Possible role of metal ionophore against zinc induced cognitive dysfunction in <Emphasis Type="SmallCaps">d-</Emphasis>galactose senescent mice

Metal ionophores are considered as potential anti-dementia agents, and some are currently undergoing clinical trials. Many metals are known to accumulate and distribute abnormally in the aging brain. Alterations in zinc metal homeostasis in the glutaminergic synapse could contribute to ageing and the pathophysiology of Alzheimer’s disease (AD). The present study was designed to investigate the effect of metal ionophores on long term administration of zinc in D-galactose induced senescent mice. The ageing model was established by combined administration of zinc and D-galactose to mice for 6 weeks. A novel metal ionophore, PBT-2 was given daily to zinc-induced d-galactose senescent mice. The cognitive behaviour of mice was monitored using the Morris Water Maze. The anti-oxidant status and amyloidogenic activity in the ageing mouse was measured by determining mito-oxidative parameters and deposition of amyloid β (Aβ) in the brain. Systemic administration of both zinc and D-galactose significantly produced memory deficits, mito-oxidative damage, heightened acetylcholinesterase enzymatic activity and deposition of amyloid-β. Treatment with PBT-2 significantly improved behavioural deficits, biochemical profiles, cellular damage, and curbed the deposition of APP in zinc-induced senescent mice. These findings suggest that PBT-2, acting as a metal protein attenuating compound, may be helpful in the prevention of AD or alleviation of ageing.     

Influence of follicular maturation on 3-hydroxy-methylglutaryl coenzyme A reductase activity in hen granulosa cells

The activity of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoA reductase: EC 1.1.1.34) was measured in a microsomal preparation of the granulosa of rapidly growing ovarian follicles of laying hens in the late preovulatory period (2-3 h before expected ovulation). The specific activity of the enzyme was measured in the five largest (F1-F5) preovulatory follicles, F1 being the follicle destined to ovulate first. Enzyme activity increased concomitantly with follicle size. The apparent Km of the enzyme decreased 60-80% from the smallest to the largest preovulatory follicle. There was no significant change in the Vmax during follicle development. Although our results have demonstrated the presence of HMG/CoA reductase in chicken granulosa cells and the progressive increase of its activity with follicular maturation, the quantitative significance of de-novo synthesized cholesterol as steroid hormone precursor remains to be ascertained.     

Influence of tea and coffee beverages on prostacyclin synthesis by the rat aorta

Influences of 2.5 and 5% (w/v) aqueous tea and coffee beverages administered ad lib. to rats for two weeks on PGI2 synthesis by the rat thoracic aorta in vitro were investigated using a rat platelet antiaggregatory bioassay and HPLC methods. The 2.5% beverages did not affect PGI2 synthesis; however, the 5% beverages significantly decreased PGI2 synthesis. The observed decreases were significantly abolished in presence of exogenous arachidonic acid suggesting a beverage-induced inhibition of precursor release. The ability of the beverages to inhibit PGI2 synthesis may partly contribute towards better understanding of the biochemical mechanisms underlying some of the beverages-induced actions in vivo.     

Cyclic adenosine monophosphate (cAMP) production in avian theca cells during follicular maturation

LH was used to stimulate cAMP production in theca cells from the 5 largest preovulatory follicles of hens and this was related to LH-stimulated androstenedione production in the same cells. cAMP production was stimulated by LH to the same extent in theca cells from each follicle. However, LH was not effective in stimulating androstenedione production in theca cells from the largest follicle (T1), although androstenedione production was greatly increased by LH in the smaller follicles (T2-T5). Effects similar to those of LH on cAMP production were observed in response to forskolin, indicating that the intrinsic adenylate cyclase activity was similar in theca cells from each follicle. In addition, forskolin was unable to stimulate androstenedione production by T1 cells. Our results provide evidence that the levels of receptor-mediated and non-receptor-mediated cAMP production are similar in theca cells from the 5 largest follicles. We conclude that the step that restricts the ability of T1 cells to produce androgen is distal to cAMP generation.     

Effect of calcium ionophore A23187 on pregnenolone metabolism to progesterone in rat granulosa cells

The effect of calcium ionophore A23187 on the metabolism of pregnenolone to progesterone was examined in rat granulosa cells during a 24-h culture period. Granulosa cells harvested from pregnant mare's serum gonadotropin treated immature rats were incubated in the presence and absence of the divalent cation ionophore A23187. The ionophore induced progesterone synthesis from both endogenous sterol substrate and exogenous pregnenolone in a time- and concentration-dependent manner. Pregnenolone metabolism was examined in the presence of aminoglutethimide phosphate, an inhibitor of endogenous pregnenolone production. Steroid secretion resulting from metabolism of endogenous substrate was more sensitive to A23187 in that a lower concentration of the ionophore was required to induce a significant increase than that noted for exogenous pregnenolone metabolism. In addition, progesterone production from endogenous sterol occurred 6 h earlier than the observed increase in the conversion of pregnenolone to progesterone. These results indicate that A23187 and therefore possibly enhanced calcium influx may play a significant role in the regulation of pregnenolone metabolism in granulosa cells depending on the duration of incubation. The earlier steroidogenic response from endogenous substrate may be a reflection of an acute effect of A23187 on certain steroidogenic steps proximal to pregnenolone production.     

Clomiphene and tamoxifen inhibit the cholesterol side-chain cleavage enzyme activity in hen granulosa cells

A radiochemical assay was utilized to study the inhibitory effects of clomiphene and tamoxifen on the cholesterol side-chain cleavage enzyme activity in a mitochondrial preparation of granulosa cells isolated from mature ovarian follicles of laying hens. At saturating substrate concentrations, both clomiphene and tamoxifen were able to suppress enzyme activity in a dose-related manner (IC50 1.8 X 10(-5) M). Double reciprocal plots of kinetic data show that the inhibition is mixed, exhibiting competitive kinetics at low concentrations, whereas at high concentrations, the inhibition is of a non-competitive nature. The competitive inhibition constants as determined from Dixon plots are 2 X 10(-5) M for clomiphene and 2.3 X 10(-5) M for tamoxifen. It is concluded that, in granulosa cells, clomiphene and tamoxifen directly inhibit the mitochondrial cholesterol side-chain cleavage activity. This inhibition may represent an important aspect of the mode of action of clomiphene and tamoxifen.     

The phagosome containing Legionella pneumophila within the protozoan Hartmannella vermiformis is surrounded by the rough endoplasmic reticulum.

Legionella pneumophila is an intracellular parasite of protozoa and human phagocytes. To examine adaptation of this bacterium to parasitize protozoa, the sequence of events of the intracellular infection of the amoeba Hartmannella vermiformis was examined. The previously described uptake phenomenon of coiling phagocytosis by human monocytes was not detected. A 1 h postinfection with wild-type strain AA100, mitochondria were observed within the vicinity of the phagosome. At 2.5 h postinfection, numerous vesicles surrounded the phagosomes and mitochondria were in close proximity to the phagosome. At 5 h postinfection, the bacterium was surrounded by a ribosome-studded multilayer membrane. Bacterial multiplication was evident by 8 h postinfection, and the phagosome was surrounded by a ribosome-studded multilayer membrane until 15 h postinfection. The recruitment of organelles and formation of the ribosome-studded phagosome was defective in an isogenic attenuated mutant of L. pneumophila (strain AA101A) that failed to replicate within amoebae. At 20 h postinfection with wild-type strain AA100, numerous bacteria were present in the phagosome and ribosome were not detected around the phagosome. These data showed that, at the ultrastructural level, the intracellular infection of protozoa by L. pneumophila is highly similar to that of infection of macrophages. Immunocytochemical studies provided evidence that at 5 h postinfection the phagosome containing L. pneumophila acquired an abundant amount of the endoplasmic reticulum-specific protein (BiP). Similar to phagosomes containing heat-killed wild-type L. pneumophila, the BiP protein was not detectable in phagosomes containing the mutant strain AA101A. In addition to the absence of ribosomes and mitochondria, the BiP protein was not detected in the phagosomes at 20 h postinfection with wild-type L. pneumophila. The data indicated that the ability of L. pneumophila to establish the intracellular infection of amoebae is dependent on its capacity to reside and multiply within a phagosome surrounded by the rough endoplasmic reticulum. This compartment may constitute a rich source of nutrients for the bacteria and is probably recognized as cellular compartment. The remarkable similarity of the intracellular infections of macrophages and protozoa by L. pneumophila strongly supports the hypothesis that adaptation of the bacterium to the intracellular environment of protozoa may be the mechanism for its ability to adapt to the intracellular environment of human alveolar macrophages and causes pneumonia.     

A rheological study on plasma lipoproteins (author's transl)]

Lipoproteins of the types LpB and LP-X are studied in a microviscometer to measure intrinsic viscosity. Up to a shear rate of 1700s-1 no shear dependence of viscosity is observed. Intrinsic viscosities are 3.5 and 4.0 for LpB, and 8.5 ml/g for LP-X. Density measurements are used to calculate apparent specific volumes. The results are compatible with a spherical model. An upper limit of 0.45 is estimated for the hydration.     

Activation of nylon by alkaline glutaraldehyde solution for enzyme immobilisation

Summary Nylon tube was directly activated by alkaline glutaraldehyde solution. PEI was utilised as a spacer molecule. Glucose oxidase was immobilised to the nylon tube after reactivating the spacer molecules with glutaraldehyde. On immobilising glucose oxidase there was more protein binding and higher immobilised enzyme activity when compared to immobilised enzyme tube activated by triethyloxonium salt. The optimal condition for direct glutaraldehyde activation of nylon was incubation with 18.5% (w/v) glutaraldehyde in 0.12M borate pH 9.0 for 15 min at 90 °.