Triglyceride enriched lipoprotein particles correlate with the severity of coronary artery disease

Applications of Genome Editing Technologies in CAD Research and Therapy with a Focus on Atherosclerosis

Cardiovascular diseases, particularly coronary artery disease (CAD), remain the leading cause of death worldwide in recent years, with myocardial infarction (MI) being the most common form of CAD. Atherosclerosis has been highlighted as one of the drivers of CAD, and much research has been carried out to understand and treat this disease. However, there remains much to be better understood and developed in treating this disease. Genome editing technologies have been widely used to establish models of disease as well as to treat various genetic disorders at their root. In this review, we aim to highlight the various ways genome editing technologies can be applied to establish models of atherosclerosis, as well as their therapeutic roles in both atherosclerosis and the clinical implications of CAD.

From Dietary Cholesterol to Blood Cholesterol

The Nutrients' Special Issue "From dietary cholesterol to blood cholesterol" aims to supply existing knowledge and novel new research data about human cholesterol (C) fluxes [...].

Measurement of Serum Low Density Lipoprotein Cholesterol and Triglyceride-Rich Remnant Cholesterol as Independent Predictors of Atherosclerotic Cardiovascular Disease: Possibilities and Limitations

The serum low density lipoprotein cholesterol (LDL-C) concentration is the dominant clinical parameter to judge a patient's risk of developing cardiovascular disease (CVD). Recent evidence supports the theory that cholesterol in serum triglyceride-rich lipoproteins (TRLs) contributes significantly to the atherogenic risk, independent of LDL-C. Therefore, combined analysis of both targets and adequate treatment may improve prevention of CVD. The validity of TRL-C calculation is solely dependent on the accuracy of the LDL-C measurement. Direct measurement of serum LDL- C is more accurate than established estimation procedures based upon Friedewald, Martin-Hopkins, or Sampson equations. TRL-C can be easily calculated as total C minus high density lipoprotein C (HDL-C) minus LDL-C. Enhanced serum LDL-C or TRL-C concentrations require different therapeutic approaches to lower the atherogenic lipoprotein C. This review describes the different atherogenic lipoproteins and their possible analytical properties and limitations.

APOC-III: a Gatekeeper in Controlling Triglyceride Metabolism

PURPOSE OF REVIEW

Apolipoprotein C-III (ApoC-III) is a widely known player in triglyceride metabolism, and it has been recently recognized as a polyhedric factor which may regulate several pathways beyond lipid metabolism by influencing cardiovascular, metabolic, and neurological disease risk. This review summarizes the different functions of ApoC-III and underlines the recent findings related to its multifaceted pathophysiological role.

RECENT FINDINGS

The role of ApoC-III has been implicated in HDL metabolism and in the development of atherosclerosis, inflammation, and ER stress in endothelial cells. ApoC-III has been recently considered an important player in insulin resistance mechanisms, lipodystrophy, diabetic dyslipidemia, and postprandial hypertriglyceridemia (PPT). The emerging evidence of the involvement of ApoC-III in the in the pathogenesis of Alzheimer's disease open the way to further study if modification of ApoC-III level slows disease progression. Furthermore, ApoC-III is clearly linked to cardiovascular disease (CVD) risk, and progression of coronary artery disease (CAD) as well as the calcification of aortic valve and recent clinical trials has pointed out the inhibition of ApoC-III as a promising approach to manage hypertriglyceridemia and prevent CVD. Several evidences highlight the role of ApoC-III not only in triglyceride metabolism but also in several cardio-metabolic pathways. Results from recent clinical trials underline that the inhibition of ApoC-III is a promising therapeutical strategy for the management of severe hypertriglyceridemia and in CVD prevention.

APOC3 genetic variation, serum triglycerides, and risk of coronary artery disease in Asian Indians, Europeans, and other ethnic groups

BACKGROUND

Hypertriglyceridemia has emerged as a critical coronary artery disease (CAD) risk factor. Rare loss-of-function (LoF) variants in apolipoprotein C-III have been reported to reduce triglycerides (TG) and are cardioprotective in American Indians and Europeans. However, there is a lack of data in other Europeans and non-Europeans. Also, whether genetically increased plasma TG due to ApoC-III is causally associated with increased CAD risk is still unclear and inconsistent. The objectives of this study were to verify the cardioprotective role of earlier reported six LoF variants of APOC3 in South Asians and other multi-ethnic cohorts and to evaluate the causal association of TG raising common variants for increasing CAD risk.

METHODS

We performed gene-centric and Mendelian randomization analyses and evaluated the role of genetic variation encompassing APOC3 for affecting circulating TG and the risk for developing CAD.

RESULTS

One rare LoF variant (rs138326449) with a 37% reduction in TG was associated with lowered risk for CAD in Europeans (p = 0.007), but we could not confirm this association in Asian Indians (p = 0.641). Our data could not validate the cardioprotective role of other five LoF variants analysed. A common variant rs5128 in the APOC3 was strongly associated with elevated TG levels showing a p-value 2.8 × 10- 424. Measures of plasma ApoC-III in a small subset of Sikhs revealed a 37% increase in ApoC-III concentrations among homozygous mutant carriers than the wild-type carriers of rs5128. A genetically instrumented per 1SD increment of plasma TG level of 15 mg/dL would cause a mild increase (3%) in the risk for CAD (p = 0.042).

CONCLUSIONS

Our results highlight the challenges of inclusion of rare variant information in clinical risk assessment and the generalizability of implementation of ApoC-III inhibition for treating atherosclerotic disease. More studies would be needed to confirm whether genetically raised TG and ApoC-III concentrations would increase CAD risk.

Apolipoprotein CIII Is an Important Piece in the Type-1 Diabetes Jigsaw Puzzle

It is well known that type-2 diabetes mellitus (T2D) is increasing worldwide, but also the autoimmune form, type-1 diabetes (T1D), is affecting more people. The latest estimation from the International Diabetes Federation (IDF) is that 1.1 million children and adolescents below 20 years of age have T1D. At present, we have no primary, secondary or tertiary prevention or treatment available, although many efforts testing different strategies have been made. This review is based on the findings that apolipoprotein CIII (apoCIII) is increased in T1D and that in vitro studies revealed that healthy β-cells exposed to apoCIII became apoptotic, together with the observation that humans with higher levels of the apolipoprotein, due to mutations in the gene, are more susceptible to developing T1D. We have summarized what is known about apoCIII in relation to inflammation and autoimmunity in in vitro and in vivo studies of T1D. The aim is to highlight the need for exploring this field as we still are only seeing the top of the iceberg.

Effect of milk fat on LDL cholesterol and other cardiovascular risk markers in healthy humans: the INNOVALAIT project

BACKGROUND

Milk has a specific saturated fatty acid profile and its calcium content may change the kinetics of fat absorption.

OBJECTIVE

The goal of this study was to compare the effect on LDL Cholesterol and other risk markers of four isolipidic diets differing by their fat food source, vegetable fat, spring milk fat, winter milk fat or winter milk fat supplemented with calcium, in healthy moderately hypercholesterolemic humans.

INDIVIDUALS AND METHODS

This double-blind, randomized trial with four parallel arms included 172 healthy adults with plasma LDL cholesterol (LDL-C) from 130 to 220 mg/dL and triglycerides below 300 mg/dL. Individual meal plans ensured a stable energy intake. In the three diets containing milk fat, milk fat provided 38% of energy. Vegetable fat and spring milk fat diets provided the same amount of saturated fatty acids while the winter milk fat diets were slightly richer in saturated fatty acids. Vegetable fat diet and winter milk fat diets provided the same amount of palmitic acid (7.0% EI), while the spring milk fat diet was slightly poorer in this fatty acid (5.1% EI). Cardiovascular risk markers were analyzed after 8 weeks of dietary intervention.

RESULTS

There was no significant difference in LDL-C and other markers, except total cholesterol (TC), apo C3 and CRP. TC was significantly higher with spring milk fat than with vegetable fat.

CONCLUSIONS

In this trial, the chosen vegetable fat did not have a significant beneficial effect on LDL-C compared to dairy fat. However, sub-group analysis showed differences in TC, apo C3 and CRP. These results need confirmation and long-term studies aiming at cardiovascular endpoints are warranted.

The role of antisense oligonucleotide therapy against apolipoprotein-CIII in hypertriglyceridemia

Increased triglyceride levels (higher than ∼1000 mg/dL) are associated with an increased risk for pancreatitis. Apolipoprotein-CIII (apo-CIII) plays a key role in the metabolism of triglycerides and triglyceride-rich lipoproteins. While loss of function mutations in the gene encoding apo-CIII (APOC3) are associated with low triglyceride levels and a decreased risk for cardiovascular disease (CVD), overexpression of APOC3 is associated with hypertriglyceridemia. Although many drugs such as fibrates, statins and omega-3 fatty acids modestly decrease triglyceride levels (and apo-CIII concentrations), there are many patients who still have severe hypertriglyceridemia and are at risk for pancreatitis and potentially CVD. The antisense oligonucleotide (ASO) against APOC3 mRNA volanesorsen (previously called ISIS 304801, ISIS-ApoCIIIRx and IONIS-ApoCIIIRx) robustly decreases both, apo-CIII production and triglyceride concentrations and is being currently evaluated in phase 3 trials. In this narrative review we present the currently available clinical evidence on the efficacy and safety of volanesorsen for the treatment of hypertriglyceridemia.

Atherogenic index as a predictor of atherosclerosis in subjects with familial Mediterranean fever

BACKGROUND AND OBJECTIVE

Numerous inflammatory and innate immune pathways are involved in atherogenesis. We aimed to investigate the atherogenic index and other lipid parameters in individuals with familial Mediterranean fever (FMF), as a predictor of atherosclerosis.

MATERIALS AND METHODS

A total of 60 patients with FMF and 60 healthy age- and sex-matched controls were included in this study. The patients with acute infection, chronic metabolic and rheumatic diseases, use of drugs other than colchicine and smoking history were excluded. CRP, ESR, total cholesterol, triglycerides, LDL-C, and HDL-C levels of patients and the control group were measured. Atherogenic index (TG/HDL-C) was calculated.

RESULTS

We found that the atherogenic index values of the patients were significantly higher than those of the control group. HDL-C levels were lower and ESR and TG levels were higher in patients. Total cholesterol, LDL-C and CRP levels did not differ significantly between the two groups. There was no significant difference in the values of total cholesterol, LDL-C, triglycerides (TG), HDL-C, and atherogenic indexes between the groups of patients with and without M694V mutation.

CONCLUSIONS

Elaboration of clinical models of inflammation-induced atherogenesis may further advance our knowledge of multiple inflammatory pathways implicated in atherogenesis and provide a useful tool for cardiovascular prevention. We believe that the atherogenic index also be used as a preliminary indication of accelerated atherosclerosis in FMF. However, large-scale prospective studies on this issue are needed.

Monogenic causes of elevated HDL cholesterol and implications for development of new therapeutics

Identification of the CETP, LIPG (encoding endothelial lipase) and APOC3 genes, and ana lysis of rare genetic variants in them, have allowed researchers to increase understanding of HDL metabolism significantly. However, development of cardiovascular risk-reducing therapeutics targeting the proteins encoded by these genes has been less straightforward. The failure of two CETP inhibitors is complex but illustrates a possible over-reliance on HDL cholesterol as a marker of therapeutic efficacy. The case of endothelial lipase exemplifies the importance of utilizing population-wide genetic studies of rare variants in potential therapeutic targets to gain information on cardiovascular disease end points. Similar population-wide studies of cardiovascular end points make apoC-III a potentially attractive target for lipid-related drug discovery. These three cases illustrate the positives and negatives of single-gene studies relating to HDL-related cardiovascular drug discovery; such studies should focus not only on HDL cholesterol and other components of the lipid profile, but also on the effect genetic variants have on cardiovascular end points.

Two novel mutations in apolipoprotein C3 underlie atheroprotective lipid profiles in families

Apolipoprotein C3 (APOC3) mutations carriers typically display high plasma high-density lipoprotein cholesterol (HDL-C) and low triglycerides (TGs). We set out to investigate the prevalence and clinical consequences of APOC3 mutations in individuals with hyperalphalipoproteinemia. Two novel mutations (c.-13-2A>G and c.55+1G>A) and one known mutation (c.127G>A;p.Ala43Thr) were found. Lipid profiles and apoCIII isoform distributions were measured. c.55+1G>A mutation carriers displayed higher HDL-C percentiles (35.6 ± 35.8 vs 99.0 ± 0, p = 0.002) and lower TGs (0.51 (0.37-0.61) vs 1.42 (1.12-1.81) mmol/l, p = 0.007) and apoCIII levels (4.24 ± 1.57 vs 7.33 ± 3.61 mg/dl, p = 0.18). c.-13-2A>G mutation carriers did not display significantly different HDL-C levels (84.0 ± 30.0 vs 63.7 ± 45.7, p = 0.50), a trend towards lower TGs [0.71 (0.54 to 0.78) vs 0.85 (0.85 to -) mmol/l, p = 0.06] and significantly lower apoCIII levels (3.09 ± 1.08 vs 11.45 ± 1.06 mg/dl, p = 0.003). p.Ala43Thr mutation carriers displayed a trend towards higher HDL-C percentiles (91.2 ± 31.8 vs 41.0 ± 29.7 mmol/l, p = 0.06) and significantly lower TGs [0.58 (0.36-0.63) vs 0.95 (0.71-1.20) mmol/l, p = 0.02] and apoCIII levels (4.92 ± 2.33 vs 6.60 ± 1.60, p = 0.25). Heterozygosity for APOC3 mutations results in high HDL-C and low TGs and apoCIII levels. This favourable lipid profile in patients with genetically low apoCIII levels holds promise for current studies investigating the potential of apoCIII inhibition as a novel therapeutic in cardiovascular disease prevention.

Atherosclerosis and physical activity

Atherosclerosis and coronary heart disease have been considered as major health problem worldwide. Abnormalities in lipids and lipoprotein metabolism and impairment of endothelial function have been implicated as the main contributing factors in atherosclerosis and its progression. Physical activity has been recognized as a preventive measure for atherosclerosis.

The mean platelet volume and atherogenic index of plasma in nondipper normotensive individuals compared to dippers

Mean platelet volume (MPV) is a determinant of platelet activation. Atherogenic index of plasma (AIP), which is defined as the logarithm of the ratio of plasma level of triglycerides to the level of high-density lipoprotein (HDL)-cholesterol (log[ TG/HDL-C]), has recently been used as a marker of atherogenicity. This study included 104 normotensive individuals. Mean platelet volume and AIP were measured in all patients. Nondipper individuals (8.6 ± 0.9 fL, 0.3 ± 0.2) demonstrated higher values of MPV and AIP compared with dippers (7.9 ± 1.1 fL, 0.1 ± 0.2) (P < .001 and < .001, respectively). Mean platelet volume and AIP have a positive correlation with insufficient decline in nocturnal blood pressure.

Apolipoprotein C-III: understanding an emerging cardiovascular risk factor

The concurrence of visceral obesity, insulin resistance and dyslipidaemia comprises the concept of the metabolic syndrome. The metabolic syndrome is an escalating problem in developed and developing societies that tracks with the obesity epidemic. Dyslipidaemia in the metabolic syndrome is potently atherogenic and, hence, is a major risk factor for CVD (cardiovascular disease) in these subjects. It is globally characterized by hypertriglyceridaemia, near normal LDL (low-density lipoprotein)-cholesterol and low plasma HDL (high-density lipoprotein)-cholesterol. ApoC-III (apolipoprotein C-III), an important regulator of lipoprotein metabolism, is strongly associated with hypertriglyceridaemia and the progression of CVD. ApoC-III impairs the lipolysis of TRLs [triacylglycerol (triglyceride)-rich lipoproteins] by inhibiting lipoprotein lipase and the hepatic uptake of TRLs by remnant receptors. In the circulation, apoC-III is associated with TRLs and HDL, and freely exchanges among these lipoprotein particle systems. However, to fully understand the complex physiology and pathophysiology requires the application of tracer methodology and mathematical modelling. In addition, experimental evidence shows that apoC-III may also have a direct role in atherosclerosis. In the metabolic syndrome, increased apoC-III concentration, resulting from hepatic overproduction of VLDL (very-LDL) apoC-III, is strongly associated with delayed catabolism of triacylglycerols and TRLs. Several therapies pertinent to the metabolic syndrome, such as PPAR (peroxisome-proliferator-activated receptor) agonists and statins, can regulate apoC-III transport in the metabolic syndrome. Regulating apoC-III metabolism may be an important new therapeutic approach to managing dyslipidaemia and CVD risk in the metabolic syndrome.

Biochemical Aspects, Laboratory Diagnosis and Follow-Up of High Blood Cholesterol: NCEP ATP III Guidelines

Treći izveštaj ekspertske grupe o detekciji, evaluaciji i tretmanu povišene koncentracije holesterola u odraslih (Adult Treatment Panel III, ATP III) predstavlja ažuriran klinički vodič Nacionalnog programa edukacije o holesterolu (National Cholesterol Education Program, NCEP), o određivanju holesterola i zbrinjavanju osoba s povišenom koncentracijom holesterola u serumu. Pored toga što preporučuje intenzivan tretman pacijenata sa koronarnom srčanom bolešću (coronary heart disease/CHD), važna karakteristika ATP III je težište na primarnoj prevenciji kod osoba sa više prisutnih faktora rizika. ATP III nastavlja da identifikuje povišene koncentracije LDL holesterola kao primarni cilj terapije za snižavanje holesterola. Osnovni princip prevencije je da se intenzitet terapije prilagođava apsolutnom riziku za CHD svake osobe pojedinačno. Procena rizika podrazumeva određivanje LDL holesterola u sklopu analize lipoproteina i identifikaciju pratećih determinanti rizika (prisustvo ili odsustvo CHD, drugih kliničkih oblika aterosklerotske bolesti i dijabetesa, pušenje, hipertenzija, niska koncentracija HDL holesterola, porodična anamneza prevremene pojave CHD, starost). U kategoriji najvišeg rizika nalaze se osobe sa CHD i CHD ekvivalentima rizika, čiji je apsolutni rizik od pojave srčane smrti ili nefatalnog infarkta miokarda u narednih 10 godina ≥20%. Drugu kategoriju čine osobe sa dva ili više faktora rizika kod kojih je 10-godišnji rizik <20%. Apsolutni rizik se procenjuje na osnovuFraminghamrizik skora. U trećoj kategoriji su osobe sa jednim ili nijednim faktorom rizika. Definisane su preporučene koncentracije LDL holesterola za svaku kategoriju i postižu se korekcijom ishrane i/ili farmakoterapijom. Evropske preporuke za prevenciju kardiovaskularne bolesti (cardiovascular disease, CVD) u kliničkoj praksi preporučuju upotrebu SCO-RE (Systematic COronary Risk Evaluation) tablica za procenu rizika za pojavu CVD, koje podrazumevaju apsolutnu verovatnoću za fatalan ishod CVD u toku 10 godina. Cilj ovog rada je predstavljanje delova NCEP ATP III i evropskih preporuka značajnih za njihovu implementaciju u laboratorijsku praksu.

Oral glucosamine in doses used to treat osteoarthritis worsens insulin resistance

BACKGROUND

Glucosamine is used to treat osteoarthritis. In animals, the compound is known to cause insulin resistance, the underlying abnormality in type 2 diabetes mellitus. Insulin resistance in humans taking oral glucosamine in doses used for osteoarthritis has not been studied.

METHODS

Volunteer human subjects (n = 38) without known abnormality of glucose homeostasis had fasting serum glucose, insulin, and lipids determined before and after taking 1500 mg glucosamine by mouth every day for 6 weeks. Fasting insulin and glucose were used to calculate homeostasis model assessment (HOMA-IR) and quantitative insulin sensitivity check index (QUICKI). Vascular elasticity was measured by pulse wave analysis. The paired Student's t test was used to compare baseline with posttreatment values. Pearson's correlation was used to determine the relation of baseline HOMA-IR with changes in other variables.

RESULTS

We found a rise in HOMA-IR after 6 weeks of glucosamine (2.8 versus 3.2, P < 0.04). The fall in HOMA-IR among the subjects was statistically related to a higher baseline HOMA-IR by Pearson's correlation(P < 0.01). A rise in serum triglycerides and a rise in LDL cholesterol were statistically related to baseline HOMA-IR. Small artery elasticity fell, and the decrease was higher in those with the highest baseline HOMA-IR.

CONCLUSIONS

Notwithstanding its efficacy remaining in question, glucosamine is widely used as treatment for osteoarthritis, which is a condition associated with both obesity and type 2 diabetes mellitus. Our data indicate that persons with underlying poorer insulin sensitivity are at risk for worsening insulin resistance and vascular function with the use of glucosamine in doses used to treat osteoarthritis.

Postprandial effect of n-3 polyunsaturated fatty acids on apolipoprotein B-containing lipoproteins and vascular reactivity in type 2 diabetes

BACKGROUND

Plasma lipoproteins may be classified by their apolipoprotein composition. The lipoprotein subclass containing apolipoproteins B and C (LpB:C) is considered the most atherogenic.

OBJECTIVE

We evaluated the acute effects of individual fatty acids on apolipoprotein B (apo B)-containing lipoproteins in adults with type 2 diabetes (n = 15).

DESIGN

We administered 3 meals in a randomized, double-blind, crossover design. Treatments contained skim milk and 50 g fat from high-oleic acid safflower and canola oils (monounsaturated fatty acid; MUFA), MUFA + 3.5 g alpha-linolenic acid (ALA; MUFA + ALA) from high-ALA canola oil, or MUFA + 4.0 g both eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA; MUFA + EPA/DHA) from sardine oil. Apo B, LpB, LpB:C, LpB:E + LpB:C:E, and LpA-II:B:C:D:E were measured at baseline and 2 and 4 h after the meal. Flow-mediated dilation was measured at baseline and 4 h after the meal.

RESULTS

The treatments significantly increased apo B and LpB postprandially (P < 0.03 for both), but the magnitude of the changes did not differ significantly between the treatments. The postprandial change in LpB:C was 23% lower after MUFA + EPA/DHA than after MUFA (treatment x time interaction, P < 0.0001). MUFA + ALA attenuated the increase in LpA-II:B:C:D:E in those with high triacylglycerols (>/=1.69 mmol/L) but was the only treatment to significantly increase this particle in those with low triacylglycerols (treatment x group interaction, P < 0.0001). Examination of change scores did not reveal the source of the interaction of treatment and time (P < 0.007) for LpB:E + LpB:C:E. Furthermore, the subjects with the largest increases in LpB:C exhibited the largest impairment in endothelial function.

CONCLUSIONS

The results suggest that unsaturated fatty acids differentially affect concentrations of apo B-containing lipoprotein subclasses. A rise in LpB:C adversely affects endothelial function. Meals containing MUFA + EPA/DHA attenuated the postprandial rise in LpB:C and the impairment of endothelial function.

Increased apoC-III production is a characteristic feature of patients with hypertriglyceridemia

Apolipoprotein (apo) C-III plays an important role in regulating plasma triglyceride (TG) metabolism. In order to further investigate the plasma metabolism of apoC-III in hypertriglyceridemic subjects, we have studied the plasma kinetics of VLDL apoC-III, HDL apoC-III and total plasma apoC-III with a primed constant intravenous infusion of deuterated leucine in a group of male patients with mixed hyperlipidemia (type IIb hyperlipoproteinemia, HLP, n=6) and in a group with type III HLP (n=6). Compared to normolipidemic control subjects (n=5), patients with type IIb and type III HLP had significantly higher levels of plasma TG (0.89 +/- 0.15 mmol/l vs 2.56 +/- 0.40 mmol/l vs 8.76 +/- 1.39 mmol/l, respectively, P <0.01), plasma apoC-III (9.5 +/- 0.8 mg/dl vs 20.8 +/- 2.5 mg/dl vs 41.7 +/- 5.6 mg/dl, P <0.01) and VLDL apoC-III (3.6 +/- 0.8 mg/dl vs 14.6 +/- 2.2 mg/dl vs 35.4 +/- 5.1 mg/dl, P <0.01). VLDL apoC-III production rates were significantly elevated in type IIb and type III patients (1.35 +/- 0.23 mg kg(-1) day(-1) vs 3.53 +/- 0.43 mg kg(-1) day(-1) vs 5.60 +/- 0.78 mg kg(-1) day(-1), P <0.01), as were total plasma apoC-III production rates (1.80 +/- 0.22 mg kg(-1) day(-1) vs 4.16 +/- 0.44 mg kg(-1) day(-1) vs 7.26 +/- 0.74 mg kg(-1) day(-1), P <0.01). VLDL apoC-III but not total plasma apoC-III fractional catabolic rates were reduced in type IIb and type III patients. Together with our previous results showing an increase of apoC-III production in patients with type IV HLP, and in overweight subjects with reduced insulin sensitivity, our data suggest that increased apoC-III production is a characteristic feature of patients with hypertriglyceridemia.

ApoC-III bound to apoB-containing lipoproteins increase with insulin resistance in Cherokee Indian youth

Because Native Americans are predisposed to obesity and type 2 diabetes associated with coronary artery disease, we assessed whether apoC-III bound to apoB-containing (LpB:C-III) and apoA-containing (LpA:C-III) lipoproteins, total apoC-III, apoB, and plasma lipids are associated with insulin resistance, body mass index (BMI), and waist circumference in Cherokee children and adolescents aged 5 to 19 years (n = 975). A cross-sectional analysis was done to determine associations of the lipoproteins with the homeostasis index (HOMA-IR) and BMI. When the data were grouped by quartiles for HOMA-IR and separated by three 5-year age groups (5-9, 10-14, and 15-19 years), the trend for LpB:C-III, triglyceride, and BMI z score to increase was significant for all age groups and both genders (P < .001). The trend to increase LpB:C-III with age was greater in boys (P < .0001) than in girls (P < .05) who tended to plateau after the age of 10 years. In contrast, the ratio of LpA:C-III to LpB:C-III decreased and the decrease was greater in boys (P < .0001) than girls (P < .01). Body mass index z score and waist circumference were correlated with LpB:C-III, triglyceride, apoB, and non-high-density lipoprotein cholesterol within each gender (P < .001). In multiple regression models, LpB:C-III, the dependent variable, was associated with HOMA-IR for both genders. We conclude that increases in LpB:C-III in childhood and adolescence are associated with insulin resistance and obesity supporting the need for prevention programs.

Apolipoprotein C-III protein concentrations and gene polymorphisms in Type 1 diabetes: associations with microvascular disease complications in the DCCT/EDIC cohort

AIM

We investigated the associations of apolipoprotein C-III (apoCIII) protein and apoCIII gene variation with microvascular disease complications in Type 1 diabetes.

METHODS

The serum apoCIII concentration, and both a T(-455)-->C and a SacI gene polymorphisms were determined in 409 patients in the DCCT/EDIC cohort of patients with Type 1 diabetes. Correlations with albumin excretion rate (AER) and the severity of retinopathy were investigated.

RESULTS

Higher apoCIII concentrations were associated (P<.0001) with increased triglycerides (r=.78), total (r=.61) and LDL (r=.40) cholesterol, apoAI (r=.26), and apoB (r=.50), AER (r=.08), and the severity of retinopathy (ETDRS score, r=.11), and these relationships persisted after controlling for age, gender, body mass index (BMI), and HbA1c level. The apoCIII concentration was significantly higher in the group of patients with macroalbuminuria (AERs 300 mg/24 h) compared to the groups with microalbuminuria (AER 40-299 mg/24 h; P<.0001) or normoalbuminuria (AER <40 mg/24 h) (P<.0001). The apoCIII concentration also was significantly higher in the group of patients with severe retinopathy (ETDRS 10-23) compared to those with moderate (ETDRS 4-9; P<.02) or mild retinopathy (ETDRS 1-3; P<.0001). Neither the T(-455)-->C polymorphism nor a SacI polymorphism in the 3' UTR were associated with circulating apoCIII concentrations, nor the severity of nephropathy or retinopathy.

CONCLUSIONS

Elevated apoCIII levels have been associated with increased macrovascular disease risk. In the DCCT/EDIC cohort of patients, there was an independent positive association of apoCIII level with microvascular complications of Type 1 diabetes.

Apolipoprotein C-III protein concentrations and gene polymorphisms in type 1 diabetes: associations with lipoprotein subclasses

Serum apolipoprotein C-III (apoCIII) concentration and apoCIII gene polymorphisms have been shown to be a risk factor for cardiovascular disease; however, the underlying mechanisms remain unclear. In addition, no studies have been performed that address these issues in type 1 diabetes. The current study investigated apoCIII protein and apoCIII gene variation in a normotriglyceridemic (82 +/- 57 mg/dL) population of patients with type 1 diabetes, the Diabetes Control and Complications Trial/Epidemiology of Diabetes Intervention and Complications (DCCT/EDIC) cohort. Blood samples were obtained in 409 patients after an overnight fast. Serum apoCIII concentration was highly correlated with multiple changes in lipids and lipoproteins that resulted in an adverse cardiovascular disease risk profile. Higher apoCIII concentrations were associated (P < .0001) with increased triglycerides (r = 0.78), total (r = 0.61) and low-density lipoprotein (LDL) (r = 0.40) cholesterol, apoA-I (r = 0.26), and apoB (r = 0.50), and these relationships persisted after controlling for age, gender, body mass index (BMI), and hemoglobin A1c (HbA1c). Nuclear magnetic resonance (NMR) lipoprotein subclass analyses demonstrated that apoCIII was correlated with an increase in very-low-density lipoprotein (VLDL) subclasses (P = .0001). There also was a highly significant positive relationship between serum apoCIII concentration and the LDL particle concentration in both men (r = 0.49, P = .001) and women (r = 0.40, P = .001), and a highly significant negative relationship between serum apoCIII levels and average LDL particle size in both men (r = -0.37, P = .001) and women (r = -0.22, P = .001) due primarily to an augmentation in the small L1 subclass (r = 0.42, P = .0001). Neither the T(-455) --> C polymorphism affecting an insulin response element in the apoCIII gene promoter nor a SacI polymorphism in the 3'UTR were associated with any alterations in circulating apoCIII concentrations, serum lipids, apolipoprotein concentrations, lipoprotein composition, or parameters measured by NMR lipoprotein subclass analyses. In summary, elevated apoCIII concentration was associated with risk factors for cardiovascular disease in normolipidemic type 1 diabetic patients through associated changes in lipoprotein subfraction distributions, which were independent of apoCIII genotype.

Storage of human plasma samples leads to alterations in the lipoprotein distribution of apoC-III and apoE

The effect of frozen storage on lipoprotein distribution of apolipoprotein C-III (apoC-III) and apoE was investigated by measuring apoC-III and apoE by ELISA in HDL and apoB-containing lipoproteins of human plasma samples (n = 16) before and after 2 weeks of frozen storage (-20 degrees C). HDLs were separated by heparin-manganese precipitation (HMP) or by fast-protein liquid chromatography (FPLC). Total plasma apoC-III and apoE levels were not affected by frozen storage. HDL-HMP apoC-III and apoE levels were significantly higher in frozen versus fresh samples: 7.7 +/- 0.7 versus 6.7 +/- 0.7 mg/dl (P < 0.05) and 2.0 +/- 0.1 versus 1.2 +/- 0.1 mg/dl (P < 0.001), respectively. HDL-FPLC apoC-III and apoE, but not triglyceride (TG) or cholesterol, levels were also higher in frozen samples: 12.0 +/- 1.2 versus 7.5 +/- 0.6 mg/dl (P < 0.001) and 2.7 +/- 0.2 versus 1.6 +/- 0.2 mg/dl (P < 0.001), respectively. Frozen storage led to a decrease in apoC-III (-17 +/- 9%) and apoE (-19 +/- 9%) in triglyceride-rich lipoprotein. Redistribution of apoC-III and apoE was most evident in samples with high TG levels. HDL apoC-III and apoE levels were also significantly higher when measured in plasma stored at -80 degrees C. Our results demonstrate that lipoprotein distribution of apoC-III and apoE is affected by storage of human plasma, suggesting that analysis of frozen plasma should be avoided in studies relating lipoprotein levels of apoC-III and/or apoE to the incidence of coronary artery disease.

Mechanism of triglyceride lowering in mice expressing human apolipoprotein A5

Overexpression of human APOA5 in mice results in dramatically decreased plasma triglyceride levels. In this study we explored the mechanism underlying this hypotriglyceridemic effect. Initially we found that triglyceride turnover was faster in hAPOA5 transgenic mice compared to controls, and this strongly correlated with increased LPL activity in postheparin plasma. Furthermore, we show that in vitro recombinant apoAV interacts physically with lipoprotein lipase and significantly increased its activity. We show that both apoB and apoCIII are decreased in hAPOA5 transgenic mice indicating a decrease in VLDL number. To further investigate the mechanism of hAPOA5 in a hyperlipidemic background, we inter-crossed hAPOA5 and hAPOC3 transgenic mice. We found a marked decrease in VLDL triglyceride and cholesterol, as well as apolipoprotein B and CIII levels. These data indicated that apoAV induces a decrease in VLDL size by activating lipolysis and an increase of VLDL clearance. In a postprandial state, the normal triglyceride response found in wild-type mice was significantly reduced in hAPOA5 transgenics. In addition, we demonstrated that in response to this fat load in hAPOA5xhAPOC3 mice, apoAV, but not apoCIII, was redistributed from primarily HDL to VLDL. This shift of apoAV in VLDL appears to limit the increase of triglyceride by activating the lipoprotein lipase.

Non-HDL cholesterol as a measure of atherosclerotic risk

Elevated triglyceride (TG) and low high-density lipoprotein cholesterol (HDL-C) levels, hallmarks of the atherogenic lipid profile found in the metabolic syndrome and type 2 diabetes, are commonly seen in Japanese patients with coronary heart disease (CHD). In the setting of mildly to moderately elevated plasma TG (150-500 mg/dl), very-low-density lipoprotein (VLDL) accumulates and so do high levels of atherogenic TG-rich, cholesterol-enriched remnant particles. Indeed, in hypertriglyceridemia, abnormalities are seen in the quantity and quality of all lipoprotein B-containing lipoproteins. Non-HDL-C (total cholesterol minus HDL-C) provides a convenient measure of the cholesterol content of all atherogenic lipoproteins, and thus incorporates the potential risk conferred by elevated levels of atherogenic TG-rich remnants that is additional to the risk associated with low-density lipoprotein cholesterol (LDL-C). Non-HDL-C level has been found to be a strong predictor of future cardiovascular risk among patients whether or not they exhibit symptoms of vascular disease, and was recently recommended as a secondary treatment target (after LDL-C) in patients with elevated TG by the National Cholesterol Education Program Adult Treatment Panel III. Adoption of this readily available measure to assess risk and response to treatment in patients with elevated TG would improve treatment of dyslipidemia in a substantial number at risk for CHD.

Fractional esterification rate of cholesterol and ratio of triglycerides to HDL-cholesterol are powerful predictors of positive findings on coronary angiography

BACKGROUND

We examined the predictive value of various clinical and biochemical markers for angiographically defined coronary artery disease (aCAD). Specifically, we assessed the value of the ratio of plasma triglyceride (TGs) to HDL-cholesterol (HDL-C) and the fractional esterification rate of cholesterol in plasma depleted of apolipoprotein B (apoB)-containing lipoproteins (FER(HDL)), a functional marker of HDL and LDL particle size.

METHODS

Patients (788 men and 320 women) undergoing coronary angiography were classified into groups with positive [aCAD(+)] and negative [aCAD(-)] findings. Patient age, body mass index, waist circumference, blood pressure (BP), medications, drinking, smoking, exercise habits, and plasma total cholesterol (TC), LDL-cholesterol (LDL-C), HDL-unesterified cholesterol, HDL-C, TGs, FER(HDL), apoB, log(TG/HDL-C), and TC/HDL-C were assessed. Lipids and apoproteins were measured by standard laboratory procedures; FER(HDL) was determined by a radioassay.

RESULTS

Members of the aCAD(+) group were older and had a higher incidence of smoking and diabetes than those in the aCAD(-) group. The aCAD(+) group also had higher TG, apoB, FER(HDL), and log(TG/HDL-C) and lower HDL-C values. aCAD(+) women had greater waist circumference and higher plasma TC and TC/HDL-C. aCAD(+) men, but not women, had higher plasma LDL-C. In the multivariate logistic model, the significant predictors of the presence of aCAD(+) were FER(HDL), age, smoking, and diabetes. If only laboratory tests were included in the multivariate logistic model, FER(HDL) appeared as the sole predictor of aCAD(+). Log(TG/HDL-C) was an independent predictor when FER(HDL) was omitted from multivariate analysis.

CONCLUSIONS

FER(HDL) was the best laboratory predictor of the presence of coronary atherosclerotic lesions.

The concept of apolipoprotein-defined lipoprotein families and its clinical significance

Classification of plasma lipoproteins on the basis of apolipoprotein (apo) composition recognizes two lipoprotein (Lp) classes, one of which is characterized by apoA-I and the other by apoB as major protein constituents. The former lipoprotein class consists of three major subclasses referred to (according to their apolipoprotein constituents) as Lp-A-I, Lp-A-I:A-II, and Lp-A-II, and the latter one of five subclasses called Lp-B, Lp-B:E, Lp-B:C, Lp-B:C:E, and Lp-A-II:B:C:D:E. As polydisperse systems of particles, the apoA-I-containing lipoproteins overlap in high-density segments and apoB- containing lipoproteins in low-density segments of the density gradient. Each subclass is characterized by a specific chemical composition and metabolic property. Normolipidemia and dyslipoproteinemias are characterized by quantitative rather than qualitative differences in the levels of apoA- and apoB-containing subclasses. Furthermore, apoA-containing subclasses seem to differ with respect to their relative antiatherogenic capacities, and apoB-containing subclasses regarding their relative atherogenic potentials. Whereas Lp-A-I may have a greater antiatherogenic capacity than other apoA-containing subclasses, the cholesterol-enriched Lp-B:C appears to be the most atherogenic subclass among apoB-containing lipoprotein families. The use of pharmacologic and/or dietary interventions to treat dyslipoproteinemias has already shown that these therapeutic modalities may affect selectively individual apolipoprotein-defined lipoproteins, and thus allow the selection of individualized treatments targeted at decreasing harmful and/or increasing beneficial lipoprotein subclasses.

Indices related to apo CII and CIII serum concentrations and coronary heart disease: a case-control study

BACKGROUND

Triglycerides (TG) are carried in the circulation by diverse lipoprotein particles, which vary in their lipid and protein content, metabolism, and atherogenicity. Several indices related to apolipoproteins (apo) CII and CIII blood concentration have been proposed to reflect TG metabolism more accurately than the blood level of TG. In the present study we compared the distribution of those indices in coronary heart disease (CHD) patients and controls..

METHODS

Ninety consecutively discharged patients with CHD and 209 healthy controls were included in the analysis. Demographic, clinical, and laboratory characteristics were obtained.

RESULTS

The CHD patients differed appreciably from controls in several TG-related variables. After adjusting for cardiovascular risk factors, significant associations were found between CHD and the following: TG, VLDL-C, apo CIII, apo CIII in HDL, apo CIII in VLDL + LDL, apo CII- to- TG ratio, and apo CIII ratio (CIII in HDL/CIII in VLDL + LDL). Further adjustment for HDL-C substantially attenuated the above associations, except for those regarding apo CIII in VLDL + LDL (odds ratio (OR): 1.69 per 1 SD increment, 95%CI: 1.03-2.77) and apo CIII ratio (OR: 0.40 per 1 SD increment, 95%CI: 0.15-1.00).

CONCLUSION

Our results add to the growing evidence which links apo CIII concentration in VLDL + LDL to CHD. Further confirmation in prospective studies would be required before considering this measurement as a screening tool.

Accuracy of lipoprotein lipids and apoproteins in predicting coronary heart disease in diabetic American Indians. The Strong Heart Study

PURPOSE

To evaluate the accuracy of lipoprotein lipids and apoproteins in predicting coronary heart disease (CHD) in diabetic American Indians.

METHODS

This study included 2099 diabetic participants of the Strong Heart Study, which is a longitudinal study of cardiovascular disease (CVD) and its risk factors in American Indians in Arizona, Oklahoma, and South and North Dakota. Diabetic participants with incident CHD (N = 126) were selected as the case group, and those without CHD or any cardiovascular events were the control group (N = 1732). Previous vascular events such as stroke were the sole exclusion criterion (N = 241). Baseline measurements of lipoprotein lipids and apoproteins were used to predict CHD diagnosed at the 4-year follow-up examination by using Receiver-Operating Characteristic (ROC) curve analysis.

RESULTS

The ratio of high-density lipoprotein (HDL) to total cholesterol had the highest area under the ROC curve (0.69 +/- 0.02). The areas for the ratios of HDL to low-density lipoprotein (LDL) cholesterol (0.68 +/- 0.02), apo AI/B (0.66 +/- 0.02), and the single component of total cholesterol (0.64 +/- 0.03) and LDL cholesterol (0.63 +/- 0.05) were not significantly different from the area for HDL/total cholesterol. However, the areas for apo B (0.64 +/- 0.02), HDL cholesterol (0.62 +/- 0.03), triglycerides (0.58 +/- 0.03), and apo AI (0.57 +/- 0.05) were significantly lower than the area for HDL/total cholesterol. Logistic regression analysis indicates that only HDL and LDL cholesterol were significant independent lipoprotein lipid and apoprotein predictors for CHD. The other significant predictors in the model were study center, age, gender, and albuminuria. The ROC area for this model is 0.75.

CONCLUSIONS

HDL and LDL cholesterol were the most important independent predictors for incident CHD in diabetic American Indians. The ratios of HDL/total cholesterol, HDL/LDL cholesterol, and apo AI/B had higher accuracy for predicting CHD. Although the values for all lipoprotein lipids and apoproteins and their ratios were not large enough to definitely predict CHD, they can be used as screening tools for CHD in diabetic American Indians.

The rise of the plasma lipid concentration elicited by dietary sodium chloride restriction in Wistar rats is due to an impairment of the plasma triacylglycerol removal rate

Studies in humans have indicated that dietary salt restriction raises plasma levels of total cholesterol (TC) and triacylglycerols (TAG). In order to explain the mechanisms involved, a rat experimental model was developed consisting of chronic feeding ad libitum isocaloric diets with variable sodium chloride contents. Rates of synthesis of plasma TAG were measured either as the increase of plasma TAG after blocking its removal from plasma by the intra-arterial pulse infusion of Triton-WR 1339, or as the plasma rate of incorporation of [(14)C]-oleic acid [(14)C]-TAG. Plasma TAG removal rate was determined by the intra-arterial pulse infusion of a lipid emulsion. Severe salt restriction increased the plasma concentrations of TAG (71%) and of TC (10%). This result was not due to modification of the rate of synthesis of plasma TAG but was attributed to a 55% slower rate of removal of the TAG-containing lipoproteins. An increased plasma non-esterified fatty acid concentration, probably due to a salt restriction-related insulin resistance, may have impaired the activity of the enzyme lipoprotein lipase.

Apoprotein c-III and E-containing lipoparticles are markedly increased in HIV-infected patients treated with protease inhibitors: association with the development of lipodystrophy

Long-term therapy with protease inhibitors (PIs) can induce hypertriglyceridemia and development of a lipodystrophy. To better understand these metabolic alterations, the apoprotein and lipoparticle profile was investigated in male HIV patients under antiretroviral therapy: 49 received PIs, and 14 were given only two reverse transcriptase inhibitors. As controls, 63 male subjects were selected from a population study carried out in the Toulouse, France, area. Fasting glucose, insulin, and C-peptide were also determined. All patients under PIs displayed low levels of plasma glucose and increased insulin. PI administration was associated with moderate hypertriglyceridemia, low high-density cholesterol and apolipoprotein (apo) A-I levels. The most striking changes were a 2- to 3-fold increase in apo E and apo C-III, essentially recovered as associated to apo B-containing lipoparticles. Levels of those lipoparticles were two to eight times above control values. About 50% of PI-treated patients had developed a patent lipodystrophy. Multivariate analysis revealed that, among the investigated parameters, apo C-III was the only one found strongly associated with the occurrence of lipodystrophy (odds ratio, 5.5; P: < 0.015). Finally, 13 PI-receiving subjects with patent hypertriglyceridemia were given fenofibrate and were reevaluated 2 months later. Triglycerides, apo E, apo C-III, and the corresponding lipoparticles had returned to nearly normal levels. These results document the accumulation of potentially atherogenic lipoparticles under PIs. Apo C-III may play a pivotal role in the development of hypertriglyceridemia and lipodystrophy.

Characterization of recombinant wild type and site-directed mutations of apolipoprotein C-III: lipid binding, displacement of ApoE, and inhibition of lipoprotein lipase

The physicochemical properties of recombinant wild type and three site-directed mutants of apolipoprotein C-III (apoC-III), designed by molecular modeling to alter specific amino acid residues implicated in lipid binding (L9T/T20L, F64A/W65A) or LPL inhibition (K21A), were compared. Relative lipid binding efficiencies to dimyristoylphosphatidylcholine (DMPC) were L9T/T20L > WT >K21A > F64A/W65A with an inverse correlation with size of the discoidal complexes formed. Physicochemical analysis (Trp fluorescence, circular dichroism, and GdnHCl denaturation) suggests that L9T/T20L forms tighter and more stable lipid complexes with phospholipids, while F64A/W65A associates less tightly. Lipid displacement properties were tested by gel-filtrating apoE:dipalmitoylphosphatidylcholine (DPPC) discoidal complexes mixed with the various apoC-III variants. All apoC-III proteins bound to the apoE:DPPC complexes; the amount of apoE displaced from the complex was dependent on the apoC-III lipid binding affinity. All apoC-III proteins inhibited LPL in the presence or absence of apoC-II, with F64A/W65A displaying the most inhibition, suggesting that apoC-III inhibition of LPL is independent of lipid binding and therefore of apoC-II displacement. Taken together. these data suggest that the hydrophobic residues F64 and W65 are crucial for the lipid binding properties of apoC-III and that redistribution of the N-terminal helix of apoC-III (L9T/T20L) enhances the stability of the lipid-bound protein, while LPL inhibition by apoC-III is likely to be due to protein:protein interactions.

Preventing, stopping, or reversing coronary artery disease--triglyceride-rich lipoproteins and associated lipoprotein and metabolic abnormalities: the need for recognition and treatment

A substantial number of treated patients with or at high risk for coronary artery disease continue to have fatal and nonfatal coronary artery events in spite of significant reduction of elevated levels of low-density lipoprotein cholesterol. Other lipoprotein abnormalities besides an elevated level of low-density lipoprotein cholesterol contribute to risk of coronary artery disease and coronary artery events, and the predominant abnormalities that appear to explain much of this continued risk are an elevated serum triglyceride level and a low level of high-density lipoprotein cholesterol. Most patients with coronary artery disease have a mixed dyslipidemia with hypertriglyceridemia, which is associated and metabolically intertwined with other atherogenic risk factors, including the presence of triglyceride-rich lipoprotein remnants, low levels of high-density lipoprotein cholesterol, small, dense, low-density lipoprotein particles, postprandial hyperlipidemia, and a prothrombotic state. Aggressive treatment of these patients needs to focus on these other lipoprotein abnormalities as much as on low-density lipoprotein cholesterol. Combination drug therapy will usually be required. Reliable assessment of risk of coronary artery disease from lipoprotein measurements and response to therapy requires inclusion of all atherogenic lipoproteins in laboratory measurements and treatment protocols. At present this may be best accomplished by use of non-high-density lipoprotein cholesterol (total cholesterol minus high-density lipoprotein cholesterol) calculated from standard laboratory lipoprotein values. Ultimately, a more comprehensive assessment of coronary artery disease risk and appropriate therapy may include measurement of lipoprotein subclass distribution including determination of low-density lipoprotein particle concentration and sizes of the various lipoprotein particles.

Plasma lipoprotein particle concentrations in postmenopausal women with unstable coronary artery disease. Analysis of diagnostic accuracy using receiver operating characteristics

BACKGROUND

The contribution of plasma lipids to cardiovascular risk is usually evaluated by measuring plasma concentrations of total cholesterol, triglycerides and HDL cholesterol, and calculating LDL cholesterol concentration. We investigated plasma concentrations of apolipoproteins and lipoprotein particles in women with unstable coronary artery disease (CAD) to evaluate whether these, better than the routine lipid status, could differentiate women with and without coronary atherosclerosis.

METHODS

Blood samples for lipid analyses were collected from 119 angiographically examined postmenopausal 49-79-year-old women with unstable CAD, and from 101 age-matched controls. Mean plasma concentrations were compared and the discriminatory ability of the different variables were tested using receiver operating characteristics (ROC).

RESULTS

At coronary angiography 19% had normal vessels and 81% had coronary atherosclerosis. A disturbed triglyceride metabolism was the most pronounced lipid abnormality in women with unstable CAD and coronary atherosclerosis. ROC showed that none of the evaluated variables had a particularly high discriminatory power regarding unstable CAD or coronary atherosclerosis. The ratio cholesterol/HDL cholesterol was best with an ROC area of 0.79. Furthermore, the newer lipid variables, i.e. lipoprotein particles and apolipoproteins, were no better than the traditional variables.

CONCLUSION

Lipoprotein changes reflecting a disturbed triglyceride metabolism are most pronounced in women with unstable CAD and coronary atherosclerosis. Lipoprotein particles and apolipoproteins alone were no better than lipids and lipoproteins in separating women with from those without coronary atherosclerosis. Our study does not support the measurement of apolipoproteins and lipoprotein particles on the basis of diagnostic accuracy alone.

Detection, quantification, and characterization of potentially atherogenic triglyceride-rich remnant lipoproteins

Triglyceride-rich lipoprotein (TRL) remnants are formed in the circulation when apolipoprotein (apo) B-48-containing chylomicrons of intestinal origin or apoB-100-containing VLDL of hepatic origin are converted by lipoprotein lipase, and to a lesser extent by hepatic lipase, into smaller and more dense particles. Compared with their nascent precursors, TRL remnants are depleted of triglyceride, phospholipid, and C apolipoproteins and are enriched in cholesteryl esters and apoE. They can thus be identified, separated, and/or quantified in plasma according to their density, charge, size, specific lipid components, apolipoprotein composition, and/or apolipoprotein immunospecificity. Each of these approaches has contributed to our current understanding of the compositional characteristics of TRL remnants and their potential to promote atherosclerosis. An ongoing search is nevertheless under way for more accurate and clinically applicable remnant lipoprotein assays that will be able to better define coronary artery disease risk in patients with hypertriglyceridemia.

Overexpression of human apolipoprotein A-II in mice induces hypertriglyceridemia due to defective very low density lipoprotein hydrolysis

Two lines of transgenic mice, hAIItg-delta and hAIItg-lambda, expressing human apolipoprotein (apo)A-II at 2 and 4 times the normal concentration, respectively, displayed on standard chow postprandial chylomicronemia, large quantities of very low density lipoprotein (VLDL) and low density lipoprotein (LDL) but greatly reduced high density lipoprotein (HDL). Hypertriglyceridemia may result from increased VLDL production, decreased VLDL catabolism, or both. Post-Triton VLDL production was comparable in transgenic and control mice. Postheparin lipoprotein lipase (LPL) and hepatic lipase activities decreased at most by 30% in transgenic mice, whereas adipose tissue and muscle LPL activities were unaffected, indicating normal LPL synthesis. However, VLDL-triglyceride hydrolysis by exogenous LPL was considerably slower in transgenic compared with control mice, with the apparent Vmax of the reaction decreasing proportionately to human apoA-II expression. Human apoA-II was present in appreciable amounts in the VLDL of transgenic mice, which also carried apoC-II. The addition of purified apoA-II in postheparin plasma from control mice induced a dose-dependent decrease in LPL and hepatic lipase activities. In conclusion, overexpression of human apoA-II in transgenic mice induced the proatherogenic lipoprotein profile of low plasma HDL and postprandial hypertriglyceridemia because of decreased VLDL catabolism by LPL.

Lipoprotein(a), homocysteine, and remnantlike particles: emerging risk factors

Although lipoprotein(a) [Lp(a)] was first described more than 35 years ago, adequate prospective data have only recently supported Lp(a) as an independent risk factor for coronary heart disease (CHD). In vitro studies suggest that Lp(a) contributes to atherogenesis directly by cholesterol uptake and indirectly by the inhibition of fibrinolysis. In patients with CHD or a significant risk for CHD, Lp(a) should be measured and treated with either niacin or estrogen if the patient has Lp(a) cholesterol levels of more than 10 mg/dL or an Lp(a) mass of more than 30 mg/dL. In addition, homocysteine and remnantlike lipoprotein cholesterol are strongly supported by prospective or population-based prevalence data as independent risk factors for CHD. Homocysteine levels of more than 14 mumol/L should be treated with vitamin supplements of folate, B6, and B12. Remnantlike lipoprotein cholesterol is the product of a novel immunoassay that separates the partially hydrolyzed triglyceride-rich remnant particles. The association of these particles with CHD risk in women may explain the small independent CHD risk that triglycerides have in women in the Framingham Heart Study. A clear therapeutic intervention has not been documented but may include diet, fibric acid derivatives, or hydroxymethylglutamyl coenzyme A reductase inhibitors.

Lipoprotein classes and coronary disease regression

Lowering LDL cholesterol (LDL-C) levels to reduce or prevent coronary artery disease (CAD) progression and cardiac events in hypercholesterolemic subjects is now widely accepted. The clinical benefit of lowering LDL-C has recently been extended to individuals with normal or mildly elevated LDL-C. Recent analyses of large primary and secondary CAD prevention trials, however, clearly demonstrated that reducing LDL-C levels does not entirely account for the coronary event reduction associated with lipid-lowering therapy. Growing and compelling evidence is emerging on the role of triglyceride-rich lipoproteins (VLDL and IDL), high density lipoproteins (HDL), and small, dense LDL, as well as non lipid risk factors, in the regression or stabilization of atherosclerotic plaques of mild/moderate severity, which are associated with clinical cardiac events. Enzymes involved in the tight metabolic interrelationship between triglyceride-rich lipoproteins, small, dense LDL and HDL levels may represent potential therapeutic targets for CAD prevention by favourably altering lipoprotein composition and physical properties in addition to the current therapeutic focus on lipoprotein levels.

Biologic markers as predictors of cardiovascular disease

Epidemiologic data obtained over the past 30 years suggest that a number of new biologic markers are associated with increased risk for cardiovascular disease. These include indices related to (1) altered glucose metabolism, particularly insulin resistance; (2) hyperlipidemia; (3) elevated levels of lipoprotein(a) and homocysteine; (4) increased levels of molecules reflecting decreased fibrinolysis and increased activation of the coagulation cascade; (5) elevations in cell adhesion molecules and other markers of endothelial function; and (6) elevations in molecules associated with infection, inflammation, and vascular remodeling. Changes in molecules associated with increased risk usually occur in clusters. This clustering suggests that effective treatment of one marker may have positive effects on multiple markers. Indeed, several studies have demonstrated that therapies designed to reduce hyperlipidemia may also lower the plasma levels of factors associated with increased coagulation and reduced fibrinolysis. Thus, careful assessment of patient risk factors, and the development of therapies directed toward chains of markers associated with increased risk, may significantly alter the course of cardiovascular disease.

Influence of fitness status on very-low-density lipoprotein subfractions and lipoprotein(a) in men and women

The purpose of this study was to examine the influence of the physical activity level of men and women on the very-low-density lipoprotein (VLDL) subfractions and lipoprotein(a) [Lp(a)]. Fifty-four men (n = 30) and women (n = 24) aged 30 to 53 years were recruited based on their level of activity over the past 2 years, and formed three groups: sedentary (S), no routine activity; recreational exercise (R), routine moderate exercise three to five times per week; and trained (T), competition-based, high-volume aerobic training five to seven times per week. Each subject underwent a maximal oxygen consumption (VO2max) test and was measured for body composition (skinfolds) and waist to hip ratio (WHR). Following a prescribed 24-hour diet and abstinence from activity, a blood sample was obtained from each subject and the plasma was analyzed for cholesterol and triglycerides (TGs) in VLDL1, VLDL2, and VLDL3 subfractions. High-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C) and Lp(a) also were analyzed. Total VLDL-C was higher in men than in women, but no gender differences were observed in VLDL subfractions. VLDL1-TG and VLDL2-TG were elevated in the S group compared with groups R and T, even though total VLDL-TG, LDL-C, and HDL-C values were not different among the groups. Values for Lp(a) were not significantly different between men and women or among the groups. The two exercising groups were not different on any lipoprotein variable or WHR. VLDL1-TG was inversely correlated with VO2max and HDL-C. These results suggest that life-style activity is associated with a favorable VLDL subfraction pattern and WHR, but not Lp(a). In addition, long-term recreational activity is associated with a lipoprotein profile and WHR similar to those obtained with higher-volume exercise training.