Hepatic glucose sensing is impaired, but can be normalized, in people with impaired fasting glucose

Abstract

Objective: Abnormal endogenous glucose production (EGP) is a characteristic feature in people with impaired fasting glucose (IFG). We sought to determine whether impaired hepatic glucose sensing contributes to abnormal EGP in IFG and whether it could be experimentally restored.

Methods: Glucose production (rate of appearance; Ra) and flux (glucose cycling) were assessed during a hyperglycemic-euinsulinemic somatostatin clamp with an infusion of [6,6-(2)H2-]glucose and [2-(2)H]glucose before and after enhanced hepatic glucokinase activity via an infusion of low-dose fructose in people with IFG and normal glucose tolerance (NGT).

Results: During euglycemia, neither endogenous glucose production [(6,6-(2)H2)-glucose Ra; P = 0.53] or total glucose output (TGO; [2-(2)H]-glucose Ra; P = .12) was different between groups, but glucose cycling ([2-(2)H]glucose Ra to [6,6-(2)H2-]glucose Ra; a surrogate measure of hepatic glucokinase activity in the postabsorptive state) was lower in IFG than NGT (P = .04). Hyperglycemia suppressed EGP more in NGT than IFG (P < .01 for absolute or relative suppression, NGT vs IFG), whereas TGO decreased similarly in both groups (P = .77). The addition of fructose completely suppressed EGP in IFG (P < .01) and tended to do the same to TGO (P = .01; no such changes in NGT, P = .39-.55). Glucose cycling (which reflects glucose-6-phosphatase activity during glucose infusion) was similar in IFG and NGT (P = .51) during hyperglycemia and was unchanged and comparable between groups with the addition of fructose (P = .24).

Conclusions: In summary, glucose sensing is impaired in IFG but can be experimentally restored with low-dose fructose. Glucokinase activation may prove to be a novel strategy for the prevention of diabetes in this high-risk group.

Figure 1.

Study design outlining the timing of the infusions, stages of the clamp, and periods of blood sampling.

Figure 2.

A, Enrichment of [2-²H]glucose (started at t = 0). B, Enrichment of [6,6-²H₂]glucose (started at t = 180) over the duration of the study. Euglycemia (t = 120–300 min), hyperglycemia (t = 300–420 min), and hyperglycemia + fructose (t = 420–540 min).

Figure 3.

A, Total glucose output as measured by the [2-²H]glucose Ra. B, EGP was determined using the [6,6-²H₂]glucose Ra. C, Glucose cycling ([2-²H]glucose, [6,6-²H₂]glucose Ra). *, P < .05, NGT vs IFG; #, P < .05 vs euglycemia.