In vitro comparison of equine granulocytes labeled with 99mTc-hexamethylpropyleneamine oxime or 111In-oxine.

This research provides comparative data on the efficiency, viability, and phagocytic function of horse white blood cells (WBCs) labeled with two different radioactive substances, 99mTc-hexamethylpropyleneamine oxime (99mTc-HMPAO) and 111In-oxine. The findings suggest that 99mTc-HMPAO-labeled WBCs hold potentially better or equivalent characteristics than the 111In-oxine-labeled WBCs after a 6-hour period, implying its suitability as a good alternative for biological cell tagging.

Overview of the Research

The researchers conducted in vitro studies to compare independent batches of equine granulocytes labeled with either 99mTc-HMPAO or 111In-oxine across three main parameters:

• Labeling efficiency of the radiotracers
• Viability of the radiolabeled granulocytes
• Phagocytic function of the radiolabeled granulocytes

Labeling Efficiency

• The 111In-oxine-labeled granulocytes demonstrated a mean labeling efficiency of 62.2%, which turned out to be considerably (with a statistical significance of less than 0.001) higher than the 32.0% achieved by 99mTc-HMPAO-labeled granulocytes.
• However, the rate of radioactive label leakage, or elution, from the granulocytes was significantly greater in the 99mTc-HMPAO-labeled cells at 0.5, 2, and 4-hour marks, but was at an equivalent rate in both types by the final 6-hour mark.

Viability Assessment

• Using trypan blue dye exclusion to measure cell viability, the researchers found that both 99mTc-HMPAO and 111In-oxine labeled granulocytes, as well as the non-labeled control cells, retained almost full viability (between 97 and 100%), indicating that the radiolabeling process did not significantly harm the cells.

Phagocytic Function

• The phagocytic function, assessed through a phagocytosis assay, was measured by the phagocytic index and showed no significant difference between the two cell groups at 0.5, 2, and 4 hours.
• However, at the 6-hour mark, the 99mTc-HMPAO-labeled WBCs demonstrated a significantly greater phagocytic index (P = 0.038), suggesting a better or equivalent cell function to their 111In-oxine labeled counterparts over a long duration.

Conclusion

Given the superior imaging characteristics, and equal or superior labeling efficiency and cell function over 6 hours, 99mTc-HMPAO-labeled equine white blood cells can be seen as a viable alternative to the traditionally used 111In-oxine-labeled cells for in vitro studies.