*3.6. The Addition of SOD and Catalase Negate the Lethal Effects of Reactive Oxygen Species against F. hepatica NEJ In Vitro*

Co-incubation of *F. hepatica* NEJ with enzymatically generated superoxide killed 98% of exposed NEJ within 24 h. There was no significant difference in NEJ survival after the addition of BS or rFhSOD1 (*p* > 0.99); however, rFhSOD3 prevented death in 30% of

NEJ (*p* = 0.0041) (Figure 8; Table S3). The addition of catalase protected NEJ in a dosedependent manner, with 73 and 43% of NEJ alive when incubated with 43 and 4.3 U/mL catalase, respectively, at 24 h (Figure S6), the effect of which was enhanced when used in the conjunction with SODs (Table S3).

**Figure 8.** Susceptibility of *F. hepatica* NEJ to superoxide and their subsequent protection via the addition of SOD and catalase. Six replicates of 10 NEJ/well were incubated in the presence of enzymatically generated superoxide for 24 h at 37 ◦C and 5% CO2. PBS; phosphate buffered saline (negative control), Vehicle; assay buffer containing enzymatically generated superoxide via the step-wise reduction of hypoxanthine into xanthine and superoxide by xanthine oxidase (positive control), CAT; recombinant catalase, BS; native bovine erythrocyte SOD, ns; not significant (0.1234), \* *p* < 0.0332.
