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An abstract of the article "Polymer Library Approaches to Gene Therapy," by Daniel G. Anderson, Andreas Zumbuehl, Weidan Peng, Janet A. Sawicki, and Robert Langer is presented.

This paper evaluates the impact of a reform which replaced universal basic grants by income-contingent loans on enrolment in Dutch higher education using administrative data of ten complete student cohorts. Estimates of differences between cohorts show no negative effect of the policy on enrolment. Moreover, difference-in-differences estimates exploiting variation in eligibility for supplementary grants show no negative effect on enrolment. These findings suggest that a system of income-contingent loans can facilitate an increase of private contributions without harming access to higher education. [ABSTRACT FROM AUTHOR]

Remote and minimally‐invasive modulation of biological systems with light has transformed modern biology and neuroscience. However, light absorption and scattering significantly prevents penetration to deep brain regions. Herein, we describe the use of gold‐coated mechanoresponsive nanovesicles, which consist of liposomes made from the artificial phospholipid Rad‐PC‐Rad as a tool for the delivery of bioactive molecules into brain tissue. Near‐infrared picosecond laser pulses activated the gold‐coating on the surface of nanovesicles, creating nanomechanical stress and leading to near‐complete vesicle cargo release in sub‐seconds. Compared to natural phospholipid liposomes, the photo‐release was possible at 40 times lower laser energy. This high photosensitivity enables photorelease of molecules down to a depth of 4 mm in mouse brain. This promising tool provides a versatile platform to optically release functional molecules to modulate brain circuits. [ABSTRACT FROM AUTHOR]

Liposomes formulated from the 1,3-diamidophospholipid Pad-PC-Pad are shear-responsive and thus promising nano-containers to specifically release a vasodilator at stenotic arteries. The recommended preclinical safety tests for therapeutic liposomes of nanometer size include the in vitro assessment of complement activation and the evaluation of the associated risk of complement activation-related pseudo-allergy (CARPA) in vivo . For this reason, we measured complement activation by Pad-PC-Pad formulations in human and porcine sera, along with the nanopharmaceutical-mediated cardiopulmonary responses in pigs. The evaluated formulations comprised of Pad-PC-Pad liposomes, with and without polyethylene glycol on the surface of the liposomes, and nitroglycerin as a model vasodilator. The nitroglycerin incorporation efficiency ranged from 25% to 50%. In human sera, liposome formulations with 20 mg/mL phospholipid gave rise to complement activation, mainly via the alternative pathway, as reflected by the rises in SC5b-9 and Bb protein complex concentrations. Formulations having a factor of ten lower phospholipid content did not result in measurable complement activation. The weak complement activation induced by Pad-PC-Pad liposomal formulations was confirmed by the results obtained by performing an in vivo study in a porcine model, where hemodynamic parameters were monitored continuously. Our study suggests that, compared to FDA-approved liposomal drugs, Pad-PC-Pad exhibits less or similar risks of CARPA. [ABSTRACT FROM AUTHOR]

This article describes four fluorescent membrane tension probes that have been designed, synthesized, evaluated, commercialized and applied to current biology challenges in the context of the NCCR Chemical Biology. Their names are Flipper-TR ® , ER Flipper-TR ® , Lyso Flipper-TR ® , and Mito Flipper-TR ® . They are available from Spirochrome.

Cellular delivery of DNA vectors for the expression of therapeutic proteins is a promising approach to treat monogenic disorders or cancer. Significant efforts in a preclinical and clinical setting have been made to develop potent nonviral gene delivery systems based on lipoplexes composed of permanently cationic lipids. However, transfection efficiency and tolerability of such systems are in most cases not satisfactory. Here, we present a one-pot combinatorial method based on double-reductive amination for the synthesis of short-chain aminolipids. These lipids can be used to maximize the DNA vector delivery when combined with the cationic lipid 1,2-dioleoyl-3-trimethylammonium propane (DOTAP). We incorporated various aminolipids into such lipoplexes to complex minicircle DNA and screened these systems in a human liver-derived cell line (HuH7) for gene expression and cytotoxicity. The lead aminolipid AL-A12 showed twofold enhanced gene delivery and reduced toxicity compared to the native DOTAP:cholesterol lipoplexes. Moreover, AL-A12-containing lipoplexes enabled enhanced transgene expression in vivo in the zebrafish embryo model., Competing Interests: The authors declare no competing financial interest.

In a biological membrane, proteins require specific lipids of distinctive length and chain saturation surrounding them. The active tuning of the membrane thickness therefore opens new possibilities in the study and manipulation of membrane proteins. Here, we introduce the concept of stapling phospholipids to different degrees of interdigitation depth by mixing 1,3-diamidophospholipids with single-chain bolalipids. The mixed membranes were studied by calorimetric assays, electron microscopy, X-ray, and infrared measurements to provide a complete biophysical characterization of membrane stapling. The matching between the diamidophospholipids and the bolalipids can be so strong as to completely induce a new phase that is more stable than the gel phase of the individual components.

Lipid bilayer membranes formed from the artificial 1,3-diamidophospholipid Pad-PC-Pad have the remarkable property that their hydrophobic thickness can be modified in situ: the particular arrangement of the fatty acid chains in Pad-PC-Pad allows them to fully interdigitate below 37 °C, substantially thinning the membrane with respect to the noninterdigitated state. Two stimuli, traversing the main phase transition temperature of the lipid or addition of cholesterol, have previously been shown to disable the interdigitated state. Both manipulations cause an increase in hydrophobic thickness of about 25 Å due to enhanced conformational entropy of the lipids. Here, we characterize the interdigitated state using electrophysiological recordings from free-standing lipid-membranes formed on micro structured electrode cavity arrays. Compared to standard membranes made from 1,2-diphytanoyl- sn -glycero-3-phosphocholin (DPhPC), pure Pad-PC-Pad membranes at room temperature had lowered electroporation threshold and higher capacitance. Ion channel formation by the peptide Gramicidin A was clearly facilitated in pure Pad-PC-Pad membranes at room temperature, with activity occurring at significantly lower peptide concentrations and channel dwell times increased by 2 orders of magnitude with respect to DPhPC-membranes. Both elevation of temperature beyond the phase transition and addition of cholesterol reduced channel dwell times, as expected if the reduced membrane thickness stabilized channel formation due to decreased hydrophobic mismatch.

Ischaemic heart disease and stroke are the most common causes of death worldwide. Anoxia, defined as the lack of oxygen, is commonly seen in both these pathologies and triggers profound metabolic and cellular changes. Sphingolipids have been implicated in anoxia injury, but the pathomechanism is unknown. Here we show that anoxia-associated injury causes accumulation of the non-canonical sphingolipid 1-deoxydihydroceramide (DoxDHCer). Anoxia causes an imbalance between serine and alanine resulting in a switch from normal serine-derived sphinganine biosynthesis to non-canonical alanine-derived 1-deoxysphinganine. 1-Deoxysphinganine is incorporated into DoxDHCer, which impairs actin folding via the cytosolic chaperonin TRiC, leading to growth arrest in yeast, increased cell death upon anoxia-reoxygenation in worms and ischaemia-reperfusion injury in mouse hearts. Prevention of DoxDHCer accumulation in worms and in mouse hearts resulted in decreased anoxia-induced injury. These findings unravel key metabolic changes during oxygen deprivation and point to novel strategies to avoid tissue damage and death.

Liposomes of specific artificial phospholipids, such as Pad-PC-Pad and Rad-PC-Rad, are mechanically responsive. They can release encapsulated therapeutics via physical stimuli, as naturally present in blood flow of constricted vessel segments. The question is how these synthetic liposomes change their structure in the medically relevant temperature range from 22 to 42 °C. In the present study, small-angle neutron scattering (SANS) was employed to evaluate the temperature-induced structural changes of selected artificial liposomes. For Rad-PC-Rad, Pad-Pad-PC, Sur-PC-Sur, and Sad-PC-Sad liposomes, the SANS data have remained constant because the phase transition temperatures are above 42 °C. For Pad-PC-Pad and Pes-PC-Pes liposomes, whose phase transitions are below 42 °C, the q -plots have revealed temperature-dependent structural changes. The average diameter of Pad-PC-Pad liposomes remained almost constant, whereas the eccentricity decreased by an order of magnitude. Related measurements using transmission electron microscopy at cryogenic temperatures, as well as dynamic light scattering before and after the heating cycles, underpin the fact that the non-spherical liposomes flatten out. The SANS data further indicated that, as a consequence of the thermal loop, the mean bilayer thickness increased by 20%, associated with the loss of lipid membrane interdigitation. Therefore, Pad-PC-Pad liposomes are unsuitable for local drug delivery in the atherosclerotic human blood vessel system. In contrast, Rad-PC-Rad liposomes are thermally stable for applications within the human body.

Phospholipids are at the heart and origin of life on this planet. The possibilities in terms of phospholipid self-assembly and biological functions seem limitless. Nonetheless, nature exploits only a small fraction of the available chemical space of phospholipids. Using chemical synthesis, artificial phospholipid structures become accessible, and the study of their biophysics may reveal unprecedented properties. In this article, the recent advances by our work group in the field of chemical lipidology are summarized. The family of diamidophospholipids is discussed in detail from monolayer characterization to the formation of faceted vesicles, culminating in the template-free self-assembly of phospholipid cubes and the possible applications of vesicle origami in modern personalized medicine.

Atherosclerosis gives rise to blood vessel occlusion associated with blood flow alteration and substantial increase of average wall shear stress. This modification was proved acting as a purely physical trigger for targeted vasodilator release from a particular type of liposomes composed of 1,3-diaminophospholipids (Pad-PC-Pad). The flow-induced structural changes of these faceted liposomes, however, are completely unknown. Therefore, spatially resolved small-angle X-ray scattering was combined with microfluidics to uniquely study the purely physical mechanisms, which give rise to the highly efficient drug release from mechanoresponsive liposomes of nanometer size. The microfluidic device, designed to mimic a stenotic blood vessel, consisted of a 1-mm-wide channel with a constriction, 125 ​μm in diameter. Here, the changes of the average bilayer thickness and the mean size of the mechanoresponsive liposomes have been locally detected under flow conditions. Overall shape and bilayer thickness do change already near the constriction inlet, but the alteration is dominant near the outlet. At a flow rate of 0.2 ​μL/s, the liposome's bilayer thickness increased by 30 % compared to the situation well before the constriction and under static condition. The detected bilayer thickness increase of the faceted liposomes is in line with the mechanically induced loss of interdigitation between the phospholipid amide chains. These results imply that rather the gradient force than the wall shear stress provokes structural changes of Pad-PC-Pad liposomes and the related drug release at stenoses. The approach, i.e. the combination of microfluidics and spatially resolved small-angle X-ray scattering, paves the way to design highly efficient and specific systems for the targeted drug delivery at constrictions with predefined morphology., (© 2019 The Authors.)

Sphingolipids are bio-active metabolites that show structural diversity among eukaryotes. They are essential for growth of all eukaryotic cells but when produced in an uncontrolled manner can lead to cell death and pathologies including auto-immune reactions, cancer, diabetes and neurodegeneration. Caenorhabditis elegans is an important genetic model organism both to find new drug-targets against parasitic nematodes and to study the conserved roles of sphingolipids in animals like their essential functions in very basic cellular processes ranging from maintenance of cell polarity and mitochondrial repair to growth and survival. C. elegans produces sphingoid bases which are structurally distinct from those of other animals as both iso- and anteiso-branched species have been reported. Using metabolic labeling we show that most worm sphingoid bases are iso-branched. We have synthesized the nematode-specific C17 iso-branched sphinganine and its 1-deoxy analogue and could show that both the iso-branch and the 1-hydroxyl group are essential to form functional nematode sphingolipids which are needed to maintain intestinal function. The organism specificity was examined by complementation experiments in Saccharomyces cerevisiae yeast cells lacking sphingoid base synthesis. We found that iso-branched sphingoid base did not support growth of mutant cells and was toxic to wild type yeast. 1-Deoxy sphingolipids have been linked to the hereditary disease HSAN1A and other metabolic disorders including diabetes. We found that in C. elegans the 1-deoxy analogue cannot rescue the intestinal phenotype caused by sphingoid base depletion. In fact, in wild-type animals with normal sphingoid base biosynthesis, exogenous 1-deoxy analogue had a disruptive effect on apical cytoskeletal organization of intestinal cells indicating that atypical bases can interfere with normal sphingolipid function.