Contamination of tissue samples with blood is hardly avoidable. The possibilities for replicate sampling and tissue washing are limited when working with resected specimens of human origin. However, its impact on metabolic profiling has rarely been addressed. In this study, we performed elemental analysis and metabolic profiling focusing on 108 hydrophilic target metabolites in 61 meningioma tissue samples obtained from a non-stratified cohort of 36 patients during neurosurgery. We used iron as an easily accessible proxy for blood. The samples were frequently and non-homogenously contaminated with blood, with iron concentrations ranging from 5 to > 160 µg/g fresh weight. Ten metabolites were significantly altered with their concentrations more than halved or more than doubled when comparing samples with low and high degrees of blood contamination. By contrast, blood contamination did not dominate the apparent metabolic heterogeneity between the samples during PCA analysis based on the metabolites targeted in this study and in the context of a heterogeneous patient cohort and non-standardized sampling. However, studies targeting the reported vulnerable metabolites should critically reflect blood contamination as a biasing factor. Moreover, we report estimated concentrations of 74 hydrophilic metabolites to give tissue-specific orientation for future quantification studies.
Fitz et al. (Wed,) studied this question.