Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:However, CP-induced free radical production and LP in tubular cells have been suggested to be responsible for the oxidative renal damage (Mansour et al., 2002; Sueishi et al., 2002; Atessahin et al., 2006).
Category: