Effects of structural modifications on the intestinal permeability of angiotensin II receptor antagonists and the correlation of in vitro, in situ, and in vivo absorption

Endothelial Senescence and Chronic Fatigue Syndrome, a COVID-19 Based Hypothesis

Myalgic encephalomyelitis/chronic fatigue syndrome is a serious illness of unknown etiology, characterized by debilitating exhaustion, memory impairment, pain and sleep abnormalities. Viral infections are believed to initiate the pathogenesis of this syndrome although the definite proof remains elusive. With the unfolding of COVID-19 pandemic, the interest in this condition has resurfaced as excessive tiredness, a major complaint of patients infected with the SARS-CoV-2 virus, often lingers for a long time, resulting in disability, and poor life quality. In a previous article, we hypothesized that COVID-19-upregulated angiotensin II triggered premature endothelial cell senescence, disrupting the intestinal and blood brain barriers. Here, we hypothesize further that post-viral sequelae, including myalgic encephalomyelitis/chronic fatigue syndrome, are promoted by the gut microbes or toxin translocation from the gastrointestinal tract into other tissues, including the brain. This model is supported by the SARS-CoV-2 interaction with host proteins and bacterial lipopolysaccharide. Conversely, targeting microbial translocation and cellular senescence may ameliorate the symptoms of this disabling illness.

Effect of dietary fibers on losartan uptake and transport in Caco-2 cells

The objective of this study was to assess the effect of dietary fibers on the transport of losartan, an angiotensin II type 1 receptor blocker, in small intestinal cells. Using Caco-2 cells in vitro, losartan uptake and transport were evaluated in the presence of various fibers (cellulose, chitosan, sodium alginate and glucomannan). Dietary fibers caused a decrease in the uptake of losartan, with chitosan causing a significant reduction. Chitosan and glucomannan significantly reduced the transport of losartan, while cellulose or sodium alginate did not. Dietary fibers also reduced the level of free losartan; however, this did not correlate with the observed reduction in losartan uptake and transport. In summary, chitosan had the greatest inhibitory effect on losartan uptake and transport, and this potential interaction should be considered in patients taking losartan. Copyright © 2016 John Wiley & Sons, Ltd.

A systematic comparison of the properties of clinically used angiotensin II type 1 receptor antagonists

Angiotensin II type 1 receptor antagonists (ARBs) have become an important drug class in the treatment of hypertension and heart failure and the protection from diabetic nephropathy. Eight ARBs are clinically available [azilsartan, candesartan, eprosartan, irbesartan, losartan, olmesartan, telmisartan, valsartan]. Azilsartan (in some countries), candesartan, and olmesartan are orally administered as prodrugs, whereas the blocking action of some is mediated through active metabolites. On the basis of their chemical structures, ARBs use different binding pockets in the receptor, which are associated with differences in dissociation times and, in most cases, apparently insurmountable antagonism. The physicochemical differences between ARBs also manifest in different tissue penetration, including passage through the blood-brain barrier. Differences in binding mode and tissue penetration are also associated with differences in pharmacokinetic profile, particularly duration of action. Although generally highly specific for angiotensin II type 1 receptors, some ARBs, particularly telmisartan, are partial agonists at peroxisome proliferator-activated receptor-γ. All of these properties are comprehensively reviewed in this article. Although there is general consensus that a continuous receptor blockade over a 24-hour period is desirable, the clinical relevance of other pharmacological differences between individual ARBs remains to be assessed.

Permeation of losartan across human respiratory epithelium: an in vitro study with Calu-3 cells

The potential for nasal delivery of losartan, a drug with poor oral bioavailability, was investigated using Calu-3 cells. Epithelial permeation of the drug with or without dimethyl-beta-cyclodextrin (DM-beta-CD) and glycocholate was investigated. Possible transport mechanism of the compound and epithelial mucosal tolerance were screened. Reversibility of epithelial membrane perturbation was also investigated by measuring transepithelial electrical resistance (TEER) recovery over a 24-h period following drug formulation exposure. The permeability coefficient of losartan was 1.3 + or - 0.5 x 10(-6) cm s(-1). This flux was not significantly different from that of formulations containing DM-beta-CD (0.5 and 1.0%) or glycocholate (0.5%). However, the formulation with 1.0% glycocholate significantly increased losartan permeation 7-fold. Losartan flux across the cells was concentration-dependent. Serosal to mucosal permeation was significantly higher than mucosal to serosal permeation. Concentration-dependency, as well as polarity in transport indicated that the flux of the compound across Calu-3 cells was not limited to passive diffusion. Cells exposed to DM-beta-CD (0.5 and 1.0%) and glycocholate (0.5%) caused no significant change in TEER and mitochondrial dehydrogenase activity (MDH). The results of the study showed that losartan may be a suitable drug candidate for nasal delivery.

Physiological models are good tools to predict rat bioavailability of EF5154 prodrugs from in vitro intestinal parameters

There are only a few reports on the methods that predict in vivo bioavailability from in vitro intestinal parameters. In the present study, we constructed physiological models where we examined if in vivo rat bioavailability was predictable from in vitro intestinal parameters using prodrugs of EF5154, a potent glycoprotein IIb/IIIa receptor antagonist, and other prodrugs. Apparent fraction absorbed (F(a),pred) was calculated using the physiological models that consist of absorption number calculated from Caco-2 cell membrane permeability (P(app)), and Damkohler number calculated from apparent degradation rate constant (K(dapp)) in rat small intestinal fluid. The predicted rat bioavailability that was calculated from F(a),pred corresponded to the observed rat bioavailability, and root mean square error (RMSE) and squared correlation coefficient (r(2)) were 4.58 and 0.904, respectively, suggesting that the physiological models consisting of the membrane permeability and degradation rate constant are good tools for predicting rat bioavailability of EF5154 prodrugs. As for other prodrugs where the chemical structure of their active forms differs from EF5154, the predicted rat bioavailability was not different from fraction absorbed (or rat bioavailability), suggesting the physiological models are generalized to various prodrugs that are not the substrates for active transporters.

Correlation of in vitro and in vivo models for the oral absorption of peptide drugs

The aim of this study was to evaluate two in vitro models, Caco-2 monolayer and rat intestinal mucosa, regarding their linear correlation with in vivo bioavailability data of therapeutic peptide drugs after oral administration in rat and human. Furthermore the impact of molecular mass (Mm) of the according peptides on their permeability was evaluated. Transport experiments with commercially available water soluble peptide drugs were conducted using Caco-2 cell monolayer grown on transwell filter membranes and with freshly excised rat intestinal mucosa mounted in Using type chambers. Apparent permeability coefficients (P (app)) were calculated and compared with in vivo data derived from the literature. It was shown that, besides a few exceptions, the Mm of peptides linearly correlates with permeability across rat intestinal mucosa (R (2) = 0.86; y = -196.22x + 1354.24), with rat oral bioavailability (R (2) = 0.64; y = -401.90x + 1268.86) as well as with human oral bioavailability (R (2) = 0.91; y = -359.43x + 1103.83). Furthermore it was shown that P (app) values of investigated hydrophilic peptides across Caco-2 monolayer displayed lower permeability than across rat intestinal mucosa. A correlation between P (app) values across rat intestinal mucosa and in vivo oral bioavailability in human (R (2) = 0.98; y = 2.11x + 0.34) attests the rat in vitro model to be a very useful prediction model for human oral bioavailability of hydrophilic peptide drugs. Presented correlations encourage the use of the rat in vitro model for the prediction of human oral bioavailabilities of hydrophilic peptide drugs.

[Novel formulations of a liver protection drug glycyrrhizin]

In Japan, glycyrrhizin injections have been used as a therapeutic drug for allergy inflammation since 1948 and for chronic hepatitis since 1979. A 20 ml injection of glycyrrhizin contains 53 mg of monoammonium glycyrrhizinate (40 mg as glycyrrhizin acid), 400 mg of glycine, and 20 mg of L-cysteine. Patients receiving glycyrrhizin injections two or three times per week are forced to accept a decline in quality of life. Because administering glycyrrhizin by injection has some disadvantages, many researchers have systematically searched for novel glycyrrhizin formulations that can be administered through oral, rectal, intranasal, and subcutaneous routes. There are two problems, however, in developing new formulations: (1) glycyrrhizin has low membrane permeability and is thus poorly absorbed, and (2) highly concentrated glycyrrhizin readily forms gels in aqueous solutions. Here, we describe the utility of glycyrrhizin formulations prepared in safe solubility agents and absorption-enhancing agents, as assessed in animal experiments. We also discuss pharmaceutical issues in developing various glycyrrhizin formulations. In the near future, convenient pharmaceutical preparations of glycyrrhizin will be developed for chronic hepatitis patients who require glycyrrhizin therapy.

Further studies on imidazo[4,5-b]pyridine AT1 angiotensin II receptor antagonists. Effects of the transformation of the 4-phenylquinoline backbone into 4-phenylisoquinolinone or 1-phenylindene scaffolds

The 4-phenylquinoline fragment of novel AT(1) receptor antagonists 4 based on imidazo[4,5-b]pyridine moiety was replaced by 4-phenylisoquinolinone (compounds 5) or 1-phenylindene (compounds 6) scaffolds to investigate the structure-activity relationships. Binding studies showed that most of the synthesized compounds display high affinity for the AT(1) receptor. Because of the in vitro high potency of carboxylic acids 5b,f, they were evaluated in permeability (in Caco-2 cells) and in pharmacokinetic studies in comparison with quinoline derivatives 4b,i,j,k. The studies showed that these compounds are characterized by rapid excretion, low membrane permeability, and low oral bioavailability. The structure optimization of the indene derivatives led to compounds 6e,f possessing interesting AT(1) receptor affinities. Optimization produced polymerizing AT(1) receptor ligand 6c, which forms a thermoreversible polymer (poly-6c) and is released from the latter by a temperature-dependent kinetics. The results suggest the possibility of developing novel polymeric prodrugs based on a new release mechanism. Finally, a set of 34 AT(1) receptor antagonists was used as a new test for the evaluation of the predictive capability of the previously published qualitative and quantitative pharmacophore models.

Exploration of orally available calpain inhibitors. Part 3: Dipeptidyl alpha-ketoamide derivatives containing pyridine moiety

Calpain-mediated proteolysis has been implicated as a major process in neuronal cell death including retinal neurological degeneration. The previously reported calpain inhibitor SJA6017 (1) showed oral efficacy in a retinal pharmacological model, but its oral bioavailability was low due to the metabolic lability and low water-solubility. The purpose of present study was to identify good orally bioavailable calpain inhibitors. A series of water-soluble dipeptidyl alpha-ketoamides containing a pyridine moiety at P3 were designed, synthesized, and evaluated for their oral bioavailability and retinal penetration. Introduction of a pyridineethanol moiety provided the potent alpha-ketoamide inhibitor 8 with good oral bioavailability. Compound 8 showed about 12-fold higher retinal AUC than 1.

Tetrazole compounds: The effect of structure and pH on Caco-2 cell permeability

A tetrazole ring is often used in drug discovery as a replacement for the carboxylic acid group. Previous work indicates that compounds containing a tetrazole moiety show asymmetric permeability in Caco-2 cells characteristic of an efflux transporter substrate. The aim of this study is to determine which transporters are responsible for polarization of transport of tetrazole-containing compounds in Caco-2 cells. Results indicate that only select compounds with tetrazole moieties display asymmetric transport. Three compounds (two commercial drug products and one druglike structure) were selected for further studies. Losartan appears to be primarily a P-glycoprotein (P-gp) substrate, as previously reported, but MRP inhibitors such as MK-571 and rifampicin also affect the difference between apical to basolateral and basolateral to apical transport. Pemirolast and phenyltetrazole derivative C are sensitive to P-gp inhibition, but transport seems to be mediated by one or more of the MRP family of transporters. Additionally, lowering the pH from 7.4 to 4.0 eliminates the polarization of permeability in Caco-2 cells. These studies indicate that some tetrazole compounds are susceptible to efflux, therefore caution should be used when choosing an appropriate functional group to replace carboxylic acids when synthesizing a drug candidate.

Exploration of orally available calpain inhibitors: peptidyl alpha-ketoamides containing an amphiphile at P3 site

A novel series of dipeptidyl alpha-ketoamide derivatives with amphiphile was designed and synthesized as water-soluble calpain inhibitors. The introduction of amphiphiles at the P3 site increased water solubility without loss of membrane permeability and provided the oral available inhibitors. Extension of the ethylene glycol chain at the P3 site led to an improvement in persistence of plasma levels. In particular, introduction of a combination of a diethylene glycol methyl ether moiety at the P3 site, a phenylalanine residue at the P1 site and a cyclopropyl moiety at the P' site was the most effective modification for an increase in plasma drug exposure.

Comparison of human duodenum and Caco-2 gene expression profiles for 12,000 gene sequences tags and correlation with permeability of 26 drugs

PURPOSE

To compare gene expression profiles and drug permeability differences in Caco-2 cell culture and human duodenum.

METHODS

Gene expression profiles in Caco-2 cells and human duodenum were determined by GeneChip analysis. In vivo drug permeability measurements were obtained through single-pass intestinal perfusion in human subjects, and correlated with in vitro Caco-2 transport permeability.

RESULTS

GeneChip analysis determined that 37, 47, and 44 percent of the 12,559 gene sequences were expressed in 4-day andl6-day Caco-2 cells and human duodenum, respectively. Comparing human duodenum with Caco-2 cells, more than 1,000 sequences were determined to have at least a 5-fold difference in expression. There were 26, 38, and 44 percent of the 443 transporters, channels, and metabolizing enzymes detected in 4-day, 16-day Caco-2 cells, and human duodenum, respectively. More than 70 transporters and metabolizing enzymes exhibited at least a 3-fold difference. The overall coefficient of variability of the 10 human duodenal samples for all expressed sequences was 31% (range 3% to 294%) while that of the expressed transporters and metabolizing enzymes was 33% (range 3% to 87%). The in vivo / in vitro drug permeability measurements correlated well for passively absorbed drugs (R2 = 85%). The permeability correlation for carrier-mediated drugs showed 3- 35-fold higher in human above the correlation of passively absorbed drugs. The 2- 595-fold differences in gene expression levels between the Caco-2 cells and human duodenum correlated with the observed 3- 35-fold difference in permeability correlation between carrier-mediated drugs and passively absorbed drugs. CONCLUSIONS; Significant differences in gene expression levels in Caco-2 cells and human duodenum were observed. The observed differences of gene expression levels were consistent with observed differences in carrier mediated drug permeabilities. Gene expression profiling is a valuable new tool for investigating in vitro and in vivo permeability correlation.

Species differences in stereoselective hydrolase activity in intestinal mucosa

PURPOSE

The aim of this study is to investigate species differences in the stereoselective hydrolysis for propranolol ester prodrugs in mammalian intestinal mucosa and Caco-2 cells.

METHODS

Hydrolase activities for propranolol prodrugs and p-nitrophenylacetate in man (age: 51-71 years), the beagle dog (age: 4 years) and Wistar rat (age: 8 weeks) intestinal mucosa, and also in Caco-2 cells (passage between 60-70) were estimated by determining the rate of production of proparanolol and p-nitrophenol, respectively.

RESULTS

The hydrolase activities for both propranolol prodrugs and p-nitrophenylacetate were in the order of man > rat >> Caco-2 cells > dog for intestinal microsomes, and rat > Caco-2 cells = man > dog for intestinal cytosol. Dog microsomes showed stereoselective hydrolysis for propranolol prodrugs, but not those from human or rat. Interestingly, both subcellular fractions of Caco-2 cells showed remarkable R-enantioselectivity except acetyl propranolol. Enzyme kinetic experiments for each enantiomer of butyryl propranolol in microsomes revealed that dog possesses both low and high affinity hydrolases. Both Km and Vmax values in rat were largest among examined microsomes, while Vmax/Km was largest in man. Finally, it was shown that the carboxylesterases might contribute to the hydrolysis of propranolol prodrug in all species by inhibition experiments.

CONCLUSIONS

The hydrolase activities for propranolol prodrugs and p-nitrophenylacetate in intestinal mucosa showed great species differences and those in human intestine were closer to those of rat intestine than dog intestine or Caco-2 cells.

Improvement of intestinal absorption of peptide drugs by glycosylation: transport of tetrapeptide by the sodium ion-dependent D-glucose transporter

A tetrapeptide (Gly-Gly-Tyr-Arg, GGYR), which is not transported by di- or tripeptide transporters, was glycosylated with p-(succinylamido)phenyl alpha- or beta-D-glucopyranoside (alpha,beta-SAPG) to investigate whether these glycosylated molecules are transported by the Na+-dependent D-glucose transporter. Their uptake into brush border membrane vesicles (BBMVs) and transport through the intestinal membrane were examined using the rapid filtration technique and the everted sac method. It was observed that glycosylation at the alpha-amino position of GGYR increased resistance to aminopeptidase activity and inhibited its degradation. When alpha- and beta-SAPG-GGYR were incubated with BBMVs, overshoot uptake was observed about 2 min after the start of incubation in the presence of an inward Na+ gradient. This uptake remained unaffected by the addition of GGYR while it was significantly inhibited when Na+ was replaced with K+ or alpha- and beta-SAPG-GGYR were incubated with BBMVs at 4 degrees C. Uptake was also markedly inhibited either with 1 mM phloridzin or 10 mM D-glucose. These findings suggested that the Na+-dependent glucose transporter (SGLT-1) played an important role in the uptake of both alpha- and beta-SAPG-GGYR into BBMVs. A comparison of alpha- with beta-SAPG-GGYR revealed that the amount of beta-SAPG-GGYR taken up was greater than that of alpha-SAPG-GGYR. From the everted sac method data, it was shown that the elimination clearance from the mucosal side, CLel, and permeation clearance to the serosal side, CLp, were 15.82+/-6.83 and 0.83+/-0.06 microL/min/cm for alpha-SAPG-GGYR and 44.52+/-3.61 and 3.50+/-0.81 microL/min/cm for beta-SAPG-GGYR, respectively, and that alpha-SAPG-GGYR was more resistant to enzymatic degradation than beta-SAPG-GGYR. Permeation of both alpha- and beta-SAPG-GGYR was inhibited in the presence of D-glucose and in the absence of a Na+ gradient, suggesting that both alpha- and beta-SAPG-GGYR were transported by the Na+-dependent D-glucose transporter. The permeation clearance transported by the Na+-dependent D-glucose transporter, (CLp)Na+, of beta-SAPG-GGYR was about 5 times greater than that for alpha-SAPG-GGYR. This result may be ascribable to the fact that the beta-form of glucose has higher affinity to SGLT-1 than the alpha-form. The results of the present study encourage further investigations on improvements in intestinal absorption of peptide drugs by glycosylation.