Endogenous tissue engineering: PTH therapy for skeletal repair

Based on its proven anabolic effects on bone in osteoporosis patients, recombinant parathyroid hormone (PTH_1-34) has been evaluated as a potential therapy for skeletal repair. In animals, the effect of PTH_1-34 has been investigated in various skeletal repair models such as fractures, allografting, spinal arthrodesis and distraction osteogenesis. These studies have demonstrated that intermittent PTH_1-34 treatment enhances and accelerates the skeletal repair process via a number of mechanisms, which include effects on mesenchymal stem cells, angiogenesis, chondrogenesis, bone formation and resorption. Furthermore, PTH_1-34 has been shown to enhance bone repair in challenged animal models of aging, inflammatory arthritis and glucocorticoid-induced bone loss. This pre-clinical success has led to off-label clinical use and a number of case reports documenting PTH_1-34 treatment of delayed-unions and non-unions have been published. Although a recently completed phase 2 clinical trial of PTH_1-34 treatment of patients with radius fracture has failed to achieve its primary outcome, largely because of effective healing in the placebo group, several secondary outcomes are statistically significant, highlighting important issues concerning the appropriate patient population for PTH_1-34 therapy in skeletal repair. Here, we review our current knowledge of the effects of PTH_1-34 therapy for bone healing, enumerate several critical unresolved issues (e.g., appropriate dosing regimen and indications) and discuss the long-term potential of this drug as an adjuvant for endogenous tissue engineering.     

Sequence heterogeneity and anomalous electrophoretic mobility of kinetoplast minicircle DNA from Leishmania tarentolae

Several unit-length minicircles from the kinetoplast DNA of Leishmania tarentolae were cloned into pBR322 and into M13 phage vectors. The complete nucleotide sequences of three different partially homologous minicircles were obtained. The molecules contained a region of approx. 80% sequence homology extending for 160–270 bp and a region unique to each minicircle. A 14-mer was found to be conserved in all kinetoplast minicircle sequences reported to date. The frequency distributions of various minicircle sequence classes in L. tarentolae were obtained by quantitative gel electrophoresis and by examination of the “T ladder” patterns of minicircles randomly cloned into M13 at several sites. By these methods we could assign approx. 50% of the total minicircle DNA into a minimum of five sequence classes. A sequence-dependent polyacrylamide gel migration abnormality was observed with several minicircle fragments both cloned and uncloned. The abnormality was dependent on the presence of a portion of the conserved region of the minicircle.     

Serum opsonic activity in rodent malaria: functional and immunochemical characteristics in vitro.

The functional and immunochemical characteristics of serum opsonic activity in rodent malaria were examined in the present study. Schizont- and late trophozoite-enriched populations of Plasmodium berghei-infected red blood cells (IRBC) were isolated on a Ficoll density-gradient and used in an in vitro phagocytosis system composed of serum and monolayer cultures of rat peritoneal macrophages. Hyperimmune serum augmented the phagocytosis of IRBC to a greater degree than did nonimmune serum. When either IRBC or macrophages were pre-incubated with serum, the phagocytosis-promoting factors acted on the IRBC rather than on the macrophages in a manner characteristic of serum opsonins. The opsonic activity was specific for IRBC since noninfected red blood cells were rarely phagocytized and were unable to absorb opsonic activity from serum. The opsonic activity of both hyperimmune and nonimmune sera was heat stable, and unaffected by agents known to inactivate or inhibit complement (cobra venom factor and ethylenediaminetetraacetic acid). Finally, the opsonic activity was identified in preparations of purified IgG isolated from both hyperimmune and nonimmune sera.