The user safety assessment of a selenized yeast feed additive

Abstract

Purpose: Of the several selenized yeasts authorised for use as feed additives in the EU, Saccharomyces cerevisiae CNCM I-3060 inactivated’ (Sel-Plex^®), was the first to be approved for use, in 2006. The additive has a concentration of selenium between 2000 and 2400 mg/kg and a selenomethionine content greater than 63%. Previous toxicological and safety studies have shown Sel-Plex^® to be safe for use for target animal species, consumers, users and the environment. A new formulation of Sel-Plex^® was recently developed however, with a minimum selenium content of 3000 mg/kg. The increase in selenium in this product, Sel-Plex^® 3000, presented the need to assess the risk for workers and users and to establish if there would be any eye and/or skin irritancy and skin sensitisation effects associated with the product. The purpose of this paper is to present the methodology and results of the user safety skin and eye studies performed on Sel-Plex^® 3000.

Materials & Methods: In vitro skin and eye models were used to assess skin and eye irritancy, while skin sensitisation was examined using an in vivo method. The acute eye irritation was evaluated using a Reconstructed human Cornea-like Epithelium (RhCE) model, which followed the OECD guideline 492. The skin irritation was assessed based on its ability to induce cell death in a commercial reconstructed human epidermis (RhE) model (EPISKIN™) according to the OECD Guideline No. 439. The skin sensitising potential was evaluated in the Guinea pig in line with OECD Guideline 406, and measured the extent and degree of skin reaction to a challenge exposure following previous topical exposure of a substance on the skin.

Results: The skin and eye irritation test results showed that Sel-Plex^® 3000 was a non-irritant in both cases. The skin sensitisation study showed that the additive did not generate a sensitisation response in the guinea pig and should not be considered a skin sensitiser.

Conclusion: These results indicate that Sel-Plex^® 3000 is safe to use for workers in an industrial setting when handling the product and the studies may be further used to support regulatory compliance in respective markets.

Keywords:

• Feed additive
• organic selenium
• selenised yeast
• toxicology
• skin and eye irritation
• skin sensitisation

Introduction

Selenium is a micronutrient essential for human and animal health. It is associated with a range of biological functions, such as reproduction and fertility, antioxidant processes, the reduction of inflammation and DNA synthesis^1,2. In livestock, selenium deficiency can lead to conditions including muscular dystrophy, pneumonia, unthriftiness and reduced weight gain³. Inorganic and organic selenium compounds are commonly used in animal nutrition to supplement livestock diets⁴. Typically, organic selenium comes in the form of selenized yeast using a specific strain of Saccharomyces cerevisiae, with selenomethionine and selenocysteine as the main organic compounds present, along with an abundance of other low molecular weight selenocompounds⁵.

There are five selenized yeasts and seven other selenium-based compounds of trace elements approved as feed additives in animal nutrition in the EU. Among these is ‘Saccharomyces cerevisiae CNCM I-3060 inactivated’ (Sel-Plex^®), which was the first selenized yeast to be approved for use in the EU under Regulation (EU) 1750/2006 and renewed for a further ten years under Regulation (EU) 2019/804^6,7. The authorised additive is characterised as having a selenium concentration between 2000 and 2400 mg/kg and a selenomethionine content greater than 63%. As part of the safety evaluation of the additive, a comprehensive range of target animal, toxicological and user safety studies have been performed. EFSA concluded in their resulting assessment of the additive that Sel-Plex^® has very low acute oral toxicity and is unlikely to have any genotoxic potential⁸. Moreover, it is considered non irritant to the eyes and skin⁹. Selenised yeast may also be used in human nutrition as a source of selenium. EFSA has assessed selenium enriched yeast for nutritional use in foods the general population and concluded it was safe for human use¹⁰. Selenium-enriched yeast is authorised in the EU as a mineral substance which may be used in the manufacture of food supplements, and which may be added to food by Regulation (EC) No 1170/2009¹¹. In the USA, selenium yeast is allowed by the United States Food and Drug Administration (FDA) as a food additive permitted for use in feed via 21 CFR 573.920 (g). It is also listed as a feed ingredient in the Association of American Feed Control Officials (AAFCO) Official Publication. In Canada, selenium enriched yeast is listed in Schedule IV of the Canadian Feeds Regulations, 1983 (SOR/83–593).

Recently, a new formulation of ‘Saccharomyces cerevisiae CNCM I-3060 inactivated’ was developed with a minimum selenium content of 3000 mg/kg (Sel-Plex^® 3000, SP3000). When considering the safety implications of this increase in selenium content, it is pertinent to note that in previous EFSA safety evaluations of selenized yeasts where new formulations of authorised additives were introduced at the concentration level of 3000 mg selenium/kg, no adverse effects were be expected for the target animal, consumer and environmental safety or efficacy^12,13. This was mainly because supplementation of feed with selenized yeast cannot exceed the maximum limit of 0.2 mg of selenium per kg of complete feed with a moisture content of 12%. This means that irrespective of the selenium content of the additive, the maximum dosage rate of selenium in animals is the same. However, the increase in selenium in SP3000 did present the need to assess the risk for workers and users when handling the product to establish if there would be any eye and/or skin irritancy and skin sensitisation associated with the new formulation.

Existing selenized yeast feed additives with a selenium concentration of 3000 mg/kg in the marketplace have comparably different safety profiles in terms of user safety. One additive was deemed to be a non-irritant for the skin but an irritant for the eyes and mucosae and a dermal sensitiser^12,14, while another additive was considered a non-irritant to skin and eyes and, due to an absence in data, no conclusion was reached on its dermal sensitising capacity^13,15. As noted in the work of Bierla et al.¹⁶, Fagan et al.² and Ward et al. ⁵, the deposition of selenium into yeast and the components obtained during production is dependent on the specific strain used in the manufacturing process. It is not surprising that differences may exist between selenized yeasts resulting in characteristic differences in safety and efficacy profiles^5,17. Previous user safety studies of Sel-Plex 2000 demonstrated that the product was non-irritant to skin and eyes whilst, hitherto, no skin sensitisation studies had been conducted⁹. This paper aims to present the methodology and outcomes of the user safety skin and eye studies on SP3000. In line with Directive 2010/63/EU on the protection of animals used for scientific purposes, in vitro systems were used where available.

Materials and methods

Test substance

The test substance was 100% selenised yeast, Saccharomyces cerevisiae CNCM I-3060, inactivated (Sel-Plex^® 3000) provided by Alltech Inc. (Nicholasville, KY, USA).

Ethics and good laboratory practice

All studies were performed in accordance with European Directive 2004/10/EC¹⁸ on the harmonisation of laws, regulations and administrative provisions relating to the application of the principles of good laboratory practice and the verification of their applications for tests on chemical substances, and with the OECD Principles of GLP¹⁹. Relevant studies were compliant with the requirements of the EU Directive 2010/63/EU on the protection of animals used for scientific purposes²⁰.

Acute eye irritation study

The acute eye hazard potential of SP3000 was evaluated in vitro using a Reconstructed human Cornea-like Epithelium (RhCE) model (EpiOcular^TM Eye Irritation Test sourced from MatTek In Vitro Life Science Laboratories, Bratislava, Slovakia) and followed the OECD guideline 492. The test predicts the hazard potential of chemicals by measuring tissue damage in the model and can be used as an alternative to the in vivo Draize Eye Irritation Test. The tissue used in the model consisted of normal human-derived keratinocytes, which had been cultured to form a stratified squamous epithelium, similar to that found in the human cornea. Tissues were prepared in cell culture inserts with a porous membrane that allows nutrients to pass through to cells. The tissue surface was 0.6 cm². The eye hazard potential of a given test substance can be evaluated by its ability to produce a decrease in cell viability. The cell viability was measured by dehydrogenase conversion of MTT (3–(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazoliumbromide) normally present in cell mitochondria, into a blue formazan salt, which was quantitatively measured after extraction from tissues. Compared to untreated negative controls, the percentage reduction of cell viability was used to predict the eye irritation potential.

SP3000 was first tested to assess its ability to reduce MTT directly. For this test, 50.8 mg of SP3000 was added to 1 ml of MTT solution in a 6-well plate, and the mixture was incubated in darkness at 37 °C with 5% CO₂ and 95% relative humidity (RH) for three hours (h). The MMT solution was prepared by dissolving MMT (MatTek In Vitro Life Science Laboratories, Bratislava, Slovakia) in Dulbecco’s Phosphate Buffered Saline (DPBS) (MatTek In Vitro Life Science Laboratories, Bratislava, Slovakia) to yield a solution of 1 mg/ml. A negative control was prepared by adding 1 ml of MTT to 50 μl of demineralised water. It was also necessary to perform a functional test with freeze-killed tissues that possess no metabolic activity to check if SP3000 could cause any non-specific colouring. Freeze-killed tissues were prepared by placing untreated tissues in the freezer (-20 ± 5 °C) overnight. The functional check employed two freeze-killed tissues treated with the MTT reducing test item and one untreated killed tissue as a negative control to show non-specific MMT reduction.

In the primary assay, viable tissues were transferred to three 6-well-plates containing 1 ml of assay medium (serum-free Dulbecco’s Modified Eagle’s Medium - MatTek In Vitro Life Science Laboratories, Bratislava, Slovakia). They were incubated at 37 °C, 5% CO₂ and 95% RH for 1 h. . After the pre-incubation, the medium was replaced, and the wells were filled with 1 ml fresh assay medium. All 6-well-plates were incubated at 37 °C and 5% CO₂ and 95% RH for 16 h and 30 min.

After incubation, 20 μL DPBS was added to the tissues and were further incubated at 37 °C, 5% CO₂ and 95% RH for 30 min. Positive (Methyl acetate - MatTek In Vitro Life Science Laboratories, Bratislava, Slovakia) and negative controls (Sterile demineralised water - LAUS GmbH, Kirrweiler, Germany) and the SP3000 test substance (50 μl of each) were applied in duplicate in one-minute-intervals. All plates were transferred into the incubator for 6 h at 37 °C, 5% CO₂ and 95% RH. At the end of exposure time, the inserts were removed from the plates using sterile forceps and rinsed immediately with DPBS. Tissues were directly transferred into 5 ml of assay medium in pre-labelled 6-well plates for 25 min at room temperature. Each insert was subsequently blotted on absorbent material and transferred into a pre-labelled 6-well plate containing 1 ml assay medium. For post-treatment incubation, the tissues were incubated for 18 h at 37 °C, 5% CO2, and 95% RH. After the post-treatment incubation, the MTT assay was performed.

A 24-well-plate was prepared with 300 μl freshly prepared MTT solution in each well. The tissue inserts were blotted on absorbent material and then transferred into the MTT solution. The plate was incubated for 180 min at 37 °C and 5% CO₂ and 95% RH. Finally, each insert was thoroughly dried and set into a pre-labelled 6-well-plate containing 1 ml isopropanol. The plate was firmly sealed to avoid evaporation of the solvent and then shaken for 2 h at room temperature, protected from light. An additional volume of 1 ml of isopropanol was pipetted into each well, and the contents of each well were thoroughly mixed to achieve homogenisation. From each well, two replicates with 200 μl solution (each) were pipetted into a 96-well-plate. The plate was read in a plate spectrophotometer at 570 nm. In addition, eight wells of the 96-well-plate were filled with 200 μl isopropanol each, which served as a blank.

Acute skin irritation study

The skin irritancy of SP3000 was measured by assessing its ability to induce cell death in a commercial reconstructed human epidermis (RhE) model (EPISKIN™) (SkinEthic Laboratories, Lyon, France) according to the OECD Guideline No. 439. The cells in the model are sourced from human-derived epidermis keratinocytes and closely mimic the biochemical and physiological properties of the upper parts of the human skin. The principle of the RhE test method is based on the premise that chemicals can penetrate the stratum corneum, and irritant chemicals are cytotoxic to the cells in the underlying layers. Cell viability is measured by dehydrogenase conversion MTT to a blue formazan salt, quantitatively measured after tissue extraction. Irritant chemicals are identified by their ability to decrease cell viability below defined threshold levels.

Before the primary skin irritancy assay, a preliminary test was carried out to evaluate the compatibility of the test item with the test system. Firstly, SP3000 was assayed to assess its ability to reduce MTT in the absence of living cells. A 2 ml solution of MTT (containing 0.3 mg MMT/ml) was incubated with 20 mg of SP3000 at 37 °C and 5% CO₂ in saturated humidity for 3 h . The solution was observed for the appearance of a blue or purple colour at the end of the incubation time. Secondly, the colouring potential of SP3000 was assessed whereby 20 ± 2 mg of SP3000 was added to 180 μL of distilled water (Baxter, Co. Mayo, Ireland) in a transparent tube and mixed by using a vortex mixer for 15 min. The colouring of the solution/suspension at the end of the incubation time was evaluated.

As some colouring was observed in the solutions prepared in the preliminary test, additional tests were carried out to verify if the test item results had to be corrected. The non-specific colour (NSC living) was evaluated using two alive treated tissues without MTT staining and compared with a DPBS negative control. Additionally, non-specific MTT reduction (NSMTT) was assessed using two killed tissues and compared with the negative control. A third control for non-specific colour in killed tissue (NSC killed) was performed to avoid a possible double correction for colour interference. The full range of samples prepared for the experiment is given in Table 1.

Table 1. Acute skin irritation study: Test samples prepared and analysed.

Sample Name	Test System	Treatment	Amount per Well	Number of Replicates
Negative control	Live tissue	DPBS	20 µL	3
Positive control	Live tissue	5% (w/v) SDS	20 µL	3
Test item	Live tissue	SP3000	20 ± 2 mg	3
Test item without MTT (NSC living)	Live tissue	SP3000	20 ± 2 mg	2
Test item (NSMMT)	Killed tissue	SP3000	20 ± 2 mg	2
Negative control	Killed tissue	DPBS	20 µL	2
Test item without MTT (NSC killed)	Killed tissue	SP3000	20 ± 2 mg	2

In the primary assay, SP3000 was applied as supplied in three replicates at the treatment level of 20 ± 2 mg/epidermis unit, each measuring 0.38cm² (treatment level: 53 mg/cm²). A positive control of 5% (w/v) sodium dodecyl sulphate (Merck S.r.l., Milan, Italy) solution in water and a negative control of DPBS were tested concurrently at the treatment level of 20 μL/epidermis unit.

At the end of the exposure, each tissue was rinsed with approximately 25 ml of DPBS. The excess liquid was carefully removed, and the sample was transferred to new wells containing 2 ml per well of maintenance medium. Samples were incubated at 37 °C and 5% CO₂ for 42 h at saturated humidity. Each tissue insert was incubated with 2 ml/well of MTT solution. Plates were incubated for approximately 3 h at standard conditions. At the end of the incubation period, tissues were placed on absorbent paper to dry. A total biopsy was carried out using a biopsy punch. The epidermis was separated from the collagen matrix, and both were put in a microtube prefilled with 500 μl of acidic isopropanol. Tubes were preserved for approximately 3 days at 4 °C to allow formazan extraction. At the end of the extraction period, debris was eliminated by centrifugation of the tubes (14000 rpm for 2 min) and 200 μl aliquots of each sample were read in duplicate for their absorbance at 595 nm. Optical Density (OD) values were recorded.

Skin sensitivity

Animals

For the skin sensitisation study, 4 to 5-week-old female (nulliparous and non-pregnant) Dunkin Hartley guinea pigs were used (Charles River Italia S.p.A, Calco, Italy). Five animals were used in a preliminary study, and 30 animals were used in the main study. In all experiments, animals were acclimatised for a minimum of five days in the area where the experiment took place. The observation was performed at the time of delivery of the animals and daily during the acclimatisation period. Five animals were housed per cage in cages of standard size. These cages were placed in an air-conditioned (22 °C ± 2 °C) animal house and kept at 55% ± 15% relative humidity. Artificial day/night cycle involved 12 h light and 12 h darkness, and feed and drinking water were available ad libitum.

The study aimed to evaluate any possible skin sensitising potential of SP3000 in the Guinea pig in line with OECD Guideline 406. The experimental design is based on measuring the extent and degree of skin reaction to a challenge exposure following previous topical exposure of a substance on intact and unabraded skin in the absence of any adjuvant.

Preliminary study

The test item concentrations used in the main study were determined by conducting a preliminary screening test. Five animals had their flanks clipped free of hair, and each animal was dosed with two preparations of the test item, with one on each flank. A gauze patch measuring at least 20 × 20 mm was soaked with 0.4 ml of the selected concentration of the test item and was placed onto the selected treatment site. A strip of synthetic film was placed over the treated sites, and the whole assembly was secured in position by encircling the trunk with a length of adhesive strapping. All animals were treated in this manner such that a total of five concentrations (50%, 20%, 10%, 5% and 1% in corn oil) of the test item were dosed each in duplicate. The adhesive strapping and patches were removed after approximately 6 h in contact with the skin. The treated sites were washed with lukewarm water to remove any remaining test item and were examined after 24 to 48 h for signs of reaction to the respective treatments.

Main study

No reactions were noted in the animals treated at any concentration of the test item tested. Consequently, the highest concentration of 50% was selected for the induction and challenge phases of the main study. On the first day of the main study, animals were divided into a treatment group of 20 animals and a control group of 10 animals. Each animal was weighed, and the hair was clipped from the anterior region of the left flank using an electric clipper and a razor. Animals of the test group were treated with the test item at a concentration of 50% in the vehicle (corn oil) following the same dosing method as performed in the preliminary study. Animals of the control group were similarly treated with the vehicle alone (negative control item, corn oil). After an exposure period of 6 h, the dressings and patches were removed. The treated sites were cleaned of the remaining test item or vehicle by washing with lukewarm water. Approximately 24 and 48 h after removing the dressings and patches, the treated sites were examined for signs of reaction to treatment. Each site was assessed and scored using the following scale: no visible change 0; discrete or patchy erythema 1; moderate and confluent erythema 2; intense erythema and swelling 3. The process was repeated at weekly intervals for a total of 3 weeks. Two weeks after the third and final induction exposure, animals of the test and control groups were challenged by topical application of the test item at 50% concentration and the vehicle alone (corn oil). On Day 29, the hair was removed with an electric clipper and a razor from both the anterior and posterior regions of the right flank of all animals of both test and control groups. A 0.4 ml aliquot of the test item at 50% concentration was spread evenly over an absorbent patch measuring approximately 20 × 20 mm. This was placed onto the skin of the posterior region of the prepared site on the right flank. A similar patch containing 0.4 ml of the vehicle alone (negative control item, corn oil), was placed onto the anterior region of the prepared site. A strip of synthetic film was placed over the treated sites, and the whole assembly was secured in position by encircling the trunk of the animal with a length of adhesive strapping. All animals of the test and control groups were treated with both the test item and vehicle in this manner. After an exposure period of approximately 6 h, the dressings were removed, and the treated sites were cleaned of the remaining test item by washing with lukewarm water. Approximately 21 h after removing the dressing and patches, the treated sites were closely clipped to remove any hair that may have grown. Approximately 3 h later, 24 h after removing the dressing and patches, the treated sites were examined for any signs of reaction to treatment.

Results

Acute eye irritation study

In the pre-test, the test item showed MTT-reducing properties. The influence of any photometric measurement, as well as a false negative result, had to be excluded. Therefore, an additional test was performed using freeze-killed tissues that possess no metabolic activity but absorb and bind the test item like viable tissues. The results from the primary test for optical density and % viability results of the negative control, positive control and SP3000 are provided in Table 2. The viability of cells after treatment with SP3000 was 86.9%. This was slightly reduced to 86.7% when corrected with the additional test result on freeze-killed tissues. This value is above the threshold for eye irritation potential (≤60%), and therefore the MTT reduction by the test item itself did not influence the result of the study. The optical density of the negative control was 1.618, which fulfilled the validity criterion for the optical density of the negative control (>0.8 and <2.8). The positive control induced a decrease in tissue viability compared to the negative control to 26.4%. The variation within the replicates of the controls and the test item was acceptable (<20%). All validity criteria were met, and therefore the test was considered valid. Under the test conditions, SP3000 is deemed to be non-eye irritant in the Epi-OcularTM Eye Irritation Test.

Table 2. The optical density and viability results of the acute eye irritation study.

Test Item (n = 4)	Optical Density	Corrected Optical Density	Viability (%)
Blank Control	0.034
Negative Control (DPBS)	1.652	1.618	100
Positive Control (5% (w/v) SDS)	0.462	0.428	26.4
SP3000	1.441	1.407	86.9

Viability (%) = COD/COD Negative Control (alive tissues)*100.

Acute skin irritation study

Before calculating the viability of the test substance SP3000, the mean optical densities of the blank control, negative control and positive control were all established. The mean optical density of the blank control was determined to be 0.037. This was lower than the maximum acceptable value of 0.1. The negative control is taken to be the baseline in terms of optical density values and thus represents 100% of cell viability. Positive control results indicated an appropriate cell death with acceptable relative cell viability (3% of the negative control value). Variability between replicates also gave acceptable results. The acceptance criterion for mean viability was set as lower or equal to 40% with a standard deviation equal to or lower than 18. As the results obtained met the acceptance criteria, the study was accepted as valid.

The NSMTT and NSC living values were lower than 5%, and therefore, only the OD-blank background subtraction was performed. The additional tests carried out to check whether the test item results had to be corrected are provided as supplementary information (Table S1).

The test item did not induce cell death in any replicate, and the mean cell viability after the blank subtraction was 98% compared to the negative control. Acceptable intra-replicate variability was obtained. The optical density and viability results of blank control, negative control, positive control and SP3000 are provided in Table 3. Based on the results obtained, the test item SP3000 was classified as non-irritant to the skin.

Table 3. The optical density and viability results of the acute eye irritation study.

Test Item (n = 3)	Optical Density	Corrected Optical Density	Viability (%)
Blank Control	0.037	–	–
Negative Control (DPBS)	0.621	0.585	100
Positive Control (5% (w/v) SDS)	0.053	0.016	3
SP3000	0.612	0.575	98

Viability (%) = COD/COD Negative Control (alive tissues)*100.

Skin sensitivity

No reactions were noted in the animals treated at any test item concentration investigated in the preliminary tolerance study. Consequently, the highest concentration of 50% was selected for the induction and challenge phases of the main study. In the induction phase, no response was seen to either the test item at 50% concentration or the negative control item (corn oil) in animals of the test and control groups following 6-h topical exposure. The results of the induction phase are included in the supplementary information tables (Table S2). The test item at 50% was further used at the challenge phase, as no irritation was noted during the induction phase. No response was observed to the test item at this selected concentration, in either test or control group animals 24 and 48 h following a 6h topical exposure (See Table S3 in supplementary information). No reaction was observed to the negative control item. The validity of the test system has been verified with the periodic testing of the positive control. A sensitisation reaction was observed in 60% of animals in the reliability check with the positive control (2-Mercaptobenzothiazole 97%). This result was in excess of the 15% positivity threshold, and therefore the test system was considered valid. The results of the induction and challenge studies indicate that the test item, SP3000, does not elicit a sensitisation response in the guinea pig, as there was no evidence of a reaction at the challenge phase following a period of induction exposure to the test item.

Discussion

The objective of the prescribed studies was to determine the skin and eye safety for workers and users of SP3000. In-vitro models were used to assess skin and eye irritation, and SP3000 was found to be a non-irritant in both studies. These results are consistent with previous in vivo studies on Sel-Plex 2000^®, which were evaluated in rabbits under OECD Guidelines 404 and 405 and considered non-irritant to skin and eyes⁹. The results from the skin and eye irritation studies are in line with those on related products and substances. The selenized yeast Saccharomyces cerevisiae CNCM I-3399 has also been found to be non-irritant to eyes and skin¹⁵. Similarly, the feed additive, DL-selenomethionine consisting of 40% selenium (DL-SeMet), did not induce ocular changes or induce skin lesions and was found to be not an irritant to skin and eyes²¹. Each of the studies referenced above used the in-vivo OECD models 404 and 405 for eye and skin respectively. In-vitro assessment methods were used to determine skin and eye irritation on the inorganic compound sodium selenate²². The additive was found to be a skin irritant but non-corrosive and, in the absence of documented evidence, was considered an irritant in the eye. As noted previously, the deposition of selenium into yeast is dependent on the specific yeast strain used in the manufacturing process^2,5,16. Speciation analysis has demonstrated significant differences in the patterns of selenocompounds obtained in alternative selenized yeast feed additives. As such, it cannot be assumed that all selenized yeast compounds possess similar safety profiles⁵. Differences in user safety data has been observed between selenized yeast products and related substances. Saccharomyces cerevisiae NCYC R397 is non-irritant for the skin but considered an irritant for the eyes and mucosae¹⁴. Similarly, the feed additive hydroxy-analogue of selenomethionine, consisting of synthetic R, S-2-hydroxy-4-methylselenobutanoic acid (HMSeBA), was found to be a non-irritant for skin but an irritant to the eye²³.

The result of the skin sensitisation study on SP3000 showed that the additive did not elicit a sensitisation response in the guinea pig and should therefore not be considered a skin sensitiser. The result was in line with the skin sensitisation study conducted on DL-SeMet, which showed no allergic reaction in guinea pigs following the OECD 406 method and was therefore not a dermal sensitiser²¹. Similarly, HMSeBA did not show any sensitisation potential in a mouse local lymph node assay (OECD 429) was not considered a dermal sensitiser²³. In contrast, Saccharomyces cerevisiae NCYC R397 was a dermal sensitiser under the subcategory 1B (‘may cause an allergic skin reaction’) following skin sensitisation analysis carried out according to the OECD guideline 429¹⁴.

In conclusion, SP3000 is non-irritant in the eye and skin and does not possess any skin sensitisation potential. This demonstrates that SP3000 is safe to use in an industrial setting for workers handling the product. The results of the tests described herein may be further used to support regulatory compliance in prospective markets.

Acknowledgements

The authors thank C. Longobardi and L. Bisini (Study Directors) and scientists, R. Zanier, F. Zeno, G.A. Marzoli, A. Parenti, V. Pentella, F.R. Calfapietra, R. Ricci and S. Cinelli of the European Research Biology Center S.r.l. (Pomezia, Italy) for conducting the skin irritation and sensitization studies and to A. Himmelsbach (Study Director), Isabelle Kiefer and Kareen Brady of Laus GmbH (Kirrweiler, Germany) for performing the eye irritation study.

Disclosure statement

The authors Gerald P. Dillon and Colm A. Moran are employees of Alltech^® which produces and markets Sel-Plex^® the commercial selenized yeast feed additive evaluated in this study.

Correction Statement

This article has been corrected with minor changes. These changes do not impact the academic content of the article.

Additional information

Funding

This work was sponsored by Alltech SARL (France).