Figure 3.

Lipid solubility determines the capacity of desferri-exochelins to enter cells and protect against oxidant injury. (A) The elution profile of the exochelins present in the filtrate of a 6-week culture of the virulent Erdman strain of M. tuberculosis, using a reverse-phase HPLC C-18 column and an acetonitrile gradient. Each 450-nm absorbance peak contains an exochelin species whose mass and structure have been determined by mass spectrometry and tandem mass spectrometry (18). The mass in daltons of the iron-loaded form of each exochelin used in this study is labeled above the peak, followed by the letter S or T to indicate whether the exochelin is a member of the serine or threonine series and C or M to indicate whether its R1 side chain terminates with a carboxylic acid or methyl ester moiety. The dashed line represents the concentration of buffer B (50% acetonitrile/0.1% trifluoroacetic acid). The most polar molecules elute early (to the left) and the least polar (most soluble in lipid) elute late. (B ) The structures of three exochelins of different lipid solubility in the iron-loaded state. These three desferri-exochelins were added 2 hr before exposure to 100 μM H₂O₂ (C) and simultaneously with H₂O₂ exposure (D) (n = 3 for each group). The cultured cardiac myocytes were studied under the same conditions as in Fig. 2. The most polar desferri-exochelin, 772SC, slightly attenuated injury when added before H₂O₂ exposure (P < 0.01 by ANOVA with group as a nominal variable) but had no effect (P = not significant) when added simultaneously with H₂O₂. The most nonpolar (most lipophilic) desferri-exochelin, 772SM, was highly effective whether added 2 hr before or simultaneously with H₂O₂ exposure (P < 0.001 for each). The desferri-exochelin of intermediate polarity, 758SM, was moderately effective when added 2 hr before (P < 0.01) and had a very small, but significant, effect when added simultaneously with H₂O₂ exposure (P < 0.05).