Inflammation and aneurysmal disease

Background  

Interleukin-6 (IL-6) is central to the inflammatory process implicated in aneurysm pathogenesis.In vitro studies demonstrate that AAA tissue secrete more IL-6 compared to normal and atherosclerotic controls.In addition, AAA patients have elevated venous IL-6 compared to healthy and atherosclerotic controls.The aim of this study was to directly measure aortic IL-6 in vivo, testing the hypothesis that aneurysms secrete IL-6 into the circulation.

Methods

27 AAA patients and 9 with thoracic aneurysms (TA) undergoing endovascular aneurysm repair participated.Prior to stent insertion, a catheter was utilised to sample blood at five sequential points within the aorta; ascending (TA only), arch or thoracic aneurysm, descending, proximal abdominal (AAA only), distal abdominal and common iliac artery. 15 patients undergoing angiography acted as controls.Additionally, CRP was measured in the AAA and controls.Plasma IL-6 was determined by ELISA.Statistical analysis utilised repeated measures ANOVA.

Results

Overall IL-6 was significantly higher in the aneurysm groups (P <0.001), with a rise in IL-6 corresponding to positions downstream to the aneurysms.In the AAA group there was a significant rise in plasma IL-6 concentration from above to below the aneurysm (P=0.002) conforming to a linear trend. In the thoracic group the levels returned to baseline further downstream.There were no differences in IL-6 with position in the controls (P=0.26)

Aorta Position	IL-6 (pg/ml)
	TA	AAA	Control
Ascending	7.51(1.75)	-	-
Arch or TA	7.60(1.64)	4.70(0.47)	2.45(0.50)
Descending	8.51(1.86)	4.73(0.48)	2.65(0.54)
Proximal Abdo	-	5.00(0.51)	2.82(0.59)
Distal Abdo	7.70(1.59)	5.09(0.50)	2.80(0.59)
Iliac	7.99(1.71)	5.17(0.46)	2.54(0.47)

Results expressed as mean + S.E.

Conclusions

As IL-6 levels correspond to aneurysm position with no differences in CRP, this suggests the aneurysm as a source of circulating IL-6, rather than these data reflecting systemic inflammation.As elevated circulating IL-6 has recently been identified as an independent risk factor for cardiovascular mortality these findings may explain the high cardiovascular mortality observed in patients with aneurysms