Increased Plasma Low-density Lipoprotein Cholesterol Research Articles

Il rischio cardiovascolare e la concentrazione plasmatica del colesterolo LDL: il ruolo dei Servizi Sanitari Regionali

Cardiovascular risk and increased plasma LDL cholesterol concentration: the role of the Regional Health ServiceThe relevance of hypercholesterolemia, as a risk factor for cardiovascular (CV) diseas...

Mechanism of impaired lipid homeostasis in MCPIP1‐deficienct mice

BackgroundMonocyte chemotactic protein‐induced protein 1 (MCPIP1) is found in monocytes/macrophages in response to MCP‐1 stimulation. Our preliminary data showed that MCPIP1 knockout mice have increased plasma LDL cholesterol and decreased HDL and total triglycerides. We have also found that mice lacking MCPIP1 display a marked loss of adipose and muscle tissues. Our current project was designed to determine whether MCPIP1‐deficiency impairs lipid homeostasis by affecting the apoprotein expression hepatic remodeling.MethodsC57/BL6 mice at 6‐8 weeks of age were used. Liver histological changes and plasma apoprotein expression were examined in samples collected from wild‐type, heterozygous, and MCPIP1 knockout mice.Resultshepatic histological staining revealed an increase in collagen and fibrous tissue and a decrease in hepatocytes in MCPIP1 knockout mice. We also found that the expression of LPL, and apoB48 is increased but the apoB100 and apoA‐1 is decreased in the plasma from MCPIP1 knockout mice.ConclusionsThe data collected so far suggest that the impaired lipid homeostasis observed in MCPIP1 deficient mice may occur through hepatic remodeling and alteration of apoprotein expression and/or function.

Insulin Resistance Causes Posttranslational Downregulation of Hepatic Sortilin 1 in Diabetic Mice

Dyslipidemia increases the risk of cardiovascular diseases in diabetes. Hepatic Sortilin 1 decreases hepatic apoB production, and its liver expression is associated with plasma LDL cholesterol and cardiovascular disease risk in humans. The goal of this study is to investigate the insulin regulation of hepatic Sortilin 1 in diabetes. Insulin treatment rapidly induced Sortilin 1 protein, but not mRNA, in AML12 cells. A PI3K inhibitor or an AKT inhibitor treatment rapidly reduced, while overexpression of a constitutively active AKT induced Sortilin 1 protein in AML12 cells. LC-MS/MS analysis showed that Sortilin 1 was phosphorylated at serine 825. Previous studies have shown that phosphorylation of S825 by casein kinase II promotes the cellular trafficking function of Sortilin 1 via enhancing its interaction with other trafficking adaptor proteins. Interestingly, abolishing S825 phosphorylation by S825A mutation or by a casein kinase 2 inhibitor prevented insulin induction of Sortilin1 in AML12 cells. High fat diet-fed obese mice and streptozocin-treated mice showed decreased hepatic Sortilin 1 protein. Treating mice with a PI3K inhibitor rapidly decreased hepatic Sortilin 1 protein and increased plasma LDL-cholesterol and triglyceride levels. Furthermore, over-expression of Sortilin 1 in mouse livers with adenovirus-mediated gene delivery prevented PI3K inhibitor inhibition of hepatic Sortilin 1. This prevented the PI3K inhibitor-induced elevation of plasma triglyceride, but not cholesterol in mice, suggesting that Sortilin 1-independent mechanisms also mediate the cholesterol-raising effect of PI3K inhibitor. In summary, insulin regulation of Sortilin 1 may be a novel link between insulin resistance and increased hepatic apoB production in insulin resistance.

G-protein estrogen receptor as a regulator of low-density lipoprotein cholesterol metabolism: cellular and population genetic studies.

Estrogen deficiency is linked with increased low-density lipoprotein (LDL) cholesterol. The hormone receptor mediating this effect is unknown. G-protein estrogen receptor (GPER) is a recently recognized G-protein-coupled receptor that is activated by estrogens. We recently identified a common hypofunctional missense variant of GPER, namely P16L. However, the role of GPER in LDL metabolism is unknown. Therefore, we examined the association of the P16L genotype with plasma LDL cholesterol level. Furthermore, we studied the role of GPER in regulating expression of the LDL receptor and proprotein convertase subtilisin kexin type 9. Our discovery cohort was a genetically isolated population of Northern European descent, and our validation cohort consisted of normal, healthy women aged 18 to 56 years from London, Ontario. In addition, we examined the effect of GPER on the regulation of proprotein convertase subtilisin kexin type 9 and LDL receptor expression by the treatment with the GPER agonist, G1. In the discovery cohort, GPER P16L genotype was associated with a significant increase in LDL cholesterol (mean±SEM): 3.18±0.05, 3.25±0.08, and 4.25±0.33 mmol/L, respectively, in subjects with CC (homozygous for P16), CT (heterozygotes), and TT (homozygous for L16) genotypes (P<0.05). In the validation cohort (n=339), the GPER P16L genotype was associated with a similar increase in LDL cholesterol: 2.17±0.05, 2.34±0.06, and 2.42±0.16 mmol/L, respectively, in subjects with CC, CT, and TT genotypes (P<0.05). In the human hepatic carcinoma cell line, the GPER agonist, G1, mediated a concentration-dependent increase in LDL receptor expression, blocked by either pretreatment with the GPER antagonist G15 or by shRNA-mediated GPER downregulation. G1 also mediated a GPER- and concentration-dependent decrease in proprotein convertase subtilisin kexin type 9 expression. GPER activation upregulates LDL receptor expression, probably at least, in part, via proprotein convertase subtilisin kexin type 9 downregulation. Furthermore, humans carrying the hypofunctional P16L genetic variant of GPER have increased plasma LDL cholesterol. In aggregate, these data suggest an important role of GPER in the regulation of LDL receptor expression and consequently LDL metabolism.

Canadian Cardiovascular Society Position Statement on Familial Hypercholesterolemia

Familial hypercholesterolemia (FH) is the most common genetic disorder causing premature cardiovascular disease and death. Heterozygous FH conservatively affects approximately 1:500 Canadians, and the more serious homozygous form affects approximately 1:1,000,000 Canadians, although these numbers might be underestimated. Of approximately 83,500 Canadians estimated to have FH, most are undiagnosed, which represents a simultaneous public health deficit and opportunity, because early treatment of heterozygous FH can normalize life expectancy. Diagnostic algorithms for FH incorporate increased plasma low-density lipoprotein cholesterol, pathognomonic clinical features, and family history of early cardiovascular disease and hyperlipidemia. DNA-based detection of causative mutations in FH-related genes can help with diagnosis. Maximizing diagnosis and treatment of FH in Canada will involve a multipronged approach, including: (1) increasing awareness of FH among health care providers and patients; (2) creating a national registry for FH individuals; (3) setting standards for screening, including cascade screening in affected families; (4) ensuring availability of standard-of-care therapies, in particular optimization of plasma low-density lipoprotein cholesterol levels and timely access to future validated therapies; (5) promoting patient-based support and advocacy groups; and (6) forming alliances with international colleagues, resources, and initiatives that focus on FH. This document aims to raise awareness of FH nationally, and to mobilize knowledge translation, patient support, and availability of treatment and health care resources for this underrecognized, but important medical condition.

PCSK9 inhibition with evolocumab (AMG 145) in heterozygous familial hypercholesterolaemia (RUTHERFORD-2): a randomised, double-blind, placebo-controlled trial

Heterozygous familial hypercholesterolaemia is characterised by low cellular uptake of LDL cholesterol, increased plasma LDL cholesterol concentrations, and premature cardiovascular disease. Despite intensive statin therapy, with or without ezetimibe, many patients are unable to achieve recommended target levels of LDL cholesterol. We investigated the effect of PCSK9 inhibition with evolocumab (AMG 145) on LDL cholesterol in patients with this disorder. This multicentre, randomised, double-blind, placebo-controlled trial was undertaken at 39 sites (most of which were specialised lipid clinics, mainly attached to academic institutions) in Australia, Asia, Europe, New Zealand, North America, and South Africa between Feb 7 and Dec 19, 2013. 331 eligible patients (18-80 years of age), who met clinical criteria for heterozygous familial hypercholesterolaemia and were on stable lipid-lowering therapy for at least 4 weeks, with a fasting LDL cholesterol concentration of 2·6 mmol/L or higher, were randomly allocated in a 2:2:1:1 ratio to receive subcutaneous evolocumab 140 mg every 2 weeks, evolocumab 420 mg monthly, or subcutaneous placebo every 2 weeks or monthly for 12 weeks. Randomisation was computer generated by the study sponsor, implemented by a computerised voice interactive system, and stratified by LDL cholesterol concentration at screening (higher or lower than 4·1 mmol/L) and by baseline ezetimibe use (yes/no). Patients, study personnel, investigators, and Amgen study staff were masked to treatment assignments within dosing frequency groups. The coprimary endpoints were percentage change from baseline in LDL cholesterol at week 12 and at the mean of weeks 10 and 12, analysed by intention-to-treat. This trial is registered with ClinicalTrials.gov, number NCT01763918. Of 415 screened patients, 331 were eligible and were randomly assigned to the four treatment groups: evolocumab 140 mg every 2 weeks (n=111), evolocumab 420 mg monthly (n=110), placebo every 2 weeks (n=55), or placebo monthly (n=55). 329 patients received at least one dose of study drug. Compared with placebo, evolocumab at both dosing schedules led to a significant reduction in mean LDL cholesterol at week 12 (every-2-weeks dose: 59·2% reduction [95% CI 53·4-65·1], monthly dose: 61·3% reduction [53·6-69·0]; both p<0·0001) and at the mean of weeks 10 and 12 (60·2% reduction [95% CI 54·5-65·8] and 65·6% reduction [59·8-71·3]; both p<0·0001). Evolocumab was well tolerated, with rates of adverse events similar to placebo. The most common adverse events occurring more frequently in the evolocumab-treated patients than in the placebo groups were nasopharyngitis (in 19 patients [9%] vs five [5%] in the placebo group) and muscle-related adverse events (ten patients [5%] vs 1 [1%]). In patients with heterozygous familial hypercholesterolaemia, evolocumab administered either 140 mg every 2 weeks or 420 mg monthly was well tolerated and yielded similar and rapid 60% reductions in LDL cholesterol compared with placebo. Amgen Inc.

Transgenic expression of dominant-active IDOL in liver causes diet-induced hypercholesterolemia and atherosclerosis in mice.

The E3 ubiquitin ligase inducible degrader of the low-density lipoprotein receptor (IDOL) triggers lysosomal degradation of the low-density lipoprotein receptor. The tissue-specific effects of the IDOL pathway on plasma cholesterol and atherosclerosis have not been examined. Given that the liver is the primary determinant of plasma cholesterol levels, we sought to examine the consequence of effect of chronic liver-specific expression of a dominant-active form of IDOL in mice. We expressed a degradation-resistant, dominant-active form of IDOL (super IDOL [sIDOL]) in C57Bl/6J mice from the liver-specific albumin promoter (L-sIDOL transgenics). L-sIDOL mice were fed a Western diet for 20 or 30 weeks and then analyzed for plasma lipid levels and atherosclerotic lesion formation. L-sIDOL mice showed dramatic reductions in hepatic low-density lipoprotein receptor protein and increased plasma low-density lipoprotein cholesterol levels on both chow and Western diets. Moreover, L-sIDOL mice developed marked atherosclerotic lesions when fed a Western diet. Lesion formation in L-sIDOL mice was more robust than in apolipoprotein E*3 Leiden mice and did not require the addition of cholate to the diet. Western diet-fed L-sIDOL mice had elevated expression of liver X receptor target genes and proinflammatory genes in their aortas. Liver-specific expression of dominant-active IDOL is associated with hypercholesterolemia and a marked elevation in atherosclerotic lesions. Our results show that increased activity of the IDOL pathway in the liver can override other low-density lipoprotein receptor regulatory pathways leading to cardiovascular disease. L-sIDOL mice are a robust, dominantly inherited, diet-inducible model for the study of atherosclerosis.

Abstract 43: The Hypofunctional GPER P16L Variant is Associated With a Gene Dosage-Related Increase in Plasma LDL Cholesterol

Introduction: Estrogen deficiency is linked with dyslipidemia, especially in postmenopausal women, through a poorly understood mechanism. GPER is a recently recognized GPCR which is activated by estrogens. However, the role of GPER in mediating estrogen’s effects on lipid metabolism is unknown. We recently identified a common hypofunctional missense variant of GPER, namely P16L (allele frequency ~ 20%). We studied association of this with plasma LDL cholesterol levels. Further, we studied the role of GPER in regulating expression of the LDL receptor. Methods: Our discovery cohort was a genetically isolated population of Northern European descent (n=415), and our validation cohort consisted of 505 normal, healthy subjects 18-56 years of age from London, Ontario. Genomic DNA was extracted from whole blood and genotyped for GPER using a dedicated TaqMan assay. Additionally we examined the role of GPER on the regulation of LDL receptor expression by treatment with the GPER agonist, G1. Results: In the discovery cohort, the GPER P16L genetic variant was associated with a significant gene-dosage related increase in LDL cholesterol (CC [homozygous wild type] =3.18±0.84 (mean+SD); CT [heterozygote] =3.25±0.80; and TT [homozygous variant] =4.25±0.87 mmol/L, p&lt;0.05). Total cholesterol concentrations followed a similar gradient across genotypes. In the validation cohort, the GPER P16L genetic variant was associated with a similar significant gene-dosage related increase in LDL cholesterol (CC =2.16±0.67; CT [heterozygote] =2.29±0.67; TT =2.40±0.84 mmol/L, p&lt;0.05). In HepG2 cells expressing GPER, G1 mediated a concentration-dependent increase in LDL receptor expression. Pre-treating the cells with the GPER antagonist G15 attenuated the effect of G1 on LDL receptor upregulation. Further, downregulation of GPER expression via infection with a shGPER construct also attenuated G1's effect on LDL receptor upregulation. Conclusion: GPER activation upregulates LDL receptor expression. Further, carrying the hypofunctional P16L genetic variant of GPER, increases plasma LDL cholesterol in humans. In aggregate these data suggest an important role of GPER in regulation of LDL receptor expression and consequently LDL metabolism.

Gender specific association of ABCA1 gene R219K variant in coronary disease risk through interactions with serum triglyceride elevation in Turkish adults

ATP binding cassette transporter A1 (ABCA1) controls the reverse cholesterol transport. Some ABCA1 variants are correlated with serum high-density lipoprotein cholesterol (HDL-C) and other lipid concentrations. We aimed to explore the relationship of ABCA1 gene with both the lipid profile and coronary heart disease (CHD) risk. Selected 627 individuals of the Turkish Adult Risk Factor Study were genotyped for ABCA1 R219K polymorphism using PCR-RFLP (polymerase chain reaction-restriction fragment length polymorphism) method. Student's t-test, one-way ANOVA, Chi-square test, linear and logistic regression was used for statistical analysis. We demonstrated a gender-specific effect of the R219K polymorphism on plasma lipids and CHD. In men, while homozygosity of the K allele was associated with increased plasma low-density lipoprotein cholesterol (LDL-C) (p<0.05) and total cholesterol concentrations (p<0.05), carriage of this allele was associated with higher HDL-C concentrations (p<0.05) after adjustment for associated risk factors, but not with CHD. In women, however, without being related to HDL-C levels, each 219K allele was associated with 10% higher triglycerides (TG) concentrations (p<0.05). R219K heterozygosity in women independently doubled (95% CI 1.00; 3.80) the odds ratio for CHD risk in regression models, after adjustment for several variables. Interaction of TG elevation (>140 mg/dL) with CHD was demonstrated in female 219RK genotype carriers. R219 allele of the ABCA1 gene independently confers CHD risk in heterozygote Turkish women, not via reduced HDL-C, but interacting with elevated TG expressed by the 219K allele, but not in men.

The M2 Module of the Cys-His-rich Domain (CHRD) of PCSK9 Protein Is Needed for the Extracellular Low-density Lipoprotein Receptor (LDLR) Degradation Pathway

PCSK9 enhances the cellular degradation of the LDL receptor (LDLR), leading to increased plasma LDL cholesterol. This multidomain protein contains a prosegment, a catalytic domain, a hinge region, and a cysteine-histidine rich domain (CHRD) composed of three tightly packed modules named M1, M2, and M3. The CHRD is required for the activity of PCSK9, but the mechanism behind this remains obscure. To define the contribution of each module to the function of PCSK9, we dissected the CHRD structure. Six PCSK9 deletants were generated by mutagenesis, corresponding to the deletion of only one (ΔM1, ΔM2, ΔM3) or two (ΔM12, ΔM13, ΔM23) modules. Transfection of HEK293 cells showed that all deletants were well processed and expressed compared with the parent PCSK9 but that only those lacking the M2 module were secreted. HepG2 cells lacking endogenous PCSK9 (HepG2/shPCSK9) were used for the functional analysis of the extracellular or intracellular activity of PCSK9 and its deletants. To analyze the ability of the deletants to enhance the LDLR degradation by the intracellular pathway, cellular expressions revealed that only the ΔM2 deletant retains a comparable total LDLR-degrading activity to full-length PCSK9. To probe the extracellular pathway, HepG2/shPCSK9 cells were incubated with conditioned media from transfected HEK293 or HepG2/shPCSK9 cells, and cell surface LDLR levels were analyzed by FACS. The results showed no activity of any secreted deletant compared with PCSK9. Thus, although M2 is dispensable for secretion, its presence is required for the extracellular activity of PCSK9 on cell surface LDLR.

Furin-cleaved Proprotein Convertase Subtilisin/Kexin Type 9 (PCSK9) Is Active and Modulates Low Density Lipoprotein Receptor and Serum Cholesterol Levels

Proprotein convertase subtilisin/kexin 9 (PCSK9) regulates plasma LDL cholesterol levels by regulating the degradation of LDL receptors. Another proprotein convertase, furin, cleaves PCSK9 at Arg(218)-Gln(219) in the surface-exposed "218 loop." This cleaved form circulates in blood along with the intact form, albeit at lower concentrations. To gain a better understanding of how cleavage affects PCSK9 function, we produced recombinant furin-cleaved PCSK9 using antibody Ab-3D5, which binds the intact but not the cleaved 218 loop. Using Ab-3D5, we also produced highly purified hepsin-cleaved PCSK9. Hepsin cleaves PCSK9 at Arg(218)-Gln(219) more efficiently than furin but also cleaves at Arg(215)-Phe(216). Further analysis by size exclusion chromatography and mass spectrometry indicated that furin and hepsin produced an internal cleavage in the 218 loop without the loss of the N-terminal segment (Ser(153)-Arg(218)), which remained attached to the catalytic domain. Both furin- and hepsin-cleaved PCSK9 bound to LDL receptor with only 2-fold reduced affinity compared with intact PCSK9. Moreover, they reduced LDL receptor levels in HepG2 cells and in mouse liver with only moderately lower activity than intact PCSK9, consistent with the binding data. Single injection into mice of furin-cleaved PCSK9 resulted in significantly increased serum cholesterol levels, approaching the increase by intact PCSK9. These findings indicate that circulating furin-cleaved PCSK9 is able to regulate LDL receptor and serum cholesterol levels, although somewhat less efficiently than intact PCSK9. Therapeutic anti-PCSK9 approaches that neutralize both forms should be the most effective in preserving LDL receptors and in lowering plasma LDL cholesterol.

Rethinking dietary cholesterol

The perceived notion that dietary cholesterol is associated with increased risk for coronary heart disease (CHD) has led to dietary recommendations of no more than 300 mg/day for healthy populations in the USA. This study will review the recent evidence that challenges the current dietary restrictions regarding cholesterol while it presents some beneficial effects of eggs (an icon for dietary cholesterol) in healthy individuals. The European countries, Australia, Canada, New Zealand, Korea and India among others do not have an upper limit for cholesterol intake in their dietary guidelines. Further, existing epidemiological data have clearly demonstrated that dietary cholesterol is not correlated with increased risk for CHD. Although numerous clinical studies have shown that dietary cholesterol challenges may increase plasma LDL cholesterol in certain individuals, who are more sensitive to dietary cholesterol (about one-quarter of the population), HDL cholesterol also rises resulting in the maintenance of the LDL/HDL cholesterol ratio, a key marker of CHD risk. The lines of evidence coming from current epidemiological studies and from clinical interventions utilizing different types of cholesterol challenges support the notion that the recommendations limiting dietary cholesterol should be reconsidered.

Effects of antinutritional factors on plasma lipoprotein levels in Japanese flounder Paralichthys olivaceus

This study examined the effects of four types of antinutritional factor (phytic acid, stachyose, soy saponins and soy isoflavones) on lipoprotein levels in plasma of Japanese flounder Paralichthys olivaceus. A basal diet was prepared with fish meal as primary protein source, the other diets were supplemented with 0·2, 0·4 or 0·8% phytic acid, 0·4, 0·8 or 1·5% stachyose, 0·1, 0·35 or 0·7% soy saponins and 0·10, 0·35 or 0·70% soy isoflavones, by dry mass, in place of white flour in the basal diet. Total cholesterol (TC) and triglyceride (TG) levels in plasma of P. olivaceus were not affected by phytic acid or stachyose. In general, addition of 0·2-0·8% phytic acid or 0·4-1·5% stachyose decreased plasma high-density lipoprotein cholesterol (HDL-C) levels, increased plasma low-density lipoprotein cholesterol (LDL-C) levels, thereby increasing the LDL-C:HDL-C ratio. By contrast, supplementation with 0·35-0·7% soy saponins generally depressed plasma TC levels and the LDL-C:HDL-C ratio. Supplementation with 0·35-0·7% soy isoflavones, however, increased plasma TC and TG levels. These results indicate that soy saponins may be partly responsible for the cholesterol-lowering effects of soybean meal.

Abstract 8706: Impact of Small Dense Low-Density Lipoproteins Cholesterol on Cardiovascular Disease in an Urban Japanese Cohort: The Suita Study

Aim: Increased plasma low-density lipoprotein cholesterol (LDL-C) concentrations have been shown to be one of the major risk factors for cardiovascular disease (CVD). Clinical evidence also indicates that small dense LDL (sd-LDL) particles are more atherogenic than large buoyant LDL particles. Because there was no easy assay to measure the amount of sd-LDL-C, few studies have addressed the association between sd-LDL-C and CVD. In this study, we hypothesized that higher sd-LDL-C is associated with increased risk for CVD. To this end, we examined the association between sd-LDL-C and CVD in Japanese by using a new kit to measure sd-LDL-C. Methods: We studied 2034 Japanese individuals (30 to 79 years old without stroke or coronary heart disease (CHD)) in the Suita Study, who completed measurement of direct LDL-C and sd-LDL-C by a kit based on the precipitation method with filtration, and then followed for 11.7 years on average. We calculated the Cox proportional adjusted hazard ratios (HRs) of LDL-C, sd-LDL-C, and sd-LDL-C/LDL-C ratio quartiles for incident CAD, stroke, and CVD (CHD + stroke) adjusting for age, sex, body mass index, diabetes, blood pressure category (defined on the basis of the ESH-ESC 2007 criteria), smoking and drinking at baseline. Results: The mean age of this cohort was 59.3 years old and 52.4% was women. The HR of the 4th quartile of sd-LDL-C for the development of CAD was 3.35 (95% confidence intervals: 1.38 to 8.13), which was higher than that in the analysis using LDL-C quartiles. In multivariable adjustment, the HR of the 4th quartile was almost similar. When we used the quartiles of sd-LDL/LDL ratio, increased sd-LDL/LDL ratio was associated with the incidence of CVD, CAD, and stroke. Sex-specific analysis showed that the association of sd-LDL-C with CAD and CVD was statistically significant in men, but not in women. Conclusions: We demonstrated that increased levels of sd-LDL-C are significantly associated with the development of CVD. Our data indicate that sd-LDL-C is a better risk factor for CVD than LDL-C for risk assessment.

Dietary polyunsaturated fatty acids may increase plasma LDL-cholesterol and plasma cholesterol concentrations in carriers of an ABCG1 gene single nucleotide polymorphism: Study in two Spanish populations

BackgroundABCG1 mediates cellular cholesterol transport, but there is very little known about the influence of ABCG1 polymorphisms on human plasma lipoprotein cholesterol concentrations or on the interactions of these polymorphisms with diet. ObjectiveOur objective was to investigate whether interactions between PUFA intake and ABCG1 polymorphisms modulate associations with plasma total cholesterol (TC), LDL- and HDL-cholesterol in two Spanish populations. MethodsWe grounded our investigation on two general population-based studies: the Hortega study (population A) and the Pizarra study (population B). Participants included 1178 individuals (50.0% women, age range 21–85 years) and 763 individuals (66% women, age range 23–73 years) from populations A and B, respectively, without lipid lowering drugs. Subjects were genotyped for ABCG1 variants. Biochemical measurements were taken by standard procedures. Dietary intakes were estimated with a validated questionnaire. ResultsIn population A, the A allele homozygotes of SNP rs4148102 had higher TC and LDLc concentrations in subjects on a high PUFA diet than did the carriers of the G allele (242.1±38.9 vs. 198.0±36.0mg/dL, p=0.003, and 149.8±37.9 vs. 111.4±32.1mg/dL, p=0.005, respectively), and significant gene–diet interactions were observed (p=0.020 and p=0.013, respectively). In population B, similar differences in TC and LDLc concentrations were also found in association with this SNP under a high PUFA diet (253.2±24.9 vs. 197.7±39.9mg/dL, p=0.009, and 171.8±20.5 vs. 120.4±34.2mg/dL, p=0.004, respectively), but the gene–diet interactions observed were not significant (p=0.379 and p=0.422, respectively). In the pooled populations, differences in the TC and LDLc concentrations increased (246.8±32.9 vs. 198.0±37.5, p=6×10−5, and 159.0±32.6 vs. 114.3±33.1, p=3×10−5, respectively), and significant gene–diet interactions were maintained (p=0.006 and p=0.003, respectively). ConclusionIn two Spanish populations, the ABCG1 polymorphism rs4148102 was associated with variations in plasma lipoprotein cholesterol concentrations in subjects with high PUFA intakes. Carriers of the AA genotype consuming high PUFA diet showed higher plasma LDLc concentrations.

Development of Apolipoprotein E–Deficient Mice

The first mouse carrying a deletion mutation in its apolipoprotein E (apoE) gene was born in our mouse colony in the summer of 1991. Our ongoing experiments to that point had indicated that this would happen, but the realization that the mouse in front of my eyes had inherited a mutation that we had designed and made in the laboratory filled me with awe. It did not occur to me immediately that this mouse would develop hypercholesterolemia and atherosclerosis and dictate the direction of my research for the next 20 years. I here briefly describe the background and my personal experience that led to the development of apoE-deficient mice as a model for human atherosclerosis. As a research scientist in the Department of Genetics at the University of Wisconsin, my main interest during the early 1980s was directed toward understanding how different types of DNA recombination contribute to the architecture and diversity of individual genomes within human populations and to DNA differences between humans and nonhuman primates. My studies clearly showed that new alleles and new genes are constantly being formed in the human genome by recombinational events, particularly between existing members of multigene families. There also appeared to be hot spots for recombination. By tracing a history of the human haptoglobin-gene cluster from the present-day structures in human populations and in other primates, I found that a single recombination event between related genes often produces much more drastic changes in the genome than those that result from simple point mutations.1 Whether this frequent yet natural occurrence of homologous recombination in the mammalian genome could be used to alter the genome of mammalian cells in culture in a preplanned fashion became a question of interest to several laboratories.2,3 An affirmative answer was first obtained in 1985, …

Studies in mice, hamsters, and rats demonstrate that repression of hepatic apoA-I expression by taurocholic acid in mice is not mediated by the farnesoid-X-receptor

It is claimed that apoA-I expression is repressed in mice by cholic acid (CA) and its taurine conjugate, taurocholic acid (TCA) via farnesoid X receptor (FXR) activation. We measured apoA-I expression in mice, hamsters, and rats treated with highly potent and selective synthetic FXR agonists or with TCA. All of the synthetic agonists bound to FXR with high affinity in a scintillation proximity assay. However, TCA did not compete with the radioligand up to the highest concentration used (100 μM). The C-site regulatory region of apoA-I, through which FXR has been reported to regulate its expression, is completely conserved across the species investigated. In both male and female human apoA-I-transgenic mice, we reproduced the previously reported strong inhibition of human apoA-I expression upon treatment with the typical supraphysiological dose of TCA used in such studies. However, in contrast to some previous reports, TCA did not repress murine apoA-I expression in the same mice. Also, more-potent and -selective FXR agonists did not affect human or murine apoA-I expression in this model. In LDL receptor-deficient mice and Golden Syrian hamsters, selective FXR agonists did not affect apoA-I expression, whereas in Wistar rats, some even increased apoA-I expression. In conclusion, selective FXR agonists do not repress apoA-I expression in rodents. Repression of human apoA-I expression by TCA in transgenic mice is probably mediated through FXR-independent mechanisms.

PCSK9: an emerging target for treatment of hypercholesterolemia

Introduction: Increased plasma low-density lipoprotein (LDL) cholesterol is a significant risk factor for cardiovascular disease. Plasma LDL-cholesterol is controlled through its uptake into cells upon binding the LDL receptor (LDLR). Proprotein convertase subtilisin/kexin type 9 (PCSK9) binds to the LDLR and promotes its degradation, resulting in increased plasma LDL-cholesterol. Inhibiting the action of PCSK9 on the LDLR has emerged as a novel therapeutic target for hypercholesterolemia.Areas covered: We briefly describe the identification and initial characterisation of PCSK9, before detailing the molecular mechanisms involved in its interaction with the LDLR. We highlight the potential sites for therapeutic intervention in this pathway and describe the current status of therapeutic approaches, including blocking antibodies, siRNA, antisense oligonucleotides and small-molecule inhibitors. The potential limitations of such approaches are also discussed.Expert opinion: There is a wealth of evidence indicating that inhibition of PCSK9 is a highly desirable approach to combat hypercholesterolemia, with several agents in preclinical and clinical development. However, further research is required to fully understand the biological role of PCSK9 and whether its inhibition may have adverse effects in certain groups of patients, for example, those with liver disease.

The unique role of proprotein convertase subtilisin/kexin 9 in cholesterol homeostasis

The LDL receptor (LDLR) plays an essential role in the regulation of plasma (LDL) cholesterol concentrations by virtue of its ability to clear plasma LDL. Down-regulation of the LDLR by proprotein convertase subtilisin/kexin 9 (PCSK9) has recently emerged as a regulatory mechanism that controls plasma LDL cholesterol concentrations. Studies in which PCSK9 is over-expressed in mice, have demonstrated that PCSK9, by enhancing hepatic LDLR degradation, decreases the availability of the LDLR for LDL uptake, resulting in increased plasma LDL cholesterol levels. However, PCSK9 has also recently been shown to mediate down-regulation of surface receptors other than the LDLR, suggesting that it may have much broader roles than initially thought.

Plasma PCSK9 Is Associated with Age, Sex, and Multiple Metabolic Markers in a Population-Based Sample of Children and Adolescents

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a protein convertase that posttranslationally promotes the degradation of the low-density lipoprotein receptor (LDLR) in hepatocytes and increases plasma LDL cholesterol (LDL-C). Heterozygote gain-of-function mutations of PCSK9 are associated with the familial hypercholesterolemia phenotype, whereas loss-of-function variants are associated with reduced LDL-C concentrations and lower coronary risk. Plasma PCSK9 correlates with body mass index, triglyceridemia, total cholesterol, and LDL-C in adults, but no data are available in youth. We studied 1739 French Canadian youth ages 9, 13, and 16 years who participated in the Quebec Child and Adolescent Health and Social Survey, a province-wide school-based survey conducted in 1999. An ELISA assay was used to measure plasma PSCK9. The mean (SD) plasma PCSK9 concentration was 84.7 (24.7) microg/L in the sample. In boys, plasma PCSK9 decreased with age, whereas the inverse was true for girls. There were statistically significant positive associations between PCSK9 and fasting glucose, insulin, and HOMA-IR (homeostasis model assessment of insulin resistance). In multivariable analysis, a 10% higher fasting insulin was associated with a 1%-2% higher PCSK9 in both sexes. There were also positive associations between PCSK9 and total cholesterol, LDL-C, and triglycerides, as well as with HDL-C and apolipoproteins A1 and B. PCSK9 is associated with age, sex, and multiple metabolic markers in youth. A novel finding is that PCSK9 is associated with fasting insulinemia, which suggests that PCSK9 could play a role in the development of dyslipidemia associated with the metabolic syndrome. .