Does familial hypertriglyceridemia predispose to NIDDM?

The Causal Relationship of Circulating Triglyceride and Glycated Hemoglobin: A Mendelian Randomization Study

CONTEXT

The association between circulating triglyceride (TG) and glycated hemoglobin A1c (HbA1c), a biomarker for type 2 diabetes, has been widely addressed, but the causal direction of the relationship is still ambiguous.

OBJECTIVE

To confirm the causal relationship between TG and HbA1c by using bidirectional and 2-step Mendelian randomization (MR) approaches.

METHODS

We carried out a bidirectional MR approach using the summarized results from the public database to examine any potential causal effects between serum TG and HbA1c in 16 000 individuals of the Taiwan Biobank cohort. We used the MR estimate and the MR inverse variance-weighted method to reveal that relationship between TG and HbA1c. To further determine whether the DNA methylation at specific sequences mediate the causal pathway between TG and HbA1c, using the 2-step MR approach.

RESULTS

We identified that a single-unit increase in TG measured via log transformation of mg/dL data was associated with a significant increase of 10 units of HbA1c (95% CI = 1.05-18.95, P = 0.029). In contrast, the genetic determinants of HbA1c do not contribute to the amount of circulating TG (beta = 1.75, 95% CI = -11.50 to 14.90). Sensitivity analyses, included the weighted-median approach and MR-Egger regression, were performed to confirm no pleiotropic effect among these instrumental variables. Furthermore, we identified the genetic variant, rs1823200, is associated with both methylation of the CpG site adjacent to CADPS gene and HbA1c level.

CONCLUSION

Our study suggests that higher circulating TG can have an affect on genomic methylation status, ultimately causing elevated level of circulating HbA1c.

A Case-Control Study on Risk Factors and Their Interactions with Prediabetes among the Elderly in Rural Communities of Yiyang City, Hunan Province

BACKGROUND

The prevalence of prediabetes has been increasing significantly in recent years. Individuals with prediabetes have an increased risk of developing diabetes and cardiovascular diseases. The objectives of this study were to identify risk factors for prediabetes and their interactions among the elderly in rural communities of Hunan Province and to provide a scientific basis for prediabetes prevention.

METHODS

A case-control study was conducted to explore risk factors for prediabetes among the elderly in rural areas. The general sociodemographic information, lifestyle behaviours, and physiological results of elderly individuals with prediabetes and controls were collected by a questionnaire and laboratory testing. Conditional logistic regression was performed to identify the risk factors for prediabetes among the elderly, and additive interactions were used to analyse the interactions between risk factors.

RESULTS

A total of 425 elderly subjects with prediabetes were included in the case group, and 425 elderly subjects with normal plasma glucose levels were included in the control group. The main risk factors for prediabetes among the elderly in rural communities of Hunan Province were a family history of diabetes (OR = 2.48; 95% CI: 1.13, 5.46), physical inactivity (OR = 3.27; 95% CI: 1.95, 5.49), a lack of health literacy on diabetes prevention and control (OR = 3.26; 95% CI: 1.62, 6.55), hypertension (OR = 2.01; 95% CI: 1.38, 2.93), overweight (OR = 2.53; 95% CI: 1.67, 3.81), obesity (OR = 3.08; 95% CI: 1.48, 6.40), and a high waist-to-hip ratio (WHR) (OR = 2.26; 95% CI: 1.45, 3.51). Additive interactions for prediabetes were detected between a high WHR and physical inactivity, with a relative excess risk due to interaction (RERI) of 6.30 (95% CI: 0.42, 12.18), and between a high WHR and overweight or obesity, with an RERI of 2.92 (95% CI: 0.56, 5.29).

CONCLUSION

The independent risk factors for prediabetes are a family history of diabetes, physical inactivity, a lack of health literacy on diabetes prevention and control, hypertension, overweight or obesity, and a high WHR. A high WHR has additive interactions with physical inactivity and overweight or obesity for the risk of prediabetes. These findings have significant implications for prediabetes prevention among the elderly in rural areas.

Effects of Sanyaku and Its Constituent Diosgenin on the Fasted and Postprandial Hypertriacylglycerolemia in High-Fat-Diet-Fed KK- A y Mice

In this study, we examined the fasted and postprandial triacylglycerol (TG) levels in KK- A ^y mice fed a high-fat diet (HFD) or a HFD containing either 500 ppm (0.05%) of diosgenin or 500 ppm (0.05%) of diosgenin-containing Chinese yam sanyaku. Oral fat tolerance tests revealed that, not only in the fasting state but also after loading of lipid emulsion, plasma levels of TG were significantly reduced in sanyaku- and diosgenin- fed mice. Levels of fat oxidation, especially in the dark phase (from 7 p.m. to 7 a.m.), were increased in the sanyaku and diosgenin groups. Moreover mRNA levels of lipoprotein lipase and peroxisome proliferator-activated receptor γ, coactivator 1α were moderately upregulated in the liver of sanyaku- and diosgenin-ingested mice. These results suggest that consecutive ingestion of diosgenin or diosgenin-containing sanyaku at the dose achievable in a human diet potentially ameliorates fasted and postprandial hypertriacylglycerolemia, which could be associated with the improvement of TG metabolism.

Effects of Fiber Purified Extract of Carob Fruit on Fat Digestion and Postprandial Lipemia in Healthy Rats

Increased postprandial lipemia is a cardiovascular disease (CVD) risk factor. Carob fruit extract (CFE) contains condensed tannins, and their intake has been inversely related to CVD. The objective was to evaluate the in vitro pancreatic lipase activity in the presence of CFE and the in vivo effect of CFE on postprandial lipemia of healthy Wistar rats in acute and subchronic digestibility studies and to relate it with changes in fat digestion and absorption. CFE significantly reduced pancreatic lipase activity. A peak delay and a dose-dependent decrease in plasma triglyceride and cholesterol areas under the curve were observed, effects that increased after the subchronic treatment. The levels of nondigested, nonabsorbed triglycerides of the remaining intestinal lumen fat were significantly higher in the maximum dose of CFE administrated versus the control ( P < 0.05). This study demonstrates for the first time the hypolipemic properties of CFE from the first administration, modifying postprandial lipemia by reducing the extents of fat digestion and absorption.

Diabetes in China: Epidemiology and Genetic Risk Factors and Their Clinical Utility in Personalized Medication

The incidence of type 2 diabetes (T2D) has rapidly increased over recent decades, and T2D has become a leading public health challenge in China. Compared with European descents, Chinese patients with T2D are diagnosed at a relatively young age and low BMI. A better understanding of the factors contributing to the diabetes epidemic is crucial for determining future prevention and intervention programs. In addition to environmental factors, genetic factors contribute substantially to the development of T2D. To date, more than 100 susceptibility loci for T2D have been identified. Individually, most T2D genetic variants have a small effect size (10-20% increased risk for T2D per risk allele); however, a genetic risk score that combines multiple T2D loci could be used to predict the risk of T2D and to identify individuals who are at a high risk. Furthermore, individualized antidiabetes treatment should be a top priority to prevent complications and mortality. In this article, we review the epidemiological trends and recent progress in the understanding of T2D genetic etiology and further discuss personalized medicine involved in the treatment of T2D.

Postprandial Hypertriglyceridemia Predicts Development of Insulin Resistance Glucose Intolerance and Type 2 Diabetes

Insulin resistance (IR) and type 2 diabetes mellitus (T2DM) have been found to be associated with postprandial hypertriglyceridemia (PPHTg). However, whether PPHTg can cause IR and diabetes is not clear. We therefore investigated the role of PPHTg in development of T2DM in rat model of T2DM. 96 male Wistar rats were randomized into four groups (24 rats each). Control Group A, high sucrose diet (HSD) Group B, HSD+Pioglitazone (10mg/kg/day) Group C and HSD+Atorvastatin (20mg/kg/day) Group D. Fat and glucose tolerance tests were done at regular intervals in all groups besides insulin and body weight measurement. At 26 weeks, low dose streptozotocin (15mg/kg,i.p.) was given to half of the rats. All rats were followed up till 48 weeks. PPHTg developed as early as week 2 in Group B and stabilized by week 14. Group B displayed highest PPHTg compared to other groups. Atorvastatin treatment (Group D) abolished PPHTg which became comparable to controls, pioglitazone treatment partially blunted PPHTg resulting in intermediate PPHTg. Group B with highest PPHTg showed highest subsequent IR, glucose intolerance (GI) and highest incidence of prediabetes at week 26 and diabetes at week 34 and 46 compared to other groups. Group D rats displayed lower IR, GI, low incidence of prediabetes and diabetes at these time points compared to Groups B and C. ROC analysis showed that triglyceride area under the curve of each time point significantly predicts the risk of diabetes. Present study provides the evidence that PPHTg predicts the development of IR, GI and T2DM in rat model of diet induced T2DM.

Impact of metabolic syndrome risk factors in first-degree relatives of type 2 diabetic patients

OBJECTIVE

Family members of patients with an established diagnosis of type 2 diabetes mellitus (T2DM) are theoretically at risk of having the metabolic syndrome (MetS). A sample of these family members was studied from a population in a small township in Argentina, which has a high prevalence of T2DM.

METHODS

We examined the clinical and metabolic characteristics of 132 first-degree relatives of T2DM patients (FDR) and 112 age-matched controls. The subjects were categorized according to the International Diabetes Federation (IDF) and National Cholesterol Education Program Adult Treatment Panel III (NCEP-ATPIII) criteria for MetS.

RESULTS

The prevalence of MetS in the FDR group was 34.8 (IDF) and 26.5% (NCEP-ATPIII) respectively, which was significantly different to the prevalence in controls (p < 0.025). According to IDF criteria, the most prevalent factors among FDR subjects with MetS were low HDL-cholesterol (87%) followed by hypertriglyceridemia (69.5%). In the MetS group, which ranged between 20-29 years old (36%), the major risk factor in women was a low HDL-cholesterol serum level. In the MetS group, which ranged between 30-39 years old (44.4%), the most important risk factor in men was hypertriglyceridemia.

CONCLUSION

This study revealed that the prevalence of MetS is high in young FDR adults, who need urgent preventive treatment, including lifestyle changes. The risk of developing T2DM is five times higher in non-diabetic people with MetS than in those without the syndrome.

Postprandial lipaemia induces an acute decrease of insulin sensitivity in healthy men independently of plasma NEFA levels

AIMS/HYPOTHESIS

Typical Western diets cause postprandial lipaemia for 18 h per day. We tested the hypothesis that postprandial lipaemia decreases insulin sensitivity.

SUBJECTS, MATERIALS AND METHODS

Employing a randomised crossover design, we administered two types of virtually isocaloric meals to ten healthy volunteers on two separate occasions. The meals (Meals 1 and 2) were both designed to produce a rise in triglycerides, but only Meal 1 generated a rise in NEFA, too. Insulin sensitivity, as quantified by an IVGTT with minimal model analysis, was calculated postabsorptively at 08.00 h and postprandially at 13.00 h, i.e. 3 h after meal ingestion.

RESULTS

Triglycerides rose from 0.91+/-0.31 mmol/l postabsorptively to 2.08+/-0.70 mmol/l postprandially with Meal 1 (p=0.005) and from 0.92+/-0.41 to 1.71+/-0.79 mmol/l with Meal 2 (p=0.005). Neither the triglyceride levels at 13.00 h, nor the post-meal AUCs for triglycerides were statistically different between Meal 1 and Meal 2. NEFA rose from 0.44+/-0.17 mmol/l postabsorptively to 0.69+/-0.16 mmol/l postprandially with Meal 1 (p=0.005) and showed no significant change with Meal 2 (0.46+/-0.31 mmol/l postabsorptively vs 0.36+/-0.32 mmol/l postprandially, p=0.09). Both the NEFA level at 13.00 h and the post-meal AUC for NEFA were significantly higher after Meal 1 than Meal 2. Compared with the postabsorptive state, insulin sensitivity decreased postprandially after each of the two meals to a comparable degree (Meal 1: -53%, p=0.02; Meal 2: -45%, p=0.005).

CONCLUSIONS/INTERPRETATION

Our study reveals a drop in insulin sensitivity during postprandial lipaemia and strongly suggests that decreased insulin sensitivity is brought about by elevated plasma levels of triglyceride-rich lipoproteins independently of plasma NEFA levels.

Glucose-stimulated insulin response in non-diabetic patients with lipoprotein lipase deficiency and hypertriglyceridemia

Elevations in plasma triglyceride (TG) and free fatty acid (FFA) concentrations are generally thought to play a role in the pathogenesis of insulin-resistant diabetes. The objective of this study was to investigate the relationship between hypertriglyceridemia and glucose-stimulated insulin responsiveness in non-diabetic patients. Forty subjects were divided into three BMI-matched groups as follows: one group consisted of 8 patients with a lipoprotein lipase (LPL) deficiency, another consisted of 12 patients with hypertriglyceridemia and a third consisted of 20 subjects with normal TG levels. In response to a 75 g oral glucose tolerance test, plasma insulin levels in the LPL-deficient subjects were higher (106+/-11 microU/ml) than those in the hypertriglyceridemic (69+/-16 microU/ml) and normolipidemic (29+/-3 microU/ml) subjects, at 30 min. On the other hand, their plasma glucose levels (127+/-6 mg/dl) were less than those seen in the normolipidemic group (165+/-9 mg/dl) after 90 min. Thus, LPL-deficient subjects with hypertriglyceridemia displayed an enhanced glucose-stimulated insulin response as well as lower blood glucose levels, the latter of which is not generally seen in those with hypertriglyceridemia and normolipidemia.

Relation between insulin resistance and fast-migrating LDL subfraction as characterized by capillary isotachophoresis

The proportion of the electronegative low density lipoprotein [LDL(-)] subfraction, which is atherogenic, is increased in type 2 diabetes but is not reduced by glycemic control. Therefore, we evaluated the ability of a new technique, capillary isotachophoresis (cITP), to quantify charge-based LDL subfractions and examined the relation between insulin resistance and the cITP fast-migrating (f) LDL levels. Seventy-five 10-year-old boys were included. The two cITP LDL subfractions, fLDL and major LDL subfractions, were proportional to the LDL protein content within the range of 0.1-0.8 mg/ml LDL protein. Levels of cITP fLDL were positively correlated with triglyceride (TG) levels and negatively correlated with LDL size. Insulin resistance as assessed by the homeostasis model assessment (HOMA-IR) was positively correlated (P < 0.01) with cITP fLDL levels (r = 0.41). The relation between HOMA-IR and cITP fLDL levels depended on TG levels but was independent of body mass index and LDL size. cITP lipoprotein analysis is an accurate and sensitive method for quantifying charge-based LDL subfractions in human plasma, and insulin resistance is related to cITP fLDL independent of LDL size.

Influence of obesity on plasma lipid and lipoprotein concentrations in dogs

OBJECTIVE

To determine effects of obesity and diet in dogs on plasma lipid and lipoprotein concentrations by assaying plasma leptin and ghrelin concentrations and determining total plasma cholesterol and triglyceride concentrations as well as the concentrations of cholesterol and triglycerides in various lipoprotein classes (ie, very-low-density, low-density, and high-density lipoproteins).

ANIMALS

24 Beagles; 12 lean (mean [+/- SEM] body weight, 12.7 +/- 0.7 kg) and 12 chronically obese (21.9 +/- 0.8 kg) dogs of both sexes, between 1 and 9 years old.

PROCEDURES

Total plasma cholesterol and triglyceride concentrations; lipoprotein cholesterol and triglyceride concentrations; and plasma ghrelin, leptin, free fatty acids, insulin, and glucose concentrations were measured and compared between lean and obese dogs, both of which were fed a complete and balanced maintenance diet. Chronically obese dogs were subsequently fed a high-protein low-energy diet to evaluate effects of diet composition on plasma lipid and lipoprotein measurements.

RESULTS

Chronic obesity resulted in a significant decrease in plasma ghrelin concentration and a significant increase in plasma leptin, cholesterol, and triglyceride concentrations in dogs. High total plasma cholesterol and triglyceride concentrations resulted from increased cholesterol and triglyceride concentrations in all lipoprotein fractions. In obese dogs, modification of diet composition resulted in beneficial effects on plasma lipid and leptin concentrations, even before weight loss was observed.

CONCLUSIONS AND CLINICAL RELEVANCE

Correlations exist between obesity and plasma measurements (ie, lipoproteins, leptin, insulin, and ghrelin) commonly associated with obesity. Modification of diet composition to control energy intake improves plasma lipid and leptin concentrations in obese dogs.

Recurrent hypoglycaemic episodes in a patient with Type 2 diabetes under fibrate therapy

The causal relationship between dyslipidaemia and insulin resistance, two central components of the metabolic syndrome, is still poorly understood. We describe a 76-year-old patient with Type 2 diabetes mellitus and pronounced hypertriglyceridaemia. The patient required a total insulin dose of 148 IU/day for decent glycaemic control. The addition of the fibrate gemfibrozil to her medication resulted in a remarkable reduction in triglyceride levels (from 31.7 to 7.1 mmol/l). Consequently, the patient experienced recurrent hypoglycaemic episodes concurrent with a massive reduction in insulin requirements. Eventually, the insulin dosage was reduced by more than 65% to 48 IU/day, and HbA1c levels dropped from 9% to 6.5% over a period of 5 months without alterations in lifestyle, diet, body weight, or any other blood chemical values. Thus, this case report illustrates that treatment of hypertriglyceridaemia can reduce insulin requirements and harbours the risk of hypoglycaemia in patients with insulin-treated Type 2 diabetes mellitus.

Insulin resistance in the St. Thomas' mixed hyperlipidaemic (SMHL) rabbit, a model for familial combined hyperlipidaemia

The St. Thomas mixed hyperlipidaemic (SMHL) rabbit exhibits an inherited hyperlipidaemia similar to that seen in familial combined hyperlipidaemia (FCHL). In this study, we investigated whether the SMHL rabbit is insulin resistant, a condition often associated with FCHL. Six young and six mature combined hyperlipidaemic SMHL rabbits, age/sex matched New Zealand White (NZW) control rabbits and six young hypercholesterolaemic Watanabe heritable hyperlipidaemic (WHHL) control rabbits were fed a 0.08% (w/w) cholesterol-enriched diet for at least 1 month prior to the start of the experiment. We performed an oral glucose tolerance test after an overnight fast by dosing the rabbits with a solution of 1 g of glucose per kg body weight. Blood was withdrawn just before and 15, 30, 45, 60 and 120 min after administration of the oral glucose dose. Plasma glucose levels were similar in SMHL, WHHL and NZW rabbits throughout the oral glucose tolerance test. Fasting glucose levels were slightly increased in WHHL rabbits but not in young and adult SMHL rabbits as compared to NZW rabbits. The area under the curve (AUC) for the insulin response was significantly increased for both young (P<0.05) and mature (P<0.05) SMHL rabbits, and in WHHL rabbits, compared with NZW rabbits. The AUC for the ratio of glucose:insulin response to the glucose dose was decreased in young and mature SMHL rabbits (P<0.05 and P<0.01, respectively) and in young WHHL rabbits (P<0.05), compared with NZW rabbits. Only WHHL rabbits showed an increased AUC for the non-esterified fatty acid response compared to NZW rabbits. Log-transformed plasma triglycerides values were significantly correlated with the log-transformed AUC for the insulin response in young SMHL rabbits (r=0.81; P<0.05) and with the AUC for the insulin response in mature SMHL rabbits (r=0.84; P<0.05). WHHL rabbits showed no significant correlation. In conclusion, SMHL rabbits are insulin resistant, the severity of which appears to increase with age. Therefore, the SMHL rabbit offers a valuable animal model in which to study the relation between hypertriglyceridaemia and insulin resistance.

Insulin resistance directly correlates with increased saturated fatty acids in skeletal muscle triglycerides

A close relationship between elevated plasma free fatty acid (FFA) levels and insulin resistance is commonly reported in obese subjects. The aim of the present study was to evaluate the role of intramuscular triglyceride (mTG) and FFA levels in insulin sensitivity in 30 nondiabetic normal-weight or obese subjects (18 with body mass index [BMI] = 21.8 +/- 3.3 kg/m2 and 12 with BMI = 34.6 +/- 2.7 kg/m2) who underwent minor abdominal surgery. Body composition was estimated by isotopic dilution, substrate oxidation by indirect calorimetry, and whole-body glucose uptake by euglycemic-hyperinsulinemic clamp (EHC). Glucose uptake (M) value negatively correlated with the MTG level (R2 = -.56, P < .0001), which was increased in obese patients (11.6 +/- 2.2 v 6.2 +/- 1.4 micromol/g wet weight muscle tissue, P < .0001). The TG fatty acid profile was significantly different in the 2 groups: an increased concentration of saturated fat was present in obese patients (unsaturated to saturated ratio, 1.89 +/- 0.40 v2.19 +/- 0.07, P < .0001). Stepwise linear regression analysis of total mTGs and palmitic and oleic fractions on the M value showed that only TGs and palmitic acid were significantly related to glucose uptake (R2 = .66, P < .0001). Furthermore, among the other anthropometric variables, only the BMI was significantly correlated with MTGs (R2 = .71, P < .0001). In conclusion, not only the MTG concentration but also the FFA pattern seems to affect insulin-mediated glucose uptake. A pivotal role might be played by a high saturated fatty acid content in the TGs.

Glucose intolerance in familial combined hyperlipidaemia. EUFAM study group

BACKGROUND

Familial combined hyperlipidaemia (FCHL) is a common hereditary disorder. Hypertriglyceridaemia is associated with glucose intolerance and insulin resistance.

METHODS

To study glucose tolerance in FCHL patients with different lipid phenotypes [hypercholesterolaemia (IIA), mixed hyperlipidaemia (IIB), hypertriglyceridaemia (IV)], we investigated 253 family members and 92 spouses arising from 33 well-defined Finnish FCHL pedigrees.

RESULTS

In oral glucose tolerance tests the affected family members had higher values for glucose area under the curve than did non-affected family members [673+/-127 min mmolL(-1), 754+/-145 min mmol L(-1), 846+/-180 min mmol L(-1) and 838+/-183 min mmol L(-1) for phenotypes normal, IIA, IIB and IV respectively; P < 0.001 after adjustment for body mass index, waist circumference and age]. Impaired glucose tolerance and diabetes were more common among affected than non-affected family members (prevalences of normal glucose tolerance 94.0%, 80.0%, 54.3% and 58.5% for phenotypes normal, IIA, IIB and IV).

CONCLUSION

Affected FCHL family members were more glucose intolerant than non-affected family members. In men, this disturbance was not related to lipid phenotype nor was it explained by obesity.