Publications by authors named "Scott Wasdo"

16 Publications

  • Page 1 of 1

Feasibility of a breath test for monitoring adherence to vaginal administration of antiretroviral microbicide gels.

J Clin Pharmacol 2013 Jan 24;53(1):103-11. Epub 2013 Jan 24.

Department of Anesthesiology, University of Florida College of Medicine, Gainesville, FL, USA.

Adherence to microbicide gel use is critical to optimizing effectiveness in preventing human immunodeficiency virus transmission. The authors hypothesized that ester taggants added to vaginal gels would generate exhaled alcohol and ketone metabolites and provide a "breath test" for vaginal gel use. This 2-arm (vaginal and dermal), randomized, participant-blinded, pilot study tested this hypothesis. On 8 visits, healthy women (n = 8) received intravaginal taggant (2-butyl acetate, 2-pentyl acetate, isopropyl butyrate, or 2-pentyl butyrate; 30 mg) formulated in hydroxyethylcellulose or tenofovir placebo gel. A second group (n = 4) of women received the same formulations administered dermally on the forearm to determine if skin administration might confound the system. Breath samples were collected using bags before and after taggant administration for 1 hour. Samples were measured using a miniature gas chromatograph and/or gas chromatography-mass spectroscopy for ester taggant, alcohol, and ketone concentrations. After vaginal administration, 2-butyl acetate, 2-pentyl acetate, and metabolites were observed in breath, whereas isopropyl butyrate, 2-pentyl butyrate, and metabolites were not. Some women reported self-resolving, mild burning (24/64 visits) with vaginal administration or a "bubblegum" taste (7/64 visits). No taggants or metabolites were detected following dermal application. A "breath test" for adherence to antiretroviral vaginal gel application appears physiologically and technically feasible.
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http://dx.doi.org/10.1177/0091270011434157DOI Listing
January 2013

A novel breath test to directly measure use of vaginal gel and condoms.

AIDS Behav 2013 Jul;17(6):2211-21

Women's Global Health Imperative, RTI International, 114 Sansome Street, Suite 500, San Francisco, CA 94104, USA.

We assessed the feasibility of a breath test to detect women's single or concurrent use of vaginal products by adding ester taggants to vaginal gel and condom lubricant. Healthy non-pregnant women were enrolled into a two-day cohort (N = 13) and a single-day cohort (N = 12) in San Francisco. Within each cohort, women were randomized (5:1) to tagged or untagged products, and inserted in a clinical setting: 4 mL of tenofovir placebo gel (ten tagged with 15 mg 2-pentyl acetate; three untagged), and an artificial phallus with a lubricated condom (11 tagged with 15 mg 2-butyl acetate; two untagged), on two separate days (two-day cohort) or concurrently (single-day cohort). Using a portable mini-gas chromatograph, the presence/absence of taggants was determined in breath specimens collected prior to, and at timed intervals following product exposure. Demographic, clinical and product use experience data were collected by structured interview. All participants completed all visits and inserted their assigned products. At 5 min post-insertion, the breath test was 100% accurate in identifying insertion of the tagged (or untagged) gel and/or condom. The half-life in breath of the two esters tested was <1 h with large variability between individuals, taggants and cohorts. Overall, among those receiving tagged product, six mild and two moderate product-related AEs were reported. All were transient and resolved spontaneously. Additional sensations included taste in mouth (N = 4) and scent (N = 5). The tagged products were well tolerated. This breath test has the potential to accurately and objectively monitor adherence to vaginal gel and condom used separately or concurrently.
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http://dx.doi.org/10.1007/s10461-012-0390-zDOI Listing
July 2013

Oral adherence monitoring using a breath test to supplement highly active antiretroviral therapy.

AIDS Behav 2013 Jan;17(1):298-306

Department of Anesthesiology, University of Florida College of Medicine, P.O. Box 100254, Gainesville, FL 32610-0254, USA.

A breath-based adherence system to document ingestion of oral medications (e.g., HAART) was investigated. Specifically, the food additive 2-butanol, which can be easily packaged with a drug, is converted via alcohol dehydrogenase to the volatile metabolite 2-butanone that rapidly appears in breath, indicating adherence. In healthy adults using a portable sensor and GC-MS, the following experiments were performed: yield of 2-butanone in breath following ingestion of 2-butanol, adherence system accuracy, and potential interference of the adherence system by food or misplacement of 2-butanol on the tongue. During feasibility testing, every subject exhaled 2-butanone with 6.6 ± 1.5 min to peak concentrations of 548 ± 235 ppb following ingestion of 2-butanol (40 mg). ROC areas at 5 and 10 min were 0.95 (0.86-1.00) and 1.00 (1.00-1.00). Food did not interfere. Tongue application resulted in large concentrations of 2-butanol, but not 2-butanone. A breath test to provide definitive evidence of oral medication adherence appears technically feasible.
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http://dx.doi.org/10.1007/s10461-012-0318-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3548996PMC
January 2013

The effect of lipid and aqueous solubilities on flux of nicotinic acid esters from water through silicone membrane.

Drug Dev Ind Pharm 2013 Sep 8;39(9):1494-7. Epub 2012 Jun 8.

Department of Medicinal Chemistry, University of Florida, Gainesville, Florida, USA.

Objective: The maximum fluxes (J(M)) of nicotinic acid esters (NAE) across silicone membranes from water (J(MPAQ)) have been measured to determine how well they correlate with J(M) of NAE across human skin from water in vitro (J(MHAQ)) and in vivo (J(MHAQ1)) and with J(M) of NAE across hairless mouse skin from water (J(MMAQ)).

Materials And Methods: The NAE were all commercially available. Solubilities in water (S(AQ)), isopropyl myristate (S(IPM)) and octanol (S(OCT)) were obtained from literature sources. J(MPAQ) were measured at saturation for all the esters except the methyl ester. In that case, flux was measured at a concentration (C) less than saturation (J(PAQ)) and converted to J(MPAQ) = (J(PAQ))(S(AQ)/C(AQ)).

Results And Discussion: J(MPAQ) values predicted from the previously reported coefficients to the parameters in the Roberts-Sloan (RS) equation (PRE J(MPAQ)) were substantially lower than the experimental J(MPAQ) values (EXP J(MPAQ)) values obtained here. The EXP J(MPAQ) were incorporated into the previous J(MPAQ) database and new coefficients were obtained: x = -1.837; y = 0.742; z = 0.00435; r² = 0.86. Correlation of J(MPAQ) values with J(MHAQ), J(MHAQ1), and J(MMAQ) values show the same trend as the J(MPAQ) values.

Conclusions: The inclusion of the NAE n = 6 data into the previous n = 32 database for the permeation of the prodrugs through a silicone membrane from water (J(MPAQ)) greatly improved the fit of the n = 38 database to the RS equation: r² = 0.86 vs r² = 0.77. The correlation between log J(MHAQ) and log J(MPAQ) gave r² = 0.98. This suggests that J(MPAQ) values are good predictors of J(MHAQ) values.
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http://dx.doi.org/10.3109/03639045.2012.694590DOI Listing
September 2013

Dermal and transdermal delivery: prodrugs.

Ther Deliv 2011 Jan;2(1):83-105

Department of Medicinal Chemistry, University of Florida, PO Box 100485, Gainesville, Fl 32610, USA.

Attempts to deliver drugs into and through the skin (dermal and transdermal delivery) have not been very successful because the physicochemical properties of drugs are often not optimal. Prodrugs can be used to optimize those physicochemical properties of drugs and optimize their delivery by transiently masking their polar functional groups. For a drug to cross the rate-limiting barrier to delivery (the stratum corneum) it must dissolve in and cross multiple lipid and aqueous phases within the stratum corneum. Prodrugs can be designed to exhibit increased lipid and aqueous solubilities resulting in increased delivery. In order to identify the optimal prodrugs, they must be evaluated as saturated solutions where their thermodynamic activities are maximal in the solution and in the skin. If prodrugs are evaluated at concentrations less than at saturation, inaccurate conclusions about the optimal physicochemical properties may result. Prodrugs must be designed to optimize both their lipid and aqueous solubilities to optimize their delivery into and through the skin.
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http://dx.doi.org/10.4155/tde.10.83DOI Listing
January 2011

A correlation of flux through a silicone membrane with flux through hairless mouse skin and human skin in vitro.

Int J Pharm 2009 May 12;373(1-2):62-7. Epub 2009 Feb 12.

Department of Medicinal Chemistry, University of Florida, P.O. Box 100485, Gainesville, FL 32610, USA.

The maximum fluxes of 32 prodrugs and parabens through polydimethylsiloxane membranes from water (EXP log J(MPAQ)) have been correlated with the maximum flux of the same prodrugs and parabens through hairless mouse skin from water (EXP log J(MMAQ)): EXP log J(MMAQ)=0.608 EXP log J(MPAQ)-0.636, r(2)=0.743. The average of the absolute values for the differences between the EXP log J(MMAQ) and the log J(MMAQ) calculated from EXP log J(MPAQ) (Delta log J(MMAQ)) was 0.227 log units. Similarly the maximum fluxes of 11 unrelated permeants through human skin from water (EXP log J(MHAQ)) was correlated with the EXP log J(MPAQ) for the same permeants: EXP log J(MHAQ)=0.516 EXP log J(MPAQ)-0.922, r(2)=0.82 and Delta log J(MHAQ)=0.252 log units. Since the best fit of the databases for EXP log J(MPAQ), log J(MMAQ) and log J(MHAQ) was to the Roberts-Sloan (RS) model, and the dependency of RS on a balance in lipid and aqueous solubility for optimization of topical delivery has been established, the present correlation suggests that the flux through a silicone can be used to predict flux through mouse or human and that the physicochemical properties that lead to optimized flux through one membrane will lead to optimized flux through the others.
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http://dx.doi.org/10.1016/j.ijpharm.2009.02.004DOI Listing
May 2009

A comparison of the fit of flux through hairless mouse skin from water data to three model equations.

Int J Pharm 2009 Jan 9;366(1-2):65-73. Epub 2008 Sep 9.

Department of Medicinal Chemistry, University of Florida, Gainesville, FL 32610, USA.

Data for the delivery of total species containing parent drugs from water through hairless mouse skin by prodrugs, logJ(MMAQ), has been fitted to the Roberts-Sloan, RS, the Kasting-Smith-Cooper, KSC, and Magnusson-Anissimov-Cross-Roberts, MACR, equations. The RS model which contains a parameter for the dependence of flux on solubility in water, S(AQ), as well as solubility in the lipid isopropyl myristate, S(IPM), gave the best fit: logJ(MMAQ)=-2.30+0.575 logS(IPM)+0.425 logS(AQ)-0.0016MW, r(2)=0.903. The values for the coefficients to the parameters are quite similar to those obtained when the RS model was fit to flux of solutes from water through human skin, logJ(MHAQ). There was no trend in predicting the under or over-performance of prodrugs based on their fit to the RS model and whether they were more or less soluble than their parent drugs. There was an inverse dependence of logJ(MMAQ) on partition coefficients or permeability coefficients similar to that observed for logJ(MHAQ). The similarities in trends for results for logJ(MMAQ) and logJ(MHAQ) suggests that design directives obtained from mouse skin can be extended to design new prodrugs or select new drugs for delivery through human skin.
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http://dx.doi.org/10.1016/j.ijpharm.2008.08.045DOI Listing
January 2009

Modeling of flux through silicone membranes from water.

Eur J Pharm Sci 2008 Aug 5;34(4-5):321-32. Epub 2008 Jun 5.

Department of Medicinal Chemistry, University of Florida, P.O. Box 100485, Gainesville, FL 32610, USA.

Do the Roberts-Sloan (RS) or modified Kasting-Smith-Cooper (KSC) equations that provide good fit to data for maximum flux, from water through mouse or human skin also provide a good fit to data for maximum fluxes through silicone membranes (polydimethylsiloxane, PDMS). The maximum fluxes through silicone membranes from water (J(MPAQ)), molecular weights (MW), solubilities in isopropyl myristate (S(IPM)) and water (S(AQ)) of 31 prodrugs and one parent drug have been fitted to the RS equation, which includes a parameter for dependence on S(AQ), and the KSC equation, which does not, to determine which equation gave the better fit. In addition, the J(MPAQ), MW, S(AQ) and solubilities in octanol (S(OCT)) of 26 diverse molecules from other laboratories were collected and fitted to the RS and KSC equations to determine if the choice of lipid parameter (S(IPM) or S(OCT)) had an effect on which equation gave the better fit. RS gave the better fit to the present prodrug database where: logJ(MPAQ)=-2.454+0.716 logS(IPM)+0.284 logS(AQ)+0.00208 MW, r(2)=0.77. RS also gave the better fit to the database from other laboratories where: logJ(MPAQ)=-2.046+0.667 logS(OCT)+0.333 logS(AQ)-0.00374 MW, r(2)=0.878 after four obvious outliers were removed to give n=22. Thus, data for J(MPAQ) can be fitted to the RS equation, which also provides the best fit to maximum flux from water through mouse or human skin and includes a dependence on S(AQ).
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http://dx.doi.org/10.1016/j.ejps.2008.05.008DOI Listing
August 2008

The effect of water solubility of solutes on their flux through human skin in vitro: an extended Flynn database fitted to the Roberts-Sloan equation.

Int J Pharm 2007 Jul 3;339(1-2):157-67. Epub 2007 Mar 3.

Department of Medicinal Chemistry, University of Florida, PO Box 100485, Gainesville, FL 32610, USA.

The edited Flynn database (n=62) for determining the effect of the physicochemical properties of solutes on their skin absorption has been extended (n=114) to give a database for which solubilities of the solutes in water, S(AQ), and their maximum fluxes from water through human skin in vitro, J(MAQ), are known or can be calculated. Besides the six major contributors to the original and edited Flynn database, nine more contributors have been included in the extended database to give 15 contributors. As in the edited Flynn database, data for solutes that were significantly ionized or for experiments using different thicknesses of skin were not excluded from the extended database so that the diversity of the original database was maintained. The extended database was fit to five equations where the independent variables were solubility in octanol (S(OCT)), in water (S(AQ)) or molecular weight (MW) and combinations of those three variables; and the dependent variable was J(MAQ). The best fit was obtained from the Roberts-Sloan (RS) equation: logJ(MAQ) = x + ylogS(OCT) + (1 - y)logS(AQ) - z MW, x = -2.574, y = 0.586, z = 0.00440, r(2) = 0.887, S.D. = 0.399, F = 139. This result is comparable to the best fit published using permeability coefficients, P, as the dependent variable, but gives greater insight into the factors affecting permeation. J(MAQ) is more important clinically because it described how much is permeating per unit area and time, while P is in the units of speed (cmh(-1)). Because of the dependence of J(MAQ) on S(AQ), the selection of new drugs with improved topical delivery should include considerations of their S(AQ) in their design.
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http://dx.doi.org/10.1016/j.ijpharm.2007.02.031DOI Listing
July 2007

Design for optimized topical delivery: Prodrugs and a paradigm change.

Pharm Res 2006 Dec 16;23(12):2729-47. Epub 2006 Nov 16.

Department of Medicine Chemistry, University of Florida, PO Box 100485, Gainesville, Florida 32610, USA.

In theory, topical delivery has substantial potential to treat local and some systemic disease states more effectively than systemic delivery. Unfortunately many, if not most, drug candidates for topical delivery lack the requisite physicochemical properties that would allow them to permeate the skin to a clinically useful extent. One way to overcome this obstacle to effective topical delivery is to make a transient derivative of the drug, a prodrug, with the correct physicochemical properties. But what are those correct properties and can the directives for the design of prodrugs be applied to the design of new drugs, their analogs or homologs? For some time increasing the lipid solubility (S (LIPID)) or its surrogate, the partition coefficient between a lipid (LIPID) and water (AQ) (K (LIPID:AQ)), has been the standard working paradigm for increasing permeation of the skin, and the permeability coefficient (P = distance/time) has been the quantitative measure of the result. However, even the earliest reports on non-prodrugs such as alcohols showed that working paradigm was incorrect and that P should not be the relevant measure of permeation. The shorter chain and more water soluble alcohols exhibiting lower K (LIPID:AQ) values gave the greater flux values (J = amount/area x time; the more clinically relevant measure of permeation), regardless of whether they were applied neat or in an aqueous vehicle, while P showed opposite trends for the two applications. Subsequently a large volume of work has shown that, for prodrugs and non-prodrug homologs or analogs alike, S (AQ) (not solubility in the vehicle, S (VEH)) as well as S (LIPID) should be optimized to give maximum flux from any vehicle, J (MVEH): a new working paradigm. The dependence of J (MVEH) on S (AQ) is independent of the vehicle so that S (AQ) as well as S (LIPID) are descriptors of the solubilizing capacity of the skin or S (M1) in Fick's law. The inverse dependence of J (or P) on molecular weight (MW) or volume (MV) remains. Here we review the literature that leads to the conclusion that a new working paradigm is necessary to explain the experimental data, and argue for its use in the design of new prodrugs or in the selection of candidate analogs or homologs for commercialization.
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http://dx.doi.org/10.1007/s11095-006-9108-0DOI Listing
December 2006

The effect of water solubility of solutes on their flux through human skin in vitro.

Int J Pharm 2007 Feb 22;329(1-2):25-36. Epub 2006 Aug 22.

Department of Medicinal Chemistry, University of Florida, P.O. Box 100485, Gainesville, FL 32610, USA.

The Flynn database (n=97) for determining the effect of the physicochemical properties of solutes on their skin absorption has been edited to give a database for which the solubilities of the solutes in water, S(AQ), and their maximum fluxes from water through human skin in vitro, J(MAQ), are known or can be calculated (n=76). Data from the six major contributors to the original Flynn database have been included. Data for solutes, which were significantly ionized or for experiments using different thicknesses of skin were not excluded so that the edited database is as diverse as the original. The edited database was fit to five equations where the independent variables were solubility in octanol (S(OCT)) in water (S(AQ)) or molecular weight (MW), and combinations of those three variables; and the dependent variable was J(MAQ). The best fit was obtained from the Roberts-Sloan (RS) equation: logJ(MAQ)=x+ylogS(OCT)+(1-y)logS(AQ)-zMW, x=-3.00, y=0.73, z=0.0048, r(2)=0.934, S.D.=0.37 and F=274. This result is important because J (amount/area time) is the more clinically useful descriptor of permeation compared to P (distance/time); and because the identification of S(AQ) as a significant variable in predicting flux changes the design parameters for optimizing topical delivery of drugs from solubility in lipids (or partition coefficients between OCT and AQ, K(OCT:AQ)) and MW, to solubility in lipids, S(OCT), and in water, S(AQ), as well as MW.
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http://dx.doi.org/10.1016/j.ijpharm.2006.08.015DOI Listing
February 2007

Research strategies for safety evaluation of nanomaterials. Part VI. Characterization of nanoscale particles for toxicological evaluation.

Toxicol Sci 2006 Apr 11;90(2):296-303. Epub 2006 Jan 11.

Particle Engineering Research Center, University of Florida, Gainesville, Florida 32611, USA.

To properly assign mechanisms or causes for toxic effects of nanoscale materials, their properties and characteristics both outside and within the biological environment must be well understood. Scientists have many tools for studying the size, shape, and surface properties of particulates outside of the physiological environment; however, it is difficult to measure many of these same properties in situ without perturbing the environment, leading to spurious findings. Characterizing nanoparticle systems in situ can be further complicated by an organism's active clearance, defense, and/or immune responses. As toxicologists begin to examine nanomaterials in a systematic fashion, there is consensus that a series of guidelines or recommended practices is necessary for basic characterization of nanomaterials. These recommended practices should be developed jointly by physical scientists skilled in nano characterization and biological scientists experienced in toxicology research. In this article, basic nanoparticle characterization techniques are discussed, along with the some of the issues and implications associated with measuring nanoparticle properties and their interactions with biological systems. Recommendations regarding how best to approach nanomaterial characterization include using proper sampling and measurement techniques, forming multidisciplinary teams, and making measurements as close to the biological action point as possible.
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http://dx.doi.org/10.1093/toxsci/kfj099DOI Listing
April 2006

Topical delivery of a model phenolic drug: alkyloxycarbonyl prodrugs of acetaminophen.

Pharm Res 2004 Jun;21(6):940-6

Department of Medicinal Chemistry, University of Florida, Gainesville, Florida 32610, USA.

Purpose: To determine whether the delivery of a phenolic parent drug by its alkyloxycarbonyl (AOC) prodrugs through hairless mouse skin would show similar dependencies on water and lipid solubilities that similar prodrugs of more polar heterocyclic amide and imide parent drugs have shown.

Methods: Flux through hairless mouse skin from suspensions in isopropyl myristate (J(MIPM)), solubilities in IPM (S(IPM)) and water (S(AQ)), and partition coefficients between isopropyl myristate (IPM) and pH 4.0 buffer (K(IPM:4.0)) were measured for two series of AOC derivatives of acetaminophen (APAP); their solubilities in pH 4.0 buffer (S4.0) were estimated from S(IPM)/K(IPM:4.0). Log J(MIPM) values were calculated from the n = 43 coefficients for the parameters in the transformed Potts-Guy (Roberts-Sloan) equation, and the average error of prediction (delta log J'(IPM)) was calculated. The J(MIPM), S(IPM), S4.0, and molecular weight (MW) data for this series and two other series were combined with the n = 43 database to give a n = 61 database, and new best fit coefficients were determined for the Roberts-Sloan equation: log J(MIPM) = x + y log S(IPM) + (1 - y) log S4.0 - z MW.

Results: All of the 4-AOC-APAP derivatives underperformed based on their predicted log J(MIPM) (delta log J'(MIPM) = 0.275 +/- 0.147 log units) and, although the two more water soluble members of this more lipid soluble series were more effective than APAP, they were only marginally so: <2 times. Addition of three new series to the n = 43 database for the Roberts-Sloan equation did not substantially change the coefficients to the parameters: x, y, z, and r2 = -0.322, 0.530, 0.00337 and 0.92, respectively.

Conclusions: The topical delivery of a model phenolic drug by its AOC prodrugs through hairless mouse skin from IPM shows the same dependence on S(IPM), S4.0, and MW as the delivery of polar heterocycles by their similar prodrugs.
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http://dx.doi.org/10.1023/b:pham.0000029281.12753.25DOI Listing
June 2004

Distinctive patterns of autoimmune response induced by different types of mineral oil.

Toxicol Sci 2004 Apr 12;78(2):222-8. Epub 2004 Jan 12.

Division of Rheumatology and Clinical Immunology, Department of Medicine, University of Florida, Gainesville, Florida 32610-0221, USA.

Although mineral oils are generally considered nontoxic and have a long history of use in humans, the mineral oil Bayol F (incomplete Freund's adjuvant, IFA) and certain mineral oil components (squalene and n-hexadecane) induce lupus-related anti-nRNP/Sm or -Su autoantibodies in nonautoimmune mice. In the present study, we investigated whether medicinal mineral oils can induce other types of autoantibodies and whether structural features of hydrocarbons influence autoantibody specificity. Female 3-month-old BALB/c (16-45/group) mice each received an i.p. injection of pristane (C19), squalene (C30), IFA, three medicinal mineral oils (MO-F, MO-HT, MO-S), or PBS. Sera were tested for autoantibodies and immunoglobulin levels. Hydrocarbons were analyzed by gas chromatography/mass spectrometry. IFA contained mainly C15-C25 hydrocarbons, whereas MO-HT and MO-S contained C20-C40, and MO-F contained C15-C40. Pristane and n-hexadecane were found in IFA (0.17% and 0.10% w/v, respectively) and MOs (0.0026-0.027%). At 3 months, pristane and IFA induced mainly IgG2a, squalene IgG1, and MOs IgG3 and IgM in sera. Anti-cytoplasmic antibodies were common in mice treated with MO-F, as well as those treated with pristane, squalene, and IFA. Anti-ssDNA and -chromatin antibodies were higher in MO-F and MO-S than in untreated/PBS, squalene-, or IFA-treated mice, suggesting that there is variability in the induction of anti-nRNP/Sm versus -chromatin/DNA antibodies. The preferential induction of anti-chromatin/ssDNA antibodies without anti-nRNP/Sm/Su by MO-S and MO-F is consistent with the idea that different types of autoantibodies are regulated differently. Induction of autoantibodies by mineral oils considered nontoxic also may have pathogenetic implications in human autoimmune diseases.
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http://dx.doi.org/10.1093/toxsci/kfh063DOI Listing
April 2004

Designing for topical delivery: prodrugs can make the difference.

Med Res Rev 2003 Nov;23(6):763-93

Department of Medicinal Chemistry, P.O. Box 100485, University of Florida, Gainesville, Florida 32610, USA.

It has been shown for homologous series of prodrugs that those members who were the more water soluble ones gave the greatest enhancement in topical delivery of the parent drug and not the more lipophilic ones. However, until recently models for topical delivery and equations to predict topical delivery focused only on lipid solubility (S(LIPID)) or partition coefficient (K(OCT:AQ)) and molecular volume (or molecular weight, MW) as parameters. Now several equations (transformed Potts-Guy or Series/Parallel) have been developed which include aqueous solubility (SAQ) as a parameter for predicting flux through skin. Experimental fluxes, solubilities, and MW from seven series of prodrugs have been fit to the transformed Potts-Guy equation to give coefficients for log solubility in isopropyl myristate (log SIPM) and log solubility in water (log SAQ) (0.53 and 0.47, respectively) which show, for parent drugs delivered by prodrugs from IPM in vitro through hairless mouse skin, that water solubility is almost as important as lipid solubility. When the transformed Potts-Guy equation was fit to data for the delivery of NSAID from mineral oil (MO) in vivo through human skin, the coefficients were 0.72 log SMO and 0.28 log SAQ. When the transformed Potts-Guy equation was fit to data for the delivery of their parent drugs by three series of prodrugs from water in vitro through hairless mouse skin the coefficients were 0.66 log S(IPM) and 0.34 log SAQ. Numerous recent examples are also given where more water-soluble members of homologous series of prodrugs give higher flux values from water vehicles in vitro through human skin than the more lipid soluble ones.
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http://dx.doi.org/10.1002/med.10048DOI Listing
November 2003

Topical delivery of 5-fluorouracil and 6-mercaptopurine by their alkylcarbonyloxymethyl prodrugs from water: vehicle effects on design of prodrugs.

Pharm Res 2003 Apr;20(4):639-45

Department of Medicinal Chemistry, PO Box 100485, University of Florida, Gainesville, Florida 32610, USA.

Purpose: To determine whether the fluxes through hairless mouse skin for three homologous series of prodrugs of 5-fluorouracil (5-FU, 1) and 6-mercaptopurine (6-MP, 2) from saturated aqueous suspensions show dependencies on aqueous (SAQ) and isopropyl myristate (SIPM) solubilities similar to those shown by the identical compounds delivered from IPM.

Methods: Flux through hairless mouse skin from water (JMAQ) and solubility data were measured for a homologous series of six 3-alkylcarbonyloxymethyl (ACOM) prodrugs of 5-FU (3-ACOM-5-FU), and five 6-ACOM-6-MP prodrugs, then combined with literature data for five bis-6,9-ACOM-6-MP prodrugs to give a data base. Multiple linear regression using SPSS 7.5 was performed on log SIPM, log SAQ, molecular weight and log JMAQ data to determine the best fit coefficients to the transformed Potts-Guy equation: log JMAQ = x + y log SIPM + (1 - y) log SAQ + z MW. Permeability coefficients (PMAQ) were calculated from JMAQ/SAQ.

Results: The best fit coefficients for the flux from AQ(JMAQ) were x = -1.497, y = 0.660 and z = -0.00469 (r2 = 0.765) with an average error of prediction equal to 0.193 log units. The best fit coefficients for the flux from IPM (JMIPM) were x = -0.557, y = 0.536 and z = -0.00261 (r2 = 0.941) with an average error of prediction equal to 0.109 log units. For all three series, log PMAQ increased whereas log PMIPM decreased with increasing alkyl chain lengths in the promoiety and with decreasing solubility parameter values.

Conclusions: The transformed Potts-Guy equation can be used to predict JMAQ but with less certainty than JMIPM. SIPM and SAQ have consistently been shown to have a positive influence on JMIPM, and now on JMAQ, with a balance between the two solubilities being obviously important. The previous observation that log PMAQ increased with lipophilicity is an artifact of normalizing JMAQ by SAQ.
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http://dx.doi.org/10.1023/a:1023207118209DOI Listing
April 2003
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