Calvarial bone repair with porous D,L-polylactide.

Bone is a storehouse of biologic factors enabling it to regenerate without scar formation. Recombinant technology has made many of these factors available in significant quantity for therapeutic applications. However, a system to deliver recombinant bone-regenerating factors is needed. Biodegradable, biocompatible polymers have shown promise for delivering bone regenerative factors, such as bone morphogenetic protein. The polymer we selected to investigate was racemic D,L-polylactide. Our immediate objective was to engineer porous D,L-polylactide to promote bone ingrowth (osteoconduction). We tested the hypothesis that porous D,L-polylactide implanted in a standard intraosseous calvarial wound would not hinder but would support bone regeneration. Therefore porous polylactide disks (65% void volume) were manufactured with pores < or = 100 microns, < or = 200 microns, and < or = 350 microns; implanted in rabbits' calvariae, and retrieved 1, 2, 4, and 6 months after insertion. Quantitative histomorphometry revealed a possible relationship in the amount of bone ingrowth with increasing pore size over time. The D,L-polylactide disks < or = 350 microns had the greatest quantity of bone ingrowth (< or = 0.05). However, a disturbing finding was the multinucleated giant cell response associated with all implanted disks. We speculate these cells may have produced an inhospitable environment stifling osteoconduction. Consequently, postsynthesis engineering refinements of D,L-polylactide to eliminate the giant cell response are crucial before loading with bone morphogenetic protein.

Rheumatoid arthritis and positional vertebrobasilar insufficiency. Case report.

The authors report a case of positional occlusions of the vertebral arteries in a 45-year-old patient with juvenile rheumatoid arthritis. The occlusions were documented angiographically by placing the head in various positions during digital subtraction angiography using aortic arch injections.

Kinetics of cholesterol and phospholipid exchange from membranes containing cross-linked proteins or cross-linked phosphatidylethanolamines.

Mono- and dipalmitoylphosphatidylethanolamine derivatives have been synthesized and used to evaluate the role of cross-links between the amino groups of two phospholipid molecules in the rate of cholesterol movement between membranes. Incorporation of the cross-linked phospholipids into small unilamellar vesicles (the donor species) decreased the rate of spontaneous cholesterol exchange with acceptor membranes (small unilamellar vesicles or Mycoplasma gallisepticum cells). These results suggest that the cross-linking of aminophospholipids by reactive intermediates, which may be one of the degenerative transformations associated with peroxidation of unsaturated lipids and cellular aging, can inhibit cholesterol exchangeability in biological membranes. The rates of spontaneous [14C]cholesterol and protein-mediated 14C-labeled phospholipid exchange from diamide-treated mycoplasma and erythrocyte membranes have also been measured. The formation of extensive disulfide bonds in the membrane proteins of M. gallisepticum enhanced the 14C-labeled phospholipid exchange rate but did not affect the rate of [14C]cholesterol exchange. The rates of radiolabeled cholesterol and phospholipid exchange between erythrocyte ghosts and vesicles were both enhanced (but to different extents) when ghosts were treated with diamide. These observations suggest that diamide-induced oxidative cross-linking of sulfhydryl groups in membrane proteins does not lead to random defects in the lipid domain.