Abstract
Albumin is the most abundant plasma protein and functions as a transport molecule that continuously interacts with various cell types. Because of these properties, albumin has been exploited by the pharmaceutical industry to improve drug delivery into target cells. The immediate effects of albumin on cells, however, require further understanding. The cell interacting properties and pharmaceutical applications of albumin incentivises continual research into the immediate effects of albumin on cells. The HepG2/C3A hepatocellular carcinoma cell line is used as a model for studying cancer pathology as well as liver biosynthesis and cellular responses to drugs. Here we investigated the direct effect of purified albumin on HepG2/C3A cell proliferation in the absence of serum, growth factors and other serum originating albumin bound molecules. We observed that the reduced cell counts in serum starved HepG2/C3A cultures were increased by the inclusion of albumin. Cell cycle analysis demonstrated that the percentage of cells in G1 phase during serum starvation was reduced from 86.4 ± 2.3% to 78.3 ± 3.2% by the inclusion of albumin whereas the percentage of cells in S phase was increased from 6.5 ± 1.5% to 14.3 ± 3.6%. A significant reduction in the cell cycle inhibitor protein, P21, accompanied the changes in the proportions of cell cycle phases upon treatment with albumin. We have also observed that the levels of dead cells determined by DNA fragmentation and membrane permeabilization caused by serum starvation (TUNEL: 16.6 ± 7.2%, ethidium bromide: 13.8 ± 4.8%) were not significantly altered by the inclusion of albumin (11.6 ± 10.2%, ethidium bromide: 16.9 ± 8.9%). Therefore, the increase in cell number was mainly caused by albumin promoting proliferation rather than protection against cell death. These primary findings demonstrate that albumin has immediate effects on HepG2/C3A hepatocellular carcinoma cells. These effects should be taken into consideration when studying the effects of albumin bound drugs or pathological ligands bound to albumin on HepG2/C3A cells.
Highlights
Albumin comprises half of the plasma proteins in healthy individuals at concentrations of circa g/L (0.6 mmol/L) and is produced by hepatocytes and exported through the blood to the rest of the cells in the body (Margarson & Soni, 1998; Quinlan, Martin & Evans, 2005)
We have selected HepG2/C3A carcinoma cells because they originate from hepatocytes (Aden et al, 1979) and have been used as a model for studying hepatocellular carcinoma (Chen et al, 2015; Ao et al, 2017) as well as normal hepatocyte functions (Nibourg et al, 2012; Gaskell et al, 2016)
Hepatocytes play an important role in the clearance of albumin bound substances (Meijer & van der Sluijs, 1989), some of these albumin interacting properties can potentially be used in targeting hepatocellular carcinoma or studying the effects of pathologically modified albumin on cellular function
Summary
Albumin comprises half of the plasma proteins in healthy individuals at concentrations of circa g/L (0.6 mmol/L) and is produced by hepatocytes and exported through the blood to the rest of the cells in the body (Margarson & Soni, 1998; Quinlan, Martin & Evans, 2005). Albumin’s ability to transport between different cell occurs through endocytosis and transcytosis and is controlled by several cellular receptors These interactions dictate whether albumin should be internalised or cross the vascular endothelial barrier to extravascular compartments (Schnitzer et al, 1992; Schnitzer & Oh, 1994; Vogel et al, 2001). Albumin with high affinity was recycled whereas low affinity albumin underwent lysosomal degradation (Schmidt et al, 2017) These cellular interactions with albumin demonstrate that cells selectively dictate the fate of albumin based on the albumin’s ligand conformation. This raises the question of whether the cells in turn respond physiologically to albumin
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