Percutaneous Absorption of [14C]DDT and [14C]Benzo[a]pyrene from Soil

Percutaneous Absorption of [¹⁴C]DDT and [¹⁴C]Benzo[a]pyrenefrom Soil. WESTER, R. C, MAIBACH, H. I., BUCKS, D. A. W., SEDIK,L., MELENDRES, J., LIAO, C, AND DIZIO, S. (1990). Fundam. Appl.Toxicol. 15, 510–516. The objective was to determine percutaneousabsorption of DDT and benzo[a]pyrene in vitro and in vivo fromsoil into and through skin. Soil (Yolo County 65-California-57-8;26% sand, 26% clay, 48% silt) was passed through 10-, 20-, and48-mesh sieves. Soil then retained by 80-mesh was mixed with[¹⁴C]-labeled chemical at 10 ppm. Acetone solutions at 10 ppmwere prepared for comparative analysis. Human cadaver skin wasdermatomed to 500 µm and used in glass diffusion cellswith human plasma as the receptor fluid (3 ml/hr flow rate)for a 24-hr skin application time. With acetone vehicle, DDT(18.1 ± 13.4%) readily penetrated into human skin. Significantlyless DDT (1.0 ± 0.7%) penetrated into human skin fromsoil. DDT would not partition from human skin into human plasmain the receptor phase (<0.1%). With acetone vehicle, benzo[a]pyrene(23.7 ± 9.7%) readily penetrated into human skin. Significantlyless benzo[a]pyrene (1.4 ± 0.9%) penetrated into humanskin from soil. Benzo[a]pyrene would not partition from humanskin into human plasma in the receptor phase (<0.1 %). Substantivity(skin retention) was investigated by applying ¹⁴C-labeled chemicalto human skin in vitro for only 25 min. After soap and waterwash, 16.7 ± 13.2% of DDT applied in acetone remainedabsorbed to skin. With soil only 0.25 ±0.11% of DDT remainedabsorbed to skin. After soap and water wash 5.1 ±2.1%of benzo[a]pyrene applied in acetone remained absorbed to skin.With soil only 0.14 ±0.13% of benzo[a]pyrene remainedabsorbed to skin. In vivo percutaneous absorption of DDT inrhesus monkey was significantly less (p < 0.02) from soil(3.3 ± 0.5%) than from acetone solution (18.9 ±9.4%). DDT in vitro skin penetration values into human skinwere similar to in vivo absorption values in the rhesus monkey.In vivo absorption in the rhesus was not statistically differentfrom published in vivo absorption in man (10.4 ± 3.6%).In vivo percutaneous absorption of benzo[a]pyrene in rhesusmonkey was significantly less (p < 0.015) from soil (13.2± 3.4%) than from acetone solution (51.0 ± 13.2%).Thus, with in vitro and animal in vivo systems relevant to man,skin absorption of DDT and benzo[a]pyrene from soil was significantlyless than when the chemicals were applied to skin in acetoneSolvent.     

Percutaneous Absorption of Pentachlorophenol from Soil

Pentachlorophenol (PCP) is one of the most heavily used pesticides.About 80% of PCP is used for wood preservation, whereas theremainder is used as an herbicide, fungicide, and disinfectant.PCP is a probable human carcinogen, based on animal studies.Illness and death have been reported where PCP is in directcontact with skin. PCP is the most ubiquitous compound foundwhen the general population is screened for pesticide residue.PCP is found in soil as well as other environmental sources.Our objective was to determine the skin bioavailability of PCPfrom soil and from the control vehicle acetone. In vivo in theRhesus monkey, percutaneous absorption of PCP was 24.4±6.4%of applied dose from soil and 29.2±5.8% of applied dosefrom acetone vehicle for a 24-hr exposure period. This amountof absorption makes PCP one of the more extensively absorbedcompounds to date. Additionally, the ¹⁴C half-life was 4.5 daysfollowing both intravenous and skin administration of [¹⁴C]PCP.These data suggest high bioavailability and an extended biologicalinteraction period with the long half-life. In vitro percutaneousabsorption with human cadaver skin and human plasma receptorfluid underestimated the in vivo absorption. Receptor fluidaccumulation was 0.6±0.09% and 1.5±0.2% for twoskin sources for PCP in acetone vehicle and 0.01±0.00%and 0.00±0.08% for two skin sources with soil vehicle.Skin content after skin surface wash ranged from 2.6 to 3.7%for acetone vehicle and 0.07–0.11% for soil vehicle. Overallaccountability for in vitro dose ranged from 81 to 96%.     

Glyphosate Skin Binding, Absorption, Residual Tissue Distribution, and Skin Decontamination

Glyphosate Skin Binding, Absorption, Residual Tissue Distribution,and Skin Decontamination. Wester, R. C., Melendres, J., Sarason,R., McMaster, J., and Maibach, H. I. (1991). Fundam. Appl. Toxicol.16, 725–732. Glyphosate is a broad-spectrum postemergencetranslocated herbicide. Its interactions with skin and potentialsystemic availability through percutaneous absorption was studiedby skin binding, skin absorption, residual tissue distribution,and skin decontamination. Glyphosate in a final formulation(Roundup) undiluted and diluted with water 1:20 and 1:32, wouldnot partition into powdered human stratum corneum (<1%).In vitro percutaneous absorption through human skin into humanplasma as receptor fluid was no more than 2% over a concentrationrange of 0.5–154 µg/cm² and a topical volume rangeof 0.014–0.14 ml/cm². Disposition of glyphosate followingiv administration of 93 and 9 µg doses to rhesus monkeyswas mainly through urine excretion, 95 ± 8 and 99 ±4% in 7 days, respectively. Percutaneous absorption in vivoin rhesus monkey was 0.8 ± 0.6% for the low dose (25µg/cm²) and 2.2 ± 0.8% for the high dose (270 µg/cm²).No residual ¹⁴C was found in organs of the monkeys euthanized7 days after the topical application. Washing the skin applicationsite with soap and water removed 90 ± 4% of applied dose,and washing with water only removed 84 ± 3% of applieddose. Both soap and water and water only were equal in abilityto remove glyphosate from skin over a 24 hr skin applicationperiod. About 50% of the initially applied dose could be recoveredafter 24 hr. Glyphosate is very soluble in water and insolublein most organics (octanol/water log P = –1.70) and thereforenot compatible with the lipid-laden stratum corneum. This isconsistent with the low skin binding and skin absorption andalso consistent with the efficient removal from skin with soapand water or water-only wash.     

In Vivo and in Vitro Percutaneous Absorption and Skin Decontamination of Arsenic from Water and Soil

The objective was to determine the percutaneous absorption ofarsenic-73 as H₃A_sO₄ from water and soil. Soil (Yolo County65-California-57-8) was passed through 10-, 20-, and 48-meshsieves. Soil retained by 80 mesh was mixed with radioactivearsenic-73 at a low (trace) level of 0.0004 µg/cm² (microgramsarsenic per square centimeter skin surface area) and a higherdose of 0.6 µg/cm². Water solutions of arsenic-73 at alow (trace) level of 0.000024 µg/cm² and a higher doseof 2.1 µg/cm² were prepared for comparative analysis.In vivo in Rhesus monkey a total of 80.1 ± 6.7% (SD)intravenous arsenic-73 dose was recovered in urine over 7 days;the majority of the dose was excreted in the first day. Withtopical administration for 24 hr, absorption of the low dosefrom water was 6.4 ± 3.9% and 2.0 ± 1.2% fromthe high dose. In vitro percutaneous absorption of the low dosefrom water with human skin resulted in 24-hr receptor fluid(phosphate-buffered saline) accumulation of 0.93 ± 1.1%dose and skin concentration (after washing) of 0.98 ±0.96%. Combining receptor fluid accumulation and skin concentrationgave a combined amount of 1.9%, a value less than that in vivo(6.4%) in the Rhesus monkey. From soil, receptor fluid accumulationwas 0.43 ± 0.54% and skin concentration was 0.33 ±0.25%. Combining receptor fluid plus skin concentrations gavean absorption value of 0.8%, an amount less than that with invivo absorption (4.5%) in the Rhesus. These absorption valuesdid not match current EPA default assumptions. Washing withsoap and water readily removed residual skin surface arsenic,both in vitro and in vivo. The partition coefficient of arsenicin water to powdered human stratum corneum was 1.1 x 10⁴andfrom water to soil it was 2.5 x 10⁴. This relative similarityin arsenic binding to powdered human stratum corneum and soilmay indicate why arsenic absorption was similar from water andsoil. This powdered human stratum corneum partition coefficientmodel may provide a facile method for such predictions.     

In Vitro Percutaneous Absorption of Cadmium from Water and Soil into Human Skin

The objective was to determine percutaneous absorption of cadmiumas the chloride salt from water and soil into and through humanskin. Soil (Yolo County 65-California-57-8) was passed through10-, 20-, and 48-mesh sieves. Soil retained by 80 mesh was mixedwith radioactive cadmium-109 at 13 ppb. Water solutions of cadmium-109at 116 ppb were prepared for comparative analysis. Human cadaverskin was dermatomed to 500-µm, and used in glass diffusioncells with human plasma as the receptor fluid (3 ml/hr flowrate) for a 16-hr skin application time. Cadmium in water (5µ1/cm²) penetrated skin to concentrations of 8.8 ±0.6 and 12.7 ± 11.7% of the applied dose from two humanskin sources. Percentage doses absorbed into plasma were 0.5± 0.2 and 0.6 ± 0.6%, respectively. Cadmium fromsoil (0.04 g soil/cm²) penetrated skin at concentrations of0.06 ± 0.02 and 0.13 ± 0.05% for the two humanskin sources. Amounts absorbed into plasma were 0.01 ±0.01 and 0.07 ± 0.03%. Most of the non-absorbed cadmiumwas recovered in the soap and water skin surface wash. Bindingof cadmium from water to soil was greater than binding fromwater to powdered human stratum corneum, supporting the lowerabsorption from soil than from water. Short-term exposure ofcadmium in water to human skin for 30 min (bath or swim) resultedin skin uptake, which upon further perfusion (48 hr), absorbedinto the plasma receptor fluid (systemic). Cadmium in soil wasincreased from 6.5 to 65 ppb. Skin levels correspondently increased,but plasma receptor fluid levels remained constant. Soil capacitywas decreased from 40 to 4 mg/cm². Skin levels correspondinglydecreased, suggesting decreased skin contact, but plasma receptorfluid levels remained constant. The above suggest that, within vitro diffusion, the surface concentration of cadmium willinfluence skin cadmium concentration, but that absorption intoplasma receptor fluid is relatively independent of skin surfaceconcentrations. Calculations suggest that a daily whole bodyexposure to cadmium at 116 ppb with 0.5% absorption will resultin daily systemic intake of about 10 µg Cadmium.     

Further Validation of an in Vitro Method to Reduce the Need for in Vivo Studies for Measuring the Absorption of Chemicals through Rat Skin

Current requirements for the registration of agrochemicals,particularly in the U.S.A., often require the provision of dermalabsorption data. In this process the rat is often used and complexin vivo studies, using large numbers of animals, are performed.We have compared the data obtained from in vivo and in vitrodermal absorption studies using eight pesticides with a rangeof physicochemical properties. Measurements were made of the¹⁴C-labeled pesticides which could be washed from the skin,were associated with (on/in) skin, or absorbed through the skinfollowing dermal applications in vivo and in vitro at varioustime points over a 24-hr exposure period. Good agreement wasfound between the amounts washed from and associated with theskin in vivo and in vitro. Over the time period 4–24 hrafter application the in vitro experiments predicted the invivo absorption within a factor of 2–3. These resultsshow that, with a range of pesticide molecules, the in vitromethod accurately predicted in vivo absorption supporting theutilization of the in vitro method for risk assessment fromexposure to pesticides and other chemicals.     

Age-Related Percutaneous Penetration of 2-sec-Butyl-4,6-dinitrophenol (Dinoseb) in Rats

[¹⁴C]Dinoseb was applied to previously clipped back skin of33- and 82-day-old female Fischer 344 rats at a dosage rangeof 210–2680 nmol/cm². Radioactivity in the treated skin,tissues, urine, and feces was determined at 1, 6, 24, 48, 72,and 120 hr following dermal application. In vitro dermal absorptionof [¹⁴C]dinoseb was also measured in rats of the same age bystatic and flow-through methods. In vivo dermal absorption inboth young and adults appeared biphasic with 55.6 and 82.7%of the recovered dose, respectively, penetrating in 72 hr. Invitro measurements of skin absorption at 72 hr with static cellsshowed higher values in young and lower values in the adultcompared to in vivo dermal absorption values, In vitro flow-throughmeasurements at 72 hr gave lower dermal absorption values forboth young and adult rats, compared to In vivo values. Followingin vivo application, adults excreted about 70% of the totalrecovered dose in urine, 16% in feces, and retained 7% in thebody at 120 hr. HPLC analysis of urine collected at 24 hr fromadults administered [¹⁴C]dinoseb showed extensive metabolismof parent. Excretion and retention results for young were about80% of the adult values, which also was the young to adult ratioof dermal penetration. Blood had the highest concentration ofdinoseb-derived radioactivity of the tissues examined. The kidneyto blood ratio averaged 0.60 in young and 0.41 in adults, whilethe liver and carcass to blood ratio averaged 0.18 in youngand 0.11 in adult. Dermal absorption in young rats was slightlyless than that in adults, and the subsequent kinetics of retentionand excretion appeared different, In vitro dermal penetrationof dinoseb was usually lower than In vivo absorption.     

Percutaneous Absorption/Metabolism of Phenanthrene in the Hairless Guinea Pig: Comparison of in Vitro and in Vivo Results

Percutaneous Absorption/Metabolism of Phenanthrene in the HairlessGuinea Pig: Comparison of in Vitro and in Vivo Results. NG,K. M. E., CHU, I., BRONAUGH, R. L., FRANKLIN, C. A., AND SOMERS,D. A. (1991). Fundam. Appl. Toxicol. 16, 517–524. Thein vitro and in vivo percutaneous absorption/metabolism of phenanthrenewas investigated in hairless guinea pigs. Flow-through diffusioncells and Hepes-buffered Hanks' balanced salt solution (HHBSS)as receptor fluid were used in the in vitro system. When phenanthrenewas applied to excised guinea pig skin mounted on the cellsat dose levels of 6.6 and 15.2 µg/cm², 89.7 and 79.1%of the administered doses were respectively absorbed into theskin and receptor fluids during a 24-hr perfusion period. Theseresults are consistent with the in vivo data which showed approximately80% absorption over the same period of time. Phenanthrene wasmetabolized in vitro into phenanthrene 9,10-dihydrodiol, 3,4-dihydrodiol,1,2-dihydrodiol, and traces of hydroxy phenanthrenes. Of thematerials absorbed in vitro, 92% was the parent compound and7% the dihydrodiol metabolites. When a nonviable in vitro systemwas used, 68% of the applied 15.2 µg/cm² dose was absorbed.Data from the present study demonstrate that the in vitro systemis a good model for predicting in vivo percutaneous absorptionof phenanthrene, and that penetration of phenanthrene throughthe skin is controlled more by the passive rate of diffusionthan by metabolism.     

The Predictive Accuracy of in Vitro Measurements for the Dermal Absorption of a Lipophilic Penetrant (Fluazifop-Butyl) through Rat and Human Skin

The predictive accuracy of in vitro measurements in estimatingdermal absorption has been evaluated in rat and human skin usingfluazifop-butyl (FB), a lipophilic model compound, at dosagerates of 2.5, 25, and 250 µg/cm² In vitro studies usedrat and human epidermal membranes mounted in static diffusioncells with radiolabeled FB and receptor fluids of 50% aqueousethanol (Aq Et), 6% polyethylene glycol 20 oleyl ether in saline(PEG), or tissue culture medium (TCM). In vivo rat studies withradiolabeled FB were carried out to parallel previously publishedhuman volunteer studies. For rat skin, in vitro measurementswith all types of receptor fluid provide an adequate prediction(generally within a factor of 3) of in vivo absorption. Absorptiondata for human epidermal membranes with a receptor fluid ofAq Et were adequately predictive of the in vivo absorption.In contrast, membranes with PEG or TCM significantly underestimatedthe in vivo absorption. The results support the conclusion thatin vitro studies are useful to predict in vivo dermal absorptionin rat and man, when appropriate receptor fluids are used.     

Percutaneous Absorption, Metabolism, and Hemolytic Activity of n-Butoxyethanol

Percutaneous Absorption, Metabolism, and Hemolytic Activityof n-Butoxyethanol. BARTNIK, F. G., REDDY, A. K., KLECAK, G.,ZIMMERMANN, V., HOSTYNEK, J. J., and KUNSTLER, K. (1987). Fundam.Appl. Toxicol. 8, 59–70. A series of studies was conductedto examine the percutaneous absorption, distribution, excretion,and hemolytic activity of n-butoxyethanol (BE). Rats receivinga subcutaneous dose of ¹⁴C-labeled BE excreted the radioactivityin the urine (79%), expired air (10%), and feces (0.5%) within72 hr. Of the organs analyzed, thymus and spleen showed elevatedspecific radioactivities as compared with blood. A percutaneousapplication of BE on rats, under nonocclusive conditions, showed25–29% absorption within 48 hr. Peak blook levels of BEoccurred at 2 hr after application; butoxyacetic acid (BAA)was found to be the major metabolite. Comparison of in vitroskin penetration data showed the following absorption patternof BE: hairless rat >> pig > human skin. Hemolysisand associated hematological changes were noted in the ratswhich received single dermal applications of 260–500 mg/kgof BE. In vitro, BAA showed markedly greater hemolytic abilityon rat erythrocytes than did BE. Human erythrocytes showed nohemolysis when incubated with BE or BAA at concentrations thatare hemolytic to rat erythrocytes. An intravenous dose of 62.5mg/kg of BE does not result in hemolysis or hemoglobinuria inthe rat. The rat may be an animal model with increased susceptibilityto the effects of BE compared with humans because of its rapidpercutaneous absorptive ability and its greater hemolytic sensitivity.     

In Vivo percutaneous absorption of acetochlor in the rhesus monkey: Dose-response and exposure risk assessment

Percutaneous absorption of three topical dose levels of [¹⁴C]acetochlor in the rhesus monkey were determined for exposure risk assessment. The topical doses were 30.7, 0.43 and 0.03 mg acetochlor in 40 μl commercial formulation and aqueous dilutions thereof, spread over 10 cm³ skin surface area (lower abdominal). The dosing area was not covered. The skin application time was 24 hr. The dosed skin surface area was washed with 50% soap (Ivory^R Liquid) and water at the end of the 24-hr dosing period. An intravenous dose of 0.43 mg was also administered to determine the excretory kinetics of acetochlor in the rhesus monkey. The same four monkeys were used for all dose administrations. Bioavailability was determined by radioactivity disposition in blood, urine and faeces. Percutaneous absorption was 23.1 ± 8.7, 17.3 ±5.9 and 4.9 ± 1.4% for 0.03, 0.43 and 30.7 mg doses, respectively. Assuming a constant state of absorption, the hourly exposure flux (μmg/cm²/hr) was 0.03 ± 0.01 for the 0.03 mg dose (3 μg/cm²). Increasing the dose approximately 15-fold to 0.43 mg (43 μg/cm²) resulted in a 10-fold increase in flux to (0.3 μg/cm²/hr). Increasing the dose a further 70-fold to 30.7 mg (3070 μg/cm²) resulted in only another 21-fold increase in flux (6.3 ±1.8 μg/cm²/hr). Thus, the efficiency of absorption (%) decreased with increased topical dose, but the amount (mass/flux) of acetochlor absorbed always increased with increased dose. Plasma levels of topical acetochlor at the high dose were detectable at 1 hr and continued at a relatively steady level through the 24-hr dosing period. After the skin surface wash (24 hr) plasma levels decreased but were still detectable at the last 168-hr sampling period. Acetochlor, recently EPA approved as an herbicide for corn crops, is carcinogenic; however, farmers will use half as much acetochlor/acre as other herbicides. The percutaneous absorption of acetochlor is equal to that of alachlor. Therefore, human exposure based on one-half usage suggests that human risk assessment should be one-half all other factors being equal.     

Cutaneous corticosteroid-induced glaucoma

Skin contact with nonylphenol ethoxylates (NPE), a group of widely used surfactants, is the primary source of human exposure. Previous studies have shown that the absorption of NPE through human and animal skin in vitro is limited (<1% over 8 hr) [Monteiro-Riviere et al. Toxicol Indust Health 2000; 16:49–57]. The purpose of this study was to examine the percutaneous absorption of NPE and the chemical precursor, nonylphenol (NP), in the isolated perfused porcine skin flap (IPPSF) model for comparison to the in vitro porcine skin flow through (PSFT) diffusion studies. The IPPSF model is considered to accurately predict absorption of chemicals through human skin. The IPPSF was dosed with 100 μl of 1% ¹⁴C ring-labeled NP, ¹⁴C ring-labeled NPE-4, or ¹⁴C ring-labeled NPE-9 in aqueous polyethylene glycol (PEG-400) solution and perfused for 8 hr. All three chemicals were minimally absorbed, with only approximately 0.1% of the applied dose found in the perfusate over the 8-hr collection. This absorbed material represents the systemic exposure expected following skin contact in humans. In addition, less than 1% of the applied dose penetrated into the stratum corneum and underlying dermis, but remained within the skin and did not go through to the perfusate. Thus, the overall potential systemic exposure to these chemicals from skin contact, using a model considered similar to human skin in vivo, is less than 1%. The absorption results of this study were consistent with previous studies in the PSFT model. The penetration of NPEs and NP in the IPPSF was less than the PSFT and is probably more predictive of in vivo human absorption as this model is physiologically closer to human skin. This suggests that the overall potential for skin absorption of these chemicals in humans is even lower than previous estimates.     

Percutaneous Absorption of Parathion in Vitro in Porcine Skin: Effects of Dose, Temperature, Humidity, and Perfusate Composition on Absorptive Flux

Percutaneous Absorption of Parathion in Vitro in Porcine Skin:Effects of Dose, Temperature, Humidity, and Perfusate Compositionon Absorptive flux. CHANG, S. K., AND RIVIERE, J. E. (1991).Fundam. Appl. Toxicol. 17, 494–504. The effect of environmentalfactors on the percutaneous absorption of parathion in excisedporcine skin was assessed in a flow-through diffusion cell systemby varying the temperature (T), relative humidity (%RH), perfusateflow rate (F), and composition (porcine serum) at three parathiondoses (4, 40, and 400 µ/cm²) compared to standard conditions(air temperature = 37°C, perfusate temperature = 37°C,%RH = 60, flow rate = 4 ml/hr, and standard bovine serum albuminmedium). Parathion absorption was assessed by monitoring totalradiolabeled activity appearing in the perfusate over time.High relative humidity significantly increased parathion penetration,as did two elevated temperature conditions. The effects of flowrate and perfusate composition were variable and dose dependent.In the present studies, lower applied doses appeared to be moresensitive to changes in the environmental conditions studied.These results suggest that these parameters have independentand different degrees of effect on parathion percutaneous absorption.Experimental conditions should be strictly controlled and dose-responsestudies need to be conducted when evaluating transdermal studies.Finally, if simi1ar effects occur in vivo, the risk assessmentcalculations on percutaneous absorption should take these parametersinto consideration.     

In Vivo Percutaneous Absorption of Boric Acid, Borax, and Disodium Octaborate Tetrahydrate in Humans Compared to in Vitro Absorption in Human Skin from Infinite and Finite Doses

Literature from the first half of this century report concernfor toxicity from topical use of boric acid, but assessmentof percutaneous absorption has been impaired by lack of analyticalsensitivity. Analytical methods in this study included inductivelycoupled plasma-mass spectrometry which now allows quantitationof percutaneous absorption of ¹⁰B in ¹⁰B-enriched boric acid,borax, and disodium octaborate tetrahydrate (DOT) in biologicalmatrices. This made it possible, in the presence of comparativelylarge natural dietary boron intakes for the in vivo segmentof this study, to quantify the boron passing through skin. Humanvolunteers were dosed with ¹⁰B-enriched boric acid, 5.0%, borax,5.0%, or disodium octaborate tetrahydrate, 10%, in aqueous solutions.Urinalysis, for boron and changes in boron isotope ratios, wasused to measure absorption. Boric acid in vivo percutaneousabsorption was 0.226 (SD = 0.125) mean percentage dose, withflux and permeability constant (K_p) calculated at 0.009 µg/cm²/hand 1.9 x 10^–7 cm/h, respectively. Borax absorption was0.210 (SD = 0.194) mean percentage of dose, with flux; and K_pcalculated at 0.009 µg/cm²/h and 1.8 x 10^–7 cm/h,respectively. DOT absorption was 0.122 (SD = 0.108) mean percentage,with flux and K_p calculated at 0.01 µg/cm²/h and 1.0 x10^–7 cm/h, respectively. Pretreatment with the potentialskin irritant 2% sodium lauryl sulfate had no effect on boronskin absorption. In vitro human skin percentage of doses ofboric acid absorbed were 1.2 for a 0.05% solution, 0.28 fora 0.5% solution, and 0.70 for a 5.0% solution. These absorptionamounts translated into flux values of, respectively, 0.25,0.58, and 14.58     

Vitamin A Potentiation of Vinylidene Chloride Hepatotoxicity in Rats and Precision-Cut Rat Liver Slices

Pretreatment of large doses of vitamin A (VA) is known to potentiatethe hepatotoxicity of carbon tetrachloride. Therefore the effectsof 1-day VA pretreatment on VDC hepatotoxicity was examinedboth in vivo and in an in vitro system of precision-cut ratliver slices. Male Sprague-Dawley rats were pretreated with250,000 IU/kg VA by oral gavage. After 24 hr rats were administered50, 100, or 200 mg/kg VDC ip. Precision-cut liver slices wereprepared from VA pretreated rats 24 hr later and the liver sliceswere exposed for 2–8 hr to 0.025–1.0 µl VDCevaporated into the gas phase of the incubation vials. VA pretreatmentresulted in an enhancement of VDC toxicity, both in vivo andin vitro. There was a dose-dependent increase in plasma ALT24 hr after VDC treatment of rats and an increase in K⁺ leakagefrom liver slices after VDC exposure. Histological analysisof the liver or the liver slices revealed that VA+VDC treatmentresulted in centrilobular necrosis of the liver. When GdCl₃(10 mg/kg iv) was administered just before VA pretreatment ofrats, VDC toxicity was partially reversed as observed by a decreasein ALT in vivo and a decrease in the loss of K⁺ in vitro. Theseresults indicated that Kupffer cells, the resident macrophagesof the liver, were partially responsible for the VA-potentiatedVDC hepatotoxicity. One-day pretreatment of VA induced cytochromeP450IIE1 protein content as well as its enzymatic activity asmeasured by p-nitrophenol hydroxylation. Because VDC is bioactivatedby cytochrome P450IIE1, the increase in VDC hepatotoxicity afterVA may be due to an increased bioactivation of VDC in the liverand in precision-cut liver slices. Thus, more than one mechanismmay be involved in the VA enhancement of VDC hepatotoxicity.     

Metabolic Alterations Induced by Topical Dimethylacetylenedicarboxylate

Metabolic Alterations Induced by Topical Dimethylacetylenedicarboxylate.KLAIN, G. J., BONNER, S. J., AND BELL, W. G. (1988). Fundam.Appl Toxicol 10, 730–735. The disposition of topical dimethylacetylenedicarboxylate(DMAD) in tissue and its effect on glucose metabolism were studiedin vivo, using skin grafted athymic nude mice, and in vitro,using excised pig skin. [¹⁴C]DMAD that penetrated skin graftswas distributed throughout the body. At 24 hr, the liver contained15.62% of the applied dose. The kidneys, lungs, brain, and theheart contained 12.73, 5.61,0.36, and 3.24% of the dose, respectively.One hour postapplication, DMAD markedly decreased [U-¹⁴C]glucoseoxidation and the syntheses of fatty acids and glycogen in thelivers and skin grafts. Similar effects were observed in excisedpig skin. In addition, the activities of hepatic glucose-6-phosphatedehydrogenase, isocitric and NADP-mahc dehydrogenase, and acetyl-CoAcarboxylase were significantly reduced in DMAD-treated mice.In contrast, no effect was observed on the activity of glucokinase.The data indicate that DMAD rapidly penetrates the skin andcauses aberrations in the activities of the glycogenic. lipogenic,and tricarboxylic acid metabolic pathways.     

Time Course of Inhibition of Cholinesterase and Aliesterase Activities, and Nonprotein Sulfhydryl Levels Following Exposure to Organophosphorus Insecticides in Mosquitofish (Gambusia affinis)

Cholinesterase (ChE) in brain and muscle was quickly inhibitedduring a 48-hr in vivo exposure to chlorpyrifos (0.1 ppm), parathion(0.15 ppm), and methyl parathion (8 ppm) in mosquitofish (Gambusiaaffinis). ChE remained inhibited during a 96-hr nonexposureperiod. Brain ChE reached peak inhibition by 12 hr after exposureto parathion and chlorpyrifos and by 4 hr after exposure tomethyl parathion. All insecticides caused greater than 70% ChEinhibition by 4 hr in muscle. There was no recovery of ChE after4 days of nonexposure in either brain or muscle. Hepatic aliesterases(AliE) were quickly and greatly inhibited (>70% by 4 hr)after exposure to parathion and chlorpyrifos but not after exposureto methyl parathion. Exposure to methyl parathion required 24–36hr to inhibit hepatic AliE to the same level as that followingparathion and chlorpyrifos exposures at 4 hr. Exposure to allinsecticides eventually resulted in greater than 80% inhibitionof AliE. None of the test groups treated with insecticides showedany signs of significant recovery of AliE during the 4 daysof nonexposure. Nonprotein sulfhydryl (NPSH) concentrationswere lower than controls after 24 hr of exposure and 96 hr afterrecovery for all compounds. Exposure to methyl parathion loweredNPSH concentrations greater than the other compounds. HepaticAliE appear capable of affording some protection of ChE frominhibition following parathion or chlorpyrifos exposures, butconsiderably less protection against methyl parathion.     

Oral absorption of CGS-20625, an insoluble drug,in dogs and man

Oral bioavailability of highly water-insoluble drugs is often quite limited and variable, requiring the development of improved formulations. Animal models are an essential aspect of the design and testing of such formulations designed to improve absorption in man. The present report compares the absorption of CGS-20625, an insoluble drug, in dog and man after oral administration of the drug as a powder, a solid dispersion capsule, and after gastric and duodenal administration in PEG 400 solution. CGS-20625 powder (20 mg) given orally exhibited slow, delayed absorption in both dog and man, with aC _max of 0.26±0.07 μg/ml atT _max of 3 hr in dog, and 0.01±0.004 μg/ml at 2 hr in man. Administration of CGS-20625 in PEG 400 solution improved absorption in dog and man, with aC _max of 1.2±0.10 μg/ml atT _max of 0.25 hr in dog, and aC _max of 0.10±0.04 μg/ml at 0.5 hr in man.T _max after administration of the hard gelatin capsule formulation was 0.9 and 1.0 hr in dog and man, withC _max of 0.89±0.16 and 0.052±0.014 μg/ml, respectively. Absolute bioavailability of CGS-20625 powder in the dog was 0.67±0.21, whereas the bioavailabilities of the powder and the capsule relative to the PEG 400 solution were 0.84 and 1.1, respectively, in dog, and 0.41 and 0.85 respectively, in man. No significant benefits of duodenal administration were observed. Plasma levels were approximately 10-fold greater and oral clearance was approximately 5-fold less in the dog than in man. Furthermore, pharmacokinetic data were less variable and relative bioavailability was greater in dogs than in humans. Physiological factors in the gastrointestinal tract or greater first-pass metabolism in man may account for these species differences. The relative rate and extent of CGS-20625 absorption were similar between dog and man, in the order of powder <capsule<PEG 400 solution. In addition,in vivo absorption rates in both species reflectin vitro dissolution differences between the powder and the capsule. These data strongly support the use of the dog as a model for developing improved formulations of CGS-20625. Further investigation of the dog as a model to evaluate insoluble drug absorption is warranted.     

Evaluation of Monkey Skin as a Model for in Vitro Percutaneous Penetration and Metabolism of [3H]T-2 Toxin in Human Skin

Evaluation of Monkey Skin as a Model for in Vitro PercutaneousPenetration and Metabolism of [³H]T-2 Toxin in Human Skin. KEMPPAINEN,B.W., RILEY, R.T., PACE, J.G., HOERR, F.J., AND JOYAVE, J. (1986).Fundam. Appl. Toxicol. 7, 367–375. Discs of abdominalskin (obtained from humans and hybrid monkeys at autopsy) weremounted on diffusion cells. The epidermal surfaces were dosedwith [³H]T-2 dissolved in dimethyl sulfoxide (DMSO). The rateof [³H]T-2 penetration (expressed as ng/cm²/hr) through humanskin was 0.38±0.10 and 3.85±0.96 (x±95percnt;confidence limit) when dosed with 74 and 582 ng/cm², respectively.[³H]T-2 penetrated through monkey skin at the rate of 0.37±0.14,0.80±0.43, 4.13±1.71, and 6.55±3.45 whendosed with 70, 155, 555 and 1063 ng/cm², respectively. Analysisof the receptor fluid bathing human skin revealed 15% of theradioactivity was associated with T-2, 71% with HT-2 toxin (HT-2),and 6.3% with an unknown metabolite more polar than HT-2. Theradioactivity in the receptor fluid bathing monkey skin wasassociated with T-2 (87%) and HT-2 (1.0%). The results are consistentwith the hypothesis that metabolism of T-2 occurred during penetrationthrough the excised skin and did not occur in the receptor fluiddue to enzymes leaching out of the skin. These findings indicatethat excised monkey skin is a good model for T-2 penetrationthrough human skin when DMSO is the vehicle, but that dermalmetabolism of T-2 is different in these two species.     

The Relationship between pKa and Skin Irritation for a Series of Basic Penetrants in Man

The Relationship between pK_a and Skin Irritation for a Seriesof Basic Penetrants in Man. BERNER, B., WILSON, D. R., STEFFENS,R. J., MAZZENGA, G. C., HINZ, R., GUY, R. H., AND MAIBACH, H.I. (1990). Fundam. Appl. Toxicol 15, 760–766. For a seriesof bases, which penetrate through human skin in vitro at similarrates (0.056–0.49 µM/cm²/hr), penetrant pK_ais shown to correlate with erythema, edema, and color meterreadings. As estimates of irritation, erythema, edema, and rednessmeasurements are highly linearly correlated. For the selectedseries, irritation becomes significant for bases with a pK_a> 8. The irritation potential of acids with pK_a 4 has beenpreviously reported; pK_a appears highly predictive of acuteskin irritation for acids and bases in man.