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 occurs. It has been hypothesized that the crosslinking agent, GA, stabilizes and perhaps modifies phosphorus-rich calcifiable structures in the bioprosthetic tissue. This is supported by our findings that calcium deposition is induced 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 microg/cm3 in GA-pretreated, 57.7 +/- 10.2 microg/cm3 in the control, and 108.6 +/- 7.6 microg/cm3 in 24 h UV irradiated leaflets. 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 deposition on the GA-pretreated leaflets may be due to residual aldehyde groups after pretreatment. The exposure time of UV irradiation was not significantly 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 microg/cm3, 547.5 +/- 34.1 microg/cm3, 564.3 +/- 26.1 microg/cm3, and 543.0 +/- 55.5 microg/cm3. In all test groups, [Ca]/[P] molar ratio decreased toward that of hydroxyapatite as the predominant mineral phase as time proceeds. This study suggests that UV irradiation can be considerable as an efficient crosslinking method to surmount the side effects induced by GA-pretreatment and may endow tissue with mechanical property.