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Calcium channel blockers modify jejunal uptake of D-galactose in rabbits.

Calcium channel blockers modify the intestinal uptake of lipids. This study was undertaken to test the hypothesis that two different types of calcium channel blockers influence the uptake of D-galactose, a sugar absorbed by the sodium-dependent glucose transporter (SGLT1) in the intestinal brush border membrane. Nisoldipine (1 mg/kg/day) or verapamil (4 mg/kg/day) were given by mouth to New Zealand white rabbits for three weeks, and then the rates of uptake of varying concentrations (2-64 mM) of galactose were examined in an in vitro preparation of jejunum using the incorporation of 14C-labeled substrate into intact tissue segments. The maximal transport capacities (Vmax) for D-galactose were increased in animals given nisoldipine or verapamil, as compared to controls. The value of the apparent Michaelis constant Km* for D-galactose was higher with nisoldipine group and lower with verapamil, than in controls. The apparent passive permeability (Pd*) of D-galactose was estimated from the uptake of L-glucose: Pd* was lower with nisoldipine and higher with verapamil, as compared to controls. The effect of these drugs on sugar uptake is not due to differences in the animals' food intake, body weight gain, or mucosal surface area. Thus, the two different classes of calcium channel blockers, the dihydropyridine nisoldipine and the phenylalkylamine verapamil, have different effects on the K(m)* and Pd*, but not on the Vmax of D-galactose uptake.

Animals↗

In utero galactose intoxication in animals.

To assess in utero effects of galactose, diets containing large amounts of the sugar have been fed to pregnant rats with examination of the fetuses and newborns. Galactose levels in fetal blood parallel those of the dam and amniotic fluid contains high concentrations of galactose and galactitol. In the offspring and in the fetuses cataracts, and a decrease in brain weight, protein content and DNA are observed. There is an elevated content of galactitol and decrease in myo-inositol in the brain of galactose-intoxicated newborns. Brain synaptosomes of young rats whose mothers were fed galactose show a reduced response in vitro to acetylcholine as evidenced by a decrease in incorporation of myo-inositol into phosphatidylinositol and an inappropriate change in phosphatidylinositol content. The data indicate that there can be significant effects in the offspring of pregnant rats fed a high galactose diet. The findings support the concept that in utero toxicity may occur in the human galactosemic fetus.

Animals↗

Leptin effect on intestinal galactose absorption in ob/ob and db/db mice.

Our previous works demonstrated that leptin inhibits galactose absorption in rat and mice intestinal rings. Here, we have studied the effect of exogenous leptin on intestinal galactose absorption in the genetically obese db/db (leptin-resistant) and ob/ob (leptin-deficient) mice. Assays were performed by incubating the intestinal rings in saline solution containing 5 mM galactose in the absence or presence of 0.2 or 0.4 nM leptin. Basal galactose uptake was similar in the wild-type and the two obese groups. Contrarily to what happens in wild-type mice, leptin increased galactose uptake in db/db animals; since these mice lack the functional long leptin receptor, the measured effect may be due to the short receptor signaling. In the ob/ob mice, 0.2 nM leptin also increased galactose absorption whereas 0.4 nM did not have any effect, suggesting that in the genetically obese animals the expression and regulation of leptin receptors may be altered.

Animals↗

Reactive, degenerative, and proliferative Schwann cell responses in experimental galactose and human diabetic neuropathy.

Despite early descriptions of hypertrophic Schwann cells and onion-bulb formation in patients with diabetic neuropathy, clinical and experimental studies have emphasized axonal pathology. In recent years, the Schwann cell has been further implicated in diabetic neuropathy because it is the primary intrafascicular location for the first enzyme of the polyol pathway, aldose reductase, which appears to have a role in modulating a variety of complications of diabetes, including diabetic neuropathy. To further explore the role of polyol pathway flux in the pathogenesis of Schwann cell injury, ultrastructural abnormalities of Schwann cells in human diabetic neuropathy (HDN) were compared with those in experimental galactose neuropathy (EGN), a well-characterized model of hyperglycemia without hypoinsulinemia. Similar to previous studies of EGN, reactive, degenerative and proliferative changes of Schwann cells were observed after 2, 4 and 24 months of galactose intoxication. Reactive changes included accumulation of lipid droplets, pi granules of Reich and glycogen granules, increased numbers of subplasmalemmal vesicles, cytoplasmic expansion, and capping. Degenerative changes included enlargement of mitochondria and effacement of cristae, and disintegration of both abaxonal and adaxonal cytosol and organelles. Both demyelination and onion-bulb formation were seen at all time points, although supernumerary Schwann cells and axonal degeneration were most numerous after 24 months of galactose feeding. In sural nerve biopsy samples from patients with diabetes and progressive worsening of neuropathy, ultrastructural abnormalities in Schwann cells encompassed the full range of reactive, degenerative and proliferative changes described in galactose-fed rats. The concordance of fine-structural observations in nerves from galactose-fed rats and these adult-onset diabetic patients emphasizes the role of flux through aldose reductase in the complex pathology of diabetic neuropathy and points to the utility of galactose intoxication in helping to understand this metabolic disorder.

Adult↗

Effect of quercetin on galactose-induced hyperglycaemic oxidative stress in hepatic and neuronal tissues of Wistar rats.

In recent times there has been great demand for natural products that have possible preventive action against diabetes and its secondary complications. Keeping this in mind, this study was undertaken to investigate the influence of the flavonoid, quercetin, on oxidative stress markers and the antioxidant defence system of hepatic and neuronal tissues from galactose-induced hyperglycaemic rats. Weanling male Wistar rats were treated with 30% galactose in AIN 93 diet (group B, n=8) to induce hyperglycaemia. Control rats received normal Stock AIN 93 diet (group A, n=8). The third set of rats received group B diet with quercetin at 400 mg/100 g diet (group C, n=8). Glucose levels and body weights were measured on a weekly basis for four weeks to monitor the hyperglycaemia induced by galactose feeding. Parameters involved in the pathogenesis of galactose-induced hyperglycaemia, which included organosomatic index, protein content, antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px), tryptophan fluorescence, content of protein carbonyls, prooxidant malonaldehyde (MDA) and glutathione (GSH) in hepatic and neuronal tissues were determined at the end of the fourth week. The study suggest that quercetin counters the pro-oxidant effects of galactose-induced hyperglycaemic stress, as there was a significant reversal of changes with respect to body weights, organosomatic index of hepatic and neuronal tissues, lipid peroxidation, protein carbonyl content, reduced glutathione and activities of antioxidant enzymes. In addition, treatment with quercetin appears to reduce the osmotic stress induced by hyperglycaemia, as assessed by polyol pathway enzyme aldose reductase. These results imply that inclusion of quercetin in the diet controls, to some extent, galactose-induced hyperglycaemia and its attendant complications.

Animal Feed↗

D-galactose-caused life shortening in Drosophila melanogaster and Musca domestica is associated with oxidative stress.

D-galactose causes aging acceleration in different animal models but the mechanism is unclear. In the present study, we investigated the effects of D-galactose on lifespan and oxidative stress biomarkers in the fruit fly (Drosophila melanogaster) and housefly (Musca domestica). D-galactose was added to drinking water (20 mg/ml) for housefly and to culture medium (6.5%) for fruit fly from 24 h after emergence. Oxidative stress was estimated by measuring the activity of Cu-Zn-superoxide dismutase (SOD) and the levels of lipid peroxidation products, namely malondialdehyde (MDA) and lipofuscin in housefly brain (male) and in fruit fly (male and female). D-galactose caused a significant decrease in mean lifespan (by 12.6% of male and 15.9% of female) and maximum lifespan (by 12.9% of male and 17.1% of female) in fruit fly, and also a significant decrease in mean lifespan (by 27.1% of male, 19.8% of female) and maximum lifespan (by 27.1% of male, 21.9% of female) in housefly. MDA and lipofuscin increased with age in fruit fly and in housefly brains while change of the SOD activity showed a biphasic shape with age. D-galactose caused a significant increase in MDA and lipofuscin and decrease in SOD activity in the age-matched fruit flies and houseflies. These data indicate that D-galactose shortens the lifespan of the two different fly species and that the life shortening effect is associated with an increase in oxidative stress.

Animals↗

Aldose reductase inhibition prevents galactose-induced ovarian dysfunction in the Sprague-Dawley rat.

OBJECTIVE: Our objective was to determine whether impaired ovarian function induced by short-term creation of a galactosemic state in the rat might be prevented by the coadministration of an aldose reductase inhibitor. STUDY DESIGN: Prepubertal Sprague-Dawley rats were fed four different diets including (1) control, (2) 40% galactose, (3) 40% galactose and an aldose reductase inhibitor, and (4) an aldose reductase inhibitor with the control diet. Percentage germinal vesicle breakdown, postovulatory oocyte quantities, hormonal parameters, ovarian histologic evaluation, and ovarian galactitol concentrations were determined. RESULTS: The galactose-fed animals (group 2) had decreased germinal vesicle breakdown (47%) versus control (69%, p < 0.05). Galactose-exposed animals had significantly decreased quantities of postovulatory eggs (6.4 per animal) after menotropin ovarian stimulation in comparison with controls (14.1, p < 0.01). In rats exposed to high dietary levels of galactose (group 2) ovarian galactitol concentrations were significantly higher (protein 42.12 mumol/gm versus 0.0 for controls, p < 0.005). When galactose-fed animals received the aldose reductase inhibitor, ovarian accumulation of galactitol was significantly reduced and the observed detrimental effects on the oocyte were prevented. CONCLUSION: Galactitol accumulation or metabolic flux through aldose reductase in galactosemic rodents may be involved in the demonstrated ovarian dysfunction.

Aldehyde Reductase↗

Purification of galactose oxidase from Dactylium dendroides by affinity chromatography on melibiose-polyacrylamide.

Galactose oxidase is a fungal enzyme which is known to oxidize the C-6 hydroxymethyl of galactose and galactosamine to an aldehyde group. It has been widely used in glycoconjugate research, for example in the labeling of asialoglycoproteins. We have developed a simple affinity purification for galactose oxidase using melibiose-polyacrylamide. This affinity procedure was used to purify the enzyme from ammonium sulfate precipitates of culture filtrates of Dactylium dendroides. The material containing proteases and other contaminants is eluted in the buffer wash. The galactose oxidase is then specifically eluted from the column with buffer containing 0.1 M D-fucose or D-galactose. Using this procedure, the enzyme was also purified from commercial samples of galactose oxidase which contain high proteolytic activity.

Acrylic Resins↗

Resting membrane potential in 41A3 mouse neuroblastoma cells. Effect of increased glucose and galactose concentrations.

Neuroblastoma cells were used to examine the effect of high concentrations of glucose or galactose and accumulation of polyols on the resting membrane potential. Polyol levels are increased and myo-inositol content decreased when neuroblastoma cells are chronically exposed to media containing 30 mM glucose or 30 mM galactose compared to cells grown in media containing 30 mM fructose. Furthermore, the 6 h accumulation and incorporation into phospholipid of extracellular myo-inositol is decreased in cells exposed to media containing 30 mM glucose or 30 mM galactose compared to cells grown in media containing 30 mM fructose. The resting membrane potential was determined by examining the steady-state accumulation of the lipophilic cation tetra[3H]phenylphosphonium bromide (TPP+). The resting membrane potential of cells grown in media containing 30 mM fructose is about -70 mV which is very similar to the resting membrane potential of cells grown in unsupplemented media. The resting membrane potential is significantly decreased in cells grown in media containing 30 mM glucose or 30 mM galactose. myo-Inositol metabolism and content and polyol levels are maintained at near normal values and the resting membrane potential is improved when media containing 30 mM glucose or 30 mM galactose are supplemented with 0.4 mM sorbinil. Acute exposure of neuroblastoma cells to 2 mM ouabain had no significant effect on [3H]TPP+ accumulation. This suggests that acute inhibition of Na+/K+ pump activity does not decrease the resting membrane potential of neuroblastoma cells. The decrease in resting membrane potential may be induced by the metabolic abnormalities and/or chronic decrease in Na+/K+ pump activity which occur when neuroblastoma cells are chronically exposed to increased glucose or galactose concentrations.

Animals↗

Accumulation of galactonate in liver of suckling rats perfused with galactose.

Livers of 14-day-old suckling rats were perfused for 30 min in the nonrecirculating (once-through) mode with media containing 0-60 mM galactose. Galactonate was detected in livers perfused with as little as 1 mM galactose and increased with higher perfusate galactose to 178 nmoles per gram of liver at 60 mM hexose. Tissue galactonate levels were as high as 60% of galactose-1-phosphate which also accumulated under the same conditions. Galactonate was also found to be present in the effluent perfusate. The perfused suckling rat liver appears to be a physiological model for assessing the role of galactose oxidation to galactonate as an alternate metabolic pathway of galactose metabolism.

Animals↗

Effects of a membrane sugar analogue, 6-deoxy-6-fluoro-D-galactose, on the L1210 leukemic cell ectosialyltransferase system.

In L1210 leukemia cells, 6-deoxy-6-fluoro-D-galactose specifically inhibited the incorporation of [3H]-D-galactose, while that of other precursors of glycoconjugate biosynthesis, including mannose and glucosamine, was unaffected. The activation of [6-3H]-6-deoxy-6-fluoro-D-galactose to a nucleotide sugar was similar to that found for [3H]-D-galactose. The incorporation of either sugar after 1 hr was visualized by electron microscopic autoradiography to be in the Golgi region. Treatment of L1210 cells with 6-deoxy-6-fluoro-D-galactose in vitro or in vivo resulted in a specific, dose- and time-dependent decrease in the activity of cell surface sialyltransferase (ectosialyltransferase) but not of 5'-nucleotidase, a plasma membrane marker enzyme. The decrease in ectosialyltransferase activity appeared to be selective and is suggested to be due to structural modification of the cell surface galactoprotein acceptors for this enzyme. The data indicate that 6-deoxy-6-fluoro-D-galactose is an effective modifier of cellular glycoconjugate in that its incorporation into certain cell surface components results in a modification of plasma membrane structure and function.

Animals↗

Inhibition of galactose-induced alterations in ocular lens with sorbinil.

Lens ultrastructure and Na- K-ATPase activity in the lenses of rats fed galactose and a galactose + sorbinil diet (aldose reductase inhibitor) were studied. Lenses of rats on the galactose diet exhibited development of peripheral opacity within 3-4 days. This opacity progressed with the continuation of the galactose feeding, and by 20 days mature cataracts were observed in these animals. The formation of vacuoles, cysts, membrane disruption in the epithelium and fibers, and swelling of fibers accompanied the development of opacity. With the progression of opacity there was a considerable drop in lens Na- K-ATPase activity in the galactose-fed animals. However, the lenses of rats that were treated with sorbinil did not show any of the alterations in the ultrastructure of the epithelium and fibers that accompany galactose cataractogenesis. The level of Na-K-ATPase activity in the sorbinil-treated animals was similar to that found in lenses from the laboratory chow-fed group of rats. These observations further substantiate the role of aldose reductase in sugar-cataract development.

4-Nitrophenylphosphatase↗

Modelling cortical cataractogenesis VII: Effects of vitamin E treatment on galactose-induced cataracts.

The possibility that vitamin E or other antioxidants might prevent cataracts was tested by incubating rat lenses in vitro in galactose-enriched medium or by treating rats fed a diet containing 50% galactose (w/w). The vitamin E was added to the medium at 2.4 microM, and to the diet at a level of 5 g kg-1 diet. In vitro, lenses incubated with 55.6 mM galactose underwent globular degeneration, which was partially prevented by addition of vitamin E (2.4 microM). Even in such vitamin E-protected lenses, which appeared clear, many small globules could be seen in the region of interdigitation at the 'corners' where hexagonal cells intersected. In vivo, in dietary experiments, a dense nuclear opacity of the lens was observed after approximately 5 weeks; unlike diabetic cataracts, this was not prevented by the addition of vitamin E to the diet. The extensive globular degeneration observed was typical of that found in long-term (21-week diabetic) cataracts. Although no significant difference in cataract incidence was observed, the extent of damage in vitamin E-treated rat lenses appeared to be less. The difference in effectiveness of vitamin E in galactose-induced cataracts, as compared to diabetic cataracts, is tentatively ascribed to (1) the more severe osmotic stress expected from the products of the aldose reductase pathway for galactose and (2) the greater depletion of reduced pyridine nucleotides (NADPH + NADH) expected of galactose as compared to glucose.

Animals↗

Rat lens prostaglandin biosynthesis during galactose-induced cataractogenesis.

The relationship between the development of galactose-induced cataractogenesis and rat lens microsomal prostaglandin (PG) biosynthesis was studied. Within 24 hr of the introduction of 50% galactose to the rat's diet, lens PGF2 alpha production fell dramatically to 31% of control. Following the initial depression of PGF2 alpha biosynthesis, the ability to generate PGF2 alpha in lens microsomes slightly recovered reaching 58- and 53% of controls at day 2 and day 5 on the sugar diet, respectively. Determination of microsomal PGF2 alpha biosynthesis at 9- and 21 days revealed a continued decline in PG synthesis with complete cessation of PGF2 alpha synthesis by day 36 (hypermature cataracts, +5). The decreased PGF2 alpha biosynthetic capacity was a result of decreased cyclo-oxygenase activity since: PGE2 production demonstrated a similar time course for inhibition; and lens microsomes from control and galactose fed rats revealed no difference in the PGs produced from PGH2 endoperoxide. Neither galactose (1 mM) nor galactitol (1 mM), when added to control microsomal preparations inhibited PG biosynthesis, eliminating the possibility of a direct effect of the sugar, or its metabolite, on cyclo-oxygenase activity. While PG biosynthesis was rapidly inhibited by the galactose feeding no changes were observed in basal lens cyclic AMP levels measured during the first 5 days of the feedings. These results demonstrate that depressed PG biosynthesis is an early consequence of galactose feeding.

Animals↗

Increases in collagen type IV and laminin in galactose-induced retinal capillary basement membrane thickening--prevention by an aldose reductase inhibitor.

Biochemical alterations in the composition of retinal capillary basement membrane components were investigated in galactosemic rats, an animal model that develops basement membrane lesions comparable to those of diabetic retinopathy. Normotensive Wistar-Kyoto rats fed a 30% galactose diet for 9 months developed significant thickening of retinal capillary basement membranes by comparison with animals fed a control test diet (P less than 0.001), or animals on a diet containing 30% galactose and 250 mg kg-1 of the aldose reductase inhibitor sorbinil (P less than 0.001). A quantitative electron microscopic immunogold technique applied on ultrathin sections of the retinas of these animals showed that the labeling densities of collagen type IV and laminin per unit cross-sectional area (which is presumably proportional to the concentrations of these molecules) were significantly increased in the retinal capillary basement membranes of galactose-fed rats, compared with animals on the control test diet. Increases in these two components of basement membranes were prevented by addition of sorbinil to the diet. However, there was no significant change in the labeling density of heparan sulfate proteoglycan (HSPG) core protein in the basement membranes of galactose-fed rats in comparison to animals on either the control diet or galactose-sorbinil diet. Two types of striated fibrillar materials were frequently found in areas of focal thickening of basement membranes of galactose fed rats only. Thinner fibrils reacted strongly with collagen type III antibody, whereas thicker fibrils reacted weakly with collagen type I antibody. Our results indicate that there is an increase in labeling densities of collagen type IV and laminin in thickened basement membranes of retinal capillaries of galactosemic rats along with the expression of interstitial collagens like collagen type III and an abnormal collagen that weakly cross-reacts with antibody to collagen type I, and these effects of galactosemia on the basement membranes are preventable by an aldose reductase inhibitor.

Aldehyde Reductase↗

Modification by site-directed mutagenesis of the specificity of Erythrina corallodendron lectin for galactose derivatives with bulky substituents at C-2.

Examination of the three-dimensional structure of Erythrina corallodendron lectin (ECorL) in complex with a ligand (lactose), the first of its kind for a Gal/GalNAc-specific lectin [(1991) Science 254, 862-866], revealed the presence of a hydrophobic cavity, surrounded by Tyr108 and Pro134-Trp135, which can accommodate bulky substituents such as acetamido or dansylamido (NDns) at C-2 of the lectin-bound galactose. Comparison of the primary sequence of ECorL with that of soybean agglutinin, specific for galactose and its C-2 substituted derivatives, and of peanut agglutinin, specific for galactose only, showed that in soybean agglutinin, Tyr108 is retained, and Pro134-Trp135 is replaced by Ser-Trp, whereas in peanut agglutinin, the former residue is replaced by Thr and the dipeptide by Ser-Glu- Tyr-Asn. Three mutants of ECorL were therefore constructed: L2, in which Pro134-Trp135 was replaced by Ser-Glu-Tyr-Asn; Y108T, in which Tyr108 was replaced by Thr and the double mutant L2; Y108T. They were expressed in Escherichia coli, as done for recombinant ECorL [(1992) Eur. J. Biochem. 205, 575-581]. The mutants had the same hemagglutinating activity as native or rECorL. Their specificity for galactose, GalNAc and Me beta GalNDns was examined by inhibition of hemagglutination and of the binding of the lectin to immobilized asialofetuin; in addition, their association constants with Me alpha GalNDns and Me beta GalNDns were measured by spectrofluorimetric titration. The results showed that Y108T had essentially similar specificity as the native and recombinant lectins. The affinity of L2 and L2;Y108T for galactose was also the same as ECorL, but they had a lower affinity for GalNAc and markedly diminished affinity for the dansyl sugars (up to 43 times, or 2 kcal, less). This appears to be largely due to steric hindrance by the two additional amino acids present in the cavity region in these mutants. Our findings also provide an explanation for the inability of PNA to accommodate C-2-substituted galactose derivatives at its primary subsite.

Amino Acid Sequence↗

Assessment of lactose absorption by measurement of urinary galactose.

Individuals with sufficient intestinal lactase hydrolyze ingested lactose to galactose and glucose and these monosaccharides are absorbed. Lactose is not digested completely when intestinal lactase activity is low and the disaccharide is malabsorbed. Breath hydrogen excretion after lactose ingestion is used commonly to diagnose lactose malabsorption. However, no direct tests are currently used to assess lactose absorption. We tested a new method of assessing lactose absorption in 26 healthy individuals. Each subject ingested 50 g of lactose. Participants were evaluated for lactose malabsorption using a standard 3-h breath hydrogen test. In addition, the urinary excretions of galactose, lactose, and creatinine were quantitated for 3-5 h after lactose ingestion. On the basis of breath hydrogen analysis after lactose ingestion, 12 individuals were lactose malabsorbers (defined as a rise in the breath hydrogen concentration of greater than 20 parts per million above the baseline value). The 14 subjects who did not malabsorb lactose by breath hydrogen testing (defined as a rise in the breath hydrogen concentration of less than or equal to 20 parts per million above the baseline value), had significantly more galactose in their urine 1, 2, and 3 h after lactose ingestion than lactose malabsorbers. The ratio of excreted lactose to excreted galactose was significantly decreased in lactose absorbers compared with lactose malabsorbers (p less than 0.001). Determination of the ratio of urinary galactose to urinary creatinine separated lactose absorbers from lactose malabsorbers completely (p less than 0.001). We conclude from this study that the determination of urinary galactose, urinary lactose/galactose ratio, and urinary galactose/creatinine ratio may be used to assess lactose digestion and absorption in healthy adults.

Adolescent↗

Regulation of rat liver glycogen synthesis and activities of glycogen cycle enzymes by glucose and galactose.

Direct regulation of rat liver glycogen metabolism by glucose and galactose was studied using an isolated liver perfusion system. Activation of glycogen synthase and net glycogen synthesis increased linearly when perfusate glucose concentration was increased from 125 to 500 mg/100 ml. Galactose, rapidly taken up by isolated rat liver regardless of circulating glucose concentration, increased these responses to glucose. In the presence of galactose (greater than or equal to 5 mg/100 ml), activation of synthase and glycogen synthesis were 1.5-fold higher at any given glucose concentration. The addition of insulin did not appreciably after synthase activation by glucose and galactose. Phosphorylase activity, low at circulating glucose levels above 125 mg/100 ml, was further decreased as glucose was increased or when galactose was added to the perfusate. Release of glucose into the perfusate in response to aglycemia was increased in the presence of galactose.

Animals↗