International Congress on "Vitamins and Biofactors in Life Science"

The first International Congress on "Vitamins and Biofactors in Life Science" (ICVB) officially get underway on Monday morning, Sept. 16, 1991, with a brief welcoming speech by the Congress' Organizing Committee's President, Dr. Kunio Okuda at the Main Hall of the International Conference Center Kobe.
In his remarks, Dr. Okuda expressed his pleasure that this conference, the first of its kind, had attracted so many eminent people and leading scientists - a total of 800 including more than 200 from nearly 30 countries around the world.
The purpose of the conference in his words is "to inaugurate a new discipline to integrate the immense amount of scientific information gained by in vitro and animal experiments on vitamins, trace elements, and bioactive substances into more practical and useful forms applicable to the health and well-being of humans."
He went on to say that the concept of "specialization turned into integration" had been widely accepted by leading scientists in the medical, untritional, biochemical, and pharmaceutical sciences, and that there had been a momentum building to organize a conference in order to close the gaps existing between basic studies and human applications.
Expressing the hope that this conference would be the catalyst towards establishing a new international organization that would be concerned with promoting ways of making full use of basic studies, he also voiced his desire to have another conference in three years.
ICVB will continue through Friday, Sept. 20. During the five-day conference there will be 10 plenary lectures and 21 symposia as well as related communications and poster sessions.
The conference has been organized by The Vitamin Society of Japan and the Organizing Committee for the First International Congress on "Vitamins and Biofactors in Life Science." The Committee President is Dr. Okuda and the Secretary General is Dr. Nobuhiko Katunuma. Along the organizations supporting the conference is the Foundation for Advancement of International Science.

Vitamin B12 - Transport and Hemopoietic Role
By Kunio Okuda
Chiba University School of Medicine
B12 (cobalamin, Cbl) exists in the body mainly in two coenzyme forms, deoxyadenosyl-Cbl and methyl-Cbl. The liver contains the largest amount mainly in the form of the former and the latter is the main Cbl in plasma. There are many corrinoid analogues in nature and in human gut where intestinal flora produce them.
Cbl is an essential micronutrient for man in whom it has a biological half-life of about one year. Physiological gut absorption of Cbl required intrinsic factor (IF), a glycoprotein which is secreted by stomach parietal cells. Body fluids contain another Cbl-binding glycoprotein called R-binder or haptocorrin (HC) ; it is ubiquitous and saliva in particular contains high concentrations of HC.
Bulk of Cbl in food freed by digestion in the stomach and gut is first bound to HC, and Cbl-HC in then digested by pancreatic proteases that effect intraluminal transfer of Cbl from HC to IF; IF resists digestion in the gut. In man, physiological doses of Cbl are absorbed from the ileum with the aid of IF, whereas large unphysiological doses are absorbed by a non-IF mediated concentration gradient which is very inefficient quantitatively.
Coenzyme forms of Cbi, which are labile outside tissues, may be absorbed unchanged from the gut under IF exists in the intramicrovillous pits of enterocytes in the ileum. According to Grasbeck, it consists of alpha and beta subunits arranged in a 4-leaved clover-like structure. Cbl-IF is attached to it as a third unit through Ca++. Cbl-IF is then internalized and Cbl released.
In plasma, there are two major Cbl binding proteins, transcobalamin I/III which is immunologically identical to HC, and TC II which lacks sugar moiety. Absorbed Cbl is first bound to TC II and transported to target cells where it is taken up by absorptive endocytosis.
In the cell, TC II is degraded and Cbl is released to be utilized for several biochemical reactions. TCI/III binds unphysiological Cbl analogues in plasma which are derived from the gut and may exert toxic effects in hepatocytes; the complex enters the hepatocytes through the asialoglycoprotein receptor and are secreted into bile in a teleological fashion.
Thus, absorption of Cbl is unique in that an elaborate mechanism operates by which minute quantities of Cbl which otherwise would be taken up by microorganisms contaminating the human body, are preferentially absorbed under protection by IF.
Megaloblastic anemia due to Cbl deficiency which was called "pernicious anemia" in the past but is currently least pernicious, is a result of impaired DNA synthesis.
Bone-marrow megaloblastosis is characterized by large basophilic erythroblasts showing an immature nucleus in the face of a maturing cytoplasm with normally proceeding RNA and protein synthesis (nuclear-cytoplasm synchronism), similar synchronism in the granulocyte series, and large megakaryocytes.
Peripheral blood reflects these changes with normochromic macrocytic anemia and hypersegmented granulocytes. Erythrokinetically, inefficient erythropoiesis and hemolysis of circulating erythrocytes are the main features.
There is no basic difference hematologically between folate and Cbl deficiencies, whereas the latter causes certain neurological disorders. Of the two enzyme systems that require Cbl, only 5-CH3-THF homocystein methyltransferase (methionine synthetase) is involved in DNA synthesis.
In Cbl deficiency, this enzyme activity is markedly reduced, 5-CH3-THF accumulates, resulting in THF deficiency that leads to reduced formate production, hence reduced purine and thimidine synthesis and other metabolic alterations that encompass reduced formation of folate polyglutamate, reduced DNA replication fork movement, accumulation of dUMP and dUTP, uracil misincorporation into DNA, failure of repair of DNA strand breaks owing to lack of dITT, etc. The exact reason why anemia occurs only in man is not known. The details of reactions that lead to altered nucleotide metabolism are as yet to be fully elucidated.

Family of Protein Kinase C in Transmembrane Signalling for Cellular Regulation
By Yasutomi Nishizuka
Department of Biochemistry, Kobe University School of Medicine
Physiological importance of protein kinase C activation in transmembrane signalling is now well documented and widely appreciated. Although the hydrolysis of inositol phospholipids was once thought to be the sole mechanism leading to the activation of protein kinase C, there appear to be several additional routes to provide the diacyglycerol that is needed for enzyme activation. It is now also clear that there is more than one species of protein kinase C molecule, and several discrete subspecies have been defined.
These proteins are derived from both multiple genes and from alternative splicing of a single mRNA transcript, yet possess a primary structure containing conserved structural motifs with a high degree of sequence homology. In the brain tissues, for example, at least seven subspecies can distinguished, one of which is expressed only in the central nervous tissues.
Biochemical and immunocytochemical studies have revealed that these protein kinase C subspecies are differently located in particular cell types, and at limited intracellular locations.
The enzyme subspecies purified from tissues show subtle differences in their mode of activation, sensitivity to Ca2+, and catalytic activity. It is worth nothing that, in synergy with diacylglycerol, unsaturated free fatty acids such as arachidonic, oleic, and linoleic acids dramatically activate some members of the protein kinase C family at the basal level of Ca2+
concentration.
It is thus possible that activation of the enzyme is an integral part of the signal-induced degradation cascade of various membrane phospholipids catalyzed by phospholipases C, A3, and perhaps D.
Evidence now accumulates that protein kinase C plays roles in the control of a number of membrane functions, such as release reactions and ion channel conductivity, as well as in the cross-talk of various cell-signalling systems. It is also clear that protein kinase C plays roles of crucial importance for regulation of gene expression and cell differentiation. The heterogeneity of this enzyme family in signal transduction cascade for cellular regulation will be summarized.

Biosynthesis and Functions of Glutathione, as Essential Biofactor
By Alton Meister
Cornell University Medical College
Glutathione, an essential biofactor that is synthesized within many types of cells, provides the reducing milieu important for the maintenance of cellular thiols and antionxidants such as ascorbate and a- tocopherol. GSH protects cells against oxidative and free-radical-induced damage and other types of toxicity. GSH interacts with many types of drugs.
Studies on GSH synthesis and utilization have elucidated the biochemistry and functions of this biofactor, and have led to effective methods for decreasing, and also for increasing, cellular GSH.
Such modulation of cellular GSH has provided a new approach to the treatment of certain tumors (including cell types that are resistant to drugs and to radiation). Other therapeutically useful effects of modulation of GSH metabolism have also been observed. Thus, normal cells may be selectively protected against toxic compounds including antitumor agents, and against the effects of radiation by cysteine-delivery and GSH-delivery compounds.
An experimental model has been designed in which GSH synthesis is selectively inhibited by administration of buthionine sulfoximine, a transition-state inactivator of r- glutamylcysteine synthetase. This leads to GSH deficiency, which is not prevented or reversed by administration of GSH because there is very little transport of intact GSH into cells. Cellular utilization of GSH requires its extracellular degradation , uptake of products, and intracellular GSH synthesis.
GSH deficiency induced by inhibition of its synthesis may, however, be prevented or reversed by giving GSH esters such as glutathione (glycyl) monoethylester. In contrast to GSH, GSH esters are readily transported into cells and are hydrolyzed to GSH intracellularly. This model, in which GSH deficiency is produced in the absence of applied stress by inhibition of r -gultamylcysteine synthetase and reversed by giving GSH esters, has been applied to adult mice and newborn mice and rats. Newborns treated with buthionine sulfoximine develop cataracts which are prevented by giving GSH esters. In adult mice, GSH deficiency leads to cellular damage in muscle, lung, lymphocytes, jejunum, and colon, and in newborn rats to cellular damage in these organs and also in liver, kidney and brain.
Cellular damage, which is presented by GSH esters, is invariably associated with mitochondrial degeneration. In GSH deficiency, hydrogen peroxide (normally produced by mitochondria) accumulates and leads mitochondria damage. Mithchondrial GSH is normally imported from the cytosol by a system that contains a high-affinity transporter.
GSH deficiency also leads to decrease of tissue ascorbate levels and to increase of dehydroascorbate levels indicating that reduction of dehydroascorbate is an important physiological function of GSH. GSH deficiency induced by giving buthionine sulfoximine to newborn rats leads to mortality that is prevented by giving GSH esters or by giving high doses of ascorbate.
Ascorbate was found to spare GSH; thus, ascorbate and GSH have similar antioxidant actions. Although GSH functions normally to maintain ascorbate, a - tocopherol and other cellular components in reduced states, ascorbate can serve as an essential antioxidant when there is severe GSH deficiency.

Recent Advances in Our Understanding of the Mechanism of Action of Vitamin D
By Hecter F. DeLuca
Department of Biochemistry, University of Wisconsin
The availability of antibodies directed against various epitopes of the 1,25-dihydroxyvitamin D3 receptor and the successful cloning of the rat and human 1,25-dihydroxyvitamin D3 receptor has provided new and important tools for deciphering the molecular mechanism of action of vitamin D. With these tools, it can be shown that phosphorylation of the 1,25-dihydroxyvitamin D3 receptor is an early event in the response of 1,25-dihydroxyvitamin D3.
By means of activators of protein kinases and inhibitors of protein phosphatases, the essentiality of phosphorylation to the activation of target genes by 1,25-dihydroxyvitamin D3 can be demonstrated. These experiments were carried out using contransfection of the cDNA encoding the 1,25-dihydroxyvitamin D3 receptor and a reporter gene system containing the 1,25-dihydrozyvitamin D3 response element from the rat osteocalcin gene. The cDNA encoding for the rat 1,25-dihydroxyvitamin D3 receptor has been successfully expressed in a baculovirus system in insect cells. Large amounts of the receptor (nmol/mg protein) can be produced. The recombinant receptor is identical to rat receptor from in vivo sources as demonstrated by ligand binding characteristics. This receptor, however, does not produce gel shifts with the D-response element of the osteocalcin gene but requires a factor(s) present in nuclear extracts to initiate binding and hence transcription of target genes.
The nature of these factors and their interaction with the receptor will be described. Based on new results obtained using these systems, a hypothesis of the molecular mechanism of action of 1,25-dihydroxyvitamin D3 will be presented. This mechanism will also discuss the differential activity of different anologs in causing expression of some genes and not others.