Deletion of glycine N-methyltransferase (GNMT), the main gene involved in liver S-adenosylmethionine (SAM) catabolism, leads to the hepatic accumulation of this molecule and the development of fatty liver and fibrosis in mice. To demonstrate that the excess of hepatic SAM is the main agent contributing to liver disease in GNMT knockout (KO) mice, we treated 1.5-month-old GNMT-KO mice for 6 weeks with nicotinamide (NAM), a substrate of the enzyme NAM N-methyltransferase. NAM administration markedly reduced hepatic SAM content, prevented DNA hypermethylation, and normalized the expression of critical genes involved in fatty acid metabolism, oxidative stress, inflammation, cell proliferation, and apoptosis. More importantly, NAM treatment prevented the development of fatty liver and fibrosis in GNMT-KO mice. Because GNMT expression is down-regulated in patients with cirrhosis, and because some subjects with GNMT mutations have spontaneous liver disease, the clinical implications of the present findings are obvious, at least with respect to these latter individuals. Because NAM has been used for many years to treat a broad spectrum of diseases (including pellagra and diabetes) without significant side effects, it should be considered in subjects with GNMT mutations. Conclusion: The findings of this study indicate that the anomalous accumulation of SAM in GNMT-KO mice can be corrected by NAM treatment leading to the normalization of the expression of many genes involved in fatty acid metabolism, oxidative stress, inflammation, cell proliferation, and apoptosis, as well as reversion of the appearance of the pathologic phenotype. (HEPATOLOGY 2010;52:105-114) Abbreviations: 5mC, 5-methyl-cytosine; a-SMA, a-smooth muscle actin; ADFP, adipose differentiation-related protein; COL1A1, pro-a1-collagen type I; CYP2E1, cytochrome P4502E1; CYP39A1, cytochrome P45039A1; CYP4A10, cytochrome P4504A10; CYP4A14, cytochrome P4504A14; CD36, fatty acid translocase CD36; ERK, extracellular signal-regulated kinase; GAPDH, glyceraldehyde 3-phosphate dehydrogenase; GNMT, glycine N-methyltransferase; GSH, glutathione; HCC, hepatocellular carcinoma; IL6, interleukin-6; iNOS, inducible nitric oxide synthase; JAK, Janus kinase; KO, knockout; MAT, methionine adenosyltransferase; NAM, nicotinamide; NNMT, nicotinamide N-methyltransferase; PARP, poly(ADP-ribose) polymerase; PCR, polymerase chain reaction; PPAR, peroxisome proliferator-activated receptor; RASSF1A, Ras-association domain family/tumor suppressor-1A; SAH, S-adenosylhomocysteine; SAM, Sadenosylmethionine; SEM, standard error of the mean; SIRT1, sirtuin-1; SOCS1, suppressor of cytokine signaling-1; STAT, signal transducer and activator of transcription; TIMP-1, TIMP tissue inhibitor of metalloproteinase-1; TUNEL, terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling; UCP2, uncoupling protein-2; WT, wild-type.From the

Scope Interventions that boost NAD+ availability are of potential therapeutic interest for obesity treatment. The potential of nicotinamide (NAM), the amide form of vitamin B3 and a physiological precursor of nicotinamide adenine dinucleotide (NAD)+, in preventing weight gain has not previously been studied in vivo. Other NAD+ precursors have been shown to decrease weight gain; however, their impact on adipose tissue is not addressed. Methods and results Two doses of NAM (high dose: 1% and low dose: 0.25%) are given by drinking water to C57BL/6J male mice, starting at the same time as the high‐fat diet feeding. NAM supplementation protects against diet‐induced obesity by augmenting global body energy expenditure in C57BL/6J male mice. The manipulation markedly alters adipose morphology and metabolism, particularly in inguinal (i) white adipose tissue (iWAT). An increased number of brown and beige adipocyte clusters, protein abundance of uncoupling protein 1 (UCP1), mitochondrial activity, adipose NAD+, and phosphorylated AMP‐activated protein kinase (P‐AMPK) levels are observed in the iWAT of treated mice. Notably, a significant improvement in hepatic steatosis, inflammation, and glucose tolerance is also observed in NAM high‐dose treated mice. Conclusion NAM influences whole‐body energy expenditure by driving changes in the adipose phenotype. Thus, NAM is an attractive potential treatment for preventing obesity and associated complications.

The potential of nicotinamide (NAM) to prevent atherosclerosis has not yet been examined. This study investigated the effect of NAM supplementation on the development of atherosclerosis in a mouse model of the disease. The development of aortic atherosclerosis was significantly reduced (NAM low dose: 45%; NAM high dose: 55%) in NAM-treated, apolipoprotein (Apo)E-deficient mice challenged with a Western diet for 4 weeks. NAM administration significantly increased (1.8-fold) the plasma concentration of proatherogenic ApoB-containing lipoproteins in NAM high-dose (HD)-treated mice compared with untreated mice. However, isolated ApoB-containing lipoproteins from NAM HD mice were less prone to oxidation than those of untreated mice. This result was consistent with the decreased (1.5-fold) concentration of oxidized low-density lipoproteins in this group. Immunohistochemical staining of aortas from NAM-treated mice showed significantly increased levels of IL-10 (NAM low-dose (LD): 1.3-fold; NAM HD: 1.2-fold), concomitant with a significant decrease in the relative expression of TNFα (NAM LD: −44%; NAM HD: −57%). An improved anti-inflammatory pattern was reproduced in macrophages cultured in the presence of NAM. Thus, dietary NAM supplementation in ApoE-deficient mice prevented the development of atherosclerosis and improved protection against ApoB-containing lipoprotein oxidation and aortic inflammation.

Our data indicate that the HDL from methionine-induced hyperhomocysteinemic mice was more prone to oxidation and displayed lower capacity to protect LDL against oxidative modification than that of control mice, highlighting a mechanism by which a diet-induced HHcy may facilitate progression of atherosclerosis.

Introducción. La concentración plasmática elevada de homocisteína (Hcy) o hiperhomocisteinemia se asocia a un aumento del riesgo de enfermedad vascular en estudios de casos y controles, y, en menor grado, en estudios prospectivos. Desarrollo. Han finalizado ya diversos grandes estudios aleatorios, doble ciego y controlados con placebo, que se realizaron con el objetivo de estudiar si había una reducción del riesgo vascular al disminuir la concentración plasmática de Hcy mediante tratamientos vitamínicos específicos (folatos y/o vitaminas B 12 y B 6). Su objetivo era analizar si esta estrategia reducía el riesgo de enfermedad cardiovascular (estudios HOPE, NORVIT, WAFACS y WENBIT) y cerebrovascular (estudio VISP) en un contexto de prevención secundaria. Los resultados obtenidos a partir de estos estudios y un metaanálisis, que incluye otros más pequeños hasta un total de 12, mostraron que el tratamiento disminuye la concentración plasmática de Hcy, pero no el riesgo vascular. Es, sin embargo, interesante señalar que un metaanálisis reciente que analizó los efectos de estos tratamientos vitamínicos detectó un efecto protector significativo en la prevención primaria del ictus. Estos datos son consistentes con el hecho de que la hiperhomocisteinemia se relaciona más con el riesgo cerebrovascular que con el cardiovascular. Y también con la observación reciente de que la suplementación con ácido fólico en las harinas está asociada con una disminución en la mortalidad por ictus en Estados Unidos y Canadá. Conclusiones. Obviamente, estos datos requerirán de posterior confirmación, pero parece que ahora existen razones que permiten esperar un desenlace positivo de los estudios de intervención para disminuir la Hcy. Palabras clave. Ácido fólico. Enfermedad cardiovascular. Enfermedad cerebrovascular. Enfermedad vascular. Hiperhomocisteinemia. Vitaminas.