Randomised clinical trial: low-volume bowel preparation for colonoscopy - a comparison between two different PEG-based formulations.

BACKGROUND: Low-volume bowel preparations with polyethylene glycol (PEG) have been shown to provide an equivalent cleansing with improved tolerability as compared with standard PEG bowel preparation for colonoscopy. A new iso-osmotic sulphate-free formulation of PEG-Citrate-Simethicone (PEG-CS) in combination with bisacodyl has been recently developed. AIM: To compare the quality of bowel cleansing with PEG-CS with bisacodyl vs. PEG-Ascorbate (PEG-ASC) in adult out-patients undergoing colonoscopy. METHODS: Randomised, observer-blind, parallel group study in adult out-patients undergoing colonoscopy in five Italian centres. Both preparations were taken the evening before the procedure. Subjects were instructed to take 2-4 tablets of 5 mg bisacodyl at 16:00 hours and 2 L of PEG-CS at 20:00 hours or 2 L of PEG-ASC plus 1 L of additional water the day before colonoscopy. Bowel cleansing was evaluated according to the Boston Bowel Preparation Scale (≥6 scores were considered as 'clinical success'), and mucosal visibility according to a 3-point scale. Tolerability, acceptability and compliance were also evaluated. RESULTS: Four hundred and eight patients were randomly allocated to PEG-CS and bisacodyl (n = 204, male patient 48%, mean age 59.1 years) or PEG-ASC (n = 204, male patient 51%, age 59.4 years). In the planned per-protocol analysis, the rate of successful preparation was 79.1% following PEG-CS with bisacodyl, and 70% following PEG-ASC (P < 0.05). Mucosal visibility was evaluated as optimal in 56.1% in the PEG-CS and bisacodyl and 46.3% in the PEG-ASC group (P < 0.05). There were no serious adverse events (AE) in each of the two experimental groups. Two subjects in the PEG-ASC group discontinued the study because of AE. CONCLUSIONS: Polyethylene glycol-Citrate-Simethicone in combination with bisacodyl was more effective for bowel cleansing than PEG-ASC for out-patient colonoscopy. Tolerability, safety, acceptability and compliance of the two low-volume bowel preparations were similar.

Nitric oxide synthesis in retinal photoreceptor cells.

Nitric oxide (NO) is known to be synthesized in several tissues and to increase the formation of cyclic GMP through the activation of soluble guanylate cyclases. Since cyclic GMP plays an important role in visual transduction, we investigated the presence of nitric oxide synthesizing activity in retinal rod outer segments. Bovine rod outer segments were isolated intact and separated into membrane and cytosolic fractions. Nitric oxide synthase activity was assayed by measuring the conversion of L-arginine to L-citrulline. Both membrane and cytosolic fractions were active in the presence of calcium and calmodulin. The activity in both fractions was stimulated by the nitric oxide synthase cofactors FAD, FMN, and tetrahydrobiopterin and inhibited by the L-arginine analog, L-monomethyl arginine. The Km for L-arginine was similar, about 5 microM for the enzyme in both fractions. However, the two fractions differed in their calcium/calmodulin dependence: the membrane fraction exhibited basal activity even in the absence of added calcium and calmodulin while the cytosolic fraction was inactive. But the activity increased in both fractions when supplemented with calcium/calmodulin: in membranes from about 40 to 110 fmol/min/mg of protein and in the cytosol from near zero to about 350 fmol/min/mg of protein in assays carried out at 0.3 microM L-arginine. The two enzymes also responded differently to detergent: the activity of the membrane enzyme was doubled by Triton X-100 while that of the cytosolic enzyme was unaffected. These results show that NO is produced by cytosolic and membrane-associated enzymes with distinguishable properties.(ABSTRACT TRUNCATED AT 250 WORDS)

The redox couple between glutathione and ascorbic acid: a chemical and physiological perspective.

This article provides a comprehensive analysis of the redox reaction between glutathione/glutathione disulfide and ascorbic acid/dehydroascorbic acid. It includes an historical perspective of the progression of the experiments, first begun more than 60 years ago and continuing today with heightened importance. Indeed, the antioxidant capacity of glutathione and ascorbic acid, whether singly or in combination, linked via the redox couple, is a subject of intense interest for studies by bench scientists and clinicians, particularly because a growing body of evidence suggests that free radicals may be involved in a variety of diseases. The authors begin with a detailed summary of "test tube" experiments (the chemical perspective) that have revealed the conditions that regulate the rate of the redox coupling between glutathione and dehydroascorbic acid and that promote or inhibit the decomposition of dehydroascorbic acid in ordinary, buffered aqueous media; results obtained in the authors' laboratory are used for illustration purposes and uniformity of presentation. The authors then proceed to a critical examination of the extent to which the redox couple between glutathione and ascorbic acid operates in a cell, using the often published antioxidant cascade (See Fig. 1) as the model for the analysis (the physiological perspective). The evidence for and the evidence against the presence of the enzyme dehydroascorbate reductase in animal cells is outlined in a balanced way in an attempt to make sense of this continuing controversy. Next, the authors carefully document the many studies showing that exogenous dehydroascorbic acid is transported into cells where it is reduced to ascorbic acid by glutathione. Finally, they probe the functional significance and efficiency of the redox couple in monolayer cultures of human retinal pigment epithelial (RPE) cells, as a prototypical cellular model. The authors include the results of new experiments showing that incubation of RPE cells with a nitroxide, TEMPOL, leads to the selective oxidation of intracellular ascorbic acid. This approach is desirable because it dissects the cascade at a specific site and permits measurements of the levels of ascorbic acid and glutathione in the cells before, during, and after oxidation. The results show that only partial regeneration of ascorbic acid is obtained when control conditions are restored. However, if either ascorbic acid or dehydroascorbic acid is added to the media during the recovery period following treatment of cells with TEMPOL, then full recovery of ascorbic acid is observed.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of oxidized glutathione on ATPase activities in rat retina.

The activities of Mg(2+)-dependent and Na(+)-K(+)-stimulated ATPase in homogenates of rat retina were measured in the presence of increasing concentrations of oxidized glutathione (GSSG). The Mg(2+)-ATPase was not inhibited by GSSG at any of the concentrations tested. The Na(+)-K(+)-stimulated ATPase was not inhibited by 1 mM GSSG, but its activity was decreased by 20 and 35%, respectively, in the presence of 5 and 10 mM GSSG. Other enzymatic measurements using supernatant fractions of rat retina showed that 1-10 mM GSSG did not inhibit the activities of hexokinase, glucose-6-phosphate dehydrogenase, or glyceraldehyde-3-phosphate dehydrogenase. These results suggest that GSSG is not likely to exert significant deleterious changes on cellular processes, at least in cells and tissues in which normal glutathione (GSH) concentration is 2 mM or lower.

DNA methylation of embryogenic carrot cell cultures and its variations as caused by mutation, differentiation, hormones and hypomethylating drugs.

The level of auxin - both natural and synthetic - in the medium has a strong effect on the level of 5-methyl-cytosine in the DNA of carrot cells in culture. This level may vary from approximately 15% to 70% of total cytosine without apparent effects on growth rate and cell morphology. No effect was seen with cytokinin. During somatic embryogenesis, in the absence of hormones, variations were seen in the level of methylation according to a characteristic pattern. If hypomethylation is induced with drugs such as azacytidine, ethionine or ethoxy-carbonyl-pyrimidine, embryogenesis is immediately blocked. A mutant was isolated which is resistant to the action of hypomethylating drugs. It shows variations in the methylation pattern and variations in indole-acetic acid metabolism. In addition its regeneration is often associated with the production of tumors.