One-year real-life efficacy of sitagliptin revealed importance of concomitant pioglitazone use in Japanese patients with type 2 diabetes mellitus.

AIMS: Dipeptidyl-peptidase 4 inhibitors have become one of the most popular antidiabetic drugs. However, what kind of combinations with other drugs were advantageous was not known. Here, we tried to elucidate it in a real-life clinical setting. METHODS: We retrospectively studied efficacies of sitagliptin in 87 Japanese patients with type 2 diabetes mellitus for 52 weeks. We divided subjects into excellent, effective and unresponsive subgroups according to glycemic responses to sitagliptin. RESULTS: In the excellent and effective groups the minimum HbA1c values were attained at 16 weeks while HbA1c levels in the unresponsive group kept increasing during the study period. There was a significant difference in the baseline HbA1c values between the excellent and unresponsive groups (p=0.02). Interestingly, the mean doses of pioglitazone were highest in the excellent group and lowest in the unresponsive group (p=0.02). When we compared the effective and unresponsive groups, the mean doses of sulfonylureas were constantly higher in the effective group than in the unresponsive group (p=0.05). CONCLUSIONS: These data suggest that the baseline HbA1c value can be a factor that predicts the extent of HbA1c reduction and reveal a possibility that the concomitant use of pioglitazone augments glycemic responsiveness to sitagliptin.

Critical promoter region for statin-induced human endothelial nitric oxide synthase (eNOS) transcription in EA.hy926 cells.

AIM: Statins have many anti-atherogenic effects apart from reducing the serum level of low density lipoprotein cholesterol (LDL-C). For instance, statins can enhance the expression of endothelial nitric oxide synthase (eNOS), at least partly by upregulating its transcription. Although it has been reported that -786 T/C polymorphism of the promoter region has an important influence on statininduced transcription of the human eNOS gene, much remains unclear about statin-induced eNOS transcription. We tried to identify other statin-responsive promoter regions. METHODS: A human endothelial cell line (EA.hy926 cells) was treated with pitavastatin, atorvastatin, or fluvastatin, after which eNOS mRNA levels were assessed by quantitative real-time RT-PCR. EA.hy926 cells were also transiently transfected with luciferase reporter genes driven by various lengths of the human eNOS promoter and were treated with statins before luciferase activity was measured. RESULTS: Statin treatment increased eNOS mRNA levels in EA.hy926 cells. In addition, cells transfected with the reporter gene driven by the eNOS promoter fragment starting from position -740 exhibited a pitavastatin-induced increase of luciferase activity, which was not observed in cells transfected with the reporter gene driven by the fragment starting from -727. Similar results were also obtained with atorvastatin and fluvastatin. CONCLUSIONS: Statins enhanced eNOS expression in EA.hy926 cells, at least partly by inducing its transcription. Although a statin-responsive sequence that could function even in a heterologous promoter was not precisely identified, the region of the human eNOS promoter around position -730 seems to be critical for statin-induced transcriptional activation.

Serum from methimazole-treated patients induces activation of aryl hydrocarbon receptor, a transcription factor that binds to dioxin-response elements.

BACKGROUND: The aryl hydrocarbon receptor (AhR) is a transcription factor that is activated by xenobiotic substances such as dioxin. After activation, it binds to dioxin response elements of DNA, thereby inducing transcription of a variety of xenobiotic metabolizing enzymes. To investigate whether AhR-activating substances accumulate in patients with endocrine disorders, we tested serum samples for AhR-stimulating activity. METHODS: Serum AhR-stimulating activity was evaluated by exposing the HepG2 cells transiently transfected with an AhR-responsive reporter plasmid to serum samples. On the basis of preliminary findings that implicated methimazole (MMI), wild-type and AhR-null mice were treated with MMI, and their plasma AhR-stimulating activities and thyroxine levels were quantified. RESULTS: In 28 randomly chosen patients, 7 out of 10 Graves' disease patients exhibited increased serum AhR-stimulating activity. The increased activity did not correlate with thyroid hormone status. However, we hypothesized that it might be caused by MMI. Subsequent analyses revealed that in 25 of 26 MMI-treated Graves' patients, serum samples collected after the MMI treatment had significantly higher AhR-stimulating activity compared to samples obtained when the same patients were not on MMI. By contrast, serum AhR-stimulating activity was unchanged in samples from the seven patients on propylthiouracil (PTU) compared to serum taken before the PTU treatment. In vitro experiments demonstrated that an MMI metabolite 3-methyl-2-thiohydantoin, but not MMI, activated AhR. MMI increased plasma AhR-stimulating activities and reduced plasma thyroxine concentrations, in both wild-type and AhR-deficient mice. CONCLUSIONS: Graves' patients taking MMI have increased serum AhR-stimulating activity, which is unrelated to thyroid hormone status, but correlates with MMI treatment. The AhR activation is likely caused by 3-methyl-2-thiohydantoin. Further studies are required to determine the potency of 3-methyl-2-thiohydantoin as an AhR activator and the significance of the differences between MMI and PTU observed in this study.