Rat Serum Lipoproteins Research Articles

Changes in serum lipids and lipoproteins of rats after ovariectomy and administration of the methyl ester of 6-oxy-D-homo-8-isoestrone

Changes in serum lipids and lipoproteins of rats after ovariectomy and administration of the methyl ester of 6-oxy-D-homo-8-isoestrone

Adult rat Leydig cell cultures: Minimum requirements for maintenance of luteinizing hormone responsiveness and testosterone production

The aim of this study was to establish the minimum conditions required to maintain adult rat Leydig cell testosterone production and luteinizing hormone (LH) responsiveness in short term culture, at a level similar to that observed in vivo, which could be used to study factors which may have a delayed or chronic effect on Leydig cell function. Percoll gradient-purified adult rat Leydig cells (5.0 × 10 4/250 μl) were cultured in Dulbecco's modified Eagle's medium/Ham's F12 (DMEM/F12) with 0.1% bovine serum albumin at 32°C for up to 3 days, with daily medium changes. A combination of submaximal rat LH (0.1 ng/ml) and a maximal concentration of rat serum lipoproteins (0.5 mg/ml) maintained testosterone production at between 5 and 15 ng/10 6 cells/h; subsequent stimulation of the Leydig cells with a maximum dose of rat LH (8 ng/ml) over 24 h resulted in testosterone production of 75–240 ng/10 6 cells/h on all 3 days of culture. However, the addition of 0.1% fetal calf serum instead of rat lipoproteins could not maintain LH-stimulated testosterone production in the same culture period. In cultures containing submaximal LH and lipoproteins, levels of testosterone production and responses to maximal LH stimulation were constant over the culture period when expressed as either testosterone production per 10 6 cells plated, or testosterone production per μg DNA recovered at end of incubation. Reduction of the oxygen tension from 19% to 5%, or to 1% did not significantly alter testosterone production by Leydig cells under these established conditions. Although LH-stimulated immunoactive inhibin secretion by the cultured Leydig cells was enhanced by the presence of lipoprotein, maximal LH-stimulated inhibin levels were only partially maintained, and submaximal LH-stimulated inhibin secretion was non-detectable after the initial 24 h. This suggests that not all functions of the Leydig cells were maintained. Nevertheless, these culture conditions provide a simple, effective means of maintaining adult rat Leydig cell testosterone production and LH responsiveness for a period of at least 3 days in culture.

実験的ネフローゼラットの血清リポ蛋白の性状について

実験的ネフローゼラットの血清リポ蛋白の性状について

The hypolipidemic activity of heterocyclic amine boranes in rodents

Heterocyclic amine boranes were observed to be potent hypolipidemic agents in rodents at 8 mg kg per day lowering both serum cholesterol and triglyceride levels. These agents were also effective in lowering tissue lipids. Rat serum lipoprotein cholesterol levels were reduced in the low density lipoprotein (LDL) and very low density lipoprotein (VLDL) fractions and elevated in the high density lipoprotein (HDL) fraction after 14 days. The modes of action of the agents appear to accelerate excretion of lipids in the bile and the suppression of the activities of key hepatic regulatory enzymes of lipids synthesis.

Association between rat serum cholinesterase and some phospholipid components of lipoproteins in thioacetamide-induced hepatic injury

Rat serum lipoprotein phospholipids and serum cholinesterase activity in control and thioacetamide-treated rats (50 mg/kg/day for 30 days) were studied. Analyses were done after 1, 3, 8 and 30 intraperitoneal doses of thioacetamide or 0.15 mol/l NaCl. Cholinesterase activity significantly increased with thioacetamide treatment. Only two phospholipids: LDL-phosphatidylcholine and HDL-lysophosphatidylcholine appeared associated with cholinesterase activity. LDL-phosphatidylcholine increased through the action of hepatotoxic thioacetamide while HDL-lysophosphatidylcholine significantly decreased. Because of the high statistically significant association between changes in these lipoprotein phospholipids and in cholinesterase in this model of hepatic injury, we conclude that cholinesterase could be involved in the regulation of these phospholipid levels.

Structure activity relationships of imidoN‐alkyl semicarbazones, thiosemicarbazones and acethydrazones as hypolipidemic agents in rodents

A series of nitrogen substituted N-butan-3-one derivatives of cyclic imides (phthalimide, substituted phthalimide, o-benzosulfimide, 1,8-naphthalimide, 2,3-dihydrophthalazine-1,4-dione and diphenimide) and their semicarbazone, thiosemicarbazone and acethydrazone derivatives were investigated for hypolipidemic activity in rodents. These compounds were generally potent hypolipidemic agents, lowering serum cholesterol levels on an average of 37% and serum triglyceride levels on an average of 29% after 16 days dosing at 20 mg/kg day intraperitoneally (I.P.) in mice. Several analogs, most notably the semicarbazone and acethydrazone derivatives of 1-N-(1,8-naphthalimido)-butan-3-one, demonstrated improved hypocholesterolemic activity relative to their ketone precursors. Similarly, the acethydrazone derivatives generally resulted in improved hypotriglyceridemic activity in each series of 2-(3-oxobutyl)-2,3-dihydrophthalazone-1,4-dione analogs tested. The thiosemicarbazones in mice generally resulted in a loss in hypolipidemic activity. Select compounds, 1-N-3-methylphthalimido butan-3-semicarbazone (Ig) and 1-(4-methoxyphthalazine-1(2H)-one)yl butan-3(N-acetyl)hydrazone (IVg), at 10 mg/kg/day orally administered to rats demonstrated potent hypolipidemic activity after 14 days. These compounds lowered liver, small intestine mucosa and aorta wall tissue lipids, e.g. cholesterol and triglycerides, and raised fecal excretion of cholesterol moderately and of triglyceride significantly. Rat serum lipoprotein fractions after treatment for 14 days showed that the two agents lowered VLDL cholesterol and raised HDL cholesterol content.

Growth hormone and thyroxine affect lipoprotein metabolism in hypothyroid and hypophysectomized rats

The aim of this study was to evaluate the effect of thyroxine (T4) and GH replacement therapy on serum lipoproteins in rats with primary and secondary hypothyroidism and to see whether recovery of GH activity was associated with normalization of serum lipoproteins. In both the primary and secondary hypoproteins. In both the primary and secondary hypothyroid rats, total cholesterol (TC) was higher than in normal controls, due to an increase in low-density lipoprotein cholesterol (LDL-c) and to a lesser extent also in high-density lipoprotein cholesterol (HDL-c). Treatment of hypophysectomized rats with GH induced a decrease in the concentration of TC, LDL-c and HDL-c, while liver lipase activity (LLA) increased. The effect of GH on HDL-c was correlated with the increase in LLA. T4 replacement therapy of hypophysectomized rats normalized LDL-c, but HDL-c and LLA were unaffected. During primary hypothyroidism, T4 treatment induced GH activity, increased LLA and reduced the HDL-c concentration. GH treatment of primary hypothyroid rats had a similar influence on the lipid levels and LLA as in hypophysectomized animals, although the lowering of HDL-c was less prominent. These results demonstrate that GH determines serum lipoproteins during both primary and secondary hypothyroidism.

Identification and characterization of rat serum lipoprotein subclasses. Isolation by chromatography on agarose columns and sequential immunoprecipitation.

Lipoproteins, present in serum of chow-fed rats, were fractionated according to size by chromatography of serum on 6% agarose columns. The distributions of apolipoprotein (apo) A-I, E, and A-IV within the high density lipoprotein (HDL) size range (i.e., lipoprotein complexes smaller than low density lipoproteins) showed the existence of lipoprotein subclasses with different size and chemical composition. Sequential immunoprecipitations were performed on these fractions obtained by agarose column chromatography, using specific antisera against apoA-I, apoE, and apoA-IV. The resulting precipitates and supernatants were analyzed for cholesteryl esters, unesterified cholesterol, phospholipids, triglycerides, and specific lipoproteins. The following conclusions were drawn from these experiments. Sixty-three +/- 3% of apoE in the total HDL size range is present on a large particle (mol wt 750,000). This lipoprotein contains apoE as its sole protein constituent and is called LpE. Thirty-nine +/- 4% of the cholesterol found in the HDL size range is present in this fraction. The cholesterol:phospholipid ratio is 1:1.1. Sixty-nine +/- 8% of apoA-I in the total HDL size range is present on a smaller particle (mol wt 250,000). This apoA-I-HDL has apoA-I as its major protein component and possibly contains minor amounts of C apoproteins and A-II, but neither apoE nor apoA-IV. It contains 39 +/- 8% of the total cholesterol found in the HDL size range and the cholesterol:phospholipid ratio is 1:1.6.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypolipidemic Activity in Rodents of Phenobarbital and Related Derivatives

A series of 5-alkyl-5-phenylbarbituric acid analogues were shown to be potent hypolipidemic agents in rats and mice at 20 mg/kg/day. This dose is lower than that required for hypolipidemic activity for clofibrate and nicotinic acid derivatives in rodents and man. These new derivatives reduced both serum cholesterol and triglyceride levels in rodents by either the oral or intraperitoneal route of administration. Previous studies have demonstrated that similar heterocyclic compounds, i.e. cyclic imides, glutarimides and hydantoins are potent hypolipidemic agents in rodents. The barbituric acid derivatives probably interfered with de novo synthesis of cholesterol and fatty acids in the early steps since the agents inhibit the activities of ATP-dependent citrate lyase and acetyl-CoA synthetase. Triglyceride synthesis may be blocked since the agents inhibited the rate limiting enzyme, sn-glycerol-3-phosphate-acyl-transferase. Rat tissue lipids especially cholesterol and triglycerides were reduced after 14 days treatment. Fecal lipids were increased in cholesterol and phospholipid content by selected compounds. The rat serum lipoprotein after 14 days drug administration showed reduced VLDL-cholesterol and HDL-triglyceride contents. The modulation of the lipid content of the serum lipoproteins by the barbituric acids suggest that these agents may be helpful in treating clinical hyperlipidemic disease states.

The effect of gossypol on serum lipoproteins of adult rats.

It has been shown that gossypol treatment brings about marked changes in plasma lipoproteins of certain species causing a marked fall in total cholesterol and LDL-cholesterol levels. Using Helena electrophoretic system the lipoprotein pattern in serum of adult rats treated with gossypol was studied. Gossypol treatment for 1 day and 7 days continuously did bring about changes in serum lipoprotein profile. A marked increase in VLDL-cholesterol and fall in LDL-cholesterol was observed in rats treated with gossypol which was more pronounced in the 7 days treated group. It did not bring about any marked change in total cholesterol level. It did cause an increase in serum triglyceride level. Heparin injection which brought about a fall in VLDL-cholesterol with a concomitant increase in HDL-cholesterol in control rats did not elicit changes in gossypol-treated rats. Thus, gossypol treatment appears to alter serum lipoprotein metabolism in rats also.

Cholesterol transfer from mitochondrial membranes and cells to human and rat serum lipoprotein fractions.

We have investigated the transfer of [14C]cholesterol from labeled bovine heart mitochondria and Friend erythroleukemic cells to high density lipoprotein (HDL), low density lipoprotein (LDL), and very low density lipoprotein (VLDL) fractions from human and rat plasma. The lipoprotein fractions were obtained by molecular sieve chromatography of plasma on agarose A-5m columns. For either membrane system, the highest rate of [14C]cholesterol transfer was observed with the human and the rat HDL fraction. Since the mitochondria lack the receptors for HDL, one may conclude that the observed preferential transfer is not governed by a receptor-controlled interaction of HDL with the membrane. Under conditions where the pool of free cholesterol in the lipoprotein fractions was the same, HDL was a much more efficient acceptor of [14C]cholesterol from mitochondria than LDL or VLDL. Similarly, transfer of [14C]cholesterol proceeded at a higher rate to HDL than to sonicated egg phosphatidylcholine (PC) vesicles, even under conditions where there was a tenfold excess of the vesicle-PC pool over the HDL phospholipid pool. This preferred transfer of [14C]cholesterol to HDL cannot be explained by a random diffusion of monomer cholesterol molecules. Rather, it shows that HDL has a specific effect on this process in the sense that it most likely enhances the efflux of cholesterol from the membrane. Treatment of HDL with trypsin reduced the rate of [14C]cholesterol transfer by 40-50%, indicating that protein component(s) are involved. One of these components appears to be apoA-I, as this protein was shown to enhance the transfer of [14C]cholesterol from mitochondria to lipid vesicles.

Cholesterol binding reserve of hyperlipemic rat serum lipoproteins in chronic ethanol administration

Chronic administration of ethanol in rats caused the reduction of serum cholesterol binding reserve. The very low density and high density lipoproteins, main serum cholesterol binding reserves, were slightly increased with corresponding increases in their lipid and protein components during initial stage of alcohol consumption. However, these capacities get deminished during reversal of hyperlipemia induced by prolonged action of ethanol. This situation may be an early indicator for the initiation of hepatic damage and a variety of secondary effects of ethanol.

Effects of chronic ethanol consumption in atherosclerosis-prone JCR:LA-corpulent rat.

Rats of the atherosclerosis-prone JCR:LA-corpulent strain were subjected to long-term low (0.5% wt/vol) or high (4% wt/vol) consumption of ethanol from 1 to 12 months of age. The corpulent rats are hyperphagic, obese, and insulin-resistant; exhibit a marked very low density lipoprotein hyperlipidemia; and develop both vascular and myocardial lesions while eating a normal rat chow. The total lipid profile of the rat sera showed only limited changes with ethanol consumption. There were also no significant effects on high density lipoprotein lipids. Ethanol consumption was associated with elevated fasting glucose concentrations in both lean and corpulent rats and a strong decrease in fasting insulin levels and pancreatic B-cell volume density in the hyperinsulinemic corpulent rats. The relative frequency of myocardial nodules of chronic inflammatory cells was increased in the ethanol-consuming rats, both lean and corpulent. In contrast, old organized lesions (scars) were absent in the ethanol-consuming corpulent rats. Thus, ethanol consumption had no major effect on serum lipids or lipoproteins in the corpulent rat but was associated with a reduction in insulin resistance and islet cell hyperplasia, with an associated decreased incidence of myocardial lesions.

Lipid peroxidation of hyperlipemic rat serum lipoproteins in chronic ethanol and acetaldehyde administration

The levels of lipid peroxides in circulatory lipoproteins increased with chronic administration of ethanol or acetaldehyde. Low density lipoprotein showed a greater increase in its content of lipid peroxides than very low density lipoprotein or high density lipoprotein. However, very low density lipoprotein was more prone to lipid peroxidationin vitro than low density lipoprotein or high density lipoprotein. The effect of acetaldehyde was more marked than that of ethanol. Lipoproteins of control and hyperlipemic groups were partially protected against peroxidation by butyrated hydroxytoluene and serum high density lipoprotein of normal rats.

Effects of 2-(2,4-dimethylphenyl)indan-1,3-dione on serum lipoprotein and lipid metabolism of rodents.

2-(2,4-Dimethylphenyl)indan-1,3-dione was shown to be a potent hypolipidemic agent in rodents, lowering significantly both serum cholesterol and triglyceride levels at 20 mg/kg/day. The agent in vivo inhibited the enzymatic activities of ATP-dependent citrate lyase, acetyl-CoA synthetase, cholesterol-7-alpha-hydroxylase, acyl-CoA cholesterol acyl transferase, sn-glycerol-3-phosphate acyl transferase and phosphatidylate phosphohydrolase. Tissue lipid levels of liver and small intestine also were reduced by the agent. The rat serum lipoprotein lipid content was modulated by the drug, which should be favorable for the removable of cholesterol from peripheral tissue for conduction to the liver for clearance from the body. Low density lipoprotein (LDL) cholesterol levels were reduced after treatment, which suggests that the agent potentially reduces deposition of cholesterol in plaques. If chemotherapy for atherosclerosis is to be successful, then the high density lipoprotein (HDL) cholesterol level needs to be elevated more than 16% to 25%, the level produced by current hypolipidemic agents. 2-(2,4-Dimethylphenyl)indan-1,3-dione offers a 75% increase in HDL cholesterol levels and a 30% reduction of LDL cholesterol levels with a suppression of de novo synthesis of lipids and a reduction of tissue cholesterol deposition.

Effect of pectin, wheat bran and cellulose on serum lipids and lipoproteins in rats fed on a low- or high-fat diet.

1. Four groups of adult male Sprague-Dawley rats were fed for 6 weeks on a diet with a low-fat content (50 g/kg) and another four groups were given a diet rich in fat (250 g/kg) and cholesterol (12 g/kg). In both cases, the basal diets were either fibre-depleted or supplemented with cellulose (60 g/kg), wheat bran (100 g/kg) or low-methoxyl pectin (100 g/kg). 2. Low-methoxyl pectin displayed the most hypocholesterolaemic effect and decreased the cholesterol content of the very-low-density lipoproteins (VLDL) and low-density lipoproteins (LDL), when the low-fat diet was given. When rats were fed on the high-fat diet, pectin no longer had a hypocholesterolaemic effect but still decreased the VLDL-cholesterol content. Pectin lowered serum triglyceride and VLDL-triglyceride levels only when the low-fat diet was given. 3. Wheat bran exerted no hypocholesterolaemic effect in rats fed on the low- and high-fat diets, but decreased the cholesterol content of VLDL and lowered serum triglycerides and VLDL-triglycerides when the high-fat diet was given. 4. Purified cellulose had no significant effect on plasma lipids. 5. As shown by multivariance analysis, low-methoxyl pectin and wheat bran both beneficially modified the serum triglyceride and cholesterol variables except VLDL-triglycerides. However, the magnitude of the effect of each individual type of fibre was dependent on the fat and cholesterol content of the diet, suggesting the existence of different mechanisms of action.

Enzymatically induced alterations in the structure of rat serum lipoproteins

Incubation of freshly isolated rat serum induces a large number of changes in the properties of the serum lipoproteins, especially the high density lipoproteins (HDL). The particle diameter of the HDL increases from about 10.4 nm to 12.3 nm and the protein content appears to increase by about 60,000 Daltons. Reactions catalyzed by lecithin:cholesterol acyltransferase (LCAT) lead to a marked decrease in cholesterol and phospholipid content, and an even greater increase in cholesteryl ester content. Especially noteworthy are the marked increases in apoE and apoA-IV which are found associated with HDL as a result of this process. Data indicate that the affinity of apoE and apoA-IV for the HDL particles may be influenced by the proportion of surface to core lipid and by the presence of products of the LCAT reaction. Changes in the apoprotein content of very low density lipoproteins are also observed, with A-I and A-IV appearing in this density interval. All of the above changes can be prevented by the inclusion of 5,5'dithiobis(2-nitrobenzoate) or p-chloromercuriphenylsulfonate during the incubation, or by heat treatment of serum at 56 degrees C for 30 min; these treatments are known to inhibit LCAT activity. It is concluded that LCAT action is the major cause of the various changes in HDL structure that are observed and that alterations in apoprotein content occur to correct the resultant imbalance between core lipid and coverage of this core by amphiphilic components. Increased apoE association with cholesteryl ester-rich HDL may provide an efficient means for receptor-mediated removal of cholesterol from the circulation.

Acetaldehyde binding increases the catabolism of rat serum low-density lipoproteins

Acetaldehyde was found to form adducts with rat serum lipoproteins. The binding of [ 14C] acetaldehyde to lipoproteins was studied at low concentrations which are known to exist during ethanol oxidation. The amount of lipoprotein adducts was a linear function of acetaldehyde concentration up to 250 μM. Incubation of rat plasma low-density lipoproteins (LDL) with 200 μM acetaldehyde increased the disappearance rate of the 3H-label from the cholesterol ester moiety of LDL injected into normal rats. The data show that even low concentrations of acetaldehyde are capable of affecting LDL metabolism. These findings may provide an explanation for the low concentrations of serum LDL in alcoholics. The alcohol-induced hyperlipidemia includes either a lack of increase or a decrease in the low-density lipoprotein (LDL) concentration, but the underlying mechanism is not known (1,2). It has been shown previously, that the acetylation of lysine residues of LDL apoprotein (apoB) by acetanhydride leads to rapid uptake of LDL particles by macrophages through a non-LDL receptor pathway (3). Since acetaldehyde, the first toxic metabolite of ethanol, is a chemically reactive compound capable of binding to proteins (4–6), we tested whether acetaldehyde forms adducts with serum lipoproteins and subsequently alters the catabolism of LDL.

Lipoproteins and liposomes as in vivo cholesterol vehicles in the rat: preferential use of cholesterol carried by small unilamellar liposomes for the formation of muricholic acids

Hepatic cholesterol metabolism was studied in rats with a permanent biliary drainage. Three cholesterol vehicles were used to discriminate between metabolic pathways of cholesterol in the liver. [ 3H]Cholesterol was administered intravenously associated with rat serum lipoproteins, multilamellar (MLV) or small unilamellar (SUV) liposomes. The liposomes were made from cholesterol, sphingomyelin and phosphati-dylserine in a 5:4:1 molar ratio. Initial blood elimination differed markedly for the three vehicles: 15 min after injection the 3H radioactivity content of blood for MLV, SUV and lipoprotein was 3, 50 and 54% of the injected dose, respectively. After about 30 min, MLV-cholesterol label started to reappear in the blood, probably after processing of the vehicle by the Kupffer cells. For all vehicles about 80% of the cholesterol label had been excreted in bile after 120 h, predominantly as bile acids. Initial biliary excretion was highest for lipoproteins (5.7% at 1 h), followed by MLV and SUV (1.3 and 1.2%, respectively). No differences in the radioactivity of excreted bile acids were detectable between the three vehicles at 12 h after injection. However, at 1 h the radioactivity in the muricholic acid fraction was markedly increased, as compared to the other bile acids after injection of SUV-cholesterol, but not after injection of MLV- or lipoprotein-cholesterol. Also, the glycine/taurine conjugation ratio of bile acids was increased for SUV-cholesterol at 1 h as compared to that for the other two vehicles. Since SUV appear to donate their cholesterol to a pool which preferentially supplies cholesterol for muricholic acid synthesis, we conclude that more than one cholesterol pool exists in the hepatocytes from which cholesterol can be recruited for bile acid synthesis. Zonal heterogeneity might be responsible for the observed differences.

Comparison of the metabolic behavior of rat apolipoproteins A-I AND A-IV, isolated from both lymph chylomicrons and serum high density lipoproteins

1. 1. Rat apolipoprotein (apo) A-I and A-IV, isolated from both lymph chylomicrons and serum high density lipoproteins (HDL) were analyzed by isoelectric focusing. 2. 2. Lymph chylomicron apo A-I consisted for 81 ± 2% of the pro form and for 19 ± 2% of the mature form, while apo A-I isolated from serum HDL was present for 36 ± 4% in the pro form and for 64 ± 4% in the mature form. Apo A-IV also showed two major protein bands after analysis by isoelectric focusing. 3. 3. The most prominent component is the more basic protein that amounts to 80 ± 2% in apo A-IV isolated from lymph chylomicrons and to 60 ± 3% in apo A-IV isolated from serum HDL. 4. 4. Apo A-I (or apo A-IV), isolated from both sources (lymph chylomicrons or serum HDL), was iodinated and the radioactive apolipoproteins were incorporated into rat serum lipoproteins. 5. 5. The resulting labeled HDL was isolated from serum by molecular sieve chromatography on 6% agarose columns and injected intravenously into rats. 6. 6. No difference in the fractional turnover rate or the tissue uptake of the two labeled HDL preparations was observed, neither for apo A-I nor for apo A-IV. 7. 7. It is concluded that the physiological significance of the extracellular pro apo A-I conversion or the post-translational modification of apo A-IV is not related to the fractional turnover rate in serum or to the rate of catabolism in liver and kidneys.