Effect of submaximal exercise on horse homocysteinaemia: possible implications for immune cells.

Physical exercise induces a reduction of immune defences and an imbalance of red-ox status. In this study plasma levels of cysteine and homocysteine (Hcy) were determined in horses before and after submaximal treadmill exercise as well as the effect on horse lymphocyte proliferation. The exercise induced a significant increase in plasma Hcy levels, which remained high both after the 20 min recovery period and after 2 h of rest. Moreover, a reduction of lymphocyte responsiveness to the proliferative stimulus induced by Concanavalin A was observed. The effects of different Hcy concentrations on the proliferative capacity of lymphocytes in culture were also tested. The results indicated that 10 microM of this amino acid can reduce the proliferative capacity of resting lymphocytes as well as their responsiveness to mitogen. Moreover, our results suggest that homocysteinaemia could be considered one of the parameters affected by physical exercise in horses and that this amino acid could be implicated in the effects of physical exercise on the immune system.

Plasma sulfate concentration and hyperhomocysteinemia in hemodialysis patients.

BACKGROUND: Severe hyperhomocysteinemia is common in hemodialysis patients, who also present a dramatic increase in plasma concentrations of sulfate, one of the main products of methionine and cysteine catabolism. The aim of this study was to verify the relationship between high plasma sulfate levels and cysteine or homocysteine concentrations in hemodialysis patients. METHODS: Plasma sulfate, cysteine and homocysteine concentrations and some renal efficiency parameters were determined in 18 patients with end-stage renal failure, all undergoing 4h hemodialysis three times a week. The pattern of post-dialysis rises on plasma concentrations of sulfate, cysteine and homocysteine was established. RESULTS: Plasma sulfate, cysteine and homocysteine levels were significantly higher in patients than in normal controls. Plasma sulfate concentrations positively correlated with cysteinemia (p = 0.031; r = 0.482) which, in turn correlated with homocysteinemia (p = 0.042; r = 0.460). Sulfate levels also correlated with blood creatinine (p = 0.004; r = 0.630), nitrogen (p = 0.000; r = 0.899), protein (p = 0.014; r = 0.555), and albumin (p = 0.003; r = 0.642). Post-dialysis rises in sulfate and cysteine were detected some hours before homocysteine. CONCLUSION: The results suggest that high sulfate levels, due mainly to impaired renal function, are involved in the altered metabolism of homocysteine in hemodialysis patients.

Possible involvement of L-glycero-phosphoryl-ethanolamine in the phospholipid methylation pathway.

It is usually accepted that GPEtn is only an intermediate in glycerophospholipid degradation. However, some years ago J. P. Infante published a review-hypothesis concerning the possible involvement of GPEtn and GPCho in the biosynthesis of acyl-specific glycerophospholipids in mammalian tissues. This paper reports the results obtained by incubating brain cortex slices in the presence of labeled GPEtn. GPEtn enters the cells and the radioactivity of the precursor is found in both PE and PC. When these results were compared with those obtained by incubating brain slices in the presence of 3H-Etn, a significantly higher amount of radioactivity was found in PC, mainly after short incubations in the presence of low concentrations of the precursors. The slopes of the methylated forms of PE further underline the above differences found by comparing the results obtained with the two precursors. The results presented in this paper suggest a possible role of GPEtn in phospholipid biosynthesis and methylation pathway of PE.

Phospholipid base-exchange in brain microvessels.

The capillary endothelium of cerebral microvessels plays an important role in homeostasis within the central nervous system. The flux of fluids and solutes takes place through the lipid matrix of plasma membranes and the maintenance of their structural composition is necessary for cell membrane permeability and the cellular transport systems. Few studies have been carried out to clarify the relationships between brain microvessel lipid metabolism and the role of this metabolism. We have studied a particular aspect of the phospholipid metabolism, i.e. their hydrosoluble head group exchange with free choline, ethanolamine or serine, in capillaries from brains of both 4 month- old and 24 month-old rats. The results obtained indicate that microvessels possess the biochemical machinery of base-exchange reaction, whose activity rate appears unaffected by age.

Linoleic acid passage through the blood-brain barrier and a possible effect of age.

It has already been established that the blood-brain barrier is readily crossed by unsaturated fatty acids, while saturated fatty acid transport appears to be protein mediated. When the passage of the fatty acids is tested in vivo by using perfusion buffers containing both linoleate and palmitate in different concentrations, linoleate is able to decrease the palmitate passage, while palmitate increases the linoleate passage. These results could be related to the effect of two fatty acids on the ratio between the fatty acids bound to the serum albumin and the free fatty acid pool, which is only available for transport through membranes. However, on the basis of some results obtained with aged rats, the possibility that a relationship may exist between palmitate and linoleate during their passage through the BBB is discussed. Moreover, it seems likely that in aged rats a moderate modification for fatty acids takes place in the BBB.

Arachidonic and palmitic acid utilization in aged rat brain areas.

We have previously demonstrated that the arachidonic acid (20:4) incorporation into brain lipids differs according to the age of the animals used and the experimental conditions adopted. These differences led to a further investigation of arachidonic acid uptake in both aged and adult rat brains, its transformation into CoA derivatives, its incorporation into diacyl-glycerols and polar lipids, and finally its oxidation to CO2. These metabolic parameters were then compared with those obtained after using the saturated fatty acid palmitate (16:0). In both cases slices or mitochondria from different brain areas of 24-month-old and 4-month-old rats were examined. The results obtained indicate that the uptake of the fatty acids into cells is not modified by age. However, the successive metabolic transformations of the acids are altered to a considerable extent. In particular, in 24-month-old animals (compared with 4-month-old rats) there is a significant decrease of 20:4 in its incorporation into lipids as well as its oxidation to CO2, while arachidonoyl-CoA content increases by about 50%. This increased amount of CoA derivative, which has a potent detergent effect, may interfere with membrane structure and affect membrane physiological functions. Furthermore, because the free arachidonate pool is maintained in a dynamic equilibrium with its esterified forms, the final result may be a perturbation of this equilibrium.

Linoleic acid metabolism in brain cortex of aged rats.

The linoleic acid metabolism was examined in the brain cortex of 4 month-old and 24 month-old rats. After the injection of [1-14C]-linoleate into the lateral ventricle of the brain the animals were sacrificed at 1,3 and 6 hours from the injection. The linoleate (18:2) incorporation into lipids, the presence of fatty acid peroxidation products, as well as the 18:2 transformation into elongated and desaturated derivatives were determined. Both an age-related reduction in linoleate incorporation rate into glycerophospholipids and a decrease in fatty acid turnover were found. Furthermore, in glycerophospholipids from 24 month-old rat brain cortex a higher level of hydroperoxide derivative of linoleate was found as compared to 4 month-old animals, and this damaged fatty acid is eliminated more slowly in aged rats than in adults. Finally, unlike 4 month-old animals, a stimulation of the transformation rate of linoleate into desaturation (6,9,12-C18:3) and elongation (8,11,14,C20:3) products was found in 24 month-old rat brain cortex. On the contrary, as far as arachidonic acid (one of the most important end products of the mechanism of linoleate modification) is concerned, the differences between aged and control animals were small, making it quite difficult to attribute a physiological meaning to this phenomenon.

Choline incorporation into phospholipids in brain areas from spontaneously hypertensive rats: effect of oxiracetam treatment.

It has been demonstrated that spontaneously hypertensive rats (SHR) develop severe hypertension and cerebrovascular lesions on drinking 1% NaCl from weaning. These animals present a learning and memory impairment as well as impairment of both energy metabolism and membrane phospholipid turnover. We tested both choline uptake into the cells and incorporation into choline phosphoglyceride (CPG) by incubating slices from hippocampus and cortex. After 5 min of incubation, a noticeable decrease in free labelled choline content inside the cells as well as its incorporation into phospho-choline (PC) and CPG were found in the brain of SHR, as compared to Wistar-Kyoto (WK) rats. This may indicate that in the SHRs with cerebrovascular lesions there is a reduction in choline uptake which in turn causes a decline in CPG biosynthesis through de novo pathway. Oxiracetam treatment is able to restore the labeled choline content in the cells from SH rats, as well as the incorporation of choline into its derivatives PC and CPG, to the levels found in the WK or more. Tests performed in the presence of such a high affinity choline uptake as hemicholinium (HC) confirmed the capacity of oxiracetam to stimulate choline uptake into the cells even if the results obtained up to now are not sufficient to hypothesize a direct effect of oxiracetam on acetylcholine metabolism. In conclusion, from the results obtained it would seem reasonable to hypothesize that the effects of the drug above mentioned on the cholinergic system may be secondary to its effect on choline phosphoglycerides biosynthesis.