Relationship between serum bilirubin and albuminuria in patients with type 2 diabetes

Association of bilirubin and malondialdehyde levels with retinopathy in type 2 diabetes mellitus

INTRODUCTION

Bilirubin as an antioxidant and malondialdehyde (MDA) as an oxidant have been shown to be associated with various complications of type 2 diabetes mellitus (DM).

AIMS AND OBJECTIVES

The aim was to measure the levels of serum bilirubin and MDA in type 2 DM patients with and without diabetic retinopathy (DR) and to correlate them with severity of DR.

MATERIALS AND METHODS

A total number of 120 subjects out of which 40 were controls without type 2 DM and the rest 80 were type 2 DM patients were included in the study. Of those 80 diabetics, 44 patients did not have DR and 36 patients had DR.

RESULTS

The total bilirubin, direct bilirubin, indirect bilirubin were higher in controls as compared to cases (P = 0.017, 0.033, 0.024). Serum MDA levels were found to be higher in diabetics as compared to controls (P = 0.00). The values of all the three parameters, that is, total bilirubin, direct bilirubin and indirect bilirubin were lower in patients with retinopathy as compared to those without retinopathic changes (P = 0.00, 0.020, and 0.007). Subjects were assigned to quartiles based on serum total bilirubin concentration. The prevalence of DR was significantly lower among persons with the highest bilirubin quartile compared to those with the lowest quartile. The severity of DR was inversely proportional to the total bilirubin levels (P = 0.001). The multiple logistic regression analysis showed total bilirubin to be associated with prevalence of DR (P = 0.035).

CONCLUSIONS

The levels of total bilirubin were significantly lower in patients with DR and also in the late stages of retinopathy as compared to those without retinopathy and in controls but MDA levels did not show any association with DR.

Prognostic impact of serum bilirubin level on long-term renal survival in IgA nephropathy

BACKGROUND

Serum bilirubin has been recognized as a novel endogenous antioxidant. The aim of our study was to evaluate the impact of serum bilirubin on kidney prognosis in IgA nephropathy (IgAN).

METHODS

We followed retrospectively 694 patients with IgAN diagnosed by renal biopsy between 1982 and 2010. The risk factors for developing end-stage renal disease (ESRD) were estimated using a Cox proportional hazard model. Predictive performance between models with or without serum bilirubin was evaluated by calculating the net reclassification improvement (NRI) and integrated discrimination improvement (IDI).

RESULTS

Seventy-seven patients developed ESRD during the median 4.9 years of follow-up. Estimated glomerular filtration rate, proteinuria and histological severity were inversely related to bilirubin levels. In multivariate analysis, serum bilirubin was an independent risk factor for ESRD (hazard ratio for every 0.1 mg/dL decrease in serum bilirubin, 1.18; 95 % CI, 1.04-1.33). The incidence rate of ESRD decreased linearly with the increases in bilirubin levels (P for trend <0.01). When bilirubin was incorporated into a model with conventional ESRD risk factors, the NRI and IDI were 0.281 (P = 0.02) and 0.019 (P = 0.01), respectively.

CONCLUSIONS

We demonstrated that lower bilirubin levels were significantly associated with higher risk of ESRD in IgAN. In addition, bilirubin provided incremental predictive value in the risk assessment for progression of IgAN beyond that provided by standard risk factors.

Association between Serum Bilirubin and Estimated Glomerular Filtration Rate among Diabetic Patients

The subjects comprised 230 men aged 77 ± 10 (range: 50-100) years and 279 women aged 81 ± 10 (50-101) years that visited the medical department. We examined the relationship between increased serum bilirubin and renal function evaluated by estimated glomerular filtration rate (eGFR) using CKD-EPI equations modified by a Japanese coefficient. Compared with the fourth quartile in serum bilirubin (1.01-1.97 mg/dL), the nonadjusted, age and gender-adjusted, and multivariate-adjusted odds ratios {95% confidence interval (CI)} of eGFR <60 mL/min/1.73 m(2) for the first quartile in serum bilirubin (0.13-0.50 mg/dL) were 2.08 (1.25-3.44), 1.82 (1.07-3.09), and 1.53 (0.83-2.81), respectively. Moreover, compared with the fourth quartile, nonadjusted, age and gender-adjusted, and multivariate-adjusted odds ratios (95% CI) of eGFR <45 mL/min/1.73 m(2) for the first quartile were 3.50 (1.95-6.23), 3.12 (1.72-5.65), and 3.53 (1.71-7.26), respectively. The data were further stratified by gender, age, medication (antihypertensive, antidyslipidemic, and antidiabetic agents), and prevalence of cardiovascular disease (CVD). The standardized coefficients for eGFR were significant in all the subgroups other than the prevalence of CVD, and there were significant interactions between the two groups regarding CVD. Our data demonstrated an independent positive association between serum bilirubin and eGFR among diabetic patients.

The duration of diabetes is inversely associated with the physiological serum bilirubin levels in patients with type 2 diabetes

OBJECTIVE

The aim of this study was to assess the relationship between the duration of diabetes and the physiological serum bilirubin concentration in association with antioxidant properties in patients with type 2 diabetes.

METHODS

A total of 1,746 patients with type 2 diabetes were investigated in this cross-sectional study. An analysis of covariance was performed after adjusting for other covariates. Simple correlation analyses and a multivariate regression model were used to assess the association between the duration of diabetes and the serum bilirubin concentration.

RESULTS

The mean total bilirubin value differed significantly according to the tertile of diabetes duration (<5 years, 12.38 μmol/L, 95% confidence interval (CI) 12.02-12.76; 5-11.9 years, 12.33 μmol/L, 95% CI 11.97-12.69; ≥12 years, 11.73 μmol/L, 95% CI 11.35-12.11; p for trend =0.033), after adjustment for other covariates. In addition, an inverse correlation was found between the serum bilirubin concentration and diabetes duration (ρ=-0.211, p<0.001). According to a multivariate model, the association between the diabetes duration and serum bilirubin concentration remained significant, even after adjustment for confounding factors (β=-0.074, p=0.008).

CONCLUSION

The duration of diabetes is inversely associated with a serum bilirubin concentration within the physiologic range in patients with type 2 diabetes.

Association between serum bilirubin and estimated glomerular filtration rate among elderly persons

Chronic kidney disease (CKD) is a major public health problem. However, few studies have examined the significance of serum bilirubin as a risk factor for the development of CKD in the general Japanese population. The subjects comprised 413 men (mean age: 79±9 years; (range, 60-100 years) and 637 women (mean age: 81±8 years; range, 60-106 years) who visited the medical department of Seiyo Municipal Nomura Hospital. We examined the relationship between increased serum bilirubin and renal function that was evaluated by estimated glomerular filtration rate (eGFR) using CKD-EPI equations modified by a Japanese coefficient. Stepwise multiple regression analysis with eGFR as the objective variable, and adjusted risk factors as the explanatory variables, showed that serum bilirubin (β = 0.11, P<0.001) was significantly and independently associated with eGFR, in addition to gender, age, prevalence of antihypertensive medication, triglycerides, prevalence of antidiabetic medication, and serum uric acid. Compared with stages 1+2 (eGFR ≥60.0 ml/min/1.73 m2), mean multivariate-adjusted odds ratio {95% (confidence interval (CI)} for hypobilirubinemia (first quartile, <0.52 mg/dL) was 3.52 (range: 1.88-6.59). Next, to control potential confounding factors, data were further stratified by gender, age, medication (antihypertensive, antidyslipidemic, and antidiabetic agents), and prevalence of cardiovascular disease. The standardized coefficient for eGFR was significant in both groups, and there was no interaction between the groups. Our data demonstrated an independent positive association between serum bilirubin and eGFR in both genders. Low serum bilirubin level would be useful as a potential risk factor for renal function.

Serum bilirubin concentrations are positively associated with serum C-peptide levels in patients with Type 2 diabetes

AIMS

To investigate the relationship between physiological serum total bilirubin concentrations and serum C-peptide levels in Korean patients with Type 2 diabetes.

METHODS

A total of 588 patients with Type 2 diabetes were investigated in this cross-sectional study. Fasting C-peptide level, 2-h postprandial C-peptide level and ΔC-peptide (postprandial C-peptide minus fasting C-peptide) level were measured in all patients.

RESULTS

Fasting C-peptide level, postprandial C-peptide level and ΔC-peptide level tended to be higher in patients with higher bilirubin concentrations. Partial correlation analysis showed that serum bilirubin levels were significantly correlated with fasting C-peptide level (r = 0.159, P < 0.001), postprandial C-peptide level (r = 0.209, P < 0.001) and ΔC-peptide level (r = 0.186, P < 0.001) after adjustment for other covariates. In the multivariate model, the association between serum bilirubin concentrations and serum C-peptide levels remained significant after adjustment for confounding factors including age, gender, familial diabetes, hypertension, hyperlipidaemia, BMI, HbA1c , duration of diabetes and associated liver function tests (fasting C-peptide level: β = 0.083, P = 0.041; postprandial C-peptide level: β = 0.106, P = 0.005; ΔC-peptide level: β = 0.096, P = 0.015, respectively).

CONCLUSIONS

Serum bilirubin concentrations within the physiological range were positively associated with serum C-peptide levels in patients with Type 2 diabetes.

Inverse association between serum bilirubin levels and arterial stiffness in Korean women with type 2 diabetes

BACKGROUND

Considerable evidence suggests that bilirubin is a potent physiologic antioxidant that may provide important protection against cardiovascular disease (CVD) and inflammation. We investigated the relationship between serum total bilirubin (TB) levels and arterial stiffness, measured by the brachial-ankle pulse wave velocity (baPWV), in patients with type 2 diabetes.

METHODS

We conducted a cross-sectional analysis of 1,711 subjects with type 2 diabetes (807 men and 904 women; mean age, 57.1 years). The subjects were stratified based on gender-specific tertiles of TB values, and a high baPWV was defined as greater than 1,745 cm/s ( >75th percentile).

RESULTS

The serum TB concentration was negatively correlated with the duration of diabetes, HbA1c, the 10-year Framingham risk score, and baPWV and was positively correlated with high-density lipoprotein cholesterol and the eGFR in both genders. Inverse association between TB categories and unadjusted prevalence of high PWV was only observed in women. After adjusting for confounding factors, the TB levels were inversely associated with a greater risk of a high baPWV, both as a continuous variable [a 1-SD difference; odds ratio (OR), 0.70; 95% confidence interval (CI), 0.54-0.90; P = 0.005] and when categorized in tertiles (the highest vs. the lowest tertile; OR, 0.49; 95% CI, 0.28-0.85; P = 0.011) in women but not in men. The relationship remained significant even after adjusting for retinopathy and nephropathy.

CONCLUSIONS

Low TB levels were significantly associated with arterial stiffness in Korean women with type 2 diabetes. Our data suggested that bilirubin may protect against macrovascular disease in diabetic women.

Bilirubin activates transcription of HIF-1α in human proximal tubular cells cultured in the physiologic oxygen content

The expression of hypoxia-inducible factor (HIF) is influenced by reactive oxygen species (ROS). Effect of bilirubin on HIF-1 expression in proximal tubular cells was investigated under physiological oxygen concentration, which is relative hypoxic condition mimicking oxygen content in the medulla of renal tissue. The human kidney (HK2) cells were cultured in 5% oxygen with or without bilirubin. HIF-1α protein expression was increased by bilirubin treatment at 0.01-0.2 mg/dL concentration. The messenger RNA expression of HIF-1α was increased by 1.69±0.05 folds in the cells cultured with 0.1 mg/dL bilirubin, compared to the control cells. The inhibitors of PI3K/mTOR, PI3K/AKT, and ERK 1/2 pathways did not attenuate increased HIF-1α expression by bilirubin. HIF-1α expression decreased by 10 µM exogenous hydrogen peroxide (H2O2); scavenger of ROS with or without bilirubin in the HK2 cells increased HIF-1α concentration more than that in the cells without bilirubin. Exogenous H2O2 decreased the phosphorylation of P70S6 kinase, which was completely reversed by bilirubin treatment. Knockdown of NOX4 gene by small interfering RNA (siRNA) increased HIF-1α mRNA expression. In coonclusion, bilirubin enhances HIF-1α transcription as well as the up-regulation of HIF-1α protein translation through the attenuation of ROS and subunits of NADPH oxidase.

Bilirubin and progression of nephropathy in type 2 diabetes: a post hoc analysis of RENAAL with independent replication in IDNT

Bilirubin, a potent endogenous antioxidant, was found to protect against the development of diabetic nephropathy (DN) in rodents. In humans, cross-sectional studies found an inverse relation between bilirubin and DN. We prospectively investigated whether bilirubin is associated with progression of DN toward end-stage renal disease (ESRD). To this end, we performed a post hoc analysis in the Reduction of Endpoints in NIDDM with the Angiotensin II Antagonist Losartan (RENAAL) trial with independent replication in the Irbesartan Diabetic Nephropathy Trial (IDNT). Subjects with type 2 diabetes and nephropathy with alanine aminotransferase, aspartate aminotransferase (AST), and bilirubin levels <1.5 times the upper limit of normal were included. The renal end point was defined as the composite of confirmed doubling of serum creatinine or ESRD. Bilirubin was inversely associated with the renal end point in RENAAL independent of age, sex, race, BMI, smoking, total cholesterol, diastolic blood pressure, HbA1c, treatment, estimated glomerular filtration rate, albumin-to-creatinine ratio, and AST. These results were confirmed in IDNT. This study indicates an independent inverse association of bilirubin with progression of nephropathy in RENAAL and IDNT. These data suggest a protective effect of bilirubin against progression of nephropathy in type 2 diabetes. The well-established role of bilirubin as an antioxidant is a potential explanation for the findings.

Circulating bilirubin and defense against kidney disease and cardiovascular mortality: mechanisms contributing to protection in clinical investigations

Unconjugated bilirubin is an endogenous circulating antioxidant, bound to albumin, and therefore is retained in the vascular compartment. Bilirubin has well-documented neurotoxic effects in infants; however, current evidence indicates mildly elevated bilirubin is associated with protection from cardiovascular disease and all-cause mortality in adults. Recent clinical studies show mildly elevated bilirubin is associated with protection from kidney damage and dysfunction, in addition to cardiovascular events and all-cause mortality in patients undergoing hemodialysis. This is the first review to examine the clinical evidence and summarize the potential mechanisms of action that link bilirubin to protection from kidney damage, subsequent kidney failure, and dialysis-related mortality. With this understanding, it is hoped that new therapies will be developed to prevent renal dysfunction and mortality from cardiovascular disease in at-risk individuals.

Serum total bilirubin levels and prevalence of diabetic retinopathy in a Chinese population

BACKGROUND

Patients with type 2 diabetes (T2D) are at a high risk of developing microvascular complications, such as diabetic retinopathy (DR). Previous studies have shown that low serum bilirubin concentrations in T2D patients may increase the risk of diabetic complications. Thus, the aim of the present was to investigate the association between the prevalence of DR and serum concentrations of total bilirubin in a Chinese population.

METHODS

The present study was a population-based cross-sectional study on 1761 T2D patients aged ≥40 years from the Jiading district of Shanghai, China. Fundus photographs were taken to confirm the presence and severity of DR. Subjects were assigned to quartiles based on serum total bilirubin concentrations (Quartile (Q) 1 <0.60 mg/dL; Q2 0.60-0.76 mg/dL; Q3 0.77-0.99 mg/dL; Q4 >0.99 mg/dL). Logistic regression models were used to explore the association between bilirubin concentrations and the prevalence of DR.

RESULTS

The prevalence of DR in the entire study population was 9.6%. The prevalence of DR was significantly lower in Q4 compared with the other three quartiles (Ptrend  = 0.004). After adjustment for multiple confounding factors, T2D patients in Q4 (i.e. serum bilirubin >0.99 mg/dL) were less likely (odds ratio 0.55; 95% confidence interval 0.33-0.91) to suffer from DR than patients in Q1 (i.e. serum bilirubin <0.60 mg/dL).

CONCLUSION

Serum bilirubin concentrations were inversely associated with DR in an elderly Chinese population, independent of traditional risk factors for microvascular complications.

Low serum bilirubin concentration is a predictor of chronic kidney disease

OBJECTIVE

Chronic kidney disease (CKD) is a worldwide public health problem. It is very important to identify the factors that affect CKD. Previous studies have reported that serum bilirubin concentration was positively correlated with renal function in a cross-sectional study. The aim of this study was to investigate the relationship between serum bilirubin concentration and the progression of CKD.

METHODS

A cohort study was performed on a consecutive series of 2784 subjects without CKD, defined as estimated glomerular filtration rate (eGFR) < 60 ml/min/1.73 m(2), at baseline. We analyzed the relationship between serum total bilirubin concentration at baseline and new-onset CKD in the general population.

RESULTS

We followed the subjects for a median period of 7.7 years. There were 1157 females and 1627 males, and 231 females and 370 males developed CKD during this period. Multiple Cox regression analyses revealed that serum total bilirubin concentration (hazard ratio (HR) per 1.0 μmol/L increase 0.97 (95% CI 0.95-0.99), P = 0.0084) in addition to age, gamma-glutamyl transpeptidase (GGT), uric acid (UA), creatinine and medication for hypertension in men and serum total bilirubin concentration (HR per 1.0 μmol/L increase 0.96 (95% CI 0.93-1.00), P = 0.0309) in addition to age, GGT, alanine aminotransferase, UA, creatinine and medication for dyslipidemia in women were independent predictors of new-onset CKD, after adjusting for confounders.

CONCLUSION

Our study demonstrated that serum total bilirubin concentration could be a novel risk factor for the progression of CKD, defined as eGFR <60 ml/min/1.73 m(2), in the general population.

Association of serum bilirubin levels with development and progression of albuminuria, and decline in estimated glomerular filtration rate in patients with type 2 diabetes mellitus

AIMS/INTRODUCTION

Recent observational studies suggest elevated levels of bilirubin, an endogenous anti-oxidant, might protect against kidney disease. We carried out an observational cohort study to assess whether higher baseline levels of bilirubin, within normal range, could predict the rate of development and progression of diabetic nephropathy in patients with type 2 diabetes.

MATERIALS AND METHODS

Japanese type 2 diabetic patients with normo- or microalbuminuria and normal serum bilirubin (<1.2 mg/dL) were recruited from a single center, and categorized according to baseline serum bilirubin levels. Two independent end-points were specified: development or progression of diabetic nephropathy, based on transition to a more advanced stage of albuminuria (albuminuria cohort), and the rate of change in estimated glomerular filtration rate (eGFR cohort).

RESULTS

Albuminuria and eGFR cohorts were constructed consisting of 1,915 patients and 1,898 patients, respectively, with 1,738 patients overlapping. Mean follow up was 4.4 and 5.4 years for the two cohorts, respectively. Within the albuminuria cohort, 132 (9%) of 1,418 patients with normoalbuminuria developed microalbuminuria, and 56 (11%) of 497 patients with microalbuminuria developed macroalbuminuria. Higher baseline bilirubin levels were associated with significantly lower risk of progression from microalbuminuria to macroalbuminuria in both the univariate and multivariate analyses. In normoalbuminuric patients, an inverse association was found when restricted to a subgroup with elevated hemoglobin A1c levels. There was no relationship between bilirubin levels and the rate of change in eGFR.

CONCLUSIONS

Higher serum bilirubin levels, within normal range, might be predictive of a lower risk of progression of nephropathy in type 2 diabetic patients.

Bilirubin increases insulin sensitivity in leptin-receptor deficient and diet-induced obese mice through suppression of ER stress and chronic inflammation

Obesity-induced endoplasmic reticulum (ER) stress causes chronic inflammation in adipose tissue and steatosis in the liver, and eventually leads to insulin resistance and type 2 diabetes (T2D). The goal of this study was to understand the mechanisms by which administration of bilirubin, a powerful antioxidant, reduces hyperglycemia and ameliorates obesity in leptin-receptor-deficient (db/db) and diet-induced obese (DIO) mouse models. db/db or DIO mice were injected with bilirubin or vehicle ip. Blood glucose and body weight were measured. Activation of insulin-signaling pathways, expression of inflammatory cytokines, and ER stress markers were measured in skeletal muscle, adipose tissue, and liver of mice. Bilirubin administration significantly reduced hyperglycemia and increased insulin sensitivity in db/db mice. Bilirubin treatment increased protein kinase B (PKB/Akt) phosphorylation in skeletal muscle and suppressed expression of ER stress markers, including the 78-kDa glucose-regulated protein (GRP78), CCAAT/enhancer-binding protein (C/EBP) homologous protein, X box binding protein (XBP-1), and activating transcription factor 4 in db/db mice. In DIO mice, bilirubin treatment significantly reduced body weight and increased insulin sensitivity. Moreover, bilirubin suppressed macrophage infiltration and proinflammatory cytokine expression, including TNF-α, IL-1β, and monocyte chemoattractant protein-1, in adipose tissue. In liver and adipose tissue of DIO mice, bilirubin ameliorated hepatic steatosis and reduced expression of GRP78 and C/EBP homologous protein. These results demonstrate that bilirubin administration improves hyperglycemia and obesity by increasing insulin sensitivity in both genetically engineered and DIO mice models. Bilirubin or bilirubin-increasing drugs might be useful as an insulin sensitizer for the treatment of obesity-induced insulin resistance and type 2 diabetes based on its profound anti-ER stress and antiinflammatory properties.

Low serum bilirubin concentration is a novel risk factor for the development of albuminuria in patients with type 2 diabetes

OBJECTIVE

Bilirubin has been recognized as an important endogeneous antioxidant. Previous studies reported that bilirubin could prevent atherosclerosis. The aim of this study was to investigate if serum bilirubin concentration could be a predictor for the development of albuminuria in patients with type 2 diabetes.

MATERIALS AND METHODS

We measured serum bilirubin in 320 consecutive patients with normoalbuminuria. We performed follow-up study to assess the development of albuminuria, mean interval of which was 3.2±0.9years. Cox proportional hazards regression was used to examine the relationship between serum bilirubin concentration and the development of albuminuria.

RESULTS

During follow-up duration, 43 patients have developed albuminuria. In multivariate analysis, after adjusting for comprehensive risk factors, the risk of developing albuminuria was higher in the lowest quartile of serum bilirubin concentrations than that in the highest quartile of serum bilirubin concentrations (Hazard ratio, 5.76; 95% CI, 1.65 to 24.93).

CONCLUSIONS

Low serum bilirubin concentration could be a novel risk factor for the development of albuminuria in patients with type 2 diabetes.

Higher serum direct bilirubin levels were associated with a lower risk of incident chronic kidney disease in middle aged Korean men

Background

The association between serum bilirubin levels and incident chronic kidney disease (CKD) in the general population is unknown. We aimed to examine the association between serum bilirubin concentration (total, direct, and indirect) and the risk of incident CKD.

Methods and Findings

Longitudinal cohort study of 12,823 Korean male workers 30 to 59 years old without CKD or proteinuria at baseline participating in medical health checkup program in a large worksite. Study participants were followed for incident CKD from 2002 through 2011. Estimated glomerular filtration rate (eGFR) was estimated by using the CKD-EPI equation. CKD was defined as eGFR <60 mL/min per 1.73 m². Parametric Cox models and pooled logistic regression models were used to estimate adjusted hazard ratios for incident CKD. We observed 238 incident cases of CKD during 70,515.8 person-years of follow-up. In age-adjusted models, the hazard ratios for CKD comparing quartiles 2–4 vs. quartile 1 of serum direct bilirubin were 0.93 (95% CI 0.67–1.28), 0.88 (0.60–1.27) and 0.60 (0.42–0.88), respectively. In multivariable models, the adjusted hazard ratio for CKD comparing the highest to the lowest quartile of serum direct bilirubin levels was 0.60 (95% CI 0.41–0.87; P trend = 0.01). Neither serum total nor indirect bilirubin levels were significantly associated with the incidence of CKD.

Conclusions

Higher serum direct bilirubin levels were significantly associated with a lower risk of developing CKD, even adjusting for a variety of cardiometabolic parameters. Further research is needed to elucidate the mechanisms underlying this association and to establish the role of serum direct bilirubin as a marker for CKD risk.

Physiological serum bilirubin concentrations are inversely associated with the prevalence of cardiovascular autonomic neuropathy in patients with Type 2 diabetes

AIMS

Although severe hyperbilirubinaemia causes kernicterus in neonates, normal to modestly elevated bilirubin concentrations have been reported to be neuroprotective. However, the relationship between serum bilirubin concentrations and cardiovascular autonomic neuropathy in patients with Type 2 diabetes is currently unknown. This study assessed the relationships between physiological serum total bilirubin concentrations and cardiovascular autonomic neuropathy in patients with Type 2 diabetes.

METHODS

A total of 2991 patients with Type 2 diabetes were investigated in this cross-sectional study. Cardiovascular autonomic neuropathy was diagnosed by a cardiovascular reflex test. According to the American Diabetes Association criteria, the degree of cardiovascular autonomic dysfunction was graded into normal, early, definite and severe. Cardiovascular autonomic neuropathy was either definite or severe in the present study. An analysis of covariance after adjustment for other covariates was performed. A logistic regression model was used to assess an association of cardiovascular autonomic neuropathy with serum total bilirubin tertiles.

RESULTS

Serum total bilirubin concentrations were significantly lower in subjects with cardiovascular autonomic neuropathy. The mean total bilirubin values differed significantly according to the severity of cardiovascular autonomic dysfunction (normal 13.0 μmol/l; early 12.3 μmol/l; definite 11.8 μmol/l; severe 10.1 μmol/l; P for trend < 0.001) after adjustment for other covariates. In multivariate analysis, serum total bilirubin levels were significantly associated with cardiovascular autonomic neuropathy (odds ratio 0.36; 95% CI 0.21-0.63 for the highest vs. the lowest bilirubin tertile, P < 0.001).

CONCLUSIONS

Serum total bilirubin concentrations within the physiologic range are inversely associated with the prevalence of cardiovascular autonomic neuropathy in patients with Type 2 diabetes.

Correlations between serum bilirubin levels and diabetic nephropathy progression among Japanese type 2 diabetic patients: a prospective cohort study (Diabetes Distress and Care Registry at Tenri [DDCRT 5])

OBJECTIVE To assess the correlations between serum bilirubin levels and diabetic nephropathy development and progression in type 2 diabetic patients. RESEARCH DESIGN AND METHODS Longitudinal data were obtained from 2,511 type 2 diabetic patients registered in a Japanese diabetes registry. To assess the independent correlations between serum bilirubin levels and either the development or progression of diabetic nephropathy, we used logistic regression analysis adjusted for potential confounders. RESULTS The median follow-up period was 503.4 days (range 238-777). The mean patient age, BMI, and HbA1c level was 65.2 years, 24.7 kg/m(2), and 7.5% (58.5 mmol/mol), respectively. Baseline serum bilirubin levels were significantly associated with the urinary albumin-creatinine ratio at baseline (P < 0.001) and 1 year after registration (P < 0.001). Multivariable adjusted odds ratios for progression from microalbuminuria to macroalbuminuria for the second, third, and fourth quartile of serum bilirubin levels were 0.89 (95% CI 0.49-1.58), 0.93 (0.47-1.83), and 0.33 (0.13-0.84), respectively, showing a statistically significant linear trend across categories (P = 0.032). However, this trend disappeared after adjustment for hemoglobin levels. CONCLUSIONS Serum bilirubin levels were associated with diabetic nephropathy progression in type 2 diabetic patients independent of possible confounders. Serum bilirubin levels might be the link in the correlation between hemoglobin levels and nephropathy progression.

Unconjugated bilirubin, a potent endogenous antioxidant, is decreased in patients with non-alcoholic steatohepatitis and advanced fibrosis

BACKGROUND AND AIM

Oxidative stress is considered a key element in the progression of non-alcoholic fatty liver to non-alcoholic steatohepatitis (NASH). Unconjugated bilirubin is the main endogenous lipid antioxidant and is cytoprotective in different tissues and organs. In this study, it was evaluated if unconjugated bilirubin levels are associated with the degree of liver injury in patients with non-alcoholic fatty liver disease.

METHODS

Two hundred and eighty-five patients were retrospectively evaluated with biopsy-confirmed non-alcoholic fatty liver disease. Multiple logistic regression models were used to assess the relationship of steatosis, inflammation, and fibrosis levels to the features of patients.

RESULTS

Unconjugated bilirubin levels differed significantly according to inflammation and fibrosis scores. Unconjugated bilirubin was lower in patients with moderate-severe inflammation compared with those with absent-mild (P = 0.001) and in patients with moderate-severe fibrosis compared with those with absent-mild (P < 0.001), whereas no difference was observed for steatosis grades. At logistic regression analysis, low unconjugated bilirubin levels were associated with moderate-severe inflammation (odds ratio, 0.11; 95% confidence interval 0.02-0.76; P = 0.025) and moderate-severe fibrosis (odds ratio, 0.013; 95% confidence interval 0.001-0.253; P = 0.004).

CONCLUSIONS

Low unconjugated bilirubin levels are independent predictors of advanced inflammation and fibrosis in patients with steatohepatitis, indicating the lack of antioxidant protection as a possible molecular determinant for the progression of liver injury.

A bilirubin-inducible fluorescent protein from eel muscle

The fluorescent protein toolbox has revolutionized experimental biology. Despite this advance, no fluorescent proteins have been identified from vertebrates, nor has chromogenic ligand-inducible activation or clinical utility been demonstrated. Here, we report the cloning and characterization of UnaG, a fluorescent protein from Japanese eel. UnaG belongs to the fatty-acid-binding protein (FABP) family, and expression in eel is restricted to small-diameter muscle fibers. On heterologous expression in cell lines or mouse brain, UnaG produces oxygen-independent green fluorescence. Remarkably, UnaG fluorescence is triggered by an endogenous ligand, bilirubin, a membrane-permeable heme metabolite and clinical health biomarker. The holoUnaG structure at 1.2 Å revealed a biplanar coordination of bilirubin by reversible π-conjugation, and we used this high-affinity and high-specificity interaction to establish a fluorescence-based human bilirubin assay with promising clinical utility. UnaG will be the prototype for a versatile class of ligand-activated fluorescent proteins, with applications in research, medicine, and bioengineering.

Total bilirubin is inversely associated with metabolic syndrome but not a risk factor for metabolic syndrome in Japanese men and women

Serum total bilirubin (TB) is a potent antioxidant and inversely associated with metabolic syndrome (MetS) in Asian populations. However, there has been no study which is aimed to investigate whether TB is a risk factor for MetS or not. We investigated cross-sectional and longitudinal associations between TB and MetS in 2,435 Japanese men and 1,436 Japanese women. The odds ratios [95 % confidence interval (CI)] of coexisting MetS for each 1 SD increase in log TB were 0.850 (0.754-0.958) (p = 0.008) in men and 0.809 (0.656-0.998) (p = 0.047) in women adjusted for sex, age, smoking, and other confounding covariates. Those for the third and fourth quartiles of TB compared with the lowest quartile were 0.720 (0.537-0.965) (p = 0.028) and 0.737 (0.530-1.052) (p = 0.095), respectively, in men and 0.822 (0.473-1.427) (p = 0.486) and 0.704 (0.362-1.369) (p = 0.301), respectively, in women. There was a tendency that TB and MetS changed inversely to each other. The similarly adjusted hazard ratios of developing MetS for each 1 SD increase in log TB and for the higher quartiles of TB compared with the lowest quartile were not significant either in men or in women. TB is inversely associated with MetS but not a risk factor for MetS in Japanese men and women.

Phycocyanin and phycocyanobilin from Spirulina platensis protect against diabetic nephropathy by inhibiting oxidative stress

We and other investigators have reported that bilirubin and its precursor biliverdin may have beneficial effects on diabetic vascular complications, including nephropathy, via its antioxidant effects. Here, we investigated whether phycocyanin derived from Spirulina platensis, a blue-green algae, and its chromophore phycocyanobilin, which has a chemical structure similar to that of biliverdin, protect against oxidative stress and renal dysfunction in db/db mice, a rodent model for Type 2 diabetes. Oral administration of phycocyanin (300 mg/kg) for 10 wk protected against albuminuria and renal mesangial expansion in db/db mice, and normalized tumor growth factor-β and fibronectin expression. Phycocyanin also normalized urinary and renal oxidative stress markers and the expression of NAD(P)H oxidase components. Similar antioxidant effects were observed following oral administration of phycocyanobilin (15 mg/kg) for 2 wk. Phycocyanobilin, bilirubin, and biliverdin also inhibited NADPH dependent superoxide production in cultured renal mesangial cells. In conclusion, oral administration of phycocyanin and phycocyanobilin may offer a novel and feasible therapeutic approach for preventing diabetic nephropathy.

The role of oxidative stress in the pathogenesis of diabetic vascular complications

Oxidative stress has been paid increasing attention to as an important causative factor for diabetic vascular complications. Among possible various sources, accumulating evidence has indicated that NAD(P)H oxidase may be the most important source for reactive oxygen species production in diabetic vascular tissues. The mechanisms underlying activation and up-regulation of NAD(P)H oxidase has been supposed to be mediated by high glucose-induced protein kinase C (PKC) activation. In this review article, activation of local renin-angiotensin II system induced by chymase activation is also shown to amplify such a PKC-dependent activation of NAD(P)H oxidase. Additionally, human evidence showing the beneficial effect of antioxidants on diabetic vascular complications. Bilirubin has been recognized as a strong endogenous antioxidant. Here markedly lower prevalence of vascular complications is shown in diabetic patients with Gilbert syndrome, a congenital hyperbilirubinemia, as well as reduced markers of oxidative stress and inflammation. Lastly, statin, angiotensin II receptor blocker, chymase inhibitor, bilirubin and biliverdin, PKC β isoform inhibitor, and glucagon-like peptide-1 analog, are shown to serve as antioxidants and have some beneficial effect on diabetic vascular complications, via inhibiting PKC-NAD(P)H oxidase activation, supporting the notion that this mechanism may be an effective therapeutic target for preventing diabetic vascular complications.

The role of bilirubin in diabetes, metabolic syndrome, and cardiovascular diseases

Bilirubin belongs to a phylogenetically old superfamily of tetrapyrrolic compounds, which have multiple biological functions. Although for decades bilirubin was believed to be only a waste product of the heme catabolic pathway at best, and a potentially toxic compound at worst; recent data has convincingly demonstrated that mildly elevated serum bilirubin levels are strongly associated with a lower prevalence of oxidative stress-mediated diseases. Indeed, serum bilirubin has been consistently shown to be negatively correlated to cardiovascular diseases (CVD), as well as to CVD-related diseases and risk factors such as arterial hypertension, diabetes mellitus, metabolic syndrome, and obesity. In addition, the clinical data are strongly supported by evidence arising from both in vitro and in vivo experimental studies. This data not only shows the protective effects of bilirubin per se; but additionally, of other products of the heme catabolic pathway such as biliverdin and carbon monoxide, as well as its key enzymes (heme oxygenase and biliverdin reductase); thus, further underlining the biological impacts of this pathway. In this review, detailed information on the experimental and clinical evidence between the heme catabolic pathway and CVD, and those related diseases such as diabetes, metabolic syndrome, and obesity is provided. All of these pathological conditions represent an important threat to human civilization, being the major killers in developed countries, with a steadily increasing prevalence. Thus, it is extremely important to search for novel markers of these diseases, as well as for novel therapeutic modalities to reverse this unfavorable situation. The heme catabolic pathway seems to fulfill the criteria for both diagnostic purposes as well as for potential therapeutical interventions.

Physiological antioxidative network of the bilirubin system in aging and age-related diseases

Oxidative stress is detrimental to life process and is particularly responsible for aging and age-related diseases. Thus, most organisms are well equipped with a spectrum of biological defense mechanisms against oxidative stress. The major efficient antioxidative mechanism is the glutathione system, operating a redox cycling mechanism for glutathione utilization, which consists of glutathione and its peroxidase and reductase. However, this system is mainly effective for hydrophilic oxidants, while lipophilic oxidants require another scavenging system. Since many age-related pathological conditions are related to lipid peroxidation, especially in association with the aging process, the physiological role of the scavenging system for lipophilic oxidants should be considered. In this regard, the biliverdin to bilirubin conversion pathway, via biliverdin reductase (BVR), is suggested to be another major protective mechanism that scavenges lipophilic oxidants because of the lipophilic nature of bilirubin. The efficiency of this bilirubin system might be potentiated by operation of the intertwined bicyclic systems of the suggested redox metabolic cycle of biliverdin and bilirubin and the interactive control cycle of BVR and heme oxygenase. In order to combat oxidative stress, both antioxidative systems against hydrophilic and lipophilic oxidants are required to work cooperatively. In this regard, the roles of the bilirubin system in aging and age-related diseases are reassessed in this review, and their interacting networks are evaluated.

Bile pigments in pulmonary and vascular disease

The bile pigments, biliverdin, and bilirubin, are endogenously derived substances generated during enzymatic heme degradation. These compounds have been shown to act as chemical antioxidants in vitro. Bilirubin formed in tissues circulates in the serum, prior to undergoing hepatic conjugation and biliary excretion. The excess production of bilirubin has been associated with neurotoxicity, in particular to the newborn. Nevertheless, clinical evidence suggests that mild states of hyperbilirubinemia may be beneficial in protecting against cardiovascular disease in adults. Pharmacological application of either bilirubin and/or its biological precursor biliverdin, can provide therapeutic benefit in several animal models of cardiovascular and pulmonary disease. Furthermore, biliverdin and bilirubin can confer protection against ischemia/reperfusion injury and graft rejection secondary to organ transplantation in animal models. Several possible mechanisms for these effects have been proposed, including direct antioxidant and scavenging effects, and modulation of signaling pathways regulating inflammation, apoptosis, cell proliferation, and immune responses. The practicality and therapeutic-effectiveness of bile pigment application to humans remains unclear.

Relationship of serum bilirubin concentration to kidney function and 24-hour urine protein in Korean adults

Background

The relationships among serum bilirubin concentration, kidney function and proteinuria have yet to be fully elucidated, nor have these relationships been investigated in Korean adults.

Method

We retrospectively reviewed the medical records of Korean adults who were evaluated at Kosin University Gospel Hospital (Busan, Republic of Korea) during a five-year period from January 2005 to December 2009. We evaluated the relationships among serum bilirubin concentration, estimated glomerular filtration rate (eGFR) and 24-hour urinary protein excretion in a sample of 1363 Korean adults aged 18 years or older.

Results

The values of eGFR <60 mL/min/1.73 m² and 24-hour urine albumin ≥150 mg/day were observed in 26.1% (n = 356) and 40.5% (n = 553) of subjects, respectively. Fasting glucose levels ≥126 mg/dL were observed in 44.9% (n = 612) of the total sample. After adjustment for potential confounding factors including demographic characteristics, comorbidities and other laboratory measures, total serum bilirubin was positively associated with eGFR and negatively associated with proteinuria both in the whole cohort and in a subgroup of diabetic individuals.

Conclusions

To our knowledge, this is the first hospital-based study specifically aimed at examining the relationships among serum total bilirubin concentration, 24-hour urine protein and kidney function in Korean adults. We demonstrated that serum total bilirubin concentration was negatively correlated with 24-hour urine protein and positively correlated with eGFR in Korean non-diabetic and diabetic adults.

High serum bilirubin levels and diabetic retinopathy: the Hisayama Study

PURPOSE

To assess the association between serum total bilirubin levels and diabetic retinopathy prevalence in participants of the Hisayama Study who had diabetes and impaired glucose metabolism.

DESIGN

Population-based, cross-sectional study.

PARTICIPANTS

Of 3119 participants of the Hisayama Study Eye Examinations in 2007, Japan, 1672 aged ≥40 years with either diabetes or impaired glucose metabolism (defined by a 75-g oral glucose tolerance test) were enrolled in the present study.

METHODS

Diabetic retinopathy was assessed via ophthalmic examination after pupil dilatation. The presence and the severity of diabetic retinopathy were determined by grading of color fundus photographs using the modified Airlie House classification system. Association of diabetic retinopathy with serum bilirubin quartiles was assessed using logistic regression model adjusting for age and known risk factors for diabetic retinopathy.

MAIN OUTCOME MEASURES

Prevalent diabetic retinopathy.

RESULTS

Diabetic retinopathy was present in 70 of 1672 (4.2%) participants. The prevalence of diabetic retinopathy in persons with the highest bilirubin quartile (≥0.9 mg/dL) was 2.7%, compared with the prevalence of 3.4%, 5.1%, and 5.1% in those with the first (<0.6 mg/dL), second (0.6-0.69 mg/dL), and third quartiles (0.7-0.89 mg/dL). After adjusting for factors known to be associated with diabetic retinopathy, the prevalence was significantly lower among persons with the highest bilirubin quartile compared with those with the lowest quartile (odds ratio [OR], 0.25; 95% confidence interval [CI], 0.09-0.72) or compared with those in the 3 lower quartiles (OR, 0.25; 95% CI, 0.11-0.58).

CONCLUSIONS

Elevated serum bilirubin levels may be protective against diabetic retinopathy among persons with either diabetes or impaired glucose metabolism, independent of known risk factors for diabetic retinopathy.

High serum bilirubin is associated with the reduced risk of diabetes mellitus and diabetic nephropathy

Several studies have suggested a potential effect of serum bilirubin as an antioxidant and cytoprotectant factor. For the results presented here, we evaluated the correlation between serum bilirubin and diabetes mellitus (DM) or chronic kidney disease originated from DM (DMCKD) in a Korean population. We used a cross-sectional, population-based design to examine 93,909 subjects (aged 18-96 years, 53.0% male). The trend of P values in the odds ratios for being DM and DMCKD was calculated using patients separated into five groups based on individual serum bilirubin concentrations. The prevalence of DM and DMCKD was 6.7% and 0.8%, respectively. Higher serum bilirubin levels were significantly associated with decreased prevalence of DM in both men (P trend < 0.001) and women (P trend = 0.014). The risk of DMCKD also decreased as bilirubin levels increased in women (P trend = 0.011), but not in men (P trend = 0.467). Serum bilirubin level was inversely related to insulin resistance using the homeostasis model assessment (HOMA-IR), serum insulin, and C-reactive protein (CRP) levels in multiple linear regression analyses. The regression coefficients (B) of log-HOMA-IR, log-insulin, and log-CRP were as follows: -0.09, -0.13, and -0.60 in men; -0.07, -0.09, and -0.50 in women, respectively. All the regressions were statistically significant (P < 0.001). These results indicate that serum bilirubin might have some protective function against DM and DMCKD, although the association between high serum bilirubin and decreased prevalence of DMCKD is observed only in women.

Serum bilirubin and genes controlling bilirubin concentrations as biomarkers for cardiovascular disease

BACKGROUND

Serum bilirubin has been consistently shown to be inversely related to cardiovascular disease (CVD). Recent studies showed serum bilirubin to be associated with CVD-related factors such as diabetes, metabolic syndrome, and body mass index. Although the association of serum bilirubin with CVD has been found in both retrospective and prospective studies, less information is available on the role of genes that control bilirubin concentrations and their association with CVD.

CONTENT

In this review, we provide detailed information on the identity of the major genes that control bilirubin concentrations and their association with serum bilirubin concentrations and CVD risk. We also update the results of the major studies that have been performed on the association between serum bilirubin, CVD, and CVD-related diseases such as diabetes or metabolic syndrome. Studies consistently indicate that bilirubin concentrations are inversely associated with different types of CVD and CVD-related diseases. A conditional linkage study indicates that UGT1A1 is the major gene controlling serum bilirubin concentrations, and this finding has been confirmed in recent genomewide association studies. Studies also indicate that individuals homozygous for UGT1A1*28 have a significantly lower risk of developing CVD than carriers of the wild-type alleles.

SUMMARY

Serum bilirubin has a protective effect on CVD and CVD-related diseases, and UGT1A1 is the major gene controlling serum bilirubin concentrations. Pharmacologic, nonpharmacologic, or genetic interventions that increase serum bilirubin concentrations could provide more direct evidence on the role of bilirubin in CVD prevention.

Renal function in diabetic nephropathy

Diabetic nephropathy is the kidney disease that occurs as a result of diabetes. Cardiovascular and renal complications share common risk factors such as blood pressure, blood lipids, and glycemic control. Thus, chronic kidney disease may predict cardiovascular disease in the general population. The impact of diabetes on renal impairment changes with increasing age. Serum markers of glomerular filtration rate and microalbuminuria identify renal impairment in different segments of the diabetic population, indicating that serum markers as well as microalbuminuria tests should be used in screening for nephropathy in diabetic older people. The American Diabetes Association and the National Institutes of Health recommend Estimated glomerular filtration rate (eGFR) calculated from serum creatinine at least once a year in all people with diabetes for detection of kidney dysfunction. eGFR remains an independent and significant predictor after adjustment for conventional risk factors including age, sex, duration of diabetes, smoking, obesity, blood pressure, and glycemic and lipid control, as well as presence of diabetic retinopathy. Cystatin-C (Cys C) may in future be the preferred marker of diabetic nephropathy due differences in measurements of serum creatinine by various methods. The appropriate reference limit for Cys C in geriatric clinical practice must be defined by further research. Various studies have shown the importance of measurement of albuminuria, eGFR, serum creatinine and hemoglobin level to further enhance the prediction of end stage renal disease.

Inverse associations of serum bilirubin with high sensitivity C-reactive protein, glycated hemoglobin, and prevalence of type 2 diabetes in middle-aged and elderly Japanese men and women

AIM

The aim of this study was to examine the association of serum bilirubin, an endogenous antioxidant, with serum high sensitivity C-reactive protein (hs-CRP) level, HbA(1c), and the prevalence of type 2 diabetes in middle-aged and elderly Japanese men and women (n=12,400).

METHODS

Analysis of covariance and logistic regression analysis were used to estimate geometric means of hs-CRP and HbA(1c) and odds ratios of prevalent diabetes according to bilirubin concentrations, respectively, with statistical adjustment for behavioral factors and liver enzymes.

RESULTS

Geometric means of hs-CRP and HbA(1c) were progressively lower with increasing concentrations of serum bilirubin in men and women each. An inverse association between serum bilirubin and HbA(1c) was slightly attenuated after adjustment for hs-CRP, but still remained highly significant (trend P=0.0004 in men and trend P=10(-5) in women). Multivariate-adjusted odds ratios of prevalent diabetes for the lowest to highest quintiles of serum total bilirubin were 1.00, 1.00, 0.73, 0.80, and 0.73 (trend P=0.002), without adjustment for hs-CRP, and 1.00, 1.04, 0.76, 0.86, and 0.79 (trend P=0.01), with adjustment for hs-CRP.

CONCLUSIONS

Higher concentrations of serum bilirubin probably confer protection against the development of type 2 diabetes.

Hyperglycemia and glycation in diabetic complications

Diabetes mellitus is a multifactorial disease, classically influenced by genetic determinants of individual susceptibility and by environmental accelerating factors, such as lifestyle. It is considered a major health concern,as its incidence is increasing at an alarming rate, and the high invalidating effects of its long-term complications affect macro- and microvasculature, heart, kidney, eye, and nerves. Increasing evidence indicates that hyperglycemia is the initiating cause of the tissue damage occurring in diabetes, either through repeated acute changes in cellular glucose metabolism, or through the long-term accumulation of glycated biomolecules and advanced glycation end products (AGEs). AGEs represent a heterogeneous group of chemical products resulting from a nonenzymatic reaction between reducing sugars and proteins, lipids, nucleic acids, or a combination of these.The glycation process (glucose fixation) affects circulating proteins (serum albumin, lipoprotein, insulin, hemoglobin),whereas the formation of AGEs implicates reactive intermediates such as methylglyoxal. AGEs form cross-links on long-lived extracellular matrix proteins or react with their specific receptor RAGE, resulting inoxidative stress and proinflammatory signaling implicated in endothelium dysfunction, arterial stiffening, and microvascular complications. This review summarizes the mechanism of glycation and of AGEs formation and the role of hyperglycemia, AGEs, and oxidative stress in the pathophysiology of diabetic complications.

Relationship of serum bilirubin concentrations to kidney function and albuminuria in the United States adult population. Findings from the National Health and Nutrition Examination Survey 2001-2006

BACKGROUND

The association of serum bilirubin concentrations with kidney function and albuminuria has not been established in the US general population.

METHODS

We performed a cross-sectional analysis of data from the National Health and Nutrition Examination Survey (NHANES) 2001-2006 and examined the associations of serum total bilirubin concentrations with estimated glomerular filtration rate (eGFR) and albuminuria in a nationally representative sample of 13,184 adults aged 20 years or older. eGFR was estimated using the abbreviated Modification of Diet in Renal Disease equation. Urinary albumin excretion was measured using the albumin/creatinine ratio.

RESULTS

An eGFR < 60 mL/min/1.73 m(2) and urinary albumin/creatinine ratio > or = 30 mg/g were present in 8.1% (n=1072) and 10.6% (n=1402) of participants, respectively. A total of 427 (3.2%) individuals had a serum total bilirubin concentration >22.23 micromol/L. After adjustment for demographics, comorbidities, alcohol consumption, viral hepatitis status and other laboratory measures, serum bilirubin was negatively associated with eGFR, and positively with albuminuria both in the whole cohort and in the subgroup of non-diabetic individuals. In contrast, serum bilirubin was not significantly associated with eGFR or albuminuria in persons with diabetes (n=1253).

CONCLUSIONS

Increasing serum concentrations of total bilirubin are independently associated with decreasing eGFR and increasing albuminuria in the US adult population.

Molecular mechanisms underlying the antiatherosclerotic and antidiabetic effects of probucol, succinobucol, and other probucol analogues

PURPOSE OF REVIEW

New therapies for the management of cardiovascular disease remain highly desirable, yet the recently developed agents, such as the cholesterylester transfer protein inhibitor torcetrapib, the antidiabetic agent rosiglitazone, and anti-inflammatory inhibitors of cyclooxygenase-2, have failed. In this review, the more recent developments in the molecular mechanisms underlying the beneficial activities of probucol and related compounds are described.

RECENT FINDINGS

In-vivo and in-vitro studies have revealed that several of the protective activities of probucol can be explained by the ability of this drug to induce the enzyme heme oxygenase-1. It is now apparent that the sulfur atoms, rather than the phenol moieties of probucol, are required for its antiatherogenic and antirestenotic activities. Compounds related to probucol that have improved efficacy without the adverse effects offer promise as novel therapies of cardiovascular disease. Recent results suggest these compounds may also be used for the prevention of type-2 diabetes, a disease that is increasing in prevalence and importance worldwide.

SUMMARY

The development of derivatives of probucol targeting anti-inflammatory and antioxidant processes, perhaps via induction of heme oxygenase-1, may add to the armamentarium of current agents used in treatment of atherosclerotic disease and diabetes.