The isolated perfused equine distal limb as an ex vivo model for pharmacokinetic studies

Development of a constant pressure perfused ex vivo model of the equine larynx

Distal axonopathy is seen in a broad range of species including equine patients. In horses, this degenerative disorder of the recurrent laryngeal nerve is described as recurrent laryngeal neuropathy (RLN). The dysfunctional innervation of the cricoarytenoideus dorsalis muscle (CAD) leads to a loss of performance in affected horses. In general, ex vivo models of the larynx are rare and for equine patients, just one short report is available. To allow for testing new therapy approaches in an isolated organ model, we examined equine larynges in a constant pressure perfused setup. In order to check the vitality and functionality of the isolated larynx, the vessels´ reaction to norepinephrine (NE) and sodium nitroprusside (NP) as vasoactive agents was tested. Additionally, the contractility of the CAD was checked via electrical stimulation. To determine the extent of hypoxic alterations, lactate dehydrogenase (LDH) and lactate were measured and an immunofluorescent analysis of hypoxia-inducible factor (HIF-1α), a key transcription factor in hypoxia, was performed. For this, a hypoxia-induced cell culture for HIF-1α was developed. The application of NE led to an expected vasoconstriction while NP caused the expected vasodilation. During a perfusion period of 352 ±20.78 min, LDH values were in the reference range and lactate values slightly exceeded the reference range at the end of the perfusion. HIF-1α nuclear translocation could reliably be detected in the hypoxia-induced cell cultures, but not in sections of the perfused CAD. With the approach presented here, a solid basis for perfusing equine larynges was established and may serve as a tool for further investigations of equine larynx disorders as well as a transferrable model for other species.

Revealing the influence of glucocorticoid treatment on the excretion of anabolic-androgenic steroids in horses through in vitro digestive simulations and an in vivo case study

Anabolic-androgenic steroids (AAS) are strictly forbidden in equine sports because of their stimulating effect on muscle growth and performance. Nevertheless, low levels of AAS have been found in some horses, untreated with AAS. Glucocorticoids (GC), used as an anti-inflammatory therapy and structurally related to AAS, might play a role in this phenomenon. In order to unravel this possible correlation the influence of glucocorticoid treatment on the excretion of AAS was studied both in vivo and in vitro. In vivo effects were investigated by analysing urine samples collected from a gelding treated with betamethasone. Additionally, multiple in vitro digestion simulations were set up, according to a previously validated protocol, to study the possibility of a direct biotransformation of glucocorticoids to AAS, by the microbiota of the equine hindgut. Urine and in vitro digestion samples were extracted and analysed with UHPLC-MS/MS and UHPLC-Orbitrap-HRMS analytical methods. A significant influence on the urinary excretion of α-testosterone (αT), β-testosterone (βT) and androsta-1,4-diene-3,17-dione (ADD) was seen. αT-concentrations up to 20ng/mL were detected. ADD was not found before treatment but could be detected post-treatment. Cortisone and cortisol also peaked (>30ng/mL) between day 37 and 48 post-treatment. The in vitro digestion results however revealed no direct biotransformation of glucocorticoids to AAS by the microbiota of the equine hindgut. This study shows that a glucocorticoid treatment can disrupt the synthesis and excretion of AAS, not by direct biotransformation upon gastrointestinal digestion, but more likely by influencing the hypothalamic-pituitary-adrenal axis.

Synovial distribution of "systemically" administered acetylsalicylic acid in the isolated perfused equine distal limb

Background

This study investigated synovial concentrations of acetylsalicylic acid (ASA) and its metabolite salicylic acid (SA) in the equine fetlock joint following systemic administration of ASA. Salicylates were chosen because SA is the only nonsteroidal anti-inflammatory drug for which threshold levels exist for plasma and urine in equine sports. To avoid animal experiments, the study was conducted using an ex vivo model of the isolated perfused equine distal limb in combination with plasma concentrations obtained from literature.

Salicylate concentrations in the joint were determined using microdialysis and high performance liquid chromatography (HPLC). Any anti-inflammatory effect of synovial ASA concentrations was assessed using an ASA EC₅₀ (half maximal effective concentration) determined in equine whole blood.

Results

The ASA concentration in the synovial fluid (n = 6) reached a maximum of 4 μg/mL, the mean concentration over the entire perfusion period was 2 μg/mL. Maximum SA concentration was 17 μg/mL, the average was 14 μg/mL. ASA and SA concentration in the synovial fluid exceeded systemic concentrations 2 h and 3.5 h after “systemic” administration, respectively.

Conclusions

ASA and SA accumulated in the in the synovial fluid of the ex vivo model despite decreasing systemic concentrations. This suggests a prolonged anti-inflammatory effect within the joint that remains to be further elucidated.