Assessment of antimutagenic and genotoxic potential of senna (Cassia angustifolia Vahl.) aqueous extract using in vitro assays

Senna (Cassia angustifolia Vahl.) is widely used as a laxative, although potential side effects, such as toxicity and genotoxicity, have been reported. This study evaluated genotoxic and mutagenic effects of senna aqueous extract (SAE) by means of four experimental assays: inactivation of Escherichia coli cultures; bacterial growth inhibition; reverse mutation test (Mutoxitest) and DNA strand break analysis in plasmid DNA. Our results demonstrated that SAE produces single and double strand breaks in plasmid DNA in a cell free system. On the other hand, SAE was not cytotoxic or mutagenic to Escherichia coli strains tested. In effect, SAE was able to avoid H(2)O(2)-induced mutagenesis and toxicity in Escherichia coli IC203 (uvrA oxyR) and IC205 (uvrA mutM) strains, pointing to a new antioxidant/antimutagenic action of SAE.

Cytotoxic and genotoxic effects induced by stannous chloride associated to nuclear medicine kits

At present, more than 75% of routine nuclear medicine diagnostic procedures use technetium-99m (99mTc). The binding between 99mTc and the drug to obtain the radiopharmaceutical needs a reducing agent, with stannous chloride (SnCl2) being one of the most used. There are controversies about the cytotoxic, genotoxic and mutagenic effects of SnCl2 in the literature. Thus, the approaches below were used to better understand the biological effects of this salt and its association in nuclear medicine kits [methylenediphosphonate (MDP) bone scintigraphy and diethylenetriaminepentaacetic acid (DTPA) kidney and brain scintigraphy]: (i) bacterial inactivation experiments; (ii) agarose gel electrophoresis of supercoiled and linear plasmid DNA and (iii) bacterial transformation assay. The Escherichia coli strains used here were AB1157 (wild type) and BW9091 (xthA mutant). Data obtained showed that both MDP and SnCl2 presented a high toxicity, but this was not observed when they were assayed together in the kit, thereby displaying a mutual protect effect. DTPA salt showed a moderate toxicity, and once more, the DTPA kit provided protection, compared to the SnCl2 effect alone. The results suggest a possible complex formation, either MDP-SnCl2 or DTPA-SnCl2, originating an atoxic compound. On the other hand, SnCl2-induced cell inactivation and the decrease in bacterial transformation generated by DTPA found in XthA mutant strain suggest that the lack of this enzyme could be responsible for the effects observed, being necessary to induce DNA damage repair.

Biological effects of stevioside on the survival of Escherichia colistrains and plasmid DNA

Stevioside is widely used daily in many countries as a non-caloric sugar substitute. Its sweetening power is higher than that of sucrose by approximately 250-300 times, being extensively employed as a household sweetener, or added to beverages and food products. The purpose of this study was to ascertain stevioside genotoxic and cytotoxic potentiality in different biological systems, as its use continues to increase. Agarose gel electrophoresis and bacterial transformation were employed to observe the occurrence of DNA lesions. In addition to these assays, Escherichia coli strains were incubated with stevioside so that their survival fractions could be obtained. Results show absence of genotoxic activity through electrophoresis and bacterial transformation assays and drop of survival fraction of E. coli strains deficient in rec A and nth genes, suggesting that stevioside (i) is cytotoxic; (ii) could need metabolization to present deleterious effects on cells; (iii) is capable of generating lesions in DNA and pathways as base excision repair, recombination and SOS system would be important to recover these lesions.

Interaction of stannous chloride leads to alteration in DNA, triphosphate nucleotides and isolated bases

Stannous chloride (SnCl2) is a reducing chemical agent used in several man-made products. SnCl2 can generate reactive oxygen species (ROS); therefore, studies have been carried out in order to better understand its damaging action in biological systems. In this work, calf thymus DNA, triphosphate nucleotides and isolated bases were incubated with SnCl2 and the results were analyzed through UV spectrophotometry. The presence of stannous ions altered the absorption spectra of all three isolates. The amount of stannous ions associated to DNA was measured by atomic absorption spectrophotometry. Data showed that more than 40% of the initial SnCl2 concentration was present in the samples. Our results are in accordance with the damaging potential of this salt and present evidence that stannous ions can complex with DNA, inducing ROS in its vicinity, which may be responsible for the observed lesions.

Assessment of Aloe vera (L.) genotoxic potential on Escherichia coli and plasmid DNA

Aloe vera is a tropical plant, known in Brazil as babosa and several reputable suppliers produce a stabilized aloe gel for topic use. Since people use Aloe vera topically, they could be exposed to solar ultraviolet light in addition and it might cause a cross damage effect between these agents. The aim of this work was to investigate the biological effects of Aloe vera pulp extract, associated or not to UVA radiation, on Escherichia coli-deficient repair mutants and plasmid DNA, in order to test its genotoxic potential. Data obtained from analysis of survival fractions, bacterial transformation and agarose gel electrophoresis suggest that Aloe vera has genotoxic properties, but it seems not to be able to damage the cell membrane.

Genotoxic potentiality of aqueous extract prepared from Chrysobalanus icaco L. leaves

Plants have been related to our lives, being used as medicine, regardless of scientific evidence of side effects. This work analyses the toxicological effects of Chrysobalanus icaco L. aqueous extract, used in different pathologies. It was studied through: (i) alteration of plasmid pUC 9.1 topology; (ii) survival of bacterial strains submitted, or not, to previous treatment with SnCl2; (iii) transformation efficiency of E. coli strain by the treatment with the plasmid pUC 9.1. In (i), the treatment of the plasmid resulted in DNA single-strand breaks (SSB). A decrease of the lethal effect induced by SnCl2 in presence of the extract was found, while no C. icaco bacterial survival reduction was observed. The transformation efficiency of the plasmid was also reduced. Results suggest that the extract could present a potential genotoxic effect, as demonstrated either by the induction of SSB in plasmid or in transformation efficiency experiments. Finally, it presents an antioxidant action.

Biological effects of stannous chloride, a substance that can produce stimulation or depression of the central nervous system

It was demonstrated that tin, as stannous chloride (SnCl(2)), can facilitate the neuromuscular transmission by accelerating the transmitter release from the nerve terminals in the mouse. When this salt is injected into laboratory animals, it can produce stimulation or depression of the central nervous system. Because calcium (Ca(2+)) influx into the cytoplasm is indispensable to release the transmitter, it would be possible that SnCl(2) increases the Ca(2+) influx at the nerve terminals but not by blocking the K(+) channels. SnCl(2) is known to inhibit the immune response in rodents and to induce tumor generation in thyroid gland. There is no general agreement regarding its genotoxicity and it was discussed that the effects of this salt might depend on the physicochemical conditions and the route of its administration. SnCl(2) has been used in many sectors of human interest, such as food industry and nuclear medicine. This salt is directly administered to human beings endovenously, when it is used as a reducing agent to prepare 99mTc-radiopharmaceuticals which are also used for cerebral studies. SnCl(2) is capable to promote the generation of reactive oxygen species (ROS) that are responsible for the oxidative stress. Oxidative stress has been related with aging and other neurological diseases. So, it is relevant to evaluate other biological effects of SnCl(2). We decided to study these effects using Escherichia coli mutant strains, deficient in DNA repair genes, and supercoiled plasmid DNA. We evaluated the influence of medicinal plants, metal chelating agents, and ROS scavengers against the SnCl(2) deleterious effects. Our results show that SnCl(2) produced lesions in vitro as well as in vivo. This inactivation may be due to the production of ROS. We observed that the genotoxic effect of SnCl(2) was partly inhibited or disappeared, when the treatments were done in the presence of medicinal plants, metal chelating agents, and ROS scavengers. In conclusion, these findings suggest that the SnCl(2) biological effects may be associated with the generation of ROS. Moreover, we can speculate that ROS could be associated with the detrimental effects in the brain due to exogenous or endogenous metals.

Dna damage in peripheral blood nuclear cells assessed by comet assay from individuals submitted to scintigraphic examinations

Stannous chloride (SnCl2) is employed as a reducing agent to obtain Technetium-99m-labelled radiophamaceuticals in nuclear medicine kits, being injected endovenously in humans. Toxic effects of these kits were not studied, thus making it important to evaluate their impact in humans. In this study, the toxic effects were evaluated from peripheral blood nuclear cells (PBNC) from patients who received radiopharmaceuticals obtained using such kits. The analyses included results performed by comet assay. DNA damage was visualized in PBNC samples collected within a time up to 2 hr, and 24 hr after radiopharmaceutical injection in the patients. Initially we observed an increase of comet signals, which subsequently were reduced to zero after 24 hr. The diminishing of comet amounts probably is associated with DNA repair of damaged cells or with the elimination by apoptosis of cells whose DNA are not repaired.

Adaptive response to H(2)O(2) protects against SnCl(2) damage: the OxyR system involvement

The stannous ion, mainly the stannous chloride (SnCl(2)) salt form, is widely used as a reducing agent to label radiotracers with technetium-99m ((99m)Tc). These radiotracers can be employed as radiopharmaceuticals in nuclear medicine procedures. In this case, there is no doubt about absorption of this complex, because it is intravenously administered in humans, although biological effects of these agents have not been fully understood. In this work we used a bacterial system to study the cytotoxic potential of stannous chloride. It is known that SnCl(2) induces lesions that could be mediated by reactive oxygen species (ROS). We, thus, investigated the existence of cross-adaptive response between hydrogen peroxide (H(2)O(2)) and SnCl(2) and the role of the OxyR system known to promote cellular protection against oxidative damages. Here we describe the results obtained with prior treatment of different Escherichia coli strains with sub-lethal doses of H(2)O(2), followed by incubation with SnCl(2). Our data show that H(2)O(2) is capable of inducing cross-adaptive response against the lethality promoted by SnCl(2), suggesting the OxyR system participation through catalase, alkyl hydroperoxide reductase and superoxide dismutase enzymes