Asymmetric Dimethylarginine.

ADMA is a competitive inhibitor at nitric oxide synthase, occupying the site arginine binds. Raising arginine shifts the ratio back toward normal nitric oxide output.

Citrulline escapes first-pass arginase and is recycled to arginine in the kidney and endothelium, raising the local arginine to ADMA ratio more reliably than oral arginine. It works on the same competition from upstream.

The citrulline portion regenerates arginine and lifts the arginine to ADMA ratio at the enzyme. The malate portion feeds the citric acid cycle and does not act on this competition.

The hydrochloride salt delivers the same arginine that competes with ADMA at nitric oxide synthase. The counter-ion changes solubility, not the mechanism.

ADMA is produced when arginine residues are methylated and is cleared largely by DDAH, whose activity is sensitive to the homocysteine and methylation state. Folate status shapes both ends of that balance.

Dietary nitrate is reduced to nitrite and then to nitric oxide without passing through nitric oxide synthase at all. That route is untouched by ADMA competition at the enzyme.

Betaine donates a methyl group to remethylate homocysteine back to methionine. Homocysteine inhibits the enzyme DDAH that clears ADMA, so anything that lowers homocysteine sits upstream of ADMA clearance. The chemistry is established; whether a betaine dose moves a person's ADMA is a separate question that the candidate papers here do not answer.

Trimethylglycine feeds the betaine homocysteine methyltransferase route, which is one of two ways the body disposes of homocysteine. Because homocysteine inhibits DDAH, the enzyme that degrades ADMA, this route touches ADMA handling indirectly. It is an upstream mechanistic link rather than a measured effect on the marker.

Methionine synthase requires methylcobalamin to transfer a methyl group from 5-methyltetrahydrofolate to homocysteine. Without adequate B12 the folate route stalls and homocysteine rises. Since homocysteine inhibits ADMA clearance by DDAH, B12 status sits two steps upstream of this marker.

Cystathionine beta-synthase and cystathionine gamma-lyase both require pyridoxal 5-phosphate, and together they route homocysteine irreversibly to cysteine. That is the disposal arm rather than the recycling arm of the pathway. Its relevance here is the same indirect link through homocysteine and DDAH activity.

Methionine is converted to S-adenosylmethionine, the methyl donor that protein arginine methyltransferases use to methylate arginine residues in proteins. Proteolysis of those methylated proteins is what releases free ADMA. So methionine sits upstream of ADMA production, not of its clearance, which is the opposite direction from the B vitamins.

S-adenosylmethionine is the methyl donor PRMT enzymes use when they methylate arginine residues, the reaction that ultimately generates ADMA when those proteins are broken down. This means the methylation supply side and the clearance side of ADMA respond to different inputs. Worth stating plainly because it is easy to assume every methylation-supporting nutrient pushes the marker the same way.

Choline is oxidised to betaine, which then donates a methyl group in homocysteine remethylation. That places choline on the same route as betaine, one step earlier. The connection to ADMA runs through homocysteine and DDAH and is mechanistic rather than measured.

DDAH, the enzyme that degrades ADMA to citrulline and dimethylamine, carries an active site cysteine that is sensitive to oxidative modification. Thiol availability affects how much of the enzyme stays in its active form. N-acetylcysteine supplies cysteine for glutathione synthesis, which is the reasoning behind the pairing; the step from that to a measured ADMA change has not been shown in the papers available here.

Oxidative modification of the DDAH active site cysteine reduces its activity, and glutathione is the main intracellular buffer against that modification. This is why oxidative stress and ADMA are frequently reported together. The relationship is mechanistic and observational, not a demonstrated effect of a glutathione dose on the marker.

Dihydrolipoate regenerates other antioxidants and supports the intracellular thiol pool that keeps thiol-dependent enzymes active. DDAH is one such enzyme. The link is indirect and no candidate paper here measures the pairing.

Nitric oxide synthase needs tetrahydrobiopterin as a cofactor, and ascorbate helps keep that cofactor in its reduced form. ADMA acts on the same enzyme from the other side, competing with arginine at the substrate site. The two therefore touch NOS function by different routes; a supplementation study of L-arginine plus vitamin C in adults recovering from a viral illness reported on arginine pathway metabolites including ADMA.

A vitamin D supplementation study in ultramarathon runners reported changes in serum amino acid profiles, including methylarginine measures, around the exercise bout. What is measured is a circulating marker panel, not a performance or vascular outcome. Endurance exercise itself moves these values, so attributing a shift to the supplement alone would overstate the finding.

Long chain omega-3 fatty acids have been reported to influence endothelial function measures such as flow-mediated dilation, which is the same functional readout that ADMA is used to explain. The two connect at the level of the endothelium rather than by a shared enzyme. Flow-mediated dilation is a physiological marker, not a clinical outcome.

Garlic preparations have been reported to influence nitric oxide related endpoints in small human studies. ADMA is a competitive inhibitor of the enzyme that makes nitric oxide, so the two sit on the same pathway from different directions. The supporting work is small and the endpoints are markers.

Pine bark polyphenols have been studied for effects on endothelial nitric oxide availability. That is the same output that ADMA restricts by competing with arginine at NOS. The relationship is pathway-level and the human evidence base is small.

Taurine has been examined for effects on endothelial function markers in small trials. It does not act on ADMA metabolism directly and no shared enzyme links them. Included as a pathway-adjacent partner rather than a mechanistic one.

Arginase converts arginine to ornithine and urea, competing with nitric oxide synthase for the same substrate. ADMA restricts the NOS arm from the other side by competitive inhibition. Together they describe why the arginine to ADMA ratio, rather than either value alone, is what gets reported.

Lysine, arginine and the methylarginines all move on the y+ cationic amino acid transporter system. A large lysine load competes for that carrier. This is established transport biochemistry and it is one reason cellular arginine availability does not track plasma arginine exactly.