Reduced motor nerve conduction velocity and Na(+)-K(+)-ATPase activity in rats maintained on L-fucose diet. Reversal by myo-inositol supplementation

Is metformin a possible treatment for diabetic neuropathy?

Metformin is a hypoglycemic drug widely used in the treatment of type 2 diabetes. It has been proven to have analgesic and neuroprotective effects. Metformin can reverse pain in rodents, such as diabetic neuropathic pain, neuropathic pain caused by chemotherapy drugs, inflammatory pain and pain caused by surgical incision. In clinical use, however, metformin is associated with reduced plasma vitamin B12 levels, which can further neuropathy. In rodent diabetes models, metformin plays a neuroprotective and analgesic role by activating adenosine monophosphate-activated protein kinase, clearing methylgloxal, reducing insulin resistance, and neuroinflammation. This paper also summarized the neurological adverse reactions of metformin in diabetic patients. In addition, whether metformin has sexual dimorphism needs further study.

Trans-synaptic spreading of alpha-synuclein pathology through sensory afferents leads to sensory nerve degeneration and neuropathic pain

Pain is a common non-motor symptom of Parkinson’s disease (PD), with current limited knowledge of its pathophysiology. Here, we show that peripheral inoculation of mouse alpha-synuclein (α-Syn) pre-formed fibrils, in a transgenic mouse model of PD, elicited retrograde trans-synaptic spreading of α-Syn pathology (pSer129) across sensory neurons and dorsal nerve roots, reaching central pain processing regions, including the spinal dorsal horn and the projections of the anterolateral system in the central nervous system (CNS). Pathological peripheral to CNS propagation of α-Syn aggregates along interconnected neuronal populations within sensory afferents, was concomitant with impaired nociceptive response, reflected by mechanical allodynia, reduced nerve conduction velocities (sensory and motor) and degeneration of small- and medium-sized myelinated fibers. Our findings show a link between the transneuronal propagation of α-Syn pathology with sensory neuron dysfunction and neuropathic impairment, suggesting promising avenues of investigation into the mechanisms underlying pain in PD.

Insulin Treatment Attenuates Small Nerve Fiber Damage in Rat Model of Type 2 Diabetes

INTRODUCTION

Current clinical guidelines for management of diabetic peripheral neuropathy (DPN) emphasize good glycemic control. However, this has limited effect on prevention of DPN in type 2 diabetic (T2D) patients. This study investigates the effect of insulin treatment on development of DPN in a rat model of T2D to assess the underlying causes leading to DPN.

METHODS

Twelve-week-old male Sprague-Dawley rats were allocated to a normal chow diet or a 45% kcal high-fat diet. After eight weeks, the high-fat fed animals received a mild dose of streptozotocin to induce hyperglycemia. Four weeks after diabetes induction, the diabetic animals were allocated into three treatment groups receiving either no insulin or insulin-releasing implants in a high or low dose. During the 12-week treatment period, blood glucose and body weight were monitored weekly, whereas Hargreaves' test was performed four, eight, and 12 weeks after treatment initiation. At study termination, several blood parameters, body composition, and neuropathy endpoints were assessed.

RESULTS

Insulin treatment lowered blood glucose in a dose-dependent manner. In addition, both doses of insulin lowered lipids and increased body fat percentage. High-dose insulin treatment attenuated small nerve fiber damage assessed by Hargreaves' test and intraepidermal nerve fiber density compared to untreated diabetes and low-dose insulin; however, neuropathy was not completely prevented by tight glycemic control. Linear regression analysis revealed that glycemic status, circulating lipids, and sciatic nerve sorbitol level were all negatively associated with the small nerve fiber damage observed.

CONCLUSION

In summary, our data suggest that high-dose insulin treatment attenuates small nerve fiber damage. Furthermore, data also indicate that both poor glycemic control and dyslipidemia are associated with disease progression. Consequently, this rat model of T2D seems to fit well with progression of DPN in humans and could be a relevant preclinical model to use in relation to research investigating treatment opportunities for DPN.

Expression of myo-inositol cotransporters in the sciatic nerve and dorsal root ganglia in experimental diabetes

The transport of myo-inositol is the main mechanism for the maintenance of its high intracellular levels. We aimed to measure the mRNA and protein levels of myo-inositol cotransporters in the sciatic nerve (SN) and dorsal root ganglia (DRG) during experimental diabetes. Streptozotocin-induced (STZ; 4, 8, and 12 weeks; 65 mg/kg; ip) diabetic rats (DB) and age-matched euglycemic (E) rats were used for the analysis of mRNA and protein levels of sodium myo-inositol cotransporters 1, 2 (SMIT1, SMIT2) or H⁺/myo-inositol cotransporter (HMIT). There was a significant reduction in the mRNA levels for SMIT1 in the SN and DRG (by 36.9 and 31.0%) in the 4-week DB (DB4) group compared to the E group. SMIT2 was not expressed in SN. The mRNA level for SMIT2 was up-regulated only in the DRG in the DB4 group. On the other hand, the protein level of SMIT1 decreased by 42.5, 41.3, and 44.8% in the SN after 4, 8, and 12 weeks of diabetes, respectively. In addition, there was a decrease of 64.3 and 58.0% of HMIT in membrane and cytosolic fractions, respectively, in the SN of the DB4 group. In the DRG, there was an increase of 230 and 86.3% for SMIT1 and HMIT, respectively, in the DB12 group. The levels of the main inositol transporters, SMIT1 and HMIT, were greatly reduced in the SN but not in the DRG. SMIT-1 was selectively reduced in the sciatic nerve during experimental STZ-induced diabetes.

High fructose-induced metabolic changes enhance inflammation in human dendritic cells

Dendritic cells (DCs) are critical antigen-presenting cells which are the initiators and regulators of the immune response. Numerous studies support the idea that dietary sugars influence DC functions. Increased consumption of fructose has been thought to be the leading cause of metabolic disorders. Although evidence supports their association with immune dysfunction, the specific mechanisms are not well understood. Fructose is one of the main dietary sugars in our diet. Therefore, here we compared the effect of fructose and glucose on the functions of human DCs. High levels of D-fructose compared to D-glucose led to activation of DCs in vitro by promoting interleukin (IL)-6 and IL-1β production. Moreover, fructose exposed DCs also induced interferon (IFN)-γ secretion from T cells. Proinflammatory response of DCs in high fructose environment was found to be independent of the major known metabolic regulators or glycolytic control. Instead, DC activation on acute exposure to fructose was via activation of receptor for advanced glycation end product (RAGE) in response to increased accumulation of advanced glycation end products (AGE). However, chronic exposure of DCs to high fructose environment induced a shift towards glycolysis compared to glucose cultured DCs. Further investigations revealed that the AGEs formed by fructose induced increased levels of inflammatory cytokines in DCs compared to AGEs from glucose. In summary, understanding the link between metabolic changes and fructose-induced DC activation compared to glucose has broad implications for immune dysfunction associated with metabolic disorders.

Anti-inflammatory effect of AMPK signaling pathway in rat model of diabetic neuropathy

Diabetic neuropathy (DN) is characterized as Hyperglycemia activates thdisturbed nerve conduction and progressive chronic pain. Inflammatory mediators, particularly cytokines, have a determinant role in the pathogenesis of neuropathic pain. The activity of adenosine monophosphate protein kinase (AMPK), an energy charge sensor with neuroprotective properties, is decreased in diabetes. It has been reported that activation of AMPK reduces the systemic inflammation through inhibition of cytokines. In this study, we aimed to investigate the probable protective effects of AMPK on DN in a rat of diabetes. DN was induced by injection of streptozotocin (65 mg/kg, i.p.). Motor nerve conduction velocities (MNCV) of the sciatic nerve, as an electrophysiological marker for peripheral nerve damage, were measured. Plasma levels of IL-6, TNF-α, CRP were assessed as relevant markers for inflammatory response. Also, the expression of phosphorylated AMPK (p-AMPK) and non-phosphorylated (non-p-AMPK) was evaluated by western blotting in the dorsal root ganglia. Histopathological assessment was performed to determine the extent of nerve damage in sciatic nerve. Our findings showed that activation of AMPK by metformin (300 mg/kg) significantly increased the MNCV and reduced the levels of inflammatory cytokines. In addition, we showed that administration of metformin increased the expression of p-AMPK as well as decline in the level of non p-AMPK. Our results demonstrated that co-administration of dorsomorphin with metformin reversed the beneficial effects of metformin. In conclusion, the results of this study demonstrated that the activation of AMPK signaling pathway in diabetic neuropathy might be associated with the anti-inflammatory response.

Diabetic foot ulcer--A review on pathophysiology, classification and microbial etiology

As the prevalence of diabetes is increasing globally, secondary complications associated to this endocrinal disorder are also ascending. Diabetic foot ulcers are potentially modifying complications. Disruption of harmony in glucose homeostasis causes hyperglycemic status, results in activation of certain metabolic pathways which in their abnormal state subsequently leads to development of vascular insufficiency, nerve damages headed by ulceration in lower extremity due to plantar pressures and foot deformity. Insult to foot caused by trauma at the affected site goes unnoticeable to patient due to loss of sensation. Among the above mention causes, resistance to infection is also considered as chief modulator of pathophysiological image of diabetic foot lesions. Healing as well as non-healing nature of ulcer relies upon the wound microbial communities and the extent of their pathogenicity. A validated classification system of foot ulcer is primarily necessary for clinicians in management of diabetic foot problems. Another aspect which needs management is proper identification of causative pathogen causing infection. The way of approaches presently employed in the diagnosis for treatment of foot ulcer colonized by different microbes is conventional techniques. Conventional diagnostic methods are widely acceptable since decades. But in recent years newly invented molecular techniques are exploring the use of 16S ribosomal regions specific to prokaryotes in bacterial identification and quantification. Molecular techniques would be a better choice if engaged, in finding the specific species harboring the wound.

Protective effect of Jiaweibugan decoction against diabetic peripheral neuropathy

Oxygen free radical damage is regarded as a direct or indirect common pathway associated with diabetic neuropathy and is the main cause of complications in peripheral neuropathies. We speculate that Jiaweibugan decoction has a significant effect in treating diabetic peripheral neuropathy through an anti-oxidative stress pathway. In this study, a diabetic rat model was established by intraperitoneal injection of streptozotocin. Rats were treated with Jiaweibugan decoction via intragastric administration. The levels of malondialdehyde and glutathione, which are indirect indexes of oxidative stress, in serum were determined using a colorimetric method. The expression levels of nuclear factor kappa B p65 mRNA and p38 mitogen-activated protein kinase, which are oxidative stress associated factors, in the dorsal root ganglion of spinal S_4–6 segments were evaluated by reverse-transcriptase polymerase chain reaction and immunohistochemistry. Results showed that, Jiaweibugan decoction significantly ameliorated motor nerve conduction velocity in diabetic rats, effectively decreased malondialdehyde levels in serum and the expression of nuclear factor kappa B p65 mRNA and p38 mitogen-activated protein kinase mRNA in the dorsal root ganglion, and increased glutathione levels in serum. Therefore, our experimental findings indicate that Jiaweibugan decoction plays an anti-oxidative stress role in the diabetic peripheral neuropathy process, which has a protective effect on peripheral nerve injury.

Vascular risk factors and Alzheimer's disease

Vascular cognitive impairment risk factors include stroke, hypertension, diabetes and atherosclerosis. In the elderly, vascular risk factors occur in the presence of high levels of amyloid in the aging brain. Stroke alters the clinical expression of a given load of Alzheimer's disease (AD) pathology. Experimentally, large vessel infarcts or small striatal infarcts are larger in the presence of amyloid. Patients with minor cerebral infarcts and moderate AD lesions will develop the clinical manifestations of dementia. Moreover, there is also an association between other vascular risk factors and the clinical expression of cognitive decline and dementia. The risk of AD is increased in subjects with adult-onset diabetes mellitus, hypertension, atherosclerotic disease and atrial fibrillation. Experimentally, small striatal infarcts in the presence of high levels of amyloid in the brain exhibit a progression in infarct size over time with enhanced degree of cognitive impairment, AD-type pathology and neuroinflammation compared with striatal infarcts or high amyloid levels alone.

Progression of vascular and neural dysfunction in sciatic nerves of Zucker diabetic fatty and Zucker rats

We have examined the progression of vascular and neural deficits in Zucker rats, Zucker diabetic fatty (ZDF) diabetic rats, and age-matched lean ZDF rats from 8 to 40 wk of age. Both the ZDF diabetic and Zucker rats were glucose intolerant at 8 wk of age. The Zucker rats did not become hyperglycemic but were hyperinsulinemic through 32 wk of age. All ZDF diabetic rats became hyperglycemic by 8 wk of age. Through their life span, serum free fatty acids and triglycerides levels were significantly higher in Zucker and ZDF diabetic rats compared with age-matched lean ZDF rats. After 24 and 28 wk of age, endoneurial blood flow was significantly decreased in ZDF diabetic and Zucker rats. Motor nerve conduction velocity was significantly decreased after 12-14 wk of age in ZDF diabetic rats and at 32 wk of age in Zucker rats. ACh-mediated vascular relaxation of epineurial arterioles of the sciatic nerve was impaired after 8-10 wk of age in ZDF diabetic rats and after approximately 16 wk of age in Zucker rats. In contrast, vascular relaxation mediated by calcitonin gene-related peptide was impaired significantly after 28 wk of age in ZDF diabetic rats but not impaired in Zucker rats up to 40 wk of age. Markers of oxidative stress were differentially elevated in ZDF diabetic rats and Zucker rats. These data indicate that vascular and neural dysfunction develops in both Zucker and ZDF diabetic rats but at different rates, which may be the result of hyperglycemia.

Inositol and higher inositol phosphates in neural tissues: homeostasis, metabolism and functional significance

Inositol phospholipids and inositol phosphates mediate well-established functions in signal transduction and in Ca2+ homeostasis in the CNS and non-neural tissues. More recently, there has been renewed interest in other roles that both myo-inositol and its highly phosphorylated forms may play in neural function. We review evidence that myo-inositol serves as a clinically relevant osmolyte in the CNS, and that its hexakisphosphate and pyrophosphorylated derivatives may play roles in such diverse cellular functions as DNA repair, nuclear RNA export and synaptic membrane trafficking.

Changes in endoneurial blood flow, motor nerve conduction velocity and vascular relaxation of epineurial arterioles of the sciatic nerve in ZDF-obese diabetic rats

BACKGROUND

We have previously reported that in streptozotocin-induced diabetic rats, reduction in endoneurial blood flow (EBF) and impairment of acetylcholine-mediated vascular relaxation of arterioles that provide circulation to the sciatic nerve precedes slowing of motor nerve conduction velocity (MNCV). However, in animal models of type 2 diabetes it is unknown whether slowing of MNCV is accompanied by vascular dysfunction.

METHODS

Using ZDF-lean and ZDF-obese diabetic rats we examined whether diabetes-induced slowing in MNCV was associated with a reduction in EBF and impaired vascular relaxation in epineurial arterioles of the sciatic nerve. We measured MNCV in the sciatic nerve using a non-invasive procedure, and sciatic nerve nutritive blood flow using microelectrode polarography. In vitro videomicroscopy was employed to quantify arteriolar diameter responses to acetylcholine in arterioles overlying the sciatic nerve.

RESULTS

MNCV and EBF in hyperglycemic (4-week duration) ZDF-obese diabetic rats were significantly decreased by 30% and 63%, respectively, compared to age-matched ZDF-lean rats. Acetylcholine elicited a dose-dependent dilation of epineurial vessels from ZDF-lean and ZDF-obese diabetic rats, although acetylcholine-induced dilation was significantly reduced in ZDF-obese diabetic rats. Determination of markers of oxidative stress provided ambiguous results. Superoxide levels were increased in epineurial vessels from ZDF-obese diabetic rats. Lens glutathione levels were decreased and serum thiobarbituric acid reactive substances increased in ZDF-obese diabetic rats but sciatic nerve conjugated diene and glutathione levels were not significantly different compared to ZDF-lean rats.

CONCLUSIONS

Diabetes causes a reduction in EBF and impairment in vascular relaxation in epineurial vessels in ZDF-obese diabetic rats. This impaired vascular response is associated with neural dysfunction.

Effect of M40403 treatment of diabetic rats on endoneurial blood flow, motor nerve conduction velocity and vascular function of epineurial arterioles of the sciatic nerve

1. To further explore the effect of antioxidants in preventing diabetes-induced vascular and neural dysfunction we treated streptozotocin-induced diabetic rats daily with subcutaneous injections of 10 mg kg(-1) of M40403 (n=11) and compared the results obtained from 17 control rats and 14 untreated diabetic rats. M40403 is a manganese(II) complex with a bis(cyclo-hexylpyridine)-substituted macrocyclic ligand that was designed to be a selective functional mimetic of superoxide dismutase. Thus, M40403 provides a useful tool to evaluate the roles of superoxide in disease states. 2. Treatment with M40403 significantly improved diabetes-induced decrease in endoneurial blood flow, acetylcholine-mediated vascular relaxation in arterioles that provide circulation to the region of the sciatic nerve, and motor nerve conduction velocity (P<0.05). M40403 treatment also reduced the appearance of superoxide in the aorta and epineurial vessels and peroxynitrite in epineurial vessels. Treating diabetic rats with M40403 reduced the diabetes-induced increase in thiobarbituric acid reactive substances in serum but did not prevent the decrease in lens glutathione level. Treating diabetic rats with M40403 did not improve sciatic nerve Na(+)/K(+) ATPase activity or the sorbitol, fructose or myo-inositol content of the sciatic nerve. 3. These studies provide additional evidence that diabetes-induced oxidative stress and the generation of superoxide and perhaps peroxynitrite may be partially responsible for the development of diabetic vascular and neural complications.

Wortmannin and LY294002 inhibit myo-inositol accumulation by cultured bovine aorta endothelial cells and murine 3T3-L1 adipocytes

We have previously reported that myo-inositol uptake and metabolism is reduced in human fibroblasts derived from patients with ataxia telangiectasia (AT). Treating normal fibroblasts with 10-100 microM wortmannin duplicates some of the phenotypic properties of AT fibroblasts including the decrease in myo-inositol accumulation. In the present study we examined whether treatment of other types of mammalian cells with wortmannin or LY294002 altered myo-inositol uptake. Cultured bovine aorta endothelial cells or 3T3-L1 adipocytes were incubated with either wortmannin or LY294002, and afterwards, myo-inositol uptake and SMIT mRNA levels were determined. Incubating cultured bovine aorta endothelial cells and 3T3-L1 adipocytes with either wortmannin or LY294002 caused a time- and concentration-dependent decrease in myo-inositol accumulation that was independent of changes in SMIT mRNA levels. The effect of wortmannin and LY294002 on myo-inositol accumulation was not due to an increase in myo-inositol secretion. The effect of LY294002 on myo-inositol accumulation was reversible. Furthermore, the LY294002-induced decrease in myo-inositol accumulation was specific since the uptake of serine or choline by cultured bovine aorta endothelial cells and 3T3-L1 adipocytes treated with LY294002 was not significantly decreased. Co-incubation of cultured bovine aorta endothelial cells and 3T3-L1 adipocytes with either wortmannin or LY294002 and hyperosmotic medium caused a significant decrease in the induction of myo-inositol accumulation by hyperosmolarity without significantly affecting the hyperosmotic-induced increase in SMIT mRNA levels. These data suggest that myo-inositol accumulation is regulated post-translationally by wortmannin and LY294002.

Correction of Leukocyte Adhesion Deficiency Type II With Oral Fucose

We describe a simple, noninvasive, and effective therapy for leukocyte adhesion deficiency type II (LAD II), a rare inherited disorder of fucose metabolism. This disorder leads to an immunodeficiency caused by the absence of carbohydrate-based selectin ligands on the surface of neutrophils as well as to severe psychomotor and mental retardation. The fucosylation defect in LAD II fibroblasts can be corrected by addition of L-fucose to the culture medium. This prompted us to initiate dietary fucose therapy on a patient with LAD II. Oral supplementation of fucose in this patient induced the expression of fucosylated selectin ligands on neutrophils and core fucosylation of serum glycoproteins. During 9 months of treatment, infections and fever disappeared, elevated neutrophil counts returned to normal, and psychomotor capabilities improved.

Correction of Leukocyte Adhesion Deficiency Type II With Oral Fucose

We describe a simple, noninvasive, and effective therapy for leukocyte adhesion deficiency type II (LAD II), a rare inherited disorder of fucose metabolism. This disorder leads to an immunodeficiency caused by the absence of carbohydrate-based selectin ligands on the surface of neutrophils as well as to severe psychomotor and mental retardation. The fucosylation defect in LAD II fibroblasts can be corrected by addition of L-fucose to the culture medium. This prompted us to initiate dietary fucose therapy on a patient with LAD II. Oral supplementation of fucose in this patient induced the expression of fucosylated selectin ligands on neutrophils and core fucosylation of serum glycoproteins. During 9 months of treatment, infections and fever disappeared, elevated neutrophil counts returned to normal, and psychomotor capabilities improved.

Acetylcholine-induced arteriolar dilation is reduced in streptozotocin-induced diabetic rats with motor nerve dysfunction

1. Diabetes mellitus produces marked abnormalities in motor nerve conduction, but the mechanism is not clear. In the present study we hypothesized that in the streptozotocin (STZ)-induced diabetic rat impaired vasodilator function is associated with reduced endoneural blood flow (EBF) which may contribute to nerve dysfunction. 2. We examined whether diabetes-induced reductions in sciatic nerve conduction velocity and EBF were associated with impaired endothelium-dependent dilation in adjacent arterioles. We measured motor nerve conduction velocity (MNCV) in the sciatic nerve using a non-invasive procedure, and sciatic nerve nutritive blood flow using microelectrode polarography and hydrogen clearance. In vitro videomicroscopy was used to quantify arteriolar diameter responses to dilator agonists in arterioles overlying the sciatic nerve. 3. MNCV and EBF in 4-week-STZ-induced diabetic rats were decreased by 22% and 49% respectively. Arterioles were constricted with U46619 and dilation to acetylcholine (ACh), aprikalim, or sodium nitroprusside (SNP) examined. All agonists elicited dose-dependent dilation in control and diabetic rats, although ACh-induced dilation was significantly reduced in diabetic rats. Treating vessels from normal or diabetic rats with indomethacin (INDO) alone did not significantly affect ACh-induced relaxation. However, ACh-induced vasodilation was significantly reduced by treatment with KCl or Nomega-nitro-L-arginine (LNNA) alone. Combining LNNA and KCl further reduced ACh-induced dilation in these vessels. 4. Diabetes causes vasodilator dysfunction in a microvascular bed that provides circulation to the sciatic nerve. These studies imply that ACh-induced dilation in these vessels is mediated by multiple mechanisms that may include the endothelial-dependent production of nitric oxide and endothelial-derived hyperpolarizing factor. This impaired vascular response is associated with neural dysfunction.

Abnormal myo-inositol and phospholipid metabolism in cultured fibroblasts from patients with ataxia telangiectasia

Ataxia telangiectasia (AT) is a complex autosomal recessive disorder that has been associated with a wide range of physiological defects including an increased sensitivity to ionizing radiation and abnormal checkpoints in the cell cycle. The mutated gene product, ATM, has a domain possessing homology to phosphatidylinositol-3-kinase and has been shown to possess protein kinase activity. In this study, we have investigated how AT affects myo-inositol metabolism and phospholipid synthesis using cultured human fibroblasts. In six fibroblast lines from patients with AT, myo-inositol accumulation over a 3-h period was decreased compared to normal fibroblasts. The uptake and incorporation of myo-inositol into phosphoinositides over a 24-h period, as well as the free myo-inositol content was also lower in some but not all of the AT fibroblast lines. A consistent finding was that the proportion of 32P in total labeled phospholipid that was incorporated into phosphatidylglycerol was greater in AT than normal fibroblasts, whereas the fraction of radioactivity in phosphatidic acid was decreased. Turnover studies revealed that AT cells exhibit a less active phospholipid metabolism as compared to normal cells. In summary, these studies demonstrate that two manifestations of the AT defect are alterations in myo-inositol metabolism and phospholipid synthesis. These abnormalities could have an effect on cellular signaling pathways and membrane production, as well as on the sensitivity of the cells to ionizing radiation and proliferative responses.

Effect of L-fucose and D-glucose concentration on L-fucoprotein metabolism in human Hep G2 cells and changes in fucosyltransferase and alpha-L-fucosidase activity in liver of diabetic rats

L-Fucose is a monosaccharide that is present at low concentrations in serum and is a normal constituent of glycoproteins. In some pathological conditions, such as cancer, rheumatoid arthritis, and diabetes, there is an abnormal fucosylation of acute phase serum proteins. Because most serum proteins are produced in the liver, we have examined L-fucose accumulation, metabolism, and secretion of L-fucose-containing proteins in human Hep G2 liver cells. Accumulation of L-fucose by Hep G2 cells approached 3.5 nmol/mg protein after a 48 h incubation. This accumulation appears similar to accumulation in other cells, which we have shown occurs via a specific transport protein. Exogenous L-fucose was incorporated into protein in both O- and N-linked glycosidic linkages. After a 48 h incubation, 61% of the accumulated L-fucose was incorporated into protein and secreted into the medium, whereas 39% of the L-fucose remaining in the cells was incorporated into integral membrane proteins. Utilizing reverse-phase high-performance liquid chromatographic separation of L-[5,6-(3)H]fucose-containing proteins and detection by scintillation counting, we determined that two major fucoproteins and numerous minor fucoproteins were produced and secreted by normal Hep G2 cells. This elution profile was unchanged when glucose-conditioned cells were examined. By size-separating secreted proteins by nondenaturing HPLC we determined that the size of the two major fucoproteins were approximately 60 and approximately 100 kDa. In these studies we also examined the effect of diabetes on hepatic fucosyltransferase and serum alpha-L-fucosidase activity and found that the activity of these enzymes is increased by 40 and 100%, respectively in diabetic rats.

Regulation of gene expression by hypertonicity

Adaptation of cells to hypertonicity often involves changes in gene expression. Since the concentration of salt in the interstitial fluid surrounding renal inner medullary cells varies with operation of the renal concentrating mechanism and generally is very high, the adaptive mechanisms of these cells are of special interest. Renal medullary cells compensate for hypertonicity by accumulating variable amounts of compatible organic osmolytes, including sorbitol, myo-inositol, glycine betaine, and taurine. In this review we consider how these solutes help relieve the stress of hypertonicity and the nature of transporters and enzymes responsible for their variable accumulation. We emphasize recent developments concerning the molecular basis for osmotic regulation of these genes, including identification and characterization of osmotic response elements. Although osmotic stresses are much smaller in other parts of the body than in the renal medulla, similar mechanisms operate throughout, yielding important physiological and pathophysiological consequences.

The aldose reductase inhibitor sorbinil does not prevent the impairment in nitric oxide-mediated neurotransmission in anococcygeus muscle from diabetic rats

This study investigated whether increased polyol pathway activity could contribute to alterations in nitrergic neurotransmission in anococcygeus muscles from 8-week diabetic rats. In the presence of guanethidine (10-30 microM) and clonidine (0.01-0.05 microM), relaxations obtained to nitrergic nerve stimulation (0.5-5 Hz, 10-s train), to sodium nitroprusside (5-500 nM) and to nitric oxide (0.1-3 microM) were significantly reduced in muscles from diabetic rats compared to responses from control rats. Treatment of diabetic rats with the aldose reductase inhibitor sorbinil (42 mg/kg per day via feed for 8 weeks) did not affect impaired reactivity to nitrergic nerve stimulation, sodium nitroprusside or nitric oxide. The results suggest increased polyol pathway activity does not contribute to the alterations in nitrergic neurotransmission in anococcygeus muscles from diabetic rats.

Reducing sugars trigger oxidative modification and apoptosis in pancreatic beta-cells by provoking oxidative stress through the glycation reaction

Several reducing sugars brought about apoptosis in isolated rat pancreatic islet cells and in the pancreatic beta-cell-derived cell line HIT. This apoptosis was characterized biochemically by inter-nucleosomal DNA cleavage and morphologically by nuclear shrinkage, chromatin condensation and apoptotic body formation. N-Acetyl-L-cysteine, an antioxidant, and aminoguanidine, an inhibitor of the glycation reaction, inhibited this apoptosis. We also showed directly that proteins in beta-cells were actually glycated by using an antibody which can specifically recognize proteins glycated by fructose, but not by glucose. Furthermore, fluorescence-activated cell sorting analysis using dichlorofluorescein diacetate showed that reducing sugars increased intracellular peroxide levels prior to the induction of apoptosis. Levels of carbonyl, an index of oxidative modification, and of malondialdehyde, a lipid peroxidation product, were also increased. Taken together, these results suggest that reducing sugars trigger oxidative modification and apoptosis in pancreatic beta-cells by provoking oxidative stress mainly through the glycation reaction, which may explain the deterioration of beta-cells under conditions of diabetes.

Localization and regulation of renal Na+/myo-inositol cotransporter in diabetic rats

We have examined the effect of diabetes on sodium/myo-inositol cotransporter (SMIT) mRNA levels and myo-inositol content in the kidney to test the hypothesis that diabetes-induced changes in renal myo-inositol levels are due to the regulation of SMIT mRNA levels. In streptozotocin-induced diabetic rats, after 3, 7 and 28 days of diabetes, SMIT mRNA levels in the whole kidney were increased three to fivefold, and remained increased by about twofold after six months of diabetes. Insulin treatment of diabetic rats normalized blood glucose levels and prevented the increase in SMIT mRNA levels. Treating diabetic rats with sorbinil, an aldose reductase inhibitor, corrected the abnormal accumulation of sorbitol but had no effect on the diabetes-induced increase in renal SMIT mRNA levels. The regional distribution of SMIT mRNA from normal rats showed a relative abundance in cortex, outer medulla, and inner medulla of 1.0:3.4:7.0. After seven days of diabetes, the levels of SMIT mRNA and myo-inositol content were significantly increased only in the outer medulla. In situ hybridization studies revealed that SMIT mRNA in the outer medulla was predominately localized to the medullary thick ascending limbs of Henle's loop and was not localized to any specific cell in the inner medulla. This distribution pattern was unchanged in diabetic rats. These studies show that diabetes causes an increase in renal SMIT mRNA, which is primarily localized to the outer medulla. Accumulation of myo-inositol by the thick ascending limb of Henle's loop may account for most of the increase caused by diabetes.

L-fucose reduces collagen and noncollagen protein production in cultured cerebral microvessel endothelial cells

L-fucose is a monosaccharide which is present in low concentrations in normal serum but is increased in diabetes, cancer, and inflammatory diseases. The contribution that abnormal L-fucose levels make to the progression of these disorders is unknown. In a previous study we showed that increased L-fucose concentration reduced proliferation and proteoglycan production by cultured cerebral microvessel endothelial cells. In the present study we show that exposing cerebral microvessel endothelial cells for 2 weeks to medium containing an increased concentration of L-fucose causes a significant decrease in collagen and to a lesser extent noncollagen protein production. The effect of L-fucose on collagen and noncollagen protein production is concentration-dependent: 1 mM L-fucose causes a significant decrease in collagen production but has no effect on noncollagen protein production; a 5 mM L-fucose concentration causes a maximum decrease in both collagen and noncollagen protein production. This defect is unrelated to the reduction in myo-inositol uptake caused by L-fucose and is not prevented by aminoguanidine. Collagen production can be improved by restoring L-fucose-conditioned cells to normal medium. Culturing cells for 2 weeks in medium containing 10 mM L-fucose resulted in a 50% decrease in collagen production, which was restored to 75% of control after cells were transferred to normal medium for 7 days. In contrast, noncollagen protein production was totally restored after 3 days in normal medium. Increasing levels of L-fucose in serum of rats also resulted in a decrease in collagen production. Collagenase digestible incorporation of L-[2,3,4,5-3H]proline into protein of the articular cartilage from rats fed a diet containing 20% L-fucose for 3 weeks was reduced by about 40% compared to rats fed a normal diet. The decrease in collagen production in L-fucose fed rats was less than the reduction that occurred in streptozotocin-induced diabetic rats. These data suggest that changes in L-fucose concentration itself may be a factor in the regulation of collagen production.