Pharmacokinetics of tacrolimus and mycophenolic acid are altered, but recover at different times during hepatic regeneration in rats

Pregnane X receptor activation induces liver enlargement and regeneration and simultaneously promotes the metabolic activity of CYP3A1/2 and CYP2C6/11 in rats

Human pregnane X receptor (PXR) is critical for regulating the expression of key drug-metabolizing enzymes such as CYP3A and CYP2C. Our recent study revealed that treatment with rodent-specific PXR agonist pregnenolone-16α-carbonitrile (PCN) significantly induced hepatomegaly and promoted liver regeneration after two-thirds partial hepatectomy (PHx) in mice. However, it remains unclear whether PXR activation induces hepatomegaly and liver regeneration and simultaneously promotes metabolic function of the liver. Here, we investigated the metabolism activity of CYP1A2, CYP3A1/2 and CYP2C6/11 during PXR activation-induced liver enlargement and regeneration in rats after cocktail dosing of CYP probe drugs. For PCN-induced hepatomegaly, a notable increase in the metabolic activity of CYP3A1/2 and CYP2C6/11, as evidenced by the plasma exposure of probe substrates and the AUC ratios of the characteristic metabolites to its corresponding probe substrates. The metabolic activity of CYP1A2, CYP3A1/2 and CYP2C6/11 decreased significantly after PHx. However, PCN treatment obviously enhanced the metabolic activity of CYP2C6/11 and CYP3A1/2 in PHx rats. Furthermore, the protein expression levels of CYP3A1/2 and CYP2C6/11 in liver were up-regulated. Taken together, this study demonstrates that PXR activation not only induces hepatomegaly and liver regeneration in rats, but also promotes the protein expression and metabolic activity of the PXR downstream metabolizing enzymes such as CYP3A1/2 and CYP2C6/11 in the body.

Physiologically based pharmacokinetic model combined with reverse dose method to study the nephrotoxic tolerance dose of tacrolimus

Nephrotoxicity is the most common side effect that severely limits the clinical application of tacrolimus (TAC), an immunosuppressive agent used in kidney transplant patients. This study aimed to explore the tolerated dose of nephrotoxicity of TAC in individuals with different CYP3A5 genotypes and liver conditions. We established a human whole-body physiological pharmacokinetic (WB-PBPK) model and validated it using data from previous clinical studies. Following the injection of 1 mg/kg TAC into the tail veins of male rats, we developed a rat PBPK model utilizing the drug concentration-time curve obtained by LC-MS/MS. Next, we converted the established rat PBPK model into the human kidney PBPK model. To establish renal concentrations, the BMCL5 of the in vitro CCK-8 toxicity response curve (drug concentration range: 2-80 mol/L) was extrapolated. To further investigate the acceptable levels of nephrotoxicity for several distinct CYP3A5 genotypes and varied hepatic function populations, oral dosing regimens were extrapolated utilizing in vitro-in vivo extrapolation (IVIVE). The PBPK model indicated the tolerated doses of nephrotoxicity were 0.14-0.185 mg/kg (CYP3A5 expressors) and 0.13-0.155 mg/kg (CYP3A5 non-expressors) in normal healthy subjects and 0.07-0.09 mg/kg (CYP3A5 expressors) and 0.06-0.08 mg/kg (CYP3A5 non-expressors) in patients with mild hepatic insufficiency. Further, patients with moderate hepatic insufficiency tolerated doses of 0.045-0.06 mg/kg (CYP3A5 expressors) and 0.04-0.05 mg/kg (CYP3A5 non-expressors), while in patients with moderate hepatic insufficiency, doses of 0.028-0.04 mg/kg (CYP3A5 expressors) and 0.022-0.03 mg/kg (CYP3A5 non-expressors) were tolerated. Overall, our study highlights the combined usage of the PBPK model and the IVIVE approach as a valuable tool for predicting toxicity tolerated doses of a drug in a specific group.

Approaching treatment for immunological rejection of living-donor liver transplantation in rats

Background

The anti-immunological rejection therapy for small-for-size syndrome (SFSS) after live donor liver transplantation (LDLT) play a central role in keeping graft survival. The hepatocyte number and grafts function has undergone real-time changes with the proliferation and apoptosis of the grafts after reperfusion. Lacking an accurate and effective treatment regiments or indicators to guide the use of immunosuppressive drugs in SFS liver transplantation has made immunotherapy after SFS liver transplantation an urgent problem to be solved. Herein, we established small-for-size (SFS) and normal size liver transplantation model in rats to explore the effective indicators in guiding immunotherapy, to find an effective way for overcoming SFSS.

Methods

Lewis rats (donors) and BN rats (recipients) were used to mimic allograft liver transplantation and treated with tacrolimus. Local graft immune response was analyzed through haematoxylin and eosin and immunohistochemistry. Flow cytometry was used to assess the overall immune status of recipient. The pharmacokinetics mechanism of immunosuppressive drugs was explored through detecting CYP3A2 expression at mRNA level and protein levels.

Results

The results showed the local immune reaction of SFS grafts and systemic immune responses of recipient were significantly increased compared with those in normal size grafts and their recipient at four days after liver transplantation. Regression equation was used to regulate the tacrolimus dose which not only controlled tacrolimus serum concentration effectively but alleviated liver damage and improved survival rate.

Conclusions

This study showed that AST level and tacrolimus serum concentrations are effective indicators in guiding immunotherapy. Regression equation (T_D = − 0.494T_C-0.0035AST + 260.487) based on AST and tacrolimus serum concentration can be used as a reference for adjustment of immunotherapy after SFS liver transplantation, which is applicable in clinical practice.

Clickable, acid labile immunosuppressive prodrugs forin vivotargeting

Clickable immunosuppressive prodrugs enablein vivoreplenishment of drugs in biomaterial depots to maintain long-term immunosuppression in tissue/organ transplantation.

Pharmacokinetics of drugs in adult living donor liver transplant patients: regulatory factors and observations based on studies in animals and humans

INTRODUCTION

Limited information is available on the pharmacokinetics of drugs in the donors and recipients following adult living donor liver transplantation (LDLT). Given that both the donors and recipients receive multiple drug therapies, it is important to assess the pharmacokinetics of drugs used in these patients.

AREAS COVERED

Pathophysiological changes that occur post-surgery and regulatory factors that may influence pharmacokinetics of drugs, especially hepatic drug metabolism and transport in both LDLT donors and the recipients are discussed. Pharmacokinetic data in animals with partial hepatectomy are presented. Clinical pharmacokinetic data of certain drugs in LDLT recipients are further reviewed.

EXPERT OPINION

It takes up to six months for the liver volume to return to normal after LDLT surgery. In the LDLT recipients, drug exposure generally is higher with lower clearance during early period post-transplant; lower initial dosages of immunosuppressants are used than deceased donor liver transplant recipients during the first six months post-transplantation. In animals, the activities of hepatic drug metabolizing enzymes and transporters are known to be altered differentially during liver regeneration. Future studies on the actual hepatic function with reference to drug metabolism, drug transport, and biliary secretion in both LDLT donors and recipients are required.

Effects of Pringle maneuver and partial hepatectomy on the pharmacokinetics and blood-brain barrier permeability of sodium fluorescein in rats

Liver diseases are known to affect the function of remote organs. The aim of the present study was to investigate the effects of Pringle maneuver, which results in hepatic ischemia-reperfusion (IR) injury, and partial hepatectomy (Hx) on the pharmacokinetics and brain distribution of sodium fluorescein (FL), which is a widely used marker of blood-brain barrier (BBB) permeability. Rats were subjected to Pringle maneuver (total hepatic ischemia) for 20 min with (HxIR) or without (IR) 70% hepatectomy. Sham-operated animals underwent laparotomy only. After 15 min or 8h of reperfusion, a single 25-mg/kg dose of FL was injected intravenously and serial (0-30 min) blood and bile and terminal brain samples were collected. Total and free (ultrafiltration) plasma, total brain homogenate, and bile concentrations of FL and/or its glucuronidated metabolite (FL-Glu) were determined by HPLC. Both IR and HxIR caused significant reductions in the biliary excretions of FL and FL-Glu, resulting in significant increases in the plasma AUC of the marker. Additionally, the free fraction of FL in plasma was significantly increased by HxIR. Although the brain concentrations of FL were increased by almost twofold in both IR and HxIR animals, the brain concentrations corrected by the free FL AUC (and not the total AUC) were similar in both groups at either time points. It is concluded that Pringle maneuver and/or partial hepatectomy substantially alters the hepatobiliary disposition, plasma AUC, plasma free fraction, and brain accumulation of FL without altering the BBB permeability to the marker.

Comparison of pharmacokinetics of mycophenolic acid and its metabolites between living donor liver transplant recipients and deceased donor liver transplant recipients

Living-donor liver transplantation (LDLT) has been considered an alternative method for treatment of patients with end-stage liver disease. However, the characteristics of pharmacokinetics of mycophenolic acid (MPA) in patients who underwent LDLT were not clear. This study was designed to compare the pharmacokinetics of MPA and its metabolites between LDLT patients and deceased donor liver transplant (DDLT) patients after oral administration of mycophenolate mofetil (MMF). Thirteen patients who underwent LDLT and 14 patients who underwent DDLT were enrolled prospectively. All patients received oral MMF administration (1.0 g, twice daily) in combination with tacrolimus (TAC). The plasma concentrations of MPA, free MPA, glucuronide (MPAG), and acyl glucuronide (AcMPAG) was determined by high-performance liquid chromatography method. There was a wide variation in various pharmacokinetic parameters of MPA and its metabolites in patients who underwent LDLT and DDLT after oral MMF administration. Although mean MPA area under the plasma concentration time curve for 0-12 hours (AUC(0-12h)) of MPA and MPAG in DDLT patients were higher than those in LDLT patients, there was no significant difference between the two groups. MPA concentration at 6 hours (C(6h)), C(10h), C(12h), and MPA AUC(6-12h) were significantly higher in DDLT group than those in LDLT group (P < 0.05). Inversely, higher free MPA AUC(0-12h) and significant free MPA fraction (P < 0.05) in LDLT patients were observed in DDLT patients when compared with DDLT group. AcMPAG concentrations at 4, 8, and 10 hours and AcMPAG AUC(0-12h) were significantly higher in the DDLT group (P < 0.05). In conclusion, after a fixed oral dose of MMF, DDLT patients had higher enterohepatic recycling contributing to total MPA exposure compared with LDLT patients. The function of glucuronide conjugation in LDLT patients was decreased compared with that in DDLT patients. Higher free MPA AUC(0-12h) and a significantly higher fraction of free MPA in LDLT patients suggested that a lower oral dose of MMF may be administered for patients who underwent LDLT.

Optimal administration of tacrolimus in reduced-size liver

The optimal administration of immunosuppressants such as tacrolimus (Tac) for small-for-size (SFS) grafts, where the functional liver mass is small and must regenerate, has not been reported so far. The aim of this study is to clarify the characteristics of Tac metabolism according to liver volume. Seven-week-old male Wistar rats were randomly divided into three groups: (1) Tac administrated and 70% Hx group (Tac 70% Hx group), (2) Tac administrated and 90% Hx group (Tac 90% Hx group), and (3) vehicle administrated and 90% Hx group (control 90% Hx group). In both the Tac groups, Tac (0.3 mg/kg) was given daily for 3 days before operation, and daily after surgery until sacrifice (each time point; n = 5). The plasma concentration of Tac (trough level), as well as liver toxicity, were measured. The plasma concentration of Tac in the Tac 90% Hx group was significantly higher than in the Tac 70% Hx group from 24 to 72 h after operation. Furthermore, expression of CYP3AII mRNA was significantly lower in the Tac 90% Hx group than in the Tac 70% Hx group. Regarding the liver toxicity, there was no significant difference in both the Tac 90% Hx and the control 90% Hx groups. In this experimental study, the plasma concentration of Tac was dependent on the remnant liver volume. Therefore, special attention in regard to Tac administration should also be taken for patients with SFS grafts in living-donor liver transplantation (LDLT).

Pharmacokinetics of diclofenac in rats intoxicated with CCL4, and in the regenerating liver

The pharmacokinetics of an intravenous and oral diclofenac dose of 3.2 mg/kg was studied in male Wistar rats under control conditions, 1 and 3 days after liver damage and regeneration induced by an oral injection of CCl(4). One day after CCl(4) administration, indicators of necrosis (alanine aminotransferase), cholestasis (gamma-glutamyl transpeptidase) and regeneration (alpha-fetoprotein) were significantly increased; these effects were reversed after 3 days. In nonintoxicated rats, t(1/2) was 43.83 +/- 4.95 min, V(d) was 0.37 +/- 0.04 l/kg, Cl was 129.21 +/- 9.20 ml/min kg, AUC(i.v.) was 25.62 +/- 1.45 microg/min ml, and AUC(p.o.) was 20.21 +/- 1.03. One day after intoxication, when the liver was damaged and regenerating, the metabolism was decreased: diclofenac t(1/2) was increased to 258.21 +/- 30.80 min but V(d) did not change significantly, therefore Cl was reduced to 32.81 +/- 3.38 ml/min kg. By day 3 after intoxication, liver function, regeneration and pharmacokinetics returned to normal. The results show that liver damage and regeneration increases the bioavailability by decreasing elimination. The present observations suggest that reduction of the pharmacokinetic parameters may lead to drug accumulation in the regenerating-damaged liver with an attendant possible increase in toxic effects. The results in rats, also suggest that once hepatic injury is finished and regeneration is complete, diclofenac can be administered normally.

Factors affecting the apparent clearance of tacrolimus in Korean adult liver transplant recipients

STUDY OBJECTIVE

To identify the factors affecting tacrolimus apparent total body clearance (Cl/F [F = bioavailability]) in adult liver transplant recipients.

DESIGN

Population pharmacokinetic analysis using data from a retrospective chart review.

SETTING

University-affiliated hospital in Seoul, South Korea.

PATIENTS

Fifty-one adult liver transplant recipients who had received tacrolimus after transplantation.

MEASUREMENTS AND MAIN RESULTS

Data on 35 adult liver transplant recipients for model building and 16 patients for model validation were obtained retrospectively. Population average parameter estimates of Cl/F and apparent volume of distribution (V/F) were sought by using the nonlinear mixed-effect model (NONMEM) program. A number of clinical covariates were screened for their influence on these pharmacokinetic parameters. The final optimal population model related Cl/F to total bilirubin, early (< or = 3 days) and late (> 35 days) postoperative days, international normalized ratio (INR), and graft:recipient weight ratio (GRWR). The NONMEM estimates indicated that the Cl/F of tacrolimus was decreased in patients with a small graft, hyperbilirubinemia, and a high INR. In addition, the Cl/F of tacrolimus almost doubled 4 days after transplantation, but decreased with an increase in duration of therapy after day 35. Mean prediction error and mean absolute prediction error were 0.26 and 3.78 ng/ml, respectively, for the validation sample. A final analysis in all 51 patients, which consisted of 1775 blood samples for concentration measurements, identified the following regression model: Cl/F (L/hr) = (0.36 + 2.01/POD * L) * TBIL(-0.23 (TBIL = 1 if TBIL level < or = 1.2 mg/dl, otherwise TBIL = TBIL level)) *49((if POD < or = 3 days)) * 0.75((if INR > 1.4)) * 0.86((if GRWR < or = 1.25%)) * WT, where L was 1 if postoperative day (POD) was greater than 35 days, otherwise L was 0; V/F was 568 L, TBIL was total bilirubin, and WT was body weight. The interindividual variabilities (coefficients of variation) in Cl/F and V/F were 35.35% and 68.12%, respectively. The residual variability was 3.14 ng/ml.

CONCLUSION

These findings could be useful to the health care provider for adjustment of tacrolimus dosage in adult liver transplant recipients with various clinical factors.

Immunosuppression using the mTOR inhibition mechanism affects replacement of rat liver with transplanted cells

Successful grafting of tissues or cells from mismatched donors requires systemic immunosuppression. It is yet to be determined whether immunosuppressive manipulations perturb transplanted cell engraftment or proliferation. We used syngeneic and allogeneic cell transplantation assays based on F344 recipient rats lacking dipeptidyl peptidase IV enzyme activity to identify transplanted hepatocytes. Immunosuppressive drugs used were tacrolimus (a calcineurin inhibitor) and its synergistic partners, rapamycin (a regulator of the mammalian target of rapamycin [mTOR]) and mycophenolate mofetil (an inosine monophosphate dehydrogenase inhibitor). First, suitable drug doses capable of inducing long-term survival of allografted hepatocytes were identified. In pharmacologically effective doses, rapamycin enhanced cell engraftment by downregulating hepatic expression of selected inflammatory cytokines but profoundly impaired proliferation of transplanted cells, which was necessary for liver repopulation. In contrast, tacrolimus and/or mycophenolate mofetil perturbed neither transplanted cell engraftment nor their proliferation. Therefore, mTOR-dependent extracellular and intracellular mechanisms affected liver replacement with transplanted cells. In conclusion, insights into the biological effects of specific drugs on transplanted cells are critical in identifying suitable immunosuppressive strategies for cell therapy.

Activity and expression of various isoforms of uridine diphosphate glucuronosyltransferase are differentially regulated during hepatic regeneration in rats

PURPOSE

Glucuronidation pathway is very important in the detoxification of endogenous and exogenous compounds. The objective of this study was to evaluate the activity and expression of various hepatic uridine diphosphate glucuronosyltransferases (UGTs) in rats at various time points after initiation of hepatic regeneration by partial hepatectomy (PHx).

METHODS

The mRNA expression of various UGTs was evaluated using real-time polymerase chain reaction (real-time PCR) with specific primers. The in vitro activity of UGTs was evaluated using different substrates such as estradiol (UGT1A1), acetaminophen (UGT1A6/7), morphine (UGT2B1), testosterone (UGT2B1/3/6), androsterone (UGT2B2), and (-)-borneol (UGT2B12).

RESULTS

Whereas the activity and mRNA expression of UGT1A1, UGT2B1, UGT2B1/3/6, UGT2B2, and UGT2B12 were lower, the activity and mRNA expression of UGT1A6/7 were preserved during hepatic regeneration. The mRNA expression of UGT2B8 was down-regulated, whereas the mRNA expression of UGT1A5 and UGT1A8 was not altered by PHx. The mRNA expression of UGT1A2 and UGT1A3 was increased during hepatic regeneration.

CONCLUSION

UGT-mediated drug-metabolizing ability of the liver was altered differentially in the regenerating rat liver. Individualized dosing regimen for different UGT substrates may be needed when using such substrates of these enzymes in patients with a regenerating liver, especially during the early postoperative period. However, the glucuronide conjugating capacity of the liver in the donor of a living donor liver transplantation is expected to completely return to normal with time after surgery.

AN INVESTIGATION OF HUMAN AND RAT LIVER MICROSOMAL MYCOPHENOLIC ACID GLUCURONIDATION: EVIDENCE FOR A PRINCIPAL ROLE OF UGT1A ENZYMES AND SPECIES DIFFERENCES IN UGT1A SPECIFICITY

Mycophenolic acid (MPA; 1,3-dihydro-4-hydroxy-6-methoxy-7-methyl-3-oxo-5-isobenzylfuranyl)-4-methyl-4-hexenoate), the active metabolite of the immunosuppressant prodrug, mycophenolate mofetil, undergoes glucuronidation to its 7-O-glucuronide as a primary route of metabolism. Because differences in glucuronidation may influence the efficacy and/or toxicity of MPA, we investigated the MPA UDP-glucuronosyltransferase (UGT) activities of human liver microsomes (HLMs) and rat liver microsomes with the goal of identifying UGTs responsible for MPA catalysis. HLMs (n = 23) exhibited higher average MPA glucuronidation rates (14.7 versus 6.0 nmol/mg/min, respectively, p < 0.001) and higher apparent affinity for MPA (K(m) = 0.082 mM versus 0.20 mM, p < 0.001) compared with rat liver microsomes. MPA UGT activities were reduced >80% in liver microsomes from Gunn rats. To identify the active enzymes, human and rat UGT1A enzymes were screened for MPA-glucuronidating activity. UGT1A9 was the only human liver-expressed UGT1A enzyme with significant activity and exhibited both high affinity (K(m) = 0.077 mM) and high activity (V(max) = 28 nmol x min(-1) x mg(-1)). Spearman correlation analyses revealed a stronger relationship between HLM MPA UGT activities and 1A9-like content (r(2) = 0.79) relative to 1A1 (r(2) = 0.20), 1A4-like (r(2) = 0.22), and 1A6 (r(2) = 0.41) protein. A different profile was observed for rat with three active liver-expressed UGT1A enzymes: 1A1 (medium affinity/capacity), 1A6 (low affinity/medium capacity), and 1A7 (high affinity/capacity). Our data suggest that UGT1A enzymes are the major contributors to hepatic MPA metabolism in both species, but 1A9 is dominant in human, whereas 1A1 and 1A7 are likely the principal mediators in control rat liver. This information should be useful for interpretation of MPA pharmacokinetic and toxicity data in clinical and animal studies.