Antiremodeling Effect of Xanthine Oxidase Inhibition in a Canine Model of Atrial Fibrillation

The Relationship between Uric Acid and the Development, Complication, and Prognosis of Atrial Fibrillation: The Views from a Clinical Study

A large number of studies suggest that uric acid (UA) is related to the occurrence, complications, and prognosis of atrial fibrillation (AF). However, the guidelines did not clearly elaborate on this issue. The current research results need to be summarized to analyze the association between UA and AF. This study found that in the current clinical research on the relationship between UA and AF, studies mainly focus on the development or complications of AF. A lot of repetitive work does not deepen awareness of this question. In contrast, studies investigating the effects of UA-lowering therapy on the management of AF are limited. The only reports deny the protective effect of UA-lowering therapy. For now, we suggest that UA is close to the occurrence and progression of AF; therefore, it may have important significance as a clinical marker. The role of UA-lowering therapy in the management of AF is one of the next key issues to be explored. It will be a meaningful topic to focus on the latest research on AF ablation and to conduct a secondary analysis to explore the prognostic impact of UA on the latest treatment methods for AF. Multiomics techniques may allow us to have a deeper understanding of the role of UA in AF management in the future.

Xanthine oxidase inhibitor febuxostat reduces atrial fibrillation susceptibility by inhibition of oxidized CaMKII in Dahl salt-sensitive rats

Oxidative stress could be a possible mechanism and a therapeutic target of atrial fibrillation (AF). However, the effects of the xanthine oxidase (XO) inhibition for AF remain to be fully elucidated. We investigated the effects of a novel XO inhibitor febuxostat on AF compared with allopurinol in hypertension rat model. Five-week-old Dahl salt-sensitive rats were fed either low-salt (LS) (0.3% NaCl) or high-salt (HS) (8% NaCl) diet. After 4 weeks of diet, HS diet rats were divided into three groups: orally administered to vehicle (HS-C), febuxostat (5 mg/kg/day) (HS-F), or allopurinol (50 mg/kg/day) (HS-A). After 4 weeks of treatment, systolic blood pressure (SBP) was significantly higher in HS-C than LS, and it was slightly but significantly decreased by treatment with each XO inhibitor. AF duration was significantly prolonged in HS-C compared with LS, and significantly suppressed in both HS-F and HS-A (LS; 5.8 ± 3.5 s, HS-C; 33.9 ± 23.7 s, HS-F; 15.0 ± 14.1 s, HS-A; 20.1 ± 11.9 s: P<0.05). Ca2+ spark frequency was obviously increased in HS-C rats and reduced in the XO inhibitor-treated rats, especially in HS-F group. Western blotting revealed that the atrial expression levels of Met281/282-oxidized Ca2+/Calmodulin-dependent kinase II (CaMKII) and Ser2814-phosphorylated ryanodine receptor 2 were significantly increased in HS-C, and those were suppressed in HS-F and HS-A. Decreased expression of gap junction protein connexin 40 in HS-C was partially restored by treatment with each XO inhibitor. In conclusion, XO inhibitor febuxostat, as well as allopurinol, could reduce hypertension-related increase in AF perpetuation by restoring Ca2+ handling and gap junction.

Quality and Quantity-Cultured Human Mononuclear Cells Improve Human Fat Graft Vascularization and Survival in an In Vivo Murine Experimental Model

BACKGROUND

Fat graft ischemia impedes us from having satisfying long-term results. The quality and quantity culture is a 1-week cell culture that increases the vasculogenic potential of peripheral blood mononuclear cells (PBMNC). This in vivo murine model investigates whether enrichment with quality and quantity-cultured human mononuclear cells (MNC-QQ) improves the vascularization in the human fat graft and whether this decreases the tissue loss.

METHODS

Human adipose tissue, PBMNC, MNC-QQ, and stromal vascular fraction were prepared. First, PBMNC, MNC-QQ, and stromal vascular fraction were compared in vitro for vasculogenic potential by endothelial progenitor cell colony-forming and culture assays. Second, 0.25-g fat grafts were created with 1 × 106 PBMNC (n = 16), 1 × 106 MNC-QQ (n = 16), 1 × 106 stromal vascular fraction (n = 16), or phosphate-buffered saline as control (n = 16) before grafting in BALB/c nude mice. Grafts were analyzed for weight persistence, vessel formation by CD31 immunohistochemistry, and angiogenic markers by quantitative polymerase chain reaction.

RESULTS

MNC-QQ develop more definitive endothelial progenitor cell colonies and more functional endothelial progenitor cells compared to PBMNC and stromal vascular fraction. Weight persistence after 7 weeks was significantly higher in grafts with MNC-QQ (89.8 ± 3.5 percent) or stromal vascular fraction (90.1 ± 4.2 percent) compared with control (70.4 ± 6.3 percent; p < 0.05). MNC-QQ-enriched grafts had the highest vessel density (96.6 ± 6.5 vessels/mm2; control, 70.4 ± 5.6 vessels/mm2; p < 0.05). MNC-QQ exerted a direct vasculogenic effect through vascular integration and a potential paracrine vascular endothelial growth factor-mediated effect.

CONCLUSION

Quality and quantity-cultured human mononuclear cells containing endothelial progenitor cells stimulate fat graft vascularization and enhance graft survival in a rodent recipient.

Cannabinoid Receptor Agonist Inhibits Atrial Electrical Remodeling in a Tachypaced Ex Vivo Rat Model

Introduction: Atrial fibrillation (AF) leads to rate-dependent atrial changes collectively defined as atrial remodelling (AR). Shortening of the atrial effective refractory period (AERP) and decreased conduction velocity are among the hallmarks of AR. Pharmacological strategies to inhibit AR, thereby reducing the self-perpetual nature of AF, are of great clinical value. Cannabinoid receptor (CBR) ligands may exert cardioprotective effects; CB13, a dual CBR agonist with limited brain penetration, protects cardiomyocytes from mitochondrial dysfunction induced by endothelin-1. Here, we examined the effects of CB13 on normal physiology of the rat heart and development of tachypacing-induced AR.

Methods: Rat hearts were perfused in a Langendorff set-up with CB13 (1 µM) or vehicle. Hemodynamic properties of non-paced hearts were examined conventionally. In a different set of hearts, programmed stimulation protocol was performed before and after atrial tachypacing for 90 min using a mini-hook platinum quadrupole electrode inserted on the right atrium. Atrial samples were further assessed by western blot analysis.

Results: CB13 had no effects on basal hemodynamic properties. However, the compound inhibited tachypacing-induced shortening of the AERP. Protein expression of PGC1α was significantly increased by CB13 compared to vehicle in paced and non-paced hearts. Phosphorylation of AMPKα at residue threonine 172 was increased suggesting upregulation of mitochondrial biogenesis. Connexin43 was downregulated by tachypacing. This effect was diminished in the presence of CB13.

Conclusion: Our findings support the notion that peripheral activation of CBR may be a new treatment strategy to prevent AR in patients suffering from AF, and therefore warrants further study.

Serum uric acid and incident atrial fibrillation: A systematic review and dose-response meta-analysis

The exposure-effect association between serum uric acid and atrial fibrillationis not well known. We conduct a meta-analysis to quantitatively examine the exposure-effect relationship between serum uric acid and atrial fibrillation. Prospective studies (including cohort or nested case-control) that reported the serum uric acid and atrial fibrillation were identified through electronic searches using EMBASE, PubMed, and the Cochrane Library database. The exposure-effect analysis was performed using a stage robust error meta-regression. Eleven studies were included, with a total of 6831 cases of atrial fibrillation among 527 908 individuals. Both the highest (risk ratio (RR), 1.9; 95% confidence interval (CI), 1.64-2.23; I²  = 0%) and intermediate (RR, 1.36; 95% CI, 1.16-1.59; I²  = 36%) level of serum uric acid were associated with increased risks of atrial fibrillation compared to the patients with the lowest level of serum uric acid. In the exposure-effect analysis, for each 1 mg/dL increase in serum uric acid level, the incidence of atrial fibrillation increased by 21% (RR, 1.21; 95% CI, 1.12-1.32; I²  = 78%). Furthermore, a significant positive linear relationship between serum uric acid and the risk of atrial fibrillation, P_nonlinearity  = 0.47 was found. The exposure-effect analysis demonstrated that serum uric acid over 5.0 mg/dL significantly increased the risk of atrial fibrillation. There was a positive linear association between serum uric acid and risk of atrial fibrillation, both in subjects with noruricaemia and hyperuricaemia. More studies are needed to explore the impact of serum uric acid reduction on the incidence of atrial fibrillation.

Spontaneous Atrial Fibrillation in Transgenic Goats With TGF (Transforming Growth Factor)-β1 Induced Atrial Myopathy With Endurance Exercise

BACKGROUND

There is increasing evidence that endurance exercise is associated with increased risk of atrial fibrillation (AF). However, it is unknown if the relationship between endurance exercise and AF is dependent on an atrial myopathy.

METHODS

Six cardiac-specific TGF (transforming growth factor)-β1 transgenic and 6 wild-type (WT) goats were utilized for these studies. Pacemakers were implanted in all animals for continuous arrhythmia monitoring and AF inducibility. AF inducibility was evaluated using 5 separate 10 s bursts of atrial pacing (160-200 ms). Three months of progressive endurance exercise (up to 90 minutes at 4.5 mph) was performed. Quantitative assessment of circulating microRNAs and inflammatory biomarkers was performed.

RESULTS

Sustained AF (≥30 s) was induced with 10 s of atrial pacing in 4 out of 6 transgenic goats compared with 0 out of 6 WT controls at baseline (P<0.05). No spontaneous AF was observed at baseline. Interestingly, between 2 and 3 months of exercise 3 out of 6 transgenic animals developed self-terminating spontaneous AF compared with 0 out of 6 WT animals (P<0.05). There was an increase in AF inducibility in both transgenic and WT animals during the first 2 months of exercise with partial normalization at 3 months (transgenic 67%; 100%; 83% versus WT 0%; 67%; 17%). These changes in AF susceptibility were associated with a decrease in circulating microRNA-21 and microRNA-29 during the first 2 months of exercise with partial normalization at 3 months in both transgenic and WT animals. Finally, MMP9 (matrix metallopeptidase 9) was increased during the second and third months of exercise training.

CONCLUSIONS

This study demonstrates a novel transgenic goat model of cardiac fibrosis (TGF-β1 overexpression) to demonstrate that endurance exercise in the setting of an underlying atrial myopathy increases the incidence of spontaneous AF. Furthermore, endurance exercise seems to increase inducible AF secondary to altered expression of key profibrotic biomarkers that is independent of the presence of an atrial myopathy.