Chapter 3.1: Diagnosis of CKD–MBD: biochemical abnormalities

Mineral bone disorder in children with chronic kidney disease: Data from the KNOW-Ped CKD (Korean cohort study for outcome in patients with pediatric chronic kidney disease) study

BACKGROUND

Children with chronic kidney disease (CKD) are at high risk of mineral bone disorder (MBD), which leads to fractures, growth retardation, and cardiovascular disease. We aimed to comprehensively understand the relationship between renal function and factors related to MBD and evaluate the prevalence and distribution characteristics of MBD, specifically among Korean patients from the KNOW-PedCKD cohort.

METHODS

From the baseline data of the KNOW-PedCKD cohort, we examined the prevalence and distribution of MBD in 431 Korean pediatric CKD patients, including the level of corrected total calcium, serum phosphate, serum alkaline phosphatase, serum intact parathyroid hormone (iPTH), fibroblast growth factor 23 (FGF-23), serum vitamin D, fractional excretion of phosphate (FEP), and bone densitometry Z-scores.

RESULTS

The median serum calcium level remained relatively normal regardless of the CKD stage. The levels of 1,25-dihydroxy vitamin D, urine calcium-to-creatinine ratio, and bone densitometry Z-score significantly decreased with advancing CKD stage, while those of serum phosphate, FGF-23, and FEP significantly increased with CKD stage. The prevalence of hyperphosphatemia (17.4%, 23.7%, and 41.2% from CKD stages 3b, 4, and 5, respectively) and hyperparathyroidism (37.3%, 57.4%, 55.3%, and 52.9% from CKD stages 3a, 3b, 4, and 5, respectively) significantly increased with the CKD stage. Prescriptions of medications, such as calcium supplements (39.1%, 42.1%, 82.4%), phosphate binders (39.1%, 43.4%, 82.4%), and active vitamin D (21.7%, 44.7%, and 64.7%) significantly increased with CKD stage 3b, 4, and 5, respectively.

CONCLUSIONS

The results demonstrated the prevalence and relationship of abnormal mineral metabolism and bone growth according to CKD stage in Korean pediatric CKD patients for the first time.

oxLDL inhibits differentiation of mesenchymal stem cells into osteoblasts via the CD36 mediated suppression of Wnt signaling pathway

Bone abnormalities as a consequence of osteoblast deregulation are associated with several diseases such as diabetes and chronic kidney disease. Important role for oxidized low density lipoproteins (oxLDL) in the pathophysiology of bone disorders has been reported. However, little is known about the effects and mechanisms of oxLDL on the process of osteoblastogenesis in human mesenchymal stem cells (MSCs). We show that oxLDL concentrations of ~ 10-25 µg protein (0.43-1.0 µM MDA/mg protein) inhibited the differentiation of MSCs to osteoblasts. We demonstrate that the underlying mechanism entails the suppression of the Wnt signaling through the down-regulation of β-catenin. Further, we show the association of scavenger receptor CD36 with the receptors LRP5/6 and Frizzled in mediating the oxLDL effects on the differentiation of MSCs to pre-osteoblasts. Inhibiting CD36 restored osteoblasts differentiation in the presence of oxLDL. Our findings suggest that oxLDL interferes with the canonical Wnt signaling pathway in a CD36 dependent manner leading to an inhibition of osteoblastogenesis.

Abdominal aortic calcification score can predict future coronary artery disease in hemodialysis patients: a 5-year prospective cohort study

BACKGROUND

Abdominal aortic calcification (AAC) has been known to be associated with cardiovascular mortality in hemodialysis. However, the association between AAC and future coronary artery disease (CAD) occurrence is not clear. We aimed to clarify the association of AAC severity and the occurrence of future CAD events in hemodialysis patients.

METHODS

Hemodialysis (HD) patients were recruited in this prospective cohort study. AAC severity was quantified by AAC score, which was measured by lateral lumbar radiography. We used receiver operation curve (ROC) analysis to find the cutoff AAC value for CAD prediction. CAD-free survival was analyzed by Kaplan-Meier study.

RESULTS

There were 303 patients recruited for study with a median (interquartile range) follow-up of 95 (65-146) months. The AAC score in patients with occurrence of new CAD [9 (3-15.25), n = 114] was higher than in patients without new CAD occurrence [5 (1-9) n = 189], p < 0.001. Multivariate hazard ratio of AAC score for CAD was 1.039 (p = 0.016). ROC study showed that an AAC score of 5.5 had a sensitivity of 0.658 and a specificity of 0.587 in the prediction of new CAD occurrence. Patients with AAC score above 5.5 had significantly higher cumulative incidence of CAD than patients with AAC score below 5.5. Age, diabetes, prior history of CAD, and longer dialysis vintage were major factors associated with higher AAC score.

CONCLUSIONS

AAC score can predict the occurrence of future CAD events in HD patients. The best cut-off value of AAC score is 5.5. AAC score greater than 5.5 is a reliable abdominal aortic calcification marker, and can predict future CAD in ESRD patients. Major contributive factors for higher AAC score were age, presence of diabetes, prior history of CAD, and longer dialysis vintage.

The efficacy and safety of sevelamer and lanthanum versus calcium-containing and iron-based binders in treating hyperphosphatemia in patients with chronic kidney disease: a systematic review and meta-analysis

Background

It remains unclear which phosphate binders should be preferred for hyperphosphatemia management in chronic kidney disease (CKD).

Methods

We performed a systematic review and meta-analysis of randomized trials comparing sevelamer or lanthanum with other phosphate binders in CKD.

Results

Fifty-one trials (8829 patients) were reviewed. Compared with calcium-based binders, all-cause mortality was nonsignificantly lower with sevelamer {risk ratio [RR] 0.62 [95% confidence interval (CI) 0.35-1.08]} and lanthanum [RR 0.73 (95% CI 0.18-3.00)], but risk of bias was concerning. Compared with calcium-based binders, sevelamer reduced the risk of hypercalcemia [RR 0.27 (95% CI 0.17-0.42)], as did lanthanum [RR 0.12 (95% CI 0.05-0.32)]. Sevelamer reduced hospitalizations [RR 0.50 (95% CI 0.31-0.81)], but not lanthanum [RR 0.80 (95% CI 0.34-1.93)]. The presence/absence of other clinically relevant outcomes was infrequently reported. Compared with calcium-based binders, sevelamer reduced serum calcium, low-density lipoprotein and coronary artery calcification, but increased intact parathyroid hormone. The clinical relevance of these changes is unknown since corresponding clinical outcomes were not reported. Lanthanum had less favorable impact on biochemical parameters. Sevelamer hydrochloride and sevelamer carbonate were similar in three studies. Sevelamer was similar to lanthanum (three studies) and iron-based binders (three studies).

Conclusion

Sevelamer was associated with a nonsignificant reduction in mortality and significantly lower hospitalization rates and hypercalcemia compared with calcium-based binders. However, differences in important outcomes, such as cardiac events, fractures, calciphylaxis, hyperchloremic acidosis and health-related quality of life remain understudied. Lanthanum and iron-based binders did not show superiority for any clinically relevant outcomes. Future studies that fail to measure clinically important outcomes (the reason why phosphate binders are prescribed in the first place) will be wasteful.

Osteoporosis in patients with diabetes after kidney transplantation

Preexisting diabetes increases risk of fractures after kidney transplantation (KT). However, little is known about mechanisms and prevention of increased fragility in these patients. Pathophysiology of osteoporosis after KT is complex and characterized by high prevalence of adynamic bone disease. Despite high prevalence of preexisting diabetes in KT recipients, diabetes patients were underrepresented in the studies that explored mechanisms and treatments of osteoporosis after KT. Therefore, caution should be exercised before considering conventional fracture prevention strategies in this unique group of patients. Many traditional osteoporosis medications reduce bone turnover and, hence, can be ineffective or even harmful in diabetic patients after KT. Contrary to predictions, evidence from the studies conducted in mostly non-diabetic subjects demonstrated that bisphosphonates failed to reduce fracture rates after KT. Therefore, bisphosphonates use should be limited in diabetic patients until more evidence supporting their post-transplant efficacy is available. We recommend the following strategies that may help reduce fracture risk in diabetes subjects after KT such as adequate management of calcium, parathyroid hormone, and vitamin D levels, optimization of glycemic control, use of steroid-sparing immunosuppressive regimens, and fall prevention.

Brown tumor at the jaw in patients with secondary hyperparathyroidism due to chronic renal failure

Brown tumors are bony lesions caused by rapid osteoclastic activity, which rare involved jaws. Renal osteodystrophy (ROD) is associated with different pathogenetic mechanisms--disorder of calcium-phosphate metabolism, impaired metabolism of vitamin D, increased parathyroid activity that lead to extreme concentrations of parathormone. The authors report two cases of jaw enlargement in patients received haemodialysis with excessive increase values of alkaline phosphatase and parathormone in serum. The patients were treated surgically with corrective procedures in maxillo-facial area. ROD of the jaws could be severe complication in dialysis patients with end stage of CKD if no appropriate care aimed at correction or prevention of parathyroid hyperfunction was applied to them.

Randomized clinical trial of the iron-based phosphate binder PA21 in hemodialysis patients

BACKGROUND AND OBJECTIVES

A dose-finding study was undertaken to investigate the efficacy of PA21, a novel polynuclear iron(III)-oxyhydroxide phosphate binder.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

In a randomized, active-controlled, multicenter, open-label study at 50 clinical sites in Europe and the United States, hemodialysis patients were randomized to PA21 at dosages of 1.25, 5.0, 7.5, 10.0, or 12.5 g/d or sevelamer-HCl 4.8 g/d for 6 weeks. The primary efficacy endpoint was the change in serum phosphorus concentration from baseline.

RESULTS

There were 154 participants who were randomized and received the study drug. All groups except PA21 1.25 g/d showed a significant decrease in serum phosphorus. Mean decreases in serum phosphorus in PA21 10 g/d and 12.5 g/d were -2.00±1.71 mg/dl and -1.69±1.81 mg/dl, respectively. A similar decrease to sevelamer-HCl (-1.06±1.35 mg/dl) was seen with PA21 5.0 g/d (-1.08±2.12 mg/dl) and 7.5 g/d (-1.25±1.21 mg/d). Overall, 60.9% of participants randomized to PA21 and 57.7% randomized to sevelamer-HCl reported ≥1 adverse event. The most frequent adverse events were hypophosphatemia (18.0%) and discolored feces (11.7%) for the pooled PA21 dose groups, and diarrhea, hypophosphatemia, and hypotension (each 11.5%) for sevelamer-HCl. Discontinuation due to adverse events occurred at a similar rate in PA21-treated (21.1%) and sevelamer-HCl-treated (23.1%) participants.

CONCLUSIONS

PA21 5-12.5 g/d significantly reduces serum phosphorus in hemodialysis patients. The 5 g/d and 7.5 g/d dosages showed similar efficacy to 4.8 g/d of sevelamer-HCl. The adverse events rate was similar for PA21 and sevelamer-HCl.

Hyperparathyroidism in chronic kidney disease: complexities within the commonplace

Secondary hyperparathyroidism in patients with chronic kidney disease (CKD) is common and usually caused by associated metabolic abnormalities, in particular, hypocalcaemia and hyperphosphataemia. Nevertheless, other causes of hyperparathyroidism can exist concurrently with CKD, challenging diagnostic interpretation and therapeutic intervention. We present four cases of hyperparathyroidism in patients with CKD that highlight some of these dilemmas.

Discriminants of prevalent fractures in chronic kidney disease

Patients with chronic kidney disease (CKD) have higher rates of fracture than the general population. Increased bone remodeling, leading to microarchitectural deterioration and increased fragility, may accompany declining kidney function, but there are no reliable methods to identify patients at increased risk for fracture. In this cross-sectional study of 82 patients with predialysis CKD, high-resolution imaging revealed that the 23 patients with current fractures had significantly lower areal density at the femoral neck; total, cortical, and trabecular volumetric bone density; cortical area and thickness; and trabecular thickness. Compared with levels in the lowest tertile, higher levels of osteocalcin, procollagen type-1 N-terminal propeptide, and tartrate-resistant acid phosphatase 5b were associated with higher odds of fracture, even after adjustment for femoral neck T-score. Discrimination of fracture prevalence was best with a femoral neck T-score of -2.0 or less and a value in the upper two tertiles for osteocalcin, procollagen type-1 N-terminal propeptide, or tartrate-resistant acid phosphatase 5b; these values corresponded to the upper half of the normal premenopausal reference range. In summary, these cross-sectional data suggest that measurement of bone turnover markers may increase the diagnostic accuracy of densitometry to identify patients with CKD at high risk for fracture.

FGF-23 and osteoprotegerin are independently associated with myocardial damage in chronic kidney disease stages 3 and 4. Another link between chronic kidney disease-mineral bone disorder and the heart

BACKGROUND

Extra-skeletal calcification and disordered phosphate metabolism are hallmarks of chronic kidney disease-mineral bone disorder (CKD-MBD). Osteoprotegerin (OPG) and fibroblast growth factor 23 (FGF-23) are increased in chronic kidney disease (CKD) and have been associated with arterial and cardiac dysfunction and reduced survival. Troponin T (cTnT) is released from cardiac myocytes under conditions of stress and is predictive of mortality across a range of renal functions. However, the utility of this biomarker was formerly limited by the lower limit of assay detection. The introduction of a high-sensitivity assay has enabled more detailed study of myocyte stress below the previous limit of detection. We studied the association of mediators of CKD-MBD with arterial stiffness and also of these mediators and arterial stiffness with myocardial damage in patients with CKD stages 3-4.

METHODS

OPG and FGF-23 were measured in 200 CKD stages 3-4 patients. cTnT was measured using a high-sensitivity assay. Aortic stiffness was assessed using aortic pulse wave velocity (APWV).

RESULTS

Mean age was 69 ± 11 years, mean systolic and diastolic blood pressure was 151 ± 22/81 ± 11 mmHg and renal function was 33 ± 11 mL/min/1.73 m(2). OPG, FGF-23, high-sensitivity troponin T (hs-cTnT) and APWV all correlated with renal function. After multivariate analysis, OPG and age remained independently associated with aortic stiffness. OPG and FGF-23 were independently associated with hs-cTnT in addition to other non-traditional risk factors (Model R(2) = 0.596).

CONCLUSION

We have shown that changes in bone mediators and phosphate metabolism induced by CKD are independently associated with vascular and cardiomyocyte dysfunction. Our findings suggest that cardiac dysfunction may be specifically associated with such abnormalities in addition to recognized increases in vascular stiffness.

Cardiorenal syndrome type 4-cardiovascular disease in patients with chronic kidney disease: epidemiology, pathogenesis, and management

The term cardiorenal syndrome refers to the interaction between the heart and the kidney in disease and encompasses five distinct types according to the initial site affected and the acute or chronic nature of the injury. Type 4, or chronic renocardiac syndrome, involves the features of chronic renal disease (CKD) leading to cardiovascular injury. There is sufficient epidemiologic evidence linking CKD with increased cardiovascular morbidity and mortality. The underlying pathophysiology goes beyond the highly prevalent traditional cardiovascular risk burden affecting renal patients. It involves CKD-related factors, which lead to cardiac and vascular pathology, mainly left ventricular hypertrophy, myocardial fibrosis, and vascular calcification. Risk management should consider both traditional and CKD-related factors, while therapeutic interventions, apart from appearing underutilized, still await further confirmation from large trials.