Taurine supplementation enhances nutrient-induced insulin secretion in pancreatic mice islets.
ABSTRACT Taurine (TAU), a naturally occurring sulfur-containing amino acid, is found at high concentrations in plasma and mammalian tissues and regulates osmolarity, ion channel activity, and glucose homeostasis. Several reports have shown that physiological plasma TAU levels seem to be important for adequate beta (beta)-cell function and insulin action, since low concentrations of TAU in the plasma have been reported in the pre-diabetic and diabetic states.
Glucose tolerance and insulin sensitivity were investigated in mice supplemented with 2% (w/v) TAU in their drinking water for 30 days, as well as the insulin secretion from isolated islets stimulated by glucose or L-leucine.
TAU-supplemented mice demonstrated improved glucose tolerance and higher insulin sensitivity, compared to controls (CTL). In addition, their islets secreted more insulin in response to high concentrations of glucose and L-leucine. L-[U-(14)C]leucine oxidation was higher in TAU than in CTL islets, whereas D-[U-(14)C]glucose oxidation, ATP levels, glucose transporter (GLUT) 2 and glucokinase (GCK) protein expressions were similar in both types of islets. The L-type beta(2) subunit voltage-sensitive Ca(2+) channel protein, as well as (45)Ca uptake, were significantly higher in TAU-supplemented than CTL islets. In addition, islets from TAU-supplemented mice secreted more glucagon than CTL islets at low glucose.
TAU supplementation improves glucose tolerance and insulin sensitivity in mice, as well as insulin secretion from isolated islets. The latter effect seems to be, at least in part, dependent on a better Ca(2+) handling by the islets.
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ABSTRACT: Taurine is a semi-essential sulfonic acid found at high concentrations in plasma and mammalian tissues which regulates osmolarity, ion channel activity and glucose homeostasis. The structural requirements of GABAA-receptors (GABAAR) gated by taurine are not yet known. We determined taurine potency and efficacy relative to GABA at different types of recombinant GABAAR occurring in central histaminergic neurons of the mouse hypothalamic tuberomamillary nucleus (TMN) which controls arousal. At binary α1/2β1/3 receptors taurine was as efficient as GABA, whereas incorporation of the γ1/2 subunit reduced taurine efficacy to 60-90% of GABA. The mutation γ2F77I, which abolishes zolpidem potentiation, significantly reduced taurine efficacy at recombinant and native receptors compared to the wild type controls. As taurine was a full- or super- agonist at recombinant αxβ1δ-GABAAR, we generated a chimeric γ2 subunit carrying the δ subunit motif around F77 (MTVFLH). At α1/2β1γ2(MTVFLH) receptors taurine became a super-agonist, similar to δ-containing ternary receptors, but remained a partial agonist at β3-containing receptors. In conclusion, using site-directed mutagenesis we found structural determinants of taurine's partial agonism at γ-containing GABAA receptors. Our study sheds new light on the β1 subunit conferring the widest range of taurine-efficacies modifying GABAAR function under (patho)physiological conditions.PLoS ONE 01/2013; 8(4):e61733. · 3.73 Impact Factor
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ABSTRACT: SCOPE: Poor nutrition during the perinatal period is associated with an increased risk for metabolic syndrome in adulthood. Taurine (TAU) regulates β-cell function and glucose homeo-stasis. Here, we assessed the effects of TAU supplementation upon adiposity and glucose control in malnourished mice fed a high-fat diet (HFD). METHODS AND RESULTS: Weaned male C57BL/6J mice were fed a control (14% protein - C) or a protein-restricted (6% protein - R) diet for 6 weeks. Afterwards, mice received or not an HFD for 8 weeks (CH and RH). Half of the HFDmice were supplemented with 5% TAU after weaning (CHT and RHT). Protein restriction led to typical malnutrition features. HFD increased body weight, adiposity, and led to hyperleptinemia, hyperphagia, glucose intolerance, and higher liver glucose output in RH and CH groups. Fasted R mice showed higher plasma adiponectin levels and increased phosphorylation of the AMP-activated protein kinase (p-AMPK) in the liver. These parameters were reduced in RH mice and increased p-AMPK persisted in RHT. TAU prevented obesity and improved glucose tolerance only in CHT, but liver glucose control was ameliorated in both supplemented groups. Better CHT liver glucose control was linked to increased Akt (thymoma viral proto-oncogene/protein kinase B) phosphorylation. CONCLUSION: Malnourished mice fed an HFD developed obesity, glucose intolerance, and increased liver glucose output. TAU preserved only normal liver glucose control in RHT mice, an effect associated with increased liver p-AMPK content.Molecular Nutrition & Food Research 12/2012; · 4.31 Impact Factor
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ABSTRACT: Pancreatic β-cells are highly sensitive to suboptimal or excess nutrients, as occurs in protein-malnutrition and obesity. Taurine (Tau) improves insulin secretion in response to nutrients and depolarizing agents. Here, we assessed the expression and function of Cav and KATP channels in islets from malnourished mice fed on a high-fat diet (HFD) and supplemented with Tau. Weaned mice received a normal (C) or a low-protein diet (R) for 6 weeks. Half of each group were fed a HFD for 8 weeks without (CH, RH) or with 5 % Tau since weaning (CHT, RHT). Isolated islets from R mice showed lower insulin release with glucose and depolarizing stimuli. In CH islets, insulin secretion was increased and this was associated with enhanced KATP inhibition and Cav activity. RH islets secreted less insulin at high K(+) concentration and showed enhanced KATP activity. Tau supplementation normalized K(+)-induced secretion and enhanced glucose-induced Ca(2+) influx in RHT islets. R islets presented lower Ca(2+) influx in response to tolbutamide, and higher protein content and activity of the Kir6.2 subunit of the KATP. Tau increased the protein content of the α1.2 subunit of the Cav channels and the SNARE proteins SNAP-25 and Synt-1 in CHT islets, whereas in RHT, Kir6.2 and Synt-1 proteins were increased. In conclusion, impaired islet function in R islets is related to higher content and activity of the KATP channels. Tau treatment enhanced RHT islet secretory capacity by improving the protein expression and inhibition of the KATP channels and enhancing Synt-1 islet content.Amino Acids 05/2014; · 3.91 Impact Factor