Postheparin Plasma Hepatic Triglyceride Lipase Research Articles

Reduced Hepatic Triglyceride Secretion in Rats Fed Docosahexaenoic Acid–Rich Fish Oil Suppresses Postprandial Hypertriglyceridemia

To evaluate the mechanisms of suppression of postprandial hypertriglyceridemia by fish oil rich in docosahexaenoic acid, the effect on the intestinal absorption of triglyceride, activities of lipoprotein lipase (LPL) and hepatic triglyceride lipase (HTGL) and metabolism of chylomicrons (CM) and CM remnants were compared with that of safflower oil in Sprague-Dawley rats in a series of studies. The feeding of fish oil for 3 wk suppressed postprandial hypertriglyceridemia (study 1). Dietary fish oil did not alter the rate of lymphatic absorption of triglyceride (study 2). The activities of LPL and HTGL were measured at 5 h after the beginning of feeding, when serum triglyceride concentrations were highest in both dietary groups. The activities of LPL in adipose tissue and heart were greater (P < 0.05) and those of HTGL were lower (P < 0.05) in the rats fed fish oil (study 3). In contrast, there were no differences in the activities of LPL and HTGL in postheparin plasma between the fish and safflower oil groups (study 4). The clearance rates of CM and CM remnants were measured by injecting intravenously CM collected from rats fed safflower or fish oils with [14C]triolein and [3H]cholesterol (study 5). Dietary oil did not influence the half-lives of CM or CM remnants. The secretion of triglyceride from the liver of rats injected with Triton WR-1339 was lower (P < 0.05) in the rats fed docosahexaenoic acid, a major component of fish oil, than those fed linoleic acid, a major component of safflower oil (study 6). These observations strongly support the hypothesis that in rats, the principal cause of the suppression of postprandial hypertriglyceridemia by fish oil is the depression of triglyceride secretion from the liver.

Lipoprotein metabolism in postmenopausal and oophorectomized women

To investigate the mechanisms of accumulating cholesterol, and to analyze the metabolism of excess tissue cholesterol in women with low plasma levels of sex steroid hormones. We measured plasma concentrations of cholesterol, triglyceride, apolipoproteins, sex steroid hormones, and lecithin cholesterol acyltransferase activity in 20 premenopausal, ten postmenopausal, and ten bilaterally oophorectomized women. Lipoprotein lipase and hepatic triglyceride lipase activities were measured in postheparin plasma. We compared the three groups and evaluated a correlation between lipid metabolism and sex steroid hormone concentrations. The mean plasma low-density lipoprotein (LDL) cholesterol level, lecithin cholesterol acyltransferase activity, and postheparin plasma lipoprotein lipase activity were higher in the postmenopausal and surgically menopausal groups. The mean plasma high-density lipoprotein (HDL) cholesterol concentration and postheparin plasma hepatic triglyceride lipase activity did not differ significantly among the three groups. The plasma LDL cholesterol level and postheparin plasma lipoprotein lipase activity showed a significantly negative correlation with plasma concentration of estrone (LDL: r = 0.64, P < .001; lipoprotein lipase: r = 0.54, P < .005) and estradiol (LDL: r = 0.65, P < .001; lipoprotein lipase: r = 0.47, P < .01), but not with that of testosterone. There was no significant relationship between postheparin plasma hepatic triglyceride lipase activity and plasma sex steroid hormones. Plasma lecithin cholesterol acyltransferase activity correlated significantly with plasma LDL cholesterol concentration, but not with levels of sex steroid hormones. Because of low endogenous estrogens, enhanced postheparin plasma lipoprotein lipase activity may lead to an elevated plasma LDL cholesterol concentration in postmenopausal and bilaterally oophorectomized women. We demonstrated an accelerated cholesterol esterification in HDL cholesterol that may have been induced by LDL cholesterol accumulation, although the HDL cholesterol concentration remained unchanged.

Loss of abdominal fat and metabolic response to exercise training in obese women

Numerous studies have shown that a high accumulation of abdominal fat is associated with metabolic complications and with an increased risk of coronary heart disease. The present study examined the effects of changes in body fatness and in the level of abdominal fat on metabolic variables in a sample of 13 obese premenopausal women, aged 38.8 +/- 5.3 (SD) yr. Women exercised for 90 min at approximately 55% of maximal aerobic power (VO2 max) four to five times a week for a period of 14 mo. The training program induced a significant increase in VO2 max and a mean reduction in body fat mass of 4.6 kg (P less than 0.01), with no change in fat-free mass. Measurement of adipose tissue areas by computed tomography indicated a greater loss of abdominal fat compared with midthigh adipose tissue (P less than 0.05). The training program also produced significant reductions in the insulinogenic index measured during an oral glucose tolerance test and in plasma cholesterol (Chol), low-density lipoprotein (LDL)-Chol, and apolipoprotein (apo) B levels (P less than 0.05). Training also significantly increased plasma high-density lipoprotein (HDL)-apo A-I and HDL2-Chol levels and decreased plasma HDL3-Chol concentration (P less than 0.05). Whereas no change in postheparin plasma lipoprotein lipase activity was noted, a significant decrease in postheparin plasma hepatic triglyceride lipase activity was observed after training (P less than 0.005). Metabolic responses were not correlated with changes in VO2 max but were significantly correlated with the reduction in body fat mass and/or with the loss of deep abdominal fat.(ABSTRACT TRUNCATED AT 250 WORDS)

A sandwich-enzyme immunoassay for the quantification of lipoprotein lipase and hepatic triglyceride lipase in human postheparin plasma using monoclonal antibodies to the corresponding enzymes

We have developed a sandwich-enzyme immunoassay (EIA) for the quantification of lipoprotein lipase (LPL) and hepatic triglyceride lipase (HTGL) in human postheparin plasma (PHP) using monoclonal antibodies (MAbs) directed against the corresponding enzymes purified from human PHP. The sandwich-EIA for LPL was performed by using the combination of two distinct types of anti-LPL MAbs that recognize different epitopes on the LPL molecule. The immunoreactive mass of LPL was specifically measured using a beta-galactosidase-labeled anti-LPL MAb as an enzyme-linked MAb, an anti-LPL MAb linked with the bacterial cell wall as an insolubilized MAb, and purified human PHP-LPL as a standard. The sandwich-EIA for HTGL was carried out by using two distinct anti-HTGL MAbs that recognize different epitopes on HTGL. The limit of detection was 20 ng/ml for LPL and 60 ng/ml for HTGL. Each method yielded a coefficient of variation of less than 6% in intra- and inter-assays, and a high concentration of triglyceride did not interfere with the assays. The average recovery of purified human PHP-LPL and -HTGL added to human PHP samples was 98.8% and 97.5%, respectively. The immunoreactive masses of LPL and HTGL in PHP samples, obtained at a heparin dose of 30 IU/kg, from 34 normolipidemic and 20 hypertriglyceridemic subjects were quantified by the sandwich-EIA. To assess the reliability of the measured mass values, they were compared with the corresponding enzyme activities measured by selective immunoinactivation assay using rabbit anti-human PHP-LPL and -HTGL polyclonal antisera. Both assay methods yielded a highly significant correlation in either normolipidemic (r = 0.945 for LPL; r = 0.932 for HTGL) or hypertriglyceridemic subjects (r = 0.989 for LPL; r = 0.954 for HTGL). The normal mean (+/- SD) level of lipoprotein lipase mass and activity in postheparin plasma was 223 +/- 66 ng/ml and 10.1 +/- 2.9 mumol/h per ml, and that of hepatic triglyceride lipase mass and activity was 1456 +/- 469 ng/ml and 26.4 +/- 8.7 mumol/h per ml, respectively. The present sandwich-enzyme immunoassay methods make it possible to study the molecular nature of LPL and HTGL in PHP from patients with either primary or secondary hyperlipoproteinemia.

High-density lipoprotein cholesterol is not decreased if an aromatizable androgen is administered

We examined the influence of aromatization of testosterone on serum high-density lipoprotein cholesterol (HDL-C) and postheparin plasma hepatic triglyceride lipase activity (HTLA) in men. Eighteen healthy lean nonsmokers (ages, 20 to 33) were administered androgens in a weekly total dose of 280 mg for 12 weeks in one of three groups: testosterone enanthate (TE) (280 mg/wk intramuscularly [IM]); TE (280 mg/wk IM) + testolactone (TL) (250 mg orally [PO] four times daily); or methyltestosterone (MeT) (20 mg PO twice daily). Serum testosterone achieved steady state levels by 4 weeks with >40 nmol/L (TE and TE + TL) and <15 nmol/L (MeT) while 17b-estradiol (E2) rose to >250 pmol/L (TE) or remained below 70 pmol/L (TE + TL and MeT). LH fell to less than 5 U/L (TE and TE + TL) but remained unchanged with MeT. By 4 weeks, HDL-C had decreased significantly from 1.20 ± 0.13 to 0.77 ± 0.13 mmol/L (MeT), from 1.18 ± 0.15 to 0.89 ± 0.13 mmol/L (TE + TL), and demonstrated no decrease in the TE group across the time course of the study. These changes were preceded by mean increases in HTLA of 102% (MeT) and 55% (TE + TL) over baseline, and no significant change with TE. The changes in HDL-C and HTLA returned to baseline within 2 weeks of steroid cessation. There were no changes in total cholesterol, triglycerides, or insulin in any group but, in the MeT group, apo AI levels decreased and low-density lipoprotein cholesterol (LDL-C) increased. After 12 weeks of treatment, sex hormone binding globulin (SHBG) levels were decreased to 37% (MeT), 54% (TE + TL), and 73% (TE) of baseline levels; these changes were evident by the second week of treatment and returned to baseline by the second week following treatment cessation. These results suggest that TE has little effect on HTLA but when a corresponding increase in E2 levels is prevented, HTLA increases. MeT, which is not metabolized to E2, produced the most dramatic HTLA increases, even at a dose that did not reduce serum LH; thus, hepatic specific properties of 17-alkylated androgens may further increase the atherogenic potential of this class of androgens.

Lipoprotein, apolipoprotein, and lipolytic enzyme changes following estrogen administration in postmenopausal women.

To test whether estrogen can modulate the cholesterolemic response to an Occidental diet, six healthy postmenopausal women were studied for 84 days while ingesting a solid food diet of constant composition high in cholesterol content (995 mg/d). In the middle of the study, estrogen (17 alpha-ethinyl estradiol, 1 microgram/kg per day) was administered orally. Ingestion of the diet for the initial 28 days did not alter lipoprotein lipid or apolipoprotein (apo) levels. However, with just 4 days of estrogen use there were significant decreases in apoE (-36%), low density lipoprotein cholesterol (-26%), and postheparin plasma hepatic triglyceride lipase activity (HTGL) (-61%), and an increase in high density lipoprotein (HDL) triglyceride (72%). These changes persisted throughout the estrogen use. The percent change in HTGL with 4 days of estrogen correlated inversely with the percent change in HDL triglyceride (rs = -0.94). After 28 days of estrogen there were also significant increases in HDL cholesterol (21%), HDL2 cholesterol (42%), apoA-I (37%), and apoA-II (9%), and a decrease in apoB (-11%). The level of apoE at this juncture correlated inversely with the level of HDL cholesterol (rs = -0.90), and the levels of HTGL and apoA-I correlated with HDL2 cholesterol (rs = -0.89 and rs = 0.89, respectively). Thus, HTGL may play a role in both the early estrogen-related changes in HDL triglyceride and apoE and the late estrogen-related changes in HDL cholesterol, apoA-I, and apoA-II.

Isolation and cDNA sequence of human postheparin plasma hepatic triglyceride lipase.

Hepatic triglyceride lipase (H-TGL) was isolated from human postheparin plasma by column chromatography on heparin-Sepharose and phenyl-Sepharose and immunoaffinity chromatography with monoclonal antibodies. The purified enzyme had an apparent molecular weight of 65,000 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis and an amino-terminal sequence of Leu-Gly-Gln-Ser-Leu-Lys-Pro-Glu. Partial amino acid sequences of seven cyanogen bromide peptides were obtained. A human hepatoma cDNA library was screened with synthetic oligonucleotides derived from the partial protein sequence. The cloned H-TGL cDNA of 1569 nucleotides predicts a mature protein of 477 amino acids plus a leader sequence of 22 amino acids. Blot hybridization analysis of poly(A)+ mRNA with a putative H-TGL cDNA clone gave a single hybridizing band of 1.7 kilobases. The protein contains four consensus N-glycosylation sequences based on the cDNA sequence. Comparison of the enzyme sequence with that of other lipases reveals highly conserved sequences in regions of putative lipid and heparin binding. The carboxyl terminus of H-TGL contains a highly basic sequence which is not reported to be present in rat H-TGL or other members of the lipase gene family.

Monoclonal antibodies that distinguish between active and inactive forms of human postheparin plasma hepatic triglyceride lipase.

Hepatic triglyceride lipase (H-TGL) was purified from human postheparin plasma. Specific monoclonal antibodies (MAbs) were produced that discriminate between active (native) and inactive (denatured) forms of the enzyme. Mice immunized with native H-TGL resulted in MAbs that recognized only the native protein. The antibodies did not react with H-TGL treated with 1% sodium dodecyl sulfate or heated at 60 degrees C. The loss of immunoreactivity with heating correlated directly with the loss of enzyme activity and there was a corresponding increase in immunoreactivity with the MAbs prepared against the denatured enzyme. Western blot analysis of postheparin plasma with the MAbs against denatured H-TGL gave a single protein band of 65 kD; preheparin plasma showed no detectable immunoreactivity with either MAb. These immunochemical studies suggest that there are no circulating active or inactive forms of H-TGL in man. Furthermore, the MAbs provide the necessary reagents for development of immunoassays for H-TGL.

The dyslipoproteinemia of anabolic steroid therapy: Increase in hepatic triglyceride lipase precedes the decrease in high density lipoprotein 2 cholesterol

Administration of the androgenic anabolic steroid, stanozolol, is associated with decreased high density lipoprotein (HDL) cholesterol (primarily due to decreased HDL 2 cholesterol) and increased levels of postheparin plasma hepatic triglyceride lipase (HTGL) activity. Since HTGL appears to play a role in HDL metabolism, we examined the temporal relationship between these changes. HDL cholesterol remained stable during the first two days of stanozolol administration, but decreased 14% ( P < .01) by the third day and 39% ( P < .01) by the seventh day of stanozolol. HDL 2 cholesterol paralleled the total HDL cholesterol level and remained stable for the first two days, but decreased 22% ( P < .01) after three days and 71% ( P < .01) after seven days of stanozolol. In contrast, HTGL increased 62% ( P < .001) during the first day, 161% ( P < .001) with two days, 230% ( P < .001) with three days of stanozolol administration, and remained elevated thereafter. Thus, during stanozolol administration HTGL increased dramatically and clearly before any change in HDL or HDL 2 cholesterol.

Effects of estrogen/progestin agents on plasma retinoids and chylomicron remnant metabolism

Women using estrogen-progestin oral contraceptive agents have a marked decrease in the activity of hepatic triglyceride lipase, an enzyme believed to be involved in the catabolism of lipoprotein remnants. The hypothesis that women receiving these agents have defective remnant processing resulting in elevated chylomicron remnant concentrations in plasma was tested. Retinyl esters, which in humans are transported by intestinally-derived lipoproteins, were used to estimate chylomicron and chylomicron remnant concentrations. Women on a variety of oral contraceptive agents had increased plasma triglyceride concentrations, but only minimally increased fasting retinyl ester concentrations. Retinol and retinyl binding protein were elevated to about 150% of controls (p < 0.001). Retinyl ester concentrations during active fat absorption were then measured in a second group of women taking a single preparation. Three-hour retinyl ester levels were lower in the treated group than control (p < 0.05), but the difference had disappeared at six hours. Postheparin plasma hepatic triglyceride lipase was reduced by 46% in the treated group (p < 0.05). Thus despite reduction in hepatic lipase activity, there was no accumulation of retinyl esters in the contraceptive-treated women to suggest impaired remnant processing.

The role of hepatic triglyceride lipase in the metabolism of intermediate-density lipoprotein—Postheparin lipolytic activities determined by a sensitive, nonradioisotopic method in hyperlipidemic patients and normals

With a view to elucidating the physiologic role of hepatic triglyceride lipase (H-TGL), we studied the relationship between the activity of H-TGL and the concentrations of the lipids of ultracentrifugally separated lipoprotein fractions in sera from 81 cases of primary hyperlipidemia, 5 of hypothyroidism, and 31 normal subjects. The activity of H-TGL in postheparin plasma was determined by the sensitive, nonradioisotopic method that was recently developed by us. In the entire group of subjects including the normals, the activity of H-TGL had a significant inverse correlation with the concentration of the cholesterol (r = −0.443, P < 0.001) and phospholipid (r = −0.433, P < 0.001) of intermediate density lipoprotein (IDL). When the patients were divided into subgroups according to the phenotype of hyperlipidemia, it was found that the correlation was more significant in type IIb (r = 0.695, P < 0.001) or type IV + V (r = −0.664, P < 0.0001). In the five cases of hypothyroidism, the mean IDL cholesterol level was high (28.3 ± 12.3 mg/dL) and the H-TGL activity was very low (4.6 ± 4.5 μmol/h/mL). The H-TGL activity was also significantly correlated with the ratio of high density lipoprotein-2 to high density lipoprotein-3 cholesterol (r = 0.351, P < 0.001) in the entire group. The present study provided further evidence in favor of the hyptohesis that a decrease in H-TGL activity in hyperlipidemic patients with high levels of very low density lipoprotein (VLDL), such as type IIb, IV, and V cases, contributes to IDL accumulation, and suggests that H-TGL plays an important role in IDL metabolism, especially in hyperlipidemia associated with increased levels of VLDL.

Preliminary report: Kinetic studies on the modulation of high-density lipoprotein, apolipoprotein, and subfraction metabolism by sex steroids in a postmenopausal woman

To investigate the effects of estrogens and androgens on the metabolism of high density lipoproteins (HDL) and low density lipoproteins (LDL), a normolipidemic postmenopausal woman was studied under the following conditions: (1) during supplementation with ethinyl estradiol (0.06 mg/d); (2) without sex steroid therapy; and (3) during treatment with stanozolol, an androgenic, anabolic steroid (6 mg/d). During these manipulations HDL and LDL cholesterol levels fluctuated widely but reciprocally: during estrogen supplementation HDL increased while LDL decreased; during stanozolol HDL-C decreased while LDL-C increased. Simultaneous changes in post-heparin plasma hepatic triglyceride lipase activity paralleled those of LDL (and opposed those of HDL), decreasing with estrogen and increasing with stanozolol. During all three phases, autologous 125I-HDL turnover studies disclosed similarities between HDL 2 and apolipoprotein A-I metabolism and between HDL 3 and apolipoprotein A-II metabolism. In the untreated state the residence times of HDL 2 and apo A-I were only half those of HDL 3 and apo A-II. During estrogen treatment HDL 2 and apo A-I, residence times were selectively prolonged, coming to resemble those of HDL 3 and apo A-II, which remained unchanged. By contrast, during stanozolol treatment HDL 3 and apo A-II residence times were selectively reduced, coming to resemble those of HDL 2 and apo A-I, which remained unchanged. Apo A-I levels increased on estrogen and decreased on stanozolol, while apo A-II remained stable. Hence, estrogen increased HDL primarily by retarding the catabolism of the HDL 2 subfraction rich in apo A-I, whereas stanozolol decreased HDL by accelerating the catabolism of HDL 3, relatively rich in apo A-II. These effects may have been mediated via the concomitant sex steroid-induced changes in the activity of hepatic triglyceride lipase, hypothesized to be a central enzyme in the regulation of HDL catabolism.

Studies on the mechanism of hypertriglyceridemia in the genetically obese Zucker rat.

The possibility that impaired removal of lipoprotein triglyceride from the circulation may be a participating factor in the hypertriglyceridemia of the obese Zucker rat was examined. We found no significant differences in the heparin-released lipoprotein lipase (LPL) activities of the adipose tissue, skeletal muscle, and heart (expressed per gram of tissue) from the lean and obese Zucker rats. Furthermore, the kinetic properties of adipose tissue and heart LPL from the lean and obese rats were similar, indicating that the catalytic efficiency of the enzyme was unaltered in the obese animals. The postheparin plasma LPL activities of lean and obese rats were also similar. However, the postheparin plasma hepatic triglyceride lipase (H-TGL) activity in the obese rats was elevated. The higher activity of H-TGL could not alleviate the hypertriglyceridemia in these animals. Since hypertriglyceridemia in the obese rats could also be due to the hepatic production of triglyceride-rich lipoproteins which are resistant to lipolysis, we therefore isolated very low density lipoproteins (VLDL) from lean and obese rat liver perfusates and examined their degradation by highly purified human milk LPL. Although certain differences were observed in hepatic VLDL triglyceride fatty acid composition, the kinetic patterns of LPL-catalyzed triglyceride disappearance from lean and obese rat liver perfusate VLDL were similar. The isolated liver perfusate VLDL contained sufficient apolipoprotein C-II for maximum lipolysis. These results indicate that impaired lipolysis is not a contributing factor in the genesis of hypertriglyceridemia in the genetically obese Zucker rat. The hyperlipemic state may be attributed to hypersecretion of hepatic VLDL and consequent saturation of the lipolytic removal of triglyceride-rich lipoproteins from the circulation.

肝性トリグリセライドリパーゼ活性低下を伴った家族性高HDL血症の一例

A 72-year-old woman with myocardial infarction and cerebral infarction was studied because of her markedly increased concentration of plasma high-density lipoprotein (HDL). The concentration of HDL-cholesterol was 152mg per 100ml. The cholesterol and phospholipid levels in the HDL2 fraction were greatly elevated. In contrast, the activity of post-heparin plasma hepatic triglyceride lipase (H-TGL) was only 18 per cent of normal. The daughter and the granddaughter of the proband showed a similar increase in plasma HDL2 level and also a decrease in H-TGL activity, 12.5 and 22 per cent of normal respectively. In this family, there were no causal factors that would account for the increased HDL level nor for the decreased activity of H-TGL. A physiological role for H-TGL remains obscure, a further examination of lipoprotein metabolism and abnormality in H-TGL in these patients may provide important information concerning the physiological role for this enzyme and for the relationship between plasma HDL and the progression of atherosclerosis.

Roles of lipoprotein lipase and hepatic triglyceride lipase in the catabolism in vivo of triglyceride-rich lipoproteins.

To define the roles, in vivo, of hepatic triglyceride lipase and lipoprotein lipase in the catabolism of triglyceride-rich lipoproteins, we investigated the relationship between the activities of the above enzymes in postheparin plasma and the fractional removal rates of very low density lipoproteins (VLDL) and VLDL remnant particles. In 22 patients, the fractional removal rates of VLDL and VLDL-remnant particles were determined from analyses of the disappearance of radioiodinated Sf 60-400 and Sf 12-60 lipoprotein B apoprotein. The maximal activities of hepatic triglyceride lipase and lipoprotein lipase were determined in plasma samples drawn 2-60 minutes after heparin injection (60 U/kg). A positive correlation was observed between the fractional removal rate of VLDL and postheparin plasma lipoprotein lipase activity (r = 0.65). When all 22 patients were considered together, no relationship was demonstrable between remnant fractional removal and postheparin plasma lipoprotein lipase activity. However, humans may be subdivided with respect to the way in which they catabolize remnants. In some, all remnant may be catabolized to form LDL. In others, some of the remnant may also be directly removed from the circulation. Those subjects in whom previous studies indicate that all remnant is converted to LDL demonstrated a positive correlation between remnant fractional removal rate and postheparin plasma lipoprotein lipase activity (n = 8, r - 0.83). No correlations between postheparin plasma hepatic triglyceride lipase activity and any of the fractional removal rates were found. These data are consistent with the following: 1) lipoprotein lipase plays a key regulatory role in the catabolism of triglyceride-rich lipoproteins; 2) this role applies only to those catabolic involving the formation of particles of higher density VLDL remnants and low density lipoprotein; and 3) hepatic triglyceride lipase plays no rate-limiting role in the catabolism of VLDL or VLDL-remnant particles.

低HDL血症患者のHDL代謝における肝性トリグリセリドリパーゼの役割

It has been indicated that lipoprotein lipase (LPL) and hepatic triglyceride lipase (H-TGL) play a role not only in the metabolism of triglyceride rich lipoproteins but also in HDL metabolism. The purpose of the present study was to investigate the role of LPL and H-TGL in the metabolism of HDL-subfractions, HDL2 and HDL3 in the subjects with hypo-high density lipoproteinemia. Clinical diagnosis of the 29 patients with hypohigh density lipoproteinemia studied in the present study were postapoplexy in the steady state, coronary heart disease and hypertension etc. Furthermore, seventeen hypo-high density lipoproteinemia with diabetes mellitus, 19 subjects with normal levels of HDL-cholesterol (C) and 8 diabetics with normal levels of HDL-C were studied. Hypo-high density lipoproteinemia was defined by (HDL2+HDL3)-cholesterol less than 40mg/100ml. Plasma lipoproteins were fractionated by sequential ultracentrifugation at densities 1.063 and 1.110g/ml to obtain VLDL+LDL(d<1.063g/ml), HDL2(1.063<d<1.110g/ml) and HDL3 (d>1.110g/ml). Concentrations of cholesterol, triglyceride and phospholipid in plasma and each lipoprotein fraction were measured. Activities of LPL and H-TGL in postheparin plasma obtained 10min after injection of heparin, 10U/Kg body weight, were assayed utilizing the substrate containing [14C] triolein. Separate assay of LPL and H-TGL activities were performed by inhibition of LPL activity by 1M NaCl. Cholesterol concentrations in HDL2 and HDL3 from hypohigh density lipoproteinemia were significantly lower than those from the patients with normal levels of HDL-C. Decrease of HDL2-cholesterol was more remarkable than that of HDL3-cholesterol. Therefore, HDL2-Ch/HDL3-Ch ratio was significantly lower in hypo-high density lipoproteinemia than in the patients with normal levels of HDL-Ch. As far as phospholipid is concerned, the same tendency was observed as cholesterol. There was no significant difference in triglyceride concentration in HDL2 and HDL3 between hypo- and normo-high density lipoproteinemia. LPL activity was significantly lower in hypo-high density lipoproteinemia without diabetes mellitus than in normo-high density lipoproteinemia. There were no significant differences in H-TGL activities among 4 groups. In hypo-high density lipoproteinemia, significantly negative correlations were observed between H-TGL activities and concentrations of cholesterol and phospholipid in HDL2. Significantly positive correlations were observed between LPL activities and concentrations of triglyceride and phospholipid in HDL2. However, there were no significant correlations among LPL activity, H-TGL activity and lipids concentrations in HDL3. These correlations were much more obvious in diabetics with hypo-high density lipoproteinemia. The data presented indicate the important role of LPL and H-TGL in the metabolism of HDL2 and HDL3 in the subjects with hypo-high density lipoproteinemia.

A selective decline of postheparin plasma hepatic triglyceride lipase in hypothyroid rats

The present study aimed to define the effect of thyroid status on two postheparin plasma lipases, i.e., lipoprotein lipase and hepatic triglyceride lipase. Rats with hypo- and hyperthyroidism were used for this purpose. Separate measurement of these two lipases was done by an immunochemical method utilizing antiserum specific to hepatic triglyceride lipase. The 5-wk thyroidectomized, hypothyroid rats had normal plasma concentrations of both triglyceride and cholesterol. These rats showed a selective decline in the activity of postheparin plasma hepatic triglyceride lipase with normal lipoprotein lipase activity. The rats made thyrotoxic by thyroxine treatment had normal plasma levels of both triglyceride and cholesterol. These rats showed normal activities of both hepatic triglyceride lipase and lipoprotein lipase. The observed finding of a selective decline of hepatic triglyceride lipase in hypothyroid rats is discussed in connection with the possible function of this enzyme in lipoprotein metabolism.

Postheparin plasma triglyceride lipases in chronic hemodialysis: Evidence for a role for hepatic lipase in lipoprotein metabolism

Elevated plasma triglyceride levels frequently occur in patients with chronic renal failure receiving longterm hemodialysis. Postheparin plasma lipolytic activity, an indirect measure of triglyceride removal, is low in hemodialysis patients, but this activity measures both hepatic triglyceride lipase (HTGL) and lipoprotein lipase (LPL). To determine if HTGL and/or LPL are low in hemodialysis patients and related to lipoprotein lipid levels, both activities were measured by a selective antibody-inhibition technique in postheparin plasma from 20 hemodialysis patients with a wide range of plasma triglyceride levels ( 104–676 mg 100 ml ), and the relationships between the enzyme activities and lipoprotein lipid levels were examined. To more accurately compare subjects, the heparin doses were adjusted for the differences in plasma volumes between the hemodialysis patients and the nonuremic control subjects. Hemodialysis patients with elevated plasma triglyceride levels (↑TG) had HTGL levels (148 ± 67 nmole/min/ml, n=10) which were similar to the dialysis patients with normal triglyceride levels (nlTG) (134 ± 64 nmole/min/ml, n=10) and both groups were significantly lower ( p<0.05, p<0.02, respectively) than the levels of the control subjects (208 ± 61 nmole/min/ml, n=11). The HTGL levels of the hemodialysis patients with ↑TG correlated inversely with plasma total cholesterol ( r s=−0.833, p<0.01) and the d>1.006 fraction cholesterol (low + high density lipoproteins, r s=−0.863, p<0.01), but not triglyceride. The activity of HTGL of the entire group of hemodialysis patients correlated with the plasma total cholesterol ( r s=−0.615, p<0.01), d>1.006 fraction cholesterol ( r s=−0.731, p<0.01) and low density lipoprotein cholesterol ( r s=−0.659, p<0.01). The LPL levels of the hemodialysis patients with the ↑TG (52 ± 24 nmole/min/ml) were lower than those with nlTG (70 ± 25 nmole/min/ml) and the levels of both hemodialysis groups were significantly lower ( p<0.01, p<0.02, respectively) than the LPL levels in the control subjects (110 ± 43 nmole/min/ml). The ratio of LPL to total postheparin plasma lipolytic activity was lower in the hemodialysis patients with ↑TG (0.32 ± 0.15), than in the hemodialysis patients with nlTG (0.47 ± 0.18, p<0.06) or the control subjects (0.45 ± 0.09, p<0.05). Unlike HTGL, the levels of LPL did not correlate with lipid levels in the hemodialysis patients. Thus, both postheparin plasma HTGL and LPL are low in hemodialysis patients. The relationship between HTGL and low density lipoprotein cholesterol levels suggests a possible role for HTGL in low density lipoprotein catabolism.

Hepatic triglyceride and lipoprotein lipase activities of post-heparin plasma in normals and hypertriglyceridemics.

Post-heparin plasma hepatic triglyceride lipase (H-TGL) and lipoprotein lipase (LPL) activities were 8-34 and 3.5-21 (range) mu mol/ml/hr respectively in males with normal serum lipid concentrations. In females the corresponding values were 4-25 and 4-16 mu mol/ml/hr. No significant differences were observed between ages or between the two sexes. Male patients with hypertriglyceridaemia had similar activities of H-TGL but significantly lower values for LPL activities than the control males. Significant linear correlations were found between serum triglyceride concentrations and LPL activities both for males (coefficient of correlation = r = -0.64) and for females (r = -0.62).

Triglyceride (TG) 代謝に関する研究 (第3報)

Hepatic triglyceride lipase (TGL) was extracted from acetone-ether dried powder of rat liver with 0.05M NH4Cl-NH4OH buffer (pH 8.5) containing 0.5U/ml of heparin for 60min at 0°C. The crude enzyme extracts thus obtained were partially purified on a heparin-Sepharose affinity chromatography. This gave a 78-fold purification over crude enzyme extracts. A purified enzyme did not require serum for substrate activation and was not inhibited by 1M sodium chloride, being differed from lipoprotein lipase in rat postheparin plasma.A purified enzyme had a single pH optimum at 9.0, whereas crude enzyme extracts had lipolytic activities over a wide range of pH values with two maxima at pH9.0 and 4.0. The lipolytic activities in crude enzyme extracts were separated on heparin-Sepharose column into two fractions, a breakthrough fraction and a purified hepatic TGL. In an attempt to define the location of these lipolytic activities, NaCl-noninhibitable hepatic TGL in postheparin plasma and crude enzyme extracts of postheparin liver were assayed for their activities at different pH values. The lipolytic activities of crude extracts of postheparin liver had a pH optimum at 4.0 with a marked decrease at 9.0, being the same with that of the break-through fraction of the column. Heparin-released hepatic TGL in plasma, on the other hand, had a similar pH dependence to that of a purified hepatic TGL.These results indicate that TGL activity in the liver is heterogeneous. This enzyme activity can be separated into two forms. One, having a high affinity for heparin bound to Sepharose, is in the hepatic plasma membrane and released by heparin into the circulation. The other, having no affinity for heparin, might be present intracellularly. The functional importance of the former form of enzyme was discussed.