Inflammation plays an important role in developing cardiovascular diseases and other comorbidities, such as hypertension, hypercholesterolemia, type 2 diabetes, chronic kidney disease, and obesity. Astaxanthin exerts a marked anti-inflammatory effect, which may be interrelated with its antioxidant effect and contributes to physiological changes that benefit cardiovascular function.

Atherosclerosis is a degenerative and chronic disease that affects large- and medium-caliber arteries. Atherogenesis, the initial phase of the atherosclerotic process, is characterized by the accumulation of LDL in the subendothelial layer of the vascular wall, which is responsible for inflammation mediated by the innate and adaptive immune responses. As will be detailed below, the anti-inflammatory effects promoted by astaxanthin are proved in its role in atherosclerosis prevention.

The epitopes generated from enzymatic or non-enzymatic oxidation of LDL are the main damage-associated molecular patterns recognized by macrophages and are responsible for the onset of the inflammatory cascade, with the release of cytokines and chemokines that recruit more resident vascular macrophages and monocytes from the blood. Macrophages bind to oxidized LDL via scavenger receptors, such as SR-A, SR-B2 (CD36), and LOX-1. The expression of these receptors is controlled by nuclear factor-κB (NF-κB), the primary mediator of the inflammatory response, which is activated by pattern recognition receptors and proinflammatory cytokines.

In inflammatory states, macrophages produce excessive proinflammatory mediators, such as cytokines, chemokines, NO, cyclooxygenase-2 (COX-2), and matrix metalloproteinases (MMPs). MMPs are responsible for the degradation of most extracellular matrix proteins and mediate the tissue remodeling associated with atherosclerosis.

In vitro and in vivo studies have evaluated the effect of astaxanthin on the formation of atherosclerotic plaques. Supplementation with ten µM astaxanthin significantly reduced the expression of the SR-A and CD36 scavenger receptors in the THP-1 macrophage line. It reduced the total activity of MMPs, as reflected by reduced protein expression of MMP-9 and MMP-2 and the mRNA levels of five MMPs.

Astaxanthin at this concentration also reduced the gene expression of proinflammatory markers, such as interleukin (IL)-1β, IL-6, tumor necrosis factor-α (TNF-α), inducible nitric oxide synthase (iNOS), and COX-2. These results corroborate those of other studies indicating that astaxanthin reduces the expression of proinflammatory mediators in macrophages and other cell types, such as microglia, endothelial vascular cells, and human neutrophils.

The significant decreases in the levels of MMPs and proinflammatory cytokines may result from astaxanthin’s suppression of the NF-κB transcription factor. NF-κB is frequently activated at inflammation sites associated with various pathologies, particularly cardiovascular diseases, in which the increased expression of its proinflammatory target genes plays a key role.

The inflammatory pathway of NF-κB is, at least in part, regulated by oxidative stress. Astaxanthin inhibits the activity of IκB kinase, a complex responsible for controlling NF-κB activation. This maintains NF-κB inactive in the cell cytoplasm, and its proinflammatory target genes, such as TNF-α, IL-1β, and iNOS, are downregulated.

Cholesterol uptake is balanced by transferring this molecule from macrophages to free apolipoproteins A1 or HDL, the latter being responsible for the reverse cholesterol transport process. When cholesterol uptake exceeds cholesterol efflux in macrophages, lipid droplets accumulate in the cytoplasm, forming foam cells, the primary markers of atherosclerosis. The progression of cholesterol accumulation may lead to its precipitation in the form of crystals, which activate the inflammasome, leading to cell death by apoptosis or necrosis. The atherosclerotic plaque is separated from the bloodstream by a fibrous layer, which, upon rupture, initiates intraluminal thrombosis, the initial event of stroke and other coronary syndromes.

Reverse cholesterol transport consists of HDL removing excess cholesterol from peripheral tissues and transporting it to the liver, where it is degraded by bile juice and excreted in the feces, thus preventing the accumulation of cholesterol in macrophages. The liver and intestine synthesize apolipoprotein A-I (apoA-I) and apoA-II in the plasma, incorporating free cholesterol and phospholipids through the ATP-binding cassette A1 (ABCA1) hepatic transporter originating from nascent HDL. In peripheral tissues, nascent HDL molecules recruit free cholesterol from foam cells via the macrophage ABCA1 transporter.

This reverse cholesterol transport was also observed in the lymphatic system, which is mainly responsible for removing cholesterol from different tissues. Finally, mature HDL can transport cholesterol directly to the liver via the SR-B1 scavenger receptor or transfer cholesteryl esters to very-low-density lipoprotein (VLDL) through the cholesteryl ester transfer protein. These lipoproteins are absorbed in the liver by their specific receptors, likely the predominant pathway in humans. Once in the liver, cholesterol is secreted into the bile via the ABCG5 and ABCG8 transporters. Some of these molecules can be reabsorbed by the intestine and reach the bloodstream again, while the rest is excreted in the feces.

In atherosclerosis, apolipoproteins are oxidized by the myeloperoxidase, which is expressed in macrophages during the inflammatory process, compromising cholesterol efflux via ABCA1. In individuals with heart disease, elevated levels of apoA-I modified by myeloperoxidase were identified, and their HDL molecules were dysfunctional in performing reverse cholesterol transport. In addition, an association was observed between increased cholesterol efflux via ABCA1 and reduced risk of cardiovascular diseases (OR=0.30; 95% CI: 0.14-0.66; P<0.003).

Thus, the oxidation of apolipoproteins by macrophage myeloperoxidase is a determining factor in HDL dysfunction in cholesterol transport and, therefore, in the risk of cardiovascular diseases.

The effects of astaxanthin on reverse cholesterol transport have been demonstrated in vivo. In wild-type and ApoE−/− mice, astaxanthin increased cholesterol efflux from peripheral tissues to the liver and its subsequent excretion in feces.

Additionally, in the ApoE−/− model, this carotenoid promoted a significant decline in plasma total cholesterol, triglycerides, and non-HDL cholesterol. It reduced the atherosclerotic plaque area of the aortic sinus and the cholesterol concentration in the aorta compared to controls. Thus, astaxanthin may exert antiatherosclerotic effects by increasing the activity of the reverse cholesterol transport pathway, but the molecular mechanisms underlying this action remain elusive.

In addition to its function in reverse cholesterol transport, astaxanthin is involved in certain lipid metabolism steps, a finding corroborated by a randomized, placebo-controlled clinical study of 61 adult individuals with moderate hyperlipidemia. In that study, daily supplementation with 6, 12, or 18 mg astaxanthin for 12 weeks improved the patients’ lipid profile.

Triglycerides were reduced by 25.2 and 23.8% (P<0.05) by doses of 12 and 18 mg, respectively, whereas HDL was increased by 10.6% (P<0.05) and 15.4% (P<0.01) by doses of 6 and 12 mg, respectively. Doses of 12 and 18 mg also significantly increased serum adiponectin (P<0.01 and P<0.05, respectively), a protein secreted by adipocytes with important functions in the cardiovascular and endocrine systems associated with its anti-inflammatory, atheroprotective, and insulin-sensitizing actions.

Inflammation is also involved in the pathophysiology of metabolic syndrome, a multifactorial disorder associated with glucose and lipid metabolism disorders. This disease has risk factors that are also strongly related to the development of cardiovascular complications, including type 2 diabetes, dyslipidemia, hypertension, and abdominal fat deposition. In this context, astaxanthin has been found to be promising in improving glucose and lipid metabolism in a randomized, placebo-controlled clinical study with 43 diabetic patients aged 46-62 years.

In agreement with a previous clinical study, supplementation with astaxanthin (8 mg/day for eight weeks) significantly increased serum adiponectin (47±14 vs. 45±13 and 36±15 µg/ml compared with placebo and baseline, respectively; P<0.05) and improved the lipid profile of the patients, as shown by the reductions in the levels of triglycerides (128±52 vs. 150±85 and 156±90 mg/dl compared with placebo and baseline, respectively; P<0.05) and VLDL (27±16 vs. 31±16 mg/dl compared with placebo; P<0.05).

Furthermore, astaxanthin marginally reduced fasting glucose levels (8.3±2.7 vs. 9.4±3.2 mmol/l compared with placebo; P=0.057) and significantly increased serum fructosamine levels (5.8±3.8 vs. 7.32±4.31 and 7.36±4.2 µmol/l compared with placebo and baseline, respectively; P<0.05), an important marker in the control of diabetes that reflects the mean concentration of blood glucose. Patients receiving astaxanthin supplementation also exhibited lower visceral fat deposition (11.2±3.4 vs. 11.85±3.8% compared with placebo; P<0.05) and systolic blood pressure (132±18 vs. 133±19 and 143±27 mmHg compared with placebo and baseline, respectively; P<0.05).

Disorders characterized by ischemia/reperfusion, including myocardial infarction, stroke, and peripheral vascular disease, are among the most frequent causes of morbidity and mortality worldwide. Ischemia/reperfusion is a complex inflammatory process associated with high levels of oxidative stress in the affected tissue.

In rodents with hepatic lesions induced by ischemia/reperfusion, astaxanthin not only reduced oxidative stress and histopathological damage but also exerted a significant anti-inflammatory effect, attenuating the release of inflammatory cytokines through the mitogen-activated protein kinase (MAPK) pathway.

Furthermore, astaxanthin exerted an anti-inflammatory and antioxidant influence in the context of myocardial injury due to ischemia/reperfusion in rabbits by significantly reducing the activation of the complement system associated with the reduced deposition of C-reactive protein and the membrane attack complex in the injured area of the myocardium.

In mice with non-alcoholic steatohepatitis (NASH) induced by a high-lipid diet, supplementation with astaxanthin (0.02% in the diet, ~20 mg/kg body weight) significantly improved several liver parameters: it reduced liver inflammation, decreased the proportion of pro-inflammatory M1-type macrophages, reduced stellate cell activation, and attenuated liver fibrosis, the accumulation, and peroxidation of hepatic lipids and insulin resistance.

Additionally, astaxanthin was more effective in preventing and treating NASH and improving liver inflammation and fibrosis than vitamin E (standard NASH treatment). The same study also corroborated the potential of astaxanthin to improve NASH in 12 individuals receiving this carotenoid as a supplement (12 mg/day; control: placebo) for 24 weeks.

The effects of astaxanthin on the relief of liver injury were shown to be correlated to its positive impact on the intestinal microbiota and consequent reduction of inflammation. A growing body of evidence indicates that gut microbiota plays a key role in the pathogenesis of inflammatory disorders and cardiovascular diseases, and alterations in its composition (dysbiosis) have been associated with heart failure, hypertension, atherosclerosis, and metabolic syndrome.

Several recent in vivo studies revealed that astaxanthin supplementation improved gut microbiota composition, which may contribute to its local and systemic anti-inflammatory and antioxidant effects. The beneficial effect of astaxanthin on gut microbiota is correlated with the mitigation of cardiovascular disease-related pathologies and risk factors, such as obesity, insulin resistance, and alcoholic fatty liver disease.

The anti-inflammatory and antioxidant effects of astaxanthin were also confirmed by a randomized clinical trial in 42 healthy young women receiving a placebo or astaxanthin at 2 or 8 mg/day. Compared with placebo, after eight weeks of treatment, 2 mg astaxanthin significantly lowered the plasma inflammatory marker C-reactive protein (unspecified values; P<0.05). Astaxanthin improved the immune responses of the participants, as evidenced by the increased cytotoxic activity of natural killer cells (8 mg dose, 67.9±3.0 vs. 57.8±2.7% lysis; P<0.05), levels of T and B lymphocytes (2 mg dose, 75.7±1.6 vs. 70.6±1.5 and 13.1±0.5 vs. 10.7±0.5%, respectively; P<0.05), and the production of interferon (IFN)-γ and IL-6 (dose of 8 mg, 9.55 vs. 4.68 and 25.2 vs. 13.6 pg/ml, respectively; P<0.05).

Finally, starting at four weeks, both doses drastically reduced the plasma levels of 8-OHdG (unspecified values; P<0.01), a biomarker of oxidative DNA damage.

Although macrophages are the primary type of immune cell found in atherosclerotic plaques, T lymphocytes also contribute to the development of the disease. The inflammatory response mediated by T lymphocytes plays a crucial role in the etiology of cardiovascular diseases, contributing to atherosclerosis, heart failure, and myocardial infarction. For example, T helper cells can be activated by LDL particles in the arterial wall and trigger inflammation through an autoimmune response, contributing to the development of atherosclerotic plaques. Similarly, self-reactive T helper cells may target cardiomyocytes, contributing to the development of heart failure.

Astaxanthin was shown to be effective in preventing oxidative stress in T lymphocytes and in modulating their activity. In the aforementioned clinical study on healthy young women, astaxanthin supplementation stimulated mitogen-induced lymphoproliferation. It increased the subpopulation of T lymphocytes without changing the populations of T killer or T helper cells and increased the response to tuberculin, an indicator of T lymphocyte function.

In a mouse model of NASH, astaxanthin reduced T helper and T killer cell recruitment to the liver, contributing to improving inflammation and insulin resistance. Supplementation for 45 days with fish oil containing astaxanthin (1 mg/kg of body weight) reduced the proliferative capacity of T lymphocytes in response to mitogens and RONS production compared with fish oil alone. In in vitro studies with peripheral blood mononuclear cells from patients with asthma and allergic rhinitis, it was demonstrated that astaxanthin significantly suppressed the activation of T lymphocytes induced by phytohemagglutinin.

Another in vitro and ex vivo study with cultured lymphocytes demonstrated that astaxanthin stimulated their immune response and increased the production of IL-2 and IFN-γ without inducing cytotoxicity. The administration of astaxanthin in mice prevented renal fibrosis by mechanisms involving stimulation of T killer cell recruitment and the increased output of IFN-γ. In cats, astaxanthin increased the immune response mediated by total T lymphocytes and T helper cells.

Therefore, astaxanthin was shown to exert an apparent modulatory effect on T lymphocytes, improving their immune response or downregulating their potentially pathological immune activation. However, the role of T lymphocyte modulation by astaxanthin in the risk and progression of cardiovascular diseases remains to be fully elucidated.

In summary, inflammation plays a key role in the pathophysiology of cardiovascular diseases and their risk factors, while astaxanthin exerts beneficial anti-inflammatory effects. The mechanism of action of this carotenoid involves inhibition of the NF-κB and MAPK signaling pathways, which suppresses the inflammatory process and stimulates reverse cholesterol transport, thereby attenuating the formation of foam cells.