**1. Introduction**

In the past decades, rigorous research and management strategies have been implicated in tackling the menace of diabetes mellitus (DM) [1]. According to the International Diabetes Federation, the number of diabetic patients reached 463 million in 2019, and the numbers are expected to rise by 66% by 2045 [2]. DM is a metabolic syndrome characterized by a loss of capability to oxidize carbohydrates by individuals due to altered insulin production, low insulin production and desensitized insulin receptors [3]. The inefficiency in metabolizing carbohydrates causes a surge in glucose levels in the patients' blood. Monomeric carbohydrates can undergo non-enzymatic glycation towards proteins, nucleic acids and lipids [4].

Glycation is a non-enzymatic and spontaneous reaction. It is commenced by the reaction between reducing sugars carbonyl group with a free amino group, generally

**Citation:** Khan, M.S.; Alokail, M.S.; Alenad, A.M.H.; Altwaijry, N.; Alafaleq, N.O.; Alamri, A.M.; Zawba, M.A. Binding Studies of Caffeic and p-Coumaric Acid with α-Amylase: Multispectroscopic and Computational Approaches Deciphering the Effect on Advanced Glycation End Products (AGEs). *Molecules* **2022**, *27*, 3992. https:// doi.org/10.3390/molecules27133992

Academic Editor: Michael Assfalg

Received: 8 April 2022 Accepted: 27 May 2022 Published: 21 June 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

lysine's ε-amino group and α-amino group of the protein. The process forms complex adducts referred to as Schiff base [5]. The base undergoes Amadori rearrangement to form various complex compounds known as advanced glycation end products (AGEs) [6,7]. There are a series of events that results in cellular malfunctioning as a result of high glucose, and these are not fully elucidated, thereby attracting researchers across the globe. Amongst these, a major event is the formation of AGEs that can contribute to diabetic complications in different ways. Glycation of proteins results in AGEs formation, leading to many diabetic complications. Protein glycation alters their normal functioning in various ways, viz. disruption of molecular conformation, alteration of enzymatic activity, reducing degradation capacity and others. AGEs interaction with their cellular receptors plays a crucial role in the pathogenesis of diabetic complications [8]. AGEs formation further aids the formation of reactive oxygen species (ROS), which further damages the cellular antioxidant defense mechanism and increases the oxidative load [9]. AGE formation is augmented in diabetic conditions, especially in Type 2 DM [10,11]. Glycation contributes greatly to AGE formation; highly reactive C=O species such as 3-deoxyglucosone and methylglyoxal are generated in glycation, lipid peroxidation and polyol pathway of DM type II [12]. Accumulation of AGEs contributes to many chronic diseases such as diabetes, Alzheimer's disease, heart failure and many other life-threatening conditions [13]. Further AGEs interaction with RAGEs, their specific receptors causes an onset of an inflammation cascade and further increases the oxidative load in the cells. The cascade of inflammation involves the activation of several pathways involved in diabetes, such as the MAP kinase pathway, TNF-α, NF-Kb, etc. [14]. The toxic accumulations can further contribute to pathogenesis in diabetic conditions such as decreased ligand binding, altered enzymatic activities and immunogenicity [15].

α-Amylase is an essential enzyme in carbohydrate degradation and is linked with postprandial hyperglycemia in Type-II DM patients. The enzyme hydrolyzes carbohydrates and creates a glycemic environment in the bloodstream, aiding AGEs formation and thrusting diabetic complications [16]. Constraining these enzymes' activity can subdue blood glucose levels. Investigations have shown that α-amylase inhibition aids in regulating glucose levels [17]. Polyphenols, their derivatives and other naturally derived compounds show therapeutic potential against various diseases such as cancer [18–21], neurodegenerative disorders [22,23], diabetes [24,25] and many more.

Caffeic acid (3,4-dihydroxycinnamic) is one of the most abundant hydroxycinnamate present in plant tissues. Phenolic acid caffeine is prevalent in various food sources such as apple, cider, blueberries, etc., and beverages such as tea and coffee [26]. Caffeic acid is known to cross the brain barrier and is classified as an antioxidant, antibacterial and anti-cancer compound [27,28]. Similarly, Coumaric acid is an essential polyphenol that governs the synthesis of some other important polyphenolic compounds such as sinapinic, ferulic and caffeic acid [29,30]. CA also plays an important role in lignin synthesis and is an abundant dietary polyphenol present in apples, maize, tomato and wheat [31]. The present study was designed to explore the binding mechanism of polyphenols (caffeic/coumaric acid) to α-amylase. Our study was also extended to reveal the anti-glycation activities of these structures and their modes of action. Various spectroscopic, biochemicals and computational approaches were employed.
