Effects of dexamethasone-loaded PLGA microspheres on human fetal osteoblasts

Integration of a drug delivery function into implantable medical devices enables local release of specific bioactives to control cells–surface interactions. One alternative to achieve this biofunctionality for bone implants is to incorporate particulate drug delivery systems (DDSs) into the rough or porous implant surfaces. The scope of this study was to assess the effects of a model DDS consisting of poly(D,L-lactide-co-glycolide) (PLGA) microspheres loaded with an anti-inflammatory drug, dexamethasone (DXM), on the response of Simian Virus-immortalized Human Fetal Osteoblast (SV-HFO) cells. The microspheres were prepared by the oil-in-water emulsion/solvent evaporation method, whereas cells response was investigated by Alamar Blue test for viability, alkaline phosphatase (ALP) activity for differentiation, and Alizarin Red staining for matrix mineralization. Cell viability was not affected by the presence of increased concentrations of polymeric microspheres in the culture media. Furthermore, in the cultures with DXM-loaded microspheres, ALP activity was expressed at levels similar with those obtained under osteogenic conditions, indicating that DXM released from the microsphere-stimulated cell differentiation. Matrix mineralization occurred preferentially around the DXM-loaded microspheres confirming that the released DXM could act as osteogenic supplement for the cells. These in vitro findings suggest that a particulate PLGA-DXM DDS may actually provide dual, anti-inflammatory and osteogenic functions when incorporated on the surface of bone implants.

Release of PLGA-encapsulated dexamethasone from microsphere loaded porous surfaces

The aim of the present study was to investigate the morphology and function of a drug eluting metallic porous surface produced by the immobilization of poly lactide-co-glycolide microspheres bearing dexamethasone onto plasma electrolytically oxidized Ti-6Al-7Nb medical alloy. Spheres of 20 microm diameter were produced by an oil-in-water emulsion/solvent evaporation method and thermally immobilized onto titanium discs. The scanning electron microscopy investigations revealed that the size distribution and morphology of the attached spheres had not changed significantly. The drug release profiles following degradation in phosphate buffered saline for 1000 h showed that, upon immobilisation, the spheres maintained a sustained release, with a triphasic profile similar to the non-attached system. The only significant change was an increased release rate during the first 100 h. This difference was attributed to the effect of thermal attachment of the spheres to the surface.

Size effect of PLGA spheres on drug loading efficiency and release profiles

Drug delivery systems (DDS) based on poly (lactide-co-glycolide) (PLGA) microspheres and nanospheres have been separately studied in previous works as a means of delivering bioactive compounds over an extended period of time. In the present study, two DDS having different sizes of the PLGA spheres were compared in morphology, drug (dexamethasone) loading efficiency and drug release kinetics in order to investigate their feasibility with regard to production of medical combination devices for orthopedic applications. The loaded PLGA spheres have been produced by the oil-in-water emulsion/solvent evaporation method following two different schemes. Their morphology was assessed by scanning electron microscopy and the drug release was monitored in phosphate buffer saline solution at 37 degrees C for 550 h using high performance liquid chromatography. The synthesis schemes used produced spheres with two different and reproducible size ranges (20 +/- 10 and 1.0 +/- 0.4 microm) having a smooth outer surface and regular shape. The drug loading efficiency of the 1.0 microm spheres was found to be 11% as compared to just 1% for the 20 microm spheres. Over the 550 h release period, the larger spheres (diameter 20 +/- 10 microm) released 90% of the encapsulated dexamethasone in an approximately linear fashion whilst the relatively small spheres (diameter 1.0 +/- 0.4 microm) released only 30% of the initially loaded dexamethasone, from which 20% within the first 25 h. The changes observed were mainly attributed to the difference in surface area between the two types of spheres as the surface texture of both systems was visibly similar. As the surface area per unit volume increases in the synthesis mixture, as is the case for the 1.0 microm spheres formulation, the amount of polymer-water interfaces increases allowing more dexamethasone to be encapsulated by the emerging polymer spheres. Similarly, during the release phase, as the surface area per unit volume increases, the rate of inclusion of water into the polymer increases, permitting faster diffusion of dexamethasone.

Molecular breeding of viruses

Genetic recombination is a major force driving the evolution of many viruses. Recombination between two copackaged retroviral genomes may occur at rates as high as 40% per replication cycle. This enables genetic information to be shuffled rapidly, leading to recombinants with new patterns of mutations and phenotypes. The in vitro process of DNA shuffling (molecular breeding) mimics this mechanism on a vastly parallel and accelerated scale. Multiple homologous parental sequences are recombined in parallel, leading to a diverse library of complex recombinants from which desired improvements can be selected. Different proteins and enzymes have been improved using DNA shuffling. We report here the first application of molecular breeding to viruses. A single round of shuffling envelope sequences from six murine leukaemia viruses (MLV) followed by selection yielded a chimaeric clone with a completely new tropism for Chinese Hamster Ovary (CHOK1) cells. The composition and properties of the selected clone indicated that this particular permutation of parental sequences cannot be readily attained by natural retroviral recombination. This example demonstrates that molecular breeding can enhance the inherently high evolutionary potential of retroviruses to obtain desired phenotypes. It can be an effective tool, when information is limited, to optimize viruses for gene therapy and vaccine applications when multiple complex functions must be simultaneously balanced.

Molecular evolution of an arsenate detoxification pathway by DNA shuffling

Functional evolution of an arsenic resistance operon has been accomplished by DNA shuffling, involving multiple rounds of in vitro recombination and mutation of a pool of related sequences, followed by selection for increased resistance in vivo. Homologous recombination is achieved by random fragmentation of the PCR templates and reassembly by primerless PCR. Plasmid-determined arsenate resistance from plasmid pl258 encoded by genes arsR, arsB, and arsC was evolved in Escherichia coli. Three rounds of shuffling and selection resulted in cells that grew in up to 0.5 M arsenate, a 40-fold increase in resistance. Whereas the native plasmid remained episomal, the evolved operon reproducibly integrated into the bacterial chromosome. In the absence of shuffling, no increase in resistance was observed after four selection cycles, and the control plasmid remained episomal. The integrated ars operon had 13 mutations. Ten mutations were located in arsB, encoding the arsenite membrane pump, resulting in a fourfold to sixfold increase in arsenite resistance. While arsC, the arsenate reductase gene, contained no mutations, its expression level was increased, and the rate of arsenate reduction was increased 12-fold. These results show that DNA shuffling can improve the function of pathways by complex and unexpected mutational mechanisms that may be activated by point mutation. These mechanisms may be difficult to explain and are likely to be overlooked by rational design.

Directed evolution of a fucosidase from a galactosidase by DNA shuffling and screening

An efficient beta-fucosidase was evolved by DNA shuffling from the Escherichia coli lacZ beta-galactosidase. Seven rounds of DNA shuffling and colony screening on chromogenic fucose substrates were performed, using 10,000 colonies per round. Compared with native beta-galactosidase, the evolved enzyme purified from cells from the final round showed a 1,000-fold increased substrate specificity for o-nitrophenyl fucopyranoside versus o-nitrophenyl galactopyranoside and a 300-fold increased substrate specificity for p-nitrophenyl fucopyranoside versus p-nitrophenyl galactopyranoside. The evolved cell line showed a 66-fold increase in p-nitrophenyl fucosidase specific activity. The evolved fucosidase has a 10- to 20-fold increased kcat/Km for the fucose substrates compared with the native enzyme. The DNA sequence of the evolved fucosidase gene showed 13 base changes, resulting in six amino acid changes from the native enzyme. This effort shows that the library size that is required to obtain significant enhancements in specificity and activity by reiterative DNA shuffling and screening, even for an enzyme of 109 kDa, is within range of existing high-throughput technology. Reiterative generation of libraries and stepwise accumulation of improvements based on addition of beneficial mutations appears to be a promising alternative to rational design.

PDZ domain of neuronal nitric oxide synthase recognizes novel C-terminal peptide sequences

PDZ domains are multifunctional protein-interaction motifs that often bind to the C-terminus of protein targets. Nitric oxide (NO), an endogenous signaling molecule, plays critical roles in nervous, immune, and cardiovascular function. Although there are numerous physiological functions for neuron-derived NO, produced primarily by the neuronal NO synthase (nNOS), excess nNOS activity mediates brain injury in cerebral ischemia and in animal models of Parkinson's disease. Subcellular localization of nNOS activity must therefore be tightly regulated. To determine ligands for the PDZ domain of nNOS, we screened 13 billion distinct peptides and found that the nNOS-PDZ domain binds tightly to peptides ending Asp-X-Val. This differs from the only known (Thr/Ser)-X-Val consensus that interacts with PDZ domains from PSD-95. Preference for Asp at the -2 peptide position is mediated by Tyr-77 of nNOS. A Y77D78 to H77E78 substitution changes the binding specificity from Asp-X-Val to Thr-X-Val. Guided by the Asp-X-Val consensus, candidate nNOS interacting proteins have been identified including glutamate and melatonin receptors. Our results demonstrate that PDZ domains have distinct peptide binding specificity.

Computerized evaluation of fetal heart-rate patterns

Antepartum Cardiotocography (CTG) is one of the few techniques available today to assess fetal conditions in high risk pregnancies. Visual interpretation of CTG traces has been shown to be unreliable. In order to eliminate observer variability and to increase the accuracy of CTG, numerical on-line analysis of fetal heart rate (FHR) patterns was introduced. The experience with computerized systems has shown that the best indicator of fetal conditions is variation, long- or short-term. Mean range (Long-term variation) values of less than 20 msec are associated with an increased rate of fetal acidaemia and perinatal mortality. The availability of numerical measurements enables the detection of small changes in FHR occurring in time, so when initial deterioration signs arise, the single fetus can be followed up longitudinally. Moreover, a more accurate correlation with other biophysical and biochemical parameters of the fetus can be done, as well as with perinatal outcome. In conclusion, computerized CTG improves accuracy and allows to distinguish fetuses that are truly jeopardized because of hypoxemia, from those who are not.

Umbilical artery resistance index as a screening test for fetal well-being. I: Prospective revealed evaluation

Abnormalities of the human fetoplacental circulation, a common association with fetal morbidity and mortality, can be detected by Doppler ultrasound examination of the umbilical arterial blood flow. The value of this procedure as a screening test was assessed in 369 women whose fetuses were evaluated on 1354 occasions using both computerized antenatal fetal heart rate (FHR) analysis and continuous-wave Doppler ultrasound. The FHR analyses were used to guide management, but the results of the Doppler measurements were not made available to the clinical staff. The mean duration of each nonstress test (NST) was 27 minutes, compared with 6 minutes for the Doppler examination. Increased resistance indices in the umbilical artery identified those fetuses with an abnormal NST or a clinical diagnosis of antenatal distress with a high sensitivity and negative predictive value. The high rate of false-positive results with respect to these two end points was reduced when fetal distress in labor was included as a third end point. The value of the Doppler examination in predicting fetal distress was applicable to appropriately grown as well as small for gestational age fetuses.