Abnormal Catabolism Research Articles

Abnormal degradative pathway of mitochondrial ATP synthase subunit c in late infantile neuronal ceroid‐lipofuscinosis (Batten disease)

Subunit c is normally present as an inner mitochondrial membrane component of the F0 sector of the ATP synthase complex, but in the late infantile form of neuronal ceroid-lipofuscinosis (NCL) it was also found in lysosomes in high concentrations. The rate of degradation of subunit c as measured by pulse-chase and immunoprecipitation showed a marked delay of degradation in patients' fibroblasts with late infantile form of NCL. There were no significant differences between control cells and cells with disease in the degradation of cytochrome oxidase subunit IV, an inner membrane protein of mitochondria. Measurement of labeled subunit c in mitochondrial and lysosomal fractions showed that the accumulation of labeled subunit c in the mitochondrial fraction can be detected before lysosomal appearance of radioactive subunit c, suggesting that subunit c accumulated as a consequence of abnormal catabolism in the mitochondrion and is transferred to lysosomes through an autophagic process. The biosynthetic rate of subunit c and mRNA levels for P1 and P2 genes that code for it were almost the same in both control and patient cells. These findings suggest that a specific failure in the degradation of subunit c after its normal inclusion in mitochondria and its consequent accumulation in lysosomes.

Membranous Nephropathy and a TAP1 Gene Polymorphism

To the Editor: Membranous glomerulopathy, which is characterized by immune-complex deposits on the epithelial side of the glomerular basement membrane, is one of the most frequent forms of glomerulopathy. The mechanisms responsible for abnormal antibody responses and immune-complex catabolism in this disease are unknown. Nevertheless, an association between membranous nephropathy and the HLA-DR3 class II antigen has been described1. Recently, two “new” genes (TAP1 and TAP2) have been mapped within the HLA class II region2. Each of these genes codes for a transmembrane protein located within the membrane of the endoplasmic reticulum. The noncovalent association of these two . . .

Apolipoprotein E polymorphism in patients with acute pancreatitis.

We have shown that patients with previous acute pancreatitis (AP) may have an abnormal catabolism of chylomicron remnants (CMR). Because apoprotein E (Apo E) genetic polymorphism has an important influence on CMR clearance, we compared frequency distribution of Apo E phenotypes in 52 patients with AP, 109 patients with gallstones, and 110 control subjects. Apo E phenotypes were detected by isoelectric focusing and immunoblotting. After adjusting for differences in age and gender, fasting triglyceride level was comparable between the study groups. The frequency distribution of Apo E phenotypes was not different between the three study groups and it was in Hardy-Weinberg equilibrium. The gene frequency for Apo E2 was 0.212, 0.273, and 0.243 in AP, gallstone, and control group, respectively. For Apo E3 it was 0.701, 0.627, and 0.674, and for Apo E4 0.090, 0.100, and 0.083 in the same groups, respectively. Differences were not statistically significant (chi 2). In conclusion, the abnormal catabolism of CMR in patients with AP is not attributable to Apo E polymorphism. An alternative explanation may be sought in the activity of the recently identified hepatocytic Apo E receptor [LDL-related receptor protein (LRP)].

Hepatic lipase deficiency. Clinical, biochemical, and molecular genetic characteristics.

Hepatic lipase (HL) is an important enzyme in the metabolism of triglyceride-rich lipoproteins and high density lipoproteins. The clinical syndrome of HL deficiency is rare and difficult to identify. We studied carriers of mutant HL to ascertain whether there are distinctive clinical and/or biochemical characteristics of the heterozygous state. In an Ontario kindred, compound heterozygosity for two HL mutations, S267F and T383M, underlies the clinical syndrome of complete HL deficiency. We report that simple heterozygotes for either HL mutant do not have a discrete lipoprotein abnormality, except for relative triglyceride enrichment of lipoprotein fractions with d > 1.006 g/mL. Postheparin HL activity is depressed to a greater degree in carriers of S267F compared with carriers of T383M. Retinyl palmitate loading studies in a compound heterozygote revealed impaired clearance of chylomicron remnants. The dyslipoproteinemia in a compound heterozygote was ameliorated by lovastatin. There was no difference in the quantity and distribution of HL mRNA in the liver of a compound heterozygote when compared with that of a normal subject. Thus, HL deficiency associated with structural variation of the HL gene is characterized by premature atherosclerosis, triglyceride enrichment of lipoprotein fractions with d > 1.006 g/mL, the presence of circulating beta-very low density lipoproteins, and abnormal catabolism of postprandial triglyceride-rich lipoproteins.

Is there a treatment necessity for lipid disorders of uremic patients?

In the present review, the role of lipid disturbances is evaluated as a risk factor in the pathogenesis and the potential acceleration of atherosclerosis in uremic patients undergoing long-term hemodialysis. The alteration in high density lipoprotein composition with a decrease in high density lipoprotein cholesterol but a normal apoprotein AI content may have relevance to the atherogenetic process. Moreover, the accumulation of cholesterol-rich, very low density lipoproteins and intermediate density lipoproteins may play a major role in atherosclerosis since these degradation products of triglyceride-rich particles are considered as atherogenic. The hypothesis should be tested whether a correction of the abnormal catabolism of triglyceride-rich lipoproteins in uremic patients leads to a decrease in ischemic vascular events.

Hypertriglyceridemia: lipoprotein receptors and atherosclerosis.

We have shown first, that apoB mediates the binding of small VLDL Sf 20-60 and IDL, as well as LDL, to the LDL receptor. Second, apoE of an appropriate, accessible conformation is required for the binding of large VLDL to the LDL receptor; HTG-VLDL Sf greater than 60 but not normal VLDL Sf greater than 60 have this apoE population. Third, the same population of apoE that mediates binding of HTG-VLDL Sf greater than 60 to the LDL receptor modulates its binding to the beta-VLDL receptor, but it is not required for the latter interaction. Fourth, a domain of processed apoB or apoB-48 in association with a domain of the inaccessible apoE is required for binding to and uptake by the beta-VLDL receptor. Fifth, our observations suggest that the abnormal catabolism of VLDL that occurs in hypertriglyceridemia may be explained by the abnormal uptake of HTG-VLDL by either the LDL or the beta-VLDL receptor pathway. Finally, we suggest that plasma proteases may route apoB/E-containing lipoproteins to macrophages for disposal, and this results in foam cell formation.

Abnormal cell-interactive properties of low-density lipoproteins isolated from patients with chronic renal failure

Patients with renal failure on maintenance hemodialysis have accelerated rate of atherosclerosis. This, and the fact that chemically modified low-density lipoproteins (LDL) have a better capacity than native LDL to stimulate cholesteryl ester accumulation within macrophages in the vessel wall, led us to examine the possibility that some alteration in apo-LDL may take place in chronically uremic patients. We isolated LDL (d = 1.019 − 1.063 g/mL) from 18 patients with chronic renal failure and from 13 normolipidemic controls and compared the interactive properties of the different LDL preparations with cultured fibroblasts. Our results show that “uremic” LDL associates less, is degraded less, and has diminished ability to stimulate cholesteryl ester formation in fibroblasts when compared to normal LDL. LDL carbamylated in vitro showed interactive properties with fibroblasts similar to those of uremic LDL. Uremic LDL was not taken up by scavenger receptors present on rat peritoneal macrophages, similarly to normal LDL. However, the decrease in uptake by fibroblasts of uremic LDL may increase the residence time of these particles within the subendothelial region of the vessel wall, ultimately resulting in increased atherogenicity. Carbamylation of lysine residues of apoB in vivo, abnormal catabolism of LDL due to the absence of functional renal tissue, or triglyceride enrichment of LDL are among the possible explanations for the abnormal properties of uremic LDL.

Measurements of molecular weights of low-density lipoprotein (LDL) from homozygotes for familial hypercholesterolemia and controls

Weight average molecular weights ( M r(w)) were determined for LDL and LDL 2 taken from normals and patients who were homozygotic and heterozygotic for familial cholesterolemia (FH). M r(w) were calculated using experimental estimates of S 0 20,w , D 20,w (using intensity fluctuation spectroscopy) and apparent specific volume (Φ), all made on the same samples. The results showed that although there was variability in M r(w) between individuals, these differences could not be related to the FH condition. It was also found that M r(w) for LDL and LDL 2 were surprisingly similar for individuals examined at intervals, and furthermore the values for LDL and LDL 2 were also very similar, showing that the separation into these two fractions was by density only. These findings must be considered alongside the findings that there are observable differences in the LDL between normal and FH patients when examined in the ultracentrifuge. Examination of LDL from a patient before and after plasmapheresis showed a temporal change in the LDL which would be consistent with the view that the FH patients could synthesize normal LDL but they had an abnormal catabolism; this view would also be consistent with the consistency in molecular weights for individuals.

Studies on Factor VIII Complex in Liver Diseases

Factor VIII procoagulant activity (VIII: C), factor VIII related antigen (VIII R: AG) and von Willebrand factor (VIII R: WF) were measured in patients with liver disease (33 cases of cirrhosis, 8 cases of acute hepatitis, 10 cases of chronic hepatitis, 3 cases of fulminant hepatitis and 3 cases of primary liver cancer) and in 30 normal individuals.Level of the three subunits of factor VIII complex were increased in cirrhotic patients as compared to those in normal individuals. In normal individuals there was a high degree of correlation between the three subunits, whilst this correlation was low in cirrhotic patients. In most cases with liver cirrhosis, high levels of VIII R: AG were not followed by a proportional increase in VIII R: WF or VIII: C. Similar results were obtained in the other liver diseases. These data suggest a functionally or qualitatively different factor VIII complex molecule from that found in normal plasma.The two dimensional crossed immunoelectrophoresis (CIE) of the plasmas from patients with liver disease in whom disproportionately important elevation of VIII R: AG was found as compared with VIII R: WF, revealed abnormalities of the shape and migration of the precipitin arcs with more anodal electrophoretic mobility. The elution profile of the cryoprecipitate on Sepharose 4B of the plasma of liver cirrhosis differed from normal in respect that the partially purified factor VIII protein had markedly reduced VIII R: WF. These studies indicate that some patients with liver disease may comprise both quantitative and qualitative defects of factor VIII complex, presenting discrepancy between VIII R: AG and VIII R: WF.Although the reason for the abnormality is not clear it may be related to the abnormal synthesis of factor VIII protein or to the accumulation of partially degraded protein due to normal or abnormal catabolism, or to disorder of joining or activating VIII: C. An alternative possibility is that it could be due to degradation of the protein by plasmin as the authers previously reported.

Apolipoprotein of the low density lipoprotein of human plasma: Structural study in familial hyperbetalipoproteinemia

Isolation of the low density lipoprotein (LDL) from human plasma was accomplished within a narrow density interval (1.030–1.045 g/ml). After covalent modification by maleic anhydride of the protein moiety and delipidation it was possible to fractionate, by ion-exchange chromatography, up to 35% of the protein into three peptides with distinctive amino acid compositions. These fractions appeared to be identical in normal individuals and in patients with familial hyperbetalipoproteinemia (FH). Our findings provide further evidence that in FH the abnormal catabolism of the protein moiety of LDL is not related to a modification of its structure.

Antenatal detection of the sphingolipidoses.

Antenatal diagnosis in combination with elective termination of pregnancy has become an integral part of the approach to otherwise fatal, inherited disorders. Several of these disorders (termed sphingolipidoses) are characterized by deficient activity of a specific acid hydrolase and the concomitant accumulation of a complex molecule whose catabolism is normally associated with the disease-related acid hydrolase. These complex molecules are important structural components of cell membranes and under conditions of abnormal catabolism form aggregates within the cell, particularly within membrane-bound subcellular organelles. These organelles resemble lysosomes, which are, in fact, the major subcellular localization of the various acid hydrolases.Both . . .