Functional intravital two-photon based imaging of bile salts transport in cholestasis: mechanisms and consequences of bile infarcts formation

Question:

The mechanisms of hepatocytes damage in cholestatic liver disease are not fully understood. Therefore, we here investigated the spatio-temporal processes of bile salt (BS) transport in cholestatic livers aiming to understand its pathophysiological role.

Methods:

Functional intravital two-photon based imaging of mice livers in acute and chronic cholestasis induced by common bile duct-ligated (BDL) was done using fluorescent BS analogues. Key findings were followed-up by clinical chemistry, immunostaining and gene expression analyses.

Results:

In the acute phase after BDL (days 1 to 3), individual dispersed hepatocytes lose their mitochondrial membrane potential, followed by dilatation and rupturing of their apical membranes, BS leakage and cell death. This was followed by a domino effect of further death of neighboring hepatocytes, finally leading to formation of large bile infarcts. Interestingly, bile infarcts provide a transepithelial shunt between bile canaliculi and sinusoids, by which BS leak into the blood. This resulted in decrease of BS concentrations in the biliary tract. In the chronic phase after BDL (day 21), uptake of BS tracers at the sinusoidal membrane of hepatocytes was strongly reduced. This was associated with upregulation of the basolateral efflux transporters, MRP3 and MRP4.

Conclusion:

In acute cholestasis, a limited number of hepatocytes are lost allowing leakage of BS from the biliary tract into sinusoidal blood, thereby protecting the liver from BS overloading. In chronic cholestasis, the liver adapts by reducing BS uptake via the sinusoidal hepatocytes membranes, on the expense of the kidney.