Acetaminophen elimination half-life in humans is unaffected by short-term consumption of sulfur amino acid-free diet

A new experimental model to study human drug responses

Accurate prediction of pharmacokinetic (PK) and pharmacodynamic (PD) characteristics is critical for drug development. Oral drugs are particularly difficult because they are absorbed by the intestine and metabolized in the liver before systemic metabolism in vivo; this is called the first-pass effect and is a critical factor for predicting oral bioavailability (BA). Here, we fabricated a new networking and circulating cell culture system (NCCS), mimicking the circulatory system and interaction of organs for studying the pharmacokinetic and pharmacodynamics of oral drugs in vitro. NCCS consisted of a micro-pump for circulating fluids, two types of multi-insert culture dishes for culturing different cell types, and an orbital shaker for mixing; flow rate and shaking-speed were controlled by weight-sensors and drivers. A first-pass effect test was performed using functionally differentiated HepaRG and Caco-2 cell lines, using a new modified spheroid forming unit (SFU) protocol. To verify the similarity of PK (first-pass effect) data of NCCS with the data from the human body, 15 reference drugs were chosen and their associated data were obtained by liquid chromatography-mass spectrometry analysis. NCCS generated absorption and metabolism data showed >70% similarity to human data respectively. NCCS can also be used to demonstrate species differences. Animal models are the primary basis for drug discovery, development, and testing. However, the weak correlation between humans and animals, particularly regarding absorption and metabolism, is a substantial limitation for the use of animal models. Here we compare human and mouse acetaminophen (APAP) metabolism using NCCS, and its application can be extended to assess cellular responses, such as efficacy and toxicity, simultaneously.

Co-culture with mouse embryonic fibroblasts improves maintenance of metabolic function of human small hepatocyte progenitor cells

Derivation and culture of small hepatocyte progenitor cells (SHPCs) capable of proliferating in vitro has been described in rodents and recently in humans. These cells are capable of engrafting in injured livers, however, they display de-differentiated morphology and reduced xenobiotic metabolism activity in culture over passages. Here we report that SHPCs derived from adult primary human hepatocytes (PHHs) and cultured on mouse embryonic fibroblasts (MEFs) not only display differentiated morphology and exhibit gene expression profiles similar to adult PHHs, but importantly, they retain their phenotype over several passages. Further, unlike previous reports, where extensive manipulations of culture conditions are required to convert SHPCs to metabolically functional hepatocytes, SHPCs in our co-culture system maintain expression of xenobiotic metabolism-associated genes. We show that SHPCs in co-culture are able to perform xenobiotic metabolism at rates equal to their parent PHHs as evidenced by the metabolism of acetaminophen to all of its major metabolites. In summary, we present an improved co-culture system that allows generation of SHPCs from adult PHHs that maintain their differentiated phenotype over multiple passages. Our findings would be useful for expansion of limited PHHs for use in studies of drug metabolism and toxicity testing.

Impact of sex, age and diet on the cysteine/cystine and glutathione/glutathione disulfide plasma redox couples in mice

Age, sex and diet are well-established risk factors for several diseases. In humans, each of these variables has been linked to differences in plasma redox potentials (E_h) of the glutathione/glutathione disulfide (GSH/GSSG) and cysteine/cystine (Cys/CySS) redox couples. Mice have been very useful for modeling human disease processes, but it is unknown if age, sex and diet affect redox couples in mice as they do in humans. The purpose of the present study was to examine the effects of these factors on plasma redox potentials in C57BL/6J mice. We found that age had no effect on either redox couple in either sex. Plasma E_h Cys/CySS and E_h GSH/GSSG were both more oxidized (more positive) in females than in males. A 24-hour fast negated the sex differences in both redox potentials by oxidizing both redox couples in male mice, while having no effect on E_h Cys/CySS and a smaller effect on E_h GSH/GSSG in female mice. A diet with excess sulfur amino acids reduced the plasma E_h Cys/CySS in females to a level comparable to that seen in male mice. Thus, sex-specific differences in plasma E_h Cys/CySS could be normalized by two different dietary interventions. Some of these findings are consistent with reported human studies, while others are not. Most strikingly, mice do not exhibit age-dependent oxidation of plasma redox potentials. Care must be taken when designing and interpreting mouse studies to investigate redox regulation in humans.

An Unexpected Role of Cholesterol Sulfotransferase and its Regulation in Sensitizing Mice to Acetaminophen-Induced Liver Injury

Overdose of acetaminophen (APAP) is the leading cause of acute liver failure (ALF) in the United States. The sulfotransferase-mediated sulfation of APAP is widely believed to be a protective mechanism to attenuate the hepatotoxicity of APAP. The cholesterol sulfotransferase SULT2B1b is best known for its activity in catalyzing the sulfoconjugation of cholesterol to synthesize cholesterol sulfate. SULT2B1b can be transcriptionally and positively regulated by the hepatic nuclear factor 4α (HNF4α). In this study, we uncovered an unexpected role for SULT2B1b in APAP toxicity. Hepatic overexpression of SULT2B1b sensitized mice to APAP-induced liver injury, whereas ablation of the Sult2B1b gene in mice conferred resistance to the APAP hepatotoxicity. Consistent with the notion that Sult2B1b is a transcriptional target of HNF4α, overexpression of HNF4α sensitized mice or primary hepatocytes to APAP-induced hepatotoxicity in a Sult2B1b-dependent manner. We conclude that the HNF4α-SULT2B1b axis has a unique role in APAP-induced acute liver injury, and SULT2B1b induction might be a risk factor for APAP hepatotoxicity.

Prenatal acetaminophen affects maternal immune and endocrine adaptation to pregnancy, induces placental damage, and impairs fetal development in mice

Acetaminophen (APAP; ie, Paracetamol or Tylenol) is generally self-medicated to treat fever or pain and recommended to pregnant women by their physicians. Recent epidemiological studies reveal an association between prenatal APAP use and an increased risk for asthma. Our aim was to identify the effects of APAP in pregnancy using a mouse model. Allogeneically mated C57Bl/6J females were injected i.p. with 50 or 250 mg/kg APAP or phosphate-buffered saline on gestation day 12.5; nonpregnant females served as controls. Tissue samples were obtained 1 or 4 days after injection. APAP-induced liver toxicity was mirrored by significantly increased plasma alanine aminotransferase levels. In uterus-draining lymph nodes of pregnant dams, the frequencies of mature dendritic cells and regulatory T cells significantly increased on 250 mg/kg APAP. Plasma progesterone levels significantly decreased in dams injected with APAP, accompanied by a morphologically altered placenta. Although overall litter sizes and number of fetal loss remained unaltered, a reduced fetal weight and a lower frequency of hematopoietic stem cells in the fetal liver were observed on APAP treatment. Our data provide strong evidence that prenatal APAP interferes with maternal immune and endocrine adaptation to pregnancy, affects placental function, and impairs fetal maturation and immune development. The latter may have long-lasting consequences on children's immunity and account for the increased risk for asthma observed in humans.

Favipiravir inhibits acetaminophen sulfate formation but minimally affects systemic pharmacokinetics of acetaminophen

Aims

The antiviral agent favipiravir is likely to be co-prescribed with acetaminophen (paracetamol). The present study evaluated the possiblility of a pharmacokinetic interaction between favipiravir and acetaminophen, in vitro and in vivo.

Methods

The effect of favipivir on the transformation of acetaminophen to its glucuronide and sulfate metabolites was studied using a pooled human hepatic S9 fraction in vitro. The effect of acute and extended adminstration of favipiravir on the pharmacokinetics of acetaminophen and metabolites was evaluated in human volunteers.

Results

Favipiravir inhibited the in vitro formation of acetaminophen sulfate, but not acetaminophen glucuronide. In human volunteers, both acute (1 day) and extended (6 days) administration of favipiravir slightly but significantly increased (by about 20 %) systemic exposure to acetaminophen (total AUC), whereas C_max was not significantly changed. AUC for acetaminophen glucuronide was increased by 23 to 35 % above control by favipiravir, while AUC for acetaminophen sulfate was reduced by about 20 % compared to control. Urinary excretion of acetaminophen sulfate was likewise reduced to 44 to 65 % of control values during favipiravir co-administration, while excretion of acetaminophen glucuronide increased to 17 to 32 % above control.

Conclusion

Favipiravir inhibits acetaminophen sulfate formation in vitro and in vivo. However the increase in systemic exposure to acetaminophen due to favipiravir co-administration, though statistically significant, is small in magnitude and unlikely to be of clinical importance.

Aggregate culture of human embryonic stem cell-derived hepatocytes in suspension are an improved in vitro model for drug metabolism and toxicity testing

Early phase drug development relies on primary human hepatocytes for studies of drug metabolism, cytotoxicity, and drug-drug interactions. However, primary human hepatocytes rapidly lose metabolic functions ex vivo and are refractory to expansion in culture and thus are limited in quantity. Hepatocytes derived from human pluripotent stem cells (either embryonic stem (ES) or induced pluripotent stem (iPS) cells), have the potential to overcome many of the limitations of primary human hepatocytes, but to date the use of human pluripotent stem cell-derived hepatocytes has been limited by poor enzyme inducibility and immature metabolic function. Here, we present a simple suspension culture of aggregates of ES cell-derived hepatocytes that compared to conventional monolayer adherent culture significantly increases induction of CYP 1A2 by omeprazole and 3A4 by rifampicin. Using liquid chromatography-tandem mass spectrometry, we further show that ES cell-derived hepatocytes in aggregate culture convert omeprazole and rifampicin to their human-specific metabolites. We also show that these cells convert acetaminophen (APAP) to its cytotoxic metabolite (N-acetyl-p-benzoquinone imine (NAPQI)), although they fail to perform APAP glucuronidation. In summary, we show that human pluripotent stem cell-derived hepatocytes in aggregate culture display improved enzymatic inducibility and metabolic function and is a promising step toward a simple, scalable system, but nonetheless will require further improvements to completely replace primary human hepatocytes in drug development.

Acetaminophen metabolism after major surgery: a greater challenge with increasing age

Patients undergoing major surgery represent a good model for the study of the hepatic metabolism of acetaminophen (APAP) after surgery and for the evaluation of how the detoxification process is influenced by aging. Thirty patients received intravenous APAP (1 g/6 h) for 4 days (D1-D4). Daily 24-h urinary metabolites-cysteine-APAP, mercapturate-APAP, APAP, and glucuronide and sulfate conjugates-as well as blood glutathione levels were compared with repeated-measures analysis of variance (significance, P<0.05). Between D1 and D4, cysteine-APAP increased (308±308 mg vs. 570±512 mg, P=0.005), and sulfate and glucuronide conjugates decreased (1,365±1,084 mg vs. 694±600 mg, P<0.0001 and 2,418±817 mg vs. 1,513±1,076 mg, P=0.011, respectively). Blood glutathione decreased (790±125 vs. 623±132 µmol/l, P<0.0001. These changes increased with aging. APAP disposition after major surgery shifts toward the oxidative pathways of metabolism, and this is enhanced with aging. Supplementation with sulfur-containing amino acids should be investigated further as it might minimize the effect on antioxidant defenses, especially in older persons undergoing more extensive surgical procedures.