The regeneration of bone is a remarkable, complex physiological process, and BMPs are a formidable clinical tool to promote its regeneration. By defining roles played by BMPs in developmental biology and bone regeneration, significant progress has been made to identify cell-signaling molecules and their regulators. For example, the regulators of BMPs that include noggin, chordin, cerberus, dan, and gremlin may be harnessed as therapies to offset calcification encountered after total hip arthroplasties. Furthermore, exploiting BMPs and Smads may generate new therapeutic options for bone repair. Another compelling clinical consideration is the trans-acting factor osteoblast-specific factor-2, which can promote osteoblast differentiation. Moreover, the affiliation of osteoblast-specific factor-2 with heritable disorders merits exploration. A recognized daunting challenge includes a carrier/delivery system for the powerful morphogenetic therapeutic tools, as well as osteoprogenitor cells and intracellular transduction and transcriptional factors. In addition, the long-term effects of administering superphysiological doses of rhBMPs to patients must be assessed systematically. A new generation carrier/delivery system may be the answer to offset dosing liabilities as well as to provide residence for exogenous, BMP-receptive osteoprogenitor cells (111,112). The areas highlighted in this review offer fertile territory for thought and research to develop rational clinical treatments to promote bone regeneration and to understand some of the biological roles of BMPs.

The present studies were undertaken to evaluate the in vitro gel stability of the hydrogels alginate and agarose. Gel strength (of alginate and agarose) and protein diffusion (of alginate only) were shown t o correlate with gel stability and to be useful techniques to monitor gel stability over time. The gel strengths of alginate and agarose were followed for a 90-day period using gel strength as a measure of gel stability. The gel strength of agarose diminished in the presence of cells because the cells likely interfered with the hydrogen bond formation required for agarose gelation. In the presence of cells, the gel strength of agarose decreased by an average of 25% from time 0 to 60 days, thereafter maintaining that value to 90 days. The gel strength of calcium-or barium-crosslinked alginate decreased over 90 days, with an equilibrium gel strength being achieved after 30 days. The presence of cells did not further decrease alginate gel strength. The gel strengths of calcium-and barium-crosslinked alginates were similar at 60 days-350 ? 20 g and 300 ? 60 g, respectively-indicating equivalence in their stability. The stability of calcium-crosslinked sodium alginate gels over a 60-day time period was monitored by diffusion of proteins ranging in molecular weight from 14.5 t o 155 kD. From these diffusion measurements, the average pore size of the calcium-crosslinked alginate gels was estimated, using ,a semi-empirical model, t o increase from -176 to 289 A over a period of 60 days.

No abstract

Huntington's disease is a genetic disorder that results from degeneration of striatal neurons, particularly those containing GABA (gamma-aminobutyric acid). There is no effective treatment for preventing or slowing this neuronal degeneration. Ciliary neurotrophic factor (CNTF) is a trophic factor for striatal neurons and therefore a potential therapeutic agent for Huntington's disease. Here we evaluate CNTF as a neuroprotective agent in a nonhuman primate model of Huntington's disease. We gave cynomolgus monkeys intrastriatal implants of polymer-encapsulated baby hamster kidney fibroblasts that had been genetically modified to secrete human CNTF. One week later, monkeys received unilateral injections of quinolinic acid into the previously implanted striatum to reproduce the neuropathology seen in Huntington's disease. Human CNTF was found to exert a neuroprotective effect on several populations of striatal cells, including GABAergic, cholinergic and diaphorase-positive neurons which were all destined to die following administration of quinolinic acid. Human CNTF also prevented the retrograde atrophy of layer V neurons in motor cortex and exerted a significant protective effect on the GABAergic innervation of the two important target fields of the striatal output neurons (the globus pallidus and pars reticulata of the substantia nigra). Our results show that human CNTF has a trophic influence on degenerating striatal neurons as well as on critical non-striatal regions such as the cerebral cortex, supporting the idea that human CNTF may help to prevent the degeneration of vulnerable striatal populations and cortical-striatal basal ganglia circuits in Huntington's disease.

Basic fibroblast growth factor (b-FGF) has been shown to enhance the in vitro survival and neurite extension of various types of neurons including dorsal root ganglia (DRG) cells. Alpha-1 glycoprotein (alpha 1-GP), an acute phase reactant, has been reported to enhance the in vitro neuritic extensions of chick DRG cells. In the present study, we investigated the ability of synthetic nerve guidance channels, which release sustained controlled amounts of b-FGF and/or alpha 1-GP, to support the regeneration of a transected peripheral nerve over a 15 mm long gap, a distance that does not permit regeneration in conventional polymeric tubes. Tubes releasing bovine serum albumin (BSA), cytochrome C, BSA and b-FGF, BSA and denatured b-FGF, BSA and alpha 1-GP, or BSA, b-FGF, and alpha 1-GP were fabricated by a dip-molding technique. In vitro kinetic studies of protein release from these channels showed an initial burst during the 1st day, followed by a linear release for at least 2 weeks thereafter. In vitro studies indicated that the b-FGF released from the polymer was biologically active as assessed by the ability of channels releasing b-FGF to induce neurite extensions in PC12 cells. For in vivo studies, the various types of tubes were used as nerve guidance channels for the repair of a 15 mm nerve gap in the sciatic nerve of rats. Four weeks postimplantation, only the tubes releasing b-FGF or b-FGF and alpha 1-GP displayed regenerated cables bridging both nerve stumps, which contained nerve fascicles with myelinated and unmyelinated axons.(ABSTRACT TRUNCATED AT 250 WORDS)

This study was designed to determine if the surface modification of porous poly(lactic acid) (PLA) scaffolds would enhance osteogenic precursor cell (OPC) attachment, growth, and differentiation. A covalently grafted amino group (-NH(2)), poly(L-lysine) (PLL), and the peptide arginine-glycine-aspartic acid (RGD) were selected for the evaluation. The hypothesis was that surface modification would have a positive impact on cell-substratum interactions. The experiment was performed by OPC cells being placed on PLA films and scaffolds modified with NH(2), PLL, or RGD in tissue culture media. OPC attachment to PLA films was assessed after 24 h of incubation. The growth and differentiation of the adherent OPCs on porous PLA scaffolds were assessed after 14 and 28 days for alkaline phosphatase (APase) activity and calcium levels, both of which increase as OPCs differentiate into mature bone cells. All assays were accomplished in triplicate, and data were tested with post hoc orthogonal contrasts (i.e., Fisher's least significant difference) at p < or = 0.05. The PLA film surface-modified with RGD showed better OPC cell attachment than the other films. The cells on the PLA scaffolds surface-modified with RGD also exhibited an increase in APase activity and calcium levels in comparison with those on other scaffolds. This difference was apparent at both time intervals and was especially evident in the tissue culture media containing an osteogenic supplement. The results of this study indicate that modifying the surface of PLA polymer scaffolds with RGD enhances bone cell attachment and differentiation and may improve their ability to regenerate bone tissue more efficiently in wound models.

No abstract

Delivery of neurotrophic molecules to the CNS has gained considerable attention as a potential treatment strategy for neurological disorders. In the present study, a DHFR-based expression vector containing the human ciliary neurotrophic factor (hCNTF) was transfected into a baby hamster kidney fibroblast cell line (BHK). Using a polymeric device, encapsulated BHK-control cells and those secreting hCNTF (BHK-hCNTF) were transplanted unilaterally into the rat lateral ventricle. Twelve days later, the same animals received unilateral injections of quinolinic acid (QA; 225 nmol) into the ipsilateral striatum. After surgery, animals were behaviorally tested for apomorphine-induced rotation behavior and for skilled forelimb function using the staircase test. Rats receiving BHK-hCNTF cells rotated significantly less than animals receiving BHK-control cells. No behavioral effects of hCNTF were observed on the staircase test. Nissl-stained sections demonstrated that BHK-hCNTF cells significantly reduced the extent of striatal damage produced by QA. Quantitative analysis of striatal neurons further demonstrated that both choline acetyltransferase- and GAD-immunoreactive neurons were protected by BHK-hCNTF implants. In contrast, a similar loss of NADPH-diaphorase-positive cells was observed in the striatum of both implant groups. Analysis of retrieved capsules revealed numerous viable and mitotically active BHK cells that continued to secrete hCNTF. These results support the concepts that implants of polymer-encapsulated hCNTF-releasing cells can be used to protect striatal neurons from excitotoxic damage and that this strategy may ultimately prove relevant for the treatment of Huntington's disease.