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Abstract
Background
The objective of this study was to evaluate the role of proteases on the degradation of parathyroid hormone (PTH) in blood samples.
Methods
Protease inhibitors with specificity against serine proteases (aprotinin), cysteine proteases (E-64), serine and cysteine proteases (leupeptin), metalloproteases (EDTA), or a protease inhibitor cocktail with a broad spectrum of inhibitory activity were added to blood samples. After storage at room temperature (0-48 hr), PTH levels were measured.
Results
PTH levels in samples with the protease inhibitor cocktail did not change significantly after 48 hr of storage at room temperature, but the average PTH levels decreased by 40.7% and 20.1%, in samples stored at room temperature and stored at 4°C without protease inhibitors, respectively. PTH levels in samples with leupeptin were stable for up to 24 hr. After 48 hr, the mean PTH levels decreased by 17.1%, 16.0%, 26.2%, and 32.1%, with 500 KIU/mL aprotinin, 100 μmol/L leupeptin, 10 μmol/L E-64, and 10 μmol/L EDTA, respectively, in the samples stored at room temperature.
Conclusions
The decrease in PTH levels in blood samples seemed to be due to the degradation of PTH by proteases. Various proteases, including especially serine proteases, would act together to degrade PTH in blood specimen. The PTH degradation may be inhibited in blood specimen with protease inhibitor cocktail.
REFERENCES
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Fig. 1.
Time-dependent changes of the PTH levels in samples with different kinds of protease inhibitors. Data points are the mean ±SD (error bars) of PTH levels. Six groups of samples were stored at room temperature and the other group was stored at 4°C. Abbreviation: PTH, parathyroid hormone.
Table 1.
Changes of PTH levels in blood specimen according to different storage conditions
| Storage condition | PTH levels (pg/mL)∗ | P† | |||
|---|---|---|---|---|---|
| Zero time | After 12 hr | After 24 hr | After 48 hr | ||
| Storage at room temperature | |||||
| Without protease inhibitors | 35.4±13.1 | 28.1±8.4 | 23.8±.4 | 21.0±6.2 | 0.005 |
| With protease inhibitors | |||||
| Inhibitor cocktail | 34.7±12.4 | 33.6±12.7 | 33.14±11.9 | 33.3±11.5 | 0.139 |
| Aprotinin, 500 KIU/mL | 35.6±12.6 | 33.5±11.8 | 31.8±12.7 | 29.5±11.0 | 0.005 |
| Leupeptin, 100 μmol/L | 45.0±9.0 | 43.6±15.9 | 41.9±15.7 | 37.8±14.2 | 0.028 |
| E-64, 10 μmol/L | 34.3±12.2 | 30.6±10.9 | 28.7±11.3 | 25.3±9.9 | 0.005 |
| EDTA, 10 μmol/L | 34.9±13.5 | 30.1±9.8 | 26.4±9.5 | 23.7±8.3 | 0.008 |
| Storage at 4°C | |||||
| Without protease inhibitors | 35.9±14.2 | 33.6±13.7 | 30.6±12.4 | 28.7±11.1 | 0.009 |
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