Reactive oxygen species (ROS) cause oxidative stress that contributes to the pathogenesis of various diseases, including inflammation, cancer, and neurodegenerative diseases ^[1][2][38,39]. ROS, including radical and non-radical derivatives, such as superoxide anions, hydroxyl radicals, and hydrogen peroxide, mainly derived from oxidative metabolism during inflammatory reactions ^[1][38], are generated by redox reactions during cellular metabolism. However, excess production of ROS can cause oxidative damage to essential molecules such as proteins, lipids, and DNAs ^[2][39]. Chlorogenic acids exert their antioxidant effect via their polyhydroxyl structure that directly scavenges free radicals and regulates the activity of the endogenous oxidase system and its associated proteins ^[3][4][40,41]. This natural antioxidant property depends on the chlorogenic acid’s unique molecular structure, which contains several active hydroxyl groups and one carboxyl group. Of these, the phenolic hydroxyl structure readily reacts with free radicals and forms hydrogen free radicals, which eliminate hydroxyl radicals and superoxide anions and exhibit a strong antioxidant effect ^[5][6][37,42]. Thus, under some circumstances, coffee might contribute to the endogenous systems which prevent oxidative damage to cell components, DNA, proteins, and lipids, which contribute to the pathogenesis of inflammation, cancer and neurodegenerative diseases ^[7][43]. Consequently, the consumption of instant coffee, which contains increased levels of chlorogenic acids, enables protection against oxidative damage in healthy adults ^[8][44].

Chlorogenic acids can eliminate superoxide anions and hydroxyl radicals through their antioxidant activities, rendering coffee an effective dietary antioxidant source due to its high chlorogenic acid content ^[9][45]. Chlorogenic acids directly act on the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) signaling pathway and control the expression of both pro- and anti-inflammatory factors ^[10][11][46,47]. Studies have shown that chlorogenic acids can inhibit interleukin-8 (IL-8) production in human intestinal Caco-2 cells, induced by combined stimulation with tumor necrosis factor-alpha (TNF-α) and H₂O₂ ^[12][48]. IL-8 is a cytokine similar to platelet factor 4, with a chemoattractive activity. IL-8 is produced by phagocytes and mesenchymal cells exposed to inflammatory stimuli and activates neutrophils inducing chemotaxis. These results suggest that dietary chlorogenic acids might prevent intestinal inflammation ^[12][48]. Vascular endothelial cells exhibit upregulation of adhesion molecules, such as intercellular adhesion molecule 1 (ICAM-1) and vascular cell adhesion molecule 1 (VCAM-1), which enable recruitment of immune cells, including monocytes, to the inflammation site. ICAM-1 and VCAM-1 are the members of the immunoglobulin superfamily of transmembrane adhesion molecules with an amino-terminus extracellular domain, a single transmembrane domain, and a carboxy-terminus cytoplasmic domain. VCAM-1 binds to its ligand, very late antigen-4 (VLA-4). Furthermore, chlorogenic acid attenuates the enhanced expression of ICAM-1 and VCAM-1 induced by interleukin-1β, highlighting its anti-inflammatory activities ^[13][49]. The recruitment of neutrophils to the site of inflammation is a typical process during inflammation, and the interactions of the circulating neutrophils with the vascular endothelial cells is the initial step of neutrophil recruitment, which is mediated by certain adhesion molecules expressed on the surface of neutrophils. In this context, an adhesion molecule CD62L, also called L-selectin, plays a pivotal role in cell–cell interactions. CD62L is a member of the carbohydrate-binding selectin family of cell adhesion molecules and forms a type-I transmembrane protein comprising an N-terminal lectin domain, an epidermal growth factor (EGF)- like domain, two short consensus repeats, a transmembrane region, and a short cytoplasmic domain. CD62L is expressed in leukocytes and located at the cell surface, which plays a pivotal role in multistep cell-cell adhesion interactions. A previous study reported that chlorogenic acid could attenuate the lipopolysaccharide-induced CD62L proteolytic processing of neutrophils and decrease the adhesion and chemotaxis of neutrophils to vascular endothelial cells ^[14][50]. Platelets are also key mediators of inflammation and platelet–endothelial cell interactions at the site of lesion trigger inflammatory responses. Upon platelet activation, the CD62P adhesion molecule, also called P-selectin, translocates from the Weibel–Palade bodies inside the cell body into the plasma membrane, where fibrinogen causes platelet aggregation. In addition, chlorogenic acid inhibits the expression of CD62P in human platelets and impair platelet–leukocyte interactions ^[15][51].

Numerous epidemiological studies have indicated that coffee consumption might lower the risk of certain types of cancer. For instance, coffee consumption has been found to strongly and consistently reduce the risk of endometrial and hepatocellular cancer ^[16][10], and a modest or borderline negative association with breast and colorectal cancer has been reported. Contrastingly, no association was found with pancreatic, ovarian, prostate, or gastric cancer ^[16][10]. The epidemiologic evidence of coffee on each type of cancer is summarized in the literature ^[17][52].

One of the eight distinct hallmarks of cancer involves the acquired capability for sustaining proliferative signaling ^[18][19][53,54]. The first step of cancer progression toward poorly differentiated carcinomas is dedifferentiation which is not initially associated with increased proliferation. A study showed that chlorogenic acids could inhibit the proliferation of A549 human lung cancer cells in vitro by inhibiting activator protein-1, NF-κB, and mitogen-activated protein kinases (MAP kinases) ^[20][55]. NF-κB plays critical roles in inflammation, cell proliferation, differentiation, and survival. MAP kinases have three main families, extracellular-signal-regulated kinases (ERKs), jun amino-terminal kinases (JNKs), and p38/stress-activated protein kinases (SAPKs). These respond primarily to growth factors and mitogens to induce cell growth and differentiation. This suggests that the consumption of chlorogenic acids through coffee might prevent cancer ^[21][22][56,57].

In addition, matrix metalloproteinases (MMPs) are essential enzymes employed by tumor cells during metastasis that degrade proteins and regulate various cell behaviors ^[23][24][58,59]. These proteolytic enzymes are prevalent in cancer biology due to their capacity to promote cancer-cell growth, differentiation, apoptosis, migration, and invasion while they also regulate tumor angiogenesis and immune surveillance ^[23][58]. The MMPs belong to a family of zinc-dependent endopeptidases with more than 20 different members, and play pivotal roles in the degradation of the extracellular matrix which is composed of collagens, fibronectins, and laminins, which help maintain homeostasis. Based on their sub-cellular distribution and specificity for components of the extracellular matrix, the MMPs are divided into collagenases, gelatinases, stromelysins, matrilysins, and membrane-type matrix metalloproteases: MMPs that belong to collagenases are MMP-1, MMP-8, MMP-13, and MMP-18, which degrade triple-helical fibrillar collagen; MMPs that belong to gelatinases are MMP-2 and MMP-9; stromelysins include MMP-3 and MMP-10; MMP-11, and MMP-7 and MMP-26 are matrilysins. MMPs are inhibited by endogenous protein regulators, namely, the tissue inhibitors of MMPs (TIMPs). Most MMPs have consistently increased gene expression across cancers, and MMP1, MMP9, MMP10, MMP11, and MMP13 are almost universally upregulated across a wide variety types of cancers ^[24][59]. Of all MMPs, MMP-9 is the most essential for cancer-cell invasion and tumor metastasis ^[25][60]. Chlorogenic acids have been shown to inhibit MMP-9 activity in cultured hepatoma cells, indicating a possible cancer chemoprevention mechanism ^[26][61]. Furthermore, MMP-2, also called gelatinase A, also plays a significant role in ECM degradation because it can degrade collagen type IV during cancer progression, allowing cancer cells to migrate from the primary tumor to form metastasis ^[27][62]. However, chlorogenic acids have been found to inhibit cell migration and MMP-2 secretion of human glioma cells, highlighting their anti-cancer effects ^[28][63].

The signaling pathway comprising phosphatidylinositol 3-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR)/phosphatase and tensin homologue deleted on chromosome ten (PTEN) plays a pivotal role in cancer progression, including cell proliferation and migratory activities ^[29][64]. Particularly, PI3K has been shown to induce the expression of the multidrug resistance-associated protein, suggesting that high PI3K activity facilitates drug resistance ^[29][64]. Therefore, the PI3K/AKT/mTOR/PTEN axis is an attractive target for targeted molecular therapy including cancer ^{[30][31][32][33][34][35][36]}[65,66,67,68,69,70,71]. Moreover, germline mutations in the breast cancer susceptibility gene 1 (BRCA1) considerably increase the risk of breast and ovarian cancers and, thus, modulation of PTEN/BRCA1 proteins may prove therapeutically beneficial for breast, ovarian, and prostate cancer treatment ^[37][72]. Chlorogenic acids have a biological activity to modulate signal transduction through the PI3K/AKT/PTEN pathway, thereby suppressing cancer progression. Chlorogenic acid potentiated the apoptotic effect of certain anti-cancer agents via activation of apoptosis-related molecules, namely Bcl-2-associated X protein (Bax) and Caspase 3/7, and inhibition of anti-apoptotic molecules, namely B-cell/CLL lymphoma-2 (Bcl-2) and B-cell lymphoma-extra large (Bcl-xL), by modulating the PI3K/Akt signaling pathway ^[38][73]. Moreover, chlorogenic acid could selectively suppress the proliferation of human kidney cells by modulating the PI3K/Akt/mTORC signaling pathway ^[39][74].

Wnt signaling is another signaling pathway that plays an important role in cancer-cell signaling. The Wnt signal is transferred into the cytosol and thereby further transduced to the cell nucleus via the β-catenin–T-cell factor and lymphoid enhancer factor (TCF/LEF) complex to enhance the expression of targets, including Myc and leucine-rich repeat-containing G-protein coupled receptor 5 (LGR5). The Wnt pathway is involved in cell polarity formation and cell migration, and chlorogenic acid has been found to modulate the Wnt pathway in cancer cells, including colon cancer cells ^[40][75]. More specifically, chlorogenic acid has been confirmed to decrease the viability and migratory properties of colorectal cancer cells ^[41][76]. Chlorogenic acid affects apoptosis by acting on p53, p21, JNK, and nuclear factor erythroid 2-related factor 2 (Nrf2) molecules and also by regulating microRNA expression ^{[42][43][44][45][46]}[80,81,82,83,84]. Furthermore, the combination of multiple phytochemicals is recently emerging as a promising cancer treatment therapy ^[47][85]. Chlorogenic acid in combination with cinnamaldehyde and arctigenin exhibited synergistic effects by increasing the number of pathways and systems that can be targeted at once ^[48][86].

Chlorogenic acid increases the levels of cyclic adenosine monophosphate (cAMP)-responsive element binding protein (CREB) in the hippocampus and suppresses inflammation in the old brain, facilitating a preventive effect against brain aging ^[49][92]. Alzheimer’s disease is the most common progressive neurodegenerative disorder associated with aging. The pathology of this disease is characterized by an earlier accumulation of extracellular amyloid-beta plaques and intracellular neurofibrillary tangles in the hippocampus, eventually leading to severe neurodegeneration, and cognitive and synaptic impairment over time ^[50][7]. Additionally, hyperphosphorylation of tau, neuronal inflammation, oxidative stress, and cellular apoptosis can contribute to the pathogenesis of Alzheimer’s disease ^[50][7]. Studies have shown that oxidative stress represents a major risk factor associated with the pathology of dementia ^[35][70]. More specifically, substantial evidence has confirmed that oxidative stress is associated with neuronal apoptosis and brain dysfunction in Alzheimer’s disease ^[35][70]. Due to the absence of actual treatments, brain dysfunction in Alzheimer’s disease is a prevalent public health anxiety. Therefore, a number of preventive factors have been proposed by epidemiological research, including modifiable lifestyle factors, such as healthy dietary habits. In fact, it has been revealed that dietary choices can play a certain role in neuroprotection against the Alzheimer’s disease ^[51][93]. However, the relationship between nutrient consumption and neuroprotection is fairly complex. In addition, the convolution of the human diet makes it difficult to examine its distinct effects. Although many lifestyle factors affect brain function, food-related involvements might be a promising strategy in preventing brain dysfunction ^[51][93]. Consumption of Arabian coffee containing moderate caffeine seems to ameliorate Alzheimer’s disease-induced cognitive impairment by decreasing amyloid-beta levels ^[50][7]. It is also believed that antioxidant nutraceuticals such as coffee phenolic compounds may have beneficial effects in the prevention of Alzheimer’s disease ^[52][94].

Parkinson’s disease is a brain disorder that is characterized by neuropsychiatric symptoms such as depression and anxiety preceding the onset of motor symptoms ^[53][95]. The major features of this disease include loss of dopaminergic neurons in the substantia nigra and Lewy body depositions ^[53][95]. It has been suggested that mitochondrial dysfunction, oxidative stress, and oxidative damage underlie the pathogenesis of Parkinson’s disease ^[53][95]. The activity of substantia nigra dopaminergic neurons is critical for striatal synaptic plasticity and associative learning, and degeneration of dopaminergic neurons leads to a disinhibition of the subthalamic nucleus, which in turn increases excitatory projections to the substantia nigra ^[53][95]. Environmental exposures to toxic mediators such as ROS may lead to the development of neurodegenerative disorders with similar clinical findings to Parkinson’s disease ^[53][95]. Consequently, it is critical to develop strategies to ensure that healthy neurons remain alive following ROS attack without using intricate medications ^[53][95]. Epidemiological studies have demonstrated that coffee consumption reduces the risk of Parkinson’s disease, in both case–control and cohort studies, yielding a 33% reduction in risk ^[54][96].