Yo Ishikawa

Abnormal metabolism of polyunsaturated fatty acids and phospholipids in diabetic glomeruli

Studies were done on changes in phospholipid content and fatty acid composition of phospholipids and on the role of the acylation pathway in synthesis of phospholipids in the development of abnormal fatty acid composition in the glomeruli of rats 2 and 10 mo after induction of diabetes with streptozotocin. The proportions of individual phospholipids in the glomeruli of rats were not changed 2 mo after induction of diabetes, but the proportion of phosphatidylethanolamine (PE) decreased and that of sphingomyelin increased 10 mo after induction of diabetes. In contrast, in liver the proportion of PE was increased and that of phosphatidylcholine was decreased. These results showed that changes of individual phospholipids in glomeruli were time-dependent and tissue-specific. Two mo after induction of diabetes, the main change in the phospholipid fatty acid composition of diabetic glomeruli was a decrease in arachidonic acid (AA); the main change in serum free fatty acids (FFA) was an increase in linoleic acid (LA) and a decrease in AA. Ten mo after induction of diabetes, the main changes in the phospholipid fatty acid composition of glomeruli were an increase in LA and a decrease in AA; the main change of the serum FFA composition was a decrease in AA. Thus, the fatty acid composition of glomerular phospholipids was not directly correlated to that of the serum in diabetic rats. Acyl-CoA synthetase and acyltransferase activities increased in diabetic glomeruli with either AA or LA as substrate, but activity toward LA increased more at 2 mo after induction of diabetes. Acyl-CoA synthetase activity increased in diabetic glomeruli with LA as substrate, but that did not change with AA as substrate at 10 mo after induction of diabetes. Furthermore, acyltransferase activity decreased in diabetic glomeruli with AA as substrate, although that did not change with LA as substrate at 10 mo after induction of diabetes.

Effect of Glycyrrhizin on Lysosomes Labilization by Phospholipase A2

The influence of glycyrrhizin on the effect of phospholipase A2 on lysosomes was studied. Treatment of rat liver lysosomes with venom phospholipase A2 caused release of acid phosphatase. This release of acid phosphatase was inhibited by 0.1 mM glycyrrhizin. Glycyrrhizin also inhibited acid phospholipase A2 with pH optimum of 4.5, which is thought to be present in the lysosomal membrane. These results suggest that glycyrrhizin stabilizes lysosomes by inhibiting phospholipase A2 activity in the lysosomal membrane.

Effects of long-term treatment with probucol on serum lipoproteins in cases of familial hypercholesterolemia in the elderly.

The effect of probucol in lowering serum lipoprotein in young and middle‐aged (YM) and elderly (E) patients with familial hypercholesterolemia were compared. Probucol at 1000 mg/day was administered orally to 37 YM patients and 14 E patients for an average of 10 months. Probucol treatment for this period caused significant reductions in the serum levels of total cholesterol, low density lipoprotein cholesterol (LDL‐C), high density lipoprotein cholesterol, and apoprotein AI, AII, B, and CIII in both groups. The decreases in the levels of total cholesterol, LDL‐C, and apoprotein B were greater in the E group than in the YM group (total cholesterol: YM, −19.3%, E, −31.3% [P < .001]; LDL‐C: YM −17.0%, E, −35.4% [P < .001]; apoprotein B: YM, −12.3%, E, −28.1% [P < .01]). The decreases in other parameters in the two groups were not significantly different. The serum probucol concentrations in the YM and E groups were not significantly different. No significant side effects were observed in any patient. Thus probucol reduced the serum level of LDL more in the E group than in the YM group, and did so without any increase in the serum concentration of the drug or in side effects, suggesting that probucol is safe and beneficial for use in elderly patients.

Moderate oxidation of hypertriglyceridemic low-density lipoprotein causes apolipoprotein B epitope change and enhances its uptake by macrophages.

We prepared monoclonal antibody (MabB4) that selectively binds to acetylated low-density lipoprotein (LDL). Native hypertriglyceridemic LDL (HT-LDL) obtained from IIb and native normotriglyceridemic LDL (NT-LDL) from type IIa scarcely bound with MabB4. When these LDL were oxidized moderately by incubation with copper ions, the binding of MabB4 to HT-LDL was enhanced compared to that of NT-LDL, although the contents of the hydroperoxide they produced were the same. The incorporation of moderately oxidized HT-LDL into macrophages was enhanced compared to that of NT-LDL, and the rate of incorporation parallel the binding of LDL for MabB4. These results suggested that moderate oxidation of HT-LDL expressed some apolipoprotein B epitope on the surface of acetylated LDL to a much greater degree than NT-LDL, and that this expressed epitope might work as a ligand of moderately oxidized HT-LDL for the recognition by macrophages.

Effects of chloroquine on the metabolism of phosphatidylcholine associated with low density lipoprotein in arterial smooth muscle cells

Phospholipid associated with LDL (LDL-phospholipid) has been suggested to affect metabolism of LDL in arterial smooth muscle cells. However, the metabolism of LDL-phosphatidylcholine in these cells has not been well clarified. We compared the metabolic pathway of LDL-phosphatidylcholine with that of cholesteryl ester associated with LDL (LDL-cholesteryl ester) in rabbit arterial smooth muscle cells by incubating the cells in the absence or presence of chloroquine, an inhibitor of lysosomal function. When the cells were incubated with LDL-[3H]cholesterol linoleate in the absence of chloroquine, 26.6 and 51.4% of incorporated radioactivity was found as cholesteryl ester in the lysosome-rich and microsome-rich fractions, respectively. When the cells were incubated in the presence of 50 microM chloroquine, the radioactivity found as cholesteryl ester in the lysosome-rich fraction increased to 45.5% while that in microsome-rich fraction decreased to 21.4%, indicating that LDL-cholesteryl ester accumulated in lysosomes as a consequence of inhibition of lysosomal function. When the cells were incubated with LDL-[14C]linoleoyl phosphatidylcholine in the absence of chloroquine, 25.1% of incorporated radioactivity was found as phosphatidylcholine in the lysosome-rich fraction and 24.8% in the cytosol-rich fraction. When the cells were incubated in the presence of chloroquine, phosphatidylcholine-associated radioactivity found in the lysosome-rich and cytosol-rich fractions changed only to 28.8% and 26.1%, respectively, showing that LDL-phosphatidylcholine did not accumulate in lysosomes when lysosomal function was inhibited. In conclusion, these data indicate that LDL-phosphatidylcholine, in contrast to LDL-cholesteryl ester, is not only hydrolyzed in lysosomes, but also at other subcellular sites.

Effect of Glycyrrhizin on Stability of Lysosomes in the Rat Arterial Wall

Studies were made on the effect of phospholipase A2 on the stability of arterial wall lysosomes, and the influence of glycyrrhizin on this effect. Lysosomal phospholipase A2 activity was found to be increased in the aorta of hypercholesterolemic rats. Treatment of the lysosomal fraction of the arterial wall with venom phospholipase A2 resulted in release of acid phosphatase, and addition of glycyrrhizin (0.1 mM) inhibited this release. Lysosomal phospholipase A2 in the arterial wall was also inhibited dose-dependently by glycyrrhizin. These results suggest that lysis of lysosomes was due to increase in phospholipase A2 activity, and that glycyrrhizin stabilized the lysosomes by inhibiting phospholipase A2 activity.