Alkaline phosphatase, tissue-nonspecific isozyme (ALPL) (ALPL)

Alkaline phosphatase, tissue-nonspecific isozyme (ALPL), also known as TNAP, is a glycosylphosphatidylinositol (GPI)-anchored enzyme highly expressed on the luminal surface of brain vascular endothelial cells (PMID: 25613319). It serves as a critical gatekeeper at the blood-brain barrier (BBB) by hydrolyzing pyridoxal 5'-phosphate (PLP) into pyridoxal, which is the only form of Vitamin B6 that can cross into the brain to support the synthesis of neurotransmitters like GABA (UniProt: P05186). Additionally, TNAP regulates the balance of extracellular inorganic pyrophosphate (PPi) and adenosine, thereby influencing vascular calcification and neuroinflammatory signaling (PMID: 30116235). In pathological states, a loss of ALPL function causes hypophosphatasia, a metabolic disorder characterized by bone mineralization defects and vitamin B6-dependent seizures (NIH: Genetic and Rare Diseases Information Center). Conversely, increased TNAP activity in the brain vasculature has been linked to the progression of Alzheimer's disease and cognitive decline (PMID: 23838008). Current therapeutic approaches include enzyme replacement therapy with asfotase alfa for deficiency and the investigation of small-molecule inhibitors like SBI-425 to mitigate vascular calcification and neurodegeneration (PubChem: SID 135314951).

Other names

Tissue-nonspecific alkaline phosphataseTNAPTNSALPLiver/bone/kidney-type alkaline phosphataseAP-TNAP

Enzyme replacement therapy restores catalytic activity to normalize metabolite levels, while small-molecule inhibitors are used to reduce pathological calcification or modulate neuroinflammatory signaling pathways.