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We employed broken cell liver preparations in order to investigate potential species-specific differences in the metabolism of BW 1370U87, a new selective and reversible MAO-A inhibitor. The drug metabolizing capacity of crude liver homogenates from rat, dog, cat, monkey, and man was assessed based on the utilization of BW 1370U87 and the appearance of suspected metabolites. When incubated with liver homogenates (37° C) in the presence of a cofactor preparation designed to generate TPNH, BW 1370U87 (1 or 10 μM) was metabolized in a species and time dependent manner. The rate of disappearence of BW 1370U87 was more rapid in dog and cat preparations than those of rat, monkey and man. The appearance of metabolites coincided with the disappearance of BW 1370U87. Three metabolites, identified and synthesized as BW 183U88, BW 380U88, and BW 330U88 appeared in all five species. These metabolites were also found to be selective MAO-A inhibitors both in vitro and ex vivo and may contribute to the overall activity exhibited by the parent molecule.

BW 1370U87 is a potent, reversible, selective inhibitor of rat and human brain MAO-A with a competitive mechanism of action. The ED50 of BW 1370U87 for inhibition of MAO-A in rat brain is 8 mg/kg after oral administration, and the duration of action exceeds 7 hr. The ED80 dose for inhibition of MAO-A (20 mg/kg) elevates NE, DA, and 5-HT levels in brains of rats without significantly potentiating the blood pressure effects of a 15 mg/kg oral dose of tyramine. This dose of tyramine, extrapolated to man, exceeds the amount that could be consumed at one time from dietary sources. No inhibition of MAO-B has been observed with BW 1370U87 either in vitro or ex vivo. BW 1370U87 was effective in the 5-hydroxytryptophan potentiation test over the dose range that produced MAO-A inhibition in brain in both rats and mice, and it reduced swim stress induced immobility in the Porsolt test. The compound has positive effects on abnormal social behavior produced by early social deprivation in the rhesus monkey. BW 1370U87 had no adverse cardiovascular effects in dogs or rats. It also had no significant pharmacological effects on various isolated tissue preparations and did not cause changes in the neuronal transport or the receptor systems which mediate the antidepressant effects or side effects of the tricyclic antidepressants. An acute oral dose 100 times that which produced an 80% inhibition of brain MAO-A exhibited no signs of toxicity. BW 137OU87 appears to be a safe reversible MAO-A inhibitor with potential for treating depression, anxiety conditions, panic, phobias, obsessive compulsive behaviors, and borderline personality disorders.

11192U90 was submitted to receptor binding and monoamine uptake assays. It bound potently at serotonin 5-HT2, dopaminergic D2, serotonin 5-HT1A, and adrenergic alpha 1 and alpha 2 receptors. It also bound to dopaminergic D1, serotonin 5-HT3, serotonin 5-HT4, and sigma sites, albeit with lower affinity. It was essentially inactive at 22 other sites, including those for cholinergic M1 and M2. It weakly inhibited uptake of 3H-norepinephrine, 3H-serotonin and 3H-dopamine. Acute doses of 1192U90 (5 and 20 mg/kg P.O.) increased whole-brain levels of dopamine metabolites but did not affect levels of norepinephrine, dopamine, and serotonin. Subcutaneous injection of 1192U90 (0.8 mg/kg/day) and clozapine (20 mg/kg/day) for 28 days preferentially decreased the number of spontaneously active dopamine cells in the ventral tegmental area (VTA) but not the substantia nigra (SN) of rats, as measured by population sampling. This outcome is characteristics of atypical antipsychotics like clozapine. Acute injections of 1192U90 reversed the rate-inhibiting effects of microiontophoretically applied dopamine and intravenously injected apomorphine and d-amphetamine on dopamine cell firing. Intravenous injection or iontophoretic application of 1192U90 or the 5-HT1A agonist (+/-)8-OH-DPAT inhibited the firing rates of dorsal raphe nucleus (DRN) neurons in rats, and the effects of both compounds were blocked by iontophoretically applied S(-) propranolol, a 5-HT1A antagonist. The results suggest that 1192U90 is a preferential dopamine D2 antagonist as well as a 5-HT1A agonist that may prove to be an atypical antipsychotic.

Bupropion (BW 323U66) has been considered a dopaminergic antidepressant based on its ability to inhibit the uptake of dopamine (DA) somewhat more selectively than it inhibits uptake of norepinephrine (NE) or serotonin (5-HT). This report describes new evidence that bupropion selectively inhibits firing rates of NE cells in the locus coeruleus (LC) at doses significantly lower than those that inhibit activity of midbrain DA cells or dorsal raphe 5-HT cells. The IC50 dose (13 mg/kg i.p.) for inhibition of LC firing produced plasma concentrations that were not significantly different from those generated by the ED50 in the Porsolt test (10 mg/kg i.p.). The fourfold higher dose needed to inhibit DA cell firing (IC50 = 42 mg/kg i.p.) was similar to the dose associated with locomotor stimulation in freely moving rats. Bupropion did not change the firing rates of 5-HT cells in the dorsal raphe nucleus at any dose. In both in vitro and in vivo tests, the metabolite 306U73 (hydroxybupropion), a weak inhibitor of NE uptake, was approximately equipotent to bupropion with regard to inhibition of LC cells. Another metabolite, 494U73, had no effect on LC firing rates over a wide range of doses. Because of species variation in metabolism, 306U73 was not detected in plasma of rats after i.v. doses of bupropion that inhibited LC firing. Only trace amounts of 306U73 were detected after bupropion dosing for the Porsolt test. Pretreatment with reserpine markedly depleted catecholamines and reduced (by 30-fold) the potency of bupropion to inhibit LC firing.(ABSTRACT TRUNCATED AT 250 WORDS)

A sensitive high-performance liquid chromatographic method that does not require organic extraction has been developed for the determination of propranolol levels in canine and feline plasma. Equal volumes of plasma and a mixture of methanol-acetonitrile-0.1 M sodium hydroxide (3:3:4, v/v/v) were added to a microseparation unit with a 10,000 molecular mass cut-off filter. The ultrafiltrate was analyzed by reversed-phase liquid chromatography with fluorimetric detection. The consistency of the recoveries obtained eliminated the need for an internal standard (coefficients of variation less than 4%). Linear regressions for the standard curves (2.5-100 ng/ml) gave correlation coefficients above 0.9955. The detection limit was 1 ng/ml. The assay retains high sensitivity while eliminating laborious sample preparation.

If glycolysis is inhibited in distal axonopathy, there should be a concomitant inhibition of lipogenesis from glucose. To investigate this possibility, lipogenesis from [14C]glucose and [3H]acetate was studied in sciatic nerves incubated with iodoacetate, a known inhibitor of glycolysis, in sciatic nerves incubated with 2,5-hexanedione, a putative inhibitor of glycolysis, and in sciatic nerves from rats exhibiting clinical signs of peripheral neuropathy induced by 2,5-hexanedione. Nerves incubated with 1.0 mm iodoacetate, in comparison with untreated nerves, exhibited decreased incorporation of [14C]glucose into sterols + diacylglycerols (33-fold), free fatty acids (14-fold), triacylglycerols (27-fold), and phospholipids (21-fold). In addition, these nerves exhibited decreased incorporation of [3H]acetate into sterols + diacylglycerols (30-fold), free fatty acids (2-fold), triacylglycerols (23-fold), and phospholipids (12-fold). In contrast, the incorporation of [14C]glucose into sterols + diacylglycerols, free fatty acids, and triacylglycerols was not affected by 1.0 mm 2,5-hexanedione. Compared to untreated nerves, nerves incubated with 1.0 mm 2,5-hexanedione exhibited a small decrease (15%) in the incorporation of [14C]glucose into phospholipids. Nerves from rats given 1% 2,5-hexanedione in the drinking water for 6 weeks, in comparison with those from pair-fed control rats, exhibited decreased (45%) incorporation of [14C]glucose and [3H]acetate into digitonin-precipitable sterols. Nerves from 2,5-hexanedione-treated and pair-fed control rats exhibited similar incorporation of [14C]glucose and [3C]acetate into free fatty acids, triacylglycerols, and phospholipids. The data indicate that while sterologenesis is inhibited in distal axonopathy, glycolysis is not.

Distal axonopathy induced by n-hexane and methyl n-butyl ketone has been attributed to a common metabolite, 2,5-hexanedione. Since altered lipid metabolism is frequently associated with neuropathy, the effects of 2,5-hexanedione on lipid biosynthesis from [1-14C]acetate in sciatic nerve and brain of rats given 1% 2,5-hexanedione in drinking water have been studied, in vitro. Clinical signs of neuropathy appeared after 6 weeks. Loss of body weight induced by 2,5-hexanedione was similar to that observed in pair-fed control rats. Compared to nerves from pair-fed controls, nerves from rats fed 2,5-hexanedione exhibited decreased incorporation of [1-14C]acetate into triacylglycerols (32%), total sterols + diacylglycerols (54%), digitonin-precipitable sterols (55%), squalene (55%), and ubiquinone (43%). Incorporation of [1-14C]acetate into phospholipids, fatty acids, and cholesteryl esters was similar in nerves of 2,5-hexanedione-treated rats and pair-fed controls. In brain, incorporation of [1-14C]acetate into lipids was similar in 2,5-hexanedione-treated and pair-fed control rats, except into the fatty acid fraction which was significantly decreased by 11%. The data support the hypothesis that lipid metabolism, in particular sterol metabolism, is altered in hexacarbon-induced distal axonopathy.

Buthionine sulfoximine significantly reduced the hepatic non-protein sulfhydryl (NPSH) content of male B6C3F1 mice within 2 h after intraperitoneal (i.p.) injection. This treatment did not affect the activity of several hepatic microsomal and cytosolic enzymes responsible for xenobiotic metabolism. Pretreatment of mice with buthionine sulfoximine (2 mmol/kg) increased the hepatotoxicity of chloroform, but did not affect the hepatotoxicity of carbon tetrachloride. These findings suggest that buthionine sulfoximine can be a useful agent for studying the role of glutathione (GSH) in hepatic biotransformation of xenobiotics.

Sterologenesis from [ 14 C]acetate and [ 3 H]mevalonolactone has been studied, in vitro , in sciatic nerves of rats fed 1% 2,5-hexanedione in the drinking water for 6 weeks. Nerves from rats given 2,5-hexanedione, in comparison with those from pair-fed control rats, exhibited reduced incorporation of [ 14 C]acetate, but not of [ 3 H]mevalonolactone, into the sterol precursor squalene (38%), C 30 sterols (53%), C 27 sterols (46%), and digitonin-precipitable sterols (41%). Sterologenesis was not inhibited in nerves obtained from untreated rats and incubated in vitro with 1 m m 2,5-hexanedione, nor in nerves of rats that had inhaled 1000 ppm n -hexane for 6 hr. Incorporation of [ 14 C]acetate into triacylglycerols of nerves from rats exposed to n -hexane was increased by 50%; [ 14 C]acetate incorporation into other lipid fractions was similar in n -hexane-exposed and control rats. The concentration of 2,5-hexanedione in nerves of rats receiving 1% 2,5-hexanedione in drinking water for 6 weeks or exposed to 1000 ppm n -hexane for 6 hr was determined by gas chromatography-mass spectrometry and found to be 0.8 ± 0.2 and 5.2 ± 0.6 μg/g tissue wet weight, respectively.

2,5-Hexanedione (HD) induces testicular atrophy and peripheral neuropathy in rats. Since altered lipid metabolism is frequently associated with these disease states, lipid metabolism was investigated in vitro in testes and sciatic nerves of rats fed 1% HD in the drinking water for 6 weeks. Testes from HD-treated rats were 30–60% smaller and weighed threefold less than testes from pair-fed control (PFC) rats. Compared to testes from PFC rats, testes from HD rats exhibited increased incorporation of [14C]acetate into phospholipids (344%), triacylglycerols (281%), and cholesteryl esters + hydrocarbons (246%) but decreased incorporation into free fatty acids (25%) and sterols + diacylglycerols (65%). The increased incorporation of [14C]acetate into phospholipids induced by HD reflected an approximate 300% increase into phosphatidyl choline, lysophosphatidyl choline, phosphatidyl serine + phosphatidyl inositol, and phosphatidyl ethanolamine and a disproportionate 800% increase into sphingomyelin. HD rats exhibited clinical signs of peripheral neuropathy, including everted and flat foot placement and hindlimb weakness; similar changes were not observed in PFC rats. In sciatic nerves, the incorporation of [14C]leucine was decreased into sterols + diacylglycerols (47%), digitoninprecipitable sterols (45%), and cholesteryl esters + hydrocarbons (40%) in HD compared to PFC rats; incorporation of [14C]leucine into free fatty acids, triacylglycerols, and phospholipids was similar in HD and PFC rats. In contrast to the testis and nerve, lipid metabolism in the liver was similar in HD and PFC rats. The concentrations of 2,5-hexanedione and 2,5-dimethylfuran, respectively, were 0.6 ± 0.3 and 6.5 ± 0.9 μg/g wet weight in the testes and 3.1 ± 0.4 and 3.0 ± 0.4 μg/g wet weight in the livers of HD rats. The data indicate that altered metabolism is associated with HD-induced testicular atrophy and distal axonopathy.

Previous data have demonstrated that methyl chloride (MeCl) is toxic to B6C3F1 mice under both acute and chronic exposure conditions, and that conjugation of MeCl with glutathione (GSH) is a key step in the metabolism of MeCl. This study examined the role of GSH in mediating the acute toxicity of MeCl to liver, kidney, and brain of male B6C3F1 mice. The lethal effects of a single 6-hr inhalation exposure of B6C3F1 males to 2500 ppm MeCl were completely prevented by pretreatment with the GSH synthesis inhibitor, L-buthionine-S,R-sulfoximine (4 mmol L-BSO/kg, ip 1.5 hr prior to MeCl exposure). GSH levels (measured as nonprotein sulfhydryl) in liver and kidney were depleted to 19 and 25% of control values, respectively, at the start of the exposure; the ratio of dead/exposed mice during the 18-hr postexposure declined from 14/15 mice to 0/10. Also, the LC50 for MeCl increased from 2200 to 3200 ppm in male mice pretreated with BSO. The hepatic toxicity of MeCl was detected by increased alanine aminotransferase (ALT) activities in serum 18 hr after a 6-hr exposure to 1500 ppm MeCl (2147 +/- 1327 IU/liter vs 46 +/- 6 in controls). Liver toxicity was inhibited when B6C3F1 males were depleted of GSH prior to MeCl exposure by BSO pretreatment (43 +/- 2), fasting (100 +/- 47), or injection of diethyl maleate (42 +/- 16). The effects of GSH depletion on MeCl toxicity to brain and kidney were determined in B6C3F1 males exposed to 1500 ppm MeCl 6 hr/day, 5 days/week for 2 weeks, with and without daily pretreatment with 2 mmol L-BSO/kg. This dose of BSO depleted hepatic and renal GSH by 28 and 60%, respectively, at the start of MeCl exposure. BSO-pretreated mice were protected from the central nervous system toxicity of MeCl, as assessed by microscopic examination of the granule cell layer of the cerebellum. BSO pretreatment also inhibited the renal toxicity of MeCl as measured by incorporation of [3H]thymidine ([3H]TdR) into renal DNA, an indicator of cell regeneration after cortical necrosis. [3H]TdR incorporation was 105 +/- 10,337 +/- 40, and 60 +/- 15 dpm/microgram DNA in nonexposed controls, MeCl, and MeCl + BSO treatment groups, respectively. These results indicate that GSH is an important component in the toxicity of MeCl to multiple organ systems in B6C3F1 mice. Reaction of MeCl with GSH appears to constitute a mechanism of toxication, contrary to the role usually proposed for GSH in detoxifying xenobiotics.