Kip1 (27) may mediate these cellular processes.EETs are rapidly taken up by vascular cells and converted either to the corresponding dihydroxyeicosatrienoic acids (DHETs) by soluble epoxide hydrolase (sEH) or to chainshortened fatty acid epoxides by ␤-oxidation (7,8,10,13,33). These metabolic processes likely play an important role in modulating the bioactivity of EETs. Increased excretion of 11,12-DHET and 14,15-DHET has been observed in patients with pregnancy-induced hypertension (3), suggesting a role for epoxide hydrolase in the regulation of blood pressure. Selective inhibition of sEH by N,NЈ-dicyclohexyl urea (DCU) or N-cyclohexyl-NЈ-dodecyl urea (CUDA) decreased blood pressure in rodent models of hypertension (18, 39), and sEH gene knockout reduced blood pressure in male mice (31). These observations suggest that sEH inhibition could represent a novel approach for the treatment of hypertension.Although sEH has been detected in various human cells and tissues (33), recent studies indicate that ␤-oxidation, rather than sEH, is the primary pathway for EET metabolism in cultured human vascular cells and skin fibroblasts (7, 13). Thus it is necessary to delineate the pathways of EET metabolism in intact human blood vessels to evaluate the potential utility of sEH inhibition in human vascular tissues. In the present study, we examined the metabolism of EETs and tested the effects of a novel sEH inhibitor with enhanced potency and solubility in intact human blood vessels (21,22). Our findings demonstrate that the main EET metabolic pathway in human blood vessels is conversion to DHET, that selective sEH inhibitors are effective in inhibiting this process, and that EET conversion to ␤-oxidation products only occurs in intact human vascular tissue when sEH is inhibited. METHODS Human Intact Vessel Collection and Cell CultureUnused human saphenous veins (HSVs) harvested for coronary artery bypass surgery and human aortas (HAs) and coronary arteries (HCAs) removed at the time of heart transplantation surgery were obtained from the operating room at the University of Iowa Hospitals and Clinics according to a protocol approved by the University of Iowa Human Subjects Office (28). Tissues were maintained overnight in medium 199 (M199) supplemented with 10% FBS, MEM nonessential amino acids, MEM vitamin solution, 2 mmol/l L-glutamate, 50 mol/l gentamicin, and 15 mmol/l HEPES in a humidified atmosphere containing 5% CO 2 at 37°C. HSV endothelial cells (HSVECs) and smooth muscle cells (HSVSMCs) were isolated from HSVs using the Address for reprint requests and other correspondence: X. Fang,

These findings demonstrate that defective homocysteine remethylation caused by deficiency of either MS or folate produces oxidative stress and endothelial dysfunction in the cerebral microcirculation of mice.

Summary This study compares the effect of y-linolenic acid (GLA) and its precursor linoleic acid (LA) on survival of 36B10 malignant rat astrocytoma cells and 'normal' rat astrocytes. GLA was cytotoxic to 36B10 cells but not to astrocytes. By contrast, LA supplementation did not affect the survival of either cell types. There were minor differences in the uptake, distribution and use of radiolabelled GLA and LA by the 36B1 0 cells and astrocytes. GLA and LA supplementation increased the total polyunsaturated fatty acid (PUFA) content of the cells indicating increased oxidative potential. However, elevated levels of 8-isoprostane, an indicator of increased oxidative stress, were only observed in the GLA supplemented 36B10 cells. Addition of the antioxidant trolox to GLA-enriched 36B10 cells blocked the cytotoxic effect. Further, GLA enhanced the radiation sensitivity of the astrocytoma cells but not the astrocytes; trolox blocked the GLA-mediated increase in astrocytoma cell radiosensitivity. LA did not affect the radiation response of either cell type. While cyclo-oxygenase inhibitors did not affect GLA cytotoxicity, they blocked the enhanced radiation response of GLA-supplemented cells. The lipoxygenase inhibitor NDGA did not affect the toxicity produced by GLA. Thus, GLA is toxic to the neoplastic astrocytoma cells but not to normal astrocytes.Keywords: polyunsaturated fatty acids; y-linolenic acid; linoleic acid; astrocytoma; astrocyte; radiation Gamma linolenic acid (GLA, 18:3n6) supplementation has been reported to suppress the growth of tumour cells in vitro (Fujiwara et al, 1986;Sangeetha and Das, 1992;Falconer et al, 1994) and in vivo (Karmali et al, 1985;Abou et al, 1987). Interestingly, in separate studies conducted on normal tissues in vivo, it has been reported that dietary GLA decreases the severity of radiation damage to the skin (Hopewell et al, 1993) and CNS (Hopewell et al, 1994). We have previously shown that GLA supplementation can decrease clonogenic cell survival of malignant rat astrocytoma cells and increase their radiosensitivity (Vartak et al, 1997). To determine the therapeutic potential of this observation, it is important to investigate the effect of GLA on 'normal' rat astrocytes. The purpose of this work was to compare the effects of GLA on the survival of 36B10 astrocytoma cells and astrocytes and their response to radiation. The uptake and use of GLA by astrocytoma cells has also been compared with that by astrocytes.The cytotoxic action of polyunsaturated fatty acids (PUFAs) is thought to be mediated predominantly via lipid peroxidation and free radical generation (Begin et al, 1988;Ells et al, 1996). Several studies also indicate that eicosanoid and leukotriene synthesis play an important role in tumour cell proliferation and metastasis (Earashi et al, 1995; Damtew and Spagnuolo, 1997). Arachidonic acid (AA, 20:4n6) and dihomo-y-linolenic acid (DGLA, 20:3n6) are the substrate for the biosynthesis of prostaglandins of the 2-and 1-series respectively (Crawford, 1983 Bell JG et ...

Hyperhomocysteinemia and hypercholesterolemia, alone or in combination, produce endothelial dysfunction and increased susceptibility to thrombosis in Apoe-deficient mice.