Biphasic effects of oxethazaine, a topical anesthetic, on the intracellular Ca(2+) concentration of PC12 cells

Complexation of oxethazaine with 2-hydroxypropyl-β-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-β-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-1H-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-β-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-β-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.

Oxethazaine inhibits hepatitis B virus capsid assembly by blocking the cytosolic calcium-signalling pathway

Chronic hepatitis B virus (HBV) infection is a serious public health problem and may progress to liver fibrosis, cirrhosis and hepatocellular carcinoma. It is currently treated with PEGylated IFN-α2a and nucleoside/nucleotide analogues (NAs). However, PEGylated IFN treatment has problems of high cost, low efficiency and side effects. Long-term administration of NAs is necessary to avoid virus relapse, which can cause drug resistance and side effects. New efforts are now being directed to develop novel anti-HBV drugs targeting either additional viral targets other than viral DNA polymerase or host targets to improve the treatment of chronic hepatitis B. In this study, we discovered that oxethazaine, approved for clinic use in a few countries such as Japan, India, South Africa and Brazil, can dose-dependently reduce the levels of HBV envelope antigen, extracellular HBV DNA in supernatants and intracellular HBV total DNA. However, the levels of HBV cccDNA and HBV RNAs were not affected by oxethazaine treatment. Further study confirmed that oxethazaine acts on the virus assembly stage of the HBV life cycle. A study of the mechanisms of oxethazaine suggested that this drug inhibits HBV replication and capsid assembly by blocking the cytosolic calcium-signalling pathway. Moreover, oxethazaine could inhibit the replication of lamivudine/entecavir-dual-resistant and adefovir-resistant HBV mutants. In conclusion, our study suggests that oxethazaine may serve as a promising drug, or could be used as a starting point for anti-HBV drug discovery.

Intrahepatic Flow Disturbance: Possibility of a Hidden Cause of Drug Toxicity

The liver has an intricate microvascular system that allows homogenous perfusion throughout the organ. However, the regulatory mechanisms of intrahepatic circulation are still unclear, and the effects of drugs on this system have rarely been reported. Oxethazaine, a topical anesthetic, was incidentally found to induce a consistent increase in portal pressure in the isolated perfused rat liver, which led us to characterize this phenomenon. For this, a vital staining method was developed to detect microcirculatory alterations in the isolated liver. Using this method, not only vasoconstrictors like endothelin-1, but the drugs oxethazaine and clomipramine, a tricyclic antidepressant, were found to induce flow redistribution to the deeper and hilar portions of the liver with minimal perfusion at the periphery, which was due to a short-circuit flow at the center owing to the constriction of the intrahepatic portal vein branches. Hepatic nerve stimulation also produced a similar flow disturbance. Since the portal pressure increases by these compounds were inhibited by the Rho-kinase inhibitors Y27632 and HA1077, portal vein branches may employ a Rho-kinase-dependent pathway for sustained contraction. However, oxethazaine, clomipramine, and endothelin-1 may activate this pathway differently. The intrahepatic flow disturbance could play a hidden role in drug toxicity of certain drugs.

Mechanisms involved in the contraction of intrahepatic portal vein branches by clomipramine and oxethazaine in isolated perfused rat livers

Clomipramine (CLM) and oxethazaine (OXZ) were previously reported to increase portal pressure by contracting portal vein branches (PVBs) in isolated perfused rat liver. In the present study, to characterize the contractile mechanisms, the effects of Y27632, HA1077, staurosporine, papaverine, SKF96365, and sulindac sulfide on the portal pressure increase induced by CLM and OXZ were examined comparatively with those induced by endothelin-1. The results suggest that 1) intrahepatic PVBs employ a Rho-kinase-dependent pathway for sustained contraction, 2) CLM contracts PVBs by activating a Rho-kinase pathway and Ca(2+)-channels, and 3) OXZ acts primarily by promoting Ca(2+) entry through its ionophore-like action.

Intrahepatic flow disturbance by clomipramine in the isolated perfused rat liver

Intrahepatic flow disturbance may have important pharmacological and toxicological significance. However, apart from pathological conditions, flow disturbance by drugs has received little attention. In the isolated perfused rat liver (IPRL), we found that infusion of tricyclic antidepressants increased portal perfusion pressure (PP) with a coincidental decrease in oxygen uptake at concentrations of 3-30 microM; the order of potency was clomipramine > amitriptyline > imipramine approximately nortriptyline >> desipramine. The characteristics of clomipramine action were as follows: (1) The extrahepatic portal vein was much less sensitive to clomipramine than the IPRL. (2) Changes in PP and oxygen uptake required Ca(2+) in the perfusate and were inhibited by papaverine, staurosporine, sodium nitroprusside and indomethacin. (3) Compared with endothelin-1, clomipramine produced a greater decrease in the ratio of oxygen uptake/PP together with a greater overflow of loaded indocyanine green for an increase in PP by about 2 cm H(2)O. (4) Vital staining with trypan blue and rhodamine 6G and histological examinations revealed that 3-10 microM clomipramine produced marked flow redistribution due to the constriction of portal vein branches. Portal flow was short-circuited to the hepatic vein at a deeper and hilar portion of the liver, with minimal perfusion of the periphery. These results demonstrate an example of drug-induced intrahepatic flow disturbance in vitro. Its contribution to the development of toxicity in vivo remains to be studied.

Ca2+ dependency of N-cadherin function probed by laser tweezer and atomic force microscopy

This study was undertaken to provide a biophysical basis for the hypothesis that activity-dependent modulation of cadherin-mediated adhesion by transient changes of extracellular calcium ([Ca2+]e) is causally involved in coordination of synaptic plasticity. Characterization of homophilic N-cadherin binding by atomic force microscopy and laser tweezer trapping of N-cadherin-coated microbeads attached to the cell surface of cultured neuronal cells showed that adhesive activity of N-cadherin is effectively regulated between 0.3 and 0.8 mm [Ca2+]e. Furthermore, we show that an increase of [Ca2+]i, which is known to be essential for induction of synaptic plasticity, causes significant reduction of cadherin-mediated bead adhesion that could be completely suppressed by inhibition of actin depolymerization. The results of this study show that N-cadherin has ideal biophysical properties to serve as a Ca2+-dependent sensor for synaptic activity and, at the same time, is strategically located to control synaptic adhesion. A drop of [Ca2+]e and a concomitant increase of [Ca2+]i may act in concert to modulate N-cadherin-based adhesive contacts at synaptic sites.