Intramolecular Hydrogen Bonds in Tip-Functionalized Single-Walled Carbon Nanotubes as pH-Sensitive Gates

Since their discovery, carbon nanotubes and other related nanomaterials are in the spotlight due to their unique molecular structures and properties, having a wide range of applications. The cage-like structure of carbon nanotubes is especially appealing as a route to confine molecules, isolating them from the solvent medium. This study aims to explore and characterize, through density functional theory (DFT) calculations, covalent tip-functionalization of single-walled carbon nanotubes (SWCNTS) with carboxymethyl moieties that establish pH sensitive molecular gates. The response of the molecular gate to pH fluctuations arises from variations in the noncovalent interactions between functionalized groups, which depend on the extent of protonation, leading to conformational changes. Overall, the hydrogen bonds present in the molecular models under study, as evaluated through topological analysis and pK_a calculations, suggest that functionalized SWCNTs may be suitable for the design of drug delivery systems to enhance the efficiency of some pharmacological treatments, or even in the area of catalysis and separation processes, through their incorporation in nanocomposites.

Mitochondrial disruption and DNA fragmentation in Trypanosoma cruzi induced by naphthoimidazoles synthesized from beta-lapachone

Three naphthoimidazoles presenting aromatic groups attached to the imidazole ring were the most active against trypomastigotes of Trypanosoma cruzi between 45 derivatives from beta-lapachone. N1 is active against the three forms of the parasite. In this work, we investigated N2 and N3 and analyzed the effect of the three derivatives on metacyclogenesis, endocytosis, and cell cycle. In epimastigotes, N2 and N3 blocked the cell cycle, inhibited succinate cytochrome c reductase, metacyclogenesis, and induced damage to mitochondrion, Golgi, and reservosomes. In treated trypomastigotes, there were alterations in the mitochondrion, nucleus and kinetoplast, and DNA fragmentation. Preincubation with cysteine protease inhibitors reversed the effect of N1, N2, and N3. Such reversion and ultrastructural alterations suggest the involvement of autophagy in parasite death. Ultrastructural, flow cytometry, and biochemical studies suggest that naphthoimidazoles interferes with the energetic metabolism and induces DNA fragmentation.

In vitro activity of Brazilian medicinal plants, naturally occurring naphthoquinones and their analogues, against methicillin-resistant Staphylococcus aureus

Fourteen extracts from Brazilian traditional medicinal plants used to treat infectious diseases were used to look for potential antimicrobial activity against multiresistant bacteria of medical importance. Staphylococcus aureus strains were susceptible to extracts of Punica granatum and Tabebuia avellanedae. The minimum inhibitory concentrations (MICs) of the total extracts and of additional fractions of these plants were determined by employing strains of methicillin-resistant (MRSA) and -sensitive (MSSA) S. aureus, including isolates of the PFGE clone A, which is prevalent in Brazil and two ATCC reference strains. A mixture of ellagitannins isolated from P. granatum and two naphthoquinones isolated from T. avellanedae demonstrated antibacterial activity against all S. aureus strains tested. Semi-synthetic furanonaphthoquinones (FNQs) showed lower MICs than those exhibited by natural occurring naphthoquinones. The results indicate that these natural products can be effective potential candidates for the development of new strategies to treat MRSA infections.

Chemical reactivity studies with naphthoquinones from Tabebuia with anti-trypanosomal efficacy

The biological activities of the naphthoquinones lapachol and its cyclization product beta-lapachone, extracted from trees of the genus Tabebuia, have been intensively studied. Given continuity to the studies about heterocyclic derivatives obtained from the reaction of these naphtoquinones with amino-containing reagents, 22 derivatives of beta-lapachone, nor-beta-lapachone and lapachol were synthesised and their activities against trypomastigote forms of T. cruzi were evaluated. The compounds were grouped as oxazolic, imidazolic, phenoxazinic, indolic, pyranic and cyclopentenic derivatives. The variability of the new structures is based on the great electrophilicity of 1,2-quinoidal carbonyls towards reagents containing nitrogen or carbon as nucleophilic centres. In relation to the trypanocidal activity of the synthesised compounds, in view of their structural diversity, tendencies only could be verified. Among the cyclofunctionalised products the oxazolic and imidazolic derivatives showed +/- 1.5 to 34.8 times higher activity than crystal violet, the standard drug for the sterilization of stored blood. These results corroborate the tendency of trypanocidal activity in imidazolic skeletons, and indicate that this moiety could be used as a guide for architectural delineation of molecules with potential value for the chemotherapy of Chagas disease.

Molluscicidal activity of 2-hydroxy-3-alkyl-1,4-naphthoquinones and derivatives

In the search for new molluscicidal agents we tested the activity of lapachol and other 2-hydroxy-3-alkylnaphthoquinones possessing nitrogenated alkyl chains, against the snail Biomphalaria glabrata. Lapachol, isolapachol and nor-lapachol showed strong molluscicidal activity against the adult snail (LD(90)<10 ppm) and significant toxicity against snail egg masses (LD(90)<0.2 ppm). As lapachol is easily extracted, and the derivatives can be synthesised without any difficulty, large-scale synthesis and field tests can be conducted, with a view to large-scale molluscicidal programs.

Potent inhibition of tumor survival in vivo by beta-lapachone plus taxol: combining drugs imposes different artificial checkpoints

Ablation of tumor colonies was seen in a wide spectrum of human carcinoma cells in culture after treatment with the combination of beta-lapachone and taxol, two low molecular mass compounds. They synergistically induced death of cultured ovarian, breast, prostate, melanoma, lung, colon, and pancreatic cancer cells. This synergism is schedule dependent; namely, taxol must be added either simultaneously or after beta-lapachone. This combination therapy has unusually potent antitumor activity against human ovarian and prostate tumor prexenografted in mice. There is little host toxicity. Cells can commit to apoptosis at cell-cycle checkpoints, a mechanism that eliminates defective cells to ensure the integrity of the genome. We hypothesize that when cells are treated simultaneously with drugs activating more than one different cell-cycle checkpoint, the production of conflicting regulatory signaling molecules induces apoptosis in cancer cells. beta-Lapachone causes cell-cycle delays in late G(1) and S phase, and taxol arrests cells at G(2)/M. Cells treated with both drugs were delayed at multiple checkpoints before committing to apoptosis. Our findings suggest an avenue for developing anticancer therapy by exploiting apoptosis-prone "collisions" at cell-cycle checkpoints.

Release of mitochondrial cytochrome C in both apoptosis and necrosis induced by beta-lapachone in human carcinoma cells

BACKGROUND

There are two fundamental forms of cell death: apoptosis and necrosis. Molecular studies of cell death thus far favor a model in which apoptosis and necrosis share very few molecular regulators. It appears that apoptotic processes triggered by a variety of stimuli converge on the activation of a member of the caspase family, such as caspase 3, which leads to the execution of apoptosis. It has been suggested that blocking of caspase activation in an apoptotic process may divert cell death to a necrotic demise, suggesting that apoptosis and necrosis may share some upstream events. Activation of caspase is preceded by the release of mitochondrial cytochrome C.

MATERIALS AND METHODS

We first studied cell death induced by beta-lapachone by MTT and colony-formation assay. To determine whether the cell death induced by beta-lapachone occurs through necrosis or apoptosis, we used the PI staining procedure to determine the sub-G1 fraction and the Annexin-V staining for externalization of phophatidylserine. We next compared the release of mitochondrial cytochrome C in apoptosis and necrosis. Mitochondrial cytochrome C was determined by Western blot analysis. To investigate changes in mitochondria that resulted in cytochrome C release, the mitochondrial membrane potential (delta psi) was analyzed by the accumulation of rhodamine 123, a membrane-permeant cationic fluorescent dye. The activation of caspase in apoptosis and necrosis were measured by using a profluorescent substrate for caspase-like proteases, PhiPhiLuxG6D2.

RESULTS

beta-lapachone induced cell death in a spectrum of human carcinoma cells, including nonproliferating cells. It induced apoptosis in human ovary, colon, and lung cancer cells, and necrotic cell death in four human breast cancer cell lines. Mitochondrial cytochrome C release was found in both apoptosis and necrosis. This cytochrome C release occurred shortly after beta-lapachone treatment when cells were fully viable by trypan blue exclusion and MTT assay, suggesting that cytochrome C release is an early event in beta-lapachone induced apoptosis as well as necrosis. The mitochondrial cytochrome C release induced by beta-lapachone is associated with a decrease in mitochondrial transmembrane potential (delta psi). There was activation of caspase 3 in apoptotic cell death, but not in necrotic cell death. This lack of activation of CPP 32 in human breast cancer cells is consistent with the necrotic cell death induced by beta-lapachone as determined by absence of sub-G1 fraction, externalization of phosphatidylserine.

CONCLUSIONS

beta-lapachone induces either apoptotic or necrotic cell death in a variety of human carcinoma cells including ovary, colon, lung, prostate, and breast, suggesting a wide spectrum of anti-cancer activity in vitro. Both apoptotic and necrotic cell death induced by beta-lapachone are preceded by a rapid release of cytochrome C, followed by the activation of caspase 3 in apoptotic cell death but not in necrotic cell death. Our results suggest that beta-lapachone is a potential anti-cancer drug acting on the mitochondrial cytochrome C-caspase pathway, and that cytochrome C is involved in the early phase of necrosis.

Trypanocidal activity of synthetic heterocyclic derivatives of active quinones from Tabebuia sp

Continuing a program on the chemistry and biological activity of compounds from the Brazilian flora, the lytic activity against bloodstream forms of T. cruzi of nine new heterocyclic naphthooxazole and naphthoimidazole derivatives obtained from the reaction of naphtoquinones isolated from Tabebuia sp. (Tecoma) with amino-containing reagents has been studied. Also for the first time the biological activity of allyl derivatives of lawsone, a natural quinone from Lausonia alba inactive against T. cruzi, is reported. The introduction of an allyl group in lawsone gives rise to O-allyl-lawsone and C-allyl-lawsone that showed activity against the parasite, with ID50 values of 420.7 +/- 71.1 and 330.7 +/- 62.4 mumol/l, respectively. The trypanocidal activity of the naphtho heterocyclics synthesized from the original quinones showed no concordant behavior in relation to the parent compound. Six of nine of the synthesized compounds presented lower ID50 values than crystal violet, indicating a general trend of activity among naphthalenic heterocyclics of the oxazole/imidazole type. However, their chemical structures do not endow them with the capacity of free radical generation by biological reduction as the quinoidal moiety, nor do they have chemical reducible appendage like the nitro group of nifurtimox and benznidazole, responsible for such behaviour. As a hypothesis, the pattern of their biological actions should be focused in other aspects of their chemical structures. Because of their polycyclic planar topology, these derivatives are potential candidates for experimental tests as DNA intercalating agents.

Steroidal saponins from Smilax officinalis

Three new steroidal saponins were isolated from the rhizomes of Smilax officinalis. The structures of these saponins were established by extensive spectral data, hydrolysis and chemical correlation as sarsasapogenin 3-O-beta-D-glucopyranosyl-(1-->4)-[alpha-L-arabinopyranosyl-(1-->6 )-beta- D-glucopyranoside, neotigogenin 3-O-beta-D-glucopyranosyl-(1-->4)-[alpha-L-arabinopyranosyl-(1-->6 )]-beta- D-glucopyranoside and 25S-spirostan-6 beta-ol 3-O-beta-D-glucopyranosyl-(1-->4)-[alpha-L-arabinopyranosyl-(1-->6 )]-beta- D-glucopyranoside. Acid hydrolysis of the latter compound gave a sapogenin which has a new orientation of an hydroxyl on the steroidal skeleton. A route is proposed for the biogenesis of the latter sapogenin which is an uncommon steroidal aglycone.

Screening of natural and synthetic drugs against Trypanosoma cruzi. 1. Establishing a structure/activity relationship

The activity of 45 compounds against bloodstream forms of Trypanosoma cruzi was investigated. The aim was to consider new agents which might subsequently be assayed for chemoprophylaxis in donated blood. In a preliminary screening the drugs were assayed (50 to 1,000 microM at 29 degrees C) and those active against bloodstream forms at concentrations below 600 microM were selected for further assays under blood-bank conditions (4 degrees C/24 h). Three compounds isolated from natural sources and six synthetic agents were selected. The active compounds of plant origin included purpurin, a member of the trihydroxylated anthraquinone group, which is known to exhibit trypanocidal activity. Among the active synthetic compounds, five displayed a common structural feature in that they were potentially one-electron acceptors, via reductive functional groups. All five compounds form tricentered C or N intermediates, joined in a hypothetical 'Y' radical pattern. It is possible that the trypanocidal mechanisms initiated by these compounds are similar to those found with crystal violet, since this dye, which is already used in endemic areas for the treatment of banked blood, also conforms to this general Y structural pattern.

[The prevalence of iron deficiency in pregnant women at their first consultation in health centers in a metropolitan area, Brazil. Etiology of anemia]

Three hundred and sixty-three pregnant women enrolled in the Pregnancy Medical Care Program of S. Paulo Health Department in the district of Butantan, S. Paulo city, Brazil, were studied at their first routine consultation between April and October, 1988. Their average age was 25 and 65.9% of them belonged to families with a monthly income below US$50.00 per capita. Only 3.1% presented an income above US$150.00 per capita. Taking the minimum transferrin saturation threshold of 15% as determining iron deficiency, a 4.6% prevalence of iron deficiency was observed in the first trimester, 17.3% in the second trimester and 42.8% in the third trimester, resulting in an overall prevalence of 12.4%. There was no significant difference between prevalences of iron deficiency according to the number of pregnancies. The prevalence of iron deficiency was higher in women presenting incomes below US$50.00 per capita.

NBS bromination reactions of dihydronaphthofuran quinones: a new fragmentation type reaction in the chemistry of quinones

The reactions of isomeric dihydronaphthofuran-quinones of the alpha and beta type, 1 and 5, respectively, with NBS, under visible light, gave unexpected products. These reactions represent a new route to structural types represented by naphtho[1,2-b]furan and naphtho[2,3-b]furan quinones and lead to a new assessment of biosynthetic theory concerning the furan ring in plants.

[Selection by means of KB cells of substances and extracts potentially active in cancer chemotherapy]

Several synthetic, semi-synthetic and natural compounds as well as plant extracts were screened for their growth inhibition activity on KB cells. The most active ones were naphthoquinones and derivatives of pyrido [4,3-b]carbazole alkaloids, with inhibition dose (ID50) less than 4 micrograms/ml. Of the crude extracts of several plants screened, Vellozia caput-ardeae showed to be the most active.

Activity of some naphthoquinones on blood stream forms of Trypanosoma cruzi

Accidental transmission of Chagas disease to man by blood transfusion is a serious problem in Latin America. This paper describes the testing of several naphthoquinones, some of which were active against blood trypomastigotes in vitro at 4 degrees C and might therefore warrant further study for preventing transmission of Chagas disease by blood transfusion.

[Synthesis of xyloidone and lapachone analogs]

Several xiloidone analogues were prepared, in a one step reaction, by the alkylation of lawsone with aldehydes obtained from natural essential oil sources. By Pd/C hydrogenation of these xyloidone derivatives, alpha-lapachone analogues were obtained in high yield. beta-lapachone isomers were prepared from the alpha-derivatives by treatment with sulphuric acid.

In vitro and in vivo evaluation of the toxicity of 1,4-naphthoquinone and 1,2-naphthoquinone derivatives against Trypanosoma cruzi

The toxic effect of lapachol, beta-lapachone and several 1,2-naphthoquinone derivatives on the growth, viability and infectivity of Trypanosoma cruzi were compared. beta-lapachone was the most active compound in vitro. No inhibition was observed in suspensions which contained inactivated foetal calf serum or rabbit haemoglobin solution. The infectivity of trypomastigotes in mice was not affected when cells were previously incubated with beta-lapachone or one of several other naphthoquinone derivatives in vitro in the presence of blood. It is suggested that beta-lapachone and the other compounds can be inactivated either by reduction in the presence of oxyhaemoglobin or by interaction with serum proteins. A beta-lapachone derivative, allyl-beta-lapachone, was not inactivated in the presence of blood and remained effective in suppressing trypomastigote infectivity.

Schistosomiasis mansoni: blockage of cercarial skin penetration by chemical agents: i. naphthoquinones and derivatives

Skin penetration by Schistosoma mansoni cercariae may be blocked by 1,4-and 1,2-naphthoquinones applied topically. Of 23 naphthoquinone derivatives synthesized, 15 afforded almost complete protection when applied in solution to the tails of mice 24 hours before exposure to cercariae. On the basis of present evidence the 5-carbon atom side chain present in naturally occurring lapachol seems to be important for activity, and this is in accord with the previous observation that effective protective agents are liposoluble. Topically applied cercarial penetration inhibitors are presently the only prophylactic agents available for use in the field.

[Anemia in pregnant women of Sobradinho, a satellite city of Brazilia, Brazil (author's transl)]

Four hundred and seven pregnant women, living in Sobradinho, a satellite city of Brasilia, Brazil, divided in three groups according to their gestation age: I trimester (50 cases); II trimester (140 cases); III trimester (201 cases), were studied for the hemoglobin concentration of their blood and intestinal parasitism. In nineteen of the anemic women iron, folic acid and vitamin B12 serum determinations were done. The mean hemoglobin concentration and the percentage of anemia (less than 12 g/100 ml) in the different stages of gestation, were: 13.06 g/100 ml and 22% for the first trimester: 12.49 g/100 ml and 29% for the second trimester and 12.11 g/100 ml and 34% for the third trimester. In the 19 cases of the anemic group studied we found 73.7% of iron deficiency (below 60 microg/100 ml); 26.3% of folic acid deficiency (below 4 ng/ml) and 10.5% of vitamin B12 deficiency (below 140 pg/ ml). A combined deficiency occured in two cases: iron plus folic acid (case 11, table 3) and folic acid plus vitamin B12 (case 3, table 3). The stool examination showed parasitic infection, in 51% of the women.