The role of hyaluronan in aortic stiffening in patients with rheumatoid arthritis

Kaisa Maki-Petaja, Elizabeth Ribey, Sarah Cleary, Chen Yen Ooi, Ian Wilkinson. University of Cambridge, Cambridge, UK

Introduction

Patients with rheumatoid arthritis (RA) have an increased risk of cardiovascular disease (CVD) and one of the contributing factors is thought to be increased aortic stiffness, which can be improved with anti-inflammatory therapies. Aortic stiffness is a strong, independent predictor of future CV events and therefore reduction of aortic stiffness may have beneficial effect on the CV risk. However, how inflammation leads to aortic stiffening remains unclear. One potential mechanism is by overproduction of hyaluronan (HA) in the extracellular matrix, which has been shown to result in stiffening of the arterial wall by thinning of elastic lamellae in animal models. However, the effect in man is unknown.

The aim of the study was 1) to evaluate whether serum HA concentration is a valid surrogate of aortic tissue level and 2) to compare serum HA in patients with RA and control subjects and to relate this to aortic pulse wave velocity (PWV) 3) to investigate whether anti-TNF-alpha therapy leads to a reduction of serum HA 4) to determine whether enzymatic removal of hyaluronan with hyaluronidase leads to reduction of aortic stiffness.

Methods

1) 18 human aortic tissue samples were homogenised by digesting them overnight in protease from Streptomyces Griseus and HA concentration in the homogenate, and a corresponding serum sample, was assessed using commercially available enzyme-linked immunosorbent assay (ELISA) kit (DY3614, R&D Systems, U.K). 2) In 80 patients with RA, and in 72 age- and gender-matched control subjects, blood pressure, serum C-reactive protein (CRP) and HA and aortic PWV and augmentation index were assessed using SphygmoCor device (AtCor, Australia). 3) In further 20 patients with RA aortic PWV, HA and CRP were assessed before and 8 weeks after anti-TNF-alpha therapy. 4) Elastic modulus (Em) was measured in 20 Sprague-Dawley rat aortic rings following 1 hour incubation with either Hyaluronidase or saline.

Results

The mean aortic tissue and serum HA concentrations were 128±67 and 40.4±12.0 ng/ml, respectively. There was a correlation between tissue and serum HA (R=0.68; P=0.01 n=18). RA Patients had higher serum HA in comparison to control subjects (54.8±67.5 v. 17.5±17.6 ng/ml; P<0.0001). The serum HA was, independently of age and MAP, associated with aPWV (R=0.2; P=0.02). Anti-TNF-therapy lead to a reduction of aPWV (8.99±1.83 v. 8.30±1.51 m/s; P<0.0001) and there was a trend for HA reduction following treatment, but this did not reach statistical significance (93.5±134.8 v. 78.6±82.1ng/ml; P=0.3). In the isolated rat aortas, incubation with hyaluronidase successfully removed hyaluronan (21.5±15.8 v. 0.00±0.00 ng/ml; P=0.02), but this was not associated with a reduction of aortic stiffness in the mechanical testing (Em at 100 mmHg: 2151±239 v. 2149±488 kPa; P=0.9)

Conclusion

This study demonstrates that serum HA is increased in patients with RA in comparison to control subjects, and that serum HA is associated with aortic stiffening. However, we were unable to reduce stiffness by removal of HA, suggesting that HA may not play a causal role in aortic stiffening during inflammation.