Phosphatidylserine

Phosphatidylserine (PS or PtdSer) is a phospholipid nutrient found in fish, green leafy vegetables, soybeans, and rice, and is essential for the normal functioning of neuronal cell membranes, activating protein kinase C (PKC), which has been shown to be involved in memory function. ^[1] Phosphatidylserine is usually kept on the inner-leaflet of cell membranes by any enzyme called translocase. In apoptosis, caspase 3 activation culminates in deactivation of translocase and activation of scramblase, which allows free movement of PtdSer down its concentration gradient, and activation of flippase, which transports PtdSer to the outer-leaflet of the plasma membrane. This is part of the process by which the cell is targeted for phagocytosis.

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Applications

Research

Annexin-A5 is a naturally-occurring protein with avid binding affinity for PS. Labeled-annexin-A5 enables visualization of cells in the early- to mid-apoptotic state in vitro or in vivo.

Medical

Neuronal

PS has been shown to slow cognitive decline in animal models.^[2]

PS has been investigated in a small number of double-blind placebo trials and has been shown to increase memory performance in the elderly. Because of the potential cognitive benefits of phosphatidylserine, the substance is sold as a dietary supplement to people that believe they can benefit from an increased intake.

The dietary supplement was originally processed from bovine sources, however Prion disease scares in the 1990s outlawed this process, and a soy-based alternative was adopted.^[3] The fatty acids attached to the serine in the soy product are not identical to those in the bovine product, which is also impure. Studies using the soy version indicate a possible improvement in mood, but no clear evidence of an effect on mental function.

Tumour

Technetium-labeled annexin-A5 enables distinction between malignant and benign tumours whose pathology includes a high rate of cell division and apoptosis in malignant compared with a low rate of apoptosis in benign tumours.

References