Structure and tissue distribution of some retinoid-binding proteins

Malnutrition and Allergies: Tipping the Immune Balance towards Health

Malnutrition, which includes macro- and micronutrient deficiencies, is common in individuals with allergic dermatitis, food allergies, rhinitis, and asthma. Prolonged deficiencies of proteins, minerals, and vitamins promote Th2 inflammation, setting the stage for allergic sensitization. Consequently, malnutrition, which includes micronutrient deficiencies, fosters the development of allergies, while an adequate supply of micronutrients promotes immune cells with regulatory and tolerogenic phenotypes. As protein and micronutrient deficiencies mimic an infection, the body's innate response limits access to these nutrients by reducing their dietary absorption. This review highlights our current understanding of the physiological functions of allergenic proteins, iron, and vitamin A, particularly regarding their reduced bioavailability under inflamed conditions, necessitating different dietary approaches to improve their absorption. Additionally, the role of most allergens as nutrient binders and their involvement in nutritional immunity will be briefly summarized. Their ability to bind nutrients and their close association with immune cells can trigger exaggerated immune responses and allergies in individuals with deficiencies. However, in nutrient-rich conditions, these allergens can also provide nutrients to immune cells and promote health.

Nutrition in chronic inflammatory conditions: Bypassing the mucosal block for micronutrients

Nutritional Immunity is one of the most ancient innate immune responses, during which the body can restrict nutrients availability to pathogens and restricts their uptake by the gut mucosa (mucosal block). Though this can be a beneficial strategy during infection, it also is associated with non-communicable diseases-where the pathogen is missing; leading to increased morbidity and mortality as micronutritional uptake and distribution in the body is hindered. Here, we discuss the acute immune response in respect to nutrients, the opposing nutritional demands of regulatory and inflammatory cells and particularly focus on some nutrients linked with inflammation such as iron, vitamins A, Bs, C, and other antioxidants. We propose that while the absorption of certain micronutrients is hindered during inflammation, the dietary lymph path remains available. As such, several clinical trials investigated the role of the lymphatic system during protein absorption, following a ketogenic diet and an increased intake of antioxidants, vitamins, and minerals, in reducing inflammation and ameliorating disease.

Recent insights on the role and regulation of retinoic acid signaling during epicardial development

The vitamin A metabolite, retinoic acid, carries out essential and conserved roles in vertebrate heart development. Retinoic acid signals via retinoic acid receptors (RAR)/retinoid X receptors (RXRs) heterodimers to induce the expression of genes that control cell fate specification, proliferation, and differentiation. Alterations in retinoic acid levels are often associated with congenital heart defects. Therefore, embryonic levels of retinoic acid need to be carefully regulated through the activity of enzymes, binding proteins and transporters involved in vitamin A metabolism. Here, we review evidence of the complex mechanisms that control the fetal uptake and synthesis of retinoic acid from vitamin A precursors. Next, we highlight recent evidence of the role of retinoic acid in orchestrating myocardial compact zone growth and coronary vascular development.

The nutritional biochemistry of wool and hair follicles

The rôle of various classes of nutrients (energy substrates, vitamins, minerals, amino acids) in the production of wool and hair from follicles, is considered for a variety of animal species. The wool and hair follicle have evolved a number of interesting features of carbohydrate metabolism including glutaminolysis, aerobic glycolysis, significant activity of the pentose phosphate pathway, and storage and mobilisation of glycogen. Presumably the necessity to continue to produce fibre despite fluctuations in the supply of oxygen and nutrients has resulted in some of these unique features, while others reflect the high level of DNA and protein synthesis occurring in the follicle. While it is considered that energy does not normally limit fibre growth, the relative contributions of aerobic and anerobic metabolism will greatly influence the amount of ATP available for follicle activity, such that energy availability may at times alter fibre growth. Alopecia and deficient fibre growth are consistent outcomes of deficiencies of biotin, riboflavin, pyridoxine, folate and pantothenic acid, but the precise rôles of these vitamins in follicle function await elucidation. Folate, in particular appears to play an important rôle in wool production, presumably reflecting its involvement in methionine metabolism. Cholecalciferol (vitamin D) significantly alters fibre growth in cultured follicles; vitamin D receptors are located in the outer root sheath, bulb, and dermal papilla of the follicle; and alopecia occurs in humans with defects in the vitamin D receptor. Retinol (vitamin A), too, appears to influence follicle function by altering keratinocyte proliferation and differentiation, with direct effects on the expression of keratin genes. The receptors for the retinoids are present in the keratogenous zone, the outer root sheath, the bulb, and the sebaceous glands. Vitamin A may also act indirectly on follicle function by influencing the activity of the insulin-like and epidermal growth factors and by altering vitamin D activity. At present there is little evidence implicating alpha-tocopherol (vitamin E) or phytylmenaquinone (vitamin K) in follicular events. Of the minerals, only copper and zinc have been shown to have direct effects on follicle function, independent of effects on food intake. Copper has direct effects on the activity of an unidentified enzyme on oxidation of thiol groups to form disulphide linkages. Wool produced by copper-deficient sheep lacks crimp, is weak and lustrous. Copper is also necessary for the activity of tyrosinase and the tyrosinase-related proteins involved in melanin synthesis. Zinc, like copper, is required for the normal keratinization of fibres but again, the precise rôle has yet to be elucidated. While the importance of amino acid supply for wool growth has long been established, there are still some unaswered questions such as; what are the effects of amino acids on fibre growth in animals other than sheep; what are the characteristics of the amino acid transport genes and proteins operating in the wool and hair follicle; and what are the specific rôles for amino acids in follicle function.

cDNA microarray analysis of HBV transgenic mouse liver identifies genes in lipid biosynthetic and growth control pathways affected by HBV

Hepatitis B virus (HBV) transgenic mice that replicate HBV in the liver generally do not exhibit gross liver pathology, while maintaining a high level (10(7) or greater) of viral titer in the blood. We have used this model to determine the minimum effects of HBV replication in the liver on cellular gene transcription, using cDNA microarrays. cDNA microarray data from sets of HBV versus control cDNA microarrays revealed a very small impact of HBV on the cellular transcriptome. After deletion of genes that were variable in control cDNA microarrays and applying significance analysis of microarrays (SAM), an application to detect statistically significantly regulated genes, we identified 18 upregulated genes and 14 downregulated genes. Most of the regulated genes show a change in expression with respect to control of less than 40% in either direction, demonstrating small effects of HBV. The largest functional category for upregulated genes was lipid biosynthesis, in which ATP citrate lyase, fatty acid synthase, sterol regulatory element binding factor 2, and retinol binding protein 1 were all upregulated. The most strongly downregulated genes were in the cytochrome p450 group, particularly p450, 4a14. Several growth regulatory genes including cyclin D1, IGF binding protein 3, and PCNA were moderately upregulated. These data are the first to specifically identify enzymes involved in fatty acid and NADPH-electron transport pathways that are altered by the presence of HBV. The data also demonstrates that HBV is well adapted to non-cytopathic replication in hepatocytes. Cellular genes expected to be affected by viral secretion from membranes are clearly upregulated, and upregulation of growth regulatory genes may facilitate replacement of dying hepatocytes during persistent infection.

Hair regrowth. Therapeutic agents

Today there are new classes of hair growth promotors with proven efficacy. This article reviews the current state of the art agents for treatment of two of the most common forms of hair loss encountered in clinical practice, androgenetic alopecia and alopecia areata. Current therapeutic strategies are based on recent advances in the understanding of disordered hair growth. Practical treatment protocols are presented.

Effects of vitamin A status on cellular retinoic acid-binding protein in rat skin and testes

Cellular retinoic acid-binding protein levels were determined in the skin and testes of normal and retinol-deficient rats. All-trans [3H]retinoic acid (1.1 TBq/mmol) was used to titrate the specific binding sites in tissue cytosol preparations. Scatchard plot analyses were used to determine the concentration of cellular retinoic acid-binding protein and its binding affinity (Kd) for all-trans-retinoic acid. In normal rat skin the concentration of cellular retinoic acid-binding protein was 3317 +/- 924 (SD) fmol/mg protein and the Kd was 1.98 +/- 1.0 x 10(-9) mol/l. In retinol-deficient rat skin the concentration of cellular retinoic acid-binding protein was 2584 +/- 1205 fmol/mg protein and the Kd was 3.30 +/- 3.4 x 10(-9) mol/l. In the normal rat testes the concentration of cellular retinoic acid-binding protein was 2965 +/- 1187 fmol/mg protein and the Kd was 2.30 +/- 2.1 x 10(-9) mol/l. In retinol-deficient rat testes the concentration of cellular retinoic acid-binding protein was 2439 +/- 383 fmol/mg protein and the Kd was 0.3 +/- 0.2 x 10(-9) mol/l. These findings indicate that there are no significant differences in the levels of cellular retinoic acid-binding protein between normal and deficient rat skin and testes (p greater than 0.1, by Wilcoxon rank sum test). We therefore conclude that the level of cellular retinoic acid-binding protein in skin and testes may not be controlled by the availability of vitamin A.

Polyacrylamide gradient gel electrophoresis of cytosolic retinol- and retinoic acid-binding proteins: application to rat testis and liver

Distribution and cellular levels of retinol-binding protein and retinoic acid-binding protein, involved in the molecular action of retinoids, were analyzed in rat testis and liver. Both binding proteins of cytosolic extracts were separated by linear-polyacrylamide gradient gel electrophoresis and following electrophoretic separation, could be visualized by complementary identification tests such as autoradiography and marker proteins. The concentration of the binding proteins were evaluated by scanning the polyacrylamide gradient gels and the resulting data were found to be in accordance with those obtained by counting radioactivities. Polyacrylamide gradient gel electrophoresis appears suitable to detect and quantitatively evaluate cytosolic retinol- and retinoic acid-binding proteins.

Displacement of nutritional receptors on cell membrane as an initiation factor in carcinogenesis

Carcinogenesis is a multi-step process, and initiation is the first step. The cell membrane may hold the key to the entry of carcinogens. According to our hypothesis, the cell membrane may have receptors for nutrients including the essential vitamins, in addition to hormones, immune modulators, prostaglandins and neurotransmitters. In addition, there may be cytoplasmic counter receptors to the above. Carcinogens after prolonged contact with cell membrane may displace nutritional receptors to gain an abnormal foothold on cell membrane before entering the cytoplasm and cell nucleus and activating the oncogenes. If this is proven to be correct, there is a possibility of cancer prevention at the cellular level. A possible experimental approach is also described.

Quantitation and localization of cellular retinol-binding protein in squamous-cell carcinomas of the cervix uteri and of the oral cavity

The concentration of cellular retinol-binding protein (CRBP) was determined by radioimmunoassay in biopsies of normal mucosa and squamous-cell carcinomas of cervix uteri from 30 women. The tumour tissues contained significantly higher concentrations of CRBP (median = 120 micrograms/g protein) than normal mucosa (median = 32 micrograms/g protein). The distribution of CRBP in normal mucosa and squamous-cell carcinomas from cervix uteri and from oral cavity was evaluated by immunohistochemical techniques. In tissue sections of normal epithelium from the cervix uteri and the oral cavity, the maturing keratinocytes in the prickle-cell layers were moderately or strongly stained when antiserum against CRBP was used, while the proliferating cells in the basal-cell layer were stained only lightly if at all. Squamous-cell carcinomas of the cervix uteri and the oral cavity presented much the same picture. The observed difference in CRBP concentration between squamous-cell carcinomas and normal squamous-cell mucosa may therefore be more quantitative than qualitative.

Loss of retinol-binding properties for plasma retinol-binding protein in normal human epidermis

Terminal differentiation of the keratinocytes (cornification) has been linked to a restricted supply of retinol. Retinol is distributed to target cells by the retinol-binding protein (RBP), which circulates in the plasma in complex with transthyretin (TTR). In this study we have addressed the question of retinol delivery to the epidermis via RBP. Retinol radiobinding assays, affinity chromatography with TTR coupled to Sepharose beads, polyacrylamide gel electrophoresis, and immunoblotting techniques were used to show that epidermal extracts contain retinol binding sites with no affinity for TTR. Immunoreactive RBP was detected in the epidermal extracts. The RBP in the epidermis was in the apoform (without retinol) in contrast to serum where the majority of RBP is in the holoform (with retinol). Epidermal RBP was converted in vitro into the holoform only after addition of 20 times more retinol, which was needed to reconstitute holoforms of RBP in dermal extracts, human buccal mucosal extracts, and delipidized normal serum or purified delipidized RBP. Moreover, several immunoreactive RBP bands (possibly degradation products) were identified in the epidermal but not in dermal extracts. Retinol-binding protein from nonkeratinizing human oral mucosa showed different immunoblotting patterns when compared to epidermal RBP. These results suggest that degradation of RBP within the epidermis may result in a decreased retinol supply to the keratinocytes, and may lead to the cornification of the epidermis.

Retinoic acid: biochemistry and metabolism

Retinoic acid, unlike the naturally occurring vitamin A (retinol), is a minor component of the human diet. It is formed in vivo from retinol and has many metabolites. The biological activity of the metabolites is not higher than that of retinoic acid itself, indicating that the metabolites must be products of retinoic acid catabolism. Little is known about the enzymatic systems responsible for forming retinoic acid or about how it enters the cell. Discovering the molecular mechanism(s) of retinoic acid activity in cellular metabolism is important to understanding its physiologic role. The pharmacologic effects of high doses of retinoic acid may be caused by its action on cellular membranes. Conversely, low concentrations appear to produce physiologic effects. Results of experiments with animals and with cell cultures indicate that the primary physiologic role of retinoic acid is in cellular differentiation. Retinoic acid influences genomic expression, inducing the appearance of some proteins while suppressing the expression of others. The existence of an intracellular retinoic acid-binding protein suggests that it may mediate the physiologic effects of retinoic acid on cellular differentiation.

Topical tretinoin for hair growth promotion

Topical all-trans-retinoic acid (tretinoin) alone and in combination with 0.5% minoxidil has been tested for the promotion of hair growth in 56 subjects with androgenetic alopecia. After 1 year, the combination of topical tretinoin with 0.5% minoxidil resulted in terminal hair regrowth in 66% of the subjects studied. Tretinoin was shown to stimulate some hair regrowth in approximately 58% of the subjects studied. One female subject with pronounced alopecia for more than 20 years had regrowth of hair using only tretinoin for a period of 18 months. Tretinoin has been shown to promote and regulate cell proliferation and differentiation in the epithelium and may promote vascular proliferation. These factors are important for hair growth promotion. These preliminary results indicate that more work should be done on the role of retinoids in hair growth. The synergistic effect of retinoids in combination with a low concentration of minoxidil should also be further investigated.

Cellular retinol- and retinoic acid-binding proteins in the epidermis and dermis of normal human skin

The distribution of cellular retinol- and retinoic acid-binding proteins (CRBP and CRABP) in normal human epidermis and dermis was examined by gel filtration. We showed that CRBP is entirely bound to a lipid-protein aggregate and its free form is obtained through delipidation. The type of homogenization procedure appeared to be important for the recovery of CRBP in human skin. The level of CRABP was about 3.1 pmol/mg protein in the epidermis whereas it was only sporadically detectable in the dermis. In contrast, CRBP was found in both tissues at a concentration of about 1 pmol/mg protein. The difference in CRABP concentrations between epidermis and dermis might have biological and therapeutic implications. Dissociation constants (Kd) of CRABP and CRBP were respectively 2.2 X 10(-7) M and 2.51 X 10(-7) M. This method will facilitate the study of CRABP and CRBP in retinoid- responsive dermatoses and enable us to relate the therapeutic effects of retinoids to the levels of cellular retinoid-binding proteins in the skin.