Hexacarboxyporphyrin

Hexacarboxyporphyrin is a Porphyrin. Porphyrins are precursors of heme and usually only occur in urine in negligible amounts.

What is heme?

Heme is a red pigment composed of iron linked to a chemical called protoporphyrin. Heme is the substance that gives blood its red color. The body makes heme mainly in the bone marrow and liver. Bone marrow is the soft, spongelike tissue inside the bones; it makes stem cells that develop into one of the three types of blood cells—red blood cells, white blood cells, and platelets. The process of making heme is called heme biosynthetic pathway. One of eight enzymes controls each step of the process. The body has a problem making heme if any one of the enzymes is at a low level, also called a deficiency. Porphyrins and porphyrin precursors of heme then build up in the body and cause illness. So high levels of a porphyrin can indicate that the body has trouble making heme.

Heme’s functions:

Heme has important functions in the body. The largest amounts of heme are in the form of hemoglobin, found in red blood cells and bone marrow. Hemoglobin carries oxygen from the lungs to all parts of the body. In the liver, heme is a component of proteins that break down hormones, medications, and other chemicals and keep liver cells functioning normally. Heme is an important part of nearly every cell in the body.

Disorders in the heme biosynthetic pathway:

Disorders in heme biosynthesis lead to the syndrome of porphyria with increased formation and excretion of porphyrins. Porphyrias can be hereditary-related or acquired through exogenous influences such as alcohol consumption or lead poisoning. Different enzymes of the heme biosynthesis can be deficient, thus, several different porphyrias can be distinguished. Since these share some common symptoms, chromatographic measurement of the porphyrins is the only way to enable an exact diagnosis.

Porphyrins are particularly well suited as biomarkers for two reasons. First, the pathway is highly active, so any disturbance tends to cause rapid and relatively large accumulations of intermediates. Second, the enzymes of the porphyrin-producing pathway are widely distributed in human tissues and some of them are highly sensitive to the presence of various toxins. Alterations of porphyrin synthesis that are not due to hereditary or toxic disturbances of porphyrin metabolism are adaptive responses. Such responses caused by alcohol or other drugs may not lead to clinical consequences. However, these disturbances often initiate biochemical and clinical manifestation of genetic porphyrias that previously may have been latent. Once initiated, the symptoms may be long-lasting, especially if the offending toxicant is not identified and removed or avoided. Numerous toxic porphyrias are precipitated by environmental mediators. Multiple environmental and nutritional factors can cause additive effects.

A few examples:

- Hexachlorobenzene-induced porphyria is accentuated by estrogens and attenuated by vitamin C. The estrogen effect increases the susceptibility of women to porphyrias.

- Aluminum inhibits some heme synthetic enzymes and has been implicated in causing porphyria in chronic hemodialysis patients, whom are often aluminum overloaded.

- Lead intoxication causes signs and symptoms similar to acute intermittent porphyria including abdominal pain, constipation and vomiting. However, anemia which is often found with lead intoxication may be absent in lower lead exposures that generate porphyria, indicating that the overall flux through the porphyrin pathway is not strongly reduced even though significant amounts of intermediates are spilled, due to the toxicant effect.

What causes porphyria?

Most porphyrias are inherited disorders. Scientists have identified genes for all eight enzymes in the heme biosynthetic pathway. Most porphyrias result from inheriting an abnormal gene, also called a gene mutation (from one parent). Some porphyrias, such as congenital erythropoietic porphyria, hepatoerythropoietic porphyria, and erythropoietic protoporphyria, occur when a person inherits two abnormal genes, one from each parent. The likeliness of a person passing the abnormal gene or genes to the next generation depends on the type of porphyria.

Porphyria cutanea tarda is usually an acquired disorder, meaning factors other than genes cause the enzyme deficiency.

For all types of porphyria, symptoms can be triggered by:

– use of alcohol

– smoking

– use of certain medications or hormones

– exposure to sunlight

– stress

– dieting and fasting

References:

https://www.niddk.nih.gov/health-information/liver-disease/porphyria