Amphotericin B both inhibits and enhances T-cell proliferation: Inhibitory effect is mediated through H2O2 production via cyclooxygenase pathway by macrophages

Abstract

Amphotericin B (AmB) has been shown to have both immunosuppressive and -enhancing effects, making its precise nature of action enigmatic. In the present study, we found that AmB inhibited concanavalin A (Con A)-induced T cell proliferation if added within first 30 min of stimulation, after which inhibition began to diminish rapidly. However, AmB did not inhibit T-cell proliferation induced by a combination of PMA and ionomycin. AmB inhibition of Con A-induced proliferation was completely overcome by cyclooxygenase inhibitor ibuprofen ([alpha-methyl-4-(isobutyl)phenylacetic acid]) and H(2)O(2) scavenger catalase. In fact, in the presence of ibuprofen and catalase, AmB enhanced, instead of suppressing, Con A-induced proliferation in a dose-dependent way. The effect of catalase was limited to the removal of extracellular H(2)O(2) only, as the enzyme did not enter the cells. AmB stimulated H(2)O(2) production by macrophages, but not by a lymphocyte population, which was inhibited by ibuprofen. Our T-cell preparation contained about 3% macrophages, and AmB inhibition of proliferation was further pronounced by increasing the macrophage number by as little as 1%. Finally, AmB inhibition of Con A-induced T-cell proliferation was completely overcome by 2-mercaptoethanol. On the basis of these results, we suggest that AmB stimulates H(2)O(2) production by macrophages through the activation of the cyclooxygenase pathway of arachidonate metabolism. H(2)O(2) then inhibits Con A-induced T-cell proliferation by interfering with an early step of the T-cell receptor signaling pathway through the oxidative modification of some signaling proteins. Our results also show that AmB enhances T-cell proliferation, which can be seen only after blocking its inhibitory effect.

Vitamin A as an enzyme that catalyzes the reduction of MTT to formazan by vitamin C

“…Five‐tenths millimolar H 2 O 2 was incubated with various concentration of ascorbic acid (0–0.5 mM) in the presence or absence of retinol for 30 min at 37°C. H 2 O 2 in the samples and in the standard was measured by the horseradish peroxidase method as we described previously [Kumar and Chakrabarti, 2000]. The H 2 O 2 concentration in the sample was quantitated by comparing with the standard curve of the known H 2 O 2 concentrations.…”

Management of invasive pulmonary aspergillosis in non-neutropenic critically ill patients

“…Although antifungal drugs are targeted against specific cell functions, many drugs also have pleiotropic effects that may inhibit other elements of fungal homeostasis [ 108 ]. For instance, azoles inhibit many cytochrome-dependent enzymes of the fungal respiration chain and amphotericin B generates oxidative species that damage fungal mitochondrial function and enhance macrophage fungal killing [ 109 ]. These subtle effects could be enhanced when one antifungal is applied together with a second drug, resulting in synergy.…”