High-dose vitamin therapy stimulates variant enzymes with decreased coenzyme binding affinity (increased Km): relevance to genetic disease and polymorphisms1-3

by Bruce N Ames, Ilan Elson-Schwab, and Eli A Silver

ABSTRACT As many as one-third of mutations in a gene result in the corresponding enzyme having an increased Michaelis constant, or Km, (decreased binding affinity) for a coenzyme, resulting in a lower rate of reaction. About 50 human genetic diseases due to defective enzymes can be remedied or ameliorated by the administration of high doses of the vitamin component of the corresponding coenzyme, which at least partially restores enzymatic activity. Several single-nucleotide polymorphisms, in which the variant amino acid reduces coenzyme binding and thus enzymatic activity, are likely to be remediable by raising cellular concentrations of the cofactor through high-dose vitamin therapy. Some examples include the alanine-to-valine substitution at codon 222 (A1a222->Val) [DNA: C-to-T substitution at nucleotide 677 (677C->T)] in methylenetetrahydrofolate reductase (NADPH) and the cofactor FAD (in relation to cardiovascular disease, migraines, and rages), the Pro187->4Ser (DNA: 609C->T) mutation in NAD(P):quinone oxidoreductase 1 [NAD(P)H dehydrogenase (quinone)] and FAD (in relation to cancer), the Ala44->Gly (DNA: 131C->G) mutation in glucose-6-phosphate 1-dehydrogenase and NADP (in relation to favism and hemolytic anemia), and the Glu487->Lys mutation (present in one-half of Asians) in aldehyde dehydrogenase (NAD') and NAD (in relation to alcohol intolerance, Alzheimer disease, and cancer). Am J Clin Nuir 2002;75:616-58.

KEY WORDS Genetic disease, therapeutic vitamin use, binding defect, favism, alcohol intolerance, autism, migraine headaches, single nucleotide polymorphisms, enzyme mutations, review

INTRODUCTION

High doses of vitamins are used to treat many inheritable human diseases. The molecular basis of disease arising from as many as one-third of the mutations in a gene is an increased Michaelis constant, or Km, (decreased binding affinity) of an enzyme for the vitamin-derived coenzyme or substrate, which in turn lowers the rate of the reaction. The Km is a measure of the binding affinity of an enzyme for its ligand (substrate or coenzyme) and is defined as the concentration of ligand required to fill one-half of the ligand binding sites. It is likely that therapeutic vitamin regimens increase i ntracellular ligand (cofactor) concentrations, thus activating a defective enzyme; this alleviates the primary defect and remediates the disease. We show in this review that ~50 human genetic diseases involving defective enzymes can be remedied by high concentrations of the vitamin component of the coenzyme, and that this therapeutic technique can be applied in several other cases, including polymorphisms associated with disease risks, for which molecular evidence suggests that a mutation affects a coenzyme binding site.

The nutrients discussed in this review are pyridoxine (page 618); thiamine (page 625); riboflavin (page 627); niacin (page 632); biotin (page 637); cobalamin (page 638); folic acid (page 641); vitamin K (page 643); calciferol (page 645); tocopherol (page 645); tetrahydrobiopterin (page 646); S-adenosylmethionine (page 646); pantothenic acid (page 646); lipoic acid (page 647); carnitine (page 647); hormones, amino acids, and metals (page 648); and maxi B vitamins (page 649).

The proportion of mutations in a disease gene that is responsive to high concentrations of a vitamin or substrate may be one-third or greater (1-3). Determining the true percentage from the literature is difficult because exact response rates in patients are not always reported and much of the literature deals only with individual case reports. The true percentages depend on several factors, such as the nature of the enzyme, the degree of enzyme loss that results in a particular phenotype, how much a small conformational change disrupts the binding site of the particular enzyme, whether the binding site is a hot spot for mutations, and whether dietary administration of the biochemical raises its concentration in the cell. From what is known of enzyme structure, it seems plausible that, in addition to direct changes in the amino acids at the coenzyme binding site, some mutations affect the conformation of the protein, thus causing an indirect change in the binding site.

Pantothenate kinase: Hallervorden-Spatz syndrome and pantothenate kinase-associated neurodegeneration

Pantothenate kinase is a cytosolic enzyme responsible for the first step in the biosynthesis of CoA from pantothenic acid (vitamin B-5). Four genes encoding pantothenate kinase have been identified: PANKI (expressed in heart, liver, kidney), PANK2 (ubiquitous), PANK3 (predominantly liver), and PANK4 (ubiquitous, predominantly muscle). Mutations in PANK2, which is the most abundantly expressed form in the brain, were recently implicated in pantothenate kinase-associated neurodegeneration (see OMIM 234200), an autosomal recessive neurodegenerative disorder characterized clinically by dystonia and often optic atrophy or pigmentary retinopathy and biochemically by iron deposits in the basal ganglia and globus pallidus (360). The mutations identified in PANK2 fall into exons 1C, 2, 3, 4, 5, and 6. Missense mutations resulting in nonconservative amino acid changes were found in 32 of 38 classical pantothenate kinase-associated neurodegeneration cases. All 17 mutations found in atypical cases were missense mutations. It seems plausible that some of these mutations will lower pantothenate kinase activity by affecting the affinity of the enzyme for pantothenate substrate. Such cases may prove to be responsive to high-pantothenate therapy.

References

1 From the Department of Molecular and Cellular Biology, University of California, Berkeley (BNA, IF-S, and EAS), and the Children's Hospital Oakland Research Institute, Oakland, CA (BNA and IE-S).
2 Supported by grants to BNA from the Ellison Foundation (SS0422-99), the National Foundation for Cancer Research (M2661), the Wheeler Fund of the Dean of Biology, and the National Institute of Environmental Health Sciences Center (ES01896).
3 Address reprint requests to BN Ames, Children's Hospital Oakland Research Institute, 5700 Martin Luther King Jr Way, Oakland, CA 94609. E-mail: bames@chori.org. Received September 20, 2001. Accepted for publication December 19,

Am J Clin Nutr 2002;75:616-58. Printed in USA 2002 American Society for Clinical Nutrition