Influence of the carcinogenic oestrogen diethylstilboestrol on the intracellular calcium level in C6 rat glioma cells

Evaluation of combination effects of ethanolic extract of Ziziphus mucronata Willd. subsp. mucronata Willd. and antibiotics against clinically important bacteria

A pragmatic approach to the treatment of infectious diseases with multicausal agents and prevention of the development of resistant isolates is the combination of herbal remedies with the first-line antimicrobial agents to which most of them have become resistant. This study evaluated the interactions between the ethanolic bark extract of Ziziphus mucronata with known antimicrobial agents in vitro. In this study, the results showed that varied zones of inhibitions (ZME-chloramphenicol (17-42 mm), ZME-amoxicillin (17-35 mm), ZME-tetracycline (17-36 mm), ZME-ciprofloxacin (20-41 mm), ZME-nalidixic acid (17-34 mm), and ZME-kanamycin (17-38 mm)) were produced by the antibacterial combinations. At the highest combined concentrations, 12 isolates (ZME-ciprofloxacin) > 10 isolates (ZME-chloramphenicol) = (ZME-kanamycin) > 6 isolates (ZME-amoxicillin) = (ZME-nalidixic acid) and 5 isolates (ZME-tetracycline) were inhibited with zones of inhibition greater than 20 ± 1.0 mm. Although the agar diffusion assay suggested that the interactions between the ethanolic extract of Z. mucronata and the antibiotics were both synergistic and additive in nature, the fractional inhibitory concentration indices (FICI) showed that the interactions were synergistic (54.17%), additive (27.78%), indifferent (16.67%), and antagonistic (1.39%). While the fractional inhibitory concentration indices (FICIs) for synergism ranged between 0.00391 and 0.5, that of additivity ranged between 0.516 and 1.0, indifferences ranged between 1.062 and 3.0 and antagonistic interaction was 5.0. The synergistic effects implied that the antibacterial combinations would be more effective and useful in the treatment of multicausal and multidrug-resistant bacteria than a single monotherapy of either antibacterial agent.

Phenolic content and antioxidant property of the bark extracts of Ziziphus mucronata Willd. subsp. mucronata Willd

BACKGROUND

Several plants traditionally used in treatment of a variety of infections in South Africa are reported in ethnobotanical surveys. Many of these plants including Ziziphus mucronata subsp. mucronata lack scientific reports to support their medicinal importance.

METHODS

The antioxidant activities and phenolic contents of the acetone, ethanol and aqueous extracts of the stems of Z. mucronata subsp. mucronata were evaluated using in vitro standard methods. The total phenol, total flavonoids and proanthocyanidin content were determined spectrophotometrically. Quercetin, Tannic acid and catechin equivalents were used for these parameters. The antioxidant activities of the stem bark extracts of this plant were determined by ABTS, DPPH, and ferrous reducing antioxidant property (FRAP) methods.

RESULTS

The quantity of the phenolic compounds, flavonoids and proanthocyanidins detected differ significantly in the various extracts. The phenolics were significantly higher than the flavonoids and proanthocyanidin contents in all the extracts investigated. The ferric reducing ability and the radical scavenging activities of the extracts were very high and dose-dependent. The ethanol extract had the highest antioxidant activity, followed by the acetone extract while the aqueous extract was the least active. Reacting with ABTS, the 50% inhibitory concentrations (IC50) were (0.0429 ± 0.04 mg/ml) for aqueous, (0.0317 ± 0.04 mg/ml) for acetone and (0.0306 ± 0.04 mg/ml) for ethanol extracts while they inhibited DPPH radical with 50% inhibitory concentration (IC50) values of 0.0646 ± 0.02 mg/ml (aqueous), 0.0482 ± 0.02 mg/ml (acetone) and 0.0422 ± 0.03 mg/ml (ethanol).

CONCLUSIONS

A correlation between the antioxidant activity and the total phenolic contents of the extracts indicated that phenolic compounds were the dominant contributors to the antioxidant activity of the plant. This study, therefore, demonstrated that Z. mucronata subsp. mucronata has strong antioxidant property and free radical scavenging capability.

Mechanisms of diethylstilbestrol-induced calcium movement in MG63 human osteosarcoma cells

The effect of the estrogen diethylstilbestrol (DES) on cytosolic free Ca(2+) levels ([Ca(2+)](i)) in MG63 human osteoblasts was explored by using fura-2 as a Ca(2+) indicator. DES at concentrations between 5--20 microM induced an immediate increase in [Ca(2+)](i) in a concentration-dependent manner with an EC(50) of 10 microM. Removing extracellular Ca(2+) reduced the Ca(2+) signal by 70%. Pretreatment with 50 microM La(3+) or 10 microM of nifedipine, verapamil and diltiazem did not change 20 microM DES-induced [Ca(2+)](i) increases. Addition of 3 mM Ca(2+) increased [Ca(2+)](i) in cells pretreated with 20 microM DES in Ca(2+)-free medium. Pretreatment with 1 microM thapsigargin (an endoplasmic reticulum Ca(2+) pump inhibitor) to deplete the endoplasmic reticulum Ca(2+) store partly inhibited 20 microM DES-induced Ca(2+) release, but addition of carbonylcyanide m-chlorophenylhydrazone (CCCP; a mitochondrial uncoupler) and thapsigargin together abolished DES-induced Ca(2+) release. Conversely, pretreatment with 20 microM DES abrogated CCCP- and thapsigargin-induced Ca(2+) release. Inhibition of phospholipase C activity with 2 microM U73122 did not alter 20 microM DES-induced Ca2+ release. Another estrogen 17beta-estradiol also increased [Ca(2+)](i) in a concentration-dependent manner with an EC50 of 7 microM. Together, the data indicate that in human osteoblasts, DES increased [Ca(2+)](i) via causing Ca(2+) release from both mitochondria and the endoplasmic reticulum in a phospholipase C-independent manner, and by causing Ca(2+) influx.

Nongenomic stimulation of nitric oxide release by estrogen is mediated by estrogen receptor alpha localized in caveolae

Acute administration of 17beta-estradiol (E(2)) exerts antiatherosclerotic effects in healthy postmenopausal women. The vasoprotective action of E(2) may be partly accounted for by a rapid increase in nitric oxide (NO) levels in endothelial cells (ECs). However, the signaling mechanisms producing this rise are unknown. In an attempt to address the short-term effect of E(2) on endothelial NO production, confluent bovine aortic endothelial cells (BAECs) were incubated in the absence or presence of E(2), and NO production was measured. Significant increases in NO levels were detected after only 5 min of E(2) exposure without a change in the protein levels of endothelial NO synthase (eNOS). This short-term effect of estrogen was significantly blunted by various ligands which decrease intracellular Ca(2+) concentration. Furthermore, plasma membrane-impermeable BSA-conjugated E(2) (E(2)BSA) stimulated endothelial NO release, indicating that in the current system the site of action of E(2) is on the plasma membrane rather than the classical nuclear receptor. The partial antagonist tamoxifen did not block E(2)-induced NO production; however, a pure estrogen receptor alpha (ERalpha) antagonist ICI 182,780 completely inhibited E(2)-stimulated NO release. The binding of E(2) to the membrane was confirmed using FITC-labeled E(2)BSA (E(2)BSA-FITC). Western blot analysis showed that plasmalemmal caveolae possess ERalpha in addition to well-known caveolae-associated proteins eNOS and caveolin. This study demonstrates that the nongenomic and short-term effect of E(2) on endothelial NO release is Ca(2+)-dependent and occurs via ERalpha localized in plasmalemmal caveolae.

Modulation of the intracellular calcium level in mammalian cells caused by 17beta-estradiol, different phytoestrogens and the anti-estrogen ICI 182780

In previous investigations it was shown that the synthetic estrogen diethylstilbestrol (DES) induces a rise of the intracellular calcium level ([Ca2+]i) in C6 rat glioma cells [P. Tas, H. Stopper, K. Koschel, D. Schiffmann, Influence of the carcinogenic oestrogen diethylstilboestrol on the intracellular calcium level in C6 rat glioma cells. Toxic. In vitro 5 (1991) 463-465] which is accompanied by changes of the arrangement of the cytoskeleton. In the present study, we compared the induction of these effects in COS (monkey kidney cells) lacking estrogen receptors (ER) with those in RUCA-I (rat endometrial carcinoma) cells containing ER. The [Ca2+]i in RUCA-I and COS cells following 17beta-estradiol (ES), genistein (GEN), daidzein (DZ) and coumestrol (CES) treatment was analyzed. A significant increase of [Ca2+]i induced by all compounds was observed in RUCA-I cells. No effects were detected in COS cells after ES and GEN treatment. The anti-estrogen ICI 182780 completely blocked the ES-and GEN-induced rise of [Ca2+]i. Dose and time dependencies of changes of calcium levels were analyzed and a biphasic response could be observed. The actin staining showed disintegrated stress fibers in RUCA-I cells. The degree of the observed effects correlates with the known estrogenicity of the applied compounds (DES > ES > GEN). It remains to be elucidated whether or not the effects observed are mediated by the "classic" genomic estrogen receptor pathway or by alternate nongenomic or receptor-independent pathways.

Effects of (+)-, (-)- and (+/-)-indenestrols A and B on microtubule distribution and cytotoxicity in Chinese hamster V79 cells

We have reported that (+)-, (-)- and (+/-)-indenestrols A and B (IA and IB respectively) inhibit the polymerization of microtubule proteins isolated from porcine brain in vitro. In this study, the effects of (+)-, (-)- and (+/-)-IA and IB on the relative plating efficiency, chromosome number and cellular microtubular architecture of Chinese hamster V79 cells, detected with a fluorescent anti-tubulin antibody, were investigated. The results indicated that the effect of (+/-)-IA was similar to that of diethylstilbestrol and that of (+/-)-IB was greater than that of (+/-)-IA. We also determined the effects of the optically active IA and IB isomers and found that the rank order of cytotoxic activity of the IA and IB series was: (-)-IA > (+/-)-IA > (+)-IA and (+/-)-IB > or = (-)-IB > (+)-IB. Furthermore, we studied the intracellular disturbance of microtubule formation induced by these compounds and found that (-)-IA had by far the greatest disruptive effect.