Colin R. Lenihan

Loss of Prolyl Hydroxylase-1 Protects Against Colitis Through Reduced Epithelial Cell Apoptosis and Increased Barrier Function

BACKGROUND & AIMS Hypoxia inducible factor (HIF) prolyl hydroxylase inhibitors are protective in mouse models of inflammatory bowel disease (IBD). Here, we investigated the therapeutic target(s) and mechanism(s) involved. METHODS The effect of genetic deletion of individual HIF-prolyl hydroxylase (PHD) enzymes on the development of dextran sulphate sodium (DSS)-induced colitis was examined in mice. RESULTS PHD1(-/-), but not PHD2(+/-) or PHD3(-/-), mice were less susceptible to the development of colitis than wild-type controls as determined by weight loss, disease activity, colon histology, neutrophil infiltration, and cytokine expression. Reduced susceptibility of PHD1(-/-) mice to colitis was associated with increased density of colonic epithelial cells relative to wild-type controls, which was because of decreased levels of apoptosis that resulted in enhanced epithelial barrier function. Furthermore, with the use of cultured epithelial cells it was confirmed that hydroxylase inhibition reversed DSS-induced apoptosis and barrier dysfunction. Finally, PHD1 levels were increased with disease severity in intestinal tissue from patients with IBD and in colonic tissues from DSS-treated mice. CONCLUSIONS These results imply a role for PHD1 as a positive regulator of intestinal epithelial cell apoptosis in the inflamed colon. Genetic loss of PHD1 is protective against colitis through decreased epithelial cell apoptosis and consequent enhancement of intestinal epithelial barrier function. Thus, targeted PHD1 inhibition may represent a new therapeutic approach in IBD.

An intact canonical NF-κB pathway is required for inflammatory gene expression in response to hypoxia.

Hypoxia is a feature of the microenvironment in a number of chronic inflammatory conditions due to increased metabolic activity and disrupted perfusion at the inflamed site. Hypoxia contributes to inflammation through the regulation of gene expression via key oxygen-sensitive transcriptional regulators including the hypoxia-inducible factor (HIF) and NF-κB. Recent studies have revealed a high degree of interdependence between HIF and NF-κB signaling; however, the relative contribution of each to hypoxia-induced inflammatory gene expression remains unclear. In this study, we use transgenic mice expressing luciferase under the control of NF-κB to demonstrate that hypoxia activates NF-κB in the heart and lungs of mice in vivo. Using small interfering RNA targeted to the p65 subunit of NF-κB, we confirm a unidirectional dependence of hypoxic HIF-1α accumulation upon an intact canonical NF-κB pathway in cultured cells. Cyclooxygenase-2 and other key proinflammatory genes are transcriptionally induced by hypoxia in a manner that is both HIF-1 and NF-κB dependent, and in mouse embryonic fibroblasts lacking an intact canonical NF-κB pathway, there is a loss of hypoxia-induced inflammatory gene expression. Finally, under conditions of hypoxia, HIF-1α and the p65 subunit of NF-κB directly bind to the cyclooxygenase-2 promoter. These results implicate an essential role for NF-κB signaling in inflammatory gene expression in response to hypoxia both through the regulation of HIF-1 and through direct effects upon target gene expression.

Outcomes After Warfarin Initiation in a Cohort of Hemodialysis Patients With Newly Diagnosed Atrial Fibrillation

BACKGROUND Although warfarin is indicated to prevent ischemic strokes in most patients with atrial fibrillation (AF), evidence supporting its use in hemodialysis patients is limited. Our aim was to examine outcomes after warfarin therapy initiation, relative to no warfarin use, following incident AF in a large cohort of hemodialysis patients who had comprehensive prescription drug coverage through Medicare Part D. STUDY DESIGN Retrospective observational cohort study. SETTING & PARTICIPANTS Patients in the US Renal Data System undergoing maintenance hemodialysis who had AF newly diagnosed in 2007 to 2011, with Medicare Part D coverage, who had no recorded history of warfarin use. PREDICTOR Warfarin therapy initiation, identified by a filled prescription within 30 days of the AF event. OUTCOMES Death, ischemic stroke, hemorrhagic stroke, severe gastrointestinal bleeding, and composite outcomes. MEASUREMENTS HRs estimated by applying Cox regression to an inverse probability of treatment and censoring-weighted cohort. RESULTS Of 12,284 patients with newly diagnosed AF, 1,838 (15%) initiated warfarin therapy within 30 days; however, ∼70% discontinued its use within 1 year. In intention-to-treat analyses, warfarin use was marginally associated with a reduced risk of ischemic stroke (HR, 0.68; 95% CI, 0.47-0.99), but not with the other outcomes. In as-treated analyses, warfarin use was associated with reduced mortality (HR, 0.84; 95% CI, 0.73-0.97). LIMITATIONS Short observation period, limited number of nonfatal events, limited generalizability of results to more affluent patients. CONCLUSIONS In hemodialysis patients with incident AF, warfarin use was marginally associated with reduced risk of ischemic stroke, and there was a signal toward reduced mortality in as-treated analyses. These results support clinical equipoise regarding the use of warfarin in hemodialysis patients and underscore the need for randomized trials to fill this evidence gap.

NF-κB Links CO2 Sensing to Innate Immunity and Inflammation in Mammalian Cells

Molecular O2 and CO2 are the primary substrate and product of aerobic metabolism, respectively. Levels of these physiologic gases in the cell microenvironment vary dramatically both in health and in diseases, such as chronic inflammation, ischemia, and cancer, in which metabolism is significantly altered. The identification of the hypoxia-inducible factor led to the discovery of an ancient and direct link between tissue O2 and gene transcription. In this study, we demonstrate that mammalian cells (mouse embryonic fibroblasts and others) also sense changes in local CO2 levels, leading to altered gene expression via the NF-κB pathway. IKKα, a central regulatory component of NF-κB, rapidly and reversibly translocates to the nucleus in response to elevated CO2. This response is independent of hypoxia-inducible factor hydroxylases, extracellular and intracellular pH, and pathways that mediate acute CO2-sensing in nematodes and flies and leads to attenuation of bacterial LPS-induced gene expression. These results suggest the existence of a molecular CO2 sensor in mammalian cells that is linked to the regulation of genes involved in innate immunity and inflammation.

Trends in Acute Kidney Injury, Associated Use of Dialysis, and Mortality After Cardiac Surgery, 1999 to 2008

BACKGROUND The development of acute kidney injury (AKI) after cardiac surgery is associated with significant mortality, morbidity, and cost. The last decade has seen major changes in the complexity of cardiac surgical candidates and in the number and type of cardiac surgical procedures being performed. METHODS Using data from the Nationwide Inpatient Sample, we determined the annual rates of AKI, AKI requiring dialysis (AKI-D), and inpatient mortality after cardiac surgery in the United States in the years 1999 through 2008. RESULTS Inpatient mortality with AKI and AKI-D decreased from 27.9% and 45.9%, respectively, in 1999 to 12.8% and 35.3%, respectively, in 2008. Compared with 1999, the odds of AKI and AKI-D in 2008, adjusted for demographic and clinical factors, were 3.30 (95% confidence interval [CI]: 2.89 to 3.77) and 2.23 (95% CI: 1.78 to 2.80), respectively. Corresponding adjusted odds of death associated with AKI and AKI-D were 0.31 (95% CI: 0.26 to 0.36) and 0.47 (95% CI: 0.34 to 0.65.) Taken together, the attributable risks for death after cardiac surgery associated with AKI and AKI-D increased from 30% and 5%, respectively, in 1999 to 47% and 14%, respectively, in 2008. CONCLUSIONS In sum, despite improvements in individual patient outcomes over the decade 1999 to 2008, the population contribution of AKI and AKI-D to inpatient mortality after surgery increased over the same period.

Longitudinal study of living kidney donor glomerular dynamics after nephrectomy

BACKGROUND Over 5,000 living kidney donor nephrectomies are performed annually in the US. While the physiological changes that occur early after nephrectomy are well documented, less is known about the long-term glomerular dynamics in living donors. METHODS We enrolled 21 adult living kidney donors to undergo detailed long-term clinical, physiological, and radiological evaluation pre-, early post- (median, 0.8 years), and late post- (median, 6.3 years) donation. A morphometric analysis of glomeruli obtained during nephrectomy was performed in 19 subjects. RESULTS Donors showed parallel increases in single-kidney renal plasma flow (RPF), renocortical volume, and glomerular filtration rate (GFR) early after the procedure, and these changes were sustained through to the late post-donation period. We used mathematical modeling to estimate the glomerular ultrafiltration coefficient (Kf), which also increased early and then remained constant through the late post-donation study. Assuming that the filtration surface area (and hence, Kf) increased in proportion to renocortical volume after donation, we calculated that the 40% elevation in the single-kidney GFR observed after donation could be attributed exclusively to an increase in the Kf. The prevalence of hypertension in donors increased from 14% in the early post-donation period to 57% in the late post-donation period. No subjects exhibited elevated levels of albuminuria. CONCLUSIONS Adaptive hyperfiltration after donor nephrectomy is attributable to hyperperfusion and hypertrophy of the remaining glomeruli. Our findings point away from the development of glomerular hypertension following kidney donation. TRIAL REGISTRATION Not applicable. FUNDING. NIH (R01DK064697 and K23DK087937); Astellas Pharma US; the John M. Sobrato Foundation; the Satellite Extramural Grant Foundation; and the American Society of Nephrology.

The impact of hypoxia on cell death pathways

Hypoxia is a frequently encountered feature of the cellular microenvironment in a number of pathophysiological processes in which programmed cell death (apoptosis) affects disease progression including, but not limited to, cancer, chronic inflammation, myocardial infarction, stroke and ischaemic acute kidney injury. In these diseases, the presence of hypoxia can significantly affect the rate of cell death and thus may make a significant contribution to disease progression. In the present review, we discuss the complex relationship that exists between the presence of hypoxia and the regulation of cell death pathways.

Differences in Access to Kidney Transplantation between Hispanic and Non-Hispanic Whites by Geographic Location in the United States

BACKGROUND AND OBJECTIVES Hispanic patients undergoing chronic dialysis are less likely to receive a kidney transplant compared with non-Hispanic whites. This study sought to elucidate disparities in the path to receipt of a deceased donor transplant between Hispanic and non-Hispanic whites. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS Using the US Renal Data System, 417,801 Caucasians who initiated dialysis between January 1, 1995 and December 31, 2007 with follow-up through 2008 were identified. This study investigated time from first dialysis to first kidney transplantation, time from first dialysis to waitlisting, and time from waitlisting to kidney transplantation. Multivariable Cox regression estimated cause-specific hazard ratios (HRCS) and subdistribution (competing risk) hazard ratios (HRSD) for Hispanics versus non-Hispanic whites. RESULTS Hispanics experienced lower adjusted rates of deceased donor kidney transplantation than non-Hispanic whites (HRCS, 0.77; 95% confidence interval [95% CI], 0.75 to 0.80) measured from dialysis initiation. No meaningful differences were found in time from dialysis initiation to placement on the transplant waitlist. Once waitlisted, Hispanics had lower adjusted rates of deceased donor kidney transplantation (HRCS, 0.66; 95% CI, 0.64 to 0.68), and the association attenuated once accounting for competing risks (HRSD, 0.79; 95% CI, 0.77 to 0.81). Additionally controlling for blood type and organ procurement organization further reduced the disparity (HRSD, 0.99; 95% CI, 0.96 to 1.02). CONCLUSIONS After accounting for geographic location and controlling for competing risks (e.g., Hispanic survival advantage), the disparity in access to deceased donor transplantation was markedly attenuated among Hispanics compared with non-Hispanic whites. To overcome the geographic disparities that Hispanics encounter in the path to transplantation, organ allocation policy revisions are needed to improve donor organ equity.

MDRD-Estimated GFR at One Year Post-Renal Transplant Is a Predictor of Long-Term Graft Function

Renal transplantation is the optimal mode of renal replacement. Improvements in graft survival and acute rejection rates have made these outcomes less useful for prognostication and as end-points in clinical trials; accurate surrogate markers of long-term graft outcome are therefore increasingly important. This study examines the relationship between both serum creatinine (SCr1yr) and MDRD estimated glomerular filtration rate measured at one year (eGFRMDRD1yr) as predictors of graft survival. Data on 1,110 patients who received a renal transplant between 1989 and 2005 were extracted from the Irish Renal Transplant Registry. The study group was divided into quartiles of patient numbers according to SCr1yr and eGFRMDRD1yr. Kaplan-Meier estimates of the primary end-point graft survival were constructed for each quartile. Additionally, a Cox Regression restricted cubic spline model was performed for both eGFRMDRD1yr and SCr1yr. Both overall graft outcome and outcome censored for death with a functioning graft (CDWFG) were used as endpoints. Cox regression analysis was performed along with tests for the proportionality assumption to compare the predictive value of eGFRMDRD1yrand SCr1yr. Both eGFRMDRD1yr and SCr1yr were independently associated with long-term renal transplant survival. eGFRMDRD1yr and SCr1yr had similarly strong associations with long-term outcome when the quartile variables were compared using the Bayesian Information Criterion method. The Cox regression restricted cubic spline modeling demonstrated that an eGFRMDRD1yr value < 27 mLs/min/1.73m2 and a SCr1yr value > 229 μmol/L were associated with poor graft survival.

Temporal Trends in the Incidence, Treatment and Outcomes of Hip Fracture After First Kidney Transplantation in the United States

It is currently unknown whether any secular trends exist in the incidence and outcomes of hip fracture in kidney transplant recipients (KTR). We identified first‐time KTR (1997–2010) who had >1 year of Medicare coverage and no recorded history of hip fracture. New hip fractures were identified from corresponding diagnosis and surgical procedure codes. Outcomes studied included time to hip fracture, type of surgery received and 30‐day mortality. Of 69 740 KTR transplanted in 1997–2010, 597 experienced a hip fracture event during 155 341 person‐years of follow‐up for an incidence rate of 3.8 per 1000 person‐years. While unadjusted hip fracture incidence did not change, strong confounding by case mix was present. Using year of transplantation as a continuous variable, the hazard ratio (HR) for hip fracture in 2010 compared with 1997, adjusted for demographic, dialysis, comorbid and most transplant‐related factors, was 0.56 (95% confidence interval [CI]: 0.41–0.77). Adjusting for baseline immunosuppression modestly attenuated the HR (0.68; 95% CI: 0.47–0.99). The 30‐day mortality was 2.2 (95% CI: 1.3–3.7) per 100 events. In summary, hip fractures remain an important complication after kidney transplantation. Since 1997, case‐mix adjusted posttransplant hip fracture rates have declined substantially. Changes in immunosuppressive therapy appear to be partly responsible for these favorable findings.