Nicotinamide N-methyltransferase (NNMT), which converts nicotinamide (NA) to 1-methylnicotinamide (MNA), is up-regulated in the cirrhotic liver. Because MNA displays PGI(2)-dependent anti-inflammatory effects, the up-regulation of NNMT may play a regulatory role in liver inflammation. In the present work, we analyzed changes in NNMT activity in the liver and concomitant changes in the concentration of endogenous MNA in plasma in T-cell dependent hepatitis induced by concanavalin A (ConA) in BALB/c mice. Furthermore, we tested whether exogenous MNA possessed a protective effect against ConA-induced hepatitis. Development of liver injury induced by ConA (10 mg/kg, iv) was characterized by measurements of plasma concentration of alanine aminotransaminase (ALT), inflammatory cytokines (INF gamma and TNFalpha) and by histopathological examination. ConA-induced hepatitis was characterized by an early activation of inflammatory cytokines (IFN gamma; from below 0.05 ng/ml to 23.72 +/- 8.80 ng/ml; TNFalpha;from 0.07 +/- 0.01 ng/ml to 0.71 +/- 0.12 ng/ml, 2 h after ConA), an elevation of ALT (from 40.65 +/- 3.2 U/l to 5,092.20 +/- 1,129.05 U/l, 8 h after ConA) and by morphological signs of severe liver inflammation and injury (24 h after ConA). In mice injected with ConA, NNMT activity in the liver was up-regulated approximately 2-fold to 3-fold, 8-24 h after ConA injection. The concentration of MNA and its metabolites (Met-2PY and Met-4PY) in plasma were elevated approximately 2-fold 8 h after ConA injection. Exogenous MNA (100 mg/kg, iv) diminished ConA-induced liver injury, and this effect was reversed by an antagonist of the prostacyclin receptor, RO 3244794 (10 mg/kg, po). In conclusion, the present study demonstrated that hepatic NNMT activity and MNA concentration in plasma significantly increased during the progression of ConA-induced hepatitis in mice. This response may play a hepatoprotective role compatible with the PGI(2)-releasing properties of MNA.

Abstract:Nicotinamide N-methyltrasferase (NMMT) catalyzes the conversion of nicotinamide (NA) to 1-methylnicotinamide (MNA). Recent studies have reported that exogenous MNA exerts anti-thrombotic and anti-inflammatory activity, suggesting that endogenous NMMT-derived MNA may play a biological role in the cardiovascular system. In the present study, we assayed changes in hepatic NNMT activity and MNA plasma levels along the progression of atherosclerosis in apoE/LDLR -/-mice, as compared to age-matched wild-type mice. Atherosclerosis progression in apoE/LDLR -/-mice was quantified in aortic root, while hepatic NNMT activity and MNA plasma concentrations were concomitantly measured in 2-, 3-, 4-, and 6-month-old mice. In apoE/LDLR -/-mice, atherosclerotic plaques developed in the aortic roots beginning at the age of 3 months and gradually increased in size, macrophage content, and inflammation intensity over time, as detected by Oil-Red O staining, CD68 immunostaining, and in situ zymography (MMP2/MMP9 activity). Hepatic NNMT activity was upregulated approximately two-fold in apoE/LDLR -/-mice by the age of 2 months, as compared to wild-type mice (1.03 ± 0.14 vs. 0.64 ± 0.23 pmol/min/mg, respectively). MNA plasma concentrations were also elevated approximately two-fold (0.30 ± 0.13 vs. 0.17 ± 0.04 mmol/l, respectively). As atherosclerosis progressed, hepatic NMMT activity and MNA plasma concentrations increased five-fold in 6-month-old apoE/LDLR -/-mice at the stage of advanced atherosclerotic plaques (NMMT activity: 2.29 ± 0.34 pmol/min/mg, MNA concentration: 1.083 ± 0.33 mmol/l). In summary, the present study demonstrated that the progression of vascular inflammation and atherosclerosis was associated with the upregulation of hepatic NNMT activity and subsequent increase in endogenous MNA plasma levels. Given the anti-thrombotic and anti-inflammatory properties of exogenous MNA, robust activation of an endogenous NA-MNA pathway in atherosclerosis may play an important compensatory role.

No abstract

Recent studies suggest both beneficial and detrimental role of increased reactive oxygen species and oxidative stress in heart failure (HF). However, it is not clear at which stage oxidative stress and oxidative modifications occur in the endothelium in relation to cardiomyocytes in non-ischemic HF. Furthermore, most methods used to date to study oxidative stress are either non-specific or require tissue homogenization. In this study, we used immuno-spin trapping (IST) technique with fluorescent microscopy-based detection of DMPO nitrone adducts to localize and quantify oxidative modifications of the hearts from Tgαq*44 mice; a murine model of HF driven by cardiomyocyte-specific overexpression of Gαq* protein. Tgαq*44 mice and age-matched FVB controls at early, transition, and late stages of HF progression were injected with DMPO in vivo and analyzed ex vivo for DMPO nitrone adducts signals. Progressive oxidative modifications in cardiomyocytes, as evidenced by the elevation of DMPO nitrone adducts, were detected in hearts from 10- to 16-month-old, but not in 8-month-old Tgαq*44 mice, as compared with age-matched FVB mice. The DMPO nitrone adducts were detected in left and right ventricle, septum, and papillary muscle. Surprisingly, significant elevation of DMPO nitrone adducts was also present in the coronary endothelium both in large arteries and in microcirculation simultaneously, as in cardiomyocytes, starting from 10-month-old Tgαq*44 mice. On the other hand, superoxide production in heart homogenates was elevated already in 6-month-old Tgαq*44 mice and progressively increased to high levels in 14-month-old Tgαq*44 mice, while the enzymatic activity of catalase, glutathione reductase, and glutathione peroxidase was all elevated as early as in 4-month-old Tgαq*44 mice and stayed at a similar level in 14-month-old Tgαq*44. In summary, this study demonstrates that IST represents a unique method that allows to quantify oxidative modifications in cardiomyocytes and coronary endothelium in the heart. In Tgαq*44 mice with slowly developing HF, driven by cardiomyocyte-specific overexpression of Gαq* protein, an increase in superoxide production, despite compensatory activation of antioxidative mechanisms, results in the development of oxidative modifications not only in cardiomyocytes but also in coronary endothelium, at the transition phase of HF, before the end-stage disease.

No abstract