Porphyrin Excretion Research Articles

Analysis of Urinary Porphyrins in Rats Exposed to Aluminum and Iron

The mechanism by which excess aluminum induces anemia may be aluminum overload resulting from a reversible block in heme synthesis due either to a defect in porphyrin synthesis or to impaired iron utilization. Studies were conducted to define the specific changes in the urinary porphyrin excretion pattern (porphyrin profile) and the time course of those changes in rats exposed to aluminum. In these studies, aluminum chloride (AlCl3) was orally administered to female Wistar rats at the dose of 100 mg Al/kg for 35 days with or without FeCl2 (4 mg Fe/kg). Control rats were treated with 0.9% NaCl or with FeCl2 (4 mg/kg). The dynamics of urine porphyrins (8-, 7-, 6-, 5-, and 4-carboxyporphyrins) was determined by HPLC on the 7th, 14th, 21st, 28th, and 35th days in both exposed and control groups of rats. The results of the experiment indicate that aluminum induced a statistically significant increase in the percentage of uroporphyrin and a decrease in coproporphyrin in urine (cumulative dose, 2100 mg Al/kg). Changes in urinary porphyrins were observed when the concentration of aluminum in serum was at 48 μg Al/L on average. Administration of iron together with aluminum diminished the described changes in porphyrins metabolism caused by aluminum itself.

A mouse model of familial porphyria cutanea tarda

Approximately one-third of patients with porphyria cutanea tarda (PCT), the most common porphyria in humans, inherit a single mutant allele of the uroporphyrinogen decarboxylase (URO-D) gene. PCT associated with URO-D mutations is designated familial PCT. The phenotype is characterized by a photosensitive dermatosis with hepatic accumulation and urinary excretion of uroporphyrin and hepta-carboxylic porphyrins. Most heterozygotes for URO-D mutations do not express a porphyric phenotype unless hepatic siderosis is present. Hemochromatosis gene (HFE) mutations are frequently found when the phenotype is expressed. We used homologous recombination to disrupt one allele of murine URO-D. URO-D(+/-) mice had half-wild type (wt) URO-D protein and enzymatic activity in all tissues but did not accumulate hepatic porphyrins, indicating that half-normal URO-D activity is not rate limiting. When URO-D(+/-) mice were injected with iron-dextran and given drinking water containing delta-aminolevulinic acid for 21 days, hepatic porphyrins accumulated, and hepatic URO-D activity was reduced to 20% of wt. We bred mice homozygous for an HFE gene disruption (HFE(-/-)) to URO-D(+/-) mice, generating mice with the URO-D(+/-)/HFE(-/-) genotype. These animals developed a porphyric phenotype by 14 weeks of age without ALA supplementation, and URO-D activity was reduced to 14% of wt. These data indicate that iron overload alone is sufficient to reduce URO-D activity to rate-limiting levels in URO-D(+/-) mice. The URO-D(+/-) mouse serves as an excellent model of familial PCT and affords the opportunity to define the mechanism by which iron influences URO-D activity.

The Porphyrias.

The porphyrias are a diverse group of metabolic diseases. Major manifestations are episodic neurovisceral attacks of pain or other neurologic features, and/or dermatologic abnormalities. It is essential that a clear diagnosis be established prior to planning management. In our experience, most patients referred with a presumptive diagnosis of "porphyria" do not have true porphyria at all, but rather have syndromes of other etiologies associated with mild, nonspecific increases in urinary porphyrin excretion (secondary porphyrinurias). The management of the acute or inducible porphyrias depends upon prevention and prompt, aggressive management of acute attacks. The latter includes nutrition (at least 300 g/d carbohydrate plus adequate protein), analgesia, and intravenous heme. The management of active porphyria cutanea tarda involves iron depletion by therapeutic phlebotomy and cessation of precipitating or exacerbating factors, especially alcohol and estrogens. When chronic hepatitis C and/or HIV infection are present, they should also be treated. The management of protoporphyria involves ensuring adequate iron stores, and avoidance of hepatotoxic or cholestatic factors. Liver transplantation may be life-saving in the small minority of patients who develop progressive protoporphyric liver disease. A few patients with congential erythropoietic porphyria (Günther's disease) have been treated successfully by transplantation of bone marrow from a normal donor. In the future, this and other forms of porphyria may be treated by specific gene therapy. Such efforts are now under development, but they are not yet ready for human trials in the US.

Multiple Regulatory Steps in Erythroid Heme Biosynthesis

Current models for regulation of heme synthesis during erythropoiesis propose that the first enzyme of the pathway, 5-aminolevulinate synthase (ALAS), is the rate-limiting enzyme. We have examined cellular porphyrin excretion in differentiating murine erythroleukemia cells to determine in situ rate-limiting steps in heme biosynthesis. The data demonstrate that low levels of coproporphyrin and protoporphyrin accumulate in the culture medium under normal growth conditions and that during erythroid differentiation the level of excretion of coproporphyrin increases approximately 100-fold. Iron supplementation lowered, but did not eliminate, porphyrin accumulation. While ALAS induction is necessary for increased heme synthesis, these data indicate that other enzymes, in particular coproporphyrinogen oxidase, represent downstream rate-limiting steps.

Transdermal estrogen replacement therapy in postmenopausal women previously treated for porphyria cutanea tarda

Oral contraceptives and postmenopausal estrogen replacement therapy are recognized as risk factors for the development of porphyria cutanea tarda (PCT) in women. The recommended clinical practice is to withhold estrogen therapy in women who have had phlebotomy therapy for PCT and are clinically and biochemically normal. We tested the safety and efficacy of transdermal estrogen replacement therapy in 7 women previously treated for PCT and compared them with 19 non-porphyric control subjects treated with transdermal or oral estrogens. Gonadotrophic hormone levels, estrogen levels, liver function studies, body iron stores, urine porphyrin excretion, and cytochrome P4501A2 (CYP1A2) activity were monitored for 1 year. Four of the women previously treated for PCT completed the study. None had evidence of a porphyric relapse. CYP1A2 activity, measured by three different methods, did not differ between study subjects receiving estrogens, patients with active PCT, and non-porphyric control subjects, nor did CYP1A2 activity change during the study period. Gonadotro-phic hormone levels fell and estrogen levels rose in all women receiving estrogens. The administration of estrogens by the transdermal route appeared to be safe in the small number of subjects we studied and should be considered for women previously treated for PCT. (J Lab Clin Med 2000;136:482-8)

On-line LC-MS analysis of urinary porphyrins.

A reversed-phase high-performance liquid chromatography-mass spectrometry (LC-MS) method is described for the separation and simultaneous analysis of porphyrins related to disorders of heme biosynthesis (uro-, heptacarboxylic, hexacarboxylic, pentacarboxylic, and coproporphyrins). The method involves initial porphyrin esterification and extraction from urine. Detection and quantification is performed from the extracts by separation with a Hypersil BDS column and on-line detection by MS through coupling with an atmospheric pressure chemical ionization interface. The porphyrin esters are detected as protonated molecules [M + H]+. Their mass spectra also exhibit an [M + Na]+ fragment of lower intensity. The analytical performance of this method is compared with those of LC with UV and fluorescence detection. LC-MS used in selective [M + H]+ ion monitoring provides the lowest detection and quantitation limits. In scan mode, this LC-MS method affords, without further isolation or concentration steps, the measurement of mass spectra of unknown compounds present in the urine of patients with altered porphyrin excretion.

Hereditary coproporphyria in Germany: clinical-biochemical studies in 53 patients

Objectives: To describe the biochemical and clinical features in hereditary coproporphyria (HCP). Design and method: Within the last 20 years, we investigated 53 patients (male:female = 1:2.5; age = 8–86 years) suffering from HCP. We describe the characteristic levels of urine, and fecal porphyrins and their precursors in hereditary coproporphyria and present the clinical features. Especially, we measured the coproporphyrin isomers I and III. Results and conclusion: The group of hereditary coproporphyria patients exhibited a significantly higher ( p < 0.0001) excretion of urinary porphyrin precursors, δ-aminolevulinic acid (median = 84 μmol/24 h) and porphobilinogen (median = 39 μmol/24 h), as compared to controls (δ-aminolevulinic acid: 22 μmol/24 h, porphobilinogen: 3 μmol/24 h; median, n = 20). The median of coproporphyrin in urine (1315 nmol/24 h) and feces (1855 nmol/g) were enhanced 12- and 168-fold, as compared to healthy subjects (urinary coproporphyrin: 106 nmol/24 h, fecal coproporphyrin: 11 nmol/g; median, n = 20). During therapy on one female patient, with IV application of heme arginate, a considerable decline of porphyrin precursors and porphyrin excretion was observed. The examination of urinary and fecal coproporphyrin isomers I and III revealed an excessive elevation of the coproporphyrin isomer III of 87% in urine and 94% in feces, respectively (normal: urinary isomer III = 69–83% and fecal isomer III = 25–40%). In feces the increase of isomer III caused an inversion of the physiologic coproporphyrin isomer III:I ratio that could be recognized in all various stages in hereditary coproporphyria and in children. Acute attacks of hereditary coproporphyria are accompanied by an acute polysymptomatic clinical syndrome, and this is associated with high levels of urinary porphyrin precursors. On review of our patients, the highest percentage had abdominal pain (89%), followed by neurologic (33%), psychiatric (28%), cardiovascular (25%), and skin symptoms (14%).

Cutaneous porphyria in a neonate with tyrosinaemia type 1

A term infant born to consanguineous parents presented at birth with hypoglycaemia, thrombocytopenia, coagulopathy and hyperbilirubinaemia associated with polycythaemia due to delayed cord clamping. Despite phototherapy and correction of polycythaemia by partial exchange transfusion, coagulopathy, hypoglycaemia and conjugated hyperbilirubinaemia persisted, suggesting hepatic failure. Metabolic work-up led to the diagnosis of tyrosinaemia type 1 on day 4. Two--(2-nitro-4-trifluoromethylbenzoyl)--1,3 cyclohexanedione (NTBC) treatment, started on day 5, resulted in progressive clinical improvement and unambiguous biochemical response. Severe skin purpuric lesions occurred in areas exposed to phototherapy. These resolved slowly after its discontinuation. Urine analysis sampled just before and 6 days after starting NTBC treatment showed high levels of type 1 coproporphyrin isomers. Such findings do not seem directly related to tyrosinaemia type 1 where succinylacetone inhibits delta-aminolevulinic acid (delta-ALA) dehydratase and where the accumulation of delta-ALA results in neurotoxicity without photosensitivity. We describe a cutaneous form of porphyria in a neonate presenting with severe liver failure due to tyrosinaemia type 1. This porphyria is tentatively attributed to a secondary accumulation of coproporphyrins due to cholestasis, as reported in the bronze baby syndrome and recently described in neonates with purpuric phototherapy-induced eruption, rather than to a primary defect of porphyrin metabolism. The hypothesis of a direct effect of tyrosinaemia type 1 on porphyrin excretion is also discussed.

Spontaneous Porphyria of the Long–Evans Cinnamon Rat: An Animal Model of Wilson's Disease

To confirm and extend our previous microspectrophotometric observations of 30-week-old male Long–Evans Cinnamon (LEC) rats, an animal model of human Wilson's disease, we analyzed the porphyrin patterns of the organs, urine, and plasma of LEC rats. Abnormal accumulation of porphyrins, especially highly carboxylated porphyrins (uro- and heptaporphyrin), in the kidneys and liver was seen in male and female LEC rats aged 30 weeks and also in 10-week-old rats, before the onset of spontaneous hepatic dysfunction. Accumulation of copper and iron in the kidneys was not observed in the 10-week-old rats. Massive accumulation of porphyrins was observed only in the kidneys of the 30-week-old male LEC rat, indicating that this symptom is related to sex and age. Renal accumulation of porphyrins was reflected in the rate of urinary porphyrin excretion. Hepatic accumulation of porphyrins appeared to be independent of sex and age. These results indicate that neither renal nor hepatic porphyrin accumulation is the result of renal deposition of metals or of spontaneous hepatic dysfunction and that porphyrinuria in the LEC rat is closely related to the renal accumulation of porphyrins. In contrast to these organs, a reduction in the porphyrin levels was observed in the brain of the LEC rat. This was independent of sex and age. The present work stresses the existence of an abnormal heme metabolism in the LEC rat, and thus, the necessity to study the heme metabolism in human Wilson's disease is strongly suggested.

Porphyrins, porphyrin metabolism, porphyrias. III. Diagnosis, care and monitoring in porphyria cutanea tarda - suggestions for a handling programme

Deficiency of the fifth enzyme in haem synthesis, uroporphyrinogen decarboxylase (UPGD), may give rise to accumulation and excretion of poly-carboxylated porphyrins, as well as to clinical manifestations in the form of a phototoxic skin reaction and liver engagement leading to cirrhosis and hepatocellular cancer. The cutaneous reaction, presenting as skin fragility and blisters on areas exposed to sun-porphyria cutanea tarda (PCT)-develops only in individuals with a remaining hepatic UPGD activity less than 20% of normal. Experimental results and clinical observation give evidence that PCT is a multifactorial disease. In some individuals a 50% decrease in UPGD activity is a consequence of inheritance of an allele with a mutation in the gene programming for the enzyme, but in these gene carriers, as well as in the other patients with overt PCT, the activity of the hepatic enzyme is reduced below the critical level by the action of specific inhibitors. In the generation of the enzyme inhibitors, iron plays a central role by promoting the formation of reactive oxygen species, a process where a specific class of cytochrome enzymes; cytochrome P450 1A (CYP4501A), participates. The varying individual susceptibility to development of the disease can be discussed in terms of differences in a spectrum of factors that affect the availability of the free form of this element in the liver, or its pathogenic action. In the article the roles of chronic viral infection, alcohol abuse and exposition to polyhalogenated cyclic hydrocarbons are considered in the light of effects on the availability of iron in the liver. Some genetic prerequisites for susceptibility to PCT-inducing agents are included in a tentative model for the disease, i.e. mutations in the UPGD gene and in the HFE gene affected in haemochromatosis, as well as genetically steered inducibilities of the genes programming for CYP4501A and the rate-limiting enzyme in haem synthesis, 5-aminolevulinate synthase. With the pathogenic model as a basis the different therapeutic strategies that can be applied are discussed, and suggestions for a handling programme for the patient presenting with PCT put forward.

Diagnosis of variegate porphyria - hard to get?

Variegate porphyria (VP) is an inherited metabolic disease that results from the partial deficiency of protoporphyrinogen oxidase. In this communication we have used DNA technology in the diagnosis of VP and compared the results with the biochemical and clinical data. To date, we have diagnosed 107 VP patients using either biochemical or DNA techniques or both. In addition, in 106 family members the diagnosis of VP could be excluded. The sensitivity and specificity of the biochemical screening for VP were studied among 38 family members. These individuals were either asymptomatic (n=19) or had experienced occasional skin symptoms (n=13), acute attacks (n=5) or both (n=1). The sensitivity of urinary and fecal coproporphyrin analysis was 48% and 52%, respectively. The sensitivity of urinary uroporphyrin analysis was 71% and for fecal protoporphyrin 77%. Plasma fluorescence was sensitive in symptomatic patients even in remission, but resulted in false negatives in four asymptomatic patients with normal excretion of porphyrins in the urine. In our series of mutation screening, many new asymptomatic patients were identified, and this demonstrated that DNA analysis is the only reliable way to screen (a)symptomatic patients facilitating correct treatment and proper genetic counselling of family members at risk. Biochemical analyses (e.g. plasma fluorescence, fecal protoporphyrins, urinary copro- and uroporphyrins, porphobilinogen and delta-aminolevulinic acid) are essential when the diagnosis of VP is confirmed at the symptomatic phase.

Treatment of Porphyria cutanea tarda with Oral Thalidomide

Eight male patients with overt clinical and biochemical features of porphyria cutanea tarda (PCT) were orally treated with 300 mg/day thalidomide for 1 week and with 200 mg/day for 3 more weeks. Already after the first week of treatment no new vesicles and/or bullae could be observed. Spontaneous blisters completely disappeared, increased skin fragility subsided and skin hyperpigmentation receded about 2 months after completion of therapy, whereas hypertrichosis persisted. There was a rapid decrease in the urinary total porphyrin excretion which reached normal levels in all patients by the end of the fourth week of therapy, whereas the posttreament chromatographic pattern of urinary porphyrins revealed a slight reduction of higher carboxylated porphyrin metabolites and an increase in the amount of the excreted coproporphyrin, as compared to the pretreatment period. Somnolence, intermittent constipation and dry mouth occurred in all patients, 2 patients additionally experienced dizziness. No evidence of peripheral neuropathy could be detected and laboratory investigations revealed no abnormalities, as compared to the pretreatment period. During the 16- to 28-month follow-up of the patients, no clinical or biochemical relapse was observed. In view of the encouraging results of the present investigation, further studies are now warranted in order to definitely answer the question whether oral thalidomide may be regarded as an effective alternative approach to the treatment of PCT.

Urinary porphyrin excretion in hepatitis C infection.

A high prevalence of hepatitis C virus infection in porphyria cutanea tarda in some populations suggests a close link between viral hepatitis and alteration of porphyrin metabolism. Moreover, there is evidence of a role of porphyrinopathies in hepatocarcinogenesis. The aim of our study was to obtain data on the prevalence and patterns of heme metabolism alterations in patients with chronic hepatitis C virus infection. Urinary porphyrin excretion was prospectively studied in 100 consecutive outpatients with chronic hepatitis C infection without signs of photosensitivity, using an ion-pair high-performance liquid chromatography method. Increased total porphyrin excretion was found in 41 patients, with predominant excretion of coproporphyrins (whole study group: mean 146 microg/g creatinine, interquartile range 76-186; normal < 150), in 10 patients excretion exceeded 300 microg/g creatinine. In the majority of all patients studied (75/100) an increased ratio of the relatively hydrophobic coproporphyrin isomer I to isomer III was found. In just one case, urinary porphyrin pattern characteristic for chronic hepatic porphyria was present (uroporphyrin > coproporphyrin, heptacarboxyporphyrin III increased) but the total porphyrin excretion was only slightly elevated in this case. In the whole group, total urinary porphyrin excretion correlated well with serum bilirubin and was inversely correlated with albumin and thrombin time. In conclusion, secondary coproporphyrinuria occurs frequently in heptatitis C infection, whereas in Germany, preclinical porphyria cutanea tarda seems to be rare in these patients.

Urinary porphyrin excretion measurements in healthy neonates.

The objective of this study was to establish normal reference ranges for porphyrins in healthy neonates. There is little information about urinary porphyrin excretion in this age group. This knowledge may provide an early diagnostic tool for detecting subtle alterations or latent forms in disorders of heme biosynthesis. Fifty healthy neonates were selected from the Department of Obstetrics. Total urinary porphyrins in random specimens were analysed by a spectrofluorometry method. The measurement of porphyrin fractions was made by fluorometric high-performance liquid chromatography (HPLC). The results were adjusted to urinary creatinine excretion to correct any imprecision and interindividual variation in body mass. The urinary total porphyrin had a median value of 331.50 (nmol/L). A statistically significant relationship between total porphyrin (nmol/L) and creatinine (mmol/L) was found (p < 0.01). The porphyrin/creatinine ratio showed a median value of 56.30 nmol/mmol creatinine. The study of individual porphyrins revealed that coproporphyrin and uroporphyrin were the major porphyrins excreted in neonates (coproporphyrin represents 81.98% and uroporphyrin 16.64% of total porphyrin); in both cases, isomer I was predominant with median values of 22.36 and 6.25 nmol/mmol creatinine, respectively. No significant relationships were found between porphyrin excretion and sex, gestational age, weight, or height. Our data provide the reference limits for porphyrins in neonates as a diagnostic guideline for evaluation of subtle alterations in heme biosynthesis.

Porphyrin status in aluminum foundry workers exposed to hexachlorobenzene and octachlorostyrene.

The possible interference of hexachlorobenzene and octachlorostyrene (i.e., thermal byproducts from hexachloroethane in aluminum degassing) with porphyrin metabolism was investigated in exposed workers. Urine specimens from 9 male aluminum foundry workers (i.e., smelters) at 6 different companies and from 18 controls-matched for sex, age, residence, and socioeconomic status-were analyzed for total porphyrins and porphyrin isomers. Workers exposed to hexachlorobenzene and octachlorostyrene had a statistically significant increase in urinary total porphyrins, compared with controls (mean +/- standard deviation: 13.63 +/- 11.13 micromol/mol creatinine and 6.24 +/- 3.84 micromol/mol creatinine, respectively; p = .02). The authors attributed the results mainly to differences in excretion of coproporphyrins-notably coproporphyrin III. Erythrocyte uroporphyrinogen decarboxylase activity was similar in both groups. There was a high correlation between levels of hexachlorobenzene and octachlorostyrene, respectively, in plasma and urinary excretion of porphyrins; these findings, however, relied heavily on 1 subject for whom extreme values were obtained. The results indicated that occupational exposure to hexachlorobenzene and octachlorostyrene in aluminum degassing with hexachloroethane may affect porphyrin metabolism in a manner consistent with early secondary coproporphyrinuria-the first recognized step in the development of chronic hepatic porphyria. It was also noted that changes remained detectable some years after exposure ceased.

Effect of alpha lipoic acid amide on hexachlorobenzene porphyria.

The aim of this work is to study the effect of thioctamide--the commercial form of alpha lipoic acid amide--on the porphyrinogenic action of hexachlorobenzene (HCB). For this purpose, porphyria was induced in rats by chronic HCB treatment, with or without simultaneous thioctamide administration. Two different groups of rats were used as reference: one treated with vehicle (control) and the other treated with thioctamide (TO). Urine delta aminolevulic acid, porphobilinogen, and porphyrin excretions were lower in the HCB + TO treated group than in the HCB group, and the same happened with liver uroporphyrin accumulation. On the other hand, the second stage of uroporphyrinogen-decarboxylase activity was significantly higher in the HCB + TO group than in the HCB group. delta aminolevulic acid synthase activity was higher in the HCB group. Hepatic thiobarbituric acid reactive substances were lower in HCB + TO group than in HCB group. Thus, we might suggest that TO would decrease HCB effects by means of its free radical scavenging ability, and by having a direct effect on uroporphyrinogen-decarboxylase activity.

Altered activity of heme biosynthesis pathway enzymes in individuals chronically exposed to arsenic in Mexico.

Our objective was to evaluate the activities of some enzymes of the heme biosynthesis pathway and their relationship with the profile of urinary porphyrin excretion in individuals exposed chronically to arsenic (As) via drinking water in Region Lagunera, Mexico. We selected 17 individuals from each village studied: Benito Juarez, which has current exposure to 0.3 mg As/l; Santa Ana, where individuals have been exposed for more than 35 years to 0.4 mg As/l, but due to changes in the water supply (in 1992) exposure was reduced to its current level (0.1 mg As/l), and Nazareno, with 0.014 mg As/l. Average arsenic concentrations in urine were 2058, 398, and 88 microg As/g creatinine, respectively. The more evident alterations in heme metabolism observed in the highly exposed individuals were: (1) small but significant increases in porphobilinogen deaminase (PBG-D) and uroporphyrinogen decarboxylase (URO-D) activities in peripheral blood erythrocytes; (2) increases in the urinary excretion of total porphyrins, mainly due to coproporphyrin III (COPROIII) and uroporphyrin III (UROIII); and (3) increases in the COPRO/URO and COPROIII/COPROI ratios. No significant changes were observed in uroporphyrinogen III synthetase (UROIII-S) activity. The direct relationships between enzyme activities and urinary porphyrins, suggest that the increased porphyrin excretion was related to PBG-D, whereas the increased URO-D activity would enhance coproporphyrin synthesis and excretion at the expense of uroporphyrin. None of the human studies available have reported the marked porphyric response and enzyme inhibition observed in rodents. In conclusion, chronic As exposure alters human heme metabolism; however the severity of the effects appears to depend on characteristics of exposure not yet fully characterized.

Urinary porphyrin excretion in a human population highly exposed to hexachlorobenzene.

Data from an epidemic reported in Turkey (1955-1959) is the only information about the relationship between hexachlorobenzene (HCB) intake and porphyria cutanea tarda in humans. No information is available on the HCB threshold exposure level to induce porphyria cutanea tarda. To study HCB serum levels and urinary porphyrin excretion in the inhabitants of a village located near an organochlorine compound factory with high HCB concentrations in the air and to detect possible alterations in urinary porphyrin excretion and examine their relationship with HCB serum levels. Cross-sectional study. Unit of Porphyrias of a tertiary care facility in Barcelona, Spain. Six hundred four inhabitants of the village who were older than 14 years provided serum and urine samples (185 participants were factory workers). Serum HCB was analyzed by gas chromatography coupled to electron capture detection. Quantification of urinary total porphyrins was performed by spectrofluorimetry. Porphyrin profile was determined by high-pressure liquid chromatography. Hexachlorobenzene was detected in all serum samples (mean, 39.8 ng/mL; range, 1.1-1616.0 ng/mL), and levels were higher in factory workers. Mean +/- SD level urinary total porphyrin average concentration was 98 +/- 69 nmol/L (range, 9-1009 nmol/L). Only the urine sample with the highest porphyrin concentration showed an increase of highly carboxylated porphyrins, with a typical profile of porphyria cutanea tarda. In the remaining 603 urine samples, coproporphyrin was the predominant fraction. The airborne exposure to and increased body burden of HCB in the Flix village population are not enough to trigger a significant alteration of the heme biosynthesis pathway.

Novel Single Nucleotide Polymorphism (9678G→A) for Linkage Analysis of Acute Intermittent Porphyria

Acute intermittent porphyria (AIP) is an autosomal dominant inborn error of metabolism caused by a partial deficiency of the third enzyme of the heme biosynthetic pathway, hydroxymethylbilane synthase (EC 4.3.1.8.; HMBS). This enzyme catalyzes the condensation of four molecules of porphobilinogen to a tetrapyrrole hydroxymethylbilane. Clinically, AIP is characterized by acute attacks of neurological disorders manifesting as abdominal pain, hypertension, tachycardia, peripheral neuropathy, and mental dysfunction. Biochemical diagnosis of AIP relies on increased urinary porphobilinogen and fecal porphyrin excretion within the health-related reference interval. The definitive diagnosis requires the assay of red blood cell (RBC) HMBS activity (1). AIP is a genetic disease characterized by poor penetrance; therefore, identification of presymptomatic AIP carriers in families with manifesting individuals is of utmost clinical importance because avoidance of precipitating agents, e.g., drugs and alcohol, can prevent the occurrence of the first porphyric attacks, which may be life-threatening. However, the identification of AIP carriers by assaying the RBC HMBS activity is problematic because there is substantial overlap between the enzyme activities of healthy individuals and patients with AIP (2). In addition, in one variant of AIP, the decreased enzyme activity is confined to …

Validity of spot urine samples as a surrogate measure of 24-hour porphyrin excretion rates. Evaluation of diurnal variations in porphyrin, mercury, and creatinine concentrations among subjects with very low occupational mercury exposure.

Porphyrin, mercury, and creatinine levels in single-void urine specimens ("spot samples") were compared with calculated 24-hour urine concentrations among 146 (77 male and 69 female) practicing dentists who are participating in an ongoing study of urinary porphyrin changes as a biomarker of mercury body burden. All subjects had urinary mercury concentrations < or = 5 micrograms/L, a level comparable to that of the general US population and which is below that determined to be associated with mercury-induced changes in urinary porphyrin excretion rates. The results confirmed previous findings of no significant diurnal variation in any of the porphyrin levels normally found in urine or in total porphyrin levels combined among males but describe significant diurnal variations in most porphyrin levels as well as concentrations of total porphyrins combined among females. Similarly, no evidence of large diurnal variation in mercury excretion among males was apparent, whereas significant diurnal variation in the mercury excretion rate among females was found. Creatinine adjustment of porphyrin or mercury concentrations had no significant effect on these findings. Moreover, no evidence of diurnal variation in urinary creatinine excretion among either male or female subjects was obtained, despite substantial between-subject variability in this parameter. These results support the view that spot urine samples may be utilized to derive reasonably accurate estimates of 24-hour porphyrin and mercury excretion rates in male subjects. In contrast, time of day appears to be of considerably greater importance when spot samples are utilized as 24-hour estimates of either porphyrin or mercury excretion rates among females. Additionally, time of day may be an important consideration in studies involving serial (repeated) porphyrin or mercury measurements using spot urine samples, irrespective of gender distribution of study subjects.