Blood product use for radiological/nuclear trauma: product development and US regulatory considerations

Blood products are likely to be critical components of the medical response to nuclear detonation, as the hematopoietic subsyndrome of acute radiation syndrome (H-ARS) includes depletion of platelets and red blood cells that can lead to lethal hemorrhage and anemia. There is, however, only limited clinical information on the use of blood products to treat H-ARS. As currently configured, the US blood supply cannot meet the predicted surge in blood product demand that is likely to occur short-term and possibly long-term in the event of a large nuclear detonation. As part of the Administration for Strategic Preparedness and Response within the US Department of Health and Human Services, the Biomedical Advanced Research and Development Authority (BARDA) is addressing this preparedness gap by supporting the development of novel blood products and devices with characteristics that improve blood product storage and use in austere operational environments. The US Food and Drug Administration's Center for Drug Evaluation and Research (CDER) recently issued draft guidance on the development of drugs and biologics regulated by CDER to prevent or treat Acute Radiation Syndrome under the provisions of the "Animal Rule." The commentary provided here discusses the unique regulatory scheme for transfusion components and blood products regulated as biological drugs by Center for Biologics Evaluation and Research, including the ambiguity surrounding the evidentiary requirements for their approval for H-ARS, and whether, under certain circumstances, a specific H-ARS indication is necessary if relevant commercial indications are approved.

Radiation-induced multi-organ injury

PURPOSE

Natural history studies have been informative in dissecting radiation injury, isolating its effects, and compartmentalizing injury based on the extent of exposure and the elapsed time post-irradiation. Although radiation injury models are useful for investigating the mechanism of action in isolated subsyndromes and development of medical countermeasures (MCMs), it is clear that ionizing radiation exposure leads to multi-organ injury (MOI).

METHODS

The Radiation and Nuclear Countermeasures Program within the National Institute of Allergy and Infectious Diseases partnered with the Biomedical Advanced Research and Development Authority to convene a virtual two-day meeting titled 'Radiation-Induced Multi-Organ Injury' on June 7-8, 2022. Invited subject matter experts presented their research findings in MOI, including study of mechanisms and possible MCMs to address complex radiation-induced injuries.

RESULTS

This workshop report summarizes key information from each presentation and discussion by the speakers and audience participants.

CONCLUSIONS

Understanding the mechanisms that lead to radiation-induced MOI is critical to advancing candidate MCMs that could mitigate the injury and reduce associated morbidity and mortality. The observation that some of these mechanisms associated with MOI include systemic injuries, such as inflammation and vascular damage, suggests that MCMs that address systemic pathways could be effective against multiple organ systems.

Animal Care in Radiation Medical Countermeasures Studies

Animal models are necessary to demonstrate the efficacy of medical countermeasures (MCM) to mitigate/treat acute radiation syndrome and the delayed effects of acute radiation exposure and develop biodosimetry signatures for use in triage and to guide medical management. The use of animal models in radiation research allows for the simulation of the biological effects of exposure in humans. Robust and well-controlled animal studies provide a platform to address basic mechanistic and safety questions that cannot be conducted in humans. The U.S. Department of Health and Human Services has tasked the National Institute of Allergy and Infectious Diseases (NIAID) with identifying and funding early- through advanced-stage MCM development for radiation-induced injuries; and advancement of biodosimetry platforms and exploration of biomarkers for triage, definitive dose, and predictive purposes. Some of these NIAID-funded projects may transition to the Biomedical Advanced Research and Development Authority (BARDA), a component of the Office of the Assistant Secretary for Preparedness and Response in the U.S. Department of Health and Human Services, which is tasked with the advanced development of MCMs to include pharmacokinetic, exposure, and safety assessments in humans. Guided by the U.S. Food and Drug Administration's (FDA) Animal Rule, both NIAID and BARDA work closely with researchers to advance product and device development, setting them on a course for eventual licensure/approval/clearance of their approaches by the FDA. In August 2020, NIAID partnered with BARDA to conduct a workshop to discuss currently accepted animal care protocols and examine aspects of animal models that can influence outcomes of studies to explore MCM efficacy for potential harmonization. This report provides an overview of the two-day workshop, which includes a series of special topic presentations followed by panel discussions with subject-matter experts from academia, industry partners, and select governmental agencies.

Balancing potential risks and benefits of hemoglobin-based oxygen carriers

Hemoglobin-based oxygen carriers (HBOCs) are thought to have an adverse risk:benefit profile when compared to that of transfusing stored red blood cells (RBCs). However, there are clinical circumstances when RBC transfusion is not an option (e.g., patient refusal, unavailability owing to issues of compatibility or remote location). For these circumstances assessment of the risks of an HBOC should be compared to the risks of untransfused acute anemia. In this article we compare the risk of allowing a patient with severe anemia to have a further small decrease in hemoglobin (Hb) concentration to the risk of infusing an HBOC. We conclude that at Hb concentrations less than 6 g/dL, the risk of a further decrease in Hb concentration greatly exceeds the risk of HBOC infusion. Thus, we suggest that there may be a place for use of HBOCs when RBC transfusion is not an option.

Effects of cerebral TRH on intestinal water transport: role of vagal, muscarinic, and VIP pathways

Thyrotropin-releasing hormone (TRH) is a central nervous system (CNS) transmitter that stimulates various gastrointestinal secretory and motor processes by increasing vagal outflow. In this study, the CNS effects of TRH on ileal and jejunal water transport were examined in awake rats and dogs, respectively. Cerebral but not intravenous TRH (0.1-5.0 nmol/kg) significantly (P < 0.01) reversed net water absorption from approximately 30 microliters.cm-1.h-1 in rats and 300 microliters.cm-1.h-1 in dogs toward net water secretion of 60 and 600 microliters.cm-1.h-1, respectively. Truncal vagotomy and ganglionic blockade with chlorisondamine completely abolished this stimulatory effect of cerebral TRH, whereas adrenalectomy, hypophysectomy, noradrenergic and opiate blockade, and inhibition of prostaglandin and nitric oxide synthesis did not. Atropine methylnitrate significantly (P < 0.05) attenuated the stimulatory response produced by TRH by approximately 30%. Intravenous infusion of the vasoactive intestinal peptide (VIP) receptor antagonist, [4Cl-D-Phe6, Leu17]VIP (0.05-5.0 mumol.kg-1.h-1), significantly (P < 0.01) inhibited the stimulatory response of TRH by approximately 60%. Pretreatment of the animals with both atropine and the VIP antagonist completely abolished ileal and jejunal water secretion stimulated by cerebral TRH. These results indicate that 1) TRH acts within the CNS to stimulate net ileal and jejunal water secretion in rats and dogs, respectively; 2) these actions are mediated by vagal pathways; and 3) stimulation of intestinal secretion by cerebral TRH is primarily mediated by a VIP-sensitive mechanism and, in part, by a muscarinic mechanism.

Characterization of an antisense Inr element in the eIF-2 alpha gene

We recently discovered an opposing initiator promoter (Inr) downstream of the sense promoter region of the eIF-2 alpha gene (Silverman, T., Noguchi, M., and Safer, B. (1992) J. Biol. Chem. 267, 9738-9742). By reverse transcriptase/polymerase chain reaction analysis of G0 and activated (G1) T-lymphocyte RNAs, overlapping sense and antisense transcripts are now identified. Sense transcription of the eIF-2 alpha gene proceeds from left to right to generate alpha-mRNA; antisense transcription proceeds from right to left to generate RNA, having a sequence complementary to eIF-2 alpha mRNA. Upstream indicates a position 5' relative to the transcription start site. Using DNase I footprint analysis and EMSA, we have found a potential cis-regulatory sequence immediately upstream of the Inr which binds a 43-kDa protein. In addition to conferring protection against DNase I (+457 to +474), the factor also generates hypersensitive sites directly over the Inr (+447 to +457). Insertion of the Inr footprint region into a luciferase reporter gene construct increases expression 150-fold. While mutation of the Inr conserved sequence decreases luciferase activity by 50%, mutation of the 43-kDa factor binding site inhibits luciferase activity by 20%. Sense orientation of the Inr footprint region decreases activity by 80%. The 43-kDa Inr-associated binding protein may be involved in allowing access of RNA polymerase II transcription complexes ot the initiation site of this TATA-less gene. A model for the regulation of eIF-2 alpha expression involving the rapid degradation of dsRNA generated by the relative activities of the two overlapping and opposing promoters is proposed.

Role of sequences within the first intron in the regulation of expression of eukaryotic initiation factor 2 alpha

Resting human peripheral blood T cells synthesize proteins at very low rates and contain very low levels of eukaryotic initiation factor (eIF) 2 alpha mRNA. During mitogenic activation, the level of eIF-2 alpha mRNA increases at least 50-fold, an effect thought to be due primarily to intranuclear stabilization of the primary transcript (Cohen, R. B., Boal, T. R., and Safer, B. (1990) EMBO J. 9, 3831-3837). Analysis of sequences within the first intron revealed a region with homology to the "initiator" (Inr) sequence first described by Smale and Baltimore (Smale, S. T., and Baltimore, D. (1989) Cell 57, 103-113). This Inr element is positioned 450 bases downstream of the eIF-2 alpha promoter and is oriented to generate an overlapping antisense transcript. Deletion or mutation of the Inr element results in a reproducible 5-8-fold increase in the activity of an eIF-2 alpha promoter-driven CAT reporter gene and a corresponding 2.5-fold decrease in activity of an antisense driven luciferase reporter gene in vivo in 293 cells. In vitro transcription analysis also reveals antisense transcripts which depend on an intact Inr element and whose 5' ends map to sequences surrounding the Inr consensus sequence. A potential role for double-stranded RNA generated by these overlapping divergent transcription units in the regulation of eIF-2 alpha gene expression in T cells is suggested.

Identification and characterization of a novel transcription factor participating in the expression of eukaryotic initiation factor 2 alpha

We have recently cloned and characterized the promoter region of the gene encoding eukaryotic initiation factor 2 alpha (eIF-2 alpha) to identify regulatory elements of this housekeeping gene. We compared the location of DNase I-hypersensitive (HS) sites with the distribution of protein-binding sites as revealed by footprint analysis. The eIF-2 alpha promoter contains four upstream DNase I-HS sites extending from -650 to -40 base pairs and a fifth downstream site near the first intron-exon junction. In vitro DNase I footprint analysis shows eight distinct DNA-protein interactions organized into clusters that correspond well with the distribution of the five HS sites. None of the protected regions, however, shares obvious sequence homology with the binding sites of known regulatory factors. To initiate our analysis of factors required for eIF-2 alpha expression, selected a CAP-proximal element shown by in vivo methylation protection analysis to bind a potential regulatory factor. A striking feature of this element is its palindrome sequences and eight-base pair direct repeats. We have purified to near homogeneity a 66-68-kDa protein that binds to this region and have designated it alpha-PAL. The alpha-PAL-binding site extends from -74 to -10. By methylation protection analysis and mobility shift assay, the alpha-PAL-binding site is shown to be two adjacent sites, one with high and one with lower affinity, which bind alpha-PAL in a noncooperative manner. When the high affinity binding site is cloned upstream of the adenovirus 2 core promoter, in vitro transcription is stimulated 2-3-fold. When linked to a CAT reporter gene, activity of the eIF-2 alpha promoter shows an approximate 2-fold dependence on the alpha-PAL element.

Postradiation soft tissue sarcomas. An analysis of 53 cases

The clinicopathologic features of 53 cases of postradiation soft tissue sarcoma (PRS) were correlated with the physical characteristics of the administered radiation. All but three patients received radiation for malignant processes. Of the secondary sarcomas, malignant fibrous histiocytoma (MFH) accounted for 36 cases (68%), followed by seven extraskeletal osteosarcomas (13%), six fibrosarcomas (11%), two malignant Schwannomas (4%), one extraskeletal chondrosarcoma, and one angiosarcoma. The sex incidence, age of the patient at time of diagnosis, and location of the PRS correlated only with the clinical characteristics of the initial treated condition. The latency period (mean 10 years) showed an indefinite relationship to patient survival but no definite relationship to the patient's age at the time of the initial radiation. There was no difference between patients treated with megavoltage radiation (39 patients) and with orthovoltage radiation (seven patients) in the type of sarcoma, location, or survival, although the orthovoltage group received a lower mean radiation dose (3880 rads) than the megavoltage group (4446 rads). Megavoltage radiation, however, produced deeper tissue radiation changes and was associated with a shorter latency period. Most PRS were poorly differentiated, produced abundant collagen, and had a dismal prognosis.

Postradiation soft tissue sarcomas. An analysis of 53 cases

The clinicopathologic features of 53 cases of postradiation soft tissue sarcoma (PRS) were correlated with the physical characteristics of the administered radiation. All but three patients received radiation for malignant processes. Of the secondary sarcomas, malignant fibrous histiocytoma (MFH) accounted for 36 cases (68%), followed by seven extraskeletal osteosarcomas (13%), six fibrosarcomas (11%), two malignant Schwannomas (4%), one extraskeletal chondrosarcoma, and one angiosarcoma. The sex incidence, age of the patient at time of diagnosis, and location of the PRS correlated only with the clinical characteristics of the initial treated condition. The latency period (mean 10 years) showed an indefinite relationship to patient survival but no definite relationship to the patient's age at the time of the initial radiation. There was no difference between patients treated with megavoltage radiation (39 patients) and with orthovoltage radiation (seven patients) in the type of sarcoma, location, or survival, although the orthovoltage group received a lower mean radiation dose (3880 rads) than the megavoltage group (4446 rads). Megavoltage radiation, however, produced deeper tissue radiation changes and was associated with a shorter latency period. Most PRS were poorly differentiated, produced abundant collagen, and had a dismal prognosis.

Fibrolipomatous hamartoma of nerve. A clinicopathologic analysis of 26 cases

Nineteen cases of fibrolipomatous hamartoma of nerve without macrodactyly and seven cases with macrodactyly are discussed. Twenty-five involved the hand, wrist, palm, and finger, and one case involved the foot. Nineteen patients had isolated fibrofatty enlargement of nerve, while seven had macrodactyly in addition to the peripheral nerve changes. Involved nerves included the median nerve, ulnar nerve, an unidentified nerve near the elbow, and a nerve on the dorsum of the foot. Four of nine patients with neurologic symptoms of pain or paresthesias had physical findings compatible with compression neuropathy, and two others were described as having carpal tunnel syndrome. Most patients had been aware of a mass for several years. Microscopically, the lesion was characterized by fibrofatty enlargement of nerve with massive epineural and perineural fibrosis. In two of the cases with macrodactyly, the fibrofatty enlargement of the nerve was associated with overgrowth of bone and the surrounding subcutaneous tissues. In one case, the perineural fibrosis was associated with metaplastic bone. The histogenesis of fibrofatty overgrowth of nerve has been disputed. Mature fat cells have been described within the normal nerve sheath, and it is thought that proliferation of these cells leads to the fatty enlargement of the nerve and its coverings. The relationship of these neural changes to the development of macrodactyly remains controversial. Follow-up in 18 patients (69%) reveals a benign course following biopsy, limited excision, or division of the flexor retinaculum in the wrist.

Hepatic failure secondary to indicine N-oxide toxicity. A Pediatric Oncology Group Study

Indicine N-oxide, a pyrrolizidine alkaloid, was given to a five-year-old boy with refractory acute myelocytic leukemia. Three days after receiving the drug the patient developed signs and symptoms of acute hepatic failure. The patient died nine days after receiving the drug and an autopsy showed massive hepatic necrosis. The acute hepatic failure observed in this patient may have been secondary to indicine N-oxide toxicity.

Temporal arteritis presenting with jaw claudication and normal erythrocyte sedimentation rate

We have described a case of sudden blindness of the right eye in an 81-year-old white woman with a one-month history of increasingly severe jaw claudication and a normal Westergren sedimentation rate. Isolated jaw claudication in the elderly is of diagnostic importance, and the need for temporal artery biopsy and rapid institution of high-dose steroid therapy to prevent blindness is emphasized.