Sterol biosensor reveals LAM-family Ltc1-dependent sterol flow to endosomes upon Arp2/3 inhibition.

Sterols are crucial components of biological membranes, which are synthetized in the ER and accumulate in the plasma membrane (PM). Here, by applying a genetically encoded sterol biosensor (D4H), we visualize a sterol flow between PM and endosomes in the fission yeast Schizosaccharomyces pombe. Using time-lapse and correlative light-electron microscopy, we found that inhibition of Arp2/3-dependent F-actin assembly promotes the reversible relocalization of D4H from the PM to internal sterol-rich compartments (STRIC) labeled by synaptobrevin Syb1. Retrograde sterol internalization to STRIC is independent of endocytosis or an intact Golgi, but depends on Ltc1, a LAM/StARkin-family protein localized to ER-PM contact sites. The PM in ltc1Δ cells over-accumulates sterols and upon Arp2/3 inhibition forms extended ER-interacting invaginations, indicating that sterol transfer contributes to PM size homeostasis. Anterograde sterol movement from STRIC is independent of canonical vesicular trafficking but requires Arp2/3, suggesting a novel role for this complex. Thus, transfer routes orthogonal to vesicular trafficking govern the flow of sterols in the cell

In vitro release testing as an alternative to establishing bioequivalence of drug products in vivo

Generische Arzneimittel werden als Arzneimittel definiert, die im Vergleich zu einem Referenzarzneimittel hinsichtlich der meisten pharmazeutischen Aspekte identisch sind. Um die therapeutische Äquivalenz zum Referenzprodukt sicherzustellen, sind Bioverfügbarkeitsstudien erforderlich. Für Arzneimittel, die als feste, perorale, schnell freisetzende Darreichungsformen formuliert sind, kann auf den Nachweis der Bioäquivalenz in vivo zugunsten eines vergleichenden Freisetzungstests in vitro im Rahmen eines sogenannten Biopharmaceutics Classification System (BCS) basierten Biowaivers verzichtet werden. Der BCS-basierte Biowaiver ist ein vielversprechendes Instrument, welches Kosteneinsparungen sowie eine Verringerung des regulatorischen Aufwands im Zuge der behördlichen Zulassung von Generika ermöglicht und dazu beitragen kann, die Zugänglichkeit unentbehrlicher Arzneimittel zu verbessern. Dabei gibt es jedoch auch Hürden, welche die weitläufige Anwendung des Verfahrens verhindern: Unklare Löslichkeits- und Permeabilitätsklassifizierungen von Wirkstoffen, Arzneimittel, welche die in vitro Freisetzungskriterien nicht erfüllen, sowie Zweifel an der Eignung der regulatorischen Spezifikationen, Freisetzungsunterschiede in vitro erfassen zu können, die für das Verhalten in vivo relevant sind. In der vorliegenden Dissertation werden diese Probleme thematisiert, indem eine umfassende Bewertung der Anwendbarkeit und Einschränkungen des BCS-basierten Biowaivers in seinem aktuell regulatorisch vorgeschriebenen Ablauf vorgenommen wird. Mögliche Anpassungen des Verfahrens wurden auf der Grundlage experimenteller in vitro Daten untersucht, bewertet und mithilfe von in silico Simulationsmodellen auf die Situation in vivo extrapoliert

A comprehensive study of charge transport in Au-contacted graphene on Ge/Si(001)

We investigate the electronic transport properties of Au-contacted graphene on Ge/Si(001). Kelvin probe force microscopy at room temperature with an additionally applied electric transport field is used to gain a comprehensive understanding of macroscopic transport measurements. In particular, we analyze the contact pads including the transition region, perform local transport measurements in pristine graphene/Germanium, and explore the role of the semiconducting Germanium substrate. We connect the results from these local scale measurements with the macroscopic performance of the device. We find that a graphene sheet on a 2 μm Ge film carries approximately 10% of the current flowing through the device. Moreover, we show that an electronic transition region forms directly adjacent to the contact pads. This transition region is characterized by a width of >100 μm and a strongly increased sheet resistance acting as the bottleneck for charge transport. Based on Rutherford backscattering of the contact pads, we suggest that the formation of this transition region is caused by diffusion. © 2020 Author(s)

Biowaiver Monographs for Immediate-Release Solid Oral Dosage Forms: Folic Acid.

This work presents a review of literature and experimental data relevant to the possibility of waiving pharmacokinetic bioequivalence studies in human volunteers for approval of immediate-release solid oral pharmaceutical forms containing folic acid as the single active pharmaceutical ingredient. For dosage forms containing 5 mg folic acid, the highest dose strength on the World Health Organization Essential Medicines List, the dose/solubility ratio calculated from solubility studies was higher than 250 mL, corresponding to a classification as "not highly soluble." Small, physiological doses of folic acid (≤320 μg) seem to be absorbed completely via active transport, but permeability data for higher doses of 1-5 mg are inconclusive. Following a conservative approach, folic acid is classified as a Biopharmaceutics Classification System class IV compound until more reliable data become available. Commensurate with its solubility characteristics, the results of dissolution studies indicated that none of the folic acid products evaluated showed rapid dissolution in media at pH 1.2 or 4.5. Therefore, according to the current criteria of the Biopharmaceutics Classification System, the biowaiver approval procedure cannot be recommended for immediate-release solid oral dosage forms containing folic acid