Hyperhomocysteinemia in patients with acute porphyrias: a possible effect of ALAS1 modulation by siRNAm therapy and its control by vitamin supplementation

Elevated homocysteine is negatively correlated with plasma cystathionine β-synthase activity in givosiran-treated patients

Givosiran is a subcutaneously administered, liver-targeted RNA interference (RNAi) therapeutic that has been approved for treating acute hepatic porphyria (AHP). Elevation in plasma homocysteine (hyperhomocysteinemia) has been reported in AHP patients, and treatment with givosiran has been reported to further increase homocysteine levels in some patients. The mechanism of homocysteine elevation during givosiran treatment is unknown, but has been hypothesized to be mediated by a reduction in activity of cystathionine β-synthase (CBS), which uses homocysteine as a substrate. A liquid chromatography-tandem mass spectrometry-based assay was adapted to measure circulating CBS activity. Using plasma collected from the Phase III ENVISION study, CBS activity was measured to directly evaluate whether it is associated with elevated homocysteine levels in givosiran-treated patients. CBS activity was reduced following givosiran treatment and both homocysteine and methionine levels were inversely correlated with CBS activity. Following administration of a supplement containing vitamin B6, a cofactor for CBS, in four patients during the trial, plasma CBS activity was found to increase, mirroring a corresponding decrease in homocysteine levels. These results support the hypothesis that elevated homocysteine levels following givosiran treatment result from a reduction of CBS activity and that vitamin B6 supplementation lowers homocysteine levels by increasing CBS activity.

Preventing hyperhomocysteinemia using vitamin B6 supplementation in Givosiran-treated acute intermittent porphyria: Highlights from a case report and brief literature review

Acute hepatic porphyrias are inherited metabolic disorders of heme biosynthesis characterized by the accumulation of toxic intermediate metabolites responsible for disabling acute neurovisceral attacks. Givosiran is a newly approved siRNA-based treatment of acute hepatic porphyria targeting the first and rate-limiting δ-aminolevulinic acid synthase 1 (ALAS1) enzyme of heme biosynthetic pathway. We described a 72-year old patient who presented with severe inaugural neurological form of acute intermittent porphyria evolving for several years which made her eligible for givosiran administration. On initiation of treatment, the patient developed a major hyperhomocysteinemia (>400 μmol/L) which necessitated to discontinue the siRNA-based therapy. A thorough metabolic analysis in the patient suggests that hyperhomocysteinemia could be attributed to a functional deficiency of cystathionine β-synthase (CBS) enzyme induced by givosiran. Long-term treatment with vitamin B6, a cofactor of CBS, allowed to normalize homocysteinemia while givosiran treatment was maintained. We review the recently published cases of hyperhomocysteinemia in acute hepatic porphyria and its exacerbation under givosiran therapy. We also discuss the benefits of vitamin B6 supplementation in the light of hypothetic pathophysiological mechanisms responsible for hyperhomocysteinemia in these patients. Our results confirmed the importance of monitoring homocysteine metabolism and vitamin status in patients with acute intermittent porphyria in order to improve management by appropriate vitamin supplementation during givosiran treatment.

Long-term management and treatment of acute intermittent porphyria with recurring attacks using pharmacological prophylaxis

BACKGROUND

There is no definitive guidance on whether patients with acute intermittent porphyria (AIP) with recurrent attacks need pharmacological prophylactic treatment.

METHODS

The management strategies for patients with frequent (defined as ≥4 annualized attack rate (AAR) and less frequent attacks (<4 AAR), including treatment for acute attacks and duration of prophylaxis (weekly heme arginate 3 mg/kg body weight and/or investigational drug, givosiran), were summarized. The AAR for the following periods were presented: the first 2 years after diagnosis, before/after prophylaxis, and the most recent 2 years.

RESULTS

A total of 29 patients with AIP were included, 19 (34.5%) had <4 AAR and 10 (65.6%) had ≥4 AAR in the first 2 years after diagnosis. All patients experienced reduced attacks during the treatment course, 23 (79.3%) were attack-free during the most recent 2 years. Among the 9 patients who received prophylaxis (7 heme arginate; 1 givosiran, 1 heme arginate followed by givosiran), 5 (55.6%) were attack-free in the most recent 2-year period and prophylaxis was discontinued because there had been no attacks for >1 year. For patients without prophylaxis (n = 20), 18 (90.0%) were attack-free in the most recent 2-year period and 15 (75.0%) experienced attacks only in the first 2 years after diagnosis.

CONCLUSIONS

Prophylaxis could be considered for patients with AIP with ≥4 biochemically confirmed attacks/year after routine treatment of 1-2 years, during which the severity and frequency of attacks should be closely monitored to determine the necessity of pharmacologic prophylaxis. More studies are needed to reach a consensus on the use of pharmacological prophylaxis and treatment of AIP.

RNA interference therapy in acute hepatic porphyrias

The acute hepatic porphyrias (AHPs) are inherited disorders of heme biosynthesis characterized by life-threatening acute neurovisceral attacks precipitated by factors that upregulate hepatic 5-aminolevulinic acid synthase 1 (ALAS1) activity. Induction of hepatic ALAS1 leads to the accumulation of porphyrin precursors, in particular 5-aminolevulinic acid (ALA), which is thought to be the neurotoxic mediator leading to acute attack symptoms such as severe abdominal pain and autonomic dysfunction. Patients may also develop debilitating chronic symptoms and long-term medical complications, including kidney disease and an increased risk of hepatocellular carcinoma. Exogenous heme is the historical treatment for attacks and exerts its therapeutic effect by inhibiting hepatic ALAS1 activity. The pathophysiology of acute attacks provided the rationale to develop an RNA interference therapeutic that suppresses hepatic ALAS1 expression. Givosiran is a subcutaneously administered N-acetylgalactosamine-conjugated small interfering RNA against ALAS1 that is taken up nearly exclusively by hepatocytes via the asialoglycoprotein receptor. Clinical trials established that the continuous suppression of hepatic ALAS1 mRNA via monthly givosiran administration effectively reduced urinary ALA and porphobilinogen levels and acute attack rates and improved quality of life. Common side effects include injection site reactions and increases in liver enzymes and creatinine. Givosiran was approved by the US Food and Drug Administration and European Medicines Agency in 2019 and 2020, respectively, for the treatment of patients with AHP. Although givosiran has the potential to decrease the risk of chronic complications, long-term data on the safety and effects of sustained ALAS1 suppression in patients with AHP are lacking.

Efficacy and safety of givosiran for acute hepatic porphyria: Final results of the randomized phase III ENVISION trial

BACKGROUND & AIMS

Acute hepatic porphyria (AHP) is caused by defects in hepatic heme biosynthesis, leading to disabling acute neurovisceral attacks and chronic symptoms. In ENVISION (NCT03338816), givosiran treatment for 6 months reduced attacks and other disease manifestations compared with placebo. Herein, we report data from the 36-month final analysis of ENVISION.

METHODS

Ninety-four patients with AHP (age ≥12 years) and recurrent attacks were randomized 1:1 to monthly double-blind subcutaneous givosiran 2.5 mg/kg (n = 48) or placebo (n = 46) for 6 months. In the open-label extension (OLE) period, 93 patients received givosiran 2.5 or 1.25 mg/kg for 6 months or more before transitioning to 2.5 mg/kg. Endpoints were exploratory unless otherwise noted.

RESULTS

During givosiran treatment, the median annualized attack rate (AAR) was 0.4. Through Month 36, annualized days of hemin use remained low in the continuous givosiran group (median, 0.0 to 0.4) and decreased in the placebo crossover group (16.2 to 0.4). At end of OLE, in the continuous givosiran and placebo crossover groups, 86% and 92%, respectively, had 0 attacks. AAR was lower than historical AAR in 98% and 100%, respectively (post hoc analysis), and there were 0 days of hemin use in 88% and 90%, respectively. The 12-item short-form health survey physical and mental component summary scores increased by 8.6 and 8.1, respectively (continuous givosiran) and 9.4 and 3.2, respectively (placebo crossover). EQ-5D health-related questionnaire scores increased by 18.9 (continuous givosiran) and 9.9 (placebo crossover). Lower urinary delta-aminolevulinic acid and porphobilinogen levels were sustained. Safety findings demonstrated a continued positive risk/benefit profile for givosiran.

CONCLUSIONS

Long-term monthly givosiran treatment provides sustained and continued improvement in clinical manifestations of AHP.

CLINICALTRIALS

GOV IDENTIFIER

NCT03338816.

EUDRACT NUMBER

2017-002432-17.

IMPACT AND IMPLICATIONS

Acute hepatic porphyria (AHP) is a group of rare, chronic, multisystem disorders associated with overproduction and accumulation of neurotoxic heme intermediates (delta-aminolevulinic acid and porphobilinogen), sometimes resulting in recurrent acute attacks and long-term complications. Givosiran, a small-interfering RNA that prevents accumulation of delta-aminolevulinic acid and porphobilinogen, is approved for the treatment of AHP. These final 36-month results of ENVISION, a phase III study of givosiran in patients with AHP and recurrent attacks, show that long-term monthly treatment with givosiran leads to continuous and sustained reductions in annualized attack rate and use of hemin over time, as well as improved quality of life, with an acceptable safety profile. These results are important for physicians, patients, families, and caregivers who are grappling with this debilitating and potentially life-threatening disease with few effective and tolerable treatment options.

Hyperhomocysteinemia in acute hepatic porphyria (AHP) and implications for treatment with givosiran

INTRODUCTION

Homocysteine is a sulfur-containing amino acid formed in the intermediary metabolism of methionine. Amino acid metabolism and heme biosynthesis pathways are complexly intertwined. Plasma homocysteine elevation, hyperhomocysteinemia (HHcy), has been reported in patients with acute hepatic porphyria (AHP), a family of rare genetic disorders caused by defects in hepatic heme biosynthesis.

AREAS COVERED

This article summarizes published case series in which givosiran, a subcutaneously administered small interfering RNA approved for AHP treatment, appeared to exacerbate dysregulated homocysteine metabolism in patients with AHP. A comprehensive exploratory analysis of ENVISION trial data demonstrated that on a population level, givosiran increased homocysteine but with wide interpatient variations, and there is no proof of correlations between HHcy and changes in efficacy or safety of givosiran.

EXPERT OPINION

The strong correlation and co-increase of homocysteine and methionine suggest that HHcy associated with givosiran is likely attributable to the impaired trans-sulfuration pathway catalyzed by cystathionine β-synthase, which uses vitamin B6 as a cofactor. Data-based consensus supports monitoring total plasma homocysteine and vitamin B6, B12, and folate levels before and during givosiran treatment; supplementing with pyridoxine/vitamin B6 in patients with homocysteine levels >100 μmol/L; and involving patients with homocysteine levels >30 μmol/L in decisions to supplement.

Iron Metabolism in the Disorders of Heme Biosynthesis

Given its remarkable property to easily switch between different oxidative states, iron is essential in countless cellular functions which involve redox reactions. At the same time, uncontrolled interactions between iron and its surrounding milieu may be damaging to cells and tissues. Heme—the iron-chelated form of protoporphyrin IX—is a macrocyclic tetrapyrrole and a coordination complex for diatomic gases, accurately engineered by evolution to exploit the catalytic, oxygen-binding, and oxidoreductive properties of iron while minimizing its damaging effects on tissues. The majority of the body production of heme is ultimately incorporated into hemoglobin within mature erythrocytes; thus, regulation of heme biosynthesis by iron is central in erythropoiesis. Additionally, heme is a cofactor in several metabolic pathways, which can be modulated by iron-dependent signals as well. Impairment in some steps of the pathway of heme biosynthesis is the main pathogenetic mechanism of two groups of diseases collectively known as porphyrias and congenital sideroblastic anemias. In porphyrias, according to the specific enzyme involved, heme precursors accumulate up to the enzyme stop in disease-specific patterns and organs. Therefore, different porphyrias manifest themselves under strikingly different clinical pictures. In congenital sideroblastic anemias, instead, an altered utilization of mitochondrial iron by erythroid precursors leads to mitochondrial iron overload and an accumulation of ring sideroblasts in the bone marrow. In line with the complexity of the processes involved, the role of iron in these conditions is then multifarious. This review aims to summarise the most important lines of evidence concerning the interplay between iron and heme metabolism, as well as the clinical and experimental aspects of the role of iron in inherited conditions of altered heme biosynthesis.

Therapy Follows Diagnosis: Old and New Approaches for the Treatment of Acute Porphyrias, What We Know and What We Should Know

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.

Endothelial Dysfunction in Acute Hepatic Porphyrias

Background Acute hepatic porphyrias (AHPs) are a group of rare diseases caused by dysfunctions in the pathway of heme biosynthesis. Although acute neurovisceral attacks are the most dramatic manifestations, patients are at risk of developing long-term complications, several of which are of a vascular nature. The accumulation of non-porphyrin heme precursors is deemed to cause most clinical symptoms. Aim We measured the serum levels of endothelin-1 (ET-1) and nitric oxide (NO) to assess the presence of endothelial dysfunction (ED) in patients with AHPs. Forty-six patients were classified, according to their clinical phenotype, as symptomatic (AP-SP), asymptomatic with biochemical alterations (AP-BA), and asymptomatic without biochemical alterations (AP-AC). Results Even excluding those under hemin treatment, AP-SP patients had the lowest NO and highest ET-1 levels, whereas no significant differences were found between AP-BA and AP-AC patients. AP-SP patients had significantly more often abnormal levels of ED markers. Patients with the highest heme precursor urinary levels had the greatest alterations in ED markers, although no significant correlation was detected. Conclusions ED is more closely related to the clinical phenotype of AHPs than to their classical biochemical alterations. Some still undefined disease modifiers may possibly determine the clinical picture of AHPs through an effect on endothelial functions.

Challenges in diagnosis and management of acute hepatic porphyrias: from an uncommon pediatric onset to innovative treatments and perspectives

Acute hepatic porphyrias (AHPs) are a family of four rare genetic diseases resulting from a deficiency in one of the enzymes involved in heme biosynthesis. AHP patients can experience potentially life-threatening acute attacks, characterized by severe abdominal pain, along with other signs and symptoms including nausea, mental confusion, hyponatraemia, hypertension, tachycardia and muscle weakness. Some patients also experience chronic manifestations and long-term complications, such as chronic pain syndrome, neuropathy and porphyria-associated kidney disease. Most symptomatic patients have only a few attacks in their lifetime; nevertheless, some experience frequent attacks that result in ongoing symptoms and a significant negative impact on their quality of life (QoL). Initial diagnosis of AHP can be made with a test for urinary porphobilinogen, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\delta$$\end{document}δ-aminolaevulinic acid and porphyrins using a single random (spot) sample. However, diagnosis is frequently missed or delayed, often for years, because the clinical symptoms of AHP are non-specific and mimic other more common disorders. Delayed diagnosis is of concern as some commonly used medications can trigger or exacerbate acute attacks, and untreated attacks can become severe, potentially leading to permanent neurological damage or fatality. Other attack triggers include hormonal fluctuations in women, stress, alcohol and low-calorie diets, which should be avoided in patients where possible. For the management of attacks, intravenous hemin is approved, whereas new therapeutic approaches are currently being investigated as a baseline therapy for prevention of attacks and improvement of QoL. Among these, a novel siRNA-based agent, givosiran, has shown very promising results in a recently concluded Phase III trial and has been approved for the management of AHPs. Here, we propose a challenging case study-with a very unusual pediatric onset of variegate porphyria-as a starting point to summarize the main clinical aspects (namely, clinical manifestations, diagnostic challenges, and therapeutic management) of AHPs, with a focus on the latest therapeutic innovations.

Efficacy and safety of givosiran for acute hepatic porphyria: 24-month interim analysis of the randomized phase 3 ENVISION study

BACKGROUND & AIMS

Upregulation of hepatic delta-aminolevulinic acid synthase 1 with accumulation of potentially toxic heme precursors delta-aminolevulinic acid and porphobilinogen is fundamental to the pathogenesis of acute hepatic porphyria.

AIMS

evaluate long-term efficacy and safety of givosiran in acute hepatic porphyria.

METHODS

Interim analysis of ongoing ENVISION study (NCT03338816), after all active patients completed their Month 24 visit. Patients with acute hepatic porphyria (≥12 years) with recurrent attacks received givosiran (2.5 mg/kg monthly) (n = 48) or placebo (n = 46) for 6 months (double-blind period); 93 received givosiran (2.5 mg or 1.25 mg/kg monthly) in the open-label extension (continuous givosiran, n = 47/48; placebo crossover, n = 46/46). Endpoints included annualized attack rate, urinary delta-aminolevulinic acid and porphobilinogen levels, hemin use, daily worst pain, quality of life, and adverse events.

RESULTS

Patients receiving continuous givosiran had sustained annualized attack rate reduction (median 1.0 in double-blind period, 0.0 in open-label extension); in placebo crossover patients, median annualized attack rate decreased from 10.7 to 1.4. Median annualized days of hemin use were 0.0 (double-blind period) and 0.0 (open-label extension) for continuous givosiran patients and reduced from 14.98 to 0.71 for placebo crossover patients. Long-term givosiran led to sustained lowering of delta-aminolevulinic acid and porphobilinogen and improvements in daily worst pain and quality of life. Safety findings were consistent with the double-blind period.

CONCLUSIONS

Long-term givosiran has an acceptable safety profile and significantly benefits acute hepatic porphyria patients with recurrent attacks by reducing attack frequency, hemin use, and severity of daily worst pain while improving quality of life.

Kidney Involvement in Acute Hepatic Porphyrias: Pathophysiology and Diagnostic Implications

Porphyrias are a group of rare disorders originating from an enzyme dysfunction in the pathway of heme biosynthesis. Depending on the specific enzyme involved, porphyrias manifest under drastically different clinical pictures. The most dramatic presentation of the four congenital acute hepatic porphyrias (AHPs: acute intermittent porphyria-AIP, ALAD deficiency, hereditary coproporphyria-HCP, and porphyria variegata-VP) consists of potentially life-threatening neurovisceral attacks, for which givosiran, a novel and effective siRNA-based therapeutic, has recently been licensed. Nonetheless, the clinical manifestations of acute porphyrias are multifaceted and do not limit themselves to acute attacks. In particular, porphyria-associated kidney disease (PAKD) is a distinct, long-term degenerating condition with specific pathological and clinical features, for which a satisfactory treatment is not available yet. In PAKD, chronic tubule-interstitial damage has been most commonly reported, though other pathologic features (e.g., chronic fibrous intimal hyperplasia) are consistent findings. Given the relevant role of the kidney in porphyrin metabolism, the mechanisms possibly intervening in causing renal damage in AHPs are different: among others, δ-aminolevulinic acid (ALA)-induced oxidative damage on mitochondria, intracellular toxic aggregation of porphyrins in proximal tubular cells, and derangements in the delicate microcirculatory balances of the kidney might be implicated. The presence of a variant of the human peptide transporter 2 (PEPT2), with a greater affinity to its substrates (including ALA), might confer a greater susceptibility to kidney damage in patients with AHPs. Furthermore, a possible effect of givosiran in worsening kidney function has been observed. In sum, the diagnostic workup of AHPs should always include a baseline evaluation of renal function, and periodic monitoring of the progression of kidney disease in patients with AHPs is strongly recommended. This review outlines the role of the kidney in porphyrin metabolism, the available evidence in support of the current etiologic and pathogenetic hypotheses, and the known clinical features of renal involvement in acute hepatic porphyrias.

Mechanisms of Neuronal Damage in Acute Hepatic Porphyrias

Porphyrias are a group of congenital and acquired diseases caused by an enzymatic impairment in the biosynthesis of heme. Depending on the specific enzyme involved, different types of porphyrias (i.e., chronic vs. acute, cutaneous vs. neurovisceral, hepatic vs. erythropoietic) are described, with different clinical presentations. Acute hepatic porphyrias (AHPs) are characterized by life-threatening acute neuro-visceral crises (acute porphyric attacks, APAs), featuring a wide range of neuropathic (central, peripheral, autonomic) manifestations. APAs are usually unleashed by external "porphyrinogenic" triggers, which are thought to cause an increased metabolic demand for heme. During APAs, the heme precursors δ-aminolevulinic acid (ALA) and porphobilinogen (PBG) accumulate in the bloodstream and urine. Even though several hypotheses have been developed to explain the protean clinical picture of APAs, the exact mechanism of neuronal damage in AHPs is still a matter of debate. In recent decades, a role has been proposed for oxidative damage caused by ALA, mitochondrial and synaptic ALA toxicity, dysfunction induced by relative heme deficiency on cytochromes and other hemeproteins (i.e., nitric oxide synthases), pyridoxal phosphate functional deficiency, derangements in the metabolic pathways of tryptophan, and other factors. Since the pathway leading to the biosynthesis of heme is inscribed into a complex network of interactions, which also includes some fundamental processes of basal metabolism, a disruption in any of the steps of this pathway is likely to have multiple pathogenic effects. Here, we aim to provide a comprehensive review of the current evidence regarding the mechanisms of neuronal damage in AHPs.

Porphyrias in the Age of Targeted Therapies

The porphyrias are a group of eight rare genetic disorders, each caused by the deficiency of one of the enzymes in the heme biosynthetic pathway, resulting in the excess accumulation of heme precursors and porphyrins. Depending on the tissue site as well as the chemical characteristics of the accumulating substances, the clinical features of different porphyrias vary substantially. Heme precursors are neurotoxic, and their accumulation results in acute hepatic porphyria, while porphyrins are photoactive, and excess amounts cause cutaneous porphyrias, which present with photosensitivity. These disorders are clinically heterogeneous but can result in severe clinical manifestations, long-term complications and a significantly diminished quality of life. Medical management consists mostly of the avoidance of triggering factors and symptomatic treatment. With an improved understanding of the underlying pathophysiology and disease mechanisms, new treatment approaches have become available, which address the underlying defects at a molecular or cellular level, and promise significant improvement, symptom prevention and more effective treatment of acute and chronic disease manifestations.