Phosphatidylserine

Phosphatidylserine (abbreviated Ptd-L-Ser or PS) is a phospholipid component, usually kept on the inner-leaflet (the cytosolic side) of cell membranes by an enzyme called flippase. When a cell undergoes apoptotic cell death phosphatidylserine is no longer restricted to the cytosolic part of the membrane, but becomes exposed on the surface of the cell.

Memory and cognition
Early studies of phosphatidylserine distilled the chemical from bovine brain. Because of concerns about Bovine Spongiform Encephalopathy, however, modern studies and commercially available products are made from soybeans. The fatty acids attached to the serine in the soy product are not identical to those in the bovine product, which is also impure. Preliminary studies in rats indicate that the soy product is at least as effective as that of bovine origin. However, later clinical trials in humans found that "a daily supplement of S-PS (soybean derived PS) does not affect memory or other cognitive functions in older individuals with memory complaints."

On May 13, 2003, the U.S. Food and Drug Administration stated "based on its evaluation of the totality of the publicly available scientific evidence, the agency concludes that there is not significant scientific agreement among qualified experts that a relationship exists between phosphatidylserine and reduced risk of dementia or cognitive dysfunction." FDA also stated "of the 10 intervention studies that formed the basis of FDA's evaluation, all were seriously flawed or limited in their reliability in one or more ways." It concludes that "most of the evidence does not support a relationship between phosphatidylserine and reduced risk of dementia or cognitive dysfunction, and that the evidence that does support such a relationship is very limited and preliminary." FDA did, however give "qualified health claim" status to phosphatidylserine, stating that "Consumption of phosphatidylserine may reduce the risk of dementia in the elderly" and "Consumption of phosphatidylserine may reduce the risk of cognitive dysfunction in the elderly".

Sports nutrition
Phosphatidylserine has been demonstrated to speed up recovery, prevent muscle soreness, improve well-being, and might possess ergogenic properties in athletes involved in cycling, weight training and endurance running. Soy-PS, in a dose dependent manner (400 mg), has been reported to be an effective supplement for combating exercise-induced stress by blunting the exercise-induced increase in cortisol levels. PS supplementation promotes a desirable hormonal balance for athletes and might attenuate the physiological deterioration that accompanies overtraining and/or overstretching. In recent studies, PS has been shown to enhance mood in a cohort of young people during mental stress and to improve accuracy during tee-off by increasing the stress resistance of golfers.

Attention-deficit hyperactivity disorder
First pilot studies indicate that PS supplementation might be beneficial for children with attention-deficit hyperactivity disorder.

Safety
Traditionally, PS supplements were derived from bovine cortex (BC-PS); however, due to the potential transfer of infectious diseases, soy-derived PS (S-PS) has been established as a potential safe alternative. Soy-derived PS is Generally Recognized As Safe (GRAS) and is a safe nutritional supplement for older persons if taken up to a dosage of 200 mg three times daily. Phosphatidylserine has been shown to reduce specific immune response in mice.

Dietary sources
PS can be found in meat, but is most abundant in the brain and in innards such as liver and kidney. Only small amounts of PS can be found in dairy products or in vegetables, with the exception of white beans.

Table 1. PS content in different foods.

The average daily PS intake from the diet in Western countries is estimated to be 130 mg.

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. Another PS binding protein is Mfge8.

Tumors
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 tumors.