Combination therapy with relaxin and methylprednisolone augments the effects of either treatment alone in inhibiting subepithelial fibrosis in an experimental model of allergic airways disease

Although CSs (corticosteroids) demonstrate potent effects in the control of airway inflammation in asthma, many patients continue to experience symptoms and AHR (airway hyper-responsiveness) despite optimal treatment with these agents, probably due to progressive airway remodelling. Identifying novel therapies that can target airway remodelling and/or airway reactivity may improve symptom control in these patients. We have demonstrated previously that the anti-fibrotic hormone RLN (relaxin) can reverse airway remodelling (epithelial thickening and subepithelial fibrosis) and AHR in a murine model of AAD (allergic airways disease). In the present study, we compared the effects of RLN with a CS (methylprednisolone) on airway remodelling and AHR when administered independently or in combination in the mouse AAD model. Female mice at 6–8 weeks of age were sensitized and challenged to OVA (ovalbumin) over a 9-week period and treated with methylprednisolone, RLN, a combination of both treatments or vehicle controls. Methylprednisolone was administered intraperitoneally on the same day as nebulization for 6 weeks, whereas recombinant human RLN-2 was administered via subcutaneously implanted osmotic mini-pumps from weeks 9–11. RLN or methylprednisolone alone were both able to significantly decrease subepithelial thickness and total lung collagen deposition; whereas RLN but not methylprednisolone significantly decreased epithelial thickness and AHR. Additionally, combination therapy with CS and RLN more effectively reduced subepithelial collagen thickness than either therapy alone. These findings demonstrate that RLN can modulate a broader range of airway remodelling changes and AHR than methylprednisolone and the combination of both treatments offers enhanced control of subepithelial fibrosis.