The biosynthesis of plasmalogen (alkenyl acyl glycerophosphoryl choline or ethanolamine) is independent of diacyl glycero-phospholipid synthesis and requires the coordinated activities of peroxisomal, cytosolic, and endoplasmic reticulum enzymes. This would indicate that the plasmalogens may have a unique role(s) to play in cellular functions, one different from that of the diacyl glycerophospholipids. Several functions have been assigned to plasmalogens such as antioxidants, arachidonic acid storage terminals, receptor mediators, substrate for the biosynthesis of platelet-activating-factor (PAF), and determinant of physicochemical properties of biomembranes. Except for serving as a substrate for biologically active PAF biosynthesis, none of the proposed functions have been fully validated. The purpose of this review article is to provide up-to-date knowledge of the biosynthetic pathway and functions of plasmalogens.
A carboxyfluorescein(CF)-enveloping liposome is presented as a physicochemical damage model of the biomembrane for the study of lipid peroxidation. The degree of membrane damage may be assessed by measurement of the fluorescence intensity of CF released from damaged liposomes after the interaction between the liposomal membrane and a radical initiator. The process of lipid peroxidation was biochemically confirmed by the thiobarbituric acid-reactive substances (TBARS) test done simultaneously. Three types of CF-enveloping liposomes, i.e., soybean phosphatidylcholine (SPC) containing polyunsaturated fatty acid, dipalmitoylphosphatidylcholine (DPPC) containing saturated fatty acid, and soybean phosphatidylcholine plus α-tocopherol, were exposed to a known radical initiator, ferric nitrilotriacetate with a reductant (either cysteine, reduced form glutathione, or ascorbic acid). The release of CF from the peroxidized liposome was measured with a fluorospectrophotometer. A high release of CF and a high level of TBARS were seen in the SPC liposomes, but not in the DPPC and α-tocopherol-inserted SPC liposomes. This liposome model is superior to the conventional red cell hemolysis model for several reasons: (1) the constituents of the membrane are defined; (2) CF is not a radical initiator, whereas hemoglobin is a potential radical initiator; and (3) the membrane components can be easily changed depending on the purpose of the experiment.
The influence of honey on biochemical and biophysical parameters of wounds was assessed by making an excision wound by cutting away a 4cm2 (2cm×2cm) full-thickness patch of skin from the shaven back of rats under ether anaesthesia. One milliliter of pure, commercial, unboiled honey was applied topically (Group II), or administered orally (Group III) or intraperitoneally (Group IV). The control rats were left untreated (Group I). The rate of healing was assessed by estimation of some biochemical parameters like DNA, total protein, total collagen, hexosamine and uronic acid contents of the granulation tissues formed different times after wound creation. All the biochemical parameters increased in honey-treated animals when compared with the control values. The increases were very significant with oral and intraperitoneal treatment when compared with those with the topical. Biophysical parameters like tensile strength, stress-strain behavior, rate of contraction, and period of epithelialization were also studied. There was an approximately 21% increase in tensile strength in Group II rats, whereas the increase was more in Group III (34.5%) and Group IV (52%) rats. The stress-strain behavior also followed the same trend. A significant increase in the rate of contraction was observed equally in all three honey-treated groups when their values were compared to the control. Among the three experimental groups, the intraperitoneal treatment decreased the period of epithelialization more significantly (37%) than the oral (22%) and topical (15%) treatments. The decrease in the period of epithelialization showed that the time taken by the wounds to heal was less with systemic treatment than with no treatment (control).
The effect of starvation and chronic food restriction on lipid peroxidation during treatment with ethanol was studied. The experiment was carried out on 64 female Wistar rats. The formation of malondialdehyde was determined in postmitochondrial liver fraction (basal level and after stimulation with ascorbate). The concentration of reduced glutathione was measured in the same fraction. In rats fed ad libitum, the consumption of ethanol, given with the drinking water for either 3 or 28 days, promoted a slight, but statistically nonsignificant, activation of lipid peroxidation. In animals not given ethanol, a 3-day fast increased the formation of lipid peroxides after stimulation with ascorbate. However, some tendency toward inhibition of lipid peroxidation was established after consumption of a restricted diet (6-8g standard pellet food daily) for 28 days. The treatments with alcohol for 3 and 28 days were combined respectively with a 3-day fast and a 28-day food restriction. In both a statistically significant increase in lipid peroxides was observed in comparison with the controls, which were fed ad libitum and were not given ethanol. The concentration of reduced glutathione was decreased in all experimental groups, but only with the 3-day treatments did the extent of its depletion correspond to the activation of lipid peroxidation. The results show that both starvation and chronic malnutrition potentiate lipid peroxide formation in rats treated with ethanol.
In the present study Swiss NMRI mice were fed quercetin, a naturally-occurring dietary polyphenolic flavonoid, through their drinking water at dose levels of 0, 1, 3, and 9μg/ml for 8 weeks. There was no change in the hepatic and pulmonary levels of arylhydrocarbon hydroxylase, cytochrome P-450, cytochrome b5, cytochrome c-reductase, or UDP-glucuronyltransferase due to quercetin feeding. However, hepatic activity of glutathione-S-transferase was significantly increased at 3 and 9μg/ml dose levels; and that of the pulmonary enzyme, at 9μg/ml dose. Levels of reduced glutathione were significantly elevated in liver and lungs. These increases in glutathione-S-transferase and reduced glutathione may protect the liver and lungs from the carcinogenic insult of chemicals through the detoxification process.
Change in serum lipid peroxide level was examined in rats undergoing acute or chronic rejection of heart transplants, in order to clarify the role of lipid peroxides in the development of graft coronary disease. In the rat heart transplantation model under acute rejection conditions, the serum lipid peroxide level of the recipients did not change. While, in the chronic rejection model the level of the recipients significantly increased on the 15th day after the transplantation as compared with that of sham-operated control rats. Light microscopic observations of an allograft on the 15th day after the operation revealed the presence of inflammatory lesions involving infiltration of lymphocytes into the myocardium, edema, and necrosis. On the 22nd day after the operation, intimal thickening in the coronary artery was observed, and it became more remarkable on the 50th day. These results suggest that the increase in serum lipid peroxide level could be one of the signs of graft coronary disease.
In order to study the degradation of skeletal muscle proteins during basal conditions and following surgery of moderate and major severity, we examined the proteinase activities in skeletal muscle tissue. Proteinase activities were analyzed in biopsies (30 to 60mg) taken from skeletal muscle of healthy human volunteers and from patients undergoing abdominal surgery. Acid and neutral proteinase activities toward the added substrate, hemoglobin, and autolytic degradation of intrinsic proteins were measured by analysis of the tyrosine released during incubation. Acid proteinase activity in the presence of added substrate was inhibited by pepstatin to 99% and autolytic degradation to 75%, indicating the presence of the lysosomal enzyme cathepsin D (EC 126.96.36.199) in human skeletal muscle. Storage of the biopsies prior to analysis should not exceed 3 weeks at -80°C. Reproducibility of the assay for specimens from a single individual was high, with an error of ±3%. Among the proteins degraded intrinsically at acid pH myosin heavy chain was analyzed by immunoblotting. The protein was one of the substrates of the pepstatin-insensitive pathways of protein degradation at acid pH. As neutral proteinases were lower in activity than acid proteinases, the studies on patients focused on acid proteinase activities. The analysis was applied to biopsies taken from patients undergoing abdominal surgery. Following cholecystectomy, classified as moderately severe surgery, the rate of acid proteinase activity per mg wet weight of muscle decreased significantly (p<0.05) at 24h and was marginally significantly decreased at 72h after surgery (p=0.075). Per mg of protein the values were 94.5±7.5% and 96.5±5.0% for 24 and 72h, respectively. Per mg of DNA a significant decrease (p<0.05) was noted at 24h after surgery. Autolytic degradation decreased (p<0.05) at 24h after moderately severe surgical trauma. Following major abdominal surgery acid proteinases without or with added substrate increased in activity. In the absence of added substrate the peak was at 6h, and in its presence, at 24h, following surgery. The activity of the acid proteinases appears to be a useful tool when protein metabolic events are studied in biopsy specimens of human skeletal muscle.
Previously, we reported protease changes in cerebral tissues, as well as in serum, of patients with Alzheimer-type dementia. In the present study, we investigated enzymatic activities in their cerebrospinal fluid. In the Alzheimer patients the activities of dipeptidyl peptidase III (DPP-III), DPP-IV, and cathepsin B were significantly increased when compared with those of the control subjects. In vascular dementia patients the activities of Leu-AP and cathepsin B were increased but the activity of DPP-III was decreased. These results, as well as those of a multivariate study on these enzymatic changes, suggest the independency of the cerebral changes in the Alzheimer patients from those in vascular dementia. The results may also be of use for clinical diagnoses of these pathologic states.