in mouse glomerular mesangial cells].

OBJECTIVE: To examine the role of liver X receptors (LXRs) in lipid metabolism in cultured mouse mesangial cells. METHODS: To determine whether LXRalpha and LXRbeta are expressed in the kidney, RT-PCR and western blot assay were utilized. Cultured mesangial cells were treated with either vehicle or LXR agonist TO901317(10 micromol/L) for 24 hours. Real-time PCR analysis was used to detect ABCA1 and ABCG1 expressions. Cells were also transfected with a human ABCA1 promoter driven luciferase reporter plasmid and then stimulated with or without TO901317 for 24 hours. In order to determine the effect of TO901317 on protein expression of ABCA1, LXRalpha adenovirus was used to overexpress LXRalpha in the cultured cells. Finally, [3H] cholesterol efflux assay was performed to evaluate the efflux of cholesterol upon TO901317 stimulation. RESULTS: Both LXRalpha and LXRbeta were expressed in the kidney, freshly isolated glomeruli and mesangial cells. After treatment with TO901317, both ABCA1 and ABCG1 expressions were induced. Moreover, ABCA1 protein level was increased after the cells were simultaneously treated with LXRalpha-adenovirus and TO901317. The cholesterol efflux was also significantly enhanced after TO901317 treatment. CONCLUSION: LXRalpha and LXRbeta were functionally expressed in mouse mesangial cells. Activation of LXRs enhanced cholesterol efflux possibly through upregulating ABCA1 and ABCG1 expressions in mesangial cells. Therefore, LXR agonist might ameliorate lipid accumulation and reduce related cell injury in mesangial cells.