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Prostanoid biosynthesis by blood monocytes of children with hyperprostaglandin E syndrome
R M Nüsing1, T P Schaub, T Klein
1Department of Pediatrics, Philipps University Marburg, Germany.
Insights
Hyperprostaglandin E syndrome (HPS) involves increased prostaglandin E2 (PGE2) synthesis. Studies show monocytes are not the source of this elevated PGE2 in HPS patients, ruling out a primary genetic defect in PGE synthesis.
Area of Science:
- Biochemistry
- Pediatrics
- Genetics
Background:
- Hyperprostaglandin E syndrome (HPS), a prenatal form of Bartter's syndrome, is defined by elevated prostaglandin E2 (PGE2) synthesis.
- HPS patients exhibit significantly increased urinary and plasma levels of PGE2 and its metabolite PGE-M.
Purpose of the Study:
- To investigate the cellular origin of the heightened PGE2 biosynthesis in HPS.
- To determine if monocytes contribute to the increased PGE2 production in HPS patients.
- To assess for a primary genetic defect in PGE synthesis in HPS.
Main Methods:
- Isolated CD14+ monocytes from HPS patients and controls for prostanoid synthesis analysis.
- Analyzed prostanoid synthesis from endogenous arachidonic acid and exogenous PGH2.
- Performed RT-PCR to analyze mRNA expression of cyclooxygenase-1, cyclooxygenase-2, and thromboxane synthase in monocytes.
Main Results:
- Monocytes from HPS patients did not show altered prostanoid synthesis compared to controls, from either endogenous or exogenous substrates.
- No significant differences in the expression of key enzymes (COX-1, COX-2, TXS) mRNA were found between HPS and control monocytes.
- Indomethacin treatment equally suppressed prostanoid excretion in both groups, indicating similar responsiveness.
Conclusions:
- Monocytes are not the source of elevated PGE2 biosynthesis in children with HPS.
- The findings exclude a primary genetic defect in PGE synthesis as the cause of HPS.
- Further research is needed to identify the precise origin of PGE2 overproduction in HPS.
Abstract:
Hyperprostaglandin E syndrome (HPS), the prenatal variant of Bartter's syndrome, is characterized by a marked and selective stimulation of prostaglandin E (PGE2) synthesis. In the study group HPS patients showed increased urinary levels of PGE2, an index of renal, and of 11 alpha-hydroxy-9,15-dioxo-2,3,4,5,20-pentanor-19-carboxyprostano ic acid (PGE-M), an index of systemic PGE2 synthesis of 470% and of 570%, respectively. In addition, plasma concentration of PGE-M was also elevated 6.3-fold when compared with a control group. The urinary levels of other prostanoids were unaltered. During indomethacin treatment in both groups prostanoid excretion rates were suppressed to similar levels. To investigate the origin of stimulated prostanoid biosynthesis in HPS patients CD14+ monocytes were isolated from plasma samples, and the prostanoid synthesis was analyzed. The pattern and amounts of metabolites synthesized from endogenous arachidonic acid pools did not vary significantly between monocytes of the HPS and the control group. Thromboxane A2 (TXA2) was formed as the major prostanoid product. Using PGH2 as an exogenous substrate, again no difference in PGE2 biosynthesis was observed, indicating no difference in PGE-synthetic activity between both groups. Additionally, mRNA expression analysis of CD14+ monocytes via RT-PCR delineated the constitutive expression of cyclooxygenase-1, cyclooxygenase-2, and thromboxane synthase mRNA in cells from HPS patients and controls without statistical differences between these two groups. In conclusion, our data show that monocytes are not the source for the increased PGE2 biosynthesis in children with HPS, and a genetic defect in PGE synthesis can be excluded as the primary event in the pathogenesis in HPS.