Pathophysiology of ketoacidosis in Type 2 diabetes mellitus

AIMS

Despite an increasing number of reports of ketoacidosis in populations with Type 2 diabetes mellitus, the pathophysiology of the ketoacidosis in these patients is unclear. We therefore tested the roles of three possible mechanisms: elevated stress hormones, increased free fatty acids (FFA), and suppressed insulin secretion.

METHODS

Forty-six patients who presented to the Emergency Department with decompensated diabetes (serum glucose > 22.2 mmol/l and/or ketoacid concentrations > or = 5 mmol/l), had blood sampled prior to insulin therapy. Three groups of subjects were studied: ketosis-prone Type 2 diabetes (KPDM2, n = 13) with ketoacidosis, non-ketosis-prone subjects with Type 2 diabetes (DM2, n = 15), and ketotic Type 1 diabetes (n = 18).

RESULTS

All three groups had similar mean plasma glucose concentrations. The degree of ketoacidosis (plasma ketoacids, bicarbonate and anion gap) in Type 1 and 2 subjects was similar. Mean levels of counterregulatory hormones (glucagon, growth hormone, cortisol, epinephrine, norepinephrine), and FFA were not significantly different in DM2 and KPDM2 patients. In contrast, plasma C-peptide concentrations were approximately three-fold lower in KPDM2 vs. non-ketotic DM2 subjects (P = 0.0001). Type 1 ketotic subjects had significantly higher growth hormone (P = 0.024) and FFA (P < 0.002) and lower glucagon levels (P < 0.02) than DM2.

CONCLUSIONS

At the time of hospital presentation, the predominant mechanism for ketosis in KPDM2 is likely to be greater insulinopenia.

Hepatic glucose-6-phosphatase flux and glucose phosphorylation, cycling, irreversible disposal, and net balance in vivo in rats. Measurement using the secreted glucuronate technique

Measurement of hepatic glucose production (HGP) by standard isotope dilution reveals only the net release of glucose from the liver, not the flux across glucose-6-phosphatase ([G6Pase] or total hepatic glucose output), hepatic glucose cycling (HGC), irreversible glucose disposal into glycogen in the liver (hepatic Rd), or net hepatic glucose balance. We describe two independent isotopic techniques for measuring these parameters in vivo, both of which use secreted glucuronate (GlcUA). HGC can be quantified by measuring a correction factor for glucose label retained in hepatic glucose-6-phosphate (G6P), sampled as GlcUA. A complementary technique for measuring total hepatic glucose output is also described (reverse dilution), requiring administration of no labeled glucose but instead a labeled gluconeogenic precursor and unlabeled glucose. Hepatic Rd is calculated by multiplying the rate of appearance (Ra) of hepatic UDP-glucose ([UDP-glc] based on dilution of labeled galactose in GlcUA) times the direct entry of glucose into hepatic UDP-glc and the fraction of labeled UDP-glc retained in the liver. The sum of hepatic Rd plus HGC represents the total hepatic glucose phosphorylation rate. Rats received intravenous (i.v.) glucose infusions at a rate of 15 to 30 mg/kg/min after a 24-hour fast. Despite a suppression of net HGP more than 50%, total hepatic glucose output was not significantly decreased, because of increased HGC. Total hepatic glucose output calculated by reverse dilution yielded similar results during i.v. glucose infusions at 15 mg/kg/min, although values were higher than obtained by the correction-factor method at 30 mg/kg/min. The fraction of labeled UDP-glc released into blood glucose, representing a hepatic glycogen cycle, decreased from 35% (fasted) to nearly 0% (i.v. glucose 30 mg/kg/min). Hepatic Rd was 1.4, 4.6, and 7.5 mg/kg/min (fasted and i.v. glucose 15 and 30 mg/kg/min, respectively); total hepatic glucose phosphorylation increased substantially (from 4.2 to 8.5 to 12.7 mg/kg/min) and net hepatic glucose balance changed from negative to positive during i.v. glucose. In conclusion, hepatic G6Pase flux, glucose phosphorylation, HGC, disposal of glucose into glycogen, and net glucose balance can be measured noninvasively in vivo under various metabolic conditions by techniques involving the GlcUA probe.

Hepatic gluconeogenic fluxes and glycogen turnover during fasting in humans. A stable isotope study

Fluxes through intrahepatic glucose-producing metabolic pathways were measured in normal humans during overnight or prolonged (60 h) fasting. The glucuronate probe was used to measure the turnover and sources of hepatic UDP-glucose; mass isotopomer distribution analysis from [2-13C1]glycerol for gluconeogenesis and UDP-gluconeogenesis; [U-13C6]glucose for glucose production (GP) and the direct UDP-glucose pathway; and [1-2H1]galactose for UDP-glucose flux and retention in hepatic glycogen. After overnight fasting, GP (fluxes in milligram per kilogram per minute) was 2.19+/-0.09, of which 0.79 (36%) was from gluconeogenesis, 1.40 was from glycogenolysis, 0.30 was retained in glycogen via UDP-gluconeogenesis, and 0.17 entered hepatic UDP-glucose by the direct pathway. Thus, total flux through the gluconeogenic pathway (1.09) represented 54% of extrahepatic glucose disposal (2.02) and the net hepatic glycogen depletion rate was 0.93 (46%). Prolonging [2-13C1]glycerol infusion slowly increased measured fractional gluconeogenesis. In response to prolonged fasting, GP was lower (1. 43+/-0.06) and fractional and absolute gluconeogenesis were higher (78+/-2% and 1.11+/-0.07, respectively). The small but nonzero glycogen input to plasma glucose (0.32+/-0.03) was completely balanced by retained UDP-gluconeogenesis (0.31+/-0.02). Total gluconeogenic pathway flux therefore accounted for 99+/-2% of GP, but with a glycogen cycle interposed. Prolonging isotope infusion to 10 h increased measured fractional gluconeogenesis and UDP-gluconeogenesis to 84-96%, implying replacement of glycogen by gluconeogenic-labeled glucose. Moreover, after glucagon administration, GP (1.65), recovery of [1-2H1]galactose label in plasma glucose (25%) and fractional gluconeogenesis (91%) increased, such that 78% (0.45/0.59) of glycogen released was labeled (i.e., of recent gluconeogenic origin). In conclusion, hepatic gluconeogenic flux into glycogen and glycogen turnover persist during fasting in humans, reconciling inconsistencies in the literature and interposing another locus of control in the normal pathway of GP.