Histological assessment of intermediate- and long-term creatine monohydrate supplementation in mice and rats

Creatine monohydrate (CrM) supplementation appears to be relatively safe based on data from short-term and intermediate-term human studies and results from several therapeutic trials. The purpose of the current study was to characterize pathological changes after intermediate-term and long-term CrM supplementation in mice [healthy control and SOD1 (G93A) transgenic] and rats (prednisolone and nonprednisolone treated). Histological assessment (18-20 organs/tissues) was performed on G93A mice after 159 days, and in Sprague-Dawley rats after 365 days, of CrM supplementation (2% wt/wt) compared with control feed. Liver histology was also evaluated in CD-1 mice after 300 days of low-dose CrM supplementation (0.025 and 0.05 g x kg-1x day-1) and in Sprague-Dawley rats after 52 days of CrM supplementation (2% wt/wt) with and without prednisolone. Areas of hepatitis were observed in the livers of the CrM-supplemented G93A mice (P < 0.05), with no significant inflammatory lesions in any of the other 18-20 tissues/organs that were evaluated. The CD-1 mice also showed significant hepatic inflammatory lesions (P < 0.05), yet there was no negative effect of CrM on liver histology in the Sprague-Dawley rats after intermediate-term or long-term supplementation nor was inflammation seen in any other tissues/organs (P = not significant). Dietary CrM supplementation can induce inflammatory changes in the liver of mice, but not rats. The observed inflammatory changes in the murine liver must be considered in the evaluation of hepatic metabolism in CrM-supplemented mice. Species differences must be considered in the evaluation of toxicological and physiological studies.

Coenzyme A independent acylation of phosphatidylethanolamine in isolated bovine rod cell outer segments

The acylation of membrane phospholipids in isolated bovine rod outer segments (ROS) by exogenous, radiolabeled palmitic acid (16:0) was assayed, using [14C]palmitoyl-coenzyme A (16:0-CoA), [3H]16:0 alone and [3H]16:0 with added ATP and CoA. Both [14C]16:0-CoA and [3H]16:0 with added ATP and CoA are incorporated predominantly into phosphatidylcholine (PC), whereas [3H]16:0 without added ATP and CoA is incorporated almost exclusively into phosphatidylethanolamine (PE). Without added ATP and CoA in the incubation medium, [3H]16:0 is esterified predominantly to the 2 position of PE, but with added ATP and CoA, it is esterified to both the 1 and 2 positions; the rates of esterification of [3H]16:0 to the 2 position of PE under these two conditions are similar. These results suggest that 16:0 is esterified to the 2 position of PE of ROS membranes by an acyl transferase mechanism that does not utilize an acyl-CoA intermediate. The product of this reaction is likely to be a molecular species of PE with 16:0 at the 2 position and a polyunsaturated fatty acid at the 1 position.

Phospholipid molecular species from isolated bovine rod outer segments incorporate exogenous fatty acids at different rates

The incorporation of radiolabeled palmitic (16:0), oleic (18:1), and docosahexaenoic (22:6) acids into different molecular species of membrane phospholipids was investigated in isolated bovine rod outer segments (ROS). Phosphatidylcholine (PC), phosphatidylethanolamine (PE), and phosphatidylserine (PS) were isolated, and their diacylglyceroacetate and diacylglycerobenzoate derivatives were prepared, separated by HPLC, quantified, and assayed for radioactivity. Maximal incorporation of fatty acids occurred within 15-30 min. The rate of incorporation of the fatty acids into PC was three to six times higher than it was into PS or PE. The rate of incorporation of 22:6 into the molecular species, 22:6-22:6, of PC was ten to 15 times higher than into that of PE or PS, and it was three to four times higher than the incorporation rates of 22:6 into the other 22:6-containing molecular species. Similarly, incorporation of 18:1 into 18:1-22:6 was ten to 30 times more rapid in PC than in PE and PS, but in both PE and PS, 18:1 was incorporated into 18:1-22:6 at a rate of 20 to 25 times higher than the incorporation into the other molecular species analysed. For PC, incorporation of 16:0 was most rapid into 16:0-16:0, but for PE and PS it was most rapid into 16:0-20:4; for all cases, incorporation of 16:0 into these molecular species was four to six times more rapid than into the other 16:0-containing molecular species. These results are further evidence for the presence within a membranous organelle, the ROS, of an active acylation-deacylation system that is selective with regard to phospholipid, molecular species of phospholipid, and fatty acid.

Effects of the antioxidants dithiothreitol and vitamin E on phospholipid metabolism in isolated rod outer segments

Phospholipid peroxidation and the activities of phospholipase A, acyl Coenzyme A:lysophospholipid acyltransferase and lysophospholipase were measured in isolated bovine rod outer segments (ROS) that were incubated in the presence or absence of the added antioxidants, vitamin E and dithiothreitol (DTT), and additionally in light or dark. DTT and vitamin E significantly inhibit both lipid peroxidation and the enzyme activities. These results suggest that one function of the enzymes for molecular replacement of fatty acids in ROS, is removal of peroxidized fatty acids and thus protection of the membrane phospholipids and proteins from further oxidative damage.

Lysophospholipase and the metabolism of lysophosphatidylcholine in isolated bovine rod outer segments

Incubation of bovine rod outer segments (ROS) with radiolabeled palmitic acid (16:0) and lysophosphatidylcholines (lysoPC) radiolabeled in either the fatty acid or the choline group indicated the presence of a lysophospholipase activity that is unaffected by Ca2+. In the presence of ATP, Mg2+ and CoA and acyl CoA:lysophospholipid acytransferase activity is evident, and free fatty acids, including those released by lysophospholipase activity, are esterified to membrane phospholipids. At low concentrations of lysoPC, 68% of it is acylated to form phosphatidylcholine (PC) and 24% is converted to glycerophosphocholine (GPC) and fatty acid per hour. As the concentration of lysoPC increases lysophospholipase activity increases, acyl-CoA:lysophospholipid acyltransferase activity decreases, and the proportion of lysoPC converted to PC decreases. The rate of production of lysophospholipids in vitro under phospholipase A-stimulatory conditions exceeds the rate at which it can be removed by 5-10-fold. This suggests the possibility that an early step in light, anoxia- or hypoxia-induced damage to photoreceptor cells may be activation of the phospholipase A endogenous to ROS.

Acylation and deacylation of phospholipids in isolated bovine rod outer segments

Isolated bovine rod outer segments (ROS) were incubated under different conditions with radiolabeled fatty acid-Coenzyme A (CoA) compounds, fatty acids and phospholipids in order to further investigate the rates, mechanisms and function of phospholipid metabolism within that organelle. ROS contain acyl CoA synthetase, acyl transferase, acyl CoA hydrolase, and phospholipase A activities. Although different radiolabeled fatty acid CoAs were esterified to the major ROS phospholipids (phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine) at the same rate, different free fatty acids were esterified at different rates. There was no correlation between these estimates of in vitro rates of incorporation of fatty acids and the fatty acid composition of ROS phospholipids. Both the deacylation of radiolabeled phospholipids (phospholipase A activity) and the acylation of endogenous phospholipids (acyl transferase activity) were maximally stimulated when ATP, CoA, Mg2+ and Ca2+ were present, and both processes were stimulated by pro-oxidizing conditions and exposure to light. Under phospholipase A-stimulatory conditions, there was preferential hydrolysis of polyenoic fatty acids from endogenous ROS phospholipids. Both the acylation and deacylation reactions were primarily at the sn-2 position of ROS phospholipids.

Acyl transferase and fatty acid coenzyme A synthetase activities within bovine rod outer segments

Rod outer segments purified from bovine retinal homogenates were incubated with radiolabelled fatty acids (palmitic, docosahexaenoic) and palmitoyl Coenzyme A, and were found to contain enzyme activities that catalyze addition of these compounds to the major phospholipids of rod outer segment membranes. It is suggested that these phospholipid retailoring enzymes function to establish the unique fatty acid distribution and composition of the phospholipids of vertebrate rod outer segment membranes.

The Paget Cell: Its Structure, Occurrence and Significance

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