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.

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.

Methods for improving drug release from poly(methyl)methacrylate bone cement

Poly(methylmethacrylate) (PMMA) is a widely used material with both dental and orthopaedic applications. The acrylic cement is produced by the combination of polymethylacrylate beads with methylmethacrylate monomer. After polymerisation, a heterogeneous and porous matrix is formed which can be used to deliver therapeutic agents. In this work, the release of antibiotic, growth hormone and serum albumin is demonstrated. The mechanism is similar for all agents; a rapid release followed by a slow continuous release. The quantity of drug released depends upon the formulation of both the PMMA and the drug. The polymer-to-monomer ratio can greatly affect the ratio of drug release; increased polymer-to-monomer ratio leads to increased release of antibiotic. Optimum release is achieved if a crystalline formulation of the drug is used rather than a fine powder. Experimental methods to improve the drug release performance of bone cements are presented.

Dopamine1-receptor blockade inhibits ANP-induced phosphaturia and calciuria in rats

Atrial natriuretic peptide (ANP) is known to enhance the excretion of Pi and Ca, solutes reabsorbed primarily by the proximal tubule. Previous studies have shown that proximal tubule Na transport is inhibited by dopamine (DA), and that the natriuretic action of ANP is blunted by DA-receptor blockade. However, alterations in Na reabsorption cannot localize ANP or DA action to a specific nephron site. Therefore, the possibility that DA mediates the apparent proximal tubule effects of ANP was investigated with the use of Pi and Ca as proximal tubule markers. ANP was infused into normal rats in the presence and absence of specific DA-receptor antagonists, and Na, Pi, and Ca excretion rates were determined. ANP enhanced Na, Pi, and Ca excretion at doses that failed to alter glomerular filtration rate and mean arterial pressure (MAP). DA1-receptor blockade significantly blunted the influence of ANP on urinary Na, Pi, and Ca excretion, whereas DA2-receptor blockade was without effect. MAP and inulin and p-aminohippurate (PAH) clearances remained stable during DA-receptor blockade. Because endogenous ANP levels are elevated in rats with remnant kidneys, and because blockade of endogenous ANP reduces Pi and Ca as well as Na excretion in this model, the effect of DA1-receptor blockade on solute excretion was also examined in rats with 5/6 nephrectomy. DA1-receptor blockade significantly reduced absolute and fractional Na, Pi, and Ca excretion in rats with 5/6 nephrectomy, in the absence of measurable changes in MAP, inulin, or PAH clearance.(ABSTRACT TRUNCATED AT 250 WORDS)

Growth hormone in polymethylmethacrylate cement

The in vitro release of human growth hormone (hGH) from polymethylmethacrylate bone cement was measured for up to 40 days using a specific enzyme-linked immunosorbent assay. In rabbits, hGH-loaded bone cement was inserted into one distal femur and plain cement was inserted into the contralateral distal femur as a control. The rabbits were killed at time intervals of one, two, and four months after surgery and the distal femurs embedded whole for histology. Quantitative histomorphometry indicated there was a greater percentage of osteoid present at the hGH-loaded cement surface than at the plain cement surface one month after implantation. The hGH released from bone cement may stimulate osteogenesis and new bone formation, thus improving the strength of the bone-cement interface.

Methods and basic data of case-control study of leukaemia and lymphoma among young people near Sellafield nuclear plant in West Cumbria

OBJECTIVE

To examine whether the observed excess of childhood leukaemia and lymphoma near the Sellafield nuclear plant is associated with established risk factors or with factors related to the plant.

DESIGN

A case-control study.

SETTING

West Cumbria health district.

SUBJECTS

52 Cases of leukaemia, 22 of non-Hodgkin's lymphoma, and 23 of Hodgkin's disease occurring in people born in the area and diagnosed there in 1950-85 under the age of 25 and 1001 controls matched for sex and date of birth taken from the same birth registers as the cases.

MAIN OUTCOME MEASURES

Antenatal abdominal x ray examinations, viral infections, habit factors, proximity to and employment characteristics of parents at Sellafield.

RESULTS

Ascertainment of cases through multiple sources was as complete as possible, and the diagnosis was established for nearly all cases from hospital records and by independent pathological review when suitable material (60% (58) of cases) was available. Identification and tracing of the parents of cases and controls enabled questionnaires to be forwarded to 730 (66%), and 467 (64%) of the questionnaires were returned completed. Obstetric records were located for 481 (44%) of the relevant births, more frequently in recent years. Linkage of study subjects to the Sellafield workforce file enabled dates of employment and records on external doses of whole body ionising radiation to be obtained. Concordance of information from duplicate sources (when available) was reasonably high with no indications of bias.

CONCLUSION

Overall the collected data were sufficiently reliable for detailed analysis and careful interpretation.

Results of case-control study of leukaemia and lymphoma among young people near Sellafield nuclear plant in West Cumbria

OBJECTIVE

To examine whether the observed excess of childhood leukaemia and lymphoma near the Sellafield nuclear plant is associated with established risk factors or with factors related to the plant.

DESIGN

A case-control study.

SETTING

West Cumbria health district.

SUBJECTS

52 Cases of leukaemia, 22 of non-Hodgkin's lymphoma, and 23 of Hodgkin's disease occurring in people born in the area and diagnosed there in 1950-85 under the age of 25 and 1001 controls matched for sex and date of birth taken from the same birth registers as the cases.

MAIN OUTCOME MEASURES

Antenatal abdominal x ray examinations, viral infections, habit factors, proximity to and employment characteristics of parents at Sellafield.

RESULTS

Expected associations with prenatal exposure to x rays were found, but little information was available on viral illnesses. Relative risks for leukaemia and non-Hodgkin's lymphoma were higher in children born near Sellafield and in children of fathers employed at the plant, particularly those with high radiation dose recordings before their child's conception. For example, the relative risks compared with area controls were 0.17 (95% confidence interval 0.05 to 0.53) for being born further than 5 km from Sellafield 2.44 (1.04 to 5.71) for children of fathers employed at Sellafield at their conception, and 6.42 (1.57 to 26.3) for children of fathers receiving a total preconceptual ionising radiation dose of 100 mSv or more. Other factors, including exposure to x rays, maternal age, employment elsewhere, eating seafood, and playing on the beach did not explain these relationships. Focusing on Seascale, where the excess incidence has predominantly been reported, showed for the four out of five cases of leukaemia and one case of non-Hodgkin's lymphoma whose fathers were employed at Sellafield and for whom dose information was obtained that the fathers of each case had higher radiation doses before their child's conception than all their matched control fathers; the father of the other Seascale case (non-Hodgkin's lymphoma) was not employed at the plant. These results seem to explain statistically the geographical association. For Hodgkin's disease neither geographical nor employment associations with Sellafield were found.

CONCLUSIONS

The raised incidence of leukaemia, particularly, and non-Hodgkin's lymphoma among children near Sellafield was associated with paternal employment and recorded external dose of whole body penetrating radiation during work at the plant before conception. The association can explain statistically the observed geographical excess. This result suggests an effect of ionising radiation on fathers that may be leukaemogenic in their offspring, though other, less likely, explanations are possible. There are important potential implications for radiobiology and for protection of radiation workers and their children.

Follow up study of children born to mothers resident in Seascale, West Cumbria (birth cohort)

Records on 1068 children who were born to mothers resident in Seascale Civil Parish during 1950-83 were studied. There was a large degree of mobility among the families, and nearly half of the children did not subsequently attend the main local school. Use of the National Health Service Central Register, however, enabled us to follow up the children's records regardless of place of residence. The excess of leukaemia among Seascale children first supported from the analysis of geographical areas is confirmed. There were five deaths from leukaemia identified to 30 June 1986 compared with 0.53 expected at national rates--a ratio of 9.36 (95% confidence interval 3.04 to 21.84). One of these deaths occurred after the child had left Seascale. There were four deaths from other cancers compared with 1.06 expected--a ratio of 3.76 (95% CI 1.02 to 9.63). In addition, three further cases of cancer, apart from the deaths, were reported compared with 1.19 expected since 1971--a ratio of 2.53 (95% CI 0.52 to 7.40). For other causes of death, including stillbirths and infant mortality, there was a reported deficit compared with national rates, some of which at least was to be expected on the basis of the social class composition of the population of Seascale. In view of the importance of this cohort of births continued follow up is planned, with the possibility of extending it to include births since 1983, and the methods available for this type of study will be examined further.

Follow up study of children born elsewhere but attending schools in Seascale, West Cumbria (schools cohort)

Records on 1546 children who were identified as having attended schools in Seascale up to November 1984 and were born since 1950 but not in the civil parish were studied. These children lived in or near Seascale for a period of time while they were attending one or more of three local schools and are an additional group to the 1068 children who were identified as born to mothers resident in Seascale in an accompanying study. Even though some of the schoolchildren apparently remained in the village for a short period only all but 7% were followed up through the National Health Service Central Register. Mortality among these children to 30 June 1986 is comparable to that expected at national rates. From all causes there were 10 observed deaths compared with 12.69 expected--a ratio of 0.79 (95% confidence interval 0.38 to 1.45)--and from cancer one observed death compared with 2.04 expected--a ratio of 0.49 (95% CI 0.01 to 2.73). No deaths from leukaemia or lymphoma were reported, but only 0.83 was expected. Since 1971 (the year when cases of cancer were first notified to the NHS Central Register) three non-fatal cases of cancer were reported, including two lymphomas, compared with 2.04 expected and two cases of carcinoma in situ of the cervix compared with 1.79 expected. In addition, there was a case of leukaemia among the schoolchildren which was known previously and had been diagnosed in 1968. There is an interesting difference between the results of this study and the results of the study of children born to mothers who were resident in Seascale. In the latter study there was an excess of leukaemia and of other cancers, but a similar finding is not apparent among children who spent some time at schools in Seascale but were born elsewhere. This raises the question of whether one or more aetiological factors in childhood cancer were acting on a locality specific basis before birth or early in life. This cannot be answered from these cohort studies, but it is hoped that the case-control study that is under way in West Cumbria will provide relevant information.

The clearance of gentamicin from antibiotic-loaded bone cement

The concentrations of Gentamicin in the serum, drainage fluid and urine were determined by radioimmunoassay in 40 patients after total hip replacement and 10 after knee replacement. Palacos R bone cement with added Gentamicin had been used to fix the prostheses in all cases. Two types of response were observed; in Group I the Gentamicin levels rose very rapidly, whereas in Group II a more gradual increase was seen. In all cases the level of Gentamicin had fallen to a negligible amount by the fifth day after operation.