Validation of malondialdehyde and 4-hydroxy-2-trans-nonenal measurement in plasma by NICI-GC-MS.

Measurement of the concentrations of aldehydes in biological samples has become the object of much effort due to their relevance in relation to the toxic effects of lipid peroxidation, through which a number of aldehydes are derived. We have reconsidered a previously proposed method based on gas chromatographic mass spectrometric analysis of derivatives obtained by the treatment of aldehydes with O-pentafluorobenzyl hydroxylamine followed by a trimethylsilylating agent. In view of the possible use of the method for the simultaneous evaluation of the plasma levels of malondialdehyde and 4-hydroxy-2-trans-nonenal, we have studied the linearity of the analysis using various internal standards. Commercially available, inexpensive 2,4-dihydroxybenzaldehyde gave optimal results, the correlation coefficient of the calibration curve for plasma being r > 0.995 in the 0.1-5 microM range for both the tested aldehydes. The between-day imprecision (%CV) and accuracy (%bias) of the procedure determined using plasma samples spiked with the two aldehydes and with an internal standard reached maximum values of 3 and 8%, and 5 and 12% for HNE and MDA, respectively. The results obtained on analysis of plasma samples before and after oxidation with copper ions indicate the flexibility of the method for evaluation of the levels of MDA and HNE in plasma samples both under basal conditions and after an oxidative burst.

Inhibition of cholesterol synthesis and hepatic 3-hydroxy-3-methylglutaryl--CoA reductase in rats by simvastatin and pravastatin.

In this communication we attempt to provide one possible explanation for the observed differences regarding kinetics and distribution between simvastatin and pravastatin. Rats treated with simvastatin or pravastatin exhibited a reduction in the incorporation of [2-(14)C] acetate into liver cholesterol and displayed lower plasma mevalonate levels as compared to control animals. Moreover, both the total and dephosphorylated 3-hydroxy-3-methylglutaryl--CoA (HMG-CoA) reductase (EC 1.1.1.34) activities, particularly 1 h after treatment, were greatly reduced in liver microsomes obtained from simvastatin-treated as compared to control rats. During the same time frame, these parameters were actually elevated with pravastatin treatment. It is known that HMG-CoA reductase synthesis and activity increase following their competitive inhibition. Our results suggest that pravastatin, at 1 h following treatment, was no longer bound to the enzyme; however, it had entered the liver because its inhibitory effect on cholesterol synthesis was manifest at early times after administration. These data provide a plausible rationale for the earlier observation that activity of simvastatin persists longer in plasma than does that of pravastatin.