Method to simultaneously determine the sphingosine 1-phosphate breakdown product (2E)-hexadecenal and its fatty acid derivatives using isotope-dilution HPLC-electrospray ionization-quadrupole/time-of-flight mass spectrometry

Aldehyde Dehydrogenase 2 as a Therapeutic Target in Oxidative Stress-Related Diseases: Post-Translational Modifications Deserve More Attention

Aldehyde dehydrogenase 2 (ALDH2) has both dehydrogenase and esterase activity; its dehydrogenase activity is closely related to the metabolism of aldehydes produced under oxidative stress (OS). In this review, we recapitulate the enzyme activity of ALDH2 in combination with its protein structure, summarize and show the main mechanisms of ALDH2 participating in metabolism of aldehydes in vivo as comprehensively as possible; we also integrate the key regulatory mechanisms of ALDH2 participating in a variety of physiological and pathological processes related to OS, including tissue and organ fibrosis, apoptosis, aging, and nerve injury-related diseases. On this basis, the regulatory effects and application prospects of activators, inhibitors, and protein post-translational modifications (PTMs, such as phosphorylation, acetylation, S-nitrosylation, nitration, ubiquitination, and glycosylation) on ALDH2 are discussed and prospected. Herein, we aimed to lay a foundation for further research into the mechanism of ALDH2 in oxidative stress-related disease and provide a basis for better use of the ALDH2 function in research and the clinic.

Neutron encoded derivatization of endothelial cell lysates for quantitation of aldehyde metabolites using nESI-LC-HRMS

Biological aldehydes are difficult to analyze by electrospray ionization mass spectrometry due to their poor proton affinity and low biological concentrations. Chemical derivatization with stable isotope tags is used here for sample multiplexing, increased throughput, improved signal intensity, and quantitation. Nine quaternary amine tags with mass differences as low as 0.0058 Da had no observable chromatographic shifts, small amounts of ion suppression, and minimal matrix effects. Low concentration perfluoropentanoic acid was used as an ion pairing reagent to improve the retention of derivatized aldehydes. Perfluoropentanoic acid addition showed an average of three-fold improvement in limits of detection, 50% reduction in peak width, and 2.5 fold increase in analyte retention. Analysis of fifteen tagged aldehydes yielded an average of 13 nM limit of detection, 9 %RSD, R² of 0.995, and linear dynamic range of 40-1000 nM. In a single 20 min separation, absolute quantitative data was obtained for 11 reactive aldehydes across 8 aortic endothelial cell samples. High glucose treatment produced significant changes to malondialdehyde, decanal, and (2E)-hexadecenal. These changes are consistent with glucose-induced oxidative stress. This method demonstrates that neutron encoded tagging of aldehydes is suitable for the analysis of complex samples.

S1P and plasmalogen derived fatty aldehydes in cellular signaling and functions

Long-chain fatty aldehydes are present in low concentrations in mammalian cells and serve as intermediates in the interconversion between fatty acids and fatty alcohols. The long-chain fatty aldehydes are generated by enzymatic hydrolysis of 1-alkyl-, and 1-alkenyl-glycerophospholipids by alkylglycerol monooxygenase, plasmalogenase or lysoplasmalogenase while hydrolysis of sphingosine-1-phosphate (S1P) by S1P lyase generates trans ∆2-hexadecenal (∆2-HDE). Additionally, 2-chloro-, and 2-bromo- fatty aldehydes are produced from plasmalogens or lysoplasmalogens by hypochlorous, and hypobromous acid generated by activated neutrophils and eosinophils, respectively while 2-iodofatty aldehydes are produced by excess iodine in thyroid glands. The 2-halofatty aldehydes and ∆2-HDE activated JNK signaling, BAX, cytoskeletal reorganization and apoptosis in mammalian cells. Further, 2-chloro- and 2-bromo-fatty aldehydes formed GSH and protein adducts while ∆2-HDE formed adducts with GSH, deoxyguanosine in DNA and proteins such as HDAC1 in vitro. ∆2-HDE also modulated HDAC activity and stimulated H3 and H4 histone acetylation in vitro with lung epithelial cell nuclear preparations. The α-halo fatty aldehydes elicited endothelial dysfunction, cellular toxicity and tissue damage. Taken together, these investigations suggest a new role for long-chain fatty aldehydes as signaling lipids, ability to form adducts with GSH, proteins such as HDACs and regulate cellular functions.

The first fluorogenic sensor for sphingosine-1-phosphate lyase activity in intact cells

New fluorogenic sensors with suitable kinetic parameters and sensitivity have been developed for the determination of sphingosine-1-phosphate lyase activity in cell lysates. The probe RBM148 can be efficiently loaded into cationic liposomes and used to determine S1PL activity in intact cells.

Divergent Role of Sphingosine 1-Phosphate in Liver Health and Disease

Two decades ago, sphingosine 1-phosphate (S1P) was discovered as a novel bioactive molecule that regulates a variety of cellular functions. The plethora of S1P-mediated effects is due to the fact that the sphingolipid not only modulates intracellular functions but also acts as a ligand of G protein-coupled receptors after secretion into the extracellular environment. In the plasma, S1P is found in high concentrations, modulating immune cell trafficking and vascular endothelial integrity. The liver is engaged in modulating the plasma S1P content, as it produces apolipoprotein M, which is a chaperone for the S1P transport. Moreover, the liver plays a substantial role in glucose and lipid homeostasis. A dysfunction of glucose and lipid metabolism is connected with the development of liver diseases such as hepatic insulin resistance, non-alcoholic fatty liver disease, or liver fibrosis. Recent studies indicate that S1P is involved in liver pathophysiology and contributes to the development of liver diseases. In this review, the current state of knowledge about S1P and its signaling in the liver is summarized with a specific focus on the dysregulation of S1P signaling in obesity-mediated liver diseases. Thus, the modulation of S1P signaling can be considered as a potential therapeutic target for the treatment of hepatic diseases.

The sphingosine 1-phosphate breakdown product, (2E)-hexadecenal, forms protein adducts and glutathione conjugates in vitro

Sphingosine 1-phosphate (S1P), a bioactive lipid involved in various physiological processes such as cell proliferation and apoptosis, can be irreversibly cleaved by S1P lyase, yielding phosphoethanolamine and (2E)-hexadecenal (2EHD). The latter metabolite, an α,β-unsaturated fatty aldehyde, may be susceptible to nucleophilic attack by cellular biomolecules. Hence, we studied whether 2EHD forms reaction products with GSH and proteins in vitro. Using LC-MS/MS and stable isotopically labeled reference material, we identified a total of nine novel reaction products of 2EHD in a cell-free approach: two GSH conjugates and seven l-amino acid adducts. Both GSH conjugates were also found in HepG2 cell lysates incubated with 2EHD. Likewise, we detected four out of seven amino acid adducts released from the model protein, BSA, and proteins extracted from HepG2 cells. On this occasion, the 2EHD Michael adduct with l-histidine proved to be the most prominent adduct. Most interestingly, inhibition of the enzymatically driven oxidative degradation of 2EHD resulted in increased levels of both GSH conjugates and protein adducts in HepG2 cell lysates. Hence, our data provide new insights into sphingolipid metabolism and will be useful to investigate certain disorders linked to an impaired fatty aldehyde metabolism in more detail.

Disruption of the Sjögren-Larsson Syndrome Gene Aldh3a2 in Mice Increases Keratinocyte Growth and Retards Skin Barrier Recovery

The fatty aldehyde dehydrogenase (FALDH) ALDH3A2 is the causative gene of Sjögren Larsson syndrome (SLS). To date, the molecular mechanism underlying the symptoms characterizing SLS has been poorly understood. Using Aldh3a2(-/-) mice, we found here that Aldh3a2 was the major FALDH active in undifferentiated keratinocytes. Long-chain base metabolism was greatly impaired in Aldh3a2(-/-) keratinocytes. Phenotypically, the intercellular spaces were widened in the basal layer of the Aldh3a2(-/-) epidermis due to hyperproliferation of keratinocytes. Furthermore, oxidative stress-induced genes were up-regulated in Aldh3a2(-/-) keratinocytes. Upon keratinocyte differentiation, the activity of another FALDH, Aldh3b2, surpassed that of Aldh3a2 As a result, Aldh3a2(-/-) mice were indistinguishable from wild-type mice in terms of their whole epidermis FALDH activity, and their skin barrier function was uncompromised under normal conditions. However, perturbation of the stratum corneum caused increased transepidermal water loss and delayed barrier recovery in Aldh3a2(-/-) mice. In conclusion, Aldh3a2(-/-) mice replicated some aspects of SLS symptoms, especially at the basal layer of the epidermis. Our results suggest that hyperproliferation of keratinocytes via oxidative stress responses may partly contribute to the ichthyosis symptoms of SLS.

Derivatization methods for LC–MS analysis of endogenous compounds

Sensitive and reliable analysis of endogenous compounds is critically important for many physiological and pathological studies. Methods based on LC–MS have progressed to become the method of choice for analyzing endogenous compounds. However, the analysis can be challenging due to various factors, including inherent low concentrations in biological samples, low ionization efficiency, undesirable chromatographic behavior and interferences of complex biological. The integration of chemical derivatization with LC–MS could enhance its capabilities in sensitivity and selectivity, and extend its application to a wider range of analytes. In this article, we will review the derivatization strategies in the LC–MS analysis of various endogenous compounds, and provide applications highlighting the impact of these important techniques in the evaluation of pathological events.