Calcification of leaflets from porcine aortic valves crosslinked by ultraviolet irradiation

Glutaraldehyde (GA)-pretreated porcine aortic valves are generally used as a bioprosthetic valve, but gradual calcification of the leaflets often occu rs. It has been hypothesized that the crosslinking agent, GA, stabilizes an d perhaps modifies phosphorus-rich calcifiable structures in the bioprosthe tic tissue. This is supported by our findings that calcium deposition is in duced rapidly in GA-pretreated leaflets in comparison with ultraviolet (UV) irradiated leaflets. After 3 days of in vitro calcification test, calcium levels were 257.6 +/- 23.5 mu g/cm(3) in GA-pretreated, 57.7 +/- 10.2 mu g/ cm(3) in the control, and 108.6 +/- 7.6 mu g/cm(3) in 24 h UV irradiated le aflets. The calcium level in all test groups increased as time proceeds and the calcium level of GA-pretreated leaflets was significantly higher than the control and UV irradiated leaflets during test. This rapid calcium depo sition on the GA-pretreated leaflets may be due to residual aldehyde groups after pretreatment. The exposure time of UV irradiation was not significan tly correlated with the extent of calcification. After 14 days of the test, calcium levels in leaflets UV irradiated for 1, 2, 4, and 24 h were 502.6 +/- 12.3 mu g/cm(3), 547.5 +/- 34.1 mu g/cm(3), 564.3 +/- 26.1 mu g/cm(3), and 543.0 +/- 55.5 mu g/cm(3). In all test groups, [Ca]/[P] molar ratio dec reased toward that of hydroxyapatite as the predominant mineral phase as ti me proceeds. This study suggests that UV irradiation can be considerable as an efficient crosslinking method to surmount the side effects induced by G A-pretreatment and may endow tissue with mechanical property.