Na+-dependent and phlorizin-inhibitable transport of glucose and cycasin in brain endothelial cells

Western Pacific ALS-PDC: Evidence implicating cycad genotoxins

Amyotrophic Lateral Sclerosis and Parkinsonism-Dementia Complex (ALS-PDC) is a disappearing neurodegenerative disorder of apparent environmental origin formerly hyperendemic among Chamorros of Guam-USA, Japanese residents of the Kii Peninsula, Honshu Island, Japan and Auyu-Jakai linguistic groups of Papua-Indonesia on the island of New Guinea. The most plausible etiology is exposure to genotoxins in seed of neurotoxic cycad plants formerly used for food and/or medicine. Primary suspicion falls on methylazoxymethanol (MAM), the aglycone of cycasin and on the non-protein amino acid β-N-methylamino-L-alanine, both of which are metabolized to formaldehyde. Human and animal studies suggest: (a) exposures occurred early in life and sometimes during late fetal brain development, (b) clinical expression of neurodegenerative disease appeared years or decades later, and (c) pathological changes in various tissues indicate the disease was not confined to the CNS. Experimental evidence points to toxic molecular mechanisms involving DNA damage, epigenetic changes, transcriptional mutagenesis, neuronal cell-cycle reactivation and perturbation of the ubiquitin-proteasome system that led to polyproteinopathy and culminated in neuronal degeneration. Lessons learned from research on ALS-PDC include: (a) familial disease may reflect common toxic exposures across generations, (b) primary disease prevention follows cessation of exposure to culpable environmental triggers; and (c) disease latency provides a prolonged period during which to intervene therapeutically. Exposure to genotoxic chemicals ("slow toxins") in the early stages of life should be considered in the search for the etiology of ALS-PDC-related neurodegenerative disorders, including sporadic forms of ALS, progressive supranuclear palsy and Alzheimer's disease.

Sodium-glucose cotransporter-2 inhibitors: Understanding the mechanisms for therapeutic promise and persisting risks

In a healthy person, the kidney filters nearly 200 g of glucose per day, almost all of which is reabsorbed. The primary transporter responsible for renal glucose reabsorption is sodium-glucose cotransporter-2 (SGLT2). Based on the impact of SGLT2 to prevent renal glucose wasting, SGLT2 inhibitors have been developed to treat diabetes and are the newest class of glucose-lowering agents approved in the United States. By inhibiting glucose reabsorption in the proximal tubule, these agents promote glycosuria, thereby reducing blood glucose concentrations and often resulting in modest weight loss. Recent work in humans and rodents has demonstrated that the clinical utility of these agents may not be limited to diabetes management: SGLT2 inhibitors have also shown therapeutic promise in improving outcomes in heart failure, atrial fibrillation, and, in preclinical studies, certain cancers. Unfortunately, these benefits are not without risk: SGLT2 inhibitors predispose to euglycemic ketoacidosis in those with type 2 diabetes and, largely for this reason, are not approved to treat type 1 diabetes. The mechanism for each of the beneficial and harmful effects of SGLT2 inhibitors-with the exception of their effect to lower plasma glucose concentrations-is an area of active investigation. In this review, we discuss the mechanisms by which these drugs cause euglycemic ketoacidosis and hyperglucagonemia and stimulate hepatic gluconeogenesis as well as their beneficial effects in cardiovascular disease and cancer. In so doing, we aim to highlight the crucial role for selecting patients for SGLT2 inhibitor therapy and highlight several crucial questions that remain unanswered.

An Early Fecal Microbiota Transfer Improves the Intestinal Conditions on Microflora and Immunoglobulin and Antimicrobial Peptides in Piglets

The goal of this study was to investigate the effects of early fecal microbial transfer (FMT) on the microflora of recipient piglets, where Yorkshire newborn piglets and Min sows (an indigenous pig breed in China) were used as the fecal recipients and donors, respectively, to reveal the changes in immunity and development-related functions of the intestinal mucosa driven by FMT. The recipient group was inoculated with fecal microbial fluids from days 1 to 10. On day 21, the relative abundance of the Proteobacteria was reduced; the concentrations of immunoglobulin M (IgM) and immunoglobulin G (IgG) in the jejunal mucosa, and that of IgG in the ileal mucosa of the recipient group, were increased (P < 0.05). On day 40, the relative abundance of the Firmicutes in the recipient group was increased, while that of Bacteroides was decreased. The concentrations of IgG and IgM in the ileal mucosa of the recipient group were increased. FMT protected the intestine by modulating the antimicrobial peptides of the intestinal mucosa (P < 0.05). The results of this study revealed that early FMT can improve the gut microbiota, intestinal mucosal immunity, and intestinal development-related functions of Yorkshire piglets.

Activation of c-Jun N-terminal kinase and p38 after cerebral ischemia upregulates cerebral sodium-glucose transporter type 1

Cerebral ischemic stress increases cerebral sodium-glucose transporter type 1 (SGLT-1). However, the mechanism by which cerebral ischemia leads to the up-regulation of SGLT-1 remains unclear. In peripheral tissue, the activation of mitogen-activated protein kinases (MAPKs) increases SGLT-1. MAPK pathways [c-Jun N-terminal kinase (JNK), p38 MAPK, and extracellular signal-regulated protein kinase (ERK)] are activated by cerebral ischemic stress. Therefore, we confirmed the involvement of MAPKs in the up-regulation of cerebral SGLT-1 after cerebral ischemia. Male ddY mice were subjected to middle cerebral artery occlusion (MCAO). Protein expression was assessed by western blotting. Mice received an intracerebroventricular (i.c.v.) injection of SP600125 (JNK inhibitor), SB203580 (p38 inhibitor), and PD98059 (MEK inhibitor) immediately after reperfusion. The infarction and behavioral abnormalities were assessed on days 1 and 3 after MCAO. The MAPK inhibitors suppressed the activation of JNK, p38, and ERK 3 h after MCAO. SP600125 and SB203580 administration ameliorated cerebral ischemic neuronal damage, whereas PD98059 administration exacerbated cerebral ischemic neuronal damage. SP600125 and SB203580 significantly suppressed the increase in SGLT-1 12 h after MCAO. PD98059 had no effect on SGLT-1 expression after MCAO. Our results indicate that the activation of JNK and p38 participate in the up-regulation of cerebral SGLT-1 after MCAO.

[Potential of the Cerebral Sodium-Glucose Transporter as a Novel Therapeutic Target in Cerebral Ischemia]

　Cerebral ischemic stress often induces a hyperglycemic condition. This postischemic hyperglycemia exacerbates the development of cerebral ischemic neuronal damage, although the mechanism of this exacerbation remains to be clarified. We previously discovered that the cerebral sodium-glucose transporter (SGLT) was closely involved in the development of cerebral ischemic neuronal damage. SGLT is a member of the glucose transporter family and moves glucose together with sodium ions. SGLT-1, -3, -4, and -6 are distributed in the brain. We conducted further experiments to elucidate the detailed mechanism of the exacerbation of cerebral ischemia by cerebral SGLT. The results clarified: 1) the relationship between cerebral SGLT and postischemic hyperglycemia; 2) the involvement of cerebral SGLT-1 (a cerebral SGLT isoform) in cerebral ischemic neuronal damage; and 3) the effects of sodium influx through cerebral SGLT on the development of cerebral ischemic neuronal damage. This paper presents our data on the involvement of cerebral SGLT in the exacerbation of cerebral ischemic neuronal damage.

Sodium-glucose transporter as a novel therapeutic target in disease

Glucose is the primary energy fuel of life. A glucose transporter, the sodium-glucose transporter (SGLT), is receiving attention as a novel therapeutic target in disease. This review summarizes the physiological role of SGLT in cerebral ischemia, cancer, cardiac disease, and intestinal ischemia, which has encouraged analysis of SGLT function. In cerebral ischemia and cardiomyopathy, SGLT-1 is involved in worsening of the injury. In addition, SGLT-1 promotes the development of cancer. On the other hand, SGLT-1 has a protective effect against cardiac and intestinal ischemia. Interestingly, SGLT-1 expression levels are increased in some diseased tissue, such as in cerebral ischemia and cancer. This suggests that SGLT-1 may have an important role in many diseases. This review discusses the potential of SGLT as a target for novel therapeutic agents.

Activation of cerebral sodium-glucose transporter type 1 function mediated by post-ischemic hyperglycemia exacerbates the development of cerebral ischemia

The regulation of post-ischemic hyperglycemia plays an important role in suppressing neuronal damage in therapeutic strategies for cerebral ischemia. We previously reported that the cerebral sodium-glucose transporter (SGLT) was involved in the post-ischemic hyperglycemia-induced exacerbation of cerebral ischemic neuronal damage. Cortical SGLT-1, one of the cerebral SGLT isoforms, is dramatically increased by focal cerebral ischemia. In this study, we focused on the involvement of cerebral SGLT-1 in the development of cerebral ischemic neuronal damage. It was previously reported that activation of 5'-adenosine monophosphate-activated protein kinase (AMPK) increases SGLT-1 expression. Moreover, ischemic stress-induced activation of AMPK exacerbates cerebral ischemic neuronal damage. Therefore, we directly confirmed the relationship between cerebral SGLT-1 and cerebral AMPK activation using in vitro primary culture of mouse cortical neurons. An in vivo mouse model of focal cerebral ischemia was generated using a middle cerebral artery occlusion (MCAO). The development of infarct volume and behavioral abnormalities on day 3 after MCAO were ameliorated in cerebral SGLT-1 knock down mice. Cortical and striatal SGLT-1 expression levels were significantly increased at 12h after MCAO. Immunofluorescence revealed that SGLT-1 and the neuronal nuclear antigen (NeuN) were co-localized in the cortex and striatum of MCAO mice. In the in vitro study, primary cortical neurons were cultured for five days before each treatment with reagents. Concomitant treatment with hydrogen peroxide and glucose induced the elevation of SGLT-1 and phosphorylated AMPK/AMPK ratio, and this elevation was suppressed by compound C, an AMPK inhibitor in primary cortical neurons. Moreover, compound C suppressed neuronal cell death induced by concomitant hydrogen peroxide/glucose treatment in primary cortical neurons. Therefore, we concluded that enhanced cerebral SGLT-1 function mediated by post-ischemic hyperglycemia exacerbates the development of cerebral ischemic neuronal damage. One of the mechanisms of cerebral SGLT-1 up-regulation may be involved in the AMPK activation after cerebral ischemia.

Animal models of brain maldevelopment induced by cycad plant genotoxins

Cycads are long-lived tropical and subtropical plants that contain azoxyglycosides (e.g., cycasin, macrozamin) and neurotoxic amino acids (notably β-N-methylamino-l-alanine l-BMAA), toxins that have been implicated in the etiology of a disappearing neurodegenerative disease, amyotrophic lateral sclerosis and parkinsonism-dementia complex that has been present in high incidence among three genetically distinct populations in the western Pacific. The neuropathology of amyotrophic lateral sclerosis/parkinsonism-dementia complex includes features suggestive of brain maldevelopment, an experimentally proven property of cycasin attributable to the genotoxic action of its aglycone methylazoxymethanol (MAM). This property of MAM has been exploited by neurobiologists as a tool to study perturbations of brain development. Depending on the neurodevelopmental stage, MAM can induce features in laboratory animals that model certain characteristics of epilepsy, schizophrenia, or ataxia. Studies in DNA repair-deficient mice show that MAM perturbs brain development through a DNA damage-mediated mechanism. The brain DNA lesions produced by systemic MAM appear to modulate the expression of genes that regulate neurodevelopment and contribute to neurodegeneration. Epigenetic changes (histone lysine methylation) have also been detected in the underdeveloped brain after MAM administration. The DNA damage and epigenetic changes produced by MAM and, perhaps by chemically related substances (e.g., nitrosamines, nitrosoureas, hydrazines), might be an important mechanism by which early-life exposure to genotoxicants can induce long-term brain dysfunction.

Regional distribution of SGLT activity in rat brain in vivo

Na(+)-glucose cotransporter (SGLT) mRNAs have been detected in many organs of the body, but, apart from kidney and intestine, transporter expression, localization, and functional activity, as well as physiological significance, remain elusive. Using a SGLT-specific molecular imaging probe, α-methyl-4-deoxy-4-[(18)F]fluoro-D-glucopyranoside (Me-4-FDG) with ex vivo autoradiography and immunohistochemistry, we mapped in vivo the regional distribution of functional SGLTs in rat brain. Since Me-4-FDG is not a substrate for GLUT1 at the blood-brain barrier (BBB), in vivo delivery of the probe into the brain was achieved after opening of the BBB by an established procedure, osmotic shock. Ex vivo autoradiography showed that Me-4-FDG accumulated in regions of the cerebellum, hippocampus, frontal cortex, caudate nucleus, putamen, amygdala, parietal cortex, and paraventricular nucleus of the hypothalamus. Little or no Me-4-FDG accumulated in the brain stem. The regional accumulation of Me-4-FDG overlapped the distribution of SGLT1 protein detected by immunohistochemistry. In summary, after the BBB is opened, the specific substrate for SGLTs, Me-4-FDG, enters the brain and accumulates in selected regions shown to express SGLT1 protein. This localization and the sensitivity of these neurons to anoxia prompt the speculation that SGLTs may play an essential role in glucose utilization under stress such as ischemia. The expression of SGLTs in the brain raises questions about the potential effects of SGLT inhibitors under development for the treatment of diabetes.

Addition of NMDA-receptor antagonist MK801 during oxygen/glucose deprivation moderately attenuates the upregulation of glucose uptake after subsequent reoxygenation in brain endothelial cells

During stroke the blood-brain barrier (BBB) is damaged which can result in vasogenic brain edema and inflammation. The reduced blood supply leads to decreased delivery of oxygen and glucose to affected areas of the brain. Oxygen and glucose deprivation (OGD) can cause upregulation of glucose uptake of brain endothelial cells. In this letter, we investigated the influence of MK801, a non-competitive inhibitor of the NMDA-receptor, on the regulation of the glucose uptake and of the main glucose transporters glut1 and sglt1 in murine BBB cell line cerebEND during OGD. mRNA expression of glut1 was upregulated 68.7-fold after 6h OGD, which was significantly reduced by 10μM MK801 to 28.9-fold. Sglt1 mRNA expression decreased during OGD which was further reduced by MK801. Glucose uptake was significantly increased up to 907% after 6h OGD and was still higher (210%) after the 20h reoxygenation phase compared to normoxia. Ten micromolar MK801 during OGD was able to reduce upregulated glucose uptake after OGD and reoxygenation significantly. Presence of several NMDAR subunits was proven on the mRNA level in cerebEND cells. Furthermore, it was shown that NMDAR subunit NR1 was upregulated during OGD and that this was inhibitable by MK801. In conclusion, the addition of MK801 during the OGD phase reduced significantly the glucose uptake after the subsequent reoxygenation phase in brain endothelial cells.

Functional expression of SGLTs in rat brain

This work provides evidence of previously unrecognized uptake of glucose via sodium-coupled glucose transporters (SGLTs) in specific regions of the brain. The current understanding of functional glucose utilization in brain is largely based on studies using positron emission tomography (PET) with the glucose tracer 2-deoxy-2-[F-18]fluoro-D-glucose (2-FDG). However, 2-FDG is only a good substrate for facilitated-glucose transporters (GLUTs), not for SGLTs. Thus, glucose accumulation measured by 2-FDG omits the role of SGLTs. We designed and synthesized two high-affinity tracers: one, α-methyl-4-[F-18]fluoro-4-deoxy-D-glucopyranoside (Me-4FDG), is a highly specific SGLT substrate and not transported by GLUTs; the other one, 4-[F-18]fluoro-4-deoxy-D-glucose (4-FDG), is transported by both SGLTs and GLUTs and will pass through the blood brain barrier (BBB). In vitro Me-4FDG autoradiography was used to map the distribution of uptake by functional SGLTs in brain slices with a comparable result from in vitro 4-FDG autoradiography. Immunohistochemical assays showed that uptake was consistent with the distribution of SGLT protein. Ex vivo 4-FDG autoradiography showed that SGLTs in these areas are functionally active in the normal in vivo brain. The results establish that SGLTs are a normal part of the physiology of specific areas of the brain, including hippocampus, amygdala, hypothalamus, and cerebral cortices. 4-FDG PET imaging also established that this BBB-permeable SGLT tracer now offers a functional imaging approach in humans to assess regulation of SGLT activity in health and disease.

Decomposition of α-Tocopheryl Glycosides in Rat Tissues

Background

The aim of our investigation was to estimate the stability of α-tocopheryl O-glycosides in relation to activity of exoglycosidases in selected rat tissues.

Material and Methods

Acetylated glycosides were obtained in glucosidation of α-tocopherol using the Helferich method. The activity of exoglycosidases was determined by the Zwierz et al. method. Protein concentrations were determined by the biuret method. The concentration of released α-tocopherol was determined with the HPLC method.

Results

The comparison of the amount of released α-tocopherol with the amount of released p-nitrophenol shows that glycoside bound in 2a–5a derivatives of α-tocopherol undergoes hydrolysis significantly harder than in appropriate 2b–5bp-nitrophenyl derivatives.

Conclusion

The results indicate that tocopheryl O-glycosides are more resistant to enzymatic hydrolysis than appropriate p-nitrophenol O-glycosides 2a–5a. Among examined tocopheryl O-glycosides, galactoside 4 is the only compound that caused the significant increase in tocopherol concentration, as compared to its endogenic content.

Matrix metalloproteinase-9 contributes to brain extravasation and edema in fulminant hepatic failure mice

BACKGROUND/AIMS

Fulminant hepatic failure (FHF) can be dreadful. When coma sets in, brain edema develops taking FHF into a lethal course. Mechanisms of brain extravasation leading to brain edema remain incompletely understood. Matrix metalloproteinase (MMP)-9 is implicated in various brain injuries. We hypothesized that MMP-9 contributes to brain edema in FHF.

METHODS

MMP-9 and its proform were assayed using SDS-PAGE and in situ gelatin zymographies. Brain extravasation was assessed with Evans blue. Brain water was determined by specific gravity and astrocytic endfoot swelling by electron microscopy. FHF in mice was induced by azoxymethane. MMP inhibitor GM6001 and MMP-9 monoclonal antibody were used.

RESULTS

Active MMP-9 was significantly increased at the onset of coma and brain extravasation in FHF mice. Blocking MMP-9 with either GM6001 or MMP-9 monoclonal antibody significantly attenuated brain extravasation, astrocytic endfoot swelling, and brain edema. Brains of FHF mice did not show MMP-9 activity. In contrast, livers of these animals showed marked up-regulation of MMP-9 activity.

CONCLUSIONS

Our findings suggest that MMP-9 contributes to the pathogenesis of brain extravasation and edema in FHF. The necrotic liver is the source of MMP-9 in FHF. Inhibition of MMP-9 may protect against the development of brain edema in FHF.

Phlorizin: a review

The dihydrochalcone phlorizin is a natural product and dietary constituent found in a number of fruit trees. It has been used as a pharmaceutical and tool for physiology research for over 150 years. Phlorizin's principal pharmacological action is to produce renal glycosuria and block intestinal glucose absorption through inhibition of the sodium-glucose symporters located in the proximal renal tubule and mucosa of the small intestine. This review covers the role phlorizin has played in the history of diabetes mellitus and its use as an agent to understand fundamental concepts in renal physiology as well as summarizes the physiology of cellular glucose transport and the pathophysiology of renal glycosuria. It reviews the biology and pathobiology of glucose transporters and discusses the medical botany of phlorizin and the potential effects of plant flavonoids, such as phlorizin, on human metabolism. Lastly, it describes the clinical pharmacology and toxicology of phlorizin, including investigational uses of phlorizin and phlorizin analogs in the treatment of diabetes, obesity, and stress hyperglycemia.

Characterisation of glucose transporters in the intact coronary artery endothelium in rats: GLUT-2 upregulated by long-term hyperglycaemia

AIMS/HYPOTHESIS

We have examined the effects of streptozotocin-induced type 1 diabetes on the expression and subcellular distribution of the classic sugar transporters (GLUT-1 to 5 and sodium-dependent glucose transporter-1 [SGLT-1]) in the endothelial cells of an en face preparation of septal coronary artery from Wistar rats.

METHODS

The presence of the GLUT isoforms and SGLT-1 in the endothelial cell layer was determined by immunohistochemistry using wide-field fluorescence microscopy coupled to deconvolution, and was quantified by digital image analysis.

RESULTS

We found that all of the transporters were expressed within these cells and that all except SGLT-1 were preferentially located on the abluminal side. The heaviest labelling was adjacent to the cell-to-cell junctions where the luminal and abluminal membranes are in close proximity, which may reflect a spatial organisation specialised for vectorial glucose transport across the thinnest part of the cytoplasm. Long-term hyperglycaemia, induced by streptozotocin, significantly downregulated GLUT-1, 3, 4 and 5 and dramatically upregulated GLUT-2, leaving SGLT-1 unchanged.

CONCLUSIONS/INTERPRETATION

We conclude that the high susceptibility of endothelial cells to glucose toxicity may be the result of the subcellular organisation of their GLUTs and the increased expression of GLUT-2.

Regulation of amino acid and glucose transporters in endothelial and smooth muscle cells

While transport processes for amino acids and glucose have long been known to be expressed in the luminal and abluminal membranes of the endothelium comprising the blood-brain and blood-retinal barriers, it is only within the last decades that endothelial and smooth muscle cells derived from peripheral vascular beds have been recognized to rapidly transport and metabolize these nutrients. This review focuses principally on the mechanisms regulating amino acid and glucose transporters in vascular endothelial cells, although we also summarize recent advances in the understanding of the mechanisms controlling membrane transport activity and expression in vascular smooth muscle cells. We compare the specificity, ionic dependence, and kinetic properties of amino acid and glucose transport systems identified in endothelial cells derived from cerebral, retinal, and peripheral vascular beds and review the regulation of transport by vasoactive agonists, nitric oxide (NO), substrate deprivation, hypoxia, hyperglycemia, diabetes, insulin, steroid hormones, and development. In view of the importance of NO as a modulator of vascular tone under basal conditions and in disease and chronic inflammation, we critically review the evidence that transport of L-arginine and glucose in endothelial and smooth muscle cells is modulated by bacterial endotoxin, proinflammatory cytokines, and atherogenic lipids. The recent colocalization of the cationic amino acid transporter CAT-1 (system y(+)), nitric oxide synthase (eNOS), and caveolin-1 in endothelial plasmalemmal caveolae provides a novel mechanism for the regulation of NO production by L-arginine delivery and circulating hormones such insulin and 17beta-estradiol.

Inositol stereoisomers stabilize an oligomeric aggregate of Alzheimer amyloid beta peptide and inhibit abeta -induced toxicity

Inositol has 8 stereoisomers, four of which are physiologically active. myo-Inositol is the most abundant isomer in the brain and more recently shown that epi- and scyllo-inositol are also present. myo-Inositol complexes with Abeta42 in vitro to form a small stable micelle. The ability of inositol stereoisomers to interact with and stabilize small Abeta complexes was addressed. Circular dichroism spectroscopy demonstrated that epi- and scyllo- but not chiro-inositol were able to induce a structural transition from random to beta-structure in Abeta42. Alternatively, none of the stereoisomers were able to induce a structural transition in Abeta40. Electron microscopy demonstrated that inositol stabilizes small aggregates of Abeta42. We demonstrate that inositol-Abeta interactions result in a complex that is non-toxic to nerve growth factor-differentiated PC-12 cells and primary human neuronal cultures. The attenuation of toxicity is the result of Abeta-inositol interaction, as inositol uptake inhibitors had no effect on neuronal survival. The use of inositol stereoisomers allowed us to elucidate an important structure-activity relationship between Abeta and inositol. Inositol stereoisomers are naturally occurring molecules that readily cross the blood-brain barrier and may represent a viable treatment for AD through the complexation of Abeta and attenuation of Abeta neurotoxic effects.

Interstitial glucose concentration and glycemia: implications for continuous subcutaneous glucose monitoring

The changes in plasma glucose concentration and in interstitial glucose concentration, determined with a miniaturized subcutaneous glucose sensor, were investigated in anesthetized nondiabetic rats. Interstitial glucose was estimated through two different calibration procedures. First, after a glucose load, the magnitude of the increase in interstitial glucose, estimated through a one-point calibration procedure, was 70% of that in plasma glucose. We propose that this is due to the effect of endogenous insulin on peripheral glucose uptake. Second, during the spontaneous secondary decrease in plasma glucose after the glucose load, interstitial glucose decreased faster than plasma glucose, which may also be due to the effect of insulin on peripheral glucose uptake. Third, during insulin-induced hypoglycemia, the decrease in interstitial glucose was less marked than that of plasma glucose, suggesting that hypoglycemia suppressed transfer of glucose into the interstitial tissue; subsequently, interstitial glucose remained lower than plasma glucose during its return to basal value, suggesting that the stimulatory effect of insulin on peripheral glucose uptake was protracted. If these observations obtained in rats are relevant to human physiology, such discrepancies between plasma and interstitial glucose concentration may have major implications for the use of a subcutaneous glucose sensor in continuous blood glucose monitoring in diabetic patients.

Synthesis of antioxidative and anti-inflammatory drugs glucoconjugates

Glucoconjugates of (+/-)-ibuprofen, (+/-)-alpha-tocopherol (vitamin E), gentisic acid, gallic acid, 2,6-bis(tert-butyl)-4-thiophenol, and N-acetyl-L-cysteine were prepared with the objective of increasing the bioavailability of such antioxidant and anti-inflammatory drugs. The O-glucosides were synthesized using benzylated alpha-D-glucopyranosyl trichloracetimidate as glycosyl donor. For the synthesis of the S-glucosides, the glycosyl donor 1,2,3,4,6-penta-O-acetyl-beta-D-glucopyranose provided higher yields than the corresponding O-acetylated imidate.

Damage and repair of nerve cell DNA in toxic stress

It is generally agreed that ALS/PDC is triggered by a disappearing environmental factor peculiar to the lifestyle of people of the western Pacific (i.e., Guam, Irian Jaya, Indonesia, and the Kii Peninsula of Japan). A strong candidate is the cycad plant genotoxin cycasin, the beta-D-glucoside of methylazoxymethanol (MAM). We propose that prenatal or postnatal exposure to low levels of cycasin/MAM may damage neuronal DNA, compromise DNA repair, perturb neuronal gene expression, and irreversibly alter cell function to precipitate a slowly evolving disease ("slow-toxin" hypothesis). In support of our hypothesis, we have demonstrated the following: 1. DNA from postmitotic rodent central nervous system neurons is particularly sensitive to damage by MAM. 2. MAM reduces DNA repair in human and rodent neurons, whereas DNA-repair inhibitors potentiate MAM-induced DNA damage and toxicity in mature rodent nervous tissue. 3. Human neurons (SY5Y neuroblastoma) that are deficient in DNA repair are susceptible to MAM-induced cytotoxicity and DNA damage, whereas overexpression of DNA repair in similar cells is protective. 4. MAM alters gene expression in SY5Y human neuroblastoma cells and, in the presence of DNA damage and reduced DNA repair, enhances glutamate-modulated expression of tau mRNA in rat primary neurons; the corresponding protein (TAU) is elevated in ALS/PDC and Alzheimer's disease. These findings support a direct relationship between MAM-induced DNA damage and neurotoxicity and suggest the genotoxin may operate in a similar manner in vivo. More broadly, a combination of genotoxin-induced DNA damage (via exogenous and/or endogenous agents) and disturbed DNA repair may be important contributing factors in the slow and progressive degeneration of neurons that is characteristic of sporadic neurodegenerative disease. Preliminary studies demonstrate that DNA repair is reduced in the brain of subjects with western Pacific ALS/PDC, ALS, and Alzheimer's disease, which would increase the susceptibility of brain tissue to DNA damage by endogenous/exogenous genotoxins. Interindividual differences in the extent of prior exposure to DNA-damaging agents and/or the efficiency of its repair might produce population variety in the rate of damage accumulation and explain the susceptibility of certain individuals to sporadic neurodegenerative disease. Studies are underway using DNA-repair proficient and deficient neuronal cell cultures and mutant mice to explore gene-environment interplay with respect to MAM treatment, DNA damage, and DNA repair, and the age-related appearance of neurobehavioral and neuropathological compromise.

Carrier-mediated or specialized transport of drugs across the blood-brain barrier

In the drug development process, it remains a difficult task to regulate the entry of the drugs. However, recent progress in studies of the transporter-mediated influx and efflux of endogenous and exogenous compounds, including synthetic drugs, across the blood-brain barrier (BBB) is beginning to provide a rational basis for controlling drug distribution to the brain. This paper describes mechanisms established in the last decade for carrier-mediated influx and efflux of drugs and endocytosis of biologically active peptides across the BBB. The transport systems at the BBB described here are the uptake transporters for nutrients, such as amino acids and hexoses, monocarboxylates, amines, carnitine and glutathione and efflux transporters, such as P-glycoprotein and multiple organic anion transporters. Delivery of cationized peptides across the BBB via adsorptive-mediated endocytosis is also described. By utilizing such highly specific transport mechanisms, it should be possible to establish strategies to regulate the entry of candidate drugs, including peptides, into the brain.

The Guam cycad toxin methylazoxymethanol damages neuronal DNA and modulates tau mRNA expression and excitotoxicity

As in Alzheimer's disease, brains of Guam Chamorros with amyotrophic lateral sclerosis (ALS) and Parkinsonism-dementia complex (PDC) contain intraneuronal-paired helical filaments composed of accumulated phosphorylated tau protein. Tau mRNA expression in rat neuronal cultures-normally modulated by glutamate-increases after treatment with the aglycone of cycasin, a cycad-derived toxin whose concentration in Chamorro food varies with disease incidence. Elevated Tau gene expression in vitro is coincident with increased cycasin-related DNA adducts and reduced DNA repair. Cycasin and endogenous glutamate may together promote the accumulation of tau protein and neuronal degeneration in Western Pacific ALS/PDC.