Kazutoshi Nozaki

A biodegradable polymer as a cytokine delivery system for inducing bone formation

Bone morphogenetic proteins (BMPs) that have the potential to elicit new bone in vivo have been used in a tissue-engineering approach for the repair of bone injuries and bone defects. Although it is now possible to generate large amounts of recombinant human (rh) BMPs for medical use, the major challenge remains in the development of optimal local delivery systems for these proteins. Here we describe the development of a synthetic biodegradable polymer, poly-d,l-lactic acid–p-dioxanone–polyethylene glycol block copolymer (PLA-DX-PEG). This polymer exhibits promising degradation characteristics for BMP delivery systems and good biocompatibility under test conditions. PLA-DX-PEG/rhBMP-2 composite implants induced ectopic new bone formation effectively when tested in vivo, and can repair large bone defects orthotopically. This polymeric delivery system represents an advance in the technology for the enhancement of bone repair.

Local bone formation by injection of recombinant human bone morphogenetic protein-2 contained in polymer carriers

The regenerating potential of human bone is limited. The repair of large bone defects often associated with bone tumor resections is not observed, and nonunion or delayed union of bone is a serious problem for fracture treatment. In these cases, autogeneic or allogeneic bone grafting has been routinely indicated, but these approaches require invasive surgical procedures. An alternative approach described in this paper involves the injection of bone morphogenetic proteins (BMPs) in a polymeric delivery system. We demonstrate that synthetic biodegradable polymers, poly-D,L-lactic acid-polyethylene glycol (PLA-PEG) block copolymers, which exhibit an exquisite temperature-dependent liquid-semisolid transition, work well as an injectable delivery system for recombinant human (rh) BMP-2. The thermosensitive property of the PLA-PEG/rhBMP-2 composite is permissive to percutaneous injection when heated. The fluidity of this composite decreases as it cools down to body temperature and the resultant semisolid form provides a scaffold for bone formation through the gradual local release of the rhBMP-2. This new type of injectable osteoinductive material will enable a less invasive approach to surgeries involving the restoration or repair of bone tissues.

Bone regeneration by recombinant human bone morphogenetic protein-2 and a novel biodegradable carrier in a rabbit ulnar defect model

The effects of recombinant human bone morphogenetic protein (rhBMP)-2 and a novel carrier, PLGA-coated gelatin sponge (PGS), on bone defect repair was examined. A 1.5 cm unilateral segmental bone defect was created in the ulnar diaphysis of a Japanese white rabbit. In an initial study, defects were either treated with PGS impregnated with various concentrations of rhBMP-2 (0, 0.1, 0.4 and 1 mg/cm(3)) or left untreated. Defect healing was assessed by radiographic union rate, and biomechanical properties of regenerated bones were determined at 16 weeks postoperatively. In a second study, defects were implanted with PGS with or without rhBMP-2, and histologically observed at postoperative weeks 8 and 16. Radiographic union rate increased the dose-dependently at an early time point. All defects treated with rhBMP-2 (0.4 and 1 mg/cm(3)) were radiographically repaired. Mechanical properties of regenerated bones were restored in a dose-dependent manner. Neither ulnae left untreated nor implanted PGS alone showed radiographic union. Longitudinal alignment of lamellar structure was observed histologically at 16 weeks, indicating that remodeling of regenerated bone was complete. Implanted PGS was almost completely resorbed by 8 weeks, and no abnormalities were observed in the surrounding soft tissue. These results suggest that PGS is a promising carrier for rhBMP-2.

Biodegradable poly-D,L-lactic acid-polyethylene glycol block copolymers as a BMP delivery system for inducing bone.

Background: Bone morphogenetic proteins (BMPs) are biologically active molecules capable of eliciting new bone formation. In combination with biomaterials, these proteins can be used in a clinical setting as bone-graft substitutes to promote bone repair. Collagen from animal sources has previously been the preferred carrier material in animal experiments. More recently, synthetic biodegradable polymers have been tested as a delivery vehicle for osteoinductive agents. In earlier studies performed in our laboratory, it was found that the polylactic acid homopolymers (PLA650) and poly-d,l-lactic acid-polyethylene glycol block copolymers (PLA650-PEG200) are viscous liquids that can be used as BMP delivery systems. Methods: To obtain new PLA-PEG polymers that exhibit greater plasticity, the molecular sizes of PLA and PEG segments in the copolymer chains were increased. Plastic PLA-PEG polymers with various molecular sizes and PLA/PEG ratios were synthesized, mixed with recombinant human (rh) BMP-2, and implanted into the dorsal muscles of mice for 3 weeks to evaluate their capacity to elicit new bone formation. To compare the plastic PLA-PEG polymer with the liquid PLA650-PEG200 polymer, these two polymers were combined with rhBMP-2, implanted, and harvested after 3 weeks. Bone mineral content (BMC), bone area, and bone mineral density (BMD) of the ectopic new bone were measured by means of single energy X-ray absorptiometry (SXA). Results: All of the PLA6,500-PEG3,000 implants with 10 or 20 g of rhBMP-2 showed new bone formation. In contrast, little or no bone formation was seen in other plastic PLA-PEG implants with rhBMP-2. Control implants that lacked rhBMP-2 did not show new bone formation. Radiographic and histologic examinations showed that the PLA6,500-PEG3,000 implants with rhBMP-2 harvested 3 weeks after implantation had normal bone characteristics with hematopoietic marrow and osseous trabeculae. SXA analysis showed that the values for bone mineral content (BMC), bone area, and bone mineral density (BMD) of new bone resulting from the use of plastic PLA6,500-PEG3,000 polymers with rhBMP-2 were significantly higher than those obtained with the liquid PLA650-PEG200 polymers (p < 0.001 for each of the three values). Conclusions: These results indicate that the PLA6,500-PEG3000 block copolymer with plastic properties works effectively as a BMP delivery system. These data suggest that the total molecular size and ratio of PLA size to PEG size is an essential factor in determining the efficacy of a BMP delivery system. After implantation, it is possible that the PLA6,500-PEG3,000 pellets might have absorbed tissue fluids and become swollen, resulting in bone formation that exceeded the size of the original implants. This expansion characteristic is a potentially beneficial property, given the intended practical application of the polymer in the repair of bone defects.Clinical Relevance:New synthetic biodegradable delivery systems will play an important role in the clinical applications of rhBMPs in which local formation of bone via an osteoinductive graft material is needed. Further pre-clinical and clinical work is necessary to establish the safety of these implants before they are adopted for widespread clinical use.

The effects of heat on the biological activity of recombinant human bone morphogenetic protein-2

This study was designed to investigate effects of heat on the bone-inducing activity of recombinant human bone morphogenetic protein (rhBMP)-2. rhBMP-2 samples were heated at 50, 70, 90, or 100°C for 15 min, or 1, 2, 4, or 8 h, or autoclaved at 120°C for 15 min. The bone-inducing activity of the rhBMP-2 before and after heating was assayed in in vivo and in vitro systems. For the in vivo assay, 5 µg rhBMP-2 samples were impregnated into porous collagen disks (6 mm in diameter, 1 mm thickness), freeze dried, and implanted into the back muscles of ddY mice. Three weeks later, the implant was harvested from the host and examined for ectopic new bone tissue by radiography. The new bone mass was quantified by single-energy X-ray absorptiometry. The in vitro activity of the rhBMP-2 was assayed by adding the BMP sample at a concentration of 100 ng/ml to cultures of MC3T3-E1 cells. After 48 h, the alkaline phosphatase activity was measured. After heating at 50° or 70°C, no significant reduction in bone-inducing activity was noted in either in vivo or in vitro assay systems unless the protein was exposed to sustained heat at 70°C for 8 h, based on in vitro assay data. However, heating above 90°C and for longer periods led to a decrease in the biological activity of the rhBMP-2 in a time- and temperature-dependent manner. rhBMP-2 was rendered inactive when exposed to temperatures at or in excess of 120°C.

Effects of minodronic acid and alendronate on bone remodeling, microdamage accumulation, degree of mineralization and bone mechanical properties in ovariectomized cynomolgus monkeys.

Suppression of bone remodeling by bisphosphonates leads to accumulation of microdamage in bone. If this microdamage develops due to suppressed repair of remodeling only, more potent bisphosphonates should cause more damage. In this study, we evaluated the effects of reduced bone turnover produced by a potent bisphosphonate, minodronic acid, on microdamage accumulation, the degree of mineralization and mechanical properties of bone in ovariectomized cynomolgus monkeys, and compared these effects with those of alendronate. Sixty female monkeys aged 9-17 years old were divided into five groups. The sham group and the ovariectomized group were treated daily for 17 months with lactose vehicle. The other three groups were treated daily with minodronic acid at a dose of 0.015 mg/kg or 0.15 mg/kg, or alendronate at 0.5mg/kg orally. After sacrifice, lumbar vertebrae and left femurs were subjected to histomorphometry, microdamage, mineralization analyses, and mechanical testing. Minodronic acid suppressed bone remodeling of cancellous and cortical bone in a dose-dependent manner and the higher dose of minodronic acid suppressed bone remodeling more strongly than alendronate. The lower dose of minodronic acid did not increase microdamage accumulation and compressive strength, but the higher dose of minodronic acid and alendronate resulted in similar increases in cancellous microdamage accumulation and ultimate load in lumbar vertebra. There were no significant differences among the groups in microdamage, degree of mineralization and mechanical properties in cortical bone of the femoral shaft; however, only alendronate showed a tendency to increase highly mineralized osteons and microdamage. These findings suggest that microdamage caused by minodronic acid is less than that expected based on the extent of remodeling suppression, in comparison with alendronate although this was not reflected in any significant change of mechanical properties.

Synergism between interleukin-11 and bone morphogenetic protein-2 in the healing of segmental bone defects in a rabbit model

Recombinant human interleukin-11 (rHuIL-11) and recombinant human bone morphogenetic protein-2 (rHuBMP-2) have been shown to act synergistically in the induction of osteoblast differentiation. To determine whether these two proteins can be used clinically in fracture healing and reconstructive surgery, we investigated whether rHuIL-11 and rHuBMP-2 act synergistically to heal segmental bone defects in a rabbit model. A 1.5-cm segmental defect was created in the right ulnar diaphysis of 20 Japanese white rabbits. Polylactic-co-glycolic acid (PLGA)-coated gelatin sponges (PGS) permeated with rHuBMP-2 (n = 8), rHuIL-11 plus rHuBMP-2 (n = 8), or rHuIL-11 (n = 4) were implanted into the bone defects. Radiographs were scored by two independent observers for bone formation and union rates after 2, 3, 4, and 8 weeks. Bone formation was higher in rabbits implanted with rHuBMP-2 plus rHuIL-11 than in those implanted with rHuBMP-2 alone, reaching statistical significance after 4 weeks. At early time points, the union rate in rabbits implanted with rHuBMP-2 plus rHuIL-11 was higher than in rabbits implanted with rHuBMP-2. At 2, 4, and 8 weeks, new bone volume was significantly higher in rabbits administered rHuIL-11 plus rHuBMP-2 than in those given rHuBMP-2 alone. In contrast, mechanical testing after 8 weeks showed that bone strength in the two groups of rabbits was equivalent. These findings show that rHuIL-11 and rHuBMP-2 act synergistically to accelerate bone formation without affecting bone strength. Treatment with a combination of rHuIL-11 and rHuBMP-2 may thus be of great benefit in fracture healing and for patients undergoing reconstructive surgery.

Incadronate inhibits osteoporosis in ovariectomized rats.

Incadronate is a highly effective inhibitor of stimulated bone resorption as demonstrated in a hypercalcemia model in rats, bone metastasis models in mice and rats, and an osteoporosis model in dogs. In this study, the effect of incadronate on osteoporosis in ovariectomized rats was examined. Incadronate dose-dependently inhibited decreases in second lumbar vertebrae bone mineral density (BMD) following oral administration for 4 or 12 weeks. Significant inhibition was observed at doses of more than 0.3 mg/kg. Incadronate dose-dependently inhibited the loss of distal femur metaphyseal compressive strength following 12 weeks of oral administration, and this was significant at a 3 mg/kg daily dose. Incadronate also dose-dependently inhibited the increases in urinary deoxypyridinoline levels after 4-or 12-week oral administrations. While incadronate had no effect on serum osteocalcin levels after 4 weeks of oral administration, it did dose-dependently reduce levels after 12 weeks of oral administration. These results suggested that incadronate may be a useful drug for osteoporosis due to stimulated bone resorption.

Recombinant Human Bone Morphogenetic Protein-2 as an Osteoinductive Biomaterial and a Biodegradable Carrier in a Rabbit Ulnar Defect Model

We investigated early local changes induced by recombinant human bone morphogenetic protein (rhBMP)-2 and a novel carrier, poly[L-lactide-co-glycolide] copolymer-coated gelatin sponge (PGS). A 1.5 cm segmental bone defect was created in the diaphysis of the right ulna of male Japanese white rabbit. Defects received PGS with or without rhBMP-2 (0, 0.4, or 1 mg/cm3) and were harvested at 3, 7, 14, 21, or 28 days post implantation for histological examination. Immuno-staining for vascular endothelial growth factor (VEGF) was also performed. Spindle-shaped cells were observed in the rhBMP-2-treated groups 3 and 7 days after implantation. Bone regeneration was detected after 14 days in the rhBMP-2-treated groups and the bone area increased with time and dose. Expression of VEGF was observed in all groups at 3 days and was maintained by 14 days only in the defects treated with rhBMP-2 at a dose of 1 mg. These results indicate that rhBMP-2 exert its osteo-inductive activities via the promotion of osteogenic cell mobilization, and possibly via angiogenesis based on VEGF induction. Foreign-body reactions to the implanted PGS were similar to those observed when either poly[L-lactide-co-glycolide] copolymer or gelatin was individually implanted. These results indicate that the PGS is a useful and safe carrier for rhBMP-2.

Intermittent minodronic acid treatment with sufficient bone resorption inhibition prevents reduction in bone mass and strength in ovariectomized rats with established osteopenia comparable with daily treatment

This study examined and compared the effects of four-week intermittent and daily administrations of minodronic acid, a highly potent nitrogen-containing bisphosphonate, on bone mineral density (BMD), bone strength, bone turnover, and histomorphometry on established osteopenia in ovariectomized (OVX) rats. Fourteen-week-old female F344 rats were OVX or sham-operated. At 12 weeks post surgery, minodronic acid was orally administered once every 4 weeks at 0.2, 1, and 5 mg/kg and once daily at 0.006, 0.03, and 0.15 mg/kg for 12 months. The total dosing amount was comparable between the two dosing regimens. The levels of urinary deoxypyridinoline and serum osteocalcin were measured to assess bone turnover. BMD as assessed via dual-energy X-ray absorptiometry, bone structure and dynamical changes in vertebral trabecula and biomechanical properties were measured ex vivo at 12 months to assess bone content and material properties. Minodronic acid dose-dependently ameliorated the decrease in BMD of lumbar vertebrae and the femur in both treatment regimens similarly. Minodronic acid suppressed elevated urinary levels of deoxypyridinoline, a bone resorption marker, and reduced the serum levels of osteocalcin, a bone formation marker. In the mechanical test at 12 months of treatment, minodronic acid dose-dependently ameliorated the reduction in bone strength in femur and vertebral body. There is no significant difference in parameters between the two regimens except maximal load of lower doses in lumbar vertebral body and absorption energy of middle doses in femur. With these parameters with significant differences, values of the intermittent regimen were significantly lower than that of daily repeated regimen. Bone histomorphometric analysis of the lumbar vertebral body showed that minodronic acid significantly ameliorated the decrease in bone mass, trabecular thickness and number, and the increase in trabecular separation, bone resorption indices (Oc.S/BS and N.Oc/BS), and bone formation indices (BFR/BS, MAR and OV/BV) in both regimens. Minodronic acid suppressed OVX-induced increases in bone turnover at the tissue level and ameliorated all structural indices, thereby improving the deterioration of bone quality under osteoporotic disease conditions regardless of the regimen. In conclusion, a four-week intermittent treatment of minodronic acid suppressed increased bone resorption as daily treatment when considering the total administered dose in OVX rats with established osteopenia. The improvement of microarchitectural destruction in low dose of intermittent treatment was weaker than that observed in a daily repeated regimen; however the effects of high and middle doses of intermittent treatment were equivalent to that observed in daily repeated regimen accompanied by sufficient bone resorption inhibition in rats. These findings suggest that minodronic acid at an appropriate dose in an intermittent regimen may be as clinically useful in osteoporosis therapy as in daily treatment.