Effect of t-butyl hydroperoxide on liver microsomal membranes and microsomal calcium sequestration

Chronic dietary iron overload in rats results in impaired calcium sequestration by hepatic mitochondria and microsomes [corrected]

The purpose of these experiments was to determine whether chronic dietary iron overload causes impairment of hepatic mitochondrial and/or microsomal calcium sequestration. Experimental iron overload was produced by feeding three groups of rats a chow diet supplemented with 3.0% (wt/wt) carbonyl iron for up to 8 weeks achieving graded increases in hepatic iron concentrations ranging from 1360 to 3170 micrograms/g. At low levels of iron overload, there were no changes in mitochondrial oxidative metabolism or calcium sequestration, whereas at moderate and high degrees of iron loading, both of these parameters were significantly reduced. In contrast, there were significant decreases in microsomal cytochrome P450 levels and microsomal calcium sequestration at all three levels of iron loading. These abnormalities occurred at hepatic iron concentrations at which the authors have previously found evidence of hepatic organelle lipid peroxidation. These alterations in organelle calcium sequestration may impair intracellular calcium homeostasis in the liver and contribute to subsequent cellular injury.

Elaboration of cellular DNA breaks by hydroperoxides

Cellular damage produced by ionizing radiation and peroxides, hydrogen peroxide (HOOH) and the organic peroxides tert-butyl (tBuOOH) or cumene hydroperoxide (CuOOH) were compared. DNA breaks, toxicity, malondialdehyde production, and the rate of peroxide disappearance were measured in a human adenocarcinoma cell line (A549). The alkaline and neutral filter elution assays were used to quantitate the kinetics of single and double strand break formation and repair (SSB and DSB), respectively. Peroxides, at 0.01-1.0 mM, produce multiphasic dose response curves for both toxicity and DNA SSBs. Radiation, 1-6 Gy, produced a shouldered survival curve, and both DNA SSB and DSBs produced in cells x-rayed on ice were nearly linear with dose. The peroxides produced more SSBs than radiation at equitoxic doses. X-ray induced DNA single strand breaks were rejoined rapidly by cells at 37 degrees C with approximately 80% of initial damage repaired in 20 min. Peroxide induced SSBs were maximal after 15 min at 37 degrees C. Rejoining proceeded thereafter, but at a rate less than for x-ray induced strand breaks. Significant DNA DSBs could not be achieved by peroxides even at concentrations 50-fold higher than required to produce SSBs. HOOH treatment of DNA on filters following cell lysis and proteolysis produced SSBs. CuOOH and tBuOOH produced no SSBs in lysed cell DNA. None of the peroxides produced DSBs when incubated with lysed cell DNA. Malondialdehyde was released from cells incubated with organic hydroperoxides, but not HOOH, nor up to 40 Gy of x-rays. HOOH was metabolized three times faster than the organic peroxides. The overall results demonstrate the necessity for a metabolically active cell environment to elaborate maximal DNA strand breaks and cell death at hydroperoxide concentrations of 10(-4) or greater, but prevent strand breaks and stimulate cell growth at 10(-5) M.

In vitro lipid oxidation modifies proteins and functional properties of sarcoplasmic reticulum

Changes in protein and fatty acid compositions of flounder sarcoplasmic reticulum during NADH plus ascorbate-dependent lipid peroxidation in vitro were related to the ability of the sarcoplasmic reticulum to sequester Ca+2. Progressive accumulation of high-molecular-weight protein components occurred concomitantly with loss of Ca+2-sequestering activity. Part of this polymerized protein may be the dimer or trimer of Ca+2, Mg+2-ATPase. Loss in Ca+2, Mg+2-ATPase protein could account for over 60% of the polymerized protein. Rate of loss of polyunsaturated fatty acids was C22:6 greater than C20:4 greater than C20:5 greater than C22:5. Loss of polyunsaturated fatty acids and accumulation of thiobarbituric acid-reactive substances occurred concomitantly with protein polymerization.

Effect of age of winter flounder on some properties of the sarcoplasmic reticulum

Sarcoplasmic reticulum (SR) from winter flounder (Pseudopleuronectes americanus) of various ages was investigated with regard to fluorescent age pigment (FAP), potential of enzymic lipid peroxidation, fatty acid composition, protein pattern and Ca2+-sequestering ability. FAP accumulation, protein pattern and Ca2+-sequestering ability were also evaluated after the SR were incubated in vitro with the peroxidizing cofactors: NADH, ADP and Fe3+. No difference in FAP content was observed in SR isolated from fish of different ages. However, a higher accumulation of FAP in muscle tissue from old fish was observed. A slow but significant increase in FAP in SR was observed when the SR from both young and old fish were incubated with peroxidizing cofactors. It was demonstrated that 4-year-old fish had higher levels of NADH-dependent lipid peroxidation in their SR than 2-year-old fish. No differences in fatty acid composition were observed in the SR of fish aged from 2 to 8 years old. Two species of high-molecular-weight protein were found to increase in SR isolated from aging fish. These species resembled the polymerized proteins derived after incubation of the SR with the peroxidizing cofactors. Ca2+-uptake decreased when the SR was incubated with peroxidizing cofactors, but the results are difficult to interpret since Ca2+-uptake of SR was affected by captive stress.