Homocysteine increases the production of asymmetric dimethylarginine in cultured neurons.

Increased circulating concentrations of homocysteine may be a risk factor for Alzheimer's disease and cognitive dysfunction in normal aging. Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of endothelial nitric oxide synthase (NOS). ADMA is metabolized in neurons by the enzyme dimethylarginine dimethylaminohydrolase (DDAH). Nitric oxide plays an important role in synaptic events involved in learning and memory. We determined the effect of L-homocysteine on ADMA accumulation and nitric oxide production in cultured rat neuronal granule cells. The incubation of neuronal granule cells with L-homocysteine for 24 hr caused a dose-dependent accumulation of ADMA and a dose-dependent decrease in nitric oxide production. The addition of the sulfhydryl antioxidant pyrrolidine dithiocarbamate (PDTC) attenuated the effect of homocysteine on ADMA accumulation and nitric oxide production. DDAH activity had a decreasing dose-response relationship with increasing L-homocysteine concentrations. The addition of PDTC caused a dose-dependent increase in DDAH activity. The addition of the N-methyl-D-aspartate receptor antagonists (+/-)-2-amino-5-phosphopentanoic acid and 7-chlorokynurenate had no effect on the inhibition of DDAH by homocysteine. It is concluded that L-homocysteine inhibits DDAH activity, thereby causing ADMA accumulation and decreasing nitric oxide production in cultured neurons. The protective effect of PDTC suggests that L-homocysteine inactivates DDAH in neurons by reacting with the cysteine residue in its active site. The preservation of DDAH activity and the reduction of ADMA accumulation in neurons may be a new strategy for the treatment of Alzheimer's disease and cognitive impairment in normal aging.

Selley ML 《JOURNAL OF NEUROSCIENCE RESEARCH》

Increased (E)-4-hydroxy-2-nonenal and asymmetric dimethylarginine concentrations and decreased nitric oxide concentrations in the plasma of patients with major depression.

(E)-4-Hydroxy-2-nonenal (HNE) is a highly electrophilic end-product of lipid peroxidation. Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of endothelial nitric oxide synthase (NOS). ADMA is metabolised by dimethylarginine dimethylaminohydrolase (DDAH). DDAH contains a nucleophilic cysteine residue in its active site. There is an increase in lipid peroxidation in major depression. Major depression is associated with the development of coronary heart disease (CHD) and greatly increases morbidity and mortality. There is an increase in circulating ADMA in CHD and vascular risk factors. To determine plasma HNE, ADME and nitric oxide (NO) concentrations in patients with major depression compared to normal volunteers and to examine the effect of HNE on ADMA formation and DDAH activity in cultured endothelial cells. The study was conducted in 25 patients with major depression (DSM-IV criteria) and 25 healthy control subjects. Plasma concentrations of HNE were determined as the O-pentafluorylbenzyl oxime using capillary column GC-MS and deuterated HNE as the internal standard; ADME by LC-MS-MS using 13C6-L-arginine as the internal standard; and NO by GC-MS following reduction to nitrate and nitrite and derivatisation to the pentafluorobenzyl derivative using [15N]nitrate and [15N]nitrite as the internal standards. Human umbilical vein endothelial cells were incubated in serum-free medium in the presence of HNE. The concentration of ADMA in the medium was determined by LC-MS-MS. DDAH activity was determined by measuring L-citrulline in endothelial cell lysates using LC-MS. There was a significant increase in the plasma concentration of HNE (P<0.0001) and ADMA (P<0.0002) in patients with major depression. There was a significant decrease in the plasma concentration of NO (P<0.0001). A significant positive correlation was found between the plasma concentrations of HNE and ADMA (r=0.63, P<0.0001). A significant negative correlation was detected between the plasma concentrations of ADMA and NO (r=-0.595, P<0.0001). HNE significantly increased ADMA formation (P<0.0001) and significantly decreased DDAH activity (P<0.0001) in cultured endothelial cells. The effects of HNE on DDAH activity were significantly attenuated by the addition of glutathione (P<0.0001). No allowance was made for the phase of the menstrual cycle which could influence plasma nitric oxide concentrations. There is an increase in circulating HNE in major depression. HNE inactivates the cysteine residue in the active site of endothelial DDAH leading to the accumulation of ADMA in the circulation. The ADMA then decreases the production of eNOS. This could reduce the amount of NO diffusing from cerebral blood vessels to nearby neurons and influence the release of neurotransmitters. ADMA also constricts cerebral blood vessels and may contribute to the decreased regional perfusion in major depression. The accumulation of ADMA could explain the increased risk of CHD in major depression. The preservation of DDAH activity and the reduction of ADMA accumulation may represent a novel therapeutic approach to the treatment of major depression.

Selley ML 《JOURNAL OF AFFECTIVE DISORDERS》

All-trans retinoic acid inhibits cobalt chloride-induced apoptosis in PC12 cells: role of the dimethylarginine dimethylaminohydrolase/asymmetric dimethylarginine pathway.

Previous studies have shown that the endogenous nitric oxide synthase inhibitor asymmetric dimethylarginine (ADMA) and its specific hydrolase dimethylarginine dimethylaminohydrolase (DDAH) are involved in the regulation of apoptosis in different cell types. In the present study, we investigated the role of the DDAH/ADMA pathway in cobalt chloride (CoCl(2))-induced apoptosis and the antiapoptotic effect of all-trans retinoic acid (atRA) in undifferentiated pheochromocytoma (PC12) cells. Treatment of CoCl(2) (125 microM) for 48 hr significantly induced the apoptosis of PC12 cells, concomitantly with increased intracellular reactive oxygen species (ROS) production and caspase-3 activity. CoCl(2) treatment also decreased the activity of DDAH and the expression of DDAH2 (mRNA and protein), resulting in an increased level of ADMA. All these alterations induced by CoCl(2) were attenuated by atRA (0.1, 1, or 10 microM). Interestingly, the antiapoptotic effects of atRA were inhibited by DDAH2 small RNA interference. In contrast, DDAH2 overexpression inhibited the proapoptotic effects of CoCl(2). We also found that treatment of exogenous ADMA (3, 10, or 30 microM) induced the apoptosis of PC12 cells in a concentration- and time-dependent manner, which was inhibited by the antioxidant or the caspase-3 inhibitor. These findings suggest that the modulation of the DDAH/ADMA/ROS pathway plays an important role in CoCl(2)-induced apoptosis and the antiapoptotic effects of atRA in undifferentiated PC12 cells.

Wang S ，Hu CP ，Jiang DJ ，Peng J ，Zhou Z ，Yuan Q ，Nie SD ，Jiang JL ，Li YJ ，Huang KL ... -  《-》

Protective effects of kaempferol against endothelial damage by an improvement in nitric oxide production and a decrease in asymmetric dimethylarginine level.

Xiao HB ，Jun-Fang ，Lu XY ，Chen XJ ，Chao-Tan ，Sun ZL ... -  《-》

Estradiol counteracts oxidized LDL-induced asymmetric dimethylarginine production by cultured human endothelial cells.

Monsalve E ，Oviedo PJ ，García-Pérez MA ，Tarín JJ ，Cano A ，Hermenegildo C ... -  《CARDIOVASCULAR RESEARCH》