Chronological Appearance of Endocrine and Metabolic Dysfunctions Induced by an Unhealthy Diet in Rats

Background and Objectives: The work was aimed to determine the chronological sequence of events triggered by a fructose-rich diet (FRD) (10% w/v in the drinking water) in normal rats. Material and Methods: Serum parameters, liver and islet markers of metabolism, inflammation and oxidative stress were determined weekly for 21 days. Results: At the end of the first week, rats fed with a FRD showed an early increase in circulating triglycerides, fat liver deposit, and enzymatic activity of liver glucokinase and glucose-6-phosphate dehydrogenase (G6P-DH). After two weeks of such a diet, liver glucose-6-phosphatase (G6Pase) activity and liver oxidative stress markers were significantly increased. Liver sterol regulatory element-binding protein 1c (SREBP1c) mRNA also increased in the second week while their target genes fatty acid synthase (FAS) and glycerol-3-phosphate dehydrogenase (GPAT) enhanced their expression at the third week. Liver and pancreatic inflammation markers also enhanced their gene expression in the last week of treatment. Whereas both control and FRD rats remained normoglycemic throughout the entire period of treatment, blood insulin levels were significantly higher in FRD animals at the third week, thereby evidencing an insulin-resistant state (higher HOMA-IR, HOMA-B and HIS indexes). Pancreatic islets isolated from rats fed with a FRD for 3 weeks also increased glucose-induced insulin secretion (8.3 and 16.7 mM). Conclusions: FRD induces asynchronous changes involving early hypertriglyceridemia together with intrahepatic lipid deposit and metabolic disturbances from week one, followed by enhanced liver oxidative stress, liver and pancreas inflammation, pancreatic β-cell dysfunction, and peripheral insulin-resistance registered at the third week. Knowledge of time-course adaptation mechanisms involved in our rat model could be helpful in developing appropriate strategies to prevent the progression from prediabetes to Type 2 diabetes (T2D) triggered by unhealthy diets.

SGLT2 inhibition alleviated hyperglycemia, glucose intolerance, and dumping syndrome-like symptoms in a patient with glycogen storage disease type Ia: a case report

Background Glycogen storage disease (GSD) type Ia is a glycogenesis disorder with long-term complications such as hepatomegaly and renal dysfunction and is caused by congenital loss of glucose-6-phosphatase (G6Pase) expression. G6Pase is essential for the final step of gluconeogenesis and glycogenolysis, and its deficiency causes clinical hypoglycemia in the fasting state during infancy. Contrastingly, patients also show blood glucose trends and glucose intolerance similar to those in type II diabetes. Owing to the contrasting presentation of hypoglycemia with glucose intolerance, glucose control in patients remains a challenge, requiring management of both fasting hypoglycemia and post-prandial hyperglycemia. Case presentation The patient was a 45-year old Asian (Japanese) woman who showed disease onset at 3 years of age, when hypoglycemia and hepatomegaly were observed, and GDS type Ia was diagnosed by the lack of G6Pase activity. Over the past 45 years, she presented hyperglycemia and dumping syndrome like symptoms (a feeling of fullness, even after eating just a small amount, abdominal cramping, nausea, sweating, flushing, or light-headedness and rapid heartbeat) at 2 hours after food intake. Her liver and kidney dysfunction also worsened over time. Treatment with exercise combined with a sodium-glucose co-transporter 2 inhibitor and an alpha glucosidase inhibitor alleviated her glucose intolerance and dumping syndrome-like symptoms, without increasing hypoglycemic events. Conclusion This case suggests SGLT2 inhibitor as a promising candidate for treating glucose intolerance in GSD type Ia without worsening of hypoglycemia.

Possible mechanisms of the hypoglycaemic effect of artesunate: Gender implication

Background Artesunate is an antimalarial drug that affects glucose homeostasis but the mechanism of its glucose-modulating effect is not fully understood especially with gender implication, which is the information this study sought to provide. Methods Twenty-five (25) male and 25 female rats were separately and blindly allocated into five identical groups (n = 5/group). Group I (control) received 0.2 ml/kg distilled water. Groups II and III both received 2.90 mg/kg artesunate on day one, but 1.45 mg/kg from day two till day five and day fifteen respectively. Groups IV and V both received 8.70 mg/kg artesunate on day one, but 4.35 mg/kg artesunate from day two till day five and day fifteen respectively. Results In male rats, the blood glucose was reduced by low and high doses of artesunate at 5 days but increased by high dose at 15 days. Glucose was reduced in female rats but unchanged in male rats by low dose artesunate at 15 days. Artesunate increased glycogen concentration at short duration which normalised at long duration in both genders. Artesunate increased G6P concentration only in male rats at 15 days but reduced G6Pase activity in male and female rats (except in those that received low and high doses of artesunate for 15 days). Artesunate increased insulin only in male rats treated with low dose artesunate for 5 days. Artesunate increased cortisol concentration in male but reduced it in female rats. Artesunate decreased glucagon concentration except in female rats treated with high dose for 5 days. Artesunate increased oestrogen concentration in male rats that received low dose artesunate for 5 days but reduced it in female rats that received high dose for 15 days. Except in male rats that received high dose of artesunate for 15 days where testosterone was increased, artesunate did not affect testosterone concentration in all other male and female groups Conclusions The present study suggests that artesunate causes reduction in plasma glucose by reducing plasma glucagon concentrations and inhibiting liver glycogenolysis via inhibition of G6Pase activity in both sexes. In addition, increase in plasma insulin concentration contributed to the reduction in blood glucose caused by artesunate in male but not female rats; and artesunate-induced increase in G6P, a substrate for G6PD, could enhance NADPH generation and antioxidant enzyme activation in male rats.

Anti-diabetic effect of pyroglutamic acid in type 2 diabetic Goto-Kakizaki rats and KK-Aymice

With the rapidly increasing prevalence of type 2 diabetes mellitus (T2DM), specific dietary components with anti-diabetic efficacy could be one strategy with therapeutic potential. In the present study, the anti-diabetic effects of an amino acid, pyroglutamic acid (PA), found in vegetables and fruits were investigated in T2DM models using Goto-Kakizaki (GK) rats and KK-Aymice by measuring glucose tolerance and other markers of diabetes. Moreover, the effect of PA on gene expression in GK rats was measured by DNA microarray analysis. Oral glucose tolerance and serum insulin levels were reduced by PA in both animal models. Serum and liver total cholesterol levels were also improved by PA. Expression of genes involved with gluconeogenesis and those involved with its related transcription factor were down-regulated by feeding PA. In KK-Aymice, the glucokinase:glucose-6-phosphatase (G6Pase) activity ratio increased. From these results, it is suggested that dietary PA beneficially modifies glucose and lipid metabolism in diabetic animals, and can potentially contribute to the mitigation of T2DM.

Effects of eicosapentaenoic acid ethyl ester on visfatin and apelin in lean and overweight (cafeteria diet-fed) rats

Previous studies have demonstrated that then-3 fatty acid EPA improves insulin resistance induced by high-fat diets. The aim of the present study was to investigate the potential role of visfatin and apelin in the insulin-sensitising effects of EPA ethyl ester. The effects of EPA on muscle and adipose GLUT mRNA, as well as on liver glucokinase (GK) and glucose-6-phosphatase (G6Pase) activity, were investigated. Male Wistar rats fed on a standard diet or a high-fat cafeteria diet were daily treated by oral administration with EPA ethyl ester (1 g/kg) for 5 weeks. A significant decrease (P < 0·01) in white adipose tissue (WAT) visfatin mRNA levels was found in the cafeteria-fed rats, which was reversed by EPA administration (P < 0·05). Moreover, a negative relationship was observed between homeostatic model assessment (HOMA) and the visfatin:total WAT ratio. In contrast, cafeteria-diet feeding caused a significant increase (P < 0·01) in apelin mRNA in visceral WAT. EPA increased (P < 0·01) apelin gene expression, and a negative relationship between HOMA index with visceral apelin mRNA and serum apelin:total WAT ratio was also observed. EPA treatment did not induce changes in skeletal muscle GLUT1, GLUT4 or insulin receptor mRNA levels. Neither liver GK and G6Pase activity nor the GK:G6Pase ratio was modified by EPA. These data suggest that somehow the insulin-sensitising effects of EPA could be related to its stimulatory action on both visfatin and apelin gene expression in visceral fat, while changes in skeletal muscle GLUT, as well as in hepatic glucose production, are not likely to be the main contributing factors in the improvement in insulin resistance induced by EPA.

Effects of dexamethasone on the glucogenic capacity of fetal, pregnant, and non-pregnant adult sheep

Fetal glucocorticoids have an important role in the pre-partum maturation of physiological systems essential for neonatal survival such as glucogenesis. Consequently, in clinical practice, synthetic glucocorticoids, like dexamethasone, are given routinely to pregnant women threatened with pre-term delivery to improve the viability of their infants. However, little is known about the effects of maternal dexamethasone treatment on the glucogenic capacity of either the fetus or mother. This study investigated the effects of dexamethasone treatment using a clinically relevant dose and regime on glycogen deposition and the activities of glucose-6-phosphatase (G6Pase) and phosphoenolpyruvate carboxykinase (PEPCK) in the liver and kidney of pregnant ewes and their fetuses, and of non-pregnant ewes. Dexamethasone administration increased the glycogen content of both the fetal and adult liver within 36 h of beginning treatment. It also increased G6Pase activity in the liver and kidney of the fetuses but not of their mothers or the non-pregnant ewes. Neither hepatic nor renal PEPCK activity was affected by dexamethasone in any group of animals. These changes in glycogen content and G6Pase activity were accompanied by rises in the plasma glucose and insulin concentrations and by a fall in the plasma cortisol level in the fetus and both groups of adult animals. In addition, dexamethasone treatment raised fetal plasma tri-iodothyronine (T3) concentrations and reduced maternal levels of plasma T3 and thyroxine, but had no effect on thyroid hormone concentrations in the non-pregnant ewes. These findings show that maternal dexamethasone treatment increases the glucogenic capacity of both the mother and fetus and has major implications for glucose availability both before and after birth.

Up-regulation of liver glucose-6-phosphatase in rats fed with a Pi-deficient diet

Because Pi deprivation markedly affects the Na/Pi co-transporter in kidney and has been related to insulin resistance and glucose intolerance, the effect of a Pi-deficient diet on the liver microsomal glucose-6-phosphatase (G6Pase) system was investigated. Rats were fed with a control diet (+Pi) or a diet deficient in phosphate (-Pi) for 2 days and killed on the morning of the third day, after an overnight fast (fasted) or not (fed). Kinetic parameters of Pi transport (t½ and equilibration) into liver microsomes were not changed by the different nutritional conditions. In contrast, it was found that G6Pase activity was significantly increased in the (-Pi) groups. This was due to an increase in the Vmax of the enzyme, without change in the Km for G6P. There was no correlation between liver microsomal glycogen content and G6Pase activity, but both protein abundance and mRNA of liver 36 kDa catalytic subunit of G6Pase (p36) were increased. The mRNA of the putative G6P translocase protein (p46) was changed in parallel with that of the catalytic subunit, but the p46 immunoreactive protein was unchanged. These findings indicate that dietary Pi deficiency causes increased G6Pase activity by up-regulation of the expression of the 36 kDa-catalytic-subunit gene.

Mutation/Polymorphism Scanning of Glucose-6-Phosphatase Gene Promoter in Noninsulin-Dependent Diabetes Mellitus Patients1

Glucose-6-phosphatase (G6Pase) catalyzes the rate-limiting step of gluconeogenesis, and hepatic G6Pase activity is increased in diabetes. We have cloned and analyzed the human G6Pase gene promoter region and identified putative regulatory sequences for insulin, cAMP, glucocorticoid, and hepatocyte nuclear factors. The promoter region of the G6Pase gene was analyzed in 154 noninsulin-dependent diabetes mellitus patients and 90 control subjects by PCR-single strand conformation polymorphism and direct sequencing methods. Polymorphisms were not found in any subjects. The results suggested that in noninsulin-dependent diabetic patients, the major cause of the hepatic glucose overproduction was not attributed to dysregulation of the G6Pase gene due to mutation/polymorphism of its promoter region.

High glucose-6-phosphatase activity in non-pigmented epithelial cells of rabbit ciliary body.

For study of the origin of glucose in the aqueous humor, glucose-6-phosphatase (G6Pase) and hexokinase activities, and glycogen, were cytochemically examined in the ciliary body (CB) of rabbit. G6Pase activity was also assayed biochemically. The staining reaction for G6Pase activity was strong in the non-pigmented epithelium (NPE) in the pars plana and tips of ciliary processes in the region containing large ciliary pockets within the pars plicata. NPE cells contained abundant reaction product for G6Pase activity in the endoplasmic reticulum (ER) and nuclear envelope. However, NPE in other regions of the CB and pigmented epithelium (PE) of CB, and other areas surrounding the anterior and (PE) of CB, and other areas surrounding the anterior and posterior chambers, showed weak or no G6Pase staining reaction. Biochemical G6Pase activity in the whole ciliary body was relatively high. Both NPE and PE in the pars plana and the tips showed strong staining reaction for hexokinase activity but no staining for glycogen. Furthermore, NPE cells in the tips bore large aggregates of smooth ER and many Golgi apparati. These suggest that the high G6Pase activity in NPE cells in the pars plana and the tips is related to glucose release into the aqueous humor.

Quantitative histochemical analysis of glucose-6-phosphatase activity in rat liver using an optimized cerium-diaminobenzidine method.

We have optimized a cerium-diaminobenzidine-based method for histochemical analysis of glucose-6-phosphatase (G6Pase) activity and have determined quantitative data on the zonal distribution pattern in the liver acinus of fasted male rats. In the cerium-diaminobenzidine technique, cerium instead of lead ions is used as capturing reagent for the enzymatically liberated phosphate. For light microscopy, the primary reaction product, cerium phosphate, is then visualized by conversion into cerium perhydroxide using hydrogen peroxide and subsequent oxidative polymerization of diaminobenzidine to diaminobenzidine brown as the final reaction product. Variation of the substrate (glucose-6-phosphate) concentration in the incubation medium yielded in periportal zones a KM value of 2.3 +/- 0.7 mM and a Vmax value of 0.96 +/- 0.18 (expressed as mean integrated absorbance). In perivenous zones a KM value of 1.1 +/- 0.4 mM and a Vmax value of 0.51 +/- 0.08 were calculated. The cytophotometric analysis performed in this study demonstrated for the first time that a functional difference of G6Pase, the key enzyme for gluconeogenesis, exists in the periportal and perivenous zones of the liver acinus. Periportal zones contain twice as many enzyme molecules (high Vmax) as perivenous zones, but the affinity for the substrate is twice as low. This may have important implications for the concept of metabolic zonation of the liver and also for glucose homeostasis in the blood.