Eicosapentaenoic acid enhances myo-inositol uptake in cultured human aortic smooth muscle cells

Effects of eicosapentaenoic acid on blood pressure, cell membrane fatty acids, and intracellular sodium concentration in essential hypertension

This study was designed to clarify the effects of orally administered eicosapentaenoic acid (EPA) on blood pressure, intracellular sodium content, and cell membrane fatty acid composition in patients with essential hypertension. After a 4-week run-in period, a study group of 17 male patients was assigned to an 8-week treatment with EPA (2.7 g/day) or placebo in a randomized, double-blind fashion with a crossover at week 4. Systolic blood pressure (SBP) was lower after treatment with EPA than after treatment with placebo (152.9+/-17.3 vs. 162.6+/-20.6 mmHg; p<0.01), while diastolic blood pressure was not statistically different. Compared with the placebo treatment, EPA supplementation resulted in a decrease in intraerythrocyte sodium content (R-Na; 11.17+/-0.63 vs. 10.44+/-1.28 nmol/l cells; p<0.05) accompanied by an increase (p<0.001) in erythrocyte membrane EPA content. The increase in membrane EPA content was related to the decrease in SBP (r=-0.52, p<0.05) and the decrease in R-Na (r=-0.57, p<0.02) during EPA treatment. The decrease in R-Na correlated positively with the decrease in SBP (r=0.54, p<0.05), and correlated negatively with the change in Na+-K+ ATPase activity (r= -0.59, p<0.02). However, the change in Na+-K+ ATPase activity did not directly correlate with the change in membrane EPA content. In conclusion, oral EPA supplementation increased membrane EPA content and reduced SBP in patients with essential hypertension. Based on the association between the increase in membrane EPA content and the decrease in intracellular sodium concentration, EPA may lower blood pressure by altering the activities of the membrane sodium transport systems.

Alternate splicing in human Na+-MI cotransporter gene yields differentially regulated transport isoforms

myo-Inositol is a ubiquitous intracellular organic osmolyte and phosphoinositide precursor maintained at millimolar intracellular concentrations through the action of membrane-associated Na+-myo-inositol cotransporters (SMIT). Functional cloning and expression of a canine SMIT cDNA, which conferred SMIT activity in Xenopus oocytes, predicted a 718-amino acid peptide homologous to the Na+-glucose cotransporter with a potential protein kinase A phosphorylation site and multiple protein kinase C phosphorylation sites. A consistent approximately 1.0- to 13.5-kb array of transcripts hybridizing with this cDNA are osmotically induced in a variety of mammalian cells and species, yet SMIT activity appears to vary among different tissues and species. An open reading frame on human chromosome 21 (SLC5A3) homologous to that of the canine cDNA (96.5%) is thought to comprise an intronless human SMIT gene. Recently, this laboratory ascribed multiply sized, osmotically induced SMIT transcripts in human retinal pigment epithelial cells to the alternate utilization of several 3'-untranslated SMIT exons. This article describes an alternate splice donor site within the coding region that extends the open reading frame into the otherwise untranslated 3' exons, potentially generating novel SMIT isoforms. In these isoforms, the last putative transmembrane domain is replaced with intracellular carboxy termini containing a novel potential protein kinase A phosphorylation site and multiple protein kinase C phosphorylation sites, and this could explain the heterogeneity in the regulation and structure of the SMIT.

Hypoxia and endothelin-1 induce VEGF production in human vascular smooth muscle cells

Vascular endothelial growth factor/vascular permeability factor (VEGF/VPF) is a secreted mitogen for vascular endothelial cells, and it promotes vascular permeability and neovascularization in vivo. We investigated the mechanisms by which low oxygen tension modulates the expression of VEGF in human aortic vascular smooth muscle cells (h-SMC) in vitro. Moreover, we measured VEGF levels in the cultured medium with or without endothelin-1 (ET-1) using a newly developed, highly sensitive, enzyme-linked immunosorbent assay. Hypoxia resulted in a substantial induction of VEGF transcripts at 3 and 24 hr. VEGF levels were significantly higher when h-SMC were cultured in medium containing ET-1 than when cultured in medium without ET-1. In conclusion, hypoxia and ET-1 constitute potent stimuli for VEGF production in h-SMC.

High concentration of glucose causes impairment of the function of the glutathione redox cycle in human vascular smooth muscle cells

We demonstrated that high glucose reduced H2O2 scavenge activity in human vascular smooth muscle cells. In the cells exposed to high glucose, the intracellular glutathione content decreased, although the NADPH content was unchanged. The rate of uptake of cystine, which is a rate-limiting precursor of the glutathione synthesis, decreased in the high glucose group compared with the control group. These decreases were shown to be dependent on glucose concentration. It was suggested that high glucose causes impairment of the function of the glutathione redox cycle in human vascular smooth muscle cells, resulting in reduced H2O2 scavenge activity.