2(3)-tert-butyl-4-hydroxyanisole inhibits oxidative metabolism of aflatoxin B1 in isolated rat hepatocytes

Previous studies indicate that dietary administration of phenolic antioxidants, 2(3)-tert-butyl-4-hydroxyanisole (BHA) and 3,5-di-tert-butyl-4-hydroxytoluene, inhibits the carcinogenic effect of a number of chemical carcinogens including aflatoxin B1 (AFB1). Induction of hepatic enzymes, such as glutathione S-transferase, UDP-glucuronyltransferase, and epoxide hydrolase, has been shown to be responsible for the reduction of AFB1 cytotoxic and carcinogenic effects. The effect of BHA on AFB1 activation was examined in vitro utilizing isolated rat hepatocytes and liver microsomes. In hepatocytes, the total AFB1 content and bound form of AFB1 were 3.4 and 1.4 pmol/10(6) cells, respectively. In the cell-free microsomal activating system, 2.2 pmol were activated per mg of microsomal protein during 60 min of incubation. BHA (0.1-0.5 mM) inhibited AFB1 activation and binding in both systems in a dose-dependent manner; in hepatocytes, 90% inhibition was observed at 0.5 mM. Analyzing various AFB1 adducts, BHA (0.25 mM)-treated hepatocytes contained a significantly reduced amount of AFB1 macromolecular adducts. The antioxidant neither stimulated nor inhibited the cytosolic glutathione S-transferase and microsomal UDP-glucuronyltransferase activities. Analysis of various hydroxylated (aflatoxins M1 and Q1 (AFM1 and AFQ1] and demethylated (aflatoxin P1 (AFP1] metabolites of AFB1 in both the conjugated and unconjugated form indicated that there was a 30-50% reduction of unconjugated AFP1, AFQ1, and AFM1, whereas AFB1 was increased 3-fold. There was no significant change of conjugated metabolites. The effect of BHA on AFB1 activation in hepatocytes was compared with that of other cytochrome P-450 inhibitors; the ED50 values of SKF 525A, BHA, and metyrapone were 9 microM, 40 microM, and 280 microM, respectively. In the cell-free microsomal system, biotransformation of AFB1 to AFP1, AFM1, and AFQ1 was also inhibited. Kinetic analysis of p-nitroanisole O-demethylase activity of rat liver microsomes demonstrated that BHA inhibited noncompetitively with an apparent Ki of 90 microM. In the absence of enzyme induction, the phenolic antioxidant, BHA, blocks the oxidative biotransformation of AFB1 in isolated hepatocytes.     

Handling of induced hypercalcaemia in hyperthyroidism

The mean serum calcium of 13 hyperthyroid patients was found to be significantly higher than that of controls matched for sex and age, though none of the patients'' values were outside the normal range. Nevertheless, these patients responded very promptly to hypercalcaemia (induced by an intravenous calcium load), and their serum calcium returned to normal much more rapidly compared with the matched controls. There was also increased retention of intravenous calcium load, possibly owing to increased calcitonin production. Calcium infusion may be useful in treating bone diseases in which increased bone resorption exceeds bone accretion.     

Adenosine modulates cell growth in human epidermoid carcinoma (A431) cells.

Adenosine mediates many physiological functions via activation of extracellular receptors. The modulation of cell growth by adenosine was found to be receptor-mediated. In A431 cells adenosine evoked a biphasic response in which a low concentration (approximately 10 microM) produced inhibition of colony formation but at higher concentrations (up to 100 microM) this inhibition was progressively reversed. Evidence for the involvement of A1 (inhibitory) and A2 (stimulatory) adenosine receptors in regulating cell growth of these tumor cells was obtained through plating efficiency studies based on the relative potency of adenosine agonists and antagonists. When both A1 and A2 receptors were blocked, colony formation or growth was not inhibited at low concentrations of adenosine but was inhibited at high adenosine concentrations.     

Glucan synthesis in Pneumocystis carinii.

Rat-derived Pneumocystis carinii lysed with sodium deoxycholate catalysed the incorporation of uridine diphosphoglucose into an insoluble polymer. This enzyme activity was present in both the pellet and the supernatant when the P. carinii preparations were centrifuged. The polymer whose production was catalysed by the supernatant was examined by mass spectrometry and found to be an alpha 1----4 glucan, which is either unbranched or has relatively few branches. Polymer formation was completely inhibited by the addition of alpha amyloglucohydrolase to the supernatant. Polymer formation in the pellet of deoxycholate P. carinii preparations, unlike that in the supernatant, was partially resistant to alpha amyloglucohydrolase. The soluble glucan synthase activity in the supernatant was stable for more than 30 h at room temperature and was approximately 50 times more active on a cell-to-cell basis than the supernatant from deoxycholate preparations of the yeast Saccharomyces cerevisae.     

Expression of S-antigen in retina, pineal gland, lens, and brain is directed by 5'-flanking sequences.

S-antigen (S-Ag) is an abundant protein of the retina and pineal gland that elicits experimental autoimmune uveitis and pinealocytis in several animal species. To study the elements regulating the expression of S-Ag, we generated transgenic mice expressing the chloramphenicol acetyl transferase (CAT) gene under the control of a 1.3-kilobase pair 5'-flanking segment of the mouse S-Ag gene. While all of the transgenic mice expressed CAT activity in the retina, in some animals CAT activity was also detected in the pineal gland, lens, and brain. Immunoblotting, polymerase chain reaction-mediated detection of RNA, and immunocyto-staining of transgenic tissues with antibodies to CAT and S-Ag established that the profile of expression of the transgene corresponded to that of S-Ag; both proteins were detectable in retinal photoreceptor cells, pinealocytes, lens fiber and epithelial cells, the cerebellum, and the cerebral cortex. These results indicate that S-Ag is expressed in a wider spectrum of the cell types than previously recognized and that a 1.3-kilobase pair S-Ag promoter segment contains sufficient information to direct appropriate tissue-specific gene expression in transgenic mice.     

A model-based evaluation of the single-breath CO2 ventilatory response test

The accuracy of the single-breath CO2 inhalation test as a method for determining peripheral chemoreflex gain (Gp) is evaluated through computer simulations using a mathematical model of the closed-loop respiratory control system. Estimates of Gp (G'p) are based on "corrected" changes in end-tidal PCO2, because the uncorrected end-tidal values do not accurately reflect changes in alveolar PCO2. The influence of the central chemoreflex on G'p is generally less than 10% but can become disproportionally more significant as the relative contribution of the peripheral chemoreflex diminishes. G'p tends to overestimate Gp with the inclusion of peripheral chemoreceptor rate sensitivity, but this effect is offset by the time constant for adaptation. The spontaneous variability of breathing can seriously impair the resolution of G'p. Averaging of G'p deduced from individual single-breath tests can lead to erroneous estimates of Gp even when a large number of repetitions are performed. This problem can be minimized by first ensemble averaging the data from individual single-breath tests and, then, computing G'p from the resulting mean changes.     

Direct evidence for aerial egg deposition in the burrows of the Malaysian mudskipper, <Emphasis Type="Italic">Periophthalmodon schlosseri</Emphasis>

The presence of mudskipper eggs in an air-filled chamber was confirmed by direct endoscopic observation of intact burrows of Periophthalmodon schlosseri in a mudflat in Penang, Malaysia. For all five burrows from which video images of egg chambers were successfully obtained, the presence of air was unequivocally demonstrated by the existence of an air–water interface inside the chambers. Of these burrows, eggs were found in two, but not in the others. Eggs were laid uniformly in a monolayer on the inner top surface of the chamber. The much brighter color of the surface mud of the egg chambers than the surrounding mud, irrespective of the presence or absence of the eggs, suggested that the surface mud had been oxidized by deposited air.     

Characterisation framework development for the SIMPASS (Singapore IMPact ASSessment) methodology

Purpose  

Life cycle assessment (LCA) practitioners in Singapore currently rely on foreign life cycle impact assessment (LCIA) methodologies when conducting studies, despite the fact that foreign methodologies may not be relevant, adaptable and sensitive to Singapore's circumstances. As a result, work has been undertaken to develop the Singapore IMPact ASSessment (SIMPASS) methodology by adapting and modifying existing LCIA methodologies to suit the Singaporean context. It is envisioned that the use of SIMPASS will improve the accuracy of LCA studies conducted for industries operating in Singapore.