Accumulation Of Delta-aminolevulinic Acid Research Articles

Phase 3 Trial of RNAi Therapeutic Givosiran for Acute Intermittent Porphyria

BackgroundUp-regulation of hepatic delta-aminolevulinic acid synthase 1 (ALAS1), with resultant accumulation of delta-aminolevulinic acid (ALA) and porphobilinogen, is central to the pathogenesis of acute attacks and chronic symptoms in acute hepatic porphyria. Givosiran, an RNA interference therapy, inhibits ALAS1 expression.MethodsIn this double-blind, placebo-controlled, phase 3 trial, we randomly assigned symptomatic patients with acute hepatic porphyria to receive either subcutaneous givosiran (2.5 mg per kilogram of body weight) or placebo monthly for 6 months. The primary end point was the annualized rate of composite porphyria attacks among patients with acute intermittent porphyria, the most common subtype of acute hepatic porphyria. (Composite porphyria attacks resulted in hospitalization, an urgent health care visit, or intravenous administration of hemin at home.) Key secondary end points were levels of ALA and porphobilinogen and the annualized attack rate among patients with acute hepatic porphyria, along with hemin use and daily worst pain scores in patients with acute intermittent porphyria.ResultsA total of 94 patients underwent randomization (48 in the givosiran group and 46 in the placebo group). Among the 89 patients with acute intermittent porphyria, the mean annualized attack rate was 3.2 in the givosiran group and 12.5 in the placebo group, representing a 74% lower rate in the givosiran group (P<0.001); the results were similar among the 94 patients with acute hepatic porphyria. Among the patients with acute intermittent porphyria, givosiran led to lower levels of urinary ALA and porphobilinogen, fewer days of hemin use, and better daily scores for pain than placebo. Key adverse events that were observed more frequently in the givosiran group were elevations in serum aminotransferase levels, changes in serum creatinine levels and the estimated glomerular filtration rate, and injection-site reactions.ConclusionsAmong patients with acute intermittent porphyria, those who received givosiran had a significantly lower rate of porphyria attacks and better results for multiple other disease manifestations than those who received placebo. The increased efficacy was accompanied by a higher frequency of hepatic and renal adverse events. (Funded by Alnylam Pharmaceuticals; ENVISION ClinicalTrials.gov number, NCT03338816.)

Leading RNA Interference Therapeutics Part 2: Silencing Delta-Aminolevulinic Acid Synthase 1, with a Focus on Givosiran.

In November 2019 givosiran became the second small interfering RNA (siRNA)-based drug to receive US Food and Drug Administration (FDA) approval, it has been developed for the treatment of acute intermittent porphyria (AIP), a disorder characterized by life-threatening acute neurovisceral attacks. Theporphyrias are a group of disorders in which enzymatic deficiencies in heme production lead to toxic accumulation of delta-aminolevulinic acid (ALA) and porphobilinogen (PBG), which are involved in the neurovisceral attacks. Givosiran acts as a conventional siRNA to trigger RNA interference (RNAi)-mediated gene silencing on delta-ALA synthase 1 (ALAS1), thus returning ALA and PBG metabolites to the physiological level to attenuate further neurotoxicity. Givosiran makes use of a new hepatic-delivery system that conjugates three GalNac (N-acetylgalactosamine) molecules to the siRNA passenger strand. GalNac binds to the liver asialoglycoprotein receptor, favoring the internalization of these GalNac-conjugated siRNAs into the hepatic cells. In a phase I study, subcutaneous monthly administration of givosiran 2.5mg/kg reduced > 90% of ALA and PBG content. This siRNA is being analyzed in ENVISION (NCT03338816), a phase III, multicenter, placebo-controlled randomized controlled trial. In preliminary results, givosiran achieved clinical endpoints for AIP, reducing urinary ALA levels, and presented a safety profile that enabled further drug development. The clinical performance of givosiran revealed that suppression of ALAS1 by GalNac-decorated siRNAs represents an additional approach for the treatment of patients with AIP that manifests recurrent acute neurovisceral attacks.

Drugs and Acute Porphyrias: Reasons for a Hazardous Relationship

The porphyrias are a group of metabolic diseases caused by inherited or acquired enzymatic deficiency in the metabolic pathway of heme biosynthesis. Simplistically, they can be considered as storage diseases, because the partial enzymatic defect gives rise to a metabolic “bottleneck” in the biosynthetic pathway and hence to an accumulation of different metabolic intermediates, potentially toxic and responsible for the various (cutaneous or neurovisceral) clinical manifestations observed in these diseases. In the acute porphyrias (acute intermittent porphyria, hereditary coproporphyria, variegate porphyria, and the very rare delta-aminolevulinic acid dehydratase ALAD-d porphyria), the characteristic severe neurovisceral involvement is mainly ascribed to a tissue accumulation of delta-aminolevulinic acid, a neurotoxic nonporphyrin precursor. Many different factors, both endogenous and exogenous, may favor the accumulation of this precursor in patients who are carriers of an enzymatic defect consistent with an acute porphyria, thus contributing to trigger the serious (and potentially fatal) clinical manifestations of the disease (acute porphyric attacks). To date, many different drugs are known to be able to precipitate an acute porphyric attack, so that the acute porphyrias are also considered as pharmacogenetic or toxygenetic diseases. This article reviews the different biochemical mechanisms underlying the capacity of many drugs to precipitate a porphyric acute attack (drug porphyrogenicity) in carriers of genetic mutations responsible for acute porphyrias, and addresses the issue of prescribing drugs for patients affected by these rare, but extremely complex, diseases.

Biochemical and hematological analysis in acute intermittent porphyria (AIP): a case report

Acute intermittent porphyria is the most common acute porphyria caused by a decrease in hepatic porphobilinogen deaminase activity, resulting in an accumulation of delta-aminolevulinic acid and porphobilinogen. This disease shows nonspecific signs and symptoms that can be confused with other diseases, thereby making the diagnosis difficult. We report a case of acute intermittent porphyria, reviewing clinical and laboratory aspects, highlighting the hematological and biochemical parameters during and after the crisis. A female patient, aged 28 years, suffered two crises, both presenting gastrointestinal disorders. The second presented neuropsychiatric symptoms. The analysis of hematological and biochemical parameters during the second crisis showed anemia, leukocytosis, hyponatremia, mild hypokalemia, uremia and elevated C-reactive protein. The initial treatment included glucose infusion, a diet rich in carbohydrates and interruption of porphyrinogenic drugs. Subsequently, treatment was maintained with oral contraceptive use. According to the observed data, signs and symptoms of gastrointestinal, neurological and psychiatric disorders, associated with laboratory results presented in this paper can be applied to screen acute porphyria, contributing to early diagnosis.

Necrotic cell death induced by delta-aminolevulinic acid in mouse astrocytes. Protective role of melatonin and other antioxidants.

Accumulation of delta-aminolevulinic acid (ALA), as it occurs in acute intermittent porphyria (AIP), is the origin of an endogenous source of reactive oxygen species (ROS), which can exert oxidative damage to cell structures. In the present work we examined the ability of different antioxidants to revert ALA-promoted damage, by incubating mouse astrocytes with 1.0 mM ALA for different times (1-4 hr) in the presence of melatonin (2.5 mM), superoxide dismutase (25 units/mL), catalase (200 units/mL) or glutathione (0.5 mM). The defined relative index [(malondialdehyde levels/accumulated ALA) x 100], decreases with incubation time, reaching values of 76% for melatonin and showing that the different antioxidants tested can protect astrocytes against ALA-promoted lipid peroxidation. Concerning porphyrin biosynthesis, no effect was observed with catalase and superoxide dismutase whereas increases of 57 and 87% were obtained with glutathione and melatonin, respectively, indicating that these antioxidants may prevent the oxidation of porphobilinogen deaminase, reactivating so that the AIP genetically reduced enzyme. Here we showed that ALA induces cell death displaying a pattern of necrosis. This pattern was revealed by loss of cell membrane integrity, marked nuclear swelling and double labeling with annexin V and propidium iodide. In addition, no caspase 3-like activity was detected. These findings provide the first experimental evidence of the involvement of ALA-promoted ROS in the damage of proteins related to porphyrin biosynthesis and the induction of necrotic cell death in astrocytes. Interestingly, melatonin decreases the number of enlarged nuclei and shows a protective effect on cellular morphology.

In vivo protection by melatonin against delta-aminolevulinic acid-induced oxidative damage and its antioxidant effect on the activity of haem enzymes.

Accumulation of delta-aminolevulinic acid (ALA), as it occurs in acute intermittent porphyria, is a potential endogenous source of reactive oxygen species (ROS) which can then produce oxidative damage to cell structures and macromolecules. This in vivo study investigated whether melatonin could prevent the deleterious effects of ALA. Rats were injected i.p. for 2 weeks with ALA (40 mg/kg on alternate days) and/or with melatonin (50 microg/kg or 500 microg/kg daily). Administration of pharmacological doses of melatonin reduced and/or prevented ALA-induced lipid peroxidation (LPO) in both cerebral cortex and cerebellum, providing further evidence of melatonin's action as a ROS scavenger. Administration of pharmacological concentrations of melatonin to ALA-injected rats showed the protective properties of melatonin on the activities of both porphobilinogen-deaminase and delta-aminolevulinate dehydratase (ALA-D) in the cerebral cortex; the effect on ALA-D activity was unexpectedly high (at least 6-fold), indicating that, besides acting as a scavenger of hydroxyl radicals, melatonin may exert its protection on ALA-D through other mechanisms, such as increasing mRNA levels of antioxidant enzymes or/and inducing glutathione peroxidase activity. The possibility that changes in the expression of antioxidant enzymes could affect the expression of other proteins, even those not related to the cellular ROS homeostasis, should also not be discarded. The potential use of melatonin as an antioxidant and for its reactivating properties in the treatment of acute porphyrias is considered.

Studies of Delta-Aminolevulinic Acid Dehydrase from Skeletonema costatum, a Marine Plankton Diatom

The accumulation of delta-aminolevulinic acid and activities of delta-aminolevulinic acid dehydrase were examined in the marine diatom, Skeletonema costatum, grown in the presence of levulinic acid. Levulinic acid concentrations greater than 10 mm affect growth and morphology, and inhibit chlorophyll synthesis. The algae recover from the effects of levulinic acid after 48 hours of exposure. The recovery is characterized by increased cellular cholorphyll content, decreased delta-aminolevulinic acid accumulation, decreased 3-(3,4-dichlorophenyl)-1, 1-dimethylurea-enhanced in vivo fluorescence, and the induction of a levulinic acid-activated delta-aminolevulinic acid dehydrase which does not follow Michaelis-Menten kinetics. The data indicate that levulinic acid blocks may be ineffective in vivo, and that delta-aminolevulinic acid is metabolized to amino and dicarboxylic acids. delta-Aminolevulinic acid dehydrase activities are used to estimate the capacity for chlorophyll synthesis. Results suggest this diatom may be capable of rapid chlorophyll turnover, which would allow the plant to light-shade adapt on the time scales appropriate to vertical mixing rates in the sea.

Control of δ-Aminolevulinic Acid and Chlorophyll Accumulation in Greening Maize Leaves upon Light-Dark Transitions

The accumulation of delta-aminolevulinic acid (ALA) was studied in greening maize (Zea mays) leaves which were transferred to darkness and reilluminated after various periods of time. The system synthesizing ALA decays in the dark with a half-life of about 80 minutes. The onset of enzyme decay after transfer to darkness shows a 40-minute lag. The accumulation of ALA in the presence of levulinic acid in leaves transferred to darkness corresponds to that expected from the estimated half-life of the enzyme synthesizing ALA. On the other hand, the accumulation of protochlorophyll upon transfer to darkness in the absence of levulinic acid stops much earlier. It is suggested that a control point exists in the pathway between ALA and protochlorophyll, preventing utilization of the accumulated ALA upon transfer of greening leaves to darkness. This is supported by the observed effects of low intensities of monochromatic light (648 nm) on ALA and chlorophyll accumulation.

Accumulation of δ-Aminolevulinic Acid and Its Relation to Chlorophyll Synthesis and Development of Plastid Structure in Greening Leaves

Levulinic acid inhibited the greening of etiolated maize (Zea mays) and bean (Phaseolus vulgaris) leaves and caused accumulation of delta-aminolevulinic acid (ALA). ALA accumulation in maize was equivalent to the decrease in chlorophyll, over a wide range of experimental conditions. It was saturated at low light intensities and was not limited by the supply of substrates during the early hours of greening. During 20 hours in light, levulinic acid had little effect on the structural development of thylakoids in bundle sheath chloroplasts but significantly reduced the number and size of thylakoids in grana of mesophyll chloroplasts. Recrystallization of prolamellar bodies and their reformation was inhibited. Mitochondria appeared not to be affected.The accumulation of ALA in bean leaves differed from that in maize in regard to its time course and the effect of levulinic acid concentration and light intensity. The amount of ALA accumulated exceeded that expected from the degree of inhibition of chlorophyll synthesis. Levulinic acid caused abnormalities in the structural development of bean chloroplasts and marked swelling of mitochondria.Chloramphenicol and cycloheximide inhibited ALA accumulation, while inhibitors of RNA synthesis had no effect. The extent of inhibition depended on the time the inhibitor was applied during the greening process. The use of ALA accumulation as a tool for studying the control of chlorophyll synthesis is discussed.

The Biosynthesis of δ-Aminolevulinic Acid in Higher Plants

delta-Aminolevulinic acid dehydrase activity in cucumber (Cucumis sativus L. var. Alpha green) cotyledons did not change as the tissue was allowed to green for 24 hours. delta-Aminolevulinic acid accumulated in greening cucumber cotyledons, and barley (Hordeum sativum L. var. Numar) and bean (Phaseolus vulgaris L. var. Red Kidney) leaves incubated in the presence of levulinic acid, a specific competitive inhibitor of delta-aminolevulinic acid dehydrase. The rate of delta-aminolevulinic acid accumulation in levulinic acid-treated cucumber cotyledons paralleled the rate of chlorophyll accumulation in the controls, and the quantity of delta-aminolevulinic acid accumulated compensated for the decrease in chlorophyll accumulation. When levulinic acid-treated cucumber cotyledons were returned to darkness, delta-aminolevulinic acid accumulation ceased.delta-Aminolevulinic acid accumulation showed an absolute requirement for oxygen and was inhibited drastically by cyanide and azide, and to a lesser extent by arsenite and malonate. 2,4-Dinitrophenol, 3-(3,4-dichlorophenyl)-1,1-dimethyl urea, sodium fluoroacetate, and hydroxylamine hydrochloride showed no effect under the conditions tested. Freezing and thawing of the tissue completely prevented the accumulation of delta-aminolevulinic acid.The findings of this investigation are consistent with the hypothesis that delta-aminolevulinic acid is a chlorophyll precursor in higher plants, and that chlorophyll biosynthesis is regulated at the level of the formation of delta-aminolevulinic acid.

Studies on the Biosynthesis and Metabolism of δ-Aminolevulinic Acid in Chlorella

The regulation of chlorophyll synthesis in Chlorella was examined at the level of the formation and metabolism of delta-aminolevulinic acid. delta-Aminolevulinic acid synthetase activity could not be detected in broken cell preparations, and exogenously supplied delta-aminolevulinic acid was taken up only in the presence of dimethylsulfoxide, with a corresponding production of porphobilinogen.The delta-aminolevulinic acid dehydratase of Chlorella has a pH optimum of 7.8 and at this pH the Michaelis constant for delta-aminolevulinic acid is 0.13 millimolar.delta-Aminolevulinic acid excretion in the presence of levulinic acid, a competitive inhibitor of delta-aminolevulinic acid dehydratase, allowed measurement of the relative rates of delta-aminolevulinic acid synthesis under various growth conditions. A mutant which requires light for chlorophyll synthesis also requires light for delta-aminolevulinic acid accumulation in the presence of levulinic acid. This same mutant has 40% of the delta-aminolevulinic acid dehydratase activity of the wild-type Chlorella during growth in the dark on glucose.The necessity for protein synthesis during chlorophyll synthesis is due primarily to the requirement for protein synthesis during delta-aminolevulinic acid formation.It is concluded that the rate of chlorophyll formation and the cellular chlorophyll content are regulated by the relative rates of synthesis and breakdown of an enzyme responsible for delta-aminolevulinic acid biosynthesis and that this enzyme has an in vivo lifetime of about 30 minutes.