Diabetes mellitus-induced enhancement of prostaglandin F2 alpha-responses is inhibited by lipoxygenase- but not cyclooxygenase-inhibitors in mesenteric veins and arteries of mouse and rat

Augmented contractility of murine femoral arteries in a streptozotocin diabetes model is related to increased phosphorylation of MYPT1

Diabetes mellitus (DM) is a metabolic disorder with high prevalence, and a major risk factor for macro- and microvascular abnormalities. This study was undertaken to explore the mechanisms of hypercontractility of murine femoral arteries (FA) obtained from mice with streptozotocin (STZ)-induced diabetes and its relation to the phosphorylation profile of the myosin phosphatase target subunit 1, MYPT1. The immunoreactivity of MYPT1 toward phospho-MYPT1-T696, MYPT1-T853, or MYPT1-S695, used as a read out for MYPT1 phosphorylation, has been studied by Western Blotting. Contractile activity of FA from control and STZ mice has been studied by wire myography. At basal conditions (no treatment), the immunoreactivity of MYPT1-T696/T853 was ~2-fold higher in the STZ arteries compared with controls. No changes in MYPT1-T696/853 phosphorylation were observed after stimulation with the Thromboxan-A2 analog, U46619. Neither basal nor U46619-stimulated phosphorylation of MYPT1 at S695 was affected by STZ treatment. Mechanical distensibility and basal tone of FA obtained from STZ animals were similar to controls. Maximal force after treatment of FA with the contractile agonists phenylephrine (10 μmol/L) or U46619 (1 μmol/L) was augmented in the arteries of STZ mice by ~2- and ~1.5-fold, respectively. In summary, our study suggests that development of a hypercontractile phenotype in murine FA in STZ diabetes is at least partially related to an increase in phosphorylation of MLCP at MYPT1-T696/853. Interestingly, the phosphorylation at S695 site was not altered in STZ-induced diabetes, supporting the view that S695 may serve as a sensor for mechanical activity which is not directly involved in tone regulation.

Effect of age and COX-2-derived prostanoids on the progression of adult vascular dysfunction in the offspring of diabetic rats

BACKGROUND AND PURPOSE

The present study was designed to determine how diabetes in pregnancy affects vascular function in their offspring, the influence of age and whether COX activation is involved in this effect.

EXPERIMENTAL APPROACH

Relaxation responses to ACh were analysed in mesenteric resistance arteries from the offspring of control rats (O-CR) and those of diabetic rats (O-DR) at 3, 6 and 12 months of age. TxB₂, PGE₂ and PGF(2α) release were determined by enzyme immunoassay. COX-1 and COX-2 expression were measured by Western blot analysis.

KEY RESULTS

O-DR developed hypertension from 6 months of age compared with O-CR. In O-DR, relaxation responses to ACh were impaired in all ages studied and were restored by COX-2 inhibition. TP receptor blockade (SQ29548) restored ACh relaxation in arteries from 3-month-old O-DR while TP and EP receptor blockade (SQ29548 + AH6809) was required to restore it in 6-month-old O-DR. In 12-month-old O-DR, ACh relaxation was restored when TP, EP and FP receptors were blocked (SQ29548 + AH6809 + AL8810). ACh-stimulated TxB₂ was higher in all O-DR. ACh-stimulated PGE₂ release was increased in arteries from 6- and 12-month-old O-DR, whereas PGF(2α) was increased only in 12-month-old O-DR. COX-2, but not COX-1, expression was higher in O-DR than O-CR.

CONCLUSIONS AND IMPLICATIONS

The results indicate an age-dependent up-regulation of COX-2 coupled to an enhanced formation of vasoconstrictor prostanoids in resistance arteries from O-DR. This effect plays a key role in the pathogenesis of endothelial dysfunction, which in turn could contribute to the progression of vascular dysfunction in these rats.

The contractile response of the mesenteric resistance arteries to prostaglandin F2alpha; effects of simultaneous hyperlipemia-diabetes

The effect of hyperlipemia associated with diabetes on the contractility of resistance arteries to prostaglandin F2alpha (PGF2alpha) was investigated employing 4 weeks simultaneously hyperlipemic-diabetic (HD), hyperlipemic (H), diabetic (D) and normal hamsters (controls, C). The isometric force produced by explanted arteries in the presence of 10(-8) to 10(-5) M PGF2alpha was recorded by the myograph technique. The results showed that compared with controls, the contractile response to 10(-5) M PGF2alpha was approx. 2 fold increased in HD group, and approx. 1.75 and 1.62-fold enhanced in H and D groups, respectively. Activation of protein kinase C with 10(-6) M phorbol 12-myristate 13-acetate increased the contractility to PGF2alpha in all groups and particularly in HD hamsters (approx. 10.16-fold). Inhibition of cyclooxygenase by indomethacin increased approx. 1.81-fold the arterial contractility to PGF2alpha in C group, whereas in H, D and HD hamsters had no effect. Blockage of Ca(2+)-activated K(+)-channels with 10(-3) M tetraethylammonium augmented the contraction to PGF2alpha approx. 6.43-fold in C group, and at significantly lower levels in H, D and HD groups, i.e. approx. 3.84, 3.72 and 3.33-fold, respectively. The results validate two conclusions: (i) simultaneous insult of hyperlipemia-hyperglycemia is associated with the highest contractility of the resistance arteries to PGF2alpha; the highest circulating glucose and cholesterol levels, and the enhancement in the protein kinase C pathway underlay the augmented contractility; (ii) no matter the pathology induced (hyperlipemia, diabetes or both simultaneously) a common dysfunctional response to PGF2alpha was installed; this consists in a reduced effect of cyclooxygenase inhibition, and a altered activity of Ca(2+) dependent K(+) channels.

Lipoxygenase products increase monocyte adhesion to human aortic endothelial cells

The development of atherosclerosis is accelerated in individuals with type 2 diabetes. Adhesion of monocytes to the vascular endothelium is a key initial step in atherogenesis. We have previously shown that monocyte adhesion to human aortic endothelial cells (HAECs) cultured long-term in high-glucose medium (25 mmol/L, 2 passages) is increased compared with cells grown in normal glucose (5 mmol/L). One potential mechanism for increased monocyte adhesion to HAECs under hyperglycemic conditions is via the 12-lipoxygenase (12-LO) pathway. In this study, we demonstrated in HAECs that the major LO metabolite of arachidonic acid was the 12-LO product, 12(S)-hydroxyeicosatetraenoic acid [12(S)-HETE], which was increased severalfold in HAECs cultured under high-glucose conditions. Furthermore, treatment of HAECs with 12(S)-HETE induced monocyte, but not neutrophil, adhesion an average of 3-fold (range of 1.5- to 5-fold) compared with untreated cells (75+/-5 versus 26+/-1 monocytes per field, respectively, P<0.001). Expression of the adhesion molecules vascular cell adhesion molecule-1, E-selectin, and intercellular adhesion molecule-1 was not significantly increased. However, both glucose and 12(S)-HETE induced a 60% increase in HAEC surface expression of connecting segment-1 (ie, CS-1) fibronectin, a ligand for very late-acting antigen-4 (VLA-4). The antibodies used to block monocyte integrin VLA-4 and leukocyte function-related antigen-1, a monocytic counterreceptor for intercellular adhesion molecule-1, inhibited the ability of both 12-LO products and high glucose to induce monocyte adhesion. These results definitively demonstrate for the first time in HAECs that the 12-LO pathway can induce monocyte-endothelial cell interaction and that the effects of glucose may be mediated, at least in part, through this pathway. Thus, these results suggest that the 12-LO pathway may play a role in the increased susceptibility of diabetics to atherosclerosis.

A quantitative assay for angiogenesis of cultured choroidal tissues in streptozotocin-diabetic Wistar and spontaneously diabetic GK rats

Angiogenesis of cultured choroids was quantitatively assayed in spontaneously diabetic GK and a bolus-treated streptozotocin (STZ)-diabetic Wistar rats. The number and total length of microvessels budded from cultured choroidal explants were measured to use as angiogenic indices. Both indices in 10-week-old Wistar rats were increased in parallel by 5% fetal bovine serum (FBS) from days 2 to 7 in culture. These indices in STZ-rats (10 weeks of age) were increased by 5% FBS to a greater extent than those in age-matched normal rats. These enhanced actions of FBS were concentration-dependent. The explants of 16-week-old GK rats also increased these indices to a greater extent than those of age-matched Wistar rats. Aging to 18 weeks of age also increased choroidal angiogenesis in the normal rats. In conclusion, the assay model of choroidal angiogenesis was established by determining the number and length of microvessels in cultured choroidal explants. The diabetic states of STZ-Wistar and GK rats enhanced FBS-induced choroidal angiogenesis. This assay model is useful for determining angiogenic activity of growth factors and effective drugs in diabetic choroidopathy and retinopathy.

Glycated serum stimulation of macrophages in GK- and streptozotocin-rats for the proliferation of primary cultured smooth muscle cells of the aorta

The purpose of this study was to investigate the actions of intraperitoneal macrophages and aortic endothelial cells (EC) as the cause of proliferation of primary cultured smooth muscle cells (SMC) of the aorta in non-insulin-dependent diabetes mellitus (NIDDM) models, including spontaneously diabetic GK and streptozotocin-diabetic Wistar rats. Conditioned medium derived from macrophages of GK rats increased proliferation of SMC in Wistar rats to a greater extent when compared to normal Wistar rats in conditioned medium. Serum of both GK rats and of Wistar rats which was previously exposed to 16.7 and 25 mM glucose (glycated serum) activated normal macrophages, enhancing SMC proliferation. However, glycated serum and high concentrations of glucose did not affect directly the proliferation of SMC. Conditioned medium from EC of streptozotocin-Wistar rats enhanced SMC proliferation. The enhancing activity of EC in diabetic rats was mimicked by conditioned medium from glycated EC but not from EC treated with the diabetic rat serum nor glycated bovine serum albumin. Cholesterol (39 microg/ml) potentiated the action of glycated serum on macrophages, but neither the action of normal macrophages nor the direct action of SMC was affected. Both the actions of glycated serum and cholesterol were inhibited by a polyclonal platelet-derived growth factor-BB antibody. However, low density lipoprotein (LDL), acetylated LDL and oxidized LDL (25 microg/ml) did not potentiate the action of glycated serum. These results demonstrate that glycated serum in the NIDDM model predominantly activated macrophages, resulting in proliferation of SMC by the release of platelet-derived growth factor-BB. Cholesterol potentiated the actions of glycated serum on macrophages.