Release Of Lipoprotein Lipase Research Articles

Factors affecting clinical outcomes of continuous and intermittent plasmapheresis in patients with severe hypertriglyceridemia.

Acute hypertriglyceridemia is considered a category III indication for plasmapheresis. The use of plasma as replacement fluid (RF) has been suggested to replace the consumed lipoprotein lipase. Heparin when used as an anticoagulant could possibly release lipoprotein lipase, thereby increasing triglyceride clearance. The impact of RF (albumin vs fresh frozen plasma (FFP) and anticoagulant (ACD-A vs. heparin) on triglycerides following plasmapheresis in 27 patients with severe hypertriglyceridemia (SHTG) was investigated. A paired study of four patients with recurrent SHTG was conducted, evaluating continuous (Optia) versus intermittent flow plasmapheresis (Haemonetics). Shorter procedures positively impacted triglycerides (TG) drop post-sessions p < 0.05. In albumin sessions, patients who used heparin demonstrated significantly greater drop in TG and required less sessions than did those with citrate p < 0.05. In heparin sessions, patients who used albumin demonstrated significantly greater drop in triglycerides and required less sessions than did those with FFP p < 0.05. Three of six patients who used FFP and heparin showed a triglyceride drop of 11.7% following three sessions and a 50% drop with one albumin session. Compared with Haemonetics, Optia removed comparable volumes of plasma in less time, processing smaller blood volumes and using less citrate p < 0.05. Patients demonstrated significantly lower drop in TG and required more sessions with Haemonetics than they did with Optia p < 0.05. Shorter procedure was the main predictor for effective TG clearance. This can be achieved by continuous apheresis technology, particularly when using albumin as RF. TG removal via Optia seems to be optimized by using heparin.

Investigations into the Actions of Glucose-Dependent Insulinotropic Polypeptide and Glucagon-Like Peptide-1(7–36)amide on Lipoprotein Lipase Activity in Explants of Rat Adipose Tissue

The direct actions of glucose-dependent insulinotropic polypeptide, glucagon-like peptide-1(7–36)amide and insulin on lipoprotein lipase activity in explants of rat epididymal adipose tissues were investigated. Lipoprotein lipase was extracted into the incubation medium by heparin release of lipoprotein lipase and measured by fatty acid release from a glyceroltriolein emulsion. Insulin and glucose-dependent insulinotropic polypeptide caused a significant stimulation of lipoprotein lipase activity over a dose range of 0.25–4 nmol/L and 4–8 nmol/L, respectively. Explants incubated in the presence of both insulin and glucose-dependent insulinotropic polypeptide (at 0.5 and 4 nmol/L, respectively) showed levels of lipoprotein lipase activity significantly greater than that seen with either hormone alone. Neither insulin- nor glucose-dependent insulinotropic polypeptide-stimulated lipoprotein lipase was modified by the presence of the antibiotic actinomycin-D in the incubation medium, indicating that these two hormones exert their actions on the pre-existing cellular pool of lipoprotein lipase. Glucagon-like polypeptide-1(7–36)amide, over a dose range of 1–8 nmol/L, did not stimulate lipoprotein lipase activity. This study indicates that glucose-dependent insulinotropic polypeptide, in addition to stimulating insulin secretion, has a direct biological action on adipose tissue and in vivo, together with insulin, may promote lipoprotein lipase activity postprandially.

Changes in Lipoprotein Lipase in the Heart Following Diabetes Onset

Due to its constant pumping and contraction, the heart requires a substantial amount of energy, with fatty acids (FAs) providing a major part of its adenosine triphosphate (ATP). However, the heart is incapable of making this substrate and attains its FAs from multiple sources, including the action of lipoprotein lipase (LPL). LPL is produced in cardiomyocytes and subsequently secreted to its heparan sulfate proteoglycan (HSPG) binding sites on the plasma membrane. To then move LPL to the endothelial cell (EC) lumen, glycosylphosphatidylinositol-anchored high-density lipoprotein-binding protein 1 (GPIHBP1) attaches to interstitial LPL and transfers it to the vascular lumen, where the LPL is ready to perform its function of breaking down circulating triglycerides (TG) into FAs. The endo-β-glucuronidase heparanase (Hpa) is unique in that it is the only known mammalian enzyme to cleave heparan sulfate (HS), thereby promoting the abovementioned release of LPL from the cardiomyocyte HSPG. In diabetes, it has been suggested that changes in how the heart generates energy are responsible for the development of diabetic cardiomyopathy (DCM). Following moderate diabetes, with the reduction in glucose utilization, the heart increases its LPL activity at the vascular lumen due to an increase in Hpa action. Although this adaptation might be beneficial to compensate for the underutilization of glucose by the heart, it is toxic over the long term, as harmful lipid metabolite accumulation, along with augmented FA oxidation and thus oxidative stress, leads to cell death. This coincides with the loss of a cardioprotective growth factor—namely, vascular endothelial growth factor B (VEGFB). This review discusses interconnections between Hpa, LPL, and VEGFB and their potential implications in DCM. Given that mechanism-based therapeutic care for DCM is unavailable, understanding the pathology of this cardiomyopathy, along with the contribution of LPL, will help us advance its clinical management.

Rapid Decrease and Subsequent Increase in the Serum Triglycerides Accompanied by &amp;lt;i&amp;gt;CD36&amp;lt;/i&amp;gt; Transcript Increase in an Acute Stress Mice Model

In this article, we report the changes in serum triglyceride (TG) levels that occurred during repeated tail blood sampling using a mouse restrainer. We used three groups of mice, namely, “PBS-restrained” “PBS-unrestrained” and “mock-restrained”. The mice in the PBS-restrained and PBS-unrestrained groups were intraperitoneally (i.p.) injected with 100 mL PBS and tail blood sampling was performed at 1, 5, 8, 24, and 48 h after i.p. injection. For the mock-restrained group, no i.p. injection was performed whereas the subsequent tail blood sampling was similarly performed. During the tail blood sampling, the mice of the two “restrained” groups were placed inside the restrainer designed from an open-ended 50 mL conical tube. The blood from the mice in the PBS-unrestrained group mice was sampled from the tail held by the operator’s hands while being allowed to move on a stage. Strikingly, in all of the three groups, the serum TG level initially decreased to remarkably low levels (approximately 30 mg/dL) after several blood samplings were performed over 8 h. This decrease was followed by a 2 - 3-fold increase in the levels relative to that in the control mice in the subsequent 24 - 48 h time period. We concluded that the acute stress associated with blood sampling caused alterations in TG levels. Serum levels of free fatty acid showed only modest changes. Changes in TG levels were not associated with serum corticosterone levels but with a dramatic increase in CD36 transcript levels in the liver. The relevance of this finding to the previously reported release of lipoprotein lipase (LPL) from white fatty tissue into the plasma during acute stress is also discussed.

Heparin Effects on Serum Gonadotropins.

IntroductionStudies using lipid infusions to raise fatty acid levels require heparin to release lipoprotein lipase (LPL), thus calling into question the appropriate control infusion for this type of study: saline alone or saline plus heparin. We aimed to evaluate whether the addition of heparin alone, in doses needed to release LPL, would alter circulating free fatty acids (FFAs) and/or affect gonadotropins.Materials and MethodsThis was a secondary analysis using combined data from eumenorrheic normal-weight women subjected to “control” conditions in 1 of 2 separate studies. In 1 study, participants received saline alone (group 1) as a control, and in the other study participants received saline alone and/or saline plus heparin (groups 2-3) as a control. Both studies performed early follicular phase, frequent blood sampling. FSH and LH were compared across groups and in conditions with and without heparin. Linear mixed models were used to analyze the data.ResultsLH did not differ across any of the 3 groups. Estimated means (SE) for FSH differed between groups but this difference was marginal (P = .05) after adjusting for anti-Mullerian hormone and unrelated to heparin infusion (group 1: 4.47 IU/L [SE 1.19], group 2: 8.01 IU/L [SE 1.14], group 3: 7.94 IU/L [SE 1.13]).ConclusionsHeparin does not exert major effects on gonadotropins when infused in quantities sufficient to release LPL. However, because it can release other vascular membrane-bound proteins, heparin should be considered part of the control infusions in lipid infusion studies where increased FFA levels are the goal.

Dairy Processing Affects the Gut Digestion and Microecology by Changing the Structure and Composition of Milk Fat Globules.

Milk fat globules (MFGs) are the major source of energy for infants' dietary intake. In this study, the effects of changes in the structure and composition of MFG after dairy processing on lipolysis and immune regulation were investigated. Pasteurized MFG tends to form protein aggregates to prevent lipolysis. However, the aggregate is rich in neutrophil degranulation products, which are effective in killing pathogens. Homogenized MFG has the lowest hydrolysis rate due to the reconstituted anti-lipase barrier and exposed apolipoprotein. Simultaneously, the reconstituted barrier can compensate for the lack of the complement cascade. Spray-dried MFG had the highest hydrolysis rate attributable to the disrupted MFG barrier and the release of lipoprotein lipase and endothelial lipase. The immunomodulatory properties of spray-dried MFG proteins are mainly mediated by the toll-like receptor (TLR) signaling pathway. This research provides the improvement basis of dairy processing and functional infant formulas.

Коррекция нарушений показателей свертывающей системы крови крыс, вызванных церебральной ишемией, соединением PIR-10

Нарушения антитромботической функции эндотелия сосудов вызывали моделированием окклюзии левой средней мозговой артерии у крыс-самцов линии Вистар. Первая группа — ложнооперированные особи, вторая — крысы негативного контроля. Животным третьей группе вводили препарат сравнения сулодексид (30 ЛЕ, единицы высвобождения липопротеинлипазы), четвертой — исследуемое соединение PIR-10 (50 мг/кг). Все изучаемые вещества вводили внутрибрюшинно сразу после операции и ежедневно однократно в течение 3 сут. Соединение PIR-10 в равной степени, в сравнении с сулодексидом, способствовало уменьшению АДФ-индуцированной агрегации тромбоцитов (степень на 53,63 % (p &lt; 0,05), скорость на 62,94 % (p &lt; 0,05)). Кроме того, данное соединение препятствовало гиперкоагуляционному сдвигу по параметрам: активированное частичное тромбопластиновое время, протромбиновое время, тромбиновое время — на 117,62 % (p &lt; 0,05), 57,55 % (p &lt; 0,05), 92,06 % (p &lt; 0,05), соответственно, и вызывало уменьшение концентрации фибриногена в плазме крови на 42,39 % (p &lt; 0,05) в сравнении с животными, не получавшими фармакологические вещества, соединение PIR-10 предотвращало нарушения антитромботической функции эндотелия в условиях церебральной ишемии крыс, не уступая препарату сравнения сулодексиду.

Adropin induction of lipoprotein lipase expression in tilapia hepatocytes

The peptide hormone adropin plays a role in energy homeostasis. However, biological actions of adropin in non-mammalian species are still lacking. Using tilapia as a model, we examined the role of adropin in lipoprotein lipase (LPL) regulation in hepatocytes. To this end, the structural identity of tilapia adropin was established by 5'/3'-rapid amplification of cDNA ends (RACE). The transcripts of tilapia adropin were ubiquitously expressed in various tissues with the highest levels in the liver and hypothalamus. The prolonged fasting could elevate tilapia hepatic adropin gene expression, whereas no effect of fasting was observed on hypothalamic adropin gene levels. In primary cultures of tilapia hepatocytes, synthetic adropin was effective in stimulating LPL release, cellular LPL content, and total LPL production. The increase in LPL production also occurred with parallel rises in LPL gene levels. In parallel experiments, adropin could elevate cAMP production and up-regulate protein kinase A (PKA) and PKC activities. Using a pharmacological approach, cAMP/PKA and PLC/inositol trisphosphate (IP3)/PKC cascades were shown to be involved in adropin-stimulated LPL gene expression. Parallel inhibition of p38MAPK and Erk1/2, however, were not effective in these regards. Our findings provide, for the first time, evidence that adropin could stimulate LPL gene expression via direct actions in tilapia hepatocytes through the activation of multiple signaling mechanisms.

A Pressure-dependent Model for the Regulation of Lipoprotein Lipase by Apolipoprotein C-II

Apolipoprotein C-II (apoC-II) is the co-factor for lipoprotein lipase (LPL) at the surface of triacylglycerol-rich lipoproteins. LPL hydrolyzes triacylglycerol, which increases local surface pressure as surface area decreases and amphipathic products transiently accumulate at the lipoprotein surface. To understand how apoC-II adapts to these pressure changes, we characterized the behavior of apoC-II at multiple lipid/water interfaces. ApoC-II adsorption to a triacylglycerol/water interface resulted in large increases in surface pressure. ApoC-II was exchangeable at this interface and desorbed on interfacial compressions. These compressions increase surface pressure and mimic the action of LPL. Analysis of gradual compressions showed that apoC-II undergoes a two-step desorption, which indicates that lipid-bound apoC-II can exhibit at least two conformations. We characterized apoC-II at phospholipid/triacylglycerol/water interfaces, which more closely mimic lipoprotein surfaces. ApoC-II had a large exclusion pressure, similar to that of apoC-I and apoC-III. However, apoC-II desorbed at retention pressures higher than those seen with the other apoCs. This suggests that it is unlikely that apoC-I and apoC-III inhibit LPL via displacement of apoC-II from the lipoprotein surface. Upon rapid compressions and re-expansions, re-adsorption of apoC-II increased pressure by lower amounts than its initial adsorption. This indicates that apoC-II removed phospholipid from the interface upon desorption. These results suggest that apoC-II regulates the activity of LPL in a pressure-dependent manner. ApoC-II is provided as a component of triacylglycerol-rich lipoproteins and is the co-factor for LPL as pressure increases. Above its retention pressure, apoC-II desorbs and removes phospholipid. This triggers release of LPL from lipoproteins.

Abstract 237: CAT-2003 is a Novel Small Molecule That Activates Lipoprotein Lipase and Reduces Fasting and Postprandial Triglycerides

Introduction: Triglycerides from chylomicron and VLDL particles are cleared in the periphery through Lipoprotein lipase (LPL). LPL is negatively regulated by Angiopoietin-like proteins 3 and 4 (Angptl3/4) and Apolipoprotein C3 (apoC3). CAT-2003 is an orally active small molecule that reduces fasting and postprandial triglycerides (TGs) in rat models of hypertriglyceridemia. We hypothesize that CAT-2003 activates LPL by reduction of Angptl3/4 and apoC3. Methods and Results: In vitro addition of CAT-2003 to THP-1 cells increased heparin releasable LPL activity rapidly (28% increase at 2 hr, p=0.01) and was sustained (52% increase at 20 hr, p=.0002). Angptl4 mRNA was decreased, while levels of LPL mRNA remained unchanged. In HepG2 cells CAT-2003 lowers apoC3 (94%, p&lt;0.001) and Angptl3 (99%, p&lt;0.001) mRNA. Secretion of newly made apoC3 protein was significantly inhibited (54%, p=0.004) within 1 hour of CAT-2003 treatment and was reduced by 84% (p&lt;0.0001) after 4 hours. In vivo administration of a single oral dose of CAT-2003 (100 mg/kg) reduced plasma TGs excursion by 80% (p&lt;0.014) at 2 hours and by 91% (p&lt;0.031) at 4 hours following an oral oleate challenge in Sprague-Dawley (SD) rats (n=4 per arm). In a separate SD rat study CAT-2003 (30 mg/kg) was administered as a single oral dose and a time course (0.5 to 4 hrs, n=4 per time point) of PCSK9, apoC3 and Angtpl4 gene regulation in intestine and liver was studied. Expression of these genes was reduced as rapidly as 30 minutes and the reduction was sustained through 4 hours. In a 5-day study in Zucker fa/fa rats with TGs elevated above 900 mg/dL, qd oral dosing with CAT-2003 (10, 30, 100 and 300 mg/kg, n=8 per arm) resulted in dose-dependent reductions in fed and fasted plasma TGs with fasting reductions ranging from 41% (p&lt;0.01) at 10 mg/kg to 67% (p&lt;0.0001) at 300 mg/kg. Conclusion: CAT-2003 inhibits the negative regulators of LPL in vitro and in vivo. The time course of action is rapid and sustained in vitro with a translation to in vivo SD and fa/fa rats. CAT-2003 offers a potential new therapeutic for the treatment of severe hypertriglyceridemia and is being evaluated in Phase 2 clinical studies.

Lipoprotein lipase activity is favoured by peritoneal dialysis compared to hemodialysis

Background. The lipoprotein lipase (LPL) pool is reduced by 50% in patients on hemodialysis (HD). LPL release by tinzaparin has not been investigated for peritoneal dialysis (PD). Therefore, the aim of this study was to investigate if tinzaparin differently alters the pool of LPL and triglyceride levels of patients on HD versus PD. Materials and methods. Thirty-two patients on chronic PD or HD were matched to nearest age and gender. In order to release and thereby estimate the endothelial pool of LPL, all patients received a bolus of tinzaparin (75 units/kg). Blood samples were drawn for analysis of LPL activity and triglycerides (TG) between the groups. Results. The peak level of LPL released at 40 min after tinzaparin was similar in PD and HD patients. At 180 min, a slightly higher median level of LPL activity was noted in the PD patients (6.1 mU/mL (n = 6) versus 3.4 mU/mL (n = 16), p = 0.005). The TG concentration in plasma at 40 min was reduced relatively more in the PD patients than in the HD patients (p < 0.05). At 180 min, TG had returned to start levels in HD patients while they were still lowered in PD patients. Conclusions. The negative effect of uraemia on the LPL pool in HD patients, known from other studies, here is shown to be similar in PD patients. Tinzaparin administration releases the LPL pool during each HD but does not cause an exhaustion of the LPL system over time. In contrast to HD, the LPL pool is not altered during PD.

Monascus-Fermented Yellow Pigments Monascin and Ankaflavin Showed Antiobesity Effect via the Suppression of Differentiation and Lipogenesis in Obese Rats Fed a High-Fat Diet

Monascus-fermented monascin and ankaflavin are found to strongly inhibit differentiation and lipogenesis and stimulate lipolysis effects in a 3T3-L1 preadipocyte model, but the in vivo regulation mechanism is unclear. This study uses obese rats caused by a high-fat diet to examine the effects of daily monascin and ankaflavin feeding (8 weeks) on antiobesity effects and modulation of differentiation, lipogenesis, and lipid absorption. The results show that monascin and ankaflavin had a significant antiobesity effect, which should result from the modulation of monascin and ankaflavin on the inhibition of differentiation by inhibiting CCAT/enhancer-binding protein β (C/EBPβ) expression (36.4% and 48.3%) and its downstream peroxisome proliferator-activated receptor γ (PPARγ) (55.6% and 64.5%) and CCAT/enhancer-binding protein α (C/EBPα) expressions (25.2% and 33.2%) and the inhibition of lipogenesis by increasing lipase activity (14.0% and 10.7%) and decreasing heparin releasable lipoprotein lipase (HR-LPL) activity (34.8% and 30.5%). Furthermore, monascin and ankaflavin are the first agents found to suppress Niemann-Pick C1 Like 1 (NPC1L1) protein expression (73.6% and 26.1%) associated with small intestine tissue lipid absorption. Importantly, monascin and ankaflavin are not like monacolin K, which increases creatine phosphokinase (CPK) activity, known as a rhabdomyolysis indicator.

Lipoprotein lipase responds similarly to tinzaparin as to conventional heparin during hemodialysis

BackgroundLow molecular weight (LMW) heparins are used for anticoagulation during hemodialysis (HD). Studies in animals have shown that LMW-heparins release lipoprotein lipase (LPL) as efficiently as unfractionated (UF) heparin, but are less able to retard hepatic uptake of the lipase. This raises a concern that the LPL system may become exhausted by LMW-heparin in patients on HD. We have explored this in the setting of clinical HD.MethodsTwenty patients on chronic hemodialysis were switched from a primed infusion of UF-heparin to a single bolus of tinzaparin. There were long term follow up of variables for the estimation of dialysis efficacy as well as of the LPL release during dialysis and the subsequent impact on the triglycerides.ResultsThe LPL activity in blood was higher on tinzaparin at 40 but lower at 180 minutes during HD. These values did not change during the 6 month study period. There were significant correlations between the LPL activities in individual patients at the beginning and end of the 6 month study period and between the activities on UF-heparin and on tinzaparin, indicating that tissue LPL was not being exhausted. Triglycerides were higher during the HD-session with tinzaparin than UF-heparin. The plasma lipid/lipoprotein levels did not change during the 6 month study period, nor during a 2-year follow up after the switch from UF-heparin to tinzaparin. Urea reduction rate and Kt/V were reduced by 4 and 7% after 6 months with tinzaparin.ConclusionOur data demonstrate that repeated HD with UF-heparin or tinzaparin does not exhaust the LPL-system.

Expression of Lipoprotein Lipase In Chronic Lymphocytic Leukemia Cells: Is There a Biological Function?

AbstractAbstract 3580The expression of lipoprotein lipase (LPL) in CLL cells is an established mRNA surrogate marker for immunoglobulin heavy chain (IgVH) mutational status. High expression of LPL correlates with poor prognosis. However, the possible functional role of LPL in CLL is still unclear. LPL is normally expressed in muscle cells, adipose tissue and macrophages, transported to the luminal surface of endothelial cells where it is bound heparan sulfate-proteoglycans (HSPG). Heparin competes with HSPG for the binding sites and intravenous injection leads to elevated plasma LPL protein levels and enzymatic activity (“heparin release test”). LPL mRNA levels correlate with intracellular protein expression (Heintel et al. Leukemia. 2005; Mansouri et al. Leuk Res. 2010). Moreover cellular lysates from CLL patients contain elevated LPL enzymatic activity compared to healthy donors (Pallasch et al. Leukemia. 2008.). In this study, we investigated the basal (pre-heparin) LPL protein levels by enzyme-linked immunosorbent assay in the serum of 42 CLL patients, 14 non-CLL patients (lymphoma in remission), and 4 healthy donors (HD): Median pre-heparin LPL protein levels were 40.10 ng/ml (range: 5.66–108.44), 44.11 ng/ml (18.26-84.08), and 68.14 ng/ml (33.28-174.38), respectively. Among CLL patients there were no significant differences between those with high (N=16; median LPL protein in serum: 38.10 ng/ml (8.72-73.49)) and low (N=26; 43.12 ng/ml (5.66-108.44) (p=0.354) LPL mRNA expression. Thirteen patients with known LPL mRNA expression were investigated for LPL protein “release” after heparin injection. Ten and twenty minutes after 50 U/kg heparin injection, the elevation of both parameters, LPL protein amount in serum and enzymatic activity in plasma, was similar to those of HD normal values. In detail, medium serum protein levels in samples with high LPL mRNA (N=5) increased from 16.11 to 214.33 and 332.78 ng/ml and in the samples with low mRNA (N=8) from 13.08 to 219.68 and 386.65 ng/ml, respectively. The corresponding median values of the LPL enzymatic activities in high vs. low expressors were: 7.25/15.52/20.01 and 7.45/19.13/20.57 μ M/ml/h. In addition, release of LPL from peripheral mononuclear cells (PBMC) of CLL patients (N=3) by heparin in vitro was absent. Cell viability and LPL mRNA expression remained unaffected in both in vivo and in vitro samples after heparin addition. In order to assess the impact of LPL on cell survival, CLL cells were cultured (N=3) for up to 72 hours with different doses of purified LPL protein. There was no positive effect on cell survival irrespective of primary LPL mRNA expression or culture conditions (with or without FCS). Since these results point to an intracellular effect of LPL, we aimed to identify downstream targets by knock down with siRNA against LPL in 7 CLL samples and 5 cell lines (hepatocellular carcinoma, cervix carcinoma, colon carcinoma, multiple myeloma and acute monocytic leukemia) with high LPL mRNA expression. Gene expression changes were analyzed by microarrays (GeneChip® Human Gene 1.0 ST Array, Affymetrix). Fifteen genes were up- (N=4) or downregulated (N=11) in at least 3 of 5 cell lines by more than 1.5-fold (e.g. GSTP1, COROC1). Nine genes were at least 1.5-fold downregulated in parallel with LPL in the CLL samples only. These genes belong to various pathways (e.g. cell cycle, signaling in immune system, metabolism of carbohydrates) and seem to be specific for CLL. Cross-validation of individual genes is under way.Our data suggest that (1) neither basal serum LPL protein levels nor heparin-induced LPL release in CLL patients are suitable clinical prognostic markers; (2) Stimulation with external LPL protein does not affect CLL cell survival; (3) siRNA knock-down of LPL induces changes in various functional pathways. We conclude that the key role of LPL expression in high-risk CLL is related to its (intra)cellular expression. Disclosures:No relevant conflicts of interest to declare.

Release of 12 Adipokines by Adipose Tissue, Nonfat Cells, and Fat Cells From Obese Women

The relative release in vitro of endothelin-1, zinc-alpha2-glycoprotein (ZAG), lipocalin-2, CD14, RANTES (regulated on activation, normal T cell expressed and secreted protein), lipoprotein lipase (LPL), osteoprotegerin (OPG), fatty acid-binding protein 4 (FABP-4), visfatin/PBEF/Nampt, glutathione peroxidase-3 (GPX-3), intracellular cell adhesion molecule 1 (ICAM-1), and amyloid A was examined using explants of human adipose tissue as well as the nonfat cell fractions and adipocytes from obese women. Over a 48-h incubation the majority of the release of LPL was by fat cells whereas that of lipocalin-2, RANTES, and ICAM-1 was by the nonfat cells present in human adipose tissue. In contrast appreciable amounts of OPG, amyloid A, ZAG, FABP-4, GPX-3, CD14, and visfatin/PBEF/Nampt were released by both fat cells and nonfat cells. There was an excellent correlation (r = 0.75) between the ratios of adipokine release by fat cells to nonfat cells over 48 h and the ratio of their mRNAs in fat cells to nonfat cells at the start of the incubation. The total release of ZAG, OPG, RANTES, and amyloid A by incubated adipose tissue explants from women with a fat mass of 65 kg was not different from that by women with a fat mass of 29 kg. In contrast that of ICAM-1, FABP-4, GPX-3, visfatin/PBEF/Nampt, CD14, lipocalin-2, LP, and endothelin-1 was significantly greater in tissue from women with a total fat mass of 65 kg.

PROGRESS IN UREMIC TOXIN RESEARCH: Lipoprotein Lipase Disturbances Induced by Uremia and Hemodialysis

Factors such as malnutrition, physical inactivity, uremic toxins, and inflammation are known to influence the activity of lipoprotein lipase (LPL), an important enzyme in metabolism of blood lipids. In patients with chronic kidney disease these factors are common and may result in a decreased LPL activity. This is particularly so in patients on hemodialysis. Further, during each dialysis treatment, the use of heparin (or low molecular weight heparin) induces a release of LPL from its normal binding sites at the plasma membrane of endothelial cells. This results in an increased degradation of the enzyme and a relative lack of LPL activity for up to 10 hours from the start of the dialysis. Thus, the use of conventional anticoagulation for hemodialysis, in addition to the consequences of the uremic state, may cause a severe functional deficiency of LPL. This in turn may have deleterious effects on energy metabolism and may contribute to the increased risk for cardiovascular disease in this vulnerable group of patients.

GPIHBP1 and lipolysis: an update

This review will provide an update on the structure of GPIHBP1, a 28-kDa glycosylphosphatidylinositol-anchored glycoprotein, and its role in the lipolytic processing of triglyceride-rich lipoproteins. Gpihbp1 knockout mice on a chow diet have milky plasma and plasma triglyceride levels of more than 3000 mg/dl. GPIHBP1 is located on the luminal surface of endothelial cells in tissues where lipolysis occurs: heart, skeletal muscle, and adipose tissue. The pattern of lipoprotein lipase (LPL) release into the plasma after an intravenous injection of heparin is abnormal in Gpihbp1-deficient mice, suggesting that GPIHBP1 plays a direct role in binding LPL within the tissues of mice. Transfection of CHO cells with a GPIHBP1 expression vector confers on cells the ability to bind both LPL and chylomicrons. Two regions of GPIHBP1 are required for the binding of LPL - an amino-terminal acidic domain and the cysteine-rich Ly6 domain. GPIHBP1 expression in mice changes with fasting and refeeding and is regulated in part by peroxisome proliferator-activated receptor-gamma. GPIHBP1, an endothelial cell-surface glycoprotein, binds LPL and is required for the lipolytic processing of triglyceride-rich lipoproteins.

Abnormal Patterns of Lipoprotein Lipase Release into the Plasma in GPIHBP1-deficient Mice

GPIHBP1-deficient mice (Gpihbp1(-/-)) exhibit severe chylomicronemia. GPIHBP1 is located within capillaries of muscle and adipose tissue, and expression of GPIHBP1 in Chinese hamster ovary cells confers upon those cells the ability to bind lipoprotein lipase (LPL). However, there has been absolutely no evidence that GPIHBP1 actually interacts with LPL in vivo. Heparin is known to release LPL from its in vivo binding sites, allowing it to enter the plasma. After an injection of heparin, we reasoned that LPL bound to GPIHBP1 in capillaries would be released very quickly, and we hypothesized that the kinetics of LPL entry into the plasma would differ in Gpihbp1(-/-) and control mice. Indeed, plasma LPL levels peaked very rapidly (within 1 min) after heparin in control mice. In contrast, plasma LPL levels in Gpihbp1(-/-) mice were much lower 1 min after heparin and increased slowly over 15 min. In keeping with that result, plasma triglycerides fell sharply within 10 min after heparin in wild-type mice, but were negligibly altered in the first 15 min after heparin in Gpihbp1(-/-) mice. Also, an injection of Intralipid released LPL into the plasma of wild-type mice but was ineffective in releasing LPL in Gpihbp1(-/-) mice. The observed differences in LPL release cannot be ascribed to different tissue stores of LPL, as LPL mass levels in tissues were similar in Gpihbp1(-/-) and control mice. The differences in LPL release after intravenous heparin and Intralipid strongly suggest that GPIHBP1 represents an important binding site for LPL in vivo.

Release of Lipoprotein Lipase Induced by L-Arginine in Mouse Mammary Tumor FM3A Cells

The nitric oxide (NO)/cyclic guanosine 5'-monophosphate (GMP) pathway remains undefined regarding the regulation of lipoprotein lipase (LPL) release. Here, we investigated whether L-arginine (Arg) stimulates the release of LPL from mouse mammary tumor FM3A cells in a time- and dose-dependent manner. L-Arg-stimulated release of LPL activity was inhibited by NG-monomethyl-L-Arg monoacetate, which is an endothelial NO synthase (NOS) inhibitor. Furthermore, release of enzyme activity was also suppressed by various inhibitors of guanylate cyclase and adenylate cyclase, as well as cyclic GMP- and cyclic adenosine 5'-monophosphate (AMP)-dependent protein kinases (PKG and PKA). L-Arg also increased intracellular cyclic GMP contents as well as intracellular cyclic AMP contents. In addition, the increase in the cyclic AMP contents was reduced by inhibitors of guanylate cyclase and PKG. These results suggest that the stimulatory release of LPL from tumor cells by L-Arg is partly due to activation of cyclic AMP production and PKA activity caused by elevated cyclic GMP production and PKG activity.

Nitric Oxide and the Release of Lipoprotein Lipase from White Adipose Tissue

Background/Aim: Lipoprotein lipase (LPL) is the main enzyme responsible for the distribution of circulating triacylglycerides in tissues. Its regulation via release from active sites in the vascular endothelium is poorly understood. In a previous study we reported that in response to acute immobilization (IMMO), LPL activity rapidly increases in plasma and decreases in white adipose tissue (WAT) in rats. In other stress situations IMMO triggers a generalized increase in nitric oxide (NO) production. Methods/Results: Here we demonstrate that in rats: 1) in vivo acute IMMO rapidly increases NO concentrations in plasma 2) during acute IMMO the WAT probably produces NO via the endothelial isoform of nitric oxide synthase (eNOS) from vessels, and 3) epididymal WAT perfused in situ with an NO donor rapidly releases LPL from the endothelium. Conclusion: We propose the following chain of events: stress stimulus / rapid increase of NO production in WAT (by eNOS) / release of LPL from the endothelium in WAT vessels. This chain of events could be a new mechanism that promotes the rapid decrease of WAT LPL activity in response to a physiological stimulus.