OBJECTIVE

Obeticholic acid (OCA; INT-747, 6α-ethyl-chenodeoxycholic acid) is a semisynthetic derivative of the primary human bile acid chenodeoxycholic acid, the natural agonist of the farnesoid X receptor, which is a nuclear hormone receptor that regulates glucose and lipid metabolism. In animal models, OCA decreases insulin resistance and hepatic steatosis.

METHODS

We performed a double-blind, placebo-controlled, proof-of-concept study to evaluate the effects of OCA on insulin sensitivity in patients with nonalcoholic fatty liver disease and type 2 diabetes mellitus. Patients were randomly assigned to groups given placebo (n = 23), 25 mg OCA (n = 20), or 50 mg OCA (n = 21) once daily for 6 weeks. A 2-stage hyperinsulinemic-euglycemic insulin clamp was used to measure insulin sensitivity before and after the 6-week treatment period. We also measured levels of liver enzymes, lipid analytes, fibroblast growth factor 19, 7α-hydroxy-4-cholesten-3-one (a BA precursor), endogenous bile acids, and markers of liver fibrosis.

RESULTS

When patients were given a low-dose insulin infusion, insulin sensitivity increased by 28.0% from baseline in the group treated with 25 mg OCA (P = .019) and 20.1% from baseline in the group treated with 50 mg OCA (P = .060). Insulin sensitivity increased by 24.5% (P = .011) in combined OCA groups, whereas it decreased by 5.5% in the placebo group. A similar pattern was observed in patients given a high-dose insulin infusion. The OCA groups had significant reductions in levels of γ-glutamyltransferase and alanine aminotransferase and dose-related weight loss. They also had increased serum levels of low-density lipoprotein cholesterol and fibroblast growth factor 19, associated with decreased levels of 7α-hydroxy-4-cholesten-3-one and endogenous bile acids, indicating activation of farnesoid X receptor. Markers of liver fibrosis decreased significantly in the group treated with 25 mg OCA. Adverse experiences were similar among groups.

CONCLUSIONS

In this phase 2 trial, administration of 25 or 50 mg OCA for 6 weeks was well tolerated, increased insulin sensitivity, and reduced markers of liver inflammation and fibrosis in patients with type 2 diabetes mellitus and nonalcoholic fatty liver disease. Longer and larger studies are warranted. ClinicalTrials.gov, Number: NCT00501592.

The acute response of steroidogenic cells to trophic hormone stimulation is the mobilization of cholesterol from cellular stores to the mitochondrial outer membrane and the transfer of this cholesterol to the mitochondrial inner membrane where the first enzymatic step in steroidogenesis occurs. The transfer of cholesterol across the mitochondrial membranes is dependent upon de novo protein synthesis, and this is the regulated step in the process. Although the newly synthesized regulatory protein(s) have yet to be identified, we previously have proposed a candidate protein which we identified in MA-10 cells that is synthesized in response to luteinizing hormone stimulation and that is localized to the mitochondria. In the present study, we report the isolation of a cDNA that encodes this luteinizing hormone-induced protein. Analysis of the cDNA and protein sequences reveals this is a novel protein. Importantly, we demonstrate for the first time that expression of the protein in MA-10 cells in the absence of hormone stimulation is sufficient to induce steroid production. We conclude that this protein is required in the acute regulation of steroidogenesis and propose to call this protein the Steroidogenic Acute Regulatory protein (StAR).

The treatment of ischemic strokes is limited to prophylactic agents that block the coagulation cascade. Here, we show that cholesterol-lowering agents, 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase inhibitors, protect against cerebral injury by a previously unidentified mechanism involving the selective up-regulation of endothelial NO synthase (eNOS). Prophylactic treatment with HMG-CoA reductase inhibitors augments cerebral blood flow, reduces cerebral infarct size, and improves neurological function in normocholesterolemic mice. The up-regulation of eNOS by HMG-CoA reductase inhibitors is not associated with changes in serum cholesterol levels, but is reversed by cotreatment with L-mevalonate and by the downstream isoprenoid, geranylgeranyl pyrophosphate and not by farnesyl pyrophosphate. The blood flow and neuroprotective effects of HMG-CoA reductase inhibitors are completely absent in eNOS-deficient mice, indicating that enhanced eNOS activity by HMG-CoA reductase inhibitors is the predominant if not the only mechanism by which these agents protect against cerebral injury. Our results suggest that HMG-CoA reductase inhibitors provide a prophylactic treatment strategy for increasing blood flow and reducing brain injury during cerebral ischemia.

BACKGROUND

Niacin reduces coronary heart disease morbidity and mortality when taken either alone or in combination with statins; however, the incremental impact of adding niacin to background statin therapy is unknown.

RESULTS

This was a double-blind randomized placebo-controlled study of once-daily extended-release niacin (1000 mg) added to background statin therapy in 167 patients (mean age 67 years) with known coronary heart disease and low levels of high-density lipoprotein cholesterol (HDL-C; <45 mg/dL). The primary end point was the change in common carotid intima-media thickness (CIMT) after 1 year. Baseline CIMT (0.884+/-0.234 mm), low-density lipoprotein cholesterol (89+/-20 mg/dL), and HDL-C (40+/-7 mg/dL) were comparable in the placebo and niacin groups. Adherence to niacin exceeded 90%, and 149 patients (89.2%) completed the study. HDL-C increased 21% (39 to 47 mg/dL) in the niacin group. After 12 months, mean CIMT increased significantly in the placebo group (0.044+/-0.100 mm; P<0.001) and was unchanged in the niacin group (0.014+/-0.104 mm; P=0.23). Although the overall difference in IMT progression between the niacin and placebo groups was not statistically significant (P=0.08), niacin significantly reduced the rate of IMT progression in subjects without insulin resistance (P=0.026). Clinical cardiovascular events occurred in 3 patients treated with niacin (3.8%) and 7 patients treated with placebo (9.6%; P=0.20).

CONCLUSIONS

The addition of extended-release niacin to statin therapy slowed the progression of atherosclerosis among individuals with known coronary heart disease and moderately low HDL-C.

Previous studies have indicated that human immunodeficiency virus (HIV) is enclosed with a lipid envelope similar in composition to cell plasma membranes and to other viruses. Further, the fluidity, as measured by spin resonance spectroscopy, is low and the viral envelope is among the most highly ordered membranes analyzed. However, the relationship between viral envelope lipids and those of the host cell is not known. Here we demonstrate that the phospholipids within the envelopes of HIV-1RF and HIV-2-L are similar to each other but significantly different from their respective host cell surface membranes. Further, we demonstrate that the cholesterol-to-phospholipid molar ratio of the viral envelope is approximately 2.5 times that of the host cell surface membranes. Consistent with the elevated cholesterol-to-phospholipid molar ratio, the viral envelopes of HIV-1RF and HIV-2-L were shown to be 7.5% and 10.5% more ordered than the plasma membranes of their respective host cells. These data demonstrate that HIV-1 and HIV-2-L select specific lipid domains within the surface membrane of their host cells through which to emerge during viral maturation.

Hepatitis C virus (HCV) infection is a major cause of chronic hepatitis, liver cirrhosis, and hepatocellular carcinoma. Our laboratory has previously demonstrated that high-level HCV replication during acute infection of chimpanzees is associated with the modulation of multiple genes involved in lipid metabolism, and that drugs that regulate cholesterol and fatty acid biosynthesis regulate the replication of the subgenomic HCV replicon in Huh-7 cells. In this article, we demonstrate that Huh-7 cells harboring replicating, full-length HCV RNAs express elevated levels of ATP citrate lyase and acetyl-CoA synthetase genes, both of which are involved in cholesterol and fatty acid biosynthesis. Further, we confirm that the cholesterol-biosynthetic pathway controls HCV RNA replication by regulating the cellular levels of geranylgeranyl pyrophosphate, we demonstrate that the impact of geranylgeranylation depends on the fatty acid content of the cell, and we show that fatty acids can either stimulate or inhibit HCV replication, depending on their degree of saturation. These results illustrate a complex cellular-regulatory network that controls HCV RNA replication, presumably by modulating the trafficking and association of cellular and/or viral proteins with cellular membranes, suggesting that pharmacologic manipulation of these pathways may have a therapeutic effect in chronic HCV infection.

The fate of free cholesterol released after endocytosis of low-density lipoproteins remains obscure. Here we report that late endosomes have a pivotal role in intracellular cholesterol transport. We find that in the genetic disease Niemann-Pick type C (NPC), and in drug-treated cells that mimic NPC, cholesterol accumulates in late endosomes and sorting of the lysosomal enzyme receptor is impaired. Our results show that the characteristic network of lysobisphosphatidic acid-rich membranes contained within multivesicular late endosomes regulates cholesterol transport, presumably by acting as a collection and distribution device. The results also suggest that similar endosomal defects accompany the anti-phospholipid syndrome and NPC.

Circulating levels of adiponectin, a hormone produced predominantly by adipocytes, are highly heritable and are inversely associated with type 2 diabetes mellitus (T2D) and other metabolic traits. We conducted a meta-analysis of genome-wide association studies in 39,883 individuals of European ancestry to identify genes associated with metabolic disease. We identified 8 novel loci associated with adiponectin levels and confirmed 2 previously reported loci (P = 4.5×10(-8)-1.2×10(-43)). Using a novel method to combine data across ethnicities (N = 4,232 African Americans, N = 1,776 Asians, and N = 29,347 Europeans), we identified two additional novel loci. Expression analyses of 436 human adipocyte samples revealed that mRNA levels of 18 genes at candidate regions were associated with adiponectin concentrations after accounting for multiple testing (p<3×10(-4)). We next developed a multi-SNP genotypic risk score to test the association of adiponectin decreasing risk alleles on metabolic traits and diseases using consortia-level meta-analytic data. This risk score was associated with increased risk of T2D (p = 4.3×10(-3), n = 22,044), increased triglycerides (p = 2.6×10(-14), n = 93,440), increased waist-to-hip ratio (p = 1.8×10(-5), n = 77,167), increased glucose two hours post oral glucose tolerance testing (p = 4.4×10(-3), n = 15,234), increased fasting insulin (p = 0.015, n = 48,238), but with lower in HDL-cholesterol concentrations (p = 4.5×10(-13), n = 96,748) and decreased BMI (p = 1.4×10(-4), n = 121,335). These findings identify novel genetic determinants of adiponectin levels, which, taken together, influence risk of T2D and markers of insulin resistance.

The lipid droplet (LD) is the major site of cholesterol storage in macrophage foam cells and is a potential therapeutic target for the treatment of atherosclerosis. Cholesterol, stored as cholesteryl esters (CEs), is liberated from this organelle and delivered to cholesterol acceptors. The current paradigm attributes all cytoplasmic CE hydrolysis to the action of neutral CE hydrolases. Here, we demonstrate an important role for lysosomes in LD CE hydrolysis in cholesterol-loaded macrophages, in addition to that mediated by neutral hydrolases. Furthermore, we demonstrate that LDs are delivered to lysosomes via autophagy, where lysosomal acid lipase (LAL) acts to hydrolyze LD CE to generate free cholesterol mainly for ABCA1-dependent efflux; this process is specifically induced upon macrophage cholesterol loading. We conclude that, in macrophage foam cells, lysosomal hydrolysis contributes to the mobilization of LD-associated cholesterol for reverse cholesterol transport.

OBJECTIVE

To investigate the association between stress at work and the metabolic syndrome. [table: see text].

METHODS

Prospective cohort study investigating the association between work stress and the metabolic syndrome.

METHODS

10 308 men and women, aged 35-55, employed in 20 London civil service departments at baseline (the Whitehall II study); follow-up was an average of 14 years.

METHODS

Work stress based on the iso-strain model, measured on four occasions (1985-99). Biological measures of the metabolic syndrome, based on the National Cholesterol Education Program definition, measured in 1997-9.

RESULTS

A dose-response relation was found between exposure to work stressors over 14 years and risk of the metabolic syndrome, independent of other relevant risk factors. Employees with chronic work stress (three or more exposures) were more than twice as likely to have the syndrome than those without work stress (odds ratio adjusted for age and employment grade 2.25, 95% confidence interval 1.31 to 3.85).

CONCLUSIONS

Stress at work is an important risk factor for the metabolic syndrome. The study provides evidence for the biological plausibility of the link between psychosocial stressors from everyday life and heart disease.

Plasma membrane compartmentalization imposes lateral segregation on membrane proteins that is important for regulating signal transduction. We use computational modeling of immunogold spatial point patterns on intact plasma membrane sheets to test different models of inner plasma membrane organization. We find compartmentalization at the nanoscale level but show that a classical raft model of preexisting stable domains into which lipid raft proteins partition is incompatible with the spatial point patterns generated by the immunogold labeling of a palmitoylated raft marker protein. Rather, approximately 30% of the raft protein exists in cholesterol-dependent nanoclusters, with approximately 70% distributed as monomers. The cluster/monomer ratio (number of proteins in clusters/number of proteins outside clusters) is independent of expression level. H-rasG12V and K-rasG12V proteins also operate in nanoclusters with fixed cluster/monomer ratios that are independent of expression level. Detailed calibration of the immunogold imaging protocol suggests that radii of raft and RasG12V protein nanoclusters may be as small as 11 and 6 nm, respectively, and shows that the nanoclusters contain small numbers (6.0-7.7) of proteins. Raft nanoclusters do not form if the actin cytoskeleton is disassembled. The formation of K-rasG12V but not H-rasG12V nanoclusters also is actin-dependent. K-rasG12V but not H-rasG12V signaling is abrogated by actin cytoskeleton disassembly, which shows that nanoclustering is critical for Ras function. These findings argue against stable preexisting domains on the inner plasma membrane in favor of dynamic actively regulated nanoclusters similar to those proposed for the outer plasma membrane. RasG12V nanoclusters may facilitate the assembly of essential signal transduction complexes.

OBJECTIVE

This study sought to characterize the prevalence of metabolic syndrome (MetS), its 5 components, and their pharmacological treatment in U.S. adults by sex and race/ethnicity over time.

BACKGROUND

MetS is a constellation of clinical risk factors for cardiovascular disease, stroke, kidney disease, and type 2 diabetes mellitus.

METHODS

Prevalence estimates were estimated in adults (≥ 20 years of age) from the National Health and Nutrition Examination Survey (NHANES) from 1999 to 2010 (in 2-year survey waves). The biological thresholds, defined by the 2009 Joint Scientific Statement, were: 1) waist circumference ≥ 102 cm (males adults) and ≥ 88 cm (female adults); 2) fasting plasma glucose ≥ 100 mg/dl; 3) blood pressure of ≥ 130/85 mm Hg; 4) triglycerides ≥ 150 mg/dl; and 5) high-density lipoprotein-cholesterol (HDL-C) <40 mg/dl (male adults) and <50 mg/dl (female adults). Prescription drug use was estimated for lipid-modifying agents, anti-hypertensives, and anti-hyperglycemic medications.

RESULTS

From 1999 and 2000 to 2009 and 2010, the age-adjusted prevalence of MetS (based on biologic thresholds) decreased from 25.5% (95% confidence interval [CI]: 22.5% to 28.6%) to 22.9% (95% CI: 20.3% to 25.5%). During this period, hypertriglyceridemia prevalence decreased (33.5% to 24.3%), as did elevated blood pressure (32.3% to 24.0%). The prevalence of hyperglycemia increased (12.9% to 19.9%), as did elevated waist circumference (45.4% to 56.1%). These trends varied considerably by sex and race/ethnicity. Decreases in elevated blood pressure, suboptimal triglycerides, and high-density lipoprotein-cholesterol prevalence have corresponded with increases in anti-hypertensive and lipid-modifying drugs, respectively.

CONCLUSIONS

The increasing prevalence of abdominal obesity, particularly among female adults, highlights the urgency of addressing abdominal obesity as a healthcare priority. The use of therapies for MetS components aligns with favorable trends in their prevalence.

BACKGROUND

We studied the joint effect of baseline triglyceride and lipoprotein cholesterol levels on the incidence of cardiac end points in the trial group (n = 4,081) of the Helsinki Heart Study, a 5-year randomized coronary primary prevention trial among dyslipidemic middle-aged men. The relative risks (RR) were calculated using Cox proportional hazards models with a dummy variable technique that allows simultaneous study of subgroup combinations from the placebo and treatment groups.

RESULTS

In the placebo group (n = 2,045), the low density lipoprotein cholesterol (LDL-C)/high density lipoprotein cholesterol (HDL-C) ratio was the best single predictor of cardiac events. This ratio in combination with the serum triglyceride level revealed a high-risk subgroup: subjects with LDL-C/HDL-C ratio greater than 5 and triglycerides greater than 2.3 mmol/l had a RR of 3.8 (95% CI, 2.2-6.6) compared with those with LDL-C/HDL-C ratio less than or equal to 5 and triglyceride concentration less than or equal to 2.3 mmol/l. In subjects with triglyceride concentration greater than 2.3 mmol/l and LDL-C/HDL-C ratio less than or equal to 5, RR was close to unity (1.1), whereas in those with triglyceride level less than or equal to 2.3 mmol/l and LDL-C/HDL-C ratio greater than 5, RR was 1.2. The high-risk group with LDL-C/HDL-C ratio greater than 5 and triglyceride level greater than 2.3 mmol/l profited most from treatment with gemfibrozil, with a 71% lower incidence of coronary heart disease events than the corresponding placebo subgroup. In all other subgroups, the reduction in CHD incidence was substantially smaller.

CONCLUSIONS

Serum triglyceride concentration has prognostic value, both for assessing coronary heart disease risk and in predicting the effect of gemfibrozil treatment, especially when used in combination with HDL-C and LDL-C.

Oxygenated derivatives of cholesterol (oxysterols) present a remarkably diverse profile of biological activities, including effects on sphingolipid metabolism, platelet aggregation, apoptosis, and protein prenylation. The most notable oxysterol activities center around the regulation of cholesterol homeostasis, which appears to be controlled in part by a complex series of interactions of oxysterol ligands with various receptors, such as the oxysterol binding protein, the cellular nucleic acid binding protein, the sterol regulatory element binding protein, the LXR nuclear orphan receptors, and the low-density lipoprotein receptor. Identification of the endogenous oxysterol ligands and elucidation of their enzymatic origins are topics of active investigation. Except for 24, 25-epoxysterols, most oxysterols arise from cholesterol by autoxidation or by specific microsomal or mitochondrial oxidations, usually involving cytochrome P-450 species. Oxysterols are variously metabolized to esters, bile acids, steroid hormones, cholesterol, or other sterols through pathways that may differ according to the type of cell and mode of experimentation (in vitro, in vivo, cell culture). Reliable measurements of oxysterol levels and activities are hampered by low physiological concentrations (approximately 0.01-0.1 microM plasma) relative to cholesterol (approximately 5,000 microM) and by the susceptibility of cholesterol to autoxidation, which produces artifactual oxysterols that may also have potent activities. Reports describing the occurrence and levels of oxysterols in plasma, low-density lipoproteins, various tissues, and food products include many unrealistic data resulting from inattention to autoxidation and to limitations of the analytical methodology. Because of the widespread lack of appreciation for the technical difficulties involved in oxysterol research, a rigorous evaluation of the chromatographic and spectroscopic methods used in the isolation, characterization, and quantitation of oxysterols has been included. This review comprises a detailed and critical assessment of current knowledge regarding the formation, occurrence, metabolism, regulatory properties, and other activities of oxysterols in mammalian systems.

Antidepressants targeting Na(+)/Cl(-)-coupled neurotransmitter uptake define a key therapeutic strategy to treat clinical depression and neuropathic pain. However, identifying the molecular interactions that underlie the pharmacological activity of these transport inhibitors, and thus the mechanism by which the inhibitors lead to increased synaptic neurotransmitter levels, has proven elusive. Here we present the crystal structure of the Drosophila melanogaster dopamine transporter at 3.0 Å resolution bound to the tricyclic antidepressant nortriptyline. The transporter is locked in an outward-open conformation with nortriptyline wedged between transmembrane helices 1, 3, 6 and 8, blocking the transporter from binding substrate and from isomerizing to an inward-facing conformation. Although the overall structure of the dopamine transporter is similar to that of its prokaryotic relative LeuT, there are multiple distinctions, including a kink in transmembrane helix 12 halfway across the membrane bilayer, a latch-like carboxy-terminal helix that caps the cytoplasmic gate, and a cholesterol molecule wedged within a groove formed by transmembrane helices 1a, 5 and 7. Taken together, the dopamine transporter structure reveals the molecular basis for antidepressant action on sodium-coupled neurotransmitter symporters and elucidates critical elements of eukaryotic transporter structure and modulation by lipids, thus expanding our understanding of the mechanism and regulation of neurotransmitter uptake at chemical synapses.

BACKGROUND

Calcific aortic stenosis has many characteristics in common with atherosclerosis, including hypercholesterolemia. We hypothesized that intensive lipid-lowering therapy would halt the progression of calcific aortic stenosis or induce its regression.

METHODS

In this double-blind, placebo-controlled trial, patients with calcific aortic stenosis were randomly assigned to receive either 80 mg of atorvastatin daily or a matched placebo. Aortic-valve stenosis and calcification were assessed with the use of Doppler echocardiography and helical computed tomography, respectively. The primary end points were change in aortic-jet velocity and aortic-valve calcium score.

RESULTS

Seventy-seven patients were assigned to atorvastatin and 78 to placebo, with a median follow-up of 25 months (range, 7 to 36). Serum low-density lipoprotein cholesterol concentrations remained at 130+/-30 mg per deciliter in the placebo group and fell to 63+/-23 mg per deciliter in the atorvastatin group (P<0.001). Increases in aortic-jet velocity were 0.199+/-0.210 m per second per year in the atorvastatin group and 0.203+/-0.208 m per second per year in the placebo group (P=0.95; adjusted mean difference, 0.002; 95 percent confidence interval, -0.066 to 0.070 m per second per year). Progression in valvular calcification was 22.3+/-21.0 percent per year in the atorvastatin group, and 21.7+/-19.8 percent per year in the placebo group (P=0.93; ratio of post-treatment aortic-valve calcium score, 0.998; 95 percent confidence interval, 0.947 to 1.050).

CONCLUSIONS

Intensive lipid-lowering therapy does not halt the progression of calcific aortic stenosis or induce its regression. This study cannot exclude a small reduction in the rate of disease progression or a significant reduction in major clinical end points. Long-term, large-scale, randomized, controlled trials are needed to establish the role of statin therapy in patients with calcific aortic stenosis.

Genome-wide association studies have identified a region on chromosome 9p that is associated with coronary artery disease (CAD). The region is also associated with type 2 diabetes (T2D), a risk factor for CAD, although different SNPs were reported to be associated to each disease in separate studies. We have undertaken a case-control study in 4251 CAD cases and 4443 controls in four European populations using previously reported ('literature') and tagging SNPs. We replicated the literature SNPs (P = 8x10(-13); OR = 1.29; 95% CI: 1.20-1.38) and showed that the strong consistent association detected by these SNPs is a consequence of a 'yin-yang' haplotype pattern spanning 53 kb. There was no evidence of additional CAD susceptibility alleles over the major risk haplotype. CAD patients without myocardial infarction (MI) showed a trend towards stronger association than MI patients. The CAD susceptibility conferred by this locus did not differ by sex, age, smoking, obesity, hypertension or diabetes. A simultaneous test of CAD and diabetes susceptibility with CAD and T2D-associated SNPs indicated that these associations were independent of each other. Moreover, this region was not associated with differences in plasma levels of low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, fibrinogen, albumin, uric acid, bilirubin or homocysteine, although the CAD-high-risk allele was paradoxically associated with lower triglyceride levels. A large antisense non-coding RNA gene (ANRIL) collocates with the high-risk haplotype, is expressed in tissues and cell types that are affected by atherosclerosis and is a prime candidate gene for the chromosome 9p CAD locus.

The rate-limiting enzyme of cholesterol biosynthesis, HMG CoA reductase, is controlled by negative feedback regulation of transcription. We have isolated the reductase gene from a bacteriophage lambda genomic library prepared from hamster UT-1 cells. The 25 kilobase gene is split into 20 exons. The 5' untranslated and promoter regions differ from those of previously characterized genes. The 5' untranslated region encompasses as many as 670 nucleotides; contains up to eight AUG codons upstream of the codon used to initiate translation; and has multiple transcription initiation sites as determined by S1 nuclease mapping and primer extension analysis. The promoter region lacks a characteristic TATA box and CCAAT box; is rich in G + C residues (65%); and contains repeat sequences homologous to the 21 base pair repeats of the SV40 promoter. These unusual features may be relevant to the mechanism of expression of "housekeeping" genes, particularly those that are subject to negative feedback regulation.

Cholesterol is an essential component of mammalian cell membranes and is required for proper membrane permeability, fluidity, organelle identity, and protein function. Cells maintain sterol homeostasis by multiple feedback controls that act through transcriptional and posttranscriptional mechanisms. The membrane-bound transcription factor sterol regulatory element binding protein (SREBP) is the principal regulator of both sterol synthesis and uptake. In mammalian cells, the ER membrane protein Insig has emerged as a key component of homeostatic regulation by controlling both the activity of SREBP and the sterol-dependent degradation of the biosynthetic enzyme HMG-CoA reductase. In this review, we focus on recent advances in our understanding of the molecular mechanisms of the regulation of sterol synthesis. A comparative analysis of SREBP and HMG-CoA reductase regulation in mammals, yeast, and flies points toward an equilibrium model for how lipid signals regulate the activity of sterol-sensing proteins and their downstream effectors.

OBJECTIVE

In men, hypoandrogenism is associated with features of the metabolic syndrome, but the role of sex hormones in the pathogenesis of the metabolic syndrome and diabetes is not well understood. We assessed the association of low levels of testosterone and sex hormone-binding globulin (SHBG) with the development of the metabolic syndrome and diabetes in men.

METHODS

Concentrations of SHBG and total and calculated free testosterone and factors related to insulin resistance were determined at baseline in 702 middle-aged Finnish men participating in a population-based cohort study. These men had neither diabetes nor the metabolic syndrome.

RESULTS

After 11 years of follow-up, 147 men had developed the metabolic syndrome (National Cholesterol Education Program criteria) and 57 men diabetes. Men with total testosterone, calculated free testosterone, and SHBG levels in the lower fourth had a severalfold increased risk of developing the metabolic syndrome (odds ratio [OR] 2.3, 95% CI 1.5-3.4; 1.7, 1.2-2.5; and 2.8, 1.9-4.1, respectively) and diabetes (2.3, 1.3-4.1; 1.7, 0.9-3.0; and 4.3, 2.4-7.7, respectively) after adjustment for age. Adjustment for potential confounders such as cardiovascular disease, smoking, alcohol intake, and socioeconomic status did not alter the associations. Factors related to insulin resistance attenuated the associations, but they remained significant, except for free testosterone.

CONCLUSIONS

Low total testosterone and SHBG levels independently predict development of the metabolic syndrome and diabetes in middle-aged men. Thus, hypoandrogenism is an early marker for disturbances in insulin and glucose metabolism that may progress to the metabolic syndrome or frank diabetes and may contribute to their pathogenesis.

BACKGROUND

Lower blood cholesterol concentrations have consistently been found to be strongly associated with lower risks of coronary disease but not with lower risks of stroke. Despite this observation, previous randomised trials had indicated that cholesterol-lowering statin therapy reduces the risk of stroke, but large-scale prospective confirmation has been needed.

METHODS

3280 adults with cerebrovascular disease, and an additional 17256 with other occlusive arterial disease or diabetes, were randomly allocated 40 mg simvastatin daily or matching placebo. Subgroup analyses were prespecified of first "major vascular event" (ie, non-fatal myocardial infarction or coronary death, stroke of any type, or any revascularisation procedure) in prior disease subcategories. Subsidiary outcomes included any stroke, and stroke sub-type. Comparisons are of all simvastatin-allocated versus all placebo-allocated participants (ie, "intention-to-treat"), which yielded an average difference in LDL cholesterol of 1.0 mmol/L (39 mg/dL) during the 5-year treatment period.

RESULTS

Overall, there was a highly significant 25% (95% CI 15-34) proportional reduction in the first event rate for stroke (444 [4.3%] simvastatin vs 585 [5.7%] placebo; p<0.0001), reflecting a definite 28% (19-37) reduction in presumed ischaemic strokes (p<0.0001) and no apparent difference in strokes attributed to haemorrhage (51 [0.5%] vs 53 [0.5%]; rate ratio 0.95 [0.65-1.40]; p=0.8). In addition, simvastatin reduced the numbers having transient cerebral ischaemic attacks alone (2.0% vs 2.4%; p=0.02) or requiring carotid endarterectomy or angioplasty (0.4% vs 0.8%; p=0.0003). The reduction in stroke was not significant during the first year, but was already significant (p=0.0004) by the end of the second year. Among patients with pre-existing cerebrovascular disease there was no apparent reduction in the stroke rate, but there was a highly significant 20% (8-29) reduction in the rate of any major vascular event (406 [24.7%] vs 488 [29.8%]; p=0.001). The proportional reductions in stroke were about one-quarter in each of the other subcategories of participant studied, including: those with coronary disease or diabetes; those aged under or over 70 years at entry; and those presenting with different levels of blood pressure or lipids (even when the pretreatment LDL cholesterol was below 3.0 mmol/L [116 mg/dL]).

CONCLUSIONS

Much larger numbers of people in the present study suffered a stroke than in any previous cholesterol-lowering trial. The results demonstrate that statin therapy rapidly reduces the incidence not only of coronary events but also of ischaemic strokes, with no apparent effect on cerebral haemorrhage, even among individuals who do not have high cholesterol concentrations. Allocation to 40 mg simvastatin daily reduced the rate of ischaemic strokes by about one-quarter and so, after making allowance for non-compliance in the trial, actual use of this regimen would probably reduce the stroke rate by about a third. HPS also provides definitive evidence that statin therapy is beneficial for people with pre-existing cerebrovascular disease, even if they do not already have manifest coronary disease.

BACKGROUND

Alterations in serum lipid values have been widely reported among persons infected with human immunodeficiency virus (HIV) type 1 treated with highly active antiretroviral therapy (HAART), but no data have yet been reported on changes from preseroconversion lipid values.

OBJECTIVE

To describe changes in serum cholesterol levels associated with HIV infection and antiretroviral medication exposure, and 1-time assessment of triglyceride levels post-HAART initiation.

METHODS

The Multicenter AIDS Cohort Study, a prospective study in which homosexual and bisexual men were enrolled and from which 50 of 517 HIV seroconverters were drawn for the analysis herein, who later initiated HAART, involving measurements of stored serum samples obtained between 1984 and 2002.

METHODS

Changes in levels of total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), and low-density lipoprotein cholesterol (LDL-C) at 6 time points during an average of 12 years; 1-time assessment of triglyceride levels from the third post-HAART clinic visit.

RESULTS

Among the 50 men, notable declines in mean serum TC (-30 mg/dL [-0.78 mmol/L]), HDL-C (-12 mg/dL [-0.31 mmol/L]), and LDL-C values (-22 mg/dL [-0.57 mmol/L]) were observed after HIV infection. Following HAART initiation, there were large increases in mean TC and LDL-C values (50 and 21 mg/dL [1.30 and 0.54 mmol/L], respectively); however, the mean changes from the preseroconversion values were 20 mg/dL (0.52 mmol/L) (95% confidence interval [CI], -1 to 41) and -1 mg/dL (-0.03 mmol/L) (95% CI, -25 to 22), respectively. Mean HDL-C remained below baseline levels throughout follow-up. The median value (interquartile range) of triglycerides was 225 mg/dL (2.54 mmol/L) (147-331 mg/dL).

CONCLUSIONS

Before treatment, HIV infection results in substantial decreases in serum TC, HDL-C, and LDL-C levels. Subsequent HAART initiation is associated with increases in TC and LDL-C but little change in HDL-C. Increases in TC and LDL-C observed after about 3 years of HAART possibly represent a return to preinfection serum lipid levels after accounting for expected age-related changes.

Mammalian cells acquire cholesterol from low-density lipoprotein (LDL) and from endogenous biosynthesis. The roles of the Niemann-Pick type C1 protein in mediating the endosomal transport of LDL-derived cholesterol and endogenously synthesized cholesterol are discussed. Excess cellular cholesterol is converted to cholesteryl esters by the enzyme acyl-coenzyme A:cholesterol acyltransferase (ACAT) 1 or is removed from a cell by cellular cholesterol efflux at the plasma membrane. A close relationship between the ACAT substrate pool and the cholesterol efflux pool is proposed. Sterol-sensing domains (SSDs) are present in several membrane proteins, including NPC1, HMG-CoA reductase, and the SREBP cleavage-activating protein. The functions of SSDs are described. ACAT1 is an endoplasmic reticulum cholesterol sensor and contains a signature motif characteristic of the membrane-bound acyltransferase family. The nonvesicular cholesterol translocation processes involve the START domain proteins and the oxysterol binding protein-related proteins (ORPs). The properties of these proteins are summarized.

Apolipoprotein E (APOE) is a cholesterol transport protein and an isoform-specific major risk factor for neurodegenerative diseases. The lipoprotein receptors that bind APOE have recently been recognized as pivotal components of the neuronal signalling machinery. The interaction between APOE receptors and one of their ligands, reelin, allows them to function directly as signal transduction receptors at the plasma membrane to control not only neuronal positioning during brain development, but also synaptic plasticity in the adult brain. Here, we review the molecular mechanisms through which APOE, cholesterol, reelin and APOE receptors control synaptic functions that are essential for cognition, learning, memory, behaviour and neuronal survival.