The importance of the gastrointestinal microbiota in health and disease has come to prominence in human medicine in recent years, and veterinary researchers are now recognizing its significance in animal species as well. Small cell gastrointestinal lymphoma and inflammatory bowel diseases (IBD) are commonly encountered in middle-aged and elderly feline patients. In the 40-year time span from 1964 to 2004, diagnosis of small cell gastrointestinal lymphoma (SCGIL) in cats increased six-fold; this disease is characterized by chronic weight loss, vomiting, and diarrhea. Appetite may vary from excessive to poor. IBD has a clinical presentation similar to SCGIL; the etiologies of both diseases are not well understood, but are probably multifactorial, involving such factors as genetics, diet, and chronic inflammation.
The intestinal microbiome found in healthy cats is known to be altered in IBD. In this retrospective case control study of 14 cats with IBD and 14 cats with SCGIL evaluated and diagnosed with endoscopic or laparoscopic biopsies at 3 different veterinary teaching hospitals, these researchers were interested in characterizing the microbiome of cats with SCGIL and determine whether specific bacterial groups are associated with this disease. Previous studies in cats have demonstrated that dysbiosis (alteration of the microbiome) is associated with benign mixed mucosal inflammation in the form of lymphoplasmacytic enteritis with IBD and gastrointestinal lymphoid malignancy. In addition to the biopsies, all patients were assessed with routine hematologic and biochemical analyses, including serum total T4. All cats in both study cohorts had negative fecal parasite ova tests, and were dewormed regardless of fecal test results before the biopsies were collected. Most cats were retrovirus tested as well.
The authors made efforts to include only cats who had no history of antibiotic administration for at least two weeks prior to collection of biopsies, but this information was not always present in the medical records. A diagnosis of IBD or SCGIL on each biopsy was reached by the use of routine hematoxylin-eosin staining, immunophenotyping, and in some cases, a PARR (polymerase chain reaction for antigen receptor rearrangement) assay.
Bacterial groups were identified in the biopsies by fluorescence in situ hybridization (FISH) and were correlated to CD11b+ and NF-κB expession. Differentiated myeloid cells carrying the CD11b+ marker are known to be significantly involved in tumor progression in rodents and humans with colorectal cancer, while NF-κB, a protein complex of transcription factors, has many roles, including involvement in immune regulation, DNA transcription, and pro-inflammatory cytokine and chemokine production. In humans, dysregulation of NF-κB activation is known to be associated with carcinogenesis because of resulting overproduction of pro-inflammatory cytokines and cell transformation.
The study also sought to determine if there was a relationship between gastrointestinal mucosal bacteria and the mucosal expression of NF-κB and infiltrating CD11b+ immune cells in the gastrointestinal biopsies of those cats with SCGIL in comparison with the gastrointestinal biopsies of the cats with IBD. In the intestinal biopsies of all 28 cats, the number of mucosal CD11b+ myeloid cells and NF-κB expression were quantified.
Bacteria quantified in the biopsies were divided among four well-defined mucosal compartments: (1) bacteria within free mucus; (2) bacteria within adherent mucus; (3) bacteria attached to surface epithelium; and (4) bacteria invasive within the mucosa. Only a few bacteria were identified as invasive within the mucosa. Those biopsies diagnosed as SCGIL had significantly increased numbers of Fusobacterium spp. in the three non-invasive mucosal compartments of the colon compared to the biopsies of the cats with IBD. Also in those cats with SCGIL, there were significantly increased counts of Fusobacterium spp. in the adherent mucus compartment of the ileum and colon as compared with biopsies of the cats with IBD.
Bacteroides spp. numbers were also significantly increased in the three combined non-invasive mucosal compartments of the ileum and the ileal adherent mucus in biopsies of patients with SCGIL compared to ileal biopsies of cats with IBD. However, the total counts of all bacteria, as well as numbers of Clostridium spp., Enterobacteriaceae, Helicobacter spp., and Faecalibacterium spp. were not significantly different in the colonic and ileal biopsies of the SCGIL cats relative to similar biopsies in the IBD cats. All of the above listed bacterial phyla as well as Fusobacterium spp. and Bacteroides spp. are found in the feces of healthy cats.
Those cats with SCGIL had significantly increased numbers of CD11b+ cells within the lamina propria of both ileal and colonic biopsies relative to those with IBD. Likewise, the cats with SCGIL had markedly increased expression of NF-κB in the lamina propria of both ileal and colonic biopsies compared to the IBD cats. A positive correlation was also found between the total numbers of Fusobacterium spp. and the total numbers of CD11b+ cells and cells expressing increased NF-κB.
The investigation of the relationship between the gastrointestinal microbiome and enteric health and disease is still in its infancy, especially in veterinary species. In humans, an increased risk for colorectal and pancreatic cancers as well as some oral squamous cell carcinomas is associated with some of the Fusobacterium spp. In one study of humans with late stage colorectal cancer, Fusobacterium nucleatum counts were found to be positively correlated with tumor size and shortened survival times. Based on these studies as well as others in rodent models, it appears that chronic IBD-type conditions are a potential risk factor for inflammatory and dysplastic processes that can lead to carcinogenesis.
Changes in the gastrointestinal microbiome such as increased numbers of mucosal Fusobacterium spp., which are pro-inflammatory, have virulence factors that promote invasive and adhesive properties, and have pro-oncogenic features, could reflect a progression from high grade chronic lymphoplasmacytic IBD to lymphoid intestinal cancer, or could simply be an effect of the gastrointestinal malignancy itself. The presence of increased numbers of CD11b+ myeloid cells and increased expression of NF-κB in the biopsies of cats with SCGIL was positively correlated with the numbers of Fusobacterium spp. in the same biopsies. A valuable and logical focus for future research would be to determine whether the observed increase in Fusobacterium spp. in biopsies demonstrating feline SCGIL is an etiologic factor in the development of this disease or an associated effect. [PJS]
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