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Inada and Ido identified Leptospira sp. as the pathogen responsible for Weil's Disease in 1915. Later, it was confirmed that Leptospira causes leptospirosis. The host microorganism's interaction at the cellular level remained misunderstood for many years. Although different bacterial components have been isolated and purified, the complexity of the molecular interactions between these components and the host and the molecular mechanisms responsible for the systemic dysfunctions still needs to be fully unveiled. Leptospirosis affects virtually all animal species. Its cellular pathophysiology must involve a ubiquitous cellular mechanism in all eukaryotes. Na/K-ATPase is the molecular target of the leptospiral endotoxin (glycolipoprotein-GLP). Na/K-ATPase dysfunctions on different types of cells give rise to the organ disorders manifested in leptospirosis. Concomitantly, the development of a peculiar metabolic disorder characterized by dyslipidemia, with increased levels of circulating free fatty acids and an imbalance in the fatty acid/albumin molar ratio, triggers events of cellular lipotoxicity. Synergistically, multiple molecular stimuli are prompted during the infection, activating inflammasomes and Na/K-ATPase signalosome, leading to pro-inflammatory and metabolic alterations during leptospirosis. Leptospirosis involves diverse molecular mechanisms and alteration in patient inflammatory and metabolic status. Nonetheless, Na/K-ATPase is critical in the disease, and it is targeted by GLP, its components, and other molecules, such as fatty acids, that inhibit or trigger intracellular signaling through this enzyme. Herein, we overview the role of Na/K-ATPase during leptospirosis infection as a potential therapeutic target or an indicator of disease severity.

Circulating non-esterified fatty acids (NEFA) are toxic to mammalian cells. They increase in diseases such as diabetes and sepsis. Herein we propose a serum albumin-fatty acid saturation test. •We based our test on three methodologies: isoelectric focusing (IF) of human plasma albumin, staining proteins after isoelectric focusing in gels with Coomassie Brilliant Blue, and serum albumin measurement with bromocresol green.•The test consists in the determination of albumin IF and staining with bromocresol green. If albumin is saturated with NEFA, it focuses on lower pH, meaning it is the threshold to bind to them. Excessive NEFA is free and toxic. Many other tests are available for NEFA quantification as NEFA kit assay. All colorimetric assays are used for quantification of NEFA and other tests need expensive equipment to read out the results, and they do not measure albumin levels.•Our method focused on albumin-NEFA saturation instead of just NEFA quantification. Critically ill patients have an alteration in both albumin and NEFA. Therefore, our test undergoes less daytime variation compared to assays that measure absolute NEFA values, allowing a more reliable use as an indicator of albumin-fatty acid saturation and NEFA toxicity.

Fatty acids are fundamental as energy and structural source to the human cells. They are not usually found free in human circulation. Alteration in fatty acids metabolism is linked to diseases such as diabetes, preeclampsia, heart disease, and some infectious diseases. Increased levels of non-esterified fatty acids (NEFA) may cause cell dysfunction and lipotoxicity. Since physiologically fatty acids are transported bound to albumin, we propose here a simple and cheap test that consists of albumin isoelectric focusing determination to measure the potential systemic NEFA cytotoxicity. For validation of this method, albumin isoelectric focusing in 51 serum samples from 40 critically ill patients and 11 controls was compared with NEFA/albumin ratios measured by HPLC. We called this approach an albumin saturation test. This test may indicate to physicians the potential NEFA lipotoxicity guiding them throughout better patient management. The albumin saturation test can point out serum albumin-NEFA saturation through a cheap assay that could be performed by any care facility., (Copyright © 2019 Elsevier B.V. All rights reserved.)