Modulation of Enzyme-Catalyzed Synthesis of Prostaglandins by Components Contained in Kidney Microsomal Preparations.

Hyoung-Woo Bai,Bao Ting Zhu,Yue Wang,Pan Wang,Jina Yu

doi:10.3390/molecules27010219

Abstract

In the kidney, prostaglandins formed by cyclooxygenase 1 and 2 (COX-1 and COX-2) play an important role in regulating renal blood flow. In the present study, we report our observations regarding a unique modulatory effect of renal microsomal preparation on COX-1/2-mediated formation of major prostaglandin (PG) products in vitro. We found that microsomes prepared from pig and rat kidneys had a dual stimulatory–inhibitory effect on the formation of certain PG products catalyzed by COX-1 and COX-2. At lower concentrations, kidney microsomes stimulated the formation of certain PG products, whereas at higher concentrations, their presence inhibited the formation. Presence of kidney microsomes consistently increased the Km values of the COX-1/2-mediated reactions, while the Vmax might be increased or decreased depending on stimulation or inhibition observed. Experimental evidence was presented to show that a protein component present in the pig kidney microsomes was primarily responsible for the activation of the enzyme-catalyzed arachidonic acid metabolism leading to the formation of certain PG products.

Highlights

Cyclooxygenase 1 and 2 (COX-1 and COX-2) can convert arachidonic acid (AA) into prostaglandins H2 (PGH2), which is further converted to various prostaglandins (PGs), thromboxanes (TX) and hydroxyeicosateraenoic acids (HETE)
It is of note that PGH2 is a well-known direct product of COX-1/2-mediated AA metabolism, which can undergo non-enzymatic rearrangement to form 12-hydroxyheptadecatrienoic acid (12-HHT) [26,27]
PGH2 can be enzymatically converted to prostaglandin E2 (PGE2), prostaglandin D2 (PGD2) and prostaglandin F2α (PGF2α) in the presence of the terminal synthases

Summary

Introduction

Cyclooxygenase 1 and 2 (COX-1 and COX-2) can convert arachidonic acid (AA) into prostaglandins H2 (PGH2), which is further converted to various prostaglandins (PGs), thromboxanes (TX) and hydroxyeicosateraenoic acids (HETE). COX-2, which is strongly induced by various mitogens, plays a more important role under certain pathological conditions such as inflammation, whereas COX-1, which is stably expressed in many tissues, mostly functions as a house-keeping enzyme [9,10]. These two COX enzymes are localized intracellularly to the luminal surfaces of the endoplasmic reticulum and the inner and outer membranes of the nuclear envelope [11]. The presence of the pig kidney microsomes stimulated the COX-mediated formation of major PG products (not all PG products), but at higher concentrations, the presence of the pig kidney microsomes consistently exerted an inhibitory effect on COX-mediated formation of various PG products

Results and Discussions

Materials and Methods

Assay of COX-1 and COX-2 Catalytic Activity

Preparation of Microsomes

Treatment of Pig Kidney Microsomes with Chymotrypsin