Acute effects of isolated and combinedL-alanine andL-glutamine on hepatic gluconeogenesis, ureagenesis and glycaemic recovery in experimental short-term insulin induced hypoglycaemia

Glycerol Potentiates the Effects of Glucose in Promoting Glucose Recovery During Hypoglycemia: From Basic to Clinical Investigations and Their Therapeutic Application

We compared the effect of oral glucose versus oral glucose combined with glycerol (glucose + glycerol) in promoting glucose recovery during hypoglycemia. These studies were carried out in two series of experiments. In the first series of experiments, 16 overnight fasted rats received an intraperitoneal injection of lispro insulin (1 IU/kg), and 25 min later, they received oral water (control), glucose (0.25 g/kg), glycerol (2.5 g/kg), or glucose (0.25 g/kg) + glycerol (2.5 g/kg). In the second series of experiments on 164 eligible type 1 diabetic (T1D) patients, 30 individuals with a history of hypoglycemia were recruited. Five volunteers did not meet the inclusion criteria and two subjects were excluded after starting the clinical investigation; 23 patients concluded the study. All patients with symptoms of hypoglycemia ingested oral glucose (15 g) or glucose (15 g) + glycerol (9.45 g). To treat hypoglycemia in T1D patients, preparations containing glucose alone or glucose + glycerol were used alternately (2 weeks/2 weeks) in a double-blind crossover scheme. Throughout the clinical research (4 weeks), glucose concentrations were assessed with a continuous glucose monitoring device and the results after the use of glucose alone or glucose + glycerol preparations were compared. Oral glucose combined with glycerol was more effective in promoting glucose recovery in comparison with glucose alone, not only in rats but also in T1D patients. Taken together, our experimental and clinical investigations reported the best performance of oral administration of glucose + glycerol in comparison with isolated glucose.

Oral glutamine supplementation attenuates inflammation and oxidative stress-mediated skeletal muscle protein content degradation in immobilized rats: Role of 70 kDa heat shock protein

Skeletal muscle disuse results in myofibrillar atrophy and protein degradation, via inflammatory and oxidative stress-mediated NF-kB signaling pathway activation. Nutritional interventions, such as l-glutamine (GLN) supplementation have shown antioxidant properties and cytoprotective effects through the modulation on the 70-kDa heat shock protein (HSP70) expression. However, these GLN-mediated effects on cell signaling pathways and biochemical mechanisms that control the myofibrillar protein content degradation in muscle disuse situations are poorly known yet. This study investigated the effects of oral GLN plus l-alanine (ALA; GLN ​+ ​ALA-solution) supplementation, either in their free or dipeptide (L-alanyl-l-glutamine-DIP) form, on GLN-glutathione (GSH) axis and cytoprotection mediated by HSP70 protein expression in the slow-twitch soleus and fast-twitch gastrocnemius skeletal muscle of rats submitted to 14-days of hindlimb immobilization-induced disuse muscle atrophy. Forty-eight Wistar rats were distributed into 6 groups: hindlimb immobilized (IMOB group) and hindlimb immobilized orally supplemented with either GLN (1 g kg^-1) plus ALA (0.61 g kg^-1) ​(GLN ​+ ​ALA-IMOB group) or 1.49 ​g ​kg^-1 of DIP (DIP-IMOB group) and; no-immobilized (CTRL) and no-immobilized supplemented GLN ​+ ​ALA and DIP baselines groups. All animals, including CTRL and IMOB rats (water), were supplemented via intragastric gavage for 14 days, concomitantly to immobilization period. Plasma and muscle GLN levels, lipid (thiobarbituric acid reactive substances-TBARS) and protein (carbonyl) peroxidation, erythrocyte concentration of reduced GSH and GSH disulfide (GSSG), plasma and muscle pro-inflammatory TNF-α levels, muscle IKKα/β-NF-kB signaling pathway and, the myofibrillar protein content (MPC) were measured. The MPC was significantly lower in IMOB rats, compared to CTRL, GLN ​+ ​ALA, and DIP animals (p ​< ​0.05). This finding was associated with reduced plasma and muscle GLN concentration, equally in IMOB animals. Conversely, both GLN ​+ ​ALA and DIP supplementation restored plasma and muscle GLN levels, which equilibrated GSH and intracellular redox status (GSSG/GSH ratio) in erythrocytes and skeletal muscle even as, increased muscle HSP70 protein expression; attenuating oxidative stress and TNF-α-mediated NF-kB pathway activation, fact that reverberated on reduction of MPC degradation in GLN ​+ ​ALA-IMOB and DIP-IMOB animals (p ​< ​0.05). In conclusion, the findings shown herein support the oral GLN ​+ ​ALA and DIP supplementations as a therapeutic and effective nutritional alternative to attenuate the deleterious effects of the skeletal muscle protein degradation induced by muscle disuse.

l-glutamine and l-alanine supplementation increase glutamine-glutathione axis and muscle HSP-27 in rats trained using a progressive high-intensity resistance exercise

In this study we investigated the chronic effects of oral l-glutamine and l-alanine supplementation, either in their free or dipeptide form, on glutamine-glutathione (GLN-GSH) axis and cytoprotection mediated by HSP-27 in rats submitted to resistance exercise (RE). Forty Wistar rats were distributed into 5 groups: sedentary; trained (CTRL); and trained supplemented with l-alanyl-l-glutamine, l-glutamine and l-alanine in their free form (GLN+ALA), or free l-alanine (ALA). All trained animals were submitted to a 6-week ladder-climbing protocol. Supplementations were offered in a 4% drinking water solution for 21 days prior to euthanasia. Plasma glutamine, creatine kinase (CK), myoglobin (MYO), and erythrocyte concentration of reduced GSH and glutathione disulfide (GSSG) were measured. In tibialis anterior skeletal muscle, GLN-GSH axis, thiobarbituric acid reactive substances (TBARS), and the expression of heat shock factor 1 (HSF-1), 27-kDa heat shock protein (HSP-27), and glutamine synthetase were determined. In CRTL animals, high-intensity RE reduced muscle glutamine levels and increased GSSG/GSH rate and TBARS, as well as augmented plasma CK and MYO levels. Conversely, l-glutamine-supplemented animals showed an increase in plasma and muscle levels of glutamine, with a reduction in GSSG/GSH rate, TBARS, and CK. Free l-alanine administration increased plasma glutamine concentration and lowered muscle TBARS. HSF-1 and HSP-27 were high in all supplemented groups when compared with CTRL (p < 0.05). The results presented herein demonstrate that l-glutamine supplemented with l-alanine, in both a free or dipeptide form, improve the GLN-GSH axis and promote cytoprotective effects in rats submitted to high-intensity RE training.

Kettelhut I, Navegantes LC, Chaves VE, Bertolini GL, Kawashita NH. High glucose uptake in growing rats adapted to a low-protein, high-carbohydrate diet determines low fasting glycemia even with high hepatic gluconeogenesis

The our objective was to investigate the adaptations induced by a low-protein, high-carbohydrate (LPHC) diet in growing rats, which by comparison with the rats fed a control (C) diet at displayed lower fasting glycemia and similar fasting insulinemia, despite impairment in insulin signaling in adipose tissues. In the insulin tolerance test the LPHC rats showed higher rates of glucose disappearance (30%) and higher tolerance to overload of glucose than C rats. The glucose uptake by the soleus muscle, evaluated in vivo by administration of 2-deoxy-[14C]glucose, increased by 81%. The phosphoenolpyruvate carboxykinase content and the incorporation of [1-14C]pyruvate into glucose was also higher in the slices of liver from the LPHC rats than in those from C rats. The LPHC rats showed increases in l-lactate as well as in other gluconeogenic precursors in the blood. These rats also had a higher hepatic production of glucose, evaluated by in situ perfusion. The data obtained indicate that the main substrates for gluconeogenesis in the LPHC rats are l-lactate and glycerol. Thus, we concluded that the fasting glycemia in the LPHC animals was maintained mainly by increases in the hepatic gluconeogenesis from glycerol and l-lactate, compensating, at least in part, for the higher glucose uptake by the tissues.

Investigation of glycemia recovery with oral administration of glycerol, pyruvate, and L-lactate during long-term, insulin-induced hypoglycemia

AIM

The acute effect of oral administration of isolated or combined glycerol, pyruvate, and L-lactate on glycemia recovery (GR) during long-term, insulin-induced hypoglycemia (IIH) was compared.

METHODS

Glycemia of 24 h-fasted rats that received intraperitoneal injection (1.0 U/kg) of regular insulin (IIH group) or saline (COG group) and, 15, 150, or 165 min later, oral saline (control IIH), glycerol (100 mg/kg), pyruvate (100 mg/kg), L-lactate (100 mg/kg), or combined glycerol+pyruvate+L-lactate (each 33.3 or 100 mg/kg) was compared. In addition, for comparative purposes, a group that received glucose (100 mg/kg) was included. Glycemia was measured 180 min after insulin or saline injection. To investigate the participation of the hepatic availability of gluconeogenic substrates to GR, livers from IIH and COG rats that received physiological or supraphysiological concentrations of isolated or combined glycerol, pyruvate, and L-lactate were compared. Liver experiments were done 180 min after insulin or saline injection.

RESULTS

Oral glycerol, pyruvate, and L-lactate (isolated or combined) or glucose promoted GR. Moreover, the best GR was obtained with combined glycerol+pyruvate+L-lactate (100 mg/kg). In agreement, livers that received supraphysiological concentrations of glycerol, pyruvate, and L-lactate (isolated or combined) showed higher glucose release than livers that received physiological concentrations of these substances (isolated or combined).

CONCLUSION

The best GR obtained with combined administration of glycerol, pyruvate, and L-lactate (100 mg/kg) during long-term IIH was a consequence of the higher liver availability of these substances associated with a maintained liver ability to produce glucose from gluconeogenic substrates.

Gluconeogenesis and ketogenesis in perfused liver of rats submitted to short-term insulin-induced hypoglycaemia

Gluconeogenesis and ketogenesis of in situ rat perfused liver submitted to short-term insulin-induced hypoglycaemia (IIH) were investigated. For this purpose, 24-h fasted rats that received intraperitoneal (ip) regular insulin (1.0 U kg(-1)) or saline were compared. The studies were performed 30 min after insulin (IIH group) or saline (COG group) injection. For gluconeogenesis studies, livers from the IIH and COG groups were perfused with increasing concentrations (from basal blood concentrations until saturating concentration) of glycerol, L-lactate (Lac) or pyruvate (Pyr). Livers of the IIH group showed maintained efficiency to produce glucose from glycerol and higher efficiency to produce glucose from Lac and Pyr. In agreement with these results the oral administration of glycerol (100 mg kg(-1)), Lac (100 mg kg(-1)), Pyr (100 mg kg(-1)) or glycerol (100 mg kg(-1)) + Lac (100 mg kg(-1)) + Pyr (100 mg kg(-1)) promoted glycaemia recovery. It can be inferred that the increased portal availability of Lac, Pyr and glycerol could help glycaemia recovery by a mechanism mediated, partly at least, by a maintained (glycerol) or increased (Lac and Pyr) hepatic efficiency to produce glucose. Moreover, in spite of the fact that insulin inhibits ketogenesis, the capacity of the liver to produce ketone bodies from octanoate during IIH was maintained.