Atrasentan and renal events in patients with type 2 diabetes and chronic kidney disease (SONAR): a double-blind, randomised, placebo-controlled trial

BACKGROUND

Short-term treatment for people with type 2 diabetes using a low dose of the selective endothelin A receptor antagonist atrasentan reduces albuminuria without causing significant sodium retention. We report the long-term effects of treatment with atrasentan on major renal outcomes.

METHODS

We did this double-blind, randomised, placebo-controlled trial at 689 sites in 41 countries. We enrolled adults aged 18-85 years with type 2 diabetes, estimated glomerular filtration rate (eGFR) 25-75 mL/min per 1·73 m² of body surface area, and a urine albumin-to-creatinine ratio (UACR) of 300-5000 mg/g who had received maximum labelled or tolerated renin-angiotensin system inhibition for at least 4 weeks. Participants were given atrasentan 0·75 mg orally daily during an enrichment period before random group assignment. Those with a UACR decrease of at least 30% with no substantial fluid retention during the enrichment period (responders) were included in the double-blind treatment period. Responders were randomly assigned to receive either atrasentan 0·75 mg orally daily or placebo. All patients and investigators were masked to treatment assignment. The primary endpoint was a composite of doubling of serum creatinine (sustained for ≥30 days) or end-stage kidney disease (eGFR <15 mL/min per 1·73 m² sustained for ≥90 days, chronic dialysis for ≥90 days, kidney transplantation, or death from kidney failure) in the intention-to-treat population of all responders. Safety was assessed in all patients who received at least one dose of their assigned study treatment. The study is registered with ClinicalTrials.gov, number NCT01858532.

FINDINGS

Between May 17, 2013, and July 13, 2017, 11 087 patients were screened; 5117 entered the enrichment period, and 4711 completed the enrichment period. Of these, 2648 patients were responders and were randomly assigned to the atrasentan group (n=1325) or placebo group (n=1323). Median follow-up was 2·2 years (IQR 1·4-2·9). 79 (6·0%) of 1325 patients in the atrasentan group and 105 (7·9%) of 1323 in the placebo group had a primary composite renal endpoint event (hazard ratio [HR] 0·65 [95% CI 0·49-0·88]; p=0·0047). Fluid retention and anaemia adverse events, which have been previously attributed to endothelin receptor antagonists, were more frequent in the atrasentan group than in the placebo group. Hospital admission for heart failure occurred in 47 (3·5%) of 1325 patients in the atrasentan group and 34 (2·6%) of 1323 patients in the placebo group (HR 1·33 [95% CI 0·85-2·07]; p=0·208). 58 (4·4%) patients in the atrasentan group and 52 (3·9%) in the placebo group died (HR 1·09 [95% CI 0·75-1·59]; p=0·65).

INTERPRETATION

Atrasentan reduced the risk of renal events in patients with diabetes and chronic kidney disease who were selected to optimise efficacy and safety. These data support a potential role for selective endothelin receptor antagonists in protecting renal function in patients with type 2 diabetes at high risk of developing end-stage kidney disease.

FUNDING

AbbVie.

Baseline characteristics and enrichment results from the SONAR trial

AIM

The SONAR trial uses an enrichment design based on the individual response to the selective endothelin receptor antagonist atrasentan on efficacy (the degree of the individual response in the urinary albumin-to-creatinine ratio [UACR]) and safety/tolerability (signs of sodium retention and acute increases in serum creatinine) to assess the effects of this agent on major renal outcomes. The patient population and enrichment results are described here.

METHODS

Patients with type 2 diabetes with an estimated glomerular filtration rate (eGFR) within 25 to 75 mL/min/1.73 m² and UACR between 300 and 5000 mg/g were enrolled. After a run-in period, eligible patients received 0.75 mg/d of atrasentan for 6 weeks. A total of 2648 responder patients in whom UACR decreased by ≥30% compared to baseline were enrolled, as were 1020 non-responders with a UACR decrease of <30%. Patients who experienced a weight gain of >3 kg and in whom brain natriuretic peptide exceeded ≥300 pg/mL, or who experienced an increase in serum creatinine >20% (0.5 mg/dL), were not randomized.

RESULTS

Baseline characteristics were similar for atrasentan responders and non-responders. Upon entry to the study, median UACR was 802 mg/g in responders and 920 mg/g in non-responders. After 6 weeks of treatment with atrasentan, the UACR change in responders was -48.8% (95% CI, -49.8% to -47.9%) and in non-responders was -1.2% (95% CI, -6.4% to 3.9%). Changes in other renal risk markers were similar between responders and non-responders except for a marginally greater reduction in systolic blood pressure and eGFR in responders.

CONCLUSIONS

The enrichment period has successfully identified a population with a profound UACR reduction without clinical signs of sodium retention in whom a large atrasentan effect on clinically important renal outcomes is possible. The SONAR trial aims to establish whether atrasentan confers renal protection.

Rationale and protocol of the Study Of diabetic Nephropathy with AtRasentan (SONAR) trial: A clinical trial design novel to diabetic nephropathy

AIMS

Individuals with diabetes and chronic kidney disease (CKD) are at high risk for renal events. Recent trials of novel treatments have been negative, possibly because of variability in response to treatment of the target risk factor. Atrasentan is a selective endothelin A receptor antagonist that reduces urinary albumin-to-creatinine ratio (UACR), with a large variability between patients. We are assessing its effect on renal outcomes in the Study Of diabetic Nephropathy with AtRasentan (SONAR; NCT01858532) with an enrichment design (>30% lowering of albuminuria) to select patients most likely to benefit.

MATERIALS AND METHODS

SONAR is a randomized, double-blind, placebo-controlled trial with approximately 3500 participants who have stage 2-4 CKD and macroalbuminuria and are receiving a maximum tolerated dose of a renin-angiotensin system inhibitor.

RESULTS

After 6 weeks of exposure to atrasentan 0.75 mg once daily (enrichment period), participants with ≥30% UACR decrease and no tolerability issues (responders) were randomly assigned to placebo or atrasentan 0.75 mg/day. The responder group will be used for primary efficacy and safety analyses. Approximately 1000 participants with <30% UACR reduction (non-responders) were also randomized to placebo or atrasentan. The primary endpoint is a composite of a sustained doubling of serum creatinine or end-stage renal disease. The original power calculation indicated that a total of 425 primary renal events in the responder group provides 90% power to detect a 27% reduction in relative risk (alpha level of .05).

CONCLUSION

SONAR aims to determine whether atrasentan added to guideline-recommended therapies safely reduces the risk of CKD progression and delays the onset of end-stage renal disease in patients with type 2 diabetes and nephropathy. SONAR also aims to establish whether the enrichment of patients based on their initial "surrogate" response to atrasentan will deliver a trial design in accord with personalized treatment of diabetic kidney disease.

Relationship Between Atrasentan Concentrations and Urinary Albumin to Creatinine Ratio in Western and Japanese Patients With Diabetic Nephropathy

PURPOSE

The objective of the current analyses was to characterize the pharmacokinetic properties of atrasentan and the exposure-response relationships for the efficacy end point, urinary albumin to creatinine ratio (UACR), and the treatment-emergent adverse event, peripheral edema, during 8 or 12 weeks of treatment.

METHODS

Results from 3 Phase II, randomized, double-blind, placebo-controlled studies (N = 257) were used for the population pharmacokinetic and exposure-response models. Concentration-time and response data for efficacy and tolerability were analyzed using a nonlinear mixed-effects population analysis and logistic regression approaches.

FINDINGS

The pharmacokinetic data were adequately described by a 2-compartment model with first-order absorption and elimination. After weight was accounted for, no clinically meaningful differences were found in CL/F or V_d/F of the central compartment between Western and Japanese patients. Exposure-response analyses confirmed the efficacy of atrasentan in reducing UACR, with an estimated decrease in UACR of ≥37% when the atrasentan dose was 0.75 mg or higher. No significant association between atrasentan exposure and the rate of edema was identified at atrasentan doses of 0.5, 0.75, and 1.25 mg. The rates of peripheral edema were comparable in patients receiving active treatment and placebo.

IMPLICATIONS

The exposure-response relationships for efficacy and tolerability were consistent between Western and Japanese patients. On the basis of these analyses, a dose of 0.75 mg/d was selected for the Phase III trial. ClinicalTrials.gov identifiers: NCT01356849, NCT01399580, and NCT01424319.

Number and frequency of albuminuria measurements in clinical trials in diabetic nephropathy

BACKGROUND AND OBJECTIVES

Albuminuria change is often used to assess drug efficacy in intervention trials in nephrology. The change is often calculated using a variable number of urine samples collected at baseline and end of treatment. Yet more albuminuria measurements usually occur. Because albuminuria shows a large day-to-day variability, this study assessed to what extent the average and the precision of the antialbuminuric drug effect varies with the number of urine collections at each visit and the number of follow-up visits.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This study used data from three randomized intervention trials (Aliskiren Combined with Losartan in Type 2 Diabetes and Nephropathy, Selective Vitamin D Receptor Activation for Albuminuria Lowering, and Residual Albuminuria Lowering with Endothelin Antagonist Atrasentan) including patients with type 2 diabetes and macroalbuminuria. Albuminuria-lowering drug effects were estimated from one, two, or three urine collections at consecutive days before each study visit and reported as albuminuria change from baseline to end of treatment or the change over time considering an average of all follow-up albuminuria measurements.

RESULTS

Increasing the number of urine collections for an albuminuria measurement at baseline and end of treatment or using all study visits during follow-up did not alter the average drug effect. The precision of the drug effect increased (decreased SEM) when the number of study visits and the number of urine collections per visit were increased. Using all albuminuria measurements at all study visits led to a 4- to 6-fold reduction in sample size to detect a 30% albuminuria-lowering treatment effect with 80% power compared with using baseline and end-of-treatment albuminuria measurements alone.

CONCLUSIONS

Increasing the number of urine collections per study visit and the number of visits over time does not change the average drug effect estimate but markedly increases the precision, thereby enhancing statistical power. Thus, clinical trial designs in diabetic nephropathy using albuminuria as an end point can be significantly improved, leading to smaller sample sizes and less complex trials.

Effects of paricalcitol on calcium and phosphate metabolism and markers of bone health in patients with diabetic nephropathy: results of the VITAL study

Background

Chronic kidney disease (CKD) is associated with elevations in serum phosphate, calcium–phosphorus product and bone-specific alkaline phosphatase (BAP), with attendant risks of cardiovascular and bone disorders. Active vitamin D can suppress parathyroid hormone (PTH), but may raise serum calcium and phosphate concentrations. Paricalcitol, a selective vitamin D activator, suppressed PTH in CKD patients (stages 3 and 4) with secondary hyperparathyroidism (SHPT) with minimal changes in calcium and phosphate metabolism.

Methods

The VITAL study enrolled patients with CKD stages 2–4. We examined the effect and relationship of paricalcitol to calcium and phosphate metabolism and bone markers in a post hoc analysis of VITAL. The study comprised patients with diabetic nephropathy enrolled in a double-blind, placebo-controlled, randomized trial of paricalcitol (1 or 2 μg/day). Urinary and serum calcium and phosphate, serum BAP, and intact PTH (iPTH) concentrations were measured throughout the study.

Results

Baseline demographics and calcium, phosphate, PTH (49% with iPTH <70 pg/mL), and BAP concentrations were similar between groups. A transient, modest yet significant increase in phosphate was observed for paricalcitol 2 μg/day (+0.29 mg/dL; P < 0.001). Dose-dependent increases in serum and urinary calcium were observed; however, there were few cases of hypercalcemia: one in the 1-μg/day group (1.1%) and three in the 2-μg/day group (3.2%). Significant reductions in BAP were observed that persisted for 60 days after paricalcitol discontinuation (P < 0.001 for combined paricalcitol groups versus placebo). Paricalcitol dose-dependent reductions in iPTH were observed. Paricalcitol in CKD patients (±SHPT) was associated with modest increases in calcium and phosphate.

Conclusion

Paricalcitol reduces BAP levels, which may be beneficial for reducing vascular calcification.

Trial registration

Trial is registered with ClinicalTrials.gov, number NCT00421733.

Clinical efficacy of the selective endothelin A receptor antagonist, atrasentan, in patients with diabetes and chronic kidney disease (CKD)

AIMS

Progression of chronic kidney disease (CKD) in patients with diabetes is a growing problem. Diabetes is associated with elevated endothelin-1 (ET-1) and enhanced renal expression of the endothelin A receptor (ETAR). Atrasentan, a highly selective ETAR antagonist, reduces albuminuria in patients with DN. KEY METHODS: This was a randomized, double-blind trial of subjects with type 2 diabetes on renin-angiotensin system (RAS) inhibitors having eGFR >20 ml/min, and urine albumin-to-creatinine ratio (UACR) of 100-3000 mg/g, who were allocated to placebo, 0.25, 0.75 or 1.75 mg atrasentan.

KEY FINDINGS

UACR was reduced in the 0.75 mg and 1.75 mg groups (42% and 35% vs placebo, P<0.011) over the 8 week treatment period. Edema was reported in 21 subjects: 62% of edema events emerged during the first 4 weeks. There were no significant changes in serum hsCRP, IL-6, NT-pro-BNP, ET-1, urine TGFb or MCP-1. Urine NGAL was reduced 24% in the 1.75 mg group (P=0.044). Hispanic subjects (58% of total) tended to have greater UACR reductions than non-Hispanics (0.75 mg dose: Hispanic: 41-60%; non-Hispanic: 18-37%; P=0.012 and 0.048 vs placebo, respectively) without different rates of edema. Mean UACR reduction in subjects receiving maximum doses of RAS inhibitors (38%) was 32% and 35% in the 0.75 and 1.75 mg groups, respectively, and similar to overall UACR changes.

SIGNIFICANCE

Edema formation was dose-dependent and occurred early. The decrease in urine NGAL warrants further study in renal tubular disease attenuation. UACR responses based on ethnicity need further characterization. Results suggest atrasentan may have additive effects to RAS inhibition in treatment of DN.

Paricalcitol versus ergocalciferol for secondary hyperparathyroidism in CKD stages 3 and 4: a randomized controlled trial

BACKGROUND

The efficacy of 25-hydroxyvitamin D (25[OH]D) supplementation versus vitamin D receptor activators for the treatment of secondary hyperparathyroidism (SHPT) in patients with chronic kidney disease (CKD) stages 3 or 4 and vitamin D deficiency is unclear.

STUDY DESIGN

Randomized controlled trial.

SETTING & PARTICIPANTS

80 patients with CKD stages 3 or 4, 25(OH)D level <30 ng/mL, and SHPT in a single medical center.

INTERVENTION

Ergocalciferol, 50,000 units, titrated to achieve serum levels ≥30 ng/mL versus paricalcitol, 1 or 2 μg/d, for 16 weeks.

OUTCOMES

The occurrence of 2 consecutive parathyroid hormone (PTH) levels decreased by at least 30% from baseline. All analyses were intention to treat.

RESULTS

Baseline characteristics in the 2 groups were similar. 21 patients (53%) on paricalcitol and 7 patients (18%) on ergocalciferol treatment achieved the primary outcome measure (P = 0.002). After 16 weeks, PTH levels did not decrease significantly in patients receiving ergocalciferol, but were decreased significantly in those treated with paricalcitol (mean estimate of between-group difference over 16 weeks of therapy, 43.9 pg/mL; 95% CI, 11.2-76.6; P = 0.009). Serum 25(OH)D levels increased significantly after 16 weeks in only the ergocalciferol group, but not the paricalcitol group (mean estimate of between-group difference over 16 weeks of therapy, 7.08 ng/mL; 95% CI, 4.32-9.85; P < 0.001). Episodes of hyperphosphatemia and hypercalcemia were not significantly different between the 2 groups.

LIMITATIONS

Lack of blinding and use of surrogate end points.

CONCLUSIONS

Paricalcitol is more effective than ergocalciferol at decreasing PTH levels in patients with CKD stages 3 or 4 with vitamin D deficiency and SHPT.

Addition of atrasentan to renin-angiotensin system blockade reduces albuminuria in diabetic nephropathy

Although endothelin-receptor antagonists reduce albuminuria in diabetic nephropathy, fluid retention limits their use. Here, we examined the effect of atrasentan, a selective endothelin A receptor (ET(A)R) antagonist, on albuminuria in a randomized, double-blind, placebo-controlled trial of subjects with diabetic nephropathy already receiving stable doses of renin-angiotensin system (RAS) inhibitors. We randomly assigned 89 subjects with eGFR >20 ml/min per 1.73 m(2) and a urinary albumin-to-creatinine ratio (UACR) of 100 to 3000 mg/g to placebo or atrasentan (0.25, 0.75, or 1.75 mg daily) for 8 weeks. Compared with placebo, atrasentan significantly reduced UACR only in the 0.75- and 1.75-mg groups (P=0.001 and P=0.011, respectively). Compared with the 11% reduction in the geometric mean of the UACR from baseline to final observation in the placebo group during the study, the geometric mean of UACR decreased by 21, 42, and 35% in the 0.25-, 0.75-, and 1.75-mg atrasentan groups (P=0.291, P=0.023, and P=0.073, respectively). In the placebo group, 17% of subjects achieved ≥40% reduction in UACR from baseline compared with 30, 50, and 38% in the 0.25-, 0.75-, and 1.75-mg atrasentan groups, respectively (P=0.029 for 0.75 mg versus placebo). Peripheral edema occurred in 9% of subjects receiving placebo and in 14, 18, and 46% of those receiving 0.25, 0.5, and 1.75 mg atrasentan, respectively (P=0.007 for 1.75 mg versus placebo). In summary, atrasentan, at the doses tested, is generally safe and effective in reducing residual albuminuria and may ultimately improve renal outcomes in patients with type 2 diabetic nephropathy.

Cost Effectiveness of Paricalcitol versus a non-selective vitamin D receptor activator for secondary hyperparathyroidism in the UK: a chronic kidney disease markov model

BACKGROUND

secondary hyperparathyroidism (SHPT) is a common complication of chronic kidney disease (CKD) and a frequent cause of clinically significant bone disease. Non-selective vitamin D receptor (VDR) activator treatment has been used to treat the condition but is ineffective for many patients with hypercalcaemia and hyperphosphataemia and may precipitate worsening of their condition. Compared with non-selective VDR activator treatment, use of the VDR ligand paricalcitol may increase survival and reduce the risk of morbidities in patients with SHPT, which may have health economic consequences.

OBJECTIVE

the objective of this study was to determine the cost effectiveness of paricalcitol versus a non-selective VDR activator for the treatment of SHPT in patients with CKD in the UK setting.

METHODS

A Markov process model was developed employing data sources from the published literature, paricalcitol clinical trials and observational studies, official UK price/tariff lists and national population statistics. The comparator was alfacalcidol, a non-selective VDR activator medication. The primary perspective of the study was that of the UK National Health Service (NHS). The efficacy outcomes (reductions in SHPT, proteinuria, complications and mortality) were extrapolated to: number of life-years gained (LYG) and number of quality-adjusted life-years (QALYs). Clinical and economic outcomes were discounted at 3.5%. The year of costing for costs determined in the study was 2006.

RESULTS

the reference case analysis was a 10-year time horizon, based on a comparison of paricalcitol with a non-selective VDR activator, which is started in CKD stage 3 (moderate reduction in glomerular filtration rate [GFR] with kidney damage) and continued in CKD stage 4 (severe reduction in GFR) and CKD stage 5 (established kidney failure). The use of paricalcitol leads to an additional medical cost of pound3224 ($US5970). The health benefits of paricalcitol lead to an increase in LYG of 0.52 and a gain in QALYs of 0.465. Therefore the use of paricalcitol results in an incremental cost-effectiveness ratio of pound6933/QALY ($US12 840/QALY) from the primary perspective of the NHS. One-way sensitivity analyses and probabilistic sensitivity analyses confirmed the robustness of the model.

CONCLUSION

this model showed that the favourable clinical benefit of paricalcitol results in positive short- and long-term health economic benefits. This study suggests that the use of paricalcitol in patients with early CKD may be cost effective from the UK NHS perspective versus non-selective VDR activator medication.

Vitamin D deficiency, inflammation, and albuminuria in chronic kidney disease: complex interactions

OBJECTIVE

Vitamin D may promote cardiovascular health in general population and in chronic kidney disease (CKD) through inhibition of the renin-angiotensin system and anti-inflammatory effects. Although proteinuria is a marker of kidney and cardiovascular disease, few studies have examined vitamin D levels, inflammation, and proteinuria simultaneously in CKD. We evaluated the relationship between calcidiol (25D), calcitriol (1,25D), inflammation, and albuminuria in Study of Early Evaluation of Kidney Disease, a multicenter CKD cohort.

DESIGN

A cross-sectional study was carried out.

PARTICIPANTS

A total of 1,847 participants were studied, of which 387 were randomly selected for inflammatory biomarker assessment. PREDICTORS AND OUTCOMES: The primary predictors were 25D and 1,25D. The outcome was albuminuria (urine albumin to creatinine ratio [UACR]: >30 mg/g).

RESULTS

Albuminuric patients were more likely to have decreased 25D and 1,25D levels and higher interleukin-6 (IL-6) levels compared with normoalbuminuric patients. The lowest tertiles of 25D and 1,25D were associated with 2 to 3 times increased odds of albuminuria compared with the highest tertiles when adjusted for age, gender, race, systolic blood pressure, and diabetes (OR for 25D: 3.0; 95% CI: 1.3 to 7.0; OR for 1,25D: 2.6; 95% CI: 1.7 to 3.9). In analogous linear regression models, 25D and 1,25D were significantly associated with log UACR (P < .0001, for both). In participants for whom inflammatory markers were measured, demographics-adjusted linear regression models that included IL-6 described attenuation of the relationship between 25D, 1,25D, and UACR.

CONCLUSIONS

Low 25D and 1,25D levels are independently associated with albuminuria. IL-6 may be an important intermediary between vitamin D deficiency and albuminuria, or vitamin D deficiency may contribute to inflammation and subsequent albuminuria.

Differential effects of paricalcitol and calcitriol on intestinal calcium absorption in hemodialysis patients

BACKGROUND/AIMS

Increased parathyroid activity associated with chronic kidney disease is often managed with calcitriol, which can elevate serum calcium (Ca) by increasing bone resorption and intestinal absorption, whereas paricalcitol promotes less bone resorption. This study compared intestinal Ca absorption in hemodialysis patients treated with calcitriol versus paricalcitol (dose ratio 1:3).

METHODS

Patients (n = 22) aged > or =20 years, on maintenance hemodialysis for > or =2 months with intact parathyroid hormone (iPTH) levels of >200 pg/ml were enrolled in a single-center, double-blind, active-controlled, randomized, crossover trial. Mean fractional intestinal Ca absorption (+/-SE) was measured by the single-tracer method ((42)Ca) and evaluated with an analysis of variance crossover model.

RESULTS

Mean fractional intestinal Ca absorption was significantly lower after paricalcitol (0.135 +/- 0.006) versus calcitriol treatment (0.158 +/- 0.006, p = 0.022), a 0.023 difference in absolute Ca absorption fraction. Overall Ca absorption was low in the study population, indicating that regulation of Ca absorption may be dysfunctional. There were no significant differences in serum PTH, Ca, phosphorus (P), or Ca x P.

CONCLUSION

Overall, paricalcitol-treated patients absorbed approximately 14% less Ca compared with calcitriol-treated patients with similar effects on PTH. In hemodialysis patients, paricalcitol may provide a benefit by lowering the Ca available for removal by dialysis and/or for deposit in bone or soft tissues.

Chronic kidney disease Markov model comparing paricalcitol to calcitriol for secondary hyperparathyroidism: a US perspective

OBJECTIVE

The objective of this study was to determine the cost effectiveness of paricalcitol versus calcitriol for the treatment of secondary hyperparathyroidism in patients with chronic kidney disease in the United States setting.

METHODS

A Markov process model was developed employing data sources from the published literature, paricalcitol clinical trials and observational studies, official US price/tariff lists and national population statistics. The comparator was calcitriol, a non-selective vitamin D receptor activator (VDRA) medication. The primary perspective of the study was that of the third-party payer in the US. The efficacy outcomes (reduction in secondary hyperparathyroidism (SHPT), reduction in proteinuria, complications and mortality) were extrapolated to: number of life-years gained (LYG) and number of quality-adjusted life-years (QALYs). Clinical and economic outcomes were discounted at 3.5%.

RESULTS

The reference case analysis was a 10-year time horizon based on a comparison of paricalcitol with calcitriol, which is started in chronic kidney disease (CKD) stage 3 and continued in CKD stage 4 and CKD stage 5. The use of paricalcitol leads to a cost saving of US$1941. The inclusion of indirect costs leads to a cost saving of US$2528. The use of paricalcitol leads to an increase in life-years gained (0.47 years) and a gain in QALYs (0.43). The use of paricalcitol results in a dominant outcome from the perspective of the third-party payer, as well as from the societal perspective. One-way sensitivity analyses and probabilistic sensitivity analyses confirmed the robustness of the model.

CONCLUSION

This model showed that the favorable clinical benefit of paricalcitol results in positive short and long-term health economic benefits. This study suggests that the use of paricalcitol in patients with early chronic kidney disease may be cost-effective from the third-party payer perspective in the US versus calcitriol. Additional comparative studies are necessary to validate these results.

The selective vitamin D receptor activator for albuminuria lowering (VITAL) study: study design and baseline characteristics

BACKGROUND

Patients with diabetic nephropathy are at high risk for further progressive renal function loss. Treatments that decrease albuminuria have been linked with renal and cardiovascular protection. However, even when taking optimal treatment, residual renal and cardiovascular risk remains high which correlates with the magnitude of residual albuminuria. Use of vitamin D receptor activators, such as calcitriol and paricalcitol, is associated with improved sur- vival. A small study with paricalcitol showed reductions in albuminuria. The VITAL study tests the hypothesis whether paricalcitol persistently reduces albuminuria in diabetic subjects already receiving angiotensin-converting enzyme inhibitor (ACEI) and/or angiotensin receptor blocker (ARB) therapy.

METHODS

Randomization in this double-blind trial is equal allocation to paricalcitol 1 micro/day, 2 microg/day, or placebo. Inclusion criteria include: a diagnosis of type 2 diabetes, urinary albumin/creatinine ratio (UACR) between 100-3,000 mg/g, estimated glomerular filtration rate (eGFR) between 15-90 ml/min/1.73 m(2), serum calcium <9.8 mg/dl, and parathyroid hormone (PTH) between 35-500 pg/ml.

RESULTS

Baseline characteristics of the 281 subjects are: 69% men, mean age 64.9 +/- 10.4 years, eGFR 40.7 +/- 16.7 ml/min, median UACR (interquartile range) 612.3 mg/g (281-1,181 mg/g) and PTH 98.4 +/- 63.8 pg/ml.

CONCLUSION

This trial will be the first clinical test of the hypothesis that paricalcitol possesses pleiotropic effects and can modulate albuminuria in the setting of ACEI and/or ARB therapy. Results will have important clinical implications and are expected in November 2009.

Bone and mineral guidelines for patients with chronic kidney disease: a call for revision

Recent clinical studies of mineral metabolism in patients with chronic kidney disease have helped to verify and extend the Kidney Disease Outcomes Quality Initiative practice guidelines for bone metabolism and disease that were published in 2003. In particular, investigations that examined calcium loading, vitamin D therapy, and mortality risk associated with serum calcium and phosphate in dialysis patients have been the most helpful clinically. As a consequence, there is now a growing interest to have the previous guidelines amended accordingly, which will be performed through the Kidney Disease: Improving Global Outcomes working group after a debate within the nephrology community. The new data support this call for revision in an attempt to improve survival of the dialysis patient by emphasizing the importance of intravenous vitamin D therapy and of preventing excess calcium loading. These studies also suggest avenues for future investigation into nontraditional causes and treatments of cardiovascular disease in patients with chronic kidney disease.

Superiority of the Modification of Diet in Renal Disease equation over the Cockcroft-Gault equation in screening for impaired kidney function in Japanese Americans

The Cockcroft-Gault and the Modification of Diet in Renal Disease (MDRD) Study equations have not been validated in Asian Americans with varying degrees of glucose tolerance. We compared both equations to 24-h urinary creatinine clearance, the latter as a standard measurement of glomerular filtration rate (GFR), in 398 Japanese Americans (62.1+/-5.8 years, mean+/-S.D.) who had normal glucose tolerance (NGT) (n=138), impaired glucose tolerance (IGT) (n=136) and diabetes (n=124). Although both the Cockcroft-Gault (r=0.65, P<0.001) and the MDRD (r=0.74, P<0.001) equations correlated well with creatinine clearance, the latter was significantly superior (P=0.013 between r values). Receiver operating characteristic (ROC) curve analysis showed that the area under the curve (AUC) for the MDRD equation was significantly greater than for the Cockcroft-Gault equation (AUC 0.86 versus 0.80, P=0.015) in classifying subjects as having mildly reduced GFR (<90ml/min per 1.73m(2)). However, both equations overestimated the number of individuals with decreased GFR. We conclude therefore that while the MDRD equation more accurately identifies Asians who are in the early stages of kidney disease, as for other groups, a correction term appears necessary in order to reduce the number of Asian subjects being falsely diagnosed with CKD.

Prevalence of abnormal serum vitamin D, PTH, calcium, and phosphorus in patients with chronic kidney disease: results of the study to evaluate early kidney disease

Abnormalities of mineral metabolism occur early in chronic kidney disease. Quantification of the prevalence of these abnormalities has not been described using current assays nor in large unselected populations. This outpatient cohort cross-sectional study was conducted in 153 centers, (71% primary care practices). Blood for parathyroid hormone (PTH), vitamin D metabolites, creatinine, calcium (Ca), and phosphorus (P) were drawn between June and October 2004. Low 1,25-dihydroxyvitamin D (1,25 OH2 D3) was defined as <22 pg/ml. The 1814 patients had a mean age of 71.1 years old; 48% had diabetes mellitus (DM). Low 1,25 OH2 D3 was evident at all estimated glomerular filtration rate (eGFR) levels: 13% in those with eGFR >80 ml/min, >60% in those with eGFR <30 ml/min. High PTH (>65pm/dl) occurred in 12% with eGFR >80 ml/min. Serum Ca and P were normal until eGFR was <40 ml/min. Significant differences in the mean and median values of 1,25 OH2 D3, PTH, but not 25(OH)D3 levels, were seen across deciles of eGFR (P<0.001). Multivariate analysis revealed that DM, increased urinary albumin/creatinine ratio and lower eGFR predicted lower values of 1,25 OH2 D3. A high prevalence of mineral metabolite abnormalities occurs in a large unreferred US cohort. Low 1,25 OH2 D3 and elevated PTH are common at higher eGFR than previously described. As bone, cardiovascular disease, and mineral metabolite are correlated; further studies are necessary to determine the importance of these findings relative to outcomes.

Paricalcitol capsule for the treatment of secondary hyperparathyroidism in stages 3 and 4 CKD

BACKGROUND

The safety and efficacy of paricalcitol injection have been well established for the prevention and treatment of secondary hyperparathyroidism (SHPT) in patients with chronic kidney disease (CKD) stage 5. The capsule form of paricalcitol was developed to provide a convenient dosage form for patients with stages 3 and 4 CKD.

METHODS

Three randomized, placebo-controlled, phase-3 trials were conducted in patients with stages 3 and 4 CKD with SHPT. Enrollment criteria included an estimated glomerular filtration rate between 15 and 60 mL/min/1.73 m2 (0.25 and 1.00 mL/s/1.73 m2), an average of 2 consecutive intact parathyroid hormone (iPTH) levels greater than 150 pg/mL (ng/L), 2 consecutive serum calcium levels between 8.0 and 10.0 mg/dL (2.00 and 2.50 mmol/L), and 2 consecutive serum phosphorus levels of 5.2 mg/dL or less (< or = 1.68 mmol/L). Two studies used a thrice-weekly dosing regimen and 1 study used a once-daily dosing regimen for 24 weeks. Dosing was based on serum iPTH, calcium, and phosphorus levels. The primary efficacy end point is 2 consecutive decreases in iPTH levels greater than 30% from baseline.

RESULTS

Two hundred twenty patients participated (n = 107, paricalcitol; n = 113, placebo). At least 2 consecutive decreases in iPTH levels of 30% or greater from baseline occurred in 91% of paricalcitol versus 13% of placebo patients (P < 0.001). Incidences of hypercalcemia, hyperphosphatemia, and elevated calcium-phosphorus product levels were not significantly different between groups. Similarly, no significant differences in urinary calcium and phosphorus excretion or deterioration in kidney function were detected in patients administered paricalcitol compared with placebo.

CONCLUSION

Paricalcitol capsule was well tolerated and effectively decreased iPTH levels with minimal or no impact on calcium levels, phosphorus balance, and kidney function in patients with stages 3 and 4 CKD.

Vitamin D in chronic kidney disease: A systemic role for selective vitamin D receptor activation

Hyperparathyroidism occurs in most patients during the progression of chronic kidney disease (CKD) and one of its initiating events, reduced serum levels of 1,25-dihydroxyvitamin D, results from a decrease in renal 1alpha hydroxylase activity, which converts 25-hydroxyvitamin D to its activated form. The combination of persistently high parathyroid hormone (PTH) and low 1,25-dihydroxyvitamin D is associated with bone loss, cardiovascular disease, immune suppression and increased mortality in patients with end-stage kidney failure. Recent studies in dialysis patients suggest that paricalcitol, a selective activator of the vitamin D receptor (VDR), is associated with a more favorable efficacy to side effect profile than calcitriol, with less morbidity and better survival. One hypothesis derived from such studies suggests that systemic activation of VDRs may have direct effects on the cardiovascular system to decrease mortality in CKD. Although current guidelines for regulating serum calcium, phosphate and PTH recommend specific interventions at the various stages of CKD to prevent or postpone irreversible parathyroid disease and decrease cardiovascular morbidity and mortality, emerging data suggest that vitamin D therapy may prolong survival in this patient population by mechanisms that are independent of calcium, phosphate and PTH. It is suggested that a re-evaluation of current treatment recommendations is needed and that future research should focus on mechanisms that distinguish potential tissue specific benefits of selective VDR activators in patients with CKD.

Vitamin D treatment in chronic kidney disease

Activated vitamin D continues to be the major treatment for suppressing parathyroid hormone (PTH) levels in dialysis patients who have secondary hyperparathyroidism. Active vitamin D compounds are distinguished by their ability to bind with high affinity to vitamin D receptors (VDRs) not only in the parathyroid glands, but in cells throughout the body. Because of recent data showing that pulsatile, intravenous vitamin D treatment (calcitriol or paricalcitol) confers a survival advantage in the dialysis population, there is new interest in understanding the systemic effects of VDR activation, particularly in the predialysis stages of chronic kidney disease (CKD), where high mortality rates from cardiovascular disease have recently been documented. Previous underutilization of calcitriol treatment to control PTH levels in stages 3 and 4 CKD was often due to concerns about its potential for accelerating the progression of CKD as a consequence of hypercalcemia, hypercalciuria, or hyperphosphatemia. Vitamin D analogs with selective VDR activity (such as paricalcitol) have great potential for preventing parathyroid hyperplasia and bone loss in early CKD without adversely affecting kidney function. Whether they also reduce cardiovascular morbidity and mortality in early CKD, as they appear to do in dialysis patients, remains to be determined.

Serum phosphate levels and mortality risk among people with chronic kidney disease

Elevated serum phosphate levels have been linked with vascular calcification and mortality among dialysis patients. The relationship between phosphate and mortality has not been explored among patients with chronic kidney disease (CKD). A retrospective cohort study was conducted from eight Veterans Affairs' Medical Centers located in the Pacific Northwest. CKD was defined by two continuously abnormal outpatient serum creatinine measurements at least 6 mo apart between 1999 and 2002. Patients who received chronic dialysis, those with a present or previous renal transplant, and those without a recent phosphate measurement were excluded. The primary end point was all-cause mortality. Secondary end points were acute myocardial infarction and the combined end point of myocardial infarction plus death. A total of 95,619 veterans with at least one primary care or internal medicine clinic contact from a Northwest VA facility and two or more outpatient measurements of serum creatinine, at least 6 mo apart, between January 1, 1999, and December 31, 2002, were identified. From this eligible population, 7021 patients met our definition of CKD. After exclusions, 6730 CKD patients were available for analysis, and 3490 had a serum phosphate measurement during the previous 18 mo. After adjustment, serum phosphate levels >3.5 mg/dl were associated with a significantly increased risk for death. Mortality risk increased linearly with each subsequent 0.5-mg/dl increase in serum phosphate levels. Elevated serum phosphate levels were independently associated with increased mortality risk among this population of patients with CKD.

Survival following parathyroidectomy among United States dialysis patients

BACKGROUND

Secondary hyperparathyroidism (SHPTH) is highly prevalent among persons with end-stage renal disease (ESRD). SHPTH has been linked to uremic bone disease, vascular calcification, and a higher risk of death. Parathyroidectomy (PTX) can dramatically reduce parathyroid hormone (PTH) and phosphate levels; however, the relationship between PTX and survival is not known.

METHODS

We conducted an observational matched cohort study utilizing data from the United States Renal Database System (USRDS) in which 4558 patients undergoing a first PTX while on hemodialysis or peritoneal dialysis were individually matched by age, race, gender, cause of ESRD, dialysis duration, prior transplantation status, and dialysis modality to 4558 control patients who did not undergo PTX. Patients were followed from the date of PTX until they died or were lost to follow-up.

RESULTS

The 30-day postoperative mortality rate following PTX was 3.1%. Long-term relative risks of death among patients undergoing PTX were estimated to be 10% to 15% lower than those of matched control patients not undergoing surgery. Survival curves between the 2 groups crossed 587 days following PTX. Median survival was 53.4 months (95% CI: 51.2-56.4) in the PTX group, and 46.8 months (95% CI: 44.7-48.9) in the control group.

CONCLUSION

PTX was associated with higher short-term, and lower long-term, mortality rates among U.S. patients receiving chronic dialysis. Measures to attenuate SHPTH may play an important role in reducing mortality among patients with end-stage renal disease.

Vitamin D analogs in uremia: integrating medical and nutritional issues

A system of regulatory molecules interacts at the cellular level to control and coordinate the many metabolic pathways that constitute normal mineral metabolism. Alterations that occur in uremia profoundly disrupt this intricate system of regulation. A lack of control poses serious consequences for patients with chronic renal disease, and restoring some level of control represents a significant treatment goal. To achieve adequate treatment, it is necessary to correct aberrations in the metabolism of the major regulatory molecules, parathyroid hormone, vitamin D, calcium, and phosphorus. The use of vitamin D hormone replacement therapy is one important part of this strategy, and the availability of newer vitamin D compounds may prove to be especially beneficial. The effective use of these compounds, nevertheless, depends on the coordinated efforts of each member of the health care team to design and implement an integrated treatment protocol that recognizes all aspects of intervention.

IGF-1-induced lipid accumulation impairs mesangial cell migration and contractile function

BACKGROUND

Chronic treatment of mesangial cells with insulin-like growth factor-1 (IGF-1) results in intracellular lipid accumulation. These mesangial cells resemble foam cells.

METHODS

To determine whether this phenotype affects cell function, lipid-laden mesangial cells were tested for their ability to migrate in response to IGF-binding protein-5 (IGFBP-5) and to contract in response to angiotensin II (Ang II). IGFBP-5 binding and subsequent activation of the signal transduction cascade for migration were examined. To confirm that lipid accumulation was responsible for impaired contractility, lipid was removed from lipid-laden mesangial cells and the cells were re-tested for contractile response to Ang II.

RESULTS

In comparison to control mesangial cells, lipid-laden cells failed to migrate in response to IGFBP-5. Although cellular binding of IGFBP-5 was not altered by lipid accumulation, IGFBP-5 failed to activate cdc42, a Rho GTPase required for IGFBP-5-mediated mesangial cell migration. These data indicate that lipid accumulation within the mesangial cell interferes with the signal transduction response to IGFBP-5. In addition, mesangial cells treated with IGF-1 had reduced contraction to Ang II. When lipid accumulation was exaggerated by adding cholesteryl esters to the culture medium, mesangial cells failed to contract in response to Ang II. Following removal of excess lipid from these mesangial cells, the contractile response to Ang II was restored.

CONCLUSIONS

IGF-1 induces lipid accumulation in mesangial cells, which impairs their ability to respond to specific migratory and contractile stimuli. These observations are relevant to understanding functional abnormalities in diseases where mesangial foam cells occur, such as focal and segmental glomerulosclerosis and diabetic nephropathy.

Antiepileptic drug-induced bone loss in young male patients who have seizures

BACKGROUND

Long-term antiepileptic drug (AED) therapy is a known risk factor for bone loss and fractures. Vitamin D deficiency is frequently cited as a cause for bone loss in patients who have seizures.

OBJECTIVE

To determine whether men who have seizures, but who are otherwise healthy, suffer substantial bone loss in the hip while taking AEDs.

PATIENTS AND METHODS

We prospectively examined femoral neck bone mineral density (BMD) by dual-energy x-ray absorptiometry in 81 consecutive men, aged between 25 and 54 years old (mean age, 45 years), who were attending an outpatient seizure clinic. Low BMD values were analyzed for known risk factors for bone loss. Dual-energy x-ray absorptiometry scans were repeated in 54 patients, 12 to 29 months later (mean, 19 months), to assess the rate of change in BMD over time.

RESULTS

Multivariate linear regression analysis revealed that age (P<.001) and time receiving AEDs (P<.003) were the 2 important risk factors associated with low femoral neck BMD. Neither vitamin D deficiency, hypogonadism, cigarette smoking, nor excess alcohol intake were associated with low BMD after correcting for age and time on AEDs. Longitudinal analysis of femoral neck BMD revealed that only those in the youngest age group (25-44 years) showed significant declines in femoral neck BMD (1.8% annualized loss; 95% confidence interval, -3.1 to -0.9; P<.003) while receiving AED therapy. There was no evidence that a specific type of AED was more causally related to bone loss in this group although most patients were taking phenytoin sodium or carbamazepine during the longitudinal assessment.

CONCLUSIONS

Long-term AED therapy in young male patients who have seizures causes significant bone loss at the hip in the absence of vitamin D deficiency. Dual-energy x-ray absorptiometry scanning of the hip is useful in identifying patients who are particularly susceptible to rapid bone loss while taking AEDs.

Cytokine accumulation in osteitis fibrosa of renal osteodystrophy

Bone marrow fibrosis occurs in association with a number of pathological states. Despite the extensive fibrosis that sometimes characterizes renal osteodystrophy, little is known about the factors that contribute to marrow accumulation of fibrous tissue. Because circulating cytokines are elevated in uremia, possibly in response to elevated parathyroid hormone levels, we have examined bone biopsies from 21 patients with end-stage renal disease and secondary hyperparathyroidism. Bone sections were stained with antibodies to human interleukin-1alpha (IL-1alpha), IL-6, IL-11, tumor necrosis factor-alpha (TNF-alpha) and transforming growth factor-beta (TGF-beta) using an undecalcified plastic embedding method. Intense staining for IL-1alpha, IL-6, TNF-alpha and TGF-beta was evident within the fibrotic tissue of the bone marrow while minimal IL-11 was detected. The extent of cytokine deposition corresponded to the severity of fibrosis, suggesting their possible involvement in the local regulation of the fibrotic response. Because immunoreactive TGF-beta and IL-6 were also detected in osteoblasts and osteocytes, we conclude that selective cytokine accumulation may have a role in modulating bone and marrow cell function in parathyroid-mediated uremic bone disease.

Intact IGF-binding protein-4 and -5 and their respective fragments isolated from chronic renal failure serum differentially modulate IGF-I actions in cultured growth plate chondrocytes

Impairment of longitudinal growth among children with chronic renal failure (CRF) may be partly attributable to the inhibition of insulin-like growth factor (IGF) activity by an excess amount of high-affinity IGF-binding proteins (IGFBP). Elevated levels of immunoreactive IGFBP-4 in CRF serum are inversely correlated with the standardized heights of these children, whereas levels of IGFBP-5, which circulates mainly as proteolyzed fragments, are positively correlated with growth parameters. To delineate the respective effects of these IGFBP on growth cartilage, the biologic effects of intact and fragmented forms of IGFBP-4 and IGFBP-5 on rat growth plate chondrocytes in primary cultures were characterized. Intact IGFBP-4 and IGFBP-5 and the amino-terminal fragment IGFBP-5(1-169) were recombinant proteins; the carboxy-terminal fragments IGFBP-5(144-252) and IGFBP-4(136-237) and the amino-terminal fragment IGFBP-4(1-122) were purified to homogeneity from CRF hemofiltrates. Intact IGFBP-4 and, to a lesser extent, IGFBP-4(1-122) inhibited IGF-I-induced cell proliferation. In contrast, intact IGFBP-5 was stimulatory in the absence or presence of exogenous IGF-I, whereas the amino-terminal fragment IGFBP-5(1-169) was inhibitory. Studies on the mechanism by which IGFBP-4 and IGFBP-5 exert opposite effects on chondrocyte proliferation demonstrated that intact IGFBP-4 prevented the binding of (125)I-IGF-I to chondrocytes, whereas intact IGFBP-5 enhanced ligand binding and was able to bind specifically to the cell membrane. These data suggest that intact IGFBP-4 and, to a lesser extent, IGFBP-4(1-122) act exclusively as growth-inhibitory binding proteins in the growth cartilage. IGFBP-5, however, can either stimulate (if it remains intact) or inhibit (if amino-terminal forms predominate) IGF-I-stimulated chondrocyte proliferation.

Intravenous versus oral vitamin d therapy in dialysis patients: what is the question?

The debate regarding the administration of vitamin D (parenteral versus pulse oral) in dialysis patients has centered on the efficacy of parathyroid hormone (PTH) suppression while ignoring other questions related to complications and compliance. Past studies looking at efficacy showed no differences during short-term treatment, although the small number of patients studied reduces the significance of these findings. Long-term studies with larger populations have shown that parenteral calcitriol is more effective than pulse oral calcitriol in suppressing PTH. When considering the questions of complications and compliance the current literature demonstrates that parenteral vitamin D therapy is associated with fewer episodes of hypercalcemia and hyperphosphatemia and that patients receiving pulse oral calcitriol require more phosphate binders. Because of the documented high noncompliance rate with oral medications in the dialysis population, parenterally administered vitamin D is expected to more completely suppress PTH long term and result in fewer parathyroidectomies. Based on these considerations it is suggested that parenteral vitamin D analogs are superior to pulse oral calcitriol for the long-term control of hyperparathyroidism in dialysis patients.

IGF-binding protein-5 stimulates osteoblast activity and bone accretion in ovariectomized mice

Insulin-like growth factor binding protein-5 (IGFBP-5) is an osteoblast secretory protein that becomes incorporated into the mineralized bone matrix. In osteoblast cultures, IGFBP-5 stimulates cell proliferation by an IGF-independent mechanism. To evaluate whether IGFBP-5 can stimulate osteoblast activity and enhance bone accretion in a mouse model of osteoblast insufficiency, daily subcutaneous injections of either intact [IGFBP-5 (intact)] or carboxy-truncated IGFBP-5 [IGFBP-5-(1--169)] were given to ovariectomized (OVX) mice for 8 wk. Femur and spine bone mineral density (BMD), measured every 2 wk, showed early and sustained increases in response to IGFBP-5. Bone histomorphometry of cancellous bone showed significant elevations in the bone formation rate in both the femur metaphysis [IGFBP-5- (1)] only) and spine compared with OVX controls. IGFBP-5 also stimulated osteoblast number in the femur IGFBP-5-(1--169) only) and spine. These data indicate that IGFBP-5 effectively enhances bone formation and bone accretion in OVX mice by stimulating osteoblast activity. The finding that IGFBP-5-(1--169) is bioactive in vivo indicates that the carboxy-terminal portion is not required for this bone anabolic effect.

Vitamin D analogs in uremia: integrating medical and nutritional issues

A system of regulatory molecules interacts at the cellular level to control and coordinate the many metabolic pathways that constitute normal mineral metabolism. Alterations that occur in uremia profoundly disrupt this intricate system of regulation. A lack of control poses serious consequences for patients with chronic renal disease, and restoring some level of control represents a significant treatment goal. To achieve adequate treatment, it is necessary to correct aberrations in the metabolism of the major regulatory molecules, parathyroid hormone, vitamin D, calcium, and phosphorus. The use of vitamin D hormone replacement therapy is one important part of this strategy, and the availability of newer vitamin D compounds may prove to be especially beneficial. The effective use of these compounds, nevertheless, depends on the coordinated efforts of each member of the health care team to design and implement an integrated treatment protocol that recognizes all aspects of intervention.

IGFBP-5(201-218) stimulates Cdc42GAP aggregation and filopodia formationin migrating mesangial cells

BACKGROUND

We have previously shown that insulin-like growth factor-I (IGF-I) and IGF binding protein-5 (IGFBP-5) induce mesangial cell migration using separate stimulatory and effector pathways. The IGFBP-5 stimulatory pathway is mediated by the serine/threonine kinase IGFBP-5 receptor, which is activated by the carboxy-terminal peptide IGFBP-5201-218. In this study, we examined the direct effects of IGFBP-5201-218 on stimulatory and effector pathways that lead to a change in mesangial cell (MC) phenotype.

METHODS

Rapid actin reorganization, formation of filopodia, and characterization of novel substratum attachment structures that develop during IGFBP-5-mediating migration were examined by light, immunofluorescence, and electron microscopy. Using a wounding assay, migration was measured after the addition of stimulants and inhibitors.

RESULTS

Stimulation of MCs with IGFBP-5201-218 induces rapid actin reorganization and loss of peripheral focal adhesions. The MCs develop long cellular extensions where f-actin and beta-actin terminate in unique substratum attachments. Fluorescence microscopy of stimulated cells shows that Cdc42GAP aggregates within minutes following treatment with IGFBP-5201-218. In contrast, IGF-I increases staining for Rac-1, but not Cdc42GAP, in association with the formation of prominent leading lamellae without filopodia. Staurosporin inhibits cell migration and Cdc42GAP aggregation only when added within the first hour, suggesting that it inhibits the stimulatory effect of IGFBP-5201-218 by blocking the IGFBP-5 receptor serine/threonine kinase activity.

CONCLUSIONS

These data demonstrate that IGFBP-5201-218 preferentially activates Cdc42 and induces the formation of long filopodia with unique substratum attachments that produce a novel mode of locomotion.

Insulin-like growth factor binding protein-5 proteolytic activity in ovine articular chondrocyte culture

We have previously demonstrated that ovine articular chondrocytes synthesise and release insulin-like growth factor binding protein-5 (IGFBP-5) which subsequently undergoes proteolysis in the tissue culture medium. The IGFBP-5 proteolytic activity has now been characterised and its substrate specificity analysed using recombinant IGFBP-5 and purified chondrocyte-derived IGFBPs. Iodinated human recombinant IGFBP-5 was incubated with chondrocyte culture or conditioned medium in the presence or absence of various inhibitors. Serine protease inhibitors aprotinin and heparin effectively inhibited the breakdown of IGFBP-5. Furthermore, insulin-like growth factor-I (IGF-I) but not its structural analogues with reduced affinity for IGFBP-5, was also able to partially protect IGFBP-5 from degradation indicating that the association of IGF with the binding protein was required for the inhibition of the proteolytic activity. The inflammatory cytokine interleukin-1 did not have any effect on IGFBP-5 proteolysis. The proteolytic activity appears to be IGFBP-5-specific since the incubation of chondrocyte-derived IGFBPs with chondrocyte conditioned medium resulted in the loss of IGFBP-5 while the levels of the other two IGFBPs (IGFBP-2 and a 24 kDa IGFBP) remained unchanged. In conclusion, we show that IGFBP-5 is specifically cleaved by a serine protease released by primary cultures of ovine articular chondrocytes and also demonstrate the ability of IGF-I to inhibit the proteolytic activity both in cell culture and in cell-free conditions.

Regulation of insulin-like growth factor-binding protein-5 by insulin-like growth factor I and interleukin-1alpha in ovine articular chondrocytes

Insulin-like growth factors (IGFs) contribute to the maintenance of the cartilage matrix by stimulating proteoglycan synthesis. In contrast, interleukin-1 (IL-1), an inflammatory cytokine, suppresses the synthesis of proteoglycans. In pathological conditions the chondrocytes' responsiveness to IGF-I is decreased, and elevated levels of IGF-binding proteins (IGFBPs) have been implicated as a possible cause. The aim of this study was to investigate the effects of IGF-I and IL-1 on IGFBP production by ovine articular chondrocytes (OAC) and the roles of these IGFBPs in the regulation of proteoglycan synthesis. As revealed by Western ligand and immunoblotting, OACs secreted IGFBP-2 and a 24-kDa IGFBP in culture medium under basal conditions. Exposure of the cells to IGF-I for 48 h resulted in the appearance of IGFBP-5 in the medium. Des(1-3)IGF-I, an IGF-I analog with reduced affinity for IGFBPs, also increased the level of IGFBP-5, but to a lesser extent than IGF-I, whereas LR3IGF-I, which has virtually no affinity for IGFBPs, had no effect on IGFBP-5. Furthermore, IGFBP-5 underwent a time-dependent limited proteolysis when incubated with OAC-conditioned medium, degrading into 22- and 16-kDa fragments. The degradation of IGFBP-5 was significantly inhibited by IGF-I, but not by des(1-3)IGF-I or LR3IGF-I. Basic fibroblast growth factor, transforming growth factor-beta, and platelet-derived growth factor had no effect on OAC IGFBPs. However, IL-1alpha increased the IGFBP-5 level in a dose-dependent manner, showing maximum activity at 200 U/ml. Furthermore, IL-1alpha, but not IGF-I, induced IGFBP-5 messenger RNA expression, as assessed by Northern blot analysis. Coincubation of IGF-I with IL-1alpha resulted in a substantially increased IGFBP-5 protein level, suggesting a synergism between the mechanisms of action of these two factors. Des(1-3)IGF-I and LR3IGF-I were 10 times more potent than IGF-I in stimulating proteoglycan synthesis, indicating inhibition of IGF-I activity by endogenous IGFBPs. IL-1alpha reduced the IGF-I bioactivity, but had no effect on the activities of the IGF-I analogs, thus implying that locally produced IGFBPs, particularly IGFBP-5, which was substantially increased when IGF-I and IL-1alpha were coincubated, mediated the reduction of the IGF-I activity. Our results demonstrate that IGF-I and IL-1alpha synergistically increase the level of IGFBP-5 in OAC by inhibiting the proteolysis and stimulating the expression of IGFBP-5, respectively. Furthermore, the attenuation of IGF-I-stimulated proteoglycan synthesis by IL-1alpha in OAC appears to be mediated by chondrocyte IGFBPs. We conclude that locally produced IGFBPs, in particular IGFBP-5, may play a critical role in the regulation of cartilage matrix degradation in inflammatory and degenerative arthritides.

Insulin-like growth factor-binding protein-5 (IGFBP-5) stimulates phosphorylation of the IGFBP-5 receptor

The finding that insulin-like growth factor (IGF)-binding protein-5 (IGFBP-5) binding to mouse osteoblasts was capable of being downregulated by IGFBP-5 suggested that the 420-kDa membrane protein, which interacted with IGFBP-5, may be a signaling receptor (Andress, D. L. J. Biol. Chem. 270: 28289-28296, 1995). In the current study, a carboxy-terminal IGFBP-5 peptide, IGFBP-5-(201-218), which was found to competitively inhibit 125I-IGFBP-5 binding and to specifically bind to osteoblast monolayers, was used to affinity-purify the 420-kDa membrane protein. Co-incubation of the affinity-purified membrane protein with [32P]ATP resulted in autophosphorylation at serine residues. Serine phosphorylation of the 420-kDa protein was enhanced by intact IGFBP-5, IGFBP-5-(1-169), and IGFBP-5-(201-218). When the IGFBP-5 receptor was incubated with dephosphorylated casein in the presence of [32P]ATP, casein became phosphorylated on serine residues. These data indicate that IGFBP-5 stimulates the phosphorylation of the IGFBP-5 receptor and suggest that serine/threonine kinase activation may be important in mediating some of the IGF-independent effects of IGFBP-5.

A calcimimetic agent acutely suppresses parathyroid hormone levels in patients with chronic renal failure. Rapid communication

The control of hyperparathyroidism in patients with chronic renal failure continues to be a problem, particularly when parathyroid hormone (PTH) suppression becomes refractory to calcitriol activation of parathyroid cell 1,25-dihydroxyvitamin D receptors. To evaluate whether parathyroid cell calcium receptor activation may be useful in suppressing PTH levels, we tested the safety and effectiveness of a novel calcimimetic agent in dialysis patients with hyperparathyroidism. In a prospective, dose finding study, the calcimimetic agent, NPS R-568, was administered orally to seven patients at the start of a hemodialysis session and again 24 hours later. Plasma PTH, calcitonin and ionized calcium levels were measured over a 48 hour period and patients were observed for adverse events. Plasma PTH levels fell abruptly in all patients after a single dose of the compound, with the maximum suppression occurring within one to two hours after its administration. Following the administration of low doses (40 or 80 mg), the suppressed PTH levels rose to baseline values over 48 hours, whereas in patients who received high doses (120 or 200 mg) the mean PTH level remained 51% below baseline. Plasma calcitonin increased after the administration of both low and high doses (peak effect within 4 to 6 hr), with levels always returning to baseline by 48 hours. There were no episodes of hypocalcemia and no adverse effects were reported. We conclude that the activation of parathyroid cell calcium receptors by a novel calcimimetic compound is safe and effective in acutely suppressing PTH secretion in dialysis patients with hyperparathyroidism. Whether concomitant stimulation of calcitonin secretion will provide added beneficial effects on bone remodeling remains to be determined in long-term studies.

Evidence that serum phosphate is independently associated with serum PTH in patients with chronic renal failure

There has been controversy regarding the initial pathogenic events involved with the hyperparathyroidism of chronic renal failure (CRF). Low serum levels of 1,25-dihydroxyvitamin D in uremic patients are postulated by some as having a role in permitting higher parathyroid hormone (PTH) secretion. However, recent animal and in vitro studies strongly suggest that phosphate has a direct effect on parathyroid cells to enhance PTH secretion. To evaluate the relationships among serum phosphate, calcium, PTH, and 1,25-dihydroxyvitamin D in uremic humans, we performed a cross-sectional analysis of 84 patients with varying levels of CRF. Using stepwise regression analysis after adjusting for multiple comparisons, we found that serum phosphate correlated directly with serum PTH (r = 0.62, P < 0.01) in patients with mild to moderate CRF (creatinine < or = 3.0 mg/dL), independent of serum calcium and 1,25-dihydroxyvitamin D levels. In patients with more severe renal failure (creatinine > 3.0 mg/dL), only the serum calcium correlated with serum PTH (r = -0.47, P < 0.01). While serum 1 ,25-dihydroxyvitamin D showed no correlations with PTH, phosphate, or calcium at any stage of renal failure, the mean 1,25-dihydroxyvitamin D level in patients with mild CRF was lower than that in age-matched controls (24 +/- 3 pg/mL v 37 +/- 2 pg/mL; P < 0.01), suggesting that low 1,25-dihydroxyvitamin D was permissive for enhanced PTH secretion. These data demonstrate an independent association of serum phosphate with PTH in patients with CRF and suggest that phosphate may directly enhance PTH secretion in this setting. This study supports recent animal studies showing a direct parathyroid cell effect of phosphate on PTH secretion.

Heparin binding domain of insulin-like growth factor binding protein-5 stimulates mesangial cell migration

Insulin-like growth factor I (IGF-I) binding protein-5 (IGFBP-5) is produced by mesangial cells (MCs) and likely functions to modulate glomerular IGF-I activity. Although IGFBP-5 may be inhibitory for IGF-stimulated MC activity, preliminary studies suggested that IGFBP-5 acts directly on MCs. To investigate this further, we evaluated the effects of IGFBP-5 on rat MC migration. We found that the carboxytruncated fragment, IGFBP-5-(1-169), inhibited IGF-I-stimulated migration, but intact IGFBP-5 simulated migration when IGF-I was not present. Demonstration that 125I-labeled IGFBP-5 directly binds to MCs further supports an independent role for IGFBP-5. Because heparin inhibited MC binding of 125I-IGFBP-5, we tested the heparin binding peptide, IGFBP-5-(201-218), for stimulatory activity. IGFBP-5-(201-218) stimulated MC migration, and this effect was inhibited by heparin. Because the disintegrin, kistrin, blocked IGF-I-induced migration but not migration induced by IGFBP-5-(201-218), the migratory induction mechanism for the two peptides is different. These data indicate that separate, specific regions of IGFBP-5 are responsible for interactive effects with IGF-I as well as direct effects on MC activity.

Insulin-like growth factor (IGF)-binding protein-5-(201-218) region regulates hydroxyapatite and IGF-I binding

Insulin-like growth factor-binding protein-5 (IGFBP-5), the major bone IGFBP, modifies the biological activity of IGFs within the osteoblastic pericellular environment. Because glycosaminoglycans modulate IGFBP-5 binding to osteoblast organic extracellular matrix (ECM), we assessed whether the heparin binding domain of IGFBP-5, IGFBP-5-(102-218), modifies the interaction of IGFBP-5 with the inorganic bone ECM hydroxyapatite (HA). Synthetic IGFBP-5-(201-218) peptide increased the binding of IGFBP-5 to HA as well as the binding of IGF-I to HA-bound IGFBP-5. This action was specific for the heparin-binding domain, because IGFBP-5-(130-138), IGFBP-5-(138-152), and IGFBP-5-(1-169) were without effect. IGFBP-5-(201-218) was found to bind directly to IGFBP-5 and cause a threefold enhancement of the IGF-I binding affinity for IGFBP-5, whether IGFBP-5 was bound to HA or was in a matrix-free fluid phase. Heparin inhibited the binding of IGFBP-5 to HA and blocked the interaction of IGFBP-5 with IGFBP-5-(201-218) in the fluid phase, suggesting that the primary heparin-binding domain of IGFBP-5 specifically enhances the binding of IGFBP-5 to HA and increases IGF-I binding to IGFBP-5.