Effects of reactive oxygen species on eicosanoid metabolism in human endothelial cells

Integration of plasma and CSF metabolomics with CSF proteomic reveals novel associations between lipid mediators and central nervous system vascular and energy metabolism

Integration of the omics data, including metabolomics and proteomics, provides a unique opportunity to search for new associations within metabolic disorders, including Alzheimer's disease. Using metabolomics, we have previously profiled oxylipins, endocannabinoids, bile acids, and steroids in 293 CSF and 202 matched plasma samples from AD cases and healthy controls and identified both central and peripheral markers of AD pathology within inflammation-regulating cytochrome p450/soluble epoxide hydrolase pathway. Additionally, using proteomics, we have identified five cerebrospinal fluid protein panels, involved in the regulation of energy metabolism, vasculature, myelin/oligodendrocyte, glia/inflammation, and synapses/neurons, affected in AD, and reflective of AD-related changes in the brain. In the current manuscript, using metabolomics-proteomics data integration, we describe new associations between peripheral and central lipid mediators, with the above-described CSF protein panels. Particularly strong associations were observed between cytochrome p450/soluble epoxide hydrolase metabolites, bile acids, and proteins involved in glycolysis, blood coagulation, and vascular inflammation and the regulators of extracellular matrix. Those metabolic associations were not observed at the gene-co-expression level in the central nervous system. In summary, this manuscript provides new information regarding Alzheimer's disease, linking both central and peripheral metabolism, and illustrates the necessity for the "omics" data integration to uncover associations beyond gene co-expression.

Association of plasma and CSF cytochrome P450, soluble epoxide hydrolase, and ethanolamide metabolism with Alzheimer's disease

BACKGROUND

Alzheimer's disease, cardiovascular disease, and other cardiometabolic disorders may share inflammatory origins. Lipid mediators, including oxylipins, endocannabinoids, bile acids, and steroids, regulate inflammation, energy metabolism, and cell proliferation with well-established involvement in cardiometabolic diseases. However, their role in Alzheimer's disease is poorly understood. Here, we describe the analysis of plasma and cerebrospinal fluid lipid mediators in a case-control comparison of ~150 individuals with Alzheimer's disease and ~135 healthy controls, to investigate this knowledge gap.

METHODS

Lipid mediators were measured using targeted quantitative mass spectrometry. Data were analyzed using the analysis of covariates, adjusting for sex, age, and ethnicity. Partial least square discriminant analysis identified plasma and cerebrospinal fluid lipid mediator discriminates of Alzheimer's disease. Alzheimer's disease predictive models were constructed using machine learning combined with stepwise logistic regression.

RESULTS

In both plasma and cerebrospinal fluid, individuals with Alzheimer's disease had elevated cytochrome P450/soluble epoxide hydrolase pathway components and decreased fatty acid ethanolamides compared to healthy controls. Circulating metabolites of soluble epoxide hydrolase and ethanolamides provide Alzheimer's disease predictors with areas under receiver operator characteristic curves ranging from 0.82 to 0.92 for cerebrospinal fluid and plasma metabolites, respectively.

CONCLUSIONS

Previous studies report Alzheimer's disease-associated soluble epoxide hydrolase upregulation in the brain and that endocannabinoid metabolism provides an adaptive response to neuroinflammation. This study supports the involvement of P450-dependent and endocannabinoid metabolism in Alzheimer's disease. The results further suggest that combined pharmacological intervention targeting both metabolic pathways may have therapeutic benefits for Alzheimer's disease.

Influence of different dietary fat intake on liver metastasis and hepatic lipid peroxidation in BOP-induced pancreatic cancer in Syrian hamsters

OBJECTIVES

Effects of polyunsaturated fatty acids (PUFA) on carcinogenesis are discussed controversially. Thus, tumor growth seems to be influenced by type and composition of fat dietary; however, the pathomechanism is still unknown. Therefore, we investigated the impact of different PUFAs on liver metastasis and hepatic lipid peroxidation in a solid model of ductal pancreatic cancer in Syrian hamsters.

METHODS

90 male hamsters were randomized into 6 groups (n = 15). Accordingly groups 2, 4 and 6 received 10 mg N-nitrosobis-2-oxopropylamine (BOP)/kg body weight weekly by subcutaneous injection for 12 weeks in order to induce ductal pancreatic cancer, while groups 1, 3 and 5 were treated with 0.5 ml 0.9% sodium chloride. All hamsters received a standard fat diet (SFD) rich in n-6 PUFA for 16 weeks (2.9% fat). Afterwards, groups 1 and 2 had free access to SFD, while groups 3 and 4 were given a diet enriched with n-3, n-6 and n-9 PUFA (SMOF) and groups 5 and 6 were fed a diet high in n-3 PUFA (FISH-OIL). After 32 weeks all hamsters were sacrificed in order to determine incidence of pancreatic carcinoma and liver metastasis. Furthermore hepatic activities of glutathionperoxidase (GSH-Px) and superoxiddismutase (SOD) as well as levels of lipidperoxidation were analyzed intra- and extrametastatically.

RESULTS

The incidence of liver metastasis was decreased in the FISH-OIL tumor group compared to the SFD and SMOF groups. However, GSH-Px activity was not influenced by different diets. Extrametastatic hepatic SOD activity did not differ between all groups, while intrametastatic hepatic SOD activity in the SFD-BOP group was increased. In the FISH-OIL-BOP and the SMOF-BOP group intrametastatic SOD activity was lower than in non-metastatic hepatic tissue. Furthermore levels of hepatic lipid peroxidation were decreased in the tumor groups treated with fish oil and SMOF compared to the SFD group. Comparing intra- and extrametastatic TBARS concentration there was no difference in the SFD-BOP and the SMOF-BOP groups, while in the FISH-OIL-BOP group intrametastatic TBARS concentration was increased.

CONCLUSION

Conclusively, fish oil reduced the incidence of liver metastasis in experimental ductal pancreatic cancer. Maybe this effect is caused by an increase of intrametastatic hepatic lipid peroxidation.

Prostaglandin E2 production in astrocytes: regulation by cytokines, extracellular ATP, and oxidative agents

Upregulation and activation of phospholipases A2 (PLA2) and cyclooxygenases (COX) leading to prostaglandin E2(PGE2) production have been implicated in a number of neurodegenerative diseases. In this study, we investigated PGE2 production in primary rat astrocytes in response to agents that activate PLA2 including pro-inflammatory cytokines (IL-1beta, TNFalpha and IFNgamma), the P2 nucleotide receptor agonist ATP, and oxidants (H2O2 and menadione). Exposure of astrocytes to cytokines resulted in a time-dependent increase in PGE2 production that was marked by increased expression of secretory sPLA2 and COX-2, but not COX-1 and cytosolic cPLA2. Although astrocytes responded to ATP or phorbol ester (PMA) with increased cPLA2 phosphorylation and arachidonic acid release, ATP or PMA only caused a small increase in levels of PGE2. However, when astrocytes were first treated with cytokines, further exposure to ATP or PMA, but not H2O2 or menadione, markedly increased PGE2 production. These results suggest that ATP release during neuronal excitation or injury can enhance the inflammatory effects of cytokines on PGE2 production and may contribute to chronic inflammation seen in Alzheimer's disease.

Influence of conjugated vs. conventional linoleic acid on liver metastasis and hepatic lipidperoxidation in BOP-induced pancreatic cancer in Syrian hamster

While conjugated linoleic acid (CLA) is regarded as an essential fatty acid with anticarcinogenic effects, conventional linoleic acid (LA) is reported to promote tumour growth in various experimental studies probably caused by high sensitivity to non-enzymatic lipid peroxidation. In order to evaluate the impact of dietary LA and CLA on liver metastasis and lipidperoxidation (LPO), 60 Syrian hamsters were injected with 10 mg N -nitrosobis-2-oxopropylamine (BOP)/kg body weight s.c. for 12 weeks. Animals were fed a special diet containing LA or CLA. The experiment was terminated after 24 weeks. Incidence, number and size of liver metastases were histologically determined. Furthermore, the activities of antioxidative enzymes and concentration of hepatic lipidperoxidation were measured intra- and extrametastatically. Incidence, number and size of liver metastases did not differ between the tumour groups. Otherwise, antioxidative enzyme activity of GSH-Px was higher in non-metastatic liver, while SOD activity and lipidperoxidation were increased in liver metastases. Conclusively there was no difference between the groups fed with LA and CLA according to the impact on liver metastasis in ductal pancreatic cancer.

Influence of octreotide on liver metastasis and hepatic lipid peroxidation in BOP-induced pancreatic cancer in Syrian hamsters

INTRODUCTION

In prospective clinical trials, octreotide improved quality of life and survival time in patients with pancreatic cancer.

AIMS

To analyze whether octreotide modulates the hepatic oxygen radical metabolism and thus might decrease liver metastasis in an animal model of pancreatic cancer.

METHODOLOGY

Syrian hamsters received 0.9% NaCl or N-nitrosobis(2-oxopropyl)amine (BOP) for 3 months. Therapy was performed for 12 weeks by 0.9% NaCl or octreotide. Hamsters received a standard diet (3.5% fat) or were fed a high-fat diet (21.4% fat). In the 25th week, the pancreas and liver were examined macroscopically and histologically. The level of lipid peroxidation and activities of glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD) were determined intrahepatically.

RESULTS

The number of liver metastases per animal and the size of liver metastases were increased by the high-fat diet, whereas they were decreased by octreotide. Octreotide increased activities of GSH-Px and SOD. The concentration of thiobarbituric acid reactive substances was increased by BOP and a high-fat diet and decreased by octreotide.

CONCLUSION

Octreotide decreases the number and size of liver metastases in chemically induced pancreatic cancer in Syrian hamsters. This is accompanied by high hepatic GSH-Px and SOD activity and a low level of lipid peroxidation.

*NO and oxyradical metabolism in new cell lines of rat brain capillary endothelial cells forming the blood-brain barrier

To investigate the relevance of *NO and oxyradicals in the blood-brain barrier (BBB), differentiated and well-proliferating brain capillary endothelial cells (BCEC) are required. Therefore, rat BCEC (rBCEC) were transfected with immortalizing genes. The resulting lines exhibited endothelial characteristics (factor VIII, angiotensin-converting enzyme, high prostacyclin/thromboxane release rates) and BBB markers (gamma-glutamyl transpeptidase, alkaline phosphatase). The control line rBCEC2 (mock transfected) revealed fibroblastoid morphology, less factor VIII, reduced gamma-glutamyl transpeptidase, weak radical defence, low prostanoid metabolism, and limited proliferation. Lines transfected with immortalizing genes (especially rBCEC4, polyoma virus large T antigen) conserved primary properties: epitheloid morphology, subcultivation with high proliferation rate under pure culture conditions, and powerful defence against reactive oxygen species (Mn-, Cu/Zn-superoxide dismutase, catalase, glutathione peroxidase, glutathione) effectively controlling radical metabolism. Only 100 microM H2O2 overcame this defence and stimulated the formation of eicosanoids similarly as in primary cells. Some BBB markers were expressed to a lower degree; however, cocultivation with astrocytes intensified these markers (e.g., alkaline phosphatase) and paraendothelial tightness, indicating induction of BBB properties. Inducible NO synthase was induced by a cytokine plus lipopolysaccharide mixture in all lines and primary cells, resulting in *NO release. Comparing the cell lines obtained, rBCEC4 are stable immortalized and reveal the best conservation of properties from primary cells, including enzymes producing or decomposing reactive species. These cells can be subcultivated in large amounts and, hence, they are suitable to study the role of radical metabolism in the BBB and in the cerebral microvasculature.

Influence of octreotide and tamoxifen on tumor growth and liver metastasis in N-nitrosobis(2-oxopropyl)amine-induced pancreatic cancer in Syrian hamsters

In prospective clinical trials single octreotide therapy or combined therapy with tamoxifen has improved the quality of life and survival time in patients with pancreatic cancer. In this study we analyzed the influence of octreotide and tamoxifen on tumor growth and liver metastases in chemically induced pancreatic adenocarcinoma in Syrian hamsters. Octreotide alone and the combined therapy (octreotide/tamoxifen) decreased the incidence of macroscopic pancreatic carcinomas as well as the number and size of liver metastases. The combined therapy showed no superior effect to octreotide alone. Furthermore, there was no difference between the tamoxifen and the control group.

Induction of cyclooxygenase-2 by overexpression of the human catalase gene in cerebral microvascular endothelial cells

Prostaglandin (PG) formation by the inducible (type 2) cyclooxygenase (COX-2) and reactive oxygen species (ROS) have been proposed to play important roles in cerebrovascular pathological processes. To explore the relationship between ROS and COX-2 expression, adenovirus (Ad) vectors containing cDNA for human antioxidant enzymes including catalase (AdCAT:), copper/zinc superoxide dismutase (AdCu/ZnSOD), and manganese superoxide dismutase (AdMnSOD) were transferred into murine cerebral microvascular endothelial cells. AdCAT: (100 multiplicity of infection) infection increased the content and enzymatic activity of cellular Cat threefold and decreased the intracellular peroxide level. The expression of COX-2 mRNA and protein in cell lysates was up-regulated, and the amount of PGE(2) formed from exogenous arachidonic acid increased following AdCAT: infection in a dose-dependent manner, paralleling the expression of COX-2 protein. The AdCAT:-induced increase in PGE(2) formation was inhibited by NS-398, a selective inhibitor of COX-2 enzymatic activity. AdCAT: infection did not change the expression of the constitutive (type 1) COX protein. Although AdCu/ZnSOD and AdMnSOD infection increased the expression of superoxide dismutase proteins, COX-2 expression was not induced. An in vitro nuclear transcription assay indicated that overexpression of the Cat gene increases the transcription of the COX-2 gene. Furthermore, the stability of COX-2 mRNA induced by lipopolysaccharide was increased after AdCAT: gene transfer. These results indicate that AdCAT: gene transfer induces the transcriptional activation of the COX-2 gene and increases COX-2 mRNA stability. Therefore, peroxide may have regulatory effect on COX-2 function in the cerebral microcirculation.

Does alpha-linolenic acid in combination with linoleic acid influence liver metastasis and hepatic lipid peroxidation in BOP-induced pancreatic cancer in Syrian hamsters?

Some fatty acids are reported to inhibit tumor growth of pancreatic carcinoma. However, it is still unknown if alpha-linolenic acid (ALA) and linoleic acid (LA) inhibit liver metastasis of ductal pancreatic adenocarcinoma. Therefore we studied the effect of these fatty acids on liver metastasis in the animal model of N-nitrosobis(2-oxopropyl)amine (BOP)-induced pancreatic adenocarcinoma in Syrian hamsters. Since lipid peroxidation seems to be involved in carcinogenesis and metastasis, we further analyzed the intrahepatic concentration of thiobarbituric acid-reactive substances (TBARS) and activity of glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD). We observed an increase in the incidence and the number of liver metastases in response to the combination of ALA and LA. This was accompanied by a decrease in hepatic GSH-Px activity and an increase in hepatic SOD activity and TBARS concentration. The increase in hepatic lipid peroxidation seems to be one possible mechanism of increasing liver metastasis in this study.

Markers of endothelial dysfunction

The endothelium is a functional barrier between vessel wall and blood stream. Assuming the total human vascular and capillary system occupies a surface area of more than 1,000 m2 which is covered by 1,013 endothelial cells, the complex role of the endothelium for hemostasis and immunological and metabolic processes becomes obvious. Dysfunction of the endothelium is a critical factor in the pathogenesis of vascular diseases and thrombus formation. This paper provides a brief review of physiological endothelial functions and summarizes measurable changes in products released from endothelial cells under pathological conditions which were associated with endothelial dysfunction.

Overexpression of human catalase inhibits proliferation and promotes apoptosis in vascular smooth muscle cells

The role of reactive oxygen species, such as superoxide anions (O(2). (-)) and hydrogen peroxide (H(2)O(2)), in modulating vascular smooth muscle cell proliferation and viability is controversial. To investigate the role of endogenously produced H(2)O(2), rat aortic smooth muscle cells were infected with adenoviral vectors containing cDNA for human catalase (AdCat) or a control gene, beta-galactosidase (AdLacZ). Infection with AdCat resulted in dose-dependent increases in intracellular catalase protein, which was predominantly localized to peroxisomes. After infection with 100 multiplicity of infection (MOI) of AdCat, cellular catalase activity was increased by 50- to 100-fold, and intracellular H(2)O(2) concentration was reduced, as compared with control. Infection with AdCat reduced [(3)H]thymidine uptake, an index of DNA synthesis, in cells maintained in medium supplemented with 2% serum (0.37+/-0.09 disintegrations per minute per cell [AdLacZ] versus 0.22+/-0.08 disintegrations per minute per cell [AdCat], P<0.05). Five days after infection with 100 MOI of AdCat, cell numbers were reduced as compared with noninfected or AdLacZ-infected cells (157 780+/-8413 [AdCat], P<0.05 versus 233 700+/-3032 [noninfected] or 222 410+/-5332 [AdLacZ]). Furthermore, the number of apoptotic cells was increased 5-fold after infection with 100 MOI of AdCat as compared with control. Infection with AdCat resulted in induction of cyclooxygenase (COX)-2, and treatment with a COX-2 inhibitor overcame the AdCat-induced reduction in cell numbers. These findings indicate that overexpression of catalase inhibited smooth muscle proliferation while increasing the rate of apoptosis, possibly through a COX-2-dependent mechanism. Our results suggest that endogenously produced H(2)O(2) importantly modulates survival and proliferation of vascular smooth muscle cells.

Endothelial cell compatibility of clindamycin, gentamicin, ceftriaxone and teicoplanin in Bier's arterial arrest

In patients with infected diabetic foot lesions, and gangrenous, peripheral, occlusive arterial disease, it is important to achieve high concentrations of antibiotics in the tissues, as the extent of amputation is often influenced by the presence of infection. Local transvenous pressure injection of antibiotics, in Bier's arterial arrest, allows high local tissue concentrations to be attained in the extremities. Information on the endothelial compatibility of antibiotics in high concentrations combined with the effect of reperfusion injury following tissue hypoxia is lacking. To evaluate the effect of clindamycin, gentamicin, ceftriaxone and teicoplanin injected in Bier's arterial arrest, on endothelial cells, an in-vitro model using human umbilical venous endothelial cells (HUVEC) has been devised. The intracellular levels of purine nucleotides, reflecting DNA/RNA synthesis, energy production and signal transduction of these cells were measured by means of high-performance liquid chromatography. Incubation of cells with 10 mg/mL clindamycin, gentamicin, ceftriaxone and teicoplanin for 20 min resulted in no significant decline of intracellular purines. Levels of purines obtained after exposure of the cells to 0.1 mmol/L hydrogen peroxide (H2O2), to simulate reperfusion injury, were not significantly different from those obtained from cells allowed to recover after antibiotic exposure. These findings indicate that the infusion of high doses of antibiotics, during Bier's arterial arrest, is compatible with maintenance of endothelial cell function, even in the presence of increased free radical activity, provided the exposure is limited to 20 min.

Mechanisms of hyperoxia-induced reductions in retinal blood flow in newborn pig

Although reductions in retinal blood flow (RBF) in response to acute hyperoxia are well described, the mechanistic basis of this response has yet to be clarified. The present study was undertaken in order to determine the possible involvement of two arachidonic acid-derived vasoconstrictors, the cyclooxygenase metabolite thromboxane and the cytochrome P450 metabolite 20-HETE, as well as the involvement of the peptide endothelin and superoxide free radical. Fluorescein videoangiography was performed on the intact eyes of isoflurane-anesthetized newborn piglets. RBF responses to 20 min of hyperoxia were calculated from the angiograms off-line, using changes in mean arteriovenous transit times and arteriolar and venular diameters. The effect of hyperoxia (PaO2=351+/-9 mmHg; n=39) on RBF was examined in each animal under control conditions and again after intravitreal perivascular administration of drugs that block the synthesis or receptors of known vasoconstrictors. Estimated RBF decreased by a maximum of 42+/-3% in the 7 animal groups in response to 20 min of hyperoxia. The magnitude and time course of the change in RBF resulting from two successive hyperoxic challenges did not differ, and were unaffected by intravitreal administration of vehicle. The response to hyperoxia was attenuated 46+/-6 (n=6; P=0.001) after intravitreal CGS 22652 (2 nmol), a combined thromboxane synthesis inhibitor and receptor antagonist. DDMS (12.5 nmol), a competitive inhibitor of the P450 enzyme omega-hydroxylase that forms 20-HETE, blocked hyperoxic constriction by 23+/-7% (n=6; P=0.01). Intravitreal pretreatment with TBC 1241z (2 nmol), a receptor antagonist of the peptide endothelin, blocked the hyperoxic response by 26+/-5% (n=6; P=0.01). A combination of CGS 22652 (2 nmol), DDMS (12.5 nmol), and TBC 1241z (2 nmol), blocked the hyperoxic flow response by 51+/-3% (n=5; P=0.003). Administration of a combination of superoxide dismutase (10 U intravitreally, 10000 U kg-1 of the polyethylene glycol-conjugate intravenously) and catalase (10 U intravitreally, 10000 U kg-1 intravenously) was without effect on hyperoxia-induced reductions in RBF (n=5). The present results indicate that the arachidonic acid metabolites thromboxane and 20-HETE, and the peptide endothelin, participate in mediating the acute reduction in RBF in response to hyperoxia.

Regulation of cyclo-oxygenase gene expression in rat smooth muscle cells by catalase

We have studied, in detail, the effect of catalase, one of the naturally occurring antioxidant enzymes, on the expression of cyclo-oxygenase (COX) mRNA and protein in rat aortic smooth muscle cells (RASMC). The activity of COX enzyme within the cells was also determined. Catalase either alone or in combination with interleukin-1beta (IL-1beta) enhanced mRNA and protein expression for cyclo-oxygenase 2 (COX-2) in a concentration-dependent manner. However, it did not affect the expression of mRNA or protein for cyclo-oxygenase 1 (COX-1). The expression of mRNA for COX-2 induced by catalase was blocked completely by actinomycin D (ACT) or cycloheximide (CHX). In comparison, expression of mRNA for COX-2 stimulated by IL-1beta was inhibited by actinomycin D, but not by cycloheximide. This suggests that induction of the synthesis of mRNA for COX-2 by catalase and IL-1beta involves different mechanisms. In particular, the induction of mRNA for COX-2 by catalase requires on-going protein and RNA synthesis, but the induction following exposure to IL-1beta does not. The increase in expression of mRNA for COX-2 induced by catalase may be related to the ability of catalase to stimulate cyclic AMP response element (CRE) and NF-IL6 transcription factors, but not nuclear factor kappa B (NF-kappaB), for electrophoretic mobility shift assays (EMSA) showed that catalase enhanced nuclear factor binding to cyclic AMP response element and NF-IL6 but not to NF-kappaB. Catalase exerted a biphasic effect on prostaglandin synthesis. At low concentrations it enhanced prostaglandin production, but at high concentrations it tended to inhibit it. These findings suggest that catalase has differential and multiple effects on COX expression and activity in rat aortic smooth muscle cells.

Influence of long-term supplementation with alpha-linolenic acid on myocardial lipid peroxidation and antioxidative capacity in spontaneously hypertensive rats

The ischaemic vulnerability of the heart of spontaneously hypertensive rats (SHR) is enhanced after feeding an alpha-linolenic acid (LNA) enriched diet. Because oxygen radical-induced reactions (e.g. lipid peroxidation) are involved in the ischaemic damage, an increased susceptibility of the SHR heart to such damaging reactions might be the reason. As a sign of the enhanced susceptibility to lipid peroxidation of LNA-fed SHR, we found (measured as TBARS) higher plasma and heart lipid peroxide levels (3.84 +/- 0.50 micromol/l vs 2.98 +/- 0.78 micromol/l and 507 +/- 127 nmol/g prot. vs 215 +/- 80 nmol/g prot., respectively) after feeding LNA. Using Fe2+/Vit. C to induce lipid peroxidation in myocardial tissue homogenates, we demonstrated the enhanced susceptibility to lipid peroxidation of the LNA-fed SHR heart (68 +/- 12 nmol/min x g prot. vs 40 +/- 8 nmol/min x g prot.) also in vitro. The myocardial enrichment of n-3 polyunsaturated fatty acids (PUFA) resulting in a higher peroxidation index (PI 227 vs. 170) and the loss in myocardial activities of the antioxidative enzymes (SOD: 76 +/- 24 U x 10(3)/g prot. vs 235 +/- 150 U x 10(3)/g prot.; GSH-Px: 32 +/- 5 U/g prot. vs 110 +/- 30 U/g prot.) by feeding LNA could be the cause of the increase in myocardial susceptibility to lipid peroxidation of PUFA supplemented SHR.

The ratio of formation of prostacyclin/thromboxane A2 in HUVEC decreased in each subsequent passage

In this study, we analyzed the antioxidative potential (SOD-, GSH-Px-activity) and the basal, H2O2- and ATP-stimulated formation of PGI2 and TXA2 in human umbilical vein endothelial cells (HUVEC) of different passages. The subcultivation of cells partly represents the process of aging. Both subcultivation of the cells and the H2O2 incubation did not significantly influence the activity of SOD and GSH-Px. H2O2 (0.1 mM and 1.0 mM) stimulated the generation of PGI2 and TXA2 in the cell passages time dependently. The formation ratio of PGI/TXA2 changed from 640:1 (0.1 mM H2O2) or 430:1 (1.0 mM H2O2, 40 min incubation) at the 1st passage, to 13:1 and 17:1, respectively, at the 4th passage. This resulted from the reduction of the PGI2 synthesis connected with more pronounced TXA2 formation. The same behavior was found in the basal and ATP-stimulated eicosanoid formation. Based on this, the age-dependent activation of the oxygen radical formation could be responsible for the modified eicosanoid metabolism resulting in vascular complications in the elderly.

Arachidonic acid metabolism in murine lymphoma cell sublines differing in radiation sensitivity

14C arachidonic acid incorporation and 14C radioactivity release as well as prostaglandin (PG) and 5-hydroxyeicosatetraenoic acid (5-HETE) synthesis were measured in the pair of murine lymphoma L5178Y (LY) cell sublines differing in radiation sensitivity. Both LY sublines, LY-R (resistant) and LY-S (sensitive), incorporated exogenous arachidonic acid and released it from membrane phospholipids. Ca2+ ionophores (ionomycin and A23187) but not PMA stimulated the liberation of 14C arachidonic acid in LY cells. PMA did not potentiate the 14C arachidonic acid release both in the presence or in the absence of A23187; this observation suggests that protein kinase C activation is not essential for the regulation of arachidonic acid release by LY-R and LY-S cells. X-irradiation (5 Gy) did not change the uptake of 14C arachidonic acid into LY-R and LY-S cells and did not potentiate the release of its total radioactivity from the cells. PG synthesis was stimulated in irradiated LY-R cells but not in LY-S cells. The susceptibility of eicosanoid metabolism to A23187 and H2O2 was altered in irradiated LY-R cells. A23187 stimulated only PG and 5-HETE synthesis in irradiated LY-R cells. H2O2 did not stimulate the synthesis of PG from exogenous arachidonic acid in irradiated LY-R and LY-S cells and 5-HETE synthesis in LY-R cells. An implication of the increased PG synthesis in LY-R cells in the protection against radiation is discussed.

Mechanisms of the biphasic effects of peroxides on the retinal vasculature of newborn and adult pigs

We tested whether the ontogenic differences in the constrictor effects of peroxides on the retinal vasculature were modulated by dilator cyclo-oxygenase products. Retinal arteriole (100-200 microns) vasomotor response to H2O2, t-butyl hydroperoxide, and cumene hydroperoxide were studied in isolated eyecup preparations using video camera monitoring of vessel diameter. A time- and dose-dependent biphasic retinal vasomotor response to all peroxides was observed on tissues of newborn and adult pigs. A rapid vasoconstriction (first 2 min) was followed by a relaxation which was greater in the adult than in the newborn tissues. The constrictor as well as the dilator response to peroxides and the observed increase in prostanoids were blocked by the cyclo-oxygenase inhibitor indomethacin. The peroxide-induced relaxation was inhibited or markedly attenuated by the prostaglandin I2 synthase blockers, trans-2-phenyl cyclopropylamine and minoxidil on tissues of newborn and adult animals. These agents also prevented the increase of the prostaglandin I2 receptor-coupled second messenger, cyclic 3',5'-adenosine monophosphate. Our data indicate that prostaglandin I2 plays a major role in counteracting the initial constrictor effects of peroxides in the retinal vasculature, and that the reversal of this constriction is greater in the adult than the newborn. These findings suggest that reduced reversal of vasoconstriction by the dilator prostaglandin I2 during an oxidative stress in the newborn may facilitate vasoconstriction by the dilator prostaglandin I2 during an oxidative stress in the newborn may facilitate neovascularization in retinopathy of prematurity.

In vitro effects of hypoxia and reoxygenation on human umbilical endothelial cells

We investigated metabolic changes in human umbilical venous endothelial cells, when these were incubated under hypoxic followed by hyperoxic conditions, thus simulating hypoxia and reoxygenation. The human umbilical venous endothelial cells were incubated with a degassed buffer (oxygen content: 0-0.5%) for either 3 h or 24 h, followed by a 60 min incubation with oxygen-perfused buffer (oxygen content: 100%). Three hours of hypoxia led to a slight decrease in the ATP and creatine phosphate content (-16% +/- 5%), while a pronounced decrease of high energy phosphates (-54% +/- 4%) was observed after 24 h of hypoxia. Reoxygenating the cells after 3 h of hypoxia led to restoration of the content of high energy phosphates, while reoxygenation after 24 h resulted in a strong decrease (-66% +/- 4%). The prostaglandin I2 release during the first 3 h of hypoxia exceeded the release in the following 21 h. In all cases, reoxygenation increased the prostaglandin I2 release. Under normoxic conditions the ratio between oxidised glutathione and reduced glutathione shifted from 1:100 to 1:4.5 after 3 h of hypoxia. The content of lipid peroxidation products was almost unaffected during hypoxia, whereas reoxygenation resulted in a pronounced increase (+380% +/- 60%). The results of this in vitro study suggest that relatively long periods of hypoxia lead to a deficiency of high energy phosphates in the cell. Reoxygenation leads to the formation of oxygen-derived radicals, irrespectively of a prior hypoxia.