Adriana Pabón

Oxidative stress in patients with non-complicated malaria

AIM To compare oxidative stress in adults with non-complicated malaria and healthy controls. METHODOLOGY We measured malondialdehyde (MDA), total antioxidant status (TAS), catalase, superoxide dismutase (SOD) and glutathione peroxidase (GSH-PX). Oxidative stress was calculated based on MDA/TAS, MDA/GSH-PX and SOD/catalase indexes. RESULTS Mean MDA in patients was 3.9 micromol/L (controls = 1.3 micromol/L). Mean TAS was 0.9 mmol/L in patients and controls. Malaria patients had less catalase activity when compared to controls (209.4 vs. 320.4 k/gr), while SOD and GSH-PX activity was higher (79.4 U/mL, 11,884.2U/L vs. 54.3 U/mL, 9,672.6 U/L). MDA/TAS index was 3.5 fold more in patients than in controls, MDA/GSH-PX and SOD/catalase indexes were increased by 6 and 2.8 fold. MDA levels and MDA/TAS index showed no differences according to malarial history, parasitaemia, Plasmodium species, parasites stage, place of residence and drinking or smoking habits. CONCLUSIONS During acute non-complicated P. falciparum or P. vivax malaria, we observed high oxidative stress. This resulted from lipid peroxidation rather than from a reduced TAS. We propose MDA/TAS index as a useful marker of oxidative stress during malaria infection.

New salicylamide and sulfonamide derivatives of quinoxaline 1,4-di-N-oxide with antileishmanial and antimalarial activities

Continuing with our efforts to identify new active compounds against malaria and leishmaniasis, 14 new 3-amino-1,4-di-N-oxide quinoxaline-2-carbonitrile derivatives were synthesized and evaluated for their in vitro antimalarial and antileishmanial activity against Plasmodium falciparum Colombian FCR-3 strain and Leishmania amazonensis strain MHOM/BR/76/LTB-012A. Further computational studies were carried out in order to analyze graphic SAR and ADME properties. The results obtained indicate that compounds with one halogenous group substituted in position 6 and 7 provide an efficient approach for further development of antimalarial and antileishmanial agents. In addition, interesting ADME properties were found.

Aryl piperazine and pyrrolidine as antimalarial agents. Synthesis and investigation of structure-activity relationships

Piperazine and pyrrolidine derivatives were synthesised and evaluated for their capacity to inhibit the growth of Plasmodium falciparum chloroquine-resistant (FCR-3) strain in culture. The combined presence of a hydroxyl group, a propane chain and a fluor were shown to be crucial for the antiplasmodial activity. Five compounds of the aryl-alcohol series inhibited 50% of parasite growth at doses ≤10 μM. The most active compound 1-(4-fluoronaphthyl)-3-[4-(4-nitro-2-trifluoromethylphenyl)piperazin-1-yl] propan-1-ol was almost 20-40 times more active on P. falciparum (IC(50): 0.5 μM) than on tumorogenic and non-tumorogenic cells. In vivo it has a very weak effect; inhibiting 35% of parasite growth only, at 10 mg/kg/day against Plasmodium berghei infected mice without any impact on survival time. In silico molecular docking study and molecular electrostatic potential calculation revealed that this compound bound to the active site of Plasmodium plasmepsin II enzyme.

New Amide Derivatives of Quinoxaline 1,4-di-N-Oxide with Leishmanicidal and Antiplasmodial Activities

Malaria and leishmaniasis are two of the World’s most important tropical parasitic diseases. Continuing with our efforts to identify new compounds active against malaria and leishmaniasis, twelve new 1,4-di-N-oxide quinoxaline derivatives were synthesized and evaluated for their in vitro antimalarial and antileishmanial activity against Plasmodium falciparum FCR-3 strain, Leishmania infantum and Leishmania amazonensis. Their toxicity against VERO cells (normal monkey kidney cells) was also assessed. The results obtained indicate that a cyclopentyl derivative had the best antiplasmodial activity (2.9 µM), while a cyclohexyl derivative (2.5 µM) showed the best activity against L. amazonensis, and a 3-chloropropyl derivative (0.7 µM) showed the best results against L. infantum. All these compounds also have a Cl substituent in the R7 position.

Synthesis and antiplasmodial activity of some 1-azabenzanthrone derivatives

Some synthetic 1-azabenzanthrones (7H-dibenzo[de,h]quinolin-7-ones) are weakly to moderately cytotoxic, suggesting that they might also show antiparasitic activity. We have now tested a small collection of these compounds in vitro against a chloroquine-resistant Plasmodium falciparum strain, comparing their cytotoxicity against normal human fibroblasts. Our results indicate that 5-methoxy-1-azabenzanthrone and its 2,3-dihydro analogue have low micromolar antiplasmodial activities and showed more than 10-fold selectivity against the parasite, indicating that the dihydro compound, in particular, might serve as a lead compound for further development.

Adherence to human lung microvascular endothelial cells (HMVEC-L) of Plasmodium vivax isolates from Colombia

BackgroundFor years Plasmodium vivax has been considered the cause of benign malaria. Nevertheless, it has been observed that this parasite can produce a severe disease comparable to Plasmodium falciparum. It has been suggested that some physiopathogenic processes might be shared by these two species, such as cytoadherence. Recently, it has been demonstrated that P. vivax-infected erythrocytes (Pv-iEs) have the capacity to adhere to endothelial cells, in which intercellular adhesion molecule-1 (ICAM-1) seems to be involved in this process.MethodsAdherence capacity of 21 Colombian isolates, from patients with P. vivax mono-infection to a microvascular line of human lung endothelium (HMVEC-L) was assessed in static conditions and binding was evaluated at basal levels or in tumor necrosis factor (TNF) stimulated cells. The adherence specificity for the ICAM-1 receptor was determined through inhibition with an anti-CD54 monoclonal antibody.ResultsThe majority of P. vivax isolates, 13 out of 21 (61.9%), adhered to the HMVEC-L cells, but P. vivax adherence was at least seven times lower when compared to the four P. falciparum isolates. Moreover, HMVEC-L stimulation with TNF led to an increase of 1.6-fold in P. vivax cytoadhesion, similar to P. falciparum isolates (1.8-fold) at comparable conditions. Also, blockage of ICAM-1 receptor with specific antibodies showed a significant 50% adherence reduction.ConclusionsPlasmodium vivax isolates found in Colombia are also capable of adhering specifically in vitro to lung endothelial cells, via ICAM-1 cell receptor, both at basal state and after cell stimulation with TNF. Collectively, these findings reinforce the concept of cytoadherence for P. vivax, but here, to a different endothelial cell line and using geographical distinct isolates, thus contributing to understanding P. vivax biology.

Plasmodium falciparum: Effect of Solanum nudum steroids on thiol contents and β-hematin formation in parasitized erythrocytes

We studied the effects on total thiols glutathione (GSH) and cysteine contents in Plasmodium falciparum in vitro when treated with four steroid derivatives and a sapogenin (Diosgenone) extracted from Solanum nudum. We also determined their capacity to inhibit beta-hematin formation. We showed that SN-1 (16alpha-acetoxy-26-hydroxycholest-4-ene-3,22-dione) increased total glutathione and cysteine concentrations while SN-4 (26-O-beta-d-glucopyranosyloxy-16alpha-acetoxycholest-4-ene-3,22-dione) decreased the concentration of both thiols. Acetylation in C16 was crucial for the effect of SN-1 while type furostanol and terminal glucosidation were necessary for the inhibitory properties of SN-4. The combination of steroids and buthionine sulfoximine, a specific inhibitor of a step-limiting enzyme in GSH synthesis, did not modify the glutathione contents. Finally, we found that SN-1 inhibited more than 80% of beta-hematin formation at 5.0mM, while the other steroids did not show any effect.

Diosgenone Synthesis, Anti-Malarial Activity and QSAR of Analogues of This Natural Product

Solanum nudum Dunal steroids have been reported as being antimalarial compounds; however, their concentration in plants is low, meaning that the species could be threatened by over-harvesting for this purpose. Swern oxidation was used for hemisynthesis of diosgenone (one of the most active steroidal sapogenin diosgenin compounds). Eighteen structural analogues were prepared; three of them were found to be more active than diosgenone (IC50 27.9 μM vs. 10.1 μM, 2.9 μM and 11.3 μM). The presence of a 4-en-3-one grouping in the A-ring of the compounds seems to be indispensable for antiplasmodial activity; progesterone (having the same functional group in the steroid A-ring) has also displayed antiplasmodial activity. Quantitative correlations between molecular structure and bioactivity were thus explored in diosgenone and several derivatives using well-established 3D-QSAR techniques. The models showed that combining electrostatic (70%) and steric (30%) fields can explain most variance regarding compound activity. Malarial parasitemia in mice became reduced by oral administration of two diosgenone derivatives.

Amodiaquine failure associated with erythrocytic glutathione in Plasmodium falciparum malaria

ObjectiveTo establish the relationship between production of glutathione and the therapeutic response to amodiaquine (AQ) monotherapy in Plasmodium falciparum non-complicated malaria patients.MethodologyTherapeutic response to AQ was evaluated in 32 patients with falciparum malaria in two townships of Antioquia, Colombia, and followed-up for 28 days. For every patient, total glutathione and enzymatic activity (glutathione reductase, GR, and γ-glutamylcysteine synthetase, γ-GCS) were determined in parasitized erythrocytes, non-infected erythrocytes and free parasites, on the starting day (day zero, before ingestion of AQ) and on the day of failure (in case of occurrence).ResultsThere was found an AQ failure of 31.25%. Independent of the therapeutic response, on the starting day and on the day of failure, lower total glutathione concentration and higher GR activities in parasitized erythrocytes were found, compared with non-infected erythrocytes (p < 0.003). In addition, only on the day of failure, γ-GCS activity of parasitized erythrocytes was higher, compared with that of healthy erythrocytes (p = 0.01). Parasitized and non-parasitized erythrocytes in therapeutic failure patients (TF) had higher total glutathione on the starting day compared with those of adequate clinical response (ACR) (p < 0.02). Parasitized erythrocytes of TF patients showed lower total glutathione on the failure day, compared with starting day (p = 0.017). No differences was seen in the GR and γ-GCS activities by compartment, neither between the two therapeutic response groups nor between the two treatment days.ConclusionThis study is a first approach to explaining P. falciparum therapeutic failure in humans through differences in glutathione metabolism in TF and ACR patients. These results suggest a role for glutathione in the therapeutic failure to antimalarials.

New hydrazine and hydrazide quinoxaline 1,4-di-N-oxide derivatives : in silico ADMET, antiplasmodial and antileishmanial activity

We report the design (in silico ADMET criteria), synthesis, cytotoxicity studies (HepG-2 cells), and biological evaluation of 15 hydrazine/hydrazide quinoxaline 1,4-di-N-oxide derivatives against the 3D7 chloroquine sensitive strain and FCR-3 multidrug resistant strain of Plasmodium falciparum and Leishmania infantum (axenic amastigotes). Fourteen of derivatives are novel quinoxaline 1,4-di-N-oxide derivatives. Compounds 18 (3D7 IC50=1.40μM, FCR-3 IC50=2.56μM) and 19 (3D7 IC50=0.24μM, FCR-3 IC50=2.8μM) were identified as the most active against P. falciparum, and they were the least cytotoxic (CC50-values>241μM) and most selective (SI>86). None of the compounds tested against L. infantum were considered to be active. Additionally, the functional role of the hydrazine and hydrazide structures were studied in the quinoxaline 1,4-di-N-oxide system.