Tyrosinase inhibition by a rare neolignan: Inhibition kinetics and mechanistic insights through in vitro and in silico studies

https://doi.org/10.1016/j.compbiolchem.2018.06.003Get rights and content

Highlights

  • 1 is as potent an inhibitor as the positive control, kojic acid against tyrosinase.

  • It inhibited tyrosinase in an uncompetitive manner.

  • Its inhibitory effects on α-glucosidase, AChE/BuChE were limited.

Abstract

Neolignans are a large group of polyphenols found in plants and exhibit a wide range of bioactivities including cytotoxicity, apoptosis inducer, antimalarial and antifungal effects, acetylcholinesterase, tyrosinase, and α-glucosidase inhibition. In this study we tested acetylcholinesterase (AChE), butyrylcholinesterase (BuChE), tyrosinase, and α-glucosidase inhibitory effects of a rare neolignan, (-)-4-O-methyldehydrodiconiferyl alcohol 9'-O-β-glucopyranoside (1) in search for its new pharmaceutical effects. This compound exhibited good tyrosinase inhibition with an IC50 value of 44.62 ± 3.99 μg/mL. Enzyme kinetics and molecular modelling studies were performed to provide insights into its tyrosinase inhibition mechanism.

Introduction

Neolignans are an important class of phenylpropane derivatives that widely distributed in the plant kingdom. They are derived from the shikimic acid biosynthetic pathway and exhibit a wide range of pharmacological properties such as cytotoxic, antibacterial, antioxidant, anti-inflammatory, anti-diabetic, neuroprotective, and anti-acetylcholinesterase effects (Teponno et al., 2016; Salleh et al., 2016).

Diabetes Mellitus (DM) is a degenerative disease characterized by chronic hyperglycemia. Approximately % 8.8 of world adult population (20–79 years of age) has DM, which leads to life threatening health complications, such as cardiovascular diseases, nephropathy, and neuropathy, which can be delayed or prevented by management of high glucose level (ADA, 2009; Brownlee, 2005; IDF, 2017). α-Glucosidase inhibitors are used for the treatment of DM however, side effects such as gastrointestinal system disturbances are very common (Kalra, 2014). Therefore, it is important to search for new potent α-glucosidase inhibitors with fewer side effects.

Neurodegenerative disorders are usually associated with neuron loss in the central nervous system (CNS). As the two most common neurodegenerative disorders, Alzheimer’s disease (AD) and Parkinson’s disease are usually seen among the elder population and owing to extending lifespan, the prevalence of both disorders is expected to rise in the next few decades. However, effective treatments are still lacking. Accumulation of extracellular senile plagues, intracellular neurofibrillary tangles, and acetylcholine deficiency are considered to underlie the AD pathophysiology. Acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) are two sister enzymes that catalyze the hydrolysis of acetylcholine, which is lower in the brains of AD patients than healthy people. Furthermore, AChE and BuChE play an important role in β-amyloid aggregation (Yacoubian, 2016; Chopra et al., 2011). The cholinergic hypothesis is a well-accepted strategy for the symptomatic treatment of AD and for this reason, AChE and BuChE inhibitors are known to be important targets in drug discovery challenges for AD (McGleenon et al., 1999). Parkinson’s is another common neurodegenerative disease marked by progressive and slow loss of dopaminergic neurons containing neuromelanin (Braak et al., 2004). Tyrosinase is involved in development of Parkinson’s disease by causing neurodegeneration through increasing dopamine level, inducing high production of melanine and in turn, triggering cell death in the brain (Xu et al., 1997). Tyrosinase catalyzes the hydroxylation of tyrosine to L-DOPA and the oxidation of the L-DOPA to dopaquinone. This enzyme plays key role in formation of melanin pigments which can cause hyperpigmentation and lead to esthetic problems and melanoma. Thus, tyrosinase inhibitors are also important for the treatment of skin disorders associated with excessive melanine production (Parvez et al., 2007; Solano, 2014).

Natural products have been promising model compounds for discovery and design of many novel drug molecules. Medicinal plants and their components were reported to exert cholinesterase, tyrosinase, and α-glucosidase inhibitory effects in numerous studies (Parvez et al., 2007; Murray et al., 2013; Şöhretoğlu et al., 2017, 2018). In this regard, we aimed to investigate AChE, BuChE, tyrosinase, and α-glucosidase inhibitory properties of a rare neolignan, (-)-4-O-methyldehydrodiconiferyl alcohol -9'-O-β-glucopyranoside (1), which we previously isolated from Potentilla recta L. (Rosaceae) (Şöhretoğlu and Kırmızıbekmez, 2011). Upon molecular modelling we tried to predict possible allosteric binding sites on mushroom tyrosinase X-ray structure and provide details about inhibition mechanisms of 1 and some other known non-competitive inhibitors at molecular level.

Section snippets

General experimental procedures

The isolation and structural characterization of 1 was previously described [17]. Acarbose, AChE from electric eel, acetylthiocholine iodide (AChI), BuChE, butyrylthiocholine iodide (BChI), 5,5-dithio-bis(2-nitrobenzoic)acid (DTNB), galantamine, α-1,4-glucosidase (maltase) from Saccharomyces cerevisiae, kojic acid, L-3,4-dihydroxyphenylalanine (L-DOPA), methanol, p-nitrophenyl-α-glucopyranoside (4-pNPG), trisma-base and tyrosinase from mushroom were purchased from Sigma-Aldrich (St. Louis, MO).

Inhibition of α-glucosidase, AChE/BuChE, and tyrosinase

In vitro inhibitory properties of 1 against α-glucosidase, AChE, BuChE, and tyrosinase were tested in vitro using acarbose, galantamine, and kojic acid as positive controls. The IC50 values of 1 against α-glucosidase, AChE, BuChE, and tyrosinase are summarized in Table 1. According to the results, 1 showed very little inhibition against α-glucosidase, AChE, and BuChE. However, its tyrosinase inhibition was as potent as that of kojic acid.

To understand the inhibitory mechanism and calculate the K

Conclusions

So far, there has not been any information available regarding biological effects of 1, a rare neolignan derivative. So, in the present work we report, for the first time, the α-glucosidase, AChE/BuChE, and tyrosinase inhibitory effects of this compound. Furthermore, tyrosinase inhibitory effects of neolignans are very limited and for the first time, our research provided insights into binding mechanism of 1 to mushroom tyrosinase using in vitro enzyme inhibition kinetics and molecular

Conflict of interest

The authors have declared that there is no conflict of interest.

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