Effect of omega-3 fatty acids in non-alcoholic fatty liver disease

155 Pages·2017·2.19 MB·English

UNIVERSITY OF SOUTHAMPTON
Faculty of Medicine
Human Development and Health

Effect of omega-3 fatty acids in

non-alcoholic fatty liver disease

Volume 1 of 1

by Eleonora Scorletti (MD)

June 2017

University of Southampton Research Repository
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Thesis: E. Scorletti (2018) "Effect of omega-3 fatty acids in non-alcoholic fatty liver
disease", University of Southampton, Faculty of Medicine Human Development and Health,
PhD Thesis, 1-138.

To Andrea, “per aspera ad astra”.

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UNIVERSITY OF SOUTHAMPTON
ABSTRACT
FACULTY OF MEDICINE
Human development and health
Thesis for the degree of Doctor of Philosophy
Title: EFFECT OF OMEGA-3 FATTY ACIDS IN NON-ALCOHOLIC FATTY LIVER DISEASE
Eleonora Scorletti
The first chapter (Introduction) of the thesis summarises the pathogenesis of NAFLD and its
associated risk factors such as type 2 diabetes and cardiovascular disease. Moreover, it describes:
a) the potential beneficial effects of long chain omega-3 fatty acid treatment [docosahexaenoic
acid (DHA) plus eicosapentaenoic acid (EPA)] in NAFLD; b) the effect of genotypes patatin-like
phospholipase domain-containing protein-3 (PNPLA3 I148M) and the transmembrane 6
superfamily member 2 protein (TM6SF2 E167K), on the level of DHA and EPA enrichment and end
of study liver fat percentage after DHA+EPA treatment; and c) the effect of fatty acid desaturase
(FADS) and Elongase (ELOVL) polymorphisms influencing omega-3 fatty acid metabolism. The
second chapter describes the overall aim of this thesis. The aim of my research was to investigate
in patients with NAFLD: a) the effect of long-chain omega-3 fatty acid treatment on liver fat
percentage and liver fibrosis biomarkers; b) the effect of genotypes influencing NAFLD severity on
treatment with DHA+EPA; and c) the effect of genotypes influencing omega-3 fatty acid
metabolism in NAFLD. The third chapter describes in details the design and methods used in my
research. Chapter four highlights my novel results from the WELCOME study. This chapter
describes the baseline and end of study characteristics of the WELCOME study participants and
shows the results of the DHA+EPA treatment on liver fat percentage and liver fibrosis biomarkers.
This chapter also describes the association between DHA erythrocyte enrichment and decrease in
liver fat percentage after DHA+EPA treatment. Chapter five illustrates the association between
PNPLA3 I148M and DHA erythrocyte enrichment percentage and end of study liver fat percentage
after DHA+EPA treatment. The chapter shows that PNPLA3 I148M was associated with higher end
of study liver fat percentage and lower DHA tissue enrichment. Chapter six shows the negative
association between FADS polymorphisms and omega-3 fatty acid metabolism in NAFLD. The
chapter also shows that there was a gene-DHA+EPA interaction between the minor allele of the
FADS1 rs174556 and Δ-5 desaturase activity after treatment with DHA+EPA. Finally, chapter
seven, summarises my results in the context of current evidence and knowledge about the subject
matter.

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Table of Contents
List of Tables ……………………………………………………………………………………………………………. ix
List of Figures …………………………………………………………………………………………………………… xi
List of accompanying material …………………………………………………………………………………. xiii
Author’s declaration ………………………………………………………………………………………………… xv
Acknowledgments …………………………………………………………………………………………………… xvii
List of abbreviations ………………………………………………………………………………………………... xix
Academic Thesis: Declaration Of Authorship ...................................................................... xv
1. Introduction .................................................................................................................... 1
1.1 Background and epidemiology of non-alcoholic fatty liver disease ....................... 2
1.2 Pathogenesis of non-alcoholic fatty liver disease ................................................... 6
1.2.1 Role of carbohydrates and fructose in the pathogenesis of NAFLD ................ 7
1.2.2 Lipids metabolism and the pathogenesis of NAFLD ........................................ 9
1.2.3 Hepatic and Adipose Tissue Function, Inflammation, and NAFLD ................ 10
1.2.4 Influence of genotype polymorphism on liver lipid metabolism ................... 11
1.2.5 Enterohepatic Circulation and NAFLD............................................................ 13
1.3 Omega-3 polyunsaturated fatty acids ................................................................... 17
1.3.1 Chemical structure and nomenclature .......................................................... 19
1.3.2 Synthesis and metabolism ............................................................................. 19
1.3.3 Effect of omega-3 fatty acids in NAFLD ......................................................... 22
2. Aims and Hypotheses ................................................................................................... 27
2.1 Aims ....................................................................................................................... 28
2.2 Hypotheses ............................................................................................................ 29
3. Methods ........................................................................................................................ 31
3.1 Study design .......................................................................................................... 32
3.2 Patient selection .................................................................................................... 32
3.3 Recruitment ........................................................................................................... 32
3.4 Randomisation ....................................................................................................... 32
3.5 Intervention ........................................................................................................... 33
3.5.1 Active group ................................................................................................... 33
3.5.2 Placebo group ................................................................................................ 33
3.6 Inclusion and exclusion criteria ............................................................................. 34
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3.7 Study visit overview and follow-up ....................................................................... 34
3.7.1 Detail of follow-up of non-compliant subjects & withdrawal of subjects. .... 37
3.8 Baseline and end of study measurements ............................................................ 38
3.8.1 Biochemical and anthropometric measurements ......................................... 38
3.8.2 Assessment of compliance and measurement of erythrocyte DHA and EPA
enrichment ................................................................................................................... 38
3.8.3 Body fat (total body fat, regional body fat and visceral fat) ......................... 39
3.8.4 Mean liver fat percentage ............................................................................. 40
3.8.5 Diet ................................................................................................................. 42
3.8.6 Cardiorespiratory fitness ............................................................................... 42
3.8.7 Physical activity energy expenditure ............................................................. 43
3.8.8 DNA analyses ................................................................................................. 43
3.9 Sample size and power calculation ....................................................................... 44
4. Results .......................................................................................................................... 45
4.1 The effect of highly purified high dose Docosahexaenoic acid (DHA) and
Eicosapentaenoic acid (EPA) treatment in NAFLD. .......................................................... 46
4.1.1 Introduction ................................................................................................... 46
4.1.2 Hypothesis ..................................................................................................... 47
4.1.3 Methods ......................................................................................................... 48
4.1.4 Results ............................................................................................................ 50
4.1.5 Discussion ...................................................................................................... 65
4.2 The Treating liver fat and serum triglyceride levels in NAFLD, effects of PNPLA3
and TM6SF2 genotypes .................................................................................................... 67
4.2.1 Introduction ................................................................................................... 67
4.2.2 Hypothesis ..................................................................................................... 68
4.2.3 Methods ......................................................................................................... 69
4.2.4 Results ............................................................................................................ 71
4.2.5 Discussion ...................................................................................................... 82
4.3 The effect of Fatty Acid Desaturase (FADS) and Elongase (ELOVL) polymorphisms
on indexes of desaturase activity and liver fat in NAFLD. ............................................... 86
4.3.1 Introduction ................................................................................................... 86
4.3.2 Hypotheses .................................................................................................... 88
4.3.3 Methods ......................................................................................................... 89
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