INACTIVATION OF HEART DIHYDROLIPOAMIDE DE HYDROGENASE BY LEUKOCYTE MYELOPEROXIDASE-DEPENDENT SYSTEMS - PREVENTION BY CAPTOPRIL AND OTHER THIOL COMPOUNDS
Jg. Correa et Aom. Stoppani, INACTIVATION OF HEART DIHYDROLIPOAMIDE DE HYDROGENASE BY LEUKOCYTE MYELOPEROXIDASE-DEPENDENT SYSTEMS - PREVENTION BY CAPTOPRIL AND OTHER THIOL COMPOUNDS, Medicina, 58(2), 1998, pp. 171-178
Myocardial dihydrolipoamide dehydrogenase (LADH) is inactivated after
incubation at 30 degrees C, with myeloperoxidase (MPO)-dependent syste
ms. The enzyme inactivation was a function of the pro-oxidant system c
omposition and the time of incubation. The standard inactivating syste
m contained 50 mM KH2PO4-K2HPO4, pH 7.4, 0.5-1.0 mu M LADH, and pro-ox
idant system. After 30 or 60 min of incubation with the MPO/H2O2/NaCl
system, LADH inactivation was 64 and 87%, respectively (Figure 1). In
the absence of NaCl, inactivation values were 9 and 27%, respectively,
whereas in the absence of MPO the inactivation Values were 4.0 and 11
%, respectively (Figure 1). Under similar experimental conditions, sod
ium hypochlorite significantly inactivated LADH, thus supporting the r
ole of hipochlorous acid as agent of the MPO/H2O2/ClNa system. With th
e MPO/H2O2/Kl, MPO/H2O2/KSCN or the MPO/H2O2/NaNO2 systems LADH inacti
vation depended on the anion nature, I being the most effective (Figur
e 2). NaNO2 effectively replaced halides as pro-oxidant (Figure 3). Th
e MPO/NADH/halide systems, where NADH replaced H2O2, also inactivated
LADH. Native (not denatured) catalase completely prevented the MPO/NAD
H/Kl system effect (Table 1), in close agreement with H2O2 production
by the LADH-catalysed NADH oxidation and the role of H2O2 in LADH inac
tivation. LADH was also inactivated after incubation with MPO-generate
d free radicals such as the Chloropromazine and Paracetamol radicals (
Table 2). Thiol compounds (Captopril, penicillamine, cysteine, N-acety
lcysteine and mercaptopropionylglycine) (Table 3 and Figure 4), as wel
l as taurine, ascorbate (Table 4), GSSG and trypanothione (Figure 5),
protected LADH against the MPO-dependent oxidizing systems, and also a
gainst NaClO (Table 4). The summarized observations are discussed in r
elation to MPO function in free radical production and pathologies suc
h as ischemia-reperfusion injury and inflammation.