Abnormality in prostacyclin-stimulatory activity in sera from diabetics

Lysophosphatidylcholine inhibits the expression of prostacyclin stimulating factor in cultured vascular smooth muscle cells

We have cloned a prostacyclin (PGI2) stimulating factor (PSF), which stimulates PGI2 production by vascular endothelial cells. Previous study demonstrated the reduced PSF expression in the coronary arteries from the patients with ischemic heart disease. To clarify the mechanism of reduced PSF expression in atherosclerosis, we examined the effect of lysophosphatidylcholine (lysoPC), a main component of oxidized low density lipoprotein (LDL), on PSF expression in cultured vascular smooth muscle cells. LysoPC reduced PSF expression dose-dependently. Whereas neither phosphatidylcholine nor native LDL affects the PSF expression. Calphostin C, a protein kinase C (PKC) inhibitor, restored the reduction of PSF expression by lysoPC. These results suggest that lysoPC-induced reduction of PSF expression is mediated by PKC activation and is playing a role in the initiation and progression of atherosclerotic lesions.

Prostanoid release and constrictor responses to noradrenaline in the rat mesenteric vascular bed in non-insulin-dependent diabetes mellitus

1. The administration of streptozotocin (STZ) to 2-day old rats induced a non-insulin-dependent diabetes mellitus (NIDDM)-like state, with mild hyperglycaemia and no alterations in body weight at the adult age. 2. In the isolated and perfused mesenteric vascular bed of NIDDM animals, the constrictor responses to either noradrenaline (NA) or potassium chloride (KCl) were not modified as compared with age-matched non-diabetic controls. 3. The reduction in NA contractions induced by the cyclooxygenase inhibitor, 10 microM indomethacin in the control group was absent in the NIDDM rats. 4. The increase in the NA-induced contractions caused by endothelium removal was suppressed by indomethacin in the controls but not in the NIDDM group. 5. The prostanoid release from the mesenteric vascular beds of NIDDM rats was markedly reduced as compared with non-diabetic controls. Noradrenaline increased production of the constrictor prostaglandin (PG) F2alpha in control but not in NIDDM rats. 6. In summary, these results show that in STZ-induced NIDDM rats, there is an impairment of the prostanoid production, as well as a suppression of the role of prostanoids in the contractile effects of NA in the mesenteric vascular bed. These alterations are more severe than those previously observed in a model of insulin-dependent diabetes mellitus (IDDM), in which hyperglycaemia and reduction of body weight were more marked. The conclusion is that, in these models of diabetes and in the preparation studied, vascular alterations and modifications of glycaemia and body weight are not closely related.

The insulin-like growth factor-binding protein (IGFBP) superfamily

Over the last decade, the concept of an IGFBP family has been well accepted, based on structural similarities and on functional abilities to bind IGFs with high affinities. The existence of other potential IGFBPs was left open. The discovery of proteins with N-terminal domains bearing striking structural similarities to the N terminus of the IGFBPs, and with reduced, but demonstrable, affinity for IGFs, raised the question of whether these proteins were "new" IGFBPs (22, 23, 217). The N-terminal domain had been uniquely associated with the IGFBPs and has long been considered to be critical for IGF binding. No other function has been confirmed for this domain to date. Thus, the presence of this important IGFBP domain in the N terminus of other proteins must be considered significant. Although these other proteins appear capable of binding IGF, their relatively low affinity and the fact that their major biological actions are likely to not directly involve the IGF peptides suggest that they probably should not be classified within the IGFBP family as provisionally proposed (22, 23). The conservation of this single domain, so critical to high-affinity binding of IGF by the six IGFBPs, in all of the IGFBP-rPs, as well, speaks to its biological importance. Historically, and perhaps, functionally, this has led to the designation of an "IGFBP superfamily". The classification and nomenclature for the IGFBP superfamily, are, of course, arbitrary; what is ultimately relevant is the underlying biology, much of which still remains to be deciphered. The nomenclature for the IGFBP related proteins was derived from a consensus of researchers working in the IGFBP field (52). Obviously, a more general consensus on nomenclature, involving all groups working on each IGFBP-rP, has yet to be reached. Further understanding of the biological functions of each protein should help resolve the nomenclature dilemma. For the present, redesignating these proteins IGFBP-rPs simplifies the multiple names already associated with each IGFBP related protein, and reinforces the concept of a relationship with the IGFBPs. Beyond the N-terminal domain, there is a lack of structural similarity between the IGFBP-rPs and IGFBPs. The C-terminal domains do share similarities to other internal domains found in numerous other proteins. For example, the similarity of the IGFBP C terminus to the thyroglobulin type-I domain shows that the IGFBPs are also structurally related to numerous other proteins carrying the same domain (87). Interestingly, the functions of the different C-terminal domains in members of the IGFBP superfamily include interactions with the cell surface or ECM, suggesting that, even if they share little sequence similarities, the C-terminal domains may be functionally related. The evolutionary conservation of the N-terminal domain and functional studies support the notion that IGFBPs and IGFBP-rPs together form an IGFBP superfamily. A superfamily delineates between closely related (classified as a family) and distantly related proteins. The IGFBP superfamily is therefore composed of distantly related families. The modular nature of the constituents of the IGFBP superfamily, particularly their preservation of an highly conserved N-terminal domain, seems best explained by the process of exon shuffling of an ancestral gene encoding this domain. Over the course of evolution, some members evolved into high-affinity IGF binders and others into low-affinity IGF binders, thereby conferring on the IGFBP superfamily the ability to influence cell growth by both IGF-dependent and IGF-independent means (Fig. 10). A final word, from Stephen Jay Gould (218): "But classifications are not passive ordering devices in a world objectively divided into obvious categories. Taxonomies are human decisions imposed upon nature--theories about the causes of nature's order. The chronicle of historical changes in classification provides our finest insight into conceptual revolutions

Effect of eicosapentaenoic acid on glucose-induced diacylglycerol synthesis in cultured bovine aortic endothelial cells

Hyperglycemia has been postulated to increase diacylglycerol (DAG) level through de novo synthesis pathway and subsequently activate protein kinase C (PKC) in vascular cells, possibly leading to vascular dysfunction associated with diabetes. In this study, we examined the effect of eicosapentaenoic acid (EPA) on high glucose-induced increase in DAG level in cultured aortic endothelial cells (ECs). In ECs, total DAG level was significantly increased in the cells cultured with high glucose levels (400 mg/dl) compared with the cells with normal glucose levels (100 mg/dl). The addition of EPA completely prevented high glucose-induced increase in total DAG level. In contrast, other common fatty acids such as palmitate and oleate significantly stimulated DAG syntheisis, although arachidonate did not affect it. High glucose level significantly stimulated the incorporation of 3H-palmitate into DAG, while it did not affect the incorporation of 3H-arachidonate into DAG. The addition of EPA completely prevented the high glucose-induced increase in 3H-palmitate incorporation into DAG, while it did not affect the 3H-arachidonate incorporation. These findings suggest that EPA can prevent high glucose induced-increase in DAG level in ECs, probably by specifically inhibiting de novo synthesis at the step of acylation. EPA may be one of the candidates for clinical agents normalizing activation of DAG-PKC pathway in diabetic vascular tissues and preventing vascular complications associated with diabetes.

Difference in serum-induced prostacyclin production by cultured aortic and capillary endothelial cells

Prostacyclin (PGl2) generated by vascular endothelial cells play an important role in the maintenance of vessel wall homeostasis. Human plasma-derived serum (PDS) stimulated PGl2 synthesis by both cultured bovine aortic endothelial cells (BAEC) and adrenal capillary endothelial cells (BCEC), but the PGl2 response of the latter cells was far smaller. When BAEC were cultured with a high concentration of glucose (400 mg/dl), the PGl2 synthesis induced by 20% PDS was significantly lower than in the culture with a physiological concentration of glucose (100 mg/dl) (258 +/- 45 pg/10(4) cells/h vs. 402 +/- 52 pg/10(4) cells/h, n = 4, P < 0.05). On the other hand, there was no significant difference in the PDS-induced PGl2 synthesis between BCEC cultured with high and physiological concentrations of glucose. Additionally, 10% PDS obtained from patients with non-insulin dependent diabetes mellitus (n = 6) stimulated significantly less PGl2 synthesis than that from healthy subjects (n = 4) in the case of both BAEC (133 +/- 27 pg/10(4) cells/h vs. 402 +/- 38 pg/10(4) cells/h, P < 0.05) and BCEC (72 +/- 15 pg/10(4) cells/h vs. 118 +/- 12 pg/10(4) cells/h, P < 0.05), with the difference in PGl2 synthesis being smaller for BCEC. These findings indicate that the PDS-induced PGl2 synthesis differs between cultured vascular endothelial cells from large and small vessels with the decrease in PGl2 by diabetic PDS and high glucose being more marked for BAEC than BCEC.

Is a (n inborn) deficiency of prostacyclin synthesis stimulating plasma factor associated with increased lipoprotein(a)?

Patients with the antiphospholipid syndrome as well as those with a lack in the prostacyclin synthesis stimulating plasma factor (PF) are prone to develop thrombophilia and are at a higher clinical risk for vascular disease. As patients with the antiphospholipid syndrome have been reported to show elevated lipoprotein (Lp)(a) levels, we re-examined all our patients known to have an inborn or an acquired persistent deficiency of PF. Their non-affected relatives served as controls. In addition, 36 patients suffering from clinically manifested atherosclerosis as well as 16 healthy adults, all of them having elevated Lp(a) levels (> 30 mg/dl), were screened for a PF deficiency. In fact, all the patients with a deficient PF activity showed elevated Lp(a) values. While the prevalence of PF deficiency ranges about 1-2%, in 7 (19%) patients with clinically manifested atherosclerosis and 3 (19%) healthy adults with elevated Lp(a) this defect was found. The findings demonstrate an association between PF deficiency and Lp(a), indicating a biochemical interaction which needs to be further elucidated.

Potential mechanisms promoting restenosis in diabetic patients

Diabetes is associated with greater restenosis rates after successful balloon angioplasty. The metabolic alterations that occur as a result of hyperglycemia or hyperinsulinemia can accelerate many of the pathophysiologic processes that lead to restenosis. Diabetes results in endothelial dysfunction and accelerated platelet deposition, which increase the propensity to thrombosis. Several growth factors known to promote the restenosis process are overexpressed in the presence of hyperglycemia. Advanced glycosylation promotes inflammatory cell recruitment and smooth muscle cell proliferation. Many of the potential mechanisms promoting restenosis in diabetic patients can be ameliorated by improved metabolic control.

Increased transendothelial permeation of albumin by high glucose concentration

Vascular endothelial cells, which are polyfunctional, play an important role in the pathogenesis of diabetic complications. The increase in vascular permeability, ie, regulated by vascular endothelial cells, has been reported in patients with diabetes mellitus complicated by angiopathy. To determine the role of hyperglycemia in endothelial cell permeability, we examined the effect of high concentrations of glucose on the permeability of cultured bovine aortic endothelial cells. The permeations of albumin and fluorescein-labeled dextran (FD) across endothelial cell monolayers were increased when cultured with a high concentration of glucose (400 mg/dL). This increased permeation of albumin but not FD was temperature-dependent and was partially reduced by adding 100 mumol/L ponalrestat (ICI 128,436, Statil; ICI, Cheshire, UK), which is an aldose reductase inhibitor. Stimulation or inhibition of Na,K-adenosine triphosphatase (ATPase) in bovine aortic endothelial cells failed to alter their permeability. These findings suggest that high concentrations of glucose enhance transendothelial permeability of albumin in part by activating the polyol pathway, but independently of Na,K-ATPase activity.

Enhancement of prostacyclin production in cultured bovine aortic endothelial cells by oxidized glycated low-density lipoprotein

Oxidized low-density lipoprotein (oLDL) is implicated in the pathogenesis of atherosclerosis. The serum concentration of glycated LDL (gLDL) is increased in diabetics, and it is possible that oxidative modification of gLDL contributes to the increased incidence of atherosclerosis associated with diabetes. The mechanism and effect on prostacyclin (PGI2) production by cultured bovine aortic endothelial cells of oxidized glycated LDL (ogLDL) prepared in vitro have now been examined. Glycation of LDL was performed by incubating LDL with 20 mM glucose for 3 days. ogLDL was then prepared by incubation of gLDL with 1 microM CuSO4 for 12 h. Both the electrophoretic mobility and the thiobarbituric acid reactive substance content of ogLDL were greater than those of native LDL (nLDL) or gLDL. Binding, cell-association, and degradation of ogLDL in endothelial cells were significantly greater than those of nLDL and gLDL. The stimulatory effect of ogLDL on PGI2 production was significantly greater than that of nLDL or gLDL; this effect was dose dependent. Both cell-association and the stimulatory effect on PGI2 production of oLDL were dependent on the extent of oxidation in a biphasic manner. Endothelial cells thus appear to protect against atherosclerosis by removing atherogenic lipoproteins and by producing PGI2.

Human fibroblast cells produce a factor that stimulates prostacyclin synthesis by vascular endothelial cells

The prostacyclin (PGI2) produced by vascular endothelium plays a key role in maintaining vascular homeostasis. The present study demonstrated that the conditioned medium (CM) of human diploid fibroblast cells contained PGI2-stimulatory activity (PSA) for bovine aortic endothelial cells (BAEC) and human umbilical vein endothelial cells (HUVEC). CM significantly stimulated the production of 6-keto-PGF1 alpha, a stable PGI2 metabolite, by both cultured BAEC and HUVEC in a concentration-dependent manner. Since the factor responsible for the PSA seemed to be negatively charged, PSA was partially purified using a DEAE-5PW high performance liquid chromatography column. The partially purified PSA was completely inhibited by preincubation with 15 microM indomethacin, a cyclooxygenase inhibitor. However, partially purified PSA was partially inhibited by preincubation with 50 microM mepacrine, a phospholipase A2 inhibitor. These findings suggest that PSA stimulates preferentially cyclooxygenase relative to phospholipase A2 in vascular endothelial cells. The partially purified PSA showed no effect on thromboxane A2 production by human washed platelets, and had no growth-promoting activity on BAEC. We conclude that cultured human fibroblast cells produce factor that stimulate the synthesis of prostaglandin by vascular endothelial cells but not by platelets.

Purification and molecular cloning of prostacyclin-stimulating factor from serum-free conditioned medium of human diploid fibroblast cells

We attempted to identify the factor that stimulated prostacyclin (PGI2) production using conditioned medium from cultured human diploid fibroblast cells subjected to a series of purification steps using h.p.l.c. on DEAE-5PW, Heparin-5PW, Protein-Pak 300, and an insulin-like growth factor-1 ligand affinity column. The purified prostacyclin-stimulating factor (PSF) ran as a single band with a molecular mass of 31 kDa by SDS/PAGE. Analysis of the purified PSF by C4 reversed-phase h.p.l.c. showed a single sharp peak in 31% (v/v) acetonitrile. The material was purified 8000-fold with an overall yield of about 18%. The purified PSF stimulated PGI2 production by cultured bovine aortic endothelial cells at a concentration of about 10 ng/ml; maximal stimulation was achieved at a concentration of 25 ng/ml. A cDNA coding for PSF was cloned and sequenced, revealing an apparently novel protein with no obvious sequence similarity to known proteins.

Partial purification of serum prostacyclin stimulatory activity by heparin-agarose column; abnormality detected in diabetics

Human plasma-derived serum (PDS) stimulated the production of 6-keto-PGF1 alpha (a stable metabolite of PGI2) by cultured bovine aortic endothelial cells. The stimulation was both time- and dose-dependent. The main prostacyclin stimulatory activity (PSA) in human PDS remained biologically active after dialysis and was inhibited by the simultaneous addition of heparin. The maximum inhibition of PSA was obtained with 10 micrograms/ml heparin. PDS obtained from patients with non-insulin-dependent diabetes mellitus (NIDDM, n = 24) showed significantly less PSA than that from the control subjects (n = 11). A decrease in PSA was also found in diabetic patients using dialyzed PDS. The PSA in human PDS had a specific binding affinity to heparin-agarose and the bound PSA was eluted by a linear gradient of NaCl, which showed two major PSA peaks at 1.0 and 1.5 M NaCl. The dialyzed, mixed PDS from patients with NIDDM and the control subjects was independently applied to a heparin-agarose column and eluted by a linear gradient of NaCl. Comparing the PSA in each peak between the diabetic and the control dialyzed PDS, the PSA at 1.5 M NaCl was markedly decreased in the diabetic patients, but the PSA at 1.0 M NaCl did not change significantly. These observations suggest that the decreased PSA in human diabetic PDS may result mainly from the decrease in the activity of a specific non-dialyzed factor(s) which can bind to heparin. The decreased PSA in serum seems to be responsible in part for decreased PGI2 synthesis by the vascular wall of diabetics.

Enhanced secretion of endothelin-1 by elevated glucose levels from cultured bovine aortic endothelial cells

We have investigated the effect of glucose on the release of endothelin-1-like immunoreactivity (ET-1-LI) from cultured bovine aortic endothelial cells. Elevation of glucose concentrations in cultured media from 5.5 to 11.1 or 22.2 mM significantly stimulated ET-1-LI release from cultured endothelial cells. An aldose reductase inhibitor did not affect the high glucose-induced ET-1-LI release. These findings suggest the possibility that hyperglycemia in diabetic patients enhances ET-1-LI release at the local site of vascular endothelium, which might be involved in the developments of vascular complications and atherosclerosis.

Modification of prostacyclin-stimulatory activity in sera by glucose, insulin, low density lipoprotein, linoleic acid and linoleic acid hydroperoxide

Reduced prostacyclin (PGI2) production by the vascular wall has been proposed as one of the possible causes of diabetic vascular complications. We found an activity which stimulated PGI2 production by cultured endothelial cells (PGI2-stimulatory activity, PSA) in human plasma-derived serum (PDS). The PSA was less in patients with diabetes mellitus. The present study was undertaken to evaluate how metabolic factors relevant to diabetic angiopathy modify the PSA. Pooled PDS was prepared from 10 healthy volunteers. The 6-keto-PGF1 alpha (6KF, a stable metabolite of PGI2) production by cultured bovine aortic endothelial cells was maximally stimulated by Dulbecco's modified Eagle's medium (DMEM) containing 10% pooled PDS after incubation for 60 min. The production of 6KF was reduced in a dose-dependent manner by the addition of 10% pooled PDS with glucose and linoleic acid hydroperoxide (lipid peroxide). In contrast, human low density lipoprotein (LDL) and linoleic acid (unsaturated fatty acid) enhanced the production of 6KF by 10% pooled PDS in a dose-dependent manner. Insulin, however, showed no effect on the production of 6KF by 10% pooled PDS. These results suggest that the reduced PSA in diabetics may be the result, in part, of a modification of the PSA by diabetic metabolic factors such as glucose and lipid peroxide.