Phenobarbital-induced alterations in phosphatidylcholine and triglyceride synthesis in hepatic endoplasmic reticulum

Fatty acid microemulsion for the treatment of neonatal conjunctivitis: quantification, characterisation and evaluation of antimicrobial activity

Fatty acids (FAs) are used by many organisms as defence mechanism against virulent bacteria. The high safety profile and broad spectrum of activity make them potential alternatives to currently used topical antibiotics for the treatment of eye infections in neonates. The current study utilised a Design of Experiment approach to optimise the quantification of five fatty acids namely; lauric acid, tridecanoic acid, myristoleic acid, palmitoleic acid and α-linolenic acid. The significance of the influence of the experimental parameters such as volume of catalyst, volume of n-hexane, incubation temperature, incubation time and the number of extraction steps on derivatisation was established by statistical screening with a factorial approach. Derivatisation was confirmed using attenuated total reflectance infrared (ATR) and 1H NMR spectrum. A gas chromatographic method (GC-FID) was developed and validated according to ICH guidelines for the identification and quantification of fatty acids. The results were found to be linear over the concentration range studied with coefficient of variation greater than 0.99 and high recovery values and low intra-day and inter-day variation values for all FAs. Then, different α-linolenic acid-based microemulsions (MEs) were prepared using Tween 80 as surfactant, polyethylene glycol 400 (PEG 400) as co surfactant and water as aqueous phase. The developed GC method was used to quantify the FA content in ME formulations. The results indicated that the developed GC method is very effective to quantify the FA content in the ME formulations. The antimicrobial efficacy of FA-based MEs were tested against Staphylococcus aureus. It was concluded that the FA-based MEs have strong antimicrobial effect against S. aureus.

Cytochrome P450 Organization and Function Are Modulated by Endoplasmic Reticulum Phospholipid Heterogeneity

Cytochrome P450s (P450s) comprise a superfamily of proteins that catalyze numerous monooxygenase reactions in animals, plants, and bacteria. In eukaryotic organisms, these proteins not only carry out reactions necessary for the metabolism of endogenous compounds, but they are also important in the oxidation of exogenous drugs and other foreign compounds. Eukaryotic P450 system proteins generally reside in membranes, primarily the endoplasmic reticulum or the mitochondrial membrane. These membranes provide a scaffold for the P450 system proteins that facilitate interactions with their redox partners as well as other P450s. This review focuses on the ability of specific lipid components to influence P450 activities, as well as the role of the membrane in P450 function. These studies have shown that P450s and NADPH-cytochrome P450 reductase appear to selectively associate with specific phospholipids and that these lipid-protein interactions influence P450 activities. Finally, because of the heterogeneous nature of the endoplasmic reticulum as well as other biologic membranes, the phospholipids are not arranged randomly but associate to generate lipid microdomains. Together, these characteristics can affect P450 function by 1) altering the conformation of the proteins, 2) influencing the P450 interactions with their redox partners, and 3) affecting the localization of the proteins into specific membrane microdomains.

The dynamic ER: experimental approaches and current questions

The endoplasmic reticulum (ER) is an extremely plastic and dynamic organelle. Its size and shape can undergo drastic changes to meet changing demands for ER-related functions, or as a response to drugs or pathogens. Because of the ER's key functions in protein and lipid synthesis, this organelle is a hotbed of detailed molecular analysis.

Changes by progesterone derivatives in fatty acids from phosphatidylcholine and phosphatidylethanolamine fractions in rat liver endoplasmic reticulum

The effects of two progesterone metabolites on fatty acid composition of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) from total liver and liver microsomes were studied in female rats. 16 alpha-Hydroxyprogesterone significantly increased the amount of fatty acids esterified to PC and PE fractions in total liver and liver microsomes. Both saturated and unsaturated fatty acyl components were enhanced. In contrast, 5 beta-pregnan-3 alpha-ol-20-one caused a reduction of fatty acids bound to PC and PE fractions from total liver and liver microsomes. Pregnanolone decreased both saturated and unsaturated fatty acids. Changes in specific fatty acids occurred in palmitic and stearic acids among saturated components, and palmitoleic, oleic, linoleic, eicosatrienoic, arachidonic and docosahexenoic acids among unsaturated ones. The unsaturated: saturated fatty acid ratio was raised by 16-alpha-hydroxyprogesterone and lowered by 5 beta-pregnan-3 alpha-ol-20-one in all phospholipid fractions. The induction of drug metabolizing enzymes by 16 alpha-hydroxyprogesterone may be related to an enhanced synthesis of microsomal phospholipids containing unsaturated fatty acids, particularly arachidonic and docosahexenoic acids. In contrast, the inhibition of drug metabolism by 5 beta-pregnan-3 alpha-ol-20-one is associated with reduced formation of unsaturated fatty acyl side chains.

The effect of chronic ritanserin and clorgyline administration on 5-HT2 receptor linked inositol phospholipid hydrolysis

We have previously shown that chronic administration of the 5-hydroxytryptamine (5-HT) receptor antagonist, ritanserin (10 mg/kg/day) or the monoamine oxidase type A inhibitor (MAOI), clorgyline (2 mg/kg/day), results in a reduction in 5-HT2 receptor number in rat cerebral cortex. This study investigates the effects of acute and chronic ritanserin administration, on 5-HT2 receptor linked inositol phospholipid hydrolysis in rat cortical slices and compares it with the effect of a chronic clorgyline regimen. [3H]Myo-inositol (50 microCi) was used to label inositol phospholipids. Their subsequent hydrolysis in the presence or absence of 5-HT was determined by the accumulation of [3H]myoinositol monophosphate ([3H]InsP). Addition of 5 nM ritanserin to slices had no effect on basal or 5-HT stimulated [3H]InsP accumulation whereas 100 nM ritanserin blocked the stimulated response by 65%. Acutely, ritanserin (15 mg/kg i.p.) completely blocked 5-HT stimulated [3H]InsP accumulation. Chronic ritanserin or clorgyline treatment had no effect on basal levels of [3H]InsP accumulation compared to controls (mean value 3125 +/- 298 dpm/mg protein). Ritanserin increased 5-HT stimulated [3H]InsP accumulation at 1 microM, 100 microM and 1 mM 5-HT and this effect was significant at 100 microM 5-HT. Clorgyline had no significant or consistent effect on 5-HT stimulated [3H]InsP accumulation at 1 microM, 100 microM and 1 mM 5-HT. Thus the effects of both chronic clorgyline and ritanserin administration on 5-HT2 linked inositol phospholipid hydrolysis do not correlate with their effects on 5-HT2 receptor number (Bmax). The situation is further complicated since ritanserin significantly increases phosphatidylinositol (PtdIns), phosphatidylinositol 4-phosphate (PtdIns4P) and phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2) labelling whereas clorgyline significantly increases PtdIns and PtdIns4P labelling. The implications of this are discussed.

Heightened free radical activity in pancreatitis

Three markers of free radical oxidation of lipids--9 cis, 11 trans isomer of linoleic acid, conjugated dienes and ultraviolet fluorescence products--were measured in the phospholipid fraction of duodenal juice collected in the first 10 min after an intravenous injection of secretin. The volume of aspirate was similar in 11 controls and in 25 patients who had sustained an attack of pancreatitis 6 weeks earlier--acute pancreatitis (AP) 10, chronic pancreatitis (CP) 15. The concentration of each marker was very significantly higher in the patients; the output of the isomer gave the best discrimination from controls; and ultraviolet fluorescence products were substantially higher in the subgroup with CP than with AP. The serum % molar ratio of the isomer to linoleic acid was measured in 25 controls, 14 AP and 17 CP patients: the highest levels were found in the CP group. Heightened hepatic free radical activity involving lipid isomerization as well as lipid peroxidation pathways is a feature of pancreatitis--probably antedating the attack and persisting well after clinical recovery--the difference between CP and AP being in the degree of abnormality. We argue that these hepatic changes mirror changes in pancreatic-acinar cells and that increased free radical activity in both organs is due to a shortfall of antioxidants in the face of cytochromes P450 induction by xenobiotics. Therefore, a combination of preventive and chain-breaking antioxidants may be useful in preventing further attacks of pancreatitis and controlling background pain in chronic disease.

Induction of phosphatidylcholine biosynthesis via CDPcholine pathway in lung and liver of rats following intratracheal administration of DDT and endosulfan

The induction of phosphatidylcholine (PC) biosynthesis via the CDPcholine pathway in lung and liver of rats has been shown following the intratracheal administration of 1,1,1-trichloro-2m2-bis(p-chlorophenyl) ethane (DDT) (5 mg/100 g body weight) and endosulfan (1 mg/100 g body weight) for 3 days. Controls received only the vehicle solution (groundnut oil, 0.1 m1/100 g body weight). The treatment of DDT and endosulfan significantly increased the PC contents and the incorporation of radioactive [methyl-3H]choline into PC of lung and liver microsomes. The incorporation of radioactive [methyl-14C]methionine into microsomal PC of lung and liver was not affected significantly by treatment with either of the insecticides. 1,4,5,6,7-hexachloro-5-norbornene-2,3-dimethano cyclic sulfite (endosulfan) administration significantly increased the activity of choline kinase and phosphocholine cytidylyltransferase (both cytosolic and microsomal) of lung, whereas DDT increased the activity of only latter. In liver, both DDT and endosulfan administration significantly increased the activity of choline kinase and phosphocholine cytidylyltransferase (both cytosolic and microsomal). However, the activity of phosphocholinetransferase was not affected in both lung and liver microsomes of rats treated with these insecticides. The PC precursor pool sizes, choline and phosphorylcholine, of lung and liver tissues were not altered by DDT and endosulfan treatments. The present results suggest that the increased level of PC and incorporation of radioactive [methyl-3H]choline into microsomal PC could be the result of increased activity of choline kinase and phosphocholine cytidylyltransferase of lung and liver of rats following intratracheal administration of DDT and endosulfan.

B-naphthoflavone induction and its effect on hepatic phospholipid metabolism in rainbow trout (Salmo gairdneri)

1. B-naphthoflavone (BNF) induction of microsomal cytochrome P-488 and its effect on liver phospholipid metabolism were examined in rainbow trout (Salmo gairdneri) 24 and 96 hr after intraperitoneal injection. 2. Cytochrome P-448 content increased at 96 hr to approximately double the cytochrome content of control fish. 3. Computer-analyzed laser densitometry scans of LDS-polyacrylamide gels of 96 hr BNF-treated liver microsomes showed a 90% increase in cytochrome P-448 levels. 4. A 34% increase in microsomal phospholipid (mumol/mg protein) was observed 24 hr after BNF injection, with a marked increase in choline, ethanolamine and inositol phospholipids. 5. Following 96 hr of exposure to BNF some differences in enzyme activity were noted; choline kinase and cytidylyltransferase activities were reduced, while a marked increase was observed in choline phosphotransferase activity. In light of current information on induction of liver microsomal phospholipid metabolism in mammals, the results of the this study suggest that trout do not respond like mammals to inducers of monooxygenase activity.

Comparison of hexachlorobenzene-induced alterations of microsomal membrane composition and monooxygenase activity in male and female rats

The effect of hexachlorobenzene (HCB) on microsomal cytochromes P-450 and b5, monooxygenase activity and membrane composition was examined in male and female Fischer rats. Cytochrome P-450 was induced more in male than in female animals while cytochrome b5 was induced only in males. Analysis of patterns of induction of microsomal monooxygenases showed that aminopyrine-N-demethylase activity doubled in both sexes after treatment while aryl hydrocarbon hydroxylase activity was 16 times the control value in the females and 1.5 times in the males. After HCB treatment the phospholipid content of microsomal membranes per gram of liver was increased in both sexes while cholesterol was unchanged. Analysis of the phospholipids (PL) pattern showed that the percentage of sphingomyelin (SPH) decreased significantly (50% of the control value) while phosphatidylcholine (PC), phosphatidylinositol (PI) and phosphatidylethanolamine (PE) did not change. These changes resulted in a reduction of membrane microviscosity and indicate that HCB interferes with the biosynthesis of phospholipids containing choline. Free fatty acid (FFA) content also dropped in both sexes but females were more affected; free arachidonic acid rose in females. HCB induction of microsomal cytochromes and monooxygenases is thus accompanied by marked modifications of membrane composition. Comparing the 2 sexes, HCB showed more pronounced features of 'PB type' inducers in males.

Circadian rhythm of the liver of male rats pre-treated with phenobarbital--II. Hexobarbital sleeping time and lipids content in liver and serum

The circadian rhythm of hexobarbital sleeping time and lipids content in liver and serum were studied in 226 male Sprague-Dawley rats pretreated daily at 0800-0900 with 70 mg/kg (study 1 or 3) or 50 mg/kg (study 2) phenobarbital (PB) orally for 7 days. Thereafter, eight (study 1) or five (study 2 and 3) rats each were studied at 4-hr intervals at 1000, 1400, 1800, 2200, 0200, 0600 and 1000 through the following day. The lighting schedule in the colony was 12:12 +/- light:dark (light from 0600 to 1800). The hexobarbital sleeping times of PB-pretreated rats were generally shortened compared to the controls and no circadian rhythm was observed. PB-treatment increased slightly the liver content of cholesterol, and significantly that of triglycerides and phospholipids. Liver cholesterol and phospholipids showed circadian rhythms with peaks during the dark phase. No circadian rhythm of liver triglycerides existed. In serum, levels of triglycerides and phospholipids were slightly lowered by PB-treatment, while levels of cholesterol and beta-lipoprotein were not influenced. Serum values did not exhibit circadian rhythms.

Hypersecretion of biliary fatty acids in patients with exocrine pancreatic disease

The fatty acid composition of bile secreted into the duodenum in the first 10 min after an intravenous (i.v.) injection of Boots secretin (2 CHRu kg-1) has been analysed by gas liquid chromatography in 11 healthy volunteers, 8 patients without pancreatic disease, 27 patients with exocrine pancreatic disease who had not altered their diet substantially (acute pancreatitis 8; chronic pancreatitis 16; cancer 3) and 11 patients with exocrine pancreatic disease on low fat intakes (40 g/day) for at least 6 months. The mean values for total fatty acid outputs (after back transformation of the logged data) were significantly higher in each subgroup of patients with pancreatic disease on their usual diets (acute 134, chronic 189, cancer 235 mg) than in the two subgroups of controls (30 and 55 mg), due to significant increases in the outputs of every fatty acid, C16:0 through to C22:5. This finding, which was usually not apparent in patients with pancreatic disease on low-fat diets, may reflect the combined influence of dietary fat intakes and hepatic enzyme induction. Comparison of the fatty acid outputs in endoscopically collected bile and duodenal juice after separate injections of secretin three hours apart indicate that: (a) analysis of duodenal juice within 10 min of stimulation by Boots secretin provides valuable information on the composition of hepatic bile; (b) the increased phospholipid output in the untreated patients is due to hypersecretion and does not merely represent a 'washout' phenomenon.

The role of methionine in carcinogenesis in vivo

The effects of methionine on carcinogenesis and tumor development have been studied intermittently for over 35 years. These studies have generally shown that methionine confers some degree of protection against the development of liver tumors by hepatocarcinogens. Such protective effects by supplemental dietary methionine are more pronounced in animals fed methionine- and choline-deficient diets rather than methionine- and choline-adequate diets. To date few if any protective effects of methionine have been observed against tumor formation in extrahepatic tissues. The effects of methionine on hepatocarcinogenesis appear to correlate well with its effects on the liver content of S-adenosylmethionine, the chief physiologic methyl donor. Perturbation of the methyl pool is known to alter the extent of methylation of membrane phospholipids, RNA, and DNA. Thus several plausible mechanisms by which methionine may modify the carcinogenic process center upon the aberrant methylation of macromolecules.

Relationship between lipid composition and drug metabolizing capacity of human liver

The relationship between hepatic glycerolipids and microsomal drug-metabolizing enzymes was studied in liver biopsies from 41 subjects. The series included obese, diabetic, epileptic and chronic alcoholic patients, all of whom were hospitalized for suspected hepatic ailments (fatty liver, hepatitis or cirrhosis). Therapy with enzyme-inducing anticonvulsants was associated with high phospholipid and cytochrome P-450 and low triacylglycerol concentration in the liver. In patients with fatty liver or cirrhosis low phospholipid and cytochrome P-450 and high triacylglycerol concentrations were observed. There was a significant correlation (r (Pearson's product moment correlation coefficient) = 0.91) between the hepatic phospholipid and cytochrome P-450 concentration. The cytochrome P-450 concentration was inversely related (r = -0.74) to the triacylglycerol concentration. The positive correlation between hepatic phospholipids and drug-metabolizing enzymes could be interpreted as indicating that in human liver phospholipid and cytochrome P-450 synthesis share common regulators, or that phospholipids are necessary for the maximum rate of cytochrome P-450 synthesis.

The proliferation of hepatocytes and the lipid composition of the endoplasmic reticulum after induction of drug-metabolizing enzymes with trans-stilbene oxide

Three aspects of the induction of drug-metabolizing enzymes brought about by trans-stilbene oxide have been investigated. (1) The liver hypertrophy in rats treated with trans-stilbene oxide was found to result solely from an increase in the number of cells in this organ, without any increase in the size of each individual cell. (2) Administration of trans-stilbene oxide also produces a 27% increase in the phospholipid content of the hepatic endoplasmic reticulum, i.e., a limited proliferation of this organelle occurs. (3) Furthermore, induction causes changes in the lipid composition of the endoplasmic reticulum. The cholesterol content is decreased, the relative content of sphingo-myelin is also lowered, and a number of changes in the fatty-acid composition occur as well. All of these effects would tend to increase the fluidity of the phospholipid bilayer of the endoplasmic-reticulum membrane and may thus affect drug metabolism.

Effects of ethionine and phenobarbital on the phosphatidylcholines of rat liver

The diglyceride species of phosphatidylcholines from livers of male rats after treatment of the animals with ethionine (1 mg/g divided among 4 doses 2 hr apart), phenobarbital (80 mg/kg each day for 3 days), or a combination of the two drugs were determined using gas chromatography. Ethionine treatment greatly elevated the diene species (significant at the 0.005 level for 34:2 and 0.001 level for 36:2). Phenobarbital treatment had no significant effect on the quantity of 34:2 but slightly increased that of 36:2 (significant at the 0.05 level). Both drugs caused relative decreases in the quantities of 38:4 (significant at the 0.001 level for ethionine and at the 0.01 level for phenobarbital). Ethionine decreased the content of 36:4 (significant at the 0.01 level) while phenobarbital treatment did not produce a significant effect on this fraction. Thus, while ethionine produced marked effects on the quantities of the various molecular species, the effects of phenobarbital were less dramatic. Combined treatment with both drugs generally produced levels of species similar to those produced by ethionine alone.

Mechanism of the enrichment of phosphatidylcholine in liver accompanying enzyme induction by phenobarbital

The mechanism of the increase of phosphatidylcholine in liver, accompanying enzyme induction by phenobarbital, has been studied in rats. Using radioactively labeled precursors, the two main pathways of phosphatidylcholine biosynthesis--the CDP-choline pathway and the methylation of phosphatidylethanolamine--were analyzed after pretreatment with 4 doses of phenobarbital (80 mg/kg) on 3 consecutive days. After i.v. injection of choline [Me-3H], choline [Me-14C] or NaH2[32P]O4 the specific radioactivity (sp. act.) of phosphatidylcholine (dpm/nmol) was decreased by 60%, and after methionine [Me-3H] or ethanolamine [1.2-14C] by 40% compared to control rats. These changes are partly due to the increased concentration of phosphatidylcholine and phosphatidylethanolamine, causing the incorporated precursors to dilute, and partly to a secondary effect which leads to a reduction of the sp. act. of free choline in pretreated animals. The concentration of glycerylphosphorylcholine, one of the metabolites of phosphatidylcholine catabolism, was also diminished by almost 50%. From these results it may be concluded that the increase of phosphatidylcholine is due to a retardation of its breakdown rather than to an increase of its synthesis.

Reduced response to phenobarbital by the liver of rats fed a choline-deficient diet

1. The response of the liver to phenobarbital administration was compared in rats fed either laboratory chow, a semipurified choline-supplemented diet or a semipurified choline-deficient diet. 2. The liver contents of proteins, lipids and cytochrome P-450, as well as the activity of aminopyrine and ethylmorphine demethylases, were measured after 5 days of feeding and five daily injections of phenobarbital. Liver sections were examined electron microscopically. 3. In rats fed the choline-supplemented diet, phenobarbital administration caused increases in cellular constituents, enzyme activities and smooth endoplasmic reticulum membranes as great as those seen in rats fed laboratory chow. However, in rats fed the choline-deficient diet, the response of the liver to phenobarbital administration was severely reduced in comparison to that in rats fed the other diets. 4. It is concluded that dietary choline and an adequate synthesis of lecithins are necessary for the induction of microsomal mixed-function oxidases and the concomitant accumulation of smooth endoplasmic reticulum in hepatocytes.

The effect of phenobarbital on cholesterol gallstones in hamsters

This experimental study was undertaken to follow the influence of phenobarbital on bile chemistry and gallstone formation. Phenobarbital (400 mg/kg/day) was administered to golden hamsters receiving a diet known to induce cholesterol gallstones. After a 28-day period none of the control animals had gallstones whereas five of 12 animals with added phenobarbital developed stones. Ten of 19 animals on the lithogenic diet formed gallstones but when phenobarbital was added gallstones occurred in 16 of 19 hamsters. The administration of phenobarbital resulted in the production of bile which was relatively more saturated with cholesterol, the bile salt + phospholipid: cholesterol of 24.8 +/- 12.7 in control animals altering to 9.1 +/- 6.2 in animals receiving phenobarbital. Hepatic bilirubin uridine diphosphate-glucuronyl transferase activity was not increased in animals on phenobarbital. It was concluded that, in the hamster at least, there is no indication that large doses of phenobarbital will reduce the potential for gallstone formation.