Can allopurinol improve retinopathy in diabetic rats? Oxidative stress or uric acid; which one is the culprit?

Development of diabetic macular oedema shows associations with systemic medication - An epidemiological study

PURPOSE

To identify associations between systemic drugs and the incidence of diabetic macular oedema (DME). Of interest was to find beneficial and/or deleterious associations of used drugs.

METHODS

A historic cohort design based on administrative data. Study population consisted of 150 353 individuals with diabetes. Endpoint event was the development of DME (ICD-10 H36.01), censoring events were death or study end December 2017. The follow-up started between 1997 and 2010. The systemic medication consisted of 95 substances. We constructed a nested case-control study design comparing 2630 cases with DME to 13 144 age- and sex-matched controls without DME. Results are reported as odds ratios (ORs) with 95% confidence intervals (CIs) based on conditional logistic regression models.

RESULTS

Incidence rate for DME was 1.80 per 1000 person-years (95% CI 1.73-1.87). In all, we observed a lower incidence rate of DME in females (IRR 0.57; 95% CI 0.52-0.62) compared to males. Exposure to hormone replacement therapy estradiol (OR 0.42; 0.25-0.68), temazepam (0.23; 0.08-0.62) and allopurinol (0.61; 0.43-0.86) were associated with lower risk of DME, while use of insulin or insulin analogue (3.30; 2.99-3.64), sulfonylureas (1.21; 1.05-1.40), diuretic furosemide (1.90; 1.61-2.24), calcium channel blocker amlodipine (1.53; 1.34-1.75), ACE inhibitors ramipril (1.66; 1.46-1.89) and enalapril (1.38; 1.16-1.64) were associated with an increased risk of DME.

CONCLUSIONS

Large-scale studies examining the incidence of DME are lacking. Our findings suggest that associations of systemic medications with the incidence of DME may shed light on the pathogenesis of complex DME, encouraging further studies.

Antioxidant effects of astaxanthin and metformin combined therapy in type 2 diabetes mellitus patients: a randomized double-blind controlled clinical trial

Background and purpose:

Since the critical role of oxidative stress in the pathogenesis and complications of type 2 diabetes mellitus (T2DM) has been proven, antioxidant therapy is considered an applicable strategy to control T2DM development. This study aimed at evaluating the effect of astaxanthin (AST) supplementation combined with metformin on oxidative indices and antioxidant defenses in T2DM patients.

Experimental approach:

In this randomized, double-blind placebo-controlled trial, 50 T2DM subjects receiving metformin were supplemented with 10 mg/day AST or placebo for 12 weeks. Malondialdehyde concentration and serum total antioxidant capacity (TAC) were assessed as oxidative indices. We also evaluated NF-E2-related factor2 (Nrf2) as the most critical transcription factor of antioxidant defense. Moreover, the activity of antioxidant enzymes, superoxide dismutase (SOD), and catalase were calculated.

Findings/Results:

AST supplementation-metformin combination caused a significant increase in SOD and catalase activities, as well as inducing Nrf2 protein expression compared to the placebo group. Significant changes in serum malondialdehyde and TAC between the AST group and placebo group after supplementation were not observed, although a significant increase was observed in TAC within the AST group after supplementation (32.67 ± 6.73) to before (25.86 ± 5.98). These results remained without change after adjustment for potential confounders.

Conclusion and implications:

Our study demonstrated that AST supplementation controlled oxidative stress through a synergistic effect with metformin and ameliorated overall antioxidant capacity by inducing Nrf2 transcription factor and activating SOD and catalase in T2DM patients. As a result, AST and metformin combination therapy can be considered beneficial in modifying oxidative stress and preventing T2DM complications.

Chrysin ameliorates STZ-induced diabetes in rats: possible impact of modulation of TLR4/NF-κβ pathway

Background and purpose:

Growing evidence advocates that upregulation of toll-like receptor 4 (TLR4) has been suggested as a causative influence in the development and complications of diabetes mellitus. We aimed to study the antidiabetic activity of chrysin against streptozotocin (STZ)-induced diabetes via down-regulation of TLR4/nuclear factor (NF-κβ)/heat shock protein 70 (HSP70) pathway as well as modulation of clusters of differentiation 4 (CD4+) in rats.

Experimental approach:

Fifty rats were divided into five groups (n = 10). Group I, normal rats received a single intraperitoneal injection of buffer citrate; group II, STZ-induced diabetic rats; groups III-V, diabetic rats received glimepiride (0.5 mg/kg; p.o.) or chrysin (40 and 80 mg/kg; p.o.) respectively, for 10 days. Serum samples were extracted to determine nitric oxide (NO), malondialdehyde (MDA), and reduced glutathione (GSH), insulin, CD4+, TLR4, and NF-κβ. Pancreatic tissue samples were extracted to determine glucose transporter 2 (GLUT2). Part of the pancreas was kept in formalin for pathological studies.

Findings/Results:

An elevation in blood glucose, NO, and MDA serum levels and a reduction of pancreatic GLUT2 content, insulin, and GSH serum levels were observed in diabetic rats. STZ injection, also, showed an increase in serum TLR4, NF-κβ, and HSP70 levels and a reduction in serum CD4+ levels with pancreatic cells necrosis. These biochemical and histological changes were reversed in glimepiride and chrysin groups.

Conclusion and implications:

The present study proved that chrysin has a potent anti-diabetic effect through the elevation of insulin and GLUT2 levels, the reduction of oxidative stress, and the inflammatory pathways TLR4/NF-κβ/HSP70 with the regulation of CD4+.

Xanthine Oxidoreductase Inhibitors

Xanthine oxidase inhibitors are primarily used in the clinical prevention and treatment of gout associated with hyperuricemia. The archetypal xanthine oxidase inhibitor, Allopurinol has been shown to have other beneficial effects such as a reduction in vascular reactive oxygen species and mechano-energetic uncoupling. This chapter discusses these properties and their relevance to human pathophysiology with a focus on Allopurinol as well as newer xanthine oxidase inhibitors such as Febuxostat and Topiroxostat. Xanthine oxidase (XO) and xanthine dehydrogenase (XDH) are collectively referred to as xanthine oxidoreductase (XOR). XDH is initially synthesised as a 150-kDa protein from which XO is derived, e.g. under conditions of ischemia/hypoxia either reversibly by conformational changes (calcium or SH oxidation) or irreversibly by proteolysis, the latter leading to formation of a 130-kDa form of XO. Both, XO and XDH, catalyse the conversion of hypoxanthine via xanthine to uric acid, the former by using oxygen forming superoxide and hydrogen peroxide and the latter NAD⁺. However, XDH is in principle also able to generate ROS.

Association Between Uric Acid and N-Terminal Pro-B-Type Natriuretic Peptide in Patients With Unstable Angina Pectoris

BACKGROUND

The association between uric acid and N-Terminal Pro-B-Type Natriuretic Peptide (NT-proBNP) in patients with unstable angina pectoris (UAP) is unclear.

METHODS

We recruited 260 patients with UAP admitted to the first affiliated Hospital of Guangxi Medical University from February 2018 to August 2018. According to the level of uric acid, patients were divided into 4 groups (Q1 = 48.00-305.00 μmol/L; Q2 = 310.00-405.00 μmol/L; Q3 = 408.00-513.00 μmol/L; Q4 = 514.00-4330.00 μmol/L). The differences of NT-proBNP between groups and the relationship with cardiac function were compared.

RESULTS

The average age of the 260 patients enrolled was 75.04 years. The NT-proBNP of the 4 groups showed an increasing trend, and there were significant differences between the 4 groups (<0.001). On the other hand, with the increase of cardiac function (New York Heart Association), the levels of NT-proBNP and uric acid also showed an upward trend (all P < 0.05). Pearson correlation analysis showed that there was a positive correlation between uric acid log10 transform and NT-proBNP log10 transform (r = 0.272, P < 0.001). After adjusting the potential confounding factors, elevated uric acid was still significantly related to the increase of NT-proBNP (Q2 versus [vs.] Q1: OR = 469.64, 95%CI -1396.77 to 2336.05; Q3 vs. Q1: OR = 1166.53, 95%CI -726.12 to 3059.18; Q4 vs. Q1: OR = 3204.78, 95%CI 1240.86-5168.70). In subgroup analysis, the relationship between uric acid and NT-proBNP was significant in males, but no difference was observed in females.

CONCLUSIONS

In male patients with UAP, elevated uric acid is related to the increase of NT-proBNP, but this phenomenon is not obvious in female patients.

Monosodium Urate Contributes to Retinal Inflammation and Progression of Diabetic Retinopathy

We have investigated the contributing role of monosodium urate (MSU) to the pathological processes associated with the induction of diabetic retinopathy (DR). In human postmortem retinas and vitreous from donors with DR, we have found a significant increase in MSU levels that correlated with the presence of inflammatory markers and enhanced expression of xanthine oxidase. The same elevation in MSU levels was also detected in serum and vitreous of streptozotocin-induced diabetic rats (STZ-rats) analyzed at 8 weeks of hyperglycemia. Furthermore, treatments of STZ-rats with the hypouricemic drugs allopurinol (50 mg/kg) and benzbromarone (10 mg/kg) given every other day resulted in a significant decrease of retinal and plasma levels of inflammatory cytokines and adhesion factors, a marked reduction of hyperglycemia-induced retinal leukostasis, and restoration of retinal blood-barrier function. These results were associated with effects of the hypouricemic drugs on downregulating diabetes-induced levels of oxidative stress markers as well as expression of components of the NOD-like receptor family pyrin domain-containing protein 3 (NLRP3) inflammasome such as NLRP3, Toll-like receptor 4, and interleukin-1β. The outcomes of these studies support a contributing role of MSU in diabetes-induced retinal inflammation and suggest that asymptomatic hyperuricemia should be considered as a risk factor for DR induction and progression.