Periodontal infection and dyslipidemia in type 2 diabetics: association with increased HMG-CoA reductase expression.

Recent studies have suggested that the periodontal disease, chronic sub-clinical inflammation, is associated with atherosclerosis, although "cause or effect" relationship is still unclear. The aim of this study was to assess the association between the degree of periodontal infection and lipid profiles in diabetic subjects. Additionally, the association of such sub-clinical inflammation with HMG-CoA reductase gene expression was evaluated. One hundred and thirty-one non-obese relatively well-controlled Japanese type 2 diabetic patients were enrolled for the study. Although no significant association was observed between serum triglycerides, HLD-cholesterol and antibody titer to Porphyromonas gingivalis (Pg), the most predominant periodontal pathogen in adults, LDL-cholesterol was significantly associated with antibody titer to Pg. Concomitantly, the same works out to be true for total cholesterol. To understand the possible mechanisms underlying this association, we evaluated 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase gene expression in cultured HepG2 cells stimulated by either bacterial lipopolysaccharide (LPS) or inflammatory cytokines. Although Pg and E. coli LPS had no effect on HMG-CoA reductase gene expression, both tumor necrosis factor-alpha and interleukin-6 (IL-6), especially IL-6 at low concentration, markedly up-regulated HMG-CoA reductase gene expression. It can be concluded that Pg infection is associated with increased LDL-cholesterol in diabetic subjects, which may be accompanied by increased cholesterol synthesis by inflammatory cytokines.

Soluble TNF receptors and albuminuria in non-obese Japanese type 2 diabetic patients.

The aim of this study was to investigate the relationships between albuminuria and tumor necrosis factor (TNF)-alpha or soluble TNF receptors (sTNF-R1, sTNF-R2) in eighty-eight non-obese Japanese type 2 diabetic patients stratified into two groups according to albuminuria status-microalbuminuria or normoalbuminuria. Patients with microalbuminuria were older and had significantly higher concentrations of sTNF-R1 and sTNF-R2 than those with normoalbuminuria. There was, however, no significant difference in sex, diabetes duration, smoking, BMI, systolic and diastolic blood pressure, HbA (1c), serum creatinine, and lipid profile between the two groups. Although serum TNF-alpha was positively correlated to serum sTNF-R1 and sTNF-R2, serum TNF-alpha level did not differ with respect to albuminuria. Univariate regression analysis showed that urinary albumin concentration was positively correlated to age (r=0.380, p<0.001), serum creatinine (r=0.214, p<0.05) and concentrations of sTNF-R1 (r=0.364, p<0.001) and sTNF-R2 (r=0.342, p<0.005). Other variables, including TNF-alpha, were not associated with albuminuria. Multiple regression analyses showed that urinary albumin concentration was independently predicted by the level of sTNF-R1 (F=32.1), which explained 26.3% of the variability of urinary albumin concentration. From these results, it can be concluded that serum soluble TNF receptor is an important independent factor associated with albuminuria in non-obese Japanese type 2 diabetic patients.

Prevalence of periodontal bacterial infection in non-obese Japanese type 2 diabetic patients: relationship with C-reactive protein and albuminuria.

The aim of the present study was to investigate the relationship between periodontal bacteria infection ( Porphyromonas gingivalis, Actinobacillus actinomycetemcomitans, Prevotella intermedius) and C-reactive protein (CRP) and albuminuria in non-obese Japanese type 2 diabetic patients. One hundred and thirty-four non-obese Japanese type 2 diabetic patients without evidence of current acute illness including clinically significant acute infectious disease were enrolled into the study. The degree of periodontal bacterial infection was evaluated using IgG titer against Porphyromonas gingivalis, Actinobacillus actinomycetemcomitans, or Prevotella intermedius. The bacterial sonic extracts were used as antigens. High-sensitivity CRP (hCRP), glucose, glycosylated hemoglobin (HbA (1c)), and lipids were also measured after an overnight fast. Urinary albumin excretion rate as a ratio of urinary albumin and urinary creatinine was assessed in a morning spot urine sample using a commercial enzymatic immunoassay. The prevalence of Porphyromonas gingivalis infection was 52.2 % and that of Actinobacillus actinomycetemcomitans and Prevotella intermedius was 7.5 and 14.2 %, respectively. IgG titer against Porphyromonas gingivalis significantly correlated with CRP (r = 0.225, p < 0.001) and albuminuria (r = 0.185, p < 0.05), while IgG titer against Actinobacillus actinomycetemcomitans or Prevotella intermedius was not associated with either parameter. These results suggest that among periodontal bacteria, Porphyromonas gingivalis infection is associated with atherosclerosis in non-obese Japanese type 2 diabetic patients.

Relationship of regional adiposity to serum leptin level in nonobese Japanese type 2 diabetic male patients.

BACKGROUND: The aim of the present study was to investigate the relationships between serum leptin levels and regional adipose fat area, BMI, and the measures of variables including serum insulin in nonobese Japanese type 2 diabetic patients. METHODS: A total of 121 nonobese Japanese type 2 diabetic patients [aged 35 to 83 years, body mass index (BMI) (15.4 to 26.8 kg/m(2))] were studied. They all were male patients. In conjunction with serum leptin level, BMI, glycosylated hemoglobin (HbA(1c)), and fasting concentrations of plasma glucose and serum insulin and lipids (triglycerides, total and HDL cholesterol) were measured. RESULTS: Univariate regression analysis showed that serum leptin levels were positively correlated to subcutaneous (r=0.566, P<0.0001) and visceral (r=0.481, P<0.001) fat area in our diabetic patients. Furthermore, serum leptin levels were positively correlated to serum insulin (r=0.517, P<0.0001), BMI (r=0.428, P<0.0001), serum triglycerides (r=0.279, P<0.005), and age (r=0.225, P<0.05). There was, however, no relationship between serum leptin levels and measures of other variables including total and HDL cholesterol. Multiple regression analyses showed that serum leptin levels were predicted by subcutaneous fat area (F=5.92, P<0.0001) and serum insulin level (F=5.60, P<0.0001), which explained 29.0% of the variability of serum leptin concentrations in our nonobese Japanese type 2 diabetic male patients. Visceral fat area, BMI, serum triglycerides, and age, however, were not independently associated with serum leptin levels in our patients. CONCLUSIONS: These results indicate that serum leptin levels are reflective of subcutaneous fat area in nonobese Japanese type 2 diabetic male patients.

Human TSC-22 gene: no association with type 2 diabetes.

OBJECTIVE: In order to elucidate whether or not genetic variations of TSC-22 (TGF [transforming growth factor]-beta-stimulated clone 22), which was originally identified as a TGF-beta-responsive leucine zipper protein in murine osteoblastic cells, are associated with type 2 diabetes, the genomic organization of the human TSC-22 gene was determined and the association between its polymorphisms and type 2 diabetes was examined. RESULTS: The human TSC-22 gene spans approximately 5 kilobase pairs and is encoded in three exons. Two single nucleotide polymorphisms (SNPs) were identified in the coding region of the first exon, two other SNPs in the first intron, and one SNP in the putative promoter region. There were, however, no significant differences in the frequency of these polymorphisms between patients with type 2 diabetes and non-diabetic control subjects. CONCLUSION: It is unlikely that the TSC-22 gene is a locus responsible for type 2 diabetes.

Genomic variation in pancreatic ion channel genes in Japanese type 2 diabetic patients.

BACKGROUND: Many genetic diseases are caused by mutations in ion channel genes. Because type 2 diabetes is characterized by pancreatic beta-cell insensitivity to glucose, the genes responsible for glucose metabolism and calcium signaling in pancreatic beta-cells are candidate type 2 diabetes susceptibility genes. METHODS: We have examined genomic variations in two ion channel genes relevant to the molecular pathology of diabetes mellitus, the Kir6.2 subunit of the ATP-sensitive potassium channel gene and alpha(1D) subunit of the voltage-dependent calcium channel (VDCC) gene among Japanese type 2 diabetic patients. RESULTS: There are two alleles in the Kir6.2 gene: EI, glutamic acid at codon 23 and isoleucine at codon 337 and KV, lysine at codon 23 and valine at codon 337. The allelic frequencies of these polymorphisms are similar in type 2 diabetic patients and normal subjects. We also detected trinucleotide repeat polymorphisms in the amino terminus and the carboxyl terminal region of the alpha(1D) gene. Expansion of the ATG trinucleotide repeat from seven to eight was detected only in type 2 diabetic patients, but the frequency was low and was similar in type 2 diabetic patients and normal subjects. CONCLUSIONS: Although variations of the Kir6.2 and alpha(1D) genes are not associated with the development of common type 2 diabetes, further studies may determine the role of these genomic variations, especially those in the alpha(1D) VDCC gene, in the pathogenesis of certain subsets of type 2 diabetes, or as a co-factor in the polygenic disorder generally.

Activating transcription factor-2 is a positive regulator in CaM kinase IV-induced human insulin gene expression.

Insulin plays a crucial role in the regulation of glucose-homeostasis, and its synthesis is regulated by several stimuli. The transcription of the human insulin gene, enhanced by an elevated intracellular concentration of calcium ions, was completely blocked by Ca2+/calmodulin-dependent protein kinase inhibitor. The activity of the transcription factor activating transcription factor-2 (ATF-2), which binds to the cAMP responsive elements of the human insulin gene, was enhanced by Ca2+/calmodulin-dependent protein kinase IV (CaMKIV). Mutagenesis studies showed that Thr69, Thr71, and Thr73 of ATF-2 are all required for activation by CaMKIV. CaMKIV-induced ATF-2 transcriptional activity was not altered by activation of cJun NH2-terminal protein kinase (JNK) or p38 mitogen-activated protein (MAP) kinase. Furthermore, when transfected into rat primary cultured islets, ATF-2 enhanced glucose-induced insulin promoter activity, whereas cAMP response element-binding protein (CREB) repressed it. These results suggest a mechanism in which ATF-2 regulates insulin gene expression in pancreatic beta-cells, with the transcriptional activity of ATF-2 being increased by an elevated concentration of calcium ions.

Antioxidant alpha-tocopherol ameliorates glycemic control of GK rats, a model of type 2 diabetes.

We have shown recently that oxidative stress by chronic hyperglycemia damages the pancreatic beta-cells of GK rats, a model of non-obese type 2 diabetes, which may worsen diabetic condition and suggested the administration of antioxidants as a supportive therapy. To determine if natural antioxidant alpha-tocopherol (vitamin E) has beneficial effects on the glycemic control of type 2 diabetes, GK rats were fed a diet containing 0, 20 or 500 mg/kg diet alpha-tocopherol. Intraperitoneal glucose tolerance test revealed a significant increment of insulin secretion at 30 min and a significant decrement of blood glucose levels at 30 and 120 min after glucose loading in the GK rats fed with high alpha-tocopherol diet. The levels of glycated hemoglobin A1c, an indicator of glycemic control, were also reduced. Vitamin E supplementation clearly ameliorated diabetic control of GK rats, suggesting the importance of not only dietary supplementation of natural antioxidants but also other antioxidative intervention as a supportive therapy of type 2 diabetic patients.

Glucose intolerance caused by a defect in the entero-insular axis: a study in gastric inhibitory polypeptide receptor knockout mice.

Mice with a targeted mutation of the gastric inhibitory polypeptide (GIP) receptor gene (GIPR) were generated to determine the role of GIP as a mediator of signals from the gut to pancreatic beta cells. GIPR-/- mice have higher blood glucose levels with impaired initial insulin response after oral glucose load. Although blood glucose levels after meal ingestion are not increased by high-fat diet in GIPR+/+ mice because of compensatory higher insulin secretion, they are significantly increased in GIPR-/- mice because of the lack of such enhancement. Accordingly, early insulin secretion mediated by GIP determines glucose tolerance after oral glucose load in vivo, and because GIP plays an important role in the compensatory enhancement of insulin secretion produced by a high insulin demand, a defect in this entero-insular axis may contribute to the pathogenesis of diabetes.

The MH1 domains of smad2 and smad3 are involved in the regulation of the ALK7 signals.

The biological responses of the transforming growth factor beta (TGF-beta) superfamily are induced by activation of a receptor complex and Smad proteins. We surveyed the TGF-beta superfamily receptors using the degenerate PCR strategy, and found activin receptor-like kinase 7 (ALK7) to be abundantly expressed in fetal rat pancreatic islets. ALK7 is also expressed in adult rat islets and pancreatic beta-cell-derived MIN6 cells. The constitutively active form of ALK7, ALK7(T194D), activated Smad3 and a chimeric Smad protein, Smad3-2, containing the MH1 domain of Smad3 and the MH2 domain of Smad2, and translocated them to nuclei and then induced activation of the human PAI-1 promoter. However, neither Smad2 nor Smad2-3 protein, containing the MH1 domain of Smad2 and the MH2 domain of Smad3 were activated. These results indicate that the ALK7 signal regulates nuclear localization and activation of Smad2 and Smad3, and the MH1 domain of Smad2 has inhibitory effects on the nuclear localization.

Transcriptional repressors are increased in pancreatic islets of type 2 diabetic rats.

To further clarify the mechanism of impaired insulin gene transcription in the diabetic state, we investigated the expression and function of the transcriptional repressor CREM (CRE modulator) in rat pancreatic islets. The CREM gene generates both transcriptional activators and repressors by alternative splicing and an intronic promoter. We isolated a novel alternatively spliced CREM isoform, CREM-17X, which efficiently represses insulin gene transcription, in addition to the three previously reported repressors. We also compared mRNA levels of insulin and the CREM repressors in pancreatic islets of Wistar and GK (Goto-Kakizaki) rats, the well-characterized spontaneous animal model of type 2 diabetes. The CREM repressor levels are increased, and the expression of insulin mRNA is decreased in GK rats, suggesting that increased CREM repressor expression in pancreatic islets could contribute to the decreased insulin gene transcription that results in impaired insulin secretion in type 2 diabetes.

Gastric inhibitory polypeptide activates MAP kinase through the wortmannin-sensitive and -insensitive pathways.

The signal transduction pathways of a cloned human gastric inhibitory polypeptide (GIP) receptor have been investigated in CHO cells stably expressing this receptor. Exposure of GIP receptor expressing cells to GIP significantly increased MAP kinase activity. Time course analysis showed that a rapid and marked increase in MAP kinase activation was detected and that this activation reached maximal levels 10 min after the addition of GIP. Dose-response analysis showed that GIP activated MAP kinase activity in a dose-dependent manner with an ED50 value of 5.9 x 10(-10) M of GIP. Wortmannin, a potent inhibitor of phosphatidylinositol 3-kinase (PI3-kinase), partially inhibited GIP-induced MAP kinase activation, suggesting that GIP activates MAP kinase through two different, wortmannin-sensitive and -insensitive pathways. It has been demonstrated that in CHO cells cAMP attenuates MAP kinase activity by inhibiting Raf-1. Since GIP elevates intracellular cAMP, we examined the effects of cAMP on MAP kinase activation. Interestingly, forskolin, which increased intracellular cAMP levels, significantly inhibited MAP kinase activation by GIP, but did not affect MAP kinase activation by GIP in the presence of wortmannin, suggesting that the wortmannin-sensitive pathway activates an MAP kinase cascade at or above the level of Raf-1 and that the wortmannin-insensitive pathway activates an MAP kinase cascade below the level of Raf-1. These findings demonstrate that the GIP receptor is linked to the MAP kinase cascade via at least two different pathways.