Effect of different doses of aerobic exercise training on total bilirubin levels

Eight weeks of aerobic exercise, but not four, improves insulin sensitivity and cardiovascular performance in young women

Regular aerobic exercise has a significant impact on glucose metabolism and lipid profiles, contributing to overall health improvement. However, evidence for optimal exercise duration to achieve these effects is limited. This study aims to explore the effects of 4 and 8 weeks of moderate-intensity aerobic exercise on glucose metabolism, lipid profiles, and associated metabolic changes in young female students with insulin resistance and varying body mass, seeking to determine the optimal duration for physiological adaptations. Twenty-eight physically semi-active female students were randomly assigned to 4-week (G4, n = 13, age = 23.31 ± 5.19, BMI = 24.78 ± 5.87) and 8-week (G8, n = 15, age = 21.8 ± 2.56, BMI = 24.95 ± 4.81) training groups. The aerobic intervention maintained an intensity of 40-70% of maximum heart rate (HRmax). 6-min-walk test (6MWT), handgrip strength tests, insulin, HOMA-IR, lipid profiles, and metabolic profiles were assessed pre- and post-intervention. Following the intervention, G8, but not G4, exhibited a significant decrease in HOMA-IR (-14.59%, p = 0.047). The improvement in HOMA-IR was accompanied by notable improvements in 6-MWT (+ 38.18%, p < 0.001) and handgrip strength (+ 11.62, p = 0.027 and + 17.59%, p = 0.013), and increased levels of bilirubin degradation products, ribose, and glutarate. The elevated levels of bilirubin degradation products, known for their antioxidant properties, suggested a potential antioxidative response triggered by prolonged aerobic exercise. Additionally, an increase in ribose and glutarate indicated improved metabolic flexibility and enhanced utilization of alternative energy substrates. The 8-week aerobic exercise regimen demonstrated enhanced insulin sensitivity, upper body strength, and cardiovascular performance in young females compared to a 4-week regimen by triggering specific metabolic adaptations. These findings emphasize the complex relationship between exercise duration, metabolic adaptations, and overall well-being in young women, providing valuable insights for optimizing exercise prescriptions in promoting metabolic health.

Bile Acids and Bilirubin Role in Oxidative Stress and Inflammation in Cardiovascular Diseases

Bile acids (BAs) and bilirubin, primarily known for their role in lipid metabolism and as heme catabolite, respectively, have been found to have diverse effects on various physiological processes, including oxidative stress and inflammation. Indeed, accumulating evidence showed that the interplay between BAs and bilirubin in these processes involves intricate regulatory mechanisms mediated by specific receptors and signaling pathways under certain conditions and in specific contexts. Oxidative stress plays a significant role in the development and progression of cardiovascular diseases (CVDs) due to its role in inflammation, endothelial dysfunction, hypertension, and other risk factors. In the cardiovascular (CV) system, recent studies have suggested that BAs and bilirubin have some opposite effects related to oxidative and inflammatory mechanisms, but this area of research is still under investigation. This review aims to introduce BAs and bilirubin from a biochemical and physiological point of view, emphasizing their potential protective or detrimental effects on CVDs. Moreover, clinical studies that have assessed the association between BAs/bilirubin and CVD were examined in depth to better interpret the possible link between them.

The effects of aerobic exercise on cardiometabolic health in postmenopausal females: A systematic review and meta-analysis of randomized controlled trials

BACKGROUND

After menopause, reductions in ovarian hormones increase the risk of cardiovascular disease. Aerobic exercise training has been shown to reduce cardiovascular risk in older adults, but its effectiveness in postmenopausal females is less definitive.

OBJECTIVES

The objectives of this study were to examine the: (1) effects of aerobic training, and (2) association between aerobic training intensity and cardiometabolic health outcomes in postmenopausal females.

DESIGN

Systematic review and meta-analysis of randomized controlled trials.

DATA SOURCES AND METHODS

Six electronic databases were searched from inception to July 21, 2023 for aerobic training interventions reporting cardiometabolic outcomes in postmenopausal females. Data were synthesized qualitatively and random-effects meta-analyses and subgroup analyses (light, moderate, and vigorous intensity) were performed. Grading of Recommendations, Assessment, Development and Evaluation was used to assess the certainty of evidence.

RESULTS

Fifty-nine studies (n = 4,225; 45-78 years old) were identified, 53 (n = 3,821) were included in the quantitative analyses. Aerobic training interventions varied in frequency (3-21×/week), intensity, type, time (8-60 min/session), and duration (3-52 weeks). Aerobic training improved systolic blood pressure (mean difference (MD) = -4.41 mmHg, 95% confidence interval (95%CI) [-7.29, -1.52], p = 0.01), resting heart rate (MD = -3.08 bpm, 95%CI [-5.11, -1.05], p < 0.01), body mass index (BMI, MD = -0.65 kg/m2, 95%CI [-0.99, -0.31], p < 0.01), waist circumference (MD = -2.03 cm, 95%CI [-2.65, -1.41], p < 0.01), body fat (MD = -2.57 kg, 95%CI [-3.65, -1.49], p < 0.01), low-density lipoprotein cholesterol (MD = -10.46 mg/dL, 95%CI [-16.31, -4.61], p < 0.01), high-density lipoprotein cholesterol (MD = 3.28 mg/dL, 95%CI [0.20, 6.36], p = 0.04) and cardiorespiratory fitness (standardized MD = 1.38, 95%CI [1.13, 1.64], p < 0.01). There was a very low certainty of evidence for all outcomes. In subgroup analyses, light- and vigorous intensities were beneficial for BMI with no effect for moderate-intensity exercise (p < 0.01). Light intensity showed a beneficial effect (p = 0.02) for glucose levels (p < 0.01) and triglycerides; there was no effect with moderate or vigorous intensities.

CONCLUSION

Aerobic training may improve cardiometabolic health outcomes in postmenopausal females. There may be differential effects of exercise intensity on BMI, blood triglycerides, and blood glucose; however, this warrants further investigation.

REGISTRATION

PROSPERO-CRD42022313350.

Unveiling the Dichotomy of Urinary Proteins: Diagnostic Insights into Breast and Prostate Cancer and Their Roles

This review covers the diagnostic potential of urinary biomarkers, shedding light on their linkage to cancer progression. Urinary biomarkers offer non-invasive avenues for detecting cancers, potentially bypassing the invasiveness of biopsies. The investigation focuses primarily on breast and prostate cancers due to their prevalence among women and men, respectively. The intricate interplay of urinary proteins is explored, revealing a landscape where proteins exhibit context-dependent behaviors. The review highlights the potential impact of physical activity on urinary proteins, suggesting its influence on tumorigenic behaviors. Exercise-conditioned urine may emerge as a potential diagnostic biomarker source. Furthermore, treatment effects, notably after lumpectomy and prostatectomy, induce shifts in the urinary proteome, indicating therapeutic impacts rather than activating oncogenic signaling. The review suggests further investigations into the double-sided, context-dependent nature of urinary proteins, the potential role of post-translational modifications (PTM), and the integration of non-protein markers like mRNA and metabolites. It also discusses a linkage of urinary proteomes with secretomes from induced tumor-suppressing cells (iTSCs). Despite challenges like cancer heterogeneity and sample variability due to age, diet, and comorbidities, harnessing urinary proteins and proteoforms may hold promise for advancing our understanding of cancer progressions, as well as the diagnostic and therapeutic role of urinary proteins.

How Supplementation with SOD-Rich Plant Extract, Combined with Gliadin, Can Affect Oxidative Stress Markers and Zonulin Levels in Exercise-Induced Oxidative Stress

A randomized, double-blind, placebo-controlled study was conducted to investigate the influence of supplementation with a superoxide dismutase (SOD)-rich plant extract on markers of oxidative stress, zonulin levels and the performance of elite athletes. Participants were 30 international-level rowers, divided into an experimental group (n = 15) and a control group (n = 15). The rowers performed a maximal effort incremental test on a rowing ergometer at the beginning and at the end of the study. Markers of oxidative stress (total antioxidant status (TAS), total oxidant status (TOS), oxidative stress index (OSI), superoxide dismutase (SOD), glutathione peroxidase (GPx), advanced oxidation protein products (AOPPs), malondialdehyde (MDA), sulfhydryl (SH) groups, bilirubin, uric acid, albumin and zonulin) were determined in serum. A lower TOS (p = 0.010) and OSI (p = 0.004), a lower MDA (p = 0.001) and a higher level of SH groups (p = 0.031) were observed in the experimental group after supplementation. Physical performance was evaluated through metabolic efficiency, taking lactate levels and power output on the ergometer into account. After 6 weeks of supplementation, the relative increase in metabolic efficiency at a 4 mmol/L lactate concentration and maximal effort was significantly higher in the experimental group (p = 0.004 and p = 0.015, respectively). These results suggest that supplementation with a SOD-rich extract promotes lower oxidative stress, better antioxidant protection and, consequently, the better work performance of athletes.

Habitual fish consumption and healthy lifestyle behaviours may be associated with higher total serum bilirubin level and anti-inflammatory activity: a cross-sectional study

Habitual fish consumption and a healthy lifestyle are associated with lower atherosclerotic CVD (ASCVD) risk. Mildly elevated bilirubin, an end product of Hb metabolism, may be associated with anti-inflammatory effects, suppressing ASCVD risk. No data exist on the relationship between fish consumption, total serum bilirubin (TSB) and inflammation in clinical settings. We conducted a cross-sectional study between April 2019 and March 2020 in a cohort of 8292 participants (average age, 46·7 (sd 12·9) years and 58·9 % men) with no history of ASCVD and TSB concentrations < 2·0 mg/dl. Multiple stepwise regression analysis showed Hb concentrations were a solid positive determinant of TSB concentrations (β = 0·302, P< 0·0001). Fish consumption (β = 0·025, P= 0·019) and aerobic exercise (β = 0·021, P= 0·043) were statistically weak but significantly positive determinants of TSB concentrations. Cigarette smoking negatively affected TSB concentrations (β = −0·104, P< 0·0001). Moreover, with increasing fish consumption, the proportion of participants with a habit of cigarette smoking decreased, and that of participants who engaged in aerobic exercises increased (P< 0·0001 for both). Furthermore, as TSB concentrations increased, the leukocyte counts and C-reactive protein concentrations decreased (P< 0·0001 for both). In conclusion, despite the lesser relevance given to TSB concentrations than Hb concentrations, higher fish consumption and healthier lifestyle behaviours related to fish consumption habits may be additively or synergistically associated with higher TSB concentrations and anti-inflammatory activity, leading to attenuated ASCVD risk. Further investigations are needed to clarify the causal relationships between these factors.

Physical activity interventions for cardiopulmonary fitness in obese children and adolescents: a systematic review and meta-analysis

PURPOSE

This study [PROSPERO CRD42023416272] systematically analysed the effects of a physical activity intervention on cardiorespiratory fitness in obese children and adolescents and elucidated the factors that influenced those effects.

METHODS

A systematic review of the literature on physical activity interventions for improving cardiopulmonary fitness in obese children and adolescents from January 1, 2011, to March 1, 2023, was conducted. The search was performed on the Web of Science and PubMed databases, and the selected literature was first screened and then assessed for quality. Finally, a systematic review was conducted.

RESULTS

Out of the initially identified 1424 search records, 28 studies were eventually included in the systematic review. These studies encompassed a total of 2724 participants aged 5 to 18 years, with the publication dates of the literature primarily ranging from 2011 to 2023. Physical activity was found to effectively improve the following parameters in obese children and adolescents: weight [mean difference (MD), -2.03 (95% confidence interval, -2.59 to -1.47), p < 0.00001], maximal oxygen consumption [MD, -1.95 (95% CI, -1.06 to -2.84), p < 0.0001], heart rate [MD, -2.77 (95% CI, -4.88 to -0.67), p = 0.010], systolic blood pressure [MD, -8.11 (95% CI, -11.41 to -4.81), p < 0.00001], and diastolic blood pressure [MD, -4.18 (95% CI, -5.32 to -3.03), p < 0.00001]. High-intensity exercise was found to yield greater improvements than low- to moderate-intensity exercise in maximal oxygen consumption [MD, 1.43 (95% CI, 0.04 to 2.82), p = 0.04] and diastolic blood pressure [MD, -6.94 (95% CI, -10.61 to -3.26), p = 0.0002] in obese children and adolescents.

CONCLUSION

Physical activity can effectively improve the body weight, maximal oxygen consumption, heart rate, systolic blood pressure, and diastolic blood pressure of obese children and adolescents. The type of physical activity directly influences the participation interest of obese children and adolescents, with moderate- to high-intensity physical activity showing the most significant impact on intervention outcomes. High-frequency, long-term interventions yield better results than short-term interventions.

Oxidative status alteration during aerobic-dominant mixed and anaerobic-dominant mixed effort in judokas

This study aimed to depict the oxidative status variation in judokas during aerobic-dominant mixed effort (AeDME) and anaerobic-dominant mixed effort (AnDME). It is to be expected that the sporting commitment of Judo is a stimulus of oxidative stress leading to the recruitment of antioxidant responses. Blood samples were collected from 17 athletes at rest, immediately after a training session (AeDME) and after a 5-min bout (AnDME). AeDME and AnDME caused significant increases in malondialdehyde (MDA) (p < 0.01 and p < 0.001 respectively) and glutathione (GSH) (p = 0.018 and p < 0.001 respectively). Blood thiol concentrations decreased following AeDME and AnDME (p < 0.001) whilst catalase decreased significantly after AnDME (p = 0.026) only. Uric acid increased significantly after AnDME than after AeDME (p = 0.047) while, conversely, total bilirubin was higher after AnDME than after AeDME (p = 0.02). We may ultimately summarize that AeDME and AnDME caused oxidative stress, higher in AnDME, and some antioxidant response slightly higher in AnDME compared to AeDME. In sports, monitoring of oxidative stress status is recommended as part of the training regimen.

Association of liver function with health-related physical fitness: a cross-sectional study

BACKGROUND

In this study, by analyzing the correlation between various components of health-related physical fitness (HPF) and liver function indicators, the indicators of physical fitness that were highly correlated with liver function and could be monitored at home were screened to prevent more serious liver disease in the future, and to provide experimental basis for prescribing personalized exercise.

METHODS

A total of 330 faculties (female = 198) of a university were recruited. The indicators of HPF and liver function were measured. Spearman correlation analysis, multivariate linear regression, and cross-lagged panel model was used to data statistics.

RESULTS

In males, body fat (BF) was positively correlated with alanine aminotransferase (ALT); vital capacity and the vital capacity index were positively correlated with albumin; and vertical jump was positively correlated with globulin and negatively correlated with the albumin-globulin ratio (P < 0.05). However, there was no significant correlation among all indicators controlled confounding factors. In females, BF was negatively correlated with direct bilirubin; VO2max was positively correlated with indirect bilirubin; and vertical jump was positively correlated with the albumin-globulin ratio and significantly negatively correlated with globulin (P < 0.05). Controlled confounding factors, body fat percentage was positively correlated with globulin (β = 0.174) and negatively correlated with direct bilirubin (β = -0.431), and VO2max was positively correlated with indirect bilirubin (β = 0.238, P < 0.05). Cross-lagged panel analysis showed that BF percentage can negatively predict direct bilirubin levels with great significance (β = -0.055, P < 0.05).

CONCLUSIONS

HPF may play a crucial role in liver function screening, particularly for female faculty members. For males, BF, vertical jump, vital capacity and vital capacity index could be associated with liver function but are susceptible to complex factors such as age, smoking, diabetes, and hypertension. In females, BF percentage is an important predictor of abnormal liver function in addition to VO2max and vertical jump, which are not affected by complex factors.

Effects of an aerobic training program on liver functions in male athletes: a randomized controlled trial

The optimal functioning of the liver is essential for athletic performance. It is necessary to maintain the liver's enzymes at an optimal level so that liver cells can be protected from inflammation or damage. This study investigated the effects of a 12-week aerobic exercise program on the liver function of adult athletes. A pretest-posttest experimental design was used. A total of thirty healthy male athletes (football players) aged 21 to 24 years were recruited for this study and randomly and equally divided into the experimental group (EG) and control group (CG). The CG did not participate in any special activities. The EG performed an aerobic training program consisting of several exercises for 12 weeks. Evaluation of all participants in both groups was carried out before and after the intervention by measuring the blood levels of Alkaline phosphate, AST/SGOT, ALT/SGPT, Bilirubin Total/indirect/direct, Albumin, Globulin, and Total protein using the standard methods by collecting blood samples. There was a significant decrease (p < 0.05) in Bilirubin and globulin levels in the EG after 12 weeks of aerobic training sessions. However, there was no significant difference in alkaline phosphate, AST/SGOT, ALT/SGPT Total protein, and Albumin (p > 0.05) between both groups post-treatment. The 12 weeks of aerobic training used in the study can potentially improve the liver function of adult athletes.

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.

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.

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.

Heme Oxygenase-1 and Blood Bilirubin Are Gradually Activated by Oral D-Glyceric Acid

It has been shown that small doses of oral D-glyceric acid (DGA) activate mitochondrial metabolism and reduce inflammation among 50-60-year-old healthy volunteers. The present results with the same small doses reveal that after a 4-day DGA regimen, a dose of DGA activated the HO-1 pathway acutely, while enhanced inflammatory status after the 4-day DGA regimen seemed to be able to downregulate the HO-1 pathway in non-acute measurement. Blood bilirubin was strongly upregulated towards the end of the altogether 21-day study period with positive associations towards improved inflammation and reduced blood triglycerides. After the 4-day DGA regimen, hepatic inflow of blood bilirubin with albumin as the carrier was clearly upregulated in the lower-aerobic-capacity persons. At the same time also, blood triglycerides were down, pointing possibly to the activation of liver fatty acid oxidation. The combination of activated aerobic energy metabolism with transient HO-1 pathway activation and the upregulation of blood bilirubin may reduce the risks of chronic diseases, especially in aging. Furthermore, there exist certain diseases with unsatisfactorily-met medical needs, such as fatty and cholestatic liver diseases, and Parkinson's disease, that can be possibly ameliorated with the whole-body mechanism of the action of the DGA regimen.

Does Opuntia ficus-indica Juice Supplementation Improve Biochemical and Cardiovascular Response to a 6-Minute Walk Test in Type 2 Diabetic Patients?

Background and objectives: The purpose of this study was to evaluate the effect of Opuntia ficus-indica juice (OFIJ) on performance and biochemical and physiological responses to a 6 min walking test (6MWT) in diabetic patients. Materials and Methods: Twenty diabetic patients performed a 6MWT at 07:00 h. During each test session, they were asked to drink 70 mL/day of natural OFIJ or placebo (PLA) for 4 days. Results: the results showed that cardiovascular parameters increased significantly after the 6MWT under both conditions. While, cortisol, HbA1c, cholesterol total (CT), triglycerides (TG), as well as low-density lipoprotein (LDL) were not modified between without and with supplementation. Likewise, no significant variation in performance was observed for PLA and OFIJ (p > 0.05). The cardiovascular parameters (heart rate max (HRmax), diastolic blood pressure (DBP), and systolic blood pressure (SBP)), lipid profile (CT, TG, LDL, and high-density lipoprotein HDL), hormonal parameters (insulin and glucagon), HbA1c and lactate ([La]) did not present any significant modification either between PLA or OFIJ (p > 0.05). Muscle-damage markers (creatine kinase (CK) and lactate dehydrogenase (LDH)], cortisol, and liver parameters (i.e., oxidative stress marker, γGT, and total bilirubin) as well as glucose (GLC) were affected by supplementation (p < 0.05) before and after the 6MWT, but this change was significant only for OFIJ (p < 0.05). Conclusion: OFIJ had an antioxidant capacity, improved performance of the 6MWT, and reduced muscle-damage markers and glucose level in type 2 diabetic patients.

Serum Bilirubin Concentrations and the Prevalence of Gilbert Syndrome in Elite Athletes

Objectives

Bilirubin is a potent endogenous antioxidant and immunomodulating substance, which is also implicated in both cell signalling and various metabolic pathways. Mild elevation of systemic bilirubin concentrations provides substantial protection against many diseases of civilization. Rare published reports have suggested that serum bilirubin might also be relevant to sports performance. The purpose of the current study was to evaluate serum bilirubin concentrations and the prevalence of Gilbert syndrome (GS) in elite athletes.

Methods

The study was carried out in 536 consecutive healthy elite athletes and in 2594 individuals of the Czech post-MONICA study representing the general Czech population. Serum bilirubin concentrations, the prevalence of benign hyperbilirubinemia > 17 µmol/L (1 mg/dL, a phenotypic sign of GS), and a variant of the UGT1A1 gene promoter responsible for GS manifestation in Caucasians (rs81753472) were evaluated in study subjects.

Results

Compared to the general Czech population, significantly higher serum bilirubin concentrations were found in elite athletes (9.6 vs. 11.6 µmol/L, p < 0.001), both in men (11.3 vs. 12.6 µmol/L, p < 0.001) and women (8.3 vs. 10.5 µmol/L, p < 0.001). Furthermore, the prevalence of GS was also significantly higher in elite athletes (9.6 vs. 22%, p < 0.001) together with the tendency to higher frequencies of the genotypes (TA)_7/7 and (TA)_6/7UGT1A1.

Conclusion

Elite athletes have significantly higher concentrations of serum bilirubin, the most potent endogenous antioxidant substance known. Simultaneously, the prevalence of GS syndrome is also much higher in elite athletes, suggesting that a mild elevation of serum bilirubin might predispose to better sports performance.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40798-022-00463-6.

Identifying Potential Therapeutic Applications and Diagnostic Harms of Increased Bilirubin Concentrations: A Clinical and Genetic Approach

Bilirubin has antioxidant and anti-inflammatory properties in vitro and in animal studies and protects against inflammatory, cardiovascular, and other diseases in observational studies; therefore, bilirubin has potential as a therapeutic agent. However, observational studies could be confounded by many factors. We used a genetic (n = 61,281) and clinical (n = 234,670) approach to define the association between bilirubin and 19 conditions with a putative protective signal in observational studies. We also tested if individuals with genetically higher bilirubin levels underwent more diagnostic tests. We used a common variant in UGT1A1 (rs6742078) associated with an 26% increase in bilirubin levels in the genetic studies. Carriers of the variant had higher bilirubin levels (P = 2.2 × 10-16 ) but there was no significant association with any of the 19 conditions. In a phenome-wide association study (pheWAS) to seek undiscovered genetic associations, the only significant finding was increased risk of "jaundice-not of newborn." Carriers of the variant allele were more likely to undergo an abdominal ultrasound (odds ratio = 1.04, [1.00-1.08], P = 0.03). In contrast, clinically measured bilirubin levels were significantly associated with 15 of the 19 conditions (P < 0.003) and with 431 clinical diagnoses in the pheWAS (P < 1 × 10-5 adjusted for sex, age, and follow-up). With additional adjustment for smoking and body mass index, 7 of 19 conditions and 260 pheWAS diagnoses remained significantly associated with bilirubin levels. In conclusion, bilirubin does not protect against inflammatory or other diseases using a genetic approach; the many putative beneficial associations reported clinically are likely due to confounding.

Reactive Oxygen Species (ROS) and Antioxidants as Immunomodulators in Exercise: Implications for Heme Oxygenase and Bilirubin

Exercise is commonly prescribed as a lifestyle treatment for chronic metabolic diseases as it functions as an insulin sensitizer, cardio-protectant, and essential lifestyle tool for effective weight maintenance. Exercise boosts the production of reactive oxygen species (ROS) and subsequent transient oxidative damage, which also upregulates counterbalancing endogenous antioxidants to protect from ROS-induced damage and inflammation. Exercise elevates heme oxygenase-1 (HO-1) and biliverdin reductase A (BVRA) expression as built-in protective mechanisms, which produce the most potent antioxidant, bilirubin. Together, these mitigate inflammation and adiposity. Moderately raising plasma bilirubin protects in two ways: (1) via its antioxidant capacity to reduce ROS and inflammation, and (2) its newly defined function as a hormone that activates the nuclear receptor transcription factor PPARα. It is now understood that increasing plasma bilirubin can also drive metabolic adaptions, which improve deleterious outcomes of weight gain and obesity, such as inflammation, type II diabetes, and cardiovascular diseases. The main objective of this review is to describe the function of bilirubin as an antioxidant and metabolic hormone and how the HO-1-BVRA-bilirubin-PPARα axis influences inflammation, metabolic function and interacts with exercise to improve outcomes of weight management.

Body Composition and Metabolomics in the Alberta Physical Activity and Breast Cancer Prevention Trial

BACKGROUND

Obesity is correlated with many biomarkers, but the extent to which these correlate with underlying body composition is poorly understood.

OBJECTIVES

Our objectives were to 1) describe/compare distinct contributions of fat/lean mass with BMI-metabolite correlations and 2) identify novel metabolite biomarkers of fat/lean mass.

METHODS

The Alberta Physical Activity and Breast Cancer Prevention Trial was a 2-center randomized trial of healthy, inactive, postmenopausal women (n = 304). BMI (in kg/m2) was calculated using weight and height, whereas DXA estimated fat/lean mass. Ultra-performance liquid chromatography and mass spectrometry measured relative concentrations of serum metabolite concentrations. We estimated partial Pearson correlations between 1052 metabolites and BMI, adjusting for age, smoking, and site. Fat mass index (FMI; kg/m2) and lean mass index (LMI; kg/m2) correlations were estimated similarly, with mutual adjustment to evaluate independent effects.

RESULTS

Using a Bonferroni-corrected α level <4.75 × 10-5,  we observed 53 BMI-correlated metabolites (|r| = 0.24-0.42). Of those, 21 were robustly correlated with FMI (|r| > 0.20), 25 modestly (0.10 ≤ |r| ≤ 0.20), and 7 virtually null (|r| < 0.10). Ten of 53 were more strongly correlated with LMI than with FMI. Examining non-BMI-correlated metabolites, 6 robustly correlated with FMI (|r| = 0.24-0.31) and 2 with LMI (r = 0.25-0.26). For these, correlations for fat and lean mass were in opposing directions compared with BMI-correlated metabolites, in which correlations were mostly in the same direction.

CONCLUSIONS

Our results demonstrate how a thorough evaluation of the components of fat and lean mass, along with BMI, provides a more accurate assessment of the associations between body composition and metabolites than BMI alone. Such an assessment makes evident that some metabolites correlated with BMI predominantly reflect lean mass rather than fat, and some metabolites related to body composition are not correlated with BMI. Correctly characterizing these relations is important for an accurate understanding of how and why obesity is associated with disease.

Remote Ischemic Preconditioning Reduces Marathon-Induced Oxidative Stress and Decreases Liver and Heart Injury Markers in the Serum

Clinical studies continue to provide evidence of organ protection by remote ischemic preconditioning (RIPC). However, there is lack of insight into impact of RIPC on exercise-induce changes in human organs' function. We here aimed to elucidate the effects of 10-day RIPC training on marathon-induced changes in the levels of serum markers of oxidative stress, and liver and heart damage. The study involved 18 male amateur runners taking part in a marathon. RIPC training was performed in the course of four cycles, by inflating and deflating a blood pressure cuff at 5-min intervals (RIPC group, n=10); the control group underwent sham training (n=8). The effects of RIPC on levels of oxidative stress, and liver and heart damage markers were investigated at rest after 10 consecutive days of training and after the marathon run. The 10-day RIPC training decreased the serum resting levels of C-reactive protein (CRP), alanine transaminase (ALT), γ-glutamyl transpeptidase (GGT), and malondialdehyde (MDA). After the marathon run, creatinine kinase MB (CK-MB), lactate dehydrogenase (LDH), cardiac troponin level (cTn), aspartate aminotransferase (AST), alkaline phosphatase (ALP), ALT, total bilirubin (BIL-T), and MDA levels were increased and arterial ketone body ratio (AKBR) levels were decreased in all participants. The changes were significantly diminished in the RIPC group compared with the control group. The GGT activity remained constant in the RIPC group but significantly increased in the control group after the marathon run. In conclusion, the study provides evidence for a protective effect of RIPC against liver and heart damage induced by strenuous exercise, such as the marathon.

The Protective Role of the Heme Catabolic Pathway in Hepatic Disorders

Significance: As the central metabolic organ, the liver is exposed to a variety of potentially cytotoxic, proinflammatory, profibrotic, and carcinogenic stimuli. To protect the organism from these deleterious effects, the liver has evolved a number of defense systems, which include antioxidant substrates and enzymes, anti-inflammatory tools, enzymatic biotransformation systems, and metabolic pathways. Recent Advances: One of the pivotal systems that evolved during phylogenesis was the heme catabolic pathway. Comprising the important enzymes heme oxygenase and biliverdin reductase, this complex pathway has a number of key functions including enzymatic activities, but also cell signaling, and DNA transcription. It further generates two important bile pigments, biliverdin and bilirubin, as well as the gaseous molecule carbon monoxide. These heme degradation products have potent antioxidant, immunosuppressive, and cytoprotective effects. Recent data suggest that the pathway participates in the regulation of metabolic and hormonal processes implicated in the pathogenesis of hepatic and other diseases. Critical Issues: This review discusses the impact of the heme catabolic pathway on major liver diseases, with particular focus on the involvement of cellular targeting and signaling in the pathogenesis of these conditions. Future Directions: To utilize the biological consequences of the heme catabolic pathway, several unique therapeutic strategies have been developed. Research indicates that pharmaceutical, nutraceutical, and lifestyle modifications positively affect the pathway, delivering potentially long-term clinical benefits. However, further well-designed studies are needed to confirm the clinical benefits of these approaches. Antioxid. Redox Signal. 35, 734-752.

Serum Bilirubin Levels in Overweight and Obese Individuals: The Importance of Anti-Inflammatory and Antioxidant Responses

Obesity is a chronic condition involving low-grade inflammation and increased oxidative stress; thus, obese and overweight people have lower values of serum bilirubin. Essentially, bilirubin is a potent endogenous antioxidant molecule with anti-inflammatory, immunomodulatory, antithrombotic, and endocrine properties. This review paper presents the interplay between obesity-related pathological processes and bilirubin, with a focus on adipose tissue and adipokines. We discuss potential strategies to mildly increase serum bilirubin levels in obese patients as an adjunctive therapeutic approach.

Bilirubin as a metabolic hormone: the physiological relevance of low levels

Recent research on bilirubin, a historically well-known waste product of heme catabolism, suggests an entirely new function as a metabolic hormone that drives gene transcription by nuclear receptors. Studies are now revealing that low plasma bilirubin levels, defined as "hypobilirubinemia," are a possible new pathology analogous to the other end of the spectrum of extreme hyperbilirubinemia seen in patients with jaundice and liver dysfunction. Hypobilirubinemia is most commonly seen in patients with metabolic dysfunction, which may lead to cardiovascular complications and possibly stroke. We address the clinical significance of low bilirubin levels. A better understanding of bilirubin's hormonal function may explain why hypobilirubinemia might be deleterious. We present mechanisms by which bilirubin may be protective at mildly elevated levels and research directions that could generate treatment possibilities for patients with hypobilirubinemia, such as targeting of pathways that regulate its production or turnover or the newly designed bilirubin nanoparticles. Our review here calls for a shift in the perspective of an old molecule that could benefit millions of patients with hypobilirubinemia.

Rats Genetically Selected for High Aerobic Exercise Capacity Have Elevated Plasma Bilirubin by Upregulation of Hepatic Biliverdin Reductase-A (BVRA) and Suppression of UGT1A1

Exercise in humans and animals increases plasma bilirubin levels, but the mechanism by which this occurs is unknown. In the present study, we utilized rats genetically selected for high capacity running (HCR) and low capacity running (LCR) to determine pathways in the liver that aerobic exercise modifies to control plasma bilirubin. The HCR rats, compared to the LCR, exhibited significantly higher levels of plasma bilirubin and the hepatic enzyme that produces it, biliverdin reductase-A (BVRA). The HCR also had reduced expression of the glucuronyl hepatic enzyme UGT1A1, which lowers plasma bilirubin. Recently, bilirubin has been shown to activate the peroxisome proliferator-activated receptor-α (PPARα), a ligand-induced transcription factor, and the higher bilirubin HCR rats had significantly increased PPARα-target genes Fgf21, Abcd3, and Gys2. These are known to promote liver function and glycogen storage, which we found by Periodic acid–Schiff (PAS) staining that hepatic glycogen content was higher in the HCR versus the LCR. Our results demonstrate that exercise stimulates pathways that raise plasma bilirubin through alterations in hepatic enzymes involved in bilirubin synthesis and metabolism, improving liver function, and glycogen content. These mechanisms may explain the beneficial effects of exercise on plasma bilirubin levels and health in humans.

Association of circulating total bilirubin level with ischemic stroke: a systemic review and meta-analysis of observational evidence

Background

Circulating total bilirubin is a biomarker of ischemic stroke and may serve as a potential prognostic factor. It is imperative to systemically evaluate the correlation between circulating total bilirubin and risk for stroke. This systematic review and meta-analysis investigated the relationship between total serum bilirubin and risk for stroke.

Methods

Studies published before 30 June 2017 were searched in four databases (PubMed, EMBASE, Web of Science and Cochrane Central). Additional studies were searched by reviewing references and contacting authors. Cohort, cross-sectional and case-control studies in adults that examined the association between serum total bilirubin and stroke were included irrespective of language and date of publication. The primary outcome of this study was ischemic stroke, and the secondary outcome was stroke. Abstract and full-text were reviewed by two independent reviewers, and disagreement was resolved by consulting a third reviewer. Data were extracted by two independent reviewers using a pre-designed data collection form.

Results

Eleven observational studies (5 prospective and 6 cross-sectional studies) involving 131,450 subjects were included for analysis. In four studies with 83,380 subjects, the relationship between circulating total bilirubin and ischemic stroke was investigated, ischemic stroke was found in 2,496 patients, and the total odds ratio (OR) of the highest bilirubin and the lowest bilirubin for the occurrence of ischemic stroke was 0.66 (95% CI: 0.58-0.74). Eleven studies with 131,450 subjects explored the correlation between bilirubin and stroke, stroke was reported in 5,060 patients, and the total OR of the highest bilirubin and the lowest bilirubin for the occurrence of stroke was 0.73 (95% CI: 0.68-0.79). A stratified analysis based on the gender showed that the total bilirubin level in males correlated with ischemic stroke or stroke, which was not noted in females.

Conclusions

The available studies support an inverse association between circulating total bilirubin and risk for ischemic stroke and stroke in males. Prospective studies with large sample size are needed to establish the role of circulating bilirubin in the prevention of stroke.

Induction of Mild Hyperbilirubinemia: Hype or Real Therapeutic Opportunity?

Observational epidemiological studies showed that mild hyperbilirubinemia has beneficial effects on the prevention of cardiovascular disease, type 2 diabetes mellitus, and metabolic syndrome. In mammals, bilirubin plays a major role as a potent antioxidant. Uridine 5'-diphospho-glucuronosyl transferase (UGT)1A1 variants coding for bilirubin UDP-glucuronosyl transferase resulting in mild hyperbilirubinemia (as in Gilbert syndrome (GS)) may confer a strong genetic advantage. Strategies to boost bioavailability of bilirubin or to mimic GS represent an attractive approach to prevent many oxidative stress and inflammation-mediated diseases. Even a tiny, micromolar increase in serum bilirubin concentrations substantially decreases the risk of oxidative stress-mediated diseases. There are several possible ways to achieve this, including lifestyle changes, changes in dietary patterns, regular physical activities, or use of chemical drug or of specific plant products either in the form of regular food items or nutraceuticals. Further basic and experimental research is required to fully uncover this promising therapeutic field.

Effects of Probiotic Supplementation on Selected Parameters of Blood Prooxidant-Antioxidant Balance in Elite Athletes: A Double-Blind Randomized Placebo-Controlled Study

A randomized, double-blind, placebo-controlled study was conducted, in order to evaluate if Lactobacillus helveticus Lafti® L10 (Lallemand Health Solutions, Montreal, Canada) supplementation during three months could influence oxidative markers in the population of elite athletes: triathletes, cyclists and endurance athletes. Twenty-two elite athletes were randomized to either placebo (n = 12) or probiotic (n = 10) groups. The probiotic group received 2x1010 colony forming units of Lafti® L10. Before and after the supplementation serum samples were collected. Markers of oxidative stress and anti-oxidative defense: superoxide dismutase (SOD), paraoxonase (PON), advanced oxidation protein products (AOPP), malondialdehyde (MDA), total antioxidant status, total oxidant status, pro-oxidant-antioxidant balance, oxidative stress index, bilirubin, uric acid and albumin were determined in serum. Parameters of lipid status, as well as susceptibility to copper-induced oxidation of LDL particles in vitro were also determined. There was a significant interaction effect for MDA (p = 0.039), with a decrease in MDA in the probiotic group only (p = 0.049). There was a significant interaction effect for AOPP (p = 0.037), with a significant decrease in the probiotic group (p = 0.045). Interaction effect for SOD was approaching to formal significance (p = 0.108) and the post-hoc test showed a significant decrease in the probiotic group (p = 0.041) only. A significant correlation between AOPP and SOD (p = 0.012, r = -0.40) was found in the probiotic group at the end of the study. PON1 activity was decreased in both the probiotic (p = 0.032) and placebo group (p = 0.035). No significant changes in the remainder of the evaluated parameters were noted. In conclusion, probiotic strain Lafti® L10 exerts certain antioxidant potential, but further research is needed.

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.

Circulating Total Bilirubin and Future Risk of Hypertension in the General Population: The Prevention of Renal and Vascular End-Stage Disease (PREVEND) Prospective Study and a Mendelian Randomization Approach

BACKGROUND

Circulating total bilirubin is known to be inversely and independently associated with future risk of cardiovascular disease. However, the relationship of circulating total bilirubin with incident hypertension is uncertain. We aimed to assess the association of total bilirubin with future hypertension risk and supplemented this with a Mendelian randomization approach to investigate any causal relevance to the association.

METHODS AND RESULTS

Plasma total bilirubin levels were measured at baseline in the PREVEND (Prevention of Renal and Vascular End-Stage Disease) prospective study of 3989 men and women without hypertension. Hazard ratios (95% confidence intervals) of total bilirubin with incident hypertension were assessed. New-onset hypertension was recorded in 1206 participants during a median follow-up of 10.7 years. Baseline total bilirubin was approximately log-linearly associated with hypertension risk. Age- and sex-adjusted hazard ratio for hypertension per 1-SD increase in loge total bilirubin was 0.86 (0.81-0.92; P<0.001), which was attenuated to 0.94 (0.88-0.99; P=0.040) after further adjustment for established risk factors and other potential confounders. The association was marginally significant on further adjustment for high-sensitivity C-reactive protein (0.94; 0.88-1.00; P=0.067). A genetic variant at the UGT1A1*28 locus consistently shown to be strongly associated with circulating bilirubin levels-rs6742078-was not significantly associated with blood pressure or hypertension (P>0.05 for all), arguing against a strong causal association of circulating bilirubin with blood pressure.

CONCLUSIONS

The weak and inverse association of circulating total bilirubin with future hypertension risk may be driven by biases such as unmeasured confounding and/or reverse causation. Further evaluation is warranted.

In vivo toxicity of copper oxide, lead oxide and zinc oxide nanoparticles acting in different combinations and its attenuation with a complex of innocuous bio-protectors

Stable suspensions of metal oxide nanoparticles (Me-NPs) obtained by laser ablation of 99.99% pure copper, zinc or lead under a layer of deionized water were used separately, in three binary combinations and a triple combination in two independent experiments on rats. In one of the experiments the rats were instilled with Me-NPs intratracheally (i.t.) (for performing a broncho-alveolar lavage in 24h to estimate the cytological and biochemical indices of the response of the lower airways), while in the other, Me-NPs were repeatedly injected intraperitoneally (i.p.) 18 times during 6 weeks (for estimating the accumulation of corresponding metals in the blood and their excretion with urine and feces and for assessing subchronic intoxication by a large number of functional and morphological indices). Mathematical description of the results from both experiments with the help of the Response Surface Methodology has shown that, as well as in the case of any other binary toxic combinations previously investigated by us, the response of the organism to a simultaneous exposure to any two of the Me-NPs under study is characterized by complex interactions between all possible types of combined toxicity (additivity, subadditivity or superadditivity of unidirectional action and different variants of opposite effects) depending on which effect it is estimated for as well as on the levels of the effect and dose. With any third Me-NP species acting in the background, the type of combined toxicity displayed by the other two may change significantly (as in the earlier described case of a triple combination of soluble metal salts). It is shown that various harmful effects produced by CuO-NP+ZnO-NP+PbO-NP combination may be substantially attenuated by giving rats per os a complex of innocuous bioactive substances theoretically expected to provide a protective integral and/or metal-specific effect during one month before i.t. instillation or during the entire period of i.p. injections.

Total bilirubin in athletes, determination of reference range

The purpose of this study was to determine a typical reference range for the population of athletes. Results of blood tests of 339 athletes (82 women and 257 men, aged 18-37 years) were retrospectively analysed. The subjects were representatives of different sports disciplines. The measurements of total bilirubin (BIT), iron (Fe), alkaline phosphatase (ALP), alanine aminotransferase (ALT) and gamma-glutamyltransferase (GGT) were made using a Pentra 400 biochemical analyser (Horiba, France). Red blood cell count (RBC), reticulocyte count and haemoglobin concentration measurements were made using an Advia 120 haematology analyser (Siemens, Germany). In groups of women and men the percentage of elevated results were similar at 18%. Most results of total bilirubin in both sexes were in the range 7-14 μmol·L^-1 (49% of women and 42% of men). The highest results of elevated levels of BIT were in the range 21-28 μmol·L^-1 (12% of women and 11% of men). There was a significant correlation between serum iron and BIT concentration in female and male athletes whose serum total bilirubin concentration does not exceed the upper limit of the reference range. Elevated concentrations of total bilirubin appear to be due to changes caused by regular exercise. The obtained upper limit of the reference range for total bilirubin concentration in the group of athletes is 29.0 μmol·L^-1. It seems reasonable to use dedicated reference values for total bilirubin concentration in relation to the group of athletes.

Association of circulating total bilirubin with the metabolic syndrome and type 2 diabetes: A systematic review and meta-analysis of observational evidence

OBJECTIVE

Emerging evidence suggests that bilirubin levels might be associated with the metabolic syndrome (MetS) and type 2 diabetes (T2D), although the nature of the association remains unclear.

DESIGN

This systematic review and meta-analysis investigated the relationship between total plasma bilirubin and the risk of MetS and T2D.

DATA SOURCES

Relevant studies were identified using five databases (Embase, Medline [Ovid], Web of Science, PubMed, Cochrane Central and Google Scholar), with the last search done on 21 October 2015. Study references were checked and authors contacted to identify additional studies.

STUDY SELECTION

Randomized controlled trials, and cohort, case-control and cross-sectional studies of adults examining the association between blood bilirubin levels and MetS and T2D were included, irrespective of language and date of publication. Abstract and full-text selection was done by two independent reviewers, with a third reviewer available in case of disagreement.

DATA EXTRACTION

Data were extracted by two independent reviewers using a predesigned data collection form.

MAIN OUTCOMES AND MEASURES

MetS and T2D.

METHODS

Summary estimates were obtained by random-effects meta-analysis.

RESULTS

Of the 2313 searched references, 16 observational studies (11 cross-sectional, two prospective, one that was both cross-sectional and prospective, two retrospective and one national survey) met our inclusion criteria. Overall, data were available for 175,911 non-overlapping participants, including 7414 MetS cases and 9406 T2D cases. In the meta-analysis of seven cross-sectional studies, the pooled odds ratio (95% confidence interval) for MetS in a comparison of extreme tertiles of serum bilirubin levels was 0.70 (95% CI: 0.62, 0.78), whereas no significant association was found for the pooled estimated relative risk between two prospective studies (0.57, 95% CI: 0.11, 2.94). The corresponding estimate was 0.77 (95% CI: 0.67, 0.87) for T2D from four cross-sectional studies.

CONCLUSION

The available evidence, mainly from cross-sectional studies, supports an inverse association of bilirubin levels with adverse metabolic outcomes. Large-scale prospective studies are now needed to establish whether bilirubin levels may be useful in the prevention of MetS and T2D.

Effects of clinically significant weight loss with exercise training on insulin resistance and cardiometabolic adaptations

OBJECTIVE

To determine response rates for clinically significant weight loss (CWL) following different aerobic exercise training amounts and whether enhanced cardiometabolic adaptations are observed with CWL compared to modest weight loss (MWL) or neither.

METHODS

Participants (N = 330) performed 6 months of aerobic training at 4 kcal per kilogram per week (KKW), 8 KKW, or 12 KKW (50%, 100%, and 150% of recommended levels respectively). Weight loss was categorized as CWL (≥5%) or MWL (3.0% to 4.9%) or neither.

RESULTS

The CWL response rate was greater in the 8 KKW group (20.2%, CI: 13.0% to 27.5%) compared to 4 KKW (10.3%, CI: 4.6% to 16.0%), but not compared to the 12 KKW group (14.6%, CI: 7.6% to 21.6%). Reductions in HOMA-IR were observed in participants with CWL (-0.60, CI: -0.98 to -0.22) and with MWL (-0.48, CI: -0.87 to -0.10), but not those who achieved neither (-0.06, CI -0.22 to 0.10). No changes between groups were observed for cholesterol, fitness, or blood pressure.

CONCLUSIONS

Low response rates for CWL were observed following training, even at levels above recommended levels. Achieving MWL with exercise may represent a reasonable initial weight loss target since the improvement in insulin resistance with MWL is similar to what is achieved with CWL.

Influence of Long-Distance Bicycle Riding on Serum/Urinary Biomarkers of Prostate Cancer

Herein, we present a study focused on the determination of the influence of long-distance (53 km) bicycle riding on levels of chosen biochemical urinary and serum prostate cancer (PCa) biomarkers total prostate-specific antigen (tPSA), free PSA (fPSA) and sarcosine. Fourteen healthy participants with no evidence of prostate diseases, in the age range from 49-57 years with a median of 52 years, underwent physical exercise (mean race time of 150 ± 20 min, elevation increase of 472 m) and pre- and post-ride blood/urine sampling. It was found that bicycle riding resulted in elevated serum uric acid (p = 0.001, median 271.76 vs. 308.44 µmol/L pre- and post-ride, respectively), lactate (p = 0.01, median 2.98 vs. 4.8 mmol/L) and C-reactive protein (p = 0.01, 0.0-0.01 mg/L). It is noteworthy that our work supports the studies demonstrating an increased PSA after mechanical manipulation of the prostate. The subjects exhibited either significantly higher post-ride tPSA (p = 0.002, median 0.69 vs. 1.1 ng/mL pre- and post-ride, respectively) and fPSA (p = 0.028, median 0.25 vs. 0.35 ng/mL). Contrary to that, sarcosine levels were not significantly affected by physical exercise (p = 0.20, median 1.64 vs. 1.92 µmol/mL for serum sarcosine, and p = 0.15, median 0.02 µmol/mmol of creatinine vs. 0.01 µmol/mmol of creatinine for urinary sarcosine). Taken together, our pilot study provides the first evidence that the potential biomarker of PCa-sarcosine does not have a drawback by means of a bicycle riding-induced false positivity, as was shown in the case of PSA.

Active and Passive Smoking and Serum Total Bilirubin in a Rural Korean Population

INTRODUCTION

Serum bilirubin is an endogenous antioxidant biomarker and its low level is a potential risk factor for smoking related health disorders. This study investigated the association of cigarette smoke with serum total bilirubin among Koreans.

METHODS

Between 2006 and 2011, we examined 4899 Korean adults living in a rural community. After excluding 38 participants with serum bilirubin more than 2mg/dL, 75 participants who did not report their smoking status or who had liver or bile duct disorders, and 711 participants with liver enzymes exceeding the upper reference values, we performed a cross-sectional analysis on 4075 participants. Participants were classified into four groups: never-smokers without secondhand smoke exposure (SHSE), never-smokers with SHSE, former smokers, and active smokers. Serum total bilirubin concentration was measured using the enzyme method.

RESULTS

Compared to never-smokers without SHSE, never-smokers with SHSE (β = -0.025 mg/dL), former smokers (β = -0.049 mg/dL), and active smokers (β = -0.149 mg/dL) had significantly lower serum bilirubin even after adjusting for demographic factors, study year, alanine aminotransferase, gamma-glutamyl transferase, hemoglobin, lifestyle factors, and chronic diseases. A sex-stratified analysis indicated that for men, former smokers and active smokers were significantly associated with having lower bilirubin when compared to never-smokers without SHSE. However, for women, never-smokers with SHSE and active smokers were significantly associated with having lower bilirubin when compared to never-smokers without SHSE.

CONCLUSION

Our findings suggest that both active and passive cigarette smoking are associated with low serum bilirubin among Korean adults.

IMPLICATIONS

Our results suggest that not only active smoking but also passive smoking including SHSE can have an influence on decreasing serum bilirubin levels. With this different point of view, our study supports efforts to create smoke-free environments in order to foster more favorable serum bilirubin profiles, which may improve endothelial function and reduce the risk of cardiovascular disease.

Serum bilirubin and the risk of hypertension

BACKGROUND

Experimental studies suggest oxidative stress could lead to the development of hypertension. Serum bilirubin is a major contributor to the antioxidant capacity in blood plasma and has been identified as an independent cardiovascular risk factor in cohort studies. However, data on the relationship between bilirubin and blood pressure are scarce and inconclusive.

METHODS

We analysed data from the National Health and Nutrition Examination Surveys (NHANES) 1999-2012 (N=31069). Fifty multiple imputed data sets were generated and analysed to avoid selection/confounding bias due to excluding individuals/variables with missing values. A minimal sufficient adjustment set of variables (MSAS) needed to estimate the unconfounded effect of bilirubin on blood pressure and hypertension (systolic/diastolic blood pressure ≥ 140/90 mmHg or using antihypertensive medication) was identified using the back-door criterion and included in all regression models.

RESULTS

After adjustment for the MSAS variables, systolic blood pressure decreased progressively up to -2.5 mmHg (p<0.001) and the prevalence of hypertension was up to 25% lower (P<0.001) in those with bilirubin ≥ 1.0 mg/dl-the highest two deciles-compared with those with 0.1-0.4 mg/dl-the lowest decile. Sensitivity analyses showed these results were unlikely to be explained by residual confounding or selection bias.

CONCLUSIONS

High serum bilirubin may decrease the risk of hypertension by inactivating and inhibiting the synthesis of reactive oxygen species in vascular cells. Strategies to boost the bioavailability of circulating and tissue bilirubin or to mimic bilirubin's antioxidant properties could have a significant impact on prevention and control of hypertension as well as coronary heart disease.

Body fat percentage is a major determinant of total bilirubin independently of UGT1A1*28 polymorphism in young obese

Objectives

Bilirubin has potential antioxidant and anti-inflammatory properties. The UGT1A1*28 polymorphism (TA repeats in the promoter region) is a major determinant of bilirubin levels and recent evidence suggests that raised adiposity may also be a contributing factor. We aimed to study the interaction between UGT1A1 polymorphism, hematological and anthropometric variables with total bilirubin levels in young individuals.

Methods

350 obese (mean age of 11.6 years; 52% females) and 79 controls (mean age of 10.5 years; 59% females) were included. Total bilirubin and C-reactive protein (CRP) plasma levels, hemogram, anthropometric data and UGT1A1 polymorphism were determined. In a subgroup of 74 obese and 40 controls body composition was analyzed by dual-energy X-ray absorptiometry.

Results

The UGT1A1 genotype frequencies were 49.9%, 42.7% and 7.5% for 6/6, 6/7 and 7/7 genotypes, respectively. Patients with 7/7 genotype presented the highest total bilirubin levels, followed by 6/7 and 6/6 genotypes. Compared to controls, obese patients presented higher erythrocyte count, hematocrit, hemoglobin and CRP levels, but no differences in bilirubin or in UGT1A1 genotype distribution. Body fat percentage was inversely correlated with bilirubin in obese patients but not in controls. This inverse association was observed either in 6/7 or 6/6 genotype obese patients. UGT1A1 polymorphism and body fat percentage were the main factors affecting bilirubin levels within obese patients (linear regression analysis).

Conclusion

In obese children and adolescents, body fat composition and UGT1A1 polymorphism are independent determinants of total bilirubin levels. Obese individuals with 6/6 UGT1A1 genotype and higher body fat mass may benefit from a closer clinical follow-up.

Association Between Flavonoid-Rich Fruit and Vegetable Consumption and Total Serum Bilirubin

Emerging work demonstrates that serum bilirubin is a novel biomarker implicated in cardiovascular and metabolic diseases. However, we have a limited understanding of the influence of flavonoid-rich fruit and vegetable consumption on bilirubin levels, which was the purpose of this study. Data from the 2003 to 2006 National Health and Nutrition Examination survey were used (n = 1783; 18-85 years of age), with analyses performed in 2014. Total serum bilirubin was measured from a blood sample. Using a food frequency questionnaire (FFQ), a flavonoid index variable was created summing the frequency of consumption of flavonoid-rich foods. After adjustments, greater consumption of flavonoid-rich fruits and vegetables was positively associated with bilirubin levels. Our findings suggest an association between flavonoid-rich fruit and vegetable consumption and bilirubin levels. If confirmed by prospective and experimental studies, then regular consumption of flavonoid-rich fruits and vegetables should be promoted to increase levels of bilirubin.

Physical activity and total serum bilirubin levels among insulin sensitive and insulin resistant U.S. adults

Background

Total serum bilirubin has been identified as a novel biomarker for metabolic disease, with higher levels providing protection against metabolic disease. To our knowledge, only 3 studies, to date, have examined the association between physical activity and total serum bilirubin, with these studies reporting mixed findings. One potential reason for the mixed findings may be the exclusive use of self-report physical activity methodology. The purpose of this study was to examine the association between accelerometer-assessed physical activity and total serum bilirubin among a national sample of U.S. insulin sensitive and insulin resistant adults.

Methods

Data from the 2003-2006 National Health and Nutrition Examination Survey were used. Physical activity was objectively-measured using an accelerometer over a 7 day period. Bilirubin levels were assessed from a blood sample. Data was analyzed in 2013.

Results

After adjusting for age, gender, race-ethnicity, BMI, comorbid illness, cotinine, and poverty level, moderate-to-vigorous physical activity (MVPA) was associated with bilirubin for insulin resistant individuals (β = 0.08; p = 0.04), but not insulin sensitive individuals (β = 0.02; p = 0.38).

Conclusions

MVPA is associated with total serum bilirubin levels among U.S. adults with insulin resistance. Future experimental and prospective studies are needed, with further attention focused on the mechanisms that may help to explain the association between physical activity and bilirubin.

Higher serum bilirubin level as a protective factor for the development of diabetes in healthy Korean men: a 4 year retrospective longitudinal study

OBJECTIVE

Bilirubin, a natural product of heme catabolism by heme oxygenase, one of key antioxidant enzymes, has been recognized as a substance with potent antioxidant and cytoprotective properties. Several studies have shown a significant negative relationship between serum bilirubin levels and the risk of metabolic disorders, including type 2 diabetes. However, longitudinal studies investigating the association of elevated serum bilirubin levels and type 2 diabetes are lacking. In the present study, we aimed to investigate the longitudinal effects of baseline serum bilirubin concentrations on the development of type 2 diabetes in healthy Korean men.

MATERIALS AND METHODS

This 4 year retrospective longitudinal observational study was conducted at the Asan Medical Center, Seoul, Republic of Korea. The study population consisted of 5960 men without type 2 diabetes who underwent routine health examinations in 2007 (baseline) and 2011 (follow-up). Baseline serum bilirubin concentrations were determined by the vanadate oxidation method.

RESULTS

During a 4 year period, 409 incident cases of diabetes (6.9 %) were identified. Incident type 2 diabetes decreased across the baseline bilirubin quartile categories (P for trend <0.001). In multivariable-adjusted model, the relative risk (RR) for the development of type 2 diabetes was significantly lower in the highest (i.e., 1.30-2.00 mg/dl) than in the lowest bilirubin quartile category (i.e., ≤ 0.90 mg/dl), even after adjustment for confounding variables (RR=0.69, 95% confidence interval 0.48-0.99, P for trend = 0.041).

CONCLUSIONS

The results indicate that serum total bilirubin level may provide additional information for predicting future development of type 2 diabetes in healthy subjects.

Serum bilirubin levels are lower in overweight asymptomatic middle-aged adults: an early indicator of metabolic syndrome?

OBJECTIVE

Low levels of bilirubin have recently been associated with obesity, diabetes mellitus, and metabolic syndrome. Here, we hypothesized that serum bilirubin levels might be already altered in overweight asymptomatic middle-aged individuals before full development of the metabolic syndrome.

METHODS

Healthy nonsmoking adults aged 25-49 (64 women and 32 men) participated in this cross-sectional study. All participants who reported stable weight within the last three months underwent standard anthropomorphological measurements of body composition, blood pressure measurements, aerobic and anaerobic capabilities assessment, dietary intake evaluation, and fasting serological measurements of total and direct bilirubin, glucose, insulin, triglycerides, total cholesterol, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, and C-reactive protein. Participants were divided into normal-weight and overweight groups. Linear correlation and multiple regression analyses were used to examine the association of serum bilirubin levels with all metabolic syndrome risk factor changes.

RESULTS

Serum bilirubin levels were lower in overweight healthy individuals of both sexes, and were negatively associated with abdominal obesity, insulin resistance, fasting glucose, fasting insulin, fasting triglycerides, total cholesterol, low-density lipoprotein cholesterol, and C-reactive protein levels but positively associated with aerobic body capabilities.

CONCLUSION

Our findings suggest that serum bilirubin levels have the potential to be employed as an early biomarker for indicating asymptomatic individuals at increased risk of developing metabolic syndrome.

Diabetes, bilirubin and amputations: is there a link?

A study by Chan et al in this issue of Diabetologia (DOI: 10.1007/s00125-012-2818-4 ) reports that low plasma bilirubin levels are associated with an increased risk of amputation in patients with type 2 diabetes mellitus participating in the Fenofibrate Intervention and Event Lowering in Diabetes (FIELD) study. These findings raise the interesting and clinically relevant hypothesis that bilirubin protects against risk of amputation in patients with type 2 diabetes. This commentary considers some of the limitations associated with research aiming to define any link between circulating bilirubin levels and vascular disease. Numerous confounding factors (several of which may be present in patients with type 2 diabetes) may explain why the literature regarding this potentially protective role of bilirubin remains controversial.