Biomedical subjects

R Curi

Publications and source records attributed to R Curi.

At least 73 records · Page 4Linked to original sources

PubMed1999

Superoxide dismutase, catalase and glutathione peroxidase activities in the lymphoid organs and skeletal muscles of rats treated with dexamethasone.

The effect of dexamethasone (a synthetic glucocorticoid) on the activity of antioxidant enzymes (superoxide dismutase (SOD), catalase and glutathione peroxidase) of the lymphoid organs (mesenteric lymph nodes (MLN), spleen and thymus) was investigated. For comparison with non-immune tissues, skeletal muscles (soleus and gastrocnemius (GC) were also studied. As an indication of the occurrence of lipid peroxidation, the content of thiobarbituric acid reactant substances (TBARs) was also determined. Dexamethasone treatment decreased the TBARs content of the lymphoid organs and raised it in the GC and soleus muscles. The activity of Cu/Zn-SOD was reduced in all tissues. However, the activity of Mn-SOD was decreased in the MLN and soleus muscle only. The activity of catalase was reduced in the MLN and thymus and raised in the spleen and GC and soleus muscles. The imposed treatment raised the activity of GPX in the MLN, thymus and spleen and reduced it in GC and soleus muscles. These data led us to postulate that the mechanism for the therapeutic effect of glucocorticoids as antiinflammatory and immunosuppressive agents might include modification of antioxidant enzyme activities.

Animals↗

PubMed1999

NADPH-oxidase activity and lipid peroxidation in neutrophils from rats fed fat-rich diets.

In order to investigate the effect of fat-rich diets on neutrophil functions, 21 day-aged rats were fed for 6 weeks with a control diet consisting of a regular laboratory rodent chow (4 per cent final fat content), a control diet supplied with soybean oil (15 per cent final fat content), or a control diet supplied with coconut oil (15 per cent final fat content). Glycogen-elicited peritoneal neutrophils from rats fed soybean and coconut oil-enriched diets presented a reduction in spontaneous and PMA-stimulated H2O2 generation relative to neutrophils from rats fed the control diet. The activity of superoxide dismutase, glutathione peroxidase and catalase did not change in animals fed fat-rich diets. In addition, the capacity to generate O2-, spontaneously or in response to PMA, did not change in neutrophils from animals fed fat-rich diets. Values attained matched those observed in animals fed the control diet, regardless of the method used to measure O2-, the superoxide dismutase-inhibitable reduction of cytochrome c or the lucigenin-dependent chemiluminescence. However, the initial rate of O2- generation both in resting neutrophils and in PMA-stimulated cells was significantly reduced when animals were fed with coconut or soybean oil-enriched diets due, at least in part, to a reduction in the activity of glucose-6-phosphate dehydrogenase. The concentration of thiobarbituric acid reactive substances, an index of lipid peroxidation, was increased in animals fed both fat-rich diets. This was accompanied by an increase in arachidonic acid content in these cells. Results presented suggest that lipid peroxidation in neutrophils from animals fed fat-rich diets may be associated with a consumption of H2O2 yielding more reactive oxygen-derived species such as the hydroxyl radical.

Animals↗

PubMed1999

Cholesterol inhibits glutamine metabolism in LLC WRC256 tumour cells but does not affect it in lymphocytes: possible implications for tumour cell proliferation.

The effect of cholesterol on proliferation and glutamine metabolism of lymphocytes and tumour cells was investigated. The addition of cholesterol to the culture medium did not cause a significant effect on [2-(14)C]-thymidine incorporation in lymphocytes. In the presence of concanavalin A, lymphocyte proliferation was increased by cholesterol (from 0.013 up to 1.3 microm). At high concentrations (234 and 468 microm), however, a marked inhibition of lymphocyte proliferation occurred. The same inhibitory effect was observed in the presence of lipopolysaccharides. Cholesterol also caused a marked decrease of LLC WRC256 tumour cell growth at 117 and 234 microm. The same findings were obtained by the measurement of [2-(14)C]-thymidine incorporation in these cells. The effect of cholesterol on phosphate-dependent glutaminase activity was then tested in cultured lymphocytes and LLC WRC256 tumour cells. Cholesterol at concentrations of 117 and 234 microm did not alter this enzyme activity in lymphocytes. However, this sterol, already at 26 microm, caused a 44 per cent reduction in glutaminase activity. Similar to the changes observed for glutaminase, cholesterol reduced glutamine oxidation in LLC WRC256 tumour cells, whereas no effect was observed on lymphocytes. Therefore, cholesterol might control lymphocyte and tumour cells proliferation by different mechanisms. The significance of these findings for the immune function in tumour-bearing patients remains to be investigated.

Animals↗

PubMed1999

Thioglycolate-elicited rat macrophages exhibit alterations in incorporation and oxidation of fatty acids.

Incorporation and oxidation of fatty acids (FA) were investigated in resident and thioglycolate-elicited (TG-elicited) rat macrophages (Mphi). Both cell types presented a time-dependent incorporation of [14C]-labeled palmitic acid (PA), oleic acid (OA), linoleic acid (LA), and arachidonic acid (AA) up to 6 h. The total amount of [14C]-FA incorporated by resident Mphi after 6 h was: AA > PA = LA > OA. TG-elicited cells presented a 50% reduction in the incorporation of LA, PA, and AA, whereas that of OA remained unchanged as compared to resident Mphi. The FA were oxidized by resident Mphi as follows: LA > OA > PA > AA. TG elicitation promoted a reduction of 42% in LA oxidation and a marked increase in AA oxidation (280%). The increased oxidation of AA in TG-elicited cells may account for the lower production of prostaglandins in Mphi under these conditions. The full significance of these findings for Mphi function, however, remains to be examined.

Animals↗

PubMed1999

Modulation of insulin secretion by leptin.

The present study examines the acute effect of leptin (50 nM) on insulin secretion and on the fractional outflow rates of 45Ca2+ and 86Rb+ from pancreatic islets isolated from male lean albino rats. Under a constant physiological glucose concentration (5.6 mM), the addition of leptin to the perifusion medium led to an increment in 45Ca2+ fractional outflow rate followed by a significant (p < 0.05) increase (26%) in the insulin release. At low glucose concentration (2.8 mM), leptin also elicited a significant (p < 0.05; 50-60%) increase in insulin secretion. However, under supraphysiological (16.7 mM) glucose concentration, the rapid first-phase insulin secretion response was abolished. At low glucose levels, islets perifused in the presence of leptin presented a lower 86Rb+ fractional outflow rate compared with perifused controls. In contrast, when glucose was switched to 16.7 mM, compared with controls, a slight increase in the 86Rb+ fractional outflow rate was observed instead. These in vitro data provide evidence that, by changing K+ fluxes, leptin might modulate insulin secretion from pancreatic islets.

Animals↗

PubMed1999

Modulation of hypersensitivity reaction by lipids given orally.

The effect of lipids administration by gavage (0.4% body weight) given daily during four weeks on the hypersensitivity reaction in trachea, upper and lower bronchi, liver, kidney, mesentery, and pancreas was investigated in male rats. The plasma exudation was assessed by using Evans blue (EB) dye extravasation method. There was a significant difference in the permeability of the organs in nonimmunized rats. The immunization increased the vascular permeability and the response with the organs varied greatly. The effect of lipids on anaphylactic reaction was compared to those of untreated rats (control group). The EB extravasation was significantly increased in the trachea obtained from rats treated with cocoa butter and soybean oil. In the upper bronchi of rats treated with soybean oil, the EB extravasation was increased. However, in the lower bronchi, none of the treatments with lipids changed the extravasation of EB. The same was observed in the liver and kidney. The animals treated with lipids by gavage did not present differences in EB extravasation in the mesentery. However, in the pancreas and duodenum, the treatment with fish and soybean oils and cocoa butter markedly lowered EB extravasation.

Administration, Oral↗

PubMed1999

Glutamine metabolism by lymphocytes, macrophages, and neutrophils: its importance in health and disease.

Many aspects of the cell biology of lymphocytes, macrophages, and neutrophils have been studied extensively. Our recent work on these cells has investigated how fuel metabolism, especially glutamine metabolism, is related to the specific function of these cells in the inflammatory response. The high rate of glutamine utilization and its metabolism in such immune cells has raised the question of why glutamine is responsible for these functions. The macrophage has access to a variety of metabolic fuels both in vivo and in vitro. The quantitatively important role of glutamine in the processes of free radical and cytokine production has been established in our laboratories. Our current understanding of the rate of utilization and the pathway of metabolism of glutamine by cells of the immune system raises some intriguing questions concerning therapeutic manipulation of utilization of this amino acid, specifically the phagocytic and secretory capacities of cells of the defense system can be beneficially altered.

Journal Article↗

PubMed1999

Comparing effects of leptin and insulin on glucose metabolism in skeletal muscle: evidence for an effect of leptin on glucose uptake and decarboxylation.

OBJECTIVE: To investigate the effects of leptin and the combination of insulin and leptin on glucose metabolism in incubated rat soleus muscle. ANIMALS: Male lean albino rats (50-70 g) of the Wistar strain were used in all experiments. MEASUREMENTS: 2-Deoxy-D-[3H]-glucose (2-DG) uptake, glycogen synthesis, lactate synthesis, glucose and pyruvate decarboxylation. RESULTS: Leptin (1, 10 and 100 nM), increased 2-Deoxyglucose uptake from 4.07+/-0.23 micromol/h(-1)/g(-1) (basal) to 5.88+/-0.29 micromol/h(-1)/g(-1) (100 nM) (P < 0.05); however, leptin did not potentiate the effect of either physiological (100 microU/ml) or supra-physiological (10000 microU/ml) insulin concentrations on glucose uptake. Glycogen synthesis rose almost 2-fold in the presence of supra-physiological leptin concentrations (100 nM). The combination of insulin and leptin did not present any additional effect on glycogen synthesis beyond that caused by insulin. Compared to the control group, the decarboxylation of [U-14C] D-glucose increased 75%, 246% and 304% (P < 0.05) in the presence of 1, 10 and 100nM leptin, respectively. When leptin (100 nM) was combined with insulin in the incubation medium, the 14CO2 production rose almost 4-fold (397%) (P < 0.05) and more than 5-fold (527%) (P < 0.05) for the 100 microU/ml and 10000 microU/ml insulin concentrations, respectively. In the presence of leptin (100 nM), the decarboxylation of [1-14C]- and [2-14C]-pyruvate in incubated muscles rose 89% and 49%, respectively, indicating that both pyruvate dehydrogenase and Krebs cycle are activated by leptin. CONCLUSION: These data demonstrate that, in soleus muscle, leptin per se exerts a direct and acute insulin-like effect, stimulating glucose uptake, glycogen synthesis, lactate formation and glucose oxidation.

Animals↗

PubMed1999

Acute effects of leptin on glucose metabolism of in situ rat perfused livers and isolated hepatocytes.

OBJECTIVE: To investigate whether leptin interferes directly with glycogenolysis and gluconeogenesis in isolated rat hepatocytes and also in in situ rat perfused livers. ANIMALS: Male albino rats (200-250 g) were used in all experiments. MEASUREMENTS: D-glucose, L-lactate and pyruvate production. RESULTS: In the present study, no differences were found for the rates of glycolysis, as expressed by the areas under the curves, among control (24.2+5.0 mmol¿g), leptin (32.0+4.5 mmol¿g), glucagon (24.7+3.0 mmol¿g), and the leptin + glucagon (23.8+3.4 mmol¿g) groups. No difference was found for the rates of glycogenolysis between the control and the leptin perfused livers (15.2+3.9 and 15.0+3.2 mmol¿g, respectively). In the presence of glucagon, the areas under the curves for the rate of glycogenolysis rose to 108.6+3.8 mmol¿g. When leptin was combined with glucagon, the area under the curve for glycogenolysis was 43. 7+4.3 mmol¿g. In fact, leptin caused a reduction of almost 60% (P<0. 001) in the rate of glucagon-stimulated glycogenolysis. Under basal conditions, the addition of leptin (100 ng¿ml) to the incubation medium did not elicit any alteration in glucose production by isolated hepatocytes. However, in the presence of leptin, the production of glucose from glycerol (2 mM), L-lactate (2 mM). L-alanine (5 mM) and L-glutamine (5 mM) by the isolated hepatocytes was significantly reduced (30%, 30%, 23% and 25%, respectively). The rate of glucose production (glycogenolysis) by isolated hepatocytes was not different between the control and the leptin incubated groups (445.0+/-91.0 and 428.0+/-72.0 nmol¿106 cells¿h, respectively). CONCLUSION: We conclude that leptin per se does not directly affect either liver glycolysis or its glucose production, but a physiological leptin concentration is capable of acutely inducing a direct marked reduction on the rate of glucagon-stimulated glucose production in in situ rat perfused liver. Leptin is also capable of reducing glucose production from different gluconeogenic precursors in isolated hepatocytes.

Alanine↗

PubMed1999

Glucose induces an acute increase of superoxide dismutase activity in incubated rat pancreatic islets.

The activity of superoxide dismutase (SOD), catalase, and glutathione peroxidase (GSP) in isolated rat pancreatic islets exposed to high glucose concentration for a short period of time (60 min) was determined. High glucose concentration (16.7 mM) did not significantly alter catalase activity. GSP activity was increased by glucose at 5.6 mM, remaining elevated at higher concentrations up to 16.7 mM. However, the activity of SOD increased with glucose concentration, and this increment was closely correlated with the rate of insulin secretion (r = 0.96). High potassium (30 mM) did not increase SOD activity, suggesting that the increase in intracellular ionic calcium concentration does not stimulate this enzyme activity. alpha-Ketoisocaproic acid and pyruvate, which are metabolized through the TCA cycle, did not increase SOD activity, indicating that the stimulation of SOD activity might be triggered by a factor produced through glycolysis or the pentose phosphate pathway.

Animals↗

PubMed1999

Metabolic fate of glutamine in lymphocytes, macrophages and neutrophils.

Eric Newsholme's laboratory was the first to show glutamine utilization by lymphocytes and macrophages. Recently, we have found that neutrophils also utilize glutamine. This amino acid has been shown to play a role in lymphocyte proliferation, cytokine production by lymphocytes and macrophages and phagocytosis and superoxide production by macrophages and neutrophils. Knowledge of the metabolic fate of glutamine in these cells is important for the understanding of the role and function of this amino acid in the maintenance of the proliferative, phagocytic and secretory capacities of these cells. Glutamine and glucose are poorly oxidized by these cells and might produce important precursors for DNA, RNA, protein and lipid synthesis. The high rate of glutamine utilization and its importance in such cells have raised the question as to the source of this glutamine, which, according to current evidence, appears to be muscle.

Cell Division↗

PubMed1999

Effects of adrenaline on glucose and glutamine metabolism and superoxide production by rat neutrophils.

Despite the large body of information on the role of corticosteroids in regulating lymphocyte and phagocyte function, the role of the hormone adrenaline in immunoregulation is an under-investigated topic. The present study has addressed the effects of adrenaline on the rates of utilization and oxidation of glucose and glutamine, the phagocytic capacity and the rate of superoxide production by rat neutrophils. Incubation of rat neutrophils in the presence of 50 microM adrenaline caused a marked elevation in glucose metabolism, an effect that could be blocked by propranolol. Adrenaline caused a partial inhibition of glutamine utilization by neutrophils, an effect that was also blocked by propranolol. These effects of adrenaline could be mimicked by 100 microM dibutyryl cAMP. Phosphate-dependent glutaminase activity was significantly elevated in neutrophils incubated in the presence of 50 microM adrenaline or 100 microM dibutyryl cAMP for 1 h, whereas glutamine oxidation was significantly depressed (P<0.05) under these conditions. The elevation in enzyme activity was only partially blocked by propranolol. The phagocytic activity of rat neutrophils was not altered by adrenaline in the presence of either glucose or glutamine. The rate of phorbol 12-myristate 13-acetate-induced superoxide production in the presence of glucose was potently reduced by the addition of 5 nM or 50 microM adrenaline. This effect could be mimicked by dibutyryl cAMP. However, when rat neutrophils were incubated in the presence of glutamine plus adrenaline (5 nM or 50 microM), the rate of superoxide production was only marginally reduced. These findings support the proposition that adrenaline may deviate the flux of glucose from the NADPH-producing pentose phosphate pathway, thus reducing substrate availability for the superoxide-generating NADPH oxidase. However, glutamine metabolism may still give rise to substantial quantities of NADPH from the glutaminolysis pathway. We postulate that glutamine metabolism may thus provide a protective mechanism against the inhibitory effect of adrenaline on superoxide production by neutrophils.

Adrenergic beta-Agonists↗

PubMed1998

Soybean- and olive-oils-enriched diets increase insulin secretion to glucose stimulus in isolated pancreatic rat islets.

Islets isolated from rats fed a lipid-enriched diet have shown an impairment of insulin secretion, but there is no available data comparing the effect of diet containing different dietary fat. This may be important in preventing or facilitating the establishment of diabetes. In this study, the effect of diets enriched (10%) with different fatty acids on insulin secretion by isolated pancreatic islets was investigated. The sources of the fatty acids tested were: saturated long chain from animal fat (AF), polyunsaturated from soybean oil (SO), and monounsaturated from olive oil (OL). The results were compared with those from rats receiving a diet enriched (10%) with a balanced mixture of fatty acids (the same proportion of AF, SO, and OL). The effect of fat-rich diets on insulin release was tested in vivo by giving a glucose load (glucose tolerance test-GTT) and in vitro in perfused islets. The mechanism involved was also examined by measuring 45Ca2+ and 86Rb+ fluxes, GLUT-2 content, and glucose oxidation in isolated islets. A significant increase of insulin secretion and glucose oxidation without any alteration of the ionic movements were detected in islets from SO and OL rats. GLUT-2 content was increased in islets of the OL group but diminished in AF rats. The results led us to postulate that soybean and olive oils may increase the response of insulin secretion to glucose stimulus in pancreatic islets.

Animals↗

PubMed1998

Percentage of phagocytosis, production of O2.-, H2O2 and NO, and antioxidant enzyme activities of rat neutrophils in culture.

Changes in the integrity, ultrastructure, phagocytosis capacity, and production of H2O2, O2.- and NO2- were evaluated in cultured neutrophils. The activities of the antioxidant enzymes (catalase-CAT, superoxide dismutase-SOD and glutathione-dependent peroxidase-GSH-Px) were measured under similar conditions. The integrity of the cells remained unchanged up to 18 h. After 24 h, the number of viable cells in culture dropped by 16 per cent. The percentage of viable cells in culture was of 72 per cent even after 72 h. An ultrastructural analysis of the cells was carried out after 3, 6, 12, 24, 48, and 72 h in culture. Neutrophils started developing morphologic changes after 24 h: decreased cell volume, abundant vacuoles (mainly around the nucleus), and also the presence of autophagic vacuoles. This period was then chosen for the study of neutrophil function and antioxidant enzyme activities. Neutrophils cultured for 24 h presented reduced phagocytosis capacity. The rates of production of H2O2 and O2.- remained unchanged after 24 h in culture. Concomitantly, these cells were also able to produce NO in significant amounts. The production of O2.- in response to PMA stimulus was lowered in 24-h cultured cells. Possibly, the production of oxygen and nitrogen reactive species accomplished with a decrease in the activities of CAT and GSH-Px play a key role for the process of apoptosis which takes place in neutrophils under these conditions.

Animals↗

PubMed1998

Effect of dietary fat on lymphocyte proliferation and metabolism.

The effect of diets enriched with fat containing different fatty acids on glucose and glutamine metabolism of mesenteric lymph nodes lymphocytes, spleen, and thymus and lymphocyte proliferation was examined. The following fat-rich diets were tested: (1) standard chow (CC); (2) medium chain saturated fatty acids (MS)--coconut fat oil; (3) long chain saturated fatty acids (LS)--cocoa butter; (4) monounsaturated fatty acids (MU)--canola oil (n-9); (5) polyunsaturated fatty acids (PU)--soybean oil (n-6). Of the fat-rich diets tested, MS was the one to present the least pronounced effect. Lymphocyte proliferation was reduced by LS (64 per cent), MU (55 per cent), and PU (60 per cent). Hexokinase activity was enhanced in lymph node lymphocytes by PU (67 per cent), in the spleen by MS (42 per cent), and in the thymus by PU (30 per cent). This enzyme activity was reduced in the spleen (33 per cent) by LS and MU (35 per cent). In the thymus, this enzyme activity was reduced by LS (26 per cent) and MU (13 per cent). Maximal phosphate-dependent glutaminase activity was raised in lymphocytes by MS (70 per cent) and MU (20 per cent). This enzyme activity, however, was decreased in lymphocytes by PU (26 per cent), in the spleen by LS (15 per cent), and in the thymus by MU (44 per cent). Citrate synthase activity was increased in lymphocytes by MU (35 per cent), in the spleen by LS (56 per cent) and MU (68 per cent), and in the thymus by LS (42 per cent). This enzyme activity was decreased in lymphocytes by PU (24 per cent) only. [U-14C]-Glucose decarboxylation was raised by all fat-rich diets; MS (88 per cent). LS (39 per cent), MU (33 per cent), and PU (50 per cent), whereas [U-14C]-glutamine decarboxylation was increased by LS (53 per cent) and MU (55 per cent) and decreased by MS (17 per cent). The results presented indicate that the reduction in lymphocyte proliferation due to LS, LU and PU could well be a consequence of changes in glucose and glutamine metabolism.

Animals↗

PubMed1998

Effects of saturated and polyunsaturated fatty acids on human tumor-cell proliferation.

1. Fatty acids of varying chain length and degree of unsaturation were found to inhibit the proliferation of T24/83, Hep2 and LLC-WRC256 tumor cell lines. 2. There was a strong correlation (r2= -0.956 to -0.995) between the degree of inhibition of proliferation and the degree of unsaturation of 18-carbon fatty acids for all the cell lines studied. No correlation existed in this respect for the 20-carbon fatty acids. 3. Tumor cells can differentiate between the degree of unsaturation of the 18-carbon fatty acids, and this ability is ultimately manifested in the rate of proliferation; however, the mechanisms remain to be identified.

Animals↗

PubMed1998

Effect of the administration of fish oil by gavage on activities of antioxidant enzymes of rat lymphoid organs.

1. The effect of administration of fish oil by gavage on catalase (CAT), glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD) activities of the lymphoid organs and liver was compared with those of soybean oil and cocoa butter. 2. Fish oil did not affect the activities of SOD and CAT but reduced that of GSH-Px in the spleen. In contrast, cocoa butter reduced the CAT activity in the thymus and liver, and soybean oil decreased CAT activity in the thymus. 3. The content of thiobarbituric acid reactive substances of the lymphoid organs was not modified but was increased in plasma.

Animals↗

PubMed1998

Fish oil given by gavage increases lymphocyte proliferation and production of hydrogen peroxide by rat macrophages.

1. The effect of fish oil (FO) administration by gavage (0.4% body weight) on macrophage and lymphocyte function was investigated in young male rats. The results were compared with those obtained by administration of soybean oil (SB) and cocoa butter (CB). 2. Lymphocyte proliferation was markedly increased by FO administration compared with control and other oils. 3. Macrophage phagocytosis capacity was not affected by FO, but it was increased by CB and SB. 4. The oils did not affect the production of O2.- but increased the production of H2O2 in the presence of PMA. 5. The administration of the oils did not markedly affect the activity of antioxidant enzymes in macrophages, except for a decrease in superoxide dismutase activity by FO.

Animals↗