Hepatocyte Concentrations of Indocyanine Green Reflect Transfer Rates Across Membrane Transporters

Abstract

Perioperative imaging with indocyanine green (ICG) is developing to increase safety in dissecting anatomical structures during hepatobiliary surgery. Images obtained with the fluorescence camera rely on concentrations measured in liver regions of interest. However, how ICG sinusoidal uptake and hepatocyte elimination rates generate ICG hepatocyte concentrations is largely unknown. To investigate such issue and better understand the role of membrane transporters in generating ICG hepatocyte concentrations, we perfused ICG in livers isolated from normal livers. Whether the well-known transporter inhibitor rifampicin modifies hepatocyte ICG concentrations was also studied. The dye has a very high and constant extraction ratio (96%) into hepatocytes. This persistent high extraction ratio generates a huge uphill concentration gradient across the sinusoidal membrane: from 5 μM (sinusoids) to 1600 μM (liver). When inside hepatocytes, ICG has low hepatocyte elimination (7 nmol/min.) and liver concentrations do not decrease much over time. Moreover, the tiny hepatocyte ICG efflux is mainly due to ICG return back to sinusoids (90%). Rifampicin slightly inhibits ICG uptake into hepatocytes and when inside hepatocytes blocks ICG efflux into bile canaliculi. In contrast, it increases ICG efflux back to sinusoids with significant decrease in ICG liver concentrations. Imaging with ICG in the perioperative period reflects the high hepatocyte concentrations and relies on the high extraction ratio across hepatocyte sinusoidal membrane. Although ICG concentrations are low in bile ducts, they are adequate for a good visualization and avoid bile duct injury.

Effect of Chronic Kidney Disease on Hepatic Clearance of Drugs in Rats

“…ICG has been commonly used for assessment of liver function, especially hepatic blood flow in clinical. 22) ICG is transported by several transporters. It is reported that ICG enters through organic anion transporting polypeptides (OTAP1B1/3) and Na(+)/taurocholate cotransporter polypeptide (NTCP) expressed on the sinusoidal membrane of hepatocytes.…”

“…It is reported that ICG enters through organic anion transporting polypeptides (OTAP1B1/3) and Na(+)/taurocholate cotransporter polypeptide (NTCP) expressed on the sinusoidal membrane of hepatocytes. 23) Besides, it is also reported ICG elimination from hepatocytes is mainly due to efflux back to sinusoids, and biliary transport across the canalicular occurs across P-glycoprotein 2 (Mdr2). 24) In this study, ICG clearance from the plasma was delayed in the CKD group (Fig.…”

Hepatocyte Concentrations of Imaging Compounds Associated with Transporter Inhibition: Evidence in Perfused Rat Livers

“…The gamma counter placed over the liver detects the concentrations of both imaging compounds, avoiding the collection of serial liver biopsy samples. Indeed, serial biopsies alter the liver structure over the period of the protocol (Cusin et al, 2017). This improved experimental model directly measures the effects of RIF on fluxes across hepatocyte membranes and is a new tool for the understanding of transporter-mediated drugdrug interactions.…”

Hepatobiliary MRI: Signal intensity based assessment of liver function correlated to 13C-Methacetin breath test

“…In general, the ICG clearance test has certain limitations, as constant hemodynamic conditions (stable liver perfusion rate and hepatic blood flow) are required for liver function analysis 40 – 42 and, in cases of cholestasis and hyperbilirubinemia, carrier competition of bilirubin and ICG at the OATP1 transporter might occur 43 , 44 . It is also known that various drugs (e.g., rifampicin) exert inhibitory effects on the OATP pathway and might influence hepatocyte ICG uptake 45 , 46 . Similar to the findings of Tamada et al .…”