Inhibition of pancreatic α-amylase activity by a 2 weight-loss herbal formula RCM-107 3

14 Reducing carbohydrates digestion by having low glycaemic index (GI) foods has been linked to 15 weight loss. Inhibiting related enzymes is an alternative way to decrease carbohydrate digestion. 16 RCM-107, an eight-herb formula that is modified from the RCM-104, has indicated significant 17 weight-loss action in clinical trials. However, no research has been conducted to study its effect on 18 the activity of porcine pancreatic alpha-amylase (PPA), which is involved in carbohydrate 19 absorption. In this paper, we used fluorescence PPA inhibition assay to investigate the inhibitory 20 effects of RCM-107 and the individual herbs present in this herbal mixture on amylase activity. 21 Subsequently, molecular docking predicted the key active compounds that may be responsible for 22 the enzyme inhibition. According to our results, both the RCM-107 formula and several individual 23 herbs displayed α-amylase inhibitory effects. Also, marginal synergistic effects of RCM-107 were 24 also detected. In addition, alisol B, (-)-epigallocatechin-3-gallate (EGCG) and plantagoside have 25 been predicted as the key active compounds that may be responsible for the α-amylase inhibition 26 effect of RCM-107 according to inter-residue contact analysis. Finally, Glu233, Gln63, His305, 27 Asp300 and Tyr151 are predicted to be markers of important areas with which potential amylase 28 inhibitors would interact. 29


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Obesity has been defined as a chronic disease by the Obesity Society (TOS) in 2018 due to its 33 emerging epidemiological trend [1]. It increases the risk of developing other metabolic disorders 34 such as hypertension, type 2 diabetes, cardiovascular diseases and myocardial infarction [2,3]. At 35 least 2.8 million adults die due to being overweight or obese each year [4]. Globally, over 1.9 billion 36 adults were overweight while more than 650 million adults were obese in 2016 [4].

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Currently there is a variety of therapeutic targets available for weight reduction, such as 38 pancreatic lipase, alpha-amylase, glucagon like peptide-1 (GLP-1) receptor and serotonin 2C 39 receptor [5][6][7]. Along with the general reduction in use of appetite suppressants which act on the 40 central nervous system (CNS), eg: fenfluramine, d-fenfluramine and rimonabant [5], drugs that act 41 on the periphery have gained wider use [5]. Some periphery-acting drugs have proven successful in 42 weight management with mild intolerances, especially those which reduce the digestion and 43 absorption of nutrients [6].

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In humans, various forms of carbohydrates account for between 40% to 80% of total caloric 45 intake [5,6]. Low GI foods (GI value < 55), polymeric form of carbohydrates that are absorbed 46 slowly, have been linked to glycemic control and weight loss [8]. An alternative to low GI foods are 47 products that can decrease carbohydrate absorption via suppressing related enzymes such as 48 pancreatic α-amylase [6,8]. Αlpha-amylase is responsible for catalysing the hydrolysis of α-(1, 49 4)-glycosidic linkages of starch components and glycogen. Therefore, suppressing this enzyme could 50 result in a general decrease of the main dietary carbohydrates absorption [5]. The known 51 alpha-amylase inhibitors such as acarbose have been used as an off-label agent to assist weight loss 52 [9]. In addition, the supplement Phase2 ® Phaseolus vulgaris white bean extract demonstrated 53 weight-loss effects in human clinical trials via its amylase inhibitory activity [     143 macromolecules (target proteins) required to initiate structure-based virtual screening were 144 obtained and pre-processed as follows.

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The structures of small molecule were obtained from Pubchem or TCMSP. The RCM-107 formula and 6 individual herbs present in this formula displayed significant PPA 169 inhibitory activities after screening at 300µ g/mL (Figure 1). The RCM-107 formula exhibited the 170 highest inhibition rate followed by Gardeniae fructus (64%), lotus leaf and green tea (60%, 54% and 171 51%, respectively). However, our data has shown that differences between those three herbs and the 172 RCM-107 formula were not statistically significant (P > 0.05). Sophorae flos did present significant 173 PPA inhibition (P < 0.0001) but at a much lower inhibition rate (29%) compared to the above four 174 samples. In addition, Cassiae semen and Plantaginis semen displayed an inhibition rate of 17% and 175 16%, respectively and were statistically significant (P < 0.05).

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Only two single herbs Poria and Alismatis rhizome were statistically non-significant (P > 0.05) on 177 PPA. Alismatis rhizome slightly increased the enzyme activity rather than suppressing it. Even

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It is worthy to note that RCM-107 is an 8-herb combination at 2:1(w/w) ratio, in which the 189 proportion of green tea is 2-fold higher than the other 7 herbs in this formula, due to its role as a key    (Table 1).

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The present work examined the alpha-amylase inhibition of the herbal formula RCM-107 and 278 its constituent herbs, and showed that the RCM-107 can be applied as an effective α-amylase