Hyperbilirubinemia modulates myocardial function, aortic ejection, and ischemic stress resistance in the Gunn rat

Cardiovascular and metabolic effects of hyperbilirubinemia in a cohort of Italian Olympic athletes

INTRODUCTION

Bilirubin was supposed to have cardio-metabolic protective role by signaling functions. Indeed, mild hyperbilirubinemia has immunosuppressive and endocrine activities and may offer protection against oxidative stress-mediated diseases. Gilbert syndrome (GS) has been hypothesized to provide cardio-metabolic benefits.

OBJECTIVE

To investigate the prevalence of hyperbilirubinemia and its cardio-metabolic effects in a cohort of elite Italian athletes engaged in different sports disciplines.

METHODS

We enrolled 1492 elite athletes (age 25.8 ± 5.1) practising different disciplines (power, skills, endurance, and mixed) underwent blood, echocardiographic, and exercise tests. GS was diagnosed per exclusionem in athletes with isolated asymptomatic unconjugated hyperbilirubinemia.

RESULTS

GS was highlighted in 91 athletes (6%; globally 9% male and 2.4% female); 82% were males (p < 0.0001) showing higher indirect bilirubin (0.53 ± 0.4 vs. 0.36 ± 0.24 mg/dL in females, p < 0.0001). GS athletes had fewer platelets (201 ± 35 vs. 214 ± 41, p = 0.01), higher iron (male: 124 ± 44 vs. 100.9 ± 34 mcg/dL, p < 0.0001; female: 143.3 ± 35 vs. 99.9 ± 42 mcg/dL, p < 0.0001), and lower erythrocyte sedimentation rate, (1.93 ± 0.9 vs. 2.80 ± 2.7 mm/H, p = 0.03). At multivariate analysis, male (OR 3.89, p = 0.001) and iron (OR 3.47, p = 0.001) were independently associated with GS. No significant differences were found in cardiac remodeling, heart rate, blood pressure, arrhythmias, or power capacity at stress test. Endurance athletes (313) presented higher total (p = 0.003) and indirect bilirubin (p = 0.001).

CONCLUSION

Bilirubin has several metabolic effects (including immunosuppressive and endocrine) and plays a role in regulating antioxidant pathways exercise-related with hematological consequences but seems not to affect significantly cardiovascular remodeling. Endurance athletes present higher bilirubin concentrations, likely as an adaptive mechanism to counteract increased oxidative stress.

The physiology of bilirubin: health and disease equilibrium

Bilirubin has several physiological functions, both beneficial and harmful. In addition to reactive oxygen species-scavenging activities, bilirubin has potent immunosuppressive effects associated with long-term pathophysiological sequelae. It has been recently recognized as a hormone with endocrine actions and interconnected effects on various cellular signaling pathways. Current studies show that bilirubin also decreases adiposity and prevents metabolic and cardiovascular diseases. All in all, the physiological importance of bilirubin is only now coming to light, and strategies for increasing plasma bilirubin levels to combat chronic diseases are starting to be considered. This review discusses the beneficial effects of increasing plasma bilirubin, incorporates emerging areas of bilirubin biology, and provides key concepts to advance the field.

Cutting edge concepts: Does bilirubin enhance exercise performance?

Exercise performance is dependent on many factors, such as muscular strength and endurance, cardiovascular capacity, liver health, and metabolic flexibility. Recent studies show that plasma levels of bilirubin, which has classically been viewed as a liver dysfunction biomarker, are elevated by exercise training and that elite athletes may have significantly higher levels. Other studies have shown higher plasma bilirubin levels in athletes and active individuals compared to general, sedentary populations. The reason for these adaptions is unclear, but it could be related to bilirubin's antioxidant properties in response to a large number of reactive oxygen species (ROS) that originates from mitochondria during exercise. However, the mechanisms of these are unknown. Current research has re-defined bilirubin as a metabolic hormone that interacts with nuclear receptors to drive gene transcription, which reduces body weight. Bilirubin has been shown to reduce adiposity and improve the cardiovascular system, which might be related to the adaption of bilirubin increasing during exercise. No studies have directly tested if elevating bilirubin levels can influence athletic performance. However, based on the mechanisms proposed in the present review, this seems plausible and an area to consider for future studies. Here, we discuss the importance of bilirubin and exercise and how the combination might improve metabolic health outcomes and possibly athletic performance.

Bilirubin Levels Are Negatively Correlated with Adiposity in Obese Men and Women, and Its Catabolized Product, Urobilin, Is Positively Associated with Insulin Resistance

Bilirubin levels in obese humans and rodents have been shown to be lower than in their lean counterparts. Some studies have proposed that the glucuronyl UGT1A1 enzyme that clears bilirubin from the blood increases in the liver with obesity. UGT1A1 clearance of bilirubin allows more conjugated bilirubin to enter the intestine, where it is catabolized into urobilin, which can be then absorbed via the hepatic portal vein. We hypothesized that when bilirubin levels are decreased, the urobilin increases in the plasma of obese humans, as compared to lean humans. To test this, we measured plasma levels of bilirubin and urobilin, body mass index (BMI), adiposity, blood glucose and insulin, and HOMA IR in a small cohort of obese and lean men and women. We found that bilirubin levels negatively correlated with BMI and adiposity in obese men and women, as compared to their lean counterparts. Contrarily, urobilin levels were positively associated with adiposity and BMI. Only obese women were found to be insulin resistant based on significantly higher HOMA IR, as compared to lean women. The urobilin levels were positively associated with HOMA IR in both groups, but women had a stronger linear correlation. These studies indicate that plasma urobilin levels are associated with obesity and its comorbidities, such as insulin resistance.

Bilirubin Nanoparticles Protect Against Cardiac Ischemia/Reperfusion Injury in Mice

Background

Ischemia/reperfusion (I/R) injury causes overproduction of reactive oxygen species, which are the major culprits of oxidative stress that leads to inflammation, apoptosis, myocardial damage, and dysfunction. Bilirubin acts as a potent endogenous antioxidant that is capable of scavenging various reactive oxygen species. We have previously generated bilirubin nanoparticles (BRNPs) consisting of polyethylene glycol–conjugated bilirubin. In this study, we examined the therapeutic effects of BRNPs on myocardial I/R injury in mice.

Methods and Results

In vivo imaging using fluorophore encapsulated BRNPs showed BRNPs preferentially targeted to the site of I/R injury in the heart. Cardiac I/R surgery was performed by first ligating the left anterior descending coronary artery. After 45 minutes, reperfusion was achieved by releasing the ligation. BRNPs were administered intraperitoneally at 5 minutes before and 24 hours after reperfusion. Mice that received BRNPs showed significant improvements in their cardiac output, assessed by echocardiogram and pressure volume loop measurements, compared with the ones that received vehicle treatment. BRNPs treatment also significantly reduced the myocardial infarct size in mice that underwent cardiac I/R, compared with the vehicle‐treatment group. In addition, BRNPs effectively suppressed reactive oxygen species and proinflammatory factor levels, as well as the amount of cardiac apoptosis.

Conclusions

Taken together, BRNPs could exert their therapeutic effects on cardiac I/R injury through attenuation of oxidative stress, apoptosis, and inflammation, providing a novel therapeutic modality for myocardial I/R injury.

Physiologically increased total bilirubin is associated with reduced risk of first myocardial infarction: A meta-analysis and dose-response analysis

AIM

Bilirubin has potential predictive and prognostic value for myocardial infarction (MI), but the clinical evidence remains controversial. We performed this meta-analysis to systematically quantify the relationships between circulating bilirubin levels and the incidence of MI and post-MI adverse events.

DATA SYNTHESIS

We searched the PubMed, Cochrane Library, Embase, and Web of Science databases for ad-hoc studies, published up to October 17, 2020, recording bilirubin before MI (predictive analyses) or adverse events (prognostic analyses). Relative risks (RR) were pooled by a random-effects model. The dose-response analysis was conducted by restricted cubic splines. In patients without previous MI, increased total bilirubin (TB) reduced the risk of long-term (>3 year) first MI by 22% (95% confidence interval [CI]: 0.69-0.88, n = 4). The dose-response analysis indicated that the RR for first MI decreased by 2.7% per each 2 μmol/L increment of TB (three studies, 95% CI: 1.3%-4.1%, P < 0.001), with a cut-off value of 12.60 μmol/L for RR > 1.00. Elevated bilirubin reduced the incidence of first and recurrent MI by 36% (95% CI: 0.42-0.98, n = 7). However, after suffering MI, higher TB concentrations could not decrease the risk of recurrent MI (RR: 1.02, 95% CI: 0.67-1.55, n = 5) and increased the incidence of short-term (<1 year) post-MI major adverse cardiovascular events, all-cause mortality, and cardiovascular mortality, but not long-term (≥1 year).

CONCLUSION

Higher TB levels within a physiological range reduced the incidence of long-term first MI, with a cut-off value of 12.60 μmol/L.

Lower Serum Indirect Bilirubin Levels are Inversely Related to Carotid Intima-Media Thickness Progression

BACKGROUND

Bilirubin has been recognized as a potential endogenous inhibitor of atherosclerosis, being inversely associated with carotid intima-media thickness (CIMT). However, little information is available concerning the correlation between serum indirect bilirubin (IBIL), especially long-term IBIL level, and early atherosclerosis progression. This study was designed to evaluate the relationship between serum IBIL level and CIMT progression.

METHODS

A total of 2205 participants were enrolled in this Asymptomatic Polyvascular Abnormalities Community study (APAC study). CIMT was measured at baseline and 2-year follow-up. The participants were divided into four groups based on their serum IBIL levels at baseline. Both baseline and average serum IBIL values during the 2-year follow up were used in the analysis. Multivariable logistic regression and linear regression were used to assess the associations between serum IBIL and CIMT progression.

RESULTS

The results showed that 51.93% (1145/2205) of participants were diagnosed with CIMT progression during the 2-year follow-up. Baseline serum IBIL level was significantly associated with the incidence of CIMT progression after adjusting for other potential confounding factors. Compared with the first quartile, adjusted odds ratios (OR) of the second, third, and fourth quartiles of IBIL were 0.70 [95% confidence interval (CI), 0.55-0.90], 0.68 (95% CI, 0.52-0.87), and 0.63 (95% CI, 0.49-0.82) (P = 0.0006), respectively. Serum IBIL level during the follow-up was also associated with CIMT progression in the univariate analysis (P = 0.0022), although no longer significant after adjusting for potential confounders in the multiple linear regression.

CONCLUSION

The study demonstrated the inverse relationship between serum IBIL and CIMT progression. Lower serum IBIL level is an independent predictor of subclinical atherosclerosis.

Heme Oxygenase-1 Upregulation: A Novel Approach in the Treatment of Cardiovascular Disease

Significance: Heme oxygenase (HO) plays a pivotal role in both vascular and metabolic functions and is involved in many physiological and pathophysiological processes in vascular endothelial cells (ECs) and adipocytes. Recent Advances: From the regulation of adipogenesis in adipose tissue to the adaptive response of vascular tissue in the ECs, HO plays a critical role in the capability of the vascular system to respond and adjust to insults in homeostasis. Recent studies show that HO-1 through regulation of adipocyte and adipose tissue functions ultimately aid not only in local but also in systemic maintenance of homeostasis. Critical Issues: Recent advances have revealed the existence of a cross talk between vascular ECs and adipocytes in adipose tissue. In the pathological state of obesity, this cross talk contributes to the condition's adverse chronic effects, and we propose that specific targeting of the HO-1 gene can restore signaling pathways and improve both vascular and adipose functions. Future Directions: A complete understanding of the role of HO-1 in regulation of cardiovascular homeostasis is important to comprehend the homeostatic regulation as well as in cardiovascular disease. Efforts are required to highlight the effects and the ability to target the HO-1 gene in models of obesity with an emphasis on the role of pericardial fat on cardiovascular health.

Bilirubin Safeguards Cardiorenal and Metabolic Diseases: a Protective Role in Health

PURPOSE OF REVIEW

To discuss recent advances indicating that bilirubin safeguards against cardiorenal and metabolic diseases.

RECENT FINDINGS

Several investigations from human patient populations and experimental animal models have shown that bilirubin improves cardiorenal and metabolic dysfunction. The latest studies found an entirely new function of bilirubin suggesting that it acts as a hormone signaling molecule capable of activating nuclear receptors for burning fat, which may explain several of its protective actions. This review highlights the current findings (within the last 3 years) regarding cardiorenal and metabolic protective effects of bilirubin and the latest mechanism(s) that may be mediating these effects.

Cardioprotective Heme Oxygenase-1-PGC1α Signaling in Epicardial Fat Attenuates Cardiovascular Risk in Humans as in Obese Mice

OBJECTIVE

This study investigated whether levels of signaling pathways and inflammatory adipokines in epicardial fat regulate cardiovascular risks in humans and mice.

METHODS

Epicardial fat was obtained from the hearts of patients with heart failure requiring coronary artery bypass surgery, and signaling pathways were compared with visceral fat. The genetic profile of epicardial and visceral fat from humans was also compared with genetic profiles of epicardial and visceral fat in obese mice. Left ventricular (LV) fractional shortening was measured in obese mice before and after treatment with inducers of mitochondrial signaling heme oxygenase 1 (HO-1)-peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1α). An RNA array/heat map on 88 genes that regulate adipose tissue function was used to identify a target gene network.

RESULTS

Human epicardial fat gene profiling showed decreased levels of mitochondrial signaling of HO-1-PGC1α and increased levels of the inflammatory adipokine CCN family member 3. Similar observations were seen in epicardial and visceral fat of obese mice. Improvement in LV function was linked to the increase in mitochondrial signaling in epicardial fat of obese mice.

CONCLUSIONS

There is a link between cardiac ectopic fat deposition and cardiac function in humans that is similar to that which is described in obese mice. An increase of mitochondrial signaling pathway gene expression in epicardial fat attenuates cardiometabolic dysfunction and LV fractional shortening in obese mice.

Targeting Heme Oxygenase-1 in Cardiovascular and Kidney Disease

Heme oxygenase (HO) plays an important role in the cardiovascular system. It is involved in many physiological and pathophysiological processes in all organs of the cardiovascular system. From the regulation of blood pressure and blood flow to the adaptive response to end-organ injury, HO plays a critical role in the ability of the cardiovascular system to respond and adapt to changes in homeostasis. There have been great advances in our understanding of the role of HO in the regulation of blood pressure and target organ injury in the last decade. Results from these studies demonstrate that targeting of the HO system could provide novel therapeutic opportunities for the treatment of several cardiovascular and renal diseases. The goal of this review is to highlight the important role of HO in the regulation of cardiovascular and renal function and protection from disease and to highlight areas in which targeting of the HO system needs to be translated to help benefit patient populations.

Bilirubin acts as a multipotent guardian of cardiovascular integrity: more than just a radical idea

Bilirubin, a potentially toxic catabolite of heme and indicator of hepatobiliary insufficiency, exhibits potent cardiac and vascular protective properties. Individuals with Gilbert's syndrome (GS) may experience hyperbilirubinemia in response to stressors including reduced hepatic bilirubin excretion/increased red blood cell breakdown, with individuals usually informed by their clinician that their condition is of little consequence. However, GS appears to protect from all-cause mortality, with progressively elevated total bilirubin associated with protection from ischemic heart and chronic obstructive pulmonary diseases. Bilirubin may protect against these diseases and associated mortality by reducing circulating cholesterol, oxidative lipid/protein modifications, and blood pressure. In addition, bilirubin inhibits platelet activation and protects the heart from ischemia-reperfusion injury. These effects attenuate multiple stages of the atherosclerotic process in addition to protecting the heart during resultant ischemic stress, likely underpinning the profound reduction in cardiovascular mortality in hyperbilirubinemic GS. This review outlines our current knowledge of and uses for bilirubin in clinical medicine and summarizes recent progress in revealing the physiological importance of this poorly understood molecule. We believe that this review will be of significant interest to clinicians, medical researchers, and individuals who have GS.

Association of serum bilirubin with longevity: Evidence from a retrospective longitudinal study and cross-sectional data

Bilirubin is a potent antioxidant and an important anti-inflammatory factor. Therefore, there has been an increasing focus on serum bilirubin as a negative risk factor of cardiovascular mortality in men and an indicator of improved survival in both sexes, but the direct mechanisms of these links and the causes of sex differences are not well understood. Moreover, the evidence from longitudinal studies on effects of bilirubin on longevity is limited. In this study, we retrospectively analyzed two groups of older adults to explore age-dependent changes in serum bilirubin levels and their associations with long-term survival in both sexes. Longitudinal data from 142 individuals (68 men and 74 women) aged 45 to 70 years were compared with cross-sectional data from 225 individuals (113 men and 112 women). The latter group was divided into four categories of survival, i.e. 53, 63, 68, and 76+ based on data on lifespan. ANOVA, t-test, and regression analysis were run. The analysis of the longitudinal data showed an increase in serum total bilirubin levels in men (0.3038e0.093x, R2 = 0.667) and women (0.1838e0.0187x, R2 = 0.950), while the analysis of cross-sectional data revealed a U-shaped pattern of age-related changes in men (0.001x2 - 0.1263x + 4.4524, R2 = 0.999) but an inverted U-shaped pattern in women (0.0006x2 + 0.072x - 1.6924, R2 = 0.195). On balance, these results suggest that elevated but normal bilirubin levels might confer a survival advantage in older men but not women. Alternatively, the positive relationship between serum total bilirubin and lifespan was not causal but coincidental. Further studies are needed to elucidate the direct mechanisms of the association between serum bilirubin levels and longevity in elderly people of both sexes.

Chronically elevated bilirubin protects from cardiac reperfusion injury in the male Gunn rat

AIMS

Bilirubin is associated with reduced risk of cardiovascular disease, as evidenced in conditions of mild hyperbilirubinaemia (Gilbert's Syndrome). Little is known regarding myocardial stress resistance in hyperbilirubinaemic conditions or whether life-long exposure modifies cardiac function, which might contribute to protection from cardiovascular disease.

METHODS

Hyperbilirubinaemic rats and littermate controls underwent echocardiography at 3, 6 and 12 months of age, with hearts subsequently assessed for resistance to 30 min of ischaemia. Heart tissue was then collected for assessment of bilirubin content.

RESULTS

No difference in baseline cardiac function was evident until 6 months onwards, where Gunn rats demonstrated aortic dilatation and reduced peak ejection velocities. Additionally, duration of ventricular ejection increased progressively, indicating a negative inotropic effect of bilirubin in vivo. Ex vivo analysis of baseline function revealed reduced left ventricular pressure development (LVDP) and contractility in hyperbilirubinaemic rats. Furthermore, stress resistance was improved in Gunn hearts: post-ischaemic recoveries of LVDP (76 ± 22% vs. 29 ± 17% Control, P < 0.01) and coronary flow (96 ± 9% vs. 86 ± 16% Control, P < 0.01) were improved in Gunn hearts, accompanied by reduced infarct area (21 ± 5% vs. 47 ± 15% Control, P < 0.01), and ventricular malondialdehyde and protein carbonyl content. Expression of myocardial nitric oxide-regulating genes including Nos1 and Noa1 were not significantly different.

CONCLUSIONS

These data reveal life-long hyperbilirubinaemia induces age-dependent hypocontractility in male Gunn rats, and improved stress resistance. In addition, bilirubin exerts sex-independent effects on vascular structure, myocardial function and ischaemic tolerance, the latter likely mediated via bilirubin's antioxidant properties.

Bilirubin Decreases Macrophage Cholesterol Efflux and ATP-Binding Cassette Transporter A1 Protein Expression

BACKGROUND

Mild but chronically elevated circulating unconjugated bilirubin is associated with reduced total and low-density lipoprotein cholesterol concentration, which is associated with reduced cardiovascular disease risk. We aimed to investigate whether unconjugated bilirubin influences macrophage cholesterol efflux, as a potential mechanism for the altered circulating lipoprotein concentrations observed in hyperbilirubinemic individuals.

METHODS AND RESULTS

Cholesterol efflux from THP-1 macrophages was assessed using plasma obtained from normo- and hyperbilirubinemic (Gilbert syndrome) humans (n=60 per group) or (heterozygote/homozygote Gunn) rats (n=20 per group) as an acceptor. Hyperbilirubinemic plasma from patients with Gilbert syndrome and Gunn rats induced significantly reduced cholesterol efflux compared with normobilirubinemic plasma. Unconjugated bilirubin (3-17.1 μmol/L) exogenously added to plasma- or apolipoprotein A1-supplemented media also decreased macrophage cholesterol efflux in a concentration- and time-dependent manner. We also showed reduced protein expression of the ATP-binding cassette transporter A1 (ABCA1), a transmembrane cholesterol transporter involved in apolipoprotein A1-mediated cholesterol efflux, in THP-1 macrophages treated with unconjugated bilirubin and in peripheral blood mononuclear cells obtained from hyperbilirubinemic individuals. Furthermore, we demonstrated that bilirubin accelerates the degradation rate of the ABCA1 protein in THP-1 macrophages.

CONCLUSIONS

Cholesterol efflux from THP-1 macrophages is decreased in the presence of plasma obtained from humans and rats with mild hyperbilirubinemia. A direct effect of unconjugated bilirubin on cholesterol efflux was demonstrated and is associated with decreased ABCA1 protein expression. These data improve our knowledge concerning bilirubin's impact on cholesterol transport and represent an important advancement in our understanding of bilirubin's role in cardiovascular disease.

Impairment of enzymatic antioxidant defenses is associated with bilirubin-induced neuronal cell death in the cerebellum of Ugt1 KO mice

Severe hyperbilirubinemia is toxic during central nervous system development. Prolonged and uncontrolled high levels of unconjugated bilirubin lead to bilirubin-induced encephalopathy and eventually death by kernicterus. Despite extensive studies, the molecular and cellular mechanisms of bilirubin toxicity are still poorly defined. To fill this gap, we investigated the molecular processes underlying neuronal injury in a mouse model of severe neonatal jaundice, which develops hyperbilirubinemia as a consequence of a null mutation in the Ugt1 gene. These mutant mice show cerebellar abnormalities and hypoplasia, neuronal cell death and die shortly after birth because of bilirubin neurotoxicity. To identify protein changes associated with bilirubin-induced cell death, we performed proteomic analysis of cerebella from Ugt1 mutant and wild-type mice. Proteomic data pointed-out to oxidoreductase activities or antioxidant processes as important intracellular mechanisms altered during bilirubin-induced neurotoxicity. In particular, they revealed that down-representation of DJ-1, superoxide dismutase, peroxiredoxins 2 and 6 was associated with hyperbilirubinemia in the cerebellum of mutant mice. Interestingly, the reduction in protein levels seems to result from post-translational mechanisms because we did not detect significant quantitative differences in the corresponding mRNAs. We also observed an increase in neuro-specific enolase 2 both in the cerebellum and in the serum of mutant mice, supporting its potential use as a biomarker of bilirubin-induced neurological damage. In conclusion, our data show that different protective mechanisms fail to contrast oxidative burst in bilirubin-affected brain regions, ultimately leading to neurodegeneration.

Looking to the horizon: the role of bilirubin in the development and prevention of age-related chronic diseases

Bilirubin, the principal tetrapyrrole, bile pigment and catabolite of haem, is an emerging biomarker of disease resistance, which may be related to several recently documented biological functions. Initially believed to be toxic in infants, the perception of bilirubin has undergone a transformation: it is now considered to be a molecule that may promote health in adults. Data from the last decade demonstrate that mildly elevated serum bilirubin levels are strongly associated with reduced prevalence of chronic diseases, particularly cardiovascular diseases (CVDs), as well as CVD-related mortality and risk factors. Recent data also link bilirubin to other chronic diseases, including cancer and Type 2 diabetes mellitus, and to all-cause mortality. Therefore, there is evidence to suggest that bilirubin is a biomarker for reduced chronic disease prevalence and a predictor of all-cause mortality, which is of important clinical significance. In the present review, detailed information on the association between bilirubin and all-cause mortality, as well as the pathological conditions of CVD, cancer, diabetes and neurodegenerative diseases, is provided. The mechanistic background concerning how bilirubin and its metabolism may influence disease prevention and its clinical relevance is also discussed. Given that the search for novel biomarkers of these diseases, as well as for novel therapeutic modalities, is a key research objective for the near future, bilirubin represents a promising candidate, meeting the criteria of a biomarker, and should be considered more carefully in clinical practice as a molecule that might provide insights into disease resistance. Clearly, however, greater molecular insight is warranted to support and strengthen the conclusion that bilirubin can prevent disease, with future research directions also proposed.

Bilirubin, platelet activation and heart disease: a missing link to cardiovascular protection in Gilbert's syndrome?

Gilbert's syndrome (GS) is a relatively common condition, inducing a benign, non-hemolytic, unconjugated hyperbilirubinemia. Gilbert's Syndrome is associated with mutation in the Uridine Glucuronosyl Transferase 1A1 (UGT1A1) gene promoter, reducing UGT1A1 activity, which normally conjugates bilirubin allowing its elimination from the blood. Individuals with GS demonstrate mildly elevated plasma antioxidant capacity caused by elevated levels of unconjugated bilirubin (UCB), reduced thiols and glutathione. Interestingly, the development of, and risk of mortality from, cardiovascular disease is remarkably reduced in GS individuals. An explanation for this protection may be explained by bilirubin's ability to inhibit multiple processes that induce platelet hyper-reactivity and thrombosis, thus far under-appreciated in the literature. Reactive oxygen species are produced continuously via metabolic processes and have the potential to oxidatively modify proteins and lipids within cell membranes, which may encourage the development of thrombosis and CVDs. Oxidative stress induced platelet hyper-reactivity significantly increases the risk of thrombosis, which can potentially lead to tissue infarction. Here, we discuss the possible mechanisms by which increased antioxidant status might influence platelet function and link this to cardiovascular protection in GS. In summary, this is the first article to discuss the possible role of bilirubin as an anti-thrombotic agent, which inhibits platelet activation and potentially, organ infarction, which could contribute to the reduced mortality rate in mildly hyperbilirbinemic individuals.