[Tissue engineering of parathyroid gland]

The postoperative hypoparathyroidism is a not rare complication after total thyroidectomy and/or total parathyroidectomy. Attempts to transplant parathyroid tissue began in 1975 with the work of Wells, but still today results are disappointing. However, with the development of tissue engineering techniques, some experimental approaches to build artificial parathyroid are been made. Bioengineered device, actively secreting PTH, for transplant in patients with iatrogenic hypoparathyroidism is unavailable.

Parathyroid cells were obtained from three chronic uremic patients in hemodialysis, operated for secondary hyperparathyroidism. Cell cultures in RPMI medium were subsequently seeded on collagen scaffold (three-dimensional matrix with slow biodegradation). Collagen is the major component of the extracellular matrix and thus is a good substrate for cell adhesion and growth. Culture media, with a low calcium concentration, were optimised to physiologically stimulate parathyroid hormone secretion. Cell cultures were morphologically observed in optical and electron (ESEM) microscopy and metabolically assayed by MTT method until the tenth week. Besides, concentration of parathyroid hormone in the culture medium has been measured for several weeks.

After 24 hours of culture in RPMI, cells extracted from human parathyroid glands were nearly all adherent and organised in clusters to resemble the glandular organization. The cellular population consisted predominantly of parathyroid cells (90-95%). On collagen scaffolds, cells maintains an epithelial-like morphology also after 10 weeks, colonizing the scaffold surface and keeping a good proliferative rate with a discrete production of parathyroid hormone.

The use of parathyroid cells extracted from patients with secondary hyperparathyroidism was certainly an appropriate choice that enabled us to achieve these results, that albeit partial bode well for the experimental in vivo animal model. The bioengineered scaffolds when implanted in the subcutaneous can avoid the dispersion of parathyroid cells, assuring also the possibility to easily remove the implant in case of complications. Our research was aimed primarily to the optimisation of PTH secreting human parathyroid cells cultures and then to the in vitro engineering of human parathyroid glands in three-dimensional collagen scaffolds.