|Year : 2019 | Volume
| Issue : 1 | Page : 48-51
Periodontal implications of argyrophilic nucleolar organizer region: A mini reviewPeriodontal implications of argyrophilic nucleolar organizer region: A mini review
Vandana Kharidi Laxman1, GS Madhushankari2, Mini Saluja3, Shivani Singh1
1 Department of Periodontics, College of Dental Sciences, Davangere, Karnataka, India
2 Department of Oral Pathology and Microbiology, College of Dental Sciences, Davangere, Karnataka, India
3 Faculty of Dental Sciences, SGT University, Gurgaon, Haryana, India
|Date of Submission||18-Mar-2018|
|Date of Acceptance||30-Nov-2018|
|Date of Web Publication||6-Mar-2019|
Vandana Kharidi Laxman
Department of Periodontics, College of Dental Sciences, Davangere . 577 004, Karnataka
Source of Support: None, Conflict of Interest: None
The periodontal lesions with cellular proliferation can be assessed by various methods. One of the methods to determine the proliferative activity is silver-staining argyrophilic nucleolar organizer region (AgNOR) staining. AgNOR can be used as diagnostic and prognostic tool for many of periodontal lesions which are proliferative in nature and may be quantitative marker of incipient cellular alterations before the histologic hallmarks appear. Hence, this paper reviewed about the periodontal applications of AgNOR staining.
Keywords: Histology, periodontal lesions, proliferative marker, silver staining
|How to cite this article:|
Laxman VK, Madhushankari G S, Saluja M, Singh S. Periodontal implications of argyrophilic nucleolar organizer region: A mini reviewPeriodontal implications of argyrophilic nucleolar organizer region: A mini review. J Oral Res Rev 2019;11:48-51
|How to cite this URL:|
Laxman VK, Madhushankari G S, Saluja M, Singh S. Periodontal implications of argyrophilic nucleolar organizer region: A mini reviewPeriodontal implications of argyrophilic nucleolar organizer region: A mini review. J Oral Res Rev [serial online] 2019 [cited 2020 Apr 7];11:48-51. Available from: http://www.jorr.org/text.asp?2019/11/1/48/253434
| Introduction|| |
The clinical presentation of hyperplastic (inflammatory and neoplastic) lesions affecting periodontium may generate diagnostic challenges for the periodontist. Several methods have been used in the past for the identification of proliferating cells in tissue sections such as assessment of mitosis, use of DNA flow cytometry, autoradiographic methods, application of RNA and DNA, and use of monoclonal antibodies to detect proliferating-related antigens. The major disadvantages in the above techniques are that they are time-consuming, expensive and require sophisticated equipment with technical expertise. Various other methods which have been employed to indicate the proliferative activity in normal tissues and both benign and malignant tumors are immunohistochemical staining for proliferating cell nuclear antigen, Ki67, bromodeoxyuridine-labelling (Brdu), and AgNOR staining. Silver-staining argyrophilic nucleolar organizer regions (AgNORs) have recently been utilized in the healthy status,, and diagnosis of periodontal lesions.,, The early attraction of this method was that it was inexpensive and needed no special resources other than time and patience. An attempt is made in this short communication to provide periodontal application of AgNOR staining.
| Nucleolar Organizer Regions|| |
Nucleolar organizer regions (NORs) are loops of ribosomal DNA which occur in the nuclei of cells possessing the genes for synthesizing r-RNA. These genes are transcribed by RNA polymerase I and ultimately direct ribosome formation and protein synthesis.
In the homosapiens, they are located on the short arm of five acrocentric chromosomes, i.e., chromosome numbers 13, 14, 15, 21, and 22. Many of these bind silver, a property attributed to proteins attributed to these sites, particularly the acidic nonhistone compounds. The amount of silver deposited in this cytochemical reaction is a reflection of the transcriptional activity of ribosomal genes, and the frequency of NORs per nucleus may prove useful as replicatory marker.
Physiologic consideration of argyrophilic nucleolar organizer region
Although 20 AgNOR sites should theoretically be present in a human diploid nucleus, AgNORs are typically aggregated within one or two nuclei during interphase in normal cells. The number of AgNORs visualized depend on (a) the number of NOR-bearing chromosomes in the karyptope, (b) the level of (RNA) transcriptional activity, and (c) the stage of cell cycle, as the nucleolus disperses before mitosis and reorganizes afterward.
A decreased size of AgNOR which is normally 0.3–1.5 μ, an increased number, and more dispersed distribution has been reported in malignant lesions and the converse for benign lesions. However, AgNORs staining is also useful for studying normal proliferating cells, as it may be a quantitative marker of incipient cellular alterations before the histological hallmarks appear.
| Implications of Argyrophilic Nucleolar Organizer Region|| |
Diagnostic implications of argyrophilic nucleolar organizer region
AgNOR count is more commonly used for the diagnostic purpose as compared to the prognostic determination. Crocker demonstrated that malignant cells can be distinguished from corresponding benign or normal cells on the basis of a higher quantity of interphase. It has been suggested that AgNOR count may be more reflective of the biologic nature of the condition, and hence, the degree of malignant potential rather than proliferative status.
It has been employed to study the proliferative activity of various other tumor cells, including malignant lymphoma, salivary gland, sarcoma, breast cancer, and pleural malignancy. It has also been used in the diagnosis of cutaneous tumors.
It has been reported that difference in AgNOR number is not of diagnostic significance and cannot be used to distinguish various odontogenic cysts from one another nor from unicystic ameloblastoma.
Prognostic implication of argyrophilic nucleolar organizer region
Although AgNOR estimation is used for diagnostic aspect, it has been found to serve as a reliable prognostic marker too. The prognostic significance of the AgNOR technique was reported in carcinomas of the sigmoid colon and rectum. AgNOR count may provide information on breast cancer prognosis supplementary to that obtained from DNA flow cytometric analysis.
Implications in oral conditions
Different Implications of silver-staining nucleolar organizer region in other oral conditions are presented in [Table 1].
|Table 1: Implications of silver-staining nucleolar organizer region in other oral conditions|
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Various Implications of silver-staining nucleolar organizer region in healthy and periodontal conditions are presented in [Table 2]
|Table 2: Implications of silver-staining nucleolar organizer region in healthy and periodontal conditions|
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Oral medicine and oral pathology
- Studies on oral malignancies and submucous fibrosis have revealed high count in squamous cell carcinoma with the AgNOR count increasing further with poor differentiation of the neoplasm
- The lesions with higher counts were reported to exhibit poor prognosis
- The increased proliferative activity and poor prognosis of ossifying fibroma compared with peripheral ossifying fibroma was suggested through AgNORs expression. 
In healthy situations
AgNOR in periodontics was a new found interest in the 80s and 90s, as many periodontal lesions are proliferative in nature. In few studies, the proliferative activity of long junctional epithelium (LJE) using AgNOR method has been reported.,, Uno et al. in 1998 conducted a study to examine the proliferative activity of the LJE in rats using stains for argyrophilic proteins of the nucleolar organizer region (AgNORs protein). The results suggested that the proliferative activity of the LJE is maintained continuously at a high level on the connective tissue interface supplying the epithelial cells. Usuda et al. in 2004 showed that LJE could not supply sufficient epithelial cells because of their significantly low rates of proliferation, consequently LJE becomes shorter after 12 weeks whereas the proliferative activity of regenerative connective tissue maintains the same level of proliferation, and ultimately, LJE is replaced by regenerative connective tissue.
AgNOR count can be used as a histopathological indicator in cases of nonresponsive gingivitis to assess the severity of gingival inflammation.
Neoplastic and nonneoplastic periodontal conditions
A study by Saluja and Vandana evaluated the diagnostic and prognostic ability of AgNOR in various neoplastic (squamous cell carcinoma) and nonneoplastic periodontal conditions (fibrous hyperplasia, peripheral ossifying fibroma, gingival bromatosis, pyogenic granuloma, drug-induced enlargement, and gingival polyp) showed that AgNOR has a limited diagnostic value, with a definite prognostic value in nonneoplastic periodontal lesions.
| Indications|| |
AgNOR estimation can be additional diagnostic criteria histologically. Its feasible indications are
- All types of gingival/periodontal enlargements which undergoes excision or biopsy
It is not popular because it's time-consuming and its implications are minimally understood specially in the periodontal field
- It is a useful tool to assess gingival changes pre- to post-treatment (scaling and root planing)
- Its not expensive but laborious so usually not considered. However, after trying out in two of our projects, it is valuable more of prognostic criteria than diagnostic criteria.
| Argyrophilic Nucleolar Organizer Region Evaluation Methods|| |
It includes enumeration of AgNOR dots, measurement of area of AgNORs, and analysis of their distribution pattern. Microscopically, the AgNOR were clearly recognized as variable sized black dots with yellowish background in the nuclei and the counting was done using two methods-individual count and cluster count [Figure 1]a and b].
|Figure 1: Histological section (argyrophilic nucleolar organizer region staining) showing increased argyrophilic nucleolar organizer region count pretreatment (a) and posttreatment (b)|
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| Significance of Argyrophilic Nucleolar Organizer Region|| |
AgNOR count rise with increased cell ploidy, with increased transcriptional activity and stages of active cell proliferation. Thus, AgNOR counting may enable to predict the biologic behavior of various periodontal lesions and to correlate the clinical and histologic grading of the condition, thus rendering prognosis more reliably. However, further investigations are required to clarify these techniques in large series of periodontal lesions.
Limitations of argyrophilic nucleolar organizer region
As the AgNOR depends on active cell proliferation, the specific range of AgNOR count is not determined so far. There is a need to study the normal healthy tissue and to determine the normal range of AgNOR count. This will facilitate the oral pathologists and clinicians to discriminate healthy and diseased tissues. It may be a difficult issue since cell proliferation in health itself is variable.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2]