Preprints (www.preprints.org) | NOT PEER-REVIEWED | Posted: 2 August 2018 doi:10.20944/preprints201808.0032.v1 1 Type of the paper: Review 2 3 Physiological effects of caffeine and its congeners 4 present in tea and coffee beverages 5 6 I. Iqbal1, M. N. Aftab2, M. A. Safer3, M. Menon4, M. Afzal5⌘ 7 1Department of Life Sciences, Lahore College for Women, Lahore, Pakistan 8 2Institute of Biochemistry and Biotechnology, Government College University, 9 Lahore 54000, Pakistan 10 3Department of Biological Sciences, Faculty of Science, Kuwait University, Kuwait 11 4Plamer University (West Campus) San Jose, CA 12 5Department of Biological Sciences, Faculty of Science, Kuwait University, Kuwait 13 ⌘ Correspondence: [email protected], Tel. +1 352 681 7347 14 15 16 Running title: Caffeine 17 18 19 20 21 22 23 Corresponding author: 24 M. Afzal, 25 10547 NW 14th PL. 26 Gainesville, FL. USA 27 email: [email protected] 28 Tel. +1 352 681 7347 29 30 1 © 2018 by the author(s). Distributed under a Creative Commons CC BY license. Preprints (www.preprints.org) | NOT PEER-REVIEWED | Posted: 2 August 2018 doi:10.20944/preprints201808.0032.v1 31 Abstract: Tea and coffee are the most commonly used beverages throughout the 32 world. Both decoctions are rich in small organic molecules such as 33 phenolics/polyphenolics, purine alkaloids, many methylxanthines, substituted 34 benzoic and cinnamic acids. Many of these molecules are physiologically 35 chemopreventive and chemoprotective agents against many severe conditions such 36 as cancer, Alzheimer, Parkinsonism, inflammation, sleep apnea, cardiovascular 37 disorders, bradycardia, fatigue, muscular relaxation, and oxidative stress. Caffeine, a 38 purine alkaloid, is a common metabolite of both tea and coffee aqueous decoctions 39 and its concentration in tea/coffee depends on the fermentation process, 40 preparation of the water extract and quality of tea leaves/coffee beans. A 250 ml of a 41 coffee cup contains 100-150 mg caffeine while the same volume of strong tea 42 contains 25-40 mg caffeine. The present paper presents the potential of caffeine as 43 a potent chemopreventive agent that can be used for numerous physiological 44 disorders. 45 46 Keywords: Caffeine, methylxanthine, chlorogenic acid, caffeic acid, inflammation, 47 antimutagen, anticancer, antioxidant. 48 49 50 51 2 Preprints (www.preprints.org) | NOT PEER-REVIEWED | Posted: 2 August 2018 doi:10.20944/preprints201808.0032.v1 52 1. Introduction 53 Caffeine from cocoa beans was first discovered in Ethiopia, and since then it has been 54 a part of the global history for thousands of years. German scientist Friedrich Ferdinand 55 Runge was the first to isolate pure caffeine in 1820 and the word caffeine is derived from 56 the German word ‘Kaffee’ and the French word ‘Café.' Since then, the psychoactive 57 substance caffeine is one of the most researched medications with more than 30,200 58 research publications. During 2016 more than 2000, while in 2017 in access of 1200, and 59 in 2018 till March, more 300 publications have appeared on different aspects of caffeine. 60 This data shows the global research interest in caffeine and related methylxanthines. On a 61 daily basis, around the world, more than two billion cups of tea and coffee are consumed 62 making it the most frenzied beverage after water and the second most traded commodity 63 after oil when both are deliberated as black gold. Due to its diverse pharmacological 64 activities, caffeine merits a focus for further scientific research. 65 The black decoction of coffee contains hundreds of compounds, the composition, and 66 concentration of which depends upon many factors including cultivar, the origin of coffee 67 and the method of its preparation. Roasting of coffee beans results in about 1000 volatile 68 compounds, and 35 aroma compounds and caffeine is a common metabolite in both tea 69 leaves and coffee bean. On the average, tea leaves contain 3% caffeine depending upon 70 the tea quality and method of its preparation. An 8 fl oz. cup of coffee contains 100-150 71 mg caffeine while black and green tea provides 40-60 mg and 25-40 mg of caffeine, 72 respectively. The total phenolic content of varies 19.2-108.6 mg mL-1 with an abundance 73 of quinic acid and gallic acids (1). The seasonal variation of theanine, methylxanthines, 74 and catechins such as Afzelechin (1a), in 21 cultivars of Camellia Sinensis, has been 75 recently published [1, 1a]. 76 Caffeine, a 1,3,7-trimethylxanthine (C8H10N4O2), purine alkaloid (2) and structurally 77 related to adenosine (5), has an astringent taste. It is produced in more than 60 distantly 78 related plant species such as coffee beans, tea leaves, kola nuts (Cola acuminate, Beauv 79 and Cola nitida, Vent), cocoa beans (Theobroma cacao) and even in some citrus species 80 [2]. In some cases, methylxanthines are recognized as remarkable markers for facilitating 81 chemotaxonomy of plants while caffeine (2), theophylline (17), saxitoxin, and 82 theobromine (4) are the representative examples of this class of methylxanthines. 3 Preprints (www.preprints.org) | NOT PEER-REVIEWED | Posted: 2 August 2018 doi:10.20944/preprints201808.0032.v1 83 The bitter taste of black tea (Camellia Sinensis) and roasted coffee (two species of 84 Coffee; C. arabica and C. robusta), is recognized due to the variable amounts of caffeine 85 and 5-caffeoylquinic acid (6). A link between the mouth cavity, nasal cavity, and the 86 brain is known, and caffeine can cross the blood-brain barrier [3]. 87 OH O CH3 H C 3 N HO O N N O N OH 88 HO CH3 89 (1) (2) 90 O CH3 NH2 H H N HO N N O N O O N 91 CH3 92 (3) (4) 93 94 NH2 OH N N HO OH O N O N OH H HO O O O H 95 HO OH HO 96 97 (5) (6) 98 99 4 Preprints (www.preprints.org) | NOT PEER-REVIEWED | Posted: 2 August 2018 doi:10.20944/preprints201808.0032.v1 100 Caffeine is frequently used as a CNS stimulant with numerous physiological 101 consequences on cardiovascular, renal, respiratory, immuno-modulation, smooth muscle, 102 mood forming, memory, alertness, and cognitive performance [4]. Due to their ergogenic 103 effect, caffeine and creatine (10) are the two most widely used compounds in sports with 104 a sizeable interindividual variation of caffeine absorption within and between groups [5]. 105 As complex forming agents, methylxanthines, like caffeine can interact with lysozyme, 106 bringing about a conformational change in the cationic proteins, thus lowering the 107 antimicrobial activity. Synergistic cytotoxicity and mechanism of caffeine and lysozyme 108 on hepatoma cells have been recently reported [6]. 109 Tea and coffee extract, apart from methylxanthines, contain many other 110 phytochemicals such as L-theanine (N-ethyl-L-glutamine) (3) that also affect mood, 111 cognition, sustained attention and suppression of distraction [7]. Theanine enhances the 112 toxicity when combined with strychnine or phenobarbital sodium [8]. The other tea 113 congener, theobromine (4), is an inhibitor of physiologically essential phosphodiesterases 114 and it increases intracellular second messenger molecules cAMP and cGMP in mice [9]. 115 In green coffee beans, along with caffeine, chlorogenic acid, the most popular weight loss 116 ingredient and its derivatives have also been identified [10]. 117 While hot tea and coffee extracts contain variable amounts of caffeine, heating, and 118 processing of coffee beans convert 5-caffeoylquinic acid (neochlorogenic acid, 6) into 119 various phenylindanes (7) and lactones such as 3-caffeoylquinic-1,5-lactone (8) and 4- 120 caffeoylquinic-1,5-lactone (9) [11]. Melanoidins, present in coffee, are the byproducts 121 produced by Millard reaction between amino groups of proteins and carbonyl groups of 122 reducing sugars and are poorly understood [12]. This convolution of the tea and coffee 123 extracts shows a highly complicated mixture of hundreds of small molecules that have 124 not even been investigated. 5 Preprints (www.preprints.org) | NOT PEER-REVIEWED | Posted: 2 August 2018 doi:10.20944/preprints201808.0032.v1 CH3 O HO O 1 O 2 HO 3 OH HO O 6 5 4 HO OH R OH 125 OH 126 127 (7) (8) 128 129 130 O 1 O 3 2 NH O OH HO 6 HO HO 5 O 4 N NH2 O CH 131 HO 3 132 133 (9) (10) 134 135 136 137 2. Caffeine: Bioavailability and dose response 138 For healthy adults, the recommended amount of caffeine is around 400 mg/day, and 139 an overdose may occur if one absorbs more than this amount. A moderate dose of 140 caffeine may cause anxiety in consumers, and it can lead to central nervous system 141 consequences in heavy consumers. Liver diseases, pregnancy, oral use of contraceptives, 142 and interaction with therapeutic drugs may lower the metabolism and its excretion 143 consequently increasing its concentration in the body. The safe amount of caffeine differs 144 for everyone, and it depends on age, weight, gender and the state of general health. These 145 variables make it difficult to know the exact amount of caffeine that can lead to an 6 Preprints (www.preprints.org) | NOT PEER-REVIEWED | Posted: 2 August 2018 doi:10.20944/preprints201808.0032.v1 146 overdose or an inevitable consequence. Therefore, at a young age, a dose of 100 mg/day 147 is safer. 148 The half-life of caffeine (HLC) is species dependent and is recorded as 3-5 hr. Thus, 149 in an adult human, HLC is 0.7-1.0 hr., rats, and mice, 1-1.6 hr., rabbits 3-5 hr., monkeys, 150 and baboons, 4-4.3 hr., while in dogs it is 11-12 hr [13].