Akihiro Matsuura

Preferential pharmacological inhibition of macrophage ACAT increases plaque formation in mouse and rabbit models of atherogenesis.

The cholesteryl ester, foam cell-enriched vulnerable plaque is a principle pharmacological target for reducing athero-thrombosis. Acyl CoA:cholesterol Acyl Transferase (ACAT) catalyzes the esterification of free cholesterol in intestine, liver, adrenal and macrophages, leading in the latter cells to intracellular cholesteryl ester accumulation and foam cell formation in the arterial intima. Previous studies suggested the existence of several isoforms of ACAT with different tissue distribution and this has largely been confirmed by molecular cloning of ACAT-1 and ACAT-2. We developed a series of ACAT inhibitors that preferentially inhibited macrophage ACAT relative to hepatic or intestinal ACAT based on in vitro assays and ex vivo bioavailability studies. Four of these compounds were tested in three models of atherosclerosis at oral doses shown to give sufficient bioavailable monocyte/macrophage ACAT inhibitory activity. In fat-fed C57BL/6 mice, chow fed apo E-/- mice and KHC rabbits, the various ACAT inhibitors had either no effect or increased indices of atherosclerotic foam cell formation. Direct and indirect measurements suggest that the increase in plaque formation may have been related to inhibition of macrophage ACAT possibly leading to cytotoxic effects due to augmented free cholesterol. These results suggest that pharmacological inhibition of macrophage ACAT may not reduce, but actually aggravate, foam cell formation and progression.

Amelioration of neurovascular deficits in diabetic rats by a novel aldose reductase inhibitor, GP-1447: Minor contribution of nitric oxide

The effects of a novel potent aldose reductase inhibitor, GP-1447 [3-[(4,5,7-trifluorobenzothiazol-2-yl)methyl]-5-methylphenylace tic acid] on the sciatic nerve blood flow in streptozotocin-induced diabetic rats were examined. Blood flow was analyzed in terms of mass, i.e. the volume of blood in tissue, and of velocity, i.e. the velocity of the blood flow. In diabetic rats, a 63% decrease in blood flow due to a decrease in velocity was observed. The blood mass in the same animals fluctuated, thereby increasing its range of values. Treatment with GP-1447 at a dose of 30 mg/kg per day for 4 consecutive weeks following a 3-week period without treatment ameliorated the reduced blood flow by 51%, and was accompanied by a recovery of velocity. The increase in the range of blood mass values was reversed by treatment with GP-1447. The restoration of the range of blood mass values, but not that of the blood flow, by GP-1447 was blocked by treatment with the nitric oxide (NO) synthase inhibitor, NG-nitro-L-arginine. Motor nerve conduction velocity (MCV) changes in parallel with blood flow values, while it is inversely proportionate to alterations in the range of blood mass values. It is suggested that the observed beneficial effect of GP-1447 on blood flow is involved in the restoration of decreased MCV in diabetes. It would appear that GP-1447-induced amelioration of neurovascular defects is not mediated solely by the improvement of the NO system.

Big endothelin-1-induced sudden death is inhibited by phosphoramidon in mice

The lethal activity of big endothelin-1 (bET-1) was examined in mice and compared with endothelin-1 (ET-1). Like ET-1, intravenous administration of bET-1 produced sudden death with an approximate LD50 value at 21.0 nmol/kg, higher than that of ET-1 (3.8 nmol/kg). At doses above the respective LD90 value, the latency to death was much longer in bET-1-treated mice with sustained elevation of plasma immunoreactive ET-1 (IR-ET-1). A metalloproteinase inhibitor, phosphoramidon, although failing to inhibit sudden death induced by ET-1, suppressed bET-1-induced lethality and elevation of plasma IR-ET-1 probably due to an inhibition of the enzymatic conversion of bET-1 to ET-1.

Comparison of haemoconcentration induced by big endothelin-1 and endothelin-1 in mice

1 The profile of haemoconcentration induced by big endothelin‐1 (big ET‐1), a precursor of endothelin‐1 (ET‐1), was compared with that induced by endothelin‐1 in mice. 2 ET‐1(1.5 nmol kg−1, i.v.) increased haematocrit in mice, which reached a maximum at 5 min and then returned to the control value within 30 min after the administration, this occurred at the same time as changes in the plasma immunoreactive endothelin‐1 and rat atrial natriuretic peptide (rANP)‐like activities (IR‐ET‐1 and IR‐rANP, respectively). 3 Big ET‐1(2.5–15 nmol kg−1, i.v.) also caused a significant and dose‐dependent increase in haematocrit, that lasted over 3 h although elevated plasma IR‐ET‐1 and IR‐rANP had almost been restored to the initial levels within 10 min after big ET‐1 injection. 4 A metalloproteinase inhibitor, phosphoramidon (10 mg kg−1, i.v.), which inhibits the activity of endothelin converting enzyme (ECE), delayed the onset of big ET‐1‐induced haemoconcentration, but failed to alter the maximal value and the duration of the haemoconcentration. 5 Pretreatment with phosphoramidon (10 mg kg−1, i.v.) did not affect the big ET‐1‐induced change in plasma IR‐ET‐1, while significant delay of the disappearance of plasma IR‐rANP and significant suppression of a sustained increase in tissue IR‐ET‐1 were observed. 6 These results suggest that ET‐1, not in plasma but in tissue, plays an important role in the pathogenesis of big ET‐1‐induced long‐lasting haemoconcentration, in which unknown factors besides rANP are involved.

Diltiazem facilitates endothelin clearance from the blood stream to reduce toxic elevation of plasma endothelin level in rodents

Abstract— Pretreatment with diltiazem at a dose of 2 mg kg−1 intravenously protected against sudden death induced by intravenous administration of endothelin‐1 (ET‐1, 5 nmol kg−1), with an apparent decrease in the plasma immunoreactive‐ET‐1 (IR‐ET‐1) in mice. These effects, which were also observed in anaesthetized rats, disappeared in rats with bilateral ligation of the renal arteries. In the latter, the exogenous ET‐1‐induced elevation of plasma IR‐ET‐1 tended to be higher than that in the sham‐operated controls. Furthermore, in anaesthetized rats, diltiazem inhibited ET‐1‐induced decreases in renal blood flow and increased renal accumulation of IR‐ET‐1. These results indicate that part of the clearance of ET‐1 from the bloodstream occurs in the kidney, and that diltiazem enhances the elimination of the peptide, presumably by improvement in the renal circulation, this action leading to alleviation of the toxic effects of ET‐1.