Hypertriglyceridemic very low density lipoproteins induce triglyceride synthesis and accumulation in mouse peritoneal macrophages

Sirt6 enhances macrophage lipophagy and improves lipid metabolism disorder by regulating the Wnt1/β-catenin pathway in atherosclerosis

Lipid metabolism disorders are considerably involved in the pathology of atherosclerosis; nevertheless, the fundamental mechanism is still largely unclear. This research sought to examine the function of lipophagy in lipid metabolism disorder-induced atherosclerosis and its fundamental mechanisms. Previously, Sirt6 has been reported to stimulate plaque stability by promoting macrophage autophagy. However, its role in macrophage lipophagy and its relationship with Wnt1 remains to be established. In this study, ApoE-/-: Sirt6-/- and ApoE-/-: Sirt6Tg mice were used and lipid droplets were analysed via transmission electron microscopy and Bodipy 493/503 staining in vitro. Atherosclerotic plaques in ApoE-/-: Sirt6-/- mice showed greater necrotic cores and lower stability score. Reconstitution of Sirt6 in atherosclerotic mice improved lipid metabolism disorder and prevented the progression of atherosclerosis. Furthermore, macrophages with Ac-LDL intervention showed more lipid droplets and increased expression of adipophilin and PLIN2. Reconstitution of Sirt6 recruited using SNF2H suppressed Wnt1 expression and improved lipid metabolism disorder by promoting lipophagy. In addition, downregulation of Sirt6 expression in Ac-LDL-treated macrophages inhibited lipid droplet degradation and stimulated foam cell formation. Innovative discoveries in the research revealed that atherosclerosis is caused by lipid metabolism disorders due to downregulated Sirt6 expression. Thus, modulating Sirt6's function in lipid metabolism might be a useful therapeutic approach for treating atherosclerosis.

Impact of triglyceride levels on plaque characteristics in patients with coronary artery disease

BACKGROUND

High triglyceride (TG) levels have been demonstrated to be a risk factor for coronary artery disease. This study aimed to clarify the impact of TG levels on the characteristics of coronary plaques.

METHODS

A total of 850 consecutive patients who underwent optical coherence tomography (OCT) imaging of the culprit lesion were included. The morphologies of culprit plaques were compared between the higher TG group (nonfasting TG levels ≥150 mg/dL, n = 337) and the lower TG group (nonfasting TG <150 mg/dL, n = 513).

RESULTS

The prevalence of lipid-rich plaques (43% vs. 33%, p = 0.005), thin-cap fibroatheromas (TCFAs) (24% vs. 17%, p = 0.015) and macrophages (40% vs. 31%, p = 0.006) was significantly higher in the higher TG group than in the lower TG group. In addition to a high low-density lipoprotein cholesterol (LDL-C) level (≥140 mg/dL), high TGs (≥150 mg/dL) were identified as an independent factor for the presence of TCFAs (odds ratio 1.465, 95% confidence interval 1.004-2.137, p = 0.048). Among patients with lower LDL-C levels (<100 mg/dL), the prevalence of macrophages (38% vs. 26%, p = 0.007) and layered plaques (48% vs. 38%, p = 0.019) was significantly higher in the higher TG group than in the lower TG group.

CONCLUSIONS

Higher TG levels were associated with a higher prevalence of TCFAs in culprit coronary lesions. The prevalence of macrophages and layered plaques was more frequently observed in patients with higher TGs than those with lower TGs among patients with LDL-C < 100 mg/dL.

Fasting, non-fasting and postprandial triglycerides for screening cardiometabolic risk

Fasting triacylglycerols have long been associated with cardiovascular disease (CVD) and other cardiometabolic conditions. Evidence suggests that non-fasting triglycerides (i.e. measured within 8 h of eating) better predict CVD than fasting triglycerides, which has led several organisations to recommend non-fasting lipid panels as the new clinical standard. However, unstandardised assessment protocols associated with non-fasting triglyceride measurement may lead to misclassification, with at-risk individuals being overlooked. A third type of triglyceride assessment, postprandial testing, is more controlled, yet historically has been difficult to implement due to the time and effort required to execute it. Here, we review differences in assessment, the underlying physiology and the pathophysiological relevance of elevated fasting, non-fasting and postprandial triglycerides. We also present data suggesting that there may be a distinct advantage of postprandial triglycerides, even over non-fasting triglycerides, for early detection of CVD risk and offer suggestions to make postprandial protocols more clinically feasible.

Pro-atherogenic and pro-oxidant crosstalk between adipocytes and macrophages

PURPOSE

Obesity, which is characterized by triglyceride accumulation mainly in adipocytes but also in arterial wall cells such as macrophages, is a major risk factor for developing atherosclerosis. We aimed to identify the crosstalk related to lipid metabolism and oxidation status between adipocytes and macrophages.

METHODS

We used a co-culture model system with J477A.1 cultured macrophages and 3T3L1 cultured adipocytes. For an in-vivo co-culture system, we used C57BL/6 mouse peritoneal macrophages and visceral or subcutaneous adipose tissue.

RESULTS

Adipocytes significantly increased reactive oxygen species generation, up to twofold, and decreased cholesterol content by 22% in the co-cultured macrophages. Macrophages significantly increased triglyceride-biosynthesis rate by twofold and decreased triglyceride-degradation rate by 30%, resulting in increased triglyceride accumulation in the co-cultured adipocytes by up to 72%. In the in-vivo mouse model, visceral adipose tissue crosstalk with macrophages resulted in a significant pro-atherogenic phenotype with respect to cellular cholesterol metabolism. In contrast, the interaction between subcutaneous adipose tissue and macrophages mostly affected cellular triglyceride metabolism. There were no significant effects on mitochondrial respiration capacity in the macrophages. Upon oxidative-stress reduction in the co-cultured cells using the polyphenol-rich antioxidant, pomegranate juice, the expression of genes related to cellular lipid accumulation was significantly reduced.

CONCLUSIONS

We reveal, for the first time, that paracrine interactions between adipocytes and macrophages result in oxidative stress and lipids metabolic alterations in both cells, toward increased atherogenicity which can be reversed by phenolic antioxidants.

Prolonged pretreatment of mice with cholera toxin, but not isoproterenol, alleviates acute lethal systemic inflammatory response

Isoproterenol, a synthetic non-selective β-adrenergic agonist, is often used during the immediate postoperative period after open heart surgery for its chronotropic and vasodilatory effects. It has been demonstrated that isoproterenol pretreatment followed by immediate LPS administration leads to reduced tumor necrosis factor-α (TNF-α) response in vivo. However, sepsis never happens immediately after the surgery, but rather severe immune dysfunction occurs at least 24h later. It remains elusive what effects isoproterenol might exert to innate immunity during the period. In this scenario, we investigated the effects of 24-h isoproterenol pretreatment on septic shock induced by experimental endotoxemia and bacterial peritonitis, with cholera toxin as another cAMP elevator. Unexpectedly, we found that isoproterenol and cholera toxin exhibited distinct effects in acute lethal systemic inflammatory response. Isoproterenol worsened liver injury without enhancing NK/NKT activity. Meanwhile, cholera toxin but not isoproterenol showed dramatically reduced TNF-α response in LPS induced septic shock. Our data provide a caution for the clinical use of isoproterenol and suggest that isoproterenol has cAMP-independent functions.

Very low density lipoproteins derived from periodontitis patients facilitate macrophage activation via lipopolysaccharide function

OBJECTIVE

Periodontitis, a chronic oral infection caused mainly by gram-negative bacteria, induces endotoxemia and associates with the risk for atherosclerosis. We investigated the effect of periodontal treatment on proatherogenic properties of very low density lipoproteins (VLDL).

METHODS

VLDL were isolated from 30 systemically healthy periodontitis patients before (pre-treatment) and 3 months after treatment (post-treatment). The mass compositions were analyzed, and VLDL-induced changes in cellular cholesterol content and expression of selected genes of human THP-1 macrophages were measured.

RESULTS

Periodontal treatment decreased the local inflammation in the periodontium, but did not have a significant effect on C-reactive protein (CRP) levels, VLDL composition, or VLDL potential to induce cholesterol uptake or gene expression by the macrophages. Incubation of macrophages in the presence of VLDL resulted in more than twofold increase in their cellular cholesterol content. Uptake of VLDL with ensuing macrophage cholesterol accumulation correlated positively with VLDL-associated lipopolysaccharide (LPS) activity (r=0.436, P=.016) and apolipoprotein E content (r=0.374, P=.046). Pre-treatment VLDL derived from the patients with high CRP levels displayed higher LPS activity than that of VLDL derived from patients with low CRP (above vs. below median, P=.007). In addition, pre-treatment VLDL isolated from patients with high systemic inflammation induced higher relative mRNA expression of CD14, TNF-α, MCP-1, and IL-6 in the macrophages.

CONCLUSION

Inflammation and endotoxemia induced by severe periodontitis may increase VLDL-dependent macrophage activation and cellular cholesterol accumulation, and thereby atherogenesis.

Exploring the value of apoB48 as a marker for atherosclerosis in clinical practice

BACKGROUND

  Postprandial accumulation of atherogenic remnants has been described in patients with type 2 diabetes mellitus (T2DM), familial combined hyperlipidaemia (FCH), familial hypercholesterolaemia (FH) and coronary artery disease (CAD). Scarce data are available on fasting plasma apolipoprotein (apo) B48 levels in relation to these conditions and atherosclerosis.

DESIGN

  Treated patients with FCH (18), FH (20), T2DM (26), CAD (65), T2DM with CAD (T2DM/CAD) (28) and 33 healthy controls were included. Intima-media thickness (IMT) measurements were carried out to investigate subclinical atherosclerosis.

RESULTS

  LDL-C and total apoB were lowest in patients with T2DM/CAD owing to the more frequent use of lipid-lowering medication. Fasting plasma apoB48 was elevated in patients with FCH (11·38 ± 1·50 mg/L) and T2DM/CAD (9·65 ± 1·14 mg/L) compared with the other groups (anova, P < 0·01). CAD patients (8·09 ± 0·57 mg/L) had higher apoB48 levels than controls (5·74 ± 0·55 mg/L) and FH patients (5·40 ± 0·51 mg/L) (P = 0·02). IMT was highest in subjects with T2DM/CAD (0·77 ± 0·03 mm) (P < 0·01). The lowest IMT was measured in controls (0·56 ± 0·02 mm) and FCH patients (0·60 ± 0·03 mm). In the total group, the best association for apoB48 was found with fasting triglyceride (Pearson's r = 0·72, P < 0·001). In the subjects not using statins (n = 74), the best correlation was found with IMT (r = 0·52; P < 0·001), whereas total apoB was not associated with IMT (r = 0·20, P = 0·12).

CONCLUSIONS

  ApoB48 concentrations are highest in patients with FCH and in atherosclerotic subjects with T2DM. In patients not using statins, the surrogate atherosclerosis marker IMT correlates best with apoB48, suggesting that fasting apoB48 may help to detect subjects at risk.

Triacylglycerol-rich lipoproteins derived from healthy donors fed different olive oils modulate cytokine secretion and cyclooxygenase-2 expression in macrophages: the potential role of oleanolic acid

PURPOSE

Current evidence suggests that consumption of virgin olive oil (VOO) helps to protect against the development of atherosclerosis and that minor components such as oleanolic acid contribute to this effect. In this study, the effects of triacylglycerol-rich lipoproteins (TRLs) derived from olive oil on inflammatory processes in macrophages and how they are modulated by oleanolic acid was investigated.

METHODS

TRLs isolated from healthy volunteers 2 and 4 h after a test meal containing VOO, pomace olive oil (POO) (the second pressing of olive oil, enriched in minor components) or POO enriched with oleanolic acid (OPOO) were incubated with macrophages derived from the human monocyte cell line, THP-1.

RESULTS

All types of TRLs caused a decrease of about 50% in the secretion of monocyte chemoattractant protein-1 (MCP-1) by the cells. Interleukin (IL)-6 secretion was also significantly decreased by 2 and 4 h VOO TRLs and by 4 h OPOO TRLs. In contrast, increased IL-1β secretion was observed with all 2 h TRL types, and increased tumour necrosis factor-α (TNF-α) production with 2 h VOO and POO, but not OPOO, TRLs. TRLs isolated after 4 h, however, had no significant effects on TNF-α secretion and increased IL-1β secretion only when they were derived from VOO. Cyclooxygenase-2 (COX-2) mRNA expression was strongly down-regulated by all types of TRLs, but protein expression was significantly depressed only by 4 h OPOO TRLs.

CONCLUSION

These findings demonstrate that TRLs derived from olive oil influence inflammatory processes in macrophages and suggest that oleanolic acid may have beneficial effects.

Angptl4 protects against severe proinflammatory effects of saturated fat by inhibiting fatty acid uptake into mesenteric lymph node macrophages

Dietary saturated fat is linked to numerous chronic diseases, including cardiovascular disease. Here we study the role of the lipoprotein lipase inhibitor Angptl4 in the response to dietary saturated fat. Strikingly, in mice lacking Angptl4, saturated fat induces a severe and lethal phenotype characterized by fibrinopurulent peritonitis, ascites, intestinal fibrosis, and cachexia. These abnormalities are preceded by a massive acute phase response induced by saturated but not unsaturated fat or medium-chain fat, originating in mesenteric lymph nodes (MLNs). MLNs undergo dramatic expansion and contain numerous lipid-laden macrophages. In peritoneal macrophages incubated with chyle, Angptl4 dramatically reduced foam cell formation, inflammatory gene expression, and chyle-induced activation of ER stress. Induction of macrophage Angptl4 by fatty acids is part of a mechanism that serves to reduce postprandial lipid uptake from chyle into MLN-resident macrophages by inhibiting triglyceride hydrolysis, thereby preventing macrophage activation and foam cell formation and protecting against progressive, uncontrolled saturated fat-induced inflammation.

Inhibition of long-chain acyl coenzyme A synthetases during fatty acid loading induces lipotoxicity in macrophages

OBJECTIVE

Obesity is often associated with hypertriglyceridemia and elevated free fatty acids (FFAs), which are independent risk factors for cardiovascular disease and diabetes. Although impairment of cholesterol homeostasis is known to induce toxicity in macrophages, the consequence of altered fatty acid homeostasis is not clear.

METHODS AND RESULTS

Long-chain acyl CoA synthetases (ACSLs) play a critical role in fatty acid homeostasis by channeling fatty acids to diverse metabolic pools. We treated mouse peritoneal macrophages (MPMs) with VLDL or FFAs in the presence of triacsin C, an inhibitor of the 3 ACSL isoforms present in macrophages. Treatment of macrophages with VLDL and triacsin C resulted in reduced TG accumulation but increased intracellular FFA levels, which induced lipotoxicity characterized by apoptosis. Treatment of MPMs with the saturated fatty acid stearic acid in the presence of triacsin C increased intracellular stearic acid and induced apoptosis. Stromal vascular cells collected from high-fat diet-fed mice displayed foam cell morphology and exhibited increased mRNA levels of macrophage markers and ACSL1. Importantly, all of these changes were associated with increased FFA level in AT.

CONCLUSIONS

Inhibition of ACSLs during fatty acid loading results in apoptosis via accumulation of FFAs. Our data have implications in understanding the consequences of dysregulated fatty acid metabolism in macrophages.

Pathophysiology of triglyceride-rich lipoproteins in atherothrombosis: cellular aspects

Elevated plasma levels of triglyceride-rich lipoproteins (TGRLP), including very low-density lipoproteins (VLDL), chylomicrons, and their remnants, are now acknowledged as risk factors for cardiovascular disease. Interactions of TGRLP with lipoprotein receptors on monocytes, macrophages, and endothelial cells may be mechanistically linked to this risk. Triglyceride-rich lipoproteins from hypertriglyceridemic (HTG) subjects have the abnormal ability to bind to low-denisty lipoprotein receptors via apoE, and plasma chylomicrons from all subjects bind to a new, distinct receptor for apoB48 that is expressed specifically by monocytes, macrophages, and endothelial cells. Receptor binding and uptake of TGRLP by these cells are likely mechanisms involved in the formation of lipid-filled, macrophage-derived "foam cells" of atherosclerotic lesions and for defective fibrinolysis due to endothelial dysfunction. Recognition of the atherothrombogenic potential of TGRLP may lead to improved interventions to lessen or prevent the often fatal sequelae of coronary atherosclerosis and thrombosis associated with elevated plasma triglyceride levels.

Therapeutic effects of fibrates in postprandial lipemia

Hypertriglyceridemia is observed in many metabolic diseases such as the metabolic syndrome, diabetes mellitus, or mixed dyslipidemia frequently leading to premature coronary heart disease (CHD). Additionally, several studies have shown that postprandial hypertriglyceridemia is pronounced in patients with CHD, metabolic syndrome, hypertension, and other pathologic conditions. The triglyceride-rich lipoprotein remnants accumulating in the postprandial state seem to be involved in atherogenesis and in events leading to thrombosis. Since abnormal postprandial lipemia is associated with pathologic conditions, its treatment is of clinical importance.Fibrates are of significant help in managing hypertriglyceridemia. This review summarizes the effect of fibric acid derivatives on postprandial lipemia. Fibrates decrease the production of and enhance the catabolism of triglyceride-rich lipoproteins through the activation of peroxisome proliferator-activated receptor-alpha. Results of clinical studies with fibrates have confirmed their action in decreasing postprandial triglyceride levels by increasing lipoprotein lipase activity, decreasing apolipoprotein CIII production, and by increasing fatty acid oxidation in the liver.It is concluded that fibrates are effective agents in lowering the postprandial increase in remnant lipoprotein particles and retinyl palmitate. Furthermore, fibrates can also affect the postprandial lipid profile by increasing hepatic lipase levels and in some cases, by reducing cholesterol ester transfer protein activity. The main target of fibrate therapy is to improve fasting hypertriglyceridemia, which is an essential component associated with improving postprandial lipemia. Fibrates are well tolerated by patients and adverse effects have been reported rarely after their administration.

A novel peptide binding to the cytoplasmic domain of class A scavenger receptor reduces lipid uptake in THP-1 macrophages

Class A scavenger receptor (SR-A) contributes primarily to lipid accumulation in cells. The cytoplasmic domain of SR-A (CSR-A) is responsible for internalization of the receptor-ligand complex into cells. In the present study we tried to reduce cellular uptake of acetylated low density lipoprotein (AcLDL) by inducing the interaction between the CSR-A and a novel peptide H11, which was screened from a phage-displayed peptide library. When H11 was fused with a cross membrane peptide TAT, the fusion peptide could enter cell efficiently. The peptide H11 inhibited the binding and uptake of DiI-AcLDL and attenuated lipid accumulation in the differentiated human acute monocytic leukemia cell line (THP-1) macrophages. Furthermore, the interaction of peptide H11 with the CSR-A inhibited the expression of SR-A protein as well as the phosphorylation of c-jun N-terminal kinase 2 (JNK2) in cells, which mediates cellular lipid accumulation-related signaling pathways. These results suggest that the CSR-A can be a potential target to prevent lipid accumulation in cells. The peptide H11 may be useful in regulating SR-A functions in macrophages.

Adiponectin and the metabolic syndrome: mechanisms mediating risk for metabolic and cardiovascular disease

PURPOSE OF REVIEW

Adiponectin is secreted exclusively by adipocytes, aggregates in multimeric forms, and circulates at high concentrations in blood. This review summarizes recent studies highlighting cellular effects of adiponectin and its role in human lipid metabolism and atherosclerosis.

RECENT FINDINGS

Adiponectin is an important autocrine/paracrine factor in adipose tissue that modulates differentiation of preadipocytes and favors formation of mature adipocytes. It also functions as an endocrine factor, influencing whole-body metabolism via effects on target organs. Adiponectin multimers exert differential biologic effects, with the high-molecular-weight multimer associated with favorable metabolic effects (i.e. greater insulin sensitivity, reduced visceral adipose mass, reduced plasma triglycerides, and increased HDL-cholesterol). Adiponectin influences plasma lipoprotein levels by altering the levels and activity of key enzymes (lipoprotein lipase and hepatic lipase) responsible for the catabolism of triglyceride-rich lipoproteins and HDL. It thus influences atherosclerosis by affecting the balance of atherogenic and antiatherogenic lipoproteins in plasma, and by modulating cellular processes involved in foam cell formation.

SUMMARY

Recent studies emphasize the role played by adiponectin in the homeostasis of adipose tissue and in the pathogenesis of the metabolic syndrome, type 2 diabetes, and atherosclerosis. These pleiotropic effects make it an attractive therapeutic target for obesity-related conditions.

Atherosclerosis is accelerated in patients with long-term well-controlled systemic lupus erythematosus (SLE)

BACKGROUND

It is uncertain whether atherosclerosis is accelerated in premenopausal and postmenopausal patients with long-term well-controlled systemic lupus erythematosus (SLE).

METHODS

We measured the intima-media thickness (IMT) of the carotid arteries and the cardio-ankle vascular index (CAVI) in 39 women with SLE and in age- and sex-matched controls.

RESULTS

In the premenopausal state, carotid plaque was detected only in SLE patients (36%). In the postmenopausal state, the maximum IMT was about 2-fold greater in SLE patients than in control subjects (1.3+/-0.7 vs. 0.7+/-0.2 mm, p<0.001). CAVI was higher in both the premenopausal and postmenopausal SLE patients. The serum amyloid A protein (SAA) was higher in SLE patients in the premenopausal state (p=0.025), while remnant like particle-cholesterol (RLP-C), the homeostasis model assessment of insulin resistance (HOMA-IR), and SAA were significantly increased in postmenopausal SLE patients (p=0.001, p<0.001 and p<0.05, respectively). Multiple regression analysis revealed that the maximum IMT was associated with cumulative PSL dosage (p=0.027) and SAA (p=0.074) in the premenopausal SLE patients, and with HOMA-IR (p<0.001) in the postmenopausal SLE patients.

CONCLUSION

Atherosclerosis is accelerated in long-term well-controlled SLE. More attention should be given to subclinical inflammation and insulin resistance in the management of SLE patients.

The role of lipolysis in mediating the proinflammatory effects of very low density lipoproteins in mouse peritoneal macrophages

Hypertriglyceridemia is an important risk factor for atherosclerosis, especially in obesity. Macrophages are one of the primary cell types involved in atherogenesis and are thought to contribute to lesion formation through both lipid accumulation and proinflammatory gene expression. In this study, we sought to determine the direct impact of triglyceride (TG)-rich VLDL-induced lipid accumulation on macrophage proinflammatory processes. Incubation of mouse peritoneal macrophages with 100 microg/ml VLDL for 6 h led to 2.8- and 3.7-fold increases in intracellular TGs and FFAs, respectively (P < 0.05). The inflammatory proteins tumor necrosis factor-alpha, interleukin-1beta, monocyte chemoattractant protein-1, intercellular adhesion molecule-1, matrix metalloproteinase 3 (MMP3), and macrophage inflammatory protein-1alpha (MIP-1alpha) were all upregulated by at least 2-fold (P < 0.05) in a dose-dependent manner in VLDL-treated macrophages. The increase in inflammatory gene expression coincided with the phosphorylation of the mitogen-activated protein kinase (MAPK) pathway members extracellular signal-regulated kinase (ERK) 1/2, stress-activated protein kinase/c-Jun NH2-terminal kinase, and p38 MAPK and was ameliorated by U0126, an inhibitor of ERK1/2. Inhibition of extracellular TG hydrolysis with tetrahydrolipstatin (Orlistat) resulted in the absence of intracellular TG and FFA accumulation and was accompanied by the amelioration of ERK1/2 phosphorylation and MIP-1alpha gene expression. These data indicate that VLDL hydrolysis, and the subsequent accumulation of intracellular FFAs and TGs, plays a substantive role in mediating the proinflammatory effects of VLDL. These data have important implications for the direct proatherogenic effects of VLDL on macrophage-driven atherosclerosis.

New insight into the pathophysiology of lipid abnormalities in type 2 diabetes

Lipid abnormalities in patients with type 2 diabetes are likely to play an important role in the development of atherogenesis. These lipid disorders include not only quantitative but also qualitative abnormalities of lipoproteins which are potentially atherogenic. The main quantitative abnormalities are increased triglyceride levels, related to an augmented hepatic production of VLDL and a reduction of both VLDL and IDL catabolism, and decreased HDL-Cholesterol levels due to an accelerated HDL catabolism. The main qualitative abnormalities include large VLDL particles (VLDL1), relatively rich in triglycerides, small dense LDL particles, increase in triglyceride content of LDL and HDL, glycation of apolipoproteins and increased susceptibility of LDL to oxidation. Moreover, although plasma LDL-cholesterol level is usually normal in type 2 diabetic patients, LDL particles show significant kinetic abnormalities, such as reduced turn-over, which is potentially harmful. The pathophysiology of lipid abnormalities in type 2 diabetes is not yet totally explained. However, insulin resistance and the "relative" insulin deficiency, observed in patients with type 2 diabetes, are likely to play a crucial role since insulin has an important function in the regulation of lipid metabolism. In addition, it is not excluded that adipocytokines, such as adiponectin, could play a role in the pathophysiology of lipid abnormalities in type 2 diabetes.

Pitavastatin inhibits remnant lipoprotein-induced macrophage foam cell formation through ApoB48 receptor-dependent mechanism

OBJECTIVE

Atherogenic remnant lipoproteins (RLPs) are known to induce foam cell formation in macrophages in vitro and in vivo. We examined the involvement of apoB48 receptor (apoB48R), a novel receptor for RLPs, in that process in vitro and its potential regulation by pitavastatin.

METHODS AND RESULTS

THP-1 macrophages were incubated in the presence of RLPs (20 mg cholesterol/dL, 24 hours) isolated from hypertriglyceridemic subjects. RLPs significantly increased intracellular cholesterol ester (CE) and triglyceride (TG) contents (4.8-fold and 5.8-fold, respectively) in the macrophages. Transfection of THP-1 macrophages with short interfering RNA (siRNA) against apoB48R significantly inhibited RLP-induced TG accumulation by 44%. When THP-1 macrophages were pretreated with pitavastatin (5 micromol/L, 24 hours), the expression of apoB48R was significantly decreased and RLP-induced TG accumulation was reduced by 56%. ApoB48R siRNA also inhibited TG accumulation in THP-1 macrophage induced by beta-very-low-density lipoprotein derived from apoE-/- mice by 58%, supporting the notion that apoB48R recognizes and takes-up RLPs in an apoE-independent manner.

CONCLUSIONS

RLPs induce macrophage foam cell formation via apoB48R. Pitavastatin inhibits RLP-induced macrophage foam cell formation. The underlying mechanism involves, at least in part, inhibition of apoB48R-dependent mechanism. Our findings indicate a potential role of apoB48R in atherosclerosis. RLPs induced macrophage foam cell formation via apoB48R. Pitavastatin inhibited RLP-induced macrophage foam cell formation, at least in part, via inhibition of apoB48R expression. Our findings indicate a potential role of apoB48R in atherosclerosis.

PPAR(alpha) and PPAR(gamma) activators suppress the monocyte-macrophage apoB-48 receptor

Certain triglyceride-rich lipoproteins (TRLs), specifically chylomicrons, dyslipemic VLDLs, and their remnants, are atherogenic and can induce monocyte-macrophage foam cell formation in vitro via the apolipoprotein B-48 receptor (apoB-48R). Human atherosclerotic lesion foam cells express the apoB-48R, as determined immunohistochemically, suggesting it can play a role in the conversion of macrophages into foam cells in vivo. The regulation of the apoB-48R in monocyte-macrophages is not fully understood, albeit previous studies indicated that cellular sterol levels and state of differentiation do not affect apoB-48R expression. Since peroxisome proliferator-activated receptors (PPARs) regulate some aspects of cellular lipid metabolism and may be protective in atherogenesis by up-regulation of liver X-activated receptor alpha and ATP-binding cassette transporter A1, we examined the regulation of apoB-48R by PPAR ligands in human monocyte-macrophages. Using real-time PCR, Northern, Western, and functional cellular lipid accumulation assays, we show that PPARalpha and PPARgamma activators significantly suppress the expression of apoB-48R mRNA in human THP-1 and blood-borne monocyte-macrophages. Moreover, PPAR activators inhibit the expression of the apoB-48R protein and, notably, the apoB-48R-mediated lipid accumulation of TRL by THP-1 monocytes in vitro. If PPAR activators also suppress the apoB-48R pathway in vivo, diminished apoB-48R-mediated monocyte-macrophage lipid accumulation may be yet another antiatherogenic effect of the action of PPAR ligands.

Report of the Japan Atherosclerosis Society (JAS) Guideline for Diagnosis and Treatment of Hyperlipidemia in Japanese adults

This paper described the Guideline for Diagnosis and Management of Hyperlipidemias for Prevention of Atherosclerosis proposed by The Japan Atherosclerosis Society (JAS) Guideline Investigating Committee (1,995-2,000) under the auspices of the JAS Board of Directors. 1) The guideline defines the diagnostic criteria for serum total cholesterol (Table 1), LDL-cholesterol (Table 1), triglycerides (Table 4) and HDL-cholesterol (Table 7). It also indicates the desirable range (Table 1), the initiation levels of management (Table 2) and the target levels of treatment (Table 2) for total and LDL-cholesterol. 2) Though both total and LDL-cholesterol are shown as atherogenic parameter in the guideline, the use of LDL-cholesterol, rather than total cholesterol, is encouraged in daily medical practice and lipid-related studies, because LDL-cholesterol is more closely related to atherosclerosis. 3) Elevated triglycerides and low HDL-cholesterol are included in the risk factors, since no sufficient data have been accumulated to formulate the guideline for these two lipid disorders. 4) Emphasis is laid on evaluation of risk factors of each subject before starting any kind of treatment (Table 2). 5) This guideline is applied solely for adults (age 20-64). Lipid abnormalities in children or the youth under age 19, and the elderly with an age over 65 have to be evaluated by their own standard. 6) This part of the guideline gives only the diagnostic aspects of hyperlipidemias. The part of management and treatment will follow in the second section of the guideline that will be published in future.

Effects of insulin lispro and chronic vitamin C therapy on postprandial lipaemia, oxidative stress and endothelial function in patients with type 2 diabetes mellitus

BACKGROUND

Insulin therapy may influence cardiovascular disease (CVD) and lipid metabolism in type 2 diabetes (T2D). Exaggerated postprandial lipaemia (PPL) is a feature of diabetic dyslipidaemia affecting CVD via enhanced oxidative stress (OS) and endothelial dysfunction. We assessed endothelial function and OS during PPL following insulin and vitamin C. Twenty (17 M) T2D patients were studied (mean Hba1c 8.4%) at baseline, following 6 weeks of insulin lispro (0.2 Iu kg-1) and vitamin C 1-g daily. Eight-h lipid and glucose profiles were measured following a fatty meal. Endothelial function (flow-mediated vasodilatation: FMD) and OS were measured at fasting, 4 h and 8 h.

MATERIALS AND METHODS

Glucose, body mass index, and total and LDL cholesterol remained unchanged. FMD improved. Placebo group: fasting, 1.1 +/- 1.2 to 4.2 +/- 1.1% (P < 0.001); 4-h, 0.3 +/- 1.2 to 3.1 +/- 0.9% (P < 0.01); 8-h, 0.7 +/- 1.1 to 3.76 +/- 1.1% (P < 0.001). Vitamin C group: fasting, 0.9 +/- 1.1 to 6.1 +/- 1.3% (P < 0.001); 4-h, 0.7 +/- 1.5 to 4.9 +/- 2.1% (P < 0.001); 8-h, 0.8 +/- 0.9 to 5.8 +/- 0.6% (P < 0.01). Post-prandial lipaemia was attenuated: TG area-under-curve (mmol L-1 8 h-1), 52.6 +/- 11 to 39.1 +/- 12.5 (placebo group), P < 0.02; and 56.9 +/- 8 to 40.1 +/- 10.3 (vitamin C group), P < 0.02. Oxidative stress was reduced, with greater changes in the vitamin C group.

CONCLUSION

Insulin may thus exert vascular benefits in T2D, by modifying fasting and postprandial lipid metabolism resulting in reduced OS and improved EF. Vitamin C therapy may augment the vascular benefits of insulin in T2D through additional effects on OS and EF.

VLDL-induced triglyceride accumulation in human macrophages is mediated by modulation of LPL lipolytic activity in the absence of change in LPL mass

Mixed dyslipidemia of phenotype IIB is characterized by elevated levels of very low density lipoprotein (VLDL)-1 and VLDL-2 subfractions and of low density lipoprotein (LDL), which are associated with premature formation of atherosclerotic plaques, characterized by the presence of lipid-rich macrophage foam cells. Lipoprotein lipase (LPL) is a key factor in mediating macrophage lipid accumulation and foam-cell formation from native VLDL particles. The action of macrophage-derived LPL in the induction of intracellular lipid accumulation from triglyceride-rich lipoprotein (TRL) subfractions (VLDL-1, VLDL-2) is, however, indeterminate, as is the potential role of VLDL-1 and VLDL-2 in modulating macrophage LPL expression. We evaluated the role of LPL in the interaction of type IIB VLDL-1 and VLDL-2 with human macrophages. Both VLDL-1 and VLDL-2 subfractions induced significant accumulation of triglyceride (9.8-fold, P<0.0001, and 4.8-fold, P<0.0001, respectively) and of free cholesterol content (1.4-fold, P<0.001, and 1.2-fold, P=0.02, respectively). Specific inhibition (90%) of the lipolytic activity of endogenous LPL by tetrahydrolipstatin (THL) in the presence of VLDL-1 or VLDL-2 resulted in marked reduction in cellular loading of both triglycerides (-89%, P=0.008, and -89%, P=0.015, respectively) and free cholesterol (-76%, P=0.02, and -55%, P=0.06 respectively). Furthermore, VLDL-1 and VLDL-2 induced marked increase in macrophage-derived LPL enzyme activity (+81%, P=0.002, and +45%, P=0.02), but did not modulate macrophage-derived LPL mRNA and protein expression; consequently, LPL specific activity was significantly increased from 1.6 mU/microg at baseline to 4.1 mU/microg (P=0.01) and 3.1 mU/microg (P=0.05), in the presence of VLDL-1 and VLDL-2, respectively. We conclude that type IIB VLDL-1 and VLDL-2 induce triglyceride accumulation in human monocyte-macrophages primarily via the lipolytic action of LPL, which may involve stabilization and activation of the macrophage-secreted enzyme, rather than via modulation of enzyme production.

Early kinetic abnormalities of apoB-containing lipoproteins in insulin-resistant women with abdominal obesity

OBJECTIVE

The kinetic abnormalities of apolipoprotein B (apoB)-containing lipoproteins in abdominally obese insulin-resistant individuals remain poorly understood. To determine the influence of insulin resistance, linked with abdominal obesity, on apoB metabolism at an early stage, we performed a stable isotope kinetic study of apoB in very low density lipoproteins (VLDLs), intermediate density lipoproteins (IDLs), and low density lipoproteins (LDLs) in 5 abdominally obese insulin-resistant women with normal fasting triglyceride levels and without impaired glucose tolerance and in 5 age-matched control women.

METHODS AND RESULTS

Each subject received an intravenous injection of a 0.7 mg/kg bolus of L-[1-(13)C]leucine, immediately followed by a 16-hour constant infusion at 0.7 mg/kg per hour. Compared with control women, insulin-resistant women with abdominal obesity showed a significant 84% increase of the VLDL apoB production rate (27.18+/-11.53 versus 14.80+/-1.94 [control] mg/kg per day, P=0.009), a significant 54% increase of the IDL apoB production rate (20.63+/-3.66 versus 13.39+/-3.99 [control] mg/kg per day, P=0.009), and a significant 63% increase of the LDL apoB production rate (18.49+/-1.70 versus 11.33+/-3.79 [control] mg/kg per day, P=0.009), leading to significantly higher VLDL, IDL, and LDL apoB concentrations. The fractional catabolic rates of VLDL, IDL, and LDL apoB were not significantly different between abdominally obese insulin-resistant women and control women.

CONCLUSIONS

Our study shows that patients at an early stage of insulin resistance linked with abdominal obesity (without glucose intolerance or fasting hypertriglyceridemia) already have an altered metabolism of the VLDL-IDL-LDL cascade (increased VLDL, IDL, and LDL apoB production rates), which is consistent with the augmented risk of atherosclerosis observed in this population.

Peroxisome proliferator-activated receptor (PPAR) agonists decrease lipoprotein lipase secretion and glycated LDL uptake by human macrophages

Lipoprotein lipase (LPL) acts independently of its function as triglyceride hydrolase by stimulating macrophage binding and uptake of native, oxidized and glycated LDL. Peroxisome proliferator-activated receptors (PPARs) are nuclear receptors expressed in monocyte/macrophages, where they control cholesterol homeostasis. Here we study the role of PPARs in the regulation of LPL expression and activity in human monocytes and macrophages. Incubation of human monocytes or macrophages with PPARalpha or PPARgamma ligands increases LPL mRNA and intracellular protein levels. By contrast, PPAR activators decrease secreted LPL mass and enzyme activity in differentiated macrophages. These actions of PPAR activators are associated with a reduced uptake of glycated LDL and could influence atherosclerosis development associated with diabetes.

Targeting triglycerides as prognostic indicators and determining lowest values for patient benefit

A number of reports demonstrate the importance of serum triglyceride values in predicting the clinical onset of vascular disease. However, adjustment for measurements highly correlated with triglyceride (TG) levels, such as history of diabetes, body mass index, and high-density lipoprotein cholesterol (HDL-C), lessen if not remove the TG contribution to outcomes. More recently, improved analytic approaches have more persuasively implicated triglycerides as independently relevant to the onset of cardiovascular disease. Elevated TG values are the consequence of larger TG-rich particles, including very low density lipoprotein and atherogenic intermediate particles, which are in turn associated with dense low-density lipoprotein. It has been observed that a reduction in TG concentrations often proceeds in parallel with improved clinical outcomes; however, direct correlation between the two has been elusive. This has been demonstrated in multiple pharmacologic trials. However, an improvement in these relationships has been observed when TG-correlated measurements of intermediate particles, low-density lipoprotein density, and HDL-C have been made. National guidelines for cholesterol treatment have now incorporated a TG greater than 200 mg/dL as a secondary treatment trigger, which targets apolipoprotein B-related particles, represented by non-HDL-C (total cholesterol minus HDL-C), as the suggested goal of therapy.

Hypertriglyceridemia: associated risks and effect of drug treatment

Accumulating evidence indicates that hypertriglyceridemia (HTG) is a risk factor for cardiovascular disease. This increased risk is probably substantially mediated through the metabolic interrelationships between serum triglyceride (TG) levels and other risk factors, such as the atherogenic lipid profile (low high density lipoprotein-cholesterol levels and elevated small dense low density lipoprotein levels), insulin resistance, a prothrombotic propensity and low grade systemic inflammation. TG-lowering strategy in patients with HTG encompasses dietary modification and pharmacological agents, such as fibric acid derivatives, fish-oil and hydroxymethylglutaryl coenzyme A reductase inhibitors, which have, besides their known effects on the atherogenic lipid profile, beneficial effects on other determinants of cardiovascular disease. However, in spite of data from trials investigating fibric acid derivative-induced reduction in coronary events in patients with distinct types of hyperlipidemia, no specific trials have been performed that investigated this risk reduction in patients with HTG, in whom other cardiovascular risk factors are clustered as well. Small-scale studies on determinants of cardiovascular disease in patients with HTG and post-hoc analyses of the Helsinki Heart, Veterans Affairs High-Density Lipoprotein Cholesterol Intervention Trial and Bezafibrate Infarction Prevention trials in patients with high serum TG levels suggest a drug-induced reduction in cardiovascular events. However, a specific trial should be conducted to investigate the effects of lipid-lowering therapy on clinical end-points in patients with HTG of defined types.

A macrophage receptor for apolipoprotein B48: cloning, expression, and atherosclerosis

We have cloned a human macrophage receptor that binds to apolipoprotein (apo)B48 of dietary triglyceride (TG)-rich lipoproteins. TG-rich lipoprotein uptake by the apoB48R rapidly converts macrophages and apoB48R-transfected Chinese hamster ovary cells in vitro into lipid-filled foam cells, as seen in atherosclerotic lesions. The apoB48R cDNA (3,744 bp) encodes a protein with no known homologs. Its approximately 3.8-kb mRNA is expressed primarily by reticuloendothelial cells: monocytes, macrophages, and endothelial cells. Immunohistochemistry shows the apoB48R is in human atherosclerotic lesion foam cells. Normally, the apoB48R may provide essential lipids to reticuloendothelial cells. If overwhelmed, foam cell formation, endothelial dysfunction, and atherothrombogenesis may ensue, a mechanism for cardiovascular disease risk of elevated TG.

Ciprofibrate therapy improves endothelial function and reduces postprandial lipemia and oxidative stress in type 2 diabetes mellitus

BACKGROUND

Exaggerated postprandial lipemia (PPL) is a factor in atherogenesis, involving endothelial dysfunction and enhanced oxidative stress. We examined the effect of ciprofibrate therapy on these parameters in type 2 diabetes mellitus.

METHODS AND RESULTS

Twenty patients entered a 3-month, double-blind, placebo-controlled study. Each subject was studied fasting and after a fatty meal, at baseline, and after 3 months of treatment. Glucose and lipid profiles were measured over an 8-hour postprandial period. Endothelial function (flow-mediated endothelium-dependent vasodilatation [FMD]) and oxidative stress (electron paramagnetic resonance spectroscopy) were measured after fasting and 4 hours postprandially. At baseline, both groups exhibited similar PPL and deterioration in endothelial function. After ciprofibrate, fasting and postprandial FMD values were significantly higher (from 3.8+/-1. 8% and 1.8+/-1.3% to 4.8+/-1.1% and 3.4+/-1.1%; P<0.05). This was mirrored by a fall in fasting and postprandial triglycerides (3. 1+/-2.1 and 6.6+/-4.1 mmol/L to 1.5+/-0.8 and 2.8+/-1.3 mmol/L, P<0. 05). Fasting and postprandial HDL cholesterol was also elevated (0. 9+/-0.1 and 0.8+/-0.1 mmol/L and 1.2+/-0.2 and 1.2+/-0.1 mmol/L, P<0. 05). There were no changes in total or LDL cholesterol. Fasting and postprandial triglyceride enrichment of all lipoproteins was attenuated, with cholesterol depletion of VLDL and enrichment of HDL. There were similar postprandial increases in oxidative stress in both groups at baseline, which was significantly attenuated by ciprofibrate (0.3+/-0.6 versus 1.5+/-1.1 U, P<0.05).

CONCLUSIONS

This study demonstrates that fibrate therapy improves fasting and postprandial endothelial function in type 2 diabetes. Attenuation of PPL and the associated oxidative stress, with increased HDL cholesterol levels, may be important.

Structural peculiarities of the binding of very low density lipoproteins and low density lipoproteins to the LDL receptor in hypertriglyceridemia: role of apolipoprotein E

Very low (VLDL) and low density lipoproteins (LDL) were isolated from plasma of patients with the E3/3 phenotype which were divided into three groups based on their plasma triglyceride content: low (TG<200 mg/dl, TG(l)), intermediate (200<300 mg/dl, TG(i)300 mg/dl, TG(h)). The protein density (PD) on the VLDL and LDL surface was calculated from lipoprotein composition and protein location was studied by tryptophan fluorescence quenching by I(-) anions at 25 degrees C and 40 degrees C. A comparison of the TG(h) with the TG(l) group revealed a significant (<0.05) increase of the PD parameter as much as 21% for VLDL, but not for LDL where this parameter did not change for any group; generally, PD(LDL) values were 3.2-3.8-fold lower than PD(VLDL). In accordance with this difference, the tryptophan accessibility f in VLDL vs. LDL was lower at both temperatures. There were temperature-induced changes of the f parameter in opposite directions for these lipoproteins. The difference in f value gradually decreased for VLDL in the direction TG(l)TG(i)TG(h) while for LDL there was a U-shaped dependence for these groups. The Stern-Volmer quenching constant K(S-V) which is sensitive to both temperature and viscosity, did not change for VLDL, but K(S-V)(LDL) was 2-3-fold higher for the TG(i) group compared to the other two. The efficiencies of VLDL and LDL binding to the LDL receptor (LDLr) in vitro were compared by solid-phase assay free of steric hindrance observed in cell binding. The maximal number of binding sites did not change for either type of particles and between groups. The association constant K(a) and apolipoprotein (apo) E/apoB mole ratio values all increased significantly for VLDL, but not for LDL, in comparison of the TG(i+h) with the TG(l) group. Based on VLDL and LDL concentrations in serum and on the affinity constant values obtained in an in vitro assay, VLDL concentrations corresponding to 50% inhibition of LDL binding (IC(50)) were calculated in an assumption of the competition of both ligands for LDLr in vivo; the mean values of IC(50) decreased 2-fold when plasma TG exceeded 200 mg/dl. The functional dependences of K(a)(VLDL), IC(50) and apoE content in VLDL (both fractional and absolute) and in serum on TG content in the whole concentration range studied were fitted to a saturation model. For all five parameters, the mean half-maximum values TG(1/2) were in the range 52-103 mg/dl. The efficiency of protein-protein interactions is suggested to differ in normolipidemic vs. HTG-VLDL and apoE content and/or protein density on VLDL surface may be the primary determinant(s) of the increased binding of HTG-VLDL to the LDL receptor. ApoCs may compete with apoE for the binding to the VLDL lipid surface as plasma triglyceride content increases. The possible competition of VLDL with LDL for the catabolism site(s) in vivo, when plasma TG increases, could explain the atherogenic action of TG-rich lipoproteins. Moreover, the 'dual action' hypothesis on anti-atherogenic action of apoE-containing high density lipoproteins (HDL) in vivo is suggested: besides the well-known effect of HDL as cholesteryl ester catabolic outway, the formation of a transient complex of apoE-containing discs appearing at the site of VLDL TG hydrolysis by lipoprotein lipase with VLDL particles proposed in our preceding paper promotes the efficient uptake of TG-rich particles; in hypertriglyceridemia due to the diminished HDL content this uptake seems to be impaired which results in the increased accumulation of the remnants of TG-rich particles. This explains the observed increase in cholesterol and triglyceride content in VLDL and LDL, respectively, due to the CETP-mediated exchange of cholesteryl ester and triglyceride molecules between these particles.

Diabetic dyslipidaemia and coronary heart disease: new perspectives

Atherosclerotic macrovascular disease is the leading cause of both morbidity and mortality in non-insulin dependent diabetes mellitus. Endothelial dysfunction is a key, early and potentially reversible event in pathogenesis of atherosclerosis. Its occurrence in non-insulin dependent diabetes mellitus is well supported by both in-vitro and in-vivo studies. Non-insulin dependent diabetes mellitus results in diverse abnormalities of lipid and lipoprotein metabolism, in particular hypertriglyceridaemia, low levels of high density lipoprotein and abnormalities of post-prandial lipaemia. A variety of studies demonstrate the presence of enhanced oxidative stress in non-insulin dependent diabetes mellitus, with recent data implying an association between oxidative stress, post-prandial lipaemia and endothelial dysfunction in non-diabetic subjects. In this article based on in-vitro and human studies, we develop the hypothesis that endothelial dysfunction in non-insulin dependent diabetes mellitus is the consequence of the diabetic dyslipidaemia, in particular post-prandial lipaemia, and of oxidative stress on the action of nitric oxide. The practical applications of this theory provide potential therapeutic options which may reduce the risk of vascular disease in non-insulin dependent diabetes mellitus.

Hypertriglyceridemia: changes in the plasma lipoproteins associated with an increased risk of cardiovascular disease

There is a growing body of evidence from epidemiologic, clinical, and laboratory data that indicates that elevated triglyceride levels are an independent risk factor for cardiovascular disease. Identification and quantification of atherogenic lipoproteins in patients with hypertriglyceridemia are important steps in the prevention of cardiovascular disease. Increased levels of apoC-III, apoC-I, or apoA-II on the apoB-containing lipoproteins may alter lipoprotein metabolism and result in the accumulation of atherogenic remnants. Hypertriglyceridemic patients at risk for cardiovascular disease often develop a lipoprotein profile characterized by elevated triglyceride, dense LDL, and low HDL cholesterol. Understanding that each of these factors contributes separately to the patient's risk of cardiovascular disease can help physicians provide patients with more effective risk-reduction programs for cardiovascular disease.

Modification of type III VLDL, their remnants, and VLDL from ApoE-knockout mice by p-hydroxyphenylacetaldehyde, a product of myeloperoxidase activity, causes marked cholesteryl ester accumulation in macrophages

Very low density lipoproteins (VLDLs) from apolipoprotein (apo) E2/E2 subjects with type III hyperlipoproteinemia, VLDL remnants, and VLDL from apoE-knockout (EKO) mice are taken up poorly by macrophages. The present study examined whether VLDL modification by the reactive aldehyde p-hydroxyphenylacetaldehyde (pHA) enhances cholesteryl ester (CE) accumulation by J774A.1 macrophages. pHA is the major product derived from the oxidation of L-tyrosine by myeloperoxidase and is a component of human atherosclerotic lesions. Incubation of J774A.1 cells with native type III VLDL, their remnants, and EKO-VLDL increased cellular CE by only 3-, 5-, and 5-fold, respectively, compared with controls. In striking contrast, cells exposed to VLDL modified by purified pHA (pHA-VLDL) exhibited marked increases in cellular CE of 38-, 47-, and 35-fold, respectively (P</=0.0001). Addition of the lipoprotein lipase inhibitor tetrahydrolipstatin decreased cellular CE accumulation induced by the 3 pHA-modified VLDL preparations by 73%, 59%, and 73%, respectively. Addition of the acyl coenzyme A:cholesterol acyltransferase inhibitor DuP 128 to cells incubated with the pHA-modified lipoproteins decreased cellular CE by 100%, 82%, and 95%, respectively, but had no effect on cellular triglycerides. To examine whether the type A scavenger receptors (SR-As) mediated the uptake of pHA-VLDL, incubations were performed in the presence of polyinosine (poly I), a polynucleotide known to block binding to SR-As (types I and II), or in cells preincubated with interferon-gamma (IFN-gamma), a cytokine known to decrease expression of SR-A type I. Coincubation of pHA-VLDL with poly I reduced cellular CE by only 38%, 44%, and 49%, respectively, whereas coincubation with IFN-gamma reduced CE by only 18%, 27%, and 65%, respectively. In marked contrast to pHA-VLDL, both poly I and IFN-gamma inhibited, by>95%, CE accumulation induced by copper-oxidized VLDL. These results demonstrate a novel mechanism for the conversion of type III VLDLs, their remnants, and EKO-VLDL into atherogenic particles and suggest that macrophage uptake of pHA-VLDL (1) requires catalytically active lipoprotein lipase, (2) involves acyl coenzyme A:cholesterol acyltransferase-mediated cholesterol esterification, and (3) involves pathways distinct from the SR-A.

Triglycerides as a risk factor for coronary artery disease

Triglyceride has not traditionally been considered the cornerstone of lipid risk factors for coronary artery disease. Yet emerging evidence from epidemiologic, clinical, cellular, genetic, and molecular studies suggests otherwise, namely, that levels of triglyceride and triglyceride-rich lipoproteins such as very-low-density lipoprotein (VLDL) are indeed independent risk factors for coronary artery disease. Further, triglyceride metabolism is associated with atherogenesis, and diminishing triglyceride levels is pivotal in decreasing the incidence of coronary artery disease, particularly in early-evolving atherosclerotic lesions.

Evaluation of an immunoseparation method for quantitative measurement of remnant-like particle-cholesterol in serum and plasma

Substantial evidence indicates that triglyceride-rich lipoprotein remnants are atherogenic. Additional research has, however, been limited by available methods for separation and quantification of remnants. We have evaluated an immunoseparation assay developed to measure cholesterol in remnant-like particles (RLP-C). This method uses monoclonal antibodies to human apolipoproteins B-100 and A-I to remove most of the apolipoprotein B-100-containing lipoproteins (namely LDL and nascent VLDL) and apolipoprotein A-I-containing lipoproteins (namely chylomicrons and HDL), leaving behind a fraction of triglyceride-rich lipoproteins, including chylomicron and VLDL remnants, both of which are enriched in apolipoprotein E. Cholesterol in the unbound fraction is measured with a sensitive enzymatic assay. The RLP-C concentration was highly correlated with total triglyceride-rich lipoproteins (sum of VLDL-cholesterol and IDL-cholesterol) separated by ultracentrifugation and by polyacrylamide gel electrophoresis (r = 0.86 and 0.76, respectively). The within-run and run-to-run imprecision (CV) of the assay was ∼6% and 10%, respectively. The assay was not affected by hemoglobin up to 5000 mg/L (500 mg/dL), bilirubin up to 342 mmol/L (20 mg/dL), glucose up to 67 mmol/L (1200 mg/dL), or ascorbic acid up to 170 mmol/L (3.0 mg/dL). In 726 subjects (men, n = 364; women, n = 362) in the US, the 75th percentiles of RLP-C concentration were 0.17 mmol/L (6.6 mg/dL) and 0.23 mmol/L (8.8 mg/dL) in sera obtained after overnight fasting or randomly, respectively. A group of 151 patients from nine US centers and one Canadian center with coronary artery atherosclerosis established by angiography had higher median RLP-C concentrations than 302 gender- and age-matched controls (P &lt;0.05). We conclude that the RLP-C assay compares favorably to ultracentrifugation and electrophoresis and provides a convenient and economical approach to measure triglyceride-rich lipoprotein remnants in routine clinical laboratories.

The atherogenic significance of an elevated plasma triglyceride level

The importance of hypertriglyceridemia as an independent predictor of coronary artery disease (CAD) remains unsettled. Hypertriglyceridemia, with or without associated hypercholesterolemia, occurs more frequently in premature CAD subjects than does hypercholesterolemia alone. With univariate analysis, most studies show a positive correlation between plasma triglyceride (TG) level and risk for CAD, but with multivariate analysis plasma TG level is no longer an independent risk factor except in women and diabetics. Prospective studies have shown that subjects with a high LDL/HDL cholesterol ratio and a high plasma TG level have the highest risk for CAD. Hypertriglyceridemia signifies the presence of excess triglyceride-rich lipoproteins (TRL), including chylomicrons, VLDL, and their remnants. The question then becomes one of whether TRL are directly or indirectly involved in atherogenesis. TRL were thought to be too big to infiltrate the arterial wall, and histopathological studies have shown cholesterol but not triglyceride accumulation in the atherosclerotic plaque. However, there was a recent demonstration of undegraded VLDL and IDL in atherosclerotic plaques. Larger TRL may undergo hydrolysis on the arterial surface to become smaller particles before entry into the intima. Possible cellular pathways for the uptake of TRL by macrophages have been described. The smaller TRL (Sf 20-60), including postprandial chylomicron remnants, are believed to be the most atherogenic of all TRL particles. Because large amounts of TRL are produced in the postprandial period, atherogenesis involving TRL may be primarily a postprandial phenomenon. Once in the intima, TG may undergo hydrolysis, releasing free fatty acids and mono- and diacyl glycerol, accounting for the dearth of TG in atherosclerotic lesions. Particle for particle, VLDL delivers five times as much cholesterol as LDL does to the macrophage.

Normal triglyceride levels and coronary artery disease events: the Baltimore Coronary Observational Long-Term Study

OBJECTIVES

This study sought to evaluate long-term predictors of coronary events in men and women with arteriographically defined coronary artery disease (CAD).

BACKGROUND

There is conflicting evidence of the role of triglycerides (TGs) as a prognosticator of CAD, and no studies have examined the long-term outcome of "normal" levels in predicting new coronary events.

METHODS

This was a retrospective cohort study that evaluated 740 consecutive patients presenting for diagnostic coronary arteriography between 1977 and 1978. Beginning in 1988, patients with arteriographic CAD (n=350) were recontacted and asked to complete detailed medical questionnaires. Case and control patients were stratified by development of new coronary events, including death from ischemic heart disease, nonfatal myocardial infarction and revascularization.

RESULTS

There were 199 events during the 18-year follow-up period. The mean high density lipoprotein cholesterol (HDL-C) was significantly lower (35 vs. 39 mg/dl; p=0.002) and TGs higher (160 vs. 137 mg/dl; p=0.03) in case patients than in control patients; After adjusting for age, gender and beta-adrenergic blocking agent use, multiple logistic regression analysis revealed the following independent predictors of CAD events: diabetes mellitus (relative risk [RR] 2.1, 95% confidence interval [CI] 1.4% to 3.1%), HDL-C <35 mg/dl (RR 1.5, 95% CI 1.1% to 2.00) and TGs >100 mg/dl (RR 1.5, 95% CI 1.1% to 2.1%). A Kaplan-Meier analysis revealed significantly reduced survival from CAD events in patients with baseline TG levels > or = 100 mg/dl compared with TG levels <100 mg/dl (p=0.008).

CONCLUSIONS

TG levels previously considered "normal" are predictive of new CAD events. The cutpoints established by the National Cholesterol Education Program for elevated TGs (>200 mg/dl) may need to be refined.

VLDL compositional changes and plasma levels of triglycerides and high density lipoprotein

VLDL chemical composition is related to plasma levels of triglycerides and HDL-cholesterol. We evaluated patients with primary hypertriglyceridemia with or without hypoalphalipoproteinemia and subjects with normotriglyceridemia with hypoalphalipoproteinemia. The pattern observed in all the groups was an enrichment in the triglyceride content of VLDL and in apo B-VLDL. Compared to controls, LpC-III:B levels were higher in hypertriglyceridemic patients with low or normal HDL-cholesterol levels (7.3 +/- 0.6 vs. 14.9 +/- 1.8 and 12.3 +/- 2.8 mg/dl; P < 0.005 and P < 0.01, respectively) and LpE:B concentration was only increased in patients with hypertriglyceridemia and normal HDL-cholesterol levels (3.1 +/- 0.5 vs. 6.3 +/- 1.0 mg/dl; P < 0.01). The activity of the cholesteryl ester transfer protein was higher in hypertriglyceridemic patients with low HDL-cholesterol levels than in controls (380 +/- 25 vs. 262 +/- 14% cholesteryl esters/ml.h; P < 0.001). The most atypical VLDL particle was found in patients who combined an accumulation of VLDL particles and a reduction in HDL-cholesterol concentration. These two parameters represent both ends of the cholesteryl ester-triglyceride transfer, a crucial factor for VLDL chemical composition and HDL levels.

Association of vitamin K-dependent coagulation proteins and C4b binding protein with triglyceride-rich lipoproteins of human plasma

The triglyceride (TG) concentration in plasma is an independent risk factor for coronary heart disease. There is evidence that TG-rich lipoprotein (TGRLP), ie, chylomicrons (CMs), chylomicron remnants (CMRs), and VLDLs associate with factor VII and prothrombin and that the association enhances a platelet factor Xa-mediated prothrombin activation when the CM-prothrombin complex is exposed to platelets. In this study, we examined the association of the vitamin K-dependent coagulation factors VII, IX, X, and prothrombin, as well as the anticoagulation protein C and its cofactor protein S, in plasma lipoproteins obtained from human fasting and postprandial plasma. We also analyzed some other proteins that are related to the coagulation system but not to vitamin K-dependent proteins, including factor V, serum amyloid P component (SAP), C4b binding protein (C4BP), and thrombomodulin (TM), and as a control, Ig G. Human TGRLP (d < 1.006 kg/L), LDL (d = 1.006 to 1.063 kg/L), and HDL (d = 1.063 to 1.210 kg/L) were separated from normal subjects both in fasting and 2 to 3 hours after the ingestion of a meal containing 100 g fat. The different coagulation proteins, SAP, C4BP, TM, and Ig G were determined by SDS-polyacrylamide gel electrophoresis combined with Western blotting, using specific polyclonal or monoclonal antibodies, and were visualized by peroxidase staining. All the vitamin K-dependent proteins associate with TGRLP in both fasting and postprandial plasma, but not with LDL or HDL. Factor V, SAP, TM, and Ig G were not found in any lipoprotein classes. C4BP, which is a regulatory protein of the classic pathway of the complement system and which binds protein S in vivo to regulate blood coagulation, was present in TGRLP, especially postprandial, but not in LDL or HDL. The amounts of prothrombin, protein S, and C4BP in postprandial TGRLP were larger than those in fasting TGRLP. Vitamin K-dependent procoagulation and anticoagulation proteins, as well as C4BP, could be associated with TGRLP in vivo. If the association enhances prothrombin activation, this effect may thus be counteracted by simultaneous binding of protein S.

Heterozygous lipoprotein lipase deficiency: frequency in the general population, effect on plasma lipid levels, and risk of ischemic heart disease

BACKGROUND

Patients with mutations on both alleles of the lipoprotein lipase gene resulting in complete lipoprotein lipase deficiency exhibit the chylomicronemia syndrome with severe hypertriglyceridemia and increased risk of pancreatitis and possibly of ischemic heart disease. This study examined frequency, lipid levels, and risk of ischemic heart disease for heterozygous carriers of lipoprotein lipase mutations known to cause the chylomicronemia syndrome in the homozygous state.

METHODS AND RESULTS

Two mutations were screened for in 9259 individuals in a general population sample and in 948 patients with verified ischemic heart disease. The percent frequencies of heterozygous individuals with the Gly188-->Glu and Ile194-->Thr substitutions in the general population were 0.06% (95% CI, 0.04% to 0.23%) and 0% (95% CI, 0.00% to 0.12%), respectively. The Gly188-->Glu substitution was associated with an increase in plasma triglycerides of 0.8+/-0.3 mmol/L (mean+/-SEM) and a decrease in plasma HDL cholesterol, apo A-I, and glucose levels of 0.45+/-0.07 mmol/L, 17+/-6 mg/dL, and 1.1+/-0.2 mmol/L, respectively. On multiple logistic regression analysis allowing for age, sex, plasma cholesterol, plasma lipoprotein (a), hypertension, diabetes mellitus, smoking, and body mass index, both plasma triglycerides and HDL cholesterol levels were independent predictors of ischemic heart disease. Finally, the Gly188-->Glu substitution was more common among patients with verified ischemic heart disease (percent frequency of heterozygous individuals, 0.32%) than among individuals from the general population (odds ratio, 4.9; 95% CI, 1.2 to 19.6). The effects of the Gly188-->Glu substitution were more pronounced than those of the common Asn291-->Ser substitution.

CONCLUSIONS

Heterozygous lipoprotein lipase deficiency due to the Gly188-->Glu substitution appears to increase plasma triglycerides and reduce HDL levels and may thereby predispose carriers to ischemic heart disease.