Hepatocytes hepatic clearance

As described above, it will be normal to assume that the dose interval is 24 hours, i.e., once-a-day dosing. Absorption can be estimated with good confidence from absorption in the rat (see Section 6.1). Clearance is the sum of the predicted hepatic, renal, biliary and extrahepatic clearance. Hepatic clearance can be derived from in vitro studies with the appropriate human system, using either microsomes or hepatocytes. We prefer to use an approach based on that described by Houston and Carlile [83], Renal clearance can be predicted allometrically (see section 6.8.1). The other two potential methods of clearance are difficult to predict. To minimize the risks, animal studies can be used to select compounds that show little or no potential for clearance by these routes. As volume can be predicted from that measured in the dog, after correction for human and dog plasma protein binding (see Section 6.2), it is possible to make predictions for all of the important parameters necessary. 

Houston, J. B., Carlile, D. J., Prediction of hepatic clearance from micro-somes, hepatocytes and liver slices, Drug Metab. Rev. 1997, 29, 891-922. 

An important DMPK property of a NCE is oral bioavailability (F) of the compound in various pre-clinical species.3 The oral bioavailability of a compound is dependent on several factors including intestinal permeability (estimated by the Caco-2 assay) and hepatic clearance (estimated with an in vitro metabolic stability assay).3 30 The metabolic stability assay is typically performed by incubating test compounds in liver microsomes or hepatocytes. The results can provide estimates of in vivo stability in terms of metabolic liabilities.3 8 59 62 Several authors described this assay as an important tool for the rapid assessment of the DMPK properties of NCEs.3 6 8111819 26 44 59 62-65... 

Lau, Y.Y. et al. 2002. Development of a novel in vitro model to predict hepatic clearance using fresh, cryopreserved, and sandwich-cultured hepatocytes. Drug Met. Disp. 30 1446. 

Figure 6 Well-stirred model of hepatic clearance. The exchange of a drug between plasma and hepatocyte and its removal from this cell involves an unbound compound. Intrinsic clearance, CLint, relates the rate of the elimination (by formation of metabolites, CLint>f, and secretion of unchanged compound into bile, CLint5ex) to the unbound drug in the cell, CUr Cbout and CUout are the bound and unbound concentrations of the drug leaving the liver at total concentration Cout.

Niro, R., Byers, J., Fournier, R., and Bachmann, K., Application of a convective-dispersion model to predict in vivo hepatic clearance from in vitro measurements utilizing cryopreserved human hepatocytes, Current Drug Metabolism, Vol. 4, No. 5, 2003, pp. 357-369. 

Equation 7.13 emphasizes the central point that changes in perfusion and protein binding, as well as intrinsic clearance, will affect the hepatic clearance of a number of drugs. The intact hepatocyte theory has been proposed as a means of simplifying this complexity (33). This theory is analogous to the intact nephron theory (see Chapter 5) in that it assumes that the increase in portocaval shunting parallels the loss of functional cell mass, and that the reduced mass... 

Hepatic clearance can also be estimated from in vitro intrinsic metabolic CL obtained by incubation of a compound with hepatocytes or liver microsomes. This method requires fewer resources than the in vivo approach and is more suitable for screening a large number of compounds however, there are documented cases when in vitro clearance does not accurately predict in vivo. Intrinsic metabolic CL (CLint) is a parameter that only reflects the intrinsic ability of liver to metabolize... 

Hepatic clearance is the net result of drug uptake into the hepatocyte, followed hy metabolism and biliary excretion, with possible efflux of drug back into the circulation from the liver cell. Overall, hepatic clearance is traditionally described using the venous equilibration model ... 

Explain the role of sinusoidal transport on hepatic clearance, and list the various transporters that mediate drug uptake into the hepatocyte. 

This model for predicting hepatic clearance has allowed simple enzyme (e.g. cytochrome P450 enzymes for phase 1 metabolism), sub-cellular (microsomes for phase 1 metabolism) or cellular assays (hepatocytes for phase 1 and 2 metabolism) to be established in drug discovery cascades to enable the identification of low clearance compounds, with the ability to predict the consequent expected in vivo clearance. Results from in vitro assays based on rat or dog microsomes or hepatocytes for a particular compound can be validated with... 

The second caveat is that, in order to accurately predict hepatic clearance, the correct in vitro system must be chosen. If the candidate drug is primarily oxidatively metabolized, then liver microsomes will be sufficient. However, if the potential for non-microsomal biotransformation exists, then a different in vitro system, such as hepatocyte suspensions, should be used. In the illustration above, it turned out, as far as clearance of Compound X is concerned, man is specifically like a rat, and unlike a dog. 

Transporters are involved in biliary and renal excretions that are the two common routes of drug elimination. In the liver, a drug is first taken up into hepatocytes, then either secreted back to the systemic circulation or excreted to the bile in an intact form or as metabolites via Phase I and/or Phase II enzymes. Given the involvement of transporters in both uptake at the sinusoidal membrane and efflux at the sinusoidal and canulicular membranes (Fig. 6.1c), the hepatic clearance can be expressed based on well-stirred model as the following equation (Shitara et al., 2005 Yamazaki et al., 1996) ... 

Zomorodi, K. CarlUe, DJ. Houston, J.B. Kinetics of diazepam metabolism in rat hepatic microsomes and hepatocytes and their use in predicting in vivo hepatic clearance. Xenobiotica, 1995, 25, 907-916... 

Bachmann K, Byers J, Ghosh R. Prediction of in vivo hepatic clearance from in vitro data using cryopreserved human hepatocytes. Xenobiotica 2003 33 475-483. 

Shibata Y, Takahashi H, Chiba M, Ishii Y. Prediction of hepatic clearance and availability by cryopreserved human hepatocytes An application of serum incubation method. Drug Metab Dispos 2002 30 892-896. 

Chao P, Maguire T, Novik E, Cheng KC, Yarmush ML. Evaluation of a microfluidic based cell culture platform with primary human hepatocytes for the prediction of hepatic clearance in human. Biochem Pharmacol 2009 78(6) 625—632. 

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