Parathyroid hormone-related protein analog RS-66271 is an effective therapy for impaired bone healing in rabbits on corticosteroid therapy.

A new class of parathyroid hormone-related protein (PTHrP) analogs has been developed that causes a rapid gain in both trabecular and cortical bone in models of osteopenia. This study investigates the efficacy of the PTHrP analog, RS-66271 ([MAP(1-10)]22-31 hPTHrP(1-34)-NH(2)), as systemic therapy for impaired bone healing in corticosteroid-treated rabbits. A 1 mm defect was created bilaterally in the ulnae of 30 rabbits. Delayed healing was induced by daily injections of prednisone (0.15 mg/kg) beginning 2 months prior to surgery and continuing until killing. Rabbits in the experimental group received daily subcutaneous injections of PTHrP analog RS-66271 (0.01 mg/kg) starting 1 day after surgery. Control animals received subcutaneous normal saline. At the 6 week timepoint, nine of ten ulnae from PTHrP-treated rabbits achieved radiographic union, whereas only two of ten limbs achieved union in control rabbits (p < 0.01). In a separate part of the study, 20 animals (10 control, 10 RS-66271-treated) were killed when radiographic union was achieved bilaterally. In this portion of the study, all limbs in animals treated with PTHrP achieved union by 6 weeks. In the control animals that were allowed to heal for 10 weeks, only 20% of the limbs achieved radiographic union. In addition, ulnae in the PTHrP-analog-treated rabbits showed greater radiographic intensity (20%-40%), larger callus area (209% anteroposterior view, 417% lateral view) (mean area on AP radiographs: control, = 387 +/- 276 mm(2); PTHrP analog, 1195 +/- 408 mm(2)), and greater stiffness (64%) and torque (87%) when compared with controls. RS-66271 was shown to be an effective therapy for preventing impaired bone healing caused by prednisone in a rabbit model.

Uveitis induction in the rabbit by muramyl dipeptides.

Intraocular inflammation (uveitis) was produced in rabbits by intravenous or subcutaneous treatment with N-acetylmuramyl-L-alanyl-D-isoglutamine and several of its synthetic analogs at doses of greater than or equal to 0.2 mg/kg in saline. A dose-dependent increase in permeability of the ocular blood-aqueous barrier as measured by leakage of protein or fluoresceinated dextran from the serum into the eye was observed from 2 to 14 h after glycopeptide treatment. Peak response occurred at approximately 3 h postdose. The lowest dose found to produce maximal vascular leakage for the most active glycopeptide analogs was 1 mg/kg. The adjuvant-inactive L-L stereoisomer of N-acetylmuramyl-L-alanyl-D-isoglutamine was inactive, even at doses as high as 10 mg/kg. Analogs of N-acetylmuramyl-L-alanyl-D-isoglutamine which were homologous in the lactyl side chain were found to cause less uveitis. Chronic biweekly intravenous treatment of rabbits for 1 month with either N-acetyl-L-alpha-aminobutyryl-D-isoglutamine or its lipophilic 6-O-stearoyl derivative at 1 mg/kg, but not with murabutide, resulted in leukocytic inflammatory lesions unique to the uveal tract of the eye. The uveitis was potentially reversible and occurred with decreased severity as long as 2 months after cessation of chronic treatment. Vascular leakage but not cellular infiltrate in the choroid could be modulated by pharmacologic means. Pyrogenicity but not adjuvanticity correlated with ability of glycopeptides to induce vascular leakage. Several adjuvant-active muramyl dipeptide analogs with minimal ability to cause acute vascular leakage or chronic inflammation in the rabbit eye have been identified.

Correlation between in vivo anti-Pseudomonas and anti-Candida activities and clearance of carbon by the reticuloendothelial system for various muramyl dipeptide analogs, using normal and immunosuppressed mice.

A linear correlation coefficient analysis, comparing in vivo anti-infective and reticuloendothelial stimulating activity of several different analogs of N-acetylmuramyl-L-alanyl-D-isoglutamine (muramyl dipeptide) suggests that the macrophage is an important target cell for these immunomodulating compounds. The increase in protection against infections of Candida albicans or Pseudomonas aeruginosa in normal or immunosuppressed mice after treatment with 18 different glycopeptides was found to correlate with the degree of clearance of colloidal carbon particles from the blood by the reticuloendothelial system after treatment with the same muramyl dipeptide analogs. The compound which gave the greatest protection in all four assays was N-acetylmuramyl-L-alpha-aminobutyryl-D-isoglutamine followed by N-acetyl-nor-muramyl-L-alanyl-D-isoglutamine. Both analogs were better than the parent muramyl dipeptide. Whether macrophage stimulation alone is responsible for the anti-infective properties of these compounds has not yet been determined.

Vascular clearance of embolic tumor cells and colloidal carbon and the levels of serum lysozyme following muramyl dipeptide administration.

Various doses of coded samples of the parent muramyl dipeptide entity and eight synthetic analogues were injected intravenously into C57BL/6J mice, and the extent of clearance of intravenously injected 5-[125I]iodo-2-deoxyuridine (125I-dUrd) radioactively labeled B16 tumor cells from the lung was measured 3 days later. The results of between one and four experiments with each compound demonstrated that five compounds, including the parent compound, produced dose-dependent increases in the loss of tumor cells from the lung. The same five compounds also caused an increase in the clearance of intravascular carbon clearance. Monitoring of serum lysozyme levels revealed no significant increases compared to controls at doses of up to 1 mg/mouse following muramyl dipeptide (MDP) administration i.v., i.p. or s.c. at any time up to 30 days after administration. Increased pulmonary tumor cell clearance did not occur after s.c. MDP administration and peaked 3 days after i.p. or i.v. MDP, reaching near normal levels by Day 7.

Systemic corticosteroids inhibit bone healing in a rabbit ulnar osteotomy model.

Prolonged systemic administration of corticosteroids causes osteoporosis and increased risk of fracture. Despite this well documented side effect of systemic corticosteroids, the effect of these compounds on fracture healing is not well defined. The goal of this study was to test the hypothesis that systemic corticosteroid therapy adversely affects fracture healing in a rabbit ulnar osteotomy model. Non-critical sized (1 mm) defects were created bilaterally in 18 adult female New Zealand White rabbits. Starting 2 months before operative intervention and continuing for 6 weeks during healing of the osteotomies, a subcutaneous dose of either sterile saline or prednisone (0.15 mg/kg) was administered daily. Serial radiographs of the forelimb were taken immediately postoperatively and weekly beginning the second week postoperatively. After killing at 6 weeks, only 3 of 20 limbs from animals treated with prednisone achieved radiographic union while 13 of 16 control limbs achieved union. The radiographic density of bone in the defect as well as callus size were greater in the control limbs than in the limbs from prednisone-treated animals. DEXA confirmed that the bone mineral content was lower in the ulnae of prednisone-treated rabbits both within the defect and in adjacent ulnar bone. Mechanical data indicated that osteotomies from rabbits chronically treated with prednisone were weaker than in controls. In this rabbit ulnar osteotomy model, chronic prednisone treatment clearly inhibited bone healing.