Background:
Paraoxonase (PON; arilesterase, [EC 3.1.8.1]) is an enzyme from the group
arilesterases (ARE). This enzyme is capable of hydrolyzing paraoxone which is the active metabolite
of parathion, an organic phosphorus insecticide. PON activity was found to be low in individuals
prone to development of atherosclerosis such as diabetes, familial hypercholesterolemia and
kidney disorders. It was noted that PON enzyme activity decreases in relation to age increase in
adults. PON enzyme activity is approximately half of that in newborns and premature babies. Approximately
one year after birth, it reaches the adult level. It can be said that PON1 has significant
role on living organisms. For this reason, many studies on interactions of PON-drugs are needed.
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Objective: In this article, our aim is to investigate in vitro effects of four pharmaceutically active
agents (fosfomycin, cefuroxime axetil, cefaclor monohydrate, and cefixime) which are often used in
patients after surgery on human serum paraoxanase-I (PON1) enzyme activity.
Methods:
In this article, we purify paraoxonase-I enzyme from human serum by using ammonium
sulfate precipitation (in the range of 60-80%), ion exchange and gel filtration chromatography. We
use electrophoresis to check the purity of the enzyme. We investigate the paraoxonase activity of
the enzyme at 412 nm the inhibition effects of the active substances. Paraoxone is used as the substrate.
Activity measurements arw made at different inhibitor concentrations related to inhibitor
studies and % Activity- [I] graphs are drawn for drug active substances. Lineweaver-Burk graphics
are used to determine the Ki constants. Finally, to determine the types of inhibition we interpret
these graphs.
Results:
The active agents used after surgery decreased the PON1 enzyme activity. They showed
different inhibition mechanism. The inhibition mechanism of fosfomycin and cefaclor monohydrate
was noncompetitive, cefixime was uncompetitive and cefuroxime axetil was a competitive inhibitor.
The IC50 values for fosfomycin, cefuroxime axetil, cefaclor monohydrate, and cefixime were
calculated to be 31.5 mM, 1.03 mM, 4.18 mM and 0.781 mM, respectively, and the Ki constants
were determined to be 27.98 ± 12.25 mM, 2.20 ± 0.22 mM, 4.81 ± 2.25 mM and 1.12 ± 0.32 mM,
respectively. The IC50 and Ki values showed that cefixime active agent has the maximum inhibition.
Conclusion:
In this study, we have detected that cefuroxime axetil inhibited competitively in vitro
paraoxonase activity of this enzyme. According to this information, we thought that cefuroxime
axetil linked to the active site of the enzyme. Fosfomycin and cefaclor monohydrate can be attached
with amino acids out of the active site of the enzyme because they inhibit enzyme noncompetitively.
Cefixime can be attached only to the enzyme-substrate complex because it inhibits enzyme
uncompetitively.
Inhibition Effect of Copper (II) Theophylline Nanocomplex on Phosphodiesterase (PDE) Enzyme Activity in Human Serum of Iraqi Patients with Asthma Disease
