Local release of masitinib alters in vivo implantable continuous glucose sensor performance

Continuous glucose monitoring (CGM) sensors are often advocated as a clinical solution to improve long-term glycemic control in the context of diabetes. Subcutaneous sensor inflammatory response, fouling and fibrous encapsulation resulting from the host foreign body response (FBR) reduce sensor sensitivity to glucose, eventually resulting in sensor performance compromise and device failure. Several combination device strategies load CGM sensors with drug payloads that release locally to tissue sites to mitigate FBR-mediated sensor failure. In this study, the mast cell-targeting tyrosine kinase inhibitor, masitinib, was released from degradable polymer microspheres delivered from the surfaces of FDA-approved human commercial CGM needle-type implanted sensors in a rodent subcutaneous test bed. By targeting the mast cell c-Kit receptor and inhibiting mast cell activation and degranulation, local masitinib penetration around the CGM to several hundred microns sought to reduce sensor fibrosis to extend CGM functional lifetimes in subcutaneous sites. Drug-releasing and control CGM implants were compared in murine percutaneous implant sites for 21 days using direct-wire continuous glucose reporting. Drug-releasing implants exhibited no significant difference in CGM fibrosis at implant sites but showed relatively stable continuous sensor responses over the study period compared to blank microsphere control CGM implants.

Foreign body response to subcutaneous biomaterial implants in a mast cell-deficient Kit(w-Sh) murine model

Mast cells (MCs)_are recognized for their functional role in wound-healing and allergic and inflammatory responses - host responses that are frequently detrimental to implanted biomaterials if extended beyond acute reactivity. These tissue reactions impact especially on the performance of sensing implants such as continuous glucose monitoring (CGM) devices. Our hypothesis that effective blockade of MC activity around implants could alter the host foreign body response (FBR) and enhance the in vivo lifetime of these implantable devices motivated this study. Stem cell factor and its ligand c-KIT receptor are critically important for MC survival, differentiation and degranulation. Therefore, an MC-deficient sash mouse model was used to assess MC relationships to the in vivo performance of CGM implants. Additionally, local delivery of a tyrosine kinase inhibitor (TKI) that inhibits c-KIT activity was also used to evaluate the role of MCs in modulating the FBR. Model sensor implants comprising polyester fibers coated with a rapidly dissolving polymer coating containing drug-releasing degradable microspheres were implanted subcutaneously in sash mice for various time points, and the FBR was evaluated for chronic inflammation and fibrous capsule formation around the implants. No significant differences were observed in the foreign body capsule formation between control and drug-releasing implant groups in MC-deficient mice. However, fibrous encapsulation was significantly greater around the drug-releasing implants in sash mice compared to drug-releasing implants in wild-type (e.g. MC-competent) mice. These results provide insights into the role of MCs in the FBR, suggesting that MC deficiency provides alternative pathways for host inflammatory responses to implanted biomaterials.

Poly(amido amine) dendrimers as absorption enhancers for oral delivery of camptothecin

Oral delivery of camptothecin has a treatment advantage but is limited by low bioavailability and gastrointestinal toxicity. Poly(amido amine) or PAMAM dendrimers have shown promise as intestinal penetration enhancers, drug solubilizers and drug carriers for oral delivery in vitro and in situ. There have been very limited studies in vivo to evaluate PAMAM dendrimers for oral drug delivery. In this study, camptothecin (5 mg/kg) was formulated and co-delivered with cationic, amine-terminated PAMAM dendrimer generation 4.0 (G4.0) (100 and 300 mg/kg) and anionic, carboxylate-terminated PAMAM generation 3.5 (G3.5) (300 and 1000 mg/kg) in CD-1 mice. Camptothecin associated to a higher extent with G4.0 than G3.5 in the formulation, attributed to an electrostatic interaction on the surface of G4.0. Both PAMAM G4.0 and G3.5 increased camptothecin solubilization in simulated gastric fluid and caused a 2-3 fold increase in oral absorption of camptothecin when delivered at 2 h. PAMAM G4.0 and G3.5 did not increase mannitol transport suggesting that the oral absorption of camptothecin was not due to tight junction modulation. Histologic observations of the epithelial layer of small intestinal segments of the gastrointestinal tract (GIT) at 4 h post dosing supported no evidence of toxicity at the evaluated doses of PAMAM dendrimers. This study demonstrates that both cationic (G.4) and anionic (G3.5) PAMAM dendrimers were effective in enhancing the oral absorption of camptothecin. Results suggest that drug inclusion in PAMAM interior controlled solubilization in simulated gastric and intestinal fluids, and increased oral bioavailability.

Thermal injury by in vitro incision of equine skin with electrosurgery, radiosurgery, and a carbon dioxide laser

Freshly harvested equine skin incised with an electrosurgical unit, a radiosurgical device, or a carbon dioxide (CO2) laser was examined by light microscopy to determine the extent of thermal injury caused by each instrument. There was no significant difference between the thermal injury caused by the electrosurgical unit in the pure-cut mode and the CO2 laser in the superpulse mode, or between the electrosurgical unit and the radiosurgical device in the fully filtered cut mode. However, thermal injury caused by the CO2 laser was significantly less than that caused by the radiosurgical device. The amount of thermal injury in this in vitro study was similar to that found in vivo with other species.

Organ-selective switching of 3-methylindole toxicity by glutathione depletion

A high dose (550 mg/kg) of 3-methylindole (3MI) specifically damaged pulmonary tissue in Swiss-Webster mice without causing any hepatic or renal necrosis. When a glutathione depleter, L-buthionine-(S,R)-sulfoximine (BSO, 1.0 mmol/kg), was administered to mice 3 hr before a low dose of 3-methylindole (75 mg/kg), significant renal damage was observed by histopathological examination after 4 hr. The nephrotoxicity occurred without any observable pathological damage to lung tissues. Increased doses of BSO caused dose-dependent increases in renal toxicity. A low dose of BSO (1.0 mmol/kg) caused no depletion of renal glutathione levels, a large depletion of hepatic glutathione levels (60% of control values), and much larger increases in covalent binding of [methyl-14C]3-methylindole to renal tissues (3.4-fold) than to hepatic tissues (1.5-fold) or pulmonary tissues (2.1-fold). No evidence of hepatic or pulmonary histopathological damage was observed at any dose of BSO with 75 mg/kg 3MI. These results indicate that a shift in organ selectivity of 3MI-induced toxicity from pulmonary to renal sites occurs as a result of glutathione depletion in hepatic tissues. The production of a toxic metabolite in the livers of glutathione-depleted mice that is circulated to susceptible renal cells may be the mechanism of this interesting organ-selective shift in toxicity of 3MI.

Comparison of results using electron microscope, immunodiffusion and fluorescent antibody analyses to detect rotavirus in diarrheic fecal samples of calves

Seventy-nine diarrheic calf fecal samples were examined by electron microscopy, immunodiffusion and the fluorescent antibody technique for the presence of rotavirus (reovirus-like agent). Thirty-eight (48%) of the samples were positive by electron microscopy, 59% by immunodiffusion and 20% positive by fluorescent antibody technique analyses. Another 9% were suspect-positive by fluorescent antibody technique. Chymotrypsin treatment of the fecal samples increased the ease of observing the viral particles by electron microscopy and also intensified the immunodiffusion arcs obtained. Immunodiffusion analyses using specific antisera to the virus would appear to be a practical method of detecting rotavirus in diarrheic fecal samples.