Glycemic effects of simvastatin: Where do we stand?

ABSTRACT In clinical practice, simvastatin is usually used in the treatment of dyslipidemia patients and those at risk of or with established cardiovascular disease. However, previous studies have shown that simvastatin has the potential to affect glycemic parameters as it reportedly reduced insulin secretion and sensitivity. The exact mechanism by which simvastatin affects glycemia is still unknown, but previous studies have postulated the involvement of the glucose-insulin secretion mechanism. This review focuses on the effects of simvastatin, either alone or in combination with other lipid lowering agents, antidiabetics and antihypertensives, on glucose homeostasis. Some studies have reported that simvastatin might impair the levels of glucose metabolism markers in the blood while others have reported no effect or improvement in glycemia.

A Journey to Understand Glucose Homeostasis: Starting from Rat Glucose Transporter Type 2 Promoter Cloning to Hyperglycemia

My professional journey to understand the glucose homeostasis began in the 1990s, starting from cloning of the promoter region of glucose transporter type 2 (GLUT2) gene that led us to establish research foundation of my group. When I was a graduate student, I simply thought that hyperglycemia, a typical clinical manifestation of type 2 diabetes mellitus (T2DM), could be caused by a defect in the glucose transport system in the body. Thus, if a molecular mechanism controlling glucose transport system could be understood, treatment of T2DM could be possible. In the early 70s, hyperglycemia was thought to develop primarily due to a defect in the muscle and adipose tissue; thus, muscle/adipose tissue type glucose transporter (GLUT4) became a major research interest in the diabetology. However, glucose utilization occurs not only in muscle/adipose tissue but also in liver and brain. Thus, I was interested in the hepatic glucose transport system, where glucose storage and release are the most actively occurring.

SLC2A2 gene analysis in three Chinese children with Fanconi-Bickel syndrome / 中国当代儿科杂志

Fanconi-Bickel syndrome (FBS, OMIM 227810), a rare autosomal recessive disorder of carbohydrate metabolism, is caused by SLC2A2 (GLUT2) mutations. The study reported 3 cases of FBS who were confirmly diagnosed by SLC2A2 gene analysis. The three patients showed typical features like glycogen storage disease and proximal renal tubular nephropathy. Homozygous splice-site mutation IVS8+5G>C (c.1068+5 G>C) was found in patient A and homozygous nonsense mutation c.1194T>A (p.Tyr398X) in patient B. Patient C harboured a missense mutation c.380C>A (p.Ala127Asp) and a de novo insertion c.970dupT (p.324TyrfsX392) which was not inherited from her parents. Four mutations were identified in the 3 Chinese FBS patients. Except IVS8+5G>C mutation, the other 3 mutations were novel in Chinese population. To the best of our knowledge, patient C may be the first FBS case worldwide with de novo mutation.

Chlorogenic Acid Maintains Glucose Homeostasis through Modulating the Expression of SGLT-1, GLUT-2, and PLG in Different Intestinal Segments of Sprague-Dawley Rats Fed a High-Fat Diet / 生物医学与环境科学（英文）

<p><b>OBJECTIVE</b>To reveal the effects and related mechanisms of chlorogenic acid (CGA) on intestinal glucose homeostasis.</p><p><b>METHODS</b>Forty male Sprague-Dawley rats were randomly and equally divided into four groups: normal chow (NC), high-fat diet (HFD), HFD with low-dose CGA (20 mg/kg, HFD-LC), and HFD with high-dose CGA (90 mg/kg, HFD-HC). The oral glucose tolerance test was performed, and fast serum insulin (FSI) was detected using an enzyme-linked immunosorbent assay. The mRNA expression levels of glucose transporters (Sglt-1 and Glut-2) and proglucagon (Plg) in different intestinal segments (the duodenum, jejunum, ileum, and colon) were analyzed using quantitative real-time polymerase chain reaction. SGLT-1 protein and the morphology of epithelial cells in the duodenum and jejunum was localized by using immunofluorescence.</p><p><b>RESULTS</b>At both doses, CGA ameliorated the HFD-induced body weight gain, maintained FSI, and increased postprandial 30-min glucagon-like peptide 1 secretion. High-dose CGA inhibited the HFD-induced elevation in Sglt-1 expression. Both CGA doses normalized the HFD-induced downregulation of Glut-2 and elevated the expression of Plg in all four intestinal segments.</p><p><b>CONCLUSION</b>An HFD can cause a glucose metabolism disorder in the rat intestine and affect body glucose homeostasis. CGA can modify intestinal glucose metabolism by regulating the expression of intestinal glucose transporters and Plg, thereby controlling the levels of blood glucose and insulin to maintain glucose homeostasis.</p>

Effect of small interfering RNA-mediated angiotensin II type 1 receptor knockdown on first-phase insulin secretion in isolated diabetic rat islets / 南方医科大学学报

<p><b>OBJECTIVE</b>To investigate the effects of angiotensin II type 1 receptor (AT1R) knockdown on the first-phase insulin secretion in isolated islets of db/db mice and explore the possible mechanisms.</p><p><b>METHODS</b>Islets were isolated from db/db and db/m mice and the expression level of AT1R in the islets was assayed. A recombinant adenovirus containing siRNA targeting AT1R (Ad-siAT1R) and a recombinant adenovirus with nonspecific siRNA (Ad-siControl) were constructed to infect the isolated islets for 72 h. AT1R, GLUT-2, and GCK expressions in the islets were investigated and islet perifusion was performed to evaluate the kinetics of insulin release.</p><p><b>RESULTS</b>The expression level of AT1R in the isolated islets from db/db mice was twice that of islets from db/m mice. The islets treated with Ad-siAT1R showed significantly decreased AT1R mRNA and protein levels and significantly increased expression of GLUT-2 (by 190%) and GCK (by 121%) compared to those treated with Ad-siControl (P<0.05). In response to stimulation with 16.7 mmol/L glucose, the first-phase insulin secretion was impaired in both Ad-siControl group and mock infected group with the peak insulin levels only 1.8 times of the basal level; the first-phase insulin secretion was markedly improved in islets treated with Ad-siAT1R, with a peak insulin level reaching 2.8 times of the basal level.</p><p><b>CONCLUSIONS</b>In isolated islets of db/db mice, selective AT1R inhibition can restore the first phase insulin secretion by up-regulating GLUT-2 and GCK, which may be one of the potential mechanisms by which AT1R blockers improve insulin secretion function.</p>

Effects of ursolic acid on glucose metabolism, the polyol pathway and dyslipidemia in non-obese type 2 diabetic mice.

Ursolic acid (UA) is a pentacyclic triterpenoid compound that naturally occurs in fruits, leaves and flowers of medicinal herbs. This study investigated the dose-response efficacy of UA (0.01 and 0.05%) on glucose metabolism, the polyol pathway and dyslipidemia in streptozotocin/nicotinamide-induced diabetic mice. Supplement with both UA doses reduced fasting blood glucose and plasma triglyceride levels in non-obese type 2 diabetic mice. High-dose UA significantly lowered plasma free fatty acid, total cholesterol and VLDL-cholesterol levels compared with the diabetic control mice, while LDL-cholesterol levels were reduced with both doses. UA supplement effectively decreased hepatic glucose-6-phosphatase activity and increased glucokinase activity, the glucokinase/glucose-6-phosphatase ratio, GLUT2 mRNA levels and glycogen content compared with the diabetic control mice. UA supplement attenuated hyperglycemia-induced renal hypertrophy and histological changes. Renal aldose reductase activity was higher, whereas sorbitol dehydrogenase activity was lower in the diabetic control group than in the non-diabetic group. However, UA supplement reversed the biochemical changes in polyol pathway to normal values. These results demonstrated that low-dose UA had preventive potency for diabetic renal complications, which could be mediated by changes in hepatic glucose metabolism and the renal polyol pathway. High-dose UA was more effective anti-dyslipidemia therapy in non-obese type 2 diabetic mice.

Identification and Functional Characterization of P159L Mutation in HNF1B in a Family with Maturity-Onset Diabetes of the Young 5 (MODY5)

Mutation in HNF1B, the hepatocyte nuclear factor-1beta (HNF-1beta) gene, results in maturity-onset diabetes of the young (MODY) 5, which is characterized by gradual impairment of insulin secretion. However, the functional role of HNF-1beta in insulin secretion and glucose metabolism is not fully understood. We identified a family with early-onset diabetes that fulfilled the criteria of MODY. Sanger sequencing revealed that a heterozygous P159L (CCT to CTT in codon 159 in the DNA-binding domain) mutation in HNF1B was segregated according to the affected status. To investigate the functional consequences of this HNF1B mutation, we generated a P159L HNF1B construct. The wild-type and mutant HNF1B constructs were transfected into COS-7 cells in the presence of the promoter sequence of human glucose transporter type 2 (GLUT2). The luciferase reporter assay revealed that P159L HNF1B had decreased transcriptional activity compared to wild-type (p < 0.05). Electrophoretic mobility shift assay showed reduced DNA binding activity of P159L HNF1B. In the MIN6 pancreatic beta-cell line, overexpression of the P159L mutant was significantly associated with decreased mRNA levels of GLUT2 compared to wild-type (p < 0.05). However, INS expression was not different between the wild-type and mutant HNF1B constructs. These findings suggests that the impaired insulin secretion in this family with the P159L HNF1B mutation may be related to altered GLUT2 expression in beta-cells rather than decreased insulin gene expression. In conclusion, we have identified a Korean family with an HNF1B mutation and characterized its effect on the pathogenesis of diabetes.

Fanconi-Bickel syndrome versus osteogenesis imperfeeta: An Iranian case with a novel mutation in glucose transporter 2 gene, and review of literature.

Fanconi-Bickel syndrome is an extremely rare hereditary metabolic disease, characterized by hepatomegaly due to glycogen storage, refractory hypophosphatemic rickets, marked growth retardation and proximal renal tubular acidosis. Recurrent bone fractures are one of the hallmark findings. It is a single gene disorder; the responsible gene belongs to the facilitative glucose transporters 2 (GLUT2) family gene or (SLC2A2) mapped to the q26.1-26.3 locus on chromosome 3, and encodes the GLUT protein 2. This protein is expressed in pancreatic ί-cells, hepatocytes, renal tubules, and intestinal mucosa. Several mutations in the GLUT2 gene have been reported in different ethnicities. Herein we report an Iranian girl with a missed diagnosis of osteogenesis imperfecta. She was referred with the history of frequent fractures, and severe motor delay and was suspected to osteogenesis imperfecta. Following the case we detected refractory rickets instead of OI, sever growth failure, proximal renal tubulopathy and RTA, and enlarged kidneys, progressive hepatomegaly, and GSD on liver biopsy. Glucose and galactose tolerance tests confirmed abnormal carbohydrate metabolism. Molecular analysis on GLUT2 gene revealed a homozygous novel mutation in exon 5; it was 15 nucleotide deletion and 7 nucleotide insertion and caused a frame shift mutation, produced a premature truncated protein (P.A229QFsX19). This mutation has not been reported before in the relevant literature.

A Case of Fanconi-Bickel Syndrome with Mild Clinical Signs / 대한내과학회지

Fanconi-Bickel syndrome is a rare autosomal recessive disorder caused by a mutation in the facilitative glucose transporter 2 gene (GLUT2 or SLC2A2 gene) that codes for the glucose transporter protein 2 expressed in hepatocytes, pancreatic beta-cells, enterocytes, and renal tubular cells. Mutation of this gene leads to defective carbohydrate metabolism, hepatomegaly, glucose intolerance, proximal renal tubular dysfunction, and hypophosphatemic rickets. We report a case of Fanconi-Bickel syndrome in an 18-year-old man who presented due to renal glycosuria; a mutation was identified in the GLUT2 gene (c.482C > A + c.1556G > A). To the best of our knowledge, unlike previous reports of Fanconi-Bickel syndrome, this case was relatively unusual in that it caused only mild clinical signs.

Effect of sijunzi decoction on the intestinal glucose absorption in model rats of Pi-qi deficiency syndrome: an experimental research / 中国中西医结合杂志

<p><b>OBJECTIVE</b>To observe the effect of Sijunzi Decoction (SD) on the intestinal absorption of glucose in model rats of Pi-qi deficiency syndrome (PQDS).</p><p><b>METHODS</b>PQDS rat model was established by subcutaneous injection of reserpine from the neck. The body weight and urine D-xylose excretion rates were measured. The glucose uptake rate was measured by jejunum perfusion. The intestinal mucosa was collected. The glucose transporter-2 (GLUT2) protein and mRNA expression levels were detected.</p><p><b>RESULTS</b>Compared with the normal control group, the body weight and D-xylose excretion rates decreased in the model group. Meanwhile, the glucose uptake and GLUT2 protein and mRNA expression levels decreased in the model group. The aforesaid indices were improved in the SD group.</p><p><b>CONCLUSION</b>SD could promote the recovery of glucose uptake in the small intestine of reserpine induced PQDS rats.</p>

Hypoglycemic effect of Octomeles sumatrana aqueous extract in streptozotocin-induced diabetic rats and its molecular mechanisms

OBJECTIVE@#To investigate the hypoglycemic effect of the aqueous extract of Octomeles sumatrana (O. sumatrana) (OS) in streptozotocin-induced diabetic rats (STZ) and its molecular mechanisms.@*METHODS@#Diabetes was induced by intraperitoneal (i.p.) injection of streptozotocin (55 mg/kg) in to male Sprague-Dawley rats. Rats were divided into six different groups; normal control rats were not induced with STZ and served as reference, STZ diabetic control rats were given normal saline. Three groups were treated with OS aqueous extract at 0.2, 0.3 and 0.5 g/kg, orally twice daily continuously for 21 d. The fifth group was treated with glibenclamide (6 mg/kg) in aqueous solution orally continuously for 21 d. After completion of the treatment period, biochemical parameters and expression levels of glucose transporter 2 (Slc2a2), glucose-6-phosphatase (G6Pase) and phosphoenolpyruvate carboxykinase (PCK1) were determined in liver by quantitative real time PCR.@*RESULTS@#Administration of OS at different doses to STZ induced diabetic rats, resulted in significant decrease (P<0.05) in blood glucose level in a dose dependent manner by 36%, 48%, and 64% at doses of 0.2, 0.3 and 0.5 g/kg, respectively, in comparison to the STZ control values. Treatment with OS elicited an increase in the expression level of Slc2a2 gene but reduced the expression of G6Pase and PCK1 genes. Morefore, OS treated rats, showed significantly lower levels of serum alanine transaminase (ALT), aspartate aminotransferase (AST) and urea levels compared to STZ untreated rats. The extract at different doses elicited signs of recovery in body weight gain when compared to STZ diabetic controls although food and water consumption were significantly lower in treated groups compared to STZ diabetic control group.@*CONCLUSIONS@#O. sumatrana aqueous extract is beneficial for improvement of hyperglycemia by increasing gene expression of liver Slc2a2 and reducing expression of G6Pase and PCK1 genes in streptozotocin-induced diabetic rats.

In vitro potential of human bone marrow and umbilical cord vein mesenchymal stem cells to differentiate into insulin producing cells

Mesenchymal stem cells [MSCs] derived from bone marrow are multi potent cells that have the capacity to trans-different!ate into a variety of cell types including insulin islet cells. However the efficiency is low. The aim of this study is to explore the potential of Marrow and Umbilical cord vein MSC to differentiate into functional islet like cells in vitro. BM-MSCs and UC-MSCs were obtained from healthy donors and were cultured. MSCs with high CD90, CD73, CD105, CD44 and very low CD34 and CD45 expression were differentiated into Islet-like cells, under defined conditions. Insulin and c-peptide positive cells were evaluated with immune-florescence and insulin release after glucose challenge was tested by ELISA. QRT-PCR was done to detect expression of insulin, Glut2, Nkx6.1 and Nkx2.2 at mRNA level. Our results showed that only BM-MSC can be differentiated to insulin secreting cells. About 15.8% +/- 2.6 and 13.5% +/- 5.5 of cells were positive for insulin and c-peptide, respectively. Our results revealed that expression of Insulin and Glut2 upregulated 20 fold changes at mRNA level. However they were not functional when treated by different concentration of glucose. Our results showed that only Human BM-MSCs, compared to umbilical cord vein MSCs, are able to differentiate into insulin producing cells in vitro

[Effect of metformin on the Pdx-1 gene expression during development of mouse pancreas]

Metformin, an oral medicine used to treat type 2 diabetes, is a Glucagon-Like Peptide-1 [GLP-1] analogue, which has been demonstrated to stimulate the expression of Pancreatic duodenal homeobox-1 [Pdx-1], Insulin and Glucose transporter 2 [Glut-2] genes. In this study, the regulatory effect of metformin on beta cells function through the expression of Pdx-1, Insulin and Glut-2 genes was investigated. Pregnant C57BL/6 mice were randomly divided into 2 groups. Normal saline was given to the control group and the experimental group received 75, 150 and 250 mg/kg metformin daily by intraperitoneal injection from day 8.5 of pregnancy. Half the pregnant animals were then sacrificed by cervical dislocation or day 19.5 of pregnancy and the pancreases of embryos were dissected. The other half of pregnant animals were allowed to deliver their pups and the pancreases of one day old mice were dissected. The dissected pancreases were then used for assessment of Pdx-1, Insulin and Glut-2 genes expression by semi-quantitative RT-PCR method. Results showed that the administration of various doses of metformin caused no changes in the expression of Pdx-1, Insulin and Glut-2 genes compared to the control group [P>0.05]. The regulatory effect of metformin on beta cells function might not be related to the expression of Pdx-1, Insulin and Glut-2 genes and may be related to the expression of gloconeogenesis pathway genes

Influence of modified qianjin huanglian pill on pancreas of mice with insulin resistance / 中国中西医结合杂志

<p><b>OBJECTIVE</b>To investigate the influence of modified Qianjin Huanglian Pill (QJHL), a Chinese herbal compound, on pancreas in mice with monosodium L-glutamate (MSG) induced insulin resistance (IR) and its molecular mechanism.</p><p><b>METHODS</b>Controlled by rosiglitazone (Ros), the MSG indiced IR mice were treated with QJHL for 28 days. The laboratory indices were examined including fasting serum glucose (FSG), fasting serum insulin (FSI), insulin sensitivity index (ISI), and morphological changes of pancreas, and levels of insulin receptor (InsR), insulin receptor substrate (IRS1/2) and glucose transporter (GLUT2) mRNA expression in pancreas tissue were determined by the reverse transcriptase polymerase chain reaction (RT-PCR).</p><p><b>RESULTS</b>As compared with the model group, the level of FSG was lower (P < 0.01) and ISI was higher (P < 0.05) after treatment in the QJHL treated group, with pancreatic islet hyperplasia and hypertrophy ameliorated significantly (P < 0.01). And these changes were similar to those in the Ros treated group (P > 0.05). Moreover, the level of GLUT2 mRNA expression in pancreas of the QJHL group increased significantly (P < 0.01), while it was unchanged in the Ros group.</p><p><b>CONCLUSION</b>QJHL could reduce IR, ameliorate pathological changes of pancreas, which is possibly related with its action on increasing GLUT2 mRNA expression in the pancreas tissue.</p>

Effects of pentoxifylline on hepatic nuclear factor-kappa B signaling pathway and insulin resistance in nonalcoholic steatohepatitis rats induced by fat-rich diet / 中华肝脏病杂志

<p><b>OBJECTIVE</b>To explore the effects of pentoxifylline (PTX) on nuclear factor-kappa B (NF-kB) signaling pathway, insulin receptor substrates (IRSs) and glucose transporter 2 (GLUT2) expressions in livers in a rat model of nonalcoholic steatohepatitis (NASH).</p><p><b>METHODS</b>Rats fed a fat-rich diet for 4 weeks were randomly allocated into two groups; the model group rats (n = 12) were fed a high-fat diet alone and the PTX group rats (n = 12) were fed a high-fat diet plus PTX (100 mg x kg(-1)/d(-1)) in drinking water. Meanwhile, rats (n = 6) fed a standard diet from the start served as controls. All the rats were sacrificed at the end of the 24th week. Hepatic NF-kappaB binding activity was measured by electrophoretic mobility shift assay (EMSA). The expression of tumor necrosis factor (TNF) alpha and inhibitor kappaB (IkappaBalpha) proteins in livers were determined by Western blot. Messenger RNA of IRS-1, IRS-2 and GLUT2 expressions were examined by RT-PCR.</p><p><b>RESULTS</b>NF-kappaB binding activity was higher in the model group than that in the controls, while it was lower in the PTX group compared with that in the model group. The expression of TNFalpha protein was markedly increased in the model group (vs. the control group) but decreased in the PTX group (vs. the model group). The expression of IkappaBaalpha protein was decreased in the model group (vs. the control group) but increased in the PTX group (vs. the model group) to a certain extent. IRS-2 mRNA expression was markedly increased in the model group, and significantly decreased in the PTX group when compared with the model group (P less than 0.01).</p><p><b>CONCLUSIONS</b>PTX could influence NF-kappaB signaling pathway and IRS expression in livers of NASH rats, which might be involved in the improvement of hepatic insulin resistance.</p>