Metabolic syndrome and T2D produce significant health and economic issues. Many available animal models have monogenic leptin pathway mutations that are absent in the human population. Development of the ZDSD rat model was undertaken to produce a model that expresses polygenic obesity and diabetes with an intact leptin pathway. A lean ZDF rat with the propensity for beta-cell failure was crossed with a polygenetically obese Crl:CD (SD) rat. Offspring were selectively inbred for obesity and diabetes for >30 generations. In the current study, ZDSD rats were followed for 6 months; routine clinical metabolic endpoints were included throughout the study. In the prediabetic metabolic syndrome phase, ZDSD rats exhibited obesity with increased body fat, hyperglycemia, insulin resistance, dyslipidemia, glucose intolerance, and elevated HbA1c. As disease progressed to overt diabetes, ZDSD rats demonstrated elevated glucose levels, abnormal oral glucose tolerance, increases in HbA1c levels, reductions in body weight, increased insulin resistance with decreasing insulin levels, and dyslipidemia. The ZDSD rat develops prediabetic metabolic syndrome and T2D in a manner that mirrors the development of metabolic syndrome and T2D in humans. ZDSD rats will provide a novel, translational animal model for the study of human metabolic diseases and for the development of new therapies.

In a pilot single-blind study, gamma-vinyl GABA, an enzyme-activated irreversible inhibitor of GABA-transaminase (GABA-T), was administered orally to 10 epileptic patients who were refractory to conventional anticonvulsant therapy. Daily doses of 1 g and 2 g for 2 weeks each as add-on therapy were followed by 2 weeks of placebo treatment. CSF obtained from suboccipital and lumbar punctures demonstrated dose-related increases in concentrations of free and total GABA and homocarnosine with treatment, but no changes in 5-hydroxyindoleacetic acid or homovanillic acid levels, indicating effective and selective CNS GABA-T inhibition. These biochemical changes were associated with decreased seizure frequency in seven patients, decreased seizure severity in one, no change in one, and possible worsening in one. gamma-Vinyl GABA may be useful in the therapy of epilepsy.

ABSTRACT:A new glutathione adduct (M4) was tentatively identified, likely as 2-hydroxy-3-(glutathione-S-yl)-monoclofenac, using liquid chromatography-tandem mass spectrometry analysis of incubations of diclofenac with human liver microsomes. The same conjugate was not detected in incubations with either rat or monkey liver microsomes. Formation of M4 was mediated specifically by CYP2C9 in human liver microsomes, as evidenced by the following observations: 1) cDNA-expressed CYP2C9-catalyzing formation of M4; 2) inhibition of M4 formation by sulfaphenazole, a CYP2C9-selective inhibitor; and 3) strong correlation between the production of M4 and CYP2C9-mediated tolbutamide 4-hydroxylase activities in a panel of human liver microsome samples. Formation of M4 suggests the existence of a new reactive intermediate as diclofenac-2,3-oxide. A tentative pathway states that diclofenac is oxidized to diclofenac-2,3-oxide that reacts with glutathione (GSH) to form a thioether conjugate at the C-3 position, followed by a concomitant loss of chlorine to give rise to M4. Furthermore, a likely mechanism leading to the formation of diclofenac oxides is rationalized: CYP2C9-catalyzed oxidation at the C-3 position of the dichlorophenyl ring to form a cationic -complex that subsequently results in diclofenac-3,4-oxide and diclofenac-2,3-oxide; the former oxide is converted to 4-hydroxy-diclofenac as a major metabolite and can be trapped by GSH to produce 4-hydroxy-3-glutathione-S-yl diclofenac (M2), whereas the latter oxide forms 3-hydroxy-diclofenac and can be trapped by GSH to produce M4. This mechanism is consistent with the structural modeling of the CYP2C9-diclofenac complex, which reveals that both the C-3 and C-4 of the dichlorophenyl ring are proximate to the heme group.

Stable-isotope trapping combined with mass spectrometry (MS) neutral loss scanning has recently been developed as a high-throughput method for the in vitro screening of major reactive metabolites. In fact, detection and identification of minor reactive metabolites are equally important since the minor metabolites, even though at low levels, may be highly reactive and also play an important role in drug-induced adverse reactions. In this study, 2-acetylthiophene, clozapine, troglitazone and 7-methylindole were selected as model compounds to further validate the advantages of this method for rapid detection and structural characterization of minor glutathione (GSH) adducts derived from reactive metabolites. The utility of the current method was clearly demonstrated by successful identification of novel reactive metabolites at low levels and also minor ones either masked by non-specific responses or co-eluted with other conjugates. In comparison with existing methods, this method is sensitive, efficient, and suitable for rapid screening and more complete profiling of reactive metabolites.

Metabolism and bioactivation of 3-methylindole (3MI) were investigated in human liver microsomes. The metabolism of two deuterium-labeled analogues of 3MI permitted a relatively unambiguous identification of multiple metabolites and glutathione (GSH) adducts of reactive intermediates. A total of eight oxidized metabolites were detected, five of which were assigned as previously identified 3-methyloxindole, 3-hydroxy-3-methylindolenine, 3-hydroxy-3-methyloxindole, 5-hydroxy-3-methylindole, and 6-hydroxy-3-methylindole. Among the three new metabolites, one was either 4- or 7-OH-3-methylindole, and the other two were derived from additional oxidation on the phenyl ring of 3-methyloxindole. When GSH was added to the microsomal incubations, seven conjugates that had molecular ions corresponding to the incorporation of GSH and an atom of oxygen at m/z 453 (group I) were produced, and two additional conjugates had molecular ions at m/z 437 that corresponded to the incorporation of GSH with no additional oxygen (group II). Two conjugates in group I (m/z 453) were apparently derived by GSH addition to the 5,6-epoxide metabolite of 3-methyloxindole. These two GSH adducts were tentatively identified as 5-(glutathione-S-yl)-3-methyloxindole and 6-(glutathione-S-yl)-3-methyloxindole. The most abundant conjugate in group I was identified as 3-(glutathione-S-yl)-3-methyloxindole, which substantiated the presence of the putative 2,3-epoxy-3-methylindole intermediate. The remaining four adducts in group I were likely formed by conjugation of GSH at different positions of the phenyl ring, possibly via oxidation of 5-hydroxy-3-methylindole and 6-hydroxy-3-methylindole to two very interesting new electrophilic benzoquinone imine intermediates. For the group II conjugates (m/z 437), two isomers were identified as 2-(glutathione-S-yl)-3-methylindole and 3-(glutathione-S-yl-methyl)-indole. The former adduct was primarily derived from the 2,3-epoxide intermediate by thiol conjugation followed by dehydration. The latter adduct was consistent with our previously published work on the dehydrogenation of 3MI. In those studies, we showed that the reactive intermediate, 3-methylenenindolenine, was formed by hydrogen abstraction at the methyl group and was trapped with GSH. The putative dehydrogenation bioactivation mechanism is also substantiated by the finding that CYP2E1 selectively generated 2-(glutathione-S-yl)-3-methylindole but did not produce 3-(glutathione-S-yl-methyl)-indole. In summary, the results not only confirmed the formation of 2,3-epoxide-3-methylindole in human liver microsomes but also suggested that the phenolic metabolites of 3-methylindole were dehydrogenated to previously uncharacterized reactive intermediates.

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Glutathione (GSH) has been widely used for in vitro trapping and subsequently detecting reactive metabolites using liquid chromatography-mass spectrometry. A major drawback of GSH is its low trapping efficiency for "hard" reactive metabolites such as reactive aldehydes. In the present study, a bifunctional trapping agent (gamma GSK, gamma-glutamylcysteinlysine) is investigated as an alternative of GSH for simultaneous trapping both "hard" and "soft" reactive metabolites. In microsomal incubations, soft and hard reactive metabolites are captured by conjugation to the free thiol and the amine group of gamma GSK, respectively, resulting in formation of stable peptide adducts. Similar to GSH conjugates, all gamma GSK adducts derived from both soft and hard reactive metabolites contain a gamma-glutamyl moiety and, thus, undergo a neutral loss of 129 Da under collision-induced dissociation. As a result, an NL MS/MS scan can be utilized as a generic method for rapid detecting of both hard or soft reactive metabolites. As demonstrated by a number of model compounds, this approach, in combination with the isotope trapping technique, is reliable, sensitive, and efficient and can be potentially utilized as a high-throughput method for screening and rapid identification of both soft and hard reactive metabolites. In comparison with other methods, this approach is highly efficient and suitable in drug discovery for screening a wide variety of compounds for different reactive metabolites.

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