Vitamin E: Regulatory role of metabolites

Immunomodulation through Nutrition Should Be a Key Trend in Type 2 Diabetes Treatment

An organism's ability to function properly depends not solely on its diet but also on the intake of nutrients and non-nutritive bioactive compounds that exert immunomodulatory effects. This principle applies both to healthy individuals and, in particular, to those with concomitant chronic conditions, such as type 2 diabetes. However, the current food industry and the widespread use of highly processed foods often lead to nutritional deficiencies. Numerous studies have confirmed the occurrence of immune system dysfunction in patients with type 2 diabetes. This article elucidates the impact of specific nutrients on the immune system function, which maintains homeostasis of the organism, with a particular emphasis on type 2 diabetes. The role of macronutrients, micronutrients, vitamins, and selected substances, such as omega-3 fatty acids, coenzyme Q10, and alpha-lipoic acid, was taken into consideration, which outlined the minimum range of tests that ought to be performed on patients in order to either directly or indirectly determine the severity of malnutrition in this group of patients.

Vitamin E reduces inflammation and improves cognitive disorder and vascular endothelial functions in patients with leukoaraiosis

BACKGROUND

Leukoaraiosis (LA) is a disease manifested by demyelination and gliosis in white matter, mainly caused by cerebrovascular diseases. LA is closely related to the expression level of inflammatory factors, oxidative stress, and vascular endothelial dysfunction in patients. Vitamin E may play antioxidant and anti-inflammatory roles in various diseases. We aimed to explore the effects of vitamin E on the patients with LA.

METHODS

A total of 160 patients with LA were recruited in this research. Matrix metalloproteinase-9 (MMP-9), MMP-2, C-reactive protein (CRP), complement 3 (C3), C4, nitric oxide (NO), and endothelin (ET) levels were evaluated by ELISA. The Mini-Mental State Examination (MMSE) was used for cognitive impairment assessment. Superoxide dismutase (SOD) and malondialdehyde (MDA) concentrations were analyzed by commercial kits.

RESULTS

The levels of CRP, C3, and C4 significantly decreased in the serum of LA patients after the administration of vitamin E. The levels of MMP-2 and MPP-9 showed a significant decrease in the administered group. Vitamin E significantly inhibited the expression of MDA, while significantly upregulated the expression of SOD. Significant increase in NO production and significant downregulation of ET expression occurred in vitamin E groups. MMSE score was significantly increased by vitamin E.

CONCLUSION

In conclusion, vitamin E showed effects on the alleviation of inflammatory response, oxidative stress, endothelial damage, and cognitive dysfunction. Thus, vitamin E could be a potential drug for the clinical treatment of LA patients.

Lester Packer and Vitamin E: Editorial

The inspiring ideas of Professor Lester Packer (1929-2018) substantially enriched our understanding of biological systems. One of the most important contributions of Lester is the role of vitamin E in biological membranes. Lester started early in the 1970s with the development and use of a preparatory technique for electron microscopy of biological membranes, the "freeze fracture." This made it possible to detect inner and outer membranes of mitochondria as well as associated compounds in other biological organelles. Lester also considered the effect of tocols on entire animals and thereby initiated the field of exercise biology. An important finding was the loss of vitamin E and of muscle mitochondria after exhaustive exercise. In the 1990s, he and his group worked on the intermembrane exchange and membrane stabilization by tocols. They also determined the specific activities of various tocols including tocotrienols. In the later years they embarked on the role of vitamin E in redox signaling and gene expression, topics fundamental to our understanding of the role of vitamin E in membranes and in general. Lester, his group, and international guests tried to answer the still open question how vitamin E protects biomembranes. The numerous possibilities they offered will help to find a final solution. Lester always engaged himself at the forefront of science and in scientific exchange on meetings and in societies. Antioxid. Redox Signal. 39, 771-776.

Serum Vitamins A and E at Mid-Pregnancy and Their Relationships with Both Maternal and Cord Blood Antioxidant Status and Perinatal Conditions: The NELA Cohort

INTRODUCTION

Most of the pregnant women do not achieve the recommended dietary intake of vitamins A and E. These vitamins may counteract oxidative stress involved in some adverse perinatal outcomes. We aimed to assess the associations between maternal vitamin A and E at mid-pregnancy with both maternal and fetal outcomes and to identify possible early biomarkers during pregnancy to predict and prevent oxidative stress in the offspring.

METHODS

Data on dietary and serum levels of vitamins A and E were collected from 544 pregnant women from the Nutrition in Early Life and Asthma (NELA) study, a prospective mother-child cohort set up in Spain.

RESULTS

There were large discrepancies between low dietary vitamin E intake (78% of the mothers) and low serum vitamin E levels (3%) at 24 weeks of gestation. Maternal serum vitamins A and E at mid-pregnancy were associated with higher antioxidant status not only in the mother at this time point (lower hydroperoxides and higher total antioxidant activity [TAA]) but also with the newborn at birth (higher TAA). Gestational diabetes mellitus (GDM) was negatively associated with maternal serum vitamin A (OR: 0.95 CI: 0.91-0.99, p = 0.009) at mid-pregnancy. Nevertheless, we could not detect any association between GDM and oxidative stress parameters.

CONCLUSIONS

In conclusion, maternal vitamin A and E serum levels may be used as an early potential biomarker of antioxidant status of the neonate at birth. Control of these vitamins during pregnancy could help avoid morbid conditions in the newborn caused by oxidative stress in GDM pregnancies.

Construction and evaluation of an antioxidant synergistic system containing vitamin C and vitamin E

AIMS

The aim of this study is to develop a liposome that could exert unparalleled antioxidant effects. In the present study, a vitamin C (VC)/vitamin E (VE)-co-loaded multivesicular liposome (VCVE-MVL) was constructed.

METHODS

Vitamins were encapsulated in soybean phosphatidylcholine (SPC) and cholesterol (CHO) by multi-emulsification method. The concentration of VC was determined by Fast Blue method. The concentration of VE was determined by high performance liquid chromatography (HPLC). Vitamin antioxidant capacity in vitro and in vivo was determined using β-carotene bleaching.

RESULTS

VCVE-MVL with particle diameter of 848.55 ± 0.29 nm and SPAN of 0.16 ± 0.11 were obtained. The encapsulation efficiency of VC reached 48.51% (w/w)±0.15. Compared with VC/VE solution, VCVE-MVL had a higher permeation efficiency. In addition, the in vitro and ex-vivo antioxidant tests verified the adequate antioxidant activity of VCVE-MVL.

CONCLUSIONS

In conclusion, the antioxidant synergistic system we constructed and demonstrated its potential applications in the cosmetics industry.

Iron and atrial fibrillation: A review

Atrial fibrillation (AF), one of the most common arrhythmias in clinical practice, is classified into paroxysmal, persistent, and permanent AF according to its duration. The development of AF is associated with increased cardiovascular morbidity and mortality. However, the exact etiology of this disease remains poorly understood. Recent studies found disorders of iron metabolism might be involved in the progression of AF. Abnormal iron metabolism in cardiomyocytes provides arrhythmogenic substrates through a variety of mechanisms, including calcium mishandling, ion channel remodeling, and oxidative stress overaction. Interestingly, in AF patients with iron overload, interventions on iron metabolism, such as iron chelators and ferroptosis inhibitors, has been shown to prevent AF via reducing ferroptosis. Herein, we review the possible mechanisms, consequences, and therapeutic implications of altered atrial iron handling for AF pathophysiology.

Fat-soluble vitamin and phytochemical metabolites: Production, gastrointestinal absorption, and health effects

Consumption of diets rich in fruits and vegetables, which provide some fat-soluble vitamins and many phytochemicals, is associated with a lower risk of developing certain degenerative diseases. It is well accepted that not only the parent compounds, but also their derivatives formed upon enzymatic or nonenzymatic transformations, can produce protective biological effects. These derivatives can be formed during food storage, processing, or cooking. They can also be formed in the lumen of the upper digestive tract during digestion, or via metabolism by microbiota in the colon. This review compiles the known metabolites of fat-soluble vitamins and fat-soluble phytochemicals (FSV and FSP) that have been identified in food and in the human digestive tract, or could potentially be present based on the known reactivity of the parent compounds in normal or pathological conditions, or following surgical interventions of the digestive tract or consumption of xenobiotics known to impair lipid absorption. It also covers the very limited data available on the bioavailability (absorption, intestinal mucosa metabolism) and summarizes their effects on health. Notably, despite great interest in identifying bioactive derivatives of FSV and FSP, studying their absorption, and probing their putative health effects, much research remains to be conducted to understand and capitalize on the potential of these molecules to preserve health.

Vitamin E and Metabolic Health: Relevance of Interactions with Other Micronutrients

A hundred years have passed since vitamin E was identified as an essential micronutrient for mammals. Since then, many biological functions of vitamin E have been unraveled in both cell and animal models, including antioxidant and anti-inflammatory properties, as well as regulatory activities on cell signaling and gene expression. However, the bioavailability and physiological functions of vitamin E have been considerably shown to depend on lifestyle, genetic factors, and individual health conditions. Another important facet that has been considered less so far is the endogenous interaction with other nutrients. Accumulating evidence indicates that the interaction between vitamin E and other nutrients, especially those that are enriched by supplementation in humans, may explain at least some of the discrepancies observed in clinical trials. Meanwhile, increasing evidence suggests that the different forms of vitamin E metabolites and derivates also exhibit physiological activities, which are more potent and mediated via different pathways compared to the respective vitamin E precursors. In this review, possible molecular mechanisms between vitamin E and other nutritional factors are discussed and their potential impact on physiological and pathophysiological processes is evaluated using published co-supplementation studies.

Natural Antioxidant Evaluation: A Review of Detection Methods

Antioxidants have drawn the attention of the scientific community due to being related to the prevention of various degenerative diseases. The antioxidant capacity has been extensively studied in vitro, and different methods have been used to assess its activity. However, the main issues related to studying natural antioxidants are evaluating whether these antioxidants demonstrate a key role in the biological system and assessing their bioavailability in the organism. The majority of outcomes in the literature are controversial due to a lack of method standardization and their proper application. Therefore, this study aims to compile the main issues concerning the natural antioxidant field of study, comparing the most common in vitro methods to evaluate the antioxidant activity of natural compounds, demonstrating the antioxidant activity in biological systems and the role of the main antioxidant enzymes of redox cellular signaling and explaining how the bioavailability of bioactive compounds is evaluated in animal models and human clinical trials.

Vitamin E Levels in Preterm and Full-Term Infants: A Systematic Review

Vitamin E deficiency (VED) is associated with clinical repercussions in preterm newborns (PTN), but low levels are also found in full-term newborns (TN). As this inadequacy can compromise neurogenesis in childhood, studies are needed to assess whether there is a difference in vitamin E status among newborns according to gestational age to provide support for neonatal monitoring protocols. This systematic review presents a synthesis of the available information on the vitamin E status among PTN and TN. The review was performed according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). Observational studies that evaluated alpha-tocopherol levels were searched in the databases reported in the protocol registered in PROSPERO (CRD42021165152). The Newcastle–Ottawa Scale was used to assess the methodological quality. Overall, 1809 articles were retrieved; 10 were included in the systematic review. In the PTN, the alpha-tocopherol levels ranged from 3.9 to 8.5 mmol/L, while in TN, they were 4.9 to 14.9 mmol/L, and VED ranged from 19% to 100% in newborns. Despite substantial heterogeneity in research methodology and VED classification, the results suggest that the alpha-tocopherol levels among preterm and full-term newborns is below the recommended levels. Our findings demonstrate that further investigations are needed to standardize this classification and to monitor vitamin E status in birth and postnatal with adequate bias control.

The α-tocopherol-derived long-chain metabolite α-13'-COOH mediates endotoxin tolerance and modulates the inflammatory response via MAPK and NFκB pathways

SCOPE

The long-chain metabolites of (LCM) vitamin E are proposed as the active regulatory metabolites of vitamin E providing, with their anti-inflammatory properties, an explanatory approach for the inconsistent effects of vitamin E on inflammatory-driven diseases. We examined the modulation of cytokine expression and release from macrophages, a fundamental process in many diseases, to gain insights into the anti-inflammatory mechanisms of the α-tocopherol-derived LCM α-13'-COOH.

METHODS AND RESULTS

Suppressed gene expression of C-C motif chemokine ligand 2 (Ccl2), tumor necrosis factor (Tnf), and interleukin (Il) 6 in response to lipopolysaccharides by 24 h pre-treatment with α-13'-COOH in RAW264.7 macrophages was revealed using quantitative reverse transcription PCR. Further, reduced secretion of IL1β and CCL2 was found in this setup using flow cytometry. In contrast, 1 h pre-treatment suppressed only CCL2. Consequent gene expression analysis within 24 h of α-13'-COOH treatment revealed the induction of mitogen-activated protein kinases (MAPK) and nuclear factor kappa-light-chain-enhancer of activated B cells (NFκB) negative feedback regulators including the 'master regulators' dual-specificity phosphatase 1 (Dusp1/Mkp1) and tumor necrosis factor induced protein 3 (Tnfaip3/A20). Approaches with immunoblots and chemical antagonists suggest a feedback induction via activation of extracellular-signal regulated kinase (ERK), p38 MAPK and NFκB pathways.

CONCLUSIONS

CCL2 is suppressed in murine macrophages by α-13'-COOH and the indirect suppression of MAPK and NFκB pathways is likely a relevant process contributing to anti-inflammatory actions of α-13'-COOH. These results improve the understanding of the effects of α-13'-COOH and provide a basis for new research strategies in the context of inflammatory diseases.

Vitamin E research: Past, now and future

The early history of vitamin E from its discovery by Herbert M. Evans and Katharine J. S. Bishop in 1922 up to its chemical synthesis by Paul Karrer and coworkers in 1938 and the development of the concept that vitamin E acts as an antioxidant in vivo are recalled. Some more recent results shedding doubt on this hypothesis are reviewed. They comprise influence of vitamin E on enzyme activities, signaling cascades, gene expression and bio-membrane structure. The overall conclusion is that our knowledge of the vitamin's mechanism of action still remains fragmentary. The metabolism of tocopherols and tocotrienols is presented and discussed in respect to bioactivity of the metabolites, interference with drug metabolism and the future design of clinical trials. Some strategies are recommended how to reach the final goal: the identification of the primary vitamin E target(s) and the analysis of the downstream events up to the physiological phenomena.

Lipid oxidation that is, and is not, inhibited by vitamin E: Consideration about physiological functions of vitamin E

Lipids are oxidized in vivo by multiple oxidizing species with different properties, some by regulated manner to produce physiological mediators, while others by random mechanisms to give detrimental products. Vitamin E plays an important role as a physiologically essential antioxidant to inhibit unregulated lipid peroxidation by scavenging lipid peroxyl radicals to break chain propagation independent of the type of free radicals which induce chain initiation. Kinetic data suggest that vitamin E does not act as an efficient scavenger of nitrogen dioxide radical, carbonate anion radical, and hypochlorite. The analysis of regio- and stereo-isomer distribution of the lipid oxidation products shows that, apart from lipid oxidation by CYP enzymes, the free radical-mediated lipid peroxidation is the major pathway of lipid oxidation taking place in humans. Compared with healthy subjects, the levels of racemic and trans,trans-hydro (pero)xyoctadecadienoates, specific biomarker of free radical lipid oxidation, are elevated in the plasma of patients including atherosclerosis and non-alcoholic fatty liver diseases. α-Tocopherol acts as a major antioxidant, while γ-tocopherol scavenges nitrogen dioxide radical, which induces lipid peroxidation, nitration of aromatic compounds and unsaturated fatty acids, and isomerization of cis-fatty acids to trans-fatty acids. It is essential to appreciate that the antioxidant effects of vitamin E depend on the nature of both oxidants and substrates being oxidized. Vitamin E, together with other antioxidants such as vitamin C, contributes to the inhibition of detrimental oxidation of biological molecules and thereby to the maintenance of human health and prevention of diseases.

Reflections on a century of vitamin E research: Looking at the past with an eye on the future

The name vitamin E, was given by Barnett and Sure who suggested that the factor proposed by Evans and Bishop as substance "X," be termed vitamin "E" as the next vitamin after the A, B, C and D vitamins had been already described. The identification of vitamin E with a-tocopherol was made in 1936 by Evans' group. One year later β-tocopherol and 11 years later δ-tocopherol were isolated. Tocotrienol (named zetatocopherol) was first described in 1957 and later isolated in 1961. The antioxidant property of tocopherols was reported by Olcott and Emerson in 1937. Inherited vitamin E deficiency, AVED, characterized by a form of neuromyopathy was first described in 1981. The disease, was localized to chromosome 8q and found to be caused by a mutation of the a-TTP gene. The subsequent paragraphs are not a comprehensive review but only critical reflections on some important aspects of vitamin E research.

The Association Between Vitamin E Deficiency and Critically Ill Children With Sepsis and Septic Shock

Background: Literature is scarce on the assessment of vitamin E status in septic children. We aim to investigate the prevalence of vitamin E deficiency in critically ill children with sepsis and septic shock and its association with clinical features and outcomes.

Methods: We compared serum vitamin E status between the confirmed or suspected infection and no infection groups, the sepsis shock and no sepsis shock groups upon pediatric intensive care unit admission. Clinical characteristics were compared in subgroup patients with and without vitamin E deficiency. The association between vitamin E deficiency and septic shock were evaluated using univariate and multivariable methods.

Results: 182 critically ill children with confirmed or suspected infection and 114 without infection were enrolled. The incidence of vitamin E deficiency was 30.2% in the infection group and 61.9% in the septic shock subgroup (P < 0.001). Thirty-days mortality in critically ill children with vitamin E deficiency was significantly higher than that without vitamin E deficiency (27.3 vs. 14.2%, P < 0.05). Vitamin E levels were inversely associated with higher pediatric risk of mortality (r = − 0.238, P = 0.001) and cardiovascular sequential organ failure assessment (r = −0.249, p < 0.001) scores in critically ill children with infection. In multivariable logistic regression, vitamin E deficiency showed an independent effect on septic shock (adjusted OR: 6.749, 95%CI: 2.449–18.60, P < 0.001).

Conclusion: Vitamin E deficiency is highly prevalent in critically ill children with sepsis and contributed to the septic shock.

Tocopherols and Tocotrienols-Bioactive Dietary Compounds; What Is Certain, What Is Doubt?

Tocopherols and tocotrienols are natural compounds of plant origin, available in the nature. They are supplied in various amounts in a diet, mainly from vegetable oils, some oilseeds, and nuts. The main forms in the diet are α- and γ-tocopherol, due to the highest content in food products. Nevertheless, α-tocopherol is the main form of vitamin E with the highest tissue concentration. The α- forms of both tocopherols and tocotrienols are considered as the most metabolically active. Currently, research results indicate also a greater antioxidant potential of tocotrienols than tocopherols. Moreover, the biological role of vitamin E metabolites have received increasing interest. The aim of this review is to update the knowledge of tocopherol and tocotrienol bioactivity, with a particular focus on their bioavailability, distribution, and metabolism determinants in humans. Almost one hundred years after the start of research on α-tocopherol, its biological properties are still under investigation. For several decades, researchers' interest in the biological importance of other forms of vitamin E has also been growing. Some of the functions, for instance the antioxidant functions of α- and γ-tocopherols, have been confirmed in humans, while others, such as the relationship with metabolic disorders, are still under investigation. Some studies, which analyzed the biological role and mechanisms of tocopherols and tocotrienols over the past few years described new and even unexpected cellular and molecular properties that will be the subject of future research.

Endogenous vitamin E metabolites mediate allosteric PPARγ activation with unprecedented co-regulatory interactions

Vitamin E exhibits pharmacological effects beyond established antioxidant activity suggesting involvement of unidentified mechanisms. Here, we characterize endogenously formed tocopherol carboxylates and the vitamin E mimetic garcinoic acid (GA) as activators of the peroxisome proliferator-activated receptor gamma (PPARγ). Co-stimulation of PPARγ with GA and the orthosteric agonist pioglitazone resulted in additive transcriptional activity. In line with this, the PPARγ-GA complex adopted a fully active conformation and interestingly contained two bound GA molecules with one at an allosteric site. A co-regulator interaction scan demonstrated an unanticipated co-factor recruitment profile for GA-bound PPARγ compared with canonical PPARγ agonists and gene expression analysis revealed different effects of GA and pioglitazone on PPAR signaling in hepatocytes. These observations reveal allosteric mechanisms of PPARγ modulation as an alternative avenue to PPARγ targeting and suggest contributions of PPARγ activation by α-13-tocopherolcarboxylate to the pharmacological effects of vitamin E.

Cardiovascular and Metabolic Protection by Vitamin E: A Matter of Treatment Strategy?

Cardiovascular diseases (CVD) cause about 1/3 of global deaths. Therefore, new strategies for the prevention and treatment of cardiovascular events are highly sought-after. Vitamin E is known for significant antioxidative and anti-inflammatory properties, and has been studied in the prevention of CVD, supported by findings that vitamin E deficiency is associated with increased risk of cardiovascular events. However, randomized controlled trials in humans reveal conflicting and ultimately disappointing results regarding the reduction of cardiovascular events with vitamin E supplementation. As we discuss in detail, this outcome is strongly affected by study design, cohort selection, co-morbidities, genetic variations, age, and gender. For effective chronic primary and secondary prevention by vitamin E, oxidative and inflammatory status might not have been sufficiently antagonized. In contrast, acute administration of vitamin E may be more translatable into positive clinical outcomes. In patients with myocardial infarction (MI), which is associated with severe oxidative and inflammatory reactions, decreased plasma levels of vitamin E have been found. The offsetting of this acute vitamin E deficiency via short-term treatment in MI has shown promising results, and, thus, acute medication, rather than chronic supplementation, with vitamin E might revitalize vitamin E therapy and even provide positive clinical outcomes.

Inflammatory Diseases and Vitamin E-What Do We Know and Where Do We Go?

Inflammation-driven diseases and related comorbidities, such as the metabolic syndrome, obesity, fatty liver disease, and cardiovascular diseases cause significant global burden. There is a growing body of evidence that nutrients alter inflammatory responses and can therefore make a decisive contribution to the treatment of these diseases. Recently, the inflammasome, a cytosolic multiprotein complex, has been identified as a key player in inflammation and the development of various inflammation-mediated disorders, with nucleotide-binding domain and leucine-rich repeat pyrin domain (NLRP) 3 being the inflammasome of interest. Here an overview about the cellular signaling pathways underlying nuclear factor "kappa-light-chain-enhancer" of activated B-cells (NF-κB)- and NLRP3-mediated inflammatory processes, and the pathogenesis of the inflammatory diseases atherosclerosis and non-alcoholic fatty liver disease (NAFLD) is provided; next, the current state of knowledge for drug-based and dietary-based interventions for treating cardiovascular diseases and NAFLD is discussed. To date, one of the most important antioxidants in the human diet is vitamin E. Various in vitro and in vivo studies suggest that the different forms of vitamin E and also their derivatives have anti-inflammatory activity. Recent publications suggest that vitamin E-and possibly metabolites of vitamin E-are a promising therapeutic approach for treating inflammatory diseases such as NAFLD.

Dietary intervention reduces left atrial enlargement in dogs with early preclinical myxomatous mitral valve disease: a blinded randomized controlled study in 36 dogs

Background

Myxomatous mitral valve disease (MMVD), the most common naturally-occurring heart disease in dogs, is associated with alterations in energy metabolism, oxidative stress and inflammation. Energy deprivation plays a causal role in the development of heart failure. This study was designed to determine if a cardiac protection blend (CPB) of nutrients containing medium-chain triglycerides as an alternative energy source, fish oil to reduce inflammation, antioxidants, and other key nutrients important to cardiac health and function could slow or prevent MMVD progression. Nineteen dogs with early stage MMVD and 17 breed-, age-, and sex-matched healthy dogs were enrolled for a 6-month blinded, placebo-controlled study. Dogs in each cardiac health group were randomly assigned to either control diet (CON) or CPB-supplemented diet. Echocardiography was performed at baseline, 3 months and 6 months.

Results

No changes were found in healthy dogs. While MMVD-CON dogs had an average 10% increase over baseline in left atrial diameter (LAD) and left atrial to aortic root ratio (LA/Ao) at 6 months, MMVD-CPB dogs showed 3% decreases, resulting significant diet by time interactions (P = 0.037, P = 0.005, respectively). More MMVD-CON dogs progressed from stage B1 to B2 during the study. A positive correlation was found between 6-month changes in LAD and blood pressures in MMVD-CPB dogs (systolic: P = 0.050, diastolic: P = 0.035) but not MMVD-CON dogs.

Conclusions

Our results demonstrated efficacy of CPB-based dietary intervention in reducing LA size and mitral regurgitation, and in slowing or preventing the progression of early MMVD in dogs.

Vitamin E analogues differentially inhibit human cytochrome P450 3A (CYP3A)-mediated oxidative metabolism of lithocholic acid: Impact of δ-tocotrienol on lithocholic acid cytotoxicity

Lithocholic acid is a cytotoxic bile acid oxidized at the C-3 position by human cytochrome P450 3A (CYP3A) to form 3-ketocholanoic acid, but it is not known whether this metabolite is cytotoxic. Tocotrienols, in their various isomeric forms, are vitamin E analogues. In the present study, the hypothesis to be tested is that tocotrienols inhibit CYP3A-catalyzed lithocholic acid 3-oxidation, thereby influencing lithocholic acid cytotoxicity. Our enzyme catalysis experiments indicated that human recombinant CYP3A5 in addition to CYP3A4, liver microsomes, and intestinal microsomes catalyzed lithocholic acid 3-oxidation to form 3-ketocholanoic acid. Liver microsomes with the CYP3A5*1/*3 and CYP3A5*3/*3 genotypes were associated with decreased lithocholic acid 3-oxidation. α-Tocotrienol, γ-tocotrienol, δ-tocotrienol, and a tocotrienol-rich vitamin E mixture, but not α-tocopherol (a vitamin E analogue), differentially inhibited lithocholic acid 3-oxidation catalyzed by liver and intestinal microsomes and recombinant CYP3A4 and CYP3A5. Compared to lithocholic acid 3-oxidation, CYP3A-catalyzed testosterone 6β-hydroxylation was inhibited to a lesser extent by α-tocotrienol, γ-tocotrienol, δ-tocotrienol, and a tocotrienol-rich vitamin E mixture. δ-Tocotrienol inhibited lithocholic acid 3-oxidation by a mixed mode. Like lithocholic acid, 3-ketocholanoic acid was also cytotoxic in human intestinal and liver cell models. δ-Tocotrienol decreased the extent of lithocholic acid 3-oxidation and this inhibition was associated with enhanced cytotoxicity in LS180 cells treated with δ-tocotrienol and lithocholic acid. Overall, vitamin E analogues inhibited in vitro lithocholic acid 3-oxidation in an isomer-dependent manner, with inhibition occurring with tocotrienols, but not α-tocopherol. The enhanced lithocholic acid toxicity by δ-tocotrienol in a human intestinal cell model warrants future investigations in vivo.

Transcriptomic Analysis of MAPK Signaling in NSC-34 Motor Neurons Treated with Vitamin E

Vitamin E family is composed of different tocopherols and tocotrienols that are well-known as antioxidants but that exert also non-antioxidant effects. Oxidative stress may be involved in the progression of neurodegenerative disorders including amyotrophic lateral sclerosis (ALS), characterized by motor neuron death. The aim of the study was the evaluation of the changes induced in the transcriptional profile of NSC-34 motor neurons treated with α-tocopherol. In particular, cells were treated for 24 h with 10 µM α-tocopherol, RNA was extracted and transcriptomic analysis was performed using Next Generation Sequencing. Vitamin E treatment modulated MAPK signaling pathway. The evaluation revealed that 34 and 12 genes, respectively belonging to “Classical MAP kinase pathway” and “JNK and p38 MAP kinase pathway”, were involved. In particular, a downregulation of the genes encoding for p38 (Log₂ fold change −0.87 and −0.67) and JNK (Log₂ fold change −0.16) was found. On the contrary, the gene encoding for ERK showed a higher expression in cells treated with vitamin E (Log₂ fold change 0.30). Since p38 and JNK seem more involved in cell death, while ERK in cell survival, the data suggested that vitamin E treatment may exert a protective role in NSC-34 motor neurons. Moreover, Vitamin E treatment reduced the expression of the genes which encode proteins involved in mitophagy. These results indicate that vitamin E may be an efficacious therapy in preventing motor neuron death, opening new strategies for those diseases that involve motor neurons, including ALS.