Parathyroid Allotransplantation: A Systematic Review

Development and application of primary rat parathyroid cells for transplantation in hypoparathyroidism

Background

Hypoparathyroidism (HPO) is characterized by deficient secretion of parathyroid hormone (PTH), leading to hypocalcemia and disrupted calcium homeostasis. Current treatments rely on calcium and vitamin D supplementation, which do not adequately mimic physiological PTH function. Cell-based therapies offer a potential solution, but optimal culture conditions to preserve the functional properties of primary parathyroid cells remain unclear. This study aims to develop primary rat parathyroid cell cultures that maintain hormone secretion and calcium-sensing abilities and to evaluate their therapeutic potential in a rat model of HPO.

Methods

An HPO model was established in rats through surgical excision of the parathyroid glands. Primary parathyroid cells were isolated from these rats and sorted by flow cytometry using epithelial cell adhesion molecule (EpCAM) and calcium-sensing receptor (CaSR) markers. Four different culture media (CM) were tested to determine optimal conditions for sustaining cell functionality. The most effective CM was supplemented with Sonic Hedgehog (Shh), Activin A, and inhibitors of epithelial-mesenchymal transition (EMT). The cultured cells were then transplanted into HPO rats, and serum calcium and PTH levels were monitored to assess therapeutic efficacy.

Results

The optimized CM successfully preserved the hormone-secreting and calcium-sensing functions of primary parathyroid cells over multiple passages. Transplanted cells in HPO rats led to a significant increase in serum calcium and PTH levels compared to untreated controls. The restoration of these levels correlated with the alleviation of hypocalcemic symptoms, indicating effective functional integration of the transplanted cells.

Conclusions

Primary rat parathyroid cells cultured under optimized conditions retained essential functional properties and, upon transplantation, effectively restored calcium homeostasis in an HPO rat model. These results highlight the potential of using cultured primary parathyroid cells as a viable cell-based therapy for HPO, offering a promising alternative to conventional treatments.

Hypoparathyroidism: an update on new therapeutic approaches

BACKGROUND

Hypoparathyroidism is a rare endocrine disease characterized by insufficient parathyroid hormone (PTH) secretion by the parathyroid glands, leading to hypocalcemia. In contrast to most hormone deficiencies for which hormone replacement is currently the mainstay of therapy, hypoparathyroidism has conventionally been treated with calcium supplements and active analogs of vitamin D. Although the advent of a replacement therapy with 1-34 and 1-84 PTH represented a major step in the therapeutic history of hypoparathyroidism, several new molecules and different management strategies have recently been developed.

PURPOSE

This review investigates the therapeutic approaches currently under investigation for the treatment of hypoparathyroidism. Clinical trials results have been considered and discussed.

The Challenge of Preoperative Panel Reactive Antibody Positivity in Parathyroid Transplantation

OBJECTIVES

Identifying suitable recipient criteria and matching recipients with appropriate donors are required to increase survival for parathyroid transplant. This study was undertaken to evaluate transplant survival rates while comparing preoperative panel reactive antibody positivity.

MATERIALS AND METHODS

The study included 14 hypoparathyroidism patients who presented to our clinic for parathyroid transplant. Preoperative ABO compatibility and negative cross-match tests were prioritized for recipient-donor matching, and panel reactive antibody screening tests were performed. During the 24-month follow-up, we evaluated medication use and serum calcium, phosphorus, and parathormone levels of patients.

RESULTS

Preoperative panel reactive antibody positivity was assessed in 3 groups. The HLA class I-positive group (mean fluorescence intensity range, 179-1770) showed decreased medication use and stability in serum calcium levels. The HLA class IIpositive (mean fluorescence intensity range, 85-3959) showed decreased medication use by 25% to 50% and returned to their former prescription doses after 12 months. An opposite pattern was observed in 2 patients with panel reactive antibody positivity for both HLA classes (mean fluorescence intensity range, 462-2289), with 1 patient requiring medication for continuing symptoms and the other patient occasionally taking additional magnesium supplementation, despite decreased medication doses after 12 months. Serum calcium levels remained normal, and parathormone and phosphorus levels were elevated.

CONCLUSIONS

Improving patient symptoms and having no requirement for intravenous calcium replacement are priorities, and monitoring serum levels is the next important step. Varied panel reactive antibody positivities and survival rates indicate a requirement, and each HLA class could require a proper limitation for the mean fluorescence intensity. Preoperative mean fluorescence intensity cut-off value should be <900. Higher mean fluorescence intensity values in panel reactive antibody screenings could increase risk of short-term graft survival after parathyroid transplant. Further studies should include immunological risk assessments by individualizing the outcome with donor-specific antibodies.

Is parathyroid allotransplantation a viable option in the treatment of permanent hypoparathyroidism? A review of the literature

BACKGROUND

The standard clinical treatment for hypoparathyroidism, replacement of calcium and vitamin metabolites (calcitriol), has been used for decades; however, evidence points to its inefficiency in acting on the pathophysiology of the disease, which may precipitate or aggravate conditions already related to hypoparathyroidism. Therapies based on recombinant human parathyroid hormone have emerged in recent years but still have low availability due to their high cost. Parathyroid allotransplantation (Pt-a) has been reported as a strategy for treating more severe cases.

METHODS

This narrative review highlights relevant aspects of conventional permanent hypoparathyroidism treatment and provides a comprehensive and critical review of the reports of applications of Pt-a, especially those carried out in recent years. Particular focus is placed on the following key points: parathyroid immunogenicity, immunosuppression regimens (short-term or chronic), techniques to reduce the expression of immunogenic molecules, follow-up time, and reductions in calcium and vitamin D supplementation.

CONCLUSION

Pt-a has been considered a safe and relatively low-cost therapy and is believed to have the potential to cure the disease, in addition to treating symptoms. However, there is considerable heterogeneity in treatment protocols; therefore, more studies are required to improve the standardization of the procedure and thus improve the consistency of outcomes.