Postmortem chondrocyte viability in porcine articular cartilage: Influence of time, temperature, and burial under winter conditions.

The aim of the present study was to investigate the effects of time, temperature, and burial in a natural environment on the viability of chondrocytes in porcine femoral condyles using confocal laser scanning microscopy. Hind trotters from 10 pigs were buried or left unburied. Samples were collected daily and stained with a combination of vital dyes (calcein-AM and ethidium homodimer-1). The chondrocytes showed an intense staining corresponding to their vitality. In the first 3 days, viability decreased slowly and showed no statistical difference between buried and unburied samples. After the first 3 days, it decreased rapidly, with the viability of the buried samples being 66% on day 4, decreasing to 25% on day 8 and to 16% on day 10, while in the unburied samples it decreased to 43% on day 4, 13% on day 8 and 5% on day 10. Our results indicate a time, temperature, and burial dependent decrease in chondrocyte viability and suggest the use of chondrocyte viability as a marker for estimating PMI in both the natural environment and in animals, as well as its potential use in humans.

Inhibition of P-glycoprotein-mediated efflux by thiolated cyclodextrins.

Overcoming P-glycoprotein (P-gp)-mediated efflux poses a significant challenge for the pharmaceutical industry. This study investigates the potential of thiolated ß-cyclodextrins (ß-CD-SHs) as inhibitors of P-gp-mediated efflux in Caco-2 cells. Through a series of transport assays, intracellular accumulation, and efflux of the P-gp substrates Rhodamine 123 (Rh123) and Calcein-AM with and without co-administration of ß-CD-SHs were assessed. The results revealed that the cellular uptake of Rh123 and Calcein-AM were enhanced up to 7- and 3-fold, compared to the control, respectively. In efflux studies an up to 2.5-fold reduction of the Rh123 efflux was reached compared the control, indicating a substantial decrease of Rh123 efflux by ß-CD-SHs. Furthermore, it was observed that ß-CD-SHs led to a decrease in the reactivity of fluorescence-labeled anti-P-gp, suggesting additional effects on the conformation of P-gp. Overall, this study demonstrates the potential of ß-CD-SHs as effective modulator of P-gp-mediated drug efflux in Caco-2 cells.

Establishment of a new method to isolate viable x-ray-sensitive cells from planarian by fluorescence-activated cell sorting.

Planarians show outstanding regenerative ability due to the proliferation of neoblasts. Hence the method to isolate planarian neoblasts is important to understand the regeneration process. In our previous study, we reported a method to isolate planarian neoblasts of Dugesia japonica using fluorescence-activated cell sorting (FACS). However, we have not yet succeeded in cultivating these cells even under in vivo conditions after transplantation into x-ray-irradiated planarians. This suggests that dissociated cells might enter apoptotic or necrotic states in the process of fluorescent dye staining and sorting. Here, we developed a new method to isolate viable neoblasts, which can proliferate in the x-ray-irradiated planarians. First, the toxicity of various fluorescence dyes was investigated. All nuclear fluorescent dyes such as Hoechst 33342, DRAQ5, and DyeCycle, showed, more or less, toxicity to mammalian culture cells. In contrast, cytoplasmic fluorescent dye for live cells, calcein AM, was less toxic on these cells. Next, we stained the dissociated planarian cells with only calcein AM, and then collected the x-ray-sensitive fraction. Although the purity of neoblasts was slightly lower than that of the original staining method (ca. 97% → ca. 89%), the sorted cells could actively proliferate when they were injected into x-ray-irradiated planarians. This simple staining and sorting method will provide new opportunities to isolate viable neoblasts and understand regenerating processes.

Drug-free and non-crosslinked chitosan/hyaluronic acid hybrid hydrogel for synergistic healing of infected diabetic wounds.

The management of infected diabetic wounds remains a major challenge in clinical practice. Recently, multifunctional hydrogels have attracted much attention in the area of wound healing. Herein, we developed the drug-free and non-crosslinked chitosan (CS)/hyaluronic acid (HA) hybrid hydrogel, so as to combine the multiple functions of CS and HA for synergistic healing of the methicillin-resistant Staphylococcus aureus (MRSA)-infected diabetic wound. As a result, CS/HA hydrogel showed the broad-spectrum antibacterial activity, the great capacity for promoting fibroblasts proliferation and migration, the excellent reactive oxygen species (ROS) scavenging ability, and the great cell-protection effects under oxidative stress. In the MRSA-infected diabetic mouse wounds, CS/HA hydrogel significantly promoted the wound healing via eliminating MRSA infection and enhancing epidermal regeneration, collagen deposition and angiogenesis. Considering the drug-free feature, the ready availability, the great biocompatibility and the excellent wound healing efficacy, CS/HA hydrogel may have great potentials in clinical use for the management of chronic diabetic wounds.

Overexpression of a GIPC glycosyltransferase gene, OsGMT1, suppresses plant immunity and delays heading time in rice.

Glycosylinositol phosphorylceramides (GIPCs) are the major sphingolipids in the plant plasma membrane. In Arabidopsis, mutations of genes involved in the synthesis of GIPCs affect many physiological aspects of plants, including growth, pollen fertility, defense, and stress signaling. Loss of function of the GIPC MANNOSYL-TRANSFERASE1 (AtGMT1) results in GIPC misglycosylation and induces plant immune responses accompanied by a severely dwarfed phenotype, thus indicating that GIPCs play important roles in plant immunity. Here, we investigated the enzymatic activity and phenotypes of transgenic lines of OsGMT1, the ortholog of AtGMT1. Sphingolipidomic analysis indicated that OsGMT1 retained the enzymatic activity of GIPC hexose (Hex) glycosylation, but the knockout lines did not accumulate H2O2. In contrast, the OsGMT1 overexpression lines showed significant down-regulation of several defense-associated or cell wall synthesis-associated genes, and enhanced sensitivity to rice blast. Furthermore, we first demonstrated the sensitivity of rice cells to MoNLP1 protein through calcein AM release assays using rice protoplasts, thus legitimizing the presence of MoNLPs in rice blast fungus. In addition, yeast two-hybrid screens using OsGMT1 as bait revealed that OsGMT1 may regulate heading time through the OsHAP5C signaling pathway. Together, our findings suggested clear physiological functional differentiation of GMT1 orthologs between rice and Arabidopsis.

Carboxymethyl chitosan-assisted MnOx nanoparticles: Synthesis, characterization, detection and cartilage repair in early osteoarthritis.

While the early detection and repair of cartilage lesions are crucial in the treatment of osteoarthritis (OA), they remain challenging because neither clinically used medicines nor magnetic resonance (MR) contrast agents can achieve detection and repair simultaneously. Here, we conjugated carboxymethyl chitosan (CMC) with a cartilage-targeting peptide (WYRGRL, termed WY) and then synthesized CMC-assisted manganese oxide nanoparticles (MnOx NPs). The resultant WY-CMC-MnOx NPs demonstrated an excellent biocompatibility and a good T1 relaxivity of 1.72 mM-1·s-1. Owing to their ultrasmall size and cartilage-targeting ability, the WY-CMC-MnOx NPs considerably increased the MR imaging quality of cartilage lesions compared to non-cartilage-targeting NPs. In contrast, clinically used gadolinium-diethylenetriamine pentaacetic acid (Gd-DPTA) failed to detect the cartilage lesions. Furthermore, WY-CMC-MnOx promoted chondrogenesis in mesenchymal stem cells, thereby enhancing OA therapy through efficient cartilage regeneration after intraarticularly injection in destabilization of medial meniscus (DMM) rat models. Our results indicate that WY-CMC-MnOx NPs are promising for use in the diagnosis and treatment of early OA.

Measurement of canine blood microparticles by flow cytometry: effect of anticoagulants and staining reagents.

Microparticles (MPs) are released from budding plasma membranes into body fluids. The use of flow cytometry for the measurement of MP in canines has not been standardized. In this fundamental study, we compared the effect of anticoagulant agents, such as acid-citrate-dextrose (ACD) and heparin on the measurement of canine MPs in platelet-free plasma (PFP) using flow cytometry. In addition, we used annexin V, carboxyfluorescein succinimidyl ester (CFSE), or calcein tetraacetoxymethyl ester (calcein-AM), and explored the characteristics of the staining reagents in MP detection using flow cytometry. We were able to measure canine MPs in PFP prepared from ACD-anticoagulated blood using flow cytometry, in which the highest positive rate for fluorescent staining was observed when CFSE was used.

Nuclear receptor coactivator 4-mediated ferritinophagy contributes to cerebral ischemia-induced ferroptosis in ischemic stroke.

Ischemic stroke poses a significant health risk due to its high rate of disability and mortality. To address this problem, several therapeutic approaches have been proposed, including interruption targeting programmed cell death (PCD). Ferroptosis is a newly defined PCD characterized by iron-dependent accumulation of lipid peroxidation, and is becoming a promising target for treating numerous diseases. To explore the underlying mechanisms of the initiation and execution of ferroptosis in ischemic stroke, we established stroke models in vivo and in vitro simulating ischemia/reperfusion (I/R) neuronal injury. Different from previous reports on stroke, we tested ferroptosis by measuring the levels of core proteins, such as ACSL4, 15-LOX2, Ferritin and GPX4. In addition, I/R injury induces excessive degradation of ferritin via the autophagy pathway and subsequent increase of free iron in neurons. This phenomenon has recently been termed ferritinophagy and reported to be regulated by nuclear receptor coactivator 4 (NCOA4) in some cell lines. Increased NCOA4 in cytoplasm was detected in our study and then silenced by shRNA to investigate its function. Both in vivo and in vitro, NCOA4 deletion notably abrogated ferritinophagy caused by I/R injury and thus inhibited ferroptosis. Furthermore, we found that NCOA4 was upregulated by ubiquitin specific peptidase 14 (USP14) via a deubiquitination process in damaged neurons, and we found evidence of pharmacological inhibition of USP14 effectively reducing NCOA4 levels to protect neurons from ferritinophagy-mediated ferroptosis. These findings suggest a novel and effective target for treating ischemic stroke.

Interaction of Commonly Used Oral Molecular Excipients with P-glycoprotein.

P-glycoprotein (P-gp) plays a critical role in drug oral bioavailability, and modulation of this transporter can alter the safety and/or efficacy profile of substrate drugs. Individual oral molecular excipients that inhibit P-gp function have been considered a mechanism for improving drug absorption, but a systematic evaluation of the interaction of excipients with P-gp is critical for informed selection of optimal formulations of proprietary and generic drug products. A library of 123 oral molecular excipients was screened for their ability to inhibit P-gp in two orthogonal cell-based assays. ß-Cyclodextrin and light green SF yellowish were identified as modest inhibitors of P-gp with IC50 values of 168 µM (95% CI, 118-251 µM) and 204 µM (95% CI, 5.9-1745 µM), respectively. The lack of effect of most of the tested excipients on P-gp transport provides a wide selection of excipients for inclusion in oral formulations with minimal risk of influencing the oral bioavailability of P-gp substrates.

Boosting 5-ALA-based photodynamic therapy by a liposomal nanomedicine through intracellular iron ion regulation.

5-Aminolevulinic acid (5-ALA) has been approved for clinical photodynamic therapy (PDT) due to its negligible photosensitive toxicity. However, the curative effect of 5-ALA is restricted by intracellular biotransformation inactivation of 5-ALA and potential DNA repair of tumor cells. Inspired by the crucial function of iron ions in 5-ALA transformation and DNA repair, a liposomal nanomedicine (MFLs@5-ALA/DFO) with intracellular iron ion regulation property was developed for boosting the PDT of 5-ALA, which was prepared by co-encapsulating 5-ALA and DFO (deferoxamine, a special iron chelator) into the membrane fusion liposomes (MFLs). MFLs@5-ALA/DFO showed an improved pharmaceutical behavior and rapidly fused with tumor cell membrane for 5-ALA and DFO co-delivery. MFLs@5-ALA/DFO could efficiently reduce iron ion, thus blocking the biotransformation of photosensitive protoporphyrin IX (PpIX) to heme, realizing significant accumulation of photosensitivity. Meanwhile, the activity of DNA repair enzyme was also inhibited with the reduction of iron ion, resulting in the aggravated DNA damage in tumor cells. Our findings showed MFLs@5-ALA/DFO had potential to be applied for enhanced PDT of 5-ALA.

Scaffold fragmentation and substructure hopping reveal potential, robustness, and limits of computer-aided pattern analysis (C@PA).

Computer-aided pattern analysis (C@PA) was recently presented as a powerful tool to predict multitarget ABC transporter inhibitors. The backbone of this computational methodology was the statistical analysis of frequently occurring molecular features amongst a fixed set of reported small-molecules that had been evaluated toward ABCB1, ABCC1, and ABCG2. As a result, negative and positive patterns were elucidated, and secondary positive substructures could be suggested that complemented the multitarget fingerprints. Elevating C@PA to a non-statistical and exploratory level, the concluded secondary positive patterns were extended with potential positive substructures to improve C@PA's prediction capabilities and to explore its robustness. A small-set compound library of known ABCC1 inhibitors with a known hit rate for triple ABCB1, ABCC1, and ABCG2 inhibition was taken to virtually screen for the extended positive patterns. In total, 846 potential broad-spectrum ABCB1, ABCC1, and ABCG2 inhibitors resulted, from which 10 have been purchased and biologically evaluated. Our approach revealed 4 novel multitarget ABCB1, ABCC1, and ABCG2 inhibitors with a biological hit rate of 40%, but with a slightly lower inhibitory power than derived from the original C@PA. This is the very first report about discovering novel broad-spectrum inhibitors against the most prominent ABC transporters by improving C@PA.

Comparative Evaluation of Natural Killer Cell-mediated Cell Killing Assay Based on the Leakage of an Endogenous Enzyme or a Pre-loaded Fluorophore.

A cell-killing ability of natural killer (NK) cells has been evaluated by the leakage of marker molecules from target cells. Lactate dehydrogenase (LDH) and calcein are two major non-radioisotope markers used for the killing assay. The spontaneous death of NK cells during the killing-assay of cells is a major issue in the assay because it provides background signals to increase errors. In this study, the effect of the spontaneous death of NK cells on the killing assays based on LDH and the calcein method was comparatively evaluated. We found that the calcein method is much less sensitive to the spontaneous death of NK cells to enable an accurate evaluation of the cell killing.

Endothelial Cell Viability after DMEK Graft Preparation.

Aim: To evaluate the effect of graft preparation and organ-culture storage on endothelial cell density (ECD) and viability of Descemet membrane endothelial keratoplasty (DMEK) grafts.Materials and methods: DMEK grafts (n = 27) were prepared at Amnitrans EyeBank Rotterdam from 27 corneas (15 donors) that were eligible for transplantation but could not be allocated due to the Covid-19-related cancellation of elective surgeries. Cell viability (by Calcein-AM staining) and ECD of five grafts originally scheduled for transplantation were evaluated on the originally planned surgery day, whereas 22 grafts from paired donor corneas were evaluated either directly post-preparation or after 3-7 days of storage. ECD was analyzed by light microscopy (LM ECD) and Calcein-AM staining (Calcein-ECD).Results: Light microscopy (LM) evaluation of all grafts showed an unremarkable endothelial cell monolayer directly after preparation. However, median Calcein-ECD for the five grafts initially allocated for transplantation was 18% (range 92-73%) lower than median LM ECD. For the paired DMEK grafts, Calcein-ECD determined by Calcein-AM staining on the day of graft preparation and after 3-7 days of graft storage showed a median decrease of 1% and 2%, respectively. Median percentage of central graft area populated by viable cells after preparation and after 3-7 days of graft storage was 88% and 92%, respectively.Conclusion: Cell viability of most of the grafts will not be affected by preparation and storage. Endothelial cell damage may be observed for some grafts within hours after preparation, with insignificant additional ECD changes during 3-7 days of graft storage. Implementing an additional post-preparation step in the eye bank to evaluate cell density before graft release for transplantation may help to reduce postoperative DMEK complications.

Exogenic production of bioactive filamentous biopolymer by monogonant rotifers.

The chemical ecology of rotifers has been little studied. A yet unknown property is presented within some monogonant rotifers, namely the ability to produce an exogenic filamentous biopolymer, named 'Rotimer'. This rotifer-specific viscoelastic fiber was observed in six different freshwater monogonants (Euchlanis dilatata, Lecane bulla, Lepadella patella, Itura aurita, Colurella adriatica and Trichocerca iernis) in exception of four species. Induction of Rotimer secretion can only be achieved by mechanically irritating rotifer ciliate with administering different types (yeast cell skeleton, denatured BSA, epoxy, Carmine or urea crystals and micro-cellulose) and sizes (approx. from 2.5 to 50 µm diameter) of inert particles, as inductors or visualization by adhering particles. The thickness of this Rotimer is 33 ± 3 nm, detected by scanning electron microscope. This material has two structural formations (fiber or gluelike) in nano dimension. The existence of the novel adherent natural product becomes visible by forming a 'Rotimer-Inductor Conglomerate' (RIC) web structure within a few minutes. The RIC-producing capacity of animals, depends on viability, is significantly modified according to physiological- (depletion), drug- (toxin or stimulator) and environmental (temperature, salt content and pH) effects. The E. dilatata-produced RIC is affected by protein disruptors but is resistant to several chemical influences and its Rotimer component has an overwhelming cell (algae, yeast and human neuroblastoma) motility inhibitory effect, associated with low toxicity. This biopolymer-secretion-capacity is protective of rotifers against human-type beta-amyloid aggregates.

Evaluation of NK cell cytotoxic activity against malignant cells by the calcein assay.

The immune system exerts a tight cancer surveillance to eradicate nascent and developing tumors. Natural killer (NK) cells rely on their cytotoxic activity to eliminate abnormal or stressed cells, including those undergoing malignant transformation. Thereupon, NK cells, along with CD8+ T cells, are effector immune cells with a pivotal role in cancer immunosurveillance. Due to the outstanding effectivity of immunotherapy in cancer management, strategies aimed at boosting NK cell-mediated tumor recognition and elimination are being thoroughly studied, such as approaches to induce tumor surface expression of NK cell activating ligands. Additionally, the development of methods to evaluate NK cell cytotoxic responses towards malignant cells with distinct immunogenic profiles is of paramount relevance. In this chapter, we detail a simple but highly sensitive and reproducible methodological approach to quantify in vitro NK cell-mediated lysis of a given target cell, e.g. a tumor cell, based on calcein-AM staining and fluorescence detection. Further, this method can be employed to determine the impact of chemical modulators or antibodies blocking cell surface proteins on the antitumor capacity of NK cells, with the aim to improve anticancer immune responses and elucidate the underlying mechanisms regulating NK cell activity.

Analyzing the Quenchable Iron Pool in Murine Macrophages by Flow Cytometry.

Tissue-resident macrophages are pivotal for a tightly-regulated iron metabolism at a cellular and systemic level, since subtle iron alterations increase the susceptibility for microbial infections or drive multiple diseases. However, research on cellular iron homeostasis in macrophages remains challenging due to the limited amount of available methods using radioactive 59Fe isotopes or strong iron chelators, which might be inapplicable in certain experimental settings. This protocol describes the analysis of the quenchable iron pool (QIP) in macrophages by loading these cells with exogenous iron-complexes. Thereby, the cytoplasmic iron pool can be determined, since the iron uptake ability of macrophages inversely correlates with intracellular iron levels. Thus, this assay enables the accurate analysis of even minor alterations in cytoplasmic iron fluxes and is applicable in almost every laboratory environment. In addition, the protocol can also be adopted for other immune cell types in vitro and in vivo.

Nisin penetration and efficacy against Staphylococcus aureus biofilms under continuous-flow conditions.

Biofilms may enhance the tolerance of bacterial pathogens to disinfectants, biocides and other stressors by restricting the penetration of antimicrobials into the matrix-enclosed cell aggregates, which contributes to the recalcitrance of biofilm-associated infections. In this work, we performed real-time monitoring of the penetration of nisin into the interior of Staphylococcus aureus biofilms under continuous flow and compared the efficacy of this lantibiotic against planktonic and sessile cells of S. aureus. Biofilms were grown in Center for Disease Control (CDC) reactors and the spatial and temporal effects of nisin action on S. aureus cells were monitored by real-time confocal microscopy. Under continuous flow, nisin caused loss of membrane integrity of sessile cells and reached the bottom of the biofilms within ~20 min of exposure. Viability analysis using propidium iodide staining indicated that nisin was bactericidal against S. aureus biofilm cells. Time-kill assays showed that S. aureus viability reduced 6.71 and 1.64 log c.f.u. ml-1 for homogenized planktonic cells in exponential and stationary phase, respectively. For the homogenized and intact S. aureus CDC biofilms, mean viability decreased 1.25 and 0.50 log c.f.u. ml-1, respectively. Our results demonstrate the kinetics of biofilm killing by nisin under continuous-flow conditions, and shows that alterations in the physiology of S. aureus cells contribute to variations in sensitivity to the lantibiotic. The approach developed here could be useful to evaluate the antibiofilm efficacy of other bacteriocins either independently or in combination with other antimicrobials.

A platelet viability assay (PVA) for the diagnosis of heparin-induced thrombocytopenia.

Diagnosing heparin-induced thrombocytopenia (HIT) requires functional assays measuring platelet activation as they are highly specific and sensitive. A useful functional test for diagnosing HIT is the serotonin release assay (SRA), but this assay is technically demanding and requires a radioactive marker. We describe an alternate functional HIT assay, the platelet viability assay (PVA), that overcomes the need for a radioactive marker by using a viability dye endpoint to measure platelet activation. We compared the performance characteristics of the PVA to the SRA. Serum samples from 76 patients with suspected HIT were tested in both the PVA and the SRA. The PVA uses calcein-AM as a marker of platelet viability, with decreases in fluorescence and cell size as surrogate markers for platelet activation. A significant linear correlation (Spearman correlation, r = -0.78, P < 0.0001) was observed between the PVA and SRA. Calcein-AM fluorescence decreased in a negative linear relationship with platelet activation as measured by 14C-serotonin release. The PVA detected all positive SRA samples, with an overall sensitivity of 100% and a specificity of 97% in comparison to the SRA. The measurement of platelet viability using the PVA provided similar results to the SRA when testing suspected HIT patient samples.

5-Oxo-hexahydroquinoline derivatives as modulators of P-gp, MRP1 and BCRP transporters to overcome multidrug resistance in cancer cells.

Multidrug resistance (MDR) in cancer cells is often associated with overexpression of ATP-binding cassette (ABC) transporters, including P-glycoprotein (P-gp/ABCB1), multidrug resistance-associated protein 1 (MRP1/ABCC1) and breast cancer resistance protein (BCRP/ABCG2). Modulators of these transporters might be helpful in overcoming MDR. Moreover, exploiting collateral sensitivity (CS) could be another approach for efficient treatment of cancer. Twelve novel 5-oxo-hexahydroquinoline derivatives bearing different aromatic substitutions at C4, while having 2-pyridyl alkyl carboxylate substituents at the C3 were synthesized and evaluated for MDR reversal activity by flow cytometric determination of rhodamine 123, calcein and mitoxantrone accumulations in P-gp, MRP1 and BCRP-overexpressing cell lines, respectively. Furthermore, to confirm the P-gp inhibitory activity, the effect of compounds on the reduction of doxorubicin's IC50 of drug-resistant human uterine sarcoma cell line, MES-SA/DX5, was evaluated. Compounds D6, D5 and D3 (bearing 3-chlorophenyl, 2,3-dichlorophenyl and 4-chlorophenyl substituents at C4 position of 5-oxo-hexahydroquinoline core) were the most potent P-gp, MRP1 and BCRP inhibitors, respectively, causing significant MDR reversal at concentrations of 1-10 µM. Additionally, D4 (containing 3-flourophenyl) was the most effective MRP1-dependent CS inducing agent. Overall, chlorine containing compounds D6, C4 and D3 were capable of significant inhibition of all 3 important efflux pumps in cancer cells. Moreover, D6 also induced CS triggered by reducing glutathione efflux. In conclusion, some of the 5-oxo-hexahydroquinoline derivatives are effective efflux pump inhibitors capable of simultaneously blocking 3 important ABC transporters involved in MDR, and represent promising agents to overcome MDR in cancer cells.

Nonionic surfactants increase digoxin absorption in Caco-2 and MDCKII MDR1 cells: Impact on P-glycoprotein inhibition, barrier function, and repeated cellular exposure.

Nonionic surfactants commonly used in pharmaceutical formulations may have P-glycoprotein (P-gp) inhibiting and/or permeation enhancing effects. The present work aims to distinguish these effects and assess the degree of cellular recovery after multiple exposures to nonionic surfactants. The investigated surfactants were polysorbates (PS): PS20, PS40, PS60, PS65, PS80 and PS85; monosaccharide-based: lauroyl methyl glucamide and n-nonyl-ß-D-glucopyranoside; or disaccharide-based: lauryl-ß-D-maltoside and trehalose 6-laurate. Bi-directional permeability studies of digoxin and mannitol, and calcein-AM efflux assay were performed in cell cultures. Cellular recovery was evaluated by continuous measurements of transepithelial electrical resistance (TEER) in Caco-2 cell monolayers. Polysorbates with one fatty acid chain decreased the efflux of digoxin through P-gp inhibition in MDCKII MDR1 cells. Mono- and di-saccharide-based surfactants, in a dose dependent manner, enhanced digoxin absorptive permeability without decreasing the secretory permeability in Caco-2 cells, suggesting that the surfactants had a transcellular permeation enhancing effect. Caco-2 cell monolayers recovered to different degrees of 60-100% of the initial TEER values. Calcein-AM assay was found to be non-predictive to surfactants influence on digoxin permeability across cell monolayers. In conclusion, these results may assist, in a mechanism-based, selection of suitable surfactants for formulating oral dosage forms to enhance the absorption of low bioavailable P-gp substrates.