Effect on endometrial histology and pharmacokinetics of different dose regimens of progesterone vaginal pessaries, in comparison with progesterone vaginal gel and placebo.

STUDY QUESTION: Which progesterone vaginal pessary dose regimen induces adequate secretory transformation of the endometrium, in comparison with progesterone vaginal gel and placebo? SUMMARY ANSWER: The best secretory transformation of the endometrium was observed during treatment with 400 mg progesterone vaginal pessaries, administered twice daily. WHAT IS KNOWN ALREADY: Vaginally administered progesterone is widely used for luteal phase support (LPS) in assisted reproductive techniques (ART). Although several vaginal formulations using various doses are available, little is known on the impact of formulation and doses at the endometrial level. STUDY DESIGN, SIZE, DURATION: The study had a randomised, observer-blind design and comprised two parts. The participants used study medication during two or three treatment periods, separated by washout periods. Subjects in Part 1 (n = 61 treated) received 200 mg progesterone vaginal pessaries twice daily (bid), 400 mg pessaries bid and the comparator 90 mg progesterone vaginal gel once daily (od) in a 3-way crossover design. Subjects in Part 2 (n = 64 treated) received 100 mg pessaries bid in one period and 400 mg pessaries od in the other period in a 2-way crossover design. A subgroup of these subjects (n = 22 treated) received placebo vaginal pessaries bid in a third period in a non-randomised manner. The study was performed from May 2012 until April 2013. PARTICIPANTS/MATERIALS, SETTING, METHODS: The study was performed at a clinical research centre in healthy female volunteers of reproductive age. The subjects used 2 mg estradiol bid for 24 days in each treatment cycle. Progesterone or placebo was administered vaginally from Day 15 onwards during 10 days. In each treatment period, an endometrial biopsy for histological evaluation was performed on Day 23 and pharmacokinetic parameters were determined after the first progesterone dose on Day 15 and after the last dose on Day 24. MAIN RESULTS AND THE ROLE OF CHANCE: Frequencies of (early and late) secretory transformation of the endometrium, i.e. adequate responses, during treatment with 200 mg and 400 mg vaginal pessaries bid were comparable with those during 90 mg vaginal gel treatment (90-94%), whereas lower secretory transformation rates were observed during treatment with 100 mg bid and 400 mg od (64-75%). At the time of the endometrial biopsy in the cycle the late secretory state of the endometrium, which is characteristic of adequate luteal support, was observed more often with 400 mg pessaries bid (90%) than with vaginal gel (82%) and with lower pessary doses (64-78%). Pharmacokinetic parameters after repeated dosing of vaginal pessaries showed a dose-dependent, but not dose-proportional, increase of plasma progesterone levels. The lowest incidence of bleeding and spotting was reported during treatment with 400 mg pessaries bid. LIMITATIONS REASONS FOR CAUTION: The primary outcome parameter, rate of secretory transformation of the endometrium, is a surrogate for endometrial receptivity and for the actual clinical efficacy. WIDER IMPLICATIONS OF THE FINDINGS: Delivery of progestesterone through 400 mg pessaries bid is an effective alternative method for luteal support in ART. STUDY FUNDING/COMPETING INTEREST(S): The study was funded by Actavis Group PTC ehf., Iceland, part of Teva Pharmaceuticals, and L.D. Collins. I.D. and C.K. are directors of Dinox, a contract research organisation. I.K. is Managing Director of Pharmaplex and M.W. is Managing Director of M.A.R.C.O., service organisations involved in organisation/supervision and evaluation/reporting of clinical trials. All received funding for the conduct of the study from Actavis. S.H. and Th.M. are employees of Actavis. TRIAL REGISTRATION NUMBER: EudraCT number 2012-001726-95.

Lipid distribution and transport across cellular membranes.

In eukaryotic cells, the membranes of different intracellular organelles have different lipid composition, and various biomembranes show an asymmetric distribution of lipid types across the membrane bilayer. Membrane lipid organization reflects a dynamic equilibrium of lipids moving across the bilayer in both directions. In this review, we summarize data supporting the role of specific membrane proteins in catalyzing transbilayer lipid movement, thereby controlling and regulating the distribution of lipids over the leaflets of biomembranes.

Reconstitution and partial characterization of phospholipid flippase activity from detergent extracts of the Bacillus subtilis cell membrane.

In bacteria, phospholipids are synthesized on the inner leaflet of the cytoplasmic membrane and must translocate to the outer leaflet to propagate a bilayer. Transbilayer movement of phospholipids has been shown to be fast and independent of metabolic energy, and it is predicted to be facilitated by membrane proteins (flippases) since transport across protein-free membranes is negligible. However, it remains unclear as to whether proteins are required at all and, if so, whether specific proteins are needed. To determine whether bacteria contain specific proteins capable of translocating phospholipids across the cytoplasmic membrane, we reconstituted a detergent extract of Bacillus subtilis into proteoliposomes and measured import of a water-soluble phospholipid analog. We found that the proteoliposomes were capable of transporting the analog and that transport was inhibited by protease treatment. Active proteoliposome populations were also able to translocate a long-chain phospholipid, as judged by a phospholipase A(2)-based assay. Protein-free liposomes were inactive. We show that manipulation of the reconstitution mixture by prior chromatographic fractionation of the detergent extract, or by varying the protein/phospholipid ratio, results in populations of vesicles with different specific activities. Glycerol gradient analysis showed that the majority of the transport activity sedimented at approximately 4S, correlating with the presence of specific proteins. Recovery of activity in other gradient fractions was low despite the presence of a complex mixture of proteins. We conclude that bacteria contain specific proteins capable of facilitating transbilayer translocation of phospholipids. The reconstitution methodology that we describe provides the basis for purifying a facilitator of transbilayer phospholipid translocation in bacteria.

Specific proteins are required to translocate phosphatidylcholine bidirectionally across the endoplasmic reticulum.

BACKGROUND: A long-standing problem in understanding the mechanism by which the phospholipid bilayer of biological membranes is assembled concerns how phospholipids flip back and forth between the two leaflets of the bilayer. This question is important because phospholipid biosynthetic enzymes typically face the cytosol and deposit newly synthesized phospholipids in the cytosolic leaflet of biogenic membranes such as the endoplasmic reticulum (ER). These lipids must be transported across the bilayer to populate the exoplasmic leaflet for membrane growth. Transport does not occur spontaneously and it is presumed that specific membrane proteins, flippases, are responsible for phospholipid flip-flop. No biogenic membrane flippases have been identified and there is controversy as to whether proteins are involved at all, whether any membrane protein is sufficient, or whether non-bilayer arrangements of lipids support flip-flop. RESULTS: To test the hypothesis that specific proteins facilitate phospholipid flip-flop in the ER, we reconstituted transport-active proteoliposomes from detergent-solubilized ER vesicles under conditions in which protein-free liposomes containing ER lipids were inactive. Transport was measured using a synthetic, water-soluble phosphatidylcholine and was found to be sensitive to proteolysis and associated with proteins or protein-containing complexes that sedimented operationally at 3.8S. Chromatographic analyses indicated the feasibility of identifying the transporter(s) by protein purification approaches, and raised the possibility that at least two different proteins are able to facilitate transport. Calculations based on a simple reconstitution scenario suggested that the transporters represent approximately 0.2% of ER membrane proteins. CONCLUSIONS: Our results clearly show that specific proteins are required to translocate a phosphatidylcholine analogue across the ER membrane. These proteins are likely to be the flippases, which are required to translocate natural phosphatidylcholine and other phospholipids across the ER membrane. The methodology that we describe paves the way for identification of a flippase.

Transbilayer movement of fluorescent phospholipids in Bacillus megaterium membrane vesicles.

We investigated the transbilayer movement or flip-flop of phospholipids in vesicles derived from the cytoplasmic membrane of Bacillus megaterium. Since common assay techniques were found to be inapplicable to the Bacillus system, we exploited and elaborated a newly described method in which fluorescent phospholipids (1-myristoyl-2-C6-NBD phospholipids) are used as tracers to monitor flip-flop. These lipids were introduced into Bacillus vesicles from synthetic donor vesicles containing a fluorescence quencher. Transport was measured by monitoring the increase in fluorescence as the tracers departed the quenched environment of the donor vesicle and entered first the outer membrane leaflet and subsequently the inner leaflet of Bacillus vesicles. Independent experiments involving cobalt quenching of NBD fluorescence provided results consistent with the existence of pools of fluorescent phospholipid in the outer and inner leaflets of Bacillus vesicles at the completion of transport. Using the assay we show that phospholipid flip-flop in Bacillus vesicles occurs rapidly (half-time approximately 30 s at 37 degrees C) with no preference for a particular phospholipid headgroup and that it is sensitive to proteolysis. We also establish that flip-flop does not occur in synthetic phospholipid vesicles or vesicles made from Bacillus phospholipids. We conclude that Bacillus vesicles possess the ability to promote rapid transbilayer movement of phospholipids, and that the transport is probably protein (flippase)-mediated.