Alexander S. Petrides

Role of free fatty acids and insulin in determining free fatty acid and lipid oxidation in man.

Plasma FFA oxidation (measured by infusion of 14C-palmitate) and net lipid oxidation (indirect calorimetry) are both inhibited by insulin. The present study was designed to examine whether these insulin-mediated effects on lipid metabolism resulted from a decline in circulating FFA levels or from a direct action of the hormone on FFA/lipid oxidation. Nine subjects participated in two euglycemic insulin clamps, performed with and without heparin. During each insulin clamp study insulin was infused at two rates, 4 and 20 mU/m2.min for 120 min. The studies were performed with indirect calorimetry and 3-3H-glucose and 14C-palmitate infusion. During the control study plasma FFA fell from 610 +/- 46 to 232 +/- 42 to 154 +/- 27 mumol/liter, respectively. When heparin was infused basal plasma FFA concentration remained constant. During the control study, FFA/lipid oxidation rates decreased in parallel with the fall in the plasma FFA concentration. During the insulin/heparin study, plasma 14C-FFA oxidation remained unchanged while net lipid oxidation decreased. In conclusion, when the plasma FFA concentration is maintained unchanged by heparin infusion, insulin has no direct effect on FFA turnover and disposal. These results thus suggest that plasma FFA oxidation is primarily determined by the plasma FFA concentration, while net lipid oxidation is regulated by both the plasma FFA and the insulin level.

Glucose and insulin metabolism in cirrhosis

Glucose intolerance, overt diabetes mellitus, and insulin resistance are characteristic features of patients with cirrhosis. Insulin secretion, although increased in absolute terms, is insufficient to offset the presence of insulin resistance. The defect in insulin-mediated glucose disposal involves peripheral tissues, primarily muscle, and most likely reflects a disturbance in glycogen synthesis. Hepatic glucose production is normally sensitive to insulin; at present, it is unknown whether hepatic glucose uptake is impaired in cirrhosis. One of the more likely candidates responsible for the insulin-resistant state is insulin itself. The hyperinsulinemia results from three abnormalities: diminished hepatic extraction, portosystemic/intrahepatic shunting, and enhanced insulin secretion.

Effect of physiologic hyperinsulinemia on glucose and lipid metabolism in cirrhosis.

Insulin secretion and insulin sensitivity were evaluated in eight clinically stable cirrhotic patients and in 12 controls. OGTT was normal in cirrhotics but plasma insulin response was increased approximately twofold compared with controls. Subjects received a three-step (0.1, 0.5, 1.0 mU/kg.min) euglycemic insulin clamp with indirect calorimetry, [6-3H]-glucose, and [1-14C]-palmitate. During the two highest insulin infusion steps glucose uptake was impaired (3.33 +/- 0.31 vs. 5.06 +/- 0.40 mg/kg.min, P less than 0.01, and 6.09 +/- 0.50 vs. 7.95 +/- 0.52 mg/kg.min, P less than 0.01). Stimulation of glucose oxidation by insulin was normal; in contrast, nonoxidative glucose disposal (i.e., glycogen synthesis) was markedly reduced. Fasting (r = -0.553, P less than 0.01) and glucose-stimulated (r = -0.592, P less than 0.01) plasma insulin concentration correlated inversely with the severity of insulin resistance. Basal hepatic glucose production was normal in cirrhotics and suppressed normally with insulin. In postabsorptive state, plasma FFA conc (933 +/- 42 vs. 711 +/- 44 mumol/liter, P less than 0.01) and FFA turnover (9.08 +/- 1.20 vs. 6.03 +/- 0.53 mumol/kg.min, P less than 0.01) were elevated in cirrhotics despite basal hyperinsulinemia; basal FFA oxidation was similar in cirrhotic and control subjects. With low-dose insulin infusion, plasma FFA oxidation and turnover failed to suppress normally in cirrhotics. During the two higher insulin infusion steps, all parameters of FFA metabolism suppressed normally. In summary, stable cirrhotic patients with normal glucose tolerance exhibit marked insulin resistance secondary to the impaired nonoxidative glucose disposal. Our results suggest that chronic hyperinsulinism may be responsible for the insulin resistance observed in cirrhosis.

Different Sensitivity of Glucose and Amino Acid Metabolism to Insulin in NIDDM

NIDDM subjects are characterized by impaired glucose tolerance and insulin resistance with respect to glucose metabolism. To examine whether the defect in glucose utilization extends to amino acid metabolism, 6 NIDDM subjects (64 ± 4 yr of age; ideal body weight of 107 ± 3%) and 7 control subjects (58 ± 4 yr of age; ideal body weight of 105 ± 2%) were studied with the euglycemic insulin clamp technique, in combination with [1-14C]leucine and indirect calorimetry. All subjects participated in two studies. In study 1, after 3 h of tracer equilibration, a 3-h insulin clamp (40 mU · m−2 · min−1) was performed to define the effect of insulin on leucine kinetics and glucose metabolism. In study 2, subjects received a repeat 3-h insulin clamp, and a balanced amino acid solution was infused to increase the plasma amino acid concentrations ∼ 2-fold to examine the effect of combined physiological hyperinsulinemia-hyperaminoacidemia on the rate of leucine and glucose disposal. Insulin-mediated total body glucose uptake was significantly reduced in NIDDM during both study 1 (5.6 ± 0.4 vs. 6.9 ± 0.6 mg · kg−1 · min−1 P < 0.01) and study 2 (5.2 ± 0.4 vs. 6.8 ± 0.6, P < 0.01). Basal plasma leucine (120 ± 10 vs. 123 ± 11 μM) and α-ketoisocaproic acid concentrations (28 ± 3 vs. 25 ± 2 μM) were similar in NIDDM and control subjects, respectively. In contrast, the basal plasma glucose concentration (8.9 ± 0.8 vs. 4.7 ± 0.2 μM) and the HbA1c (8.5 ± 0.2 vs. 5.7 ± 0.2%) were significantly increased in NIDDM (P < 0.01). In the postabsorptive state, endogenous leucine flux, leucine oxidation, and nonoxidative leucine disposal were similar in NIDDM and control subjects. When insulin was infused without amino acids (study 1), the decrement in plasma leucine (53 ± 5 vs. 48 ± 4 μM), endogenous leucine flux (13 ± 2 vs. 11 ± 1 μmol · m−2 · min−1), leucine oxidation (1.6 ± 0.2 vs. 1.3 ± 0.1 μmol · m−2 · min−1), and nonoxidative leucine disposal (10 ± 1 vs. 8 ± 1 μmol · m−2 · min−1) was comparable in both groups. During combined insulin and amino acid infusion (study 2), plasma leucine concentration (185 ± 20 vs. 190 ± 15 μM) rose similarly in NIDDM and control subjects. In NIDDM, the increment in leucine oxidation (9.0 ± 0.7 vs. 8.5 ± 0.6 μmol · m−2 · min−1) and nonoxidative leucine disposal (9.3 ± 0.7 vs. 10.5 ± 0.9 μmol · m−2 · min−1) was similar to that observed in control subjects; the decrement in endogenous leucine flux (22.3 ± 2.1 vs. 20.2 ±1.9 μmol · m−2 · min−1) was comparable in both groups. We conclude that 1) insulin-mediated glucose disposal is significantly impaired in NIDDM and 2) the effect of insulin on endogenous leucine flux (protein degradation), nonoxidative leucine disposal (protein synthesis), and leucine oxidation is similar in NIDDM and control subjects. These results indicate a clear-cut dissociation between the effect of insulin on glucose and protein metabolism in NIDDM.

Leucine metabolism in IDDM: Role of insulin and substrate availability

The effect of insulin on plasma amino acid concentrations and leucine metabolism was examined in 18 healthy nondiabetic young volunteers and in 7 subjects with insulin-dependent diabetes mellitus (IDDM) with the euglycemic insulin-clamp technique (40 mU · m−2 · min−1) in combination with [1-14C]leucine. All diabetic subjects were studied while in poor metabolic control (fasting glucose 13.3 ± 1.1 mM; HbA1c 10.8 ± 0.2%) and again after 2 mo of intensified insulin therapy (fasting glucose 7.2 ± 0.5 mM; HbA1c 8.0 ± 0.2%). Insulin-mediated total-body glucose uptake in poorly controlled diabetic subjects (3.6 ± 0.5 mg · kg−1 · min−1) was significantly reduced compared with control subjects (7.5 ± 0.2 mg · kg−1 · min−1; P < .001) and improved slightly after insulin therapy (4.8 ± 0.3 mg · kg−1 · min−1; P < .05), although it still remained significantly lower than in control subjects (P < .01). During the insulin-clamp study performed in subjects with poorly controlled IDDM, endogenous leucine flux (ELF), leucine oxidation (LO), and nonoxidative leucine disposal (NOLD) all decreased (50.1 ± 2.0 to 26.4 ± 0.4; 9.2 ± 0.4 to 6.0 ± 0.3; 40.9 ± 2.0 to 20.4 ± 2.0 μmol · m−2 · min−1, respectively) to the same extent as in control subjects. After 2 mo of intensified insulin therapy, the effect of acute hyperinsulinemia on ELF, LO, and NOLD was comparable to that of control subjects, whereas insulin-stimulated glucose metabolism was still impaired. To examine the effect of substrate availability on leucine turnover, well-regulated IDDM and control subjects underwent a repeat insulin-clamp study combined with a balanced amino acid infusion designed to increase circulating plasma amino acid levels approximately twofold. Under these conditions, NOLD was equally enhanced above baseline in both control and IDDM subjects (P < .01), whereas ELF was inhibited to a greater extent (P < .01) than during the insulin clamp performed without amino acid infusion (control vs. diabetic subjects, NS). In conclusion, insulin-mediated glucose metabolism is severely impaired in subjects with both poorly controlled and well-controlled IDDM, whereas the effect of acute insulin infusion on leucine turnover is normal, and combined hyperaminoacidemia/hyperinsulinemia stimulated NOLD to a similar extent in both IDDM and control subjects.

Hepatic microsomal ethanol oxidizing system (MEOS): Respective roles of ethanol and carbohydrates for the enhanced activity after chronic alcohol consumption

Abstract To study whether the inductive effect of alcohol containing diets is due to ethanol itself or to the decreased carbohydrate content of these diets, female rats were group-fed for five weeks liquid diets containing various amounts of carbohydrates and, when indicated, ethanol. Compared to the control diet, supplementation of the control diet by additional carbohydrates failed to alter MEOS activity, whereas a hypocaloric diet with a decreased carbohydrate content led to a significant increase of MEOS activity by 72% (P

Hepatic gamma-glutamyltransferase activity: Its increase following chronic alcohol consumption and the role of carbohydrates

Prolonged feeding of diets containing ethanol leads to a significant increase of hepatic gamma-glutamyltransferase (GGT) activity which has been ascribed either to ethanol itself or to dietary imbalance with respect to carbohydrates. Hepatic GGT activity was therefore determined in Sprague-Dawley rats fed for five weeks liquid diets containing various amounts of protein, fat and vitamins. Compared to the normal control diet containing 47% of total calories as carbohydrates, a hypocaloric diet with 11% of total calories of the control diet as carbohydrates failed to result in major alterations of hepatic GGT activity (0.27 +/- 0.04 Units/g liver wet weight vs 0.35 +/- 0.06; N.S.). Similarly, hepatic GGT activity remained virtually unchanged under a hypercaloric carbohydrate rich diet. However, hepatic GGT activity was strikingly enhanced by a diet in which carbohydrates were replaced to the extent of 36% of total calories by ethanol to achieve a carbohydrate content of 11% (0.66 +/- 0.12 Units/g liver; P less than 0.005), indicating that alcohol itself is capable of increasing hepatic GGT activity. However, alcohol given with a high carbohydrate diet was shown to be incapable of increasing the hepatic activity of GGT. These data therefore indicate that upon chronic intake ethanol itself enhances hepatic GGT activity provided that the carbohydrate content of the diet is low, whereas such an effect could not be observed with ethanol in a high carbohydrate diet.

Insulin Resistance in Noncirrhotic Idiopathic Portal Hypertension

To explore further the pathogenesis of glucose intolerance and insulin resistance observed in patients with cirrhosis and portal hypertension, we studied a 35-year-old woman with presinusoidal portal hypertension without cirrhosis due to nodular regenerative hyperplasia of the liver. After oral glucose ingestion, glucose tolerance remained normal; however, this occurred at the expense of a markedly hyperinsulinemic plasma response, suggesting the presence of insulin resistance. To examine this question more directly, we performed a stepwise euglycemic insulin clamp study in combination with an infusion of [6-3H]glucose and [1-14C]palmitate and indirect calorimetry. The ability of insulin to promote total body (primarily muscle) glucose uptake was markedly impaired, whereas its effect to suppress hepatic glucose production was normal compared with results obtained in nine healthy subjects. Moreover, insulin failed to normally suppress plasma free fatty acid turnover and oxidation in this patient. This informative case demonstrates that portal hypertension alone, without hepatic dysfunction from cirrhosis, is associated with impaired insulin-mediated glucose and plasma free fatty acid metabolism and may also play a predominant role in the development of insulin resistance in many cirrhotic patients.

Alcoholic Liver Disease Associated with Increased Gamma-Glutamyltransferase Activities in Serum and Liver

Chronic alcohol consumption leads to increased activities of gamma-glutamyltransferase (GGT) in the serum which are associated with an enhancement of GGT activities in the liver. These findings suggest that increased GGT activities commonly found in alcoholic liver disease can be ascribed primarily to hepatic enzyme induction rather than to liver cell injury, since hepatic GGT activities were increased but not reduced. Moreover, at the fatty liver stage the fetal form of GGT in the serum is much higher in activity that the adult form, whereas the reverse constellation can be found in patients with alcoholic liver cirrhosis. Thus, these preliminary data suggest that the determination of various forms of GGT in the serum of alcoholics may be useful in establishing the particular stage of alcoholic liver disease by a simple enzyme test in the serum.