Relapsing-Remitting Multiple Sclerosis Natalizumab Treatment in Enhanced Axonal Metabolism during Early

BACKGROUND AND PURPOSE: The considerable clinical effect of natalizumab in patients with relapsing-remitting multiple sclerosis might be explained by its possible beneficial effect on axonal functioning. In this longitudinal study, the effect of natalizumab on absolute concentrations of total N-acetylaspartate, a marker for neuronal integrity, and other brain metabolites is investigated in patients with relapsing-remitting multiple sclerosis by using MR spectroscopic imaging. MATERIALS AND METHODS: In this explorative observational study, 25 patients with relapsing-remitting multiple sclerosis initiating natalizumab treatment were included and scanned every 6 months for 18 months. Additionally 18 matched patients with relapsingremitting multiple sclerosis continuing treatment with interferonor glatiramer acetate were included along with 12 healthy controls. Imaging included short TE 2D-MR spectroscopic imaging with absolute metabolite quantification of total N-acetylaspartate, creatine and phosphocreatine, choline-containing compounds, myo-inositol, and glutamate. Concentrations were determined for lesional white matter, normal-appearing white matter, and gray matter. RESULTS: At baseline in both patient groups, lower concentrations of total N-acetylaspartate and creatine and phosphocreatine were found in lesional white matter compared with normal-appearing white matter and additionally lower glutamate in lesional white matter of patients receiving natalizumab. In those patients, a significant yearly metabolite increase was found for lesional white matter total N-acetylaspartate (7%, P .001), creatine and phosphocreatine (6%, P .042), and glutamate (10%, P .028), while lesion volumes did not change. In patients receiving interferon/glatiramer acetate, no significant change was measured in lesional white matter for any metabolite, while whole-brain normalized lesion volumes increased. CONCLUSIONS: Patients treated with natalizumab showed an increase in total N-acetylaspartate, creatine and phosphocreatine, and glutamate in lesional white matter. These increasing metabolite concentrations might be a sign of enhanced axonal metabolism. ABBREVIATIONS: GA glatiramer acetate; Glu glutamate; IFNb interferon ; LWM lesional white matter; NAWM normal-appearing white matter; MRSI MR spectroscopic imaging; PVE partial volume estimation; tCr total creatine (creatine and phosphocreatine); tNAA total N-acetylaspartate; RRMS relapsing-remitting multiple sclerosis Multiple sclerosis is an inflammatory and neurodegenerative disease of the central nervous system. The acute pathology of the disease is characterized by focal lesions in the white matter, while accumulation of gray matter damage is more prominent in the progressive stage of the disease. Previous spectroscopy studies found that lesional WM (LWM) (ie, only lesions or WM directly surrounding lesions) is characterized by decreased levels of total N-acetylaspartate (tNAA), a marker of neuronal integrity, and decreased total creatine (tCr), a marker of energy metabolism, combined with higher levels of choline-containing compounds, a marker of cell membrane turnover. In the WM, an increased Cho/tCr ratio has been detected before the lesions are visible on conventional Received September 11, 2014; accepted after revision December 19. From the Departments of Radiology and Nuclear Medicine (O.T.W., G.J.A.N., M.D.S., F.B.), Anatomy and Neurosciences (O.T.W., A.M.K., M.M.S., G.J.A.N., J.J.G.G.), Neurology (J.A.v.R., C.H.P.), and Physics and Medical Technology (P.J.W.P.), Neuroscience Campus Amsterdam and VU University Medical Center, Amsterdam, the Netherlands. † Deceased. O.T. Wiebenga and A.M. Klauser contributed equally to this article. This work was sponsored by the Dutch MS Research Foundation, grant number 09-358d. MR imaging was partly sponsored by Biogen Idec. Biogen Idec did not participate in any aspect of the design or performance (including data collection, data management, data analysis and interpretation, or preparation) of this investigator initiated study. Final approval for the work and manuscript was given by the authors. Please address correspondence to Oliver T. Wiebenga, MD, VU University Medical Center, Department of Radiology and Nuclear Medicine, PO Box 7057, 1007 MB, Amsterdam, the Netherlands; e-mail: o.wiebenga@vumc.nl Indicates article with supplemental on-line appendix. http://dx.doi. org/10.3174/ajnr.A4252 1116 Wiebenga Jun 2015 www.ajnr. org MR imaging. In the normal-appearing WM (NAWM), decreased tNAA and increased mIns, a marker of gliosis, have been found and have shown correlations with clinical disability scores. The anti-inflammatory effect of natalizumab, second-line therapy for relapsing-remitting MS (RRMS) in most countries, leads to a dramatic reduction in the formation of WM lesions, a decrease in the whole-brain atrophy rate, and improved rates of clinical progression and relapses. Previous studies have shown that interferon -1b (IFNb) and glatiramer acetate (GA) increase tNAA concentrations in MS, but the effect of natalizumab remains unclear. We, therefore, performed MR spectroscopic imaging (MRSI) in patients starting natalizumab treatment and repeated measurements every 6 months in LWM, NAWM, and GM. Measurements were compared with those in healthy controls. Additionally, patients with RRMS continuing on IFNb/GA were followed during the same period. MATERIALS AND METHODS Subjects Three groups of subjects were investigated in this observational study: patients with RRMS starting natalizumab at baseline, those continuing IFNb/GA, and healthy controls (Table 1), as described separately (O.T.W. et al, unpublished data, 2015). The study was approved by the ethics review board of the VU University Medical Center, and all subjects gave written informed consent before participation. Inclusion criteria for the study were an age between 18 and 65 years and a diagnosis of clinically definite MS (for patients only). Exclusion criteria were a history of psychiatric or neurologic disease (other than MS for patients), contraindications for MR imaging, and a history of alcohol or drug abuse. Patients starting natalizumab (n 25; 300 mg intravenously every 4 weeks) had at least 1 prior period of IFNb/GA treatment with breakthrough disease or rapidly evolving active RRMS before starting treatment. These patients were included after the decision to start natalizumab had already been made. At baseline, 6 patients were treatment-naïve for natalizumab, 14 patients had received 1, and 3 patients had received 2 infusions. Two patients who had already received 6 infusions when they joined the study were only analyzed at the 6-month visit and onward. All patients continued natalizumab treatment for the duration of the study. Patients receiving IFNb/GA (n 18) continued this treatment at baseline. Twelve patients used IFN-b, the dose and route of administration dependent on type, and 6 patients used GA, 20 mg subcutaneously, daily. Patients receiving IFNb/GA were matched to those receiving natalizumab for age, sex, disability (Expanded Disability Status Scale), and duration of therapy. Two patients discontinued IFNb/GA treatment but remained in the study. One discontinued GA after baseline because of side effects (necrosis and scarring of skin at injection sites) combined with stable disease; another discontinued IFNb at month 12 due to conversion to secondary-progressive MS. Healthy controls (n 12) were ageand sex-matched to patients receiving natalizumab at baseline. MR Imaging Acquisition MR imaging was performed on a 1.5T whole-body scanner (Sonata; Siemens, Erlangen, Germany) with an 8-channel receiver head coil. Sequences included a 3D T1-weighted MPRAGE sequence (TR, 2700 ms; TE, 5 ms; TI, 950 ms; 176 sagittal sections; 1.3-mm section thickness; 1.3 1.3 mm in-plane resolution), and a proton-attenuation/T2-weighted turbo spin-echo sequence (TR, 3130 ms; TE, 24 and 85 ms; 46 contiguous 3-mm axial sections; 1 1 mm in-plane, aligned to the pituitary-fastigium line as outlined in Fig 1A). 2D-MRSI included a point-resolved spectroscopy sequence (TR/TE, 3000/30 ms) on a single 15-mm slab aligned to the sections of the proton-attenuation/T2 sequence, with the center touching the top of the corpus callosum. Depending on head size, the FOV was 160 160 or 140 160 mm and the corresponding volume of interest was 70 100 or 80 100 mm. The use of 16 16 phase-encodings resulted in a voxel size of 1.3 or 1.5 mL. Reference 2D-MRSI datasets without water suppression were measured by using both head and body coils as a