Plasma porphyrin concentrations in porphyria cutanea tarda

1. Plasma porphyrin concentrations in twelve patients with porphyria cutanea tarda (symptomatica) were compared with twenty normal controls.

2. The concentrations in porphyria cutanea tarda were significantly elevated.

Erythropoietic porphyria of the fox squirrel Sciurus niger

Uroporphyrin I is found in high concentration in the bones, teeth, blood, soft tissues, and urine of the fox squirrel, Sciurus niger. The concentration of uroporphyrin in fox squirrel spleen is much higher than in liver, kidney or bone marrow, probably because of accumulation from phagocytosed red cells. Bleeding causes a marked increase in the uroporphyrin concentration of red cells and spleen, and a 3-8-fold increase in uroporphyrin excretion. Urinary excretion of delta-aminolevulinic acid and porphobilinogen is not greater in fox squirrels than in nonporphyric gray squirrels. Sciurus carolinensis, used as controls. In all these characteristics, as well as in the previously demonstrated deficiency of the enzyme uroporphyrinogen III cosynthetase in red cells, the physiological porphyria of fox squirrels resembles congenital erythropoietic porphyria, a hereditary disease of man and cattle. For squirrels differ in showing no evidence of cutaneous photosensitivity or hemolytic anemia. Uroporphyrinogen III cosynthetase activity is present in fox squirrel bone marrow at 1/10 its concentration in gray squirrel marrow. The fox squirrel enzyme is much more unstable than the gray squirrel enzyme, which provides a possible explanation for its low activity and for the overproduction of uroporphyrin I. It is unlikely that the deficiency of cosynthetase is due to its inactivation by excessive amounts of uroporphyrinogen I synthetase, because activity of the latter enzyme is the same in blood from fox and gray squirrels.Fox squirrel porphyria provides a convenient model for studies of pathogenesis of human congenital erythropoietic porphyria.

Coproporphyrin I and 3 excretion in bile and urine

The excretion of coproporphyrin isomers I and III was studied in the rat. Both isomers were found to bind equally to rat plasma and liver cytosol in vitro and to disappear from plasma at equal rates after single injections in vivo. During equimolar infusions of isomers into bile fistula animals, both the I and III isomers were excreted in bile in a concentration ratio of 2:1, respectively. Pretreatment of animals with ethinylestradiol or simultaneous infusions of phenoldibromophthalein disulfonate caused a reduction in total hepatic excretion with no change in the 2:1 ratio in bile. As hepatic excretion fell, excretion of both isomers in urine rose, with an increase in the proportion of the I isomer. The findings mimic those reported to occur in man and can be explained by inhibition of a common carrier which requires a stereospecific configuration that statistically favors the hepatic transport of the symmetrical coproporphyrin I isomer.

Quantitative studies of the delivery of hepatic-synthesized bilirubin to plasma utilizing -aminolevulinic acid-4- 14 C and bilirubin- 3 H in man

After the simultaneous intravenous administration of unconjugated bilirubin-(3)H and delta-aminolevulinic acid-4-(14)C, the plasma disappearance curves of unconjugated bilirubin-(3)H and the plasma appearance curves of biosynthesized unconjugated bilirubin-(14)C have been defined in seven patients, three of whom had acute intermittent porphyria (AIP). The incorporation of (14)C into plasma unconjugated bilirubin, derived by an analysis which involves deconvolution of the two plasma curves, varied between 13.1 and 23.5% (mean 19.3%) of the injected dose in the nonporphyric patients and between 5.4 and 13.6% (mean 8.3%) of the injected dose in the porphyric patients. In five of the patients, the stercobilin-(14)C specific activity in a pooled specimen of feces was measured, enabling the following further values to be calculated: (a) the total (14)C radioactivity incorporated into bilirubin (21.0 and 25.3% [mean 23.2%] of the injected dose in two of the nonporphyric patients and between 8.5 and 25.3% [mean 14.2%] of the injected dose in the porphyric patients), and (b) the proportion of hepatic synthesized bilirubin delivered directly to plasma in the unconjugated form (between 0.520 and 0.904; mean for nonporphyric patients 0.712; mean for porphyric patients 0.614). The results demonstrate that a large proportion of bilirubin derived from hepatic hemes passes through the plasma in the unconjugated form before conjugation and secretion into bile.

Assays for porphyrins, delta-aminolevulinic-acid dehydratase, and porphyrinogen synthetase in microliter samples of whole blood: applications to metabolic defects involving the heme pathway

Three micromethods are described for the assay of enzymes or products of the heme biosynthetic pathway in blood. A fluorometric method for the assay of protoporphyrin may be applied to the rapid screening of children for chronic lead poisoning. A colorimetric assay for delta-aminolevulinic-acid dehydratase may be applied to the detection of acute and chronic lead poisoning. A fluorometric assay for porphyrin formation from prophobilinogen is also described.