Associations among plasma homocysteine, amino acids and nutritional status in hemodialysis

188 Pages·2002·10.75 MB·English

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ASSOCIATIONS AMONG PLASMA HOMOCYSTEINE, AMINO ACDS
AND NUTRITIONAL STATUS INHEMODIALYSIS PATENTS
Karen Sarita Burleigh
A thesis subrnitted in conformity with the requirements
for the degree of Masters of Science
Graduate Department of Nutritional Sciences
University of Toronto
O Copyright by Karen Sarita Burleigh 2001
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ASSOCIATiONS AMONG PLASMA HOMOCYSTEINE, AMKNO ACIDS
AND NUTRITIONAL STATUS IN HEMODIALYSIS PATIENTS
Masters of Science, 2001
Karen Sarita Burleigh
Graduate Department of Nuîritional Sciences,
University of Toronto
Hyperhomocysteinemia and cardiovascular disease are prevalent among hemodialysis
(HD) patients. The influence of amino acid metabolisrn and nutritional status on plasma
homocysteine (Mcy) was examined in 45 HD patients prescribed 1m g/d folate and 6&d
vitamin B 12 (B 12). A pre-dialysis blood sample was analyzed for tHcy, amino acids,
folate, and B 12. tHcy was elevated in 89% of patients (27.3&12.6poVL, meRn+SD),
and was 42% higher in 7 patients who were noncornpliant with vitamin supplementation
versus cornpliers (p=0.003). tHcy correlated with serum folate, plasma methionine and
cystine @<0.01 each). îHcy was similar in well-nourished vs. malnourished patients,
based on subjective global assessment. Intakes of energy, protein, folate and B 12
determined fiom weighed 3-day food records and food fiequency questionnaires, were
inversely correlated with tHcy (~60.02e ach). B 12 intake and plasma cystine accounted
for 53.6% of the variance in tHcy, suggesting that diet and altered amho acid metabolism
contribute to hyperhomocysteinemia in HD patients.
Acknowledgemeats
"It takes a community to raise a chi1d "... and clearly, it also takes a comunity to ensure
the successfùi completion of a research thesis.
1 wish to extend immense gratitude to my thesis supe~sorDs r Rhona Hanning and Dr
Pauline Darling for their wisdom, great enthusiasm, cornmitment and resourcefidness.
They guided me with patience, and chaüenged me to new heights, professionally and
persodly. 1 thank them for inspiring me to master the skills required to conduct a hi&
calibre of research, so that 1 may continue making a clifference in the world by pumiing
answers to questions. My sincere thanks to my advisors, Dr Paul Pencharz and Dr
Young-In Kim for their keen interest and valuable contributions.
1 am gratefiil to Dr Marc Goldstein for his collaboration, permission to conduct this
research in the Hemodialysis Unit at St Michael's Hospital, and for generously sharing
his genotype data. 1 am ais0 indebted to the Hemodiaiysis Unit nurses who cheerfully
assisted in obtaining patients' blood samples for the study.
My sincere thanks go to the hemodialysis patients who participated in the study. They
made this work possible by t&g me, and being willing to contribute to other patient's
health through this research.. 1 am also indebted to the staff of the Diet Office at SMH
who went out of their way to provide individuaiized breakfasts for the study participants.
Among those who provided me with technical support, 1 am especially gratehil to Dr
David Cole, and Dr Jovan Evrovski fiom Dr Cole's laboratory at the Departments of
Clinical Biochemistry, Medicine and Pediatrics (Genetics), University of Toronto, and
the Banting Institute, Toronto, for their expert assistance with homocysteine analysis, and
their enthusiastic support throughout the study. Sincere thanks are also extended to David
Bassford of the Biochemical Genetics Laboratory, McMaster University Medical Centre,
Hamilton, Ontario, for his advice and assistance with amino acid anaiysis; to Betty Wong
fiom Dr David Cole's laboratory at the Departments of Clinical Biochemistry, Medicine
and Pediatrics (Genetics), University Health Network, Toronto, for her assistance with
MTHFR genotyping; to Dr Art Vandenbroucke and the technicians of the Clinical
Chemistry Laboratones of St Michael's Hospital for theu advice and assistance with the
andysis of blood folate and vitamin B 12, urea, creatinine, and albumin; and to Tamara
Arenovich and Dr Aida Barr for their advice with statistical analysis.
1 am also gratefid to Dr David Jenkuis at the Clinicai Risk Factor Modification Centre of
St Michael's Hospital for the loan of the electronic scales used to weigh patients' food; to
Elizabeth Warwick RD for her advice in the nutritional analysis of food records and food
fiequency questionnaires; and to Karen Fogei and Charlene Waker for their assistance
with data entry. 1 wish to thank Nom Lee and Stephanie Charron at Health Canada for
sharing their expertise and preIiminary data on folate fortification of foods in Canada-
A special thank you to my Directors, Joan McLaughlin RD MBA, and Bea Mudge RN
MBA, and to my Clinical Leader Manager Nancy Webster RN MSc, who provided
practical support and encouragement throughout my studies.
My great appreciation is also extended to my fellow graduate students and colleagues,
including: Wantanee Kriengsinyos MSc RD, Shelly Perry RD, Carol Huang RD, Donna
Lum MSc RD, Michelle McCall MSc RD, Crystal O'Leary RD and Linda Cohen MSW
who generously provided me with advice, fiiendship and practical support in jugghg my
studies and work responsibilities.
The research in this thesis was made possible by fiinding fiom the Canadian Foundation
for Dietetic Research. Personal bding was awarded by the McCain Foundation
Graduate Award for Dietitians, and St Michael's Hospital Tuition Assistance Program.
1 dedicate this thesis to my parents, brother and sister for their extraordinary gifts of love,
respect, and generosity. They instilled in me an enquinng mind and the confidence to
succeed.
TABLE OF CONTENTS
1. INTRODUCTION 1
2. LITERATURE REVJEW
2.1. Hyperhomocysteinemia: Association with Cardiovascular Disease Risk 5
2.2. Homocysteine Metabolism and Regdation 7
2.3. Hyperhomocys teinemia in Chronic Rend Failure 10
2.4. Determinants of Hyperhomocysteinemia 15
2.4.1. FoIate and vitamin B lz insufficiency 15
2.4.1.1. Trials of B vitamin supplementation in CRF 18
2.4.2. Altered amino acid metabolism in HD patients 22
2.4.3. Nutrient intake of HD patients 25
2.4.3.1. Energy and protein intakes 25
2.4.3.2. Vitamin intakes 27
2.4.4. Malnutrition in HD patients 29
2.4.5. MTHFR genotype 32
2.4.6. Lifestyle (coffee and alcohol consumption, and smoking status) 33
2.5. Surnmary 35
3. RATIONALE, HYPOTHESIS AND OBJECTIVES
3.1. Rationale
3.2. Hypothesis
3.3. Objectives
4. METHODS
4.1. Subjects
4.2. Study Design
4.3. Study Procedures and Sample Collection
4.3.1. Blood sample collection
4.3.2. Collection of nutrient intake data
4.3.3. Physical assessment of nutritional status
4.3 -3.1. Subjective global assessment
4.3 -3.2. Height and weight measurements
4.3 -3.3. TSF and MAMC measurements
4.4. Anaiyticai Procedures
4.4.1. Erythrocyte and senun folate, and serum vitamin B iz analysis
4.4.2. Plasma homocysteine analysis
4.4.3. Plasma itmùio acid analysis
4.4.4. S e ma lbumin and creatinine, and dialysis adequacy (üRR)
4.4.5. Analysis of nutrient intake
4.4.5.1. Caiculation of energy and protein intake
4.4.5.2. Calculation of vitamin intake
4.4.5.3. Calculation of coffee and alcohol consumption
4.4.6. Nutritional status assessment
4.4.6.1. Determination of subjective global assessment
4.4.6.2. Calculation of body mass index
4.4.6.3. Calculation of TSF percentile
4.4.6.4. Calculation of MAMC percentile
4.4.7. Genetic analysis
4.4.7.1. Amplification of DNA fÏagments
4.4.7.2. Identification of MTHFR polymorphisms
4.5. Statistical Analysis
4.5.1. Sample size calculation
5. RESULTS
5.1. Subjects 67
5.1 .l. Patient characteristics 68
5.1.2. Duration ofH D, biochemical indices of CRF and HD adequacy 70
5.1.3. Cornpliance with vitamin supplementation 70
5.2. Plasma tHcy and vitamin status 70
5.2.1. Plasma tHcy concentrations 70
5.2.2. Vitamin status and the relationship with plasma tHcy concenration 72
5.3. Plasma amino acids and the relationship with plasma tHcy 76
5.3.1. Associations between plasma amino acids and tHcy 79
5.4. Nutritional status and the relationship with plasma tHcy 83
5.4.1. Association between Body Mass Index and plasma tHcy 83
5.4.2. Association between Subjective Global Assessrnent and plasma tHcy 83
5.4.3. Association between anthropometrics and plasma tHcy 83
5.5. Nutrient intake and the relationship with plasma tHcy 87
5.5.1. Associations between energy and protein intake and plasma tHcy 87
5.5.2. Associations between protein and plasma amino acids, BUN
and serum albumin and plasma tHcy 87
5 -5.3. Association between vitamin intake and plasma tHcy 92
5.6. MTHFR genotype and its associations with plasma tHcy and folate status 95
5.7. Associations among potential confounding variables and plasma tHcy 98
5.7.1. Patient gender and age 98
5.7.2. Dialysis treatment and serum albumin 98
5.7.3. Diabetes 98
5.7.4. Smoking status 98
5.7.5. Coffee and alcohol consuniption 98
5.8. Multiple regression of deterrninants of plasma tHcy 101
6. DISCUSSION
6.1. Prevalence of hyperhomocysteinemia 10 4
6.2. Response to vitamin supplementation 105
6.3. Association between tHcy and vitamin B 12 intake 10 7
6.4. Association between tHcy and RBC and senun folate 110
6.5. Association between tHcy and key amino acids in Hcy metabolism 112
6.5.1. Plasma concentrations of sulfùr amino acids, taurine and glutathione 1 12
6.5.1.1. Association between tHcy and amino acids in Hcy metabolism 11 3
6.5.1.2. Plasma serine concentrations 114
6.5.1.3. Association between tHcy and serine 114
6.6. Association between tHcy and macronutrient intake 115
6.6.1. Association between tHcy and protein intake 116