Vikram Arya

Contrary to adult, neonatal rats show pronounced brain uptake of corticosteroids.

Neurotoxic adverse effects after systemic corticosteroid administration are elevated in preterm infants. To test whether this might be related to an immature blood-brain barrier (BBB) that permits corticosteroids to enter the brain and induce neurotoxic effects, this study assessed the differences in brain permeability of triamcinolone acetonide after intratracheal administration to neonatal (10- to 11-day-old) and adult rats. Triamcinolone acetonide (or the phosphate prodrug in the case of neonatal rats) was administered intratracheally to neonatal rats at doses of 2.5, 25, or 50 μg/kg and to adult rats at 100 μg/kg. An ex vivo receptor binding assay was used to monitor the cumulative brain and liver glucocorticoid receptor occupancies over 6 h. Brain and liver receptor occupancies in neonates were similar for the 25 and 50 μg/kg triamcinolone acetonide phosphate (brain/liver receptor occupancy ratio, 1.10 ± 0.14 and 0.87 ± 0.13, respectively), whereas some reduction in the brain permeability was seen at the lower dose. After intratracheal administration of 100 μg/kg triamcinolone acetonide to adult rats, receptor occupancies in the brain were significantly lower (brain/liver ratio, 0.21 ± 0.14; p < 0.001). The study demonstrated that glucocorticoids enter the brain of neonatal rats because of an immature BBB. The results of this study support the hypothesis that neurotoxic adverse effects in preterm infants after systemic corticosteroid administration might be related to an immature BBB.

Brain permeability of inhaled corticosteroids

The aim of this study was to evaluate if the permeability of inhaled corticosteroids entering the brain is reduced and if P‐glycoprotein (P‐gp) transporters are involved. Currently employed inhaled corticosteroids were given intravenously and intratracheally to rats at a dose of 100 μg kg−1. An ex‐vivo receptor binding assay was used to monitor over 12 h the glucocorticoid receptor occupancy in the brain and a systemic reference organ (kidney). The involvement of P‐gp in the brain permeability of triamcinolone acetonide was assessed in wild‐type mice and mdr1a(‐/‐) knockout mice (mice lacking the gene for expressing P‐gp). After both forms of administration, the average brain receptor occupancies were 20–56% of those of the reference organ, with the more lipophilic drugs showing a more pronounced receptor occupation. While the receptor occupancies in the liver of wild‐type and mdr1a(‐/‐) mice were similar after administration of triamcinolone acetonide, brain receptor occupancies in mdr1a(‐/‐) mice were significantly greater (mdr1a(‐/‐): 47.6%, 40.2–55.0%, n = 2; wild‐type: 11.5±33.0%, n = 3). Penetration into the brain for inhaled corticosteroids (especially those of lower lipophilicity) is reduced. Experiments in mdr1a(‐/‐) mice confirmed the involvement of P‐gp transporters. Further studies are needed to assess whether potential drug interactions at the transporter level are of pharmacological significance.

Pulmonary targeting of sustained release formulation of budesonide in neonatal rats

Systemic corticosteroids are widely used for the treatment/prevention of chronic lung disease (CLD) in premature infants. The use of the inhalation route for delivering corticosteroids has been widely recognized, however so far pre-term babies continue to be treated with oral glucocorticoids, such as dexamethasone. We hypothesize that the pulmonary administration of sustained release formulations of inhaled corticosteroids to pre-term infants will result in a higher benefit/risk ratio as compared to traditional inhalation therapy. To achieve a slow release formulation budesonide particles were coated with a very thin film of polylactic acid using a pulse laser ablation technique. Coated material was characterized with respect to the dissolution behavior and particle size. Ex vivo receptor binding studies were performed to monitor the cumulative lung, liver and brain receptor occupancies after adminstration in neonatal (10–11 days old) rats after intratracheal instillation of either uncoated budesonide or poly (l-lactic acid) (PLA) coated budesonide. The mean dissolution timed for the uncoated and the polymer coated formulations were 1.2 ± 0.5 and 4.7 ± 0.1 h, respectively (p < 0.05). No significant differences in the respirable fraction were found between coated and uncoated formulation (p>0.05). The average receptor occupancies in the lung, liver and brain after administration of uncoated budesonide were 58.4 ± 12.9, 56.4 ± 6.8 and 38.3 ± 6.7%, respectively. However, after administration of PLA coated budesonide, the average AUC estimates in the lung, liver and brain were 75.8 ± 3.7%, 46.6 ± 14.5 and 29 ± 7, respectively. The results from our study suggest sustained receptor occupancy in the lungs of neonatal rats after administration of PLA coated budesonide results in lower systemic exposure (as indicated by low liver receptor occupancy). The data strongly underscore the urgent need to develop sustained release pulmonary-targeted delivery systems of corticosteroids for the treatment of CLD in pre-term infants. The administration of inhaled corticosteroids using targeted drug-delivery systems will potentially result in higher local effects and a reduction in systemic exposure.

Stabilized dynorphin derivatives for modulating antinociceptive activity in morphine tolerant rats: effect of different routes of administration.

Dynorphins, such as dynorphin A(1–13) (Dyn A(1–13)), have been shown to enhance analgesia in morphine-tolerant animals, despite their very short half-life after intravenous administration. The potential use of dynorphins in humans is therefore of interest. This laboratory has recently evaluated the metabolic fate of stabilized dynorphin derivatives. This study was conducted to evaluate whether such stabilized derivatives, ie, [N-Met-Tyr1]-Dynorphin A(1–13) (N-MT Dyn A, stabilized at the N-terminal end) and [N-Met-Tyr1]-Dynorphin A(1–13) amide (N-MT Dyn A amide, stabilized at the C-and N-terminal ends), would enhance the antinociceptive activity of morphine not only after intravenous administration but also after subcutaneous and pulmonary delivery. Intravenous administration of N-MT Dyn A (5 μmol/kg) and N-MT Dyn A amide (5 μmol/kg) to morphine-tolerant rats resulted in significantly higher tail-flick latencies than those observed for the saline group. These effects could be observed for up to 2.0±0.1 hours after intravenous administration of N-MT Dyn A and for up to 3.4±1.4 hours for N-MT Dyn A amide. The time-averaged effects of both peptides were similar. After pulmonary delivery of the same dose, derivatives remained active. The duration of the effects after pulmonary administration of the amide was 4.4±2.5 hours while that of N-MT Dyn A was slightly shorter (2.8±0.9 hours). No effect was observed after subcutaneous administration of N-MT Dyn A. These results suggest that pulmonary delivery of stabilized dynorphin derivatives represents a possible alternative to intravenous administration.

Identification of Stabilized Dynorphin Derivatives for Suppressing Tolerance in Morphine-Dependent Rats

AbstractPurpose. Modulatory actions on morphine-induced effects, such as tolerance and withdrawal, have been noted for dynorphin A(1-13) [Dyn A(1-13)] and similar peptides. These are currently of limited therapeutic potential due to extensive metabolism by human metabolic enzymes resulting in a half-life of less than 1 min in human plasma. The purpose of this study was to identify stabilized dynorphin A (Dyn A) derivatives, to determine their metabolic routes in human plasma, and to assess whether the pharmacodynamic activity is retained. Methods. The stability of peptides in human plasma was tested using in vitro metabolism studies with and without enzyme inhibitors. Identification of the generated metabolites was performed by mass spectrometry after high performance liquid chromatography (HPLC) separation. The in vivo activity of a stabilized dynorphin was tested by tail-flick assay in morphine-tolerant rats. Results. Though amidation of the Dyn A(1-13) was able to stop the majority of C-terminal degradation, metabolism of Dyn A(1-10) amide continued by captopril sensitive enzymes, suggesting that Dyn A(1-13) amide is a better candidate for additional stabilization. Two Dyn A(1-13) amide derivatives further stabilized at the N-terminal end, [D-Tyr1]-Dyn A(1-13) amide and [N-Met-Tyr1]-Dyn A(1-13) amide, showed half-lives in plasma of 70 and 130 min, respectively. The most stable derivative [N-Met-Tyr1]-Dyn A(1-13) amide was tested successfully for retention of the pharmacological activity in modulating antinociceptive activity. Conclusions. [N-Met-Tyr1]-Dyn A(1-13) amide showed significant stability and antinociceptive activity in the tail-flick test, thus pointing to the clinical potential of this derivative in the management of pain as well as its potential activity in suppressing opiate tolerance and withdrawal.

Laser-ablated nanofunctional polymers for the formulation of slow-release powders for dry powder inhalers: physicochemical characterization and slow-release characteristics

Recently, dry powder inhalation (DPI) powders coated with nanometre‐thin layers of biodegradable polymers, prepared using pulse laser deposition (PLD), have been evaluated as a slow‐release formulation for DPI use, with the goal of improving pulmonary selectivity. This paper describes evaluation of the chemical stability of one potential polymer, poly lactic acid (PLA), during the ablation process, the resulting respirable properties and potential cytotoxicity of coated glucocorticoid powders, and the resulting sustained‐release characteristics of PLA‐coated glucocorticoids creating using PLD. Triamcinolone acetonide (TA) and budesonide (BUD) were used as two model glucocorticoids to determine pulmonary targeting (PT) in‐vivo.