Acute intravenous L-arginine infusion decreases endothelin-1 levels and improves endothelial function in patients with angina pectoris and normal coronary arteriograms: correlation with asymmetric dimethylarginine levels.

BACKGROUND: We tested the hypothesis that asymmetric dimethylarginine (ADMA) levels could be elevated and influence endothelin-1 and nitric oxide release and action in patients with cardiac syndrome X (CSX). In addition, we evaluated whether an intravenous infusion of L-arginine would improve endothelial function in these subjects. METHODS AND RESULTS: Nine patients with CSX and 14 control subjects underwent a continuous infusion of L-arginine (0.125 g/min) or saline for 120 minutes. Sixty minutes after L-arginine or saline infusions, an intravenous insulin bolus (0.1 U/kg) combined with a euglycemic clamp was performed. Basal ADMA and endothelin-1 levels were higher in patients with CSX than in controls. At the end of the first hour of infusion, compared with saline, L-arginine infusion increased basal forearm blood flow, nitrite and nitrate (NOx), and forearm cGMP release and decreased endothelin-1. After insulin bolus, during saline, insulin-induced NOx, endothelin-1, and forearm cGMP release was almost abolished. Conversely, L-arginine restored a physiological profile of all endothelial variables compared with control subjects. In control subjects, compared with saline infusion, L-arginine infusion did not modify any parameter. ADMA levels were positively correlated with basal endothelin-1 levels and negatively correlated with insulin-induced incremental levels of NOx and forearm cGMP release. CONCLUSIONS: Plasma ADMA levels are increased in patients with CSX, and they are correlated with increases in endothelin-1 and reductions in insulin-induced increments in plasma NOx and cGMP, effects that are reversed by intravenous L-arginine. These data suggest that increased ADMA levels play a role in the abnormal vascular reactivity that is observed in patients with CSX.

Endothelial nitric oxide synthase polymorphisms are associated with type 2 diabetes and the insulin resistance syndrome.

Endothelial nitric oxide synthase (eNOS) variants were previously demonstrated in cardiovascular disease. To evaluate whether eNOS gene variants are associated with insulin resistance and type 2 diabetes, we evaluated polymorphisms in Exon7 (E298D), intron 18 (IVS18 + 27A-->C), and intron 23 (IVS23 + 10G-->T) in 159 type 2 diabetic patients without macrovascular complications and in 207 healthy control subjects. Samples for all hormonal and metabolic variables were obtained after an overnight fast. The D298 and IVS18 + 27C alleles, but not the IVS23 + 10G-->T variant, were significantly more frequent in type 2 diabetic patients than in control subjects. The two- and three-loci haplotype analysis showed that there is a statistically significant association between the eNOS variants and type 2 diabetes. No significant differences were observed in the clinical characteristics of type 2 diabetic patients according to genotypes (except for visceral obesity [waist-to-hip ratio], which was significantly more present in D298 homozygotes). Healthy control subjects homozygous for both D298 and IVS18 + 27C presented higher insulin, C-peptide, and nitric oxide levels, as well as higher HOMA (homeostasis model assessment) values than the double wild-type homozygotes, with values superimposable on those found in type 2 diabetic patients. In conclusion, we described a significant association between eNOS gene polymorphisms and type 2 diabetes, suggesting a new genetic susceptibility factor for hyperinsulinemia, insulin resistance, and type 2 diabetes.

Acute effects of heparin administration on the ischemic threshold of patients with coronary artery disease: evaluation of the protective role of the metabolic modulator trimetazidine.

OBJECTIVES: We sought to assess the effects of heparin and the potential protective effects of trimetazidine (TMZ) on exercise performance, plasma nitric oxide (NO), endothelin-1 (ET-1) and free fatty acid (FFA) release in patients with stable coronary artery disease (CAD). BACKGROUND: Heparin has been shown to reduce the ischemic threshold in patients with CAD. Trimetazidine may affect myocardial substrate utilization by shifting energy production from FFA to glucose oxidation. METHODS: In four consecutive days, nine patients with CAD each received one of the following four regimens: 1) one tablet of placebo the evening before and at 8 AM and 4 PM on the day of the study, 10 ml of saline in a bolus 10 min before exercise, followed by an infusion of the same preparation; 2) placebo at the same times as in the first regimen, 5,000 IU of heparin 10 min before exercise, followed by 1,000 IU/h; 3) 20 mg TMZ at the same times as in the first regimen, 5,000 IU of heparin 10 min before exercise, followed by 1,000 IU/h; or 4) TMZ at the same times as in the first regimen, 10 ml of saline 10 min before exercise, followed by an infusion of the same preparation. RESULTS: During placebo (test 2), heparin reduced the time to 1-mm ST-segment depression and prolonged the recovery time, as compared with the results of test 1. When heparin was administered after TMZ (test 3), the time to 1-mm ST-segment depression and the recovery time were similar to those recorded during saline (test 1). Finally, compared with all study phases, TMZ during saline (test 4) prolonged the time to 1 mm. No changes in NO release were found, whereas ET-1 was decreased at peak exercise and during recovery, when the patients were receiving TMZ (tests 3 and 4). Free fatty acids increased after heparin, both with placebo and TMZ. CONCLUSIONS: In patients with CAD, heparin reduces the ischemic threshold. Trimetazidine reduces the effects of heparin, probably by inhibiting FFA oxidation and enhancing glucose metabolism. The concomitant novel observation of reduced ET-1 release is likely to be also dependent on TMZ-induced improvement of endothelial metabolism or reduction of myocardial ischemia.

Chronic hyperglycemia impairs insulin secretion by affecting insulin receptor expression, splicing, and signaling in RIN beta cell line and human islets of Langerhans.

Recent evidence suggests that insulin signaling through the insulin receptor A type (Ex11-), regulates insulin gene transcription. Because chronic hyperglycemia negatively affects insulin receptor function and regulates alternative splicing of the insulin receptor, we inquired whether chronic exposure of pancreatic beta-cells to high glucose results in alterations in insulin signaling due to changes in insulin receptor expression and relative abundance of its spliced isoforms. Our results demonstrate that the insulin receptor is localized in insulin secretory vescicles in human pancreatic beta-cells. Furthermore, we find that alterations in insulin expression and secretion caused by chronic exposure to high glucose are paralleled by decreased insulin receptor expression and increased relative abundance of the Ex11+ isoform in both human islets and RIN beta-cells. PDX-1 and HMGI(Y) transcription factors are down-regulated by high glucose. These changes are associated with defects in insulin signaling involving insulin receptor-associated PI 3-kinase/Akt/PHAS-I pathway in RIN beta-cells. Re-expression in RIN beta-cells chronically exposed to high glucose of the Ex11-, but not the Ex11+, isoform restored insulin mRNA expression. These data suggest that changes in early steps of insulin receptor signaling may play a role in determining beta-cell dysfunction caused by chronic hyperglycemia.

Antitumorigenic and antiinsulinogenic effects of calcitriol on insulinoma cells and solid beta-cell tumors.

Malignant insulinoma is a rare form of cancer with a poor prognosis because of metastatic dissemination and untreatable hypoglycemia. Effective chemotherapy of patients who are not cured by surgery is needed. Calcitriol has known anticancer properties on different neoplastic cell lines, but no data are available regarding its activity on tumorigenic pancreatic beta-cells. We analyzed the in vitro effects of calcitriol on the murine insulinoma cell line betaTC(3) and primary cultures of human isolated islets and benign insulinoma. The effect of in vivo calcitriol administration on insulinoma of recombinant insulin/Simian virus 40 oncogene-expressing transgenic mice was also investigated. In betaTC(3), calcitriol induced growth inhibition; apoptosis; down-regulation of insulin gene expression; and nongenomic activation of the MAPK pathway. MAPK kinase inhibitor (UO126) and staurosporine reduced calcitriol-mediated betaTC(3) death, and down-regulation of insulin gene transcription was prevented by staurosporine but not UO126. Calcitriol significantly decreased insulin release and mRNA levels of human islets and insulinoma cells. Finally, recombinant insulin/Simian virus 40 oncogene-expressing transgenic mice treated with calcitriol showed reduced insulinoma volumes because of increased apoptosis of adenomatous cells. Together, these findings provide the rationale for testing the efficacy of calcitriol in the treatment of patients with solid beta-cell tumors.

Magnetic resonance image (MRI) of an acquired aorto-pulmonary fistula, associated with cerebral and paradoxical embolism.

Aorto-pulmonary fistula has been described in Marfan's syndrome, with severe degeneration of connective tissue, particularly severe at the aortic site. Rarely, the chronic evolution of this condition could determine the formation of a fistula between the aorta and the adjacent anatomic structures [Ann Thorac Surg 59 (1995) 1563; J Cardiovasc Surg 29 (1988) 403; Thorax 28 (1973) 521]. Here, we describe the first case of aorto-pulmonary fistula, with cerebral and paradoxical embolism, described with angio-nuclear magnetic resonance (MRI) of the heart.