Prevention and reversal of experimental posthemorrhagic vasospasm by the periadventitial administration of nitric oxide from a controlled-release polymer

OBJECTIVE

Despite improvements in the care of patients with aneurysmal subarachnoid hemorrhage, delayed cerebral vasospasm remains a major cause of morbidity and death. There is now evidence that a decrease in the local availability of nitric oxide (NO) plays a role in delayed cerebral vasospasm. We evaluated a controlled-release polymer containing the NO donor (Z)-1-[2-(2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-ium-1,2-diolate (DETA/NO) for the treatment of chronic posthemorrhagic vasospasm in the rat femoral artery model.

METHODS

The release kinetics of ethylene/vinyl acetate copolymers loaded with 20% (w/w) DETA/NO were determined in vitro. Chronic vasospasm was induced in the left femoral artery of adult male Fischer 344 rats (n = 35) by exposure to autologous blood. At 1, 3, or 7 days after blood exposure, either a 5-mg polymer loaded with 20% (w/w) DETA/NO or an empty 5-mg polymer was placed in the periadventitial space next to the left femoral artery. At the same time, an empty 5-mg polymer was placed next to the right femoral artery. On the 8th day after blood exposure (at the peak of vasospasm in this model), rats were transcardially perfused with 4% paraformaldehyde, and the left and right femoral arteries were removed for histological processing and morphometric analyses. Vasospasm was expressed as the percent lumen patency of the treated left artery, compared with the control right artery.

RESULTS

The in vitro release kinetics demonstrated that the 20% DETA/NO-loaded polymers released up to 15% of their total drug load during a 9-day period. DETA/NO treatments initiated at 1, 3, or 7 days after blood deposition all significantly inhibited vasospasm, compared with control values (94.6 +/- 7.2% versus 67.6 +/- 5.8%, 104.6 +/- 5.5% versus 64.9 +/- 1.7%, and 102.4 +/- 5.1% versus 73.6 +/- 1.4%, respectively; mean +/- standard error of the mean percent lumen patency; P < 0.001). No adverse effects of treatment were observed.

CONCLUSION

The diazeniumdiolate NO donor DETA/NO can be effectively released from ethylene/vinyl acetate polymers. Administration of DETA/NO into the periadventitial space can prevent the development of chronic posthemorrhagic vasospasm in the rat femoral artery and can reverse established vasospasm. No adverse effects of DETA/NO were observed in this model.

Inhibition of experimental vasospasm in rats with the periadventitial administration of ibuprofen using controlled-release polymers

BACKGROUND AND PURPOSE

The chronic phase of vasospasm after an aneurysmal subarachnoid hemorrhage may be mediated in part by early leukocyte-endothelial cell interactions. Ibuprofen is an anti-inflammatory agent that inhibits expression of certain cell adhesion molecules and therefore disrupts leukocyte-endothelial cell interactions. Its systemic administration, however, has dose-limiting side effects. We evaluated the effect of the periadventitial delivery of ibuprofen using controlled-release polymers in the rat femoral artery model of chronic posthemorrhagic vasospasm.

METHODS

Before the animal studies, the release pharmacokinetics of the ibuprofen-loaded ethylene-vinyl acetate polymers were determined in vitro. Subsequently, the femoral arteries (n=266) of Fischer 344 rats (n=133) were enclosed in latex pouches bilaterally. In the toxicity study (n=15 rats), the animals were randomized into 5 dose groups in which 0%-, 10%-, 20%-, 30%-, or 50%-loaded ibuprofen polymers were evaluated. In the efficacy study, the animals were randomized into 5 time groups in which 50%-loaded ibuprofen polymers were inserted at 0 (n=58 rats), 6 (n=16), 12 (n=13), 24 (n=11), or 48 hours (n=12) after blood injection into the pouch. The rats were killed 12 days after blood exposure, at the time of maximal vasospasm in this model. Vasospasm was expressed as percent lumen patency. To evaluate the effect of ibuprofen on leukocyte migration, 8 rats were randomized into 2 groups. Macrophages and granulocytes were stained by immunohistochemistry with the use of a mouse OX-41 monoclonal antibody and counted in the periadventitial space 24 hours after blood exposure.

RESULTS

In vitro pharmacokinetics showed that the 50%-loaded ibuprofen polymer released its total drug load over a 12-day period. In the toxicity study, a nonsignificant arterial vasodilatation with ibuprofen treatment was seen at higher doses, and no deleterious effects were noted on the vessel wall histologically. In the efficacy study, ibuprofen treatment resulted in significant vasospasm inhibition when treatment was initiated at 0 hour (73.7+/-4.9% versus 94.5+/-3.3% [mean+/-SEM percent lumen patency]; P<0.001) and 6 hours (69.2+/-5.7% versus 98.0+/-3.9%; P=0. 002) after blood exposure, but not at 12, 24, or 48 hours. Leukocyte immunohistochemistry showed that ibuprofen treatment resulted in significantly lower periadventitial macrophage and granulocyte counts of 25.0+/-3.9 cells per high-powered field compared with counts of 140.5+/-18.2 cells per high-powered field in the untreated vessels (P<0.001).

CONCLUSIONS

The periadventitial, controlled release of ibuprofen from surgically implanted polymers significantly inhibits chronic posthemorrhagic vasospasm in this model when treatment is initiated within 6 hours of blood exposure. Vasospasm inhibition with ibuprofen correlates with a significant decrease in the number of macrophages and granulocytes in the periadventitial space. This study supports the hypothesis that inflammation mediates in part the chronic phase of posthemorrhagic vasospasm and suggests a potential alternative treatment for this condition.

Tonic protein kinase C-mediated vasoconstriction is unmasked when nitric oxide synthase is inhibited in cerebral microvessels

Recent evidence indicates that nitric oxide participates in the modulation of vascular tone in a variety of vascular beds, including the parenchymal microvasculature of the brain. The present study examined the role of protein kinase activity in the induction and maintenance of the contractile response when endogenous nitric oxide production is inhibited in parenchymal microvessels of the rat hippocampus. Microvessels in in vitro slices of the hippocampus were monitored using computer-assisted video microscopy. The effects of inhibitors of two kinases, protein kinase C and calcium/calmodulin-dependent protein kinase, on the vasoconstrictor response to NG-nitro-L-arginine (L-NNA) were investigated. The resting luminal diameter of the microvessels examined in this study ranged from 9 to 29 microns. Addition of 100 microM L-NNA to the medium superfusing the slice constricted microvessels by 38.8 +/- 0.6%. The addition of protein kinase inhibitors reversed this constriction in a dose-dependent manner. H-7 (50 microM), a relatively non-selective protein kinase C inhibitor, elicited an 81.4 +/- 10.0% reversal of the L-NNA-induced constriction. Bisindolylmaleimide (5 microM), a selective protein kinase C inhibitor, reversed the constriction by 69.1 +/- 13.7%. KN-62, an inhibitor of calcium/calmodulin-dependent protein kinase II, elicited a smaller yet statistically significant reversal of 17.1 +/- 5.1%. Pretreatment with H-7 or bisindolyl-maleimide blocked the LNNA-induced constriction entirely, while KN-62 did not significantly inhibit the response. These findings indicate that the contractile response observed upon removal of endogenous nitric oxidergic vasodilation is mediated by protein kinase activity, and the contribution of protein kinase C to this effect is greater than that of calcium/calmodulin-dependent protein kinase II. The results suggest that a tonic nitric oxidergic influence serves to mask the potential for protein kinase C-mediated vasoconstriction in cerebral microvessels.

Histological changes in the normal rat brain after gamma irradiation

Radiation-induced changes in the parietal cortex of Wistar rats were observed at various time points after gamma surgery. Maximum dosages of 50, 75, and 120 Gy were given at the iso-center of the radiation using a 4-mm collimator. Conventional histochemical and immunocytochemical analyses, and computer-assisted videomicroscopy were utilized to examine perfusion-fixed brain tissue. Irradiation at a dosage of 50 Gy elicited morphological changes of astrocytes in the parietal cortex at 3 months. Vasodilatation became obvious at 12 months; fibrin deposition was observed in the dilated capillary wall. Neither leakage of Evans Blue from the vasculature into the tissue nor necrosis was observed across the 12 month observation period. Irradiation at a dosage of 75 Gy resulted in morphological changes of astrocytes within 1 month. Dilatation of vessels and capillary thickening were observed at 3 months. Evans Blue leakage and necrosis were observed at 4 months after 75 Gy irradiation. At this time, the walls of arterioles became thickened by subintimal accumulation of fibrin and hyaline substance; this sometimes resulted in occlusion of the lumen. Significant hemispheric swelling was observed at 4 months. Irradiation at a dosage of 120 Gy elicited changes in astrocytic morphology within 3 days. Evans Blue leakage into the tissue was observed by 3 weeks. Vasodilation became marked at this time point and rarefaction was observed in the irradiated cortex. Necrosis was observed at 4 weeks, however, no significant swelling was observed. Taken together, these findings demonstrate time-dependent and dosage-dependent changes in normal cerebral tissue after Gamma Knife irradiation. These results provide a basis for gauging the impact of gamma surgery in regions of eloquent tissue. An enhanced understanding of the cellular responses to radiosurgery will contribute to developing and evaluating future applications for gamma surgery.

Vasodilatory actions of calcitonin gene-related peptide and nitric oxide in parenchymal microvessels of the rat hippocampus

Calcitonin gene-related peptide (CGRP) and nitric oxide (NO) are potent dilators in a variety of vascular beds. Recent evidence suggests that NO may serve as an intermediary messenger for CGRP and/or CGRP may serve as an intermediary messenger for NO in the expression of vasodilation. The present study was designed to provide an initial characterization of the responses to NO and CGRP in parenchymal microvessels and to determine whether NO and/or CGRP act as intermediaries for one another. Microvessels in the parenchyma of in vitro hippocampal slices from rat brain were examined using computer-assisted videomicroscopy. The resting diameter of the microvessels ranged from 9 to 26 microm. Treatment with the nitric oxide synthase inhibitor, N(G)-nitro-L-arginine (L-NNA; 100 microM) constricted vessels to 64.2% +/- 3.0% of resting luminal diameter. Sodium nitroprusside (SNP; 1 microM), a donor of NO, reversed the L-NNA-induced vasoconstriction by 77.0% +/- 15.0%. CGRP alone (10 nM) elicited a small but significant vasodilatory effect on resting vascular tone (2.3% +/- 0.6%). In the presence of L-NNA, CGRP elicited a significant dose-dependent vasodilatory response, and 10 nM CGRP elicited a sizeable response, reversing the L-NNA-induced constriction by 84.3% +/- 15.5%. This CGRP-induced dilation was inhibited by pretreatment with the CGRP receptor antagonist, CGRP fragment (8-37) (1 microM). In contrast, pretreatment with 1 microM CGRP fragment (8-37) did not attenuate the SNP-induced dilation in the presence of L-NNA. Taken together, these findings demonstrate that CGRP and NO are potent dilators of parenchymal microvessels, and that NO provides a substantial relaxant effect on resting tone. In addition, the results indicate that CGRP is not a necessary intermediary in NO-induced dilation, and that NO is not a necessary intermediary in CGRP-induced dilation in parenchymal microvessels.

The effects of papaverine on phorbol dibutyrate-induced vasoconstriction in brain slice microvessels

Papaverine (PPV) is a nonspecific vasodilator with widespread clinical uses in the treatment of arterial spasm. It has also been utilized in an attempt to reverse cerebral vasospasm. Recent angiographic results have demonstrated significant reversal of vasospasm in large vessels after selective intra-arterial application of PPV; however, these impressive results lacked good clinical correlation. In this study, phorbol dibutyrate was used to stimulate protein kinase C in an in vitro model of cerebral microvessels. Papaverine was found to elicit a dose-dependent exacerbation of phorbol dibutyrate-induced microvascular constriction in this model system. Because protein kinase C is thought to play a key role in the development of cerebral vasospasm, PPV-induced vasoconstriction represents a potentially important deleterious effect that may not be apparent on angiography. Such a constrictor response may compromise the beneficial vasodilatory effect seen with intra-arterial injection of PPV.

Cerebral microvascular responses to endothelins: the role of ETA receptors

The regulatory role of endothelins in cerebral microvessels was investigated in a recently developed model system which allows the study of small cerebral vessels in their normal microenvironment. Using brain slices of the rat neocortex, it was shown that the isopeptide endothelin-3 (ET-3) had no effect on cerebral microvessels, while the isopeptide endothelin-1 (ET-1) produced a potent, dose-dependent vasoconstriction. When a recently developed antagonist of ETA receptors (cyclo-[D-Asp-L-Pro-D-Val-L-Leu-D-Trp]; ETant) was administered prior to treatment with ET-1, the vasoconstrictor response to ET-1 was inhibited in a dose-dependent manner. When ETant was administered after the establishment of a constriction by ET-1, the constrictor response to ET-1 was partially reversed, and this effect was weaker than that seen in the pre-treatment paradigm. These findings indicate that constrictor responses to ET-1 in cerebral microvessels are mediated by ETA receptors. Inasmuch as endothelins have been implicated in pathological forms of vasoconstriction in the CNS, the present findings also suggest that endothelin antagonists may be useful in the treatment of cerebral ischemia.

Live computerized videomicroscopy of cerebral microvessels in brain slices

A model system for studying cerebral microvasculature is presented in which submerged in vitro brain slices are examined by computerized videomicroscopy. Brain slices are superfused continuously with artificial cerebrospinal fluid, while blood vessels are monitored using a transmission light microscope with water immersion objectives. The responses to well-characterized vasoactive compounds indicate that basic physiological characteristics are maintained in this preparation. This model system represents a simple and rapid technique for studying cerebrovascular responses under conditions in which vessels are surrounded by their normal cellular microenvironment. An additional advantage of this technique is the ability to perform simultaneous electrophysiological recordings in identified neurons. This will facilitate the study of interactions between neuronal and vascular elements and may help elucidate mechanisms underlying the local regulation of cerebral microvasculature.