The effect of acute caffeine administration on insulin sensitivity is mediated by A1 and A2B adenosine receptors

JF Sacramento, MJ Ribeiro, MP Guarino, SV Conde. CEDOC, Faculdade Ciências Médicas, Universidade Nova de Lisboa, Pharmacology, 1169-056 Lisboa, Portugal

Background and aims: Caffeine is the most widely behaviorally active substance consumed in the world and when consumed chronically appears to have minor negative consequences on human health. Several epidemiological studies showed that chronic caffeine intake decreases the risk of type 2 diabetes and metabolic syndrome (Lopez-Garcia et al., 2006, Am J Clin Nutr, 84: 888-93; van Dam et al., 2006, Diabetes Care, 29: 398-403) and recently, our group showed that chronic caffeine intake prevents the development of insulin resistance (IR) in diet-induced IR rats (Conde et al., 2012, Br J Nutr, 107:86-95). This sensitizer effect of chronic caffeine intake contrasts with the acute caffeine administration that has been associated with an increase in IR (Graham et al., 2001; Can J Physiol Pharmacol, 79: 559-65; Moisey et al., 2008, Am J Clin Nutr, 87: 1254-61).The aim of the present work was to investigate the effect of acute caffeine administration on insulin sensitivity and also if this effect is mediated by adenosine receptors.

Methods: In vivo experiments were performed in Wistar rats of both sexes, aged 3 months (200-350g) anaesthetized with pentobarbitone (60 mg/Kg) and breathing spontaneously. To evaluate the effect of acute caffeine administration as well as to investigate the subtype(s) of adenosine receptors involved in this effect, the animals were submitted to i.v. administration of the different adenosine receptors antagonists: caffeine (non-selective, 0.001-5 μM), DPCPX (A1 antagonist, 0.0005 -5 μM), MRS1754, (A2B antagonist, 0.001 – 5 μM), 15 minutes prior to insulin sensitivity evaluation. DPCPX and MRS 1754 were dissolved in DMSO. Insulin sensitivity was measured by an insulin tolerance test. After insulin sensitivity test, blood was collected by heart puncture and skeletal muscle and adipose tissue were removed for Western-blot detection and quantification of adenosine receptors, Glut4 transporters and AMPK. One and Two-Way ANOVA with multicomparison post-tests were used to perform statistical analysis.

Results: Acute administration of caffeine, DPCPX and MRS1754 did not modified basal glycemia in all concentrations tested. Caffeine decreased insulin sensitivity in a dose dependent manner with a maximal effect of 61.95% (p<0.001) and an IC50 of 6.98 nM. Also, DPCPX and MRS1754 decreased insulin sensitivity with Emax of 58.74% (p<0.001) and 62.31% (p<0.001), respectively and an IC50 of 21.44nM and 94.28 nM, respectively. Acute caffeine administration did not modify Glut4 expression (n = 3-4), however AMPK expression (n = 2-3) increased in a concentration dependent manner (p<0.05) with an Emax of 72%.

Conclusions: Our results suggest that the effects of acute caffeine administration on insulin sensitivity are mediated by both A1 and A2B adenosine receptors. The profile of dose response curves for adenosine antagonists on insulin sensitivity suggest that an effect on A2A receptors can also be involved. Additionally, an effect of caffeine on AMPK can also account for the effects of this xanthine on insulin sensitivity.

Supported by Portuguese Foundation for Science and Technology - PTDC/SAU-ORG/111417/2009