Myeloperoxidase Molecular MRI Reveals Synergistic Combination Therapy in Murine Experimental Autoimmune Neuroinflammation.

Background Despite advances in immunomodulatory agents, most current therapies for multiple sclerosis target lymphocytes or lymphocytic function. However, therapy response may be less than optimal due to demyelination and axonal damage caused by myeloid cells. Purpose To determine if myeloperoxidase (MPO) molecular MRI can evaluate whether combination therapy targeting both lymphoid and myeloid inflammation can improve autoimmune neuroinflammation compared with either drug alone, even at suboptimal doses. Materials and Methods Four groups of 94 female mice (8-10 weeks old) were induced with experimental autoimmune encephalomyelitis (EAE) from August 2, 2016, to March 30, 2018, and divided into saline control (n = 22), 4-aminobenzoic acid hydrazide (ABAH) therapy group (n = 19), glatiramer acetate (GA) therapy group (n = 22), and combination therapy group (n = 31). Mice were administered suboptimal doses of ABAH, an irreversible inhibitor of MPO; GA, a first-line multiple sclerosis drug; both ABAH and GA; or saline (control). Mice were imaged with bis-5-hydroxytryptamide-diethylenetriaminepentaacetate gadolinium (hereafter, MPO-Gd) MRI. One-way analysis of variance, two-way analysis of variance, Kurskal-Wallis, and log-rank tests were used. P < .05 was considered to indicate statistical significance. Results The combination-treated group showed delayed disease onset (day 11.3 vs day 9.8 for ABAH, day 10.4 for GA, day 9.9 for control; P < .05) and reduced disease severity (clinical score during the acute exacerbation period of 1.8 vs 3.8 for ABAH, 3.1 for GA, 3.9 for control; P < .05). The combination-treated group demonstrated fewer MPO-positive lesions (30.2 vs 73.7 for ABAH, 64.8 for GA, 67.2 for control; P < .05), smaller MPO-positive lesion volume (16.7 mm3 vs 65.2 mm3 for ABAH, 69.9 mm3 for GA, 66.0 mm3 for control; P < .05), and lower intensity of MPO-Gd lesion activation ratio (0.7 vs 1.9 for ABAH, 3.2 for GA, 2.3 for control; P < .05). Reduced disease severity in the combination group was confirmed at histopathologic analysis, where MPO expression (1779 vs 2673 for ABAH, 2898 for GA; P < .05) and demyelination (5.3% vs 9.0% for ABAH, 10.6% for GA; P < .05) were ameliorated. Conclusion Myeloperoxidase molecular MRI can track the treatment response from immunomodulatory drugs even if the drug does not directly target myeloperoxidase, and establishes that combination therapy targeting both myeloid and lymphocytic inflammation is effective for murine autoimmune neuroinflammation, even at suboptimal doses. © RSNA, 2019 Online supplemental material is available for this article. See also the editorial by Walczak in this issue.