Proposal for risk-based scientific approach on full and partial validation for general changes in bioanalytical method

Impact of introducing a new biological matrix into a validated bioanalytical method: Focus on matrix protein content

International guidance on bioanalytical method validation recommends the practice of partial validation when introducing a new matrix from the same species into a previously fully validated assay. Planning the partial validation protocol should include an evaluation of analyte chemistry, consideration of sample container materials, and a comparison of properties between the relevant biological matrices. Transition of a serum/plasma-validated bioanalytical method to analysis from a low-protein matrix, such as urine, cerebral spinal fluid, or oral fluid can result in inconsistent analyte recovery. The low recovery can potentially be mistaken for signal suppression or lack of drug stability and may be more pronounced in low-concentration or low-volume samples. In addition, adsorption and absorption interactions with containers may be exacerbated in low-protein matrices. Several possibilities exist for mitigating the impact of non-specific binding and low-protein matrices, including surfactants, bovine serum albumin, and β-cyclodextrin. Finally, higher matrix protein can facilitate analyte stability. Given all this, matrix protein content should not be overlooked when anticipating a partial bioanalytical method validation.

Effect of Stool Sampling on a Routine Clinical Method for the Quantification of Six Short Chain Fatty Acids in Stool Using Gas Chromatography-Mass Spectrometry

Short chain fatty acids (SCFAs) are primarily produced in the caecum and proximal colon via the bacterial fermentation of undigested carbohydrates that have avoided digestion in the small intestine. Increasing evidence supports the critical role that SCFAs play in health and homeostasis. Microbial SCFAs, namely butyric acid, serve as a principal energy source for colonocytes, and their production is essential for gut integrity. A direct link between SCFAs and some human pathological conditions, such as inflammatory bowel disease, irritable bowel syndrome, diarrhea, and cancer, has been proposed. The direct measurement of SCFAs in feces provides a non-invasive approach to demonstrating connections between SCFAs, microbiota, and metabolic diseases to estimate their potential applicability as meaningful biomarkers of intestinal health. This study aimed to adapt a robust analytical method (liquid-liquid extraction, followed by isobutyl chloroformate derivatization and GC-MS analysis), with comparable performances to methods from the literature, and to use this tool to tackle the question of pre-analytical conditions, namely stool processing. We focused on the methodology of managing stool samples before the analysis (fresh stool or dilution in either ethanol/methanol, lyophilized stool, or RNAlater®), as this is a significant issue to consider for standardizing results between clinical laboratories. The objective was to standardize methods for future applications as diagnostic tools. In this paper, we propose a validated GC-MS method for SCFA quantification in stool samples, including pre- and post-analytical comparison studies that could be easily used for clinical laboratory purposes. Our results show that using lyophilization as a stool-processing method would be the best method to achieve this goal.