Fenofibrate-associated changes in renal function and relationship to clinical outcomes among individuals with type 2 diabetes: the Action to Control Cardiovascular Risk in Diabetes (ACCORD) experience.

AIMS/HYPOTHESIS: Fenofibrate has been noted to cause an elevation in serum creatinine in some individuals. Participants in the Action to Control Cardiovascular Risk in Diabetes Lipid Study were studied to better characterise who is at risk of an increase in creatinine level and to determine whether those with creatinine elevation have a differential risk of adverse renal or cardiovascular outcomes. METHODS: A fenofibrate-associated creatinine increase (FACI) was defined as an increase in serum creatinine of at least 20% from baseline to month 4 in participants assigned to fenofibrate. Baseline patient characteristics, and baseline and 4-month drug, clinical, laboratory characteristics and study outcomes were examined by FACI status. RESULTS: Of the sample, 48% of those randomised to receive fenofibrate had at least a 20% increase in serum creatinine within 4 months. In multivariable analysis, participants who were older, male, used an ACE inhibitor at baseline, used a thiazolidinedione (TZD) at 4 months post-randomisation, had baseline CVD, and had lower baseline serum creatinine and LDL-cholesterol levels were all more likely to meet the criteria for FACI. Participants in the FACI group were also more likely to have a decrease in their serum triacylglycerol level from baseline to 4 months. No differences in study outcomes were seen by FACI criteria. CONCLUSIONS/INTERPRETATION: Several characteristics predict a rapid rise in serum creatinine upon starting fenofibrate. Participants who met the criteria for FACI also had a greater change in triacylglycerol levels. In the setting of careful renal function surveillance and reduction of fenofibrate dose as indicated, no increase in renal disease or cardiovascular outcome was seen in those individuals demonstrating FACI. TRIAL REGISTRATION: ClincalTrials.gov: NCT00000620. FUNDING: The ACCORD Trial was supported by grants (N01-HC-95178, N01-HC-95179, N01-HC-95180, N01-HC-95181, N01-HC-95182, N01-HC-95183, N01-HC-95184, IAA-Y1-HC-9035 and IAA-Y1-HC-1010) from the National Heart, Lung, and Blood Institute; by the National Institute of Diabetes and Digestive and Kidney Diseases, the National Institute on Aging, and the National Eye Institute; by the Centers for Disease Control and Prevention; by General Clinical Research Centers and by the Clinical and Translational Science Awards. Abbott Laboratories, Amylin Pharmaceutical, AstraZeneca Pharmaceuticals LP, Bayer HealthCare LLC, Closer Healthcare, GlaxoSmithKline Pharmaceuticals, King Pharmaceuticals, Merck, Novartis Pharmaceuticals, Novo Nordisk, Omron Healthcare, sanofi-aventis US and Takeda Pharmaceuticals provided study medications, equipment or supplies.

HIV protease inhibitors protect apolipoprotein B from degradation by the proteasome: a potential mechanism for protease inhibitor-induced hyperlipidemia.

Highly active anti-retroviral therapies, which incorporate HIV protease inhibitors, resolve many AIDS-defining illnesses. However, patients receiving protease inhibitors develop a marked lipodystrophy and hyperlipidemia. Using cultured human and rat hepatoma cells and primary hepatocytes from transgenic mice, we demonstrate that protease inhibitor treatment inhibits proteasomal degradation of nascent apolipoprotein B, the principal protein component of triglyceride and cholesterol-rich plasma lipoproteins. Unexpectedly, protease inhibitors also inhibited the secretion of apolipoprotein B. This was associated with inhibition of cholesteryl-ester synthesis and microsomal triglyceride transfer-protein activity. However, in the presence of oleic acid, which stimulates neutral-lipid biosynthesis, protease-inhibitor treatment increased secretion of apolipoprotein B-lipoproteins above controls. These findings suggest a molecular basis for protease-inhibitor-associated hyperlipidemia, a serious adverse effect of an otherwise efficacious treatment for HIV infection.

Overexpression of the A1 adenosine receptor in adipose tissue protects mice from obesity-related insulin resistance.

In-vitro studies have implicated the A(1) adenosine receptor (A(1)AR) of adipocytes in inhibition of lipolysis, stimulation of lipogenesis and enhancement of the action of insulin on glucose metabolism. To determine whether any of these activities were physiologically relevant in an intact animal, A(1)AR was overexpressed in adipose tissue of transgenic mice. Lower plasma free fatty acid (FFA) levels were observed in the transgenic mice relative to the litter-matched controls, supporting a significant physiological role for adipocyte A(1)AR in the control of lipolysis. However, no differences were observed in body weights or body composition. On a high fat diet, both the transgenic mice and the litter matched controls, male and female, became equally obese. Unlike the control mice, however, the transgenic mice did not develop insulin resistance, as demonstrated by serum glucose and insulin levels and glucose and insulin tolerance tests. These findings demonstrate that adipocyte A(1)AR plays an important physiological role in the control of insulin sensitivity in an intact animal and therefore should be considered to be a potential therapeutic target for the treatment of obesity-related insulin resistance and type 2 diabetes.

Post-transcriptional stimulation of the assembly and secretion of triglyceride-rich apolipoprotein B lipoproteins in a mouse with selective deficiency of brown adipose tissue, obesity, and insulin resistance.

A mouse model of insulin resistance and its associated dyslipidemia was generated by crossing mice expressing human apolipoprotein B (apoB) with mice lacking only brown adipose tissue (BATless). On a high fat diet, male apoB/BATless mice became obese, hypercholesterolemic, hypertriglyceridemic, and hyperinsulinemic compared with control apoB mice. Fast performance liquid chromatography revealed increased triglyceride concentrations in intermediate density lipoprotein/low density lipoprotein (LDL) and reduced high density lipoprotein cholesterol concentrations. Inhibition of lipolysis by the drug, tetrahydrolipostatin, demonstrated that very low density lipoprotein-sized particles were initially secreted. Metabolic studies employing Triton WR-1339 and either [(3)H]glycerol or [(3)H]palmitate showed that the hypertriglyceridemia in apoB/BATless mice was due to the increased synthesis and secretion of triglyceride. Furthermore, lipoprotein lipase and hepatic lipase activities were not defective. ApoB was also secreted at increased rates in the apoB/BATless mice. Similar levels of apoB mRNA in apoB and apoB/BATless mice indicated that apoB secretion was regulated post-transcriptionally. LDL receptor mRNA was increased in the apoB/BATless mice, indicating that the observed increase in apoB-lipoprotein secretion was not due to their decreased reuptake. Finally, mRNA levels of the large subunit of microsomal triglyceride transfer protein, a required component for very low density protein assembly, were not different between apoB and apoB/BATless mice. This rodent model should prove useful in exploring mechanisms underlying the regulation of apoB secretion in the context of insulin resistance.

Postprandial dyslipidemia: an atherogenic disorder common in patients with diabetes mellitus.

The increased risk of coronary artery disease among patients with diabetes mellitus is attributable, in part, to specific disorders of lipoprotein metabolism that are common in this population. These include disordered metabolism of very-low-density lipoprotein and/or chylomicrons that may be proatherogenic. Elevated postprandial triglycerides, peak postprandial triglyceridemia, and late postprandial triglyceride levels have been associated in clinical trials with both early coronary artery and carotid artery atherosclerosis for persons with normal lipid profiles and those with mild-to-moderate hyperlipidemia, independently of established risk factors. If hyperlipidemia cannot be managed through better glycemic control, diet, and exercise, then hepatic 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors, fibric acid derivatives, and omega-3 fatty acids are safe and effective lipid-altering agents that can be used to correct these disorders.

Age-related effects of genetic variation on lipid levels: The Columbia University BioMarkers Study.

OBJECTIVES: To examine the genotype:phenotype association in children compared with their parents. METHODS: Variations at 4 key gene loci, namely lipoprotein lipase (LPL S447X), hepatic lipase (HL -480C>T), cholesteryl ester transfer protein (CETP TaqIB), and apolipoprotein CIII (APOC3 -455T>C and -482C>T), were examined in children (n = 495) and their parents (n = 353) in the Columbia University BioMarkers Study, 1994 to 1998. RESULTS: The frequencies of the rare alleles of the HL -480C>T and APOC3 -455T>C and -482C>T (but not LPL S447X or CETP TaqIB) were significantly lower in non-Hispanic white participants compared with Hispanics. Overall, genotype effects seen in the adults were weaker in the children, although similar trends were seen. In an examination of the effect of body fat on the genotypic effects in the children, there was significant HL -480C>T:sum of skinfold interaction. CONCLUSIONS: All genotypes were associated with clear relationships to plasma lipid levels in adults, but the effects were weaker in their children, unless stressed by body fat. atherosclerosis, cardiovascular disease, child, lipids, genetics.

Microsomal triglyceride transfer protein binding and lipid transfer activities are independent of each other, but both are required for secretion of apolipoprotein B lipoproteins from liver cells.

Recent studies indicate that microsomal triglyceride transfer protein (MTP) and apolipoprotein B (apoB) interact physically via two specific binding sites located within the amino-terminal globular region of apoB100. The first site is thought to be within the first 5.8% of the amino-terminal sequence, and the second site is between 9 and 16% of the amino-terminal sequence. It is not clear from prior studies whether these sites have unique or overlapping functions. Furthermore, there are no data differentiating between lipid transfer and potential chaperone functions of MTP. In the present study we have attempted to further characterize the physiologic interaction between apoB and MTP and to determine the relationship between the binding and lipid transfer aspects of the interaction. HepG2 cells were transiently transfected with apoB cDNAs, and MTP binding to apoB polypeptides was determined by two-step immunoprecipitation. MTP bound equally well to apoB polypeptides with (apoB13, 16,beta, apoB34, and apoB42) or without (apoB16, apoB13, and 16 or apoB13, 13, and 16) beta sheet domains. When proteasomal degradation of newly synthesized apoB polypeptides was blocked, MTP binding to all of the apoB polypeptides was only modestly affected by lipid availability and was independent of MTP-associated lipid transfer. Furthermore, MTP did not bind directly to a portion of the first beta sheet domain. We created two apoB constructs (apoB16del and apoB34del) by deleting the first 210 amino acids of apoB16 and apoB34. These apoB polypeptides, therefore, lacked the putative first MTP binding site. MTP binding to apoB16del and apoB34del was decreased significantly. However, the secretion of apoB16del was not different from apoB16, whereas the secretion of apoB34del was impaired significantly. Our results indicate that the interaction between MTP and apoB involves independent binding and lipid transfer activities but that both activities are required for the secretion of apolipoprotein B from liver cells.

Variation in the human ApoB signal peptide modulates ApoB17 translocation.

The functional effects of the common 27- or 24-amino-acid (aa) variants in the human apoB signal peptide (SP) on intracellular and secreted apoB17 were investigated in vitro. Only in the presence of oleate was a significant difference in intracellular and secreted SP27-B17 compared to SP24-B17 observed (P = 0.01 and P < 0.0007, respectively), although in the presence or absence of oleate mRNA levels from the two constructs were similar. After fractionation, oleate treatment enhanced microsomal SP27-B17 by 150% (P < 0.0005) with a modest but significant effect on SP24-B17 (32% P = 0.007). Oleate stimulated SP24-B17 accumulation in the nonmicrosomal fraction. The data suggest that the presence of oleate leads to inefficient translocation of the 24-amino-acid signal peptide, possibly resulting in increased retrograde translocation into the cytoplasm and reduced intracellular and secreted levels compared to the "wildtype" 27 aa SP. This implies a direct role of the SP variants in the regulation of apoB intracellular metabolism.

Co-translational interactions of apoprotein B with the ribosome and translocon during lipoprotein assembly or targeting to the proteasome.

Hepatic lipoprotein assembly and secretion can be regulated by proteasomal degradation of newly synthesized apoB, especially if lipid synthesis or lipid transfer is low. Our previous studies in HepG2 cells showed that, under these conditions, newly synthesized apoB remains stably associated with the endoplasmic reticulum (ER) membrane (Mitchell, D. M., Zhou, M., Pariyarath, R., Wang, H., Aitchison, J. D., Ginsberg, H. N., and Fisher, E. A. (1998) Proc. Natl. Acad. Sci. U. S. A. 95, 14733-14738). We now show that independent of lipid synthesis, apoB chains that appear full-length are, in fact, incompletely translated polypeptides still engaged by the ribosome and associated with the ER translocon. In the presence of active lipid synthesis and transfer, translation and lipoprotein assembly are completed, and the complexes exit the ER. Upon omitting fatty acids from, or adding a microsomal triglyceride transfer protein inhibitor to, culture media to reduce lipid synthesis or transfer, respectively, apoB was degraded while it remained associated with the ER and complexed with cytosolic hsp70 and proteasomes. Thus, unlike other ER substrates of the proteasome, such as major histocompatibility complex class I molecules, apoB does not fully retrotranslocate to the cytosol before entering the ubiquitin-proteasome pathway. Although, upon immunofluorescence, apoB in proteasome-inhibited cells accumulated in punctate structures similar in appearance to aggresomes (cytosolic structures containing molecules irreversibly lost from the secretory pathway), these apoB molecules could be secreted when lipid synthesis was stimulated. The results suggest a model in which 1) apoB translation does not complete until lipoprotein assembly terminates, and 2) assembly with lipids or entry into the ubiquitin-proteasome pathway occurs while apoB polypeptides remain associated with the translocon and attached to the ribosome.

Diabetes and dyslipidemia.

Numerous prospective cohort studies have indicated that diabetes mellitus (DM), particularly type-2 DM (the type of diabetes associated with insulin resistance that usually strikes adults), is associated with a 3-4-fold increase in risk for coronary heart disease (CHD) [1-3]. The increase in risk is particularly evident in younger-age groups, and in women: females with type-2 DM appear to lose a great deal of the protection that characterizes non-diabetic females. Furthermore, patients with DM have a 50% greater in-hospital mortality, and a 2-fold increased rate of death within 2 years of surviving a myocardial infarction. Overall, CHD is the leading cause of death in individuals with DM who are >35 years old. Although a significant portion of this increased risk is associated with the presence of well-characterized risk factors for CHD, a significant proportion remains unexplained. Patients with DM, particularly those with type-2 DM, have abnormal plasma lipid and lipoprotein concentrations that are less commonly present in non-diabetics [4-6]. Patients with poorly controlled type-1 DM can also have a dyslipidemic pattern, but, in this review, we will focus on the dyslipidemia seen commonly in patients with type-2 DM. In particular, we will describe the pathophysiology underlying the increase in plasma very low-density lipoprotein triglyceride levels, the reductions in plasma high-density lipoprotein cholesterol levels, and the abnormal, small, dense low-density lipoproteins that are the central components of diabetic dyslipidemia. The dyslipidemia of DM clearly adds significantly to the high risk for CHD in this group, and must be treated aggressively with diet, weight loss and lipid-altering medications. Combinations of lipid-altering medications, particularly statins and fibrates, can markedly change plasma lipid levels, often bringing them all into the normal range.

Predictors of postprandial triacylglycerol response in children: the Columbia University Biomarkers Study.

BACKGROUND: Predictors of postprandial lipemia have not been explored in children. OBJECTIVE: Our objective was to determine whether the postprandial triacylglycerol response is associated with low HDL-cholesterol and high fasting triacylglycerol concentrations and family history of early-onset ischemic heart disease (IHD) in children. DESIGN: We administered a standardized fat load (52.5 g fat/m(2)) to 60 children (mean age: 14.0 y), 20 with and 40 without a family history of early-onset IHD, and to 29 mothers, all recruited from families enrolled in the Columbia University Biomarkers Study. Plasma lipid and retinyl palmitate concentrations were measured in the fasting state and 3, 6, and 8 h after the oral fat load. RESULTS: In children, postprandial lipemia, as indicated by the incremental area under the triacylglycerol response curve, was associated with elevated fasting triacylglycerol concentrations (>/=1.13 mmol/L; P: < 0.01), with low fasting HDL-cholesterol concentrations (

Acute elevations of plasma asymmetric dimethylarginine and impaired endothelial function in response to a high-fat meal in patients with type 2 diabetes.

Asymmetric dimethylarginine (ADMA), a compound detectable in human plasma, is an endogenous inhibitor of NO synthase. Endothelial dysfunction is an early event in atherogenesis, and large-vessel atherosclerosis is a major cause of morbidity and mortality in patients with type 2 diabetes mellitus. Fifty patients with type 2 diabetes mellitus were studied at baseline and 5 hours after ingestion of a high-fat meal. Plasma ADMA measured by using high-performance liquid chromatography increased from 1.04+/-0.99 to 2.51+/-2.27 micromol/L (P:<0.0005). Brachial arterial vasodilation after reactive hyperemia, a NO-dependent function, measured by high-resolution ultrasound, decreased from 6.9+/-3.9% at baseline to 1.3+/-4.5% (P:<0.0001). These changes occurred in association with increased plasma levels of triglycerides and very low density lipoprotein triglycerides, with reduced low density lipoprotein cholesterol and high density lipoprotein cholesterol, and with no changes in total cholesterol. The increase in plasma ADMA in response to a high-fat meal was significantly and inversely related to the decrease in percent vasodilation. In 10 of the subjects studied with a similar protocol on another day, no significant changes in the brachial artery flow responses or in plasma ADMA were observed 5 hours after ingestion of a nonfat isocaloric meal. The data suggest that ADMA may contribute to abnormal blood flow responses and to atherogenesis in type 2 diabetics.

The amino-terminal domain of apolipoprotein B does not undergo retrograde translocation from the endoplasmic reticulum to the cytosol. Proteasomal degradation of nascent apolipoprotein B begins at the carboxyl terminus of the protein, while apolipoprotein B is still in its original translocon.

We studied the sequential topology of the NH(2) and COOH termini of apoB during translocation by expressing, in Chinese hamster ovary (CHO) and HepG2 cells, an apoB42 construct with c-Myc and hemagglutinin (HA) tags at 2 and 41% (relative to apoB100) of its amino acid sequence. We conducted similar studies using monoclonal antibodies against the NH(2) and COOH termini of apoB100 in HepG2 cells. After radiolabeling, microsomes were immunoisolated from transfected CHO cells using anti-c-Myc or anti-HA antibodies. Throughout a 60-min chase in the presence of N-acetyl-leucyl-norleucinal, more than 90% of microsomes were isolated by anti-HA antibodies, whereas less than 10% were isolated by anti-c-Myc antibodies. Proteinase K digestion of total microsomes consistently generated two fragments ( approximately 70 and approximately 120 kDa) of apoB42 containing the NH(2) terminus throughout the chase; no fragments containing the COOH terminus were detected. Immunofluorescent studies of transfected CHO cells were consistent with results from the labeling studies. Essentially identical results were obtained from pulse-chase studies in both native and apoB42-transfected HepG2 cells. The present studies support a model in which, in the absence of adequate core lipid synthesis, there is partial translocation of apoB leading to cytosolic exposure, ubiquitination, and proteasomal degradation directly from the original translocation channel.

Inhibition of translocation of nascent apolipoprotein B across the endoplasmic reticulum membrane is associated with selective inhibition of the synthesis of apolipoprotein B.

In HepG2 cells, inhibition of apolipoprotein B100 (apoB) translocation across the endoplasmic reticulum by an microsomal triglyceride transfer protein (MTP) inhibitor (CP-10447) in the presence of N-acetyl-leucinyl-norleucinal, a proteasomal inhibitor, results in accumulation of newly synthesized apoB in the translocation channel. Here we demonstrated that such accumulation led to a specific reduction of apoB synthesis. ApoB mRNA levels remained unchanged, but we observed reduced rates of elongation of nascent apoB in puromycin-synchronized cells pretreated with MTP inhibitor. This observation was consistent with a longer half-ribosome transit time for the synthesis of apoB in MTP-inhibited cells. Initiation of translation of apoB mRNA was not impaired by MTP inhibition. Overall, these findings suggest that translocation arrest of apoB in the endoplasmic reticulum channel can exert a selective and negative effect on the synthesis of apoB at the stage of elongation.

Circulating lipoprotein profiles are modulated differently by lipoprotein lipase in obese humans.

BACKGROUND: Several genetic analyses have suggested that lipoprotein lipase (LpL) genotypes causing decreased LpL activity correlate with increased triglyceride concentrations and risk for coronary artery disease. In contrast, in some other studies LpL activity was positively correlated with plasma low-density lipoprotein (LDL) cholesterol concentrations. OBJECTIVE: To assess whether these different associations represent physiologic differences in lipoprotein metabolism. METHODS: We correlated postheparin lipase activities, postprandial lipemia, and fasting lipoprotein concentrations in obese (BMI > or = 30 kg/m2, n = 26) and non-obese (BMI < or = 30 kg/m2, n = 57) individuals. LpL was measured using specific inhibitory antibodies. RESULTS: Surprisingly, LpL activity was significantly correlated with triglyceride area under the curve after a fat load in the non-obese, but not the entire group. Moreover, in non-obese individuals, LpL activity correlated directly (r = 0.40) and hepatic lipase activity correlated inversely (r = -0.32) with high-density lipoprotein (HDL) cholesterol concentrations. These relationships were not found in the obese group, in whom LpL correlated with LDL cholesterol concentrations (r = 0.54). CONCLUSIONS: We conclude that postheparin LpL activity relates to different lipoproteins in obese and non-obese individuals. In obesity, greater LpL activity may enhance conversion of very-low-density lipoprotein cholesterol to LDL cholesterol, whereas in non-obese individuals the correlation is with HDL cholesterol. Whether this is due to differences in the source of LpL (muscle or fat), or to other associated alterations in lipoprotein metabolism is unknown. These results may explain the non-uniformity of correlations between LpL and atherogenic lipoproteins in different populations.

The insulin resistance syndrome: impact on lipoprotein metabolism and atherothrombosis.

Insulin resistance is a common metabolic abnormality that is associated with an increased risk of both atherosclerosis and type 2 diabetes. The phenotype of insulin resistance includes a dyslipidemia characterized by an elevation of very low-density lipoprotein triglyceride, a reduction in high-density lipoprotein cholesterol, and the presence of small, triglyceride-enriched low-density lipoproteins. The underlying metabolic abnormality driving this dylipidemia is an increased assembly and secretion of very low-density lipoprotein particles, leading to an increased plasma level of triglyceride. Hypertriglyceridemia, in turn, results in a reduction in the high-density lipoprotein level and the generation of small, dense low-density lipoproteins; these events are mediated by cholesteryl ester transfer protein. In addition, hypertension, obesity, and a prothrombotic state are also integral components of the insulin resistance syndrome. In this review, we will provide a pathophysiologic basis, based on studies on humans and in tissue culture, for the dyslipidemia of insulin resistance. We will also review the effects of insulin resistance on the coagulation and fibrinolytic pathways. It is hoped that this review will allow health professionals better to evaluate and treat their patients with insulin resistance, thereby reducing the very much increased risk of atherosclerotic cardiovascular disease carried by these individuals.

Nonpharmacologic management of low levels of high-density lipoprotein cholesterol.

Several nonpharmacologic approaches can effectively increase low serum levels of high-density lipoprotein cholesterol (HDL-C), including weight control, specific nutritional choices, exercise, alcohol consumption, and smoking cessation. Increased visceral fat is inversely associated with HDL-C in both men and women. During weight reduction, HDL-C, HDL2-C, and apolipoprotein A-1 (apo A-1) tend to decrease, but levels increase with sustained weight loss. Overall, weight cycling is not detrimental in terms of serum lipids. Increasing monounsaturated fat intake and reducing carbohydrates increases HDL-C levels. Lowering trans-fatty acid intake also improves serum lipids. A very low-fat diet combined with stress-lowering lifestyle changes has been shown to cause regression of coronary artery disease. Moderate alcohol consumption, even in diabetic patients, and smoking cessation can increase serum HDL-C levels.