Selective measurement of two lipase activities in postheparin plasma from normal subjects and patients with hyperlipoproteinemia

The early years of lipoprotein research: from discovery to clinical application

This review outlines major milestones in the first four decades of lipoprotein research beginning with their discovery nearly 90 years ago. It focuses on the contributions of some of the key investigators during this era, and findings that set the stage for widespread clinical implementation of lipoprotein testing for evaluation and management of CVD risk.

Aging and dyslipidemia: a review of potential mechanisms

Elderly adults constitute a rapidly growing part of the global population, thus resulting in an increase in morbidity and mortality related to cardiovascular disease (CVD), which remains the major cause of death in elderly population, including men and women. Dyslipidemia is a well-established risk factor for CVD and is estimated to account for more than half of the worldwide cases of coronary artery disease (CAD). Many studies have shown a strong correlation between serum cholesterol levels and risk of developing CAD. In this paper, we review the changes of plasma lipids that occur in men and women during aging and the potential mechanisms of age-related disorders of lipoprotein metabolism covering humans and/or animals, in which changes of the liver sinusoidal endothelium, postprandial lipemia, insulin resistance induced by free fatty acid (FFA), growth hormone (GH), androgen (only for men) and expression and activity of peroxisome proliferator-activated receptor α (PPARα) are mainly focused.

HDL biogenesis, remodeling, and catabolism

In this chapter, we review how HDL is generated, remodeled, and catabolized in plasma. We describe key features of the proteins that participate in these processes, emphasizing how mutations in apolipoprotein A-I (apoA-I) and the other proteins affect HDL metabolism. The biogenesis of HDL initially requires functional interaction of apoA-I with the ATP-binding cassette transporter A1 (ABCA1) and subsequently interactions of the lipidated apoA-I forms with lecithin/cholesterol acyltransferase (LCAT). Mutations in these proteins either prevent or impair the formation and possibly the functionality of HDL. Remodeling and catabolism of HDL is the result of interactions of HDL with cell receptors and other membrane and plasma proteins including hepatic lipase (HL), endothelial lipase (EL), phospholipid transfer protein (PLTP), cholesteryl ester transfer protein (CETP), apolipoprotein M (apoM), scavenger receptor class B type I (SR-BI), ATP-binding cassette transporter G1 (ABCG1), the F1 subunit of ATPase (Ecto F1-ATPase), and the cubulin/megalin receptor. Similarly to apoA-I, apolipoprotein E and apolipoprotein A-IV were shown to form discrete HDL particles containing these apolipoproteins which may have important but still unexplored functions. Furthermore, several plasma proteins were found associated with HDL and may modulate its biological functions. The effect of these proteins on the functionality of HDL is the topic of ongoing research.

Role of SN1 lipases on plasma lipids in metabolic syndrome and obesity

OBJECTIVE

To assess the phospholipase activity of endothelial (EL) and hepatic lipase (HL) in postheparin plasma of subjects with metabolic syndrome (MS)/obesity and their relationship with atherogenic and antiatherogenic lipoproteins. Additionally, to evaluate lipoprotein lipase (LPL) and HL activity as triglyceride (TG)-hydrolyses to complete the analyses of SN1 lipolytic enzymes in the same patient.

APPROACH AND RESULTS

Plasma EL, HL, and LPL activities were evaluated in 59 patients with MS and 36 controls. A trend toward higher EL activity was observed in MS. EL activity was increased in obese compared with normal weight group (P=0.009) and was negatively associated with high-density lipoprotein-cholesterol (P=0.014 and P=0.005) and apolipoprotein A-I (P=0.045 and P=0.001) in control and MS group, respectively. HL activity, as TG-hydrolase, was increased in MS (P=0.025) as well as in obese group (P=0.017); directly correlated with low-density lipoprotein-cholesterol (P=0.005) and apolipoprotein B (P=0.003) and negatively with high-density lipoprotein-cholesterol (P=0.021) in control group. LPL was decreased in MS (P<0.001) as well as in overweight and obese compared with normal weight group (P=0.015 and P=0.004, respectively); inversely correlated %TG-very low-density lipoproteins (P=0.04) and TG/apolipoprotein B index (P=0.013) in control group. These associations were not found in MS.

CONCLUSIONS

We describe for the first time EL and HL activity as phospholipases in MS/obesity, being both responsible for high-density lipoprotein catabolism. Our results elucidate part of the remaining controversies about SN1 lipases activity in MS and different grades of obesity. The impact of insulin resistance on the activity of the 3 enzymes determines the lipoprotein alterations observed in these states.

Postprandial VLDL lipolysis products increase monocyte adhesion and lipid droplet formation via activation of ERK2 and NFκB

Postprandial lipemia is characterized by a transient increase in circulating triglyceride-rich lipoproteins such as very low-density lipoprotein (VLDL) and has been shown to activate monocytes in vivo. Lipolysis of VLDL releases remnant particles, phospholipids, monoglycerides, diglycerides, and fatty acids in close proximity to endothelial cells and monocytes. We hypothesized that postprandial VLDL lipolysis products could activate and recruit monocytes by increasing monocyte expression of proinflammatory cytokines and adhesion molecules, and that such activation is related to the development of lipid droplets. Freshly isolated human monocytes were treated with VLDL lipolysis products (2.28 mmol/l triglycerides + 2 U/ml lipoprotein lipase), and monocyte adhesion to a primed endothelial monolayer was observed using a parallel plate flow chamber coupled with a CCD camera. Treated monocytes showed more rolling and adhesion than controls, and an increase in transmigration between endothelial cells. The increased adhesive events were related to elevated expression of key integrin complexes including Mac-1 [α(m)-integrin (CD11b)/β2-integrin (CD18)], CR4 [α(x)-integrin (CD11c)/CD18] and VLA-4 [α4-integrin (CD49d)/β1-integrin (CD29)] on treated monocytes. Treatment of peripheral blood mononuclear cells (PBMCs) and THP-1 monocytes with VLDL lipolysis products increased expression of TNFα, IL-1β, and IL-8 over controls, with concurrent activation of NFkB and AP-1. NFκB and AP-1-induced cytokine and integrin expression was dependent on ERK and Akt phosphorylation. Additionally, fatty acids from VLDL lipolysis products induced ERK2-dependent lipid droplet formation in monocytes, suggesting a link to inflammatory signaling pathways. These results provide novel mechanisms for postprandial monocyte activation by VLDL lipolysis products, suggesting new pathways and biomarkers for chronic, intermittent vascular injury.

Effect of treatment of overt hypothyroidism on insulin resistance

AIM: To investigate the impact of hypothyroidism and thyroxine therapy on insulin sensitivity in patients with overt hypothyroidism.

METHODS: The study included twenty seven overtly hypothyroid and fifteen healthy euthyroid South Western Asian females. Both groups had matching age and body mass index. Physiological and pathological conditions as well as medications that may alter thyroid function, glucose homeostasis or serum lipids were ruled out. Serum thyrotropin (TSH), free tetraiodothyronine (FT4), free triiodothyronine (FT3), fasting insulin (FI), fasting plasma glucose (FPG), total cholesterol and triglycerides were measured before and six months after initiating thyroxine therapy for hypothyroid patients and once for the control group. Insulin resistance (IR) was estimated using homeostasis model assessment (HOMA-IR) and Body mass index (BMI) was calculated.

RESULTS: Both study groups, hypothyroid patients and euthyroid control subjects, had matching age and body mass index (P-value 0.444, 0.607 respectively). No significant difference was found between the hypothyroid patients and the euthyroid control group regarding fasting plasma glucose, fasting insulin, insulin resistance, total cholesterol and triglycerides (P-values 0.432, 0.621, 0.883, 0.586, 0.05 respectively). In the hypothyroid patients, triglycerides showed direct correlation to TSH and inverse correlation to FT3. Similarly total cholesterol inversely correlated to FT3 but its direct correlation to TSH did not reach statistical significance. After thyroxine replacement and reaching an euthyroid state as confirmed by clinical and laboratory data, there was no significant change in fasting plasma glucose, insulin resistance or triglyceride level (P-value 0.216, 0.204, 0.175 respectively) while total cholesterol significantly decreased (P-value 0.043) and fasting insulin significantly increased (P-value 0.047).

CONCLUSION: Hypothyroidism has no impact on insulin sensitivity. Correction of hypothyroidism is not associated with a significant change of insulin sensitivity or triglycerides, but with a significant reduction of total cholesterol.

Hepatic lipase activity is increased in non-alcoholic fatty liver disease beyond insulin resistance

BACKGROUND AND OBJECTIVE

Hepatic lipase is a lipolytic enzyme mostly synthesized and localized at the surface of liver sinusoidal capillaries, which hydrolyses triglycerides and phospholipids of intermediate density, large low density (LDL) and high density lipoproteins. Hepatic lipase activity is increased in insulin resistant states. Non-alcoholic fatty liver disease (NAFLD) is characterized by insulin resistance. However, at present, no data are available regarding the behaviour of hepatic lipase with regard to the degree of hepatic steatosis. Our aim was to evaluate hepatic lipase activity in NAFLD patients and its relationship to the severity of hepatic steatosis.

DESIGN AND PATIENTS

We studied 48 patients with NAFLD (diagnosed by ultrasonography and confirmed by liver biopsy) and 30 controls. Steatosis was semi-quantitatively assessed and considered as mild or grade 1, moderate or grade 2 and severe or grade 3.

MEASUREMENTS

hepatic lipase activity, lipid and lipoprotein profile (including intermediate density lipoproteins and dense LDL), adiponectin, insulin, glucose and high sensitivity C-reactive protein were measured. Homeostasis model assessment for insulin resistance (HOMA) index was calculated.

RESULTS

Patients with hepatic steatosis presented with higher hepatic lipase activity, HOMA and dense LDL and lower levels of adiponectin, high density lipoproteins, cholesterol and apoA-I. Hepatic lipase activity positively correlated significantly with the severity of hepatic steatosis. Hepatic lipase correlated with a more atherogenic profile and persisted higher in patients even after corrected for age, gender, body mass index, HOMA and adiponectin.

CONCLUSION

The higher hepatic lipase activity in NAFLD patients contributes to a more atherogenic profile linked to increased cardiovascular risk, beyond the insulin resistance and the reduction in adiponectin.

Lipid abnormalities and cardiometabolic risk in patients with overt and subclinical thyroid disease

Dyslipidemia is a common finding in patients with thyroid disease, explained by the adverse effects of thyroid hormones in almost all steps of lipid metabolism. Not only overt but also subclinical hypo- and hyperthyroidism, through different mechanisms, are associated with lipid alterations, mainly concerning total and LDL cholesterol and less often HDL cholesterol, triglycerides, lipoprotein (a), apolipoprotein A1, and apolipoprotein B. In addition to quantitative, qualitative alterations of lipids have been also reported, including atherogenic and oxidized LDL and HDL particles. In thyroid disease, dyslipidemia coexists with various metabolic abnormalities and induce insulin resistance and oxidative stress via a vice-vicious cycle. The above associations in combination with the thyroid hormone induced hemodynamic alterations, might explain the increased risk of coronary artery disease, cerebral ischemia risk, and angina pectoris in older, and possibly ischemic stroke in younger patients with overt or subclinical hyperthyroidism.

Blood and tissue lipid composition and lipase activity in wether lambs treated with trenbolone acetate combined with oestradiol-17 β at two different live weights

Thirty-two Border Leicester ♂ × Scottish Blackface ♀ wether lambs aged about 5 months, were divided on the basis of live weight such that group G1 contained the 16 lightest lambs and group G2 the 16 heaviest lambs. Lambs in group G1 were subdivided equally at random to be either sham-implanted controls (group C1) or to be implanted with 35 mg trenbolone acetate (TBA) + 5 mg oestradiol-17β (OE) (group T1) at 24 kg initial live weight. Lambs in group G2 were also subdivided into two groups (C2 and T2) and similarly treated approximately 1 month later at 37 kg initial live weight. Animals were offered ad libitum, a diet containing an estimated 12·5 MJ metabolizable energy and 140 g crude protein per kg dry matter. The experimental treatments lasted for 60 days.

Samples of pre-heparin plasma were analysed for free fatty acid (FFA) and triglycerides (TG). Post-heparin plasma was analysed for lipoprotein lipase (LPL) activity. Samples of subcutaneous (SCAT), perinephric (PNAT), mesenteric (MAT) and intermuscular (IMAT) adipose tissue, liver and muscle, taken immediately post mortem, were analysed for total lipid concentration and fatty acid composition. Comparisons were made for the main effects of hormonal treatment and live weight.

Plasma FFA concentrations in heavier lambs (group G2) were significantly higher than in group G1 from week 1 pre-implantation to week 3 post implantation. Compared with group G1, animals in group G2 had significantly higher plasma TG concentrations at weeks 1, 2, 5 and 8 when data was analysed using pre-implantation values as covariates. The lipid concentration was lower in group G1 than in group G2. In group G1 compared with group G2 there were greater proportions of C12:0 and C18:2 in SCAT and C16:1 in PNAT and lesser proportions of C18:0 in SCAT and PNAT.

Significant effects due to hormonal treatment were recorded for plasma TG at weeks 1, 5, 6, 7 and 8 mainly due to increases in group T1 compared with group C1. Hormonal treatment increased the proportions of C12:0, C15:0, C16:1 and C18:1 in SCAT and C16:1 and C18:1 in IMAT; reduced the proportions of C16:0 and C18:0 in SCAT and C18:0 in MAT and IMAT and reduced the ratio of saturated to unsaturated fatty acids in SCAT and IMAT and to a lesser extent in MAT.

Triglyceride-rich lipoproteins and plasma lipid transport

This memoir provides a history of the triglyceride-rich lipoproteins of blood plasma over the last half-century. As precursors of low-density lipoproteins and in their own right, triglyceride-rich lipoproteins are essential to the formation of atherosclerotic plaques and to consequent ischemic vascular disease. The author recounts research at the National Heart Institute during 1953 to 1956 and continuing thereafter at the University of California San Francisco. Emphasis is placed on key insights arising from investigations of human disease, the interplay of fatty acid and triglyceride-transport involving the liver, small intestine, adipose tissue and muscle, and the role of the liver in the synthesis and catabolism of atherogenic lipoproteins.

Extreme hyperalphalipoproteinaemia in a patient with a solitary paraspinal lipoma

Increased high-density lipoprotein (HDL)-cholesterol (hyperalphalipoproteinaemia; HALP) is commonly genetic, but may have secondary causes. An association between multiple lipomatosis and HALP has been reported; however, the mechanism for this is unclear. We report the case of a 69-year-old Cook Island woman with extreme HALP who presented with a large paraspinal lipoma. Magnetic resonance imaging showed no other lipomas. She had the metabolic syndrome, a family history suggestive of lipomas and was on lipid-lowering and antihypertensive therapy. Her plasma HDL-cholesterol concentration was 4.9 mmol/L (>95th percentile for age and sex) and was not explained by typical secondary causes. HDL(2) and HDL(3) subfractions were increased, with HDL(2) predominance. The excised lipoma histology demonstrated benign tissue and normal karyotype. Postoperative lipid profiles showed no change in HDL-cholesterol concentrations. In summary, we report a case of extreme HALP that persisted after excision of a solitary paraspinal lipoma.

Two novel mutations and functional analyses of the CETP and LIPC genes underlying severe hyperalphalipoproteinemia

Previous studies have shown that CETP and LIPC mutations contribute to hyperalphalipoproteinemia (HALP) in some populations. We investigated whether activities in cholesteryl ester transfer protein (CETP) and hepatic lipase (HL) contribute to HALP in the Thai population and performed genetic analyses of the CETP and LIPC genes. We recruited 38 individuals with high-density lipoprotein cholesterol (HDL-C) levels of at least 2.59 mmol/L (100 mg/dL) (HALP group) and an equal number of individuals with normal serum HDL-C levels (control group). The CETP and HL activities were determined in both groups. Genetic analyses covering all the coding regions and exon-intron junctions of the CETP and LIPC genes were performed in subjects who had low CETP activity and HL activity, respectively. The mean CETP and HL activities were significantly lower in the HALP group than in the control group (34 +/- 4 vs 44 +/- 3 pmol/[microL h], P = .04 and 150 +/- 17 vs 227 +/- 16 nmol free fatty acid/[mL min] P = .002, respectively). Of the 38 individuals with HALP, 19 and 16 were found to have low CETP activity and HL activity, respectively. Of the 19 subjects with low CETP activity, 6 subjects were found to be heterozygous for a known functionally relevant c.1325A>G (D442G) mutation. The other subject was found to be heterozygous for a novel deletion mutation, c.734_737delTCCC mutation. Of the 16 subjects with low HL activity, 8 and 2 subjects were found to be heterozygous for known variants, c.283 G>A (V73M) and c.1068A>C (L334F), respectively. These variants have previously been shown not to be associated with HALP. Another subject was found to be heterozygous for a novel missense mutation, c.421G>A (G119S). Its amino acid change, absence in controls, evolutionary conservation, occurrence in functionally important domain, and predicted damaging function suggested that the G119S mutation is functionally relevant. Two novel mutations in the CETP and LIPC genes found in this study are likely to be the causes of low enzyme activities and elevated HDL-C levels.

Hypertriglyceridemia: impact and treatment

The treatment of elevated levels of low-density lipoprotein cholesterol is standard medical practice supported by conclusive outcome data. Less definitive information exists for hypertriglyceridemia. Only in the setting of severe hyperchylomicronemia is the benefit of triglyceride lowering clear: it is a means to reduce the risk of pancreatitis. The relationship of triglycerides and cardiovascular disease is still unclear. Moreover, the cardiovascular benefits of reducing triglycerides and of using triglyceride-lowering medications remain unproved. Nonetheless it has become almost standard to reduce the levels of triglyceride-rich lipoproteins that are a major component of plasma non-high-density lipoprotein cholesterol.

HDL composition regulates displacement of cell surface-bound hepatic lipase

HDL is able to displace cell surface-bound hepatic lipase (HL) and stimulate vascular triglyceride (TG) hydrolysis, much like heparin. Displacement appears to be a result of a high-affinity association of HL and apoA-I. HDL varies in its ability to displace HL, and therefore experiments were undertaken to evaluate the impact of HDL composition and structure on HL displacement from cell surface proteoglycans. HDL apolipoprotein and lipid composition directly affect HL displacement. ApoA-II and apoC-I significantly increase HL displacement from the cell surface. While changes in HDL cholesteryl ester and fatty acid content have no effect on HL displacement, increases in HDL phospholipid and TG content significantly inhibit HL displacement. HDL fractions from hyperlipidemic patients are unable to displace HL from the cell surface. These results indicate that the structure and composition of HDL particles in plasma are central to regulation of HL displacement and the hydrolytic activity of HL.

Lipoprotein alterations, hepatic lipase activity, and insulin sensitivity in subclinical hypothyroidism: response to L-T(4) treatment

Subclinical hypothyroidism (sH) has been associated with atherosclerotic cardiovascular disease even in the absence of hypercholesterolemia.

OBJECTIVE

Our study was designed to assess the hypothesis that other pro-atherogenic parameters, such as qualitative lipoprotein changes and insulin resistance, might be present in sH.

DESIGN AND METHODS

Twenty-one sH women were compared to 11 female controls matched for body mass index, menopausal status, and age. Before and after 6 months of levothyroxine (L-T(4)) treatment, we determined total cholesterol, low-density lipoprotein (LDL) cholesterol, high-density lipoprotein (HDL) cholesterol, triglycerides (TG), apoB levels, hepatic lipase (HL) activity in postheparin plasma samples, the chemical composition and copper-induced oxidation in isolated LDL and homeostasis model assessment (HOMA), quantitative insulin sensitivity check index, and insulinogenic index.

MAIN OUTCOME

Lipid profiles were similar between the two groups. No differences in LDL oxidability or the insulin sensitivity assessment parameters were found. HL activity was significantly lower in the sH patients: median (range), 13.1 (2.5-26.7) vs. 18.7 (7.9-28.1) micromol free fatty acids/mL, p < 0.04. The LDL-cholesterol/LDL-TG ratio was decreased in sH: 3.9 (1.8-5.5) vs. 4.7 (3.5-6.8), p < 0.02. HL negatively correlated with thyroid-stimulating hormone (TSH) levels (r = - 0.504, p < 0.01) and positively with LDL-cholesterol/LDL-TG (r = 0.46, p < 0.02). Posttreatment results for all these parameters did not differ significantly compared to baseline.

CONCLUSIONS

Increased levels of TSH are associated to a decrease in HL activity, explaining our findings of an LDL particle rich in TG. This qualitative lipoprotein alteration suggests a pro-atherogenic pattern in sH. Treatment with L-T(4), however, did not correct the basal lipid derangement.

Lipid lowering effect of S-methyl cysteine sulfoxide from Allium cepa Linn in high cholesterol diet fed rats

The lipid lowering action of S-methyl cysteine sulfoxide (SMCS) isolated from Allium cepa Linn (family: Liliaceae) was investigated in Sprague-Dawley rats fed on 1% cholesterol diet, in comparison to the hypolipidemic drug gugulipid. Administration of SMCS at a dose of 200mg/kg body weight for 45 days ameliorated the hyperlipidemic condition. The lipid profile in serum and tissues showed that concentrations of cholesterol, triglyceride and phospholipids were significantly reduced when compared to their untreated counterparts. The total lipoprotein lipase activity in the adipose tissue was decreased with also a decrease in the free fatty acid levels in serum and tissues. The activities of the lipogenic enzymes glucose 6-phosphate dehydrogenase and malic enzyme as also of HMG CoA reductase in the tissues remained low on treatment indicating that both the drugs did not favor lipogenesis and cholesterogenesis in the hyperlipidemic animals. The fecal excretion of bile acids and sterols was further increased upon treatment with the drugs. The results are directive to that both gugulipid and SMCS cause reduction of endogenous lipogenesis, increase catabolism of lipids and subsequent excretion of metabolic by-products through the intestinal tract. However, gugulipid is a better drug than SMCS at a low dose of 50mg/kg body weight.

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.

Blood lipid responses to plant stanol ester supplementation and aerobic exercise training

The purpose of this study was to determine the independent and combined effects of plant stanol ester (PSE) margarine and aerobic exercise on blood lipid concentrations and related intravascular enzymes in 26 healthy sedentary, middle-aged men and postmenopausal women (age, 53 +/- 8 years; body mass index, 27 +/- 1.0, % fat, 28.5 +/- 2). In a stratified double-blind manner, participants were randomly assigned to either a PSE (n = 17) or a placebo (CON, n = 9) margarine group. Participants supplemented their daily diets with 42 g of margarine spread (PSE = 3 g; CON, PSE = 0 g, of approximately equal energy content) for 9 weeks. During the last 4 weeks of margarine supplementation (MS), participants expended 400 kcal on a treadmill 5 d/wk at 65% of VO(2) reserve (2000 kcal/wk). Fasting blood samples were obtained before initiating and after 4 weeks of MS and after exercise training. All blood samples were analyzed for total cholesterol, low-density lipoprotein cholesterol, triglyceride, high-density lipoprotein cholesterol (HDL-C), hepatic lipase, lipoprotein lipase, and cholesterol ester transfer protein activities. Total cholesterol (-10%), low-density lipoprotein cholesterol (-13%), and triglyceride (-18%) concentrations decreased after 4 weeks of MS in the PSE group, but not in the CON group (P < .05 for all). Four weeks of aerobic exercise increased HDL-C by 21% in the CON group (P < .05) and by 4% in the PSE group (P > .05). Total cholesterol-HDL-C ratio decreased significantly (P < .05) in the PSE group, but not in the CON group. No other significant alterations were observed with either PSE or exercise. Our findings suggest that PSE is effective in reducing blood cholesterol concentrations and that exercise can increase HDL-C in middle-aged men and postmenopausal women. Our findings also suggest that PSE supplementation may attenuate the exercise-induced increase in HDL-C.

Role of apoA-I, ABCA1, LCAT, and SR-BI in the biogenesis of HDL

The concentration, composition, shape, and size of plasma high-density lipoprotein (HDL) are determined by numerous proteins that influence its biogenesis, remodeling, and catabolism. The discoveries of the HDL receptor (scavenger receptor class B type I, SR-BI) and the ABCA1 (ATP-binding cassette transporter A1) lipid transporter provided two missing links that were necessary to understand the biogenesis and some of the functions of HDL. Existing data indicate that functional interactions between apoA-I and ABCA1 are necessary for the initial lipidation of apoA-I. Through a series of intermediate steps, lipidated apoA-I proceeds to form discoidal HDL particles that can be converted to spherical particles by the action of lecithin:cholesterol acyltransferase (LCAT). Discoidal and spherical HDL can interact functionally with SR-BI and these interactions lead to selective lipid uptake and net efflux of cholesterol and thus remodel HDL. Defective apoA-I/ABCA1 interactions prevent lipidation of apoA-I that is necessary for the formation of HDL particles. In the same way, specific mutations in apoA-I or LCAT prevent the conversion of discoidal to spherical HDL particles. The interactions of lipid-bound apoA-I with SR-BI are affected in vitro by specific mutations in apoA-I or SR-BI. Furthermore, deficiency of SR-BI affects the lipid and apolipoprotein composition of HDL and is associated with increased susceptibility to atherosclerosis. Here we review the current status of the pathway of HDL biogenesis and mutations in apoA-I, ABCA1, and SR-BI that disrupt different steps of the pathway and may lead to dyslipidemia and atherosclerosis in mouse models. The phenotypes generated in experimental mouse models for apoA-I, ABCA1, LCAT, SR-BI, and other proteins of the HDL pathway may facilitate early diagnosis of similar phenotypes in the human population and provide guidance for proper treatment.

Intra-individual fasting versus postprandial variation of biochemical markers of liver fibrosis (FibroTest) and activity (ActiTest)

BACKGROUND: Biochemical marker combinations, including alpha2-macroglobulin, haptoglobin, apolipoprotein A1, gamma-glutamyl transpeptidase, and total bilirubin (all part of FibroTest) plus alanine aminotransferase (all part of ActiTest), are being developed as alternatives to liver biopsy in patients with chronic hepatitis C and other various chronic liver diseases. Considering this premise, the primary aim of this study was to assess the impact of meal intake on FibroTest and ActiTest results. Such studies are very important for patients, as many clinical errors have been related to the absence of baseline evidence. RESULTS: Intra-individual variation was assessed for the 6 above components and for FibroTest and ActiTest, by measuring time dependent variations before and one hour after a standard meal in 64 subjects. These consisted of 29 healthy volunteers and 35 patients with chronic liver diseases. Meal intake had no significant impact on any of the six components, or on FibroTest or ActiTest, as assessed by repeated measure variance analyses (ANOVA all p > 0.90); the Spearman correlation coefficient ranged from 0.87 (total bilirubin) to 0.995 (gamma-glutamyl transpeptidase). The coefficients of variation (CV) between fasting and postprandial measurements fluctuated for the six components from 0.09 (apolipoprotein A1) to 0.14 (alpha2-macroglobulin), and from 0.09 for FibroTest to 0.13 for ActiTest. In contrast, meal intake had a significant impact on triglycerides (ANOVA p = 0.01, CV = 0.65) and glucose (ANOVA p = 0.04, CV = 0.31). As for the prediction of liver injury, the concordance between fasting and postprandial predicted histological stages and grades was almost perfect, both for FibroTest (kappa = 0.91, p < 0.001) and ActiTest (kappa = 0.80, p < 0.001). CONCLUSIONS: The intra-individual variation of biochemical markers was low, and it was shown that measurements of FibroTest, ActiTest and their components are not significantly modified by meal intake. This fact makes the screening of patients at risk of chronic liver diseases more convenient.

Effects of low and moderate exercise intensity on postprandial lipemia and postheparin plasma lipoprotein lipase activity in physically active men

This study was designed to assess differences in the intensity of exercise to attenuate postprandial lipemia (PPL). Thirteen healthy men (age 23.8 +/- 0.9 yr) participated in three random-ordered trials: in low-(25% peak oxygen consumption; Low) and moderate-intensity (65% peak oxygen consumption; Mod) exercise trials, which were completed 1 h before a high-fat meal (1.3 g fat/kg body mass), and a control (Con), fat meal only, trial. Venous blood samples were obtained before the fat meal, and at 2, 4, 6, 8, and 20 h after the fat meal. PPL in the Mod trial (267 +/- 50 mg.dl-1.8 h) was lower compared with that in either Con (439 +/- 81 mg.dl-1.8 h) or Low (403 +/- 91 mg.dl-1.8 h) trials (P < 0.05), whereas there was no difference in PPL between Con and Low trials (P > 0.05). High-density lipoprotein cholesterol (HDL-C) and HDL subtype 2 cholesterol were not different between or within trials (P > 0.05). Postprandial insulinemia was lower in the Mod trial (20.5 +/- 5.7 microIU.ml-1.8 h; P < 0.05), but not in the Low trial (31.4 +/- 4.7 microIU.ml-1.8 h), compared with that in the Con trial (34.9 +/- 5.0 microIU.ml-1.8 h). Postheparin lipoprotein lipase activity at 8 h was higher in the Low trial compared with that in either Con or Mod trials, whereas there were no differences between trials at 20 h. These results suggest that, when exercise is performed 1 h before a fat meal, only exercise of moderate but not of low intensity attenuates PPL and that this effect is not associated with changes in postheparin lipoprotein lipase activity.

Apolipoprotein CIII deficiency prevents the development of hypertriglyceridemia in streptozotocin-induced diabetic mice

To explore the role of apolipoprotein (apo) CIII in the development of hypertriglyceridemia associated with diabetes mellitus, we examined triglyceride (TG) kinetics in apo CIII - deficient mice (apo CIII - null) and wild-type (WT) (C57BL/6J) mice with diabetes induced by the injection of streptozotocin (STZ). Plasma TG levels increased significantly in WT mice after diabetes was induced (102 +/- 29 v 65 +/- 33 mg/dL, P <.01). Apo CIII-null mice had a significantly lower TG level (35 +/- 9 mg/dL) that remained unchanged even when diabetes was induced (35 +/- 8 mg/dL). The TG secretion rate (TGSR) measured by the Triton WR1339 method tended to decrease in diabetic WT, indicating that catabolism of TG was impaired. Apo CIII-null mice showed 2-fold higher TG production than WT mice, indicating markedly faster clearance of TG. The high TGSR was halved when diabetes was induced in apo CIII-null mice, and the fractional catabolic rate (FCR) of TG was also halved, although it was still significantly higher than in WT mice. Lipoprotein lipase (LPL) activity in postheparin plasma was not significantly altered in WT or apo CIII-null mice regardless of the presence or absence of diabetes. [(3)H] very-low-density lipoprotein (VLDL)-TG from WT or apo CIII-null mice showed similar clearance by WT recipients, and this was also observed when VLDL was obtained from diabetic counterparts. In contrast, VLDL-TG was cleared faster by apo CIII-null recipients compared with WT recipients, regardless of the VLDL donors. These results suggest that apo CIII deficiency prevents the development of hypertriglyceridemia associated with diabetes by stimulating TG removal, possibly by promoting the interaction of VLDL with the TG removal system.

Characterization of a novel mutation causing hepatic lipase deficiency among French Canadians

Individuals with hepatic lipase (HL) deficiency are often characterized by elevated levels of triglycerides (TGs) and cholesterol. The aim of the present study was to characterize the molecular defect leading to severe HL deficiency in a Québec-based kindred. In the proband and two of her brothers, the very low to undetectable HL activity resulted from compound heterozygosity for two rare HL gene mutations, a previously unknown missense mutation in exon 5 designated A174T and the previously reported T383M mutation in exon 8 of the HL gene. The mutation at codon 174 resulted in the substitution of alanine for threonine, a polar amino acid, in a highly conserved nonpolar region of the protein involved in the catalytic activity of the enzyme. The severe HL deficiency among the three related compound heterozygotes was associated with a marked TG enrichment of LDL and HDL particles. The two men with severe HL deficiency also presented with abdominal obesity, which appeared to amplify the impact of HL deficiency on plasma TG-rich lipoprotein levels. Our results demonstrated that HL deficiency in this Québec kindred is associated with an abnormal lipoprotein-lipid profile, which may vary considerably in the presence of secondary factors such as abdominal obesity.

Lipoprotein lipase mRNA in white adipose tissue but not in skeletal muscle is increased by pioglitazone through PPAR-gamma

Lipoprotein lipase (LPL), a key enzyme for triglyceride hydrolysis, is an insulin-dependent enzyme and mainly synthesized in white adipose tissue (WAT) and skeletal muscles (SM). To explore how pioglitazone, an enhancer of insulin action, affects LPL synthesis, we examined the effect of pioglitazone on LPL mRNA levels in WAT or SM of brown adipose tissue (BAT)-deficient mice, which develop insulin resistance and hypertriglyceridemia. Both LPL mRNA of WAT and SM were halved in BAT-deficient mice. Pioglitazone increased LPL mRNA in WAT by 8-fold, which was substantially associated with a 4-fold increase of peroxisome proliferator activated receptor (PPAR)-gamma mRNA (r=0.97, p<0.0001), whereas pioglitazone did not affect LPL mRNA in SM. These results suggest that pioglitazone exclusively increases LPL production in WAT via stimulation of PPAR-gamma synthesis. Since pioglitazone does not affect LPL production in SM, this would contribute to prevent the development of insulin resistance due to lipotoxicity.

Analysis of lipoprotein lipase activity using high-performance liquid chromatography

Lipoprotein lipase (LPL) is a key enzyme which regulates the plasma triglyceride concentration by hydrolyzing triglycerides in chylomicrons and very-low-density lipoprotein (VLDL). The activity of LPL was conventionally analyzed using radio-labeled residues or direct sandwich-ELISA. An assay for lipoprotein lipase activity which used a nonradioactive substrate, tri-olein, is described. In this method, LPL activity was detected fluorometrically by reacting 9-anthryldiazomethane (ADAM) with the oleic acid generated from tri-olein by enzyme activity and separated by reversed-phase HPLC. This method has been optimized and the optimum enzyme incubation time and reaction time of the generated oleic acid with ADAM were both at 20 min. The method correlated well with the conventional method.

Butter differs from olive oil and sunflower oil in its effects on postprandial lipemia and triacylglycerol-rich lipoproteins after single mixed meals in healthy young men

Accumulation of postprandial triacylglycerol-rich lipoproteins is generated by assimilation of ingested dietary fat and has been increasingly related to atherogenic risk. Nevertheless, the influence of different kinds of dietary fatty acids on postprandial lipid metabolism is not well established, except for (n-3) polyunsaturated long-chain fatty acids. Our goal was to evaluate the effects of test meals containing a common edible fat source of saturated (butter), monounsaturated (olive oil) or (n-6) polyunsaturated (sunflower oil) fatty acids on postprandial lipid and triacylglycerol-rich lipoprotein responses. After a 12-h fast, 10 healthy young men ingested mixed meals containing 0 g (control) or 40 g fat, provided as butter, olive oil or sunflower oil in a random order. Fasting and postmeal blood samples were collected for 7 h. The no-fat test meal did not elicit any change over baseline except for plasma phospholipids, insulin and nonesterified fatty acids. Conversely, the three fat-containing meals elicited bell-shaped postprandial changes (P < 0.05) in serum triacylglycerols, free and esterified cholesterol, and nonesterified fatty acids. The butter meal induced a lower postprandial rise of triacylglycerols in serum and chylomicrons (incremental AUC, mmol.h/L: 0.72) than the two unsaturated oils (olive oil: 1.6, sunflower oil: 1.8), which did not differ. Circulating chylomicrons were smaller after the butter meal than after the two vegetable oil meals. The in vitro susceptibility of circulating chylomicrons to hydrolysis by postheparin plasma was higher after sunflower oil than after butter or olive oil. We conclude that butter results in lower postprandial lipemia and chylomicron accumulation in the circulation of young men than olive or sunflower oils after consumption of a single mixed meal.

Ferrocenylnaphthalene diimide-based electrochemical hybridization assay for a heterozygous deficiency of the lipoprotein lipase gene

An electrochemical hybridization assay has been devised that enables the rapid analysis of a heterozygous deficiency of the human lipoprotein lipase (LPL) gene. PCR products of 350 base pairs (bp) containing the wild-type sequence, a mutated G(818) --> A transition or a G(916) deletion of the LPL gene were subjected to hybridization with a probe DNA of 13 or 15 bases that represented either the wild-type or the mutated sequence immobilized on a gold electrode. The differential pulse voltammetry of the electrode before and after hybridization was determined in the presence of ferrocenylnaphthalene diimide (FND) at 460 mV. The measured change in peak current, Deltai, was defined by (i - i(o))/i(o) x 100%, where i(o) and i represent the current before and after hybridization, respectively. Matched combinations of sample and probe gave Deltai values of 40-90%, whereas mismatched combinations gave values of 20-35%, enabling the discrimination of matched hybrids from mismatched ones across a slim margin. Because the heterozygote contains both the wild-type and mutated sequences, however, it alone gives large Deltai values with both the wild- and mutant-type probes. This system was validated on 10 unknown samples of each of the two types of LPL mutation, which were correctly identified in every case.

Effects of fenofibrate on high-density lipoprotein particle size in patients with hyperlipidemia: a randomized, double-blind, placebo-controlled, multicenter, crossover study

BACKGROUND

Fenofibrate lowers serum total cholesterol and triglyceride levels while it elevates serum high-density lipoprotein cholesterol (HDL-C) level.

OBJECTIVE

The aim of this study was to investigate the effects of fenofibrate on the particle size of high-density lipoprotein (HDL).

METHODS

Patients with hyperlipidemia (as defined by serum triglyceride level > or = 150 mg/dL in the fasting state) were enrolled in this randomized, double-blind, placebo-controlled, multicenter, crossover study. Fenofibrate 300 mg (corresponding to 200 mg of micronized fenofibrate) or placebo was administered orally once daily after dinner for 8 weeks, followed by crossover of the 2 drugs for an additional 8 weeks.

RESULTS

Fifty hyperlipidemic patients (31 men, 19 women; mean [SD] age, 54.6 [12.7] years) were enrolled. Serum total cholesterol and triglyceride levels were significantly reduced with fenofibrate treatment compared with placebo (9.4% [P = 0.007] and 34.4% [P < 0.001], respectively), whereas HDL-C levels were significantly elevated (by 25.8% [P < 0.001]). Lipoprotein lipase (LPL) activity, LPL protein level, and hepatic triglyceride lipase activity increased by 10.5%, 13.4%, and 11.4%, respectively, with fenofibrate compared with placebo. HDL was classified into 3 groups by particle size: HDL3 <88 A; HDL2a > or = 88 A but <98 A; and HDL2b > or = 98 A. The amount of HDL3 increased significantly with fenofibrate compared with placebo (P < 0.001). Fenofibrate was well tolerated during the study. Abnormal clinical laboratory values were noted in 20 of 48 patients (41.7%), but these events were mild and not clinically significant.

CONCLUSION

Taken together, these findings indicate that fenofibrate therapy increased the HDL subfraction with the smallest diameter (HDL3), which is largely responsible for withdrawing cholesterol from peripheral cells.

Flavonoids from Emblica officinalis and Mangifera indica-effectiveness for dyslipidemia

Flavonoids from Emblica officinalis and Mangifera indica effectively reduce lipid levels in serum and tissues of rats induced hyperlipidemia. Hepatic HMG CoA reductase activity was significantly inhibited in rats fed E. officinalis flavonoids. But increase of this enzyme was observed in rats administered M. indica flavonoids. LCAT showed elevated levels in rats fed flavonoids from E. officinalis and M. indica. The degradation and elimination of cholesterol was highly enhanced in both the groups. In E. officinalis, the mechanism of hypolipidemic action is by the concerted action of inhibition of synthesis and enhancement of degradation. In the other group (M. indica) inhibition of cholesterogenesis was not encountered but highly significant degradation of cholesterol was noted, which may be the pivotal factor for hypolipidemic activity in this case. Though the mechanisms differ in the two cases, the net effect is to lower lipid levels.

Hypogonadism and androgen replacement therapy in elderly men

The decrease in testosterone levels with age is both central (pituitary) and peripheral (testicular) origin. Because serum levels of sex-hormone-binding globulin increase with aging, the decrease in free testosterone is of even greater magnitude. Recent long-term studies of testosterone therapy in hypogonadal elderly men have shown beneficial effects on bone density, body composition, and muscle strength without any substantial adverse effects on lipids and the prostate. Total testosterone level is the test of choice for initial screening of elderly men who present with signs and symptoms of hypogonadism. If the level is below 300 ng/dL, replacement therapy should be initiated. If the level is normal in a symptomatic patient, free or bioavailable testosterone should be determined. The pros and cons of testosterone therapy should be discussed in depth with every patient, and decisions should be made on an individual basis. This review summarizes the trials of testosterone replacement therapy in elderly men and outlines a diagnostic approach to these patients.

A newly identified lipoprotein lipase (LPL) gene mutation (F270L) in a Japanese patient with familial LPL deficiency

We have systematically investigated the molecular defects resulting in a primary lipoprotein lipase (LPL) deficiency in a Japanese male infant (proband SH) with fasting hyperchylomicronemia. Neither LPL activity nor immunoreactive LPL mass was detected in pre- or postheparin plasma from proband SH. DNA sequence analysis of the LPL gene of proband SH revealed homozygosity for a novel missense mutation of F270L (Phe(270)-->Leu/TTT(1065)-->TTG) in exon 6. The function of the mutant F270L LPL was determined by both biochemical and immunocytochemical studies. In vitro expression experiments on the mutant F270L LPL cDNA in COS-1 cells demonstrated that the mutant LPL protein was synthesized as a catalytically inactive form and its total amount was almost equal to that of the normal LPL. Moreover, the synthesized mutant LPL was non-releasable by heparin because the intracellular transport of the mutant LPL to the cell surface - by which normal LPL becomes heparin-releasable - was impaired due to the abnormal structure of the mutant LPL protein. These findings explain the failure to detect LPL activities and masses in pre- and postheparin plasma of the proband. The mutant F270L allele generated an XcmI restriction enzyme site in exon 6 of the LPL gene. The carrier status of F270L in the proband's family members was examined by digestion with XcmI. The proband was ascertained to be homozygous for the F270L mutation and his parents and sister were all heterozygous. The LPL activities and masses of the parents and the sister (carriers) were half or less than half of the control values. Regarding the phenotype of the carriers, the mother with a sign of hyperinsulinemia manifested hypertriglyceridemia (type IV hyperlipoproteinemia), whereas the healthy father and the sister were normolipidemic. Hyperinsulinemia may be a strong determinant of hypertriglyceridemia in subjects with heterozygous LPL deficiency.

Race, visceral adipose tissue, plasma lipids, and lipoprotein lipase activity in men and women: the Health, Risk Factors, Exercise Training, and Genetics (HERITAGE) family study

Abdominal obesity is associated with numerous metabolic alterations, such as hypertriglyceridemia and low levels of high density lipoprotein (HDL) cholesterol. However, compared with abdominally obese white individuals, abdominally obese black individuals have been characterized by higher plasma HDL cholesterol levels, suggesting that the impact of abdominal fat accumulation on the lipoprotein-lipid profile may differ among ethnic groups. Therefore, we have compared the associations between body fatness, visceral adipose tissue (AT) accumulation, and metabolic risk variables in a sample of 247 white men and 240 white women versus a sample of 93 black men and 143 black women. Although no difference in mean total body fatness was found between the 2 race groups, white men had higher levels of visceral AT than did black men (P<0.001). Despite the fact that black women had a greater body fat content than did white women, black women had levels of visceral AT that were similar to those of white women, suggesting a lower susceptibility to visceral obesity in black women. This lower accumulation of visceral AT in blacks was accompanied by significantly reduced apolipoprotein B concentrations and ratios of total cholesterol to HDL cholesterol as well as higher plasma HDL cholesterol levels (P<0.05) compared with those values in whites. Irrespective of sex, higher postheparin plasma hepatic lipase (HL) and lower lipoprotein lipase (LPL) activities were found in whites, resulting in an HL/LPL ratio that was twice as high in whites as in blacks (P<0.005). Although differences in lipoprotein-lipid levels were noted between whites and blacks, results from multiple regression analyses revealed that after control for morphometric and metabolic variables of the study (body fat mass, visceral AT, LPL, HL, and age), ethnicity had, per se, only a minor contribution to the variance in plasma lipoprotein levels. Thus, our results suggest that the higher plasma HDL cholesterol levels and the generally more cardioprotective plasma lipoprotein profile found in abdominally obese black versus white individuals are explained, at least to a certain extent, by a lower visceral AT deposition and a higher plasma LPL activity in black individuals.

Influence of cholesterol status on blood lipid and lipoprotein enzyme responses to aerobic exercise

To compare postexercise changes in plasma lipids and lipoprotein enzymes in 13 hypercholesterolemic (HC) and 12 normocholesterolemic men [total cholesterol (TC) 252 +/- 5 vs. 179 +/- 5 mg/dl], fasting blood samples were obtained 24 h before, immediately, 24, and 48 h after a single bout of treadmill walking (70% peak O(2) consumption, 500 kcal expenditure). Significant findings (P < 0.05 for all) for plasma volume-adjusted lipid and enzyme variables were that TC, low-density-lipoprotein cholesterol, and cholesterol ester transfer protein activity were higher in the HC group but did not influence the lipid responses to exercise. Across groups, TC was transiently reduced immediately after exercise but returned to baseline levels by 24 h postexercise. Decreases in triglyceride and increases in high-density-lipoprotein cholesterol (HDL-C) and HDL(3)-C were observed 24 h after exercise and lasted through 48 h. Lipoprotein lipase activity was elevated by 24 h and remained elevated 48 h after exercise. HDL(2)-C, cholesterol ester transfer protein activity, hepatic triglyceride lipase, and lecithin: cholesterol acyltransferase activities did not change after exercise. These data indicate that the exercise-induced changes in HDL-C and triglyceride are similar in HC and normocholesterolemic men and may be mediated, at least in part, by an increase in lipoprotein lipase activity.

Estrogen effects on triglyceride metabolism in analbuminemic rats

BACKGROUND

Triglyceride (TG) levels are normally lower in female rats, while the opposite is the case in the Nagase analbuminemic rats (NAR). Increased TG levels in normal males are caused by a testosterone-mediated decrease in postheparin (PH) lipoprotein lipase (LpL). Castration of males reduces TG, while castration of females is without effect. TG levels are reduced by castration of the female NAR, suggesting that estrogen rather than testosterone causes hypertriglyceridemia in this strain. The mechanism for this increase is unknown.

METHODS

We measured secretion of very-low density lipoprotein (VLDL) TG using Triton WR 1339 clearance as the disappearance from blood of 3H-trioleate and 14C-cholesterol-labeled chylomicrons (CM), and the activity of the PH lipases: LpL and hepatic lipase (HL). All were determined in Sprague-Dawley (SD) and NAR female, male, and ovariectomized (OVX) rats.

RESULTS

TG levels were significantly greater in female NAR in comparison to all other groups. Ovariectomy of NAR significantly ameliorated hypertriglyceridemia. VLDL TG secretion was significantly greater in intact female NAR compared with all other groups. There were no other differences in VLDL TG secretion among the other groups. The clearance of CM was greatest in female SD rats, and OVX had no effect. NAR cleared CM less well than did SD rats (P < 0.001), but among NAR, clearance was greatest in OVX NAR and male NAR (P < 0. 002). Both PH LpL activity and HL activity were lowest in female NAR (P < 0.05). Ovariectomy partially corrected the defect in HL (P < 0. 05).

CONCLUSION

TG levels in female NAR are in part a result of increased VLDL-TG secretion, an effect mediated by estrogen. The presence of an estrogen-mediated catabolic defect that was alleviated by OVX was also observed. This catabolic defect is likely a result of an estrogen-mediated decrease both in LpL and HL expressed only in the presence of analbuminemia.

Development and evaluation of a direct sandwich-enzyme-linked immunosorbent assay for the quantification of human hepatic triglyceride lipase mass in human plasma

We have developed a direct sandwich-enzyme-linked immunosorbent assay (ELISA) for quantification of the hepatic triglyceride lipase (HTGL) immunoreactive mass in human plasma. This direct sandwich-ELISA uses a combination of two distinct monoclonal antibodies (MAbs), which recognize different epitopes on the HTGL molecule: a horseradish peroxidase (HRP)-labeled anti-human HTGL MAb (2(4)F12C12) as an enzyme-linked MAb, and an anti-human HTGL MAb (1(11)A3H3) coated on a microtiter plate as a solid-phase MAb. Purified human post-heparin plasma (PHP)-HTGL was used as the standard material. The detection range of the sandwich-ELISA was 40-800 ng of HTGL protein per ml of plasma. The intra- and inter-assay coefficients of variation were less than 2.0% and 2.3%, respectively. The recovery tests resulted in variation only between 97.7% and 103.5%. No significant assay interference was caused by a high concentration of triglyceride, hemoglobin, bilirubin, uric acid, or creatinine. The reliability of the HTGL mass values obtained with the direct sandwich-ELISA was assessed by comparison with the HTGL mass values determined by our earlier one-step sandwich-enzyme immunoassay (EIA). The two sets of values showed a highly significant correlation (r=+0.952, n=64). Strong correlation (r=+0. 959, n=50) was also found between the HTGL masses with the direct sandwich-ELISA and the HTGL activities determined with a selective immunoinactivation assay. The HTGL mass concentrations in PHP from 64 healthy subjects were 1916+/-841 ng/ml by the direct sandwich-ELISA and 1925+/-785 ng/ml (mean+/-standard deviation (SD)) by the one-step sandwich-EIA. The present direct sandwich-ELISA permits rapid identification of certain HTGL abnormalities in PHP samples from patients with hypertriglyceridemia or diseases such as hypothyroidism or renal failure, which affect HTGL.

Carbohydrate-induced hypertriacylglycerolemia: historical perspective and review of biological mechanisms

Current trends in health promotion emphasize the importance of reducing dietary fat intake. However, as dietary fat is reduced, the dietary carbohydrate content typically rises and the desired reduction in plasma cholesterol concentrations is frequently accompanied by an elevation of plasma triacylglycerol. We review the phenomenon of carbohydrate-induced hypertriacylglycerolemia, the health effects of which are among the most controversial and important issues in public health nutrition today. We first focus on how seminal observations made in the late 1950s and early 1960s became the basis for subsequent important research questions and areas of scientific study. The second focus of this paper is on the current knowledge of biological mechanisms that contribute to carbohydrate-induced hypertriacylglycerolemia. The clinical rationale behind mechanistic studies is this: if carbohydrate-induced hypertriacylglycerolemia shares a metabolic basis with endogenous hypertriacylglycerolemia (that observed in subjects consuming high-fat diets), then a similar atherogenic risk may be more likely than if the underlying metabolic mechanisms differ. The third focus of the paper is on both the positive metabolic changes that occur when high-carbohydrate diets are consumed and the potentially negative health effects of such diets. The review concludes with a summary of some important research questions that remain to be addressed. These issues include the level of dietary carbohydrate that induces carbohydrate-induced hypertriacylglycerolemia, whether the phenomenon is transient or can be avoided, whether de novo lipogenesis contributes to the phenomenon, and what magnitude of triacylglycerol elevation represents an increase in disease risk.

Genomic interval engineering of mice identifies a novel modulator of triglyceride production

To accelerate the biological annotation of novel genes discovered in sequenced regions of mammalian genomes, we are creating large deletions in the mouse genome targeted to include clusters of such genes. Here we describe the targeted deletion of a 450-kb region on mouse chromosome 11, which, based on computational analysis of the deleted murine sequences and human 5q orthologous sequences, codes for nine putative genes. Mice homozygous for the deletion had a variety of abnormalities, including severe hypertriglyceridemia, hepatic and cardiac enlargement, growth retardation, and premature mortality. Analysis of triglyceride metabolism in these animals demonstrated a several-fold increase in hepatic very-low density lipoprotein triglyceride secretion, the most prevalent mechanism responsible for hypertriglyceridemia in humans. A series of mouse BAC and human YAC transgenes covering different intervals of the 450-kb deleted region were assessed for their ability to complement the deletion induced abnormalities. These studies revealed that OCTN2, a gene recently shown to play a role in carnitine transport, was able to correct the triglyceride abnormalities. The discovery of this previously unappreciated relationship between OCTN2, carnitine, and hepatic triglyceride production is of particular importance because of the clinical consequence of hypertriglyceridemia and the paucity of genes known to modulate triglyceride secretion.

Development and evaluation of a direct sandwich enzyme-linked immunosorbent assay for the quantification of lipoprotein lipase mass in human plasma

OBJECTIVE

The purpose of this study was to develop and evaluate a direct sandwich enzyme-linked immunosorbent assay (ELISA) for quantification of the lipoprotein lipase (LPL) immunoreactive mass in human plasma using monoclonal antibodies (MAbs) directed against LPL purified from human postheparin plasma (PHP) [corrected].

METHODS AND RESULTS

The direct sandwich-ELISA was performed using a combination of two distinct types of MAbs that recognize different epitopes on the LPL molecule. The immunoreactive mass of human LPL was specifically measured using a horseradish peroxidase-labeled anti-human LPL MAb [1(1)D2B2] as an enzyme-linked MAb, and an anti-human LPL MAb [2(10)F8F9] coated on a polystyrene microtiter plate as a solid-phase MAb. Purified human PHP-LPL was used as a standard material. The detection range of the sandwich-ELISA was 3.6-460 ng of LPL protein per mL of plasma. The intra- and interassay coefficients of variation were less than 5.9% and 3.3%, respectively. The validity of this method was additionally assured by the recovery test, which resulted in the variation only between 97.5% and 105.1%, and also by the interference test, which resulted in noninterference of LPL assay with a high concentration of triglyceride, hemoglobin, bilirubin, uric acid, or creatinine. To assess the reliability of the LPL mass values obtained with the direct sandwich-ELISA, they were compared with LPL mass values determined by the one-step sandwich-EIA (MARKIT-F LPL EIA kit) previously established by us. This comparison showed a highly significant correlation (r = +0.990) between the two sets of values. The LPL mass concentrations in PHP from 33 healthy subjects were 267 +/- 53 and 257 +/- 59 ng/mL (mean +/- SD), respectively.

CONCLUSION

The present direct sandwich-ELISA is useful for rapidly identifying certain abnormalities of LPL in PHP samples from patients with hypertriglyceridemia [corrected].

Non-insulin-dependent diabetes mellitus and hypertriglyceridemia impair lipoprotein metabolism in chronic hemodialysis patients

Patients with diabetes mellitus undergoing chronic hemodialysis treatment have the worst outcome on dialysis due to an increased rate of cardiovascular complications. Nearly all patients present with dyslipidemia, a prominent vascular risk factor, probably responsible for the high rate of vascular injury. Since both uremia and diabetes predispose to hypertriglyceridemia, the present study was conducted to investigate the influence of diabetes mellitus and/or hypertriglyceridemia on lipoprotein metabolism in hemodialysis patients. LDL was isolated and characterized from hyper- and normotriglyceridemic diabetic and nondiabetic hemodialysis patients (n = 40; 10 in each group); also, LDL-receptor-dependent uptake and intracellular cholesterol metabolism were studied in HepG2 cells. In addition, scavenger-receptor-mediated uptake was examined in mouse peritoneal macrophages. LDL isolated from nondiabetic normotriglyceridemic hemodialysis patients exhibited impaired cellular uptake via the LDL receptor. Additionally, intracellular sterol synthesis was less inhibited and cholesterol esterification was reduced compared with LDL from healthy control subjects. Reduction of catabolic capacities was more marked in hemodialysis patients who were either diabetic or hypertriglyceridemic and even more pronounced in patients presenting with a combination of both diabetes and hypertriglyceridemia. Hypertriglyceridemic and diabetic patients showed reduced lipase activity and increased LDL oxidation. Furthermore, they accumulated a fraction of small, dense LDL, and LDL was predominantly taken up via the scavenger-receptor pathway in peritoneal macrophages. This study elucidates the distinct influence of diabetes and/or hypertriglyceridemia in hemodialysis patients on cellular LDL metabolism via specific and nonspecific metabolic pathways. Furthermore, it underscores the cumulative impact of these pathologic entities on impairment of lipoprotein metabolism and increase of cardiovascular risk.

Familial lipoprotein lipase deficiency in infancy: clinical, biochemical, and molecular study

OBJECTIVES

To describe the characteristics of lipoprotein lipase (LPL)-deficient patients seen in infancy and to evaluate the safety and efficacy of severe fat restriction.

METHODS

Children <1 year old presenting with chylomicronemia between 1972 and 1995 were identified, and their clinical courses were reviewed retrospectively.

RESULTS

LPL deficiency was demonstrated in 16 infants who presented with irritability (n = 7), lower intestinal bleeding (n = 2), pallor, anemia, or splenomegaly (n = 5), and a family history or fortuitous discovery (n = 2). All plasma samples were lactescent at presentation. Chylomicronemia responded rapidly to dietary fat restriction, and it was possible to maintain satisfactory metabolic control for a prolonged period of time. Only 1 adolescent girl had an episode of pancreatitis associated with the use of oral contraceptives. No persistent adverse effects on growth were seen. We obtained abnormal values for serum iron, alkaline phosphatase, and total calcium.

CONCLUSIONS

The presentation of LPL deficiency is heterogeneous during infancy. Close dietary monitoring is required to avoid nutritional deficiencies. Estrogen therapy should be avoided in LPL-deficient patients.