A pharmacokinetic model of the liver

The liver is the major organ where chemical breakdown of organic and inorganic compounds takes place. A pharmacokinetic heterogeneous model was developed for the local anesthetic and antiarrhythmic drug lidocaine. It was assumed that transport and elimination of lidocaine and its metabolites are linear with concentration. Simulations were done using VisSim software on a 486 based personal computer to obtain concentration profiles for hepatic clearance and for step input of the drug and its metabolites. It was found that the rate of uptake and rate of breakdown were 0.48 min-1 and 0.49 min-1 respectively for lidocaine. The results are consistent with published data. Similar simulations were done for the lidocaine metabolites MEGX and 3-OHLID. The same heterogeneous model was used with appropriate changes to include cellular inactivation of the drug and urine output in order to model another antiarrthymic drug, procainamide. Simulations were done for hepatic clearance and for bolus (impulse) input to the model. The rate of uptake and rate of release for procainamide were found to be 9.35 min-1. The rate of breakdown and urine output were 0.0053 min-1 and 0.0013 min-1 respectively.Finally, a parameter sensitivity study was done for both lidocaine and its metabolites and procainamide in order to determine sensitivity of the model to the parameters used. The maximum values of rate constants for which the model can operate in stable range were determined. Finally, a parameter sensitivity study was done for both lidocaine and its metabolites and procainamide in order to determine sensitivity of the model to the parameters used. The maximum values of rate constants for which the model can operate in stable range were determined

An Evaluation of the Disposition of R941000, a Tetrazolone-Telmisartan Analog: A Case Study of the Suitability of Tetrazolone As a Carboxylic Acid Bioisostere

Carboxylic acids are ubiquitous in medicinal compounds, such as nonsteroidal anti-inflammatories, statins, hypertensives, and anticoagulants. Despite their prolific use, unfavorable characteristics such as metabolic instability, poor membrane permeability, and toxicity have been associated with this moiety in some instances. Bioisosteres have been employed to attenuate these issues. However, bioisostere use can alter drug potency and disposition. Recently, our company demonstrated the feasibility of the tetrazolone moiety as a carboxylic acid bioisostere for the angiotensin II antagonist telmisartan. R941000 (telmisartan-tetrazolone analog) was a potent in vitro inhibitor of angiotensin II and possessed a similar disposition to telmisartan. To the best of our knowledge, no studies of the changes in disposition caused by bioisosteric replacement of a carboxylic acid with a tetrazolone have been published. In this work, the disposition of R941000 was evaluated in Sprague Dawley rats, and in vitro metabolism was conducted using human and rat hepatocytes and supplemented microsomes. Results indicated comparable PK parameters for R941000 relative to telmisartan, respectively, bioavailability (64.7% vs 59.2%), exposure (2610 ngL/h vs 1850 ngL/h) Clpred (4.51 ml/min vs 7.23 ml/min) t1/2 (5.37h vs 3.64 h) and Vss (1.67L/kg vs 1.59L/kg). Both compounds underwent biliary excretion, and glucuronide metabolites were found in rat bile; however, no significant glucuronidation was observed in in vitro assays. Additional studies utilizing tetrazolone bioisosteres in other species and classes of compounds are needed to further characterize their utility as a carboxylic acid substitute

High Resolution Maps of the Vasculature of An Entire Organ

The structure of vascular networks represents a great, unsolved problem in anatomy. Network geometry and topology differ dramatically from left to right and person to person as evidenced by the superficial venation of the hands and the vasculature of the retinae. Mathematically, we may state that there is no conserved topology in vascular networks. Efficiency demands that these networks be regular on a statistical level and perhaps optimal. We have taken the first steps towards elucidating the principles underlying vascular organization, creating the rst map of the hierarchical vasculature (above the capillaries) of an entire organ. Using serial blockface microscopy and fluorescence imaging, we are able to identify vasculature at 5 μm resolution. We have designed image analysis software to segment, align, and skeletonize the resulting data, yielding a map of the individual vessels. We transformed these data into a mathematical graph, allowing computationally efficient storage and the calculation of geometric and topological statistics for the network. Our data revealed a complexity of structure unexpected by theory. We observe loops at all scales that complicate the assignment of hierarchy within the network and the existence of set length scales, implying a distinctly non-fractal structure of components within

Nrf2/HO-1, NF-κB and PI3K/Akt signalling pathways decipher the therapeutic mechanism of pitavastatin in early phase liver fibrosis in rats

Liver fibrosis is a common chronic hepatic disease. This study aimed to investigate the effect of pitavastatin (Pit) against thioacetamide (TAA)-induced liver fibrosis. Rats were divided into four groups: (1) control group; (2) TAA group (100 mg/kg, i.p.) three times weekly for 2 weeks; (3 and 4) TAA/Pit-treated group, in which Pit was administered orally (0.4 and 0.8 mg/kg/day) for 2 weeks following TAA injections. TAA caused liver damage manifested by elevated serum transaminases, reduced albumin and histological alterations. Hepatic malondialdehyde (MDA) was increased, and glutathione (GSH) and superoxide dismutase (SOD) were decreased in TAA-administered rats. TAA upregulated the inflammatory markers NF-κB, NF-κB p65, TNF-α and IL-6. Treatment with Pit ameliorated serum transaminases, elevated serum albumin and prevented histopathological changes in TAA-intoxicated rats. Pit suppressed MDA, NF-κB, NF-κB p65, the inflammatory cytokines and PI3K mRNA in TAA-intoxicated rats. In addition, Pit enhanced hepatic antioxidants and boosted the nuclear factor erythroid 2–related factor 2 (Nrf2) and heme oxygenase-1 (HO-1) mRNA. Moreover, immunohistological studies supported the ability of Pit to reduce liver fibrosis via suppressing p-AKT expression. In conclusion, Pit effectively prevents TAA-induced liver fibrosis by attenuating oxidative stress and the inflammatory response. The hepatoprotective efficacy of Pit was associated with the upregulation of Nrf2/HO-1 and downregulation of NF-κB and PI3K/Akt signalling pathways

Emulsion Templated Porous Polymers as Scaffolds for 3D Hepatocyte Culture

Hepatocytes are the main functional cells of the liver and are used extensively in vitro for predicting in vivo drug toxicity profiles. However, the predictive accuracy of in vitro hepatocyte models depends on the physiological relevance of the artificial growth environment. Conventional in vitro hepatocyte models have employed monolayer cultures on two-dimensional (2D) substrates, forcing cells into a flattened morphology that is far removed from the in vivo scenario. Unsurprisingly, 2D cultures often show significant deviations from native liver genotype and phenotype and so are unable to accurately predict drug toxicity. Accordingly, it is hypothesised that approximating the native liver three-dimensional (3D) tissue architecture in vitro will help to preserve genotype and phenotype and so improve predictive accuracy. In this study, emulsion templated porous polymers were investigated as scaffolds for 3D hepatocyte culture. In particular, porous polystyrene scaffolds were explored due to their high porosity, reproducibility and suitable mechanical strength properties. Hepatocytes were cultured on polystyrene scaffolds under a range of culture conditions and were found to approximate native liver density and architecture. The morphology of hepatocytes in scaffolds was representative of in vivo, unlike the flattened morphology of 2D cultures. Crucial ultrastructural features involved in drug detoxification such as bile canaliculi were also present in scaffold cultures, but almost absent from 2D cultures. Importantly, these representative structural features translated into functional and genetic improvements in vitro. Hepatocytes in scaffolds displayed increased albumin synthesis, a key marker of hepatocyte function. Hepatic cell lines also showed increased resistance to drug toxicity compared to 2D cultures. Hepatic drug metabolising genotype was also increased to more physiologically relevant levels in scaffolds compared to 2D cultures. In addition, emulsion templated polystyrene scaffolds were also made more biochemically relevant by surface functionalising with galactose, a ligand known to selectively bind to hepatocytes in vivo via the asialoglycoprotein receptor (ASGP-R). Scaffold morphology was maintained with the incorporation of galactose, allowing cells to approximate native liver tissue architecture. Moreover, the pendent galactose ligands were found to be accessible to hepatocytes adhering onto the scaffold. In summary, this thesis has shown that emulsion templated porous polymers can offer a more physiologically relevant growth environment for hepatocytes in vitro. This could have a profound effect on improving drug toxicity predictions and so reducing the dependence on animal testing

Observations on the metabolism of cholecystokinin

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Novel Insights in Retinoid Homeostasis during the Feeding-Fasting Transition of Mice

Vitamin A, which is also known as retinol, is an essential vitamin and needed for the functionality of vision, immune cells, reproduction, embryonic development, and regulation of cell proliferation and differentiation. Retinol is mobilized from the liver while bound to retinol binding protein 4 (RBP4) and transthyretin (TTR) in order to ensure a successful transport to extrahepatic tissues and to maintain these physiological functions. During fasting, the dietary intake of essential retinol is lacking, which was shown in a preliminary study in mice to induce a shift in the retinoid homeostasis in order to ensure retinoid availability for the organism. It was hypothesized that retinol is reversely transported from adipose tissue to replenish hepatic stores. Moreover, it was suggested that fibroblast growth factor 21 (FGF21) is secreted by the liver to induce this reverse transport. This study aimed to illuminate which mechanism underlies the changes of hepatic mRNA expression and protein levels of RBP4 and TTR in the fasted state observed in a preliminary study in mice. Therefore, primary murine hepatocytes were used as a model to investigate hepatic regulations. Insulin, glucagon, and their related signaling pathways were identified to regulate RBP4 and TTR. In addition, the question whether there are alterations in the concentrations of apo-RBP4 and holo-RBP4 in serum in times of fasting was investigated, since the export of hepatic retinol was hypothesized to be reduced and repartitioning thereof from adipose tissue was suggested to be enhanced. This was done by using non-denaturing immunoblotting and immunoprecipitation. Also, it was investigated whether FGF21 can mediate a signal and its enhanced secretion can induce reverse transport from adipose tissue to the liver. For this reason, an adeno-associated virus (AAV) was injected into mice, resulting in liver-specific overexpression of FGF21, which led to minor changes in the retinoid homeostasis. The amount of retinoids in the liver and subcutaneous white adipose tissue did not change and the expression of retinol metabolism-associated target genes was induced. In epididymal white adipose tissue, retinyl ester stores were found to have reduced while retinol metabolism-associated target genes remained unaltered. Moreover, hepatic FGF21 overexpression was found to promote the gene and protein expression of uncoupling protein 1 (UCP1) and, thus, so-called browning in subcutaneous white adipose tissue. Overall, this study found that the ratio of insulin and glucagon, which shifts during the feeding-fasting-transition, can regulate the gene and protein expressions of RBP4 and TTR. Moreover, it was shown that FGF21 can induce minor changes in retinoid homeostasis, but was not identified as the primary regulator of the fasting-induced influences affecting retinoid homeostasis