• The effect of dietary carbohydrate and fat manipulation on the metabolome and markers of glucose and insulin metabolism: A randomised parallel trial

      McCullough, Deaglan; Harrison, Tanja; Boddy, Lynne M.; Enright, Kevin J.; Amirabdollahian, Farzad; Schmidt, Michael A.; Doenges, Katrina; Quinn, Kevin; Reisdorph, Nichole; Mazidi, Mohsen; et al. (MDPI, 2022-09-07)
      High carbohydrate, lower fat (HCLF) diets are recommended to reduce cardiometabolic disease (CMD) but low carbohydrate high fat (LCHF) diets can be just as effective. The effect of LCHF on novel insulin resistance biomarkers and the metabolome has not been fully explored. The aim of this study was to investigate the impact of an ad libitum 8-week LCHF diet compared with a HCLF diet on CMD markers, the metabolome, and insulin resistance markers. n = 16 adults were randomly assigned to either LCHF (n = 8, <50 g CHO p/day) or HCLF diet (n = 8) for 8 weeks. At weeks 0, 4 and 8, participants provided fasted blood samples, measures of body composition, blood pressure and dietary intake. Samples were analysed for markers of cardiometabolic disease and underwent non-targeted metabolomic profiling. Both a LCHF and HCLF diet significantly (p < 0.01) improved fasting insulin, HOMA IR, rQUICKI and leptin/adiponectin ratio (p < 0.05) levels. Metabolomic profiling detected 3489 metabolites with 78 metabolites being differentially regulated, for example, an upregulation in lipid metabolites following the LCHF diet may indicate an increase in lipid transport and oxidation, improving insulin sensitivity. In conclusion, both diets may reduce type 2 diabetes risk albeit, a LCHF diet may enhance insulin sensitivity by increasing lipid oxidation.
    • Regulation of beta-cell viability and gene expression by distinct agonist fragments of adiponectin

      Brown, James E. P.; Conner, Alex C..; Digby, Janet E.; Ward, Kenya L.; Ramanjaneya, Manjunath; Randeva, Harpal S.; Dunmore, Simon J. (2010)
      Obesity is an established risk factor for type 2 diabetes. Activation of the adiponectin receptors has a clear role in improving insulin resistance although conflicting evidence exists for its effects on pancreatic beta-cells. Previous reports have identified both adiponectin receptors (ADR-1 and ADR-2) in the betacell. Recent evidence has suggested that two distinct regions of the adiponectin molecule, the globular domain and a small N-terminal region, have agonist properties. This study investigates the effects of two agonist regions of adiponectin on insulin secretion, gene expression, cell viability and cell signalling in the rat beta-cell line BRIN-BD11, as well as investigating the expression levels of adiponectin receptors (ADRs) in these cells. Cells were treated with globular adiponectin and adiponectin (15-36)±leptin to investigate cell viability, expression of key beta-cell genes and ERK1/2 activation. Both globular adiponectin and adiponectin (15-36) caused significant ERK1/2 dependent increases in cell viability. Leptin co-incubation attenuated adiponectin (15-36) but not globular adiponectin induced cell viability. Globular adiponectin, but not adiponectin (15-36), caused a significant 450% increase in PDX-1 expression and a 45% decrease in LPL expression. ADR-1 was expressed at a higher level than ADR-2, and ADR mRNA levels were differentially regulated by non-esterified fatty acids and peroxisome-proliferator-activated receptor agonists. These data provide evidence of roles for two distinct adiponectin agonist domains in the beta-cell and confirm the potentially important role of adiponectin receptor agonism in maintaining beta-cell mass.
    • The Role of adipokines in obesity related beta-cell failure of diabetes mellitus and endothelial cell dysfunction of cardiovascular diseases.

      Majebi, Andrew (2014-11)
      Obesity affects about 520 million people world-wide and more recently studies have shown that fat cells produce proteins called adipokines which have various influences on the human metabolism and has helped to change the perspectives of researchers on the concept of the adipose tissue being just a store of energy. As a result of this, adipokines have been reported to represent a connection between obesity and cardiovascular diseases (CVD) and diabetes mellitus. The concentrations and the bases of the effects of the adipokines in beta cell failure of diabetes mellitus and endothelial cell dysfunction of cardiovascular diseases are still not fully understood. The effect of leptin and adiponectin, which are two adipokines with opposing effects, has been explored in this study. In the present study, therefore, the concentrations of leptin and adiponectin with significant effect on beta cell and endothelial cell function and the basis of these functions were explored. Also, attempts were made in the present study to correlate the concentrations of leptin and adiponectin with possible clinical pointers to complications. In order to achieve this, beta cells (BTC) were grown, made into pseudo-islets (which are said to produce more insulin) and treated with various concentrations of leptin and adiponectin and cells assayed for insulin and amylin (to investigate the role of amylin in insulin secretion). Also the cells were collected and mRNA extracted from these cells, reverse transcription PCR carried out to find out the role of protein phosphatase 1 (PP-1) in the effect of leptin on insulin secretion. PP-1 is a substrate that increases insulin secretion by allowing calcium influx into the cell and is said to be blocked by leptin). Leptin at 500ng/ml was found to significantly (p<0.05) inhibit the secretion of insulin and the expression of PP1 gene, thus supporting this as a basis for the effect of leptin on insulin secretion. Adiponectin however increased insulin secretion significantly but was not as consistent in its effect as leptin was in inhibiting insulin secretion. In order to explore the role of adipokines in cardiovascular diseases, EAHY human endothelial cells were cultured and treated with various concentrations of adiponectin and leptin both individually and in combinations and cells collected and mRNA extracted in order to carry out a reverse transcription PCR for the expression of angiogenic (TIMP2, TIMP3 and MMP2) genes and atherosclerotic (LPA and LPL) genes. Leptin (1nM) was shown to increase the expression of atherosclerotic and angiogenic genes while adiponectin (100nM) inhibited the expression of the atherosclerotic and angiogenic genes. A combination of leptin and adiponectin caused a reduction in the stimulatory effect of leptin on the expression of atherosclerotic and angiogenic genes. This shows that leptin may predispose to CVD while adiponectin reduces the risk of CVD. The clinical part of this study involved recruiting 150 patients with diabetes after the ethical approval for the clinical study was granted. The data collected from the patients included their age, sex, race, and physical parameters like the body mass index (BMI). Also blood samples were collected to measure the clinical indicators for CVD and renal function such as cholesterol, HDL levels, eGFR, albumin levels and their retinopathy status checked as these are the common complications seen in diabetic patients. The blood samples were also assayed in the laboratory for leptin and adiponectin levels and the leptin, adiponectin and the leptin/adiponectin ratio (LAR) were then correlated with the laboratory determinants of CVD, renal and retinopathy risks. It was found that the LAR and the leptin levels correlates significantly with the BMI, while the leptin levels were significantly correlated with the risk of nephropathy in diabetic patients while adiponectin levels correlated significantly with a reduced risk for developing CVD. The role of the enzymes in the leptin and adiponectin signaling pathway was also explored and it was discovered that ERK, P38 and AMPK all had roles in the effect of leptin and adiponectin on the expression of atherosclerotic and angiogenic genes. These data indicate that leptin and adiponectin play significant roles in the beta cell and endothelial cell function and are links between obesity and CVD and diabetes mellitus.