Glucose metabolism by lymphocytes, macrophages, and tumor cells from Walker 256 tumor-bearing rats supplemented with fish oil for one generation

Here we investigated the effect of lifelong supplementation of the diet with coconut fat (CO, rich in saturated fatty acids) or fish oil (170, rich in n-3 polyunsaturated fatty acids) on tumor growth and lactate production from glucose in Walker 256 tumor cells, peritoneal macrophages, spleen, and gut-associated lymphocytes. Female Wistar rats were supplemented with CO or FO prior to mating and then throughout pregnancy and gestation and then the male offspring were supplemented from weaning until 90 days of age. Then they were inoculated subcutaneously with Walker 256 tumor cells. Tumor weight at 14 days in control rats (those fed standard chow) and CO supplemented was approximately 30 g. Supplementation of the diet with FO significantly reduced tumor growth by 76%. Lactate production (nmol h(-1) mg(-1) protein) from glucose by Walker 256 cells in the group fed regular chow (W) was 381.8 +/- 14.9. Supplementation with coconut fat (WCO) caused a significant reduction in lactate production by 1.6-fold and with fish oil (WFO) by 3.8-fold. Spleen lymphocytes obtained from W and WCO groups had markedly increased lactate production (553 +/- 70 and 635 +/- 150) when compared to non-tumor-bearing rats (similar to 260 +/- 30). FO supplementation reduced significantly the lactate production (297 +/- 50). Gut-associated lymphocytes obtained from W and WCO groups increased lactate production markedly (280 +/- 31 and 276 +/- 25) when compared to non-tumor-bearing rats (similar to 90 +/- 18). FO supplementation reduced significantly the lactate production (168 +/- 14). Lactate production by peritoneal macrophages was increased by tumor burden but there was no difference between the groups fed the various diets. Lifelong consumption of FO protects against tumor growth and modifies glucose metabolism in Walker tumor cells and lymphocytes but not in macrophages. Copyright (C) 2008 John Wiley & Sons, Ltd.

Intensive insulin treatment induces insulin resistance in diabetic rats by impairing glucose metabolism-related mechanisms in muscle and liver

Insulin replacement is the only effective therapy to manage hyperglycemia in type 1 diabetes mellitus (T1DM). Nevertheless, intensive insulin therapy has inadvertently led to insulin resistance. This study investigates mechanisms involved in the insulin resistance induced by hyperinsulinization. Wistar rats were rendered diabetic by alloxan injection, and 2 weeks later received saline or different doses of neutral protamine Hagedorn insulin (1.5, 3, 6, and 9 U/day) over 7 days. Insulinopenic-untreated rats and 6U- and 9U-treated rats developed insulin resistance, whereas 3U-treated rats revealed the highest grade of insulin sensitivity, but did not achieve good glycemic control as 6U- and 9U-treated rats did. This insulin sensitivity profile was in agreement with glucose transporter 4 expression and translocation in skeletal muscle, and insulin signaling, phosphoenolpyruvate carboxykinase/glucose-6-phosphatase expression and glycogen storage in the liver. Under the expectation that insulin resistance develops in hyperinsulinized diabetic patients, we believe insulin sensitizer approaches should be considered in treating T1DM. Journal of Endocrinology (2011) 211, 55-64

Regulation of glycolysis and expression of glucose metabolism-related genes by reactive oxygen species in contracting skeletal muscle cells

Contractile activity induces a marked increase in glycolytic activity and gene expression of enzymes and transporters involved in glucose metabolism in skeletal muscle. Muscle contraction also increases the production of reactive oxygen species (ROS). In this study, the effects of treatment with N-acetylcysteine (NAC), a potent antioxidant compound, on contraction-stimulated glycolysis were investigated in electrically stimulated primary rat skeletal muscle cells. The following parameters were measured: 2-[(3)H]deoxyglucose (2-DG) uptake; activities of hexokinase, phosphofructokinase (PFK), and glucose-6-phosphate dehydrogenase (G6PDH); lactate production; and expression of the glucose transporter 4 (GLUT4), hexokinase II (HKII), and PFK genes after one bout of electrical stimulation in primary rat myotubes. NAC treatment decreased ROS signal by 49% in resting muscle cells and abolished the muscle contraction-induced increase in ROS levels. In resting cells, NAC decreased mRNA and protein contents of GLUT4, mRNA content and activity of PFK, and lactate production. NAC treatment suppressed the contraction-mediated increase in 2-DG uptake; lactate production; hexokinase, PFK, and G6PDH activities; and gene expression of GLUT4. HKII, and PFK. Similar to muscle contraction, exogenous H(2)O(2) (500 nM) administration increased 2-DG uptake; lactate production; hexokinase, PFK, and G6PDH activities; and gene expression of GLUT4. HKII, and PFK. These findings support the proposition that ROS endogenously produced play an important role in the changes in glycolytic activity and gene expression of GLUT4, HKII, and PFK induced by contraction in skeletal muscle cells. (C) 2010 Elsevier Inc. All rights reserved.

Low doses of hydrogen peroxide impair glucose-stimulated insulin secretion via inhibition of glucose metabolism and intracellular calcium oscillations

The inhibitory effect of hydrogen peroxide (H(2)O(2)) on glucose-stimulated insulin secretion was previously reported. However, the precise mechanism involved was not systematically investigated. In this study, the effects of low concentrations of H(2)O(2) (5-10 mu mol/L) on glucose metabolism, intracellular calcium ([Ca(2+)](i)) oscillations, and dynamic insulin secretion in rat pancreatic islets were investigated. Low concentrations of H(2)O(2) impaired insulin secretion in the presence of high glucose levels (16.7 mmol/L). This phenomenon was observed already after 2 minutes of exposure to H(2)O(2). Glucose oxidation and the amplitude of [Ca(2+)](i); oscillations were dose-dependently suppressed by H(2)O(2). These findings indicate that low concentrations of H(2)O(2) reduce insulin secretion in the presence of high glucose levels via inhibition of glucose metabolism and consequent impairment in [Ca(2+)](i); handling. (C) 2010 Elsevier Inc. All rights reserved.

Effect of prior exercise on glucose metabolism in trained men.

Several studies have demonstrated that oral glucose tolerance is impaired in the immediate postexercise period. A double-tracer technique was used to examine glucose kinetics during a 2-h oral glucose (75 g) tolerance test (OGTT) 30 min after exercise (Ex, 55 min at 71 ± 2% of peak O₂ uptake) and 24 h after exercise (Rest) in endurance-trained men. The area under the plasma glucose curve was 71% greater in Ex than in Rest (P = 0.01). The higher glucose response occurred even though whole body rate of glucose disappearance was 24% higher after exercise (P = 0.04, main effect). Whole body rate of glucose appearance was 25% higher after exercise (P = 0.03, main effect). There were no differences in total (2 h) endogenous glucose appearance (R_aE) or the magnitude of suppression of R_aE, although R_aE was higher from 15 to 30 min during the OGTT in Ex. However, the cumulative appearance of oral glucose was 30% higher in Ex (P = 0.03, main effect). There were no differences in glucose clearance rate or plasma insulin responses between the two conditions. These results suggest that adaptations in splanchnic tissues by prior exercise facilitate greater glucose output from the splanchnic region after glucose ingestion, resulting in a greater glycemic response and, consequently, a greater rate of whole body glucose uptake.

Elevation in tanis expression alters glucose metabolism and insulin sensitivity in H4IIE cells

Increased hepatic glucose output and decreased glucose utilization are implicated in the development of type 2 diabetes. We previously reported that the expression of a novel gene, Tanis, was upregulated in the liver during fasting in the obese/diabetic animal model Psammomys obesus. Here, we have further studied the protein and its function. Cell fractionation indicated that Tanis was localized in the plasma membrane and microsomes but not in the nucleus, mitochondria, or soluble protein fraction. Consistent with previous gene expression data, hepatic Tanis protein levels increased more significantly in diabetic P. obesus than in nondiabetic controls after fasting. We used a recombinant adenovirus to increase Tanis expression in hepatoma H4IIE cells and investigated its role in metabolism. Tanis overexpression reduced glucose uptake, basal and insulin-stimulated glycogen synthesis, and glycogen content and attenuated the suppression of PEPCK gene expression by insulin, but it did not affect insulin-stimulated insulin receptor phosphorylation or triglyceride synthesis. These results suggest that Tanis may be involved in the regulation of glucose metabolism, and increased expression of Tanis could contribute to insulin resistance in the liver.

Physical activity and television viewing in relation to risk and undiagnosed abnormal glucose metabolism in adults

OBJECTIVE--The goal of this study was to assess the associations of physical activity time and television (TV) time with risk of "undiagnosed" abnormal glucose metabolism in Australian adults.

RESEARCH DESIGN AND METHODS--This population-based cross-sectional study using a stratified cluster design involving 42 randomly selected Census Collector Districts across Australia included 8,299 adults aged 25 years or older who were free from new type 2 diabetes and self-reported ischemic disease and did not take lipid lowering or antihypertensive drugs. Abnormal glucose metabolism (impaired fasting glycetnia [IFG], impaired glucose tolerance [IGT], or new type 2 diabetes) was based on an oral glucose tolerance test Self reported physical activity time and TV time (previous week) were assessed using interviewer administered questionnaires.

RESULTS--Alter adjustment for known confounders and TV time, the odds ratio (OR) of having abnormal glucose metabolism was 0.62 (95% CI 0.41-0.96) in men and 0.71 (0.501.00) in women for those engaged in physical activity [greater than or equal to] 2.5 h/week compared with those who were sedentary (0 h/week). The ORs of having abnormal glucose metabolism were 1.16 (0.791.70) in men and 1.49 (1.12-1.99) in women who watched TV > 14 h/week compared with those who watched [less than or equal to] 7.0 h/week. Higher TV viewing (> 14 h/week) was also associated with an increased risk of new type 2 diabetes in men and women and IGT in women compared with those watching < 14 h/week. Total physical activity of [greater than or equal to] 2.5 h/week was associated with a reduced risk of IFG, IGT, and new type 2 diabetes in both sexes: however, only the association with IGT in women was statistically significant.

CONCLUSIONS--These findings suggest a protective effect of physical activity and a deleterious effect of TV time on the risk of abnormal glucose metabolism in adults. Population strategies to reduce risk of abnormal glucose metabolism should focus on reducing sedentary behaviors such as TV time, as well as increasing physical activity.

Impact of in vivo fatty acid oxidation blockade on glucose turnover and muscle glucose metabolism during low-dose AICAR infusion

AMPK plays a central role in influencing fuel usage and selection. The aim of this study was to analyze the impact of low-dose AMP analog 5-aminoimidazole-4-carboxamide-1-ß-D-ribosyl monophosphate (ZMP) on whole body glucose turnover and skeletal muscle (SkM) glucose metabolism. Dogs were restudied after prior 48-h fatty acid oxidation (FAOX) blockade by methylpalmoxirate (MP; 5 x 12 hourly 10 mg/kg doses). During the basal equilibrium period (0–150 min), fasting dogs (n = 8) were infused with [3-³H]glucose followed by either 2-h saline or AICAR (1.5–2.0 mg·kg^–1·min^–1) infusions. SkM was biopsied at completion of each study. On a separate day, the same protocol was undertaken after 48-h in vivo FAOX blockade. The AICAR and AICAR + MP studies were repeated in three chronic alloxan-diabetic dogs. AICAR produced a transient fall in plasma glucose and increase in insulin and a small decline in free fatty acid (FFA). Parallel increases in hepatic glucose production (HGP), glucose disappearance (Rd tissue), and glycolytic flux (GF) occurred, whereas metabolic clearance rate of glucose (MCR_g) did not change significantly. Intracellular SkM glucose, glucose 6-phosphate, and glycogen were unchanged. Acetyl-CoA carboxylase (ACC~pSer²²¹) increased by 50%. In the AICAR + MP studies, the metabolic responses were modified: the glucose was lower over 120 min, only minor changes occurred with insulin and FFA, and HGP and Rd tissue responses were markedly attenuated, but MCR_g and GF increased significantly. SkM substrates were unchanged, but ACC~pSer²²¹ rose by 80%. Thus low-dose AICAR leads to increases in HGP and SkM glucose uptake, which are modified by prior FA_ox blockade.

Association between impaired glucose metabolism and quality of life

Aims
We examined the association of quality of life with glucose tolerance status in an Australian population to determine the stage in the development of diabetes that quality of life is impaired.

Methods
The Australian Diabetes, Obesity and Lifestyle study (AusDiab) was a population-based study of 11,247 people from randomly selected areas of Australia. As part of the study, participants underwent an oral glucose tolerance test and completed the SF-36 quality of life questionnaire.

Results
Previously diagnosed diabetes was associated with a significantly greater risk of being in the lowest quartile of each dimension of the SF-36 scale (except for mental health) and this association was only partially attenuated by adjustment for age, sex, body mass index (BMI), physical activity and treatment for hypertension and lipid abnormalities (adjusted odds ratios [95% CI]: bodily pain, 1.51 [1.18–1.94]; general health, 2.20 [1.64–2.95]; physical functioning, 1.50 [1.10–2.05]; role limitation (emotional), 1.43 [1.07–1.91]; role limitation (physical), 1.57 [1.13–2.18]; social functioning, 1.93 [1.46–2.54] and vitality, 2.24 [1.56–3.22]. Among those with newly diagnosed diabetes (NDM) and impaired glucose tolerance (IGT), there was also evidence of reduced quality of life on some dimensions of the SF-36 scale (NDM, general health, physical functioning and role limitation (physical); IGT, physical functioning and social functioning) after adjustment for confounders.

Conclusion
These findings show that diabetes is associated with a reduced quality of life and that this is evident in the early stage of the disease, particularly in relation to the ability to perform physical activities.

Screening for type 2 diabetes and impaired glucose metabolism – the Australian experience

OBJECTIVE--To assess the Australian protocol for identifying undiagnosed type 2 diabetes and impaired glucose metabolism.

RESEARCH DESIGN AND METHODS--The Australian screening protocol recommends a stepped approach to detecting undiagnosed type 2 diabetes based on assessment of risk status, measurement of fasting plasma glucose (FPG) in individuals at risk, and further testing according to FPG. The performance of and variations to this protocol were assessed in a population-based sample of 10,508 Australians.

RESULTS--The protocol had a sensitivity of 79.9%, specificity of 79.9%, and a positive predictive value (PPV) of 13.7% for detecting undiagnosed type 2 diabetes and sensitivity of 51.9% and specificity of 86.7% for detecting impaired glucose tolerance (IGT) or impaired fasting glucose (IFG). To achieve these diagnostic rates, 20.7% of the Australian adult population would require an oral glucose tolerance test (OGTT). Increasing the FPG cut point to 6.1 mmol/l (110 mg/dl) or using Hb[A.sub.1c], instead of FPG to determine the need for an OGTT in people with risk factors reduced sensitivity, increased specificity and PPV, and reduced the proportion requiring an OGTT. However, each of these protocol variations substantially reduced the detection of IGT or IFG.

CONCLUSIONS--The Australian screening protocol identified one new case of diabetes for every 32 people screened, with 4 of 10 people screened requiring FPG measurement and 1 in 5 requiring an OGTT. In addition, 1 in 11 people screened had IGT or IFG. Including Hb[A.sub.1c] measurement substantially reduced both the number requiring an OGTT and the detection of IGT or IFG.

Are barriers to physical activity similar for adults with and without abnormal glucose Metabolism?

Purpose The purpose of this study was to examine perceived barriers to physical activity among adults with and without abnormal glucose metabolism (AGM), and whether barriers varied according to physical activity status.
Methods The 1999 to 2000 Australian Diabetes, Obesity, and Lifestyle Study (AusDiab) was a population-based cross-sectional study among adults aged ≥25 years. AGM was identified through an oral glucose tolerance test. The previous week’s physical activity and individual, social, and environmental barriers to physical activity were self-reported. Logistic regression analyses examined differences in barriers to physical activity between those with and without AGM, and for those with and without AGM who did and did not meet the minimum recommendation of 150 minutes/week of moderate-to-vigorous intensity physical activity.
Results Of the 7088 participants (47.5 ± 12.7 years; 46% male), 18.5% had AGM. Approximately 47.5% of those with AGM met the physical activity recommendation, compared to 54.7% of those without AGM (P < .001). Key barriers to physical activity included lack of time, other priorities, and being tired. Following adjustment for sociodemographic and behavioral factors, there were few differences in barriers to physical activity between those with and without AGM, even after stratifying according to physical activity.
Conclusions Adults with AGM report similar barriers to physical activity, as do those without AGM. Programs for those with AGM can therefore focus on the known generic adult-reported barriers to physical activity.

Area-level socioeconomic status and incidence of abnormal glucose metabolism : the Australian diabetes, obesity and lifestyle (AusDiab) study

OBJECTIVE--To examine the role of area-level socioeconomic status (SES) on the development of abnormal glucose metabolism (AGM) using national, population-based data.

RESEARCH DESIGN AND METHODS--The Australian Diabetes, Obesity and Lifestyle (AusDiab) study is a national, population-based, longitudinal study of adults aged [greater than or equal to] 25 years. A sample of 4,572 people provided complete baseline (1999 to 2000) and 5-year follow-up (2004 to 2005) data relevant for these analyses. Incident AGM was assessed using fasting plasma glucose and 2-h plasma glucose from oral glucose tolerance tests, and demographic, socioeconomic, and behavioral data were collected by interview and questionnaire. Area SES was defined using the Index of Relative Socioeconomic Disadvantage. Generalized linear mixed models were used to examine the relationship between area SES and incident AGM, with adjustment for covariates and correction for cluster design effects.

RESULTS--Area SES predicted the development of AGM, after adjustment for age, sex, and individual SES. People living in areas with the most disadvantage were significantly more likely to develop AGM, compared with those living in the least deprived areas (odds ratio 1.53; 95% CI 1.07-2.18). Health behaviors (in particular, physical activity) and central adiposity appeared to partially mediate this relationship.

CONCLUSIONS--Our findings suggest that characteristics of the physical, social, and economic aspects of local areas influence diabetes risk. Future research should focus on identifying the aspects of local environment that are associated with diabetes risk and how they might be modified.