Effects of statins on regeneration of olfactory epithelium

Potential pharmacologic treatments for COVID-19 smell and taste loss: A comprehensive review

The acute loss of taste and smell following COVID-19 are hallmark symptoms that affect 20-85% of patients. However, the pathophysiology and potential treatments of COVID-19 smell and taste loss are not fully understood. We searched the literature to review the potential pathologic pathways and treatment options for COVID-19 smell and taste loss. The interaction of novel coronavirus with ACE-2 receptors expressed on sustentacular cells and taste buds results in direct damage to the olfactory and gustatory systems. Also, the invasion of the virus to the olfactory neurons and consequent local inflammation are other proposed mechanisms. Therefore, COVID-19 patients with smell or taste loss may benefit from neuroprotective, anti-inflammatory, or depolarizing agents. Based on the current evidence, phosphodiesterase inhibitors, insulin, and corticosteroids can be promising for the management of COVID-19 smell and taste loss. This review provided crucial information for treating COVID-19-related smell and/or taste loss, urging to perform large clinical trials to find optimum treatment options.

Mechanisms Linking Olfactory Impairment and Risk of Mortality

Olfaction is a sense involved in a complex set of tasks, influencing eating behavior, increasing awareness of environmental hazards and affecting social communication. Surprisingly, smell disorders are very frequent, especially in the elderly population. Several recent studies conducted mostly in older subjects have demonstrated a strong association between olfactory impairment and overall mortality risk, with anosmia being even more predictive of 5 years mortality risk than cardiovascular disease. Presently, the underlying pathophysiology linking olfactory impairment to mortality remains unknown and only putative mechanisms are suggested. This review aims to examine the link between olfactory impairment and mortality and to discuss existing ideas on underlying existing mechanisms including, (1) the effect of olfactory loss on nutrition, life-threatening situations and social interactions, (2) associated neurodegenerative diseases, (3) accelerated brain aging, and (4) reflection of general health status being reflected in olfactory function.

Effects of statins on the recovery of olfactory function in a 3-methylindole-induced anosmia mouse model

BACKGROUND

Despite the importance of olfactory function, no effective medications have been identified to treat olfactory disorders. This study was performed to evaluate the functional recovery of olfaction damaged by 3-methylindole (3MI) in a mouse model with hydroxymethylglutaryl-coenzyme A reductase inhibitors (statins).

METHODS

In a randomized placebo-controlled trial, 24 healthy female BALB/c mice (aged 9-10 weeks and weighing 18-20 g each) were randomly allocated to statin-treated or control groups. Olfactory loss was induced by i.p. injections of 3MI. Atorvastatin (10 mg/kg) or normal saline was then administered per os with a gastric tube for 3 weeks. The effects of treatment were evaluated by food-finding tests and Western blot analysis.

RESULTS

Both groups showed complete losses of olfactory function 1 week after 3MI injection. Three weeks after 3MI injection, 9 of the 12 mice in the statin-treated group (75%) passed a food-finding test, in which they were able to find the food within 3 minutes, at least two times out of three trials. However, only two mice in the control group (16.6%) passed the food-finding test, and this difference was statistically significant (p = 0.004; chi-square test). The expression level of the olfactory marker protein was also elevated in the statin-treated group (p = 0.030; Wilcoxon rank sum test).

CONCLUSION

Statins are associated with recovery of olfaction after 3MI injection in a mouse model.

Effect of Simvastatin on Transforming Growth Factor Beta-1–Induced Myofibroblast Differentiation and Collagen Production in Nasal Polyp-Derived Fibroblasts

Background

Statins are the most commonly prescribed drugs for the treatment of hypercholesterolemia. Statins exert not only lipid-lowering but also other cellular effects, including antifibrotic properties. The purpose of this study was to determine the effect of simvastatin on transforming growth factor (TGF)-beta-1–induced myofibroblast differentiation and collagen production in nasal polyp-derived fibroblasts (NPDFs) and to verify the mechanism of the effect of simvastatin in TGF-beta-1–induced myofibroblast differentiation in NPDFs.

Methods

NPDFs were pretreated with simvastatin with or without mevalonate or Y-27643 for 2 hours before induction by TGF-beta-1. The expression of alpha-smooth muscle actin (SMA) and collagen type IV mRNA was determined by a reverse transcription-polymerase chain reaction, and the expression of alpha-SMA protein was determined by immunofluorescent cytochemical staining. Total soluble collagen production was analyzed by the SirCol collagen dye-binding assay (Biocolor, Belfast, U.K.). Phosphorylation of Smad 2/3 was evaluated by Western blot analysis.

Results

In TGF-beta-1–induced NPDFs, simvastatin significantly inhibited the expressions of α-SMA and collagen type IV mRNA and reduced alpha-SMA and collagen protein levels. Pretreatment with mevalonate reversed the effect of simvastatin. The expression of alpha-SMA mRNA and protein was significantly decreased by pretreatment with Y-27632. The TGF-beta-1–induced expression of pSmad 2/3 protein was notably decreased by pretreatment with simvastatin.

Conclusion

We showed that simvastatin inhibits TGF-beta-1–induced myofibroblast differentiation (expression of alpha-SMA) and collagen production in NPDFs and Rho/Rock and TGF-β/Smad signaling is involved as an underlying mechanism. The results of our study suggest that simvastatin is a possible candidate for the suppression of nasal polyp formation.