Cannabinoid receptor antagonist-induced striated muscle toxicity and ethylmalonic-adipic aciduria in beagle dogs.

Ibipinabant (IBI), a potent cannabinoid-1 receptor (CB1R) antagonist, previously in development for the treatment of obesity, causes skeletal and cardiac myopathy in beagle dogs. This toxicity was characterized by increases in muscle-derived enzyme activity in serum and microscopic striated muscle degeneration and accumulation of lipid droplets in myofibers. Additional changes in serum chemistry included decreases in glucose and increases in non-esterified fatty acids and cholesterol, and metabolic acidosis, consistent with disturbances in lipid and carbohydrate metabolism. No evidence of CB1R expression was detected in dog striated muscle as assessed by polymerase chain reaction, immunohistochemistry, Western blot analysis, and competitive radioligand binding. Investigative studies utilized metabonomic technology and demonstrated changes in several intermediates and metabolites of fatty acid metabolism including plasma acylcarnitines and urinary ethylmalonate, methylsuccinate, adipate, suberate, hexanoylglycine, sarcosine, dimethylglycine, isovalerylglycine, and 2-hydroxyglutarate. These results indicated that the toxic effect of IBI on striated muscle in beagle dogs is consistent with an inhibition of the mitochondrial flavin-containing enzymes including dimethyl glycine, sarcosine, isovaleryl-CoA, 2-hydroxyglutarate, and multiple acyl-CoA (short, medium, long, and very long chain) dehydrogenases. All of these enzymes converge at the level of electron transfer flavoprotein (ETF) and ETF oxidoreductase. Urinary ethylmalonate was shown to be a biomarker of IBI-induced striated muscle toxicity in dogs and could provide the ability to monitor potential IBI-induced toxic myopathy in humans. We propose that IBI-induced toxic myopathy in beagle dogs is not caused by direct antagonism of CB1R and could represent a model of ethylmalonic-adipic aciduria in humans.

Predicted regional flux of hydrogen sulfide correlates with distribution of nasal olfactory lesions in rats.

Hydrogen sulfide (H(2)S) is a toxic gas that is released by both natural and industrial sources. H(2)S selectively targets the olfactory system in humans and rodents. The purpose of this study was to test the hypothesis that the distribution of H(2)S-induced nasal pathology is correlated with the location of high-flux areas within the upper respiratory tract. To investigate whether the location of the olfactory lesion is dependent on regional gas uptake patterns, a comparison was made between lesion locations and regions of high H(2)S flux predicted using a 3-dimensional, anatomically accurate computational fluid dynamics (CFD) model of rat nasal passages. Rats were exposed by inhalation to 0, 10, 30, or 80 ppm H(2)S for 6 h/day for 70 days. The regional incidence of olfactory lesions and predicted H(2)S flux were determined at the mid-dorsomedial meatus and the middle portion of the ethmoid recess, and their rank correlation was evaluated. At these 2 levels, regions lined by respiratory epithelium were predicted to exhibit the highest mass flux values; however, H(2)S exposure elicited little or no response in this tissue. In contrast, regions lined by olfactory epithelium showed a close correlation between H(2)S flux and lesion incidence (p < 0.005) for both the 30 and 80-ppm exposure groups. These results indicate that airflow-driven patterns of H(2)S uptake within the inherently sensitive olfactory epithelium play an important role in the distribution of H(2)S-induced lesions and should therefore be taken into consideration when extrapolating from nasal lesions in rats to estimates of risk to human health.

Cytochrome oxidase inhibition induced by acute hydrogen sulfide inhalation: correlation with tissue sulfide concentrations in the rat brain, liver, lung, and nasal epithelium.

Hydrogen sulfide (H2S) is an important brain, lung, and nose toxicant. Inhibition of cytochrome oxidase is the primary biochemical effect associated with lethal H2S exposure. The objective of this study was to evaluate the relationship between the concentration of sulfide and cytochrome oxidase activity in target tissues following acute exposure to sublethal concentrations of inhaled H2S. Hindbrain, lung, liver, and nasal (olfactory and respiratory epithelial) cytochrome oxidase activity and sulfide concentrations were determined in adult male CD rats immediately after a 3-h exposure to H2S (10, 30, 80, 200, and 400 ppm). We also determined lung sulfide and sulfide metabolite concentrations at 0, 1.5, 3, 3.25, 3.5, 4, 5, and 7 h after the start of a 3-h H2S exposure to 400 ppm. Lung sulfide concentrations increased during H2S exposure and rapidly returned to endogenous levels within 15 min after the cessation of the 400-ppm exposure. Lung sulfide metabolite concentrations were transiently increased immediately after the end of the 3-h H2S exposure. Decreased cytochrome oxidase activity was observed in the olfactory epithelium following exposure to > or = 30 ppm H2S. Increased olfactory epithelial sulfide concentrations were observed following exposure to 400 ppm H2S. Hindbrain and nasal respiratory epithelial sulfide concentrations were unaffected by acute H2S exposure. Nasal respiratory epithelial cytochrome oxidase activity was reduced following acute exposure to > or = 30 ppm H2S. Liver sulfide concentrations were increased following exposure to > or = 200 ppm H2S and cytochrome oxidase activity was increased following inhalation exposure to > or = 10 ppm H2S. Our results suggest that cytochrome oxidase inhibition is a sensitive biomarker of H2S exposure in target tissues, and sulfide concentrations are unlikely to increase postexposure in the brain, lung, or nose following a single 3-h exposure to < or = 30 ppm H2S.