Increased expression of cytosolic phospholipase A2, 5-lipoxygenase and 5-lipoxygenase-activating protein in rat peritoneal macrophages during ovalbumin-induced sensitization.

BACKGROUND: Macrophages are involved in immediate hypersensitivity reactions by their ability to release leukotrienes involved in the symptomatology of allergy. To date it is unknown whether this ability to secrete leukotrienes has been favoured by modifications, occurring during the sensitization phase, of the enzymes involved in leukotriene metabolism. OBJECTIVE: We used ovalbumin-sensitized rats to study the expression of cytosolic phospholipase A2 (cPLA2), 5-lipoxygenase (5-LO) and 5-lipoxygenase-activating protein (FLAP) in peritoneal macrophages during active sensitization. We compared basal and challenged (PMA, A23187 and allergen) arachidonic acid (AA) metabolism of macrophages from control (cPM) and sensitized (sPM) rats. Then we tested, in cultured cPM, whether IL-4, the predominant cytokine of sensitization process, could reproduce the enzymatic modifications occurring in macrophages during sensitization. METHODS: cPLA2, 5-LO and FLAP expression was assessed by Western blotting. The arachidonic acid (AA) metabolism study was performed after incorporation of tritiated AA in macrophages and analysis of secreted tritiated eicosanoids. RESULTS: Ovalbumin-sensitization of rats increased cPLA2, 5-LO and FLAP expression in peritoneal macrophages. These increased expressions were not paralleled by modifications of basal and PMA- or A23187-stimulated AA metabolism of sPM. However, when macrophages encountered the specific allergen for a second time, sPM secreted higher levels of leukotrienes than cPM. IL-4 induced FLAP expression in cPM but had no effect on cPLA2 and 5-LO expression. CONCLUSION: Active sensitization of rats induces an increase, in peritoneal macrophages, of the enzymes involved in leukotriene metabolism. The increased leukotriene secretion of sPM in response to ovalbumin challenge may be favoured by this increased expression of cPLA2, 5-LO and FLAP that, however, is not able to lead to modifications of macrophage AA metabolism in any circumstance. Our results also suggest that IL-4 is not the major element originating the enzymatic modification induced by sensitization in peritoneal macrophages.

Contrasting effect of interleukin-4 on the expression of cytosolic phospholipase A2, 5-lipoxygenase and 5-lipoxygenase-activating protein in peritoneal macrophages from control and ovalbumin-sensitized rats.

Interleukin-4 (IL-4), which has been widely described as an anti-inflammatory cytokine, can also exert proinflammatory effects. In this study, we extend these findings to demonstrate, in an allergic model, the dual effect of IL-4 on arachidonic acid (AA) metabolism in macrophages. In peritoneal macrophages from control rats (cPM), IL-4 had no effect on cPLA2 and 5-LO expression, but increased FLAP expression without affecting basal and A23187- or PMA-challenged arachidonic acid (AA) metabolism. In contrast, in peritoneal macrophages from ovalbumin-sensitized rats (sPM), IL-4 decreased cPLA2, 5-LO and FLAP expression and PMA-challenged eicosanoid production. A23187-challenged AA metabolism of sPM was not affected by IL-4 pretreatment. Thus, IL-4 acts differently on cPLA2, 5-LO and FLAP expression and AA metabolism in peritoneal macrophages depending on their resident or sensitization-induced differentiated status.

Nonstructural 3 protein of hepatitis C virus triggers an oxidative burst in human monocytes via activation of NADPH oxidase.

It has been shown that oxidative stress occurs in chronic hepatitis C. Release of reactive oxygen species (ROS) from sequestered phagocytes and activated resident macrophages represents the predominant component of oxidative stress in the liver. However, little is known about the ability of the monocyte to produce ROS in response to protein of hepatitis C virus. In this study, we investigated the ROS production in human monocytes stimulated by several viral proteins of hepatitis C virus. Human monocytes from healthy blood donors were incubated with recombinant viral protein: Core, NS3, NS4, and NS5. ROS production was measured by chemiluminescence. Only NS3 triggered ROS production in human monocytes. Generated ROS were mainly the anion superoxide. NS3 also induced a rapid and transient increase in intracellular calcium concentration measured by a video digital microscopy technique. By using different metabolic inhibitors, we showed that ROS production requires calcium influx, tyrosine kinases, and the stress-activated protein kinase, p38. The study of p47(PHOX) phosphorylation and translocation showed that NADPH oxidase was activated and involved in ROS production induced by NS3. In a second experiment, NS3 inhibited the oxidative burst induced by phorbol 12-myristate 13-acetate. These results indicate that NS3 activates NADPH oxidase and modulates ROS production, which may be involved in the natural history of hepatitis C infection.

Study of host- and virus-related factors associated with spontaneous hepatitis C virus clearance.

Epidemiologic parameters, virologic characteristics and frequency of HLA class II DR and DQ antigens were compared between 63 subjects with spontaneous hepatitis C virus clearance (group 1) and 282 patients with chronic active hepatitis C virus infection (group 2). DRB1*1101 and moreover DQB1*0301 alleles were more frequent in group 1 than in group 2 (33.8% vs. 14.7% and 64.4% vs. 28.6%; P=0.012 and P=0.003, respectively). The frequency of DQB1*02 was lower in group 1 than in group 2 (25.4% vs. 49%; P=0.04). No difference was observed in viral genotype distribution between group 1 and group 2. Univariate analysis showed that female sex and contamination by intravenous drug use were associated with self limited infection. However, by multivariate analysis, the only independent factor associated with hepatitis C virus RNA clearance was female sex (P=0.004). In conclusion, spontaneous hepatitis C virus RNA clearance is determined by class II antigens (mainly DQB1*0301) and female sex, while viral genotype plays no role.

Reactive oxygen intermediates and eicosanoid production by kupffer cells and infiltrated macrophages in acute and chronic liver injury induced in rats by CCl4.

OBJECTIVE AND DESIGN: The aim of the present study was to characterize during acute and chronic liver injury induced by CCl4, macrophage phenotypes and whether a change in reactive oxygen intermediates (ROI) and eicosanoids production by Kupffer cells (KC) was observed. MATERIAL AND METHODS: Liver steato-necrosis and cirrhosis were induced in rats after 3 weeks and 9 weeks of CCl4 intoxication, respectively. Monocytes and tissue macrophages were identified by immunohistochemical study using monoclonal antibodies ED-1 and tissue macrophages using the antibody ED-2. The release of ROI and eicosanoids in response to the phorbol ester TPA (protein kinase activator) and to the calcium ionophore A23187 was assessed in cultivated cells. RESULTS: As compared to healthy controls, livers of rats with steato-necrosis or cirrhosis exhibited a significant increase of ED-1 and ED-2 positive cells. Only KC from rats with liver steato-necrosis were found to have higher A23187, TPA + A23187 or opsonized zymosan induced ROI production than healthy controls (p < 0.01). After TPA + A23187 or opsonized zymosan stimulation, KC from both rats with steato-necrosis or cirrhosis produced more TxB2 and leukotrienes and less PGE2 as compared to healthy controls (p <0.05). CONCLUSIONS: These results suggest an influx of monocytes into the liver during acute and chronic injury induced by CCl4. Functional changes of this inflammatory infiltrate have been demonstrated with an increase of ROI production only in the early stage of liver injury whereas a rise in KC leukotriene production and an imbalance between cytoprotective and cytotoxic prostanoids were observed at all stages of liver disease.

Expression of TNF-alpha and immunohistochemical distribution of hepatic macrophage surface markers in carbon tetrachloride-induced chronic liver injury in rats.

In liver injury induced by carbon tetrachloride, secondary hepatic injury occurs from inflammatory processes originating from products released by activated Kupffer cells, which play a central role in hepatic inflammation. The purpose of our study was to demonstrate, in rats, the relationships between a function of the hepatic macrophages, TNF-alpha production and the state of activation of these cells, characterized by their phenotype, in the different phases of the process and development of fibrosis in a carbon tetrachloride-induced cirrhosis model. The immunohistochemical localization of proinflammatory cytokine TNF-alpha and surface surface makers (ED1 and ED2) was studied in hepatitis and cirrhosis in response to 3 and 9 weeks ingestion of carbon tetrachloride. After carbon tetrachloride ingestion, accompanying the increased necrosis, immunohistochemical analysis of liver tissue sections demonstrated the significantly increased number of cells expressing ED1, ED2 and TNF-alpha, compared to normal. The number of cells expressing the surface phenotypic markers of liver macrophages increased and this change was concomitantly associated with an increased cellular expression of TNF-alpha. Local macrophage proliferation and influx of newly recruited blood monocytes resulted in an increase of the macrophage population. The populational changes involved difference in functional activity and enhanced TNF-alpha expression. This cytokine expressed in the carbon tetrachloride-induced inflammatory process is associated with the development of fibrosis and may contribute to disease severity.

IL-13 increases the cPLA2 gene and protein expression and the mobilization of arachidonic acid during an inflammatory process in mouse peritoneal macrophages.

Pretreatment of mouse peritoneal macrophages with interleukin-13 (IL-13) potentiates the mobilization of arachidonic acid (AA) and the production of HETEs but does not affect the production of cyclooxygenase metabolites triggered by the suboptimal concentration of an inflammatory agonist (opsonized-zymosan). Cycloheximide suppresses these effects of IL-13 suggesting that de novo protein synthesis is involved. Indeed, IL-13 induces a time-dependent increase in the levels of cytosolic PLA2 (cPLA2) protein and mRNA. This study demonstrates a new pathway for IL-13 to modulate the inflammatory process in macrophages via modifications of cPLA2 expression and subsequent AA mobilization.

Effect of interleukin-4 on allergen-induced arachidonic acid metabolism of rat peritoneal macrophages during immediate hypersensitivity reactions.

The aim of this study was to investigate the [3H]arachidonic acid metabolism of rat peritoneal macrophages, induced by allergen (ovalbumin) and the impact of interleukin-4 on this process. We established that ovalbumin induces an increase of [3H]arachidonic acid mobilisation from membrane lipids and of [3H]arachidonic acid catabolism, principally by the 5-lipoxygenase pathway, when the macrophages are sensitized and when serum is present. The allergen effect is not modified by the presence of interleukin-4 in the culture medium of macrophages 15 h before the allergen challenge. We also showed that, whereas the basal [3H]arachidonic acid metabolism of macrophages from control and actively sensitized rats is not different, interleukin-4 increases the [3H]arachidonic acid mobilisation and catabolism by cyclooxygenase and 5-lipoxygenase pathways in macrophages from control rats although it does not in macrophages from actively sensitized rats. In macrophages from control rats, the interleukin-4 effect is diminished by the addition of IgEs to their culture medium. In summary, interleukin-4 has an enhancer effect on the macrophage arachidonic acid catabolism that depends on the sensitization condition of the cell but that has no consequences on the further increased arachidonic acid metabolism induced by the allergen.

Involvement of calcium in macrophage leukotriene release during experimental cirrhosis.

The aim of the present study was to assess the mechanism of 5-lipoxygenase metabolites (LT) secretion by peritoneal macrophages in rats wih CC14 induced cirrhosis. After stimulation with calcium ionophore A23187 or opsonized zymosan, [3H] arachidonic acid labeled macrophages from cirrhotic rats presented a significantly greater secretion of LT than macrophages from healthy controls. In addition, the phorbol ester TPA (protein kinase C activator) increased LT production only in macrophages from cirrhotic animals and not in controls. Although Ca2+ is thought to be involved in 5 lipoxygenase activation, the role of Ca2+ in LT production was studied. The use of a Ca2+-free medium as well as the addition of TMB-8 (an inhibitor of intra-cellular Ca2+ movements and of plasma membrane Ca2+ fluxes) resulted in a fall in LT production greater for macrophages from cirrhotic animals than for controls. The measurement of cytosolic Ca2+ concentration by cytofluorimetry showed that Fluo-3 loaded macrophages from cirrhotic rats had a greater cytosolic CA2+ concentration than macrophages from control animals both in basal conditions and after A23187 stimulation. Study of 45Ca2+ uptake suggest, that extra-cellular Ca2+ is implicated in the elevated cytosolic Ca2+ observed in macrophages from cirrhotic animals as compared to healthy controls. The greater Ca2+ concentration observed in macrophages from cirrhotic rats was not related to a difference in phospholipase C activation because inositol phosphate production did not differ between macrophages from healthy and cirrhotic animals. Taken together these results suggest that as compared to healthy animals, the greater LT production during cirrhosis could be dependent upon a difference in 5-lipoxygenase activation related to a rise in cytosolic Ca2+ concentration independently of inositol phosphates generation.

Eicosanoid production by mouse peritoneal macrophages during Toxoplasma gondii penetration: role of parasite and host cell phospholipases.

The metabolism of endogenous arachidonic acid by mouse resident peritoneal macrophages infected in vitro with Toxoplasma gondii was studied. Prelabeling of macrophages with [5,6,8,9,11,12,14,15-3H]arachidonic acid and challenge with tachyzoites for 15 min resulted in a high mobilization of free labeled arachidonic acid (178%) in the culture medium. The parasites also triggered the synthesis of 6-keto-prostaglandin F1 alpha (47%), prostaglandin E2 (44%), leukotrienes C4 and D4 (33%) and 5-, 12-hydroxyeicosatetraenoic acids (155%). The study indicated that during the intracellular development phase of the parasites, 6-keto-prostaglandin F1 alpha (38%), prostaglandin E2 (31%) leukotrienes C4 and D4 (15%), hydroxyeicosatetraenoic acids (43%), and free arachidonic acid (110%) were secreted into the culture medium. Pretreatment of tachyzoites with phospholipase A2 inhibitors (4-p-bromophenacyl bromide and quinacrine) and no calcium in the culture medium resulted in inhibition of tachyzoite penetration into the macrophages and a decrease of the arachidonic acid metabolism. The triggering of the arachidonic acid cascade by T. gondii was dependent on the active penetration of the parasites into the macrophages, whereas preincubation of the macrophages with phospholipase A2 inhibitors did not affect penetration or free arachidonic acid release, thereby supporting a role for parasite phospholipase in the penetration process and in arachidonic acid mobilization from macrophage membrane phospholipids. Moreover, treatment of macrophages with phospholipase A2 inhibitors decreased the activities of the cyclooxygenase and lipoxygenase pathways, also suggesting an activation of host cell phospholipase A2 by the parasite.

Possible implication of arachidonic acid metabolism in the decrease of chemiluminescence production after exposure of murine peritoneal macrophages to diethylnitrosamine and tumour promoter, 12-O-tetradecanoylphorbol-13-acetate.

The effect of the carcinogen diethylnitrosamine (DEN) on prostaglandins (PGs), leukotrienes (LTs) and reactive oxygen intermediates production by murine peritoneal macrophages was assessed. In vitro exposure to DEN (0.8, 1.6 and 8 mM) resulted in a dose-dependent stimulation of the PGs and LTs generation by macrophages. DEN-exposed peritoneal macrophages demonstrated enhanced production of arachidonic acid (AA) metabolites following stimulation with 12-O-tetradecanoylphorbol 13-acetate (TPA) as compared to macrophages stimulated with TPA alone. Studies of [3H]AA release from glycerolipids of prelabelled macrophages and of the distribution of AA metabolites between intra and extracellular compartments indicated that DEN induced de novo synthesis of AA metabolites. The stimulation of AA metabolism by DEN was decreased by H-7 and staurosporine, protein kinase C (PKC) inhibitors, and so could be dependent on PKC activation. The generation of PGs by macrophages after DEN exposure was also inhibited by indomethacin (cyclo-oxygenase inhibitor). DEN at high concentrations (1.6-16 mM) inhibited chemiluminescence production by peritoneal macrophages in a dose-dependent manner, triggered by tumour promoter TPA; lower concentrations (0.8 and 1.2 mM) increased this reactive oxygen intermediates dependent chemiluminescence production induced by TPA. The role of AA metabolism in the alteration of chemiluminescence production by murine peritoneal macrophages treated in vitro with DEN and triggered by TPA has been evaluated by using AA metabolism inhibitors. The stimulation of chemiluminescence by TPA was inhibited by the addition of phospholipase A2 (PLA2) inhibitor, 4-p-BPB; this metabolic inhibitor did not affect the decrease of chemiluminescence production induced by DEN. The cyclo-oxygenase (CO) inhibitor, indomethacin, reversed the inhibition of TPA-induced chemiluminescence caused by DEN. These results suggest that AA and/or a lipoxygenase product can potentiate the reactive oxygen intermediates production by macrophages stimulated by TPA. The CO pathway could be involved in the inhibition by DEN of the reactive oxygen intermediates generating enzyme system. It is suggested that this inhibition could be related to AA metabolites issued from the CO pathway or to DEN oxygenated metabolites issued from the co-oxidation of the DEN by the PGs endoperoxide synthase. These results also raise the problem of macrophage dysfunction by chemical carcinogens and the implication of the CO pathway in this process.

The lavage fluid from a patient with alveolar proteinosis inhibits the in vitro chemiluminescence response and arachidonic acid metabolism of normal guinea pig alveolar macrophages.

Pulmonary alveolar proteinosis is characterized by the accumulation of a lipoproteinaceous material within the alveoli of the lung. It is well established that patients with pulmonary alveolar proteinosis have a high incidence of complicating pulmonary infections possibly resulting from defects of antibacterial functions of alveolar macrophages. Moreover, for unclear reasons, an inflammatory response in the airways is frequently absent. In order to investigate the role of the lipoproteinaceous material in these two patterns, we tested the in vitro effects of a lavage fluid from a human pulmonary alveolar proteinosis on the secretion of reactive oxygen intermediates and arachidonic acid metabolites by normal guinea pig alveolar macrophages. After incubation with the lipoproteinaceous material, the luminol-enhanced chemiluminescence of zymosan-triggered alveolar macrophages was reduced in a dose-dependent fashion. The lipoproteinaceous material similarly reduced the chemiluminescence response in a cell-free xanthine-xanthine oxidase system generating superoxide anions. This latter observation suggests that the lipoproteinaceous material acts as a scavenger for superoxide anions produced by alveolar macrophages. Its purified protein or phospholipid fractions also resulted in a general inhibition of the secretion of arachidonic acid metabolites by alveolar macrophages challenged in vitro with zymosan. Our results suggest that the alveolar filling material of pulmonary alveolar proteinosis may inhibit the action of antibacterial and/or proinflammatory agents produced by alveolar macrophages. We speculate that such effects of the lipoproteinaceous material may play a role in vivo in the high incidence of pulmonary infections and in the absence of discernible interstitial or intraalveolar inflammation seen in pulmonary alveolar proteinosis.

[Effects of cotrimoxazole on some macrophage functions: microbicide, tumoricide, production of free oxygen radicals, prostaglandins and leukotrienes]. / Effets du cotrimoxazole sur certaines fonctions de macrophages: microbicidie, tumoricidie, production de radicaux libres oxygénés, de prostaglandines et de leucotriènes.

In order to demonstrate an immunomodulating effect of cotrimoxazole, we investigated its influence on some macrophage (M phi) functions in culture: P815 tumor cells killing, Toxoplasma gondii killing, production of free oxygen radicals by luminol-dependent chemiluminescence, prostaglandins and leukotrienes secretion evaluated after incorporation of tritiated arachidonic acid. In vitro, cotrimoxazole inhibited in a dose-dependent fashion the chemiluminescence of murine resident peritoneal or guinea pig alveolar M phi. Production of prostaglandin (PG) 6-keto-F1 alpha, PGF2 alpha, and 5-hydroxyeicosatetraenoic acid by resident peritoneal M phi was also inhibited. However, PGD2 synthesis by alveolar M phi was enhanced. A second study was performed on peritoneal M phi, resident or elicited in vivo by one intra-peritoneal injection of an extract from Mycobacterium Tuberculosis membranes and obtained from mice pretreated or not by cotrimoxazole per os. Resident M phi from cotrimoxale-treated animals showed increased production of leucotriene B4 compared to M phi from controls. 6-keto-PGF1 alpha and free oxygen radicals production by elicited M phi was greatly enhanced by cotrimoxazole whereas thromboxane B2 was reduced. Finally cotrimoxazole enhanced intracellular killing of Toxoplasma gondii and cytotoxicity for tumor cells P815 by resident but not by elicited M phi. It is concluded that cotrimoxazole can modulate MO activation and some M phi functions involved in immune homeostasis. This data could help to understand why an antibiotic such as cotrimoxazole, which is known to be frequently used in immunocompromised hosts, is also efficient in Wegener's granulomatosis.

1-naphthyl N-methyl carbamate effect on intra- and extracellular concentrations of arachidonic acid metabolites, and on the chemiluminescence generation by mouse peritoneal macrophages.

1-Naphthyl N-methyl carbamate (carbaryl), potent carbamate insecticide with anticholinesterase activity, was tested for its ability to affect mouse peritoneal macrophages in particular arachidonic acid (AA) metabolism and oxidative burst. Carbaryl inhibited in a dose-related manner the reactive oxygen intermediate dependent chemiluminescence (CL) induced by opsonized zymosan (OZ), 12-O-tetradecanoyl phorbol-13-acetate (TPA) and calcium ionophore (A23187); this carbamate did not affect CL-mediated by AA. The intracellular and extracellular concentrations of prostaglandins (PGs) and 5-hydroxyeicosatetraenoic (5-HETE) generated in macrophages stimulated with OZ has been investigated for various periods. Carbaryl effect displayed two successive phases on AA metabolism stimulation. In a first phase (up to 2-15 min), carbaryl did not alter the rapid AA metabolite synthesis (total amount of intra- and extracellular metabolites) but it increased intracellular concentration of PGE2, PGA2, PGF2 alpha and decreased 5-HETE intracellular concentration. In a second phase (after 2-15 min), carbaryl inhibited AA metabolite synthesis. The release of cyclooxygenase (CO) and lipoxygenase (LO) metabolites decreased, in particular PGF2 alpha and PGD2 which in addition seemed to be submit to a cellular retention; the inhibition of other metabolite release appeared essentially related to the inhibition of their synthesis since the intracellular amount did not augment. The inhibition by carbaryl of the NADPH-oxidase dependent CL induced by OZ may be related to the alteration of the intra- and extracellular concentrations of AA metabolites.

Chemiluminescence response and arachidonic acid metabolism of macrophages induced by gamma-hexachlorocyclohexane (lindane).

The influence of gamma-hexachlorocyclohexane (gamma-HCCH) on arachidonic acid (AA) metabolism and oxygen metabolite production was investigated on mouse peritoneal macrophages gamma-HCCH stimulated 6KPGF1 alpha, PGE2, LTC4, LTB4 and HETEs production and increased the luminol-dependent chemiluminescence (CL). Lindane acted synergistically with phorbol ester on prostaglandins-leukotrienes (PGs-LTs) and CL production. Similar stimulation of CL and PGs-LTs production was found after challenge by the calcium ionophore A23187. The implication of calcium mobilization in lindane effects was proposed.

Lipid peroxidation in rat liver microsomes: influence of carcinogenic N-nitrosocarbaryl.

The reactivities of carbaryl, N-methyl 1-naphthylcarbamate insecticide and its N-nitrosated derivative carcinogenic, N-nitrosocarbaryl, were investigated on the microsomal hepatic lipid peroxidation and NADPH-dependent reductase activities. The in vivo treatment by N-nitrosocarbaryl produced a reduction in lipoperoxidative degradation induced in vitro by NADPH with regard to the formation of malonaldehyde and conjugated dienes. Carbaryl, its precursor did not affect lipid peroxidation under the same in vivo conditions. Moreover, following administration of the 2 compounds, the activities of NADPH-cytochrome c reductase as well as NADPH-neotetrazolium reductase were significantly decreased by N-nitrosocarbaryl but not influenced by carbaryl. Correspondingly, in vitro studies were performed; different action patterns of the 2 tested xenobiotics were also noted after treatment of rat liver microsomes in vitro by carbaryl and N-nitrosocarbaryl especially in their ability to cope with microsomal oxygen activation. N-Nitrosocarbaryl proved to have a potent inhibitor concentration effect on NADPH-dependent chemiluminescence response in vitro; carbaryl was virtually ineffective on this parameter. No significant difference appeared in the affinity of N-nitrosocarbaryl and carbaryl for the microsomal phospholipids. From the in vitro explorations, it was suggested that carcinogenic N-nitrosocarbaryl may be involved in the inhibition mechanism of microsomal lipid peroxidation through decreases in both NADPH-dependent reductase activities and superoxide generation.

Interaction of carbaryl and N-nitrosocarbaryl with microsomal monooxygenase activities.

The in vitro interactions of carbaryl and carcinogenic N-nitrosocarbaryl with rat liver microsomal monooxygenase activities are compared. The inhibitory effect of the nitroso-compound is demonstrated to be non-competitive on aminopyrine N-demethylase, p-nitroanisole O-demethylase and aniline hydroxylase. The nature of the inhibition induced by the parent amide is found to be competitive on aminopyrine N-demethylase and p-nitroanisole O-demethylase. Correspondingly, in vitro studies of the metabolism of the two compounds were carried out: they both yield formaldehyde. Moreover, N-nitrosocarbaryl is denitrosated through a NO-cytochrome P-450 complex during microsomal metabolism. The toxic effects and biological activities of the two compounds are discussed on the basis of data of metabolic studies and different patterns of enzyme inhibition.

In vitro influence of molybdenum on benzo[a]pyrene metabolism in hepatic and pulmonary rat microsomes.

Our study presents the in vitro molybdenum influence on benzo[a]pyrene (BaP) microsomal metabolism. Addition of various concentrations of different molybdenum salts [MoS2, MoCl5, (NH4)6Mo7O24 . 4H2O] to liver and lung microsomal fractions of rats previously treated with 3-methylcholanthrene produces a decrease in the different BaP metabolites assessed by high-performance liquid chromatography (HPLC) analysis. This inhibition varies, depending on the considered metabolite and in relation to both the molybdenum level and the origin of the microsomal suspension. The minimum effective concentration is 0.26 and 0.52 mM Mo from liver and lung, respectively. The inhibitory potencies of the +5 (chloride) and +6 (ammonium heptamolybdate) molybdenum compounds are comparable; that of the sulfide is lower.

The effect of carbaryl on the arachidonic acid metabolism and superoxide production by mouse resident peritoneal macrophages challenged by zymosan.

Carbaryl, a broad spectrum insecticide with anticholinesterase activity, was tested for its ability to disturb resident peritoneal macrophages stimulated by opsonized zymosan. The effect of carbaryl on superoxide production and on the release of [1-14C] arachidonic acid and 14C-labelled prostaglandins was dose-dependent. For 2.5 X 10(-6) M of carbaryl, superoxide production and prostaglandin release were not significantly inhibited. At 12.5 X 10(-6) M, the inhibitory effect was apparent for superoxide production (33%) and for the release of 6 KPGF1 alpha (60%), PGE2 (42%), PGF2 alpha (38%), PGD2 (33%). Carbaryl had no effect on the level of free arachidonic acid. Insecticide at 12.5 X 10(-6) M significantly decreased the deacylation of the phosphatidylcholine (20%). Incubation of resident peritoneal macrophages with indomethacin studied conjointly decreased only the prostaglandin release. These results suggest that carbaryl decreases the sequence of events following the binding of a particulate agent to its receptor and leading to the induction of phospholipase activity and the subsequent release of 20:4 and the oxidative burst in the cells. The effect of this pesticide on phospholipid metabolism and its consequences on macrophage stimulation are discussed. Ecto-serine esterase inhibition in the effect mechanism of the pesticide was suggested.