Modeling Principle

The Beagle Dermatitis Model is a SCI gold-standard large-animal cutaneous inflammatory pathological model established by skin barrier destruction combined with repeated allergen stimulation, mainly used to simulate clinical atopic dermatitis (AD). It fully recapitulates the full-stage pathological progression of human dermatitis including skin barrier defect, epidermal hyperkeratosis, dermal inflammatory cell infiltration, persistent pruritus, erythema and exudation, chronic lichenification, and compensates for experimental defects of rodent small animals with remarkable differences from humans in stratum corneum thickness, epidermal layered structure, immune response and pruritus behavioral pattern.

The epidermal-dermal layered structure, stratum corneum lipid composition, Th2 immune imbalance pathway, cutaneous nerve ending distribution and pruritus reflex regulation mechanism of Beagle dogs are highly homologous to human skin. The temporal sequence of dry scaling, erythema and edema, scratching pruritus and chronic thickened lichenification after repeated cutaneous stimulation is completely consistent with the disease course of moderate to severe clinical atopic dermatitis. The modeling procedure firstly uses sodium dodecyl sulfate (SDS) local wiping to destroy stratum corneum barrier and reduce transepidermal water loss barrier function. Then repeated topical stimulation with ovalbumin/dust mite extract allergen is performed. Cutaneous Langerhans cells capture antigens to initiate systemic Th2-dominant immune response, secrete massive type 2 inflammatory factors such as IL-4, IL-5 and IL-13, induce mast cell degranulation and dermal infiltration of eosinophils and lymphocytes. Long-term continuous antigen stimulation activates NF-κB inflammatory pathway, disturbs proliferation of epidermal keratinocytes, and leads to hyperkeratosis, epidermal hypertrophy and fissure exudation. Persistent scratching of animals further aggravates epidermal damage and recurrent inflammation, and gradually forms progressive dermatitis lesions including acute erythema and exudation stage, subacute dry scaling stage and chronic skin thickening lichenification stage, which fully recapitulates the classic pathogenic cascade of human atopic dermatitis: barrier damage-antigen sensitization-Th2 immune imbalance-inflammatory infiltration-chronic lichenification.

Beagle dogs possess sufficient body surface skin area and wide observation field for modeling, with slow progression of dermatitis lesions and minimal individual differences without spontaneous cutaneous inflammation. It can clearly distinguish three-stage phenotypes of acute inflammatory stage, subacute proliferative stage and terminal chronic lichenification stage, serving as a standardized gold-standard large-animal model for preclinical pharmacodynamic evaluation of topical and oral new drugs for skin barrier repair, anti-inflammation and anti-pruritus, abnormal keratin hyperplasia inhibition and anti-allergy.

Modeling Success Criteria

Macroscopic Clinical Cutaneous Lesion Phenotype

The back skin of blank control group was smooth and flat without erythema, edema, scaling and scratch marks, soft and lustrous with TEWL value maintained at normal low level. At Day 28 terminal point, the modeling area skin of model group presented large-area erythema, local edema and dry scaling, multiple epidermal broken scratch marks left by frequent daily scratching of animals, thickened and rough skin with deepened texture showing typical lichenification changes. TEWL was significantly elevated and stratum corneum water content decreased sharply. The macroscopic dermatitis score was remarkably higher than blank group with typical lesion grading characteristics and extremely significant inter-group difference, confirming preliminary successful model construction.

Quantitative Biochemical Gold-Standard Indexes of Serum and Cutaneous Th2 Immunity

The expression of core Th2 inflammatory factors IL-4, IL-5 and IL-13 in cutaneous tissues and serum of model group was extremely significantly upregulated, pro-inflammatory factors TNF-α and IL-6 increased synchronously, and the activation and degranulation level of mast cells increased remarkably. Massive accumulation of cutaneous oxidative stress products ROS and MDA, decreased SOD antioxidant activity and blocked stratum corneum barrier lipid synthesis fully match the core biochemical diagnostic characteristics of clinical atopic dermatitis: Th2 immune shift, barrier destruction and chronic inflammation.

Cutaneous Histopathological Characteristics

Combined HE, toluidine blue and Masson staining of full-thickness cutaneous tissues showed characteristic pathological evolution of atopic dermatitis:

1. Day 7 acute stage: mild epidermal edema, diffuse massive infiltration of eosinophils, lymphocytes and mast cells in superficial dermis, telangiectasia and congestion;
2. Day 21 subacute stage: epidermal acanthosis, parakeratosis of stratum corneum accompanied by massive scaling, persistent dermal inflammatory cell infiltration and mild collagen disorder;
3. Day 28 terminal chronic lichenification stage: remarkably thickened epidermis with elongated epidermal processes, stratum corneum hyperkeratosis, persistent dermal inflammatory cell infiltration, disorderly proliferated collagen fibers and significantly increased number of mast cells, which fully recapitulates graded pathological changes of epidermal proliferation, dermal Th2 inflammatory infiltration and cutaneous fibrotic thickening in human chronic atopic dermatitis.

Core Immune Inflammation and Keratin Proliferation Pathway Indexes

The NF-κB inflammatory pathway of model group was persistently overactivated with massive release of downstream Th2 inflammatory factors. The expression of keratinocyte proliferation marker Ki67 was significantly elevated, barrier lipid synthesis-related protein was downregulated, and mast cell activation pathway remained continuously open. Oxidative stress imbalance further amplified cutaneous inflammation and epidermal hyperplasia, which fully conforms to the complete pathogenic mechanism induced by compound modeling: barrier defect-antigen sensitization-Th2 immune shift-dermal inflammatory infiltration-epidermal keratin thickening-chronic lichenification, serving as core academic criterion for confirming successful modeling.

Model Advantages

This model is a well-recognized exclusive large-animal gold-standard dermatitis model for atopic dermatitis in SCI dermatology field. Two-step compound induction of barrier destruction and repeated sensitization stably forms chronic pruritic dermatitis lichenified lesions highly homologous to humans within 28 days. The stratum corneum, immune typing, pruritus behavior and barrier lipid metabolism of Beagle dog skin are close to human body, with gentle and uniform dermatitis progression gradient, extremely low intra-group data dispersion and excellent experimental reproducibility. The modeling inducing factors conform to the dual pathogenesis of clinical atopic dermatitis (congenital barrier defect + environmental allergen stimulation), without one-sidedness caused by single drug induction, which is more suitable for in-vivo pharmacodynamic verification of topical repair, oral anti-allergy, anti-pruritus and anti-inflammatory preparations. The large lesion area of large animals allows multi-concentration administration control in the same individual to reduce animal consumption. The clinical transformation credibility of data is far higher than mice and rats, with high recognition in high-score dermatology SCI journals, suitable for National Natural Science Foundation, master/doctor project opening, graduation thesis of cutaneous pharmacology/allergic dermatoses and translational medical research of skin regeneration and anti-inflammation.

Research Applications

The Beagle Dermatitis Model is corely applied to basic research on stratum corneum barrier lipid defect, exogenous allergen-induced Th2 immune shift, dermal mast cell and eosinophil infiltration, epidermal hyperkeratosis proliferation and secondary cutaneous damage mediated by chronic pruritus. It is specially used for screening and evaluating topical cutaneous gels, creams, medical dressings, active extracts of traditional Chinese medicine and oral anti-allergic small-molecule drugs with effects of repairing stratum corneum barrier, inhibiting release of Th2 inflammatory factors, reducing mast cell degranulation, alleviating cutaneous pruritus, inhibiting abnormal epidermal keratinization and relieving erythema and lichenification. It is widely adopted for excavation of pathogenic targets of allergic dermatitis, elucidation of skin barrier regulation mechanisms and large-animal preclinical in-vivo pharmacodynamic verification of anti-inflammatory and anti-pruritus preparations, serving as a scarce and essential standardized large-animal gold-standard model in the fields of allergic dermatoses, skin barrier pharmacology and dermatological regenerative repair research.

beagle dog atopic dermatitis model，cutaneous barrier dysfunction，epidermal inflammatory infiltration，pruritus and hyperkeratosis，dermatological drug preclinical evaluation