ALS is a heterogeneous disease that is not well understood. Epigenetic rearrangements are important in complex disorders including motor neuron diseases. The aim of this study was to determine whether whole-blood DNA methylation (DNA MET %) is a potential modifier of age at onset in ALS. DNA MET % was measured as incorporation of [(3)H]dCTP following HpaII cut in 96 ALS patients and 87 controls, comprising: early-onset (< 55 years of age) and late-onset (> 74 years of age). Methionine (Met) and homocysteine (Hcy) plasma levels were assessed by liquid chromatography selected reaction monitoring coupled with isotope-dilution mass spectrometry. Results showed that DNA MET % was increased in ALS patients independently of age of onset. Compared to the other three groups, Hcy plasma levels were reduced in early-onset ALS patients but Met levels were similar. ROC analysis reported Met levels and DNA MET %, respectively, with a slight and moderate discriminative power. In conclusion, increased DNA MET % is a possible marker of epigenetic dysfunction in ALS independently of age of onset. Further studies dissecting biological determinants of phenotypic complexity in ALS may help in developing successful therapeutic strategies.

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Purpose Indoleamine 2,3-dioxygenase-1 (IDO1) and more recently, tryptophan 2,3-dioxygenase (TDO), are tryptophancatabolizing enzymes with immunoregulatory properties in cancer. IDO1 is more expressed than TDO in many tumours including melanomas; however, IDO inhibitors did not give expected results in clinical trials, highlighting the need to consider TDO. We aimed to characterize both TDO expression and function in a melanoma cell line, named SK-Mel-28, with the purpose to compare it with a colon cancer cell line, HCT-8, and with a human endothelial cell line (HUVEC). Methods TDO expression was assessed as real time-PCR and western blot, for mRNA and protein expression, respectively. While cell proliferation was assessed as cell duplication, cell apoptosis and cell cycle were analysed by means of flow cytometry. Results SK-Mel-28 cells showed higher TDO levels compared to HCT-8 and to HUVEC cells. A selective TDO inhibitor, 680C91, significantly impaired cell proliferation in a concentration-dependent manner, by inducing cell arrest during the G2 phase for SK-Mel-28 and HUVEC cells, while an early apoptosis was increasing in HCT-8 cells. No toxic effects were observed. These data demonstrated that TDO is highly expressed in SK-Mel-28 cells and may be involved in the regulation of their proliferation. Conclusion TDO may directly modulate cancer cell function rather than immune suppression and can be considered as a target for melanoma progression together with IDO1.

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