Molecular mechanisms of membrane transport of vitamin E

Recent advances in the screening methods of NPC1L1 inhibitors

NPC1L1 is a crucial protein involved in sterol lipid absorption and has been shown to play an important role in intestinal cholesterol absorption. Hypercholesterolemia is a significant risk factor for cardiovascular diseases such as coronary heart disease. Screening of NPC1L1 inhibitors is critical for gaining a full understanding of lipid metabolism, developing new cholesterol-lowering medicines, and treating cardiovascular diseases. This work summarized existing methodologies for screening NPC1L1 inhibitors and evaluated their challenges, and will assist the development of novel cholesterol-lowering medications and therapeutic strategies for hypercholesterolemia and other cholesterol-related metabolic disorders.

Modulation of CD36-mediated lipid accumulation and senescence by vitamin E analogs in monocytes and macrophages

The CD36/FAT scavenger receptor/fatty acids transporter regulates cellular lipid accumulation important for inflammation, atherosclerosis, lipotoxicity, and initiation of cellular senescence. Here we compared the regulatory effects of the vitamin E analogs alpha-tocopherol (αT), alpha-tocopheryl phosphate (αTP), and αTP/βCD (a nanocarrier complex between αTP and β-cyclodextrin [βCD]) and investigated their regulatory effects on lipid accumulation, phagocytosis, and senescence in THP-1 monocytes and macrophages. Both, αTP and αTP/βCD inhibited CD36 surface exposition stronger than αT leading to more pronounced CD36-mediated events such as inhibition of DiI-labeled oxLDL uptake, phagocytosis of fluorescent Staphylococcus aureus bioparticles, and cell proliferation. When compared to βCD, the complex of αTP/βCD extracted cholesterol from cellular membranes with higher efficiency and was associated with the delivery of αTP to the cells. Interestingly, both, αTP and more so αTP/βCD inhibited lysosomal senescence-associated beta-galactosidase (SA-β-gal) activity and increased lysosomal pH, suggesting CD36-mediated uptake into the endo-lysosomal phagocytic compartment. Accordingly, the observed pH increase was more pronounced with αTP/βCD in macrophages whereas no significant increase occurred with αT, alpha-tocopheryl acetate (αTA) or βCD. In contrast to αT and αTA, the αTP molecule is di-anionic at neutral pH, but upon moving into the acidic endo-lysosomal compartment becomes protonated and thus is acting as a base. Moreover, it is expected to be retained in lysosomes since it still carries one negative charge, similar to lysosomotropic drugs. Thus, treatment with αTP or αTP/βCD and/or inhibition of conversion of αTP to αT as it occurs in aged cells may counteract CD36-mediated overlapping inflammatory, senescent, and atherosclerotic events.

Absorption, transportation, and distribution of vitamin E homologs

Vitamin E has eight different naturally occurring forms: four tocopherols and four tocotrienols. Because α-tocopherol has three asymmetric carbons, both natural α-tocopherol (RRR-α-tocopherol) and synthetic α-tocopherol (all-rac-α-tocopherol) are utilized in both pharmaceutical products and food additives. Therefore, determining the distribution of vitamin E in the body is very important. With regard to absorption, and transportation of vitamin E, it is suggested that the pathways mediated by three proteins (CD36, SR-BI, and NPC1L1) as well as passive diffusion affect absorption of vitamin E. Vitamin E homologs are mainly transported by very low-density lipoprotein (VLDL) with the α-tocopherol being recognized by the α-tocopherol transfer protein in liver. However, it is also suggested that chylomicrons (CMs) and high-density lipoprotein (HDL) are involved in transportation of vitamin E homologs from the small intestine to each section of peripheral tissue. In particular, it is speculated that vitamin E homologs transportation by CMs and HDL from enterocytes to peripheral tissues such as adipose tissue greatly affects the distribution of vitamin E homologs, excluding α-tocopherol. However, how lipoprotein lipase affects the incorporation of vitamin E homologs containing lipoprotein into peripheral tissues is unclear. Whether there is biodiscrimination when vitamin E homologs are incorporated into peripheral tissues from lipoprotein is an interesting question. It is likely that future research will reveal how individual vitamin E homologs are incorporated into peripheral tissue, especially the brain, adipose tissue, and skin.

Novel α-tocopherol-ferrocene conjugates for the specific delivery of transgenes in liver cancer cells under high serum conditions

The delivery of therapeutic genes to a specific organ has drawn significant research attention. Among the pool of various delivery vectors, cationic liposomes (non-viral) are potential candidates for delivering therapeutic genes due to their low immunogenic response. Here, we have developed novel ferrocene-conjugated cationic tocopheryl aggregates as non-viral vectors. These formulations can transfer a reporter gene (pGL3; encoded for luciferase protein) specifically to liver cancer cells (HepG2 and Huh7) instead of non-hepatic cancer cells, such as Caco-2 (human colon carcinoma) and HeLa (cervical cancer) cells. The transfection efficiency (TE) of the optimum liposomal formulation is more significant than commercially available Lipofectamine 2000 (L2K). Notably, it retains its TE under high serum conditions (up to 50% FBS). A coupled effect from conjugated ferrocene and tocopherol in the cationic liposomal formulation might be responsible for the cell-specific delivery and higher serum compatibility. Therefore, the present proposed delivery system may provide a platform for further progress in terms of developing hepatotropic gene delivery systems.

NPC1L1 Facilitates Sphingomyelin Absorption and Regulates Diet-Induced Production of VLDL/LDL-associated S1P

Niemann-Pick C1-Like 1 (NPC1L1) is a cholesterol importer and target of ezetimibe, a cholesterol absorption inhibitor used clinically for dyslipidemia. Recent studies demonstrated that NPC1L1 regulates the intestinal absorption of several fat-soluble nutrients, in addition to cholesterol. The study was conducted to reveal new physiological roles of NPC1L1 by identifying novel dietary substrate(s). Very low-density lipoprotein and low-density lipoprotein (VLDL/LDL) are increased in Western diet (WD)-fed mice in an NPC1L1-dependent manner, so we comprehensively analyzed the NPC1L1-dependent VLDL/LDL components. Apolipoprotein M (apoM), a binding protein of sphingosine-1-phosphate (S1P: a lipid mediator), and S1P were NPC1L1-dependently increased in VLDL/LDL by WD feeding. S1P is metabolized from sphingomyelin (SM) and SM is abundant in WD, so we focused on intestinal SM absorption. In vivo studies with Npc1l1 knockout mice and in vitro studies with NPC1L1-overexpressing cells revealed that SM is a physiological substrate of NPC1L1. These results suggest a scenario in which dietary SM is absorbed by NPC1L1 in the intestine, followed by SM conversion to S1P and, after several steps, S1P is exported into the blood as the apoM-bound form in VLDL/LDL. Our findings provide insight into the functions of NPC1L1 for a better understanding of sphingolipids and S1P homeostasis.

[Translational Research Based on Understanding the Regulatory Mechanisms of in Vivo Behaviors of Fat-soluble Compounds]

Several fat-soluble compounds such as cholesterol and fat-soluble vitamins have important physiological activities in the body, and their excess and/or deficiency have been reported to be closely associated with the onset and progression of several conditions such as lifestyle-related diseases. It is important to clarify not only the physiological activities but also in vivo kinetics of fat-soluble compounds to understand their in vivo activity (toxicity). This review introduces our recent (reverse) translational research in a combination of basic and clinical studies to reveal the regulatory mechanisms of in vivo behaviors of fat-soluble compounds and effects of their disruption in humans.

TPGS-grafted and acid-responsive soy protein nanogels for efficient intracellular drug release, accumulation, penetration in 3D tumor spheroids of drug-resistant cancer cells

The frequent occurrence of multidrug resistance (MDR) in solid tumors is the major obstacle for nano-drug delivery systems (nDDS) to realize the successful cancer chemotherapy. Herein, we had prepared pH-responsive nanogels via cross-linking TPGS-grafted soy protein with an acid-labile ortho ester cross-linker (OEAM) to realize the efficient intracellular drugs release and accumulation, and subsequently enhance therapeutic effect in MDR tumor cells. These nanogels displayed a uniform size (~200 nm) and morphology, and the introduction of ortho ester bonds endowed nanogels stability in neutral environment and acid-degradability in acidic conditions. Cisplatin (CDDP) was successfully loaded into nanogels, which exhibited an accelerated drug release at low pH. The modification of TPGS efficiently improved cellular internalization and drug accumulation in A549/DDP cells by inhibiting the function of drug efflux pumps (MRP2 and ATP7A/7B), leading to higher cytotoxicity and apoptosis. Moreover, TPGS-grafted nanogels also showed better drug accumulation and penetration in tumor-like spheroids, and then remarkably inhibited tumor growth owing to the rapid drug release in acidic organelles. As a result, the TPGS-grafted and pH-sensitive soy protein nanogels have a great potential as a drugs carrier for the efficient cancer treatment.

Hepatic Expression of Niemann-Pick C1-Like 1, a Cholesterol Reabsorber from Bile, Exacerbates Western Diet-Induced Atherosclerosis in LDL Receptor Mutant Mice

Westernization of dietary habits increases lipid intake and is responsible for increased numbers of patients with atherosclerotic diseases. Niemann-Pick C1-Like 1 (NPC1L1)-a cholesterol importer-plays a crucial role in dietary cholesterol absorption in the intestine and is closely associated with several lipid-related diseases, including atherosclerosis. NPC1L1 is highly expressed in the liver and intestine in humans, whereas NPC1L1 expression is low in the rodent liver. Due to species differences in the tissue distribution of NPC1L1, there are limited studies on the pathophysiological role of hepatic NPC1L1, a cholesterol reabsorber from bile. In the present study, to explore whether hepatic NPC1L1 is involved in the development/progression of atherosclerosis, we compared four kinds of atherosclerosis mouse models with different expression levels of NPC1L1 in the intestinal and liver tissues in a genetic background of dysfunctional low-density lipoprotein receptor mutation. Western diet (WD)-induced hyperlipidemia and atherosclerotic plaque formation were more severe in mice expressing NPC1L1 in both the liver and intestine (plasma cholesterol, 839.5 mg/dl; plaque area, 29.5% of total aorta), compared with mice expressing NPC1L1 only in the intestine (plasma cholesterol, 573.1 mg/dl; plaque area, 13.3% of total aorta). Such hepatic NPC1L1-mediated promotion of hyperlipidemia and atherosclerosis was not observed in mice not expressing intestinal NPC1L1 and mice treated with ezetimibe, an NPC1L1 inhibitor used clinically for dyslipidemia. These results suggested that hepatic NPC1L1 promotes WD-induced dyslipidemia and atherosclerosis in concert with intestinal NPC1L1. Our findings provide novel insights into the pathophysiological importance of hepatic NPC1L1 in development/progression of atherosclerosis. SIGNIFICANCE STATEMENT: Niemann-Pick C1-Like 1 (NPC1L1) protein, a cholesterol importer and a molecular target of ezetimibe clinically used for dyslipidemia, is highly expressed not only in the intestine, but also in the liver in humans, although the pathophysiological importance of hepatic NPC1L1 in atherosclerotic diseases remained unclear. By using novel mouse models to separately analyze the effects of hepatic and intestinal NPC1L1 on the development/progression of atherosclerosis, we first demonstrated that hepatic NPC1L1 accelerates Western diet-induced atherosclerotic plaque formation in an intestinal NPC1L1-dependent and an ezetimibe-sensitive manner.

Vitamin E: Regulatory Role on Signal Transduction

Vitamin E modulates signal transduction pathways by several molecular mechanisms. As a hydrophobic molecule located mainly in membranes it contributes together with other lipids to the physical and structural characteristics such as membrane stability, curvature, fluidity, and the organization into microdomains (lipid rafts). By acting as the main lipid-soluble antioxidant, it protects other lipids such as mono- and poly-unsaturated fatty acids (MUFA and PUFA, respectively) against chemical reactions with reactive oxygen and nitrogen species (ROS and RNS, respectively) and prevents membrane destabilization and cellular dysfunction. In cells, vitamin E affects signaling in redox-dependent and redox-independent molecular mechanisms by influencing the activity of enzymes and receptors involved in modulating specific signal transduction and gene expression pathways. By protecting and preventing depletion of MUFA and PUFA it indirectly enables regulatory effects that are mediated by the numerous lipid mediators derived from these lipids. In recent years, some vitamin E metabolites have been observed to affect signal transduction and gene expression and their relevance for the regulatory function of vitamin E is beginning to be elucidated. In particular, the modulation of the CD36/FAT scavenger receptor/fatty acids transporter by vitamin E may influence many cellular signaling pathways relevant for lipid homeostasis, inflammation, survival/apoptosis, angiogenesis, tumorigenesis, neurodegeneration, and senescence. Thus, vitamin E has an important role in modulating signal transduction and gene expression pathways relevant for its uptake, distribution, metabolism, and molecular action that when impaired affect physiological and patho-physiological cellular functions relevant for the prevention of a number of diseases. © 2018 IUBMB Life, 71(4):456-478, 2019.

Vitamin E Metabolic Effects and Genetic Variants: A Challenge for Precision Nutrition in Obesity and Associated Disturbances

Vitamin E (VE) has a recognized leading role as a contributor to the protection of cell constituents from oxidative damage. However, evidence suggests that the health benefits of VE go far beyond that of an antioxidant acting in lipophilic environments. In humans, VE is channeled toward pathways dealing with lipoproteins and cholesterol, underlining its relevance in lipid handling and metabolism. In this context, both VE intake and status may be relevant in physiopathological conditions associated with disturbances in lipid metabolism or concomitant with oxidative stress, such as obesity. However, dietary reference values for VE in obese populations have not yet been defined, and VE supplementation trials show contradictory results. Therefore, a better understanding of the role of genetic variants in genes involved in VE metabolism may be crucial to exert dietary recommendations with a higher degree of precision. In particular, genetic variability should be taken into account in targets concerning VE bioavailability per se or concomitant with impaired lipoprotein transport. Genetic variants associated with impaired VE liver balance, and the handling/resolution of oxidative stress might also be relevant, but the core information that exists at present is insufficient to deliver precise recommendations.

Associations between Lifestyle-Related Diseases and Transporters Involved in Intestinal Absorption and Biliary Excretion of Cholesterol

Westernization of dietary habits leads to an increase in lipid intake and is thought to be responsible for an increase in patients with dyslipidemia. It is a well-known fact that the impaired cholesterol homeostasis is closely related to the development of various lifestyle-related diseases such as fatty liver, diabetes, and gallstone as well as dyslipidemia leading to atherosclerosis and cardiovascular diseases such as heart attack and stroke. Therefore, appropriate management of cholesterol levels in the body is considered important in prevention and treatments of these lifestyle-related diseases and in addition, molecular mechanisms controlling plasma (and/or hepatic) cholesterol levels have been intensively studied. Due to its hydrophobicity, cholesterol was long believed to pass through cell membranes by passive diffusion. However, recent studies have identified a number of plasma membrane transporters that are responsible for the cellular uptake or efflux of cholesterol and involved in developments of lifestyle-related diseases. In this review, we focus on Niemann-Pick C1 Like 1 (NPC1L1) and a heterodimer of ATP-binding cassette transporter G5 and G8 (ABCG5/G8), both of which are responsible for intestinal cholesterol absorption and biliary cholesterol secretion, and discuss the relationship between these cholesterol transporters and lifestyle-related diseases. In addition, we also discuss the related uncertainties that need to be explored in future studies.

Clinically Relevant Herb-Micronutrient Interactions: When Botanicals, Minerals, and Vitamins Collide

The ability of certain foods to impair or augment the absorption of various vitamins and minerals has been recognized for many years. However, the contribution of botanical dietary supplements (BDSs) to altered micronutrient disposition has received little attention. Almost half of the US population uses some type of dietary supplement on a regular basis, with vitamin and mineral supplements constituting the majority of these products. BDS usage has also risen considerably over the last 2 decades, and a number of clinically relevant herb-drug interactions have been identified during this time. BDSs are formulated as concentrated plant extracts containing a plethora of unique phytochemicals not commonly found in the normal diet. Many of these uncommon phytochemicals can modulate various xenobiotic enzymes and transporters present in both the intestine and liver. Therefore, it is likely that the mechanisms underlying many herb-drug interactions can also affect micronutrient absorption, distribution, metabolism, and excretion. To date, very few prospective studies have attempted to characterize the prevalence and clinical relevance of herb-micronutrient interactions. Current research indicates that certain BDSs can reduce iron, folate, and ascorbate absorption, and others contribute to heavy metal intoxication. Researchers in the field of nutrition may not appreciate many of the idiosyncrasies of BDSs regarding product quality and dosage form performance. Failure to account for these eccentricities can adversely affect the outcome and interpretation of any prospective herb-micronutrient interaction study. This review highlights several clinically relevant herb-micronutrient interactions and describes several common pitfalls that often beset clinical research with BDSs.

Key Pathways and Regulators of Vitamin K Function and Intermediary Metabolism

Vitamin K (VK) is an essential cofactor for the post-translational conversion of peptide-bound glutamate to γ-carboxyglutamate. The resultant vitamin K-dependent proteins are known or postulated to possess a variety of biological functions, chiefly in the maintenance of hemostasis. The vitamin K cycle is a cellular pathway that drives γ-carboxylation and recycling of VK via γ-carboxyglutamyl carboxylase (GGCX) and vitamin K epoxide reductase (VKOR), respectively. In this review, we show how novel molecular biological approaches are providing new insights into the pathophysiological mechanisms caused by rare mutations of both GGCX and VKOR. We also discuss how other protein regulators influence the intermediary metabolism of VK, first through intestinal absorption and second through a pathway that converts some dietary phylloquinone to menadione, which is prenylated to menaquinone-4 (MK-4) in target tissues by UBIAD1. The contribution of MK-4 synthesis to VK functions is yet to be revealed.

pH-sensitive micelles with charge-reversible property for tumor growth inhibition and anti-metastasis

Biocompatible VE-based micelles with charge-reversible property for PTX delivery demonstrating effective antitumor and anti-metastasis effects.

Recent developments in d-α-tocopheryl polyethylene glycol-succinate-based nanomedicine for cancer therapy

Cancer remains an obstacle to be surmounted by humans. As an FDA-approved biocompatible drug excipient, d-α-tocopheryl polyethylene glycol succinate (TPGS) has been widely applied in drug delivery system (DDS). Along with in-depth analyses of TPGS-based DDS, increasingly attractive results have revealed that TPGS is able to act not only as a simple drug carrier but also as an assistant molecule with various bio-functions to improve anticancer efficacy. In this review, recent advances in TPGS-based DDS are summarized. TPGS can inhibit P-glycoprotein, enhance drug absorption, induce mitochondrial-associated apoptosis or other apoptotic pathways, promote drug penetration and tumor accumulation, and even inhibit tumor metastasis. As a result, many formulations, by using original TPGS, TPGS-drug conjugates or TPGS copolymers, were prepared, and as expected, an enhanced therapeutic effect was achieved in different tumor models, especially in multidrug resistant and metastatic tumors. Although the mechanisms by which TPGS participates in such functions are not yet very clear, considering its effectiveness in tumor treatment, TPGS-based DDS appears to be one of the best candidates for future clinical applications.

Effects of lipoic acid and n-3 long-chain polyunsaturated fatty acid on the liver ovariectomized rat model of menopause

BACKGROUND

Bilateral ovariectomy is an experimental model used to analyse the effects of menopause and develop strategies to mitigate the deleterious effects of this condition. Supplementation of the diet with antioxidants has been used to reduce potential oxidative stress caused by menopause. The purpose of the study was to analyse the effects of α-lipoic acid (LA), docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), dietary supplementation on oxidative stress in the livers of ovariectomized rats.

METHODS

In this study, we evaluated the effect of dietary supplementation with LA, DHA and EPA for a period of 16 weeks on oestrogen levels and oxidative stress biomarkers in the livers of ovariectomized 25 three-month-old rats.

RESULTS

Serum oestrogen levels were lower after ovariectomy but were not altered by dietary treatments. LA was capable of acting in the liver, recovering the activity of the antioxidant enzymes superoxide dismutase and glutathione peroxidase, and reducing protein oxidative damage. Moreover, LA supplementation reduced nitrite and nitrate levels. DHA and EPA recovered the antioxidant activity of cytosolic and mitochondrial superoxide dismutase, decreasing protein oxidation. Protection against lipid oxidation differed between treatments. The DHA-treated group showed increased levels of the lipid peroxidation biomarker malondialdehyde compared to the ovariectomized group. However, malondialdehyde levels were not altered by EPA treatment.

CONCLUSIONS

The results suggest that the antioxidant response varies among evaluated supplementations and all supplements were able to alter enzymatic and non-enzymatic antioxidants in the livers of ovariectomized rats. DHA presented the most evident antioxidant effect, decreasing protein and lipid damage.

A New Horizon in Vitamin K Research

Vitamin K is a cofactor for γ-glutamyl carboxylase, which catalyzes the posttranslational conversion of specific glutamyl residues to γ-carboxyglutamyl residues in a variety of vitamin K-dependent proteins (VKDPs) involved in blood coagulation, bone and cartilage metabolism, signal transduction, and cell proliferation. Despite the great advances in the genetic, structural, and functional studies of VKDPs as well as the enzymes identified as part of the vitamin K cycle which enable it to be repeatedly recycled within the cells, little is known of the identity and roles of key regulators of vitamin K metabolism in mammals and humans. This review focuses on new insights into the molecular mechanisms underlying the intestinal absorption and in vivo tissue conversion of vitamin K1 to menaquinone-4 (MK-4) with special emphasis on two major advances in the studies of intestinal vitamin K transporters in enterocytes and a tissue MK-4 biosynthetic enzyme UbiA prenyltransferase domain-containing protein 1 (UBIAD1), which participates in the in vivo conversion of a fraction of dietary vitamin K1 to MK-4 in mammals and humans, although it remains uncertain whether UBIAD1 functions as a key regulator of intracellular cholesterol metabolism, bladder and prostate tumor cell progression, vascular integrity, and protection from oxidative stress.

Transporters for the Intestinal Absorption of Cholesterol, Vitamin E, and Vitamin K

Humans cannot synthesize fat-soluble vitamins such as vitamin E and vitamin K. For this reason, they must be obtained from the diet via intestinal absorption. As the deficiency or excess of these vitamins has been reported to cause several types of diseases and disorders in humans, the intestinal absorption of these nutrients must be properly regulated to ensure good health. However, the mechanism of their intestinal absorption remains poorly understood. Recent studies on cholesterol using genome-edited mice, genome-wide association approaches, gene mutation analyses, and the development of cholesterol absorption inhibitors have revealed that several membrane proteins play crucial roles in the intestinal absorption of cholesterol. Surprisingly, detailed analyses of these cholesterol transporters have revealed that they can also transport vitamin E and vitamin K, providing clues to uncover the molecular mechanisms underlying the intestinal absorption of these fat-soluble vitamins. In this review, we focus on the membrane proteins (Niemann-Pick C1 like 1, scavenger receptor class B type I, cluster of differentiation 36, and ATP-binding cassette transporter A1) that are (potentially) involved in the intestinal absorption of cholesterol, vitamin E, and vitamin K and discuss their physiological and pharmacological importance. We also discuss the related uncertainties that need to be explored in future studies.

Complexity of vitamin E metabolism

Bioavailability of vitamin E is influenced by several factors, most are highlighted in this review. While gender, age and genetic constitution influence vitamin E bioavailability but cannot be modified, life-style and intake of vitamin E can be. Numerous factors must be taken into account however, i.e., when vitamin E is orally administrated, the food matrix may contain competing nutrients. The complex metabolic processes comprise intestinal absorption, vascular transport, hepatic sorting by intracellular binding proteins, such as the significant α-tocopherol-transfer protein, and hepatic metabolism. The coordinated changes involved in the hepatic metabolism of vitamin E provide an effective physiological pathway to protect tissues against the excessive accumulation of, in particular, non-α-tocopherol forms. Metabolism of vitamin E begins with one cycle of CYP4F2/CYP3A4-dependent ω-hydroxylation followed by five cycles of subsequent β-oxidation, and forms the water-soluble end-product carboxyethylhydroxychroman. All known hepatic metabolites can be conjugated and are excreted, depending on the length of their side-chain, either via urine or feces. The physiological handling of vitamin E underlies kinetics which vary between the different vitamin E forms. Here, saturation of the side-chain and also substitution of the chromanol ring system are important. Most of the metabolic reactions and processes that are involved with vitamin E are also shared by other fat soluble vitamins. Influencing interactions with other nutrients such as vitamin K or pharmaceuticals are also covered by this review. All these processes modulate the formation of vitamin E metabolites and their concentrations in tissues and body fluids. Differences in metabolism might be responsible for the discrepancies that have been observed in studies performed in vivo and in vitro using vitamin E as a supplement or nutrient. To evaluate individual vitamin E status, the analytical procedures used for detecting and quantifying vitamin E and its metabolites are crucial. The latest methods in analytics are presented.

NPC1L1 is a key regulator of intestinal vitamin K absorption and a modulator of warfarin therapy

Vitamin K (VK) is a micronutrient that facilitates blood coagulation. VK antagonists, such as warfarin, are used in the clinic to prevent thromboembolism. Because VK is not synthesized in the body, its intestinal absorption is crucial for maintaining whole-body VK levels. However, the molecular mechanism of this absorption is unclear. We demonstrate that Niemann-Pick C1-like 1 (NPC1L1) protein, a cholesterol transporter, plays a central role in intestinal VK uptake and modulates the anticoagulant effect of warfarin. In vitro studies using NPC1L1-overexpressing intestinal cells and in vivo studies with Npc1l1-knockout mice revealed that intestinal VK absorption is NPC1L1-dependent and inhibited by ezetimibe, an NPC1L1-selective inhibitor clinically used for dyslipidemia. In addition, in vivo pharmacological studies demonstrated that the coadministration of ezetimibe and warfarin caused a reduction in hepatic VK levels and enhanced the pharmacological effect of warfarin. Adverse events caused by the coadministration of ezetimibe and warfarin were rescued by oral VK supplementation, suggesting that the drug-drug interaction effects observed were the consequence of ezetimibe-mediated VK malabsorption. This mechanism was supported by a retrospective evaluation of clinical data showing that, in more than 85% of warfarin-treated patients, the anticoagulant activity was enhanced by cotreatment with ezetimibe. Our findings provide insight into the molecular mechanism of VK absorption. This new drug-drug interaction mechanism between ezetimibe (a cholesterol transport inhibitor) and warfarin (a VK antagonist and anticoagulant) could inform clinical care of patients on these medications, such as by altering the kinetics of essential, fat-soluble vitamins.

[Transporter-mediated regulation of pharmacokinetics of lifestyle-related substances]

Recent studies revealed the importance of transporters in the behaviors of small molecules in the body. In mammals, the presence of a lot of transporters has been suggested, such as ATP-binding cassette (ABC) transporters and solute ligand carrier (SLC) transporters, some of which are clarified to be causative genes for various kinds of genetic disorders. In addition, a lot of transporters are known to mediate cellular import or export of drugs, to contribute to the pharmacokinetics of substrate drugs and to be involved in the interindividual differences of drug responses. In this review, I introduce our recent work on the transporter-mediated regulation of pharmacokinetics of lifestyle-related substances, such as cholesterol and urate.

Unsaturated fatty acids promote bioaccessibility and basolateral secretion of carotenoids and α-tocopherol by Caco-2 cells

Bioavailability of carotenoids and tocopherols from foods is determined by the efficiency of transfer from food/meal to mixed micelles during digestion, incorporation into chylomicrons for trans-epithelial transport to lymphatic/blood system, and distribution to target tissues.

A question of balance: achieving appropriate nutrient levels in biofortified staple crops

The biofortification of staple crops with vitamins is an attractive strategy to increase the nutritional quality of human food, particularly in areas where the population subsists on a cereal-based diet. Unlike other approaches, biofortification is sustainable and does not require anything more than a standard food-distribution infrastructure. The health-promoting effects of vitamins depend on overall intake and bioavailability, the latter influenced by food processing, absorption efficiency and the utilisation or retention of the vitamin in the body. The bioavailability of vitamins in nutritionally enriched foods should ideally be adjusted to achieve the dietary reference intake in a reasonable portion. Current vitamin biofortification programmes focus on the fat-soluble vitamins A and E, and the water-soluble vitamins C and B9 (folate), but the control of dosage and bioavailability has been largely overlooked. In the present review, we discuss the vitamin content of nutritionally enhanced foods developed by conventional breeding and genetic engineering, focusing on dosage and bioavailability. Although the biofortification of staple crops could potentially address micronutrient deficiency on a global scale, further research is required to develop effective strategies that match the bioavailability of vitamins to the requirements of the human diet.

Vitamin E: a dark horse at the crossroad of cancer management

It appears that the story on vitamin E and its role in human health remains incomplete. It is apparent that vitamin E supplementation involves many variables, some of which include its uptake from the intestine, the preference for α-tocopherol, transport by tocopherol specific proteins and lipid transporters and the differential metabolism of different vitamin E isoforms. The fundamental differences within population genetics can have significant implications for the effect that dietary supplementation might have on human health. When evaluating the efficacy of vitamin E prophylactic or therapeutic use in previous and future studies, it is critical to consider dosage to be administered, form of vitamin E and source (such as whether from synthetic or purified from natural sources). Further studies are needed to determine the effects of all vitamin E isoforms on cell growth, tumorigenicity, to clarify its possible use as an adjuvant to existing chemotherapeutics. The Alpha-Tocopherol, Beta Carotene (ATBC) Cancer Prevention Study Group and Selenium and Vitamin E Cancer Prevention Trial (SELECT) studies along with the numerous studies of vitamin E should help guide the next chapter of vitamin E research.

β-Carotene Attenuates Angiotensin II-Induced Aortic Aneurysm by Alleviating Macrophage Recruitment in Apoe(-/-) Mice

Abdominal aortic aneurysm (AAA) is a common chronic degenerative disease characterized by progressive aortic dilation and rupture. The mechanisms underlying the role of α-tocopherol and β-carotene on AAA have not been comprehensively assessed. We investigated if α-tocopherol and β-carotene supplementation could attenuate AAA, and studied the underlying mechanisms utilized by the antioxidants to alleviate AAA. Four-months-old Apoe^−/− mice were used in the induction of aneurysm by infusion of angiotensin II (Ang II), and were orally administered with α-tocopherol and β-carotene enriched diet for 60 days. Significant increase of LDL, cholesterol, triglycerides and circulating inflammatory cells was observed in the Ang II-treated animals, and gene expression studies showed that ICAM-1, VCAM-1, MCP-1, M-CSF, MMP-2, MMP-9 and MMP-12 were upregulated in the aorta of aneurysm-induced mice. Extensive plaques, aneurysm and diffusion of inflammatory cells into the tunica intima were also noticed. The size of aorta was significantly (P = 0.0002) increased (2.24±0.20 mm) in the aneurysm-induced animals as compared to control mice (1.17±0.06 mm). Interestingly, β-carotene dramatically controlled the diffusion of macrophages into the aortic tunica intima, and circulation. It also dissolved the formation of atheromatous plaque. Further, β-carotene significantly decreased the aortic diameter (1.33±0.12 mm) in the aneurysm-induced mice (β-carotene, P = 0.0002). It also downregulated ICAM-1, VCAM-1, MCP-1, M-CSF, MMP-2, MMP-9, MMP-12, PPAR-α and PPAR-γ following treatment. Hence, dietary supplementation of β-carotene may have a protective function against Ang II-induced AAA by ameliorating macrophage recruitment in Apoe^−/− mice.

Bioavailability of vitamin E in humans: an update

Vitamin E is essential for human health and may play a role in the prevention of some degenerative diseases. Its bioavailability, however, is wide ranging and is affected by numerous factors. Recent findings showing that the intestinal absorption of vitamin E involves proteins have raised new relevant questions about factors that can affect bioavailability. It is, therefore, opportune to present a current overview of this topic. This review begins by exploring what is known, as well as what is unknown, about the metabolization of vitamin E in the human upper gastrointestinal tract and then presents a methodical evaluation of factors assumed to affect vitamin E bioavailability. Three main conclusions can be drawn. First, the proteins ABCA1, NPC1L1, and SR-BI are implicated in the absorption of vitamin E. Second, the efficiency of vitamin E absorption is widely variable, though not accurately known (i.e., between 10% and 79%), and is affected by several dietary factors (e.g., food matrix, fat, and fat-soluble micronutrients). Finally, numerous unanswered questions remain about the metabolization of vitamin E in the intestinal lumen and about the factors affecting the efficiency of vitamin E absorption.

Vitamin E and nonalcoholic fatty liver disease

PURPOSE OF REVIEW

Oxidative stress plays a central role in the transition from simple steatosis to nonalcoholic steatohepatitis (NASH). An effective therapeutic strategy is to target reduction in oxidative stress in NASH patients. The aim of this review is to discuss the role of oxidative stress in NASH and biological activities of vitamin E and present available evidence on the therapeutic efficacy of vitamin E in NASH.

RECENT FINDINGS

In Pioglitazone versus Vitamin E versus Placebo for the Treatment of Nondiabetic Patients with Nonalcoholic Steatohepatitis (PIVENS) trial, vitamin E therapy demonstrated a significant improvement in steatosis, inflammation, ballooning, and resolution of steatohepatitis in adult patients with aggressive NASH, who do not have diabetes or cirrhosis. Although vitamin E showed a significant resolution of NASH in children, a sustained reduction of alanine aminotransferase was not attained in The Treatment of nonalcoholic fatty liver disease (NAFLD) in Children (TONIC) trial.

SUMMARY

The prevalence of NAFLD is likely to increase over time due to the epidemics of obesity and diabetes. Presently, there is no definitive treatment for NAFLD. Based on available evidence, vitamin E (RRR-α-tocopherol) is only recommended in NASH adults without diabetes or cirrhosis and with aggressive histology. Validation is needed in children before its use can be recommended. Longer follow-up of randomized controlled trials are needed to assess long-term vitamin E safety.

Differential changes of fat-soluble vitamins and pollutants during lactation in northern elephant seal mother-pup pairs

We investigated the changes of vitamins A and E as well as PCBs and DDTs during lactation in northern elephant seal (Mirounga angustirostris) mother-pup pairs. On average, milk vitamin A concentrations were 6 times higher during late lactation than during early lactation, a pattern that differs dramatically from terrestrial mammals. Vitamin A concentrations also significantly increased in the inner blubber throughout lactation, whereas they remained constant in the outer blubber. Similar dynamics were observed for PCBs and DDTs in maternal blubber and milk. Blubber appears to be an important storage site for vitamin A and organochlorines in seals and a direct transfer of those molecules to the mammary gland may occur. The dynamics of vitamin A, PCBs and DDTs differed from those of vitamin E. There was a significant drop in milk vitamin E concentrations between early and late lactation, which is the usual pattern observed in terrestrial mammals. The dynamics of vitamin E in the blubber layers also differed from those of vitamin A, suggesting different mechanisms of mobilization and transfer into the milk.

Toxicogenomics and metabolomics of pentamethylchromanol (PMCol)-induced hepatotoxicity

Pentamethyl-6-chromanol (PMCol), a chromanol-type compound related to vitamin E, was proposed as an anticancer agent with activity against androgen-dependent cancers. In repeat dose-toxicity studies in rats and dogs, PMCol caused hepatotoxicity, nephrotoxicity, and hematological effects. The objectives of this study were to determine the mechanisms of the observed toxicity and identify sensitive early markers of target organ injury by integrating classical toxicology, toxicogenomics, and metabolomic approaches. PMCol was administered orally to male Sprague-Dawley rats at 200 and 2000 mg/kg daily for 7 or 28 days. Changes in clinical chemistry included elevated alanine aminotransferase, total bilirubin, cholesterol and triglycerides-indicative of liver toxicity that was confirmed by microscopic findings (periportal hepatocellular hydropic degeneration and cytomegaly) in treated rats. Metabolomic evaluations of liver revealed time- and dose-dependent changes, including depletion of total glutathione and glutathione conjugates, decreased methionine, and increased S-adenosylhomocysteine, cysteine, and cystine. PMCol treatment also decreased cofactor levels, namely, FAD and increased NAD(P)+. Microarray analysis of liver found that differentially expressed genes were enriched in the glutathione and cytochrome P450 pathways by PMCol treatment. Reverse transcription-polymerase chain reaction of six upregulated genes and one downregulated gene confirmed the microarray results. In conclusion, the use of metabolomics and toxicogenomics demonstrates that chronic exposure to high doses of PMCol induces liver damage and dysfunction, probably due to both direct inhibition of glutathione synthesis and modification of drug metabolism pathways. Depletion of glutathione due to PMCol exposure ultimately results in a maladaptive response, increasing the consumption of hepatic dietary antioxidants and resulting in elevated reactive oxygen species levels associated with hepatocellular damage and deficits in liver function.

Behavioral and neurochemical effects of proline

Proline is an amino acid with an essential role for primary metabolism and physiologic functions. Hyperprolinemia results from the deficiency of specific enzymes for proline catabolism, leading to tissue accumulation of this amino acid. Hyperprolinemic patients can present neurological symptoms and brain abnormalities, whose aetiopathogenesis is poorly understood. This review addresses some of the findings obtained, mainly from animal studies, indicating that high proline levels may be associated to neuropathophysiology of some disorders. In this context, it has been suggested that energy metabolism deficit, Na(+),K(+)-ATPase, kinase creatine, oxidative stress, excitotoxicity, lipid content, as well as purinergic and cholinergic systems are involved in the effect of proline on brain damage and spatial memory deficit. The discussion focuses on the relatively low antioxidant defenses of the brain and the vulnerability of neural tissue to reactive species. This offers new perspectives for potential therapeutic strategies for this condition, which may include the early use of appropriate antioxidants as a novel adjuvant therapy, besides the usual treatment based on special diets poor in proline.

Quantitation of [5-14CH3]-(2R, 4'R, 8'R)-α-tocopherol in humans

Half-lives of α-tocopherol in plasma have been reported as 2-3 d, whereas the Elgin Study required >2 y to deplete α-tocopherol, so gaps exist in our quantitative understanding of human α-tocopherol metabolism. Therefore, 6 men and 6 women aged 27 ± 6 y (mean ± SD) ingested 1.81 nmol, 3.70 kBq of [5-(14)CH(3)]-(2R, 4'R, 8'R)-α-tocopherol. The levels of (14)C in blood plasma and washed RBC were monitored frequently from 0 to 460 d while the levels of (14)C in urine and feces were monitored from 0 to 21 d. Total fecal elimination (fecal + metabolic fecal) was 23.24 ± 5.81% of the (14)C dose, so feces over urine was the major route of elimination of the ingested [5-(14)CH(3)]-(2R, 4'R, 8'R)-α-tocopherol, consistent with prior estimates. The half-life of α-tocopherol varied in plasma and RBC according to the duration of study. The minute dose coupled with frequent monitoring over 460 d and 21 d for blood, urine, and feces ensured the [5-(14)CH(3)]-(2R, 4'R, 8'R)-α-tocopherol (the tracer) had the chance to fully mix with the endogenous [5-(14)CH(3)]-(2R, 4'R, 8'R)-α-tocopherol (the tracee). The (14)C levels in neither plasma nor RBC had returned to baseline by d 460, indicating that the t(1/2) of [5-CH(3)]-(2R, 4'R, 8'R)-α-tocopherol in human blood was longer than prior estimates.

NPC2 regulates biliary cholesterol secretion via stimulation of ABCG5/G8-mediated cholesterol transport

BACKGROUND & AIMS

Biliary cholesterol secretion helps maintain cholesterol homeostasis; it is regulated by the cholesterol exporter adenosine triphosphate-binding cassettes G5 and G8 (ABCG5/G8) and the cholesterol importer Niemann-Pick C1-like 1 (NPC1L1). We studied another putative regulator of cholesterol secretion into bile, Niemann-Pick C2 (NPC2)--a cholesterol-binding protein secreted by the biliary system--and determined its effects on transporter-mediated biliary secretion of cholesterol.

METHODS

Mice with hepatic knockdown of Npc2 or that overexpressed NPC2 were created using adenovirus-mediated gene transfer; biliary lipids were characterized. The effects of secreted NPC2 on cholesterol transporter activity were examined in vitro using cells that overexpressed ABCG5/G8 or NPC1L1.

RESULTS

Studies of mice with altered hepatic expression of NPC2 revealed that this expression positively regulates the biliary secretion of cholesterol, supported by the correlation between levels of NPC2 protein and cholesterol in human bile. In vitro analysis showed that secreted NPC2 stimulated ABCG5/G8-mediated cholesterol efflux but not NPC1L1-mediated cholesterol uptake. Consistent with these observations, no significant changes in biliary cholesterol secretion were observed on hepatic overexpression of NPC2 in ABCG5/G8-null mice, indicating that NPC2 requires ABCG5/G8 to stimulate cholesterol secretion. Analyses of NPC2 mutants showed that the stimulatory effect of biliary NPC2 was independent of the function of lysosomal NPC2 as a regulator of intracellular cholesterol trafficking.

CONCLUSIONS

NPC2 is a positive regulator of biliary cholesterol secretion via stimulation of ABCG5/G8-mediated cholesterol transport.

Human NPC1L1 expression is positively regulated by PPARα

PURPOSE

Niemann-Pick C1-like 1 (NPC1L1), a pharmacological target of ezetimibe, is responsible for cholesterol absorption in enterocytes and hepatocytes. In the present study, the involvement of peroxisome proliferator-activated receptor α (PPARα) and its cofactor, PPARγ coactivator 1α (PGC1α) in the transcriptional regulation of human NPC1L1 was analyzed.

METHODS

Reporter gene assays and electrophoretic mobility shift assays (EMSAs) were performed with the 5'-flanking region of the human NPC1L1 gene and the effect of siPPARα was examined.

RESULTS

PPARα-mediated transactivation was observed with human NPC1L1 promoter constructs. Detailed analyses using deletion- and mutated-promoter constructs revealed the presence of a functional PPARα-response element (PPRE) upstream of the human NPC1L1 gene (-846/-834), a direct binding of PPARα and RXRα to which was confirmed by EMSAs. Moreover, PPARα-specific knockdown resulted in a significant decrease in the endogenous expression of NPC1L1 mRNA and protein in human-derived HepG2 cells. Furthermore, cotransfection of PGC1α stimulated the SREBP2/HNF4α- and PPARα/RXRα-mediated activation of the human NPC1L1 promoter.

CONCLUSIONS

We found that PPARα positively regulates human NPC1L1 transcription via direct binding to a PPRE. Additionally, PGC1α stimulates the SREBP2/HNF4α- and PPARα/RXRα-mediated transactivation of human NPC1L1. These findings may provide new insights into the close relationship of glucose, fatty acids and cholesterol homeostasis.

Human NPC1L1 expression is positively regulated by PPARα

PURPOSE

Niemann-Pick C1-like 1 (NPC1L1), a pharmacological target of ezetimibe, is responsible for cholesterol absorption in enterocytes and hepatocytes. In the present study, the involvement of peroxisome proliferator-activated receptor α (PPARα) and its cofactor, PPARγ coactivator 1α (PGC1α) in the transcriptional regulation of human NPC1L1 was analyzed.

METHODS

Reporter gene assays and electrophoretic mobility shift assays (EMSAs) were performed with the 5'-flanking region of the human NPC1L1 gene and the effect of siPPARα was examined.

RESULTS

PPARα-mediated transactivation was observed with human NPC1L1 promoter constructs. Detailed analyses using deletion- and mutated-promoter constructs revealed the presence of a functional PPARα-response element (PPRE) upstream of the human NPC1L1 gene (-846/-834), a direct binding of PPARα and RXRα to which was confirmed by EMSAs. Moreover, PPARα-specific knockdown resulted in a significant decrease in the endogenous expression of NPC1L1 mRNA and protein in human-derived HepG2 cells. Furthermore, cotransfection of PGC1α stimulated the SREBP2/HNF4α- and PPARα/RXRα-mediated activation of the human NPC1L1 promoter.

CONCLUSIONS

We found that PPARα positively regulates human NPC1L1 transcription via direct binding to a PPRE. Additionally, PGC1α stimulates the SREBP2/HNF4α- and PPARα/RXRα-mediated transactivation of human NPC1L1. These findings may provide new insights into the close relationship of glucose, fatty acids and cholesterol homeostasis.