Physiological factors predisposing to neurotoxicity

Identification and interpretation of developmental neurotoxicity effects

The reliable detection, measurement, and interpretation of treatment-related developmental neurotoxicity (DNT) effects depend on appropriate study design and execution, using scientifically established methodologies, with appropriate controls to minimize confounding factors. Appropriate statistical approaches should be optimized for the specific endpoints in advance, analyzing effects across time and functional domains as far as possible. If available, biomarkers of exposure are useful to assess the bioavailability of toxicants to the dam and offspring in utero and after birth. Finally, "weight of evidence" principles are used to aid assessment of the biological significance of differences from concurrent controls. These effects should be interpreted in light of available information from historical controls, positive controls, maternal and offspring systemic toxicity, and other relevant toxicological data. This review provides a framework for the integration of all these types of information in the interpretation of DNT studies.

Carbon monoxide specifically inhibits cytochrome c oxidase of human mitochondrial respiratory chain

Carbon monoxide (CO) toxicity is the result of a combination of tissue hypoxia and direct CO-mediated damage at a cellular level, since not all the signs and symptoms presented can be explained only by the formation of carboxyhaemoglobin. Mitochondria, specially the electron transport chain, seem to be the target for CO at a subcellular level. However, the direct effect of CO in individual complexes of the human mitochondrial respiratory chain has not been completely elucidated. We here studied the in vitro effect of CO on individual complexes of the mitochondrial respiratory chain of human mitochondria. We obtained muscle tissue from 10 healthy people who underwent orthopaedic surgery for hip replacement. Isolated mitochondria were incubated for 5 min. under CO concentrations of 50, 100 and 500 ppm. Afterwards, enzymatic activities of individual complexes of the mitochondrial respiratory chain were assessed in vitro and compared with those obtained in basal (synthetic air without CO) conditions. Cytochrome c oxidase (complex IV of the mitochondrial respiratory chain) activity showed a decrease from 836+/-439 nmol/min./mg of mitochondrial protein after air incubation to 670+/-401, 483+/-182, and 379+/-131 nmol/min./mg after 50, 100 and 500 ppm of CO incubation, respectively (20%, 42% and 55% decrease in cytochrome c oxidase activity). This gradual decrease in cytochrome c oxidase was found to be statistically significant (P<0.001). Other complex activities showed no any significant variation. Carbon monoxide is toxic for mitochondria in man, altering the mitochondrial respiratory chain at the cytochrome c oxidase level. This inhibition in cytochrome c oxidase may play a role in the development of the symptoms observed in acute CO poisoning, and in some diseases related to smoking.