A combination treatment of low-dose dexamethasone and aspirin-triggered resolvin D1 reduces Sjögren syndrome–like features in a mouse model

**Background:** Sjögren syndrome (SS) is an autoimmune disease characterized by lymphocytic infiltration and diminished secretory function of salivary glands. Dexamethasone (DEX) reduces inflammation and lymphocytic infiltration but causes significant adverse effects (e.g., osteoporosis, skin thinning) with long-term use. Aspirin-triggered resolvin D1 (AT-RvD1), a proresolving lipid mediator, increases saliva secretion but cannot eliminate lymphocytic infiltration. A prior study showed that combination treatment before disease onset prevents SS-like features, but this is not clinically practical due to lack of reliable early markers. The present study tested the combination at disease onset to evaluate efficacy and tolerability for potential lifelong use.

**Methods:** Forty female 12-week-old NOD/ShiLtJ mice were randomly divided into four groups (n=10 each): ethanol vehicle control, high-dose DEX (8.25 mg/kg), AT-RvD1 alone (0.1 mg/kg), or low-dose DEX (4.125 mg/kg) combined with AT-RvD1 (0.1 mg/kg). Treatments were administered twice weekly via tail vein injection for 8 weeks. At 20 weeks of age, submandibular glands (SMGs) were harvested for histologic analyses. Saliva flow rate was measured after stimulation with pilocarpine (50 mg/kg) and isoproterenol (0.5 mg/kg). Lymphocytic infiltration was assessed by hematoxylin-eosin staining and quantified as foci area/total SMG area using ImageJ. Mast cell degranulation was evaluated by toluidine blue staining and confocal microscopy for chymase. Aquaporin-5 (AQP5) localization was examined by confocal microscopy.

**Key Results:** - **Lymphocytic infiltration:** SMGs from vehicle and AT-RvD1–treated mice showed extensive infiltration covering >40% of glandular tissue. High-dose DEX and low-dose DEX+AT-RvD1 significantly reduced foci size (P = .001 for both vs. vehicle; AT-RvD1 alone not significant). - **Mast cell degranulation:** Toluidine blue staining showed extensive degranulation in vehicle controls. High-dose DEX and low-dose DEX+AT-RvD1 significantly diminished degranulation. Confocal chymase quantification confirmed significant reduction in all treatment groups vs. vehicle (P = .05). - **Saliva flow rate:** All treatments significantly increased saliva secretion vs. vehicle (P = .01). - **Aquaporin-5 localization:** AT-RvD1 alone and low-dose DEX+AT-RvD1 restored apical AQP5 expression, whereas high-dose DEX and vehicle showed basolateral or diffuse staining.

**Clinical Implications:** The combination of low-dose DEX with AT-RvD1 at disease onset effectively reduces lymphocytic infiltration and mast cell degranulation (benefits of high-dose DEX) while restoring apical AQP5 and increasing saliva secretion (benefits of AT-RvD1). This approach avoids the adverse effects of high-dose DEX and overcomes AT-RvD1's inability to control lymphocytic infiltration. The treatment is intended for indefinite administration, making tolerability critical. Limitations include lack of direct proof that lymphocytic infiltration causes dysfunction (though prior studies support this), potential unresponsiveness of lymphocyte receptors to AT-RvD1, and need for dose-response studies to determine the minimal effective DEX dose. Future studies should extend to male mice and late-stage disease.