Kidney Transplantation in a Patient Lacking Cytosolic Phospholipase A₂ Proves Renal Origins of Urinary PGI-M and TX-M.

Abstract

The balance between vascular prostacyclin, which is antithrombotic, and platelet thromboxane A₂, which is prothrombotic, is fundamental to cardiovascular health. Prostacyclin and thromboxane A₂ are formed after the concerted actions of cPLA₂α (cytosolic phospholipase A₂) and COX (cyclooxygenase). Urinary 2,3-dinor-6-keto-PGF_1α (PGI-M) and 11-dehydro-TXB₂ (TX-M) have been taken as biomarkers of prostacyclin and thromboxane A₂ formation within the circulation and used to explain COX biology and patient phenotypes, despite concerns that urinary PGI-M and TX-M originate in the kidney. We report data from a remarkable patient carrying an extremely rare genetic mutation in cPLA₂α, causing almost complete loss of prostacyclin and thromboxane A₂, who was transplanted with a normal kidney resulting in an experimental scenario of whole-body cPLA₂α knockout, kidney-specific knockin. By studying this patient, we can determine definitively the contribution of the kidney to the productions of PGI-M and TX-M and test their validity as markers of prostacyclin and thromboxane A₂ in the circulation. Metabolites were measured using liquid chromatography-tandem mass spectrometry. Endothelial cells were grown from blood progenitors. Before kidney transplantation, the patient's endothelial cells and platelets released negligible levels of prostacyclin (measured as 6-keto-prostaglandin F_1α) and thromboxane A₂ (measured as TXB₂), respectively. Likewise, the urinary levels of PGI-M and TX-M were very low. After transplantation and the establishment of normal renal function, the levels of PGI-M and TX-M in the patient's urine rose to within normal ranges, whereas endothelial production of prostacyclin and platelet production of thromboxane A₂ remained negligible. These data show that PGI-M and TX-M can be derived exclusively from the kidney without contribution from prostacyclin made by endothelial cells or thromboxane A₂ by platelets in the general circulation. Previous work relying on urinary metabolites of prostacyclin and thromboxane A₂ as markers of whole-body endothelial and platelet function now requires reevaluation.