Pantethine: A Review of its Biochemistry and Therapeutic Applications Gregory S. Kelly, N.D. Abstract Pantethine is the stable disulfate form of pantetheine, the metabolic substrate which constitutes the active part of coenzyme A (CoA) molecules and acyl carrier proteins. Because pantethine is located nearer to CoA than is pantothenic acid in the biosynthetic pathway of CoA, it has been suggested it will have clinical benefits in conditions where pantothenic acid is not effective, and clinical trials with pantethine appear to prove this argument. Oral administration of pantethine has consistently shown an ability to favorably impact a variety of lipid risk factors in persons with hypercholesterolemia, arteriosclerosis, and diabetes. Pantethine administration positively affects parameters associated with platelet lipid composition and cell membrane fluidity. In several animal models, preliminary studies have indicated pantethine can inhibit cataract formation. Pantethine is capable of lipotropic activity, and in experimental models exerts hepato-protective action and impacts adrenal cortex function. The intravenous administration of pantethine has been shown to impact several central nervous system neurotransmitters and hormones; however, oral doses of pantethine have not demonstrated a similar action, suggesting cysteamine, a metabolite of pantethine, is responsible for these actions. (Alt Med Rev 1997;2(5):365-377) Introduction As the stable disulfate form of pantetheine, pantethine is the metabolic substrate which constitutes the active part of coenzyme A (CoA) molecules and acyl carrier proteins (ACP). The reactive component of both CoA and ACP is not the pantothenic acid molecule but rather it is the sulfhydryl (SH) group donated from cysteine. Although pantothenic acid is commonly known as Vitamin B5,, pantethine, or its reduced-SH form pantetheine, contain the SH mol- ecule required for enzyme activity. Pantethine, as opposed to pantothenic acid, bypasses the cysteine reactions required to form pantetheine from pantothenic acid, providing a more meta- bolically active form of the vitamin. See Figure 1 for the chemical composition of CoA, pantethine, pantetheine, and pantothenic acid. The metabolic activity of Vitamin B5 is due to its role in the synthesis of CoA and ACP. CoA is a cofactor in over 70 enzymatic pathways, including fatty acid oxidation, carbohydrate metabolism, pyruvate degradation, amino acid catabolism, heme synthesis, acetylcholine Gregory S. Kelly, N.D.—Associate Editor, Alternative Medicine Review; Private Practice, San Diego, CA. Correspondence address: 937 South Coast Highway 101, Suite 205. Encinitas, CA 92024. [email protected] Alternative Medicine Review ◆ Volume 2, Number 5 ◆ 1997 Page 365 Copyright©1997 Thorne Research, Inc. All Rights Reserved. No Reprint Without Written Permission Figure 1. Chemical composition of CoA and its constituents: pantetheine and pantothenic acid. acid with b-alanine. Mammals lack the enzyme for this synthetic step, so are unable to syn- NH2 thesize pantothenic acid. N Although foods contain CoA, ACP, N pantetheine, and pantethine, as well as pan- O tothenic acid, endogenous synthesis of both N N CoA and ACP can begin with pantothenic acid HO P O CH in humans. After pantothenic acid is absorbed 2 O and transported into cells, it can be converted O to either CoA or ACP by a synthetic process HH H requiring several enzymatic steps. Described HO P O H below is the most common biosynthetic path- O O OH way; however, the initial phosphorylation re- action can also occur after pantetheine, the re- CH2 O P OH duced form of pantethine, is formed or pro- vided exogenously. H3CCHC 3 OH The first step is a phosphorylation re- H C OH action catalyzed by pantothenate kinase, a magnesium-dependent enzyme, resulting in C O the formation of 4'-phosphopantothenic acid (4'-PPA). High levels of CoA can inhibit this antothenic acid NH P enzymatic step; however, carnitine has been CH2 shown to reverse the inhibitory action under antetheine 1 P experimental conditions in rat hearts. CH2 The next step in CoA or ACP biosyn- C thesis is a condensation reaction with cysteine, producing 4'-phosphopantothenoyl cysteine. NH The enzyme needed for this synthetic step is also magnesium dependent. In the absence of CH2 cysteine, 4'-PPA will accumulate, suggesting, in biological systems, an absence of cysteine CH2 Cysteamine beta-Alanine acid Pantoic as a substrate is the limiting factor in biosyn- SH thesis of pantothenic acid’s down-line metabo- lites. 4'-phosphopantetheine (4'-PP) is then synthesis, and phase II detoxification formed by a decarboxylation reaction. The acetylations. ACP is an essential component reaction rate of this enzymatic step is increased of the fatty acid synthase complex required for by the availability of protein-SH compounds, fatty acid elongation. such as cysteine, suggesting the importance of these compounds for the activity of this de- Biosynthesis of Pantetheine and carboxylase enzyme.2 The final two steps in the synthesis of Related Compounds CoA involve the addition of an adenosyl group Biosynthesis of pantothenic acid can derived from ATP and the phosphorylation of be accomplished by most plants and microor- this molecule. Both of these enzymatic ganisms by enzymatically combining pantoic Page 366 Alternative Medicine Review ◆ Volume 2, Number 5 ◆ 1997 Copyright©1997 Thorne Research, Inc. All Rights Reserved. No Reprint Without Written Permission Pantethine reactions require magnesium as a cofactor. See Ono et al have suggested pantethine is Figure 2 for the synthetic pathway for CoA. more readily absorbed than calcium Although degradative enzymes exist pantothenate, a commonly-used form of for the breakdown of CoA, the scattered loca- Vitamin B5 supplementation, when given tion of these enzymes within the cell appear to indicate the cell is geared to minimize deg- radation of CoA once it has been formed.3 While CoA accounts for a large pro- Figure 2. Coenzyme A biosynthesis. portion of cellular pantothenic acid, ACP also contains the pantothenic acid molecule. The synthesis of ACP is not completely elaborated; Pantothenic acid however, as in CoA, 4'-PP has been identified ATP as the prosthetic group.3 Evidence suggests mg2+ ACP, in addition to its role in fatty acid syn- ADP thase, might be associated with a number of protein complexes. Observations also indicate ACP levels are maintained at the expense of 4'-Phosphopantothenic acid 3 CoA in bacteria; however, it is unclear CTP whether this is also the case in mammals. mg2+ Several hormones might impact the CDP+Pi synthesis of pantothenic acid-dependent en- zymes. In experimental models, glucagon in- creases, while insulin decreases, the incorpo- 4'-Phosphopantothenylcysteine ration of pantothenic acid into CoA. Gluco- corticoids appear to potentiate the effects of glucagon.3 Hyperthyroidism is also reported to CO2 increase CoA synthesis.4 4'-Phosphopantetheine Metabolism of Pantethine The metabolic fate of an oral dose of ATP pantethine in humans has not been clearly de- mg2+ scribed. However, because pantethine is closer PPi to CoA than is pantothenic acid in the biosyn- thetic pathway of CoA, it has been suggested Dephosphocoenzyme A that pantethine will have clinical benefits in conditions where pantothenic acid is not ef- ATP fective. Based on clinical trials with mg2+ pantethine, this theoretical argument appears ADP to be true. It is generally accepted that a portion Coenzyme A of pantethine is hydrolyzed to pantetheine and a portion is degraded to pantothenic acid prior to intestinal absorption. The pantetheine can then be phosphorylated to provide the active orally to rats. In these animals, pantethine was 4'-PP moiety of CoA and ACP.5 hydrolyzed to pantetheine and pantothenic acid prior to absorption.6 Shigeta et al have also Alternative Medicine Review ◆ Volume 2, Number 5 ◆ 1997 Page 367 Copyright©1997 Thorne Research, Inc. All Rights Reserved. No Reprint Without Written Permission Figure 3. CoA and ACP dependent pathways ACP Directly or indirectly, Carbohydrates Tr iglycerides Doliquol Bile Salts Amino Acids Phospholipids CoQ-10 Vitamin D CoA is involved in the (Glucogenic) Prostaglandins Squalene Pantethine Fatty Acids Steroid Hormone breakdown of the carbon skeleton of most amino Pyrurate Acetyl-CoA 34mg-CoA Cholesterol acids. Alanine, cystine, CoA cysteine, glycine, serine, threonine, and hydrox- Lipids Ketones Amino Acids yproline are metabolized (Ketogenic) TCA Acetylation of Amino Sugars to pyruvate and then en- CYCLE ter the TCA cycle with Acetylcholine Succinyl the help of CoA. CoA is CoA Acetylation of Xenobiotics directly involved with the CoA breakdown of leucine, lysine, and tryptophan. α - Keto Acids CoA Porphyrin The degradation of the pyrimidine bases, cy- Branched Chain Adapted from: Smith CA, Song WO. Comparative Nutrition of Pantothenic Acid. Amino Acids Nutr. Bioch. 1996; 7:312-321 tosine, uracil, and thym- ine, is also dependent on CoA. CoA can direct acetyl suggested pantethine, following intramuscular groups into the formation injection in healthy subjects, is retained longer of all the polyisoprenoid-containing in the blood and has more tissue affinity than compounds, which include dolichol, pantothenic acid.5 ubiquinone (CoQ10), squalene, and cholesterol. Dolichol is a sugar carrier used in Biochemical Functions of the synthesis of glycoproteins. In addition to this indirect role in the formation of Pantethine and CoA glycoproteins, CoA is also used in the The biological