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. 99m Tc-galactosyl-serum albumin ( 99m Tc-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 99m Tc-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 99m Tc-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 99m Tc-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 99m Tc-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 99m Tc-GSA in all three cell types. A mean of 18.5% of the radioactivity was released over 120 min when 99m Tc-GSA - labeled hepatocytes were shaken in vitro at 37°C. Conclusions: Human and rat hepatocytes can be labeled with 99m Tc-GSA, which may have potential application for in vivo imaging after hepatocyte transplantation.