Coproporphyrin, and uroporphyrin

Coproporphyrins and uroporphyrins are of chnical interest because they are excreted in increased amounts in... 

It may be noted that although the human organism is capable of degrading metal-containing porphyrins such as heme, it has no means of degrading porphyrins containing no metal, for example coproporphyrins and uroporphyrins. These must be excreted as such. The latter two are water-soluble and are thus found in urine and to some extent in the feces. Protoporphyrins, however, are largely water-insoluble and are excreted in the feces. Finally, it may be mentioned that porphyrias make their appearance after puberty. This has been associated with the appearance of 5/3-steroid reductases, as discussed above. 

Menon lA, Becker MAC, Persad SD, Haberman HF. Quantitation of hydrogen peroxide formed during UV-visible irradiation of protoporphyrin, coproporphyrin and uroporphyrin. Clin Chim Acta 1989 186 375-81. 

The use of chick embryo liver culture in vitro as contrasted to induction in the whole animal permitted the inference that the inducing chemicals acted directly on the hepatic cells and not via other stimuli generated from other organs. The porphyrins formed could be seen by fluorescence microscopy to accumulate in the c)doplasm of the liver parenchyma cells and were identified mainly as coproporphyiin with some protoporphyrin [25]. However, Doss [70] found mainly protoporphyrin. This difference may depend on conditions of culture the older cultures had more coproporphyrin and uroporphyrin. The increase in porphyrins in tissue culture has been assumed to be a result of an increase in ALA-synthetase. With the aid of 13-cm-diameter petri dishes, it has been possible to grow sufficient numbers of cells and demonstrate with inducing chemicals an increase in vitro of ALA-synthetase activity of seven to ten times that of controls, in a 20-hour period [21]. 

The first porphyrin intermediate of the biosynthetic pathway is uroporphyrinogen, which is stepwise decarboxylated by uroporphyrinogen decarboxylase to heptacarboxy-, hexacarboxy-, pentacarboxy-, and coproporphyrinogen. This latter compound proceeds, as indicated in Fig. 7.3.1, to protoporphyrinogen and protoporphyrin. The oxidized uroporphyrin and its decarboxylation products up to coproporphyrin are assayed in urine. Coproporphyrin and the further downstream intermediaries can be recovered from feces as described below. 

Commercial PCB Mixtures. Urinary coproporphyrin levels were increased in rats that ingested 0.3 or 1.5 mg/kg/day Aroclor 1242 in the diet for 2-6 months (Bruckner et al. 1974). Rats treated with 5 mg/kg/day Aroclor 1254 in the diet had maximum increases in liver microsomal P-450 concentration and liver weight after 1 week, but onset of porphyria and induction of 5-aminolevulinic acid (ALA) synthetase was delayed until 2-7 months of treatment (Goldstein et al. 1974). A marked accumulation of uroporphyrins occurred in the liver, and urinary excretion of coproporphyrin and other porphyrins was increased the largest increase was in uroporphyrins. The uroporphyrins in the liver and urine of the treated rats consisted primarily of 8- and 7-carboxyporphyrins. 

Mg-PPIX, or Mg-PPIXME. Furthermore, neither of the photodynamic precursors of PPIX, coproporphyrinogen nor uroporpophyrinogen (extracted as coproporphyrin III and uroporphyrin III) accumulate in diphenyl ether herbicide-treated plant tissues (Table IV). All of our data are consistent with the view that PPIX is the primary photodynamic pigment involved in the mechanism of action of these herbicides. 

Porphyrins are widely spread natural compounds. They are found in feces (coproporphyrin), urine (uroporphyrin), amniotic fluid, meconium, hemoglobin, and cytochromes. They are all formed by the condensation of four pyrrole rings, but differ from each other in the nature of their side chains. As it appears from the formula, the pyrrole ring that constitutes the unit structure of the porphyrin is the same ring that appears in proline, hydroxyproline, and indole. 

The pattern of porphyrin excretion in the urine can also be helpful in identifying lead intoxication. With lead poisoning, the urine concentrations of coproporphyrins I and II, porphobilinogen and uroporphyrin I rise. The most important increase, however, is that of coproporphyrin iii levels may exceed 5,000 pg/l in the urine in lead poisoned individuals, but its correlation with blood lead levels and ZPP are not as good as those of ALA. Increases in urinary porphyrins are not diagnostic of lead toxicity and may be seen in porphyria, some liver diseases, and in patients with high reticulocyte counts. 

There are many porphyrins, which differ from one another in the nature and disposition of the attached groups (vinyl, propionic acid, and methyl in protoporphyrin). Coproporphyrin 1, the principal porphyrin in human feces, has four methyl groups and four propionic acid groups in alternation around the molecule, and uroporphyrin I, sometimes present in human urine, has four acetic acid groups and four propionic acid groups in alternation. In the disease congenital porphyria there is a defect in the enzyme that normally catalyzes the conversion of uroporphyrin to-coproporphyrin. 

Porphyrins can be detected in urine and faeces by extraction into an organic solvent which is then examined for fluorescence. Coproporphyrins, protoporphyrins and uroporphyrins can also be measured separately in urine and faeces. This involves their differential extraction, using a number of different solvent systems, followed by measurement of their absorbance using a spectrophotometer. Various chromatographic procedures can also be used for their separation. 

Two coproporphyrins and two uroporphyrins have been found in nature. 

An early account194 describes an attempt to use 64Cu complexes of haematoporphyrin, protoporphyrin, uroporphyrin, and coproporphyrin to detect tumors preferential localization in tumors was not observed. It needs to be recognized that metalation can change solution... 

Increased porphyrins in clear fluid such as urine may be detected directly by their pink fluorescence if exposed to long ultraviolet (Fig. 7.3.2). The specificity of this screening assay may be improved if porphyrins are extracted by talcum [8]. These isolated porphyrins may be quantified using a spectrofluorimeter. As different porphyrias show specific excretion patterns, separation of the main porphyrins is desirable. The formerly used fractionated extraction enabled to separate the uroporphyrin fraction from the coproporphyrin fraction. In addition to uroporphyrin, the first fraction includes heptacarboxy- and part of hexacarboxyporphyrins, and in addition to coproporphyrin, the second fraction includes part of hexacarboxy- and pentacar-boxyporphyrins. Later on, thin-layer chromatography of methylester derivatives is used. 

All acute porphyrias show similar urinary porphyrin patterns with predominant elevation of uroporphyrin and coproporphyrin III isomer in addition, hepta-, hexa-, and especially pentacarboxyporphyrins are increased (see Fig. 7.3.3). 

Table 7.3.3 Example mean reference values for uroporphyrin, coproporphyrin I, and coproporphyrin III (these can only be interpreted as a guidance) collected by means of high-performance liquid chromatography (HPLC). The intermediary porphyrins were below the detection limit...

Side chains Different porphyrins vary in the nature of the side chains that are attached to each of the four pyrrole rings. For example, uroporphyrin contains acetate (-CH2-COO-) and propionate (-CH2-CH2-COO-) side chains, whereas coproporphyrin, is substituted with methyl (-CH3) and propionate groups. 

Methods using condensations of two dipyrrolic units suffer from inherent symmetry restrictions, though these are of course less serious than those involved in the use of monopyrrole tetramerization. Thus the routes through dipyrroles are limited to synthesis of porphyrins which are centrosymmetrically substituted (by way of self-condensation of a suitably activated dipyrrole), or to porphyrins which possess subunit symmetry in one or both halves of the molecule. It is very fortunate that this latter restriction is not serious for the synthesis of porphyrins from natural materials because rings c and d of uroporphyrin-III, coproporphyrin-III and protoporphyrin-IX (Table 1), for example, are symmetrically substituted about the C-15 atom. 

Uroporphyrins I and III are both excreted in small amounts in the urine. Another excretion product is coproporphyrin III, in which all of the carboxymethyl side chains have been decarboxylated to methyl groups. The feathers of the tropical touraco are colored with copper(II) complex of coproporphyrin III and this... 

Uroporphyrin I and coproporphyrin I will be present in the urine. In the absence of uroporphyrinogen cosynthase, hydroxymethyl bilane will spontaneously cyclyze into uroporphyrinogen I. Some of it will be oxidized to uroporphyrin I. Some will be decarboxylated by uroporphyrinogen decarboxylase to coproporphyrinogen I and then oxidized to coproporphyrin I. None of these will be degraded by heme oxidase. 

This rare form shows a very varied symptomatology. The disease may become manifest during puberty with severe pain or it may present later in life (beyond the 5 decade) with the clinical picture of moderate polyneuritis. ALA as well as uroporphyrins and coproporphyrins are augmented in the urine, whereas no abnormalities are evident in faeces or plasma. 

Figure 32-4 Representative HPLC chromatograms for (a) working standard b, norma) feces c, normal urine d, feces—hereditary coproporphyria e, urine—congenita erythropoietic porphyria f, feces—variegata porphyria g, urine—porphyria cutanea tarda and h, feces—porphyria cutanea tarda chromatographic conditions as described in the appendix on the Evolve site that accompanies this book. Peaks are I, uroporphyrin- 2, uroporphyrin-l 3, heptacarboxyiate porphyrin-l 4, heptacarboxylate porphyrin-tl 5, hexacarboxylate porphyrin 6, pentacarboxylate porphyrin 7, coproporphyrin-1 8, coproporphyrin- ll 9, deuteroporphyrin-IX ...

Porphyrias are inherited or acquired disorders caused by a deficiency of enzymes in the heme biosynthetic pathway. Porphyrin is synthesized in both the erythroblasts and the liver, and either one may be the site of a disorder. Congenital erythropoietic pOTjdtyria, for example, prematurely destroys eythrocytes. This disease results from insufficient cosynthase. In this porphyria, the synthesis of the required amount of uroporphyrinogen III is accompanied by the formation of very large quantities of uroporphyrinogen I, the useless symmetric isomer. Uroporphyrin I, coproporphyrin I, and other symmetric derivatives also accumulate. The urine of... 

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