Protection of the Cyp1a2(-/-) null mouse against uroporphyria and hepatic injury following exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin.

The effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on the liver of C57BL/6J mice is a model for clinical sporadic porphyria cutanea tarda (PCT). There is massive uroporphyria, inhibition of uroporphyrinogen decarboxylase (UROD) activity, and hepatocellular damage. A variety of evidence implicates the CYP1A2 enzyme as necessary for mouse uroporphyria. Here we report that, 5 weeks after a single oral dose of TCDD (75 microg/kg), Cyp1a2(+/+) wild-type mice showed severe uroporphyria and greater than 90% decreases in UROD activity; in contrast, despite exposure to this potent agent Cyp1a2(-/-) knockout mice displayed absolutely no increases in hepatic porphyrin levels, even after prior iron overload, and no detectable inhibition of UROD activity. Plasma levels of alanine-aminotransferase (ALT) and aspartate aminotransferase (AST)-although elevated in both genotypes after TCDD exposure-were significantly less in Cyp1a2(-/-) than in Cyp1a2(+/+) mice, suggesting that the absence of CYP1A2 also affords partial protection against TCDD-induced liver toxicity. Histological examination confirmed a decrease in hepatocellular damage in TCDD-treated Cyp1a2(-/-) mice; in particular, there was no bile duct damage or proliferation that in the Cyp1a2(+/+) mice might be caused by uroporphyrin. We conclude that CYP1A2 is both necessary and essential for the potent uroporphyrinogenic effects of TCDD in mice, and that CYP1A2 also plays a role in contributing to TCDD-induced hepatocellular injury. This study has implications for both the toxicity assessment of TCDD and the hepatic injury seen in PCT patients.

Targeted knockout of Cyp1a1 gene does not alter hepatic constitutive expression of other genes in the mouse [Ah] battery.

Using the Cre-lox system, we have generated a cytochrome P450 1A1 Cyp1a1(-/-) knockout mouse by deletion of the translated portions of the Cyp1a1 gene. These mice are viable and demonstrate no obvious phenotype, compared with wild-type littermates. As a first step toward characterizing genes that might be expected to compensate for loss of CYP1A1, constitutive expression of [Ah] gene battery members was examined. In a cultured hepatoma CYP1A1 metabolism-deficient mutant line that does not express Cyp1a2, we have previously shown that constitutive transcriptional up-regulation of other [Ah] gene battery members occurs; these results are consistent with the elevation of a putative endogenous ligand (EL) for the Ah receptor that is a substrate for CYP1A1. The [Ah] battery includes Cyp1a2, NAD(P)H:quinone oxidoreductase (Nqo1), and three other Phase II genes. Examining mRNA, protein, and enzyme activity, we demonstrate that the absence of CYP1A1 has no effect on the hepatic constitutive expression of Cyp1a2 or Nqo1. We postulate that CYP1A1 and CYP1A2 might have overlapping substrate specificity for metabolism of the EL, such that basal CYP1A2 in the liver can compensate for the loss of CYP1A1.

Cerebrospinal fluid monoamine metabolites and glucose metabolism in posttraumatic aggression.

BACKGROUND: This pilot study was conducted to determine if aggressive, post brain-injured patients have abnormal glucose metabolism or abnormal CSF monoamine metabolite concentrations as compared with non-aggressive, post brain-injured controls. METHODS: Subjects with a history of traumatic brain injury underwent a lumbar puncture and glucose tolerance test after a three-week medication wash-out period. Monoamine metabolite concentrations and glucose nadirs were compared between aggressive and control subjects. RESULTS: There were no statistical differences between the aggressive (n = 4) and control (n = 6) group with respect to age (28.5 +/- 15.7 versus 28.0 +/- 10.8), weight (72.5 kg +/- 14.1 versus 67.7 kg +/- 10.1) or number of months since brain injury (31.8 +/- 26.1 versus 33.3 +/- 23.3). There were no significant differences between the two groups in glucose nadirs following oral glucose challenge or in levels of CSF monoamine metabolite concentrations of 5-hydroxyindoleacetic acid (5-HIAA), homovanillic acid (HVA), or 3-methoxy-4-hydroxyphenylglycol (MHPG), although a trend toward significance was noted between the MHPG groups (higher MHPG within aggressive group). CONCLUSIONS: The preliminary data suggest that glucose metabolism and CSF monoamine metabolite concentrations do not differ significantly from aggressive subjects to controls in persons with brain injury. Follow-up prospective studies with larger sample sizes are needed to evaluate these preliminary findings.

Accuracy of diagnosis of persistent vegetative state.

We reviewed pre-admission diagnosis in all patients referred for inpatient brain injury neurorehabilitation over a 5-year period (n = 193). All patients more than 1 month postinjury with diagnosis of coma or persistent vegetative state were selected for review (n = 49). We found that 18 (37%) of these patients were diagnosed inaccurately. Inaccurate diagnosis was more likely if the injury was more than 3 months before admission and the etiology of injury was trauma (48%). Results were statistically significant when traumatic injuries were compared with anoxic injuries (p < 0.10). Errors in diagnosis may result from confusion in terminology, lack of extended observation of patients, and lack of skill or training in the assessment of neurologically devastated patients.