Andrew T. Blair

A multi-center, dose-escalation study of human type I pancreatic elastase (PRT-201) administered after arteriovenous fistula creation

Purpose To explore the safety and efficacy of PRT-201. Methods Randomized, double-blind, placebo-controlled, single-dose escalation study of PRT-201 (0.0033 to 9 mg) applied after arteriovenous fistula (AVF) creation. Participants were followed for one year. The primary outcome measure was safety. Efficacy measures were the proportion with intra-operative increases in AVF outflow vein diameter or blood flow ≥25% (primary), changes in outflow vein diameter and blood flow, AVF maturation and lumen stenosis by ultrasound criteria and AVF patency. Results The adverse events in the PRT-201 group (n=45) were similar to those in the placebo group (n=21). There were no differences in the proportion with ≥25% increase in vein diameter or blood flow, successful maturation or lumen stenosis. There was no statistically significant difference in primary patency between the dose groups (placebo n=21, Low Dose n=16, Medium Dose n=17 and High Dose n=12). In a subgroup analysis that excluded three participants with early surgical failures, the hazard ratio (HR) for primary patency loss of Low Dose compared with placebo was 0.38 (95% CI 0.10-1.41, P=0.15). In a Cox model, Low Dose (HR 0.27, 95% CI 0.04-0.79, P=0.09), white race (HR 0.17, 95% CI 0.03-0.79, P=0.02), and age <65 years (HR 0.25, CI 0.05-1.15, P=0.08) were associated (P<0.10) with a decreased risk of primary patency loss. Conclusions PRT-201 was not different from placebo for safety or efficacy measures. There was a suggestion for improved AVF primary patency with Low Dose PRT-201 that is now being studied in a larger clinical trial.

Application of human type I pancreatic elastase (PRT-201) to the venous anastomosis of arteriovenous grafts in patients with chronic kidney disease

Purpose To explore the safety and efficacy of PRT-201 applied to the outflow vein of a newly created arteriovenous graft (AVG). Methods Randomized, double-blind, placebo-controlled, single-dose escalation study of PRT-201 (0.01 to 9 mg) applied to the graft-vein anastomosis and adjacent outflow vein immediately after AVG placement. The primary outcome measure was safety. The efficacy measures were intraoperative increases in outflow vein diameter and blood flow rate, primary unassisted patency, and secondary patency by dose groups (placebo, low, medium, high and All PRT-201). Results A total of 89 patients were treated (28 placebo and 61 PRT-201). There were no significant differences in the proportion of placebo and PRT-201 patients reporting adverse events. Intraoperative outflow vein diameter increased 5% (p=0.14) in the placebo group compared with 13% (p=0.01), 15% (p=0.07) and 12% (p<0.001), in the low, medium and high groups, respectively. The comparison between the high and placebo groups was marginally statistically significant (p=0.06). The intraoperative blood flow did not change in the placebo group, and increased in the low, medium and high groups by 19% (p=0.34), 36% (p=0.09) and 46% (p=0.02), respectively. The low group had the longest primary unassisted and secondary patency and the fewest procedures to restore or maintain patency; however, the differences between groups were not statistically significant. Conclusions PRT-201 was well tolerated and increased AVG intraoperative outflow vein diameter and blood flow. Low dose tended to increase secondary patency and decrease the rate of procedures to restore or maintain patency. Larger studies with these doses will be necessary to confirm these results.

Sevelamer Restores Bone Volume and Improves Bone Microarchitecture and Strength in Aged Ovariectomized Rats

Sevelamer hydrochloride, a noncalcium phosphate binder, has been shown to reduce coronary artery and aortic calcification, and to improve trabecular bone mineral density in hemodialysis patients with chronic kidney disease. Here, we examined whether sevelamer given orally for 12 wk with normal food could restore bone volume (BV) and strength in aged ovariectomized (OVX) rats starting at 4 wk after OVX. Dual-energy x-ray absorptiometry, microcomputerized tomography, and bone histomorphometry analyses showed that OVX animals receiving sevelamer had increased trabecular BV (51%), trabecular number (43%), trabecular thickness (9%), cortical thickness (16%), mineral apposition rate (103%), bone formation rate (25%), and enhanced cortical and trabecular bone mechanical strength as compared with OVX rats. Sevelamer decreased collagen C telopeptide, increased osteocalcin levels, and decreased phosphate and magnesium levels without affecting calcium levels in the blood. Although sevelamer was not absorbed systemically, it stimulated osteoblast differentiation in BM-derived mesenchymal stem cell cultures, as evaluated by alkaline phosphatase positive colony-forming units, and inhibited recombinant human soluble receptor activator of nuclear factor-kappaB ligand-induced osteoclast differentiation, as evaluated by tartrate-resistant acid phosphatase positive cells in bone mineral-hematopoietic stem cell cultures. Surface enhanced laser desorption/ionization time-of-flight mass spectrometry analysis revealed that 69 proteins were differently expressed after OVX, of which 30% (20 of 69) were reversed to sham activity after sevelamer intake. PTH, fibroblast growth factor-23, and cytokine profile in serum were not significantly changed. Together, these results suggest that sevelamer in food increases the BV and improves biomechanical properties of bone in OVX rats.

The ability of serum from alpha 1-antitrypsin-deficient patients to inhibit PRT-201, a recombinant human type I pancreatic elastase.

PRT‐201 is a recombinant human pancreatic elastase under development as a treatment for blood vessels to promote hemodialysis access patency. Proteases such as elastase are normally inactivated by antiproteases such as alpha 1‐antitrypsin. It is unknown if serum from patients with alpha 1‐antitrypsin deficiency will inhibit PRT‐201 elastase activity. An assay for PRT‐201 elastase activity in the presence of serum was developed and validated. PRT‐201 elastase activity inhibition curves were developed using serum and also using purified alpha 1‐antitrypsin and alpha 2‐macroglobulin. Serum from 15 patients with documented alpha 1‐antitrypsin deficiency, some of whom were receiving alpha 1‐antitrypsin augmentation therapy, and four normal volunteers was analyzed. Serum from normal volunteers and patients with alpha 1‐antitrypsin deficiency completely inactivated PRT‐201 elastase activity in vitro. In the alpha 1‐antitrypsin–deficient patients, the volume of serum necessary to inhibit elastase activity was related to the serum concentration of alpha 1‐antitrypsin and augmentation therapy. Purified alpha 1‐antitrypsin and alpha 2‐macroglobulin were each alone capable of completely inhibiting PRT‐201 elastase activity. It is unlikely that the use of PRT‐201 will be associated with negative outcomes in patients with alpha 1‐antitrypsin deficiency.

Comparison of postoperative ultrasound criteria to predict unassisted use of arteriovenous fistulas for hemodialysis

Introduction: Arteriovenous fistulas (AVF) frequently fail to mature. Postoperative ultrasounds provide objective measurements to predict unassisted AVF use for hemodialysis (unassisted use) and guide interventions to salvage nonmaturing AVFs. The optimal ultrasound criteria to assess AVF maturation are uncertain. We analyzed data from a multicenter, randomized, controlled, clinical trial to compare 2 published ultrasound maturation criteria used to predict unassisted AVF use for hemodialysis. Methods: We retrospectively analyzed prospective data on 105 patients undergoing new AVF creation, who underwent standardized postoperative ultrasounds at 6 and 12 weeks to measure AVF diameter and blood flow. Unassisted AVF use was defined as successful cannulation for ≥90 days without requiring prior surgical or percutaneous interventions. Two ultrasound criteria were assessed: (i) National Kidney Foundation (NKF) Kidney Disease Outcome Quality Initiative criteria: AVF outflow vein lumen diameter ≥6 mm and blood flow ≥600 mL/min; and (ii) University of Alabama at Birmingham (UAB) criteria: AVF outflow vein lumen diameter ≥4 mm and blood flow ≥500 mL/min. Performance characteristics were calculated for both criteria. Results: Compared to the NKF criteria, the UAB criteria had a higher sensitivity (89 vs.68%), but a lower specificity (42 vs. 70%) for unassisted AVF use. For radiocephalic AVFs, the UAB criteria had higher sensitivity (86 vs. 46%) and lower specificity (58 vs. 83%). For brachiocephalic AVFs, both UAB and NKF had high sensitivity (90 and 80%) but low specificity (21 and 53%), respectively. Conclusions: Using the UAB ultrasound criteria would minimize unnecessary early interventions in AVFs likely to mature without an intervention, but would delay interventions in AVFs that are unlikely to mature. The UAB criteria may be preferred in patients receiving a radiocephalic AVF.

Comparison of in Vivo Arteriovenous Fistula Volume Flow Measurements Using a Transonic Transit-Time Ultrasound Flow Device and Doppler Ultrasound

Introduction Doppler ultrasound (US) is extensively validated for classification of vascular disease based on velocity calculations. Although widely used to evaluate dialysis access arteriovenous fistulas (AVF), accurate volume flow measurements have proved more elusive, with significant variability resulting in large thresholds for differentiation of normally functioning from failing fistulae. We sought to compare in vivo measurements of AVF blood flow volume measured by the Transonic transit-time ultrasound flow device with those of Doppler US. Methods Bilateral femoral AVFs (n = 6) were created in swine (n = 3). Comparative volume flow measurements were made at baseline, 15, 30, 60, and 120 minutes after the creation of AVFs with the Transonic device and with Doppler US using an estimated time averaged velocity and the diameter of the vessel to calculate volume flow using the formula: Q = v A = v (πr2), where Q = volume flow, v = time and spatial averaged mean velocity, A = cross-sectional area, and r = radius of the vessel. Repeat measurements (minimum 3) were performed at each time point. Linear and multiple linear regression analyses were performed. Results Linear regression analyses showed a weak correlation (R2 = 0.103, p = 0.002) between Transonic and Doppler volume flow measurements. Doppler consistently showed greater volume flow over all time points than Transonic data. Average Transonic values had less variability over time (R2 = 0.9505) compared with average Doppler measurements (R2 = 0.7601). Average flow increased over time, regardless of the flow measurement device, consistent with reported clinical observation of AVF maturation process. Multiple linear regression analysis demonstrated correlation between Doppler and Transonic data (R2 = 0.197, p = 0.013), and provided a formula to estimate Transonic flow measurement from the Doppler data. [Transonic = 113.742 + (0.334 * Doppler)]. Conclusions Transonic data demonstrated a stronger relationship between volume flow and time than Doppler data, suggesting transit time ultrasound volume flow measurements may be more accurate. Doppler data tended to overestimate volume flow measurements; however, it may be feasible to use a correction factor for Doppler data that predicts Transonic results.