3-H-[1,2]Dithiole as a New Anti-Trypanosoma cruzi Chemotype: Biological and Mechanism of Action Studies.

The current pharmacological Chagas disease treatments, using Nifurtimox or Benznidazole, show limited therapeutic results and are associated with potential side effects, like mutagenicity. Using random screening we have identified new chemotypes that were able to inhibit relevant targets of the Trypanosoma cruzi. We found 3H-[1,2]dithioles with the ability to inhibit Trypanosoma cruzi triosephosphate isomerase (TcTIM). Herein, we studied the structural modifications of this chemotype to analyze the influence of volume, lipophilicity and electronic properties in the anti-T. cruzi activity. Their selectivity to parasites vs. mammalian cells was also examined. To get insights into a possible mechanism of action, the inhibition of the enzymatic activity of TcTIM and cruzipain, using the isolated enzymes, and the inhibition of membrane sterol biosynthesis and excreted metabolites, using the whole parasite, were achieved. We found that this structural framework is interesting for the generation of innovative drugs for the treatment of Chagas disease.

Arylnitroalkenes as scavengers of macrophage-generated oxidants.

Oxygen and nitrogen derived molecules mediated oxidation and nitration have been involved in several pathological conditions. Conversely, nitric oxide and hydrogen peroxide are important signalization intermediates, whose concentrations are tightly regulated by specialized enzyme repertoires and should remain undisturbed by the addition of exogenous antioxidant molecules, as already demonstrated by intervention studies with antioxidant vitamins. Our goal was to develop specific antioxidants able to scavenge peroxynitrite anion, as well the radicals derived from the homolytic decomposition of its conjugated acid, nitrogen dioxide and hydroxyl radical. Fourteen substituted nitroalkenes, seven 4-substituted 1-(2-nitro-1Z-ethenyl)benzene, and seven 4-substituted (2-nitro-1Z-propenyl)benzene, with different stereochemical and electronic characteristics were synthesized and tested. Compounds with the electron donor group N,N-dimethylamino showed the highest reaction rates against peroxynitrite, and also reacted with its homolytic decomposition products, OH and NO2. While 1,1-dimethylamino-4-(2-nitro-1Z-ethenyl)benzene came up as a lead for future developments without the risk of interfering with signalization pathways, since it was highly specific for peroxynitrite and peroxynitrite derived radicals, its methylated analogous 1,1-dimethylamino-4-(2-nitro-1Z-propenyl)benzene was less specific and also reacted with NO and O2(-), the biological precursor of H2O2.

Analysis of two methods to evaluate antioxidants.

This exercise is intended to introduce undergraduate biochemistry students to the analysis of antioxidants as a biotechnological tool. In addition, some statistical resources will also be used and discussed. Antioxidants play an important metabolic role, preventing oxidative stress-mediated cell and tissue injury. Knowing the antioxidant content of nutritional components can help make informed decisions about diet design, and increase the commercial value of antioxidant-rich natural products. As a reliable and convenient technique to evaluate the whole spectrum of antioxidants present in biological samples is lacking, the general consensus is to use more than one technique. We have chosen two widely used and inexpensive methods, Trolox-equivalent antioxidant capacity and the ferric reducing antioxidant power assays, to evaluate the antioxidant content of several fruits, and to compare and analyze the correlation between both assays.

Identification of chalcones as in vivo liver monofunctional phase II enzymes inducers.

Cancer preventive agents (CPA) are drugs able to suppress the carcinogen metabolic activation or block the formation of ultimate carcinogens. CPA could act through various molecular mechanisms, for example by interfering with the action of procarcinogen. This could be attained by increasing the phase II enzymes levels of quinone reductase (QR) and glutathione S-transferase (GST). New flavonoids, especially chalcones, have been identified as in vivo monofunctional phase II enzymes inducers. Oral administration of chalcone, 4, and both p-methoxy-substituted chalcones, 6 and 14, increased hepatic QR activity with concomitant decrease in CYP1A1 activity, a member of the most important group of phase I enzymes cytochrome P450. Among them, 4 also increased GST activity. While p-bromo-substituted chalcone 8 was the best inducer of QR it decreased hepatic GST expression and cytochrome P450, being the most effective decreasing cytochrome P450-expression. Thienyl-chalcone 20 being the bioisostere of chalcone 4 did not display the same in vivo profile in the phase I level modification. As chalcone 4 its bioisostere, chalcone 20, displayed low DNA strand breakage and absence of mutagenicity. Also, in our preliminary in vivo tumourigenesis/chemopreventive and acute-toxicity studies, chalcones 4, 6 and 8 showed the best behaviours as CPA justifying additional studies that are ongoing.

Inactivation of cystathionine beta-synthase with peroxynitrite.

Cystathionine beta-synthase (CBS) is a homocysteine metabolizing enzyme that contains pyridoxal phosphate (PLP) and a six-coordinate heme cofactor of unknown function. CBS was inactivated by peroxynitrite, the product of nitric oxide and superoxide radicals. The IC(50) was approximately 150microM for 5microM ferric CBS. Stopped-flow kinetics and competition experiments showed a direct reaction with a second-order rate constant of (2.4-5.0)x10(4)M(-1)s(-1) (pH 7.4, 37 degrees C). The radicals derived from peroxynitrite, nitrogen dioxide and carbonate radical, also inactivated CBS. Exposure to peroxynitrite did not modify bound PLP but led to nitration of Trp208, Trp43 and Tyr223 and alterations in the heme environment including loss of thiolate coordination, conversion to high-spin and bleaching, with no detectable formation of oxo-ferryl compounds nor promotion of one-electron processes. This study demonstrates the susceptibility of CBS to reactive oxygen/nitrogen species, with potential relevance to hyperhomocysteinemia, a risk factor for cardiovascular diseases.