Previous reports of unmodified rhTIMP-1 pharmacokinetics in rodents have varied considerably; an early study found an elimination half-life of 4 h in mice, while another group recently reported a half-life of 42 h in an ischemia-reperfusion model in rats. Both of these values are considerably longer than the 1.1 h elimination half-life that we measured for rhTIMP- 1. Major differences include that both prior studies employed 125I-labelled rhTIMP-1 to follow distribution and clearance while we used an ELISA with high specificity for human TIMP-1, and that the prior studies administered much lower doses. A caveat in the interpretation of radiolabelling studies is that the assay does not specifically monitor intact or active rhTIMP-1 molecules, but inflammatory diseases including osteoarthritis, rheumatoid arthritis, multiple sclerosis, chronic obstructive pulmonary disease and other conditions of pulmonary inflammation and fibrosis. Among TIMPs, native TIMP-1 has the Bortezomib strongest preexisting affinity for MMP-9, and possesses the unique ability to bind to proMMP-9 through an interaction between the C-terminal domain of TIMP-1 and the C-terminal hemopexin domain of the proenzyme. This highaffinity interaction substantially accelerates the kinetics of MMP- 9/TIMP-1 association, likely contributing to selectivity of TIMP-1 toward MMP-9 in vivo. The N-terminal domain of TIMP- 1 in the proMMP-9/TIMP-1 complex remains available and competent for inhibiting other active MMP molecules including MMP-3, a physiological activator of MMP-9 the interaction with TIMP-1 therefore protects proMMP-9 from enzymatic activation in vitro and in vivo. While native TIMP-1 therefore offers special advantages where targeting of MMP-9 is desired, we found that the PEG20K-TIMP-1 preparation inhibited MMP-9 somewhat less effectively than it inhibited MMP-3cd. This was possibly due to steric incompatibility between one or more sites of TIMP-1 lysine PEGylation and the MMP-9 PEX domain. For retention of optimal activity toward MMP-9, it may be advantageous for future studies to further pursue approaches for more regioselective PEGylation of rhTIMP-1. Although we did not find success with PEGylation of an introduced Cys residue, the most common approach toward sitespecific PEGylation, another possible approach might pursue PEGylation on the two glycosyl groups of TIMP-1, both of which lie within the N-terminal domain and well removed from the inhibitory site. Yet another possibility could involve mutational studies to identify which of the TIMP-1 Lys residues interferes with MMP-9 association upon PEGylation, and then specifically removing that site of modification by mutagenesis. TIMP-1 offers a potential biopharmaceutical MMP inhibitor but is rapidly eliminated; our results indicate that PEGylation is one feasible approach to improve its pharmacokinetic profile while preserving activity. Several recent publications have suggested other biopharmaceutical approaches to MMP inhibition. Nanoparticles loaded with mouse TIMP-1 were shown to provide neuroprotection in an organotypic hippocampal slice culture model. A fusion protein formed from human TIMP-2 and human serum albumin was found to provide an improved pharmacokinetic profile and biodistribution in a tumor model and to provide an antiangiogenic effect. Furthermore, TIMPs are not the only biomolecules to be investigated as scaffolds for development of MMP inhibitors. An inhibitory human antibody targeting MMP-14, developed using phage display technology, has shown in vivo activity in mouse xenograft tumor models. Mouse monoclonal antibodies, raised against a synthetic antigen that mimics the MMP catalytic site, were shown to inhibit gelatinases via a TIMP-like binding mechanism, and to show therapeutic promise in a mouse model of inflammatory bowel disease. The methods tested and developed in the present work will contribute to the developing biotechnological arsenal for creating next-generation MMP inhibitors. Accumulating evidence suggests that dysfunction of the glutamate neurotransmitter system is associated with the pathophysiology of mood disorders, such as major depressive disorder and bipolar disorder. Levels of glutamate are altered in blood, cerebrospinal fluid, and brains of patients with MDD and BP. Furthermore, clinical studies including double-blind, placebo-controlled randomized trials, demonstrate the efficacy of a single dose of the ionotrophic N-methyl-Daspartate receptor antagonist, ketamine, in treating patients with refractory MDD and bipolar depression.