Rune Blomhoff

Transport and storage of vitamin A

The requirement of vitamin A (retinoids) for vision has been recognized for decades. In addition, vitamin A is involved in fetal development and in the regulation of proliferation and differentiation of cells throughout life. This fat-soluble organic compound cannot be synthesized endogenously by humans and thus is an essential nutrient; a well-regulated transport and storage system provides tissues with the correct amounts of retinoids in spite of normal fluctuations in daily vitamin A intake. An overview is presented here of current knowledge and hypotheses about the absorption, transport, storage, and metabolism of vitamin A. Some information is also presented about a group of ligand-dependent transcription factors, the retinoic acid receptors, that apparently mediate many of the extravisual effects of retinoids.

Is serum gamma glutamyltransferase a marker of oxidative stress

The primary role of cellular gamma glutamyltransferase (GGT) is to metabolize extracellular reduced glutathione (GSH), allowing for precursor amino acids to be assimilated and reutilized for intracellular GSH synthesis. Paradoxically, recent experimental studies indicate that cellular GGT may also be involved in the generation of reactive oxygen species in the presence of iron or other transition metals. Although the relationship between cellular GGT and serum GGT is not known and serum GGT activity has been commonly used as a marker for excessive alcohol consumption or liver diseases, our series of epidemiological studies consistently suggest that serum GGT within its normal range might be an early and sensitive enzyme related to oxidative stress. For example, serum and dietary antioxidant vitamins had inverse, dose-response relations to serum GGT level within its normal range, whereas dietary heme iron was positively related to serum GGT level. More importantly, serum GGT level within its normal range positively predicted F2-isoprostanes, an oxidative damage product of arachidonic acid, and fibrinogen and C-reactive protein, markers of inflammation, which were measured 5 or 15 years later, in dose–response manners. These findings suggest that strong associations of serum GGT with many cardiovascular risk factors and/or events might be explained by a mechanism related to oxidative stress. Even though studies on serum and/or cellular GGT is at a beginning stage, our epidemiological findings suggest that serum GGT might be useful in studying oxidative stress-related issues in both epidemiological and clinical settings.

The total antioxidant content of more than 3100 foods, beverages, spices, herbs and supplements used worldwide

BackgroundA plant-based diet protects against chronic oxidative stress-related diseases. Dietary plants contain variable chemical families and amounts of antioxidants. It has been hypothesized that plant antioxidants may contribute to the beneficial health effects of dietary plants. Our objective was to develop a comprehensive food database consisting of the total antioxidant content of typical foods as well as other dietary items such as traditional medicine plants, herbs and spices and dietary supplements. This database is intended for use in a wide range of nutritional research, from in vitro and cell and animal studies, to clinical trials and nutritional epidemiological studies.MethodsWe procured samples from countries worldwide and assayed the samples for their total antioxidant content using a modified version of the FRAP assay. Results and sample information (such as country of origin, product and/or brand name) were registered for each individual food sample and constitute the Antioxidant Food Table.ResultsThe results demonstrate that there are several thousand-fold differences in antioxidant content of foods. Spices, herbs and supplements include the most antioxidant rich products in our study, some exceptionally high. Berries, fruits, nuts, chocolate, vegetables and products thereof constitute common foods and beverages with high antioxidant values.ConclusionsThis database is to our best knowledge the most comprehensive Antioxidant Food Database published and it shows that plant-based foods introduce significantly more antioxidants into human diet than non-plant foods. Because of the large variations observed between otherwise comparable food samples the study emphasizes the importance of using a comprehensive database combined with a detailed system for food registration in clinical and epidemiological studies. The present antioxidant database is therefore an essential research tool to further elucidate the potential health effects of phytochemical antioxidants in diet.

Vitamin A in Health and Disease

Introduction Overview of Vitamin A Metabolism and Function Metabolism of Vitamin A Absorption of Vitamin A Role of Perisinusoidal Stellate Cells in Vitamin A Storage The Retinol-Binding Protein Superfamily Dynamic and Control of Plasma Retinol Retinoic Acid Homeostasis: Prospective Roles of b-Carotene, Retinol, CRBP, and CRABP Mechanism of Action of Vitamin A and Carotenoids Role of Nuclear Retinoic Acid Receptors in the Regulation of Gene Expression The Retinoid X Receptors: Modulators of Multiple Hormonal Signaling Pathways Retinoylation of Proteins in Mammalian Cells Role of Carotenoids in Antioxidant Defense Embryonic Development Role of Retinoids in Embryonic Development Vitamin A in Lung Development and Bronchopulmonary Dysplasia Are Ethanol-Induced Birth Defects Caused by Functional Retinoic Acid Deficiency? Skin and Epithelial Cells Role of Retinoids in Normal and Diseased Skin Regulation of Epithelial Differentiation by Retinoids Blood Cells Role of Retinoids in Normal Hematopoiesis and the Immune System Retinoids and Acute Myeloid Leukemia Vision Retinoid Isomerization Reactions in the Visual System Reproduction Vitamin A Functions in the Reproductive Organs Intake and Cancer Incidence Vitamin A and Cancer: Epidemiological Evidence in Humans Deficiency and Toxicity Vitamin A Deficiency: Its Epidemiology and Relation to Child Mortality and Morbidity Teratogenicity of Vitamin A and Retinoids Requirements Dietary Vitamin A Requirements

Perisinusoidal stellate cells of the liver: important roles in retinol metabolism and fibrosis.

In mammals, liver perisinusoidal stellate cells play an important role as a main store of body retinol (vitamin A). This fat‐soluble vitamin is essential for vision, and regulates differentiation and growth of many cell types during embryonal development as well as in adult tissues. Thus, many cell types require a continuous supply of retinol. The storage of retinol (as retinyl esters) in stellate cells ascertains ample access of retinol to such cells also during periods with a low dietary intake. In lower vertebrates such as fish, vitamin A‐storing stellate cells are found not only in the hepatic lobule, but also in the connective tissues of organs like intestine, kidney, ovaries, testes, and gills. Extrahepatic vitamin A‐storing stellate cells are found in higher vertebrates when excessive doses of vitamin A are administered. It is not clear at present whether these cells also play a role in retinol metabolism under normal conditions. Stellate cells proliferate in a fibrotic liver, and they have been found to synthesize connective tissue compounds such as collagen. It was recently demonstrated that stellate cells are the principal cellular source of collagen and other extracellular substances in normal as well as fibrotic livers. Therefore, stellate cells, which seem to be a specialized type of pericyte, have a central role in the pathological changes observed during the development of liver fibrosis.—Blomhoff, R.; Wake, K. Perisinusoidal stellate cells of the liver: important roles in retinol metabolism and fibrosis. FASEB J. 5: 271–277; 1991.

Polyphenols and glutathione synthesis regulation

Polyphenols in food plants are a versatile group of phytochemicals with many potentially beneficial activities in terms of disease prevention. In vitro cell culture experiments have shown that polyphenols possess antioxidant properties, and it is thought that these activities account for disease-preventing effects of diets high in polyphenols. However, polyphenols may be regarded as xenobiotics by animal cells and are to some extent treated as such, ie, they interact with phase I and phase II enzyme systems. We recently showed that dietary plant polyphenols, namely, the flavonoids, modulate expression of an important enzyme in both cellular antioxidant defenses and detoxification of xenobiotics, ie, gamma-glutamylcysteine synthetase. This enzyme is rate limiting in the synthesis of the most important endogenous antioxidant in cells, glutathione. We showed in vitro that flavonoids increase expression of gamma-glutamylcysteine synthetase and, by using a unique transgenic reporter mouse strain, we showed increased expression in vivo, with a concomitant increase in the intracellular glutathione concentrations in muscles. Because glutathione is important in redox regulation of transcription factors and enzymes for signal transduction, our results suggest that polyphenol-mediated regulation of glutathione alters cellular processes. Evidently, glutathione is important in many diseases, and regulation of intracellular glutathione concentrations may be one mechanism by which diet influences disease development. The aim of this review is to discuss some of the mechanisms involved in the glutathione-mediated, endogenous, cellular antioxidant defense system, how its possible modulation by dietary polyphenols such as flavonoids may influence disease development, and how it can be studied with in vivo imaging.

Flavonoids increase the intracellular glutathione level by transactivation of the γ-glutamylcysteine synthetase catalytical subunit promoter

Fruits and vegetables protect against cancer by so far not well-characterized mechanisms. One likely explanation for this effect is that dietary plants contain substances able to control basic cellular processes such as the endogenous defense against oxidative stress. Oxidative stress is pivotal in many pathological processes and reduced oxidative stress is implicated in prevention of disease. Our results demonstrate that extract from onion and various flavonoids induce the cellular antioxidant system. Onion extract and quercetin were able to increase the intracellular concentration of glutathione by approximately 50%. Using a reporter construct where reporter expression is driven by the gamma-glutamylcysteine synthetase (GCS) heavy subunit (GCS(h)) promoter we show that onion extract, quercetin, kaempferol, and apigenin increased reporter gene activity, while a fourth flavonoid, myricetin and sugar conjugates of quercetin were unable to increase reporter expression. Quercetin was also able to induce a distal part of the GCS(h) promoter containing only two antioxidant-response/electrophile-response elements (ARE/EpRE). Our data strongly suggest that flavonoids are important in the regulation of the intracellular glutathione levels. This effect may be exerted in part through GCS gene regulation, and may also contribute to the disease-preventing effect of fruits and vegetables.

In Vivo Imaging of NF-κB Activity

A wide range of human disorders involves inappropriate regulation of NF-κB, including cancers and numerous inflammatory conditions. Toward our goal to define mechanisms through which NF-κB leads to the development of disease, we have developed transgenic mice that express luciferase under the control of NF-κB, enabling real-time in vivo imaging of NF-κB activity in intact animals. We show that in the absence of extrinsic stimulation, strong luminescence is evident in lymph nodes in the neck region, thymus, and Peyer’s patches. Treating mice with TNF-α, IL-1α, or LPS increased the luminescence in a tissue-specific manner, with the strongest activity observed in skin, lungs, spleen, Peyer’s patches, and the wall of the small intestine. Liver, kidney, heart, muscle, and adipose tissue displayed less intense activities. Also, exposure of skin to a low dose of UV radiation increased luminescence in the exposed areas. Furthermore, induction of chronic inflammation resembling rheumatoid arthritis produced strong NF-κB activity in the affected joints, as revealed by in vivo imaging. Thus, we have developed a versatile model for monitoring NF-κB activation in vivo.

Health benefits of nuts : potential role of antioxidants

A diet rich in fruits, vegetables and minimally refined cereals is associated with lower risk for chronic degenerative diseases. Since oxidative stress is common in chronic degenerative disease, it has been assumed that dietary antioxidants may explain this protective effect. Every dietary plant contains numerous types of antioxidants with different properties. Many of these antioxidants cooperate in oxidative stress reduction in plants, and we hypothesize that many different antioxidants may also be needed for the proper protection of animal cells. To test this hypothesis, it is useful to identify dietary plants with high total antioxidant content. Several nuts are among the dietary plants with the highest content of total antioxidants. Of the tree nuts, walnuts, pecans and chestnuts have the highest contents of antioxidants. Walnuts contain more than 20 mmol antioxidants per 100 g, mostly in the walnut pellicles. Peanuts (a legume) also contribute significantly to dietary intake of antioxidants. These data are in accordance with our present extended analysis of an earlier report on nut intake and death attributed to various diseases in the Iowa Womens Health Study. We observed that the hazard ratio for total death rates showed a U-shaped association with nut/peanut butter consumption. Hazard ratio was 0.89 (CI = 0.81-0.97) and 0.81 (CI = 0.75-0.88) for nut/peanut butter intake once per week and 1-4 times per week, respectively. Death attributed to cardiovascular and coronary heart diseases showed strong and consistent reductions with increasing nut/peanut butter consumption. Further studies are needed to clarify whether antioxidants contribute to this apparent beneficial health effect of nuts.

Flagellin Promotes Myeloid Differentiation Factor 88-Dependent Development of Th2-Type Response

Activation of dendritic cells (DC) by microbial products via Toll-like receptors (TLR) is instrumental in the induction of immunity. In particular, TLR signaling plays a major role in the instruction of Th1 responses. The development of Th2 responses has been proposed to be independent of the adapter molecule myeloid differentiation factor 88 (MyD88) involved in signal transduction by TLRs. In this study we show that flagellin, the bacterial stimulus for TLR5, drives MyD88-dependent Th2-type immunity in mice. Flagellin promotes the secretion of IL-4 and IL-13 by Ag-specific CD4+ T cells as well as IgG1 responses. The Th2-biased responses are associated with the maturation of DCs, which are shown to express TLR5. Flagellin-mediated DC activation requires MyD88 and induces NF-κB-dependent transcription and the production of low levels of proinflammatory cytokines. In addition, the flagellin-specific response is characterized by the lack of secretion of the Th1-promoting cytokine IL-12 p70. In conclusion, this study suggests that flagellin and, more generally, TLR ligands can control Th2 responses in a MyD88-dependent manner.