-
Cd chloride (CdCl2) was purchased from Serva (Serva, Feinbiochemica, Heidelberg, Germany); 3-(4,5-dimethyl-thiazol-2-yl)-2,5 diphenyl-tetrazolium bromide (MTT) was purchased from SigmaAldrich (St. Louis, MO, USA); 1-chloro-2,4 dinitrochlorobenzene (DNCB) was obtained from BDH Chemicals Ltd.; 2,4-dinitrobenzenesulfonic acid (DNBS) was purchased from Aldrich Chemical Company (Milwaukee, WI, USA); and N,N,N,N-ethylenediaminetetraacetic acid (EDTA) disodium salt dihydrate was obtained from USB Corporation (Cleveland, OH, USA). Sucrose was obtained from Lachner (Neratovice, Czech Republic). Dispase II was obtained from Boehringer (Manheim, Germany), and collagenase IV and DNase I were obtained from Sigma (Sigma Chemical Co, St. Louis, MO, USA). RPMI-1640 culture medium (Biowest, Nuaillé, France) supplemented with 2 mmol/L glutamine, 20 μg/mL gentamicine (Galenika a.d., Zemun, Serbia) and 5% (v/v) heat-inactivated fetal calf serum (Biowest, Nuaillé, France) were used. Phosphate buffered saline, pH 7.4, contained NaCl (137 mmol/L), KCl (2.7 mmol/L), Na2HPO4x2H2O (8.1 mmol/L) and KH2PO4 (1.76 mmol/L; purchased from LachNer, Neratovice, Czech). For use in experiments, Dispase II was dissolved in RPMI-1640 medium. All solutions for cell culture experiments were prepared under sterile conditions and were sterile filtered (Minisart, pore size 0.20 µm, Sartorius Stedim Biotech, Goettingen, Germany) before use. Commercially available enzyme-linked immunosorbent assay (ELISA) kits for rat IFN-γ and IL-10 were purchased from R&D (Minneapolis, USA), whereas kits for mouse IL-17 (cross-reactive with rat IL-17) and rat TNF were obtained from eBioscience (San Diego, CA, USA). Mouse anti-rat anti-CD4 and anti-CD8 antibodies for flow cytometry analysis were purchased from eBioscience (San Diego, CA, USA).
-
Animal treatments and experimental procedures were performed in compliance with Directive 2010/63/EU on the protection of animals used for experimental and other scientific purposes, and were approved by the Ethical Committee of the Institute for Biological Research “Sinisa Stankovic” (IBISS), University of Belgrade, Serbia. Male DA and AO rats (ethical clearance number 01-05/18) 8–10 weeks of age, used in experiments, were conventionally housed at IBISS under a controlled environment (21–24 °C temperature, a 60% relative humidity and 12 h light/dark cycle). Four animals were assigned to each treatment group per experiment, and at least two independent experiments were performed. Both strains of rats were exposed to 5 ppm (5 mg/L) of Cd (II) ion prepared in distilled water over a period of 30 days, whereas control rats were given only distilled water. In experiments examining both the sensitization phase and the challenge phase, we also had an AO group of rats exposed to a higher dose of Cd (50 ppm), in addition to a group exposed to a lower dose (5 ppm), because higher doses induce more pronounced dermatotoxicity in this strain, as previously demonstrated[29]. Doses used in this study are relevant to human exposure: 5 ppm is considered to correspond to the environmental pollution exposure of women in Japan with itai itai disease[39], and 50 ppm is equivalent to the concentration of Cd in highly polluted areas or environments in which humans are professionally exposed to this metal[40]. Twice per week, the Cd solution and water were replaced with freshly prepared solution/water. All rats were given ad libitum access to standard rodent pellets and water/Cd solution throughout the study.
-
After Cd or water treatment (at day 30) CHS reaction was performed by application of a low DNCB dose sensitization/challenge regime, as described previously[41]. Animals whose fur was previously clipped were sensitized by application of 100 μL of 0.4% DNCB dissolved in a solution containing acetone and olive oil, to the upper part of the dorsum (approximately 16 cm2) for 2 consecutive days. Five days after sensitization, the animals were challenged by application of 50 μL of 0.13% DNCB (also dissolved in a solution of acetone and olive oil) to the ventral and dorsal surfaces of the right ear. The left ear was treated with vehicle (acetone and olive oil solution). All functional measurements were performed 24 h and 72 h after the second DNCB application on dorsal skin (for the sensitization phase) or 24 h after DNCB application on right ears (for the challenge phase; Figure 1). Experimental groups are explained in Table 1. Animals were anesthetized by i.p. injection of 40 mg/kg bw of thiopental sodium (Rotexmedica, Tritau, Germany).
Figure 1. Experimental flow chart. DLN, draining lymph nodes; CHS, contact hypersensitivity reaction.
Parameters DA rats AO rats Cd (0 ppm) Cd (5 ppm) Cd (0 ppm) Cd (5 ppm) Cell number (× 106) 1.23 ± 0.11 1.83 ± 0.05* 1.46 ± 0.08 1.68 ± 0.07 CD8+ cell number, % 1.56 ± 0.04 2.11 ± 0.11*** 1.37 ± 0.16 1.43 ± 0.08 CD8+ cell number (× 104) 1.92 ± 0.05 3.86 ± 0.19** 2.00 ± 0.22 2.53 ± 0.13 CD4+ cell number, % 3.11 ± 0.04 5.67 ± 0.14*** 1.26 ± 0.01 2.04 ± 0.14** CD4+ cell number (× 104) 3.83 ± 0.04 10.36 ± 0.24** 1.87 ± 0.01 3.43 ± 0.23* Note. Results are presented as mean ± SEM. Significance at: *P < 0.05, **P < 0.01, and ***P < 0.001 vs. control (Cd 0 ppm) (Mann-Whitney U test corrected with the Bonferroni adjustment). Table 1. Experimental animal groups
-
Ear swelling (an in vivo measure of contact hypersensitivity response) was assessed in a blinded fashion by measurement of the pinnal thickness before and 24 h after ear challenge, with a hand-held engineer’s micrometer (six measurements per ear). An increase in ear swelling, defined as a difference in ear thickness 24 h after vs. before the challenge, is expressed as a relative value compared with the respective control (i.e., Cd nonexposed animals), which was normalized to 1.
-
Ear skin samples were collected 24 h after challenge, fixed in 4% buffered formalin (pH 6.9), treated with an ethanol series (concentration 30%–100%), then washed in xylene and embedded in paraffin. Five micrometer thick tissue sections were mounted on glass slides and stained with hematoxylin and eosin. Pathohistological analysis was performed by a certified specialist using a Coolscope digital light microscope (Nikon, Tokyo, Japan).
-
Suprascapular and axillary lymph nodes (that drain sensitized skin) were harvested 24 h and 72 h after sensitization. Cell suspensions were prepared by mechanical teasing of DLNs over nylon mesh (70 μm nylon, BD Bioscience, Bedford, USA). After washing and resuspension in medium, cells were counted with an improved Neubauer hemocytometer. The number of viable cells, determined with a trypan blue exclusion assay, always exceeded 95%. DLN cell viability was measured with MTT reduction assays[42]. Cells (0.1 × 106) were incubated with 500 µg/mL of MTT (added immediately in culture) in a 96-well plate, for 3 h at 37 °C under a humidified atmosphere of 5% CO2. Formed formazan was dissolved by overnight incubation with 10% sodium dodecyl sulfate and 0.01 N HCl, and the absorbance of extracted chromogen was read spectrophotometrically at 540 nm (with correction at 670 nm).
DLN cells (1.2 × 106/well) were cultured in 96-well plates (Sarstedt Inc., Newton, NC, USA) for 48 h (at 37 °C under a humidified 5% CO2 atmosphere) in the presence of 10 μg/mL of DNBS (hapten-specific production). Cytokine production was determined in medium conditioned by DLN cells with commercially available ELISA kits. Cytokine titers were calculated through reference to a standard curve constructed with known amounts of kit-provided recombinant cytokines.
-
A mixed population of epidermal and dermal cells from right ears (treated with DNCB) was isolated for analysis of the skin response to the challenge, as described in other studies[43]. Ears were split into dorsal and ventral halves with forceps and digested with Dispase II (2.5 mg/mL) for 90 min at 37 °C, to separate the epidermis and dermis. The separated epidermal and dermal sheets were cut into small pieces and digested with collagenase type IV (1 mg/mL) and DNase I (1 mg/mL) for 45 min at 37 °C to release cells. To obtain single-cell suspensions, we filtered the tissues through a nylon mesh (70 μm nylon, BD Bioscience, Bedford, USA), then washed and resuspended the cells in medium. Cells were counted with an improved Neubauer hemocytometer, whereas metabolic viability was measured with MTT reduction assays, as previously described.
Ear cells (0.1 × 106/well) were cultured for 48 h (at 37 °C in a humidified atmosphere of 5% CO2) in 96-well plates (Sarstedt Inc., Newton, NC, USA) in medium alone (spontaneous production for TNF) or in medium with 10 μg/mL of DNBS (hapten-specific production for IFN-γ and IL-17). Cytokine production was determined with commercially available ELISA kits in medium conditioned by ear cells. Cytokine titers were calculated by reference to a standard curve constructed with known amounts of kit-provided recombinant cytokines.
-
The isolated right (treated with DNCB) ear cells (1 × 106) were incubated on ice with mouse anti-rat anti-CD4 (fluorescein isothiocyanate conjugated) and anti-CD8 (phycoerythrin conjugated) antibodies, for 30 minutes. After washing with phosphate buffered saline, the cells were fixed with 1% paraformaldehyde and assayed for fluorescence intensity on a CyFlow Space flow cytometer (Partec, Munster, Germany).
-
Results are expressed as means ± standard error. Statistical analysis was performed in STATISTICA 7.0 (StatSoft Inc., Tulsa, OK), and statistical significance between groups was defined by a Mann-Whitney U test with Bonferroni correction for multiple comparisons. Corrected P-values less than 0.05 were considered significant.
-
To determine whether oral Cd consumption might affect the CHS reaction to DNCB, we first analyzed the ear swelling response after challenge (Figure 1). Greater ear swelling was observed in Cd-exposed DA rats than Cd-nonexposed (treated only with DNCB) controls, and no changes were observed in AO rats (Figure 2). No differences were seen in the thickness of ears treated with vehicle (olive oil and acetone) between rats receiving only water or water with Cd (1.00 ± 0.06 and 0.88 ± 0.11 in Cd-nonexposed and Cd-exposed DA rats, and 1.00 ± 0.11 and 0.93 ± 0.04 in Cd-nonexposed and Cd-exposed AO rats, respectively). Histological examination of the challenged ears in DA rats showed edema and dilatation of subcutaneous vascular spaces with congestion (Figure 3A–B), which were more pronounced in Cd-exposed animals (compared with controls), in which infiltration of inflammatory cells was detected (Figure 3B). In sensitized AO rats, after challenge, edema was present, but differences were not observed between Cd-nonexposed (Figure 3C) and Cd-exposed animals (Figure 3D). Cutaneous ear skin response to the challenge was much more pronounced in Cd-exposed DA than Cd-exposed AO rats.
Figure 2. Effects of oral Cd on the ear swelling response during the challenge phase of the CHS reaction in DA (n = 12) and AO (n = 8) rats. Ear swelling was defined as a difference in ear thickness 24 hours after the challenge vs. before the challenge. Results are presented as mean ± SEM. **P < 0.01 vs. control (Cd 0 ppm; Mann-Whitney U test with Bonferroni correction).
Figure 3. Histological analysis of challenged ears (n = 8). Collagen homogenization (edema; arrows) in (A) control (Cd-nonexposed) rats and (B) Cd-exposed DA rats. (B) Pronounced subcutaneous vascular congestion (asterisk), intravascular aggregation of neutrophils (inset, left) and perivascular infiltration of mononuclear cells (inset, right) in Cd-exposed DA rats. Edema (arrow) in (C) control and (D) Cd-exposed AO rats (original magnification × 200).
-
Total number of ear cells obtained from DA rats, including the absolute and relative number of both CD4+ and CD8+ cells, were greater compare to the cell number obtained from control animals (Table 2). In contrast, no change was observed between control and Cd-exposed AO rats, in either the total number of ear skin cells or CD8+ cell number. However, an increase in number (absolute and relative) of CD4+ cells was observed in Cd-exposed AO rats compared to control animals. The viability of ear skin-derived cells was unchanged between Cd-exposed and Cd-nonexposed animals in either strain (0.190 ± 0.007 and 0.170 ± 0.006 in control and Cd-exposed DA rats, and 0.210 ± 0.007 and 0.230 ± 0.01 in control and Cd-exposed AO rats, respectively).
Phase DA rats AO rats Challenge
(24 h post challenge)0.4%/0.13%
DNCB (control)0.4%/0.13%
DNCB + 5 ppm Cd0.4%/0.13%
DNCB (control)0.4/%/0.13%
DNCB + 5 ppm Cd0.4/%/0.13%
DNCB + 50 ppm Cdn = 12 n = 12 n = 8 n = 8 n = 8 Sensitization
(24 h and 72 h post
sensitization)0.4%
DNCB (control)0.4%
DNCB + 5 ppm Cd0.4%
DNCB (control)0.4%
DNCB + 5 ppm Cd0.4%
DNCB + 50 ppm Cdn = 10/term n = 10/term n = 8/term n = 8/term n = 8/term Table 2. Oral Cd effect on ear CD4+ and CD8+ cells number following challenge of CHS
Since ear skin inflammation in CHS includes a pro-inflammatory cytokine response, we determined the level of TNF, IFN-γ and IL-17 in ear cell culture, the most relevant cytokines for CHS reaction (Figure 4). Significantly higher production of these cytokines was found in Cd-exposed DA rats than controls, whereas no differences were seen in AO rats (Figure 4A–C).
Figure 4. Effects of oral Cd on pro-inflammatory cytokine production by ear skin cells during the challenge phase of CHS. (A) TNF, (B) IFN-γ and (C) IL-17 production in DA (n = 8) and AO rats (n = 6). Results are presented as mean ± SEM. **P < 0.01 vs. control (Cd 0 ppm; Mann-Whitney U test with Bonferroni correction).
-
Development of a CHS reaction is determined by the sensitization phase, and the generation of effector cytokine (IFN-γ and IL-17)-producing cells occurs in skin DLNs. Thus, we next explored the effect of oral Cd intake on DLN cell activity during the sensitization phase (Figure 5). No differences were observed in the viability of DLN cells between Cd-exposed animals and Cd-nonexposed animals, at either time point after sensitization (0.15 ± 0.02 and 0.13 ± 0.01 in control and Cd-exposed DA rats, and 0.13 ± 0.03 and 0.15 ± 0.02 in control and Cd-exposed AO rats, respectively, at day 1 post sensitization; 0.62 ± 0.03 and 0.59 ± 0.03 in control and Cd-exposed DA rats, and 0.63 ± 0.05 and 0.65 ± 0.03 in control and Cd-exposed AO rats, respectively, at day 3 post sensitization).
Figure 5. Effects of oral Cd on DLN cell activity during the sensitization phase of CHS. (A) Cell number, and (B) IFN-γ and (C) IL-17 production by DLN cells in DA (n = 10) and AO (n = 8) rats. Results are presented as mean ± SEM. *P < 0.05 and **P < 0.01 vs. control (Cd 0 ppm); #P < 0.05 and ##P < 0.01 vs. day 1 after sensitization (Mann-Whitney U test with Bonferroni correction).
At 1 day after sensitization, greater cellularity of DLNs was observed in DA rats exposed previously to Cd than in Cd-nonexposed animals. In DA rats, 3 days after sensitization, the DLN cellularity was generally higher than that on day 1 after sensitization; however, the number of DLN cells was similar between groups (Figure 5A). In contrast, no differences in DLN cellularity were observed between control and Cd-exposed rats at both time points after sensitization in AO rats (although the values were higher at day 3 than day 1 post sensitization in controls; Figure 5A).
No changes in IFN-γ production by DLN cells were seen on the first day, but the level of this cytokine were greater 3 days after sensitization in the Cd-exposed group than in controls in DA rats, and was generally higher than that on the first day post sensitization (Figure 5B). IL-17 production was higher in DA animals receiving Cd 1 day after sensitization, and were unchanged 3 days after sensitization (although the values were higher than those on day 1 in controls; Figure 5C). No changes in DLN cell production of pro-inflammatory cytokines at either time point after sensitization were observed in AO rats (Figure 5B–C). IFN-γ production was generally higher 3 days after sensitization than 1 day after sensitization in AO rats.
Measurements of the anti-inflammatory/immunoregulatory cytokine IL-10 revealed an inverse pattern of production by DLN cells in two strains 1 day after sensitization (lower in Cd-exposed DA rats and higher in Cd-exposed AO rats than in the respective controls), whereas no differences between groups were observed later in the sensitization phase. Significantly higher IL-10 production was observed on the third day than the first day post sensitization in DA rats (Figure 6A). Calculation of the ratio of pro-inflammatory cytokines to IL-10 indicated significantly higher values for IFN-γ/IL-10 (Figure 6B) and IL-17/IL-10 (Figure 6C) in Cd-exposed than control DA rats 1 day after sensitization, and for IFN-γ/IL-10 3 days after sensitization. The IFN-γ/IL-10 and IL-17/IL-10 ratios were lower in Cd-exposed AO rats than control rats throughout the sensitization phase (Figure 6B–C, respectively).
Figure 6. Effects of oral Cd on IL-10 production by DLN cells during the sensitization phase of CHS. (A) IL-10 production by DLN cells in DA (n = 10) and AO (n = 8) rats. The ratio of (B) IFN-γ and IL-10, and (C) IL-17 and IL-10 production by DLN cells. Results are presented as mean ± SEM. *P < 0.05, **P < 0.01 and ***P < 0.001 vs. control (Cd 0 ppm); #P < 0.05, ##P < 0.01 vs. day 1 after sensitization (Mann-Whitney U test with Bonferroni correction).
-
Given the lack of effect of 5 ppm of Cd on the CHS reaction in AO rats, we examined whether skin reactivity might be provoked by a higher Cd dose of 50 ppm (Table 3). Most parameters relevant to ear skin swelling had significantly higher values in the higher Cd dose-exposed group than the control group of the same strain, except for the number of CD8+ cells (although a tendency toward an increased absolute number was observed, P = 0.057) and the IFN-γ production by ear-derived cells. No effect of high Cd dose was observed during the sensitization phase in this strain regarding cell number and pro-inflammatory cytokine production. However, greater production of IL-10 by DLN cells was seen during this phase of CHS reaction in higher Cd dose-exposed AO rats than controls. Consequently, lower ratios of pro-inflammatory cytokines to IL-10 were observed in Cd-exposed AO rats than controls, at both time points during the sensitization phase (Table 4).
Parameters Cd dose (ppm) 0 50 Ear thickness (relative value) 1.00 ± 0.06 2.25 ± 0.31** Ear cells response Cells number (× 106) 1.46 ± 0.08 2.61 ± 0.16** CD8+ cells number, % 1.37 ± 0.16 1.28 ± 0.09 CD8+ cells number (× 104) 2.00 ± 0.22 3.20 ± 0.23 CD4+ cells number, % 1.26 ± 0.01 1.76 ± 0.09* CD4+ cells number (× 104) 1.83 ± 0.01 4.59 ± 0.24* TNF (pg/mL) 53.6 ± 7.80 91.91 ± 11.7* IFN-γ (pg/mL) 268.89 ± 5.70 375.00 ± 25.0 IL-17 (pg/mL) 285.67 ± 22.8 367.75 ± 16.03 Note. Results are presented as mean values ± S.E.M. Significance at: *P < 0.05 and **P < 0.01 vs. control (Cd 0 ppm) (Mann-Whitney U test corrected with the Bonferroni adjustment). Table 3. High Cd dose effect on challenge phase of CHS in AO rats
Parameters One day following sensitization Three days following sensitization Cd (0 ppm) Cd (50 ppm) Cd (0 ppm) Cd (50 ppm) Cell number (× 106) 43.12 ± 5.49 32.08 ± 2.95 63.35 ± 4.77 69.24 ± 3.50# IFN-γ (pg/mL) 284.07 ± 12.29 245.00 ± 6.20 476.67 ± 16.56# 460.67 ± 13.91 IL-17 (pg/mL) 301.95 ± 16.18 311.50 ± 9.82 299.17 ± 8.96 269.17 ± 23.56 IL-10 (pg/mL) 125.67 ± 19.37 435.00 ± 70.99* 218.60 ± 25.37 424.67 ± 9.51* IFN-γ/IL-10 2.24 ± 0.09 0.58 ± 0.02* 2.16 ± 0.08 1.15 ± 0.04*# IL-17/IL-10 2.37 ± 0.13 0.72 ± 0.02* 1.37 ± 0.04 0.70 ± 0.06* Note. Results are presented as mean ± SEM. Significance at: *P < 0.05 vs. control (Cd 0 ppm); #P < 0.05 vs. one day following sensitization (Mann-Whitney U test corrected with the Bonferroni adjustment). Table 4. High Cd dose effect on DLN cells activity during sensitization phase of CHS in AO rats
Oral Cadmium Intake Enhances Contact Allergen-induced Skin Reaction in Rats
doi: 10.3967/bes2022.132
- Received Date: 2022-01-18
- Accepted Date: 2022-06-14
Abstract:
Citation: | Dina Tucovic, Jelena Kulas, Ivana Mirkov, Dusanka Popovic, Lidija Zolotarevski, Marta Despotovic, Milena Kataranovski, Aleksandra Popov Aleksandrov. Oral Cadmium Intake Enhances Contact Allergen-induced Skin Reaction in Rats[J]. Biomedical and Environmental Sciences, 2022, 35(11): 1038-1050. doi: 10.3967/bes2022.132 |