Comparative in vitro metabolism of 14C-ciclesonide in hepatocytes from the mouse, rat, rabbit, dog, and human

Hepatotoxicological potential of P-toluic acid in humanised-liver mice investigated using simplified physiologically based pharmacokinetic models

p-Toluic acid, a metabolite of organic solvent xylene, has a high reported no-observed-effect level (NOEL, 1000 mg/kg) in rats, possibly because of direct glycine conjugation to methylhippuric acid. In this study, plasma levels of p-toluic acid and its glycine conjugate in mice and humanised-liver mice were evaluated after oral administrations.Although rapid conversion of p-toluic acid to its glycine conjugate was evident from mouse plasma concentrations, the biotransformation of p-toluic acid was slower in humanised-liver mice. The input parameters for physiologically based pharmacokinetic (PBPK) models were determined using fitting procedures to create PBPK-generated plasma concentration curves.The PBPK-modelled hepatic concentrations of p-toluic acid in humanised-liver mice were higher than those observed in plasma. PBPK-modelled hepatic and plasma concentrations of p-toluic acid also indicated slow elimination in humans.These results suggest that rapid conjugations of p-toluic acid reportedly observed in rats could result in overestimation of NOELs for conjugatable chemicals when extrapolated to humanised-liver mice or humans.

Allometric modeling of ciclesonide, a nonhalogenated glucocorticoid, and its active metabolite, desisobutyrylciclesonide, using animal-derived pharmacokinetic parameters

Ciclesonide, a novel glucocorticosteroid, through a rapid metabolism to desisobutyryl-ciclesonide (des-ciclesonide), provides an effective treatment option for asthma episodes by the inhaled route of administration. The availability of pharmacokinetic parameters (clearance [CL/F]; volume of distribution [Vd/F]; elimination half-life [T(½)]; and elimination rate constant [Kel]) in mice, rats, rabbits, and dogs enabled the prediction of human parameter values for des-ciclesonide using the well-accepted tool of allometry after intravenous administration of ciclesonide. However, as a result of the rapid conversion of ciclesonide, it was possible to perform allometry for the CL parameter only. Simple allometry (CL = 4.781W⁰·⁷⁸⁷⁴; R² = 0.9968) appeared to predict the CL of ciclesonide in close proximity of the observed value (observed: 101.25 L/h versus predicted: 135.62 L/h). In a similar manner, simple allometry predicted the human pharmacokinetic parameters of des-ciclesonide (CL/F, Vd/F, T(½), and Kel) within a two- to threefold range of the observed values. The allometric equations for des-ciclesonide parameter values were: CL/F = 4.8166W⁰·⁴⁹² (R² = 0.8598); Vd/F = 19.052W⁰·⁶³² (R² = 0.9049); T(½) = 3.7598W⁻⁰·¹⁶¹¹(R² = 0.8551); and Kel = 0.1832W⁰·¹⁵⁹⁶ (R² = 0.8632). In conclusion, the data suggested that allometry tool may be amenable for the prediction of the pharmacokinetic parameters of des-ciclesonide despite differences in the conversion rates and bioavailability of the active metabolite in various animal species.

Tissue accumulation kinetics of ciclesonide-active metabolite and budesonide in mice

Inhaled corticosteroids (ICS) are mainstay treatment of asthma and chronic obstructive pulmonary disease. However, highly lipophilic ICS accumulate in systemic tissues, which may lead to adverse systemic effects. The accumulation of a new, highly lipophilic ICS, ciclesonide and its active metabolite (des-CIC) has not yet been reported. Here, we have compared tissue accumulation of des-CIC and an ICS of a moderate lipophilicity, budesonide (BUD), after 14 days of once-daily treatment in mice. Single, three or 14 daily doses of [(3) H]-des-CIC or [(3) H]-BUD were administered subcutaneously to male CD1 albino mice, which were killed at 4 hr, 24 hr or 5 days after the last dose. Distribution of tissue concentration of radioactivity was studied by quantitative whole-body autoradiography. Pattern of radioactivity distribution across most tissues was similar for both corticosteroids after a single as well as after repeated dosing. However, tissue concentration of radioactivity differed between des-CIC and BUD. After a single dose, concentrations of radioactivity for both corticosteroids were low for most tissues but increased over 14 days of daily dosing. The tissue radioactivity of des-CIC at 24 hr and 5 days after the 14th dose was 2-3 times higher than that of BUD in majority of tissues. Tissue accumulation, assessed as concentration of tissue radioactivity 5 days after the 14th versus 3rd dose, showed an average ratio of 5.2 for des-CIC and 2.7 for BUD (p < 0.0001). In conclusion, des-CIC accumulated significantly more than BUD. Systemic accumulation may lead to increased risk of adverse systemic side effects during long-term therapy.

Clinical pharmacokinetic and pharmacodynamic profile of inhaled ciclesonide

Asthma is a chronic inflammatory disease of the airways, and inhaled corticosteroids (ICSs) are recommended as first-line therapy for persistent asthma of all severities. Ciclesonide is a novel ICS, which is administered as an aerosol solution in a metered-dose inhaler, using hydrofluoroalkane-134a as a propellant. Because of the high respirable particle fraction, high pulmonary deposition is obtained in patients, which constitutes the basis of effective therapeutic action. The parent compound, ciclesonide, is pharmacologically inactive and is activated in the target organ, the lung, to form its only pharmacologically active metabolite, desisobutyryl-ciclesonide (des-CIC). Low oral deposition combined with minimal formation of des-CIC in the oropharynx may minimize the typical oropharyngeal adverse events associated with ICSs. Low oral bioavailability, rapid clearance and high protein binding reduce pharmacologically relevant systemic exposure. The unique pharmacokinetic and pharmacodynamic profile of ciclesonide offers a rationale that supports the favourable risk-benefit profile observed in clinical trials in patients with persistent asthma.

Metabolism of ciclesonide in the upper and lower airways: review of available data

Ciclesonide is a novel corticosteroid (CS) for the treatment of asthma and allergic rhinitis. After administration, the parent compound ciclesonide is converted by intracellular airway esterases to its pharmacologically active metabolite desisobutyryl-ciclesonide (des-CIC). We investigated the in vitro activation of ciclesonide and further esterification of des-CIC to (mainly) des-CIC oleate in several human target organ test systems. Human precision-cut lung slices, alveolar type II epithelial cells (A549), normal bronchial epithelial cells (NHBE), and nasal epithelial cells (HNEC) were incubated with ciclesonide. Enzymes characterization and the determination of the reversibility of fatty acid esterification was investigated in HNEC and NHBE. Ciclesonide was taken up and converted to des-CIC in all cellular test systems. Intracellular concentrations of des-CIC were maintained for up to 24 h. Formation of des-CIC oleate increased over time in HNEC, A549 cells, and lung slices. The formed des-CIC fatty acid conjugates were reconverted to des-CIC. Increasing concentrations of carboxylesterase and cholinesterase inhibitors progressively reduced the formation of metabolites. The results derived from these studies demonstrate the activation of ciclesonide to des-CIC in the upper and lower airways. The reversible formation of des-CIC fatty acid conjugates may prolong the anti-inflammatory activity of des-CIC and may allow for once-daily dosing.

Identification of enzymes involved in phase I metabolism of ciclesonide by human liver microsomes

Ciclesonide, a novel inhaled corticosteroid, is currently being developed for the treatment of asthma. Here, the enzymes catalysing the human hepatic metabolism of ciclesonide were investigated. When incubated with human liver microsomes (HLM), [14C]ciclesonide was first metabolised to the active metabolite M1 (des-isobutyryl-ciclesonide, des-CIC) and to at least two additional metabolites, M2 and M3. M3 comprises a 'family' of structurally similar metabolites that are inactive. 16-Hydroxyprednisolone was also formed in microsomal incubations of [14C]des-CIC, but at approximately one-tenth the amount of both M2 and M3. bis-p-Nitrophenylphosphate and SKF 525-A respectively inhibited des-CIC formation from [14C]ciclesonide by 82% and 49% and M2/M3 formation by 82-84% and 87-89%. Regression analysis showed significant negative correlations (r = -0.96, -0.79 and -0.71, respectively) of M2 formation with CYP3A4/5, CYP2B6 and CYP2C8 activities; M3 formation significantly correlated with CYP4A9/11 (r = 0.47). Troleandomycin and diethyldithiocarbamate inhibited M2 and M3 formation by 85% and 45%, respectively. Sulphaphenazole and quinidine had no inhibitory effects. CYP3A4 Supersomes catalysed notable formation of both M2 and M3 from [14C]des-CIC; CYP2C8 and CYP2D6, but not CYP4A11 formed smaller amounts. It is concluded that the human hepatic metabolism of ciclesonide is primarily catalysed by one or more esterases and, subsequently, by CYP3A4.