The GI-MAP™ 2.0
The GI Microbial Assay Plus (GI-MAP™) now includes two new markers, in addition to the original analytes.
Beta-glucuronidase is an enzyme produced by cells in the liver, kidney, intestinal epithelium, endocrine, and reproductive organs (1). However, the major producers of beta-glucuronidase are these bacteria: Bacteroides fragilis, Bacteroides vulgatus, Bacteroides uniformis, Clostridium paraputrificum, Clostridium clostridioforme, Clostridium perfringens, Escherichia coli, Eubacterium, Peptostreptococcus, Ruminococcus, and Staphylococcus. It is found in 97% of E.coli strains (2). The enzyme hydrolyzes B-glucuronide to make glucuronic acid and an aglycone, such as imine, thiol, or alcohol. Glucuronidation by way of beta-glucuronidase is a major route of detoxification in the human body (2). However, this enzyme can also convert pro-carcinogens to carcinogenic compounds (1).
High levels of faecal beta-glucuronidase can indicate unfavorable changes in the colon. When the enzyme is elevated in plasma, there is an increased risk of hormone-sensitive cancers, such as those of the breast or prostate (1). Deconjugation of a variety of toxins, carcinogens, hormones and drugs in the gut permits their reabsorption via enterohepatic recirculation, producing higher than desired blood levels of these potentially harmful compounds. Evidence of increased enzymatic activity of intestinal microorganisms may suggest increased risk of digestive tract cancer (3). Patients with diagnosed tumors of the large intestine had high activity of B-glucuronidase (3).
Toxins stimulate B-glucuronidase activity and dietary red meat and protein increases the enzyme. Antibiotics increase B-glucuronidase levels. A low-calorie, vegetarian diet can reduce faecal B-glucuronidase levels (1).
Evaluating B-glucuronidase may be of interest to clinicians interested in evaluating substances that require deconjugation of glucuronide molecules, such as hormones, vitamin D, toxins, and phytonutrients.
Interpretation: Abnormally high levels of this biomarker warrant further investigation; abnormally low levels may diminish the bioavailability of many phytonutrients.
Further evaluation of patients with elevated faecal B-glucuronidase includes consideration of exposure to and intake of toxins, hormones, and drugs.
For patients with elevated faecal B-glucuronidase, the following may be helpful:
- Milk thistle
- Probiotics (Lactobacilli and Bifidobacteria)
- Increased consumption of vegetables and insoluble fiber
B-glucuronidase may be lower following antibiotic administration, which may reduce B-glucuronidase activity due to reduction of gut bacteria (4-7)
Steatocrit has been used widely since 1981 to detect steatorrhea in patients with pancreatic insufficiency and small intestinal malabsorption (8). It is a simple test that uses centrifugation to separate the solid, aqueous, and lipid layers of the stool. The lipid layer is measured in the steatocrit and this makes up the total faecal fat (8). Acidification of the stool dramatically improved the performance of this method. The acid steatocrit method has been shown to correlate well with 24-hour and 72-hour faecal fats; therefore, it is modulated by recent diet (9, 10).
The GI-MAP™ 2.0 also now measures calprotectin instead of lactoferrin.
Fecal calprotectin is the most studied marker of gastrointestinal inflammation (11) and the gold standard marker for the diagnosis and monitoring of inflammatory bowel disease (IBD) (12). It is used to discriminate IBD from irritable bowel syndrome (IBS) (11, 12). Calprotectin is a calcium- and zin-binding protein that is found at high concentration in neutrophils. Calprotectin is also found in monocytes, macrophages, and gut epithelial cells (13). In IBD, there is a migration of inflammatory cells such as neutrophils to the inflamed intestinal mucosa. Because leukocytes are shed into the intestinal lumen, pro-inflammatory proteins such as calprotectin can be identified and measured in stool specimens (14). Fecal calprotectin levels are proportional to the level of neutrophil infiltration and inflammation in the gut (13).
Calprotectin has been shown to correlate with histologic and endoscopic measures of inflammatory bowel disease severity (14). It is non-invasive, stable (12) and shows a considerable sensitivity and specificity of 93% and 96%, respectively, when used to screen for IBD activity (15). High calprotectin can also be detected in colorectal cancers, diverticular disease, and infectious gastroenteritis (11). When IBD is suspected based on clinical presentation, a fecal calprotectin level <50 ug/g stool suggests IBS, not IBD. Calprotectin levels between 50 and 150 ug/g indicate GI inflammation and deserve treatment and follow-up testing. Calprotectin levels greater than 150 ug/g suggest organic disease such as IBD or colorectal cancer and follow-up colonoscopy is recommended (See Figure 1) (11). Fecal calprotectin can elevate with enteropathy caused by excessive non-steroidal anti-inflammatory medication use (13). For this reason, it may be beneficial to temporarily discontinue NSAIDs, when possible in select patients, prior to measuring fecal calprotectin (13).
Figure 1. The algorithm used to differentiate IBD from IBS using fecal calprotectin. Adapted from Walsham et al. (11).
Zonulin - New Add on Marker for the GI-MAP
Fecal zonulin testing is now available to practitioners as an add-on to the GI-MAP for £65, or as a standalone test for £95.
Zonulin is a protein secreted by intestinal cells that regulates intercellular tight junctions (16, 17). Tight junctions are the connections between epithelial cells that make up the gastrointestinal lining. Zonulin increases intestinal permeability in the jejunum and ileum (18) and is considered a biomarker for barrier permeability (16, 17). Tight junctions can be opened or closed, depending on the physiological need. Zonulin’s role is to open tight junctions in the gut. In the case of enteric infections, high zonulin can “open the floodgates” and flush out bacteria and toxins (16). Certain gut bacteria and gliadin (the main staple protein from wheat) can activate the zonulin system (17, 19).
The intestinal barrier is a critical interface between the lumen of the gut and the internal milieu. Dysfunction of this barrier is believed to initiate immune dysfunction because it allows macromolecules from the gut lumen to pass into the bloodstream (20). Intestinal permeability, also known as “leaky gut,” has been associated with inflammatory bowel disease, celiac disease, food allergy, irritable bowel syndrome, critical illness, autoimmune diseases (21) and obesity and metabolic disease (22). In many cases, permeability precedes disease (16).
Zonulin regulates barrier permeability. Serum zonulin correlates with intestinal permeability and lactulose/mannitol tests for intestinal permeability (18, 23). High serum zonulin has been associated with celiac disease, type 1 diabetes (23) insulin resistance and type I diabetes (18), cancers, neurological conditions, and autoimmune diseases (see Table 1) (16).
Fecal zonulin is available for investigational use but has not been correlated with circulating (serum) levels as of this writing. Serum zonulin may constitute zonulin secretion not only from intestinal cells, but also from extraintestinal tissues such as the liver, heart and brain (24). Stool may therefore present an appropriate specimen for analyzing only intestinal production of zonulin. Fecal zonulin has been used in human studies as a marker of intestinal permeability. In athletes, fecal zonulin levels improved (decreased) after 14 weeks of probiotic supplementation (17). Treatment with zeolite lowered stool levels of zonulin in athletes and presumably improved intestinal barrier function (25).
Serum zonulin is high in a number of immune-mediated conditions (16):
Celiac diseaseAnkylosing spondylitisInflammatory bowel diseaseType 1 diabetesRheumatoid arthritisSystemic lupus erythematousNeurological diseasesMultiple sclerosisChronic inflammatory demyelinating polyneuropathy Schizophrenia
Brain (gliomas)BreastLung adenocarcinomaOvarianPancreatic
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