Hepatic Bioavailability Research Articles

Evaluating in vivo data for drug metabolism and transport: lessons from Kirchhoff’s Laws

Mechanistic models of hepatic clearance have been evaluated for more than 50 years, with the first author of this mini-review serving as a co-author of the first paper proposing such a model. However, published quality experimental data are only consistent with the first of these models, designated as the well-stirred model, despite the universal recognition that this model is physiologically unrepresentative of what occurs with respect to liver metabolism and transport. Within the last 3 years, our laboratory has recognized that it is possible to derive clearance equations employing the concepts of Kirchhoff’s Laws from physics, independent of the differential equation approach that has been utilized to derive reaction rates in chemistry. Here we review our published studies showing that the equation previously believed to be the well-stirred model, when hepatic basolateral transporters are not clinically relevant, is in fact the general equation for hepatic clearance when only systemic drug concentrations are measured, explaining why all experimental data fit this equation. To demonstrate that the equations deriving the mechanistic models of hepatic elimination for the past 50 years are not valid, we show that when calculating Kpuu, the ratio of unbound drug concentration in the liver to the unbound concentration of drug in the systemic circulation, for the well-stirred, parallel tube and dispersion models, Kpuu surprisingly can never exceed 1 and is a function of FH, the hepatic bioavailability following oral dosing. We believe that knowledgeable drug metabolism scientist and clinical pharmacologist will agree that this outcome is nonsensical.

Does high hepatic bioavailability enhance the effect of oral compared to subcutaneous glucocorticoids?

Glucocorticoids (GC) are important in the treatment of autoinflammatory disorders. Oral prednisolone ≤5 mg/day can be effective, but such doses are at or even below physiological daily endogenous GC production. We hypothesised that their immunosuppressive effect might be explained by high hepatic bioavailability of oral GC, exposing the liver to supraphysiological GC via the portal circulation. We tested this by comparing the effect of oral versus subcutaneous low-dose prednisolone, on erythrocyte sedimentation rate (ESR). Patients with rheumatoid arthritis or psoriatic arthritis, elevated ESR (≥30 mm/h) and no current or recent GC therapy were eligible. In a pilot study (n=5), 5 mg/day oral prednisolone decreased ESR significantly, suggesting a sample size of 10 patients for a randomised, non-blinded crossover trial. Patients received 5 mg/day prednisolone for 2 periods of 4 days: one treatment period orally and one subcutaneously with a 10-day washout period between treatments. ESR was measured before (day 1 and 15) and after (day 5 and 19) each treatment course. 10 patients were included. ESR decreased after both oral and subcutaneous prednisolone, by -5.6 (20.9) and -5.8 (3.0) mm/h, respectively (p=0.98). The treatment order had no effect on the outcome. . Short-term oral low-dose GC therapy is not more effective than parental GC in decreasing ESR, arguing against therapeutic high hepatic bioavailability effects. More likely, systemic concentration peaks following administration explain why oral physiological steroid doses are clinically effective.

Are all measures of liver Kpuu a function of FH, as determined following oral dosing, or have we made a critical error in defining hepatic drug clearance?

Here we present, utilizing universally accepted relationships for hepatic clearance at steady state, that for all models of hepatic elimination the ratio of unbound liver drug concentration to unbound systemic blood concentration, Kpuu, is a function of or related to the hepatic bioavailability for that drug, FH. According to the derivation for the well-stirred model, Kpuu can never exceed unity, can frequently be a function of hepatic blood flow, and is equivalent to the value of FH as determined following oral dosing. For the parallel tube model, Kpuu will not equal FH but will be a function of FH and will also never be a value greater than 1. When hepatic clearance is rate limited by basolateral transporters, Kpuu will be less than 1, and less than FH. We believe that such outcomes are highly unlikely, and that the error arises from a basic assumption concerning hepatic clearance that leads to the mechanistic models of hepatic elimination, the well-stirred, parallel tube and dispersion models. That basic assumption is that the steady-state systemic concentration multiplied by the hepatic systemic clearance is equal to the product of the average unbound liver steady-state concentration and the intrinsic hepatic clearance (Css · CL = CH,u · CLint). Calculations of Kpuu and FH based on present methods of analysis provide a strong argument as to why this universally accepted relationship is not correct. Alternatively, we have shown in recent publications that hepatic clearance may be adequately determined based on Kirchhoff's Laws where no assumption of the above equality concerning hepatic intrinsic clearance is required, and where Kpuu is independent of hepatic extraction ratio and FH.

Enhancement of Liver Targetability through Statistical Optimization and Surface Modification of Biodegradable Nanocapsules Loaded with Lamivudine.

The intention of the current work was to develop and optimize the formulation of biodegradable polymeric nanocapsules for lamivudine (LMV) in order to obtain desired physical characteristics so as to have improved liver targetability. Nanocapsules were prepared in this study as aqueous-core nanocapsules (ACNs) with poly(lactide-co-glycolide) using a modified multiple emulsion technique. LMV was taken as a model drug to investigate the potential of ACNs developed in this work in achieving the liver targetability. Three formulations factors were chosen and 33 factorial design was adopted. The selected formulation factors were optimized statistically so as to have the anticipated characteristics of the ACNs viz. maximum entrapment efficiency, minimum particle size, and less drug release rate constant. The optimized LMV-ACNs were found to have 71.54 ± 1.93% of entrapment efficiency and 288.36 ± 2.53 nm of particle size with zeta potential of -24.7 ± 1.2 mV and 0.095 ± 0.006 h-1 of release rate constant. This optimized formulation was subjected to surface modification by treating with sodium lauryl sulphate (SLS), which increased the zeta potential to a maximum of -41.6 ± 1.3 mV at a 6 mM concentration of SLS. The results of in vivo pharmacokinetics from blood and liver tissues indicated that hepatic bioavailability of LMV was increased from 13.78 ± 3.48 μg/mL ∗ h for LMV solution to 32.94 ± 5.12 μg/mL ∗ h for the optimized LMV-ACNs and to 54.91 ± 6.68 μg/mL ∗ h for the surface-modified LMV-ACNs.

Infused aqueous curry tea extracts ameliorate Nω -Nitro-L-Arginine Methyl Ester-induced liver dysfunction in male albino Wistar rats.

Murraya koenigii (L.) Spreng. (Rutaceae) has been reported to positively affect liver function. However, the effect of M. koenigii leaves on Nω -Nitro-L-Arginine Methyl Ester (L-NAME) induced liver dysfunction is unknown. The aim of the present study was therefore to investigate the effect of M.koenigii leaves as tea on L-NAME induced liver dysfunction. Two variants of curry tea were formulated; one was formulated entirely from leaves of M. koenigii, the other was formulated with thaumatin-rich aril obtained from seeds of Thaumatococcus danielii (Benn.) Benth. (Marantaceae). Group I animals served as control and were untreated. Groups II and V animals were administered curry tea (CT). Group III and VI animals received curry-thaumatin tea (CTT). Concurrently, L-NAME (40 mg/kg) was administered to groups IV-VI respectively for 21 days. Blood and liver samples were collected at the end of the study for biochemical, histological, and immunohistochemical analysis. L-NAME induced liver dysfunction evidenced by liver histology, increased activities of ALT, AST, hyperlipidemia, hepatic oxidative stress and increased hepatic NF-kB expression. Administration of CT and CTT ameliorated the L-NAME induced liver dysfunction evidenced by liver histology, increased NO hepatic bioavailability, reduced activity of ALT and AST, increased hepatic antioxidant system and decreased hepatic NF-kB expression. Thaumatin taste/flavor enhancer did not significantly reduce or potentiate the hepatoprotective, antioxidant and anti-lipidemic property of aqueous curry tea extracts in rats. L-NAME impaired liver function in rats. CT and CTT interfered with the ability of L-NAME to inhibit NO synthesis which was associated with ameliorated hepatic dysfunction. The study reports that non-selective inhibition of nitric oxide by L-NAME in rats impairs liver function and formulated curry tea types interfered with the ability of L-NAME to inhibit NO synthesis which was associated with ameliorated hepatic dysfunction in rats.

Contributions of intestine and liver to the absorption and disposition of FZJ-003, a selective JAK1 inhibitor with structure modification of filgotinib

FZJ-003 is a selective Janus kinase 1 (JAK1) inhibitor with structural modification of filgotinib for rheumatoid arthritis (RA) treatment. In this study, a series of in vivo and in vitro experiments were conducted to investigate the specific contribution of the intestine and liver to the disposition of FZJ-003 compared with filgotinib. Results showed that FZJ-003 exhibited over 2-fold higher systemic exposure and lower clearance than those of filgotinib, after intravenous or intragastric administration at the equivalent mole dose level to conscious rats. In anesthetized rats treated with different dosing routes, FZJ-003 exhibited higher intestinal bioavailability (Fa·Fg, 98.47 vs 34.54%) but lower hepatic bioavailability (Fh, 61.45 vs 92.07%). Permeability test in Caco-2 cells indicated that FZJ-003 was probably transported by passive diffusion (efflux ratio 1.37 < 2, indicating the approximately equivalent Papp values in two directions) with a little higher permeability (Papp,AP-to-BL, 1.42 × 10−6vs 1.01 × 10−6 cm·s−1, FZJ-003 vs filgotinib). Metabolic studies in pre-systemic incubation systems showed that FZJ-003 experienced more NADPH-dependent metabolism, especially in hepatic microsomes fractions. Unlike filgotinib, there was no obvious amide-hydrolyzed metabolite of FZJ-003 detected throughout the pre-systemic metabolic sites. Collectively, these data suggest that the higher systemic exposure of FZJ-003 than filgotinib is mainly attributed to the higher intestinal bioavailability including bypassing the amide hydrolysis and possible efflux by intestinal epithelial cells, which strongly support the structural design purpose in terms of pharmacokinetics.

Rapeseed and Soy Lecithin As Food Additives Vectors of α-Linolenic Acid: Impacts on High-Fat Induced Adiposity, Inflammation and Gut Microbiota in Mice

Abstract Objectives Dietary synthetic emulsifiers have recently been shown to promote metabolic syndrome and alter gut microbiota. The effects of natural emulsifiers, such as vegetable lecithin, remain, however, poorly described. Our objective was to evaluate, in mice, the impact of soy and rapeseed lecithin, both rich in essential α-linolenic acid (ALA), when incorporated in high-fat (HF) Western diets on the bioavailability of ALA, as well as on HF-induced adiposity, inflammation and gut microbiota. Methods For 13 weeks, male Swiss mice (n = 72) were fed either a standard Chow diet, a control semi-synthetic HF-diet (25 wt% lipids) poor in ALA (HFC), or different ALA-enriched (4.7% of total fatty acids) HF-diets containing 0% lecithin (HFA-L0), a nutritional dose of soy or rapeseed lecithin (10 wt% of lipids; HFA-SL10, HFA-RL10), or a 20 wt% supplemental dose of RL (HFA-RL20). Histomorphology of the epididymal adipose tissue (EAT) was analysed; hepatic lipid composition was determined by GC-FID, gene expression by RT-PCR, and faecal microbiota composition by 16S sequencing. Results Within ALA-rich HF diets, the hepatic bioavailability of ALA was similar whether ALA was vectorised as lecithin (HFA-RL10, HFA-RL20, HFA-SL10) or as oil only (HFA-L0) (yet, all higher than HFC). Similarly to HFC, HFA-SL10 and HFA-RL20, but not HFA-RL10, increased body weight gain (P &amp;lt; 0.001), visceral adiposity (P &amp;lt; 0.001) and adipocyte hypertrophy (P &amp;lt; 0.05), compared to Chow. The addition of lecithin in HF-diets, regardless of origin or dose, cancelled the anti-inflammatory effect of ALA observed in HFA-L0 on the expression of genes involved in macrophage infiltration in the EAT (e.g., Tnfα, Cd11c). Only HFA-RL10 increased gut microbiota α-diversity compared to HFC (P &amp;lt; 0.05), and altered the abundance of several gut bacterial groups, such as Lachnospiraceae and Desulfovibrionaceae. Conclusions Although the incorporation of neither soy nor rapeseed lecithin in HF-diets improved ALA hepatic bioavailability, the two lecithins exerted differential metabolic effects in mice. At a nutritional dose, rapeseed lecithin, unlike soy lecithin, did not significantly enhance visceral adiposity comparatively to a Chow diet, and increased gut bacterial diversity. Rapeseed lecithin may therefore be considered as a promising food ingredient. Funding Sources ANRT CIFRE PhD grant (UMT ACTIA BALI).

Predicting human pharmacokinetics from preclinical data: absorption.

Predicting the rate and extent of oral absorption of drugs in humans has been a challenging task for new drug researchers. This tutorial reviews in vitro and PBPK methods reported in the past decades that are widely applied to predicting oral absorption in humans. The physicochemical property and permeability (typically obtained using Caco-2 system) data is the first necessity to predict the extent of absorption from the gut lumen to the intestinal epithelium (Fa). Intrinsic clearance measured using the human microsome or hepatocytes is also needed to predict the gut (Fg) and hepatic (Fh) bioavailability. However, there are many issues with the correction of the inter-laboratory variability, hepatic cell membrane permeability, CYP3A4 dependency, etc. The bioavailability is finally calculated as F = Fa × Fg × Fh. Although the rate of absorption differs by micro-environments and locations in the intestine, it may be simply represented by ka. The ka, the first-order absorption rate constant, is predicted from in vitro and in vivo data. However, human PK-predicting software based on these PBPK theories should be carefully used because there are many assumptions and variances. They include differences in laboratory methods, inter-laboratory variances, and theories behind the methods. Thus, the user's knowledge and experiences in PBPK and in vitro methods are necessary for proper human PK prediction.

Organotropism of total mercury (THg) in Cichla pinima, ecological aspects and human consumption in fish from Amazon region, Brazil

Specimens of the Cichla pinima are of ecological and economic importance in the Amazon region and are a good bioindicator species of Hg bioaccumulation. Adult specimens of Cichla pinima were obtained by fisheries in the Tapajós river region's impacted gold mining area. Tissues such as muscle, liver, skin, and gill were submitted for total mercury (THg) analysis. For hepatic bioavailability, assays were carried out in the whole liver and in the sub-cellular hepatic fraction. The weight-length relationship showed an equation of W = 2E - 06L3.3002 (R2 = 0.856) indicating an allometric growth. The mean THg values found in the muscle tissue of 676 ± 258μgkg-1 were below the maximum limit established for human consumption, but were similar to Cichla fish from other areas impacted by Hg in the Amazon region. The trends of levels in the tissues were as follows: liver>muscle>gonads>skin>gill, with no significant differences between the gills and skin. A significant and positive correlation as rs = 0.65 was obtained between the THg contents in cytosolic fraction and the total hepatic THg (liver homogenate). However, only 7% of the THg were found and were available to the sub-cellular hepatic fraction. This profile can be an indicative of a hepatic cellular transference in fish exposed to high Hg levels in the Amazon region now that low concentrations of Hg have been found in the sub-cellular fraction. However, data of differential THg partition in the subcellular compartments should be considered, since others' hepatic fractions can act in the Hg linkage into the cell.

Mechanistic study of absorption and first-pass metabolism of GL-V9, a derivative of wogonin.

GL-V9, a derivative of wogonin, has potent anti-cancer activity. The absorption and metabolism of this compound have not been investigated systematically. This study aims to illustrate the pharmacokinetic characters of GL-V9 by exploring its metabolic status under different administration routes. To further clarify the absorption mechanism of GL-V9, an in situ single-pass perfusion model and a Caco-2 cell monolayer model were used. Meanwhile, a microsomal incubation system was used to evaluate the enzyme kinetic parameters. In vivo, the obtained gastrointestinal availability (Fa × Fg ) was 21.28±5.38%. The unmetabolized fraction in the gut wall (Fgut wall ) was 98.59±9.74%, while the hepatic bioavailability (Fh ) was 29.11±5.22%. These results indicated that poor absorption and extensive metabolism may contribute greatly to the low bioavailability of GL-V9. The effective permeability (Peff ) in the duodenum and jejunum was 1.34±0.50×10-4 and 0.90±0.27×10-4 cm/s, respectively. The high permeability of GL-V9 indicated that other unknown factors (such as metabolism) may account for its systemic exposure problem. Studies in rat liver microsomal (RLMs) confirmed this hypothesis, and the Clint, CYP450s and UGT of GL-V9 was 0.20ml/min/mg protein. In conclusion, these results suggest that GL-V9 possesses higher permeability than wogonin and the metabolism of GL-V9 is related to its disposition in rat intestine and liver.

Design and development of transdermal drug delivery of nonsteroidal anti-inflammatory drugs: Lornoxicam

Background: Conventional route, the most common route of administration, has drawbacks such as hepatic first-pass metabolism, poor bioavailability, and ability to alter drug concentrations in the blood. These problems can be overcome by a controlled-release drug delivery system, which can be accomplished with the development of transdermal drug delivery system. Objective: The objective of this study was to design and develop a lornoxicam-loaded matrix-type transdermal films with different permeation enhancers and determine their physicochemical characteristics. Materials and Methods: Lornoxicam-loaded transdermal films were prepared by the solvent evaporation technique. The Fourier transform infrared spectroscopic studies were performed to determine the drug–excipient interactions. Six formulations were prepared with different permeation enhancers such as propylene glycol, dimethylformamide, dimethyl sulfoxide (DMSO), sodium lauryl sulfate, Span 20, and TWEEN 80 by using 500 mg of sodium alginate as the polymer and 60% w/w glycerin as the plasticizer. The prepared formulations were evaluated for thickness, uniformity of weight, moisture loss, moisture uptake, drug content, and tensile strength. The effect of different permeation enhancers on diffusion was determined through a shed snakeskin by using Franz diffusion cells. Results: The preformulation studies conducted were fulfilled to design a matrix-type transdermal film. In vitro diffusion 24 h indicated that the steady state flux were in the order of F3 > F2 > F1 > F6 > F5 > F4. It was observed that the film prepared with DMSO showed higher diffusion than the formulations with other permeation enhancers. Conclusion: It was concluded that permeation enhancer to prepare lornoxicam-loaded matrix-type transdermal film to improve patient compliance.

The effects of lapatinib on CYP3A metabolism of midazolam in patients with advanced cancer

The potential inhibition of CYP3A4 by lapatinib was studied using midazolam as a probe substrate in patients with cancer. This was a partially randomized, 4-period, 4-sequence, 4-treatment, cross-over study in 24 patients with advanced cancer. Single 1-mg IV and 3-mg oral doses of midazolam were given 2 days apart, in a partially random order, on study days 1, 3, 9, and 11. Lapatinib 1500-mg was administered orally once daily on study days 4 through 11. Midazolam plasma concentrations were measured up to 24-h post dosing, and lapatinib plasma concentrations measured prior to each midazolam dose. Lapatinib increased the geometric mean (95% CIs) midazolam AUC(o-∞) by 45% (31-60%) after the oral dose and by 14% (0-29%) after the IV dose, and prolonged the midazolam elimination half-life by 48% (22-81%) after the oral dose and by 20% (2-40%) after the IV dose. Lapatinib decreased midazolam total clearance by 13% (1-23%), while total bioavailability was increased 23% (4-46%) without changes in apparent volume of distribution or hepatic bioavailability. These data show that lapatinib caused weak inhibition of gastrointestinalCYP3A4 in vivo. This suggests that oralCYP3A4 drug substrates with a narrow therapeutic index may need dose reduction if lapatinib is to be co-prescribed.

Revisiting the well-stirred model of hepatic clearance: QH, CLHand F changing in the same direction

This tutorial examines the relationship between CL, F, and hepatic blood flow (QH) quantitatively at oral and i.v. administration as an answer to the quiz set for KSCPT members. In case of oral dosing, when hepatic blood flow increases, the hepatic clearance (CL) and bioavailability (F) increases in high-extraction ratio drugs according to the well-stirred model equations for hepatic clearance: CLH = QH·ER = QH∙fu∙CLint/(QH+fu∙CLint) and F = 1 − ER Despite such a clear relationship, many students may feel it rather paradoxical that the increased CL (thus decreasing the AUC) causes increased F and thus the AUC (F∙Dose/CLH) remains unchanged. This tutorial clarifies that the degree to which CL increase fails to match that of the QH increase, and thus the decreased ER (= CL/QH) that results in the increased F. Contemplating this simple, but seemingly paradoxical phenomenon may help students gain a deeper understanding of the first-pass effect.

Improvement of hepatic bioavailability as a new step for the future of statin.

Statins (HMG-CoA reductase inhibitors) are a group of highly efficient pharmacological agents used for reducing blood cholesterol level and prevention/treatment of cardiovascular disease. Adverse reactions during statin treatment affect quite significant numbers of patients (reportedly from 5% to 20%), with more side effects occurring at higher doses. Reduced statin dosing can be achieved by improved bioavailability of statins, which is fairly low due to poor aqueous solubility, low permeability and high molecular weight of some members of the statin family. Moreover, since hepatic cholesterologenesis is a main target of statin action and extrahepatic inhibition of HMG-CoA reductase has no effect on plasma lipids, hepatic bioavailability, in our opinion, becomes a new important modality of statins maximizing their potential effect on the plasma lipid profile and diminishing their extrahepatic toxicity. Therefore efficient delivery systems of statins into hepatocytes need to be developed and introduced. Uses of nano-emulsifying statin delivery systems which may include vectors of intrahepatic transport, in particular lycopene, are discussed. As a proof of concept, some preliminary results revealing the effect of a lycopene-containing nanoformulation of simvastatin (designated as Lyco-Simvastatin) on LDL in mildly hypercholesterolemic patients are shown.

Quantitative Determination of Absorption and First-Pass Metabolism of Apicidin, a Potent Histone Deacetylase Inhibitor

Apicidin, a potential oral chemotherapeutic agent, possesses potent anti-histone-deacetylase activity. After oral administration, the total bioavailability of apicidin is known to be low (14.2%-19.3%). In the present study, we evaluated the factors contributing to the low bioavailability of apicidin by means of quantitative determination of absorption fraction and first-pass metabolism after oral administration. Apicidin was given to rats by five different routes: into the femoral vein, duodenum, superior mesenteric artery, portal vein, and carotid artery. Especially, the fraction absorbed (FX) and the fraction that is not metabolized in the gut wall (FG) were separated by injection of apicidin via superior mesenteric artery, which enables bypassing the permeability barrier. The FX was 45.9% ± 9.7%, the FG was 70.9% ± 8.1% and the hepatic bioavailability (FH) was 70.6% ± 12.3%, while the pulmonary first-pass metabolism was minimal (FL = 102.8% ± 7.4%), indicating that intestinal absorption was the rate-determining step for oral absorption of apicidin. The low FX was further examined in terms of passive diffusion and transporter-mediated efflux by in vitro immobilized artificial membrane (IAM) chromatographic assay and in situ single-pass perfusion method, respectively. Although the passive diffusion potential of apicidin was high (98.01%) by the IAM assay, the in situ permeability was significantly enhanced by the presence of the P-glycoprotein (P-gp) inhibitor elacrider. These data suggest that the low bioavailability of apicidin was mainly attributed to the P-gp efflux consistent with the limited FX measured in vivo experiment.

Intestinal and hepatic first-pass extraction of the 11β-HSD1 inhibitor AMG 221 in rats with chronic vascular catheters

1. A catheterized rat model was used to define the intestinal and hepatic components of oral bioavailability for an 11β-HSD1 inhibitor, AMG 221. These data were integrated with standard in vivo metabolism studies to elucidate the components contributing to the oral disposition of a novel drug candidate.2. Intestinal and hepatic extraction ratios of AMG 221 obtained using a five-catheter rat model were 0.56 and 0.32, respectively. Therefore, both intestinal and hepatic extraction contributed to the first-pass component of oral bioavailability. There was no evidence for significant gut extraction of systemically administered drug.3. Mass balance data and in vivo metabolite characterization obtained after administration of [14C] AMG 221 to rat showed that AMG 221 was completely absorbed from the gut lumen following an oral dose, primarily excreted in urine and was almost completely metabolized prior to excretion.4. Hepatic bioavailability (FH), measured in two animals at various time points after oral dose administration was somewhat variable but generally characterized by an initial reduction during the absorption phase followed by an increase during the elimination phase, consistent with hepatic distribution of AMG 221.5. The five-catheter rat model afforded estimates of hepatic and intestinal contribution to oral bioavailability that were used with other data to define the preclinical ADME characteristics of a drug candidate.

Mecanismos moleculares de la esteatosis en la patología de hígado graso no alcohólico

Nonalcoholic fatty liver disease (NAFLD) is the most important cause of chronic liver disease and is considered the hepatic manifestation of the metabolic syndrome associated with diabetes mellitus type 2. The prevalence of NAFLD in the general population reaches 15-20%. It is also estimated that nonalcoholic steatohepatitis (NASH) affects 3% of the population. NAFLD refers to a wide spectrum of liver damage, which ranges from simple steatosis or intracellular triglyceride accumulation, to inflammation (NASH), fibrosis and cirrhosis. The mechanisms involved in the accumulation of triglycerides in the liver and subsequent hepatocellular damage are multifactorial and are not completely understood. However, metabolic changes such as insulin resistance (IR) are developed, being a common factor in the retention of fatty acids (FA) within the hepatocytes with oxidation and production of free radicals at the mitochondrial level, which are capable of causing lipid peroxidation, cytokine production, and necrosis. In addition, there are alterations in the hepatic bioavailability of long chain n-3 polyunsaturated fatty acids, conditions that alter the expression of a series of transcriptional factors involved in lipolytic and lipogenic processes in the liver. A greater knowledge of the etiopathogenic mechanisms of NAFLD is fundamental for the development of future effective therapeutic strategies. The pathophysiological fundamentals of liver steatosis are analyzed in this study.

Molecular mechanisms of steatosis in nonalcoholic fatty liver disease.

Nonalcoholic fatty liver disease (NAFLD) is the most important cause of chronic liver disease and is considered the hepatic manifestation of the metabolic syndrome associated with diabetes mellitus type 2. The prevalence of NAFLD in the general population reaches 15-20%. It is also estimated that nonalcoholic steatohepatitis (NASH) affects 3% of the population. NAFLD refers to a wide spectrum of liver damage, which ranges from simple steatosis or intracellular triglyceride accumulation, to inflammation (NASH), fibrosis and cirrhosis. The mechanisms involved in the accumulation of triglycerides in the liver and subsequent hepatocellular damage are multifactorial and are not completely understood. However, metabolic changes such as insulin resistance (IR) are developed, being a common factor in the retention of fatty acids (FA) within the hepatocytes with oxidation and production of free radicals at the mitochondrial level, which are capable of causing lipid peroxidation, cytokine production, and necrosis. In addition, there are alterations in the hepatic bioavailability of long chain n-3 polyunsaturated fatty acids, conditions that alter the expression of a series of transcriptional factors involved in lipolytic and lipogenic processes in the liver. A greater knowledge of the etiopathogenic mechanisms of NAFLD is fundamental for the development of future effective therapeutic strategies. The pathophysiological fundamentals of liver steatosis are analyzed in this study.

Preparation of PLGA Microspheres Encapsulating Highly Concentrated Glycyrrhizin and the Bile Elimination of Glycyrrhizin after Subcutaneous Administration in Rats

The aim of this study was to prepare poly (lactide-co-glycolide) (PLGA) microspheres encapsulating highly concentrated glycyrrhizin (GZ), a hydrophilic drug, and to compare the release characteristics of GZ in in vitro experiments and GZ elimination into bile after subcutaneous administration in rats. The preparation was carried out based on water drying using a (w/o)/w emulsion. The encapsulation rate of GZ in microspheres was 76% when the GZ concentration in the outer water phase was equal to that in the inner water phase for the preparation of (w/o)/w emulsion. The release of GZ from the microspheres showed a biphasic zero-order profile, that is, the behavior boundary was approximately 12 h. The release of GZ from the microspheres at the periods of 0.5-8 h and 12-672 h was 0.18 mg/h and 0.0012 mg/h, respectively. On the other hand, 0.25% of GZ administered (5.0 mg) was eliminated into bile by 12 h, and the bile clearance rate (1.13 ml/h) of GZ after the subcutaneous administration of the microspheres was the same as that (1.13 ml/h) after the administration of GZ solution. From the results, it is suggested that the initial controlled release (0.18 mg/h) of GZ from microspheres may be beneficial for the hepatic bioavailability of GZ.

Stereoselective First-Pass Metabolism of Verapamil in the Small Intestine and Liver in Rats

Verapamil (VP) is used as a racemate but shows stereoselective pharmacokinetics and pharmacodynamics. It undergoes extensive first-pass metabolism. Stereoselective first-pass metabolism in the intestine and liver was investigated in vivo and in vitro to determine its impact on the disposition of VP and its main metabolite, norverapamil (NVP). VP racemate was administered to rats i.v., p.o., and via the portal vein. The formation rates of the main metabolites of the VP enantiomers were estimated in an in vitro intestinal microsomal study. The hepatic bioavailability of VP showed saturable metabolism, and the hepatic bioavailability of R-VP was higher than that of S-VP. Conversely, the intestinal bioavailability of R-VP was lower than that of S-VP, resulting in a higher systemic bioavailability of S-VP. The pharmacokinetics of the NVP enantiomers was similar. These results suggest that the stereoselectivity of the total bioavailability of VP is determined by first-pass metabolism in the small intestine and liver, and that the NVP enantiomers observed in the systemic circulation after p.o. administration of VP racemate originate mainly from the liver in rats.