Detection of IgE-reactive proteins in hydrolysed dog foods

Evaluation of hydrolyzed salmon and hydrolyzed poultry feather diets in restrictive diet trials for diagnosis of food allergies in pruritic dogs

Introduction

Canine cutaneous adverse food reaction (CAFR) is a common disorder caused by abnormal and unwanted skin reactions to ingested dietary allergens. Whereas other forms of allergic dermatitis may require drug therapy, CAFR is best treated with dietary change. Therefore, early and accurate diagnosis and treatment of CAFR are critical. The gold standard test for CAFR is a 6-12 week elimination diet trial using limited and known hypoallergenic proteins.

Method

A multicenter, triple-blinded, randomized, crossover prospective clinical study was conducted in dogs suspected to have cutaneous adverse food reaction. The study utilized a hydrolyzed salmon (HS) diet and a hydrolyzed poultry feather (HPF) diet in separate elimination diet trials to determine if the HS diet would be efficacious and well-tolerated, compared with the established HPF diet, to diagnose and treat CAFR.

Results

Fifty-seven dogs were enrolled, and 47 dogs completed the study. HS was well-tolerated, similar to HPF. Pruritus scores during the initial elimination diet trial were reduced with both diets, and dermatitis severity scores during both diet trials were reduced with both diets in the 47 dogs diagnosed with either CAFR, CAFR with atopic dermatitis (AD), or AD. Over half of the subjects diagnosed with CAFR or CAFR with AD required >4 weeks to show PVAS score decreases ≥2 or any decrease in CADESI-4 score.

Discussion

HS, like HPF, presents a valuable diagnostic and treatment tool for dogs suffering from CAFR. Both hydrolyzed diets tested also improved clinical signs in dogs diagnosed with AD and may be useful adjunctive tools in the management of canine AD.

Evaluation of the theoretical risk of cross-reactivity among recently identified food allergens for dogs

BACKGROUND

There is increasing evidence of cross-reactivity between allergens of close or distant species. The A-RISC (Allergens'-Relative Identity, Similarity and Cross-reactivity) index helps evaluate the risk of theoretical cross-reactivity between proteins of the same family among different species.

OBJECTIVES

To report the A-RISC indices for several food allergens of dogs between multiple food sources.

MATERIALS AND METHODS

We selected several recently characterised food allergens for dogs from fish and chicken (ACTA1, ALDOA, CKM, ENO3, GAPDH, PKM and TPI1), fish (TPM1/2), beef/lamb (PGM1) and corn/potato (WAXY). When quality sequence data were available, A-RISC indices were calculated between multiple animal and plant species that can be used as food sources. For the TPM subunits, A-RISC indices also were calculated with the environmental allergens Bla g 4 and Der f 10, and the Toxocara canis nematode.

RESULTS

The A-RISC indices suggest a substantial theoretical risk of cross-reactivity between species for all allergens considered. For TPM, this risk also extends to the environmental and nematode allergens.

CONCLUSIONS AND CLINICAL RELEVANCE

There is a high theoretical risk of cross-reactivity between allergens of different species used as food sources. The clinical relevance of these elevated A-RISC indices should be studied further.

Hydrolyzed diets may stimulate food-reactive lymphocytes in dogs

Hydrolyzed proteins are often prescribed for dogs with food hypersensitivity in food elimination programs. However, the potential of these diets to stimulate lymphocyte-mediated hypersensitivity is currently unknown. In this study, two commercially available hydrolyzed diets for dogs, D-1 (Aminopeptide Formula Dry, Royal Canin Japon, Tokyo, Japan), and D-2 (Canine z/d Ultra Dry, Hill's-Colgate (Japan) Ltd., Tokyo, Japan), were analyzed to identify residual proteins or peptides, as well as activated helper T-lymphocyte reactions in dogs with suspected food hypersensitivity. Proteins and peptides with molecular weights >1 kDa (majority 1.5-3.5 kDa) were detected in both diet extracts with sodium dodecyl sulfate polyacrylamide gel electrophoresis, and size exclusion chromatography. When peripheral blood mononuclear cells (PBMC's) from 316 dogs with suspected food allergies were cultured with hydrolyzed diet extracts, flow cytometry analysis revealed detectable levels of CD25^low helper T-lymphocytes stimulated by D-1 and D-2 in 91 of 316, (28.8%), and 75 of 316 (23.7%) samples, respectively. These data indicated that the extracts contained proteins or peptides large enough to activate the lymphocytes. The percentages of CD25^low helper T-lymphocytes stimulated by D-1 and D-2 extracts increased to 38.7% and 29.6%, respectively, in 186 of the original 316 samples (186/316, 58.9%), also reactive to poultry-related antigens. Thus, both poultry-related antigens, and D-1 and D-2 diet extracts may activate helper T-lymphocytes. These results demonstrate that hydrolyzed diets may contain proteins that stimulate helper T-lymphocytes, and may not be effective for treating all dogs with food hypersensitivity.

Cross-contamination in canine and feline dietetic limited-antigen wet diets

Background

Adverse food reactions (AFRs) are defined as abnormal responses to an ingested food or food additive. Diagnosis and treatment of AFRs consist of the complete elimination of these ingredients in the dietary trial. Previous studies have demonstrated the presence of undeclared ingredients in commercial limited-antigen dry food diets that can compromise the results and efficacy of dietary elimination trails. The aim of this study was to assess a selection of commercial canine and feline dietetic limited-antigen wet foods for the potential cross-contamination of animal proteins from origins not mentioned on the label.

Results

Eleven canine and feline dietetic limited-antigen wet foods (9 novel animal protein foods, 1 vegetarian and 1 hydrolyzed) were analyzed by polymerase chain reaction (PCR) to detect the presence DNA of animal and vegetal origins. PCR analysis confirmed the contamination of 6 of the 11 (54.5%) limited-antigen wet diets with undeclared animal protein. One of these 6 diets was solely composed of animal protein sources completely unrelated to those declared on the label. None of the foods containing horse meat or fish were contaminated, and neither were the vegetarian or the hydrolyzed food products. Moreover, the results show that had zoological class primers only been used to check for cross-class contaminations, as are generally used in the pet food industry for in-house checks, the apparent contamination rate would have been significantly underestimated: less than 20% (3/11), instead of the actual rate of 54.7% using species-specific primers.

Conclusion

This study reveals a high rate of cross-contamination in dietetic limited-antigen wet canine and feline foods, as previously described for dietetic dry limited-antigen foods (reported to be more than 80%). These results add new fuel to the discussion about the potential causes underlying the failure of elimination diets, since animal protein contaminants may actually be present in the commercial dietetic limited-antigen diets. AFRs may therefore occur as a result of inadequate practices in the pet food industry.

An open label clinical trial to evaluate the utility of a hydrolysed fish and rice starch elimination diet for the diagnosis of adverse food reactions in dogs

BACKGROUND

The diagnosis of adverse food reaction (AFR) is based on an eight week elimination diet (ED) and is confirmed by relapse upon re-challenge with the previously fed diet. Hydrolysed EDs are commonly used for this purpose.

OBJECTIVE

To evaluate a commercially available hydrolysed fish protein and rice starch ED for the diagnosis of AFR.

ANIMALS

Fifty nonseasonally pruritic dogs.

METHODS AND MATERIALS

Pruritus was assessed with a Visual Analog Scale, lesions with the Canine Atopic Dermatitis Lesions Index and quality of life with a validated questionnaire on days 0 and 56. Antimicrobial treatments were permitted during the first four weeks, and corticosteroids and oclacitinib during the first six weeks. Dogs showing at least 50% pruritus improvement were separately challenged with their prior diet, fish and rice.

RESULTS

Thirty eight dogs completed the ED, four were dropped out due to worsening clinical signs, three to low palatability and five were lost to follow-up. In 24 dogs, pruritus improved by >50% and 22 underwent dietary challenges. Of these, 15 reacted to their prior diets and were diagnosed with AFR, whereas seven did not relapse (and a diagnosis of AFR was considered to be doubtful). Five dogs reacted to fish and four to rice. Of the 14 dogs in which pruritus did not improve, some underwent a second ED and others were successfully treated for atopic dermatitis.

CONCLUSION AND CLINICAL IMPORTANCE

The hydrolysed fish and rice diet seemed to be a useful ED for the diagnosis of AFR, even in dogs allergic to fish or rice.

Cornstarch is less allergenic than corn flour in dogs and cats previously sensitized to corn

Background

Corn appears to be an uncommon food source of allergens in dogs and cats. There is limited information on the nature of the corn allergens in dogs and cats and their presence in the various foodstuffs used in commercial pet foods. The aim of this study was to determine if serum IgE from corn-sensitized dogs and cats recognized proteins in corn flour and cornstarch, which are common sources of carbohydrates in pet foods.

Results

We selected archived sera from allergy-suspected dogs (40) and cats (40) with either undetectable, low, medium or high serum levels of corn-specific IgE. These sera were tested then by ELISA on plates coated with extracts made from corn kernels, corn flour, cornstarch and the starch used in the commercially-available extensively-hydrolyzed pet food Anallergenic (Royal Canin). Immunoblotting was then performed on the same extracts with some of the sera from moderate-to-high corn-sensitized dogs and cats. Using ELISA, it is mostly the dogs and cats with moderate and high corn-specific IgE levels that also had IgE identifying allergens in the flour (dogs: 20/30 sera, 67% - cats: 20/29, 69%). In contrast, none of the tested sera had measurable IgE against proteins isolated from the cornstarch. Immunoblotting confirmed the existence of numerous major corn allergens in the corn kernel extract, fewer in that of the corn flour, while such allergens were not detectable using this technique in the two cornstarch extracts.

Conclusions

In this study, ELISA and immunoblotting results suggest that IgE from corn-sensitized dogs are less likely to recognize allergens in cornstarch than in kernel and flour extracts. As corn is not a common allergen source in dogs and cats, and as its starch seems to be less allergenic than its flour, pet foods containing cornstarch as a carbohydrate source are preferable for dogs and cats suspected of suffering from corn allergy.

Electronic supplementary material

The online version of this article (10.1186/s12917-018-1538-5) contains supplementary material, which is available to authorized users.

DNA and Protein Analyses to Confirm the Absence of Cross-Contamination and Support the Clinical Reliability of Extensively Hydrolysed Diets for Adverse Food Reaction-Pets

Adverse food reactions (AFR) are a common cause of skin diseases in cats and dogs. The correct diagnosis and management of AFR relies upon clinical nutrition. The reliability of commercial hypoallergenic diets commonly used in AFR has been questioned because studies have shown the presence of proteins not declared on the label ingredients. It is proposed that extensively hydrolysed protein-based diets constitute a reliable nutritional solution. Royal Canin Anallergenic™ Canine and Feline diets are formulated with very low molecular weight feather protein and purified corn starch. Protein gel electrophoresis and thin layer paper chromatography were used to characterize protein hydrolysis in these diets and their hydrolysed raw materials; protein species were identified by mass spectrometry. To detect cross-contaminating protein, species-specific DNA was measured and correlated with ancillary protein content using calibration curves. The only protein components detected in the extensively hydrolysed feather protein raw material were amino acids and small oligopeptides. GBSS-I (Granule-bound starch synthase 1) was detected in the finished diets; this has not been reported as a clinically apparent allergen in dogs or cats. The DNA threshold corresponding to the maximum acceptable level of ancillary protein was not exceeded in 99.9% of more than 2150 product batches tested and no products were released to the market with cross-contaminating proteins. These results demonstrate the extensive level of protein hydrolysis in Royal Canin Anallergenic™ Canine and Feline diets and the absence of cross-contaminating protein, both key requirements for a diet to be used during diagnosis and for management of pets with AFR.

Critically appraised topic on adverse food reactions of companion animals (5): discrepancies between ingredients and labeling in commercial pet foods

Background

Elimination dietary trials for the diagnosis of adverse food reactions (food allergies) in dogs and cats are often conducted with commercial pet foods while relying on their label to select those not containing previously-eaten ingredients. There are concerns that industrial pet foods might contain unlisted food sources that could negate the usefulness of performing food trials. Furthermore, unidentified ingredients might cause clinical reactions in patients hypersensitive to such items.

Results

We searched two article databases on July 7, 2017 and January 12, 2018 for relevant articles, and we screened abstracts from the leading international veterinary dermatology congresses for suitable material. Additional citations were found in the selected papers. In all, we extracted data from 17 articles and one abstract. The studies varied both in the number of pet foods tested (median: 15; range: 1 to 210) and that of ingredients specifically evaluated (median: 4; range: 1 to 11). Studies most often employed either PCR to detect DNA or ELISA to identify proteins from one or more vegetal or animal species; two studies used mass spectrometry to increase the number of detectable proteins. The various methods found ingredients that were not on the label in 0 to 83% (median: 45%) of tested diets; this percentage varied between 33 and 83% in pet foods with “novel/limited” ingredients proposed for elimination diets. Similarly, ingredients were found to be missing from the label in 0 to 38% (median: 1%) of tested foods. Finally, six studies evaluated, among others, several hydrolysate-containing pet foods: mislabeling with unlabeled or missing ingredients was found only in one diet.

Conclusions

The mislabeling of pet foods appears rather common, even in those with “novel” or “limited” ingredients proposed for elimination diets. Unexpected added ingredients are more frequently detected than those missing from the label. There is insufficient information to determine if the presence of a contaminating component will lead to a clinical reaction in a patient allergic to it, as challenges with the mislabeled foods were not performed in dogs or cats allergic to such ingredients. The testing of hydrolysate-containing pet foods found only one instance of possible mislabeling.

Electronic supplementary material

The online version of this article (10.1186/s12917-018-1346-y) contains supplementary material, which is available to authorized users.