Triglyceride lipases in acute hepatitis

Two triglyceride lipases in postheparin plasma, the lipoprotein lipase (LPL) and the hepatic triglyceride lipase (H-TGL) were separated by heparin-sepharose affinity chromatography and studied in controls and patients during the course of acute hepatitis. All three patients had increased content of triglycerides in the low density lipoproteins, and two of them had hypertriglyceridemia. Low activities of both lipases were found in the acute stage of the disease in all three patients. Concomitantly one of the patients had absolute low lecithin: cholesterol acyltransferase (LCAT) activity, and in the two other patients a relative LCAT deficiency was present. The increased content of triglycerides in LDL that may be found in liver disease, may not only be due to low H-TGL and LPL, but also LCAT deficiency.     

Increased lipase inhibition in uremia: identification of pre-beta-HDL as a major inhibitor in normal and uremic plasma

The hypertriglyceridemia commonly observed in uremia has been attributed to an abnormally high inhibitor activity in plasma for lipoprotein lipase (LPL) and hepatic lipase (HL), both of which have a key role in lipoprotein metabolism. The purpose of this investigation was to establish a relationship between plasma lipase inhibitor activity and hypertriglyceridemia, identify the main plasma lipase inhibitor, and determine the basis for the greater inhibitor activity in uremia. In a mixed population of normal (N = 8) and uremic subjects (N = 12), log-transformed plasma triglycerides correlated with both inhibitor activity and uremic status. However, inhibitor activity was the only retained predictor variable for triglycerides in a multiple linear regression model (r = 0.91; P < 0.0001). An inhibitor isolated from normal plasma was identified as a particle containing apolipoprotein A-I (apo A-I) and 3% phospholipid. This particle, which has pre-beta electrophoretic mobility and a Stokes' radius of 54 A, therefore corresponds to a form of the previously described pre-beta-HDL (free apo A-I) in the non-lipoprotein fraction of plasma. Comparison of normal and uremic plasma indicated that the greater lipase inhibitor activity in the latter could be attributed to an increased concentration of apo A-I in the non-lipoprotein fraction of plasma (pre-beta-HDL), as well as to increased inhibition by the uremic lipoproteins. The increased plasma lipase inhibitor activity may be important in the pathogenesis of hypertriglyceridemia in chronic renal failure.     

Release of nonesterified fatty acids during cerulein-induced pancreatitis in rats

During acute pancreatitis, data obtained in vitro suggest that pancreatic lipase, acting on circulating or tissular triglycerides, might generate nonesterified fatty acids (NEFA) that could promote pancreatic and fat tissue necrosis. This work determined whether NEFA were actually produced in vivo in pancreatic tissue and in blood during cerulein-induced pancreatitis in rats. Intraperitoneal injections of cerulein induced pancreatitis. To promote the possible NEFA release by pancreatic lipase, a venous infusion of human very low density lipoprotein (VLDL) was used to cause hypertriglyceridemia. NEFA were measured in portal and aortic blood and in tissue extracts prepared from pancreas homogenates. NEFA did not increase either in peripheral or in portal blood. In pancreatic tissue, NEFA levels did not differ from controls. The major hypertriglyceridemia produced by human VLDL intravenous infusion neither altered the course of the disease nor promoted plasma NEFA release. The role commonly attributed to NEFA in acute pancreatitis seems questionable.     

Effect of tamoxifen on serum lipid metabolism

The effect of tamoxifen, an antiestrogenic agent, on lipid metabolism was studied in postmenopausal patients with breast cancer who received the drug for postoperative adjuvant treatment following mastectomy. To measure total cholesterol and triglyceride concentrations, fasting blood samples were collected before and 2 months after the initiation of tamoxifen therapy from 16 patients who satisfied the study criteria. All patients were normolipidemic before tamoxifen was administered. Control samples were obtained from hypertriglyceridemia patients who were free from breast cancer. Marked hypertriglyceridemia was observed in 3 of 16 patients after tamoxifen treatment. The activity of lipoprotein lipase and hepatic triglyceride lipase, the key enzymes of triglyceride metabolism, decreased significantly in all of 16 patients as a result of tamoxifen treatment (P = 0.008 and P = 0.007, respectively). However, the mean mass of lipoprotein lipase significantly increased (P = 0.011) after tamoxifen treatment. We therefore conclude that tamoxifen might increase inactive lipoprotein lipase. Because marked hyperlipidemia is a potent risk factor for life-threatening acute pancreatitis and arteriosclerosis, plasma lipid levels should be tested periodically during tamoxifen treatment, even if the patients are normolipidemic during the pretreatment stage.     

Verapamil prevents chronic renal failure-induced abnormalities in lipid metabolism

Hypertriglyceridemia is common in chronic renal failure (CRF); this derangement is due to decreased peripheral removal of triglycerides. Certain data indicate that the state of secondary hyperparathyroidism of CRF is, at least in part, responsible for derangements in lipid metabolism. It has been proposed that chronic excess of parathyroid hormone exerts its deleterious effects on many organs through its ability to raise basal levels of cytosolic calcium. Prevention of the latter by a calcium channel blocker is followed by the correction of organ dysfunctions. The present study examined the effect of treatment of CRF rats with verapamil on several parameters of lipid metabolism. Chronic renal failure rats displayed hypertriglyceridemia, fat intolerance, reduced postheparin plasma lipoprotein and hepatic lipase activities, decreased hepatic lipase in liver homogenate, and elevated calcium content in liver and epididymal fat. Treatment of the CRF rats with verapamil prevented all these derangements in lipid metabolism. These effects of verapamil were similar to those produced by parathyroidectomy of CRF rats. The data are consistent with the formulation that chronic excess of parathyroid hormone increases the calcium burden of liver and adipose tissue and consequently impairs the synthesis and/or release of lipoprotein and hepatic lipases. Reduced availability of these enzymes in plasma results in impared peripheral removal of triglycerides, leading to hypertriglyceridemia.     

Severe hypertriglyceridemia caused by tamoxifen-treatment after breast cancer surgery

Tamoxifen, a nonsteroidal estrogen antagonist, has been widely used in a hormonal treatment for breast cancer. The side effects of tamoxifen are generally recognized to be mild. However, we experienced three cases of severe hypertriglyceridemia and/or hyperglycemia induced by tamoxifen. For normalization of their hypertriglyceridemia we need to stop giving tamoxifen. In one of three cases we analyzed her lipoprotein profile in detail with lipoprotein lipase activities and apolipoprotein E phenotype. The case was a 49 year-old woman. After 15 months of tamoxifen administration, she was diagnosed as severe hypertriglyceridemia. Consecutively, severe hyperglycemia was occurred to need insulin therapy. After tamoxifen withdrawal, her triglyceride and glucose levels improved. Her lipolytic enzyme was reduced during tamoxifen treatment. Apolipoprotein E phenotype was uncommon E4/2. Although hypertriglyceridemia was not considered to be a risk factor for coronary heart disease, a marked hypertriglyceridemia might occasionally produce severe lethal pancreatitis. We recommend that a periodic plasma lipid analysis is needed for patients treated with tamoxifen, especially for diabetic and hypertriglyceridemic patients, to avoid such complications.     

The role of xenobiotic metabolizing enzymes in arylamine toxicity and carcinogenesis: functional and localization studies

Familial apolipoprotein C-II (apo C-II) deficiency is an autosomal recessive genetic disorder characterized by fasting hypertriglyceridemia and accumulation of chylomicrons in the plasma. To elucidate the genetic defect, the apo C-II gene of a neonatal Japanese patient (C-IITokyo) was analyzed. Nucleotide sequence analysis showed a G+1 to C transversion at the donor splice site of intron 2 (INT2 G+1 to C). Restriction fragment length polymorphism analyses of the patient's family members with Hph I showed that the patient was homozygous and the parents were heterozygous for the INT2 G+1 to C mutation. Although consanguinity could not be demonstrated, haplotype analysis of the C-II gene revealed the identity of the patient's alleles on the mutation, suggesting that the parents had a common Japanese ancestor. Sequence analysis of the patient's cDNA isolated from peripheral blood lymphocytes revealed that the INT2 G+1 to C mutation causes skipping of exon 2, which encodes the initiation codon, and results in deficiency of apo C-II proteins. The outstanding feature of our patient was that he showed severe hypertriglyceridemia beginning in the neonatal period, a feature not reported in a case of apo C-II deficiency (C-IIHamburg) with the same mutation as our patient. A previous report of another case of apo C-II deficiency (C-IIToronto) suggested that the apo E4 isoform is associated with higher levels of plasma triglycerides in subjects heterozygous for the apo C-II mutation. Determination of the apo E isoform of our patient revealed that apo E4 was coinherited with the INT2 G+1 to C mutation, whereas the apo E isoform has been reported to be E2/3 in C-IIHamburg. We speculate that apo E4/4 aggravated the hypertriglyceridemia in our patient with apo C-II deficiency.     

Failure of the nonselective beta-blocker propranolol to affect lipoprotein lipase gene expression in the rat

Treatment with beta-blockers has been reported to be associated with the development of hypertriglyceridemia. The etiology, even the existence, of this phenomenon is controversial. The purpose of our study was to examine whether the nonselective beta-blocker propranolol causes hypertriglyceridemia in the rat and whether its action is mediated by the modulation of lipoprotein lipase (LPL) messenger RNA (mRNA) accumulation or activity. LPL activity was assayed in fresh tissue by incubation with tritiated triglycerides. LPL mRNA was quantified in total RNA by slot-blot analysis using a mouse LPL complementary DNA probe. We have conducted three series of experiments in unanaesthetized rats in order to study the effects of different single doses of propranolol (1.5 to 6 mg i.p.) and different durations of treatment (15 min to 4 wk). We measured triglyceride and cholesterol levels in plasma as well as the LPL activity and mRNA levels in the heart and adipose tissue before and after propranolol administration. In these experiments we did not find any significant decrease in either the activity or the amount of mRNA of lipoprotein lipase nor was there any change in plasma lipids following treatment. Our results lead us to the conclusion that the nonselective beta-blocker propranolol affects neither the activity nor the mRNA level of LPL in the rat.     

Short-term effects of a high-sucrose diet on plasma lipid, lipoprotein cholesterol, tissue lipoprotein lipase and hepatic triglyceride lipase in rats

Short-term (2 weeks) effects of a high-sucrose diet on plasma lipids, lipoproteins, tissue lipoprotein lipase (LPL) and hepatic triglyceride lipase (HTGL) activities were investigated in rats. Three days of sucrose feeding significantly increased plasma TG (42 +/- 3 mg/dl vs. 56 +/- 2 mg/dl, p = 0.032), while TC increased significantly after 10 days of the diet (50 +/- 2 mg/dl vs. 62 +/- 2 mg/dl, p = 0.0001). HDL-C increased significantly after 3 days of sucrose feeding (36.2 +/- 0.9 mg/dl vs. 42.4 +/- 2.7 mg/dl, p = 0.011). Although LDL-C tended to decrease on days 3, 7 and 10, these changes were not significant. The plasma glucose level did not change during the study. Increased LPL activity in adipose tissue and decreased enzyme activities in skeletal and heart muscles were observed. Adipose tissue LPL returned to the baseline value after 14 days of the diet treatment, while LPL in skeletal and heart muscles remained at the decreased level. HTGL and HTGL/total liver lipase activities were significantly increased after 14 days of the diet. The different responses of lipase activities in various tissues may help to regulate serum lipid and lipoprotein levels in sucrose-fed rats.     

Association of hyperuricemia with hyperlipidemia and obesity

Various epidemiological evidences have shown the increased incidence of hyperuricemia in the subjects with hyperlipidemia and/or obesity. Our clinical study indicated the association was more close in hypertriglyceridemia to hyperuricemia than in hypercholesterolemia. Serum uric acid level increased more in Type IIb with elevated lipoprotein lipase (LPL) than those with low or normal LPL. Elevated LPL may be involved in the retarded uric acid clearance due to increased free fatty acids (FFA) in the serum, resulting in the elevation of uric acid and may be linked to the obesity-insulin resistance syndrome. Increased FFA may play an important role on the association of hyperuricemia with hypertriglyceridemia.     

Isochromosome 15q of maternal origin in a Prader-Willi patient with pituitary adenoma

The inoculation of the Yoshida AH-130 ascites hepatoma to rats resulted in an important loss of adipose tissue associated with a decrease in lipoprotein lipase (LPL) activity. Tumour burden also resulted in an important hyperlipidemia which affected both triglyceride and free fatty acids. Administration of phentolamine (an alpha-adrenergic antagonist) to tumour-bearing rats did not influence LPL activity, but it reversed the increase in plasma triglycerides associated with tumour burden. It is suggested that the hypertriglyceridemia associated with tumour growth may be, in part, a consequence of the effect of catecholamines on hepatic triglyceride secretion, via alpha-adrenergic receptors.     

Enhanced lipolysis in normal mice expressing liver-derived human lipoprotein lipase after adenoviral gene transfer

The authors previously demonstrated that the gene for human lipoprotein lipase (hLPL), an enzyme crucial to the breakdown of triglyceride (TG)-rich dietary fats, corrects the hypertriglyceridemia in lipoprotein lipase (LPL)-deficient knockout mice after adenoviral (Ad)-mediated LPL gene transfer. They have now extended their observations to primary cultured mouse hepatocytes and intact animals of normal LPL genotype, and confirm effective overexpression of hLPL from the liver and a sustained TG-lowering effect in plasma over 60 days. A typical first-generation Ad-vector containing the hLPL cDNA (Ad-LPL) resulted in efficient gene transfer into isolated mouse hepatocytes and significant de novo synthesis of active hLPL protein. In this experiment, 5 x 10(9) viral particles (5 x 10(7) pfu) of either Ad-LPL or an Ad-LacZ control vector were injected into CD1 mice of normal LPL genotype. Hepatic expression of hLPL was confirmed at Day 7 postinjection by in situ hybridization and direct measurement of LPL in the liver. This correlated with a total LPL activity (human + mouse) in postheparin plasma (PHP) of 1020.5 standard deviation [SD] 93.6 mU/mL, versus 479.5 SD 129.7 mU/mL (p < 0.001) in Ad-LacZ controls at Day 7. Respective hLPL activity comprised 49% of the total. Significantly raised levels of hLPL protein mass persisted until Day 60. Corresponding plasma TGs decreased to 39% of Ad-LacZ controls at Day 7, and, despite absent hLPL activity from Day 28 on, serum TGs remained significantly lower in Ad-LPL mice up to Day 42. Fast phase liquid chromatography analysis showed a dramatic depletion in TG-rich lipoproteins, mainly very low density lipoproteins (VLDL) and chylomicron fractions. Therefore, Ad-mediated overexpression of hepatic LPL was found to significantly decrease plasma TG levels unrelated to primary LPL deficiency.     

Three polymorphisms associated with low hepatic lipase activity are common in African Americans

We have shown previously that a hepatic lipase allele (designated -514T) is common among African Americans and contributes to low hepatic lipase activity in this population. To identify other hepatic lipase alleles associated with low hepatic lipase activity in this population, the coding region and intron-exon boundaries of the hepatic lipase gene were sequenced in 20 African American men with low hepatic lipase activity. Two polymorphisms (N193S and L334F) were associated with low post-heparin plasma hepatic lipase activity and were much more common in African Americans than in whites. This finding, together with our previous data on the -514T allele, indicates that at least three different hepatic lipase polymorphisms associated with low hepatic lipase activity are common among African Americans. Analysis of hepatic lipase haplotypes revealed that 97% of African Americans have at least one hepatic lipase allele that is associated with low hepatic lipase activity.     

Symmetry and pH dependency of the lactate/proton carrier in skeletal muscle studied with rat sarcolemmal giant vesicles

To study the pathogenesis of hyperlipoidemia and atheromatosis and the metabolism of lipoprotein, we have developed a colorimetric method for simultaneously determining the activities of post-heparinplasma lipoprotein lipase (LPL) and hepatic lipase (HL). The intralipid was kept for LPL and HL at 37 degrees C, pH8.3 for 30 min, with 100 microliters post-heparin plasma. The LPL and HL in the post-heparin plasma could hydrolyse the triglyceride in intralipid into glycerine and free fatty acid (FFA). Determining the amount of FFA by copper-reagent method, we could measure the activities of LPL and HL. The kinetics of LPL and HL in post-heparin plasma was observed. K(m) values for LPL and HL were 0.9 mumol/L and 2.4 mumol/L respectively. The C. V. for LPL and HL were 4.5% (n = 4), 2.9% (n = 6) and 6.4% (n = 6), 4.8% (n = 6) respectively.     

Hepatic lipase activity is lower in African American men than in white American men: effects of 5' flanking polymorphism in the hepatic lipase gene (LIPC)

Plasma high density lipoprotein cholesterol (HDL-C) concentrations are higher in African American men than in white men, but the mechanism(s) responsible for this ethnic difference has not been elucidated. This study examined the relationship between hepatic lipase activity, plasma HDL-C concentrations, and a hepatic lipase polymorphism (-514T) in African American and white American men. Consistent with previous reports, plasma HDL-C concentrations were significantly higher in African American men than in white American men. Mean post-heparin plasma hepatic lipase activity was significantly lower in African American than in white American men (27 +/- 12 vs. 44 +/- 17 mmol x h(-1) x l(-1), P < 0.001). The -514T hepatic lipase allele was associated with low hepatic lipase activity in both populations, and was 3-fold more common among African Americans than white Americans. Taken together, these data suggest that genetic differences in hepatic lipase activity contribute to the differences in plasma HDL-C concentrations between African American men and white American men.     

Elevated LDL triglyceride concentrations in subjects heterozygous for the hepatic lipase S267F variant

Although naturally occurring loss-of-function mutations in human hepatic lipase (HL) have been described, the biochemical phenotype of heterozygous HL deficiency remains ill defined. This may be due to the relatively small numbers of heterozygous adult carriers of HL mutations in index kindreds. We have identified several new heterozygotes for the catalytically inactive, nonsecreted HL variant S267F in the kindred that was originally ascertained because of hypertriglyceridemia due to the mutant, secreted, circulating apolipoprotein (apo) CII variant apo CII-T. Pairwise comparisons with family controls showed that only the plasma low density lipoprotein triglycerides (LDL TGs) were higher in 11 simple heterozygotes for HL S267F (P=0.002). In contrast, both plasma total TGs and LDL TGs were significantly higher in 12 simple heterozygotes for apo CII-T than in family-matched control subjects (P=0.005 and 0.009, respectively). These findings suggest that the TG content of LDL is increased by heterozygosity for 2 different mutations that affect different proteins involved in lipolysis. However, the mechanisms underlying this compositional change in LDL appear to be different for the 2 mutations, because the total TGs are also elevated in subjects heterozygous for apo CII-T but not in subjects heterozygous for HL S267F.     

Polymorphic markers in apolipoprotein C-III gene flanking regions and hypertriglyceridemia

Hypertriglyceridemia and hyperlipidemia are common disorders associated with coronary artery disease and premature death. The proteins encoded by the apolipoprotein (apo) A-I/C-III/A-IV gene cluster are involved in the metabolism of both triglycerides and cholesterol. In a large sample of individuals from the ARIC study, six polymorphic markers were typed and plasma lipid values were measured to determine whether the well-established association between the Sst I S2 allele in the 3'-untranslated region of the apo C-III gene and hypertriglyceridemia was due to disequilibrium with variation in the 5' regulatory region of the apo C-III gene. The Sst I polymorphism was significantly associated with hypertriglyceridemia (P = .006) but not with carotid artery wall thickness, plasma apo C-III levels, or elevated cholesterol. The frequency of the S2 allele was 0.14 in those with high triglyceride levels and 0.05 in those with low triglyceride levels. None of the 5' flanking polymorphisms were significantly associated with any of the plasma lipids studied. There was substantial linkage disequilibrium between the Sst I polymorphism and each of the 5' apo C-III polymorphisms; however, the significant association between the apo C-III haplotypes and hypertriglyceridemia (odds ratio, 4.0; P < .0001) was solely attributable to the effects of the Sst I polymorphism (odds ratio, 3.96). As a part of these analyses, we also defined a unique haplotype that is inversely associated with the occurrence of hypertriglyceridemia, suggesting further molecular analyses of this important gene region.     

Decreased release of lipoprotein lipase is associated with vascular endothelial damage in NIDDM patients with microalbuminuria

OBJECTIVE: To explore mechanisms for hypertriglyceridemia in diabetic patients with microalbuminuria, we examined an association between heparin-releasable lipoprotein lipase (LPL) and the von Willebrand factor (vWF), based on the hypothesis that LPL bound to endothelium is decreased by generalized endothelial damage. RESEARCH DESIGN AND METHODS: A total of 37 NIDDM patients with microalbuminuria and 69 patients with normoalbuminuria were studied. Plasma LPL mass in post-heparin plasma and plasma vWF antigen were quantified by sandwich-enzyme immunoassay and enzyme-linked immunosorbent assay, respectively. RESULTS: The NIDDM patients with microalbuminuria had higher plasma triglyceride (TG) and lower HDL cholesterol concentrations compared with the patients with normoalbuminuria. Heparin-releasable LPL mass was significantly lower in the microalbuminuric than in the normoalbuminuric subjects. Plasma level of vWF, a marker for endothelial damage, was significantly increased in microalbuminuric subjects compared with their normoalbuminuric counterparts. The LPL mass was inversely correlated with plasma vWF level at a high correlation coefficient value. The LPL mass was inversely related to TG and positively to HDL cholesterol concentrations. CONCLUSIONS: These results suggest that widespread endothelial damage occurred in NIDDM patients with microalbuminuria, thereby LPL moiety bound to the endothelium is decreased, which results in an impaired catabolism of TG-rich lipoproteins.     

VLDL triglyceride kinetics in Wistar fatty rats, an animal model of NIDDM: effects of dietary fructose alone or in combination with pioglitazone

The effects of dietary fructose alone or in combination with a new oral agent, pioglitazone, on VLDL-triglyceride (TG) turnover were studied in genetically obese Wistar fatty rats characterized by hyperinsulinemia (7,488 +/- 954 pmol/l), hyperglycemia, (22.5 +/- 1.4 mmol/l), and hypertriglyceridemia (4.39 +/- 0.54 mmol/l). They had an increased hepatic TG production (16.2 +/- 0.1 micromol/min; lean rats, 5.4 +/- 0.3 micromol/min) as well as a longer half-life of VLDL-TG from lean donors (8.8 +/- 1.4 min, lean recipients; 2.3 +/- 0.9 min). In addition, in lean recipients, the half-life of VLDL-TG from fatty donors was longer than that from lean donors (4.80 +/- 0.56 vs. 3.14 +/- 0.23 min). Although feeding fructose into fatty rats did not change plasma glucose and insulin levels, it produced a twofold increase in TG levels (8.74 +/- 1.15 mmol/l). This was associated with a 1.7-fold increase in TG production to 27.5 +/- 1.2 micromol/min, while no significant change was found in the half-life of lean VLDL-TG in fructose-fed fatty recipients (10.9 +/- 2.4 min) or in that of VLDL-TG from fructose-fed fatty donors in lean recipients (4.46 +/- 0.76 min). Daily administration of pioglitazone (3 mg/kg body weight) in fructose-fed fatty rats ameliorated glycemia and triglyceridemia to the level of lean rats (8.1 +/- 0.7 and 1.18 +/- 0.05 mmol/l, respectively) and insulinemia to a lesser extent (2,712 +/- 78 pmol/l). A fall in TG levels was associated with improvement of an impairment in the ability of fructose-fed fatty rats to remove lean VLDL-TG (half-fife: 2.6 +/- 0.6 min). Pioglitazone, however, produced no change in TG production (25.9 +/- 2.7 micromol/min), the half-life of VLDL-TG from fructose-fed fatty donors in lean recipients (4.17 +/- 0.38 min), or the activity of lipoprotein lipase and hepatic lipase in postheparin plasma. We conclude that in Wistar fatty rats 1) hypertriglyceridemia is attributed to TG overproduction and impaired TG catabolism, and the latter is due to changes in both VLDL, such that they are less able to be removed, and changes in the nature of Wistar fatty rats, such that they are less able to remove VLDL-TG; 2) fructose further increases hepatic TG production with a resultant deterioration in hypertriglyceridemia; 3) pioglitazone normalizes TG levels by altering the physiology of the Wistar fatty rats in a manner that increases their ability to remove VLDL-TG from the circulation.     

The familial chylomicronemia syndrome

The chylomicronemia syndrome is a disorder characterized by severe hypertriglyceridemia and fasting chylomicronemia. Genetic causes of the syndrome are rare and include deficiency of lipoprotein lipase (LPL), apolipoprotein C-II, and familial inhibitor of LPL. Patients with familial forms of hypertriglyceridemia in combination with secondary acquired disorders account for most individuals presenting with chylomicronemia. The clinical manifestations--lipid and other biochemical abnormalities--as well as treatment options for chylomicronemic patients are discussed.