Plasma Apolipoprotein C-III Research Articles

Apolipoprotein C-III and hepatic triglyceride-rich lipoprotein production

A strong positive correlation between plasma apolipoprotein (apo) C-III and triglyceride concentrations has been invariably observed in human and animal studies. The hypertriglyceridemic effect of apo C-III has been conventionally explained by its extracellular roles in inhibiting lipolysis catalysed by lipoprotein lipase and attenuating triglyceride-rich lipoprotein clearance through receptor-dependent and/or independent mechanisms. However, recent experimental evidence suggests that apo C-III may also play an intracellular role in promoting hepatic triglyceride-rich lipoprotein production. Kinetic studies with humans and genetically modified mice have shown that apo C-III is linked with increased production of triglyceride-rich lipoproteins, such as very-low-density lipoprotein 1 (VLDL1). Mutational studies on human apo C-III variants (originally identified in humans with hypotriglyceridemia or hyperalphalipoproteinemia) provide the structure-function analysis of human apo C-III, demonstrating that loss-of-function mutations within human apo C-III impair the assembly and secretion of triglyceride-rich VLDL1 under lipid-rich conditions. The current review summarizes recent experimental evidence for an intrahepatic role of human apo C-III in promoting mobilization and utilization of triglyceride during VLDL1 assembly/secretion. Understanding mechanisms by which hepatic apo C-III expression is regulated under insulin resistance and diabetic conditions will lead to better and more rational strategies for the prevention and treatment of diabetic hypertriglyceridemia that is closely related to premature atherosclerosis.

Elevated Ratio of Maternal Plasma ApoCIII to ApoCII in Preeclampsia

Preeclampsia is a hypertensive disorder unique to pregnancy. Although the pathogenesis of the disease begins with aberrant spiral artery invasion in the first trimester, clinical symptoms usually do not present until late in pregnancy. Apolipoprotein CII (ApoCII) and its negative regulator, apolipoprotein CIII (ApoCIII), have recently been described as atherogenesis biomarkers in models of cardiovascular disease. Given the similarities in pathology, etiology, and clinical presentation between cardiovascular disease and preeclampsia, we hypothesized that the ratio of ApoCIII to ApoCII in maternal first trimester plasma would predict preeclampsia later in pregnancy. To test this hypothesis, plasma was prospectively collected from 311 nulliparas at 8 to 12 weeks gestation. After delivery, patients were divided into cohorts based on preeclampsia diagnosis. Conditioning monocytes with preeclamptic plasma potentiated monocyte adhesion to endothelial cells in an in vitro model. The ratio of ApoCIII to ApoCII was significantly elevated in patients with severe preeclampsia relative to normotensive and gestational hypertensive individuals (P < .05) as determined by mass spectrometry and competitive enzyme-linked immunosorbent assay (ELISA) assays. These results support a predictive change in the ratio of ApoCIII to ApoCII in pregnancies complicated by severe preeclampsia.

Plasma apolipoprotein C-III metabolism in patients with chronic kidney disease

Moderate chronic kidney disease (CKD) (defined by an estimated glomerular filtration rate of 30-60 ml/min) is associated with mild hypertriglyceridemia related to delayed catabolism of triglyceride-rich lipoprotein particles. Altered apolipoprotein C-III (apoC-III) metabolism may contribute to dyslipidemia in CKD. To further characterize the dyslipidemia of CKD, we investigated the kinetics of plasma apoC-III in 7 nonobese, nondiabetic, non-nephrotic CKD subjects and 7 age- and sex-matched healthy controls, using deuterated leucine ([5, 5, 5, ²H₃]leucine), gas chromatography-mass spectrometry, and multicompartmental modeling. Compared with controls, CKD subjects had higher concentrations of plasma and VLDL triglycerides and plasma and VLDL apoC-III (P < 0.05). The increased plasma apoC-III concentration was associated with a decreased apoC-III fractional catabolic rate (FCR) (1.21 ± 0.15 vs. 0.74 ± 0.12 pools/day, P = 0.03). There were no differences between apoC-III production rates of controls and those of CKD subjects. In CKD subjects, plasma apoC-III concentration was significantly and negatively correlated with apoC-III FCR (r = -0.749, P = 0.05) but not with apoC-III production rate. Plasma apoC-III concentration was positively correlated with plasma and VLDL triglycerides and VLDL apoB concentrations and negatively correlated with VLDL apoB FCR (P < 0.05 for all). ApoC-III FCR was negatively correlated with plasma and VLDL triglycerides and VLDL apoB concentration and positively correlated with VLDL apoB FCR (P < 0.05 for all). Altered plasma apoC-III metabolism is a feature of dyslipidemia in moderate CKD. Modification of apoC-III catabolism may be an important therapeutic target for reducing cardiovascular disease risk in moderate CKD.

Individual Differences in Hyperlipidemia and Vitamin E Status in Response to Chronic Alcohol Self-Administration in Cynomolgus Monkeys

Chronic ethanol self-administration induces oxidative stress and exacerbates lipid peroxidation. α-Tocopherol is a potent lipid antioxidant and vitamin that is dependent upon lipoprotein transport for tissue delivery. To evaluate the extent to which vitamin E status is deranged by excessive alcohol consumption, monkeys voluntarily drinking ethanol (1.36 to 3.98 g/kg/d for 19 months, n = 11) were compared with nondrinkers (n = 5, control). Three alcohol-drinking animals developed hyperlipidemia with plasma triglyceride levels (1.8 ± 0.9 mM) double those of normolipidemic (NL) drinkers (0.6 ± 0.2) and controls (0.6 ± 0.3, p < 0.05); elevated plasma cholesterol (3.6 ± 0.5 mM) compared with NL drinkers (2.3 ± 0.2, p < 0.05) and controls (2.9 ± 0.3); and lower plasma α-tocopherol per triglycerides (14 ± 6 mmol/mol) than controls (27 ± 8) and NL drinkers (23 ± 6, p < 0.05). Hyperlipidemic monkey liver α-tocopherol (47 ± 15 nmol/g) was lower than NL drinkers (65 ± 13) and controls (70 ± 15, p = 0.080), as was adipose α-tocopherol (84 ± 37 nmol/g) compared with controls (224 ± 118) and NL drinkers (285 ± 234, p < 0.05). Plasma apolipoprotein (apo) CIII increased compared to baseline at both 12 and 19 months in the normolipidemic (p = 0.0016 and p = 0.0028, respectively) and in the hyperlipidemic drinkers (p < 0.05 and p < 0.05, respectively). Plasma apo H concentrations at 19 months were elevated hyperlipidemics (p < 0.05) relative to concentrations in control animals. C-reactive protein (CRP), a marker of inflammation, was increased compared to baseline at both the 12- and 19-month time points in the normolipidemic (p = 0.005 and p = 0.0153, respectively) and hyperlipidemic drinkers (p = 0.016 and p = 0.0201, respectively). A subset of alcohol-drinking monkeys showed a predisposition to alcohol-induced hyperlipidemia. The defect in lipid metabolism resulted in lower plasma α-tocopherol per triglycerides and depleted adipose tissue α-tocopherol, and thus decreased vitamin E status.

Chronic kidney disease delays VLDL-apoB-100 particle catabolism: potential role of apolipoprotein C-III

To determine the relative contribution of obesity and/or insulin resistance (IR) in the development of dyslipidemia in chronic kidney disease (CKD), we investigated the transport of apolipoprotein (apo) B-100 in nonobese, nondiabetic, nonnephrotic CKD subjects and healthy controls (HC). We determined total VLDL, VLDL(1), VLDL(2), intermediate density lipoprotein (IDL), and LDL-apoB-100 using intravenous D3-leucine, GC-MS, and multicompartmental modeling. Plasma apoC-III and apoB-48 were immunoassayed. In this case control study, we report higher plasma triglyceride, IDL-, VLDL-, VLDL(1)-, and VLDL(2)-apoB-100 concentrations in CKD compared with HC (P < 0.05). This was associated with decreased fractional catabolic rates [FCRs (pools/day)] [IDL:CKD 3.4 (1.6) vs. HC 5.0 (3.2), P < 0.0001; VLDL:CKD 4.8 (5.2) vs. HC 7.8 (4.8), P = 0.038; VLDL(1):CKD 10.1 (8.5) vs. HC 29.5 (45.1), P = 0.007; VLDL(2):CKD 5.4 (4.6) vs. HC 10.4 (3.4), P = 0.001] with no difference in production rates. Plasma apoC-III and apoB-48 were significantly higher in CKD (P < 0.001) and both correlated with impaired FCRs of VLDL, VLDL(1), and VLDL(2) apoB-100 (P < 0.05). In CKD, apoC-III concentration was the only independent predictor of clearance defects in VLDL and its subfractions. Moderate CKD in the absence of central adiposity and IR is associated with mild hypertriglyceridemia due to delayed catabolism of triglyceride rich lipoproteins, IDL, and VLDL, without changes in production rate. Altered apoC-III metabolism may contribute to dyslipidemia in CKD, and this requires further investigation.

Nitric oxide-releasing agent, LA419, reduces atherogenesis in apolipoprotein E-deficient mice

LA419 is a novel nitric oxide-donor with antioxidant properties. The effect of this compound on the development of atherosclerosis was investigated in apolipoprotein E-deficient mice. Male mice were randomized to receive vehicle or 5 mg/kg/day LA419 for 12 weeks. At the end of this period, plasma lipid and lipoprotein parameters, oxidative stress markers and hepatic fat, and mRNA levels were measured as well as en face and cross-sectional lesion areas of the aorta. Data showed that LA419 administration reduced atherosclerotic foci and cross-sectional lesion areas by decreasing the intimae presence of macrophage-derived foam cells despite an increase in plasma cholesterol. This agent induced a significant reduction in body weight gain and mass of adipose tissue. Furthermore, compared with placebo, LA419 administration significantly reduced plasma triglycerides and apolipoprotein C-III levels as well as systemic oxidative stress, estimated by plasma 8-isoprostane. Conversely, nonesterified fatty acid and HDL cholesterol levels remained unchanged, as well as apolipoproteins A-I, A-IV, and B and paraoxonase activity. Plasma triglycerides were significantly associated with plasma levels of apolipoprotein C-III and hepatic Fsp27 mRNA expression. These results indicate that administration of LA419 modulates lesion development. These actions are partly independent of total cholesterol as well as HDL particles and related to triglyceridemia and oxidative stress. Hypotriglyceridemia is associated with an equal number of apoB-containing particles. Hence, LA419 administration could be used as a safe alternative to control the metabolic syndrome and atherosclerosis.

Disturbance of Apolipoprotein B100 Containing Lipoprotein Metabolism in Severe Hyperlipidemic and Lipodystrophic HIV Patients on Combined Antiretroviral Therapy: Evidences of Insulin Resistance Effect

The aim was to study the mechanisms involved in the dyslipidemia associated with lipodystrophy in HIV infected patients on antiretroviral therapy (ART). We investigated the in vivo kinetics of apolipoprotein B100 (apoB) containing lipoproteins using a 14 h primed constant infusion of [5,5,5, (2)H(3)] leucine and compartmental modelling in normolipidemic without lipodystrophy (7 patients, NLD) or dyslipidemic with lipodystrophy (7 patients, LD) treated with ART. Subjects in group LD showed higher plasma triglycerides (5.73+/-3.58 vs 1.29+/-0.54 g/L, p<0.005), total cholesterol (2.98+/-0.95 vs 1.74+/-0.26 g/L, p<0.05), apoB (1.49+/-1.11 vs 0.51+/-0.11 g/L, p<0.005) and apolipoprotein CIII in apoB containing lipoproteins (117.7+/-42.2 vs 22.6+/-23.9 g/L, p<0.005). LD subjects exhibited an insulin resistant as observed by higher HOMA (3.44+/-1.62 vs 1.60+/-0.61, p<0.05). They exhibited an increase in VLDL (1.24+/-0.33 vs 0.80+/-0.21 mg/kg/h, p<0.05), decrease in IDL (0.20+/-0.10 vs 0.48+/-0.24 mg/kg/h, p<0.05) and no difference in LDL (0.38+/-0.19 vs 0.45+/-0.25 mg/kg/h) production rate. LD subject also showed a dramatic decrease in transformation of VLDL to IDL (0.013+/-0.010 vs 0.258+/-0.206 h(-1), p<0.005) and IDL to LDL (0.088+/-0.093 vs 0.366+/-0.189 h(-1), p<0.05) and a decrease in fractional catabolic rate (FCR) of VLDL (0.199+/-0.132 vs 0.555+/-0.398 h(-1), p<0.05), IDL (0.110+/-0.08 vs 0.523+/-0.275 h(-1), p<0.05) and LDL (0.010+/-0.005 vs 0.025+/-0.014 h(-1), p<0.05). These disturbances, overproduction and an overall delayed catabolism of apoB, are similar to those observed using the same protocol in insulin resistant subjects. Our study suggests that metabolic disturbance of apoB100 observed in lipodystrophic HIV in combined antiretroviral therapy are consecutive to insulin resistance induced by the treatment.

Plasma Apolipoprotein CI and CIII Levels Are Associated With Increased Plasma Triglyceride Levels and Decreased Fat Mass in Men With the Metabolic Syndrome

OBJECTIVE—To determine whether, in accordance with observations in mouse models, high concentrations of the lipoprotein lipase inhibitors apolipoprotein (Apo) CI and ApoCIII are associated with increased triglyceride concentrations and decreased fat mass in men with the metabolic syndrome.RESEARCH DESIGN AND METHODS—Plasma ApoCI, ApoCIII, and triglyceride concentrations were measured in the postabsorptive state in 98 men with the metabolic syndrome. Subcutaneous and visceral fat areas were measured by 3T-magnetic resonance imaging.RESULTS—Triglyceride concentrations were 49% higher, and the average visceral fat area was 26% lower (both P < 0.001), in subjects with high ApoCI and ApoCIII compared with low ApoCI and ApoCIII. Subjects with either high ApoCI or ApoCIII had 16% (P < 0.05) and 18% (P < 0.01) decreased visceral fat area, respectively.CONCLUSIONS—High concentrations of ApoCI and ApoCIII are associated with increased triglycerides and decreased visceral fat mass in men with the metabolic syndrome. These findings translate mouse studies into human pathophysiology.

Inhibition of apoB secretion from HepG2 cells by insulin is amplified by naringenin, independent of the insulin receptor

Hepatic overproduction of apolipoprotein B (apoB)-containing lipoproteins is characteristic of the dyslipidemia associated with insulin resistance. Recently, we demonstrated that the flavonoid naringenin, like insulin, decreased apoB secretion from HepG2 cells by activation of both the phosphoinositide-3-kinase (PI3-K) pathway and the mitogen-activated protein kinase/extracellular-regulated kinase (MAPK(erk)) pathway. In the present study, we determined whether naringenin-induced signaling required the insulin receptor (IR) and sensitized the cell to the effects of insulin, and whether the kinetics of apoB assembly and secretion in cells exposed to naringenin were similar to those of insulin. Immunoblot analysis revealed that insulin stimulated maximal phosphorylation of IR and IR substrate-1 after 10 min, whereas naringenin did not affect either at any time point up to 60 min. The combination of naringenin and submaximal concentrations of insulin potentiated extracellular-regulated kinase 1/2 activation and enhanced upregulation of the LDL receptor, downregulation of microsomal triglyceride transfer protein expression, and inhibition of apoB-100 secretion. Multicompartmental modeling of apoB pulse-chase studies revealed that attenuation of secreted radiolabeled apoB in naringenin- or insulin-treated cells was similar under lipoprotein-deficient or oleate-stimulated conditions. Naringenin and insulin both stimulated intracellular apoB degradation via a kinetically defined rapid pathway. Therefore, naringenin, like insulin, inhibits apoB secretion through activation of both PI3-K and MAPK(erk) signaling, resulting in similar kinetics of apoB secretion. However, the mechanism for naringenin-induced signaling is independent of the IR. Naringenin represents a possible strategy for reduction of hepatic apoB secretion, particularly in the setting of insulin resistance.

Cutis laxa with frontoparietal cortical malformation: A novel type of congenital disorder of glycosylation

This report describes a female infant with cutis laxa, short stature, microcephaly, wide anterior fontanel and bifrontal cortical malformation. Isoelectrofocusing of plasma transferrin and apolipoprotein C-III showed abnormal patterns suggesting defective N- and O-glycosylation. Together with recently reported patients, this patient represents a novel type of congenital disorder of glycosylation.

Polymorphisms in the peroxisome proliferator activated receptor α gene are associated with levels of apolipoprotein CIII and triglyceride in African-Americans but not Caucasians

Background We tested whether single nucleotide polymorphisms (SNPs) in the PPARα gene ( PPARA) are associated with variations in levels of plasma apolipoprotein CIII (apoCIII) levels, as well as other lipids and lipoproteins, in African-Americans and Caucasians. Methods and results We initially identified an intronic SNP (rs4253728) in PPARA that was associated with plasma apoCIII level ( p < 0.05) in a subset of 435 individuals from the total study population ( n = 944; 335 African-Americans and 609 Caucasians). This SNP was then genotyped in a second subset of 476 individuals (total 911 subjects with available data), and a previously described PPARA coding SNP (L162V) which was shown to be in moderate linkage disequilibrium with the intronic SNP ( r 2 = 0.18) was genotyped in 928 subjects from the same study population. The minor allele frequencies for both SNPs were significantly lower in African-Americans compared with Caucasians (7.2% vs. 27.3% for rs4253728, 1.5% vs. 6.1% for L162V, both p < 0.0001). African-Americans had significantly lower levels of TG and apoCIII compared with Caucasians after adjusting for age, sex, body mass index (BMI), waist circumference and other baseline characteristics. However, racial differences in TG levels were attenuated after adjusting for apoCIII levels. The minor alleles for both PPARA SNPs were associated with higher TG and apoCIII levels. Race modified the associations of L162V with TG ( p for interaction = 0.0056) and apoCIII ( p for interaction = 0.0011). Levels of both TG and apoCIII were lower in African-American but not Caucasian homozygotes for the major allele compared with carriers of the minor allele. Similar results were obtained for the intronic SNP, but the findings were no longer significant in a model that also contained L162V. Conclusions Two PPARA SNPs, L162V and rs4253728 (intronic), are less prevalent in African-Americans than in Caucasians and in African-Americans only are associated with higher apoCIII and TG levels.

Peroxisome proliferator-activated receptor α polymorphisms and postprandial lipemia in healthy men

Peroxisome proliferator-activated receptor alpha (PPARalpha) is a ligand-dependent transcription factor that plays a key role in lipid and glucose homeostasis. This study evaluated whether variants of PPARalpha are associated with postprandial lipemia. Subjects were given a single fat load composed of 60% calories as fat, 15% as protein, and 25% as carbohydrate. Blood was drawn every hour from baseline to 6 h, then every 2.5 h to 11 h to determine triglyceride (TG) levels. The minor allele of the nonsynonymous p.Leu162Val variant was associated with higher fasting total cholesterol, LDL-cholesterol, and apolipoprotein B. There were no significant associations with all of the postprandial parameters examined. Conversely, the noncoding variant c.140+5435T>C was not associated with fasting lipid concentrations but was significantly associated with decreased postprandial TG and cholesterol in the small TG-rich lipoprotein particle. Although the minor allele carriers displayed lower mean concentrations of TG and cholesterol throughout the postprandial period, the differences were most pronounced in the latter period. These data suggest that PPARalpha variants may modulate the risk of cardiovascular disease by influencing both fasting and postprandial lipid concentrations.

Kinetics of plasma apolipoprotein C-III as a determinant of diet-induced changes in plasma triglyceride levels

To compare the effect of a high monounsaturated fatty acid (MUFA) diet and of a control low-fat diet consumed under ad libitum conditions on plasma apolipoprotein (apo) C-III metabolism. Randomized, two-arm parallel dietary trial. Diets were prepared and consumed at the metabolic kitchen of the Department of Food Sciences and Nutrition, and laboratory analyses were performed at the Institute of Nutraceuticals and Functional Foods at Laval University. Eighteen men were randomly assigned to either the high MUFA diet or the low-fat control diet, which they consumed for 6-7 weeks. Before and after the dietary intervention, subjects received a primed-constant infusion of [5,5,5-D(3)]-L-leucine for 12 h under constant feeding conditions for the determination of plasma apoC-III kinetics. The high-MUFA diet and the low-fat control diet had no significant impact on plasma apoC-III production rate (PR) or fractional catabolic rate. However, diet-induced variations in plasma apoCIII PR predicted the reduction in plasma triglycerides and apoC-III levels (r=0.85, P<0.01 and r=0.73, P<0.05, respectively) in the high MUFA group only. These results suggest that the hypotriglyceridemic effect of a high-MUFA diet may be attributable in part to a reduced hepatic production of apoC-III. This study was supported in part by an operating grant from the Canadian Institutes of Health Research (CIHR), and the Canada Research Chair in Nutrition and Cardiovascular Health (B Lamarche).

Apolipoprotein CIII-Induced THP-1 Cell Adhesion to Endothelial Cells Involves Pertussis Toxin-Sensitive G Protein- and Protein Kinase Cα-Mediated Nuclear Factor-κB Activation

Plasma apolipoprotein CIII (apoCIII) independently predicts risk for coronary heart disease (CHD). We recently reported that apoCIII directly enhances adhesion of human monocytes to endothelial cells (ECs), and identified the activation of PKC alpha as a necessary upstream event of enhanced monocyte adhesion. This study tested the hypothesis that apoCIII activates PKC alpha in human monocytic THP-1 cells, leading to NF-kappaB activation. Among inhibitors specific to PKC activators, phosphatidylcholine-specific phospholipase C (PC-PLC) inhibitor D609 limited apoCIII-induced PKC alpha activation and THP-1 cell adhesion. ApoCIII increased PC-PLC activity in THP-1 cells, resulting in PKC alpha activation. Pertussis toxin (PTX) inhibited apoCIII-induced PC-PLC activation and subsequent PKC alpha activation, implicating PTX-sensitive G protein pathway. ApoCIII further activated nuclear factor-kappaB (NF-kappaB) through PKC alpha in THP-1 cells and augmented beta1-integrin expression. The NF-kappaB inhibitor peptide SN50 partially inhibited apoCIII-induced beta1-integrin expression and THP-1 cell adhesion. ApoCIII-rich VLDL had similar effects to apoCIII alone. PTX-sensitive G protein pathway participates critically in PKC alpha stimulation in THP-1 cells exposed to apoCIII, activating NF-kappaB, and increasing beta1-integrin. This action causes monocytic cells to adhere to endothelial cells. Furthermore, because leukocyte NF-kappaB activation contributes to inflammatory aspects of atherogenesis, apoCIII may stimulate diverse inflammatory responses through monocyte activation.

Variations in plasma apolipoprotein C-III levels are strong correlates of the triglyceride response to a high-monounsaturated fatty acid diet and a high-carbohydrate diet

The objective of this study was to examine how a diet rich in carbohydrates (high-CHO) vs a diet rich in monounsaturated fatty acids (high MUFA) consumed ad libitum modulated plasma apolipoprotein C-III (apo C-III) levels and to examine the extent to which diet-induced changes in plasma apo C-III were associated with concurrent variations in plasma triglyceride (TG) levels. Forty-seven men (mean age, 35.7 ± 11.4 years; body mass index, 29.0 ± 5.1 kg/m 2) were randomly assigned to either a high-CHO diet (CHO, 58%; fat, 26%; n = 23) or a high-MUFA diet (CHO, 45%; fat, 40%; MUFA, 22.5%; n = 24), which they consumed for 6 to 7 weeks. Fasting and postprandial lipemia after an oral fat load and fasting plasma apo C-III were measured at the beginning and at the end of the dietary intervention. Ad libitum consumption of the high-CHO diet induced a significant reduction in body weight (−2.6%, P < .0001), but had no impact on plasma apo C-III concentrations and on fasting and postprandial plasma TG levels. In contrast, ad libitum consumption of the high-MUFA diet also resulted in a significant reduction in body weight (−2.3%, P < .01) as well as in significant reductions in plasma apo C-III (−11%, P = .05) and fasting plasma TG (−17%, P < .01). Diet-induced variations in plasma apo C-III concentrations were correlated with changes in fasting and postprandial TG levels both in the high-CHO ( r > 0.70, P < .001) and the high-MUFA groups ( r > 0.42, P < .05). These results indicate that variations in plasma apo C-III levels are strong correlates of the fasting and postprandial plasma TG responses to high-MUFA and high-CHO diets.

Patients with unsolved congenital disorders of glycosylation type II can be subdivided in six distinct biochemical groups

Defects in the biosynthesis of N- and core 1 O-glycans may be found by isoelectric focusing (IEF) of plasma transferrin and apolipoprotein C-III (apoC-III). We hypothesized that IEF of transferrin and apoC-III in combination with sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) of apoC-III may provide a classification for congenital disorders of glycosylation (CDG) patients. We analyzed plasma from 22 patients with eight different and well-characterized CDG subtypes and 19 cases with unsolved CDG. Transferrin IEF (TIEF) has been used to distinguish between N-glycan assembly (type 1 profile) and processing (type 2 profile) defects. We differentiated two different CDG type 2 TIEF profiles: The "asialo profile" characterized by elevated levels of asialo- and monosialotransferrin and the "disialo profile" characterized by increased levels of disialo- and trisialotransferrin. ApoC-III IEF gave two abnormal profiles ("apoC-III(0)" and "apoC-III(1)" profiles). The results for the eight established CDG forms exactly matched the theoretical expectations, providing a validation for the study approach. The combination of the three electrophoretic techniques was not additionally informative for the CDG-Ix patients as they had normal apoC-III IEF patterns. However, the CDG-IIx patients could be further subdivided into six biochemical subgroups. The robustness of the methodology was supported by the fact that three patients with similar clinical features ended in the same subgroup and that another patient, classified in the "CDG-IIe subgroup," turned out to have a similar defect. Dividing the CDG-IIx patients in six subgroups narrows down drastically the options of the primary defect in each of the subgroups and will be helpful to define new CDG type II defects.

Polyunsaturated Fatty Acids Interact with the PPARA-L162V Polymorphism to Affect Plasma Triglyceride and Apolipoprotein C-III Concentrations in the Framingham Heart Study

Peroxisome proliferator-activated receptor alpha (PPARalpha) is a nuclear transcription factor regulating multiple genes involved in lipid metabolism. It was shown that a common leucine to valine (L162V) substitution at the PPARalpha gene (PPARA) is functional and affects transactivation activity of PPARalpha ligands, such as PUFA, on a concentration-dependent basis. The current study examined this gene-nutrient interaction in relation to plasma lipid variables in a population-based study consisting of 1003 men and 1103 women participating in the Framingham cohort and consuming their habitual diets. We found significant gene-nutrient interactions between the L162V polymorphism and total PUFA intake, which modulated plasma triglycerides (TG; P < 0.05) and apolipoprotein C-III (apoC-III; P < 0.05) concentrations. The 162V allele was associated with greater TG and apoC-III concentrations only in subjects consuming a low-PUFA diet (below the population mean, 6% of energy). However, when PUFA intake was high, carriers of the 162V allele had lower apoC-III concentrations. This interaction was significant even when PUFA intake was considered as a continuous variable (P = 0.031 for TG and P < 0.001 for apoC-III), suggesting a strong dose-response effect. When PUFA intake was <4%, 162V allele carriers had approximately 28% higher plasma TG than did 162L homozygotes (P < 0.01). Conversely, when PUFA intake was >8%, plasma TG in 162V allele carriers was 4% lower than in 162L homozygotes. Similar results were obtained for (n-6) and (n-3) fatty acids. Our data show that the effect of the L162V polymorphism on plasma TG and apoC-III concentrations depends on the dietary PUFA, with a high intake triggering lower TG in carriers of the 162V allele.

A combined defect in the biosynthesis of N- and O-glycans in patients with cutis laxa and neurological involvement: the biochemical characteristics

Based on our preliminary observation of abnormal glycosylation in a cutis laxa patient, nine cutis laxa patients were analyzed for congenital defects of glycosylation (CDG). Isoelectric focusing of plasma transferrin and apolipoproteinC-III showed that three out of nine patients had a defect in the biosynthesis of N-glycans and core 1 mucin type O-glycans, respectively. Mass spectrometric N-glycan analyses revealed a relative increase of glycans lacking sialic acid and glycans lacking sialic acid and galactose residues. Mutation analysis of the fibulin-5 gene (FBLN5), which has been reported in cases of autosomal recessive cutis laxa, revealed no mutations in the patients' DNA. Evidence is presented that extracellular matrix (ECM) proteins of skin are likely to be highly glycosylated with N- and/or mucin type O-glycans by using algorithms for predicting glycosylation. The conclusions in this study were that the clinical phenotype of autosomal recessive cutis laxa seen in three patients is not caused by mutations in the FBLN5 gene. Our findings define a novel form of CDG with cutis laxa and neurological involvement due to a defect in the sialylation and/or galactosylation of N- and O-glycans. Improper glycosylation of ECM proteins of skin may form the pathophysiological basis for the cutis laxa phenotype.

THE APOLIPOPROTEIN CIII T-2854G VARIANTS MODULATE FASTING AND POSTPRANDIAL TRIGLYCERIDE CONCENTRATIONS, BUT NOT EXERCISE-INDUCED HYPOTRIGLYCERIDEMIA

Elevated triglyceride (TG) and reduced HDLC in fasting plasma are the major risk factors of nonfatal myocardial infarction and coronary artery disease. Plasma apolipoprotein CIII (apoCIII) can play an important role in TG metabolism and thereby TG concentrations in circulating plasma. PURPOSE To study an influence of the apoCIII T-2854G variants on fasting and postprandial TG concentrations and exercise-induced hypotriglyceridemia. METHODS Healthy Korean men (n = 120) participated in the study. Polymerase chain reaction followed by a restriction fragment length genotyping was performed. PCR products were digested with 7 units of Alw26I (MBI Fermentas, USA) for 2 hr at 37°C. Digested fragments were separated by 2% agarose gel and visualized by ethidium bromide staining. A subgroup of 30 subjects (10 = GG homozygotes, 10 = GT heterozygotes, 10 = TT homozygotes) was further invited to participate in two separate fat-meal tests performed before and after 3-d exercise. Fasting and postprandial blood samples were collected for TG, TC, HDLC, and LDLC measurements. RESULTS No significant deviation from Hardy-Weinberg equilibrium was observed in the study population. The GG allele carriers, compared to the TT or GT allele carriers, had significantly higher TG and lower HDLC concentrations in fasting plasma (p < 0.05) and higher postprandial TG concentrations after a fat meal test performed before the 3-d exercise (p < 0.05). However, there were no significant differences among the specific allele carriers in postprandial TG concentrations during a fat meal test performed after the 3-day exercise. CONCLUSION This study suggests that while the T-2854G polymorphism is an important modulator of fasting and postprandial TG metabolism, other factors may be more important in determining exercise-induced hypotriglyceridemia in Korean adults.

APOLIPOPROTEIN C-III AND THE METABOLIC SYNDROME IN POSTMENOPAUSAL SEDENTARY WOMEN

It has been shown that apolipoprotein C-III (apo C-III) inhibits the uptake of the triglyceride-rich (Tg) very low density lipoproteins (VLDL) by the liver and also inhibits lipoprotein lipase activity in vivo. These two factors may induce hypertriglyceridaemia, a biological marker of the metabolic syndrome. PURPOSE: To analyse the association between plasma triglycerides (Tg) and apolipoprotein C-III (apo C-III) and study the relationship between these measures and other cardiovascular risk factors that characterize the metabolic syndrome (high density lipoprotein cholesterol [HDL-chol], insulin, and low density lipoprotein cholesterol (LDL-chol]) in postmenopausal women. METHODS: Subjects were 123 women (age: 61.2 ± 6.3 years; weight: 66.5 ± 11.5 kg; height: 154.1 ± 5.9 cm; BMI: 27.9 ± 4.3 kg/m2), 35 of whom were on hormone replacement therapy (HRT). Tg and HDL-chol were quantified by enzymatic colorimetric methods, LDL-Chol was calculated with the Friedwald equation, insulin was determined by RIA, and apo C-III assessed with a immunoturbidimetric assay. RESULTS: Positive partial correlations, controlling for age and HRT, were observed between apo C-III and triglycerides, r = 0.31, p < 0.05. Tg was significantly (p < 0.05) associated with HDL-chol (r = −0.55), insulin (r = 0.47) and LDL-chol (r = 0.21), while apo C-III was not related (p > 0.05) with HDL-chol, insulin, and LDL-chol. CONCLUSION: In this sample of postmenopausal sedentary women with and without HRT, apo C-III was directly associated with Tg but not with any other marker of the metabolic syndrome. Triglyceride level was associated with these variables, reinforcing the current knowledge that hypertriglyceridaemia tends to cluster with high levels of LDL-chol, hyperinsulinemia, and low levels of HDL-chol. Apo C-III may have a regulatory effect that influences Tg levels, suggesting that it has an indirect role within the scope of the metabolic syndrome.