Introduction: We have demonstrated that nanoscale PEG-ylated oxidized carbon materials, which we refer to as hydrophilic carbon clusters (PEG-HCCs), have antioxidant characteristics favorable for their use in ischemia. These materials are rich in conjugated carbon double bond domains, and unlike conventional antioxidants, are able to quench rather than transfer oxidative radicals thus not requiring regeneration (Marcano et al, JNT in press). They have shown no acute or 6 week toxicity in rodents, excellent uptake into endothelial cells and protection against TBI-induced neurovascular dysfunction (Bitner et al, ACS Nano, 2012), but were not designed for blood-brain barrier (BBB) transport. We were able to synthesize PEG-HCCs bound to adamantane (ADM), a well characterized moiety that increases lipophilicity. We tested these agents in a severe example of oxidative stress, reversible middle cerebral artery occlusion (MCAO) in acutely hyperglycemic rats (Martini and Kent, JCBFM 2006).
Methods: 16 Male, Long Evans rats received an ip injection of streptozotocin or vehicle 2 days prior to 90 minutes MCAO using the suture technique. Physiological and post-op monitoring was performed. PEG-HCCs or ADM-PEG-HCCs were injected IV at suture removal. The endpoints investigated thus far are: mortality; nitric oxide (NO) expression, reflected in the ratio of perivascular DAF-2AC intensity in penumbra to contralateral region after 5 min. circulation (Fabian and Kent AJP 2008); and presence of the PEG-HCCs detected by reaction product from an anti-PEG antibody to the tightly bound PEG moiety.
Results: Mortality by 24 hours was 100% in untreated hyperglycemic rats, 66% with PEG-HCCs and 33% after ADM-PEG-HCCs. Ratio of penumbral perivascular NO expression to control hemisphere was: untreated: 0.29; PEG-HCCs: 0.52; and ADM-PEG-HCCs: 0.59. There was considerable vascular and parenchymal staining with ADM-PEG-HCC but was restricted to the vasculature with PEG-HCCs.
Conclusion: Addition of an ADM moiety to PEG-HCCs reduced mortality. This may have occurred because of BBB transport and partial recoupling of endothelial NO synthase, thought to be impaired in hyperglycemic stroke. Further characterization of the range of actions of these materials is underway.