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Congenital adrenal hyperplasia (CAH) is the most common form of adrenal insufficiency in childhood; it requires cortisol replacement therapy with hydrocortisone (HC, synthetic cortisol) from birth and therapy monitoring for successful treatment. In children, the less invasive dried blood spot (DBS) sampling with whole blood including red blood cells (RBCs) provides an advantageous alternative to plasma sampling. Potential differences in binding/association processes between plasma and DBS however need to be considered to correctly interpret DBS measurements for therapy monitoring. While capillary DBS samples would be used in clinical practice, venous cortisol DBS samples from children with adrenal insufficiency were analyzed due to data availability and to directly compare and thus understand potential differences between venous DBS and plasma. A previously published HC plasma pharmacokinetic (PK) model was extended by leveraging these DBS concentrations. In addition to previously characterized binding of cortisol to albumin (linear process) and corticosteroid-binding globulin (CBG; saturable process), DBS data enabled the characterization of a linear cortisol association with RBCs, and thereby providing a quantitative link between DBS and plasma cortisol concentrations. The ratio between the observed cortisol plasma and DBS concentrations varies highly from 2 to 8. Deterministic simulations of the different cortisol binding/association fractions demonstrated that with higher blood cortisol concentrations, saturation of cortisol binding to CBG was observed, leading to an increase in all other cortisol binding fractions. In conclusion, a mathematical PK model was developed which links DBS measurements to plasma exposure and thus allows for quantitative interpretation of measurements of DBS samples.

Skeletal muscle function is inferred from the spatial arrangement of myofiber architecture and the molecular and metabolic features of myofibers. Features of myofiber types can be distinguished by the expression of myosin heavy chain (MyHC) isoforms, indicating contraction properties. In most studies, a local sampling, typically obtained from the median part of the muscle, is used to represent the whole muscle. It remains largely unknown to what extent this local sampling represents the entire muscle. Here we studied myofiber architecture over the entire wild type mouse tibialis anterior muscle, using a high-throughput procedure combining automatic imaging and image processing analyses. We reconstructed myofiber architecture from consecutive cross-sections stained for laminin and MyHC isoforms. The data showed a marked variation in myofiber geometric features, as well as MyHC expression and the distribution of neuromuscular junctions, and suggest that muscle regions with distinct properties can be defined along the entire muscle. We show that in these muscle regions myofiber geometric properties align with biological function and propose that future studies on muscle alterations in pathological or physiological conditions should consider the entire muscle.