The biochemical basis of anesthetic toxicity

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.

Pulmonary toxicity and environmental contamination: radicals, electron transfer, and protection by antioxidants

The atmosphere is replete with a mixture of toxic substances, both natural and man-made. Inhalation of toxic substances produces a variety of insults to the pulmonary system. Lung poisons include industrial materials, particulates from mining and combustion, agricultural chemicals, cigarette smoke, ozone, and nitrogen oxides, among a large number of other chemicals and environmental contaminants. Many proposals have been advanced to explain the mode of action of pulmonary toxicants. In this review we focus on mechanisms of pulmonary toxicity that involve ET, ROS, and OS. The vast majority of toxicants or their metabolites possess chemical ET functionalities that can undergo redox cycling. Such recycling may generate ROS that can injure various cellular constituents in the lung and in other tissues. ET agents include quinones, metal complexes, aromatic nitro compounds, and conjugated iminium ions. Often, these agents are formed metabolically from parent toxicants. Such metabolic reactions are often catalytic and require only small amounts of the offending material. Oxidative attack is commonly associated with lipid peroxidation and oxidation of DNA, and it may result in strand cleavage and 8-OH-DG production. Toxicity is often accompanied by depletion of natural AOs, which further exacerbates the toxic effect. It is not surprising that the use of AOs, both natural in fruits and vegetables, as well as synthetic, may provide protection from the adverse effects of toxicant exposure. The mechanistic framework described earlier is also applicable to some of the more prominent pulmonary illnesses, such as asthma, COPD, and cancer.

Sevoflurane depolarizes pre-synaptic mitochondria in the central nervous system

BACKGROUND

Volatile anaesthetics protect the heart from ischaemic injury by activating mitochondrial signalling pathways. The aim of this study was to test whether sevoflurane, which is increasingly used in neuroanaesthesia, affects mitochondrial function in the central nervous system by altering the mitochondrial membrane potential (DeltaPsi(m)).

METHODS

In order to correlate free cytosolic Ca(2+) ([Ca(2+)](i)) and DeltaPsi(m), rat neural presynaptic terminals (synaptosomes) were loaded with the fluorescent probes fura-2 and JC-1. During sevoflurane exposure, 4-aminopyridine (4-AP) 500 micro M to induce pre-synaptic membrane depolarization or carbonylcyanide-p-(trifluoromethoxy)-phenylhydrazone (FCCP) 1 micro M to induce maximum mitochondrial depolarization was added. In order to block mitochondrial ATP-regulated K(+)-channels (mitoK(ATP)), the antagonist 5-hydroxydecanoate (5-HD) 500 micro M was added.

RESULTS

In Ca(2+)-containing medium, both sevoflurane 1 and 2 MAC gradually decreased the normalized JC-1 ratio from 0.96 +/- 0.01 in control to 0.92 +/- 0.01 and 0.89 +/- 0.01, representing a depolarization of DeltaPsi(m) (n = 9, P < 0.05). Sevoflurane 2 MAC increased [Ca(2+)](i). In Ca(2+)-depleted medium, sevoflurane 1 and 2 MAC depolarized DeltaPsi(m), while [Ca(2+)](i) remained unaltered. Sevoflurane 2 MAC attenuated the 4-AP-induced depolarization of DeltaPsi(m). When mitoK(ATP) was blocked, the sevoflurane-induced depolarization of DeltaPsi(m) was attenuated, but not blocked. The depolarizing effect of sevoflurane on DeltaPsi(m) compared with FCCP was calculated to 13.2 +/- 1.3% in Ca(2+)-containing and 15.1 +/- 1.2% in Ca(2+)-depleted medium (n = 7).

CONCLUSIONS

Sevoflurane depolarizes DeltaPsi(m) in rat synaptosomes, and the effect is not dependent on Ca(2+)-influx to the cytosol. Opening of mitoK(ATP) is partly responsible for the depolarizing effect of sevoflurane.