Cystathionine (Plasma)

Elevated blood levels of cystathionine can occur for several reasons related to vitamin status, enzyme activity, or metabolic regulation.

A deficiency in vitamin B6, vitamin B12, or folate can impair normal amino acid metabolism, leading to increased cystathionine levels.

Higher cystathionine concentrations have also been observed in certain neural tumors, kidney dysfunction, and metabolic defects affecting the conversion of homocysteine to methionine.

Because cystathionine is an intermediate in the transsulfuration pathway, its elevation often reflects a metabolic bottleneck or backup in this pathway. The conversion of cystathionine into glutathione and other downstream metabolites requires adequate levels of key cofactors, including vitamin B6, zinc, glycine, and magnesium. When these nutrients are insufficient or demand is increased, cystathionine may temporarily accumulate.

Genetic factors can also play a role. Individuals with a CBS gene variant (SNP) that increases CBS enzyme activity may show higher cystathionine due to accelerated conversion of homocysteine to cystathionine. Similarly, elevated S-adenosylmethionine (SAM) levels can stimulate the CBS enzyme, further increasing cystathionine production.

Supplementation with dimethylglycine (DMG) or trimethylglycine (betaine) can enhance the methylation cycle. When methylation functions efficiently, the transsulfuration pathway becomes more active, which can also lead to higher cystathionine levels.

In cases of vitamin B12 or folate deficiency, homocysteine often rises. The body may then divert more homocysteine into the transsulfuration pathway, leading to a secondary elevation in cystathionine.

- A cystathionine beta-synthase (CBS) deficiency can lead to a decrease in cystathionine.

- Abnormalities within the methylation cycle can result in lower levels of cystathionine. Low levels of SAM, or methylation imbalances, result in the body preferentially deferring transsulfuration to maintain methylation. Because the CBS enzyme requires vitamin B6 as a cofactor, deficiencies in vitamin B6 may result in lower cystathionine.

Cystathionine is an intermediate dipeptide within the process of transsulfuration. Transsulfuration is the main route for irreversible homocysteine disposal, glutathione production, and energy. The initial step involves the enzyme cystathionine β-synthase enzyme (CBS). This reaction requires nutrient cofactors such as vitamin B6 and iron. Cystathionine is then converted to cysteine, and eventually goes on to either make glutathione or feed the Kreb’s cycle. Currently, there is no known source or physiologic function for cystathionine other than serving as a transsulfuration intermediate. Some literature suggests that cystathionine may exert protection against endoplasmic reticulum stress-induced tissue damage and cell death, but studies are sparse.