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Although considered as a poison for long time, the importance of selenium as an essential trace element is now well recognized. In proteins, the redox active selenium moiety is incorportated as selenocysteine (Sec), the 21st amino acid. In mammals, selenium exerts its redox activities through several selenocysteine-containing enzymes, which include glutathione peroxidase (GPx), iodothyronine deiodinase (ID) and thioredoxin reductase (TrxR). Although these enzymes have Sec in their active sites, they catalyze completely different reactions and their substrate specificity and cofactor or co-substrate systems are significantly different. The most widely studied selenoenzyme GPx protects various organisms from oxidative stresses by catalyzing the reduction of hydroperoxides by using glutathione (GSH) as cofactor. The chemical aspects of the reduction of hydroperoxide by GPx have been extensively studied with the help of synthetic selenium and tellurium compounds. For example, 2-phenyl, 1, 2-benzoisoselenazol-3(2H)-one, commonly known as ebselen exhibits significant GPx activity by using GSH as cofactor. The anti-inflammatory, antiatherosclerotic and cytoprotective properties of ebselen have led to the design and synthesis of nex GPx mimics for potential therapeutic applications. In the first chapter, the importance of selenium in biochemistry in general and the function of selenoenzyme GPx and its synthetic mimics in particular are discussed. In the second chapter, the importance of ebselen as a GPx mimic and how thiol exchange reaction in the selenenyl sulfide intermediate deactivates its catalytic cycle and the possible ways to overcome thiol exchange reaction are described. The third chapter deals with the first synthetic chemical model that effectively mimics the unusual cyclization of sulfenic acid to a sulfenyl amide in protein Tyrosien Phosphatase 1B(PTP1B). PTP1B is a cysteine containing enzyme where the sulfenic acid (PTP1B-SOH) intermediate produced in response to its oxidation by H2O2 is rapidly converted into a sulfenyl amide species, in which sulfur atom of the catalytic cysteine is covalently bonded to the main chain nitrogen of an adjacent serine residue. This unusual protein modification in PTP1B has been proposed to protect the sulfur centre from irreversible oxidation to sulfinic acid and and sulfonic acids. In the fourth chapter, it is shown that not only the catalytic efficiency of ebselen but also its phosphatase like behavior is important for its antioxidant activity. Ebselen is regenerated from selenenic acid (R-SeOH) under a verity of conditions, which protects its selenium centre from irreversible oxidation and thus reduces its toxicity. The fifth chapter deals with spirodizaselenurane and Spirodiazatellurane. Although the chemistry of spirodioxyselenuranes and spirodiazasulfuranes has been studied extensively due to their interesting structural and stereochemical properties, there is no example of stable spirodiazaselenurane and its tellurium analogues. In the fifth chapter, the synthesis, structure and GPx-like activity of the spirodizzaselenurane and spirodiazatellurane are discussed. In summary, the synthetic sulfenic acids and seleneric acids undergo cyclization to their corresponding sulfenyl amides and selenenyl amides and thus protect their sulfur and selenium centers from irreversible inactivation. We have also observed that selenoxides and telluroxides with nearby amide moieties undergo cyclization to their corresponding cyclic spiro compounds. This unusual transformation of sulfenic acids has been recently discovered in PTP1B. As the redox regulation cycle of PTP1B and the catalytic cycle of GPx are similar we believe that GPx may involve a selenenyl amide intermediate in its catalytic cycle.

Reactive oxygen species (ROS) such as superoxide radical anion (O2•¯), hydroxylradical (OH•), hydrogen peroxide (H2O2) and peroxynitrite (ONOO-) that are produced during the metabolism of oxygen under oxidative stress in aerobic organisms destroy several key biomolecules and lead to a number of disease states. Mammalian systems possess several effective defense mechanisms including antioxidant enzymes to detoxify these ROS. The selenocysteine-containing Glutathione peroxidase (GPx) is particularly an efficient enzyme in the detoxification of H2O2 and other hydroperoxides by using glutathione (GSH) as cofactor. The chemistry at the active siteof GPx has been extensively investigated with the help of synthetic selenium compounds. Although the anti-inflammatory compound ebselen(2-phenyl-1,2-benzoisoselenazol-3(2H)-one) is undergoing phase III clinical trial as antioxidant, the chemistry of ebselen is still not understood. The present study on a number of ebselen derivatives with various N-substitutions reveals that the substitution at the N atom is important for the antioxidant activity. This study also suggests that the nature for thiol cofactor has a dramatic effect on the GPx activity of ebselen derivatives. It has been shown that ebselen exhibits very poor catalytic activity in the presence of aromatic thiols mainly due to strong Se….O nonbonded interactions that lead to extensive thiol exchange reactions in the selenenyl sulfide intermediate. To prevent the se….O interactions, a series of tertiary amide-based diselenides have been synthesized along with their secondary amide counterparts. Detailed structure-activity correlation studies reveal that the GPx-like activity of the sec-amide-based compounds can be significantly enhanced by the substitution at the free-NH group of sec-amide functionality. The N,N-dialkylbenzylamine-based diselenides exhibit their catalytic activities via the generation of selenols which was confirmed by the reaction with anti-arthritic gold(I) compounds. Interestingly, the replacement of the hydrogen atom at the 6th position of the benzene ring of N,N-dialkylbenzylamine-based diselenides by a methoxy group prevents the thiol exchange reactions mainly be weakening the Se…N interactions and thus enhances the GPx activity. On the other hand, the catalytic activity of the tert-amine-based diselenides can also be increased by replacing the tert-amino groups with the corresponding sec-amine moieties. It has been observed that the basic amino group in the amine-based diselenides deprotonates the selenol and also the thiol cofactor, which is crucial for the higher catalytic activities of the amine-based compounds. Peroxynitrite (PN, ONOO), a strong nitrating agent, is known to inactivate a number of proteins, enzymes and other biomolecules by nitration of tyrosine residues. In this study, we have shown that the commonly used antithyroid drugs and their analogues inhibit protein tyrosine nitration. This study reveals that antithyroid agents having PN scavenging activity may be beneficial of hyperthyroidism as these compounds may protect the thyroid gland from nitrative or nitrosative stress.

MATOS, Mayara Patrícia Viana de. Aspectos bioquímicos e etnofarmacológicos do látex de Himatanthus drasticus Mart. (Plumel). 2013. xix, 89 f. : Dissertação (Mestrado) - Universidade Federal do Ceará, Centro de Ciências, Departamento de Bioquímica e Biologia Molecular, Programa de Pós-Graduação em Bioquímica. Fortaleza-CE, 2013. / Submitted by Eric Santiago (erichhcl@gmail.com) on 2016-06-20T13:34:18Z No. of bitstreams: 1 2013_dis_mpvmatos.pdf: 2159476 bytes, checksum: ddbc07e064712e575447b91164349d1e (MD5) / Approved for entry into archive by José Jairo Viana de Sousa (jairo@ufc.br) on 2016-07-26T20:01:21Z (GMT) No. of bitstreams: 1 2013_dis_mpvmatos.pdf: 2159476 bytes, checksum: ddbc07e064712e575447b91164349d1e (MD5) / Made available in DSpace on 2016-07-26T20:01:21Z (GMT). No. of bitstreams: 1 2013_dis_mpvmatos.pdf: 2159476 bytes, checksum: ddbc07e064712e575447b91164349d1e (MD5) Previous issue date: 2013 / Himatanthus drasticus (Apocynaceae) is traditionally used in folk medicine in Northeastern Brazil. The plant is wildly distribuited from Guianas until Southeast Brazil. Latex obtained by cutting its stem bark is mixed with water and extensively sold in public markets. People use Janaguba milk (“Leite de Janaguba”- LJ) to treat or prevent different inflammatory disorders such as gastritis, ulcers as well as cancer, among other uses. Despite, there is not enough scientific data confirming these pharmacological properties. In this work, Janaguba milk was preliminarily investigated in an attempt to validate its anti- inflammatory activity. Its major protein fraction (HdLP) was assessed for the presence of anti- inflammatory, anti-nociceptive and toxicological effects. LJ inhibited the inflammatory response induced by carrageenan in rats (98%, p < 0.05), whereas HdLP did it independent of the route of administration. HdLP significantly reduced the infiltration of neutrophils into the peritoneal cavity (96%, p < 0.05) concomitant with increased nitric oxide synthesis in plasma and decrease of pro-inflammatory cytokines IL- 1 and TNF-α in peritoneal fluid. This fraction also prevented vacuolization and Kupfer cell hyperplasia caused by carrageenan in liver. Further, the anti-inflammatory properties were shown to be associated with the protein fraction of LJ. HdLP exhibited anti-inflammation, even after heat-treatment (100 C, 30 min) or proteolysis. Moreover, a pro-inflammatory effect was observed after HdLP treatment. It also suppressed abdominal constrictions in acetic acid-treated mice and reduced paw licking induced by formalin, both in a dose-dependent manner. An acute toxicological evaluation demonstrated no toxic effects after 14 days from LJ and HdLP administration by oral route even when high doses were tested. A qualitative phytochemical analysis showed the absence of lupeol and presence of saponinas, tannins and free steroids in HdLP. However, pharmacological properties are probably not related to them. It is therefore concluded that the latex of Himatanthus drasticus exhibits both the anti-inflammatory and anti-nociceptive activities claimed by its users. The protein fraction of the latex is an important contributor to the pharmacological properties of LJ. Resistance to heat and proteolytic treatment can explain the effectiveness of HdLP even when administered orally. The absence of toxic effects by oral route confirms the potential use of this plant as a phytotherapic agent. / Himatanthus drasticus (Apocynaceae) é uma espécie tradicionalmente utilizada na medicina popular da região nordeste deste país. Sua distribuição ocorre das Guianas ao sudeste do Brasil. O látex desta planta é obtido após uma injúria no caule e amplamente comercializado em mercados públicos. As pessoas ingerem o látex, conhecido como Leite de Janaguba (LJ), para o tratamento e/ou prevenção de diferentes doenças inflamatórias, gastrite, úlcera, câncer, entre outras. Apesar das diversas informações oriundas da medicina popular, não existem relatos científicos suficientes confirmando tais propriedades farmacológicas. Neste trabalho, LJ foi investigado com o propósito de validar sua tão popularmente relatada atividade anti-inflamatória. A fração proteica deste látex (HdLP) também foi investigada quanto à presença de atividades anti-inflamatória, antinociceptiva, além de seus efeitos toxicológicos. LJ inibiu a resposta inflamatória induzida por carragenina em ratos (98%, p < 0.05), assim como o fez a fração HdLP, independente da rota de administração. HdLP reduziu a infiltração de neutrófilos na cavidade peritoneal (96%, p < 0.05). Paralelamente a isto, ocorreu o aumento da síntese de óxido nítrico no plasma e a redução de citocinas pró-inflamatórias (IL-1 e TNF-α) no fluido peritonal. Esta fração também preveniu a vacuolização e hiperplasia das células de Kupfer, causadas pelo efeito da carragenina no fígado. Atividade anti-inflamatória está provavelmente associada com a fração proteica de LJ. HdLP exibiu um efeito anti-inflamatório mesmo após aquecimento (100 C, 30 minutos) ou proteólise. Além desta atividade, um efeito pró-inflamatório foi observado após o tratamento com HdLP. Esta também suprimiu contrações abdominais induzidas por ácido acético e reduziu a lambedura de pata induzida por formalina, ambos de maneira dose-dependente. A avaliação da toxicidade aguda demonstrou a ausência de efeitos tóxicos após tratamento com LJ e HdLP (v.o.) mesmo utilizando doses 5000 vezes maiores que as recomendadas. Uma dosagem qualitativa de fitoquímicos em HdLP mostrou a ausência de lupeol e presença de saponinas, taninos e esteróides livres. Entretanto, as propriedades farmacológicas provavelmente não estão relacionadas com estas moléculas. Desta forma, concluímos que o látex de H. drasticus exibe duas das atividades farmacológicas relatadas por seus usuários e a fração proteica deste látex é um importante contribuinte para tais propriedades medicinais. A resistência ao aquecimento e à proteólise pode explicar a efetividade de HdLP quando administrada oralmente. A ausência de efeitos tóxicos por via oral torna esta planta uma potencial candidata a fitoterápico.

PhD (Microbiology) / Department of Microbiology / See the attached abstract below