Mycobacterium avium subspecies paratuberculosis and goblet cells: are Barrett's esophagus and esophageal adenocarcinoma zoonotic infectious diseases?

Ellen S. Pierce*

13212 East Blossey Avenue, Spokane Valley, Washington, USA

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Abstract

Infectious agents are known causes of human cancers. Human papillomaviruses and species of fungi are associated with esophageal squamous cell carcinoma. Esophageal adenocarcinoma is a complication of Barrett’s esophagus, the replacement of the normal squamous epithelium lining the esophagus by gastric or intestinal columnar mucous epithelium with or without goblet cells. As intestinal metaplasia of the stomach is the precursor lesion of Helicobacter Pylori-associated gastric cancer, a microorganism may cause the metaplasias of the esophagus that are the precursors of esophageal adenocarcinoma. Mycobacterium avium subspecies paratuberculosis (MAP), the cause of a chronic gastrointestinal enteropathy in domestic ruminants and a suspected zoonosis, results in bovine small and large intestinal goblet cell hyperplasia. MAP colonization of human gastric mucus and/or invasion of cardiac surface mucus cells, and resulting proliferation and proximal migration, may result in the metaplasias of Barrett’s esophagus. MAP therefore may be one infectious cause of Barrett’s esophagus-associated esophageal adenocarcinoma.

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There has been a great increase in the incidence of esophageal adenocarcinoma (EAC) in western so-called developed countries in the past several decades^1-3. This marked increase has led some to speculate that “changing environmental factors and microbial agents”⁴ may be contributing factors.

A possible infectious cause of EAC and associated Barrett’s esophagus (BE) is Mycobacterium avium subspecies paratuberculosis (MAP). MAP, a long suspected cause of Crohn’s disease, is a probable zoonosis⁵, a microorganism that causes disease in humans and is transmitted to humans from animals.

MAP is present in an infected domestic ruminant’s manure, milk, and muscle tissue. Humans can become infected with MAP by swallowing MAP organisms in MAP-contaminated potable water, MAP-contaminated milk and other dairy products, and MAP-contaminated meat, or inhaling and then swallowing MAP-contaminated water aerosolized from rivers and lakes.

Presumably MAP-associated Crohn’s disease is known to cause oral⁶, esophageal⁷, and gastric lesions⁸. MAP organisms are present in oral biopsies from patients with Crohn’s disease⁹.

Goblet cell proliferation that occurs in locations where goblet cells already exist is called goblet cell hyperplasia. Goblet cell hyperplasia of the small and large intestines is a known result of infection with enteropathogenic bacteria and parasites¹⁰. MAP has the little-known ability to cause acute¹¹ and chronic¹² goblet cell hyperplasia in the small and large intestines of its natural hosts, domestic ruminants.

MAP has a predilection for human intestinal goblet cells. A single striking study shows MAP organisms actively migrating within the mucus of human fetal small intestines to a position directly above goblet cells, gathering in dense aggregations, and then heavily invading the goblet cells¹³. MAP also appears perfectly capable of invading not just goblet cells, but every cell type in the intestines. A single study documents that MAP can directly infect all cell types of bovine intestinal epithelium, but causes the proliferation or hyperplasia only of infected goblet cells¹¹.

As MAP organisms actively migrate within human fetal small intestinal mucus to the apical surface of goblet cells and then actively invade the apical granule portion of those goblet cells, MAP organisms may be able to migrate within the mucus layer of the stomach to the apical surface of cardiac surface mucus cells and then actively invade those cardiac surface mucus cells. If MAP preferentially colonizes the mucus above or the mucus within cardiac surface mucus cells, then the pathologic changes MAP causes will begin in the gastric cardia and work their way up. MAP infected cardiac surface mucus cells that proliferate and ‘spill’ upward would explain why BE begins at the esophagogastric junction and spreads proximally, referred to as “proximal migration”¹⁴.

MAP infection of the gastric cardia mucus or surface mucus cells, causing their proximal migration, explains what is referred to as the “multilayered epithelium”¹⁵ of BE, with columnar-lined epithelium overlying and slightly compressing the underlying squamous epithelium. Possibly MAP-infected cardiac surface mucus cells sometimes migrate underneath rather than over esophageal squamous epithelium, referred to as “subsquamous”¹⁶ or “buried” BE, which while usually considered a post-ablation artifact is actually common in untreated BE patients¹⁷.

In contrast to goblet cell hyperplasia, the proliferation of intestinal-type goblet cells in the stomach, a location where intestinal goblet cells don’t normally exist, is called intestinal metaplasia or goblet cell metaplasia. The possibility that MAP can cause the proliferation of gastric or intestinal type columnar-lined epithelium is suggested by the known ability of Helicobacter pylori (HP) to cause intestinal metaplasia. Long term gastric HP infection results first in complete metaplasia, consisting of small intestinal enterocytes and small intestinal-type goblet cells, and then incomplete metaplasia, consisting of colonic-type goblet cells. These colonic-type goblet cells are the immediate precursor lesion of HP-associated gastric cancer¹⁸. After first causing the proximal proliferation of gastric cardiac mucus cells, MAP may ‘do’ the same thing as HP, causing their complete, and then incomplete, intestinal metaplasia.

Depending on the country, the diagnosis of BE requires the presence of goblet cells. Goblet cell-containing columnar-lined epithelium or intestinal metaplasia is a requirement for the diagnosis of BE in the United States and continental Europe, but in the United Kingdom and Japan only columnar-lined epithelium is required¹⁹. Columnar-lined epithelium in Barrett’s esophagus has four histologic subtypes, two gastric metaplasias and two intestinal metaplasias. The two types of gastric metaplasia, gastric cardia-type epithelium and gastric fundic-type epithelium, do not contain goblet cells. The two types of intestinal metaplasia, incomplete or small intestinal type, and complete or large intestinal type, do contain goblet cells²⁰. Just as chronic HP infection results in the two histologic subtypes of intestinal metaplasia in the stomach, chronic MAP infection of the gastric cardia and esophagus may cause all of the histologic subtypes of gastric and intestinal columnar-lined epithelium in the esophagus, all of which are precursors of EAC.

Researchers are divided on the relationship between gastroesophageal reflux disease (GERD), BE and EAC. Some researchers believe that all cases of BE are preceded by GERD or reflux esophagitis. They explain the lack of preceding GERD in some patients with BE or EAC by arguing that not all cases of GERD are symptomatic. If GERD is a necessary precursor of BE, then MAP must be able to invade squamous epithelium, causing the acute inflammation of reflux esophagitis. There are no studies of MAP infection of the upper gastrointestinal tract in animals, despite the common perception that MAP infection in animals occurs exclusively by the fecal-oral route. Esophageal Crohn’s disease is characterized by ulcers and chronic inflammation as well as strictures⁷. It is possible that MAP infection of esophageal squamous epithelium may result in the acute inflammation of GERD.

Pathologist have, however, noted that the damaged squamous epithelium, including ulcers and erosion, of reflux esophagitis/GERD in humans is replaced by regenerating squamous epithelium, not by Barrett’s columnar mucus epithelium²¹. The majority of patients with EAC and BE do not have a clinical history of GERD²¹. If BE is not a direct pathologic sequela of GERD, what aspect of MAP might explain the close association between MAP and GERD?

The usually close association between GERD and BE may be explained by MAP’s requirement for exogenous iron and MAP’s possible preference for acidic environments. MAP can’t make its own iron and therefore requires exogenous iron. The acid of GERD may ‘help’ MAP by making iron more soluble and therefore absorbable²², which may enhance the growth and/or persistence of MAP in the esophagus. Acidity enhances but is not required for the growth of MAP in soil²³. Acidity enhances but is not required for the growth of nontuberculous mycobacteria such as MAP in natural bodies of water²⁴. Similarly, the acidic environment of GERD may enhance MAP’s ability to colonize gastric cardia surface mucus or surface mucus cells but is probably not required.

The majority of EAC cases that arise in BE don’t actually arise in goblet cell-containing epithelium. Instead, cardiac mucus epithelium surrounds the majority of minute esophageal adenocarcinomas²⁵. A recent study showed that the greater the number of goblet cells in BE, the less the risk of EAC²⁶. The presence of goblet cells may indicate a more ‘successful’ immune response to continuing MAP infection, as goblet cell hyperplasia is a protective mechanism of the intestines against other enteric pathogens¹⁰. In murine intestinal Citrobacter rodentium (CR) infection, for example, goblet cell hyperplasia occurs not during the initial phases of the infection, but only during the resolving phase when the CR organism has been successfully eliminated²⁷. Goblet cell hyperplasia is a mechanism by which the intestines successfully expel the rodent helminth Nippostrongylis brasiliensis²⁸. The studies showing MAP causing acute and chronic goblet cell hyperplasia place MAP organisms in the underlying lamina propria^{11, 12}, suggesting MAP-induced goblet cell hyperplasia does not successfully expel the organism, but may indicate a more aggressive immune response to MAP that helps contain the organism.

Why MAP may have a predilection for gastric cardiac mucus surface cells rather than fundic or pyloric surface mucus cells is unknown, but may involve MAP’s possible preference for the sulphomucins and sialomucins produced by cardiac glands.

HP infection is inversely correlated with Barrett’s esophagus²⁹, suggesting HP colonization of gastric mucus precludes MAP colonization. HP colonization of gastric mucus may crowd out MAP from doing so.

MAP’s perhaps preferential colonization of the acidic cardiac mucus and/or cardiac mucous surface cells may also explain the inverse relationship between idiopathic inflammatory bowel disease and BE³⁰. Having colonized MAP’s perhaps preferred location, MAP organisms may not descend further into the intestinal tract.

The common assumption that cancers in general are a result of unspecified chronic inflammation is not supported by the pathology. GERD for example is chronically inflamed squamous epithelium, yet GERD is not associated with an increased risk of esophageal squamous cell carcinoma. Instead, species of fungi³¹ and human papillomavirus types 16 and 18³² are associated with esophageal squamous cell carcinoma.

The possibility that MAP may be involved in the pathogenesis of BE and associated EAC does not rule out the effect of co-factors on the development of EAC. As high salt diets and smoking ‘help’ HP cause gastric cancer³³, co-factors including obesity and high sucrose diets may ‘help’ MAP cause EAC. Obesity is associated with an increased risk of infection³⁴. Adipocytes are storage cells for Mycobacterium tuberculosis organisms³⁵; similarly, adipocytes may be storage cells for MAP organisms, possibly explaining the relationship between obesity and EAC³⁶. MAP is more invasive in hyperosmolar, high lactose, environments³⁷, and may be more invasive in high sucrose western diet environments, possibly explaining the relationship between high sugar diets and an increased risk of BE^{38, 39} and EAC⁴⁰.

As an enteric pathogen, MAP organisms or antibodies to MAP organisms may be present in EAC and BE patients’ esophagi, serum and feces. The regression or resolution of BE, and an improved survival rate of EAC patients treated with anti-MAP therapies in addition to standard surgical and chemotherapy, including dietary alterations such as the specific carbohydrate diet, anti-MAP antibiotics such as RedHill Biopharma’s RHB-104 triple antibiotic combination and anti-infective ultraviolet blood irradiation would lend additional support to this hypothesis.

Acknowledgments

As always, my research would not be possible without the assistance of Dr. Beth Hill at the Providence Sacred Heart Medical Center and Children’s Hospital’s Health Sciences Library in Spokane, Washington as well as the other libraries that participate in the FreeShare Library group within the DOCLINE National Network of Libraries of Medicine. My personal gastroenterologist, Ajay Pabby, M.D., M.P.H. heard about MAP and the goblet cell hyperplasia lesion of colorectal cancer and immediately thought of this idea.

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