The treatment of renal hyperparathyroidism.

Renal hyperparathyroidism (rHPT) is a complex and challenging disorder. It develops early in the course of renal failure and is associated with increased risks of fractures, cardiovascular disease and death. It is treated medically, but when medical therapy cannot control the hyperparathyroidism, surgical parathyroidectomy is an option. In this review, we summarize the pathophysiology, diagnosis, and medical treatment; we describe the effects of renal transplantation; and discuss the indications and strategies in parathyroidectomy for rHPT. Renal hyperparathyroidism develops early in renal failure, mainly as a consequence of lower levels of vitamin D, hypocalcemia, diminished excretion of phosphate and inability to activate vitamin D. Treatment consists of supplying vitamin D and reducing phosphate intake. In later stages calcimimetics might be added. RHPT refractory to medical treatment can be managed surgically with parathyroidectomy. Risks of surgery are small but not negligible. Parathyroidectomy should likely not be too radical, especially if the patient is a candidate for future renal transplantation. Subtotal or total parathyroidectomy with autotransplantation are recognized surgical options. Renal transplantation improves rHPT but does not cure it.

Cardiovascular and Cerebrovascular Events After Parathyroidectomy in Patients on Renal Replacement Therapy.

BACKGROUND: A majority of patients with end-stage renal disease suffer from secondary hyperparathyroidism, which is associated with osteoporosis and cardiovascular disease. Parathyroidectomy (PTX) is often necessary despite medical treatment. However, the effect of PTX on cardio- and cerebrovascular events (CVE) remains unclear. Data on the effect of PTX from population-based studies are scarce. Some studies have shown decreased incidence of CVE after PTX. The aim of this study was to evaluate the effect of PTX on risk of CVE in patients on renal replacement therapy. METHODS: We performed a nested case-control study within the Swedish Renal Registry (SRR) by matching PTX patients on dialysis or with functioning renal allograft with up to five non-PTX controls for age, sex and underlying renal disease. To calculate time to CVE, i.e., myocardial infarct, stroke and transient ischemic attack, control patients were assigned the calendar date (d) of the PTX of the case patient. Crude and adjusted proportional hazards regressions with random effect (frailty) were used to calculate hazard ratios for CVE. RESULTS: The study cohort included 20,056 patients in the SRR between 1991 and 2009. Among these, 579 patients had undergone PTX, 423 during dialysis and 156 during time with functioning renal allograft. These patients were matched with 1234 dialysis and 736 transplanted non-PTX patients. The adjusted hazard ratio (HR) with 95% confidence interval (CI) of CVE after PTX was 1.24 (1.03-1.49) for dialysis patients compared with non-PTX patients. Corresponding results for patients with renal allograft at d were HR (95% CI) 0.53 (0.34-0.84). CONCLUSIONS: PTX patients on dialysis at d had a higher risk of CVE than patients without PTX. Patients with renal allograft at d on the other had a lower risk after PTX than patients without PTX.

Total versus subtotal parathyroidectomy for secondary hyperparathyroidism.

BACKGROUND: It remains unclear whether total or subtotal parathyroidectomy for secondary hyperparathyroidism yields the best outcomes. We investigated mortality, cardiovascular events, hip fracture, and recurrent parathyroidectomy after total versus subtotal parathyroidectomy in patients on renal replacement therapy. METHODS: Using the Swedish Renal Registry, the surgical registry for thyroid and parathyroid surgery, and the National Inpatient Registry, we identified patients who underwent parathyroidectomy between 1991 and 2013. We calculated the risk of outcome after total versus subtotal parathyroidectomy using COX's regression, adjusting for age, sex, cause of renal disease, time with a functioning graft before and after parathyroidectomy, Charlson comorbidity index, year of surgery, prevalent cardiovascular disease, time on dialysis, renal transplantation at parathyroidectomy, and treatment with calcimimetics before parathyroidectomy. RESULTS: There were 824 patients who underwent parathyroidectomy, 388 total and 436 subtotal. There was no difference in mortality or risk of incident hip fracture between groups. Comparing the subtotal with the total parathyroidectomy, the adjusted hazard ratio (95% confidence interval) for cardiovascular events was 0.43 (0.25-0.72) and for recurrent parathyroidectomy 3.33 (1.33-8.32). CONCLUSION: There was a higher risk of cardiovascular events in patients after total parathyroidectomy compared with subtotal parathyroidectomy, but a lower risk of recurrent parathyroidectomy.

Is low pre-transplant parathyroid hormone a risk marker for cardiovascular disease in long-term follow-up of renal transplant recipients?

BACKGROUND: Secondary hyperparathyroidism and altered levels of parathyroid hormone (PTH) are associated with vascular events in chronic kidney disease. After renal transplantation, this association is not clear. Pre-transplant parathyroidectomy (PTX) is common, but post-transplant data are scarce. We aimed to study the effect of PTH at the time of transplantation on risk of post-transplant vascular events in renal transplant recipients with and without pre-transplant PTX. METHODS: 258 patients from two Swedish transplant units were followed for 6 years. Separate analyses were made for patients with or without pre-transplant PTX. Patients with no pre-transplant PTX were stratified by quartiles of PTH at time of transplantation and patients with pre-transplant PTX were stratified by above and below median levels of PTH at time of transplantation. Hazard ratios for vascular events, mortality, and graft failure were calculated in adjusted Cox regression models. RESULTS: In patients with no pre-transplant PTX, the lowest quartile of PTH at transplantation had a higher risk of cardiovascular events compared to quartile 3 with an adjusted hazard ratio (95% CI) of 2.63 (1.04-6.67). In patients with pre-transplant PTX, the group below median of PTH had a higher risk of cardiovascular events with an adjusted hazard ratio (95% CI) of 18.15 (1.62-203.82) compared to patients above median of PTH. CONCLUSION: Low levels of parathyroid hormone before transplantation were associated with increased risk of post-transplant vascular events both in patients with and without pre-transplant parathyroidectomy. Any conclusions on causal or direct effect of PTH on outcome cannot be drawn from this observational study.

High doses of cholecalciferol alleviate the progression of hyperparathyroidism in patients with CKD Stages 3-4: results of a 12-week double-blind, randomized, controlled study.

Background: Calcidiol insufficiency may accelerate the development of secondary hyperparathyroidism (SHPT). We tested the effect of a substantial increase in calcidiol on mineral metabolism in patients with chronic kidney disease (CKD). Methods: Ninety-five patients with CKD Stages 3-4, parathyroid hormone (PTH) above 6.8 pmol/L and calcidiol below 75 nmol/L were randomized to receive either cholecalciferol 8000 IU/day or placebo for 12 weeks. The primary endpoint was difference in the mean change in iPTH after 12 weeks. The proportion of participants having a 30% reduction in PTH and the effect on hand grip strength, fatigue and different biochemical variables were also investigated. Results: Baseline calcidiol was 57.5 ± 22 and 56.8 ± 22 nmol/L in the cholecalciferol and placebo groups, respectively. The corresponding concentrations of PTH were 10.9 ± 5 and 13.1 ± 9 pmol/L. Calcidiol increased to 162 ± 49 nmol/L in patients receiving cholecalciferol, and PTH levels remained constant at 10.5 ± 5 pmol/L. In the placebo group, calcidiol remained stable and PTH increased to 15.2 ± 11 pmol/L. The mean change in PTH differed significantly between the two groups (P < 0.01). The proportion of subjects reaching a 30% decrease in PTH did not differ. No effect on grip strength, fatigue, phosphate or fibroblast growth factor 23 was observed. Cholecalciferol treatment resulted in stable calcium concentrations and a substantial increase in calcitriol. Conclusion: Treatment with high daily doses of cholecalciferol in patients with CKD Stages 3-4 halts the progression of SHPT and does not cause hypercalcaemia or other side effects.

The Effect of Parathyroidectomy on Risk of Hip Fracture in Secondary Hyperparathyroidism.

BACKGROUND: Secondary hyperparathyroidism increases the risk for fractures. Despite improvement in medical therapy, surgical parathyroidectomy (PTX) often becomes necessary, but its effect on risk of fractures is not clear. Our aim was to study the effect of parathyroidectomy on the risk of hip fractures in patients on dialysis or with a functioning renal graft at time of parathyroidectomy. DESIGN: In a cohort of 20,056 patients on dialysis or with functioning renal allograft, we identified 590 patients who underwent parathyroidectomy between 1991 and 2009. Of these, 579 were matched with 1970 non-PTX patients on age, sex, cause of renal disease and functioning renal allograft or not at the time of PTX or at the corresponding time for non-PTX patients (t). We calculated the risk for hip fracture after PTX using crude and adjusted Cox proportional hazards regressions, adjusting for time in renal replacement therapy before t, time with functioning renal allograft before and after t, comorbidity at t and a hip fracture before t. RESULTS: The adjusted hazard ratio (95% confidence interval) for hip fracture was 0.40 (0.18-0.88) for PTX patients, compared to non-PTX patients. When analyses were performed separately for sex, only women had a lower risk of hip fracture after PTX compared to non-PTX patients. The risk of hip fracture after PTX was similar in patients with or without functioning renal allograft at time for PTX. CONCLUSION: Parathyroidectomy is associated with a lower risk of hip fracture in female patients with secondary hyperparathyroidism.

The effect of parathyroidectomy on patient survival in secondary hyperparathyroidism.

BACKGROUND: Secondary hyperparathyroidism is a common condition in patients with end-stage renal disease and is associated with osteoporosis and cardiovascular disease. Despite improved medical treatment, parathyroidectomy (PTX) is still necessary for many patients on renal replacement therapy. The aim of this study was to evaluate the effect of PTX on patient survival. METHODS: A nested index-referent study was performed within the Swedish Renal Registry (SRR). Patients on maintenance dialysis and transplantation at the time of PTX were analysed separately. The PTX patients in each of these strata were matched for age, sex and underlying renal diseases with up to five referent patients who had not undergone PTX. To calculate survival time and hazard ratios, indexes and referents were assigned the calendar date (d) of the PTX of the index patient. The risk of death after PTX was calculated using crude and adjusted Cox proportional hazards regressions. RESULTS: There were 20 056 patients in the SRR between 1991 and 2009. Of these, 579 (423 on dialysis and 156 with a renal transplant at d) incident patients with PTX were matched with 1234/892 non-PTX patients. The adjusted relative risk of death was a hazard ratio (HR) of 0.80 [95% confidence interval (CI) 0.65-0.99] for dialysis patients at d who had undergone PTX compared with matched patients who had not. Corresponding results for the patients with a renal allograft at d were an HR of 1.10 (95% CI 0.71-1.70). CONCLUSIONS: PTX was associated with improved survival in patients on maintenance dialysis but not in patients with renal allograft.

Early development of secondary hyperparathyroidism following renal transplantation.

BACKGROUND: Optimal levels of intact parathyroid hormone (iPTH) in the post-transplant period are not known due to insufficient data. Therefore, we aimed to describe secondary hyperparathyroidism (SHPT) in Swedish renal transplant (RT) recipients and also report events of fractures and vascular events potentially related to levels of iPTH. METHODS: Medical charts from 132 RT recipients were retrospectively reviewed. Laboratory/clinical data were obtained at regular points up to 12 months post RT. Three groups were created based on pre-RT levels of iPTH based on KDOQI recommended levels of iPTH in CKD 5. RESULTS: One year post RT 69% had iPTH above levels recommended by KDOQI. A multiple regression analysis showed a strong relation between pre-transplant iPTH levels and iPTH levels at 12 months (ß coefficient = 0.323, p < 0.001). Patients with low pre-transplant levels of iPTH had a higher rate of fractures during follow up compared to patients with higher pre-transplant levels of iPTH (P = 0.034) [corrected]. CONCLUSION: SHPT is common in Swedish RT recipients. Pre-transplant regulation of SHPT is of great importance to determine outcome post RT. Low levels of iPTH in the pre-transplant period could be associated with a high risk of fracture in the first post-transplant year.

The RACK1 signaling scaffold protein selectively interacts with Yersinia pseudotuberculosis virulence function.

Many gram-negative bacteria use type III secretion systems to translocate effector proteins into host cells. These effectors interfere with cellular functions in a highly regulated manner resulting in effects that are beneficial for the bacteria. The pathogen Yersinia can resist phagocytosis by eukaryotic cells by translocating Yop effectors into the target cell cytoplasm. This is called antiphagocytosis, and constitutes an important virulence feature of this pathogen since it allows survival in immune cell rich lymphoid organs. We show here that the virulence protein YopK has a role in orchestrating effector translocation necessary for productive antiphagocytosis. We present data showing that YopK influences Yop effector translocation by modulating the ratio of the pore-forming proteins YopB and YopD in the target cell membrane. Further, we show that YopK that can interact with the translocators, is exposed inside target cells and binds to the eukaryotic signaling protein RACK1. This protein is engaged upon Y. pseudotuberculosis-mediated ß1-integrin activation and localizes to phagocytic cups. Cells with downregulated RACK1 levels are protected from antiphagocytosis. This resistance is not due to altered levels of translocated antiphagocytic effectors, and cells with reduced levels of RACK1 are still sensitive to the later occurring cytotoxic effect caused by the Yop effectors. Further, a yopK mutant unable to bind RACK1 shows an avirulent phenotype during mouse infection, suggesting that RACK1 targeting by YopK is a requirement for virulence. Together, our data imply that the local event of Yersinia-mediated antiphagocytosis involves a step where YopK, by binding RACK1, ensures an immediate specific spatial delivery of antiphagocytic effectors leading to productive inhibition of phagocytosis.

The membrane localization domain is required for intracellular localization and autoregulation of YopE in Yersinia pseudotuberculosis.

Recent work has shown that a domain of YopE of Yersinia pseudotuberculosis ranging from amino acids 54 to 75 (R. Krall, Y. Zhang, and J. T. Barbieri, J. Biol. Chem. 279:2747-2753, 2004) is required for proper localization of YopE after ectopic expression in eukaryotic cells. This domain, called the membrane localization domain (MLD), has not been extensively studied in Yersinia. Therefore, an in cis MLD deletion mutant of YopE was created in Y. pseudotuberculosis. The mutant was found to secrete and translocate YopE at wild-type levels. However, the mutant was defective in the autoregulation of YopE expression after the infection of HeLa cells. Although the mutant translocated YopE at wild-type levels, it showed a delayed HeLa cell cytotoxicity. This delay was not caused by a change in GTPase activating protein (GAP) activity, since the mutant showed wild-type YopE GAP activity toward Rac1 and RhoA. The MLD mutant displayed a changed intracellular localization pattern of YopE in HeLa cells after infection, and the YopEDeltaMLD protein was found to be dispersed within the whole cell, including the nucleus. In contrast, wild-type YopE was found to localize to the perinuclear region of the cell and was not found in the nucleus. In addition, the yopEDeltaMLD mutant was avirulent. Our results suggest that YopE must target proteins other than RhoA and Rac1 and that the MLD is required for the proper targeting and hence virulence of YopE during infection. Our results raise the question whether YopE is a regulatory protein or a "true" virulence effector protein.

Regulation of Yersinia Yop-effector delivery by translocated YopE.

The bacterial pathogen Yersinia pseudotuberculosis uses a type III secretion (T3S) system to translocate Yop effectors into eukaryotic cells. Effectors are thought to gain access to the cytosol via pores formed in the host cell plasma membrane. Translocated YopE can modulate this pore formation through its GTPase-activating protein (GAP) activity. In this study, we analysed the role of translocated YopE and all the other known Yop effectors in the regulation of effector translocation. Elevated levels of Yop effector translocation into HeLa cells occurred by YopE-defective strains, but not those defective for other Yop effectors. Only Yersinia devoid of YopK exhibits a similar hyper-translocation phenotype. Since both yopK and yopE mutants also failed to down-regulate Yop synthesis in the presence of eukaryotic cells, these data imply that translocated YopE specifically regulates subsequent effector translocation by Yersinia through at least one mechanism that involves YopK. We suggest that the GAP activity of YopE might be working as an intra-cellular probe measuring the amount of protein translocated by Yersinia during infection. This may be a general feature of T3S-associated GAP proteins, since two homologues from Pseudomonas aeruginosa, exoenzyme S (ExoS) and exoenzyme T (ExoT), can complement the hyper-translocation phenotypes of the yopE GAP mutant.

Functional analysis of the YopE GTPase-activating protein (GAP) activity of Yersinia pseudotuberculosis.

YopE of Yersinia pseudotuberculosis inactivates three members of the small RhoGTPase family (RhoA, Rac1 and Cdc42) in vitro and mutation of a critical arginine abolishes both in vitro GTPase-activating protein (GAP) activity and cytotoxicity towards HeLa cells, and renders the pathogen avirulent in a mouse model. To understand the functional role of YopE, in vivo studies of the GAP activity in infected eukaryotic cells were conducted. Wild-type YopE inactivated Rac1 as early as 5 min after infection whereas RhoA was down regulated about 30 min after infection. No effect of YopE was found on the activation state of Cdc42 in Yersinia-infected cells. Single-amino-acid substitution mutants of YopE revealed two different phenotypes: (i) mutants with significantly lowered in vivo GAP activity towards RhoA and Rac1 displaying full virulence in mice, and (ii) avirulent mutants with wild-type in vivo GAP activity towards RhoA and Rac1. Our results show that Cdc42 is not an in vivo target for YopE and that YopE interacts preferentially with Rac1, and to a lesser extent with RhoA, during in vivo conditions. Surprisingly, we present results suggesting that these interactions are not a prerequisite to establish infection in mice. Finally, we show that avirulent yopE mutants translocate YopE in about sixfold higher amount compared with wild type. This raises the question whether YopE's primary function is to sense the level of translocation rather than being directly involved in downregulation of the host defence.