Catabolism Of Lipoproteins Research Articles

Structure-function analyses of microsomal triglyceride transfer protein missense mutations in abetalipoproteinemia and hypobetalipoproteinemia subjects

We describe two new hypolipidemic patients with very low plasma triglyceride and apolipoprotein B (apoB) levels with plasma lipid profiles similar to abetalipoproteinemia (ABL) patients. In these patients, we identified two previously uncharacterized missense mutations in the microsomal triglyceride transfer protein (MTP) gene, R46G and D361Y, and studied their functional effects. We also characterized three missense mutations (H297Q, D384A, and G661A) reported earlier in a familial hypobetalipoproteinemia patient. R46G had no effect on MTP expression or function and supported apoB secretion. H297Q, D384A, and G661A mutants also supported apoB secretion similarly to WT MTP. Contrary to these four missense mutations, D361Y was unable to support apoB secretion. Functional analysis revealed that this mutant was unable to bind protein disulfide isomerase (PDI) or transfer lipids. The negative charge at residue 361 was critical for MTP function as D361E was able to support apoB secretion and transfer lipids. D361Y most likely disrupts the tightly packed middle α-helical region of MTP, mitigates PDI binding, abolishes lipid transfer activity, and causes ABL. On the other hand, the hypolipidemia in the other two patients was not due to MTP dysfunction. Thus, in this study of five missense mutations spread throughout MTP's three structural domains found in three hypolipidemic patients, we found that four of the mutations did not affect MTP function. Thus, novel mutations that cause severe hypolipidemia probably exist in other genes in these patients, and their recognition may identify novel proteins involved in the synthesis and/or catabolism of plasma lipoproteins.

Triglyceride-Rich Lipoproteins and Remnants: Targets for Therapy?

It is now evident that elevated circulating levels of triglycerides in the non-fasting state, a marker for triglyceride (TG)-rich remnant particles, are associated with increased risk of premature cardiovascular disease (CVD). Recent findings from basic and clinical studies have begun to elucidate the mechanisms that contribute to the atherogenicity of these apoB-containing particles. Here, we review current knowledge of the formation, intravascular remodelling and catabolism of TG-rich lipoproteins and highlight (i) the pivotal players involved in this process, including lipoprotein lipase, glycosylphosphatidylinositol HDL binding protein 1 (GPIHBP1), apolipoprotein (apo) C-II, apoC-III, angiopoietin-like protein (ANGPTL) 3, 4 and 8, apoA-V and cholesteryl ester transfer protein; (ii) key determinants of triglyceride (TG) levels and notably rates of production of very-low-density lipoprotein 1 (VLDL1) particles; and (iii) the mechanisms which underlie the atherogenicity of remnant particles. Finally, we emphasise the polygenic nature of moderate hypertriglyceridemia and briefly discuss modalities for its clinical management. Several new therapeutic strategies to attenuate hypertriglyceridemia have appeared recently, among which those targeted to apoC-III appear to hold considerable promise.

Abstract 192: Characterization of Microsomal Triglyceride Transfer Protein Missense Mutations Found in Abetalipoproteinemia and Hybobetalipoproteinemia Subjects

We describe two new hypolipidemic patients with very low plasma triglyceride and apolipoprotein B (apoB) levels and lipid malabsorption with plasma lipid profiles similar to abetalipoproteinemia (ABL) patients. In these patients, we identified two previously uncharacterized missense mutations in the microsomal triglyceride transfer protein (MTP) gene, R46G and D361Y, and studied their effects on function. We also characterized three missense mutations (H297Q, D384A, and G661A) reported earlier in a familial hypobetalipoproteinemia patient. R46G had no effect on MTP expression or function and supported apoB secretion. Similarly, H297Q, D384A, and G661A mutants supported apoB secretion similarly to WT MTP. Contrary to these four missense mutations, D361Y was unable to support apoB secretion. Functional analysis revealed that this mutant was unable to bind protein disulfide isomerase (PDI) or transfer lipids. The negative charge at residue 361 was critical for MTP function as D361E was able to support apoB secretion and transfer lipids. D361Y most likely disrupts the tightly packed middle α-helical region of MTP, mitigates PDI binding, abolishes lipid transfer activity, and causes ABL. On the other hand, the hypolipidemia in the other two patients was not due to MTP dysfunction. Thus, in this study of five missense mutations spread throughout MTP’s three structural domains found in three hypolipidemic patients, we found that four of the mutations did not affect MTP function. Thus, there probably exist novel mutations in other genes that cause severe hypolipidemia and their recognition may identify novel proteins involved in the synthesis and/or catabolism of plasma lipoproteins.

Genetic and Functional investigation of LPL Independent Pathways of TG-Rich Lipoproteins Catabolism in Severe Hypertriglyceridemia and Chylomicronemia

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Mutations causative of familial hypercholesterolaemia: screening of 98 098 individuals from the Copenhagen General Population Study estimated a prevalence of 1 in 217.

Ideally, familial hypercholesterolaemia (FH) is diagnosed by testing for mutations that decrease the catabolism of low-density lipoprotein (LDL) cholesterol; however, genetic testing is not universally available. The aim of the present study was to assess the frequency and predictors of FH causing mutations in 98 098 participants from the general population, the Copenhagen General Population Study. We genotyped for LDLR[W23X;W66G;W556S] and APOB[R3500Q] accounting for 38.7% of pathogenic FH mutations in Copenhagen. Clinical FH assessment excluded mutation information. The prevalence of the four FH mutations was 0.18% (1:565), suggesting a total prevalence of FH mutations of 0.46% (1:217). Using the Dutch Lipid Clinic Network (DLCN) criteria, odds ratios for an FH mutation were 439 (95% CI: 170-1 138) for definite FH, 90 (53-152) for probable FH, and 18 (13-25) for possible FH vs. unlikely FH. Using the Simon Broome criteria, the odds ratio was 27 (20-36) for possible vs. unlikely FH, and using the Make Early Diagnosis to Prevent Early Death (MEDPED) criteria, 40 (28-58) for probable vs. unlikely FH. Odds ratios for an FH mutation were 17 (9-31) for LDL-cholesterol of 4-4.9 mmol/L, 69 (37-126) for LDL-cholesterol of 5-5.9 mmol/L, 132 (66-263) for LDL-cholesterol of 6-6.9 mmol/L, 264 (109-637) for LDL-cholesterol of 7-7.9 mmol/L, and 320 (129-798) for LDL-cholesterol above 7.9 mmol/L vs. LDL-cholesterol below 4 mmol/L. The most optimal threshold for LDL-cholesterol concentration to discriminate between mutation carriers and non-carriers was 4.4 mmol/L. Familial hypercholesterolaemia-causing mutations are estimated to occur in 1:217 in the general population and are best identified by a definite or probable phenotypic diagnosis of FH based on the DLCN criteria or an LDL-cholesterol above 4.4 mmol/L.

FGF21 Lowers Plasma Triglycerides by Accelerating Lipoprotein Catabolism in White and Brown Adipose Tissues

FGF21 decreases plasma triglycerides (TGs) in rodents and humans; however, the underlying mechanism or mechanisms are unclear. In the present study, we examined the role of FGF21 in production and disposal of TG-rich lipoproteins (TRLs) in mice. Treatment with pharmacological doses of FGF21 acutely reduced plasma non-esterified fatty acids (NEFAs), liver TG content, and VLDL-TG secretion. In addition, metabolic turnover studies revealed that FGF21 facilitated the catabolism of TRL in white adipose tissue (WAT) and brown adipose tissue (BAT). FGF21-dependent TRL processing was strongly attenuated in CD36-deficient mice and transgenic mice lacking lipoprotein lipase in adipose tissues. Insulin resistance in diet-induced obese and ob/ob mice shifted FGF21 responses from WAT toward energy-combusting BAT. In conclusion, FGF21 lowers plasma TGs through a dual mechanism: first, by reducing NEFA plasma levels and consequently hepatic VLDL lipidation and, second, by increasing CD36 and LPL-dependent TRL disposal in WAT and BAT.

Increased HDL Size and Enhanced Apo A‐I Catabolic Rates Are Associated With Doxorubicin‐Induced Proteinuria in New Zealand White Rabbits

The catabolism and structure of high-density lipoproteins (HDL) may be the determining factor of their atheroprotective properties. To better understand the role of the kidney in HDL catabolism, here we characterized HDL subclasses and the catabolic rates of apo A-I in a rabbit model of proteinuria. Proteinuria was induced by intravenous administration of doxorubicin in New Zealand white rabbits (n = 10). HDL size and HDL subclass lipids were assessed by electrophoresis of the isolated lipoproteins. The catabolic rate of HDL-apo A-I was evaluated by exogenous radiolabelling with iodine-131. Doxorubicin induced significant proteinuria after 4 weeks (4.47 ± 0.55 vs. 0.30 ± 0.02 g/L of protein in urine, P < 0.001) associated with increased uremia, creatininemia, and cardiotoxicity. Large HDL2b augmented significantly during proteinuria, whereas small HDL3b and HDL3c decreased compared to basal conditions. HDL2b, HDL2a, and HDL3a subclasses were enriched with triacylglycerols in proteinuric animals as determined by the triacylglycerol-to-phospholipid ratio; the cholesterol content in HDL subclasses remained unchanged. The fractional catabolic rate (FCR) of [(131)I]-apo A-I in the proteinuric rabbits was faster (FCR = 0.036 h(-1)) compared to control rabbits group (FCR = 0.026 h(-1), P < 0.05). Apo E increased and apo A-I decreased in HDL, whereas PON-1 activity increased in proteinuric rabbits. Proteinuria was associated with an increased number of large HDL2b particles and a decreased number of small HDL3b and 3c. Proteinuria was also connected to an alteration in HDL subclass lipids, apolipoprotein content of HDL, high paraoxonase-1 activity, and a rise in the fractional catabolic rate of the [(131)I]-apo A-I.

Understanding of Diabetic Dyslipidemia by Using the Anion-Exchange High Performance Liquid Chromatography Data.

Type 2 diabetes and dyslipidemia are cardiovascular risk factors which should be managed [1]. However, the precise lipoprotein profiles and the underlying mechanisms for diabetic dyslipidemia remain largely unknown. We previously developed an anion-exchange liquid chromatographic method (AEX-HPLC) which can measure cholesterol levels of triglyceride (TG)-rich lipoproteins such as very low-density lipoprotein (VLDL), intermediate-density lipoprotein (IDL) and chylomicron (CM) in addition to low-density lipoprotein (LDL) and high-density lipoprotein (HDL) [2]. Here we compared lipoprotein profiles obtained by our previous studies using AEX-HPLC in young lean men [3], subjects with low Framingham risk score (FRS) [4, 5], type 2 diabetic patients without obesity and type 2 diabetic patients with obesity [6, 7]. The mean ± SD values of age, body mass index, HbA1c in in young lean men (n = 7) [3], low FRS subjects (n = 304) [4], type 2 diabetic patients without obesity (n = 194) [6], and type 2 diabetic patients with obesity (n = 5) [7] were 24 ± 2, 51 ± 8, 63 ± 13, and 60 ± 9 years old, 20.8 ± 2.2, 23.8 ± 3.0, 23.1 ± 2.0, and 29.5 ± 7.0 kg/m2, 5.0 ± 0.2, 5.4 ± 0.5, 6.3 ± 1.0, and 9.1±2.1%, respectively. HDL-cholesterol (HDL-C) in type 2 diabetes (49.9 ± 16.6 mg/dL (1.29 ± 0.43 mmol/L)), especially in type 2 diabetic patients with obesity (36.4 ± 5.3 mg/dL (0.94 ± 0.14 mmol/L)) was lower than young lean men (59.4 ± 10.1 mg/dL (1.54 ± 0.26 mmol/L)) and low FRS subjects (57.6 ± 14.7 mg/dL (1.49 ± 0.38 mmol/L)). IDL-C in type 2 diabetes was higher than other two groups, and IDL-C was higher in the order of type 2 diabetic patients with obesity (9.8 ± 3.0 mg/dL (0.25 ± 0.08 mmol/L)), type 2 diabetic patients without obesity (9.3 ± 4.6 mg/dL (0.24 ± 0.12 mmol/L)), low FRS subjects (7.3 ± 3.1 mg/ dL (0.19 ± 0.08 mmol/L)), young lean men (4.3 ± 2.2 mg/dL (0.11 ± 0.06 mmol/L)). VLDL-C clearly showed higher values in the order of type 2 diabetic patients with obesity (27.3 ± 22.7 mg/dL (0.71 ± 0.59 mmol/L)), type 2 diabetic patients without obesity (20.1 ± 16.2 mg/dL (0.52 ± 0.42 mmol/L)), low FRS subjects (16.6 ± 12.8 mg/dL (0.43 ± 0.33 mmol/L)), and young lean men (4.0 ± 4.6 mg/dL (0.10 ± 0.12 mmol/L)). LDL-C and CM-C did not show the characteristic profile for diabetes. According to accumulation of our previous AEX-HPLC data [3, 4, 6, 7], the characteristics in diabetic dyslipidemia is reduced HDL-C, and increased IDL-C and VLDL-C, which is further deteriorated by complication with obesity. Relative insulin deficiency due to insulin resistance increases activity and expression of hormone-sensitive lipase (HSL) in adipose tissue, which catalyzes the breakdown of TG, releasing free fatty acids (FFA) (Fig. 1) [8]. Insulin promotes apoB100 degradation, and hepatic insulin resistance causes reduction of apoB100 degradation [9]. Insulin resistance also induces an enhanced expression of microsomal TG transfer protein (MTP), a key enzyme involved in VLDL assembly [10]. In type 2 diabetes, increased FFA entry to liver, reduced degradation of apoB100 and enhanced expression of MTP may elevate hepatic production of VLDL. Relative insulin deficiency also decreases the activity of lipoprotein lipase (LPL), the rate-limiting enzyme of the catabolism of TG-rich lipoproteins such as CM, VLDL and IDL [11]. The formation of HDL is related with the catabolism of TG-rich lipoproteins by LPL [12]. Therefore, reduced LPL activity increases IDL and VLDL, and reduces HDL. The activity of hepatic TG lipase (HTGL), the enzyme that facilitates the catabolism of HDL, is correlated with insulin requirement [13]. In type 2 diabetes, low serum HDL-C may be partially due to an increased rate of clearance by HTGL [13]. LDL size and buoyancy are inversely proportional to HTGL activity [14], and patients with high HTGL have smaller, denser LDL particles, as compared with subjects with low HTGL activity [15]. Increased HTGL activity due Manuscript accepted for publication March 03, 2016

Abstract 18667: Lipoprotein(a) Catabolism and Apolipoprotein(a) Secretion is Regulated by Sortilin

Elevated levels of lipoprotein(a) (Lp(a)) in plasma have been identified as an independent, causal risk factor for coronary heart disease. Lp(a) consists of a low-density lipoprotein (LDL)-like particle whose apolipoproteinB-100 (apoB-100) moiety is covalently linked to the unique glycoprotein apolipoprotein(a) (apo(a)). Recently, Lp(a) internalization by the LDL-receptor (LDLr) in hepatic cells and primary human fibroblasts has been shown to be regulated by proprotein convertase subtilisin/kexin type 9 (PCSK9). However, Lp(a)/apo(a) internalization still occurs even with a defective LDLr or in the presence of PCSK9 (in fibroblasts and hepatic cells, respectively), indicating a role for receptors other than the LDLr in Lp(a) catabolism. Hepatic sortilin has been identified as a potential receptor mediating LDL catabolism as well as the regulation of apoB-100 secretion. Sortilin localizes to the Golgi apparatus where it mediates trafficking of specific bound ligands to the lysosome. Sortilin also localizes to clathrin-coated pits in the plasma membrane where it can act as an internalization receptor. We demonstrate in the current study that Lp(a), but not apo(a), internalization in hepatic cells is influenced by sortilin overexpression. In the presence of PCSK9, Lp(a) internalization greatly increases with sortilin overexpression compared to control. These results suggest that hepatic sortilin has the ability to act as a receptor for Lp(a) catabolism, through the LDL-like moiety, in a manner that is not dependent on the LDLr. Furthermore, Lp(a) internalization increases with sortilin overexpression in primary human fibroblasts with a defective LDLr, again emphasizing an LDLr-independent role for sortilin as a receptor for Lp(a). Interestingly, an increase in apo(a) secretion is observed with sortilin overexpression in hepatic cells. Removal of the carboxyl-terminal tail of sortilin results in an inability to promote the secretion of apo(a), indicating a direct role for the sorting motifs present in this region of sortilin for the regulation of apo(a) secretion. Taken together, these results indicate novel roles for sortilin in both Lp(a) catabolism and apo(a) secretion.

PCSK9 inhibitors and cardiovascular disease: heralding a new therapeutic era.

Purpose of reviewThe first monoclonal antibodies targeting proprotein convertase subtilisin/kexin type 9 (PCSK9) have been approved for clinical use. This timely review highlights recent developments.Recent findingsLow-density lipoprotein cholesterol (LDL-C) is the primary driver of atherosclerosis and the key target for intervention. Yet despite best treatment including statins, attaining sufficient LDL-C lowering can be problematic for high cardiovascular risk patients. The development of PCSK9 inhibitors, driven by novel genetic and mechanistic insights, offers an answer. Removal of circulating PCSK9 increases LDL receptor availability, and thus markedly decreases plasma LDL-C levels (by ∼50–60%), and is additive to the lipid lowering effects of statins and ezetimibe. PCSK9 inhibition also reduces (by 25–30%) plasma levels of lipoprotein(a), a causal factor in atherosclerotic vascular disease, suggestive of partial catabolism of lipoprotein(a) by LDL receptors. The ODYSSEY and PROFICIO (Programme to Reduce LDL-C and Cardiovascular Outcomes Following Inhibition of PCSK9 In Different Populations) clinical trial programmes involving a wide range of high-risk patients, including statin intolerant patients, have confirmed the consistency of the LDL response, even with concomitant high-intensity statin or nonstatin therapy. Extensive evidence to date attests to a favourable safety and tolerability profile for these innovative agents.SummaryThe new pharmacotherapeutic era of PCSK9 inhibition is upon us, promising major reduction in cardiovascular events across a wide spectrum of high-risk patients.

Gender specific effect of LIPC C-514T polymorphism on obesity and relationship with plasma lipid levels in Chinese children.

Hepatic lipase (LIPC) is a key rate-limiting enzyme in lipoprotein catabolism pathways involved in the development of obesity. The C-514T polymorphism in the promoter region is associated with decreased LIPC activity. We performed a case-controlled study (850 obese children and 2119 controls) and evaluated the association between LIPC C-514T polymorphism, obesity and plasma lipid profile in Chinese children and adolescents. Additionally, we conducted a meta-analysis of all results from published studies as well as our own data. A significant association between the polymorphism and obesity is observed in boys (P = 0.042), but not in girls. And we observed a significant relationship of the polymorphism with total cholesterol (TC) and high density lipoprotein cholesterol (HDL-C) independent of obesity in boys. The T allele carriers have higher levels of low density lipoprotein cholesterol (LDL-C) in obese boys, and triglyceride (TG), TC and LDL-C in non-obese girls (all P < 0.05). In the meta-analysis, under dominant model the T allele increased body mass index (BMI) level in boys, while it decreased BMI in girls, and increased the levels of TC both in the overall and subgroups, TG and HDL-C in the overall and boys, and LDL-C in the overall (all P < 0.05). Our results suggest that the T allele might carry an increased risk of obesity in Chinese boys. The meta-analysis suggests that T allele acts as a risk allele for higher BMI levels in male childhood, while it is a protective allele in female childhood. And the polymorphism is associated with the levels of plasma lipids, which may be modulated by obesity and gender.

Dietary Lipid Levels Influence Lipid Deposition in the Liver of Large Yellow Croaker (Larimichthys crocea) by Regulating Lipoprotein Receptors, Fatty Acid Uptake and Triacylglycerol Synthesis and Catabolism at the Transcriptional Level.

Ectopic lipid accumulation has been observed in fish fed a high-lipid diet. However, no information is available on the mechanism by which dietary lipid levels comprehensively regulate lipid transport, uptake, synthesis and catabolism in fish. Therefore, the present study aimed to gain further insight into how dietary lipids affect lipid deposition in the liver of large yellow croaker(Larimichthys crocea). Fish (150.00±4.95 g) were fed a diet with a low (6%), moderate (12%, the control diet) or high (18%) crude lipid content for 10 weeks. Growth performance, plasma biochemical indexes, lipid contents and gene expression related to lipid deposition, including lipoprotein assembly and clearance, fatty acid uptake and triacylglycerol synthesis and catabolism, were assessed. Growth performance was not significantly affected. However, the hepato-somatic and viscera-somatic indexes as well as plasma triacylglycerol, non-esterified fatty acids and LDL-cholesterol levels were significantly increased in fish fed the high-lipid diet. In the livers of fish fed the high-lipid diet, the expression of genes related to lipoprotein clearance (LDLR) and fatty acid uptake (FABP11) was significantly up-regulated, whereas the expression of genes involved in lipoprotein assembly (apoB100), triacylglycerol synthesis and catabolism (DGAT2, CPT I) was significantly down-regulated compared with fish fed the control diet, and hepatic lipid deposition increased. In fish fed the low-lipid diet, the expression of genes associated with lipoprotein assembly and clearance (apoB100, LDLR, LRP-1), fatty acid uptake (CD36, FATP1, FABP3) and triacylglycerol synthesis (FAS) was significantly increased, whereas the expression of triacylglycerol catabolism related genes (ATGL, CPT I) was reduced compared with fish fed the control diet. However, hepatic lipid content in fish fed the low-lipid diet decreased mainly due to low dietary lipid intake. In summary, findings of this study provide molecular insight into the role of lipid deposition in the liver in response to different dietary lipid contents.

Effect of dietary Fatty acids on human lipoprotein metabolism: a comprehensive update.

Dyslipidemia is a major risk factor for cardiovascular disease (CVD). Dietary fatty-acid composition regulates lipids and lipoprotein metabolism and may confer CVD benefit. This review updates understanding of the effect of dietary fatty-acids on human lipoprotein metabolism. In elderly participants with hyperlipidemia, high n-3 polyunsaturated fatty-acids (PUFA) consumption diminished hepatic triglyceride-rich lipoprotein (TRL) secretion and enhanced TRL to low-density lipoprotein (LDL) conversion. n-3 PUFA also decreased TRL-apoB-48 concentration by decreasing TRL-apoB-48 secretion. High n-6 PUFA intake decreased very low-density lipoprotein (VLDL) cholesterol and triglyceride concentrations by up-regulating VLDL lipolysis and uptake. In a study of healthy subjects, the intake of saturated fatty-acids with increased palmitic acid at the sn-2 position was associated with decreased postprandial lipemia. Low medium-chain triglyceride may not appreciably alter TRL metabolism. Replacing carbohydrate with monounsaturated fatty-acids increased TRL catabolism. Trans-fatty-acid decreased LDL and enhanced high-density lipoprotein catabolism. Interactions between APOE genotype and n-3 PUFA in regulating lipid responses were also described. The major advances in understanding the effect of dietary fatty-acids on lipoprotein metabolism has centered on n-3 PUFA. This knowledge emphasizes the importance of regulating lipoprotein metabolism as a mode to improve plasma lipids and potentially CVD risk. Additional studies are required to better characterize the cardiometabolic effects of other dietary fatty-acids.

Lipoprotein(a) Catabolism Is Regulated by Proprotein Convertase Subtilisin/Kexin Type 9 through the Low Density Lipoprotein Receptor

Elevated levels of lipoprotein(a) (Lp(a)) have been identified as an independent risk factor for coronary heart disease. Plasma Lp(a) levels are reduced by monoclonal antibodies targeting proprotein convertase subtilisin/kexin type 9 (PCSK9). However, the mechanism of Lp(a) catabolism in vivo and the role of PCSK9 in this process are unknown. We report that Lp(a) internalization by hepatic HepG2 cells and primary human fibroblasts was effectively reduced by PCSK9. Overexpression of the low density lipoprotein (LDL) receptor (LDLR) in HepG2 cells dramatically increased the internalization of Lp(a). Internalization of Lp(a) was markedly reduced following treatment of HepG2 cells with a function-blocking monoclonal antibody against the LDLR or the use of primary human fibroblasts from an individual with familial hypercholesterolemia; in both cases, Lp(a) internalization was not affected by PCSK9. Optimal Lp(a) internalization in both hepatic and primary human fibroblasts was dependent on the LDL rather than the apolipoprotein(a) component of Lp(a). Lp(a) internalization was also dependent on clathrin-coated pits, and Lp(a) was targeted for lysosomal and not proteasomal degradation. Our data provide strong evidence that the LDLR plays a role in Lp(a) catabolism and that this process can be modulated by PCSK9. These results provide a direct mechanism underlying the therapeutic potential of PCSK9 in effectively lowering Lp(a) levels.

Circulating PCSK9 levels are positively correlated with NMR-assessed atherogenic dyslipidaemia in patients with high cardiovascular risk.

The proprotein convertase subtilisin/kexin type 9 (PCSK9) gene regulates cholesterol homoeostasis by accelerating low-density lipoprotein receptor (LDLR) degradation resulting in the decreased catabolism of low-density lipoprotein (LDL) leading to hypercholesterolaemia. PCSK9 has also been related to other metabolic risk factors such as triglycerides (TGs) and glucose levels and body mass index (BMI). Therefore, our aim was to study the relationship between the PCSK9 and the lipid and lipoprotein profile. We studied 267 diabetic and metabolic syndrome patients who were not receiving any lipid-lowering therapy. We measured circulating lipids, cholesterol in remnant lipoproteins (RLPc) and PCSK9 levels. A detailed lipoprotein profile was determined based on NMR. Plasma PCSK9 levels were significantly and positively correlated with TG (r=0.136, P=0.033), total cholesterol (r=0.219, P<0.001) and apoB (apolipoprotein B; r=0.226, P=0.006) circulating levels and with an atherogenic profile of lipoprotein subclasses. In further detail, circulating PCSK9 levels were positively correlated with large very-low density lipoprotein (VLDL) particles, (r=0.210, P=0.001) and with their remnants, the intermediate-density lipoprotein (IDL) particles (r=0.206, P=0.001); positively correlated with smaller LDL particles (for small LDL: r=0.224, P<0.001; for medium small LDL: r=0.235, P<0.001; and for very small LDL: r=0.220, P<0.001); and with high-density lipoprotein (HDL) particles (r=0.146, P<0.001), which is mainly explained by the PCSK9 correlation with the smallest HDL particles (r=0.130, P=0.037). In addition, circulating PCSK9 levels were positively correlated with the pro-atherogenic circulating RLPc levels (r=0.171, P=0.006). All of the correlations were adjusted by age, gender and BMI. PCSK9 levels are significantly and positively correlated with atherogenic lipoproteins such as large VLDL, IDL, the smallest LDL, the smallest HDL particles and RLPc levels.

Effectiveness of genetic cascade screening for familial hypercholesterolaemia using a centrally co-ordinated clinical service: An Australian experience

BackgroundFamilial hypercholesterolaemia (FH) is a co-dominantly inherited disorder of low-density lipoprotein (LDL) catabolism, causing elevated LDL-cholesterol and premature coronary artery disease (CAD). Several guidelines recommend genetic cascade screening relatives of probands (index cases) with genetically proven FH, but experience in a clinical service setting is limited. MethodsRelatives from 100 index cases with genetically confirmed FH underwent genetic and lipid testing via a centralised screening program in Western Australia. The program's effectiveness was evaluated as the number of newly diagnosed relatives with FH per index case and the proportional reduction in LDL-cholesterol after treatment. ResultsOf 366 relatives tested for FH, 188 (51.4%) were found to have a pathogenic mutation. On average, 2 cases were detected per index case. Affected relatives were younger and less likely to have physical stigmata of FH and premature CAD than index cases (p < 0.001). Of the new cases, 12.8% had hypertension, 2.7% had diabetes and 16.0% were smokers; 48.4% were already on statin therapy and these were older (p < 0.001) and had more vascular risk factors and CAD (p < 0.01) than those not on therapy. Significant reductions in LDL-cholesterol (−24.3%, p < 0.001) were achieved overall, with previously untreated new cases of FH attaining a maximal average reduction of 42.5% in LDL-cholesterol after drug therapy. Over 90% of subjects were satisfied with screening and care. ConclusionGenetic cascade screening co-ordinated by a centralised service is an effective and acceptable strategy for detecting FH in an Australian setting. A significant proportion of new cases exhibit other CAD risk factors and are already on statins, but have not received a prior diagnosis of FH.

A computational model for the analysis of lipoprotein distributions in the mouse: translating FPLC profiles to lipoprotein metabolism.

Disturbances of lipoprotein metabolism are recognized as indicators of cardiometabolic disease risk. Lipoprotein size and composition, measured in a lipoprotein profile, are considered to be disease risk markers. However, the measured profile is a collective result of complex metabolic interactions, which complicates the identification of changes in metabolism. In this study we aim to develop a method which quantitatively relates murine lipoprotein size, composition and concentration to the molecular mechanisms underlying lipoprotein metabolism. We introduce a computational framework which incorporates a novel kinetic model of murine lipoprotein metabolism. The model is applied to compute a distribution of plasma lipoproteins, which is then related to experimental lipoprotein profiles through the generation of an in silico lipoprotein profile. The model was first applied to profiles obtained from wild-type C57Bl/6J mice. The results provided insight into the interplay of lipoprotein production, remodelling and catabolism. Moreover, the concentration and metabolism of unmeasured lipoprotein components could be determined. The model was validated through the prediction of lipoprotein profiles of several transgenic mouse models commonly used in cardiovascular research. Finally, the framework was employed for longitudinal analysis of the profiles of C57Bl/6J mice following a pharmaceutical intervention with a liver X receptor (LXR) agonist. The multifaceted regulatory response to the administration of the compound is incompletely understood. The results explain the characteristic changes of the observed lipoprotein profile in terms of the underlying metabolic perturbation and resultant modifications of lipid fluxes in the body. The Murine Lipoprotein Profiler (MuLiP) presented here is thus a valuable tool to assess the metabolic origin of altered murine lipoprotein profiles and can be applied in preclinical research performed in mice for analysis of lipid fluxes and lipoprotein composition.

Inhibition of Glycosphingolipid Synthesis Ameliorates Atherosclerosis and Arterial Stiffness in Apolipoprotein E −/− Mice and Rabbits Fed a High-Fat and -Cholesterol Diet

Glycosphingolipids, integral components of the cell membrane, have been shown to serve as messengers, transducing growth factor-initiated phenotypes. Here, we have examined whether inhibition of glycosphingolipid synthesis could ameliorate atherosclerosis and arterial stiffness in transgenic mice and rabbits. Apolipoprotein E(-/-) mice (12 weeks of age; n=6) were fed regular chow or a Western diet (1.25% cholesterol, 2% fat). Mice were fed 5 or 10 mg/kg of an inhibitor of glycosphingolipid synthesis, D-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (D-PDMP), solubilized in vehicle (5% Tween-80 in PBS); the placebo group received vehicle only. At 20 and 36 weeks of age, serial echocardiography was performed to measure aortic intima-media thickening. Aortic pulse-wave velocity measured vascular stiffness. Feeding mice a Western diet markedly increased aortic pulse-wave velocity, intima-media thickening, oxidized low-density lipoprotein, Ca(2+) deposits, and glucosylceramide and lactosylceramide synthase activity. These were dose-dependently decreased by feeding D-PDMP. In liver, D-PDMP decreased cholesterol and triglyceride levels by raising the expression of SREBP2, low-density lipoprotein receptor, HMGCo-A reductase, and the cholesterol efflux genes (eg, ABCG5, ABCG8). D-PDMP affected very-low-density lipoprotein catabolism by increasing the gene expression for lipoprotein lipase and very-low-density lipoprotein receptor. Rabbits fed a Western diet for 90 days had extensive atherosclerosis accompanied by a 17.5-fold increase in total cholesterol levels and a 3-fold increase in lactosylceramide levels. This was completely prevented by feeding D-PDMP. Inhibition of glycosphingolipid synthesis ameliorates atherosclerosis and arterial stiffness in apolipoprotein E(-/-) mice and rabbits. Thus, inhibition of glycosphingolipid synthesis may be a novel approach to ameliorate atherosclerosis and arterial stiffness.

Role of SN1 Lipases on Plasma Lipids in Metabolic Syndrome and Obesity

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. 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. 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.

SMITH-LEMLI-OPITZ syndrome, caused by deficiency in the last step of cholesterol biosynthesis: The bristol UKGTN DHCR7 mutation service

SMITH-LEMLI-OPITZ syndrome, caused by deficiency in the last step of cholesterol biosynthesis: The bristol UKGTN DHCR7 mutation service