Hepatocyte labeling with ⁹⁹mTc-GSA: a potential non-invasive technique for tracking cell transplantation.

BACKGROUND

Hepatocyte transplantation is a promising alternative to orthotopic liver transplantation, however, the fate of transplanted hepatocytes is not well defined. ⁹⁹mTc-galactosyl-serum albumin (⁹⁹mTc-GSA) is a clinical scintigraphic agent which is specifically taken up by the hepatocyte asialoglycoprotein receptor (ASGPR).

AIMS

To investigate labeling of fresh and cryopreserved human hepatocytes and fresh rat hepatocytes in vitro using ⁹⁹mTc-GSA.

METHODS

Human and rat hepatocytes were isolated from liver tissue by collagenase perfusion. The ASGPR were characterized using immunohistochemistry and RT-PCR. Hepatocytes were incubated with ⁹⁹mTc-GSA in suspension at 4°C and 37°C. Cell viability and function was determined using cell mitochondrial dehydrogenase (MTS) and sulphorhodamine B (SRB) assays.

RESULTS

Fresh and cryopreserved human hepatocytes expressed the ASGPR. Incubation of hepatocytes in suspension with ⁹⁹mTc-GSA reduced the viability of hepatocytes, but this was similar to unlabeled control cells. Greater loss of viability was seen on incubation at 37°C compared to 4°C, but there was a significantly greater uptake of ⁹⁹mTc-GSA at the physiological temperature (6.6 ± SE 0.6-fold increase, p<0.05) consistent with ASGPR-mediated endocytosis. MTS and SRB assays were not significantly affected by labeling with ⁹⁹mTc-GSA in all three cell types. A mean of 18.5% of the radioactivity was released over 120 min when ⁹⁹mTc-GSA -labeled hepatocytes were shaken in vitro at 37°C.

CONCLUSIONS

Human and rat hepatocytes can be labeled with ⁹⁹mTc-GSA, which may have potential application for in vivo imaging after hepatocyte transplantation.