Association between serum lipids and survival in hemodialysis patients and impact of race

Metabolic abnormalities in chronic kidney disease that contribute to cardiovascular disease, and nutritional initiatives that may diminish the risk

PURPOSE OF REVIEW

Chronic kidney disease (CKD) is associated with a wide range of severe metabolic and nutritional disturbances that directly or indirectly contribute to left ventricular hypertrophy, ischemic heart disease, vascular calcification, heart failure and other manifestations of cardiovascular disease (CVD). The CVD mortality rate in CKD patients is far higher than in the general population, and CKD is today recognized as one of the most important risk factors for CVD. In this review, we discuss the links between metabolic abnormalities and CVD in CKD patients and nutritional initiatives that may reduce this risk.

RECENT FINDINGS

Certain nontraditional risk factors, such as protein-energy wasting, inflammation, and biomarkers reflecting bone and mineral disorders, are strong predictors of CVD mortality in CKD patients. Although several small nutritional intervention studies have been performed and nutritional guidelines have been introduced in order to minimize metabolic disorders and improve nutritional status, they have so far not been proven to reduce morbidity nor mortality.

SUMMARY

Although the pathophysiological mechanisms involved in the markedly increased CVD risk of CKD patients are becoming more evident, still few nutritional randomized controlled studies have been conducted in this high-risk patient group.

Fluid retention is associated with cardiovascular mortality in patients undergoing long-term hemodialysis

BACKGROUND

Patients with chronic kidney disease (stage 5) who undergo hemodialysis treatment have similarities to heart failure patients in that both populations retain fluid frequently and have excessively high mortality. Volume overload in heart failure is associated with worse outcomes. We hypothesized that in hemodialysis patients, greater interdialytic fluid gain is associated with poor all-cause and cardiovascular survival.

METHODS AND RESULTS

We examined 2-year (July 2001 to June 2003) mortality in 34,107 hemodialysis patients across the United States who had an average weight gain of at least 0.5 kg above their end-dialysis dry weight by the time the subsequent hemodialysis treatment started. The 3-month averaged interdialytic weight gain was divided into 8 categories of 0.5-kg increments (up to > or =4.0 kg). Eighty-six percent of patients gained >1.5 kg between 2 dialysis sessions. In unadjusted analyses, higher weight gain was associated with better nutritional status (higher protein intake, serum albumin, and body mass index) and tended to be linked to greater survival. However, after multivariate adjustment for demographics (case mix) and surrogates of malnutrition-inflammation complex, higher weight-gain increments were associated with increased risk of all-cause and cardiovascular death. The hazard ratios (95% confidence intervals) of cardiovascular death for weight gain <1.0 kg and > or =4.0 kg (compared with 1.5 to 2.0 kg as the reference) were 0.67 (0.58 to 0.76) and 1.25 (1.12 to 1.39), respectively.

CONCLUSIONS

In hemodialysis patients, greater fluid retention between 2 subsequent hemodialysis treatment sessions is associated with higher risk of all-cause and cardiovascular death. The mechanisms by which fluid retention influences cardiovascular survival in hemodialysis may be similar to those in patients with heart failure and warrant further research.

Why is protein-energy wasting associated with mortality in chronic kidney disease?

Observational studies in chronic kidney disease (CKD) populations consistently have shown the strong mortality-predictability of such markers of protein-energy wasting (PEW) as hypoalbuminemia, low serum cholesterol levels, low body mass index, and reduced dietary protein intake. Even though the PEW-mortality association data traditionally are reported mostly in maintenance dialysis patients, emerging studies extend the existence of these associations to predialysis stages of CKD. Paradoxic risk factor patterns (reverse epidemiology) for both obesity and cholesterol recently have been reported in predialysis CKD, underscoring the overwhelming impact of PEW, a short-term killer, on reversing the long-term effect of conventional cardiovascular risk factors. Multiple pathophysiologic mechanisms have been suggested to explain the link between PEW and mortality in CKD, including derangements in muscle, adipose tissue, and the gastrointestinal, hematopoietic, and immune systems; complications related to deficiencies of multiple micronutrients; and the maladaptive activation of the inflammatory cascade. In addition to well-described pathophysiologic mechanisms involved in the higher mortality seen with PEW, we also discuss the potential role of novel factors such as circulating actin, gelsolin, and proinflammatory high-density lipoprotein. Whether PEW is causally related to adverse outcomes in CKD needs to be verified in randomized controlled trials of nutritional interventions. The initiation of major clinical trials targeting nutritional interventions with the goal of improving survival in CKD offer the promise of extending the survival of this vulnerable patient population.

Association of Malnutrition-Inflammation Score with quality of life and mortality in hemodialysis patients: a 5-year prospective cohort study

BACKGROUND

The Malnutrition-Inflammation Score (MIS), an inexpensive and easy-to-assess score of 0 to 30 to examine protein-energy wasting (PEW) and inflammation, includes 7 components of the Subjective Global Assessment, body mass index, and serum albumin and transferrin concentrations. We hypothesized that MIS risk stratification of hemodialysis (HD) patients in predicting outcomes is better than its components or laboratory markers of inflammation.

STUDY DESIGN

5-Year cohort study.

SETTING & PARTICIPANTS

We examined 809 stable HD outpatients and followed them for up to 5 years (October 2001 to December 2006).

PREDICTORS

MIS and other nutritional and inflammatory markers.

OUTCOMES & MEASUREMENTS

Prospective all-cause mortality, health-related quality of life using the 36-Item Short Form Health Survey (SF-36), and tests of body composition.

RESULTS

The MIS correlated with logarithm of serum interleukin 6 level (r = +0.26; P < 0.001), logarithm of C-reactive protein level (r = +0.16; P < 0.001), and several measures of nutritional status. Patients with a higher MIS had lower SF-36 scores. After multivariate adjustment for case-mix and other measures of PEW, HD patients in the second (3 to 4), third (5 to 7), and fourth (>or=8) quartiles of MIS had worse survival rates than those in the first (0 to 2) quartile (P < 0.001). Each 2-unit increase in MIS was associated with a 2-fold greater death risk, ie, adjusted death hazard ratio of 2.03 (95% confidence interval, 1.76 to 2.33; P < 0.001). Cubic spline survival models confirmed linear trends. Adding MIS to the constellation of age, sex, race/ethnicity, and vintage significantly improved the area under the receiver operating characteristic curve developed for predicting mortality (0.71 versus 0.67; P < 0.001).

LIMITATIONS

Selection bias and unknown confounders.

CONCLUSIONS

In HD patients, the MIS is associated with inflammation, nutritional status, quality of life, and 5-year prospective mortality. The mortality predictability of the MIS appears equal to serum interleukin 6 and somewhat greater than C-reactive protein levels. Controlled trials are warranted to examine whether interventions to improve the MIS can also improve clinical outcomes in HD patients.

Association of serum prealbumin and its changes over time with clinical outcomes and survival in patients receiving hemodialysis

BACKGROUND

In patients receiving maintenance hemodialysis (MHD), a low serum prealbumin is an indicator of protein-energy wasting.

OBJECTIVE

We hypothesized that baseline serum prealbumin correlates independently with health-related quality of life (QoL) and death and that its change over time is a robust mortality predictor.

DESIGN

Associations and survival predictability of serum prealbumin at baseline and its changes over 6 mo were examined in a 5-y (2001-2006) cohort of 798 patients receiving MHD.

RESULTS

Patients with serum prealbumin >or= 40 mg/dL had greater mid-arm muscle circumference but lower percentage of total body fat. Both serum interleukin-6 and dietary protein intake correlated independently with serum prealbumin. Measures of QoL indicated better physical health, physical function, and functionality with higher prealbumin concentrations. Although baseline prealbumin was not superior to albumin in predicting survival, in both all and normoalbuminemic (albumin >or= 3.5 g/dL; n = 655) patients, prealbumin < 20 mg/dL was associated with higher death risk in adjusted models, but further adjustments for inflammatory cytokines mitigated the associations. In 412 patients with baseline prealbumin between 20 and 40 mg/dL whose serum prealbumin was remeasured after 6 mo, a >or=10-mg/dL fall resulted in a death hazard ratio of 1.37 (95% CI: 1.02, 1.85; P = 0.03) after adjustment for baseline measures, including inflammatory markers.

CONCLUSIONS

Even though baseline serum prealbumin may not be superior to albumin in predicting mortality in MHD patients, prealbumin concentrations <20 mg/dL are associated with death risk even in normoalbuminemic patients, and a fall in serum prealbumin over 6 mo is independently associated with increased death risk.

Serum alkaline phosphatase predicts mortality among maintenance hemodialysis patients

Several observational studies have demonstrated that serum levels of minerals and parathyroid hormone (PTH) have U- or J-shaped associations with mortality in maintenance hemodialysis patients, but the relationship between serum alkaline phosphatase (AlkPhos) and risk for all-cause or cardiovascular death is unknown. In this study, a 3-yr cohort of 73,960 hemodialysis patients in DaVita outpatient dialysis were studied, and the hazard ratios for all-cause and cardiovascular death were higher across 20-U/L increments of AlkPhos, including within the various strata of intact PTH and serum aspartate aminotransferase. In the fully adjusted model, which accounted for demographics, comorbidity, surrogates of malnutrition and inflammation, minerals, PTH, and aspartate aminotransferase, AlkPhos > or =120 U/L was associated with a hazard ratio for death of 1.25 (95% confidence interval 1.21 to 1.29; P < 0.001). This association remained among diverse subgroups of hemodialysis patients, including those positive for hepatitis C antibody. A rise in AlkPhos by 10 U/L during the first 6 mo was incrementally associated with increased risk for death during the subsequent 2.5 yr. In summary, high levels of serum AlkPhos, especially >120 U/L, are associated with mortality among hemodialysis patients. Prospective controlled trials will be necessary to test whether serum AlkPhos measurements could be used to improve the management of renal osteodystrophy.

Nutritional and anti-inflammatory interventions in chronic heart failure

Currently, there are 5 million individuals with chronic heart failure (CHF) in the United States who have poor clinical outcomes, including high death rates. Observational studies have indicated a reverse epidemiology of traditional cardiovascular risk factors in CHF; in contrast to trends seen in the general population, obesity and hypercholesterolemia are associated with improved survival. The temporal discordance between the overnutrition (long-term killer) and undernutrition (short-term killer) not only can explain some of the observed paradoxes but also may indicate that malnutrition, inflammation, and oxidative stress may play a role that results in protein-energy wasting contributing to poor survival in CHF. Diminished appetite or anorexia and nutritional deficiencies may be both a cause and a consequence of this so-called malnutrition-inflammation-cachexia (MIC) or wasting syndrome in CHF. Neurohumoral activation, insulin resistance, cytokine activation, and survival selection-resultant genetic polymorphisms also may contribute to the prominent inflammatory and oxidative characteristics of this population. In patients with CHF and wasting, nutritional strategies including amino acid supplementation may represent a promising therapeutic approach, especially if the provision of additional amino acids, protein, and energy includes nutrients with anti-inflammatory and antioxidant properties. Regardless of the etiology of anorexia, appetite-stimulating agents, especially those with anti-inflammatory properties such as megesterol acetate or pentoxyphylline, may be appropriate adjuncts to dietary supplementation. Understanding the factors that modulate MIC and body wasting and their associations with clinical outcomes in CHF may lead to the development of nutritional strategies that alter the pathophysiology of CHF and improve outcomes.

Cardiovascular disease in dialysis patients: do some antihypertensive drugs have specific antioxidant effects or is it just blood pressure reduction? Does antioxidant treatment reduce the risk for cardiovascular disease?

PURPOSE OF REVIEW

Patients with end-stage renal disease have an extremely high cardiovascular disease mortality. Oxidative stress is one of the 'nontraditional' risk factors for cardiovascular disease mortality in dialysis patients. This review discusses antioxidant activity of the commonly prescribed antihypertensive agents and the effects of antioxidant interventions on cardiovascular disease mortality in patients with end-stage renal disease.

RECENT FINDINGS

Several lines of evidence confirm antioxidant activity of the renin-angiotensin-aldosterone antagonists, some of the calcium channel blockers, carvedilol, and hydralazine. This appears to be independent of their antihypertensive activity. Clinical evidence of their superiority in improving cardiovascular disease endpoints in end-stage renal disease, however, is lacking. There are no randomized trials that have examined the effect of correcting oxidative stress on clinical endpoints. One randomized study in patients on hemodialysis reported a reduction in oxidative stress and the plasma methylarginines with valsartan and amlodipine but no clinical endpoints were examined.

SUMMARY

The effects of the antihypertensive agents with antioxidant activity on cardiovascular disease mortality in end-stage renal disease have not been examined in randomized clinical trials. These agents may offer specific clinical advantage in addition to lowering the blood pressure, but this remains to be proven. Two studies show a reduction in cardiovascular disease events with vitamin E and N-acetylcysteine in patients on hemodialysis without an effect on overall mortality.

Misleading associations between cholesterol and vascular outcomes in dialysis patients: the need for randomized trials

Higher cholesterol is strongly associated with an increased risk of coronary heart disease (CHD) in nonrenal populations, so the lack of a clear positive association between total cholesterol and mortality among dialysis patients is unexpected. This review of prospective studies of the association between total cholesterol and mortality among dialysis patients suggests that there is a negative association at below average cholesterol levels and a flat or weakly positive association at higher levels. In nonrenal populations total cholesterol is not positively associated with vascular causes of death other than CHD, so the lack of a strongly positive association at above average cholesterol concentrations in dialysis patients may be explained by the high proportion of deaths due to non-CHD vascular causes. The observation of a negative association between total cholesterol and mortality at below average cholesterol concentrations in some studies is consistent with confounding by both vascular and nonvascular morbidity (i.e., reverse causality). We argue that evaluating the importance of cholesterol for vascular disease risk in dialysis patients can only be achieved through the eradication of confounding by randomization, and that ongoing trials of cholesterol-lowering therapy will provide a definitive answer to this question.

Racial and ethnic disparities in end-stage kidney failure-survival paradoxes in African-Americans

The risk of death is nearly 45% lower in African-Americans than Caucasians undergoing chronic hemodialysis. In light of the higher mortality rate in African-Americans in the general US population, this paradox requires explanation and further investigation. Factors that may contribute to this survival advantage include a younger age at which African-Americans arrive at end-stage renal disease (ESRD) and the slightly higher body mass index. On the other hand, factors, such as lower residual renal function, lower mean hemoglobin and hematocrit, increased prevalence of hypertension, a higher prevalence of catheter use for initial dialysis, and generally lower dose of dialysis should put African-Americans on dialysis at a higher risk of death. This survival advantage seems to be completely annulled with a successful renal transplant. Finally, it should be noted that ESRD carries with it a very high mortality rate in all racial and ethnic groups. A successful renal transplant improves but does not restore the expected remaining life times. Therefore, aggressive approach is required in investigating the factors that confer such high mortality risk on ESRD patients.

How to reconcile conventional and altered risk factor patterns in dialysis patients

Epidemiological relationships between risk factors and outcome in patients with chronic kidney failure (CKF), including individuals with end-stage kidney failure, can be categorized into three types: risk factor relationships that are similar to those observed in the general population; risk factor relationships that differ from those observed in the general population; and risk factor patterns that are difficult or not possible to compare to the general population, possibly because such risk factors have not been studied or are not capable of being studied in normal individuals. These latter risk factor patterns may or may not be different from what might commonly be anticipated. It is recommended that risk factor relationships in CKF patients which differ from those observed in the general population should be referred to as altered risk factor patterns (ARFPs). The causes for ARFPs include protein-energy wasting and inflammatory disorders, which occur commonly in patients with CKF. Epidemiological and other evidence is presented suggesting that the ARFPs may also have other causes. Since ARFPs are common in CKF, it is important to understand the causes and appropriate therapeutic goals concerning these risk factors. Studies, including interventional clinical trials, are indicated to ascertain the causes of ARFPs and the therapeutic targets for these risk factors for individuals with chronic kidney disease and CKF.

A proposed nomenclature and diagnostic criteria for protein-energy wasting in acute and chronic kidney disease

The recent research findings concerning syndromes of muscle wasting, malnutrition, and inflammation in individuals with chronic kidney disease (CKD) or acute kidney injury (AKI) have led to a need for new terminology. To address this need, the International Society of Renal Nutrition and Metabolism (ISRNM) convened an expert panel to review and develop standard terminologies and definitions related to wasting, cachexia, malnutrition, and inflammation in CKD and AKI. The ISRNM expert panel recommends the term 'protein-energy wasting' for loss of body protein mass and fuel reserves. 'Kidney disease wasting' refers to the occurrence of protein-energy wasting in CKD or AKI regardless of the cause. Cachexia is a severe form of protein-energy wasting that occurs infrequently in kidney disease. Protein-energy wasting is diagnosed if three characteristics are present (low serum levels of albumin, transthyretin, or cholesterol), reduced body mass (low or reduced body or fat mass or weight loss with reduced intake of protein and energy), and reduced muscle mass (muscle wasting or sarcopenia, reduced mid-arm muscle circumference). The kidney disease wasting is divided into two main categories of CKD- and AKI-associated protein-energy wasting. Measures of chronic inflammation or other developing tests can be useful clues for the existence of protein-energy wasting but do not define protein-energy wasting. Clinical staging and potential treatment strategies for protein-energy wasting are to be developed in the future.

Effects of sevelamer and calcium-based phosphate binders on lipid and inflammatory markers in hemodialysis patients

INTRODUCTION

Cardiovascular disease accounts for almost half of all deaths in individuals with chronic kidney disease stage 5 despite advances in both dialysis treatment and cardiology. A combination of lipid-lowering and anti-inflammatory effects along with avoidance of hypercalcemia should be taken into account when choosing phosphorus binders for maintenance hemodialysis (MHD) patients.

METHODS

We examined the association of sevelamer versus calcium-based phosphorus binders with lipid profile, inflammatory markers including C-reactive protein (CRP), and mineral metabolism in MHD patients who participated in the Nutritional and Inflammatory Evaluation of Dialysis Patients (NIED) study from October 2001 to July 2005.

RESULTS

Of the 787 MHD patients in the NIED study, 697 were on either sevelamer, a calcium-based binder, or both and eligible for this study. We compared the groups based on taking sevelamer monotherapy (n = 283) or calcium binder monotherapy (n = 266) for serum phosphate control. There were no differences between the groups on dialysis vintage. There were significant differences in age, serum calcium and phosphorus levels, as well as intact parathyroid hormone levels. Using a logistic regression models, the sevelamer group had a higher odds of serum CRP <10 mg/l [odds ratio (OR): 1.06, 95% CI: 1.02-1.11] and LDL cholesterol <70 mg/dl (OR: 1.33, 95% CI: 1.19-1.47) when compared to the calcium binder group independent of age, vintage, body mass index, statin use or other variables.

CONCLUSION

The improvements in multiple surrogate markers of inflammation and lipids in the NIED study make sevelamer a promising therapy for treatment in MHD patients with high risk of cardiovascular disease and mortality.

Racial and survival paradoxes in chronic kidney disease

Most of the 20 million people in the US with chronic kidney disease (CKD) die before commencing dialysis. One of every five dialysis patients dies each year in the US. Although cardiovascular disease is the most common cause of death among patients with CKD, conventional cardiovascular risk factors such as hypercholesterolemia, hypertension and obesity are paradoxically associated with better survival in hemodialysis populations. Emerging data indicate the existence of this 'reverse epidemiology' in earlier stages of CKD. There are also paradoxical relationships between outcomes and race and ethnicity. For example, the survival rate of African American dialysis patients seems to be superior to that of whites on dialysis. Paradoxes-within-paradoxes have been detected among Hispanic and Asian American CKD patients. These survival paradoxes might evolve and change over the natural course of CKD progression as a result of the time differentials of competing risk factors and the overwhelming impact of malnutrition, inflammation and wasting. Reversal of the reverse epidemiology as a result of successful kidney transplantation underscores the role of nutritional status and kidney function in engendering these paradoxes. The observation of paradoxes and their reversal might lead to the formulation of new paradigms and management strategies to improve the survival of patients with CKD. Such movement away from the use of targets set on the basis of data gathered in general populations (e.g. the Framingham cohort) would be a major paradigm shift in clinical medicine and public health.

HDL-inflammatory index correlates with poor outcome in hemodialysis patients

Oxidative stress and cardiovascular disease are risk factor of patients with chronic kidney disease (CKD) on maintenance hemodialysis. We used the fluorescence of low-density lipoprotein as an index of its proinflammatory potential to examine any role that high-density lipoprotein (HDL) might have in promoting this effect. The total body fat of the patients was measured by means of near-infrared interactance and their quality of life by means of SF36 questionnaires. In 189 randomly selected patients, followed for 30 months, HDL was found to be significantly anti-inflammatory but with a large standard deviation. Fully 17% of the patients had a decidedly proinflammatory index along with inferior SF36 scores. The patients were divided into 10% increments of total body fat percentages up to 40%. HDL was found to be progressively proinflammatory the higher the body fat content. Patients with a higher HDL proinflammatory index had a higher 30-month adjusted hazard ratio for death than those whose HDL were seen to be anti-inflammatory. Our findings suggest an important role of inflammatory HDL in patients with CKD leading to poor outcome.

Risk factor paradox in wasting diseases

PURPOSE OF REVIEW

Emerging data indicate that conventional cardiovascular risk factors (e.g. hypercholesterolemia and obesity) are paradoxically associated with better survival in distinct populations with wasting. We identify these populations and review survival paradoxes and common pathophysiologic mechanisms.

RECENT FINDINGS

A 'reverse epidemiology' of cardiovascular risk is observed in chronic kidney disease, chronic heart failure, chronic obstructive lung disease, cancer, AIDS and rheumatoid arthritis, and in the elderly. These populations apparently have slowly progressive to full-blown wasting and significantly greater short-term mortality than the general population. The survival paradoxes may result from the time differential between the two competing risk factors [i.e. over-nutrition (long-term killer but short-term protective) versus undernutrition (short-term killer)]. Hemodynamic stability of obesity, protective adipokine profile, endotoxin-lipoprotein interaction, toxin sequestration of fat, antioxidation of muscle, reverse causation, and survival selection may also contribute.

SUMMARY

The seemingly counterintuitive risk factor paradox is the hallmark of chronic disease states or conditions associated with wasting disease at the population level. Studying similarities among these populations may help reveal common pathophysiologic mechanisms of wasting disease, leading to a major shift in clinical medicine and public health beyond the conventional Framingham paradigm and to novel therapeutic approaches related to wasting and short-term mortality.

A1C and survival in maintenance hemodialysis patients

OBJECTIVE

The optimal target for glycemic control has not been established in diabetic dialysis patients.

RESEARCH DESIGN AND METHODS

To address this question, the national database of a large dialysis organization (DaVita) was analyzed via time-dependent survival models with repeated measures.

RESULTS

Of 82,933 patients undergoing maintenance hemodialysis (MHD) in DaVita outpatient clinics over 3 years (July 2001 through June 2004), 23,618 diabetic MHD patients had A1C measurements at least once. Unadjusted survival analyses indicated paradoxically lower death hazard ratios (HRs) with higher A1C values. However, after adjusting for potential confounders (demographics, dialysis vintage, dose, comorbidity, anemia, and surrogates of malnutrition and inflammation), higher A1C values were incrementally associated with higher death risks. Compared with A1C in the 5-6% range, the adjusted all-cause and cardiovascular death HRs for A1C > or = 10% were 1.41 (95% CI 1.25-1.60) and 1.73 (1.44-2.08), respectively (P < 0.001). The incremental increase in death risk for rising A1C values was monotonic and robust in nonanemic patients (hemoglobin > 11.0 g/dl). In subgroup analyses, the association between A1C > 6% and increased death risk was more prominent among younger patients, those who had undergone dialysis for > 2 years, and those with higher protein intake (> 1 g x kg(-1) x day(-1)), blood hemoglobin (> 11 g/dl), or serum ferritin values (> 500 ng/ml).

CONCLUSIONS

In diabetic MHD patients, the apparently counterintuitive association between poor glycemic control and greater survival is explained by such confounders as malnutrition and anemia. All things equal, higher A1C is associated with increased death risk. Lower A1C levels not related to malnutrition or anemia appear to be associated with improved survival in MHD patients.