Complexation of oxethazaine with 2-hydroxypropyl-ß-cyclodextrin: increased drug solubility, decreased cytotoxicity and analgesia at inflamed tissues.

OBJECTIVES: Oxethazaine (OXZ) is one of the few local anaesthetics that provides analgesia at low pH, but presents poor solubility, cytotoxicity and no parenteral formulations. To address these issues, we aimed to prepare OXZ host-guest inclusion complex with hydroxypropyl-beta-cyclodextrin (HP-ß-CD). METHODS: The inclusion complex was formed by co-solubilization, followed by a job plot analysis to determine stoichiometry of complexation and dialysis equilibrium analysis (based on UV/VIS absorption and fluorescence profiles of OXZ). Complex formation was confirmed by phase-solubility data, X-ray, Scanning Electron Microscopy and DOSY-1 H-NMR experiments. In vitro cytotoxicity was analysed by MTT test in 3T3 fibroblasts. In vivo analgesia was tested by Von Frey test (inflammatory wounds - rats). KEY FINDINGS: Oxethazaine complexed (1 : 1 molar ratio) with HP-ß-CD, as indicated by loss of OZX crystalline structure (X-ray) and strong host: guest interaction (NMR, K = 198/M), besides increased solubility. In vitro cell survival improved with the complex (IC50 OXZ = 28.9 µm, OXZ : HP-ß-CD = 57.8 µm). In addition, the complex (0.1% OXZ) promoted in vivo analgesia for the same time that 2% lidocaine/epinephrine did. CONCLUSION: Our results show that complexation improved physicochemical and biological properties of OXZ, allowing its application to inflamed tissues by parenteral routes.

In situ quantification of Cu(II) during an electrodeposition reaction using time-domain NMR relaxometry.

The use of a low-cost benchtop time-domain NMR (TD-NMR) spectrometer to monitor copper electrodeposition in situ is presented. The measurements are based on the strong linear correlation between the concentration of paramagnetic ions and the transverse relaxation rates (R(2)) of the solvent protons. Two electrochemical NMR (EC-NMR) cells were constructed and applied to monitor the Cu(2+) concentration during the electrodeposition reaction. The results show that TD-NMR relaxometry using the Carr-Purcell-Meiboom-Gill pulse sequence can be a very fast, simple, and efficient technique to monitor, in real time, the variation in the Cu(2+) concentration during an electrodeposition reaction. This methodology can also be applied to monitor the electrodeposition of other paramagnetic ions, such as Ni(2+) and Cr(3+), which are commonly used in electroplating.

Liposome-prilocaine interaction mapping evaluated through STD NMR and molecular dynamics simulations.

We have examined the interaction of the neutral and protonated species of the local anesthetic prilocaine (PLC) with phosphatidylcholine (PC) bilayers combining experimental ((1)H NMR) and theoretical (molecular dynamics simulations) approaches. DOSY experiments allowed the determination of the association constants of protonated (Ka = 9 L/mol) and neutral (Ka = 21 L/mol) PLC to egg PC liposomes. Saturation transfer difference (STD) experiments showed a different trend depending on pH: At high pH the PLC hydrogen saturation was essentially uniform and at pH 5.5 the experiments show an enhancement of the aromatic moiety hydrogen saturation, with respect to the tail. Molecular dynamics simulations, performed with PLC molecules on planar bilayers of palmitoyloleyl-PC, revealed a preferential orientation for the protonated PLC species at the polar interface of the bilayer, and a nonoriented and deeper insertion for neutral PLC. Such preferential location of protonated and neutral PLC inside the bilayer can be described as different transient sites which could modulate the access of these molecules to their binding site(s) in the voltage-gated sodium channel, justifying differences in the anesthetic's potency upon ionization.