Impact of Anticholinergic Medication on Salivary Function; Exploring Potential Genetic Markers for Dry Mouth

The growing medication use in all ages led to the fact that 20% of the US adult population take five or more drugs (polypharmacy). Over 500 medications commonly prescribed in polypharmacy (e.g., antidepressants, urinary antispasmodics, and psycholeptics) possess anticholinergic (AC) properties blocking the muscarinic signaling of neural regulation. Due to the scattered distribution of muscarinic receptors in the body, AC medications have a wide range of side effects. Besides the most severe central toxicity of cognitive impairment, dyskinesia, and psychosis, which can lead to delirium, the most frequent peripheral side effect is dry mouth. Dry mouth is characterized by reduced saliva secretion (hyposalivation), impaired quality of life by causing chewing or swallowing problems, complaints of oral dryness (xerostomia), speaking difficulties, mucosal changes, increased rate of dental caries, and tooth loss. Dry mouth causes increased susceptibility to bacterial colonization and infections in the oral cavity and the upper respiratory tract. However, no data are available on predicting medication-induced dry mouth severity or determining the AC burden from these medications among dental patients. There is a significant research gap in identifying high-risk xerostomia patients in the middle-aged population before reaching older ages when damage to oral health is irreversible. We designed a prospective cohort study with two aims for addressing these questions. In Aim 1., we will evaluate the correlation between AC burden and dry mouth outcomes, including the flow rates of the minor salivary glands (SG) in 90 middle- aged patients (45-64 years). We will determine whether high AC burden, quantified by the AC drug score (ADS) and serum AC activity (SAA) in blood, is associated with more severe dry mouth symptoms, measured at baseline and follow-ups for two years. We will assess dry mouth using saliva flow rates (unstimulated whole saliva and minor SGs) and oral health measures associated with dry mouth, including xerostomia, dental caries, and oral health impact profile. In this aim, we will examine the feasibility of minor SG flow screening as a point- of-care test for dry mouth. In Aim 2., we will explore whether CYP450 genetic polymorphisms predict dry mouth severity. Recent studies reported an increased prevalence of AC side effects in patients with inactive genetic variants of liver cytochrome P450 enzymes responsible for the metabolic clearance of AC drugs. We will analyze DNA from patients’ blood for the genetic variations of CYP2D6 and CYP2C19 enzymes and compare oral health outcomes associated with dry mouth between poor and normo-metabolizing phenotypes. We propose to study whether dry-mouth pharmacogenetics provides evidence for inter-individual variability in oral health outcomes to identify patients with predictable severity of AC medication-induced dry mouth. The overarching goal of our explorative study is to establish clinically relevant associations between AC burden and oral health outcomes, which can support future investigations of potential causal relationships and risk calculations for dry mouth development.