Özet
Amaç: Nikele maruz kalmanın getirdiği tehlikeler, direkt ve otoimmün reaksiyon nedeniyle, büyümekte olan bir problemdir. Bu çalışmanın amacı, nikelin otoimmün tiroid hastalığını başlatıp başlatmadığını araştırmaktır.  
Gereç ve Yöntemler: Bu çalışmada, daha önceki çalışmamızdan (Almogairen at al., Lupus, 2009 Nisan) 12 kahverengi Norveç sıçanı seçildi. Sıçanlar nikele maruz bırakıldıktan sonra öldürüldü ve tiroidektomize edildi. Nikele pozitif cevap veren gruptaki 6 sıçan üzerinde histolojik incelemeler yapıldı ve aynı sayıdaki antikor negatif kontrol grubu sıçanları ile karşılaştırıldı.
Bulgular: Histolojik olarak, subkutan nikel uygulanan grubun tiroid bezinde epitelyal follikuler proliferasyon anlamlıydı.
Sonuç: Yukarıdaki sonuçlar, aynı sıçanların serum antinükleer antikor (ANA) cevabı ile ilişkilendirildiğinde, nikel klorürün immünosensitif sıçanlarda otoimmün tiroid hastalığının indüklenmesinde önemli rol oynayabileceği sonucuna varılabilir. Türk Jem 2009; 13: 71-4
Anahtar kelimeler: Otoimmün, tiroid, ANA, nikel

Introduction

Nickel allergy is the most common cause of allergic contact dermatitis. It’s prevalence in the general population is about 7-10% with predominance in females (female: male ratio of 7-14:1) (1).
Nickel is used for making stainless steel which is used for production of equipments, fashion jewelry, coins, metal eyeglasses, prosthetic implants, as well as dental crown, bridges and implants (1-6). 
One of the target organs to toxins and drugs is the thyroid gland, which dysfunction is manifested as hypothyroidism, hyperthyroidism, c-cell hyperplasia (7,8). Thyroid diseases are associated with drugs such as interferon-alpha, interleukin-2, lithium, cyclosporine and amiodarone, or toxins such as organochlorine (9-16).
Chronic interferon-alpha exposure leads to changes in thyroid gland, including enlarged follicles lined by thickened granular and oxyphilic thyrocytes with diffuse mononuclear infiltrates of the stroma (8). Organochlorine induces thyroid gland cysts and c-cell hyperplasia (7).
The objective of this experimental study is to demonstrate whether nickel would induce autoimmune thyroid disease in Brown Norway rats. This study is an extension of our previous study (Almogairen et al, Lupus 2009 April) 17,but examining the correlation between the autoimmune response and the histopathological changes in the thyroid gland.   

Materials and Methods

Brown Norway rats (BN) were purchased from Charles Rivers Laboratories, Wilmington, U.S.A.  They were kept in polycarbonate metrolon plastic cages covered with stainless steel cover in the animal house in the College of Medicine, King Saud University, Riyadh, Saudi Arabia.  They were maintained under 12-hr dark: 12-hr light cycles and were kept under observation for three weeks.  No evidence of sickness was observed. All rats were 8-11 weeks old at the onset of the experiment. There were a total number of twelve rats with an average weight of 157 g.  There were four groups: the first and the second groups (six rats) were called  subcutaneous nickel group (three rats) and oral nickel group (three rats).  The third and the fourth groups (six rats) were called subcutaneous normal saline control group (three rats) and oral normal saline control group (three rats).
All the above groups were selected for thyroid histological studies from our previous study, where the first and the second nickel groups were autoantibody-positive for serum ANA, anti-dsDNA, anti-Smith, anti-SSA and anti-SSB. On the other hand, the third and the fourth control normal saline groups were overall  autoantibody-negative.  The above selected groups were sacrificed after fourteen weeks of exposure to nickel chloride or normal saline and then thyroidectomized.  The tissues taken from them were bisected and fixed in 10% buffered formalin for 24 hours. The tissues were then processed in the Tissue-Tek vacuum infiltration processor and stained using hematoxylin and eosin stain.  The slides were examined blindly by histopathologist using light microscope.

Results
 
The maximum serum antibody titers in the selected rats from our previous study are shown in Table 1.
The histopathological results are shown in Table 2.  The changes in the thyroid gland were accepted as negative if all of the parameters shown in Table 2 were negative, otherwise, positive.  Positive changes in the thyroid gland depicted in Figure 1 were observed in 3/3 (p=0.05) of subcutaneous nickel chloride group, on the other hand, p value was 0.49 in the oral nickel group.
 
Discussion

There are a limited number of publications concerning the structure of thyroid gland following the exposure to some drugs and toxins (7,10,12-14). To our knowledge, this is the first experimental animal study showing the correlation between the histopathological changes in the thyroid gland secondary to challenge with nickel and  the serum autoimmune response. One study showed that in rats, injection of nickel sulfate (NISO4) induced the epithelial proliferation in the thyroid glands (16).
In our previous study, almost all serum autoantibodies in Brown Norway rats were undetectable prior to intervention. After challenge with nickel chloride, serum ANA appeared early and in a significant number of rats (p<0.05) in both subcutaneous and orally treated rats. The same response (p<0.05) was seen with anti-SSA in the subcutaneous nickel chloride group. Other serum autoantibodies including anti-dsDNA, anti-Smith and anti-SSB were insignificant (17). The main histopathological finding of the present study was increased epithelial follicular proliferation in the subcutaneous nickel group (p=0.05).  In the oral nickel group, increased epithelial follicular changes were observed only in one rat, which was probably due to the processing of nickel chloride substance by gastrointestinal M-cells (18).
The mechanism causing these effects could be due to direct toxic injury, autoimmunity or due to disruption of the hypothalamic-pituitary-thyroid (HPT) axis, a disturbance in the calcium homeostasis or in the energy metabolism (7).
With the above significant response of Serum ANA and anti-SSA, the autoimmunity is probably playing a role in the epithelial follicular proliferation in the thyroid gland.
In conclusion, the findings from this study indicate that nickel chloride might induce autoimmune thyroid disease and we recommend, in the future, a immunohistochemical tissue study to be conducted on murine antithyroid antibodies,  if available.   
Acknowledgement
The study was supported by a grant from Research Center, College of Medicine, King Saud University.  The author is grateful to Dr. Sufia Husain, FRC Path for reporting histology.  The author is also grateful for the following:  Dr. B. Al-Mohaimeed, Dr. N. Khalil, Mr. M. Marzook, and Mr. S. Abu-al-Ghaith, S. Seno, Mitzi Guinto, Joann Octubre for their cooperation, and the Research Ethic Committee, College of Medicine for the approval of this study.  

Address for Correspondence: Sultan Al-Mogairen, MD, Department of Medicine, Faculty of Medicine, King Saud University, Saudi Arabia  E-mail: almogairin@hotmail.com-salmogairin@ksu.edu.sa Recevied: 18.01.2010 Accepted: 26.01.2010

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