Kinetics and metabolic activity of biosynthetic NPH insulin evaluated by the glucose clamp technique

The glucose clamp technique has been used to evaluate the metabolic activity of NPH biosynthetic insulin in diabetic subjects free from anti-insulin antibodies. After overnight blood glucose normalization with a glucose-controlled insulin infusion system (Biostator), an s.c. injection of NPH insulin was given in the abdominal region. The insulin dose (0.236 +/- 0.05 U/kg body wt) was related to the usual intermediate-acting insulin requirement in the morning. Glucose was clamped at 100 mg/dl by a feedback i.v. glucose infusion. The end of the action of s.c. injected insulin considered conventionally to be the time of the spontaneous rise of blood glucose to 110 mg/dl. Free insulin levels were higher and the length of action was longer after NPH porcine than after NPH biosynthetic human insulin (BHI) (area under the free insulin curve: porcine 1423 +/- 556 mU/L/h; BHI 1045 +/- 338 mU/L/h, P less than 0.05; length of action: porcine 16.0 +/- 3.2 h; BHI 13.7 +/- 0.9 h, P less than 0.05); the glucose requirement was higher after porcine (76.8 +/- 13.5 g) than after BHI (58.5 +/- 14.6 g) without reaching statistical significance. However, the metabolic activity of the bioavailable insulin (index of plasma free insulin activity) was similar for the two insulins (porcine 381 +/- 77.4, BHI 342.8 +/- 54.2 mU/L/g of glucose/h). We conclude that a difference in pharmacokinetics exists between NPH BHI and porcine NPH insulin, which makes the latter metabolically more active. The different behavior does not seem to be related to the insulin molecule itself but could be a consequence of the unequal content of protamine in the two pharmacologic preparations.

Erythromycin estolate impairs the mitochondrial and microsomal calcium homeostasis: correlation with hepatotoxicity

The effects of erythromycin estolate, a well known hepatotoxic macrolide antibiotic, on isolated rat hepatocyte viability and on subcellular Ca2+ transport have been investigated. Erythromycin estolate (0.5 mM), but not erythromycin base and erythromycin ethylsuccinate, induced 100% cell death after 60 min incubation, and caused maximal inhibition of mitochondrial and microsomal Ca2+ sequestration activities at 0.1 mM concentration. Sodium lauryl sulphate, which is the surfactant moiety of the erythromycin estolate molecule, caused effects similar to those exhibited by erythromycin estolate. Disorders of the intracellular calcium homeostasis seem to play a role in the lauryl sulphate-mediated hepatotoxic action of erythromycin estolate.

Insulin degradation in human erythrocytes. Effect of triton X-100 treatment on insulin-degrading activity of membranes

Human erythrocyte membrane has been demonstrate to possess an insulin-degrading activity. This activity is not due to a contamination by cytosolic factors and seems to be specific toward insulin. The fractionation of the erythrocyte membrane by Triton X-100 leads to the appraisal of an insulin-degrading activity in the Triton-extracted membranes higher than that present in the solubilized protein fraction. The degrading activity found in the extracted membranes is inhibited by the addition of the solubilized material. This last fraction seems to modulate, in the intact membrane, the whole insulin-degrading system.

Critical role of sulfhydryl group(s) in ATP-dependent Ca2+ sequestration by the plasma membrane fraction from rat liver

The ATP-dependent sequestration of Ca2+ by the plasma membrane fraction from rat liver is stimulated by reduced glutathione and dithiothreitol and inhibited by diamide and t-butyl hydroperoxide. The inhibitory effect on Ca2+ sequestration by the oxidizing agents is prevented in the presence of the thiols. Our results therefore suggest that free sulfhydryl group(s) may be critical for the activity of hepatic plasma membrane Ca2+ translocase, and that inhibition of this activity by the oxidation of such group(s) may contribute to the perturbation of Ca2+ homeostasis during oxidative stress.

[Use of the endocrine artificial pancreas (GCIIS; Biostator) in heart surgery]

It is well known that deep hypothermia used in open-heart surgery is usually associated with a marked reduction in carbohydrate tolerance, especially dangerous in the diabetic patient, since it might result in severe metabolic complications, namely ketosis and hyperosmolar coma. In order to prevent the occurrence of such complications we treated an insulin-dependent diabetic patient undergoing cardiovascular surgery, with a feed-back insulin infusion operated by an artificial pancreas (GCIIS, Biostator). The Biostator was then used to perform a continuous (minute by minute) blood glucose monitoring in 2 more patients, a type II (non insulin-dependent) diabetic and a non diabetic. Blood samples were drawn sequentially in order to determine plasma free insulin concentration. The glycemic profile observed in the insulin-dependent diabetic under artificial pancreas treatment was similar to that in the non-diabetic. Plasma free insulin levels dropped near to zero during by-pass cooling, returning toward basal level during the rewarming phase. Such results are then discussed by the Authors and given a pathogenetic interpretation.

Effects of different beta-receptor antagonists on handgrip in essential hypertension

To assess the influence of selective and nonselective beta blockers with or without ISA we evaluated the extent of pressor responses to isometric exercise in 15 hypertensive patients who had first been treated with atenolol (100 mg/day) and subsequently with mepindolol (15 mg/day) for 2 months each following placebo administration for 2 weeks. Isometric handgrip was always performed in a supine position. Blood pressure and heart rate were measured at 30% of the maximal voluntary contraction. The percentages of blood pressure increases associated with the isometric test were similar during treatment with the two beta blockers; only heart rate was significantly lower. Systolic and diastolic blood pressures showed a lower increase with mepindolol than with atenolol, but the differences were not statistically significant. In conclusion, cardioselective beta blockers without ISA and nonselective beta blockers with ISA influence systolic and diastolic blood pressure responses to a handgrip of 30% in the same way. Only heart rate shows a lower but rather small increase during the cardioselective drug treatment.

Regulation of intracellular calcium compartmentation: studies with isolated hepatocytes and t-butyl hydroperoxide

In suspensions of isolated hepatocytes, two intracellular Ca2+ pools were distinguished in the presence of the metallochrome indicator arsenazo III, first by treatment with the uncoupler carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP) and then with the Ca2+ ionophore A23187. The available evidence indicates that the two pools are of mitochondrial and extramitochondrial origin. Metabolism of t-butyl hydroperoxide by hepatocytes caused release of Ca2+ from both compartments concomitant with oxidation of cellular glutathione and NADPH, which was followed by characteristic alterations in cell surface structure. When NADPH oxidation was prevented by selective inactivation of glutathione reductase, t-butyl hydroperoxide metabolism was without effect on the mitochondrial Ca2+ pool, whereas the loss from the extramitochondrial pool was accelerated. Our results suggest that different regulatory mechanisms modulate mitochondrial (NADPH-dependent) and extramitochondrial (thiol-dependent) Ca2+ compartmentation and that disturbance of normal Ca2+ homeostasis may be critical in peroxide-induced cytotoxicity.

The metabolism of menadione (2-methyl-1,4-naphthoquinone) by isolated hepatocytes. A study of the implications of oxidative stress in intact cells

The cytotoxic effects of many quinones are thought to be mediated through their one-electron reduction to semiquinone radicals, which subsequently enter redox cycles with molecular oxygen to produce active oxygen species and oxidative stress. The two-electron reduction of quinones to diols, mediated by DT-diaphorase (NAD(P)H: (quinone-acceptor) oxidoreductase), may therefore represent a detoxifying pathway which protects the cell from the formation of these reactive intermediates. By using menadione (2-methyl-1,4-naphthoquinone) and isolated hepatocytes, the relative contribution of the two pathways to quinone metabolism has been studied and a protective role for DT-diaphorase demonstrated. Moreover, in the presence of cytotoxic concentrations of menadione rapid changes in intracellular thiol and Ca2+ homeostasis were observed. These were associated with alterations in the surface structure of the hepatocytes which may be an early indication of cytotoxicity.

The metabolism of menadione impairs the ability of rat liver mitochondria to take up and retain calcium

The ability of mitochondria to take up and retain Ca2+, and thereby to effect the free intracellular concentration of this ion, is well established. More recently, it has been reported (Lehninger, A. L., Vercesi, A., and Bababunmi, E. A. (1978) Proc. Natl. Acad. Sci. U. S. A. 75, 1690-1696) that the redox state of pyridine nucleotides modulates mitochondrial Ca2+ balance, since the oxidation of mitochondrial NAD(P)H is associated with the release of Ca2+ from these organelles. The latter may be achieved by a variety of treatments including the incubation of Ca2+-loaded liver mitochondria with hydroperoxides, the metabolism of which by the glutathione peroxidase-glutathione reductase system results in NADPH consumption. The metabolism of menadione (2-methyl-1,4-naphthoquinone) by Ca2+-loaded rat liver mitochondria results in rapid oxidation and loss of pyridine nucleotides and a decrease in ATP level. It is also associated with Ca2+ release and an impaired ability of the mitochondria to take up and retain Ca2+. The effects of menadione on mitochondrial Ca2+ balance are more rapid and pronounced than those of t-butylhydroperoxide, and in contrast to those observed with the hydroperoxide, they are not abolished by pretreatment with a glutathione-depleting agent. The effects of menadione on Ca2+ homeostasis are probably initiated by NAD(P)H oxidation linked to the reduction of menadione by both NADH-ubiquinone oxidoreductase and NAD(P)H:(quinone-acceptor) oxidoreductase.

Improvement of artificial endocrine pancreas (Biostator; GCIIS) performance combining feedback controlled insulin administration with a pre-programmed insulin infusion

It is well known that the glycemic control accomplished by the artificial endocrine pancreas (Biostator; GCIIS), requires an excessive insulin consumption. In order to improve the Biostator performance, we have studied 5 insulin dependent diabetic patients on anticipated automatic pre-programmed insulin infusion starting at the beginning of breakfast. Such an operating method allowed us to obtain a significant reduction in insulin requirements (from 17,3 +/- 2,2 U to 13,3 +/- 2,2 U), and a better glycemic control (MBG 98,7 +/- 5,4 vs 111,1 +/- 5,6; M 2,34 +/- 0,9 vs 6,96 +/- 1,7; delta G 43,8 +/- 3 vs 73,4 +/- 9,7), as compared to those observed under conventional feed-back control in relation to breakfast.

Bleb formation in hepatocytes during drug metabolism is caused by disturbances in thiol and calcium ion homeostasis

A wide variety of toxic chemicals cause blebbing of the plasma membrane in isolated hepatocytes. These alterations in surface structure occur well before cell death. The formation of blebs appears to be directly related to changes in the concentration of extramitochondrial calcium ions. These changes probably reduce the ability of the hepatocyte cytoskeleton to maintain normal surface morphology. The concentration of soluble thiols, notably glutathione, appears to regulate the size of the extramitochondrial calcium ion pool. Disturbances in intracellular thiol and calcium ion homeostasis therefore seem to be responsible for the surface blebbing observed during toxic injury to isolated hepatocytes.

Binding and degradation of 125I-insulin in human erythrocytes. Comparative studies with hemolysate and membranes

Insulin degradation in human erythrocytes obtained from normal subjects is studied. Under the experimental conditions used, insulin binding and insulin degradation are strictly correlated, and no degrading activity is released in incubation medium. Comparative analysis of hemolysate and membranes shows that hemolysate possesses a definite insulin-degrading activity which is not linked to the hemoglobin molecule; the km of this enzymatic activity is of the same order of magnitude as that reported in other cells. At the concentration and in the condition used in this study, membranes degrade insulin at a lower rate than hemolysate.

Insulin receptors in myotonic dystrophy: a study with mononuclear leucocytes and erythrocytes

We evaluated insulin receptor activity on mononuclear leucocytes and erythrocytes in 9 patients with myotonic dystrophy and in 9 controls. The results demonstrated that in myotonic dystrophy: 1. insulin binding to specific receptors was significantly impaired (P less than 0.01) because of a reduction in the number of high and low affinity receptors. 2. the affinity constants were not significantly affected 3. there was no correlation between receptor activity, insulin behaviour and glucose tolerance. These data obtained in two different cellular systems suggest that the constant numerical reduction of insulin receptors was probably due to a systemic membrane defect, typical of myotonic dystrophy.

Insulin degradation in human erythrocyte. Effects of reduced glutathione on insulin degradation by hemolysate

In this study the Authors have evaluated the effects of reduced glutathione on insulin-degrading activity of hemolysate. The GSH increases, in a manner proportional to its concentration, the insulin degradation and this effect is due to the increase the Vmax of the same enzymatic system responsible of insulin degradation observed in absence of exogenous glutathione.

Insulin degradation in human erythrocyte. Effects of reduced glutathione on insulin degradation by membrane fractions

In this study the Authors have evaluated the effects of reduced glutathione on insulin-degrading activity of erythrocyte membrane fractions. The GSH increases, in a manner proportional to its concentration, the insulin degradation by intact membranes, solubilized proteins and membranes treated with Triton X-100. The net increase of degradation is greater for intact and extracted membranes than for solubilized proteins. These data suggest that in human erythrocyte membrane exists an enzymatic system GSH-dependent for insulin degradation and that this system is only partially solubilized by Triton X-100 treatment.

[The hematic histamina in malignant tumors of alimentary canal and respiratory apparatus (author's transl)]

The Authors estimated the blood histamine level in 39 subjects with malignant tumors of the lung (19), Sthomac (11) and colon (9) and found a significant increase with respect to normal values. Among the groups investigated, the subjects with gastric tumors presented the greatest values. The results show a significant relationship between tumor and hyperhistaminemia as demonstrated by other Authors in experimental animals.

[Total hematic histamine in gastrectomized patients]

The Authors estimated the blood histamine in 15 patients after gastric-resection and found a significant decrease in all the cases with respect either to basal valus or to normal subjects. The autors suppose it is due to a lower presence of istidin-decarbojlase, owing to removal of gastric tissue where such enzime is placed.

Insulin receptors in human mononuclear leucocytes. II. Binding and degradation of insulin in obese subjects

The binding of insulin to the receptors on circulating mononuclear cells of obese subjects is significantly decreased when compared to the binding in normal subjects. This fenomenon is due to the reduction of the number of insulin receptors rather than reduction in affinity. The insulin degradation is also reduced, but a very strong correlation, similar to that demonstrated in normal subjects exist between insulin binding to its receptors and insulin degradation.

Insulin receptors in human mononuclear leucocytes. I. Binding and degradation of insulin in normal subjects

The binding and degradation of 125I-Insulin were investigated in mononuclear leukocytes of normal subjects. The binding data analysis show that the insulin degradation is strictly correlated with the binding of the hormone to its receptors: these data suggest that the binding of insulin to specific receptor is the possible first step for its degradation.