The generic term “melanin“ describes a black pigment of biological origin, although some melanins can be brown or even yellow. The pigment is characterized as a heterogenic polymer of phenolic or indolic nature, and the classification of eu-, pheo- and allo- melanin is broadly accepted. This classification is based on the chemical composition of the monomer subunit structure of the pigment. Due to the high heterogeneity of melanins, their analytical characterization can be a challenging task. In the present work, we synthesized the current information about the analytical methods which can be applied in melanin analysis workflow, from extraction and purification to high-throughput methods, such as matrix-assisted laser desorption/ionization mass-spectrometry or pyrolysis gas chromatography. Our thorough comparative evaluation of analytical data published so far on melanin analysis has proven to be a difficult task in terms of finding equivalent results, even when the same matrix was used. Moreover, we emphasize the importance of prior knowledge of melanin types and properties in order to select a valid experimental design using analytical methods that are able to deliver reliable results and draw consistent conclusions.

Lab-on-a-chip (LOC) and organ-on-a-chip (OOC) devices are highly versatile platforms that enable miniaturization and advanced controlled laboratory functions (i.e., microfluidics, advanced optical or electrical recordings, high-throughput screening). The manufacturing advancements of LOCs/OOCs for biomedical applications and their current limitations are briefly discussed. Multiple studies have exploited the advantages of mimicking organs or tissues on a chip. Among these, we focused our attention on the brain-on-a-chip, blood–brain barrier (BBB)-on-a-chip, and neurovascular unit (NVU)-on-a-chip applications. Mainly, we review the latest developments of brain-on-a-chip, BBB-on-a-chip, and NVU-on-a-chip devices and their use as testing platforms for high-throughput pharmacological screening. In particular, we analyze the most important contributions of these studies in the field of neurodegenerative diseases and their relevance in translational personalized medicine.

In ischemic or hypoxic tissues, elevated Ca²⁺levels have emerged as one of the main damaging agents among other Ca²⁺-independent mechanisms of cellular injury. Because mitochondria, besides the endoplasmic reticulum, play a key role in the maintainance of cellular Ca²⁺homeostasis, alterations in the mitochondrial Ca²⁺content ([Ca²⁺]_m) were monitored in addition to changes in cytosolic Ca²⁺concentration ([Ca²⁺]_i) during metabolic inhibition (MI) in renal epithelial Madin-Darby canine kidney (MDCK) cells. [Ca²⁺]_iand [Ca²⁺]_mwere monitored via, respectively, fura 2 and rhod 2 measurements. MI induced an increase in [Ca²⁺]_ireaching 631 ± 78 nM in ∼20 min, followed by a decrease to 118 ± 9 nM in the next ∼25 min. A pronounced drop in cellular ATP levels and a rapid increase in intracellular Na⁺concentrations in the first 20 min of MI excluded Ca²⁺efflux in the second phase via plasma membrane ATPases or Na⁺/Ca²⁺exchangers (NCE). Mitochondrial rhod 2 intensities increased to 434 ± 46% of the control value during MI, indicating that mitochondria sequester Ca²⁺during MI. The mitochondrial potential (ΔΨ_m) was lost in 20 min of MI, excluding mitochondrial Ca²⁺uptake via the ΔΨ_m-dependent mitochondrial Ca²⁺uniporter after 20 min of MI. Under Na⁺-free conditions, or when CGP-37157, a specific inhibitor of the mitochondrial NCE, was used, no drop in [Ca²⁺]_iwas seen during MI, whereas the MI-induced increase in mitochondrial rhod 2 fluorescence was strongly reduced. To our knowledge, this study is the first to report that in metabolically inhibited renal epithelial cells mitochondria take up Ca²⁺via the NCE acting in the reverse mode.