Protective effect of Actinidia arguta in MPTP-induced Parkinson's disease model mice

Parkinson's disease (PD) is a neurodegenerative disease characterized by the progressive degeneration of dopaminergic neurons in the substantia nigra. Oxidative stress-induced neuronal death has been identified as one of the major causes of nigrostriatal degeneration in PD. The fruit of Actinidia arguta (A. arguta), known as sarunashi in Japan, has been reported to show beneficial health effects such as antioxidant, anti-inflammatory, anti-mutagenic, and anticholinergic effects. In this study, we investigated the neuroprotective effects of A. arguta in 1-methyl-4-phenyl-1,2,3,6-tetrahydropypridine (MPTP)-induced PD model mice. A. arguta juice was administered to 7-week-old C57BL/6J mice continuously for 10 days before the first MPTP injection. The degeneration of dopaminergic neurons in the substantia nigra was induced by MPTP (30 mg/kg, i. p.) once daily for five consecutive days. We found that the administration of A. arguta ameliorated MPTP-induced motor impairment and suppressed the MPTP-induced reductions of tyrosine hydroxylase-positive neurons and tyrosine hydroxylase protein expression in the substantia nigra. Our findings suggest that taking A. arguta could provide neuroprotection that delays or prevents the neurodegenerative process of PD.

Hepatocarcinogen 4-methylquinoline induced G:C to C:G transversions in the cII gene in the liver of lambda/lacZ transgenic mice (Muta™Mouse)

We have previously reported that quinoline increased the mutation frequency of the cII gene in the liver of lambda/lacZ transgenic mice (Muta™Mouse), and G:C to C:G transversions were the molecular signature of quinoline-induced mutations. 4-Methylquinoline (4-MeQ) has the highest mutagenicity among quinoline and isomeric methylquinolines according to the Ames test using Salmonella typhimurium TA 100, in the presence of rat liver microsomal enzymes. In this report, we examined the effect of 4-MeQ on mutagenesis in the lambda cII gene in the liver of the Muta™Mouse, and we analyzed the sequences of the mutated genes. The mutation frequency of the liver cII gene was seven times higher in 4-MeQ-treated mice than in control mice. Sequence analysis revealed that 4-MeQ primarily induced G:C to C:G transversions (37 of 45). The specificities of 4-MeQ for target organ and mutation pattern were very consistent with those of quinoline. Thus, we showed that 4-MeQ was also genotoxic in the liver of the Muta™Mouse, and as with quinoline, the G:C to C:G transversion was the molecular signature of the 4-MeQ-induced mutations.

Nitrogen-substitution effects on the mutagenicity and cytochrome P450 isoform-selectivity of chrysene analogs

Nitrogen-containing analogs of chrysene, 1,10-diazachrysene (1,10-DAC) and 4,10-DAC, were tested for mutagenicity in Salmonella typhimurium TA100 in the presence of rat liver S9 and human liver microsomes to investigate the effect of nitrogen-substitution. Although these DACs could not be converted to the bay-region diol epoxide because of their nitrogen atoms in the bay-region epoxide or diol moiety, DACs were mutagenic in the Ames test with rat liver S9. Both DACs also showed mutagenicity in the Ames test using pooled human liver microsomes, although chrysene itself was not mutagenic in the presence of pooled human liver microsomes. The mutagenicity of DACs (50nmol/plate) in Ames tests using human liver microsome preparations from 10 individuals was compared with cytochrome P450 (CYP) activity in each microsome preparation to investigate the CYP isoform involved in the activation of DACs to the genotoxic forms. The numbers of induced revertants obtained by 1,10-DAC varied 6.2-folds (109-680) and those by 4,10-DAC 4.8-folds (155-751) among the 10 individuals. The number of induced revertants obtained by 1,10-DAC significantly correlated with the CYP1A2-selective catalytic activity (r=0.84, P<0.01) in each microsome preparation. On the other hand, the number of induced revertants obtained by 4,10-DAC significantly correlated with the combined activity of CYP2A6 and 1A2 (CYP2A6+0.51xCYP1A2; r=0.75, P<0.01). However, in Ames tests using microsomes from insect cells expressing various human CYP isoforms, the mutagenicity of 1,10-DAC was induced only by recombinant human CYP1A2, whereas both recombinant human CYP2A6 and 1A2 contributed to the mutagenicity of 4,10-DAC. These results suggest that 1,10-DAC shows the mutagenicity through involvement of CYP1A2 in human liver, and 4,10-DAC does so through both CYP2A6 and 1A2. In conclusion, our results suggested that the difference in the nitrogen-substituted position in the chrysene molecule might affect the mutagenic activity through influencing the ratio of participation of the metabolic activation enzyme isoforms of CYP.

Nitrogen-substitution effect on in vivo mutagenicity of chrysene

We have previously reported the in vivo mutagenicity of aza-polycyclic aromatic hydrocarbons (azaPAHs), such as quinoline, benzo[f]quinoline, benzo[h]quinoline, 1,7-phenanthroline and 10-azabenzo[a]pyrene. The 1,10-diazachrysene (1,10-DAC) and 4,10-DAC, nitrogen-substituted analogs of chrysene, were shown to exhibit mutagenicity in Salmonella typhimurium TA100 in the presence of rat liver S9 and human liver microsomes in our previous report, although DACs could not be converted to a bay-region diol epoxide, the ultimate active form of chrysene, because of their nitrogen atoms. In the present study, we tested in vivo mutagenicity of DACs compared with chrysene using the lacZ transgenic mouse (Mutatrade markMouse) to evaluate the effect of the nitrogen substitution. DACs- and chrysene-induced mutation in all of the six organs examined (liver, spleen, lung, kidney, bone marrow and colon). The mutant frequencies obtained with chrysene showed only small differences between the organs examined and ranged from 1.5 to 3 times the spontaneous frequency. The 4,10-DAC was more mutagenic than chrysene in all the organs tested. The highest lacZ mutation frequency was observed in the lung of 4,10-DAC-treated mice and it was 19 and 6 times the spontaneous frequency and the frequency induced by chrysene, respectively. The 1,10-DAC induced lacZ mutation in the lung with a frequency 4.3- and 1.5-fold higher than in the control and chrysene-treated mice, respectively, although the mutant frequencies in the other organs of 1,10-DAC-treated mice were almost equivalent to those of chrysene-treated mice. Not only chrysene but also DACs depressed the G:C to A:T transition and increased the G:C to T:A transversion in the liver and lung. These results suggest that the two types of nitrogen substitutions in the chrysene structure may enhance mutagenicity in the mouse lung, although they showed no difference in the target-organ specificity and the mutation spectrum.

In vivo mutagenicity of benzo[f]quinoline, benzo[h]quinoline, and 1,7-phenanthroline using the lacZ transgenic mice

Phenanthrene, a simplest angular polycyclic aromatic hydrocarbon with a bay-region in its molecule, is reported to be non-mutagenic, although most angular (non-linear) polycyclic aromatic hydrocarbons, such as benzo[a]pyrene and chrysene, are known to show genotoxicity after metabolic transformation into a bay-region diol epoxide. On the other hand, benzo[f]quinoline (BfQ), benzo[h]quinoline (BhQ), and 1,7-phenanthroline (1,7-Phe), which are all aza-analogs of phenanthrene, are mutagenic in the Ames test using Salmonella typhimurium TA100 in the presence of a rat liver S9 fraction. In this report, we undertook to investigate the in vivo mutagenicity of BfQ, BhQ and 1,7-Phe by an in vivo mutation assay system using the lacZ transgenic mouse (Muta Mouse). BfQ and BhQ only slightly induced mutation in the liver and lung, respectively. BfQ- and BhQ-induced cII mutant spectra showed no characteristics compared with that of the control. These results suggest that the in vivo mutagenicities of BfQ and BhQ were equivocal. On the other hand, 1,7-Phe induced a potent mutation in the liver and a weak mutation in the lung. Furthermore 1,7-Phe depressed the G:C to A:T transition and increased the G:C to C:G transversion in the liver like quinoline, a hepatomutagen possessing the partial structure of 1,7-Phe, compared with the spontaneous mutation spectrum. These results suggest that the in vivo mutagenicity of 1,7-Phe might be caused by the same mechanism as that of quinoline, which induced the same mutational spectrum change (G:C to C:G transversion).