MMP9 and schizophrenia: Hence, we recruited male patients with chronic schizophrenia to determine (1) whether plasma OS parameters and serum MMP-9 and TIMP-1 differed between schizophrenia patients and healthy controls; (2) whether alterations in plasma OS parameters and serum MMP-9 and TIMP-1 were related to the severity of clinical symptoms; (3) whether serum MMP-9 or TIMP-1 and plasma OS parameters levels were independently or interactively correlated with clinical features.