Aspartate aminotransferase and cardiovascular disease—a narrative review

This narrative review summarized the existing knowledge on the association between aspartate aminotransferase (AST) and cardiovascular disease (CVD). AST plays a key role in the metabolism of amino acids, maintenance of NAD+/NADH ratio in cells, Krebs cycle activity, synthesis of purine/pyrimidine bases, urea and protein synthesis and gluconeogenesis. In humans, AST exists as two genetically and immunologically distinct isoenzymes: cytoplasmic AST and mitochondrial AST and both forms are found in circulation. AST activity is widely distributed across human tissues with the highest activity found in heart, liver, skeletal muscle, kidney and brain. An elevated AST activity may reflect tissue damage (plasma membrane disruption or apoptosis), plasma membrane bleb formation, increased tissue expression and macroenzymes (complexes of AST with plasma proteins). Serum AST activity is increased in patients with acute myocardial infarction in proportion with the extent of myocardial necrosis. Epidemiological evidence suggests the existence of an association between AST activity and CVD or mortality with positive, inverse or U (or J)-shaped association patterns. An elevated AST level not occurring in the setting of inflammatory liver disease may signify an increased cardiovascular risk related to nonalcoholic fatty liver disease (NAFLD), cardiometabolic risk factors (metabolic syndrome, abdominal obesity, insulin resistance and diabetes), chronic alcoholism and structural heart disease (myocardial infarction or congestive heart failure). A positive association between AST and CVD is more common in epidemiological studies in Asian population. Low AST levels may reflect increased cardiovascular risk related to vitamin B6 deficiency, advanced chronic kidney or liver diseases and inflammatory diseases. High and low AST levels have clinical meaning and both of them should be analyzed.