Biocompatibility studies of low temperature nitrided and collagen-I coated AISI 316L austenitic stainless steel

The biocompatibility of austenitic stainless steels can be improved by means of surface engineering techniques. In the present research it was investigated if low temperature nitrided AISI 316L austenitic stainless steel may be a suitable substrate for bioactive protein coating consisting of collagen-I. The biocompatibility of surface modified alloy was studied using as experimental model endothelial cells (human umbilical vein endothelial cells) in culture. Low temperature nitriding produces modified surface layers consisting mainly of S phase, the supersaturated interstitial solid solution of nitrogen in the austenite lattice, which allows to enhance surface microhardness and corrosion resistance in PBS solution. The nitriding treatment seems to promote the coating with collagen-I, without chemical coupling agents, in respect of the untreated alloy. For biocompatibility studies, proliferation, lactate dehydrogenase levels and secretion of two metalloproteinases (MMP-2 and MMP-9) were determined. Experimental results suggest that the collagen protection may be favourable for endothelial cell proliferation and for the control of MMP-2 release.

Biocompatibility evaluation of surface-treated AISI 316L austenitic stainless steel in human cell cultures

The effects of AISI 316L austenitic stainless steel, tested in untreated state or subjected to glow-discharge nitriding (at 10 or 20 hPa) and nitriding + post-oxidizing treatments, on human umbilical vein endothelial cells (HUVEC) and on peripheral blood mononuclear cells (PBMC) were evaluated. All the treated samples showed a better corrosion resistance in PBS and higher surface hardness in comparison with the untreated alloy. In HUVEC put in contact for 72 h with the sample types, proliferation and apoptosis decreased and increased, respectively, in the presence of the nitrided + post-oxidized samples, while only slight differences in cytokine (TNF-alpha, IL-6, and TGF-beta1) release were registered. Intercellular adhesion molecule-1 (ICAM-1) increased in HUVEC incubated with all the treated samples, while vascular cell adhesion molecule-1 (VCAM-1) and E-selectin increased in the presence of all the sample types. PBMC incubated for 48 h with the samples showed a decrease in proliferation and an increase in apoptosis in the presence of the untreated samples and the nitrided + post-oxidized ones. All the sample types induced a remarkable increase in TNF-alpha and IL-6 release in PBMC culture medium, while only the untreated sample and the nitrided at 10 hPa induced an increase in ICAM-1 expression. In HUVEC cocultured with PBMC, previously put in contact with the treated AISI 316L samples, increased levels of ICAM-1 were detected. In HUVEC coincubated with the culture medium of PBMC, previously put in contact with the samples under study, a noteworthy increase in ICAM-1, VCAM-1, and E-selectin levels was always registered, with the exception of VCAM-1, which was not affected by the untreated sample. In conclusion, even if the treated samples do not show a marked increase in biocompatibility in comparison with the untreated alloy, their higher corrosion resistance may suggest a better performance as the contact with physiological environment becomes longer.

Synergistic anti-proliferative effects of vitamin D derivatives and 9-cis retinoic acid in SH-SY5Y human neuroblastoma cells

This study examines the effect of 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)], 24,25-dihydroxyvitamin D(3) [24,25(OH)(2)D(3)], two vitamin D analogues (KH 1060 and EB 1089, which are 20-epi-22-oxa and 22,24-diene-analogues, respectively), 9-cis retinoic acid and all-trans retinoic acid on proliferation of SH-SY5Y human neuroblastoma cells, after treatment for 7 days. Cell number did not change when the cells were incubated with 1, 10 or 100 nM 1,25(OH)(2)D(3) or its derivatives, but significantly decreased in the presence of the two retinoids (0.001--10 microM final concentration). A synergistic inhibition was observed, when SH-SY5Y cells were treated combining 0.1 microM 9-cis retinoic acid and 10 nM 1,25(OH)(2)D(3) or 10 nM KH 1060, and 1 microM 9-cis retinoic acid and 10 nM 1,25(OH)(2)D(3) or 10 nM EB 1089. Acetylcholinesterase activity showed a significant increase, in comparison with controls, after treatment of the cells for 7 days with 0.1 or 1 microM 9-cis retinoic acid, alone or combined with 10 nM 1,25(OH)(2)D(3) or 10 nM KH 1060 or 10 nM EB 1089. This increase was synergistic, combining 1 microM 9-cis retinoic acid and 10 nM 1,25(OH)(2)D(3) or EB 1089. The levels of the c-myc encoded protein remarkably decreased after treatment of SH-SY5Y cells for 1, 3, 7 days with 0.1 and 1 microM 9-cis retinoic acid, alone or combined with 10 nM 1,25(OH)(2)D(3) or 10 nM KH 1060 or 10 nM EB 1089. In particular, the association of 1 microM 9-cis retinoic acid and 10 nM 1,25(OH)(2)D(3) or 10 nM EB 1089 resulted in a synergistic c-myc inhibition, in comparison with that obtained in the presence of the retinoid alone. These findings may have therapeutic implications in human neuroblastoma.

Suppressive effect of 1,25-dihydroxyvitamin D3 and its analogues EB 1089 and KH 1060 on T lymphocyte proliferation in active ulcerative colitis

This study examined the effect exerted by 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] and two vitamin D analogues, EB 1089 and KH 1060, on the proliferation of T lymphocytes obtained from ulcerative colitis (UC) patients and healthy controls. The proliferative response of T lymphocytes to phytohaemagglutinin treatment was first analyzed on days three, five, and seven of culture. Cell proliferation was significantly lower in UC patients than that observed in healthy controls. The highest proliferation value, in either controls or patients, was registered on day five of culture. On day seven, a decrease in proliferation occurred, less evident in patients with respect to controls, whereas on day three, controls and patients showed the same proliferation value. The response of T lymphocytes of either healthy controls or UC patients to 1,25(OH)2D3, EB 1089, or KH 1060 was then investigated, treating the cells for three, five, and seven days with 10 nM vitamin D derivatives. In the presence of these compounds, cell proliferation was significantly inhibited in both groups, but on day seven, the inhibition of lymphocyte proliferation was remarkable in controls, whereas in patients it was similar to that registered on day five. The highest inhibition values were always obtained in the presence of KH 1060, and the time dependence was continuous in controls, but in the presence of EB 1089 only in patients. T lymphocytes prepared from healthy controls and UC patients were then cultured for five days in the presence of vitamin D derivatives at three different concentrations (0.1, 1, and 10 nM). In the two groups, a dose-dependent inhibition was registered in the presence of 1,25(OH)2D3 or EB 1089, while the inhibition of proliferation exerted by KH 1060 was not dose-dependent. The results obtained suggest an option for the use of the two non-hypercalcemic vitamin D analogues in the therapy of UC patients, perhaps in association with other immunosuppressive drugs.

Role of 1,25-dihydroxyvitamin D3 and extracellular calcium in the regulation of proliferation in cultured SH-SY5Y human neuroblastoma cells

This study examines the effects of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] on SH-SYSY human neuroblastoma cells cultured in the presence of medium containing varying concentrations of calcium (0.1, 0.9, 1.4, 1.8 mM). Pyruvate kinase activity was assayed in SH-SY5Y cells incubated in variable calcium medium with or without 1, 10 or 100 nM 1,25(OH)2D3 for 48 h. The enzyme levels showed a significant increase in comparison with control, when the cells were incubated with 100 nM hormone in the presence of 0.1 mM calcium, while pyruvate kinase activity decreased, when the cells were treated with 100 nM 1,25(OH)2D3 in the presence of 1.8 mM calcium. The proliferative activity of SH-SY5Y was dependent on the extracellular concentration of calcium, being the highest at 1.8 mM calcium and completely absent at 0.1 mM calcium. In the presence of 1,25(OH)2D3, at the three concentrations used and after 48 h incubation, a significant decrease in cell number was always observed, without a direct correlation between 1,25(OH)2D3 effect and calcium concentration in the medium. [3H]Thymidine incorporation in SH-SY5Y cells significantly increased in comparison with control, when the 48 h incubation with 1, 10 or 100 nM 1,25(OH)2D3 was carried out in the presence of 0.1 mM calcium, while, at the other calcium concentrations, the hormone did not cause any significant change in this parameter. The treatment of SH-SYSY cells with 1 nM 1,25(OH)2D3 for 48 h did not affect cell morphology, when 0.1 mM calcium was present, while, in the medium containing 1.8 mM calcium, the treated cells showed a slight trend to differentiation. The differentiating effect of 10 microM all-trans retinoic acid, even if incomplete after 48 h treatment, was only observed in the cultures grown in 1.8 mM calcium, in comparison with those maintained in 0.1 mM calcium.

Vitamin D receptor in SH-SY5Y human neuroblastoma cells and effect of 1,25-dihydroxyvitamin D3 on cellular proliferation

This study examines the effect of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] on proliferation of SH-SY5Y human neuroblastoma cells and demonstrates, for the first time, the presence of vitamin D receptor (VDR) in this cell line. Cell number showed a significant decrease, when the cells were incubated with 1 or 10 nM 1,25(OH)2D3 for 24, 48, 72, 96 and 144 h, while 100 nM 1,25(OH)2D3 was ineffective after 24 and 96 h incubation. The highest inhibition (about 35%) was observed after 72 h treatment with the hormone at the three concentrations used. Protein content per cell increased, in comparison with controls, after treatment of SH-SY5Y neuroblastoma cells with 1,25(OH)2D3, at the three concentrations, up to 96 h incubation. 1, 10 or 100 nM 1,25(OH)2D3 positively affected [3H]thymidine incorporation after treatment of the cells for 48 and 72 h, while, after 24 h, only 10 nM 1,25(OH)2D3 exerted a stimulatory action. To study the expression of the VDR gene, Northern blot analysis was performed. Subconfluent SH-SY5Y neuroblastoma cells were treated for 24 h with medium containing 10 nM 1,25(OH)2D3 or vehicle alone. A main transcript of an approximate size of 4.5 kb, present either in controls or in cells incubated with the hormone, was revealed. A limited increase in VDR mRNA levels was observed in the cells treated with 1,25(OH)2D3, fetal bovine serum or forskolin. Only slight differences in morphology were perceived between SH-SY5Y cultures maintained with or without 10 nM 1,25(OH)2D3 for 7 days.

Vitamin D receptor in IMR-90 human fibroblasts and antiproliferative effect of 1,25-dihydroxyvitamin D3

This study examines the effect of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], serum or forskolin on the proliferation of IMR-90 fetal lung fibroblasts and demonstrates, for the first time, the presence of 1,25(OH)2D3 receptor (VDR) in this cell line. In quiescent, subconfluent cultures neither the treatment with 100 nM 1,25(OH)2D3 nor that with 50 microM forskolin influenced proliferation, while a significant increase was observed after incubation of the cells with 10% fetal bovine serum. Either cell number, determined on growing IMR-90 human fibroblasts after 48 or 72 h incubation with 100 nM 1,25(OH)2D3 or [3H]thymidine incorporation (24, 48 or 72 h incubation) significantly decreased, while protein content per cell increased. Northern blot analysis revealed the expression of the VDR gene, the VDR mRNA bands being prominent in 1,25(OH)2D3, serum or forskolin treated fibroblasts. VDR mRNA levels slightly decreased, when growing fibroblasts were exposed to 100 nM 1,25(OH)2D3 for 48 or 72 h.

Effect of 1,25-dihydroxyvitamin D3 on proliferation in senescent IMR-90 human fibroblasts

The response of IMR-90 human fetal lung fibroblasts at high population doubling level (PDL > 42) to 1,25-dihydroxyvitamin D3[1,25(OH)2D3] was investigated to clarify whether some metabolic and molecular parameters of senescent cells are affected by the hormone treatment. Pyruvate kinase, lactate dehydrogenase and glucose-6-phosphate dehydrogenase activity significantly increased after treatment of confluent-phase cells with 10 nM 1,25(OH)2D3 for 24 h. Steroid specificity was established by the failure of 10 nM levels of 25-hydroxyvitamin D3 to affect the enzyme activities, while estradiol-17 beta and progesterone produced a slight increase in glucose-6-phosphate dehydrogenase and lactate dehydrogenase levels, respectively. 1,25(OH)2D3 also affected fibroblast proliferation, protein content/cell and DNA synthesis. The cell number significantly decreased after a 48 h incubation with 1,25(OH)2D3 at various concentrations (0.01-1 nM) when compared with control fibroblasts, while an increase in the protein content/cell was demonstrated. The same experiment, carried out by protracting the incubation with the hormone for 72 h, showed a similar trend, but 10 nM 1,25(OH)2D3 was also able to inhibit cell proliferation and to stimulate protein synthesis. The incorporation of [3H]thymidine into DNA increased after the treatment of high PDL fibroblasts with 0.01-1 nM of hormone for 48 h in comparison with controls.

1,25-dihydroxyvitamin D3 inhibits proliferation of IMR-90 human fibroblasts and stimulates pyruvate kinase activity in confluent-phase cells

This study tested the hypothesis that 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) plays a role in regulating some aspects of metabolism in IMR-90 normal human fetal lung fibroblasts. Among the enzymes studied, only pyruvate kinase showed a significant increase after treatment of confluent-phase cells with 1,25(OH)2D3 at various concentrations (0.1-100 nM range) for 24 h. A parallel increase in lactate output was observed. Steroid specificity was established by the failure of 10 nM levels of 25-hydroxyvitamin D3, estradiol-17 beta and progesterone to affect pyruvate kinase activity. The determination of the time course of [3H]-2-deoxy-D-glucose transport indicated that the hormone did not influence the transmembrane transport system of D-glucose. The addition of the inhibitors cycloheximide and actinomycin D to the culture medium abolished, at least in part, the 1,25(OH)2D3 stimulation of pyruvate kinase activity, suggesting the probable dependence of the hormone effect on cellular RNA and protein synthesis. 1,25(OH)2D3 also affected fibroblast growth and DNA synthesis. Cell number significantly decreased after 2-5 days treatment with 10 nM hormone in comparison with control fibroblasts, and also the incorporation of [3H]thymidine into DNA decreased after treatment of the cells with 1 and 10 nM hormone for 48 h. In conclusion, these data demonstrate that 1,25(OH)2D3 stimulates pyruvate kinase activity in confluent-phase IMR-90 human fibroblasts by a mechanism probably dependent on de novo protein synthesis, and also affects cell growth and DNA synthesis in sub-confluent-phase cells.

Vitamin D--related modification of enzyme activities in synaptosomes and mitochondria isolated from rat cerebral cortex

We previously demonstrated that feeding rats the Steenbock and Black rickets-inducing diet produces remarkable changes in the metabolic pattern of intestinal mucosa, kidney, liver, cerebral cortex and heart. We have now determined the levels of calcium, phosphorus and citrate in cerebral cortex and the activity of some enzymes in synaptosomes and cerebral cortex mitochondria of three rat groups: control (Group A), fed a vitamin D-deficient diet (Group B), fed a vitamin D-deficient diet and treated with 1,25-dihydroxyvitamin D3 (Group C). While calcium content increased in Groups B and C, phosphorus concentration increased only in Group C and citrate in Group B in comparison with control. The increase in acetylcholinesterase and citrate synthase registered in Group B was restored to control values by 1,25-dihydroxyvitamin D3 treatment, while, neither the decrease in cytochrome c oxidase, nor the increase in glucose-6-phosphate dehydrogenase, acid phosphatase and NADP+(-)isocitrate dehydrogenase observed in Group B were corrected by 1,25-dihydroxyvitamin D3 supply. Acyl phosphatase showed a remarkable increase in consequence of 1,25-dihydroxyvitamin D3 administration.

Effect of vitamin D deficiency and 1,25-dihydroxyvitamin D3 on rat heart metabolism

The purpose of this study was to investigate whether vitamin D3 deficiency and 1,25-dihydroxyvitamin D3 treatment affect some aspects of heart metabolism in the rat. To this end, five experimental groups were studied: (1) the control group of the vitamin D3 supplemented rats (Group A); (2) rachitic rats (Group B); (3) rachitic rats treated with 1,25-dihydroxyvitamin D3 (Group C); (4) rats fed a vitamin D-deficient diet (Group D); (5) rats fed a vitamin D-deficient diet and treated with 1,25-dihydroxyvitamin D3 (Group E). The five groups were compared by checking in the heart some metabolic parameters, i.e. citrate content, and enzyme activities in cytosol and mitochondria. Citrate content was higher in the heart of treated animals when compared with the control. As regards the enzymatic activities in heart mitochondria, NAD(+)-dependent isocitrate dehydrogenase remarkably decreased in Group B rats and 1,25-dihydroxyvitamin D3 restored quite normal values. NADP(+)-dependent isocitrate dehydrogenase decreased in Group B and Group D animals, and 1,25-dihydroxyvitamin D3 treatment was effective in restoring control values. Cytochrome c oxidase activity did not change, while citrate synthase showed an increase in all the treated rats. As regards the cytosolic enzymes, fructose-6-phosphate kinase increased in the two groups of vitamin D-deplete rats in comparison with the control. Glyceraldehyde-3-phosphate dehydrogenase and 3-phosphoglycerate kinase showed a similar trend: an increase in all the treated animals. In heart homogenate, acylphosphatase and acid phosphatase activities were also determined. Acylphosphatase increased in the treated rats, while acid phosphatase decreased in the rats injected with 1,25-dihydroxyvitamin D3. These results support the hypothesis of a participation of 1,25-dihydroxyvitamin D3 in some aspects of heart metabolism.

Relationship between age and GSH metabolism in synaptosomes of rat cerebral cortex

A comprehensive analysis on glutathione metabolism in rat cerebral cortex synaptosomes as a function of age was performed. All different glutathione system components (GSH, GSSG, total GSH, and GSH redox index) changed significantly only during aging. GSH, total GSH, and GSH redox index decreased by about 40%, 24%, and 52%, respectively, while GSSG showed a remarkable increase of about 60%. On the contrary, some GSH-related enzyme activities showed characteristic changes both during growth and aging. GSH peroxidase and GSH-S-transferase activities significantly increased both during growth and aging, GSH reductase and gamma-glutamylcysteine synthetase activities showed lower levels only during aging, while glucose-6-phosphate dehydrogenase activity did not change throughout the life of the rat. The results obtained suggest an increase of the oxidative status due to a reduced antioxidant capacity of the GSH system in the synaptosomal compartment during aging. The main cause of these metabolic modifications is a lowering of the rates of both GSSG reduction to GSH and GSH synthesis. Moreover, an irreversible loss of GSH as GSH-S-conjugates due to a high detoxification mechanism during aging is also possible. These alterations in glutathione metabolism, found mainly during aging in rat cerebral cortex synaptosomes may contribute to clarify some aspects of cerebral diseases.

Glutathione metabolism in heart and liver of the aging rat

A comprehensive study on glutathione metabolism in rat heart and liver as a function of age was performed. In the heart, reduced glutathione, total glutathione, and the glutathione redox index showed a decrease during aging, while oxidized glutathione levels increased in 5-month-old rats with respect to the young animals and remained quite constant in 14- and 27-month-old rats. In the liver, the highest levels of reduced glutathione were found in the 2-month-old rats, while oxidized glutathione reached a peak at 5 months. Glutathione-associated enzymes showed age-related changes. Glutathione peroxidase, unaffected by aging in the heart, decreased in the liver of the 27-month-old rats. In the heart and the liver, the highest values of glutathione S-transferase were found at 5 months and 27 months, respectively. Glucose-6-phosphate dehydrogenase followed a similar trend in both heart and liver. Glutathione reductase also showed the same behaviour in heart and in liver, increasing in old rats with respect to the other age groups. A decrease in gamma-glutamylcysteine synthetase was found in the heart and liver of 27-month-old rats in comparison with the 2-month-old ones. In conclusion, a decreased antioxidant capability has been demonstrated in both heart and liver of old rats.

Effect of vitamin D deficiency and 1,25-dihydroxyvitamin D3 on metabolism and D-glucose transport in rat cerebral cortex

We previously demonstrated that feeding rats Steenbock and Black's rickets-inducing diet produces remarkable changes in the metabolic pattern of the intestinal mucosa, kidney, and liver and in some membrane transport systems of intestinal mucosa and kidney. 1,25-Dihydroxyvitamin D3 administration to rachitic rats did not always prove to be effective in restoring normal values. We have now investigated the effect of 1,25-dihydroxyvitamin D3 on the levels of some metabolites in rat cerebral cortex, on the activity of some enzymes, and on the transport of 2-deoxy-D-glucose and D-glucose in synaptosomes. Our experiments were carried out on three rat groups: control, rachitic, and rachitic treated with 1,25-dihydroxyvitamin D3. The decrease in phosphorus content and the increase in citrate concentration observed in rachitic rat cerebral cortex were corrected by 1,25-dihydroxyvitamin D3 treatment. The activity of acetylcholinesterase, glucose-6-phosphate dehydrogenase, and acyl phosphatase significantly increased in rachitic rat synaptosomes, as well as NAD(+)-dependent isocitrate dehydrogenase in cerebral cortex mitochondria; the administration of 1,25-dihydroxyvitamin D3 to rachitic rats restored enzyme levels to normal. The transport of 2-deoxy-D-glucose and D-glucose in rachitic rat synaptosomes was lower than in the control group and returned to control values in consequence of 1,25-dihydroxyvitamin D3 treatment. The results reported here support the hypothesis of a participation of 1,25-dihydroxyvitamin D3 in some aspects of cerebral cortex metabolism.

Age and GSH metabolism in rat cerebral cortex, as related to oxidative and energy parameters

A comprehensive study on GSH metabolism in relation to some markers of oxidative and energy status in rat cerebral cortex as a function of age was performed. Reduced GSH, total GSH and the GSH Redox Index decreased both during growth (defined as the period between 1 and 5 months) and during aging (defined as the period between 5 and 27 months) while GSSG levels increased during the two periods, but most significantly during aging. Also GSH-associated enzymes and adenine-pyridine nucleotide levels show age characteristic changes. The obtained results suggest that decreases in oxidative and energy metabolism occur during aging. They probably contribute to decreases in the activity of the biosynthetic processes (i.e., NADP+(H) and GSH synthesis) and in the antioxidant capacity of the GSH system. However, the oxidative stress does not seem to be a typical characteristic of the aging period; as an oxidative status is present during the growth period too. Typical parameters of aging process are mainly the low levels of reduced GSH, total GSH and GSH Redox Index and the high levels of GSSG as well as the high levels of GSH peroxidase and GSH transferase and the low levels of gamma-glutamylcysteine synthetase.

Effect of vitamin D deficiency on D-glucose and citrate transport in rat renal basolateral membrane vesicles

We had previously reported that feeding rats on Steenbock and Black's rickets-inducing diet markedly influences the metabolic picture of the kidney and the transmembrane transport systems of D-glucose and citrate in renal brush-border membrane vesicles. We have now studied D-glucose and citrate transport into basolateral membrane vesicles prepared from kidney cortex of control and rachitic rats and the effect of 1,25-dihydroxyvitamin D3 on these transport systems was also investigated. D-glucose and citrate uptake, determined in the presence of a Na(+)-gradient, was lowered in rachitic animals and 1,25-dihydroxyvitamin D3 administration proved to be ineffective in restoring normal values. Citrate transport, determined in the presence of a K(+)-gradient, was not influenced by both rickets and 1,25-dihydroxyvitamin D3 supply. The in vitro addition to vesicle preparations of calcium or phosphate or citrate or 1,25-dihydroxyvitamin D3 did not show a selective influence on D-glucose and citrate uptake.

Intestinal glutathione transport system: a possible detoxication role

The epithelium of the small intestine act by the formation of GSH-S-conjugation, as a first line of defence against various ingested toxic chemicals. GSH and GSH-dependent enzymes are present in the gastrointestinal wall. We and others have characterized the GSH-specific transport systems in intestinal brush-border and in basolateral membrane vesicles, in which gamma-glutamyltranspeptidase (gamma-GT) activity was inactivated by AT-125. In the present study we use inhibition experiments, kinetic studies, trans-stimulation of GSH uptake and HPLC determination to demonstrate (for the first time) that GSH and two GSH-S-conjugates (chosen as model compounds) share a common transport system. Plasma GSH-S-conjugates that may enter the intestinal cells via basolateral membrane, and GSH-S-conjugates that form in intestinal cells, may be eliminated directly by this GSH transporter across brush-border membranes or transported into lumen to the active site of gamma-GT; they are then further metabolized and excreted by various routes. This transport system may thus contribute to the intestinal detoxication role.

Changes in metabolite transport by small intestine and kidney of young and old rats

We have studied the influence of the ageing phenomenon on metabolite absorption by the small intestine and the kidney of the rat, using isolated brush-border membrane vesicles prepared from 2 groups, one composed of 2 month, and the other of 24 month, animals. "Overshoot", which is typical of Na(+)-glucose cotransporter activity, disappeared in the duodenum and decreased in the kidney of the old rats. Short-circuiting of vesicles with valinomycin showed that, in the presence of K+ and valinomycin, "overshoot" decreased in both groups by about the same percentage. The Na(+)-dependent uptake of aspartate and phenylalanine showed contrasting pictures in the jejunum and kidney of the aged animals: aspartate transport decreased only in the kidney, while phenylalanine uptake was negatively affected in the jejunum. Na(+)-dependent citrate uptake, studied in renal brush-border membrane vesicles, was lower in the old rats. The Km values determined for Na(+)-dependent D-glucose and citrate uptake in the kidney did not meaningfully differ between the two groups. A continuous decrease in Na(+)-dependent D-glucose and citrate uptake in the rat kidney, during ageing, was demonstrated.

Glucose transport during ageing by human intestinal brush-border membrane vesicles

Glucose absorption by the small intestine is a complex phenomenon, that can be successfully studied by means of isolated brush-border and basolateral membrane vesicles of the enterocytes. We have carried out transport experiments on isolated brush-border membrane vesicles from the human small intestine, taking into account the age of the subjects. Our studies demonstrated that Na+-glucose cotransporter activity decreased as age increased with the "overshoot" phenomenon disappearing altogether in the oldest subjects. This effect was compared to that observed in intestinal membrane vesicles of young patients suffering from Crohn's disease; in this case there was a marked decrease in the Na+-dependent D-glucose uptake, but the "overshoot", even though low, was present. K+-dependent D-glucose transport, diffusion of L-glucose and the levels of some enzyme markers for intestinal brush-border membranes were also studied.

A continuous spectrophotometric assay for the enzymatic marker glucose 6-phosphatase

A continuous spectrophotometric assay for glucose 6-phosphatase is described. The method uses glucose dehydrogenase and mutarotase as ancillary enzymes. Glucose 6-phosphatase activity is measured by following NADH formation at 340 nm. The method is linear, at least up to 38 mU in the test which corresponds to a delta E of 0.24 min-1, when the enzyme is assayed in a microsomal fraction. We also discuss the method's suitability for subcellular fractionation. No other continuous assay for this important enzymatic marker of the endoplasmic reticulum is currently available.

Neutral maltase of human granulocytes: localization on the extracytoplasmic side of the plasma membrane and some properties

Neutral maltase is an alpha-glucosidase (alpha-D-glucoside glucohydrolase, EC 3.2.1.20) which is present in human granulocytes and B-lymphocytes but not in T-lymphocytes. These cells have been reported to contain a renal-type neutral maltase which cross-reacts with an antiserum raised against kidney brush-border enzyme. No study has been performed to assess the subcellular localization of the enzyme. Molecular properties of leukocyte neutral maltase from any species are unknown. We report in this paper that neutral maltase is present on the extracytoplasmic side of human granulocyte plasma membrane. These results are supported by subcellular fractionation on Percoll gradient and by papain digestion of intact granulocytes. The enzyme is probably an integral membrane protein. The anchorage to the lipid bilayer may be similar to that of the stalked brush-border hydrolases. Some properties of granulocyte neutral maltase were also determined on a plasma membrane-enriched fraction. The enzyme cleaves maltose and nigerose but not other glucosides disaccharides and oligosaccharides. The Km for maltose is (+/- SD) 0.78 (+/- 0.06) mM, that for nigerose 21.05 (+/- 1.43) mM. The Vmax for nigerose is 0.83-fold that for maltose. Tris, maltotriose, maltotetraose, and maltopentaose were inhibitors of granulocyte neutral maltase.

Effect of 25-hydroxyvitamin D3 on Na+-dependent D-glucose transport in rachitic rats

We have previously reported that feeding rats on Steenbock and Black's rickets-inducing diet, deficient in vitamin D and with an altered Ca/P ratio, leads to metabolic consequences and a marked decrease of Na+-dependent D-glucose uptake at the jejunum-ileum level. To clarify the relationship between experimental rickets and D-glucose uptake, 25-hydroxyvitamin D3 (25-OH-D3) was given to rats fed on the rickets inducing diet. In the jejunum-ileum of these animals Na+-dependent D-glucose uptake returned to the values of the controls while the decrease in D-glucose uptake in the brush-border membrane vesicles prepared from kidney cortex of rachitic animals was not corrected by the administration of 25-OH-D3.

1-O-n-octyl-beta-D-glucopyranoside as a competitive inhibitor of Na+-dependent D-glucose cotransporter in the small intestine brush-border membrane

1-O-n-Octyl-beta-D-glucopyranoside is a competitive inhibitor of the Na+-dependent D-glucose uptake into rabbit, rat and human intestinal brush-border membrane vesicles. The lack of effect on the equilibrium uptake demonstrates that the detergent does not act by rupturing the vesicles; no membrane leakiness was apparent at the concentrations of octylglucopyranoside used, since D-glucose uptake is not inhibited even in the absence of the Na+ gradient (in K+ solution). There is a competitive interaction between octylglucopyranoside and D-glucose, as shown by Dixon and by Hunter and Down plots. The selectivity of the detergent effect is confirmed by its modest influence on amino acid uptake.

D-glucose uptake in intestinal brush-border membrane vesicles of rachitic rats

We have previously reported the metabolic consequences of feeding rats Steenbock and Black's rickets-inducing diet, deficient in vitamin D and with an altered Ca/P ratio. Using isolated brush-border membrane vesicles prepared from the jejunum, ileum and duodenum of control and rachitic rats, we have demonstrated a marked decrease of Na+-dependent D-glucose uptake at jejunum-ileum level of rachitic rats. At duodenum level Na+-dependent D-glucose transport was not influenced by rickets. A lack of any significant difference between the two animal groups was observed studying the facilitated transport of D-glucose, the diffusion of L-glucose and the Na+-dependent uptake of phenylalanine and aspartate.

Activities of NAD-and NADP-specific isocitrate dehydrogenases in kidney mitochondria of rachitic rat

In the previous research we have demonstrated that rats fed on a rickets-inducing diet show increasing citrate levels in kidney and intestinal mucosa. The study of the enzymes related to citrate metabolism has shown that both NAD+-and NADP+-dependent isocitrate dehydrogenases decrease in kidney mitochondria of rachitic rat. The inhibitory effect of Ca2+ and citrate on the activity of the two dehydrogenases has been also investigated; these metabolites behave as competitive inhibitors against Mg2+ both in normal and in rachitic rats.