2020 O'Brien Kidney Center Annual Retreat

BACKGROUND Despite recent guidelines promoting “permanent access” in the form of AVFs and AVGs, tunneled catheters remain an access option in incident (upto 80%) and prevalent (up to 20%) of ESRD patients. Catheter use for vascular access in dialysis patients is associated with a great deal of mortality and morbidity as well as tremendous cost to the health care system. Most of this morbidity and cost is mediated by inflammation and infection that attend catheter use. We developed a novel nitric oxide (NO) eluting catheter insert and tested its effects in vitro and in a sheep model of catheter infection. METHODS We prepared 1.8 cm long inserts (ranging from 0.64 mm to 1.96 mm in diameter) using a variety of silicone and polyurethane tubings. The inserts were filled with a mixture of GSNO (as the NO-donor, 25-75 wt%), ZnO nanoparticles (as a solid phase catalyst, 0-25 wt%), and PEG (to increase water uptake, 0-20 wt%) and were sealed at both ends with silicone adhesive. Total NO release after different storage periods (measure by chemiluminescence NO measurements) was assed. Real-time in vitro testing of these devices as inserts submerged in saline solution at 24°C for 3 days were performed to determine the relationship between polymer tubing type, powder filling mixture, and the flux of NO released at a given time-point. Using the same experimental parameters, cell counts of Staphylococcus aureus (Gram-positive) and Pseudomonas aeruginosa (Gram-negative) were measured after incubation of the insert devices inside of the hub region of Permcath catheters (Medtronic silicone catheter). Finally, the insert devices were tested in a 14 day sheep model of infection. RESULTS We determined that silicone tubing yielded the highest NO flux because of water and NO permeability. The mixture that yielded the highest flux of NO over a 72 hour period consisted of 75 wt% GSNO and 25 wt% ZnO nanoparticles. Initial stability studies indicate greater than 5 months of stability when stored in the dark, at room temperature (24°C), and under dry conditions. Cell counts revealed a log reduction of 6.6 for S.aureus and 6.7 for P. aeruginosa when compared to a control of no insert device for the 3 day in vitro tests. The 14 day sheep model yielded a log reduction of 3 and showed no biofilm formation from the hub region to the distal tip when the insert device was utilized. When the insert device was not utilized (control) mature biofilm formation was observed in the hub region as well as at the distal tip of the TDC catheters. CONCLUSION The NO-eluting catheter insert performed well in reducing bacterial cell counts as well as biofilm in vitro as well as in a fourteen day sheep model.

Karthik Ramani <ramanik@umich.edu>

Division of Nephrology, University of Michigan Hospital & Health Systems, Ann Arbor, MI, USA

Hypertension-associated progressive glomerulosclerosis is a significant driver of both de novo and all-cause chronic kidney disease leading to end-stage kidney failure. The progression of glomerular disease proceeds via continuing depletion of podocytes from the glomeruli into the ultrafiltrate. To non-invasively assess injury patterns associated with mean arterial pressure (MAP), we conducted an observational study of 87 healthy normotensive individuals who were cleared for living kidney donation. Urine pellet podocin and aquaporin2 mRNAs normalized to the urine creatinine concentration (UPod:Creat ratio and UAqp2:Creat ratio) were used as markers of podocyte detachment and tubular injury, respectively. The ratio of two podocyte mRNA markers, podocin to nephrin (UPod:Neph) as well as the ratio of podocin to the tubular marker aquaporin2 (UPod:Aqp2) estimated the relative rates of podocyte stress and glomerular vs. tubular injury. The MAP was positively correlated with the UPod:Neph and UPod:Aqp2, thereby confirming the relationship of MAP with podocyte stress and the preferential targeting of the glomerulus by higher MAP. In multivariable linear regression analysis, both UPod:Neph and UPod:Creat, but not UAqp2:Creat or proteinuria, were both significantly related to a range of normal MAP (70 to 110 mm Hg). Systolic, as opposed to diastolic or pulse pressure was associated with UPod:Creat. Thus, higher podocyte stress and detachment into the urine are associated with MAP even in a relatively “normal” range of MAP. Hence, urine pellet mRNA monitoring can potentially identify progression risk before the onset of overt hypertension, proteinuria or chronic kidney disease.

Jeet Naik <abhinaik@umich.edu>

University of Michigan, University of Kansas and Henry Ford Hospital

Yousef Ibrahim <yibrahim@oakland.edu>

University of Michigan School of Medicine

Jeffrey Beamish <jebeamis@umich.edu>

University of Michigan

The use of a numerical coefficient for Black race in equations meant to estimate glomerular filtration rate (GFR) have recently come under criticism. This numerical correction was established due to evidenced-based studies that included representative samples of Black Americans. Some of these studies included validation with direct measurement of GFR with isotope clearance techniques. The impact of removing the Black race coefficient from the Chronic Kidney Disease Epidemiology (CKD-EPI) equation is still uncertain. This analysis sought to understand the epidemiological impact of removing the Black race coefficient from the CKD-EPI equation in both the US general population and in United States Veterans who utilize the VA Health system.

Dao Le <daole@usf.edu>

University of Michigan

Non-traditional risk factors like inflammation and oxidative stress contribute to the increased cardiovascular disease (CVD) burden observed in patients with chronic kidney disease (CKD). In our earlier work, we demonstrated that low tryptophan levels associated with incident CVD in CKD. Altered tryptophan catabolism via the kynurenine and indole pathways associates with CVD, but the ability of these specific metabolites to act as biomarkers to predict incident CVD in CKD warrants further research. We measured indole and kynurenine metabolites using targeted mass spectrometry in two independent cohorts of CKD patients—the Clinical Phenotyping Resource and Biobank Core (CPROBE; n=184; follow up 1-7 years) and Renal Research Institute (RRI-CKD; n=325; median follow up 3 years). We assessed the relationship of indole metabolites in predicting incident CVD in CPROBE and both indole and kynurenine metabolites in RRI-CKD. The CPROBE cohort included age, gender, race, diabetes status, and CKD stage matched groups—with prior history of CVD (old CVD; n=92), no history of CVD at baseline or during follow up (no CVD; n=46), and no history of CVD at baseline who developed CVD in the follow up period (incident CVD). While plasma indoxyl sulfate increases with advancing CKD stage (p<0.025) in the CPROBE cohort, indoxyl sulfate and indole-3-acetate were not found to associate with incident CVD. Our preliminary results suggest that an increased baseline levels of kynurenine metabolites—quinolinic acid and anthranilic acid—not indole metabolites predict time to first CVD event (HR: 1.56 (95% CI: 1.07, 2.28); HR: 1.88 (95% CI: 1.10, 3.19)) in the RRI-CKD cohort. In summary, our study finds elevated metabolites of the kynurenine pathway and not the indole pathway predict incident CVD events in CKD.

Trista Benitez <benitezt@umich.edu>

University of Michigan Medical School

BACKGROUND UTI is the most common hospital acquired infection with indwelling catheters being a major risk factor and are difficult to treat due to the formation of bacterial biofilms which are resistant to systemic antibiotics. NO is an endogenously formed gas molecule known to play a key role in preventing infection by dispersing biofilm formed by a variety of bacterial strains. In this abstract, we describe the effectiveness of a novel urinary catheter balloon inflation fluid to effectively reduce catheter associated urinary tract infections (CAUTI) by providing up to 7 days of bactericidal effect via NO release. METHODS Our innovative approach to prevent CAUTI involves employing a balloon inflation fluid using novel NO secreting materials based on using S-nitrosothiol type NO donors like S-nitrosoglutathione (GSNO) within the balloon of urinary catheters that slowly releases NO over a period of up to one week. The advantages of the use of NO in CAUTI prevention is its short half-life with a very low steady-state level immediately adjacent to the surface of the device required to achieve the desired anti-microbial effect with no risk of systemic effects when using NO secreting materials with fluxes that are near physiological levels. RESULTS We performed in vitro studies using a Foley catheter placed in a long-necked flask with a shape resembling the urinary bladder and the urethra. The Foley catheter retention balloon was filled with GSNO solution and the balloon was used to seal the neck of the flask.Then the flask was filled with synthetic urine inoculated with E. coli and incubated for seven days at 37 0C with horizontal shaking at 80 rpm. The results showed a 7-log reduction in planktonic bacterial growth and a 3-log reduction in biofilm of the GSNO Foley balloon solution compared to the control. CONCLUSION These data suggest that NO-based urinary catheter balloon fluid results in significant anti-microbial effects in our in vitro model of CAUTI.

Karthik Ramani <ramanik@umich.edu>

Division of Nephrology, University of Michigan Hospital & Health Systems, Ann Arbor, MI, USA

Background:

The novel coronavirus disease (COVID-19), also known as Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) is an evolving pandemic with significant mortality. Information about the impact of infection on glomerular disease patients in particular has been lacking. Understanding the virus’s effect in glomerular disease is constantly changing. This review article summarizes the data published thus far on COVID-19 and its manifestations in pre-existing and de novo glomerular disease.

Summary:

While patients with glomerular disease may be at higher risk of severe COVID-19 due to their immunosuppressed status, some data suggest that a low amount of immunosuppression may be helpful in mitigating the systemic inflammatory response which is associated with high mortality rates in COVID-19. There have been a few case reports on COVID-19 causing glomerular disease relapse in patients. Multiple mechanisms have been proposed for kidney injury, proteinuria and hematuria in the setting of COVID-19. More commonly, these are caused by direct tubular injury due to hemodynamic instability and hypoxic injury. However, the cytokine storm induced by COVID-19 may trigger common post viral glomerular disease such as IgA nephropathy, Anti-GBM and ANCA vasculitis have also been described in COVID-19 patients. Collapsing glomerulopathy, a hallmark of HIV associated nephropathy, is being reported SARS-CoV-2 cases, particularly inpatients with high risk APOL1 alleles. Direct viral invasion of glomerular structures is hypothesized to cause a podocytopathy due to virus’s affinity to ACE2, but evidence for this remains under study.

Key Messages:

Infection with SARS-CoV-2 may cause glomerular disease in certain patients. The mechanism of de novo glomerular disease in the setting of COVID-19 remains under study. The management of patients with existing glomerular disease poses unique challenges, especially with regards to immunosuppression management. Further studies are needed to inform clinician decisions about the management of these patients during the COVID-19 pandemic.

Allison Shimmel <Allison.Shimmel@rockets.utoledo.edu>

University of Michigan Health System Department of Nephrology, Ann Arbor, MI 


Sadia Tahir <Sadia.Tahir@rockets.utoledo.edu>

University of Toledo College of Medicine, University of Michigan Ann Arbor

Renal cystic disease is characterized by the development and progressive enlargement of multiple fluid-filled cysts in the kidney that can lead to end-stage renal disease. Although activation of the mTOR pathway has been demonstrated in multiple pre-clinical models of polycystic kidney disease (PKD), the clinical utility of mTOR inhibitors in human ADPKD patients has proven disappointing and to date only a single drug (tolvaptan), a vasopressin V2 receptor antagonist, is FDA-approved for use in human ADPKD patients. As such, the community is in desperate need of additional targets that offer the potential for therapeutic intervention. Ideally, such a target should be expressed specifically in renal cystic epithelial cells, exhibit minimal expression in normal renal epithelial cells, and be a central player influencing multiple cellular pathways. Given the connection between mTOR and transcription factor EB (TFEB), especially at the nexus of the lysosome, we have investigated whether TFEB, a central transcription factor involved in many downstream outputs, is activated during renal cystogenesis by assessing its expression and subcellular localization in multiple models of renal cystic disease. We demonstrate here that TFEB is upregulated and translocates to the nucleus in cystic renal epithelial cells and further show that known downstream targets are upregulated at the protein level in renal cysts in mouse models of renal cystic disease and in human ADPKD samples. These data provide evidence that the TFEB pathway represents a potential therapeutic target for interventional strategies in renal cystic disease states.

Jonathan Shillingford <jonshi@umich.edu>

University of Michigan, Department of Internal Medicine, Division of Nephrology