Insulin-induced up-regulation of lipoprotein lipase messenger ribonucleic acid and activity in mammary gland

The effects of insulin on lipoprotein lipase (LPL) messenger RNA (mRNA) were studied in mammary glands from virgin and late-pregnant rats. Virgin and pregnant rats (at 17 days of gestation) were subjected to a continuous infusion (35 ml/day) with 50% glucose for 72 h to produce a prolonged hyperinsulinemic-euglycemic condition. Gestation causes a 4-fold increase in LPL mRNA accompanied by a 3- to 4-fold increase in total LPL activity. Experimental hyperinsulinemia, generated by the 50% glucose infusion, had a similar effect in both pregnant and virgin rats, by enhancing (2- to 3-fold) both their LPL activity and LPL mRNA. Thus, total LPL activity and LPL mRNA significantly correlated with plasma insulin (r = 0.789, P < 0.001; and r = 0.772, P < 0.001, respectively). Furthermore, total LPL activity was correlated with LPL mRNA (r = 0.765, P = 0.001). In conclusion, the present study shows that insulin participates in the control of LPL expression in mammary glands, revealing its role as a modulator of the enzyme at a mRNA level.

Functional analysis of vaccinia virus B5R protein: role of the cytoplasmic tail

Vaccinia extracellular enveloped virus (EEV) is important for cell-to-cell and long-range virus spread both in vitro and in vivo. Six genes have been identified that encode protein constituents of the EEV outer membrane, and some of these proteins are critical for EEV formation. The B5R gene encodes an EEV-specific type I membrane protein, and deletion of this gene markedly decreases EEV formation and results in a small plaque phenotype. Data suggest that the transmembrane domain, cytoplasmic tail, or both contain the EEV localization signals that are required for targeting of the B5R protein to EEV and for EEV formation. Here, we report the construction of mutant vaccinia viruses in which the wild-type B5R gene was replaced with a mutated one that encodes a protein with the putative cytoplasmic tail deleted. The mutated protein showed normal intracellular distribution and was properly incorporated into EEV. Vaccinia viruses expressing the B5R protein lacking the cytoplasmic tail formed plaques that were similar in type and size to those formed by wild-type viruses and produced equivalent amounts of infectious EEV. These results indicate that the B5R cytoplasmic tail is not necessary for EEV formation and points to the transmembrane domain as the major determinant for targeting the B5R protein to the outer membrane of EEV and for supporting EEV formation.

Simplified method for vitamin E determination in rat adipose tissue and mammary glands by high-performance liquid chromatography

A method for vitamin E (alpha-tocopherol) measurement in rat adipose tissue and mammary gland has been developed and validated. Tissues were homogenized in ethanol-water (1:1) and extracted with n-hexane. Vitamin K1 was used as internal standard. Separation was performed by HPLC with methanol-water (96.5:3.5) as eluent in a Nucleosil C18 column (15 x 0.46 cm) at 40 degrees C. Detection was by fluorescence with excitation at 295 nm and emission at 350 nm for vitamin E and at 330 and 440 nm for vitamin K1. Standards and tissue extracts were checked for linearity giving correlation coefficients over 0.99 in a range of concentrations from 0.56 to 4.51 nmol/g in adipose tissue and from 2.18 to 17.4 nmol/g in mammary gland tissue. Intra-assay precision (R.S.D.) varied between 3 and 4%, whereas inter-assay precision was between 8 and 9%. Recoveries ranged between 95 +/- 3% and 98 +/- 11% for the two tissues, respectively. Vitamin E was measured in rats that had previously received one oral dose of this vitamin. Whereas vitamin E content in adipose tissue did not differ between late-pregnant and virgin rats, it was significantly higher in mammary gland of pregnant rats, and this difference could be related to the enhanced lipoprotein lipase activity in this group.

Aerobic exercise during pregnancy reverts maternal insulin resistance in rats

PURPOSE AND METHODS

To determine whether pregnancy modifies the effect of aerobic exercise on insulin responsiveness, female rats were mated or kept nonpregnant and exercised or not on a treadmill (10 degrees slope, 20 m.min-1) 5 d.wk-1 during a 20-min period that was increased progressively up to 70 min on the 19th d. On day 20, a hyperinsulinemic euglycemic clamp was performed with 0.8 IU insulin.h-1.kg-1 under conscious conditions.

RESULTS

Food intake and body weight, circulating lactic acid, glucose, and insulin as well as fetal body weight and number were unaffected by the exercise protocol. The rate of glucose infusion required to maintain basal glucose levels during the clamp was similar in exercised and nonexercised virgin rats and significantly lower in pregnant than in virgin nonexercised rats. However, in exercised pregnant rats the glucose infusion rate was almost as high as in the exercised virgin rats.

CONCLUSIONS

The results show that although our aerobic exercise protocol does not affect insulin responsiveness in nonpregnant rats, it completely reverts the insulin resistance present in late pregnant rats.

Expression of mouse telomerase catalytic subunit in embryos and adult tissues

Telomerase is a ribonucleoprotein complex that elongates telomeres, allowing the stable maintenance of chromosomes during multiple cell divisions. Here, we describe the isolation and characterization of the catalytic subunit of mouse telomerase, mTERT (mouse telomerase reverse transcriptase), an essential protein component of the telomerase complex. During embryonic development, mTERT mRNA is abundantly expressed in the whole embryo, especially in regions of intense proliferation. We found that the mTERT mRNA expression in both embryonic and adult tissues is independent of the essential RNA component of telomerase, mTR, and therefore, of the formation of active telomerase complexes. mTERT protein is present exclusively in tissues with telomerase activity, such as testis, spleen, and thymus. mTERT protein is barely detectable in the thymus of mTR-/- mice, suggesting that mTERT protein stability in this tissue may depend on the actual assembly of active telomerase complexes. Finally, we found that mouse and human telomerase catalytic subunit is located in the cell nucleus, and its localization is not regulated during cell cycle progression.

Lipid composition and vitamin E content in human colostrum and mature milk

Lipidic components, as well as fatty acid composition and vitamin E content were determined in colostrum (days 3-5 of postpartum) and mature milk (day 21) in 8 women from Murcia (Spain). Triglycerides concentration was higher and cholesterol and esterified cholesterol were lower in mature milk than in colostrum, whereas phospholipid content was similar. These differences indicate that the diameter of milk fat globules increases in mature milk. The percentage of medium-chain fatty acids (12:0 and 14:0) increased in mature milk as compared to colostrum, reflecting de novo synthesis of fatty acids. With the only exception of stearic acid which was lower in mature milk than in colostrum, the remaining long-chain fatty acids was similar. The proportion of both linoleic (18:2) and eicosapentaenoic (20:5) acids found in mature milk and colostrum is higher than in studies from other countries and may reflect the intake of high proportions of polyunsaturated fat from vegetable oils and fish in the studied women. Both vitamin E content and vitamin E/linoleic acid ratio in mature milk are lower than in colostrum, evidencing the efficient mechanism of mammary gland vitamin E uptake around parturition.

Pantethine stimulates lipolysis in adipose tissue and inhibits cholesterol and fatty acid synthesis in liver and intestinal mucosa in the normolipidemic rat

In vitro effects of pantethine on adipose tissue lipolysis and on both hepatic and intestinal cholesterol and fatty acid synthesis in normolipidemic rats are determined and related to their respective in vivo hypolipidemic effects after acute oral administration. At 3, 5, 7 and 24 h after a single high dose of pantethine to rats, free fatty acids (FFA), cholesterol and triglycerides levels decreased whereas plasma glycerol increased, the effect becoming significant at 7 h. The release of glycerol and FFA by epididymal fat pad pieces from rats was measured in Krebs Ringer bicarbonate-albumin buffer supplemented or not with epinephrine and several concentrations of pantethine (0, 10(-5), 10(-4), or 10(-3) M), and it turned out to be enhanced as pantethine concentration increased. Besides, when glucose was present in the medium, this drug lowered fatty acid re-esterification in a dose-dependent manner, the effect being specially evident in the presence of epinephrine. In vitro synthesis of both cholesterol and fatty acids by slices of liver or intestinal epithelial cells was depressed as the concentration of pantethine increased in the medium. Thus, an inhibition of both cholesterolgenesis and lipogenesis seems to contribute to the hypocholesterolemic and hypotriglyceridemic effects of pantethine. On the other hand, the stimulation of lipolysis and the inhibition of fatty acid re-esterification on adipose tissue caused by pantethine must be counteracted by a high fatty acid oxidation in the liver which would explain the decrease in FFA and the increase in glycerol levels detected in the plasma of the pantethine-treated animals.

Tropisetron for treating established postoperative nausea and vomiting: a randomized, double-blind, placebo-controlled study

Tropisetron can prevent postoperative nausea and vomiting (PONV) at doses smaller than those used to control chemotherapy-induced nausea and vomiting. In this placebo-controlled study, the efficacy and tolerability of three different doses of tropisetron were compared for the treatment of established PONV after surgical procedures in general anesthesia. Of 1513 patients who satisfied inclusion criteria, 314 experiencing PONV during the first 2 h after recovery from anesthesia were treated with one of three different doses of tropisetron (0.5, 2, or 5 mg) or placebo, administered i.v. as a single dose. Patients were then observed during 24 h for efficacy and tolerability. All three doses of tropisetron were significantly better than placebo in controlling emetic episodes and in reducing the need for rescue treatment. There were no significant differences among the three doses. However, in the subgroup of patients who had previous PONV, and in those randomized for nausea alone, the 2-mg and 5-mg doses controlled emetic episodes better than the 0.5-mg dose. All studied doses of tropisetron were well tolerated and did not affect vital signs. We conclude that a single i.v. administration of tropiestron significantly reduces the recurrence of emetic episodes in patients with established PONV after elective surgery with general anesthesia. Its optimal dose seems to be 2 mg.

IMPLICATIONS

Three hundred-fourteen patients suffering from postoperative nausea and vomiting received different i.v. doses of a new antiemetic drug, tropisetron, to determine the lowest effective dose. We found that a single i.v. administration of tropisetron significantly reduced postoperative nausea and vomiting after elective surgery with general anesthesia.

Changes in the kinase activity of the insulin receptor account for an increased insulin sensitivity of mammary gland in late pregnancy

Mammary gland is an organ that undergoes cycles of growth, differentiation, and function during pregnancy and lactation. Although it is known that the gland enhances its sensitivity to insulin during lactation, it remains to be investigated whether this increased sensitivity develops during pregnancy and which are the molecular mechanisms underlying such a change. To address this issue, virgin and late-pregnant rats were subjected to a continuous infusion with 50% glucose for 72 h to produce a prolonged hyperinsulinemic-euglycemic condition. Insulin sensitivity in mammary gland was determined as the glucose utilization index by using 2-[3H]-deoxyglucose. Furthermore, binding characteristics and kinase activity were studied by means of both [125I]insulin binding and in vitro phosphorylation studies with insulin receptors partially purified from mammary gland. Whereas the glucose utilization index in mammary gland from nonpregnant rats remained unaffected by hyperinsulinemia, glands from pregnant rats displayed a high insulin-dependent glucose uptake. This effect was not paralleled by changes in the binding characteristics of insulin to the high-affinity receptor, suggesting that the high insulin sensitivity of mammary gland in pregnancy is not accounted for by changes at the level of hormone-receptor interaction. Autophosphorylation studies showed that insulin-stimulated kinase activity of insulin receptors from mammary gland was 6- and 20-fold higher in pregnant than in virgin animals under normo- and hyperinsulinemic conditions, respectively. Moreover, insulin dose-response curves revealed that the efficacy of insulin to stimulate kinase activity of the insulin receptor was markedly higher in pregnant than in virgin rats, whereas its potency (ED50 approximately 15 nM) was not changed. These data, therefore, show that mammary glands develop increased insulin sensitivity during late pregnancy, caused by an augmented kinase activity of the insulin receptor.

Functional analysis of vaccinia virus B5R protein: essential role in virus envelopment is independent of a large portion of the extracellular domain

Vaccinia virus has two forms of infectious virions: the intracellular mature virus and the extracellular enveloped virus (EEV). EEV is critical for cell-to-cell and long-range spread of the virus. The B5R open reading frame (ORF) encodes a membrane protein that is essential for EEV formation. Deletion of the B5R ORF results in a dramatic reduction of EEV, and as a consequence, the virus produces small plaques in vitro and is highly attenuated in vivo. The extracellular portion of B5R is composed mainly of four domains that are similar to the short consensus repeats (SCRs) present in complement regulatory proteins. To determine the contribution of these putative SCR domains to EEV formation, we constructed recombinant vaccinia viruses that replaced the wild-type B5R gene with a mutated gene encoding a B5R protein lacking the SCRs. The resulting recombinant viruses produced large plaques, indicating efficient cell-to-cell spread in vitro, and gradient centrifugation of supernatants from infected cells confirmed that EEV was formed. In contrast, phalloidin staining of infected cells showed that the virus lacking the SCR domains was deficient in the induction of thick actin bundles. Thus, the highly conserved SCR domains present in the extracellular portion of the B5R protein are dispensable for EEV formation. This indicates that the B5R protein is a key viral protein with multiple functions in the process of virus envelopment and release. In addition, given the similarity of the extracellular domain to complement control proteins, the B5R protein may be involved in viral evasion from host immune responses.

Antioxidant and prooxidant effects of ascorbic acid, dehydroascorbic acid and flavonoids on LDL submitted to different degrees of oxidation

Although a high intake of antioxidants may decrease the risk of developing cardiovascular diseases, under certain circumstances they may promote free radical generation and lipid peroxidation. The objectives of the present study were to determine the antioxidant effects of ascorbic acid (AA), dehydroascorbic acid (DHA) and flavonoids on LDL submitted to different degrees of oxidation. LDL was submitted to oxidation with CuCl2 (2.4 microM). Before or at different times after the propagation of the oxidation process, 28 microM (5 micrograms/ml) of either AA or DHA or 5 micrograms/mL flavonoids extract were added. Alpha-tocopherol, conjugated dienes, thiobarbituric acid reacting substances (TBARS) and LDL electrophoretic mobility were determined as indices of LDL oxidation. The presence of any of the three antioxidants from the onset of the incubation delayed the oxidation process. However, the addition of both DHA and flavonoids to the oxidation process when it was already initiated and alpha-tocopherol consumed, accelerated the oxidation. In contrast, AA delayed the oxidation process even when added after alpha-tocopherol was consumed. Nevertheless, it also accelerated LDL oxidation when added during the propagation phase of the oxidation process.

IN CONCLUSION

although AA, DHA and flavonoids delay LDL oxidation when added before the initiation of the process, they accelerate the process if added to minimally oxidized LDL.

A cholesterol-rich diet causes a greater hypercholesterolemic response in pregnant than in nonpregnant rats and does not modify fetal lipoprotein profile

To determine whether pregnancy modifies the hyperlipidemic response to a cholesterol-rich diet, pregnant and virgin rats were fed a semisynthetic diet supplemented (CRD) or not (CD) with 2% cholesterol and 1% cholic acid and studied at d 20 of treatment and/or gestation. Plasma triglycerides, free fatty acids and glycerol and liver triglycerides were greater in pregnant than in virgin rats fed CRD. The increase in both plasma and liver cholesterol caused by CRD did not differ in the two groups. In rats fed CD, hepatic lipase activity in liver was lower in pregnant than in virgin rats, while in those fed CRD, virgin rats had lower activity than those fed CD. Plasma VLDL-triglycerides were higher and LDL-triglycerides lower in pregnant than in virgin rats fed CD. Among those fed CRD, pregnant rats had a higher triglyceride concentration in VLDL and HDL than virgin rats. Cholesterol concentration was higher in VLDL and IDL and lower in HDL in both groups fed CRD than in those fed CD, while cholesterol level in LDL was higher only in pregnant rats fed CRD than in those fed CD. Whereas placental cholesterol concentration was higher in pregnant rats fed CRD than CD, maternal CRD intake did not modify fetal plasma lipoprotein concentrations, fetal body weight or litter size, indicating a lack of cholesterol transfer by the rat placenta. Results therefore show a greater responsiveness to CRD in pregnant than in virgin rats, and we propose that CRD promotes greater liver VLDL-production and lower LDL removal in pregnant than in virgin rats.

Simultaneous determination of vitamins A and E in rat tissues by high-performance liquid chromatography

A high-performance liquid chromatographic (HPLC) method to determine vitamins A, Ap and E simultaneously was developed with direct extraction of vitamins from rat tissues with n-hexane and probe sonicating. The dry residue was redissolved in chloroform-methanol. Vitamins A and Ap were detected by UV-Vis and vitamin E by fluorescence. Vitamin K, used as internal standard, was detected both the UV-Vis and by fluorescence. Standards and samples were checked for linearity giving correlation coefficients that were higher than 0.99 in the concentration range of 3.1-9.4 for vitamin A, 8.2-24.7 for vitamin Ap and 0.6-1.7 nmol/g in the case of liver extracts and 0.5-3.0 nmol/g in the case of placenta. The inta-assay precision (R.S.D) varied between 1.48 and 7.25, whereas inter-assay precision was between 4.99 and 7.03. Recoveries ranged between 94 +/- 8 and 107 +/- 5%. Results from the application of this method to different rat tissues having wide range of vitamin content are presented.

Comparative study on the in vivo and in vitro antilipolytic effects of etofibrate, nicotinic acid and clofibrate in the rat

The release of both glycerol and free fatty acids (FFA) into a medium by epididymal fat pad pieces from fed rats incubated in Krebs Ringer bicarbonate-albumin buffer supplemented or not with epinephrine decreased more in the presence of etofibrate than in the presence of equimolecular doses of nicotinic acid or clofibrate. The first drug was the only one to stimulate the rate of fatty acid re-esterification when incubations were done under basal conditions. By 3 h after their acute oral administration all three drugs decreased plasma FFA levels, although the effect from etofibrate was largest, the drugs enhanced or decreased plasma glycerol levels depending on both the dose and the time after treatment. Plasma triglycerides also decreased at 3 h after oral drug administration, and this effect was similar with etofibrate and nicotinic acid but less with clofibrate. With the exception of a decrease at 7 h after the highest dose (1.2 mmol/kg) of either etofibrate or nicotinic acid (but not clofibrate), plasma cholesterol levels remained stable at 7 h after the respective treatments. Thus, the hypocholesterolemic effect of these drugs seems secondary to their hypotriglyceridemic effect, which would be a consequence of their respective antilipolytic actions, and follows an efficiency sequence of etofibrate, nicotinic acid and clofibrate.

A sucrose-rich diet affects triglyceride metabolism differently in pregnant and nonpregnant rats and has negative effects on fetal growth

A sucrose-rich diet (SRD) causes hypertriglyceridemia in nonpregnant rats. To determine whether a SRD further enhances gestational hypertriglyceridemia, female rats were divided into the following two groups: 1) rats fed a SRD (63 g sucrose/100 g), and 2) rats that received the same diet except that the sucrose was replaced by an equal amount of cornstarch (CD). Half of the rats were mated and studied at d 20 of gestation. Body weight increase did not differ between virgin rats fed either diet, but the final body weight of pregnant rats fed SRD was lower than that of rats fed CD due to fewer fetuses per litter and lower fetal and placental weights. The SRD enhanced plasma glucose and insulin concentrations in virgin but not in pregnant rats; plasma triglycerides and FFA concentrations and the rate of triglyceride secretion into the plasma were higher in pregnant than in virgin rats fed SRD, but the increase in liver triglycerides due to SRD was higher in virgin rats. Both removal rate of a fat emulsion and adipose tissue lipoprotein lipase activity (LPL) were lower in virgin rats fed SRD than in those fed CD. They were lower in pregnant than in virgin rats fed CD. Placental and fetal liver triglyceride concentration and placental LPL were higher in rats fed SRD than in those fed CD. Both the increased triglyceride secretion by the liver and the decreased triglyceride removal from blood resulting in maternal hypertriglyceridemia may contribute to the negative effect of SRD on the developing fetus.

Fatty acid composition of lipoprotein lipids in hepatobiliary diseases

Liver damage and alterations in the exocrine function of the gland lead to a profound alteration of the plasma lipoprotein profile. To determine whether hepatic disease results in changes in the lipoprotein fatty acid composition, i.e. to determine whether liver function influences the homeostasis of complex lipids in plasma, we studied the fatty acid profile of lipids from VLDL, LDL and HDL, as well as from total plasma, in thirty-one patients of both sexes with hepatobiliary pathology (compensated liver cirrhosis, uncompensated liver cirrhosis, primary biliary cirrhosis, other intrahepatic cholestasis, and acute viral hepatitis). We also studied a group of healthy adults as controls. We present the lipoprotein profile and the fatty acid composition (myristic C14, palmitic C16, palmitoleic C16: 1, stearic C18, oleic C18: 1, linoleic C18: 2, eicosatrienoic C20: 3 omega 6 and arachidonic C20: 4) of lipoprotein and total plasma triacylglycerols, cholesteryl esters and phospholipids. The main observation of this study is that, despite the profound changes in the lipoprotein profile and the lower abundance of polyunsaturated fatty acids in complex lipids, the composition of all triacylglycerols, cholesteryl esters and phospholipids is very similar for the corresponding lipoproteins of patients with hepatobiliary disease and of control subjects. This indicates that in the controls as in the studied patients, the exchange of lipids between plasmatic lipoproteins is very rapid and demonstrates the possible importance of the extrahepatic synthesis of cholesteryl ester transfer protein.

Teratogenic effects of diabetes mellitus in the rat. Prevention by vitamin E

We wanted to determine whether administration of vitamin E could reduce the production of free radicals which could play a role in the teratogenic effects of diabetes mellitus. Diabetes was induced in Wistar rats by the intravenous administration of streptozotocin. The animals were divided into six groups: one with no supplement (D) and two, supplemented during pregnancy either with oral vitamin E (150 mg/day) (D + E) or with a placebo (safflower oil) (D + O). Three other groups were kept under the same conditions, but were treated with insulin: D + I, D + I + E and D + I + O. There were three groups of matched controls: C, C + E and C + O. All animals were killed on day 11.5 of pregnancy. In C animals the percentages of reabsorptions and malformations were 1.3 and 2%, respectively, compared with 23.6, 24.3, 6.2 and 13.2%, respectively in D and D + I groups. The crown-rump length, number of somites, and protein and DNA content were higher in C animals than in the diabetic rats, independent of insulin treatment. When vitamin E was administered no changes in these parameters were observed in C and D + I animals; however, in the D mothers it reduced the rate of embryo malformations to 4.6% and increased the crown-rump length and the number of somites. However, vitamin E did not modify the protein and DNA content and the percentage of reabsorptions. In conclusion, administration of vitamin E to diabetic animals decreases the rate of embryo malformations and increases their size and maturation, supporting a role for free radicals in the teratogenic effects of diabetes.

Effects of ethanol intake on lipid metabolism in the lactating rat

Female rats receiving alcohol (20%) in drinking water during lactation (AL) were compared to pair-fed animals (PF) and normal controls (C) fed ad lib. All animals were killed on the 12th day of lactation. When compared to C rats, food intake decreased in both AL and PF groups, and this effect was followed by a lower body weight and mammary gland (MG), liver, and parametrial adipose tissue weights. Mammary glands triacylglyceride concentration (TG) was much lower in PF than in AL, although in the latter, values did not reach those of C, and had higher liver TG concentration than any of the other groups. Both PF and AL rats had lower plasma TG, glycerol, and free fatty acid concentrations and higher beta-hydroxybutyrate concentration than C rats. When compared to C rats, the rate of lipogenesis in MG was higher in both PF and AL rats, whereas in liver it was higher in PF and lower in AL rats, and in adipose tissue it was higher in PF and unchanged in AL rats. The appearance of 14C lipids 4 h after oral [14]triolein in both MG and liver was lower in AL and PF rats and only lower in adipose tissue of AL rats as compared to the c rats. Lipoprotein lipase and hormone-sensitive lipase activities were lower in MG in both PF and AL rats than in C, whereas in adipose tissue the activity of lipoprotein lipase did not differ between AL and C rats and the activity of HSL was lower in the former. These findings therefore show that in spite of reduced uptake of orally administered triglycerides due to decreased LPL activity, maternal alcohol feeding during lactation in the rat preserves the mammary gland triglyceride content thanks to enhanced lipogenetic activity. On the other hand, it causes liver triglycerides accumulation, probably as a result of the decreased rate of triglycerides released into circulation, and these changes are not caused by the reduced food intake of the animals.

In vitro effects of a flavonoid-rich extract on LDL oxidation

Flavonoids are phenolic compounds of vegetable origin with antioxidant effects. The present study aimed to determine their properties as LDL antioxidants. LDL were incubated with increasing concentrations of flavonoids (0-16 micrograms/ml) and LDL oxidation was started by adding CuCl2 (2 microM) to the media. When flavonoids were present in the media, vitamin E consumption, the lag phase of conjugated diene formation, LDL electrophoretic mobility in agarose gels and the appearance of thiobarbituric acid reacting substances (TBARS) were delayed in a concentration-dependent manner. To determine whether flavonoids could terminate LDL oxidation once initiated, two sets of experiments were performed. In the first, LDL oxidation was initiated as described above. At 2 or 4 h of incubation, flavonoids were added (4 micrograms/ml) and their effect compared to samples where butylated hydroxytoluene or EDTA were added. At 5 h, in the LDL samples where flavonoids were added, the electrophoretic mobility and TBARS production were the same as those present in LDL samples incubated for the whole period in the absence of flavonoids. However, when either butylate hydroxytoluene or EDTA was added, as would be expected, the LDL oxidation process was completely arrested as shown by a reduction in the appearance of TBARS and a lower LDL electrophoretic mobility. In the second experiment, LDL oxidation was initiated as described above and at 0, 10 and 20 min, flavonoids were added (4 micrograms/ml). When vitamin E was still present in the LDL solution, the flavonoids were able to both increase the lag phase in the formation of conjugated dienes and to delay the consumption of vitamin E. The present results show that in vitro, flavonoids prevent LDL oxidation in a concentration-dependent manner, delaying the consumption of vitamin E, but they cannot terminate or delay LDL oxidation once vitamin E in LDL is consumed.

Cholesteryl ester transfer activity in liver disease and cholestasis, and its relation with fatty acid composition of lipoprotein lipids

Liver disease is accompanied by major qualitative and quantitative disturbances in plasma lipoprotein metabolism, the extent and intensity of which depend on the degree of parenchymal damage, cholestasis, or both. The main objective of this study was to determine the cholesteryl ester transfer CETP activity and its association with the lipoprotein neutral lipid composition in patients with either liver cirrhosis or cholestasis, as compared to normal controls. Lipoproteins were isolated by ultracentrifugation, lipids and apolipoproteins were measured by conventional methods, and the fatty acid composition was established by gas chromatography; CETP activity in lipoprotein-deficient plasma was measured by determining the transfer of [3H]cholesteryl esters from HDL to VLDL. Lipoprotein lipase and hepatic lipase activities were measured in post-heparin plasma by radiochemical methods. In patients with liver cirrhosis, low levels of VLDL, HDL, apo B, and Lp(a) were observed, as well as a change in the composition of HDL particles, with increases in the relative proportion of triglyceride and free cholesterol. Respectively, the last two changes could be attributed in part to the low hepatic lipase activity observed in this study, and to the low lecithin:cholesterol acyltransferase activity previously observed by others. In patients with cholestasis, a moderate hyperlipidemia due to the elevation of LDL was found. In contrast, HDL and apo A-I levels were very low reflecting a low number of HDL particles, which also had altered compositions with increases in the triglyceride and free cholesterol contents relative to apo A-I and esterified cholesterol, respectively. As regards the fatty acid composition of lipoprotein lipids, the two groups of patients showed, in general, a lower proportion of linoleic acid and a compensating higher proportion of oleic acid as compared to the controls, changes that were observed in both cholesteryl esters and triglycerides. In contrast, the proportions of oleic and palmitoleic acids in phospholipids were increased, whereas that of stearic acid was decreased in patients as compared to controls. In patients with liver cirrhosis, as well as in controls, no changes were observed in the fatty acid compositions of cholesteryl ester, triglycerides, or phospholipids among the different lipoproteins, which probably reflects the equilibration reached by the action of CETP. In patients with cholestasis, no differences were observed in fatty acid composition among the lipoprotein phospholipids but, interestingly, cholesteryl esters from VLDL had a significantly lower linoleic acid content than those from HDL, whereas triglycerides from VLDL had significantly higher oleic acid and lower linoleic acid contents than those from HDL. This distinct fatty acid composition of the neutral lipids between lipoproteins was associated with a significant decrease (25%) in the cholesteryl ester transfer activity in patients with cholestasis. We suggest that fat malabsorption due to the biliary defect may induce a decrease in cholesteryl ester transfer protein synthesis or section, which in turn would slow the equilibration of the neutral lipids among plasma lipoproteins.