Kathleen A. Thompson

Human sperm glutathione reductase activity in situ reveals limitation in the glutathione antioxidant defense system due to supply of NADPH

In order to characterize further the antilipoperoxidative enzyme system of human sperm, that part of the system designed to provide reducing equivalents for the reduction of highly reactive and potentially damaging lipid hydroperoxides to relatively inert hydroxylipids was examined. The substrate that provides the reducing equivalents directly to glutathione peroxidase (GPX) is reduced glutathione (GSH), which is in turn oxidized to glutathione disulfide (GSSG). The reducing equivalents needed for regeneration of GSH through the action of glutathione reductase (GRD) are provided by NADPH, produced by the action of glucose‐6‐phosphate dehydrogenase (G6P‐DH) on substrates glucose‐6‐phosphate and NADP+. The kinetic properties of the enzymes GRD and G6P‐DH were determined by standard enzyme activity assay at 24 and 37°C. At 37°C, the Vmax for GRD was found to be 36 nmol/min · 108 cells, with Km values for GSSG and NAPH of 150 μM and 16 μM, respectively; the Vmax for G6P‐DH was 3.3 nmol/min · 108 cells with Km for NADP+ of 8 μM. This suggested that G6P‐DH activity was limiting in this reductive pathway. The activity of GRD in situ in intact cells was estimated using the thiol‐reactive fluorogenic probe ThioGlo‐1, which is cell permeant and reacts rapidly with GSH to give a highly fluorescent adduct. Mixing a suspension of human sperm with the fluorogenic reagent at 37°C gave an initial rapid increase in fluorescence, followed by a slower one. The rapid phase is due to reaction with intracellular GSH already present; the slow phase is due to reaction with GSH generated by the GRD‐catalyzed reduction of GSSG. Both rates showed first‐order kinetics. Calculation of the maximal rate as NADPH oxidation, attributable to in situ GRD activity, gave the value of 1.0 nmol/min · 108 cells, less than the maximum for NADPH production by the dehydrogenase. These results support the suggestion that NADPH production limits the capacity of the pathway leading to hydroperoxide reduction in human sperm. We propose that the antilipoperoxidative defense system of human sperm has just sufficient capacity to allow these cells to fulfill their function but is limited to allow their timely disposal from the female reproductive tract. Mol. Reprod. Dev. 49:400–407, 1998.

Assessment of the anti-microbial agent C31G as a spermicide: Comparison with nonoxynol-9

The broad-spectrum anti-microbial agent, C31G, containing an equimolar mixture of n-dodecyl-dimethylamine-N-oxide (C12-N-O) and N-(n-dodecyl), N-dimethyl-glycine (C12-betaine), was tested for spermicidal activity in comparison with the currently used spermicide, nonoxynol-9 (N-9). The rate of sperm cell permeabilization by the spermicides, as assayed with the fluorescent probe, TO-PRO-1, increased as the cube of the C31G concentration, while the rate increase was linear with N-9 concentration. At 0.04%, the rate of sperm cell permeabilization with both spermicides is at the limit of rapid measurement. C31G diffuses through cervical mucus at a more rapid rate than does N-9. C31G has long been known to aid wound healing and reduce inflammation, whereas N-9 has been reported to induce vaginal irritation. C31G would, thus, seem to have the spermicidal efficacy, the broad range of anti-microbial activity, and the lack of inflammatory activity that is sought in the ideal vaginal spermicide.

Rosiglitazone has no clinically significant effect on nifedipine pharmacokinetics.

To examine the effects of repeat oral dosing of rosiglitazone on the pharmacokinetics of nifedipine, a prototype CYP3A4 substrate, a randomized, open‐label, crossover study was performed with two treatment phases separated by a washout period of at least 14 days. Twenty‐eight healthy male volunteers received either a single 20 mg oral nifedipine dose or rosiglitazone 8 mg orally once daily for 14 days with a single 20 mg oral nifedipine dose administered on day 14. Plasma nifedipine concentrations were determined over the 24‐hour period following administration of the nifedipine doses. Lack of effect was defined as the demonstration that the 90% CI was contained entirely within a symmetrical 30% range either side of unity on the loge‐scale. Following rosiglitazone + nifedipine administration, the area under the nifedipine concentration‐time curve from time zero to infinity (AUC0‐∞;) was 13% lower than that after administration of nifedipine alone. This difference in nifedipine AUC0‐∞; was not deemed to be clinically significant since the 90% CI was contained within the protocol‐defined 30% range (point estimate for ratio of geometric means 0.87; 90% CI: 0.79, 0.96). Rosiglitazone had no marked effect on nifedipine peak plasma concentration (point estimate: 0.99; 90% CI: 0.73, 1.34) or time to peak concentration compared with nifedipine alone. Rosiglitazone coadministration produced a small decrease in the mean nifedipine half‐life (point estimate: −0.77; 90% CI: mean difference −1.29 h, −0.25 h). Both treatment regimens were well tolerated and associated with a favorable safety profile. Rosiglitazone, at the highest dose used in clinical studies, produced a small, clinically insignificant decrease in nifedipine exposure. The very small effect on nifedipine pharmacokinetics suggests that rosiglitazone is an extremely weak inducer of CYP3A4, a characteristic that distinguishes rosiglitazone from troglitazone.

Pharmacokinetics and pharmacodynamics of SB 209670, an endothelin receptor antagonist: effects on the regulation of renal vascular tone.

To evaluate the pharmacokinetics and pharmacodynamics of an infusion of SB 209670, a nonpeptide endothelin‐A/endothelin‐B receptor antagonist.

The accumulation of free and phosphorylated sugars in adipocytes based on a dynamic diffusion barrier

The simple theory of a dynamic diffusion barrier is described and it is shown how this could account for the accumulation, in adipocytes, of those free sugars which are also phosphorylated. The standing concentration gradient established by this mechanism depends on the recycling of free sugar and sugar phosphate in submembrane structures which start in juxtaposition to conventional membrane hexose transporters. Although a continual expenditure of metabolic energy is involved, there can be a net gain from the potential-energy store of accumulated substrates. The hypothesis leads to a series of simple equations which can be used as the basis for computer simulations of experimental procedures.

2-Deoxy-D-glucose accumulation in adipocytes: apparent transport discrimination between 2-deoxy-D-glucose and 3-O-methyl-D-glucose.

The uphill accumulation of free 2-deoxy-D-glucose and 2-deoxy-D-glucose 6-phosphate in rat adipocytes was found not to affect the steady-state distribution of 3-O-methyl-D-glucose although both hexoses share a common transport pathway. This observation argues against a possible effect of 2-deoxy-D-glucose phosphate on the equilibrating nature of the carrier. The results are discussed in light of hypotheses advanced to explain free 2-deoxy-D-glucose accumulation in a variety of cells.

Safety, Pharmacokinetics and Antigenicity of Single and Repeat IM Injections of a Reshaped Human Monoclonal Antibody (RSHZ19) in Healthy Volunteers

Clinical Pharmacology & Therapeutics (1996) 59, 144–144; doi: 10.1038/sj.clpt.1996.76