Helicobacter hepaticus, a recently recognized bacterial pathogen, associated with chronic hepatitis and hepatocellular neoplasia in laboratory mice

Bacterial-Mediated Tumor Therapy: Old Treatment in a New Context

Targeted therapy and immunotherapy have brought hopes for precision cancer treatment. However, complex physiological barriers and tumor immunosuppression result in poor efficacy, side effects, and resistance to antitumor therapies. Bacteria-mediated antitumor therapy provides new options to address these challenges. Thanks to their special characteristics, bacteria have excellent ability to destroy tumor cells from the inside and induce innate and adaptive antitumor immune responses. Furthermore, bacterial components, including bacterial vesicles, spores, toxins, metabolites, and other active substances, similarly inherit their unique targeting properties and antitumor capabilities. Bacteria and their accessory products can even be reprogrammed to produce and deliver antitumor agents according to clinical needs. This review first discusses the role of different bacteria in the development of tumorigenesis and the latest advances in bacteria-based delivery platforms and the existing obstacles for application. Moreover, the prospect and challenges of clinical transformation of engineered bacteria are also summarized.

Helicobacter hepaticus infection induces chronic hepatitis and fibrosis in male BALB/c mice via the activation of NF-κB, Stat3, and MAPK signaling pathways

BACKGROUND

It has been documented that Helicobacter hepaticus (H hepaticus) infection is linked to chronic hepatitis and liver cancer. However, our understanding of the molecular mechanisms underlying progression of the H hepaticus-induced hepatic inflammation to cellular hepatocarcinoma is still limited.

MATERIALS AND METHODS

In our study, male BALB/c mice were infected by H hepaticus for 8, 12, 16, 20, and 24 weeks. Histopathology, H hepaticus colonization dynamics, select signaling pathways, and expression of key inflammatory cytokines in the liver were examined.

RESULTS

We found that H hepaticus was detectible in feces of mice at 7 days postinfection (DPI) by PCR, but it was not detected in the livers by PCR until 8 weeks postinfection (WPI). In addition, abundance of colonic and hepatic H hepaticus was progressively increased over the infection duration. H hepaticus-induced hepatic inflammation and fibrosis were aggravated over the infection duration, and necrosis or cirrhosis developed in the infected liver at 24 WPI H hepaticus infection increased levels of alanine aminotransferase and aspartate aminotransferase. Moreover, mRNA levels of Il-6 and Tnf-α were significantly elevated in the livers of H hepaticus-infected mice compared to uninfected control from 8 WPI to 24 WPI. Furthermore, Stat3, nuclear factor-κB (p65), and MAPK (Erk1/2 and p38) were activated by H hepaticus infection.

CONCLUSIONS

These data demonstrated that male BALB/c mice can be used as a new mouse model of H hepaticus-induced liver diseases and that the H hepaticus-induced liver injury is triggered by NF-κB, Jak-Stat, and MAPK signaling pathways.

Pathological Findings in Lowland Tapirs (Tapirus terrestris) Killed by Motor Vehicle Collision in the Brazilian Cerrado

The lowland tapir (Tapirus terrestris) is the largest land mammal in South America. The species faces steady population decline due to poaching, habitat loss and fragmentation, road-kill, pesticide pollution, competition with domestic livestock and fires, among other threats. The lowland tapir is currently listed as vulnerable to extinction. Little information is available about natural disease processes for the species. This study aimed to report the pathological findings recorded in a cohort of 35 lowland tapirs killed by motor vehicle collision (MVC) on highways of Mato Grosso do Sul State, Brazil, between 2015 and 2018. The main gross pathological findings were those associated with MVC, primarily involving skeletal fractures and internal multiorgan damage with extensive bleeding and/or severe central nervous system injury. The most prevalent concurrent histopathological findings, unrelated to the cause of death, were: adrenal gland degeneration, necrosis and loss of fascicular and reticular cells with replacement fibrosis and cortical atrophy (9/15; 60%); interstitial pneumonia (20/34; 59%); glossitis (9/24; 38%); pulmonary anthracosis (12/34; 35%); colitis (9/28; 32%); and cholangitis/pericholangitis (9/35; 26%). The aetiopathogeneses and clinicopathological significance of some of these findings are unclear; however, parasitic infections appear to be common. Our results highlight the importance of wildlife health information obtained through the study of carcasses of roadkills.

Association between Helicobacter spp. infections and hepatobiliary malignancies: a review

Hepatobiliary cancers are highly lethal cancers that comprise a spectrum of invasive carcinomas originating in the liver hepatocellular carcinoma, the bile ducts intrahepatic cholangiocarcinoma and extrahepatic cholangiocarcinoma, the gallbladder and the ampulla of Vater (collectively known as biliary tract cancers). These tumors account for approximately 13% of all annual cancer-related deaths worldwide and for 10%-20% of deaths from hepatobiliary malignancies. Cholangiocarcinoma (CCA) is a devastating disease that displays a poor survival rate for which few therapeutic options are available. Population genetics, geographical and environmental factors, cholelithiasis, obesity, parity, and endemic infection with liver flukes have been identified as risk factors that influence the development of biliary tract tumors. Other important factors affecting the carcinogenesis of these tumors include chronic inflammation, obstruction of the bile ducts, and impaired bile flow. It has been suggested that CCA is caused by infection with Helicobacter species, such as Helicobacter bilis and Helicobacter hepaticus, in a manner that is similar to the reported role of Helicobacter pylori in distal gastric cancer. Due to the difficulty in culturing these Helicobacter species, molecular methods, such as polymerase chain reaction and sequencing, or immunologic assays have become the methods of choice for diagnosis. However, clinical studies of benign or malignant biliary tract diseases revealed remarkable variability in the methods and the findings, and the use of uniform and validated techniques is needed.

Pathogenicity of Helicobacter ganmani in mice susceptible and resistant to infection with H. hepaticus

Helicobacter spp. are some of the most prevalent bacterial contaminants of laboratory mice. Although abundant data regarding the diseases associated with H. hepaticus infection are available, little is known about the pathogenicity of H. ganmani, which was first isolated in 2001 from the intestines of laboratory mice. The objective of this study was to evaluate the host response to H. ganmani colonization in H. hepaticus disease-resistant C57BL/6 and disease-susceptible A/J and IL10-deficient mice. Mice were inoculated with H. ganmani, H. hepaticus, or Brucella broth. Cecal lesion scores, cecal gene expression, and Helicobacter load were measured at 4 and 90 d after inoculation. At both time points, mice inoculated with H. ganmani had similar or significantly more copies of cecum-associated Helicobacter DNA than did mice inoculated with H. hepaticus. When compared with those of sham-inoculated control mice, cecal lesion scores at 4 and 90 d after inoculation were not significantly greater in H. ganmani-inoculated A/J, C57BL/6, or IL10-deficient mice. Analysis of cecal gene expression demonstrated that H. ganmani infection failed to cause significant elevations of IFNγ in A/J, C57BL/6, or IL10-deficient mice. However, in IL10-deficient mice, H. ganmani infection was associated with a significant increase in the expression of the proinflammatory cytokine IL12/23p40. Although H. ganmani infection in this study failed to induce the typhlitis that is the hallmark of H. hepaticus infection, infection with H. ganmani was associated with alterations in inflammatory cytokines in IL10-deficient mice.

Human O6 -methylguanine-DNA methyltransferase containing C145A does not prevent hepatocellular carcinoma in C3HeB/FeJ transgenic mice

The prevalence of hepatocellular carcinoma (HCC) was diminished from 60% to 18% at 15 months of age in C3HeB/FeJ male transgenic mice expressing hMGMT in our previous studies. To directly test if the methyltransferase activity is required for diminished tumor prevalence, two separate lines of transgenic mice bearing an enzymatically inactive form of hMGMT were used. In these lines, cysteine 145 was substituted with alanine (C145A). Expression of the hMGMT C145A transgene in liver was demonstrated by Northern blots and Western blots. Immunohistochemistry revealed predominantly nuclear localization of the hMGMT C145A protein. hMGMT C145A transgenic mice were crossed with lacI transgenic mice to assess mutant frequencies in the presence of the mutant protein. Mutant frequencies were similar among livers of lacI × hMGMT C145A bi-transgenic mice and lacI × wild-type (WT) mice. DNA sequence analysis of recovered lacI mutants revealed similar mutation spectra for hMGMT C145A and WT mice. The prevalence of HCC was also similar for the two tested lines of hMGMT C145A mice, 45% and 48% prevalence with median tumor sizes of 11 and 8 mm, and WT mice, 40% prevalence and median tumor size of 10 mm. These results provide evidence that residue C145 in hMGMT is required to reduce the prevalence of HCC in C3HeB/FeJ mice transgenic for hMGMT.

Marked liver tumorigenesis by Helicobacter hepaticus requires perinatal exposure

BACKGROUND

Although severe hepatitis and liver tumors occur in a high percentage of A/J male mice naturally infected with Helicobacter hepaticus, these effects have not been observed after injection of adult mice with the bacteria.

OBJECTIVES

We tested the hypothesis that perinatal exposure to the bacteria is required for liver tumorigenesis.

METHODS

A/J female mice were infected by intragastric (ig) or intraperitoneal (ip) treatment with 1.5 x 10(8) H. hepaticus before pregnancy. We examined offspring at progressive time intervals, including some kept until natural death in old age. A/J, BALB/c, and C57BL/6 weanling male mice were similarly treated ig with the bacteria and observed for up to 2 years.

RESULTS

After ip bacterial infection of A/J females, 41% of their male offspring developed hepatitis and 33% had hepatocellular tumors, including 18% with hepatocellular carcinoma. Treatment by the ig route resulted in a similar incidence of hepatitis in offspring (35%) but fewer total liver tumors (8%) and carcinomas (4%). By contrast, ig instillation of H. hepaticus in weanling A/J, C57BL/6, or BALB/c mice resulted in low incidence of hepatitis (0-20%) and few liver tumors, despite presence of bacteria confirmed in feces.

CONCLUSIONS

Results indicate that a high incidence of liver tumors in mice infected with H. hepaticus requires perinatal exposure. Contributing perinatal factors could include known high sensitivity of neonatal liver to tumor initiation, and/or modulation of immune response to the bacterium or its toxins. Mechanisms of human perinatal sensitivity to such phenomena can be studied with this model.

Characterization of a Helicobacter hepaticus putA mutant strain in host colonization and oxidative stress

Helicobacter hepaticus is a gram-negative, spiral-shaped microaerophilic bacterium associated with chronic intestinal infection leading to hepatitis and colonic and hepatic carcinomas in susceptible strains of mice. In the closely related human pathogen Helicobacter pylori, L-proline is a preferred respiratory substrate and is found at significantly high levels in the gastric juice of infected patients. A previous study of the proline catabolic PutA flavoenzymes from H. pylori and H. hepaticus revealed that Helicobacter PutA generates reactive oxygen species during proline oxidation by transferring electrons from reduced flavin to molecular oxygen. We further explored the preference for proline as a respiratory substrate and the potential impact of proline metabolism on the redox environment in Helicobacter species during host infection by disrupting the putA gene in H. hepaticus. The resulting putA knockout mutant strain was characterized by oxidative stress analysis and mouse infection studies. The putA mutant strain of H. hepaticus exhibited increased proline levels and resistance to oxidative stress relative to that of the wild-type strain, consistent with proline's role as an antioxidant. The significant increase in stress resistance was attributed to higher proline content, as no upregulation of antioxidant genes was observed for the putA mutant strain. The wild-type and putA mutant H. hepaticus strains displayed similar levels of infection in mice, but in mice challenged with the putA mutant strain, significantly reduced inflammation was observed, suggesting a role for proline metabolism in H. hepaticus pathogenicity in vivo.

In vitro and in vivo characterization of alkyl hydroperoxide reductase mutant strains of Helicobacter hepaticus

Mutant strains in the tsaA gene encoding alkyl hydroperoxide reductase were more sensitive to O(2) and to oxidizing agents (paraquat, cumene hydroperoxide and t-butylhydroperoxide) than the wild type, but were markedly more resistant to hydrogen peroxide. The mutant strains resistance phenotype could be attributed to a 4-fold and 3-fold increase in the catalase protein amount and activity, respectively compared to the parent strain. The wild type did not show an increase in catalase expression in response to sequential increases in O(2) exposure or to oxidative stress reagents, so an adaptive compensatory mutation has probably occurred in the mutants. In support of this, chromosomal complementation of tsaA mutants restored alkyl hydroperoxide reductase, but catalase was still up-expressed in all complemented strains. The katA promoter sequence was the same in all mutant strains and the wild type. Like its Helicobacter pylori counterpart strain, a H. hepaticus tsaA mutant contained more lipid hydroperoxides than the wild type strain. Hepatic tissue from mice inoculated with a tsaA mutant had lesions similar to those inoculated with the wild type, and included coagulative necrosis of hepatocytes. The liver and cecum colonizing abilities of the wild type and tsaA mutant were comparable. Up-expression of catalase in the tsaA mutants likely permits the bacterium to compensate (in colonization and virulence attributes) for the loss of an otherwise important oxidative stress-combating enzyme, alkyl hydroperoxide reductase. The use of erythromycin resistance insertion as a facile way to screen for gene-targeted mutants, and the chromosomal complementation of those mutants are new genetic procedures for studying H. hepaticus.

Progressive proliferative and dysplastic typhlocolitis in aging syrian hamsters naturally infected with Helicobacter spp.: a spontaneous model of inflammatory bowel disease

Helicobacter spp. have been implicated in a variety of gastrointestinal tract diseases, including peptic ulcer disease, gastric cancer, and inflammatory bowel disease (IBD), in humans and animals. Although most models of IBD are experimentally induced, spontaneous or natural models of IBD are rare. Herein, we describe a long-term study of chronic, progressive lesions that develop in the distal portion of the large bowel of unmanipulated Syrian hamsters naturally infected with Helicobacter spp. Twenty-four Syrian hamsters of three age groups (group A, 1 month [n = 4], group B, 7-12 months [n = 12], group C, 18-24 months [n = 12]), underwent complete postmortem examination. Results of microbial isolation and polymerase chain reaction and restriction fragment length polymorphism analyses confirmed the presence of Helicobacter spp. infection in the distal portion of the large bowel of all animals. Additionally, confounding pathogens, such as Clostridium difficile, Lawsonia intracellularis, and Giardia spp. that can cause proliferative enteritis, were absent in the hamsters of this study. Histopathologic scores for inflammation (P < 0.01), hyperplasia (P < 0.01), and dysplasia (P < 0.05) were significantly higher in the ileocecocolic (ICC) junction of animals in group C, relative to group A. Dysplastic lesions of various grades were detected in 5 of 11 hamsters in group C. Interestingly, the segment of the bowel that is usually colonized by Helicobacter spp. in hamsters had the most severe lesions. One hamster of group C developed a malignant fibrous histiocytoma, whereas another hamster developed a round cell sarcoma originating from the ICC junction. Thus, lesions in the distal portion of the large bowel of aging hamsters naturally colonized with Helicobacter spp. warrants developing the hamster as an animal model of IBD and potentially IBD-related cancer.

Progression of chronic hepatitis and preneoplasia in Helicobacter hepaticus-infected A/JCr mice

Helicobacter hepaticus infection induces sustained inflammation and carcinoma of the liver in A/JCr mice, and serves as a model of human cancers associated with viral hepatitis and H. pylorichronic gastritis. Here we describe the pathogenesis of premalignant disease in A/JCr mice infected with H. hepaticus. We inoculated dams intragestationally and/or pups postnatally, and evaluated offspring at 3, 6, or 12 months. Mice infected at or before 3 weeks of age, but not at 12 weeks, developed disease. Male mice were most affected, but expressed a bimodal pattern of susceptibility. Males exhibited lobular necrogranulomatous and interface (chronic active) hepatitis, while females usually developed intraportal (chronic persistent) hepatitis. Portal inflammation was slowly progressive, with tertiary lymphoid nodule development by 12 months. Hepatic bacterial load and preneoplastic lesions, including clear and tigroid cell foci of cellular alteration, were correlated with lobular hepatitis severity. No extrahepatic surrogate disease marker reliably predicted individual hepatitis grade. In conclusion, gender and bacterial exposure timing are key determinants of H. hepaticus disease outcomes. Intrahepatic inflammation is driven by local signals characterized by a vigorous but nonsterilizing immune response. Continued study of chronic hepatitis progression may reveal therapeutic targets to reduce the risk of hepatocellular carcinoma.

Role of Se-dependent glutathione peroxidases in gastrointestinal inflammation and cancer

Increase in reactive oxygen species plays an integral part in the inflammatory response, and chronic inflammation increases cancer risk. Selenium-dependent glutathione peroxidase (GPX) is well recognized for its antioxidant, and thus anti-inflammatory, activity. However, due to the multiple antioxidant families present in the gastrointestinal tract, it has been difficult to demonstrate the importance of individual antioxidant enzymes. Using genetically altered mice deficient in individual Gpx genes has provided insight into the physiological functions of these genes. Insufficient GPX activity in the mucosal epithelium can trigger acute and chronic inflammation. The presence of certain microflora, such as Helicobacter species, may affect cancer risk significantly. However, when damaged cells have progressed into a precancerous status, increased GPX activity may become procarcinogenic, presumably due to inhibition of hydroperoxide-mediated apoptosis. This review summarizes the current view of GPX in inflammation and cancer with emphasis on the GI tract.

Immunohistochemical study of retinol-binding protein in livers of polar bears (Thalarctos maritimus)

Liver tumors of unknown cause have frequently been described in polar bears. Concurrent decrease of vitamin A levels and chronic liver disease are associated with hepatic carcinogenesis in humans. More than 90% of the body's vitamin A is stored in the liver, where it is bound to an intracellular retinol-binding protein (RBP). Therefore, in this retrospective study, RBP was assessed by immunohistochemistry in liver sections of 11 polar bears. Two of these polar bears had hepatocellular carcinoma, four showed other chronic liver changes, and five had normal livers. In normal livers, the cytoplasm stained diffusely positive with intensely staining cytoplasmic granules. RBP staining was evaluated and the abundance of diffuse cytoplasmic staining and intracytoplasmic large granules was determined. All cases with pathologic liver changes had markedly decreased staining intensities for RBP compared with normal livers. The findings of this study suggest that in polar bears, as in humans, vitamin A metabolism may play a role in hepatic carcinogenesis.

Serum antibodies to Helicobacter hepaticus and Helicobacter pylori in patients with chronic liver disease

BACKGROUND

Bile tolerant helicobacter species such as H hepaticus and H bilis have frequently been reported to cause hepatitis in mice and other rodents.

AIMS

To investigate the possible pathogenic role of these and other helicobacter species in chronic liver disease in humans.

METHODS

Serum samples from 144 patients with various chronic liver diseases, 30 patients with primary sclerosing cholangitis (PSC), and 48 healthy blood donors were analysed for antibodies against H hepaticus murine strain CCUG 33637 and H pylori strain CCUG 17874. Cell surface proteins of H hepaticus were extracted by acid glycine buffer and used in an enzyme immunoassay (EIA) and immunoblot (IB).

RESULTS

56 of 144 (39%) patients with chronic liver diseases and six of 30 (20%) with PSC showed increased antibody concentrations in the H hepaticus EIA; in the H pylori EIA the numbers were 58% and 13% respectively. Compared with the healthy blood donors the antibody reactivity against the two helicobacter species was not increased (46% and 48% respectively). Patient serum samples retested by the H hepaticus EIA after absorption with sonicated H pylori cells remained positive in 12 of 37 (33%) serum samples. Distinct antibody reactivity to 55-65 kDa proteins was observed by H hepaticus IB, after the absorption step, and was considered specific for H hepaticus. These 12 serum samples were from patients with chronic alcoholic liver disease.

CONCLUSIONS

Antibodies to H hepaticus, often cross reacting with H pylori, occur frequently in patients with chronic liver diseases, with no clear cut relation to specific diagnostic groups. The pathogenic significance of these findings is not known.

Cloning and expression of an immunogenic membrane-associated protein of Helicobacter hepaticus for use in an enzyme-linked immunosorbent assay

Helicobacter hepaticus is a bacterial pathogen that causes chronic active hepatitis and inflammatory bowel disease in mice. The purpose of this study was to develop a recombinant antigen-based enzyme-linked immunosorbent assay (ELISA) to detect H. hepaticus-infected mice. A genomic library of H. hepaticus was constructed and was screened with sera from H. hepaticus-infected mice. A 459-bp open reading frame that coded for an 18-kDa immunoreactive protein, MAP18, was identified. The gene had high identity with genes coding for outer membrane proteins of other bacteria, and the predicted amino acid sequence of MAP18 had a putative membrane-trafficking signal sequence and a putative signal peptidase II cleavage site. The recombinant protein was expressed in Escherichia coli as a glutathione S-transferase (GST) fusion protein, GST-MAP18, and purified by affinity chromatography. The 44-kDa fusion protein was detected on Western blots probed with sera from H. hepaticus-infected mice but was not detected on blots probed with sera from mice infected with Helicobacter muridarum or Helicobacter bilis or with sera from mice free of Helicobacter infection. The GST-MAP18 fusion protein was used as an antigen in an ELISA to detect anti-H. hepaticus antibodies in sera from infected mice. This ELISA was compared to an H. hepaticus-specific ELISA that uses a detergent extract of H. hepaticus as the antigen. Sera from mice naturally and experimentally infected with H. hepaticus, H. bilis, or H. muridarum and sera from mice free of Helicobacter infection were evaluated. Both ELISAs performed with a high specificity (98%); however, the detergent extract-based ELISA performed with a higher sensitivity (89%) than the recombinant protein-based ELISA (sensitivity, 66%). These data indicate that H. hepaticus carries a gene that encodes an immunogenic 18-kDa membrane-associated protein; however, antibodies to this protein are not detected in all infected mice.

Pathology, diagnosis and epidemiology of the rodent Helicobacter infection

Since the first isolation of Helicobacter pylori from humans in 1983, 18 Helicobacter species have been identified during the last decade in domestic and laboratory animals. Several Helicobacter species have been isolated from the gastrointestinal tracts of various mammalian species and birds. Helicobacter hepaticus, H. muridarum, H. bilis, H. rodentium and Flexispira rappini have been isolated from mice. Among these species, only H. hepaticos has been clearly recognized as a pathogen. Indeed, it displays the pathogenic potential to elicit hepatitis in several strains of mice; moreover in A/JCr mice, it is strongly associated with hepatic cancer. Among the five murine helicobacter species, apart from H. hepaticus, F. rappini has not been found associated with lesions, H. muridarum has been observed in gastric glands of mice with chronic gastritis, and H. bilis has been reported in the liver of mice with chronic hepatitis. When associated with H. rodentium, H. bilis is able to induce diarrhea in SCID mice. In no case has pathogenicity of a single species been clearly proven. In rats, H. trogontum and H. muridarum have been isolated from the intestine, without any information concerning their respective pathogenicity. H. cinaedi and H. cholecystus have been identified from the intestine and the gallbladders of hamsters, respectively. The diagnosis of Helicobacter species by polymerase chain reaction (PCR) is a rapid, specific and sensitive technique. One of the most promising diagnostic techniques of these infections seems to be the PCR detection of Helicobacter sp. from feces based on the 16S rRNA sequences, then a restriction enzyme analysis to identify the actual species. Several drug regimens have also been evaluated to eradicate H. hepaticus from mice. Helicobacter infections, particularly H. hepaticus and H. bilis, seem to be widespread in laboratory mouse colonies and have also been detected from commercial breeders.

Chronic active hepatitis induced by Helicobacter hepaticus in the A/JCr mouse is associated with a Th1 cell-mediated immune response

Helicobacter hepaticus infection in A/JCr mice results in chronic active hepatitis characterized by perivascular, periportal, and parenchymal infiltrates of mononuclear and polymorphonuclear cells. This study examined the development of hepatitis and the immune response of A/JCr mice to H. hepaticus infection. The humoral and cell-mediated T helper immune response was profiled by measuring the postinfection (p.i.) antibody response in serum, feces, and bile and by the production of cytokines and proliferative responses by splenic mononuclear cells to H. hepaticus antigens. Secretory immunoglobulin A (IgA) and systemic IgG2a antibody developed by 4 weeks p.i. and persisted through 12 months. Splenocytes from infected mice proliferated and produced more gamma interferon (IFN-gamma) than interleukin-4 (IL-4) or IL-5 when cultured with H. hepaticus outer membrane proteins. The predominantly IgG2a antibody response in serum and the in vitro production of IFN-gamma in excess of IL-4 or IL-5 are consistent with a Th1 immune response reported in humans and mice infected with Helicobacter pylori and Helicobacter felis, respectively. Mice infected with H. hepaticus developed progressively severe perivascular, periportal, and hepatic parenchymal lesions consisting of lymphohistiocytic and plasmacytic cellular infiltrates. In addition, transmural typhlitis was observed at 12 months p.i. The characterization of a cell-mediated Th1 immune response to H. hepaticus infection in the A/JCr mouse should prove valuable as a model for experimental regimens which manipulate the host response to Helicobacter.

Alteration in cell kinetics in control B6C3F1 mice infected with Helicobacter hepaticus

The discovery of Helicobacter hepaticus infection, H. hepaticus hepatitis, and increased incidence of liver tumors in control males from several recent National Toxicology Program B6C3F1 mouse carcinogenicity bioassays raised questions regarding the suitability of these bioassays for hazard identification. The purpose of this study was to determine if changes in cell proliferation and death at terminal sacrifice might be linked to the increased liver tumor incidences among control males. In control males, enhanced rates of hepatocyte proliferation, as assessed by immunostaining for proliferating cell nuclear antigen (PCNA), and apoptosis, as assessed from hematoxylin and eosin- and TUNEL-stained preparations, were seen in 3 bioassays with H. hepaticus hepatitis. One bioassay with H. hepaticus infection without attendant hepatitis and one bioassay without H. hepaticus or hepatitis did not have elevated rates of hepatocyte proliferation or apoptosis. There was no significant effect on PCNA cell proliferation indices or apoptosis in females. The present findings are indicative of a clear association between the presence of H. hepaticus infection with attendant hepatitis, increased cell proliferation and apoptosis, and increased incidences of hepatocellular neoplasia in males but not in females. Thus, the interpretation of liver tumor responses in H. hepaticus-infected studies is considered to be confounded in male mice. The lack of enhanced cell proliferation or hepatocellular neoplasia in control females suggests that bioassay results from females are valid for hazard identification. Furthermore, the absence of enhanced cell proliferation in lungs and kidneys of male and females suggests that neoplastic effects at these sites are not exacerbated by H. hepaticus infection.

Increased oxidative DNA damage and hepatocyte overexpression of specific cytochrome P450 isoforms in hepatitis of mice infected with Helicobacter hepaticus

A recently discovered bacterium, Helicobacter hepaticus, infects the intrahepatic bile canaliculi of mice, causing a severe chronic hepatitis culminating in liver cancer. Thus, it affords an animal model for study of bacteria-associated tumorigenesis including H. pylori-related gastric cancer. Reactive oxygen species are often postulated to contribute to this process. We now report that hepatitis of male mice infected with H. hepaticus show significant increases in the oxidatively damaged DNA deoxynucleoside 8-hydroxydeoxyguanosine, with the degree of damage increasing with progression of the disease. Perfusion of infected livers with nitro blue tetrazolium revealed that superoxide was produced in the cytoplasm of hepatocytes, especially in association with plasmacytic infiltrates near portal triads. Contrary to expectations, Kupffer cells, macrophages, and neutrophils were rarely involved. However, levels of cytochrome P450 (CYP) isoforms 1A2 and 2A5 in hepatocytes appeared to be greatly increased, as indicated by the number of cells positive in immunohistochemistry and the intensity of staining in many cells, concomitant with severe hepatitis. The CYP2A5 immunohistochemical staining co-localized with formazan deposits resulting from nitro blue tetrazolium reduction and occurred in nuclei as well as cytoplasm. These findings suggest that CYP2A5 contributes to the superoxide production and 8-hydroxydeoxyguanosine formation, although reactive oxygen species from an unknown source in the hepatocytes leading to CYP2A5 induction or coincidental occurrence of these events are also possibilities. Three glutathione S-transferase isoforms, mGSTP1-1 (pi), mGSTA1-1 (YaYa), and mGSTA4-4, also showed striking increases evidencing major oxidative stress in these livers.

Studies of oncogene activation and tumor suppressor gene inactivation in normal and neoplastic rodent tissue

Emerging short-term bioassays for chemically-induced carcinogenesis are dependent for their relevance to human risk assessment on the degree of coincidence of human and rodent tumor pathways. Since these pathways do not always converge, these new tests may have a number of unanticipated pitfalls. Models of liver and renal tumors are described. The results from Rb and p53 tumor suppressor gene transgenic animals are compared to human tumor syndromes. The question of mutagenic and epigenetic fingerprints of chemicals versus the cell-specific selection of spontaneous mutations is debated. Examples of specific pitfalls, such as the recently discovered Helicobacter hepaticus promoted liver tumors in mice are presented. The rat pseudogenes for p53 and the rare role of p53 in most important rodent tumor models other than epithelial tumors present experimental quandaries. The differential effects of carcinogens during various stages of rodent perinatal and adult development are also discussed. It is concluded that the pathways of both animal models and their human counterparts should be better identified so that realistic endpoint markers can be chosen for human carcinogenic risk assessment.