Biomedical subjects

L Di Silvio

Publications and source records attributed to L Di Silvio.

At least 37 records · Page 2Linked to original sources

PubMed2000

Surface topography and HA filler volume effect on primary human osteoblasts in vitro.

HAPEX, a bone analog material, with similar properties to cortical bone, has been studied in vitro with particular reference to the effect of surface topography. The stimulation of a favorable bone response by this composite depends on optimization of the hydroxyapatite (HA) content in relation to the material bioactivity without compromising the mechanical characteristics. In this study we have started to investigate the effects of surface topography on cell attachment and subsequent cellular behavior in relation to proliferation. Different volumes of HA (20% and 40%) were added to a high density polyethylene (HDPE) matrix to produce the test materials. Scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM) were used to examine cell morphology on HAPEX, and the surface characteristics produced by different machining protocols. The measurement of cellular DNA and tritiated thymidine ([3H]-TdR) incorporation has been used to asses cell proliferation upon the materials. The results show that the material surface topography has a large influence on cell proliferation and attachment, and with a controlled material topography the 40% vol HA/HDPE composite gives the greater biological response compared to the 20% vol HA/HDPE composite.

Journal Article↗

PubMed1999

In vitro evaluation of a new polymethylmethacrylate cement reinforced with hydroxyapatite.

The nature of the orthopedic implant surface affects the interaction between cells and subsequent bone formation. The bone/cement interface in cement-held prostheses is considered to be the main cause of fracture leading to implant revision. It is thought that the introduction of a bioactive phase, such as hydroxyapatite (HA), to cement may permit a stronger implant by encouraging direct bone apposition rather than encapsulation of the implant by fibrous tissue. Thus, a poly(methylmethacrylate) (PMMA) cement incorporating 17.5% HA by weight has been investigated. In this study, in order to analyze the interaction at the cellular level, the in vitro biological response of the HA/PMMA to a similar PMMA without HA incorporation has been studied. Primary human osteoblast-like cells (HOB) were used as they are a model of the cell type the cements might encounter in vivo. Cell proliferation and growth were assessed by measurement of total cellular DNA and tritiated thymidine ([3H]-TdR) incorporation. Alkaline phosphatase (ALP) production was measured as an indicator of HOB phenotype upon the cements. The results showed that HA/PMMA was a better substrate for HOB cells, resulting in increased proliferation and ALP activity. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that HOB cells cultured on the HA-filled PMMA preferentially anchored to HA particles exposed at the cement surface, with a close intimacy observed between HA and HOB cells.

Journal Article↗

PubMed1998

In vitro response of osteoblasts to hydroxyapatite-reinforced polyethylene composites.

A primary human cell culture model was used to investigate a range of hydroxyapaptite (HA)-reinforced high-density polyethylene (HDPE) composites (HAPEX). These materials are being developed as potential bone-substitute materials. When designing and optimizing a second-generation biomaterial, it is important to achieve a balance between mechanical and biological properties without compromising either. Biochemical and histological parameters have been used to compare the biological response of 20% and 40% volume HA in HDPE. Cellular DNA and incorporation of tritiated thymidine was measured to assess cell proliferation. Alkaline phosphatase (ALP) production was used as a marker of osteoblast phenotype expression. In this preliminary study, osteoblasts cultured on the 20% HAPEX showed a greater increase in the rate of proliferation and osteoblast expression as indicated by an increase in ALP activity compared to the 40% HAPEX over the time period studied. Osteoblast-like cells showed a flattened morphology on both composites and in some cases a greater covering was observed on the 20% HAPEX. These results indicate that the composites may not be identical in terms of bioactivity and that further research on surface topography and physico-chemical properties is required to assess fully the biological response of these composites.

Journal Article↗

PubMed1997

In vitro mechanical and biological assessment of hydroxyapatite-reinforced polyethylene composite.

In vitro performance of hydroxyapatite (HA)-reinforced polyethylene (PE) composite (HAPEX) has been characterized from both mechanical and biological aspects. The mechanical properties of HAPEX, such as tensile strength and Young's modulus, showed little change after immersion in a physiological solution at 37 and 70 degrees C for various periods. In addition, the biological response of primary human osteoblast-like (HOB) cells in vitro on HAPEX was assessed by measuring DNA synthesis and osteoblast phenotype expression. Cell proliferation rate on HAPEX was demonstrated by an increase in DNA content with time. A high tritiated thymidine ([3H]-TdR) incorporation/DNA rate was observed on day 1 for HAPEX, indicating a stimulatory effect on cell proliferation. The alkaline phosphatase (ALP) activity was expressed earlier on HAPEX than on unfilled PE and increased with time, indicating that HOB cells had commenced differentiation. Furthermore, it was found that the HA particles in the composite provided favourable sites for cell attachment. It appears that the presence of HA particles in HAPEX may have the advantage of acting as microanchors for bone bonding in vivo.

Journal Article↗

PubMed1997

Evaluation of in vitro bioactivity and biocompatibility of Bioglass-reinforced polyethylene composite.

The bioactivity and biocompatibility of Bioglass-reinforced high-density polyethylene composite (Bioglass/HDPE) have been evaluated in simulated body fluid (SBF) and by in vitro cell culture, respectively. The formation of a biologically active hydroxy-carbonate apatite (HCA) layer on the composite surface after immersion in SBF was demonstrated by thin-film X-ray diffraction, infrared spectroscopy and scanning electron microscopy, indicating the in vitro bioactivity of Bioglass/HDPE composites. The HCA layer was formed on the 40 vol% composite surface within 3 days immersion in SBF at a formation rate comparable to those on bioactive glass-ceramics, showing that in vitro bioactivity could be obtained in a composite. Furthermore, the composite was biocompatible to primary human osteoblast-like cells. In comparison with unfilled HDPE and tissue culture plastic control, a significant increase in cellular metabolic activity was found on the composite. Therefore, Bioglass/HDPE composites have a promising biological response as a potential implant material.

Journal Article↗

PubMed1995

Modifications of the hydrophilicity of heterocyclic methacrylate copolymers for protein release.

A series of copolymers comprising ethyl methacrylate (EM) and tetrahydrofurfuryl methacrylate (THFMA) gelled with either THFMA monomer or hydroxyethyl methacrylate (HEMA) monomer have been developed. In this paper, we examine the water uptake characteristics of the polymer systems and address the possibility of increasing the hydrophilicity of the systems by changing the ratios of the copolymers. We have investigated whether protein release from the polymers is related to the composition of the polymer systems. More protein was released from the polymers gelled with the more hydrophilic monomer (HEMA) than with THFMA. This was consistent with the calculated diffusion coefficients, which were 10 times greater for the polymers gelled with HEMA than those gelled with THFMA. Interestingly, the water uptake and protein release profiles were not dependent on the ratio of EM and THFMA in the copolymers. This is probably due to the conflicting roles of THFMA in the copolymer; it is both the more hydrophilic component as well as a cross-linking agent. In addition, it would appear that the structural and surface topography of these polymers had more significant effects on protein release than copolymer composition.

Absorption↗

PubMed1994

Biodegradable microspheres: a new delivery system for growth hormone.

A drug delivery system for biologically active agents targeted to specific cells could be used to improve tissue repair in orthopaedics. The system should be controllable and capable of drug release over an extended period of time. Biodegradable, membrane-moderated, monolithic microspheres for the controlled release of growth hormone (GH) were developed and the release of GH was monitored in vitro. Cross-linked gelatin microspheres were used as the vehicle, with the drug dispersed within the gelatin. The amount of GH released from the microspheres was increased following ultrasonication. The release of growth hormone was monitored in phosphate buffered saline and horse serum. Interestingly, a higher level of GH was detected in the phosphate buffered saline than in serum. In addition, both pH and enzyme-induced degradation had an effect on the swelling kinetics of the gelatin microspheres. The release of GH from the microspheres was diffusion controlled, during the time period studied.

Biocompatible Materials↗

PubMed1994

Validation and optimization of a polymer system for potential use as a controlled drug-delivery system.

A room temperature polymerizing system consisting of polyethylmethacrylate (PEM) and tetrahydrofurfuryl methacrylate (THFMA) monomer was validated for use as a drug-delivery system. The effect of gelling PEM/THFMA copolymers with a more hydrophilic monomer, hydroxyethyl methacrylate (HEMA), was also investigated. The release of growth hormone (GH) and bovine serum albumin (BSA) protein from this polymer has been studied. The polymer has the advantage of high water absorption and low shrinkage properties. Changes in release profiles have been studied by introducing structural differences in the polymer by changing the mixing technique. The stability and bioactivity of the GH incorporated have been examined at various temperatures. To optimize release profiles further, the possibility of attaining a more sustained and controllable release by varying the ratios of polymer used has also been investigated.

Drug Delivery Systems↗

PubMed1992

Analysis of trough serum growth hormone concentrations: comparison of an immunoradiometric assay and a sensitive ELISA for growth hormone.

OBJECTIVES: We compared a sensitive assay for GH (ELISA) with a conventional immunoradiometric (IRMA) assay with particular reference to the oscillatory activity detected by Fourier transformation and the estimation of trough concentrations using occupancy analysis. DESIGN: Eight healthy adult male volunteers underwent 24-hour profiles during which samples were drawn at 20-minute intervals. Samples were analysed by an ELISA and an IRMA system. MEASUREMENTS: The 24-hour serum GH concentration profiles were subjected to Fourier transformation and to occupancy analysis. RESULTS: No additional GH periodicities could be determined in the ELISA data other than the well documented 180-200-minute periodicity. Median observed concentrations (OC) at 5% occupancy were 0.035 mU/l (range 0.004-0.22) for the ELISA and 0.035 mU/l (range 0.001-0.50) for the IRMA. For all OC parameters, 5, 50 and 95%, there was a good correlation between the ELISA and IRMA systems. The mean difference (bias) between the ELISA and IRMA were -0.05, -0.28 and -1.40 mU/l at OC values of 5, 50 and 95% respectively and the standard deviations of the difference at the same OC values were 0.10, 0.50 and 1.61 mU/l. CONCLUSION: Although there is a qualitative improvement on visual inspection of individual 24-hour serum GH profiles obtained using the ELISA system, there is little additional information gained in terms of pulse periodicity or occupancy analysis.

Adult↗

PubMed1991

Short stature in a patient with cystic fibrosis caused by a 6.7-kb human growth hormone gene deletion.

A recent longitudinal study in children with cystic fibrosis (CF) challenged the common idea that CF is causing short stature. The data, however, showed clearly that short stature cannot be explained by CF alone after the first year of life. We report on a girl suffering from CF and short stature in whom DNA analysis using polymerase chain reaction and Southern blot techniques of the human growth hormone (hGH) gene cluster revealed a 6.7-kb gene deletion encompassing the hGH-1 gene. Anti-hGH antibodies of polyclonal origin developed, leading to a growth arrest after only 2 months of hGH replacement. In addition, a family study was performed, and the haplotypes of the CF gene and hGH gene cluster were analyzed.

Blotting, Southern↗

PubMed1990

A preliminary report on the role of somatostatin analogue (SMS 201-995) in the management of children with tall stature.

We have studied the effect of somatostatin analogue (SMS 201-995) given as a subcutaneous injection on the growth and growth hormone secretion in seven tall children (two male; five female). SMS 201-995 was given in doses of 37.5 or 50 micrograms on a once or twice-daily regimen. Growth velocity decreased from a pretreatment median of 8.3 cm/year (range 5.5-12.2) to 3.0 cm/year (range 0.2-4.5) after 6 months treatment (Wilcoxon, P = 0.02). In three of the children therapy was discontinued for the next 6 months with restoration of growth rate to pretreatment values in two of the three. Growth hormone secretion decreased as a result of SMS 201-995 therapy although one child needed a twice-daily regimen to achieve long-term suppression. Final height measurements were reduced in four of five patients with an overall reduction between 1.1 and 6.3 cm and no change in the other. No effects of treatment on fasting glucose and insulin, glycosylated haemoglobin or serum thyroxine concentrations were observed. These preliminary studies suggest that SMS 201-995 may have a role in the management of the growth of tall children but the optimum mode of administration remains to be established.

Adolescent↗

PubMed1990

Effects of 3 years of growth hormone therapy in short normal children.

The effect of 3 years of growth hormone (GH) treatment on growth rate, predicted height, carbohydrate and metabolic status, and thyroid function was studied in 16 short prepubertal children growing with a normal pretreatment growth rate. The height velocity SDS increased from a pretreatment value of -0.44 +/- 0.33 (mean +/- SD) to a value of +2.20 +/- 1.03 during the first year of treatment. It was maintained at a value above zero over the subsequent 2 years. By the end of the third year of treatment, the predicted final height had increased by 6.8 cm in the boys and by 4.2 cm in the girls (p less than 0.001 and p less than 0.01, respectively). Increasing the dose of GH on a body surface area basis reduced the deceleration of growth observed during the second year of treatment, leading to an improvement in height prognosis over that year. Glucose homoeostasis was achieved initially at the expense of an elevation in fasting serum insulin concentration, but this had returned to pretreatment values by the end of the second year of therapy.

Blood Glucose↗

PubMed1989

The measurement and effect of growth hormone in the presence of growth hormone-binding antibodies.

We have developed methods for measuring the concentrations of free GH in plasma using a polyethylene glycol (PEG) separation procedure to remove antibody-bound GH within 1 h of collection. Total GH concentrations were obtained by acidification of the GH-antibody complex to release the GH followed by PEG precipitation of the antibody. The plasma GH assay had a within-assay coefficient of variation (C.V.) of 6.8% at 4.6 mU/l and a between-assay C.V. of 9.2% at 4.0 mU/l. The PEG-modified assay had a within-assay C.V. of 4.3% at 6.3 mU/l and a between-assay C.V. of 10.9% at 5.3 mU/l. Both assays had a sensitivity of 1.3 mU/l. There was good correlation between plasma and free GH concentrations in 24-h profiles in two tall children (r = 0.98; P less than 0.001) and between total and free GH in the same profiles (r = 0.97; P less than 0.001). GH antibodies were measured using a highly sensitive radioimmunoassay. In children who did not develop GH antibodies there was no difference between total, plasma and free GH concentrations. In contrast, in those who developed GH antibodies both total and plasma GH concentrations were markedly increased compared with free GH concentrations. The presence of GH antibodies did not affect the growth, plasma insulin-like growth factor-I concentrations or fasting serum insulin concentration responses to 1 year of therapy with biosynthetic human GH.

Autoantibodies↗

PubMed1988

Changes in serum insulin concentration during puberty and their relationship to growth hormone.

In 40 tall and short children we have demonstrated using oral glucose tolerance tests that there is an increase in serum insulin concentration during puberty with no change in blood glucose concentration. Fasting serum insulin concentration rose from a pre-pubertal value between 4.0 and 5.7 mU/l to values between 11.0 and 14.6 mU/l during puberty. This rise in both fasting serum insulin concentration and the incremental area under the insulin curve is probably due to changes in circulating GH concentrations. In 16 tall girls a rise in serum GH concentration was observed during pubertal growth and the rise was accompanied by a two- to three-fold increase in fasting serum insulin concentration. In 13 children in whom 24 h growth hormone profiles were recorded higher insulin concentrations were seen in those who secreted the most growth hormone. These data suggest that during pubertal growth in diabetic children the standard dosage of insulin administered (0.9 units/kg per day) should be doubled or possibly tripled to maintain good metabolic control and maximize pubertal growth.

Adolescent↗

PubMed1988

Somatostatin analogue in short term management of hyperinsulinism.

Five infants with hypoglycaemia due to hyperinsulinism were treated for between three and 11 days with a somatostatin analogue, which raised the mean blood glucose concentration and lowered the glucose requirements in all. Somatostatin analogue appears to be useful in the short term management of these patients.

Dose-Response Relationship, Drug↗

PubMed1988

Relation between height velocity and fasting insulin concentrations.

A linear relation between fasting serum insulin concentration and height velocity was found in 47 normal children. This suggests that doubling of growth velocity at puberty is accompanied by a two to threefold rise in insulin. This implies that insulin dosage should be increased by a similar magnitude in pubertal diabetic children during their growth spurt.

Adolescent↗

PubMed1985

Metabolic and haemodynamic effects of alpha 2-adrenoceptor stimulation and antagonism in man.

Six healthy volunteers received a 60 min infusion of guanfacine (alpha 2-agonist) on two occasions, preceded by either idazoxan (alpha 2-antagonist) or vehicle. Idazoxan elevated blood pressure by 8/7 mmHg, but there was no change on either day during guanfacine infusion. Guanfacine reduced plasma noradrenaline by approximately 30%, and this was not antagonized by idazoxan. By contrast, the 30-fold increase in plasma growth hormone caused by guanfacine was almost completely blocked by idazoxan. Guanfacine caused a two- to three-fold increase in plasma glucagon and a similar reduction in plasma insulin. Only the latter was antagonized by idazoxan. No consistent changes in plasma ACTH were observed after either idazoxan or guanfacine. Idazoxan itself elevated plasma noradrenaline up to twice baseline values, but did not affect the other metabolic measurements. alpha 2-Adrenoceptor stimulation plays a minor role in control of hormone release but has a greater physiological role in regulating release of the neurotransmitter, noradrenaline.

Adrenergic alpha-Agonists↗

PubMed1985

The physiological and pharmacological role of presynaptic alpha- and beta-adrenoceptors in man.

Two studies were performed each in six normal volunteers in order to find evidence of either a physiological or pharmacological role of presynaptic alpha- and presynaptic beta-adrenoceptors in man. In Study 1 subjects received a 60 min infusion of guanfacine 3 mg (alpha 2-adrenoceptor agonist) preceded by either idazoxan (alpha 2-adrenoceptor antagonist) or vehicle. Guanfacine reduced plasma noradrenaline concentration by approximately 30% and this fall was not antagonised by the alpha 2-receptor antagonist. The 30-fold increase in plasma growth hormone, measured as a marker of the central action of guanfacine, was almost completely blocked by idazoxan. A comparison of the drug concentrations of idazoxan and guanfacine, together with their relative affinities for alpha 2-adrenoceptors, suggested that the idazoxan could not block the peripheral actions of guanfacine and that these were responsible for the fall in plasma noradrenaline concentration. In Study 2 adrenaline 0.05 micrograms kg-1 min-1 was infused for 80 min preceded by either idazoxan or vehicle. After vehicle, adrenaline caused no change in plasma noradrenaline concentration whereas it rose approximately 25% after administration of idazoxan. This was probably due to unmasking of presynaptic beta-adrenoceptor stimulation by adrenaline when the opposing inhibitory autoreceptor was blocked.

Adrenergic beta-Antagonists↗