Systematic study of long-term stability of 3,4-dihydroxyphenylglycol in plasma for subsequent determination with liquid chromatography

LC–MS/MS method for quantification of 3,4-dihydroxyphenylglycol, a norepinephrine metabolite in plasma and brain regions

Aim: To evaluate suitability of the LC–MS/MS method to quantify 3,4-dihydroxyphenylglycol (DHPG) that is used as a biomarker for monoamine oxidase (MAO) inhibition. Methods: DHPG was extracted using alumina basic cartridges and quantified on a triple quadrupole mass spectrometer using negative electrospray ionization, without the use of derivatization reagents. Results: Modulation of DHPG levels was observed following administration of selective and nonselective MAO inhibitors and results were in correlation with historical MAO inhibition potential of compounds. Conclusion: The proposed method is sensitive enough to measure plasma DHPG levels and DHPG can be used as a biomarker to assess MAO inhibition potential of new therapeutic agents.

Circulating epinephrine is not required for chronic stress to enhance metastasis

Signaling through β-adrenergic receptors drives cancer progression and β-blockers are being evaluated as a novel therapeutic strategy to prevent metastasis. Orthotopic mouse models of breast cancer show that β-adrenergic signaling induced by chronic stress accelerates metastasis, and that β₂-adrenergic receptors on tumor cells are critical for this. Endogenous catecholamines are released during chronic stress: norepinephrine from the adrenal medulla and sympathetic nerves, and epinephrine from the adrenal medulla. β₂-adrenergic receptors are much more sensitive to epinephrine than to norepinephrine. To determine if epinephrine is necessary in the effects of stress on cancer progression, we used a denervation strategy to eliminate circulating epinephrine, and quantified the effect on metastasis. Using both human xenograft and immune-intact murine models of breast cancer, we show that circulating epinephrine is dispensable for the effects of chronic stress on cancer progression. Measured levels of circulating norepinephrine were sufficiently low that they were unlikely to influence β₂-adrenergic signaling, suggesting a possible role for norepinephrine release from sympathetic nerve terminals.

Factors affecting the stability of drugs and drug metabolites in biological matrices

Evaluation of the stability of drugs and drug metabolites in a biological matrix is a critical element to bioanalytical method validation. It is critical to understand the most common factors that affect the stability of such analytes in order to properly develop methods for their detection and measurement. The degradation of drugs and drug metabolites in samples can occur through either reversible or irreversible processes. Common factors that affect this stability include temperature, light, pH, oxidation and enzymatic degradation. Special considerations are also required when dealing with chiral molecules, deuterated internal standards and large biomolecules. Relevant examples of these degradation effects and approaches for dealing with them are presented is this review as taken from the fields of pharmaceutical testing, clinical research and forensic analysis. It is demonstrated through these examples how an understanding of the chemical and physical factors that affect sample stability can be used to avoid stability problems and to create robust and accurate methods for the analysis of drugs and related compounds.

Stabilizing Drug Molecules in Biological Samples

Stability is one of the basic parameters, along with accuracy, precision, selectivity, and sensitivity, for bioanalytic method validation in nonhuman and clinical pharmacology/toxicology, bioavailability (BA), bioequivalence (BE), and other studies related to the drug approval process. In the drug development stage where stability evaluation is obligatory, instability of drug candidates in biologic samples will seriously complicate assay validation. In this article, we review the general strategies and methodologies such as temperature adjustment, pH control, derivatization, and addition of inhibitors and oxidant that are commonly employed to stabilize pharmaceuticals that might be unstable in biologic samples.