Safety and feasibility of long-term intravenous sodium nitrite infusion in healthy volunteers

Abstract

Background: Infusion of sodium nitrite could provide sustained therapeutic concentrations of nitric oxide (NO) for the treatment of a variety of vascular disorders. The study was developed to determine the safety and feasibility of prolonged sodium nitrite infusion.

Methodology: Healthy volunteers, aged 21 to 60 years old, were candidates for the study performed at the National Institutes of Health (NIH; protocol 05-N-0075) between July 2007 and August 2008. All subjects provided written consent to participate. Twelve subjects (5 males, 7 females; mean age, 38.8±9.2 years (range, 21-56 years)) were intravenously infused with increasing doses of sodium nitrite for 48 hours (starting dose at 4.2 µg/kg/hr; maximal dose of 533.8 µg/kg/hr). Clinical, physiologic and laboratory data before, during and after infusion were analyzed.

Findings: The maximal tolerated dose for intravenous infusion of sodium nitrite was 267 µg/kg/hr. Dose limiting toxicity occurred at 446 µg/kg/hr. Toxicity included a transient asymptomatic decrease of mean arterial blood pressure (more than 15 mmHg) and/or an asymptomatic increase of methemoglobin level above 5%. Nitrite, nitrate, S-nitrosothiols concentrations in plasma and whole blood increased in all subjects and returned to preinfusion baseline values within 12 hours after cessation of the infusion. The mean half-life of nitrite estimated at maximal tolerated dose was 45.3 minutes for plasma and 51.4 minutes for whole blood.

Conclusion: Sodium nitrite can be safely infused intravenously at defined concentrations for prolonged intervals. These results should be valuable for developing studies to investigate new NO treatment paradigms for a variety of clinical disorders, including cerebral vasospasm after subarachnoid hemorrhage, and ischemia of the heart, liver, kidney and brain, as well as organ transplants, blood-brain barrier modulation and pulmonary hypertension.

Clinical trial registration information: http://www.clinicaltrials.gov; NCT00103025.

Conflict of interest statement

Competing Interests: A patent titled “Treatment of Specific Cardiovascular Conditions with Nitrite” has been granted for the following co-inventors: Mark T. Gladwin, Alan N. Schechter, Christian Hunter, Ryszard M. Pluta, and Edward H. Oldfield. This research was performed under a cooperative research and development agreement between the National Institute of Neurological Disorders and Stroke at the National Institutes of Health and Hope Pharmaceuticals, Inc. This does not alter our adherence to all the PLoS ONE policies on sharing data and materials.

Figures

Figure 1. Clinical and biochemical data for the Maximal Tolerated Dose (MTD) group.

This composite graph depicts the mean values and standard deviations (bars) of: A; mean arterial blood pressure and methemoglobin. B; NO metabolome concentrations in plasma (nitrite, nitrate, S-nitrosothiols), red blood cells (C; nitrite and nitrate) and whole blood (D; nitrite and nitrate) in three subjects who did not develop nitrite-related toxicity during sodium nitrite infusion at 266.9 µg/kg/hr [maximal tolerated dose (MTD)] Note that in this group all NO metabolome concentrations returned to baseline levels within 12 hours after completion of sodium nitrite infusion.

Figure 2. Clinical and biochemical data for Subject 8 (Dose Limiting Toxicity; DLT).

This composite graph depicts: A; mean arterial blood pressure and methemoglobin; and NO metabolome concentrations in plasma (B; nitrite, nitrate, S-nitrosothiols), red blood cells (C; nitrite and nitrate) and whole blood (D; nitrite and nitrate) in subject 8 who had a drop of mean arterial blood pressure during sodium nitrite infusion at 533.8 µg/kg/hr and then again with the half-dose infusion (266.9 µg/kg/hr; MTD) despite 6 hours of rest between the infusions. The baseline values of mean arterial blood pressure and methemoglobin levels in this subject were 93 mmHg and 0.7%, respectively. He started sodium nitrite infusion at 533.8 µg/kg/hr. After 8 hours of sodium nitrite infusion, mean arterial blood pressure decreased by 15 mmHg and the infusion was stopped at the 9th hour. After 6 hours of rest, the infusion was re-started at the half dose (266.9 µg/kg/hr). At this time blood pressure and methemoglobin levels, as well as nitrite and nitrate concentrations in plasma all returned to baseline levels. But nitrite in red blood cells and S-nitrosothiols in plasma as well as nitrate in red blood cells and whole blood remained elevated (B–D). Immediately after initiation of the second infusion, nitrite concentration in plasma increased rapidly. However, nitrate concentrations in plasma, red blood cells, and whole blood remained stable. At 2.25 hours the half-dose infusion was stopped because of a significant (this time more than 20 mmHg) decrease in blood pressure; methemoglobin barely increased at that time and nitrite and nitrate concentrations, despite being 2 and 8 times higher than at the beginning of the second infusion, remained well below the highest level during the first infusion (A–D). The subject remained asymptomatic during and after both infusions. All concentrations, except nitrite and nitrate in whole blood, returned to normal levels within 12 hours after stopping the infusion.

Figure 3. Clinical and biochemical data for Subject 11 (Dose Limiting Toxicity; DLT).

This composite graph depicts: A; mean arterial blood pressure and methemoglobin and NO metabolome concentrations in plasma (B; nitrite, nitrate, S-nitrosothiols), red blood cells (C; nitrite and nitrate) and whole blood (D; nitrite and nitrate) in subject 11 who developed significant methemoglobinemia during sodium nitrite infusion at 445.7 µg/kg/hr. Mean arterial blood pressure remained stable during the infusion. The infusion remained uneventful until 2 and 5 minutes after the infusion cessation when methemoglobin level increased above 5% (A). However, it decreased during the next 5 minutes and returned to baseline at 8 hours after stopping sodium nitrite infusion. The subject remained asymptomatic. Within the NO metabolome only nitrite concentrations in plasma and red blood cells returned to baseline values; plasma nitrate, whole blood nitrite and nitrate, and S-nitrosothiols concentrations in plasma remained higher than the initial values until the end of the observation interval.

Figure 4. Clinical and biochemical data for Subject 12 (Dose Limiting Toxicity; DLT).

This composite graph depicts: A; mean arterial blood pressure and methemoglobin and NO metabolome concentrations in plasma (B; nitrite, nitrate, S-nitrosothiols), red blood cells (C; nitrite and nitrate) and whole blood (D; nitrite and nitrate) in subject 12 who developed toxicity (significant drop of blood pressure) during sodium nitrite infusion at 445.7 µg/kg/hr. She was the second subject to have a sodium nitrite infusion at this dose. Three hours after initiation of sodium nitrite infusion, her mean arterial blood pressure decreased by 20 mmHg and the infusion was stopped. At this time her methemoglobin level was 2%, plasma level of nitrite was several times higher than baseline but nitrate remained unchanged. In the red blood cells, nitrite increased but nitrate remained at baseline level. Nitrite in whole blood was also several times higher than baseline and nitrate concentration was unchanged compared with baseline. S-nitrosothiol concentrations in plasma were at 37 nmol/L and well below the peak of 61 nmol/L reached a few hours earlier (A–D). This subject was observed for an additional 12 hours and remained asymptomatic. Among NO metabolome measurements in this subject, only S-nitrosothiols remained high 12 hours after stopping the infusion.

Figure 5. Nitrite pharmacokinetics in plasma and whole blood.

Dose proportionality of nitrite in plasma (left panel) and in whole blood (right panel) was assessed using the area under the concentration-time curves AUC0-last as a function of dose in milligrams. The estimated power coefficient (β1) for plasma and whole blood nitrite was significantly less than 1, indicating nonlinear pharmacokinetics of nitrite. This nonlinearity could be attributed to the increased nitrite clearance at the higher dose compared with the lowest dose, which strongly suggests that nitrite is much more rapidly removed from the body at higher doses.

Figure 6. Time schedule of procedures and blood sampling for subjects participating in the safety, feasibility and pharmacokinetic study of long-term intravenous infusion of sodium nitrite.

MICU; Medical Intensive Care Unit. H&P; history and physical. BP; arterial blood pressure. Mo; a month.