Alanine aminotransferase and mortality in patients with type 2 diabetes (ZODIAC-38).

INTRODUCTION: Combined data suggest a bimodal association of alanine aminotransferase (ALT) with mortality in the general population. Little is known about the association of ALT with mortality in patients with type 2 diabetes. We therefore investigated the association of ALT with all-cause, cardiovascular and noncardiovascular mortality in patients with type 2 diabetes. DESIGN: A prospective study was performed in patients with type 2 diabetes, treated in primary care, participating in the Zwolle Outpatient Diabetes project Integrating Available Care (ZODIAC) study. Cox regression analyses were performed to determine the associations of log2 -transformed baseline ALT with all-cause, cardiovascular and noncardiovascular mortality. RESULTS: In 1187 patients with type 2 diabetes (67 ± 12 years, 45% female), ALT levels were 11 (8-16) U/L. During median follow-up for 11.1 (6.1-14.0) years, 553 (47%) patients died, with 238 (20%) attributable to cardiovascular causes. Overall, ALT was inversely associated with all-cause mortality (hazard ratio [HR] 0.81; 95% confidence interval [CI] 0.72-0.92), independently of potential confounders. This was less attributable to cardiovascular mortality (HR 0.87; 95% CI 0.72-1.05), than to noncardiovascular mortality (HR 0.77; 95% CI 0.65-0.90). Despite the overall inverse association of ALT with mortality, it appeared that a bimodal association with all-cause mortality was present with increasing risk for levels of ALT above normal (P = 0.003). DISCUSSION: In patients with type 2 diabetes, low levels of ALT are associated with an increased risk of all-cause mortality, in particular noncardiovascular mortality, compared to normal levels of ALT, while risk again starts to increase when levels are above normal.

Causal path analyses of the association of protein intake with risk of mortality and graft failure in renal transplant recipients.

The effect of a low protein intake on survival in renal transplant recipients (RTR) is unknown. A low protein intake may increase risks of malnutrition, low muscle mass, and death. We aimed to study associations of protein intake with mortality and graft failure and to identify potential intermediate factors. Protein intake was estimated from 24-h urinary urea excretion (24-h UUE). Graft failure was defined as return to dialysis or retransplantation. We used Cox regression analyses to analyze associations with outcome and potential intermediate factors in the causal path. In 604 RTR, mean ± SD 24-h UUE was 380 ± 114 mmol/24-h. During median follow-up for 7.0 yr (interquartile range: 6.2-7.5 yr), 133 RTR died and 53 developed graft failure. In univariate analyses, 24-h UUE was associated with lower risk of mortality (HR [95% CI] = 0.80 [0.69-0.94]) and graft failure (HR [95% CI] = 0.72 [0.56-0.92]). These associations were independent of potential confounders. In causal path analyses, the association of 24-h UUE with mortality disappeared after adjustment for muscle mass. Low protein intake is associated with increased risk of mortality and graft failure in RTR. Causal path analyses reveal that the association with mortality is explained by low muscle mass. These findings suggest that protein intake restriction should not be advised to RTR.

High sensitive C-reactive protein and serum amyloid A are inversely related to serum bilirubin: effect-modification by metabolic syndrome.

BACKGROUND: Bilirubin has been implicated in cardiovascular protection by virtue of its anti-inflammatory and anti-oxidative properties. The metabolic syndrome is featured by enhanced low-grade systemic inflammation and oxidative stress. Serum amyloid A (SAA) impairs anti-oxidative properties of high-density lipoprotein (HDL). We determined relationships of high sensitive C-reactive protein (hs-CRP) and SAA with bilirubin in subjects with and without metabolic syndrome (MetS). METHODS: Serum total bilirubin, hs-CRP, SAA and homeostasis model assessment- insulin resistance (HOMA-IR) were documented in 94 subjects with and in 73 subjects without MetS (26 and 54 subjects with type 2 diabetes mellitus (T2DM), respectively). RESULTS: Bilirubin was lower in MetS (P = 0.013), coinciding with higher hs-CRP (P < 0.001) and SAA levels (P = 0.002). In all subjects combined, hs-CRP was inversely related to bilirubin (r = -0.203, P = 0.008), irrespective of the presence of MetS or T2DM (interaction terms: P ≥ 0.75). The inverse relationship of bilirubin with SAA was confined to subjects without MetS (r = -0.267, P = 0.009). Furthermore, the presence of either MetS or T2DM modified the relationship of bilirubin with SAA (interaction terms: ß = 0.366, P = 0.003 and ß = 0.289, P = 0.025, respectively) in age- and sex-adjusted analyses. Effect modification was also found for HOMA-IR (ß = 0.790, P = 0.020). Of the individual MetS components, the strongest interaction of bilirubin on SAA was observed with low HDL cholesterol (ß = 0.435, P < 0.001). CONCLUSIONS: hs-CRP is inversely related to bilirubin, suggesting that low bilirubin is implicated in enhanced low-grade systemic inflammation. The inverse relationship of SAA with bilirubin was found to be absent in MetS, which could be attributable to MetS-associated abnormalities in HDL characteristics.

Plasma bilirubin and late graft failure in renal transplant recipients.

Exogenous bilirubin has been shown to protect against oxidative stress in ischemia-reperfusion injury. Oxidative stress has been implicated in the pathophysiology of chronic transplant dysfunction leading to late graft failure after renal transplantation. We prospectively investigated whether high endogenous bilirubin is protective against development of late graft failure in renal transplant recipients (RTR). Baseline data were collected between August 2001 and July 2003 in nonicteric outpatient RTR with a functioning graft for >1 year. At baseline, bilirubin and liver enzymes were measured using routine assays on a Merck Mega analyzer. Graft failure was prospectively recorded until May 19 2009. During follow-up for 7.1 [6.2-7.2] years, 55 RTR developed graft failure. We found that circulating levels of bilirubin are inversely associated with late graft failure in RTR (HR = 0.29 [95% CI: 0.16-0.52], P < 0.001). This association was independent of potential confounders, including creatinine clearance, urinary protein excretion, calcineurin inhibitors, and gender (HR = 0.31 [95% CI: 0.15-0.62] P = 0.001). Our findings are consistent with a protective effect of increased endogenous bilirubin against development of late graft failure in RTR. If our findings are confirmed by other studies, intervention with endogenous or exogenous bilirubin may be of interest for long-term preservation of renal function in RTR.

Post-Transplant Hypophosphatemia and the Risk of Death-Censored Graft Failure and Mortality after Kidney Transplantation.

BACKGROUND AND OBJECTIVES: Hypophosphatemia is common in the first year after kidney transplantation, but its clinical implications are unclear. We investigated the relationship between the severity of post-transplant hypophosphatemia and mortality or death-censored graft failure in a large cohort of renal transplant recipients with long-term follow-up. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: We performed a longitudinal cohort study in 957 renal transplant recipients who were transplanted between 1993 and 2008 at a single center. We used a large real-life dataset containing 28,178 phosphate measurements (median of 27; first to third quartiles, 23-34) serial measurements per patient) and selected the lowest intraindividual phosphate level during the first year after transplantation. The primary outcomes were all-cause mortality, cardiovascular mortality, and death-censored graft failure. RESULTS: The median (interquartile range) intraindividual lowest phosphate level was 1.58 (1.30-1.95) mg/dl, and it was reached at 33 (21-51) days post-transplant. eGFR was the main correlate of the lowest serum phosphate level (model R2 =0.32). During 9 (5-12) years of follow-up, 181 (19%) patients developed graft failure, and 295 (35%) patients died, of which 94 (32%) deaths were due to cardiovascular disease. In multivariable Cox regression analysis, more severe hypophosphatemia was associated with a lower risk of death-censored graft failure (fully adjusted hazard ratio, 0.61; 95% confidence interval, 0.43 to 0.88 per 1 mg/dl lower serum phosphate) and cardiovascular mortality (fully adjusted hazard ratio, 0.37; 95% confidence interval, 0.22 to 0.62) but not noncardiovascular mortality (fully adjusted hazard ratio, 1.33; 95% confidence interval, 0.9 to 1.96) or all-cause mortality (fully adjusted hazard ratio, 1.15; 95% confidence interval, 0.81 to 1.61). CONCLUSIONS: Post-transplant hypophosphatemia develops early after transplantation. These data connect post-transplant hypophosphatemia with favorable long-term graft and patient outcomes.

Urinary potassium excretion, renal ammoniagenesis, and risk of graft failure and mortality in renal transplant recipients.

BACKGROUND: Renal transplant recipients (RTRs) have commonly been urged to limit their potassium intake during renal insufficiency and may adhere to this principle after transplantation. Importantly, in experimental animal models, low dietary potassium intake induces kidney injury through stimulation of ammoniagenesis. In humans, low potassium intake is an established risk factor for high blood pressure. OBJECTIVE: We hypothesized that low 24-h urinary potassium excretion [UKV; urinary potassium concentration × volume], the gold standard for assessment of dietary potassium intake, represents a risk factor for graft failure and mortality in RTRs. In secondary analyses, we aimed to investigate whether these associations could be explained by ammoniagenesis, plasma potassium, or blood pressure. DESIGN: In a prospective cohort of 705 RTRs, we assessed dietary potassium intake by a single 24-h UKV and food-frequency questionnaires. Cox regression analyses were used to investigate prospective associations with outcome. RESULTS: We included 705 stable RTRs (mean ± SD age: 53 ± 13 y; 57% men) at 5.4 y (IQR: 1.9-12.0 y) after transplantation and 253 kidney donors. Mean ± SD UKV was 73 ± 24 mmol/24 h in RTRs compared with 85 ± 25 mmol/24 h in kidney donors. During follow-up for 3.1 y (IQR: 2.7-3.9 y), 45 RTRs developed graft failure and 83 died. RTRs in the lowest sex-specific tertile of UKV (women, <55 mmol/24 h; men, <65 mmol/24 h) had an increased risk of graft failure (HR: 3.70; 95% CI: 1.64, 8.34) and risk of mortality (HR; 2.66; 95% CI: 1.53, 4.61), independent of potential confounders. In causal path analyses, 24-h urinary ammonia excretion, plasma potassium, and blood pressure did not affect these associations. CONCLUSIONS: Our results indicate that low UKV is associated with a higher risk of graft failure and mortality in RTRs. Specific attention for adequate potassium intake after transplantation seems warranted. This trial was registered at clinicaltrials.gov as NCT02811835.

Plasma Vitamin D Level and Change in Albuminuria and eGFR According to Sodium Intake.

BACKGROUND AND OBJECTIVES: Low circulating 25-hydroxyvitamin D [25(OH)D] and high sodium intake are both associated with progressive albuminuria and renal function loss in CKD. Both vitamin D and sodium intake interact with the renin-angiotensin-aldosterone system. We investigated whether plasma 25(OH)D or 1,25-dihydroxyvitamin D [1,25(OH)2D] is associated with developing increased albuminuria or reduced renal function and whether these associations depend on sodium intake. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: Baseline plasma 25(OH)D and 1,25(OH)2D were measured by liquid chromatography tandem mass spectrometry, and sodium intake was assessed by 24-hour urine collections in the general population-based Prevention of Renal and Vascular End-Stage Disease cohort (n=5051). Two primary outcomes were development of urinary albumin excretion >30 mg/24 h and eGFR (creatinine/cystatin C-based CKD Epidemiology Collaboration) <60 ml/min per 1.73 m(2). Participants with CKD at baseline were excluded. In Cox regression analyses, we assessed associations of vitamin D with developing increased albuminuria or reduced eGFR and potential interaction with sodium intake. RESULTS: During a median follow-up of 10.4 (6.2-11.4) years, 641 (13%) participants developed increased albuminuria, and 268 (5%) participants developed reduced eGFR. Plasma 25(OH)D was inversely associated with increased albuminuria (fully adjusted hazard ratio [HR] per SD higher, 0.86; 95% confidence interval [95% CI], 0.78 to 0.95; P=0.003) but not reduced eGFR (HR, 0.99; 95% CI, 0.87 to 1.12; P=0.85). There was interaction between 25(OH)D and sodium intake for risk of developing increased albuminuria (P interaction =0.03). In participants with high sodium intake, risk of developing increased albuminuria was inversely associated with 25(OH)D (lowest versus highest quartile: adjusted HR, 1.81; 95% CI, 1.20 to 2.73, P<0.01), whereas this association was nonsignificant in participants with low sodium intake (HR, 1.29; 95% CI, 0.94 to 1.77; P=0.12). Plasma 1,25(OH)2D was not significantly associated with increased albuminuria or reduced eGFR. CONCLUSIONS: Low plasma 25(OH)D is associated with higher risk of developing increased albuminuria, particularly in individuals with high sodium intake, but not of developing reduced eGFR. Plasma 1,25(OH)2D is not associated with risk of developing increased albuminuria or reduced eGFR.

Bilirubin as a potential causal factor in type 2 diabetes risk: a Mendelian randomization study.

Circulating bilirubin, a natural antioxidant, is associated with decreased risk of type 2 diabetes (T2D), but the nature of the relationship remains unknown. We performed Mendelian randomization in a prospective cohort of 3,381 participants free of diabetes at baseline (age 28-75 years; women 52.6%). We used rs6742078 located in the uridine diphosphate-glucuronosyltransferase locus as an instrumental variable (IV) to study a potential causal effect of serum total bilirubin level on T2D risk. T2D developed in a total of 210 participants (6.2%) during a median follow-up period of 7.8 years. In adjusted analyses, rs6742078, which explained 19.5% of bilirubin variation, was strongly associated with total bilirubin (a 0.68-SD increase in bilirubin levels per T allele; P < 1 × 10(-122)) and was also associated with T2D risk (odds ratio [OR] 0.69 [95% CI 0.54-0.90]; P = 0.006). Per 1-SD increase in log-transformed bilirubin levels, we observed a 25% (OR 0.75 [95% CI 0.62-0.92]; P = 0.004) lower risk of T2D. In Mendelian randomization analysis, the causal risk reduction for T2D was estimated to be 42% (causal OR for IV estimation per 1-SD increase in log-transformed bilirubin 0.58 [95% CI 0.39-0.84]; P = 0.005), which was comparable to the observational estimate (Durbin-Wu-Hausman χ(2) test, P for difference = 0.19). These novel results provide evidence that an elevated bilirubin level is causally associated with the risk of T2D and support its role as a protective determinant.

Urinary Urea Excretion and Long-term Outcome After Renal Transplantation.

BACKGROUND: Little is known about optimal protein intake after transplantation. The aim of this study was to prospectively investigate associations of urinary urea excretion, a marker for protein intake, with graft failure and mortality in renal transplant recipients (RTR) and potential effect modification by body mass index (BMI) and estimated glomerular filtration rate (eGFR). METHODS: Urinary urea excretion was measured in repeated 24-hr urine collections between 6 and 18 months after transplantation. RESULTS: In total, 940 RTR were included. During 4.4 (2.3-7.8) years of follow-up for graft failure and 4.8 (2.5-8.3) years for all-cause mortality, 78 RTR developed graft failure and 158 RTR died. Urinary urea excretion was not associated with graft failure in the overall population, but was inversely associated with graft failure in RTR with BMI less than 25 kg/m (hazard ratio [HR], 0.64 [0.28-1.50] and 0.27 [0.09-0.83] for the second and third tertiles, respectively, P < 0.001), and in RTR with eGFR of 45 mL per min per 1.73 m or higher (HR, 0.34 [0.15-0.79], P = 0.015 and HR, 0.31 [0.11-0.86], P = 0.025 for the second and third tertiles, respectively), both independent of potential confounders. Compared to the first tertile, RTR in the second and third tertiles of urinary urea excretion were at a lower risk of all-cause mortality (HR, 0.47 [0.32-0.69]; P < 0.001 and HR, 0.42 [0.26-0.68]; P < 0.001, respectively), independent of potential confounders. Body mass index and eGFR did not influence this association. CONCLUSION: Urinary urea excretion, a marker for protein intake, was inversely related to graft failure in RTR with BMI less than 25 kg/m and in RTR with an eGFR of 45 mL per min per 1.73 m or higher. In addition, urinary urea excretion was inversely related to mortality.

The relationship of the anti-oxidant bilirubin with free thyroxine is modified by insulin resistance in euthyroid subjects.

BACKGROUND: The strong anti-oxidative properties of bilirubin largely explain its cardioprotective effects. Insulin resistance is featured by low circulating bilirubin. Thyroid hormone affects both bilirubin generation and its biliary transport, but it is unknown whether circulating bilirubin is associated with thyroid function in euthyroid subjects. Aim is to determine relationships of bilirubin with TSH, free T4 and free T3 in euthyroid subjects without type 2 diabetes mellitus (T2DM), and to assess whether such a relationship would be modified by the degree of insulin resistance. METHODS: Total bilirubin, TSH, free T4, free T3, glucose, insulin, lipids and transaminases were measured in 1854 fasting euthyroid subjects without T2DM, recruited from the general population (PREVEND cohort). Insulin resistance was assessed by homeostasis model assessment. RESULTS: Bilirubin was positively related to free T4 (ß = 0.116, P<0.001) and free T3 (ß = 0.078, P = 0.001), but bilirubin was unrelated to TSH. The relationship of bilirubin with free T4 was modified by insulin resistance with a larger effect in more insulin resistant individuals (adjusted for age and sex: ß = 0.043, P = 0.056 for interaction; additionally adjusted for smoking, alcohol intake, transaminases and total cholesterol (ß = 0.044, P = 0.044 for interaction). The association of bilirubin with free T4 was also modified by high density lipoprotein cholesterol (age- and sex-adjusted: ß = 0.040, P = 0.072). CONCLUSIONS: Low bilirubin relates to low free T4 in euthyroid non-diabetic subjects. Low normal free T4 may particularly confer low bilirubin in more insulin resistant individuals.

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.

Low-normal free thyroxine confers decreased serum bilirubin in type 2 diabetes mellitus.

BACKGROUND: Bilirubin may confer cardiovascular protection because of its strong antioxidative properties. Both thyroid dysfunction and the diabetic state affect bilirubin metabolism. Here we tested whether low-normal thyroid function affects serum bilirubin among euthyroid subjects with and without type 2 diabetes mellitus (T2DM). METHODS: Serum total bilirubin, thyrotropin and free thyroxine (free T4), transaminases, insulin sensitivity (homeostasis model assessment), and lipids were measured in 74 T2DM and 82 nondiabetic subjects with thyrotropin and free T4 levels within the euthyroid range. RESULTS: Bilirubin was positively related to free T4 in T2DM subjects (r = 0.370, p < 0.001), but not in nondiabetic subjects (r = 0.047, p = 0.68). In age- and sex-adjusted multiple linear regression analysis, free T4 was found to interact positively with the presence of T2DM on serum bilirubin (interaction term: ß = 0.251, p = 0.024). This interaction remained present after additional adjustment for alcohol intake, aspartate aminotransferase and insulin sensitivity (interaction term: ß = 0.222, p = 0.043), or alternatively for cholesterol and triglycerides (interaction term: ß = 0.203, p = 0.057). CONCLUSIONS: Lower free T4 levels within the euthyroid range confer decreased bilirubin in T2DM. Low-normal thyroid function could enhance atherosclerosis susceptibility in T2DM by decreasing serum bilirubin.