Activity In Postheparin Plasma Research Articles

Development of a hamster model of spontaneous hypertriglyceridemia in diabetes.

Hypertriglyceridemia (HTG) often accompanies diabetes and is considered a risk factor for diabetic vascular complications. However, inducing diabetic HTG typically requires high-fat diets in certain animal models. Leveraging our newly developed LDL receptor knockout hamster model, which exhibits features akin to human lipid metabolism, we sought to determine whether these animals would develop HTG without dietary manipulations in diabetes. Diabetes was induced via intraperitoneal injection of STZ in wild type and heterozygous LDL receptor deficient hamsters. Blood glucose, triglyceride, and cholesterol were measured over 60 days. Plasma TG clearance was determined via olive oil gavage. The effect of insulin on diabetic HTG was assessed on Day 60 post-diabetes induction. Blood glucose increased over threefold, while plasma insulin decreased to 30% of controls after STZ injection in both wild type and heterozygous hamsters by Day 7, remaining stable for 60 days. Plasma TG in wild-type hamsters remained unchanged at Day 7 post-STZ injection but increased slightly thereafter. Conversely, heterozygous hamsters exhibited severe HTG by Day 7 until the end of the study. Olive oil gavage revealed much slower plasma triglyceride clearance in heterozygous hamsters compared to WT animals, despite significantly reduced lipoprotein lipase activity in post-heparin plasma in both animals. Hyperglycemia and HTG in heterozygous hamsters were reversed to pre-diabetic levels following intraperitoneal insulin administration. In conclusion, severe HTG in diabetic heterozygous LDL receptor deficient hamsters developed spontaneously and was insulin-dependent. Thus, this hamster model holds promise for effectively studying the complications associated with human diabetic HTG.

The zinc finger and BTB domain containing protein ZBTB20 regulates plasma triglyceride metabolism by repressing lipoprotein lipase gene transcription in hepatocytes.

Lipoprotein lipase (LPL) is responsible for the lipolytic processing of triglyceride-rich lipoproteins, the deficiency of which causes severe hypertriglyceridemia. Liver LPL expression is high in suckling rodents but relatively low at adulthood. However, the regulatory mechanism and functional significance of liver LPL expression are incompletely understood. We have established the zinc finger protein ZBTB20 as a critical factor for hepatic lipogenesis. Here, we evaluated the role of ZBTB20 in regulating liver Lpl gene transcription and plasma triglyceride metabolism. Hepatocyte-specific inactivation of ZBTB20 in mice led to a remarkable increase in LPL expression at the mRNA and protein levels in adult liver, in which LPL protein was mainly localized onto sinusoidal epithelial cells and Kupffer cells. As a result, the LPL activity in postheparin plasma was substantially increased, and postprandial plasma triglyceride clearance was significantly enhanced, whereas plasma triglyceride levels were decreased. The dysregulated liver LPL expression and low plasma triglyceride levels in ZBTB20-deficient mice were normalized by inactivating hepatic LPL expression. ZBTB20 deficiency protected the mice against high-fat diet-induced hyperlipidemia without causing excessive triglyceride accumulation in the liver. Chromatin immunoprecipitation and gel-shift assay studies revealed that ZBTB20 binds to the LPL promoter in the liver. A luciferase reporter assay revealed that ZBTB20 inhibits the transcriptional activity of LPL promoter. The regulation of LPL expression by ZBTB20 is liver-specific under physiological conditions. Liver ZBTB20 serves as a key regulator of LPL expression and plasma triglyceride metabolism and could be a therapeutic target for hypertriglyceridemia.

Novel mutations in the GPIHBP1 gene identified in 2 patients with recurrent acute pancreatitis

Glycosylphosphatidylinositol-anchored high-density lipoprotein-binding protein 1 (GPIHBP1) has been demonstrated to be essential for the invivo function of lipoprotein lipase (LPL), the major triglyceride (TG)-hydrolyzing enzyme involved in the intravascular lipolysis of TG-rich lipoproteins. Recently, loss-of-function mutations of GPIHBP1 have been reported as the cause of type I hyperlipoproteinemia in several patients. Two unrelated patients were referred to our Lipid Units because of a severe hypertriglyceridemia and recurrent pancreatitis. We measured LPL activity in postheparin plasma and serum ApoCII and sequenced LPL, APOC2, and GPIHBP1. The 2 patients exhibited very low LPL activity not associated with mutations in LPL gene or with ApoCII deficiency. The sequence of GPIHBP1 revealed 2 novel point mutations. One patient (proband 1) was found to be homozygous for a C>A transversion in exon 3 resulting in the conversion of threonine to lysine at position 80 (p.Thr80Lys). The other patient (proband 2) was found to be homozygous for a G>T transversion in the third base of the ATG translation initiation codon in exon 1, resulting in the conversion of methionine to isoleucine (p.Met1Ile). In conclusion, we have identified 2 novel GPIHBP1 missense mutations in 2 unrelated patients as the cause of their severe hypertriglyceridemia.

Acute alcohol consumption downregulates lipoprotein lipase activity in vivo

ObjectiveAcute alcohol consumption can induce hypertriglyceridemia. Such an effect could be explained in part by the influence of alcohol on lipoprotein lipase (LPL) – the key enzyme responsible for triglyceride hydrolysis in circulation. Therefore, we have studied the effects of acute moderate alcohol consumption on LPL activity and on the concentrations of angiopoietin-like proteins 3 and 4 (ANGPTL3 and ANGPTL4), which are known to inhibit LPL. MethodsTwo experiments were carried out in 8 healthy volunteers. They received 25g of alcohol (vodka) in one experiment and water in the other (control). The in vivo function of LPL was estimated using intravenous fat tolerance tests (IVFTT) carried out before, 2 and 4hours after alcohol administration. At the end of each experiment, LPL activity and mass were measured in post-heparin plasma (PHP). The concentrations of ANGPTL3 and ANGPTL4 in blood were measured before alcohol consumption and at the end of the experiments. ResultsLPL activity, as estimated using the IVFTT, was reduced by 25% and 24% two and four hours after the administration of alcohol, respectively, and was not affected in the control experiment. At the end of the experiment, LPL activity in PHP was 23% lower after alcohol consumption than in the controls. The concentrations of ANGPTL3 and ANGPTL4 had dropped to 67% and 86% of baseline values, respectively, at 280min after alcohol consumption. These levels were not affected in the control experiment. The levels of ANGPTL4 but not those of ANGPTL3 were increased in PHP compared to both baseline values and values at 280min. ConclusionThe capacity for triglyceride clearance seemed to be acutely reduced by alcohol consumption and the effect persisted for several hours. The levels of LPL activity in PHP were reduced to a similar extent. This reduction in LPL activity could not be explained by the changes in the levels of ANGPTL3 or ANGPTL4, which both decreased.

In vivo structure-function studies of human hepatic lipase: the catalytic function rescues the lean phenotype of HL-deficient (hl-/-) mice.

The lean body weight phenotype of hepatic lipase (HL)–deficient mice (hl−/−) suggests that HL is required for normal weight gain, but the underlying mechanisms are unknown. HL plays a unique role in lipoprotein metabolism performing bridging as well as catalytic functions, either of which could participate in energy homeostasis. To determine if both the catalytic and bridging functions or the catalytic function alone are required for the effect of HL on body weight, we studied (hl−/−) mice that transgenically express physiologic levels of human (h)HL (with catalytic and bridging functions) or a catalytically-inactive (ci)HL variant (with bridging function only) in which the catalytic Serine 145 was mutated to Alanine. As expected, HL activity in postheparin plasma was restored to physiologic levels only in hHL-transgenic mice (hl−/−hHL). During high-fat diet feeding, hHL-transgenic mice exhibited increased body weight gain and body adiposity relative to hl−/−ciHL mice. A similar, albeit less robust effect was observed in female hHL-transgenic relative to hl−/−ciHL mice. To delineate the basis for this effect, we determined cumulative food intake and measured energy expenditure using calorimetry. Interestingly, in both genders, food intake was 5–10% higher in hl−/−hHL mice relative to hl−/−ciHL controls. Similarly, energy expenditure was ∼10% lower in HL-transgenic mice after adjusting for differences in total body weight. Our results demonstrate that (1) the catalytic function of HL is required to rescue the lean body weight phenotype of hl−/− mice; (2) this effect involves complementary changes in both sides of the energy balance equation; and (3) the bridging function alone is insufficient to rescue the lean phenotype of hl−/−ciHL mice.

Characterization of a hypertriglyceridemic transgenic miniature pig model expressing human apolipoprotein CIII

Hypertriglyceridemia has recently been considered to be an independent risk factor for coronary heart disease, in which apolipoprotein (Apo)CIII is one of the major contributory factors, as it is strongly correlated with plasma triglyceride levels. Although ApoCIII transgenic mice have been generated as an animal model for the study of hypertriglyceridemia, the features of lipoprotein metabolism in mice differ greatly from those in humans. Because of the great similarity between pigs and humans with respect to lipid metabolism and cardiovascular physiology, we generated transgenic miniature pigs expressing human ApoCIII by the transfection of somatic cells combined with nuclear transfer. The expression of human ApoCIII was detected in the liver and intestine of the transgenic pigs. As compared with nontransgenic controls, transgenic pigs showed significantly increased plasma triglyceride levels (83 ± 36 versus 38 ± 4 mg·dL(-1), P < 0.01) when fed a chow diet. Plasma lipoprotein profiling by FPLC in transgenic animals showed a higher peak in large-particle fractions corresponding to very low-density lipoprotein/chylomicrons when triglyceride content in the fractions was assayed. There was not much difference in cholesterol content in FPLC fractions, although a large low-density lipoprotein peak was identified in both nontransgenic and transgenic animals, resembling that found in humans. Further analysis revealed markedly delayed clearance of plasma triglyceride, accompanied by significantly reduced lipoprotein lipase activity in post-heparin plasma, in transgenic pigs as compared with nontransgenic controls. In summary, we have successfully generated a novel hypertriglyceridemic ApoCIII transgenic miniature pig model that could be of great value for studies on hyperlipidemia in relation to atherosclerotic disorders.

Hypertriglyceridemia and delayed clearance of fat load in transgenic rabbits expressing human apolipoprotein CIII

Apolipoprotein CIII (apoCIII) has been implicated in hypertriglyceridemia and plasma apoCIII independently predicts risk for coronary heart disease. While hypertriglyceridemia in patients has been demonstrated to correlate with elevated plasma apoCIII levels and reduced lipoprotein lipase (LPL) activity, apoCIII transgenic mice show elevated LPL activity. In this study, we generated transgenic (Tg) rabbits expressing human apoCIII gene exclusively in liver and investigated the effect of apoCIII overexpression on lipid metabolism of rabbits. In comparison with non-Tg littermates, Tg rabbits had 3- and 3.2-fold increases in fed and fasted plasma triglycerides, respectively. In contrast, no significant differences were observed in plasma total cholesterol and high density lipoprotein cholesterol levels between Tg and non-Tg rabbits. Analysis of lipoprotein fractions revealed that elevated plasma triglyceride levels in Tg rabbits were mainly attributed to an increase in very low density lipoprotein/chylomicron-sized particles. Furthermore, Tg rabbits showed markedly delayed clearance of plasma triglycerides accompanied with significantly reduced LPL activity in post-heparin plasma compared to that in non-Tg controls. In conclusion, these results indicate apoCIII transgenic rabbits develop hypertriglyceridemia with similar mechanism in hypertriglyceridemic patients via delayed clearance of plasma triglycerides, and could be used as a valuable tool for the study of human hyperlipidemia in relation with atherosclerotic disorders.

Pathogenetic role of adipose tissue lipase deficit for development of hypertriglyceridaemia.

In 87 patients (74 males, 13 females; age 43 +/- 9.2 years) covering a wide range of triglyceride (TG) concentrations (8.8 to 80.7 mmol/l) the turnover of total serum TG has been measured using the technique of labelling endogenously synthesized TG with 3H-glycerol. In parallel, lipoprotein lipase activity in adipose tissue and the adipose-tissue lipase activity in post-heparin plasma have been assessed following an oral 50 g glucose load. Despite the well-recognized function of this enzyme for intravascular lipolysis no direct relationship between lipase activities and fractional catabolic rates (FCR), reflecting TG removal processes, was found. On the other hand, relative enzyme activities (per TG moles) are positively correlated with the FCR. However, a detailed analysis of this relationship revealed that only in HTG patients whose FCR are below 0.210 h-1 a rate-limiting influence of a relative lipase deficit can be shown. In these patients, a statistically significant elevation of concentrations of free fatty acids is supposed to contribute to the impairment of the TG removal.

Abstract: 556 TRIACYLGLYCEROL-RICH LIPOPROTEINS INFLUENCE THE INACTIVATION OF LIPOPROTEIN LIPASE BY ANGPTL 3 AND ANGPTL 4

Acute alcohol consumption can induce hypertriglyceridemia. Such an effect could be explained in part by the influence of alcohol on lipoprotein lipase (LPL) – the key enzyme responsible for triglyceride hydrolysis in circulation. Therefore, we have studied the effects of acute moderate alcohol consumption on LPL activity and on the concentrations of angiopoietin-like proteins 3 and 4 (ANGPTL3 and ANGPTL4), which are known to inhibit LPL.Two experiments were carried out in 8 healthy volunteers. They received 25 g of alcohol (vodka) in one experiment and water in the other (control). The in vivo function of LPL was estimated using intravenous fat tolerance tests (IVFTT) carried out before, 2 and 4 hours after alcohol administration. At the end of each experiment, LPL activity and mass were measured in post-heparin plasma (PHP). The concentrations of ANGPTL3 and ANGPTL4 in blood were measured before alcohol consumption and at the end of the experiments.LPL activity, as estimated using the IVFTT, was reduced by 25% and 24% two and four hours after the administration of alcohol, respectively, and was not affected in the control experiment. At the end of the experiment, LPL activity in PHP was 23% lower after alcohol consumption than in the controls. The concentrations of ANGPTL3 and ANGPTL4 had dropped to 67% and 86% of baseline values, respectively, at 280 min after alcohol consumption. These levels were not affected in the control experiment. The levels of ANGPTL4 but not those of ANGPTL3 were increased in PHP compared to both baseline values and values at 280 min.The capacity for triglyceride clearance seemed to be acutely reduced by alcohol consumption and the effect persisted for several hours. The levels of LPL activity in PHP were reduced to a similar extent. This reduction in LPL activity could not be explained by the changes in the levels of ANGPTL3 or ANGPTL4, which both decreased.

Determination of lipoprotein lipase activity in post heparin plasma of streptozotocin‐induced diabetic rats by high‐performance liquid chromatography with fluorescence detection

The activity of lipoprotein lipase (LPL), an enzyme responsible for lipoprotein metabolism, would vary in diseases and metabolic disorders. For determination of LPL activity, a highly sensitive high performance liquid chromatography (HPLC) method using a fluorescent reagent, 4-nitro-7-piperazino-2,1,3-benzoxadiazole (NBD-PZ) was applied to determinate the oleic acid (OA) generated from triolein by LPL activity without multiple solvents extraction step. We studied the optimal conditions of the reaction including the effect of emulsifiers, deproteinizing solvents, and the concentration of bovine serum albumin (BSA). Ten millimolar concentrations of triolein, 5% of BSA, 1% of Gum arabic (GA), and acetonitrile showed the optimum conditions for measuring the LPL activity. The accuracy values for the determination of LPL activity in 10 microL of rat post heparin plasma were 108.73 approximately 114.36%, and the intra- and inter-day precision values were within 1.28% and 2.91%, respectively. The limit of detection was about 4.53 nM (signal-to-noise ratio 3). The proposed method was applied to determination of LPL activity in post heparin plasma of normal and streptozotocininduced diabetic rats associated with 52.3% reduction. The established assay system could be used for determining LPL activity in different physiological and pathological conditions to clarify the relationship between LPL activity and diabetes mellitus.

Appraisal of hepatic lipase and lipoprotein lipase activities in mice

A variety of methods are currently used to analyze HL and LPL activities in mice. In search of a simple methodology, we analyzed mouse preheparin and postheparin plasma LPL and HL activities using specific polyclonal antibodies raised in rabbit against rat HL (anti-HL) and in goat against rat LPL (anti-LPL). As an alternative, we analyzed HL activity in the presence of 1 M NaCl, a condition known to inhibit LPL activity in humans. The assays were validated using plasma samples from wild-type and HL-deficient C57BL/6 mice. We now show that the use of 1 M NaCl for the inhibition of plasma LPL activity in mice may generate incorrect measurements of both LPL and HL activities. Our data indicate that HL can be measured directly, without heparin injection, in preheparin plasma, because virtually all HL is present in an unbound form circulating in plasma. In contrast, measurable LPL activity is present only in postheparin plasma. Both HL and LPL can be measured using the same assay conditions (low salt and the presence of apolipoprotein C-II as an LPL activator). Total lipase activity in postheparin plasma minus preheparin HL activity reflects LPL activity. Specific antibodies are not required.

A novel complex deletion–insertion mutation mediated by Alu repetitive elements leads to lipoprotein lipase deficiency

Lipoprotein lipase (LPL) deficiency is a rare autosomal recessive inherited disorder, characterized by marked hypertriglyceridemia, eruptive xanthoma, hepatosplenomegaly, recurrent attacks of pancreatitis, and markedly low or absent LPL activity in postheparin plasma. A majority of LPL deficient patients have been reported to have point mutations in the LPL gene; however, we find a complex deletion–insertion mutation by Alu elements, mobile retrotransposons, in a patient with LPL deficiency. This patient suffered from acute pancreatitis, showed chylomicronemia and lacked detectable LPL activity or mass in her postheparin plasma. Southern blot analysis and long-range PCR of the patient’s DNA demonstrated a 2.2-kb deletion encompassing exon 2. Sequence analysis revealed (1) a 2.3-kb deletion between an AT-rich region adjacent to an Alu element in intron 1 and another Alu element in intron 2; (2) an insertion of approximately 150 bp 5′-truncated Alu sequence with a poly (A) tail at the deletion point. The inserted sequence belongs to Alu Yb9, the youngest subfamily of Alu elements. The deletion occurred at the consensus cleavage site (3′-A|TTTT-5′) without target site duplication. These findings indicated that Alu retrotransposition caused the complex deletion–insertion. The patient was homozygous for this complex mutation, which eliminates exon 2 and leads to LPL deficiency. To our knowledge, the patient is the first case with LPL deficiency due to a complex deletion–insertion mediated by Alu repetitive elements.

Therapeutic effect of osthole on hyperlipidemic fatty liver in rats

To study the effects of osthole on hyperlipidemic fatty liver and investigate the possible mechanisms. A rat model with hyperlipidemic fatty liver was successfully established by feeding fatty milk for 6 weeks. The experimental rats were then treated with 5-20 mg/kg osthole for 6 weeks. The mouse hyperlipidemic model was induced by feeding fatty milk when they were treated with 10-20 mg/kg osthole for 3 weeks. After treatment with osthole, the levels of rat serum total cholesterol (TC), triglyceride (TG) and low density lipoprotein-cholesterol significantly decreased as compared with the fatty liver model group (P< 0.05 or P< 0.01). Hepatic weight and its coefficient, the hepatic tissue contents of TC, TG, and malondialdehyde, also significantly decreased (P< 0.05 or P< 0.01). In fatty milk-induced hyperlipidemic mice, the post-heparin plasma activities of lipoprotein lipase (LPL), hepatic lipase (HL), and total lipase (TL) significantly increased after treatment with 10-20 mg/kg osthole for 3 weeks (P< 0.05 or P< 0.01). Importantly, the histological evaluation of rat liver demonstrated that osthole dramatically decreased lipid accumulation (P< 0.01). Osthole was found to have therapeutic effects on fatty milk-induced rat fatty liver; the mechanisms might be associated with its anti-oxidation and the elevation of the activities of LPL and HL.

A novel method for measuring human hepatic lipase activity in postheparin plasma

The objective of this study was to establish a hepatic lipase (HL) assay method that can be applied to automatic clinical analyzers. Seventy-four hyperlipidemic subjects (men/women 45/29) were recruited. Lipase activity was assayed measuring the increase in absorbance at 546 nm due to quinonediimine dye production. Reaction mixture R-1 contained 50 mM Tris-HCl (pH 9.5), 0.5 mM glycerol-1,2-dioleate, 0.4% (unless otherwise noted) polyoxyethylene-nonylphenylether, 3 mM ATP, 3 mM MgCl(2), 1.5 mM CaCl(2), monoacylglycerol-specific lipase, glycerol kinase, glycerol-3-phosphate oxidase, 0.075% N,N-bis-(4-sulfobutyl)-3-methylaniline-2 Na, peroxidase, ascorbic acid oxidase. Reaction mixture R-2 contained 50 mM Tris-HCl (pH9.5), 0.15% 4-aminoantypirine. Automated assay for activity was performed with a Model 7080 Hitachi analyzer. In the lipase assay, 160 microl of R-1 was incubated at 37 degrees C with 3 microl of samples for 5 min, and 80 microl of R-2 was added. Within-run coefficient of variations was 0.9-1.0%. Calibration curve of lipase activity was linear (r = 0.999) between 0 and 320 U/l. Analytical recoveries of purified HL added to plasma were 96.6-99.8%. HL activity in postheparin plasma measured in this method had a closer correlation with HL mass by a sandwich ELISA (r = 0.888, P < 0.0001) than those in the conventional method using [(14)C-]triolein (r = 0.730, P < 0.0001). This assay method for HL activity can be applied to an automatic clinical analyzer.

Reduction of plasma triglycerides in apolipoprotein C-II transgenic mice overexpressing lipoprotein lipase in muscle

LPL and its specific physiological activator, apolipoprotein C-II (apoC-II), regulate the hydrolysis of triglycerides (TGs) from circulating TG-rich lipoproteins. Previously, we developed a skeletal muscle-specific LPL transgenic mouse that had lower plasma TG levels. ApoC-II transgenic mice develop hypertriglyceridemia attributed to delayed clearance. To investigate whether overexpression of LPL could correct this apoC-II-induced hypertriglyceridemia, mice with overexpression of human apoC-II (CII) were cross-bred with mice with two levels of muscle-specific human LPL overexpression (LPL-L or LPL-H). Plasma TG levels were 319 +/- 39 mg/dl in CII mice and 39 +/- 5 mg/dl in wild-type mice. Compared with CII mice, apoC-II transgenic mice with the higher level of LPL overexpression (CIILPL-H) had a 50% reduction in plasma TG levels (P = 0.013). Heart LPL activity was reduced by approximately 30% in mice with the human apoC-II transgene, which accompanied a more modest 10% decrease in total LPL protein. Overexpression of human LPL in skeletal muscle resulted in dose-dependent reduction of plasma TGs in apoC-II transgenic mice. Along with plasma apoC-II concentrations, heart and skeletal muscle LPL activities were predictors of plasma TGs. These data suggest that mice with the human apoC-II transgene may have alterations in the expression/activity of endogenous LPL in the heart. Furthermore, the decrease of LPL activity in the heart, along with the inhibitory effects of excess apoC-II, may contribute to the hypertriglyceridemia observed in apoC-II transgenic mice.

Activity and tissue-specific expression of lipases and tumor-necrosis factor α in lean and obese cats

Post-heparin plasma activity of lipoprotein lipase (LPL) and hepatic lipase (HL), and fat and muscle activity of LPL were measured in neutered lean and obese cats. Lipoprotein lipase, hormone-sensitive lipase (HSL), and tumor necrosis factor a (TNF) mRNA were measured in muscle and fat tissue with real-time PCR using primers for feline LPL, HSL, and TNF. Lipoprotein lipase plasma and fat activity and fat mRNA levels were significantly lower (50, 80, and 50%, respectively) in obese cats than lean cats, whereas the muscle/fat ratio of LPL was significantly higher in obese compared to lean cats. The activity of HL was not different between the groups. Hormone-sensitive lipase mRNA levels were significantly higher in obese than lean cats. The level of fat TNF also was significantly higher in obese cats than in lean cats, whereas the level in muscle was not different. The lower LPL activity and mRNA expression in fat and the higher LPL and HSL mRNA expression in muscle in obese cats compared to lean cats expectedly favor a redistribution of fatty acids from fat to muscle tissue where they can be deposited or used for energy in times of need. Tumor necrosis factor α may regulate this repartitioning process through suppression of adipocyte LPL.

Long-Term Course of Lipoprotein Lipase (LPL) Deficiency Due to Homozygous LPLAritain a Patient with Recurrent Pancreatitis, Retained Glucose Tolerance, and Atherosclerosis

Lipoprotein lipase (LPL) deficiency is a rare autosomal recessive disorder caused by LPL gene mutation and is characterized by severe hyperchylomicronemia. Patients with LPL deficiency suffer from the frequent recurrence of acute pancreatitis, but the underlying mechanisms are not fully understood. A 22-yr-old male Japanese patient with severe hyperchylomicronemia was admitted to our hospital in 1973. He had no consanguinity and no family history of hyperlipidemia. He was genetically diagnosed as LPL deficiency (homozygous for LPL(Arita)) with no LPL mass or activity in postheparin plasma. He has experienced recurrent acute pancreatitis 22 times during our 31-yr clinical follow-up, but no pancreatic pseudocyst, irregularity of the pancreatic duct, or abnormal pancreatic calcification was observed in computed tomography. Moreover, his pancreatic endocrine function, as assessed by the oral glucose tolerance test, has preserved more than 30 yr. Although he was a current smoker, no clinically significant atherosclerotic lesion had been observed. From the long-term observation of this patient, we propose that LPL deficiency is not invariably associated with high mortality and that even with repeated episodes of acute pancreatitis, pancreatic function may be slow to decline.

Relationship of Lipoprotein Lipase and Hepatic Triacylglycerol Lipase Activity to Serum Adiponectin Levels in Japanese Hyperlipidemic Men

The aim of this study was to determine how lipoprotein lipase (LPL) and hepatic triacylglycerol lipase (HTGL) activity relate to serum adiponectin levels. Fifty-five hyperlipidemic Japanese men were recruited for this study. LPL and HTGL activity in post-heparin plasma (PHP) was measured using Triton X-100 emulsified-[14C] triolein. The remaining activity in the presence of 1M NaCl was defined as HTGL activity. Serum adiponectin levels were determined by an enzyme-linked immunosorbent assay system. LPL activity had a positive relationship with HDL2, but had no relation with HDL3, while HTGL had positive relationship with HDL3, but had no relationship with HDL2. LPL activity showed a positive relationship [r = 0.345, p = 0.010] to serum adiponectin levels, while and HTGL activity showed an inverse relationship [r = - 0.365 p = 0.006]. Multiple regression analysis with LPL and HTGL as dependent variables and age, BMI, serum adiponectin and the homeostasis model assessment of insulin resistance (HOMA-IR) as independent variables showed LPL and HTGL's association to adiponectin did not persist after adjustments for these covariants. However, the association of LPL activity to HOMA-IR was found to persist after adjustments of age, BMI, and serum adiponectin. There was a co-linearity between insulin sensitivity and adiponectin as well as insulin sensitivity and LPL/HTGL activity.

Complete Rescue of Lipoprotein Lipase–Deficient Mice by Somatic Gene Transfer of the Naturally Occurring LPLS447XBeneficial Mutation

The naturally occurring human lipoprotein lipase S447X variant (LPLS447X) exemplifies a gain-of function mutation with significant benefits including decreased plasma triglycerides (TG), increased high-density lipoprotein (HDL) cholesterol, and reduced risk of coronary artery disease. The S447X variant may be associated with higher LPL catalytic activity; however, in vitro data supporting this hypothesis are contradictory. We wanted to investigate the in vivo mechanism by which the LPLS447X variant improves the lipid profile of S447X carriers. We conducted a functional assessment of human LPLS447X compared with LPLWT in mice. LPL variants were compared in the absence of endogenous mouse LPL in newborn LPL(-/-) mice by adenoviral-mediated gene transfer. LPL(-/-) mice normally exhibit severe hypertriglyceridemia and die within 48 hours of birth. LPLWT gene transfer prolonged the survival of mice up to 21 days. In contrast, LPLS447X completely rescued 95% of the mice to adulthood and increased LPL catalytic activity in postheparin plasma 2.1-fold compared with LPLWT at day 3 (P=0.003). LPLS447X also reduced plasma TG 99% from baseline (P<0.001), 2-fold more than LPLWT, (P<0.01) and increased plasma HDL cholesterol 2.9-fold higher than LPLWT (P<0.01). These data provide in vivo evidence that the increased catalytic activity of LPLS447X improves plasma TG clearance and increases the HDL cholesterol pool compared with LPLWT.

Tissue‐specific regulation of lipoprotein lipase in humans: effects of fasting

We have previously reported that the activity of lipoprotein lipase (LPL) measured in postheparin plasma from humans fasted for 30 h is increased relative to the fed state. This is in contrast to laboratory animals, where the strong down-regulation of LPL in their adipose tissue on fasting is reflected in decreased levels of LPL activity in postheparin plasma. To search for the tissue source of the increase in LPL activity on fasting of humans, young, healthy subjects were fasted for 10, 20 or 30 h, and LPL was measured in plasma (pre- and postheparin) and in biopsies from subcutaneous adipose tissue (abdominal) and from a skeletal muscle (tibialis anterior). Both LPL activity and LPL protein mass were measured in the tissue homogenates. Values after fasting were compared with values from postprandial samples obtained 2 h after a meal. Fasting for up to 30 h did not alter LPL activity in basal plasma (preheparin). LPL activity in postheparin plasma remained unchanged after 10 and 20 h of fasting, but was increased by 50% after 30 h (P < 0.05). Ten hours of fasting caused a 25% (P < 0.05) decrease in LPL activity in subcutaneous adipose tissue, while LPL activity in skeletal muscle remained unchanged. After 30 h of fasting, both LPL activity and mass had decreased by approximately 50% (P < 0.05) in adipose tissue, but had increased by approximately 100% (P < 0.05) in muscle. The increase in postheparin plasma LPL activity after 30 h of total food deprivation of healthy human subjects seemed to reflect an increased activity and mass of LPL in skeletal muscle.