Differential effects of nitric oxide on blood-brain barrier integrity and cerebral blood flow in intracerebral C6 gliomas

Abstract

Nitric oxide (NO) signaling in tumors and endothelial cells regulates vascular permeability and blood flow and therefore influences tumor uptake and response to therapeutic compounds. As delivery and efficacy of chemotherapy is impaired in CNS neoplasms due to a partially intact blood-brain barrier (BBB), we studied the effects of NO released by the short-acting NO donor disodium 1-[2-(carboxylato)pyrrolidin-1-yl]diazen-1-ium-1,2-diolate methanolate (PROLI/NO) on BBB integrity and blood flow in C6 gliomas using [¹⁴C]-aminoisobutyric acid (AIB) and [¹⁴C]-iodoantipyrine quantitative autoradiography. PROLI/NO selectively increased intratumoral uptake of [¹⁴C]AIB and [¹⁴C]sucrose when given as a 3-minute intracarotid infusion or a 15-minute i.v. infusion (AIB: tumor, K₁ = 68.7 ± 3.2 vs 24.9 ± 0.9 µL g⁻¹ min⁻¹, P < .0001; sucrose, K₁ = 16.9 ± 0.9 vs 11.5 ± 0.9 µL g⁻¹ min⁻¹, P = .0007). This effect was achieved without significant changes in cerebral and tumor blood flow or arterial blood pressure, which indicates that the effect on vascular permeability is independent of changes in vascular tone induced by NO. This effect was mediated by activation of the NO/3',5'-cyclic guanosine monophosphate (cGMP) pathway, as it was blocked by guanylate cyclase inhibition by LY83583 and reproduced by the delivery of 8-bromoguanosine 5'-monophosphate or inhibition of cGMP degradation by the phosphodiesterase inhibitor zaprinast. Inhibition of inducible NO synthase by aminoguanidine or cyclooxygenase inhibition by indometacin or dexamethasone did not reduce the blood-tumor barrier (BTB) response to PROLI/NO. PROLI/NO, and perhaps other NO-donating compounds, can be used to selectively increase BTB permeability in gliomas through the NO/cGMP pathway at doses that do not cause unwanted vasodilatory changes in blood flow and that do not affect the systemic circulation.

Fig. 1.

(A) K₁ values for [¹⁴C]AIB (µL g⁻¹ min⁻¹) in tumor (T), brain around tumor (BAT), cortex (C), and white matter (WM) after a 3-minute ICA or a 15-minute i.v. infusion of saline (NaCl 0.9%) or 10⁻⁶ M PROLI/NO. The values are expressed as the mean ± SEM. **P < .0001 compared with saline infusion. (B) K₁ values for [¹⁴C]sucrose (µL g⁻¹ min⁻¹) in tumor (T), brain around tumor (BAT), cortex (C), and white matter (WM) after a 3-minute ICA or a 15-minute i.v. infusion of saline (NaCl 0.9%) or 10⁻⁶ M PROLI/NO. The values are expressed as the mean ± SEM. *P < .05 and **P < .0001 compared with saline infusion.

Fig. 2.

Representative autoradiographs of coronal brain sections through a C6 glioma showing uptake of the permeability marker [¹⁴C]AIB after infusion of saline (NaCl 0.9%) (A) or 10⁻⁶ M PROLI/NO (B), and uptake of the blood flow marker [¹⁴C]IAP after infusion of NaCl 0.9% (C) or 10⁻⁶ M PROLI/NO (D). The white lines in (C) and (D) indicate the tumor margins according to the corresponding histological section superimposed by image fusion. rCBF in tumor was not significantly higher than in normal cortex.

Fig. 3.

K₁ values for [¹⁴C]AIB (µL g⁻¹ min⁻¹) in tumor (T), brain around tumor (BAT), cortex (C), and white matter (WM) after saline (NaCl 0.9%), PROLI/NO (10⁻⁶ M), zaprinast (20 mg/kg), and LY83583 (1 mg/kg) alone or in combination with PROLI/NO and 8-bromo cGMP (10⁻³ M). The values are expressed as the mean ± SEM. P < .05 or P < .0001 compared with saline infusion (* or **) or with PROLI/NO (^# or ^##).

Fig. 4.

Mean arterial blood pressure (MABP) measured before and after infusion of drug or vehicle as well as at the end of the experiment. Values are expressed in mm Hg and given as mean ± SEM. *P < .05 and **P ≤ .0001.

Fig. 5.

K₁ values for [¹⁴C]AIB (µL g⁻¹ min⁻¹) in tumor (T), brain around tumor (BAT), cortex (C), and white matter (WM) after saline (NaCl 0.9%), PROLI/NO (10⁻⁶ M), aminoguanidine (200 mg/kg), indometacin (7 mg/kg), and dexamethasone (10 mg/kg) alone or in combination with PROLI/NO. The values are expressed as the mean ± SEM. P < .05 or P < .0001 compared with saline infusion (* or **) or with PROLI/NO (^# or ^##).

Fig. 6.

rCBF (F) values for [¹⁴C]IAP (mL 100 g⁻¹ min⁻¹) in tumor (T), brain around tumor (BAT), cortex (C), and white matter (WM) after a 3-minute ICA infusion of saline (NaCl 0.9%) or 10⁻⁶ M PROLI/NO. The values are expressed as the mean ± SEM.