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Rationale: Dysregulation of the one carbon cycle is documented in depression. Thereby, S-adenosylmethionine (SAMe), a one-carbon cycle nutraceutical compound with a favourable side effect profile, has a theoretical rationale for efficacy. However, further controlled studies are required to confirm SAMe's efficacy., Objectives: To test the efficacy of SAMe versus placebo in unmedicated DSM-5 diagnosed (major depressive disorder) (MDD) patients with mild-to-moderate levels of depressive symptoms., Methods: We conducted an 8-week, double-blind, randomised controlled trial testing 800 mg/day of SAMe monotherapy versus placebo in 49 patients with MDD (Montgomery-Åsberg Depression Rating Scale [MADRS] score 14-25) who were not currently taking antidepressants. One-carbon cycle biomarkers, brain-derived neurotropic factor (BDNF), and relevant single nucleotide polymorphisms (SNPs) were analysed as potential treatment moderators., Results: A clinically relevant differential reduction from baseline to week 8 of 3.76 points occurred on the primary outcome (MADRS) in favour of SAMe. This however was not significant (p = 0.13) on an adjusted linear mixed model, notwithstanding a medium to large effect size of 0.72. A high placebo response rate of 53% occurred (> 50% reduction on MADRS). Exploratory analyses showed that SAMe was however effective in reducing depression amongst participants with milder depression severity (MADRS ≤ 22, p = 0.045). Response was not moderated by BDNF, SNPs, or one-carbon cycle biomarkers, although increased folate concentrations were correlated with improved symptoms in the SAMe group (r = - 0.57, p = 0.026). The treatment was safe and well tolerated., Conclusions: Although a differential reduction in depression symptoms between groups was observed in favour of SAMe, the results of this pilot study were not statistically significant., Trial Registration: ANZCTR-Australian New Zealand Clinical Trials Registry; No.: ACTRN12613001299796; URL: https://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?id=364900.

In the cases that have been studied so far, S-adenosylhomocysteine (SAH) is a powerful inhibitor of S-adenosylmethionine (SAM) binding to SAM-dependent methyltransferases. We deduced, from the available data on the binding of SAM and SAH analogues to SAM dependent methyltransferases, that linkage of SAH through the carboxyl group to an immobilized support would lead to a more general affinity adsorbent for SAM-dependent methyltransferases than linkage through other functional groups. This paper describes the synthesis of this affinity adsorbent and its use to purify the two indolethylamine N-methyltransferases of Phalaris tuberosa.