Parathyroid-produced angiopoietin-2 modulates angiogenic response

The Evaluation of Neovessel Angiogenesis Behavior at Tissue Interfaces

Angiogenesis, the formation of new vessel elements from existing vessels, is important in homeostasis and tissue repair. Dysfunctional angiogenesis can contribute to numerous pathologies, including cancer, ischemia, and chronic wounds. In many instances, growing vessels must navigate along or across tissue-associated boundaries and interfaces tissue interfaces. To understand this dynamic, we developed a new model for studying angiogenesis at tissue interfaces utilizing intact microvessel fragments isolated from adipose tissue. Isolated microvessels retain their native structural and cellular complexity. When embedded in a 3D matrix, microvessels, sprout, grow, and connect to form a neovasculature. Here, we discuss and describe methodology for one application of our microvessel-based angiogenesis model, studying neovessel behavior at tissue interfaces.

Parathyroid Hormone Derivative with Reduced Osteoclastic Activity Promoted Bone Regeneration via Synergistic Bone Remodeling and Angiogenesis

Osteogenesis, osteoclastogenesis, and angiogenesis are the most important processes in bone repair. Parathyroid hormone (PTH) has pro-osteogenic, pro-osteoclastogenic, and proangiogenic effects and may be a candidate for use in bone defect repair. However, the local application of PTH to bone defects is counterproductive due to its excessive osteoclastic and bone resorptive effects. In this study, a PTH derivative, PTHrP-2, is developed that can be applied to local bone defects. First, a modified peptide with a calcium-binding repeat glutamine tail undergoes controlled local release from a ceramic material and is shown to be a better fit for the repair process than the unmodified peptide. Second, the modified peptide is shown to have strong pro-osteogenic activity due to mineralization and its facilitation of serine (Ser) phosphorylation. Third, the modified peptide is shown to maintain the pro-osteoclastogenic and proangiogenic properties of the unmodified peptide, but its pro-osteoclastogenic activity is reduced compared to that of the unmodified peptide. The reduced pro-osteoclastogenic and increased pro-osteogenic properties of the modified peptide reverse the imbalance between osteoblasts and osteoclasts with local PTH application and shift bone resorption to bone regeneration.

Angiogenesis inhibitor attenuates parathyroid hormone-induced anabolic effect

In vivo osteogenic responses to anabolic stimuli are expected to be accompanied by angiogenesis as well as in the process of remodeling of bone. Consequently, angiogenesis might play an important role in mediating bone forming stimulating effect of parathyroid hormone (PTH). To investigate this relationship, we used actively growing young Sprague-Dawley rats and CKD-732, one of the angiogenesis inhibitor (AI) to reveal the relationship of angiogenesis in the effect of PTH. The groups were divided as (1) vehicle [VEH group], (2) PTH(1-84) [PTH group], (3) AI alone [AI group], (4) PTH(1-84)+AI concomitance [PTH-AI group] and were treated for 6 weeks. The bone mineral density (BMD) of PTH group was higher than VEH group and the gain of bone mass was attenuated in PTH-AI group. The maximal failure load in PTH group was higher than VEH group, but it was definitely attenuated by concurrent use of AI. Moreover, the toughness showed similar significant deterioration in PTH-AI group. General bone turnover was also significantly decreased in PTH-AI group as shown by the absence of increase in osteocalcin and beta-crosslaps and by decrease in metaphyseal length. The BMD or the biomechanic data of AI only group were similar to the VEH group, suggesting the minimal effect of AI itself on the normal modeling phase of the growing rats. In conclusion, the angiogenesis seemed to contribute to completing the anabolic effect of PTH especially for bone strength.

A new animal model to assess angiogenesis and endocrine function of parathyroid heterografts in vivo

BACKGROUND

It is still a matter of investigation how angiogenesis and restoration of gland perfusion determine graft function after free parathyroid autotransplantation. We provide a new animal model allowing simultaneous and repetitive in vivo assessment of angiogenesis and endocrine function of parathyroid transplants.

METHODS

Fresh human parathyroid tissue from patients with secondary hyperparathyroidism was grafted into dorsal skinfold chamber preparations of athymic nude mice (CD1-nu; n=8). Equivalent pieces of the same human donor specimens were heat-inactivated and served as control grafts (n=7).

RESULTS

In all animals receiving parathyroid transplants, intact human parathyroid hormone levels were detectable by species-specific enzyme-linked immunosorbent assay analysis of plasma samples on day 5 after transplantation and increased by 2.5-fold over the observation period (19 days) in contrast with controls. Plasma Ca levels revealed no differences between the groups. On day 5 after transplantation, intravital fluorescence microscopy revealed murine angiogenic microvessels sprouting along nonperfused human donor vessels, and 1 week later functional microvasculature was established in all parathyroid transplants. Histologic analysis revealed well-vascularized endocrine tissue. In contrast, control grafts were necrotic and partly resorbed; they exhibited no angiogenic activity or well-vascularized fat cells indicating fatty degeneration. In addition, species-specific Western blot analysis revealed vascular endothelial growth factor expression of parathyroid transplants rather than functional vessel density as the functional parameter of angiogenesis determining transplant function in vivo.

CONCLUSION

This model may serve to understand mechanisms associated with specific parathyroid transplant angiogenesis and its significance for transplant function to optimize clinical success of autotransplantation in therapy-resistant patients.