13,14-Dihydro-prostaglandin E1 decreases low-density lipoprotein influx into rabbit aorta

Isradipine lowers human arterial low density lipoprotein retention in vivo

During the recent past it has been discussed that calcium antagonists may exert antiatherosclerotic actions at the vessel wall. Apolipoprotein B containing lipoproteins were isolated by immunoaffinity chromatography and radiolabeled with 123-iodine. The effect of 2 x 2.5 mg isradipine on the low density lipoproteins (LDL) entry into the carotid and femoral arteries of 12 hypertensive patients with primary hyperlipoproteinemia (total cholesterol >6.5 mmol/l [250 mg/dL) was examined. Cholesterol -1.7% (P< 0.05 664), high density lipoprotein (HDL) cholesterol +4.5% (P< 0.01 123), and LDL cholesterol -1% (P< 0.01 563) did not change, nor did any of the safety parameters. The types of entry kinetics reflecting vascular surface lining did not change while the LDL retention 20 h after tracer application was depressed by up to 23.5%. The data were comparable in the carotid and femoral artery segments, the significance level ranging up to 0.0009. These results indicate a decreased LDL retention in the arterial wall of hypertensive patients induced by isradipine. The clinical implications of the findings ought to be pursued in properly designed clinical trials.

Effects of prostaglandin E1 metabolites on the induction of arterial thromboresistance

Prostaglandin (PG) E1 has been shown to induce arterial thromboresistance in experimental animals and in man. It is known to be degraded in vivo to metabolites which have comparable (13,14-dihydro-PGE1) or no (15-keto-PGE1, 15-keto-13,14-dihydro-PGE1) biological activity. It was the goal of this study to examine whether 13,14-dihydro-PGE1 and its derivatives might share biological activity in rendering the arterial wall less thrombogenic. Using a cross-perfusion technique the aorta and iliac artery surface were exposed to a donor rabbits' blood. We examined the intact endothelial lining and a surface which had been deendothelialized before by means of a Fogarty catheter. Donor animals and/or receiver animals were treated daily for 1 week with 13,14-dihydro-PGE1, PGE1, 15-keto-PGE1, 15-keto-13,14-dihydro-PGE1, or the vehicle only, respectively. From the group of the receiver animals, a subgroup of 6 animals each was treated for the same period of time with either 13,14-dihydro-PGE1, PGE1, 15-keto-PGE1, 15-keto-13,14-dihydro-PGE1, or the vehicle. Immediately after the last administration of the respective PG or solvent, native blood from a donor rabbit was circulated [30 mL/min. under in vivo flow conditions (60 Hz)] over an arterial segment of a receiver animal. Deposition of 111Indium-oxine labeled autologous platelets per surface unit was quantitatively assessed. In vitro perfusion data were morphometrically analysed. In animals pretreated with 13,14-dihydro-PGE1 the thromboresistance was almost comparable to that achieved with PGE1. In contrast, pretreatment of the donor animals (platelet) had only minor effects on the thromboresistance. The other compounds showed no effects. In vitro perfusion of human saphenous vein segments revealed PGE1 and 13,14-dihydro-PGE1 again to be of comparable potency, while 15-keto-PGE1 and 15-keto-13,14-dihydro-PGE1 were only active at concentrations being several orders of magnitude higher. Not only PGE1 but also its in vivo formed metabolite PGE0 may play an important role in inducing improvement of haemostatic balance via the vascular wall rather than the platelets. The other metabolites, however, are unlikely to exhibit an effect at biologically relevant concentrations.

The effect of a synthetic 7-thiaprostaglandin E1 derivative, TEI-6122, on monocyte chemoattractant protein-1 induced chemotaxis in THP-1 cells

1 The ability of various prostaglandins (PGs) to inhibit monocyte chemotaxis induced by monocyte chemoattractant protein-1 (MCP-1) was investigated with a human monocytic leukaemia cell line, THP-1. Moreover, to investigate the mechanism of the inhibitory action of PGs the involvement of either intracellular adenosine 3': 5'-cyclic monosphosphate (cyclic AMP) accumulation or intracellular Ca2+ mobilization was studied. 2 TEI-6122, a synthetic 7-thia-PGE1 derivative, inhibited chemotaxis of THP-1 cells induced by MCP-1 with an IC50 of 1.5 pM. Its inhibitory activity was 1000 fold more than that of PGE1 and PGE2 (IC50 = 2.8 nM and 0.9 nM, respectively), which were more potent than other PGs such as PGA1, PGA2, PGF2 alpha and PGI2 (IC50 > or = 1 microM). 3 With respect to the effect on intracellular cyclic AMP accumulation in THP-1 cells, TEI-6122 was as potent as PGE1 and PGE2, which were approximately 100 to 1000 fold more potent than the other PGs such as PGA1, PGA2 and PGI2. The minimum concentration of TEI-6122 required to increase intracellular cyclic AMP accumulation in THP-1 cells was 1 nM. 4 TEI-6122 and PGE1 (4 microM) transiently increased intracellular calcium levels in THP-1 cells. When added prior to MCP-1, both PGs partially suppressed the increased in Ca2+ caused by this cytokine. There were no significant differences between the activity of TEI-6122 and PGE1 in either respect. 5 It is concluded that TEI-6122, a synthetic 7-thia-PGE1 derivative is a much more potent inhibitor of MCP-1-induced THP-1 cell chemotaxis than PGEI and PGE2 which are the best inhibitors among the natural PGs tested, while neither intracellular cyclic AMP accumulation nor effects on Ca2+ mobilization account for the extremely potent inhibitory activity of TEI-6122. Thus, either a novel PGE2 receptor (EPreceptor) or a novel intracellular signal transduction system may be involved in the extremely potent chemotaxis inhibitory activity of TEI-6122.

Evidence for lipid regression in humans in vivo performed by 123iodine-low-density lipoprotein scintiscanning

Radiolabeling of autologous LDL allows in vivo characterization of arterial wall lipid metabolism and LDL receptor imaging. Different kinetic types of arterial wall LDL entry reflect the de-, re-, and endothelialized segments in both animals and humans. In 36 male cholesterol-fed rabbits being treated with the calcium channel blocker isradipine (0.3 mg/kg daily), the retention of the radiolabeled (125I-LDL) was reduced, being related to the reduction in arterial wall cholesterol ester content and the decreased extent of Sudan III-positive areas. In parallel, a significant (p < 0.01) increase in vascular prostaglandin I2 (PGI2) generation was seen in endothelialized and reendothelialized segments of the abdominal aorta. These effects were completely abolished by concomitant treatment with acetylicsalicylic acid (ASA). These data could be confirmed in humans, too: a 4-week treatment with prostaglandin E1 (PGE1:5 ng/kg/min iv, 5 days/week, 6 h/day for 6 weeks) and isradipine (2 x 2.5 mg po daily for 4 weeks) did not change arterial 123I-LDL influx kinetics, which were examined over a total of 60 (PGE1) and 96 (isradipine) vascular regions. In contrast to this, the retention of the tracer was significantly diminished in different arterial segments. In isradipine-treated patients, 20 hours after reinjection of radiolabeled LDL, the quantitative LDL entry was reduced by at least 4.7% with a maximum of 23.5% (p < 0.01) in type I (n = 50 lesions) or type II lesions (n = 41). PGE1 treatment induced a 16.9% to 30.7% (p < 0.01) decrease of LDL retention in type I (n = 36 lesions) or type II lesions (n = 24), respectively. These findings support the hypothesis derived from earlier experimental studies that the antiatherosclerotic effects are likely to be due to the increase in PGE1 and/or PGI2 availability mediated by an increase in cAMP. The results demonstrate the potential of 123I-LDL scintigraphy for the characterization of vascular LDL kinetics and the monitoring of functional lipid lesion regression.