Cerebral circulation during diabetes mellitus

Cardiovascular disease risk is associated with middle cerebral artery blood flow velocity in older adults

PURPOSE

The aim of this study was to evaluate the relationship of cardiovascular disease (CVD) on middle cerebral blood flow velocity (MCAv) at rest and during exercise. A secondary aim was to explore the relationship between MCAv and 1) the presence of white matter lesions and 2) cognitive function.

METHODS

We recruited individuals who were cognitively normal older adults. CVD risk was assessed by the Pooled Cohort atherosclerotic cardiovascular disease (ASCVD) risk score. Transcranial Doppler ultrasound measured middle cerebral artery at rest and during a bout of moderate intensity exercise. We quantified white matter lesions from MRI and cognitive function outcomes included executive function, language, processing speed, and attention.

RESULTS

Seventy-two participants 70.1 ± 4.7 years of age completed the study protocol. ASCVD risk score was significantly associated with resting and exercise MCAv (p<0.01) but not associated with white matter lesions (p>0.468). We observed a significant association between resting and exercise MCAv and language processing (p=0.010) but not other cognitive domains.

CONCLUSION

In cognitively normal older adults, higher ASCVD risk score was associated with blunted resting and exercise MCAv and with lower language processing performance. These results highlight the need for CVD risk management to maintain optimal brain health.

Cerebrovascular complications of diabetes: focus on cognitive dysfunction

The incidence of diabetes has more than doubled in the United States in the last 30 years and the global disease rate is projected to double by 2030. Cognitive impairment has been associated with diabetes, worsening quality of life in patients. The structural and functional interaction of neurons with the surrounding vasculature is critical for proper function of the central nervous system including domains involved in learning and memory. Thus, in this review we explore cognitive impairment in patients and experimental models, focusing on links to vascular dysfunction and structural changes. Lastly, we propose a role for the innate immunity-mediated inflammation in neurovascular changes in diabetes.

Role of dietary and endogenous antioxidants in diabetes

Diabetes affects different people of all ages, race, and sex. This is a condition characterized by a state of chronic hyperglycaemia that leads to an increase of intracellular oxidative stress linked to the overproduction of free radicals. In the present review, we focus our attention on the molecular mechanisms leading to oxidative stress-mediates complications with particular regard to central nervous system (CNS). Furthermore, the present review reports the effects of different kind of antioxidants with enzymatic and nonenzymatic action that may significantly decrease the intracellular free radicals' overproduction and prevents the hyperglycaemia-mediated complications.

HCV, but not HIV, is a risk factor for cerebral small vessel disease

OBJECTIVES

With the aging of HIV populations, vascular contributions to neuropathogenesis are increasingly important. Indirect analyses of cerebral small vessel disease have been performed, but there have been no direct studies of human brain to elucidate risk factors for arteriolar sclerosis.

METHODS

Mean arteriolar wall thickness (sclerotic index, SI) was measured in the deep cerebral white matter of 126 brains (96 HIV+, 30 HIV-). Correlations with SI were performed for age, sex, race, hypertension, hyperlipidemia, diabetes, obesity, cirrhosis, hepatitis C virus (HCV) infection, herpes infection, HIV infection, HIV risk, cocaine use, CD4 count, plasma HIV load, and combination antiretroviral therapy (cART) at the time of death.

RESULTS

Age, hypertension, race, HCV, and cirrhosis were associated with SI; of the HIV variables, only cART at death was associated with SI. To address colinearity, partial correlations were run with HCV and cirrhosis, hypertension and race, and hypertension and age. With HCV controlled, cirrhosis lost significance; with hypertension controlled, age lost significance. For the entire sample, HCV, African American race, and hypertension accounted for 15% of SI variance in multivariate analysis. Each was independently associated with SI, and HCV had the largest effect. For the HIV sample, inclusion of cART in the model increased R (2) to 0.205, with only HCV, hypertension, and cART remaining significant or trend level.

CONCLUSIONS

This tissue-based analysis of cerebral arteriolar disease demonstrates that HCV constitutes an independent risk, in addition to African American race, hypertension, and cART. Further study is needed to understand what aspects of HCV and cART contribute to cerebrovascular neuropathogenesis.

Effect of hyperglycemia on brain penetrating arterioles and cerebral blood flow before and after ischemia/reperfusion

The effect of preexisiting hyperglycemia on cerebral blood flow (CBF) and brain penetrating arterioles before and after 2 h of ischemia and 30 min of reperfusion was determined. Male Wistar rats that were either hyperglycemic (50 mg/kg streptozotocin; n=24) or normoglycemic (n=24) were subjected to transient ischemia by filament occlusion or nonischemic. CBF was measured prior to ischemia using microspheres and during transient ischemia using laser Doppler. Edema was compared by wet/dry weights. Constriction to apamin, TRAM-34, and L-NNA, inhibitors of small- and intermediate-conductance calcium-activated potassium channels (SK and IK) and nitric oxide, were compared in penetrating arterioles from the ischemic hemisphere to investigate changes in basal tone and endothelium-dependent vasodilator responses. Preexisiting hyperglycemia did not affect CBF in non-ischemic animals or after transient ischemia; however, edema was significantly greater. Ischemia and reperfusion caused decreased basal tone in penetrating arterioles similarly in normoglycemic and hyperglycemic animals that was restored by apamin, and further increased by TRAM-34 and L-NNA. The restoration of tone in penetrating arterioles by apamin and TRAM-34 suggests that transient ischemia activates SK and IK channels in penetrating arterioles. This effect of ischemia was not different between normoglycemic and hyperglycemic animals, suggesting that it was related to ischemia and reperfusion rather than hyperglycemia.

Cerebrovascular complications of diabetes: focus on stroke

Cerebrovascular complications make diabetic patients 2-6 times more susceptible to a stroke event and this risk is magnified in younger individuals and in patients with hypertension and complications in other vascular beds. In addition, when patients with diabetes and hyperglycemia experience an acute ischemic stroke they are more likely to die or be severely disabled and less likely to benefit from the one FDA-approved therapy, intravenous tissue plasminogen activator. Experimental stroke models have revealed that chronic hyperglycemia leads to deficits in cerebrovascular structure and function that may explain some of the clinical observations. Increased edema, neovascularization and protease expression as well as altered vascular reactivity and tone may be involved and point to potential therapeutic targets. Further study is needed to fully understand this complex disease state and the breadth of its manifestation in the cerebrovasculature.

Cerebral myogenic reactivity and blood flow in type 2 diabetic rats: role of peroxynitrite in hypoxia-mediated loss of myogenic tone

Dysregulation of cerebral vascular function and, ultimately, cerebral blood flow (CBF) may contribute to complications such as stroke and cognitive decline in diabetes. We hypothesized that 1) diabetes-mediated neurovascular and myogenic dysfunction impairs CBF and 2) under hypoxic conditions, cerebral vessels from diabetic rats lose myogenic properties because of peroxynitrite (ONOO(-))-mediated nitration of vascular smooth muscle (VSM) actin. Functional hyperemia, the ability of blood vessels to dilate upon neuronal stimulation, and myogenic tone of isolated middle cerebral arteries (MCAs) were assessed as indices of neurovascular and myogenic function, respectively, in 10- to 12-week control and type 2 diabetic Goto-Kakizaki rats. In addition, myogenic behavior of MCAs, nitrotyrosine (NY) levels, and VSM actin content were measured under normoxic and hypoxic [oxygen glucose deprivation (OGD)] conditions with and without the ONOO(-) decomposition catalyst 5,10,15,20-tetrakis(4-sulfonatophenyl) prophyrinato iron (III), chloride (FeTPPs). The percentage of myogenic tone was higher in diabetes, and forced dilation occurred at higher pressures. Functional hyperemia was impaired. Consistent with these findings, baseline CBF was lower in diabetes. OGD reduced the percentage of myogenic tone in both groups, and FeTPPs restored it only in diabetes. OGD increased VSM NY in both groups, and although FeTPPs restored basal levels, it did not correct the reduced filamentous/globular (F/G) actin ratio. Acute alterations in VSM ONOO(-) levels may contribute to hypoxic myogenic dysfunction, but this cannot be solely explained by the decreased F/G actin ratio due to actin nitration, and mechanisms may differ between control and diabetic animals. Our findings also demonstrate that diabetes alters the ability of cerebral vessels to regulate CBF under basal and hypoxic conditions.

Effects of First- and Second-Generation Histamine-H1-Receptor Antagonists on the Pentobarbital-Induced Loss of the Righting Reflex in Streptozotocin-Induced Diabetic Mice

The second-generation histamine-H(1)-receptor antagonists, such as epinastine and cetirizine, are used as non-sedating antihistamines for treating allergic symptoms due to their poor ability to penetrate blood-brain barrier. Because it has been reported that the blood-brain barrier system is disturbed in diabetes, it is possible that second-generation histamine-H(1)-receptor antagonists may easily penetrate the blood-brain barrier and cause potent sedation in diabetics. In the present study, we investigated the effects of first-generation (diphenhydramine) and second-generation (epinastine and cetirizine) histamine-H(1)-receptor antagonists on the duration of pentobarbital-induced loss of the righting reflex (LORR) in non-diabetic and diabetic mice. Systemic treatment with diphenhydramine (3 - 30 mg/kg, s.c.), and intracerebroventricular treatment with epinastine (0.03 - 0.3 microg/mouse) and cetirizine (0.03 - 0.3 microg/mouse) dose-dependently and significantly increased the duration of pentobarbital-induced LORR in both non-diabetic and diabetic mice. Although systemic treatment with epinastine (3 - 30 mg/kg, s.c.) and cetirizine (3 - 30 mg/kg, s.c.) did not affect the duration of pentobarbital-induced LORR in non-diabetic mice, these treatments significantly prolonged it in diabetic mice. Our results suggest that the systemic administration of second-generation histamine-H(1)-receptor antagonists may produce a central nervous system depressant effect in diabetes.

Aminoguanidine suppresses basal macromolecular extravasation during diabetes mellitus

The goal of this study was to determine the effect of aminoguanidine on basal macromolecular efflux from the microcirculation of the hamster cheek pouch during diabetes mellitus. We used intravital fluorescent microscopy and fluorescein isothiocyanate dextrans (FITC-dextran; mw = 70 and 20K) to examine basal macromolecular extravasation in nondiabetic hamsters, nondiabetic hamsters treated with a topical application of aminoguanidine (0.5 mM), diabetic hamsters (6-10 weeks after injection of streptozotocin), and diabetic hamsters treated with a topical application of aminoguanidine (0.5 mM). Increases in macromolecular efflux were quantitated by calculating the clearance (ml/s x 10(-6)) of FITC-dextran-70K and -20K. In nondiabetic hamsters, the clearance of FITC-dextran-70K and -20K remained relatively constant during the experimental period, although the clearance of FITC-dextran-70K was less than that for FITC-dextran-20K. Topical application of aminoguanidine did not alter basal permeability characteristics in nondiabetic hamsters. In diabetic hamsters, clearance of FITC-dextran-70K and -20K also remained relatively constant during the experimental period. However, the magnitude of clearance of FITC-dextran-70K and and -20K was significantly greater in diabetic compared to nondiabetic hamsters (P < 0.05). Topical application of aminoguanidine restored basal permeability characteristics of diabetic hamsters to that observed in nondiabetic hamsters. These findings suggest that acute treatment of the microcirculation in vivo with aminoguanidine ameliorates basal increases in extravasation of macromolecules during diabetes mellitus. We suggest that aminoguanidine suppresses basal macromolecular efflux in diabetic hamsters via inhibition of nitric oxide synthase. Thus, it appears that the use of aminoguanidine may be an important therapeutic approach for the treatment of diabetes-related vascular dysfunction.

Computer analysis of magnetic resonance imaging of the brain in children and adolescents after treatment of diabetic ketoacidosis

Cerebral vascular accidents are one of the causes of morbidity and mortality in children with diabetic ketoacidosis. We investigated the possible occurrence of asymptomatic cerebrovascular infarcts and the course of subclinical brain edema in six patients. Neurologic examinations and computer analysis of magnetic resonance imaging were performed immediately after, and again at 14 days after, correction of DKA. None of the patients had clinical evidence of a neurologic deficit. Neither radiologic evaluation nor computer analysis of MRI identified changes indicating asymptomatic ischemic events. However, a computer analysis of the MRI identified a significant increase of the total ventricle area between Day one and Day 14. Our study does not establish whether this change is a return to the baseline prior to DKA or a new baseline, representing an early manifestation of diabetic encephalopathy.

Spreading depression-induced gene expression is regulated by plasma glucose

BACKGROUND AND PURPOSE

Plasma glucose and spreading depression (SD) are both determinants of brain ischemia. The purpose of this study was to examine whether plasma glucose affects SD-induced gene expression in the cortex.

METHODS

SD was induced by topical application of KCl. Hyperglycemia and hypoglycemia were induced by intraperitoneal injection of glucose and insulin, respectively. The expression of c-fos, cyclooxygenase-2 (COX-2), protein kinase C-delta (PKCdelta), and heme oxygenase-1 (HO-1) was determined by in situ hybridization.

RESULTS

SD alone induced expression of c-fos (by 340%), COX-2 (210%), HO-1 (470%), and PKCdelta (410%). Hypoglycemia (2.4+/-0.9 mmol/L) alone did not induce gene expression, and hyperglycemia (22.1+/-3.7 mmol/L) alone induced only c-fos by 42%. When hypoglycemia was induced 30 minutes before SD, c-fos induction was enhanced by 145%, but the induction of HO-1 and PKCdelta was reduced to 43% and 64%, respectively. When hyperglycemia was induced 30 minutes before SD, c-fos induction was enhanced by 388% and COX-2 expression by 53%, whereas the induction of PKCdelta and HO-1 was reduced to 54% and 51%, respectively. The frequency, amplitude, and duration of direct current potentials were unaltered in hyperglycemic SD animals, whereas in hypoglycemic animals the duration was increased by 47%.

CONCLUSIONS

While SD induces expression of several genes, the availability of glucose regulates the extent of the gene induction. The effect of glucose is different on early-response genes (c-fos and COX-2) compared with late-response genes. Plasma glucose may contribute to neuronal damage partially by regulating gene expression.

Superoxide dismutase partially restores impaired dilatation of the basilar artery during diabetes mellitus

The goal of this study was to test the hypothesis that administration of superoxide dismutase restores nitric oxide synthase-mediated dilatation of the basilar artery during diabetes mellitus. We measured the diameter of the basilar artery in vivo in nondiabetic and diabetic rats (streptozotocin; 50-60 mg/kg i.p.) in response to nitric oxide synthase-dependent agonists (acetylcholine and bradykinin) and a nitric oxide synthase-independent agonist (nitroglycerin) before and during application of superoxide dismutase. Topical application of acetylcholine (1.0 and 10 microM) and bradykinin (1.0 and 10 microM) produced dose-related dilatation of the basilar artery in nondiabetic and diabetic rats. However, the magnitude of vasodilation produced by acetylcholine and bradykinin was significantly less in diabetic rats. Topical application of nitroglycerin (0.1 and 1.0 microM) produced similar dose-related dilatation of the basilar artery in nondiabetic and diabetic rats. Treatment with superoxide dismutase (150 U/ml) did not alter baseline diameter of the basilar artery in nondiabetic and diabetic rats. However, topical application of superoxide dismutase partially restored nitric oxide synthase-dependent dilatation of the basilar artery in diabetic rats towards that observed in nondiabetic rats. Superoxide dismutase did not alter dilatation of the basilar artery in nondiabetic rats. These findings suggest that impaired nitric oxide synthase-dependent dilatation of the basilar artery during diabetes mellitus may be related, in part, to enhanced release of oxygen-derived free radicals.

Central nervous system complications of diabetes mellitus--a perspective from the blood-brain barrier

A host of diabetes-related changes in the central nervous system (CNS) has been recognized. The underlying causes of these changes are multiple. An important contributor to the changes in the CNS is the blood-brain barrier (BBB). Diabetes is associated with changes in both the barrier and transport functions of the cerebral microvessels. Structural changes in cerebral microvessels may account for some of the observed changes. Additional mechanisms include alterations in hemodynamic variables such as arteriovenous shunting, changes in biophysical properties and biochemical compositions of the endothelial cells including changes in lipid fluidity and composition, and alterations of neurotransmitter activity in the cerebral microvessels, notably altered beta adrenergic neurotransmission. These observations indicate that the CNS is not immune against the microangiopathic complications commonly found in various tissues of diabetic animals.

L-Arginine does not restore dilatation of the basilar artery during diabetes mellitus

The goal of this study was to test the hypothesis that administration of L-arginine, a substrate for the synthesis of nitric oxide, restores endothelium-dependent dilatation of the basilar artery during diabetes mellitus. We measured the diameter, of the basilar artery in vivo in nondiabetic and diabetic (streptozotocin; 50-60 mg/kg i.p.) rats in response to endothelium-dependent agonists (acetylcholine and bradykinin) and an endothelium-independent agonist (nitroglycerin) before and during application of L-arginine. Topical application of acetylcholine (1.0 and 10 muM) and bradykinin (1.0 and 10 microM) produced dilatation in nondiabetic rats of the basilar artery which was impaired in diabetic rats. Topical application of nitroglycerin (0.1 and 1.0 microM) produced similar dilatation of the basilar artery in nondiabetic and diabetic rats. Topical application of L-arginine (0.1 and 3 mM) did not enhance dilatation of the basilar artery in response to acetylcholine and bradykinin in diabetic rats. Thus, impairment of dilatation of the basilar artery in diabetic rats in response to acetylcholine and bradykinin appears to be related to a mechanism unrelated to the availability of L-arginine for nitric oxide synthase.

Poor hemodynamic and metabolic recovery after global incomplete cerebral ischemia associated with short-term diabetes in dogs

We determined the effect of 4-5 weeks of diabetes on ATP recovery following global incomplete cerebral ischemia. 31P magnetic resonance spectra of ATP, intracellular pH (pHi), and CBF (radiolabeled microspheres) were measured in three groups of anesthetized dogs (n = 8/group): chronic hyperglycemic diabetes (pancreatectomy followed by blood glucose of > 10 mM for 4-5 weeks); acute hyperglycemia (blood glucose of > 10 mM) during ischemia and reperfusion in nondiabetic dogs; and normoglycemic controls. Twenty minutes of incomplete ischemia was produced by ventricular fluid infusion to keep cerebral perfusion pressure (CPP) at 10 mm Hg during spontaneous variations in MABP. Intracranial pressure was increased initially to similar levels, resulting in a similar Cushing response among the groups. However, during the final 8 min of ischemia, MABP decreased to a greater extent in diabetic (86 +/- 42 mm Hg) than in hyperglycemic (162 +/- 30 mm Hg) and normoglycemic (135 +/- 54 mm Hg) groups and remained lower throughout 3 h of reperfusion. CPP was kept constant during ischemia, but was lower throughout reperfusion in diabetic dogs. During ischemia CBF was reduced similarly among groups: 5 +/- 3 ml.min-1 x 100 g-1 in hyperglycemic and normoglycemic and 4 +/- 3 ml.min-1 x 100 g-1 in diabetic dogs. During reperfusion early hyperemia was attenuated and delayed hypoperfusion was augmented (7 +/- 17 ml.min-1 x 100 g-1 by 180 min) as a result of low perfusion pressure in diabetics. However, medullary blood flow was similar among groups.(ABSTRACT TRUNCATED AT 250 WORDS)