Serum carnosinase activity in plasma and serum: validation of a method and values in cardiopulmonary bypass surgery.

Abstract

Serum carnosinase (EC 3.4.13.20) is synthesized in the brain, where it is secreted into cerebrospinal fluid and then into the systemic circulation. Its deficiency has been associated with neurologic deficits (1)(2), and decreased concentrations have been observed in patients with Parkinson disease or multiple sclerosis and in patients after a cerebrovascular accident (3). It has also been suggested that measurement of serum carnosinase together with neuron-specific enolase, or their ratio, may be useful in the assessment of patients with acute stroke with respect to diagnosis and prediction of clinical outcome (4). Carnosinase exists in two isoforms (5). Tissue carnosinase is found in the liver, kidney, and spleen, and serum carnosinase is found in serum (plasma), as well as in the brain and spinal fluid (6). These enzymes result from different gene products and differ not only in their distribution but also in their enzymatic properties (7)(8)(9). Specifically, although under appropriate conditions both isoforms catalyze the hydrolysis of the dipeptide carnosine (β-alanyl-l-histidine), only serum carnosinase is able to hydrolyze homocarnosine (γ-aminobutyryl-l-histidine) (2)(9)(10). It is believed that carnosine and homocarnosine have the ability to protect neuronal cells against ischemic injury (11) and oxidative stress (12)(13) as well as to increase their resistance toward functional exhaustion and accumulation of senile features (14). Ischemic-reperfusion injury is a major adverse event that causes morbidity and mortality after cardiac surgery, especially when extracorporeal circuits are used. Cerebral damage has been correlated to this type of injury and leads to a decrease in neurocognitive function (15). Currently, the possible relationships between cerebral damage, neurocognitive function, carnosine and homocarnosine concentrations, and serum carnosinase activity during (open) heart surgery are not well understood. Several methods have been described to determine …