Connections between vascular calcification and progression of chronic kidney disease: therapeutic alternatives

Vascular calcification: When should we interfere in chronic kidney disease patients and how?

Chronic kidney disease (CKD) patients are endangered with the highest mortality rate compared to other chronic diseases. Cardiovascular events account for up to 60% of the fatalities. Cardiovascular calcifications affect most of the CKD patients. Most of this calcification is related to disturbed renal phosphate handling. Fibroblast growth factor 23 and klotho deficiency were incriminated in the pathogenesis of vascular calcification through different mechanisms including their effects on endothelium and arterial wall smooth muscle cells. In addition, deficient klotho gene expression, a constant feature of CKD, promotes vascular pathology and shares in progression of the CKD. The role of gut in the etio-pathogenesis of systemic inflammation and vascular calcification is a newly discovered mechanism. This review will cover the medical history, prevalence, pathogenesis, clinical relevance, different tools used to diagnose, the ideal timing to prevent or to withhold the progression of vascular calcification and the different medications and medical procedures that can help to prolong the survival of CKD patients.

High-phosphorus/zinc-free diet aggravates hypertension and cardiac dysfunction in a rat model of the metabolic syndrome

BACKGROUND

Cardiac dysfunction is reported in patients with the metabolic syndrome. We assessed the effects of high-phosphorus and zinc-free diet on cardiovascular system in spontaneously hypertensive rats (SHR)/NDmcr-cp (SHR/cp), a rat model of the metabolic syndrome. We also investigated the effects of N-acetyl-L-cysteine (NAC), an antioxidant, on the development of cardiac dysfunction under such conditions.

METHODS

Male SHR/cp and control [Wistar Kyoto (WKY)] rats were divided into three groups and fed control diet (P 0.3% w/w, Zn 0.2% w/w) or high-phosphorus and zinc-free (P 1.2% w/w, Zn 0.0% w/w) diet. The latter group was treated with either NAC (1.5 mg/g per day) or vehicle from 6 to 18 weeks of age (n=6 or 8 for each group).

RESULTS

High-phosphate and zinc-free diet increased systolic blood pressure in both WKY and SHR/cp. Echocardiography showed that high-phosphate and zinc-free diet markedly reduced left ventricular systolic and diastolic function in SHR/cp. Histopathologically, the same diet induced severe myocardial fibrosis in SHR/cp, and this effect was prevented by NAC. Whereas treatment with NAC prevented diastolic dysfunction induced by the same diet in WKY, it only improved systolic function but not diastolic function in SHR/cp.

CONCLUSIONS

High-phosphate and zinc-free diet induced hypertension and cardiac dysfunction. These changes hamper the protective effects of NAC in the metabolic syndrome.

SUMMARY

The present study showed that consumption of high-phosphorus and zinc-free diet increased the myocardial expression of connective tissue growth factor and reduced the expression of metallothionein, which enhanced the development of severe cardiac dysfunction in rats with the metabolic syndrome. The results suggest that the metabolic syndrome seems to aggravate cardiac dysfunction and hamper the protective effects of antioxidant, NAC.

Phylloquinone and vitamin D status: associations with incident chronic kidney disease in the Framingham Offspring cohort

BACKGROUND

Cardiovascular risk factors are associated with the development of chronic kidney disease (CKD), and CKD and vascular disease are etiologically linked. Evidence suggests deficiencies of vitamins D and K may adversely affect the cardiovascular system, but data from longitudinal studies are lacking. We hypothesized that deficiencies of vitamins D and K may be associated with incident CKD and/or incident albuminuria amongst members of the general population.

METHODS

We analyzed 1,442 Framingham Heart Study participants (mean age 58 years; 50.5% women), free of CKD (eGFR <60 ml/min/1.73 m(2)), with a mean follow-up of 7.8 years in 2005-2008. Incident albuminuria was defined using sex-specific cut-offs of urine albumin-to-creatinine ratio (≥17 mg/g men and ≥25 mg/g women). Baseline log plasma phylloquinone (vitamin K(1)) and 25(OH)D levels, analyzed as continuous variables and by quartile, were related to risk of incident CKD (n = 108) and incident albuminuria (n = 106) using logistic regression models adjusted for standard risk factors.

RESULTS

Participants in the highest phylloquinone quartile (≥1.78 nmol/l) had an increased risk of CKD (multivariable-adjusted OR Q(4) vs. Q(1) 2.39; p = 0.006) and albuminuria at follow-up (multivariable-adjusted OR Q(4) vs. Q(1) 1.95; p = 0.05), whereas no association was observed with continuous phylloquinone levels for either endpoint. Deficiency of 25(OH)D was not associated with incident CKD or albuminuria in either analysis.

CONCLUSIONS

Contrary to our hypothesis, higher plasma phylloquinone levels are associated with an increased risk of incident CKD. Whether plasma phylloquinone is a marker for another unmeasured risk factor requires further study. External validation is necessary given the unexpected nature of these results.

Risk factors for progression of aortic arch calcification in patients on maintenance hemodialysis and peritoneal dialysis

Vascular calcification is accelerated during dialysis and is known to be an important risk factor for cardiovascular disease. Progression of aortic arch calcification (AoAC) can be simply estimated with an AoAC score (AoACS) using plain chest radiography. The objective of this study was to evaluate risk factors for AoAC progression. The enrolled subjects were 125 newly treated hemodialysis patients and 59 peritoneal dialysis patients. In the patients who had undergone chest radiography before initial dialysis therapy and every year, we estimated AoACS and then divided the patients into two groups based on the presence or absence of AoAC progression. We also compared the baseline clinical and biochemical profiles in the two groups. Eighty-five (46.2%) were men (mean age, 58.6 ± 12.7 years). Seventy-six patients (41.3%) had AoAC before initial dialysis, with a mean AoACS of 13.0 ± 20.4%. The mean duration of follow-up was 2.7 ± 1.0 years. Half of the patients (50%) had progressive AoAC. Age >65 years (p = 0.003), dialysis duration (p = 0.004), diabetes (p = 0.015), and the presence of AoAC at baseline (p = 0.001) were related to AoAC progression. No significant association was found between AoAC progression and the baseline clinical parameters, including gender, obesity, hypertension, and dialysis modality. In a multivariate analysis, dialysis duration (p = 0.003) and the presence of AoAC at baseline (p < 0.001) were independent risk factors for AoAC progression in patients undergoing dialysis. The duration of dialysis and the presence of AoAC before initial dialysis were significantly related to the progression of AoAC in these patients. The results suggest that patients should be carefully managed from the predialysis stage to prevent AoAC progression and to reduce cardiovascular morbidity.

Achievements and challenges in bioartificial kidney development

Bioartificial kidneys (BAKs) combine a conventional hemofilter in series with a bioreactor unit containing renal epithelial cells. The epithelial cells derived from the renal tubule should provide transport, metabolic, endocrinologic and immunomodulatory functions. Currently, primary human renal proximal tubule cells are most relevant for clinical applications. However, the use of human primary cells is associated with many obstacles, and the development of alternatives and an unlimited cell source is one of the most urgent challenges. BAKs have been applied in Phase I/II and Phase II clinical trials for the treatment of critically ill patients with acute renal failure. Significant effects on cytokine concentrations and long-term survival were observed. A subsequent Phase IIb clinical trial was discontinued after an interim analysis, and these results showed that further intense research on BAK-based therapies for acute renal failure was required. Development of BAK-based therapies for the treatment of patients suffering from end-stage renal disease is even more challenging, and related problems and research approaches are discussed herein, along with the development of mobile, portable, wearable and implantable devices.

Bone markers predict cardiovascular events in chronic kidney disease

Recent studies have indicated a link between bone metabolism and cardiovascular events in patients with chronic kidney disease (CKD). CKD is a major health problem worldwide. This study evaluates the role of noninvasive markers of bone metabolism in predicting cardiovascular morbidity (coronary artery disease, peripheral vascular disease, stroke) and mortality in patients with mild to severe forms of CKD. In a prospective cohort study, 627 patients with CKD were screened. To focus on bone metabolism, traditional risk factors for cardiovascular events were excluded, and 135 patients with CKD stages 1-5 were followed for 4 yr. Glomerular filtration rate was calculated by the Modification of Diet in Renal Disease formula. PTH (measured by four different assays), vitamin D 25 and 1,25, bone-specific alkaline phosphatase (BSALP), TRACP-5b, osteocalcin, serum collagen cross-link molecules, RANKL, and osteoprotegerin were determined. Predictors of cardiovascular events were evaluated by multivariable logistic regression, Kaplan-Meier survival, and Cox regression analysis. There were a total of 45 cardiovascular events (33%). Event rates were 5.6%, 29.1%, 45.2%, and 45.0% in CKD stages 1-2, 3, 4, and 5, respectively. In logistic regression, cardiovascular events were predicted only by (1) CKD stage (independent of age or sex; p < 0.001); (2) BSALP (p = 0.03); and (3) TRACP-5b (p = 0.04). Markers of bone formation (BSALP) and resorption (TRACP-5b) can serve as predictors of cardiovascular morbidity and mortality in CKD.

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.

An economic evaluation of sevelamer in patients new to dialysis

OBJECTIVE

The overall objective of this study was to estimate the costs and outcomes associated with treatment with sevelamer for hyperphosphataemia compared with calcium-based binders.

METHODS

Using published data on mortality and hospitalisation rates, a Markov model was developed to predict health outcomes and associated costs for the treatment of hyperphosphataemia using either sevelamer or calcium binders in chronic kidney disease patients who had recently started haemodialysis. Patient outcomes were modelled for 5 years, and incremental cost-effective ratios (ICERs) were calculated for sevelamer relative to calcium carbonate and calcium acetate binders. The perspective adopted was that of the UK National Health Service.

RESULTS

The total 5-year discounted treatment cost for patients treated with sevelamer is pound 24,216, while for the calcium carbonate group total cost was pound 17,695. This is an incremental cost of pound 6521 per sevelamer-treated patient over 5 years. Patients receiving sevelamer can be expected to experience 2.70 quality-adjusted life years (QALYs) compared to 2.46 for those treated with calcium carbonate (i.e. an incremental gain of 0.24 QALYs). This results in an incremental cost per QALY of pound 27,120 and an incremental cost per life year gained of pound 15,508. Results were similar with calcium acetate.

CONCLUSION

Together with the unique morbidity and mortality benefits, this study suggests that treatment with sevelamer confers clinical benefits with a modest investment of additional economic resources.

Arterial calcification and stiffness in chronic kidney disease

1. Patients with chronic kidney disease (CKD) demonstrate a high burden of vascular disease. This vascular disease is unusual by way of a preponderance of medial calcification. Further, traditional cardiovascular risk factors fail to fully explain the high cardiovascular event rate in this population. 2. The present review examines the problem of medial calcification and arterial stiffness evident in patients with CKD and explores evidence for its existence and the potential pathological process involved. Many factors are emerging as potential culprits in this disease entity, although the specific roles of components such as fetuin-A, matrix Gla protein, osteopontin and fibroblast growth factor-23 have yet to be determined. Calcium and phosphate balance remains integral to the pathological process. 3. Pulse wave velocity has proven to be a useful tool to assess and follow arterial stiffness in CKD patients and is discussed. 4. Finally, techniques aimed at reducing or reversing arterial calcification and stiffness are discussed, with as yet no definitive answers available.

Conflicting dietary advice for adhering to low-sodium and low-phosphorus diets

OBJECTIVE

To elucidate conflicts that patients face when advised to limit multiple nutrients in their diet.

DESIGN

We analyzed the phosphorus content of low-sodium foods compared with their regular-sodium content counterparts, and the sodium content of low-phosphorus foods compared with foods containing higher levels of phosphorus. Low-sodium and low-phosphorus foods were identified with the use of recommendations from National Kidney Foundation patient information Web sites. Content of sodium and phosphorus was quantified with use of the US Department of Agriculture (USDA) Nutrient Database.

SETTING

Review and analysis of publicly available patient information Web sites and nutrient databases.

MAIN OUTCOME MEASURE

Phosphorus content of low- versus regular-sodium-containing foods, and sodium content of low- versus high-phosphorus-containing foods.

RESULTS

Of 47 low-sodium foods, 32 had identical phosphorus content--8 higher and 7 lower--compared with regular-sodium alternatives. Of 9 foods recommended as low-phosphorus alternatives to high-phosphorus choices, 4 had higher sodium content and 5 had lower, with considerable variability. However, choosing servings of 4 low-sodium alternatives could increase ingestion of phosphorus by up to 16% of recommended intake, and choosing servings of 4 low-phosphorus alternatives could increase ingestion of sodium by more than 20% of recommended intake.

CONCLUSION

Adhering to a complex renal diet is extremely difficult for patients with chronic kidney disease. Balancing sodium and phosphorus restrictions is particularly challenging, especially as food choices low in one nutrient may not be low in the other. To help patients follow these diets, alternative methods of achieving dietary restrictions of multiple, often conflicting, components may be needed.

Mechanisms of vascular calcification

Vascular calcification is highly prevalent and correlated with high rates of cardiovascular mortality in chronic kidney disease patients. Recent evidence suggests that mineral, hormonal, and metabolic imbalances that promote phenotype change in vascular cells as well as deficiencies in specific mineralization inhibitory pathways may be important contributory factors for vascular calcification in these patients. This article reviews current mechanisms proposed for the regulation of vascular calcification and data supporting their potential contribution to this process in chronic kidney disease.