Biomedical subjects

R M Brand

Publications and source records attributed to R M Brand.

9 recordsLinked to original sources

PubMed1999

Transdermally delivered peroxovanadium can lower blood glucose levels in diabetic rats.

The element vanadium can have insulin mimetic properties and therefore has been suggested as a possible therapeutic agent for treatment of diabetes. A series of peroxovanadium compounds that are more potent at lowering blood glucose levels than sodium metavanadate, sodium orthovanadate and vanadyl sulfate have recently been synthesized. These compounds probably will not be orally active so transdermal administration is a potential option. A patch containing either the peroxovanadium compound [VO(O2)2 1-10 phenanthroline], abbreviated bpV(phen), or placebo was placed on the back of streptozotocin induced diabetic rats and was delivered either passively (16 h) or iontophoretically (0.5 mA/cm2 for 4 h). Blood samples were analyzed for glucose and vanadium levels. Mean blood glucose levels were 83+/-1% and 109+/-1% of the starting values for animals iontophoretically treated with bpV(phen) and vehicle, respectively. The compound's insulin mimetic properties were evident within 60 min of current initiation. Blood glucose levels were reduced to 74+/-14% of the original level after 16 h of passive treatment. The compound was ineffective when fed to animals. Transdermal delivery of bpV(phen) resulted in significantly greater blood levels of vanadium than the orally delivered compound (P<0.05). Overall these experiments demonstrate that peroxovanadium delivered through the skin can lower blood glucose levels in rats. Further experiments are warranted to better characterize the nature of the response and to determine the potential for using these compounds in humans.

Administration, Cutaneous↗

PubMed1998

Effects of size and sequence on the iontophoretic delivery of oligonucleotides.

Adequate cellular availability of synthetic oligonucleotides is crucial to their success as therapeutic agents. These compounds, however, are not expected to be orally active. This has led to interest in a variety of alternate drug delivery methods, including iontophoretically enhanced transdermal delivery. The purpose of this work is to begin characterizing the structure-activity relationship for iontophoresis of oligonucleotides through the skin. The in vitro permeation of 16 biologically relevant phosphorothioate oligonucleotides across hairless mouse skin was studied. Oligonucleotides with less than 20 bases (n = 10) had a wide range of steady-state flux levels (2.1-26.2 pmol/ cm2 h). A lower flux differential was observed for compounds ranging from 20 to 40 bases long (1.2-2.2 pmol/cm2 h). For the smaller compounds, transport, in general, decreased with increasing size; however, there were several oligonucleotides that did not follow this pattern. These data indicate that factors other than size influence transport and that the impact is greater at shorter lengths. Differential penetration between equal sized oligonucleotides synthesized with identical bases in reversed order indicates that sequences and not simply base composition affects steady-state flux across skin. Molecular structure, therefore, is a key contributor to iontophoretically assisted transport. Further studies are necessary to develop more precise predictions about the relationship between oligonucleotide structure and transdermal delivery.

Animals↗

PubMed1998

An experimental model for interpreting percutaneous penetration of oligonucleotides that incorporates the role of keratinocytes.

Oligonucleotides have been extensively studied for their potential as therapeutic agents. Phosphorothioate oligonucleotides have been demonstrated to be particularly useful due to their stability against nucleases, their ability to be internalized by many cell types, and the ease with which they hybridize with target mRNA. These compounds have previously been delivered across the skin with the aid of iontophoresis. During transdermal delivery, the first viable cells exposed to the oligonucleotides are the keratinocytes. The purpose of this study was to determine the relationship between internalization of these compounds by keratinocytes and their transport across the skin. The in vitro uptake of 15 different fluorescently labeled phosphorothioate oligonucleotides into human keratinocytes was quantitatively measured with a fluorometer. Photomicrographs of keratinocytes indicate diffuse cytoplasmic and nuclear localization. The ability of these molecules to enter cells was linearly related to size. Cellular uptake data were inversely correlated with previously reported steady-state transport levels of oligonucleotides that had been transdermally delivered by iontophoresis across hairless mouse skin. Oligonucleotides that readily entered keratinocytes had a decreased ability to penetrate skin under iontophoretic conditions. The results indicate that oligonucleotide sequences may be designed for treating skin diseases (high uptake, low transport) or systemic disorders (low uptake, high transport).

Animals↗

PubMed1997

Transdermal delivery of erythromycin lactobionate--implications for the therapy of gastroparesis.

BACKGROUND: The treatment of many diseases may be complicated by abnormalities in gastric emptying. Gastric motor dysfunction may lead to unpredictable food and medication delivery to the small intestine, their site of absorption. Prokinetic agents improve gastric motility, but orally administered drugs are unreliably absorbed, thereby limiting their effectiveness. A method of delivering prokinetic agents which bypasses the gastrointestinal tract could lead to more effective treatment. METHODS: Skin samples from rat, hairless mouse and man were placed in an in vitro diffusion chamber. The epidermal side of the skin was exposed to erythromycin lactobionate and passage of the drug across the skin sample monitored and quantitated by high-performance liquid chromatography with UV detection. RESULTS: Erythromycin passes across all skin types tested. Steady-state flux across hairless mouse skin was greater than for rat, full thickness human skin and human epidermis. In the first 3 h following introduction of erythromycin lactobionate, 1.85 mg/cm2 crossed human epidermis. Given that a dose of 50 mg may exert prokinetic effects in vivo in man, increasing the patch size to approximately equal to 28 cm2 should provide therapeutic levels of drug within 3 h. CONCLUSIONS: Erythromycin lactobionate, when administered transdermally, can be delivered at levels sufficient to treat gastroparesis. This technique warrants in vivo investigation.

Administration, Cutaneous↗

PubMed1996

Iontophoretic delivery of a telomeric oligonucleotide.

PURPOSE: To evaluate the feasibility of iontophoretically enhanced transdermal delivery of a phosphorothioate oligonucleotide across hairless mouse skin. METHODS: The phosphorothioate sequence, 5'-d(TTAGGG)-3' (TAG-6) which mimics the repeat sequence of the telomere was used as a model compound. Iontophoresis was performed on hairless mouse skin using as in vitro flow-through diffusion system. Both 5'-FITC and uniformly 35S labeled oligonucleotide were used to monitor transdermal flux. RESULTS: Cathodal delivery of TAG-6 resulted in substantial oligonucleotide flux. The molecular label did not alter transport properties. No flux was measured with either anodal or passive delivery. The oligonucleotide was not degraded as it crossed the skin. Molecular transport was donor condition dependent, with pH and salt concentration both having significant effects. Pre-treating the skin with ethanol reduced iontophoretic transport. CONCLUSIONS: These data demonstrate that iontophoresis can enhance transdermal flux of an intact phosphorothioate oligonucleotide and that this penetration is donor condition dependent. Furthermore, iontophoretically enhanced transdermal delivery is a feasible approach to the administration of phosphorothioate oligonucleotides.

Administration, Cutaneous↗

PubMed1994

Understanding the dynamics of cellular responsiveness to modifications of metabolic substrates in perifusion.

A novel microperifusion system with capabilities for continuous, real-time, potentiometric monitoring of extracellular hydrogen ion concentration has been used to define the response of HeLa cells to abrupt changes in extracellular energy sources or introduction of an inhibitor of glycolysis. Glycolytic inhibition, induced by removal of glucose or introduction of iodoacetate, each led to a rapid, continuous decrease in acid release. The response to iodoacetate took longer than removal of glucose, perhaps due to the time required for binding and activation. Once inhibition began, however, the rate of change was greater than following glucose removal. Conversely, recovery time following iodoacetate inhibition was much slower than with glucose removal. Unlike the response to short-term glucose depletion, a second pulse of iodoacetate resulted in a faster response followed by an even longer recovery time. The response to switching between glucose and glutamine began almost without evident delay. The response patterns revealed that HeLa cells prefer glutamine to glucose, but, in the presence of both energy sources, some glucose continues to be used. In summary, these results indicate that continuous, real-time monitoring of the kinetics of hydrogen-ion release can be used to gain new insights into the dynamics of cellular response to perturbations of extracellular energy sources.

Energy Metabolism↗

PubMed1994

Continuous on-line hydrogen ion monitoring to study flow dynamics of perifusion systems and cellular metabolism.

Time-dependent concentration profiles of input signals and feedback of metabolic products can strongly influence cellular responsiveness. To study these parameters, we developed a perifusion system that can deliver biological signals to cells with minimal dispersion, monitor real time responses, and remove waste products continuously. By monitoring pH with miniature hydrogen ion-selective electrodes at intervals of 1 s, effects of dispersion, flow rate, pumping system, and changes in cellular metabolism were demonstrated. Dynamic responses of a human cell line to a series of 10-min pulses of the metabolic uncoupler carbonyl cyanide m-chlorophenylhydrazone (CCCP) were monitored. A rapid 1-min increase in acid release occurred on exposure to CCCP, followed by a decrease in acidification and then a gradual return to a baseline slightly more acidic than before administration of CCCP. These observations demonstrate that this perifusion system can reveal small changes in pH (+/- 0.0005 units) induced by metabolic perturbations and has the potential to reveal the dynamics of cellular responsiveness to a wide range of hormonal, metabolic, and other chemical signals.

Carbonyl Cyanide m-Chlorophenyl Hydrazone↗

PubMed1994

Convolution: a method for data analysis in perifusion systems.

Considerable interest has developed in defining how imposed stimuli effect dynamic changes in cellular metabolism. We have developed a miniature perifusion system that can reveal alterations in extracellular protons within seconds after application of metabolic perturbants. This perifusion system contains two pH sensors: one before the cells records changes between medium and test solutions, and one, located just past the cells, records these alterations plus cellular modifications. Because distortion occurs as chemicals pass through perifusion systems, the shape of pH changes induced by switching from medium to test solutions is different at each electrode. This study describes and validates convolution to correct this distortion. Data from HeLa cells exposed to the metabolic uncoupler of oxidative phosphorylation carbonyl cyanide m-chlorophenyl hydrazone have been analyzed with convolution. Cellular response to oxidative phosphorylation removal is comprised of multiple components, is consistent with a rapid uncoupling, and is followed by cellular adaptation. Therefore convolutional analysis can provide an important adjunct to the analysis of data acquired by perifusion and can provide new insights into cellular responsiveness and metabolism.

Carbonyl Cyanide m-Chlorophenyl Hydrazone↗

PubMed1992

Dynamics of gonadotropin-releasing hormone release during a pulse.

This study examined the nature of the GnRH signal that travels down the pituitary portal vessels and causes an LH pulse. Individual GnRH pulses were described in terms of abruptness of increase and decrease, amplitude, duration, and amount of GnRH released. Pituitary portal blood was obtained at 30-sec intervals for 2.5 or 5 h from five short-term ovariectomized ewes. Jugular blood was sampled every 10 min for LH. We examined 13 GnRH pulss; each produced an LH pulse. The contour of most GnRH pulses approximated a square wave. The rising edge of the GnRH pulse was very abrupt; GnRH secretion increased as much as 50-fold within 1 min. The mean peak amount of GnRH collected during pulses (24 pg/min, range 2-66) was 70-fold greater than the interpulse baseline (0.2-0.5 pg/min). The release period was sustained an average of 5.5 min; thereafter, GnRH fell to prepulse levels within 3 min. Overall, the larger and more prolonged pulses of GnRH were associated with higher amplitude LH pulses. To assess the distortion of the GnRH signal by the collection procedure, samples were obtained in vitro using the same technique during application of 4- and 7-min square wave GnRH pulses by means of a syringe pump. Signals were carried as square-waves through the sampling operation with minimal distoration, with the exception that amplitude decreased during the collection procedure. Our findings indicate the square-wave pulses observed in vivo are an accurate description of the dynamics of GnRH release during a pulse in short-term overiectomized ewes.

Animals↗