In vitro testing of tensides employing monolayer cultures: a comparison with results of patch tests on human volunteers

Comparative evaluation of six commercial adult toothpaste formulations reveals cytotoxicity and altered functions in a human oral melanocyte model: an in vitro study

This study aims to compare six commercial adult toothpaste (labeled as A, B, C, D, E, and F) for cytotoxicity and melanocyte function alterations in vitro using primary human epidermal melanocytes from a Caucasian donor (HEMn-LP cells) as a model of oral melanocytes. Cells were incubated with toothpaste extracts (50% w/v) in culture media at dilutions (1:25, 1:50, 1:100, 1:200, 1:500, 1:800, and 1:1000) for 24 h. MTS and LDH assays were used to assess cytotoxicity. The effects of noncytotoxic toothpaste concentrations on melanocyte functional endpoints were then examined using spectrophotometric methods. All toothpaste showed concentration-dependent cytotoxicity that was heterogeneous across toothpaste containing SLS detergent. IC50 values of cytotoxicity followed the order: A = E > C > B > D > F. To compare toothpaste, they were tested at 1:800 and 1:1000 dilutions that were noncytotoxic after 24 h. None of the toothpaste affected cellular melanin production. However, toothpaste A, C, and D suppressed tyrosinase activity at both dilutions, while toothpaste B suppressed tyrosinase activity only at 1:800 dilution. Toothpaste A, C, E, and F elevated ROS production at 1:800 dilution, with no change at 1:1000 dilution. Toothpaste has a heterogeneous effect on melanocytes. Toothpaste B, E, and F at 1:1000 dilution were the safest as they did not alter melanocyte functions at this dilution, although toothpaste F is the least cytotoxic of these. Future studies are necessary to expand these results in a physiological environment of oral tissue. The findings of this study provide novel insight into the biocompatibility studies of toothpaste on oral melanocytes. They can aid dental practitioners and consumers in selecting noncytotoxic toothpaste that do not contribute to ROS generation by melanocytes in the oral cavity or lead to cytotoxicity and impaired cellular function.

Evaluation of Ocular Irritation Sensitivity: Implications of Clinical Parameters, Pain Sensitivity, and Tear Neuromediator Profiles

Background/Objectives: Sensitivity to ocular irritation varies among individuals, being influenced by clinical, subjective, and biochemical factors. This study aimed to evaluate individual variability in ocular irritation sensitivity, focusing on clinical parameters, pain perception, and tear neuromediator profiles. Methods: Sixty female participants aged 20-40 were classified into high-sensitivity and low-sensitivity groups based on their response to an irritant (Tween20). Clinical assessments included the ocular surface disease index (OSDI), tear break-up time (TBUT), Schirmer test, and corneal touch threshold measured with the Cochet-Bonnet esthesiometer. Pain sensitivity was assessed using the pain sensitivity questionnaire (PSQ), and tear neuromediators were quantified in tear samples before and after stimulation. The concentrations of calcitonin gene-related peptide (CGRP), nerve growth factor, neuropeptide Y, vasoactive intestinal peptide (VIP), and substance P were measured using an enzyme-linked immune sorbent assay (ELISA). Results: The high-sensitivity group exhibited significantly higher OSDI scores (p = 0.038). No significant differences were observed in TBUT, corneal staining scores, or Schirmer's test results. The PSQ results revealed that the high-sensitivity group had lower total and moderate pain scores (p = 0.037 and p = 0.040, respectively). An analysis of the tear neuromediator showed elevated baseline CGRP levels (p = 0.017) and a significant post-stimulation increase in substance P (p = 0.021) in the high-sensitivity group. Conclusions: These findings emphasize the value of combining clinical, subjective, and biochemical measures to understand sensitivity to ocular irritation. This comprehensive approach may guide the development of safer cosmetic formulations and improve safety assessment protocols.

Validation study of a new reconstructed human epidermis model EPiTRI for in vitro skin irritation test according to OECD guidelines

Following the global trend of reducing animal testing, various reconstructed human epidermis (RHE) models for skin irritation test (SIT) have been developed, verified, validated and included in OECD TG 439. We developed a new RHE called EPiTRI and a SIT method using EPiTRI (EPiTRI-SIT model) following the OECD guidelines. EPiTRI possesses morphological, biochemical and physiological properties similar to human epidermis with well-differentiated multilayered viable cells with barrier function. The EPiTRI-SIT model was tested for 20 reference chemicals in Performance Standard of OECD TG 439 (GD 220), showing good predictive capacity with 100% sensitivity, 70% specificity and 85% accuracy. EPiTRI had sensitivity in detecting di-n-propyl disulphate, as an irritant chemical (UN GHS Category 2), whereas most validated reference methods detected it as a non-irritant. An international validation study of EPiTRI-SIT was conducted in four laboratories to confirm the within- and between-laboratory reproducibility, as well as predictive capacity. The phase I/II within-laboratory and between-laboratory reproducibility was 100%/95% and 95%, respectively. The overall sensitivity, specificity and accuracy of EPiTRI-SIT was 96%, 70% and 83%, respectively, which fulfilled the OECD criteria. Thus, EPiTRI, meets the criteria of Performance Standards of OECD TG 439 (GD 220) and is suitable for screening irritating chemicals in vitro.

Improved metal allergen reactivity of artificial skin models by integration of Toll-like receptor 4-positive cells

BACKGROUND

Reconstructed human epidermis (RhE) is widely used to replace animal models in order to assess the proinflammatory and allergenic effects of chemicals. Unfortunately, RhE lacks proinflammatory responsiveness for metal haptens, which are the most prevalent human contact allergens, raising concerns about its reliability for predicting skin allergens.

OBJECTIVES

To investigate whether this limitation of RhE might be attributable to a lack of functional expression of Toll-like receptor 4 (TLR4), which governs proinflammatory sensitivity to nickel and cobalt.

MATERIALS AND METHODS

RhE, dendritic cell (DC)-containing RhE and full-thickness skin equivalent (FTSE) were compared regarding their proinflammatory responsiveness to metal allergens.

RESULTS

The incorporation of dermal fibroblasts was sufficient to confer metal sensitivity to RhE. Unlike keratinocytes, normal human fibroblasts expressed high levels of TLR4 mRNA and induced interleukin-8 expression upon stimulation with nickel or cobalt. Consistently, dermal isolates from FTSE expressed considerable amounts of TLR4 mRNA, whereas RhE or epidermis isolated from FTSE, normal human epidermis or inflamed human epidermis failed to express TLR4. Similarly, co-culture with TLR4-positive DCs bestowed RhE with proinflammatory responsiveness to metals.

CONCLUSION

Our data suggest that FTSE or DC/RhE co-culture models can circumvent the shortcomings of RhE assays, and combine the benefits of complex and monoculture-based test systems in a single assay.

In vivo evaluation of fluoride and sodium lauryl sulphate in toothpaste on buccal epithelial cells toxicity

OBJECTIVES

The present study addresses the effect of fluoride and sodium lauryl sulphate content of toothpaste on oral epithelial cells in vivo conditions.

SUBJECTS AND METHOD

Forty volunteers were assigned into two experimental groups, each of them applying the different brand of toothpaste. Every group has been using three different types of toothpaste (non-fluoride and non-SLS, fluoride and non-SLS, and the fluoride and SLS) of the same brand for 6 months, each for 2 months. The buccal epithelial cells were sampled at baseline and 30, 60, 90, 120, 150 and 180 days after the beginning of the research. Effect on DNA damage was analyzed by micronucleus assay Results: After 60 days of use, for both tested kinds of toothpaste with fluoride and without SLS, all studied parameters were not significantly different from the results obtained at the time when the participants used a non-fluoride toothpaste. While, after 60 days of use, for one kind of toothpaste with SLS and fluoride, was observed significantly higher incidence of pyknotic cells (2.20 ± 0.95, 0.00 ± 0.00 vs. 0.05 ± 0.22, respectively; p = .001), cells with karyorrhexis (2.35 ± 1.14, 0.85 ± 0.93 vs. 0.40 ± 0.68, respectively; p = .001), and nuclear buds (1.35 ± 0.68, 0.45 ± 0.51 vs. 0.45 ± 0.60, respectively; p = .001), compared to toothpastes of the same brand with fluoride and without SLS, and without fluoride and without SLS, for the same period.

CONCLUSIONS

Based on the results, can be concluded that there is no fluorine-dependent cytotoxic or genotoxic effect, while SLS dentifrice increases the number of nuclear morphological changes in buccal epithelial cells.

Formulation, development, and optimization of a novel octyldodecanol-based nanoemulsion for transdermal delivery of ceramide IIIB

This research aimed to develop and optimize a nanoemulsion-based formulation containing ceramide IIIB using phase-inversion composition for transdermal delivery. The effects of ethanol, propylene glycol (PG), and glycerol in octyldodecanol and Tween 80 systems on the size of the nanoemulsion region in the phase diagrams were investigated using water titration. Subsequently, ceramide IIIB loading was kept constant (0.05 wt%), and the proposed formulation and conditions were optimized via preliminary screening and experimental design. Factors such as octyldodecanol/(Tween 80:glycerol) weight ratio, water content, temperature, addition rate, and mixing rate were investigated in the preliminary screening experiment. Response surface methodology was employed to study the effect of water content (30%–70%, w/w), mixing rate (400–720 rpm), temperature (20°C–60°C), and addition rate (0.3–1.8 mL/min) on droplet size and polydispersity index. The mathematical model showed that the optimum formulation and conditions for preparation of ceramide IIIB nanoemulsion with desirable criteria were a temperature of 41.49°C, addition rate of 1.74 mL/min, water content of 55.08 wt%, and mixing rate of 720 rpm. Under optimum formulation conditions, the corresponding predicted response values for droplet size and polydispersity index were 15.51 nm and 0.12, respectively, which showed excellent agreement with the actual values (15.8 nm and 0.108, respectively), with no significant (P>0.05) differences.

KeraSkin-VM: a novel reconstructed human epidermis model for skin irritation tests

Several alternative in vitro methods to evaluate skin irritants have been developed recently. In July 2010, OECD officially endorsed the validated reference method (VRM) that uses reconstituted human epidermis (RhE) models as replacements for the in vivo skin irritation test. This study evaluated the KeraSkin-VM model, a novel human epidermis model that was reconstructed with Asian skin tissue using 20 reference chemicals according to the OECD TG 439 performance standard. The test chemicals were applied to the epidermal surface side for 45 min and then rinsed, and then incubated for 42 h post-treatment. An overall accuracy of 80%, sensitivity of 90% and specificity of 70% were obtained when the results from KeraSkin-VM were compared with UN GHS categories, which was comparable to the EpiDerm Skin irritation test (SIT) rates. Furthermore, KeraSkin-VM demonstrated good performance in terms of within-laboratory reproducibility and predictive capacity to screen skin irritants.

Detergents with different chemical properties induce variable degree of cytotoxicity and mRNA expression of lipid-metabolizing enzymes and differentiation markers in cultured keratinocytes

The knowledge how detergents with different chemical properties influence epidermal keratinocytes is sparse. In the present study, the effects of five detergents were examined with respect to cell-toxicity and mRNA expression of key-enzymes in barrier lipid production and keratinocyte differentiation markers. First, the LD(50) for each detergent were determined. Secondly, keratinocytes were exposed to sub-toxic concentrations and the mRNA expression was analysed by real-time PCR after 24 h exposure to the detergents. SLS and CAPB induced a concentration-dependent increase in the expression of enzymes producing cholesterol and ceramides, while transcripts of enzymes producing fatty acids were unaffected. SLES and cocoglucoside increased the expression of certain enzymes involved in cholesterol and fatty acid synthesis while sodium cocoamphoacetate (SCAA) stimulated expression of transcripts involved in fatty acid synthesis. The expression of differentiation markers were increased by SLS, SLES and CAPB, while SCAA and cocoglucoside exhibited no effect. The present findings show that detergents have variable effects on lipid synthesis and keratinocyte differentiation, which could partly explain their barrier destruction potential in vivo.

Variations in the mRNA expression of inflammatory mediators, markers of differentiation and lipid-metabolizing enzymes caused by sodium lauryl sulphate in cultured human keratinocytes

Detergents are well known irritants. Effects of the detergent sodium lauryl sulphate (SLS) on cell toxicity using the XTT assay and mRNA expression of inflammatory mediators, markers of keratinocyte differentiation and enzymes synthesizing barrier lipids using real-time PCR were studied in cultured differentiated keratinocytes. After exposure for 24 h to SLS concentrations at 0.002% or above, toxic effects were observed. When a lower SLS concentration (0.00075%) was used the mRNA expression of inflammatory mediators peaked around 4-8 h. The expression of enzymes involved in the synthesis of cholesterol, fatty acids and ceramides and markers of keratinocyte differentiation also increased but after 24 h. In cells exposed to 0.000125-0.0015% SLS, a concentration-dependent induction of the expression of inflammatory mediators was found after 4 h. Similar changes were found after 24 h for involucrin and enzymes involved in ceramide synthesis. The mRNA expression of HMG-CoA synthase and reductase, long-chain acyl-CoA synthase and transglutaminase also peaked after 24 h, but maximal induction was observed already at 0.00075% SLS. In conclusion, SLS induces an inflammatory response in keratinocytes and alters the mRNA expression of important barrier lipid enzymes and markers of keratinocyte differentiation, of possible importance for the irritant properties of SLS.

Evaluation of eye and skin irritation of arginine-derivative surfactants using different in vitro endpoints as alternatives to the in vivo assays

Arginine-derivative surfactants constitute a novel class of surfactants, which can be regarded as an alternative to conventional surfactants. Prior to human exposure, it is necessary to assess their irritation potential. The classical in vivo evaluation of the irritancy potential via the Draize test has been extensively criticized. In that regard, a great number of in vitro alternatives have been developed. Erythrocytes were chosen as the target cells for eye irritation assessment and hemolysis and hemoglobin denaturation were selected as appropriate endpoints. For skin irritancy assessment, the keratinocyte cell line NCTC 2544 was used and different in vitro endpoints were measured: two cytotoxicity assays (NRU and MTT) and the synthesis of the proinflammatory cytokine IL-1alpha. The eye and skin Draize tests were also performed for comparative purposes. The results point out that, according to in vivo and in vitro assays, the new arginine-derivative surfactants have lower eye and skin irritation potential than the synthetic surfactant SDS. Furthermore, in vitro methods were also able to detect differences in irritancy among the new surfactants not noticeable by the Draize tests, indicating that in vitro methods can be more sensitive than the in vivo test, offering the opportunity to detect subtle differences in irritancy.

The benefits of the 3T3 NRU test in the safety assessment of cosmetics: long-term experience from pre-marketing testing in the Czech Republic

We have introduced the 3T3 NRU cytotoxicity test for methodological, economical and ethical reasons as a regular part of tier pre-marketing testing to assess local tolerance of raw materials for cosmetics, household chemicals and final cosmetic products. Using the 3T3 cell line according to the standard INVITTOX protocol No.64 (NRU Assay) the borderline concentration, relevant to the highest tolerated dose, is determined for each material. The toxic effect is reached at different concentration levels specific for individual cosmetics categories, depending on their chemical characteristics. Typical ranges of cytotoxicity for specific categories of cosmetics were established after testing of hundreds of materials. The range lies between 1 microg/ml (anti-dandruff shampoos), up to 2000 microg/ml (toothpastes and mouthwashes). The 3T3 NRU cytotoxicity test is a sensitive tool able to identify more aggressive products, that are also more likely to evoke irritation in human skin. It was even possible to detect protective effects of one natural herbal ingredient. The comparative study of cytotoxicity test results and human patch test results from a group of essential oils is presented. Cytotoxicity tests represent a highly ethical approach for estimation of irritancy. On the basis of in vitro test results suggesting low risk we can proceed to confirmatory tests in human volunteers.

Quantitative assessment of primary skin irritants in vitro in a cytotoxicity model: comparison with in vivo human irritation tests

BACKGROUND

While great efforts have been made in recent years to develop in vitro methods for assessing skin irritation potential, there are relatively few data that correlate in vitro data with in vivo data.

OBJECTIVES

To expand our previously reported investigations on in vitro vs. in vivo correlation of a series of homologous N-alkyl sulphates of different alkyl chain length to include primary skin irritants of different chemical classes.

METHODS

Anionic surfactants (three different sodium alkyl sulphonates and sodium lauryl sulphate), cationic surfactants (three alkyl trimethyl ammonium bromides), non-ionic surfactants (polyoxyethylene-20-cetyl ether and Tween 20), benzoic acid, dimethyl sulphoxide and phenol were chosen as model irritants. A spontaneously immortalized human keratinocyte line, HaCaT, was used as an in vitro model to predict the cutaneous irritation. The end-point used to assess toxicity was uptake of the vital dye neutral red (NR) 24 h after dosing. The cytotoxicity data from these assays were compared with the irritant responses (as evaluated by measurement of erythema and transepidermal water loss) obtained after 24-h application of the same compounds (100 microL of 20 mmol L(-1) aqueous solution) to the volar forearm of human volunteers.

RESULTS

All tested irritants had cytotoxic effects as demonstrated by a decreased NR uptake, which showed a clear dose-response relationship. Concentrations resulting in 50% inhibition of NR uptake (IC(50)) ranged from 8 micromol L(-1) (hexadecyl trimethyl ammonium bromide) to 328 mmol L(-1) (dimethyl sulphoxide). We found a good overall correlation between in vitro cytotoxicity (NR uptake IC(50) values) and in vivo irritation potential in humans. Only the high molecular weight compounds Tween 20 and polyoxyethylene-20-cethyl ether were problematic, as their irritation potential was overestimated by the in vitro assay. This non-conformity of these high molecular weight (> 1000) compounds was expected, and can be largely attributed to the epidermal permeability barrier. The epidermal barrier, which greatly limits the percutaneous penetration of xenobiotics in vivo, does not exist in cell culture models.

CONCLUSIONS

The in vitro cytotoxicity model is a useful screening tool, but data should be interpreted critically and require confirmation by appropriate in vivo studies.