Metabolism of 125I-labeled lipoproteins by the isolated rat lung.

The capacity of the isolated perfused rat lung to metabolize the protein moieties of serum lipoproteins was assessed using homologous (rat) and heterologous (human) plasma lipoproteins. The protein and lipid moieties of the plasma lipoproteins were labeled in vivo with Na[125I]. In selected cases the lipoprotein peptides were labeled in vivo with 14C- or 3H-labeled amino acids. Uptake of lipoprotein label during perfusion was monitored by measure of losses in perfusate label and by rises in pulmonary tissue labeling as shown by radioassay and by light and electron microscope radioautography. Lipoprotein degradation was assessed by fractionation of perfusate and lung tissue radioactive material into trichloroacetic acid (TCA)-isoluble, TCA-soluble, and ether-ethanol-soluble fractions. When heparin was included in the perfusion medium, there was selective degradation of the protein portion of very low density lipoprotein (VLDL) in the perfusate and concomitant uptake of radioactive label by the lungs. Low density lipoprotein (LDL)) was neither taken up nor catabolized by the isolated rat lung in the absence or presence of heparin. By light and electron microscopy, the label was localized over the interalveolar septa, predominantly the capillary endothelium. Disappearance of TCA-insoluble radioactivity from the perfusate was associated with the generation of both TCA-soluble iodide and noniodide radioactivity. Greater than 50% of the radioactive label taken up by the lungs was found in the delipidated TCA-insoluble fraction. This study provides in vitro evidence for pulmonary catabolism of VLDL apolipoproteins and uptake of peptide catabolic products of VLDL by the lung.

Hepatic secretion of lipoproteins in the rat and the effect of experimental nephrosis.

Livers from normal and nephrotic rats were perfused by the nonrecirculating technique. Nephrosis was studied on the 7th d after the injection of puromycin animonucleoside. Amino acid-labeled lipoproteins (d < 1.21) were isolated from the perfusion medium by agarose column chromatography or by sequential density ultracentrifugation. In both groups of animals, in addition to very low density lipoproteins and nascent high density lipoproteins, column chromatography revealed the presence of a peak of 2-3 x 10(6) daltons. This peak contained lipoproteins of densities corresponding to <1.006, 1.006 < d < 1.02, and 1.02 < d < 1.06, which indicated that rat liver secretes a heterogeneous mixture of triglyceride-rich lipoproteins. The amount of these lipoprotein density classes was measured and their lipid and apoprotein composition and their apoprotein specific activity were determined. In both groups of rats there was a progressive rise in phospholipid and decrease in triglyceride content as the isolation density increased from 1.006 and 1.06. The lipoproteins from the nephrotics had higher amounts of cholesterol. The livers from the nephrotic rats secreted two to three times as much lipoprotein as controls in all density classes in the first 20 min, but during the next 40 min only the 1.02 < d < 1.06 and nascent high density lipoproteins remained at this high level compared to controls. A larger total liver pool of apolipoproteins in nephrotic livers was inferred from their lower specific activities during the first 20 min. The apoprotein composition of liver perfusate lipoproteins from nephrotics differed from controls. There was a 40% decrease in the amount of low molecular weight apoproteins in all density classes, with corresponding increases in apo B and apo E in the triglyceride-rich fractions. The apo A-1 content of nascent HDL was increased from 16% in controls to 52% in nephrotics, with corresponding decreases in apo C and apo E. When these results were combined with specific activity measurements of the individual apoproteins and the net secretion rate of total protein in each lipoprotein class, it was possible to estimate the total amount of each apoprotein secreted and the total incorporation of labeled amino acids into each. The incorporation of label gave results similar to those obtained by direct measurement of the amounts of apoproteins. Apo E secretion was increased by a factor of 1.8, apo B by 2.8, and apo A-1 by 8.4, whereas the secretion of apo C was not significantly altered. We explain these results by postulating that the primary stimulus to hepatic plasma protein synthesis in response to proteinuria is general and that subsequent negative feedback regulation affects individual apolipoprotein synthesis rates. A corollary of this hypothesis is that the biosynthesis and secretion of an apoprotein may be regulated independently of the lipoprotein density class in which it is found.

Catabolism of very low density lipoproteins in experimental nephrosis.

The effects of experimental nephrosis in rats, produced by puromycin aminonucleoside, include an elevation of plasma levels of all lipoprotein density classes and the appearance of high density lipoprotein (HDL) rich in apoprotein (apo) A-I and deficient in apo A-IV and apo E. The hyperlipoproteinemia is associated with an increase in hepatic synthesis of lipoproteins. The possible role of decreased very low density lipoprotein (VLDL were obtained from nonfasting animals by ultracentrifugation at d 1.006 and included chylomicrons) catabolism and its relationship to the apolipoprotein composition of nephrotic high density lipoproteins (1.063 less than d less than 1.210, or 1.072 less than d less than 1.210 [HDL]) was explored. When 125I-VLDL was injected, the faster plasma clearance of lower molecular weight apolipoprotein B (apo BL) compared with that of higher molecular weight apo BH which is seen in normal rats was not observed in nephrotic rats. Less labeled phospholipid, apo C, and apo E were transferred from VLDL to higher lipoprotein density classes. Heparin-releasable plasma lipoprotein lipase and hepatic lipase activities were decreased by 50% in nephrotic rats compared with pair-fed controls. Perfusion of livers with medium that contained heparin released 50% less lipase activity in nephrotic rats than in controls. When heparin was injected intravenously, significant decreases in plasma levels of triglycerides and significant increases in levels of free fatty acids were observed in both groups of animals. In the nephrotic rats, 86% of the free fatty acids were in the lipoprotein fractions, as compared with 16% in the controls. Heparin treatment did not restore to normal the decreased apo BL clearance in nephrotic rats but it produced an increased amount of apo A-IV and apo E in the plasma HDL. In vitro addition of partially pure lipoprotein lipase to whole serum from nephrotic rats significantly increased the content of apo E in HDL. We conclude that the abnormal apoprotein composition of HDL in experimental nephrosis is the result of altered entry of apolipoproteins from triglyceride-rich lipoproteins, probably because of decreased lipolysis.

Effects of nonketotic streptozotocin diabetes on apolipoprotein B synthesis and secretion by primary cultures of rat hepatocytes.

The effects of hypoinsulinemic nonketotic streptozotocin diabetes on hepatic apo B synthesis and secretion was studied in primary cultures of rat hepatocytes. Diabetic rats were characterized by their significantly elevated serum glucose, apo B, and triglyceride levels, while serum insulin levels were less than a third of normal. Serum transminase activities of diabetic rats were significantly elevated when compared with control rats, which was attributed to an increase in liver transaminase activity in diabetic rats. The pattern of enzyme activities of hepatocytes reflected that observed in livers of donor rats and the pattern was retained by primary cultures of hepatocytes over the culture period. Hepatocytes from diabetic rats secreted only one third of the apo B secreted by hepatocytes from control rats, which was determined by monoclonal immunoassay of rat total apo B. Decreases in secretion were confirmed by measurement of secretory [35S]methionine-labeled lipoprotein apo B radioactivity. The decreased apo B content of media of hepatocytes from diabetic rats was not due to increased apo B catabolism since hepatocytes from diabetic rats were shown to degrade less lipoprotein-apo B than hepatocytes from normal rats in control experiments. In addition, the apo B content of detergent-solubilized hepatocytes from diabetic rats was significantly less than that of hepatocytes from control rats. These results suggest that insulin is necessary for normal hepatic apo B synthesis and secretion and that the hyperlipidemia associated with hypoinsulinemia in vivo is primarily of intestinal origin.

Impaired hepatic apolipoprotein B and E translation in streptozotocin diabetic rats.

Studies of streptozotocin-induced diabetes in rats have demonstrated that hepatic apo B and apo E production are reduced. To determine if reductions are related to decreases in hepatic mRNAs, we performed blotting analysis of total liver RNA with rat apo B, apo E, and albumin cDNA probes. The expected reduction in albumin mRNA levels to 48% of control livers occurred in diabetic rat liver, while apo B and apo E mRNA levels were unchanged. The proportion of translational stop codon (BSTOP) mRNA averaged 43% of total in diabetic rats similar to control levels. Long-term labeling experiments using [35S]methionine in primary cultures of rat hepatocytes and specific immunoprecipitations demonstrated production of apo B and apo E, and albumin by hepatocytes from diabetic rats was reduced to 37%, 53%, and 23% of controls. Pulse-chase studies, together with mRNA analyses, suggest that reduced hepatic secretion of apo B and apo E in diabetics is primarily a result of impaired translation and not intracellular degradation. Ribosome transit studies directly confirmed the prolonged elongation rates for apo B and apo E mRNAs in hepatocytes derived from diabetic rats. This effect was more pronounced on apo BH (higher molecular weight) than on apo BL (lower molecular weight). Treatment of diabetic rats with insulin for 7 d led to normalization of hepatic albumin mRNA levels with no substantial change in apo E mRNA levels. In contrast, insulin treatment resulted in significant increases in hepatic apo B mRNA over control levels. Results suggest hepatic albumin and apo B mRNA levels are responsive to insulin in the diabetic state.

Insulin regulation of triacylglycerol-rich lipoprotein synthesis and secretion.

This review has considered a number of observations obtained from studies of insulin in perfused liver, hepatocytes, transformed liver cells and in vivo and each of the experimental systems offers advantages. The evaluation of insulin effects on component lipid synthesis suggests that overall, lipid synthesis is positively influenced by insulin. Short-term high levels of insulin through stimulation of intracellular degradation of freshly translated apo B and effects on synthesis limit the ability of hepatocytes to form and secrete TRL. The intracellular site of apo B degradation may involve membrane-bound apo B, cytoplasmic apo B and apo B which has entered the ER lumen. How insulin favors intracellular apo B degradation is not known. An area of recent investigation is in insulin-stimulated phosphorylation of intracellular substrates such as IRS-1 which activates insulin specific cellular signaling molecules [245]. Candidate molecules to study insulin action on apo B include IRS-1 and SH2-containing signaling molecules. Insulin dysregulation in carbohydrate metabolism occurs in non-insulin-dependent diabetes mellitus due to an imbalance between insulin sensitivity of tissue and pancreatic insulin secretion (reviewed in Refs. [307,308]). Insulin resistance in the liver results in the inability to suppress hepatic glucose production; in muscle, in impaired glucose uptake and oxidation and in adipose tissue, in the inability to suppress release of free FA. This lack of appropriate sensitivity towards insulin action leads to hyperglycemia which in turn stimulates compensatory insulin secretion by the pancreas leading to hyperinsulinemia. Ultimately, there may be failure of the pancreas to fully compensate, hyperglycemia worsens and diabetes develops. The etiology of insulin resistance is being intensively studied for the primary defect may be over secretion of insulin by the pancreas or tissue insulin resistance and both of these defects may be genetically predetermined. We suggest that, in addition to effects in carbohydrate metabolism, insulin resistance in liver results in the inability of first phase insulin to suppress hepatic TRL production which results in hypertriglyceridemia leading to high levels of plasma FA which accentuate insulin resistance in other target organs. As recently reviewed [17,254] the role of insulin as a stimulator of hepatic lipogenesis and TRL production has been long established. Several lines of evidence support that insulin is stimulatory to the production of hepatic TRL in vivo. First, population based studies support a positive relationship between plasma insulin and total TG and VLDL [253]. Second, there is a strong association between chronic hyperinsulinemia and VLDL overproduction [309].(ABSTRACT TRUNCATED AT 400 WORDS)

A comparison of the surface activities of rat plasma apolipoproteins C-II, C-III-0, C-III-3.

Rat apolipoproteins C-II, C-III-0 and C-III-3 give similar surface pressure (pi)-molecular area isotherms when spread at the air/water interface. When allowed to adsorb to the clean air/water interface, the intrinsic surface activity of apolipoprotein C-II is somewhat higher than that of apolipoprotein C-III. All three apolipoprotein C molecules can penetrate an egg phosphatidylcholine monolayer spread at the air/water interface causing an increase (delta pi) in surface pressure. Increasing the initial surface pressure (pi i) of the lipid monolayer decreases delta pi, and delta pi = 0 when pi i greater than or equal to 32 +/- 2 mN . m-1 for all three apolipoprotein C proteins. This implies that apolipoproteins C-II, C-III-0 and C-III-3 would adsorb and desorb similarly from the surfaces of lipoprotein particles during metabolism.

Catabolism of the apolipoproteins of HDL in control and nephrotic rats.

125I-labeled high density lipoprotein (HDL) from control rats, or from rats made nephrotic by puromycin aminonucleoside, was injected into control or nephrotic rats. At 5 and 20 h, the amount and distribution of label remaining in apolipoproteins HDL, A-I, E, A-IV and the C apolipoproteins was measured after ultracentrifugal isolation of HDL and SDS-polyacrylamide gel electrophoretic separation of each apolipoprotein. There were no significant differences in the removal rates of apolipoprotein HDL or of the individual apolipoproteins when the removal of HDL of controls was compared to HDL of nephrotics. HDL from nephrotic rats contains less than 10% of either the apolipoprotein A-IV or apolipoprotein E content of control HDL, indicating that neither apolipoprotein A-IV nor apolipoprotein E play a significant role in determining the catabolic fate of rat HDL. In severely nephrotic animals the apoliprotein C content of HDL was reduced to 50% of control values and the apolipoprotein A-I content of HDL rose to 87% of the total apolipoprotein. The individual apolipoproteins of HDL from either nephrotics or controls were catabolized at the same rates irrespective of the degrees of nephrosis or altered HDL apolipoprotein composition. The apparent fractional catabolic rates for apolipoprotein HDL and for each of the apolipoproteins, determined after 20 h, did not differ from one another, and all were reduced by half in the nephrotic rats compared to the normal controls. These results support the concept that HDL is catabolized as a particle mediated by apolipoprotein A-I recognition, and they reinforce earlier work indicating that increased synthesis is the dominant factor responsible for increased plasma HDL concentrations in experimental nephrosis.

Lipoprotein apolipoprotein synthesis by human hepatoma cells in culture.

Lipoprotein synthesis was demonstrated by double diffusion with low density lipoprotein antibody, and by 3H-labeled amino acid incorporation into proteins of the d less than 1.063 g/ml centrifugally isolated lipoprotein fraction. Radioactive label was incorporated predominantly into apolipoprotein B (60%), apolipoprotein A-I (20%) and apolipoprotein C (12%), as determined by Sepharose column chromatography and polyacrylamide gel electrophoresis. Incorporation of radioactive label into apolipoprotein B was inhibited by the presence of albumin in the medium, and was restored to control levels with the addition of 1 mM oleic acid, indicating that cell synthesis of apolipoproteins could be modified by culture conditions. The human hepatoma cell line, Hep G2, provides a potential in vitro model for the study of regulation of human hepatic lipoprotein and apolipoprotein synthesis.

Proteolysis of very low density lipoprotein in perfused lung.

Perfusion of homologous 125I-labeled rat very low density lipoprotein through isolated rat lungs in the presence of heparin resulted in apoprotein proteolysis. At least the apoprotein C was degraded into two peptides smaller than 7500 daltons as measured by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The lung uptake of radioactivity was small and due mainly to the presence of the larger of the two peptides. The lung protease was not active against an 125-I-labeled albumin substrate and was not released into the medium by heparin.

Effects of fatty acids on apolipoprotein B secretion by McArdle RH-7777 rat hepatoma cells.

The effect of oleic acid (OA), stearic acid (SA) and elaidic acid (EA) on cellular and secreted apolipoprotein (apo) B was examined in McArdle RH-7777 (McArdle) hepatoma cells and in primary rat hepatocytes. ApoB secretion by McArdle cells was significantly inhibited by 20% in 8 h incubations in medium containing EA and SA and by 50% in medium containing OA. In contrast, apo B secretion and cellular apo B of primary rat hepatocytes was relatively unaffected by incubations in medium containing fatty acids. Both B100 and B48 secretion in McArdle wild type and B48 in apo B mRNA editing enzyme catalytic polypeptide transfectants expressing B48 were inhibited to a similar extent indicating an effect of OA on both apo B species. The effect of OA occurred without changes in cellular apo B or in apo B mRNA abundance suggesting a post-transcriptional mechanism. Time course studies indicate that the suppressive effect of OA requires 4 h of incubation suggesting the depletion of a limiting factor important in apoB secretion. By increasing the proportion of palmitic acid to OA in the medium, apoB secretion by McArdle cells was progressively restored to control levels implicating an unique role for newly synthesized saturated fatty acid.

Insulin-mimetic effects of vanadate in primary cultures of rat hepatocytes.

To evaluate possible mechanisms by which insulin inhibits hepatic apolipoprotein B (apoB) secretion, we incubated primary cultures of rat hepatocytes with sodium orthovanadate, a phosphotyrosine phosphatase inhibitor and insulin-mimetic agent. Vanadate (10 microM) and insulin (10 nM) inhibited the medium accumulation of apoB (secretion) by 21 and 37%, respectively, without increasing intracellular apoB. The effects of insulin and vanadate together were not additive. Both insulin and vanadate enhanced intracellular glycogen accumulation by 82 and 37%, respectively. Unlike insulin, vanadate, at a concentration that inhibited apoB secretion (10 microM), had no effect on intracellular lipogenesis, inhibited the secretion of newly synthesized hepatic proteins, and had a delayed onset and termination of action on inhibition of apoB secretion. At higher concentrations (40 and 80 microM), vanadate stimulated intracellular lipogenesis. In conclusion, our data indicate that vanadate mimics insulin action in hepatocytes with regard to the inhibition of medium accumulation of apoB. These data are consistent with the hypothesis that inhibition of apoB secretion may be secondary to an increase in phosphotyrosine content at its site of synthesis. The kinases responsible for this effect have not been identified. Several effects of vanadate, however, are different from those of insulin, suggesting a differential sensitivity to vanadate, a divergence of the signal transfer by insulin and vanadate at the insulin-receptor or postreceptor level, or both.

Hypercholesterolemia and aortic glycosaminoglycans of rabbits fed semi-purified diets containing sucrose and lactose.

This study was designed to evaluate the role of dietary sucrose and lactose in a semipurified diet as initiating factors for aortic glycosaminoglycan (GAG) and lipid changes. Rabbits were fed sucrose or lactose as 40% by weight of a semi-purified, cholesterol-free diet for 10 weeks. At the end of the feeding period there was no macroscopic evidence of atherosclerosis. Sucrose-fed rabbits had significantly higher plasma cholesterol and phospholipid levels than the lactose-fed rabbits and triglyceride levels were variably elevated in the sucrose group. Analysis of plasma lipoproteins indicated that sucrose elevated VLDL and LDL when compared to lactose. Only the higher molecular weight form of apo B (apo BH) could be demonstrated when apo B components of isolated lipoproteins were analyzed. Sucrose-fed rabbits had significantly more aortic cholesterol, cholesteryl ester and phospholipid and tended to have more GAG/mg dry defatted aorta than the lactose-fed rabbits. Plasma cholesterol levels correlated with aortic lipids and in the sucrose group, aortic cholesteryl ester and cholesterol were strongly correlated with aortic GAG particularly hyaluronic acid. Results suggest that the semi-purified diet alters aortic GAG composition but in order for the initiation of cholesterol accumulation a significant increase in plasma lipoprotein cholesterol is necessary.

The production and utility of monoclonal antibodies to rat apolipoprotein B lipoproteins.

Murine hybridomas were prepared by fusion of azaguanine-resistant plasmacytoma cells and spleen cells from BALB/c mice immunized with intact rat lipoproteins (Lp). Seventeen stable hybridomas from 5 fusions producing antibody against rat apolipoprotein B (apo B)-containing Lp were prepared. The distribution of antigenic determinants of rat apo B variants defined by these antibodies was similar to that found for human apo B. Thirteen mAbs were reactive to epitopes found on both the higher (apo BH) and lower (apo BL) molecular weight forms of rat apo B; two were reactive to apo BH-specific epitopes and two were reactive to apolipoprotein E. No antibodies reactive to unique apo BL epitopes were found. One anti-rat apo B mAb (1.34.3) of high affinity and avidity was reactive to denatured and intact Lp-apo B. Reactivity towards Lp-apo B was independent of variant composition and density class of Lp. The mAb was subsequently used to develop a radioimmunoassay (RIA) which was sensitive down to 5 ng apo B. The assay was used successfully to measure total nascent Lp-apo B secreted by hepatocytes in culture.

Effect of dietary fat on the development of non-insulin dependent diabetes mellitus in obese Zucker diabetic fatty male and female rats.

The obese Zucker diabetic fatty male rat (ZDF/Gmi¿trade mark omitted¿-fa) has become a widely used animal model of NIDDM, in contrast to the obese ZDF females that rarely develop NIDDM. However, preliminary observations suggest that obese ZDF females may become diabetic on high-fat diets. Therefore, we studied the effect of dietary fat on development of NIDDM, dyslipidemia, and alterations in organ-specific serum panels in obese ZDF males and females. Results indicated different effects of dietary fat-content on development of diabetes in males and females. Males, even on low fat-content diets, developed diabetes but the process was accelerated as a function of dietary fat-content, whereas only the highest fat-content diet induced development of NIDDM in obese ZDF females. Additionally, triglyceride/apolipoprotein B ratios demonstrated gender-specific differences in the nature of circulating lipoprotein particles independent of diabetic state with values for females approximately twice those of males indicating more highly triglyceride-enriched lipoprotein particles in females. We conclude that the obese ZDF female rat has the potential to become an important animal model of NIDDM especially in women where few models currently exist.

Increased level of von Willebrand factor is significantly and independently associated with diabetes in postinfarction patients. THROMBO Investigators.

Diabetes is an established risk factor for reinfarction and cardiac death in postinfarction patients. Since the underlying mechanism of diabetes-related risk is not fully understood we aimed to evaluate the association between lipids, thrombogenic factors and diabetes in postinfarction patients. The study population consisted of 1,045 postinfarction patients (846 non-diabetic, 125 non-insulin- and 74 insulin-requiring diabetics) with the following blood tests performed 2 months after an index myocardial infarction: lipoprotein (a), apolipoprotein-B, apolipoprotein-A, cholesterol, HDL cholesterol, triglycerides, insulin, von Willebrand factor (vWF), fibrinogen, factor VII, D-dimer, and plasminogen activator inhibitor (PAI-1). After adjustment for relevant clinical covariates, non-insulin-requiring diabetes was significantly (p < 0.05) associated with elevated levels of (odd ratios per 1 log unit increase in parenthesis) vWF (1.74) and PAI-1 (1.42) whereas insulin requiring diabetes was associated with even more elevated levels of vWF (4.68), but not with increased levels of PAI-1. No significant differences in lipid levels were observed among three groups. In conclusion, increased level of von Willebrand factor is significantly and independently associated with diabetes in postinfarction patients, suggesting that endothelial damage is the primary mechanisms contributing to an increased occurrence of vascular and cardiac events in diabetic postinfarction patients.

Effect of smoking on lipid and thrombogenic factors two months after acute myocardial infarction.

Cigarette smoking is linked to increased cardiac morbidity and mortality, and has been shown to affect both lipid profiles and thrombotic factors in healthy subjects. However, the influence of smoking on the atherothrombotic environment has not been studied in a large population of patients after acute myocardial infarction (AMI). Blood samples and medical history, including smoking status, were obtained from 1,045 patients at a 2-month visit after AMI. Smokers were asked to refrain 24 hours before the visit, but not all complied. Measurements included total cholesterol, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, apolipoprotein-B, apolipoprotein-A, triglycerides, factor VII, factor VIIa, von Willebrand factor, D-dimer, and plasminogen activator inhibitor. There were 247 current, 443 past, and 349 nonsmokers. After adjustment for clinical variables, current smokers had higher levels of total cholesterol and apolipoprotein-B than past and nonsmokers (p <0.01). High-density lipoprotein cholesterol and apolipoprotein-A levels were similar between groups. Fibrinogen was elevated in current (p = 0.001) and past (p = 0.029) smokers, compared with nonsmokers. Smokers who smoked within 24 hours of blood sampling had higher apolipoprotein-B (p = 0.005), total cholesterol (p = 0.001), and fibrinogen (p = 0.015) levels than those who refrained from smoking. In conclusion, postinfarction patients, who historically have higher levels of atherogenic lipids than healthy subjects, have increased levels of these lipids attributed to active smoking. After smoking cessation, lipid profiles approach nonsmoker levels, but fibrinogen remains elevated. Smoking within 24 hours of blood sampling was associated with further adverse prothrombotic and lipogenic effects.

Gender-related differences in thrombogenic factors predicting recurrent cardiac events in patients after acute myocardial infarction. The THROMBO Investigators.

Thrombosis contributes to recurrent coronary events in patients after acute myocardial infarction (AMI), but prognostic significance of thrombogenic factors by gender is unknown. This study aimed to determine gender-related differences in the prognostic significance of thrombogenic factors for predicting cardiac events (nonfatal reinfarction or cardiac death) in postinfarction patients. Blood levels of the following factors were measured 2 months after AMI in 791 men and 254 women: fibrinogen, von Willebrand factor, factor VII and VIIa, plasminogen activator inhibitor, D-dimer, cholesterol, apolipoprotein A-1, apolipoprotein B, lipoprotein(a), triglycerides, and high-density lipoprotein cholesterol. After adjustment for clinical covariates, levels of apolipoprotein A, high-density lipoprotein cholesterol, fibrinogen, and factor VIIa were significantly higher in postinfarction women than men. During a mean 26-month follow-up, there were 67 cardiac events (8.5%) in men and 14 (5.5%) in women (p = 0.11). In the multivariate Cox model, elevated levels of factor VIIa were a significant predictor of cardiac events in women (p = 0.022) but not in men (p = 0.80), with significant gender-related effect (hazard ratio 2.80 vs 0.92, respectively; p <0.05). D-dimer had prognostic value in men (p = 0. 006) but not in women (p = 0.36), although the difference between hazard ratios for men and women was not significant (2.35 vs 1.58, respectively; p = 0.49). In conclusion, elevated levels of factor VIIa are associated with an increased risk of recurrent cardiac events in postinfarction women, but not in men. D-dimer is more predictive for cardiac events in postinfarction men than women. These observations indicate possible gender-related differences in the pathophysiologic mechanisms of recurrent cardiac events.

Lipoproteins in experimental nephrosis: plasma levels and composition.

Experimental nephrosis was induced in rats by administration of puromycin aminonucleoside and the levels of plasma lipoproteins were examined 7 days later and compared to controls. As determined by density ultracentrifugation, VLDL, IDL, LDL, and HDL protein levels were increased by 8, 4, 5, and 5 times, respectively. These increases were accompanied by changes in lipid and apoprotein composition. The VLDL, IDL, and LDL fractions contained less triglyceride and more phospholipid and cholesterol, while HDL lipid composition was not altered. The apoprotein composition of VLDL and IDL were not measurably altered, but LDL contained less apoE. HDL had a markedly abnormal composition characterized by an almost complete absence of apoA-IV and apoE, increased apoA-1, and decreased apoC. While increased hepatic synthesis can account for much of the observed hyperlipoproteinemia in nephrosis, the changes in lipoprotein composition suggest impaired catabolism as a contributory factor.

Liver regrowth and apolipoprotein B secretion by rat hepatocytes following partial hepatectomy.

Apolipoprotein (apo) B is an essential component for the assembly and secretion of lipoproteins. The current report examines apo B production using primary cultures of hepatocytes derived from rats 3 to 21 days after partial hepatectomy (PH) to determine the effects of liver regrowth on apo B. Studies indicate that hepatocytes stimulated by PH have a two-thirds reduction in net apo B production 3 to 7 days after surgery, which coincides with the period of maximum rate of liver regrowth. Both higher (apo BH)- and lower-molecular-weight (apo BL) apo B are synthesized and secreted after PH, indicating the presence of edited apo B mRNA in hepatocytes. Hepatocytes derived from PH rats are more sensitive to insulin inhibition of apo B secretion compared with controls, suggesting an enhanced effect of insulin on newly replicated hepatocytes. Epidermal growth factor (EGF), a key regulator of liver regrowth following PH, potentiates the inhibitory action of insulin on apo B secretion in control hepatocytes and those derived from rats 2 to 3 weeks after PH. However, the potentiating effect of EGF on insulin inhibition of apo B is not discernible in hepatocytes 3 to 7 days after PH. The short-term in vitro hormonal effects occurring even with decreased apo B production suggest that this pathway remains available following PH to balance lipoprotein secretion with lipid and energy requirements necessary for liver regeneration.