Location of the Positive Charges in Cationic Amphiphiles Modulates Their Mechanism of Action against Model Membranes.

Synthetic cationic amphiphiles (CAms) with physicochemical properties similar to antimicrobial peptides are promising molecules in the search for alternative antibiotics to which pathogens cannot easily develop resistance. Here, we investigate two types of CAms based on tartaric acid and containing two hydrophobic chains (of 7 or 11 carbons) and two positive charges, located either at the end of the acyl chains (bola-like, B7 and B11) or at the tartaric acid backbone (gemini-like, G7 and G11). The interaction of the CAms with biomimetic membrane models (anionic and neutral liposomes) was studied with zeta potential and dynamic light scattering measurements, isothermal titration calorimetry, and a fluorescent-based leakage assay. We show that the type of molecule determines the mechanism of action of the CAms. Gemini-like molecules (G7 and G11) interact mainly via electrostatics (exothermic process) and reside in the external vesicle leaflet, altering substantially the vesicle surface potential but not causing significant membrane lysis. On the other hand, the interaction of bola-like CAms (B7 and B11) is endothermic and thus entropy-driven, and these molecules reach both membrane leaflets and cause substantial membrane permeabilization, likely after clustering of anionic lipids. The lytic ability is clearly higher against anionic membranes as compared with neutral membranes. Within each class of molecule, longer alkyl chains (i.e., B11 and G11) exhibit higher affinity and lytic ability. Overall, the molecule B11 exhibits a high potential as antimicrobial agent, since it has a high membrane affinity and causes substantial membrane permeabilization.

PolyMorphine provides extended analgesic-like effects in mice with spared nerve injury.

Abstract: Morphine is a well-characterized and effective analgesic commonly used to provide pain relief to patients suffering from both acute and chronic pain conditions. Despite its widespread use and effectiveness, one of the major drawbacks of morphine is its relatively short half-life of approximately 4 h. This short half-life often necessitates multiple administrations of the drug each day, which may contribute to both dependence and tolerance to morphine. Here, we tested the analgesic properties of a new polymer form of morphine known as PolyMorphine. This polymer has monomeric units of morphine incorporated into a poly(anhydride-ester) backbone that has been shown to hydrolyze into free morphine in vitro. Using an animal model of chronic pain, the spared nerve injury surgery, we showed that PolyMorphine is able to block spared nerve injury-induced hypersensitivity in mice for up to 24-h post-administration. Free morphine was shown to only block spared nerve injury-induced hypersensitivity for up to 2-h post-injection. PolyMorphine was also shown to act through the mu opioid receptor due to the ability of naloxone (a mu opioid receptor antagonist) to block PolyMorphine-induced analgesia in spared nerve injury animals pretreated with PolyMorphine. Additionally, we observed that PolyMorphine causes similar locomotor and constipation side effects as free morphine. Finally, we investigated if PolyMorphine had any effects in a non-evoked pain assay, conditioned place preference. Pretreatment of spared nerve injury mice with PolyMorphine blocked the development of conditioned place preference for 2-methyl-6-(phenylethynyl)pyridine (MPEP), a short-lasting mGluR5 antagonist with analgesic-like properties. Free morphine does not block the development of preference for MPEP, suggesting that PolyMorphine has longer lasting analgesic effects compared to free morphine. Together, these data show that PolyMorphine has the potential to provide analgesia for significantly longer than free morphine while likely working through the same receptor.