Evaluation of Serum-Derived Bovine Immunoglobulin Protein Isolate in Subjects With Decompensated Cirrhosis With Ascites

The Gut Barrier and Pathological Bacterial Translocation: The "Achilles Heel" of Hepatology

The intestinal wall is a complex barrier that exists between humans and their environment. Inside the intestinal lumen, the commensal flora exposes the epithelium to nearly 100 trillion bacteria.1 This epithelial layer provides a surface area of 400 square meters, lined with tight junctions that prevent the translocation and paracellular transport of luminal antigens including bacteria.2 In addition to this mechanical barrier, the wall of the intestine is lined with mucosal immune defenses, notably gut-associated lymphoid tissue (GALT), the largest immunologic organ in the body.1 Under normal circumstances, this functional and efficient barrier prevents entry of bacteria from the outside world.

Failure of this intestinal barrier, along with an increased rate of pathological bacterial translocation, has been shown to be associated with increasing severity of liver disease and the development of decompensated cirrhosis.3 Factors thought to contribute to bacterial translocation in subjects with cirrhosis include small intestinal bacterial overgrowth (SIBO), which is known to have an increased prevalence in subjects with cirrhosis compared to those without4, hyperdynamic portal status, alterations in the GALT tissue altering the immune response, and impaired intestinal permeability seen in subjects with ascites.3 This increased permeability is believed to result from structural abnormalities in the intestinal mucosa, including widening of intercellular spaces, edema, inflammation, and vascular congestion.5-7

Failure of the intestinal barrier is routinely thought to play an important role in the natural course of cirrhosis, so much so that this has been referred to as hepatology's "Achilles heel."8 Pathologic bacterial translocation across the intestinal epithelium is suspected to impact the clinical course of liver cirrhosis by triggering encephalopathy, hepatic failure, and hepatorenal syndrome, in addition to having a long known role as an underlying mechanism of the development of spontaneous bacterial peritonitis (SBP) and other bacterial infections in this population.9 Given that SBP is associated with high mortality rates ranging from 10-42%,10 and that subjects with cirrhosis have increased susceptibility to infections, antibiotic prophylaxis has emerged as a widely accepted strategy in subjects at increased risk for bacterial translocation, such as those with active gastrointestinal bleeding and low protein content ascites. However, this therapeutic strategy has the potential of selecting resistant bacterial strains and increasing the risk of subjects developing Clostridium difficile associated diarrhea.

Alternative methods for the prevention of SBP and bacterial infections in subjects with cirrhosis could prove to be very beneficial in reducing mortality and preventing the development of antibiotic resistance. In particular, preventing pathological bacterial translocation at the intestinal barrier could be highly effective.

Serum-Derived Bovine Immunoglobulin: a Logical Therapy to Improve Gut Barrier Function

Immunoglobulins taken orally are known to play a prominent role in health and development given the known benefits of human milk and colostrum, a form of milk produced by mammals which contains significant amounts of antibodies.11 Recognition of the essential nature of these antibodies led to the development of commercial plasma-derived protein concentrates containing immunoglobulins, which have been used for decades in animal husbandry to promote growth and manage intestinal inflammation in immune-compromised young animals.12-14

Serum-derived bovine immunoglobulin / protein isolate (SBI) is a novel medical food marketed under the brand name, EnteraGam®. This product is currently indicated (see EnteraGam package insert for details) for the clinical dietary management of several forms of enteropathy, including diarrhea predominant irritable bowel syndrome (IBS-D) and intestinal bowel disease (IBD). While the term, enteropathy, refers to any pathology or disease of the intestines, known histological features can include blunting of intestinal villi, increased intra-epithelial lymphocytes causing reduced absorptive capacity, and increased gut permeability.12 In cases of enteropathy, a combination of factors including altered gut microbiota, increased intestinal inflammation, and worsening gut barrier dysfunction are known to increase the risk of bacterial translocation.12 Each of these factors is a potential target for SBI. In terms of altered gut microbiota, extensive literature has demonstrated broad bacterial antigen neutralizing capacity of ingested immunoglobulins.15-17 Likewise, many non-clinical studies have shown that SBI can reduce intestinal inflammation by decreasing mucosal cytokines and dampening immune activation.18-19 Furthermore, the available data suggest that oral immunoglobulin therapy benefits tight-junction integrity in epithelial barriers, as evidenced through increased transepithelial electrical resistance and reduction in radiolabeled 14C-inulin permeability across the intestine.19

To date, there is a large body of evidence showing that serum- or plasma-derived bovine immunoglobulin preparations can effectively manage the symptoms and harmful effects of enteropathy in both animals and humans. Animal studies include data regarding barrier function and nutrient absorption in animals including mice, rats, and pigs.12 Studies performed in children show promising results in terms of weight gain and the underlying problem of malabsorption.22-23 Among adults, preliminary studies show promising results of SBI in the management of HIV enteropathy in addition to diarrhea-predominant Irritable Bowel Syndrome.24,25 Collectively, there is strong evidence to support the theory that ingestion of oral immunoglobulins such as SBI could reduce the risk of bacterial translocation in patients with cirrhosis, namely by neutralizing bacterial antigen in the intestine, reducing intestinal inflammation, and decreasing permeability of the gut barrier.