Menadione Suppresses Benzo(α)pyrene-Induced Activation of Cytochromes P450 1A: Insights into a Possible Molecular Mechanism.

Oxidative reactions that are catalyzed by cytochromes P450 1A (CYP1A) lead to formation of carcinogenic derivatives of arylamines and polycyclic aromatic hydrocarbons (PAHs), such as the widespread environmental pollutant benzo(α)pyrene (BP). These compounds upregulate CYP1A at the transcriptional level via an arylhydrocarbon receptor (AhR)-dependent signaling pathway. Because of the involvement of AhR-dependent genes in chemically induced carcinogenesis, suppression of this signaling pathway could prevent tumor formation and/or progression. Here we show that menadione (a water-soluble analog of vitamin K3) inhibits BP-induced expression and enzymatic activity of both CYP1A1 and CYP1A2 in vivo (in the rat liver) and BP-induced activity of CYP1A1 in vitro. Coadministration of BP and menadione reduced DNA-binding activity of AhR and increased DNA-binding activity of transcription factors Oct-1 and CCAAT/enhancer binding protein (C/EBP), which are known to be involved in negative regulation of AhR-dependent genes, in vivo. Expression of another factor involved in downregulation of CYP1A-pAhR repressor (AhRR)-was lower in the liver of the rats treated with BP and menadione, indicating that the inhibitory effect of menadione on CYP1A is not mediated by this protein. Furthermore, menadione was well tolerated by the animals: no signs of acute toxicity were detected by visual examination or by assessment of weight gain dynamics or liver function. Taken together, our results suggest that menadione can be used in further studies on animal models of chemically induced carcinogenesis because menadione may suppress tumor formation and possibly progression.

Novel and direct access to the human locomotor spinal circuitry.

The degree of automaticity of locomotion in primates compared with other mammals remains unclear. Here, we examine the possibility for activation of the spinal locomotor circuitry in noninjured humans by spinal electromagnetic stimulation (SEMS). SEMS (3 Hz and 1.3-1.82 tesla) at the T11-T12 vertebrae induced involuntary bilateral locomotor-like movements in the legs of individuals placed in a gravity-neutral position. The formation of locomotor-like activity during SEMS started with a latency of 0.68 +/- 0.1 s after delivering the first stimulus, unlike continuous vibration of muscles, which requires several seconds. The first EMG burst in response to SEMS was observed most often in a proximal flexor muscle. We speculate that SEMS directly activates the circuitry intrinsic to the spinal cord, as suggested by the immediate response and the electrophysiological observations demonstrating an absence of strictly time-linked responses within the EMG burst associated with individual stimuli during SEMS. SEMS in the presence of vibration of the leg muscles was more effective in facilitating locomotor-like activity than SEMS alone. The present results suggest that SEMS could be an effective noninvasive clinical tool to determine the potential of an individual to recover locomotion after a spinal cord injury, as well as being an effective rehabilitation tool itself.

Species-specific induction of CYP2B by 2,4,6-tryphenyldioxane-1,3 (TPD).

AIM: The aim of the current study was to investigate the species-specific induction of CYP2B by 2,4,6-tryphenyldioxane-1,3 (TPD) in relation to activation of CAR. MAIN METHODS: 7-Pentoxyresorufin O-dealkylase (PROD) activity, RT-PCR, Western blot, Electrophoretic mobility shift assays (EMSA). KEY FINDINGS: Phenobarbital-like inducer administration significantly up-regulated CYP2B activity in rat and mouse liver in a species-specific manner, in contrast to the effects on CYP2B in lungs, kidneys and brains. In parallel, Western blot analysis showed that the species-specific increase of PROD in liver is related to the high content of CYP2B: phenobarbital (PB) and TPD increased CYP2B in rat liver, PB and 1,4-bis[2-(3,5-dichloropyridyloxy)]benzene (TCPOBOP) - in mouse liver. The CYP2B protein level was unchanged in the lungs of rats and mice after inducer treatment, whereas it was not detected in the kidney and brain of control and treated animals. The hepatic CYP2B activity in both species paralleled the increase of CYP2B mRNA. A detectable CYP2B mRNA level was measured in the lungs of untreated mice and rats, though it was unchanged during induction. Noninducibility of CYP2B in extrahepatic tissues accompanied an absence of constitutive androstane receptor (CAR) gene expression in these tissues. In liver CYP2B induction paralleled the high level of CAR expression detected by RT-PCR. Moreover, PB, TPD and TCPOBOP treatment stimulated nuclear accumulation of CAR and increased CAR receptor NR1-binding activity in animal liver in a species-specific manner. SIGNIFICANCE: We have shown that the increased nuclear accumulation and binding activity of CAR are associated with the species-specific up-regulation of CYP2B by TPD in rat liver.