Differential effects of arginine methylation on diastolic dysfunction and disease progression in patients with chronic systolic heart failure.

AIMS: To investigate the association of arginine methylation with myocardial function and prognosis in chronic systolic heart failure patients. METHODS AND RESULTS: Asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA), as well as N-mono-methylarginine (MMA) and methyl-lysine, were simultaneously measured by tandem mass spectrometry in 132 patients with chronic systolic heart failure with echocardiographic evaluation and follow-up. Increasing ADMA and SDMA levels were associated with elevated natriuretic peptide levels (both P < 0.001), and increasing SDMA levels were associated with worsening renal function (P < 0.001). Higher plasma levels of methylated arginine metabolites (but not methyl-lysine) were associated with the presence of left ventricular (LV) diastolic dysfunction (E/septal E', Spearman's r = 0.31-0.36, P < 0.001). Patients taking beta-blockers had lower ADMA levels than those not taking beta-blockers [0.42 (0.33, 0.50) vs. 0.51 (0.40, 0.58), P < 0.001]. Only increasing ADMA levels were associated with advanced right ventricular (RV) systolic dysfunction. Elevated ADMA levels remained a consistent independent predictor of adverse clinical events (hazard ratio = 1.64, 95% CI: 1.20-2.22, P = 0.002). CONCLUSION: In chronic systolic heart failure, accumulation of methylated arginine metabolites is associated with the presence of LV diastolic dysfunction. Among the methylated derivatives of arginine, ADMA provides the strongest independent prediction of disease progression and adverse long-term outcomes.

Metabolic profiling of arginine and nitric oxide pathways predicts hemodynamic abnormalities and mortality in patients with cardiogenic shock after acute myocardial infarction.

BACKGROUND: It is unclear whether abnormalities of arginine and nitric oxide metabolism are related to hemodynamic dysfunction and mortality in patients with cardiogenic shock (CS) after acute myocardial infarction. METHODS AND RESULTS: Plasma metabolites reflecting arginine bioavailability, nitric oxide metabolism, and protein oxidation were analyzed by mass spectrometry in patients with CS (n=79) and age- and gender-matched patients with coronary artery disease and normal left ventricular function (n=79). CS patients had higher levels of asymmetric dimethylarginine (ADMA; P<0.0001), symmetric dimethylarginine (P<0.0001), monomethylarginine (P=0.0003), nitrotyrosine (P<0.0001), and bromotyrosine (P<0.0001) and lower levels of arginine (P<0.0001), ratio of arginine to ornithine (P=0.03), and ratio of arginine to ornithine plus citrulline) (P=0.0003). CS patients with elevated ADMA levels were 3.5-fold (95% confidence interval, 1.4 to 11.3; P=0.02) more likely to die in 30 days than patients with low ADMA levels. ADMA remained the only independent predictor of mortality on multiple logistic regression analysis. In patients with normal renal function, symmetric dimethylarginine levels inversely correlated with mean arterial pressure and systemic vascular resistance, whereas levels of ADMA correlated with pulmonary capillary wedge pressure and both systolic and diastolic pulmonary artery pressures. Despite dramatic elevations, levels of protein oxidation products did not predict hemodynamic dysfunction or mortality in CS patients. CONCLUSIONS: CS is characterized by an arginine-deficient and highly specific pro-oxidant state, with elevated levels of methylated arginine derivatives, including endogenous nitric oxide synthase inhibitors. Levels of methylated arginine derivatives strongly correlate with hemodynamic dysfunction. Among all clinical and laboratory parameters monitored, ADMA levels were the strongest independent predictor of 30-day mortality.

A novel enzyme complex of orotate phosphoribosyltransferase and orotidine 5'-monophosphate decarboxylase in human malaria parasite Plasmodium falciparum: physical association, kinetics, and inhibition characterization.

Human malaria parasite, Plasmodium falciparum, can only synthesize pyrimidine nucleotides using the de novo pathway, whereas mammalian cells obtain pyrimidine nucleotides from both the de novo and salvage pathways. The parasite's orotate phosphoribosyltransferase (PfOPRT) and orotidine 5'-monophosphate decarboxylase (PfOMPDC) of the de novo pyrimidine pathway are attractive targets for antimalarial drug development. Previously, we have reported that the two enzymes in P. falciparum exist as a multienzyme complex containing two subunits each of 33-kDa PfOPRT and 38-kDa PfOMPDC. In this report, the gene encoding PfOPRT has been cloned and expressed in Escherichia coli. An open reading frame of PfOMPDC gene was identified in the malaria genome database, and PfOMPDC was cloned from P. falciparum cDNA, functionally expressed in E. coli, purified, and characterized. The protein sequence has <20% identity with human OMPDC and four microbial OMPDC for which crystal structures are known. Recombinant PfOMPDC was catalytically active in a dimeric form. Both recombinant PfOPRT and PfOMPDC monofunctional enzymes were kinetically different from the native multienzyme complex purified from P. falciparum. Oligomerization of PfOPRT and PfOMPDC cross-linked by dimethyl suberimidate indicated that they were tightly associated as the heterotetrameric 140-kDa complex, (PfOPRT)2(PfOMPDC)2. Kinetic analysis of the PfOPRT-PfOMPDC associated complex was similar to that of the native P. falciparum enzymes and was different from that of the bifunctional human enzymes. Interestingly, a nanomolar inhibitor of the yeast OMPDC, 6-thiocarboxamido-uridine 5'-monophosphate, was about 5 orders of magnitude less effective on the PfOMPDC than on the yeast enzyme. Our results support that the malaria parasite has unique structural and functional properties, sharing characteristics of the monofunctional pyrimidine-metabolizing enzymes in prokaryotes and bifunctional complexes in eukaryotes.

Hydrogen isotope tracing in the reaction of orotidine-5'-monophosphate decarboxylase.

The mechanism of the enzyme orotidine-5(')-monophosphate decarboxylase (OMP decarboxylase, ODCase) is not fully characterized; some of the proposed mechanisms suggest the possibility of hydrogen rearrangement (shift from C5 to C6 or loss of H5 to solvent) during catalysis. In this study, we sought mechanistic information for the ODCase reaction by examining the extent of hydrogen exchange in the product uridine-5(')-monophosphate, in combination with ODCase, at the H5 and H6 positions. In a subsequent experiment, partially deuterated OMP was prepared, and the extent of 2H5 rearrangement or loss to solvent was examined by integration of 1H nuclear magnetic resonance signals in the substrate and the resulting enzymatically decarboxylated product. The absence of detectable hydrogen exchange in these experiments limits somewhat the possible mechanisms for ODCase catalysis.