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Leukotriene (LT) A(4) hydrolase is a dual function enzyme that is essential for the conversion of LTA(4) to LTB(4) and also possesses an aminopeptidase activity. SC-57461A (3-[methyl[3-[4-phenylmethyl)phenoxy]propyl]amino]propanoic acid HCl) is a potent inhibitor of human recombinant LTA(4) hydrolase (epoxide hydrolase and aminopeptidase activities, K(i) values = 23 and 27 nM, respectively) as well as calcium ionophore-induced LTB(4) production in human whole blood (IC(50) = 49 nM). In the present study, we investigated its action in several animal models. Oral activity was evident from the ability of the compound to inhibit mouse ex vivo calcium ionophore-stimulated blood LTB(4) production with ED(50) values at 1.0 and 3.0 h of 0.2 and 0.8 mg/kg, respectively. A single oral dose of 10 mg/kg SC-57461A blocked mouse ex vivo LTB(4) production 67% at 18 h and 44% at 24 h, suggesting a long pharmacodynamic half-life. In a rat model of ionophore-induced peritoneal eicosanoid production, SC-57461 inhibited LTB(4) production in a dose-dependent manner (ED(50) = 0.3-1 mg/kg) without affecting LTC(4) or 6-keto-prostaglandin F(1alpha) production. Oral pretreatment with SC-57461 in a rat reversed passive dermal Arthus model blocked LTB(4) production with an ED(90) value of 3 to 10 mg/kg, demonstrating good penetration of drug into skin. Plasma level of intact SC-57461 (3 h after oral gavage dosing with 3 mg/kg) was 0.4 microg/ml, which corresponds to >80% inhibition of dermal LTB(4) production. Oral or topical pretreatment with SC-57461A 1 h before challenge with arachidonic acid blocked ear edema in the mouse. SC-57461A is a competitive, selective, and orally active inhibitor of LTA(4) hydrolase in vivo, making it useful to explore the contribution of LTB(4) to a number of inflammatory diseases.

Leukotriene (LT) B(4) is an inflammatory mediator that has been implicated in the pathogenesis of various diseases, including inflammatory bowel disease and psoriasis. As the rate-limiting step for LTB(4) production, LTA(4) hydrolase represents an attractive target for therapeutic agents that interfere with LTB(4) production. In the present study we evaluated a chemically novel compound designated SC-57461A (3-[methyl[3-[4-(phenylmethyl)phenoxy]propyl]amino]propanoic acid HCl) as an inhibitor of LTA(4) hydrolase. Pharmacological comparisons are made to its free acid SC-57461. SC-57461A is a potent competitive inhibitor of recombinant human LTA(4) hydrolase when either LTA(4) (IC(50) = 2.5 nM, K(i) = 23 nM) or peptide substrates (IC(50) = 27 nM) are used. In human whole blood, the IC(50) for calcium ionophore-induced LTB(4) production was 49 nM, indicative of good cell penetration. Whole blood production of the cyclooxygenase metabolite thromboxane B(2) was not affected. SC-57461A was also active in several other species, including mouse, rat, dog, and rhesus monkey. The data indicate that SC-57461A is a potent and selective inhibitor of LTA(4) hydrolase.

The effects of selective nicotinic acetylcholine (ACh) receptor (nAChR) agonists and antagonists on the stimulation-evoked release of [3H]ACh were studied in rat isolated superior cervical ganglion loaded with [3H]choline and superfused in a 2-ml chamber. Nicotine and 1,1-dimethyl-4-phenylpiperazinium iodide (DMPP), but not cytisine, increased the stimulation (2 Hz)-evoked release of [3H]ACh in a concentration-dependent manner. The rank order of potency to increase stimulation-evoked release for the nAChR agonists (nicotine > DMPP >> cytisine) suggests that the beta4 subunit of nAChRs is not involved in the release. The finding that alpha-bungarotoxin was effective in preventing the effect of DMPP and itself significantly reduced the release indicates that the alpha7 subunit is located presynaptically and may be involved in the positive feedback modulation. Hexamethonium inhibited the effect of DMPP with an apparent dissociation constant (Kd) of 11.5 +/- 1.5 microM. Hexamethonium and other nAChR antagonists, i.e., (+)-tubocurarine (100 microM), mecamylamine (3 microM), dihydro-beta-erythroidine (3 microM), pancuronium (10 microM) and alpha-bungarotoxin (2 microM), also decreased the stimulation-evoked release of [3H]ACh. The effect of hexamethonium was independent of stimulation frequency (2, 10 and 30 Hz) applied. Atropine enhanced the stimulation-evoked release of ACh, indicating that there is negative feedback modulation of ACh release associated with neuronal activity. In contrast, when the nicotinic positive feedback was prevented by hexamethonium, atropine failed to enhance the release. These findings indicate that muscarinic receptor-mediated inhibition of ACh release functions in cases in which the release is enhanced by ACh via stimulation of presynaptic nAChRs. A similar interaction was found between A1 receptor-mediated reduction and nAChR-mediated positive feedback modulation of [3H]ACh release. The results suggest the presence of positive feedback modulation of ACh release via presynaptic nAChRs in rat superior cervical ganglion.

The structural basis for depressive disorders remains unknown. Studies using neuroimaging and postmortem brain tissue indicate that anatomic substrates may contribute to major depression disorder (MDD) and bipolar disorder (BD). The present study used design-based stereology to assess neuron loss in 2 well-defined hypothalamic structures, the paraventricular nucleus (PVN) and supraoptic nucleus (SON), in clinically well-studied cases with severe depression. The left or right diencephalon was blocked from 26 brains removed at autopsy from age-matched controls (5 male/3 female) and patients with MDD (6 male/5 female) and BD (5 male/2 female). Serial sections were cut at an instrument setting of 60 μm through the entire PVN and SON from left hypothalamus and 8 to 10 sections per brain were systematic-random sampled and stained with cresyl violet. A trained operator blind to clinical diagnosis used computerized stereology to estimate total neuron numbers in PVN and SON. The results revealed a selective, robust reduction of approximately 50% in total neuron number in the PVN for major depression and bipolar cases compared with age-matched controls, with no differences in neuron numbers in the SON. This selective neuronal loss in the PVN appears to identify an important neurobiologic substrate for the behavioral manifestations of depression.