Prediction of human pharmacokinetics for low‐clearance compounds using pharmacokinetic data from chimeric mice with humanized livers

Development of low‐clearance (CL) compounds that are slowly metabolized is a major goal in the pharmaceutical industry. However, the pursuit of low intrinsic CL (CL_int) often leads to significant challenges in evaluating the pharmacokinetics of such compounds. Although in vitro–in vivo extrapolation is widely used to predict human CL, its application has been limited for low‐CL_int compounds because of the low turnover of parent compounds in metabolic stability assays. To address this issue, we focused on chimeric mice with humanized livers (PXB‐mice), which have been increasingly reported to accurately predict human CL in recent years. The predictive accuracy for nine low‐CL_int compounds with no significant turnover in a human hepatocyte assay was investigated using PXB‐mouse methods, such as single‐species allometric scaling (PXB‐SSS) approach and a novel physiologically based scaling (PXB‐PBS) approach that assumes that the CL_int per hepatocyte is equal between humans and PXB‐mice. The percentages of compounds with predicted CL within 2‐ and 3‐fold ranges of the observed CL for low‐CL_int compounds were 89% and 100%, respectively, for both PXB‐SSS and PXB‐PBS approaches. Moreover, the predicted CL was mostly consistent among the methods. Conversely, the percentages of compounds with predicted CL within 2‐ and 3‐fold ranges of the observed CL for low‐CL_int compounds were 50% and 63%, respectively, for multispecies allometric (MA) scaling. Overall, these PXB‐mouse methods were much more accurate than conventional MA scaling approaches, suggesting that PXB‐mice are useful tools for predicting the human CL of low‐CL_int compounds that are slowly metabolized.

Study Highlights

• WHAT IS THE CURRENT KNOWLEDGE ON THE TOPIC?

It is important to identify low‐clearance (CL) compounds that are slowly metabolized during the drug discovery process, but the ability of in vitro–in vivo extrapolation to predict human CL decreases as the value of intrinsic CL (CL_int) decreases. Although chimeric mice with humanized livers (PXB‐mice) have been reported to be useful for predicting human CL, their applicability to low‐CL_int compounds with no significant turnover in human hepatocyte assays has not been clarified.

• WHAT QUESTION DID THIS STUDY ADDRESS?

This study examined the predictive accuracy of PXB‐mouse methods for low‐CL_int compounds.

• WHAT DOES THIS STUDY ADD TO OUR KNOWLEDGE?

In addition to the previously reported single‐species allometric scaling approach, we proposed a novel physiologically based scaling approach. Both methods displayed much greater predictive accuracy for low‐CL_int compounds than conventional multispecies allometric scaling approaches.

• HOW MIGHT THIS CHANGE CLINICAL PHARMACOLOGY OR TRANSLATIONAL SCIENCE?

The findings should improve the accuracy of human pharmacokinetic prediction and enable efficient and safe first‐in‐human studies.     

Deprenyl decreases an endogenous parkinsonism-inducing compound, 1-benzyl-1,2,3,4-tetrahydroisoquinoline in mice: in vivo and in vitro studies

We examined the effect of deprenyl, a promising drug for the therapy of Parkinson's disease on the formation of a parkinsonism-inducing compound, 1-benzyl-1,2,3,4-tetrahydroisoquinoline (1BnTIQ). The 1BnTIQ content was significantly decreased in the brain of deprenyl-treated mouse in vivo, and deprenyl also inhibited 1BnTIQ formation from phenethylamine by a mouse brain homogenate supernatant in vitro. In vivo, the content of a parkinsonism-preventing compound, 1-methyl-1,2,3,4-tetrahydroisoquinoline (1MeTIQ) was slightly increased in mice injected with deprenyl. The marked decrease of the ratio of 1BnTIQ to 1MeTIQ might play a role in the clinical effect of deprenyl.     

Neuroprotective effect of 1-methyl-1,2,3,4-tetrahydroisoquinoline on cultured rat mesencephalic neurons in the presence or absence of various neurotoxins

1-Methyl-1,2,3,4-tetrahydroisoquinoline (1MeTIQ) is an endogenous brain amine and its content in parkinsonian brain is decreased compared with that in control brain. There is some evidence that 1MeTIQ protects dopaminergic neurons against dysfunction such as that seen in Parkinson's disease. In this study, we examined the neuroprotective effect of 1MeTIQ against four dopaminergic neurotoxins, 1-methyl-4-phenylpyridinuim ion, 6-hydroxydopamine, rotenone, and l-benzyl-1,2,3,4-tetrahydroisoquinoline, in cultured rat mesencephalic neurons. 1MeTIQ exerted neuroprotective action against all these toxins. Furthermore, (R)-1MeTIQ was neuroprotective, while (S)-1MeTIQ had little effect, indicating that the effect is stereoselective. The protective action of 1MeTIQ was most effective in mesencephalic neurons, especially in tyrosine hydroxylase-positive neurons. 1MeTIQ showed no affinity for dopamine receptors and did not influence the inhibition of mitochondrial respiratory complex I by rotenone, 1-methyl-4-phenylpyridinuim ion, or 1-benzyl-1,2,3,4-tetrahydroisoquinoline. These results raise the possibility that 1MeTIQ indirectly acts as an anti-oxidant such as the induction of anti-oxidative enzymes, because all these four neurotoxins can burden oxidative stress in common. This is the first report to confirm a protective effect of 1MeTIQ at the cultured neuron level, and it may have potential as a lead compound for the development of new agents to treat Parkinson's disease.     

Customized,degradable, functionally graded scaffold for potential treatment of early stage osteonecrosis of the femoral head

Osteonecrosis of the femoral head (ONFH) is a debilitating disease that results in progressive collapse of the femoral head and subsequent degenerative arthritis. Few treatments provide both sufficient mechanical support and biological cues for regeneration of bone and vascularity when the femoral head is still round and therefore salvageable. We designed and 3D printed a functionally graded scaffold (FGS) made of polycaprolactone (PCL) and β‐tricalcium phosphate (β‐TCP) with spatially controlled porosity, degradation, and mechanical strength properties to reconstruct necrotic bone tissue in the femoral head. The FGS was designed to have low porosity segments (15% in proximal and distal segments) and a high porosity segment (60% in middle segment) according to the desired mechanical and osteoconductive properties at each specific site after implantation into the femoral head. The FGS was inserted into a bone tunnel drilled in rabbit femoral neck and head, and at 8 weeks after implantation, the tissue formation as well as scaffold degradation was analyzed. Micro‐CT analysis demonstrated that the FGS‐filled group had a significantly higher bone ingrowth ratio compared to the empty‐tunnel group, and the difference was higher at the distal low porosity segments. The in vivo degradation rate of the scaffold was higher in the proximal and distal segments than in the middle segment. Histological analysis of both non‐decalcified and calcified samples clearly indicated new bone ingrowth and bone marrow‐containing bone formation across the FGS. A 3D printed PCL‐β‐TCP FGS appears to be a promising customized resorbable load‐bearing implant for treatment of early stage ONFH. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1002–1011, 2018.

     

Tributyltin-induced endoplasmic reticulum stress and its Ca-mediated mechanism

Organotin compounds, especially tributyltin chloride (TBT), have been widely used in antifouling paints for marine vessels, but exhibit various toxicities in mammals. The endoplasmic reticulum (ER) is a multifunctional organelle that controls post-translational modification and intracellular Ca^2 + signaling. When the capacity of the quality control system of ER is exceeded under stress including ER Ca^2 + homeostasis disruption, ER functions are impaired and unfolded proteins are accumulated in ER lumen, which is called ER stress. Here, we examined whether TBT causes ER stress in human neuroblastoma SH-SY5Y cells. We found that 700 nM TBT induced ER stress markers such as CHOP, GRP78, spliced XBP1 mRNA and phosphorylated eIF2α. TBT also decreased the cell viability both concentration- and time-dependently. Dibutyltin and monobutyltin did not induce ER stress markers. We hypothesized that TBT induces ER stress via Ca^2 + depletion, and to test this idea, we examined the effect of TBT on intracellular Ca^2 + concentration using fura-2 AM, a Ca^2 + fluorescent probe. TBT increased intracellular Ca^2 + concentration in a TBT-concentration-dependent manner, and Ca^2 + increase in 700 nM TBT was mainly blocked by 50 μM dantrolene, a ryanodine receptor antagonist (about 70% inhibition). Dantrolene also partially but significantly inhibited TBT-induced GRP78 expression and cell death. These results suggest that TBT increases intracellular Ca^2 + concentration by releasing Ca^2 + from ER, thereby causing ER stress.     

International comparison of medical students' perceptions of HIV infection and AIDS.

This analysis compared medical students'' perceptions of human immunodeficiency virus (HIV) infection and acquired immunodeficiency syndrome (AIDS) in two cities in two countries with different cultural and educational backgrounds. A total of 292 first- and second-year medical students (45% sample) were surveyed from New Jersey Medical School and from Benin Medical School, Nigeria. Compared with the Benin students, the Newark medical students were significantly more knowledgeable and had more positive attitudes and behaviors regarding HIV infection and AIDS. Misperceptions regarding certain modes of transmission of HIV were significantly higher among the Benin students than the Newark students. Compared with the Benin students, the Newark students had more frequent sexual intercourse and used condoms more frequently, but the Benin students had more sex partners. Perception of personal risk and concern of contracting AIDS was significantly higher among the Newark students than the Benin students. These results indicate it is important that medical educators in medical schools convey accurate information to improve medical students'' perception regarding HIV infection and AIDS.     

Cytotoxicity of 17 tetrahydroisoquinoline derivatives in SH-SY5Y human neuroblastoma cells is related to mitochondrial NADH-ubiquinone oxidoreductase inhibition

Since the first report that 1-methyl-4-phenyl-l,2,3,6-tetrahydropyridine induces parkinsonism, various kinds of low-molecular-weight neurotoxins, such as tetrahydroisoquinoline derivatives, have been identified as possible Parkinson's disease-inducing substances. In the present study, we measured four parameters of 17 tetrahydroisoquinoline derivatives, i.e., cytotoxicity in SH-SY5Y human neuroblastoma cells, inhibitory activity towards mitochondrial NADH-ubiquinone oxidoreductase (complex I), affinity for dopamine transporter, and 1-butanol-H2O partition coefficient (as an index of lipophilicity). Six of the derivatives showed comparatively strong inhibitory activity towards complex I (IC50 values<100 microM) and five of them were cytotoxic to SH-SY5Y cells (TC50 values<200 microM). Some of these compounds are endogenous. We found good correlations between cytotoxicity and complex I inhibitory activity, but not between cytotoxicity and affinity for dopamine transporter. Since cytotoxicity to SH-SY5Y neuroblastoma cells was related to inhibitory activity towards mitochondrial complex I, complex I inhibition is likely to be involved, at least in part, in the mechanism of TIQ derivative-induced cell death. Uptake of most of these compounds seems to be dependent on lipophilicity, rather than active transport via dopamine transporter.     

Accuracy of PET for diagnosis of solid pulmonary lesions with 18F-FDG uptake below the standardized uptake value of 2.5.

Benign and malignant pulmonary lesions usually are differentiated by 18F-FDG PET with a semiquantitative 18F-FDG standardized uptake value (SUV) of 2.5. However, the frequency of malignancies with an SUV of <2.5 is significant, and pulmonary nodules with low 18F-FDG uptake often present diagnostic challenges. METHODS: Among 360 consecutive patients who underwent 18F-FDG PET to evaluate pulmonary nodules found on CT, we retrospectively analyzed 43 who had solid pulmonary lesions (excluding lesions with ground-glass opacity, infiltration, or benign calcification) with an SUV of <2.5. The uptake of 18F-FDG was graded by a visual method (absent, faint, moderate, or intense) and 2 semiquantitative methods (SUV and contrast ratio [CR]). Final classification was based on histopathologic findings or at least 6 mo of clinical follow-up. RESULTS: We found 16 malignant (diameter, 8-32 mm) and 27 benign (7-36 mm) lesions. When faint visual uptake was the cutoff for positive 18F-FDG PET results, the receiver-operating-characteristic (ROC) analysis correctly identified all 16 malignancies and yielded false-positive results for 10 of 27 benign lesions. Sensitivity was 100%, specificity was 63%, and the positive and negative predictive values were 62% and 100%, respectively. When an SUV of 1.59 was the cutoff for positive 18F-FDG PET results, the ROC analysis revealed 81% sensitivity, 85% specificity, and positive and negative predictive values of 77% and 89%, respectively. At a cutoff for positive 18F-FDG PET results of a CR of 0.29, the ROC analysis revealed 75% sensitivity, 82% specificity, and positive and negative predictive values of 71% and 85%, respectively. The areas under the curve in ROC analyses did not differ significantly among the 3 analyses (visual, 0.84; SUV, 0.81; and CR, 0.82). Analyses of intra- and interobserver variabilities indicated that visual and SUV analyses were quite reproducible, whereas CR analysis was poorly reproducible. CONCLUSION: These results suggested that for solid pulmonary lesions with low 18F-FDG uptake, semiquantitative approaches do not improve the accuracy of 18F-FDG PET over that obtained with visual analysis. Pulmonary lesions with visually absent uptake indicate that the probability of malignancies is very low. In contrast, the probability of malignancy in any visually evident lesion is about 60%.     

Defective Hepatic Anion Transport in Variegate Porphyria

A 29-yr-old man with neurological symptoms that included tremor, dysarthria, and loss of consciousness was diagnosed as having variegate porphyria, because of increased urinary excretion of delta-aminolevulinic acid, porphobilinogen, uroporphyrin, and coproporphyrin, and increased fecal uro-, copro-, and protoporphyrins. He showed marked retention of indocyanine green (R15 min: 53%-78%) and bromosulfophthalein (R45 min: 24%-10%) as well. The kinetic analysis revealed that both hepatic uptake and hepatic excretion were decreased for both dyes. Results of other liver function tests were unremarkable except for intermittent hyperbilirubinemia (0.7-3.3 mg/100 ml), of which the ratio of conjugated and unconjugated fraction was between 0.7 and 1.2. Binding of serum protein and indocyanine green or bromosulfophthalein was normal. An angiographic and scintigraphic study of the liver was normal. A minimal deposition of hemosiderin pigment was found in liver biopsy specimen without other abnormalities. Deposition of porphyrin was not present in the liver. Plasma exchange and erythrocytapheresis did not show any beneficial effects on the clinical and laboratory abnormalities of the patient. A possible relationship between variegate porphyria and defective hepatic anion transport is discussed.     

An enzymatic defect in the obese (ob/ob) mouse: Loss of thyroid-induced sodium- and potassium-dependent adenosinetriphosphatase

Genetically obese (ob/ob) mice, mice that became obese after treatment with gold thioglucose, and lean animals were studied in the euthyroid state, after induction of hypothyroidism, and after treatment with triiodothyronine. The activity of glycerol 3-phosphate dehydrogenase (sn-glycerol-3-phosphate:(acceptor) oxidoreductase; EC 1.1.99.5] was reduced in the livers from hypothyroid animals and was increased by treatment with triiodothyronine in all groups. The activity of the ouabain-suppressible sodium- and potassium-dependent ATPase (ATP phosphohydrolase; EC 3.6.1.3) was increased by triiodothyronine and reduced by hypothyroidism in the lean and gold thioglucose-treated obese animals. In the obese (ob/ob) mice, on the other hand, treatment with triiodothyronine did not increase the activity of this enzyme, which remained at the level found in hypothyroid animals. This enzymatic activity was reduced in both liver and kidney. Adenylate cyclase [ATP pyrophosphate-lyase (cyclizing); EC 4.6.1.1] activity in liver membranes, however, was similar in all three groups of mice. This enzyme complex was activated by glucagon and was unaffected by treatment with thyroid hormones. The lack of a thyroid-dependent ouabain-suppressible (Na(+) + K(+))-ATPase in the tissues of the obese (ob/ob) mouse could explain most, if not all, of the abnormalities that have been described in this animal.