Human splanchnic metabolism during diabetic ketoacidosis

Errors in measuring plasma free fatty acid concentrations with a popular enzymatic colorimetric kit

OBJECTIVES

Our goal was to test whether an enzymatic, colorimetric assay, the WAKO NEFA kit, provides information equivalent to liquid chromatography (LC) LC-based measures of free fatty acid (FFA).

DESIGN & METHODS

We reanalyzed nadir FFA samples from 109 volunteers from a previous study where we demonstrated that maximal suppression of FFA concentrations predicts metabolic abnormalities in humans; the results from the WAKO NEFA kit, which has been widely used for over three decades, could not replicate our findings. We conducted additional studies to directly compare results from this kit to our LC-mass spectrometry (LC/MS) method that was validated by our LC-UV detection method.

RESULTS

Plasma samples with FFA concentrations ranging from 0.015 to 1.813 mmol/L were measured both by LC-mass spectrometry (LC/MS) and by the WAKO NEFA kit. Despite good overall agreement (R² = 0.86), the slope was significantly different from 1.0 and the intercept was significantly different from zero. The results from the kit were especially discrepant with FFA concentrations <0.200 and >1.000 mmol/L. Some of the discrepancy was related to the use of oleate as the standard solution for the kit and the substrate specificity of the kit enzymes for different fatty acids. Despite attempts to improve the kit by modifying the reaction time, sample volume and the types of standard solutions, we could not obtain a satisfactory agreement between the WAKO NEFA results and LC/MS.

CONCLUSIONS

The WAKO NEFA kit should not be used when high precision and accuracy of FFA concentrations over a wide range is required.

Newer Perspectives of Mechanisms for Euglycemic Diabetic Ketoacidosis

Euglycemic diabetic ketoacidosis (EDKA) was considered a rare condition with its specific definition and precipitating factors. However, with the wide use of sodium glucose cotransporter 2 (SGLT-2) inhibitors, the newest class of antidiabetic agents, EDKA has come back into the spotlight. Relevant cases are increasingly being reported along with insights into the mechanism of EDKA. It seems increasingly clear that EDKA is more common than we used to believe. The SGLT-2 inhibitor-associated EDKA also indicates a necessary review of our previous understanding of "diabetic" ketoacidosis, since the SGLT-2 inhibitor predisposes patients to DKA in a "starvation" way. Actually, there are growing reports about starvation-induced ketoacidosis as well. The previously "exclusive" nomenclature and cognition of these entities need to be reexamined. That the hormonal interactions in DKA may differ from the severity of insulin deficiency also may have served in the scenario of EDKA. The SGLT-2 inhibitors are newly approved in China. The main purpose of this work is to have a better understanding of the situation and update our knowledge with a focus on the pathogenesis of EDKA.

Regional variations in the concentrations of ketone bodies in cirrhosis and hepatic encephalopathy: a study in patients with TIPSS

BACKGROUND

Little is known about the metabolism of acetoacetate and β-hydroxybutyrate in patients with cirrhosis and encephalopathy.

AIMS

We investigated the fate of ketone bodies in these conditions.

MATERIALS AND METHODS

We studied 18 cirrhotic patients with encephalopathy and 17 cirrhotics without. At the time of insertion of a transjugular intrahepatic portosystemic stent shunt (TIPSS) or at the time of portographical assessment of the shunt's patency, we collected blood from the internal jugular, the right atrium, the inferior vena cava, the hepatic, the portal, the splenic veins and the radial artery. We used nuclear magnetic resonance spectroscopy to measure the concentrations of acetoacetate and β-hydroxybutyrate.

RESULTS

There was no difference in the total ketone body concentrations between the two groups. The mitochondrial redox potential was significantly higher in the encephalopathics (142/54=2.63 vs 52/83=0.62) (P<0.01). β-hydroxybutyrate was significantly lower in the portal vein of encephalopathics (52 ± 4 vs 28 ± 3) (P<0.02) and in the splenic vein (48 ± 6 vs 32 ± 5) (P<0.04). Acetoacetate was significantly higher in encephalopathics in the internal jugular vein (134 ± 12 vs 92 ± 16) (P<0.03), the right atrium (112 ± 18 vs 68 ± 11) (P<0.03), the hepatic vein (162 ± 25 vs 115 ± 19) (P<0.05), the portal vein (133 ± 20 vs 81 ± 14) (P<0.02) and the splenic vein (167 ± 24 vs 122 ± 21) (P<0.04). All measurements are expressed in μmols/L.

CONCLUSIONS

There are significant variations in the regional concentrations of the ketone bodies in encephalopathy.

Effects of free fatty acids, insulin, glucagon and adrenaline on ketone body production in humans

In normal human subjects, when plasma insulin, glucagon and growth hormone were 'clamped' at basal concentrations (by infusion of somatostatin plus replacement infusion of these hormones), infusion of Intralipid and heparin increased plasma free fatty acid (FFA) concentrations to approx. 1.3 mM, and ketone body production increased 4-5 fold to approx. 11 mumol . kg -1 . min-1. Hyperglucagonaemia did not further increase ketogenesis. In conditions of combined insulin and glucagon deficiency (by infusion of somatostatin without insulin and glucagon), administration of Intralipid and heparin increased plasma FFA concentrations to approx. 2.2 mM but a further increase in ketone body production did not accompany this increase. In these conditions hyperglucagonaemia increased ketogenesis by 2-3 fold the increment seen in control studies. Infusion of adrenaline (epinephrine) in conditions in which insulin secretion was not inhibited caused only a transient increase in plasma FFA concentrations and in ketone body production. These data indicate: (1) that in humans increased FFA availability can markedly augment ketogenesis in the absence of insulin deficiency and without hyperglucagonaemia; (2) that glucagon can increase ketone body production during insulin deficiency but not in its absence; and (3) that insulin deficiency may be accompanied by increased ketogenesis only because of a lack of its restraint on lipolysis and because of the action of glucagon. Glucagon may be important in determining the magnitude of ketone body production for a given degree of FFA availability and insulin deficiency, and may be necessary for attainment of maximal rates of ketogenesis. Adrenaline increases ketone body production in humans, but whether this is primarily due to a direct effect on the liver or is mediated through enhancement of lipolysis remains to be determined.

Physical training reverses the increased activity of the hepatic ketone body synthesis pathway in chronically diabetic rats

This study was designed to examine whether the training-induced improvement in the plasma concentration of ketone bodies in experimental diabetes mellitus could be explained by changes in the activity of the hepatic ketone body synthesis pathway and/or the plasma free fatty acid levels. Diabetes mellitus was induced by an intravenous injection of streptozotocin (50 mg/kg), and training was carried out on a treadmill. The plasma concentration of beta-hydroxybutyric acid was increased (P < 0.001) in sedentary diabetic rats, and this was partly reversed by training (P < 0.001). The plasma concentration of free fatty acids was increased (P < 0.001) in sedentary diabetic rats, and this was reversed to normal by training (P < 0.001). Diabetes was also associated with an increased activity of the hepatic ketone body synthesis pathway. When the data are expressed as per total liver, physical training decreased the activity of the hepatic ketone body synthesis pathway by 18% in nondiabetic rats (P < 0.05) and by 22% in diabetic rats (P < 0.01), the activity present in trained diabetic rats being not statistically different from that of sedentary control rats. These data suggest that the beneficial effects of physical training on the plasma beta-hydroxybutyric acid levels in the diabetic state are probably explained in part by a decrease in the activity of the hepatic ketone body synthesis pathway and in part by a decrease in plasma free fatty acid levels.

Physical training reverses defect in 3-ketoacid CoA-transferase activity in skeletal muscle of diabetic rats

To investigate one potential mechanism whereby physical training improves the plasma concentration of ketone bodies in experimental diabetes mellitus, we measured the activity of 3-ketoacid CoA-transferase, the key enzyme in the peripheral utilization of ketone bodies. Diabetes was induced with streptozotocin (50 mg/kg) and training carried out on a treadmill with a progressive 10-wk program. Diabetes resulted in an increase (P < 0.001) in plasma concentration of beta-hydroxybutyric acid in sedentary rats, which was partly reversed by training (P < 0.001). Diabetes was also associated with a decreased activity of 3-ketoacid CoA-transferase in gastrocnemius muscle. When expressed per total gastrocnemius, training increased the activity of 3-ketoacid CoA-transferase by 66% in nondiabetic rats (P < 0.001) and by 150% in diabetic rats (P < 0.001), the decrease present in diabetic rats being fully reversed by training. Simple linear regression between the log of 3-ketoacid CoA-transferase activity and the log of plasma beta-hydroxybutyric acid levels showed a statistically significant (r = 0.563, P < 0.001) negative correlation. The beneficial effects of training on plasma ketone bodies in diabetic rats are probably explained, at least in part, by an increase in ketone body utilization, mediated by an increase in skeletal muscle 3-ketoacid CoA-transferase activity.

Diabetic ketoacidosis and hyperglycemic hyperosmolar nonketotic syndrome

Diabetic ketoacidosis (DKA) and hyperglycemic hyperosmolar nonketotic syndrome (HHNS) are life-threatening acute metabolic complications of diabetes mellitus. Although there are some important differences, the pathophysiology, the presenting clinical challenge, and the treatment of these metabolic derangements are similar. Each of these complications can be seen in type 1 or type 2 diabetes, although DKA is usually seen in patients with type 1 diabetes and HHNS in patients with type 2 disease. The clinical management of these syndromes involves careful evaluation and correction of the metabolic and volume status of the patient, identification and treatment of precipitating and comorbid conditions, a smooth transition to a long-term treatment regimen, and a plan to prevent recurrence.

Lipoprotein disorders in diabetes mellitus

In IDDM or NIDDM, the total plasma cholesterol and triglycerides are usually within normal limits when the blood glucose is controlled. Marked hypertriglyceridemia can develop with loss of glycemic control and is often due to superimposed genetic abnormalities in lipoprotein metabolism. Tight control in IDDM usually reduces LDL and VLDL to normal levels and may raise HDL above the normal range. Low HDL cholesterol and mild to moderate elevations of VLDL triglyceride are common in NIDDM if obesity or proteinuria is also present. Both HDL and LDL may be smaller and more dense and may be enriched with triglyceride as compared with cholesterol. These abnormalities may require weight loss for control. The increased incidence of cardiovascular disease in diabetes is unexplained but is amplified by the well-defined cardiovascular risk factors. The new American Diabetes Association guidelines call for treatment of high triglycerides and LDL cholesterol to be aggressively reduced. Triglycerides should be under 200 mg/dL, are considered borderline high between 200 and 400 mg/dL, and high when above 400 mg/dL. Low HDL is defined as less than 35 mg/dL. Control of obesity with diet and exercise and reduced intake of saturated fat and cholesterol are important first steps. If needed, drug therapy is appropriate to reduce LDL to levels below 130 mg/dL in all adult diabetics and below 100 mg/dL in those with cardiovascular disease.

Uptake of beta-hydroxybutyrate in perfused hindquarter of starved and diabetic rats

To elucidate the peripheral ketone body uptake and the role of insulin in regulating peripheral ketone body utilization in starvation and diabetes mellitus, uptake of beta-hydroxybutyrate (BOHB) was investigated in the perfused hindquarter of starved (72 hour) or streptozotocin-induced (65 mg/kg, intraperitoneally) diabetic rats. Blood concentration of BOHB was significantly higher in diabetic (1,380 +/- 250 mumol/L) and starved (1,229 +/- 245 mumol/L) rats than in controls (104 +/- 8 mumol/L). The hindquarter was perfused with synthetic medium at a flow rate of 0.5 mL/g muscle weight/min. BOHB was added to the medium at a concentration of 0.1, 0.5, 2, or 10 mmol/L, and insulin was added at a concentration of 20, 100, or 500 microU/mL. In the hindquarter perfused with 0.1, 0.5, 2, or 10 mmol/L BOHB, fractional uptake of BOHB in the absence or presence of insulin was significantly lower in diabetic and starved rats than in controls. The addition of 100 or 500 microU/mL insulin significantly increased BOHB uptake in the perfused hindquarter of control rats; however, insulin addition did not significantly increase BOHB uptake in the perfused hindquarter of starved and diabetic rats. These results suggest that BOHB uptake is markedly reduced in the perfused hindquarter of starved and diabetic rats, and that physiological dose of insulin stimulates BOHB uptake in control rats, but not in starved and diabetic rats.

Hyperlipidaemia in diabetes

Currently our knowledge of the role of lipid abnormalities as risk factors for CHD in diabetes is insufficient. We need to define exact risk parameters to target correctly the therapy of lipid disorders and to outline optimum therapeutic strategies. Therefore it is necessary to identify quantitative and qualitative abnormalities of lipoproteins and apoproteins which signify the risk of CHD and to define their predictive power in prospective trials. Obviously we need to know more about the pathophysiology of lipid abnormalities and the action of insulin. Because diabetic patients carry a high inherent risk of CHD, target values recommended for non-diabetic populations may not be optimal for diabetic populations, but should be lower. To date no primary or secondary intervention trials in diabetic populations have been carried out to show that the lowering of lipid values (serum and LDL cholesterol) will reduce the risk of CHD morbidity or mortality or will prevent the progression of CHD in diabetes. Since hypertriglyceridaemia and low HDL levels are typical abnormalities in NIDDM it is a unique target group to test whether lowering of triglycerides and raising of HDL cholesterol levels will reduce the risk of CHD. Therefore there is a pressing need for clinical trials in both IDDM and NIDDM to provide adequate information on the benefits of lipid-lowering therapy and to confirm treatment strategies.

Validation of two-pool model for in vivo ketone body kinetics

Previous studies have indicated that simultaneous infusions of two ketone body tracers ([13C]acetoacetate and [14C]beta-hydroxybutyrate) provide accurate estimates of exogenous ketone body inflow when an open two-pool model is employed. In the present studies, net hepatic ketone body production was determined from surgically placed arterial, portal venous, and hepatic venous catheters in conscious diabetic (n = 6) and 4-day fasted (n = 7) dogs. [13C]acetoacetate and [14C]beta-hydroxybutyrate were infused simultaneously, and ketone body production was calculated from either acetoacetate (AcAc) single-isotope data, beta-hydroxybutyrate (beta-OHB) single-isotope data, the sum of individual fluxes, or the two-pool model. In fasted animals, both the AcAc single-isotope calculation and the sum of individual fluxes overestimated net hepatic production by approximately 50% (P less than 0.05), whereas the beta-OHB single-isotope calculation and the two-pool model gave accurate estimates. In the diabetic animals, the beta-OHB single-isotope calculation underestimated net hepatic production by approximately 30% (P less than 0.05). The sum of individual fluxes overestimated net hepatic production by approximately 46% (P less than 0.05), whereas both the AcAc single-isotope calculation and the two-pool model gave accurate estimates. In conclusion, single-isotope methods give erroneous estimates of net hepatic production of ketone bodies. In contrast, a two-pool model provided an accurate estimate of net hepatic production and thus appears to be suitable for determination of ketone body kinetics in humans.

Alcoholism, ketoacidosis, and lactic acidosis

Alcoholic ketoacidosis is a metabolic disorder that occurs in acute-on-chronic ethanol abusers who become acutely starved because of cessation of all caloric intake (including ethanol) owing to gastric intolerance or to an intercurrent acute illness. The precise pathogenesis, and especially the cause of the increased lipolysis, is not known, but several factors known or believed to promote ketogenesis are present in those patients. These are particularly starvation and recent ethanol ingestion. The metabolic disorder responds rapidly to rehydration and administration of glucose intravenously, which stops the ketogenesis. The prognosis in these patients depends on the presence and severity of any underlying illness and the adequacy and effectiveness of treatment for that illness. Patients rarely if ever die from either the ketoacidosis or the lactic acidosis associated with ethanol abuse, but they may succumb to other precipitating or coexisting illnesses.

Ketone body production and disposal: effects of fasting, diabetes, and exercise

Turnover studies performed during progressive fasting in normal subjects indicate that the production rate and the concentration of KB rise markedly during the early phase of fasting and start reaching a plateau after about 5 days. In addition to increased production, a reduction in the metabolic clearance rate of KB contributes to the hyperketonemia. This reduced metabolic clearance rate reflects essentially the progressive saturation of muscular ketone uptake that occurs with increasing ketonemia. The hormonal and metabolic environment of fasting plays only a minor role in this process, since a fall in KB metabolic clearance similar to that observed during fasting is observed if hyperketonemia is artificially induced in the postabsorptive state by the infusion of exogenous ketones. As extraction of KB by muscle becomes limited during ongoing fasting, KB are preferentially taken up by the brain to serve as a substrate replacing glucose. The remarkable stability of ketonemia during prolonged fasting is maintained through the operation of a negative feedback mechanism whereby KB tend to restrain their own production rate. The antilipolytic and insulinotropic effects of KB are instrumental in this process. This homeostatic mechanism maintains ketogenesis only slightly above the maximal metabolic disposal rate, the difference corresponding to urinary excretion, which is always below 10% of total turnover under physiologic conditions. When type I insulin-deprived diabetic patients are compared at the same KB concentration with control subjects with fasting ketosis, the characteristics of KB kinetics are comparable in the two groups. The maximal KB removal capacity is identical in the two situations, and it is not possible to identify a ketone removal defect specific to diabetes. Thus, these data favor the concept that excessive production of KB represent the main factor leading to uncontrolled hyperketonemia. It should be realized that a production exceeding only slightly that prevailing during prolonged fasting is sufficient to cause a progressive build-up in concentration, leading to uncontrolled diabetic ketosis. In the overnight-fasted state, a prolonged exercise (2 h) performed at moderate intensity (50% VO2 max) stimulates the capacity of muscle to extract ketones from blood as evidenced by a stimulation of the metabolic clearance rate.(ABSTRACT TRUNCATED AT 400 WORDS)

The effect of glucose and insulin infusion on the fall of ketone bodies during treatment of diabetic ketoacidosis

During the treatment of diabetic ketoacidosis intravenous glucose is infused when blood glucose has fallen to around 14 mmol l-1. The use of hypertonic (10%) glucose has been recommended in order to hasten the clearance of blood ketone bodies. In a randomized controlled study 17 patients presenting with severe diabetic ketoacidosis were allocated to one of two regimens of intravenous glucose and insulin when blood glucose had fallen to less than 14 mmol l-1. Nine patients were given 5% glucose containing 10 U l-1 insulin and 8 patients received 10% glucose with 40 U l-1 insulin. Fluid was infused at a rate of 250 ml h-1 for 6 h. At the start of the infusions blood glucose had fallen from levels at presentation to 12.8 +/- 1.1 mmol l-1 (mean +/- SE) in the group which subsequently received the low infusion rate and to 13.7 +/- 0.9 mmol l-1 in the subsequent high infusion rate group. With glucose/insulin infusion blood glucose after 6 h was 11.5 +/- 0.9 mmol l-1 (low infusion rate group) and 15.7 +/- 1.3 mmol l-1 (high infusion rate group). This difference between groups at 6 h was significant (p less than 0.05). Over the 6 h of infusion the fall in blood total ketone bodies was significantly greater in the group receiving the higher rate of glucose/insulin infusion (7.34 +/- 0.57 vs 5.18 +/- 0.57 mmol l-1; p less than 0.05). Despite the greater fall in total ketone bodies in this group there was no difference in the improvement in capillary blood pH or bicarbonate.(ABSTRACT TRUNCATED AT 250 WORDS)

Relationship between severity of hyperglycemia and metabolic acidosis in diabetic ketoacidosis

We evaluated 114 hospital admissions for diabetic ketoacidosis (occurring in 78 patients) retrospectively by using the Mayo Clinic medical records system. Initial plasma glucose and serum bicarbonate values were examined by using regression analysis. No correlation was found between these two measurements (r = -0.03). The reason for this dissociation between hyperglycemia and hyperketonemia needs further elucidation, but it may be related to impaired hepatic glucose production in some patients.

Whole body glucose kinetics in type I diabetes studied with [6,6-2H] and [U-13C]-glucose and the artificial B-cell

Dynamic aspects of whole body glucose metabolism were assessed in ten young adult insulin-dependent (type I) diabetic men. Using a primed, continuous intravenous infusion of [6,6-2H]glucose and [U-13C]glucose, endogenous production, tissue uptake, carbon recycling, and oxidation of glucose were measured in the postabsorptive state. These studies were undertaken after blood glucose had been maintained overnight at 5.9 +/- 0.4 mmol/L (n = 10), and on another night at 10.5 +/- 0.4 mmol/L (n = 4) or 15.2 +/- 0.6 mmol/L (n = 6). In the normoglycemic state, endogenous glucose production averaged 2.15 +/- 0.13 mg x kg-1 x min-1. This value, as well as the rate of glucose carbon recycling (0.16 +/- 0.04 mg x kg-1 x min-1) and glucose oxidation (1.52 +/- 0.16 mg x kg-1 x min-1) are comparable to those found in nondiabetic controls. In the hyperglycemic states at 10 or 15 mmol/L, endogenous glucose production was increased by 11% (P less than .01) and 60% (P less than .01) compared to the normoglycemic states, respectively. Glucose carbon recycling contributed only a small percentage to this variation in glucose production (15% at the 15 mmol/L glucose level). This suggests that if gluconeogenesis participates in the increased glucose output, it is not dependent on a greater systemic supply of three-carbon precursors. The increased rate of glucose production in the hyperglycemic state was quantitatively offset by a rise in urinary glucose excretion. Glucose tissue uptake, as well as glucose oxidation, did not vary between normoglycemic and hyperglycemic states.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of insulin on ketone body clearance studied by a ketone body "clamp" technique in normal man

The effect of elevated plasma insulin concentration (55 +/- 2 mU/l) on peripheral clearance and production of total ketone bodies was determined using 3-14C-acetoacetate tracer infusions. Nine normal subjects were studied twice, once during insulin infusion (20 mU.m-2.min-1), once during basal plasma insulin concentrations (controls). Blood total ketone body concentrations (sum of acetone, acetoacetate and beta-hydroxybutyrate) were maintained in both studies at 2 mmol/l by feedback-controlled sodium acetoacetate infusions. The coefficient of variation of total ketone body concentrations during the two clamp studies was 10 and 11% respectively. The sodium acetoacetate infusion rate required during the clamp was 55 +/- 4% higher during hyperinsulinaemia than in controls (p less than 0.005). This was due to increased total ketone body clearance (8.4 +/- 0.7 vs 6.7 +/- 0.4 ml.kg-1.min-1, p less than 0.015), and to enhanced suppression of ketone body production (p less than 0.01). Hyperketonaemia alone decreased ketone body production by 42% and diminished ketone body clearance by 46%, the former being enhanced, the latter being in part antagonised by insulin. Since the plasma insulin concentrations were within those observed in patients treated for diabetic ketoacidosis, the data suggest that the antiketotic effect of insulin therapy results in part from an increase in peripheral ketone body disposal.

Mechanism of the hyperketonaemic effect of prolonged exercise in insulin-deprived type 1 (insulin-dependent) diabetic patients

The effects of moderate exercise of 2-h duration on the concentration and turnover rate of total ketone bodies were assessed in 7 acutely insulin-deprived Type 1 (insulin-dependent) diabetic patients with an isotope tracer technique using a constant infusion of 14C-beta-hydroxybutyrate. These results were compared to those obtained in 13 normal control subjects in whom a similar range of hyperketonaemia (approximately 1-6 mmol/l) was induced by fasting. In all subjects, the concentration and the rate of production of ketone bodies followed a biphasic pattern with an initial fall lasting for about 20 min followed by a secondary rise. When integrated over the entire working period, the exercise-induced changes in ketone turnover were markedly dependent on the initial ketone body concentrations in both groups: at low ketonaemia (approximately 1 mmol/l), exercise increased the rate of production and disposal of ketones. These effects were progressively attenuated as basal ketonaemia rose and were reversed to an inhibitory action in markedly ketotic subjects (greater than 4 mmol/l). Despite the finding that, at high ketosis, exercise inhibited ketogenesis to a similar degree in control subjects and diabetic patients, the changes in concentration recorded at the end of exercise were different in the 2 groups: ketonaemia was reduced in fasted control subjects and increased in the diabetic patients. These data suggest that, contrary to a widely accepted opinion, the hyperketonaemic effect of prolonged exercise in ketotic diabetic patients does not result from an exaggerated stimulation of ketogenesis, but from some defect in their removal capacities for ketones, possibly related to insulinopenia.

A dual-isotope technique for determination of in vivo ketone body kinetics

"Total ketone body specific activity" has been widely used in studies of ketone body metabolism to circumvent so-called "isotope disequilibrium" between the two major ketone body pools, acetoacetate and beta-hydroxybutyrate. Recently, this approach has been criticized on theoretical grounds. In the present studies, [13C]acetoacetate and beta-[14C]hydroxybutyrate were simultaneously infused in nine mongrel dogs before and during an infusion of either unlabeled sodium acetoacetate or unlabeled sodium beta-hydroxybutyrate. Ketone body turnover was determined using total ketone body specific activity, total ketone body moles % enrichment, and an open two-pool model, both before and during the exogenous infusion of unlabeled ketone bodies. Basal ketone body turnover rates were significantly higher using [13C]acetoacetate than with either beta-[14C]hydroxybutyrate alone or the dual-isotope model (3.6 +/- 0.5 vs. 2.2 +/- 0.2 and 2.7 +/- 0.2 mumol X kg-1 X min-1, respectively, P less than 0.05). During exogenous infusion of unlabeled sodium acetoacetate, the dual-isotope model provided the best estimate of ketone body inflow, whereas 14C specific activity underestimated the known rate of acetoacetate infusion by 55% (P less than 0.02). During sodium beta-hydroxybutyrate infusion, [13C]-acetoacetate overestimated ketone body inflow by 55% (P = NS), while better results were obtained with 14C beta-hydroxybutyrate alone and the two-pool model. Ketone body interconversion as estimated by the dual-isotope technique increased markedly during exogenous ketone body infusion. In conclusion, significant errors in estimation of ketone body inflow were made using single-isotope techniques, whereas a dual-isotope model provided reasonably accurate estimates of ketone body inflow during infusion of exogenous acetoacetate and beta-hydroxybutyrate.(ABSTRACT TRUNCATED AT 250 WORDS)

Hepatic and renal metabolism before and after portasystemic shunts in patients with cirrhosis

Hepatic cirrhosis with portal hypertension and gastroesophageal hemorrhage is a disease complex that continues to be treated by surgical portasystemic shunts. Whether or not a reduction or diversion of portal blood flow to the liver adversely affects the ability of the liver to maintain fuel homeostasis via gluconeogenesis, glycogenolysis, and ketogenesis is unknown. 11 patients with biopsy-proven severe hepatic cirrhosis were studied before and after distal splenorenal or mesocaval shunts. Hepatic, portal, and renal blood flow rates and glucose, lactate, pyruvate, glycerol, amino acids, ketone bodies, free fatty acids, and triglyceride arteriovenous concentration differences were determined to calculate net precursor-product exchange rates across the liver, gut, and kidney. The study showed that hepatic contribution of glucose and ketone bodies and the caloric equivalents of these fuels delivered to the blood was not adversely affected by either a distal splenorenal or mesocaval shunt. In addition to these general observations, isolated findings emerged. Mesocaval shunts reversed portal venous blood and functionally converted this venous avenue into hepatic venous blood. The ability of the kidney to make a substantial net contribution of ketone bodies to the blood was also observed.

Determination of ketone body turnover in vivo with stable isotopes, utilizing gas chromatography/mass spectrometry

JH imple and reliable method for the determination of ketone body turnover in vivo using a primed, continuous infusion of [3,4-13C2]acetoacetate is described. Mole percent enrichment of beta-[13C2]hydroxybutyrate and [13C2]acetoacetate is determined by gas chromatography/mass spectrometry using electron-impact ionization and selected ion monitoring. Ketone body flux data are provided from preliminary dog experiments. The method is readily applicable to the study of ketone body metabolism in both laboratory animals and humans.

Glucose and ketone body kinetics in diabetic ketoacidosis

The hyperglycaemia and hyperketonaemia of diabetic ketoacidosis are initiated primarily by overproduction of these substrates; subsequent maintenance of hyperglycaemia occurs, in large part, due to impaired utilization of glucose, whereas overproduction of ketone bodies continues to be the major mechanism for maintenance of hyperketonaemia. Insulin deficiency results in increased rates of lipolysis and provides increased substrate (free fatty acids) for ketogenesis. Hyperglucagonaemia can augment ketogenesis further in the setting of insulin deficiency. It is likely that other counter-insulin hormones (growth hormone, catecholamines) also contribute to the pathogenesis of DKA, though their role is less well defined. Insulin corrects DKA largely via suppression of lipolysis (and thus ketone body production); insulin suppresses glucose production at lower levels than it does ketone body production.

Biochemistry and differential diagnosis of metabolic acidoses

This paper reviews the biochemical background of metabolic acidoses. The rate of development is judged from production and/or elimination rate of organic acids, particularly carboxylic acids, namely lactate, ketoacids, acetate, formate and glycollate. Further, acid production from changes in the chemical state of phosphate in tissue is evaluated. The main conclusion is that pathological conditions with acidoses are always accompanied by changes in the rate of elimination of the carboxylic acids, whereas changes in the chemical state of phosphate is of quantitatively minor importance. Further, metabolic effects of metabolic acidoses are described with special reference to the effect of low pH in the extra cellular fluid on glycolysis, gluconeogenesis, lipolysis and ketogenesis. A short outline of the differential diagnostic problems in metabolic acidoses due to changes in carbohydrate and lipid metabolism or intoxication is given.

Hepatic, gut, and renal substrate flux rates in patients with hepatic cirrhosis

The roles of liver, kidney, and gut in maintaining fuel homeostasis were studied in 28 patients with severe hepatic cirrhosis, 25 of whom had alcohol-induced cirrhosis. Hepatic, portal, and renal blood flow rates were measured and combined with substrate concentration differences across liver, gut, and kidney to calculate the net flux of free fatty acids, ketone bodies, triglycerides, and glucose with selected glucose precursors, including glycerol, lactate, pyruvate, and amino acids. Data from the catheterization studies were related to hepatic histology, glycogen content, and activities of gluconeogenic enzymes and compared with data obtained from control patients. The effects of food deprivation on net flux of fuels across the liver, gut, and kidney were assessed after overnight and after 3d of fasting. Activities of gluconeogenic enzymes were normal, but hepatic glycogen content was diminished in cirrhotic livers, probably as a consequence of extensive hepatic fibrosis. Extrahepatic splanchnic tissues (gut) had only a small influence on total splanchnic flux rates of carbohydrates, lipids and, amino acids. In cirrhotic patients, there was no mean renal glucose contribution to the bloodstream after an overnight or after a 3-d fast. After an overnight fast hepatic glucose production in patients with cirrhosis was diminished as a result of low-rate glycogenolysis. Hepatic gluconeogenesis and ketogenesis were increased. This pattern of hepatic metabolism mimics that seen in "normal" patients after more advanced stages of starvation. After 3 d of starvation, patients with hepatic cirrhosis have hepatic gluconeogenic and ketogenic profiles comparable to those of normal patients undergoing starvation of similar duration. Nevertheless, the total number of caloric equivalents derived from ketone bodies plus glucose corrected for recycled lactate and pyruvate added to the bloodstream by the cirrhotic livers that could be terminally oxidized by peripheral tissues was less than the contributions made by the normal livers, both after and overnight and after a 3-d fast.

Substrate, hormone, and temperature responses in males and females to a common breakfast

To evaluate the response to a mixed meal we studied oral temperature, metabolite, and hormonal responses to a common American breakfast containing 11 kcal/kg body weight (carbohydrate 43%, fat 42%, and protein 15%) in 12 normal volunteers (6 males and 6 females). There was a significant rise in oral temperature during the postcibal period. This change in oral temperature did not depend upon food consumption in males but was meal-dependent in females. Food ingestion caused increases in the peripheral circulating concentrations of glucose, lactate, pyruvate, and amino acids and reciprocal decreases in the concentrations of free fatty acids, glycerol, and urea nitrogen. Acetoacetate and beta-hydroxybutyrate decreased during the postcibal period but the changes were not statistically significant. Although peripheral venous serum insulin and plasma glucagon concentrations were indistinguishable between the sexes, males had higher concentrations of plasma triglycerides, plasma amino acids, and serum urea nitrogen. Peripheral venous plasma somatostatin and secretin remained unchanged, but pancreatic polypeptide hormone showed a large biphasic response to the meal. After breakfast the blood glucose concentration tended to be greater in males than in females and this difference was significant at 60 and 120 min postcibal. Furthermore, every female had a 120 min postcibal glucose concentration that was lower than her basal fasting glucose concentration. This suggests that postcibal glucose concentrations should be related to gender in making the diagnosis of carbohydrate intolerance or reactive hypoglycemia.

Energy metabolism in feasting and fasting

During feasting on a balanced carbohydrate, fat, and protein meal resting metabolic rate, body temperature and respiratory quotient all increase. The dietary components are utilized to replenish and augment glycogen and fat stores in the body. Excessive carbohydrate is also converted to lipid in the liver and stored along with the excessive lipids of dietary origin as triglycerides in adipose tissue, the major fuel storage depot. Amino acids in excess of those needed for protein synthesis are preferentially catabolized over glucose and fat for energy production. This occurs because there are no significant storage sites for amino acids or proteins, and the accumulation of nitrogenous compounds is ill tolerated. During fasting, adipose tissue, muscle, liver, and kidneys work in concert to supply, to convert, and to conserve fuels for the body. During the brief postabsorptive period, blood fuel homeostasis is maintained primarily by hepatic glycogenolysis and adipose tissue lipolysis. As fasting progresses, muscle proteolysis supplies glycogenic amino acids for heightened hepatic gluconeogenesis for a short period of time. After about three days of starvation, the metabolic profile is set to conserve protein and to supply greater quantities of alternate fuels. In particular, free fatty acids and ketone bodies are utilized to maintain energy needs. The ability of the kidney to conserve ketone bodies prevents the loss of large quantities of these valuable fuels in the urine. This delicate interplay among liver, muscle, kidney, and adipose tissue maintains blood fuel homeostasis and allows humans to survive caloric deprivation for extended periods.