Evidence for a novel pentyl radical adduct of the cyclic nitrone spin trap MDL 101,002

Use of spectroscopic probes for detection of reactive oxygen species

The detection and quantitation of reactive oxygen species (ROS) receives a great deal of interest because of their importance in a wide range of physiological and pathogenic events. Probe-assisted spectroscopy (electron spin resonance, spectrophotometry, fluorescence and luminescence) is the main tool for this application. This review discusses the properties of spectroscopic probes most commonly used for ROS detection and highlights their limitations in cellular systems. These include poor stability of some probes and/or products that may be subjected to cellular metabolism and lack of specificity in their reactions with oxidants or reductants. Additional problems often arise from undesired reactions of the probes and from their non-homogeneous distribution in the studied system, production of ROS by the probes themselves, perturbation of the systems under investigation by the probes, and artifacts due to the presence of ROS in the reaction medium. The limits imposed by these difficulties on the precise evaluation of the amounts and rates of formation of ROS are discussed critically.

Pharmacological effects of the spin trap agents N-t-butyl-phenylnitrone (PBN) and 2,2,6, 6-tetramethylpiperidine-N-oxyl (TEMPO) in a rabbit thromboembolic stroke model: combination studies with the thrombolytic tissue plasminogen activator

BACKGROUND AND PURPOSE

It has been proposed that spin trap agents such as N:-t-butyl-phenylnitrone (PBN) may be useful as neuroprotective agents in the treatment of ischemia and stroke. However, to date, there is little information concerning the effectiveness of spin trap agents when administered in combination with the only Food and Drug Administration-approved pharmacological agent for the treatment of stroke, the thrombolytic tissue plasminogen activator (tPA). Thus, we determined the effects of PBN when administered before tPA on hemorrhage and infarct rate and volume. We also compared the effects of PBN with those of 2,2,6, 6-tetramethylpiperidine-N:-oxyl (TEMPO), another spin trap agent that has a different chemical structure and trapping profile, on the incidence of infarcts and hemorrhage.

METHODS

One hundred sixty-five male New Zealand White rabbits were embolized by injecting a blood clot into the middle cerebral artery via a catheter. Five minutes after embolization, PBN or TEMPO (100 mg/kg) was infused intravenously. Control rabbits received saline, the vehicle required to solubilize the spin traps. In tPA studies, rabbits were given intravenous tPA starting 60 minutes after embolization. Postmortem analysis included assessment of hemorrhage, infarct size and location, and clot lysis.

RESULTS

In the control group, the hemorrhage rate after a thromboembolic stroke was 24%. The amount of hemorrhage was significantly increased to 77% if the thrombolytic tPA was administered. The rabbits treated with PBN in the absence of tPA had a 91% incidence of hemorrhage compared with 33% for the TEMPO-treated group. In the combination drug-treated groups, the PBN/tPA group had a 44% incidence of hemorrhage, and the TEMPO/tPA group had a 42% incidence of hemorrhage. tPA, PBN/tPA, and TEMPO/tPA were similarly effective at lysing clots (49%, 44%, and 33%, respectively) compared with the 5% rate of lysis in the control group. There was no significant effect of drug combinations on the rate or volume of infarcts.

CONCLUSIONS

This study suggests that certain spin trap agents may have deleterious effects when administered after an embolic stroke. However, spin trap agents such as PBN or TEMPO, when administered in combination with tPA, may improve the safety of tPA by reducing the incidence of tPA-induced hemorrhage. Overall, the therapeutic benefit of spin trap agents for the treatment of ischemic stroke requires additional scrutiny before they can be considered "safe" therapeutics.