Tumour necrosis factor-alpha infusion produced insulin resistance but no change in the incretin effect in healthy volunteers.

BACKGROUND: Type 2 diabetes mellitus (T2DM) is associated with peripheral insulin resistance, impaired incretin effect, and increased plasma levels of tumour necrosis factor-alpha (TNF-α). Although TNF-α infusion at a dose that induces systemic inflammation in healthy volunteers has been demonstrated to induce peripheral insulin resistance, the influence of this cytokine on the incretin effect is unknown. METHODS: We investigated whether systemic inflammation induced by TNF-α infusion in healthy volunteers alters the incretin hormone response to oral and intravenous glucose loads in a crossover study design with ten healthy male volunteers (mean age 24 years, mean body mass index 23.7 kg/m(2) ). The study consisted of four study days: days 1 and 2, 6-h infusion of saline; days 3 and 4, 6-h infusion of TNF-α; days 1 and 3, 4-h oral glucose tolerance test; and days 2 and 4, 4-h corresponding intravenous isoglycaemic glucose tolerance test. Glucose tolerance tests were initiated after 2 h of saline/TNF-α infusion. Plasma concentrations of TNF-α, interleukin 6, glucose, incretin hormones, and cortisol, and serum concentrations of C-peptide and insulin were measured throughout the study days. Insulin sensitivity was estimated by the Matsuda index and homeostasis model assessment of insulin resistance (HOMA-IR). Prehepatic insulin secretion rates were calculated. RESULTS: TNF-α infusion induced symptoms of systemic inflammation; increased plasma levels of cortisol, TNF-α, and interleukin 6; and increased the HOMA-IR. The secretion of incretin hormones as well as the incretin effect remained unchanged. CONCLUSION: In healthy young male volunteers, acute systemic inflammation induced by infusion of TNF-α is associated with insulin resistance with no change in the incretin effect.

The effects of TNF-α on GLP-1-stimulated plasma glucose kinetics.

CONTEXT: Glucagon-like peptide-1 (GLP-1) analogs have recently been promoted as antihyperglycemic agents in critically ill patients with systemic inflammation, but the effects of TNF-α on glucose metabolism during GLP-1 administration are unknown. OBJECTIVE: The objective of the study was to determine whether the infusion of TNF-α at high physiological levels impairs GLP-1's effects on glucose metabolism. DESIGN: This was a randomized, controlled, cross-over trial. SETTING: The study was conducted at a hospital clinical research laboratory. PARTICIPANTS: Twelve healthy males (aged 24 ± 3 y; body mass index 22.9 ± 1.3 kg/m(2)). INTERVENTIONS: After an overnight fast, either saline (0.9%) or recombinant human TNF-α (1000 ng/m(2) · h) was infused from t = 0-6 hours. At t = 2 hours, GLP-1 infusion (0.5 pmol/kg · min) began. From t = 4-6 hours, the GLP-1 infusion rate was increased to 1.2 pmol/kg · min. Plasma glucose was clamped at 5 mmol/L throughout via a variable rate 20% dextrose infusion. Trials were 7-14 days apart. MAIN OUTCOME MEASURES: Endogenous glucose production (EGP) was measured by the [6,6-(2)H2]glucose isotope tracer dilution method. RESULTS: GLP-1 infusion suppressed plasma glucagon (P < .01), elevated plasma insulin, and C-peptide (P < .01) and suppressed EGP (P < .001) during the saline infusion. In contrast, the infusion of TNF-α increased plasma TNF-α and IL-6, elevated body temperature, and blunted the GLP-1-induced suppression of EGP during high-dose GLP-1 infusion (all P < .05, TNF-α vs saline). However, TNF-α infusion lowered plasma GLP-1 during high-dose GLP-1 infusion (P < .001). CONCLUSIONS: TNF-α induces systemic inflammation and reduces plasma GLP-1, thereby reducing the suppression of EGP during GLP-1 infusion. This may have clinical relevance if GLP-1 analog drugs are used for the treatment of hyperglycemia in critically ill patients.

Normal physical activity obliterates the deleterious effects of a high-caloric intake.

A high-caloric intake combined with a sedentary lifestyle is an important player in the development of type 2 diabetes mellitus (T2DM). The present study was undertaken to examine if the level of physical activity has impact on the metabolic effects of a high-caloric (+2,000 kcal/day) intake. Therefore, healthy individuals on a high-caloric intake were randomized to either 10,000 or 1,500 steps/day for 14 days. Step number, total energy expenditure, dietary records, neuropsychological tests, maximal oxygen uptake (Vo2max), whole body dual-energy X-ray absorptiometry (DXA) and abdominal magnetic resonance imaging (MRI) scans, continuous glucose monitoring (CGM), and oral glucose tolerance tests (OGTT) with stable isotopes were performed before and after the intervention. Both study groups gained the same amount of body weight. However, the inactive group accumulated significantly more visceral fat compared with the active group. Following the 2-wk period, the inactive group also experienced a poorer glycemic control, increased endogenous glucose production, decreased hepatic insulin extraction, increased baseline plasma levels of total cholesterol and LDL, and a decreased cognitive function with regard to capacity of attention. In conclusion, we find evidence to support that habitual physical activity may prevent pathophysiological symptoms associated with diet-induced obesity.