The effects of varying dietary n-6 to n-3 fatty acid ratios on platelet reactivity, coagulation screening assays, and antithrombin III activity in dogs

Thirty beagles were placed on diets containing ratios of n-6 to n-3 fatty acids ranging from 5:1 to 100:1 for 12 weeks to determine the effects of these diets on platelet reactivity, coagulation screening assays, and antithrombin III activity. Although small changes were observed in adenosine diphosphate (ADP)-, collagen-, and arachidonic acid-induced platelet aggregation and 14C-serotonin release, fibrinogen concentrations, and antithrombin III activities during the 12-week study, these changes were not of clinical significance and did not correlate with the varying ratios of n-6 to n-3 fatty acids.

Identification of the novel antimicrobial fatty acid (5Z,9Z)-14-methyl-5,9-pentadecadienoic acid in Eunicea succinea

The phospholipid fatty acid composition of Eunicea succinea was investigated, and the novel (5Z,9Z)-14-methyl-5,9-pentadecadienoic acid was identified. Structural characterization was accomplished by means of mass spectrometry of its pyrrolidide derivative, NMR, FT1R, and total synthesis. Other interesting phospholipid fatty acids in E. succinea were the tetracosapolyenoic acids 6,9,12,15,18,21-tetracosahexaenoic acid (24:6) and 6,9,12,15,18-tetracosapentaenoic acids (24:5). The title compound was particularly active against Gram-positive bacteria such as Staphylococcus aureus (MIC 0.24 mumol/mL) and Streptococcus faecalis (MIC 0.16 mumol/ mL).

Dietary fatty acids in human thrombosis and hemostasis

The effects of fatty acids on hemostasis are controversial. It has been difficult to show convincing effects of saturated or monounsaturated fatty acids that are clearly related to hemostatic variables in humans. Unsaturated fatty acids alter platelet aggregation and processes related to coagulation and fibrinolysis. Indirect evidence exists that n-6 polyunsaturated fatty acids may exert favorable effects on thrombotic processes in vivo, but large clinical trials have failed to show benefits of 5-6 g linoleic acid (18:2n-6) or linolenic acid (18:3n-3)/d. Only long-chain n-3 fatty acids prolong the template bleeding time, and they may exert some beneficial effect on erythrocyte flexibility. It appears unlikely that n-3 fatty acids lower fibrinogen or interact with the fibrinolytic system directly. One prospective secondary prevention trial showed benefits that may have resulted from either an improved hemostatic profile or an antiarrhythmic effect. A similar time course of clinical improvement was noted with reduced rates of cardiac mortality and postoperative thrombosis in Norway during World War II, and this was associated with a drastic dietary alteration involving increased consumption of n-3 fatty acids and reduced consumption of saturated fatty acids. Further work is needed to develop better tools to examine in vivo hemostasis so that the mechanisms and eventual clinical utility of n-3 fatty acids can be elucidated in well-designed clinical trials.

Suppression of voltage-gated L-type Ca2+ currents by polyunsaturated fatty acids in adult and neonatal rat ventricular myocytes

Our recent data show that in cardiac myocytes polyunsaturated fatty acids (PUFAs) are antiarrhythmic. They reduce I(Na), shorten the action potential, shift the threshold for excitation to more positive potentials, and prolong the relative refractory period. In this study we use patch-clamp techniques in whole-cell mode and confocal Ca2+ imaging to examine the effects of PUFAs on the voltage-gated L-type Ca2+ current (I(Ca,L)), elementary sarcoplasmic reticulum Ca2+-release events (Ca2+-sparks), and [Ca2+]i transients in isolated rat ventricular myocytes. Extracellular application of eicosapentaenoic acid (EPA; C20:5 n - 3) produced a prompt and reversible concentration-dependent suppression of I(Ca,L). The concentration of EPA to produce 50% inhibition of I(Ca) was 0.8 microM in neonatal rat heart cells and 2.1 microM in adult ventricular myocytes. While the EPA induced suppression of I(Ca,L), it did not significantly alter the shape of the current-voltage relation but did produce a small, but significant, negative shift of the steady-state inactivation curve. The inhibition of I(Ca,L) was voltage- and time-dependent, but not use- or frequency-dependent. Other PUFAs, such as docosahexaenoic acid, arachidonic acid, linolenic acid, linoleic acid, conjugated linoleic acid, and eicosatetraynoic acid had similar effects on I(Ca,L) as EPA. All-trans-retinoic acid, which had been shown to suppress induced arrhythmogenic activity in rat heart cells, also produced a significant inhibition of I(Ca,L). The saturated stearic acid and the monounsaturated oleic acid had no effect on I(Ca,L). Because both I(Ca,L) and sarcoplasmic reticulum Ca2+-release underlie many cardiac arrhythmias, we examined the effects of EPA on I(Ca,L) and Ca2+-sparks. While EPA suppressed both, it did not change the temporal or spatial character of the Ca2+-sparks, nor did it alter the ability of I(Ca,L) to trigger Ca2+-sparks. We conclude that PUFAs may act as antiarrhythmic agents in vivo in normal and Ca2+-overloaded cells principally because they reduce Ca2+ entry by blocking I(Ca,L). Furthermore, PUFAs act directly to decrease I(Na) and I(Ca,L), but indirectly to reduce the [Ca2+]i transients and [Ca2+]i-activated membrane current. Although a negative inotropic action is associated with application of PUFAs, it is clear that by reducing I(Ca,L), I(Na) and Ca2+-sparks, PUFAs can reduce spontaneous extrasystoles in the heart. The mechanisms by which PUFAs act are discussed.

Transcriptional regulatory regions for expression of the rat fatty acid synthase

We previously mapped the sequences responsive to insulin/glucose stimulation and polyunsaturated fatty acid (PUFA) suppression in proximal promoter region from -57 to -35 of fatty acid synthase (FAS) gene of rat liver [Fukuda et al. (1996) Biochem. Mol. Biol. Int. 38, 987-9961. When two copies of the sequences spanning -57 to -35 were linked to a reporter gene containing heterologous promoter and were used for transfection, the reporter activity significantly increased in response to insulin/glucose treatment in hepetocytes. This increase was inhibited by addition of PUFA. Gel mobility shift assays using the sequence from -57 to -35 as a probe revealed nuclear factor(s) from rat liver that specifically complexed with the sequences. In addition, by antibody supershift assays, we have detected the binding of the transcriptional factor Sp1 at the GC-rich region located within -57 to -35 of the FAS promoter. Cotransfection studies in rat hepatocytes, with the Sp1 expression vector and FAScat constructs, showed the inactivation of the promoter. These results were similar to those for the region from -68 to -52 of FAS gene (an insulin response element). The region from -68 to -52 of FAS gene competed for the formation of DNA-protein complexes to the region from -57 to -35 in the gel shift assay. Mutational analysis showed that the overlapping region of these two sequences was essential for the binding of Sp1. It has been demonstrated that both the regions from -57 to -35 and from -68 to -52 of the FAS gene are responsible for regulation due to insulin/glucose and PUFA, and Sp1 may be involved in the regulation.

Effects of the incubation of long-chain polyunsaturated fatty acids on platelet lipids and thromboxane release

Alterations of dietary lipids have been advocated to manipulate platelet release of thromboxane A2. We studied the effects of incubating platelets with several different polyunsaturated fatty acids on platelet-lipid profile and release of thromboxane A2 in response to platelet stimulation. Porcine platelets were isolated by centrifugation, washed three times in Tyrode's solution, and incubated with fatty acids (500 microM) in Tyrode's solution with albumin. Seven polyunsaturated fatty acids of varying lengths (18-, 20-, and 22-carbon chain) of the omega3 and omega6 families were incubated for 60 min at concentrations of 0, 10, 30, and 100 microM with saturated fatty acids comprising the remainder of the 500 microM fatty acids. The platelets were then stimulated for 5 min with A23187 (30 microM). Indomethacin was added, and the platelets were pelleted. Platelet lipids were extracted in hexane, transesterified and quantified by gas chromatography. Using radioimmunoassay, we measured thromboxane B2, the stable metabolite of thromboxane A2, in the platelets' supernatant. A 1-h incubation in each of the seven polyunsaturated fatty acids had no significant effect on platelet-lipid composition. We found a significant increase in thromboxane B2 production in arachidonic acid (100 microM) incubated platelets (324.0 +/- 63.8% of baseline) that was inhibited by eicosapentaenoic acid (81.0 +/- 26.8%, P < 0.01) and to a lesser extent by dihomogammalinolenic acid (189.8 +/- 28.3%, P < 0.03). We conclude that in altering diets to affect platelet release of thromboxane, the two fatty acids of interest are the 20-carbon chain fatty acids, dihomogammalinolenic acid and eicosapentaenoic acid. The ideal amount of each of these fatty acids to be incorporated entails supraphysiologic but pharmacologically achievable levels of fatty acids in plasma.

Cytotoxic action of alpha-linolenic and eicosapentaenoic acids on myeloma cells in vitro

Both alpha-linolenic (ALA) and eicosapentaenoic acids (EPA) were toxic to SP 2/0 mouse myeloma cells in vitro. On the other hand, linoleic acid (LA), gamma-linolenic acid (GLA), di-homo-gamma linolenic acid (DGLA), arachidonic acid (AA), docosahexaenoic acid (DHA) and oleic acid (OA) were much less effective in their growth suppressive actions. Both nordihydroguaiaretic acid (NDGA) and Indomethacin (IM) could block the action of the fatty acids indicating a role for prostaglandins (PGs) and leukotrienes (LTs) in the growth suppressive action of ALA and EPA. Superoxide dismutase (SOD) completely blocked, while vitamin E and reduced glutathione (GSH) could prevent to a limited extent the anti-proliferative effects of ALA and EPA. Catalase, mannitol, chlorpromazine (CPZ) and trifluoperazine (TFP) did not block the cytotoxic actions of ALA and EPA. N(G)-mono-methyl L-arginine (N(G)MMA), an analogue of L-arginine, which inhibits nitric oxide synthase, was ineffective in preventing the cytotoxicity induced by ALA and EPA. Fatty acid analysis of the various lipid fractions of SP 2/0 cells treated with ALA and EPA showed significant incorporation of these fatty acids in the cell membrane lipid pools. These results suggest that ALA and EPA induced suppression of SP 2/0 cell proliferation is cyclo-oxygenase (CO), lipoxygenase (LO) and superoxide dependent. Lipid peroxidation has only a limited role in this process. Both calmodulin dependent process and L-arginine derived nitric oxide do not seem to have a role in the cytotoxic action of ALA and EPA in these cells.

Effect of cis-unsaturated fatty acids, prostaglandins, and free radicals on angiotensin-converting enzyme activity in vitro

Angiotensin-converting enzyme (ACE) is known to play an important role in the pathobiology of human essential hypertension. Similarly, cis-unsaturated fatty acids, prostaglandins, and free radicals are believed to play a role in the control of blood pressure. It was observed that all the cis-unsaturated fatty acids tested can inhibit ACE activity to a significant degree. On the other hand, prostaglandins and free radicals, superoxide anion, hydrogen peroxide, and hydroxyl radical did not show significant inhibitory effects on ACE activity in vitro. But, the nitric oxide donor sodium nitroprusside showed a potent inhibitory action on ACE activity, suggesting that one of the possible mechanism(s) by which nitric oxide can bring about its anti-hypertensive action might be by modulating ACE activity in addition to its direct vasodilator action. These results indicate that there is a close interaction among ACE activity, cis-unsaturated fatty acids, and nitric oxide, which may have relevance to the pathobiology of human essential hypertension.

The effects of unsaturated fatty acids, oxidizing agents and Michael reaction acceptors on the induction of N-ethylmaleimide reductase in Escherichia coli: possible application for drug design of chemoprotectors

Menadione and dimethyl maleate, Michael reaction acceptors, induced N-ethylmaleimide (NEM) reductase activity in Escherichia coli strain DH5a. Linoleic acid also induced NEM reductase activity, but oleic acid, which is less susceptible to lipid peroxidation than linoleic acid, did not induce NEM reductase activity. In addition, NEM reductase activity was induced by menadione and linoleic acid also in strain DH5, Y1088 and Y1090. Linoleic acid is not a Michael reaction acceptor, but is known to produce Michael reaction acceptors such as alkenals and 4-hydroxyalkenals as a result of free-radical-initiated lipid peroxidation. Thus, our findings suggested that lipid peroxidation was involved in the induction of NEM reductase by linoleic acid. The electrophilic property of Michael reaction acceptors provides the signal for induction of phase II enzymes such as glutathione S-transferase and quinone reductase in mammals. The inducer potency of phase II enzymes has been used to design chemoprotective drugs. Therefore, the inducible nature of this enzyme will serve not only for the elucidation of its physiological function, but also for the evaluation of chemoprotective drugs.

Arachidonic acid activation of potassium channels in rat visual cortex neurons

We investigated the effects of arachidonic acid on K+ channels in freshly dissociated neurons of 10- to 20-day-old rat visual cortex, using a perforated and conventional whole-cell patch-clamp and inside-out excised patch configurations. Arachidonic acid at 5-30 microM induced an outward current in 88.1% of the neurons in whole-cell mode, and evoked channel opening with a conductance of 170-238 pS in 90.5% of neurons under inside-out patch recording. Arachidonic acid-activated K+ channels were partially blocked by extracellular administration of 1 mM tetraethylammonium and 100 nM charybdotoxin. However, Ba2+ completely blocked the channel in all cases. None of the other K+ channel blockers, including 4-aminopyridine, quinidine, apamin and glibenclamide, inhibited the arachidonic acid-activated channels. Intracellular perfusion with Ca2+-free and 5 mM BAPTA in Ca2+-free extracellular perfusate containing 2 mM EGTA in conventional whole-cell recording did not inhibit the K+ channel, implying that the channel is not Ca2+ dependent. Neither guanosine 5'-O-(2-thiodiphosphate) nor staurosporine applied in inside-out mode affected the arachidonic acid-activated channels, indicating that G-protein and protein kinase C are not involved in this phenomenon. In addition, neither indomethacin nor nordihydroguaiaretic acid blocked the channel currents, demonstrating that it is arachidonic acid itself but not its metabolites that induced the effect. Among the fatty acids tested, only cis-unsaturated fatty acids, having more than two double bonds, such as arachidonic acid, docosahexaenoic acid and linolenic acid, activated the K+ channels. These findings suggest that there exists a novel type of K+ channel activated by arachidonic acid which may play a critical role in modulating neuronal excitability in cortical neurons.

Involvement of juvenile hormone in regulation of prothoracicotropic hormone transduction during the early last larval instar of Bombyx mori

We previously reported that a deficiency in prothoracicotropic hormone (PTTH) transduction during the early last larval instar of Bombyx mori plays a role in leading to very low ecdysteroid levels in the hemolymph, inactivation of corpora allata, as well as larval-pupal transformation. In the present study, the role of juvenile hormone (JH) in the regulation of PTTH transduction was clarified. When JH analog (hydroprene) was applied to early last instar larvae, the development of larvae was greatly inhibited. It was found that it was not PTTH release, but prothoracic gland competency in both cAMP generation and ecdysteroidogenesis to the stimulation of PTTH which was developmentally inhibited by hydroprene application. Glands in hydroprene-treated larvae showed no response in ecdysteroidogenesis to either PTTH or 1-methyl-3-isobutylxanthine (MIX) until day 7, 4 days later than those of control larvae. JH-I application showed the same effects as those of hydroprene. By contrast, allatectomy on day 0 of the last instar accelerated development, and glands showed the activation response to either PTTH or MIX in both cAMP generation and ecdysteroidogenesis 1 day after allatectomy. From these results, we conclude that the absence of JH is a prerequisite for successful PTTH transduction and for acquisition of the cAMP generating system of gland cells.

Effect of aeration and unsaturated fatty acids on expression of the Saccharomyces cerevisiae alcohol acetyltransferase gene

The reduction of acetate ester synthesis by aeration and the addition of unsaturated fatty acids to the medium has been reported to be the result of the reduction in alcohol acetyltransferase (AATase) activity induced by inhibition of this enzyme. However, regulation of the AATase gene ATF1 has not been reported. In this study, ATF1 gene expression was studied by Northern analysis, and the results showed that the ATF1 gene was repressed both by aeration and by unsaturated fatty acids. The results also showed that the reduction of AATase activity is closely related to the degree of repression of ATF1 mRNA, which suggested that the gene repression is the primary means of reducing AATase activity in vivo. Using the Escherichia coli lacZ gene as a reporter gene, it was shown that a 150-bp fragment of the 5' flanking sequence played a major role in the repression by aeration and unsaturated fatty acid addition.

Unsaturated fatty acids enhance cell yields and perturb the energy metabolism of an antibody-secreting hybridoma

Growth of the murine B-lymphocyte cell line CC9C10 and the myeloma SP2/0 was enhanced significantly by the presence of the unsaturated fatty acids, oleic and linoleic acids in serum-free culture. The cellular content of linoleic and oleic acids gradually increased during continuous culture passage, with no evidence of regulatory control. Over 10 culture passages in the presence of these fatty acids, the unsaturated/saturated fatty acid ratio of all cellular lipid fractions increased substantially. Most of the fatty acid accumulated in the polar lipid fraction (more than 74%) and only a small proportion was oxidized to CO2 (0.5%). Linoleic acid caused a decrease to one-eighth in the rate of metabolism of glutamine and a 1.4-fold increase in the rate of metabolism of glucose. There was no change in the relative flux of glucose through the pathways of glycolysis, pentose phosphate or the tricarboxylic acid cycle. The changes in energy metabolism were reversed when the cells were removed from fatty acid-supplemented medium. The most plausible explanation for these effects is the observed decrease in the rate of uptake of glutamine into cells loaded with linoleic acid. Growth of the CC9C10 cells in linoleic acid caused the Km of glutamine uptake to increase from 2.7 to 23 mM, whereas glucose uptake was unaffected.

Incorporation of long-chain n-3 fatty acids in tissues and enhanced bone marrow cellularity with docosahexaenoic acid feeding in post-weanling Fischer 344 rats

We wanted to examine the effects of an oil rich in docosahexaenoic acid (DHA), without eicosapentaenoic acid, on the composition of membrane phospholipid in a variety of tissues. Our in vitro studies had previously shown that DHA could modify glucose and nucleoside transport in cells in culture and also increase selectivity of the nucleoside drug, arabinosylcytosine (araC) toward tumor cells. Here we wanted to examine what effect DHA supplementation would have in the whole animal in terms of the chemosensitivity of normal bone marrow, the dose-limiting tissue during chemotherapy, to araC. The purpose was to determine whether fatty acid supplementation might be useful as an adjuvant to chemotherapy. We fed diets containing 5% (w/w) low fat-corn oil (LF-CO group), 10% moderate fat-safflower oil (MF-SO group), or 10% DHASCO (MF-DHA group) to weanling Fischer 344 rats for 8-9 wk. Feed intake and growth were not different between the different diets. Similarly, treatment of animals with the chemotherapeutic drug araC did not differentially affect growth, feed intake, or tissue fatty acid composition for the different diet groups. Fatty acid compositions of bone marrow, liver, red blood cells, plasma phospholipid and triglyceride, as well as skeletal and cardiac muscle, were substantially different between the dietary groups. The DHASCO oil contained 46% DHA (22:6n-3) and resulted in profound incorporation of DHA in all tissues examined. The most dramatic response was seen in skeletal muscle of MF-DHA fed animals where DHA represented 46% of membrane phospholipid fatty acids. This is likely to have consequences to muscle function. Although DHASCO contains a similar level of saturated fatty acids (42%), few differences in saturates were noted between the various dietary groups for most of the tissues examined. Both LF-CO and MF-SO diets were hypercholesterolemic, and the LF-CO was also hypertriglyceridemic compared to the chow-fed animals. Animals fed the MF-DHA diet had the lowest triglyceride levels of any of the treatment groups and cholesterol levels comparable to chow-fed animals. MF-DHA had substantially higher numbers of colony-forming units-granulocyte macrophage (CFU-GM) as reflected in a twofold higher bone marrow cellularity than either chow or LF-CO animals, suggesting expansion of the bone marrow compartment with DHA feeding. Although higher than LF-SO, the number of CFU-GM in MF-SO animals was not significantly higher than animals fed chow. Bone marrow from LF-CO animals appeared to be more resistant to araC treatment than either MF group. Thus, DHA, fed as DHASCO, has advantages over low or moderate n-6 diets and chow as it is has both hypolipidemic- and bone marrow-enhancing properties in weanling Fischer 344 rats. This suggests that DHA supplementation may be useful in adjuvant chemotherapy.

Polyunsaturated fatty acids increase the sensitivity of 36B10 rat astrocytoma cells to radiation-induced cell kill

Polyunsaturated fatty acids (PUFA) such as gamma-linolenic acid (GLA, 18:3n-6), eicosapentaenoic acid (EPA, 20:5n-3), and docosahexaenoic acid (DHA, 22:6n-3) have been shown to be cytotoxic to tumor cells. The objective of this work was to study the effects of PUFA on the radiation response of a 36B10 rat astrocytoma cell line. Supplementation of the astrocytoma cells with 15-45 microM GLA, EPA, or DHA produced marked changes in the fatty acid profiles of their phospholipids and neutral lipids. The methylene bridge index of these lipids increased significantly. These PUFA also exerted cytotoxic effects, as determined using the clonogenic cell survival assay. While GLA and DHA produced a moderate cell-killing effect, EPA was extremely cytotoxic, especially at a concentration of 45 microM. The monounsaturated oleic acid (OA, 18:1n-9) did not affect cell survival. Further, all three PUFA, and particularly GLA, increased the radiation-induced cell kill; OA did not enhance the effect of radiation. alpha-Tocopherol acetate blocked the enhanced radiation sensitivity of GLA- and DHA-supplemented cells. In conclusion, GLA, EPA, and DHA supplementation prior to, during, and after irradiation can enhance the radiation-induced cytotoxicity of rat astrocytoma cells. GLA and DHA supplementation post-irradiation also enhanced the radiation response of the 36B10 cells. Because GLA maximally increases the radioresponsiveness of a rat astrocytoma, this PUFA might prove useful in increasing the therapeutic efficacy of radiation in the treatment of certain gliomas.

[Artificially functionalized polyenoic fatty acids--a new lipid bioregulators]

Dopamine, histamine, serotonin, and serotonin analogs were acylated with arachidonic and eicosapentaenoic acids, and the reaction products were named as artificially functionalized fatty acids (AFFA). The amides of arachidonic acid with serotonin, dopamine, and histamine were found to inhibit human platelet aggregation induced by ADP, arachidonic acid and adrenaline. Amides of arachidonic and eicosapentaeonic acids with serotonin and dopamine protect sea urchin early embryos against cytotoxic action of serotonin and histamine antagonists. These effects are not connected with the possible hydrolytic cleavage of AFFA to their constituent polyenoic fatty acids and amines. Arachidonic acid dopaminamide was shown to be a substrate of soybean 15-lipoxygenase, whereas the arachidonic acid amides with serotonin and its derivatives were resistant to this enzyme. Moreover, arachidonic acid serotoninamide turned out to be an irreversible lipoxygenase inhibitor. Considerable amount of hydroxyl radicals (fluorescent assay) were found for the first time to accompany lipoxygenase oxidation of linoleic acid; arachidonic acid serotoninamide blocked this process completely. Therefore, it was concluded that AFFA possess specific biological activity and can be considered as a novel group of lipid bioregulators.

Effects of fatty acids on human platelet glutathione peroxidase: possible role of oxidative stress

Highly polyunsaturated fatty acids of the n-3 family are known to be inhibitors of platelet functions, but these fatty acids (FA) may alter the platelet antioxidant status, depending on their concentrations. The present study was aimed to investigate the effect of various FA on glutathione-dependent peroxidase (GPx), the required antioxidant enzyme for degrading FA hydroperoxides. Human platelets were enriched in vitro with either n-3 (18:3, 20.5, or 22.6), n-6 (18:2 or 18:3) FA, 18:1 n-9 or 16:0, and the GPx activity was then measured. It was found that n-3 FA enhanced the GPx activity whereas the others did not affect the enzyme activity. The increased GPx activity was associated with an increased amount of the enzyme measured by Western blotting. The enhanced activity and amount of GPx induced by 22:6n-3, the most potent activator among the n-3 FA, was completely abolished in the presence of cycloheximide at a concentration known to inhibit platelet protein synthesis. Because platelets are devoid of nucleus, which rules out the involvement of transcriptional factors, this suggests that 22:6n-3 might act at a translational level. On the other hand, 22:6n-3 treatment increased the malondialdehyde formation and decreased the vitamin E level in platelets, both events that could be prevented by the antioxidant epicatechin. Because epicatechin also suppressed the enhancement of both the activity and amount of GPx induced by 22:6n-3, we conclude that the increased GPx activity (possibly via protein synthesis) might be associated with an oxidative stress induced by 22:6n-3 and/or 20:4n-6 released from the platelet endogenous pool in the course of the 22:6n-3 enrichment.

P450 arachidonate metabolites mediate bradykinin-dependent inhibition of NaCl transport in the rat thick ascending limb

Recent studies from this laboratory demonstrated that bradykinin transiently elevates intracellular Ca2+ and inhibits Cl-reabsorption in the in vitro microperfused medullary thick ascending limb (mTAL) of the rat. The present study was designed to identify the intracellular signaling mechanism(s) that mediate this response. Preincubation with the intracellular calcium chelator BAPTA (10(-5) M) completely eliminated the bradykinin-dependent increase in intracellular Ca2+ and the suppression of Cl- transport. Preincubation with the cGMP-dependent protein kinase inhibitor H-89 (10(-5) M) had no effect on the transport response to bradykinin. In contrast, 17-octadecynoic acid (17-ODYA; 10(-5) M), a suicide-substrate inhibitor of renal cytochrome P450 omega-hydroxylase, completely blocked the transport response to bradykinin, while the cyclooxygenase inhibitor sodium meclofenamate (10(-5) M) had no effect. Finally, addition of the cytochrome P450 omega-hydroxylase metabolite 20-hydroxyeicosatetraenoic acid (20-HETE; 10(-8) M) to the bathing medium significantly inhibited Cl- transport in the mTAL (delta -39 +/- 6.0%; p < 0.05), while the epoxygenase metabolite 5,6-epoxyeicosatrienoic acid (5,6-EET; 10(-8) M) had no effect. These data suggest that the bradykinin-dependent inhibition of Cl- transport in the mTAL of the rat is mediated by cytochrome P450 dependent metabolite(s) of arachidonic acid.

Use of a fluorescent probe to assess the activities of candidate agents against intracellular forms of Encephalitozoon microsporidia

Microsporidia are obligate intracellular protozoan parasites. Three species of the genus Encephalitozoon are among the microsporidia that infect immunodeficient humans. These species, Encephalitozoon cuniculi, Encephalitozoon hellem, and Encephalitozoon intestinalis, all develop in a parasitophorous vacuole within a host cell. The present study describes a method that uses the fluorescent probe calcein and confocal microscopy to detect drug-induced effects in Encephalitozoon-infected green monkey kidney cells. The effects were as follows: (i) changes in parasite organization within the parasitophorous vacuole; (ii) swelling and gross morphological changes of parasite developing stages in situ; (iii) killing of developing parasite stages in situ, detected by their uptake of the fluorescent probe; and (iv) reduction in the viability of the host cell population, assessed by the loss of the probe. Verapamil and itraconazole were used to increase the vital dye loading by both uninfected and infected cells. Agents with known antimicrosporidial activity, albendazole and fumagillin, caused all three types of parasite changes at concentrations that had no detectable effect on host cell viability. The effective doses of albendazole and fumagillin that caused swelling and disorganization of parasite developing stages were 5 x 10(-7) and 10(-6) M respectively. Killing of developing stages was detected at 10-fold-higher concentrations for these agents and at 10(-5) M for metronidazole. This method can be used to screen candidate antimicrosporidial agents in infected cultured cells.

Essential fatty acid metabolism in cardiomyocytes grown in media enriched with different N-6/N-3 fatty acid combinations

We have evaluated the effects of three different 18:3n-6, 20:5n-3 and 22:6n-3 fatty acid combinations on essential fatty acid (EFA) metabolism in rat cultured cardiomyocytes. The desaturating/elongating activities for linoleic (LA) and alpha-linolenic acid (ALA) were evaluated by radiolabeling the cells with 1-[14C]LA or 1-[14C]ALA and the fatty acid pattern of cardiomyocytes was assessed by gas chromatography. LA and ALA conversion to more unsaturated metabolites was reduced by increasing respectively n-3 and n-6 fatty acid concentration in the media. The all three combinations used reduced the saturated and increased the polyunsaturated fatty acid content of cardiomyocytes. The n-6/n-3 fatty acid ratio did not change compared to control cells in cardiomyocytes receiving the highest amount of 18:3n-6 and the lowest amounts of n-3 fatty acids. This combination may be suitable for modifying EFA desaturating/elongating activities without altering the physicochemical parameters which are related to the correct balance between n-6 and n-3 fatty acid content.

Inotropic response of rat heart papillary muscle to alpha 1- and beta-adrenoceptor stimulation in relation to dietary n-6 and n-3 polyunsaturated fatty acids (PUFA) and age

The effect of dietary n-6 and n-3 polyunsaturated fatty acids (PUFA) and age on inotropic responses of heart papillary muscle to alpha 1-or beta-adrenoceptor stimulation was examined in young (4 months), middle-aged (12 months) and senescent (27 months) male Wistar rats. From the age of two months the rats were fed a diet containing 2% or 12% of fat by weight varying in PUFA type: a) standard low-fat n-6 PUFA diet, b) high-fat n-6 PUFA diet or c) high-fat n-3 PUFA diet. The inotropic responses to alpha 1-adrenoceptor stimulation with phenylephrine were triphasic (positive, negative, then positive). Young, high-fat n-3 PUFA-fed rats exhibited significantly lower negative and higher positive responses to phenylephrine stimulation, and higher positive responses to isoprenaline stimulation than young, high-fat n-6 PUFA-fed rats. On the other hand, no such dietary-related difference was found between young rats fed a high-fat n-3 PUFA diet and a standard low-fat n-6 PUFA diet. The young high-fat n-6 PUFA-fed rats exhibited inotropic responses similar to those of the middle-aged and senescent rats within the three dietary groups. The time to peak force and the time of half relaxation did not differ within dietary and age groups. The findings indicate that dietary n-6 PUFA-rich supplementation at a young age induces changes resembling the effects of age, as evidenced by decreasing cardiac responses to adrenoceptor agonists, such as phenylephrine or isoprenaline.

Leptomycin B is an inhibitor of nuclear export: inhibition of nucleo-cytoplasmic translocation of the human immunodeficiency virus type 1 (HIV-1) Rev protein and Rev-dependent mRNA

BACKGROUND

The human immunodeficiency virus type 1 (HIV-1) regulatory protein Rev is required for unspliced and incompletely spliced viral mRNAs to appear in the cytoplasm and thus for viral replication. Translocation of Rev from the nucleus to the cytoplasm is essential if Rev is to function. We wanted to identify inhibitors of this transport process because they would be potential antiviral agents.

RESULTS

The Streptomyces metabolite, leptomycin B, and other antibiotics of the leptomycin/kazusamycin family were identified as inhibitors of the nucleo-cytoplasmic translocation of Rev at nanomolar concentrations. Rev-dependent export of mRNA into the cytoplasm is also blocked by leptomycin B, which inhibits Rev-dependent, but not Rev-independent gene expression in a short-term transfection assay. In primary human monocytes, leptomycin B suppresses HIV-1 replication.

CONCLUSIONS

Leptomycin B is the first low molecular weight inhibitor of nuclear export to be identified. Although it cannot be used therapeutically, it should serve as a valuable tool for dissecting nuclear export pathways.

Thromboxane A2 induces cell signaling but requires platelet-derived growth factor to act as a mitogen

This study investigates thromboxane A2-induced cell signaling and mitogenesis of bovine coronary artery smooth muscle cells. The thromboxane mimetic U 46619 [(15S)-hydroxy-11,9-(epoxymethano) prosta-5Z,13E-dienoic acid] (10 microM) stimulated [Ca2+]i signals, phosphorylation of MAP kinase (mitogen-activated protein kinase), and expression of c-fos mRNA in smooth muscle cells. In contrast, no stimulation of DNA synthesis or cell proliferation by U 46619 was observed. However, platelet-derived growth factor-BB (20 ng/ml)-induced mitogenesis was potentiated by U 46619. Similar results were obtained with I-BOP [1S-(1 alpha,2 beta(5Z),3 alpha(1E,3R*), 4 alpha)]-7-[3-(3-hydroxy-4-(4'-iodophenoxy)-1-butenyl)-7-oxabicyclo [2.2.1] heptan-2-yl]-5-heptenoic acid]. These potentiating effects were abrogated by a specific thromboxane receptor antagonist, suggesting that the potentiation of platelet-derived growth factor-BB-induced smooth muscle cell mitogenesis by U 46619 and I-BOP was mediated by thromboxane receptors. It is concluded that thromboxane A2 generated by blood platelets at the site of vessel injury induces cell signaling in smooth muscle cells but acts as a mitogen only in the presence of growth factor(s).

Differential effects of polyunsaturated fatty acids on chemosensitivity of NIH3T3 cells and its transformants

Polyunsaturated fatty acids (PUFAs) have been suggested, on the basis of animal-model studies, to be related not only to cancer development but also to chemotherapeutic effects. Controversy persists, however, as to which types of PUFAs are beneficial in terms of chemosensitivity. In this study, we used the NIH3T3 cell line and its SIC(sigmoid colon cancer)-oncogene transformants to investigate the effects of PUFAs on the chemosensitivity of non-malignant and malignant cells in terms of cell proliferation. We also determined the fatty-acid composition of cells by high-performance liquid chromatography (HPLC). The results revealed that the sensitivity of SIC transformants to mitomycin C (MC) was lower than that of NIH3T3 cells cultured in 10% calf-serum DMEM without PUFA supplementation. When cells were cultured in DMEM supplemented with eicosapentaenoic acid (EPA) at a concentration (2 micrograms/ml) that does not influence cell proliferation, the sensitivity of SIC transformants to MC increased, whereas that of NIH3T3 cells decreased in comparison with the sensitivity of cells cultured without PUFA supplementation (p < 0.05). There was no difference between the 2 cell lines in the chemosensitivity of cells cultured in medium supplemented with arachidonic acid (ARA). The SIC transformants contained more stearic acid (C:18) and less lauric acid (C:12) than NIH3T3 cells cultured without PUFA. Culturing the cells in medium supplemented with EPA or ARA modified the cellular fatty-acid composition. EPA caused the relative combined percentage of lauric acid and myristic acid (C:14) in SIC transformants to decrease significantly, and the SIC transformants tended to accumulate additional EPA, in contrast to the NIH3T3 cells. We conclude that the alterations in fatty-acid composition in malignant transformants caused by exogenous EPA differ from those in non-malignant cells, and that these changes account for the increased chemosensitivity of malignant transformants. Although preliminary, these findings imply that EPA specifically enhances the chemosensitivity of malignant cells.