Microvascular diseases: is a new era coming?

The microvascular bed is an anatomical entity which comprises myriads of small arterioles, capillaries and venules. Microvessels and surrounding tissue metabolism are tightly coupled; consequently they are equipped with many, very specific and fine-tuned mechanisms allowing permanent, precise regulation of nutrient delivery. The review thoroughly describes the structure and physiology of arterioles and capillaries as well as the specialized means to investigate them. Microcirculation has been largely neglected for decades, mainly because of lack of technical possibilities for visualization and quantitation. However the past years have completely renewed the scientific interest, due to the combination of the availability of new techniques in human research and the recognition that the microcirculation is autonomically and causally involved in diseases previously thought to be essentially a question of macrocirculation. Today we start to see that microangiopathy is not only a consequence of large vessel diseases but can be the source of many pathologies in both cardiovascular and metabolic disorders, the best example -developed here- being the cardiometabolic syndrome or prediabetes. With very few exceptions, pentoxifylline and the antidiabetic metformin, no specific treatments have been developed for treating disorders at the microcirculatory level. Metformin has unique, intrinsic actions specifically at the level of terminal arterioles, which are completely independent of its antidiabetic effect. Other drugs are shortly described which have revealed a potential interest in this field. Our review aims at showing that microcirculation is entering a new era, starting with rapidly increasing knowledge of its intimate functioning and worth specific pharmacological developments.

Improvement of neurobehavioral disorders in children supplemented with magnesium-vitamin B6. I. Attention deficit hyperactivity disorders.

Some previous studies have reported the involvement of magnesium (Mg) deficiency in children with ADHD syndrome. In this work, 40 children with clinical symptoms of ADHD were followed clinically and biologically during a magnesium-vitamin B6 (Mg-B6) regimen (6 mg/kg/d Mg, 0.6 mg/kg/d vit-B6) which was set up for at least 8 weeks. Symptoms of ADHD (hyperactivity, hyperemotivity/ aggressiveness, lack of attention at school) were scored (0-4) at different times; in parallel, intraerythrocyte Mg2+ (Erc-Mg) and blood ionized Ca2+ (i-Ca) were measured. Children from the ADHD group showed significantly lower Erc-Mg values than control children (n = 36). In almost all cases of ADHD, Mg-B6 regimen for at least two months significantly modified the clinical symptoms of the disease: namely, hyperactivity and hyperemotivity/aggressiveness were reduced, school attention was improved. In parallel, the Mg-B6 regimen led to a significant increase in Erc-Mg values. When the Mg-B6 treatment was stopped, clinical symptoms of the disease reappeared in few weeks together with a decrease in Erc-Mg values. This study brings additional information about the therapeutic role of a Mg-B6 regimen in children with ADHD symptoms.

Improvement of neurobehavioral disorders in children supplemented with magnesium-vitamin B6. II. Pervasive developmental disorder-autism.

Previous studies reported positive results with the use of Mg-vitamin B6 in autism. Despite these reports, this intervention remains controversial. In order to study relationships between changes in clinical symtoms and biological parameters, 33 children (mean age: 4 [1-10] years old) with clinical symptoms of pervasive developmental disorder or autism (PDD, as defined in DSM-IV) were followed for at least 6 months; another group of 36 children (same age) devoided of any known pathology was used as control. All PDD children received a magnesium-vit B6 (Mg-B6) regimen (6 mg/kg/d Mg and 0.6 mg/kg/d vit B6). Intraerythrocyte Mg2+ (Erc-Mg), serum Mg2+ (s-Mg) and blood ionized Ca2+ (i-Ca) were measured before and after treatment. Clinical symptoms of PDD were scored (0 to 4). In contrast to s-Mg or i-Ca, PDD children exhibited significantly lower Erc-Mg values than controls (2.17 +/- 0.4 versus 2.73 +/- 0.23 mmol/L; 16/33). The Mg-B6 regimen led to an increase in Erc-Mg values (2.42 +/- 0.41 (after) versus 2.17 +/- 0.4 mmol/l (before), 11/17) and this supplementation improved PDD symptoms in 23/33 children (p < 0.0001) with no adverse effects: social interactions (23/33), communication (24/33), stereotyped restricted behavior (18/33), and abnormal/delayed functioning (17/33); 15/33 children were improved in the first three groups of symptoms. When the Mg-B6 treatment was stopped, PDD symtoms reappeared in few weeks. A statistically significant relationship was found in Erc-Mg values from children before treatment and their mothers. In conclusion, this study suggests that the behavioral improvement observed with the combination vitamin B6-magnesium in PDD/autism is associated with concomitant modifications of Erc-Mg values.

Mild acute renal failure potentiates metformin accumulation in the diabetic rat kidney without further impairment of renal function.

OBJECTIVES: To analyze, in acute renal failure (ARF) in diabetic rats, how moderate functional ARF would modify metformin (MET) pharmacokinetics and if plasma and renal tissue MET accumulation could aggravate renal insufficiency and/or elicit plasma lactate accumulation. METHODS: Streptozotocin-induced diabetic rats were allocated to four groups: control, MET, ARF, ARF-MET (6-7 rats per group). MET (100 mg/kg/day) was given per os for two weeks before ARF was induced by drinking restriction and enalapril treatment. The effects of MET and/or ARF were examined in vivo on renal function in conscious rats (metabolic cages) and ex vivo on renal vascular reactivity (isolated kidney). RESULTS: MET treatment (plasma level: 5.3 +/- 1.4 microg/ml, mean+/-SEM), resulted in biguanide accumulation in cortex and medulla (53 +/- 17 and 80 +/- 40 microg/g respectively). MET was devoid of any effect on creatinine clearance, mean blood pressure or renal vascular resistance, but moderately increased plasma lactate (3.8 +/- 0.5 vs 3.2 +/- 0.2 mM, P<0.05) and decreased angiotensin II-induced renal vasoconstriction. ARF, although mild, decreased renal MET clearance (0.29 +/- 0.05 vs 1.01 +/- 0.31 ml/min/100 g, P<0.05) and increased plasma and renal tissue MET levels (x 2-4). MET however did not worsen the fall in glomerular filtration rate, nor modify renal vascular reactivity. ARF did not change the MET-elicited moderate increase in plasma lactate. CONCLUSION: Despite the increase in MET plasma and renal tissue levels subsequent to moderate ARF, no harmful metabolic effect on plasma lactate and no further impairment of renal function was observed in MET-treated diabetic rats subjected to ARF.

Effect of the extract of Ginkgo biloba (EGb 761) on the circulating and cellular profiles of polyunsaturated fatty acids: correlation with the anti-oxidant properties of the extract.

Ginkgo biloba extract (EGb 761) has beneficial effects on cognitive functions in aging patients, and on various pathologies, including cardiovascular diseases. Although the extract is known to have antioxidant properties and improve membrane fluidity, the cellular mechanisms underlying these effects have not been determined. Here, we examined the in vivo effects of EGb 761 on circulating and cellular lipids. EGb 761 treatment induced significant increases in the levels of circulating polyunsaturated fatty acids (PUFAs), and a decrease in the saturation index SI (saturated/polyunsaturated species). Plasma triglycerides and cholesterol were not affected, while phospholipids were slightly increased at the higher dose of EGb 761. EGb 761 treatment also induced a significant increase in the levels of PUFAs in erythrocyte membranes, especially for the eicosapentaenoic acid (EPA omega 3), and a decrease in the saturation index. Moreover, the response of erythrocytes to oxidative stress was improved in EGb 761-treated animals (H(2)O(2)-induced cell lysis decreased by 50%). Considering that PUFAs are known to improve membrane fluidity and response to oxidative damage, and are precursors of signaling molecules such as prostaglandins, the effects of EGb 761 on circulating and cellular PUFAs may explain some of the pharmacological properties of Ginkgo biloba.

A new approach for clinical biological assay comparison and standardization: application of principal component analysis to a multicenter study of twenty-one carcinoembryonic antigen immunoassay kits.

BACKGROUND: Principal component analysis (PCA) is a powerful mathematical method able to analyze data sets containing a large number of variables. To our knowledge, this method is applied here for the first time in the field of medical laboratory analysis. METHODS: PCA was used to evaluate the results of a blind comparative study of 21 carcinoembryonic antigen (CEA) reagent kits used to determine CEA concentration in a panel of sera from 80 patients. RESULTS: The mathematical technique first eliminated the variations attributable to the use of different calibrators. The PCA representation then gave a global view of the dispersion of the kits and allowed the identification of a main homogeneous group and of some discrepant kits. CONCLUSIONS: PCA applied to the in vitro diagnostic reagent field could contribute to the standardization process and improve the quality of medical laboratory analyses. A standardization method using a panel of patient sera is proposed.

Hyperglycaemia modifies the reaction of microvessels to insulin in rat skeletal muscle.

The role played by glucose and/or insulin in local vascular regulation of tissue glucose uptake is largely unknown. Thus, the aim of this study was to examine microvascular changes induced either by hyperinsulinaemia alone or in combination with hyperglycaemia. The effects of insulin or glucose on the diameter and periodic vasomotion of precapillary arterioles (diameter < 20 microm) were determined by using the spinotrapezius muscle preparation in fasted, anaesthetized rats. Ten minutes after s.c. insulin administration, the blood insulin level was greatly increased whereas plasma glucose remained unchanged. This was associated with a marked and durable vasodilation of terminal arterioles without significant changes in vasomotion. When similar plasma insulin levels were attained by glucose infusion, tissue glucose uptake was increased in spite of a partial constriction and increased vasomotion of precapillary arterioles. Importantly, local tissue blood flow was not reduced despite the diminution in microvascular diameters. These results indicate that hyperinsulinaemia alone produces an increase in the diameter of terminal arterioles. This effect seems to be offset when the same level of hyperinsulinaemia is associated with hyperglycaemia (such as occurs postprandially), as illustrated by vasoconstriction of the muscle terminal arterioles. Our data suggest that the vasoconstriction of precapillary arterioles may be part of an active regulation for optimal glucose supply to the tissue in acute hyperglycaemic episodes. These data provide the first direct evidence that insulin and glucose can act as regulators of microflow in the skeletal muscle, as illustrated by changes in precapillary haemodynamics.

Tetanie latente: action d'une eau minerale naturelle magnesienne (hydroxydase) / Tetany: action of natural magnesian mineral water (hydroxydase)

Chez un groupe de 10 sujets dont la tetanie latente a ete verifiee par une echelle specifique validee, appelee echelle de spasmophilie, un traitement par deux cures d'eau d'Hydroxydase a ete mis en place. Cette... (AU)

Metformin induces an agonist-specific increase in albumin production by primary cultured rat hepatocytes.

Metformin (MET) is known to increase several biological effects of insulin (INS), but there is no information concerning its direct effects on protein synthesis. We studied the action of MET on albumin production by primary cultures of freshly isolated rat hepatocytes, alone or in combination with various agonists: INS, IGF-1, EGF, thyroxin, and dexamethasone. While having no effect alone, MET in vitro potentiates the effects of INS, IGF-1, and EGF. When this increasing effect toward INS was studied over a broad concentration range, MET appeared to improve low-acting INS levels and to intensify the maximal INS effects. In contrast, MET did not change the production of albumin stimulated by thyroxin or dexamethasone. Animals chronically pretreated with MET in vivo showed a higher yield of isolated hepatocytes, better attachment, and especially higher viability after liver perfusion and during cell culture. This may largely explain why basal albumin rates were higher than in in vitro-treated cells. The effect of MET in the presence of the agonists exhibited the same agonist-specificity as in vitro. Our data provide new insights into the pharmacology of MET by showing that hepatic protein synthesis is increased by MET and INS. From the specificity of action of MET towards INS, IGF-1, and EGF (but not thyroxin or dexamethasone), we hypothesize that this biguanide may act on intracellular pathways located between membrane receptors and sites of branching in the signaling cascades shared by these agonists.

Metabolic and drug distribution studies do not support direct inhibitory effects of metformin on intestinal glucose absorption.

In an attempt to clarify the question of an involvement of the inhibition of intestinal glucose absorption in the mechanism of action of Metformin, we used several experimental approaches: 1 glucose/lactate measurement in rat portal blood in vivo and 2 in the venous effluent of an isolated perfused rat intestinal segment; 3 metabolism of freshly isolated enterocytes in vitro and tissue distribution of 3H-labeled Metformin was investigated both in vivo and in vitro. Metformin applied intraluminally had no significant effect on portal glycaemia after a glucose load, but lactate increased, whereas in vivo only a high Metformin dosage reduced portal glucose appearance significantly. Although high Metformin concentrations were found in gut biopsies, precise histological analysis in the isolated intestine revealed that it was absent from enterocytes; however the drug accumulated in villous lacteals. Intrarterially applied Metformin decreased glucose absorption in the isolated perfused ileo-jejunal segment. These data suggested that vascular Metformin boosted intestinal anaerobic glucose metabolism. Biochemical measurements performed on freshly isolated enterocytes showed that even high Metformin levels did not interfere with cell respiration or with Na+/K+ ATPase activity. Thus, our data agree with other recent reports, suggesting that even at nontherapeutic concentrations Metformin has no relevant inhibitory effect on intestinal glucose absorption. The data are discussed in the frame of previous divergent observations. The results suggest however that Metformin of vascular origin stimulates glucose consumption by the intestine, which then increases lactate output from the gut.

Demonstration of the "anti-stress" activity of an extract of Ginkgo biloba (EGb 761) using a discrimination learning task.

1. Young (4-month-old) and old (20-month-old) rats, maintained under water restriction, were trained to discriminate to obtain a small amount of drinking water as a reward. Each animal had to learn to press a lever corresponding to a light that was randomly distributed on the left or right. 2. Introduction of an auditory perturbation ("stress") during the discriminative phase of learning modified the capacity and rate of acquisition in both young and old animals, changes that were correlated with increases in plasma concentrations of epinephrine, norepinephrine and corticosterone. 3. Stress-induced detrimental changes in both discrimination learning and plasma hormones were suppressed by 20 days of oral treatment with an extract of Ginkgo biloba leaves (EGb 761; 50 or 100 mg/kg/day) in both young and old rats, effects that became statistically significant by the third day of learning (time of maximal acquisition rate). 4. EGb 761 treatment was less effective in increasing the percentage of efficient lever presses in old than in young rats, but more effective in decreasing the number of inefficient lever presses and reaction time in the older animals. 5. These results indicate that EGb 761 can facilitate behavioral adaptation despite adverse environmental influences, a property that supports its clinical use in treating cognitive impairment, especially in elderly patients.

Retracted: Influence of volume replacement with different HES-solutions on microcirculatory blood flow in cardiac surgery.

A variety of hydroxyethyl starch HES preparations with different molecular weight average (Mw) and molar substitution (MS) is available for volume replacement during acute normovolemic haemodilution (ANH). Particularly with regard to microcirculation, the ideal solution for volume therapy has not been found. The influence of four different HES preparations on macro- and microcirculation was investigated in 40 patients scheduled for elective aorto-coronary bypass grafting and undergoing ANH (preoperative withdrawn blood: 10 ml.kg-1): 1) 6% HES with Mw of 450,000 dalton and MS of 0.7; 2) 6% HES with Mw of 200,000 dalton and MS of 0.5; 3) 6% HES with Mw of 200,000 dalton and MS of 0.62; 4) 6% HES with Mw of 40,000 dalton and MS of 0.5. A 5th group without ANH served as a control (10 patients in each group). In addition to systemic haemodynamics and various laboratory parameters, skin capillary blood flow was measured by laser Doppler flowmetry. Laser Doppler flow (LDF) was monitored simultaneously at the patient's forehead and forearm. Changes in systemic haemodynamics were similar in all ANH-patients. Systemic vascular resistance (SVR) was lowest after infusion of HES 200/0.5. The most pronounced increase in plasma viscosity was in patients of group 1 (450/0.7) (P < 0.05) and plasma viscosity remained highest during the entire investigation period in these patients. After ANH, skin capillary blood flow measured at the forehead decreased in all patients except in patients of group 2 (200/0.5: max. +18%). Group 3 (200/0.62) showed the highest decrease in forehead-LDF. During CPB, forehead-LDF decreased significantly in groups 3 (200/0.62) and 4 (40/0.5).(ABSTRACT TRUNCATED AT 250 WORDS)

Demonstration of defective glucose uptake and storage in erythrocytes from non-insulin dependent diabetic patients and effects of metformin.

1. Red blood cells can store glucose and may thus participate in blood glucose homeostasis. We investigated if a defect in this process exists in non-insulin dependent diabetes (NIDD). 2. Blood was obtained in fasting conditions from 10 normal and 10 newly diagnosed NIDD patients (before and after 4 weeks Metformin therapy). Washed erythrocytes were resuspended in media containing various glucose concentrations (4.4, 6.6, 8.8 and 13.2 mmol/L). Total glucose uptake was calculated as the sum of the measurements of lactate as well as free glucose, the latter being determined before and after addition of amyloglucosidase to the pellet. 3. Cells from diabetics showed a pronounced reduction in glucose uptake, particularly in their capacity to store glucose as glycogen (reactive to amyloglucosidase). Metformin treatment almost normalized glycogen levels, whereas lactate declined concomitantly in the pellet. 4. Our data demonstrate that a defect in glucose uptake exists in erythrocytes from NIDD patients, affecting both free and stored glucose, and that this defect is reversed by Metformin treatment, indicating that this drug can increase glycogen levels even in insulin-insensitive cells. 5. Thus, in view of their total mass, erythrocytes may be important in the impaired glucose homeostasis in NIDD, in particular in marked hyperglycaemia such as after a meal.

Postischemic breakdown in hippocampal protein synthesis and mnesic deficits in rats: pharmacological improvement by curative naftidrofuryl treatment.

This work was designed to investigate the effects of brain ischemia on mnesic retention in the model of unilateral microsphere embolization in rats. Using various radioactive tracers as well as a learning/memory test, we could correlate following parameters: regional blood flow, protein synthesis and memory retention. All were severely impaired by the hemispheric multi-infarction. A curative treatment with naftidrofuryl (15 mg/kg i.p.) for 3 consecutive days strongly improved the mnesic capacities of the animals, and this effect was corroborated by a marked protective drug action on protein synthesis in the hippocampus. Indeed, studies on valine incorporation into proteins revealed that, despite having no quantitative effect on regional blood flow, naftidrofuryl allowed an almost normal functioning of protein synthesis. As naftidrofuryl had also no direct effect on protein synthesis in the intact contralateral hemisphere, this effect was consequently attributed to the metabolic and/or antiserotoninergic effects of the drug.

Erythrocyte glucose consumption in insulin-dependent diabetes: effect of metformin in vitro.

Erythrocyte glucose consumption in red blood cells from healthy donors or insulin-dependent diabetics with stable glycemia was measured using the 2-deoxyglucose technique. Data showed that the formation of glucose-6P was severely impaired in diabetic red blood cells in both normo- and hyperglycemic incubation conditions. This defect seems to be inherent to the disease. Coincubation with Metformin (6.4 ug/ml) did not modify the G6P levels in RBCs from healthy donors and in RBCs from diabetics when incubated in normoglycemic conditions. However, when diabetics RBCs were incubated in a hyperglycemic medium, addition of Metformin strongly improved the intracellular levels of G6P. The underlying mechanism for the defect and the correction by Metformin remains to be determined. This study shows that also red blood cells may be involved in the failure of glucose homeostasis in diabetes and thus this may represent an additional target for therapy.