Studies on the mechanism of experimental porphyria produced by 3,5-diethoxycarbonyl-1,4-dihydrocollidine. Role of a porphyrin-like inhibitor of protohaem ferro-lyase

Abstract

A green porphyrin-like pigment with inhibitory properties towards protohaem ferro-lyase activity was isolated from the livers of mice and rats after treatment with 3,5-diethoxycarbonyl-1,4-dihydrocollidine. Mice, which are more sensitive to the porphyrogenic properties of the drug, produce more inhibitor. The non-porphyrogenic analogue 3,5-diethoxycarbonylcollidine does not cause accumulation of the pigment in the liver. The inhibitory substance is present in control liver at low but measurable concentrations.

Liver production of N‐alkylated porphyrins caused in mice by treatment with substituted dihydropyridines

“…The livers of 25 mice were pooled for each batch of green pigments; these were isolated by column chromatography of a liver extract and further purified by TLC, as in [6] The neutral spectrum of all porphyrins listed here is of an aetio type with very similar absorption maxima to those reported for the griseofulvin-induced pigment or for synthetic N-methyl protoporphyrin [7,13]. The dication and zinc complexes of the various porphyrins were prepared [ 131 and their spectra determined in CHCl,, using the porphyrin methyl ester protoporphyrin in vivo [5], as this drug already possesses the aromatic structure and, on account of this, the 4.methyl substituent will not be readily eliminated. A monooxygenated intermediate such as formaldehyde is less likely, as this would entail loss of one of the 3 deuteriums present in the original methyl group.…”

“…We have isolated a potent inhibitor of protohaem ferro-lyase from the liver of mice made porphyric by treatment with this drug [5,6] and have identified the inhibitor as N-methyl protoporphyrin [7]. Inhibition of protohaem ferro-lyase has also been obtained both in vivo and in vitro with synthetic N-alkylated porphyrins , and the size of the alkyl group present on the pyrrole nitrogen atom has been shown to be important for the inhibitory effect, N-ethylmesoporphyrin being less active than N-methylmesoporphyrin [8].…”

“…Inhibition of protohaem ferro-lyase has also been obtained both in vivo and in vitro with synthetic N-alkylated porphyrins , and the size of the alkyl group present on the pyrrole nitrogen atom has been shown to be important for the inhibitory effect, N-ethylmesoporphyrin being less active than N-methylmesoporphyrin [8]. Isotopic experiments have suggested that the N-methylated protoporphyrin produced by treatment with 3,5-diethoxycarbonyl-1,4-dihydro-2,4,6-trimethylpyridine originates from liver haem [5,6,10], but the source of the methyl group bound onto the pyrrole nitrogen atom has not yet been determined. The following findings have raised the possibility that the methyl group may originate from the 4-methyl substituent of the drug: under relatively mild chemical conditions certain dihydropyridines lose their 4-alkyl substituent on oxidation and that this alkyl group can be donated to suitable nucleophiles [ 111.…”

Foxl1-Cre-marked adult hepatic progenitors have clonogenic and bilineage differentiation potential

“…In order to induce liver injury and Foxl1 expression, Foxl1-Cre; RosaYFP mice were fed a DDC-supplemented diet. DDC inhibits protoheme ferro-lyase activity, resulting in accumulation of protoporphyrin in hepatocytes, eventually leading to a ductular reaction and cholangitis (Tephly et al 1979;Fickert et al 2007). Treatment with DDC has been reported to induce proliferation of bipotent progenitor cells ).…”

Studies in porphyria: functional evidence for a partial deficiency of ferrochelatase activity in mitogen-stimulated lymphocytes from patients with erythropoietic protoporphyria.

“…In the case of EPP the nature of the factor(s) that influence the clinic-al expression of the gene defect of the disease is not known. In an experimental hepatic porphyria induced in mice and rats by treatment with 3,5-diethoxy-carbonyl-1,4-dihydrocollidine, a green porphyrin-like heme breakdown product that potently inhibits ferrochelatase activity is known to be produced in the liver (25). In addition to the primary genetic deficiency of ferrochelatase in EPP, there may also be other factors which affect the activity of the enzyme and identification and characterization of such factors would clearly be important in understanding the mechanism of clinical expression of this disorder.…”