Canadian Society of Nephrology Commentary on the Kidney Disease Improving Global Outcomes 2017 Clinical Practice Guideline Update for the Diagnosis, Evaluation, Prevention, and Treatment of Chronic Kidney Disease-Mineral and Bone Disorder

Purpose of review:

(1) To provide commentary on the 2017 update to the Kidney Disease Improving Global Outcomes (KDIGO) 2017 Clinical Practice Guideline Update for the Diagnosis, Evaluation, Prevention, and Treatment of Chronic Kidney Disease-Mineral and Bone Disorder (CKD-MBD); (2) to apply the evidence-based guideline update for implementation within the Canadian health care system; (3) to provide comment on the care of children with chronic kidney disease (CKD); and (4) to identify research priorities for Canadian patients.

Sources of information:

The KDIGO 2017 Clinical Practice Guideline Update for the Diagnosis, Evaluation, Prevention, and Treatment of CKD-MBD.

Methods:

The commentary committee co-chairs selected potential members based on their knowledge of the Canadian kidney community, aiming for wide representation from relevant disciplines, academic and community centers, and different geographical regions.

Key findings:

We agreed with many of the recommendations in the clinical practice guideline on the diagnosis, evaluation, prevention, and treatment of CKD-MBD. However, based on the uncommon occurrence of abnormalities in calcium and phosphate and the low likelihood of severe abnormalities in parathyroid hormone (PTH), we recommend against screening and monitoring levels of calcium, phosphate, PTH, and alkaline phosphatase in adults with CKD G3. We suggest and recommend monitoring these parameters in adults with CKD G4 and G5, respectively. In children, we agree that monitoring for CKD-MBD should begin in CKD G2, but we suggest measuring ionized calcium, rather than total calcium or calcium adjusted for albumin. With regard to vitamin D, we suggest against routine screening for vitamin D deficiency in adults with CKD G3-G5 and G1T-G5T and suggest following population health recommendations for adequate vitamin D intake. We recommend that the measurement and management of bone mineral density (BMD) be according to general population guidelines in CKD G3 and G3T, but we suggest against routine BMD testing in CKD G4-G5, CKD G4T-5T, and in children with CKD. Based on insufficient data, we also recommend against routine bone biopsy in clinical practice for adults with CKD or CKD-T, or in children with CKD, although we consider it an important research tool.

Limitations:

The committee relied on the evidence summaries produced by KDIGO. The CSN committee did not replicate or update the systematic reviews.

Retention in a 10-year cohort of internationally trained family physicians licensed in Manitoba

INTRODUCTION

International medical graduates (IMGs) seeking licensure in Canada have been recruited to practise in medically underserviced areas, but retention of these physicians remains a concern. This study explored retention of IMG family physicians in Manitoba and its predictors.

METHODS

We used data from the University of Manitoba, provincial registries and Manitoba Health. Inclusion criteria were IMGs who completed University of Manitoba IMG training or assessment programs, and their return-of-service. Practice location, certification and licensure status were examined. We used logistic regression to consider the effects of a mentorship program, Manitoba residency at application, IMG program and years since program graduation on retention.

RESULTS

A total of 197 IMGs met the inclusion criteria. Most IMGs (63.5%) remained in Manitoba, and 59.2% of this group practised outside of Winnipeg. Of those remaining in Manitoba, most (69.6%) held full provincial licensure and national certification. The regression model was significant (χ²₄ = 13.94, p = 0.007), explaining 10% of the variance in retention. Two predictors were significant: years since program graduation and Manitoba residency at the time of application.

CONCLUSION

Long-term retention of IMG physicians remains a concern. Potential interventions likely to increase retention, such as Manitoba residency at application and a focus on mentorship programs, should be further explored.

Proteomic characterization of serine hydrolase activity and composition in normal urine

Background

Serine hydrolases constitute a large enzyme family involved in a diversity of proteolytic and metabolic processes which are essential for many aspects of normal physiology. The roles of serine hydrolases in renal function are largely unknown and monitoring their activity may provide important insights into renal physiology. The goal of this study was to profile urinary serine hydrolases with activity-based protein profiling (ABPP) and to perform an in-depth compositional analysis.

Methods

Eighteen healthy individuals provided random, mid-stream urine samples. ABPP was performed by reacting urines (n = 18) with a rhodamine-tagged fluorophosphonate probe and visualizing on SDS-PAGE. Active serine hydrolases were isolated with affinity purification and identified on MS-MS. Enzyme activity was confirmed with substrate specific assays. A complementary 2D LC/MS-MS analysis was performed to evaluate the composition of serine hydrolases in urine.

Results

Enzyme activity was closely, but not exclusively, correlated with protein quantity. Affinity purification and MS/MS identified 13 active serine hydrolases. The epithelial sodium channel (ENaC) and calcium channel (TRPV5) regulators, tissue kallikrein and plasmin were identified in active forms, suggesting a potential role in regulating sodium and calcium reabsorption in a healthy human model. Complement C1r subcomponent-like protein, mannan binding lectin serine protease 2 and myeloblastin (proteinase 3) were also identified in active forms. The in-depth compositional analysis identified 62 serine hydrolases in urine independent of activity state.

Conclusions

This study identified luminal regulators of electrolyte homeostasis in an active state in the urine, which suggests tissue kallikrein and plasmin may be functionally relevant in healthy individuals. Additional serine hydrolases were identified in an active form that may contribute to regulating innate immunity of the urinary tract. Finally, the optimized ABPP technique in urine demonstrates its feasibility, reproducibility and potential applicability to profiling urinary enzyme activity in different renal physiological and pathophysiological conditions.

Serum creatinine measurement immediately after cardiac surgery and prediction of acute kidney injury

BACKGROUND

After heart surgery, acute kidney injury (AKI) confers substantial long-term risk of death and chronic kidney disease. We hypothesized that small changes in serum creatinine (SCr) levels measured within a few hours of exit from the operating room could help discriminate those at low versus high risk of AKI.

STUDY DESIGN

Prospective cohort of 350 elective cardiac surgery patients (valve or coronary artery bypass grafting) recruited in Winnipeg, Canada. Baseline SCr level was obtained at the preoperative visit 2 weeks before surgery. The postoperative SCr level was drawn within 6 hours of completion of surgery and then daily while the patient was in the hospital.

PREDICTOR

Immediate (ie, <6 hours) postoperative SCr level change (ΔSCr), categorized as within 10% (reference), decrease >10%, or increase >10% relative to baseline.

OUTCOME

AKI, defined according to the new KDIGO (Kidney Disease: Improving Global Outcomes) consensus definition as an increase in SCr level >0.3 mg/dL within 48 hours or >1.5 times baseline within 1 week.

MEASUREMENTS

We compared the C statistic of logistic models with and without inclusion of immediate postoperative ΔSCr.

RESULTS

After surgery, 176 patients (52%) experienced a decrease >10% in SCr level, 26 (7.4%) experienced an increase >10%, and 143 had ΔSCr within ±10% of baseline. During hospitalization, 53 (14%) developed AKI. Bypass pump time, baseline estimated glomerular filtration rate, and European System for Cardiac Operative Risk Evaluation (euroSCORE) were associated with AKI in a parsimonious base logistic model. Added to the base model, immediate postoperative ΔSCr was associated strongly with subsequent AKI and significantly improved model discrimination over the base model (C statistic, 0.78 [95% CI, 0.71-0.85] vs 0.69 [95% CI, 0.62-0.77]; P < 0.001). A ≥10% SCr level decrease predicted significantly lower AKI risk (OR, 0.37; 95% CI, 0.18-0.76), whereas a ≥10% SCr level increase predicted significantly higher (OR, 6.38; 95% CI, 2.37-17.2) AKI risk compared with the reference category.

LIMITATIONS

We used a surrogate marker of AKI. External validation of our results is warranted.

CONCLUSION

In elective cardiac surgery patients, measurement of immediate postoperative ΔSCr improves prediction of AKI.

Urinary hepcidin-25 and risk of acute kidney injury following cardiopulmonary bypass

BACKGROUND AND OBJECTIVES

Acute kidney injury (AKI) complicating cardiopulmonary bypass (CPB) results in increased morbidity and mortality. Urinary hepcidin-25 has been shown to be elevated in patients who do not develop AKI after CPB using semiquantitative mass spectrometry (SELDI TOF-MS). The goals of this study were to quantitatively validate these findings with ELISA and evaluate the diagnostic performance of hepcidin-25 for AKI.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

A nested, case-control analysis of urinary hepcidin-25 in AKI (n = 22) and non-AKI (n = 22) patients was conducted to validate the SELDI TOF-MS data at the following times: preoperatively; the start of CPB; 1 hour on CPB; on arrival to the intensive care unit; and postoperative days (POD) 1 and 3 to 5. The diagnostic performance of hepcidin-25 was then evaluated in the entire prospective observational cohort (n = 338) at POD 1. AKI was defined as Cr >50% from baseline, within 72 hours postoperatively.

RESULTS

Urinary hepcidin-25/Cr ratio was significantly elevated in all patients at POD 1 compared with baseline (P < 0.0005) and was also significantly elevated in non-AKI versus AKI patients at POD 1 (P < 0.0005). Increased log(10) hepcidin-25/Cr ratio was strongly associated with avoidance of AKI on univariate analysis. On multivariate analysis, the log(10) hepcidin-25/Cr ratio (P < 0.0001) was associated with avoidance of AKI with an area under the curve of 0.80, sensitivity 0.68, specificity 0.68, and negative predictive value 0.96.

CONCLUSIONS

Elevated urinary hepcidin-25 on POD 1 is a strong predictor of avoidance of AKI beyond postoperative day 1.

Long-term outcomes of end-stage renal disease patients admitted to the ICU

BACKGROUND

End-stage renal disease (ESRD) patients admitted to the intensive care unit (ICU) have poor survival and high rates of readmission; however, little evidence exists on long-term outcomes. We set out to investigate the long-term (6 and 12 months) survival of ESRD patients admitted to the ICU and whether differential survival could be explained by dialysis modality and vascular access.

METHODS

We compared the admission characteristics, outcomes and readmission rates of 619 ESRD [95 peritoneal dialysis (PD), 334 hemodialysis with a catheter (HD CVC), 190 hemodialysis with an AV fistula (HD AVF)] patients admitted to 11 ICU's in Winnipeg, Manitoba, Canada. Parametric and nonparametric tests were used as appropriate to determine differences in baseline characteristics. Multivariable Cox and logistic regression was used to assess outcomes between the groups.

RESULTS

The 6- and 12-month crude survival was 62 and 52%, respectively. In a univariate model, modality and vascular access were associated with an increased hazard ratio (HR) of death [PD HR 1.60 95% confidence interval (CI) 1.20-2.13, HD CVC HR 1.55 95% CI 1.25-1.93] compared to patients on HD with an AVF. In three different multivariate adjusted models, this association persisted with HRs for death of 1.63-1.75 for PD and 1.50-1.58 for HD CVC.

CONCLUSIONS

Overall long-term survival of ESRD patients after admission to the ICU is poor. Being on PD or being dialyzed with a catheter was independently associated with an increased mortality.

Sodium thiosulfate-based treatment in calcific uremic arteriolopathy: a consecutive case series

BACKGROUND

Calcific uremic arteriolopathy (CUA) is a rare complication in end stage renal disease with high mortality. Numerous case reports and one case series of 3 patients report the benefit of sodium thiosulfate (STS) for treatment of CUA. The purpose of this evaluation was to examine the response to a STS-based treatment approach in patients with CUA with 1 year follow up.

METHODS

A retrospective case series of 6 consecutive patients from Manitoba, Canada who met predefined diagnostic criteria for CUA and received STS between 2006 and 2008 were included. STS responders were defined as improvement in at least one of the following three parameters: pain severity, wound size and diagnostic imaging/radiography. Mortality, STS dose, duration, adverse events and cost were also collected.

RESULTS

Four patients were classified as responders. The 2 responders who survived at 1 year of follow-up demonstrated an improvement in all 3 parameters examined including an improvement in their follow-up diagnostic imaging results within the first 4 - 6 weeks of STS treatment. At 1 year of follow-up, 3 patients died.

CONCLUSION

Using an STS-based multifaceted treatment approach for CUA, 4 patients responded but 3 of 6 patients died within 1 year. Further larger prospective studies are needed to delineate STS responders from non-responders.

End-stage renal disease status and critical illness in the elderly

BACKGROUND AND OBJECTIVES

Elderly patients (> 65 years old) are a rapidly growing demographic in the ESRD and intensive care unit (ICU) populations, yet the effect of ESRD status on critical illness in elderly patients remains unknown. Reliable estimates of prognosis would help to inform care and management of this frail and vulnerable population.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

The effect of ESRD status on survival and readmission rates was examined in a retrospective cohort of 14,650 elderly patients (>65 years old) admitted to 11 ICUs in Winnipeg, Manitoba, Canada between 2000 and 2006. Logistic regression models were used to adjust odds of mortality and readmission to ICU for baseline case mix and illness severity.

RESULTS

Elderly ESRD patients had twofold higher crude in-hospital mortality (22% versus 13%, P < 0.0001) and readmission rate (6.4 versus 2.7%, P = 0.001). After adjustment for illness severity alone or illness severity and case mix, the odds ratio for mortality decreased to 0.85 (95% CI: 0.57 to 1.25) and 0.82 (95% CI: 0.55 to 1.23), respectively. In contrast, ESRD status remained significantly associated with readmission to ICU after adjustment for other risk factors (OR 2.06 [95% CI: 1.32, 3.22]).

CONCLUSIONS

Illness severity on admission, rather than ESRD status per se, appears to be the main driver of in-hospital mortality in elderly patients. However, ESRD status is an independent risk factor for early and late readmission, suggesting that this population might benefit from alternative strategies for ICU discharge.

Cardiovascular disease in end-stage renal disease: the challenge of assessing and managing cardiac disease in dialysis patients

Cardiovascular disease (CVD) is the leading cause of mortality in end-stage renal disease (ESRD), approximating a 10- to 20-fold higher risk of death in dialysis patients than in the general population. Despite this, dialysis patients often undergo fewer investigations, receive less invasive procedures, and are prescribed fewer medications compared with age-matched non-ESRD patients. A lack of randomized control trials for evidence-based treatment strategies in this population may explain some of these discrepancies, but there is concern that an attitude of "therapeutic nihilism" may be impacting on the medical care of these patients. In this review, we will explore CVD in the ESRD population. Specifically, we will try to address the following issues in patients with ESRD: (1) mechanisms of CVD, (2) cardiac evaluation and the role of coronary revascularization with percutaneous or coronary artery bypass procedures, and (3) cardiac pharmacotherapy use.

Peritonitis and exit site infections in First Nations patients on peritoneal dialysis

BACKGROUND AND OBJECTIVES

First Nations (FN) patients on peritoneal dialysis experience poor outcomes. Whether discrepancies exist regarding the microbiology, rate of infections, and outcomes between FN and non-FN peoples remains unknown. Design, setting, participants, & measures: All adult peritoneal dialysis patients (n = 727) from 1997 to 2007 residing in Manitoba, Canada, were included. Parametric and nonparametric tests were used as necessary. Negative binomial regression was used to determine the relationship of rates of exit site infections (ESIs) and peritonitis between FN and non-FN peoples.

RESULTS

A total of 161 FN and 566 non-FN subjects were included in the analyses. The unadjusted relative rates of peritonitis and ESIs in FN subjects were 132.7 and 86.0/100 patient-years compared with 87.8 and 78.2/100 patient-years in non-FN populations, respectively. FN subjects were more likely to have culture-negative peritonitis (36.5 versus 20.8%, P < 0.0001) and Staphylococcus ESIs (54.1 versus 32.9%, P < 0.0001). The crude and adjusted rates of peritonitis were higher in FN subjects for total episodes and culture-negative and gram-negative peritonitis. Catheter removal because of peritonitis was similar in both groups (42.9 versus 38.1% for FN and non-FN subjects, respectively; P = 0.261).

CONCLUSIONS

FN patients experience higher rates of peritonitis and similar rates of ESIs compared with non-FN patients. Interventions to improve outcomes and prevent infections should specifically be targeted to the FN population.

Adverse outcomes among Aboriginal patients receiving peritoneal dialysis

BACKGROUND

The Aboriginal population in Canada experiences high rates of end-stage renal disease and need for dialytic therapies. Our objective was to examine rates of mortality, technique failure and peritonitis among adult aboriginal patients receiving peritoneal dialysis in the province of Manitoba. We also aimed to explore whether differences in these rates may be accounted for by location of residence (i.e., urban versus rural).

METHODS

We included all adult patients residing in the province of Manitoba who received peritoneal dialysis during the period from 1997-2007 (n = 727). We extracted data from a local administrative database and from the Canadian Organ Replacement Registry and the Peritonitis Organism Exit-sites/Tunnel infections (POET) database. We used Cox and logistic regression models to determine the relationship between outcomes and Aboriginal ethnicity. We performed Kaplan-Meier analyses to examine the relationship between outcomes and urban (i.e., 50 km or less from the primary dialysis centre in Winnipeg) versus rural (i.e., more than 50 km from the centre) residency among patients who were aboriginal.

RESULTS

One hundred sixty-one Aboriginal and 566 non-Aboriginal patients were included in the analyses. Adjusted hazard ratios for mortality (HR 1.476, CI 1.073-2.030) and adjusted time to peritonitis (HR 1.785, CI 1.352-2.357) were significantly higher among Aboriginal patients than among non-Aboriginal patients. We found no significant differences in mortality, technique failure or peritonitis between urban- or rural-residing Aboriginal patients.

INTERPRETATION

Compared with non-Aboriginal patients receiving peritoneal dialysis, Aboriginal patients receiving peritoneal dialysis had higher mortality and faster time to peritonitis independent of comorbidities and demographic characteristics. This effect was not influenced by place of residence, whether rural or urban.

Acute kidney injury in critically ill patients infected with 2009 pandemic influenza A(H1N1): report from a Canadian Province

BACKGROUND

2009 pandemic influenza A(H1N1) has led to a global increase in severe respiratory illness. Little is known about kidney outcomes and dialytic requirements in critically ill patients infected with pandemic H1N1.

STUDY DESIGN

Prospective observational study.

SETTING & PARTICIPANTS

50 patients with pandemic H1N1 admitted to any of 7 intensive care units in Manitoba, Canada, were prospectively followed.

OUTCOME & MEASUREMENTS

Outcomes were kidney injury and kidney failure defined using RIFLE (risk, injury, failure, loss, end-stage disease) criteria or need for dialysis therapy.

RESULTS

The pandemic H1N1 group was composed of 50 critically ill patients with pandemic H1N1 with severe respiratory syndrome (47 confirmed cases, 3 probable). Kidney injury, kidney failure, and need for dialysis occurred in 66.7%, 66%, and 11% of patients, respectively. Mortality was 16%. Kidney failure was associated with increased death (OR, 11.29; 95% CI, 1.29-98.9), whereas the need for dialysis was associated with an increase in length of stay (RR, 2.38; 95% CI, 2.13-25.75).

LIMITATIONS

Small population studied from single Canadian province; thus, limited generalizability.

CONCLUSIONS

In critically ill patients with pandemic H1N1, kidney injury, kidney failure, and the need for dialysis are common and associated with an increase in mortality and length of intensive care unit stay.

An unusual cause of acute renal failure in sickle cell disease

A young female with sickle cell disease was treated for biopsy-proven IgA nephropathy. Serum creatinine levels resolved to normal range, but a year later, she presented with oedema, hypertension and acute renal failure. A repeat renal biopsy showed acute-on-chronic thrombotic microangiopathy (TMA). We suggest that circulating microparticles could be a pathophysiological link between sickle cell disease and the development of renal TMA. This case emphasizes the importance of a further biopsy for acutely declining renal function, even when a definite diagnosis has been made from a previous biopsy.

Outcomes of chronic dialysis patients admitted to the intensive care unit

Admission rates and outcomes of patients who have ESRD and are admitted to an intensive care unit (ICU) are not well defined. We conducted a historical cohort study using a prospective regional ICU database that captured all 11 adult ICUs in Winnipeg, Canada. Between 2000 and 2006, there were 34,965 total admissions to the ICU, 1173 (3.4%) of which were patients with ESRD. The main admission diagnoses among patients with ESRD were cardiac disease (31%), sepsis (15%), and arrest (10%). Compared with other patients in the ICU, those with ESRD were significantly younger but had more diabetes, peripheral arterial disease, and higher APACHE II (Acute Physiology and Chronic Health Evaluation II) scores; mean length of stay in the ICU was similar, however, between these two groups. Restricting the analysis to first admissions to the ICU, unadjusted in-hospital mortality was higher for patients with ESRD (16 versus 11%; P < 0.0001), but this difference did not persist after adjustment for baseline illness severity. In conclusion, although ESRD associates with increased mortality among patients who are admitted to the ICU, this effect is mostly a result of comorbidity.

Toward point-of-care diagnostic metabolic fingerprinting: quantification of plasma creatinine by infrared spectroscopy of microfluidic-preprocessed samples

Infrared (IR) spectroscopy has previously been established as a means to accurately quantify several serum and urine metabolites, based upon spectroscopy of dry films. The same technique has also provided the basis to develop certain diagnostic tests, developed in the 'metabolomics' spirit. Here, we report on the further development of an integrated microfluidic-IR technology and technique, customized with the aim of dramatically extending the capabilities of IR spectroscopy in both analytical and diagnostic (metabolomic) applications. By exploiting the laminar fluid diffusion interface (LFDI), serum specimens are processed to yield product streams that are better suited for metabolic fingerprinting; metabolites are captured within the aqueous product stream, while proteins (which otherwise dominate the spectra of films dried from serum) are present in much reduced concentration. Spectroscopy of films dried from the aqueous stream then provides enhanced diagnostic and analytical sensitivity. The manuscript introduces an LFDI card design that is customized for integration with IR spectroscopy, and details the development of a quantitative assay for serum creatinine--based upon LFDI-processed serum samples--that is substantially more accurate (standard error of calibration, SEC = 43 micromol/L) than the corresponding assay based upon unprocessed serum specimens (SEC = 138 micromol/L). Preliminary results of diffusion modeling are reported, and the prospects for further optimization of the technique, guided by accurate modeling, are discussed.

Mass spectrometry-based proteomic analysis of urine in acute kidney injury following cardiopulmonary bypass: a nested case-control study

BACKGROUND

The early evolution of acute kidney injury (AKI) in humans is difficult to study noninvasively. We hypothesized that urine proteomics could provide insight into the early pathophysiology of human AKI.

STUDY DESIGN

A prospective nested case-control study (n = 250) compared serial urinary proteomes of 22 patients with AKI and 22 patients without AKI before, during, and after cardiopulmonary bypass surgery.

OUTCOMES

AKI was defined as a greater than 50% increase in serum creatinine level, and non-AKI, as less than 10% increase from baseline.

MEASUREMENTS

Serum creatinine, urine protein-creatinine ratio, neutrophil gelatinase-associated lipocalin (NGAL), alpha1-microglobulin, interferon-inducible protein-10 (IP-10), monokine induced by interferon gamma (Mig), interferon-inducible T cell alpha chemoatractant (I-TAC), interleukin 6 (IL-6), IL-1beta, and IL-10. Urine protein profiling by means of surface-enhanced laser desorption/ionization time-of-flight mass spectrometry (SELDI-TOF-MS).

RESULTS

SELDI-TOF-MS showed intraoperative tubular stress in both groups on arrival to the intensive care unit, evidenced by beta2-microglobulinuria. Non-AKI proteomes returned toward baseline postoperatively. In contrast, AKI proteomes showed a second phase of tubular injury/stress with the reappearance of beta2-microglobulin and multiple unidentified peaks (3 to 5 and 6 to 8 kDa) and the appearance of established tubular injury markers: urinary protein, alpha1-microglobulin, and NGAL. Furthermore, 2 novel peaks (2.43 and 2.78 kDa) were found to be dominant in postoperative non-AKI urine samples. The 2.78-kDa protein was identified as the active 25-amino acid form of hepcidin (hepcidin-25), a key regulator of iron homeostasis. Finally, an inflammatory component of reperfusion injury was evaluated by means of enzyme-linked immunosorbent assay analysis of candidate chemokines (IP-10, I-TAC, and Mig) and cytokines (IL-6, IL-1beta, and IL-10). Of these, IP-10 was upregulated in patients with versus without AKI postoperatively.

LIMITATIONS

This is an observational study. SELDI-TOF-MS is a semiquantitative technique.

CONCLUSIONS

Evaluation of human AKI revealed early intraoperative tubular stress in all patients. A second phase of injury observed in patients with AKI may involve IP-10 recruitment of inflammatory cells. The enhancement of hepcidin-25 in patients without AKI may suggest a novel role for iron sequestration in modulating AKI.

Role of calcification inhibitors in the pathogenesis of vascular calcification in chronic kidney disease (CKD)

BACKGROUND

The majority of patients with chronic kidney disease (CKD) have excessive vascular calcification; however, most studies demonstrate that a subset of CKD patients do not have, nor develop, vascular calcification despite similar exposure to the uremic environment. This suggests protective mechanisms, or naturally occurring inhibitors, of calcification may be important.

METHODS

In order to determine the role of three inhibitors, fetuin-A, matrix gla protein (MGP), and osteoprotegerin (OPG) in the vascular calcification observed in patients with CKD-5, we (1) measured serum levels of these inhibitors and compared the levels to calcification assessed by computed tomography (CT); (2) examined arteries from CKD-5 patients by immunostaining for these inhibitors; and (3) examined the expression and effect of these inhibitors in cultured bovine vascular smooth muscle cells (BVSMCs) incubated in serum pooled from uremic patients compared to healthy controls.

RESULTS

There was a negative correlation of coronary artery calcification scores with serum fetuin-A levels (r=-0.30, P= 0.034) and a positive association with OPG levels (r= 0.29, P= 0.045). There was increasing immunostaining for both fetuin-A and MGP in arteries with increasing calcification graded semiquantitatively (P < 0.003). In vitro, fetuin-A added to mineralizing BVSMCs inhibited mineralization (P < 0.001). Compared to normal serum, BVSMCs incubated with uremic serum had a progressive increase in MGP expression with mineralization (P < 0.001) and increased expression of OPG in BVSMCs (P < 0.04).

CONCLUSION

These data demonstrate that fetuin-A, OPG, and MGP play an important role in the pathogenesis of uremic vascular calcification.

Natural history of vascular calcification in dialysis and transplant patients

BACKGROUND

The purpose of the present study was to determine the natural history of coronary artery and aorta calcification by spiral computed tomography (CT) in patients who undergo a renal transplant and patients on haemodialysis.

METHODS

Two cohorts were evaluated for the natural history of vascular calcification: (i) 23 patients who underwent a baseline CT scan at the time of renal transplant and a repeat evaluation 15-20 months later; and (ii) 33 chronic kidney disease, stage 5 haemodialysis subjects who underwent a baseline CT scan, all followed for a minimum of 15 months, and 17 of whom underwent a second CT scan.

RESULTS

In the patients undergoing a renal transplant, there was no net change in CAC with time, suggesting stabilization of calcification. In the haemodialysis patients, the median CAC increased by 1.27+/-1.88 score/days, P = 0.013. There was a trend towards increasing AoC score in both groups. All patients without calcification at baseline remained calcification free at follow-up. In the 15 months following baseline, the six dialysis patients who died had a significantly greater CAC score at baseline compared with the 24 patients who remained alive. Similarly, those patients who were hospitalized had a greater baseline CAC than patients who were not hospitalized.

CONCLUSION

In this preliminary study, renal transplantation appears to slow down or arrest CAC, whereas CAC progresses in haemodialysis patients. In haemodialysis patients, CAC was greater in patients who died or were hospitalized compared with those who remained alive or were not hospitalized.

Vascular calcification in dialysis patients: pathogenesis and consequences

BACKGROUND

Vascular calcification is believed to have a crucial role in the excess cardiovascular mortality and morbidity in patients with end-stage renal disease (ESRD).

METHODS AND RESULTS

Recent evidence suggests that uremic vascular calcification is an active cell-mediated process resembling osteogenesis in bone, rather than passive precipitation of calcium and phosphorus in the setting of deranged mineral metabolism. To date, several bone-associated proteins (osteopontin, bone sialoprotein, alkaline phosphatase, and type I collagen) have been shown in histological sections of vessels obtained from patients with ESRD or calcific uremic arteriolopathy. In in vitro experiments, the addition of uremic serum upregulates osteopontin expression by cultured vascular smooth muscle cells (VSMCs).

CONCLUSION

We are only beginning to understand the process by which VSMCs transform into osteoblast-like cells, although phosphorus may have a key role. Additional factors mediating or modulating the development of vascular calcification in patients with ESRD remain to be identified. Further understanding of the pathophysiological state of uremic vascular calcification is needed to design effective therapeutic strategies to intervene with this devastating condition in the ESRD population.

Renal microvascular actions of calcitonin gene-related peptide

Calcitonin gene-related peptide (CGRP) is a potent vasodilator that is suggested to act via ATP-sensitive K channels (KATP). In the present study, we examined the actions of CGRP on pressure- and angiotensin II-induced vasoconstriction, using the in vitro perfused hydronephrotic rat kidney. Elevated pressure (from 80 to 180 mmHg) and 0.1 nM angiotensin II elicited similar decreases in afferent diameter in this model. CGRP inhibited myogenic reactivity in a concentration-dependent manner, completely preventing pressure-induced constriction at 10 nM (95 +/- 10% inhibition). These effects were partially attenuated by 10 microM glibenclamide (62 +/- 16% inhibition, P = 0.025), indicating both KATP-dependent and -independent actions of CGRP. In contrast, 10 nM CGRP inhibited angiotensin II-induced vasoconstriction by only 54 +/- 11%, and this action was not affected by glibenclamide (41 +/- 11%, P = 0.31). CGRP also inhibited the efferent arteriolar response to angiotensin II in the absence and presence of glibenclamide. Pinacidil (1.0 microM), a KATP opener also preferentially inhibited pressure- vs. angiotensin II-induced vasoconstriction (97 +/- 5 and 59 +/- 13% inhibition, respectively; P = 0.034). We conclude that the renal vasodilatory mechanisms of CGRP are pleiotropic and involve both KATP-dependent and -independent pathways. The effectiveness of CGRP in opposing renal vasoconstriction and the role of KATP in this action appear to depend on the nature the underlying vasoconstriction. We suggest that this phenomenon reflects an inhibition of KATP activation by angiotensin II.

Divergent mechanisms of ATP-sensitive K+ channel-induced vasodilation in renal afferent and efferent arterioles. Evidence of L-type Ca2+ channel-dependent and -independent actions of pinacidil

K+ channel openers (PCOs), such as pinacidil, elicit vasodilation primarily by hyperpolarization-induced inhibition of L-type Ca2+ channel activation. The physiological role of other mechanisms suggested to contribute to PCO-induced vasodilation is not well established. In the renal microcirculation, L-type Ca2+ channels play a prominent role in vasoconstriction of the afferent arteriole (AA) but are absent or physiologically silent in the efferent arteriole (EA). Thus, L-type Ca2+ channel-dependent and -independent mechanisms can readily be distinguished in this model. In the present study, we found that pinacidil potently inhibited Bay K 8644-induced AA vasoconstriction. Pinacidil also preferentially inhibited angiotensin II-induced AA vasoconstriction (approximately ninefold greater potency than EA). These results are consistent with an AA effect of pinacidil on L-type Ca2+ channel activation. Unexpectedly, 10 mumol/L pinacidil inhibited AA and EA responses to similar extents (84 +/- 10% and 71 +/- 9%, respectively). In both AAs and EAs, glibenclamide restored normal reactivity, indicating an involvement of the ATP-sensitive K+ channels. In the EA, however, pretreatment with diltiazem did not alter the effects of pinacidil. Nevertheless, 45 mmol/L KCl reversed the EA actions of pinacidil, indicating an essential requirement for a normal K+ gradient. These findings suggest that the EA actions of pinacidil involve alterations in membrane potential but not changes in L-type Ca2+ channel activity. Overall, our findings do support the premise that L-type Ca2+ channel modulation is involved in PCO-induced vasodilation in the renal microcirculation.(ABSTRACT TRUNCATED AT 250 WORDS)