Diabetes, bilirubin and amputations: is there a link?

Contrast-induced nephropathy in non-cardiac vascular procedures, a narrative review: Part 2

This is Part 2 of a narrative review summarizing the literature on CIN after non-cardiac vascular diagnostic or therapeutic procedures, focusing on peripheral artery disease (PAD) and renal artery stenosis (RAS). Part 1 discussed CIN in relation to aortic aneurysms and carotid stenosis. We comment on the incidence, biomarkers, risk factors, and consequences of CIN in patients with PAD or RAS, as well as on strategies to prevent CIN. Future perspectives in the field of CIN in relation to non-cardiac vascular procedures are also considered.

Sodium-glucose co-transporter-2 inhibitors (SGLT2i) use and risk of amputation: an expert panel overview of the evidence

Sodium-glucose co-transporter-2 inhibitors (SGLT2i) are oral antidiabetic agents that exert their glucose-lowering effect by increasing renal excretion of glucose. These drugs have been reported to beneficially affect cardiovascular (CV) and renal outcomes. However, concerns have recently been raised in relation to increased risk of lower-extremities amputation with canagliflozin and it remains unclear whether and to what extent this side effect could also occur with other SGLT2i. The present expert panel overview focuses on the three SGLT2i available and widely used in the US and Europe, i.e. empagliflozin, canagliflozin and dapagliflozin and only refers briefly to other SGLT2i for which less data are available. The results of large CV outcome trials with these SGLT2i are presented, focusing specifically on the data in relation to amputation risk. The potential pathophysiological mechanisms involved in this side effect are discussed. Furthermore, available data reporting amputation cases in SGLT2i users are critically reviewed. The expert panel concludes that, based on current data, increased amputation risk seems to be related only to canagliflozin, thus representing a drug-effect rather than a SGLT2i class-effect. The exact pathways underlying this drug-induced adverse event, possibly related to off-target drug effects rather than SGLT2 inhibition per se, should be elucidated in future studies. Continuous monitoring and pharmacovigilance is necessary and head to head trials would also be essential to provide definitive conclusions.

Contributions of Nrf2 to Puerarin Prevention of Cardiac Hypertrophy and its Metabolic Enzymes Expression in Rats

Previous evidence has suggested that puerarin may attenuate cardiac hypertrophy; however, the potential mechanisms have not been determined. Moreover, the use of puerarin is limited by severe adverse events, including intravascular hemolysis. This study used a rat model of abdominal aortic constriction (AAC)-induced cardiac hypertrophy to evaluate the potential mechanisms underlying the attenuating efficacy of puerarin on cardiac hypertrophy, as well as the metabolic mechanisms of puerarin involved. We confirmed that puerarin (50 mg/kg per day) significantly attenuated cardiac hypertrophy, upregulated Nrf2, and decreased Keap1 in the myocardium. Moreover, puerarin significantly promoted Nrf2 nuclear accumulation in parallel with the upregulated downstream proteins, including heme oxygenase 1, glutathione transferase P1, and NAD(P)H:quinone oxidoreductase 1. Similar results were obtained in neonatal rat cardiomyocytes (NRCMs) treated with angiotensin II (Ang II; 1 μM) and puerarin (100 μM), whereas the silencing of Nrf2 abolished the antihypertrophic effects of puerarin. The mRNA and protein levels of UGT1A1 and UGT1A9, enzymes for puerarin metabolism, were significantly increased in the liver and heart tissues of AAC rats and Ang II-treated NRCMs. Interestingly, the silencing of Nrf2 attenuated the puerarin-induced upregulation of UGT1A1 and UGT1A9. The results of chromatin immunoprecipitation-quantitative polymerase chain reaction indicated that the binding of Nrf2 to the promoter region of Ugt1a1 or Ugt1a9 was significantly enhanced in puerarin-treated cardiomyocytes. These results suggest that Nrf2 is the key regulator of antihypertrophic effects and upregulation of the metabolic enzymes UGT1A1 and UGT1A9 of puerarin. The autoregulatory circuits between puerarin and Nrf2-induced UGT1A1/1A9 are beneficial to attenuate adverse effects and maintain the pharmacologic effects of puerarin.

Serum Bilirubin Levels and the Presence and Progression of Abdominal Aortic Aneurysms

The relationship between bilirubin levels and peripheral artery disease has been documented. Our aim was to demonstrate the possible relationship between serum bilirubin levels and abdominal aortic aneurysms (AAAs). The study included 219 patients, 110 had a previous diagnosis of AAA and 109 patients were normal controls. Only patients with AAAs which had a size of 40 to 54 mm were included in the study. Baseline laboratory values and 2 computerized tomographic measurements 12 months apart were recorded. Patients with AAA had significantly higher white blood cell (WBC) counts and neutrophil-lymphocyte ratio (NLR) but lower total and direct bilirubin levels compared with the control patients ( P < .05). Multivariate logistic regression analysis showed that WBC, NLR, and total and direct bilirubin levels were independent predictors of the presence of an AAA ( P = .03, P = .001, P = .001, and P = .001, respectively). White blood cells and total bilirubin level were independent predictors of a rapidly enlarging AAA (>10 mm/y, P = .002 and P < .001, respectively). This study demonstrated that increased WBC and decreased total bilirubin levels were independent predictors of an AAA, especially the subgroup in which the AAA was rapidly expanding.

Does bilirubin protect against developing diabetes mellitus?

After 25 years of evaluating bilirubin as a possible protective agent in neonatal and cardiovascular disease, interest has moved on to a exploring a possible protective role in diabetes mellitus (DM). This review finds conflicting prospective data for a protective relationship though there are retrospective, case-controlled data, that can only show association, which is not causality. Only prospective studies can show causality. Also, it would appear that the underlying biochemical assumptions do not readily translate from the animal to the human setting. Given that many factors impact on circulating bilirubin levels, it is not surprising that a clear-cut answer is not available; the jury is still out. Any relationship between DM and bilirubin might relate to intermediates in bilirubin metabolism, including relationships involving the genes for the enzymes participating in those steps. Nevertheless, the pursuit of bilirubin in disease causation is opening new avenues for research and if it is established that serum bilirubin can predict risks, much will have been achieved. The answer may have to come from molecular genetic analyses.

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 (β = 0.116, P<0.001) and free T₃ (β = 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: β = 0.043, P = 0.056 for interaction; additionally adjusted for smoking, alcohol intake, transaminases and total cholesterol (β = 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: β = 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.

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: β = 0.366, P = 0.003 and β = 0.289, P = 0.025, respectively) in age- and sex-adjusted analyses. Effect modification was also found for HOMA-IR (β = 0.790, P = 0.020). Of the individual MetS components, the strongest interaction of bilirubin on SAA was observed with low HDL cholesterol (β = 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.

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: β = 0.251, p = 0.024). This interaction remained present after additional adjustment for alcohol intake, aspartate aminotransferase and insulin sensitivity (interaction term: β = 0.222, p = 0.043), or alternatively for cholesterol and triglycerides (interaction term: β = 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.