Mamoru Matsumoto

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

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‐β‐D‐glycopyranoside)) were examined in C57BL/KsJ‐db/db (db/db) mice, a genetic animal model of obese type 2 diabetes. 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. 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. Chronic administration of T‐1095 (0.1% w w−1 pellet chow, for 12 weeks) decreased blood glucose and haemoglobin A1C 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. 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. 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.

Enzymatic synthesis of poly-β-hydroxybutyrate inZoogloea ramigera

The enzyme activity synthesizing poly-β-hydroxybutyrate (PHB) was mainly localized in the PHB-containing particulate fraction ofZoogloea ramigera I-16-M, when it grew flocculatedly in a medium supplemented with glucose. On the other hand, the enzyme activity remained in the soluble fraction, when the bacterium grew dispersedly in a glucose-starved medium.The soluble PHB synthase activity became associated with the particulate fraction as PHB synthesis was initiated on the addition of glucose to the dispersed culture. Conversely, the enzyme activity was released from the PHB-containing granules to the soluble fraction when the flocculated culture was kept incubated without supplementing the medium with glucose.PHB synthase was also incorporated into the newly formed PHB fraction when partially purified soluble PHB synthase was incubated withd(-)-β-hydroxybutyryl CoA in vitro.Although attempts to solubilize the particulate enzyme were unsuccessful, and the soluble enzyme became extremely unstable in advanced stages of purification, both PHB synthases had the same strict substrate specificity ford(-)-β-hydroxybutyryl CoA, and showed the same pH optimum at 7.0.