PTH-receptors regulate norepinephrine release in human heart and kidney

Cardiovascular autonomic nervous system dysfunction in chronic kidney disease and end-stage kidney disease: disruption of the complementary forces

PURPOSE OF REVIEW

Several nontraditional risk factors have been the focus of research in an attempt to understand the disproportionately high cardiovascular morbidity and mortality in chronic kidney disease (CKD) and end-stage kidney disease (ESKD) populations. One such category of risk factors is cardiovascular autonomic dysfunction. Its true prevalence in the CKD/ESKD population is unknown but existing evidence suggests it is common. Due to lack of standardized diagnostic and treatment options, this condition remains undiagnosed and untreated in many patients. In this review, we discuss current evidence pointing toward the role of autonomic nervous system (ANS) dysfunction in CKD, building off of crucial historical evidence and thereby highlighting the areas in need for future research interest.

RECENT FINDINGS

There are several key mediators and pathways leading to cardiovascular autonomic dysfunction in CKD and ESKD. We review studies exploring the mechanisms involved and discuss the current measurement tools and indices to evaluate the ANS and their pitfalls. There is a strong line of evidence establishing the temporal sequence of worsening autonomic function and kidney function and vice versa. Evidence linking ANS dysfunction and arrhythmia, sudden cardiac death, intradialytic hypotension, heart failure and hypertension are discussed.

SUMMARY

There is a need for early recognition and referral of CKD and ESKD patients suspected of cardiovascular ANS dysfunction to prevent the downstream effects described in this review.There are many unknowns in this area and a clear need for further research.

Neurohumoral Control of Sinoatrial Node Activity and Heart Rate: Insight From Experimental Models and Findings From Humans

The sinoatrial node is perhaps one of the most important tissues in the entire body: it is the natural pacemaker of the heart, making it responsible for initiating each-and-every normal heartbeat. As such, its activity is heavily controlled, allowing heart rate to rapidly adapt to changes in physiological demand. Control of sinoatrial node activity, however, is complex, occurring through the autonomic nervous system and various circulating and locally released factors. In this review we discuss the coupled-clock pacemaker system and how its manipulation by neurohumoral signaling alters heart rate, considering the multitude of canonical and non-canonical agents that are known to modulate sinoatrial node activity. For each, we discuss the principal receptors involved and known intracellular signaling and protein targets, highlighting gaps in our knowledge and understanding from experimental models and human studies that represent areas for future research.

Should We Consider the Cardiovascular System While Evaluating CKD-MBD?

Cardiovascular (CV) disease is highly prevalent in the population with chronic kidney disease (CKD), where the risk of CV death in early stages far exceeds the risk of progression to dialysis. The presence of chronic kidney disease-mineral and bone disorder (CKD-MBD) has shown a strong correlation with CV events and mortality. As a non-atheromatous process, it could be partially explained why standard CV disease-modifying drugs do not provide such an impact on CV mortality in CKD as observed in the general population. We summarize the potential association of CV comorbidities with the older (parathyroid hormone, phosphate) and newer (FGF23, Klotho, sclerostin) CKD-MBD biomarkers.

Severe hypertension-An infantile feature of Jansen metaphyseal chondrodysplasia?

Jansen metaphyseal chondrodysplasia (JMC) is a rare autosomal dominant skeletal dysplasia caused by gain-of-function mutations in the parathyroid hormone receptor 1 gene, PTH1R. We report on a patient presenting in the neonatal period with clinical signs of JMC in addition to severe hypertension. A pathogenic mutation in PTH1R was demonstrated, but investigations for hypertension yielded normal results. Hypertension has not been previously associated with JMC. Given aberration of the parathyroid hormone (PTH)/parathyroid-related protein pathway is the underlying pathogenic mechanism attributed to JMC, and also given evidence that hyperparathyroidism plays an important role in blood pressure homeostasis, we propose that hypertension is a hitherto unrecognized feature of JMC.

Parathyroid Hormone and Cardiac Electrophysiology: A Review

Calcium has long been known to be essential to cardiac electrical activity. Parathyroid hormone (PTH) is the main regulator of serum calcium and is central to calcium homeostasis. Although there are significant data linking parathyroid disease states with changes in cardiac electrophysiology, most data have focused on how PTH modulates serum calcium to produce these effects. Close scrutiny of early literature demonstrates that the relationship between PTH and electrocardiographic changes is not straightforward, and numerous studies have linked PTH to arrhythmia. Basic science research has demonstrated that there is a basis for a direct role of PTH on cardiac electrophysiology outside of its effect on serum calcium. Later studies in secondary hyperparathyroidism indicate that PTH disturbances could have important implications for broad categories of patients with cardiovascular disease. The current review summarizes the existing literature on PTH and electrophysiology based on clinical and basic science studies of various parathyroid states, providing directions for future study.

Parathyroidectomy improves cardiovascular risk factors in normocalcemic and hypercalcemic primary hyperparathyroidism

Background

Parathyroidectomy has ameliorated cardiovascular risk factors in patients with hypercalcemic primary hyperparathyroidism (PHPT), but the effect of parathyroidectomy on normocalcemic PHPT is not exactly known. This case-controlled study aimed to investigate the effect of parathyroidectomy on cardiovascular risk factors in patients with normocalcemic and hypercalcemic PHPT.

Methods

Subjects with normocalcemic PHPT (n = 35), age- and sex-matched hypercalcemic PHPT (n = 60) and age- and sex-matched control (n = 60) were included. Cardiometabolic disorders were investigated with traditional cardiometabolic risk factors and the Framingham cardiovascular risk score (CRS) before and 6 months after parathyroidectomy.

Results

Diabetes, dyslipidemia, hypertension, obesity, insulin resistance, osteoporosis, having fractures were similarly increased in the hypercalcemic and normocalcemic PHPT groups (p > 0.05) compared with the controls (p < 0.05). Blood pressures, glucose metabolism (glucose, insulin, HOMA-IR) and lipid profiles were similarly increased in the PHPT groups (p > 0.05) compared with the controls (p < 0.05). After parathyroidectomy, blood pressures, serum total cholesterol, and HOMA-IR were decreased in both PHPT groups (p < 0.05). CRS was lower in the controls (5.74 ± 3.24, p < 0.05). After parathyroidectomy, CRS was decreased in the normocalcemic (11.98 ± 10.11 vs. 7.37 ± 4.48) and hypercalcemic (14.62 ± 11.06 vs. 8.05 ± 7.72) PHPT groups. Increased blood pressures were independent predictors of serum iPTH.

Conclusion

The normocalcemic and hypercalcemic PHPT groups had similarly increased cardiovascular risk factors, even independently of serum calcium. Parathyroidectomy ameliorated the increased cardiovascular risk factors in both normocalcemic and hypercalcemic PHPT.

Effect of general anesthesia and intubation on parathyroid levels in normal patients and those with hyperparathyroidism

BACKGROUND

Induction of general anesthesia and endotracheal intubation may precipitate parathyroid hormone (PTH) elevation in patients with primary hyperparathyroidism (HPT). The purposes of this study were to revisit this observation and to study its impact in healthy patients.

METHODS

Patients with primary HPT who underwent parathyroidectomy were retrospectively studied. The PTH was sampled and compared: before, immediately after general anesthesia and endotracheal intubation, and 15 minutes after parathyroidectomy. Healthy adults who underwent elective operations were prospectively studied. The PTH was sampled before general anesthesia and endotracheal intubation, immediately after, and 15 minutes later.

RESULTS

Thirty-one patients, aged 28-89 years (mean 60.1 ± 13 years), were retrospectively studied. The PTH was significantly elevated after general anesthesia and endotracheal intubation (P = .014). Fifty patients, aged 21-86 years (mean 54 ± 15 years), were prospectively studied. The PTH elevation after general anesthesia and endotracheal intubation was not significant.

CONCLUSION

General anesthesia and endotracheal intubation causes an immediate, steep, and significant PTH elevation in patients with primary HPT but only a minor change in healthy adults. The difference may be attributed to an impaired adrenergic response in patients with primary HPT.

Parathyroid hormone is related to QT interval independent of serum calcium in patients with coronary artery disease

BACKGROUND

Elevated serum parathyroid hormone (PTH) is associated with increased risk of cardiovascular death, including sudden cardiac death, in patients with and without parathyroid disease. In small studies, PTH levels have been associated with changes in cardiac conduction and repolarization. Changes in the corrected QT interval (QTc) in particular are thought to be mediated by the effect of PTH on serum calcium. There is limited evidence to suggest PTH may affect cardiac physiology independent of its effects on serum calcium, but there is even less data linking PTH to changes in electrical conduction and repolarization independent of serum calcium.

METHODS

ECG data were examined from the PULSE database-an observational cohort study designed to examine depression after acute coronary syndromes (ACS) at a single, urban American medical center. In all, 407 patients had PTH and ECG data for analysis.

RESULTS

The QTc was longer in patients with elevated PTH levels compared with those without elevated PTH levels (451 ± 38.6 ms vs. 435 ± 29.8 ms; p < .001). The difference remained statistically significant after controlling for calcium, vitamin D, and estimated glomerular filtration rate (p = .007). Inclusion of left ventricular ejection fraction in the model attenuated the association (p = .054), suggesting that this finding may be partly driven by changes in cardiac structure.

CONCLUSIONS

In one of the largest series to examine PTH, calcium, and QT changes, we found that elevated PTH is associated with longer corrected QT interval independent of serum calcium concentration in ACS survivors.

Human presynaptic receptors

Presynaptic receptors are sites at which transmitters, locally formed mediators or hormones inhibit or facilitate the release of a given transmitter from its axon terminals. The interest in the identification of presynaptic receptors has faded in recent years and it may therefore be justified to give an overview of their occurrence in the autonomic and central nervous system; this review will focus on presynaptic receptors in human tissues. Autoreceptors are presynaptic receptors at which a given transmitter restrains its further release, though in some instances may also increase its release. Inhibitory autoreceptors represent a typical example of a negative feedback; they are tonically activated by the respective endogenous transmitter and/or are constitutively active. Autoreceptors also play a role under pathophysiological conditions, e.g. by limiting the massive noradrenaline release occurring during congestive heart failure. They can be used for therapeutic purposes; e.g., the α₂-adrenoceptor antagonist mirtazapine is used as an antidepressant and the inverse histamine H₃ receptor agonist pitolisant has been marketed as a new drug for the treatment of narcolepsy in 2016. Heteroreceptors are presynaptic receptors at which transmitters from adjacent neurons, locally formed mediators (e.g. endocannabinoids) or hormones (e.g. adrenaline) can inhibit or facilitate transmitter release; they may be subject to an endogenous tone. The constipating effect of the sympathetic nervous system or of the antihypertensive drug clonidine is related to the activation of inhibitory α₂-adrenoceptors on postganglionic parasympathetic neurons. Part of the stimulating effect of adrenaline on the sympathetic nervous system during stress is related to its facilitatory effect on noradrenaline release via β₂-adrenoceptors.

Bovine parathyroid hormone enhances osteoclast bone resorption by modulating V-ATPase through PTH1R

The vacuolar-type H⁺ adenosine triphosphatase (V-ATPase) plays an important role in cellular acidification and bone resorption by osteoclasts. However, the direct effect of bovine parathyroid hormone (bPTH) on V-ATPase has not yet been elucidated. The aim of the present study was to assess the effects of bPTH on V-ATPase and osteoclasts. Osteoclasts from bone marrow (BM)-derived monocytes of C57BL/6 mice were cultured with or without bPTH. The mRNA and protein expression levels of the V-ATPase a₃-subunit and d₂-subunit (by RT-qPCR and western blot analysis), V-ATPase activity (using the V type ATPase Activity Assay kit) and the bone resorption function of osteoclasts (by bone resorption assay) were examined following treatment with various concentrations of bPTH (0.1, 1.0, 10 and 100 ng/ml) alone or with bPTH and its inhibitor, bafilomycin A₁. Furthermore, the expression of parathyroid hormone (PTH) receptors in osteoclasts was also detected. The results revealed that the mRNA and protein expression levels of V-ATPase a₃-subunit and d₂-subunit increased in a dose-dependent manner, paralleling the level of bPTH present. In addition, an increase in the concentration of bPTH was accompanied by the increased resorption capability of osteoclasts, whereas bone resorption was inhibited in the presence of bafilomycin A₁. In addition, we confirmed the existence of parathyroid hormone 1 receptor (PTH1R) in osteoclasts using three different methods (RT-qPCR, western blot analysis and immunofluorescence staining). We found that bPTH enhanced the bone resorption capability of osteoclasts by modulating the expression of V-ATPase subunits, intracellular acidification and V-ATPase activity. Thus, we propose that PTH has a direct effect on osteoblasts and osteoclasts, and that this effect is mediated through PTH1R, thus contributing to bone remodeling.

Serum parathyroid hormone and 25-hydroxyvitamin D concentrations and risk of incident heart failure: the Multi-Ethnic Study of Atherosclerosis

Background

Heart failure (HF) is common and is associated with high mortality. We aimed to determine associations of serum parathyroid hormone (PTH) and 25‐hydroxyvitamin D (25[OH]D) with incident HF and left ventricular mass.

Methods and Results

Among 6459 participants in the community‐based Multi‐Ethnic Study of Atherosclerosis, all of whom were free of prevalent clinical cardiovascular disease, we measured serum concentrations of PTH and 25(OH)D at the baseline examination. In longitudinal analyses, we tested associations of PTH and 25(OH)D with incident HF events, adjudicated by a panel of physicians. In cross‐sectional analyses of a subset of 4763 participants, we tested associations of PTH and 25(OH)D with left ventricular mass, measured by cardiac magnetic resonance imaging at baseline. Multivariable Cox proportional hazard and linear regression models were adjusted for demographics, physical examination measures, comorbidity, kidney function, and other mineral metabolism markers. Mean age was 62 years and 53% of participants were female. There were 180 incident HF events over a median (interquartile range) follow‐up time of 8.46 (7.67 to 8.63) years. Compared with participants with PTH <65 pg/mL, PTH ≥65 pg/mL was associated with a 50% greater risk of incident HF (95% CI: 3% to 210%) and a 5.3 g higher left ventricular mass (95% CI: 2.6, 7.9 g). In contrast, there was no association of 25(OH)D with risk of incident HF or elevated left ventricular mass.

Conclusions

In a racially/ethnically diverse population without prevalent cardiovascular disease, higher serum PTH concentration was associated with increased left ventricular mass and increased risk of incident HF. Further studies should be pursued to determine whether PTH excess may be a modifiable risk factor for HF.

The effect of renin-angiotensin system inhibitors on intact parathyroid hormone levels in peritoneal dialysis patients

HYPOTHESIS/INTRODUCTION

The objective of this article is to investigate the effect of renin-angiotensin system inhibitors (RASIs) on intact parathyroid hormone (iPTH) levels in continuous ambulatory peritoneal dialysis (CAPD) patients.

MATERIALS AND METHODS

All patients were divided into RASI-treated and non-treated groups. The relationships between the iPTH levels in CAPD patients and the clinical parameters and medication use were analyzed via linear regression.

RESULTS

A total of 149 CAPD patients were included in this study. The average iPTH level of the entire group was 189.4 pg/ml (range, 102.8-373.4 pg/ml). There were 79 (53.0%) and 70 (47.0%) cases in the RASI-treated and non-treated groups, respectively, with average iPTH levels of 139.0 pg/ml (range, 91.6-258.4 pg/ml) and 253.0 pg/ml (range, 134.3-467.2 pg/ml), respectively; this difference was statistically significant (p = 0.001). Multilinear regression analysis showed that age, dialysis vintage, serum phosphatemia, ALP, Hb and RASI use were independent factors that were associated with iPTH level.

CONCLUSION

RASI use may be associated with a lower iPTH level in CAPD patients, although the underlying mechanism requires further study.

PTH: Potential role in management of heart failure

Biomarkers play an important role for the diagnosis and prognosis of heart failure (HF), a disease with high morbidity and mortality as well as a huge impact on healthcare budgets. Parathyroid hormone (PTH) is a major systemic calcium-regulating hormone and an important regulator of bone and mineral homeostasis. PTH testing is important for differential diagnosis of calcemia related disorders and for the management of patients with chronic kidney disease. As secondary hyperparathyroidism has been evidenced in HF patients, PTH testing might be relevant in HF patients for risk stratification and more personalized selection of treatment.

Parathyroid hormone and heart rate variability in haemodialysis patients

BACKGROUND

Depressed heart rate variability (HRV) reflects abnormal cardiac autonomic regulation and has been linked with increased cardiovascular risk and sudden cardiac death. High parathyroid hormone (PTH) levels have also been associated with an increased risk of sudden cardiac death in haemodialysis (HD) patients. Our aim was to investigate the association between HRV indices and PTH in HD patients.

METHODS

Continuous intradialytic electrocardiograms were repeated in stable HD patients 5 times every 2 weeks. The absolute values of high-frequency (HF) and low-frequency (LF) HRV components were calculated every 5 min and averaged during the first and last hour of each recording (distinguished by subscripts F and L, respectively). Pre-HD PTH, corrected calcium, and phosphate levels were measured before the first recording.

RESULTS

Data were analysed for 75 subjects aged 60 ± 15, 32% females, 37% diabetics. Baseline biochemical parameters were PTH 44 ± 32 pmol/l, calcium 2.3 ± 0.2 mmol/l, and phosphate 1.6 ± 0.4 mmol/l. All HRV indices showed intra-subject stability over the 5 recordings. Diabetics had lower LFL compared to non-diabetics (-5.5 ± 0.5 vs. -5.2 ± 0.5 after logarithmic transformation, p = 0.012). In non-diabetics, PTH correlated negatively with LFL and HFL (LFL r = -0.340, p = 0.020, HFL r = -0.325, p = 0.026) and phosphate correlated negatively with LFF (r = -0.427, p = 0.003), HFF (r = -0.442, p = 0.002) and HFL (r = -0.307, p = 0.040).

CONCLUSION

High PTH and phosphate are associated with depressed HRV in non-diabetic dialysis patients. Prospective studies are needed to evaluate the role of mineral abnormalities in autonomic imbalance and arrhythmic risk in HD patients.

Parathyroid hormone and cardiovascular disease events: A systematic review and meta-analysis of prospective studies

BACKGROUND

Parathyroid hormone (PTH) excess might play a role in cardiovascular health. We therefore conducted a systematic review and meta-analysis to evaluate the association between PTH and cardiovascular disease (CVD) events, and intermediate outcomes.

METHODS

We conducted a systematic and comprehensive database search using MEDLINE and Embase between 1947 and October 2012. We included English-language prospective studies that reported risk estimates for PTH and CVD events, and intermediate outcomes. The characteristics of study populations, exposure, and outcomes of total CVD events, fatal and non-fatal CVD events were reported, and a quality assessment was conducted. Results were extracted for the highest versus lowest PTH concentrations, and meta-analyses were carried out using random effects models.

RESULTS

The systematic literature search yielded 5770 articles, and 15 studies were included. Study duration ranged between 2 and 14 years. All studies were performed primarily in whites with a mean age between 55 and 75 years. The meta-analyses included 12 studies, of which 10 investigated total CVD events; 7, fatal CVD events; and 3, non-fatal CVD events. PTH excess indicated an increased risk for total CVD events: pooled HR (95% CI), 1.45 (1.24-1.71). The results for fatal CVD events and non-fatal CVD events were: HR 1.50 (1.18-1.91) and HR 1.48 (1.14-1.92). Heterogeneity was moderately present; however, sensitivity analyses for follow-up duration, prior CVD, or PTH as dichotomous values showed similar results.

CONCLUSIONS

The meta-analysis indicates that higher PTH concentrations are associated with increased risk of CVD events.

Cardiovascular diseases in older patients with osteoporotic hip fracture: prevalence, disturbances in mineral and bone metabolism, and bidirectional links

BACKGROUND

Considerable controversy exists regarding the contribution of mineral/bone metabolism abnormalities to the association between cardiovascular diseases (CVDs) and osteoporotic fractures.

AIMS AND METHODS

To determine the relationships between mineral/bone metabolism biomarkers and CVD in 746 older patients with hip fracture, clinical data were recorded and serum concentrations of parathyroid hormone (PTH), 25-hydroxyvitamin D, calcium, phosphate, magnesium, troponin I, parameters of bone turnover, and renal, liver, and thyroid functions were measured.

RESULTS

CVDs were diagnosed in 472 (63.3%) patients. Vitamin D deficiency was similarly prevalent in patients with (78.0%) and without (82.1%) CVD. The CVD group had significantly higher mean PTH concentrations (7.6 vs 6.0 pmol/L, P < 0.001), a higher prevalence of secondary hyperparathyroidism (SPTH) (PTH > 6.8 pmol/L, 43.0% vs 23.3%, P < 0.001), and excess bone resorption (urinary deoxypyridinoline corrected by creatinine [DPD/Cr] > 7.5 nmol/μmol, 87.9% vs 74.8%, P < 0.001). In multivariate regression analysis, SHPT (odds ratio [OR] 2.6, P = 0.007) and high DPD/Cr (OR 2.8, P = 0.016) were independent indictors of CVD. Compared to those with both PTH and DPD/Cr in the normal range, multivariate-adjusted ORs for the presence of CVD were 17.3 (P = 0.004) in subjects with SHPT and 9.7 (P < 0.001) in patients with high DPD/Cr. CVD was an independent predicator of SHPT (OR 2.8, P = 0.007) and excess DPD/Cr (OR 2.5, P = 0.031). CVD was predictive of postoperative myocardial injury, while SHPT was also an independent predictor of prolonged hospital stay and in-hospital death.

CONCLUSION

SHPT and excess bone resorption are independent pathophysiological mediators underlying the bidirectional associations between CVD and hip fracture, and therefore are important diagnostic and therapeutic targets.

The vitamin D receptor activator paricalcitol prevents fibrosis and diastolic dysfunction in a murine model of pressure overload

BACKGROUND

Activation of the vitamin D-vitamin D receptor (VDR) axis has been shown to reduce blood pressure and left ventricular (LV) hypertrophy. Besides cardiac hypertrophy, cardiac fibrosis is a key element of adverse cardiac remodeling. We hypothesized that activation of the VDR by paricalcitol would prevent fibrosis and LV diastolic dysfunction in an established murine model of cardiac remodeling.

METHODS

Mice were subjected to transverse aortic constriction (TAC) to induce cardiac hypertrophy. Mice were treated with paricalcitol, losartan, or a combination of both for a period of four consecutive weeks.

RESULTS

The fixed aortic constriction caused similar increase in blood pressure, both in untreated and paricalcitol- or losartan-treated mice. TAC significantly increased LV weight compared to sham operated animals (10.2±0.7 vs. 6.9±0.3 mg/mm, p<0.05). Administration of either paricalcitol (10.5±0.7), losartan (10.8±0.4), or a combination of both (9.2±0.6) did not reduce LV weight. Fibrosis was significantly increased in mice undergoing TAC (5.9±1.0 vs. sham 2.4±0.8%, p<0.05). Treatment with losartan and paricalcitol reduced fibrosis (paricalcitol 1.6±0.3% and losartan 2.9±0.6%, both p<0.05 vs. TAC). This reduction in fibrosis in paricalcitol treated mice was associated with improved indices of LV contraction and relaxation, e.g. dPdtmax and dPdtmin and lower LV end diastolic pressure, and relaxation constant Tau. Also, treatment with paricalcitol and losartan reduced mRNA expression of ANP, fibronectin, collagen III and TIMP-1.

DISCUSSION

Treatment with the selective VDR activator paricalcitol reduces myocardial fibrosis and preserves diastolic LV function due to pressure overload in a mouse model. This is associated with a reduced percentage of fibrosis and a decreased expression of ANP and several other tissue markers.

Secondary hyperparathyroidism: benign bystander or culpable contributor to adverse health outcomes?

Elevation in serum parathyroid hormone (PTH) often accompanies vitamin D deficiency and renal impairment. PTH elevation in renal failure is viewed as an unfavorable development. Evidence is increasing that PTH elevation may be associated with increased morbidity and mortality. In many instances these PTH effects appear to be independent of vitamin D status. PTH mediates its effects through the ubiquitous type 1 PTH/PTH-related peptide receptor, which is notably present in the cardiovascular system. Increased PTH may promote cardiovascular disease through diminished cardiac contractility, enhanced coronary risk, and cardiac valvular and vascular calcification. High PTH levels appear to be linked to the metabolic syndrome and are aligned with hyperlipidemia, decreased insulin sensitivity, and, perhaps, decreased insulin secretion. Increased PTH also is associated with neuroendocrine activation, increased sympathetic activity, and endothelial stress. The relation between PTH and vitamin D is complex and may show significant threshold variations, especially when calcium intake, age, and race are considered. Moreover, evidence is increasing that fragments of PTH may not only be hormonally active but also may have opposing effects to PTH. Despite these caveats, PTH values provide useful clinical diagnostic and prognostic information in monitoring many chronic ailments such as heart and renal failure and multiple sclerosis.