Cytostatic, cytotoxic and mutagenic effects of voacristine, an indole alkaloid in wild-type and repair-deficient yeasts

Bioactivity-guided isolation of cytotoxic constituents from three medicinal plants

CONTEXT

The ethanol extracts and their fractions of three Indian medicinal plants, Ervatamia coronaria (Jacq.) Stapf, (Apocynaceae), Mimosa pudica L. (Mimosaceae) and Caesalpinia bonduc (L.) Roxb. (Caesalpiniaceae) were tested for their cytotoxic activity in the brine shrimp lethality (BSL) bioassay and in various cancer cell lines. The plants were selected based on their traditional use in the treatment of cancer/tumors.

OBJECTIVES

To investigate the in vitro cytotoxicity of Ervatamia coronaria, Mimosa pudica and Caesalpinia bonduc.

MATERIALS AND METHODS

Ethanolic extracts and their fractions of E. coronaria, M. pudica and C. bonduc were subjected to cytotoxicity studies using BSL bioassay method with concentrations of 10, 50, 100, 500 and 1000 µg/ml. The alkaloid fraction of E. coronaria with significant cytotoxicity in BSL bioassay was subjected to in vitro cytotoxicity studies with HT-29, A-549, HepG-2, MCF-7 and L-6 cell lines at concentrations of 12.5, 25, 50, 100 and 200 µg/ml and a DNA fragmentation study using the HT-29 cell line.

RESULTS

The alkaloid fractions of E. coronaria and M. pudica showed significant cytotoxicity with LC50 values of 65.83 and 85.10 µg/ml in the BSL bioassay, respectively. The purified alkaloid fraction of E. coronaria exhibited highest cytotoxicity in HT-29, A-549 and MCF-7 cell lines with IC50 values of 32.5, 47.5 and 72.5 µg/ml, respectively, and induced DNA fragmentation in the HT-29 cell line at a concentration of 65 µg/ml.

CONCLUSION

The alkaloid fraction of E. coronaria exhibited significant cytotoxicity. Alkaloids such as ervatamine, apparicine and coronaridine that were earlier reported may be responsible for this activity.

The effects of Tabernaemontana divaricata root extract on amyloid beta-peptide 25-35 peptides induced cognitive deficits in mice

ETHNOPHAMACOLOGICAL RELEVANCE: Tabernaemontana divaricata (TD), a Thai medicinal herb, has been widely used as an analgesic, sedative, or a cough syrup. Moreover, it has been used in traditional rejuvenation remedies as for preventing forgetfulness and improving the memory.

AIM OF STUDY

The present study aimed to determine the effect of TD on Abeta25-35 peptides induced cognitive deficits and acetylcholinesterase activity in mice.

MATERIALS AND METHODS

Mice were pretreated with TDE (250, 500 and 1,000 mg/kg body weight) for 28 days and then received i.c.v. injection of Abeta25-35 peptides. Cognitive performance was evaluated using the Morris water maze (MWM) and step-down avoidance test. The Ellman's colorimetric method was used to investigate the levels of cortical and hippocampal AChE activity.

RESULTS

Abeta25-35 peptides induced the memory impairment and the increased levels of cortical and hippocampal AChE activity. The consumption of TDE significantly improved the memory impairment and attenuated the brain levels of AChE activity induced by Abeta25-35 peptides.

CONCLUSIONS

These findings suggest that subchronic administration of TDE might prevent the Abeta25-35 peptides induced memory deficits by decreasing the AChE activity level. Therefore TDE could potentially be one of nootropic supplements for those elderly people suffering from dementia such as the AD patients.

Vobasinyl-iboga bisindole alkaloids, potent acetylcholinesterase inhibitors from Tabernaemontana divaricata root

The roots of the Thai medicinal plant, Tabernaemontana divaricata (L.) R. Br. ex Roem. & Schult., were investigated for their content of acetylcholinesterase inhibitors. Bioassay-guided fractionation using the Ellman colorimetric method led to the isolation of two bisindole alkaloids, 19,20-dihydrotabernamine and 19,20-dihydroervahanine A. The compounds showed higher inhibitory activity on acetylcholinesterase in comparison with galanthamine, a well-known acetylcholinesterase inhibitor. The inhibitory activity of 19,20-dihydroervahanine A was proved to be specific, reversible and competitive. During the separation process, two inactive bisindole alkaloids, conodurine and tabernaelegantine A, were also isolated. The data suggest that the substitutions at the carbons 11', 12' and 16' might affect the acetylcholinesterase inhibitory activity.

Dose finding in the Ames Salmonella assay

Threshold dose/concentration values, such as the lowest effective dose, minimum effective dose or the lowest effective concentration (LED, MED or LEC, respectively) are in use as an alternative to the mutagen potency measures based on the 'rate' measurements (e.g., the slope of the initial part of the dose-response curve). In this respect, several statistical procedures for the corresponding so-called 'dose finding' were proposed during the last decades. However, most of them disregard the discrete nature of responses such as the plate colony count in the Ames Salmonella assay. When the plate counts agree with the Poisson assumption, two procedures considered here seem to be appropriate for the dose finding. One is based on the stepwise collapsing of the homogeneous control and dose counts; another consists of constructing the confidence limits for the mutation induction factor (MIF). When the dose and control counts are non-overlapping, the simple 'visual' non-parametric estimation of LED is possible. Applicability and validity of the methods is demonstrated with the two data sets on the mutagenicity of the beta-carboline alkaloid, harmine, and one of the oxidation products of apomorphine.

Ervatamia coronaria: chemical constituents and some pharmacological activities

A new bisindole alkaloid, 19,20-dihydroervahanine A was isolated from the stems of Ervatamia coronaria grown in Brazil, together with five known alkaloids: coronaridine, heyneanine, voacristine, voacamine, descarbomethoxyvoacamine and five phenolic acids: vanillic, gentisic, syringic, 4-hydroxybenzoic and salicylic acid. The aqueous and alcoholic extracts, when administered p.o. or i.p. to rats 1 h before subplantar injection of carrageenin had a significant anti-inflammatory effect. The alcoholic extract also had an analgesic effect and increased the pentobarbital induced sleeping time.

Genotoxicity of the isoquinoline alkaloid berberine in prokaryotic and eukaryotic organisms

Berberine, a medically important isoquinoline alkaloid, was tested for the presence of genotoxic, mutagenic and recombinogenic activities in microorganisms. This alkaloid did not show genotoxic activity with or without metabolic activation in the SOS chromotest. It was also unable to induce significant cytotoxic, mutagenic or recombinogenic effects during treatments performed under nongrowth conditions. However, in dividing cells, this alkaloid induced important cytotoxic and cytostatic effects in proficient and repair-deficient Saccharomyces cerevisiae strains. Among the different repair-deficient mutants examined, a mutant blocked in the DNA strand-break repair pathway (rad52-1) was found to be the most sensitive to the cytotoxic effect of berberine. A triple mutant blocked in the excision (rad2-6), in the mutagenic (rad6-1) and in the recombinogenic (rad52-1) repair pathways demonstrated the same sensitivity as the single rad52-1 mutant. In dividing cells, the induction of frameshift and mitochondrial mutations, as well as crossing over, showed that this alkaloid is not a potent mutagenic agent. The possible implication of DNA topoisomerases in berberine toxicity mechanisms is discussed.

Chapter 1 Allelochemical Properties or the Raison D'être of Alkaloids

This chapter provides evidence that alkaloids are not waste products or functionless molecules as formerly assumed, but rather defense compounds employed by plants for survival against herbivores and against microorganisms and competing plants. These molecules were developed during evolution through natural selection in that they fit many important molecular targets, often receptors, of cells, which are seen in molecules that mimic endogenous neurotransmitters. The chapter discusses that microorganisms and herbivores rely on plants as a food source. Since both have survived, there must be mechanisms of adaptations toward the defensive chemistry of plants. Many herbivores have evolved strategies to avoid the extremely toxic plants and prefer the less toxic ones. Many herbivores have potent mechanisms to detoxify xenobiotics, which allow the exploitation of at least the less toxic plants. In insects, many specialists evolved that are adapted to the defense chemicals of their host plant, in that they accumulate these compounds and exploit them for their own defense. Alkaloids function as defense molecules against insect predators in the examples studied, and this is further support for the hypothesis that the same compound also serves for chemical defense in the host plant. It needs more experimental data to understand fully the intricate interconnections between plants, their alkaloids, and herbivores, microorganisms, and other plants.

Genotoxicity of the boldine aporphine alkaloid in prokaryotic and eukaryotic organisms

The aporphine alkaloid boldine, present in Peumus boldus (boldo-do-Chile) widely used all over the world, was tested for the presence of genotoxic, mutagenic and recombinogenic activities in microorganisms. This alkaloid did not show genotoxic activity with or without metabolic activation in the SOS chromotest and Ames tester strains TA100, TA98 and TA102. It was not able to induce point and frameshift mutations in haploid Saccharomyces cerevisiae cells. However, mitotic recombinational events such as crossing-over and gene conversion were weakly induced in diploid yeast cells by this alkaloid. Also, boldine was able to induce weakly cytoplasmic 'petite' mutation in haploid yeast cells.

Genotoxic, mutagenic and recombinogenic effects of rauwolfia alkaloids

In the last decade, the possible correlation between the use of reserpine and rauwolfia drugs as antihypertensive agents and breast cancer incidence has been investigated. For the purpose of evaluating the mutagenic and genotoxic effects of these drugs, reserpine and ajmalicine were studied using the SOS Chromotest and the induction of gene conversion, crossing-over and reverse mutation in the yeast diploid strain XS2316. The results indicated a lack of genotoxic, mutagenic and recombinogenic effects.

New pathway for the biodegradation of indole in Aspergillus niger

Indole and its derivatives form a class of toxic recalcitrant environmental pollutants. The growth of Aspergillus niger was inhibited by very low concentrations (0.005 to 0.02%) of indole, even when 125- to 500-fold excess glucose was present in the medium. When 0.02% indole was added, the fungus showed a lag phase for about 30 h and the uptake of glucose was inhibited. Indole was metabolized by a new pathway via indoxyl (3-hydroxyindole), N-formylanthranilic acid, anthranilic acid, 2,3-dihydroxybenzoic acid, and catechol, which was further degraded by ortho cleavage. The enzymes N-formylanthranilate deformylase, anthranilate hydroxylase, 2,3-dihydroxybenzoate decarboxylase, and catechol dioxygenase were induced by indole as early as after 5 h of growth, and their activities were demonstrated in a cell-free system.