Pathology and Neurotoxicity in Dogs after Repeat Dose Exposure to a Serotonin 5-HT1B Inhibitor.

AZD3783, a cationic amphiphilic drug and a potent inhibitor of the 5-hydroxytryptamine (5-HT1B) receptor, was explored as a potential treatment for depression. To support clinical trials, repeat dose toxicity studies in rats and dogs were conducted. Here we report toxicity findings in dogs after dosing from 1 to 3 months. In the 1-month study, there were minimal neuronal vacuolation in the brain, a marked increase in liver enzymes accompanied by hepatocellular degeneration/necrosis and phospholipidosis (PLD), and PLD/cholecystitis in the gallbladder of animals dosed at 47 mg/kg/day. In the 3-month study, neurotoxicity resulted in euthanasia of one animal dosed at 30 mg/kg/day after 86 days. Extensive pathologic changes were seen in all animals in retina epithelium (inclusion bodies), brain (neuronal vacuolation, degeneration, or necrosis and nerve fiber degeneration), spinal ganglia (vacuolation, degeneration, or necrosis), as well as sciatic and optic nerves (degeneration). Pigment-laden macrophages were observed in the lung, kidney, liver, gallbladder, bone marrow, gastrointestinal tract, and lymphoid tissues. Also seen were vitrel and retinal hemorrhage in the eyes. A brain concentration and pathology study showed that the concentration of AZD3783 in the brain was approximately 4 times higher than in the plasma after 4 weeks of dosing, however, they were similar in all regions examined, and did not correlate with areas with pathologic findings. Our findings with AZD3783 in dogs have not been reported previously with other CNS compounds that effect through serotonergic pharmacology.

Characterization of fibrodysplasia in the dog following inhibition of metalloproteinases.

Musculoskeletal side effects are a widely reported consequence of administration of particular matrix metalloproteinase inhibitors (MMPi) in clinical trials. We describe here histopathological findings during dog studies with a fairly selective MMPi AZM551248, that are consistent with these human clinical changes. They were characterized by a dose-and time-dependent formative connective tissue alteration we have termed "fibrodysplasia." The most sensitive site was the subcuticular connective tissue, although musculoskeletal tissues were also extensively involved. In the subcutis, changes occurred initially around pre-existing blood vessels, but then more diffusely. There was proliferation of cells showing myofibroblast differentiation identified by elevated levels of alpha-smooth muscle actin, fibronectin, and transforming growth factor beta, and the deposition of collagen type III with a lesser quantity of collagen type I. On longer-term administration at lower doses, there was evidence of active fibrodysplasia arising and resolving during the dosing period, resulting in the multifocal deposition of mature collagen. Although there was organ specificity, essentially identical changes occurred at multiple connective tissue sites. We conclude that MMPi-induced fibrodysplasia in animals and, by inference, musculoskeletal side effects in humans are potentially diffuse connective tissue disorders.

Structural pathology in a rodent model of osteoarthritis is associated with neuropathic pain: increased expression of ATF-3 and pharmacological characterisation.

Intra-articular injection of mono-iodoacetate (MIA) in the rat knee joint induces a histopathology with similarities to osteoarthritis (OA). Typically, a synovitis (days 1-3) is observed followed by thinning of articular cartilage and subsequent lesion of subchondral bone at days 8-14 onwards. Behaviourally, weight-bearing asymmetry is observed, which is sensitive to anti-inflammatory pharmacology at early but not later (days 14+) time points. As subchondral bone is densely innervated, an intriguing possibility is that focal bone pathology may cause neuropathy in this model. In male Wistar rats, activating transcription factor (ATF)-3-immunofluorescence was used as a marker of nerve injury in lumber (L)4 and L5 dorsal root ganglia of the ipsilateral knee. Significantly increased ATF-3-immunoreactivity following MIA treatment was measured in L5 on days 8 and 14 (P<0.05, Kruskal-Wallis and Mann-Whitney U-test), compared to saline controls. Furthermore, in an additional study animals were orally dosed vehicle (5 ml/kg), naproxen (0.3-10 mg/kg), celecoxib (1-10 mg/kg), amitriptyline (3-30 mg/kg) and gabapentin (10-100mg/kg) and evaluated for weight-bearing asymmetry on days 14, 21 and 28 post-MIA. Significant resolution of weight-bearing was observed at high and intermediate doses of amitriptyline and gabapentin at all time points (P<0.05, ANOVA, post-hoc Bonferroni's, vs pre-dose measurements). Transient and weak effects were observed with naproxen (10mg/kg) on days 14 and 28, whereas celecoxib showed no significant effects. Collectively, these data suggest that this putative model of OA is associated with an early phase neuropathy in the L5 innervation territory of the knee.