A Pharmacologic "Stress Test" for Assessing Select Antioxidant Defenses in Patients with CKD.

BACKGROUND AND OBJECTIVES: Oxidative stress is a hallmark and mediator of CKD. Diminished antioxidant defenses are thought to be partly responsible. However, there is currently no way to prospectively assess antioxidant defenses in humans. Tin protoporphyrin (SnPP) induces mild, transient oxidant stress in mice, triggering increased expression of select antioxidant proteins (e.g., heme oxygenase 1 [HO-1], NAD[P]H dehydrogenase [quinone] 1 [NQO1], ferritin, p21). Hence, we tested the hypothesis that SnPP can also variably increase these proteins in humans and can thus serve as a pharmacologic "stress test" for gauging gene responsiveness and antioxidant reserves. DESIGN: , setting, participants, & measurementsA total of 18 healthy volunteers and 24 participants with stage 3 CKD (n=12; eGFR 30-59 ml/min per 1.73 m2) or stage 4 CKD (n=12; eGFR 15-29 ml/min per 1.73 m2) were injected once with SnPP (9, 27, or 90 mg). Plasma and/or urinary antioxidant proteins were measured at baseline and for up to 4 days post-SnPP dosing. Kidney safety was gauged by serial measurements of BUN, creatinine, eGFR, albuminuria, and four urinary AKI biomarkers (kidney injury molecule 1, neutrophil gelatinase-associated lipocalin, cystatin C, and N-acetyl glucosaminidase). RESULTS: Plasma HO-1, ferritin, p21, and NQO1 were all elevated at baseline in CKD participants. Plasma HO-1 and urine NQO1 levels each inversely correlated with eGFR (r=-0.85 to -0.95). All four proteins manifested statistically significant dose- and time-dependent elevations after SnPP injection. However, marked intersubject differences were observed. p21 responses to high-dose SnPP and HO-1 responses to low-dose SnPP were significantly suppressed in participants with CKD versus healthy volunteers. SnPP was well tolerated by all participants, and no evidence of nephrotoxicity was observed. CONCLUSIONS: SnPP can be safely administered and, after its injection, the resulting changes in plasma HO-1, NQO1, ferritin, and p21 concentrations can provide information as to antioxidant gene responsiveness/reserves in subjects with and without kidney disease. CLINICAL TRIAL REGISTRY NAME AND REGISTRATION NUMBER: A Study with RBT-1, in Healthy Volunteers and Subjects with Stage 3-4 Chronic Kidney Disease, NCT0363002 and NCT03893799.

Parenterial iron sucrose-induced renal preconditioning: differential ferritin heavy and light chain expression in plasma, urine, and internal organs.

Experimental data suggest that iron sucrose (FeS) injection, used either alone or in combination with other prooxidants, can induce "renal preconditioning," in part by upregulating cytoprotective ferritin levels. However, the rapidity, degree, composition (heavy vs. light chain), and renal ferritin changes after FeS administration in humans remain to be defined. To address these issues, healthy human volunteers (n = 9) and patients with stage 3-4 chronic kidney disease(n = 9) were injected once with FeS (120, 240, or 360 mg). Plasma ferritin was measured from 0 to 8 days postinjection as an overall index of ferritin generation. Urinary ferritin served as a "biomarker" of renal ferritin production. FeS induced rapid (≤2 h), dose-dependent, plasma ferritin increases in all study participants, peaking at approximately three to five times baseline within 24-48 h. Significant urinary ferritin increases (~3 times), without dose-dependent increases in albuminuria, neutrophil gelatinase-associated lipocalin, or N-acetyl-ß-d-glucosaminidase excretion, were observed. Western blot analysis with ferritin heavy chain (Fhc)- and light chain (Flc)-specific antibodies demonstrated that FeS raised plasma Flc but not Fhc levels. Conversely, FeS increased both Fhc and Flc in urine. To assess sites of FeS-induced ferritin generation, organs from FeS-treated mice were probed for Fhc, Flc, and their mRNAs. FeS predominantly raised hepatic Flc. Conversely, marked Fhc and Flc elevations developed in the kidney and spleen. No cardiopulmonary ferritin increases occurred. Ferritin mRNAs remained unchanged throughout, implying posttranscriptional ferritin production. We conclude that FeS induces rapid, dramatic, and differential Fhc and Flc upregulation in organs. Renal Fhc and Flc increases, in the absence of nephrotoxicity, suggest potential FeS utility as a clinical renal "preconditioning" agent.