Prof. Lipid Res. Vol. 31, No. I, pp. 1-51, 1992 Printed in Great Britain. All rights reserved
0163-7827/92/$15.00 © 1992 Pergamon Press pk
THE FATTY ACID CHAIN ELONGATION SYSTEM OF MAMMALIAN ENDOPLASMIC RETICULUM DOMINICK L. CINTI,* LYNDA COOK,* MAnMOUD N . N A G I t a n d SANOJ K . S t r a t A *
*Department of Pharmacology, University of Connecticut Health Center, Farmington, CT 06030, U.S.A. tSchool of Pharmacy, Mansoura University, Mansoura, Egypt
CONTENTS I. INTRODUCTION II. I 3 ~ v ~ y OF ~ MEI~RANE-BOUND(ENDOPLASMlC RETICULUM) FACES: A B ~ HISTORY III. PREPARATIONOF THE SUBSTRATEFOR CHAIN ELONGATION
A. Activation of the fatty acid B. Coenzyme A derivatives as substrates for microsomal FACES IV. Rv.Ac'nolcs CATALYZFDBY THE HEPATICFACES A. The first elongation step: condensation reaction B. The second fatty acid chain elongation step: reduction of the B-ketoacyl CoA C. The third reaction step: p-hydroxyacyl CoA dehydrase D. The terminal step: reduction of trans-2-enoyl CoA E. Membrane topography of FACES V. DEVELOPMENT,MULTIPLICITY AND REGULATIONOF HEPATIC F A C E S
A. Development B. Age-related alteration C. Multiplicity and regulation 1. Diet 2. Hormones (a) Insulin (b) Thyroid hormone (c) Glucagon and cAMP 3. Hepatoma tissue culture 4. Xenobiotics (a) Clofibrate (2-(4-chlorophenoxy)-2-methyl propanoic acid ethyl ester) (b) DEHP (di(2-ethylhexyl)phthalate) (c) Ebselen (2-phenyl-l,2-benzoisoselenazol-3(2H)-one) (d) Acetylenic acid derivatives VI. ELONGATION-DEsATURATIONAND SPECIFIC ACTIVITIES OMERVED IN RAT HEPATIC MtCROSOMm
VII. BRAINFATTYACID CHAINELONGATIONSYSTEM A. Introduction and general properties B. The rate-limiting step of brain microsomal FACES C. Reduction of chain elongation intermediates in brain microsomes D. Physiological importance of FACES in the brain VIII. KJDI~nBYCOR~BXFATTYACID CHAINELONGATIONS~TI~ IX. FACES IN OTnr~ ORGANSA ~ Tmsur~s A. Lung B. Small intestine C. Cultured mammalian cells I. Skin fibroblasts 2. Aortic fibroblasts 3. Adren~ortical cells from zona fasciculata and zona reticularis D. Aorta E. Nentrophils F. T Lymphocytes G. Retina H. Placenta I. Testis X. MmouoLOGY FOR ~ MICROSOtUd.FACES A. Determination of total chain elongation activity B. Measurement of the condensation reaction C. Measurement of p-ketoacyl CoA reductase activity D. Determination of #.hydroxyacyl CoA dehydrase activity E. Determination of trans-2-enoyl CoA reductase activity
4 6 6 8 8 8
10 14 15 17 17 17 18 18 18
2O 2O 21 21 22 22 22 22 23 24 25 25 25 28
30 32 34 35 35 37 37 37 38
39 39 39 39 40 40 40 41 41 41 41 41 42
2
D.L. CINTIet
al.
F. Synthesisof substrates of the FACES 1. Chemical synthesis of CoA derivatives 2. Synthesisof/~-ketoacylCoA derivatives 3. Synthesisof/~-hydroxyacylCoA derivatives 4. Synthesisof trans-2-enoyl CoA derivatives XI. NONENDOPLASMICRETICULUMFATTYACID CHAIN ELONGATIONSYSTEMS A. Mitochondria
B. Peroxisomes XII. SUMMARYAND CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES
42 42 42 43 43 44 44 45 46 46 46
I. INTRODUCTION Before delving into the details of the mammalian enzyme system that is responsible for the biotransformation, specifically chain elongation of the lipid constituents, namely the fatty acids, an overview of the sources and levels of fatty acids in the food supply and in body tissues appears appropriate. The ensuing tables depicting fatty acid composition will provide a ready reference when substrates of and their metabolism by the fatty acid chain elongation system (FACES) are discussed below. Over the past 70 years, the quantity of fat in the food supply of the United States has increased about 35%, from a value of ca. 125 g per capita per day in 1910 to nearly 170 g in 1980.271'277In terms of food energy in the U.S. food supply, fat represents about 42% of the total kilocalories, up from 32% in 1910, whereas the proportion of calories attributed to carbohydrate has decreased from 56% in 1910 to 46% in 1980.277The energy obtained from protein has remained stable at 12%. Although the U.S. food supply data suggest an available fat supply of about 160-166 g per individual per day, actual consumption of£at per individual is significantly lower. Data from the Nationwide Food Consumption survey of 1977-1978277'331'332showed that females consumed ca. 70 g of fat per day, while males consumed 110 g per day. Hence, the average fat intake per individual per day for all individuals is 80-90 g. Based on the inherent difficulties in the methodologies employed in determining food consumption, the values 80-90 g and 160-166 g may represent the extremes and the average of the two (120-130 g) may represent a more realistic value of daily fat consumption. In any event, the food energy derived from protein, fat and carbohydrate data obtained from the food consumption survey331-334indicate that in 1977, 16% of the energy was provided by protein, 42% by fat and 41% by carbohydrate. Data obtained in 1985-1986, indicate that the energy derived from protein remained at ca. 16%, whereas energy provided by fat decreased 5% to 37% and energy from carbohydrate increased to 46%. 333`334The ingested fat is predominantly in the form of triglycerides, and the fatty acid composition of the various food fats is depicted in Tables 1 and 2. Whether the fats are of animal, vegetable or aquatic origin, with the exception of coconut oil, the predominant saturated fatty acid is palmitic acid (16:0). Whereas the major monounsaturate of all the fats is oleic acid (9-18:1), in aquatic oils there are also significant quantities of palmitoleic (9-16:1), eicosenoic (11-20:1) and docosenoic (9/11-22:1) acids. Linoleic acid (9,12-18:2) is the most abundant polyunsaturated fatty acid in animal, vegetable and fruit and nut fats; however, in marine fats, the major polyunsaturates consist of chain lengths of 20 and 22 carbons and 4, 5 or 6 double bonds (Table 2). The fatty acid composition of various mammalian tissues (Table 3) differs slightly from that of the foodstuffs (Tables 1 and 2). Both palmitic and stearic acids are present in similar amounts, except for adipose tissue which contains a higher percentage of palmitic acid. As in foodstuffs, oleic acid is the major monounsaturated fatty acid; however, whereas in vegetable oils, fruit and nut oils and animal fats, the only significant polyunsaturated fatty acid is linoleic acid; in mammalian tissues, there are large amounts of arachidonate and docosahexenoate (Tables 3 and 4). From the analysis of the fatty acid content of oils and fats (Tables 1 and 2), various mammalian tissues (Table 3) and subcellular membranes (Table 4), the fatty acyl groups
Fatty acid chain elongation TABLE 1. Composition of Major Fatty Acids of Vegetable, Fruit and Nut Oils and Animal Fats63,,z6,m,t4s.tss,176 % Saturated 16:0 18:0 Vegetable oils Corn, cottonseed, safflower, sesame, soybean,* sunflower Fruit and nut oils Olive Nutst Grapeseed Coconut + Animal fats Butter~ Beef Chickenll Lard Mutton
% Monounsaturated % Polyunsaturated 9-18:1 9,12-18:2
7-16
2-7
18-47
37-65
8-20 5-12 6-11 4-12
1-4 1-4 3-6 1-5
56-83 50-68 12-28 4-12
4-20 18-25 58-78 1-4
25-28 27-29 24-26 20-32 25-27
11-13 7-21 4-6 5-24 30-32
27-29 41-47 36-43 35-62 30-32
-2 14-21 3-16 2
*Soybean oil also contains 6% 9,12,15-18:3. tAlmond, cashew, peanut, pecan, pistachio. ~/Coconut oil--contains predominantly saturated fatty acids with carbon lengths < 16; for example, Ct4 = 13-23%, Cl2 = 41-56%, Ci0 = 4-15%, C 8 = 4-15%. §Butter also contains 10-12% Ct4 and about 13% Cc-Ct2. ItChicken contains about 9% Ct2--CI4 and 8% Ct6:t.
are derived from three different processes: (1) diet, which can provide the bulk of the fatty acids observed in the phospholipids, triacylglycerols and cholesteryl esters; (2) de n o v o fatty acid synthesis, in which the predominant product is palmitic acid; and (3) modification of both dietary and newly synthesized fatty acids by enzymes present in the endoplasmic reticulum of the mammalian cell. These enzymes catalyze a series of desaturation and chain elongation reactions to yield the required acyl (enoyl) group. Some of the biochemical transformations are shown in the scheme below (Scheme 1). The present review will focus on the current state of knowledge of the fatty acid chain elongation system. FACES has been studied extensively in both liver and brain, and also found to be present in a variety of other tissues, such as kidney, small intestine, adrenal cortex, neutrophil, cultured skin fibroblasts, aorta, placenta, testis, retina and lung. Each one of these will be discussed separately. TABLE 2. Fatty Acid Composition of Aquatic Animal Oils6,ss,m,m
Fatty acid 14:0 16:0 18:0 Total saturated mean 9-16:1 9-18:1 11-20:1 9/11-22:1 Total monounsaturated mean 9,12-18:2 9,12,15-18:3 5,8,11,14-20:4 5,8,11,14,17-20: 5 7,10,13,16,19-22:5 4,7,10,13,16,19-22: 6 Total polyunsaturated mean
Marine oils Salt water fish* Fresh water fish'}" (%) (%) 7-9 9-23 1-3 26 7-15 4-29 2-15 2-20 47 -0--4 0-2 3-16 -2-12 19
2-4 17-20 3-5 25 8-11 9-29 --29 2-6 2-6 4-8 7-12 2-4 9-26 44
*Salt water fish including menhaden, sardine, Atlantic and Pacific herring, mackerel and copelin. tFresh water fish include bass, perch, pike and trout.
D. L. CINTI et al. TAeLE 3. Fatty Acid Composition of Rat Liver, Heart, Brain, Kidney and Adipose Tissues from Several Species 88,10~,126.140,232,255,315a,325 Liver
Plasma
Heart
Fatty acid
Brain
Kidney
Adipose*
19 -18 8 13 29 1 1 3
20-28 2-10 6-16 33-50 5-30
0163-7827/92/$15.00 © 1992 Pergamon Press pk
THE FATTY ACID CHAIN ELONGATION SYSTEM OF MAMMALIAN ENDOPLASMIC RETICULUM DOMINICK L. CINTI,* LYNDA COOK,* MAnMOUD N . N A G I t a n d SANOJ K . S t r a t A *
*Department of Pharmacology, University of Connecticut Health Center, Farmington, CT 06030, U.S.A. tSchool of Pharmacy, Mansoura University, Mansoura, Egypt
CONTENTS I. INTRODUCTION II. I 3 ~ v ~ y OF ~ MEI~RANE-BOUND(ENDOPLASMlC RETICULUM) FACES: A B ~ HISTORY III. PREPARATIONOF THE SUBSTRATEFOR CHAIN ELONGATION
A. Activation of the fatty acid B. Coenzyme A derivatives as substrates for microsomal FACES IV. Rv.Ac'nolcs CATALYZFDBY THE HEPATICFACES A. The first elongation step: condensation reaction B. The second fatty acid chain elongation step: reduction of the B-ketoacyl CoA C. The third reaction step: p-hydroxyacyl CoA dehydrase D. The terminal step: reduction of trans-2-enoyl CoA E. Membrane topography of FACES V. DEVELOPMENT,MULTIPLICITY AND REGULATIONOF HEPATIC F A C E S
A. Development B. Age-related alteration C. Multiplicity and regulation 1. Diet 2. Hormones (a) Insulin (b) Thyroid hormone (c) Glucagon and cAMP 3. Hepatoma tissue culture 4. Xenobiotics (a) Clofibrate (2-(4-chlorophenoxy)-2-methyl propanoic acid ethyl ester) (b) DEHP (di(2-ethylhexyl)phthalate) (c) Ebselen (2-phenyl-l,2-benzoisoselenazol-3(2H)-one) (d) Acetylenic acid derivatives VI. ELONGATION-DEsATURATIONAND SPECIFIC ACTIVITIES OMERVED IN RAT HEPATIC MtCROSOMm
VII. BRAINFATTYACID CHAINELONGATIONSYSTEM A. Introduction and general properties B. The rate-limiting step of brain microsomal FACES C. Reduction of chain elongation intermediates in brain microsomes D. Physiological importance of FACES in the brain VIII. KJDI~nBYCOR~BXFATTYACID CHAINELONGATIONS~TI~ IX. FACES IN OTnr~ ORGANSA ~ Tmsur~s A. Lung B. Small intestine C. Cultured mammalian cells I. Skin fibroblasts 2. Aortic fibroblasts 3. Adren~ortical cells from zona fasciculata and zona reticularis D. Aorta E. Nentrophils F. T Lymphocytes G. Retina H. Placenta I. Testis X. MmouoLOGY FOR ~ MICROSOtUd.FACES A. Determination of total chain elongation activity B. Measurement of the condensation reaction C. Measurement of p-ketoacyl CoA reductase activity D. Determination of #.hydroxyacyl CoA dehydrase activity E. Determination of trans-2-enoyl CoA reductase activity
4 6 6 8 8 8
10 14 15 17 17 17 18 18 18
2O 2O 21 21 22 22 22 22 23 24 25 25 25 28
30 32 34 35 35 37 37 37 38
39 39 39 39 40 40 40 41 41 41 41 41 42
2
D.L. CINTIet
al.
F. Synthesisof substrates of the FACES 1. Chemical synthesis of CoA derivatives 2. Synthesisof/~-ketoacylCoA derivatives 3. Synthesisof/~-hydroxyacylCoA derivatives 4. Synthesisof trans-2-enoyl CoA derivatives XI. NONENDOPLASMICRETICULUMFATTYACID CHAIN ELONGATIONSYSTEMS A. Mitochondria
B. Peroxisomes XII. SUMMARYAND CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES
42 42 42 43 43 44 44 45 46 46 46
I. INTRODUCTION Before delving into the details of the mammalian enzyme system that is responsible for the biotransformation, specifically chain elongation of the lipid constituents, namely the fatty acids, an overview of the sources and levels of fatty acids in the food supply and in body tissues appears appropriate. The ensuing tables depicting fatty acid composition will provide a ready reference when substrates of and their metabolism by the fatty acid chain elongation system (FACES) are discussed below. Over the past 70 years, the quantity of fat in the food supply of the United States has increased about 35%, from a value of ca. 125 g per capita per day in 1910 to nearly 170 g in 1980.271'277In terms of food energy in the U.S. food supply, fat represents about 42% of the total kilocalories, up from 32% in 1910, whereas the proportion of calories attributed to carbohydrate has decreased from 56% in 1910 to 46% in 1980.277The energy obtained from protein has remained stable at 12%. Although the U.S. food supply data suggest an available fat supply of about 160-166 g per individual per day, actual consumption of£at per individual is significantly lower. Data from the Nationwide Food Consumption survey of 1977-1978277'331'332showed that females consumed ca. 70 g of fat per day, while males consumed 110 g per day. Hence, the average fat intake per individual per day for all individuals is 80-90 g. Based on the inherent difficulties in the methodologies employed in determining food consumption, the values 80-90 g and 160-166 g may represent the extremes and the average of the two (120-130 g) may represent a more realistic value of daily fat consumption. In any event, the food energy derived from protein, fat and carbohydrate data obtained from the food consumption survey331-334indicate that in 1977, 16% of the energy was provided by protein, 42% by fat and 41% by carbohydrate. Data obtained in 1985-1986, indicate that the energy derived from protein remained at ca. 16%, whereas energy provided by fat decreased 5% to 37% and energy from carbohydrate increased to 46%. 333`334The ingested fat is predominantly in the form of triglycerides, and the fatty acid composition of the various food fats is depicted in Tables 1 and 2. Whether the fats are of animal, vegetable or aquatic origin, with the exception of coconut oil, the predominant saturated fatty acid is palmitic acid (16:0). Whereas the major monounsaturate of all the fats is oleic acid (9-18:1), in aquatic oils there are also significant quantities of palmitoleic (9-16:1), eicosenoic (11-20:1) and docosenoic (9/11-22:1) acids. Linoleic acid (9,12-18:2) is the most abundant polyunsaturated fatty acid in animal, vegetable and fruit and nut fats; however, in marine fats, the major polyunsaturates consist of chain lengths of 20 and 22 carbons and 4, 5 or 6 double bonds (Table 2). The fatty acid composition of various mammalian tissues (Table 3) differs slightly from that of the foodstuffs (Tables 1 and 2). Both palmitic and stearic acids are present in similar amounts, except for adipose tissue which contains a higher percentage of palmitic acid. As in foodstuffs, oleic acid is the major monounsaturated fatty acid; however, whereas in vegetable oils, fruit and nut oils and animal fats, the only significant polyunsaturated fatty acid is linoleic acid; in mammalian tissues, there are large amounts of arachidonate and docosahexenoate (Tables 3 and 4). From the analysis of the fatty acid content of oils and fats (Tables 1 and 2), various mammalian tissues (Table 3) and subcellular membranes (Table 4), the fatty acyl groups
Fatty acid chain elongation TABLE 1. Composition of Major Fatty Acids of Vegetable, Fruit and Nut Oils and Animal Fats63,,z6,m,t4s.tss,176 % Saturated 16:0 18:0 Vegetable oils Corn, cottonseed, safflower, sesame, soybean,* sunflower Fruit and nut oils Olive Nutst Grapeseed Coconut + Animal fats Butter~ Beef Chickenll Lard Mutton
% Monounsaturated % Polyunsaturated 9-18:1 9,12-18:2
7-16
2-7
18-47
37-65
8-20 5-12 6-11 4-12
1-4 1-4 3-6 1-5
56-83 50-68 12-28 4-12
4-20 18-25 58-78 1-4
25-28 27-29 24-26 20-32 25-27
11-13 7-21 4-6 5-24 30-32
27-29 41-47 36-43 35-62 30-32
-2 14-21 3-16 2
*Soybean oil also contains 6% 9,12,15-18:3. tAlmond, cashew, peanut, pecan, pistachio. ~/Coconut oil--contains predominantly saturated fatty acids with carbon lengths < 16; for example, Ct4 = 13-23%, Cl2 = 41-56%, Ci0 = 4-15%, C 8 = 4-15%. §Butter also contains 10-12% Ct4 and about 13% Cc-Ct2. ItChicken contains about 9% Ct2--CI4 and 8% Ct6:t.
are derived from three different processes: (1) diet, which can provide the bulk of the fatty acids observed in the phospholipids, triacylglycerols and cholesteryl esters; (2) de n o v o fatty acid synthesis, in which the predominant product is palmitic acid; and (3) modification of both dietary and newly synthesized fatty acids by enzymes present in the endoplasmic reticulum of the mammalian cell. These enzymes catalyze a series of desaturation and chain elongation reactions to yield the required acyl (enoyl) group. Some of the biochemical transformations are shown in the scheme below (Scheme 1). The present review will focus on the current state of knowledge of the fatty acid chain elongation system. FACES has been studied extensively in both liver and brain, and also found to be present in a variety of other tissues, such as kidney, small intestine, adrenal cortex, neutrophil, cultured skin fibroblasts, aorta, placenta, testis, retina and lung. Each one of these will be discussed separately. TABLE 2. Fatty Acid Composition of Aquatic Animal Oils6,ss,m,m
Fatty acid 14:0 16:0 18:0 Total saturated mean 9-16:1 9-18:1 11-20:1 9/11-22:1 Total monounsaturated mean 9,12-18:2 9,12,15-18:3 5,8,11,14-20:4 5,8,11,14,17-20: 5 7,10,13,16,19-22:5 4,7,10,13,16,19-22: 6 Total polyunsaturated mean
Marine oils Salt water fish* Fresh water fish'}" (%) (%) 7-9 9-23 1-3 26 7-15 4-29 2-15 2-20 47 -0--4 0-2 3-16 -2-12 19
2-4 17-20 3-5 25 8-11 9-29 --29 2-6 2-6 4-8 7-12 2-4 9-26 44
*Salt water fish including menhaden, sardine, Atlantic and Pacific herring, mackerel and copelin. tFresh water fish include bass, perch, pike and trout.
D. L. CINTI et al. TAeLE 3. Fatty Acid Composition of Rat Liver, Heart, Brain, Kidney and Adipose Tissues from Several Species 88,10~,126.140,232,255,315a,325 Liver
Plasma
Heart
Fatty acid
Brain
Kidney
Adipose*
19 -18 8 13 29 1 1 3
20-28 2-10 6-16 33-50 5-30
