Hypertriglyceridemia: a review beyond low-density lipoprotein

Nrf2 Signaling Pathway as a Key to Treatment for Diabetic Dyslipidemia and Atherosclerosis

Diabetes mellitus (DM) is a chronic endocrine disorder that affects more than 20 million people in the United States. DM-related complications affect multiple organ systems and are a significant cause of morbidity and mortality among people with DM. Of the numerous acute and chronic complications, atherosclerosis due to diabetic dyslipidemia is a condition that can lead to many life-threatening diseases, such as stroke, coronary artery disease, and myocardial infarction. The nuclear erythroid 2-related factor 2 (Nrf2) signaling pathway is an emerging antioxidative pathway and a promising target for the treatment of DM and its complications. This review aims to explore the Nrf2 pathway's role in combating diabetic dyslipidemia. We will explore risk factors for diabetic dyslipidemia at a cellular level and aim to elucidate how the Nrf2 pathway becomes a potential therapeutic target for DM-related atherosclerosis.

Obesity induction in hamster that mimics the human clinical condition

Although obesity is well established in hamsters, studies using diets with high levels of simple carbohydrate associated with lipids are necessary to assess the impact of this type of food in the body. In this study a high sugar and butter diet (HSB) and high temperature were employed towards this end. Obesity was successfully induced at a temperature of 30.3°C to 30.9°C after 38 days feeding the animals an HSB diet. It was shown that although diet is important for the induction of obesity, temperature is also essential because at a temperature slightly below the one required, obesity was not induced, even when the animals were fed for a longer period (150 days).The obese clinical condition was accompanied by biochemical and hematological changes, as increased cholesterol and triglyceride levels and increased leukocyte numbers, similar to alterations observed in obese humans. Furthermore, it was demonstrated that increasing the intake of simple carbohydrates associated with lipids provided evidence of inflammation in obese animals.

Targeting inflammation in metabolic syndrome

The metabolic syndrome (MetS) is comprised of a cluster of closely related risk factors, including visceral adiposity, insulin resistance, hypertension, high triglyceride, and low high-density lipoprotein cholesterol; all of which increase the risk for the development of type 2 diabetes and cardiovascular disease. A chronic state of inflammation appears to be a central mechanism underlying the pathophysiology of insulin resistance and MetS. In this review, we summarize recent research which has provided insight into the mechanisms by which inflammation underlies the pathophysiology of the individual components of MetS including visceral adiposity, hyperglycemia and insulin resistance, dyslipidemia, and hypertension. On the basis of these mechanisms, we summarize therapeutic modalities to target inflammation in the MetS and its individual components. Current therapeutic modalities can modulate the individual components of MetS and have a direct anti-inflammatory effect. Lifestyle modifications including exercise, weight loss, and diets high in fruits, vegetables, fiber, whole grains, and low-fat dairy and low in saturated fat and glucose are recommended as a first line therapy. The Mediterranean and dietary approaches to stop hypertension diets are especially beneficial and have been shown to prevent development of MetS. Moreover, the Mediterranean diet has been associated with reductions in total and cardiovascular mortality. Omega-3 fatty acids and peroxisome proliferator-activated receptor α agonists lower high levels of triglyceride; their role in targeting inflammation is reviewed. Angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, and aldosterone blockers comprise pharmacologic therapies for hypertension but also target other aspects of MetS including inflammation. Statin drugs target many of the underlying inflammatory pathways involved in MetS.

Incident hypertension and its predictors: the Isfahan Cohort Study

OBJECTIVES

The present study aimed to investigate the incidence and predictors of hypertension in an Iranian adult population.

METHODS

Isfahan Cohort Study was a longitudinal population-based study that was conducted on adults aged 35 years or older, living in urban and rural areas of three districts in central Iran. After 7 years of follow-up, 3283 participants were re-evaluated using a standard protocol similar to the baseline. At both measurements, participants underwent medical interview, physical examination, and fasting blood measurements. Participants (n = 833) with prevalent hypertension were excluded from the analysis, resulting in a sample size of 2450.

RESULTS

The participants' age was 47.3 ± 9.4 years (mean ± SD) and 50.7% were men. During the follow-up period, 542 (22.1%) individuals developed hypertension, 49.6% of whom were aware of their disease, 42.4% were treated, but only 24.9% were controlled. Incidence rates have shown no sex-specific difference across age and blood pressure (BP) categories. Multivariate-adjusted model controlled for all study covariates showed that age, male sex, general and central obesity, hypertriglyceridemia, impaired fasting glucose, diabetes mellitus, baseline BP at least 120/80  mmHg (nonoptimal BP), and parental history of hypertension independently contributed to the development of hypertension. Higher education level and more than 10% decrease in waist circumference over 7-year follow-up represented protective effects. In men, weight loss decreased and weight gain increased the risk of developing hypertension. Nonoptimal BP along with central obesity and hypertriglyceridemia together were responsible for 71% of the burden of hypertension.

CONCLUSION

Our findings imply that there are other factors in addition to nonoptimal BP that deserve integrating into the risk assessment criteria for developing hypertension.

How do elevated triglycerides and low HDL-cholesterol affect inflammation and atherothrombosis?

This review article summarizes recent research into the mechanisms as to how elevated levels of triglyceride (TG) and low levels of high- density- lipoprotein cholesterol (HDL-C) contribute to inflammation and atherosclerosis. Evidence supports the role of TG-rich lipoproteins in signaling mechanisms via apolipoproteins C-III and free fatty acids leading to activation of NFKβ, VCAM-1 and other inflammatory mediators which lead to fatty streak formation and advanced atherosclerosis. Moreover, the cholesterol content in TG-rich lipoproteins has been shown to predict CAD risk better than LDL-C. In addition to reverse cholesterol transport, HDL has many other cardioprotective effects which include regulating immune function. The "functionality" of HDL appears more important than the level of HDL-C. Insulin resistance and central obesity underlie the pathophysiology of elevated TG and low HDL-C in metabolic syndrome and type 2 diabetes. Lifestyle recommendations including exercise and weight loss remain first line therapy in ameliorating insulin resistance and the adverse signaling processes from elevated levels of TG-rich lipoproteins and low HDL-C.

Effect of ABT-335 (fenofibric acid) on meal-induced oxidative stress in patients with metabolic syndrome

OBJECTIVE

Examine the effect of ABT-335 (fenofibric acid) on postprandial lipemia and susceptibility of plasma lipoproteins to Cu(++)-mediated oxidation in patients with metabolic syndrome.

METHODS AND RESULTS

This is a randomized double-blind, placebo-controlled study with cross-over and includes a 4-week wash-out period between the two treatment periods. At the end of each 8-week treatment period, subjects were challenged with a standardized mixed meal followed by blood collection over the ensuing 6 h. Plasma lipoproteins were isolated by a combination of ultracentrifugation and FPLC for the continuous monitoring of conjugated dienes formation as an assessment of oxidative susceptibility. Fasting plasma TG was reduced by 20% (p < 0.0002) and there was a modest reduction in hsCRP (6.1%, p < 0.06). There was no change in either HDLc or LDLc in these subjects. Postprandial lipemia was reduced with ABT-335 as demonstrated by a 28.5% reduction (p < 0.0005) in incremental area under the curve for TG during the 6-h period after the meal challenge. Lag times for both fasting LDL (+16%) and postprandial LDL (+28%) were increased with the ABT-335 therapy, suggestive of reduced oxidative susceptibility. Co-incubation with autologous HDL did not reduced LDL oxidative susceptibility in these patients.

CONCLUSION

ABT-335 therapy reduced fasting and postprandial triglycerides in patients with metabolic syndrome. Autologous HDL may be dysfunctional in these patients as co-incubation with HDL failed to reduce oxidative susceptibility of LDL. During ABT-335 therapy, LDL was less susceptible to Cu(++)-mediated oxidative modification, in spite of the lack of changes in LDLc levels.

NADPH oxidase 2 plays a critical role in dysfunction and apoptosis of pancreatic β-cells induced by very low-density lipoprotein

In type 2 diabetes, pancreatic β-cells cannot secret enough insulin compensate for insulin resistance, which are often accompanied by abnormality in lipid metabolism such as hypertriglyceridemia. It is reported that oxidative stress is involved in pancreatic β-cell dysfunction. However, molecular mechanisms linking between excessive generations of reactive oxygen species (ROS) and β-cell dysfunction and apoptosis induced by high levels of very low-density lipoprotein (VLDL) are poorly understood. In this study, we test the hypothesis that NADPH oxidase 2 (NOX2)-derived ROS may play a key role in dysfunction and apoptosis of pancreatic β-cell induced by VLDL. Our results show that the ApoCIII transgenic mice displayed increased serum TG levels, enhanced generation of ROS and impaired insulin content in pancreatic β-cells. In vitro, the treatment of pancreatic NIT-1 cells with 1 mg/ml VLDL for 12 h stimulated NOX2-derived ROS generation, decreased expression and secretion of insulin. Furthermore, we found that VLDL induced dysfunction and apoptosis of pancreatic β-cells through JNK and p53 pathways, which were rescued by siRNA-mediated NOX2 reduction. In conclusion, our data demonstrate a critical role of NOX2-derived ROS in dysfunction and apoptosis through JNK and p53 pathways in pancreatic β-cells induced by VLDL.

Effect of functional yogurt NY-YP901 in improving the trait of metabolic syndrome

BACKGROUND/OBJECTIVES

This study was aimed to assess the beneficial effects on metabolic syndrome of functional yogurt NY-YP901 (Namyang Dairy Product Co. Ltd and Nutra R&BT Inc., Seoul, Korea) supplemented with mixture of Streptococcus thermophilus, Lactobacillus acidophilus, Bifidobacterium infantis and extra-ingredients containing Bifidobacterium breve (CBG-C2), Enterococcus faecalis FK-23, fibersol-2 and so on.

SUBJECTS/METHODS

This study was designed as an 8-week randomized, double-blind, placebo-controlled, parallel study. Treatment and control groups consumed a functional yogurt NY-YP901 (150 ml) and a placebo yogurt twice a day, respectively, for 8 weeks. Body weight and body mass index (BMI), blood pressure, lipid profiles, fasting glucose with HbA1C and waist circumference were measured before and after treatment. Inclusion criteria were healthy individuals between the ages 20-65 years old who submitted an informed consent.

RESULTS

During the period August 2009 to December 2009, 101 healthy participants (31 males and 70 females) finished the study. Treatment group were 53 individuals, and the control group were 48 individuals. In the treatment group consuming NY-YP901, statistically significant beneficial changes were observed in body weight (treatment group vs control group=-0.24±1.50 vs +0.64±1.39 kg, P<0.05), BMI (-0.10±0.58 vs +0.24±0.50 kg/m(2), P<0.05 ) and low-density lipoprotein (LDL)-cholesterol (-7.71±14.14 vs -0.43±15.32 mg/dl, P<0.05) after 8 weeks. The change in other parameters was not different between the treatment and the control groups.

CONCLUSIONS

The functional yogurt NY-YP901 reduced LDL-cholesterol, body weight and BMI in the subjects at a 300-ml consumption daily for 8 weeks. From these findings, regular intake of functional yogurt NY-YP901 may be consequently related to improve metabolic syndrome.

FoxO1 integrates insulin signaling to VLDL production

Very low-density lipoproteins (VLDL) are triglyceride-rich particles. VLDL is synthesized in hepatocytes and secreted from the liver in a pathway that is tightly regulated by insulin. Hepatic VLDL production is stimulated in response to reduced insulin action, resulting in increased release of VLDL into the blood under fasting conditions. Circulating VLDL serves as a vehicle for transporting lipids to peripheral tissues for energy homeostasis. Conversely, hepatic VLDL production is suppressed in response to increased insulin release after meals. This effect is critical for preventing prolonged excursion of postprandial plasma lipid profiles in normal individuals. In subjects with obesity and type 2 diabetes, the ability of insulin to regulate VLDL production becomes impaired due to insulin resistance in the liver, resulting in excessive VLDL secretion and accumulation of triglyceride-rich particles in the blood. Such abnormality in lipid metabolism characterizes the pathogenesis of hypertriglyceridemia and accounts for increased risk of coronary artery disease in obesity and type 2 diabetes. Nevertheless, the molecular basis that links insulin resistance to VLDL overproduction remains poorly understood. Our recent studies illustrate that the forkhead transcription factor FoxO1 acts in the liver to integrate hepatic insulin action to VLDL production. Augmented FoxO1 activity in insulin resistant livers promotes hepatic VLDL overproduction and predisposes to the development of hypertriglyceridemia. These new findings raise an important question: Is FoxO1 a therapeutic target for ameliorating hypertriglyceridemia? Here we discuss this question in the context of recent advances toward our understanding of the pathophysiology of hypertriglyceridemia.

Post-prandial endothelial dysfunction in hypertriglyceridemic subjects: Molecular mechanisms and gene expression studies

OBJECTIVE

Triglyceride-rich lipoproteins (TGRLs) are a cardiovascular risk factor and induce endothelial dysfunction. In the present study, we investigated the effects of post-prandial TGRLs from type IV hyperlipidemic subjects on endothelial activation addressing the effects of the lipoproteins on intracellular pathways and gene expression.

METHODS

Thirty fasted hypertriglyceridemic patients were given an oral fat load (OFL) and blood samples were collected before the OFL (T0) and 2, 4, 6 and 8h thereafter. Endothelial function, determined as flow-mediated dilatation of the brachial artery, was assessed at the same time points. TGRLs were isolated at T0 and T4 (PP-TGRL) for in vitro studies.

RESULTS

Compared with TGRLs, PP-TGRLs induced to a larger extent phosphorylation of p38 MAPK, CREB and IKB-alpha in human endothelial cells and increased the DNA binding activity of CREB, NFAT and NF-kappaB. Furthermore, PP-TRGLs upregulated the expression of several pro-inflammatory genes including vascular cell adhesion molecule-1 (VCAM-1), PECAM-1, ELAM-1, intercellular adhesion molecule-1 (ICAM-1), P-selectin, MCP-1, interleukin-6 (IL-6), TLR-4, CD40, ADAMTS1 and PAI-1.

CONCLUSION

These effects may relate to the severe impairment of endothelial function seen during the post-prandial phase in hypertriglyceridemic patients.

Effects of apoA-V on HDL and VLDL metabolism in APOC3 transgenic mice

Apolipoprotein A-V (apoA-V) and apoC-III are exchangeable constituents of VLDL and HDL. ApoA-V counteracts the effect of apoC-III on triglyceride (TG) metabolism with poorly defined mechanisms. To better understand the effects of apoA-V on TG and cholesterol metabolism, we delivered apoA-V cDNA into livers of hypertriglyceridemic APOC3 transgenic mice by adenovirus-mediated gene transfer. In response to hepatic apoA-V production, plasma TG levels were reduced significantly as a result of enhanced VLDL catabolism without alternations in VLDL production. This effect was associated with reduced apoC-III content in VLDL. Increased apoA-V production also resulted in decreased apoC-III and increased apoA-I content in HDL. Furthermore, apoA-V-enriched HDL was associated with enhanced LCAT activity and increased cholesterol efflux. This effect, along with apoE enrichment in HDL, contributed to HDL core expansion and alpha-HDL formation, accounting for significant increases in both the number and size of HDL particles. As a result, apoA-V-treated APOC3 transgenic mice exhibited decreased VLDL-cholesterol and increased HDL-cholesterol levels. ApoA-V-mediated reduction of apoC-III content in VLDL represents an important mechanism by which apoA-V acts to ameliorate hypertriglyceridemia in adult APOC3 transgenic mice. In addition, increased apoA-V levels accounted for cholesterol redistribution from VLDL to larger HDL particles. These data suggest that in addition to its TG-lowering effect, apoA-V plays a significant role in modulating HDL maturation and cholesterol metabolism.

Peroxisome proliferator-activated receptor delta promotes very low-density lipoprotein-derived fatty acid catabolism in the macrophage

Significant attention has focused on the role of low-density lipoprotein (LDL) in the pathogenesis of atherosclerosis. However, recent advances have identified triglyceride-rich lipoproteins [e.g., very LDL (VLDL)] as independent risk predictors for this disease. We have previously demonstrated peroxisome proliferator-activated receptor (PPAR)delta, but not PPARgamma, is the major nuclear VLDL sensor in the macrophage, which is a crucial component of the atherosclerotic lesion. Here, we show that, in addition to beta-oxidation and energy dissipation, activation of PPARdelta by VLDL particles induces key genes involved in carnitine biosynthesis and lipid mobilization mediated by a recently identified TG lipase, transport secretion protein 2 (also named desnutrin, iPLA2zeta, and adipose triglyceride lipase), resulting in increased fatty acid catabolism. Unexpectedly, deletion of PPARdelta results in derepression of target gene expression, a phenotype similar to that of ligand activation, suggesting that unliganded PPARdelta suppresses fatty acid utilization through active repression, which is reversed upon ligand binding. This unique transcriptional mechanism assures a tight control of the homeostasis of VLDL-derived fatty acid and provides a therapeutic target for other lipid-related disorders, including dyslipidemia and diabetes, in addition to coronary artery disease.

FR177391, A New Anti-hyperlipidemic Agent from Serratia

The pharmacological effect of FR177391, isolated from Serratia liquefaciens No. 1821, was studied in normal animals and various types of animal models of hypertriglyceridemia. Treatment of normal mice with FR177391 resulted in an increase in heparin-releasable lipoprotein lipase (LPL) activity in the blood and epididymal fat tissue. FR177391 treatment decreased triglyceride (TG) and increased high-density lipoprotein cholesterol in the blood in normal rats following 7 days treatment, suggesting potent LPL activating properties of FR177391. Both Triton WR1339-induced severe and fructose-induced mild hypertriglyceridemia in rats were attenuated by FR177391 treatment. Severely elevated levels of TG in db/db mice, an insulin resistant diabetic animal model, also significantly decreased from 14 days of treatment with FR177391. FR177391 treatment for 9 days caused a decrease in the elevated levels of TG in mice induced by intraperitoneal inoculation of murine lymphoma EL-4. Overall, this study demonstrated that FR177391 can be possibly a LPL activating agent and that FR177391 treatment improved hypertriglyceridemia in various rat and mouse animal models. These results suggest that FR177391 is a promising candidate compound for the management of hypertriglyceridemia.

Possible role of ubiquinone in the treatment of massive hypertriglyceridemia resistant to PUFA and fibrates

OBJECTIVE

To describe the effect of Coenzyme Q10 (CoQ10) (added to either a fibrate, or polyunsaturated fatty acids (PUFA) or association of both) in patients affected by massive hypertriglyceridemia (MHTG) resistant to fibrates and PUFA.

DESIGN

Open, sequential, comparative intervention study.

SETTING

Specialised centres for dyslipidemia management.

SUBJECTS

Fifteen subjects (mean age: 45.1+/-12.5 years) affected by MHTG and hyporesponsive to either fibrates, or PUFA, or fibrates-PUFA association, and 15 age-matched subjects regularly responders to PUFA and fenofibrate treatment.

INTERVENTIONS

Treatment for periods of 6 weeks each with the following consecutive treatments: CoQ10 150 mg/day, PUFA 3000 mg/day, fenofibrate 200 mg/day, PUFA 3000 mg/day+fenofibrate 200 mg/day, PUFA 3000 mg/day+CoQ10 150 mg/day, fenofibrate 200 mg/day+CoQ10 150 mg/day, and finally, fenofibrate 200 mg/day+PUFA 3000 mg/day + CoQ10 150 mg/day.

RESULTS

CoQ10 supplementation did not improve any monitored parameter in the control group except for systolic and diastolic blood pressure, creatinine and Lp(a) plasma levels, both during fenofibrate and/or PUFA treatment. In MHTG group, CoQ10 supplementation significantly improved TG, TC, Lp(a), uric acid and blood pressure during fenofibrate treatment, but only Lp(a) and blood pressure during PUFA treatment. Fenofibrate appeared to have better effect on hsCRP and gamma-GT plasma levels than PUFA. No significant change was observed in any group and under any treatment in regards to homocysteinemia, PAI-1, or t-PA.

CONCLUSION

Even though the mechanism of action through which the effects were obtained is yet to be elucidated, adding CoQ10 to fenofibrate could improve the drug's efficacy in MHTG patients not responding to fenofibrate alone.

Treatment of massive hypertriglyceridemia resistant to PUFA and fibrates: a possible role for the coenzyme Q10?

OBJECTIVE

To describe the effect of CoQ10 (added to either a fibrate, or PUFA or association of both) in patients affected by massive hypertriglyceridemia (MHTG) resistant to fibrates and PUFA.

DESIGN

Open, sequential, comparative intervention study.

SETTING

Specialised centres for dyslipidemia management.

SUBJECTS

15 subjects (mean age: 45.1 +/- 12.5 years) affected by MHTG and hyporesponsive to either fibrates, or PUFA, or fibrates-PUFA association, and 15 age-matched subjects regularly responders to PUFA and fenofibrate treatment.

INTERVENTIONS

Treatment for periods of 6 weeks each with the following consecutive treatments: CoQ10 150 mg/day, PUFA 3000 mg/day, fenofibrate 200 mg/day, PUFA 3000 mg/day + fenofibrate 200 mg/day, PUFA 3000 mg/day + CoQ10 150 mg/day, fenofibrate 200 mg/day + CoQ10 150 mg/day, and finally, fenofibrate 200 mg/day + PUFA 3000 mg/day + CoQ10 150 mg/day.

RESULTS

CoQ10 supplementation improved, in the control group, systolic and diastolic blood pressure, creatinine and Lp(a) plasma levels, both during fenofibrate and/or PUFA treatment. In MHTG group, CoQ10 supplementation significantly improved TG, TC, Lp(a), uric acid and blood pressure during fenofibrate treatment, but only Lp(a) and blood pressure during PUFA treatment. Fenofibrate appeared to have better effect on hsCRP and gamma-GT plasma levels than PUFA. No significant change was observed in any group and under any treatment in regards to homocysteinemia, PAI-1, or t-PA.

CONCLUSION

Even though the mechanism of action through which the effects were obtained is yet to be elucidated, adding CoQ10 to fenofibrate could improve the drug's efficacy in MHTG patients not responding to fenofibrate alone.

From degeneration to infection/inflammation, and from individual-centered to ecologic approaches to investigation of evolving patterns of diseases occurrences in populations

Variation in attributes of CHD cases over time suggests a temporal change in the source sub-population of cases. It is proposed that an early 20th century expansion of a CHD-prone sub-population, characterized by high-serum cholesterol phenotype and high case-fatality - and which contributed with most of the CHD cases and deaths during the 1960s - may have followed the 1918 Influenza Pandemic. The extinction of those birth-cohorts would have resulted in a relative increase in cases coming from a second source sub-population, characterized by insulin resistance and chronic expression of low grade inflammation markers, comparatively less vulnerable to acutely die from CHD. This re-interpretation of the CHD trend, and the abandonment of the idea of degeneration for inflammation/infection calls for a change in epidemiology. Besides exposures (diet, infection...), temporal variations in proportional representations of inherited and acquired phenotypes associated with individual resistance/vulnerability, would be important determinants of evolving patterns of diseases occurrences in populations.

Dietary virgin olive oil triacylglycerols as an independent determinant of very low-density lipoprotein composition

OBJECTIVE

We examined the effects of virgin olive oil (VOO) triacylglycerols (TGs) on the lipid composition of human very low-density lipoprotein (VLDL).

METHODS

Twenty-one normocholesterolemic, normotensive, non-diabetic elderly subjects were recruited for the study. Two VOOs (VOO1 and VOO2) of the same variety, with an equivalent composition in minor components and differing only in the oleic and linoleic acid concentrations, were administered for 4 wk each to assess the effect of their TG molecular species compositions. Blood was collected after an overnight fast, VLDLs were isolated by ultracentrifugation, and lipid classes, TG molecular species, and TG fatty acid composition were determined.

RESULTS

Dietary VOOs significantly differed in TG molecular species composition. VOO1 represented larger amounts of triolein (P < 0.01), whereas VOO2 was significantly enriched with dilinoleoyl-oleoyl-glycerol, linoleoyl-dioleoyl-glycerol, and linoleoyl-oleoyl-palmitoyl-glycerol (P < 0.01). For VLDL, intake of VOO1 caused an increase of total TG (P < 0.01) due mainly to increases in triolein and linoleoyl-dioleoyl-glycerol. Conversely, VOO2 increased VLDL cholesteryl esters (P < 0.01) and TG rich in arachidonic acid (P < 0.01).

CONCLUSIONS

The different TG molecular species compositions of dietary oils may be an independent determinant of the lipid composition of VLDL in elderly people and therefore may play a role in regulating lipoprotein metabolism in these subjects.

Effect of Acanthopanax senticosus on lipoprotein lipase in 3T3-L1 adipocytes

The effect of Acanthopanax senticosus (AS) leaves on lipoprotein lipase (LPL) was investigated in 3T3-L1 adipocytes. A water extract of AS leaves increased the LPL activity in culture medium of adipocytes in a dose- and time-dependent manner. The AS extract contained heparin-like LPL releasing components, however, the increase of medium LPL activity was continued up until 12 h, in contrast to the rapid decline after heparin treatment. The increase of LPL mRNA was also observed after AS extract treatment, suggesting that LPL induction occurs at the transcriptional level. The AS extract could partially reverse the LPL suppression by tumour necrosis factor-alpha in 3T3-L1 adipocytes. These results of an AS extract-induced increase of LPL activity in vitro suggest the possible action of AS as a facilitator of plasma triglyceride clearance.

Arterial retention of apolipoprotein B(48)- and B(100)-containing lipoproteins in atherogenesis

PURPOSE OF REVIEW

The "response to retention" hypothesis of atherosclerosis suggests that the arterial deposition of cholesterol is directly proportional to the concentration of circulating plasma lipoproteins. However, there is increasing evidence to support the concept that specific lipoproteins may be preferentially retained within the arterial wall, possibly as a result of greater affinity for cell surface and extracellular matrices.

RECENT FINDINGS

Recently, key studies have provided insight into mechanisms involved in the interaction of apolipoprotein B (apoB)-containing lipoproteins with extracellular matrices. In addition, novel methods and innovative experimental design has enabled us to differentiate between the delivery, retention and efflux of apoB(48)- and apoB(100)-containing lipoproteins. Other studies have demonstrated a relationship between extracellular matrix proteoglycan expression and the development of atherosclerosis. Discussion in the present review also extends to the mechanisms that are involved in the relative intimal retention of apoB(48)- and apoB(100)-containing lipoproteins in order to explain the atherogenicity of these macromolecules.

SUMMARY

The perspective of this review is to highlight recent advances in the area of arterial lipoprotein retention and the physiological significance these processes may have in the aetiology of cardiovascular disease. Importantly, an understanding of the mechanisms responsible for the retention of apoB(48)/B(100)-containing lipoproteins will enable new strategies to be developed for the future management of cardiovascular disease.