Evaluation of Function

Assessing the function of transplants with fresh parathyroid tissue can be difficult because normocalcemia attributed to transplanted tissue may be due to residual in situ parathyroid tissue. Evaluating the function of cryopreserved transplants is usually more straightforward because patients receive cryopreserved grafts only for well-established hypoparathyroidism. In this setting, one may reasonably consider that return of serum calcium, parathyroid hormone, or urine cyclic adenosine monophosphate (cyclic AMP) toward normal after these transplants is a reflection of successful cryopreservation. Clinical results with cryopreserved auto-transplants are displayed in Table 60-2.

Several studies also provide confidence that cryopreserved parathyroid tissue retains the same (but not necessarily normal) physiology that it displays in the fresh state (Table 60-3). Several investigators have demonstrated preservation of calcium-mediated suppression of parathyroid hormone (Fig. 60-1).11"15 McHenry and coauthors" reported that parathyroid tissue cryopreserved as tissue pieces better preserved calcium-mediated suppression than the same tissue first dispersed and cryopreserved as cell suspensions. Wagner and colleagues12 found that cryopreservation preserved the parathyroid hormone secretory rate (parathyroid hormone release per 105 viable cells) but that the number of nonviable cells varied with both freezing rate and other poorly understood factors. Saxe and Gibson16 found no difference between fresh and cryopreserved human parathyroid tissue with respect to lithium-stimulated tritiated thymidine incorporation. On the other hand,

TABLE 60-1. Viability of Cryopreserved Parathyroid Tissue

Study

Model

Viability

Method

In Vitro

Brennan et al33 McHenry et al15

Herrera et al11 Saxe et al7 Ulrich et al34 Wagner et al12

Study

Cell suspension Cell suspension

Cell suspension Cell suspension Cell suspension Cell suspension

Model

95% "except where otherwise noted"

"70% to 90% reduction in live cell yield observed following cryopreservation" Mean of 91% 71% ± 15% 54,9% 80%-97%

Trypan blue dye exclusion Trypan blue dye exclusion

Propidium iodide Trypan blue dye exclusion

Trypan blue dye exclusion

Success

Proof of Function

In Vivo

Basile et al9

Rat: Wells technique:

4/14 (29%)

Postparathyroidectomy restoration of serum calcium

placed in -80°C freezer

during calcium-poor diet

Goudet et al'8

Nude mouse

6/13 (46%)

Parathyroid hormone secretion

Kapur et al10

Rat

7/10(70%)

Postparathyroidectomy restoration of serum calcium

Leight et al35

Dog

10/18 (56%)

Postparathyroidectomy restoration of serum calcium

5/6 (83%)

Parathyroid hormone

Smeds et al22

Nude mouse

20/26 (77%)

Morphologic appearance

Sonoda et al36

Dog

15 animals

Postparathyroidectomy restoration of serum calcium

Tanaka et al23

Nude mouse

6/8 (75%)

Morphologic appearance

6/8 (75%)

Parathyroid hormone

Walgenbach et ai32

Nude rat

"Programmed

Serum calcium

cryopreservation"

10/15 (67%)

Parathyroid hormone

14/15 (93%)

Serum calcium

"Modified

Parathyroid hormone

cryopreservation "

12/15 (80%)

15/15 (100%)

Wells and

Rat

28/42 (67%)

Postparathyroidectomy restoration of serum calcium

Christiansen4

Christiansen4

Hetrakul and coworkers'7 reported loss of mitochondrial activity as assessed by sestamibi uptake in cryopreserved versus fresh human parathyroid tissue.

Although few studies have been designed to address the question directly, there is evidence from several investigators that the length of storage does not affect the viability or function of cryopreserved parathyroid tissue.4'711121518'23 It appears that tissue is lost during the freezing and thawing processes rather than by attrition during storage.

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