A resorbable antibiotic eluting bone void filler for periprosthetic joint infection prevention

Authors

Zachary Jones, Amanda E. Brooks, Zachary Ferrell, David W. Grainger and Kristofer D. Sinclair

Abstract

Periprosthetic joint infection (PJI) following total knee arthroplasty is a globally increasing procedural complication. These infections are difficult to treat and typically require revision surgery. Antibiotic-loaded bone cement is frequently utilized to deliver antibiotics to the site of infection; however, bone cement is a nondegrading foreign body and known to leach its antibiotic load, after an initial burst release, at subtherapeutic concentrations for months. This work characterized a resorbable, antibiotic-eluting bone void filler designed to restore bone volume and prevent PJI. Three device formulations were fabricated, consisting of different combinations of synthetic inorganic bone graft material, degradable polymer matrices, salt porogens, and antibiotic tobramycin. These formulations were examined to determine the antibiotic's elution kinetics and bactericidal potential, the device's degradation in vitro, as well as osteoconductivity and device resorption in vivo using a pilot rabbit bone implant model. Kirby-Bauer antibiotic susceptibility tests assessed bactericidal activity. Liquid chromatography with tandem mass spectrometry measured antibiotic elution kinetics, and scanning electron microscopy was used to qualitatively assess degradation. Results indicated sustained antibiotic release from all three formulations above the Staphylococcus aureus minimum inhibitory concentration for a period of 5 to 8 weeks. Extensive degradation was observed with the Group 3 formulation after 90 days in phosphate-buffered saline, with a lesser degree of degradation observed in the other two formulations. Results from the pilot rabbit study showed the Group 3 device to be biocompatible, with minimal inflammatory response and no fibrous encapsulation in bone. The device was also highly osteoconductive—exhibiting an accelerated mineral apposition rate.

Link to Article

http://dx.doi.org/10.1002/jbm.b.33513

Treatment with curcumin alleviates sublesional bone loss following spinal cord injury in rats

Authors

Xiaobin Yang, Baorong He, Peng Liu, Liang Yan, Ming Yang, Dichen Li

Abstract

This work aimed to investigate the therapeutic effect of curcumin on sublesional bone loss induced by spinal cord injury (SCI) in rats. SCI model in this work was generated in rats by surgical transaction of the cord at the T10–12 level. After the surgery, animals were treated with curcumin (110 mg/kg body mass/day, via oral gavages) for 2 weeks. Treatment of SCI rats with curcumin prevented the reduction of bone mass in tibiae and femurs, preserved bone microstructure including trabecular bone volume fraction, trabecular number, and trabecular thickness in proximal tibiae, and preserved mechanical properties of femoral midshaft. Treatment of SCI rats with curcumin increased osteoblast surface and reduced osteoclast surface in proximal tibiae. Treatment of SCI rats with curcumin increased osteocalcin mRNA expression and reduced mRNA levels of tartrate-resistant acid phosphatase and mRNA ratio of receptor activator of NF-κB ligand/osteoprotegerin in distal femurs. Treatment of SCI rats with curcumin reduced serum and femoral levels of thiobarbituric acid reactive substances. Treatment of SCI rats with curcumin had no significant effect on serum 25(OH)D, but enhanced mRNA and protein expression of vitamin D receptor (VDR) in distal femurs. Treatment of SCI rats with curcumin enhanced mRNA levels of Wnt3a, Lrp5, and ctnnb1 and upregulated protein expression of β-catenin in distal femurs. In conclusions, treatment with curcumin abated oxidative stress, activated VDR, and enhanced Wnt/β-catenin pathway, which might explain its beneficial effect against sublesional bone loss following SCI in rats, at least in part.

Link to Article

http://dx.doi.org/10.1016/j.ejphar.2015.08.036

Vitamin D and calcium regulation of epidermal wound healing

Authors

Yuko Oda , Chia-Ling Tu , Alicia Menendez, Thai Nguyen, Daniel D. Bikle

Abstract

Wound healing is essential for survival. This is a multistep process involving a number of different cell types. In the skin wounding triggers an acute inflammatory response, with the innate immune system contributing both to protection against invasive organisms and to triggering the invasion of inflammatory cells into the wounded area. These cells release a variety of cytokines and growth factors that stimulate the proliferation and migration of dermal and epidermal cells to close the wound. In particular, wounding activates stem cells in the interfollicular epidermis (IFE) and hair follicles (HF) to proliferate and send their progeny to re-epithelialize the wound. β-catenin and calcium signaling are important for this activation process. Mice lacking the VDR when placed on a low calcium diet have delayed wound healing. This is associated with reduced β-catenin transcriptional activity and proliferation in the cells at the leading edge of wound closure. These data suggest that vitamin D and calcium signaling are necessary components of the epidermal response to wounding, likely by regulating stem cell activation through increased β-catenin transcriptional activity.

Link to Article

http://dx.doi.org/10.1016/j.jsbmb.2015.08.011

In vivo effects of two novel ALN-EP4a conjugate drugs on bone in the ovariectomized rat model for reversing postmenopausal bone loss

Authors

S. Hu, C. C. Liu, G. Chen, T. Willett, R. N. Young, M. D. Grynpas

Abstract

Two alendronate-EP4 agonist (ALN-EP4a) conjugate drugs, C1 and C2, which differ in structure by a short linker molecule, were evaluated in ovariectomized (OVX) rats for their anabolic effects. We showed that C1 led to significant anabolic effects on cortical and trabecular bone while anabolic effects associated with C2 were minimal.

EP4as were covalently linked to ALN to create ALN-EP4a conjugate anabolic bone drugs, C1 and C2, which differ in structure by a short linker molecule in C1. When administered systemically, C1 and C2 are delivered to bone through targeted binding of ALN, where local hydrolytic enzymes liberate EP4a from ALN to exert anabolic effects. Here, we compare effects of C1 to C2 in a curative in vivo study.

Three-month-old female Sprague Dawley rats were OVX or sham operated and allowed to lose bone for 3 months. Animals were then treated via tail vein injections for 3 months and sacrificed. Treatment groups were as follows: C1L (5 mg/kg biweekly), C1H (5 mg/kg weekly), C2L (15 mg/kg monthly), C2H (15 mg/kg biweekly), OVX and sham control (phosphate-buffered saline (PBS) biweekly), and ALN/EP4a-unconjugated mixture (0.75 mg/kg each biweekly).

MicroCT analysis showed that C1H treatment significantly increased vertebral bone mineral density (vBMD) and trabecular bone volume versus OVX controls while C2 treatments did not. Biomechanical testing showed that C1H treatment but not C2 treatments led to significant improvement in the load bearing abilities of the vertebrae compared to OVX controls. C1 stimulated endocortical bone formation and increased load bearing in femurs, while C2 did not.

We showed that C1 led to significant anabolic effects on cortical and trabecular bone while anabolic effects associated with C2 were minimal. These results led us to hypothesize a mode of action by which presence of a linker is crucial in facilitating the anabolic effects of EP4a when dosed as a prodrug with ALN.

Link to Article

http://dx.doi.org/10.1007/s00198-015-3284-x

IGF-1 Regulates Vertebral Bone Aging Through Sex-Specific and Time-Dependent Mechanisms

Authors

Nicole M Ashpole PhD, Jacquelyn C Herron MS, Matthew C Mitschelen, Julie A Farley, Sreemathi Logan PhD, Han Yan PhD, Zoltan Ungvari MD/PhD, Erik L. Hodges, Anna Csiszar MD/PhD, Yuji Ikeno MD/PhD, Mary Beth Humphrey PhD and William E Sonntag PhD

Abstract

Advanced aging is associated with increased risk of bone fracture, especially within the vertebrae, which exhibit significant reductions in trabecular bone structure. Aging is also associated with a reduction in circulating levels of insulin-like growth factor (IGF-1). Studies have suggested that the reduction in IGF-1 compromises healthspan, while others report that loss of IGF-1 is beneficial as it increases healthspan and lifespan. To date, the effect of decreases in circulating IGF-1 on vertebral bone aging has not been thoroughly investigated. Here, we delineate the consequences of a loss of circulating IGF-1 on vertebral bone aging in male and female Igff/f mice. IGF-1 was reduced at multiple specific time points during the mouse lifespan- early in postnatal development (crossing albumin-Cre mice with Igff/f mice), or early adulthood, and late adulthood using hepatic-specific viral vectors (AAV8-TBG-Cre). Vertebrae bone structure was analyzed at 27 months of age using microCT and quantitative bone histomorphometry. Consistent with previous studies, both male and female mice exhibited age-related reductions in vertebral bone structure. In male mice, reduction of circulating IGF-1 induced at any age did not diminish vertebral bone loss. Interestingly, early-life loss of IGF-1 in females resulted in a 67% increase in vertebral bone volume fraction, as well as increased connectivity density and increased trabecular number. The maintenance of bone structure in the early-life IGF-1-deficient females was associated with increased osteoblast surface and an increased ratio of osteoprotegerin/receptor-activator of NFkB-ligand levels in circulation. Within 3 months of a loss of IGF-1, there was a 2.2 fold increase in insulin receptor expression within the vertebral bones of our female mice, suggesting that local signaling may compensate for the loss of circulating IGF-1. Together, these data suggest the age-related loss of vertebral bone density in females can be reduced by modifying circulating IGF-1 levels early in life.

Link to Article

http://dx.doi.org/10.1002/jbmr.2689

A Histomorphometric Analysis of Radiation Damage in an Isogenic Murine Model of Distraction Osteogenesis

Authors

Alexander R. Zheutlin, BS, Sagar S. Deshpande, BS, Noah S. Nelson, BS, Yekaterina Polyatskaya, MD, Jose J. Rodriguez, MD, Alexis Donneys, MD, MS, Steven R. Buchman, MD

Abstract

Purpose The devastation radiation therapy (XRT) causes to endogenous tissue in head and neck cancer (HNC) patients can be a prohibitive obstacle in reconstruction of the mandible, demanding a better understanding of XRT-induced damage and options for reconstruction. Our study investigates the cellular damage caused by radiation in an isogenic murine model of mandibular distraction osteogenesis (DO). We posit that radiation will result in reduced osteocytes, with elevated empty lacunae and immature osteoid.

Methods Twenty Lewis rats were randomly assigned to two groups: DO (n=10) and XRT/DO (n=10). Both groups underwent an osteotomy and mandibular DO across a 5.1 mm gap. XRT was administered to the XRT/DO group at a fractionated, human equivalent dose of 35 Gy prior to surgery. Animals were sacrificed on postoperative day 40 and mandibles were harvested and sectioned for histological analysis.

Results Bone that underwent radiation revealed a significantly decreased osteocyte count and complementary increase in empty lacunae when compared to non-XRT bone (p=0.019, p=0.000). Additionally, XRT bone demonstrated increased immature osteoid and decreased mature woven bone when compared to non-radiated bone (p=0.001 and p=0.003, respectively). Furthermore, analysis of the ratio of immature osteoid to woven bone volume exhibited a significant increase in the XRT bone, further revealing the devastating damage brought by XRT (p=0.001).

Conclusion These results clearly demonstrate the cellular diminution that occurs as a result of radiation. This foundational study provides the groundwork upon which to investigate cellular therapies in an immunoprivileged model of mandibular DO.

Link To Article

http://dx.doi.org/10.1016/j.joms.2015.08.002