Uric acid increases cellular and humoral alloimmunity in primary human peripheral blood mononuclear cells

High uric acid promotes dysfunction in pancreatic β cells by blocking IRS2/AKT signalling

Hyperuricaemia is a disorder of purine metabolism. Elevated serum uric acid is strongly associated with many diseases, including gout, abdominal obesity, insulin resistance, and cardiovascular and kidney disease. Our previous studies showed that high uric acid (HUA) induced insulin resistance in several peripheral organs, including the liver, myocardium and adipose tissue. However, whether HUA directly induces insulin resistance of pancreatic β cells, the only source of insulin in the body and also a sensitive insulin target, is unknown. In this study, pancreatic β cells pretreated with HUA showed impaired insulin expression/secretion, glucose uptake and the glycolytic pathway. RNA-seq revealed that HUA affected the biological processes of INS-1 cells broadly, including oxidoreduction coenzyme metabolic process, pyruvate metabolic process, and glycolytic process. In addition, HUA reduced mitochondrial membrane potential and increased the production of reactive oxygen species(ROS) in INS-1 cells. INS-1 cells pretreated with probenecid, an organic anion transporter inhibitor, protected INS-1 cells against HUA-induced insulin secretion decrease, Pretreatment with N-acetyl-L-cysteine(NAC), a globally used antioxidant, recovered HUA-decreased insulin secretion and glucose uptake by pancreatic β cells. Insulin-like growth factor 1 (IGF-1), the phosphatidylinositol 3-kinase (PI3K) activator, rescues HUA-decreased insulin secretion by re-activating AKT phosphorylation. Thus, HUA induce insulin resistance, impaired insulin secretion and glycolytic pathway of pancreatic ꞵ cell through IRS2/AKT pathway.

The role of serum uric acid in the prediction of graft-versus-host disease in allogeneic hematopoietic stem cell transplantation

Background

Uric acid (UA) level is of the valuable signs of inflammation. However, the role of UA in the outcomes of hematopoietic stem cell transplantation (HSCT) such as GVHD and patients’ overall survival is still a matter of debate. In this study, we aimed to evaluate the relationship between UA levels and GVHD incidence and overall survival in allogeneic HSCT patients.

Methods

A total of 201 patients who were admitted for allogeneic transplantation at Taleghani hospital, Tehran, Iran, were considered for retrospective analysis. Serum UA levels from 1 week before transplantation until 2 weeks after transplantation were used to determine thresholds and find out the association of serum UA levels with GVHD and overall survival.

Results

We showed that the determined thresholds using receiver operating characteristic curves have poor predictive value for GVHD and overall survival. The patients with serum UA higher than 3.4 mg/dL had 37% lower odds of GVHD incidence and 35% lower hazard of death than patients with UA lower than 3.4 mg/dL.

Conclusion

Our results indicated that serum UA levels lower than 3.4 mg/dL could significantly increase the incidence of GVHD and hazard of death. The antioxidant functions of UA could explain the lower incidence of GVHD in hyperuricemic patients. However, the inconsistencies of the previous studies require further investigation to elucidate the role of UA in the prediction of GVHD.

Urate crystals trigger B-cell receptor signal transduction and induce B-cell proliferation

Background Urate in its crystal form is a known danger-associated molecular pattern, which after its internalization activates cells of the innate immune system. However, by inducing lipid raft sequestration and clustering of membrane-bound proteins with immunoreceptor tyrosine-based activation motifs, urate crystals can also activate cells of the innate immune system without previous internalization. Also, urate crystals trigger T-cell receptor signal transduction and induce T-cell proliferation. In this study, we evaluated whether urate crystals can also initiate B-cell receptor (BCR) signal transduction and promote B-cell proliferation. Methods B cells were isolated from the blood of 10 individuals and cultured with or without urate at a concentration of 10 mg/dL, at which crystallization occurs. Phosphorylated Igα (CD79A) and c-Myc were assessed by Western blotting and B-cell proliferation with BrdU assay. Results Urate increased the level of phosphorylated Igα, a component of the BCR complex. Phosphorylation of Igα is the very proximal event in BCR signal transduction. Also, urate increased the expression of c-Myc, an essential transcription factor for BCR-induced B-cell proliferation. Finally, urate induces B-cell proliferation. Conclusions Urate crystals trigger BCR signal transduction and induce B-cell proliferation. The clinical significance of urate-induced B-cell activation remains to be elucidated.

Allopurinol protects human glomerular endothelial cells from high glucose-induced reactive oxygen species generation, p53 overexpression and endothelial dysfunction

PURPOSE

Mitochondrial reactive oxygen species (ROS) overproduction in capillary endothelial cells is a prerequisite for the development of diabetic nephropathy. Inhibition of xanthine oxidase, another ROS generator, ameliorates experimental diabetic nephropathy. To test the hypothesis that the initial high glucose-induced ROS production by the mitochondria activates xanthine oxidase, which afterward remains as the major source of ROS, we cultured primary human glomerular endothelial cells (GEnC) under normal or high-glucose conditions, with or without the xanthine oxidase inhibitor allopurinol.

METHODS

ROS generation and nitric oxide synthase (NOS) activity were assessed by chemiluminescence or colorimetrically. Levels of intercellular adhesion molecule 1 (ICAM-1), p53 and phosphorylated p53 (p-p53) were assessed by western blotting.

RESULTS

Allopurinol prevented high glucose-induced ROS generation indicating that xanthine oxidase is the major source of ROS. Allopurinol protected GEnC from endothelial dysfunction since it prevented the high glucose-induced decrease in NOS activity and increase in ICAM-1 expression. Allopurinol reduced p53 and p-p53 levels induced by high glucose suggesting an axis of xanthine oxidase-derived ROS, DNA damage, p53 stabilization and endothelial dysfunction that may contribute to the pathogenesis of diabetic nephropathy.

CONCLUSIONS

Allopurinol protects GEnC from high glucose-induced ROS generation, p53 overexpression and endothelial dysfunction. These data provide a pathogenetic mechanism that supports the results of experimental and clinical studies about the beneficial effect of xanthine oxidase inhibitors on the development of diabetic nephropathy.

Mendelian randomization analysis indicates serum urate has a causal effect on renal function in Chinese women

PURPOSE

High levels of serum uric acid can predict the progression of stage I and II chronic kidney disease (CKD), but whether serum urate is an independent risk factor or has causal impact on serum creatinine (SCr) and renal function remains unclear.

METHODS

Mendelian randomization was used to determine whether serum uric acid had a causal effect on renal function, represented by estimated glomerular filtration rate (eGFR), with potential confounding factors, in 3734 subjects from the Taizhou Longitudinal Study. In the two-stage least squares method of Mendelian randomization, serum uric acid level was selected as the exposure, genetic risk score of uric acid transporters was selected as the instrumental variable, and SCr and eGFR were selected as the outcomes.

RESULTS

The result of the analysis showed that increased serum uric acid was not a causal effect on renal function, but it was a causal effect on reducing estimated glomerular filtration rate in both the female population and the subjects who were under 65 years old. We also found that increased serum uric acid levels led to impaired renal function only in the subjects with normal eGFR values. In addition, the serum uric acid was a risk factor for renal function in the subjects with relatively high levels of fasting glucose or who were currently smokers.

CONCLUSIONS

Although serum urate is not an independent risk factor for renal dysfunction, it has a causal effect on renal dysfunction in either female or individuals of under 65, or normal eGFR, or high level of fasting glucose, or current smokers.