Differences in ICAM-1 and TNF-alpha expression between large single fraction and fractionated irradiation in mouse brain.

PURPOSE: To elucidate the brain molecular response to irradiation. The expression of the intercellular adhesion molecule (ICAM-1) and tumour necrosis factor-alpha (TNF-alpha) in the mouse brain was compared after single-dose and fractionated whole-brain irradiation. MATERIALS AND METHODS: Mice received a single dose of 2, 10 or 20 Gy or a fractionated dose (2 Gy day(-1)) of 10, 20 or 40 Gy. ICAM-1, and TNF-alpha mRNA expression were quantified by the highly sensitive real-time polymerase chain reaction technique. Expression of ICAM-1 protein was quantified by dual-labelled monoclonal antibody assay. RESULTS: After a 20-Gy single dose, there was an increase in ICAM-1 and TNF-alpha mRNA levels (14- and 11-fold, respectively) as well as a significant increase in the level of ICAM-1 protein (p=0.0243). The expression of ICAM-1 and TNF-alpha mRNA increased at the end of the 40-Gy fractionated regimen (3.55- and 2.30-fold, respectively). CONCLUSIONS: The molecular response of the brain to single-dose irradiation was rapid, while its response to fractionated irradiation was slow. This finding is consistent with clinical observations and could be of use when designing strategies to mitigate radiation sequelae.

Increased hepatic VLDL secretion, lipogenesis, and SREBP-1 expression in the corpulent JCR:LA-cp rat.

The corpulent JCR:LA-cp rat (cp/cp) is a useful model for study of the metabolic consequences of obesity and hyperinsulinemia. To assess the effect of hyperinsulinemia on VLDL secretion in this model, we measured rates of secretion of VLDL in perfused livers derived from cp/cp rats and their lean littermates. Livers of cp/cp rats secreted significantly greater amounts of VLDL triglyceride and apolipoprotein, compared with lean littermates. The content of apoB, apoE, and apoCs in both perfusate and plasma VLDL was greater in the cp/cp rat, as was the apolipoprotein (apo)C, apoA-I, and apoA-IV content of plasma HDL. Triglyceride content was also greater in cp/cp livers, as was hepatic lipogenesis and expression of lipogenic enzymes and sterol regulatory element binding protein-1 (SREBP-1). Hepatic mRNAs for apoE, and apoA-I were higher in livers of cp/cp rats. In contrast, the steady state levels of apoC-II, apoC-III, and apoB mRNAs were unchanged. Thus, livers of obese hyperinsulinemic cp/cp JCR:LA-cp rats secrete a greater number of VLDL particles that are enriched in triglyceride, apoE, and apoC. Greater secretion of VLDL in the cp/cp rat in part results from higher endogenous fatty acid synthesis, which in turn may occur in response to increased expression of the lipogenic enzyme regulator SREBP-1c.

Lack of enteral feeding increases expression of E-selectin after LPS challenge.

BACKGROUND: Total parenteral nutrition (IV-TPN) increases neutrophil accumulation in the small intestine, expression of intestinal ICAM-1 and P-selectin, and upregulates E-selectin expression in the lung. Endothelial activation induced by lack of enteral nutrition may change the response to injury or infection. This study investigated whether nutrition influenced the expression of the adhesion molecule, E-selectin and ICAM-1, following endotoxin challenge. MATERIALS AND METHODS: Forty-three mice were injected with saline, 2, 20, 200, 2000, or 10000 microg/kg lipopolysaccharide (LPS) intraperitoneally. E-selectin expression in the lung, small intestine, and heart was quantified at 3 h after challenge, while ICAM-1 was measured at 5 h, using the dual-radiolabeled monoclonal antibody technique. Next, 80 mice were fed chow, intragastric (IG)-TPN, or IV-TPN for 5 days, and then received intraperitoneal 2 or 200 microg/kg LPS. E-selectin and ICAM-1 expression in organs was measured at 3 and 5 h after endotoxin, respectively. RESULTS: E-selectin expression in organs increased LPS dose dependently. ICAM-1 levels reached early peaks in the lung and in the intestine. Also, IV-TPN significantly increased E-selectin expression in the small intestine and tended to increase pulmonary E-selectin, when compared to chow or IG-TPN animals. There were no significant differences in E-selectin expression among three diet groups after 200 microg/kg LPS challenge. No differences in ICAM-1 expression were observed in any organ among the three groups after 2 or 200 microg/kg LPS injection. CONCLUSIONS: E-selectin rather than ICAM-1, because of the expression pattern after various dosages of LPS challenge, may be a determining factor for the degree of LPS-induced inflammation at the early phase. Lack of enteral nutrition may increase inflammatory response through enhanced gut E-selectin levels after a small dose of LPS.

Enteral nutrition prevents remote organ injury and death after a gut ischemic insult.

OBJECTIVE: To determine whether parenteral feeding (IV-TPN) influences the local and systemic response to an intestinal insult. SUMMARY BACKGROUND DATA: Parenteral feeding increases ICAM-1 expression and attracts neutrophils (PMNs) to the intestine compared with enterally fed animals. Because the gut is a priming bed for PMNs, the authors hypothesized that IV-TPN may affect organ injury after gut ischemia-reperfusion (I/R). METHODS: Mice were randomized to chow, IV-TPN, intragastric TPN, or complex enteral diet for 5 days' feeding. In experiment 1, 162 mice underwent 15 or 30 minutes of gut I/R, and death was recorded at 72 hours. In experiment 2, 43 mice underwent 15 minutes of gut ischemia and permeability was measured by 125I-labeled albumin at 3 hours after reperfusion. Lung PMN accumulation was measured by myeloperoxidase assay. In experiment 3, albumin leak was tested in the complex enteral diet group (n = 5) and the intragastric TPN group (n = 5) after 30 minutes of gut ischemia and 1 hour of reperfusion. RESULTS: In experiment 1, enteral feeding significantly reduced the death rate compared with IV-TPN after 15 minutes of I/R. After 30 minutes of gut ischemia, the IV-TPN and intragastric TPN groups showed a higher death rate than the chow and enteral diet groups. In experiment 2, IV-TPN significantly increased pulmonary and hepatic 125I albumin leak compared with enteral feeding without increasing pulmonary myeloperoxidase levels. In experiment 3, there were no differences in 125I albumin leak between the complex enteral diet and intragastric TPN groups. CONCLUSION: Enteral feeding reduced the death rate and organ permeability after 15 minutes of ischemia. However, prolonged ischemia (30 minutes) eliminated any benefits of intragastric TPN on survival.

Modulation of organ ICAM-1 expression during IV-TPN with glutamine and bombesin.

The gut primes neutrophils (PMNs) during injury, which can then induce distant organ damage after a second insult. ICAM-1 is an important adhesion molecule in PMN attachment to the vascular endothelium. Parenteral nutrition (TPN) decreases gut levels of interleukin (IL)-4 and IL-10, two cytokines that are normal inhibitors of ICAM-1 expression. TPN also increases gut ICAM-1 expression and PMN accumulation. Since glutamine (GLN) and bombesin (BBS) prevent TPN-associated impairment of mucosal immunity, we hypothesized that GLN and BBS would modulate organ ICAM-1 expression in association with normalization of IL-4 and IL-10 levels. Forty-four mice were fed chow, TPN, or GLN-TPN (isonitrogenous 2% GLN-enriched TPN). After 5 days of diets, ICAM-1 expression was quantified in organs using the dual radiolabeled monoclonal antibody technique. In the next experiment, 29 mice were fed chow, TPN, or BBS-TPN (BBS 15 microg/kg TID) for 5 days to measure organ ICAM-1 expression. Total IL-4 and IL-10 levels were measured with ELISA from intestinal homogenates of another set of 52 mice fed chow, TPN, GLN-TPN, or BBS-TPN. TPN significantly increased ICAM-1 expression in the lung, kidney, and intestine compared with chow mice. GLN-TPN decreased intestinal, but not lung, ICAM-1 expression, while BBS-TPN reduced pulmonary, but not gut, ICAM-1 levels. GLN- and BBS-TPN returned gut IL-4 levels to normal, but failed to increase IL-10 levels. GLN and BBS had different effects on organ ICAM-1 expression induced by lack of enteral nutrition. Mechanisms other than recovery of IL-4 alone may be responsible for gut ICAM-1 expression.

Differential regulation of carnitine palmitoyltransferase-I gene isoforms (CPT-I alpha and CPT-I beta) in the rat heart.

Carnitine palmitoyltransferase-I (CPT-I) is a major control point for fatty acid oxidation. Two kinetically different isoforms, CPT-I alpha and CPT-I beta, have been identified. Cardiac ventricular myocytes are the only cells known to express both CPT-I isoforms. In this study, we characterized the differential regulation of CPT-I alpha and CPT-I beta expression in the heart. Expression of the CPT-I alpha gene was very high in the fetal heart and declined following birth. CPT-I beta was also highly expressed in fetal myocytes and remained so throughout development. CPT-I alpha mRNA abundance was increased in both the liver and heart of diabetic or fasted rats, but CPT-I beta mRNA levels were not altered in these states. A high fat diet elevated expression of the CPT-I alpha gene in the liver but not in the heart. The fat content of the diet did not affect the expression of CPT-I beta. Cultures of neonatal rat cardiac myocytes were transfected with luciferase reporter genes driven by CPT-I alpha or CPT-I beta promoters. Two regions of the CPT-I alpha promoter, including an upstream region (-1300/-960) and a region in the proximal promoter (-193/-52) contributed equally to basal expression in cardiac myocytes. Basal transcription of CPT-I alpha was dependent on Sp1 sites and a CCAAT box in the proximal promoter. Our data indicate that the CPT-I beta gene is expressed in a tissue specific manner, but that it is not subject to the same developmental or hormonal controls imposed on CPT-I alpha. In addition some aspects of CPT-I alpha expression are confined to the liver. The data presented here thus suggest that two types of differential regulation of CPT-I genes exist: (a) differential control of CPT-I alpha and CPT-I beta gene expression in the heart and (b) differential regulation of CPT-I alpha expression in the heart and liver.

Increased expression of intestinal P-selectin and pulmonary E-selectin during intravenous total parenteral nutrition.

HYPOTHESIS: Intravenous total parenteral nutrition (TPN) induces intestinal polymorphonuclear neutrophil recruitment with increased intestinal intercellular adhesion molecule-1 expression. While intercellular adhesion molecule-1 causes firm adhesion of leukocytes to the endothelial cells, P- and E-selectin mediate leukocyte recruitment via rolling. Therefore, manipulation of nutrition may also affect P- and E-selectin expression in organs. DESIGN: Prospective randomized experimental trials. SETTING: Laboratory. MATERIALS: Male mice. INTERVENTIONS: Fifty-three mice were randomized to chow, intravenous TPN, or intragastric TPN. MAIN OUTCOME MEASURES: After 5 days of diet, mice were administered iodine 125-labeled anti-P-selectin antibody (or iodine 125-labeled anti-E-selectin antibody) and iodine 131-labeled nonbinding antibody to quantify P-selectin (or E-selectin) expression in organs (lung, liver, kidney, small intestine, colon, stomach, pancreas, mesentery, heart, and skeletal muscle). RESULTS: P-selectin in small intestine, colon, stomach, and pancreas in the intravenous TPN group increased significantly as compared with the chow and the intragastric TPN groups. E-selectin expression was up-regulated after intravenous TPN in the lung but not in other sites. CONCLUSIONS: In a time frame (5 days) when intercellular adhesion molecule-1 expression and neutrophil recruitment are increased, intestinal expression of P-selectin remains up-regulated. Early lung inflammatory changes are reflected by increases in E-selectin. This change may reflect early pulmonary dysfunction with intravenous TPN, but its significance requires further study.

Intracellular supply of phospholipids for biliary secretion: evidence for a nonvesicular transport component.

Phospholipids (PL) for biliary secretion could be supplied from the endoplasmic reticulum (ER) to the plasma membrane by cytosolic transfer proteins or transport vesicles. Therefore, we studied whether biliary secretions of PL and apolipoprotein A-I (apo A-I), as markers for the ER-to-Golgi vesicular transport pathway, are tightly coupled in isolated perfused rat livers with enhanced secretion (+60%) of PL after withdrawal of the cholesterol synthesis inhibitor pravastatin (0.1% of chow, fed for 7 days). Blocking agents dissociated the secretion of apo A-I and PL. Brefeldin A as well as cycloheximide inhibited biliary secretion of apo A-I (-52%; -68%), however, not of PL. Both bilirubin ditaurate and taurodehydrocholic acid reduced biliary secretion of PL (-27%; -79%), but not of apo A-I. The data support the concept that PL destined for biliary secretion bypass the vesicular transport pathway of apo A-I through the Golgi compartment, most likely via cytosolic transfer proteins.

Apolipoprotein B mRNA editing and apolipoprotein gene expression in the liver of hyperinsulinemic fatty Zucker rats: relationship to very low density lipoprotein composition.

We previously demonstrated increased apolipoprotein B (apoB) mRNA editing, elevated levels of mRNA for the catalytic component of the apoB mRNA editing complex, apobec-1, and increased secretion of the product of the edited mRNA, apoB48, in very low density lipoproteins (VLDL) in primary cultures of Sprague-Dawley rat hepatocytes following insulin treatment. In order to determine the effect of in vivo hyperinsulinemia on these processes, we determined apoB mRNA editing, apobec-1 expression, hepatic expression of mRNA for apoB and other VLDL apoproteins, and the quantity and composition of plasma VLDL in the hyperinsulinemic fatty Zucker rat. Total apoB mRNA content of the livers of the fatty rats and lean littermates did not differ; however, edited apoB message coding for hepatic apo B48, and abundance of mRNA for the catalytic subunit of the apoB mRNA editing complex, apobec-1, was increased by 1.7- and 3.3-fold, respectively, in fatty rats. ApoCIII mRNA abundance was increased in livers of fatty rats as well, but the abundance of hepatic apoE mRNA in the fatty animal was not different from that of the lean rat. Hepatic apoAI mRNA abundance was also increased in the fatty rats. Associated with increased apoB mRNA editing, was the 1.7-fold increase in the fraction of apoB in plasma as apoB48 in fatty rats. VLDL-triglyceride and -apoB in plasma were 15- and 3-fold higher, respectively, in fatty Zucker rats compared to lean littermates, indicating both enrichment of VLDL with triglycerides and increased accumulation of VLDL particles. Increased hepatic expression of mRNA for apoCIII and apoAI was associated with increased content of apoC (and relative depletion of apoE) in VLDL of fatty rats, and plasma apoAI was increased in fatty Zucker rats, primarily in the HDL fraction. The current study provides further evidence that chronic exposure to high levels of insulin influences both the quantity of and lipid/apoprotein composition of VLDL in plasma. The increased apoC and decreased apoE (as well as increased triglyceride) content of VLDL in the fatty Zucker rat observed in the current study may affect VLDL clearance and therefore may be a factor in the observed accumulation of VLDL in the plasma of the fatty hyperinsulinemic Zucker rats.

Route of nutrition influences intercellular adhesion molecule-1 expression and neutrophil accumulation in intestine.

HYPOTHESIS: The levels of intestinal interleukin 10 and interleukin 4, inhibitors of intercellular adhesion molecule-1 (ICAM-1) expression, decline with total parenteral nutrition (TPN). These cytokine changes induced by lack of enteral nutrition may increase ICAM-1 expression, resulting in polymorphonuclear neutrophil accumulation in intestine. DESIGN: Prospective randomized experimental trials. SETTING: Laboratory. MATERIALS: Male mice. INTERVENTIONS: Sixty-three mice were randomized to chow, intravenous TPN, or intragastric TPN. MAIN OUTCOME MEASURES: Experiment 1: After diet manipulation, iodine 125-labeled anti-ICAM-1 antibody and iodine 131-labeled nonbinding antibody were injected to quantify ICAM-1 expression on endothelial cells in the lung, liver, kidney, and small intestine. Measurement of myeloperoxidase was used to quantify polymorphonuclear neutrophil accumulation in the organs. Experiment 2: Intestine was harvested for both ICAM-1 and myeloperoxidase levels after chow refeeding of mice in the intravenous TPN group. RESULTS: In experiment 1, uninjured mice fed intravenous TPN showed significantly increased intestinal ICAM-1 expression and polymorphonuclear neutrophil accumulation with no significant changes in the lung, liver, or kidney. No changes occurred in mice fed chow or intragastric TPN. In experiment 2, reinstitution of enteral feeding returned intestinal ICAM-1 and myeloperoxidase levels to normal. CONCLUSION: Gut changes associated with lack of enteral feeding induce endothelial changes and an immunologic response, which may influence subsequent responses to injury.

Insulin increases expression of apobec-1, the catalytic subunit of the apolipoprotein B mRNA editing complex in rat hepatocytes.

We have previously shown that chronic insulin treatment of rat hepatocytes increases the fraction of edited apolipoprotein B (apoB) mRNA from approximately 50% to as much as 90%. We have now examined the effect of insulin on apobec-1 mRNA abundance and demonstrate that increased editing of apoB mRNA following insulin treatment is accompanied by elevated apobec-1 mRNA levels in primary rat hepatocytes. Time-course measurements of the effects of insulin on apoB mRNA editing and apobec-1 mRNA abundance showed that both were elevated almost maximally within 48 hours and sustained for at least 5 days of insulin treatment.

Insulin promotes the biosynthesis and secretion of apolipoprotein B-48 by altering apolipoprotein B mRNA editing.

Long-term insulin treatment selectively stimulates secretion of the truncated form of apolipoprotein B (apoB), apoB-48, from primary rat hepatocytes in culture. Chronic treatment with insulin at 400 ng/ml causes a 3-fold increase in total apoB secretion, with apoB-48 making up about 75% of that increase. apo-B-48 is the protein product generated by translation of full-length apoB mRNA which has been modified by a posttranscriptional editing mechanism. Editing changes codon 2153 in the middle of the apoB-100 coding region from CAA, coding for glutamine, to UAA, a translation stop signal. We therefore examined the effect of insulin treatment on the ratio of edited to nonedited apoB mRNA in RNA isolated from primary rat hepatocyte cultures. There was a dramatic shift in the ratio of edited versus nonedited forms of apoB mRNA, from about 1:1 in untreated cells to 7:1 in insulin-treated cells. Insulin exerted a dose-dependent effect on apoB secretion and apoB mRNA editing over the range of insulin concentrations studied (0.4-400 ng/ml). In contrast, oleic acid, which also increased apoB (B-48 and B-100) secretion, had no significant effect on the ratio of apoB-48 to apoB-100 particles secreted and no effect on the proportion of edited apoB mRNA. Neither insulin nor oleic acid affects total apoB mRNA levels as assayed by Northern blot analysis. These data strongly suggest that insulin stimulates biosynthesis and secretion of apoB-48 in rat hepatocytes by regulating the proportion of edited apoB mRNA.

Effects of dietary cholesterol on hepatic metabolism of free fatty acid and secretion of VLDL in the hamster.

We reported previously that dietary cholesterol produces hepatic steatosis, increased secretion of the VLDL, and hypertriglyceridemia in the rat, the result of reduced oxidation of fatty acids, stimulation of fatty acid synthesis, and increased incorporation of fatty acid into hepatic triglyceride. The present study was conducted to determine whether these regulatory actions of dietary cholesterol on fatty acid metabolism also occur in the Golden Syrian hamster. In the hamster, dietary cholesterol (0.5%) induced hypertriglyceridemia and hypercholesterolemia. Incorporation of [1-14C] oleate into plasma and hepatic triglyceride was enhanced by dietary cholesterol. Experiments with perfused livers confirmed the stimulatory effect of dietary cholesterol on synthesis and secretion of VLDL-triglyceride and other lipids. These data indicate that increased formation of triglyceride in response to dietary cholesterol is not confined to the rat but may be a more general phenomenon.

Altered hepatic catabolism of low-density lipoprotein subjected to lipid peroxidation in vitro.

Recent evidence suggests that oxidatively modified forms of low-density lipoprotein (LDL) may be particularly atherogenic. In this investigation, the catabolism of human LDL modified by lipid peroxidation in vitro was studied with a recirculating rat liver perfusion system. A dual-labelling technique was used that permitted native LDL and modified LDL to be studied simultaneously in the liver perfusion system. Native human LDL was found to have a fractional catabolic rate (FCR) of 1.00 +/- 0.21%/h, in agreement with other investigators. Subjecting LDL to oxidation for 12 h in the presence of 30 microM FeEDTA did not significantly affect its FCR. LDL treated with a superoxide-generating system (xanthine oxidase, hypoxanthine, O2) in the presence of 30 microM FeEDTA did, however, show a significant increase in FCR (3.23 +/- 0.19%/h). The hepatic uptakes of native LDL and LDL oxidized with FeEDTA+O2 were similar, but both were significantly lower than the hepatic uptake of LDL treated with the superoxide-radical-generating system. The proteolysis of LDL with pancreatin did not influence either its susceptibility to oxidation or its FCR. LDL oxidation resulted in the preferential loss of alpha-tocopherol rather than gamma-tocopherol. These data indicate that the rat liver effectively catabolizes LDL oxidatively modified by treatment with the superoxide-generating system. Furthermore, our results suggest that only very low plasma levels of highly oxidized LDL could be found under conditions in vivo. The liver may therefore play a major role in protecting the arterial vasculature from highly atherogenic forms of LDL.

Stimulation of fatty acid biosynthesis by dietary cholesterol and of cholesterol synthesis by dietary fatty acid.

We reported previously that dietary cholesterol produces hypertriglyceridemia in the rat, accompanied by reduced oxidation and increased incorporation of exogenous fatty acid into hepatic triglyceride and increased secretion of very low density lipoprotein. We now report that dietary cholesterol also increases net hepatic fatty acid synthesis and the incorporation of newly synthesized fatty acid into hepatic triglyceride in vivo. Male rats were fed a cholesterol-free, semisynthetic diet (5% [w/w] corn oil) for 7 days, or the same diet supplemented with 0.5% cholesterol. On the day of the experiments, fed animals received 5 mCi 3H2O intraperitoneally (i.p.) either at 1200 h (6 h into the light cycle) or at 2400 h (6 h into the dark cycle). Animals were killed 1 h after receiving the radioisotope. Feeding cholesterol increased hepatic triglyceride and cholesteryl ester concentrations, moderately elevated the content of free cholesterol, but did not affect phospholipid levels. Increased net synthesis of fatty acids by livers of animals receiving cholesterol was observed during the dark period; a similar increase during the light period was also observed for incorporation of newly synthesized fatty acid into hepatic phospholipid and cholesteryl ester, although incorporation into triglyceride was of borderline significance (P < 0.06). In other experiments male rats were fed similar diets for 3, 7, or 21 days. Fed animals received 10 mCi 3H2O, i.p. (900-1000 h), and were killed 24 h later. Duration of feeding did not influence rates of net fatty acid synthesis or the stimulation by cholesterol of incorporation of newly synthesized fatty acid into hepatic triglyceride and cholesteryl ester.(ABSTRACT TRUNCATED AT 250 WORDS)

Dietary cholesterol stimulates hepatic biosynthesis of triglyceride and reduces oxidation of fatty acids in the rat.

Experiments were conducted in the intact rat and in the isolated, perfused rat liver to investigate the possibility that the increase in the concentration of hepatic triglyceride and increase in the secretion of the very low density lipoprotein (VLDL)-triglyceride (TG) resulting from addition of cholesterol to the diet are due to stimulation of synthesis of triglyceride, reduced fatty acid oxidation, or both. Male rats were fed for 7 days with either a cholesterol-free diet to which 5% (w/w) corn oil was added, or with the same diet supplemented with 0.5% cholesterol. Fed animals received [1-14C]oleic acid via the tail vein, as a complex with rat serum, and were killed 2 h later. Feeding cholesterol for 7 days increased hepatic triglyceride and cholesteryl ester (CE) concentrations, moderately elevated free cholesterol, but did not affect phospholipid (PL) levels, as we had previously observed after a feeding period of 3 weeks. Incorporation of [1-14C]oleic acid into hepatic and plasma triglyceride increased significantly (60 and 48%, respectively) with cholesterol feeding. Incorporation of [1-14C]oleic acid into hepatic and plasma cholesteryl esters increased by 63 and 79%, respectively, while incorporation into phospholipid was unaffected. Increasing the fat (corn oil) content of the diet to 20% (w/w) did not change these effects of dietary cholesterol. Studies using isolated, perfused rat livers were carried out in vitro after rats were fed the 5% corn oil diet for 3 weeks. [Perfusions lasted 4 h. The perfusion medium contained 3% bovine serum albumin and 30% washed bovine erythrocytes in Krebs-Henseleit-HCO3 buffer.(ABSTRACT TRUNCATED AT 250 WORDS)

Concentration-dependent effects of eicosapentaenoic acid on very low density lipoprotein secretion by the isolated perfused rat liver.

The effects of increasing concentrations of eicosapentaenoic acid (20:5n-3; EPA) and oleic acid (18:1n-9; OA) on esterification to triacylglycerols (TG) and phospholipids (PL), and the relationship to formation and secretion of the very low density lipoproteins (VLDL) were compared in the isolated perfused rat liver. Mixtures of EPA and OA were also studied to determine whether substrate levels of one fatty acid might influence the metabolism of the other. The basal perfusion medium, which contained 30% (vol/vol) washed bovine erythrocytes, 6% (wt/vol) bovine serum albumin (BSA), and 100 mg glucose/dL in Krebs-Henseleit bicarbonate buffer (pH 7.4) was recycled through the liver for 2 h. EPA or OA, as a complex with 6% BSA, was infused at rates of 70, 105, 140 and 210 mumol/h. In other experiments, mixtures of EPA and oleic acid (70 mumol total), with molar percentages of 100, 75, 50, 25 and 0% of each fatty acid were infused per hour. BSA (6%) in the buffer was infused alone and served as the control. At an infusion rate of 70 mumol EPA per hour, hepatic VLDL lipid output was not different from that when fatty acid was not infused (approximately half that when 70 mumol OA/h was infused). However, when larger amounts of EPA and OA were infused individually, rates of VLDL secretion were stimulated to a similar extent with either fatty acid. The apparent inhibitory influence of EPA on TG synthesis and VLDL lipid output when 70 mumol EPA were infused per hour could also be overcome by the presence of as little as 25 mol% OA in a mixture.(ABSTRACT TRUNCATED AT 250 WORDS)

In vivo growth hormone treatment stimulates secretion of very low density lipoprotein by the isolated perfused rat liver.

We have previously demonstrated in hepatocyte suspensions prepared after in vivo GH deprivation [hypophysectomy (hypox)] that rates of esterification of [1-14C]oleic acid into triglyceride (TG) and phospholipid (PL) were diminished, and that these esterification rates were correspondingly restored by repletion with recombinant GH. The current studies were designed to determine if GH exerts a similar effect on the secretion of very low density lipoprotein (VLDL), the primary plasma carrier of TG. We assessed rates of secretion of VLDL lipid and apoprotein by perfused livers prepared from cortisol/T3-replaced hypox female rats in the presence and absence of recombinant human (h) GH infusion. We also determined rates of synthesis and secretion of VLDL TG from infused [1-14C]oleic acid. After hypox, rates of secretion of VLDL lipid (TG, PL, and cholesterol) and apoprotein (total) were significantly decreased. In addition, VLDL secreted under these conditions was depleted of PL, relative to the other lipid components. Secretion of newly synthesized VLDL TG from [1-14C]oleic acid was also decreased; however, neither intracellular accumulation of labeled TG nor absolute tissue levels of TG were significantly changed. Conversely, GH treatment of hypox rats effectively restored rates of secretion of VLDL TG, PL, cholesterol (C) and apoprotein to control levels. These findings support the putative role of GH in regulating VLDL secretion in vivo by demonstrating that alterations in plasma GH are accompanied by changes in VLDL secretion. The findings further suggest that GH may regulate VLDL secretion by altering the amount of PL and/or apoprotein available for formation of the VLDL particle.

Regulation of hepatic secretion of very low density lipoprotein by dietary cholesterol.

Male rats were fed a cholesterol-free diet or the same diet supplemented with either 0.05, 0.1, 0.25, 0.5, 1, or 2% C for 21 days to investigate the effects of cholesterol on secretion of very low density lipoprotein (VLDL). Cholesterol feeding increased plasma and hepatic concentrations of triglyceride (TG) and cholesteryl esters (CE) in a dose-dependent manner. Plasma VLDL and low density lipoprotein (LDL) lipids were elevated by cholesterol feeding, while the high density lipoprotein (HDL) lipids were reduced. The secretion of the VLDL by perfused livers from these cholesterol-fed rats was examined to establish the relationship between the accumulation of lipids in the liver and the concurrent hyperlipemia. Liver perfusions were carried out for 4 h with a medium containing bovine serum albumin (3% w/v), glucose (0.1% w/v), bovine erythrocytes (30% v/v), and a 10-mCi 3H2O initial pulse. Oleic acid was infused to maintain a concentration of 0.6 mM. Hepatic secretion of VLDL-TG, PL (phospholipid), free cholesterol (FC), and CE increased in proportion to dietary cholesterol and was maximal at 0.5% cholesterol in these experiments in which TG synthesis was stimulated by oleic acid. Secretion of VLDL protein and apoB by the perfused liver was also increased. The molar ratios of surface (sum of PL and cholesterol) to core (sum of TG and CE) lipid components of the secreted VLDL, regardless of cholesterol feeding, were the same, as were the mean diameters of the secreted particles. The molar ratios of surface to core lipid of VLDL isolated from the plasma also were not affected by cholesterol feeding. During perfusion with oleic acid of livers from the rats fed the higher levels of cholesterol, the hepatic concentration of CE decreased, while the level of TG was not changed. We conclude that the hypercholesterolemia and hypertriglyceridemia that occur in vivo from cholesterol feeding, concurrent with accumulation of CE and TG in the liver, must result, in part, from increased hepatic secretion of all VLDL lipids and apoB. The VLDL particles produced by the liver of the cholesterol-fed rat are assembled without modification of the surface lipid ratios (PL/FC), but contain a greater proportion of cholesteryl esters compared to triglyceride in the core, because of the stimulated transport of CE from the expanded pool in the liver.(ABSTRACT TRUNCATED AT 400 WORDS)

Biphasic effect of oleic acid on hepatic cholesterogenesis.

Livers isolated from adult male rats were perfused in vitro with oleic acid (0.6 mM) as a complex with bovine serum albumin. Albumin alone was infused in control experiments. Oleic acid exerted a biphasic effect on incorporation of 3H2O into cholesterol, which was inhibitory during the first hour of perfusion, but exhibited a net stimulatory effect over a four hour period. No differences were observed in total activity or apparent phosphorylation state of HMG-CoA reductase after one hour of perfusion, with or without addition of oleic acid, implying that some other step limits the rate of cholesterol synthesis during this interval. After four hours of perfusion, HMG-CoA reductase activity was higher in livers perfused with oleic acid than in those perfused in its absence, in agreement with the observed differences in rates of cholesterol synthesis.