Furosemide Increases the Risk of Hyperparathyroidism in Chronic Kidney Disease

NHE3 in the thick ascending limb is required for sustained but not acute furosemide-induced urinary acidification

The Na⁺/H⁺ exchanger isoform 3 (NHE3) facilitates Na⁺ reabsorption and H⁺ secretion by the kidneys. Despite stronger NHE3 abundance in the thick ascending limb (TAL) compared to the S1 and S2 segments of the proximal tubule, the role of NHE3 in the TAL is poorly understood. To investigate the role of NHE3 in the TAL, we generated and phenotyped TAL-specific NHE3 knockout mice (NHE3^TAL-KO). Compared to control mice, NHE3^TAL-KO mice did not show significant differences in body weight, blood pH or plasma Na⁺, K⁺ or Cl^- levels. Fluid intake trended to be higher and urine osmolality was significantly lower in NHE3^TAL-KO mice. Despite a similar GFR, NHE3^TAL-KO mice had a greater urinary K⁺/creatinine ratio. One proposed role of NHE3 relates to furosemide-induced urinary acidification. Acute bolus treatment with furosemide under anesthesia did not result in differences in the dose dependence of urinary flow rate, Cl^- excretion or maximal urinary acidification between genotypes; however, in contrast to control mice, urinary pH returned immediately towards baseline levels in NHE3^TAL-KO mice. Chronic furosemide treatment reduced urine osmolality similarly in both genotypes but metabolic alkalosis, hypokalemia and calciuresis were absent in NHE3^TAL-KO mice. Compared to vehicle, chronic furosemide treatment in control mice resulted in greater NKCC2 and lower Npt2a abundances, effects that were absent in NHE3^TAL-KO mice. In summary, NHE3 in the TAL plays a role for the sustained acidification effect of furosemide. Consistent with this, long-term treatment with furosemide did not result in metabolic alkalosis in NHE3^TAL-KO mice.

Vitamin D Effects on Bone Homeostasis and Cardiovascular System in Patients with Chronic Kidney Disease and Renal Transplant Recipients

Poor vitamin D status is common in patients with impaired renal function and represents one main component of the complex scenario of chronic kidney disease-mineral and bone disorder (CKD-MBD). Therapeutic and dietary efforts to limit the consequences of uremia-associated vitamin D deficiency are a current hot topic for researchers and clinicians in the nephrology area. Evidence indicates that the low levels of vitamin D in patients with CKD stage above 4 (GFR < 15 mL/min) have a multifactorial origin, mainly related to uremic malnutrition, namely impaired gastrointestinal absorption, dietary restrictions (low-protein and low-phosphate diets), and proteinuria. This condition is further worsened by the compromised response of CKD patients to high-dose cholecalciferol supplementation due to the defective activation of renal hydroxylation of vitamin D. Currently, the literature lacks large and interventional studies on the so-called non-calcemic activities of vitamin D and, above all, the modulation of renal and cardiovascular functions and immune response. Here, we review the current state of the art of the benefits of supplementation with native vitamin D in various clinical settings of nephrological interest: CKD, dialysis, and renal transplant, with a special focus on the effects on bone homeostasis and cardiovascular outcomes.

Effects of diuretics furosemide and hydrochlorothiazide on CKD-MBD: A prospective randomized study

Although diuretics are often prescribed to control fluid overload, they can change Chronic kidney disease-mineral and bone disorder (CKD-MBD) parameters. Previous studies have shown an association between diuretic prescription and changes in both calciuria and parathormone levels. However, the causal relationship could not be confirmed. In addition, the effects of diuretics on bone mineral density and turnover markers are yet to be established. To evaluate the effects of diuretics on CKD-MBD, we have performed a prospective randomized trial comparing hydrochlorothiazide with furosemide in a stage 3CKD population followed for 1 year. Furosemide increased bone remodeling and parathormone levels, whereas hydrochlorothiazide attenuated parathyroid hormone rise and decreased bone turnover markers.

•

Diuretics may change parathormone (PTH), although a randomized trial was missing.

•

Patients with CKD were randomized to either Furosemide or Hydrochlorothiazide.

•

Furosemide increased PTH levels, CTx and P1NP.

•

Hydrochlorothiazide attenuated PTH rise and decreased CTx and P1NP.

Calcitriol and FGF-23, but neither PTH nor sclerostin, are associated with calciuria in CKD

PURPOSE

The recent observation that urinary calcium excretion (UCE) drops considerably with CKD and that this effect may occur beyond compensation for reduced intestinal calcium absorption suggests that CKD per se is a state of sustained positive calcium balance, a mechanism likely to contribute to vascular calcification and CVD in CKD. However, the determinants of UCE reduction in CKD are not well understood and there is a lack of clinical studies, particularly in the CKD population. Therefore, in this study, we aimed to evaluate variables associated with UCE in a CKD cohort.

METHODS

Baseline data on 356 participants of the Progredir Study, Sao Paulo, Brazil, essentially composed of CKD G3a-G4, were analyzed according to UCE (24 h urine collection).

RESULTS

Median 24 h UCE was 38 mg/day (IQR 21-68 mg/day) and 0.48 mg/kg/day (IQR 0.28-0.82 mg/kg/day). In univariate analysis, UCE was inversely related to age, phosphorus, 1-84 PTH, FGF-23 and sclerostin, and positively associated with eGFR, DBP, 1,25(OH)_2-vitamin D, calcium, bicarbonate, total calorie intake and spironolactone use. After adjustments for age, sex and eGFR, only 1,25(OH)₂-vitamin D, calcium, FGF-23, bicarbonate and total calorie intake remained associated with it, but not PTH nor sclerostin. Lastly, in a multivariable model, eGFR, serum 1,25(OH)₂-vitamin D, calcium, and FGF-23 remained associated with UCE. Similar results were observed when calcium fractional excretion was used instead of UCE, with eGFR, 1-25-vitamin D and FGF-23 remaining as independent associations.

CONCLUSION

Our results showed that CKD is associated with very low levels of UCE and that 1,25(OH)₂-vitamin D, serum calcium and FGF-23 were independently associated with UCE in this population, raising the question whether these factors are modulators of the tubular handling of calcium in CKD.

Association of Continuation of Loop Diuretics at Hemodialysis Initiation with Clinical Outcomes

BACKGROUND AND OBJECTIVES

Loop diuretics are commonly used to manage nondialysis-dependent CKD. Despite benefits of augmented urine output, loop diuretics are often discontinued after dialysis initiation. Here, we assessed the association of the early decision to continue loop diuretics at hemodialysis start with clinical outcomes during the first year of dialysis.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We considered all patients on in-center hemodialysis at a large dialysis organization (2006-2013) with Medicare Part A and D benefits who had an active supply of a loop diuretic at dialysis initiation (n=11,297). Active therapy was determined on the basis of whether loop diuretic prescription was refilled after dialysis initiation and within 30 days of exhaustion of prior supply. Patients were followed under an intention-to-treat paradigm for up to 12 months for rates of death, hospitalization, and intradialytic hypotension and mean monthly values of interdialytic weight gain, serum potassium, predialysis systolic BP, and ultrafiltration rates.

RESULTS

We identified 5219 patients who refilled a loop diuretic and 6078 eligible controls who did not. After adjustments for patient mix and clinical differences, continuation of loop diuretics was associated with lower hospitalization (adjusted incidence rate ratio, 0.93; 95% confidence interval, 0.89 to 0.98) and intradialytic hypotension (adjusted incidence rate ratio, 0.95; 95% confidence interval, 0.92 to 0.99) rates, no difference in death rate (adjusted hazard ratio, 0.92; 95% confidence interval, 0.84 to 1.01), and lower interdialytic weight gain (P=0.03).

CONCLUSIONS

Continuation of loop diuretics after hemodialysis initiation was associated with lower rates of hospitalization and intradialytic hypotension as well as lower interdialytic weight gain, but there was no difference in mortality over the first year of dialysis.

CKD-MBD: from the Pathogenesis to the Identification and Development of Potential Novel Therapeutic Targets

PURPOSE OF REVIEW

Although we have seen tremendous advances in the comprehension of CKD-MBD pathophysiology during the last few years, this was not accompanied by a significant change in mortality rate and quality of life. This review will address the traditional and updated pathophysiology of CKD-MBD along with the therapeutic limitations that affect CKD-MBD and proposed alternative treatment targets.

RECENT FINDINGS

An innovative concept brings the osteocyte to the center of CKD-MBD pathophysiology, in contrast to the traditional view of the skeleton as a target organ for disturbances in calcium, phosphate, parathyroid hormone, and vitamin D. Osteocytes, through the synthesis of FGF-23, sclerostin, among others, are able to interact with other organs, making bone an endocrine organ. Thus, osteocyte dysregulation might be an early event during the course of CKD. This review will revisit general concepts on the pathophysiology of CKD-MBD and discuss new perspectives for its treatment.

Successful Reversal of Furosemide-Induced Secondary Hyperparathyroidism With Cinacalcet

Secondary hyperparathyroidism (SHPT) is a rare complication of furosemide therapy that can occur in patients treated with the loop diuretic for a long period of time. We report a 6-month-old 28-weeks premature infant treated chronically with furosemide for his bronchopulmonary dysplasia, who developed hypocalcemia and severe SHPT, adversely affecting his bones. Discontinuation of the loop diuretic and the addition of supplemental calcium and calcitriol only partially reversed the SHPT, bringing serum parathyroid hormone level down from 553 to 238 pg/mL. After introduction of the calcimimetic Cinacalcet, we observed a sustained normalization of parathyroid hormone concentration at 27 to 63 pg/mL and, with that correction, of all biochemical abnormalities and healing of the bone disease. No adverse effects were noted. We conclude that in cases of SHPT due to furosemide in which traditional treatment fails, there may be room to consider the addition of a calcimimetic agent.

Thiazide increases serum calcium in anuric patients: the role of parathyroid hormone

We evaluated the effect of hydrochlorothiazide in a sample of anuric patients on hemodialysis and found an increase in serum calcium, which occurred only in those with parathyroid hormone >300 pg/ml. This finding highlights the extra-renal effect of this diuretic and a possible role of parathyroid hormone in the mechanism.

PURPOSE

Thiazide diuretics are commonly used in patients with chronic kidney disease to treat hypertension. Their effects on calcium and bone metabolism are not well established, once calciuria may not fully explain levels of calcium and parathyroid hormone (PTH) in this population. A previous study has suggested that thiazides require the presence of PTH as a permissive condition for its renal action. In anuric patients, however, the role of PTH, if any, in the thiazide effect is unknown.

METHODS

To assess thiazide extra renal effect on serum calcium and whether such an effect is reliant on PTH, hydrochlorothiazide (HCTZ) 100 mg was given orally once a day to a sample of 19 anuric patients on hemodialysis for 2 weeks. Laboratories' analyses were obtained in three phases: baseline, after diuretic use, and after a 2-week washout phase.

RESULTS

We demonstrated that serum calcium (Ca) increased in ten patients (52.6%) after HCTZ use, returning to previous levels after the washout period. Out of the 19 patients, ten presented PTH ≥ 300 pg/ml, and Ca has increased in eight of them, whereas in the other nine patients with PTH < 300 pg/ml, serum Ca has increased only in two individuals (RR risk of increase Ca 3.9; p = 0.012).

CONCLUSIONS

HCTZ was capable of increasing serum Ca in a sample of anuric patients on hemodialysis and seems this effect is highly dependent on PTH levels. Caution is required while interpreting this result, as the small sample size might implicate in a finding caused by chance.

Elderly patients with chronic kidney disease have higher risk of hyperparathyroidism

PURPOSE

As the world's population ages, the incidence of chronic kidney disease (CKD) is growing. There is ongoing debate regarding whether high levels of parathyroid hormone (PTH) would be more common in elderly than young patients, and which factors are driven the risk of secondary hyperparathyroidism (SHPT), independent of renal function.

METHODS

Elderly patients (age ≥ 65 years, N = 518) were compared to a 1:1 sex- and estimated glomerular filtration rate (eGFR)-matched sample of young patients (age < 65 years), in a cross-sectional analysis. Demographic, biochemical and drug prescription data were collected from electronic charts. The main outcome measure was the prevalence of SHPT, defined as PTH > 65 pg/mL.

RESULTS

Elderly patients presented higher serum calcium and PTH levels and lower serum phosphate, and were taking more diuretics than young patients. SHPT was more frequent among elderly patients (49.4 vs. 38.6%, p = 0.005), and it was associated with lower eGFR, low levels of 25(OH) vitamin D and with furosemide therapy, while thiazide use was a protector factor. Elderly patients with 25(OH) vitamin D > 40 ng/mL were protected against SHPT. The Ca/PTH ratio was lower in elderly than in young patients [0.15 (0.10, 0.20) vs. 0.16 (0.11, 0.23), respectively, p = 0.003].

CONCLUSION

CKD elderly patients have higher risk of SHPT than young, which cannot be explained solely by renal function. Besides low levels of vitamin D, furosemide therapy and a distinct relationship between calcium and PTH are possible factors contributing to SHPT. Whether this is a result of renal resistance to PTH or an altered set point to calcium deserves further investigation.