Sulfadimethoxine and rhodamine B as oral biomarkers for European badgers (Meles meles)

A field study was carried out on Little Island (County Waterford, Ireland) in June 2000 to evaluate the potential of a bait-marking system for use in European badgers (Meles meles). Two oral biomarkers, sulfadimethoxine (SDM) and rhodamine B, were incorporated into fishmeal baits and distributed by hand at main sets in five test territories for 3 consecutive days. In parallel, non-biomarked baits were distributed at a single control territory. The objectives of the study were to: (1) assess the effects of SDM and rhodamine B on palatability and thus bait acceptance, and (2) investigate the marking capacity of SDM and rhodamine B in serum and hair samples taken from badgers. Trapping was carried out in each territory for 5 consecutive days immediately after bait distribution. Analysis of data revealed that 90-100% of baits were removed in four of the test territories and from the control territory. In the fifth test territory, 61% of baits were removed. Of the badgers (n = 26) trapped in the test territories, 18 (69%) were positive when tested for both biomarkers. In contrast, the remaining eight animals and those captured in the control territory (n = 6 badgers) were negative. In the marked animals, the highest levels of SDM were recorded in serum samples taken soon after bait distribution. Thereafter, the levels declined in each badger over the course of the study. In contrast, rhodamine B was readily detectable by fluorescence microscopy of hair samples throughout the period of study. The results indicate that SDM and rhodamine B act as systemic markers in badgers and have potential future applications for monitoring of oral vaccine uptake.

Intestinal patches for oral drug delivery

PURPOSE

Oral route offers an attractive mode of drug administration, although its applications are limited by poor stability of peptides and proteins in the gastrointestinal tract. In this article, we report a novel method based on intestinal patches for oral drug delivery. This method involves the use of millimeter size mucoadhesive patches that adhere to the intestinal wall and direct solute diffusion towards the wall similar to that observed in the case of a transdermal patch.

METHODS

Intestinal patches were prepared by sandwiching a film of cross-linked bovine serum albumin microspheres between a film of ethyl cellulose and Carbopol/pectin. Delivery of three model drugs, sulforhodamine B. phenol red, and dextran was assessed in vitro using rat intestine.

RESULTS

In vitro tests confirmed substantial unidirectional diffusion of model drugs from the patch across the intestinal wall. The presence of ethyl cellulose layer minimized release from the edges as well as from the back side of the patch into the intestinal lumen. In vitro experiments with rat intestine showed that patches were effective in delivering model drugs across the intestine. Trans-lumenal flux of model drugs from intestinal patches was about 100-fold higher compared to that from a solution due to localization of the solute near the intestinal wall and due to minimization of drug loss into the intestinal lumen.

CONCLUSIONS

Intestinal patches offer a novel approach for oral drug delivery.

Regulation of MRP2-mediated transport in shark rectal salt gland tubules

We examined endothelin-1 (ET-1) regulation of the xenobiotic efflux pump, multidrug resistance-associated protein isoform 2 (MRP2), in intact dogfish shark rectal salt gland tubules using a fluorescent substrate sulforhodamine 101 and confocal microscopy. Subnanomolar to nanomolar concentrations of ET-1 rapidly reduced the cell-to-lumen transport of sulforhodamine 101. These effects were prevented by an ET(B) receptor antagonist but not by an ET(A) receptor antagonist. Immunostaining with an antibody to mammalian ET(B) receptors showed specific localization to the basolateral membrane of the shark rectal gland epithelial cells. ET-1 effects on transport were blocked by a protein kinase C (PKC)-selective inhibitor, implicating PKC in ET-1 signaling. A protein kinase A (PKA)-selective inhibitor had no effect. Forskolin reduced luminal accumulation of sulforhodamine 101, but inhibition of PKA did not block the forskolin effect. Consistent with this observation, a cAMP analog that does not activate PKA reduced luminal accumulation of sulforhodamine 101. These results indicate that shark rectal gland transport on MRP2 is regulated by ET acting through an ET(B) receptor and PKC. In addition, cAMP affects transporter function through a PKA-independent mechanism, possibly by competition for transport.

Simultaneous detection of both nitric oxide and reactive oxygen species in guinea pig vestibular sensory cells

Gentamicin-induced production of reactive oxygen species (ROS) and of nitric oxide (NO) in the vestibular end organs of the guinea pig was investigated by applying two new fluorescence indicators, 4,5-diaminofluorescein diacetate for direct detection of NO and dihydrotetramethylrosamine for ROS. The vestibular sensory cells produced both NO and ROS after exposure to gentamicin. A nonspecific inhibitor of NO synthase, L-NAME, inhibited the production of NO but did not appear to affect the production of ROS following exposure to gentamicin. In contrast, a radical scavenger, D-methionine, or the neurotrophin BDNF suppressed the production of ROS, in turn stimulating NO production. These findings could indicate that both NO and ROS play an important role in aminoglycoside ototoxicity.

Intracellular generation of free radicals and modifications of detoxifying enzymes in cultured neurons from the developing rat forebrain in response to transient hypoxia

To address the influence of oxidative stress and defense capacities in the effects of transient hypoxia in the immature brain, the time course of reactive oxygen species generation was monitored by flow cytometry using dihydrorhodamine 123 and 2',7'-dichlorofluorescein-diacetate in cultured neurons issued from the fetal rat forebrain and subjected to hypoxia/reoxygenation (6 h/96 h). Parallel transcriptional and activity changes of superoxide dismutases, glutathione peroxidase and catalase were analyzed, in line with cell outcome. The study confirmed hypoxia-induced delayed apoptotic death, and depicted increased mitochondrial and cytosolic productions of free radicals (+30%) occurring over the 48-h period after the restoration of oxygen supply, with sequential stimulations of superoxide dismutases. Whereas catalase mRNA levels and activity were augmented by cell reoxygenation, glutathione peroxidase activity was transiently repressed (-24%), along with reduced glutathione reductase activity (-27%) and intracellular glutathione depletion (-19%). Coupled with the neuroprotective effects of the glutathione precursor N-acetyl-cysteine (50 microM), these data suggest that hypoxia/reoxygenation-induced production of reactive oxygen species can overwhelm glutathione-dependent antioxidant capacity, and thus may contribute to the resulting neuronal apoptosis.

Frequency dependence of sonophoresis

PURPOSE

Application of low-frequency ultrasound has been shown to increase skin permeability, thereby facilitating delivery of macromolecules (low-frequency sonophoresis). In this study, we sought to determine the dependence of low-frequency sonophoresis on ultrasound frequency, intensity and energy density.

METHODS

Pig skin was exposed to low-frequency ultrasound over a range of ultrasound frequency and intensity conditions. The degree of skin permeabilization was measured using its conductivity. Imaging experiments were also carried out to visualize the transport pathways created by ultrasound.

RESULTS

The data showed that for each frequency (in the range of 19.6-93.4 kHz), there exists a threshold intensity below which no detectable conductivity enhancement was observed. The threshold intensity increased with frequency. It is feasible to achieve the desired conductivity (permeability) enhancement regardless of the choice of frequency, although the necessary energy density is higher at higher frequencies. Low frequencies (approximately 20 kHz) induced localized transport compared to a more dispersed effect seen with higher frequencies (approximately 58.9 kHz).

CONCLUSIONS

This study provides a quantitative understanding of the effects of low-frequency ultrasound on skin permeability.

Static compression of articular cartilage can reduce solute diffusivity and partitioning: implications for the chondrocyte biological response

Chondrocytes depend upon solute transport within the avascular extracellular matrix of adult articular cartilage for many of their biological activities. Alterations to bioactive solute transport may, therefore, represent a mechanism by which cartilage compression is transduced into cellular metabolic responses. We investigated the effects of cartilage static compression on diffusivity and partitioning of a range of model solutes including dextrans of molecular weights 3 and 40 kDa, and tetramethylrhodamine (a 430 Da fluorophore). New fluorescence methods were developed for real-time visualization and measurement of transport within compressed cartilage explants. Experimental design allowed for multiple measurements on individual explants at different compression levels in order to minimize confounding influences of compositional variations. Results demonstrate that physiological levels of static compression may significantly decrease solute diffusivity and partitioning in cartilage. Effects of compression were most dramatic for the relatively high molecular weight solutes. For 40 kDa dextran, diffusivity decreased significantly (p<0.01) between 8% and 23% compression, while partitioning of 3 and 40 kDa dextran decreased significantly (p<0.01) between free-swelling conditions and 8% compression. Since diffusivity and partitioning can influence pericellular concentrations of bioactive solutes, these observations support a role for perturbations to solute transport in mediating the cartilage biological response to compression.

Culture model of human corneal epithelium for prediction of ocular drug absorption

PURPOSE

The main purpose of this study was to develop a cell culture model of immortalized epithelium from the human cornea for drug permeability testing.

METHODS

Immortalized human corneal epithelial (HCE) cells were grown on filters, with various filter materials and coating procedures. In the optimal case, HCE cells were grown on polyester filters coated with rat tail collagen gel containing fibroblast cells. Transepithelial electrical resistance (TER) was measured during the growth of the cells to evaluate the epithelial differentiation and tightness of the epithelial cell layers. Transmission electron microscopy (TEM) was used to show the formation of tight junctions, desmosomes, and microvilli. Cellular morphology was characterized by light microscopy. Permeabilities of (3)H-mannitol and 6-carboxyfluorescein were determined, to evaluate the intercellular spaces of the epithelium. Rhodamine B was used as a lipophilic marker of transcellular permeability. Permeabilities of the excised rabbit corneas were determined in side-by-side diffusion chambers.

RESULTS

The TER values of the corneal epithelial cultures were 200 to 800 Omega x cm(2), depending on the culture conditions. In optimal conditions, cultured corneal epithelium consisted of five to eight cell layers, TER was at least 400 Omega x cm(2), and the most apical cells were flat, with tight junctions, microvilli, and desmosomes. The permeability coefficients (P(cell), 10(-6) cm/sec) for (3)H-mannitol, 6-carboxyfluorescein, and rhodamine B were 1.42 +/- 0.36, 0.77 +/- 0.40, and 16.3 +/- 4.0, respectively. Corresponding values (at 10(-6) cm/sec) for the isolated rabbit corneas were 0.38 +/- 0.16, 0.46 +/- 0.27, and 18.1 +/- 4.0, respectively.

CONCLUSIONS

The TER, morphology, and permeability of the cultured corneal epithelial cells resemble those of the intact cornea. This cell culture model may be useful in evaluation of corneal drug permeation and its mechanisms.

Poly(D,L-lactide) foams modified by poly(ethylene oxide)-block-poly(D,L-lactide) copolymers and a-FGF: in vitro and in vivo evaluation for spinal cord regeneration

The first goal of this study was to examine the influence that poly(ethylene oxide)-block-poly(D,L-lactide) (PELA) copolymer can have on the wettability, the in vitro controlled delivery capability, and the degradation of poly(D,L-lactide) (PDLLA) foams. These foams were prepared by freeze-drying and contain micropores (10 microm) in addition of macropores (100 microm) organized longitudinally. Weight loss, water absorption, changes in molecular weight, polymolecularity (Mw/Mn) and glass transition temperature (Tg) of PDLLA foams mixed with various amounts of PELA were followed with time. It was found that 10wt% of PELA increased the wettability and the degradation rate of the polymer foams. The release of sulforhodamine (SR) was compared for PDLLA and PDLLA-PELA foams in relation with the foam porosity. An initial burst release was observed only in the case of the 90:10 PDLLA/PELA foam. The ability of the foam of this composition to be integrated and to promote tissue repair and axonal regeneration in the transected rat spinal cord was investigated. After implantation of ca. 20 polymer rods assembled with fibrin-glue, the polymer construct was able to bridge the cord stumps by forming a permissive support for cellular migration, angiogenesis and axonal regrowth.

Microcirculatory responses to repeated embolism-reperfusion in cerebral microvessels of cat: a fluorescence videomicroscopic study

Intra-carotid injections of degradable starch microspheres (DSMs) can induce DSM embolism-reperfusion in the level of cerebral arterioles. Vascular responses of cerebral arterioles to repeated DSM embolism (ischemia)-reperfusion were examined when DSMs were injected twice through a carotid artery with a time interval of 30 min. Arteriolar diameter was measured from images of arterioles filled with rhodamine-B isothiocyanate dextran and red cell velocity was measured with a dual window technique using FITC-labeled red cells as a flow tracer. DSM embolization induced ischemia (flow reduction including stasis) for approximately 10 min in the level of microvessels (arterioles). Cerebral arterioles began to dilate immediately after embolism induced by the DSM injection and vasodilation was sustained until reperfusion. After reperfusion the arteriole began to constrict and the arteriolar diameter returned to the initial diameter level at approximately 20 min after the DSM injection. The arteriolar diameters for the second DSM embolism showed a similar response to those for the first embolism in 7 out of 8 cats. It can be concluded that the vascular response of cerebral arterioles to the second embolism-reperfusion could not be affected by the first embolism-reperfusion.

Anatomical evidence for brainstem circuits mediating feeding motor programs in the leopard frog, Rana pipiens

Using injections of small molecular weight fluorescein dextran amines, combined with activity-dependent uptake of sulforhodamine 101 (SR101), brainstem circuits presumed to be involved in feeding motor output were investigated. As has been shown previously in other studies, projections to the cerebellar nuclei were identified from the cerebellar cortex, the trigeminal motor nucleus, and the vestibular nuclei. Results presented here suggest an additional pathway from the hypoglossal motor nuclei to the cerebellar nucleus as well as an afferent projection from the peripheral hypoglossal nerve to the Purkinje cell layer of the cerebellar cortex. Injections in the cerebellar cortex combined with retrograde labeling of the peripheral hypoglossal nerve demonstrate anatomical convergence at the level of the medial reticular formation. This suggests a possible integrative region for afferent feedback from the hypoglossal nerve and information through the Purkinje cell layer of the cerebellar cortex. The activity-dependent uptake of SR101 additionally suggests a reciprocal, polysynaptic pathway between this same area of the medial reticular formation and the trigeminal motor nuclei. The trigeminal motor neurons innervate the m adductor mandibulae, the primary mouth-closing muscle. The SR101 uptake clearly labeled the ventrolateral hypoglossal nuclei, the medial reticular formation, and the Purkinje cell layer of the cerebellar cortex. Unlike retrograde labeling of the peripheral hypoglossal nerve, stimulating the hypoglossal nerve while SR101 was bath-applied labeled trigeminal motor neurons. This, combined with the dextran labeling, suggests a reciprocal connection between the trigeminal motor nuclei and the cerebellar nuclei, as well as the medulla. Taken together, these data are important for understanding the neurophysiological pathways used to coordinate the proper timing of an extremely rapid, goal-directed movement and may prove useful for elucidating some of the first principles of sensorimotor integration.

Structure and functional connections of presynaptic terminals in the vertebrate retina revealed by activity-dependent dyes and confocal microscopy

The fluorescent dyes sulforhodamine 101 (SR 101) and FM1-43 were used as activity-dependent dyes (ADDs) to label presynaptic terminals in the retinas of a broad range of animals, including amphibians, mammals, fish, and turtles. The pattern of dye uptake was studied in live retinal preparations by using brightfield, fluorescence, and confocal microscopy. When bath-applied to the retina-eyecup, these dyes were avidly sequestered by the presynaptic terminals of virtually all rods, cones, and bipolar and amacrine cells; ganglion cell dendrites and horizontal cells lacked significant dye accumulation. Other structures stained with these dyes included pigment epithelial cells, cone outer segments, and Müller cell end-feet. Studies of dye uptake in dark- and light-adapted preparations showed significant differences in the dye accumulation pattern in the inner plexiform layer (IPL), suggesting a dynamic, light-modulated control of endocytotic activity. Presynaptic terminals in the IPL could be segregated on the basis of volume: bipolar varicosities in the IPL were typically larger than those of amacrine cells. The combination of retrograde labeling of ganglion cells and presynaptic terminal labeling with ADDs served as the experimental preparation for three-dimensional reconstruction of both structures, based on dual detector, confocal microscopy. Our results demonstrate a new approach for studying synaptic interactions in retinal function. These findings provide new insights into the likely number and position of functional connections from amacrine and bipolar cell terminals onto ganglion cell dendrites.

In vitro visualization and quantification of oleic acid induced changes in transdermal transport using two-photon fluorescence microscopy

In a novel application of two-photon scanning fluorescence microscopy, three-dimensional spatial distributions of the hydrophilic and hydrophobic fluorescent probes, sulforhodamine B and rhodamine B hexyl ester, in excised full-thickness human cadaver skin were visualized and quantified. Both sulforhodamine B and rhodamine B hexyl ester were observed to lie primarily in the lipid multilamellae region surrounding the corneocytes within the stratum corneum. From the two-photon scanning fluorescence microscopy scans, the changes in the concentration gradient and the vehicle to skin partition coefficient of each probe induced by the oleic acid enhancer action were calculated relative to the control sample (not exposed to oleic acid), and subsequently applied to theoretically derived mathematical expressions of transdermal transport to quantitatively characterize the oleic acid-induced relative changes in the skin diffusion coefficient and the skin barrier diffusion length of the permeant. For the hydrophobic probe rhodamine B hexyl ester, the permeability enhancement was primarily driven by an increase in the vehicle to skin partition coefficient, leading to an increase in the steepness of the concentration gradient across the skin. The primary oleic acid-induced changes in the transport properties of the hydrophilic probe sulforhodamine B included increases in the vehicle to skin partition coefficient and the skin diffusion coefficient. These findings utilizing the two-photon scanning fluorescence microscopy methodology and data analysis described here demonstrate that, in addition to providing three-dimensional images that clearly delineate probe distributions in the direction of increasing skin depth, the subsequent quantification of these images provides additional important insight into the mechanistic changes in transdermal transport underlying the visualized changes in probe distributions across the skin.

A novel screening for inhibitors of a pleiotropic drug resistant pump, Pdr5, in Saccharomyces cerevisiae

Yeast is an excellent model system of eukaryotes for the study of molecular mechanisms of ATP-binding cassette transporters. Pdr5 protein is a yeast Saccharomyces cerevisiae ATP-binding cassette transporter conferring resistance to several unrelated drugs. Here, we described a novel drug screening system designated to detect compounds that inhibit the function of Pdr5. An indicator strain with increased drug sensitivity was constructed with an ergosterol-deficient background (delta syr1/erg3 null mutation). The sensitivity of the indicator strain (delta syr1/erg3 delta pdr5 delta snq2) to the Pdr5 substrates, cycloheximide and cerulenin, was increased 16-fold and 4-fold against wild type, respectively. The screening system is mainly based on the growth inhibition of the PDR5-overexpressed indicator strain with the combination of a sample and cycloheximide or cerulenin. The effect of an mdr inhibitor, FK506 on the screening system was clearly detected even at a low concentration (approximately 0.5 microg/ml). In addition, accumulation of rhodamine 6G in the cells was detected as a result of Pdr5 inhibition by FK506. These results indicated that the screening system is useful for a sensitive screening of Pdr5-specific inhibitors with low toxicity.

Projections from the nociceptive area of the central nucleus of the amygdala to the forebrain: a PHA-L study in the rat

The lateral capsular division (CeLC) of the central nucleus (Ce) of the amygdala, in the rat, has been shown to be the main terminal area of a spino(trigemino)-parabrachio-amygdaloid nociceptive pathway [Bernard & Besson (1990) J. Neurophysiol. 63, 473-490; Bernard et al. (1992) J. Neurophysiol. 68, 551-569; Bernard et al. (1993) J. Comp. Neurol. 329, 201-229]. The projections to the forebrain from the CeLC and adjacent regions were studied in the rat by using microinjections of Phaseolus vulgaris leucoagglutinin (PHA-L) restricted in subdivisions of the Ce and the basolateral amygdaloid nucleus anterior (BLA). Our data showed that the entire CeLC projects primarily and extensively to the substantia innominata dorsalis (SId). The terminal labelling is especially dense in the caudal aspect of the SId. The other projections of the CeLC in the forebrain were dramatically less dense. They terminate in the bed nucleus of the stria terminalis (BST) and the posterior hypothalamus (pLH). No (or only scarce) other projections were found in the remaining forebrain areas. The Ce lateral division (CeL) and the Ce medial division (CeM), adjacent to the CeLC, also project to the SId with slightly lower density labelling. However, contrary to the case of the CeLC, both the CeL and the CeM extensively project to the ventrolateral subnucleus of the BST (BSTvl) with a few additional terminals found in other regions of the lateral BST. Only the CeM projects densely to both the interstitial nucleus of the posterior limb of the anterior commissure and the caudal most portion of the pLH. The projections of the BLA are totally different from those of the Ce as they terminate in the dorsal striatum, the accumbens nucleus, the olfactory tubercle, the nucleus of olfactory tract and the rostral pole of the cingulate/frontal cortex. This study demonstrates that the major output of the nociceptive spino(trigemino)-parabrachio-CeLC pathway is to the SId. It is suggested that the CeLC-SId pathway could have an important role in anxiety, aversion and genesis of fear in response to noxious stimuli.

Entorhinal cortex projection cells to the hippocampal formation in vitro

Retrogradely labeled cells in superficial and deep layers of the entorhinal cortex (EC) were analyzed following application of the fluorescent tracer rhodamine-dextran-amine in different sites of the hippocampal formation in a slice preparation. The results demonstrate a strong projection from layer IV/V to the dentate gyrus, that is in slices significantly stronger than that from layer II. In deep layers a large number of multipolar cells were found which were only labeled by dye application to the subiculum. Patch-clamp recordings from these cells revealed intrinsic low threshold membrane potential oscillations, suggesting their possible contribution to oscillatory network activity of the EC and subiculum.

Phase I study of infusional paclitaxel in combination with the P-glycoprotein antagonist PSC 833

PURPOSE

PSC 833 (valspodar) is a second-generation P-glycoprotein (Pgp) antagonist developed to reverse multidrug resistance. We conducted a phase I study of a 7-day oral administration of PSC 833 in combination with paclitaxel, administered as a 96-hour continuous infusion.

PATIENTS AND METHODS

Fifty patients with advanced cancer were enrolled onto the trial. PSC 833 was administered orally for 7 days, beginning 72 hours before the start of the paclitaxel infusion. Paclitaxel dose reductions were planned because of the pharmacokinetic interactions known to occur with PSC 833.

RESULTS

In combination with PSC 833, maximum-tolerated doses were defined as paclitaxel 13.1 mg/m(2)/d continuous intravenous infusion (CIVI) for 4 days without filgrastim, and paclitaxel 17.5 mg/m(2)/d CIVI for 4 days with filgrastim support. Dose-limiting toxicity for the combination was neutropenia. Statistical analysis of cohorts revealed similar mean steady-state concentrations (C(pss)) and areas under the concentration-versus-time curve (AUCs) when patients received paclitaxel doses of 13.1 or 17.5 mg/m(2)/d for 4 days with PSC 833, as when they received a paclitaxel dose of 35 mg/m(2)/d for 4 days without PSC 833. However, the effect of PSC 833 on paclitaxel pharmacokinetics varied greatly among individual patients, although a surrogate assay using CD56+ cells suggested inhibition of Pgp was complete or nearly complete at low concentrations of PSC 833. Responses occurred in three of four patients with non-small-cell lung cancer, and clinical benefit occurred in five of 10 patients with ovarian carcinoma.

CONCLUSION

PSC 833 in combination with paclitaxel can be administered safely to patients provided the paclitaxel dose is reduced to compensate for the pharmacokinetic interaction. Surrogate studies with CD56+ cells indicate that the maximum-tolerated dose for PSC 833 gives serum levels much higher than those required to block Pgp. The variability in paclitaxel pharmacokinetics, despite complete inhibition of Pgp in the surrogate assay, suggests that other mechanisms, most likely related to P450, contribute to the pharmacokinetic interaction. Future development of combinations such as this should include strategies to predict pharmacokinetics of the chemotherapeutic agent. This in turn will facilitate dosing to achieve comparable CPss and AUCs.

A new drug-screening procedure for photosensitizing agents used in photodynamic therapy for CNV

PURPOSE

Because vascular occlusion has been observed as a consequence of photodynamic therapy (PDT), this method has been successfully used for the treatment of choroidal neovascularization (CNV) in age-related macular degeneration (AMD). However, most conventional photosensitizers, primarily developed for tumor PDT, lack selectivity for the targeting of neovascularization. An experimental model has been developed for drug screening of new photosensitizers for the treatment of CNV associated with AMD. It consists of intravenous (IV) injection of photosensitizers and fluorescent dyes into the chick's chorioallantoic membrane (CAM), followed by measurement of fluorescence pharmacokinetics, leakage from the vascular system, and photothrombic efficacy.

METHODS

Fertilized chicken eggs were placed under a fluorescence microscope. After intravenous injection of different dyes, time-dependent fluorescence angiography was performed. The effect of PDT parameters was assessed by fluorescence angiography 24 hours after PDT.

RESULTS

Although fluorescence of lipophilic benzoporphyrin derivative monoacid ring A (BPD-MA) remained intravascular during 2 hours, hydrophilic dyes tended to leak through the fenestrated neovascularization. By variation of PDT parameters, vascular damage could be directed toward closure of vessels with a diameter smaller than 10 microm, as measured 24 hours after PDT. High photosensitizer concentrations and high light doses resulted in blood flow stasis within 60 minutes, confirmed by fluorescence angiography.

CONCLUSIONS

Fluorescence angiography and PDT after IV injection into the CAM showed strong similarities to results obtained in clinical tests of PDT in CNV associated with AMD. Thus, this model can provide valuable information about PDT mechanisms and can be used for drug-screening purposes in development of improved sensitizers for the PDT of CNV.

The applicability of rat and human liver slices to the study of mechanisms of hepatic drug uptake

In the present study we investigated the applicability of the liver slice model to study mechanisms of drug uptake. Four model compounds were investigated that enter hepatocytes via entirely different membrane transport mechanisms. Rhodamine B (RB), which enters hepatocytes by passive diffusion, was homogeneously distributed throughout the rat liver slice (250 microm thickness) within 5 min, indicating that the penetration rate into the slice and the diffusion rate into the cells are rapid. In contrast, lucigenin (LU), which is taken up by hepatocytes through adsorptive endocytosis, was detected in the inner cell layers after 15 min. Digoxin uptake into the slice showed a temperature-dependent component and was stereoselectively inhibited by quinine, which is compatible with the involvement of a carrier-mediated uptake mechanism. The neo-glycoalbumin Lactose(27)-Human Serum Albumin (Lact(27)-HSA) and the negatively charged Succinylated-Human Serum Albumin (Suc-HSA) entered the slices and were taken up temperature-dependently into hepatocytes and endothelial cells, respectively. The liver slice preparation is a valuable tool to investigate the mechanisms of cellular uptake of drugs. Moreover, the precision-cut liver slices offer the unique possibility to study both hepatocyte and endothelial cell function in human and rat liver.

Microdialysis in the study of drug transporters in the CNS

Quantitative microdialysis in the central nervous system (CNS) has recently provided evidence for the existence of transporters as they relate to the brain distribution of a variety of drugs. Support for the existence of drug transporters in the blood-brain barrier (or in the blood-CSF barrier) comes from investigations that have found: unbound drug concentrations in brain fluids that are lower than corresponding levels in plasma; saturability of transport clearances across the blood-brain barrier and; the regulation of transport by putative inhibitors. Additional confirmatory evidence for the existence of active transport or carrier-mediated processes has also been derived from models that relate observed drug levels in the CNS with those in plasma or blood. The conclusion that reduced drug levels in brain fluids generally indicate the existence of active efflux transport is questioned. In the case of relatively polar compounds with modest blood-brain barrier permeability, lower unbound concentrations in brain may be a consequence of dilution by turnover of brain fluids. This review summarizes recent reports (grouped by class of compounds) where investigators have used microdialysis to examine the distribution of therapeutic agents to the CNS, and have reached conclusions regarding the functional presence of drug transporters in the brain.

The gapped xylem mutant identifies a common regulatory step in secondary cell wall deposition

The phenotype of the novel gapped xylem (gpx) mutant is described. gpx plants exhibit gaps in the xylem in positions where xylem elements would normally be located. These gaps are not part of the transpiration stream and result in gpx plants having fewer functional xylem elements. The gaps are due to the absence of a secondary cell wall in developing xylem elements, resulting in complete degradation of these elements during cell death, and illustrate the importance of the secondary cell wall in retaining a functional xylem element following programmed cell death. Consequently the gpx phenotype suggests that the processes of secondary cell wall formation and cell death are independently regulated in developing xylem. gpx plants also exhibit a highly irregular pattern of secondary cell wall thickening in interfascicular cells, with some cells apparently undergoing little or no secondary cell wall deposition. Secondary cell wall deposition in plants involves the co-ordinate regulation of several complex metabolic pathways. The gpx mutant identifies a key step involved in regulating the deposition of secondary cell wall material in both xylem and interfascicular cells, and suggests that a common regulatory step controls secondary cell wall formation in these diverse cell types. The gpx mutant offers a unique opportunity to elucidate the mechanism by which the complex processes involved in secondary cell wall formation are co-ordinately regulated.

Anaerobic and aerobic pathways for salvage of proximal tubules from hypoxia-induced mitochondrial injury

We have further examined the mechanisms for a severe mitochondrial energetic deficit, deenergization, and impaired respiration in complex I that develop in kidney proximal tubules during hypoxia-reoxygenation, and their prevention and reversal by supplementation with alpha-ketoglutarate (alpha-KG) + aspartate. The abnormalities preceded the mitochondrial permeability transition and cytochrome c loss. Anaerobic metabolism of alpha-KG + aspartate generated ATP and maintained mitochondrial membrane potential. Other citric-acid cycle intermediates that can promote anaerobic metabolism (malate and fumarate) were also effective singly or in combination with alpha-KG. Succinate, the end product of these anaerobic pathways that can bypass complex I, was not protective when provided only during hypoxia. However, during reoxygenation, succinate also rescued the tubules, and its benefit, like that of alpha-KG + malate, persisted after the extra substrate was withdrawn. Thus proximal tubules can be salvaged from hypoxia-reoxygenation mitochondrial injury by both anaerobic metabolism of citric-acid cycle intermediates and aerobic metabolism of succinate. These results bear on the understanding of a fundamental mode of mitochondrial dysfunction during tubule injury and on strategies to prevent and reverse it.

The lipopolysaccharide barrier: correlation of antibiotic susceptibility with antibiotic permeability and fluorescent probe binding kinetics

Lipopolysaccharide (LPS), the primary lipid on the surface of Gram-negative bacteria, is thought to act as a permeability barrier, making the outer membrane relatively impermeable to hydrophobic antibiotics, detergents, and host proteins. Mutations in the LPS biosynthetic apparatus increase bacterial susceptibility to such agents. To determine how this increased susceptibility is mediated, we have correlated antibiotic susceptibilities of rough (antibiotic resistant) and deep rough (antibiotic susceptible) bacterial strains with antibiotic permeabilities and fluorescent probe binding kinetics for bilayers composed of LPS purified from the same strains. Bilayer permeabilities of two hydrophobic beta-lactam antibiotics were measured by encapsulating the appropriate beta-lactamases in large unilamellar vesicles. In the presence of MgCl(2), permeabilities of LPS bilayers from rough and deep rough bacteria were similar and significantly lower than those of bacterial phospholipids (BPL). Addition of BPL to the LPS bilayers increased their antibiotic permeability to approximately the level of the BPL bilayers. Binding rates of the fluorescent probe bis-aminonaphthylsulfonic acid (BANS) were 2 orders of magnitude slower for both rough and deep rough LPS bilayers compared to that of bilayers composed of BPL or mixtures of LPS and BPL. On the basis of these results and the observation that deep rough bacteria have higher levels of phospholipid on their surface than do rough bacteria (Kamio, Y., and Nikaido, H. (1976) Biochemistry 15, 2561-2569), we argue that the high susceptibility of deep rough bacteria is due to the presence of phospholipids on their surface. Experiments with phospholipid bilayers showed that the addition of PEG-lipids (containing covalently attached hydrophilic polymers) had little effect on permeability and binding rates, whereas the addition of cholesterol reduced permeability and slowed binding to levels approaching those of LPS. Therefore, we argue that the barrier provided by LPS is primarily due to its tight hydrocarbon chain packing (Snyder et al., (1999) Biochemistry 38, 10758-10767) rather than to its polysaccharide headgroup.

Enhancement of topical delivery of a lipophilic drug from charged multilamellar liposomes

To enhance the topical delivery of rhodamine B base (Rho), a model lipophilic compound, the electrostatic interaction between the positive and negative components incorporated in the liposomal bilayer was utilized. The higher in vitro permeability to Rho in rat skin was observed with positive and neutral multilamellar liposomal preparations, the former was prepared with phosphatidylcholine (PC) and stearylamine (SA) and the latter with PC alone, than that given as a solution. Negative liposome composed of PC and dicetyl phosphate (DCP) showed lower skin permeability to Rho. To enhance the Rho retention in the skin, the electrostatic interaction between SA and DCP, which was confirmed by in vitro partition study, was utilized. By pretreating the skin surface with SA solution or empty SA liposome, the skin distribution of Rho given as DCP liposome was substantially enhanced, with increase in the PC distribution into the skin. The pretreatment effect of empty SA liposome was also observed in rats in vivo. In conclusion, it was found that negative DCP liposome provides better drug retention in the skin with lower skin permeability, and the topical drug delivery from DCP liposome was further enhanced by the pretreatment of the skin surface with empty SA liposome.

Alterations of intracellular calcium homeostasis and mitochondrial function are involved in ruthenium red neurotoxicity in primary cortical cultures

Ruthenium red (RR) is a polycationic dye that induces neuronal death in vivo and in primary cultures. To characterize this neurotoxic action and to determine the mechanisms involved, we have analyzed the ultrastructural alterations induced by RR in rat cortical neuronal cultures and measured its effect on cytoplasmic Ca(2+) concentration ([Ca(2+)](i)) and on mitochondrial function. RR produced a dose-dependent, progressive disruption of neurites and plasma membrane of neuronal somata after 8-24 hr of incubation. RR caused also an elevation of both the basal [Ca(2+)](i) and its maximal levels after K(+) depolarization. Mitochondrial oxidative function, assessed by reduction of 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide and by changes in dihydrorhodamine-123 fluorescence, was significantly diminished after treatment with RR, both in cultured neurons and in isolated brain mitochondria. La(3+) did not prevent but rather potentiated RR-induced cell death. Glutamate receptor antagonists also failed to prevent RR neurotoxicity. Apoptotic electron microscope images were not observed, and protein synthesis inhibitors did not show any protective effect. It is concluded that RR penetrates neurons and that its neurotoxic damage probably is due to intracellular Ca(2+) dishomeostasis and disruption of mitochondrial oxidative function. These results enhance our understanding of the intracellular mechanisms underlying neuronal death.

Cell viability and growth in a battery of human breast cancer cell lines exposed to 60 Hz magnetic fields

Epidemiological data suggest that exposure to power-frequency (50/60 Hz) magnetic fields (MFs) may be a risk factor for breast cancer in humans. To determine whether MFs affect human breast cancer cells, we measured viability, growth and cytotoxicity in a battery of breast cancer cell lines after in vitro MF and sham exposure. Cells of three estrogen receptor-positive human breast cancer cell lines (MCF-7, ZR-75-1 and T-47D) and one estrogen receptor-negative human breast cancer cell line (MDA-MB-231) and normal (nontransformed) human breast epithelial cells were exposed to MFs (1 mT) or sham fields (<0.0001 mT) for 72 h. Cell viability was determined using the sulforhodamine B (SRB) assay at 0 and 72 h after the MF exposure period. Cell growth was measured as the change in SRB dye uptake over 72 h after MF exposure. MF exposure had no effect on cell viability or growth in any cell type examined. Similarly, MF exposure had no effect on cytotoxicity induced by exposure to the retinoid N-(4-hydroxyphenyl)retinamide. These data do not support the hypothesis that MF exposure stimulates growth of breast cancer cells.

Gap junction-mediated coupling in the postnatal anterior subventricular zone

We have studied gap junctional communication in the anterior subventricular zone (SVZa) of postnatal rodents, revealed by intercellular diffusion of dyes in brain slices. Extensive intercellular dye spread was evident in the SVZa. Coupling was not uniform, being characteristically larger in the outer borders of this layer, overlapping the previously described peripheral zone of concentration of S-phase cells. Intercellular spread of the dye was unaffected by acidification, but totally blocked by high Ca(2+) concentrations. In addition, application of some known uncoupling agents as carbenoxolone and halothane led to a marked reduction of dye spread in the SVZa. Our results demonstrate the presence of dye coupling mediated by gap junctions in the SVZa. Furthermore, the spatial organization of dye coupling in these slices strongly suggests the existence of cell compartments in the postnatal SVZa.

Free radical production correlates with cell death in an in vitro model of epilepsy

Free radical (FR) production, a major step in calcium-dependent neurodegeneration, has been linked to the generation of epileptiform activity and seizure-induced cell death. However, direct evidence of FR production in neurons during seizures has never been presented. Using hippocampal cultured slices we demonstrate that FRs are produced in CA3 but not CA1 pyramidal neurons during the rhythmic synchronous activity induced by the GABAA receptor antagonist bicuculline. The production of FRs (measured as changes in the fluorescence emission of dihydrorhodamine 123) was correlated with an increase in the baseline levels of intracellular calcium ([Ca2+]i) estimated by fluo-3 injected into individual neurons via a patch pipette. [Ca2+]i increased during spike bursting and returned to baseline levels after the burst termination in CA1, but not in CA3, pyramidal neurons where 'interburst' calcium concentrations progressively increased. Measurement of cell death, performed with propidium iodide 48 h after a 30-min exposure to bicuculline, revealed most prominent degeneration of pyramidal neurons in the CA3 pyramidal layer. The FR scavengers vitamin E and glutathione significantly reduced the seizure-induced neurodegeneration without supressing spontaneous epileptiform activity. These observations indicate that FR overproduction is related to seizure-induced neuronal death.

Spectral fluctuation of a single fluorophore conjugated to a protein molecule

We have measured the fluorescence spectra of a single fluorophore attached to a single protein molecule in aqueous solution using a total internal reflection fluorescence microscope. The most reactive cysteine residue of myosin subfragment-1 (S1) was labeled with tetramethylrhodamine. The spectral shift induced by a change in solvent from aqueous buffer to methanol in both single-molecule and bulk measurements were similar, indicating that, even at the single molecule level, the fluorescence spectrum is sensitive to microenvironmental changes of fluorophores. The time dependence of the fluorescence spectra of fluorophores attached to S1 molecules solely showed a fluctuation with time over a time scale of seconds. Because the fluorescence spectra of the same fluorophores directly conjugated to a glass surface remained constant, the spectral fluctuation observed for the fluorophores attached to S1 is most likely due to slow spontaneous conformational changes in the S1 molecule. Thus, single-molecule fluorescence spectroscopy appears to be a powerful tool to study the dynamic behavior of single biomolecules.

Labelling of retinal microglial cells following an intravenous injection of a fluorescent dye into rats of different ages

Retinal microglia were selectively and sequentially labelled in different layers of the retina of postnatal rats following a single intravenous injection of the fluorescent dye, rhodamine isothiocyanate (RhIc). The fluorescent cells were doubly immunostained with OX-42 and ED-1 antibodies that recognise complement type 3 (CR3) receptors and macrophage antigen, respectively. RhIc was first detected in the retinal blood vessels 5 min after injection. At 1 h, a variable number of microglia in the inner layers of the retina, namely, the nerve fibre and ganglion cell layers appeared to emit weak fluorescence. Labelled microglial cells in the inner nuclear and outer plexiform layers were not detected until 1 and 2 d had elapsed following RhIc injection. The number of labelled retinal microglia was progressively increased with time, peaking at 4 d after RhIc injection. The frequency of RhIc labelled cells also increased with age, with the largest number of cells occurring in 7-d-old rats but declined thereafter. In 11 d or older rats, RhIc was confined to the retinal blood vessels. It is concluded that when injected into the circulation, RhIc could readily gain access into the retina tissues due to an inefficient blood-retina barrier in early postnatal stages. It became impeded with maturation of the blood-retina barrier, which was established between 11 and 13 d of age. RhIc that inundated the retinal tissues was thoroughly sequestered by the resident microglial cells. It is therefore suggested that the latter could play a protective role against serum-derived substances that may be deleterious to the developing retina.

The 2-phenylbenzotriazole-type water pollutant PBTA-2 has cytochalasin B-mimetic activity

The 2-phenylbenzotriazole (PBTA)-type water pollutant, 2-[2-(acetylamino)-4-[N-(2-cyanoethyl)ethylamino]-5-methoxyphenyl]-5- amino-7-bromo-4-chloro-2H-benzotriazole (PBTA-2), has been recently identified in samples from the Nishitakase River in Kyoto, Japan, and shows potent mutagenic activities in Salmonella typhimurium in the presence of a microsomal metabolizing system (S9 mix). In the present study, we conducted the in vitro micronucleus (MN) test on PBTA-2 in the absence and presence of S9 mix in two Chinese hamster cell lines, CHL and V79-MZ. In the MN test, PBTA-2 was weakly positive in CHL cells and strongly positive in V79-MZ cells. Because the positive results were accompanied by a statistically significant increase in the number of polynuclear (PN) and/or mitotic (M) cells, we examined treated cells in metaphase to see if numerical chromosome aberrations were being induced. We found that PBTA-2 induces polyploidy in both CHL and V79-MZ cells. A detailed analysis of MN preparations showed that in CHL cells, PBTA-2 predominantly induces equal-sized binucleated cells. Rhodamine phalloidin staining revealed that PBTA-2 causes actin filament abnormalities in both cell lines similar to those caused by cytochalasin B. Cytochalasin B induced PN cells predominantly and dose dependently, and almost all the cells were equal-sized and binucleate. The results suggest that PBTA-2 has cytochalasin B-mimetic activity, although agents affecting actin filaments, such as cytochalasins, phallotoxins and chloropeptide, have been derived only from molds so far. This study also suggests that our MN test protocol may be used to identify chemicals that have cytochalasin B-mimetic activity as well as those that induce numerical aberrations.

The incorporation of dyes into hair as a model for drug binding

The binding of charged substances from external aqueous media to hair has been investigated through the use of fluorescence microscopy. Eleven hair samples, reflecting various ethnic groups and cosmetic treatments, were tested. Rhodamine 6G, a cationic dye representative of drugs such as cocaine and opiates, showed incorporation throughout the hair of all samples except one. In contrast, fluorescein, an anionic dye representative of drugs such as THC carboxylic acid, was not readily incorporated. The incorporation of rhodamine 6G was faster for chemically 'straightened' and bleached African-American female hair than for untreated hair. Incorporation of rhodamine 6G followed a pH dependence, but an ionic strength dependence could not be established. These studies support three postulates: (1) electrostatic interactions explain the preferential binding of cationic drugs of abuse to hair; (2) the hair matrix, or the non-helical portion of hair, is accessible to external solutions and thus subject to contamination; and (3) cosmetic treatments may alter the helical portion of hair thereby increasing its accessibility to external contamination.

A new method for direct introduction of chemicals into a single sieve tube of intact rice plants

We present a novel method for direct introduction of chemicals into a sieve tube of intact rice plants-namely, the method of micro-introduction using stylet of insect (the MUSI method). Fluorescent dyes were successfully introduced into a sieve tube through a severed stylet of planthopper and the distribution of the dyes was observed.

A non-covalently cross-linked chitosan based hydrogel

Hydrogels are normally formed by the covalent cross-linking of linear polymers. In the case of chitosan based hydrogels this cross-linking is often achieved with glutaraldehyde, glyoxal or other reactive cross-linking agents. Such hydrogel materials have limited biocompatibility and biodegradability. However by the attachment of hydrophobic palmitoyl groups to glycol chitosan, a water soluble chitosan derivative, we have produced a version of the amphiphilic vesicle forming polymer-palmitoyl glycol chitosan (Uchegbu et al., 1998, J Pharm Pharmacol 58, 453-458). The level of palmitoylation in this variant of the polymer (GCP11), as determined by proton neutron magnetic resonance spectroscopy, is 19.62+/-2.42% (n=4). GCP11 has been used to prepare soft, slowly eroding hydrogels suitable for drug delivery by simply freeze-drying an aqueous dispersion of the polymer. Non-covalent cross-linking to form the gel matrix is achieved by the hydrophobic interactions of the palmitoyl groups. The resulting material, as examined by scanning electron microscopy, is porous and may be hydrated to up to 20x its weight in aqueous media without any appreciable change in volume-transforming from an opaque to a translucent solid. The slow erosion of this material in aqueous environments gives a biodegradable and ultimately more biocompatible material than covalently cross-linked hydrogels. Unlike most chitosan-based gels, the gel is hydrated to 20x its weight at alkaline pH but only 10x its weight at neutral and acid pH. This is as a result of the gradual erosion of the gel at lower pH values. Hydration is also reduced from 20x the dry gel weight in water to 10x the dry gel weight in the presence of dissolved salts such as sodium chloride. GCP11 hydrogels have been loaded to 0.1% w/w with a model fluorophore, rhodamine B, by simply freeze-drying an aqueous dispersion of GCP11 in the presence of a solution of rhodamine B dissolved in either water or phosphate buffered saline (PBS, pH=7.4). The release of this model fluorophore was retarded by between 8 and 12% when PBS was contained in the gel in accordance with the hydration profiles. Rhodamine B release was also reduced by between 13 and 25% in the presence of acid as a result of the reduced solubility of rhodamine B at acid pH.

Primitive, crustacean-like state of blood-brain barrier in the eye of the apterygote insect Petrobius (Archaeognatha) determined from uptake of fluorescent tracers

Compound eyes of insects in 16 orders were tested for the presence of a blood-retina barrier (BRB) by injecting the hemolymph with Procion yellow, which was excluded from the eye in all Neoptera but not in two apterygotes. A primitive apterygote (Petrobius, Machilidae) was investigated further. Epifluorescence observations with small dyes Lucifer yellow (LY) and sulforhodamine 101 (SR) confirmed uptake by the eye within 3 min of injection. LY and SR both penetrated the eye, particularly the cornea, examined in sections. Uptake was quantified by microfluorometry, yielding entry half-times (t(1/2)) of 1-1.4 min, fitting predictions for a model where tracer uptake is limited by passive diffusion. A much larger fluorescent dextran entered at a similar rate (t(1/2) = 1.70 +/- 0.77 min; n = 22), too fast to be diffusion-limited, pointing to an active process, probably flushing of hemolymph through the retina. This is not an artifact associated with tracer injection and may be the natural result of circulatory pressures. Microfluorometry gave a first estimate of hemolymph volume (2.9% of body weight), of hemolymph mixing time (t(0.95) = 77 min); the eyes' receptive fields were also determined. All results point to a primitive crustacean-like condition in Petrobius, with open access of hemolymph to the eye and no BRB. An evolutionary hypothesis is suggested to explain how a primitive central nervous system barrier later extended to cut off the eye in Neoptera, in the face of access problems for respiratory gases and metabolites.

A study of the ability of tissue plasminogen activator to diffuse into the subretinal space after intravitreal injection in rabbits

PURPOSE

Intravitreal injections of tissue plasminogen activator have been used to lyse fibrin from blood in the subretinal space, despite the lack of proof that tissue plasminogen activator can diffuse across the retina. We tested whether tissue plasminogen activator injected into the vitreous could penetrate the neural retina and enter the subretinal space.

METHODS

We injected a mixture of 50 microg of tissue plasminogen activator (70 kD) labeled with fluorescein isothiocyanate and rhodamine B isothiocyanate-labeled dextran, which has a lower molecular weight (20 kD), into the midvitreous cavity of one eye in each of 18 rabbits. The eyes were enucleated after 3, 6, and 24 hours, and cryosections were examined with epifluorescent microscopy to determine the distribution of the labeled molecules. We also evaluated tissue plasminogen activator pharmacokinetics in one eye each of 18 rabbits in which a subretinal clot was induced by injecting autologous blood (50 microL) into the subretinal space through the sclera. Fluorescein isothiocyanate-labeled tissue plasminogen activator was injected into the vitreous 2 days after induction of the subretinal clot.

RESULTS

Fluorescein isothiocyanate-labeled tissue plasminogen activator was present at the vitreal surface of the retina in a linear array in all 36 eyes studied, whereas the rhodamine B isothiocyanate-labeled dextran had diffused throughout the neural retina in the same sections. No fluorescein isothiocyanate signal was observed in the neural retina or in the subretinal clot. Vitreous hemorrhage caused by retinal perforation was observed in all eyes with intraretinal hemorrhage in which fluorescein isothiocyanate fluorescence was seen in the neural retina and inside the clot.

CONCLUSION

Intravitreal tissue plasminogen activator did not diffuse through the intact neural retina to reach a subretinal clot. This study demonstrates no scientific rationale for the intravitreal tissue plasminogen activator treatment of submacular hemorrhage without vitreous hemorrhage presumably caused by an overlying retinal break.

Mapping of capillary flow, cellular redox state, and resting membrane potential in hypoperfused rat myocardium

The influence on myocyte viability of ischemia-induced changes in capillary perfusion was studied in the hearts of anesthetized rats subjected to partial occlusion of the left coronary artery for 45 min. Timed plasma labeling was applied to determine perfusion patterns. Changes in the fluorescence of preloaded potential-sensitive dyes [tetramethylrhodamine methyl ester (TMRM) and bis-oxonol], of trypan blue, and of endogeneous NADH were utilized in characterizing myocyte viability in histological sections of the heart. Within the hypoperfused zone, localized areas appeared vascularly nonlabeled for periods of at least 10 min. Within these areas a reduction in TMRM fluorescence occurred in 82. 5% of the tissue, signaling a reduced resting membrane potential. In the same areas 37.7% of the myocytes revealed an NADH fluorescence lower than that regularly found in anoxic tissues. This correlated with an especially low level of TMRM, with increased fluorescence bis-oxonol and with an accumulation of trypan blue. In conclusion, in localized hypoperfusion-induced zones lacking capillary flow, an inhomogeneous pattern of reductions in myocyte viability develops, which appears to be relevant in ischemia-induced arrhythmias.

Morphological evidence of the inhibitory effect of taxol on the fast axonal transport

The short term effects of taxol, a stabilizing drug of microtubules, on the peripheral nerves in the rat was investigated using a new chamber system which can be applied to incubate a sciatic nerve with various solutions in vivo. A functional analysis of retrograde axonal transport using rhodamine-labeled wheat germ agglutinin (WGA-rhodamine) showed the inhibitory effect of the drug. An electron microscopic study also revealed that a variety of vesicles were observed to accumulate on both the proximal and the distal sides of the chamber, however, no significant increase in the number of microtubules in the axons, based on the pharmacological effect of the drug, was observed even though one had been expected. These findings support the inhibitory effect of taxol on the fast axonal transport of the neurons. Furthermore, the accumulated vesicles were morphologically different from those accumulated by ligation. These results suggest that a special component of the fast axonal transport was thus selectively blocked by the drug.

The fluorescent cationic dye rhodamine 6G as a probe for membrane potential in bovine aortic endothelial cells

The membrane potential of cultured bovine aortic endothelial cells was assessed by a fluorescent probe as an alternative to direct methods. We used the fluorescent cationic dye rhodamine 6G, a lipophilic probe with high permeability in cell membranes. A linear relationship was obtained between fluorescence intensity (F.I.) and membrane potential (Em) as a function of the extracellular Na(+) concentration in the presence of the ionophore gramicidin. From the equation derived from the linear relationship F.I. = -0.004 Em + 0. 03 (P < 0.001), the fluorescence measurements could be converted to membrane potential. The resting plasma membrane potential obtained was -65 +/- 7 mV. Nigericin (27 microM), ouabain (1 mM), and bradykinin (20 nM) induced a decrease in F.I. (depolarization), while ATP (25-100 microM) induced an increase in F.I. (hyperpolarization). Mitochondrial membrane potential inhibitors myxothiazol (3 microM) and oligomycin (4 microM) did not influence F. I. measured in the cultured bovine aortic endothelial cells. The results indicate that rhodamine 6G can be used as a sensitive and specific dye in studies of substances that affect the membrane potential of endothelial cells.

Changes in mitochondrial mass, membrane potential, and cellular adenosine triphosphate content during the cell cycle of human leukemic (HL-60) cells

Oxidative phosphorylation within the inner mitochondrial membrane generates the majority of cellular adenosine triphosphate (ATP) required for normal physiological functions (including regulation of cell volume and solute concentration, maintenance of cellular architecture, and synthesis of essential macromolecules). Its efficient functioning depends on the maintenance of an electrochemical gradient and is tightly coupled to the energetic demands of the cell and/or tissue. Commitment to and completion of the cell division cycle are sensitive to changes in the availability of mitochondrially derived ATP, although the relationship between cell cycle and mitochondrial physiology is poorly understood. Using vital, mitochondrial-specific fluorochromes to differentiate between mitochondrial mass (10-N-nonyl acridine orange) and mitochondrial membrane potential (Rhodamine 123), together with a quantification of total cellular ATP levels, it was possible to generate profiles of these mitochondrial characteristics in HL-60 cells at different stages of their cell cycle. The data suggest that the availability of ATP changes in a cell cycle-specific manner and cannot be predicted by changes in mitochondrial mass or membrane potential. Furthermore, transition points in the cell cycle where ATP availability is low with respect to the amount of functional inner mitochondrial membrane have been observed. We suggest that these cell cycle phase transitions are sensitive to inhibition of mitochondrial activity because the basal levels of available ATP at these points are nearer to a theoretical "minimal threshold" below which cell cycle progression is inhibited.

Endocytic active zones: hot spots for endocytosis in vertebrate neuromuscular terminals

We have used a sensitive activity-dependent probe, sulforhodamine 101 (SR101), to view endocytic events within snake motor nerve terminals. After very brief neural stimulation at reduced temperature, SR101 is visualized exclusively at punctate sites located just inside the presynaptic membrane of each terminal bouton. The number of sites (approximately 26 sites/bouton) and their location (in register with postsynaptic folds) are similar to the number and location of active zones in snake motor terminals, suggesting a spatial association between exocytosis and endocytosis under these stimulus conditions. With more prolonged stimulation, larger SR101-containing structures appear at the bouton margins. Thus endocytosis occurs initially at distinct sites, which we call "endocytic active zones," whereas further stimulation recruits a second endocytic paradigm.

Fibroblast response to rapid decompression and hyperbaric oxygenation

INTRODUCTION

The cellular basis for symptoms associated with rapid decompression and the use of hyperbaric oxygenation treatment (HBO) is not established.

METHODS

Image analysis, sulforhodamine B assay and bromodeoxyuridine (BrDU) incorporation were used to identify cellular changes associated with rapid decompression (RD) or hyperbaric oxygenation (HBO). Human fibroblasts were exposed to RD or HBO and compared with untreated cells. Immediately following treatment, the fraction of cells synthesizing DNA was measured by detection of cells incorporating the BrDU. At 1 d and 3 d following the treatments, total cell protein adherent to the bottom of wells was measured using a sulforhodamine B assay. Cell density was observed with light microscopy and quantified with image analysis.

RESULTS

RD increased total protein significantly, (p < 0.05) relative to control, while HBO had less effect. The fraction of cells synthesizing DNA was increased by HBO and reduced by RD relative to control (p < 0.05). Image analysis showed that cell density at day 1 was: control>HBO>RD; and at day 3: RD>HBO>control, indicating an increase in proliferation induced by the treatments.

CONCLUSION

This data shows that HBO and RD increase the proliferation of fibroblasts for 24 h following treatment. HBO increased DNA replication. While there was a decrease in DNA replication following RD, protein synthesis was enhanced.

Investigation of the positive response of ethyl acrylate in the mouse lymphoma genotoxicity assay

To develop a better understanding of the relationship between ethyl acrylate (EA)-induced cytotoxicity and mutation frequency in the mouse lymphoma assay (MLA) we measured the effects of EA treatment to ML cells on: (1) nonprotein sulfhydryl (NPS) levels; (2) mitochondrial rhodamine 123 (Rh123) uptake; (3) the DNA elution slope (single-strand breakage) and Y intercept of fitted curves (cytotoxicity and double-strand breakage) in the alkaline elution assay; (4) the appearance of apoptosis; and (5) the pulsed-field gel electrophoretic resolution of high-molecular-weight DNA. EA reduced NPS in both a time- and concentration-dependent manner. By 30 min, > or = 20 micrograms/ml EA reduced NPS by 50% or greater. By 4 h, > or = 10 micrograms/ml markedly decreased both NPS cell content (> or = 71.5% reduction) and mitochondrial Rh123 uptake (10-50 micrograms/ml; 9-62%), the latter effect being further enhanced by washing and incubation for an additional 2 h (12-85%). EA did not induce single-strand breaks in the alkaline elution assay. Only highly cytotoxic EA concentrations (80-87% reduction in RCG at 40-50 micrograms/ml) caused both increases in the elution slope and parallel drops (Y intercept) in the elution curve in the alkaline elution assay. Conventional agarose gel electrophoretic analysis of the DNA neutral fraction of these high dose preparations showed evidence for both apoptosis (180-bp oligonucleosomal DNA laddering effect) and random smearing of DNA (necrosis). Pulsed-field gel electrophoresis of directly loaded high dose cell preparations revealed both high- and low-molecular-weight DNA double-strand breaks, but only at the highest concentrations. These observations indicated that the EA-induced mutagenic response correlated best with cellular cytotoxicity mediated by NPS depletion and mitochondrial membrane impairment.

Does the lack of the P-glycoprotein efflux pump in neutrophils explain the efficacy of colchicine in familial Mediterranean fever and other inflammatory diseases?

Colchicine is an alkaloid drug commonly used in familial Mediterranean fever (FMF), gout, Behcet's syndrome, psoriasis and Sweet's syndrome. The exact mechanism of its action in these diseases is not entirely known. However, it has been shown that colchicine may inhibit neutrophil chemotaxis, thereby decreasing the inflammatory process. Recently, it was shown that colchicine accumulates in neutrophils in higher concentrations than in lymphomonocytes. Studies dealing with the multiple drug resistance (MDR) issue disclosed that neutrophils lack the P-glycoprotein (P-gly) membranal pump (encoded by the MDR1 gene). We propose that the preferential accumulation of colchicine in neutrophils compared with lymphomonocytes is due to the absence of the P-gly efflux pump in the former. This may explain the effectiveness of colchicine in diseases where increased chemotaxis is evident. The hypothesis may also provide an explanation for FMF patients who do not respond to the drug.

Comparison of in vivo and in vitro deposition of rhodamine and fluorescein in hair

A direct differentiation of the internal and external drug-deposition pattern into hair was made using two fluorescent dyes and fluorescence microscopy after systemic administration to mice or external exposure of untreated hair. Mice (23 days old, C57 and Balb/C) were administered either rhodamine or fluorescein intraperitoneally at varied doses on 3 consecutive days of 3 weeks, and hair was sampled 1 week later. Another group was given 10 mg/kg rhodamine or 100 mg/kg fluorescein and sampled at time points from 5 min to 168 hr. The time courses of external deposition of rhodamine and fluorescein into untreated hair were examined after hair was soaked in 0.1 mg/ml solutions at pH 3, pH 6, and pH 9 aqueous buffer or methanol. The hair was then extracted in pH 6 phosphate buffer or methanol for 24 hr. In vivo accumulation was distinguishable as fluorescent bands along the length of the hair for rhodamine and fluorescein. The pattern of in vivo deposition appears to arise from the rapid accumulation within the cortex and medulla, with little deposition evident in the cuticle. Neither phosphate buffer nor methanol washes affected the intensity of fluorescence in the hair. External loading of rhodamine into the hair resulted in staining of the junctions of cuticle scales. This pattern persisted even after 12 hr of solution exposure. Extraction with pH 6 phosphate buffer or methanol did not remove rhodamine. Fluoroscein followed a similar pattern, with maximum fluorescence when hair was loaded in pH 6 100mM phosphate buffer and nominal staining when loaded in pH 9 100 mM Tris buffer or methanol. Soaking the hair in pH 6 buffer, but not methanol, removed some fluorescein. These results demonstrate that compounds in the circulation can rapidly diffuse into the forming cortex and medulla, where rapid associations occur with elongating intermediate filaments specific to the medulla and cortex. These compounds can become significantly occluded within the mature matrix and are resistant to removal in aqueous or methanolic solutions.

Saquinavir, an HIV protease inhibitor, is transported by P-glycoprotein

Saquinavir, a peptidomimetic HIV protease inhibitor, has been shown to be effective in reducing patient viral load and reducing mortality. In this report we investigated whether saquinavir is a substrate for the multidrug resistance transporter P-glycoprotein (P-gp), which may reduce the effective intracellular concentration of the drug. G185 cells, which highly express P-gp, are resistant to saquinavir-mediated cytotoxicity, and co-administration of cyclosporine reversed this resistance. Saquinavir and saquinavir mesylate inhibited basolateral to apical transport of the fluorescent dye rhodamine 123 in a polarized epithelial transport assay, a result that suggests competition of these drugs for the P-gp transporter. Finally, we measured specific, directional transport of saquinavir and saquinavir mesylate in an epithelial monolayer model. Transport in the basolateral to apical direction was 3-fold greater than apical to basolateral flux for both saquinavir and saquinavir mesylate and was blocked by co-incubation with the established P-gp reversal agents cyclosporine and verapamil. These data provide evidence that saquinavir is a substrate for the P-gp transporter and suggest that this protein may affect intracellular accumulation of the drug and contribute to its poor oral bioavailability.

Induction of mdr1b mRNA and P-glycoprotein expression by tumor necrosis factor alpha in primary rat hepatocyte cultures

Mammalian liver exhibits expression of members of the family of multidrug resistance (mdr) transporters (P-glycoproteins). P-glycoprotein isoforms encoded by mdr1 genes participate in extrusion of an array of xenobiotics into the bile. Induction of mdr1b mRNA expression has been shown to occur in rat hepatocytes in response to hepatotrophic growth factors. As the cytokine tumor necrosis factor alpha (TNF-alpha) is known to exert a direct mitogenic effect on hepatocytes, its influence on mdr1b expression was investigated. In primary rat hepatocytes cultured in the absence of TNF-alpha, a time-dependent increase in basal expression of mdr1b mRNA and in immunodetectable P-glycoprotein was observed. In cells treated with TNF-alpha (4,000 U/ml) for 3 days, expression of mdr1b mRNA and of immunodetectable P-glycoprotein was induced approximately twofold. Moreover, intracellular steady-state levels of the mdr1 substrate rhodamine 123 were decreased in cells pretreated with TNF-alpha in comparison to controls, indicating an increase in functional transporter(s) mediating dye extrusion. Treatment of hepatocytes with antioxidants (1 mM ascorbic acid and 2% dimethyl sulfoxide) for 3 days markedly suppressed mdr1b mRNA and P-glycoprotein expression both in cells cultured in the presence of TNF-alpha and in the absence of the cytokine, but did not fully abolish mdr1b mRNA induction by TNF-alpha, supporting the notion that reactive oxygen species participate in regulation of basal mdr1b gene expression during hepatocyte culture. In conclusion, the present data indicate that by inducing mdr1b expression in hepatocytes, TNF-alpha may affect the capacity of the liver for extrusion or detoxification of endogenous or xenobiotic mdr1 substrates.

Induction of mdr1b mRNA and P-glycoprotein expression by tumor necrosis factor alpha in primary rat hepatocyte cultures

Mammalian liver exhibits expression of members of the family of multidrug resistance (mdr) transporters (P-glycoproteins). P-glycoprotein isoforms encoded by mdr1 genes participate in extrusion of an array of xenobiotics into the bile. Induction of mdr1b mRNA expression has been shown to occur in rat hepatocytes in response to hepatotrophic growth factors. As the cytokine tumor necrosis factor alpha (TNF-alpha) is known to exert a direct mitogenic effect on hepatocytes, its influence on mdr1b expression was investigated. In primary rat hepatocytes cultured in the absence of TNF-alpha, a time-dependent increase in basal expression of mdr1b mRNA and in immunodetectable P-glycoprotein was observed. In cells treated with TNF-alpha (4,000 U/ml) for 3 days, expression of mdr1b mRNA and of immunodetectable P-glycoprotein was induced approximately twofold. Moreover, intracellular steady-state levels of the mdr1 substrate rhodamine 123 were decreased in cells pretreated with TNF-alpha in comparison to controls, indicating an increase in functional transporter(s) mediating dye extrusion. Treatment of hepatocytes with antioxidants (1 mM ascorbic acid and 2% dimethyl sulfoxide) for 3 days markedly suppressed mdr1b mRNA and P-glycoprotein expression both in cells cultured in the presence of TNF-alpha and in the absence of the cytokine, but did not fully abolish mdr1b mRNA induction by TNF-alpha, supporting the notion that reactive oxygen species participate in regulation of basal mdr1b gene expression during hepatocyte culture. In conclusion, the present data indicate that by inducing mdr1b expression in hepatocytes, TNF-alpha may affect the capacity of the liver for extrusion or detoxification of endogenous or xenobiotic mdr1 substrates.

Linear and cyclic peptides as substrates and modulators of P-glycoprotein: peptide binding and effects on drug transport and accumulation

One cause of multidrug resistance (MDR) in human cancers is the overexpression of the P-glycoprotein multidrug transporter, a member of the ABC superfamily of membrane proteins. Natural products and chemotherapeutic drugs are pumped out of the cell by P-glycoprotein in an ATP-dependent fashion. There is growing evidence that many hydrophobic peptides are also P-glycoprotein substrates. With the use of a fluorescence-quenching assay, we have shown that some linear and cyclic hydrophobic peptides interact with P-glycoprotein, whereas others do not. The measured values of the quenching constant, Kq, for interaction of peptides with P-glycoprotein ranged from 200 nM for cyclosporine A to 138 microM for the tripeptide N-acetyl-leucyl-leucyl-norleucinal. Peptides that interacted with P-glycoprotein in the fluorescence assay also blocked colchicine transport into plasma membrane vesicles from MDR cells. The values of Dm, the peptide concentration causing 50% inhibition of drug uptake, were highly correlated with the values of Kq, over three orders of magnitude. The P-glycoprotein ATPase stimulation/inhibition profile of the peptides was not helpful in making a quantitative assessment of the ability of a peptide to interact with P-glycoprotein or to block drug transport. Some hydrophobic peptides were able to restore accumulation in MDR cells of the chemotherapeutic drug daunorubicin and the fluorescent dye rhodamine 123 to the levels observed in the drug-sensitive parent. Peptides that interacted with P-glycoprotein also displayed a relatively low overall toxicity to intact MDR cells, and inhibited drug transport at concentrations below the toxic range. Hydrophobic peptides should be given serious consideration for development as clinical chemosensitizing agents.

Skin electroporation causes molecular transport across the stratum corneum through localized transport regions

High voltage pulsing of human skin (approximately 100 V across the skin, 1 ms pulses) has been hypothesized to cause electroporation of the stratum corneum, and to cause large fluxes of drugs and other molecules across the skin, through newly created aqueous pathways. In contrast, iontophoresis (<0.5 mA per cm2, <1 V across the skin) has long been used in transdermal drug delivery, and is believed to involve pre-existing pathways associated with hair follicles and sweat ducts. Either high voltage pulsing or iontophoresis was applied to human, hairless rat, or black rat snake skin. Hairless rat skin contains more hair follicles than human skin, and snake skin does not contain any hair follicles. All three types of skin had comparable electrical resistances at low voltages; however, the iontophoretic transport of charged fluorescent molecules was significant for human and hairless rat skin, but no transport occured across snake skin, indicating that hair follicles and sweat ducts play a major role in iontophoresis. Electroporation caused large molecular transport for all three types of skin, and involved spontaneously forming localized transport regions, not associated with appendages. These experiments thus provide further support for the hypothesis that high voltage pulsing causes electroporation in the stratum corneum, and that this transport mechanism is fundamentally different from iontophoresis.