Alkaline phosphatase, placental type

Alkaline Phosphatase, Placental Type (PLAP) is an isoenzyme of the alkaline phosphatase family that is particularly expressed in the placenta. It is a glycoprotein linked to the cell membrane, which is involved in the process of transporting molecules across the cell membrane. PLAP plays a significant role in the fetal development process, contributing to the nutrient transport between the mother and the fetus. Due to its high expression in the placenta and its almost negligible presence in other tissues, PLAP is used as a tumor marker for certain types of cancers, particularly those originating in the germ cells.

Structure and Function

PLAP, like other members of the alkaline phosphatase family, is a dimeric enzyme that catalyzes the hydrolysis of phosphate esters at an alkaline pH. It is anchored to the cell membrane via a glycosylphosphatidylinositol (GPI) anchor. This enzyme is crucial for the normal functioning of the placenta, aiding in the transfer of molecules that are essential for fetal development. Its expression is highly regulated and is typically restricted to the placental tissue during pregnancy.

Clinical Significance

The clinical significance of PLAP lies in its utility as a biomarker for certain types of cancers, especially germ cell tumors and tumors of placental origin like choriocarcinoma. Elevated levels of PLAP in the blood can be indicative of the presence of these tumors, making it a valuable tool in the diagnosis and monitoring of cancer treatment. Additionally, PLAP levels can be elevated in certain non-tumorous conditions, such as smoking, renal failure, and in some liver diseases, which necessitates careful interpretation of test results.

Diagnostic Use

In the clinical setting, PLAP levels are measured using blood tests. These tests are particularly useful in the diagnosis and monitoring of germ cell tumors, including testicular cancer and ovarian germ cell tumors. The measurement of PLAP, often in conjunction with other tumor markers, can help in assessing the tumor's response to treatment and in detecting recurrences.

Research Directions

Research into PLAP is ongoing, with studies aimed at better understanding its role in placental function and its potential use in cancer therapy. Investigations are also being conducted into the development of more sensitive and specific assays for PLAP, to improve its diagnostic and prognostic utility.

See Also

• Alkaline Phosphatase
• Placenta
• Tumor Marker
• Germ Cell Tumor