MMP9 and chronic obstructive pulmonary disease: Translational respiratory data point out the same way—probiotic blends in COPD models decreased lung MMP-9 mRNA/protein and inflammatory cytokines, supporting a gut–lung axis in which probiotics/prebiotics dampen MMP-9-linked remodeling; human COPD trials increasingly show safety and anti-inflammatory signals, though standardized MMP-9 endpoints remain uncommon [151].