We introduce a method, single-particle profiler, that provides single-particle information on the content and biophysical properties of thousands of particles in the size range 5–200 nm. We use our single-particle profiler to measure the messenger RNA encapsulation efficiency of lipid nanoparticles, the viral binding efficiencies of different nanobodies, and the biophysical heterogeneity of liposomes, lipoproteins, exosomes and viruses.

Phospholipids and their derivatives represent a broad range of multifunctional substances used as excipients or active ingredients by different industries due to their natural origin and unique properties. A fast and reliable quantification as well as comprehensive stability evaluation are of major importance in the process of development and quality control of lipid-based systems. Therefore, the present study is focused on the development and validation of a rapid ultra-high performance liquid chromatography - charged aerosol detector based (UHPLC-CAD) method for simultaneous detection of a multitude of natural and synthetic lipids, (charged) phospholipids, lipophilic fluorescent markers and their possible degradation products. Twenty-two compounds were characterized by a strong linear response of the detector (R² > 0.97). Moreover, remarkable limits of detection (≤10 μg mL^-1) and limits of quantification (≤25 μg mL^-1) associated with a consistent reproducibility were achieved for all tested molecules. The performance of the analytical method was demonstrated by analyzing the lipid composition (after different production stages and photodegradation) of both bupivacaine loaded liposomes and a Doxil®-like formulation. The newly developed method combines a rapid, comprehensive, and efficient quantification with minimal economic effort and ecologic consequences, meeting the requirements of modern analytical processes and offering a broad range of possible applications in various industrial sectors and scientific laboratories.

Despite enormous efforts to improve therapeutic options, pancreatic cancer remains a fatal disease and is expected to become the second leading cause of cancer-related deaths in the next decade. Previous research identified lipid metabolic pathways to be highly enriched in pancreatic ductal adenocarcinoma (PDAC) cells. Thereby, cholesterol uptake and synthesis promotes growth advantage to and chemotherapy resistance for PDAC tumor cells. Here, we demonstrate that high-density lipoprotein (HDL)–mediated efficient cholesterol removal from cancer cells results in PDAC cell growth reduction and induction of apoptosis in vitro. This effect is driven by an HDL particle composition–dependent interaction with SR-B1 and ABCA1 on cancer cells. AAV-mediated overexpression of APOA1 and rHDL injections decreased PDAC tumor development in vivo. Interestingly, plasma samples from pancreatic-cancer patients displayed a significantly reduced APOA1-to-SAA1 ratio and a reduced cholesterol efflux capacity compared with healthy donors. We conclude that efficient, HDL-mediated cholesterol depletion represents an interesting strategy to interfere with the aggressive growth characteristics of PDAC.

Due to the global rise of type 2 diabetes mellitus (T2DM) in combination with insulin resistance, novel compounds to efficiently treat this pandemic disease are needed. Screening for compounds that induce the translocation of glucose transporter 4 (GLUT4) from the intracellular compartments to the plasma membrane in insulin-sensitive tissues is an innovative strategy. Here, we compared the applicability of three fluorescence microscopy-based assays optimized for the quantitation of GLUT4 translocation in simple cell systems. An objective-type scanning total internal reflection fluorescence (TIRF) microscopy approach was shown to have high sensitivity but only moderate throughput. Therefore, we implemented a prism-type TIR reader for the simultaneous analysis of large cell populations grown in adapted microtiter plates. This approach was found to be high throughput and have sufficient sensitivity for the characterization of insulin mimetic compounds in live cells. Finally, we applied confocal microscopy to giant plasma membrane vesicles (GPMVs) formed from GLUT4-expressing cells. While this assay has only limited throughput, it offers the advantage of being less sensitive to insulin mimetic compounds with high autofluorescence. In summary, the combined implementation of different fluorescence microscopy-based approaches enables the quantitation of GLUT4 translocation with high throughput and high content.

The Tweety homologues (TTYHs) constitute a family of eukaryotic membrane proteins that, on the basis of structural features, were recently proposed to contribute to lipid transfer between soluble carriers and cellular membranes¹. However, in the absence of supporting data, this function was hypothetical. Here through pull-down of endogenous proteins, we identify APOE as the interaction partner of human TTYH2. Subcellular fractionation and immunocytochemistry assays showed that both proteins colocalize in endosomal compartments. Characterization of the specific interaction between APOE and TTYH2 through binding assays and structural studies enabled us to identify an epitope in an extended domain of TTYH2 that faces the endosomal lumen. Structures of complexes with APOE-containing lipoprotein particles revealed a binding mode that places lipids in a suitable position to facilitate their diffusion into the membrane. Moreover, in vitro studies revealed that lipid transfer is accelerated by TTYH2. Collectively, our findings indicate that TTYH2 has a role in the unloading of APOE-containing lipoproteins after they are endocytosed. These results define a new protein class that facilitates the extraction of lipids from and their insertion into cellular membranes. Although ubiquitous, this process could be of particular relevance in the brain, where APOE is involved in the transfer of lipids between astrocytes and neurons.