Host specificity of Helicobacter pylori strains and host responses in experimentally challenged nonhuman primates.

BACKGROUND & AIMS: The specificity of colonization by Helicobacter pylori and complex host-bacterium interactions cannot be readily examined in humans. The aim of this study was to perform such analyses in rhesus monkeys. METHODS: Four animals that had been cured of natural H. pylori colonization were challenged with a mixture of 7 strains of human origin, and bacteria recovered during periodic videogastroscopy were DNA fingerprinted. RESULTS: Three animals carried mixtures of several strains for 4 months, after which strain J166 predominated. In the fourth animal, only strain J238 was isolated from the earliest phase of colonization through 7 months, but strain J166 again became predominant by 10 months after the challenge. Gastritis scores and plasma gastrin and anti-H. pylori immunoglobulin G titers reached levels observed in naturally colonized animals by 4 months after the challenge; however, no plasma immunoglobulin A response was observed up to 10 months. CONCLUSIONS: These results show that (1) natural colonization does not elicit protective immunity against subsequent H. pylori challenge; (2) individuals differ in susceptibility to different H. pylori strains during initial stages of colonization; and (3) certain strains are better suited than others for long-term survival in different hosts. These observations show the complexity of H. pylori-host interactions.

Immunization against natural Helicobacter pylori infection in nonhuman primates.

Helicobacter pylori infection is widespread in some breeding groups of a rhesus monkey colony (71% H. pylori positive by 1 year), and the rate of seroconversion is also high. As a result, these groups can be used to test the safety and efficacy of an anti-H. pylori vaccine. Nine-month-old female animals were randomized to receive either 8 mg of recombinant urease (rUre) plus 25 microg of Escherichia coli heat-labile enterotoxin (LT) (n = 26) or placebo plus LT (n = 29), given four times at 1-week intervals followed by a booster 1 month later. Ten months after the start of the immunization, the animals were subjected to endoscopy and biopsy samples were obtained. H. pylori negativity was defined as no H. pylori growth by culture and no H. pylori observed at histology. By this criterion, 2 (7%) of 29 animals receiving placebo and 8 (31%) of 26 immunized animals were H. pylori negative (P < 0.035). In addition, antral gastritis score was significantly less in H. pylori-negative immunized monkeys than in H. pylori-positive animals, whether they were given rUre plus LT or placebo plus LT (P < 0.02 or P < 0.01, respectively). Interestingly, antral gastritis was also significantly less in H. pylori-positive animals given rUre plus LT than in H. pylori-positive animals given placebo plus LT (P < 0.02). However, quantitative cultures did not demonstrate significant differences between the two latter groups. It is concluded that oral administration of rUre vaccine plus LT significantly protects nonhuman primates against H. pylori infection while not causing undesirable side effects.

Cure of Helicobacter pylori infection by omeprazole-clarithromycin-based therapy in non-human primates.

Rhesus monkeys raised in colonies tend to become naturally infected by Helicobacter pylori early in life. Earlier attempts to cure H. pylori infection with a 10-day triple therapy (metronidazole, amoxicillin, and peptobismol) were only partially (60%) successful, probably because of preexisting metronidazole resistance. This study was carried out to determine the efficacy of an alternative clarithromycin-omeprazole-based therapy for curing H. pylori infection in Rhesus monkeys (Macaca mulatta), and to examine histologic and serologic correlates of curing. Five monkeys were endoscoped under ketamine anesthesia. Histology and culture of gastric biopsies and serologic tests demonstrated that they were H. pylori-positive. Two animals had not received prior anti-H. pylori treatment, while three other animals had failed triple therapy and carried metronidazole-resistant H. pylori strains. Quadruple therapy with omeprazole, clarithromycin, amoxicillin, and bismuth subsalicylate was given for 10 days to these five animals. All five animals were cured of the infection, and remained H. pylori-free, based on histology and culture at regular intervals for the 5 months posttherapy during which they were followed. Gastritis scores and anti-H. pylori IgG levels decreased in each animal during this period to levels characteristic of uninfected animals. These results indicate that an omeprazole-clarithromycin-based regimen can cure H. pylori infection in Rhesus monkeys, with resolution of abnormal histology and serologic responses. They suggest that this preclinical animal model is useful for testing new anti-H. pylori therapies.

Transient and persistent experimental infection of nonhuman primates with Helicobacter pylori: implications for human disease.

Helicobacter pylori can establish chronic infection in the human gastric mucosa, and it is a major cause of peptic ulcer disease and a principal risk factor for gastric cancer. This creates a need for H. pylori infection models that mimic the human condition. To test the suitability of rhesus monkeys as infection models, H. pylori-free animals were inoculated intragastrically with mixtures of H. pylori strains, bacteria recovered from colonized animals were typed by arbitrarily primed PCR, and host inflammatory and immunologic responses were monitored. Among five H. pylori-free animals inoculated with a mixture of two human strains plus one monkey strain, one became persistently infected and one became only transiently infected. The recovered bacteria matched the monkey input strain in DNA fingerprint. A subsequent trial using two new human isolates and three animals that had resisted colonization by the monkey strain resulted in persistent infection in one animal and transient infection in two others. Antral gastritis, anti-H. pylori serum immunoglobulin G, and atrophy all increased, but with patterns that differed among animals. We conclude that (i) rhesus monkeys can be infected experimentally with H. pylori, (ii) individuals differ in susceptibility to particular bacterial strains, (iii) infections may be transient, and (iv) the fitness of a particular strain for a given host helps determine the consequences of exposure to that strain.

Seroepizootiology of Helicobacter pylori gastric infection in nonhuman primates housed in social environments.

We determined the seroepizootiology of Helicobacter pylori infection in rhesus monkeys. Plasma was obtained from 196 animals (age range, 1 to 22 years) that were housed in social environments, either in indoor gang cages, in outdoor corrals, or in free-ranging forested conditions. Plasma immunoglobulin G levels were determined with a specific enzyme-linked immunosorbent assay, and the cutoff immunoglobulin G value for H. pylori seropositivity was determined from a study of 25 monkeys whose infection status was assessed by light microscopy and culture. One-year-old animals of both genders in all housing conditions had the lowest rate of positivity (60% in monkeys 1 year old versus 81% in monkeys 2 to 10 years old, P = 0.026). In addition, females tended to have higher rates of positivity than males. Seroconversion during a 1-year observation period occurred in 7 (28%) of 25 seronegative animals. Seroreversion occurred in 3 (4%) of the 78 positive animals; all 3 of these animals had received antimicrobial agents during the year. These observations demonstrate that the epizootiology of H. pylori infection in rhesus monkeys may serve as a model for human infection.

Natural gastric infection with Helicobacter pylori in monkeys: a model for spiral bacteria infection in humans.

BACKGROUND/AIMS: There is no generally accepted model for Helicobacter pylori infection in humans. The aim of this study was to examine the natural history and effect of treatment in rhesus monkeys and sequentially define the immune response to H. pylori in relation to treatment. METHODS: Infection and gastritis were graded blindly by histological analysis and culture of biopsy specimens harvested during gastroduodenoscopies in 26 anesthetized colony-bred monkeys. Plasma H. pylori-specific immunoglobulin (Ig) G levels were determined by enzyme-linked immunosorbent assay. RESULTS: H. pylori and Gastrospirilum hominis-like organisms were present in 13 and 9 monkeys, respectively; 3 animals harbored both organisms, whereas 4 monkeys were not infected. Gastritis score was < or = 1.5 in animals uninfected or infected only with G. hominis-like organisms and > or = 2.0 in all H. pylori-infected animals. IgG ratios were > or = 0.5 in 12 of 13 H. pylori-infected animals and in 2 of 13 H. pylori-negative animals (P < 0.001). One monkey became infected with H. pylori during the observation period, with concurrent increase of gastritis and plasma IgG levels. In untreated animals, infection, gastritis, and plasma IgG levels remained unchanged over 7-15 months. Triple therapy eradicated H. pylori at 6 months in 4 of 6 animals while suppressing gastritis and plasma IgG levels. CONCLUSIONS: Rhesus monkeys harboring H. pylori are persistently infected and have gastritis and elevated specific IgG levels, all of which may respond to appropriate therapy, whereas G. hominis infection is associated with little inflammation.

Gastric injury and invasion of parietal cells by spiral bacteria in rhesus monkeys. Are gastritis and hyperchlorhydria infectious diseases?

The possibility of using the rhesus monkey as a model for studying gastric function in the presence of infection with spiral bacteria was studied. Endoscopic evaluation of the gastric mucosa was performed under general anesthesia in 29 colony-bred rhesus monkeys, and gastric pinch biopsy specimens were obtained from each animal. On a separate day, gastric emptying and acid output were determined using a 99mTc dilution technique. Biopsy samples were fixed for light microscopy (H&E, Gram, and Warthin-Starry stains) and for transmission electron microscopy. The presence of spiral bacteria and gastritis was assessed and rated on coded slides. In 8 of 29 monkeys, Helicobacter pylori-like organisms were observed in close proximity to the mucosal epithelial cells or in the lumen of the gastric pits. In 14 other monkeys, "Gastrospirillum hominis"-like organisms were observed in the mucus covering the surface of epithelial cells, in the lumina of the gastric glands, and overlying parietal cells. Gastritis was present in 8 of 8 animals positive for H. pylori-like organisms, in 2 of 14 animals positive for "G. hominis"-like organisms, and in none of the uninfected monkeys, and the mean gastritis index was significantly greater in animals positive for H. pylori-like organisms. Moreover, acid output was significantly higher in monkeys positive for "G. hominis"-like organisms than in controls or animals positive for H. pylori-like organisms. Gastric emptying was not significantly different in the three groups. In conclusion, (a) H. pylori-like, but not "G. hominis"-like, organisms cause gastritis while not modifying acid output; (b) "G. hominis"-like, but not H. pylori-like organisms, invade and on occasion damage parietal cells while apparently causing hyperchlorhydria; and (c) the rhesus monkey appears to be a good model for the study of gastric infection with spiral bacteria.

Prevention and treatment of the gastric symptoms of radiation sickness.

Currently available treatments for radiation-induced nausea and vomiting either are ineffective or reduce performance. The new antiemetic and gastrokinetic agent zacopride was tested in rhesus monkeys to assess its behavioral toxicity and its ability to inhibit radiation-induced emesis. Zacopride (intragastric, 0.3 mg/kg) or a placebo was given blindly and randomly in the basal state and 15 min before a whole-body 800 cGy 60Co gamma-radiation dose (except for the legs which were partially protected to permit survival of some bone marrow). We determined (1) gastric emptying rates; (2) the presence and frequency of retching and vomiting; and (3) the effect of zacopride on the performance of a visual discrimination task in nonirradiated subjects. No vomiting, retching, or decreased performance was observed after either placebo or zacopride in the control state. Following irradiation plus placebo, 70 emeses were observed in 5 of 6 monkeys, and 353 retches were observed in all 6 monkeys. In contrast, only 1 emesis was observed in 1 of 6 monkeys and 173 retches were seen in 4 of 6 monkeys after irradiation plus zacopride (P less than 0.01). Zacopride also significantly inhibited radiation-induced suppression of gastric emptying. When given after the first vomiting episode in a separate group of irradiated monkeys, zacopride completely prevented any subsequent vomiting. The present results demonstrate that intragastric administration of zacopride significantly inhibited radiation-induced retching, vomiting, and suppression of gastric emptying in rhesus monkeys and did not cause detectable behavioral side effects when given to nonradiated monkeys. This observation has important implications in the treatment of radiation sickness.

Effect of ionizing radiation on prostaglandins and gastric secretion in rhesus monkeys.

Early radiation toxicity is characterized by nausea and vomiting. We have previously shown that gastric emptying, gastric motility, and gastric secretion were suppressed after total body exposure to irradiation. In the present studies, we evaluated the relation between vomiting and gastric function in nine rhesus monkeys and explored the possible role of prostaglandins (PG) in these phenomena. The concentration of PG in plasma and gastric juice was determined using a standard radioimmunoassay and gastric acid output was measured concurrently using a marker dilution technique. The animals were studied in the basal state and after total body exposure to 800 cGy 60Co delivered at a rate of 500 cGy/min. Acid output was abolished from 40 min to 2 h after irradiation but had returned to preirradiation levels 2 days later. Plasma PGE2 and PGI2 (as measured by 6-keto-PGF1 alpha determination) were not significantly modified by irradiation. In contrast, irradiation produced an immediate significant increase (P less than 0.05) in gastric juice concentration of PGE2 (318 +/- 80 to 523 +/- 94 pg/ml; mean +/- SE) and PGI2 (230 +/- 36 to 346 +/- 57 pg/ml); both had returned to basal levels 2 days later. Thus, an increase in gastric juice concentration of both PGE2 and PGI2 is associated with the radiation induced suppression of acid output.