Identification of trans,trans-2,4-decadienal metabolites in mouse and human cells using liquid chromatography-mass spectrometry

Impaired Detoxification of Trans, Trans-2,4-Decadienal, an Oxidation Product from Omega-6 Fatty Acids, Alters Insulin Signaling, Gluconeogenesis and Promotes Microvascular Disease

Omega-6 fatty acids are the primary polyunsaturated fatty acids in most Western diets, while their role in diabetes remains controversial. Exposure of omega-6 fatty acids to an oxidative environment results in the generation of a highly reactive carbonyl species known as trans, trans-2,4-decadienal (tt-DDE). The timely and efficient detoxification of this metabolite, which has actions comparable to other reactive carbonyl species, such as 4-hydroxynonenal, acrolein, acetaldehyde, and methylglyoxal, is essential for disease prevention. However, the detoxification mechanism for tt-DDE remains elusive. In this study, the enzyme Aldh9a1b is identified as having a key role in the detoxification of tt-DDE. Loss of Aldh9a1b increased tt-DDE levels and resulted in an abnormal retinal vasculature and glucose intolerance in aldh9a1b-/- zebrafish. Transcriptomic and metabolomic analyses revealed that tt-DDE and aldh9a1b deficiency in larval and adult zebrafish induced insulin resistance and impaired glucose homeostasis. Moreover, alterations in hyaloid vasculature is induced by aldh9a1b knockout or by tt-DDE treatment can be rescued by the insulin receptor sensitizers metformin and rosiglitazone. Collectively, these results demonstrated that tt-DDE is the substrate of Aldh9a1b which causes microvascular damage and impaired glucose metabolism through insulin resistance.

Rapid identification and monitoring of cooking oil fume-based toxic volatile organic aldehydes in lung tissue for predicting exposure level and cancer risks

Cooking oil fumes (COFs) comprised of a mixture of cancer-causing volatile organic aldehydes (VOAs), particularly trans, trans-2,4-decadienal (t,t-DDE), 4-hydroxy-hexenal (4-HHE), and 4-hydroxy-nonenal (4-HNE). Monitoring toxic VOAs levels in people exposed to different cooking conditions is vital to predicting the cancer risk. For this purpose, we developed a fast tissue extraction (FaTEx) technique combined with UHPLC-MS/MS to monitor three toxic VOAs in mice lung tissue samples. FaTEx pre-treatment protocol was developed by combining two syringes for extraction and clean-up process. The various procedural steps affecting the FaTEx sample pre-treatment process were optimized to enhance the target VOAs' extraction efficiency from the sample matrix. Under the optimal experimental conditions, results exhibit good correlation coefficient values > 0.99, detection limits were between 0.5-3 ng/g, quantification limits were between 1-10 ng/g, and the matrix effect was <18.1%. Furthermore, the extraction recovery values of the spiked tissue exhibited between 88.9-109.6% with <8.6% of RSD. Cooking oil fume (containing t,t-DDE) treated mice at various time durations were sacrificed to validate the developed technique, and it was found that t,t-DDE concentrations were from 14.8 to 33.8 μg/g. The obtained results were found to be a fast, reliable, and semi-automated sample pre-treatment technique with good extraction efficiency, trace level detection limit, and less matrix effect. Therefore, this method can be applied as a potential analytical method to determine the VOAs in humans exposed to long-term cooking oil fumes.

Theaphenon E prevents fatty liver disease and increases CD4+ T cell survival in mice fed a high-fat diet

BACKGROUND & AIMS

Obesity is a major cause of non-alcoholic fatty liver disease (NAFLD). NAFLD is an epidemic affecting nearly 34% of the adult population in the US. As a chronic inflammatory disease, NAFLD influences the immune system by dysregulating T-cell activity. Remedies for the adverse effects on the immune system are urgently needed. We studied Theaphenon E (TE), a standardized formulation of green tea extract, on the adverse effects of NAFLD in C57BL/6J mice fed a high fat diet (HFD).

METHODS

Mice received HFD, low fat diet (LFD) or HFD+2% TE for 35 weeks. Hepatic lipid accumulation, cell proliferation, apoptosis and CD4+T lymphocytes were measured throughout the bioassay. The hepatic composition of fatty acids was determined. The effects of epigallocatechin gallate (EGCG) metabolites on lipid accumulation in mouse and primary human liver cells were studied.

RESULTS

Unlike mice receiving HFD, mice on HFD+2% TE maintained normal liver to body weight ratios with low levels of alanine and aspartate aminotransferase (ALT and AST). Hepatic lipid accumulation was observed in HFD mice, accompanied by increased proliferation, reduced apoptosis and loss of CD4+ T lymphocytes. TE significantly inhibited lipid accumulation, decreased proliferation, induced apoptosis and increased CD4+ T cell survival in HFD mice. It was found that the EGCG metabolite EGC-M3 reduced lipid accumulation in mouse and human hepatocytes. Linoleic acid showed the largest increase (2.5-fold) in livers of mice on a HFD and this increase was significantly suppressed by TE.

CONCLUSIONS

Livers of HFD-fed mice showed lipid accumulation, increased proliferation, reduced apoptosis, elevated linoleic acid and loss of CD4+ T cells. TE effectively ameliorated all of these adverse effects.

Monoclonal Antibodies for the Detection of a Specific Cyclic DNA Adduct Derived from ω-6 Polyunsaturated Fatty Acids

Lipid peroxidation of polyunsaturated fatty acids (PUFAs) is an endogenous source of α,β-unsaturated aldehydes that react with DNA producing a variety of cyclic adducts. The mutagenic cyclic adducts, specifically those derived from oxidation of ω-6 PUFAs, may contribute to the cancer promoting activities associated with ω-6 PUFAs. ( E)-4-Hydroxy-2-nonenal (HNE) is a unique product of ω-6 PUFAs oxidation. HNE reacts with deoxyguanosine (dG) yielding mutagenic 1, N²-propanodeoxyguanosine adducts (HNE-dG). Earlier studies showed HNE can also be oxidized to its epoxide (EH), and EH can react with deoxyadenosine (dA) forming the well-studied εdA and the substituted etheno adducts. Using a liquid chromatography-based tandem mass spectroscopic (LC-MS/MS) method, we previously reported the detection of EH-derived 7-(1',2'-dihydroxyheptyl)-1, N⁶-ethenodeoxyadenosine (DHHεdA) as a novel endogenous background adduct in DNA from rodent and human tissues. The formation, repair, and mutagenicity of DHHεdA and its biological consequences in cells have not been investigated. To understand the roles of DHHεdA in carcinogenesis, it is important to develop an immuno-based assay to detect DHHεdA in cells and tissues. In this study we describe the development of monoclonal antibodies specifically against DHHεdA and its application to detect DHHεdA in human cells.

Chemistry and analysis of HNE and other prominent carbonyl-containing lipid oxidation compounds

The process of lipid oxidation generates a diverse array of small aldehydes and carbonyl-containing compounds, which may occur in free form or esterified within phospholipids and cholesterol esters. These aldehydes mostly result from fragmentation of fatty acyl chains following radical oxidation, and the products can be subdivided into alkanals, alkenals (usually α,β-unsaturated), γ-substituted alkenals and bis-aldehydes. Isolevuglandins are non-fragmented di-carbonyl compounds derived from H₂-isoprostanes, and oxidation of the ω-3-fatty acid docosahexenoic acid yield analogous 22 carbon neuroketals. Non-radical oxidation by hypochlorous acid can generate α-chlorofatty aldehydes from plasmenyl phospholipids. Most of these compounds are reactive and have generally been considered as toxic products of a deleterious process. The reactivity is especially high for the α,β-unsaturated alkenals, such as acrolein and crotonaldehyde, and for γ-substituted alkenals, of which 4-hydroxy-2-nonenal and 4-oxo-2-nonenal are best known. Nevertheless, in recent years several previously neglected aldehydes have been investigated and also found to have significant reactivity and biological effects; notable examples are 4-hydroxy-2-hexenal and 4-hydroxy-dodecadienal. This has led to substantial interest in the biological effects of all of these lipid oxidation products and their roles in disease, including proposals that HNE is a second messenger or signalling molecule. However, it is becoming clear that many of the effects elicited by these compounds relate to their propensity for forming adducts with nucleophilic groups on proteins, DNA and specific phospholipids. This emphasizes the need for good analytical methods, not just for free lipid oxidation products but also for the resulting adducts with biomolecules. The most informative methods are those utilizing HPLC separations and mass spectrometry, although analysis of the wide variety of possible adducts is very challenging. Nevertheless, evidence for the occurrence of lipid-derived aldehyde adducts in biological and clinical samples is building, and offers an exciting area of future research.

Diunsaturated Aldehyde, trans,trans-2,4-Decadienal in the Intestinal Lumen Suppresses Gastric Emptying through Serotonin Signaling in Rats

We recently demonstrated that a diunsaturated aldehyde, trans,trans-2,4-decadienal (2,4-decadienal), potently stimulated secretion of cholecystokinin in the enteroendocrine cell line. Gut hormones such as cholecystokinin and serotonin play critical roles in reducing postprandial gastric emptying. In the present study, we first demonstrated that oral administration of 2,4-decadienal (50-100 mg/kg) reduced gastric emptying rate in rats, assessed by both the acetaminophen absorption test and the phenol red recovery method. In contrast, saturated aldehyde, alcohol, and fatty acids having the same chain length as 2,4-decadienal did not affect the gastric emptying rate. Duodenal administration of 2,4-decadienal potently reduced gastric emptying rate, but intraperitoneal administration did not. Furthermore, the gastric inhibitory effect of 2,4-decadienal was attenuated by treatment with a serotonin receptor antagonist. These results demonstrated that 2,4-decadienal in the small intestinal lumen has a potent inhibitory effect on gastric emptying, possibly through stimulation of the serotonin-producing enteroendocrine cells.