Drug repurposing has gained significant interest in recent years due to the high costs associated with de novo drug development; however, comprehensive pharmacological information is needed for the translation of pre-existing drugs across clinical applications. In the present study, we explore the current pharmacological understanding of the orphan drug, hemin, and identify remaining knowledge gaps with regard to hemin repurposing for the treatment of cardiovascular disease. Originally approved by the United States Food and Drug Administration in 1983 for the treatment of porphyria, hemin has attracted significant interest for therapeutic repurposing across a variety of pathophysiological conditions. Yet, the clinical translation of hemin remains limited to porphyria. Understanding hemin\'s pharmacological profile in health and disease strengthens our ability to treat patients effectively, identify therapeutic opportunities or limitations, and predict and prevent adverse side effects. However, requirements for the pre-clinical and clinical characterization of biologics approved under the U.S. FDA\'s Orphan Drug Act in 1983 (such as hemin) differed significantly from current standards, presenting fundamental gaps in our collective understanding of hemin pharmacology as well as knowledge barriers to clinical translation for future applications. Using information extracted from the primary and regulatory literature (including documents submitted to Health Canada in support of hemin\'s approval for the Canadian market in 2018), we present a comprehensive case study of current knowledge related to hemin\'s biopharmaceutical properties, pre-clinical/clinical pharmacokinetics, pharmacodynamics, dosing, and safety, focusing specifically on the drug\'s effects on heme regulation and in the context of acute myocardial infarction.

Heme, iron protoporphyrin IX, is one of life\'s most central molecules. Hence, availability of the enzymatic machinery necessary for its synthesis is crucial for every cell. Consequently, inborn errors of porphyrin metabolism that compromise normal synthesis, namely the family of porphyrias, undermine normal cellular metabolism given that heme has functions in catalytic centers, signal transduction and functional regulation and its synthesis is fully integrated into the center of intermediary metabolism. Very often, diagnosis of porphyrias is difficult and therefore delayed. Therapy can be as complicated. Over the last 50 years, several strategies have been developed: because of its integration with other parts of intermediary metabolism, the infusion of glucose (glucose effect) was one of the first attempts to counterbalance the dysregulation of porphyrin synthesis in porphyrias. Since heme synthesis is impaired, infusional replacement of heme was the next important therapeutic step. Recently, siRNA technology has been introduced in order to downregulate 5-ALA-synthase 1, which contributes to the patho-physiology of these diseases. Moreover, other novel therapies using enzyme protein replacement, mRNA techniques or proteostasis regulators are being developed.

Porphyrias are a group of rare, mostly inherited metabolic disorders of heme biosynthesis. Each type of porphyria results from a specific deficiency of one of the pathway enzymes, causing a characteristic accumulation and excretion of heme precursors. Diagnosis is confirmed by the biochemical detection of these porphyrins and the precursors in urine, feces and blood. Porphyrias can be classified into acute and non-acute forms. The clinical presentation is unspecific and includes acute neurovisceral and/or cutaneous symptoms. The latent phase can evolve into a potentially life-threatening acute crisis, which is often misdiagnosed. The four acute hepatic porphyrias are relevant for anesthesiologists as precipitating factors are commonly found in the perioperative setting. Safe anesthetic management in cases of known porphyria is possible by adherence to current recommendations. The immediate administration of heme arginate as specific treatment for acute attacks is decisive for the outcome.
Porphyrien sind eine Gruppe seltener, meist erblicher Stoffwechselstörungen der Hämbiosynthese. Jede Porphyrie beruht auf einem spezifischen Enzymdefekt und zeigt eine charakteristische Akkumulation und Ausscheidung von Hämvorstufen. Der biochemische Nachweis dieser Porphyrine und der Präkursoren in Urin, Stuhl und Blut ist Grundlage der Diagnosestellung. Man unterscheidet akute von nichtakuten Formen. Das klinische Bild ist unspezifisch und umfasst neuroviszerale und/oder kutane Symptome. Die latente Phase kann in eine potenziell letale akute Krise übergehen, die häufig fehlinterpretiert wird. Für AnästhesistInnen sind aufgrund vieler potenzieller Trigger-Faktoren im perioperativen Umfeld die 4 akuten hepatischen Porphyrien von Bedeutung. Unter Einhaltung aktueller Empfehlungen ist bei bekannter Erkrankung eine sichere Narkoseführung möglich. Bei Auftreten einer Attacke ist die unverzügliche Gabe von Hämarginat als spezifische Therapie entscheidend für das Outcome.

The acute porphyrias are a group of four metabolic defects in which the heme synthesis in the liver is disrupted. They are characterized by massively painful acute attacks, which can be life-threatening if not diagnosed. To raise the awareness for these rare disorders, a heme molecule in cartoon style is introduced, which accurately explains the basic biochemical processes in the body and mediates important information on the acute hepatic porphyrias in a simplified and attractive way. The article is complemented by a case report.
UNASSIGNED: Die akuten Porphyrien sind eine Gruppe von vier Stoffwechseldefekten, bei denen die Synthese von Häm in der Leber gestört ist. Sie äußern sich durch massiv schmerzhafte akute Attacken, die undiagnostiziert lebensbedrohlich werden können. Um das Bewusstsein für diese seltenen Erkrankungen zu erhöhen, wird ein Hämmolekül im Cartoonstil vorgestellt, das die biochemischen Prozesse im Körper veranschaulicht und wichtige Informationen zu den akuten Porphyrien auf einfache und attraktive Weise vermittelt. Der Beitrag wird durch eine Fallbeschreibung vervollständigt.

Objectives: This study aimed to evaluate the efficacy of long-term weekly prophylactic heme arginate (HA) infusions in reducing attack frequency and severity in female AIP patients. Methods: We report the results of five female AIP patients with frequent recurrent attacks (>9/year) before and after institution of weekly prophylaxis with heme arginate (3 mg/kg body weight). All five cases had confirmed disease-associated mutations in the porphobilinogen deaminase gene, and all had received genetic and clinical counseling about AIP. Results: In the five included patients, average annual attack rate (AAR) in the year prior to HA prophylaxis was 11.82 (range 9.03-17.06), and average total HA usage was 32.60 doses (range: 13.71-53.13). After 2.58-14.64 years of HA prophylaxis, average AAR was reduced to 2.23 (range 0.00-5.58), and attack severity (i.e., doses required per attack) was reduced from 2.81 to 1.39 doses/attack. Liver and renal function remained stable during weekly administration of HA prophylaxis. The most common complications were port-A catheter-related events. No other complications or safety concerns occurred with long-term use of HA prophylaxis. Conclusion: Our study demonstrated women with AIP receiving weekly prophylactic HA infusions resulted in fewer episodes that required acute HA treatment while maintaining stable renal and liver function. Weekly prophylactic HA infusions effectively prevent frequent porphyric attacks and reduce attack severity.

A 26-year-old female presented to the emergency department due to abdominal pain in spite of painkillers. After extensive clinical diagnostics, no specific cause could be found. The further course was aggravated by a seizure due to hyponatremia. The combination of abdominal and neurological symptoms as well as darkening of the urine led to the diagnosis of porphyria. Drugs that were known to be triggers were avoided and treatment with heme arginate and glucose was started. In addition, treatment of the delirium and infection led to a complete remission of symptoms.
UNASSIGNED: Eine 26-jährige Patientin wurde mit stärksten abdominellen Schmerzen aufgenommen, die trotz Schmerztherapie progredient waren. Nach umfangreicher Diagnostik blieb die Genese unklar. Der Verlauf wurde durch einen Krampfanfall aufgrund einer massiven Hyponatriämie aggraviert. Die Kombination aus abdominellen und neurologischen Symptomen sowie ein Nachdunkeln des Urins führten schließlich zur Diagnose einer akuten hepatischen Porphyrie. Die Meidung von Triggerfaktoren, eine Therapie mit Hämarginat und Glukose sowie die Therapie des begleitenden Infekts und Delirs führten zu einer kompletten Remission.

Acute intermittent porphyria (AIP) is a rare metabolic disease caused by mutations within the hydroxymethylbilane synthase gene. Previous studies have reported increased levels of plasma total homocysteine (tHcy) in symptomatic AIP patients. In this study, we present long-term data for tHcy and related parameters for an AIP patient cohort (n = 37) in different clinical disease-states. In total, 25 patients (68%) presented with hyperhomocysteinemia (HHcy; tHcy > 15 μmol/L) during the observation period. HHcy was more frequent in AIP patients with recurrent disease receiving heme arginate, than in nonrecurrent (median tHcy: 21.6 μmol/L; range: 10-129 vs median tHcy: 14.5 μmol/L; range 6-77). Long-term serial analyses showed a high within-person tHcy variation, especially among the recurrent patients (coefficient of variation: 16.4%-78.8%). HHcy was frequently associated with low blood concentrations of pyridoxal-5\'-phosphate and folate, while cobalamin concentration and the allele distribution of the methylene-tetrahydrofolate-reductase gene were normal. Strikingly, 6 out of the 9 recurrent patients who were later included in a regime of givosiran, a small-interfering RNA that effectively reduced recurrent attacks, showed further increased tHcy (median tHcy in 9 patients: 105 μmol/L; range 16-212). Screening of amino acids in plasma by liquid-chromatography showed co-increased levels of methionine (median 71 μmol/L; range 23-616; normal <40), suggestive of acquired deficiency of cystathionine-β-synthase. The kynunerine/tryptophan ratio in plasma was, however, normal, indicating a regular metabolism of tryptophan by heme-dependent enzymes. In conclusion, even if HHcy was observed in AIP patients receiving heme arginate, givosiran induced an aggravation of the dysregulation, causing a co-increase of tHcy and methionine resembling classic homocystinuria.

In cases of recurrent attacks of acute porphyria during pregnancy, prophylactic administration of heme arginate should be considered. Clinical and biochemical monitoring of the disease and a close collaboration with a porphyria center are crucial.

A small proportion of patients with acute intermittent porphyria (AIP) suffer from recurrent porphyric attacks, with a severely diminished quality of life. In this retrospective case-control study, the burden of disease is quantified and compared among three AIP patient subgroups: cases with recurrent attacks, cases with one or occasional attacks and asymptomatic carriers.
Data from patient records and questionnaires were collected in patients between 1960 and 2016 at the Erasmus Medical Center, Rotterdam, the Netherlands. We collected symptoms related to porphyria, porphyria related complications, attack frequency, hospitalisation frequency, hospitalisation days related to acute porphyric attacks, frequency of heme infusions and medical healthcare costs based on hospitalisations and heme therapy.
In total 11 recurrent AIP cases, 24 symptomatic AIP cases and 53 AIP carriers as controls were included. All recurrent patients reported porphyria related symptoms, such as pain, neurological and/or psychiatric disorders, and nearly all developed complications, such as hypertension and chronic kidney disease. In the recurrent cases group, the median lifelong number of hospitalisation days related to porphyric attacks was 82 days per patient (range 10-374), and they spent a median of 346 days (range 34-945) at a day-care facility for prophylactic heme therapy; total follow-up time was 243 person-years (PYRS). In the symptomatic non-recurrent group the median lifelong number of hospitalisation days related to porphyric attacks was 7 days per patient (range 1-78), total follow-up time was 528 PYRS. The calculated total medical healthcare cost for recurrent cases group was €5.8 million versus €0.3 million for the symptomatic cases group.

Ischemia reperfusion injury (IRI) contributes to partial flap and solid organ transplant failure. Heme-oxygenase 1 (HO-1) is an inducible, cytoprotective enzyme which protects against IRI in solid organ transplant models. Heme arginate (HA), a HO-1 inducer, is a promising, translatable, preconditioning agent. This study investigated the effects of preconditioning with HA on the clinical outcome of a myocutaneous IRI model. Forty male Lewis rats were randomized to intravenously receive 1) Control-NaCl, 2) HA, 3) HA and tin mesoporphyrin (SnMP), a HO-1 inhibitor; and 4) SnMP alone. Twenty-four hours later, an in situ transverse rectus abdominis myocutaneous flap was performed under isoflurane anesthesia. Viability of flaps was measured clinically and by laser-Doppler perfusion scanning. In vitro work on human epidermal keratinocytes (HEKa) assessed the effects of HA, SnMP, and the iron chelator desferrioxamine on 1) cytotoxicity, 2) intracellular reactive oxygen species (ROS) concentration, and 3) ROS-mediated DNA damage. In contrast to our hypothesis, HA preconditioning produced over 30% more flap necrosis at 48 h compared with controls (P = 0.02). HA-containing treatments produced significantly worse flap perfusion at all postoperative time points. In vitro work showed that HA is cytotoxic to keratinocytes. This cytotoxicity was independent of HO-1 and was mediated by the generation of ROS by free heme. In contrast to solid organ data, pharmacological preconditioning with HA significantly worsened clinical outcome, thus indicating that this is not a viable approach in free flap research.