In vivo and in vitro activity by diverse chelators against Trypanosoma brucei brucei

Triclosan-caffeic acid hybrids: Synthesis, leishmanicidal, trypanocidal and cytotoxic activities

The synthesis, cytotoxicity, anti-leishmanial and anti-trypanosomal activities of twelve triclosan-caffeic acid hybrids are described herein. The structure of the synthesized products was elucidated by a combination of spectrometric analyses. The synthesized compounds were evaluated against amastigotes forms of L. (V) panamensis, which is the most prevalent Leishmania species in Colombia, and against Trypanosoma cruzi, which is the pathogenic species to humans. Cytotoxicity was evaluated against human U-937 macrophages. Eight compounds were active against L. (V) panamensis (18-23, 26 and 30) and eight of them against T. cruzi (19-22, 24 and 28-30) with EC₅₀ values lower than 40 μM. Compounds 19-22, 24 and 28-30 showed higher activities than benznidazole (BNZ). Esters 19 and 21 were the most active compounds for both L. (V) panamensis and T. cruzi with 3.82 and 11.65 μM and 8.25 and 8.69 μM, respectively. Compounds 19-22, 24 and 28-30 showed higher activities than benznidazole (BNZ). Most of the compounds showed antiprotozoal activity and with exception of 18, 26 and 28, the remaining compounds were toxic for mammalian cells, yet they have potential to be considered as candidates for anti-trypanosomal and anti-leishmanial drug development. The activity is dependent on the length of the alkyl linker with compound 19, bearing a four-carbon alkyl chain, the most performing hybrid. In general, hydroxyl groups increase both activity and cytotoxicity and the presence of the double bond in the side chain is not decisive for cytotoxicity and anti-protozoal activity.

Chemical constituents of Lychnophora pohlii and trypanocidal activity of crude plant extracts and of isolated compounds

Crude extracts of Lychnophora pohlii were tested in vitro against trypomastigote forms of Trypanosoma cruzi, and the dichloromethane and methanol crude extracts from leaves plus inflorescences were found to have trypanocidal activity. The bioassay-guided fractionation of the extracts yielded seven active compounds: the sesquiterpene lactones lychnopholide, centratherin, goyazensolide and 15-desoxygoyazensolide in the dichloromethane extract, and caffeic acid and the flavonoids luteolin and vicenin-2 in the methanol extract. One active caffeoyl quinic acid derivative was isolated from the inactive hydroalcoholic extract of leaves plus inflorescences. Chemically, the plant has sesquiterpene lactone type furanoheliangolides, flavonoids, caffeic acid, a caffeoyl quinic acid derivative, which are characteristic of the Vernonieae.

Studies on the protective effects of caffeic acid and quercetin on chemical-induced hepatotoxicity in rodents

Caffeic acid and quercetin, the well-known phenolic compounds widely present in the plant kingdom, were investigated for their possible protective effects against paracetamol and CCl4-induced hepatic damage. Paracetamol at the oral dose of 1 g/kg produced 100% mortality in mice while pretreatment of separate groups of animals with caffeic acid (6 mg/kg) and quercetin (10 mg/kg) reduced the death rate to 20% and 30%, respectively. Oral administration of sub-lethal dose of paracetamol (640 mg/kg) produced liver damage in rats as manifested by the significant (P<0.01) rise in serum levels of aminotransferases (aspartate transaminase (AST) and alanine transaminase (ALT)) compared to respective control values. The serum enzyme values were significantly (P<0.01) lowered on pretreatment of rats with either caffeic acid (6 mg/kg) or quercetin (10 mg/kg). Similarly, the hepatotoxic dose of CCl4 (1.5 ml/kg; orally) also raised significantly (P<0.05) the serum AST and ALT levels as compared to control values. The same dose of the caffeic acid and quercetin was able to prevent CCl4-induced rise in serum enzymes. Caffeic acid and quercetin also prevented the CCl4-induced prolongation in pentobarbital sleeping time confirming their hepatoprotectivity. These results indicate that caffeic acid and quercetin exhibited hepatoprotective activity possibly through multiple mechanisms.

Inhibition of prokaryotic and eukaryotic transcription by the 2:1 2,9-dimethyl-1,10-phenanthroline-cuprous complex, a ligand specific for open complexes

The redox-stable, tetrahedral cuprous chelate of neocuproine (2,9-dimethyl-1,10-phenanthroline) binds to the single-stranded DNA formed in open complexes and is an effective inhibitor of eukaryotic and prokaryotic transcription. Despite the many kinetic and structural differences between prokaryotic and eukaryotic transcription systems, they are all similarly inhibited by neocuproine copper, suggesting that all open complexes may share a homologous structure.

A transcription inhibitor specific for unwound DNA in RNA polymerase-promoter open complexes

The kinetically component open complexes formed at prokaryotic and eukaryotic transcription start sites are efficiently nicked by the chemical nuclease activity of the 2:1 1,10-phenanthroline-copper(I) complex [(OP)2Cu+] and hydrogen peroxide. This reaction specificity has been attributed to the creation of a binding site(s) for redox-active tetrahedral (OP)2Cu+ when RNA polymerase form productive complexes with promoters. This proposal has been confirmed for the Escherichia coli lac UV-5 promoter by the demonstration that the 2:1 2,9-dimethyl-1,10-phenanthroline-copper(I) complex [(Me2OP)2Cu+], a redox-inactive isostere of (OP)2-Cu+, protects the transcription start site from scission by the chemical nuclease activity. (Me2OP)2Cu+ is also an effective inhibitor of transcription. The inhibition of transcription and the protection from scission of the open complex by (OP)2Cu+ exhibit the same dependence on the concentration of (Me2OP)2Cu+. This redox- and exchange-stable species is a previously undescribed transcription inhibitor that binds to a site generated by the interaction of RNA polymerase with the promoter. Unlike the intercalating agent proflavine, which is also an effective transcription inhibitor, it does not displace the enzyme from the promoter. The ability of (Me2OP)2Cu+ to inhibit transcription may be partially responsible for its potent cytotoxicity.

Drug antioxidant effects. A basis for drug selection?

A free radical is any species capable of independent existence that contains one or more unpaired electrons. Free radical reactions have been implicated in the pathology of more than 50 human diseases. Radicals and other reactive oxygen species are formed constantly in the human body, both by deliberate synthesis (e.g. by activated phagocytes) and by chemical side-reactions. They are removed by enzymic and nonenzymic antioxidant defence systems. Oxidative stress, occurring when antioxidant defences are inadequate, can damage lipids, proteins, carbohydrates and DNA. A few clinical conditions are caused by oxidative stress, but more often the stress results from the disease. Sometimes it then makes a significant contribution to the disease pathology, and sometimes it does not. Several antioxidants are available for therapeutic use. They include molecules naturally present in the body [superoxide dismutase (SOD), alpha-tocopherol, glutathione and its precursors, ascorbic acid, adenosine, lactoferrin and carotenoids] as well as synthetic antioxidants [such as thiols, ebselen (PZ51), xanthine oxidase inhibitors, inhibitors of phagocyte function, iron ion chelators and probucol]. The therapeutic efficacy of SOD, alpha-tocopherol and ascorbic acid in the treatment of human disease is generally unimpressive to date although dietary deficiencies of the last two molecules should certainly be avoided. Xanthine oxidase inhibitors may be of limited relevance as antioxidants for human use. Exciting preliminary results with probucol (antiatherosclerosis), ebselen (anti-inflammatory), and iron ion chelators (in thalassaemia, leukaemia, malaria, stroke, traumatic brain injury and haemorrhagic shock) need to be confirmed by controlled clinical trials. Clinical testing of N-acetylcysteine in HIV-1-positive subjects may also be merited. A few drugs already in clinical use may have some antioxidant properties, but this ability is not widespread and drug-derived radicals may occasionally cause significant damage.