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Biomedical subjects

F Belfiore

Publications and source records attributed to F Belfiore.

At least 55 records · Page 3Linked to original sources
PubMed1987

Metabolic effects of short-term fasting in obese hyperglycaemic humans and mice.

The aim of this study was to investigate the metabolic effects of short-term fasting in obese diabetic patients and to correlate the observed changes with the activity of hepatic key enzymes in an animal model of obesity-associated diabetes (ob/ob mice, C57BL/6J strain). In obese diabetic patients (ODP), a 72-h fast (causing slight change in body weight) decreased fasting glycemia by 3.82 +/- 0.79 mmoles/l and significantly improved glucose tolerance (OGTT) while reducing basal and stimulated insulinemia, whereas in obese non-diabetic patients (ONDP) only a small decrease in fasting glycemia (1.24 +/- 0.51 mmoles/l) occurred. This suggests that in ODP hyperphagia is a factor contributing to maintain hyperglycaemia and glucose intolerance (in the face of hyperinsulinaemia, indicating insulin resistance). In fed obese hyperglycaemic mice (OHM), which are a good model of the human obesity-associated diabetes, hepatic fructose-1,6-diphosphatase (F16Pase) and glucose-6-phosphatase (G6Pase), involved in glucose production, showed increased activity (+52 and +200 per cent, respectively) compared to control mice (CM), and the ratios of F16Pase and G6Pase to the opposing enzymes phosphofructokinase (PFK1) and glucokinase (GK), i.e. the F16Pase/PFK1 and G6Pase/GK ratios, were increased by 38 and 101 per cent, respectively, suggesting increase in gluconeogenesis and perhaps in glycogenolysis. In the 48-h fasted OHM, F16Pase activity was decreased (-30 per cent) compared to the fed animals, while the activity of G6Pase showed a smaller and statistically not significant change (-22 per cent). In contrast, in the CM a 48-h fasting was associated with a trend toward increased F16Pase (+22 per cent) and G6Pase (+173 per cent). However, since PFK1 and GK decreased to a similar extent in OHM and CM, the F16Pase/PFK1 and G6Pase/GK ratios, basally elevated in the OHM, did not change with fasting, whereas in the CM they showed a striking elevation (+71 and +274 per cent, respectively). The basally elevated F16Pase/PFK1 and G6Pase/GK ratios (functionally linked to glucose production) in the OHM may contribute to maintain hyperglycaemia; in these mice, the lack of further increase in the glucose production-related F16Pase/PFK1 and G6Pase/GK ratios (which occurs in CM) with fasting might allow that the interruption of the afflux of dietary carbohydrates ameliorates the glycaemic level. Similar mechanisms might occur also in the ODP.

Adult↗
PubMed1986

Anabolic response of some tissues to diabetes.

In contrast to liver, adipose tissue, and muscle, in which the diabetic state is associated with a "catabolic response," some tissues, typically the kidney and perhaps the intestinal mucosa and some vascular cell types, show an "anabolic response" to diabetes, with enhanced activity of the anabolic pathways and diminished activity of the catabolic ones. The kidney of alloxan or streptozotocin diabetic rats is hypertrophied, and shows enrichment in intracellular glycogen and abundant accumulation of glycoprotein material at the basement membrane level. Accordingly, protein synthesis and the enzymes of glucose utilization as well as those engaged in UDP sugar formation or in the hydroxylation and glycosylation processes (required for glycoprotein synthesis) show increased activity in the diabetic kidney, while the catabolic, lysosomal enzymes (cathepsin D and several glycosidases) are depressed. We observed a reduction of -24% in the activity of cathepsin D and -23% in that of galactosidase in the kidney of streptozotocin diabetic mice, as opposed to increases of +135 and +32%, respectively, found in liver. It is not known which factor(s) may be responsible for such an anabolic response of some tissues to diabetes, but persistent hyperglycemia and/or some hormonal abnormalities may be involved. The above data refer to changes in tissue enzyme content caused by induction-repression mechanisms, but rapid (activation-inhibition) effects may also occur. We observed that preincubation of slices of mouse kidney cortex for 10 min with 20.8 mmole/liter glucose resulted in a 80% activation of phosphofructokinase, as assayed in the tissue homogenate at physiological (50 mumole/liter) concentration of the substrate fructose-6-P, suggesting that hyperglycemia may be responsible for some of the metabolic changes occurring in the diabetic kidney.

Animals↗
PubMed1985

Cathepsin D and other hydrolases in the kidney of streptozotocin-diabetic mice. Possible relevance to microangiopathy.

The lysosomal enzymes cathepsin D (E.C. 3.4.23.5), alpha-glucosidase (E.C. 3.2.1.20) and beta-galactosidase (E.C. 3.2.1.23), potentially involved in the breakdown of the peptide component and the disaccharide units of basement membrane glycoproteins, were studied in the kidney cortex and liver of streptozotocin-diabetic mice. In the liver of diabetic mice, as compared to controls, an increase was found for the total activity (measured in frozen-thawed homogenates) of cathepsin D (+135%, P less than 0.01) and beta-galactosidase (+32%, P less than 0.05). In the kidney a decrease was observed for both the free activity (measured in 12,000 g supernatant) and the total activity of these two enzymes (cathepsin D: -62% and -24%; beta-galactosidase: -29% and -23%; P less than 0.05 in all instances). Alpha-glucosidase did not show significant changes in either tissues. Total protein content of the two organs did not change significantly with diabetes and therefore cannot account for the enzyme alterations observed. These data indicate that the response of kidney to diabetes is opposite to that of liver (decrease versus increase in catabolic enzymes), and suggest decreased degradation of basement membrane in some tissues in diabetes, which may contribute to the thickening of basement membrane and therefore to the development of microangiopathy.

Animals↗
PubMed1984

Insulin resistance in the obese hyperglycemic (ob/ob) mouse. Failure of hyperinsulinemia to activate hepatic pyruvate kinase (PK).

In obese hyperglycemic (ob/ob) mice, as compared to controls, hepatic pyruvate kinase (PK) activity was enhanced by 35.63% (214.75 +/- 13.60 nmol/min/mg protein v 158.33 +/- 10.47, P less than 0.01) when measured at saturating (6.6 mmol/L) concentration of the substrate phosphoenolpyruvate (total activity), but the activity recorded at subsaturating (1.3 mmol/L) substrate concentration (active fraction) was unchanged (86.37 +/- 6.42 v 85.66 +/- 13.59) or even decreased if expressed as percent of the total activity (40.21 +/- 2.56% v 54.10 +/- 5.07, P less than 0.05). Since insulin induces the synthesis of hepatic PK and favors the conversion of the inactive (phosphorylated) to the active (dephosphorylated) form, these findings suggest that in ob/ob mice the striking hyperinsulinemia, although it is able to increase the hepatic content of PK, fails to activate this enzyme. This may favor gluconeogenesis in these animals. The hepatic concentration of PK effectors (fructose-1,6-P2 and phosphoenolpyruvate) was unchanged in ob/ob mice, and the in vitro effect of the activator fructose-1,6-P2 (15 mumol/L), which would favor the activation (dephosphorylation) of PK, was preserved. It is suggested that hepatic PK in ob/ob mice is resistant to activation by insulin.

Animals↗
PubMed1980

Defects in enzyme regulation versus defects in enzyme synthesis as cause of metabolic disorders.

Based on the consideration that normal metabolic processes depend upon the activity of key enzymes (and membrane carriers) as modulated by regulatory factors (hormones, diet, endogenous compounds, age, physical activity, environmental agents), metabolic disorders might be classified into two groups: (I) defects in enzyme synthesis, leading to enzyme deficiency (classical inborn errors of metabolism) or to qualitative (structural) enzyme alterations (entailing unresponsiveness to regulation), in the presence of normal regulatory factors; (II) defects in enzyme regulation, which include metabolic syndromes such as diabetes mellitus, obesity and hyperlipoproteinemias (other than type I), and are due to changes in enzyme activities caused by alterations in regulatory factor(s) (secondary to various causes), in the presence of normally responsive enzymes.

Allosteric Regulation↗
PubMed1979

Insulin resistance in obesity: a critical analysis at enzyme level. A review.

Based on the consideration that insulin does not act directly on metabolic processes but affects membrane carriers and key-enzymes that regulate metabolic pathways, determination of insulin responsiveness of the various key-enzymes is suggested as a very appropriate method for studying insulin resistance. Insulin resistance, as it occurs in obese or obese-diabetic humans and animals, is most often associated with hyperinsulinemia, and is characterized not only by increased activity of key-enzymes of pathways known to be stimulated by insulin (glycolysis, lipogenesis), with the possible exception of glycogen synthesis, but also by a trend towards increased activity of key-enzymes of 'catabolic pathways', normally depressed by insulin. In the adipose tissue there is a normal-to-enhanced basal lipolysis, which in man would result from the prevalence of the active over the inactive form of triacylglycerol lipase. In muscle, the increased amino-acid release that can be inferred from the elevated blood level of both alanine and branched-chain amino acids suggests an enhanced proteolysis. In liver, there is an elevation in the activity of the key gluconeogenic enzymes, which forms the basis of the augmented gluconeogenesis. In both muscle and liver, phosphorylase is also elevated with no change in glycogen synthase. Therefore, insulin resistance seems to consist of the failure of insulin to depress the key-enzymes of catabolic pathways. Possible resistance of glycogen synthetase, which might account for decreased glucose utilization in muscle, may be due to the opposing effects of the phosphorylation process on glycogen synthetase and phosphorylase, implying that activation of phosphorylase (which occurs in obesity) entails inhibition of the synthetase. The fact that insulin insensitivity concerns only the 'catabolic' but not most 'anabolic' pathways makes it unlikely that the unresponsiveness is due to a reduction in insulin receptors or increase in insulin degradation. Since resistance to insulin is shown by enzymes regulated by such different mechanisms as induction-repression (gluconeogenic enzymes), covalent modifications (lipase, phosphorylase), and changes in lysosome stability (lysosomal proteases responsible for proteolysis, a single basic mechanism for explaining insulin insensitivity cannot be envisaged at present.

Adipose Tissue↗
PubMed1977

Enzymes of citrate-cleavage pathway in liver of subjects with adult-onset diabetes.

In the liver of adult diabetics, the activity of two enzymes of the citrate-cleavage pathway was increased, the change being statistically significant for NADP-malate dehydrogenase (+ 46%, p less than 0.05) but not significant for ATP citrate-lyase (+ 55%, p greater than 0.10). The increased activity of NADP-malate dehydrogenase, together with the previously described elevation of pentose cycle dehydrogenases, suggests enhanced NADPH generation. Considering the recently proposed possibility of extramitochondrial acetyl-CoA formation by routes other than the citrate-cleavage (i.e., via cytoplasmic acetyl-CoA synthetase), our data is consistent with the occurrence of increased lipogenetic capacity.

ATP Citrate (pro-S)-Lyase↗
PubMed1976

Enzymes related to lipogenesis in the adipose tissue of obese subjects.

In a group of ten adult obese subjects, maintained for 15 days on a normal caloric intake and balanced diet, the activity of hexokinase (EC 2.7.1.1),6-phosphofructokinase (EC 2.7.1.11), and ATP citratelyase (EC 4.1.3.8) in the adipose tissue was significantly increased, both on a protein and on a fat cell number basis, compared to matched normal subjects. The activity of glucose-6-phosphate dehydrogenase (EC 1.1.1.49), malate dehydrogenase (EC 1.1.1.37), and malate dehydrogenase (decarboxylating) (NADP) (EC 1.1.1.40), on the other hand, was unchanged. Since both hexokinase and 6-phosphofructokinase are rate-limiting in glycolysis, their enhanced activity would indicate the occurrence of an increased capacity to metabolize glucose and therefore to generate alpha-glycerophosphate. The elevation of ATP citrate-lyase would suggest increased lipogenesis, owing to the regulatory role that this enzyme plays in fatty acid synthesis. The normal activity of glucose-6-phosphate dehydrogenase and malate dehydrogenase (decarboxylating) (NADP), which supply NADPH for the reduction of acetyl-CoA to fatty acids, would suggest that the change in lipogenesis is of moderate degree, thereb) affecting only the most rate-limiting enzyme, ATP citrate-lyase. These data, on the whole, are consistent with the occurrence of enhanced triglyceride formation. Whether the enzyme changes observed are adaptive or genetic in nature remains to be clarified.

ATP Citrate (pro-S)-Lyase↗
PubMed1976

NADPH-forming dehydrogenases in the adipose tissue of obese and nonobese diabetics.

The activity of glucose-6-phosphate dehydrogenase (EC 1.1.1.49) of adipose tissue was markedly decreased, both on a protein and on a fat cell number basis, in nonobese diabetics compared to control subjects, but was unchanged in obese diabetics. Average value in the obese diabetics was about fourfold higher than in nonobese diabetics. On the other hand, the activity of malate dehydrogenase (decarboxylating) (NADP) (EC 1.1.1.40) was reduced by about 50% in both groups of diabetics. These findings suggest that in obese diabetics NADPH-generation in the adipose tissue, necessary for several biosynthetic processes, might be less severely depressed than in lean diabetics.

Adipose Tissue↗
PubMed1975

Enzymes of glucose metabolism and of the citrate cleavage pathway in adipose tissue of normal and diabetic subjects.

Enzyme activities operative in glucose degradation and citrate cleavage pathway were studied in the adipose tissue of twenty-four patients with adult-onset diabetes and normal body weight, aged 59+/-9 years, and twenty-four matched controls. In normal tissue, type II (heat-inactivated) hexokinase moderately predominated over type I (heat-resistant). 6-Phosphofructokinase had an extremely low activity, which was by far the lowest among the ten glycolytic enzyme activities investigated, and which therefore might greatly limit the glycolytic rate. The level of glucose-6-phosphate dehydrogenase and phosphogluconate dehydrogenase (decarboxylating) was elevated above that occurring in other tissues. This, especially if considered together with the low 6-phosphofructokinase activity, would suggest a major role of pentose cycle in glucose degradation. Of the citrate cleavage pathway enzymes, ATP citrate-lyase, although having a lower activity than malate dehydrogenase and malate dehydrogenase (decarboxylating) (NADP), was readily measurable, which contrasts with previous data by others. This finding is consistent with the occurrence of lipogenetic capacity in human adipose tissue. In diabetic tissue, there was a decreased activity, both on a protein and on a wet-weight basis, of enzymes concerned with the glucose entry into metabolic pathways, namely hexokinase (both type I and, especially, type II) and pentose cycle dehydrogenases, as well as of pyruvate kinase. This could be connected with the defective glucose utilization by adipose tissue in diabetes. Beside the above-mentioned dehydrogenases, malate dehydrogenase (decarboxylating) (NADP) was also diminished. The reduction of these NADPH-forming enzymes, which supply reducing equivalents for fatty acid synthesis, would suggest a depressed lipogenesis.

ATP Citrate (pro-S)-Lyase↗
PubMed1975

Enzyme activities of NADPH-forming metabolic pathways in normal and leukemic leukocytes.

With respect to the enzymes of NADPH-forming metabolic pathways in human leukocytes: (a) Glucose-6-phosphate dehydrogenase and phosphogluconate dehydrogenase (decarboxylating) were less active in leukocytes (mostly myeloblasts) from eight patients with acute myeloblastic leukemia (I) than in leukocytes (mostly granulocytes) from 16 normal subjects (II). (b) Of the enzymes of the citrate cleavage pathway, ATP citrate lyase and malate dehydrogenase (decarboxylating) (NADP+) were virtually absent in the cells studied. (c) Isocitrate dehydrogenase (NADP+), aspartate aminotransferase, and alanine aminotransferase, which, together with the much more active malate dehydrogenase, constitute a newly proposed NADPH-forming metabolic cycle, showed a higher activity in I than in II or III, and therefore could compensate, as concerns NADPH-generation, for the low activity of pentose cycle dehydrogenases. We are not sure whether the enzymatic characteristic of I cells is attributable to their immaturity or to their leukemic nature.

ATP Citrate (pro-S)-Lyase↗