Histamine Quantification in Human Blood Sample

Abstract

Histamine is a short-acting biogenic amine that elicits pleiotropic actions mainly through binding to four receptor types designated as H1–H4. Since its discovery more than a century ago, it has been one of the most studied molecules in biomedical sciences and has provided blockbuster therapeutic drugs for the management of allergies, gastric ulcers, and more recently for narcolepsy. The discovery of the high affinity H4 receptor at the turn of the millennium revived the interest in histamine research and translational potential, particularly in the expanding field of immunopharmacology. Among the various methods developed for the quantification of histamine in human whole blood, plasma, and serum, the fluorometric assay that was developed more than 65 years ago still remains popular in biomedical and clinical protocols. The common basis of the several available modifications is the reaction of the extracted histamine with ophthalaldehyde (o-PΤ) in an alkaline environment to produce fluorescent condensation derivatives. These are stabilized by acidification commonly 4 min after the addition of o-PΤ and measured using a fluorospectrophotometer at excitation and emission wavelengths of 360 and 450 nm, respectively. The histamine concentration in the unknown sample is read off a standard curve. A number of factors that may potentially influence the level of circulating histamine should be considered when designing the investigation or evaluating the outcome, including patient information and medical history, as well as blood sampling, handling, and storage conditions.