Association between serum total bilirubin levels and the morphology of corneal nerve fibers in Japanese patients with uncontrolled type 2 diabetes

Insights into the liver-eyes connections, from epidemiological, mechanical studies to clinical translation

Maintenance of internal homeostasis is a sophisticated process, during which almost all organs get involved. Liver plays a central role in metabolism and involves in endocrine, immunity, detoxification and storage, and therefore it communicates with distant organs through such mechanisms to regulate pathophysiological processes. Dysfunctional liver is often accompanied by pathological phenotypes of distant organs, including the eyes. Many reviews have focused on crosstalk between the liver and gut, the liver and brain, the liver and heart, the liver and kidney, but with no attention paid to the liver and eyes. In this review, we summarized intimate connections between the liver and the eyes from three aspects. Epidemiologically, we suggest liver-related, potential, protective and risk factors for typical eye disease as well as eye indicators connected with liver status. For molecular mechanism aspect, we elaborate their inter-organ crosstalk from metabolism (glucose, lipid, proteins, vitamin, and mineral), detoxification (ammonia and bilirubin), and immunity (complement and inflammation regulation) aspect. In clinical application part, we emphasize the latest advances in utilizing the liver-eye axis in disease diagnosis and therapy, involving artificial intelligence-deep learning-based novel diagnostic tools for detecting liver disease and adeno-associated viral vector-based gene therapy method for curing blinding eye disease. We aim to focus on and provide novel insights into liver and eyes communications and help resolve existed clinically significant issues.

Correlation between serum bilirubin levels and the severity as well as the prognosis of idiopathic pulmonary fibrosis

Bilirubin exerts antioxidant activity that has been associated with respiratory diseases. However, the relationship between serum bilirubin levels and idiopathic pulmonary fibrosis (IPF) is not clear. Therefore, in this study, we evaluated the relationship between serum bilirubin levels and the severity as well as the prognosis of IPF. One hundred and forty-six patients with IPF and 69 healthy individuals as the control group were enrolled as a derivation cohort. Routine blood examination and pulmonary function tests were performed and serum bilirubin levels were measured. To validate the value of serum bilirubin levels to predict the survival of patients with IPF, 40 additional IPF patients were included as a validation cohort. IPF patients were followed-up. Patients with IPF had significantly lower levels of serum total bilirubin (TBIL) and direct bilirubin (DBIL) than those in the control group (P < 0.05). Patients with acute exacerbation of IPF (AE-IPF) had significantly lower levels of serum TBIL and IBIL than those in patients with stable IPF (P < 0.05). The area under the receiver operating characteristic curve (AUROC) of serum TBIL levels for the prediction of the incidence of AE-IPF was 0.72 (95% CI: 0.56–0.87, P = 0.0057). The best cutoff value of serum TBIL level to predict the survival of patients with IPF was 8.8 μmol/l (AUC = 0.75, 95% CI: 0.64–0.87, P = 0.022). The log-rank test showed a significant difference in survival between the two groups (TBIL ≤8.8 μmol/l and TBIL >8.8 μmol/l) in derivation and validation cohort. Cox multiple regression analysis indicated that serum TBIL levels were an independent prognostic factor for IPF prognosis (HR = 0.582, P = 0.026). Serum TBIL levels might be useful for reflecting the severity and predicting the survival of patients with IPF.

Physiological serum total bilirubin concentrations were inversely associated with diabetic peripheral neuropathy in Chinese patients with type 2 diabetes: a cross-sectional study

BACKGROUND

Although bilirubin has been generally regarded as a waste with potential neurotoxicity at high levels, a few clinical studies suggest a potential protective role of physiological serum total bilirubin (TBIL) concentrations in diabetic peripheral neuropathy (DPN). However, the pathological mechanisms underlying the relationship remain poorly understood. The objective of this study was to explore the relationship between serum TBIL and DPN, and clinical and laboratory parameters.

METHODS

Serum TBIL was measured in 1342 patients with type 2 diabetes mellitus (T2DM). The relationship between TBIL and DPN and other parameters was analyzed.

RESULTS

Serum TBIL levels were significantly lower in T2DM patients with DPN, and were independently and negatively associated with vibration perception thresholds (VPT) (P < 0.01 or P < 0.05). Moreover, serum TBIL was negatively associated with neutrophil and white blood cell counts, fibrinogen, and the prevalence of hypertension, diabetic foot ulceration, peripheral arterial disease, diabetic nephropathy and diabetic retinopathy (P < 0.01 or P < 0.05). Additionally, serum TBIL was an independent decisive factor for the presence of DPN after multivariate adjustment. Compared to the highest quartile of TBIL, the lower quartiles were associated with a significantly increased risk of DPN (P < 0.01). Last but most importantly, the analysis of receiver operating characteristic curves revealed that the best cutoff value for serum TBIL to predict DPN was 10.75 μmol/L (sensitivity 54.6% and specificity 62.9%).

CONCLUSIONS

These findings suggest that lower physiological serum TBIL may be associated with the presence of DPN due to its decreased anti-inflammatory and vascular protective effects.

Association between serum total bilirubin levels and the risk of type 2 diabetes mellitus

AIM

To confirm whether serum bilirubin is an independent risk factor of type 2 diabetes mellitus (T2DM) onset in patients with impaired fasting glycemia (IFG) and impaired glucose tolerance (IGT).

METHODS

This was a prospective cohort study carried out at the Diabetic Identification Center of Tianjin Metabolic Diseases Hospital. Serum total bilirubin (TBIL) was measured at baseline and the patients were grouped according to baseline bilirubin quartiles. The outcome was the confirmation of T2DM by oral glucose tolerance test (OGTT) during the 3-year follow-up. Logistic regression was used to determine the risk factors for T2DM development and whether bilirubin levels are independently associated with T2DM development.

RESULTS

Finally, 523 patients were analyzed. After 3 years, 310 participants were diagnosed with diabetes based on OGTT. Baseline quartiles of total bilirubin were inversely associated with diabetes risk, even after multivariable adjustment. The adjusted ORs for diabetes were 1.0 (reference), 0.83 (95% CI 0.74-0.96), 0.78 (95% CI 0.68-0.90), 0.74 (95% CI 0.64-0.87) for the 1st, 2nd, 3rd, and 4th quartiles of baseline serum total bilirubin, respectively (P < 0.001).

CONCLUSION

In patients with IFG or IGT, low levels of serum total bilirubin were associated with a significantly increased risk of T2DM.

Serum bilirubin levels are negatively associated with diabetic retinopathy in patients with type 1 diabetes and normal renal function

INTRODUCTION

Previous studies suggested that total serum bilirubin levels are negatively associated with diabetic retinopathy (DR) and nephropathy in patients with diabetes mellitus. The objective of this study was to explore the relationship between serum total bilirubin levels and prevalence of DR in patients with type 1 diabetes (T1DM) and normal renal function.

METHODS

Study included 163 T1DM with normal renal function (urinary albumin excretion rate <30 mg/24 h, estimated glomerular filtration rate (eGFR) >60 ml min^-11.73 m^-2). Photo-documented retinopathy status was made according to the EURODIAB protocol.

RESULTS

Patients with DR were older (49 vs 42 years, p = 0.001), had higher systolic blood pressure (130 vs 120 mmHg, p = 0.001), triglycerides (0.89 vs 0.77 mmol/L, p = 0.01), and lower serum total bilirubin (12 vs 15 U/L, p = 0.02) and eGFR (100 vs 106 ml min^-11.73 m^-2, p = 0.03). In multivariate logistic regression analysis, only total serum bilirubin was significantly associated with risk of DR in our subjects (OR 0.88, CI 0.81-0.96, p = 0.006).

CONCLUSION

These data suggest that serum total bilirubin levels are independently negatively associated with DR in T1DM with normal renal function. Prospective studies are needed to confirm whether lower serum total bilirubin has predictive value for the development of DR in T1DM with normal renal function.

Association between Hemoglobin Levels and Diabetic Peripheral Neuropathy in Patients with Type 2 Diabetes: A Cross-Sectional Study Using Electronic Health Records

OBJECTIVE

To investigate the relationship between hemoglobin levels and diabetic peripheral neuropathy (DPN) in type 2 diabetes mellitus (T2DM).

METHODS

1511 patients with T2DM were included in the study. DPN was diagnosed based on symptoms, signs, and laboratory tests. Hemoglobin was defined as both a continuous variable and a quartile category variable. We compared patient characteristics between the no diabetic peripheral neuropathy (NDPN) and DPN groups. Logistic regression was conducted to investigate the association of DPN with hemoglobin in all T2DM patients. Linear regression was also performed to investigate the impact of hemoglobin on the vibrating perception threshold (VPT).

RESULTS

Compared with the NDPN group, hemoglobin level in the DPN group was significantly lower (118.54 ± 16.91 versus 131.62 ± 18.32 g/L, P < 0.01). The prevalence of DPN increased by 50.1% (95% CI: 42.2-57.0%; P < 0.001) per standard deviation decrease in hemoglobin. Compared to the highest quartile of hemoglobin, the lower quartiles were associated with a significantly increased risk of DPN in the entire T2DM population (all P < 0.01). A per unit decrease in hemoglobin leads to a 0.12 (95% CI: 0.07-0.168) unit increase in VPT after adjustment for possible confounders (P < 0.001).

CONCLUSIONS

Lower hemoglobin levels were associated with increased prevalence of DPN and higher VPT.