Isoform patterns of apolipoprotein E in diabetes mellitus.

Apolipoproteins in delipidated VLDL preparations from normal, diabetic, and non-diabetic hyperlipidaemic subjects were analysed by SDS-polyacrylamide gel electrophoresis, and by isoelectric focusing. On electrophoresis, diabetic VLDL contained more apolipoprotein E (17.3 +/- 7.3 (+/- SD) %, n = 54) than did VLDL from hyperlipidaemic (13.4 +/- 4.2%, n = 52; p less than 0.005) or normal (12.4 +/- 2.6%, n = 29; p less than 0.001) subjects. Apolipoprotein E excess was also seen when subgroups were characterized by apolipoprotein E phenotype. In diabetic patients of E3/E3 phenotype, apolipoprotein E was 16.4 +/- 6.0% (n = 25), compared with 12.9 +/- 2.5% in control subjects (n = 14; p = 0.008). Acidic isoforms were more common in 44 diabetic patients with E3/E3 phenotype; E3, E2, E1, and E1' as percentage of total E apolipoprotein were 58.3 +/- 7.6, 24.5 +/- 4.4, 13.7 +/- 4.5, and 3.8 +/- 4.3% respectively, compared with 63.5 +/- 10.4 (p = 0.034), 19.1 +/- 5.3 (p less than 0.001), 13.7 +/- 6.5 (NS), and 3.7 +/- 2.1% (NS) in 21 normal subjects. In 31 diabetic patients, of apolipoprotein E3/E3 phenotype, E3, E2, E1 and E1' were 60.2 +/- 7.3, 23.4 +/- 9.4, 11.1 +/- 4.1, and 5.4 +/- 3.7%, respectively, compared with 68.0 +/- 7.1 (p less than 0.001), 21.9 +/- 6.4 (NS), 6.3 +/- 3.9 (p less than 0.001), and 3.7 +/- 2.5 (p less than 0.05) % in 32 hyperlipidaemic patients. Diabetic patients of E3/E2 phenotype showed less apolipoprotein E3 than normal or hyperlipidaemic subjects, with a similar trend for apolipoprotein E4 in those of E4/E3 phenotype.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of calcium antagonists on the activities of lipid metabolizing enzymes in the isolated ischaemically perfused and reperfused rat heart.

Isolated rat hearts were perfused with various external Ca2+ concentrations and with various Ca2+ uptake antagonists. Compared to control activities (at 1.2 mM Ca2+), 0.6 mM Ca2+ and Ca2+ antagonists inhibited triglyceride lipase (TGL) and stimulated glycerol 3-phosphate acyltransferase (GPAT). Raising external Ca2+ concentration above the control value had no effect on TGL activity but GPAT activity was greatly reduced. Therefore, it appears that GPAT, but not TGL, will respond to increases in [Ca2+]. During ischaemia the activity of TGL is increased and that of GPAT is inhibited by beta-adrenergic activation. On reperfusion, TGL activity returns to pre-ischaemic values but GPAT activity is further reduced. In this study pre-perfusion of hearts with the Ca2+ antagonist diltiazem (10(-6) M) produced the following effects on enzyme activity during ischaemia and reperfusion: after 10 min ischaemia, TGL activity was increased and GPAT activity decreased to the same extent as seen during ischaemia in control hearts; however, on reperfusion of diltiazem-perfused hearts, the activities of both TGL and GPAT returned to pre-ischaemic values. These results suggest that Ca2+ entry on reperfusion is responsible for the reperfusion-induced decrease in GPAT activity.

Identification of ADPR-transferase activity in the rat tapeworm, Hymenolepis diminuta.

1. The nuclear fraction of the rat tapeworm Hymenolepis diminuta (Cestoda) contains the enzyme adenosine diphosphoribosyl transferase (ADPR-transferase). 2. The enzyme catalyzes the postsynthetic modification of some nuclear proteins by the covalent attachment of the (ADP-ribose) moiety of NAD to such proteins. 3. The reaction is dependent on DNA which contains strand-breaks, and chain lengths equivalent to (ADP-ribose) is estimated. 4. The formation of polynucleotide products was competitively inhibited by 3-acetamidobezamide, with a Km of 125 microM. 5. The catalytic properties of ADPR-transferase in Hymenolepis diminuta are similar to those in T. brucei.

The effect of coronary artery occlusion and reperfusion on the activities of triglyceride lipase and glycerol 3-phosphate acyl transferase in the isolated perfused rat heart.

Glycerol 3-phosphate acyltransferase (GPAT) and Triglyceride lipase (TGL) were measured in homogenates from non-ischaemic and ischaemic tissue from the isolated perfused rat heart. Ischaemia was produced by occlusion of the left descending coronary artery for 10 min. Compared to activities measured in tissue from normally perfused hearts, GPAT activity measured in tissue from the ischaemic area was considerably reduced. TGL activity in the ischaemic area was markedly increased compared to activity measured in normally perfused hearts. No change was seen in GPAT or TGL activity measured in tissue from the non-ischaemic area. The change in activities produced by ischaemia were prevented by pre-perfusion with the cardio-selective beta-antagonist Atenolol. Reperfusion of the ischaemic area resulted in TGL activity returning to the value measured in tissue from normally perfused hearts. However, GPAT activity, after 1 min of reperfusion, fell to a value lower than after 10 min ischaemia. The reperfusion-induced fall in GPAT activity was prevented by pre-perfusion with the alpha 1 antagonist Doxasozin. Pre-perfusion of the alpha 2 antagonist Yohimbine resulted in a prolongation of the increased TGL activity in the ischaemic area during reperfusion. All changes in enzyme activities were prevented by injection of 6 OH-dopamine 24 h before hearts were removed. These changes in enzyme activities show that during ischaemia there is an increased beta-adrenergic drive. On reperfusion the beta-adrenergic drive is removed but an alpha 1 adrenergic drive becomes apparent.

The effect of adrenergic agents on the activities of glycerol 3-phosphate acyltransferase and triglyceride lipase in the isolated perfused rat heart.

Glycerol 3-phosphate acyltransferase (GPAT) activity and triglyceride lipase (TGL) activity were measured in homogenates from hearts perfused with adrenergic agonists and antagonists. Perfusion with adrenalin or the beta-agonist isoprenaline produced an increase in TGL activity and a fall in GPAT activity. These changes could be imitated by incubation of heart homogenates with cAMP-dependent protein kinase. The alpha 2-agonist clondine produced the opposite effect, thus it increased GPAT activity and decreased TGL activity. Methoxamine, an alpha 1-agonist, had no effect on TGL activity but reduced GPAT activity. Continuous perfusion of the beta-antagonist atenolol reduced TGL activity to half that found in controls but also reduced GPAT activity. No change was seen on continuous perfusion of alpha 1- or alpha 2-antagonists. Changes in GPAT activity were localized mainly in the microsomal enzyme. These changes are consistent with both enzymes being regulated via a cyclic-AMP dependent protein kinase system and via alpha-adrenergic mechanisms.