Quantitative evaluation of hepatic morphological alterations and pharmacokinetic changes of cationic drugs in fibrosis-inducing hepatic diseases

Chang, Ping. (2002). Quantitative evaluation of hepatic morphological alterations and pharmacokinetic changes of cationic drugs in fibrosis-inducing hepatic diseases PhD Thesis, School of Medicine, The University of Queensland.

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Author Chang, Ping.
Thesis Title Quantitative evaluation of hepatic morphological alterations and pharmacokinetic changes of cationic drugs in fibrosis-inducing hepatic diseases
School, Centre or Institute School of Medicine
Institution The University of Queensland
Publication date 2002
Thesis type PhD Thesis
Supervisor Michael S. Roberts
Total pages 191
Collection year 2002
Language eng
Subjects L
320500 Pharmacology and Pharmaceutical Sciences
730118 Organs, diseases and abnormal conditions not elsewhere classified
Formatted abstract

Liver cirrhosis and fibrosis are the ultimate results of chronic hepatic injury representing a common and difficult worldwide clinical challenge. There is no effective pharmaceutical curative for either of these conditions at this point in time and the only promising treatment in the final stages of cirrhosis is liver transplantation. Hepatic fibrosis represents basically the dynamic liver wound-healing response to a chronic insult. The morphological and architectural changes that are associated with cirrhosis and fibrosis of the liver impact severely on the exchange of substances between the vascularity and hepatic tissue and their characterization is therefore of the utmost importance for an understanding of altered solute exchange in the diseased liver. It was therefore the aim of this study to determine various aspects of altered hepatic solute exchange in chronic and acute liver disease and to describe the changes using a mathematical model. There are therapeutic strategies aimed at treating cirrhosis. Some of them are undergoing clinical study currently and may be developed as practical treatments of cirrhosis in the future. One of these attempts is snake venom enzyme (Svate-3) treatment which has been used in China to treat thromboembolic and cirrhotic disease for many years. The efficacy of snake venom treatment and outcome in fibrosis was assessed in this work. The following aspects of hepatic drug disposition in health and disease and treatment commodities were determined and evaluated.

Experimental animal models (chapter 2). The carbon tetrachloride rat model was established following a procedure established by Proctor and Chatamra. Male Wistar rats were caged in groups of 6 each (2 groups) and given sodium phenobarbital in their drinking water ad libitum; the first dose of carbon tetrachloride was administered 10 days later. Group 1: Animals were given carbon tetrachloride once a week for 12 weeks. Body weight was monitored daily, the weight versus time curve showed a steady increase following a zigzag pattern. A short period of weight loss was associated with the administration of the carbon tetrachloride dose. Each subsequent dose was adjusted weekly according to the weight loss associated with the preceding dose. The total dose volume was 1.0 mL. All 6 animals treated with carbon tetrachloride developed fibrosis. Group 2: Animals in this control group were treated identically to Group 1, except that they were given a 1.0 mL dose of com oil weekly without carbon tetrachloride. The alcohol rat model was developed following a procedure described by Takeyama et al. Male Wistar rats were housed in individual cages. Group 1: Rats were fed a nutritionally liquid high-fat alcohol diet containing ethanol (36% of the total caloric intake) for 12 weeks. The intake volume of this liquid diet for the individual rat was 100 mL/day. If the animal did not consume all the diet, the remaining liquid diet was gavage-fed ensuring exactly 100 mL was consumed over the 24-hour period. Group 2: Rats in this control group were treated identically to Group 1, except that they were given a control diet which contains no ethanol. The body weights of the alcohol-fed rats closely paralleled that of their pair-fed controls.

Hepatic pharmacokinetics (chapter 3). Barrier-limited tissue distribution is conventionally used in most organ models of solute disposition such as the two-compartment dispersion model and the "Goresky" model. However, it is well recognised that the conventional barrier limited approach inadequately describes the tail part of outflow curves. The two-phase stochastic model of drug transport was used in this work to integrate cytoplasmic binding kinetics into the conventional barrier-limited tissue distribution model. Consequently, this model perfectly fitted the data from the peak to the tail part of outflow curves.

Evaluation of altered hepatic spaces and membrane transport in fibrotic/cirrhotic rat live (chapter 4). Four animal models were used to quantitatively evaluate hepatic alterations in chronic and acute fibrotic liver disease: (i) a carbon tetrachloride (CC14)-control group (phenobarbital treatment only); (ii) a CC14-treated group (phenobarbital with CC14 treatment); (iii) an alcohol-treated group (liquid diet with alcohol treatment); and (iv) a pair-fed alcohol-control group (liquid diet only). At the end of induction, single pass perfused livers were used to conduct multiple indicator dilution studies. Hepatic spaces (vascular space, extravascular albumin space, extravascular sucrose space, and cellular distribution volume) and water hepatocyte permeability-surface area product were estimated from non-linear regression of outflow concentration versus time profile data. Livers were dissected for histopathological analyses (fibrosis index). In the four models, the CC14-treated rats were found to have the smallest vascular space, extravascular albumin space, water hepatocyte permeability-surface area product but the largest extravascular sucrose space and cellular distribution volume. In addition, a linear relationship was found to exist between histopathological analyses (fibrosis index) and hepatic spaces. The hepatic water hepatocyte permeability-surface area product also correlated to the severity of fibrosis as defined by the fibrosis index. In conclusion, the multiple indicator dilution studies data obtained from the in situ perfused rat liver could be directly related to histopathological analyses.

Structure-hepatic disposition relationships for cationic drugs of varying lipophilicity using a single-pass, in-situ rat liver preparation (chapter 5). The lipophilicity among the cationic drugs studied was in the following order: diltiazem > propranolol > labetalol > prazosin > antipyrine >atenolol. Parameters characterising the hepatic distribution and elimination kinetics of the drugs were estimated using the multiple indicator dilution method. The kinetic model used to describe dmg transport (the "two-phase stochastic model") integrated cytoplasmic binding kinetics and belongs to the class of barrier-limited and space-distributed liver models. Hepatic extraction ratio was found to increase with lipophilicity. The intracellular binding rate constant and the equilibrium amount ratios characterising the slowly and rapidly equilibrating binding sites increased with the lipophilicity of drug, whereas the intracellular unbinding rate constant decreased with the lipophilicity of drug . The partition ratio of influx and efflux rate constant, increased with increasing pKa value of the drug, the ratios for the different drugs mainly arising from ion-trapping in the mitochondria and lysosomes. The value of intrinsic elimination clearance, permeation clearance, and permeability-surface area product all increased with the lipophilicity of drug. It was concluded that cationic drug kinetics in the liver can be modelled using models which integrate the presence of cytoplasmic binding, a hepatocyte barrier and a vascular transit density function.

Disposition kinetics of six cationic model drugs in perfused diseased and normal rat livers (chapter 6). The structure-penetration and cytoplasmic binding relationships for model cationic drugs of varying lipophilicity in diseased rat livers were determined using MID study and histopathology. Three animal models were investigated in this work: i) acute hepatocellular injury model induced by carbon tetrachloride; ii) chronic hepatocellular injury model induced by alcohol; and iii) controls. The kinetic model used to describe drug transport was a heterogeneous (barrier-limited and space-distributed) transit time model. The histopathology showed: i) the carbon tetrachloride-treated group had a higher severity of liver disease than did the alcoholtreated group, ii) the carbon tetrachloride-treated group has the highest fibrosis index, iii) the alcohol-treated group has the highest hepatic a 1-acid glycoprotein tissue level. Pharmacokinetic analysis showed: i) the hepatic extraction ratio, intrinsic clearance, permeability surface area product, and slow binding constants all increased with the lipophilicity of the dmg in all animal models, ruii) the carbon tetrachloride-treated group had a significantly lower hepatic extraction ratio, intrinsic clearance, permeability surface area product, and slow binding constants than other groups for the same lipophilic dmg (e.g. diltiazem) but not for the same polar drug (e.g. atenolol), iii) the alcohol-treated group has a significantly higher hepatic extraction ratio, intrinsic clearance and slow binding constants than other groups for the same lipophilic drug but not for the same polar dmg. Iv) the partition ratio of influx and efflux rate constant increased with increasing pKa if the dmg in the normal and alcohol-treated group but no significant difference was found in the carbon tetrachloride-treated group, v) Good linear relationships existed between the histopathological results (fibrosis index and a 1-acid glycoprotein) and the pharmacokinetic parameters (permeability surface area product and slow binding constants) of the model cationic drugs. It was concluded that the findings could assist in understanding how fibrosis-inducing hepatic diseases affect hepatic drug disposition and, relevant to preclinical drug development, may assist in predicting hepatic first pass.

Snake venom enzyme treatment in the fibrotic rat
(chapter 7). Hepatic fibrosis in the rat was induced by carbon tetrachloride. Snake venom enzyme (Svate-3) was administered concomitantly to examine whether it provided any protection against this hepatotoxic agent. Initial dose ranging studies showed in vivo fibrinogen and thromboxane B2 production was reduced in a dose dependent manner. The efficacy of high dose Svate-3 as a hepatoprotectant to carbon tetrachloride was confirmed in five aspects: i) liver biochemistry, ii) histopathological examination, iii) microcirculation assessment, iv) pharmacokinetic evaluation, and v) bile production. The Svate-3- treated group had intermediate enzyme levels (alanine aminotransferase, aspartate aminotransferase), fibrosis indices, venular/extravenular/hepatocellular spaces and propranolol disposition kinetics between the normal and the control (carbon tetrachloride alone treated) group. The Svate-3-treated group showed a significantly higher bile production than the normal and control groups. It was hypothesised that Svate-3 reversal or alleviation of fibrosis might be related to one or a combination of either i) inhibition of thrombosis by inhibiting platelet aggregation; ii) improvement of microcirculation of liver; iii) inhibition of fibrin formation by fibrinogenolysis; and iv) increase of bile production (works as a chologogue).

In conclusion, this thesis has shown that a quantitative relationship exists between liver fibrosis and distribution spaces of physiological markers. Cationic drug disposition in liver fibrosis can also be related to the physicochemical properties of the drug. Finally, it was shown that a snake venom treatment improved outcome in fibrosis as assessed by a fibrosis index and assessment of vascular space and propranolol disposition.

Keyword Liver function tests
Liver cirrhosis
Additional Notes Variant title: Quantitative evaluation of hepatic pharmacokinetics in fibrosis-inducing hepatic diseases.

Document type: Thesis
Collection: UQ Theses (RHD) - UQ staff and students only
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Created: Fri, 24 Aug 2007, 17:53:43 EST