High-dose busulfan (Bu) is frequently used in preparative myeloablative conditioning (MAC) regimens for patients undergoing hematopoietic stem cell transplantation (HSCT). MAC and reduced-intensity conditioning (RIC) protocols for i.v. Bu infusion have been developed to achieve reliable systemic exposure while minimizing toxicity and treatment failure (relapse). The objectives of the present study were to (1) compare the pharmacokinetics (PK) of i.v. Bu in different dosing protocols, (2) compare intrasubject variability of Bu PK over repeated administrations; (3) examine the effect of concomitant administration of fludarabine on Bu PK, and (4) examine the effect of plasma concentrations of glutathione (GSH), the cosubstrate in Bu metabolism, on Bu clearance. We studied Bu PK twice in each of 46 HSCT patients (after the first and then after the middle dose of the treatment cycle) receiving one of 4 dosing protocols, 2 MAC (cumulative dose, 12.8 mg/kg) and 2 RIC (cumulative dose, 6.4 mg/kg), with daily doses administered either as an individual infusion (3.2 mg/kg) or as 4 infusions of 0.8 mg/kg each. Blood samples were obtained for 6-24 hours after dosing for measurement of Bu plasma concentrations. PK parameters were estimated using compartmental analyses. In a subgroup of patients (n = 14), GSH blood concentrations were determined before Bu administration. Dose- and weight-corrected Bu PK parameters (clearance, 0.173 ± 0.051 L/hour · kg; volume of distribution, 0.71 ± 0.17 L/kg; half-life time, 3.0 ± 0.7 hours) did not differ among treatment protocols (all P >.14) and remained stable between the first and mid-cycle doses. Fludarabine did not affect Bu PK. Blood GSH concentrations before Bu dosing were positively correlated with Bu clearance (adjusted R(2) = 0.45; P = .009). Our data indicate that Bu PK parameters are linear, stable, and predictable in different i.v. protocols and are unaffected by coadministration of fludarabine. Differences in whole blood GSH might contribute to variability in Bu clearance.

Current non-invasive diagnostic methods of fibrosis are limited in their ability to identify early and intermediate stages of fibrosis and assess the efficacy of therapy. New biomarkers of fibrosis are therefore constantly sought for, leading us to evaluate procollagen C-proteinase enhancer 1 (PCPE-1), a fibrosis-related extracellular matrix glycoprotein, as a plasma marker of fibrosis. A sandwich ELISA that permitted accurate measurements of PCPE-1 concentrations in mouse plasma was established. Tissue fibrosis was assessed using histochemical, immunofluorescence, and immunoblotting analyses for type I collagen and PCPE-1. The normal plasma concentration of PCPE-1 in 6 weeks to 4 months old mice was ~200 ng/ml (189.5 ± 11.3 to 206.8 ± 13.8 ng/ml). PCPE-1 plasma concentrations in four and 8.5 months old mdx mice displaying fibrotic diaphragms increased 27 and 40% respectively relatively to age-matched control mice, an increase comparable to that of the N-propeptide of procollagen type III (PIIINP), a known blood marker of fibrosis. PCPE-1 plasma levels in mice with CCl4-induced liver fibrosis increased 34 to 50% relatively to respective controls and reflected the severity of the disease, namely increased gradually during the progression of fibrosis and went down to basal levels during recovery, in parallel to changes in the liver content of collagen I and PCPE-1. The results favor PCPE-1 as a potential new clinically valuable fibrosis biomarker.

This article provides a protocol for determination of human procollagen C-proteinase enhancer 1 (PCPE-1) concentrations by ELISA. The inter-assay and intra-assay coefficients of variability are given and so are the average plasma concentrations of PCPE-1 in healthy (control) individuals and liver fibrosis patients.