Marisabel Mourelle

L-arginine: nitric oxide pathway in endotoxemia and human septic shock.

OBJECTIVE To investigate the relationship between nitric oxide production, endotoxemia, and hemodynamic alterations in human septic shock. DESIGN Prospective study. SETTING A 32-bed intensive care unit in a university referral hospital. PATIENTS Two groups of septic patients with shock (n = 13) or without shock (n = 16) and an additional group of nonseptic patients as control group (n = 25). MEASUREMENTS Plasma nitrite and nitrate concentrations were measured as an index of nitric oxide generation. Nitrite and nitrate concentrations were correlated with plasma endotoxin and hemodynamic variables. MAIN RESULTS Increased plasma nitrite and nitrate concentrations were found in patients with septic shock (p < .01). Nitrite and nitrate correlated directly with endotoxin concentration (r2 = .21, p < .05) and cardiac output (r2 = .49, p < .05), and inversely with systolic blood pressure (r2 = .24, p < .01). CONCLUSIONS This study demonstrated the activation of the L-arginine:nitric oxide pathway in human endotoxemic septic shock, suggesting that nitric oxide may be an important mediator of the hemodynamic disturbances in this pathophysiologic situation.

PREVENTION OF CCL4‐INDUCED LIVER CIRRHOSIS BY SILYMARIN

Summary— The efficacy of silymarin treatment in preventing biochemical and histological alterations in CCl4‐induced liver cirrhosis in rats was studied. Four groups of rats were treated with: (1) CCl4; (2) mineral oil; (3) CCl4 + silymarin; and (4) silymarin. All animals were sacrificed 72 h after the end of treatments. The activities of alkaline phosphatase (alk. phosp.), gamma‐glutamyl transpeptidase (GGTP), glutamic pyruvic transaminase (GPT) and glucose‐6‐phosphatase (G6Pase), and bilirubin content were determined in serum. Na+, K+‐ATPase and Ca++‐ATPase activities were measured in isolated plasma membranes. Lipoperoxidation, triglycerides (TG), and glycogen contents were also measured in liver homogenates.

Induction of nitric oxide synthase in colonic smooth muscle from patients with toxic megacolon.

BACKGROUND & AIMS Colonic inflammation may lead to motility disturbances, including severe atony. Nitric oxide is released by inflamed tissue and induces smooth muscle relaxation. The aim of this study was to analyze NO generation pathways in colonic tissue from patients who had ulcerative colitis with or without toxic megacolon and in tumor-free samples from patients with colonic neoplasm. METHODS Enzymatic activity was determined by transformation of [14C]arginine to [14C]citrulline in mucosa and muscular layer samples. Immunostaining of tissue sections with antibody against inducible NO synthase was investigated. The effects of endotoxin on NO synthase activity was tested in muscle strips from human colon. RESULTS Ca(2+)-independent NO synthase was undetectable or very low in muscularis propria from tumor and colitis controls. In contrast, specimens from patients with toxic megacolon had high activity (P < 0.05). Positive immunostaining for inducible NO synthase was found in muscular layers from patients with megacolon but not in tumor and colitis controls. Finally, endotoxin induced Ca(2+)-independent NO synthase activity in colonic muscle. CONCLUSIONS Toxic megacolon is associated with the appearance of inducible NO synthase in the colonic muscularis propria. Local generation of excessive amounts of NO may be responsible for the colonic dilatation that is the hallmark of this syndrome.

Stimulation of transforming growth factor β1 by enteric Bacteria in the pathogenesis of rat intestinal fibrosis

BACKGROUND & AIMS Bacteria and their products stimulate inflammatory responses. Certain mediators, such as transforming growth factor beta1 (TGF-beta1), induce collagen synthesis. Excess collagen deposition results in bowel strictures. The aim of this study was to investigate the role of bacteria and TGF-beta1 in the pathogenesis of intestinal fibrosis. METHODS In rats with colitis, the effects of bowel decontamination with antibiotics on TGF-beta1, tumor necrosis factor alpha (TNF-alpha), and collagen content in colonic tissue were studied. In normal rats, bacteria of the predominant flora were inoculated into the colonic wall. The effect of neutralizing antibody to TGF-beta1 on tissue collagen deposition was studied. RESULTS Rats with chronic colitis showed increased levels of TGF-beta1, TNF-alpha, and collagen in the tissue and a high rate of bowel strictures. Antibiotic treatment significantly prevented the increase in TGF-beta1 and collagen and the formation of strictures. Inoculation of bacterial suspensions into the colonic wall increased tissue TGF-beta1 and collagen content. Neutralizing antibody to TGF-beta1 prevented collagen deposition. Colonic wall inoculations with single anaerobic strains (Clostridium ramosum, Bacteroides fragilis, and Bacteroides uniformis), but not with aerobes, induced collagen deposition. CONCLUSIONS Certain strains of the common flora stimulate TGF-beta1 and induce deposition of collagen in the colonic wall.

Regulation of gall bladder motility by the arginine-nitric oxide pathway in guinea pigs.

Nitric oxide (NO) synthesised from L-arginine is an intercellular messenger in various biological actions including endothelial dependent relaxation and inhibition of platelet aggregation. This study explored the role of the L-arginine-NO pathway in the regulation of gall bladder motility. Intraluminal gall bladder pressure was recorded in anaesthetised guinea pigs in response to cholecystokinin or bethanechol before and after treatment with specific NO synthase inhibitors (NG-nitro-L-arginine, NG-nitro-L-arginine methyl ester, or NG-monomethyl-L-arginine), or with an NO donor (sodium nitroprusside). Baseline gall bladder pressure significantly increased after treatment with the NO synthase inhibitors. Responses to cholecystokinin (0.025-1.25 nmol/kg) were significantly enhanced after treatment with NG-nitro-L-arginine methyl ester and lasted two to threefold longer than in control experiments. The effect of the inhibitor both on resting pressure and on cholecystokinin induced changes was reversed by L-arginine but not by D-arginine. Pretreatment with the inhibitors also induced a significant enhancement of the response to bethanechol. On the other hand, sodium nitroprusside abolished the response to low dose cholecystokinin and reduced the response to a high dose by about 80%. In vitro experiments with isolated gall bladder strips showed a significant enhancement of the contractile response to cholecystokinin or bethanechol after preincubation with the NO synthase inhibitor. Calcium dependent activity of NO synthase was detected in fresh homogenates from gall bladder tissue and incubation with endotoxin induced considerable calcium independent activity. These findings support the existence of a key L-arginine-nitric oxide pathway regulating gall bladder contraction.

Colchicine prevents D-galactosamine-induced hepatitis.

The hepatoprotective effect of colchicine in a model of liver intoxication with galactosamine (GalN), 375 mg/kg, i.p., was studied in rats. At 0.5, 1, 3, 6, 18 and 24 h after GalN intoxication the following markers of liver damage were measured: serum activity of alanine aminotransferase, alkaline phosphatase, gamma-glutamyltranspeptidase, hepatic calcium and glycogen contents, liver lipoperoxidation, and liver plasma membrane activity of alkaline phosphatase, gamma-glutamyltranspeptidase and high-affinity Ca2+-ATPase. 24 h after GalN intoxication increases in serum levels of alanine aminotransferase, alkaline phosphatase and gamma-glutamyltranspeptidase were observed along with decreases in plasma membrane activities of alkaline phosphatase, gamma-glutamyltranspeptidase, and high-affinity Ca2+-ATPase. A sharp increase of lipoperoxidative processes measured as malondialdehyde production was also observed. Pretreatment of rats with colchicine 10 micrograms/rat/day p.o. for 7 days before GalN injection prevented partially the toxic effects of GalN. When a dose of 50 micrograms/rat/day for 7 days was given the drug prevented almost completely the damage induced by galactosamine, with the exception of glycogen and serum alkaline phosphatase that remained different from controls. Time-course experiments showed that malondialdehyde formation increased 30 min after intoxication while all other changes became apparent from 6 h after treatment, suggesting that lipoperoxidation may be a prerequisite for galactosamine-induced damage. The protection offered by colchicine was related to its capacity to inhibit lipoperoxidation. Histochemical findings paralleled the biochemical results. The possible role of lipoperoxidation in galactosamine-induced liver damage is discussed.

Characterization of membrane fraction lipid composition and function of cirrhotic rat liver: Role of S-adenosyl-l-methionine

The effect of S-adenosyl-L-methionine (SAM) administration on the lipid composition of the membrane fraction obtained from livers of cirrhotic rats was studied. Four groups of animals were used: group 1 received CCl4 for 8 weeks to induce cirrhosis. Animals in group 2 received 3 daily i.m. injections of SAM 20 mg/kg in addition to CCl4. Groups 3 and 4 were control groups of SAM and vehicles. Seventy-two h after the end of treatment all animals were killed and livers were studied to measure glycogen, cAMP contents and to isolate membrane fractions. The membrane activity of Na+,K(+)- and Ca(2+)-ATPases was measured and the lipid content was analyzed in extracts. Phospholipids were determined by thin-layer chromatography and fatty acids by gas chromatography. Chronic CCl4 treatment led to increases in cholesterol and in the cholesterol/phospholipid ratio. Analysis of phospholipids revealed an increase in phosphatidylserines. Saturated fatty acids increased, while unsaturated decreased significantly. The CCl4-treated group showed a decrease in glycogen and an increase in cAMP contents. Na+,K(+)- and Ca(2+)-ATPases activity were highly reduced in cirrhotic membranes. In the group receiving CCl4 + SAM the lipid composition and the function of liver membrane fraction showed no difference compared to normal controls, except for fatty acid composition which was similar to concentrations in the CCl4-treated group. Glycogen depletion was only partially prevented whereas cAMP levels were normalized in the CCl4 + SAM group. Our results showed that membrane lipid alterations were accompanied by changes in the activity of enzymes embedded in the membrane fraction derived from CCl4-cirrhotic rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Protective effect of colchicine on acute liver damage induced by carbon tetrachloride.

Pretreatment of rats with colchicine (10 micrograms/day) for 7 days protected against CCl4-induced acute liver damage. CCl4 intoxication was demonstrated histologically and by increased serum activities of glutamic-pyruvic transaminase, alkaline phosphatase and gamma-glutamyl transpeptidase. Furthermore, an increase in liver lipid peroxidation and a decrease in plasma membrane gamma-glutamyl transpeptidase activity were found. Colchicine increased the LD50 of CCl4 2.5-fold and prevented the release of intracellular enzymes, as well as the decrease in gamma-glutamyl transpeptidase activity in the plasma membrane. It also completely prevented the lipid peroxidation produced by CCl4 and limited the extent of the histological changes. Our results suggest that the protective effect of colchicine may be mediated through its action on an early toxic event, because treatment of the animals with colchicine produced a significant decrease in CCl4-induced lipid peroxidation.

Erythrocyte defects precede the onset of CCl4-induced liver cirrhosis. Protection by silymarin

The time-course of some alterations produced in erythrocytes during the onset of CCl4-induced liver cirrhosis was studied in rats. Erythrocyte membranes were isolated to measure Na+, K+ and Ca+2-ATPase activities. Membrane lipid composition was determined to calculate the cholesterol/phospholipid ratio and serum samples were used to measure lipoperoxidation. The results demonstrated that as CCl4 treatment progressed, serum lipoperoxidation and membrane cholesterol/phospholipid ratio increased while ATPase activities decreased. ATPase activities in red blood cells of cirrhotic rats were 50% below normal values but those determined in cells of animals treated simultaneously with CCl4 + silymarin were significantly improved. Silymarin co-treatment also preserved the normal cholesterol/phospholipid ratio in the membranes. Our results suggest that the measure of ATPase activities in erythrocytes membranes could be a simple, safe and useful early marker of liver damage and also valuable to test the effectiveness of a given drug therapy.

Sea urchin sperm head plasma membranes: characteristics and egg jelly induced Ca2+ and Na+ uptake

Sea urchin sperm respond to egg factors with changes in the ionic permeability of their plasma membrane. It has been previously shown that plasma membranes isolated preferentially from sea urchin sperm flagella respond to egg jelly increasing their Ca2+ and Na+ uptake (Darszon et al. (1984) Eur. J. Biochem. 144, 515-522). However, the egg jelly induced acrosome reaction occurs in the sperm head, and there is evidence for an heterogeneous distribution of plasma membrane components within the various regions of this cell. We here report a method for purifying sperm head membranes using positively charged beads according to Jacobson (1977) Biochim. Biophys. Acta 471, 331-335). Under the transmission electron microscope these membranes appeared homogeneous and apparently free of internal membranes. The yield of the preparation was 0.9% of the total protein in the sperm homogenate. The preparation contained less than 5% of the mitochondrial marker cytochrome oxidase, and 10% of the total DNA/mg protein. Surface labeling with 125I indicated a 2.5-3-fold enrichment in specific activity of the head membranes with respect to whole sperm. The SDS band pattern and the lipid composition of this preparation were different from those of isolated flagellar membranes. Phosphatidylcholine was higher in the head membranes, while phosphatidylserine and phosphatidylethanolamine were lower. The head membranes displayed a 1.7-2.3-fold higher Ca2+-ATPase activity and a 2.5-fold lower Na+/K+-ATPase activity, than the flagellar membranes. These results are consistent with a heterogeneous distribution of membrane components along the sea urchin sperm plasma membranes. Isolated head membranes sonicated in the presence of soybean phospholipid liposomes responded to egg jelly with a species-specific increase in Ca2+ and Na+ uptake. As in whole sperm, Ca2+ uptake was inhibited by the Ca2+ channel blocker nisoldipine. A close analog of this compound, [3H]nitrendipine, binds with high affinity to head membranes in a saturable, reversible manner, showing a Kd and Bmax of 31 nM and 5.3 pmol/mg protein, respectively.