Increased expression of inducible nitric oxide synthase for human oral submucous fibrosis, verrucous hyperplasia, and verrucous carcinoma

A Case-control Study Comparing and Correlating iNOS Expression among Various Clinicopathological Variants of Oral Leukoplakia and Oral Squamous Cell Carcinoma: A Immunohistochemistry Study

Background and Objective

The role of inducible nitric oxide synthase (iNOS) has been implicated in various pathological processes including oral carcinoma. Oral premalignancy being its precursor lesion is also expected to show similar pattern. This study attempts to appraise the iNOS expression in various clinicopathological stages and grades of oral leukoplakia (OL) and oral squamous cell carcinoma (OSCC).

Materials and Methods

A case-control study design was adopted for this study with a total sample of 90 subjects, distributed equally into the three study groups, namely controls, OL, and OSCC. Clinical staging and histopathological grading for both the case groups were performed. Representative tissue samples from all groups were obtained and studied for iNOS expression using immunohistochemistry (IHC). Data were presented in mean and percentages accordingly. Inferential analysis was performed using Kruskal-Wallis test, Mann-Whitney test, and Spearman rank correlation test.

Results

Significant (P < 0.001) difference was observed among the groups, where 83.3% of OSCC and 73.3% of OL epithelial cells showed iNOS expression. The normal cells did not show up any expression. The expression was found to rise with the progressing clinical stages of OL (P < 0.05) and OSCC (P < 0.01). Similar pattern was observed with respect to advancing dysplasia in OL (P < 0.01) and cell differentiation in OSCC (P < 0.01). Significant positive correlation was found in clinicopathological categories of OL and OSCC. Considering the risk assessment, iNOS staining was found to be significantly raised in advanced cases of OSCC (P < 0.01) and high-risk cases of OL (P < 0.01).

Conclusion

Increased expression of iNOS can be an early diagnostic marker in OL and as prognostic marker in OSCC.

Verrucous Hyperplasia: Case report and differential diagnosis

Verrucous hyperplasia (VH) is a rare exophytic oral mucosal lesion which can transform into verrucous carcinoma (VC), its malignant but clinically similar counterpart. These entities can be distinguished by the lack of invasive growth in VH cases; as such, it is essential to include a margin with adequate depth when performing a biopsy of the epithelium of the lesion. We report an 80-year-old male patient who presented to the Bapuji Dental College & Hospital, Davangere, Karanataka, India, in 2011 with a warty whitish-pink growth on the inside of his cheek. The patient was treated with wide surgical excision of the lesion and a diagnosis of VH was made based on histopathological features. There was no evidence of recurrence at a five-year follow-up. This report highlights the histological variations, pathogenesis and differential diagnosis of VH.

Oral verrucous carcinoma: From multifactorial etiology to diverse treatment regimens (Review)

Oral verrucous carcinoma (OVC) is a verrucous variant of oral squamous cell carcinoma (OSCC), which accounts for 2-12% of all oral carcinomas with a 5-year survival rate of only approximately 50%. Enormous effort has been dedicated to this cancer, and the past decades have witnessed significant advances in relevant diagnostic and therapeutic approaches. Currently, there exist three challenges from primary sub-fields of research and clinical practice of the cancer, namely multifactorial etiology, complex molecular mechanism, and deficient treatment. This study reviews the existing literature on the cancer, encompassing its etiology, clinical manifestations and pathology, molecular mechanism, diagnosis and differential diagnosis, and treatment. For improved treatment of OVC, multifactorial etiology analysis, incorporation of effective biomarkers for mechanism illustration, and integration of multidisciplinary modalities are expounded, in an attempt to resolve the challenges and to provide a useful guide for future research in the field.

Estimation of salivary nitric oxide in oral precancer patients

The role of nitric oxide (NO) in the initiation, promotion and progression of cancer has been the subject of speculation and conflicting reports in the literature. The high incidence of oral cancer and precancer has been linked to tobacco chewing and smoking habits; NO is considered an indicator of tobacco-related diseases. We compared salivary NO levels in oral precancer and normal patients. Unstimulated whole saliva was collected from 15 patients with oral precancer (group 1) and 15 healthy age and sex matched subjects (group 2). Salivary nitrite levels were estimated using a colorimetric method and a spectrophotometer. The salivary nitrite concentration of group 2 (median = 4.21 μg/ml) was significantly less than for group 1 (median = 12.91 μg/ml). We have added evidence concerning involvement of NO in the pathogenesis of oral cancer, but whether it is a potentially carcinogenic agent at the concentration at which it is present in oral precancer patients requires further evaluation.

Nitric oxide and oral cancer: a review

Nitric oxide (NO), a short-lived, endogenously produced gas, plays key role in various physiological as well as pathological processes. NO-inducing cell signaling events within the cell producing it and the diffusibility of it in other cells have led to the discovery of various physiological functions of NO including vasodilation, respiration, cell migration, immune response and apoptosis. On the other hand, excessive and unregulated NO synthesis has been implicated in many pathophysiological conditions including cancer. Research on NO, during the past few years is one of the growing areas in cancer biology. The high incidence of oral cancer and precancer has been linked with habits of tobacco chewing and smoking and NO has been said as the "messenger of death" in tobacco related diseases. NO seems to play a part in various stages of carcinogenesis from initiation to progression. However, there is considerable controversy and confusion in understanding its role in cancer biology. It is said to have both, tumoricidal as well as tumor promoting effects and these depend on its timing, location and concentration. Further, NO has also been shown to have antitumor, chemopreventive and therapeutic abilities. Here is an overview in which efforts are made to understand the role of this molecule in oral carcinogenesis.

Zyflamend reduces LTB4 formation and prevents oral carcinogenesis in a 7,12-dimethylbenz[alpha]anthracene (DMBA)-induced hamster cheek pouch model

Aberrant arachidonic acid metabolism, especially altered cyclooxygenase and 5-lipoxygenase (LOX) activities, has been associated with chronic inflammation as well as carcinogenesis in human oral cavity tissues. Here, we examined the effect of Zyflamend, a product containing 10 concentrated herbal extracts, on development of 7,12-dimethylbenz[alpha]anthracene (DMBA)-induced inflammation and oral squamous cell carcinoma (SCC). A hamster cheek pouch model was used in which 0.5% DMBA was applied topically onto the left cheek pouch of male Syrian golden hamsters either three times per week for 3 weeks (short term) or 6 weeks (long term). Zyflamend was then applied topically at one of three different doses (25, 50 and 100 microl) onto the left cheek pouch three times for 1 week (short-term study) or chronically for 18 weeks. Zyflamend significantly reduced infiltration of inflammatory cells, incidence of hyperplasia and dysplastic lesions, bromodeoxyuridine-labeling index as well as number of SCC in a concentration-dependent manner. Application of Zyflamend (100 microl) reduced formation of leukotriene B(4) (LTB(4)) by 50% compared with DMBA-treated tissues. The reduction of LTB(4) was concentration dependent. The effect of Zyflamend on inhibition of LTB(4) formation was further confirmed with in vitro cell-based assay. Adding LTB(4) to RBL-1 cells, a rat leukemia cell line expressing high levels of 5-LOX and LTA(4) hydrolase, partially blocked antiproliferative effect of Zyflamend. This study demonstrates that Zyflamend inhibited LTB(4) formation and modulated adverse histopathological changes in the DMBA-induced hamster cheek pouch model. The study suggests that Zyflamend might prevent oral carcinogenesis at the post-initiation stage.

Human gingival mucosal keratinocytes exhibiting anchorage-independent growth express increased inducible nitric oxide synthase: regulation by MAP kinases

Inducible nitric oxide synthase (iNOS) has been implicated in cancer formation because of its vast presence cancer tissues. Studies to support such a role during transformation of human cells are very limited. We have developed a cell culture system, which renders a more transformed epithelial phenotype. The model cells generated from immortalized human gingival mucosal (GM) keratinocytes are consisted of less transformed epithelial-like (EPI) cells and more transformed fibroblast-like (FIB) cells. The latter exhibit anchorage independent growth (AIG). Our data showed that iNOS at mRNA and protein levels was up-regulated in more transformed FIB cells in comparison with less transformed EPI cells. FIB cells at low passages (p<22) were unstable being able to morphologically and functionally revert back to EPI phenotype, while no reversion was observed in FIB cells at high passages (p>43). The morphological reversion of FIB cells was associated with the reversal of vimentin expression as well as AIG. More importantly, these revertants showed reduced levels of iNOS mRNA as well as MAP kinase ERK and phospho-ERK protein expression, while FIB cells without reversion maintained the expression. Furthermore, the MEK1/2 inhibitor U0126 could reduce detectable iNOS mRNA levels suggesting that MAP kinases were upstream regulators of iNOS transcription. U0126 caused both morphological and functional reversion of FIB cells indicating involvement of MAP kinases in these functions. Taken together, we provide evidence for an up-regulation of iNOS in cultured human keratinocytes which exhibit AIG. This up-regulation may reflect progressive transformation which still requires further changes to reach tumorigenic conversion.

Inhibitory effect of inducible nitric oxide synthase inhibitors on DMBA-induced hamster buccal-pouch squamous-cell carcinogenesis

We investigated the effects of two NOS inhibitors (AG and l-NAME) on DMBA-induced hamster buccal-pouch carcinogenesis. Six hundred Syrian golden hamsters were split into two divisions (I and II); divisions split into three groups (experimental groups A and B, control group C); and each group into subgroups of 20 (A1-A6, B1-B6 and C1-C3). The pouches of animals in groups A1-A3 were painted first with AG of differing concentrations (10, 20, and 30 micromol/ml) and then 30 min later with DMBA (0.5%), thrice weekly for 9 weeks. Subgroups A4-A6 only received AG treatment. Groups B1 to B6 were similarly treated with l-NAME. Animals in division II were treated in the same manner for 13 weeks. Post-mortem analysis revealed that both inhibitors can suppress the development of epithelial dysplasias and squamous-cell carcinomas. An associated increase in the numbers of epithelial hyperplasias was paralleled by a decrease in iNOS protein expression. This animal model can be employed to evaluate the potential use of iNOS inhibitors as novel therapeutic tools for oral squamous-cell carcinogenesis.

Expression of p63 (TA and ▴N isoforms) in human primary well differentiated buccal carcinomas

Abnormalities in the p53 gene have been regarded as the most consistent genetic abnormalities detected in head and neck squamous cell carcinogenesis. Two new members of the p53 gene family, p73 and p63, have recently been identified. We investigated the expression of the two N-terminal p63 isoforms (TA and deltaN isoforms) in human primary well-differentiated buccal squamous cell carcinoma. Both TAp63 and deltaNp63 isoforms were detected in the basal/suprabasal layers of all of the five specimens of normal buccal mucosa. The deltaNp63 isoform was found in all of the 23 specimens of human primary well-differentiated buccal carcinoma whereas TAp63 isoform was absent in 18 (78.3%) of the 23 specimens. The immunostaining patterns of both TAp63 and deltaNp63 isoforms were similar in that the p63 positivity was noted mainly in the peripheral cells of tumor nests whereas negative staining was observed in the areas with keratin pearl formation. A higher number of T3-T4 patients and patients with recurrence showed negative staining of TAp63 than T1-T2 patients and patients without recurrence but the difference was not statistically significant. These results suggested that specific p63 isoforms were associated with human oral squamous cell carcinogenesis. The deltaNp63 isoforms might be involved in epithelial differentiation and proliferation in human oral carcinogenesis whereas there was evidence for a possible role of TAp63 under-expression in human oral tumorigenesis.

Correlation between inducible nitric oxide synthase and p53 expression for DMBA-induced hamster buccal-pouch carcinomas

Three isoforms of nitric oxide synthase (NOS) have been identified previously--endothelial NOS, neuronal NOS, and inducible NOS (iNOS). It has been reported previously that there may be a negative feedback loop existing between nitric oxide (NO) production and wild-type p53 tumor-suppressor gene, but the relationship has not previously been studied for oral experimental carcinogenesis. The purpose of the present study is to assess whether iNOS expression correlates with p53 expression at both protein and mRNA levels for 7,12-dimethylbenz[a]anthracene (DMBA)-induced hamster buccal-pouch carcinomas.

MATERIALS AND METHODS

Thirty-five out-bred, young (6 week old), male, Syrian golden hamsters (Mesocricatus auratus) were randomly divided into one experimental group (15 animals), and two control groups (10 animals each). Bilaterally, the pouches of a group of 15 animals from the experimental group were painted with a 0.5% DMBA solution three times a week for 12 weeks whilst each animal from one of the control groups was similarly treated with only mineral oil. Another control group of 10 animals remained untreated throughout the experimental procedure. Specimens obtained from the hamster buccal-pouch mucosa were evaluated using immunohistochemical assessment of iNOS and p53 protein and in situ reverse transcription-polymerase chain reaction (IS RT-PCR), as well as reverse transcription-polymerase chain reaction (RT-PCR) for iNOS and p53 mRNA.

RESULTS

Two of the 15 animals of the DMBA-treated group died during the experiment. Squamous-cell carcinomas with a 100% tumor incidence were apparent for all of the 15-week DMBA pouch-treated animals. Animals from the mineral oil-treated and untreated pouch groups revealed no obvious changes. Inducible NOS mRNA was identified as a band corresponding to a 499-bp PCR product and was observed for all 13 of the hamster buccal-pouch tissue specimens treated with DMBA for 15 weeks. The p53 mRNA was found as a band corresponding to a 370-bp polymerase chain reaction (PCR) product and was noted for nine (9/13, 69%) of the 15-week DMBA-treated pouches. No such bands (iNOS and p53) were noted for the untreated animals, the mineral oil-treated tissues and the negative-control samples. Using IS RT-PCR, the proportional (percentage) expression of iNOS (13/13, 100%) and p53 (8/13, 62%) mRNA observed for the hamster buccal-pouch tissue specimens treated with DMBA for 15 weeks was noted to be consistent with the findings using RT-PCR. Furthermore, the proportional expression of iNOS (13/13, 100%) and p53 (8/13, 62%) proteins for the 15-week DMBA-treated hamster buccal-pouch tissue specimens was noted to be consistent with the findings using RT-PCR and IS RT-PCR. A significant association between iNOS and p53 expression (at both protein and mRNA levels) was noted (Fisher's exact probability test, P < 0.05). Neither iNOS nor p53 activity (at both protein and mRNA levels) was found for any of the untreated and mineral oil-treated pouches.

CONCLUSIONS

Enhanced expression of iNOS and p53 at both protein and mRNA levels in DMBA-induced hamster buccal-pouch carcinomas compared with the untreated and mineral oil-treated counterparts, has been demonstrated in the current study. Furthermore, we report what is, to the best of our knowledge, the first identification of a significant association between iNOS and p53 expression (at both protein and mRNA levels) in this experimental model system for oral carcinogenesis, although their precise interactions remain to be clarified.