Oral Submucous Fibrosis: Etiopathogenesis

ByHarsh Deep Singh

Submitted to:Department of oral pathology

FACULTY OF DENTISTRY, JMI

Content 1.Introduction2.Etiology • Chili• Nutritional deficiencies• Genetic Susceptibility• Autoimmunity• Areca Nut2. Pathogenesis

What is OSMF?An insidious, chronic disease affecting any part of the cavity and sometimes the pharynx. Occasionally it is preceded by and/or associated with vesicle formation and is always associated with a juxta-epithelial inflammatory reaction followed by fibroelastic change of lamina propria, with epithelial atrophy leading to stiffness of the oral mucosa and causing trismus and inability to eat

EtiologySeveral factors such as• Chili consumption, •Nutritional deficiency states, •Areca nut chewing, •Genetic susceptibility •Autoimmunity and •Collagen disorders have been suggested to be involved in the pathogenesis of this condition. Some of these suggestions were based on ecological observations, others were more or less speculative.

Chilli

•Capsaicin, which is vanillylamide of 8-methyl-6-nonenic acid, is the active ingredient of chillies, play an etiological role in oral submucous fibrosis (Rajendran, 1994

•OSMF is found mostly among Indians and other population groups who use chilies to spice their food.

• OSMF patients are unable to tolerate spicy food containing chilies before they develop disease

• Histologic observations : tissue eosinophils in the biopsy specimens suggested an allergic nature of this disease possibly due to chili intake.

•epithelial hyperplasia, presence of a chronic inflammatory cell exudate, and dense fibrogenesis with elastic degeneration of collagen; these changes were thought to indicate a simultaneous defense and repair mechanism, similar to the chronic productive response.

Q. When are these changes present ?A. Agent responsible for exciting an inflammatory reaction is mild and continues to operate over a prolonged period of time

Animal experimental studyTest : capsaicin, an active principle of chilies, as a test substance has been conducted on Wistar ratsObservation : elastic degeneration of palatal collagen, and ultra structurally partial or complete degeneration of the collagen into elastin like filaments, sheets, or dense amorphous materialInference: limited connective tissue response in an unimpaired animal system enhanced in protein- or vitamin-deficient animal systems

Against the hypothesis :Mexico or other South American countries where chilli consumption is widespread, there is no report of this condition

Nutritional deficienciesObservations suggesting hypothesis• Reports of anemia, vitamin, iron and protein deficiencies among OSF patients

• A higher frequency of clinical manifestations of deficiency of vitamins A, B and C, and lower serum vitamin levels were found in cases as compared to controls by WAHI et al.

Observations against hypothesis•In a South African study: no difference in the prevalence of iron deficiency anemia between that observed cases and the general population.

• Inability to tolerate spicy food, which is a normal family and community diet.

• The deficiency of these factors observed among OSF patients may be secondary

Conclusion : This functional impairment may affect normal food intake and lead to nutritional deficiencies.

Genetic Susceptibility

Observation suggesting hypothesis• Familial occurrence seen in India and South Africa .

• The occurrence of OSF among individuals without areca nut chewing habits has also been thought to be due to genetic factors

•Polymorphism of the genes coding for TNF-α is significant risk factor for OSMF

•TNF-α is known to stimulate fibroblastic proliferation in vitro suggesting active role for TNF-α in the pathogenesis of OSMF

• Observations suggest a possible genetic susceptibility to the action of extrageneous factors such as areca alkaloids and tannins.

Autoimmunity Reasons for investigating as an autoimmune disorders included 1. Slight female predilection2. Occurrence in middle age group3. Presence of circulating immune complexes4. Immunoglobin contents 5. Detection of various autoantibodies in patients sera

Observation suggesting hypothesis•Similarities of this condition with other collagen disorders, namely scleroderma, having an autoimmune pathogenesis.

• Antibodies which showed increased frequency were anti gastric-parietal cell (GPCA), anti thyroid microsomal, anti-nuclear (ANA), anti reticulin and anti smooth muscle (SMA) antibodies

• Increased levels of immune complexes and serum levels of IgG, IgA. And IgM when compared with control groups

Areca Nut

Areca nut (often erroneously referred to as betel nut) is the endosperm of the fruit of the Areca catechu tree.

Contents Areca nut contains 1. Tannins • gallotannic acid• D-Catechol are important 2. Alkaloids • arecoline is the most abundant• arecaidine• guvacine• isoguvacine• arecolidine • guvacoline are also present in small quantities. Other substances comprise fats,

carbohydrates, proteins, and mineral matter

Areca Nut Preparations

• In India areca nut is chewed by itself

• in the form of various areca nut preparations such as 1. scented supari2. mawa3. Manipuri tobacco,4. pan masala5. betel quid, either with or without tobacco

Epidemiologic studies

Ecological Observations •The occurrence of OSMF in an area or population in which areca nut chewing is popular, compared to its rarity in populations or areas where areca nut chewing is unknown or less common

• South Africa: common among women of Indian origin and rare among blacks

Dose-response relationship

The relationship between the degree of exposure and the risk of a disease is an important criterion for causal inferenceThe relative risk increased with the duration as well as the frequency of the areca nut chewing habit.*

Regional variationsFrequency of OSMF and arecoline content of the areca nut varies from place to place in India and perhaps this may have some influence on the prevalence rates.

Clinical StudyPune, Maharashtra Ernakulum, Kerala

Areca nut preparation

67% chewed only areca nut 77% chewed areca nut as an ingredient of betel quid with tobacco

Area affected this condition affected the posterior one-third of the buccal mucosa, soft palate, the uvula, and retromolar areas significantly more often than in Ernakulum

tongue, floor of the mouth and the hard palate were not involved in Pune

Explanation when individuals chew areca nut without tobacco, as in Pune, they generally swallow the juice, thus exposing the posterior part of the oral mucosa (to areca nut contents much more than the anterior parts

areca nut is chewed in betel quid with tobacco, therefore the quid and the juice are held for a longer time and are spat out when they become bland. This results in a more generalized contact of the quid with the oral mucosa, perhaps leading to its generalized involvement in OSF

Animal experiments and tissue-culture studies• In animal models the submucosal collagen showed altered staining similar to that seen in human OSF only in two rats, and therefore the investigators opined it was improbable that arecoline per se played any part in the causation of human OSF. They pointed out, however, that tissue changes brought about in animal systems by a test substance cannot be identically correlated to those in man.

•Tissue culture experiments using human fibroblasts suggested demonstrated that ethanolic extracts of three varieties of areca nut stimulated collagen synthesis to the extent of 170% over that in control cultures

•Interestingly, it was suggested that the addition of slaked lime to areca nut in pan (betel quid) hydrolyses arecoline to arecaidine . This means that the hydrolysis of arecoline could occur in the saliva as well as in fibroblasts. It was suggested that the inflamed oral mucosa has enhanced permeability to arecoline and arecaidine

Pathogenesis• Fibrosis and hyalisation of sub epithelial tissues account for most of the clinical features

•Increased collagen synthesis or reduced collagen degradation are possible mechanism in the development of the disease

• Numerous biological pathways are involved in the above processes and the normal regulatory mechanisms are either down regulated or up regulated at different stages of disease

Areca alkaloids causing fibroblast proliferation and increased collagen synthesis

•In vitro studies on human fibroblast using areca extracts or chemically purified arecolin suggest the theory of fibroblastic proliferation and increased collagen formation that is also demonstrable histologically in human OSMF tissue • Concentration dependent stimulation of collagen synthesis when fibroblast were exposed to both arecoline and arecaidine. The stimulation was always greater with arecaidine

•There is a correlation between the hydrolysis rates of different esters and the extent to which they stimulate collagen synthesis , suggest that hydrolysis of arecoline in arecaidine is necessary before fibroblast stimulation. This suggest that arecaidine is the active metabolite for fibroblats prolliferation

Flow chart : Role of areca nut in oral submucous fibrosis (Ghom & Mhaske, 2008)

Areca nut

Fibroblast prolieration

Alkaloids

Arecoline etc

trauma Flavanoids copper

chewing tanins, catechins

inflammation

Growth factorsStabilization cross linking

Increased collagen synthesis Decreased phagocytosis

Collagen accumulation

OSMF

Stabilization of collagen structure by tannins(and catachins polyphenols)

Treatment of reconstituted collagen fibrils and pieces of rat dermis with crude extracts of nut or purified tannins from areca nut increased their resistance to both human and bacterial collagenase

Possible mechanisms

•by reduced degradation of collagen by forming a more stable collagen structure

•tannin present in areca nut reduces collagen degradation by inhibiting collagenase

•It was postulated that the reason for high level of collagen production in OSMF because these fibroblast are a subset with increased potential among heterogenetic fibroblast

Copper in nut and fibrosis

•The copper content of areca nut is high and the levels of soluble copper in saliva may rise in volunteers who chew areca quid.

• The enzyme lysyl oxidase is found to be up regulated in OSMF . This is a copper dependent enzyme and plays a key role in collagen synthesis and its cross linkage

• The fibroblast in OSMF have not only increased lysyl oxidase activities but also specific growth characteristics. This was evident with reported cell doubling time of 3.2 days for OSMF and 3.6 days for normal fibroblast

Upregulation of cyclo-oxygenase (Cox-2)

•It is known that OSMF is associated with inflammatory changes in at least some stages of the disease. Prostaglandins is one of the main inflammatory mediators and its production is controlled by various enzymes such cyclooxygenase (COX)

Experimental Finding• Immunochemistry : increased expression of the enzyme COX-2 in moderate fibrosis and this disappeared in advanced fibrosis

• Compatible with the histology of the disease as there is lack of disease in advanced disease.

Fibrigenetic cytokines• Changes in cytokines secretion in OSF has been investigated. Endothelin and tgf β-1 estimated by radioimmunoassay and ELISA respectively were increased in OSF fibroblast compared to fibroblast of normal individuals. Therefore it has been postulated that external stimuli such as areca nut may induce the development of the disease by increased levels of cytokines in the lamina propria• It has been shown that there has been increased expression of fibrogenic cytokines namely TGF-β, PGDF and bFGF in OSF tissues compared to normal

•These observation suggest that disease process in OSMF may be an altered version of wound healing as our recent finding show that the expression of various ECM molecules are similar to those seen in maturation of granulation tissue

Genetic polymorphism predisposing to OSMF

•Polymorphism of the genes coding for TNF-α has been reported as a significant risk factor for OSMF

•TNF-α is known to stimulate fibroblastic proliferation in vitro providing evidence for an active role for TNF-α in the pathogenesis of OSMF

Inhibition of collagen phagocytosis

• Degradation of collagen by fibroblast phagocytosis is an important pathway of physiological remodeling of extracellular matrix (ECM) in connective tissue. OSMF shows a gross imbalance in ECM remodeling

• Reduction of phagocytic cell was strongly related to arecoline levels in fibroblast culture

• Dose- dependent enhancement of phagocytic cells when the cultures were treated with corticosteroids

Stabilization of extracellular matrix

• Increased and continuous deposition of extracellular matrix may take place as a result of disruption of the equilibrium between matrix metalloprotinases (MMPs) and tissue inhibitors of matrix metalloproteinase (TIMP)

• Although the main pathological change present in OSMF appears to be markedly increased production of extracellular matrix (ECM), there is little information on actual remodeling of connective tissue with the progression of the disease

• The patterns of expression of several molecules were investigated in various phases of the disease. It was apparent that the expression of teascin disappeared when the lesion advanced from early to intermediate phase

• Heparin sulphate proteologlycans, fibronectin type III collagen and elastin appeared in the early and intermediate phases but there was complete replacement by collagen type I when the lesion progressed to an advanced phase. The pattern of expression of most of these molecules followed a similar pattern to the organization of granulation tissue

Collagen related genes

• Collagen related genes play an important role in homeostasis of collagen in the body. As OSMF is a disease with disregulation of collagen metabolism,

• There is evidence to suggest that collagen related genes are altered due to ingredients in quid. The genes Col1A2, Col3A1, Col6A3 and Col7A1 have been identified as definite TGF-β targets and induced in fibroblast at early stages of the disease

• The transcriptional activation of procollagen genes by TGF-β suggest that it may contribute to increased collagen levels in OSMF

Precancerous nature and malignant transformation

• Pindborg in 1972 put forward five criteria to prove that disease is precancerous

1. High occurrence of OSMF in in oral cancer patients2. Higher incidence of SCC in patients with OSMF3. Histological diagnosis of cancer without any clinical suspicion in OSMF4. High frequency of epithelial dysplasia5. Higher prevalence of leukoplakia among OSMF cases

• Recently, the carcinogenicity of areca nut without tobacco was identified

• The strong association of areca nut with OSMF , its dose dependent effects and confirmation of OSMF as potentially malignant disease leading to oral cancer provided further evidence for this assertion

References

Oral submucous fibrosis: Review on aetiology and pathogenesisTilakaratne, W.M. et al.Oral Oncology , Volume 42 , Issue 6 , 561 - 568

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