Translator Disclaimer
1 March 2005 Self-sensitized Photodegradation of Membrane-bound Protoporphyrin Mediated by Chain Lipid Peroxidation: Inhibition by Nitric Oxide with Sustained Singlet Oxygen Damage
Author Affiliations +
Abstract

In the presence of exciting light, iron and reductants, the singlet oxygen (1O2)-generating sensitizer protoporphyrin IX (PpIX) induces free radical lipid peroxidation in membranes, but gradually degrades in the process. We postulated that NO, acting as a chain-breaking antioxidant, would protect PpIX against degradation and consequently prolong its ability to produce 1O2. This idea was tested by irradiating PpIX-containing liposomes (LUVs) in the presence of iron and ascorbate, and monitoring the cholesterol hydroperoxides 5α-OOH and 7α/β-OOH as respective 1O2 and free radical reporters. 5α-OOH accumulation, initially linear with light fluence, slowed progressively after prolonged irradiation, whereas 7α/β-OOH accumulation only accelerated after an initial lag. The active, but not spent, NO donor spermine NONOate (0.4 mM) virtually abolished 7α/β-OOH buildup as well as 5α-OOH slowdown. Increasing membrane phospholipid unsaturation hastened the onset of rapid chain peroxidation and 5α-OOH slowdown. Accompanying the 5α-OOH effect was a steady decrease in 1O2 quantum yield and PpIX fluorescence at 632 nm, both of which were inhibited by NO. An NO-inhibitable decay of PpIX fluorescence was also observed during dark incubation of 5α-OOH–bearing LUVs with iron and ascorbate, confirming a link between chain peroxidation and PpIX loss. By protecting PpIX in irradiated membranes, NO might select for and prolong purely 1O2-mediated damage. Supporting this was our observation that 1O2-mediated photoinactivation of a nonmembrane target, lactate dehydrogenase, slowed concurrently with 5α-OOH accumulation and that spermine NONOate prevented this. Thus, NO not only protected membrane lipids against PpIX-sensitized free radical damage, but PpIX itself, thereby extending its 1O2-generating lifetime. Consistent findings were obtained using porphyrin-sensitized COH-BR1 cells. These previously unrecognized effects of NO could have important bearing on 5-aminolevulinate-based photodynamic therapy in which PpIX is metabolically deposited in tumor cells.

Magdalena Niziolek, Witold Korytowski, and Albert W. Girotti "Self-sensitized Photodegradation of Membrane-bound Protoporphyrin Mediated by Chain Lipid Peroxidation: Inhibition by Nitric Oxide with Sustained Singlet Oxygen Damage," Photochemistry and Photobiology 81(2), 299-305, (1 March 2005). https://doi.org/10.1562/2004-10-25-RA-351.1
Received: 25 October 2004; Accepted: 1 January 2005; Published: 1 March 2005
JOURNAL ARTICLE
7 PAGES

This article is only available to subscribers.
It is not available for individual sale.
+ SAVE TO MY LIBRARY

SHARE
ARTICLE IMPACT
RIGHTS & PERMISSIONS
Get copyright permission
Back to Top