A Rapid and Sensitive Determination of Histamine in Mast Cells Using a Didansyl Derivatization Method.

BACKGROUND: Mast cells play a central role in allergic responses such as food allergy, asthma, allergic rhinitis, and allergic conjunctivitis. Symptoms in the early phase of these allergic diseases are primarily caused by histamine. However, due to the high histidine content in the cytosol and low histamine content in secretory granules, separating and quantifying histamine from histidine is often difficult. OBJECTIVES: We studied a method for rapid and sensitive quantitation of mast cell-derived histamine and evaluated its application to allergic disease research. METHODS: Bone marrow-derived mouse mast cells (BMMCs) were employed in this study. IgE-sensitized BMMCs were activated by FcεRI cross-linking. After activation, both the histamine released to the supernatant and histamine remaining in BMMCs were didansylated and then analyzed by high-performance liquid chromatography with fluorescence detection (HPLC-FD). Didansyl histamine was synthesized as a standard material. RESULTS: Synthetic didansyl histamine was detected by HPLC-FD with a peak retention time of 18.5 min. Very high linearity of the standard curve was maintained at concentrations of 10 pg/µL or less when the didansyl histamine method was used. This method enables detection of histamine released from 1 × 105 BMMCs. In addition, the histamine concentration in the supernatant due to spontaneous release was also determined. Finally, the ratio of histamine release was highly correlated with the degranulation ratio. CONCLUSION: These results indicate that the proposed method using didansylated histamine to determine mast cell-derived histamine is highly useful for allergy research applications.

Both glimepiride and high-dose metformin are important for sustained glucose lowering in Japanese type 2 diabetes patients on glimepiride-sitagliptin-metformin therapy: subanalysis of a single-center, open-label, randomized study.

BACKGROUND: In a previous single-center, open-label randomized 3-month study of triple oral antidiabetes drug (OAD) therapy, we investigated factors affecting the glycemic control afforded by sitagliptin, high-dose metformin, and low-dose glimepiride. Patients were prospectively assigned to either Group 1 (50% reduction in metformin) or Group 2 (discontinuation of glimepiride) and compared. The results showed that the glycated hemoglobin (HbA1c) levels of patients in Group 2 deteriorated more than those in Group 1, whereas HbA1c levels were maintained in some patients in both groups. MATERIALS AND METHODS: To determine the factors associated with maintenance of HbA1c under this triple OAD regimen, data from the prospective study were further analyzed. RESULTS: In both Groups 1 and 2, the baseline HbA1c level was higher in patients with HbA1c ≥7.0% after 3 months of treatment than those with an HbA1c level of <7.0%. A generalized linear model revealed that high-dose metformin was associated with a deterioration of HbA1c levels in Group 2. CONCLUSIONS: Together, the findings indicate that glimepiride and high-dose metformin are important for sustained glycemic control in triple OAD therapy with sitagliptin, metformin, and sulfonylurea.

Glimepiride strongly enhances the glucose-lowering effect in triple oral antidiabetes therapy with sitagliptin and metformin for Japanese patients with type 2 diabetes mellitus.

BACKGROUND: After approval of sitagliptin and >750 mg of metformin in Japan, a triple oral antidiabetes drug (OAD) regimen including sulfonylurea, metformin, and sitagliptin was sometimes described. However, in the real world of clinical practice, the daily dose of sulfonylurea tended to be decreased according to the warning from the Japan Diabetes Society for avoiding hypoglycemia, instead of increasing the dose of metformin for maintaining hemoglobin A1c (HbA1c) levels with this regimen. This study examined the impact of either a small dose of glimepiride or a high dose of metformin on HbA1c in triple OAD therapy with sitagliptin in a 3-month, single-center, open-label, randomized controlled study. SUBJECTS AND METHODS: Fifty-six type 2 diabetes mellitus patients who had been treated with 50 mg of sitagliptin, ≥ 1,000 mg of metformin, and ≤ 1 mg of glimepiride with an HbA1c level of <7.4% during at least 3 months were enrolled in the study. The patients were randomly assigned to two treatment groups who either received a 50% reduced dose of metformin (n = 27) or discontinued glimepiride (n = 29), while sitagliptin administration continued in both groups. Twenty-six patients from the reduced metformin group and 27 patients from the discontinued glimepiride group completed the study. RESULTS: Significantly greater changes were observed in HbA1c and glycated albumin levels in patients who discontinued glimepiride than in patients with a 50% reduced metformin dose, during the 2-3-month period than in the 1-3-month period. CONCLUSIONS: Glimepiride is important for good glycemic control in triple OAD therapy with sitaglitpin and metformin. This regimen may be useful for those patients who do not achieve satisfactory glycemic control with dual combination therapy.

Combination Therapy with a Dipeptidyl Peptidase-4 Inhibitor, Sulfonylurea, and Metformin Markedly Improves HbA1c Levels in Japanese Patients with Type 2 Diabetes Mellitus.

Combination therapy with a dipeptidyl peptidase (DPP)-4 inhibitor and metformin or sulfonylurea results in substantial and additive glucose-lowering effects in patients with type 2 diabetes mellitus (T2DM). However, it is not known whether triple combination therapy with a DPP-4 inhibitor, metformin, and sulfonylurea has greater additive effects or synergic effects. In the present report, we investigated the effect of addition of sitagliptin, the first-in-class DPP-4 inhibitor, to ongoing metformin and sulfonylurea therapy in three female Japanese patients with T2DM who refused insulin therapy. Combined treatment with all three drugs resulted in marked improvements in HbA1c. In the first patient, HbA1c levels decreased from 11.1% to 6.1% after the addition of sitagliptin to metformin 1000 mg, glibenclamide, and miglitol, even though the dose of glibenclamide was decreased. HbA1c levels decreased similarly in the second patient, who was being treated with metformin and glibenclamide, from 7.9% to 6.0% after addition of sitagliptin and an increase in metformin to 2250 mg; this patient ceased glibenclamide because of hypoglycemia and instead was started on low-dose glimepiride. In the third patient, HbA1c levels decreased from 8.6% to 7.1% after addition of glimepiride to ongoing sitagliptin and metformin therapy. All three patients had refused insulin therapy, despite the fact that ongoing combination therapy had failed to achieve satisfactory glycemic control. Based on these results, it is likely that the addition of sitagliptin to metformin and at least a small dose of sulfonylurea may be effective in reducing HbA1c levels without weight gain. This triple combination therapy may prove useful in at least some patients who need initiation of insulin therapy.

Prostanoid EP1 receptor antagonist reduces blood-brain barrier leakage after cerebral ischemia.

Disruption of the blood-brain barrier (BBB) after cerebral ischemia is considered to be the initial step in the development of brain injuries, and an increase in the tyrosine phosphorylation of the tight junctional protein occludin has been shown to cause an increase in BBB permeability. Prostaglandin E2 (PGE2) appears to be associated with both toxic and protective effects on neuronal survival in vitro. However, it remains to be determined whether the prostanoid EP1 receptor is involved in the disruption of the BBB after cerebral ischemia. So we examined the effect of a prostanoid EP1 receptor antagonist, SC51089, on BBB leakage and tyrosine phosphorylation of occludin after cerebral ischemia. We demonstrated that SC51089 attenuated the increase in the tyrosine phosphorylation of occludin in isolated brain capillaries, which was coincident with a decrease in BBB leakage. These results suggest that the prostanoid EP1 receptor is involved in the tyrosine phosphorylation of occludin at tight junction, which may lead to disruption of the BBB and be linked to the development of cerebral infarctions.