Successful functioning of biological cells relies on efficient translocation of different materials across cellular membranes. An important part of this transportation system is membrane channels that are known as antiporters and symporters. They exploit the energy stored as a trans-membrane gradient of one type of molecules to transport the other types of molecules against their gradients. For symporters, the directions of both fluxes for driving and driven species coincide, while for antiporters, the fluxes move in opposite directions. There are surprising experimental observations that despite differing only by the direction of transport fluxes, the molecular mechanisms of translocation adopted by antiporters and symporters seem to be drastically different. We present chemical-kinetic models to quantitatively investigate this phenomenon. Our theoretical approach allows us to explain why antiporters mostly utilize a single-site transportation when only one molecule of any type might be associated with the channel. At the same time, the transport in symporters requires two molecules of different types to be simultaneously associated with the channel. In addition, we investigate the kinetic constraints and efficiency of symporters and compare them with the same properties of antiporters. Our theoretical analysis clarifies some important physical-chemical features of cellular trans-membrane transport.

In epithelial cells, the cystic fibrosis transmembrane conductance regulator (CFTR), a cAMP-regulated Cl- channel, plays a key role in water and electrolytes secretion. A dysfunctional CFTR leads to the dehydration of the external environment of the cells and to the production of viscous mucus in the airways of cystic fibrosis patients. Here, we applied the quadriwave lateral shearing interferometry (QWLSI), a quantitative phase imaging technique based on the measurement of the light wave shift when passing through a living sample, to study water transport regulation in human airway epithelial CFBE and CHO cells expressing wild-type, G551D- and F508del-CFTR. We were able to detect phase variations during osmotic challenges and confirmed that cellular volume changes reflecting water fluxes can be detected with QWLSI. Forskolin stimulation activated a phase increase in all CFBE and CHO cell types. This phase variation was due to cellular volume decrease and intracellular refractive index increase and was completely blocked by mercury, suggesting an activation of a cAMP-dependent water efflux mediated by an endogenous aquaporin (AQP). AQP3 mRNAs, not AQP1, AQP4 and AQP5 mRNAs, were detected by RT-PCR in CFBE cells. Readdressing the F508del-CFTR protein to the cell surface with VX-809 increased the detected water efflux in CHO but not in CFBE cells. However, VX-770, a potentiator of CFTR function, failed to further increase the water flux in either G551D-CFTR or VX-809-corrected F508del-CFTR expressing cells. Our results show that QWLSI could be a suitable technique to study water transport in living cells. We identified a CFTR and cAMP-dependent, mercury-sensitive water transport in airway epithelial and CHO cells that might be due to AQP3. This water transport appears to be affected when CFTR is mutated and independent of the chloride channel function of CFTR.

To study the mass transport of mucociliary clearance of the human upper respiratory tract, a two-dimensional mass transport model based on the ciliated movement was established by using the immersed boundary-lattice Boltzmann method (IB-LBM). In this model, different characteristics of the mucus layer (ML) and the periciliary liquid (PCL) were taken into account. A virtual elastic membrane was introduced to divide the two layers dynamically. All moving boundaries that were involved in the present simulation were modeled with the immersed boundary. The Newtonian fluid was used to model the flow in PCL, and the viscoelastic fluid based on the Oldroyd-B model was used for the flow in ML; the two types of flow were both solved by the LBM framework. Based on the model, the ML thickness, the cilia density, and the phase difference of adjacent cilia were regulated, respectively, to study the transport velocity of the ML. In addition, the motion law of solid particles in PCL was also studied. According to the results, four primary conclusions were drawn. (1) At a given beating pattern, the increase of the ML thickness will decrease its transport velocity. (2) Increasing the cilia density can promote the mean transport velocity of the ML. (3) By raising the phase difference of adjacent cilia to a certain scope, the transport of ML can be accelerated. (4) In PCL, particles initially located on the upper part of the cilia tend to migrate upward and then get close to the ML. The above study can provide some reasonable explanations for the mechanism of the mucociliary clearance system, which is also helpful to the further understanding of the mass transport principle of the human upper respiratory tract.

l-Type amino acid transporter 1 (LAT1), selectively expressed at the blood-brain barrier (BBB) and brain parenchymal cells, mediates brain delivery of drugs and prodrugs such as l-dopa and gabapentin. Although knowledge about BBB transport of LAT1-utilizing prodrugs is available, there is a lack of quantitative information about brain intracellular delivery and influence of prodrugs on the transporter\'s physiological state. We studied the LAT1-mediated intrabrain distribution of a recently developed prodrug of the cyclooxygenase inhibitor ketoprofen as well as its impact on transporter protein expression and function (i.e., amino acid exchange) using brain slice method in mice and rats. The intrabrain distribution of the prodrug was 16 times higher than that of ketoprofen. LAT1 involvement in brain cellular barrier uptake of the prodrug was confirmed, reflected by a higher unbound brain intracellular compared to brain extracellular fluid concentration. The prodrug did not alter LAT1 protein expression and amino acid exchange. Integration of derived parameters with previously performed in vivo pharmacokinetic study using the Combinatory Mapping Approach allowed to estimate the brain extra- and intracellular levels of unbound ketoprofen, prodrug, and released parent drug. The overall efficiency of plasma to brain intracellular delivery of prodrug-released ketoprofen was 11 times higher than after ketoprofen dosing. In summary, this study provides quantitative information supporting the use of the LAT1-mediated prodrug approach for enhanced brain delivery of drugs with intracellular targets.

Phenols are the most abundant naturally accessible antioxidants present in a human normal diet. Since numerous beneficial applications of phenols as preventive agents in various diseases were revealed, the evaluation of phenols bioavailability is of high interest of researchers, consumers and drug manufacturers. The hydrophilic nature of phenols makes a cell membrane penetration difficult, which imply an alternative way of uptake via membrane transporters. However, the structural and functional data of membrane transporters are limited, thus the in silico modelling is really challenging and urgent tool in elucidation of transporter ligands. Focus of this research was a particular transporter bilitranslocase (BTL). BTL has a broad tissue expression (vascular endothelium, absorptive and excretory epithelia) and can transport wide variety of poly-aromatic compounds. With available BTL data (pKi [mmol/L] for 120 organic compounds) a robust and reliable QSAR models for BTL transport activity were developed and extrapolated on 300 phenolic compounds. For all compounds the transporter profiles were assessed and results show that dietary phenols and some drug candidates are likely to interact with BTL. Moreover, synopsis of predictions from BTL models and hits/predictions of 20 transporters from Metrabase and Chembench platforms were revealed. With such joint transporter analyses a new insights for elucidation of BTL functional role were acquired. Regarding limitation of models for virtual profiling of transporter interactions the computational approach reported in this study could be applied for further development of reliable in silico models for any transporter, if in vitro experimental data are available.

In this paper, we report on using mass transport to control nutrition supply of colorectal cancer cells for developing a microtumor in a confined microchamber. To mimic the spatial heterogeneity of a tumor, two microfluidic configurations based on resistive circuits are designed. One has a convection-dominated microchamber to simulate the tumor region proximal to leaky blood vessels. The other has a diffusion-dominated microchamber to mimic the tumor core that lacks blood vessels and nutrient supply. Thus, the time for nutrition to fill the microchamber can vary from tens of minutes to several hours. Results show that cells cultured under a diffusive supply of nutrition have a high glycolytic rate and a nearly constant oxygen consumption rate. In contrast, cells cultured under convective supply of nutrition have a gradual increase of oxygen consumption rate with a low glycolytic rate. This suggests that cancer cells have distinct reactions under different mass transport and nutrition supply. Using these two microfluidic platforms to create different rate of nutrition supply, it is found that a continuous microtumor that almost fills the mm-size microchamber can be developed under a low-nutrient supply environment, but not for the convective condition. It also is demonstrated that microchannels can simulate the delivery of anti-cancer drugs to the microtumor under controlled mass-transport. This method provides a means to develop a larger scale microtumor in a lab-on-a-Chip system for post development and stimulations, and microchannels can be applied to control the physical and chemical environment for anti-cancer drug screening.

Drug-induced liver injury (DILI) is a leading cause of acute liver failure and transplantation. DILI can be the result of impaired hepatobiliary transporters, with altered bile formation, flow, and subsequent cholestasis. We used gadoxetate dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI), combined with pharmacokinetic modelling, to measure hepatobiliary transporter function in vivo in rats. The sensitivity and robustness of the method was tested by evaluating the effect of a clinical dose of the antibiotic rifampicin in four different preclinical imaging centers. The mean gadoxetate uptake rate constant for the vehicle groups at all centers was 39.3 +/- 3.4 s-1 (n = 23) and 11.7 +/- 1.3 s-1 (n = 20) for the rifampicin groups. The mean gadoxetate efflux rate constant for the vehicle groups was 1.53 +/- 0.08 s-1 (n = 23) and for the rifampicin treated groups was 0.94 +/- 0.08 s-1 (n = 20). Both the uptake and excretion transporters of gadoxetate were statistically significantly inhibited by the clinical dose of rifampicin at all centers and the size of this treatment group effect was consistent across the centers. Gadoxetate is a clinically approved MRI contrast agent, so this method is readily transferable to the clinic.
Rate constants of gadoxetate uptake and excretion are sensitive and robust biomarkers to detect early changes in hepatobiliary transporter function in vivo in rats prior to established biomarkers of liver toxicity.

To develop a new pesticide with phloem mobility, a series of new amino acid-fipronil conjugates were designed and synthesized based on derivatization at the 3-position of the pyrazole ring of fipronil. Experiments using a Ricinus communis seedling system showed that all tested conjugates were phloem mobile except for the isoleucine-fipronil conjugate, and that the serine-fipronil conjugate (4g) exhibited the highest concentration in phloem sap (52.00 ± 5.80 μM). According to prediction with log Cf values and uptake experiments with Xenopus oocytes, the phloem loading process of conjugate 4g involved both passive diffusion and an active carrier system (RcANT15). In particular, compared with for a previously reported glycinergic-fipronil conjugate (GlyF), passive diffusion played a more important role for conjugate 4g in the enhancement of phloem mobility. This study suggests that associating a nutrient at a different position of an existing pesticide structure could still be effective in obtaining phloem-mobile derivatives, but the distinct physicochemical properties of resultant conjugates may lead to different phloem loading mechanisms.

Ketone bodies are neuroprotective in neurological disorders such as epilepsy. We randomly studied nine healthy human subjects twice-with and without continuous infusion of 3-hydroxybutyrate-to define potential underlying mechanisms, assessed regionally (parietal, occipital, temporal, cortical grey, and frontal) by PET scan. During 3-hydroxybutyrate infusions concentrations increased to 5.5±0.4 mmol/l and cerebral glucose utilisation decreased 14%, oxygen consumption remained unchanged, and cerebral blood flow increased 30%. We conclude that acute 3-hydroxybutyrate infusion reduces cerebral glucose uptake and increases cerebral blood flow in all measured brain regions, without detectable effects on cerebral oxygen uptake though oxygen extraction decreased. Increased oxygen supply concomitant with unchanged oxygen utilisation may contribute to the neuroprotective effects of ketone bodies.

Mg-based stent is a promising candidate of the next generation fully degradable vascular stents. The latest progress includes the CE approval of the Magmaris ® WE43 based drug eluting stent. However, so far, the long term (more than 1 year implantation) in vivo degradation and the physiological effects caused by the degradation products were still unclear. In this study, a 20 month observation was carried out after the bare Mg-Nd-Zn-Zr (abbr. JDBM) stent prototype was implanted into the common carotid artery of New Zealand white rabbit in order to evaluate its safety, efficacy and especially degradation behavior. The degradation of the main second phase Mg12Nd was also studied. Results showed that the bare JDBM stent had good safety and efficacy with a complete re-endothelialization within 28 days. The JDBM stent struts were mostly replaced in situ by degradation products in 4 month. The important finding was that the volume and Ca concentration of the degradation products decreased in the long term, eliminating the clinicians\' concern of possible vessel calcification. In addition, the alloying elements Mg and Zn in the stent could be safely metabolized as continuous enrichment in any of the main organs were not detected although Nd and Zr showed an abrupt increase in spleen and liver after 1 month implantation. Collectively, the long term in vivo results showed the rapid re-endothelialization of JDBM stent and the long term safety of the degradation products, indicating its great potential as the backbone of the fully degradable vascular stent.
Mg-based stent is a promising candidate of the next generation fully degradable stents, especially after the recent market launch of one of its kind (Magmaris). However the fundamental question about the long term degradation and metabolic mechanism of Mg-based stent and its degradation products remain unanswered. We implanted our patented Mg-Nd-Zn-Zr bare stent into the common carotid artery of rabbits and conducted a 20 months observation. We found that the Ca containing degradation products could be further degraded in vivo. All the alloying elements showed no continuous enrichment in the main organs of rabbits. These findings eliminate the clinicians\' concern of possible vessel calcification and element enrichment after the implantation of Mg alloy based stents to some extent.