Recipient Organization
UNIVERSITY OF ARIZONA
888 N EUCLID AVE
TUCSON,AZ 85719-4824
Performing Department
Nutritional Sciences
Non Technical Summary
The modern Western diet (MWD) has dramatically changed the nutritional content of ingested foods in developed countries, and given the rapid nature of these nutritional transitions, mal-adaptations and related human diseases are a likely outcome of our current nutritional environment. For example, up to 72% of dietary calories consumed presently in the MWD did not exist in hunter-gatherer diets and is provided in the form of high-calorie foods high in sugars, refined grains and oils. This has led to detrimental shifts in nutrient metabolism leading to gene-diet interactions responsible for more obesity as well as localized and systemic inflammation. In turn, this inflammation contributes to a variety of disease states, including cardiovascular disease, diabetes and insulin resistance, cancer, autoimmunity, hypersensitivity disorders such as asthma and allergies, chronic joint disease, skin and digestive disorders, dementia and Alzheimer's disease.As challenging as these changes are for overall populations of developed countries such as the US, the negative effects are considerably increased for certain populations and ethnic groups, in whom a disproportionate burden of preventable disease, death, and disability now exists. One of these groups is Hispanics of Amerindian descent (such as Mexican Americans). Hispanics have a 23% higher rate of obesity, a 50% higher death rate from diabetes, and 24% more poorly controlled high blood pressure. Interestingly, health risk also depends partly on whether you were born and live in the US, or another country, with US born at significantly higher risk.Omega-3 and omega-6 long chain polyunsaturated fatty acids (LC-PUFAs) and their metabolites play important roles in human physiology and pathology as they mediate important steps in innate immunity and energy metabolism as well as brain development, and neurocognitive function. Most evidence to date indicates thatomega-3 and omega-6 LC-PUFAs and their metabolic products have not only different, but often opposing effects on immunity and inflammation. While omega-6 LC-PUFAs promote inflammation, omega-3 LC-PUFAs are considered anti-inflammatory. Humans cannot produce their own omega-3 and omega-6 LC-PUFAs. Instead they must obtain polyunsaturated fatty acids (PUFAs) from food (usually plant-based sources), which are then used by the body to create omega-3 and omega-6 LC-PUFAs. Up until recently, it was assumed that all human populations had similar capacities to convert plant-based PUFAs to LC-PUFAs. However, more recent studies indicate that there are dramatic ancestral-based genetic differences that impact the capacity of humans to synthesize LC-PUFAs. We have recently discovered that high Amerindian-Ancestry populations have a set of gene variations associated with a limited capacity to synthesize LC-PUFAs and particularly omega-3 LC-PUFAs. These are critical to reducing inflammatory reactions, as well as lowering elevated lipids, the incidence of diabetes and heart disease. Given that omega-3 LC-PUFAs are essential for a wide range of human biological functions, a reduced capacity to synthesize them has great potential to be a health risk for modern populations with Amerindian-Ancestry Hispanics including Mexican Americans. These studies will provide data to confirm the proposed gene-diet interaction in Amerindian-Ancestry Hispanic populations gives rise to omega-3 LC-PUFA deficiencies which in turn has great potential to result in numerous diseases/disorders and disparities in these populations. These findings would then facilitate gene-based nutritional and dietary supplement approaches to address these deficiencies and diseases/disorders in Hispanic population.
Animal Health Component
(N/A)
Research Effort Categories
Basic
100%
Applied
(N/A)
Developmental
(N/A)
Goals / Objectives
The long-term objective of these studies is to determine whether there is a gene-diet interaction in high Amerindian (AI)-Ancestry Hispanic (Mexican American) populations that causes deficiencies in circulating and tissue levels of omega-3 (n-3) long chain polyunsaturated fatty acids (LC-PUFA) which in turn result in numerous diseases/disorders and disparities in these populations. This finding would then facilitate gene-based nutritional and dietary supplement approaches to address these deficiencies and the diseases/disorders they cause. Future studies will examine if such deficiencies impact human physiology at critical periods of brain development and as anti-inflammatory mediators.
Project Methods
Study 1: MESA is a longitudinal study of subclinical cardiovascular disease and risk factors that predict progression to clinically overt cardiovascular disease or progression of the subclinical disease. Between 2000 and 2002, MESA recruited 6,814 men and women 45 to 84 years of age from Forsyth County, North Carolina; New York City; Baltimore; St. Paul, Minnesota; Chicago; and Los Angeles. Exclusion criteria were clinical cardiovascular disease, weight exceeding 136 kg (300 lb.), pregnancy, and impediment to long-term participation.Hispanic American participants (n = 1225) from MESA will have samples assayed by gas chromatography for plasma phospholipids to determine n-3 and n-6 PUFA levels in those phospholipids. Hispanic country of origin will be inferred using participant-reported birthplaces for their parents and grandparents. Regression analysis will be used to assess associations of LC-PUFA levels with global proportion of Amerindian ancestry, computed using ADMIXTURE and local probability of Amerindian ancestry for the FADS variant, rs174537, computed using Rfmix. FADS cluster SNPs will be available from genome-wide genotyping (Affymetrix 6.0 array) followed by imputation to the 1000 Genomes Phase 3 reference panel. Regression models will include covariate adjustment for age, sex, study site, four PCs of ancestry and batch.Study 2: We have acquired baseline plasma and red blood cell samples from 147 Mexican American participants in La Comunidad trial. Genotypes of the key FADS variant, rs174537 has been determined in all participants. Our preliminary data indicate that 51% of this cohort contain TT genotype associated with the Amerindian ancestry haplotype and deficiencies in omega-3 LC-PUFAs. As a comparison group, 100 plasma samples have been acquired from a European-Ancestry population from a screening component of Dr. Chilton's current R01, "Role of PUFA-Gene Interactions in Health Disparities."Plasma and red blood cells have been isolated from fasting whole blood samples and lipids extracted. Fatty acid methyl esters will be prepared in duplicate from samples (100 μl) in the presence of an internal standard (triheptadecanoin; NuChek Prep, Elysian, MN, USA). A panel of twenty-three fatty acids will be quantified by GC with flame ionization detection (GC-FID). Individual fatty acids will be expressed as percentage of total fatty acids in a sample. For all samples, data peaks on chromatograms will be examined to ensure peak quality and consistency of retention times. Fatty acids in samples will be identified based on the retention times of methyl ester derivatives of authenticated fatty acid standards. These standards included Supelco 37 Component FAME Mix (Supleco, Bellefonte, PA, USA) and other individual methyl ester derivatives from Supelco (oleate,cis-11-vaccenoate, linoleate, eicosapentaenoate,n-3 docosapentaenoate), Cayman Chemicals (Ann Arbor, MI, USA; stearidonate), Matreya (Pleasant Gap, PA, USA; eicosadienoate, dihomo-γ-linolenoate, arachidonate) and NuChek Prep (cis-eicosatrienoate, docosadienoate, docosatetraenoate,n-6 docosapentaenoate, docosahexaenoate, tricosanoate, tetracosanoate). Product:precursor ratios of circulating fatty acids, an estimate of enzymatic activity, will be calculated from fatty acid mass data.For statistical analyses of fatty acid data, normal kernel density estimation (implemented in S-Plus; TIBCO Software Inc., Palo Alto, CA, USA) will be used to obtain estimates of the probability density functions. Linear mixed models will be used to assess the racial difference in the fatty acids and ratios adjusting for sex and age. Family will be treated as a random effect and age, sex and race as fixed effects. Residuals will be examined to assess the model assumptions.In addition to GC-FID described above which measures total fatty acid content simultaneously in all complex lipids, lipidomic analyses will be completed to determine those individual phospholipid, lyso-phospholipid, cholesterol ester, triacylglyceride and free fatty acid molecular species that are most impacted by FADS variation and race. Twenty samples representing each genotype in both Amerindian- and European-Ancestry will be analyzed utilizing a mass spectrometry lipidomic platform that we have developed in collaboration with the Proteomics and Metabolomics Shared Resource at Wake Forest Baptist Comprehensive Cancer Center at Wake Forest Health Sciences. Plasma samples will be processed for lipidomics analysis using standard chloroform/methanol extraction after the addition of internal standards (SPLASH, Avanti Polar Lipids). The supernatant will be removed under nitrogen at room temperature. The residues will be reconstituted into 50 μL of isopropyl alcohol/methanol (1:1) giving a 1:10 dilution of the internal standards for LC-MS/MS analysis. High-resolution LC-MS/MS analysis will be performed on a Q Exactive HF hybrid quadrupole-Orbitrap mass spectrometer (Thermo Scientific) with heated electrospray ion (HESI) source and a Vanquish UHPLC system (Thermo Scientific). Lipids will be separated on a C18 column (2.1 x 100 mm, 1.8 µm) using a linear gradient with 60:40 acetonitrile/water (mobile phase A) and 90:10 isopropyl alcohol/acetonitrile (mobile phase B). Pooled samples will be introduced periodically for quality control to correct for variations in instrument performance or other systematic biases during analysis. Lipid identification and quantification will be performed using LipidSearch 4.1 (Thermo Scientific).