Jeff McKee

Gel scaffolds of BMP-2-binding peptide amphiphile nanofibers for spinal arthrodesis.

Peptide amphiphile (PA) nanofibers formed by self-assembly can be customized for specific applications in regenerative medicine through the use of molecules that display bioactive signals on their surfaces. Here, the use of PA nanofibers with binding affinity for the bone promoting growth factor BMP-2 to create a gel scaffold for osteogenesis is reported. With the objective of reducing the amount of BMP-2 used clinically for successful arthrodesis in the spine, amounts of growth factor incorporated in the scaffolds that are 10 to 100 times lower than that those used clinically in collagen scaffolds are used. The efficacy of the bioactive PA system to promote BMP-2-induced osteogenesis in vivo is investigated in a rat posterolateral lumbar intertransverse spinal fusion model. PA nanofiber gels displaying BMP-2-binding segments exhibit superior spinal fusion rates relative to controls, effectively decreasing the required therapeutic dose of BMP-2 by 10-fold. Interestingly, a 42% fusion rate is observed for gels containing the bioactive nanofibers without the use of exogenous BMP-2, suggesting the ability of the nanofiber to recruit endogenous growth factor. Results obtained here demonstrate that bioactive biomaterials with capacity to bind specific growth factors by design are great targets for regenerative medicine.

Identification of a simple and sensitive microplate method for the detection of oversulfated chondroitin sulfate in heparin products

Heparin is a commonly implemented anticoagulant used to treat critically ill patients. Recently, a number of commercial lots of heparin products were found to be contaminated with an oversulfated chondroitin sulfate (OSCS) derivative that could elicit a hypotensive response in pigs following a single high-dose infusion. Using both contaminated heparin products and the synthetically produced derivative, we showed that the OSCS produces dose-dependent hypotension in pigs. The no observed effect level (NOEL) for this contaminant appears to be approximately 1mg/kg, corresponding to a contamination level of approximately 3%. We also demonstrated that OSCS can be identified in heparin products using a simple, inexpensive, commercially available heparin enzyme immunoassay (EIA) kit that has a limit of detection of approximately 0.1%, well below the NOEL. This kit may provide a useful method to test heparin products for contamination with oversulfated GAG derivatives.

Structure Elucidation and Biological Activity of the Oversulfated Chondroitin Sulfate Contaminant in Baxter Heparin

From late December 2007 to February 2008, the number of adverse responses to heparin infusions rose noticeably above baseline levels in North America, ultimately resulting in a widespread recall of all heparin vial products made by Baxter Healthcare. Using various analytical techniques and the de novo synthesis of a fully sulfated chondroitin sulfate (FSCS) derivative, the authors have confirmed the identity of the contaminant as an oversulfated chondroitin sulfate (OSCS) and have also defined the heterogeneity and concentration of this contaminant in various lots of heparin. Using both contaminated heparin products and the synthetically produced derivative, the authors have shown that the OSCS produces a dose‐dependent hypotension in both pigs and rats and that the response in rats can be abrogated with bradyzide, a rodent‐selective B2 bradykinin receptor antagonist. The no observed effect level (NOEL) for this contaminant appears to be approximately 1 mg/kg, corresponding to a contamination level in finished lots of heparin of approximately 3%. Using human plasma, the OSCS derivative was shown to activate kallikrein. These data provide insight into the etiology of the adverse events, particularly refractory hypotension, observed in patients who were exposed to heparin contaminated with OSCS.

Acetaminophen-Induced Forestomach Lesion in Normal Rats Following Intravenous Exposure

Four groups of ten male and ten female rats each were treated intravenously with saline, 400 mg/kg/day of a commercially available injectable acetaminophen formulation, or 400 mg/kg/day of a new injectable acetaminophen formulation with (aged) or without (fresh) impurities daily for fourteen days. Gross observations of the mucosal surface of the stomachs from treated rats included multifocal to diffuse pale, elevated foci confined to the nonglandular region of the stomach. Treatment-related histologic observations consisted of epithelial hyperplasia and hyperkeratosis of the nonglandular mucosa of the stomach. The epithelial hyperplasia was characterized by a thickened epithelium, frequently accompanied by the development of undulations at the basement membrane zone, resulting in the formation of rete ridgelike structures protruding into the underlying tissue. The submucosa was usually expanded by edema and occasionally contained an infiltrate of neutrophils, eosinophils, and macrophages. The hyperplasia was usually accompanied by hyperkeratosis resulting in thickening of the stratum corneum. The incidence and severity of the gastric changes were similar across all treatment regimens. Although considered clinically irrelevant since humans do not have a forestomach equivalent, these results are significant in that this appears to be the first report of forestomach hyperplasia and hyperkeratosis following intravenous exposure to acetaminophen.

Sodium nitrite therapy fails to improve tissue perfusion in a mouse model of hind limb ischemia: Slight differences in methodology may be responsible casting suspicion on the reliability and predictive value of this model

Background: The nude mouse model of hind limb ischemia is used to evaluate human-derived, cell-based therapeutics intended to promote tissue perfusion. The criticism of the mouse model of hind limb ischemia is the absence of a well-characterized positive control. The suitability of sodium nitrite (NaNO 2 ) was evaluated. The rationale for doing so was based on a report that NaNO 2 induced unprecedented tissue perfusion in wild-type mice using a similar model. The objective was to evaluate NaNO 2 to improve tissue perfusion in nude mice as well as their wild-type counterparts. Materials and Methods: The mice underwent surgically induced, unilateral hind limb ischemia, and received either NaNO 2 or a vehicle intraperitoneally, twice daily, for seven days. Hind limb tissue perfusion was evaluated on days one, four, seven, and fourteen post-surgery. Results: No increase in tissue perfusion was observed in the nude or wild-type mice treated with NaNO 2 when compared with the vehicle. Nude mice exhibited significantly lower tissue perfusion compared to wild-type mice, irrespective of the treatment. Conclusions: NaNO 2 failed to increase tissue perfusion and, therefore, did not appear suitable for use as a positive control in this model. This is in stark contrast to a previous report indicating that NaNO 2 significantly increased tissue perfusion in wild-type mice using a similar model. The exact cause is not known, but is probably due to differences in methodology employed between laboratories. The lower tissue perfusion in nude mice is a novel finding, suggesting this strain may have less pre-existing collateral vessels and/or a reduced capacity to form new vessels as compared to wild-type mice.