Protein kinase C-β inhibition and diabetic microangiopathy: effects on endothelial permeability responses in vitro

Chronic type 2 diabetes reduces the integrity of the blood-brain barrier by reducing tight junction proteins in the hippocampus

In the present study, we investigated the effects of type 2 diabetes-induced hyperglycemia on the integrity of the blood-brain barrier and tight junction markers in the rat hippocampus. Forty-week-old diabetic (Zucker diabetic fatty, ZDF) rats and littermate control (Zucker lean control, ZLC) rats were used in this study. We evaluated the integrity of the blood-brain barrier by measuring sodium fluorescein extravasation and blood vessel ultrastructure. In addition, tight junction markers, such as zona occludens-1, occludin and claudin-5, were quantified by western blot analysis. ZDF rats showed significantly increased sodium fluorescein leakage in the hippocampus. Tight junction markers, such as occludin and claudin-5, were significantly decreased in the hippocampi of ZDF rats compared to those of ZLC rats. In addition, ZDF rats showed ultrastructural changes with phagocytic findings in the blood vessels. These results suggest that chronic untreated diabetes impairs the permeability of the hippocampal blood-brain barrier by down-regulating occludin and claudin-5, indicating that chronic untreated diabetes may cause hippocampus-dependent dysfunction.

Endothelial monocyte activating polypeptide II in children and adolescents with type 1 diabetes mellitus: Relation to micro-vascular complications

OBJECTIVES

Endothelial monocyte-activating polypeptide II (EMAP II) is a multifunctional polypeptide with proinflammatory and antiangiogenic activity. Hyperglycemia and dyslipidemia appears to be significant factors contributing to increased EMAP-II levels. We determined serum EMAP II in children and adolescents with type 1 diabetes as a potential marker for micro-vascular complications and assessed its relation to inflammation and glycemic control.

METHODS

Eighty children and adolescents with type 1 diabetes were divided into 2 groups according to the presence of micro-vascular complications and compared with 40 healthy controls. High-sensitivity C-reactive protein (hs-CRP), hemoglobin A1c (HbA1c) and EMAP II levels were assessed.

RESULTS

Serum EMAP II levels were significantly increased in patients with micro-vascular complications (1539 ± 321.5 pg/mL) and those without complications (843.6 ± 212.6 pg/mL) compared with healthy controls (153.3 ± 28.3 pg/mL; p<0.001). EMAP II was increased in patients with microalbuminuria than normoalbuminuric group (p<0.001). Significant positive correlations were found between EMAP II levels and body mass index, fasting blood glucose, HbA1c, serum creatinine, triglycerides, total cholesterol, urinary albumin creatinine ratio (UACR) and hs-CRP (p<0.05). A cutoff value of EMAP II at 1075 pg/mL could differentiate diabetic patients with and without micro-vascular complications with a sensitivity of 93% and specificity of 82%.

CONCLUSIONS

We suggest that EMAP II is elevated in type 1 diabetic patients, particularly those with micro-vascular complications. EMAP II levels are related to inflammation, glycemic control, albuminuria level of patients and the risk of micro-vascular complications.

Kallistatin as a marker of microvascular complications in children and adolescents with type 1 diabetes mellitus: Relation to carotid intima media thickness

In diabetes, angiogenesis is disturbed, contributing to proliferative retinopathy, nephropathy and neuropathy. Kallistatin, a serine proteinase inhibitor, has anti-angiogenic effects. We assessed serum kallistatin in children and adolescents with type 1 diabetes as a potential marker for microvascular complications and its relation to carotid intima media thickness (CIMT). Sixty patients with type 1 diabetes were divided into two groups according to the presence of microvascular complications and compared with 30 healthy controls. High-sensitivity C-reactive protein (hs-CRP), HbA1c, urinary albumin creatinine ratio (UACR), kallistatin levels and CIMT were assessed. Kallistatin levels were significantly higher in patients with microvascular complications (9.9 ± 2.38 ng/mL) and those without complications (5.0 ± 1.5 ng/mL) than in healthy controls (1.39 ± 0.55 ng/mL; p<0.001). Kallistatin was increased in patients with microalbuminuria compared with the normoalbuminuric group ( p<0.001). Positive correlations were found between kallistatin and disease duration, fasting blood glucose, HbA1c, triglycerides, total cholesterol, hs-CRP, UACR and CIMT ( p<0.05). A kallistatin cut-off value at 6.1 ng/mL could differentiate patients with and without microvascular complications, with a sensitivity of 96.87% and specificity of 93.75%. Increased kallistatin levels in type 1 diabetes and its relation with CIMT may reflect vascular dysfunction and suggest a link between micro- and macro-angiopathy.

Glycemic control influences lung membrane diffusion and oxygen saturation in exercise-trained subjects with type 1 diabetes: alveolar-capillary membrane conductance in type 1 diabetes

Lung diffusing capacity (DLCO) is influenced by alveolar-capillary membrane conductance (D (M)) and pulmonary capillary blood volume (V (C)), both of which can be impaired in sedentary type 1 diabetes mellitus (T1DM) subjects due to hyperglycemia. We sought to determine if T1DM, and glycemic control, affected DLNO, DLCO, D (M), V (C) and SaO(2) during maximal exercise in aerobically fit T1DM subjects. We recruited 12 T1DM subjects and 18 non-diabetic subjects measuring DLNO, DLCO, D (M), and V (C) along with SaO(2) and cardiac output (Q) at peak exercise. The T1DM subjects had significantly lower DLCO/Q and D (M)/Q with no difference in Q, DLNO, DLCO, D (M), or V (C) (DLCO/Q = 2.1 ± 0.4 vs. 1.7 ± 0.3, D (M)/Q = 2.8 ± 0.6 vs. 2.4 ± 0.5, non-diabetic and T1DM, p < 0.05). In addition, when considering all subjects there was a relationship between DLCO/Q and SaO(2) at peak exercise (r = 0.46, p = 0.01). Within the T1DM group, the optimal glycemic control group (HbA1c <7%, n = 6) had higher DLNO, DLCO, and D (M)/Q than the poor glycemic control subjects (HbA1c ≥ 7%, n = 6) at peak exercise (DLCO = 38.3 ± 8.0 vs. 28.5 ± 6.9 ml/min/mmHg, DLNO = 120.3 ± 24.3 vs. 89.1 ± 21.0 ml/min/mmHg, D (M)/Q = 3.8 ± 0.8 vs. 2.7 ± 0.2, optimal vs. poor control, p < 0.05). There was a negative correlation between HbA1c with DLCO, D (M) and D (M)/Q at peak exercise (DLCO: r = -0.70, p = 0.01; D (M): r = -0.70, p = 0.01; D (M)/Q: r = -0.68, p = 0.02). These results demonstrate that there is a reduction in lung diffusing capacity in aerobically fit athletes with T1DM at peak exercise, but suggests that maintaining near-normoglycemia potentially averts lung diffusion impairments.

PKC and MLCK-dependent, cytokine-induced rat coronary endothelial dysfunction

BACKGROUND

Heart disease is one of the leading causes of death in the United States, killing nearly one million people every year. Inflammatory mediators or cytokines are released following myocardial infarction and ischemia/reperfusion injury. These cytokines, of which interleukin-1beta, interleukin-6, and tumor necrosis factor-alpha (TNF-alpha) are among the most important, propagate the activation of a multitude of signaling pathways, such as the protein kinase C (PKC) and myosin light chain kinase (MLCK) pathways, which lead to deleterious changes in the structure and function of the coronary microvascular endothelium.

METHODS

The effects of cytokines on rat heart microvascular endothelial cell monolayer integrity, PKC activity, and adherens junction protein alteration were examined. Further, an in vivo rat coronary ischemia/reperfusion injury model was used to determine vascular leakage and TNF-alpha release.

RESULTS

Administration of the above mentioned cytokines to cell monolayers resulted in significant increases in PKC activation, gap formation, and hyperpermeability across the monolayer and beta-catenin phosphorylation/reorganization. Inhibition of conventional PKC and MLCK attenuated permeability increases. Ischemia/reperfusion injury to the left ventricle resulted in TNF-alpha release as well as conventional PKC- and MLCK-dependent protein extravasation from the circulation to the heart tissue.

CONCLUSION

These results identify the conventional PKC and MLCK pathways as important factors in coronary endothelial dysfunction elicited by IR injury and cytokine release. Further examination of these molecular signaling cascades has the potential of identifying targets for therapeutic intervention following ischemic events in the heart.

Phase I and pharmacokinetic study of UCN-01 in combination with irinotecan in patients with solid tumors

PURPOSE

7-Hydroxystaurosporine (UCN-01) is a protein kinase inhibitor that inhibits several serine-threonine kinases including PKC and PDK1. Due to the preclinical synergistic effects seen with topoisomerase I inhibitors and non-overlapping toxicity, UCN-01 and irinotecan were combined in a dose-finding study designed to determine the maximum tolerated dose (MTD), toxicity profile, and pharmacokinetics (PK) of UCN-01 and irinotecan.

METHODS

Patients with incurable solid malignancies received UCN-01 intravenously (IV) as a 3-h infusion on day 1 and irinotecan IV over 90 min on days 1 and 8 of a 21-day cycle. Doses of UCN-01 for subsequent cycles were half the starting dose. Dose level 1 (DL1) consisted of UCN-01 and irinotecan doses of 50 and 60 mg/m(2), respectively. Blood samples were collected in cycle 1 for UCN-01, irinotecan, and irinotecan metabolites.

RESULTS

A total of 16 patients were enrolled on the trial at UCN-01/Irinotecan doses of 50/60 mg/m(2) (DL1; n = 1), 70/60 mg/m(2) (DL2; n = 6), 90/60 mg/m(2) (DL3; n = 4), and 70/90 mg/m(2) (DL4; n = 5). Two dose-limiting toxicities were observed each in DL3 and DL4 (2 grade 3 hypophosphatemia, 1 grade 4 hyperglycemia and grade 3 hypophosphatemia, 1 grade 4 febrile neutropenia). Fatigue, diarrhea, nausea, and anorexia were the most prevalent toxicities. No objective responses were documented, and four patients had stable disease for at least ten cycles. The long half-life (292.0 +/- 135.7 h), low clearance (0.045 +/- 0.038 l/h), and volume of distribution (14.3 +/- 5.9 l) observed for UCN-01 are consistent with prior UCN-01 data. There was a significant decrease in C(max) of APC, AUC of APC and SN-38, and AUC ratio of SN-38:irinotecan when comparing days 1 and 8 PK.

CONCLUSIONS

APC and SN-38 exposure decreased when administered in combination with UCN-01. The MTD of the combination based on protocol criteria was defined as 70 mg/m(2) of UCN-01 on day 1 and 60 mg/m(2) of irinotecan on days 1 and 8 in a 21-day cycle.

Streptozotocin-induced diabetes progressively increases blood-brain barrier permeability in specific brain regions in rats

This study investigated the effects of streptozotocin-induced diabetes on the functional integrity of the blood-brain barrier in the rat at 7, 28, 56, and 90 days, using vascular space markers ranging in size from 342 to 65,000 Da. We also examined the effect of insulin treatment of diabetes on the formation and progression of cerebral microvascular damage and determined whether observed functional changes occurred globally throughout the brain or within specific brain regions. Results demonstrate that streptozotocin-induced diabetes produced a progressive increase in blood-brain barrier permeability to small molecules from 28 to 90 days and these changes in blood-brain barrier permeability were region specific, with the midbrain most susceptible to diabetes-induced microvascular damage. In addition, results showed that insulin treatment of diabetes attenuated blood-brain barrier disruption, especially during the first few weeks; however, as diabetes progressed, it was evident that microvascular damage occurred even when hyperglycemia was controlled. Overall, results of this study suggest that diabetes-induced perturbations to cerebral microvessels may disrupt homeostasis and contribute to long-term cognitive and functional deficits of the central nervous system.

Role of protein kinase C on the alteration of retinal endothelin-1 in streptozotocin-induced diabetic rats

Activation of protein kinase C (PKC) has been implicated in the pathogenesis of diabetic retinopathy. The purpose of this study was to investigate the role of PKC on the alteration of retinal endothelin-1 in 2-week streptozotocin (STZ)-induced diabetic rats. The measurement of retinal PKC activities from membranous and cytosolic fractions was conducted by ELISA. Retinal tissues were analysed for the expression of endothelin-1 (ET-1), endothelin-3 (ET-3), endothelin-A (ET-A), and endothelin-B (ET-B) mRNA by means of semi-quantitative RT-PCR. Retinal vasculature isolated by trypsin digest technique was immunostained for ET-1. We followed the alteration of retinal ET-1 after intravitreal injection of a general PKC inhibitor, GF109203X, in 2-week diabetic rats. Retinal PKC specific activities were significantly increased by 37% (P=0.027) in the membranous fraction in diabetic rats compared with normal rats, whereas PKC specific activities in the cytosolic fraction were unchanged. The retina from the diabetic rats showed increased ET-1 mRNA expression after 2 weeks, while no changes were found for ET-3, ET-A and ET-B. ET-1 immunoreactivity was also increased in the retinal vasculature of diabetic rats. Retinal ET-1 expression was decreased after intravitreal injection of GF109203X (10(-5), 10(-6), 10(-7) M) in a dose-dependent manner. The results from this study showed that the enhanced ET-1 expression associated with the activation of PKC has occurred in early diabetes, and PKC inhibitor could reverse the up regulation of ET-1.

The effect of ruboxistaurin on visual loss in patients with moderately severe to very severe nonproliferative diabetic retinopathy: initial results of the Protein Kinase C beta Inhibitor Diabetic Retinopathy Study (PKC-DRS) multicenter randomized clinical trial

The purpose of this study was to evaluate the Safety and efficacy of the orally administered protein kinase C (PKC) beta isoform-selective inhibitor ruboxistaurin (RBX) in subjects with moderately severe to very severe nonproliferative diabetic retinopathy (NPDR). In this multicenter, double-masked, randomized, placebo-controlled study, 252 subjects received placebo or RBX (8, 16, or 32 mg/day) for 36-46 months. Patients had an Early Treatment Diabetic Retinopathy Study (ETDRS) retinopathy severity level between 47B and 53E inclusive, an ETDRS visual acuity of 20/125 or better, and no history of scatter (panretinal) photocoagulation. Efficacy measures included progression of DR, moderate visual loss (MVL) (doubling of the visual angle), and sustained MVL (SMVL). RBX was well tolerated without significant adverse effects but had no significant effect on the progression of DR. Compared with placebo, 32 mg/day RBX was associated with a delayed occurrence of MVL (log rank, P = 0.038) and of SMVL (P = 0.226). RBX reduction of SMVL was evident only in eyes with definite diabetic macular edema at baseline (10% 32 mg/day RBX vs. 25% placebo, P = 0.017). In multivariable Cox proportional hazard analysis, 32 mg/day RBX significantly reduced the risk of MVL compared with placebo (hazard ratio 0.37 [95% CI 0.17-0.80], P = 0.012). In this clinical trial, RBX was well tolerated and reduced the risk of visual loss but did not prevent DR progression.