A prospective evaluation of insulin dosing recommendations in patients with type 1 diabetes at near normal glucose control: bolus dosing

BACKGROUND

Current bolus insulin dosing recommendations are based on retrospective studies of patients with Type 1 diabetes in whom the glucose control was not intensely established. Using continuous glucose monitoring (CGM), we prospectively studied these recommendations in patients treated with continuous subcutaneous insulin infusion.

METHODS

Thirty subjects were studied over a mean of two weeks of continuous glucose monitoring with near daily insulin adjustments. First a basal glucose goal was achieved of <5% of values <70 mg/dL and <20%>, 170 mg/dL. Then bolus dosing factors; Insulin to Carbohydrate Ratio (g of meal carbohydrates/unit of insulin, ICR) and Correction Factor (mg/dL fall in blood glucose/unit of insulin, CF); were established for each meal time to a goal of +/- 20% of premeal glucose (ICR) or 80-120 mg/dL (CF) by the fourth post bolus hour.

RESULTS

All treatment goals were achieved in each subject. Modification of formulas from ICR = 450/Total Daily Dose (TDD) to ICR = (217/TDD) + 3 and from CF = 1700/TDD to CF = (1076/TDD) + 12 more closely matched observed results than published formulas. There was no significant difference in each factor with time of day. There was a highly significant relationship between ICR and CF, ICR*4.44 = CF (r = 0.9, p < 0.0005), total basal dose (TBD) and TDD.

CONCLUSIONS

Current formulas need to be modified to provide higher insulin bolus doses. The interrelationships between ICR, CF, TBD and TDD suggest that any change in one may require a change in the others.

The artificial pancreas: how sweet engineering will solve bitter problems

An artificial pancreas is a closed-loop system containing only synthetic materials which substitutes for an endocrine pancreas. No artificial pancreas system is currently approved; however, devices that could become components of such a system are now becoming commercially available. An artificial pancreas will consist of functionally integrated components that will continuously sense glucose levels, determine appropriate insulin dosages, and deliver the insulin. Any proposed closed loop system will be closely scrutinized for its safety, efficacy, and economic impact. Closed loop control utilizes models of glucose homeostasis which account for the influences of feeding, stress, insulin, exercise, and other factors on blood glucose levels. Models are necessary for understanding the relationship between blood glucose levels and insulin dosing; developing algorithms to control insulin dosing; and customizing each user's system based on individual responses to factors that influence glycemia. Components of an artificial pancreas are now being developed, including continuous glucose sensors; insulin pumps for parenteral delivery; and control software, all linked through wireless communication systems. Although a closed-loop system providing glucagon has not been reported in 40 years, the use of glucagon to prevent hypoglycemia is physiologically attractive and future devices might utilize this hormone. No demonstration of long-term closed loop control of glucose in a free-living human with diabetes has been reported to date, but many centers around the world are working on closed loop control systems. It is expected that many types of artificial pancreas systems will eventually be available, and they will greatly benefit patients with diabetes.

A prospective evaluation of insulin dosing recommendations in patients with type 1 diabetes at near normal glucose control: Basal dosing

BACKGROUND

Current basal insulin dosing recommendations are based on retrospective studies of Type 1 patients with diabetes in whom the glucose control was not intensely established. Using continuous glucose monitoring (CGM) we prospectively studied these recommendations in patients treated with continuous subcutaneous insulin infusion.

METHODS

With CGM 30 subjects were titrated with daily insulin adjustments to achieve a basal glucose targets of <5% of values <70 mg/dl and <20%, >170 mg/dl. The basal rate during meal time was studied by a sequential daily single meal omission until the glucose goals were achieved.

RESULTS

Glucose targets were achieved in all subjects. The observed ratios of total basal dose (TBD) to total daily dose and TBD to weight, in kilograms, were 0.384 and 0.185, respectively. Previously reported formulas for estimating the TBD resulted in significantly higher values than we observed. The difference between the maximum to the minimum hourly basal insulin infusion rate was more than 100% and the peak rate was reached by 0200 hours in 73% of subjects. During the post study observation period in which there was no further study intervention and in those subjects with baseline A1C >6.9%, the A1C decreased 0.45 % (p = 0.0110) in a mean of 12.8 weeks.

CONCLUSIONS

Current literature overestimates TBD dose and underestimates the degree and the time of onset of the dawn phenomenon. Maintaining near normal glycemia in the ambulatory setting may be achieved in selected Type 1 patients for at least two weeks and maybe longer.

Interleukin-1beta-induced insulin resistance in adipocytes through down-regulation of insulin receptor substrate-1 expression

Inflammation is associated with obesity and insulin resistance. Proinflammatory cytokines produced by adipose tissue in obesity could alter insulin signaling and action. Recent studies have shown a relationship between IL-1beta level and metabolic syndrome or type 2 diabetes. However, the ability of IL-1beta to alter insulin signaling and action remains to be explored. We demonstrated that IL-1beta slightly increased Glut 1 translocation and basal glucose uptake in 3T3-L1 adipocytes. Importantly, we found that prolonged IL-1beta treatment reduced the insulin-induced glucose uptake, whereas an acute treatment had no effect. Chronic treatment with IL-1beta slightly decreased the expression of Glut 4 and markedly inhibited its translocation to the plasma membrane in response to insulin. This inhibitory effect was due to a decrease in the amount of insulin receptor substrate (IRS)-1 but not IRS-2 expression in both 3T3-L1 and human adipocytes. The decrease in IRS-1 amount resulted in a reduction in its tyrosine phosphorylation and the alteration of insulin-induced protein kinase B activation and AS160 phosphorylation. Pharmacological inhibition of ERK totally inhibited IL-1beta-induced down-regulation of IRS-1 mRNA. Moreover, IRS-1 protein expression and insulin-induced protein kinase B activation, AS160 phosphorylation, and Glut 4 translocation were partially recovered after treatment with the ERK inhibitor. These results demonstrate that IL-1beta reduces IRS-1 expression at a transcriptional level through a mechanism that is ERK dependent and at a posttranscriptional level independently of ERK activation. By targeting IRS-1, IL-1beta is capable of impairing insulin signaling and action, and could thus participate in concert with other cytokines, in the development of insulin resistance in adipocytes.

Optimizing display, analysis, interpretation and utility of self-monitoring of blood glucose (SMBG) data for management of patients with diabetes

BACKGROUND

Self-monitoring of blood glucose (SMBG) data have not been used to fullest advantage. Few physicians routinely download data from memory-equipped glucose meters and perform systematic analyses and interpretation of the data. There is need for improved methods for display and analysis of SMBG data, for a systematic approach for identification and prioritization of clinical problems revealed by SMBG, for characterization of blood glucose variability, and for clinical decision support.

METHODS

We have developed a systematic approach to the analysis and interpretation of SMBG data to assist in the management of patients with diabetes. This approach utilizes the following criteria: 1) Overall quality of glycemic control; 2) Hypoglycemia (frequency, severity, timing); 3) Hyperglycemia; 4) Variability; 5) Pattern analysis; and 6) Adequacy of monitoring. The "Pattern analysis" includes assessment of: trends by date and by time of day; relationship of blood glucose to meals; post-prandial excursions; the effects of day of the week, and interactions between time of day and day of the week.

RESULTS

The asymmetrical distribution of blood glucose values makes it difficult to interpret the mean and standard deviation. Use of the median (50(th) percentile) and Inter-Quartile Range (IQR) overcomes these difficulties: IQR is the difference between the 75(th) and 25(th) percentiles. SMBG data can be used to predict the A1c level and indices of the risks of hyperglycemia and hypoglycemia.

CONCLUSION

Given reliable measures of glucose variability, one can apply a strategy to progressively reduce glucose variability and then increase the intensity of therapy so as to reduce median blood glucose and hence A1c, while minimizing the risk of hypoglycemia.

Beta-adrenergic and atrial natriuretic peptide interactions on human cardiovascular and metabolic regulation

CONTEXT

Atrial natriuretic peptide (ANP) has well-known cardiovascular effects and modifies lipid and carbohydrate metabolism in humans.

OBJECTIVE

The objective of the study was to determine the metabolic and cardiovascular interaction of beta-adrenergic receptors and ANP.

DESIGN

This was a crossover study, conducted 2004-2005.

SETTING

The study was conducted at an academic clinical research center.

PATIENTS

PATIENTS included 10 healthy young male subjects (body mass index 24 +/- 1 kg/m2).

INTERVENTION

We infused iv incremental ANP doses (6.25, 12.5, and 25 ng/kg.min) with and without propranolol (0.20 mg/kg in divided doses followed by 0.033 mg/kg.h infusion). Metabolism was monitored through venous blood sampling, im, and sc microdialysis and indirect calorimetry. Cardiovascular changes were monitored by continuous electrocardiogram and beat-by-beat blood pressure recordings.

MAIN OUTCOME MEASURES

Venous nonesterified fatty acid, glycerol, glucose, and insulin; and microdialysate glucose, glycerol, lactate, and pyruvate were measured.

RESULTS

ANP increased heart rate dose dependently. beta-Adrenergic receptor blockade abolished the response. ANP elicited a dose-dependent increase in serum nonesterified fatty acid and glycerol concentrations. The response was not suppressed with propranolol. Venous glucose and insulin concentrations increased with ANP, both without or with propranolol. ANP induced lipid mobilization in sc adipose tissue. In skeletal muscle, microdialysate lactate increased, whereas the lactate to pyruvate ratio decreased, both with and without propranolol. Higher ANP doses increased lipid oxidation, whereas energy expenditure remained unchanged. Propranolol tended to attenuate the increase in lipid oxidation.

CONCLUSIONS

Selected cardiovascular ANP effects are at least partly mediated by beta-adrenergic receptor stimulation. ANP-induced changes in lipid mobilization and glycolysis are mediated by another mechanism, presumably stimulation of natriuretic peptide receptors, whereas substrate oxidation might be modulated through adrenergic mechanisms.

GaP Raman Terahertz high accuracy spectrometer and its application to detect organic and inorganic crystalline defects

One of the most important uses of THz spectrometry is to detect defects in molecular structure or in crystals efficiently. We applied GaP Raman THz (GRT) spectrometer to detect and evaluate defects in inorganic and organic materials. High THz-wave absorption due to high defect density of GaSe crystal lowered the efficiency of THz wave generation, when the crystal is used as nonlinear material for DFG (Difference Frequency Generation). Defects in organic molecules could be observed as changes in frequency, intensities of the absorption, and broadenings of the spectra.

Catecholamine storage vesicles and the metabolic syndrome: The role of the chromogranin A fragment pancreastatin

Chromogranins or secretogranins (granins), present in secretory granules of virtually all neuroendocrine cells and neurones, are structurally related proteins encoded by different genetic loci: chromogranins A and B, and secretogranins II through VI. Compelling evidence supports both intracellular and extracellular functions for this protein family. Within the cells of origin, a granulogenic or sorting role in the regulated pathway of hormone or neurotransmitter secretion has been documented, especially for chromogranin A (CHGA). Granins also function as pro-hormones, giving rise by proteolytic processing to an array of peptide fragments for which diverse autocrine, paracrine, and endocrine activities have been demonstrated. CHGA measurements yield insight into the pathogenesis of such human diseases as essential hypertension, in which deficiency of the catecholamine release-inhibitory CHGA fragment catestatin may trigger sympathoadrenal overactivity as an aetiologic culprit in the syndrome. The CHGA dysglycaemic fragment pancreastatin is functional in humans in vivo, affecting both carbohydrate (glucose) and lipid (fatty acid) metabolism. Pancreastatin is cleaved from CHGA in hormone storage granules in vivo, and its plasma concentration varies in human disease. The pancreastatin region of CHGA gives rise to three naturally occurring human variants, one of which (Gly297Ser) occurs in the functionally important carboxy-terminus of the peptide, and substantially increases the peptide's potency to inhibit cellular glucose uptake. These observations establish a role for pancreastatin in human intermediary metabolism and disease, and suggest that qualitative hereditary alterations in pancreastatin's primary structure may give rise to interindividual differences in glucose disposition.

Biomedical issues of dietary fiber beta-glucan

Beta-glucan is a polysaccharide in the form of fiber and the main element of fiber in grains such as barley, oats, yeast and mushrooms. Many studies have examined the efficacy of beta-glucan in terms of the lipid lowering effects, blood sugar reduction, weight reduction, immune modulator, and anticarcinogenic effect. However, there is no comprehensive review article on the biomedical issues regarding beta-glucan. The authors searched for systematic reviews and clinical experiments for each relevant topic and reviewed the biomedical effects of beta-glucan, for the purpose of developing research strategies for the future.

WY 14,643 inhibits human aldose reductase activity

Aldose reductase (AR) is implicated to play a critical role in diabetes and cardiovascular complications because of the reaction it catalyzes. Our data reveal that peroxisome proliferator WY 14,643, follows a pure non-competitive inhibition pattern in the aldehyde reduction activity as well as in the alcohol oxidation activity of AR. This finding communicates for the first time a novel feature of WY 14,643 in regulating AR activity. In addition, this observation indicates that AR, AR-like proteins and aldo-keto reductase (AKR) members may be involved in the WY 14,643 mechanism of action when it is administered as PPAR agonist.

Exercise restores skeletal muscle glucose delivery but not insulin-mediated glucose transport and phosphorylation in obese subjects

CONTEXT/OBJECTIVE

Insulin resistance in obese subjects results in the impaired disposal of glucose by skeletal muscle. The current study examined the effects of insulin and/or exercise on glucose transport and phosphorylation in skeletal muscle and the influence of obesity on these processes.

SUBJECTS/METHODS

Seven obese and 12 lean men underwent positron emission tomography with 2-deoxy-2-[(18)F]fluoro-d-glucose in resting and isometrically exercising skeletal muscle during normoglycemic hyperinsulinemia. Data were analyzed by two-tissue compartmental modeling. Perfusion and oxidative capacity were measured during insulin stimulation by [15O]H2O and [15O]O2.

RESULTS

Exercise increased glucose fractional uptake (K), inward transport rate (K(1)), and the k(3) parameter, combining transport and intracellular phosphorylation, in lean and obese subjects. In each group, there was no statistically significant difference between plasma flow and K(1). At rest, a significant defect in K(1) (P = 0.0016), k(3) (P = 0.016), and K (P = 0.022) was found in obese subjects. Exercise restored K(1), improved but did not normalize K (P = 0.03 vs. lean), and did not ameliorate the more than 60% relative impairment in k(3) in obese individuals (P = 0.002 vs. lean). The glucose oxidative potential tended to be reduced by obesity.

CONCLUSIONS/INTERPRETATION

The study indicates that exercise restores the impairment in insulin-mediated skeletal muscle perfusion and glucose delivery associated with obesity but does not normalize the defect involving the proximal steps regulating glucose disposal in obese individuals. Our data support the use of 2-deoxy-2-[18F]fluoro-d-glucose-positron emission tomography in the dissection between substrate supply and intrinsic tissue metabolism.

The dry plant extract of common bean seed (Phaseoli vulgari pericarpium) does not have an affect on postprandial glycemia in healthy human subject

The aim of present study was to assess the effects and safety of a dry Phaseoli vulgari pericarpium (PVP) extract on postprandial glycemia in healthy participants. A randomized crossover experiment where participants received either PVP extract or placebo. Chemical compounds in dry extract were assessed by established methods. Eighteen healthy participants (9 male and 9 female) aged 29+/-4,8 years, body mass index (BMI) 23+/-3,7 kg/m(2) were recruited among students and staff at the Faculty of Pharmacy, University of Belgrade. All participants were able to follow the study protocol without difficulty. The participants received either PVP extract or placebo 30 minutes before a 50g oral glucose tolerance test (OGTT). The protocol followed the guidelines for the OGTT with blood samples drawn at 0, 15, 30, 60, 90 and 120 min. This study demonstrated that there was no significantly effect of the PVP extract on incremental blood glucose (IBG) and their areas under the curve (AUC) neither male nor female participants. However, IBG together with AUC changes were significantly lower in male compared with female participants in treated and untreated groups. The presence of chrome, soluble fiber, vitamin C, protein, glucose and lectins were also quantified. The applied amount of PVP extract was unable to produce the postprandial hypoglycemia. We assumed that amounts of chrome, soluble fiber, vitamin C which have beneficial effects on diabetes treatment were sufficient to produce hypoglycemia.

Hyperglycemia as an effect of cardiopulmonary bypass: intra-operative glucose management

Cardiopulmonary bypass (CPB) is associated with surgical stress, hypothermia, hyperoxia, enhancement of neuroendocrine outflow, and administration of glucogenic catecholamines that are associated with glucogonolysis and glucogenesis that result in hyperglycemia. The hyperglycemic state during CPB has been associated with adverse outcomes, such as infection, neurological impairment, cardiac dysfunction, prolonged hospitalization, and higher mortality rates. This report justifies vigilant monitoring of blood glucose levels and a rational protocol for the treatment of hyperglycemia of all open heart surgical patients that may improve post-CPB surgical outcomes.

Glucose and potassium derangements by glucose-insulin-potassium infusion in acute myocardial infarction

BACKGROUND

High-dose glucose-insulin-potassium infusion (GIK) has been suggested to be beneficial in acute myocardial infarction (MI). Recently new large trials have shown no effect of GIK on mortality. To investigate whether metabolic derangement could have negated the potential beneficial effect, we studied the relation between systemic glucose and potassium levels and outcome.

METHODS

Patients with signs and symptoms of ST-segment-elevation MI and treated with primary percutaneous coronary intervention (PCI) were randomised to no infusion or high-dose GIK, i.e. 80 mmol potassium chloride in 500 ml 20% glucose at a rate of 3 ml/kg/hour and 50 units short-acting insulin in 50 ml 0.9% sodium chloride for 12 hours.

RESULTS

A total of 6991 glucose values and 7198 potassium values were obtained in 476 GIK patients and 464 controls. Mean serum glucose was significantly higher in the GIK group (9.3±4.5 mmol/l vs. 8.4±2.9 mmol/l, p<0.001). Mean potassium level was significantly higher in the GIK group (4.2±0.5 mmol/l vs. 3.9±0.4 mmol/l, p<0.001). Incidence of hyperglycaemia (glucose >11.0 mmol/l) occurred in 70.8% of GIK patients and 33.8% of controls (p<0.001). Hypokalaemia was less common in the GIK group (23.5 vs. 41.2%, p<0.001). Incidence of hyperkalaemia and hypoglycaemia did not differ significantly between the two groups. In multivariate analysis age, previous cardiovascular disease, Killip class >1, unsuccessful PCI and mean glucose after admission were associated with increased one-year mortality.

CONCLUSION

In ST-segment-elevation MI patients treated with primary PCI, high-dose GIK induced hyperglycaemia and prevented hypokalaemia. Derangement of the glucose metabolism was related to one-year mortality.

Shell-less chick embryo culture as an alternative in vitro model to investigate glucose-induced malformations in mammalian embryos

We have developed a simple shell-less chick embryo culture system to study glucose-induced malformations. This system involves the culturing of chick embryos from the second day to the fifth day of incubation, with associated yolk and thick and thin albumen outside the egg shell. The system allows the observation of embryonic development of chicks in a glass bowl. Developing embryos at 24 h, 48 h and 72 h incubation, corresponding to the Hamberger Hamilton (HH) stages from 7 to 21, were treated with two concentrations of glucose (50 mM and 100 mM) for 24 h. Glucose treatment resulted in a mortality rate of over 70% in younger embryos. Furthermore, a variety of malformations such as retarded growth, abnormal heart development, macrosomia, exencephaly, etc. were observed in older embryos, which were similar to those reported in mammalian embryos as a consequence of diabetic pregnancy. The glucose-induced malformations were found to be concentration- and stage-dependent, thus emphasizing the roles of the degree of hyperglycemia and the stage of embryonic development in diabetic growth anomalies. Here we demonstrate for the first time that the present system can be used (i) for experiments at early stages of chick embryo development and (ii) for assessing the effects of acute glucose toxicity similar to those reported for mammalian embryos in a hyperglycemic environment.

Refractory hyperglycaemia induced by glucose-insulin-potassium infusion in acute myocardial infarction

BACKGROUND

Recent randomised clinical trials have not confirmed the beneficial effects of glucose-insulin-potassium (GIK) infusion observed in experimental models of myocardial ischaemia and infarction.

METHODS

We investigated glucose levels and insulin dose in 107 patients treated with reperfusion therapy and GIK for acute myocardial infarction.

RESULTS

Despite high insulin infusion rates, persistent hyperglycaemia occurred in 37% of the patients. These patients had significantly larger infarctions, as measured by enzyme release (p=0.006). In a multivariate model predicting high troponin levels, refractory hyperglycaemia remained a significant parameter (p=0.02).

CONCLUSION

These findings suggest that refractory hyperglycaemia caused by high-dose glucose infusion may, at least in part, explain the discrepancy between the experimental and clinical data.

Activation of the nuclear receptor FXR improves hyperglycemia and hyperlipidemia in diabetic mice

Farnesoid X receptor (FXR) plays an important role in maintaining bile acid and cholesterol homeostasis. Here we demonstrate that FXR also regulates glucose metabolism. Activation of FXR by the synthetic agonist GW4064 or hepatic overexpression of constitutively active FXR by adenovirus-mediated gene transfer significantly lowered blood glucose levels in both diabetic db/db and wild-type mice. Consistent with these data, FXR null mice exhibited glucose intolerance and insulin insensitivity. We further demonstrate that activation of FXR in db/db mice repressed hepatic gluconeogenic genes and increased hepatic glycogen synthesis and glycogen content by a mechanism that involves enhanced insulin sensitivity. In view of its central roles in coordinating regulation of both glucose and lipid metabolism, we propose that FXR agonists are promising therapeutic agents for treatment of diabetes mellitus.

Hyperkalemia revisited

Hyperkalemia is a common clinical condition that can induce deadly cardiac arrhythmias. Electrocardiographic manifestations of hyperkalemia vary from the classic sine-wave rhythm, which occurs in severe hyperkalemia, to nonspecific repolarization abnormalities seen with mild elevations of serum potassium. We present a case of hyperkalemia, initially diagnosed as ventricular tachycardia, to demonstrate how difficult hyperkalemia can be to diagnose. An in-depth review of hyperkalemia is presented, examining the electrophysiologic and electrocardiographic changes that occur as serum potassium levels increase. The treatment for hyperkalemia is then discussed, with an emphasis on the mechanisms by which each intervention lowers serum potassium levels. An extensive literature review has been performed to present a comprehensive review of the causes and treatment of hyperkalemia.

Septal co-infusions of glucose with a GABAB agonist impair memory

Septal infusions of glucose exacerbate memory deficits produced by co-infusions of drugs that increase gamma-aminobutyric acid (GABA)(A) receptor activity. To further understand the interaction between glucose and GABA, this experiment tested whether glucose would also potentiate spatial working memory deficits produced by septal infusions of the GABA(B) receptor agonist baclofen. Fifteen minutes prior to assessing spontaneous alternation (SA), male Sprague-Dawley derived rats were given septal infusions of vehicle, glucose (33 nmol), baclofen (0.1 nmol), or glucose combined with baclofen in one solution. Septal co-infusions of glucose with baclofen, at doses that individually had no effect, significantly impaired SA. Thus, the memory-impairing effects of glucose are observed with either GABA(A) or GABA(B) receptor ligands. This raises the possibility that glucose may impair memory by increasing synaptic levels of GABA and subsequent activation of these different receptor subtypes. These effects of glucose could contribute to the memory-impairing effects of hyperglycemia.

Transient hyperglycemia in Hispanic children with acute lymphoblastic leukemia

BACKGROUND

Transient hyperglycemia occurs commonly during the treatment for childhood acute lymphoblastic leukemia (ALL). The purpose of this study was to examine the incidence of and risk factors for transient hyperglycemia during induction chemotherapy in Hispanic pediatric patients diagnosed with B-Precursor ALL.

PROCEDURE

The study cohort consisted of 155 Hispanic pediatric patients diagnosed with ALL and treated at one of two South Texas pediatric oncology centers between 1993 and 2002. Hyperglycemia was defined as > or = 2 glucose determinations of > or = 200 mg/dl during the first 28 days of induction chemotherapy.

RESULTS

Overall, 11.0% of the study cohort developed transient hyperglycemia during induction chemotherapy. Age and body mass index (BMI) were both positively associated with the risk of hyperglycemia. Females exhibited a substantially higher risk of hyperglycemia than males, but this association did not reach statistical significance after adjusting for other covariates. Among patients who developed hyperglycemia, 100% of those who required insulin were in the 13-18-year age group and reported a family history of diabetes. Hyperglycemic patients classified as obese (BMI > or = 95 centile) were more than twice as likely to have required insulin therapy compared to overweight patients (BMI 85-<95 centile) and three times as likely to have required insulin compared to normal weight (BMI < 85 centile) patients.

CONCLUSIONS

The incidence of chemotherapy-induced transient hyperglycemia in the present study cohort is comparable to that reported in previous pediatric ALL patients. This finding is interesting in view of the elevated prevalence of obesity and the underlying dietary behaviors in this Hispanic study cohort.

Imaging and quantifying carbohydrate transport to the developing ovaries of maize

BACKGROUND AND AIMS

Shade or inadequate water can inhibit photosynthesis and limit the development of maize (Zea mays) ovaries around the time of pollination, potentially reducing the number of kernels at harvest. This study investigated whether the decreased photosynthesis diminished only the sugar supply or also altered the transport path to the ovaries.

METHODS

Photosynthesis and water potentials (Psiw) were measured in the leaves while dry matter delivery was monitored in the ovaries. Ovary glucose, starch and acid invertase activities were measured in situ. Stems were fed xylem-mobile safranin or phloem-mobile carboxyfluorescein (CF), and the dye transport to the ovaries was determined.

KEY RESULTS

Under normal conditions, the ovaries gained in dry mass, and starch accumulated in the pedicel and ovary wall. Glucose accumulated in the pedicel, apparently in the apoplast where insoluble (cell-wall-bound) acid invertase acted on the arriving sucrose. A glucose gradient developed from pedicel to nucellus. Safranin moved in the xylem and did not reach the ovary, but CF moved in the phloem and arrived at the ovary. CF also spread into the pedicel but unlike glucose it did not enter the nucellus. Low Psiw or shade decreased leaf photosynthesis, ovary dry mass accumulation, invertase activities, pedicel glucose, starch accumulation and CF delivery. Removal of these treatments reversed the effects.

CONCLUSIONS

The success of CF in tracing the general path and rate of carbohydrate transport gave visual evidence that phloem transport to the ovary decreased at low Psiw or in the shade but otherwise remained functional. The decreases indicated that losses in carbohydrate delivery are central features of failed ovary development under these conditions. The selectivity of transport into the nucellus resembled the situation later when embryo and endosperm are present and selective uptake occurs from the apoplast.

Doxazosin versus bendrofluazide: a comparison of the metabolic effects in British South Asians with hypertension

BACKGROUND

People from British South Asian communities have an increased risk of mortality from coronary heart disease (CHD). Doxazosin, a selective alpha(1)-adrenergic blocker, in addition to lowering blood pressure, has been shown to have positive effects on glucose metabolism and lipid profiles in patients with hypertension.

AIM

We studied doxazosin (1-8 mg) and bendrofluazide (2.5 mg) in patients of British South Asian origin with existing mild to moderate hypertension (doxazosin n = 78; bendrofluazide n = 82), to compare their effects on glucose and lipid metabolism in this group.

DESIGN OF STUDY

A 34-week randomised, double-blind, parallel-group, multicentre study.

SETTING

Primary care in the UK.

METHOD

All doxazosin patients started with an initial dose of 1 mg once daily, titrated to a maximum 8 mg once daily if diastolic blood pressure was >90 mmHg or was not <5 mmHg of the baseline value. The primary efficacy variables were mean glucose and total cholesterol concentrations at week 21.

RESULT

Doxazosin reduced glucose, total cholesterol, low-density lipoprotein-cholesterol and triglycerides and increased high-density lipoprotein-cholesterol. There were significant differences between doxazosin and bendrofluazide for glucose concentrations at week 21 (P = 0.029) and week 34 (P = 0.015), total cholesterol at week 21 (P = 0.048) and triglycerides at week 21 (P = 0.047) and week 34 (P = 0.009). There was no significant difference in blood pressure lowering between the two treatments.

CONCLUSION

Doxazosin exhibits beneficial effects on glucose concentrations and lipid profile, in particular in lowering triglyceride concentrations in British South Asians. Whether these desirable characteristics translate to improved overall cardiovascular risk requires formal evaluation.

Post-challenge hyperinsulinaemia rather than hyperglycaemia is associated with the severity of coronary artery disease in patients without a previous diagnosis of diabetes mellitus

OBJECTIVE

To ascertain the prevalence of abnormal glucose metabolism in patients with coronary artery disease (CAD) but no previous diagnosis of diabetes mellitus (DM) and to examine the relation between the severity of CAD and responses of glucose and insulin to the glucose tolerance test.

METHODS AND RESULTS

Abnormalities of glucose metabolism and insulin response were analysed in 144 patients with CAD without a previous diagnosis of DM who underwent both coronary arteriography and 75 g oral glucose tolerance test. The proportions of impaired and diabetic glucose tolerance were very high (39% for impaired and 21% for diabetic glucose tolerance); only 40% had normal glucose tolerance. The parameters of glucose metabolism were not associated with the number of diseased coronary arteries or the presence of previous myocardial infarction (MI). However, the insulin concentration at 60 minutes or 120 minutes after glucose challenge, insulin area, and the ratio of insulin to glucose area were significantly higher in patients with significant coronary stenosis and with previous MI. Fasting glucose concentration and most conventional risk factors did not predict post-challenge hyperinsulinaemia.

CONCLUSION

Patients with CAD without a previous diagnosis of DM had a high prevalence of abnormal glucose tolerance. Post-challenge hyperinsulinaemia was associated with the number of diseased coronary arteries and the presence of previous MI. The insulin response to the glucose challenge test requires further investigation as a potential risk factor for CAD and a potential target for intervention.

Potential beneficial mechanisms of insulin (glucose-potassium) in acute myocardial infarction

In the time-span of almost a century, a large amount of experimental evidence has been accumulated that underlines the importance of glucose metabolism during ischaemia/reperfusion of the heart. As early as 1912, Goulston suggested that treatment with glucose could be beneficial in several heart diseases. The first experimental results on the mechanical effects of insulin and glucose in the isolated heart were reported by Visscher and Muller in 1926. In 1935, Evans and colleagues showed that the uptake of glucose is increased in the ischaemic myocardium. Almost 30 years later, Sodi-Pallares and colleagues suggested that metabolic interference during myocardial ischaemia with GIK infusion decreased electrocardiographic signs of ischaemia. They also showed that glucose-insulin-potassium (GIK) infusion resulted in a lower occurrence of arrhythmias. They attributed this effect mainly to the influx of potassium in ischaemic cardiomyocytes. In order to further stimulate potassium transport into the cell, insulin was administered. Consequently, the rise of intercellular calcium is curtailed by the influx of potassium and so the incidence of arrhythmias is reduced. However, systemic infusion of insulin stimulates the uptake of glucose in many celltypes, which may result in hypoglycaemic episodes. Consequently, it is not possible to administer potassium and insulin in high concentrations without adding glucose. Interventions in the glucose metabolism in the clinical arena, whether or not used to correct acute hyperglycaemia, encompass three potentially effective elements: glucose, insulin and potassium.

Emergency interventions for hyperkalaemia

BACKGROUND

Hyperkalaemia occurs in outpatients and in between 1% and 10% of hospitalised patients. When severe, consequences include arrhythmia and death.

OBJECTIVES

To review randomised evidence informing the emergency (i.e. acute, rather than chronic) management of hyperkalaemia

SEARCH STRATEGY

We searched MEDLINE (1966-2003), EMBASE (1980-2003), The Cochrane Library (issue 4, 2003), and SciSearch using the text words hyperkal* or hyperpotass* (* indicates truncation). We also searched selected journals and abstracts of meetings. The reference lists of recent review articles, textbooks, and relevant papers were reviewed for additional potentially relevant titles.

SELECTION CRITERIA

All selection was performed in duplicate. Articles were considered relevant if they were randomised, quasi-randomised or cross-over randomised studies of pharmacological or other interventions to treat non-neonatal humans with hyperkalaemia, reporting on clinically-important outcomes, or serum potassium levels within the first six hours of administration.

DATA COLLECTION AND ANALYSIS

All data extraction was performed in duplicate. We extracted quality information, and details of the patient population, intervention, baseline and follow-up potassium values. We extracted information about arrhythmias, mortality and adverse effects. Where possible, meta-analysis was performed using random effects models.

MAIN RESULTS

None of the studies of clinically-relevant hyperkalaemia reported mortality or cardiac arrhythmias. Reports focussed on serum potassium levels. Many studies were small, and not all intervention groups had sufficient data for meta-analysis to be performed. On the basis of small studies, inhaled beta-agonists, nebulised beta-agonists, and intravenous (IV) insulin-and-glucose were all effective, and the combination of nebulised beta agonists with IV insulin-and-glucose was more effective than either alone. Dialysis is effective. Results were equivocal for IV bicarbonate. K-absorbing resin was not effective by four hours, and longer follow up data on this intervention were not available from RCTs.

AUTHORS' CONCLUSIONS

Nebulised or inhaled salbutamol, or IV insulin-and-glucose are the first-line therapies for the management of emergency hyperkalaemia that are best supported by the evidence. Their combination may be more effective than either alone, and should be considered when hyperkalaemia is severe. When arrhythmias are present, a wealth of anecdotal and animal data suggests that IV calcium is effective in treating arrhythmia. Further studies of the optimal use of combination treatments and of the adverse effects of treatments are needed.

Agglutination study of poly(allyl-alpha-D-glucopyranose/styrene) latex particles in the presence of Concanavalin A

Latex agglutination of the glucose-modified latex, which were synthesized by emulsion copolymerization of allyl-modified glucose and styrene monomers by specific binding interactions between Concanavalin A (Con A) and allyl-alpha-d-glucopyranose, were investigated. The surface of the glucose-modified latex was characterized by dye-partition method and the number of glucose was 1517 per latex particle. The average particle size and the polydispersity index of the latex were 78.3 and 1.005, respectively. Time-evolution adsorption behavior of various concentrations of the Con A and the consequent latex agglutination were studied by UV spectrophotometer at 540 nm and zeta-potential analyzer at the fixed latex concentration of 0.02 wt%. Specific binding between Con A and allyl-alpha-D-glucopyranose leaded the latex particles to coagulate by decreasing the electrostatic repulsion between the particles and mobility.

Extension growth of Impatiens glandulifera at low irradiance: importance of nitrate and potassium accumulation

BACKGROUND AND AIMS

The summer annual Impatiens glandulifera can reach 3 m in height within deciduous woodland. The primary objective was to determine if NO(3)(-) accumulation, and hence its osmotic effect, is an important physiological mechanism allowing Impatiens to achieve substantial height under low irradiance.

METHODS

Stem extension, concentrations of K(+) and NO(3)(-) in leaves and concentrations of K(+), NO(3)(-) and other inorganic anions, malate, sugars, total N and total osmoticum in stem were measured in I. glandulifera sampled at different irradiance levels in deciduous woodland and in a glasshouse. Also, the energetic costs, as absorbed photons, of generating osmolarity in stem cell vacuoles with KNO(3), K(2)malate or hexose sugar were determined.

KEY RESULTS

Results were similar in the woodland and glasshouse. At 50-100 % relative irradiance (Ir; open ground PAR = 100 % Ir) and 2-10 % Ir, plant height increased from 7-14 cm to 130-154 cm in 64-67 d. Leaf and stem NO(3)(-) concentrations were negligible at 50-100 % Ir while K(+), malate(2-) and sugars, respectively, accounted for 33.2-50.1 %, 19.3-20.8 % and 2.0-2.6 % of total osmoticum in stems. At 2-10 % Ir, NO(3)(-) concentrations were four to eight times greater in stems than leaves. Here, NO(3)(-) constituted 26.7-34.3 % of the total osmotic concentration in the stem and NO(3)(-)-N constituted 69-81 % of total N in stem tissue. Also at 2-10 % Ir, K(+) comprised 44.9-45.9 % and malate plus sugars 2.2-3.1 % of total osmotic concentration. The energy cost of osmoticum as KNO(3) was calculated as less than half that of malate and less than one-seventh that for hexose. Further calculations suggest that use of KNO(3), K(2)malate or glucose as osmoticum at low irradiance would, respectively, cost approx. 7 %, 16 % and 50 % of the total construction cost of the stem.

CONCLUSIONS

It is concluded that accumulation of NO(3)(-) in place of organic molecules in stems is an important mechanism allowing I. glandulifera to achieve substantial height at low irradiance.

Effect of nutrient deprivation on the viability of intervertebral disc cells

There is evidence that a fall in nutrient supply leads to disc degeneration but little understanding of the effects of nutrient deprivation on the physiology of disc cells which govern the composition of the disc. We examined the effects of changes in glucose and oxygen concentration and pH on the viability and metabolism of cells from bovine nucleus pulposus. Cells isolated from bovine discs and embedded in alginate beads were cultured under oxygen and glucose concentrations from zero to physiological levels and maintained at pH 7.4, pH 6.7, or pH 6.2 for up to 3 days. Interactions between nutrient concentrations were examined in relation to cell viability and lactic acid production. Cell viability was significantly reduced in the absence of glucose, with or without oxygen. Disc cells survived at 0% oxygen, provided that glucose was present, as seen previously. Cell viability decreased if the medium was acidic, more so when combined with low glucose concentrations. The rate of lactic acid production also fell as the pH became acidic and after 24 h or more at low glucose concentrations, but it did not appear to vary with oxygen concentration under the culture conditions used here. Glucose, rather than oxygen, appears to be the nutrient critical for maintaining disc cell viability. However, in an avascular tissue such as the disc, it is unlikely that glucose deprivation will occur alone; it will almost certainly correlate with a fall in oxygen concentration and pH. These results indicate that the combined nutrient and metabolite environment, rather than concentrations of any single nutrient, should be considered when studying cellular physiology in the disc.

New insights concerning the glucose-dependent insulin secretagogue action of glucagon-like peptide-1 in pancreatic beta-cells

The GLP-1 receptor is a Class B heptahelical G-protein-coupled receptor that stimulates cAMP production in pancreatic beta-cells. GLP-1 utilizes this receptor to activate two distinct classes of cAMP-binding proteins: protein kinase A (PKA) and the Epac family of cAMP-regulated guanine nucleotide exchange factors (cAMPGEFs). Actions of GLP-1 mediated by PKA and Epac include the recruitment and priming of secretory granules, thereby increasing the number of granules available for Ca(2+)-dependent exocytosis. Simultaneously, GLP-1 promotes Ca(2+) influx and mobilizes an intracellular source of Ca(2+). GLP-1 sensitizes intracellular Ca(2+) release channels (ryanodine and IP (3) receptors) to stimulatory effects of Ca(2+), thereby promoting Ca(2+)-induced Ca(2+) release (CICR). In the model presented here, CICR activates mitochondrial dehydrogenases, thereby upregulating glucose-dependent production of ATP. The resultant increase in cytosolic [ATP]/[ADP] concentration ratio leads to closure of ATP-sensitive K(+) channels (K-ATP), membrane depolarization, and influx of Ca(2+) through voltage-dependent Ca(2+) channels (VDCCs). Ca(2+) influx stimulates exocytosis of secretory granules by promoting their fusion with the plasma membrane. Under conditions where Ca(2+) release channels are sensitized by GLP-1, Ca(2+) influx also stimulates CICR, generating an additional round of ATP production and K-ATP channel closure. In the absence of glucose, no "fuel" is available to support ATP production, and GLP-1 fails to stimulate insulin secretion. This new "feed-forward" hypothesis of beta-cell stimulus-secretion coupling may provide a mechanistic explanation as to how GLP-1 exerts a beneficial blood glucose-lowering effect in type 2 diabetic subjects.

Insulin changes in preeclamptic women during pregnancy

BACKGROUND

The etiology of preeclampsia remains obscure. To study the role of insulin resistance in preeclampsia, we compared fasting insulin and glucose changes during the second and third trimesters in preeclamptic women with a normal control group.

PATIENTS AND METHODS

In a nested case-control study, subjects were selected from a population-based cohort of 674 pregnant women from whom serum was collected for this study between the 20th and 24th week of gestation. For 16 women who developed preeclampsia (cases), 16 women who remained normotensive were selected as controls. Controls were matched with each case for pregestational body mass index, age, gestational age, and parity. Fasting glucose and insulin levels of the second trimester (20th to 24th weeks) of pregnancy were compared based on serological data. The comparisons were also carried out in the third trimester when preeclampsia occurred.

RESULTS

Fasting insulin levels increased from 15.3+/-1.3 microlU/mL to 25.3+/-1.4 microlU/mL between the second and third trimesters in the preeclamptic group (P<0.01) and from 10.4+/-0.9 microlU/mL to 16.2+/-1.3 microlU/mL in the control group (P<0.01). There was no significant change in glucose levels during pregnancy in either group.

CONCLUSION

Women who develop preeclampsia have higher insulin levels before clinical evidence of disease than women who remain normotensive during pregnancy. The increase in insulin levels in the third trimester was greater in preeclamptic than in non-preeclamptic women.

Emotional arousal, blood glucose levels, and memory modulation: three laboratory exercises in cognitive neuroscience

The relationships between emotional arousal and cognition in humans represent an important field in cognitive neuroscience. Studies examining the characteristics of emotion-induced memory enhancement and the mechanisms through which these effects occur are becoming increasingly common. This article describes three affordable laboratory exercises of relevance to the growing interest in this field. Specifically, Experiment one reviews a protocol for examining memory, hypermnesia, reminiscence, and primacy/recency effects for emotional and neutral words. Experiments two and three provide opportunities to examine the relationships between blood glucose level and memory for either a list of pictures or the spatial location of pictures. Each laboratory exercise contains a certain amount of flexibility and is malleable to the specific needs of the instructor. For example, the use of blood glucose monitoring may be of value to a variety of different exercises examining stress and/or emotional arousal and the stimuli used in each of the protocols may be varied, creating opportunities for a number of different novel exercises. A series of questions have been provided at the end of each exercise in order to help stimulate inclass discussion. The potential application of this line of research in cognitive neuroscience is conveyed through a list of references where glucose has been used to attenuate cognitive deficits in Alzheimer's disease, age-related cognitive decline, and other neuropsychological conditions.

Complexation of polysaccharide and monosaccharide with thiolate boronic acid capped on silver nanoparticle

Synthesized thiolate boronic acid was found to complex with both a polysaccharide (dextran) and a monosaccharide (glucose) with similar affinities but displayed more affinity with dextran than with glucose when capped as a ligand on silver nanoparticle. Coupling on multiple sites of dextran, the silver particles were aggregated. The aggregated particles displayed a decrease of absorbance at 397 nm and an increase at 640 nm. Luminescence intensity displayed an upward deviation increase with the concentration of dextran. The luminescence spectral change was ascribed to surface-enhanced fluorescence by the enhanced field from the aggregated metallic particles.

Regulation of muscle glycogen repletion, muscle protein synthesis and repair following exercise

Recovery from prolonged strenuous exercise requires that depleted fuel stores be replenished, that damaged tissue be repaired and that training adaptations be initiated. Critical to these processes are the type, amount and timing of nutrient intake. Muscle glycogen is an essential fuel for intense exercise, whether the exercise is of an aerobic or anaerobic nature. Glycogen synthesis is a relatively slow process, and therefore the restoration of muscle glycogen requires special considerations when there is limited time between training sessions or competition. To maximize the rate of muscle glycogen synthesis it is important to consume a carbohydrate supplement immediately post exercise, to continue to supplement at frequent intervals and to consume approximately 1.2 g carbohydrate·kg(-1) body wt·h(-1). Maximizing glycogen synthesis with less frequent supplementation and less carbohydrate can be achieved with the addition of protein to the carbohydrate supplement. This will also promote protein synthesis and reduce protein degradation, thus having the added benefit of stimulating muscle tissue repair and adaptation. Moreover, recent research suggests that consuming a carbohydrate/protein supplement post exercise will have a more positive influence on subsequent exercise performance than a carbohydrate supplement. Key PointsFor rapid recovery from prolonged exercise, it is important to replenish muscle glycogen stores and initiate muscle tissue repair and adaptation.To maximize muscle glycogen replenishment, it is important to consume a carbohydrate supplement as soon after exercise as possible.Consume the carbohydrate frequently, such as every 30 minutes, and provide about 1.2 to 1.5 g of carbohydrate·kg(-1) body wt·h(-1).Efficiency of muscle glycogen storage can be increased significantly with the addition of protein to a carbohydrate supplement (~4 to 1 carbohydrate to protein ratio).The addition of protein to a carbohydrate supplement also has the added advantage of limiting post exercise muscle damage and promoting muscle protein accretion.

Glucose localization in maize ovaries when kernel number decreases at low water potential and sucrose is fed to the stems

BACKGROUND AND AIMS

Around the time of anthesis, young ovary development in maize (Zea mays) is vulnerable to 2 or 3 d of water deficits that inhibit photosynthesis. Abortion can result, and fewer kernels are produced. A breakdown of stored ovary starch is associated with the abortion and was investigated in the present study by localizing the breakdown product glucose in the ovaries.

METHODS

Ovary glucose was localized with fluorescent Resorufin. Insoluble invertase was localized in vivo and soluble invertase in situ. Sucrose was infused into the stems to vary the sugar flux to the ovaries.

KEY RESULTS

At high water potential (high Psi(w)), photosynthesis was rapid in the parent. The upper pedicel of the ovaries had a high activity of insoluble acid invertase and a large amount of glucose and starch. Because the invertase was wall-bound, sucrose hydrolysis appeared to occur in the pedicel apoplast. Soluble invertase was undetected inside the pedicel cells but was present in the nucellus cells where low concentrations of glucose occurred. This created a glucose gradient between pedicel and nucellus that favoured glucose uptake by the developing ovary. At low Psi(w), photosynthesis was inhibited, pedicel glucose and starch were depleted, the glucose gradient became negligible, and abortion occurred. When sucrose was fed, glucose, starch and the glucose gradient were maintained somewhat and were normally distributed in the ovaries. Abortion was diminished.

CONCLUSIONS

The apoplast hydrolysis of sucrose unloaded from phloem is similar to that described by others during later development when embryo and endosperm are present and separated from the parent by an apoplast. The disappearance of the glucose gradient at low Psi(w) may have inhibited glucose movement into the ovary. The low glucose in the ovaries may have a role in the abortion response.

High glucose blocks the effects of estradiol on human vascular cell growth: differential interaction with estradiol and raloxifene

Because diabetic women appear not to be protected by estrogen in terms of propensity to cardiovascular disease, we tested the possibility that chronic hyperglycemia modulates the effects of E(2) on vascular cell growth in vitro. Human endothelial cells (E304) and vascular smooth muscle cells (VSMC) were grown in normal glucose (5.5 mmol/l), high glucose (22 mmol/l) or high manitol (22 nmol/l; an osmotic control) for 7 days. In endothelial cells glucose per se stimulated DNA synthesis. However E(2)- (but not RAL-) stimulated [3H] thymidine incorporation was attenuated in the presence of high glucose. In parallel, E(2)-dependent MAP-kinase-kinase activity was blocked in the presence of high glucose. High glucose increased basal creatine kinase (CK) specific activity, but E(2)-stimulated CK was not significantly impaired in the presence of high glucose. In VSMC, high glucose prevented the inhibitory effect of high E(2) (but not of high RAL) concentrations on DNA synthesis. High glucose also prevented E(2)-induced MAP-kinase-kinase activity. In contrast, while high glucose augmented basal CK, the relative E(2)-induced changes were roughly equal in normal and high high glucose media. Hence, high glucose blocks several effects of E(2) on vascular cell growth, which are mediated, in part, via the MAP-kinase system and are likely contributors to E(2)'s anti-atherosclerotic properties. Since RAL's estrogen-mimetic effects on human vascular cell growth were independent of MAP-kinase activation and were not affected by hyperglycemia, the potential use of RAL to circumvent the loss of estrogen function induced by hyperglycemia and diabetes in the human vasculature should be further explored.

Hypoglycemic neuronal death and cognitive impairment are prevented by poly(ADP-ribose) polymerase inhibitors administered after hypoglycemia

Severe hypoglycemia causes neuronal death and cognitive impairment. Evidence suggests that hypoglycemic neuronal death involves excitotoxicity and DNA damage. Poly(ADP-ribose) polymerase-1 (PARP-1) normally functions in DNA repair, but promotes cell death when extensively activated by DNA damage. Cortical neuron cultures were subjected to glucose deprivation to assess the role of PARP-1 in hypoglycemic neuronal death. PARP-1-/- neurons and wild-type, PARP-1+/+ neurons treated with the PARP inhibitor 3,4-dihydro-5-[4-(1-piperidinyl)butoxy]-1(2H)-isoquinolinone both showed increased resistance to glucose deprivation. A rat model of insulin-induced hypoglycemia was used to assess the therapeutic potential of PARP inhibitors after hypoglycemia. Rats subjected to severe hypoglycemia (30 min EEG isoelectricity) accumulated both nitrotyrosine and the PARP-1 product, poly(ADP-ribose), in vulnerable neurons. Treatment with PARP inhibitors immediately after hypoglycemia blocked production of poly(ADP-ribose) and reduced neuronal death by >80% in most brain regions examined. Increased neuronal survival was also achieved when PARP inhibitors were administered up to 2 hr after blood glucose correction. Behavioral and histological assessments performed 6 weeks after hypoglycemia confirmed a sustained salutary effect of PARP inhibition. These results suggest that PARP-1 activation is a major factor mediating hypoglycemic neuronal death and that PARP-1 inhibitors can rescue neurons that would otherwise die after severe hypoglycemia.

Signaling at the gliovascular interface

Advances in fluorescent calcium indicating dyes over the past decade have identified calcium signaling as the tool by which astrocytes communicate among themselves and with neighboring neurons. Studies of astrocyte-neuron interactions have shown that calcium signaling is a potent modulator of the strength of both excitatory and inhibitory synapses. The concept that astrocytes possess a mechanism for rapid cell communication has not been incorporated, however, into the supportive functions of astrocytes. Because many of the classical tasks of astrocytes are linked to the blood-brain barrier, we have here examined the expression of proteins required for calcium signaling in their vascular end-foot processes. The gap junction protein, Cx43, was expressed intensively around the vessels interconnecting astrocytic end-foot processes. These gap junctions permitted diffusion of Lucifer yellow, specifically along the path of glial end feet apposed to the vessel wall. The purinergic receptors, P2Y(2) and P2Y(4), were also strongly expressed at the gliovascular interface and colocalized with GFAP around larger vessels in cortex. Multiphoton imaging of freshly prepared brain slices loaded with Fluo-4/AM revealed that ATP mobilized cytosolic calcium in astrocytic end feet, whereas electrical stimulation triggered calcium waves propagating along the vessel wall. Brain endothelial cells and pericytes were physically separated from astrocytes by the basal lamina and responded only weakly to ATP. These observations identify astrocytic end-foot processes plastered at the vessel wall as a center for purinergic signaling. It is speculated that calcium signaling may play a role in astrocytic functions related to the blood-brain barrier, including blood flow regulation, metabolic trafficking, and water homeostasis.

Localized in vivo 13C NMR spectroscopy of the brain

Localized (13)C NMR spectroscopy provides a new investigative tool for studying cerebral metabolism. The application of (13)C NMR spectroscopy to living intact humans and animals presents the investigator with a number of unique challenges. This review provides in the first part a tutorial insight into the ingredients required for achieving a successful implementation of localized (13)C NMR spectroscopy. The difficulties in establishing (13)C NMR are the need for decoupling of the one-bond (13)C-(1)H heteronuclear J coupling, the large chemical shift range, the low sensitivity and the need for localization of the signals. The methodological consequences of these technical problems are discussed, particularly with respect to (a) RF front-end considerations, (b) localization methods, (c) the low sensitivity, and (d) quantification methods. Lastly, some achievements of in vivo localized (13)C NMR spectroscopy of the brain are reviewed, such as: (a) the measurement of brain glutamine synthesis and the feasibility of quantifying glutamatergic action in the brain; (b) the demonstration of significant anaplerotic fluxes in the brain; (c) the demonstration of a highly regulated malate-aspartate shuttle in brain energy metabolism and isotope flux; (d) quantification of neuronal and glial energy metabolism; and (e) brain glycogen metabolism in hypoglycemia in rats and humans. We conclude that the unique and novel insights provided by (13)C NMR spectroscopy have opened many new research areas that are likely to improve the understanding of brain carbohydrate metabolism in health and disease.

The involvement of glucose metabolism in the regulation of inducible nitric oxide synthase gene expression in glial cells: possible role of glucose-6-phosphate dehydrogenase and CCAAT/enhancing binding protein

In rat glial cells the lipopolysaccharide (LPS)-induced inducible nitric oxide synthase (iNOS) gene expression was enhanced by extracellular glucose concentration in a dose-dependent manner. On the other hand, 2-deoxy-d-glucose decreased the LPS-induced iNOS gene expression even in the presence of glucose (6 gm/l), suggesting that glucose metabolism is linked to the regulation of iNOS gene expression. The intracellular NADPH/NADP+ directly correlated with the extracellular glucose concentration, and the reduction of NADPH generation via a block of glucose-6-phosphate dehydrogenase (G6PD) by treatment with dehydroepiandrosterone or the antisense DNA oligomer of G6PD mRNA resulted in the inhibition of iNOS gene expression. Gel shift assays showed that CAAT/enhancing binding protein (C/EBP), rather than AP-1 or NF-kappaB, correlated better with a glucose-dependent increase in iNOS gene expression. The induction of C/EBP DNA binding activity by LPS and glucose was attributable mainly to the increase in C/EBP-delta protein. The cotransfection with wild-type C/EBP-delta increased the iNOS promoter activity to the level achieved with a higher glucose concentration in the presence of LPS. Therefore, our results suggest that C/EBP-delta may be a critical mediator in glucose-mediated regulation of iNOS gene expression.

Glutamate triggers rapid glucose transport stimulation in astrocytes as evidenced by real-time confocal microscopy

Glutamate stimulates glycolysis in astrocytes, a phenomenon that couples astrocytic metabolism with neuronal activity. However, it is not known whether glutamate also affects glucose transporter-1 (GLUT1), the transporter responsible for glucose entry into astrocytes. To address this question, two different real-time single-cell hexose uptake assays were applied to cultured hippocampal astrocytes using confocal epifluorescence microscopy. Glutamate caused a twofold to threefold increase in the zero-trans uptake rates of the fluorescent hexoses 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxyglucose (2-NBDG) and 6-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-6-deoxyglucose (6-NBDG). Galactose uptake, determined by the calcein volumetric assay, was stimulated to a similar extent, confirming the fluorescent hexose data, and also demonstrating that glutamate stimulation is a Vmax effect. Remarkably, glucose transport stimulation developed fully inside 10 sec, which is 100 times faster than acute stimulations of glucose transport in other cell types. Glutamate did not significantly affect the rate of 6-NBDG uptake by GLUT1-expressing epithelial Clone 9 cells, suggesting that an astrocyte-specific factor is required for transport stimulation. We conclude that glucose transport stimulation occurs early during astrocytic activation by glutamate, which provides a novel regulatory node to current models of brain energy metabolism. This mechanism should also be considered for the interpretation of functional imaging data based on hexoses.

Energy contribution of octanoate to intact rat brain metabolism measured by 13C nuclear magnetic resonance spectroscopy

Glucose is the dominant oxidative fuel for brain, but studies have indicated that fatty acids are used by brain as well. We postulated that fatty acid oxidation in brain could contribute significantly to overall energy usage and account for non-glucose-derived energy production. [2,4,6,8-13C4]octanoate oxidation in intact rats was determined by nuclear magnetic resonance spectroscopy. We found that oxidation of 13C-octanoate in brain is avid and contributes approximately 20% to total brain oxidative energy production. Labeling patterns of glutamate and glutamine were distinct, and analysis of these metabolites indicated compartmentalized oxidation of octanoate in brain. Examination of liver and blood spectra revealed that label from 13C-octanoate was incorporated into glucose and ketones, which enabled calculation of its overall energy contribution to brain metabolism: glucose (predominantly unlabeled) and 13C-labeled octanoate can account for the entire oxidative metabolism of brain. Additionally, flux through anaplerotic pathways relative to tricarboxylic acid cycle flux (Y) was calculated to be 0.08 +/- 0.039 in brain, indicating that anaplerotic flux is significant and should be considered when assessing brain metabolism. Y was associated with the glutamine synthesis compartment, consistent with the view that anaplerotic flux occurs primarily in astrocytes.

Glucose-insulin-potassium infusion in sepsis and septic shock: no hard evidence yet

There is no hard evidence yet for a positive effect of glucose–insulin–potassium infusion in sepsis, septic shock or burn patients. Each individual element of the glucose–insulin–potassium regimen, and eventually euglycaemia, should theoretically be beneficial. At present, evidence exists only for reduced mortality with strict metabolic treatment (i.e. blood glucose levels of 4.4–6.1 mmol/l) in critically ill patients admitted to surgical intensive care units, and for better metabolic regulation (i.e. blood glucose levels of 7.0–10.0 mmol/l) in patients with hyperglycaemia and/or diabetes mellitus, and in patients without signs of heart failure (i.e. Killip class I) during acute myocardial infarction.

Charge transfer fluorescent probes using boronic acids for monosaccharide signaling

We have developed a new series of glucose sensitive fluorophores that display shifts in emission wavelengths and/or intensity change upon the binding of monosaccharides. Complexation of glucose with the boronic acid moiety changes both its orbital hybridization and its ability to accept and donate electrons. This change results in distinct emission spectra for the fluorophores when free in solution or complexed with monosaccharide. The spectral changes upon saccharide binding can be modified by substitution of electron donor or acceptor group on the fluorophore allowing rational design of the spectral response.