Transformations of 2,6-diisopropylphenol by NO-derived nitrogen oxides, particularly peroxynitrite

Propofol Attenuates the Myocardial Protection Properties of Desflurane by Modulating Mitochondrial Permeability Transition

BACKGROUND

Desflurane and propofol are cardioprotective, but relative efficacy is unclear. The aim was to compare myocardial protection of single, simultaneous, and serial administration of desflurane and propofol.

METHODS

Sixty New Zealand White rabbits and 65 isolated Sprague Dawley rat hearts randomly received desflurane, propofol, simultaneous desflurane and propofol, or sequential desflurane then propofol. Rabbits were subdivided to receive either ischemia-reperfusion with temporary occlusion of the left anterior descending artery or a time-matched, nonischemic perfusion protocol, whereas rat hearts were perfused in a Langendorff model with global ischemia-reperfusion. End points were hemodynamic, functional recovery, and mitochondrial uptake of H-2-deoxy-D-glucose as an indicator of mitochondrial permeability transition.

RESULTS

In rabbits, there were minimal increases in preload-recruitable stroke-work with propofol (P < .001), desflurane (P < .001), and desflurane-and-propofol (P < .001) groups, but no evidence of increases with pentobarbitone (P = .576) and desflurane-then-propofol (P = .374). In terms of end-diastolic pressure-volume relationship, there was no evidence of increase compared to nonischemic controls with desflurane-then-propofol (P = .364), a small but significant increase with desflurane (P < .001), and larger increases with pentobarbitone (P < .001), propofol (P < .001), and desflurane-and-propofol (P < .001).In rat hearts, there was no statistically significant difference in mitochondrial H-activity between propofol and desflurane-and-propofol (165 ± 51 × 10 vs 154 ± 51 × 10 g·mL·min/μmol; P = .998). Desflurane had lower uptake than propofol (65 ± 21 × 10 vs 165 ± 51 × 10 g·mL·min/μmol; P = .039), but there was no statistically significant difference between desflurane and desflurane-then-propofol (65 ± 21 × 10 vs 59 ± 11 × 10 g·mL·min/μmol; P = .999).

CONCLUSIONS

Propofol and desflurane are cardioprotective, but desflurane is more effective than propofol. The added benefit of desflurane is lost when used simultaneously with propofol.

Effect of nitric oxide on the anticancer activity of the topoisomerase-active drugs etoposide and adriamycin in human melanoma cells

Nitric oxide (·NO) was originally identified as an innate cytotoxin. However, in tumors it can enhance resistance to chemotherapy and exacerbate cancer progression. Our previous studies indicated that (·NO/·NO-derived species react with etoposide (VP-16) in vitro and form products that show significantly reduced activity toward HL60 cells and lipopolysaccharide (LPS)-induced macrophages. Here, we further confirm the hypothesis that (÷)NO generation contributes to VP-16 resistance by examining interactions of ·NO with VP-16 in inducible nitric-oxide synthase (iNOS)-expressing human melanoma A375 cells. Inhibition of iNOS catalysis by N(6)-(1-iminoethyl)-L-lysine dihydrochloride (L-NIL) in human melanoma A375 cells reversed VP-16 resistance, leading to increased DNA damage and apoptosis. Furthermore, we found that coculturing A375 melanoma cells with LPS-induced macrophage RAW cells also significantly reduced VP-16 cytotoxicity and DNA damage in A375 cells. We also examined the interactions of (·)NO with another topoisomerase active drug, Adriamycin, in A375 cells. In contrast, to VP-16, (·)NO caused no significant modulation of cytotoxicity or Adriamycin-dependent apoptosis, suggesting that (⋅)NO does not interact with Adriamycin. Our studies support the hypothesis that (·)NO oxidative chemistry can detoxify VP-16 through direct nitrogen oxide radical attack. Our results provide insights into the pharmacology and anticancer mechanisms of VP-16 that may ultimately contribute to increased resistance, treatment failure, and induction of secondary leukemia in VP-16-treated patients.

Role of nitric oxide in the chemistry and anticancer activity of etoposide (VP-16,213)

Originally identified as an innate cytotoxin, nitric oxide ((·)NO) formation in tumors can influence chemotherapy and exacerbate cancer progression. Here, we examined the hypothesis that (·)NO generation contributes to cancer cell drug resistance toward the widely used anticancer drug Etoposide (VP-16). The UV-vis spectrum of VP-16 was not changed by exposure of VP-16 to (·)NO in aqueous buffer. In contrast, reddish-orange compound(s) characteristic of o-quinone- and nitroso-VP-16 were readily generated in a hydrophobic medium (chloroform) in an oxygen-dependent manner. Similar products were also formed when the VP-16 radical, generated from VP-16 and horseradish peroxidase/H2O2, was exposed directly to (·)NO in chloroform in the presence of oxygen. Separation and spectral analysis of VP-16 reaction extracts by electron spin resonance and UV-vis indicated the generation of the phenoxy radical and the o-quinone of VP-16, as well as putative nitroxide, iminoxyl, and other nitrogen oxide intermediates. Nitric oxide products of VP-16 displayed significantly diminished topoisomerase II-dependent cleavage of DNA and cytotoxicity to human HL-60 leukemia cells. LPS-mediated induction of nitric oxide synthase in murine macrophages resulted in VP-16 resistance compared to Raw cells. Furthermore, (·)NO products derived from iNOS rapidly reacted with VP-16 leading to decreased DNA damage and cytotoxicity. Together, these observations suggest that the formation of (·)NO in tumors (associated macrophages) can contribute to VP-16 resistance via the detoxification of VP-16.

Reaction between the anesthetic agent propofol and the free radical DPPH in semiaqueous media: kinetics and characterization of the products

The reaction of the free radical diphenylpicrylhydrazyl (DPPH ) with the anesthetic agent 2,6-diisopropylphenol (propofol, PPF) was investigated in buffered hydroalcoholic media. The kinetics was followed using a stopped-flow system. DPPH was reduced to the hydrazine analogue DPPH-H with a measured stoichiometry (DPPH /PPF) of 2. The main product of the reaction, 3,5,3',5'-tetraisopropyl-(4,4')-diphenoquinone (PPFDQ) was isolated by chromatography and its structure was fully characterized. The reaction mechanism was inferred from the stoichiometry, kinetics, and product identification. The first step, which primarily determines the kinetics, is the reaction of DPPH with PPF to produce DPPH-H and the PPF radical. The rate constant was found to be 31.8, 207, and 908 M(-1) s(-1) at pH 6.4, 7.4, and 8.4, respectively. The pH dependence is indicative of a higher reactivity of the phenolate form of PPF. Then, PPF radicals combine to form dipropofol, which is quickly oxidized to PPFDQ by the remaining DPPH . This reaction scheme is corroborated by numerical simulations of the kinetics. In the course of this study we also disclosed an unexpected effect, the photochemical degradation of PPFDQ. The need to compare antioxidants on a kinetics basis is again emphasized. In our hands, PPF presents a significantly weaker reactivity than Trolox.

Anesthetic modulation of immune reactions mediated by nitric oxide

Nitric oxide (NO), when produced via inducible NO synthase (iNOS) in excess under pathological conditions (e.g., inflammation, endotoxemia, and septic shock), may lead to tissue injury and organ dysfunction. The bioavailability of NO and the activity and expression of iNOS are regulated by anesthetic agents. Volatile anesthetics mostly suppress, but in some instances may upregulate, the lipopolysaccharide-and cytokine-induced expression of iNOS in blood vessels and macrophages. Intravenous anesthetics inhibit iNOS expression in macrophages and the liver. Local anesthetics decrease the production of NO by inhibiting iNOS expression in macrophages and increase NO production in glial cells. Based on the literature reported so far, the effects of anesthetics on iNOS expression and activity under conditions of inflammation are controversial, with the observed effects depending on the experimental methods and animal species used. On the other hand, it has been shown that volatile and intravenous anesthetics consistently prevent the development of multiple organ failure elicited by endotoxemia or septic shock. Information, although still insufficient, regarding the interactions between anesthetic agents and the detrimental effects of NO formed during inflammatory processes may help us to construct advanced strategies for anesthetizing and sedating patients with inflammation and sepsis and for anesthetic preconditioning against ischemic injury.

Propofol reduces nitric oxide-induced apoptosis in testicular ischemia-reperfusion injury by downregulating the expression of inducible nitric oxide synthase

BACKGROUND

The aim of the present study was to investigate the underlying mechanisms in the preventive effects of intravenous anesthetics on testicular ischemia-reperfusion injury.

METHODS

Forty male Wistar Albino rats were randomly assigned to four groups of 10 rats each. Anesthesia was induced and maintained with thiopental in groups 1 and 2 and with propofol in groups 3 and 4. Groups 2 and 4 received left testicular ischemia (torsion) for 1 h and reperfusion (detorsion) for 24 h. Groups 1 and 3 (control groups) had no testicular torsion and detorsion. At 24 h of reperfusion, animals were killed and ipsilateral testes were removed for determination of tissue nitric oxide (NO) levels and immunohistochemical evaluation of endothelial nitric oxide synthase (eNOS), inducible NOS (iNOS), and apoptosis protease-activating factor 1 (APAF-1).

RESULTS

Between groups 1 and 3, there were no differences in tissue NO levels and eNOS, iNOS, and APAF-1 expressions. iNOS and APAF-1 expressions were markedly increased in group 2, but these parameters were at the mild to moderate level in group 4 at 24 h of reperfusion. Also, elevated expression of iNOS was accompanied by a high NO production in group 2 compared with group 4. Although eNOS expressions were increased in both the groups (groups 2 and 4), there were no significant differences between these groups.

CONCLUSIONS

Propofol as an anesthetic agent may attenuate germ cell-specific apoptosis and decrease NO biosynthases through downregulation of iNOS expression in an animal model of testicular torsion and detorsion.

Membrane effect of lidocaine is inhibited by interaction with peroxynitrite

Inflammation is clinically well known to decrease the efficiency of local anesthesia, an effect which has been explained mechanistically by tissue acidosis in the literature. However, recent studies offer no support to such a pharmacopathological background for anesthetic failure. Because inflammatory cells produce significant amounts of peroxynitrite, the peroxynitrite could interact with local anesthetics to decrease their effects. To examine this speculated interaction, we determined whether membrane fluidization, as one mode of local anesthetic action, was influenced by peroxynitrite. The membrane effects were analyzed by measuring the fluorescence polarization of liposomes prepared with 1, 2-dipalmitoylphosphatidylcholine. Although lidocaine, at a clinically relevant concentration, fluidized liposomal membranes, its fluidizing potency was reduced to 43.6 +/- 4.4% and 58.4 +/- 7.5% of that in membranes without peroxynitrite when membranes were pretreated with 50 and 250 microM peroxynitrite, respectively, for 15 min. A significant inhibition of membrane fluidization of 27.5 +/- 6.8%, was also observed after reaction for 5 min. Peroxynitrite released by inflammatory cells may affect local anesthesia through a possible interaction with lidocaine, inhibiting its membrane-fluidizing effect.

[Mitochondria in anaesthesia and intensive care]

OBJECTIVE

Mitochondria play a key role in energy metabolism within the cell through the oxidative phosphorylation. They are also involved in many cellular processes like apoptosis, calcium signaling or reactive oxygen species production. The objectives of this review are to understand the interactions between mitochondrial metabolism and anaesthetics or different stress situations observed in ICU and to know the clinical implications.

DATA SOURCES

References were obtained from PubMed data bank (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi) using the following keywords: mitochondria, anaesthesia, anaesthetics, sepsis, preconditioning, ischaemia, hypoxia.

DATA SYNTHESIS

Mitochondria act as a pharmacological target for the anaesthetic agents. The effects can be toxic like in the case of the local anaesthetics-induced myotoxicity. On the other hand, beneficial effects are observed in the anaesthetic-induced myocardial preconditioning. Mitochondrial metabolism could be disturbed in many critical situations (sepsis, chronic hypoxia, ischaemia-reperfusion injury). The study of the underlying mechanisms should allow to propose in the future new specific therapeutics.

Transdermal absorption of propofol in rats

Propofol (PF), a highly lipophilic anesthetic, has several desirable properties, such as the rapid onset and cessation of its effects upon intravenous infusion. In this study, the transdermal absorption of PF was investigated with the aim of the development of an alternative route of administration. PF solutions containing isopropyl myristate (IPM), ethanol or propylene glycol (PG) at various concentrations were prepared and applied to the abdominal skin of rats. Petrolatum and fatty alcohol propylene glycol (FAPG) ointments containing PF were also prepared and applied to the dorsal skin. Eyelid opening was measured and the ratio of the measured value to the initial value was calculated to evaluate the level of the pharmacological effect of the preparation. The PG solution containing 80% PF achieved higher plasma PF concentrations than the 100% PF solution. The PF-FAPG ointment produced a higher plasma PF concentration than the PF-petrolatum ointment. Furthermore, a drowsy state was confirmed after transdermal administration of 42% PF-FAPG ointment. These results indicate that the combination of PF and PG was appropriate for the transdermal absorption of PF, and PF was absorbed through the rat skin to an extent sufficient to cause a continuous sedative effect.

Catalytic activation of copper (II) salts on the reaction of peroxynitrite with propofol in alkaline medium

We report here on the role of copper (II) salts on the acceleration of peroxynitrite (ONOO-) decomposition and ONOO- reaction with the anaesthetic agent propofol (2,6-diisopropylphenol) in alkaline medium. We observed a strong acceleration of the ONOO- decomposition in alkaline medium in the presence of copper (I and II) salts. After 18 h of ONOO- reaction with propofol, we observed nitrosated, nitrated, and oxidized (quinone and diphenylquinone) derivatives of propofol, but in the presence of Cu(II) (20% molar vs ONOO-), the yields of quinone and nitrosopropofol strongly increased. We also observed that the temperature and the atmosphere influenced the effects of Cu(II) on ONOO- reactions with propofol: low temperatures promoted nitrosation and high temperatures promoted oxidation; O2 atmosphere increased the general reactivity and the yield of nitrated and oxidized products. We highlighted the influence of Cu(II) salts on the radical character of the reaction by direct EPR technique. The exact mechanism of the Cu(II) catalysis remains unexplained, but we suggest the formation of a copper complex with propofol or, more probably, the oxidation of ONOO- into ONOO. by copper ions promoting the formation of quinone and nitrosopropofol according to a previously reported mechanism [M. Cudic, C. Ducrocq, Transformations of 2,6-diisopropylphenol by NO-derived nitrogen oxides, particularly peroxynitrite, Nitric Oxide 4 (2000) 147-156].

Investigation of the reaction of peroxynitrite with propofol at acid pH: predominant production of oxidized, nitrated, and halogenated derivatives

We reported here the reaction, in acidic conditions, of peroxynitrite (ONOO(-)) with the anaesthetic agent propofol (2,6-diisopropylphenol, PPF). The most interesting finding is that peroxynitrite is able to nitrate and to oxidize propofol leading to 4-nitropropofol, quinone, and diphenylquinone as the major products. More surprisingly, we also found that peroxynitrite is capable of halogenating propofol in the presence of halide ions, suggesting the formation of nitrosyl chloride (NOCl) or nitryl chloride (NO(2)Cl) from the reaction of peroxynitrite with chloride ions. A significant enhancement of the halogenation yield is observed with a simultaneous decrease of the yields of the other products in the presence of methanol or hydrogen peroxide. Increased halogenation of PPF probably results from the formation of peroxynitrate (O(2)NOO(-)), that further oxidizes chloride ions in hypochlorous acid (HOCl) or molecular chlorine (Cl(2)). Spontaneous decay of peroxynitrate is relatively slow in acidic medium, thus explaining the decrease of the yields of the other products. By direct EPR techniques, we also observed that this reaction occurs via a radical pathway.

Effects of nitrosopropofol on mitochondrial energy-converting system

Nitrosopropofol (NOPR) is a relatively stable compound obtained from the reaction between the general anesthetic 2,6 diisopropylphenol (propofol) and nitrosoglutathione (GSNO) and bearing a more acidic phenol group than propofol. It interfered with mitochondrial energetic metabolism in a concentration-dependent manner. Concentrations as high as 100 or 200 microM disrupted both oxidative phosphorylation and electron transport. Low concentrations of NOPR (50 microM) markedly slowed down the electron transport rate which was insensitive both to ADP and uncoupler stimulation and spontaneously gradually stopped. Consequently, both the transmembrane potential production and the ATP synthesis system were affected. In the presence of 10 or 20 microM NOPR, mitochondria respired but showed a worsening of the respiratory control and produced a transmembrane potential useful to respond to a phosphorylation pulse, but were not able to restore it. These results were consistent with ATP synthesis and swelling experiments. NOPR was effective at concentrations lower than those required by the combination of propofol and GSNO, suggesting that mitochondria might be able to catalyze the reaction between GSNO and propofol and that the resulting metabolite was more active on mitochondrial membrane structure than the parent compounds. Although the details of the process are yet unknown, the mechanism presented may be of potential relevance to rationalize the pathophysiological effects of propofol.

1-Nitrosomelatonin is a spontaneous NO-releasing compound

Melatonin (N-acetyl-5-methoxytryptamin), the main hormone secreted by the pineal gland in mammals, is nitrosated by nitrite at acidic pH and by NO in the presence of oxygen under neutral conditions. Melatonin is also partly converted to 1-nitrosomelatonin by oxoperoxonitrate (ONOO-, peroxynitrite) in phosphate-buffered solutions at pH 7-10 [Blanchard, B., et al. (2000) Journal of Pineal Research 29, 184-192]. In the present report, we show that 1-nitrosomelatonin in turn behaves as an NO-donor regenerating melatonin. NO-release is evidenced by the formation of nitrite in phosphate-buffered solutions and oxidation of HbO2. No peroxynitrite was formed during that decomposition because serotonin used as a probe was converted only to 4-nitroso-serotonin as expected for a true NO-donor [Blanchard, B., et al. (2001) Free Radical Research, 34, 177-188]. The spontaneous decay of 1-nitrosomelatonin is not affected by GSH and metallic ions but its decomposition is accelerated in acidic pH or in the presence of NADH or ascorbate. Furthermore, melatonin is partially or entirely recovered in the absence or presence of ascorbate, respectively. A homolytic cleavage of 1-nitrosomelatonin is strongly suggested and discussed. Formation of 1-nitrosomelatonin from melatonin and reactive nitrogen species (RNS) followed by its decay into NO demonstrates that melatonin could reduce these RNS to NO.

Combined effect of propofol and GSNO on oxidative phosphorylation of isolated rat liver mitochondria

Isolated rat liver mitochondria have been treated with the general anaesthetic propofol (2,6-diisopropylphenol, 200 microM) and the physiological NO donor nitrosoglutathione (GSNO, 200 or 250 microM). The efficiency of the oxidative phosphorylation has been evaluated by measuring the respiration and ATP synthesis rates and the behavior of transmembrane electrical potential. In mitochondria energized by succinate, the simultaneous presence of both propofol and GSNO gives rise to a synergic action in affecting the resting and the ADP-stimulated respiration, the respiratory control ratio, the ATP synthesis, and the formation and utilization of the electrochemical transmembrane potential.