Association of ethnicity and acute kidney injury after cardiac surgery in a South East Asian population.

BACKGROUND: Postoperative acute kidney injury (AKI) is a frequent and serious complication after cardiac surgery. Clinical factors alone have failed to accurately predict the incidence of AKI after cardiac surgery. Ethnicity has been shown to be a predictor of AKI in the Western population. We tested the hypothesis that ethnicity is an independent predictor of AKI in patients undergoing cardiac surgery in a South East Asian population. METHODS: A total of 1756 consecutive patients undergoing cardiac surgery were prospectively recruited. Among them, data of 1639 patients met the criteria for analysis. There were 1182 Chinese, 195 Indian, and 262 Malay patients. The main outcome was postoperative AKI, defined as a 25% or greater increase in preoperative to a maximum postoperative serum creatinine level within 3 days after surgery. RESULTS: Five hundred and seventy-nine patients (35.3%) developed AKI after cardiac surgery. Ethnicity was shown to be an independent predictor of AKI after cardiac surgery with Indians and Malays having a higher risk of developing AKI when compared with Chinese patients (odds ratio: Indian vs Chinese 1.44, Malay vs Chinese 1.51). CONCLUSIONS: Indians and Malays have a higher risk of developing AKI after cardiac surgery than Chinese in a South East Asian population. Ethnicity was shown to be an independent predictor of AKI after cardiac surgery.

Polymodal therapy for high grade gliomas: a case report of favourable outcomes following intraoperative radiation therapy.

High grade gliomas, frequently with their infiltrative nature, often make the outcome from neurosurgical intervention alone unsatisfactory. It is recognized that adjuvant radiochemotherapy approaches offer an improved prognosis. For these reasons, we opted for surgical debulking, intraoperative radiation therapy (IORT) in combination with whole brain irradiation therapy and chemotherapy (temozolamide cycles) in the management of a 42 year-old lady with Glioblastoma Multiforme (GBM). Her troublesome symptoms improved after 3 months of this polymodal therapy and remained independently functional for more than two years.

Rotenoids mediate potent cancer chemopreventive activity through transcriptional regulation of ornithine decarboxylase.

For the discovery of new cancer chemopreventive agents, we have studied the potential of plant extracts to inhibit phorbol ester-induced ornithine decarboxylase (ODC) activity in cell culture. Four active rotenoids were obtained from the African plant Mundulea sericea (Leguminosae). These isolates were highly potent when evaluated for inhibition of chemically induced preneoplastic lesions in mammary organ culture and inhibition of papillomas in the two-stage mouse skin model, and they appear to function by a unique mechanism at the level of ODC messenger RNA expression. Based on our findings, rotenoids can be regarded as promising new chemopreventive or anticancer agents.

Added value of MRI for the diagnosis of adnexal torsion in children and adolescents after inconclusive ultrasound examination.

PURPOSE: The purpose of this study was to assess the performance of magnetic resonance imaging (MRI) in children and adolescents with suspected adnexal torsion (AT) after inconclusive initial ultrasound examination. MATERIALS AND METHODS: Twenty-eight girls with a mean age of 12±4 (SD) years (range: 1 month to 18years) were included. All had clinically suspected AT and inconclusive initial ultrasound findings followed by pelvic MRI as a second-line imaging modality. The final diagnosis was obtained by surgery or follow-up. Two radiologists blinded to the clinical, ultrasound and surgical data, retrospectively and independently reviewed MRI examinations. Clinical and MRI features associated with AT were searched for using univariate analyses. RESULT: Among the 28 patients, 10/28 patients (36%) had AT and 22/28 (79%) had an ovarian or tubal mass. AT was associated with an age<13years (OR: 10.7; 95% CI: 1.3-148.2) (P=0.022) and a whirlpool sign at MRI (OR: 61.0; median unbiased estimate, 7.2) (P<0.0001). When a mass was present, the best quantitative MRI criteria for AT were mass volume and ovary-corrected volume≥30cm3 (κ=0.72 and 0.61, respectively), mass axis length≥5cm (κ=0.90), and mass surface area≥14 cm2 (κ=0.58), with moderate to almost perfect interobserver agreement. The overall sensitivity, specificity and accuracy of MRI for the diagnosis of AT were 100% (10/10; 95% CI: 69-100), 94% (17/18; 95% CI: 73-100) and 96% (27/28; 95% CI: 82-100) respectively, with perfect interobserver agreement (κ=1). CONCLUSION: In pediatric patients with suspected AT and inconclusive initial ultrasound examination, a strategy including MRI as a second-line imaging modality should be considered if MRI does not delay a potential surgery.

Early Malaysian experience on the use of head and neck localizers in the precision radiotherapy of intra and extra cranial sites for first 28 cases.

Precision Radiotherapy at high doses require a fixed, referable target point. The frame system fulfills the required criteria by making the target point relocatable and fixed within a stereotactic space. Since December 2001, we have treated 28 central and peripheral nervous system lesions using either radiosurgery as a single high dose fraction or fractionated 3-dimensional conformal radiotherapy using a lower dose and a multi-leaf collimator. Various pathological lesions either benign or malignant were treated. Eighty six percent of our treated lesions showed growth restraint, preventing them from causing new symptoms with a median follow-up duration of 20.5 months. However, the true benefit from this technique would require a long-term follow-up to document the progress.

The prognostic value of early follow-up computerized tomography of the brain in adult traumatic brain injury.

A total of 31 adult patients with moderate and severe head injury were assessed clinically on admission for Glasgow Coma Scale (GCS) and short test of mental status (STMS) on follow-up and compared to their initial and follow up CT scan. Good predictors were admission GCS, midline shift, volume of subdural haemorrhage in the initial CT scan of the brain as well as the presence of post-traumatic hydrocephalus, gliosis and site of gliosis in the follow-up CT scan. There was no direct correlation between the significant predictors on the first CT scan and the follow-up CT scan of the brain.

Inhibitory effect of munetone, an isoflavonoid, on 12-O-tetradecanoylphorbol 13-acetate-induced ornithine decarboxylase activity.

Starting with an extract derived from the bark of Mundulea sericea Willd. (Leguminosae) that was active in the process of inhibiting 12-O-tetradecanoylphorbol 13-acetate (TPA)-induced ornithine decarboxylase activity (ODC) in cultured mouse epidermal ME 308 cells, the isoflavonoid munetone was isolated and identified as an active principle (IC50 = 46 ng/ml). Topical application of munetone (0.04-5 micromol) to the skin of CD-1 mice 2 h prior to treatment with TPA (10 nmol) resulted in dose-dependent inhibition of epidermal ODC activity. In addition, munetone inhibited TPA-independent c-Myc-induced ODC activity with cultured BALB/c c-MycER cells, as well as 7,12-dimethylbenz[a]anthracene (DMBA)-induced preneoplastic lesion formation in a mouse mammary gland organ culture (MMOC) system. These data suggest the potential of munetone to serve as a cancer chemopreventive agent by virtue of blocking the process of tumor promotion.

Thromboxane A2 synthase inhibition and thromboxane A2 receptor blockade by 2-[(4-cyanophenyl)amino]-3-chloro-1,4-naphthalenedione (NQ-Y15) in rat platelets.

The effects of 2-[(4-acetylphenyl)amino]-3-chloro-1,4-naphthalenedione (NQ-Y15), a synthetic 1,4-naphthoquinone derivative, on platelet activity and its mechanism of action were investigated. NQ-Y15 caused a concentration-dependent inhibition of the aggregation induced by thrombin, collagen, arachidonic acid (AA), and A23187. The IC50 values of NQ-Y15 on thrombin (0.1 U/mL)-, collagen (10 microg/mL)-, AA (50 microM)-, and A23187 (2 microM)-induced aggregation were 36.2 +/- 1.5, 6.7 +/- 0.7, 35.4 +/- 1.7, and 93.1 +/- 1.4 microM, respectively. NQ-Y15 also inhibited thrombin-, collagen-, AA-, and A23187-stimulated serotonin secretion in a concentration-dependent manner. However, a high concentration (100 microM) of NQ-Y15 showed no significant inhibitory effect on ADP-induced primary aggregation, which is independent of thromboxane A2 (TXA2) production in rat platelets. In fura-2-loaded platelets, the elevation of intracellular free calcium concentration stimulated by AA, thrombin, and 4-bromo-A23187 was inhibited by NQ-Y15 in a concentration-dependent manner. The formation of TXA2 caused by AA, thrombin, and collagen was inhibited significantly by NQ-Y15. NQ-Y15 inhibited TXA2 synthase in intact rat platelets, since this agent reduced the conversion of prostaglandin (PG) H2 to TXA2. Similarly, NQ-Y15 selectively inhibited the TXA2 synthase activity in human platelet microsomes, whereas it had no effect on activity of phospholipase A2, cyclooxygenase, and PGI2 synthase in vitro. NQ-Y15 inhibited platelet aggregation induced by the endoperoxide analogue U46619 in human platelets, indicating TXA2 receptor antagonism, possibly of a competitive nature. These results suggest that the antiplatelet effect of NQ-Y15 is due to a combination of TXA2 synthase inhibition with TXA2 receptor blockade, and that it may be useful as an antithrombotic agent.

Excision repair of adozelesin-N3 adenine adduct by 3-methyladenine-DNA glycosylases and UvrABC nuclease.

Adozelesin is a synthetic analog of the antitumor antibiotic CC-1065, which alkylates the N3 of adenine in the minor groove in a sequence-selective manner. Since the cytotoxic potency of a DNA alkylating agent can be modulated by DNA excision repair system, we investigated whether nucleotide excision repair (NER) and base excision repair (BER) enzymes are able to excise the bulky DNA adduct induced by adozelesin. The UvrABC nuclease and 3-methyladenine-DNA glycosylase, that exhibit a broad spectrum of substrate specificity, were selected as typical NER and BER enzymes, respectively. The adozelesin-DNA adduct was first formed in the radiolabeled restriction DNA fragment and its excision by purified repair enzymes was monitored on a DNA sequencing gel. The treatment of the DNA adduct with a purified UvrABC nuclease and sequencing gel analysis of cleaved DNA showed that UvrABC nuclease was able to incise the adozelesin adduct. The incision site corresponded to the general nuclease incision site. Excision of this adduct by 3-methyladenine-DNA glycosylases was determined following the treatment of the DNA adduct with a homogeneous recombinant bacterial, rat and human 3-methyladenine-DNA glycosylases. Abasic sites generated by DNA glycosyalses were cleaved by the associated lyase activity of the E. coli formamidopyrimidine-DNA glycosylase (Fpg). Resolution of cleaved DNA on a sequencing gel showed that the DNA glycosylase from different sources could not release the N3-adenine adducts. A cytotoxicity assay using E. coli repair mutant strains showed that E. coli mutant strains defective in the uvrA gene were more sensitive to cell killing by adozelesin than E. coli mutant strain defective in the alkA gene or the wild type. These results suggest that the NER pathway seems to be the major excision repair system in protecting cells from the cytotoxicity of adozelesin.

Cell cycle was disturbed in the MNNG-induced initiation stage during in vitro two-stage transformation of Balb/3T3 cells.

In vitro two-stage transformation, an important method for the screening of carcinogens, is a valuable approach for the mechanistic study of multi-stage carcinogenesis. However, very little is known about the molecular and cellular mechanisms, particularly in terms of cell cycle control during in vitro two-stage transformation. We improved the in vitro two-stage transformation method using N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) as an initiator and cadmium as a promoter, and reconfirmed the promotional effect of cadmium (Fang et al., 2001a). To determine the alterations of cell cycle control in the MNNG-induced initiation stage during transformation, we examined the effects of MNNG on Balb/3T3 A31 cell growth, and determined the alterations of the protein and/or mRNA levels of cyclins B1, D1, E, and G, PCNA, GADD45, p27, and wild-type p53. After 4 hour treatment of MNNG, populations of G2/M phase distribution and apoptotic fraction and the cyclin G mRNA level increased, while the cyclin B1 mRNA level decreased in a concentration-dependent manner. Wild-type p53, p27, and GADD45 protein levels also increased as a function of MNNG concentrations. However, cyclin D1, cyclin E, and PCNA expressions remained unchanged. During the initiation stage, PCNA protein expression decreased on the first day after MNNG-treatment, then increased gradually during the following 6 days, and further increased on the first day after cadmium treatment. Although wild-type p53 and p27 protein expressions also showed temporary retardation on the first day after MNNG-treatment, the expressions increased gradually during the following 6 days, but decreased rapidly by the cadmium treatment. These results indicated that during the initiation stage, MNNG induced G2/M arrest and apoptosis with increased expressions of wild-type p53, p27, and GADD45 proteins; and down-regulated mRNA level of cyclin B1 and up-regulated mRNA level of cyclin G. In addition, although a few of the G2/M-arrested cells proliferated gradually, most cells continued to be suppressed and inactivated by the over-expressions of wild-type p53 and p27 until the cadmium treatment.

Cadmium-induced alterations of connexin expression in the promotion stage of in vitro two-stage transformation.

During the multistage carcinogenesis, functions of several key genes involved in the cell cycle control and cell-cell communication can be damaged. Gap junction intercellular communication (GJIC) is known to transfer small, water-soluble molecules through intercellular channels composed of proteins called connexins (Cxs). Therefore, aberrant expression of Cx may be one of the critical factors for the clonal expansion of initiated cells during the two-stage transformation. We already improved the classical in vitro two-stage transformation method using N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) as an initiator and cadmium as a promoter on Balb/3T3 A31 cells, and reconfirmed the promotional effect of cadmium with this method (Fang, M.Z., Cho, M.H., Lee, H.W., 2001. Improvement of in vitro two-stage transformation assay and detection of the promotional effect of cadmium, Toxicol. In Vitro (in press). In this study, precise roles of Cd on Cx expression in normal Balb/3T3 A31 and during the promotion stage of the in vitro two-stage transformation were elucidated. For this purpose, the Cx43, Cx32 and Cx26 protein levels, Cx43 and Cx26 mRNA levels and the cellular distribution location of Cx43 protein were determined. Normal Balb/3T3 cells expressed Cx43 and Cx32, but not Cx26. After a short-term treatment of cadmium on normal cells, phosphorylation of Cx43 protein increased and Cx32 protein level decreased. However, during the promotion stage of the in vitro two-stage transformation, transformed cells treated with cadmium for long periods expressed Cx43 and Cx32 highly, similar to the level of normal Balb/3T3 cells, compared to the nontransformed cells. Moreover, Cx43 of the transformed cells was distributed mostly in the perinuclear region rather than the intercellular membrane. These data suggest that cadmium may inhibit the GJIC by increasing the phosphorylation of Cx43 and decreasing the expression of Cx32 in the normal Balb/3T3 A31 cells. Our results also suggest that these changes are not associated with the cell transformation; transformed cells may reexpress Cx43 and Cx32 similar to the normal cells, though Cx43 protein is distributed aberrantly during the transformation process. Further studies are needed to clarify the relationship between transformation and posttranslational modification of the Cx proteins.

Effect of T-2 toxin on lipid peroxidation in rats: elevation of conjugated diene formation.

A single dose of T-2 toxin (3.6 mg/kg, oral) enhanced conjugated diene formation in rat liver, spleen, kidney, thymus and bone marrow, implying that lipid peroxidation was stimulated. Lipid peroxidation showed apparent specificity in each organ as time elapsed (1-6 h). In liver and kidney maximum stimulation (+74% and +72%, respectively) was noted at 1 h after T-2 treatment. In spleen and thymus, maximum values were observed at 3 h (+95% and +32%, respectively). In bone marrow, a continuous elevation was noted which reached a maximum at 6 h (+112%). Results obtained from serum transaminase assay and histological examination suggested that T-2 toxin exhibited low hepatotoxicity even when the rat received a dose close to the oral LD50.

Enhancement of biliary excretion of aflatoxin B(1) and suppression of hepatic ornithine decarboxylase activity by 2-(allylthio)pyrazine in rats.

2-(Allylthio)pyrazine (2-AP), a synthetic pyrazine derivative with an allylsulfur moiety, has protective effects against chemically-induced hepatic toxicity. Previous studies have shown that 2-AP significantly reduces the formation of preneoplastic foci in rats exposed to aflatoxin B(1) (AFB(1)). The present study was designed to determine whether 2-AP could increase the biliary excretion of metabolites of AFB(1) in rats treated with this carcinogen and whether the agent could alter the activity of ornithine decarboxylase (ODC), which is considered to be associated with tumor promotion. Rats were pretreated with 2-AP (p.o.) at a daily dose of 50 mg/kg for 5 consecutive days. AFB(1) (5 mg/kg) was administered intraperitoneally 2 h after the last dose of 2-AP. Amounts of principal AFB(1) metabolites, AFB(1)-glutathione and a glucuronide conjugate secreted in bile juice was increased by 56 and 50%, respectively, after the 2-AP treatment. Levels of radiolabelled AFB(1) covalently bound to calf thymus DNA catalyzed by microsomes obtained from 2-AP-treated rats (10 and 50 mg/kg, for 5 days) were reduced by 47 to 66%. ODC activity in AFB(1)-treated rats was determined by the three-step medium-term hepatocarcinogenesis assay. Rats were treated with 2-AP at the daily doses of 10, 25 and 50 mg/kg for 16 consecutive days. During this period, four repeated doses of AFB(1) (1.0 mg/kg) were given to the animals. Rats were then subjected to two-third partial hepatectomy, followed by administration of phenobarbital. 2-AP inhibited AFB(1)-induced ODC activity by 40 to 66%, as determined at the 44th day. Inhibition of AFB(1)-induced ODC activity by 2-AP in conjunction with acceleration of AFB(1) elimination through metabolic conjugation may contribute to its chemopreventive effects against this carcinogen.

Evaluation of the mutagenic and cytostatic potential of aristolochic acid (3,4-methylenedioxy-8-methoxy-10-nitrophenanthrene-1-carboxylic acid) and several of its derivatives.

Aristolochic acid (1), a constituent of Aristolochia species, has been used for medicinal purposes since the Graeco-Roman period. Following the observation that the compound was mutagenic and carcinogenic, it was removed from pharmaceutical products. Consistent with previous reports, we have found that 1 serves as a direct-acting mutagen in Salmonella typhimurium strains TA100, TA102, TA1537 and TM677, but was not active in the nitroreductase-deficient strains TA98NR and TA100NR. However, aristolic acid (2), a compound that differs in structure only by the absence of the nitro group, was also found to be a direct-acting mutagen in Salmonella strains TA98, TA100, TA102, TA1537, and TM677, as well as strains TA98NR and TA100NR. Both compounds (1 and 2) were active mutagens when evaluated with cultured Chinese hamster ovary cells. Thus, in contrast to previous suggestions, the nitro group at position 10 is not required to induce a mutagenic response. Also, a series of structural relatives (the methyl esters of 1 and 2 (3 and 4, respectively), aristolochic acid-D (5), aristolactam (6), aristolactam A-II (7), and aristolactam-N-beta-D-glucoside (8)) were evaluated for mutagenic potential with Salmonella typhimurium strain TM677 and found to be inactive. Since compounds 3 and 4 were found to be active mutagens with Salmonella typhimurium strains TA98, TA100, TA102 and TA1537 (sufficient quantities of compounds 5-8 were not available for testing), differential sensitivity of the tester strains unrelated to mutagenic potential is suggested. Further, compounds 1, 2, and 6-8 were evaluated for potential to inhibit growth with cultured KB or P388 cells. P388 cells were substantially more sensitive, and compound 1 was the most active of the materials tested (ED5 = 0.58 microM). Compound 6 also demonstrated appreciable activity (ED50 = 4.2 microM), as did compound 8 (ED50 = 6.0 microM). It therefore appears that phenanthrene-ring substituents, in addition to the nitro group at position 10, serve important roles for biological potential. In considering the carcinogenic event induced by aristolochic acid, these functionalities should also be taken into account.

Determination of metoprolol enantiomers in human urine by coupled achiral-chiral chromatography.

Achiral chiral column switching HPLC assay was developed to allow the separation and quantitation of the enantiomers of metoprolol in human urine by means of fluorescence detection. Urine samples were prepared by liquid liquid extraction, followed by HPLC. The racemic metoprolol and internal standard were separated from the interfering components in urine and quantified on the silica column, and the enantiomers were determined on a Chiralcel OD chiral stationary phase. The two columns were connected by a switching valve equipped with a silica trap column. Detection limit was 25 ng/ml for each enantiomer. The intra-day variation ranged between 0.38 and 4.94% in relation to the measured concentration and the inter-day variation was 0.15-3.13%. It has been applied to the determination of (R)-(+)-metoprolol and (S)-(-)-metoprolol in urine from healthy volunteers dosed with racemic metoprolol tartrate.

Effects of nonylphenol, bisphenol A, and their mixture on the viviparous swordtail fish (Xiphophorus helleri).

A number of fish species have been used for studies on endocrine disrupting chemicals (EDCs). However, despite the widespread use of oviparous fish, relatively little attention has been given to viviparous species. This study investigated the effects of EDCs in a viviparous fish and examined the possible usefulness of the fish as an alternative model for the studies on EDCs. Swordtails (Xiphophorus helleri) were exposed to nonylphenol (NP), bisphenol A (BPA), and their mixture. Both short-term (3-d) and relatively long-term (60-d) exposures were carried out using adult male and 30-d-old juvenile fish, respectively. Following the short-term exposure, both NP and BPA caused vitellogenin mRNA expression. Flow cytometric analysis and terminal deoxynucleotidyl transferase assay on the testes of treated fish indicated reproductive damage. Histopathological analysis found degenerative and necrotic cells in seminiferous tubules following the exposure to 100 ppb NP. The testes with lesions were also associated with highly suppressed spermatogenesis. Following the long-term exposure, both NP and BPA exposures significantly affected the growth of swordtails. In all cases, the results showed that the mixture was always more potent than a single chemical and that swordtail fish can be a useful model for the study of endocrine disruptors.

Cytotoxic constituents of Psoralea corylifolia.

A coumestan derivative, psoralidin (1) was found to be a cytotoxic principle of the seeds of Psoralea corylifolia L. (Leguminosae) with the IC50 values of 0.3 and 0.4 microg/ml against the HT-29 (colon) and MCF-7 (breast) human cancer cell lines, respectively. A coumarin, angelicin (2) was also isolated as a marginally cytotoxic agent along with an inactive compound, psoralen (3) from the plant. The isolates 1-3 were not active against the A541 (lung) and HepG2 (liver hepatoma) cancer cell lines.

Chiral separation of the enantiomers of metoprolol and its metabolites by high performance liquid chromatography.

(1'R, 2R)-, (1'R, 2S)-, (1'S, 2R)- and (1'S, 2S)-alpha-hydroxymetoprolol; (2R)- and (2S)-O-desmethylmetoprolol; and (2R)- and (2S)-metoprolol acid are major metabolites of (2R)-and (2S)-metoprolol, beta-adrenergic antagonist. The focus of most chiral separation methods until now has been on determination of the enantiomeric parent drug. However, it is just as important to be able to follow the metabolism of the enantiomers and their possible chiral metabolites. Therefore, for the study of stereoselective metabolism and pharmacokinetics of metoprolol, the chiral separation of the enantiomers of metoprolol and its metabolites has been investigated using four chiral stationary phases, i.e., Chiralcel OD, Chiral-AGP, Cyclobond I and Sumichiral OA-4900 columns. Metoprolol acid was resolved only by Sumichiral OA-4900. Chiralcel OD provided the highest separation factor and resolution value for metoprolol and O-desmethylmetoprolol and partially resolved the four stereoisomers of alpha-hydroxymetoprolol. Diastereomeric alpha-hydroxymetoprolols were resolved using the coupled column chromatographic system of two chiral stationary phases, Sumichiral OA-4900 column and Chiralcel OD column.

Reduction of radiation-induced chromosome aberration and apoptosis by dithiothreitol.

We have examined in vitro and in vivo radioprotective effects of a well-known thiol-containing compound, dithiothreitol (DTT). The treatment of both 0.5 and 1 mM of DTT significantly increased clonogenic survival of gamma-ray irradiated Chinese hamster (V79-4) cells. In order to investigate the possible radioprotective mechanism of DTT, we measured gamma-ray induced chromosome aberration by micronucleus assay. In the presence of 0.5 mM or 1 mM DTT, the frequencies of micronuclei were greatly reduced in all dose range examined (1.5-8 Gy). Slightly higher reduction in micronucleus formation was observed in 1 mM DTT-treated cells than in 0.5 mM DTT-treated cells. In addition, incubation with both 0.5 and 1 mM of DTT prior to gamma-ray irradiation reduced nucleosomal DNA fragmentation at about same extent, this result suggests that treatment of DTT at concentrations of 0.5 and 1 mM reduced radiation-induced apoptosis. In vivo experiments, we also observed that DTT treatment reduced the incidence of apoptotic cells in mouse small intestine crypts. In irradiated control group 4.4 +/- 0.5 apoptotic cells per crypt were observed. In DTT-administered and irradiated mice, only 2.1 +/- 0.4 apoptotic cells per crypt was observed. In vitro and in vivo data obtained in this study showed that DTT reduced radiation-induced damages and it seems that the possible radioprotective mechanisms of action of DTT are prevention of chromosome aberration.

Studies on the possible mechanisms of protective activity against alpha-amanitin poisoning by aucubin.

Aucubin, an iridoid glucoside, was investigated to determine whether it has a stimulating effect on alpha-amanitin excretion in alpha-amanitin intoxicated rats, and whether there is binding activity to calf thymus DNA. High-performance liquid chromatography (HPLC) analysis of alpha-amanitin in rat urine allowed quantitative measurement of the alpha-amanitin concentration with a detection limit of 50 ng/ml. In this system, a group treated with both alpha-amanitin and aucubin showed that alpha-amanitin was excreted about 1.4 times faster than in the alpha-amanitin only treated group. Our previous results showed that the toxicity of alpha-amanitin is due to specific inhibition of RNA polymerase activity and the resultant blockage of the synthesis of certain RNA species in the nucleus. However, no significant activity change on RNA polymerase from Hep G2 cells was observed when aucubin was treated with alpha-amanitin at any concentration tested. Nevertheless, aucubigenin inhibited both DNA polymerase (IC50, 80.5 microg/ml) and RNA polymerase (IC50, 135.0 microg/ml) from the Hep G2 cells. The potential of both alpha-amanitin and aucubin to interact with DNA were examined by spectrophotometric analysis. Alpha-Amanitin showed no significant binding capacity to calf thymus DNA, but aucubin was found to interact with DNA, and the apparent binding constant (Kapp) and apparent number of binding sites per DNA phosphate (Bapp) were 0.45 x 10(4) M(-1) and 1.25, respectively.