Improved diabetic syndrome in C57BL/KsJ-db/db mice by oral administration of the Na(+)-glucose cotransporter inhibitor T-1095

Abstract

1. The therapeutic effects of an orally active inhibitor of Na(+)-glucose cotransporter (SGLT), T-1095 (a derivative of phlorizin; 3-(benzo[b]furan-5-yl)-2',6'-dihydroxy-4'-methylpropiophenone 2'-O-(6-O-methoxycarbonyl-beta-D-glycopyranoside)) were examined in C57BL/KsJ-db/db (db/db) mice, a genetic animal model of obese type 2 diabetes. 2. The higher renal SGLT activity in db/db mice than normoglycaemic C57BL/KsJ-db/+m (db/+m) mice may support the rationale for using an SGLT inhibitor in the treatment regimen for type 2 diabetes. Both T-1095 and its metabolite, T-1095A, which had approximately 10 times more potency, effectively inhibited renal SGLT activity of these mice in vitro. 3. Single oral administration of T-1095 (10, 30, 100 mg kg(-1), p.o.) to db/db mice caused a dose-dependent reduction in blood glucose levels and a concomitant increase in glucose excretion into urine. In contrast, T-1095 only slightly affected blood glucose levels in db/+m mice. 4. Chronic administration of T-1095 (0.1% w w(-1) pellet chow, for 12 weeks) decreased blood glucose and haemoglobin A(1C) levels, and improved glucose intolerance in db/db mice. The age-related decrease in plasma insulin levels was markedly inhibited and there was a 2.5 fold increase of insulin content in the pancreas of T-1095-treated db/db mice. Food consumption was not changed, while impaired body weight gain was ameliorated by T-1095 treatment. 5. Both the development of albuminuria and the expansion of glomerular mesangial area in db/db mice were significantly suppressed by chronic T-1095 treatment, indicating the prevention of the progression of diabetic nephropathy. 6. These results demonstrate that the SGLT inhibitor T-1095 is able to improve the metabolic abnormalities and inhibit the development of diabetic complications in db/db mice. Thus, T-1095 can be used for therapy of type 2 diabetic patients.

Figure 1

Effect of T-1095, T-1095A and phlorizin on renal SGLT activity of db/+m (a) and db/db mice (b) in vitro. SGLT activity was assayed as Na⁺-dependent [³H]-glucose uptake (0.1 mM) in BBMV prepared from the renal cortex. Symbols represent mean values and vertical lines show s.e.mean of three observations.

Figure 2

Effect of single oral administration of T-1095 on blood glucose levels in db/+m (a) and db/db mice (b). T-1095 (10, 30 and 100 mg kg⁻¹) was orally administered and changes in blood glucose were monitored for 24 h. Symbols represent mean values and vertical lines show s.e.mean (n=5). ^*P<0.05, ^**P<0.01 versus respective control.

Figure 3

Effects of chronic T-1095 treatment on blood glucose (a), HbA_1C (b), plasma insulin (c) levels and body wt. (d) in db/db mice. T-1095 (0.03 and 0.10% in diet) was given for 12 weeks. Blood glucose, HbA_1C, plasma insulin levels and body wt. were monitored periodically. Symbols represent mean values and vertical lines show s.e.mean (n=8). ^##P<0.01 versus db/+m mice. ^*P<0.05, ^**P<0.01 versus control.

Figure 4

Effects of chronic T-1095 treatment on glucose intolerance in db/db mice. T-1095 (0.03 and 0.10% in diet) was given for 12 weeks. Mice were subjected to an OGTT after an overnight fast. Following baseline blood glucose determination, glucose (1 g kg⁻¹ body wt.) was orally administered and blood glucose levels were evaluated through 120 min. Symbols represent mean values and vertical lines show s.e.mean (n=8). ^##P<0.01 versus db/+m mice. ^*P<0.05, ^**P<0.01 versus control.

Figure 5

Effect of chronic T-1095 treatment on urine volume (a), urinary glucose (b) and albumin (c) excretion in db/db mice. T-1095 (0.03 and 0.10% in diet) was given for 12 weeks. Urine was collected using metabolic cages and urine volume, urinary glucose and albumin excretion were monitored periodically. Symbols represent mean values and vertical lines show s.e.mean (n=8). ^##P<0.01 versus db/+m mice. ^*P<0.05, ^**P<0.01 versus control.

Figure 6

Representative microphotographs of glomeruli from db/+m mice (a), control db/db mice (b), and the high dose of T-1095-treated db/db mice (c). Expansion of the PAS-positive glomerular mesangial area is apparent in the control db/db mice compared with the db/+m mice. There is minimal mesangial widening in the T-1095-treated mice. Scale bar=10 μm.