Development and validation of a sensitive ELISA for quantitation of Grastim® (rhG-CSF) in rat plasma: application to a pharmacokinetic study

Validation of a Double-Sandwich Enzyme-Linked Immunoassay for Pharmacokinetic Study of an rh-aFGF Hydrogel in Rat Skin and Serum

In this study, we validated a double-sandwich enzyme-linked immunosorbent assay (ELISA) to investigate the pharmacokinetics of a recombinant human acidic fibroblast growth factor (rh-aFGF) hydrogel in rat skin and serum. A total of 130 Sprague-Dawley rats were divided into a control group, rh-aFGF hydrogel group, and a positive-control group (commercial rh-aFGF-Ai). We first determined the dilution ratio of skin homogenate and then validated the quantitative range, specificity, precision, and accuracy of our double-sandwich ELISA method, as well as the stability of our rh-aFGF hydrogel. For our pharmacokinetic study, skin and serum samples were collected at 0.5, 1, 2, 4, 6, and 10 h after rh-aFGF administration, and the concentration of rh-aFGF was measured by ELISA. The results showed that a 10-fold dilution of the skin tissue homogenate circumvented non-specific interference with endogenous proteins. The quantitative scope of the rh-aFGF calibration curve ranged from 62.5 to 4,000 pg/mL. The precision and accuracy of rh-aFGF quality-control samples were below 20%. Furthermore, bFGF, FGF21, KGF-2, and insulin did not interfere with the detection of aFGF, confirming that our method was specific. Rh-aFGF was stable under normal storage conditions. The maximum concentration (Cmax) and time to peak (Tmax) of the rh-aFGF hydrogel were 909.2 pg/cm2 and 0.5 h, respectively. The relative bioavailability (F) of the rh-aFGF hydrogel was 120% compared with that of rh-aFGF-Ai. The serum concentration of rh-aFGF was too low to be detected. Taken together, the pharmacokinetics of this rh-aFGF hydrogel provide further support for clinical research on rh-aFGF, and our double-sandwich ELISA method may be useful for pharmacokinetic studies of other protein-based drugs.

Clozapine promotes the proliferation of granulocyte progenitors in the bone marrow leading to increased granulopoiesis and neutrophilia in rats

Clozapine is an atypical antipsychotic that is limited in its use due to the risk of idiosyncratic agranulocytosis. The bone marrow is suspected to be the site of the reaction, and indirect measurements in patients suggest that neutrophil production and maturation are altered in the marrow by clozapine. Specifically, the majority of patients have elevated neutrophil counts at the start of treatment, often paired with increased serum granulocyte-colony stimulating factor (G-CSF). Employing a rat model of clozapine treatment, we set out to determine if the neutrophilia observed at the start of treatment is characteristic of G-CSF-associated bone marrow stimulation. Female Sprague-Dawley rats were treated with 30 mg/kg/day of clozapine for 10 days, and sustained neutrophilia was evident after 1 week of treatment paired with spikes in G-CSF. Within the bone marrow, clozapine was found to induce proliferation of the granulocyte progenitor colonies as measured by a methylcellulose assay. This led to elevated granulopoiesis observed by H&E and myeloperoxidase staining of bone marrow slices. Increased release of neutrophils from the marrow to the circulation was measured through 5-bromo-2'-deoxyuridine labeling in vivo, and these neutrophils appeared to be less mature based on (a) a decrease in the nuclear lobe count and (b) increased expression of surface CD62L. Furthermore, faster transit of the neutrophils through the marrow was suggested by a shift toward elevated numbers of neutrophils in the bone marrow maturation pool and increased CD11b and CD18 staining on the less mature neutrophils residing in the marrow. Taken together, these data indicate that clozapine stimulates the bone marrow to produce more neutrophils in a manner that is characteristic of endogenous G-CSF stimulation, and it is consistent with the inflammatory response observed in patients treated with clozapine.