Microsomal Phospholipid Content Research Articles

Increase in NAD(P)H‐dependent generation of active oxygen species and changes in lipid composition of microsomes isolated from roots of zinc‐deficient bean plants

The role of zinc (Zn) in maintaining the structural and functional integrity of plant membranes was investigated in the present work. The relationship between the activity of NAD(P)H oxidases generating active oxygen species and changes in lipid composition and peroxidation was evaluated in microsomal membrane vesicles isolated from roots of Zn‐defícient bean (Phaseolus vulgaris L., cv. Bobis) plants. Zinc content of bean root microsomal membranes was decreased by about 30% by Zn deficiency. Microsomes isolated from roots of Zn‐deficient plants showed higher rates of NAD(P)H oxidation and NAD(P)H‐dependent O2 ‐ generation than Zn‐sufficient roots. Microsomal O2 ‐ consumption, measured in the presence of pyridine nucleotides, was also considerably enhanced by Zn deficiency. This latter activity was greatly stimulated by Fe(III)EDTA, while inhibited by Superoxide dismutase (SOD) and catalase, indicating that active oxygen species were produced during the oxygen consuming enzyme reaction. Zinc deficiency caused a decline in microsomal phospholipid (PL) content. In addition, saturated fatty acids were present at a higher proportion than unsaturated fatty acids in microsomes from Zn‐deficient roots. Sterol content of microsomal vesicles was also modified by Zn deficiency, which led to an increase in the planar sterol campesterol and a concomitant decrease in stigmasterol and sitosterol content. NADPH‐dependent lipid peroxidation, directly measured in microsomal vesicles as malondialdehyde (MDA) production, was slightly enhanced by Zn deficiency. These results support the idea that Zn deficiency determines an enhanced generation of harmful oxygen species by membrane‐associated enzymes and show that this activity can be more pronounced in the presence of iron (Fe), which accumulates in Zn‐deficient tissues. The relationship between the occurrence of this phenomenon and the changes in membrane lipid profile is discussed.

385 Honey Dew Fruit Senescence is Regulated by Polyamine Inhibition of Lipid Peroxidation

Polyamines are effective scavengers of activated oxygen free radicals produced by lipoxygenase (LOX) and phospholipase-D (PL-D). Activated oxygen free radicals cause peroxidative damage to membranes and hasten senescence. Exogenous polyamine spermidine (SPD) compared to spermine (SPM) at 1 mM or no polyamine was an effective inhibitor of honey dew (Cucumis melo L. var. inodorus) membrane peroxidation, as determined by malondialdehyde (MDA), following dark incubation for 6 or 48 hours of fully abscised fruit hypodermal mesocarp tissue. MDA levels in SPD-treated tissue was lowest in both 6 and 48 hours compared to SPM or no polyamine. SPD was effective in slowing lipid peroxidation as MDA was highly negatively correlated with the loss in total chlorophyll, plasma membrane H+ pumping ATPase activity, and microsomal phospholipid content (r = -0.89, -0.64 and -0.57, respectively). Both LOX and PL-D enzyme activities were not correlated with the total chlorophyll and microsomal membrane phospholipid losses or MDA levels, demonstrating that these enzymes act indirectly in the degradation of membranes through the production of lipid peroxidating free radicals. The results also demonstrate that the effect of polyamines as anti-senescence compounds is through direct inhibition of lipid peroxidation and not by affecting LOX or PL-D free radicle production.

The role of dietary choline in the beneficial effects of lecithin on the secretion of biliary lipids in rats

Earlier studies showed that dietary soybean lecithin increases biliary lipid secretion, which mainly comes from the contribution of high density lipoprotein (HDL) and hepatic microsomal pools of phosphatidylcholine and cholesterol. In addition, a lecithin diet enhances bile secretion and prevents bile acid-induced cholestasis. This study evaluated the contribution of choline, a component of lecithin, to the observed effect of lecithin on biliary secretory function. Rats were fed either a control diet (CD), a choline diet (ChD) or a lecithin-enriched diet (LD) for 2 weeks. Results showed that like LD, ChD induced an increase in bile flow and bile acid secretion rate when compared with the control diet. However, unlike LD, ChD did not significantly increase biliary phospholipids and cholesterol output. An increase of hydrophilic bile acids (i.e. ursodeoxycholic and muricholic acids) in bile of rats fed choline could explain why the biliary phospholipid and cholesterol secretion was not increased. During taurocholic acid infusion, both experimental diets increased bile flow and the bile acid secretion rate maximum (BASRm). The cholestasis usually observed after the BASRm is reached was inhibited by ChD and LD. Both diets induced a decrease in plasma cholesterol (total and HDL), however, only LD induced statistically significant changes. Analysis of total cholesterol and phospholipid content of microsomes and canalicular membranes indicated no statistically significant difference between control and experimental groups, either under basal conditions or after bile acid infusion. Similarly, the phospholipid classes and fatty acid composition of biliary phosphatidylcholine were not altered by feeding ChD and LD. We conclude that choline contributes to the beneficial effect of a lecithin diet on bile secretion. It is postulated that this effect may be attributed to modulation of HDL and an enhancement of the cholesterol and phospholipid pools destined for biliary secretion.

Physical properties, lipid composition and enzyme activities of hepatic subcellular membranes from chick embryo after ethanol treatment

Exposure of chick embryos to ethanol resulted in significant alterations to the lipid composition of various different hepatic subcellular membranes. A marked decrease in cholesterol levels and an increase in the phospholipid content of microsomes and mitochondria was observed. Ethanol also affected the fatty acid profiles, mainly by decreasing the percentage of oleic acid in phosphatidylcholine and phosphatidylethanolamine in the mitochondria and phosphatidylethanolamine in the microsomes. In spite of these changes ethanol only induced alterations in the fluidity of the mitochondrial membranes, which showed a more rigid core, in contrast to the phospholipid-head region, which was not affected. In accordance with the changes observed in the physical state of the membrane, the enzymes involved in the microsomal electron-transport systems were not modified by ethanol, while cytochrome oxidase activity decreased by 50% compared to the activity in the mitochondria from control chick embryos. These findings establish that during the chick-embryo developmental period the mitochondria are more sensitive to ethanol than are the microsomes.

Ascorbic acid deficiency and hepatic UDP-glucuronyl transferase: Qualitative and quantitative differences

The effect of dietary ascorbate on hepatic UDP glucuronyltransferase (UDPGT) appears to be selective in that only certain isozymes of UDPGT are jeopardized. In this study, ascorbic acid deficiency produced a 68% reduction in the specific activity of hepatic UDPGT towards p-nitrophenol. Earlier studies showed a reduction in UDPGT activity towards p-aminophenol in ascorbate-deficient guinea pigs, whereas bilirubin and acetaminophen glucuronidation were unaffected. Kinetic studies suggest that p-aminophenol and p-nitrophenol are metabolized by a single isozyme in tnat p-nitrophenol was found to be a competitive inhibitor of p-aminophenol glucuronidation. Both qualitative and quantitative studies on partially purified UDPGT from ascorbate-deficient and ascorbate-supplemented guinea pigs were carried out to investigate the biochemical role of the vitamin. Qualitative differences were observed in UDPGT from ascorbate-deficient animals and included an increased lability to: thermal inactivation; storage at 4°; and purification with UDP-glucuronic acid agarose column chromatography. Furthermore, an analysis of the microsomal membrane showed a 14% increase in membrane fluidity in ascorbate deficiency. Ascorbic acid added in vitro could not reverse the increase in fluidity observed in ascorbate-deficient microsomal membranes; however, ascorbylpalmitate, a more lipophilic form of the vitamin, was effective. Palmitic acid had no effect on membrane fluidity in microsomes from either the ascorbate-supplemented or ascorbate-deficient animals. This increase in membrane fluidity could not be explained by differences in cholesterol, total phospholipid, or phosphatidylcholine content of hepatic microsomes. Furthermore, a quantitative reduction in UDPGT partially purified from ascorbate-deficient guinea pigs was indicated by a marked reduction in protein banding at 55,000 daltons when compared to UDPGT partially purified from ascorbate-supplemented animals.

Toluene-induced alterations in rat synaptosomal membrane composition and function.

Toluene is a widely used organic solvent that can produce acute central nervous system (CNS) effects. Since toluene reaches relatively high concentrations in the CNS and is extremely lipophilic, we investigated its effects on rat brain membrane composition and function. Toluene (1 g/kg, lh) did not alter total brain microsomal phospholipid (PL) or cholesterol (CL) content. However, synaptosomal PL was decreased (24%), while synaptosomal CL was unaltered. The PL/CL ratio, an indirect index of membrane fluidity, did not change, suggesting that toluene did not affect membrane fluidity. Fluorescence polarization studies employing 1,6-diphenyl-1,3,5-hexatriene (DPH) showed that toluene did not alter synaptosomal membrane fluidity after administration in vivo (1 g/kg) or in vitro (0.5 to 5.0 mM). Dose-response and time-course studies showed that toluene maximally decreased synaptosomal PL after 1 g/kg, 1 h. The dose-response and time-course studies also showed that the toluene-induced decreases in PL were a result of specific decreases in phosphatidylethanolamine (PE). Since PE was decreased, we assessed whether toluene altered synaptosomal membrane function by investigating phospholipid methylation, a reaction which uses PE as its initial substrate. Toluene decreased the incorporation of methyl groups into lipid when [3H]-methionine was used as the methyl donor, but did not affect methylation when [3H]-adenosylmethionine was the methyl donor. These data suggest that toluene-induced specific decreases in synaptosomal PE and inhibition of phospholipid methylation may alter normal synaptic function and play a critical role in the mechanism(s) of action of toluene's CNS effects.

Liver cell membrane solubilization may control maximum secretory rate of cholic acid in the rat.

The factors modulating the maximum secretory rate of cholic acid were investigated. Rats were infused intravenously with cholic acid in measured stepwise increasing doses (1, 2, 3, and 4 mumol X min-1 X 100 g body wt-1). Each dose was infused for 30 min and bile samples were collected every 10 min. Bile flow, bile acid, cholesterol, individual biliary phospholipids, and the fatty acid profiles of the biliary phospholipids were determined. Microsomal and bile canalicular membrane-enriched fractions were isolated from cholic acid-treated rats at the end of the experiment. Membranes were analyzed for cholesterol, phospholipid, and phospholipid fatty acid composition. During cholic acid infusion, the secretion rates of bile acid, cholesterol, phospholipid, and bile flow initially increased and then declined. No evidence of liver cell damage was observed by light or electron microscopy. Maximum phospholipid secretion rate (13.5 nmol X min-1 X g-1) occurred before peak bile flow and bile acid secretory rate maximum (4.72 microliter X min-1 X g-1 and 375 nmol X min-1 X g-1). When phospholipid output declined, the proportion of sphingomyelins and phosphatidylethanolamine relative to phosphatidylcholine increased. This was also reflected in the fatty acid composition. Cholic acid infusion caused a decline in microsomal and bile canalicular membrane phospholipid content without affecting their phospholipid composition. Depletion of membrane phospholipid resulted in an increase in the cholesterol:phospholipid ratio, which is suggested to be the underlying mechanism for modulating cholic acid secretion.

Development of lipidic composition of neonatal chick liver and intestine microsomes: changes induced by cholesterol feeding

1. 1. Changes in cholesterol and phospholipid content of chick liver and intestine microsomes were studied throughout the two first weeks of life. 2. 2. Differences observed throughout postnatal development were mainly due to the free cholesterol. 3. 3. Cholesterol feeding resulted in a clear increase of the amounts of both free and esterified cholesterol. 4. 4. Phospholipid content of chick liver and intestine microsomes did not change significantly after hatching. 5. 5. Phosphatidylcholine and phosphatidylethanolamine were found to be the major phospholipids. 6. 6. Although the amount of each phospholipid could be affected by cholesterol feeding, its relative percentage did not change by this treatment.

Evolution of 3-hydroxy-3-methylglutaryl-CoA reductase and microsomal membrane fluidity throughout chick embryo development

1. 1. The pattern of chick liver and brain 3-hydroxy-3-methylglutaryl-CoA reductase and its relationship with changes in microsomal membrane fluidity was studied during embryonic and postnatal development. 2. 2. A peak of brain activity was found at 19 days of embryonic development, while liver activity only increased after hatching. 3. 3. A significant increase in cholesterol content of brain microsomes ocurred at about 14 days of incubation, decreasing afterwards. No significant variations were observed in liver microsomes during the same period. 4. 4. A similar profile was found in the phospholipid content of both brain and liver microsomes. 5. 5. The cholesterol/lipidic phosphorus molar ratio of brain and liver microsomes did not exhibit significant changes throughout embryonic and postnatal development. 6. 6. These results demonstrate that membrane-mediated control does not regulate the evolution of reductase activity during this developmental period.

Relationship between inhibition of 3-hydroxy-3-methylglutaryl-coa reductase by cholesterol feeding and short-term changes in membrane fluidity during neonatal development

1. 1. Both 5% cholesterol feeding and fasting produced a decrease in the hepatic 3-hydroxy-3-methylglutaryl-CoA reductase activity, although certain diurnal variations remained during the second day of treatment. 2. 2. Supplementation of 5% cholesterol to the diet produced a significant increase in cholesterol content of hepatic microsomes, whereas no significant variations were observed after fasting. 3. 3. The phospholipid content of hepatic microsomes did not change by fasting. However, cholesterol feeding produced a clear decrease in microsomal phospholipids. 4. 4. After 7 hr of cholesterol feeding, an increase of nearly 3-fold in the cholesterol/lipidic phosphorus molar ratio was found. Fasting had no effect on this molar ratio. 5. 5. The changes observed by cholesterol feeding agree with a mechanism of regulation of hepatic reductase by alteration in membrane fluidity, a mechanism that would be already operative during the neonatal period.

Phospholipid fatty acid modification of rat liver microsomes affects acylcoenzyme a: Cholesterol acyltransferase activity

The effect of phospholipid fatty acyl composition on the activity of acylcoenzyme A:cholesterol acyltransf erase was investigated in rat liver microsomes. Specific phosphatidylcholine replacements were produced by incubating the microsomes with liposomes and bovine liver phospholipid-exchange protein. Although the fatty acid composition of the microsomes was modified appreciably, there was no change in the microsomal phospholipid or cholesterol content. As compared to microsomes enriched for 2 h with dioleoylphosphatidylcholine, those enriched with dipalmitoylphosphatidylcholine exhibited 30–45% less acyl-CoA:cholesterol acyltransferase activity. Enrichment with 1-palmitoyl-2-linoleoylphosphatidylcholine increased acyl-CoA:cholesterol acyltransferase activity by 20%. By contrast, dilinoleoylphosphatidylcholine abolished microsomal acyl-CoA:cholesterol acyltransferase activity almost completely. Addition of cofactors that stimulated microsomal lipid peroxidation inhibited acyl-CoA:cholesterol acyltransferase activity by only 10%, however, and did not increase the inhibition produced by submaximal amounts of dilinoleoylphosphatidylcholine. Certain of the phosphatidylcholine replacements produced changes in palmitoyl-CoA hydrolase, NADPH-dependent lipid peroxidase, glucose-6-phosphatase and UDPglucuronyl transferase activities, but they did not closely correlate with the alterations in acyl-CoA:cholesterol acyltransferase activity. Electron spin resonance measurements with the 5-nitroxystearate probe indicated that microsomal lipid ordering was reduced to a roughly similar extent by dioleoyl- or by dilinoleoylphosphatidylcholine enrichment. Since these enrichments produce widely different effects on acyl-CoA:cholesterol acyltransferase activity, changes in bulk membrane lipid fluidity cannot be the only factor responsible for phospholipid fatty acid compositional effect on acyl-CoA:cholesterol acyltransferase. The present results are more consistent with a modulation resulting from either changes in the lipid microenvironment of acyl-CoA:cholesterol acyltransferase or a direct interaction between specific phosphatidylcholine fatty acyl groups and acyl-CoA:cholesterol acyltransferase.

Microsomal 5-ane-3β-hydroxysteroid oxidoreductase from pubertal rat leydig cells: Partial purification and characterization

A 3β-hydroxysteroid oxidoreductase which acts on 5α(β)-reduced C 19 and C 21 steroids (5-ane-3β-hydroxysteroid oxidoreductase; 5-ane-3β-HSO) has been solubilized from pubertal rat Leydig cell microsomes and purified 300-fold by ion exchange and gel filtration chormatography. The partially purified enzyme is stable only in the presence of 0.4 M NaCl and appears to exist as a molecule having a molecular weight of 35,000 or as aggregates with a molecular weight in excess of 150,000. NAD + and NADH + are used exclusively as cofactors. The velocity of the steroid oxidation reaction was unaffected by either Ca 2+ or Mg 2+. The steroid oxidation reaction has a pH optimum between 8.0 and 8.5, a temperature optimum at 35°C and an activation energy of 12,850 cal/mol. The pH optimum of the steroid reduction reaction is 6.6. A variety of 5α-reduced C 19 and C 21 steroids can be utilized as substrates. Treatment of microsomes with phospholipase A; resulted in a 26 to 90% loss of enzyme activity, paralleling decreased microsomal phospholipid content, and suggesting a role for phospholipids in 5-ane-3β-HSO activity. Assays with combined substrates indicate that one enzyme is responsible for activities observed with 5α- and 5β-reduced C 19- and 5α-reduced C 21-3β-hydroxysteroids. Purification data indicate that the 5-ane-3β-HSO and the 5-ene-3β-hydroxysteroid oxidoreductase: isomerase are distinct enzymes.

Studies of the biochemical basis of steroid sulphatase deficiency—III. Phospholipid composition of microsomes from normal and steroid sulphatase deficient placentas

The phospholipid composition has been determined for placental microsomes from 11 normal and eight pregnancies complicated by steroid sulphatase deficiency. Phosphatidylcholine, phosphatidylethanolamine and sphingomyelin were found to be the major phospholipids of normal placental microsomes, comprising respectively 41.6 ± 4.6% (mean ± SD), 30 ± 5.7% and 22.5 ± 4.9% of the total phospholipid content. There was no correlation between the steroid sulphatase activity of the microsomes and the content of any of the three phospholipids. Though their contents were significantly decreased, ( P < 0.001) phosphatidylcholine, phosphatidylethanolamine and sphingomyelin similarly constituted the major portion of the total phospholipids in sulphatase deficient microsomes, representing 36 ± 4.2%, 34 ± 6.1% and 22.4 ± 6.7% respectively. Only the percentage of phosphatidylcholine was significantly different ( P < 0.02) from normal microsomes. The results show that the decreased phospholipid content of steroid sulphatase deficient placental microsomes reflects a lower content of all major classes of phospholipids, particularly phosphatidylcholine.

Effect of ethanol consumption on the phospholipid composition of rat liver microsomes and mitochondria

Male Sprague-Dawley rats were maintained for 31 days on a liquid diet containing 36% of calories as ethanol. Pair-fed controls were administered a similar diet, but with maltose-dextrin isocalorically substituted for ethanol. A phospholipid analysis has been carried out in liver microsomes and mitochondria isolated from the two groups of animals. The phospholipid phosphorus/protein ratio was not significantly different in the organelles of the ethanol-fed animals as compared to the same organelles of liquid diet controls, which indicates that ethanol feeding did not influence the total phospholipid content of microsomes and mitochondria. The phospholipid distribution within organelles was not changed, except for a significant increase in the phosphatidylinositol content of microsomes from ethanol-fed animals. The fatty acid compositions of both microsomal and mitochondrial phospholipids were significantly altered by ethanol feeding. In microsomes from ethanol-fed rats, palmitic acid levels were lowered in the total phospholipid fraction, phosphatidylcholine and phosphatidylethanolamine; oleic acid levels were elevated in microsomal phosphatidylethanolamine. In mitochondria from ethanol-fed animals, palmitic and arachidonic acid were lowered in phosphatidylcholine and phosphatidylethanolamine. Oleic and linoleic acid were elevated in the same phospholipids. In contrast, linoleic acid levels in cardiolipin were depressed significantly. These alterations in the fatty acid composition are suggestive of ethanol-induced changes in fatty acid desaturation activities.

Comparative effect of pretreatment with phenobarbital, Aroclor 1254, and β-naphthoflavone on the metabolism of lindane

An attempt was made to distinguish different patterns of microsomal enzyme induction by phenobarbital, β-naphthoflavone, and Aroclor 1254 on the biotransformation and excretion of the organochlorine insecticide lindane. Treated groups of six weanling female Sprague-Dawley rats, individually housed in metabolism cages, received diets containing either 500 ppm Aroclor 1254, 356 ppm phenobarbital, or 418 ppm β-naphthoflavone. After 1 week all animals, except one group of controls, were dosed p.o. with 1.89 mg lindane (containing 1.63 μCi [U- 14C]lindane). Twenty-four hours later the rats were sacrificed and urine, feces, expired air, and tissue samples were taken for analysis of radioactivity. Hepatic cytochrome P-450 content, microsomal phospholipid content, and the enzyme activity involved in the dehydrogenation of lindane, the dechlorination of lindane, and the hydroxylation of the intermediate hexachlorocyclohexene were determined in vitro. Moreover, the effect of pretreatment on the excretion of radioactivity and the distribution of eight lindane metabolites was examined. Even though the rate of lindane metabolism was unchanged by the β-naphthoflavone pretreatment, results of the study indicated that all three pretreatments significantly altered lindane metabolism. The pretreatments differed from one another in that they selectively altered specific metabolic pathways.

Effect of chlorpromazine administration on enzyme activity concerning phosphatidic acid metabolism in rat liver.

The effect of chlorpromazine on phospholipid metabolism was studied in rat liver endoplasmic reticulum. Administration of chlorpromazine per os caused a marked increase in microsomal phospholipid content without affecting its composition. The rate of incorporation of both [(32)P]orthophosphate and [2-(3)H)glycerol into phosphatidic acid and phosphatidylinositol increased by the administration of chlorpromazine. Enhanced labeling of phosphatidylinositol was also observed when myo-[2-(3)H]inositol was used as a precursor. The activity of glycerophosphate acyltransferase significantly increased and that of phosphatidate phosphohydrolase markedly decreased by the administration of chlorpromazine. The activity of phosphatidate cytidylyltransferase was not affected by the drug treatment. These findings suggested that the administration of chlorpromazine increases the availability of phosphatidic acid by activating glycerophosphate acyltransferase and inhibiting phosphatidate phosphohydrolase, leading to enhanced synthesis of phosphatidylinositol.

Effects of progesterone metabolites on fatty acids of the hepatic endoplasmic reticulum membranes

The effect of 2 selected progesterone metabolites on the phospholipid fatty acid composition of the liver and microsomal function was studied in the female rat. 16α-Hydroxyprogesterone significantly increased microsomal phospholipid content and the total amount of fatty acids esterified to phospholipids parallel with aminopyrine N-demethylase activity. Phospholipid changes were attributable to phosphatidylcholine and phosphatidylethanolamine. Both saturated and unsaturated fatty acids were enhanced. In contrast, 5β-pregnane-3α-ol-20-one caused a reduction of microsomal phospholipids, phosphatidycholine, together with decreased aminopyrine N-demethylase activity and total microsomal fatty acid content. Pregnanolone decreased both saturated and unsaturated fatty acids and its action on unsaturated acyl components was greater than on the saturated ones. Changes in fatty acids were manifested in palmitic, stearic and lignoceric acids among saturated fatty acids and in palmitoleic, oleic, linoleic, eicosaenoic, eicosadienoic, eicosatrienoic, arachidonic, eicosapentenoic, docosatrienoic, docosapentenoic and docosahexenoic acids among unsaturated ones. Total liver phospholipids were unaltered by either 16α-hydroxyprogesterone or 5β-pregnane-3α-ol-20-one. These test compounds, however, modified total hepatic fatty acid content. 16α-Hydroxyprogesterone increased total fatty acids and both saturated and unsaturated acyl components, whereas 5β-pregnane-3α-ol-20-one decreased these parameters. Major changes were manifested in saturated fatty acids such as stearic, arachidic and lignoceric acids, and in unsaturated ones such as palmitoleic, linoleic, eicosatrienoic and docosapentenoic acids. The action of these compounds on phospholipid fatty acids of hepatic microsomes may be causally related to their effect on drug-metabolizing activity of the endoplasmic reticulum.

Cadmium-induced alteration of the microsomal mono-oxygenase system in male rat liver: Effects on hemoprotein turnover and phospholipid content

After cadmium treatment (2.0 mg Cd/kg, i.p.) a marked inhibition is observed in microsomal drug metabolizing enzyme activity which is correlated with a reduction in the hemoprotein, cytochrome P-450, content. Incorporation of the heme precursor, 3H-δ-aminolevulinic acid ( 3H-δ-ALA), into microsomal CO-binding particles was decreased in cadmium-treated rats. Cadmium treatment produced a differential effect in the biphasic disappearance of radioactivity from the CO-binding particles in that the metal decreased the half-life of the fast-phase component and increased the half-life of the slow-phase component. Thus, the reduction in microsomal levels of cytochrome P-450 induced by cadmium apparently results from a stimulation of the degradation of the fast-phase hemoprotein fraction and a reduction in the synthesis of the slow-phase and fast-phase hemoprotein fractions. Cadmium treatment did not quantitatively alter microsomal phospholipid content.

Regulation of Hepatic Drug Metabolism by Elaidic and Linoleic Acids in Rats

Elaidic and linoleic acids were administered at doses of 40 and 200 mg/kg i.p. every second day for 4 weeks to rats fed a fat-free diet. The fatty acids had only a slight effect on the weight gain of the animals. The amount of microsomal protein was slightly decreased with the higher dose of linoleic acid. The higher dose level of both fatty acids decreased the microsomal phospholipid content. The relative amounts of microsomal phospholipid fatty acids were also altered due to fatty acid administration. The activity of microsomal NADPH cytochrome c reductase and microsomal cytochrome P-450 contents were decreased by the higher dose of linoleic acid. The hepatic aryl hydrocarbon hydroxylase and p-nitroanisole O-demethylase activities decreased in fatty acid-treated rats. The UDP-glucuronosyltransferase activity was also lowered after the fatty acid administration. The results suggest that fatty acid-induced changes in the activities of drug-metabolizing enzymes may be due to the microenvironmental changes of membrane-bound enzymes.

Effect of dietary lipid and dimethyl sulfoxide on lindane metabolism

Previous investigations have suggested that there is a requirement of dietary polyunsaturated fatty acids for full expression of microsomal enzyme induction. The conclusions in these studies were primarily based on in vitro enzyme activity, sleeping time recovery, or hepatic cytochrome P-450 content, measured 24 hr after treatment with an inducing agent. This study set out to examine the influence of dietary lipids, containing different fatty acid compositions, on the storage and self-induction of lindane metabolism. The alteration in metabolism was followed on a daily basis throughout the treatment period. Twenty-four female weanling rats were fed fat-free diets either unsupplemented or supplemented with 7% hydrogenated coconut oil, 7% peanut oil, or 5% menhaden oil plus 2% linseed oil for 12 days prior to treatment with lindane. All rats then received a daily po dose of 2.5 mg of lindane in dimethyl sulfoxide (DMSO) for 7 days. On Day 8, all rats were treated with 2.5 mg of lindane (containing 1.93 μCi of [ 14C]lindane and they were sacrificed 24 hr later. Tissue samples were analyzed for radioactivity. Liver samples were assayed for microsomal phospholipid, protein, and cytochrome P-450 plus the enzymatic dehydrogenation of lindane. In addition, the fatty acid content of microsomal phosphatidylcholine (PC) and phosphatidylethanolamine (PE) was determined. Depressed food consumption and growth rate, an impaired metabolite excretion pattern, low specific microsomal phospholipid content, and a decreased microsomal PC PE ratio containing a reduced proportion of polyunsaturated fatty acids suggested that a toxic lindane-DMSO-dietary lipid interaction had occurred.