This work evaluated new potential inhibitors of the enzyme homoserine dehydrogenase (HSD) of Paracoccidioides brasiliensis, one of the etiological agents of paracoccidioidomycosis. The tertiary structure of the protein bonded to the analogue NAD, and L-homoserine was modeled by homology. The model with the best output was subjected to gradient minimization, redocking, and molecular dynamics simulation. Virtual screening simulations with 187,841 molecules purchasable from the Zinc database were performed. After the screenings, 14 molecules were selected and analyzed by the use of absorption, distribution, metabolism, excretion, and toxicity criteria, resulting in four compounds for in vitro assays. The molecules HS1 and HS2 were promising, exhibiting MICs of 64 and 32 g · ml Ϫ1 , respectively, for the Pb18 isolate of P. brasilensis, 64 g · ml Ϫ1 for two isolates of P. lutzii, and also synergy with itraconazole. The application of these molecules to human-pathogenic fungi confirmed that the HSD enzyme may be used as a target for the development of drugs with specific action against paracoccidioidomycosis; moreover, these compounds may serve as leads in the design of new antifungals.

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The current multidrug therapy for tuberculosis (TB) is based on the use of isoniazid (INH) in combination with other antibiotics such as rifampin, ethambutol and pyrazinamide. Literature reports have shown that Mycobacterium tuberculosis, the causative agent of TB, has become resistant to this treatment by means of point mutations in the target enzymes of these drugs, such as catalase-peroxidase (KatG). By means of equilibrium molecular dynamics in the presence of the ligand, this work evaluated ten point mutations described in the enzyme KatG that are related to resistance to INH . The results showed that the resistance mechanism is related to stereochemical modifications at the N-terminal domain of the protein, which restrict INH access to its catalytic site, not involving mechanisms of electrostatic nature. These results show insights that can be useful for the identification of new anti-TB drugs which may be able to circumvent this mechanism of resistance.

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ABSTRACT. The effects of atropine (non selective muscarinic antagonist) and ZM241385 (A 2A receptors antagonist) in the cisatracurium-induced drastic (100%) level of fade at 50 Hz (10 s) (100% Fade) were compared in the phrenic nerve-diaphragm muscle preparations of rats indirectly stimulated at a physiological tetanic frequency (50 Hz). The lowest dose and the instant cisatracurium caused 100% Fade were investigated. Cisatracurium induced 100% Fade 15 min after being administered. Atropine reduced the cisatracurium-induced 100% Fade, but the administration of ZM241385 separately, or combined with atropine, did not cause any effect in the cisatracurium-induced 100% Fade. Data indicate that the simultaneous blockage of M 1 and M 2 muscarinic receptors on motor nerve terminal by atropine is more efficient than the blockage of presynaptic A 2A receptors for a safer recovery of patients from neuromuscular blockade caused by cisatracurium.Keywords: tetanic fade, adenosine, muscarinic receptors, train-of-four, neuromuscular blocker.Atropina é mais eficiente que ZM241385 para reduzir o intenso nível de fadiga causada por cisatracurium a 50 Hz RESUMO. Os efeitos de atropina e ZM241385 (antagonistas de receptores A 2A ) no drástico (100%) nível de fadiga (100% Fadiga) produzido pelo cisatracúrio a 50 Hz (10 s) foram comparativamente investigados em preparações nervo frênico músculo diafragma isolado de ratos indiretamente estimuladas com a frequência fisiológica tetanizante de 50 Hz. A menor dose e o instante no qual cisatracúrio causou 100% Fadiga foram pesquisados. O cisatracúrio induziu 100% Fadiga 15 min depois de ser administrado. A atropina reduziu a fadiga de 100% causada pelo cisatracúrio, mas ZM241385, ou a administração combinada de atropina com ZM241385, não causou qualquer efeito na 100% Fadiga produzida pelo cisatracúrio. Os dados indicam que o bloqueio simultâneo dos receptores muscarínicos M 1 e M 2 no terminal nervoso motor pela atropina é mais eficiente do que o bloqueio dos receptores pré-sinápticos A 2A no auxilio da recuperação mais segura do bloqueio da transmissão neuromuscular causada por cisatracúrio.Palavras-chave: fadiga, adenosina, receptores muscarínicos, trem de quatro, bloqueadores neuromusculares.