Coproporphyrinogen I is a porphyrin metabolite arising from heme synthesis. Porphyrins are pigments found in both animal and plant life. Coproporphyrinogen I is a tetrapyrrole dead-end product resulting from the spontaneous oxidation of the methylene bridges of coproporphyrinogen arising from heme synthesis. It is secreted in feces and urine. Coproporphyrinogen I is biosynthesized from the tetrapyrrole hydroxymethylbilane, which is converted by the action of uroporphyrinogen synthase to uroporphyrinogen I. Uroporphyrinogen I is subsequently converted into coproporphyrinogen I through a series of four decarboxylations. Increased levels of coproporphyrinogens can indicate congenital erythropoietic porphyria or sideroblastic anemia, which are inherited disorders. Porphyria is a pathological state characterized by abnormalities of porphyrin metabolism and results in the excretion of large quantities of porphyrins in the urine and in extreme sensitivity to light. A large number of factors are capable of increasing porphyrin excretion, owing to different and multiple causes and etiologies: (1) the main site of the chronic hepatic porphyria disease process concentrates on the liver, (2) a functional and morphologic liver injury is almost regularly associated with this chronic porphyria, and (3) the toxic form due to occupational and environmental exposure takes mainly a subclinical course. Hepatic factors include disturbance in coproporphyrinogen metabolism, which results from inhibition of coproporphyrinogen oxidase as well as from the rapid loss and diminished utilization of coproporphyrinogen in the hepatocytes. This may also explain why coproporphyrin, its autoxidation product, predominates physiologically in the urine. Decreased biliary excretion of coproporphyrin leading to a compensatory urinary excretion. Therefore, the coproporphyrin ring isomer ratio becomes a sensitive index for impaired liver function, intrahepatic cholestasis, and disturbed activity of hepatic uroporphyrinogen decarboxylase. In itself, secondary coproporphyrinuria is not associated with porphyria symptoms of a hepatologic-gastroenterologic, neurologic, or dermatologic order, even though coproporphyrinuria can occur with such symptoms (PMID: 3327428). Under certain conditions, coproporphyrinogen I can act as a phototoxin, a neurotoxin, and a metabotoxin. A phototoxin leads to cell damage upon exposure to light. A neurotoxin causes damage to nerve cells and nerve tissues. A metabotoxin is an endogenously produced metabolite that causes adverse health effects at chronically high levels. Chronically high levels of porphyrins are associated with porphyrias such as porphyria variegate, acute intermittent porphyria, hereditary coproporphyria (HCP), congenital erythropoietic porphyria, and sideroblastic anemia. There are several types of porphyrias (most are inherited). Hepatic porphyrias are characterized by acute neurological attacks (seizures, psychosis, extreme back and abdominal pain, and an acute polyneuropathy), while the erythropoietic forms present with skin problems (usually a light-sensitive blistering rash and increased hair growth). The neurotoxicity of porphyrins may be due to their selective interactions with tubulin, which disrupt microtubule formation and cause neural malformations (PMID: 3441503).  Coproporphyrinogen I can be found in a number of food items, including cascade huckleberry, hyacinth bean, horseradish tree, and watercress.