Background and objectives: Recent genome-wide association (GWA) studies conducted in Caucasian populations have significantly expanded the list of confirmed and potential susceptibility genes for obesity and type 2 diabetes. The major objective of this thesis was to establish the role of the previously identified obesity- and T2DM-susceptibility genes in the Hong Kong Southern Chinese population. Major findings: In a cross-sectional case-control study of Southern Chinese which involved 470 obese cases and 700 normal-weight controls, significant associations with obesity were demonstrated in 7 of 13 single nucleotide polymorphisms (SNPs) that have shown significant associations with obesity and/or body mass index (BMI) in previous Caucasian GWA studies. These SNPs are located within or near the GNPDA2, FTO, MC4R, KCTD15, SFRS10-ETV5-DGKG, SEC16B-RASAL2 and NEGR1 loci. The combined genetic risk score (GRS) of the 13 studied SNPs was associated with an increased risk for obesity. The GNPDA2 rs10938397, FTO rs8050136, and MC4R rs17782313, which showed the most significant associations with obesity, were further examined for their associations with persistent central obesity and the metabolic syndrome (MetS). Both rs8050136 and rs10938397 were significantly associated with persistent central obesity. rs10938397 was also associated with the MetS. The combined GRS of these 3 SNPs showed significant associations with both persistent central obesity and persistent MetS. Nineteen multimarker-tagging SNPs that span a well-defined LD block of the FTO gene were evaluated for their associations with obesity in a case-control study which involved 249 cases and 400 controls. rs16952522 was found to be significantly associated with obesity, in addition to the well-known SNP rs8050136. These 2 SNPs were nominally associated with T2DM, although the associations were abolished after adjustment for age, sex and BMI. However, the GA haplotype composed of the risk alleles of these 2 SNPs was significantly associated with T2DM, independent of BMI. Seventeen previously identified T2DM-associated SNPs were investigated for the associations with glycaemic progression in an 8-year follow-up study which involved 518 cases and 998 controls. Their combined GRS was associated with an increased risk for glycaemic progression. A significant association with glycaemic progression was found with CDKN2A/B rs10811661. Moreover, KCNJ11 rs5219 and IGF2BP2 rs11711477 also showed potential associations with glycaemic progression. In the subsequent 12-year follow-up study, which involved 200 cases and 903 controls, the CDKN2A/B rs10811661 showed a significant independent association with incident T2DM. The KCNJ11 E23K (rs5219) variant was examined for its association with diabetes development in a 12-year prospective study. It was found to be significantly associated with the development of prediabetes but not with the development of T2DM. However, in a meta-analysis which involved 15680 subjects across different populations, this variant could indeed predict T2DM. Conclusions: The findings of this thesis have provided novel evidence supporting the role of the GWA studies-identified obesity- and T2DM-associated genetic variants as genetic markers of obesity and T2DM among Southern Chinese in Hong Kong, and suggest that the GNPDA2, FTO and MC4R genes confer susceptibility to obesity and that the CDKN2A/B and KCNJ11 genes may play a role in diabetes development. / published_or_final_version / Medicine / Doctoral / Doctor of Philosophy

n-3 polyunsaturated fatty acids (n-3 PUFA) have been postulated to improve the insulin resistance associated with type 2 diabetes since the 1960s when observational studies in the Alaskan Inuit noted a reduced prevalence of type 2 diabetes when this population consumed a traditional diet. These findings were supported by animal studies but results of human intervention studies have been variable with most showing no change in glucose metabolism. More recent studies in growing farm animals suggested that muscle membrane phospholipids required to be enriched to a minimum of 14% n-3 PUFA in order for a change in insulin sensitivity to occur. This study sought to establish the effect of long-term (9 month) high-dose (3g/day) supplement of the n-3 PUFA eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) on insulin sensitivity of glucose and protein metabolism. Thirty-three subjects with impaired glucose regulation underwent hyperinsulinaemic-euglycaemic-euaminoacidaemic clamps pre- and postintervention of n-3 PUFA or a control (maize) oil. A second cohort who all received n-3 PUFA supplementation underwent pre- and post-intervention muscle biopsies. Secondary outcomes included an assessment of inflammatory status and determining whether erythrocyte membrane phospholipid could act as a surrogate for muscle membrane phospholipid. In the clamp cohort, there were no changes in glucose metabolism postintervention; however, there was an increase in insulin-stimulated protein metabolism following the fish oil intervention. In the biopsy cohort, no subject achieved 14% PUFA enrichment in muscle membrane phospholipids; however, all subjects who received n-3 PUFA supplementation did achieve a minimum of 14% enrichment of n-3 PUFA in erythrocyte membrane phospholipid. In agreement with the majority of the literature, n-3 PUFA did not affect glucose metabolism. Insulin-stimulated protein metabolism was improved supporting the findings of another recent human study. These changes in protein metabolism may reduce the sarcopenia associated with aging, potentially delaying the progression of frailty.

University of Macau / Institute of Chinese Medical Sciences

Plant sterols (PS) are effective in reducing plasma lipid concentrations, however, few studies have examined their cholesterol lowering effects in type 2 diabetics. The objective was to assess whether PS consumption alters blood lipid profile in hypercholesterolemic subjects with and without type 2 diabetes. Fifteen control subjects (age = 55.1 +/- 8.5 yr and BMI = 26.9 +/- 3.0kg/m2) and fourteen diabetic subjects (age = 54.5 +/- 6.7 yr and BMI = 30.2 +/- 3.0kg/m2) participated in a double-blinded, randomized, crossover, placebo-controlled feeding trial. The Western diet included either 1.8g/d of PS or cornstarch placebo each provided over 21 d separated by a 28 d washout period. Subjects consumed only foods prepared in Mary Emily Clinical Nutrition Research Unit of McGill University. Total cholesterol (TC) decreased (p < 0.05) from baseline with PS for control and diabetic subjects by 9.7% and 13.6%, respectively. TC decreased (P < 0.05) from baseline with placebo for control and diabetic subjects by 10.9% and 11.6%, respectively. Non high density lipoprotein cholesterol (non-HDL-C) decreased (p < 0.05) from baseline with PS for diabetic subjects by 18.5%. Low density lipoprotein cholesterol (LDL-C) levels were reduced (p < 0.05) from baseline with PS for control and diabetic subjects by 14.9% and 29.8%, respectively. The reduction of LDL-C due to PS alone is greater with type 2 diabetics. There were no significant changes in HDL-C and TG across diets or treatments. It is thus concluded that PS consumption with diet enhances non-HDL-C and LDL-C reduction compared with diet alone in hypercholesterolemic individuals with and without type 2 diabetes. Demonstration for the first time that PS alone are more efficacious in lowering LDL-C and non-HDL-C in diabetic individuals compared to non-diabetics confirm the beneficial effects of PS to help prevent cardiovascular disease (CVD) for this high risk population.

The objective of this research was to examine the effects of plant sterols and glucomannan on lipid profiles, plasma plant sterol levels and glycemic control in mildly hypercholesterolemic subjects. Thirteen type 2 diabetic and sixteen non-diabetic individuals participated in a randomized crossover trial consisting of 4 phases, of 21 days each. During the study period, subjects were supplemented with plant sterols and/or glucomannan. Overall reductions of total cholesterol and low-density lipoprotein (LDL) cholesterol concentrations were greater after consumption of plant sterols and glucomannan compared to plant sterol or glucomannan supplementation alone. Plasma lathosterol levels, indicators of cholesterol biosynthesis, were decreased after combination treatment. The results suggest that a combination of glucomannan and plant sterols substantially improve plasma lipids by reducing cholesterol absorption and synthesis simultaneously. Supplementation of plant sterols and glucomannan can thus be used as an effective treatment for management of circulating cholesterol levels and prevention of cardiovascular disease.

The objective of this study was to compare the effect of phytosterols (PS) on lipid profiles and cholesterol kinetics of hypercholesterolemic individuals with or without type 2 diabetes. It was hypothesised that the response to PS would differ between both groups due to different lipid metabolism. During this randomised, double blind, crossover trial, participants consumed a controlled diet with placebo or PS for 21 days. / Plasma total cholesterol (TC) decreased with placebo and PS (10.9% and 9.7% in non-diabetic versus 11.6% and 13.6% in diabetic participants, p < 0.05). Plasma low-density lipoprotein cholesterol (LDL) significantly decreased with PS in both groups. The reduction in LDL with PS was greater in diabetic compared to non-diabetic individuals (29.8% versus 14.9%, p < 0.05). Cholesterol absorption decreased on average (p = 0.06) by 26.5% with PS compared with placebo in the diabetic group only. Therefore, a controlled heart healthy diet reduced TC and LDL concentrations in non-diabetic and diabetic individuals. Adding PS as adjuncts to a hypocholesterolemic dietary treatment was associated with lower LDL concentrations and cholesterol absorption in hypercholesterolemic participants with type 2 diabetes.

The objective of this study was to examine the effects of plant sterols and/or glucomannan on lipid profiles and cholesterol kinetics in hyperlipidemic individuals with or without type 2 diabetes. It was hypothesized that plant sterols and glucomannan reduce circulating cholesterol levels and may have an additive or synergistic effect when combined by reducing cholesterol absorption. Thirteen type 2 diabetics and sixteen non-diabetics all mildly hypercholesterolemic free living subjects participated in a randomized crossover trial consisting of 4 phases, 21 days each. Subjects consumed plant sterols and glucomannan during the trial. Overall reductions in total and LDL-cholesterol levels were greater (P<0.05) after consumption of the combination supplement. Effects of supplements were not different between diabetics and non-diabetics. No significant changes were observed in cholesterol absorption or synthesis in both diabetics and non-diabetics. The intake of plant sterols and glucomannan together may be an alternative approach in reducing blood cholesterol levels.

Daughters of gestational diabetes (GDM) affected pregnancies are at greater risk for the development of type 2 diabetes mellitus (DM) later in life. Adiponectin is an early marker of DM risk. Dietary fat quality has been proposed to be involved in the development of insulin resistance. Plasma fatty acids are a marker of recent dietary exposure. The objectives of this research were to determine whether differences in adiponectin exist in daughters of GDM pregnancies, and to describe how dietary fatty acids impact adiponectin concentrations. Fasting adiponectin and plasma fatty acids were examined for 180 adolescent daughters born to mothers with and without GDM. No differences were observed in adiponectin between study groups, however; a significant difference was detected upon comparison of daughters from mothers who were presently diabetic with those from healthy mothers. The association between fatty acids and adiponectin varied by visceral adiposity. Adiponectin was inversely associated with monounsaturated and omega-3 (n-3) fatty acids in the high waist group. Further knowledge on the interactions between fatty acids, desaturase activity and adiponectin would be helpful in planning early interventions for individuals at risk for diabetes.

This ethnobotanical project screened and evaluated the use of traditional medicine of the Cree Nation of Quebec as part of a study directed at preventing complications associated with Type 2 diabetes (T2D). Antidiabetic plants used by the Cree that treat T2D symptoms were identified. Quantitative ethnobotany and analysis of antioxidant activity were conducted. Results from Whapmagoostui were compared with those found in Mistissini and also the literature. Twenty-one plant species were cited during the survey. Although Cree medicine throughout Quebec and Canada is homogenous, geographical and vegetation gradients show some variations. Medicinal plants have better antioxidant potential than non-medicinal plants and have a higher phenolic content. Rankings based upon the ethnobotany, the bioassays and the quantitative tools showed positive correlations. This evidence supports the beneficial effects of Cree TM and medicinal plants selected by the Cree Nation in the prevention of T2D and its complications.

One of the earliest recorded references to polyuria is found in the Papyrus Ebers (1500 BC) and much later the occurrence of "honey urine" was noted by an ancient Hindu physician, Sushrutha, in old Indian Sanskrit (400 BC). However, the first good clinical description of the disease is ascribed to Celsus, although the name "diabetes" was introduced by Aretaeus of Cappadocia. The body of knowledge which has accumulated since these early recordings to the present state of the art reflects a most impressive sojourn, punctuated by many milestones, each adding impetus to future attempts in a relentless endeavour to unravel the aetiopathogenesis of this common malady. However, this "sweet evil" (diabetes) remains an enigma in many ways. There is little doubt today that there are 2 major types of diabetes: juvenile onset diabetes, presently known as insulin-dependent diabetes mellitus (IDDM) and maturity onset diabetes, referred to as non-insulin dependent diabetes mellitus (NIDDM). In NIDDM aggregation of HLA types, evidence of cell mediated immunity and the presence of circulating islet cell antibodies, which are characteristically associated with IDDM, are not found. There is also a vast difference in concordance of diabetes in the co-twins between the two types of diabetes suggesting that a different mixture of genetic and environmental factors is operative in the pathogenesis of these two types of diabetes. In I960, Fajans and Conn drew attention to the existence of a form of diabetes with an onset before the age of 35 years. Their patients showed a substantial improvement in glucose tolerance when treated with an oral hypoglycaemic agent, tolbutamide. Subsequent to this report numerous studies from various parts of the world confirmed this entity of non-insulin dependent diabetes in the young (NIDDY) in White Caucasians. There are, however, several different syndromes presenting as mild carbohydrate intolerance in the first two to three decades of life. The classical form of NIDDY is a mild non-insulin requiring form of diabetes in which the disorder is inherited as a dominant trait; there is little progression of glucose intolerance, if any, with time, and the diabetes is rarely accompanied by vascular complications. This subtype of diabetes is referred to as MODY (maturity onset diabetes in the young) and thus constitutes a subset under the broad umbrella of NIDDY. However, recently compelling evidence for heterogeneity within MODY has been presented. This evidence is based on the prevalence of certain HLA antigens, insulin responses to oral glucose, occurrence of vascular complications, progression of hyperglycaemia to the stage of insulin requirement and failure to demonstrate autosomal dominant inheritance in some families studied. In the South African Indian population which has a high prevalence of diabetes, Campbell was the first to draw attention to NIDDY in Indians more than two decades ago. Since this initial report, nobody has really studied NIDDY in any depth in South Africa and certainly not in the Indian population. NIDDY in the local Indian population is of particular interest for the obvious reason that diagnostic and management problems arise daily in a population with a high prevalence of non-insulin dependent diabetes. It is vital that the clinical features, endocrine and associated biochemical aberrations be known in detail if this condition is to be managed appropriately and adequately. A study of these aspects therefore became the primary task of this thesis. To pre-empt any challenge that patients were not really diabetic, the strict criteria of the W.H.O. for the diagnosis of diabetes were chosen. It should therefore be borne in mind throughout this study that a group of rather severe diabetics were selected by design. The patients studied represent the rather extreme end of the spectrum. But, in the event, this selection proved advantageous in that it covered an unstudied part of the spectrum and some light could be shed on the natural history of the disorder. In the long term the purpose was to prepare the ground for what must become the thrust of future studies, namely the biochemical pathogenesis of NIDDM. If it is true that some forms of NIDDY are inherited dominantly, existing techniques should make it possible to identify a gene(s) locus and if this is done the biochemical basis of this disorder must be identifiable. In the present study direct examination of these aspects were not undertaken, but an attempt was certainly made to pinpoint those biochemical abnormalities which are perhaps primary or central to the whole disorder. / Thesis (M.D.)- University of Natal, Durban. 1982.