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The glucose-6-phosphatase (G-6- Pase) system catalyzes the terminal enzymatic step of gluconeogenesis and glycogenolysis. Inhibition of the G-6- Pase system in the liver is expected to result in a reduction of hepatic glucose production irrespective of the relative contribution of gluconeogenesis or glycogenolysis to hepatic glucose output. In isolated perfused rat liver, S-3483, a derivative of chlorogenic acid, produced concentration-dependent inhibition of gluconeogenesis and glycogenolysis in a similar concentration range. In fed rats, glucagon-induced glycogenolysis resulted in hyperglycemia for nearly 2 h. Intravenous infusion of 50 mg ⋅ kg−1 ⋅ h−1S-3483 prevented the hyperglycemic peak and subsequently caused a further lowering of blood glucose. In 24-h starved rats, in which normoglycemia is maintained predominantly by gluconeogenesis, intravenous infusion of S-3483 resulted in a constant reduction of blood glucose levels. Intrahepatic concentrations of glucose-6-phosphate (G-6- P) and glycogen were significantly increased at the end of both in vivo studies. In contrast, lowering of blood glucose in starved rats by 3-mercaptopicolinic acid was accompanied by a reduction of G-6- P and glycogen. Our results demonstrate for the first time in vivo a pharmacologically induced suppression of hepatic G-6- P activity with subsequent changes in blood glucose levels.

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Mutations in the gene of the hepatic glucose-6-phosphate transporter cause glycogen storage disease type 1b. In this disease, the altered glucose homeostasis and liver functions are accompanied by an impairment of neutrophils/monocytes. However, neither the existence of a microsomal glucose-6-phosphate transport, nor the connection between its defect and cell dysfunction has been demonstrated in neutrophils/monocytes. In this study we have characterized the microsomal glucose-6-phosphate transport of human neutrophils and differentiated HL-60 cells. The transport of glucose-6-phosphate was sensitive to the chlorogenic acid derivative S3483, N-ethylmaleimide, and 4,4-diisothiocyanostilbene-2,2-disulfonic acid, known inhibitors of the hepatic microsomal glucose-6-phosphate transporter. A glucose-6-phosphate uptake was also present in microsomes from undifferentiated HL-60 and Jurkat cells, but it was insensitive to S3483. The treatment with S3484 of intact human neutrophils and differentiated HL-60 cells mimicked some leukocyte defects of glycogen storage disease type 1b patients (ie, the drug inhibited phorbol myristate acetate-induced superoxide anion production and reduced the size of endoplasmic reticulum Ca 2؉ stores). Importantly, the treatment with S3484 also resulted in apoptosis of human neutrophils and differentiated HL-60 cells, while undifferentiated HL-60 and Jurkat cells were unaffected by the drug. The proapoptotic effect of S3483 was prevented by the inhibition of nicotinamide adenine dinucleotide phosphate oxidase or by antioxidant treatment. These results suggest that microsomal glucose-6-phosphate transport has a role in the antioxidant protection of neutrophils, and that the genetic defect of the transporter leads to the impairment of cellular functions and apoptosis. IntroductionGlucose-6-phosphatase (G6Pase) catalyses the common terminal reaction of gluconeogenesis and glycogenolysis, hence it plays a major role in the maintenance of blood glucose homeostasis. 1,2 G6Pase is expressed mainly in the liver and in the kidney where it is associated with the endoplasmic reticulum (ER) and functions as a multicomponent system. 2 The system is composed of the enzyme protein with an intraluminal active site and transporters for the entry of substrate glucose-6-phosphate (G6P) and for the exit of the products, phosphate and glucose. 2,3 Both the enzyme and glucose-6-phosphate transporter (G6PT) are already known at the molecular level. 2,4,5 The deficiency of the G6Pase activity causes type 1 glycogen storage disease (GSD-1). 2,6 The genetic deficiency of the enzyme protein is termed GSD type 1a, 2,7 and mutations affecting the G6PT gene cause GSD type 1b. 2,5,[8][9][10][11][12][13] While the clinical feature in GSD-1a is dominated by metabolic alterations and hepatorenal symptoms, in GSD-1b polymorphonuclear neutrophils (PMNs) and monocytes are also affected. 2,7 Both neutropenia and functional defects of PMNs and monocytes have been observed in most GSD-1b patients, who are therefore affected by sev...