HPV associated oral lesions

 

Human papilloma virus (HPV) has a wide spectrum of diseases that affect the body's cutaneous and mucosal regions, from mild popular warts to invasive carcinoma. The most common sexually transmitted infections are caused by the human papilloma virus ( HPV). Two thirds of people who have unprotected sex with an HPV carrier are estimated to be infected.

Because HPV has epithelial tissue tropism, it can affect the skin as well as the mucosa. It causes various types of damage, from asymptomatic infection and mild warts to invasive injury. A wide range of anatomical sites have reported HPV infection: genital and anal tract, urethra, upper airways, tracheobronchial mucosa, nasal paranasal cavities, and oral cavity. Depending on the diagnostic method used, HPV on oral mucosa currently affects 1% to 43% of the general population and may even be linked with oral malignancies[1].

The purpose of this review article is to provide an updated review of HPV to the academic community, underlining its relevance as a public health issue. This review includes HPV epidemiology, virology definition of different oral lesions, clinical illustration, oncogenesis and resources for diagnosis. We have looked at current treatment options and prophylaxis, as well as HPV vaccines[2].

 

Core material

Among the most common oral lesions are the benign HPV lesions. Interestingly, although both SP and CA are caused by HPV 6 and 11 subtypes, due to differences in clinical and histological manifestations, they are distinct entities in head and neck literature. This is contradictory to genitourinary physiology, where "squamous papilloma" signifies an HPV-unrelated lesion[3].

Common oral pathology texts refer to CA as a sexually transmitted infection whereas there is no such distinction for SP. This can cause clinician misunderstanding, especially with pediatric patients where the appearance of an HPV-related lesion can suggest sexual abuse. Since it is understood that HPV 6 and 11 can be transmitted sexually, there is concern about the detection of a lesion in either appearance. However, it is important to remember that other transmission modes are possible. Recent studies have found that even at anogential sites a minority of these lesions are caused by sexual abuse, with the risk of violence rising with the child's age[4].

Oral human papillomavirus infection

If oral mucosa is considered normal, the epithelium can serve as an HPV container that is activated at some point in time and causes injury. An immense number of oral diseases may be associated with oral HPV, but they rarely cause lesions. Lesions can range from the far more common benign warts to malignant injuries[5].

transmission

Many studies have spoken about transmission of HPV but the mechanisms involved remain unknown. Unprotected sexual intercourse is its leading cause, particularly oral-genital penetration, when the virus infects the genital mucosa, which will be clinically and subclinically present in adolescents and adults alike. Early sexual intercourse, a large number of sexual partners, fertility, smoking and another sexually transmitted infection may increase the rate of viral infection[6].

Direct skin-skin contact and self-inoculation may convey oral HPV. Transmission of the upper airway has still not been established[7].

Infant HPV is transmitted mainly at birth via maternal cervix infection. And the chronic papillomatosis of the laryngeal tends to be acquired by this way. However, mother-fetus is another transmission route, before, during or after childbirth, which can be made possible by infected amniotic fluid and umbilical cord blood[8].

Methods of detecting HPV in the oral mucosa.

-         Morphological methods, including assessment of signs of HPV-induced changes by clinical or microscopic inspection of exfoliated cells, biopsy samples or both;

-         Viral nucleic acid detection;

-         Detection of HPV reaction by anticorps.

Serologic procedures, however, have no proven role in the diagnosis of individual patients with HPV infections. Our work team23 recently demonstrated that there is no type-specific concordance between oral detection of HPV DNA and serum HPV antibodies.

Cytology and histopathology.

The actual presence of HPV is not represented in cytology and histopathology. Both are secondary methods for detecting an HPV infection 's clinical sequelae. Cervical cancer screening is done by doctors by cytological analysis of cervical smears for abnormal cells and precancerous lesions. Cytology was also used to treat oral precancers and cancers. Meta-analysis in the literature, however, suggested that cytological screening is not effective for oral precancer and cancer. To date , researchers have not performed any studies merely to diagnose particular cellular modifications caused by HPV such as koilocytosis or hyperkeratosis. One explanation for this may be that oral mucosa is often subjected to mechanical trauma that induces hyperkeratosis or cellular vacuolization, mimics the cellular changes caused by HPV, leading to false-positive interpretations[9].

THE ONCOGENIC MECHANISM

The carcinogenesis process of the HPV isn't fully understood. HPV can create immortality in keratinocytes and works alone even if separate cofactors are required for malignant conversion, yet not fully located.

In the case of HPV infection at high risk and under optimal conditions, the viral genome is inserted into the host genome, which is the required occurrence for the immortality of the keratinocytes. During this integration process, the circular shape of the viral genome splits at the level of the regions E1 and E2, never at the level of the region E6 or E7. Different studies have shown that the integrated part of the genome corresponds to E1, E6, and E7 whereas the regions from E2 to E5 are lost and not transcribed in the tumours. The loss of E2 during this integration cycle causes the loss of power by E6 and E7. Consequently, the E6 and E7 sequences are directly involved in the cell cycle by inhibiting the normal functions of p53 and pRb, respectively. The protein p53 is known as the "Genome 's Guard," and in the case of DNA damage, the p53 that cause cell division to be halted and provide the time needed to repair DNA. 

If the damage can not be reversed, p53 can cause the programmed cell death and prevent the spread of DNA damage in subsequent cell generations. In the case of other tumor types, p53 is typically mutated and functions as a strong oncogene. In the case of HPV infection, E6 suppresses the properties of the product of the p53 gene, obtaining the functional equivalent of the two hits needed to knock out both tumor suppressor gene alleles. The p53 mutations are not normally found. The protein E7 interacts with the protein from retinoblastoma (pRb), which is the crucial factor for the regulation of the cell cycle. This association causes the release of the E2F transcription factor, which is now free to act and may induce the division of cells. E7 can also bind and inactivate the protein kinase inhibitors p21 and p27, and can interact with various proteins whose significance has not yet been identified. Figure 1 provides a diagrammatic representation of oral carcinogenesis caused by HPV [10].

DIAGNOSTIC METHODS TO DETECT HPV INFECTIONS

Diagnostic laboratory tests for HPV has not been available until recently, because the virus does not emerge in tissue cultures or in laboratory animals. Currently, scientists have isolated more than 120 different types of HPV with the recent technological advances in molecular biology testing techniques.

Light microscopy

Papillomaviruses cause epithelial proliferation with epithelial thickening, conspicuous granules of keratohyalin, acanthosis, and sometimes hyperkeratosis. In exfoliated cells and biopsy specimens, koilocytes indicate the presence of active HPV infection. They are squamous epithelial cells which exhibit perinuclear clearing and an increased cytoplasm density. Nuclear atypia (enlargement) hyperchromasia and double nucleation of superficial and intermediate cells are the hallmarks of successful HPV infection[11] but infection susceptibility is lower than the molecular methods discussed below.

Electron microscopy

In successful HPV infections, viral particles may be shown but HPV typing can not be achieved. HPV particles have been identified under electron microscopy in a variety of oral squamous cell lesions, suggesting their etiology for HPV. The virions in the nuclei of koilocytic and dyskeratotic cells were identified. But as a diagnostic method of HPV infection, electron microscopy is laborious , time-consuming, and restricted to active HPV infections only.[12] It is impossible to detect non-productive HPV infections that are usually caused by high-risk types.

Molecular methods

Molecular methods can be broadly categorized between non-amplified systems, and those that use amplification. No amplification is required by in situ hybridization (ISH) / Dot Blot (DB) and Southern Transfer Hybridization (STH). Amplification strategies can also be classified into three different categories: (1) reference amplification in which the assay duplicates DNA fragments from a given sequence of genes. PCR works by target amplification; (2) signal amplification, in which a compound-sample or branched-sample technology increases the signal generated from each probe. Hybrid capture operates by amplification of the signal; and (3) Sample amplification, in which the molecule of the detector itself is amplified (e.g., ligase chain response). To date, target and signal amplification techniques have been applied to the identification of HPV, in addition to non-amplified techniques[13].

Nonamplified techniques

ISH in situ hybridization can be conducted directly on biopsies to allow localization of the target sequences and compatibility with the clinical appearance and histopathology. ISH may confirm the presence of histologically equivocal lesions in biopsies that have been caused by HPV. This method can be used to study the viral transcription and incorporation in fixed tissue. Since ISH detects 25 or more HPV-DNA copies per cell, high-grade lesions that often produce lower amounts of viral HPV-DNA are ridiculous with this technique[14].

Target amplification

PCR is the most widely used tool for the detection of HPV DNA. PCR has more clearly defined the natural history of the HPV infection. In principle, PCR will take a single double-stranded piece of DNA and amplify it after 30 cycles to 1 billion copies.[48] PCR is often used as a diagnostic tool in HPV epidemiological investigations, but the related costs and equipment specifications are often impractical for broad screening programmes. The PCR-based methodology 's inherent strength lies in its capacity to detect very small amounts of HPV DNA. At the same time, strict laboratory procedures and controls are critical in reducing false-positive findings related to contamination[13].

Signal-amplified techniques

Hybrid Capture Technology

Hybrid capture technology (HC), developed by Digene Corporation, specifically detects nucleic acid targets, using signal amplification to provide equal sensitivity to target amplification methods (PCR). Digene developed two HPV detection products: the first-generation Hybrid Capture Tube (HCT) test and the second-generation Hybrid Capture II (HC II) assay.

Gene Expression: DNA Microarray

DNA microarray is a collection of microscopic DNA spots per covalent attachment to a chemical matrix on a solid surface. Each gene is normally less than 200 μm in diameter on the solid supports referred to as the spot or probe. Growing spot has a unique sequence in the series that is distinct from the others, and will only hybridize to its complimentary strand. This technique uses a DNA probe that is either labelled with a radioisotope or a fluorescent sticker. The probe is applied to the fragment of the DNA or RNA to be studied and "sticks" to its complementary sequence by the rules of base pairing (A to T, C to G). This technology has enabled the miniaturisation of DNA probe detection methods and the detection of several thousand DNA or RNA sequences in one experiment[15].

Conclusion

Recently, HPV has gained a lot of interest as it is regarded as significant markers of cervical cancer. Oral HPV infections have not been investigated to the same degree as genital tract infections, while proof of interaction between certain tumors and HPV infection is unquestionable today. Oncogenic HPVs are associated with oral malignancies but, in different studies, their occurrence varies widely. Although the results of the study are ambiguous, it appears possible that smoking and alcohol use might interfere with HPV infection to increase the risk of oral cancer in an individual. Oral HPV infections also need to be researched and investigated in depth so that they can direct us towards possible cancer prevention strategies, including oral HPV vaccination for oral HPV infections

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