Academic Appointments

Administrative Appointments

  • President, Celiac Sprue Research Foundation (2005 - Present)

Professional Education

  • M.D., University of Washington, Medicine (1959)
  • B.S., Seattle University, Chemistry & Mathematics (1955)

2021-22 Courses

All Publications

  • A Food-Grade Enzyme Preparation with Modest Gluten Detoxification Properties PLOS ONE Ehren, J., Moron, B., Martin, E., Bethune, M. T., Gray, G. M., Khosla, C. 2009; 4 (7)


    Celiac sprue is a life-long disease characterized by an intestinal inflammatory response to dietary gluten. A gluten-free diet is an effective treatment for most patients, but accidental ingestion of gluten is common, leading to incomplete recovery or relapse. Food-grade proteases capable of detoxifying moderate quantities of dietary gluten could mitigate this problem.We evaluated the gluten detoxification properties of two food-grade enzymes, aspergillopepsin (ASP) from Aspergillus niger and dipeptidyl peptidase IV (DPPIV) from Aspergillus oryzae. The ability of each enzyme to hydrolyze gluten was tested against synthetic gluten peptides, a recombinant gluten protein, and simulated gastric digests of whole gluten and whole-wheat bread. Reaction products were analyzed by mass spectrometry, HPLC, ELISA with a monoclonal antibody that recognizes an immunodominant gluten epitope, and a T cell proliferation assay.ASP markedly enhanced gluten digestion relative to pepsin, and cleaved recombinant alpha2-gliadin at multiple sites in a non-specific manner. When used alone, neither ASP nor DPPIV efficiently cleaved synthetic immunotoxic gluten peptides. This lack of specificity for gluten was especially evident in the presence of casein, a competing dietary protein. However, supplementation of ASP with DPPIV enabled detoxification of moderate amounts of gluten in the presence of excess casein and in whole-wheat bread. ASP was also effective at enhancing the gluten-detoxifying efficacy of cysteine endoprotease EP-B2 under simulated gastric conditions.Clinical studies are warranted to evaluate whether a fixed dose ratio combination of ASP and DPPIV can provide near-term relief for celiac patients suffering from inadvertent gluten exposure. Due to its markedly greater hydrolytic activity against gluten than endogenous pepsin, food-grade ASP may also augment the activity of therapeutically relevant doses of glutenases such as EP-B2 and certain prolyl endopeptidases.

    View details for DOI 10.1371/journal.pone.0006313

    View details for Web of Science ID 000268147200010

    View details for PubMedID 19621078

    View details for PubMedCentralID PMC2708912

  • A Non-Human Primate Model for Gluten Sensitivity PLOS ONE Bethune, M. T., Borda, J. T., Ribka, E., Liu, M., Phillippi-Falkenstein, K., Jandacek, R. J., Doxiadis, G. G., Gray, G. M., Khosla, C., Sestak, K. 2008; 3 (2)


    Gluten sensitivity is widespread among humans. For example, in celiac disease patients, an inflammatory response to dietary gluten leads to enteropathy, malabsorption, circulating antibodies against gluten and transglutaminase 2, and clinical symptoms such as diarrhea. There is a growing need in fundamental and translational research for animal models that exhibit aspects of human gluten sensitivity.Using ELISA-based antibody assays, we screened a population of captive rhesus macaques with chronic diarrhea of non-infectious origin to estimate the incidence of gluten sensitivity. A selected animal with elevated anti-gliadin antibodies and a matched control were extensively studied through alternating periods of gluten-free diet and gluten challenge. Blinded clinical and histological evaluations were conducted to seek evidence for gluten sensitivity.When fed with a gluten-containing diet, gluten-sensitive macaques showed signs and symptoms of celiac disease including chronic diarrhea, malabsorptive steatorrhea, intestinal lesions and anti-gliadin antibodies. A gluten-free diet reversed these clinical, histological and serological features, while reintroduction of dietary gluten caused rapid relapse.Gluten-sensitive rhesus macaques may be an attractive resource for investigating both the pathogenesis and the treatment of celiac disease.

    View details for DOI 10.1371/journal.pone.0001614

    View details for Web of Science ID 000260586400007

    View details for PubMedID 18286171

    View details for PubMedCentralID PMC2229647

  • Enhancement of dietary protein digestion by conjugated bile acids GASTROENTEROLOGY Gass, J., Vora, H., Hofmann, A. F., Gray, G. M., Khosla, C. 2007; 133 (1): 16-23


    Conjugated bile acids promote absorption of dietary lipids by solubilizing them in mixed micelles. Bile acids are not considered to facilitate the digestion of other nutrients.The effect of conjugated bile acids on the rate of protein hydrolysis by trypsin and chymotrypsin was examined in vitro. Common dietary proteins and 2 bacterial glutenases (proposed oral therapies for celiac sprue) were proteolyzed in the absence or presence of a 10 mmol/L conjugated bile acid mixture, simulating human bile composition. Lipolysis products (monoolein) and fatty acid were also evaluated to simulate postprandial intestinal contents.Conjugated bile acids dramatically enhanced the proteolysis of several dietary proteins, including beta-lactoglobulin, bovine serum albumin, myoglobin, and a commercially available dietary protein supplement. For beta-lactoglobulin, a cow's milk allergen that is resistant to pepsin cleavage, bile acids enhanced its proteolysis by pancreatic proteases even after incubation under gastric conditions. Exposure of prolyl endopeptidases to bile acids made them more susceptible to pancreatic proteases under simulated intestinal conditions. The conjugated bile acid effect was most pronounced in the presence of dihydroxy bile acids and was observable at bile concentrations below the critical micellar concentration but to a much greater extent at concentrations above the critical micellar concentration.We propose that, in addition to promoting lipid absorption, conjugated bile acids affect the digestion and assimilation of dietary proteins by accelerating hydrolysis by pancreatic proteases. These findings have implications for intraluminal protein breakdown and assimilation in the upper small intestine.

    View details for DOI 10.1053/j.gastro.2007.04.008

    View details for Web of Science ID 000248055400007

    View details for PubMedID 17631126

  • Effect of barley endoprotease EP-B2 on gluten digestion in the intact rat JOURNAL OF PHARMACOLOGY AND EXPERIMENTAL THERAPEUTICS Gass, J., Vora, H., Bethune, M. T., Gray, G. M., Khosla, C. 2006; 318 (3): 1178-1186


    Celiac Sprue is a multifactorial disease characterized by an intestinal inflammatory response to ingested gluten. Proteolytically resistant gluten peptides from wheat, rye, and barley persist in the intestinal lumen and elicit an immune response in genetically susceptible individuals. Here, we demonstrate the in vivo ability of a gluten-digesting protease ("glutenase") to accelerate the breakdown of a gluten-rich solid meal. The proenzyme form of endoprotease B, isoform 2 from Hordeum vulgare (EP-B2), was orally administered to adult rats with a solid meal containing 1 g of gluten. Gluten digestion in the stomach and small intestine was monitored as a function of enzyme dose and time by high-performance liquid chromatography and mass spectrometry. In the absence of supplementary EP-B2, gluten was solubilized and proteolyzed to a limited extent in the stomach and was hydrolyzed and assimilated mostly in the small intestine. In contrast, EP-B2 was remarkably effective at digesting gluten in the rat stomach in a dose- and time-dependent fashion. At a 1:25 EP-B2/gluten dose, the gastric concentration of the highly immunogenic 33-mer gliadin peptide was reduced by more than 50-fold within 90 min with no overt signs of toxicity. Evaluation of EP-B2 as an adjunct to diet control is therefore warranted in celiac patients.

    View details for DOI 10.1124/jpet.106.104315

    View details for Web of Science ID 000239878900029

    View details for PubMedID 16757540

  • Rational design of combination enzyme therapy for celiac sprue CHEMISTRY & BIOLOGY Siegel, M., Bethune, M. T., Gass, J., Ehren, J., Xia, J., Johannsen, A., Stuge, T. B., Gray, G. M., Lee, P. P., Khosla, C. 2006; 13 (6): 649-658


    Celiac sprue (also known as celiac disease) is an inheritable, gluten-induced enteropathy of the upper small intestine with an estimated prevalence of 0.5%-1% in most parts of the world. The ubiquitous nature of food gluten, coupled with inadequate labeling regulations in most countries, constantly poses a threat of disease exacerbation and relapse for patients. Here, we demonstrate that a two-enzyme cocktail comprised of a glutamine-specific cysteine protease (EP-B2) that functions under gastric conditions and a PEP, which acts in concert with pancreatic proteases under duodenal conditions, is a particularly potent candidate for celiac sprue therapy. At a gluten:EP-B2:PEP weight ratio of 75:3:1, grocery store gluten is fully detoxified within 10 min of simulated duodenal conditions, as judged by chromatographic analysis, biopsy-derived T cell proliferation assays, and a commercial antigluten antibody test.

    View details for DOI 10.1016/j.chembiol.2006.04.009

    View details for Web of Science ID 000238723800013

    View details for PubMedID 16793522