Heparin-releasable Lipoprotein Lipase Research Articles

Does long-term metformin treatment increase cardiac lipoprotein lipase?

Acute activation of adenosine monophosphate–activated protein kinase (AMPK) or jumps in cardiac work increased cardiac endothelial lipoprotein lipase (LPL), yet it is unclear whether chronic AMPK activation maintains this elevated LPL. To activate AMPK chronically, metformin at low (300 mg/kg/d) and high dose (600 mg/kg/d) was administered in drinking water for 14 days. Control, metformin-treated, and 5-amino-imidazole-4-carboxamide riboside (AICAR)–treated (0.5 mmol/L) ex vivo hearts were perfused to investigate uptake of triacylglycerol and cardiac LPL activity. For perfused rat hearts, increased uptake of labeled Intralipid and β-oxidation of Intralipid–fatty acid were noted for both AICAR (P < .05) and high-dose metformin (P < .01). Intralipid incorporation into tissue lipids was decreased by AICAR (P < .05) and increased after high-dose metformin (P < .05), the increase manifest as enhanced triacylglycerol deposition (P < .05). Low-dose metformin did not alter lipid uptake or tissue deposition. Both high-dose metformin and AICAR decreased cardiac acetyl–coenzyme A carboxylase activity (P < .01). Heparin-releasable LPL was increased after treatment with AICAR (P < .05) and high-dose metformin (P < .01). Low-dose metformin did not alter cardiac LPL. High-dose metformin doubled immunoreactive AMPK and phospho-AMPK protein (P < .001) and increased phosphorylation of p38–mitogen-activated protein kinase (P < .05). After heparin pretreatment, the rate of recruitment of LPL to the cardiac endothelium was increased by AICAR (P < .05) but not by high-dose metformin. These data suggest that AMPK activation increased cardiac endothelial LPL, yet acute and chronic activation of AMPK may yield increased LPL through differing mechanisms.

Effects of androgens on adipocyte differentiation and adipose tissue explant metabolism in men and women

To examine the effects of aromatizable or nonaromatizable androgens on abdominal subcutaneous (SC) and omental (OM) adipose tissue lipid metabolism and adipogenesis in men and women. Primary organ and preadipocyte cultures were established from surgical samples obtained in men (n = 22) and women undergoing biliopancreatic diversions (n = 12) or gynaecological surgeries (n = 8). Cultures were treated with testosterone, dihydrotestosterone (DHT) and methyltrienolone (R1881). Heparin-releasable lipoprotein lipase (HR-LPL) activity, glycerol release, adiponectin secretion, glycerol-3-phosphate dehydrogenase activity and lipid accumulation were measured. In organ cultures from men, DHT had a statistically significant inhibitory effect on HR-LPL activity in the OM compartment. Testosterone significantly inhibited HR-LPL activity in SC and OM cultures. In women, high DHT concentrations tended to inhibit HR-LPL activity in OM cultures. Minor androgenic effects were observed for basal and isoproterenol-stimulated lipolysis as well as adiponectin release in men. On the other hand, adipocyte differentiation was significantly and dose-dependently inhibited by DHT, testosterone and R1881 in SC and OM cultures from both sexes. These effects did not differ according to adipose tissue depot but appeared to be more pronounced in women than in men. Androgens slightly decreased HR-LPL activity in adipose tissue organ cultures, but markedly inhibited adipogenesis in SC and OM primary preadipocyte cultures in both sexes. Androgenic effects on adipose tissue in men vs. women may not differ in terms of direction but in the magnitude of their negative impact on adipogenesis and lipid synthesis.

Effect of conjugated linoleic acid supplementation on lipoprotein lipase activity in 3T3-L1 adipocyte culture

Supplementation with conjugated linoleic acid may reduce fat body mass and increase lean body mass in various species. Some studies have demonstrated that conjugated linoleic acid reduces body fat, in part, by inhibiting the activity of lipoprotein lipase in adipocytes. The objective of this work was to study the effect of conjugated linoleic acid supplementation on lipoprotein lipase activity in 3T3-L1 adipocyte culture. 3T3-L1 adipocytes received linoleic acid (group C) or conjugated linoleic acid (group AE, supplemented with AdvantEdge® CLA, and group CO, supplemented with CLA One®) in concentrations of 1 mmol/L. Heparin-releasable lipoprotein lipase activity was analyzed by means of a 3T3-L1 adipocyte culture. After 7 days, heparin-releasable lipoprotein lipase activity was lower in the groups AE and CO supplemented with conjugated linoleic acid. These results suggest that one of the mechanisms by which CLA is capable of reducing body fat is by reducing lipoprotein lipase activity.

Weak effect of trans-10, cis-12-conjugated linoleic acid on body fat accumulation in adult hamsters

It has been proposed that young animals and subjects are more responsive to conjugated linoleic acid (CLA) than the adults. Nevertheless, there is very little information concerning the effectiveness of CLA in adult animals. In the present study we aimed to explore the effects of trans-10, cis-12-CLA on body fat accumulation in adult hamsters, as well as on some of the molecular mechanisms described in young animals as responsible for the CLA body fat-lowering effect, such as lipogenesis, lipoprotein lipase (LPL)-mediated fat uptake and thermogenesis. The experiment was conducted with sixteen adult male Syrian Golden hamsters (aged 8 months) fed a high-fat diet supplemented or not with 0.5 % trans-10, cis-12-CLA for 6 weeks. Acetyl-CoA carboxylase (ACX), fatty acid synthase (FAS), LPL, PPARgamma, sterol regulatory element-binding protein (SREBP)-1a and SREBP-1c expressions were assessed in subcutaneous and perirenal adipose tissues by real-time RT-PCR. Total and heparin-releasable LPL activities were determined in subcutaneous adipose tissue by fluorimetry and FAS activity by spectrophotometry. Uncoupling protein-1 (UCP1) expression in interscapular brown adipose tissue was assessed by Western blot. Hamsters fed the trans-10, cis-12-CLA diet showed a significant reduction in subcutaneous adipose tissue. No changes were observed in the expression of ACX, FAS, LPL, SREBP-1a, SREBP-1c and PPARgamma, nor in total and heparin-releasable LPL and FAS activities. Trans-10, cis-12-CLA induced a significant increase in the amount of UCP1. These results suggest a low responsiveness to trans-10, cis-12-CLA in adults, lower than that in young hamsters. One of the reasons explaining this difference is the lack of effect on LPL.

Myocardial metabolism of triacylglycerol‐rich lipoproteins in type 2 diabetes

Cardiac utilisation of very-low-density lipoprotein (VLDL) and chylomicrons (CM) was investigated in the ZDF rat model of type 2 diabetes, in order to define the role of triacylglycerol (TAG) metabolism in the development of contractile dysfunction. Hearts from obese diabetic and lean littermate control rats were perfused with VLDL and CM from diabetic and control rats. Metabolic fate of the lipoprotein TAG and contractile function were examined. Myocardial utilisation of both VLDL- and CM-TAG was increased in the diabetic state. Diabetic hearts oxidised diabetic lipoprotein-TAG to a greater extent than control lipoproteins; glucose oxidation was decreased. There was no difference in lipoprotein-TAG assimilation into diabetic heart lipids; diabetic lipoproteins were, however, a poor substrate for control heart tissue lipid accumulation. Although the proportion of exogenous lipid incorporated into tissue TAG was increased in diabetic hearts perfused with control lipoproteins, this effect was not seen in diabetic hearts perfused with diabetic lipoproteins. Myocardial heparin-releasable lipoprotein lipase (LPL) activity was moderately increased in the diabetic state, and diabetic lipoproteins increased tissue-residual LPL activity. Cardiac hydraulic work was decreased only in diabetic hearts perfused with diabetic CM. Compositional analysis of diabetic variant lipoproteins indicated changes in size and apoprotein content. Alterations in cardiac TAG-rich lipoprotein metabolism in type 2 diabetes are due to changes in both the diabetic myocardium and the diabetic lipoprotein particle; decreased contractile function is not related to cardiac lipid accumulation from TAG-rich lipoproteins but may be associated with changes in TAG-fatty acid oxidation.

Influence Of Atherosclerosis And Exercise On Arterial Lipoprotein Lipase Activity In Pigs

INTRODUCTION: Lipoprotein lipase (LPL) has repeatedly been identified as one of the major susceptibility genes for human coronary artery disease. The LPL protein is detectable both in peripheral tissues such as adipose tissue and skeletal muscle and also in conduit arteries such as the thoracic aorta. However, the functional enzyme activity has heretofore never been quantified in arteries with respect to either vascular disease or exercise training. We have overcome prior experimental limitations by utilizing a porcine model of atherosclerosis, where the endothelium from large arterial samples could be obtained in conjunction with modifications in the LPL assay to improve accuracy. PURPOSE: The primary purpose was to determine the effects of exercise training on arterial LPL activity in a porcine model of atherosclerosis. METHODS: Heparin releasable LPL (HR-LPL) activity was measured in approximately 5.2 cm2 of the thoracic aorta, and also in skeletal muscle and adipose tissue. In keeping with the purpose, a pig strain with familial hypercholesterolemia (FH) was run trained for ∼5 months and compared to controls fed an identical diet (N=13 run trained and N=12 untrained). As a basis of comparison to generally healthy pigs, LPL was measured in another strain of pigs with substantially lower plasma cholesterol (Yucatan). RESULTS: There was about twice as much arterial HR-LPL activity in FH pigs after the exercise training compared to sedentary control FH pigs (40±4 vs. 19±3 mU/mg total protein; p<0.05). This two-fold training effect for artery HR-LPL was evident in both males and females. In contrast to this, neither skeletal muscle, nor adipose HR-LPL activity was altered by the exercise training. Blood lipoproteins were not improved by exercise. Paradoxically, arterial HR-LPL activity was 13.7 fold greater in FH pigs (21.3±4.6 mU/mg) compared to the Yucatan pigs (1.6±0.2 mU/mg). CONCLUSION: Exercise run training increased arterial HR-LPL activity in a porcine model of lipoprotein-induced atherosclerosis. Supported by NIH HL02490

브로콜리 싹 에탄올 추출물이 고지방식이를 급여한 흰쥐의 콜레스테롤 저하 및 비만 억제효과에 미치는 영향

고지방식이로 고지혈 및 비만이 유도된 흰쥐에서 브로콜리 싹 에탄올 추출물 투여로 인한 혈 중 지질대사 개선 및 지방조직의 항비만효과에 미치는 영향에 대하여 조사하였다. 5주령 된 흰쥐 수컷 36마리를 1주일간 적응시킨 후 정상식이군(ND), 고지방식이군(HFD), 정상식이와 브로콜리 싹 에탄올 추출물 저용량 병합 투여군(ND-BSL), 정상식이와 브로콜리 싹 에탄올 추출물 고용량 병합 투여군(ND-BSH), 고지방식이와 브로콜리 싹 에탄올 추출물 저용량 병합 투여군(HFD-BSL) 및 고지방식이와 브로콜리 싹 에탄올 추출물 고용량 병합 투여군(HFD-BSH)으로 나누어 4주간 사육하였다. 고지방식이로 증가되어진 체중증가량은 브로콜리 싹 에탄올 추출물 고용량 병합 투여로 유의하게 감소되었으며, 정상식이군(ND)과는 비슷한 수준으로 저하되었다. 고지방식이군들(HFD, HFD-BSL 및 HFD-BSH)이 정상식이군들(ND, ND-BSL 및 ND-BSH)에 비하여 식이섭취량은 낮았으나, 식이효율은 높게 나타났다. 간조직의 무게는 실험 군간에 유의차가 없었으나, 부고환 및 장간막지방조직의 무게는 고지방식이를 급여한 흰쥐에게 브로콜리 싹 에탄올 추출물을 고용량 병합 투여한 경우에는 고지방식이에 비하여 유의하게 저하되었다. 고지방식이로 증가되어진 혈청 중의 ALT 및 AST 활성, 중성지방, 총콜레스테롤 및 LDL-콜레스테롤 함량, 심혈관위험지수와 동맥경화지수도 브로콜리 싹 에탄올 추출물 고용량 병합 투여로 감소되었다. 혈청 중의 ALP 활성은 실험 군 간에 유의차가 없었다. 혈청 중의 HDL-콜레스테롤 함량은 정상식이군(ND)에 비하여 고지방식이군(HFD)이 유의하게 감소하였으나, 정상식이 혹은 고지방식이를 급여한 흰쥐에게 브로콜리 싹 에탄올 추출물을 투여하였을 경우에는 영향을 미치지 않았다. 고지방식이로 증가되어진 간조직과 장간막지방조직 중의 총콜레스테롤 함량은 브로콜리 싹 에탄올 추출물 병합 투여로 저하되었다. 지방조직 중의 HR-LPL과 TE-LPL 활성 모두 정상식이군(ND)에 비하여 고지방식이군(HFD)이 증가하였고, 브로콜리 싹 에탄올 추출물 고용량 병합 투여한 모든 군은 고지방식이군(HFD)에 비하여 유의하게 감소되었으나 정상식이군(ND)과는 비슷한 활성을 나타내었다. 특히 브로콜리 싹 에탄올 추출물의 효과는 고용량 병합 투여군이 저용량 병합투여군에 비하여 더 좋은 효과를 나타내었다. 혈청 및 조직중의 지질 함량 변화는 정상식이군들(ND, ND-BSL 및 ND-BSH) 간에는 유의차가 없었다. 따라서 고지방식이를 급여하면서 브로콜리 싹 에탄올 추출물을 병합 투여 시에만 효과가 있는 것으로 여겨진다. 이상의 결과 브로콜리 싹 에탄올 추출물이 체중 및 지방조직의 무게 감소와 더불어 혈청지질 개선 효과와 LPL 활성을 저하시켜 고지혈증 예방효과와 지방축적 억제 효과가 있는 것으로 사료되나 브로콜리 싹 추출물의 어떤 성분이 콜레스테롤 저하효과 및 비만을 억제시킬 수 있는지는 보다 자세한 연구가 요구된다.

Red mold rice prevents the development of obesity, dyslipidemia and hyperinsulinemia induced by high-fat diet

To investigate the influences of red mold rice (RMR) on obesity and related metabolic abnormalities. The 3T3-L1 cell line was used to examine the effects of RMR extracts on preadipocytes and on mature adipocytes. Both water and ethanol extracts of RMR had inhibitory effects on 3T3-L1 preadipocyte proliferation and differentiation. Water extracts of RMR enhanced the lipolysis activity in mature adipocytes, which negatively correlated with the triglyceride content within cells. RMR treatment did not affect heparin-releasable lipoprotein lipase activity in mature adipocytes. Furthermore, animal studies were carried out to explore the antiobesity effects of RMR. The control group of male Wistar rats were fed regular laboratory feed, whereas the other groups were fed the high-fat (HF) diet supplemented with lovastatin, rice or RMR (0.4 and 2%, w w(-1)). The relative caloric intakes of the control and HF groups were 3.34 and 4.85 kcal g(-1), respectively. After 6 weeks, rats treated with RMR at the 0.4 and 2% doses had lower weight gain and less fat pads mass accompanied with smaller fat cells than did the HF-diet rats. These effects probably resulted from an increase in the lipolysis activity of adipose tissue and a reduction in food/energy consumption. On the other hand, the RMR supplement significantly reduced serum total cholesterol, serum low-density lipoprotein (LDL) cholesterol, the ratio of LDL to high-density lipoprotein (HDL) cholesterol and serum insulin in the HF group. Moreover, the 2% RMR treatment significantly increased serum HDL cholesterol. This study reveals for the first time that RMR can prevent body fat accumulation and improve dyslipidemia. The antiobesity effects of RMR mainly derive from the lipolytic activity and mild antiappetite potency of RMR. In addition, extracts of RMR suppressed the proliferation and differentiation in 3T3-L1 preadipocytes, which might have contributed to the inhibition of new adipocyte formation or hyperplasia in adipose tissue.

Metabolism of very-low-density lipoprotein and chylomicrons by streptozotocin-induced diabetic rat heart: effects of diabetes and lipoprotein preference

Very-low-density lipoprotein (VLDL) and chylomicrons (CM) are major sources of fatty acid supply to the heart, but little is known about their metabolism in diabetic myocardium. To investigate this, working hearts isolated from control rats and diabetic rats 2 wk following streptozotocin (STZ) injection were perfused with control and diabetic lipoproteins. Analysis of the diabetic lipoproteins showed that both VLDL and CM were altered compared with control lipoproteins; both were smaller and had different apolipoprotein composition. Heparin-releasable lipoprotein lipase (HR-LPL) activity was increased in STZ-induced diabetic hearts, but tissue residual LPL activity was decreased; moreover, diabetic lipoproteins stimulated HR-LPL activity in both diabetic and control hearts. Diabetic hearts oxidized lipoprotein-triacylglycerol (TAG) to a significantly greater extent than controls (>80% compared with deposition as tissue lipid), and the oxidation rate of exogenous lipoprotein-TAG was increased significantly in diabetic hearts regardless of TAG source. Significantly increased intracardiomyocyte TAG accumulation was found in diabetic hearts, although cardiac mechanical function was not inhibited, suggesting that lipotoxicity precedes impaired cardiac performance. Glucose oxidation was significantly decreased in diabetic hearts; additionally, however, diabetic lipoproteins decreased glucose oxidation in diabetic and control hearts. These results demonstrate increased TAG-rich lipoprotein metabolism concomitant with decreased glucose oxidation in type 1 diabetic hearts, and the alterations in cardiac lipoprotein metabolism may be due to the properties of diabetic TAG-rich lipoproteins as well as the diabetic state of the myocardium. These changes were not related to cardiomyopathy at this early stage of diabetes.

Cold acclimation induces physiological cardiac hypertrophy and increases assimilation of triacylglycerol metabolism through lipoprotein lipase

The contribution of triacylglycerol to energy provision in the hypertrophied heart, mediated through lipoprotein lipase (LPL) is largely unknown and the contribution of very-low-density lipoprotein (VLDL) receptor to control of LPL presentation at the endothelium is unclear. For isolated perfused rat hearts, cold acclimation (CA) induced volume-overload hypertrophy, with decreased developed pressure (P<0.01), increased end-diastolic volume of the left ventricle (P<0.001) and a loss of contractile reserve in response to dobutamine challenge (P<0.01). Oleate utilisation by perfused hearts was unchanged by CA, however uptake of intralipid emulsion increased 3-fold (P<0.01). CA increased the proportion of lipid deposited in tissue lipids from 10% in euthermic controls to 40% (P<0.01) although the overall contribution of individual lipid classes was unaffected. Cold acclimation significantly increased heparin-releasable LPL (P<0.05) and tissue residual LPL (P<0.01). Western blot analysis indicated preserved expression of proteins coding for SERCA2, muscle-CPT1 and VLDL-receptor following CA, while AMPKα2 and phospho-AMPKα2 were unaffected. These observations indicate that for physiological hypertrophy AMPK phosphorylation does not mediate the enhanced translocation of LPL to cardiac endothelium.

Regulation of Lipoprotein Lipase by Fasting in Epididymal and Mesenteric Adipocytes of Rats

There are marked variations in the activity of lipoprotein lipase (LPL) among adipose depots. The aim of this study was to compare the mechanisms of 24 h of fasting on LPL regulation between epididymal (EPI) adipocytes and mesenteric (MES) adipocytes in rats. 1-Day fasting consistently decreased activities of heparin-releasable LPL, total extractable LPL and cellular LPL markedly in both EPI and MES fat pads. LPL activity in MES fat pads was relatively lower than in the EPI fat pads. Consistent with data on LPL activity, the levels of expression of LPL mRNA in both nutritional states were lower in MES than EPI adipose tissue and isolated adipocytes. The decreased LPL activity after 1 day of fasting in MES adipocytes was explained mainly by a 50% decrease in the relative abundance of LPL mRNA level and a parallel 50% decrease in relative rate of LPL synthesis. In contrast, fasting of 1 day in EPI adipocytes decreased total LPL activity by 47% but did not affect LPL mRNA level or relative rate of LPL synthesis. A decrease in overall protein synthesis contributed to the decreased LPL activity after 1 day fasting both in EPI and MES adipocytes. In MES adipocytes the decrease in LPL activity, LPL mRNA and LPL synthesis were comparable, but in EPI adipocytes the changes in LPL activity were substantially larger than the changes in LPL mRNA level and LPL synthesis. Therefore, fasting decreased fat cell size, LPL activity, LPL mRNA level and relative rate of LPL synthesis in rats, and these effects were more marked in the MES adipocytes. These results clearly demonstrate the regional variations in the metabolic response of adipose tissue and LPL functions to fasting.

Increased thermoregulation in cold-exposed transgenic mice overexpressing lipoprotein lipase in skeletal muscle: an avian phenotype?

LPL is an enzyme involved in the breakdown and uptake of lipoprotein triglycerides. In the present study, we examined how the transgenic (Tg) overexpression of human LPL in mouse skeletal muscle affected tolerance to cold temperatures, cold-induced thermogenesis, and fuel utilization during this response. Tg mice and their nontransgenic controls were placed in an environmental chamber and housed in metabolic chambers that monitored oxygen consumption and carbon dioxide production with calorimetry. When exposed to 4 degrees C, an attenuation in the decline in body temperature in Tg mice was accompanied by an increased metabolic rate (15%; P < 0.001) and a reduction in respiratory quotient (P < 0.05). Activity levels, the expression of uncoupling proteins in brown fat and muscle, and lean mass failed to explain the enhanced cold tolerance and thermogenesis in Tg mice. The more oxidative type IIa fibers were favored over the more glycolytic type IIb fibers (P < 0.001) in the gastrocnemius and quadriceps muscles of Tg mice. These data suggest that Tg overexpression of LPL in skeletal muscle increases cold tolerance by enhancing the capacity for fat oxidation, producing an avian-like phenotype in which skeletal muscle contributes significantly to the thermogenic response to cold temperatures.

Postprandial chylomicrons and adipose tissue lipoprotein lipase are altered in type 2 diabetes independently of obesity and whole-body insulin resistance

Background and aims Postprandial lipoprotein abnormalities in type 2 diabetes are associated with insulin resistance. The role of other diabetes-related factors is still not clear. The aim of this study is to differentiate the effects of whole-body insulin resistance, obesity, and type 2 diabetes on postprandial dyslipidaemia and lipoprotein lipase (LPL) in adipose tissue. Methods and results Ten subjects with obesity and diabetes (OD), 11 with obesity alone (O), and 11 normal-weight controls (C) – males, aged 26–59 years, with fasting normo-triglyceridaemia underwent measurements of cholesterol, triglycerides, apo B-48 and apo B-100 concentrations in plasma lipoproteins separated by density gradient ultracentrifugation before and after a fat-rich meal. Fasting and postprandial (6 h) LPL activity was determined in abdominal subcutaneous adipose tissue biopsy samples. Insulin sensitivity was measured by hyperinsulinaemic euglycaemic clamp. OD and O subjects had similar degrees of adiposity (BMI, waist circumference, fat mass) and insulin resistance (insulin stimulated glucose disposal and M/ I). They also showed a similarly higher postprandial increase in large VLDL lipids (triglyceride incremental AUC 188 ± 28 and 135 ± 22 mg/dl·6 h) than C (87 ± 13 mg/dl·6 h, M ± SEM, p < 0.05). OD had an increased chylomicron response compared to O (triglyceride incremental AUC 132 ± 23 vs. 75 ± 14 mg/dl·6 h, p < 0.05). OD had significantly lower fasting and postprandial adipose tissue heparin-releasable LPL activity than O and C. Conclusions In insulin-resistant conditions of obesity, with and without diabetes, large VLDL are increased after a fat-rich meal. In addition, diabetic patients compared to obese subjects have an increased postprandial chylomicron response and a reduced adipose tissue LPL activity.

A transcription-dependent mechanism, akin to that in adipose tissue, modulates lipoprotein lipase activity in rat heart

The enzyme lipoprotein lipase (LPL) releases fatty acids from lipoprotein triglycerides for use in cell metabolism. LPL activity is rapidly modulated in a tissue-specific manner. Recent studies have shown that in rat adipose tissue this occurs by a shift of extracellular LPL toward an inactive form catalyzed by an LPL-controlling protein whose expression changes in response to the nutritional state. To explore whether a similar mechanism operates in other tissues we injected actinomycin D to block transcription of the putative LPL controlling protein(s). When actinomycin was given to fed rats, heparin-releasable LPL activity increased by 160% in heart and by 150% in a skeletal muscle (soleus) in 6 h. Postheparin LPL activity in blood increased by about 200%. To assess the state of extracellular LPL we subjected the spontaneously released LPL in heart perfusates to chromatography on heparin-agarose, which separates the active and inactive forms of the lipase. The amount of lipase protein released remained relatively constant on changes in the nutritional state and/or blockade of transcription, but the distribution between the active and inactive forms changed. Less of the LPL protein was in the active form in perfusates from hearts from fed compared with fasted rats. When glucose was given to fasted rats the proportion of LPL protein in the active form decreased. Actinomycin D increased the proportion that was active, in accord with the hypothesis that the message for a rapidly turning over LPL-controlling protein was being removed.

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.

Endothelial bound lipoprotein lipase (LpL) depletion in hypoalbuminemia results from decreased endothelial binding, not decreased secretion

Hypertriglyceridemia in nephrotic (NS) and Nagase analbuminemic rats (Analb) results from reduced triglyceride clearance. NS and Analb have reduced or absent albumin, reduced plasma oncotic pressure (pi), but Analb lack proteinuria. The heparin releasable lipoprotein lipase (LpL) pool in both models is greatly reduced, suggesting reduced LpL is related to low albumin or pi and not proteinuria. To determine the cause of endothelial LpL reduction, we studied effectors of endothelial LpL (eLpL) levels from gene expression, to delivery and endothelial binding. eLpL was measured as heparin releasable activity. eLpL and secretion rate was measured in isolated hearts perfused with heparin. mRNA levels were measured in rat hearts by kinetic RT-PCR. Finally, binding of (125)I-LpL by competition assays rat endothelial cells measured serum-induced changes in affinity. eLpL in vivo was reduced in nephrotic and Analb rats. While the eLpL pool was reduced in isolated perfused hearts, neither LpL secretion by isolated hearts nor myocardial mRNA was reduced in NS or Analb. Binding of LpL to RAEC preincubated with serum from either NS or Analb was reduced compared to control. LpL mRNA levels and release rate was not altered in hearts from NS rats, while eLpL is depleted, suggesting that reduced eLpL in NS is not the result of reduced delivery. The finding that NS serum alters LpL binding to RAEC suggests LpL depletion results from decreased binding rather than defective delivery. This in turn is a consequence of reduced serum albumin or pi but does not require proteinuria.

Acute intralipid infusion reduces cardiac luminal lipoprotein lipase but recruits additional enzyme from cardiomyocytes

Lipoprotein lipase (LPL) metabolizes the triglyceride (TG) core of lipoproteins. We evaluated whether circulating lipids can regulate LPL by influencing the transfer of enzyme from the myocyte to the endothelial lumen. Acute intralipid (IL, 10% and 20%) infusion was performed in male Wistar rats. After 3 h, insulin resistance was assessed using a euglycemic hyperinsulinemic clamp. Cardiac LPL activity was determined by retrogradely perfusing the hearts with heparin. Immunogold electron microscopy visualized LPL, and heparanase was detected by immunofluorescence. Cardiac myocytes were also isolated, and heparin-releasable LPL activity was measured. IL infusion increased both plasma and cardiac lipids. Circulating basal plasma LPL activity increased for the duration of the infusion. Compared to control (CON) hearts, there was a substantial decrease in heparin-releasable LPL activity at the vascular lumen following 3 h of IL infusion, an effect unrelated to changes in gene and protein expression or whole-body insulin resistance. Although constant perfusion of CON hearts with heparin stripped off most of the luminal bound LPL, hearts from IL-infused animals continued to release excessive amounts of the enzyme, suggesting buildup of LPL within endothelial cells or at the endothelial basolateral surface. Immunogold labeling confirmed this observation and demonstrated robust anti-LPL staining at these sites, only in IL hearts. Perfusing hearts from IL-rats in vitro, in the absence of TG, allowed the accumulated enzyme pool to transfer to the coronary lumen. Our data suggest that acute amplification of lipids reduces cardiac luminal LPL but facilitates additional recruitment of cardiomyocyte enzyme. Should this mechanism occur globally, it could contribute towards management of hyperlipidemia.

Trans-10,cis-12 Conjugated linoleic acid inhibits lipoprotein lipase but increases the activity of lipogenic enzymes in adipose tissue from hamsters fed an atherogenic diet

The aim of the present work was to investigate the effects of trans-10,cis-12 conjugated linoleic acid (CLA) on the activity and expression of lipogenic enzymes and lipoprotein lipase (LPL), as well as on the expression of transcriptional factors controlling these enzymes, in adipose tissue from hamsters, and to evaluate the involvement of these changes in the body fat-reducing effect of this CLA isomer. Thirty male hamsters were divided into three groups and fed atherogenic diets supplemented with 0 (linoleic group), 5 or 10 g trans-10,cis-12 CLA/kg diet, for 6 weeks. Body and adipose tissue weights, food intake and serum insulin were measured. Total and heparin-releasable LPL and lipogenic enzyme activities (acetyl-CoA carboxylase (ACC); fatty acid synthase (FAS); glucose-6-phosphate dehydrogenase (G6PDH); and malic enzyme (ME)) were assessed. ACC, FAS, LPL, sterol regulatory element-binding proteins (SREBP-1a), SREBP-1c and PPARgamma mRNA levels were also determined by real-time PCR. CLA did not modify food intake, body weight and serum insulin level. CLA feeding reduced adipose tissue weight, LPL activity and expression, and increased lipogenic enzyme activities, despite a significant reduction in ACC and FAS mRNA levels. The expression of the three transcriptional factors analysed (SREBP-1a, SREBP-1c and PPARgamma) was also reduced. These results appear to provide a framework for partially understanding the reduction in body fat induced by CLA. Inhibition of LPL activity seems to be an important mechanism underlying body fat reduction in hamsters. Further research is needed to better characterize the effects of CLA on lipogenesis and the role of these effects in CLA action.

FR177391, A New Anti-hyperlipidemic Agent from Serratia

The pharmacological effect of FR177391, isolated from Serratia liquefaciens No. 1821, was studied in normal animals and various types of animal models of hypertriglyceridemia. Treatment of normal mice with FR177391 resulted in an increase in heparin-releasable lipoprotein lipase (LPL) activity in the blood and epididymal fat tissue. FR177391 treatment decreased triglyceride (TG) and increased high-density lipoprotein cholesterol in the blood in normal rats following 7 days treatment, suggesting potent LPL activating properties of FR177391. Both Triton WR1339-induced severe and fructose-induced mild hypertriglyceridemia in rats were attenuated by FR177391 treatment. Severely elevated levels of TG in db/db mice, an insulin resistant diabetic animal model, also significantly decreased from 14 days of treatment with FR177391. FR177391 treatment for 9 days caused a decrease in the elevated levels of TG in mice induced by intraperitoneal inoculation of murine lymphoma EL-4. Overall, this study demonstrated that FR177391 can be possibly a LPL activating agent and that FR177391 treatment improved hypertriglyceridemia in various rat and mouse animal models. These results suggest that FR177391 is a promising candidate compound for the management of hypertriglyceridemia.

Physical inactivity amplifies the sensitivity of skeletal muscle to the lipid-induced downregulation of lipoprotein lipase activity

Physical inactivity is a risk factor for lipoprotein disorders and the metabolic syndrome. Physical inactivity has a powerful effect on suppressing lipoprotein lipase (LPL) activity in skeletal muscle, the rate-limiting enzyme for hydrolysis of triglyceride (TG)-rich lipoproteins. We tested the ability of several compounds to prevent the decrease in LPL. The present study minimized standing and ordinary light nonexercise movements in rats to compare the effects of inactivity and nonexercise activity thermogenesis (NEAT) on LPL activity. The key new insight was that the typically quick decrease in LPL activity of oxidative muscle caused by physical inactivity was prevented by nicotinic acid (NA), whereas inhibitors of TNF-alpha, inducible nitric oxide synthase, and NF-kappaB had no such effect. NA was administered at a dose known to acutely impede the appearance of plasma TG from the liver and free fatty acids from adipose tissue, and it was effective at intentionally lowering plasma lipid concentrations to the same level in active and inactive groups. As measured from heparin-releasable LPL activity, LPL in the microvasculature of the most oxidative muscles was approximately 90% lower in the inactive group compared with controls, and this suppression was completely blocked by NA. In contrast to inactivity, NA did not raise muscle LPL in ambulatory controls, whereas a large exogenous fat delivery did decrease LPL activity. In vitro control studies revealed that NA did not have a direct effect on skeletal muscle LPL activity. In conclusion, physical inactivity amplifies the ability of plasma lipids to suppress muscle LPL activity. The light ambulatory contractions responsible for NEAT are sufficient for mitigating these deleterious effects.