Comparative pharmacokinetic studies of tixocortol pivalate and cortisol in the rat

Novel drug delivery strategies for the treatment of inflammatory bowel disease

Inflammatory bowel disease (IBD) encompasses two idiopathic inflammatory diseases of the intestinal tract: Crohn's disease and ulcerative colitis. Existing therapy for IBD consists mainly of orally or rectally administered small drug molecules, such as 5-aminosalicylates and corticosteroids, or potent systemic immune suppressants. IBD presents a challenging target for drug delivery, particularly by the oral route, as, contrary to most therapeutic regimens, minimal systemic absorption and maximal intestinal wall drug levels are desired. Several delivery strategies are employed to achieve this goal, including the chemical modification of the drug molecules, the use of controlled- and delayed-release formulations and the use of bioadhesive particles. The goal of this review is to summarise existing IBD therapy and examine novel approaches in intestinal drug delivery.

Modelling the loss of metabolic capacities of cultured hepatocytes: application to measurement of Michaelis-Menten kinetic parameters in in vitro systems

1. The loss of metabolic capacities during culture time constitutes a major limitation for the use of hepatocyte primary cultures in in vitro metabolism measurements. A new strategy is presented that permits one to calculate the Michaelis-Menten parameters V(max) and K(m) from extended experiments, by modelling V(max) as a variable dependent on time using exponential or sigmoidal equations. 2. This method was tested with cortisol depletion in cultured rat hepatocytes. V(max) and K(m) were used to calculate intrinsic clearance, and comparisons were made with methods already described in the literature. Intrinsic clearances given by our method were scaled to in vivo hepatic clearances that were close to those reported in the literature. 3. Our method could quantify the V(max) decrease with culture time from estimates of time parameters, t(1/2) or t(50). In our system, this V(max) decrease was in agreement with P450 cytochrome inactivation rates published for the rat liver. 4. In conclusion, we propose a convenient, simple and useful general method for both Michaelis-Menten parameter estimation and modelling of variations in the metabolic capacities observed in in vitro systems. Such an approach should improve the usefulness of hepatocytes in primary cultures for long-term metabolism experiments.

Effects of tixocortol pivalate on gastrointestinal disease in systemic mastocytosis: a preliminary study

Tixocortol pivalate is a steroid reportedly without significant adrenal-pituitary axis suppression when administered via the gastrointestinal tract. To determine whether this steroid would suppress the gastrointestinal manifestations of systemic mastocytosis, we performed an open clinical trial for safety and efficacy with tixocortal pivalate in four patients for periods of 8-15 weeks. All patients showed a decrease in the symptoms of abdominal pain and frequency of stools. Laboratory parameters of malabsorption improved in parallel with symptom relief. Histopathologic abnormalities of the small bowel improved in one patient. There was no significant suppression of the pituitary-adrenal axis. Two patients developed fluid retention while on tixocortol pivalate, which was attributed to a mineralocorticoid effect. One patient had a fall in AM cortisol. In summary, this study strongly suggests that tixocortol pivalate, when administered orally, has gastrointestinal anti-inflammatory activity comparable to conventional steroids, but may not be entirely without adrenal-suppressive effect and may lead to fluid retention in some patients. Further studies are warranted to assess the value of tixocortol pivalate in the therapy of inflammatory diseases of the upper gastrointestinal tract.

Direct inhibition of cyclooxygenase pathway in platelets by tixocortol 21-pivalate: comparison with related structures, steroidal and non steroidal anti-inflammatory drugs

Direct activity of the local anti-inflammatory steroid, tixocortol 21-pivalate (21 thioester derivative of cortisol) on metabolism of exogenous arachidonate by rabbit platelets was investigated in vitro. Tixocortol 21-pivalate inhibited generation of prostanoids from cyclooxygenase with an IC50 value of 19.6 microM without affecting the 12-lipoxygenase pathway. In this model, reference anti-inflammatory glucosteroids were ineffective, whereas indomethacin and aspirin inhibited the cyclooxygenase activity. Among tixocortol 21-pivalate related structures, tixocortol and its disulfide dimere or several other tixocortol esters exhibited a quite similar efficacy while S-methylation and subsequent S-oxydations of tixocortol abolished inhibitory activity. These results indicate that tixocortol 21-pivalate in contrast to other glucosteroids is able to act directly on cyclooxygenase pathway and that some specific chemical environment of the 21 thiol side chain are required for this inhibition.

Local anti-inflammatory activities of tixocortol 21-pivalate, inhibition of prostaglandins and leukotrienes synthesis, in carrageenin-induced pleurisy. Reversion of effects by RU 486

Since a direct effect of tixocortol pivalate (TP) has been described on cyclooxygenase pathway, local anti-inflammatory activities of some 21 thiol derivatives of steroids were investigated on the carrageenin-induced pleurisy model in comparison with dexamethasone (Dex) or other anti-inflammatory drugs. LTC4/D4 contents in pleural fluid were assayed by RIA as well as PGE2 levels to characterize the effects on arachidonate pathways. After oral administration, TP was inactive up to 1 g/kg on exudate volume and leukocyte migration as expected for this strict local anti-inflammatory steroid contrary to Dex (ID50 = 0.05-0.41 mg/kg). When administered locally, TP and tixocortol (T) exerted a dose dependent inhibitory activity on exudate volume (ID30 = 12.4 micrograms or 13.1 micrograms/pleural cavity) and leukocyte count (ID30 = 83 or 230 micrograms); in the same conditions. Dex was more active (ID30 = 0.7 and 2.6 micrograms). All these steroids decreased PGE2 and LTC4/D4 contents in exudate fluids, respectively TP (50 micrograms/pleural cavity) by 28 and 63%; T (100 micrograms) by 33 and 31%; Dex (5 micrograms) by 43 and 40%. Local co-administration of RU 486 (50 micrograms) with either TP, T or Dex reversed the anti-inflammatory effects of all steroids, indicating in these conditions a local activity through glucosteroid receptor occupancy.

Effect of structural alterations on the biotransformation rate of glucocorticosteroids in rat and human liver

The effect of structural alterations on the biotransformation rate of glucocorticosteroids (GCS) by rat- and human-liver 9000 g supernatant fraction was studied. Insertion of a 16 alpha-hydroxy group in the prednisolone molecule (16 alpha-hydroxyprednisolone) was found to decrease the rate of biotransformation. Substitution of the 16 alpha,17 alpha-hydroxy groups with a symmetric acetal (in, for example, desonide) or especially a non-symmetric acetal (in, for example, budesonide), enhanced the biotransformation rate several-fold, particularly in human liver. Differences in the rates of metabolism in rat and human liver were observed. Hydrogenation of the 1,2-double bond in prednisolone and budesonide (hydrocortisone and 1,2-dihydrobudesonide) enhanced the biotransformation rate nine-fold in rat liver but only two-fold in human liver. Fluorination of the steroid nucleus in 6 alpha- and 9 alpha-positions enhanced the biotransformation rate several-fold in human liver, but in rat liver fluorination marginally decreased the rate of biotransformation. These in vitro results correlate well with available data on the first-pass liver metabolism of the studied GCS. This indicates that in vitro data can be useful in predicting oral bioavailability of GCS.

Contact allergy to hydrocortisone and thixocortol pivalate: problems in the detection of corticosteroid sensitivity

Several of the difficulties involved in the detection of corticosteroid allergy are illustrated by the problems encountered in a patient sensitive to a preparation containing hydrocortisone and miconazole nitrate. The importance of appropriate concentrations and vehicles for patch testing, the possible rôle of impurities, and cross-sensitivity of corticosteroid molecules are discussed.