Michael E. Seifert

CKD-Induced Wingless/Integration1 Inhibitors and Phosphorus Cause the CKD–Mineral and Bone Disorder

In chronic kidney disease, vascular calcification, renal osteodystrophy, and phosphate contribute substantially to cardiovascular risk and are components of CKD-mineral and bone disorder (CKD-MBD). The cause of this syndrome is unknown. Additionally, no therapy addresses cardiovascular risk in CKD. In its inception, CKD-MBD is characterized by osteodystrophy, vascular calcification, and stimulation of osteocyte secretion. We tested the hypothesis that increased production of circulating factors by diseased kidneys causes the CKD-MBD in diabetic mice subjected to renal injury to induce stage 2 CKD (CKD-2 mice). Compared with non-CKD diabetic controls, CKD-2 mice showed increased renal production of Wnt inhibitor family members and higher levels of circulating Dickkopf-1 (Dkk1), sclerostin, and secreted klotho. Neutralization of Dkk1 in CKD-2 mice by administration of a monoclonal antibody after renal injury stimulated bone formation rates, corrected the osteodystrophy, and prevented CKD-stimulated vascular calcification. Mechanistically, neutralization of Dkk1 suppressed aortic expression of the osteoblastic transcription factor Runx2, increased expression of vascular smooth muscle protein 22-α, and restored aortic expression of klotho. Neutralization of Dkk1 did not affect the elevated plasma levels of osteocytic fibroblast growth factor 23 but decreased the elevated levels of sclerostin. Phosphate binder therapy restored plasma fibroblast growth factor 23 levels but had no effect on vascular calcification or osteodystrophy. The combination of the Dkk1 antibody and phosphate binder therapy completely treated the CKD-MBD. These results show that circulating Wnt inhibitors are involved in the pathogenesis of CKD-MBD and that the combination of Dkk1 neutralization and phosphate binding may have therapeutic potential for this disorder.

Effects of Phosphate Binder Therapy on Vascular Stiffness in Early Stage Chronic Kidney Disease

Background/Aims: Cardiovascular disease (CVD) is increased in chronic kidney disease (CKD), and contributed to by the CKD-mineral bone disorder (CKD-MBD). CKD-MBD begins in early CKD and its vascular manifestations begin with vascular stiffness proceeding to increased carotid artery intima-media thickness (cIMT) and vascular calcification (VC). Phosphorus is associated with this progression and is considered a CVD risk factor in CKD. We hypothesized that modifying phosphorus balance with lanthanum carbonate (LaCO3) in early CKD would not produce hypophosphatemia and may affect vascular manifestations of CKD-MBD. Methods: We randomized 38 subjects with normophosphatemic stage 3 CKD to a fixed dose of LaCO3 or matching placebo without adjusting dietary phosphorus in a 12-month randomized, double-blind, pilot and feasibility study. The primary outcome was the change in serum phosphorus. Secondary outcomes were changes in measures of phosphate homeostasis and vascular stiffness assessed by carotid-femoral pulse wave velocity (PWV), cIMT and VC over 12 months. Results: There were no statistically significant differences between LaCO3 and placebo with respect to the change in serum phosphorus, urinary phosphorus, tubular reabsorption of phosphorus, PWV, cIMT, or VC. Biomarkers of the early CKD-MBD such as plasma fibroblast growth factor-23, Dickkopf-related protein 1 (DKK1), and sclerostin were increased 2- to 3-fold at baseline, but were not affected by LaCO3. Conclusion: Twelve months of LaCO3 had no effect on serum phosphorus and did not alter phosphate homeostasis, PWV, cIMT, VC, or biomarkers of CKD-MBD.

Pathophysiology of the chronic kidney disease-mineral bone disorder.

Purpose of reviewThe causes of excess cardiovascular mortality associated with chronic kidney disease (CKD) have been attributed in part to the CKD-mineral bone disorder syndrome (CKD-MBD), wherein, novel cardiovascular risk factors have been identified. The causes of the CKD-MBD are not well known and they will be discussed in this review Recent findingsThe discovery of WNT (portmanteau of wingless and int) inhibitors, especially Dickkopf 1, produced during renal repair and participating in the pathogenesis of the vascular and skeletal components of the CKD-MBD implied that additional pathogenic factors are critical, leading to the finding that activin A is a second renal repair factor circulating in increased levels during CKD. Activin A derives from peritubular myofibroblasts of diseased kidneys, where it stimulates fibrosis, and decreases tubular klotho expression. The type 2 activin A receptor, ActRIIA, is decreased by CKD in atherosclerotic aortas, specifically in vascular smooth muscle cells (VSMC). Inhibition of activin signaling by a ligand trap inhibited CKD induced VSMC dedifferentiation, osteogenic transition and atherosclerotic calcification. Inhibition of activin signaling in the kidney decreased renal fibrosis and proteinuria. SummaryThese studies demonstrate that circulating renal repair factors are causal for the CKD-MBD and CKD associated cardiovascular disease, and identify ActRIIA signaling as a therapeutic target in CKD that links progression of renal disease and vascular disease.

Ligand trap for the activin type IIA receptor protects against vascular disease and renal fibrosis in mice with chronic kidney disease

The causes of cardiovascular mortality associated with chronic kidney disease (CKD) are partly attributed to the CKD-mineral bone disorder (CKD-MBD). The causes of the early CKD-MBD are not well known. Our discovery of Wnt (portmanteau of wingless and int) inhibitors, especially Dickkopf 1, produced during renal repair as participating in the pathogenesis of the vascular and skeletal components of the CKD-MBD implied that additional pathogenic factors are critical. In the search for such factors, we studied the effects of activin receptor type IIA (ActRIIA) signaling by using a ligand trap for the receptor, RAP-011 (a soluble extracellular domain of ActRIIA fused to a murine IgG-Fc fragment). In a mouse model of CKD that stimulated atherosclerotic calcification, RAP-011 significantly increased aortic ActRIIA signaling assessed by the levels of phosphorylated Smad2/3. Furthermore, RAP-011 treatment significantly reversed CKD-induced vascular smooth muscle dedifferentiation as assessed by smooth muscle 22α levels, osteoblastic transition, and neointimal plaque calcification. In the diseased kidneys, RAP-011 significantly stimulated αklotho levels and it inhibited ActRIIA signaling and decreased renal fibrosis and proteinuria. RAP-011 treatment significantly decreased both renal and circulating Dickkopf 1 levels, showing that Wnt activation was downstream of ActRIIA. Thus, ActRIIA signaling in CKD contributes to the CKD-MBD and renal fibrosis. ActRIIA signaling may be a potential therapeutic target in CKD.

Left ventricular mass progression despite stable blood pressure and kidney function in stage 3 chronic kidney disease.

Background/Aims: Progressive chronic kidney disease (CKD) is associated with worsening cardiovascular (CV) risk not explained by traditional risk factors. Left ventricular (LV) hypertrophy (LVH) is an important CV risk factor, but its progression has not been documented in early CKD. We explored whether progression of LVH in early CKD would occur despite stable kidney function. Methods: We conducted a post hoc analysis of a 12-month study of lanthanum carbonate in stage 3 CKD, which included longitudinal assessments of CV biomarkers. Primary outcome for the analysis was the change in LV mass (LVM) indexed to height in meters2.7 (LVM/Ht2.7). Secondary outcomes were changes in blood pressure (BP), pulse-wave velocity, LV systolic/diastolic function, fibroblast growth factor 23 (FGF23), klotho, and estimated glomerular filtration rate (eGFR). Results: Thirty-one of 38 original subjects had sufficient data for analysis. LVM/Ht2.7 increased (47 ± 13 vs. 53 ± 13 g/m2.7, p = 0.006) over 12 months despite stable BP, stable eGFR and normal LV systolic function. Vascular stiffness and LV diastolic dysfunction persisted throughout the study. Klotho levels decreased (748 ± 289 to 536 ± 410 pg/ml, p = 0.03) but were unrelated to changes in LVM/Ht2.7. The change in FGF23/klotho ratio was strongly correlated with changes in LVM/Ht2.7 (r2 = 0.582, p = 0.03). Conclusion: Subjects with stage 3 CKD exhibited increasing LVM, persistent LV diastolic dysfunction and vascular stiffness despite stable kidney function, BP and LV systolic function. Abnormal FGF23 signaling due to reduced klotho expression may be associated with increasing LVM. These findings deserve further evaluation in a larger population given the adverse prognostic value of these CV biomarkers.

The Kidney-Vascular-Bone Axis in the Chronic Kidney Disease-Mineral Bone Disorder.

The last 25 years have been characterized by dramatic improvements in short-term patient and allograft survival after kidney transplantation. Long-term patient and allograft survival remains limited by cardiovascular disease and chronic allograft injury, among other factors. Cardiovascular disease remains a significant contributor to mortality in native chronic kidney disease as well as cardiovascular mortality in chronic kidney disease more than doubles that of the general population. The chronic kidney disease (CKD)-mineral bone disorder (MBD) is a syndrome recently coined to embody the biochemical, skeletal, and cardiovascular pathophysiology that results from disrupting the complex systems biology between the kidney, skeleton, and cardiovascular system in native and transplant kidney disease. The CKD-MBD is a unique kidney disease-specific syndrome containing novel cardiovascular risk factors, with an impact reaching far beyond traditional notions of renal osteodystrophy and hyperparathyroidism. This overview reviews current knowledge of the pathophysiology of the CKD-MBD, including emerging concepts surrounding the importance of circulating pathogenic factors released from the injured kidney that directly cause cardiovascular disease in native and transplant chronic kidney disease, with potential application to mechanisms of chronic allograft injury and vasculopathy.

Polyomavirus Reactivation and Immune Responses to Kidney-Specific Self-Antigens in Transplantation

Humoral immune responses against donor antigens are important determinants of long-term transplant outcomes. Reactivation of the polyomavirus BK has been associated with de novo antibodies against mismatched donor HLA antigens in kidney transplantation. The effect of polyomavirus reactivation (BK viremia or JC viruria) on antibodies to kidney-specific self-antigens is unknown. We previously reported excellent 5-year outcomes after minimization of immunosuppression for BK viremia and after no intervention for JC viruria. Here, we report the 10-year results of this trial (n=193) along with a nested case-control study (n=40) to explore associations between polyomavirus reactivation and immune responses to the self-antigens fibronectin (FN) and collagen type-IV (Col-IV). Consistent with 5-year findings, subjects taking tacrolimus, compared with those taking cyclosporin, had less acute rejection (11% versus 22%, P=0.05) and graft loss (9% versus 22%, P=0.01) along with better transplant function (eGFR 65±19 versus 50±24 ml/min per 1.73 m2, P<0.001) at 10 years. Subjects undergoing immunosuppression reduction for BK viremia had 10-year outcomes similar to those without viremia. In the case-control study, antibodies to FN/Col-IV were more prevalent during year 1 in subjects with polyomavirus reactivation than in those without reactivation (48% versus 11%, P=0.04). Subjects with antibodies to FN/Col-IV had more acute rejection than did those without these antibodies (38% versus 8%, P=0.02). These data demonstrate the long-term safety and effectiveness of minimizing immunosuppression to treat BK viremia. Furthermore, these results indicate that polyomavirus reactivation associates with immune responses to kidney-specific self-antigens that may increase the risk for acute rejection through unclear mechanisms.

Cytomegalovirus and Anemia: Not Just for Transplant Anymore

Cytomegalovirus (CMV) is one of the most important viruses in renal transplantation that causes significant morbidity and mortality, even in the current era of effective prophylaxis and treatment. The CMV syndrome is characterized by fever, malaise, and transplant dysfunction that manifests as AKI,

Surveillance Biopsy: Boon or Bust?

UAB Transplant Nephrology. Introduction While not particularly sensitive, serum creatinine remains the primary non-invasive method of monitoring functional allograft health. Allograft biopsies are more sensitive in detecting injury, and some transplant centers use early surveillance biopsies to assess the adequacy of immunosuppression when the creatinine is stable. However, controversy exists as to whether treatment of surveillance findings has a positive impact on kidney transplant outcomes. We initiated a surveillance biopsy program at our center in May 2015 to improve clinical outcomes. This study is an interim analysis of our surveillance program to determine outcomes of subclinical inflammation. Materials and Methods We screened a clinical database of all kidney transplant biopsies performed at our center between May 2015 and December 2016. Surveillance biopsies were defined as those performed at 6 months post-transplant in the setting of normal/stable allograft function. We collected clinical and demographic data from the medical record of each participant, including up to 32 months of follow-up. The primary exposure was subclinical inflammation (SCI), which we defined as subclinical acute rejection (SC-TCMR) or borderline acute rejection (B-TCMR) based on Banff 2013 criteria. Secondary exposures included routine clinical/demographic variables and treatment of surveillance findings (clinician’s discretion). The primary outcome was a composite endpoint of acute rejection after surveillance and death-censored allograft loss. Our primary hypothesis was that subclinical B-TCMR, which is often not actively treated, will lead to worse outcomes compared to those with no major surveillance abnormalities (NOMOA). Results and Discussion We reviewed 601 kidney biopsies performed during the study period, 166 (28%) of which were 6-month surveillance biopsies. Notably, our cohort was enriched for higher immunological risk recipients (55% black and 61% deceased donors). Mean clinical follow-up was 22 months. Overall patient, graft, and rejection-free survival (after surveillance) were excellent at 99%, 96%, and 95%, respectively. The primary composite endpoint was reached in 10/166 (6%) of subjects. SCI was detected in 57/166 (34%) surveillance biopsies, of which 48 (29%) were B-TCMR and 9 (5%) were SC-TCMR. All SC-TCMR and 42% of B-TCMR were treated with increased immunosuppression at the clinician’s discretion. This included increased maintenance therapy as well as corticosteroid pulse therapy. The incidence of the composite endpoint was 15% with B-TCMR on surveillance versus 1% with NOMOA (P<0.001), and was significantly impacted by treatment at only 10% in treated B-TCMR compared to 18% in those expectantly managed (P=0.005, see Figure). Conclusions SCI was detected at 6 months in > 30% of kidney recipients, most of whom had B-TCMR. Although sample size was limited in this interim analysis, there may be long-term benefits of treating subclinical B-TCMR. Defining those that may benefit from treatment is a critical issue in kidney transplant management. UAB Kidney Undergraduate Research Program. Figure. No caption available.

Fibroblast growth factor-23 and chronic allograft injury in pediatric renal transplant recipients: a Midwest Pediatric Nephrology Consortium study.

The chronic kidney disease‐mineral bone disorder (CKD‐MBD) produces fibroblast growth factor‐23 (FGF‐23) and related circulating pathogenic factors that are strongly associated with vascular injury and declining kidney function in native CKD. Similarly, chronic renal allograft injury (CRAI) is characterized by vascular injury and declining allograft function in transplant CKD. We hypothesized that circulating CKD‐MBD factors could serve as non‐invasive biomarkers of CRAI. We conducted a cross‐sectional, multicenter case–control study. Cases (n = 31) had transplant function >20 mL/min/1.73 m2 and biopsy‐proven CRAI. Controls (n = 31) had transplant function >90 mL/min/1.73 m2 and/or a biopsy with no detectable abnormality in the previous six months. We measured plasma CKD‐MBD factors at a single time point using ELISA. Median (range) FGF23 levels were over twofold higher in CRAI vs. controls [106 (10–475) pg/mL vs. 45 (8–91) pg/mL; p < 0.001]. FGF23 levels were inversely correlated with transplant function (r2 = −0.617, p < 0.001). Higher FGF23 levels were associated with increased odds of biopsy‐proven CRAI after adjusting for transplant function, clinical, and demographic factors [OR (95% CI) 1.43 (1.23, 1.67)]. Relationships between additional CKD‐MBD factors and CRAI were attenuated in multivariable models. Higher FGF23 levels were independently associated with biopsy‐proven CRAI in children.