Progression of Hepatic Adenoma to Carcinoma in Ogg1 Mutant Mice Induced by Phenobarbital

Chlorine, chromium, proteins of oxidative stress and DNA repair pathways are related to prognosis in oral cancer

The comparison of chemical and histopathological data obtained from the analysis of excised tumor fragments oral squamous cell carcinoma (OSCC) with the demographic and clinical evolution data is an effective strategy scarcely explored in OSCC studies. The aim was to analyze OSCC tissues for protein expression of enzymes related to oxidative stress and DNA repair and trace elements as candidates as markers of tumor aggressiveness and prognosis. Tumor fragments from 78 OSCC patients that had undergone ablative surgery were qualitatively analyzed by synchrotron micro-X-ray fluorescence for trace elements. Protein expression of SOD-1, Trx, Ref-1 and OGG1/2 was performed by immunohistochemistry. Sociodemographic, clinical, and histopathological data were obtained from 4-year follow-up records. Disease relapse was highest in patients with the presence of chlorine and chromium and lowest in those with tumors with high OGG1/2 expression. High expression of SOD-1, Trx, and Ref-1 was determinant of the larger tumor. Presence of trace elements can be markers of disease prognosis. High expression of enzymes related to oxidative stress or to DNA repair can be either harmful by stimulating tumor growth or beneficial by diminishing relapse rates. Interference on these players may bring novel strategies for the therapeutic management of OSCC patients.

The role of DNA damage and repair in liver cancer

Hepatocellular carcinoma is rapidly becoming a major cause of global mortality due to the ever-increasing prevalence of obesity. DNA damage is known to play an important role in cancer initiation, however DNA repair systems are also vital for the survival of cancer cells. Given the function of the liver and its exposure to the gut, it is likely that DNA damage and repair would be of particular importance in hepatocellular carcinoma. However, many contemporary reports have neglected the role of individual pathways of DNA damage and repair in their hypotheses. This review, therefore, aims to provide a concise overview for researchers in the field of liver cancer to understand the pathways of DNA damage and repair and their individual roles in hepatocellular carcinoma.

Prognostic impact of 8-hydroxy-deoxyguanosine and its repair enzyme 8-hydroxy-deoxyguanosine DNA glycosylase in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) has a poor prognosis in the setting of chronic inflammation and fibrosis, both of which promote nuclear DNA oxidative damage. 8-hydroxy-deoxyguanosine (8-OHdG) DNA glycosylase (OGG1) enhances the repair of 8-OHdG, which is the primary oxidative stress-induced mutation that leads to malignant alterations. This study aims to clarify the relationships between oxidative stress-induced factors and HCC progression. The clinicopathological factors were compared with immunohistochemistry OGG1 and 8-OHdG expressions in 86 resected HCC specimens. High 8-OHdG expression was associated with high serum aspartate transaminase and total bilirubin levels, as well as a low platelet count, compared with low 8-OHdG expression. Histological liver cirrhosis and poor differentiation were more frequent in patients with high 8-OHdG expression than in those with low 8-OHdG expression. The 8-OHdG was negatively correlated with OGG1 expression in HCC patients. Therefore, we classified the patients into two groups, low OGG1/high 8-OHdG group and the other group. The patients with low OGG1/high 8-OHdG expressions had worse prognosis than those with the other expressions. Our results showed that low OGG1/high 8-OHdG expressions in nuclei influence HCC patient outcomes. Evaluating the patterns of OGG1 and 8-OHdG expressions might provide pivotal prognostic biomarkers in patients with HCC.

TrxR1, Gsr, and oxidative stress determine hepatocellular carcinoma malignancy

Thioredoxin reductase-1 (TrxR1)-, glutathione reductase (Gsr)-, and Nrf2 transcription factor-driven antioxidant systems form an integrated network that combats potentially carcinogenic oxidative damage yet also protects cancer cells from oxidative death. Here we show that although unchallenged wild-type (WT), TrxR1-null, or Gsr-null mouse livers exhibited similarly low DNA damage indices, these were 100-fold higher in unchallenged TrxR1/Gsr-double-null livers. Notwithstanding, spontaneous cancer rates remained surprisingly low in TrxR1/Gsr-null livers. All genotypes, including TrxR1/Gsr-null, were susceptible to N-diethylnitrosamine (DEN)-induced liver cancer, indicating that loss of these antioxidant systems did not prevent cancer cell survival. Interestingly, however, following DEN treatment, TrxR1-null livers developed threefold fewer tumors compared with WT livers. Disruption of TrxR1 in a marked subset of DEN-initiated cancer cells had no effect on their subsequent contributions to tumors, suggesting that TrxR1-disruption does not affect cancer progression under normal care, but does decrease the frequency of DEN-induced cancer initiation. Consistent with this idea, TrxR1-null livers showed altered basal and DEN-exposed metabolomic profiles compared with WT livers. To examine how oxidative stress influenced cancer progression, we compared DEN-induced cancer malignancy under chronically low oxidative stress (TrxR1-null, standard care) vs. elevated oxidative stress (TrxR1/Gsr-null livers, standard care or phenobarbital-exposed TrxR1-null livers). In both cases, elevated oxidative stress was correlated with significantly increased malignancy. Finally, although TrxR1-null and TrxR1/Gsr-null livers showed strong Nrf2 activity in noncancerous hepatocytes, there was no correlation between malignancy and Nrf2 expression within tumors across genotypes. We conclude that TrxR1, Gsr, Nrf2, and oxidative stress are major determinants of liver cancer but in a complex, context-dependent manner.

The therapeutic effects of nicotinamide in hepatocellular carcinoma through blocking IGF-1 and effecting the balance between Nrf2 and PKB

Insulin growth factor (IGF) family and their receptors play a great role in tumors' development. In addition, IGF-1 enhances cancer progression through regulating cell proliferation, angiogenesis, immune modulation and metastasis. Moreover, nicotinamide is association with protection against cancer. Therefore, we conducted this research to examine the therapeutic effects of nicotinamide against hepatocellular carcinoma (HCC) both in vivo and in vitro through affecting IGF-1 and the balance between PKB and Nrf2. HCC was induced in rats by 200 mg/kg, ip thioacetamide. The rat survival, number and size of tumors and serum α-fetoprotein (AFP) were measured. The gene and protein levels of IGF-1, Nrf2, PKB and JNK-MAPK were assessed in rat livers. In addition, HepG2 cells, human HCC cell lines, were treated with different concentrations of nicotinamide. We found that nicotinamide enhanced the rats' survival and reduced the number and size of hepatic tumors as well as it reduced serum AFP and HepG2 cells survival. Nicotinamide ameliorated HCC-induced reduction in the expression of Nrf2. Moreover, nicotinamide blocked HCC-induced elevation in IGF-1, PKB and JNK-MAPK. In conclusion, nicotinamide produced cytotoxic effects against HCC both in vivo and in vitro. The cytotoxic activity can be explained by inhibition of HCC-induced increased in the expression of IGF-1 and leads to disturbances in the balance between the cell death signal by PKB and MAPK; and the cell survival signal by Nrf2, directing it towards cell survival signals in normal liver cells providing more protection for body against tumor.

Enhanced Susceptibility of Ogg1 Mutant Mice to Multiorgan Carcinogenesis

The role of deficiency of oxoguanine glycosylase 1 (Ogg1) Mmh homolog, a repair enzyme of the 8-hydroxy-2’-deoxyguanosine (8-OHdG) residue in DNA, was investigated using the multiorgan carcinogenesis bioassay in mice. A total of 80 male and female six-week-old mice of C57BL/6J background carrying a mutant Mmh allele of the Mmh/Ogg1 gene (Ogg1^−/−) and wild type (Ogg1^+/+) mice were administered N-diethylnitrosamine (DEN), N-methyl-N-nitrosourea (MNU), N-butyl-N-(4-hydroxybutyl) nitrosamine (BBN), N-bis (2-hydroxypropyl) nitrosamine (DHPN) and 1,2-dimethylhydrazine dihydrochloride (DMH) (DMBDD) to induce carcinogenesis in multiple organs, and observed up to 34 weeks. Significant increase of lung adenocarcinomas incidence was observed in DMBDD-treated Ogg1^−/− male mice, but not in DMBDD-administered Ogg1^+/+ animals. Furthermore, incidences of lung adenomas were significantly elevated in both Ogg1^−/− males and females as compared with respective Ogg1^−/− control and DMBDD-treated Ogg1^+/+ groups. Incidence of total liver tumors (hepatocellular adenomas, hemangiomas and hemangiosarcomas) was significantly higher in the DMBDD-administered Ogg1^−/− males and females. In addition, in DMBDD-treated male Ogg1^−/− mice, incidences of colon adenomas and total colon tumors showed a trend and a significant increase, respectively, along with significant rise in incidence of simple hyperplasia of the urinary bladder, and a trend to increase for renal tubules hyperplasia in the kidney. Furthermore, incidence of squamous cell hyperplasia in the forestomach of DMBDD-treated Ogg1^−/− male mice was significantly higher than that of Ogg1^+/+ males. Incidence of small intestine adenomas in DMBDD Ogg1^−/− groups showed a trend for increase, as compared to the wild type mice. The current results demonstrated increased susceptibility of Ogg1 mutant mice to the multiorgan carcinogenesis induced by DMBDD. The present bioassay could become a useful tool to examine the influence of various targets on mouse carcinogenesis.