The uptake mechanism of gallium-67 into hepatocytes treated with carbon tetrachloride.

We have recently reported that transferrin (Tf)-unbound gallium-67 (67Ga) may be taken up into the liver of carbon tetrachloride (CCl4)-treated rats. In the present study, we attempted to clarify detailed mechanism of Tf-unbound 67Ga uptake by hepatocytes treated with CCl4 using in vitro experimental system. Hepatotoxic damages by CCl4 are mostly attributed to radical formed by an action of cytochrome P450. P450 isozymes have a higher expression in the perivenous hepatocytes (PVH) more than periportal hepatocytes (PPH). Therefore, we thought that the uptake of 67Ga which had been used for the detection of liver damage might have a zonal difference. The results of ALT activities showed that the CCl4 exposure for 4 h strongly impaired PVH more than PPH. The uptake of 67Ga by PVH treated with CCl4 was also higher than that by PPH. Moreover, the uptake of 45Ca by PVH was higher than that by PPH. In order to investigate whether 67Ga passed through calcium channel of hepatocytes, we made use of calcium channel blocker and activator. The Ca2+-channel blocker, verapamil, significantly decreased the uptakes of 45Ca and 67Ga by PPH and PVH pretreated with CCl4. The addition of the Ca2+-channel activator, Bay K8644, significantly increased the uptake both of 45Ca and 67Ga by PPH pretreated with CCl4. In the present study, it was demonstrated that the uptake of Tf-unbound 67Ga preferentially occurred in CCl4-damaged PVH and 67Ga was taken up into the hepatocytes in part through calcium channel.

The involvement of transferrin in the uptake of iron-59 by hepatocytes of carbon tetrachloride-damaged rats.

We have reported that transferrin (Tf)-unbound Gallium-67 ((67)Ga) was taken up into hepatocytes 1 d after carbon tetrachloride (CCl(4))-treatment in rats. It had been reported that the binding affinity of Iron-59 ((59)Fe) to Tf was greater than that of (67)Ga. In the present study, we investigated whether or not Tf was involved in (59)Fe uptake by hepatocytes of CCl(4)-damaged rats. The results showed that the uptake of (59)Fe by hepatocytes and the number of Tf-receptor decreased 1 d after CCl(4)-treatment and increased 2 d after the treatment. Our data demonstrated that the uptake of (59)Fe by hepatocytes differed from that of (67)Ga and Tf was involved in that of (59)Fe. We expect that these finding could serve to analyze the inflammatory stages, disorder stage at 1 d and regeneration stage at 2 d after CCl(4)-treatment.

The involvement of polyamines as substrates of transglutaminase in zonal different hepatocyte proliferation after partial hepatectomy.

We have recently demonstrated the inverse correlation between transglutaminase (TGase) activity and DNA synthesis in periportal hepatocytes (PPH) and perivenous hepatocytes (PVH) at 1 d after partial hepatectomy. In order to elucidate a role of polyamines as substrates of TGase in the differential growth capacities between PPH and PVH from regenerating liver, we investigated the zonal differences in alteration of ornithine decarboxylase (ODC) activity and polyamines. In two subpopulations, the inverse correlation between DNA synthesis and epsilon-(gamma-glutamyl) lysine (Gln-Lys) cross-linking catalyzed by TGase was demonstrated at 1 d after partial hepatectomy. ODC activity in PPH significantly increased with a peak at 1 d after partial hepatectomy, whereas did not in PVH. Protein-binding SPD in PPH also transiently increased with a peak at 1 d after partial hepatectomy, but did not in PVH. These results suggest that at 1 d after partial hepatectomy, in PPH, the inhibition of Gln-Lys cross-linking by the formation of N-gamma-glutamyl SPD leads to the increase of DNA synthesis, whereas in PVH, enhanced formation of Gln-Lys cross-linking leads to the lower DNA synthesis.

Uptake of gallium-67 by the hepatocytes during liver regeneration in carbon tetrachloride-treated mice.

Gallium-67 (67Ga) has been used as a tumor or inflammation-imaging agent in nuclear medicine. We recently reported that the peak of serum alanine aminotransferase (ALT) level was 1 d after carbon tetrachloride (CCl4) treatment in rats. However, the peak of 67Ga uptake by the liver tissue and hepatocytes was 2 d after the treatment. If 67Ga is taken in the hepatic disorder phase, the pattern of 67Ga uptake by the hepatocytes should be consistent with that of the ALT level. In order to answer why it was not, we carried out a detailed examination. The lipid peroxidation of hepatocytes from CCl4-treated mice was greatly increased 1 d after CCl4 treatment; serum ALT was also increased 1 d after the treatment. The uptake of 67Ga by the liver tissue reached a maximum 1 and 2 d after the treatment, while maximum by the hepatocytes was achieved after 2 d. The incorporation of bromodeoxyuridine into the hepatocytes also reached maximum 2 d after the treatment. These results suggest that the uptake of 67Ga by the hepatocytes is carried out during liver regeneration rather than during hepatic disorder by CCl4 treatment.

Zonal differences in DNA synthesis and in transglutaminase activity between perivenous versus periportal regions of regenerating rat liver.

We investigated a relationship within zonal differences in DNA synthesis and in transglutaminase (TGase) activity between perivenous versus periportal regions of regenerating rat liver. Using the digitonin/collagenase perfusion technique, hepatocyte subpopulations were isolated from each region at various time points after partial hepatectomy. The amounts of DNA synthesis as well as the levels of TGase mRNA and activity in each subpopulation were measured. Although increased DNA synthesis was observed in both subpopulations with a peak at 24 h after partial hepatectomy, the amount of DNA synthesis in periportal hepatocytes (PPH) was twice as much as that in perivenous hepatocytes (PVH). In PVH, TGase activity peaked at 24 h after partial hepatectomy with a preceding increase in its mRNA expression at 12 h, whereas TGase activity in PPH at 24 h was one-half of that in PVH. As TGase is known to have a growth-arresting activity, our data indicate that relatively higher TGase activity in PVH at 24 h after partial hepatectomy might correlate with relatively lower DNA synthesis in this region compared to periportal region.