Cysteamine assay for the evaluation of bioactive electrophiles

Cysteamine Chemisorption at Mercury-Solution Interfaces in the Context of Redox and Microdissociation Equilibria

The redox behavior and chemisorption of cysteamine (CA) at a charged mercury surface are described, with an emphasis on its acid-base properties supported by molecular dynamics and quantum mechanical calculations. It was found that CA forms chemisorbed layers on the surface of the mercury electrode. The formation of Hg-CA complexes is connected to mercury disproportionation, as reflected in peaks SII and SI at potentials higher than the electrode potential of zero charge (p.z.c.). Both the process of chemisorption of CA and its consequent redox transformation are proton-dependent. Also, depending on the protonation of CA, the formation of typical populations of chemisorbed conformers can be observed. In addition, cystamine (CA disulfide dimer) can be reduced on the mercury surface. Between the potentials of this reduction and peak SI, the p.z.c. of the electrode used can be found. Furthermore, CA can serve as an LMW catalyst for hydrogen evolution. The mechanistic insights presented here can be used for follow-up research on CA chemisorption and targeted modification of other metallic surfaces.

Design and evaluation of propranolol hydrochloride loaded thiolated Zein/PEO electrospun fibrous matrix for transmucosal drug delivery

Thiolated polymers have garnered wide attention from researchers on mucoadhesive drug delivery. This work explores the thiolation of zein protein using cysteine amino acid via the EDC crosslinker. The optimization of thiolation and purification have been done and confirmed using Ellman's assay and Raman spectra. The thiolated Zein/PEO polymer blend has been appraised for electrospinning to fabricate fibrous matrices. The extent of thiol modification augmented the mechanical properties and adhesion in rabbit intestinal mucosa. In vitro cytotoxicity evaluations such as direct contact assay, MTT assay, and live dead assay performed in RPMI 2650 cells corroborated the non-cytotoxicity of the fabricated matrices with and without propranolol hydrochloride (PL). Detailed drug release studies were conducted in PBS. Drug release in PBS followed the Korsmeyer Peppas model of release. On treating RPMI 2650 cells with the matrix, F-actin and adherens junctional proteins retained integrity, and consequently, drug permeation would proceed through the transcellular transport mechanism. Transepithelial electrical resistance (TEER) measurement of the RPMI 2650 cell monolayer also supported the transcellular transport mechanism. Ex vivo permeation study through porcine buccal mucosa showed 41.26 ± 0.56% PL permeation within 24 h of study. It validated the competence of the electrospun thiolated Zein/PEO matrix for transmucosal drug delivery.

Serum albumin as a primary non-covalent binding protein for nitro-oleic acid

This work explores the interaction of 9/10-nitro-oleic acid (NO₂-OA) with human serum albumin (HSA). The molecular mechanism of the biological action of NO₂-OA is to our knowledge based on a reversible covalent reaction-Michael addition of nucleophilic amino acid residues of proteins. Since HSA is an important fatty acid transporter, a key question is whether NO₂-OA can bind covalently or non-covalently to HSA, similarly to oleic acid (OA), which can interact with the FA1-FA7 binding sites of the HSA molecule. ¹H NMR studies and competition analysis with OA and the drugs ibuprofen and warfarin were used to investigate a potential non-covalent binding mode. NO₂-OA/HSA binding was confirmed to compete with warfarin for FA-7 with significantly higher affinity. NO₂-OA competes with ibuprofen for FA-3 and FA-6, however, in contrast to the situation with warfarin, the binding affinities are not significantly different. The described interactions are based exclusively on non-covalent binding. No covalent binding of NO₂-OA to HSA was detected by MS/MS. More detailed studies based on MALDI-TOF-MS and Ellman's assay indicated that HSA can be covalently modified in the presence of NO₂-OA to a very limited extent. It was also shown that NO₂-OA has a higher affinity to HSA than that of OA.