The isolated perfused bovine udder as an in vitro model of percutaneous drug absorption. Skin viability and percutaneous absorption of dexamethasone, benzoyl peroxide, and etofenamate

Strategies for organ preservation: Current prospective and challenges

In current therapeutic approaches, transplantation of organs provides the best available treatment for a myriad of end-stage organ failures. However, shortage of organ donors, lacunae in preservation methods, and lack of a suitable match are the major constraints in advocating this life-sustaining therapy. There has been continuous progress in the strategies for organ preservation since its inception. Current strategies for organ preservation are based on the University of Wisconsin (UW) solution using the machine perfusion technique, which allows successful preservation of intra-abdominal organs (kidney and liver) but not intra-thoracic organs (lungs and heart). However, novel concepts with a wide range of adapted preservation technologies that can increase the shelf life of retrieved organs are still under investigation. The therapeutic interventions of in vitro-cultured stem cells could provide novel strategies for replacement of nonfunctional cells of damaged organs with that of functional ones. This review describes existing strategies, highlights recent advances, discusses challenges and innovative approaches for effective organ preservation, and describes application of stem cells to restore the functional activity of damaged organs for future clinical practices.

Precision-cut bovine udder slices (PCBUS) as an in-vitro-model of an early phase of infection of bovine mastitis

Background

The aim of this study was to establish precision-cut bovine udder slices (PCBUS) as an in-vitro-model to investigate pathophysiological processes in the early phase of mastitis in order to have the possibility to investigate new therapeutic approaches for the treatment of such udder inflammation in later studies. Furthermore, this model should contribute to substitute in-vivo-experiments. Bovine mastitis is one of the most common and costly infectious diseases in the dairy industry, which is largely associated with the use of antimicrobial agents. Given this problem of antimicrobial resistance, it is essential to step up research into bacterial infectious diseases. Thus, the transfer of the in-vitro-model of precision-cut tissue slices to the bovine udder enables broad research into new therapeutic approaches in this area and can also be used to address issues in basic research or the characterisation of complex pathophysiological processes.

Results

A stimulation with LPS, PGN or the combination of both substances (LPS:PGN) demonstrates the ability of the PCBUS to react with a significant secretion of IL-1ß, TNF-α and PGE₂.

Conclusion

The slices represent an instrument for investigating pharmacological interactions with udder tissue, which can be useful for studies on pharmacological questions and the understanding of complex pathophysiological processes of infection and inflammation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12917-021-02817-w.

Non-clinical Models to Determine Drug Passage into Human Breast Milk

BACKGROUND

Successful practice of clinical perinatal pharmacology requires a thorough understanding of the pronounced physiological changes during lactation and how these changes affect various drug disposition processes. In addition, pharmacokinetic processes unique to lactation have remained understudied. Hence, determination of drug disposition mechanisms in lactating women and their babies remains a domain with important knowledge gaps. Indeed, lack of data regarding infant risk during breastfeeding far too often results in discontinuation of breastfeeding and subsequent loss of all the associated benefits to the breastfed infant. In the absence of age-specific toxicity data, human lactation data alone are considered insufficient to rapidly generate the required evidence regarding risks associated with medication use during lactation.

METHODS

Systematic review of literature to summarize state-of-the art non-clinical approaches that have been developed to explore the mechanisms underlying drug milk excretion.

RESULTS

Several studies have reported methods to predict (to some extent) milk drug excretion rates based on physicochemical properties of the compounds. In vitro studies with primary mammary epithelial cells appear excellent approaches to determine transepithelial drug transport rates across the mammary epithelium. Several of these in vitro tools have been characterized in terms of transporter expression and activity as compared to the mammary gland tissue. In addition, with the advent of physiology-based pharmacokinetic (PBPK) modelling, these in vitro transport data may prove instrumental in predicting drug milk concentration time profiles prior to the availability of data from clinical lactation studies. In vivo studies in lactating animals have proven their utility in elucidating the mechanisms underlying drug milk excretion.

CONCLUSION

By combining various non-clinical tools (physicochemistry-based, in vitro and PBPK, in vivo animal) for drug milk excretion, valuable and unique information regarding drug milk concentrations during lactation can be obtained. The recently approved IMI project ConcePTION will address several of the challenges outlined in this review.

Isolated perfused udder model for transcriptome analysis in response to Streptococcus agalactiae

This study aimed to evaluate the transcriptional changes occurring in isolated perfused mammary alveolar tissue in response to inoculation with S. agalactiae and to identify the most affected biological functions and pathways after 3 h. Four udders taken at slaughter from cows with healthy mammary gland were perfused ex situ with warmed and gassed Tyrode's solution. Mammary alveolar tissue samples were taken from the left fore and rear quarters (IQ-inoculated quarters) before inoculation (hour 0) and at 3 h post inoculation (hpi) and at the same times from control right fore and rear quarters (not inoculated: NIQ). A total of 1756 differentially expressed genes (DEGs) were identified between IQ and NIQ at 3 hpi using edgeR package. Within this set of DEGs, 952 were up regulated and mainly involved with innate immune response and inflammatory response, e.g., CD14, CCL5, TLR2, IL-8, SAA3, as well as in transcriptional regulation such as FOS, STAT3 and NFKBIA. Genes down-regulated (804) included those involved with lipid synthesis e.g., APOC2, SCD, FABP3 and FABP4. The most affected pathways were chemokine signaling, Wnt signaling and complement and coagulation cascades, which likely reflects the early stage response of mammary tissue to S. agalactiae infection. No significant gene expression changes were detected by RNA-Seq in the others contrasts. Real time-PCR confirmed the increase in mRNA abundance of immune-related genes: TLR2, TLR4, IL-1β, and IL-10 at 3 hpi between IQ and NIQ. The expression profiles of Casp1 and Bax for any contrasts were unaffected whereas Bcl2 was increased in IQ, which suggests no induction of apoptosis during the first hours after infection. Results provided novel information regarding the early functional pathways and gene network that orchestrate innate immune responses to S. agalactiae infection. This knowledge could contribute to new strategies to enhance resistance to this disease, such as genomic selection.

Ischaemia–Reperfusion Injury in the Isolated Haemoperfused Bovine Uterus: An In Vitro Model of Acute Inflammation

Following on from previous studies on dermal inflammation in the isolated perfused bovine udder, a new in vitro model of the isolated haemoperfused bovine uterus was established for studies on acute inflammatory reactions (for example, eicosanoid synthesis and regulation of cyclooxygenase-1 [COX-1] and COX-2) caused by ischaemia-reperfusion (I-R) injury. The organs and blood used in this study were obtained from a slaughterhouse. Within 2 hours of slaughter, uterine perfusion was re-established, by using a mixture of homologous blood and Tyrode solution (4:1). After equilibration, several deposits of arachidonic acid (5 mg and 0.1 mg) and arachidonylethanolamide (0.1 mg) were injected into the myometrial tissue. Tissue biopsies were taken from treated and untreated areas at 180 and 300 minutes after the onset of haemoperfusion, for measuring prostaglandin E(2) (PGE(2)) levels. In addition, the regulation of COX-1 and COX-2 mRNA was investigated by using the reverse transcriptase-polymerase chain reaction. Eicosanoid levels were determined by using an enzyme immunoassay (ELISA). Because both an increase in PGE(2) concentration and up-regulation of COX mRNA were observed, the inhibitory effects of dexamethasone, added to the perfusion medium, were studied. Dexamethasone caused a significant decrease in tissue PGE(2) production, but did not induce down-regulation of COX-2 mRNA. In conclusion, the isolated haemoperfused bovine uterus was introduced as an in vitro model of acute inflammation, induced by I-R injury. The suitability of the model for investigating anti-inflammatory substances was demonstrated. Use of the isolated haemoperfused bovine uterus in pharmacological research and drug screening may contribute to reducing the number of animals used for testing.

Use of the Bovine Udder Skin model to evaluate the tolerability of Mesem cosmetic cream

Observational studies of Mesem cream (based on Mesembryanthemum crystallinum L. plant extract) found that it had positive effects on skin hydration and smoothing of the skin. However, some patients reported skin irritation effects. The current study evaluated the skin tolerability of Mesem cream, as compared to the carrier cream (without the active ingredient), by using the isolated perfused bovine udder skin model. The primary outcomes investigated were cytotoxicity (i.e. cell viability), assessed with the MTT assay, and irritancy and inflammation, assessed by measuring PGE₂ tissue levels. A total reaction score was calculated by combining the results for each parameter. In the case of a single topical application, significant differences were found between the carrier cream and the Mesem cream. While the application of carrier cream resulted in low cytotoxicity (-8.4% change in viability, as compared to the untreated control), the Mesem cream was more cytotoxic (-18.7% change). In addition, one hour after application, PGE₂ levels were higher in Mesem cream-treated skin, as compared to carrier cream-treated skin (16.6% versus 11.3%). Further experiments (tape-stripped skin and repeated application) also found significant differences between the two creams in the results obtained. Evaluation of the effectiveness, safety and tolerability of phyto-cosmetic products is important. Our results confirmed the findings of two previous human observational studies (the human patch test and open application study). Future experiments to understand the underlying principles of its effectiveness, safety and tolerability should include extracts of M. crystallinum L. juice, as well as the Mesem cream itself.

The isolated perfused human skin flap model: A missing link in skin penetration studies?

Development of effective (trans)dermal drug delivery systems requires reliable skin models to evaluate skin drug penetration. The isolated perfused human skin flap remains metabolically active tissue for up to 6h during in vitro perfusion. We introduce the isolated perfused human skin flap as a close-to-in vivo skin penetration model. To validate the model's ability to evaluate skin drug penetration the solutions of a hydrophilic (calcein) and a lipophilic (rhodamine) fluorescence marker were applied. The skin flaps were perfused with modified Krebs-Henseleit buffer (pH7.4). Infrared technology was used to monitor perfusion and to select a well-perfused skin area for administration of the markers. Flap perfusion and physiological parameters were maintained constant during the 6h experiments and the amount of markers in the perfusate was determined. Calcein was detected in the perfusate, whereas rhodamine was not detectable. Confocal images of skin cross-sections shoved that calcein was uniformly distributed through the skin, whereas rhodamine accumulated in the stratum corneum. For comparison, the penetration of both markers was evaluated on ex vivo human skin, pig skin and cellophane membrane. The proposed perfused flap model enabled us to distinguish between the penetrations of the two markers and could be a promising close-to-in vivo tool in skin penetration studies and optimization of formulations destined for skin administration.

Effects of water-filtered infrared-A and of heat on cell death, inflammation, antioxidative potential and of free radical formation in viable skin--first results

The effects of water-filtered infrared-A (wIRA) and of convective heat on viability, inflammation, inducible free radicals and antioxidative power were investigated in natural and viable skin using the ex vivo Bovine Udder System (BUS) model. Therefore, skin samples from differently treated parts of the udder of a healthy cow were analyzed using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) test, by prostaglandin E2 (PGE2) measurement and by electron spin resonance (ESR) spectroscopy. Neither cell viability, the inflammation status, the radical status or the antioxidative defence systems of the skin were significantly affected by wIRA applied within 30 min by using an irradiance of 1900 W m(-2) which is of relevance for clinical use, but which exceeded the maximum solar IR-A irradiance at the Earth's surface more than 5 times and which resulted in a skin surface temperature of about 45 °C without cooling and of about 37 °C with convective cooling by air ventilation. No significant effects on viability and on inflammation were detected when convective heat was applied alone under equivalent conditions in terms of the resulting skin surface temperatures and exposure time. As compared with untreated skin, free radical formation was almost doubled, whereas the antioxidative power was reduced to about 50% after convective heating to about 45 °C.

Reconstructed skin models as emerging tools for drug absorption studies

INTRODUCTION

As humans can come into contact with xenobiotics intentionally or accidentally, knowledge about the skin absorption of these substances is crucial and requires reliable models and test procedures. Animal experiments should be avoided whenever possible, instead of making the use of in vitro systems. Furthermore, due to limited availability of normal and especially diseased human skin, alternative test systems such as reconstructed skin models are urgently required.

AREAS COVERED

This article discusses the advantages and limitations of excised human skin, animal skin and reconstructed skin models for absorption testing in vitro. Furthermore, the authors also describe the standard procedure for skin absorption testing and give an excursion to the applicability of artificial membranes. Finally, the article highlights the progress in the development of reconstructed disease models and provides an extensive overview about past and ongoing research in this field.

EXPERT OPINION

The development and validation of in vitro systems for skin absorption testing is inevitable. More research efforts are required for the development of reconstructed disease models. Reconstructed skin models need to be improved, especially in terms of complexity to mimic the in vivo situation better. It should not, however, be the main goal to imitate the in vivo situation exactly, but to establish reliable systems that ensure predictive and reliable data.

Tissue distribution of enrofloxacin after intramammary or simulated systemic administration in isolated perfused sheep udders

OBJECTIVE

To determine the tissue distribution of enrofloxacin after intramammary or simulated systemic administration in isolated perfused sheep udders by measuring its concentration at various sample collection sites.

SAMPLE

26 udders (obtained following euthanasia) from 26 healthy lactating sheep.

PROCEDURES

For each isolated udder, 1 mammary gland was perfused with warmed, gassed Tyrode solution. Enrofloxacin (1 g of enrofloxacin/5 g of ointment) was administered into the perfused gland via the intramammary route or systemically via the perfusion fluid (equivalent to a dose of 5 mg/kg). Samples of the perfusate were obtained every 30 minutes for 180 minutes; glandular tissue samples were obtained at 2, 4, 6, and 8 cm from the teat base after 180 minutes. The enrofloxacin content of the perfusate and tissue samples was analyzed via high-performance liquid chromatography with UV detection.

RESULTS

After intramammary administration, maximun perfusate enrofloxacin concentration was detected at 180 minutes and, at this time, mean tissue enrofloxacin concentration was detected and mean tissue enrofloxacin concentration was 123.80, 54.48, 36.72, and 26.42 μg/g of tissue at 2, 4, 6, and 8 cm from the teat base, respectively. Following systemic administration, perfusate enrofloxacin concentration decreased with time and, at 180 minutes, tissue enrofloxacin concentrations ranged from 40.38 to 35.58 μg/g of tissue.

CONCLUSIONS AND CLINICAL RELEVANCE

By 180 minutes after administration via the intramammary or systemic route in isolated perfused sheep mammary glands, mean tissue concentration of enrofloxacin was greater than the minimum inhibitory concentration required to inhibit growth of 90% of many common mastitis pathogens in sheep. Use of either route of administration (or in combination) appears suitable for the treatment of acute mastitis in sheep.

The isolated perfused equine distal limb as an ex vivo model for pharmacokinetic studies

Even though intra-articular injections play an important role in the treatment of joint-related lameness in horses, little is known about pharmacokinetic properties of substances used. Therefore, an ex vivo model for pharmacokinetic studies was developed using distal forelimbs of slaughtered horses. The extremity was perfused with gassed Tyrode solution for up to 8 h. Tissue viability was confirmed by measurements of glucose consumption, lactate production, and lactate dehydrogenase activity in the perfusate. Standard criteria for tissue viability had been determined in preliminary experiments (n = 11), which also included histological examinations of the joint capsule. As the model's first implementation, the articular efflux rate of betamethasone (BM), administered as BM disodium phosphate intra-articularly to the fetlock joint (4 mg BM/joint), was investigated. The concentration of BM in the venous perfusate of the radial vein was measured by means of high-performance liquid chromatography. The average BM efflux rate per minute was calculated to be 5.1 μg/min with values ranging from 9 μg/min to 2.9 μg/min. 7.5 h after i.a. application, 2.3 mg BM had left the joint via the radial vein. Using this inexpensive setup, the presented model allows studying a variety of pharmacological topics without the ethical limitations of animal studies.

The comparability of in vitro and ex vivo studies on the percutaneous permeation of topical formulations containing Ibuprofen

In order to avoid in vivo experiments and to gain information about the suitability of surrogates for skin replacement, Franz-type diffusion cell experiments were conducted by using three ibuprofen-containing formulations (cream, gel and microgel) on bovine split-skin samples and cellophane membranes. Moreover, ex vivo examinations were performed on the isolated perfused bovine udder, to study the comparability of in vitro and ex vivo experimental set-ups. Depending on the formulation, noticeable differences in the permeation of Ibuprofen occurred in vitro (udder skin) and ex vivo (isolated perfused bovine udder), but not in the cellophane membrane. The rates of ibuprofen permeability (cream > gel > microgel) and adsorption into the skin (gel > microgel > cream) varied with the formulation, and were probably caused by differences in the ingredients. Furthermore, different storage conditions and seasonal variation in the collection of the skin samples probably led to differences in the amounts of ibuprofen adsorption apparent in the isolated bovine udder and udder skin. In vitro diffusion experiments should be preferred to experiments on isolated organs with regard to the costs involved, the throughput, and the intensity of labour required, unless metabolism of the drug in the skin, or cell-cell interactions are of particular interest.

Ex vivo examination of the biocompatibility of biodegradable magnesium via microdialysis in the isolated perfused bovine udder model

PURPOSE

Being biodegradable, magnesium is considered a promising future implant material but very little is known about the biocompatibility for the tissues in direct contact with it. In this study, the degradation of pure magnesium implants in the skin of an isolated bovine udder was examined over a period of five hours.

METHODS

Microdialysis technique was used in order to investigate the reactions at the interface of implant and tissue. Pure titanium implants served as control. Degradation behavior and biocompatibility were evaluated via extracellular magnesium ion concentration and PGE2 and TNF alpha served as indicators of inflammation.

RESULTS

Concentrations of 5.5 mmol/l Mg2+ were detected at the beginning, which decreased to a plateau of about 3.5 mmol/l after approximately two and a half hours. PGE2 and TNF alpha concentrations indicated no major inflammatory tissue response to the degradation.

CONCLUSIONS

These results give an idea of the ion burden at the implantation site of degrading magnesium and suggest good biocompatibility even at the tissue-implant interface.

Absorption of Isosorbide Dinitrate after Administration as Spray, Ointment and Microemulsion Patch. An In-vitro Study Using the Isolated Perfused Bovine Udder

The isolated perfused bovine udder is an in-vitro model, which maintains bovine udder skin with an isolated vasculature in a viable state. Using this in-vitro model, the percutaneous absorption and metabolism of isosorbide dinitrate (ISDN) was studied.

The organ was perfused with gassed Tyrode solution for up to 6 h. A region of udder skin was treated topically with 60 mg ISDN as a spray, 60 mg ISDN as an ointment and with 120mg ISDN as a microemulsion patch of 30 cm2. Spray and ointment were applied onto a skin region of 400 cm2. The concentrations of ISDN and its metabolites isosorbide-2-mononitrate and isosorbide-5-mononitrate were measured in perfusate fractions by capillary column gas-liquid chromatography with electron capture detection.

Following topical administration of the different formulations, ISDN as well as its metabolites were detected in the perfusate fractions, thus demonstrating that ISDN is metabolized by the udder skin in-vitro. A maximum amount of ISDN was absorbed after administration as a spray followed by ointment and microemulsion (5, 2·5 and 1·8 μmol total organic nitrate, respectively). In contrast, the ISDN flux per cm2 skin was significantly higher after administration of the microemulsion (64·4 pmol cm−2 min−1 for the microemulsion compared with 21·9 and 10·2 pmol cm−2 min−1 for spray and ointment).

Tissue distribution of cloxacillin after intramammary administration in the isolated perfused bovine udder

Background

Various intramammary suspensions containing cloxacillin benzathine are registered for use in cattle as antibiotics for intramammary use at drying off. To ensure antibacterial efficacy, the glandular tissue concentration of an antimicrobial agent must be sufficient. Since the possibilities to measure concentrations in the different areas of the glandular tissue in vivo are very limited, it was the aim of the present study to examine the distribution of cloxacillin in vitro using the isolated perfused bovine udder.

Methods

Mammary glands taken at slaughter from healthy lactating cows were perfused in vitro with warmed and gassed Tyrode solution. 600 mg cloxacillin benzathine were administered as Orbenin Extra Dry Cow by the intramammary route to six front and rear quarters each. Samples of glandular tissue - at different distances from and vertical to the teat right up to the udder base - were gathered from the treated quarters after 6 h. Perfusate was also sampled before and hourly after treatment for 6 h. The cloxacillin content of the tissue samples and perfusate samples was analysed by high performance liquid chromatography.

Results

The concentration of cloxacillin in the glandular tissue of front quarters measured 6 h after administration tended to decrease with increasing vertical distance from the teat. The decrease pattern of the concentration was not quite clear in rear quarters. A considerable variation in the tissue concentrations of cloxacillin was obvious, which reflects in vivo conditions. The concentrations measured in the perfusate samples were below the limit of quantification at all time points, indicating limited absorption of the antibiotic from the glandular tissue.

Conclusion

After intramammary administration of the dry off product containing cloxacillin benzathine concentrations of more than 0.5 μg/g (MIC) were reached in all regions of the front and rear quarters.

Effects of steroidal and non-steroidal antiphlogistic drugs on eicosanoid synthesis in irritated skin: studies with the isolated perfused bovine udder

Using the isolated perfused bovine udder as an in-vitro model of skin inflammation, the effects of topically administered arachidonic acid on prostaglandin and leukotriene synthesis have been shown previously. In this study, the effects of indometacin (indomethacin) and clobetasol-17-propionate (administered topically) as well as flunixin meglumine and meloxicam (administered via the perfusion fluid) have been studied. Compared with controls, arachidonic acid caused a significant increase in the dermal prostaglandin E2 (PGE2) and peptidoleukotriene (LTC4/D4/E4) concentration. Topical treatment with indometacin (1.6 mg cm−2) and clobetasol-17-propionate (90 μg cm−2), which were administered 60 min before arachidonic acid administration, inhibited the inflammatory reaction. Flunixin meglumine (1 μg mL−1 perfusion fluid) was administered 30 min after and meloxicam (3 μg mL−1 perfusion fluid) was administered 60 min before arachidonic acid application. Three hours after arachidonic acid administration, a significant inhibition of PGE2 synthesis was induced by flunixin. In contrast, meloxicam showed only a slight effect. The effect of flunixin was comparable with in-vivo results. It is known from animal studies that anti-inflammatory effects of meloxicam are obvious within up to 6 h after treatment. Therefore, the incomplete effect of meloxicam may be explained pharmacokinetically. In conclusion, the described in-vitro model seems to be suitable for studies of pharmacological effects on eicosanoid synthesis in the skin.

The skin compatibility of distilled tall oils: evaluation with the bovine udder skin in vitro model system

Distilled tall oil (DTO) is a natural product, often added as an emulsifying ingredient in cutting fluids used as lubricants and coolants in metal working. The in vitro model used to test the skin compatibility of these substances, was the isolated perfused ex vivo bovine udder skin (BUS) model. After three exposure periods (0.5, 1, and 5 hours), cytotoxic effects were determined by using the 3-(4,5-dimethylthiazol- 2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, and tissue levels of the pre-inflammatory mediator prostaglandin E2 (PGE2) in treated whole skin biopsies were assessed by using an enzyme immunoassay. The BUS standard study design, involving a single application, was previously developed to investigate the skin irritation potential of cosmetics and chemicals. In the current study, four different batches of undiluted DTO, and tall oil fatty acids as a reference compound, were applied both singly and repeatedly (three times), under open conditions which were in line with the potential usage conditions in the work place. Under the standardised single application conditions, no major differences in cytotoxic effects or PGE2 levels between the samples were apparent, so no indication of a skin irritation potential could be concluded. This result is in accordance with prior in vivo studies for acute dermal toxicity. Under repeated application conditions, signs of cytotoxicity were observed after the application of one of the DTO samples, which was known to be derived from different raw materials. Therefore, it was concluded that, generally, the presence of DTO at a concentration of up to 10% in cutting fluids, is not expected to result in any DTO-related deterioration of the skin.

Tissue distribution of marbofloxacin after ‘systemic’ administration into the isolated perfused bovine udder

Mammary glands taken at slaughter from healthy lactating cows were perfused in vitro with warmed and gassed Tyrode solution. Marbofloxacin was administered "systemically" via the perfusion fluid at concentrations similar to those measured in plasma following intravenous administration of 2mg/kg marbofloxacin. Samples from the perfusate were taken over a 24h period. Glandular tissue samples at different vertical distances from the teat up to the udder base were gathered from each of the four quarters after 3, 6, 12 and 24h. The marbofloxacin content of the tissue samples was analysed by high performance liquid chromatography with UV detection. The addition of marbofloxacin to the perfusion fluid produced median concentrations above the MIC90 (0.016microg/mL) against Escherichia coli at all glandular tissue sites measured after 3 and 6h with remarkable variations. Samples taken after 12 and 24h contained marbofloxacin in concentrations (median) of 0.22 (<0.05-0.32)microg/g and 0.13 (<0.05-0.16)microg/g. It is concluded that a systemic administration of marbofloxacin is well suited for the treatment of E. coli mastitis.

Reconstructed human epidermis for skin absorption testing: results of the German prevalidation study

Exposure to chemicals absorbed by the skin can threaten human health. In order to standardise the predictive testing of percutaneous absorption for regulatory purposes, the OECD adopted guideline 428, which describes methods for assessing absorption by using human and animal skin. In this study, a protocol based on the OECD principles was developed and prevalidated by using reconstructed human epidermis (RHE). The permeation of the OECD standard compounds, caffeine and testosterone, through commercially available RHE models was compared to that of human epidermis and animal skin. In comparison to human epidermis, the permeation of the chemicals was overestimated when using RHE. The following ranking of the permeation coefficients for testosterone was obtained: SkinEthic > EpiDerm, EPISKIN > human epidermis, bovine udder skin, pig skin. The ranking for caffeine was: SkinEthic, EPISKIN > bovine udder skin, EpiDerm, pig skin, human epidermis. The inter-laboratory and intra-laboratory reproducibility was good. Long and variable lag times, which are a matter of concern when using human and pig skin, did not occur with RHE. Due to the successful transfer of the protocol, it is now in the validation process.

Tissue distribution of cefquinome after intramammary and “systemic” administration in the isolated perfused bovine udder

Mammary glands taken at slaughter from healthy lactating cows were perfused in vitro with warmed and gassed Tyrode solution. Cefquinome (88.8mg cefquinome sulphate per 8mL) was administered by the intramammary route to all quarters and/or "systemically" via the perfusion fluid at concentrations similar to those measured in plasma following intramuscular administration of 1mg cefquinome per kg body weight. Samples of the perfusate were taken over a 6-h period and from the regional lymph nodes after 6h. Using a scalpel, sections of glandular tissue - at different distances from and vertical to the teat right up to the udder base - were gathered from four quarters each per route of administration at 2, 4 and 6h. The cefquinome content of the tissue samples was analysed by high performance liquid chromatography with diode array detection and of the perfusate samples by bioassay. After intramammary administration, the concentration of cefquinome in the glandular tissue decreased exponentially with increasing distance from the teat. The addition of cefquinome to the perfusion fluid produced a mean concentration of 0.2-0.5microg/g at all glandular tissue sites. Combined intramammary and systemic treatment ensured that concentrations exceeded the MIC(90) values of the most common mastitis pathogens in all areas of the udder by 2h post-administration. There was considerable variability in the tissue concentrations of cefquinome, particularly after intramammary administration. These results suggest that for the treatment of acute mastitis a combination of both intramammary and systemic administration is likely to be advantageous in order to rapidly produce maximum cefquinome concentrations in all regions of the udder.

Tea Tree Oil Concentration in Follicular Casts After Topical Delivery: Determination by High-Performance Thin Layer Chromatography Using a Perfused Bovine Udder Model

Tea tree oil, a popular antimicrobial agent is recommended for the treatment of acne vulgaris, a disease of the pilosebaceous unit. Tea tree oil formulations (colloidal bed, microemulsion, multiple emulsion, and liposomal dispersion containing 5% w/w tea tree oil) were applied to bovine udder skin. The follicular uptake of tea tree oil upon application was determined by a cyanoacrylate method. Tea tree oil was determined by quantifying terpinen-4-ol content using high-performance thin layer chromatography. The accumulation of tea tree oil in the follicular casts was 0.43 +/- 0.01, 0.41 +/- 0.009, 0.21 +/- 0.006, and 0.16 +/- 0.005 percentage by weight (milligram oil/gram of sebum plug) for microemulsion, liposomal dispersion, multiple emulsion, and colloidal bed, respectively. This is the first study of its kind to quantify tea tree oil concentration in the follicles.

Reflectance spectroscopy can quantify cutaneous haemoglobin oxygenation by oxygen uptake from the atmosphere after epidermal barrier disruption

BACKGROUND

The supply of oxygen to the viable skin tissue within the upper layers is not only secured by the cutaneous blood vascular system, but to a significant part also by oxygen diffusion from the atmosphere through the horny layer. The aim of this study was to examine whether changes in haemoglobin oxygenation can be observed within the isolated perfused bovine udder skin used as a skin model by removing the upper horny layer by adhesive tape stripping.

METHODS

Diffuse reflectance spectroscopy in the visible spectral range was used for non-invasive characterisation of haemoglobin oxygenation in skin under in vitro conditions. Mid-infrared attenuated total reflectance spectroscopy was employed for analysing the surface layer of the stratum corneum with respect to keratin, water and lipid components. Skin barrier disruption was achieved by repeated stripping of superficial corneocyte layers by adhesive tape.

RESULTS AND CONCLUSION

Significant changes in skin haemoglobin oxygenation were observed for skin areas with reduced lipid concentration and a reduced stratum corneum layer, as determined from the quantitative evaluation of the diffuse reflectance skin spectra. The result can be interpreted as an increase of oxygen diffusion after the removal of the upper horny layer.

The release and vascular action of bradykinin in the isolated perfused bovine udder

It has been postulated that the mammary kinin system may play a role in modulating mammary blood flow. Until the present study, the local release of bradykinin (BK) or other kinin system constituents into the mammary vasculature had not been reported and there were also conflicting findings on the action of BK on udder vasculature. Udders were removed from healthy lactating cows at slaughter. Pairs of ipsilateral quarters were perfused with Tyrode solution through the external pudendalis artery and drained via the cranial superficial epigastric vein. Mammary secretion was collected through teat cannulae. The perfusion pressure was linearly related to perfusate flux between 60 and 210 ml min(-1) and the flow rate was adjusted (110-150 ml min(-1)) to give a basal pressure of 85 mmHg. PO2, PCO2 and pH in the venous effluent perfusate stabilised at 157 +/- 10 mmHg, 50.1 +/- 2.4 mmHg and 7.1 +/- 0.03, respectively. The venous effluent contained immunoreactive BK and BK precursor, tissue kallikrein activity, and bradykinin-destroying enzyme. The concentration of BK stabilised at 378 +/- 48 pg (ml perfusate)(-1), that of trypsin-activated BK precursor was 679 +/- 59 pg BK equivalents ml(-1) and that of tissue kallikrein, measured as cleavage of D-Val.Leu.Arg-p-nitroanilide (D-Val.Leu.Arg-pNA), was 5.5 +/- 1.7 nmol p-NA h(-1) ml(-1). Arterial infusion of phenylephrine (0.49-490 microM) produced increases in perfusion pressure (vasoconstriction). Acetylcholine (ACh) (0.55-55 microM) and BK (0.1-10 microM) produced only vasodilatation. BK (EC50 = 1.00+/-0.04 microM) was a more potent vasodilator than ACh (EC50 = 9.57+/-0.49 microM). The basal BK concentration was 250 times below the threshold for vasoactivity. The udder produced a milk-like secretion, which was dependent on perfusate flow and contained a concentration of BK which remained unchanged from 60 to 180 min of perfusion (231 +/- 31 pg ml(-1)) unlike that in the venous effluent which doubled between 60 and 120 min. Thus, in addition to its secretion into milk, BK, together with its precursor and tissue kallikrein, is continuously released into the vasculature of the isolated, perfused, lactating bovine udder.

Tissue distribution of benzylpenicillin after intramammary administration in the isolated perfused bovine udder

Udders from previously healthy lactating cows were perfused with warmed and gassed Tyrode solution in vitro. Benzylpenicillin was administered in three formulations: an oily suspension with micronized particles of <10 microm diameter, an oily suspension with average particle size of 40 microm and an aqueous solution (3 million IU benzylpenicillin-potassium, volume 15 mL). The antibiotics were administered intracisternally to six front and six rear quarters each. Moreover, a dry-off-ointment (100 000 IU benzylpenicillin-potassium and 100 000 IU benzylpenicillin-benzathine, volume 7.5 mL) was tested in four udder halves. Perfusate samples were collected over 3 h. Furthermore, glandular tissue at different vertical distances from the teat base and the regional lymph node were sampled after 3 h. The determination of benzylpenicillin was performed by high pressure liquid chromatography with UV detection. With increasing distance from the teat base, the concentration of benzylpenicillin in tissue exponentially decreased. Using the aqueous solution or oily suspension that contained micronized active principle, higher concentrations were reached compared to the formulation with particle sizes of 40 microm. In udder lymph nodes, the concentration was highest after treatment with the coarse suspension. The transfer from the dry-off-ointment with benzathine-salt into perfusate was very low. These results suggest that it is possible to study tissue distribution of antibiotics in the isolated perfused bovine udder.

The isolated perfused bovine udder as a model of dermal eicosanoid release

The aim of this study was to examine whether the isolated perfused bovine udder could be used as a suitable in vitro inflammation model. A common in vivo inflammation model is arachidonic acid-induced inflammation in mouse ears. As an in vitro substitute for this model, arachidonic acid was administered topically to the skin of an isolated perfused bovine udder and the subsequent changes in eicosanoid synthesis were examined. As with the mouse-ear model, there was a significant increase in eicosanoid synthesis (prostaglandins E(2) and F(2 alpha) and leukotrienes B(4) and C(4)/D(4)/E(4)) following topical irritation. This effect lasted for 3 hours. In addition, the changes in prostaglandin E(2) synthesis in the skin following irritation with arachidonic acid were measured by the microdialysis technique. In conclusion, the in vitro model described seems suitable for studies of pharmacological effects on eicosanoid synthesis.

Tissue distribution of oxacillin and ampicillin in the isolated perfused bovine udder

In vivo, tissue distribution of intra-mammarily administered antibiotics is mostly only assessed by sampling milk and blood. Therefore, the described study analysed whether measurement of tissue concentrations makes sense in vitro instead. Isolated bovine udders were perfused with gassed and warmed Tyrode solution. To four front and rear quarters each, 1000 mg oxacillin in 7.5 ml vehicle was administered intracisternally, completely formulated as sodium monohydrate in two lactation ointments (with or without sodium dodecylsulphate) or 80% as benzathine salt in a dry-off ointment. Over 3 h, perfusate and glandular tissue from different locations were sampled and analysed by high pressure liquid chromatography. With increasing vertical distance to the teat base, the tissue concentration of antibiotics decreased. With the lactation ointment containing sodium dodecylsulphate, lower oxacillin concentrations were reached in glandular tissue and lymph nodes compared to those without. The ointments led to a higher recovery of oxacillin in glandular tissue than in perfusate. Aluminium monostearate in the dry-off ointment caused an even poorer absorption of oxacillin into perfusate. The isolated perfused bovine udder is suitable to study the tissue distribution of antibiotics, since the results were mainly comparable with the few existing in vivo studies and show the influence of different formulations.

Deuterium labelled nonylphenols in an in-vitro model of percutaneous absorption of environmental xenoestrogens

A technical mixture of isomeric nonylphenols NP is formed as rather persistent degradation product of nonionic surfactants and has become widespread in the environment, e.g., in surface waters. Information about possible pathways for incorporation is needed for risk assessments, as NP has estrogenic properties. NP uptake after skin contact was determined using isolated and perfused bovine udders as models for human skin. NP-d2 labelled in the positions ortho to the OH-group was prepared by an exchange procedure which did not measurably change the relative amount of isomers. Samples of udder perfusate, milk equivalent produced during the experiments and skin tissue were taken immediately before administration of 500 mg or 50 mg NP-d2 on an udder skin area of 200 cm2 and then for 5 h. They were analyzed by GC-MS for NP and NP-d2 after cleanup by steam distillation and final extraction with SPME fibres. The results are an unambiguous proof of the penetration of NP into the capillary system of living mammals after skin contact.

Buccal mucosa in vitro experiments. I. Confocal imaging of vital staining and MTT assays for the determination of tissue viability

Delivery of drugs through the skin and the buccal mucosa has been considered as an alternative to per oral dosing for those substances that are degraded in the gastro-intestinal tract, or are subject to first-pass metabolism in the liver. In the buccal mucosa, contrary to skin, the diffusion barriers are located within living cell layers, hence the physiological state of the tissue is likely to significantly affect in vitro diffusion profiles. In this study, we were interested in assessing the viability of excised buccal mucosa and determining the limits of tissue usage under common in vitro experimental conditions. Using confocal laser scanning microscopy (CLSM), we have shown that optical sectioning of samples exposed to calcein AM and ethidium homodimer-1 (used as 'live' and 'dead' cell probes respectively) can be employed to accurately and reliably determine the viability of buccal mucosa biopsies. The results of the CLSM assay were remarkably consistent with that of an MTT assay. In both studies, viability in PBS at 34 degrees C was lost after about 8 h post-mortem, whereas it could be sustained for up to 24 h in KBR.

Application of deuterated compounds for investigations of percutaneous absorption of chemical substances

The percutaneous absorption of the xenoestrogen 2,2-bis-(4-hydroxyphenyl)-propane (bisphenol A) 1 has been studied and compared with results on dibenzoyl peroxide 2, a component of drug formulations for topical application. Isolated perfused bovine udders from slaughtered cows were employed as models for human skin. The deuterium labelled compounds 1-d14 and 2-d10 were applied to enhance the reliability of GC-MS trace determinations by use of reverse isotope dilution analysis. 1-d14 was found in perfusate and milk equivalent samples obtained between 60 and 300 min after topical application with maximum concentrations between 120 and 180 min. 1-d14 was enriched in the milk samples by a factor of about 300 compared with the perfusate. The results confirm a possible penetration of 1 from the environment through the skin into the capillary system. 2 studied on the same model system penetrated faster than 1 by a factor of about three.

Percutaneous penetration enhancement and its quantification

True penetration enhancing effects resulting from structural alterations of the barrier stratum corneum manifest themselves in an increase of the drug diffusion coefficient DB and/or of the drug solubility in the barrier csB. The quantification of enhancing effects on drug penetration is possible either by the direct determination of the drug fluxes or by an indirect determination through the measurement of the pharmacodynamic response. In both cases the thermodynamic drug activity has to be considered. In the case of pharmacodynamic measurements, enhancing effects may be determined from the horizontal distance of activity-response lines obtained without and with enhancer, respectively, i.e. the quotient of the drug concentrations that induce the same effect. The activity-standardized bioavailability factors fa obtained from the horizontal distances correspond to the enhancer-induced relative changes in the permeabilities PB, or more exactly in the product DB X csB. On the other hand, the vertical distance between the activity-response lines, i.e. the differences in the drug response after application of preparations with equal (even maximum) thermodynamic drug activities may be used to quantify penetration enhancing effects.