Telling NO to Cardiac Risk
Author-Writer-Reporter: Stephen J. Williams, PhD
Endothelium-derived nitric oxide (NO) has been shown to be vasoprotective. Nitric oxide enhances endothelial cell survival, inhibits excessive proliferation of vascular smooth muscle cells, regulates vascular smooth muscle tone, and prevents platelets from sticking to the endothelial wall. Together with evidence from preclinical and human studies, it is clear that impairment of the NOS pathway increases risk of cardiovascular disease (3-5).
This post contains two articles on the physiological regulation of nitric oxide (NO) by an endogenous NO synthase inhibitor asymmetrical dimethylarginine (ADMA) and ADMA metabolism by the enzyme DDAH(1,2). Previous posts on nitric oxide, referenced at the bottom of the page, provides excellent background and further insight for this posting. In summary plasma ADMA levels are elevated in patients with cardiovascular disease and several large studies have shown that plasma ADMA is an independent biomarker for cardiovascular-related morbidity and mortality(6-8).
Figure 1 A. Cardiac risks of ADMA B. Effects of ADMA (Photo credit: Wikipedia)
ADMA Production and Metabolism
Nuclear proteins such as histones can be methylated on arginine residues by protein-arginine methyltransferases, enzymes which use S-adenosylmethionine as methyl groups. This methylation event is thought to regulate protein function, much in the way of protein acetylation and phosphorylation (9). And much like phosphorylation, these modifications are reversible through methylesterases. The proteolysis of these arginine-methyl modifications lead to the liberation of free guanidine-methylated arginine residues such as L-NMMA, asymmetric dimethylarginine (ADMA) and symmetrical methylarginine (SDMA).
The first two, L-NMMA and ADMA, have been shown to inhibit the activity of the endothelial NOS. This protein turnover is substantial: for instance the authors note that each day 40% of constitutive protein in adult liver is newly synthesized protein. And in several diseases, such as muscular dystrophy, ischemic heart disease, and diabetes, it has been known since the 1970’s that protein catabolism rates are very high, with corresponding increased urinary excretion of ADMA(10-13). Methylarginines are excreted in the urine by cationic transport. However, the majority of ADMA and L-NMMA are degraded within the cell by dimethylaminohydrolase (DDAH), first cloned and purified in rat(14).
Figure 2. Endogenous inhibitors of NO synthase. Chemical structures generated from PubChem.
DDAH specifically hydrolyzes ADMA and L-NMMA to yield citruline and demethylamine and usually shows co-localization with NOS. Pharmacologic inhibition of DDAH activity causes accumulation of ADMA and can reverse the NO-mediated bradykinin-induced relaxation of human saphenous vein.
Two isoforms have been found in human:
- DDAH1 (found in brain and kidney and associated with nNOS) and
- DDAH2 (highly expressed in heart, placenta, and kidney and associated with eNOS).
DDAH2 can be upregulated by all-trans retinoic acid (atRA can increase NO production). Increased reactive oxygen species and possibly homocysteine, a risk factor for cardiovascular disease, can decrease DDAH activity(15,16).
- The importance of DDAH activity can also be seen in transgenic mice which overexpress DDAH, exhibiting increased NO production, increased insulin sensitivity, and reduced vascular resistance (17). Likewise,
- Transgenic mice, null for the DDAH1, showed increase in blood pressure, decreased NO production, and significant increase in tissue and plasma ADMA and L-NMMA.
Figure 3. The DDAH/ADMA/NOS cycle. Figure adapted from Cooke and Ghebremarian (1).
As mentioned in the article by Cooke and Ghebremariam, the authors state: the weight of the evidence indicates that DDAH is a worthy therapeutic target. Agents that increase DDAH expression are known, and 1 of these, a farnesoid X receptor agonist, is in clinical trials
An alternate approach is to
- develop an allosteric activator of the enzyme. Although
- development of an allosteric activator is not a typical pharmaceutical approach, recent studies indicate that this may be achievable aim(18).
1. Cooke, J. P., and Ghebremariam, Y. T. : DDAH says NO to ADMA.(2011) Arteriosclerosis, thrombosis, and vascular biology 31, 1462-1464
2. Tran, C. T., Leiper, J. M., and Vallance, P. : The DDAH/ADMA/NOS pathway.(2003) Atherosclerosis. Supplements 4, 33-40
3. Niebauer, J., Maxwell, A. J., Lin, P. S., Wang, D., Tsao, P. S., and Cooke, J. P.: NOS inhibition accelerates atherogenesis: reversal by exercise. (2003) American journal of physiology. Heart and circulatory physiology 285, H535-540
4. Miyazaki, H., Matsuoka, H., Cooke, J. P., Usui, M., Ueda, S., Okuda, S., and Imaizumi, T. : Endogenous nitric oxide synthase inhibitor: a novel marker of atherosclerosis.(1999) Circulation 99, 1141-1146
5. Wilson, A. M., Shin, D. S., Weatherby, C., Harada, R. K., Ng, M. K., Nair, N., Kielstein, J., and Cooke, J. P. (2010): Asymmetric dimethylarginine correlates with measures of disease severity, major adverse cardiovascular events and all-cause mortality in patients with peripheral arterial disease. Vasc Med 15, 267-274
6. Kielstein, J. T., Impraim, B., Simmel, S., Bode-Boger, S. M., Tsikas, D., Frolich, J. C., Hoeper, M. M., Haller, H., and Fliser, D. : Cardiovascular effects of systemic nitric oxide synthase inhibition with asymmetrical dimethylarginine in humans.(2004) Circulation 109, 172-177
7. Kielstein, J. T., Donnerstag, F., Gasper, S., Menne, J., Kielstein, A., Martens-Lobenhoffer, J., Scalera, F., Cooke, J. P., Fliser, D., and Bode-Boger, S. M. : ADMA increases arterial stiffness and decreases cerebral blood flow in humans.(2006) Stroke; a journal of cerebral circulation 37, 2024-2029
8. Mittermayer, F., Krzyzanowska, K., Exner, M., Mlekusch, W., Amighi, J., Sabeti, S., Minar, E., Muller, M., Wolzt, M., and Schillinger, M. : Asymmetric dimethylarginine predicts major adverse cardiovascular events in patients with advanced peripheral artery disease.(2006) Arteriosclerosis, thrombosis, and vascular biology 26, 2536-2540
9. Kakimoto, Y., and Akazawa, S.: Isolation and identification of N-G,N-G- and N-G,N’-G-dimethyl-arginine, N-epsilon-mono-, di-, and trimethyllysine, and glucosylgalactosyl- and galactosyl-delta-hydroxylysine from human urine. (1970) The Journal of biological chemistry 245, 5751-5758
10. Inoue, R., Miyake, M., Kanazawa, A., Sato, M., and Kakimoto, Y.: Decrease of 3-methylhistidine and increase of NG,NG-dimethylarginine in the urine of patients with muscular dystrophy. (1979) Metabolism: clinical and experimental 28, 801-804
11. Millward, D. J.: Protein turnover in skeletal muscle. II. The effect of starvation and a protein-free diet on the synthesis and catabolism of skeletal muscle proteins in comparison to liver. (1970) Clinical science 39, 591-603
12. Goldberg, A. L., and St John, A. C.: Intracellular protein degradation in mammalian and bacterial cells: Part 2. (1976) Annual review of biochemistry 45, 747-803
13. Dice, J. F., and Walker, C. D.: Protein degradation in metabolic and nutritional disorders. (1979) Ciba Foundation symposium, 331-350
14. Ogawa, T., Kimoto, M., and Sasaoka, K.: Purification and properties of a new enzyme, NG,NG-dimethylarginine dimethylaminohydrolase, from rat kidney. (1989) The Journal of biological chemistry 264, 10205-10209
15. Ito, A., Tsao, P. S., Adimoolam, S., Kimoto, M., Ogawa, T., and Cooke, J. P.: Novel mechanism for endothelial dysfunction: dysregulation of dimethylarginine dimethylaminohydrolase. (1999) Circulation 99, 3092-3095
16. Stuhlinger, M. C., Tsao, P. S., Her, J. H., Kimoto, M., Balint, R. F., and Cooke, J. P. : Homocysteine impairs the nitric oxide synthase pathway: role of asymmetric dimethylarginine.(2001) Circulation 104, 2569-2575
17. Sydow, K., Mondon, C. E., Schrader, J., Konishi, H., and Cooke, J. P.: Dimethylarginine dimethylaminohydrolase overexpression enhances insulin sensitivity. (2008) Arteriosclerosis, thrombosis, and vascular biology 28, 692-697
18. Zorn, J. A., and Wells, J. A.: Turning enzymes ON with small molecules. (2010) Nature chemical biology 6, 179-188
Other research papers on Nitric Oxide and Cardiac Risk were published on this Scientific Web site as follows:
The Nitric Oxide and Renal is presented in FOUR parts: