Lipoprotein(a) and prevalent cardiovascular disease in a dialysis population: The Choices for Healthy Outcomes in Caring for ESRD (CHOICE) study

Association between lipoprotein(a) and premature atherosclerotic cardiovascular disease: a systematic review and meta-analysis

AIMS

High lipoprotein(a) [Lp(a)] level has been demonstrated as an important risk factor for atherosclerotic cardiovascular diseases (ASCVD) amongst the older populations, whereas its effects in the younger population remain unclear. This study evaluated the associations between Lp(a) and the risk of premature ASCVD.

METHOD AND RESULTS

PubMed and Embase were searched for related studies until 12 November 2023. Fifty-one studies including 100 540 participants were included. Mean age of patients ranged from 35.3 to 62.3 years. The proportion of male participants ranged from 0% to 100%. The mean follow-up was provided in five studies ranging from 1 year to 40 years. The definition of elevated Lp(a) varied among studies, such as >30 mg/dL, >50 mg/dL, the top tertiles, the top quartiles, the top quintiles, and so on. Higher Lp(a) was significantly associated with the composite ASCVD [odds ratio (OR): 2.15, 95% confidence interval (95% CI): 1.53-3.02, P < 0.001], especially for coronary artery disease (OR: 2.44, 95% CI: 2.06-2.90, P < 0.001) and peripheral arterial disease (OR: 2.56, 95% CI: 1.56-4.21, P < 0.001). This association remained significant in familial hypercholesterolaemia (FH) (OR: 3.11, 95% CI: 1.63-5.96, P < 0.001) and type 2 diabetes mellitus (T2DM) patients (OR: 2.23; 95% CI: 1.54-3.23, P < 0.001).Significant results were observed in South Asians (OR: 3.71, 95% CI: 2.31-5.96, P < 0.001), Caucasians (OR: 3.17, 95% CI: 2.22-4.52, P < 0.001), and patients with baseline low-density lipoprotein cholesterol (LDL-c) level ≥ 2.6 mmol/L.

CONCLUSION

Elevated Lp(a) predicts the risk of the composite or individual ASCVD in young, regardless of study design, gender, population characteristics (community or hospitalized), different premature definitions, and various Lp(a) measurement approaches. This association was important in South Asians, Caucasians, FH patients, T2DM patients, and patients with baseline LDL-c level ≥ 2.6 mmol/L.

Serum lipoprotein(a) and risk of hemorrhagic stroke among incident peritoneal dialysis patients: a large study from a single center in China

Background: This retrospective study investigated whether baseline serum lipoprotein(a) (Lp(a)) may predict subsequent stroke in patients under chronic peritoneal dialysis (PD). Methods: Eight hundred and sixty incident PD patients, treated from 1 November 2005 to 28 February 2017, were enrolled, and followed until discontinuation of PD, death, or 31 May 2017. Hemorrhagic or ischemic stroke was the primary outcome. The population was stratified by baseline serum Lp(a) tertile. The risk of each stroke subtype was analyzed using the Cox proportional hazard models. Adjustments were made for: age; gender; history of stroke and hypertension; systolic blood pressure; lipid-lowering, antiplatelet and antihypertensive medications; laboratory profiles including hemoglobin, serum albumin, calcium, triglyceride, total and low-density lipoprotein cholesterol; and apolipoprotein A1. Results: Among the 860 participants, 19.3% and 4.1% had diabetes mellitus and a history of stroke, respectively. The median baseline serum Lp(a) was 328 (172-585) mg/L. After 28 (14-41) months of follow-up, 33 (3.84%) and 12 (1.40%) patients developed hemorrhagic and ischemic stroke, respectively. Participants in the highest Lp(a) tertile had a significantly lower risk of hemorrhagic stroke compared with those in the lowest tertile (hazard ratio (HR) 0.3, 95% confidence interval (CI) 0.1-0.86; p = .026); the rates of ischemic stroke were comparable among the tertiles. Each 10 mg/L rise in serum Lp(a) was associated with a 2% (95% CI 0.96-1; p = .033) lower risk of hemorrhagic stroke. Conclusions: Among patients with incident PD, a higher serum Lp(a) level may predict a lower risk of hemorrhagic stroke.

Lipoprotein(a) level as a predictor of cardiovascular disease and small apoliprotein(a) isoforms in dialysis patients: assay-related differences are important

BACKGROUND

Lipoprotein(a) assays sensitive to apolipoprotein(a) size may underestimate associations of lipoprotein(a) with cardiovascular disease (CVD) and low molecular weight (LMW) apolipoprotein(a) isoforms. This study among 629 dialysis patients compares the value of two lipoprotein(a) assays in predicting CVD events and small isoforms.

METHODS

Lipoprotein(a) level was measured by an apolipoprotein(a) size-insensitive ELISA and apolipoprotein(a) size-sensitive immunoturbidometric (IT) assay; and apolipoprotein(a) size by Western blot. Positive/negative predictive values (PPV/NPV) for small isoforms were calculated, and CVD events ascertained prospectively.

RESULTS

The ELISA assay predicted CVD more strongly [Relative Hazard, RH=1.8; p=0.045, at the 85th Lipoprotein(a) percentile] than the IT assay (RH=1.3; p=0.37). The PPV for LMW isoforms using the ELISA (Whites, 98%; Blacks, 90%) were much higher than the IT assay (Whites, 75%; Blacks, 68%). Relative to the ELISA assay values, a positive bias in the IT assay values was seen for participants with larger apolipoprotein(a) isoforms, which may explain these findings.

CONCLUSIONS

When measured by an apolipoprotein(a) size-insensitive ELISA assay, but not a size-sensitive IT assay, high lipoprotein(a) levels predict both incident CVD and LMW isoforms in dialysis patients. Clinicians ordering lipoprotein(a) levels and research studies of lipoprotein(a) should determine if an apolipoprotein(a)-size related bias is present in the assay they use.

Comparison of Lipoprotein(a) levels between elderly and middle-aged men with coronary artery disease

Lipoprotein(a) [Lp(a)] is known to be a risk factor for atherosclerotic disease in middle-aged men, but the role of Lp(a) in women and in the elderly is less clear. In most studies, excess Lp(a) is not associated with increased risk for persons >65 years of age. This study examined the strength of association of a number of risk factors to coronary artery disease (CAD) in groups of men <65 years (n = 108) and >65 of age (n = 66) with angiographically documented significant narrowing of coronary arteries. Serum Lp(a) concentrations were determined; elevated Lp(a) is positively associated with CAD for men <65 years (adjusted OR: 2.45, P <0.05) but not for men >65 of age (adjusted OR: 0.56, P = NS). For middle-aged men, elevated Lp(a) appears to be an independent risk factor for premature CAD, and the importance of Lp(a) as a risk factor appears to decrease with age. These data suggest that the utility of Lp(a) lipoprotein levels in predicting the risk of CAD in older men is limited. Factors, such as age; sex; levels of total cholesterol, low-density lipoprotein (LDL) cholesterol, and triglycerides; carotid-wall thickness; smoking status; the presence or absence of diabetes and systolic and diastolic hypertension; body mass index (BMI); and other traditional risk factors, must be evaluated together to determine the risk of CAD for the entire population.

Phenotypic and genotypic risk factors for cardiovascular events in an incident dialysis cohort

Cardiovascular disease (CVD) remains the major cause of death in patients with end-stage renal disease (ESRD). Traditional risk factors do not explain the high prevalence of CVD in this population, and other non-traditional cardiovascular (CV) risk markers have now been described. Therefore, the potential relationship between CVD and phenotypic and genotypic risk markers was investigated prospectively in incident dialysis patients cohort. The 279 patients (244 on hemodialysis, 35 on peritoneal dialysis) within the Diamant Alpin Dialysis Cohort Study were investigated. Phenotypic and genotypic parameters were determined at dialysis initiation, patients monitored over a 2-year period, and CV events (morbidity and mortality) recorded. Globally, 82 CV events occurred and 26 patients (9.3%) died from CVD, whereas 28 (10%) died from non-CV causes. Previous CV events were strongly predictive of CV events occurrence, whatever patients had had one (hazard ratio (HR) 2, 95% confidence intervals (CI) 1.1-3.5) or more (HR 3.9, 95% CI 2.1-7.1) CV accidents before starting dialysis. Both lipoprotein(a) (HR 1.67, 95% CI 1-2.5) and total plasma homocysteine at cutoff 30 micromol/l (HR 1.7, 95% CI 1.1-2.8) were independent predictors of CV events outcome. In the subgroup of patients with homocysteine < 30 micromol/l, methylenetetrahydrofolate reductase (MTHFR) TT was the sole biological parameter predictive of CV event outcome (HR 2.5, 95% CI 1.1-10, P = 0.03). ESRD patients who enter chronic dialysis with a previous CV event, high total homocysteinemia levels, or MTHFR 677TT genotype must be considered at high risk of incident CV events.

Observational research databases in renal disease

Observational, patient-oriented research is a term that describes clinical or community-based studies in that they do not involve an experiment or intervention. Observational research studies can be designed and implemented by a primary data collection or using previously collected patient data. The latter is less expensive, although it has some distinct limitations. Many research databases are readily available and can be used to answer important questions that are relevant to kidney disease. This review summarizes the types of research analyses that can be conducted using existing databases, the types of research databases available, and a general approach for addressing a proposed research question using existing data.

Dialysis water as a determinant of the adequacy of dialysis

Hemodialysis patients are exposed to large volumes of water in the form of dialysate. Contaminants from the dialysate may cross the dialyzer membrane into the blood and have the potential to compromise the adequacy of dialysis. Several chemicals found commonly in drinking water have long been known to be toxic to hemodialysis patients. More recently, it has become apparent that even low levels of bacterial products in dialysate may adversely impact dialysis adequacy through their ability to stimulate an inflammatory response. Minimum levels of water and dialysate quality have been recommended to protect patients from chemical and microbiologic contaminants. Complying with these recommendations requires an appropriately designed water purification and distribution system, combined with a surveillance program designed to maintain dialysate quality.

Role of carnitine in modulating acute-phase protein synthesis in hemodialysis patients

Increased serum levels of C-reactive protein (CRP) in uremic and dialysis patients are associated with low serum prealbumin and albumin concentrations and increased mortality and greater risk of cardiovascular disease. Proinflammatory cytokines may cause malnutrition by increasing protein catabolism. Many studies have shown that L-carnitine supplementation leads to improvements in several conditions seen in uremic patients, including cardiac complications, impaired exercise and functional capacities, muscle symptoms, increased symptomatic intradialytic hypotension, and erythropoietin-resistant anemia. L-carnitine therapy may either suppress the inflammatory response or act independently on both inflammation and appetite and/or anabolic processes. Moreover, L-carnitine may suppress proinflammatory cytokines in sick individuals without renal disease and may improve protein synthesis or nitrogen balance in patients without renal disease and in hemodialysis and peritoneal dialysis patients. In a pilot study, we provided preliminary evidence that treatment with L-carnitine, 20 mg/kg 3 times weekly at the end of each hemodialysis treatment, was associated with a reduction in serum CRP levels and improvement in anabolic status. The improvement or normalization of serum concentrations of serum CRP also was correlated with increased serum concentrations of albumin, transferrin, and blood hemoglobin. The possibility that some or all of these changes may have been caused by improved nutritional intake cannot be ruled out. Further randomized clinical trials will be necessary to confirm the role of L-carnitine as a modulator of inflammatory protein synthesis in hemodialysis patients.

POOR NUTRITIONAL STATUS AND INFLAMMATION: Ultrapure Dialysate

To prevent pyrogenic reactions during hemodialysis, it is recommended that bacteria and endotoxin in dialysate not exceed 100-200 colony forming units (CFU)/ml and 0.25-2 endotoxin units (EU)/ml, respectively. While these limits are adequate to prevent acute pyrogenic reactions, data are accumulating to suggest they may not prevent stimulation of chronic inflammation in hemodialysis patients. Fragments of endotoxin and other bacterial products capable of stimulating immune cells cross low-flux and high-flux membranes in vitro. In clinical studies, use of ultrapure dialysate (bacteria < 0.1 CFU/ml and endotoxin < 0.03 EU/ml) is associated with lower concentrations of inflammatory markers and acute phase reactants than are observed with dialysate meeting current quality recommendations. Moreover, observational studies suggest a link between clinical outcomes and dialysate purity. Treatment of patients with ultrapure dialysate is reported to improve nutritional status, increase responsiveness to erythropoietin, slow the decline in residual renal function, lessen cardiovascular morbidity, and decrease the incidence of beta(2)-microglobulin amyloidosis. To date, however, none of these studies has shown a cause-and-effect relationship between dialysate purity and outcome. Further, there are no data defining the concentration dependence of outcomes on dialysate purity and the relative importance of dialysate purity as a trigger of inflammation remains unclear. While the technology exists to routinely provide ultrapure dialysate, controlled clinical trials are still needed to answer the question of whether or not introducing ultrapure dialysate into routine clinical practice represents an efficient use of limited resources in terms of decreasing inflammation and improving outcomes in hemodialysis patients.

Epidemiology, pathophysiology and therapeutic implications of lipoprotein(a) in kidney disease

Chronic kidney disease is associated with a tremendously increased risk for cardiovascular disease. Traditional risk factors for cardiovascular disease, however, show a diminished predictive power in these patients compared with the general population. This review provides an overview of lipoprotein(a), which is considered a nontraditional risk factor. The characteristic genetic and nongenetic changes of lipoprotein(a) in kidney disease are discussed and set into the context of risk prediction. In particular, genetically determined apolipoprotein(a) polymorphism is a powerful risk predictor for cardiovascular disease and total mortality in these patients. Finally, the limited interventional strategies available to lower lipoprotein(a) are considered.

Lipoprotein(a)-associated atherothrombotic risk in hemodialysis patients

BACKGROUND

Hemodialysis patients show a considerably higher risk of atherothrombotic disease than the general population. We investigated both lipoprotein(a) [Lp(a)] plasma levels and apolipoprotein(a) [apo(a)] phenotypes in relation to occurrence of atherothrombotic events in hemodialysis patients compared with subjects showing a normal kidney function.

METHODS

Lp(a) levels and apo(a) isoforms were determined in 118 hemodialysis patients, including 59 with prior atherothrombotic events, and in 182 subjects with normal creatinine clearance, including 82 who experienced a prior atherothrombotic event.

RESULTS

Lp(a) levels in hemodialysis patients (median; 20 mg/dl) were higher (p < 0.01) than in age- and sex-matched subjects with normal renal function without a history of atherothrombosis (11.3 mg/dl). Among hemodialysis patients, median Lp(a) levels were higher in subjects with than in those without prior atherothrombosis (34 vs. 15 mg/dl, p < 0.05). In hemodialysis patients and in subjects without nephropathy, the percentage of low-molecular-weight apo(a) phenotypes were significantly higher in patients with than in those without a history of prior atherothrombotic events (56.9% vs. 33.9%, p < 0.05; 62.2% vs. 25%, p < 0.00001,respectively). Stepwise regression analysis indicated that the presence of at least one apo(a) isoform of low molecular weight was an independent predictor of atherothrombosis in hemodialysis patients (p < 0.05).

CONCLUSIONS

Elevated Lp(a) plasma levels appear to be associated with atherothrombosis, independent of their origin due to genetic factors or related to the impaired kidney function. Low-molecular-weight apo(a) isoforms are reliable genetic markers of atherothrombosis both in patients with impaired kidney function and in subjects without nephropathy.