Fasting tests of insulin secretion and sensitivity predict future prediabetes in Japanese with normal glucose tolerance.

UNLABELLED: Aims/Introduction: Reduced insulin sensitivity and secretion are important in the pathogenesis of type 2 diabetes. Their relationships to prediabetes, impaired glucose tolerance (IGT) and impaired fasting glucose (IFG) have been previously studied with the oral glucose tolerance test (OGTT). We investigated whether or not baseline measures of insulin secretion and sensitivity obtained from fasting blood specimens were related to the development of prediabetes and how these measures compared with those based on the OGTT. MATERIALS AND METHODS: In 152 Japanese subjects with normal glucose tolerance, we measured baseline plasma glucose and insulin after an overnight fast and during a 75 g OGTT, insulin resistance index (homeostasis model assessment [HOMA-IR]), and insulin secretion (insulinogenic index [30 min insulin - fasting insulin] ÷ [30 min glucose - fasting glucose] or HOMA-ß). RESULTS: At a 5-6 year (mean 5.7 years) follow-up examination, we confirmed 36 cases of prediabetes. After adjusting for age, sex, family history of diabetes, body mass index, and 2-h plasma glucose, the odds ratio comparing the lowest tertile (≤0.82) of insulinogenic index with the highest tertile (≥1.43) was 6.98 (95% confidence interval, 1.96-24.85) and was 10.72 (2.08-55.3) comparing the lowest tertile (≤76.3) of HOMA-ß with the highest tertile (≥122.1), whereas the respective odds ratios of HOMA-IR were 3.74 (1.03-13.57) and 10.89 (1.93-61.41) comparing the highest tertile (≥1.95) with the lowest tertile (≤1.25). CONCLUSIONS: Lower insulin secretion and sensitivity are independent risk factors for prediabetes. Clinically practical identification of those at risk for prediabetes is obtainable from HOMA-ß and HOMA-IR, both of which are measured in fasting state. (J Diabetes Invest, doi: 10.1111.j.2040-1124.2010.00041.x, 2010).

Genetic variations and haplotype structures of transcriptional factor Nrf2 and its cytosolic reservoir protein Keap1 in Japanese.

Transcriptional factor Nrf2 and its cytosolic reservoir protein Keap1 play important roles in induction of the expression of genes for xenobiotic metabolism and disposition, many of which are involved in protection from oxidative stress. In this study, 5 NFE2L2 (encoding Nrf2) and 6 KEAP1 exons and their flanking introns were comprehensively screened for genetic variations in 84 Japanese subjects. As for NFE2L2, 14 genetic variations were found, including 9 novel ones: 7 were located in the 5'-flanking region, 1 in the 5'-untranslated region (5'-UTR), 3 (1 synonymous and 2 nonsynonymous) in the coding exons, 1 in the intron, and 2 in the 3'-UTR. Two novel nonsynonymous variations, 697C>T (Pro233Ser) and 1094G>T (Ser365Ile), were heterozygously found with allele frequencies of 0.012 and 0.006, respectively. Regarding KEAP1, 18 genetic variations were detected, including 13 novel ones: 2 were located in the 5'-flanking region, 4 in the coding exons (4 synonymous), 5 in the introns, 4 in the 3'-UTR, and 3 in the 3'-flanking region. Based on the linkage disequilibrium (LD) profiles, both genes were analyzed as single LD blocks, where 14 (NFE2L2) and 18 (KEAP1) haplotypes were inferred. Six (NFE2L2) and 5 (KEAP1) haplotypes were relatively prevalent (>or=0.03 frequencies) and accounted for >or=88% of the inferred haplotypes. Haplotype-tagging variations of each gene were identified to capture these prevalent haplotypes. These data would be fundamental and useful information for pharmacogenetic studies on Nrf2-regulated genes for xenobiotic metabolism and disposition.

Genetic variations of the ABC transporter gene ABCC3 in a Japanese population.

An ATP-binding cassette transporter, multidrug resistance-related protein 3 (MRP3), is encoded by the ABCC3 gene. The MRP3 protein is expressed in several tissues, and functions as an efflux transporter for conjugated as well as unconjugated substrates. In this study, the 31 ABCC3 exons and their flanking introns were comprehensively screened for genetic variations in 89 Japanese subjects. Forty-six genetic variations, including 21 novel ones, were found: 8 were located in the 5'-flanking region, 14 in the coding exons (8 synonymous and 6 nonsynonymous variations), and 24 in the introns. Of these 46 variations, five novel nonsynonymous variations, 2221C>T (Gln741Stop), 2395G>A (Val799Met), 2798_2799delAG (Gln933ArgfsX64), 3657C>A (Ser1219Arg), and 4217C>T (Thr1406Met), were found as heterozygous variations. The allele frequencies were 0.011 for Ser1219Arg and 0.006 for the other four variations. Gln741Stop induces a stop codon at codon 741. Gln933ArgfsX64 causes a frame-shift at codon 933, resulting in early termination at codon 997. Both variations result in loss of 6 transmembrane helices (from the 12th to 17th helices) in the C-terminus and all regions of nucleotide binding domain 2. Thus, both variant proteins are assumed to be inactive. These data provide fundamental and useful information for pharmacogenetic studies on MRP3-transported drugs in Japanese.

Genetic variations and haplotype structures of the ABC transporter gene ABCC1 in a Japanese population.

Multidrug resistance-related protein 1 (MRP1), an ATP-binding cassette transporter encoded by the ABCC1 gene, is expressed in many tissues, and functions as an efflux transporter for glutathione-, glucuronate- and sulfate-conjugates as well as unconjugated substrates. In this study, the 31 exons and their flanking introns of ABCC1 were comprehensively screened for genetic variations in 153 Japanese subjects to elucidate the linkage disequilibrium (LD) profiles and haplotype structures of ABCC1 that is necessary for pharmacogenetic studies of the substrate drugs. Eighty-six genetic variations including 31 novel ones were found: 1 in the 5'-flanking region, 1 in the 5'-untranslated region (UTR), 20 in the coding exons (9 synonymous and 11 nonsynonymous variations), 4 in the 3'-UTR, and 60 in the introns. Of these, eight novel nonsynonymous variations, 726G>T (Trp242Cys), 1199T>C (Ile400Thr), 1967G>C (Ser656Thr), 2530G>A (Gly844Ser), 3490G>A (Val1164Ile), 3550G>A (Glu1184Lys), 3901C>T (Arg1301Cys), and 4502A>G (Asp1501Gly), were detected with an allele frequency of 0.003. Based on the LD profiles, the analyzed regions of the gene were divided into five LD blocks (Blocks -1 and 1 to 4). The multiallelic repeat polymorphism in the 5'-UTR was defined as Block -1. For Blocks 1, 2, 3 and 4, 32, 23, 23 and 13 haplotypes were inferred, and 9, 7, 7 and 6 haplotypes commonly found on > or = 10 chromosomes accounted for > or = 91% of the inferred haplotypes in each block. Haplotype-tagging single nucleotide polymorphisms for each block were identified to capture the common haplotypes. This study would provide fundamental and useful information for the pharmacogenetic studies of MRP1-dependently effluxed drugs in Japanese.

Novel genetic variations and haplotypes of hepatocyte nuclear factor 4alpha (HNF4A) found in Japanese type II diabetic patients.

Thirty-nine single nucleotide variations, including 16 novel ones, were found in the 5' promoter region, all of the exons and their surrounding introns of HNF4A in 74 Japanese type II diabetic patients. The following novel variations were identified (based on the amino acid numbering of splicing variant 2): -208G>C in the 5' promoter region; 1154C>T (A385V) and 1193T>C (M398T) in the coding exons; 1580G>A, 1852G>T, 2180C>T, 2190G>A, and 2362_2380delAAGAATGGTGTGGGAGAGG in the 3'-untranslated region, and IVS1+231G>A, IVS2-83C>T, IVS3+50C>T, IVS3-54delC, IVS5+173_176delTTAG, IVS5-181_-180delAT, IVS8-106A>G, and IVS9-151A>C in the introns. The allele frequencies were 0.311 for 2362_2380delAAGAATGGTGTGGGAGAGG, 0.054 for 1580G>A, 0.047 for 1852G>T, 0.020 for IVS1+231G>A, 0.014 for IVS9-151A>C, and 0.007 for the other 11 variations. In addition, one known nonsynonymous single nucleotide polymorphism, 416C>T (T139I), was detected at a 0.007 frequency. Based on the linkage disequilibrium profiles, the region analyzed was divided into three blocks. Haplotype analysis determined/inferred 10, 16, and 12 haplotypes for block 1, 2, and 3, respectively. Our results on HNF4A variations and haplotypes would be useful for pharmacogenetic studies in Japanese.

Four novel defective alleles and comprehensive haplotype analysis of CYP2C9 in Japanese.

Genetic variations in cytochrome P450 2C9 (CYP2C9) are known to contribute to interindividual and interethnic variability in response to clinical drugs such as warfarin. In the present study, CYP2C9 from 263 Japanese subjects was resequenced, resulting in the discovery of 62 variations including 32 novel ones. In addition to the two known non-synonymous single nucleotide polymorphisms (SNPs), Ile359Leu (*3; allele frequency=0.030) and Leu90Pro (*13; 0.002), seven novel non-synonymous SNPs, Leu17Ile (0.002), Lys118ArgfsX9 (*25; 0.002), Thr130Arg (*26; 0.002), Arg150Leu (*27; 0.004), Gln214Leu (*28; 0.002), Pro279Thr (*29; 0.002) and Ala477Thr (*30; 0.002), were found. Functional characterization of novel alleles using a mammalian cell expression system in vitro revealed that *25 was a null allele and that *26, *28 and *30 were defective alleles. The *26 product showed a 90% decrease in the Vmax value but little change in the Km value towards diclofenac. Both *28 and *30 products showed two-fold higher Km values and three-fold lower Vmax values than the *1 allele, suggesting the importance of Gln214 and Ala477 for substrate recognition. Linkage disequilibrium and haplotype analyses were performed using the detected variations. Only five haplotypes (frequency >0.02) accounted for most (>87%) of the inferred haplotypes, and they were closely associated with the haplotypes of CYP2C19 in Japanese. Although the haplotype structure of CYP2C9 was rather simple in Japanese, the haplotype distribution was quite different from those previously reported in Caucasians and Africans. Taken together, novel defective alleles and detailed haplotype structures would be useful for determining metabolic phenotypes of CYP2C9 substrate drugs in Japanese and probably Asians.

Genetic variations and haplotypes of CYP2C19 in a Japanese population.

Forty-eight single nucleotide variations, including 27 novel ones, were found in the 5'- regulatory region, all of the exons and their surrounding introns of CYP2C19 in 253 Japanese subjects (134 diabetic patients and 119 healthy volunteers). Identified novel variations were as follows: -2772G>A, 2767_-2760delGGTGAACA, -2720T>C, -2547delG, -2545G>T, -2545_-2544 delGC, and -2040C>T in the enhancer region; -778C>T, -777G>A, -529G>C, -189C>A, and -185A>G in the promoter region; 151A>G (S51G), 481G>C (A161P), 986G>A (R329H), 1078G>A (D360N), and 1119C>T (D373D) in the exons, and IVS1+128T>A, IVS3+163G>A, IVS4+271A>G, IVS5-49A>G, IVS6-210C>T, IVS6-196T>A, IVS6-32T>A, IVS7+84G>A, IVS7-174C>T, and IVS8+64C>T in the introns. Since we found no significant differences in the variation frequencies between healthy volunteers and diabetic patients, the data for all subjects were treated as one group in further analysis. The allele frequencies were 0.265 for IVS6-196T>A, 0.045 for -2772G>A and -2720T>C, 0.024 for -2040C>T, 0.014 for IVS7-174C>T, 0.010 for -529G>C, 0.006 for IVS1+128T>A and 481G>C (A161P), 0.004 for -2767_-2760delGGTGAACA and IVS6-210C>T, and 0.002 for the other 17 variations. In addition, the two known nonsynonymous single nucleotide polymorphisms, 681G>A (splicing defect, (*)2 allele) and 636G>A (W212X; (*)3 allele) were detected at 0.267 and 0.128 frequencies, respectively. No variation was detected in the known binding sites for constitutive androstane receptor and glucocorticoid receptor. Linkage disequilibrium analysis showed several close linkages of variations throughout the gene. By using the variations, thirty-one haplotypes of CYP2C19 and their frequencies were estimated. Our results would provide fundamental and useful information for genotyping CYP2C19 in the Japanese and probably other Asian populations.

HMG-CoA reductase inhibitor decreases small dense low-density lipoprotein and remnant-like particle cholesterol in patients with type-2 diabetes.

Patients with type 2 diabetes are known to have abnormalities in their remnant metabolism and low density lipoprotein (LDL) subfraction pattern, with a preponderance of small dense LDL. The effects of pitavastatin, a newly synthesized 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitor, on lipoprotein profiles in patients with type 2 diabetes were determined. Thirty-three patients were treated with pitavastatin with a daily dose of 2 mg for 8 weeks. After treatment, triglyceride, total and LDL cholesterol were significantly reduced by 28.7 +/- 36.7%, 25.2 +/- 14.3% and 36.1 +/- 14.3%, respectively. Remnant-like particle cholesterol (RLP-C), an independent risk factor for CAD which is known to be elevated in diabetic patients, was also significantly reduced (-30.9 +/- 30.5%) by the treatment and this decrease correlated well with the decrease in triglyceride level. The proportion of small dense LDL, which is known for its atherogenisity, decreased from 29.9 +/- 26.2% to 19.7 +/- 22.7% and the mean LDL particle size significantly increased from 26.36 +/- 1.13 nm to 27.10 +/- 1.36 nm. Pitavastatin, which is known to improve triglyceride levels and cholesterol levels, also improves RLP-C level and LDL subfraction profiles, and this in turn may reduce the cardiovascular risk in patients with type 2 diabetes and dyslipidemia.