Anette Varbo

Remnant cholesterol as a causal risk factor for ischemic heart disease.

OBJECTIVES The aim of this study was to test the hypothesis that elevated nonfasting remnant cholesterol is a causal risk factor for ischemic heart disease independent of reduced high-density lipoprotein (HDL) cholesterol. BACKGROUND Elevated remnant cholesterol is associated with elevated levels of triglyceride-rich lipoproteins and with reduced HDL cholesterol, and all are associated with ischemic heart disease. METHODS A total of 73,513 subjects from Copenhagen were genotyped, of whom 11,984 had ischemic heart disease diagnosed between 1976 and 2010. Fifteen genetic variants were selected, affecting: 1) nonfasting remnant cholesterol alone; 2) nonfasting remnant cholesterol and HDL cholesterol combined; 3) HDL cholesterol alone; or 4) low-density lipoprotein (LDL) cholesterol alone as a positive control. The variants were used in a Mendelian randomization design. RESULTS The causal odds ratio for a 1 mmol/l (39 mg/dl) genetic increase of nonfasting remnant cholesterol was 2.8 (95% confidence interval [CI]: 1.9 to 4.2), with a corresponding observational hazard ratio of 1.4 (95% CI: 1.3 to 1.5). For the ratio of nonfasting remnant cholesterol to HDL cholesterol, corresponding values were 2.9 (95% CI: 1.9 to 4.6) causal and 1.2 (95% CI 1.2 to 1.3) observational for a 1-U increase. However, for HDL cholesterol, corresponding values were 0.7 (95% CI: 0.4 to 1.4) causal and 1.6 (95% CI: 1.4 to 1.7) observational for a 1 mmol/l (39 mg/dl) decrease. Finally, for LDL cholesterol, corresponding values were 1.5 (95% CI: 1.3 to 1.6) causal and 1.1 (95% CI: 1.1 to 1.2) observational for a 1 mmol/l (39 mg/dl) increase. CONCLUSIONS A nonfasting remnant cholesterol increase of 1 mmol/l (39 mg/dl) is associated with a 2.8-fold causal risk for ischemic heart disease, independent of reduced HDL cholesterol. This implies that elevated cholesterol content of triglyceride-rich lipoprotein particles causes ischemic heart disease. However, because pleiotropic effects of the genetic variants studied cannot be totally excluded, these findings need to be confirmed using additional genetic variants and/or randomized intervention trials.

Triglycerides and cardiovascular disease

After the introduction of statins, clinical emphasis first focussed on LDL cholesterol-lowering, then on the potential for raising HDL cholesterol, with less focus on lowering triglycerides. However, the understanding from genetic studies and negative results from randomised trials that low HDL cholesterol might not cause cardiovascular disease as originally thought has now generated renewed interest in raised concentrations of triglycerides. This renewed interest has also been driven by epidemiological and genetic evidence supporting raised triglycerides, remnant cholesterol, or triglyceride-rich lipoproteins as an additional cause of cardiovascular disease and all-cause mortality. Triglycerides can be measured in the non-fasting or fasting states, with concentrations of 2-10 mmol/L conferring increased risk of cardiovascular disease, and concentrations greater than 10 mmol/L conferring increased risk of acute pancreatitis and possibly cardiovascular disease. Although randomised trials showing cardiovascular benefit of triglyceride reduction are scarce, new triglyceride-lowering drugs are being developed, and large-scale trials have been initiated that will hopefully provide conclusive evidence as to whether lowering triglycerides reduces the risk of cardiovascular disease.

Elevated Remnant Cholesterol Causes Both Low-Grade Inflammation and Ischemic Heart Disease, Whereas Elevated Low-Density Lipoprotein Cholesterol Causes Ischemic Heart Disease Without Inflammation

Background— Elevated nonfasting remnant cholesterol and low-density lipoprotein (LDL) cholesterol are causally associated with ischemic heart disease (IHD), but whether elevated nonfasting remnant cholesterol and LDL cholesterol both cause low-grade inflammation is currently unknown. Methods and Results— We studied 60 608 individuals from the Copenhagen General Population Study, the Copenhagen City Heart Study, and the Copenhagen Ischemic Heart Disease study, of whom 10 668 had IHD diagnosed between 1977 and 2011. We genotyped for variants affecting levels of nonfasting remnant cholesterol, LDL cholesterol, C-reactive protein by CRP alleles, and C-reactive protein by IL6R alleles. Using a multidirectional mendelian randomization design, we investigated possible causal associations between the lipoproteins and C-reactive protein and between the lipoproteins and IHD. A 1-mmol/L(39 mg/dL) higher level of nonfasting remnant cholesterol was associated observationally with a 37% (95% confidence interval, 35–39) higher C-reactive protein level and causally with a 28% (95% confidence interval, 10–48) higher level. For LDL cholesterol, a 1-mmol/L (39-mg/dL) higher level was associated observationally with a 7% (95% confidence interval, 6–7) higher C-reactive protein level, but we found no causal association. Likewise, higher levels of C-reactive protein did not associate causally with elevated nonfasting remnant cholesterol or LDL cholesterol. Finally, the causal risk ratio for IHD for a 1-mmol/L (39-mg/dL) higher level was 3.3 (95% confidence interval, 2.1–5.2) for nonfasting remnant cholesterol and 1.8 (95% confidence interval, 1.5–2.2) for LDL cholesterol. The causal associations for remnant cholesterol were present even in those without diabetes mellitus and obesity. Conclusions— Elevated nonfasting remnant cholesterol is causally associated with low-grade inflammation and with IHD, whereas elevated LDL cholesterol is associated causally with IHD without inflammation.

Remnant cholesterol as a cause of ischemic heart disease: Evidence, definition, measurement, atherogenicity, high risk patients, and present and future treatment

This review focuses on remnant cholesterol as a causal risk factor for ischemic heart disease (IHD), on its definition, measurement, atherogenicity, and levels in high risk patient groups; in addition, present and future pharmacological approaches to lowering remnant cholesterol levels are considered. Observational studies show association between elevated levels of remnant cholesterol and increased risk of cardiovascular disease, even when remnant cholesterol levels are defined, measured, or calculated in different ways. In-vitro and animal studies also support the contention that elevated levels of remnant cholesterol may cause atherosclerosis same way as elevated levels of low-density lipoprotein (LDL) cholesterol, by cholesterol accumulation in the arterial wall. Genetic studies of variants associated with elevated remnant cholesterol levels show that an increment of 1mmol/L (39mg/dL) in levels of nonfasting remnant cholesterol associates with a 2.8-fold increased risk of IHD, independently of high-density lipoprotein cholesterol levels. Results from genetic studies also show that elevated levels of remnant cholesterol are causally associated with both low-grade inflammation and IHD. However, elevated levels of LDL cholesterol are associated with IHD, but not with low-grade inflammation. Such results indicate that elevated LDL cholesterol levels cause atherosclerosis without a major inflammatory component, whereas an inflammatory component of atherosclerosis is driven by elevated remnant cholesterol levels. Post-hoc subgroup analyses of randomized trials using fibrates in individuals with elevated triglyceride levels, elevated remnant cholesterol levels, show a benefit of lowering triglycerides or remnant cholesterol levels; however, large randomized trials with the primary target of lowering remnant cholesterol levels are still missing.

Nonfasting triglycerides, cholesterol, and ischemic stroke in the general population

Current guidelines on stroke prevention have recommendations on desirable cholesterol levels, but not on nonfasting triglycerides. We compared stepwise increasing levels of nonfasting triglycerides and cholesterol for their association with risk of ischemic stroke in the general population.

Low Nonfasting Triglycerides and Reduced All-Cause Mortality: A Mendelian Randomization Study

BACKGROUND Increased nonfasting plasma triglycerides marking increased amounts of cholesterol in remnant lipoproteins are important risk factors for cardiovascular disease, but whether lifelong reduced concentrations of triglycerides on a genetic basis ultimately lead to reduced all-cause mortality is unknown. We tested this hypothesis. METHODS Using individuals from the Copenhagen City Heart Study in a mendelian randomization design, we first tested whether low concentrations of nonfasting triglycerides were associated with reduced all-cause mortality in observational analyses (n = 13 957); second, whether genetic variants in the triglyceride-degrading enzyme lipoprotein lipase, resulting in reduced nonfasting triglycerides and remnant cholesterol, were associated with reduced all-cause mortality (n = 10 208). RESULTS During a median 24 and 17 years of 100% complete follow-up, 9991 and 4005 individuals died in observational and genetic analyses, respectively. In observational analyses compared to individuals with nonfasting plasma triglycerides of 266-442 mg/dL (3.00-4.99 mmol/L), multivariably adjusted hazard ratios for all-cause mortality were 0.89 (95% CI 0.78-1.02) for 177-265 mg/dL (2.00-2.99 mmol/L), 0.74 (0.65-0.84) for 89-176 mg/dL (1.00-1.99 mmol/L), and 0.59 (0.51-0.68) for individuals with nonfasting triglycerides <89 mg/dL (<1.00 mmol/L). The odds ratio for a genetically derived 89-mg/dL (1-mmol/L) lower concentration in nonfasting triglycerides was 0.50 (0.30-0.82), with a corresponding observational hazard ratio of 0.87 (0.85-0.89). Also, the odds ratio for a genetically derived 50% lower concentration in nonfasting triglycerides was 0.43 (0.23-0.80), with a corresponding observational hazard ratio of 0.73 (0.70-0.77). CONCLUSIONS Genetically reduced concentrations of nonfasting plasma triglycerides are associated with reduced all-cause mortality, likely through reduced amounts of cholesterol in remnant lipoproteins.

Remnant Cholesterol, Low-Density Lipoprotein Cholesterol, and Blood Pressure as Mediators From Obesity to Ischemic Heart Disease

Rationale: Obesity leads to increased ischemic heart disease (IHD) risk, but the risk is thought to be mediated through intermediate variables and may not be caused by increased weight per se. Objective: To test the hypothesis that the increased IHD risk because of obesity is mediated through lipoproteins, blood pressure, glucose, and C-reactive protein. Methods and Results: Approximately 90 000 participants from Copenhagen were included in a Mendelian randomization design with mediation analyses. Associations were examined using conventional measurements of body mass index and intermediate variables and using genetic variants associated with these. During ⩽22 years of follow-up 13 945 participants developed IHD. The increased IHD risk caused by obesity was partly mediated through elevated levels of nonfasting remnant cholesterol and low-density lipoprotein cholesterol, through elevated blood pressure, and possibly also through elevated nonfasting glucose levels; however, reduced high-density lipoprotein cholesterol and elevated C-reactive protein levels were not mediators in genetic analyses. The 3 intermediate variables that explained the highest excess risk of IHD from genetically determined obesity were low-density lipoprotein cholesterol with 8%, systolic blood pressure with 7%, and remnant cholesterol with 7% excess risk of IHD. Corresponding observational excess risks using conventional body mass index were 21%, 11%, and 20%, respectively. Conclusions: The increased IHD risk because of obesity was partly mediated through elevated levels of nonfasting remnant and low-density lipoprotein cholesterol and through elevated blood pressure. Our results suggest that there may be benefit to gain by reducing levels of these risk factors in obese individuals not able to achieve sustained weight loss.

TRIB1 and GCKR Polymorphisms, Lipid Levels, and Risk of Ischemic Heart Disease in the General Population

Objective—The goal of this study was to test whether TRIB1-rs2954029 and GCKR-rs1260326 associate with lipid levels and risk of ischemic heart disease (IHD) and myocardial infarction (MI) in the general population. Methods and Results—We genotyped >71 000 individuals. Lipid levels were studied cross-sectionally. Risk of IHD and MI was examined prospectively, cross-sectionally, and in a case-control study, and a metaanalysis was performed. TRIB1 TA (50%) and AA (27%) versus TT (23%) genotypes were associated with increased levels of triglycerides (total increase, +0.16 mmol/L; trend, P<0.001), remnant cholesterol (+0.07 mmol/L; P<0.001), apolipoprotein B (+5.7 mg/dL; P<0.001), and low-density lipoprotein cholesterol (+0.11 mmol/L; P<0.001) and with decreased levels of high-density lipoprotein cholesterol (−0.04 mmol/L; P<0.001). In metaanalyses of the 3 studies combined, TRIB1 TA and AA versus TT genotypes were associated with 13% (95% CI, 5% to 20%) and 15% (7% to 23%) increased risk of IHD, and 11% (1% to 21%) and 17% (6% to 30%) increased risk of MI, respectively. Although GCKR CT (46%) and TT (14%) versus CC (40%) genotypes had effects on triglycerides (+0.17 mmol/L; trend, P<0.001), remnant cholesterol (+0.07 mmol/L; P<0.001), and apolipoprotein B (+4.6 mg/dL; P<0.001) similar to those of TRIB1, GCKR did not influence low-density lipoprotein cholesterol levels or risk of IHD or MI. Risks of IHD were similar after stratification for gender, age, body mass index, hypertension, diabetes mellitus, smoking, statin use, alcohol intake, and physical activity. Conclusion—In the general population, both TRIB1-rs2954029 and GCKR-rs1260326 were associated with lipid levels, whereas TRIB1 was also associated with increased risk of IHD and MI.

Increased Remnant Cholesterol Explains Part of Residual Risk of All-Cause Mortality in 5414 Patients with Ischemic Heart Disease

BACKGROUND Increased concentrations of remnant cholesterol are causally associated with increased risk of ischemic heart disease. We tested the hypothesis that increased remnant cholesterol is a risk factor for all-cause mortality in patients with ischemic heart disease. METHODS We included 5414 Danish patients diagnosed with ischemic heart disease. Patients on statins were not excluded. Calculated remnant cholesterol was nonfasting total cholesterol minus LDL and HDL cholesterol. During 35836 person-years of follow-up, 1319 patients died. RESULTS We examined both calculated and directly measured remnant cholesterol; importantly, however, measured remnant cholesterol made up only 9% of calculated remnant cholesterol at nonfasting triglyceride concentrations <1 mmol/L (89 mg/dL) and only 43% at triglycerides >5 mmol/L (443 mg/dL). Multivariable-adjusted hazard ratios for all-cause mortality compared with patients with calculated remnant cholesterol concentrations in the 0 to 60th percentiles were 1.2 (95% CI, 1.1-1.4) for patients in the 61st to 80th percentiles, 1.3 (1.1-1.5) for the 81st to 90th percentiles, 1.5 (1.1-1.8) for the 91st to 95th percentiles, and 1.6 (1.2-2.0) for patients in the 96th to 100th percentiles (trend, P < 0.001). Corresponding values for measured remnant cholesterol were 1.0 (0.8-1.1), 1.2 (1.0-1.4), 1.1 (0.9-1.5), and 1.3 (1.1-1.7) (trend, P = 0.006), and for measured LDL cholesterol 1.0 (0.9-1.1), 1.0 (0.8-1.2), 1.0 (0.8-1.3), and 1.1 (0.8-1.4) (trend, P = 0.88). Cumulative survival was reduced in patients with calculated remnant cholesterol ≥1 mmol/L (39 mg/dL) vs <1 mmol/L [log-rank, P = 9 × 10(-6); hazard ratio 1.3 (1.2-1.5)], but not in patients with measured LDL cholesterol ≥3 mmol/L (116 mg/dL) vs <3 mmol/L [P = 0.76; hazard ratio 1.0 (0.9-1.1)]. CONCLUSIONS Increased concentrations of both calculated and measured remnant cholesterol were associated with increased all-cause mortality in patients with ischemic heart disease, which was not the case for increased concentrations of measured LDL cholesterol. This suggests that increased concentrations of remnant cholesterol explain part of the residual risk of all-cause mortality in patients with ischemic heart disease.

Milk intake is not associated with ischaemic heart disease in observational or Mendelian randomization analyses in 98 529 Danish adults

BACKGROUND Observationally, reports on the association between milk intake and risk of ischaemic heart disease (IHD) and myocardial infarction (MI) have produced conflicting results; and no previous large-scale study using the lactase persistent/non-persistent LCT-13910 C/T genotype as a largely unconfounded proxy for milk intake free of reverse causation has been conducted. We tested the hypothesis that milk intake observationally and genetically through the LCT-13910 C/T genotype is associated with risk of IHD and MI in a Mendelian randomization design. METHODS We included 98,529 White individuals of Danish descent, aged 20-100 years, from three studies of the general population. Information on IHD (N = 10,372) and MI (N = 4188) were obtained from national Danish registries. First, we investigated observational associations between milk intake and incident IHD and MI. Second, we confirmed the association between the rs4988235 genetic variant LCT-13910 C/T, associated with lactase persistence/non-persistence, and milk intake. Finally, we tested whether LCT-13910 C/T genotype was associated with risk of IHD and MI as well as with cardiovascular risk factors. RESULTS During a mean follow-up time of 5.4 years, the observational hazard ratio for a 1 glass/week higher milk intake was 1.00 [95% confidence interval (CI): 1.00,1.01] for both IHD and MI. Median milk intake was 3 glasses/week (interquartile range: 0-7) in lactase CC non-persistent individuals compared with 5 glasses/week (0-10) in lactase TC/TT persistent individuals (P = 3*10(-60)). In the dominant genetic model comparing lactase TC/TT persistent individuals with lactase CC non-persistent individuals, the odds ratio was 1.00 (0.92,1.09) for IHD and 0.96 (0.84,1.09) for MI. Finally, in the dominant genetic model genotype was not associated convincingly with plasma levels of total cholesterol, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, triglycerides or glucose, nor with blood pressure. CONCLUSION Milk intake was not associated with risk of IHD or MI, observationally or genetically.