Multidrug resistance 1 gene polymorphism in amlodipine-induced gingival enlargement

Abstract

Gingival enlargement comprises any clinical condition in which an increase in the size of the gingiva is observed. It is a side effect associated with some distinct classes of drugs, such as anticonvulsants, immunosuppressant, and calcium channel blockers. Among calcium channel blockers, nifedipine causes gingival enlargement in about 10% of patients, whereas the incidence of amlodipine, a third-generation calcium channel blocker, induced gingival enlargement is very limited. Because the calcium antagonists, albeit to a variable degree, act as inhibitors of P-glycoprotein (P-gp), the gene product of multidrug resistance 1 (MDR1), and inflammation may modify P-gp expression. We hereby, report a case of amlodipine-induced gingival enlargement with MDR1 3435C/T polymorphism, associated with inflammatory changes due to plaque accumulation, in a 50-year-old hypertensive male patient. The genotype obtained for the polymorphism was a heteromutant genotype, thus supporting the contention that the MDR1 polymorphism may alter the inflammatory response to the drug.

INTRODUCTION

Medication-related gingival overgrowth has now metamorphosized as drug-induced gingival enlargement. Drugs associated with gingival enlargement can be broadly categorized into: Anticonvulsants, antihypertensive calcium channel blockers, and immunosuppressants.[1,2] The pathogenesis of drug-induced gingival enlargement is uncertain, and there appears to be no unifying hypothesis that links together the three commonly implicated drugs.[1,2] As a matter of fact, the pharmacologic effect of each of these drugs varies but all of them seem to act in a similar fashion on secondary target tissue, that is, the gingival connective tissue, causing common clinical histopathological findings.[2,3] Furthermore, this condition occurs exclusively in the gingival tissues associated with teeth and is not seen in edentulous areas, thus lending support to the contention that local factors like plaque work synergistically with the offending drug in inducing drug-induced gingival enlargement.

Amlodipine which is used to control hypertension and angina occasionally associated with gingival enlargement.[2,3] As the calcium antagonists act as inhibitors of P-glycoprotein (P-gp) to a variable degree, the genetic product of multidrug resistance 1 (MDR1) and inflammation may modify the P-gp expression.[3] Pharmacogenomics and pharmacogenetics studies have revealed that genetic polymorphisms of MDR1 are associated with alteration in P-gp expression and function. Further, 50 single nucleotide polymorphisms (SNPs) and 3 insertion/deletion polymorphisms have been found in the MDR1 gene and some of them, such as C3435T, have been identified to be a risk factor for drug-induced gingival enlargement.[4] The present paper reports a case of amlodipine-induced gingival enlargement with a detailed analysis for MDR1 gene polymorphism.

CASE REPORT

A 50-year-old male patient reported with a chief complaint of swollen and bleeding gums to the Department of Oral and Maxillofacial Pathology, Dr. Harvansh Singh Judge Institute of Dental Sciences, Chandigarh. The patient was hypertensive for 2 years, and he was under treatment with amlodipine (05 mg/day, single dose orally). Intraoral examination revealed a firm, resilient, pale pink generalized gingival enlargement involving the attached, interdental and marginal gingiva of the maxillary and mandibular teeth [Figure 1]. Local irritating factors like plaque were present surrounding the dentition. On probing, periodontal pockets were obvious (2.5 ± 1.3 mm). Bleeding on probing was detected which was in accordance with mild superimposed gingival inflammation. Based on clinical examination and drug history, a provisional diagnosis of combined gingival enlargement was made. Routine blood investigations were within normal limits. The histopathological examination of the incisional biopsy specimen revealed hyperplastic keratinized stratified squamous epithelium with elongated rete ridges [Figure 2]. The underlying connective tissue component exhibited evidence of hyperplasia with sparse inflammatory cells subepithelially.

Figure 1.

Diffuse gingival enlargement seen with respect to maxillary and mandibular gingiva

Figure 2.

Photomicrograph revealing hyperplastic stratified squamous epithelium with elongated rete ridges and fibrotic connective tissue with inflammation (H and E, ×10)

Based on history, clinical and histopathological findings, the present case was suspected as a combined type of gingival enlargement; a drug-induced one (amlodipine), associated with inflammatory changes. Oral prophylaxis was done, and oral hygiene instructions were given. Review after 1-week revealed resolution of gingival enlargement to some extent. At the following visit, gingivectomy was performed for the unwanted enlarged gingiva. Patient was prescribed mouthwash chlorhexidine gluconate 0.12% for 2 weeks. Patient was recalled after 3 months, which revealed no evidence of recurrence.

Since the gingival enlargement in the present case was associated with amlodipine, this prompted us to go in for appropriate pharmacogenetic studies. Written consent was obtained from the patient. 5 ml of the blood sample was collected from subject's antecubital vein under aseptic conditions in a polypropylene tube containing 100 μl of anticoagulant - 10% ethylene diamine tetraacetic acid. Genomic DNA was extracted using Phenol-chloroform method, diluted to 50 ng/μl concentration and stored at −20°C. The sample was genotyped for MDR1 3435C>T using custom TaqMan genotyping assay on a real-time thermocycler by allelic discrimination method (Bio-Rd TouchTM Thermocycler, California) and the same methodology was validated by performing direct gene sequencing. The genotype obtained for the polymorphism was a heteromutant (CT) genotype.

DISCUSSION

Amlodipine is a 3^rd generation dihydropyridine calcium antagonist that is used in the management of both hypertension and angina.[2] Jorgensen MG detected only mild hyperplasia and concluded that amlodipine did not induce gingival hyperplasia.[5] Ellis et al. first reported gingival sequestration of amlodipine and amlodipine-induced gingival overgrowth.[2,6] The mechanisms that trigger drug-induced gingival enlargement have not been completely understood, and although literature data are extensive, they are quite contradictory.[7] Some studies demonstrated that drugs associated with gingival enlargement are able to inhibit the production of extracellular matrix by gingival fibroblast and cell proliferation in vitro.[7,8] In contrast, others showed that the accumulation of proteins in extracellular matrix, particularly collagen, may occur due to an imbalance between the synthesis and the degradation of extracellular matrix, being the possible cause of the gingival enlargement.[7,9] Gingival enlargement has been proposed to have a multifactorial etiology involving an interaction of several factors. The major factors implicated in its etiology include drug metabolite interaction with the gingival fibroblasts, age, genetic predisposition, pharmacokinetic variables, drug-induced alterations in gingival connective tissue homeostasis and inflammatory changes.[1]

As a matter of fact, not all patients taking amlodipine develop gingival enlargement. Evidence suggests that genetic factors also might have a significant role in the pathogenesis of gingival enlargement and the patient's susceptibility to this unwanted effect.[10,11] A genetic predisposition could influence a variety of factors in the drug plaque-induced inflammation. These include gingival fibroblast functional heterogeneity, collagenolytic activity, drug metabolism, and collagen synthesis. It has been speculated that drug-induced gingival enlargement may occur due to differences in the cell cycle and metabolism of fibroblasts, including collagen synthesis and breakdown between responders and nonresponders resulting in individual's susceptibility to those drugs. It has also been shown that the functional heterogenicity exists in gingival fibroblasts in response to various stimuli.[2,7]

Inflammatory mechanism of drug-induced gingival enlargement includes the up-regulation of several growth factors and inflammatory cytokines such as interleukin-6 (IL-6), IL-1, IL-8, platelet-derived growth factor-β and transforming growth factor-β[7] A synergistic enhancement of collagenous protein synthesis by human gingival fibroblasts is found when these cells are exposed simultaneously to calcium channel blockers and elevated levels of interleukin-1β (a proinflammatory cytokine) in inflamed gingival tissues.[2] Furthermore, reduction of matrix metalloproteinases and augmentation of tissue inhibitors of matrix metalloproteinases is believed to influence the gingival enlargement development. Moreover, modulation of apoptosis could contribute to fibrosis in gingival tissues. It has been demonstrated that fiodulatio apoptosis is decreased in gingival enlargement and that this decrease may contribute to fibrosis.[7]

It also needs to be emphasized that as the calcium antagonists act as inhibitors of P-gp to a variable degree, the genetic product of MDR1 and inflammation may modify the P-gp expression, which is expressed in the endothelial layers of blood vessels obtained from healthy or inflamed gingiva. It is also found that deeper gingival pockets/pseudopockets existed in subjects treated with calcium antagonists (amlodipine) as compared to drug-free counterparts. It has been found that this drug-related side effect is associated with the MDR1 3435C/T gene polymorphism.[3]

CONCLUSION

The present case is an example of a drug-induced (amlodipine) gingival enlargement that might be associated with MDR1 3435C/T polymorphism, as well as inflammatory changes due to plaque accumulation. The MDR1 polymorphism may alter the inflammatory response to the drug. The definitive treatment to such cases being drug substitution which seems to be the easiest and safest norm, but having said that science today has advanced leaps and bounds and it is possible in today's day and age to determine individual SNP profiles to identify the differences in our DNA.