Porphobilinogen Concentration Research Articles

Quantification of Urine and Plasma Porphyrin Precursors Using LC-MS in Acute Hepatic Porphyrias: Improvement in Routine Diagnosis and in the Monitoring of Kidney Failure Patients.

The quantification of delta-aminolevulinic acid (ALA) and porphobilinogen (PBG) in urine are the first-line tests for diagnosis and monitoring of acute hepatic porphyrias (AHP). Ion-exchange chromatography (IEC), which is time- and staff-consuming and limited to urine, is still the preferred method in many specialized laboratories, despite the development of mass spectrometry-based methods. We describe a new LC-MS method that allows for rapid and simple quantification of ALA and PBG in urine and plasma with an affordable instrument that was used to analyze 2260 urine samples and 309 blood samples collected in 2 years of routine activity. The results were compared to those obtained with IEC, and urine reference ranges and concentrations in asymptomatic carriers were determined. Plasma concentrations were measured in healthy subjects and subgroups of symptomatic and asymptomatic AHP carriers. In urine, the clinical decision limits were not impacted by the change of method despite discrepancies in low absolute concentrations, leading to lower normal values. Two-thirds of asymptomatic AHP carriers (with the exception of coproporphyria carriers) showed an increased urine PBG concentration. Urine and plasma levels showed a good correlation except in patients with kidney disease in whom the urine/plasma ratio was relatively low. We described an LC-MS based method for the routine diagnosis and monitoring of AHP that allows for the detection of more asymptomatic carriers than the historical method. Blood analysis appears to be particularly relevant for patients with kidney disease, where urine measurement underestimates the increase in ALA and PBG levels.

Homozygous hydroxymethylbilane synthase knock-in mice provide pathogenic insights into the severe neurological impairments present in human homozygous dominant acute intermittent porphyria.

Acute intermittent porphyria (AIP) is an inborn error of heme biosynthesis due to the deficiency of hydroxymethylbilane synthase (HMBS) activity. Human AIP heterozygotes have episodic acute neurovisceral attacks that typically start after puberty, whereas patients with homozygous dominant AIP (HD-AIP) have early-onset chronic neurological impairment, including ataxia and psychomotor retardation. To investigate the dramatically different manifestations, knock-in mice with human HD-AIP missense mutations c.500G>A (p.Arg167Glu) or c.518_519GC>AG (p.Arg173Glu), designated R167Q or R173Q mice, respectively, were generated and compared with the previously established T1/T2 mice with ~30% residual HMBS activity and the heterozygous AIP phenotype. Homozygous R173Q mice were embryonic lethal, while R167Q homozygous mice (R167Q+/+) had ~5% of normal HMBS activity, constitutively elevated plasma and urinary 5-aminolevulinic acid (ALA) and porphobilinogen (PBG), profound early-onset ataxia, delayed motor development and markedly impaired rotarod performance. Central nervous system (CNS) histology was grossly intact, but CNS myelination was delayed and overall myelin volume was decreased. Heme concentrations in liver and brain were similar to those of T1/T2 mice. Notably, ALA and PBG concentrations in the cerebral spinal fluid and CNS regions were markedly elevated in R167Q+/+ mice compared with T1/T2 mice. When the T1/T2 mice were administered phenobarbital, ALA and PBG markedly accumulated in their liver and plasma, but not in the CNS, indicating that ALA and PBG do not readily cross the blood-brain barrier. Taken together, these studies suggest that the severe HD-AIP neurological phenotype results from decreased myelination and the accumulation of locally produced neurotoxic porphyrin precursors within the CNS.

Phenanthrene-triggered Chlorosis is caused by elevated Chlorophyll degradation and leaf moisture

Leaf is an important organ in responding to environmental stresses. To date, chlorophyll metabolism under polycyclic aromatic hydrocarbon (PAH) stress is still unclear. Here we reveal, for the first time, the chlorophyll metabolism of wheat seedling leaves in response to phenanthrene (a model PAH) exposure. In this study, the hydroponic experiment was employed, and the wheat seedlings were exposed to phenanthrene to observe the response at day 1, 3, 5, 7 and 9. Over the exposure time, wheat leaf color turns light. With the accumulation of phenanthrene, the concentrations of glutamate, 5-aminolevulinic acid, uroporphyrinogen III, protoporphyrin IX, Mg-protoporphyrin IX and protochlorophyllide increase while the concentrations of porphobilinogen and Chlorophyll b decrease. Also chlorophyll a content rises initially and then declines. Uroporphyrinogen III synthase and chlorophyllase are activated and porphobilinogen deaminase activity declines in the treatments. Both chlorophyll synthesis and degradation are enhanced, but the degradation rate is faster. Phenanthrene accumulation has significant and positive effects on increase of glutamate, 5-aminolevulinic acid, uroporphyrinogen III, protoporphyrin IX, Mg-protoporphyrin IX and protochlorophyllide concentrations. There is a negative correlation between phenanthrene accumulation and total chlorophyll. Additionally, the leaf moisture increases. Therefore, it is concluded that wheat leaf chlorosis results from a combination of accelerated chlorophyll degradation and elevated leaf moisture under phenanthrene exposure. Our results are helpful not only for better understanding the toxicity of PAHs to plants and crop PAH-adaptive mechanism in the environment, but also for potentially employing the changes of the chlorophyll-synthesizing precursors and enzyme activities in plant leaves as indicators of plant response to PAH pollution.

Preclinical Development of a Subcutaneous ALAS1 RNAi Therapeutic for Treatment of Hepatic Porphyrias Using Circulating RNA Quantification.

The acute hepatic porphyrias are caused by inherited enzymatic deficiencies in the heme biosynthesis pathway. Induction of the first enzyme 5-aminolevulinic acid synthase 1 (ALAS1) by triggers such as fasting or drug exposure can lead to accumulation of neurotoxic heme intermediates that cause disease symptoms. We have demonstrated that hepatic ALAS1 silencing using siRNA in a lipid nanoparticle effectively prevents and treats induced attacks in a mouse model of acute intermittent porphyria. Herein, we report the development of ALN-AS1, an investigational GalNAc-conjugated RNAi therapeutic targeting ALAS1. One challenge in advancing ALN-AS1 to patients is the inability to detect liver ALAS1 mRNA in the absence of liver biopsies. We here describe a less invasive circulating extracellular RNA detection assay to monitor RNAi drug activity in serum and urine. A striking correlation in ALAS1 mRNA was observed across liver, serum, and urine in both rodents and nonhuman primates (NHPs) following treatment with ALN-AS1. Moreover, in donor-matched human urine and serum, we demonstrate a notable correspondence in ALAS1 levels, minimal interday assay variability, low interpatient variability from serial sample collections, and the ability to distinguish between healthy volunteers and porphyria patients with induced ALAS1 levels. The collective data highlight the potential utility of this assay in the clinical development of ALN-AS1, and in broadening our understanding of acute hepatic porphyrias disease pathophysiology.

Hepatocyte Transplantation Ameliorates the Metabolic Abnormality in a Mouse Model of Acute Intermittent Porphyria

Acute intermittent porphyria (AIP) is an autosomal dominant disorder characterized by insufficient porphobilinogen deaminase (PBGD) activity. When hepatic heme synthesis is induced, porphobilinogen (PBG) and 5-aminolevulinic acid (ALA) accumulate, which causes clinical symptoms such as abdominal pain, neuropathy, and psychiatric disturbances. Our aim was to investigate if hepatocyte transplantation can prevent or minimize the metabolic alterations in an AIP mouse model. We transplanted wild-type hepatocytes into PBGD-deficient mice and induced heme synthesis with phenobarbital. ALA and PBG concentrations in plasma were monitored, and the gene transcriptions of hepatic enzymes ALAS1, PBGD, and CYP2A5 were analyzed. Results were compared with controls and correlated to the percentage of engrafted hepatocytes. The accumulation of ALA and PBG was reduced by approximately 50% after the second hepatocyte transplantation. We detected no difference in mRNA levels of PBGD, ALAS1, or CYP2A5. Engraftment corresponding to 2.7% of the total hepatocyte mass was achieved following two hepatocyte transplantations. A lack of precursor production in less than 3% of the hepatocytes resulted in a 50% reduction in plasma precursor concentrations. This disproportional finding suggests that ALA and PBG produced in PBGD-deficient hepatocytes crossed cellular membranes and was metabolized by transplanted cells. The lack of effect on enzyme mRNA levels suggests that no significant efflux of heme from normal to PBGD-deficient hepatocytes takes place. Further studies are needed to establish the minimal number of engrafted hepatocytes needed to completely correct the metabolic abnormality in AIP and whether amelioration of the metabolic defect by partial restoration of PBGD enzyme activity translates into a clinical effect in human AIP.

Urinary Metabolic Fingerprint of Acute Intermittent Porphyria Analyzed by 1H NMR Spectroscopy

(1)H NMR is a nonbiased technique for the quantification of small molecules that could result in the identification and characterization of potential biomarkers with prognostic value and contribute to better understand pathophysiology of diseases. In this study, we used (1)H NMR spectroscopy to analyze the urinary metabolome of patients with acute intermittent porphyria (AIP), an inherited metabolic disorder of heme biosynthesis in which an accumulation of the heme precursors 5-aminolaevulinic acid (ALA) and porphobilinogen (PBG) promotes sudden neurovisceral attacks, which can be life-threatening. Our objectives were (1) to demonstrate the usefulness of (1)H NMR to identify and quantify ALA and PBG in urines from AIP patients and (2) to identify metabolites that would predict the response to AIP crisis treatment and reflect differential metabolic reprogramming. Our results indicate that (1)H NMR can help to diagnose AIP attacks based on the identification of ALA and PBG. We also show that glycin concentration increases in urines from patients with frequent recurrences at the end of the treatment, after an initial decrease, whereas PBG concentration remains low. Although the reasons for this altered are elusive, these findings indicate that a glycin metabolic reprogramming occurs in AIPr patients and is associated with recurrence. Our results validate the proof of concept of the usefulness of (1)H NMR spectroscopy in clinical chemistry for the diagnosis of acute attack of AIP and identify urinary glycin as a potential marker of recurrence of AIP acute attacks.

Urinary excretion of porphyrins, porphobilinogen and δ-aminolaevulinic acid following an attack of acute intermittent porphyria

Background and objectivesThe porphyrias are a group of rare, mainly inherited, diseases caused by a deficiency of one of the enzymes of the haem biosynthesis pathway. The biochemical hallmark of...

536 – Acute intermittent porphyria and cycloid psychosis

Introduction Acute intermittent porphyria (AIP) is a rare autosomal dominant inherited metabolic disease characterized by mutations in the porphobilinogen deaminase gene. This mutation may provoke neurotoxic levels of delta-aminolevulinic-acid and porphobilinogen, potentially resulting in an acute life-threatening clinical syndrome, characterized by psychiatric, in particular atypical psychotic, symptoms as well as severe neurological and gastrointestinal symptoms. Since the clinical presentation varies and symptoms are nonspecific, diagnosis is often made late. Objectives Naming of alarm symptoms based on a recent case study. Methods Description of a recent case supplemented with data from the literature. Results The patient is a 46 year old woman who was admitted in 2007 with abdominal pain, an epileptic seizure and weakness, interpreted as a Guillain-Barre syndrome. In 2011 she was readmitted with severe abdominal pain, diarrhea, volatile psychotic symptoms and seizures, following a short period of excessive alcohol consumption. During admission she developed progressive weakness in the upper arms, shooting pains in the limbs and a feeling of tightness. Impaired abdominal breathing was suspected. Again, Guillain-Barre syndrome was considered, but additional studies did not support this diagnosis. Because of the recurrent character of symptomatology following alcohol abuse, acute (intermittent) porphyria was considered diagnostically. The dark-colored urine indeed contained significantly increased delta-aminolevulinic-acid and porphobilinogen concentrations. Additional (genetic) diagnosis follows. Conclusion A recurrent disease course with severe gastrointestinal, neurological and psychiatric symptoms, following alcoholabuse, is suspect for AIP.

Acute intermittent porphyria: fatal complications of treatment

Acute neurovisceral attacks of porphyria can be life threatening. They are rare and notoriously difficult to diagnose clinically, but should be considered, particularly in female patients with unexplained abdominal pain, and associated neurological or psychiatric features or hyponatraemia. The diagnosis might be suggested by altered urine colour and can be confirmed by finding an elevated porphobilinogen concentration in fresh urine protected from light. Severe attacks require treatment with intravenous haem arginate and supportive management with safe drugs, including adequate analgesia. Intravenous glucose in water solutions are contraindicated as they aggravate hyponatraemia, which can prove fatal.

A LC–MS/MS method for the specific, sensitive, and simultaneous quantification of 5-aminolevulinic acid and porphobilinogen

Accurate determinations of 5-aminolevulinic acid (ALA) and porphobilinogen (PBG) in physiologic fluids are required for the diagnosis and therapeutic monitoring of acute porphyrias. Current colorimetric methods are insensitive and over-estimate ALA and PBG due to poor specificity, while LC–MS/MS methods increase sensitivity, but have limited matrices. An LC–MS/MS method was developed to simultaneously determine ALA and PBG concentrations in fluids or tissues which were solid phase extracted, butanol derivatized, and quantitated by selective reaction monitoring using 13C 5, 15N-ALA and 2,4- 13C 2-PBG internal standards. ALA was separated from interfering compounds on a reverse phase C8-column. For ALA and PBG, the matrix effects (87.3–105%) and process efficiencies (77.6–97.8% and 37.2–41.6%, respectively) were acceptable in plasma and urine matrices. The assay was highly sensitive for ALA and PBG (LLOQ = 0.05 μM with 25 μL urine or 100 μL plasma), and required ∼4 h from extraction to results. ALA and PBG accuracy ranged from 88.2 to 110% ( n = 10); intra- and inter-assay coefficients of variations were <10% for urine and plasma. In clinical applications, patients with mutation-confirmed acute porphyrias had normal to slightly increased urinary ALA and PBG levels when asymptomatic, and high levels during acute attacks, which decreased with hemin therapy. In AIP mice, baseline ALA and PBG levels in urine, plasma, and liver were increased after phenobarbital induction 28-/63-, 42-/266-, and 13-/316-fold, respectively. This LC–MS/MS method is rapid, specific, highly sensitive, accurate, and simultaneously measures ALA and PBG in urine, plasma, and tissues permitting porphyria clinical diagnoses, therapeutic monitoring, and research.

Rapid Quantitative Method Using Spin Columns to Measure Porphobilinogen in Urine

Large increases of urinary porphobilinogen (PBG) indicate acute porphyria, which may be due to acute intermittent porphyria, variegate porphyria, or hereditary coproporphyria. These conditions are relatively rare but share symptoms with more common conditions, such as acute surgical abdomen, and often must be ruled out rapidly. Reported quantitative methods for PBG measurement are time-consuming and inconvenient. We developed a rapid quantitative method that uses resin-packed spin columns to measure PBG in urine. We applied urine to anion exchange resin in a spin column, then performed centrifugal separation and washing. PBG was eluted in 1 mol/L acetic acid and reacted with Ehrlich's reagent. After 5 min, we measured absorbance at 525, 555, and 585 nm. PBG concentration (mg/L) was calculated as 88 (A(555) - (1/2)(A(525) + A(585))). The reportable PBG concentration range was 0.2-15 mg/L. Between-day (total) imprecision (CV) was 8.4% at 1.2 mg/L and 3.5% at 4.4 mg/L. Comparison with our established method (x) yielded a Deming regression equation: y = 1.04x - 0.01 mg/L (R(2) = 0.98; S(y,x) = 0.87 mg/L). No interference was noted from urobilinogen or highly colored urine specimens. This method for PBG measurement is more rapid and precise than other methods. This test can serve as a quick screening test and facilitates batch analysis for routine quantitative testing.

Safety, Pharmacokinetics and Pharmocodynamics of Recombinant Human Porphobilinogen Deaminase in Healthy Subjects and Asymptomatic Carriers of the Acute Intermittent Porphyria Gene Who Have Increased Porphyrin Precursor Excretion

Acute intermittent porphyria is an autosomal dominant disorder caused by deficient activity of the third enzyme in the haem biosynthetic pathway, porphobilinogen deaminase. It is characterised by acute, potentially life-threatening neurological attacks that are precipitated by various drugs, reproductive hormones and other factors. During acute attacks, the porphyrin precursors 5-aminolevulinic acid and porphobilinogen accumulate and are excreted at high concentrations in the urine. Current treatment is based on glucose loading and parenteral haem replenishment, which reduce the accumulation of 5-aminolevulinic acid and porphobilinogen. Recently, a new form of treatment based on porphobilinogen deaminase enzyme replacement therapy has been shown to be effective in an acute intermittent porphyria mouse model which, during phenobarbital (phenobarbitone) induction of haem biosynthesis, mimics the biochemical pattern of acute porphyric attacks. The objective of the present study was to investigate the safety, pharmacokinetics and pharmacodynamics of recombinant human porphobilinogen deaminase (P 9808), administered to healthy subjects and asymptomatic porphobilinogen deaminase-deficient subjects with high concentrations of porphobilinogen, the substrate of porphobilinogen deaminase. Forty individuals participated in this two-part study: 20 asymptomatic porphobilinogen deaminase-deficient subjects (both male and female) with > or =4 times the upper reference urinary porphobilinogen level, and 20 healthy male subjects. Four different doses of recombinant human porphobilinogen deaminase were studied (0.5, 1, 2 and 4 mg/kg bodyweight). Part A included 12 asymptomatic porphobilinogen deaminase-deficient subjects, and the enzyme was administered in an open-label, single-dose design. Part B included 20 asymptomatic porphobilinogen deaminase-deficient subjects and 20 healthy subjects. The same enzyme dosages were administered as divided doses every 12 hours for 4 consecutive days in a randomised, double-blinded, placebo-controlled design. The washout period between Parts A and B was 2 weeks. The concentrations of recombinant human porphobilinogen deaminase and titres of antibodies against recombinant human porphobilinogen deaminase were analysed by ELISA. Plasma porphobilinogen and 5-aminolevulinic acid concentrations were analysed using a novel liquid chromatography-tandem mass spectrometry method. Urinary porphobilinogen, 5-aminolevulinic acid and porphyrin concentrations, as well as plasma porphyrin concentrations, were analysed using standard methods. The pharmacodynamic effect of the enzyme was studied through changes in plasma porphobilinogen concentrations. No serious adverse events were observed. Seven subjects (four healthy men and three asymptomatic porphobilinogen deaminase-deficient subjects) developed antibodies against recombinant human porphobilinogen deaminase but did not experience allergic manifestations. The mean elimination half-lives of the highest doses of recombinant human porphobilinogen deaminase ranged between 1.7 and 2.5 hours for both healthy men and asymptomatic porphobilinogen deaminase-deficient subjects. The area under the plasma concentration-time curve was proportional to the respective dose. In asymptomatic porphobilinogen deaminase-deficient subjects, plasma porphobilinogen concentrations decreased below measurable levels almost instantaneously after administration of any dose of the enzyme. The effect lasted for approximately 2 hours, after which the plasma porphobilinogen concentration slowly increased, reaching about 70% of the initial values 12 hours after administration. There was no effect on plasma 5-aminolevulinic acid concentrations, and there was a transitory increment in porphyrin concentrations. The corresponding concentrations of metabolites in the urine reflected the pattern observed in the plasma. The recombinant human porphobilinogen deaminase enzyme preparation was found to be safe to administer and effective for removal of the accumulated metabolite porphobilinogen from plasma and urine. The pharmacokinetic profile of recombinant human porphobilinogen deaminase showed dose proportionality, and the elimination half-life was about 2.0 hours for the two highest doses. Thus, clinical grounds were established for investigation of the therapeutic efficacy of the enzyme during periods of overt disease in patients with acute intermittent porphyria.

Estimation and Application of Biological Variation of Urinary δ-Aminolevulinic Acid and Porphobilinogen in Healthy Individuals and in Patients with Acute Intermittent Porphyria

Diagnosis of an attack of acute intermittent porphyria (AIP) is based on the demonstration of increased concentrations of porphobilinogen (PBG) and delta-aminolevulinic acid (ALA) in urine, but many AIP patients also have high baseline concentrations in remission. The aim of this study was to estimate the biological variations of ALA, PBG, and porphyrins in healthy individuals and AIP patients to improve interpretation of test results. Fifteen healthy individuals and 15 AIP patients were included, and biological variations were calculated based on urine samples collected weekly for 10 consecutive weeks. For the AIP patients, long-term variations were also estimated based on 7 samples collected through a 2-year period. The porphyrin variances were inhomogeneously distributed; biological variations of porphyrins were therefore not calculated. The within-subject biological variations of ALA and PBG were 16%-20% in the short-term settings and for PBG, 25% in the long-term setting, giving reference change values of approximately 50% and 70%, respectively. The probability of detecting a 100% real change in PBG was 97% in the short-term setting and 80% in the long-term setting. In an AIP patient, a 2-fold increase in PBG, independent of the baseline concentration, will be detected with a probability >80% and is most likely related to the patient's disease and not caused only by analytical and biological variation. When PBG is used in the assessment of AIP-related symptoms, both the PBG concentration in remission and the length of time since the previous sample must be considered.

Dual porphyria with mutations in both the UROD and HMBS genes

The porphyrias are a group of inborn or acquired disorders of haem synthesis that can result in neurovisceral or dermatological symptoms. Diagnosis is usually made using a combination of clinical presentation and biochemical parameters. This case report describes a 25-year-old woman clinically presenting with a rash and then found to have elevated porphobilinogen concentrations in her urine. The initial presumptive diagnosis of variegate porphyria was not supported by analysis of her plasma, urine and faeces, which suggested a combination of acute intermittent porphyria and porphyria cutanea tarda. Sequencing of the hydroxymethylbilane synthase and uroporphyrinogen decarboxylase genes confirmed the relatively rare diagnosis of dual porphyria, and revealed a novel uroporphyrinogen decarboxylase mutation.

Effect of Tiagabine and Topiramate on Porphyrin Metabolism in an in vivo Model of Porphyria

Abstract: Administration of many antiepileptic drugs to patients with porphyria can precipitate an acute porphyric crisis. Information on the porphyrogenic activity of new antiepileptic drugs is still limited. In the presented study, the effects of tiagabine and topiramate on porphyrin metabolism were evaluated in an in vivo model of porphyria. Administration of the protoporphyrinogen oxidase inhibitor oxadiazon (12.5 mg/kg/day) for four days to male Wistar rats caused a partial block of porphyrin biosynthesis, thus mimicking the condition of quiescent variegate porphyria. Administration of phenobarbital (75 mg/kg/day) to oxadiazon‐pretreated rats increased liver porphyrin content, liver porphobilinogen content (means 480 nmol/g, control less than 20 nmol/g) and urinary excretion of porphobilinogen (means 1000 μmol/l, control less than 20 μmol/l). Tiagabine (75 mg/kg/day) and topiramate (75 mg/kg/day) increased liver porphobilinogen content (means 33 and 53 nmol/g respectively) and urinary porphobilinogen concentration (240 and 490 μmol/l respectively). Similar results were obtained in oxadiazon‐treated BALB/c mice. In untreated rats, tiagabine and topiramate caused a moderate increase of hepatic pentoxyresorufin‐O‐dealkylase activity (approximately 100 and 200 pmol/min./mg respectively, controls 15 pmol/min./mg). These data demonstrate that administration of tiagabine or topiramate to oxadiazon‐treated animals can provoke a condition resembling an acute porphyric attack and suggest that administration of these drugs to patients with suspected porphyria should be avoided. However, 5‐day administration of both tiagabine and topiramate (75 mg/kg) is considerably less porphyrogenic than phenobarbital administered at the same dose.

Effect of tiagabine and topiramate on porphyrin metabolism in an in vivo model of porphyria.

Administration of many antiepileptic drugs to patients with porphyria can precipitate an acute porphyric crisis. Information on the porphyrogenic activity of new antiepileptic drugs is still limited. In the presented study, the effects of tiagabine and topiramate on porphyrin metabolism were evaluated in an in vivo model of porphyria. Administration of the protoporphyrinogen oxidase inhibitor oxadiazon (12.5 mg/kg/day) for four days to male Wistar rats caused a partial block of porphyrin biosynthesis, thus mimicking the condition of quiescent variegate porphyria. Administration of phenobarbital (75 mg/kg/day) to oxadiazon-pretreated rats increased liver porphyrin content, liver porphobilinogen content (means 480 nmol/g, control less than 20 nmol/g) and urinary excretion of porphobilinogen (means 1,000 micromol/l, control less than 20 micromol/l). Tiagabine (75 mg/kg/day) and topiramate (75 mg/kg/day) increased liver porphobilinogen content (means 33 and 53 nmol/g respectively) and urinary porphobilinogen concentration (240 and 490 micromol/l respectively). Similar results were obtained in oxadiazon-treated BALB/c mice. In untreated rats, tiagabine and topiramate caused a moderate increase of hepatic pentoxyresorufin-O-dealkylase activity (approximately 100 and 200 pmol/min./mg respectively, controls 15 pmol/min./mg). These data demonstrate that administration of tiagabine or topiramate to oxadiazon-treated animals can provoke a condition resembling an acute porphyric attack and suggest that administration of these drugs to patients with suspected porphyria should be avoided. However, 5-day administration of both tiagabine and topiramate (75 mg/kg) is considerably less porphyrogenic than phenobarbital administered at the same dose.

Herbicide-induced experimental variegate prophyria in mice: tissue porphyrinogen accumulation and response to porphyrogenic drugs

Administration of oxadiazon or oxyfluorfen (1000 ppm in the diet) to male BALB/c mice for 9 days resulted in experimental porphyria, resembling the acute phase of human variegate porphyria. Urinary concentrations of 5-aminolevulinic acid and porphobilinogen reached 1500 and 3000 mumol/L, respectively. Both herbicides caused a decrease of protoporphyrinogen oxidase activity in liver and kidney. Brain protoporphyrinogen oxidase activity was not altered. Liver and kidney porphyrin content increased to 11 and 17 nmol/g, respectively (control mice, 2 nmol/g). Over 50% of liver and kidney porphyrins were in the reduced (porphyrinogen) form. Bile of oxadiazon-treated mice contained 700 nmol/mL of protoporphyrinogen (control mice, 15 nmol/mL). Porphyrin content of the trigeminal nerve increased from 1 nmol/g in control animals to 11 nmol/g in oxadiazon-treated animals, suggesting a possible contribution of peripheral nerve porphyrins to porphyric neuropathy. Mice treated with 125 ppm of oxadiazon in the diet for 9 days excreted moderately elevated levels of porphobilinogen in urine (control mice, less than 50 mumol/L; treated mice, 330 mumol/L). Administration of phenobarbital or phenytoin (single injections on days 7, 8, and 9) increased the urinary porphobilinogen concentration to 3500 mumol/L. This response to porphyrogenic drugs resembles the response observed in human acute porphyrias.

Herbicide-induced experimental variegate prophyria in mice: tissue porphyrinogen accumulation and response to porphyrogenic drugs

Administration of oxadiazon or oxyfluorfen (1000 ppm in the diet) to male BALB/c mice for 9 days resulted in experimental porphyria, resembling the acute phase of human variegate porphyria. Urinary concentrations of 5-aminolevulinic acid and porphobilinogen reached 1500 and 3000 mumol/L, respectively. Both herbicides caused a decrease of protoporphyrinogen oxidase activity in liver and kidney. Brain protoporphyrinogen oxidase activity was not altered. Liver and kidney porphyrin content increased to 11 and 17 nmol/g, respectively (control mice, 2 nmol/g). Over 50% of liver and kidney porphyrins were in the reduced (porphyrinogen) form. Bile of oxadiazon-treated mice contained 700 nmol/mL of protoporphyrinogen (control mice, 15 nmol/mL). Porphyrin content of the trigeminal nerve increased from 1 nmol/g in control animals to 11 nmol/g in oxadiazon-treated animals, suggesting a possible contribution of peripheral nerve porphyrins to porphyric neuropathy. Mice treated with 125 ppm of oxadiazon in the diet for 9 days excreted moderately elevated levels of porphobilinogen in urine (control mice, less than 50 mumol/L; treated mice, 330 mumol/L). Administration of phenobarbital or phenytoin (single injections on days 7, 8, and 9) increased the urinary porphobilinogen concentration to 3500 mumol/L. This response to porphyrogenic drugs resembles the response observed in human acute porphyrias.

Mitral Valve Replacement in a Patient with Acute Intermittent Porphyria

Mitral Valve Replacement in a Patient with Acute Intermittent Porphyria

Sustained high plasma 5‐aminolaevulinic acid concentration in a volunteer: no porphyric symptoms

The pathogenesis of the acute porphyric attack is not known. One hypothesis is that porphyrin precursors, especially 5-aminolaevulinic acid (ALA), are toxic for neuronal tissue. This was tested by infusing ALA in a male volunteer after a loading dose at a rate of 50-80 mg h-1 for 92.5 h. During the experiment plasma ALA concentration was 9-11 mumol 1-l and porphobilinogen concentration 3-6 mumol 1-l which are the levels seen during acute attacks. Urinary excretion of these porphyrin precursors was also markedly increased. ALA infusion caused no subjective symptoms and no change in pulse rate, blood pressure, or autonomic nerve function or conduction velocity of peripheral nerves. Photosensitivity was not demonstrable. It is concluded that sustained high plasma ALA concentration does not cause porphyria-like symptoms.