Temperature dependence of anesthetic effects on succinate oxidase activity in uncoupled submitochondrial particles

Is cardiolipin the target of local anesthetic cardiotoxicity?

BACKGROUND AND OBJECTIVES

Local anesthetics are used broadly to prevent or reverse acute pain and treat symptoms of chronic pain. Local anesthetic-induced cardiotoxic reaction has been considered the accidental event without currently effective therapeutic drugs except for recently reported intralipid infusion whose possible mechanism of action is not well known.

CONTENTS

Cardiolipin, an anionic phospholipid, plays a key role in determining mitochondrial respiratory reaction, fatty acid metabolism and cellular apoptosis. Mitochondrial energy metabolism dysfunction is suggested as associated with local anesthetic cardiotoxicity, from an in vitro study report that the local anesthetic cardiotoxicity may be due to the strong electrostatic interaction of local anesthetics and cardiolipin in the mitochondria membrane, although there is a lack for experimental evidence. Herein we hypothesized that local anesthetic-cardiolipin interactions were the major determinant of local anesthetic-associated cardiotoxic reaction, established by means of theoretic and structural biological methods. This interacting model would give an insight on the underlying mechanism of local anesthetic cardiotoxicity and provide clues for further in depth research on designing preventive drugs for such inadvertent accidence in routine clinical practice.

CONCLUSIONS

The interaction between local anesthetic and mitochondrial cardiolipin may be the underlying mechanism for cardiotoxicity affecting its energy metabolism and electrostatic status.

[Molecular mechanism of action of local anesthetics]

The main target of local anaesthetics on nervous tissue is the sodium channel. Molecular biology and electrophysiology have shown different mechanisms of action on this sodium channel, which depend on the chemical structure and electrostatic charge of the local anaesthetic molecule. There are two main types of action, shown up on the isolated axon, a direct one on the sodium channel itself and an alteration in the lipids surrounding the channel. These effects have been shown on the isolated axon and explain the anaesthetic effect by an inhibition of the sodium current. Experimental studies have also shown the effects of local anaesthetics on different organelles within the cell, and so on intracellular metabolism. Mitochondrial energetic metabolism, and therefore ATP synthesis, is reduced by local anaesthetics at several levels. The respiratory enzyme chain is inhibited by small concentrations of local anaesthetic, especially NADH dehydrogenase and ubiquinone succinate dehydrogenase. Moreover, local anaesthetics increase the mitochondrial membrane permeability to protons, thus removing the moving force behind ATPase activity in ATP synthesis; this leads to a drastic fall in available energy. This effect is further increased by a direct inhibition of ATPase and ATP/ADP translocation. Other enzyme systems of other organelles are also disturbed by local anaesthetics, such as the endoplasmic reticular Ca++ ATPase, which is inhibited, so altering the calcium concentration within the cytosol. Local anaesthetics also inhibit lipolysis and glycogenesis. Receptors such as the acetylcholine receptors are blocked by local anaesthetics. The mechanism of action of these drugs on all these protein systems is two-fold: an alteration of protein structure, but also of the lipids surrounding them.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of human serum and rabbit muscle cholinesterase by local anesthetics

The effects of tertiary amine local anesthetics (procaine, mepivacaine, lidocaine, tetracaine, dibucaine, and bupivacaine) and chlorpromazine were investigated for rabbit muscle acetylcholinesterase and human serum cholinesterase. The muscle enzyme was poorly inhibited by local anesthetics containing an amide linkage. The serum cholinesterase was inhibited by all those compounds, their relative potencies being proportional to their octanol/water partition coefficients. The dissociation constants of tetracaine and procaine, ester anesthetics, were 1000-fold and 100-fold, respectively, that which would be expected from their partition coefficient basis respective to the other amide anesthetics. Procaine showed competitive inhibition of serum cholinesterase, whereas for most anesthetics a mixed type of inhibition was observed. Procaine probably binds at the main anionic site, while the other positively charged anesthetics bind to either the catalytic centre or to the peripheral or modulator anionic site, modifying the kinetic behaviour of cholinesterase as has been demonstrated by the appearance of negative cooperativity for binding to the substrate.

Local anesthetics: a new class of partial inhibitors of mitochondrial ATPase

The following characteristics are reported for mitochondrial ATPase prepared by the chloroform extraction method: (1) The pH optimum for enzyme activity is at 8.0. (2) The neutral anesthetic benzocaine inhibits the enzyme at all pH values. (3) Reciprocal plots of 1/v versus 1/[ATP] show that inhibition by lidocaine, tetracaine, dibucaine, and chlorpromazine is noncompetitive; slope and intercept replots are hyperbolic, showing that the inhibition is partial rather than complete.

Further studies on F1-ATPase inhibition by local anesthetics

We have measured the inhibitory potencies of several local anesthetics (procaine, lidocaine, tetracaine and dibucaine) and related compounds (chlorpromazine, procainamide and propranolol) on the ATPase activities of bovine heart submitochondrial particles and purified F1 extracted from these particles. All of these agents cause inhibition of ATPase in F1 as well as in submitochondrial particles. A linear relationship is found between the log of the octanol/water partition coefficients and the log of the concentrations required for 50% inhibition of F1. Sedimentation velocity ultracentrifugation and polyacrylamide gel electrophoresis showed that 1.0 mM tetracaine caused partial dissociation of the F1 complex. Complete reversibility of the enzyme inhibitory effects was demonstrated, however. This work shows that local anesthetics can affect protein structure and enzyme activity without the mediation of lipid.

Cytochrome c oxidase inhibition by anesthetics: thermodynamic analysis

The thermodynamic parameters that characterize the inhibition of cytochrome c oxidase activity, in rat liver submitochondrial particles, by n-butanol, tetracaine, and dibucaine were obtained. Three equilibria were assumed in order to account for the data: for the interaction of inhibitor with the native state of the enzyme, for the interaction of inhibitor with the thermally (reversibly) denatured state, and for the change between the native and thermally denatured states. Inhibition results from interaction with both the native and denatured states but, because the interaction is stronger with the denatured than with the native state, the native/denatured equilibrium is shifted to the right by the anesthetics. The enthalpies of interaction are -2.3, -4.7, and 3.7 kcal/mol (1 cal = 4.18 J) for the native state and -10, -6, and -14 kcal/mol for the denatured state, for n-butanol, tetracaine, and dibucaine, respectively. These values are much smaller than the previous estimates obtained by using the assumption that anesthetics interact only with the thermally denatured state of enzymes (e.g., -81 kcal/mol for tetracaine inhibition of luciferase). Our results suggest that local anesthetics inhibit enzyme activity by causing a reversible perturbation of protein conformation. The magnitude of the perturbation is much smaller (in energetic terms) than that which accompanies thermal denaturation.

Multiple sites of inhibition of mitochondrial electron transport by local anesthetics

Local anesthetics and alcohols were found to inhibit mitochondrial electron transport at several points along the chain. THe anesthetics employed were the tertiary amines procaine, tetracaine, dibucaine, and chlorpromazine, and the alcohols were n-butamol, n-pentanol, n-hexanol, and benzyl alcohol. Uncoupled sonic submitochondrial particles from beef heart and rat liver were studied. We report the following: (1) All of the anesthetics were found to inhibit each of the segments of the electron transport chain assayed; these included cytochrome c oxidase, durohydroquinone oxidase, succinate oxidase, NADH oxidase, succinate dehydrogenase, succinate-cytochrome c oxidoreductase, and NADH-cytochrome c oxidoreductase. (2) NADH oxidase and NADH-cytochrome c oxidoreductase required the lowest concentration of anesthetic for inhibition, and cytochrome c oxidase required the highest concentrations. (3) We conclude that there are several points along the chain at which inhibition occurs, the most sensitive being in the region of Complex I (NADH dehydrogenase). (4) Beef heart submitochondrial particles are less sensitive to inhibition than are rat liver particles. (5) Low concentrations of several of the anesthetics gave enhancement of electron transport activity, whereas higher concentrations of the same agents caused inhibition. (6) The concentrations of anesthetics (alcohol and tertiary amine) which gave 50% inhibition of NADH oxidase were lower than the reported concentrations required for blockage of frog sciatic nerve.

Membranes and phospholipids of liver mitochondria from chronic alcoholic rats are resistant to membrane disordering by alcohol

Using the spin probe 5-doxylstearic acid, we studied the structural perturbations of rat liver mitochondrial membranes produced by exposure to ethanol in vitro and by chronic ethanol feeding. The addition of ethanol in vitro to mitochondria from control animals appears to "fluidize" the membranes, as evidenced by a pronounced decrease in the order parameter. By contrast, in membranes from rats fed ethanol chronically, there was no effect on the order parameter. This resistance of the mitochondrial membranes from chronically intoxicated animals to the fluidizing effect of ethanol probably results from a change in the composition of the phospholipids, because the same differential response to ethanol was observed upon using vesicles of mitochondrial phospholipids extracted from control and chronically treated rats. In the presence of 0.025--0.1 M ethanol, a range that prevails in the blood of chronic alcoholics, the order parameter of mitochondrial membranes from rats fed ethanol was comparable to that of control membranes without ethanol in vitro. Analysis of extracted mitochondrial phospholipids showed that the cardiolipin from ethanol-fed animals had fatty acyl residues that are more saturated than those of controls. These findings point to the underlying molecular mechanism of our previous observation that mitochondria from chronic alcoholic rats are more resistant to uncoupling by ethanol at physiological temperature [Rottenberg, H., Robertson, D. E. & Rubin, E. (1980) Lab. Invest. 42, 318--326]. We suggest that an adaptive change in the phospholipid composition leads to structural alterations, which result in increased resistance to disruption of mitochondrial membranes by ethanol. These changes in lipid composition and structure may explain many, if not all, of the mitochondrial abnormalities that have been previously reported to result from chronic ethanol intoxication.

On the mechanism of action of anesthetics. Direct inhibition of mitochondrial F1-ATPase by n-butanol and tetracaine

The concentrations of n-butanol and tetracaine required for 50% inhibition of the ATPase activity of F1 particles isolated from bovine heart mitochondria were 160 mM and 1.1 mM, respectively. The results are offered as evidence that the physiological effects of these anesthetics may be due to direct interaction with membrane proteins rather than with the lipids.

Action of barbiturates on activity of acetylcholinesterase from synaptosomal membranes

The acetylcholinesterase from synaptosomal membranes is inhibited by anesthetics: Nembutal, brietal, and thiopental. Nembutal and brietal decrease the Km for acetylthiocholine, without changes in Vmas. A noncompetitive type of inhibition is produced by thiopental. This anesthetic decreases Arrhenius plot discontinuity by about 4 degrees C and increases activation energies. Nembutal and brietal do not change Arrhenius plot discontinuities, but they increase activation energies. These results suggest that barbiturates change lipid-protein interactions in synaptosomal membranes.

The temperature dependence of respiration and ATPase in rat liver mitochondria is altered by ethanol

We studied hepatic mitochondria to determine the effects of ethanol in vitro and of chronic ethanol consumption on the temperature dependence (10 degrees-45 degrees C) of a) substrate oxidation, and b) ATP hydrolysis, with or without CCCP. Arrhenius plots showed the characteristic breaks around 20 degrees C both for electron transport and ATP hydrolysis with high energy of activation at low temperature and low energy of activation at high temperature. Ethanol, in vitro, generally lowered the energy of activation at high temperature and shifted the break in the Arrhenius plots to lower temperatures suggesting an increase in membrane fluidity. At 40 degrees C and above ethanol accelerated electron transport and greatly stimulated ATPase activity. In mitochondria from ethanol-fed rats, Arrhenius plots showed a shift in the breaks to a higher temperature, a finding which suggests a change in membrane structure, possibly associated with decreased fluidity. This may be an adaption of the mitochondrial membranes to counter the effect of ethanol on membrane structure.