Increased aortic endothelial death and enhanced transendothelial macromolecular transport in streptozotocin-diabetic rats

Protein-bounded uremic toxin p-cresylsulfate induces vascular permeability alternations

The goal of the present studies is to investigate that the impact of p-cresylsulfate (PCS) on the endothelial barrier integrity via in situ exposure and systemic exposure. Vascular permeability changes induced by local injection of PCS were evaluated by the techniques of both Evans blue (EB) and India ink tracer. Rats were intravenously injected with EB or India ink followed by intradermal injections of various doses of PCS (0, 0.4, 2, 10 and 50 µmol/site) on rat back skins. At different time points, skin EB was extracted and quantified. The administration of India ink was used to demonstrate leaky microvessels. Skin PCS levels were also determined by liquid chromatography-mass spectrometry. We also investigated whether the increased endothelial leakage occurred in the aortic endothelium in rats treated with 5/6 nephrectomy and intraperitoneal injection of PCS 50 mg/kg/day for 4 weeks. The aortic endothelial integrity was evaluated by increased immunoglobulin G (IgG) leakage. High doses of PCS, but not lower doses, significantly induced vascular leakage as compared to saline injection and EB leakage exhibited in time-dependent manner. A time-correlated increase in leaky microvessels was detected in the tissues examined. The injected PCS declined with time and displayed an inverse relationship with vascular leakage. Chronic kidney disease (CKD) rats administered with PCS, compared to control rats, had significantly higher serum levels of PCS and apparent IgG deposition in the aortic intima. Increased endothelial leakage induced by PCS in skin microvessels and the aorta of CKD rats suggests that the PCS-induced endothelial barrier dysfunction.

Ascorbic acid repletion: A possible therapy for diabetic macular edema?

Macular edema poses a significant risk for visual loss in persons with diabetic retinopathy. It occurs when plasma constituents and fluid leak out of damaged retinal microvasculature in the area of the macula, causing loss of central vision. Apoptotic loss of pericytes surrounding capillaries is perhaps the earliest feature of diabetic vascular damage in the macula, which is also associated with dysfunction of the endothelium and loss of the otherwise very tight endothelial permeability barrier. Increased oxidative stress is a key feature of damage to both cell types, mediated by excess superoxide from glucose-induced increases in mitochondrial metabolism, as well as by activation of the receptor for advanced glycation end products (RAGE). The latter in turn activates multiple pathways, some of which lead to increased oxidative stress, such as those involving NF-ĸB, NADPH oxidase, and endothelial nitric oxide synthase. Such cellular oxidative stress is associated with low cellular and plasma ascorbic acid levels in many subjects with diabetes in poor glycemic control. Whether repletion of low ascorbate in retinal endothelium and pericytes might help to prevent diabetic macular edema is unknown. However, cell culture studies show that the vitamin prevents high-glucose and RAGE-induced apoptosis in both cell types, that it preserves nitric oxide generated by endothelial cells, and that it tightens the leaky endothelial permeability barrier. Although these findings need to be confirmed in pre-clinical animal studies, it is worth considering clinical trials to determine whether adequate ascorbate repletion is possible and whether it might help to delay or even reverse early diabetic macular edema.

[Endothelial dysfunction in type 1 diabetes]

Vascular complications are the main cause of mortality and morbidity in diabetes. Mechanisms involved in the development of micro and macrovascular disease are complex and partially understood, but invariably begin as a dysfunctional endothelium. Nitric oxide is an important regulator of endothelial function and the impairment of its activity is determinant of the endothelial dysfunction. In type 1 diabetes, many factors like acute, chronic and post-prandial hyperglycemia, as well as the duration of diabetes or autonomic neuropathy and microalbuminuria are associated to endothelial dysfunction. Oxidative stress, polyol pathway activation, protein kinase C activation and the presence of advanced glycation end-products are potential mechanisms involved in the development of endothelial dysfunction. Early detection of endothelial dysfunction has prognostic value for the development of vascular complications and may be important in strategies for primary prevention of cardiovascular endpoints in type 1 diabetes.

Mechanopathobiology of Atherogenesis: A Review

Cardiovascular disease is the number one cause of mortality in the United States. Atherosclerosis, the primary etiology of cardiovascular disease is hypothesized to be a time-dependent response to arterial injury. Although risk factors for atherosclerosis are systemic in nature, certain arteries (e.g., coronary arteries) are more susceptible to plaque formation than others. The heterogeneous distribution of atherosclerosis in the vasculature is thought to be related to biomechanical factors. A review of the relevant pathological features of atherogenesis and how physiologically-consistent mechanical stimuli can impact those processes supports this notion. However, specific investigations geared toward finding the mechanistic link between mechanical stimuli and early atherogenic processes are required to differentiate those stimuli that facilitate and those that inhibit atherogenesis. Such knowledge is required for intelligent direction in the search for potential targets for clinical intervention.

Astragaloside IV improved barrier dysfunction induced by acute high glucose in human umbilical vein endothelial cells

The purpose of the present study was to examine the effects of astragaloside IV, a saponin isolated from Astragalus membranaceus (Fisch) Bge, on the impairment of barrier function induced by acute high glucose in cultured human vein endothelial cells. High glucose (27.8 mM) induced a decrease in transendothelial electrical impedance and an increase in cell monolayer permeability in human umbilical vein endothelial cells. Endothelial barrier dysfunction stimulated by high glucose was accompanied by translocation and activation of protein kinase C (PKC), the redistribution of F-actin and formation of intercellular gaps, suggesting that increases in PKC activity and rearrangement of F-actin could be associated with endothelial barrier dysfunction induced by acute high glucose. Application of astragaloside IV inhibited high glucose-induced endothelial barrier dysfunction in a dose-dependent manner, which is compatible with inhibition of PKC translocation and improvement of F-actin rearrangements. Western blot analysis revealed that high glucose-induced PKC alpha and beta2 overexpression in the membrane fraction were significantly reduced by astragaloside IV. These findings indicate that astragaloside IV protected endothelial cells from high glucose-induced barrier impairment by inhibiting PKC activation, as well as improving cytoskeleton remodeling.

Increased transvascular lipoprotein transport in diabetes: association with albuminuria and systolic hypertension

CONTEXT

Diabetes is associated with a highly increased risk of atherosclerosis, especially if hypertension or albuminuria is present.

OBJECTIVE

We hypothesized that the increased transvascular lipoprotein transport in diabetes may be further accelerated if hypertension or albuminuria is present, possibly explaining increased intimal lipoprotein accumulation and thus atherosclerosis.

DESIGN

The study was cross-sectional and was performed in 1999-2002.

SETTING

The study took place in the referral center.

PATIENTS

The patients included 60 with diabetes mellitus (27 with type 1 diabetes and 33 with type 2 diabetes) and 42 healthy controls. All were randomly recruited.

MAIN OUTCOME MEASURE

We used an in vivo method for measurement of transvascular transport of low-density lipoprotein (LDL). Autologous 131I-LDL was reinjected iv, and the 1-h fractional escape rate was taken as an index of transvascular transport.

RESULTS

Transvascular LDL transport was 1.8 (1.6-2.0), 2.3 (2.0-2.6), and 2.6 (1.3-4.0)%/[h x (liter/m2)] in healthy controls, diabetic controls, and diabetes patients with systolic hypertension or albuminuria, respectively (P = 0.013; F = 4.5; df =2; ANOVA). These differences most likely were not caused by altered hepatic LDL receptor expression, glycosylation of LDL, small LDL size, or medicine use.

CONCLUSIONS

Transvascular LDL transport is increased in patients with diabetes mellitus, especially if systolic hypertension or albuminuria is present. Accordingly, lipoprotein flux into the arterial wall could be increased in these patients, possibly explaining accelerated development of atherosclerosis.

Effect of diabetes on aortic nitric oxide synthesis in spontaneously hypertensive rats; does captopril modulate this effect?

Nitric oxide (NO) is a potent regulator in the cardiovascular system; it is generated by the nitric oxide synthase (NOS) family of proteins. NO produced in endothelial cells plays a crucial role in vascular functions. The aim of this study was to clarify the effect of diabetes on aortic NO synthesis in a model of genetic hypertension and determine whether captopril modulates this effect. Diabetes was induced in ten weeks old spontaneously hypertensive rats (SHR) by streptozotocin injection. The rats were allocated into 3 groups: control group 1, non-diabetic SHR; group 2, diabetic SHR; group 3, diabetic SHR group receiving captopril at 80 mg/kg in drinking water for 4 weeks. Mean blood pressure (MBP) was measured once a week by tail-cuff method. Aortic NO metabolities (nitrite/nitrate) and endothelial NOS (NOS-3) were assayed by Griess reaction and by immunoblotting and immunohistochemistry, respectively. There was a significant decrease in nitrite/nitrate (NOx) in aortas of diabetic SHR compared with controls. The decrease of aortic NOx in diabetic SHR was accompanied by a decrease in NOS-3 expression. Captopril treatment reduced MBP without affecting either NOx level or NOS-3 expression in aortas of diabetic SHR. We conclude that STZ-induced diabetes decreased NO in aortas of SHR that may reflect endothelial cell dysfunction; captopril administration decreased MBP without affecting NO level in aortas of diabetic SHR which suggest that the blood pressure-lowering effects of captopril were independent of NO.

Transvascular lipoprotein transport in patients with chronic renal disease

BACKGROUND

While increased plasma cholesterol is a well-established cardiovascular risk factor in the general population, this is not so among patients with chronic renal disease. We hypothesized that the transvascular lipoprotein transport, in addition to the lipoprotein concentration in plasma, determines the degree of atherosclerosis among patients with chronic renal disease.

METHODS

We used an in vivo method for measurement of transvascular transport of low-density lipoprotein (LDL) in 21 patients with chronic renal disease and in 42 healthy control patients. Autologous 131-iodinated LDL was reinjected intravenously, and the 1-hour fractional escape rate was taken as index of transvascular transport.

RESULTS

Transvascular LDL transport tended to be lower in patients with chronic renal disease than in healthy control patients [3.3 (95% CI 2.4-4.2) vs. 4.2 (3.7-4.2)%/hour; NS]. However, this tendency disappeared when transvascular LDL transport was corrected for distribution volume of LDL [1.7 (1.2-2.2) vs. 1.8 (1.6-2.0) %/(hour x (L/m(2))); NS]. There was significant variation in transvascular LDL transport between diabetic patients with chronic renal disease, nondiabetic patients with chronic renal disease, and healthy control patients [5.0 (3.2-7.8) vs. 3.0 (2.2-3.8) vs. 4.2 (3.6-4.8) %/hour; P < 0.01 after adjustment for distribution volume of LDL]. This variation was unlikely caused by altered hepatic LDL receptor expression or glycosylation of LDL in diabetes patients.

CONCLUSION

Transvascular LDL transport may be increased in diabetic patients with chronic renal disease, suggesting that lipoprotein flux into the arterial wall is increased. A similar mechanism does not operate in nondiabetic patients with chronic renal disease.

Reduction of high glucose and phorbol-myristate-acetate-induced endothelial cell permeability by protein kinase C inhibitors LY379196 and hypocrellin A

Endothelial barrier dysfunction plays a pivotal role in the pathogenesis of diabetic vascular complications. Although recent studies have established a link between protein kinase C (PKC) pathway and hyperglycaemic-induced vascular permeability, it is unclear which PKC isoforms involve increased endothelial cell permeability. In the present study, we investigated whether high glucose induced endothelial hyperpermeability via distinct PKC isoforms in human umbilical vein endothelial cells (HUVECs) and whether increased endothelial permeability could be substantially reversed by PKC inhibitors LY379196 and hypocrellin A (HA). High glucose (20 mM) and phorbol-myristate-acetate (PMA)-induced endothelial hyperpermeability was almost abolished by 150 nM HA and partially reduced by 30 nM PKC beta inhibitor (LY379196). LY379196 and HA inhibited the membrane fraction of PKC activity in a dose-dependent manner. Western blot analysis revealed high-glucose-induced overexpression of PKC alpha and PKC beta2 in the membrane fraction of HUVECs. LY379196 (30 and 150 nM) selectively inhibited PKC beta2 with no significant effect on PKC alpha expression. HA (150 nM) significantly reduced PKC alpha expression with no inhibitory effect on PKC beta2. At higher concentrations (300 nM), both LY379196 and HA were no longer selective for PKC beta or alpha, respectively. This study showed that both PKC alpha and beta2 contributed to endothelial hyperpermeability. Since reduction of endothelial hyperpermeability was greater with inhibition of PKC alpha rather than PKC beta2, we conclude that PKC alpha may be a major isoform involved in endothelial permeability in HUVECs, and that PKC alpha-mediated endothelial permeability was significantly reversed by the PKC inhibitor HA.

Increased transvascular low density lipoprotein transport in insulin dependent diabetes: a mechanistic model for development of atherosclerosis

BACKGROUND

The increased risk of atherosclerosis associated with diabetes cannot be explained by conventional cardiovascular risk factors alone. We hypothesized that transvascular lipoprotein transport may be increased in patients with diabetes, possibly explaining increased intimal lipoprotein accumulation and thus atherosclerosis.

METHODS

We used an in vivo method for measurement of transvascular transport of low density lipoprotein (LDL) and applied it in 24 patients with insulin dependent diabetes mellitus (type 1) and in 30 healthy controls. LDL was individually sampled and autologous 131-iodinated LDL was reinjected intravenously in addition to 125-iodinated albumin, and the 1-h fractional escape rates were taken as indices of transvascular transport.

RESULTS

Transvascular LDL transport was 5.7+/-2.2 and 4.0+/-1.8%/h in patients with diabetes and controls (P<0.005); equivalent values for albumin were 6.8+/-2.5 and 5.4+/-2.0%/h (P<0.05). This difference most likely was not caused by altered hepatic LDL receptor expression, glycosylation of LDL, small LDL size, nephropathy, statin use, or different plasma insulin levels in diabetes patients.

CONCLUSION

Transvascular LDL transport may be increased in patients with type 1 diabetes. This suggests that lipoprotein flux into the arterial wall is increased in people with type 1 diabetes, possibly explaining accelerated development of atherosclerosis.

Transvascular low-density lipoprotein transport in patients with diabetes mellitus (type 2): a noninvasive in vivo isotope technique

OBJECTIVE

The increased risk of atherosclerosis associated with diabetes cannot be explained by conventional cardiovascular risk factors alone. We hypothesized that transvascular lipoprotein transport may be increased in patients with diabetes, possibly explaining increased intimal lipoprotein accumulation and, thus, atherosclerosis.

METHODS AND RESULTS

We developed an in vivo method for measurement of transvascular transport of low density lipoprotein (LDL) and applied it in 16 patients with maturity-onset diabetes (type 2) and 29 healthy control subjects. Autologous 131I-labeled LDL was reinjected intravenously in addition to 125I-labeled albumin, and the 1-hour fractional escape rates were taken as indices of transvascular transport. Both parameters were normally distributed, and they were tightly correlated (R2=0.69, P<0.0001). Transvascular LDL transport was 5.4+/-2.9%/h and 4.1+/-1.5%/h in patients with diabetes and control subjects, respectively (P<0.05); equivalent values for albumin were 6.5+/-2.5%/h and 5.3+/-1.6%/h (P<0.05). This difference most likely was not caused by altered hepatic LDL receptor expression, glycosylation of LDL, small LDL size, nephropathy, statin use, or different plasma insulin levels in diabetic patients.

CONCLUSIONS

Transvascular LDL transport may be increased in patients with type 2 diabetes. This suggests that lipoprotein flux into the arterial wall is increased in people with diabetes, possibly explaining the accelerated development of atherosclerosis.

Ozone treatment reduces markers of oxidative and endothelial damage in an experimental diabetes model in rats

Ozone has been used as a therapeutical agent and beneficial effects have been observed. However so far only a few biochemical and pharmacodynamic mechanisms have been elucidated. We demonstrate that controlled ozone administration may promote an oxidative preconditioning or adaptation to oxidative stress, preventing the damage induced by reactive oxygen species (ROS). Taking into account that diabetes is a disorder associated with oxidative stress, we postulate that ozone treatment in our experimental conditions might protect antioxidant systems and maintain, at a physiological level, other markers of endothelial cell damage associated with diabetic complications. Five groups of rats were classified as follows: (1) control group treated only with physiological saline solution; (2) positive control group using streptozotocin (STZ) as a diabetes inductor; (3) ozone group, receiving 10 treatments (1.1 mg kg(-1)), one per day after STZ-induced diabetes; (4) oxygen group (26 mg kg(-1)), one per day, as in group 3 but using oxygen only; (5) control ozone group, as group 3, but without STZ. The ozone treatment improved glycemic control and prevented oxidative stress, the increase of aldose reductase, fructolysine content and advanced oxidation protein products. Nitrite and nitrate levels were maintained without changes with regard to non-diabetic control. The results of this study show that repeated administration of ozone in non-toxic doses might play a role in the control of diabetes and its complications.

Aortic endothelial cell von Willebrand factor content, and circulating plasminogen activator inhibitor-1 are increased, but expression of endothelial leukocyte adhesion molecules is unchanged in insulin-dependent diabetic BB rats

Endothelial cell injury has been implicated in the increased incidence of vascular disease associated with diabetes mellitus. In diabetic humans, elevated plasma von Willebrand Factor (vWF) has been interpreted as an indication of endothelial damage. In contrast, in an animal model of inherited insulin-dependent diabetes, the bio-breeding (BB) rat, plasma vWF levels did not differ from those in age-matched control rats during the first 7 months of diabetes although morphological evidence of mild aortic endothelial alteration or injury was observed. In the present study efforts have been made to define the endothelial alterations in BB diabetic rats compared to controls more precisely over this time period. Thus, adhesion molecules: intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1(VCAM-1) were evaluated by in situ immunohistochemistry, vWF content was determined by biochemical analysis of aortic extracts and by quantitative immunohistochemistry, plasma vWF levels were measured by ELISA and vWF mRNA by RNAse protection assay. Neither age nor diabetic state significantly affected either the expression of adhesion molecules, or the levels of circulating vWF. Endothelial vWF content was significantly increased in the diabetic vessels, as observed by both approaches but the vWF mRNA content was not different from that in control vessels. Plasma plasminogen activator inhibitor (PAI-1) activity was significantly increased in diabetic animals. In conclusion, endothelial alterations in BB rats associated with diabetes, together with the raised plasma PAI-1 levels, promote the thrombogenic potential of the vessel wall, and are consistent with an increased risk for vascular disease.

Effects of chelator treatment on aorta and corpus cavernosum from diabetic rats

Transition-metal catalyzed reactions contribute to oxidative stress, which has been implicated in the pathogenesis of diabetic complications. The aim was to evaluate the effects of treatment with the transition metal chelator trientine on endothelium-dependent relaxation of aorta and corpus cavernosum from streptozotocin-induced diabetes of 8 weeks duration in rats. Effects on cavernosum autonomic innervation were also examined. Diabetes caused a 30.1 +/- 3.8% reduction in maximum aorta endothelium-dependent relaxation to acetylcholine (ACh), which was markedly attenuated (72.7 +/- 10.6%) by trientine treatment. Reversal treatment (4 weeks untreated diabetes, 4 weeks trientine) did not effect endothelium-dependent relaxation compared with aortas from rats with 4 weeks of diabetes, however, there was a 22.5 +/- 6.2% improvement compared with 8 weeks of diabetes. Eight weeks of diabetes caused a 41.5 +/- 6.6% reduction in corpus cavernosum endothelium-dependent maximum relaxation to ACh that was 70.1 +/- 16.9% prevented by trientine. Cavernosum nonadrenergic, noncholinergic (NANC) nerve stimulation caused frequency-dependent relaxation to a maximum of 40.9 +/- 2.4%, which was reduced by diabetes to 24.2 +/- 2.1%. Trientine partially prevented this deficit, maximum relaxation being 31.9 +/- 2.3%. Thus, metal chelator treatment has beneficial effects on aorta and cavernosum endothelium-dependent relaxation and on cavernosum NANC innervation.

Angiotensin II AT1-receptor blockade inhibits monocyte activation and adherence in transgenic (mRen2)27 rats

This study investigated whether angiotensin II AT1-receptor blockade with losartan inhibits endothelium-monocyte interactions originating from long-term activation of the renin-angiotensin system in hypertensive transgenic rats [TGR(mRen2)27]. The number of circulating activated monocytes, monocytes adhered to thoracic aorta endothelium, and the extent of endothelial cell injury were compared in adult male transgenic (mRen2)27 and age-matched Hannover Sprague-Dawley (SD) rats after 12 days of continuous subcutaneous administration of saline (120 microl/24 h), losartan (10 mg/kg/24 h), or the vasodilator hydralazine (3 mg/kg/24 h). At the doses administered in this experiment, both losartan and hydralazine normalized mRen2 rat blood pressures equal to values in similarly treated SD rats. Compared with saline infusion, administration of either antihypertensive in mRen2 rats reduced (p<0.05) endothelial cell injury, but only losartan significantly (p<0.05) decreased the number of activated circulating and endothelium-adherent monocytes. Infusion of antihypertensives in SD rats had no effect on blood pressures, monocyte activity, or endothelial injury compared with saline administration. These findings suggest that the recruitment and infiltration of leukocytes into the subendothelium associated with renin-angiotensin system-induced hypertension is partly mediated by pressure-independent AT1-receptor pathways.

Superoxide dismutase restores endothelium-dependent arteriolar dilatation during acute infusion of nicotine

We previously showed [Am. J. Physiol. 272 (Heart Circ. Physiol. 41): H2337-H2342, 1997] that nicotine impairs endothelium-dependent arteriolar dilatation. However, mechanisms that accounted for the effect of nicotine on endothelium-dependent vasodilatation were not examined. Thus the goal of this study was to examine the role of oxygen radicals in nicotine-induced impairment of arteriolar reactivity. We measured diameter of cheek pouch resistance arterioles (approximately 50 micrometer diameter) in response to endothelium-dependent (ACh and ADP) and -independent (nitroglycerin) agonists before and after infusion of vehicle or nicotine in the absence or presence of superoxide dismutase. ACh, ADP, and nitroglycerin produced dose-related dilatation of cheek pouch arterioles before infusion of vehicle or nicotine. Infusion of vehicle, in the absence or presence of superoxide dismutase (150 U/ml), did not alter endothelium-dependent or -independent arteriolar dilatation. In contrast, infusion of nicotine (2 microgram . kg-1 . min-1) impaired endothelium-dependent, but not -independent, arteriolar dilatation. In addition, the effect of nicotine on endothelium-dependent vasodilatation was reversed by topical application of superoxide dismutase. We suggest that nicotine impairs endothelium-dependent arteriolar dilatation via an increase in the synthesis/release of oxygen-derived free radicals.

Changes in the aortic endothelium and plasma von Willebrand factor levels during the onset and progression of insulin-dependent diabetes in BB rats

Endothelial injury has been implicated in the enhanced vascular disease associated with diabetes mellitus. In diabetic humans elevated plasma von Willebrand factor (vWF) levels have been interpreted as an indication of endothelial damage. Using the BB rat as a model of inherited insulin dependent-diabetes mellitus, plasma vWF and aortic endothelial ultrastructural alterations were examined during the first 7 months of diabetes. Total plasma vWF levels were determined by ELISA and vWF multimeric composition by electrophoresis. vWF was identified immunohistochemically. Following the onset of hyperglycemia, there were progressive alterations in aortic endothelial morphology, which were consistent with injury, and aortic intimal thickening was significantly greater in rats diabetic for 7 months compared to age-matched controls. Significant increases in the Weibel Palade (WP) body content of the endothelial cells were observed after 1 week and 2 months of diabetes, but not at later times. Endothelial alterations associated with the possible release of vWF appeared to involve fusion of WP bodies with other vacuoles rather than direct fusion with the cell membrane. Plasma vWF levels in diabetic rats were varied, but were not significantly different from those of control animals and did not correlate with either glucose or insulin levels. The multimeric composition of plasma vWF was also similar at all times in both diabetic and non-diabetic animals. From these observations, plasma vWF levels do not provide an indicator of the endothelial perturbations which occurs in diabetic rats.

Increase in TUNEL positive cells in aorta from diabetic rats

TUNEL staining, which allows detection of fragmented DNA in situ, is commonly used as an indication of apoptosis. Recent studies suggest that apoptosis is increased in several pathophysiological conditions. In this study we examined the hypothesis that chronic diabetes is associated with an increase in TUNEL staining of the aorta. Diabetic rats were studied 4-5 months after injection of streptozotocin (50 mg/kg). Aorta of diabetic and control rats were examined for TUNEL staining, morphology by electron microscopy, and DNA contamination in RNA preparation by polymerase chain reaction (PCR). TUNEL staining of aortic sections showed a 6 fold increase of positive cells in the media of diabetic aorta (22 +/- 6%) (mean +/- SE) compared with aorta from age-matched controls (3.6 +/- 0.9%, p < 0.05). Electron microscopy demonstrated typical apoptotic cells and bodies in the media of aorta from diabetic but not control rats. DNA contamination was found in RNA prepared from diabetic aorta, which was detected using PCR, which is consistent with increased DNA fragmentation. Increased TUNEL staining was not observed in rats with hyperglycemia 3 days after injection of streptozotocin. In conclusion, severe chronic diabetes is associated with an increase in TUNEL staining, and perhaps apoptosis, in the aorta. We speculate that increased apoptosis may compensate for increased proliferative activity in diabetic blood vessels.

Nicotine impairs histamine-induced increases in macromolecular efflux: role of oxygen radicals

Nicotine, a major component of cigarettes and smokeless tobacco, has toxic effects on endothelium and impairs reactivity of resistance arterioles in response to agonists that stimulate the synthesis and/or release of nitric oxide. However, the effect of nicotine on nitric oxide synthase-dependent increases in macromolecular transport is not known. Thus our first goal was to determine the effect of nicotine on histamine-induced increases in macromolecular efflux. We used intravital microscopy and FITC dextran (mol wt 70, 000) (FITC-dextran-70K) to examine macromolecular extravasation from postcapillary venules in response to histamine before and after intravenous infusion of vehicle or nicotine. Extravasation of macromolecules was quantitated by counting venular leaky sites and calculating clearance (ml/s x 10(-6)) of FITC-dextran-70K. Histamine elicited reproducible increases in venular leaky sites and clearance in hamsters infused with vehicle. In contrast, nicotine infusion inhibited histamine-induced increases in macromolecular efflux. Histamine (1.0 and 5.0 micro M) elicited 19 +/- 2 and 34 +/- 4 vs. 3 +/- 1 and 11 +/- 5 leaky sites per 0.11 cm2, before vs. after nicotine infusion, respectively (P < 0.05). Histamine-induced clearance of FITC-dextran-70K was also impaired after infusion of nicotine. Our second goal was to examine whether alterations in histamine-induced increases in macromolecular efflux by nicotine may be related to the production of oxygen radicals. Application of superoxide dismutase (150 U/ml) to the hamster cheek pouch restored histamine-induced increases in venular leaky sites and clearance of FITC-dextran-70K during infusion of nicotine. Thus nicotine alters agonist-induced increases in microvascular permeability, via the formation of oxygen radicals, to presumably inactivate nitric oxide.

Increased NADH oxidase activity in the retina of the BBZ/Wor diabetic rat

This morphological study demonstrates a role for endothelial cells in generating reactive oxygen species in early stages of retinopathy in the BBZ/Wor rat, an obese, noninsulin dependent model of diabetes. Hyperglycemia induced pseudohypoxia results in an imbalance in cytosolic NADH/NAD+. In the oxygen-rich environment of the retina, NADH oxidase generates superoxide radical which is dismutated to hydrogen peroxide. Localization of hydrogen peroxide by the cerium NADH oxidase enzyme activity cytochemical localization technique shows a statistically significant increase of peroxide localization in the central retina of diabetic rats as compared to age-matched, nondiabetic controls. Endothelial cell dysfunction, indicated by leakage of endogenous serum albumin, coincided with areas of NADH oxidase activity localization. In diabetic rats there are increased levels of fibronectin in areas of hydrogen peroxide localization. This in vivo, morphological study is the first demonstration of oxidative injury and endothelial cell dysfunction in the retina of a spontaneous, noninsulin dependent model of diabetes.

Apoptosis is increased in a model of diabetes-impaired wound healing in genetically diabetic mice

Impaired wound healing is a common complication of diabetes mellitus. The underlying pathophysiology of diabetes-impaired healing is poorly understood. In the present study we have compared cell proliferation rates, apoptosis (programmed cell death), the myofibroblast marker alpha-smooth muscle actin and procollagen I mRNA expression, between diabetic and control mice. Full-thickness skin wounds were made in non-obese diabetic (NOD) mice and C57B6 controls. NOD mice showed a marked retardation of wound healing at both 7 and 14 days after wounding. Comparison of cell proliferation rates 7 days after wounding, using 5-bromo-2'-deoxy-Uridine incorporation, showed higher rates of cell proliferation in controls (88.1 +/- 12.8) than in NOD wounds (52.1 +/- 9.9, p < 0.02, n = 4). Immunohistochemical detection of alpha-smooth muscle actin, showed a later onset in diabetic wounds, suggesting that wound contraction may be delayed in the diabetic animals. In situ hybridisation for alpha 1 (I) procollagen mRNA expression, showed reduced procollagen I expression in the diabetic wounds when compared with controls. Lastly, there appeared to be higher levels of apoptosis in diabetic wounds, shown by the terminal transferase mediated UTP nick end-labelling technique. Apoptotic cells were rare in control wounds confirming previous studies, which showed that apoptosis occurs late in normal wound healing as the wound matures into scar tissue. In conclusion, we hypothesize that reduced cell proliferation, retarded onset of the myofibroblast phenotype, reduced procollagen I mRNA expression and aberrant control of apoptotic cell death may contribute to impaired wound healing seen in this diabetic model.

Effect of cigarette smoke extract on arteriolar dilatation in vivo

The goal of this study was to determine whether cigarette smoke extract alters dilatation of arterioles in vivo in response to agonists that produce activation of ATP-sensitive potassium channels and activation of adenylate cyclase. By using intravital microscopy, we measured diameter of arterioles contained within the microcirculation of the hamster cheek pouch during suffusion with agonists in the absence and presence of cigarette smoke extract (0.1, 0.5, and 1.0%). Before treatment with cigarette smoke extract, activation of ATP-sensitive potassium channels with aprikalim and cromakalim produced dose-related dilatation of cheek pouch arterioles. Similarly, activation of adenylate cyclase with isoproterenol and forskolin produced dose-related dilatation of cheek pouch arterioles before treatment with cigarette smoke extract. Superfusion of 0.1% cigarette smoke extract did not change baseline diameter of arterioles and did not alter responses of cheek pouch arterioles to activation of ATP-sensitive potassium channels and adenylate cyclase. Superfusion of 0.5 and 1.0% cigarette smoke extract also did not alter baseline diameter of arterioles but did impair dilatation of arterioles in response to activation of ATP-sensitive potassium channels and adenylate cyclase. These findings suggest that cigarette smoke extract impairs dilatation of resistance arterioles in response to activation of important cellular dilator pathways.

Accelerated death of retinal microvascular cells in human and experimental diabetic retinopathy

To reconstruct the mechanisms for the vasoobliteration that transforms diabetic retinopathy into an ischemic retinopathy, we compared the occurrence of cell death in situ in retinal microvessels of diabetic and nondiabetic individuals. Trypsin digests and sections prepared from the retinas of seven patients (age 67 +/- 7 yr) with .9 +/- 4 yr of diabetes and eight age- and sex-matched nondiabetic controls were studied with the terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) reaction which detects preferentially apoptotic DNA fragmentation. The count of total TUNEL+ nuclei was significantly greater in the microvessels of diabetic (13 +/- 12 per one-sixth of retina) than control subjects (1.3 +/- 1.4, P = 0.0016), as were the counts of TUNEL+ pericytes and endothelial cells (P < 0.006). The neural retinas from both diabetic and nondiabetic subjects were uniformly TUNEL-. Retinal microvessels of rats with short duration of experimental diabetes or galactosemia and absent or minimal morphological changes of retinopathy, showed TUNEL+ pericytes and endothelial cells, which were absent in control rats. These findings indicate that (a) diabetes and galactosemia lead to accelerated death in situ of both retinal pericytes and endothelial cells; (b) the event is specific for vascular cells; (c) it precedes histological evidence of retinopathy; and (d) it can be induced by isolated hyperhexosemia. A cycle of accelerated death and renewal of endothelial cells may contribute to vascular architectural changes and, upon exhaustion of replicative life span, to capillary obliteration.

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.

Formaldehyde produced endogenously via deamination of methylamine. A potential risk factor for initiation of endothelial injury

Methylamine can be converted by semicarbazide-sensitive amine oxidase (SSAO) to formaldehyde and hydrogen peroxide, which have been proven to be toxic towards cultured endothelial cells. We investigated whether or not these deaminated products from methylamine can exert potentially hazardous toxic effects in vivo. Long lasting residual radioactivity in different tissues was detected following administration of [14C]-methylamine in the mouse. Approximately 10% of the total administered radioactivity could even be detected 5 days after injection of [14C]-methylamine. Eighty percent of the formation of irreversible adducts can be blocked by a highly selective SSAO inhibitor, (E)-2-(4-fluorophenethyl)-3-fluoroallylamine hydrochloride (MDL-72974A). The residual radioactivity was primarily associated with the insoluble tissue components and the soluble macromolecules. Radioactively labelled macromolecules were fragmented following enzymatic proteolysis. Results suggest that the formaldehyde derived from methylamine interacts with proteins in vivo. In the streptozotocin-induced diabetic mice, both SSAO activity and the formation of residual radioactivity were found to be significantly increased in the kidney. Chronic administration of methylamine enhances blood prorenin level, which strongly suggests that uncontrolled deamination of methylamine may be a risk factor for initiation of endothelial injury, and subsequent genesis of atherosclerosis.

The potential contribution of endothelin-1 to neurovascular abnormalities in streptozotocin-diabetic rats

Abnormal vascular endothelium function may contribute to the reduced nerve perfusion implicated in the aetiology of neuropathy in diabetes mellitus. The aim was to test the hypothesis that a powerful vasoconstrictor, endothelin-1, could be involved in nerve dysfunction in streptozotocin-diabetic rats. After 6 weeks of untreated diabetes, rats were implanted with osmotic minipumps which continuously delivered the endothelin-1 antagonist, BQ-123, to the circulation via a jugular vein cannula. Sciatic motor conduction velocity, monitored serially, was increased after 4 days, treatment (p = 0.028), and reached asymptote by 9-11 days (p = 0.0001), when the degree of amelioration was approximately 60% of the initial diabetic deficit. Treatment of non-diabetic rats for 13 days with BQ-123 had no significant effect on motor conduction velocity. Sensory saphenous nerve conduction velocity was measured acutely after 20 days, BQ-123 treatment. The amelioration of a sensory deficit was approximately 80% (p < 0.001); the resultant conduction velocity value was not significantly different from that of a non-diabetic control group. After 20 days, treatment, sciatic nutritive endoneurial blood flow was measured by microelectrode polarography and hydrogen clearance. A 48% deficit with untreated diabetes (p < 0.001) was 64% ameliorated by BQ-123 treatment (p < 0.001). In non-diabetic rats, BQ-123 treatment had no effect on blood flow. We conclude that endothelin-1 does not seem to be involved in the control of nerve blood flow in non-diabetic rats; however, it makes a major contribution to the perfusion deficit in experimental diabetes. This has deleterious consequences for nerve conduction, and it is possible that endothelin-1 receptor blockade may have therapeutic potential in diabetic patients.