Changes in the defense against free radicals in the liver and plasma of the dog during hypoxia and/or halothane anaesthesia

A mini-review of the effects of inhalational and intravenous anesthetics on oxidative stress in dogs

General anesthesia increases the production of reactive oxygen species (ROS), which can exacerbate or increase oxidative stress and thus affect the prognosis of surgical procedures. Oxidative stress has been implicated in the development of cardiovascular, dermatologic, oncologic, and other diseases in dogs, as well as ischemia and reperfusion injury. Some anesthetics, such as halogenated anesthetics, have been shown to stimulate the production of ROS, while others, such as propofol, have antioxidant properties. However, the antioxidant effects of these anesthetics may not be sufficient to counteract oxidative damage at the doses used clinically. Nevertheless, the effects of anesthetics should be considered to minimize oxidative damage during anesthesia in dogs to improve the outcome of procedures requiring general anesthesia. This mini-review addresses the current knowledge on oxidative stress during inhalational and intravenous anesthesia in dogs. There is still a lack of information on the management of anesthesia in dogs with respect to oxidative stress. Further research, including comprehensive clinical studies is needed to better understand oxidative injury mechanisms and improve perioperative protocols during anesthesia in dogs.

Antioxidant capacity of lipid- and water-soluble antioxidants in dogs with subclinical myxomatous mitral valve degeneration anaesthetised with propofol or sevoflurane

Background

Antioxidants located in both the hydrophilic and lipophilic compartments of plasma act as a defence system against reactive oxygen species (ROS). Excessive production of ROS during anaesthesia affects the antioxidant capacity of plasma and may result in oxidative stress. The aim of this study was to evaluate the antioxidant capacity of lipid- (ACL) and water-soluble (ACW) antioxidants in client-owned dogs diagnosed with periodontal disease and early-stage myxomatous mitral valve degeneration (MMVD) and anaesthetised for a dental procedure with propofol and sevoflurane or with propofol only.

Results

Dogs with MMVD were anaesthetised with propofol and sevoflurane (MMVD/PS, n = 8) or with propofol only (MMVD/P, n = 10). Dogs with no evidence of MMVD (PS, n = 12) were anaesthetised with propofol and sevoflurane. Blood samples for determination of ACL and ACW were collected before and 5 min, 60 min and 6 h after induction to anaesthesia. In MMVD/PS dogs, ACL was significantly higher at all sampling times when compared to PS dogs. Compared to basal values, only anaesthesia maintained with propofol significantly increased ACL at 60 min in dogs with MMVD. In MMVD/P dogs, ACW increased after induction to anaesthesia and remained elevated up to 6 h after anaesthesia. Compared to basal values, anaesthesia maintained with sevoflurane significantly increased ACW only at 60 min in both dogs with and without MMVD. The only difference between propofol and propofol/sevoflurane anaesthesia in dogs with MMVD was significantly higher ACW at 60 min after induction to anaesthesia in the propofol group.

Conclusions

Regarding antioxidant capacity, propofol could be a better choice than sevoflurane for anaesthesia of dogs with early-stage MMVD, although further studies are necessary to clarify the advantage of this antioxidant capacity.

Combined Catalase and ADH Inhibition Ameliorates Ethanol-Induced Myocardial Dysfunction Despite Causing Oxidative Stress in Conscious Female Rats

BACKGROUND

Ethanol (EtOH)-evoked oxidative stress, which contributes to myocardial dysfunction in proestrus rats, is mediated by increases in NADPH oxidase (Nox) activity, malondialdehyde (MDA), and ERK1/2 phosphorylation. Whether these biochemical responses, which are triggered by alcohol-derived acetaldehyde in noncardiac tissues, occur in proestrus rats' hearts remains unknown. Therefore, we elucidated the roles of alcohol dehydrogenase (ADH), cytochrome P4502E1 (CYP2E1), and catalase, which catalyze alcohol oxidation to acetaldehyde, in these alcohol-evoked biochemical and hemodynamic responses in proestrus rats.

METHODS

Conscious proestrus rats prepared for measurements of left ventricular (LV) function and blood pressure (BP) received EtOH (1.5 g/kg, intravenous [i.v.] infusion over 30 minutes) or saline 30 minutes after an ADH and CYP2E1 inhibitor, 4-methylpyrazole (4-MP) (82 mg/kg, intraperitoneal), a catalase inhibitor, 3-AT (0.5 g/kg, i.v.), their combination, or vehicle. LV function and BP were monitored for additional 60 minutes after EtOH or saline infusion before collecting the hearts for ex vivo measurements of LV reactive oxygen species (ROS), Nox activity, MDA, and ERK1/2 phosphorylation.

RESULTS

EtOH reduced LV function (dP/dt_max and LV developed pressure) and BP, and increased cardiac Nox activity, ROS and MDA levels, and ERK1/2 phosphorylation. Either inhibitor partially, and their combination significantly, attenuated these responses despite the substantially higher blood EtOH level, and the increased cardiac oxidative stress and reduced BP caused by 3-AT alone or with 4-MP. The inhibitors reduced cardiac MDA level and reversed EtOH effect on cardiac and plasma MDA.

CONCLUSIONS

EtOH oxidative metabolism plays a pivotal role in the EtOH-evoked LV oxidative stress and dysfunction in proestrus rats. Notably, catalase inhibition (3-AT) caused cardiac oxidative stress and hypotension.

Mechanism of Anesthetic Toxicity: Metabolism, Reactive Oxygen Species, Oxidative Stress, and Electron Transfer

There is much literature on the toxic effects of anesthetics. This paper deals with both the volatiles and locals. Adverse effects appear to be multifaceted, with the focus on radicals, oxidative stress (OS), and electron transfer (ET). ET functionalities involved are quinone, iminoquinone, conjugated iminium, and nitrone. The non-ET routes involving radicals and OS apparently pertain to haloalkanes and ethers. Beneficial effects of antioxidants, evidently countering OS, are reported. Knowledge at the molecular level should aid in devising strategies to combat the adverse effects.

Effects of tiletamine-zolazepam anaesthesia on plasma antioxidative status and some haematological parameters in sheep

It is not clear whether the anaesthetic agents tiletamine and zolazepam have antioxidant or pro-oxidant effects. Therefore, this study was carried out to investigate the effects of tiletamine-zolazepam anaesthesia on oxidant/antioxidant status in blood plasma and on haematological parameters in 10 healthy Awassi ewes. The tiletamine-zolazepam combination was administrated in a dose of 7.5 mg/kg intramuscularly. The animals were spontaneously breathing air during the procedure. Blood samples were collected by jugular venipuncture before induction and at 30, 60, 120 min, 24 h and 3 days after anaesthesia. Malondialdehyde concentration, an index of lipid peroxidation, was higher at 30, 60, 120 min and 24 h (P < 0.05) than the baseline value in the plasma. The level of glutathione decreased (P < 0.05) at 30, 60 and 120 min, then returned to the baseline level. Beta-carotene concentration was lower (P < 0.05) than the baseline value during anaesthesia with the exception of its level at 120 min. Glutathione peroxidase and catalase activities decreased (P < 0.05) at the onset of anaesthesia, then returned to baseline values. There was no significant change in vitamin A level. Red blood cell count, haematocrit and haemoglobin concentration significantly decreased (P < 0.05) only at 30 min and thereafter they gradually returned to the baseline values. Based on the results tiletamine-zolazepam anaesthesia seems to accelerate lipid peroxidation and to impair the enzymatic antioxidant defence in the blood plasma.

Halothane induces oxidative stress and NF-kappaB activation in rat liver: protective effect of propofol

We investigated the effects of propofol on markers of oxidative stress, nuclear factor kappa B (NF-kappaB) activation and inducible nitric oxide synthase (iNOS) expression in liver of rats treated with halothane under hypoxic conditions. Male Wistar rats received halothane 1%/oxygen 14%, oxygen 14%/propofol 60 mg kg(-1) i.p., or halothane 1%/oxygen 14%/propofol 60 mg kg(-1) i.p. Morphological examination showed complete loss of architecture with massive necrosis of parenchyma in the halothane group, while only minor histological abnormalities were observed in rats receiving halothane plus propofol. The cytosolic concentration of TBARS and the hydroperoxide-initiated chemiluminescence increased significantly in the liver of animals from the halothane group (+62% and +40% versus controls, respectively), and this increase was abolished by propofol administration. Halothane induced a marked activation of NF-kappaB (+180%), and resulted in a significant decrease of the nonphosphorylated form of the inhibitor IkappaBalpha (-53%), while phosphorylated IkappaBalpha protein level was markedly increased (+146%). Propofol administration lowered these effects to +30% (NF-kappaB), -26% (nonphosphorylated IkappaBalpha), and +56% (phosphorylated IkappaBalpha). The increase of iNOS protein level (+59%) induced by halothane was significantly reduced to +22% by additional administration of propofol. Results obtained show that administration of propofol inhibits oxidative stress, NF-kappaB nuclear traslocation and iNOS overexpression in liver of rats receiving halothane. Propofol treatment, by inhibiting the NF-kappaB signal transduction pathway, might block the production of noxious mediators involved in the development of halothane-induced injury.

Ca2+ cytochemical changes of hepatotoxicity caused by halothane and sevoflurane in enzyme-induced hypoxic rats

AIM: To investigat the relation between hepatotoxicity of halothane and sevoflurane and altered hepatic calcium homeostasis in enzyme-induced hypoxic rats.

METHODS: Forty-eight rats were pretreated with phen-obarbital and randomly divided into six groups (eight in each group) and exposed to O₂/ N₂/1.2 MAC anesthetics for 1 h: normal control (NC), 21% O₂/79% N₂; hypoxic control (HC), 14% O₂/86%N₂; normal sevoflurane (NS), 21% O₂/ N₂/1.2MAC sevoflurane; hypoxic sevoflurane (HS), 14% O₂/ N₂/1.2MAC sevoflurane; normal halothane (NH)21%O₂/79%N₂/1.2MAC halothane; hypoxic halothane (HH), 14% O₂/N₂/1.2MAC halothane. Liver specimens and blood were taken 24 h after exposure to calcium and determined by EDX microanalysis.

RESULTS: The liver of all rats given halothane (14% O₂) had extensive centrilobular necrosis and denaturation. Morphologic damage was accompanied with an increase in serum glutamic pyruvic transminase. In groups NH and HH, more calcium was precipitated in cytoplasm and mitochondria.

CONCLUSION: These results suggest that halothane increases cytosolic Ca²⁺ concentration in hepatocytes. Elevation in Ca²⁺ concentration is implicated in the mechanism of halothane-induced hepatotoxicity. sevoflurane is less effective in affecting hepatic calcium homeostasis than halothane.

Leukocyte-endothelial interactions in environmental hypoxia

Hypoxia induced by reducing inspired PO2 (PIO2) to 70 Torr, promotes a rapid microvascular response characterized by increased leukocyte rolling and adherence to the venular endothelium, leukocyte emigration to the perivascular space and increased vascular permeability. This appears to be a generalized response since it is observed in venules of the mesentery, cremaster muscle and pial microcirculations. After three weeks of acclimatization to hypoxia (barometric pressure 380 Torr, PIO2 70 Torr), the initial microvascular response resolves and exposure to even lower PIO2 (50 Torr) fails to elicit a microvascular response. The initial response is accompanied by a reversible increase in the generation of reactive oxygen species (ROS) and is blocked by antioxidants and by interventions that increase the tissue levels of nitric oxide (NO). In contrast to ischemia/reperfusion, ROS levels increase during hypoxia and return towards pre-hypoxic values after return to normoxia. Acclimatization involves upregulation of inducible NO synthase (iNOS): inhibition of iNOS using two different antagonists results in increased leukocyte-endothelial interactions and increased ROS generation. The results suggest that hypoxia initially leads to an alteration of the ROS/NO balance which is eventually restored during the acclimatization process. This phenomenon may have relevance to the microcirculatory alterations associated with hypoxic exposure, including acute mountain sickness and high altitude pulmonary and cerebral edema.

Hepatobiliary scintigraphy for evaluating the hepatotoxic effect of halothane and the protective effect of catechin in comparison with histo-chemical analysis of liver tissue

Halothane and its metabolites cause liver damage by decreasing liver blood flow and generating free-radical species. Catechin suppresses lipid peroxidation and increases enzyme activity, therefore it seems to be capable of protecting liver parenchyma against the direct toxic effect of halothane. The aim of this study was to investigate the role of hepatobiliary scintigraphy in detecting liver damage after halothane anaesthesia and the protective effect of catechin in comparison with histo-chemical analysis. Thirty rabbits, divided into three groups (A, controls; B, halothane; and C, catechin+halothane), were investigated. In group A no anaesthesia was administered. Group B only received halothane, while group C was pretreated with catechin and halothane anaesthesia was administered for 2 h. Dynamic scintigrams were taken for 60 min after injecting 99mTc-mebrofenin, and the time of peak uptake (TPU) and the time for half of the activity to clear from the liver (T(1/2)) were calculated. Rabbits were killed, and malondialdehyde (MDA), superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and catalase (CAT) levels were measured in hepatic tissue. The TPU and T(1/2) values of group A is significantly lower than in groups B and C (P<0.0002 and P<0.0002, respectively, for TPU; and P<0.0002 and P<0.0003, respectively, for T(1/2)). The TPU and T(1/2) values of group B were significantly higher than in group C (P<0.0003 and P<0.0003, respectively). The hepatic MDA level of group A was significantly lower than in groups B and C (P<0.0002 and P<0.0002, respectively). SOD, GSH-Px and CAT levels of group A were significantly higher than in groups B and C (P<0.0002, P<0.0001 and P<0.003, respectively, for group A vs group B; and P<0.0005, P<0.0002 and P<0.03, respectively, for group A vs group C). The MDA level of group B was significantly higher than that in group C (P<0.0002). SOD, GSH-Px and CAT levels of group B were significantly lower than in group C (P<0.0002, P<0.0002 and P<0.003, respectively). According to these results, we suggest that catechin protects liver parenchyma against the toxic effect of halothane and its metabolites, and that, compared to invasive histo-chemical analysis, hepatobiliary scintigraphy is a useful and alternative non-invasive method for detecting the protective effect of catechin on liver parenchyma after halothane anaesthesia.

Systemic hypoxia promotes leukocyte-endothelial adherence via reactive oxidant generation

We recently demonstrated that systemic hypoxia during reduced inspired PO(2) produces a rapid increase in leukocyte adherence to rat mesenteric venules. Evidence suggests that the mechanism of this response involves decreased nitric oxide (NO) levels. One possible pathway for NO depletion could involve increased reactive oxygen species (ROS) generation resulting in inactivation of NO. The overall goal of the present study was to examine the role of ROS in promoting leukocyte-endothelial adherence during systemic hypoxia. Experiments were designed to 1) evaluate changes in ROS generation in the mesenteric microcirculation during systemic hypoxia, 2) determine how the ROS signal changes when PO(2) levels return to normal after a period of systemic hypoxia, 3) assess the effect of antioxidants on ROS generation during hypoxia, and 4) utilize antioxidants to examine the functional relationship between ROS generation and leukocyte adherence during hypoxia. The major findings from this study are that systemic hypoxia increases ROS generation within the mesenteric microcirculation and that antioxidants prevent the increase in leukocyte-endothelial adhesive interactions observed in hypoxia.

21-aminosteroids prevent the down-regulation of hepatic cytochrome P450 induced by hypoxia and inflammation in conscious rabbits

1 This study was conducted to assess whether a 21-aminosteroid, U74389G, could prevent the down-regulation of hepatic cytochrome P450 (P450) induced by acute moderate hypoxia or an inflammatory reaction. 2 The rabbits of two groups (n = 6 per group) were subjected to acute moderate hypoxia (PaO2 approximately 35 mmHg), one pre-treated with U74389G (3 mg kg-1 i.v. every 6 h, for 48 h). The rabbits of two other groups received 5 ml of turpentine s.c., one of them being pre-treated with U74389G (3 mg kg-1 i.v. every 6 h, for 72 h). The kinetics of theophylline (2.5 mg kg-1) were assessed to evaluate the activity of the P450. Once the rabbits were sacrificed, the P450 content and the amount of thiobarbituric acid reactive substances (TBARS), a marker of lipid peroxidation, were estimated in the liver. 3 Compared with control rabbits, hypoxia and inflammation increased theophylline plasma concentrations, as a result of a decrease in theophylline systemic clearance (P<0.05). Both experimental conditions reduced hepatic content of P450 by 40-50% (P<0.05) and increased the amount of hepatic TBARS by around 50% (P<0.05). Pre-treatment with U74389G prevented the hypoxia- and inflammation-induced decrease in theophylline systemic clearance, the down-regulation of hepatic P450, and the increase in liver TBARS. 4 It is concluded that in the rabbit, U74389G prevents hepatic P450 depression produced by acute moderate hypoxia and a turpentine-induced inflammatory reaction, possibly by eliciting a radical quenching antioxidant activity.

Effect of hypoxia alone or combined with inflammation and 3-methylcholanthrene on hepatic cytochrome P450 in conscious rabbits

1 To investigate the effect of moderate hypoxia alone or combined with an inflammatory reaction or after 3-methylcholanthrene (3MC) pre-treatment on cytochrome P450 (P450), conscious rabbits were exposed for 24 h to a fractional concentration of inspired O2 of 10% (mean PaO2 of 34 mmHg). Hypoxia decreased theophylline metabolic clearance (ClM) from 1.73+/-0.43 to 1.48+/-0.13 ml min-1 kg-1 (P<0. 05), and reduced (P<0.05) the formation clearance of theophylline metabolites, 3-methylxanthine (3MX), 1-methyluric acid (1MU) and 1,3-dimethyluric acid (1,3DMU). Hypoxia reduced the amount of CYP1A1 and 1A2 but increased CYP3A6 proteins. 2 Turpentine-induced inflammatory reaction reduced (P<0.05) the formation clearance of 3MX, 1MU, and 1,3DMU, and diminished the amount of CYP1A1, 1A2 and 3A6 proteins. However, when combined with hypoxia, inflammation partially prevented the decrease in ClM, especially by impeding the reduction of 1,3DMU. The amount of CYP1A1 and 1A2 remained reduced but the amount of CYP3A6 protein returned to normal values. 3 Pre-treatment with 3MC augmented the ClM by 114% (P<0.05) due to the increase in the formation clearance of 3MX, 1MU and 1,3DMU. 3MC treatment increased the amount of CYP1A1 and 1A2 proteins. Pre-treatment with 3MC prevented the hypoxia-induced decrease in amount and activity of the P450. 4 It is concluded that acute moderate hypoxia and an inflammatory reaction individually reduce the amount and activity of selected apoproteins of the P450. However, the combination of hypoxia and the inflammatory reaction restores P450 activity to near normal values. On the other hand, pre-treatment with 3MC prevents the hypoxia-induced depression of the P450.