Quantitative intravital microscopy of hepatic transport

The liver performs a number of critical physiological functions. In addition to producing a variety of important proteins and cholesterol, the liver is responsible for processing nutrients, producing bile and removing toxins from the blood. It is this last function that is particularly significant medically, because the liver provides one of the major avenues of drug metabolism and excretion. Accordingly, a major component of pharmacology in drug development involves understanding how the liver transports candidate compounds. However, it is frequently equally important to understand how candidate compounds impact liver transport, effects that may manifest themselves in drug-drug interactions or in liver injury. Indeed, drug-induced liver injury is the single biggest source of failure of drugs in development and the primary reason for withdrawal of approved drugs from the market. The fundamental process of liver transport is one in which compounds present in the blood are transported into hepatocytes, where they may be metabolized and secreted into the bile. While simple in concept, the process is actually quite complex. First, the liver transports a diverse array of substrates via a large number of different transporters with overlapping specificities, making it difficult to attribute transport to a particular transporter pathway or to predict drug-drug interactions. Second, vectorial transport depends upon the abundance and polarized expression of specific transporters to either the sinusoidal (blood) or canalicular (bile) membranes, both of which are acutely regulated in timescales varying from minutes to days. Finally, while hepatic transport is generally schematized in terms of a single hepatocyte, the process is actually mediated at the functional level of the lobule; blood flowing from the periportal to pericentral veins Intravital microscopy has a long history of application to studies of the liver. here we demonstrate how intravital multiphoton microscopy may be combined with digital image analysis to quantitatively evaluate the effects of drugs on hepatocyte transport in vivo. Quantitative intravital microscopy of hepatic transport