Sanguinate, a pegylated bovine carboxyhemoglobin, was developed by Prolong Pharmaceuticals to avoid the NO scavenging complication of the earlier HBOCs without compromising efficient oxygen delivery. Sanguinate is composed of three functional components: carbon monoxide (CO), bovine Hb, and polyethylene glycol. Surface lysine residues on the purified bovine Hb undergo pegylation with 5,000 molecular weight phosphatidylglycerol-succinimidyl carbonate followed by carboxylation.[13,14] Sanguinate's key difference from its predecessors is its CO-releasing action. The CO is bound to Hb but is released within 2 hours of infusion, with most being released within 30 minutes.
Delivery of exogenous CO serves to counteract NO scavenging by the free hemoglobin. CO delivery not only prevents vasoconstriction but also has anti-inflammatory activity. In animal studies, the peak levels of CO Hb reached 5% and then declined back to baseline within 2 hours. In addition, CO improves the shelf-life of the product because it reduces auto-oxidation of Hb, and little methemoglobin is formed.
The average p50 of Sanguinate is 7 to 16 mm Hg (measured by Hemox Analyzer; TCS Scientific Corporation). This p50 is between that of human RBCs (p50 = 26 mm Hg) and ischemic tissues (p50 <5 mm Hg), and thus it serves to deliver oxygen to ischemic tissue as it travels in the plasma layer between the RBC column and vessel wall. Furthermore, Sanguinate is only 120 kD in size and thus can bypass obstructions that would block the much larger-sized RBCs (about 7 μm in size).
The first Sanguinate study in humans was a randomized phase I single-blinded placebo-controlled study in 24 healthy volunteers to assess safety and pharmacokinetics. Three dose levels (80, 120, and 160 mg/kg) were administered by intravenous infusion to three cohorts of eight patients sequentially enrolled. Six patients in each cohort received Sanguinate and two received normal saline. The researchers found no serious adverse effects with this new HBOC. Mild adverse effects included lethargy, dizziness, and transient hypertension. Of note, these events did not correlate with the dose of Sanguinate received, and all were self-resolved within 72 hours of infusion. The researchers concluded the transient increase in blood pressure was likely caused by oncotic plasma expansion because there were no clinically significant changes.
In addition, a dose-dependent decrease in serum haptoglobin was observed. This finding was as expected with haptoglobin binding to Sanguinate followed by clearance of the complex from the circulation. Importantly, only minute amounts of Sanguinate were detected in the urine (0.87–4.18 μg/mL detected by enzyme-linked immunosorbent assay), and no human Hb was detected in the urine.
In 2016, a phase Ib clinical trial was published that was performed in stable adult sickle cell patients. The study was conducted in four medical centers in Central and South America and enrolled 24 adult patients with sickle cell anemia (homozygotes for Hb SS). The patients were randomized to receive either Sanguinate in low dose (160 mg/kg) or high dose (320 mg/kg) over a 2-hour infusion or 15 mg/kg hydroxyurea. The primary end point was the safety of Sanguinate vs hydroxyurea. Sanguinate was found to be safe in these stable patients with sickle cell anemia. Mild musculoskeletal-related complaints, including arthralgia, were the most common reported adverse events. Similar to the phase I clinical trial, this study also demonstrated a transient increase in mean arterial blood pressures with no clinical signs or symptoms. In addition, the study demonstrated that the T1/2 of Sanguinate was 19.56 hours vs 13.75 hours in the phase I trial of healthy volunteers. It is thought that because of the widespread hemolysis that sickle cell patients experience, their reticuloendothelial system would be overwhelmed and the clearance of Sanguinate by this system is subsequently slowed.
Most recently, a study was published in June 2017 evaluating Sanguinate in patients with a subarachnoid hemorrhage (SAH). Dhar et al studied 12 patients with SAH at risk of delayed cerebral ischemia at three doses of Sanguinate (160, 240, and 320 mg/kg). Cerebral blood flow and the oxygen extraction fraction were assessed by O- positron emission tomography performed at baseline, immediately after Sanguinate infusion, and 24 hours postinfusion. The team reported a 16% rise in regional cerebral blood flow with associated reduction in oxygen extraction fraction in vulnerable regions. But these effects did not persist at the 24-hour evaluation. As with earlier studies, a transient increase in mean arterial pressure (from 115.5 ± 15 mm Hg at baseline to 126.5 ± 13 mm Hg after infusion; P = .002) was appreciated. However, this increase dissipated by 24 hours and was thought likely to be due to volume expansion, as some patients were receiving 500 mL or more. (Of note, Sanguinate is supplied at a concentration of 40 mg/mL in 500-mL bags.)
There have been a limited number of other case reports published on Sanguinate. For example, Holzner et al described a case of 56-year-old female Jehovah's Witness who had end-stage liver disease. She underwent liver transplantation and was administered Sanguinate by infusion during the operation. The team measured cerebral oxygen saturations intraoperatively as a surrogate for cerebral blood flow, and they noted her saturations were increasing after Sanguinate administration even with worsening anemia. As such, they emphasized Sanguinate's possible role in increasing oxygen delivery.
In addition, Brotman et al reported the use of Sanguinate postoperatively in a 77-year-old practicing Jehovah's Witness man. He underwent a cystoprostatectomy with nephrectomy for urothelial carcinoma. The patient's preoperative Hb was 10 g/dL; however, unfortunately this fell to 4.5 g/dL on postoperative day 2. Sanguinate was administered, and the next day, his clinical status significantly improved with no observed complications.
Furthermore, McConachie et al published a report on the use of Sanguinate in two patients. The first was a 65-year-old woman with an acute gastrointestinal bleed who required emergent surgical resection. She received one infusion of Sanguinate and subsequently experienced an increase in blood pressure and troponin levels. Her troponin decreased over the course of 5 days, and she was successfully discharged in stable condition. The second patient was a 67-year-old man with severe sepsis and multiple comorbidities who ultimately developed multiorgan failure and a declining Hb level despite receiving five doses of Sanguinate.
Finally, two other case reports reported successful use of Sanguinate in a 22-year-old woman with thrombotic thrombocytopenic purpura and a 43-year-old woman with postpartum hemorrhage, respectively. Both patients were eventually stabilized with no reported complications.[21,22]
The literature thus far has been very promising for Sanguinate's clinical success. Granted, one should be cautious given the history of failure in the development of artificial oxygen carriers. Our patient's success has made us highly optimistic this product can be a valuable resource, especially with regard to managing acutely anemic Jehovah's Witness patients. While our clinical team had great success with Sanguinate, it is not the only new generation of acellular HBOC with a rising future. A review article by Taguchi et al provides details on several of these products, including OxyVita Hb (Oxy Vita-Zero-Link polymerized Hb), which is in preclinical trials, and HemoAct. HemoAct, developed by Komatsu et al, is a novel HBOC with one Hb molecule in the center surrounded by three to four human serum albumins. As with previous generations of oxygen carriers, clinical trials and meta-analyses will be invaluable to further evaluate these products.
Am J Clin Pathol. 2020;153(3):287-293. © 2020 American Society for Clinical Pathology