Immunohistochemical localization of TNF-α was performed to determine the expression and activity of the protein. Staining intensity of the nucleus and cytoplasm in patients with persistent AF was more than that observed in patients with sinus rhythm (Figure 4A–D). IHC analysis showed that the protein expression of TNF-α was higher in AF patients compared to the sinus (P=0.000; Figure 4E).
In the present study, the concentration of TNF-α elevated in AF patients and so were the hsCRP and IL-6. Corresponding to the result of serum sample, the protein and mRNA expression of TNF-α of left atrium tissue increased in AF patients too. TNF-α was strongly associated with AF. Evidence7 showed that hsCRP was the independent predictive factor of AF and early recurrence of AF after cardioversion. In the present study, TNF-α was found drifted accompanying by hsCRP. We supposed that inflammation was involved in AF from the early stage. These results suggest that inflammation may be related to “burden” of AF.7 Inflammation may be one of the reasons that cause AF burgeon AF.
TNF-α was found higher in patients with persistent AF than paroxysmal AF, followed by patients with sinus rhythm.10 The result was similar to ours and suggested the association between TNF-α and AF. On the contrary, Rizos et al reported11 that it was hsCRP but not TNF-α elevated in AF patients with hypertension. Short half-time of TNF-α may be the reason in different results.10,19 Furthermore, we also found soluble receptor 1 of TNF-α (sTNFR1) level elevated in the serum of patients with AF. sTNFR1 competitively elevated when the excretion of TNF-α increased, adjusting the action of TNF-α.20 Consistency of the result of two cytokines ulteriorly confirmed the elevation of TNF-α during the process of AF. Ascending of both TNF-α and sTNFR1 made the result much credible. TNF-α adjusts synthesis and metabolism of cells according to two different receptors, TNFR1 and TNFR2. As the result shown in the present study, we presumed that TNFR1 may be the main receptor which helped TNF-α in AF. The mechanism that TNF-α was involved in AF is still not clear. Nuclear factor kappaB (NF-κB) should take part in the transcriptional regulation of TNF-α.21 Qu et al22 reported that the expression of NF-κB increased in atrial tissue of RHD patients with AF, which was accompanying with the elevation of TNF-α in the serum. The results demonstrated that TNF-α may affect the transcription of atrial myocytes by the signal pathway of NF-κB to make AF develop and maintain. On the other hand, oxidative stress may be the main mechanism. TNF-α increased the product of oxidative stress in atrial myocytes, which made the glutathione of mitochondria exhausted, and then mitochondria swelling and disintegrating.23 TNF-α could inhibit the calcium current of ventricular myocytes of mouse but the inhibition decreased by acetylcysteine.24
The present study demonstrated that no matter patients with AF before or post surgical operation had larger LAD than the sinus ones; protein level and expression of TNF-α were positively related to LAD. LAD is the mark of structural remolding in cardiac ultrasound and previous researchrd had shown that LAD related to the development and maintenance of AF.29,30 Enlarged left atrium induced volume and pressure overload and then made function failure and abnormal electrical activity.31 Structure remolding of the left atria triggered a local inflammatory response, leading to the maintaining of AF.5 Nevertheless, two atria may play different roles in AF. Right atrium might just be onlooker in AF32 but left atrium was considered as the main chamber to induce and maintain the post-surgical AF.33 Remolding of left atrium should be the substrate of AF. In the present study, the studied tissue was from left atrium which made the result much reliable. Protein and mRNA expression of TNF-α upregulated in the tissue of left atrium of patients with AF revealed that inflammation may get involved in the remolding of left atrium. TNF-α may participate in the process of atrial remodeling.
The main limitation of the study is that we did not make multivariate analysis so we could not determine if TNF-α was the most related factor to AF or AF after surgery. Because of the specimen collecting limitation, the number of subjects enrolled was quiet small. Finally, we compared TNF-α between patients with persistent AF and sinus rhythm and it would be much meaningful if a paroxysmal group enrolled.
In conclusion, the results demonstrate the association of the level and expression of TNF-α both in patients with AF. The study was carried on with human blood and tissue sample, so it may provide direct evidence that inflammation related to AF. It might provide insights into further mechanistic research and peculiar AF therapeutic targets. Nevertheless, the development of AF is a long term, multi-factorial and complicated process. We cannot tell whether TNF-α caused the disease or it was just one of the biomarkers of AF. The exact role of TNF-α in AF needs to be further studied.
1. Boos CJ, Anderson RA, Lip GY. Is atrial fibrillation
an inflammatory disorder? Eur Heart J 2006; 27: 136-149.
2. Frustaci A, Caldarulo M, Buffon A, Bellocci F, Fennici R, Melina D. Cardiac biopsy in patients with “primary” atrial fibrillation
. Histologic evidence of occult myocardial diseases. Chest 1991; 100: 303-306.
3. Aviles RJ, Martin DO, Apperson-Hansen C, Houghtaling PL, Rautaharju P, Kronmal RA, et al. Inflammation as a risk factor for atrial fibrillation
. Circulation 2003; 108: 3006-3010.
4. Asselbergs FW, van den Berg MP, Diercks GF, van Gilst WH, van Veldhuisen DJ. C-reactive protein and microalbuminuria are associated with atrial fibrillation
. Int J Cardiol 2005; 98: 73-77.
5. Dernellis J, Panaretou M. Relationship between C-reactive protein concentrations during glucocorticoid therapy and recurrent atrial fibrillation
. Eur Heart J 2004; 25: 1100-1107.
6. Wazni O, Martin DO, Marrouche NF, Shaaraoui M, Chung MK, Almahameed S, et al. C reactive protein concentration and recurrence of atrial fibrillation
after electrical cardioversion. Heart 2005; 91: 1303-1305.
7. Chung MK, Martin DO, Sprecher D, Wazni O, Kanderian A, Carnes CA, et al. C-reactive protein elevation in patients with atrial arrhythmias: inflammatory mechanisms and persistence of atrial fibrillation
. Circulation 2001; 104: 2886-2891.
8. Korantzopoulos P, Kolettis TM, Kountouris E, Siogas K, Goudevenos JA. Variation of inflammatory indexes after electrical cardioversion of persistent atrial fibrillation
: Is there an association with early recurrence rates? Int J Clin Pract 2005; 59: 881-885.
9. Prabhu SD. Cytokine-induced modulation of cardiac function. Circ Res 2004; 95: 1140-1153.
10. Li J, Solus J, Chen Q, Rho YH, Milne G, Stein CM, et al. Role of inflammation and oxidative stress in atrial fibrillation
. Heart Rhythm 2010; 7: 438-444.
11. Rizos I, Rigopoulos AG, Kalogeropoulos AS, Tsiodras S, Dragomanovits S, Sakadakis EA, et al. Hypertension and paroxysmal atrial fibrillation
: a novel predictive role of high sensitivity C-reactive protein in cardioversion and long-term recurrence. J Hum Hypertens 2010; 24: 447-457.
12. Brundel BJ, Ausma J, van Gelder IC, Van der Want JJ, van Gilst WH, Crijns HJ, et al. Activation of proteolysis by calpains and structural changes in human paroxysmal and persistent atrial fibrillation
. Cardiovasc Res 2002; 54: 380-389.
13. Buonaquro L, Barillari G, Chang HK, Bohan CA, Kao V, Morgan R, et al. Effects of the human immunodeficiency virus type 1 Tat protein on the expression of inflammatory cytokines. J Virol 1992; 66: 7159-7167.
14. Katayama A, Oqino T, Bandoh N, Nonaka S, Harabuchi Y. Expression of CXCR4 and its down-regulation by IFN-gamma in head and neck squamous cell carcinoma. Clin Cancer Res 2005; 11: 2937-2946.
15. Danesh J, Whincup P, Walker M, Lennon L, Thomson A, Appleby P, et al. Low grade inflammation and coronary heart disease: prospective study and updated meta-analyses. BMJ 2000; 321: 199-204.
16. Allessie MA, Boyden PA, Camm AJ, Kleber AG, Lab MJ, Legato MJ, et al. Pathophysiology and prevention of atrial fibrillation
. Circulation 2001; 103: 769-777.
17. Kallergis EM, Manios EG, Kanoupakis EM, Mavrakis HE, Kolyvaki SG, Lyrarakis GM, et al. The role of the post-cardioversion time course of hs-CRP levels in clarifying the relationship between inflammation and persistence of atrial fibrillation
. Heart 2008; 94: 200-204.
18. Hack CE, Wolbink GJ, Schalkwijk C, Speijer H, Hermens WT, van den Bosch H. A role for secretory phospholipase A2 and C-reactive protein in the removal of injured cells. Immunol Today 1997; 18: 111-115.
19. Ishida K, Kimura F, Imamaki M, Ishida A, Shimura H, Kohno H, et al. Relation of inflammatory cytokines to atrial fibrillation
after off-pump coronary artery bypass grafting. Eur J Cardiothorac Surg 2006; 29: 501-505. 1982 Chin Med J 2011;124(13):1976-1982
20. Krown KA, Yasui K, Brooker MJ, Dubin AE, Nguyen C, Harris GL, et al. TNF alpha receptor expression in rat cardiac myocytes: TNF alpha inhibition of L-type Ca2+ current and Ca2+ transients. FEBS Lett 1995; 376: 24-30.
21. Wu XY, Han SP, Ren MY, Chang Y, Yu FX. The role of NF-kappaB activation in lipopolysaccharide induced keratitis in rats. Chin Med J 2005; 118: 1893-1899.
22. Qu YC, Du YM, Wu SL, Chen QX, Wu HL, Zhou SF. Activated nuclear factor-kappa B and increased tumor necrosis factor-alpha in atial tissue of atrial fibrillation
. Scand Cardiovasc J 2009; 23: 1-6.
23. Mariappan N, Soorappan RN, Haque M, Sriramula S, Francis J. TNF-α induced mitochondrial oxidative stress and cardiac dysfunction: restoration by superoxide dismutase mimetic Tempol. Am J Physiol Heart Circ Physiol 2007; 293: H2726-H2737.
24. Cailleret M, Amadou A, Andrieu-Abadie N, Nawrocki A, Adamy C, Ait-Mamar B, et al. N-acetylcysteine prevents the dileteriou effect of tumor necrosis factor-αon calcium transients and contraction. Circulation 2004; 109: 406-411.
25. Dernellis J, Panaretou M. C-reactive protein and paroxysmal atrial fibrillation
: evidence of the implication of an inflammatory process in paroxysmal atrial fibrillation
. Acta Cardiol 2001; 56: 375-380.
26. Watanabe E, Arakawa T, Uchiyama T, Kodama I, Hishida H. High sensitivity C-reactive protein is predictive of successful cardioversion for atrial fibrillation
and maintenance of sinus rhythm after conversion. Int J Cardiol 2006; 108: 346-353.
27. Psychari SN, Apostolou TS, Sinos L, Hamodraka E, Liakos G, Kremastinos DT. Relation of elevated C-reactive protein and interleukin-6 levels to left atrial size and duration of episodes in patients with atrial fibrillation
. Am J Cardiol 2005; 95: 764-767.
28. Roldan V, Marin F, Martinez JG, Garcia-Herola A, Sogorb F, Lip GY. Relation of interleukin-6 levels and prothrombin fragment 1+2 to a point-based score for stroke risk in atrial fibrillation
. Am J Cardiol 2005; 95: 881-882.
29. Vaziri SM, Larson MG, Benjamin EJ, Levy D. Echocardiographic predictors of non rheumatic atrial fibrillation
: the Framingham Heart Study. Circulation 1994; 89: 724-730.
30. Parkash R, Green MS, Kerr CR, Connolly SJ, Klein GJ, Sheldon R, et al. The association of left atrial size and occurrence of atrial fibrillation
: a prospective cohort study from the Canadian Registry of Atrial Fibrillation
. Am Heart J 2004; 148: 649-654.
31. Abhayaratna WP, Seward JB, Appleton CP, Douglas PS, Oh JK, Tajik AJ, et al. Left atrial size:physiologic determinants and clinical applications. J Am Coll Cardiol 2006; 47: 2357-2363.
32. Sanders P, Berenfeld O, Hocini M, Vaidyanathan R, Hsu LF, Garrigue S, et al. Spectral analysis identifies sites of high-frequecy activity maintaining atrial fibrillation
in humans. Circulation 2005; 112: 789-797.
33. Swartz MF, Fink GW, Lutz CJ, Taffet SM, Berenfeld O, Vikstrom KL, et al. Left versus right atrial difference in dominant frequency, K+ channel transcripts, and fibrosis in patients developing atrial fibrillation
after cardiac surgery. Heart Rhythm 2009; 6: 1415-1422.