Pharmacokinetics of an oral contraceptive containing oestradiol valerate and dienogest.

OBJECTIVE: To evaluate the pharmacokinetics of a combined oral contraceptive (OC) containing oestradiol valerate/dienogest (E2V/DNG) administered according to a four-phasic dosing regimen with an oestrogen step-down and a progestin step-up over 26 days of active treatment. METHODS: This Phase I, open-label study included healthy women aged 18-50 years. Treatment consisted of the administration of E2V 3 mg for 2 days, E2V 2 mg/DNG 2 mg for 5 days, E2V 2 mg/DNG 3 mg for 17 days, E2V 1 mg for 2 days, and placebo for 2 days. RESULTS: Pharmacokinetic data were analysed in 15 women. Stable E2 concentrations were maintained throughout the study. Minimum mean serum E2 levels were 33.6-64.7 pg/ml during E2V administration. The ratio of oestrone:E2 in serum was approximately 5:1. Minimum mean serum DNG levels were 6.8-15.1 ng/ml during DNG administration. Minimum concentrations of DNG increased only slightly during each phase of the regimen during which DNG was being administered. On day 24 the geometric mean C(max), C(ave) and t((1/2)) of DNG were 82.9 ng/ml, 33.7 ng/ml and 12.2 hours, respectively; the median t(max) was 1.5 hours. Serum sex hormone-binding globulin concentrations increased by 40% (within the normal range). Cortisol binding-globulin levels remained almost unchanged. Treatment was well tolerated. CONCLUSIONS: Treatment with an OC containing E2V and DNG was well tolerated and was associated with stable E2 concentrations over 28 days. The pharmacokinetics of DNG were consistent with previous findings. Minimum serum concentrations of DNG increased only slightly during phases of the regimen during which DNG was administered.

Small, highly structured RNAs participate in the conversion of human recombinant PrP(Sen) to PrP(Res) in vitro.

We have identified a small, highly structured (shs)RNA that binds human recombinant prion protein (hrPrP) with high affinity and specificity under physiological conditions (e.g. 10% bovine calf serum (BCS), neutral pH, nanomolar concentrations of RNA and hrPrP). We also demonstrate the ability of this shsRNA to form highly stable nucleoprotein complexes with hrPrP and cellular PrP (PrP(C)) from various cell extracts and mammalian brain homogenates. The apparent mass of the nucleoprotein complex is dependent on the molar ratio of hrPrP to RNA during complex formation. The hrPrP in these complexes acquires resistance to degradation by Proteinase K (PK). Other shsRNAs, however, under identical conditions, neither form stable complexes with hrPrP nor do they induce resistance to PK digestion. We also demonstrate that the RNAs in these nucleoprotein complexes become resistant to ribonuclease A hydrolysis. These interactions between shsRNAs and hrPrP suggest possible roles of RNAs in the modulation of PrP structure and perhaps disease development. ShsRNAs that bind to hrPrP with high affinity and induce resistance to PK digestion can be used to develop molecular biology assays for the screening of compounds associated with PrP structure transformation or for drugs that inhibit this process.

Prion protein interactions with nucleic acid: possible models for prion disease and prion function.

Several models for the transmission and progression of prion diseases have arisen, evolving with the acquisition of new experimental results. It is generally accepted that the PrP(Sc) protein is at least part of the infectious particle and the major protein component of the scrapie-associated fibrils (SAFs) that characterize the disease. An additional, unknown cofactor is most likely involved in transmission of the disease, perhaps by influencing the PrP(c) --> PrP(Sc) transition. This review relates experimental observations on the interactions of nucleic acids (NAs) and PrP with specific focus on alterations in structure. In particular, NAs appear to induce PrP(c) to acquire some of the structural and biochemical characteristics of PrP(Sc). An updated hypothesis is related wherein NAs, on the basis of their structure, act in the PrP(c) --> PrP(Sc) transformation by serving as catalysts and/or chaperones and not by encoding genetic information.

Concentration and removal of prion proteins from biological solutions.

The pathogenesis of prion diseases is characterized by the accumulation of amyloid-like rods or scrapie-associated fibrils. The major protein component of scrapie-associated fibrils is an abnormally folded isoform of the normal cellular prion protein (PrP(C)) that is resistant to digestion by proteinase K and is referred to as PrP(Sc). Purified human recombinant (hr PrP) was used to characterize the binding of a set of RNAs with affinity to PrP proteins. We report here that hr PrP has two RNA-binding activities at physiological pH. One activity is capable of binding all of the screened RNAs with high affinity, whereas the other activity can bind only to a subset of the RNAs with high affinity in the presence of non-specific competitor RNAs. A novel RNA belonging to the latter class, RQ11+12, bound to hr PrP with high affinity in the presence of vast molar excesses of competing RNAs. Beads impregnated with the RQ11+12 RNA were used to construct a filtration column. The column efficiently bound hr PrP and native PrP(C) from serum and urine. Importantly, the filtration device was also capable of binding proteinase K-treated PrP(Sc) from serum and urine. The level of sensitivity of detection of PrP by standard Western blotting was increased at least 1000-fold by first concentrating PrP from solution with the filtration column.