Impaired secondary oxidant deactivation capacity and enhanced oxidative stress in serum from alveld affected lambs

• Serum form alveld lambs has a reduced secondary oxidant deactivation capacity.
• Alveld serum shows an increased intravascular hemolysis.
• Alveld photosensitivity is initiated by exogenous and endogenous photosensitizers.
• The photodynamic reaction is followed by a light-independent reaction.
• Trace metals and the Fenton reaction may contribute to the oxidative stress.

Alveld is a hepatogenous photosensitivity disorder in lambs. The aim of the study was to investigate if alveld affected lambs had a reduced capacity to handle oxidative stress induced from either endogenous and/or exogenous photosensitizers. Serum samples from alveld lambs (n = 33) were compared to serum samples from control lambs (n = 31) and exposed to a controlled amount of singlet oxygen (1O2). The sera from alveld lambs were found to have an impaired ability to deactivate reactive oxygen species (ROS) compared to control sera. A higher degree of initial hemolysis and a higher concentration of the exogenous photosensitizer phytoporphyrin (PP) were detected in alveld sera compared to the controls. The action spectrum for the formation of 1O2 indicated that PP as well as the endogenous compound protoporphyrin IX (PP IX) may act as in vivo photosensitizers. A relatively high level of iron was detected in pooled serum from alveld lambs that showed a high degree of hemolysis. It was concluded that alveld photosensitivity is likely to be initiated by a photodynamic reaction involving PP and possibly also PP IX followed by a light-independent reaction involving hemoglobin-related products and catalysis by the Fenton reaction.