Malondialdehyde and 4-hydroxy-2-hexenal are formed during dynamic gastrointestinal in vitro digestion of cod liver oils

Dual role of transient receptor potential ankyrin 1 in respiratory and gastrointestinal physiology: From molecular mechanisms to therapeutic targets

The transient receptor potential ankyrin 1 (TRPA1) channel plays a pivotal role in the respiratory and gastrointestinal tracts. Within the respiratory system, TRPA1 exhibits diverse distribution patterns across key cell types, including epithelial cells, sensory nerves, and immune cells. Its activation serves as a frontline sensor for inhaled irritants, triggering immediate protective responses, and influencing airway integrity. Furthermore, TRPA1 has been implicated in airway tissue injury, inflammation, and the transition of fibroblasts, thereby posing challenges in conditions, such as severe asthma and fibrosis. In sensory nerves, TRPA1 contributes to nociception, the cough reflex, and bronchoconstriction, highlighting its role in both immediate defense mechanisms and long-term respiratory reflex arcs. In immune cells, TRPA1 may modulate the release of pro-inflammatory mediators, shaping the overall inflammatory landscape. In the gastrointestinal tract, the dynamic expression of TRPA1 in enteric neurons, epithelial cells, and immune cells underscores its multifaceted involvement. It plays a crucial role in gut motility, visceral pain perception, and mucosal defense mechanisms. Dysregulation of TRPA1 in both tracts is associated with various disorders such as asthma, Chronic Obstructive Pulmonary Disease, Irritable Bowel Syndrome, and Inflammatory Bowel Disease. This review emphasizes the potential of TRPA1 as a therapeutic target and discusses the efficacy of TRPA1 antagonists in preclinical studies and their promise for addressing respiratory and gastrointestinal conditions. Understanding the intricate interactions and cross-talk of TRPA1 across different cell types provides insight into its versatile role in maintaining homeostasis in vital physiological systems, offering a foundation for targeted therapeutic interventions.

Major dietary lipids in nutrition and health

In this chapter, an overview of the major lipids in the diet with emphasis in nutritional aspects is provided. Triacylglycerols, i.e., glycerol esterified with three fatty acids, are the predominant constituents in dietary lipids. Therefore, this chapter focuses on the nature and nutritional significance of the main fatty acids in the diet and their possible modifications during food processing and commercialization. The main fatty acids in dietary lipids are grouped into saturated, monounsaturated and polyunsaturated fatty acids. Nutritional implications, the latest intervention trials and health recommendations will be discussed. A brief description of the major sources of lipids in the diet is included, oils and fats standing out. Other food sources shortly commented are milk and dairy products, meat, poultry and eggs, fish, and structured lipids designed to improve functional and nutritional properties. Modifications of fatty acids as a result of processing and commercialization are discussed because of their great relevance for their health implications, especially oxidation compounds and trans fatty acids.

Different Effects of Vitamin C-Based Supplements on the Advance of Linseed Oil Component Oxidation and Lipolysis during In Vitro Gastrointestinal Digestion

Although widely consumed, dietary supplements based on Vitamin C contain high doses of this compound, whose impact on lipid oxidation during digestion needs to be addressed. Therefore, the effect of seven commercial supplements and of pure l-ascorbic acid and ascorbyl palmitate on linseed oil during in vitro gastrointestinal digestion was tackled. The advance of lipid oxidation was studied through the generation of oxidation compounds, the degradation of polyunsaturated fatty acyl chains and of gamma-tocopherol, by employing Proton Nuclear Magnetic Resonance. Supplements containing exclusively l-ascorbic acid enhanced the advance of linseed oil oxidation during digestion. This was evidenced by increased formation of linolenic-derived conjugated hydroxy-dienes and alkanals and by the generation of conjugated keto-dienes and reactive alpha,beta-unsaturated aldehydes, such as 4,5-epoxy-2-alkenals; moreover, gamma-tocopherol was completely degraded. Conversely, supplements composed of mixtures of ascorbic acid/salt with citric acid and carotenes, and of ascorbyl palmitate, protected linseed oil against oxidation and reduced gamma-tocopherol degradation. The study through Solid Phase Microextraction-Gas Chromatography/Mass Spectrometry of the volatile compounds of the digests corroborated these findings. Furthermore, a decreased lipid bioaccessibility was noticed in the presence of the highest dose of l-ascorbic acid. Both the chemical form of Vitamin C and the presence of other ingredients in dietary supplements have shown to be of great relevance regarding oxidation and hydrolysis reactions occurring during lipid digestion.

Chemical Changes of Hydroperoxy-, Epoxy-, Keto- and Hydroxy-Model Lipids under Simulated Gastric Conditions

Chemical changes occurring in dietary lipid oxidation compounds throughout the gastrointestinal tract are practically unknown. The first site for potential chemical modifications is the stomach due to the strong acidic conditions. In this study, model lipids representative of the most abundant groups of dietary oxidation compounds were subjected to in vitro gastric conditions. Thus, methyl linoleate hydroperoxides were used as representative of the major oxidation compounds formed in food storage at low and moderate temperatures. Methyl 9,10-epoxystearate, 12-oxostearate and 12-hydroxystearate were selected as model compounds bearing the oxygenated functional groups predominantly found in oxidation compounds formed at the high temperatures of frying. Analyses were performed using gas-liquid chromatography/flame ionization detection/mass spectrometry and high performance-liquid chromatography/ultraviolet detection. Losses of methyl 9,10-epoxystearate and linoleate hydroperoxides in the ranges 17.8–58.8% and 42.3–61.7% were found, respectively, whereas methyl 12-oxostearate and methyl 12-hydroxystearate remained unaltered. Although quantitative data of the compounds formed after digestion were not obtained, methyl 9,10-dihydroxystearate was detected after digestion of methyl 9,10-epoxystearate, and some major volatiles were detected after digestion of linoleate hydroperoxides. Overall, the results showed that significant modifications of dietary oxidized lipids occurred during gastric digestion and supported that the low pH of the gastric fluid played an important role.

Formation of Lipid and Protein Oxidation Products during In Vitro Gastrointestinal Digestion of Dry-Cured Loins with Different Contents of Nitrate/Nitrite Added

The effect of nitrate/nitrite (0, 37.5, 75, and 150 mg/kg) in the dry-cured loin formulation on the formation of lipid and protein oxidation products during in vitro digestion was evaluated. Dry-cured loins formulated with nitrate/nitrite resulted in significantly less lipid and protein oxidation than uncured loins before and after simulated digestion. Compared to loins added with 0 mg/kg nitrate/nitrite, dry-cured loins with 37.5, 75, and 150 mg/kg contained a significantly lower content of conjugated dienes, malondialdehyde, carbonyls, and non-heme iron, and higher amounts of nitrosylmioglobin and thiols. During in vitro digestion, the content of conjugated dienes, malondialdehyde, and carbonyls increased, while thiol content decreased, indicating the development of lipid and protein oxidative processes. At the end of the intestinal phase, the 75 mg/kg digests had a significantly higher content of conjugated dienes, while no differences were found among the other digests. During the in vitro intestinal phase (180 and 240 min), nitrate/nitrite curing resulted in significantly lower malondialdehyde concentrations in the 37.5, 75, and 150 mg/kg loin digests than in the uncured loin digests. No significant differences were observed at the end of the intestinal digestion phase between the cured loin digests. Digests of dried loins without nitrate/nitrite addition showed higher carbonyl contents than the nitrate/nitrite cured counterparts. The loss of thiols was significantly higher in loin digests without added nitrate/nitrite than in loin digests with different amounts of curing salts. The addition of 37.5 mg/kg nitrate/nitrite in the cured loin formulation prevents the formation of lipid peroxidation products and carbonyls from protein oxidation and thiol loss during digestion.

Intestinal bioavailability of n-3 long-chain polyunsaturated fatty acids influenced by the supramolecular form of phospholipids

This work aims at studying the bioavailability of n-3 long-chain polyunsaturated fatty acids carried by marine phospholipids, formulated in different supramolecular forms,i.e.oil-in-water emulsion and liposomes.

Oxidation of marine oils during in vitro gastrointestinal digestion with human digestive fluids - Role of oil origin, added tocopherols and lipolytic activity

The formation of malondialdehyde (MDA), 4-hydroxy-2-hexenal (HHE), 4-hydroxy-2-nonenal (HNE), and 4-oxo-2-nonenal (ONE) in cod liver-, anchovy-, krill-, and algae oil during in vitro digestion with human gastrointestinal fluids was investigated. Adding rabbit gastric lipase, lipase inhibitor (orlistat) and tocopherols to cod liver oil, lipolysis and oxidation was also studied. Among the marine oils, the highest aldehyde levels (18 µM MDA, 3 µM HHE and 0.2 µM HNE) were detected after digestion of cod liver oil, while the lowest levels were detected in krill and algae oils. Addition of rabbit gastric lipase significantly increased the release of HNE during the digestion. Orlistat significantly reduced lipolysis and MDA formation. Formation of MDA and HHE was delayed by tocopherols, the tocopherol mix Covi-ox® T 70 EU being more effective than pure α-tocopherol.

Relative levels of dietary EPA and DHA impact gastric oxidation and essential fatty acid uptake

Previous research showed that increasing the proportion of docosahexaenoic acid (DHA) in marine lipid supplements significantly reduces associated health benefits compared with balanced eicosapentaenoic acid (EPA):DHA supplementation Dasilva et al., 2015 [1]. It was therefore hypothesized that the EPA and DHA molecules might have differential resistance to oxidation during gastric digestion and that the oxidation level achieved could be inversely correlated with intestinal absorption and, hence, with the resultant health benefits. Accordingly, we tested this proposed mechanism of action by investigating the degree of oxidation in the stomach, and the levels of bioaccessible lipids, of varying molar proportions of DHA and EPA (2:1, 1:1 and 1:2) using the dynamic gastrointestinal tract model TIM-1. In addition, small intestine enterocyte absorption and metabolism were simulated by Caco-2 cell monolayers that were incubated with these same varying proportions of DHA and EPA, and comparing oxidized and nonoxidized polyunsaturated fatty acids (PUFAs). The results show an inverse correlation between lipid oxidation products in the stomach and the levels of bioaccessible lipids. The balanced 1:1 EPA:DHA diet resulted in lower oxidation of PUFAs during stomach digestion relative to the other ratios tested. Finally, cell-based studies showed significantly lower assimilation of oxidized EPA and DHA substrates compared to nonoxidized PUFAs, as well as significant differences between the net uptake of EPA and DHA. Overall, the present work suggests that the correct design of diets and/or supplements containing marine lipids can strongly influence the stability and bioaccessibility of PUFAs during gastrointestinal digestion and subsequent absorption. This could modulate their health benefits related with inflammation, oxidative stress and metabolic disorders.

Effects of Marine Oils, Digested with Human Fluids, on Cellular Viability and Stress Protein Expression in Human Intestinal Caco-2 Cells

In vitro digestion of marine oils has been reported to promote lipid oxidation, including the formation of reactive aldehydes (e.g., malondialdehyde (MDA) and 4-hydroxy-2-hexenal (HHE)). We aimed to investigate if human in vitro digestion of supplemental levels of oils from algae, cod liver, and krill, in addition to pure MDA and HHE, affect intestinal Caco-2 cell survival and oxidative stress. Cell viability was not significantly affected by the digests of marine oils or by pure MDA and HHE (0-90 μM). Cellular levels of HSP-70, a chaperone involved in the prevention of stress-induced protein unfolding was significantly decreased (14%, 28%, and 14% of control for algae, cod and krill oil, respectively; p ≤ 0.05). The oxidoreductase thioredoxin-1 (Trx-1) involved in reducing oxidative stress was also lower after incubation with the digested oils (26%, 53%, and 22% of control for algae, cod, and krill oil, respectively; p ≤ 0.001). The aldehydes MDA and HHE did not affect HSP-70 or Trx-1 at low levels (8.3 and 1.4 μM, respectively), whilst a mixture of MDA and HHE lowered Trx-1 at high levels (45 μM), indicating less exposure to oxidative stress. We conclude that human digests of the investigated marine oils and their content of MDA and HHE did not cause a stress response in human intestinal Caco-2 cells.

HNE and cholesterol oxidation products in colorectal inflammation and carcinogenesis

Consistent experimental data suggest the importance of inflammation-associated oxidative stress in colorectal cancer (CRC) pathogenesis. Inflammatory bowel disease with chronic intestinal inflammation is now considered a precancerous condition. Oxidative stress is an essential feature of inflammation. Activation of redox-sensitive pro-inflammatory cell signals and inflammatory mediators concur to establish a pro-tumoral environment. In this frame, lipid oxidation products, namely 4-hydroxynonenal and oxysterols, can be produced in big quantity so as to be able to exert their function as inducers of cell signaling pathways of proliferation and survival. Notably, an important source of these two compounds is represented by a high fat diet, which is undoubtedly a risk factor for inflammation and CRC development. Current evidence for the emerging implication of these two oxidized lipids in inflammation and CRC development is discussed in this review.

Reactivity of Free Malondialdehyde during In Vitro Simulated Gastrointestinal Digestion

An aqueous buffer, a saturated glycerol triheptanoate oil, and a Tween 20 stabilized fully hydrogenated coconut oil-in-water emulsion, all spiked with malondialdehyde, were subjected to in vitro digestion. A dynamic equilibrium between malondialdehyde, its aldol self-condensation products, and its hydrolytic cleavage products was observed. This equilibrium depended upon the kind of sample and the temperature at which these samples were preincubated during 24 h. The presence of oil during gastric digestion protected the aldol self-condensation and cleavage products from conversion to malondialdehyde, which occurred in the aqueous acidic gastric chyme. In parallel, the presence of oil enhanced the reactivity of malondialdehyde throughout the gastrointestinal digestion process. Malondialdehyde recoveries after digestion varied between 42 and 90%, depending upon the model system studied, with the aldol self-condensation as the main reaction pathway. In conclusion, this study revealed that malondialdehyde is a very reactive molecule whose reactivity does not stop at the point of ingestion.