Monitoring Lactate in Biological Samples

Background- The concentration lactate, a byproduct of glycolysis, is a reliable biochemical indicator of anaerobic metabolism. In eukaryotes, L-Lactate is formed
from pyruvate in the cytosol in a reversible reaction catalyzed by the enzyme lactate dehydrogenase, which is often termed reaction-11 of glycolysis or anaerobic
glycolysis. If the amount of oxygen is limiting, as occurs in muscle during intense activity, much of the pyruvate is reduced to lactate. This reaction catalyzed by
L-lactate dehydrogenase regenerates NAD+ thereby allowing continued glycolysis with the continued production of ATP. This also occurs in a variety of
microorganisms which ferment glucose. For example yogurt is prepared by growing lactate-producing bacteria in skim milk; as the concentration of acid increases,
casein is denatured and coagulates.

Cultured cells produce increased levels of lactate in response to hypoxic conditions. Lactate synthesis occurs in the presence of a rapid increase in metabolic rate
or when oxygen delivery to the mitochondria declines. When the blood flow is decreased in patients, oxygen delivery is no longer adequate to maintain aerobic
glucose metabolism, thus creating an oxygen debt, which may lead to hyperlactemia (2-5 mM blood lactate) or lactic acidosis (>5 mM blood lactate). The normal
blood lactate concentration in healthy, unstressed individuals is approximately 1 mM. Patients who develop severe septic shock usually exhibit hyperlactemia and
lactic acidosis.

Lactate producers are skeletal muscle (white fiber), the gut, the brain, and mature red blood cells whereas lactate metabolizers are the liver, the kidneys, and the
heart. The amount of lactate produced is generally thought to correlate with the body oxygen debt, the degree of tissue hypoperfusion, and the severity of shock
(clinical syndrome resulting from an imbalance between tissue oxygen demand and supply). At the molecular and cellular levels, increased lactate production may
be caused by activation of glycolysis, inhibition of pyruvate dehydrogenase activity, inborn errors of metabolism, or defects in the electron transport chain.

In the past, lactate assays were difficult and tedious to perform. Although newer lactate autoanalyzers using electrochemical methods can rapidly measure lactate
concentration within minutes, the machines are not designed for research purpose and are not readily available. The Lactate Assay Kit developed by us is based on
the reduction of the tetrazolium salt INT in a NADH-coupled enzymatic reaction to formazan, which is water-soluble and exhibits an absorption maximum at 492 nm.
Since the intensity of the red color formed is proportional to the lactate concentration, the assay, using a set of lactate standards, can measure the concentration of
lactate released to the culture medium or circulation in a semi-quantitative manner. The kit can be directly used with culture medium, serum, plasma, and urine
samples. The assay time required is 30 min. In addition to the measurement of L-lactate, we also offer a
D-lactate assay kit.
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