The inhibitory effects of local anesthetics on superoxide generation of neutrophils correlate with their partition coefficients

Effect of Dental Local Anesthetics on Reactive Oxygen Species: An In Vitro Study

Introduction Oxidative stress, an imbalance between reactive oxygen species (ROS) production and antioxidant defenses, plays an important role in various dental diseases. Local anesthetics are frequently used in dentistry. The potential antioxidant activity of dental local anesthetics can contribute to dental practice. Therefore, this study aimed to investigate the ROS-scavenging activities of three commonly used dental local anesthetics, lidocaine, prilocaine, and articaine, focusing on their effects on hydroxyl radicals (HO•) and superoxide anions (O2 •-). Materials and methods The electron spin resonance (ESR) spin-trapping technique was employed to specifically measure the ROS-scavenging activities of these local anesthetics at varying concentrations. Results Lidocaine, prilocaine, and articaine exhibited concentration-dependent HO•-scavenging activities, with IC50 values of 0.029%, 0.019%, and 0.014%, respectively. Lidocaine and prilocaine showed concentration-dependent O2 •--scavenging activity, with IC50 values of 0.033% and 0.057%, respectively. However, articaine did not scavenge O2 •-. Conclusions The proactive use of dental local anesthetics may mitigate oxidative injury and inflammatory damage through direct ROS scavenging. However, further research is needed to elucidate the specific mechanisms underlying the antioxidant effects of these dental local anesthetics and their potential impact on the dental diseases associated with oxidative stress.

The dose-response relationships of the direct scavenging activity of amide-based local anesthetics against multiple free radicals

This study aimed to illustrate the dose-response relationships of the direct scavenging activity of amide-based local anesthetics against multiple free radicals in vitro. We have demonstrated that amide-type local anesthetics selectively and directly scavenge some free radicals. Three kinds of free radicals were eliminated by all the four local anesthetics examined. Mepivacaine, lidocaine, bupivacaine, and dibucaine scavenged hydroxyl radicals in dose-dependent manners. Ascorbyl free radicals were also scavenged in dose-dependent manners, and lastly singlet oxygen was scavenged in dose-dependent manners. Three other free radicals were not scavenged by all of the four local anesthetics; tert-butoxyl radical was scavenged by all the anesthetics examined but dibucaine, nitric oxide by mepivacaine but not by the other three, and tyrosyl radical by mepivacaine and lidocaine but not by the other two. Some free radicals (superoxide anion, tert-butyl peroxyl radical, DPPH) were not scavenged by any of the four local anesthetics. The local anesthetics were also shown to inhibit lipid peroxidation by TBARS assay. These results suggest that local anesthetics have antioxidant properties through their free radical scavenging activities.

Cytotoxic responses of human chondrocytes to bupivacaine, levobupivacaine, and ropivacaine

Background

Intra-articular injections of local anesthetics are used commonly in articular surgery. However, chondrocyte viability and metabolism may be adversely affected by various anesthetics.

Objectives

To assess the chondrotoxic effects of bupivacaine, levobupivacaine, and ropivacaine on human chondrocytes and elucidate possible mechanisms of chondrocyte death.

Methods

Cultured human chondrocytes (CHON-001) were exposed to 0.25% or 0.5% of bupivacaine, levobupivacaine, and ropivacaine in vitro. Cell viability was determined by flow cytometry after 15, 30, 60, and 120 min of exposure. Chondrocyte reactive oxygen species (ROS) production was measured every 10 min for up to 1 h using 2ʹ,7ʹ-dichlorodihydrofluorescein staining. Chondrocyte production of glycosaminoglycan was measured by capillary electrophoresis. NO production was measured using a colorimetric assay kit.

Results

We found a significant increase in chondrotoxicity dependent on exposure time and concentration of the anesthetic. At 60 min, chondrocyte viability was significantly (P < 0.05) decreased when exposed to 0.5% levobupivacaine (32.5%), or 0.25% or 0.5% bupivacaine (34.3% or 46.5%, respectively) compared with exposure to phosphate-buffered saline (PBS) vehicle as a control. Cell death at 120 min was mainly necrosis. There was no difference in viability after treatment with either concentration (0.25% or 0.5%) of ropivacaine at any time compared with exposure to PBS. We found increased production of NO, while ROS decreased after exposure to any of the anesthetics tested.

Conclusions

Ropivacaine may be safer than bupivacaine or levobupivacaine as an intra-articular analgesic. Chondrotoxicity of anesthetics in vitro may be mediated via a reactive nitrogen species-dependent pathway.

Blocking ion channels induced by antifungal lipopeptide syringomycin E with amide-linked local anesthetics

The effects of the amide-linked (lidocaine (LDC), mepivacaine (MPV), prilocaine (PLC)) and ester-bound local anesthetics (benzocaine (BZC), procaine (PRC), and tetracaine (TTC)) on the pore-forming activity of the antifungal lipopeptide syringomycin E (SRE) in lipid bilayers were studied. Independently on electrolyte concentration in the membrane bathing solution the observed changes in conductance of SRE channels agreed with the altered membrane dipole potential under the action of ester-bound local anesthetics. Effects of aminoamides in diluted and concentrated solutions were completely different. At 0.1 M KCl (pH 7.4) the effects of amide-linked anesthetics were in accordance with changes in the membrane surface potential, while at 2 M KCl aminoamides blocked ion passage through the SRE channels, leading to sharp reductions in pore conductance at negative voltages and 100-fold decreases in the channel lifetimes. The effects were not practically influenced by the membrane lipid composition. The interaction cooperativity implied the existence of specific binding sites for amide-bound anesthetics in SRE channels.

Effects of local anesthetics on the respiratory burst of cord blood neutrophils in vitro

BACKGROUND

Whether local anesthetics exert anti-inflammatory effects in fetal and newborn systemic neutrophils is unclear. The aim of the present study was to assess the effects of bupivacaine and lidocaine on the respiratory burst of cord blood neutrophils in vitro compared with adult cells.

METHODS

Whole cord blood (n = 12) and control adult blood samples (n = 7) were incubated with bupivacaine (0.0005, 0.005, 0.05, 1 mmol/l) and lidocaine (0.002, 0.02, 0.2, 4 mmol/l) for 1 and 4 h. The production of reactive oxygen species (ROS) by unstimulated neutrophils and the phorbol myristate acetate-induced oxidative burst were assessed by flow cytometry. A subset of neutrophils showing high fluorescence intensity (rho+) was analyzed separately.

RESULTS

After 1 h incubation, local anesthetics decreased the respiratory burst in whole cord blood and adult neutrophils in a similar manner. At the clinically relevant concentration of 0.0005 mmol/l, bupivacaine was active, but its effect in cord blood cells could not be detected after 4 h. The cord blood rho+ cell subset was unresponsive to the inhibitory action of bupivacaine. In rho+ neutrophils, basal ROS production was stimulated by lidocaine at the lowest concentration tested.

CONCLUSION

Bupivacaine and lidocaine can decrease the respiratory burst in neutrophils of term newborns.

Inhibition of voltage-gated proton channels by local anaesthetics in GMI-R1 rat microglia

Voltage-gated proton channels play crucial roles during the respiratory burst in phagocytes, such as microglia. As local anaesthetics have a variety of anti-inflammatory properties, including inhibition of phagocytosis, they may act on the proton channels. Most local anaesthetics are tertiary amines and may affect proton channels through modification of pH(i) as weak bases. To test these hypotheses, the effects of lidocaine and bupivacaine on proton channels were examined in a rat microglial cell line (GMI-R1) as a function of pH(o) and pH(i). Both lidocaine and bupivacaine reversibly decreased the current, with IC(50) values of ∼1.2 and ∼0.5 mM, respectively, at pH(o)/pH(i) 7.3/5.5. The inhibition was enhanced with either pH(o) increase or pH(i) decrease, suggesting that the protonation of the base forms inside the cell contributed to the inhibitory effects. Both local anaesthetics shifted the reversal potentials to more positive voltages, indicating increases in pH(i). The potencies of inhibition were correlated well with the degree of increase in pH(i). The lidocaine-induced inhibition was eliminated when the pH(i) increases were cancelled by co-application of a weak acid, butyrate. The cytosolic alkalizations by lidocaine and bupivacaine were confirmed using a pH-sensitive fluorescent dye, BCECF, in non-voltage-clamped cells. Furthermore, chemiluminescence measurement proved that both anaesthetics inhibited production of reactive oxygen species by the cells. In conclusion, lidocaine and bupivacaine inhibit proton channels primarily by the weak base mechanism via an increase in pH(i). This is a novel mechanism underlying actions of local anaesthtics.

Anti-inflammatory properties of local anesthetics and their present and potential clinical implications

Development of new local anesthetic agents has been focused on the potency of their nerve-blocking effects, duration of action and safety and has resulted in a substantial number of agents in clinical use. It is well established and well documented that the nerve blocking effects of local anesthetics are secondary to their interaction with the Na+ channels thereby blocking nerve membrane excitability and the generation of action potentials. Accumulating data suggest however that local anesthetics also possess a wide range of anti-inflammatory actions through their effects on cells of the immune system, as well as on other cells, e.g. microorganisms, thrombocytes and erythrocytes. The potent anti-inflammatory properties of local anesthetics, superior in several aspects to traditional anti-inflammatory agents of the NSAID and steroid groups and with fewer side-effects, has prompted clinicians to introduce them in the treatment of various inflammation-related conditions and diseases. They have proved successful in the treatment of burn injuries, interstitial cystitis, ulcerative proctitis, arthritis and herpes simplex infections. The detailed mechanisms of action are not fully understood but seem to involve a reversible interaction with membrane proteins and lipids thus regulating cell metabolic activity, migration, exocytosis and phagocytosis.

Chirality in anaesthesia - ropivacaine, ketamine and thiopentone

Drug chirality (molecular handedness) is a source of pharmacological differences between otherwise chemically identical molecules. Specific applications to the pharmacology of ropivacaine (single enantiomer), ketamine and thiopentone (both racemates) are discussed. Ropivacaine is produced as a single S-enantiomer homologue of the more toxic bupivacaine to preclude the higher central nervous system and heart toxicity found in the R-enantiomer. S-ketamine is presently undergoing trials as a potential replacement for the racemate, on the grounds that it optimizes anaesthesia and minimizes psychotomimetic phenomena. Thiopentone, previously known to have quantitative differences in the pharmacology of its enantiomers, has recently also been shown to have pharmacokinetic differences. The evidence for these claims is discussed in this review.