Management of disturbed calcium metabolism in uraemic patients: 1. Use of vitamin D metabolites

Immune Dysfunction in Uremia 2020

Cardiovascular disease and infections are major causes for the high incidence of morbidity and mortality of patients with chronic kidney disease. Both complications are directly or indirectly associated with disturbed functions or altered apoptotic rates of polymorphonuclear leukocytes, monocytes, lymphocytes, and dendritic cells. Normal responses of immune cells can be reduced, leading to infectious diseases or pre-activated/primed, giving rise to inflammation and subsequently to cardiovascular disease. This review summarizes the impact of kidney dysfunction on the immune system. Renal failure results in disturbed renal metabolic activities with reduced renin, erythropoietin, and vitamin D production, which adversely affects the immune system. Decreased kidney function also leads to reduced glomerular filtration and the retention of uremic toxins. A large number of uremic toxins with detrimental effects on immune cells have been identified. Besides small water-soluble and protein-bound compounds originating from the intestinal microbiome, several molecules in the middle molecular range, e.g., immunoglobulin light chains, retinol-binding protein, the neuropeptides Met-enkephalin and neuropeptide Y, endothelin-1, and the adipokines leptin and resistin, adversely affect immune cells. Posttranslational modifications such as carbamoylation, advanced glycation products, and oxidative modifications contribute to uremic toxicity. Furthermore, high-density lipoprotein from uremic patients has an altered protein profile and thereby loses its anti-inflammatory properties.

Immune Dysfunction and Risk of Infection in Chronic Kidney Disease

Cardiovascular disease and infections are directly or indirectly associated with an altered immune response, which leads to a high incidence of morbidity and mortality, and together, they account for up to 70% of all deaths among patients with chronic kidney dysfunction. Impairment of the normal reaction of the innate and adaptive immune systems in chronic kidney disease predisposes patients to an increased risk of infections, virus-associated cancers, and a diminished vaccine response. On the other hand, an abnormal, exaggerated reaction of the immune systems can also occur in this group of patients, resulting in increased production and decreased clearance of proinflammatory cytokines, which can lead to inflammation and its sequelae (eg, atherosclerotic cardiovascular disease). Epigenetically, modifications in hematopoietic stem cells involving a shift from lymphoid to myeloid cell lineage may underlie uremia-associated immunological senescence, which is not reversed by renal replacement therapy, including kidney transplantation. Measures aimed at attenuating the immune abnormalities in chronic kidney disease/end-stage renal disease should be an area of focused research as this could potentially lead to a better understanding and, thus, development of therapies that could reduce the disastrously high death rate in this patient population. The aim of the present article is to review the characteristics, causes, and mechanisms of the immune dysfunction related to chronic kidney disease.

Vitamin D and Anaesthesia

Vitamin D is a vitamin not only associated with calcium-phosphorus metabolism but also affects many organ systems. Because of its effect on the immune system in recent years, it has attracted much attention. Vitamin D deficiency is a clinical condition that can be widely observed in the society. Thus, patients with vitamin D deficiency are often seen in anaesthesia practice. In the absence of vitamin D, prolongation of intensive care unit stay, increase in mortality and morbidity and also association of chronic diseases further increase the importance of vitamin D deficiency. The results obtained from studies have led to the question of whether poor surgical outcome is associated with vitamin D deficiency. We assessed the vitamin D deficiency and its negative consequences for the anaesthesiologist.

Paricalcitol treatment of secondary hyperparathyroidism in hemodialysis patients: a German-Austrian, single-arm, open-label, prospective, noninterventional, observational study

BACKGROUND

Safety and efficacy of paricalcitol in hemodialysis patients with secondary hyperparathyroidism (sHPT) was investigated under routine clinical practice in German and Austrian dialysis centers.

METHODS

Hemodialysis patients with sHPT initiating intravenous paricalcitol were enrolled in this noninterventional study regardless of concomitant sHPT treatment. Prior active vitamin D therapy was discontinued. Clinical laboratory values, including intact parathyroid hormone (iPTH), total serum calcium (Ca), phosphorus (P), Ca × P product, and alkaline phosphatase (AP), were recorded for 6 months following initiation of paricalcitol treatment.

RESULTS

1,313 patients (Austria, n = 280; Germany, n = 1,033) from 169 dialysis centers were enrolled. Most patients (n = 932; 79.1%) had received dialysis for ≥1 year. Median iPTH fell from 518.9 pg/ml [55.0 pmol/l] at baseline to 264.0 pg/ml [28.0 pmol/l] after 6 months (p < 0.0001). After 6 months of treatment, ≥30 and ≥60% reductions in iPTH were observed in 63.0 and 35.9% of patients, respectively. At 6 months, 27.2% of patients achieved iPTH levels between 150 and <300 pg/ml [15.9 and <31.8 pmol/l] compared with 9.7% at baseline. Ca, P, and Ca × P levels remained stable in the majority of patients. AP levels declined from a median of 98 U/l at baseline to 83 U/l (p < 0.0001) at 6 months. Monitoring of adverse events and clinical laboratory assessments identified no unexpected safety signals for paricalcitol.

CONCLUSIONS

Paricalcitol is an effective and well-tolerated treatment option for the control of iPTH levels in hemodialysis patients with sHPT. The results of this study support the results of previous trials under real-time clinical practice conditions in Austria and Germany.

Association of serum intact parathyroid hormone with lower estimated glomerular filtration rate

BACKGROUND AND OBJECTIVES

The prevalence of mineral metabolism abnormalities is almost universal in stage 5 chronic kidney disease (CKD), but the presence of abnormalities in milder CKD is not well characterized.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Data on adults > or =20 yr of age from the National Health and Nutrition Examination Survey 2003-2004 (N = 3949) were analyzed to determine the association between moderate declines in estimated GFR (eGFR), calculated using the Modfication of Diet in Renal Disease formula, and serum intact parathyroid hormone (iPTH) > or = 70 pg/ml.

RESULTS

The geometric mean iPTH level was 39.3 pg/ml. The age-standardized prevalence of elevated iPTH was 8.2%, 19.3%, and 38.3% for participants with eGFR > or = 60, 45 to 59, and 30 to 44 ml/min/1.73 m(2), respectively (P-trend < 0.001). After adjustment for age; race/ethnicity; sex; menopausal status; education; income; cigarette smoking; alcohol consumption; body mass index; hypertension; diabetes mellitus; vitamin D supplement use; total calorie and calcium intake; and serum calcium, phosphorus, and 25-hydroxyvitamin D levels-and compared with their counterparts with an eGFR > or = 60 ml/min/1.73 m(2)-the prevalence ratios of elevated iPTH were 2.30 and 4.69 for participants with an eGFR of 45 to 59 and 30 to 44 ml/min/1.73 m(2), respectively (P-trend < 0.001). Serum phosphorus > or = 4.2 mg/dl and 25-hydroxyvitamin D < 17.6 ng/ml were more common at lower eGFR levels. No association was present between lower eGFR and serum calcium < 9.4 mg/dl.

CONCLUSIONS

This study indicates that elevated iPTH levels are common among patients with moderate CKD.

Alterations in serum phosphate levels predict the long-term response to intravenous calcitriol therapy in dialysis patients with secondary hyperparathyroidism

Calcitriol therapy is a central strategy for the treatment of uremic secondary hyperparathyroidism. Although indiscriminate use of calcitriol may lead to worse outcomes, it is difficult to make a decision to discontinue calcitriol therapy when its parathyroid suppression effect remains unsatisfactory. In this study, intravenous calcitriol was administered to 120 chronic hemodialysis patients. Therapy continued for 48 weeks or until plasma intact parathyroid hormone (iPTH) levels decreased to below 300 pg/ml or until the development of any significant adverse effect. Of the 120 patients, the treatment goal was achieved in 47 patients during the first 4 weeks, in 10 during the next 4 weeks, and in 22 patients thereafter. Logistic regression analysis and stepwise regression analysis revealed that iPTH levels were the only significant predictor of the response to calcitriol therapy at weeks 0 and 4. Besides iPTH, the inorganic phosphate (P) levels were another significant predictor of the ultimate response to calcitriol therapy at week 8. The point of best discrimination for successful treatment was P = 6.0 mg/dl at week 8, or P level at week 8/pretreatment P level = 1.0. In conclusion, the P level at week 8 is a predictor of the response to calcitriol therapy for uremic secondary hyperparathyroidism. Changes in treatment are recommended if patients show unsatisfactory parathyroid suppression with a hyperphosphatemic tendency.

Vitamin D levels and early mortality among incident hemodialysis patients

Vitamin D deficiency is associated with cardiovascular disease, the most common cause of mortality in hemodialysis patients. To investigate the relation between blood levels of 25-hydroxyvitamin D (25D) and 1,25-dihydroxyvitamin D (1,25D) with hemodialysis outcomes, we measured baseline vitamin D levels in a cross-sectional analysis of 825 consecutive patients from within a prospective cohort of incident US hemodialysis patients. Of these patients, 78% were considered vitamin D deficient with 18% considered severely deficient. Calcium, phosphorus, and parathyroid hormone levels correlated poorly with 25D and 1,25D concentrations. To test the association between baseline vitamin D levels and 90-day mortality, we selected the next 175 consecutive participants who died within 90 days and compared them to the 750 patients who survived in a nested case-control analysis. While low vitamin D levels were associated with increased mortality, significant interaction was noted between vitamin D levels, subsequent active vitamin D therapy, and survival. Compared to patients with the highest 25D or 1,25D levels who received therapy, untreated deficient patients were at significantly increased risk for early mortality. Our study shows that among incident hemodialysis patients, vitamin D deficiency is common, correlates poorly with other components of mineral metabolism and is associated with increased early mortality.

Health-economic comparison of paricalcitol, calcitriol and alfacalcidol for the treatment of secondary hyperparathyroidism during haemodialysis

This study evaluated the health-economic consequences of use of intravenous paricalcitol (Zemplar), oral calcitriol or oral and intravenous alfacalcidol for the treatment of patients with secondary hyperparathyroidism, focusing on a third-party payer perspective through inclusion of medication and hospital costs, survival rates and utilities. Cost values were based on German treatment recommendations and prices. Reference values for survival rates and utilities were based on the results of a MEDLINE search. The analysis showed a clear advantage for intravenous paricalcitol with respect to costs, effectiveness and utilities compared with treatment with oral calcitriol or intravenous alfacalcidol. Since the results were very cost sensitive with respect to selected diagnosis-related groups (DRGs) for kidney disease with dialysis, a sensitivity analysis was performed. This demonstrated first-order dominance of intravenous paricalcitol for a wide range of hospitalisation costs. In conclusion, this analysis suggested a clear benefit from the perspective of a third-party payer for intravenous paricalcitol compared with oral calcitriol and intravenous alfacalcidol in the treatment of patients with secondary hyperparathyroidism.

Effects of ACE gene polymorphism on vitamin D therapy according to parathyroid hormone level in patients on hemodialysis

Medical management is still far from optimal in secondary hyperparathyroidism. This may be explained, at least in part, by genetic differences. The aim of this study was to evaluate the association of genetic influences of angiotensinconverting enzyme (ACE) gene polymorphisms with response to vitamin D therapy among patients on hemodialysis (HD). Eighty-two patients (female/male, 34/48; mean age, 47.5+/-15.3 y; HD duration time, 76.6+/-33.2 mo) with endstage renal disease who were on maintenance HD were included in the study. Five-year retrospective demographic, clinical, laboratory, and treatment data (5-y cumulative doses of phosphate-binding drugs and oral and intravenous cumulative doses of active vitamin D) were retrieved from patients' hospital records. ACE gene polymorphisms of patients were documented and were used to group patients as follows: The insertion/deletion polymorphism group (I/D) consisted of (1) group non-DD (n=43), who had the DI or II allele, and (2) group DD (n=39), who had the DD allele. Patients with the DD allele (group DD) of ACE gene polymorphism had (1) significantly elevated mean 5-y intact parathyroid hormone levels when compared with the non-DD group (P=.009), and (2) significantly elevated oral and intravenous 5-y cumulative doses of vitamin D. Oral and intravenous 5-y cumulative doses of vitamin D used in group DD patients were significantly higher than those in group I patients (P=.038 and P=.037, respectively). Knowledge of genetic differences among patients on HD may be useful to the clinician in planning treatment strategy. ACE gene polymorphism may have an effect on hyperparathyroidism, as is seen in patients on HD. Patients from this group who have resistant hyperparathyroidism may be candidates for ACE inhibitor therapy.

Viewpoint: How Do Calcimimetics Fit Into the Management of Parathyroid Hormone, Calcium, and Phosphate Disturbances in Dialysis Patients?

As suggested by its American brand name (Sensipar), the calcimimetic cinacalcet sensitizes the parathyroid cells to the extracellular calcium signal, suppressing parathyroid hormone (PTH) release and synthesis and preventing parathyroid cell proliferation. This primary PTH suppression decreases the release of calcium and phosphate from bone without increasing intestinal absorption of calcium and phosphate. Therefore cinacalcet decreases the risk of hypercalcemia and hyperphosphatemia in contrast to 1alpha-OH vitamin D derivatives. Compared with calcium-containing oral phosphate binder (OPB), it increases the risk of hypocalcemia and may decrease the PTH-mediated phosphaturia in predialysis patients. This justifies its combined use with calcium-containing OPB in order to prevent hypocalcemia and enhance the hypophosphatemic effect of the latter, while improving PTH suppression. The National Kidney Foundation (NKF) Kidney Disease Outcomes Quality Initiative (K/DOQI) has recommended restriction of supplemental elemental calcium to 1.5 g/day, a recommendation that we believe should be revised. No pathophysiologic or randomized trial data have yet evidenced the absolute necessity for systematically using 1alpha-OH vitamin D derivatives and noncalcium-containing OPB rather than higher doses of calcium-containing OPB alone in uremic patients without vitamin D insufficiency. In patients with hyperparathyroidism as severe as in the "Treat to Goal Study," the Durham study showed that a calcium carbonate dose more than three times the K/DOQI limit could decrease PTH into the recommended range, with the advantage of a lower calcium-phosphate product compared with the combination of calcitriol and noncalcium OPB. Besides the efficient PTH suppression associated with lower calcium-phosphate product and a good gastrointestinal tolerance, long-term data suggest that cinacalcet may decrease the risk of parathyroidectomy and fracture, while high bone turnover lesions are improved. However, no long-term data on bone mineral density and cardiovascular calcification and complications are yet available. Such studies, along with those comparing cinacalcet and 1alpha-OH vitamin D-based approaches to hyperparathyroidism, are needed.

Immune dysfunction in uremia

Kidney dysfunction leads to disturbed renal metabolic activities and to impaired glomerular filtration, resulting in the retention of toxic solutes affecting all organs of the body. Cardiovascular disease (CVD) and infections are the main causes for the increased occurrence of morbidity and mortality among patients with chronic kidney disease (CKD). Both complications are directly or indirectly linked to a compromised immune defense. The specific coordinated roles of polymorphonuclear leukocytes (PMNLs), monocytes/macrophages, lymphocytes and antigen-presenting cells (APCs) in maintaining an efficient immune response are affected. Their normal response can be impaired, giving rise to infectious diseases or pre-activated/primed, leading to inflammation and consequently to CVD. Whereas the coordinated removal via apoptosis of activated immune cells is crucial for the resolution of inflammation, inappropriately high apoptotic rates lead to a diminished immune response. In uremia, the balance between pro- and anti-inflammatory and between pro- and anti-apoptotic factors is disturbed. This review summarizes the interrelated parameters interfering with the immune response in uremia, with a special focus on the non-specific immune response and the role of uremic toxins.