Coffee components and cardiovascular risk: beneficial and detrimental effects.

http://informahealthcare.com/ijf ISSN: 0963-7486 (print), 1465-3478 (electronic) Int J Food Sci Nutr, Early Online: 1–12 ! 2014 Informa UK Ltd. DOI: 10.3109/09637486.2014.940287

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Coffee components and cardiovascular risk: beneficial and detrimental effects Justyna Godos1, Francesca Romana Pluchinotta2, Stefano Marventano3, Silvio Buscemi4, Giovanni Li Volti5, Fabio Galvano5, and Giuseppe Grosso5 1

Faculty of Biochemistry, Biophysics, and Biotechnology, Jagiellonian University, Krakow, Poland, 2IRCCS Policlinico ‘‘S. Donato’’, San Donato Milanese, Milano, Italy, 3Department ‘‘G.F. Ingrassia’’, Section of Hygiene and Public Health, University of Catania, Catania, Italy, 4Department of Internal Medicine, University of Palermo, Palermo, Italy, and 5Department of Clinical and Molecular Biomedicine, Section of Pharmacology and Biochemistry, University of Catania, Catania, Italy Abstract

Keywords

Coffee consists of several biological active compounds, such as caffeine, diterpenes, chlorogenic acids, and melanoidins, which may affect human health. The intake of each compound depends on the variety of coffee species, roasting degree, type of brewing method and serving size. The bioavailability and the distribution of each compound and its metabolites also contribute to coffee mechanisms of action. The health benefits of coffee consumption regarding cardiovascular system and metabolism mostly depend on its antioxidant compounds. In contrast, diterpenes and caffeine may produce harmful effects by raising lipid fraction and affecting endothelial function, respectively. Studying the mechanism of action of coffee components may help understanding weather coffee’s impact on health is beneficial or hazardous. In this article, we reviewed the available information about coffee compounds and their mechanism of action. Furthermore, benefits and risks for cardiovascular system associated with coffee consumption will be discussed.

Antioxidant, caffeine, cardiovascular disease, nutrients, polyphenols

Introduction Coffee is among the most widely consumed beverages worldwide (Grigg, 2003). Coming from the roasted seeds of several species of the genus Coffea, the popularity of coffee is due to its aroma and flavor, despite it seems that its caffeine content plays the major role in its popularity. Coffee is a complex mixture of more than a thousand different chemicals, many of which are reported to be biologically active (Butt & Sultan, 2011). Among them, coffee provides significant amounts of phenolic compounds that exhibit strong antioxidant activity (Spiller, 1984). Discoveries gathered in recent years have generated new information regarding the effects on health of coffee consumption, demolishing the common belief that coffee is mostly harmful (Ludwig et al., 2014). A number of recent experimental and epidemiological studies reported a substantial positive effect of coffee consumption on human health, especially in relation with cardio-metabolic risk factors (Abrahao et al., 2013; Grosso et al., 2014; Salomone et al., 2013). Coffee consumption seems to be reasonably associated with decreased risk of diabetes and cardiovascular disease (CVD) (Jiang et al., 2014; O’Keefe et al., 2013). The functionality in human health is supported by the ability of coffee components to induce human protective enzyme systems and by a number of laboratory studies suggesting protective effects Correspondence: Giuseppe Grosso, MD, Department of Clinical and Molecular Biomedicine, Section of Pharmacology and Biochemistry, University of Catania, V.le A. Doria 6, 95125 Catania, Italy. Tel: +39.095.7384278. Fax: +39.095.7384220. E-mail: giuseppe.grosso@ studium.unict.it

History Received 29 April 2014 Revised 4 June 2014 Accepted 25 June 2014 Published online 21 July 2014

against diseases with an inflammatory basis (Gulcin, 2012). Nevertheless, findings of experimental studies are often contrasting, and further research is needed to clarify the nature of the mechanisms of actions of these bioactive constituents and biological systems. The aim of this article is to review the most recent discoveries regarding the components of coffee and their potential mechanisms of action in providing protection by CVD.

Coffee types and preparation methods There are two main sources of coffee beans of commercial importance, Coffea arabica and Coffea canephora, (known also as ‘‘robusta’’), which differ each other in chemical content of the green coffee bean. It has been reported that arabica coffee contains more lipids, while robusta contains more caffeine and polyphenols (Cagliani et al., 2013). Arabica coffee beans are valued most highly by the world trade (80%) as they are considered to have a more desirable flavor than robusta (Parliament & Stahl, 2005). Coffee has several preparation methods, which significantly affect aroma, flavor and composition of coffee brews. Processing of coffee involves picking of the bean, drying, roasting, grinding and brewing to produce the final coffee. Almost all methods of preparing coffee require the seeds to be ground and mixed with hot water long enough to extract the flavor. Many of the coffee compounds are formed during the roasting process, which produce the unique taste and smell of coffee (Parliament et al., 2005). On the other hand, the roasting process may cause degradation of many of other compounds, such as antioxidant polyphenols, despite the difference in total antioxidants between


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the different roasts of a bean is generally not significant (Daglia et al., 2000). Taking into account the brewing process, three main types of coffee can be distinguished: (i) boiled unfiltered coffee, (ii) filtered coffee (instant coffee) and (iii) decaffeinated coffee. Each of these types of coffee is related to specific granulation of coffee powder, water/coffee ratio, temperature and brewing time (Yuksel et al., 2010). Decaffeination and filtration is carried out to remove components such as caffeine and lipid fraction (Parras et al., 2007; Sacchetti et al., 2009). It has been reported that lipids and hydrophobic compounds practically not cross the paper filter (Gross et al., 1997). In this entire process, the coffee beans undergo several physical and chemical changes in flavor and antioxidant properties, which in turn may influence on the biological effects of coffee (Parras et al., 2007; Sacchetti et al., 2009). It has been reported that instant coffee brews possess the highest total phenolic content and the highest antioxidant capacity, whereas filter coffee brews are characterized by the lowest content of polyphenols and the lowest antioxidant capacity (Niseteo et al., 2012). Many different extraction methods have been developed, such as decoction, infusion and pressure methods. Filter instant are obtained by infusion method, while espresso, traditional Italian coffee brew, by pressure method. There are also other well-known types of coffee, such as French press or Turkish/Greek coffee. French-press coffee brewing method allows effective contact between ground coffee and water, but as mentioned before, filter may inhibit penetration of lipids (Gross et al., 1997). Turkish coffee is a method of preparation, Figure 1. Chemical structures of the most common molecules belonging to the chlorogenic acids group.

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not a kind of coffee, which requires hot, but not boiling, water and fine powdered grounds (Yuksel et al., 2010).

Chlorogenic acids A wide part of scientific literature indicates that coffee has the highest concentration of polyphenols among the overall beverages consumed by humans (Halvorsen et al., 2006). Coffee has been extensively studied for antioxidant activity (Carvalho Ddo et al., 2011; Correa et al., 2012; Viana et al., 2012) and has been reported to among the most important source of antioxidants in the US, Norway and Spain diet (Pulido et al., 2003; Svilaas et al., 2004; Vinson et al., 2006). The average 180 ml cup of brewed coffee provides 396 mg of polyphenols and instant coffee 316 mg (Vinson et al., 2006). Among the most studied polyphenols contained in coffee, chlorogenic acids (CGAs) are a family of esters of hydroxycinnamic acids [mostly caffeic acid (CA) and ferulic acid (FA)] with D-()-quinic acid (QA) (Figure 1). CGA specifically refers to the ester of CA with QA. The compound that most contributes to the polyphenol content of roasted coffee (about 2% of dry matter) is 5-O-caffeoylquinic acid (CQA, an isomer of CGA), whereas feruloylquinic acid and dicaffeoylquinic acid are present in minor percentage (50.2%) (Clifford, 1999). Despite presence of other phenolic compounds, such as tannis, lignans and anthocyaninc, CGAs are the most abundant polyphenol subclass in coffee (Campa et al., 2005; Clifford, 1999; Fujioka & Shibamoto, 2008). These compounds occur in high concentrations in green coffee seeds (up to 14%) and significantly

71% of ingested CGAs 29% of ingested CGAs as metabolites 100% reach the colon None

29% of ingested CGAs is absorbed Escape digestion

93% of amount that enters small intestine is absorbed Traces 0.4% of the ingested kahweol as metabolites None Metabolites of caffeine are present in urine Colon Bladder

Small intestine

Espresso Filtered Stomach

97–330 mg/50 ml cup No data Rapid absorption of caffeine (no specific data) 99–100% rapidly absorbed

88% of amount that enters small intestine is absorbed Traces 1.2% of ingested cafestol as metabolites

Loss of 60.9–98% 7.2 g/100 g roasted coffee

0.1–0.3% of dry matter basis in arabica beans and traces (50.01%) in robusta beans 0.09–0.18 mg/50 ml cup 0.02 mg/150 ml cup 28% degraded in gastric fluid 0.3–0.7% of dry matter in arabica beans and 0.1–0.3% in robusta beans 0.06–0.17 mg/50 ml cup 0.02 mg/150 ml cup 33% degraded in gastric fluid

45–190 mg/kg of dry matter

116 mg/50 ml cup 270 mg/150 ml cup Escape digestion

0.8–11.9% of dry matter None

Roasted been

Compounds with antioxidant activity are supposed to protect against chronic diseases with an inflammatory basis. For instance, CGA and CA may play an important role in prevention of atherosclerosis by inhibiting low-density lipoprotein (LDL) oxidation in the plasma and below the endothelial surface

3.85–4.29 mg/g (2.3% of dry matter) 4.73–9.44 mg/g

Effects of CGAs on cardiovascular risk factors

Caffeine

CGA extensively demonstrated strong antioxidant properties in vitro (Ozgen et al., 2006). CGA has been reported to exhibit anti-inflammatory activity in a concentration-dependent manner through inhibiting production of inflammatory mediators (tumor necrosis factor-a and interleukin-6) in human peripheral blood mononuclear cells (Krakauer, 2002).5TNF IL4 Among the other properties of CGA, it presented anti-edematogenic and antinociceptive activities in animal models of carrageenininduced inflammation and formalin-induced pain, respectively (dos Santos et al., 2006). CGA may also play role as an antitumor factor by inhibiting matrix metalloproteinase-9, an angiogenic enzyme involved in human hepatic tumor genesis and metastasis (Jin et al., 2005). The major metabolites generated by the metabolism of CGA demonstrate similar antioxidant activity but account to lower effects than the parent compounds (Piazzon et al., 2012). FA-40 O-sulfate and FA-40 -O-glucuronide exhibited very low antioxidant activity, while the monosulfate derivatives of CA were 4-fold less efficient as the antioxidant than CA. In contrast, the acyl glucuronide of FA showed strong antioxidant action (Piazzon et al., 2012). In addition to the previous activities, FA is able to act as an antioxidant by altering sulfate conjugation by phenol sulfotransferase, which play an important role in the detoxification of xenobiotics and endogenous compounds (Yeh & Yen, 2003).

Cafestol

Antioxidant properties of CGAs

Green bean

Kahweol

Melanoidins

Currently available studies in colostomy patients point out that about 30% of the ingested CGA and 95% of the ingested CA are absorbed in the small intestine of volunteers ingesting a massive amount of CQA (5.5 mmol equivalent to 1.5–4 L of coffee) (Olthof et al., 2001; Table 1). Minor traces of CGAs present in urine indicate that these compounds are most likely metabolized extensively into other compounds after absorption. The remaining 70% of the ingested CGA reaches the colon where it may be metabolized by intestinal microflora (hydrolyzed to CA and QA) evaluated in volunteers consuming a real amount of CGAs, as a single 200-mL serving of coffee (Stalmach et al., 2010). The major metabolites of CGA in the serum are CA-3-O-sulfate, isoferulic acid-3-O-glucuronide and dihydrocaffeic acid-3-Osulfate (Dall’Asta et al., 2012; Stalmach et al., 2009), whereas FA-4-O-sulfate and other FA conjugates are mostly representative in urine (Lang et al., 2013). It has been reported that the bioavailability of CGAs largely depends on its metabolism by the gut microflora (Calani et al., 2012; Del Rio et al., 2010).

Table 1. Content of major components in coffee beans and beverages and their metabolism in humans.


Absorption and metabolism

40–90 mg/kg of dry matter

Chlorogenic acids (CGAs)

determine coffee quality and formation of coffee aroma and flavor (Variyar et al., 2003). Two-hundred-milliliter cup of coffee provide from 70 to 350 mg of CGA and CA, taking into account that their amount depends on the variety of coffee (i.e. arabica and robusta), its roasting degree and brewing method (Clifford, 1999). Coffee variety does not significantly modify the CGA content of espresso coffee, which varies from 96 to 111 mg per 30 ml cup, but may have importance for filtered coffee, which CGA content in a 130 ml cup may range from 143 mg (arabica) to 247 mg (robusta) (Maeztu et al., 2001; Neveu et al., 2010).

160–185 mg/50 ml 165–285 mg/150 ml Possible contribution in digestion

Coffee components and cardiovascular risk

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(Laranjinha et al., 1994; Nardini et al., 1995). In addition, studies on humans have reported that coffee consumption is correlated with decrease of LDL oxidizability (Yukawa et al., 2004) and with an increase in antioxidant capacity of in plasma (Natella et al., 2002). A possible mechanism of enhanced in vivo antioxidant capacity of plasma after coffee consumption has been suggested to depend on the increase of plasma concentration of glutathione (Esposito et al., 2003). Consumption of CGAs reduced fasting plasma glucose (Andrade-Cetto & Wiedenfeld, 2001; Rodriguez de Sotillo & Hadley, 2002; Rodriguez de Sotillo et al., 2006), increased sensitivity to insulin (Shearer et al., 2003) and slowed the appearance of glucose in circulation after glucose load (Bassoli et al., 2008) in animal studies. CGA has been hypothesized to protect against type 2 diabetes mellitus through its specific competitive inhibition of the glucose-6-phosphate translocase in rat liver microsomes (Arion et al., 1997). Glucose-6-phosphate translocase is an enzyme that in humans catalyzes the terminal reactions in both glycogenolysis and gluconeogenesis, thus highly involved in the regulation of homeostasis and blood glucose levels (Herling et al., 1998). Recently, it has been reported that CGA also activate adenosine monophosphate-activated protein kinase, a sensor and regulator of cellular energy balance, leading to beneficial metabolic effects, such as suppression of hepatic glucose production and fatty acid synthesis (Ong et al., 2013). Another proposed mechanism of protection of CGA against diabetes mellitus is its inhibiting action on intestinal glucose absorption. Studies conducted on animals have shown that CGA reduce sodium-dependent glucose transport in brush border membrane vesicles isolated from rat small intestine (Welsch et al., 1989). CGA have been reported also to reduce intestinal absorption of glucose by inhibition of a-amylase (Funke & Melzig, 2005; Narita & Inouye, 2009) and a-glucosidase activity (Adisakwattana et al., 2009; Ishikawa et al., 2007), two key enzymes responsible for digestion of dietary carbohydrates. Green coffee extract containing 28% of CGAs resulted in a dose-dependent blood pressure reduction in spontaneously hypertensive rats (Suzuki et al., 2002b). Since the principal form of CGA contained in coffee is 5-CQA, both acute and chronic administration of 5-CQA alone showed almost identical results as seen with GCE administration in the same animal model (Suzuki et al., 2002b, 2006b). Finally, these results were replicated also in human studies, showing a decrease of blood pressure after 28 d of green coffee (containing 56% CGAs) consumption in a dose-dependent manner (Kozuma et al., 2005; Watanabe et al., 2006). CGAs are hypothesized to exert antihypertensive effects attenuating oxidative stress (reactive oxygen species) by reducing NAD(P)H-dependent super-oxide production (Suzuki et al., 2006a,b), thus inhibiting the proliferation of vascular smooth muscle cells (Li et al., 2005), and to interact with the renin–angiotensin aldosterone system by inhibiting angiotensin-converting enzyme activity both in vitro and in vivo (Actis-Goretta et al., 2006; Ardiansyah et al., 2008). Among the CGAs metabolites, FA seems to have the greatest effect on blood pressure (Suzuki et al., 2002a,b). The administration of FA increases nitric oxide bioavailability and enhanced acetylcholine induces endothelial-dependent vasodilation in the arterial vasculature (Suzuki et al., 2007). Experimental studies also demonstrated that the depletion of hydroxyhydroquinone (HHQ), a particular fraction of CGA produced during the roasting process, enhanced the anti-hypertensive effects of CGAs in a marginally dose-dependent manner (Yamaguchi et al., 2008). It is hypothesized that the production of HHQ-derived superoxide may neutralize NO bioactivity enhanced by CGAs, therefore counteracting the anti-hypertensive effects of CGAs (Halliwell et al., 2004; Ochiai et al., 2009).


CGAs have been demonstrated in experimental studies that may also have an influence on serum lipid metabolism and oxidative status (Meng et al., 2013). In a study conducted on lipids metabolism in an animal model of diabetes, CGA demonstrated to decrease concentrations of plasma and tissue (liver and kidney) lipids, cholesterol, triglycerides, free fatty acids and phospholipids and LDL and very low-density lipoproteins, respectively, and a decrease in the concentration of HDL (Karthikesan et al., 2010). This antihyperlipidemic effect of CGA seems to depend on its capacity to increase the activity of 3-hydroxy 3-methylglutaryl coenzyme A reductase in the liver and kidney and decrease the activities of lipoprotein lipase and lecithin cholesterol acyltransferase in the plasma (Karthikesan et al., 2010). Moreover, CGA may modestly reduce LDL oxidation susceptibility and decrease LDL-cholesterol and malondialdehyde (MDA) levels (Yukawa et al., 2004).

Caffeine Caffeine (1,3,7-trimethylxanthine) is probably one of the first components of coffee to be studied (Figure 2). This compound is a white crystalline xanthine alkaloid naturally occurring in coffee beans. Caffeine content in coffee beverages is highly variable (Campa et al., 2005; Caprioli et al., 2014; Salinas-Vargas & Canizares-Macias, 2014). It has been reported that caffeine content in caffeinated coffees ranges from 29 to 130 mg/cup (240 ml), while in espresso, coffees is ranges from 58 to 76 mg for a single shot (35–50 ml) (McCusker et al., 2003), despite the combination of different water temperatures and pressures in the settings of the espresso coffee machine has been recently considered determinant in variation of measurements (Caprioli et al., 2014). Indeed, caffeine content has been reported to reach up to about 200 mg per cup of espresso (Caprioli et al., 2014), with a variability in the same coffee beverage ranging from 130 to 282 mg/cup (McCusker et al., 2003) and up to 322 mg/cup in different commercial espresso coffee (Crozier et al., 2012). Minor caffeine content is also present in coffee sold as decaffeinated (about 17.7 mg) (McCusker et al., 2003). Among the factors that may influence the variability in caffeine content, variety of coffee beans, roasting methods, proportion of coffee to water used in preparation and length of brewing time have been proposed. Removal of caffeine from coffee beverages by decaffeination process reduces the antioxidant capacity due to the decreasing of total polyphenol content (Niseteo et al., 2012). Absorption and metabolism Caffeine is rapidly and almost completely absorbed in the stomach and small intestine to be subsequently distributed to all tissues through the total body water. It is mostly biotransformated by cytochrome P450 (isoform CYP1A2) in the liver into 13 different metabolites, and its renal excretion is negligible (Teekachunhatean et al., 2013; Table 1). Caffeine primary undergoes 3-demethylation to form 1,7-dimethyloxanthine catalyzed by CYP1A2 (17X; Figure 2). Subsequently, 1,7-dimethyloxanthine is metabolized in three reactions: (i) 8-hydroxylation catalyzed by cytochrome P4502A6 (CYP2A6) to form 1,7dimethylurate (17U); (ii) 7-demethylation catalyzed by cytochrome P4501A2 (CYP1A2) to form 1-methylxanthine (1X); and (iii) N-acetyltransferase catalyze 17X to form open ring product 5-acetylamino-6-formylamino-3-methyluracil (AFMU). AFMU is an unstable product, which therefore may be deformylated non-enzymatically to 5-acetylamino-6-amino-3-methyluracil (Crews et al., 2001; Krul & Hageman, 1998). A minor part of caffeine is transformed in theophylline (1,3-dimethylxanthine) and theobromine (3,7-dimethylxanthine; Figure 2).

Figure 2. Chemical structure of caffeine and main pathways of its metabolism.


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Mechanism of action of caffeine on humans The caffeine molecule is structurally similar to adenosine, which is an endogenous neurotransmitter with mostly inhibitory effects in the central nervous system (CNS), when acting through high-affinity (A1) receptors. In general, adenosine inhibits adenyl cyclase via A1 receptors and stimulates adenyl cyclase via low-affinity (A2) receptors. Adenosine receptors are found throughout the body including the brain, in the cardiovascular, respiratory, renal, gastrointestinal systems and in adipose tissue (Fisone et al., 2004). In humans, caffeine is capable of nonspecific binding to A1/A2A receptors and may act as a drug stimulating central nervous system via acetylcholine receptors. The sensitivity for caffeine effects varies between individuals. These differences, observed in plasmatic concentration of caffeine following the administration of an equal dose are mainly due to variations in metabolism, which in turn depend on four factors: (i) genetic polymorphisms; (ii) metabolic induction and inhibition of cytochrome P450; (iii) individual factors (weight and sex); and (iv) presence of hepatic diseases (Miners & McKinnon, 2000). However, the necessary concentration to explicate its effect at the receptor level (inhibition constant values of 44 and 40 mmol/L antagonist at adenosine A1 and A2A receptors, respectively) generally corresponds to following the consumption of average amounts of caffeine from dietary sources (Benowitz, 1990; Porkka-Heiskanen et al., 2013). Higher concentrations (4480 mmol/L) may explicate other mechanisms of action, including phosphodiesterase inhibition and calcium mobilization from intracellular storage sites in skeletal and cardiac muscles and neuronal tissue (Daly, 1993). However, this concentration is not reached at average consumption of caffeine (Daly, 1993). Effects of caffeine on blood pressure and endothelial function Caffeine may exert direct and indirect contrasting effects on the vascular tissue by different mechanisms of action and on a wide range of molecular targets. In endothelial cells, caffeine acts directly by increasing intracellular calcium and stimulating the production of nitric oxide through the expression of the endothelial nitric oxide synthase enzyme causing vasodilatation (Umemura et al., 2006). Moreover, caffeine may indirectly decrease blood pressure by enhancing excretion of water and electrolytes inducing a diuretic effect (Carrillo & Benitez, 2000). In contrast, in vascular smooth muscle cells, its effect is predominantly a competitive inhibition of phosphodiesterase, producing an accumulation of cAMP (Watanabe et al., 1992) and a blocking effect on the adenosine receptors present in the vascular tissue, both mechanisms causing vasoconstriction in general and micro circulation (Miners & McKinnon, 2000). Overall, the predominant effect that caffeine produces on blood pressure in humans is a substantial increase after acute administration (Umemura et al., 2006). On the other hand, the effects on long-term consumers of caffeinated coffee are still unclear. A pooled analysis of clinical trials conducted on humans reported that blood pressure elevations appeared to be significant only for caffeine but not for coffee intake (Noordzij et al., 2005). Intravenous caffeine is responsible of rise in muscle sympathetic activity and blood pressure in both habitual and nonhabitual coffee drinkers, but coffee intake led to increased blood pressure only in non-habitual coffee drinkers (Corti et al., 2002). These observations suggest two hypotheses: first, habitual coffee consumers may develop tolerance to caffeine, thus smoothing its effects on blood pressure (Ammon et al., 1983; Robertson et al., 1981); second, substances other than caffeine (i.e. phenolic compounds or minerals) may counteract the


pro-hypertensive effects of caffeine, leading to an overall abolition of its effects (Zhao et al., 2012). The acute ingestion of caffeinated coffee has been also reported to affect endothelial function in healthy non-obese individuals (Buscemi et al., 2010), whereas administration of decaffeinated coffee led to a significant acute favorable dosedependent effect of decaffeinated espresso coffee on endothelial function (Buscemi et al., 2009, 2010). These results suggest that the unfavorable effects observed after caffeinated coffee ingestion are due to caffeine and that the antioxidant activity is responsible for the increased flow-mediated dilation observed after decaffeinated coffee ingestion. It is also noteworthy that caffeine metabolites themselves have been demonstrated to exert anti-inflammatory effects in vitro (Geraets et al., 2006). Furthermore, clinical and epidemiological studies are needed to understand the chronic effects of coffee consumption on health.

Diterpenes Cafestol and kahweol are two diterpenes with a characteristic furan group, which naturally occurs in coffee beans (Urgert et al., 1997; Figure 3). Both are considered to be present rarely in free form and in larger quantities with fatty acids (mainly palmitic and linoleic) esterified (Kurzrock & Speer, 2011). The typical bean of C. arabica contains about 0.3–0.7% cafestol and 0.1–0.3% kahweol by weight (cafestol and kahweol with individual concentrations ranging from 0.1 to 7 mg/ml in coffee) whereas C. canephora (robusta) present decreased concentration of cafestol (0.1–0.3%) and only traces of kahweol (50.01%) (Kolling-Speer et al., 1999; Kurzrock & Speer, 2011; Rubayiza & Meurens, 2005). In addition, diterpenes are also highly contained in Turkish/Greek and French-press coffee, however, mostly removed in filtrated and instant coffee by processing (Gross et al., 1997; Naidoo et al., 2011). The total amount of these molecules also depends on the type of coffee as well as on the method of preparation (Table 2). Among other important molecules, 16-o-methylcafetol (16OMC) has been considered fundamental for the authentication of commercial blends used for certain types of coffee, such as Italian espresso coffee (Pacetti et al., 2012). Considering the difference in quality and, consequently, in prices of arabica and robusta coffee beans, the use of 16-OMC as a marker component based on its exclusive presence in robusta coffee and its stability during roasting of coffee beans represent an useful tool for rapid determination of coffee type.

Figure 3. Chemical structure of cafestol and kahweol.

Table 2. Diterpenes content in different types of coffee. Type of coffee Scandinavian Turkish/Greek French press Espresso Singapore (filtrated sock)

Cafestol mg/cup

Kahweol mg/cup

0.64–9.68 0.4–8.0 1.84–4.4 0.16–2.32 0.02–0.23

0.8–11.68 0.08–8.56 2.08–6.4 0.16–3.12 0.01–0.06

One cup ¼ 120 mL. Adapted from Naidoo et al. (2011).

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Absorption and metabolism According to studies conducted on ileostomy patients, 70% of ingested cafestol and kahweol enters small intestine, where about 90% of the amount is absorbed (Table 1). It has been reported that a very small part of diterpenes is transformed during gastrointestinal transit and excreted as conjugate of glucuronic acid or sulfate in urine. Only slight amount enter the colon, where it can be available for the supposed anticarcinogenic effects. The rest of other ingested 30% is degraded in gastric fluid, thus it is not bioavailable (De Roos et al., 1998).


Effect of diterpenes on blood lipids Studies on coffee consumption and its association with serum total and LDL cholesterol concentrations have shown conflicting results (Thelle, 1987). A meta-analysis of 14 randomized controlled trials examining the effect of coffee consumption on serum cholesterol concentrations indicate that the consumption of boiled coffee dose-dependently is associated with higher serum total and LDL cholesterol concentrations, while the consumption of filtered coffee results in slight increase in serum cholesterol (Jee et al., 2001). Indeed, filtered coffee contains minor amounts of diterpenes (Kurzrock & Speer, 2011). A possible mechanism of action is that diterpenes affect the LDL receptor, which is responsible for the endocytic process of apoB- and apoEcontaining lipoproteins. Cholesterol content of the cell is regulated via feedback repression of the LDL receptor gene. Increased concentration of cholesterol in the cell results in down regulation of the number of LDL receptors, while cholesterol continue to circulate blood, eventually making its way below the endothelial surface, where might be oxidized and participate in creating foam cells and subsequent atherosclerosis (Goldstein & Brown, 1977). In vitro cellular experiment has confirmed that diterpenes cause extra cellular accumulation of LDL by reducing the activity of LDL receptor (Rustan et al., 1997). Interestingly, a study on human has reported that coffee oils from arabica, but not robusta, raised cholesterol and triglycerides in 36 healthy individuals, reflecting the different amount of diterpenes contained in the two types of coffee (van Rooij et al., 1995).

Melanoidins Coffee brew is considered to be one of the main sources of melanoidins in the human diet (Fogliano & Morales, 2011). Melanoidins are defined as high-molecular-weight nitrogenous brown colored polymers (Nunes & Coimbra, 2010; Wang et al., 2011). During coffee processing and, especially, roasting, the chemical composition of the green beans change, and melanoidins are formed as a final products of a non-enzymatic reaction between amino acids and reducing sugars that naturally occur in coffee beans, giving coffee desirable flavor (Martins et al., 2000). However, structure of coffee melanoidins remains largely unknown and requires further research (Moreira et al., 2012). The unstable chemical structure of these compounds interferes with isolation of pure melanoidin fractions, which in turn unable estimation of their precise quantity in coffee (Belitz et al., 2009). Two quantitative methods have been established to evaluate approximate coffee melanoidins content (Belitz et al., 2009; Gniechwitz et al., 2008; Nunes & Coimbra, 2007). The first method, which involves subtracting the total percentage of known compounds from 100%, estimated melanoidins content to account for up to around 29% of the dry weight of roasted coffee beans (Belitz et al., 2009). The second method is based on spectrophotometric measurement of the brown color saturation (405 nm absorption spectrum) of the brew and its dilution analysis (Gniechwitz et al., 2008; Nunes & Coimbra, 2007). The estimated


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intake of coffee melanoidins according to average coffee consumption varies between 0.5 and 2.0 g per day (Fogliano & Morales, 2011). Absorption and metabolism Little is known about melanoidins gastric transit, their biotransformation and bioavailability. The first studies conducted on biological activities of coffee melanoidins have often been performed using high-molecular-weight material (HMWM) isolated from coffee brews, after the assumption of the melanoidins presence. HMWM contains other high-molecular-weight compounds that have impact on analysis of the final results (Somoza, 2005). The HMWM isolated from coffee brew by ultrafiltration underwent in vitro digestion stimulated by gastrointestinal enzymes. Results of this study showed that the low-molecularweight fraction recovered after digestion represented 14% of the HMWM. Referring to the results, it may be suggested that coffee melanoidins are largely resistant to digestion in the human gastrointestinal tract (Morales et al., 2012; Rufian-Henares & Morales, 2007b; Table 1). Melanoidins and antioxidant and anti-inflammatory properties There is a wide evidence of the potential antioxidant and antiinflammatory activity of melanoidins both in vitro and in vivo, despite results are not univocal (Borrelli et al., 2002; DelgadoAndrade & Morales, 2005; Delgado-Andrade et al., 2005; Gniechwitz et al., 2008; Rufian-Henares & Morales, 2007b; Vitaglione et al., 2010). The mechanism of the antioxidant action of coffee melanoidins is still unclear. It has been assumed that it is based on their radical scavenging activity and/or their metalchelating capacity (Borrelli et al., 2002; Delgado-Andrade & Morales, 2005; Delgado-Andrade et al., 2005; Rufian-Henares & Morales, 2007b). Moreover, some studies showed the protective role of melanoidins against lipid oxidation (Daglia et al., 2008; Tagliazucchi et al., 2010). There are contrasting results according to the association between degree of coffee bean roasting and antioxidant properties of melanoidins isolated both from coffee brew and coffee beans (Borrelli et al., 2002; Delgado-Andrade et al., 2005). One study has showed that the increase of the degree of roast cause reduction of the radical scavenging activity, but the ability to prevent linoleic acid peroxidation is higher in the darkroasted sample (Borrelli et al., 2002), whereas other one showed that the antioxidant activity of melanoidins isolated by ultrafiltration from instant coffees was lower in the light-roasted beans (Delgado-Andrade et al., 2005). According to the evaluation of melanoidins antioxidant activity isolated from coffee brew, it has been reported that coffee antioxidant activity decreased with roasting degree (Richelle et al., 2001). Melanoidins and diabetes In human nutrition, advanced glycation end products, known as AGEs, are substances that can be a factor in the development or worsening of many degenerative diseases, such as diabetes, atherosclerosis and chronic renal failure (Vistoli et al., 2013). Molecules that may inhibit glycation reactions are of great interest because of their preventive and therapeutic potential (Guillet, 2010). It has been reported that HMWM isolated from coffee brew are able to inhibit in vitro glycation of bovine serum albumin with glucose (Verzelloni et al., 2011b). On the other hand, the accumulation of so called Amadori products (i.e. skin collagenlinked fructosamine product; Verzelloni et al., 2011b) is a strong predictor of the risk of progression of microvascular disease in humans (Monnier et al., 2008) during glycation in the presence

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of the HMWM was observed, indicating that its antiglycative action is paramount in the post-Amadori phase of the reaction (Verzelloni et al., 2011b). A recent study investigating the inhibitory activity of some colonic microbiota-derived polyphenol catabolites against advanced glycation end products formation in vitro demonstrated that ellagitannin-derived catabolites (urolithins and pyrogallol) were the most effective antiglycative agents, whereas CGA-derived catabolites (dihydrocaffeic acid, dihydroferulic acid and feruloylglycine) were most effective in combination in protecting neuronal cells in a conservative in vitro experimental model, both key features of diabetic complications (Verzelloni et al., 2011a).


Melanoidins and hypertension A study on HMWM isolated by ultrafiltration from instant coffee has showed their potential antihypertensive activity in vitro attributed to the melanoidins. Proposed mechanism of HMWM action is via inhibition of the angiotensin-I converting enzyme (ACE) (Rufian-Henares & Morales, 2007a). ACE catalyses the conversion of angiotensin I to angiotensin II, a potent vasoconstrictor in a substrate concentration-dependent manner (Zhang et al., 2000). In addition, ACE degrades bradykinin, a potent vasodilator, and other vasoactive peptides (Imig, 2004). Moreover, ACE is a key element of the renin-angiotensin system that regulates blood pressure, thus ACE inhibitors are important for the treatment of hypertension (Riordan, 2003). The HMWM antihypertensive activity in vitro (37–45% of ACE inhibition at the concentration of 2 mg/mL) is attributed to the melanoidins. It has been also reported that the ACE-inhibitory activity of HMWM fractions increase with the degree of roast (RufianHenares & Morales, 2007a). Separate study has showed similar results: concentrations higher than 1.5 mg/mL of the HMWM isolated from coffee inhibited in vitro ACE activity by 50% (De Marco et al., 2011). Nevertheless, as mentioned before, estimated intake of coffee melanoidins varies between 0.5 and 2.0 g per day (Fogliano & Morales, 2011), therefore does not reach the required concentration for antihypertensive activity HMWM. Several molecular mechanisms have been suggested, despite the exact one is still unclear (Rufian-Henares & Morales, 2007a,c). Taking into consideration that ACE is a zinc-dependent enzyme (Spyroulias et al., 2004), the inhibitory activity of melanoidins can come from their metal-chelating properties. On the other hand, melanoidins may bind to the enzyme in an area other than the active center and act as an ACE non-competitive inhibitor (Hernańdez-Ledesma et al., 2003).

Trigonelline N-methylnicotinic acid (C7H7NO2), better known as trigonelline, is a plant alkaloid derivate of vitamin B6 with a bitter taste contained in coffee beans and most likely one of the main components that contributes to undue bitterness in coffee (Zhou et al., 2012). Its amount in green coffee beans generally range between 0.6% and 1%, but after the roasting process at 230 C, approximately 85% of the trigonelline is broken down to nicotinic acid, with few trigonelline molecules still remaining in the roasted beans (Zhou et al., 2012). Trigonelline can be formed in green coffee beans also as a secondary metabolite by nicotinic acid (pyridinium-3-carboxylic acid) methylation using methionine, a sulfur-containing amino acid (Zhou et al., 2012). Absorption and metabolism After direct injection of trigonelline into the upper end of the duodenum in specific pathogen-free and germ-free rats, the remaining trigonelline in the sac of small intestine markedly


decreased with time. Trigonelline was not destroyed by the small intestinal microflora, and the majority of the trigonelline was absorbed from the small intestine with a moderate rate of absorption and high rate of elimination in rabbit’s urine (Zhou et al., 2012). Trigonelline and diabetes Trigonelline has been reported to have hypoglycemic and hypolipidemic effects (Zhou et al., 2012). In animal models of diabetes, administration of trigonelline lowered blood glucose levels in oral glucose tolerance tests (OGTTs) indicating that improved glucose tolerance in diabetes with obesity (Yoshinari & Igarashi, 2010; Zhou et al., 2013). The effect of this compound has been reported also in humans in a study where administration of trigonelline (500 mg) led to a significant reduction of glucose and insulin concentrations 15 min following an OGTT compared with placebo (van Dijk et al., 2009). However, the treatment did not affect insulin or glucose area under the curve values during the OGTT, suggesting that its action was limited to the early glucose and insulin responses. A similar experiment in rats resulted in similar findings, with decreased insulin levels over 120 min after ingestion of trigonelline in contrast with the gradual increase observed in control rats (Yoshinari et al., 2009). Treatment with trigonelline has been shown to reduce serum cholesterol and triglyceride levels in type 2 diabetic rats (Zhou et al., 2013). It has been suggested that the suppression of both triglyceride accumulation and the progression of diabetes may depend of the inhibition of liver fatty acid synthase activity and an increase of liver carnitine palmitoyltransferase and glucokinase activities in rats (Yoshinari et al., 2009). Tissue triglycerides were also decreased in the liver and adipose tissue of mice fed with trigonelline, reinforcing the hypothesis that it can reduce the changes in lipid levels accompanied with diabetes (Yoshinari & Igarashi, 2010). Antioxidant effects of trigonelline Together with other components previously encountered, trigonelline also demonstrated antioxidant capacity on human colon cell lines (Bakuradze et al., 2010). Rats treated with trigonelline showed to decrease MDA and nitric oxide contents and increase superoxide dismutase, catalase, glutathione and inducible nitric oxide synthase activities in the pancreas (Zhou et al., 2013). These findings suggested that trigonelline may have beneficial effects in the diabetic pancreas and may exert its antioxidant action by up-regulating antioxidant enzyme activities and decreasing lipid peroxidation.

Considerations for future research Health risks and benefits of coffee consumption on cardiovascular system require reliable studies on exposure to caffeine and other compounds in coffee, both in short and, more importantly, long time consumers. Nowadays, we are assisting to the inconsistency between observational and experimental studies, as a result of the biological differences between short- versus long-term coffee consumption. Furthermore, results from laboratory studies exploring the effects of purified components of coffee cannot often be reproduced in the human system or do not correspond to equivalent effects in nutritional epidemiology studies. The differences between the laboratory setting and the ‘‘real world’’ consumption of coffee must take into account several factors. First, the potential protective (CGAs, melanoidins) and detrimental (caffeine and diterpenes) effects of single compounds should be evaluated as a whole and not at the individual extent. Second, coffee consumption may be associated with unhealthy lifestyles

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(such as smoking and alcohol drinking) that are demonstrated risk factors for CVD and, thus, may alter results from epidemiological studies. Third, the natural genetic heterogeneity in a (study) population may mask associations between dietary exposures and chronic disease risk. Future epidemiological studies should take into consideration potential interactions between coffee intake and genetic polymorphisms in order to identify specific genotypes that are more likely to suffer of detrimental effects of coffee consumption or in contrast to benefit of the protective effects related to coffee consumption.


Conclusions Overall, there is little evidence of health risks associated with coffee consumption, the most relative to excessive intakes and documentated in some at risk populations, for instance hypertensive and elderly individuals. In contrast, some health benefits may overcome by moderate coffee consumption (3–4 cups/d providing 300–400 mg/d of caffeine). Further research is needed to better identify potential daily threshold of coffee consumption and to determine whether long-term caffeine consumption may have a detrimental effect on the health. Among the main components of coffee, melanoidins require better understanding of their chemical structure to evaluate their potential antioxidant capacity, therefore to better understand their impact on human health.

Declaration of interest The authors declare that no competing interests exist. Giuseppe Grosso was supported by the International PhD Program in Neuropharmacology, University of Catania, Catania, Italy. The contributors had no role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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