Introduction. 5-HMF and novel INN-compounds are left-shifting AEH, shown to have anti-sickling action by forming transiently covalent Schiff-base adducts with hemoglobin (Hb), thereby increasing the Hb O2-affinity. They are hypothesized to be substrates for aldehyde dehydrogenase (ALDH) in the liver and red blood cells (RBC). Methods. Biopharmaceutical assessments were made for AEH, using calculated physicochemical properties. Their in-vitro hepatic metabolism (mediated by ALDH) was characterized using hepatic cytosol, and in-vitro-in-vivo extrapolations (IVIVE) were made. Inter-species differences in hepatic cytosolic ALDH activity were investigated using acetaldehyde as a model substrate in different mammalian species. Time- and concentration-dependent in-vitro disposition of 5-HMF in human whole blood was fully characterized and quantitatively modeled. In-vitro time- and concentration-dependent pharmacodynamic (PD) profiling of AEH (0.5 – 5 mM) was carried out in normal whole blood. 5-HMF binding to (normal) HbA and (sickle) HbS was studied in systematic time- and concentration-dependency studies using isolated Hb solutions. Quantitative PK/PD models were developed to fit the experimental data by nonlinear regression (Scientist®). Results. 5-HMF and the two INN-compounds were classified as BCS-I and BCS-II, respectively. All AEH were substrates for hepatic ALDH, with predicted low/intermediate hepatic extraction. Intrinsic ALDH activity varied significantly between mammalian species. In whole blood, 5-HMF plasma concentrations declined rapidly (t1/2 of 0.8 – 4 hrs), with nonlinear kinetics, due to saturable Hb-binding. AEH showed a time-dependent, biphasic PD effect in whole blood, suggesting transiently covalent Hb binding, with slow recovery to the baseline, corresponding to dissociation from Hb and subsequent metabolism by RBC-ALDH. Binding studies with HbA and HbS demonstrated slight differences in binding affinity, but sustained adduct formation - with slow dissociation t1/2. A novel semi-mechanistic target-site drug disposition (TSDD)/PD model was developed, integrating the information, for simultaneous modeling of 5-HMF concentrations in plasma, and its effect in whole blood. Conclusions. This translational research investigated in detail the in-vitro PK/PD of AEH, and systematically compared findings with older generation compounds. A (generic) novel TSDD/PD model was developed for disposition of AEH, identifying k-1 (dissociation constant of AEH from Hb) and kmet (RBC-ALDH metabolism rate constant) as key properties for the time course of PD effect.
| Identifer | oai:union.ndltd.org:vcu.edu/oai:scholarscompass.vcu.edu:etd-1541 |
| Date | 01 January 2013 |
| Creators | Parikh, Apurvasena |
| Publisher | VCU Scholars Compass |
| Source Sets | Virginia Commonwealth University |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Theses and Dissertations |
| Rights | © The Author |
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