Chocolate is usually eaten for pleasure, nevertheless it can potentially have many health effects, both positive and negative. Cocoa or dark chocolate may positively affect the circulatory system through lots of mechanisms.
According to the research, limited amounts of dark chocolate seem to help preventing heart disease.
Chocolate consumption is inversely associated with prevalent coronary heart disease, 2011.
1.EFFECTS ON LDL AND HDL
The oxidation of LDL is considered as the main factor in inducing a coronary disease. When this substance oxidizes, it tends to stick to the artery walls, increasing the risk of a heart attack or a stroke.
The oxidation of LDL is caused by enzymes and oxidative metabolite which are produced by the cell, especially by macrophages-monocytes engaged by the endothelium in order to repair the injury (that can have different causes).
Initially, LDLs are partly oxidized. They provoke the inflammatory reaction and stimulate wall cells to produce recruitment factors for monocytes and for their conversion in macrophages.
Macrophages stimulate the further oxidations that can make the protein component more negative.
Thus, LDL-OX can’t be recognized by LDL-R, they bind scavenger receptor (SR) like: SR-A, CD36 e CD68.
Scavenger receptors do not have a negative feedback so the cell introduces these active molecules (LDL-OX) but also cholesterol and fat derived from cholesterol, that transform the endothelial cell in “foam cell”, typical of atherosclerosis.
LDL-OX active in the cell (endothelial cells, macrophages, smooth muscle cells) some transcription factors (like NF-kB) that induce gene expression encoding for adhesive molecules, cytokines and growth factors (for example ICAM-1, VCAM-1 e E selettina, MCP-1 that is a chemotactic factor and tissue factor) that starts the inflammatory reaction.
LDL-OX effects are:
a. Recruitment of monocytes and lymphocytes T inducing the expression of adhesive molecules, chemotactic factors (which partly stay on the endothelial surface and are partly released in the sub endothelium) and growth factors for monocytes-macrophages and smooth muscular cells;
b. Inhibition of the mobility of macrophages with a chemotactic direct effect;
c. Direct cytotoxic activity which leads to the release of cellular lipids and lysosomal enzymes;
d. Mitogen direct activity on smooth muscular cells, macrophages, fibroblasts and endothelial cells;
e. Inhibition of vessels dilatation endothelium-dependent stimulating the production of Endothelin and inhibiting NO synthesis;
f. Formations of thrombus stimulating the synthesis of PAI-1 (plasminogen activator inhibitor-1) and Tissue Factor, that promote the coagulation, and cause the platelets aggregation activating platelets.
A lot of researches show how the polyphenols in chocolate may inhibit oxidation of LDL cholesterol.
Thanks to polyphenols, such as catechins and procyanidins, the cocoa powder can inhibit low-density lipoprotein (LDL) oxidation and atherogenesis in a variety of models.
In fact it terminates the chain reactions that can be enhanced by ROS (Reactive Oxygen Species) removing free radical intermediates, and inhibit other oxidation reactions. They do this by being oxidized themselves, so they are reducing agents.
Continuous intake of polyphenolic compounds containing cocoa powder reduces LDL oxidative susceptibility and has beneficial effects on plasma HDL-cholesterol concentrations in humans,2007
Human studies have also shown daily intake of cocoa increases plasma high-density lipoprotein (HDL) and decreases LDL levels. Cocoa polyphenols increase apolipoprotein A1 protein levels and mRNA expression, even though apolipoprotein B protein and the mRNA expression are decreased. The ApoB is the major component of the LDL while the ApoA1 is the major protein in HDL; so LDL serum level decreases while the HDL serum level increases.
In addition, cocoa polyphenols increase sterol regulatory element binding proteins (SREBPs are transcription factors that bind to the sterol regulatory element DNA sequence TCACNCCAC. SREB proteins are indirectly required for cholesterol biosynthesis and for uptake and fatty acid biosynthesis) and activated LDL receptors.
These results suggest that cocoa polyphenols may increase the production of mature form SREBPs and LDL receptor activity, thereby increasing ApoA1 and decreasing ApoB levels.
Nevertheless the entire mechanism haven’t been elucidated yet.
Dark chocolate consumption increases HDL cholesterol concentration and chocolate fatty acids may inhibit lipid peroxidation in healthy humans, 2004.
Cocoa polyphenols influence the regulation of apolipoprotein in HepG2 and Caco2 cells, 2011
2. FLAVONOIDS AND THEIR ACTION ON CARDIAC CELLS
The polyphenols’ action is mediated by their major subclasses, the flavonoids, which have a lot of functions, including antioxidant protection and modulation of vascular homeostasis. These findings are supported by similar researches on other flavonoid-rich foods.
Cocoa and chocolate flavonoids: implications for cardiovascular health, 2003.
The most important flavonoid is the epicatechin, that is linked to a variety of protective effects in humans.
In particular, its role in protection against cardiovascular disease has been demonstrated by epidemiologic studies.
Low-dose epicatechin, which has any significant antioxidant activities, is also protective; so, in addition to their antioxidant properties, they have therapeutic effects,too .
Furthermore, 3′-O-methyl epicatechin, which can’t be used as an antioxidant, produces a similar antiapoptotic effect as epicatechin, suggesting that antioxidant activity is not the primary mechanism of protection.
In order to demonstrate these effects, epicatechin was given at a low dose (1 mg/kg) with long-term administration (10 days). At this dose, an antioxidant effect that occurs with high-dose flavonoid administration likely does not appear.
So a potent protective effect was observed, indicating that two mechanisms probably exist, for flavonoids, to promote cell survival:
1. Antioxidant activity;
2. Signaling via receptor-mediated pathways to activate survival signaling.
Epicatechin-induced cardiac protection also seems to involve the activation of the mitochondrial KATP channel but the exact mechanism has not been discovered yet.
Dark chocolate receptors: epicatechin-induced cardiac protection is dependent on δ-opioid receptor stimulation, 2010.
It can be mediated via δ-opioid receptor activation.
The result of some experiments shows that infarct size was significantly reduced after somministration of epicatechin. The importance of δ-opioid receptor was demonstrated using pharmacological antagonists like naloxone, naltrindole, and 5-HD.
Opioid receptors are involved in cardiac protection via the activation of Akt and Src pathways, and epicatechin activates similar protein kinase signaling pathways as opioids.
Epicatechin induces Akt, Src, and IκB phosphorylation in the heart.
An important number of recent studies have determined an essential role for Src / phosphatidylinositol 3-kinase / Akt pathway in myocardial survival following ischemia-reperfusion injury, and Akt also functions as a nodal point to coordinate growth factor signaling with myocyte survival.
1) Bad:it results in Bad inhibition;
2) IκB (IKK): it results in IκB activation.
The phosphorylation of IκB is a prerequisite for NF-κB activation and is a surrogate marker of the induction of the survival NF-κB pathway. Increased binding of NF-κB to DNA protects myocytes from ischemic stress.
NF-κB increases and JNK decreases cell survival in animal models; we show that epicatechin reduces apoptosis via decreased JNK.
KEGG DIAGRAM: Akt
KEGG DIAGRAM: IkB/NF-κB
As these pathways show, the NFkB inhibits the apoptosis inducing the expression of IAP, Bcl-XL and Bcl-2.
Bcl-2 and Bcl-XL can inactivate the MPT (mitochondrial permeability transition pore o MPT pore), that is in the inner membrane of the mitochondria and it is involved in the regulation of Calcium concentration, ph and mitochondrial membrane voltage. Furthermore, these proteins inhibit the release of cytochrome C in the cytosol, and the consequent activation of caspase-9 and caspase-3, that lead to apoptosis (intrinsic pathway).
IAP proteins bind the caspases, reducing enzymatic activity and inducing their ubiquitination and degradation.
KEGG DIAGRAM: Akt
KEGG DIAGRAM: Jnk
As these pathways show Akt inhibits indirectly JNK, that is involved in apoptosis pathways.
JNK (in the heart there is especially the isoform JNK3) induce apoptosis phosphorylating the transcription factor c-Jun (on its N-terminal transactivation domain at two serine residues, Ser63 and Ser73) and phosphorylating and regulating the activity of transcription factors like ATF2, Elk-1 and p53.
When p53 accumulates in the nucleus, it induces the expression of BH3 proteins (family of Bcl2, for example BAD) that induce apoptosis above all inhibiting the production of Bcl2 protein antiapoptotic.
KEGG DIAGRAM: p53
Role of JNK activation in apoptosis: A double-edged sword, 2005.
3. EFFECT ON BLOOD PRESSURE
Dark chocolate and cocoa also reduce blood pressure in both overweight and normal adults.
It has been demonstrated that dark chocolate increases NOX (eNOS) serum levels which leads to a reduction of systolic blood pressure (4-5 mmHg).
When NO forms, it has a half-life of only a few seconds, in large part because superoxide anion has a high affinity for NO (both molecules have an unpaired electron, making them highly reactive).
NO also avidly binds to the heme moiety of hemoglobin (in red blood cells) and the heme moiety of the enzyme guanylyl cyclase, which is found in vascular smooth muscle cells and in most other cells of the body. Therefore, when NO is formed by vascular endothelium, it quickly diffuses into the blood where it binds to hemoglobin and subsequently breaks down. It also diffuses into the vascular smooth muscle cells adjacent to the endothelium where it binds to and activates guanylyl cyclase.
This enzyme catalyzes the dephosphorylation of GTP to cGMP, which works as second messenger for many important cellular functions, particularly for signaling smooth muscle relaxation.
Cyclic GMP induces smooth muscle relaxation by multiple mechanisms including:
1.Increased intracellular cGMP, which inhibits calcium entry into the cell, and decreases intracellular calcium concentrations;
2.Activates K+ channels, which leads to hyperpolarization and relaxation;
3.Stimulates a cGMP-dependent protein kinase that activates myosin light chain phosphatase, the enzyme that dephosphorylates myosin light chains, which leads to smooth muscle relaxation.
Effect of dark chocolate on nitric oxide serum levels and blood pressure in prehypertension subjects, 2011.
Furthermore, it has been shown that cocoa polyphenols lower arginase-2 mRNA expression and activity in primary human endothelial cells.
The arginase competes with eNOS for l-arginine as the common substrate. When the level of arginase decreases, the L-arginine is used as substrate for eNOS.
Chocolate: (un)healthy source of polyphenols?,2010.
Consumption of flavanol-rich cocoa inhibited several measures of platelet activity including, epinephrine- and ADP-induced glycoprotein (GP) IIb/IIIa and P-Selectin expression, platelet microparticle formation, and epinephrine-collagen and ADP-collagen induced primary hemostasis.
It can enhance the effects on the blood pressure.
Flavanols and Platelet Reactivity,2005
Does chocolate reduce blood pressure? A meta-analysis, 2010