Vascular Endothelial Growth Factor Receptor, fms-Like Tyrosine Kinase-1 (Flt-1), as a Novel Binding Partner for SARS-CoV-2 Spike Receptor-Binding Domain

Angiotensin-converting enzyme 2 (ACE2) and neuropilin 1, a vascular endothelial growth factor (VEGF) receptor, were identified to bind to the SARS-CoV-2 spike receptor-binding domain (spike RBD). In silico analysis based on 3D structure, multiple sequence alignment, and molecular docking of second domain of soluble Flt-1 (sFlt-1) and spike RBD revealed structural similarities, sequence homology, and protein-protein interaction. Interaction and binding of recombinant spike RBD (rspike RBD) and recombinant sFlt-1 (rsFlt-1) in vitro induced a conformational change, as revealed by spectrofluorimetric data, with increased fluorescence intensity in emission spectra as compared to either of the proteins alone. Results on ELISA confirmed the binding and cross-reactivity of rspike-RBD and rsFlt-1 as determined by using either specific antibodies towards each protein or immunized human serum. We found that polyclonal or monoclonal anti-spike RBD antibodies can recognize either rsFlt-1 or rspike RBD, showing cross-reactivity for the two proteins in a dose-dependent binding response. Recognition of bound rspike RBD or rsFlt-1 by anti-Flt-1 or anti-spike RBD antibodies, respectively, as observed by immunoblotting, further confirmed interaction between the two proteins. Immunoprecipitation and immunoblot analysis demonstrated the identification of rspike RBD binding to the Flt-1 receptor on A549 cells. Further, the binding of rspike RBD to Flt-1 receptor was shown using immunofluorescence on 2D-culture or 3D-spheroid of MDA-MB-231 cells, which over-express Flt-1 receptor. Together, our study concludes that the Flt-1 receptor is a novel binding partner for SARS-CoV-2 spike RBD.

Comparative assessment of cognitive impairment and oxidative stress markers among vitamin D insufficient elderly patients with and without type 2 diabetes mellitus (T2DM)

BACKGROUND

Disorders of mental health are known to affect cognitive functions, hence called as cognitive disorders. Impaired glucose metabolism, insulin resistance, vitamin-D deficiency and oxidative stress are some of the key early events reported to be involved in the pathogenesis of most common cognitive disorders, which include Alzheimer's disease. Type-2 diabetes mellitus (T2DM) is one of the known contributing factors of cognitive impairment and dementia.

METHODS

A cross sectional study was carried out in 145 subjects, who were assessed for cognitive function by modified mini mental status examination (3MS). In addition, measurement of fasting blood sugar (FBS), fasting insulin, HbA1c, lipid profile, vitamin D and oxidative markers was performed. Participants were divided into different groups based on (a) vitamin D insufficiency and sufficiency; (b) diabetic and non-diabetic with and without cognitive impairment.

RESULTS

The study included a total of 145 subjects; 51 males and 94 females and the mean age was 68.24±9.70 years. Among diabetics with vitamin D insufficiency, 35 subjects (71.43%) had cognitive impairment, but, among non-diabetics with vitamin D insufficiency, 27 subjects (62.79%) had cognitive impairment. Chi square test showed no significant association between diabetes, vitamin D insufficiency and cognitive impairment. Glutathione peroxidase (GPx) and superoxide dismutase (SOD) levels were non-significantly lower in cognition-impaired subjects, when compared to cognition normal subjects in diabetics with vitamin D insufficiency.

CONCLUSION

Our study showed that cognitive impairment is more predominant in individuals with diabetes. However, our study did not find any significant relationship between T2DM, vitamin D deficiency, cognitive impairment, and oxidative stress. A significant association was found only with GPx and 3MSE score in vitamin D insufficient non-diabetics.

Anti-diabetic effect of dietary mango (Mangifera indica L.) peel in streptozotocin-induced diabetic rats

BACKGROUND

In the present study, the composition of mango peel powder (MPP) collected from the mango pulp industry was determined and the effect of MPP on ameliorating diabetes and its associated complications was studied.

RESULTS

Mango peel was rich in polyphenols, carotenoids and dietary fibre. Peel extract contained various bioactive compounds and was found to be rich in soluble dietary fibre. Peel extract exhibited antioxidant properties and protected against DNA damage. Therefore, the effect of peel on ameliorating diabetes was investigated in a rat model of diabetes. A significant increase in urine sugar, urine volume, fasting blood glucose, total cholesterol, triglycerides and low density lipoprotein, and decrease in high density lipoprotein were observed in the rats; however, these parameters were ameliorated in diabetic rats fed with diet supplemented with mango peel at 5% and 10% levels in basal diet. Treatment of diabetic rats with MPP increased antioxidant enzyme activities and decreased lipid peroxidation in plasma, kidney and liver compared to untreated diabetic rats. Glomerular filtration rate and microalbuminuria levels were ameliorated in MPP treated diabetic group.

CONCLUSIONS

Mango peel, a by-product, can be used as an ingredient in functional and therapeutic foods.

Tinospora cordifolia consumption ameliorates changes in kidney chondroitin sulphate/dermatan sulphate in diabetic rats

Diabetes is known to alter kidney extracellular matrix (ECM) components. Chondroitin sulphate (CS)/dermatan sulphate (DS), an ECM component, which plays an essential role in kidney is altered during diabetes. The focus of this study has been to examine the effect of Tinospora cordifolia (TC) consumption, a potent plant widely used to treat diabetes, on kidney CS/DS. Experimentally induced diabetic rats were fed with diet containing TC at 2·5 and 5 % levels and the effect of it on kidney CS/DS was examined. The CS/DS content and CS:heparan sulphate ratio which was decreased during diabetic condition were ameliorated in TC-fed groups. Disaccharide composition analysis of CS/DS by HPLC showed that decreases in 'E' units and degree of sulphation were modulated in 5 % TC-fed groups. Apparent molecular weight of purified CS/DS from the control rat kidney was found to be 38 kDa which was decreased to 29 kDa in diabetic rat kidney. Rats in 5 % TC-fed groups showed chain length of 38 kDa akin to control rats. Expression of chondroitin 4-O-sulfotransferase-1, dermatan 4-O-sulfotransferase-1 and N-acetylgalactosamine 4 sulphate 6-O-sulfotransferase, enzymes involved in the synthesis of 'E' units which was reduced during diabetic condition, was significantly contained in the 5 % TC-fed group. Purified CS/DS from 5 % TC-fed group was able to bind higher amounts of ECM components, namely type IV collagen and laminin, when compared with untreated diabetic rats. The present results demonstrate that consumption of a diet containing TC at the 5 % level modulates changes in kidney CS/DS which were due to diabetes.

Enhancement of soluble dietary fibre, polyphenols and antioxidant properties of chapatis prepared from whole wheat flour dough treated with amylases and xylanase

BACKGROUND

Chapati preparation involves various processing steps such as mixing the flour into dough, sheeting and baking. During these processing steps, flour components are likely to undergo changes in their nutrient and polyphenol composition and their antioxidant properties due to phenol-mediated crosslinking of proteins and carbohydrates. Therefore, in the present study, changes in nutritional, nutraceutical and antioxidant properties of chapatis prepared from doughs treated with amylases and xylanase were determined.

RESULTS

An increase in insoluble dietary fibre content and a decrease in soluble polyphenol content were observed during preparation of control chapatis from whole wheat flours. However, significant increases in soluble dietary fibre and soluble polyphenol contents were observed in chapatis prepared from amylase-treated doughs compared with control chapatis. Extracts of chapatis prepared from amylase- and xylanase-treated doughs showed better antioxidant properties than extracts of control chapatis. Among these enzyme treatments, chapatis prepared from amylase-treated doughs showed better antioxidant properties than chapatis prepared from xylanase-treated doughs. High-performance liquid chromatography analysis of extracts of chapatis prepared from doughs treated with amylases showed the presence of potential antioxidant phenolic acids such as caffeic, gentisic and syringic acids in addition to the phenolic acids present in control chapatis.

CONCLUSION

Treatment of doughs with amylases increased the contents of soluble dietary fibre and soluble polyphenols as well as improving the antioxidant properties of chapatis.

Erythrocytes express chondroitin sulphate/dermatan sulphate, which undergoes quantitative changes during diabetes and mediate erythrocyte adhesion to extracellular matrix components

Glycosaminoglycans (GAGs) such as chondroitin sulphate/dermatan sulphate (CS/DS) are complex molecules that are widely expressed on the cell membrane and extracellular matrix (ECM). They play an important role in wide range of biological activities especially during pathological conditions. Diabetes, a metabolic disorder characterized by sustained hyperglycemia, is known to affect GAGs in different tissues and affect erythrocyte adhesion. The present investigation was aimed at exploring the nature of GAGs present in erythrocytes and its role on adhesion of erythrocytes from control and diabetic rats to major extracellular matrix components. GAGs isolated from erythrocytes were demonstrated to be CS/DS and a 2-fold increase was observed in erythrocytes from diabetic rats. Disaccharide composition analysis by HPLC after depolymerization by the enzyme, chondroitinase ABC showed the presence of 4-O sulphated disaccharide units with small amounts of non-sulphated disaccharides, in both control and diabetic erythrocytes. Erythrocytes from diabetic rats, however, showed significantly increased binding to poly-l-ornithine (P-orn), type IV collagen, laminin and fibronectin, which was abrogated on treatment with chondroitinase ABC to various degrees. This study sheds new light on CS/DS in erythrocytes and its likely biological implications in vivo.

Progression of early phase diabetic nephropathy in streptozotocin-induced diabetic rats: evaluation of various kidney-related parameters

Diabetic nephropathy (DN) is one of the serious secondary complications of diabetes, which results in end-stage renal failure. Reports on the progressive nature of early phase DN especially with respect to kidney parameters such as kidney weight, type IV collagen excretion, total kidney and urinary glycosaminoglycans (GAGs) are few. This work was undertaken to determine systematically the progression of early phase DN in relation to various kidney-related parameters for a period of four months. Experimentally-induced diabetic rats were grouped based on fasting blood glucose levels. Various basic and kidney-related parameters such as kidney weight, microalbuminuria, urinary excretion of GAGs and type IV collagen, total kidney GAGs, histopathology, glomerular area and glomerular volume were examined in control and diabetic rats. There was a progressive increase in fasting blood sugar, urine sugar, kidney weight, microalbuminuria, urine glycosaminoglycans, urine type IV collagen, glomerular area and glomerular volume but there was a progressive decrease in kidney glycosaminoglycans. Glomerular sclerotic condition was aggravated with the increase in duration of diabetes from 1 to 4 months. Onset of DN in rats begins subtly after one month of diabetes but gets vitiated and more pronounced at the end of four months.

Banana (Musa sp. var. elakki bale) flower and pseudostem: dietary fiber and associated antioxidant capacity

Banana flower (BF) and pseudostem (PS) are byproducts of banana cultivation and are known to have health beneficial effects. The main objective of this study was to evaluate the dietary fiber composition and antioxidant effect of BF and PS. In the present study, BF and PS were found to be rich in dietary fiber (65.6 ± 1.32 and 28.8 ± 0.98%, respectively). Dietary fiber fractions were extracted and characterized in terms of sugar profile, and antioxidant activities were determined. BF and PS fractions were rich in sugars and showed wide diversity with respect to the nature of the sugars. Hemicellulose A fraction of BF showed high amounts of total polyphenols and total antioxidants, which were 121.8 ± 1.9 and 39.03 ± 0.118 μg/mg extract, respectively. HPLC analysis showed the presence of phenolic acids in hemicellulose A and B fractions of BF. These results indicate that BF and PS are rich sources of dietary fiber associated with polyphenols, which could promote health beneficial effects.

Role of advanced glycation on aggregation and DNA binding properties of α-synuclein

Parkinson's disease (PD) is a neurodegenerative disease with multiple etiologies. Advanced glycation end products (AGEs) accumulate in the aging brain and could be one of the reasons for age-related diseases like PD. Oxidative stress also leads to the formation of AGEs and may be involved in neurodegeneration by altering the properties of proteins. α-Synuclein is involved in pathogenesis of PD and there are limited studies on the role of AGE-α-synuclein in neurodegeneration. We studied the aggregation and DNA binding ability of AGE-α-synuclein in vitro. α-Synuclein is glycated using methylglyoxal and formation of AGE-α-synuclein is characterized using fluorescence studies, intrinsic tyrosine fluorescence, and fructosamine estimation. The results indicated that AGE-α-synuclein aggregates into smaller globular-like aggregates compared to fibrils formed with native α-synuclein. Further, it is found that AGE-α-synuclein induced conformational changes in scDNA from B-form to B-C-A mixed conformation. Additionally, AGE-α-synuclein altered DNA integrity as evidenced by the melting temperature, ethidium bromide, and DNAse I sensitivity studies. AGE-α-synuclein converted biphasic Tm to higher monophasic Tm. The Tm of AGE-α-synuclein-scDNA complex is more than that of native α-synuclein-scDNA complex, indicating that AGE-α-synuclein stabilized the uncoiled scDNA. AGE-α-synuclein could stabilize the uncoiled scDNA, as shown by the decrease in the number of ethidium bromide binding molecules per base pair of DNA. DNAse I sensitive studies indicated that both AGE-α-synuclein-scDNA and α-synuclein-scDNA are resistant to DNAse I digestion. The relevance of these findings to neuronal cell death is discussed.

Stimulation of glucose uptake by Musa sp. (cv. elakki bale) flower and pseudostem extracts in Ehrlich ascites tumor cells

BACKGROUND

Glucose uptake study plays a major role in diabetes research. Impaired glucose uptake has been implicated in the development of hyperglycemia during diabetes. Banana plant is known for its anti-diabetic properties and our earlier report revealed that banana flower and pseudostem of Musa sp. cv. elakki bale is beneficial during diabetes in rat models. The present study was designed to evaluate the potential effect of banana flower and pseudostem extracts on glucose uptake in Ehrlich ascites tumor (EAT) cells using 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxy-D-glucose (2-NBDG), a fluorescent analogue of 2-deoxyglucose.

RESULTS

Methanol and aqueous extracts of banana flower and pseudostem were more potent in promoting glucose uptake in EAT cells, in comparison to acetone and ethanol extracts. At 20 µg dosage, highest net glucose uptake was observed in aqueous extracts of banana flower (18.17 ± 0.43 nmol L⁻¹) and pseudostem (19.69 ± 0.41 nmol L⁻¹). Total polyphenol content was higher in methanol (9.031 ± 0.036 g kg⁻¹) and aqueous (6.862 ± 0.024 g kg⁻¹) extracts of banana flower compared to pseudostem, which were 0.442 ± 0.006 and 0.811 ± 0.011 g kg⁻¹, respectively.

CONCLUSION

Banana flower and pseudostem extracts are able to promote glucose uptake into the cells, presumably through glucose transporters 1 and 3, which could be beneficial in diabetes. Glucose uptake is likely promoted by phenolic acids besides other bioactives. It can be hypothesized that consumption of nutraceutical-rich extract of banana flower and pseudostem could replace some amount of insulin being taken for diabetes.

Diabetes results in structural alteration of chondroitin sulfate/dermatan sulfate in the rat kidney: effects on the binding to extracellular matrix components

Chondroitin sulfate (CS)/dermatan sulfate (DS) is a group of sulfated polymers, which play an essential role in various biological phenomena. In the kidney, they are present in small but significant amounts. Studies on their structure-function relationship in the kidney and their changes during diabetic conditions have not been rigorously looked into, which is the focus of this paper. The CS/DS content decreased significantly (14%) during diabetic conditions. This was accompanied by a decrease in the CS/heparan sulfate ratio. Disaccharide composition analysis revealed fine structural changes especially with respect to the E unit [glucuronic acid β1-3 N-acetyl d-galactosamine (4,6-O-sulfate)] and the degree of sulfation. The mRNA expression levels of major enzymes involved in the synthesis of the "E"-disaccharide unit showed a decrease during diabetes. The changes in CS/DS had implications on ligand-binding properties when tested in vitro for binding to major extracellular matrix (ECM) components such as type IV collagen, laminin and fibronectin. Thus, this study provides insights into the structure-function relationship of CS/DS in the kidney during diabetes and alterations of which could aggravate conditions such as diabetic nephropathy by virtue of them being a part of ECM components.

Structural characterization of N-linked oligosaccharides of laminin from rat kidney: changes during diabetes and modulation by dietary fiber and butyric acid

Carbohydrates of laminin, a family of large multidomain glycoproteins, have been implicated in various cellular activities including maintaining the protein structure, its function and also basement membrane integrity. During the course of our investigation, we observed that purified laminin from kidneys of control, diabetic, and dietary fiber- and butyric acid-treated diabetic rats showed differences in binding to extracellular matrix components. This prompted us to determine whether there are structural changes in laminin oligosaccharides. In this study, we have characterized a few major N-linked oligosaccharides isolated from purified laminin in various experimental groups, viz. normal, diabetic and diabetic rats fed with dietary fiber and butyric acid. Sugar composition, as identified by GLC, revealed the presence of mannose, galactose and N-acetylglucosamine. In order to study fine structures of the oligosaccharides, N-linked oligosaccharides of laminin were released by Peptide-N-glycosidase F digestion, end-labeled with 2-anthranilic acid and fractionated by lectin affinity chromatography. Furthermore, structural elucidation carried out by MALDI-TOF MS/MS analysis showed variations in the oligosaccharide sequence of laminin during diabetes which were altered by the feeding of dietary fiber and butyric acid.

Purification and characterization of endo-beta-1,4 mannanase from Aspergillus niger gr for application in food processing industry

A thermostable extracellular beta-mannanase from the culture supernatant of a fungus Aspergillus niger gr was purified to homogeneity. SDS-PAGE of the purified enzyme showed a single protein band of molecular mass 66 kDa. The beta- mannanase exhibited optimum catalytic activity at pH 5.5 and 55 degrees C. It was thermostable at 55 degrees C, and retained 50% activity after 6 h at 55 degrees C. The enzyme was stable at a pH range of 3.0 to 7.0. The metal ions Hg(2+), Cu(2+), and Ag(2+) inhibited complete enzyme activity. The inhibitors tested, EDTA, PMSF, and 1,10-phenanthroline, did not inhibit the enzyme activity. N-Bromosuccinimide completely inhibited enzyme activity. The relative substrate specificity of enzyme towards the various mannans is in the order of locust bean gum>guar gum>copra mannan, with K(m) of 0.11, 0.28, and 0.33 mg/ml, respectively. Since the enzyme is active over a wide range of pH and temperature, it could find potential use in the food-processing industry.

Effect of bitter gourd and spent turmeric on glycoconjugate metabolism in streptozotocin-induced diabetic rats

AIM

Changes in glycoconjugate metabolism during the development of diabetic complications and their modulation by feeding bitter gourd and spent turmeric as fiber-rich source.

METHOD

This was studied by measuring the contents of total sugar, uronic acid, amino sugar, and sulfate in the streptozotocin-induced diabetic rats.

RESULTS

Total sugar content decreased in liver, spleen, and brain, while an increase was observed in heart and lungs. Uronic acid content in liver, spleen, and brain decreased, and marginal increase was observed in testis. Amino sugar content decreased in liver, spleen, lungs and heart during diabetes, and augmentation was observed to different extents. Decrease in sulfation of glycoconjugates was observed in liver, spleen, lungs and heart during diabetes and was significantly ameliorated by bitter gourd and spent turmeric, except brain. Protein content decreased in liver, while an increase was observed in brain. The studies clearly showed alteration in glycoconjugate metabolism during diabetes and amelioration to different extents by feeding bitter gourd and spent turmeric.

CONCLUSION

Improvement is due to slow release of glucose by fiber in the gastrointestinal track and short-chain fatty acid production from fiber by colon microbes.

Modulatory effect of bitter gourd (Momordica charantia LINN.) on alterations in kidney heparan sulfate in streptozotocin-induced diabetic rats

Glycoconjugates in the kidney play an important role in the maintenance of glomerular filtration barrier. Thickening of the glomerular basement membrane (GBM) is well characterized in diabetic nephropathy. Changes in GBM mainly include reduction and undersulfation of heparan sulfate, and laminin with accumulation of type IV collagen leading to kidney dysfunction and there is a need to identify therapies that arrest disease progression to end-stage renal failure. In the present investigation, effect of bitter gourd on streptozotocin-induced diabetic rats with particular emphasis on kidney heparan sulfate (HS) was studied. Earlier, our study showed partial reversal of all the diabetes-induced effects by bitter gourd. Increase in the components of glycoconjugates during diabetes was significantly decreased by bitter gourd feeding. Diabetes associated elevation in the activities of enzymes involved in the synthesis and degradation of glycosaminoglycans (GAGs) were significantly lowered by bitter gourd supplementation. GAGs composition revealed decrease in amino sugar, and uronic acid contents during diabetes and bitter gourd feeding was effective in countering this reduction. Decrease in sulfate content in the GAGs during diabetes was ameliorated by bitter gourd feeding. HS decreased by 43% in diabetic rats while bitter gourd feeding to diabetic rats showed 28% reduction. These results clearly indicate beneficial role of bitter gourd in controlling glycoconjugate and heparan sulfate related kidney complications during diabetes thus prolonging late complications of diabetes.

Effect of bitter gourd and spent turmeric on constituents of glycosaminoglycans in different tissues in streptozotocin induced diabetic rats

Diet is now one of the well established means in the management of diabetes. Bitter gourd and spent turmeric at 10% level were tested for their efficacy on glycosaminoglycan metabolism in various tissues viz., liver, spleen, lungs, heart and testis in control, diabetic and treated rats. The glycosaminoglycans (GAGs) were isolated from defatted and dried tissues. The contents of sulfated GAGs decreased in all the tissues and the decrease was more prominent in heart and testis. In the isolated GAGs, contents of total sugar, amino sugar, uronic acid and sulfate were studied. Decrease in total sugar content was maximum in testis. Amino sugar content decreased considerably in testis (38%) and lungs (15%). The content of uronic acid also decreased in testis (33%) besides heart (29%) and liver (25%). Sulfate groups in GAGs perform pivotal functions in many biological events and decrease in sulfate content was significant in heart (40%), testis (37%) and liver (37%). GAGs profile on the cellulose acetate electrophoresis revealed that heparan sulfate (HS), hyaluronic acid (HA) and chondroitin sulfate/dermatan sulfate (CS/DS) were present in liver, spleen and lungs. HS, CS were present in heart, DS/CS was observed in testis. The observed beneficial effects in GAGs metabolism during diabetes may be due to the presence of high amounts of dietary fibres present in bitter gourd and spent turmeric, besides, possible presence of bioactive compounds in one or both of them.

Effect of bitter gourd (Momordica charantia) on glycaemic status in streptozotocin induced diabetic rats

Bitter gourd (Momordica charantia), a commonly consumed vegetable is used as an adjunct in the management of diabetes mellitus. A study was carried out to examine the effect of edible portion of bitter gourd at 10% level in the diet in streptozotocin induced diabetic rats. To evaluate the glycaemic control of bitter gourd during diabetes, diet intake, gain in body weight, water intake, urine sugar, urine volume, glomerular filtration rate and fasting blood glucose profiles were monitored. Water consumption, urine volume and urine sugar were significantly higher in diabetic controls compared to normal rats and bitter gourd feeding alleviated this rise during diabetes by about 30%. Renal hypertrophy was higher in diabetic controls and bitter gourd supplementation, partially, but effectively prevented it (38%) during diabetes. Increased glomerular filtration rate in diabetes was significantly reduced (27%) by bitter gourd. An amelioration of about 30% in fasting blood glucose was observed with bitter gourd feeding in diabetic rats. These results clearly provided experimental evidence that dried bitter gourd powder in the diet at 10% level improved diabetic status signifying its beneficial effect during diabetes.

Modulatory effect of fenugreek seed mucilage and spent turmeric on intestinal and renal disaccharidases in streptozotocin induced diabetic rats

To elucidate the effect of feeding fenugreek seed mucilage and spent turmeric (10%) on disaccharidases activities, the specific activities of intestinal and renal disaccharidases viz., sucrase, maltase and lactase were measured in streptozotocin induced diabetic rats. Specific activities of intestinal disaccharidases were increased significantly during diabetes and amelioration of these activities during diabetes was clearly visible by supplementing fenugreek seed mucilage and spent turmeric in the diet. However during diabetes renal disaccharidases activities were significantly lower than those in the control rats. Fenugreek seed mucilage and spent turmeric supplementations were beneficial in alleviating the reduction in maltase activity during diabetes, however not much change in the activities of sucrase and lactase was observed upon feeding. This positive influence of feeding fenugreek seed mucilage and spent turmeric on intestinal and renal disaccharidases clearly indicates their beneficial role in the management of diabetes.

Quercetin alleviates activities of intestinal and renal disaccharidases in streptozotocin-induced diabetic rats

Specific activities of both intestinal and renal dissacharidases, such as sucrase, maltase, and lactase, were altered in diabetic rats. Our study was focused to evaluate the effect of feeding quercetin - a bioflavanoid on intestinal and renal dissacharidases in streptozotocin-induced diabetic rats. The rats were fed with 0.1% quercetin in diet. A reduction in intestinal maltase and sucrase, activities in quercetin-fed diabetic rats was observed in contrast to the increased activities in the starch-fed diabetic rats. A significant amelioration in renal dissacharidase activities in quercetin-fed diabetic rats was observed when compared to decreased activity in starch-fed diabetic rats.

Dietary fibres ameliorate decreased synthesis of heparan sulphate in streptozotocin induced diabetic rats

The role of dietary fibers in diabetes has been studied by several workers. Long term dietary treatment with increased amounts of fiber-rich low-glycaemic index natural foods improves blood glucose and reduces the number of hypoglycemic events in type I diabetic patients. On the other hand Rohrbach and Martin and Cohen and Surma described changes in the general and biochemical structure of renal tissues such as the glomerular basement membranes. One of these changes was the reduction and undersulfation of the glycoconjugate and glycosaminoglycan heparan sulfate, which plays an important role in renal structure and function. The purpose of the present study was to determine specific effects of two types of dietary fiber on the composition of kidney glycoconjugates in an animal model of diabetes type I. Streptozotocin-treated diabetic rats were fed either a control diet or diets containing 10% wheat bran (insoluble dietary fiber) or 5% guar gum (soluble dietary fiber). Effects of these fibers on glycaemic control and nephropathy were assessed using previously described methodologies. The effect of dietary fiber in the glycoconjugate composition of kidneys of control and diabetic animals was studied by estimating their total hexose content, sulfated glycosaminoglycans, hexosamines and uronic acids. The activities of enzymes that participate in the synthesis of saccharides and glycoconjugates (L-glutamine-fructose-6-phosphate aminotransferase) and their degradation (N-acetyl-beta-glucosaminidase and beta-glucuronidase) were also evaluated. Results indicated that both soluble and insoluble dietary fibers ameliorated a significant increase in the activity of GFAT. Heparan sulfate was also isolated and quantified. Results indicated that the renal content of heparan sulfate decreased in diabetic animals and that this decrement was ameliorated by the ingestion of both soluble and insoluble fiber in the diet.

Structural features of arabinoxylans from bajra (pearl millet)

Structures of arabinoxylans (AX) from bajra, from a variety known to have characteristic quality in the making of roti, an unleavened flat bread, were elucidated by a combination of methylation analysis, (13)C NMR, FT-IR, etc. Arabinoxylans isolated from barium hydroxide-extracted polysaccharides and hemicellulose B had a backbone of xylose residues with beta-(1,4) linkages and were branched mainly through alpha-(1,3) linkages by arabinofuranosyl residues. Completely branched xylose residues were also present. The AX from bajra characteristically had large numbers of branches, and this may be one of the reasons for the crispiness of the rotis.

A lysosomal cysteine proteinase from Dictyostelium discoideum contains N-acetylglucosamine-1-phosphate bound to serine but not mannose-6-phosphate on N-linked oligosaccharides

Previous studies showed that vegetative Dictyostelium discoideum cells make a lysosomal proteinase, proteinase-1, that contains multiple GlcNAc-alpha-1-P residues in phosphodiester linkage to serine. We extended these studies and, in contrast to earlier reports, found that proteinase-1 contains 7.5 mol of Fuc, 8 mol of Man, 2 mol of Xyl, and 30 mol of GlcNAc per calculated mol of protein but no Man-6-P residues. The protein binds to concanavalin A and wheat germ agglutinin lectin affinity columns, and PNGase-F digestion released most of the mannose and xylose but little of the GlcNAc. beta-Elimination under reducing conditions released only GlcNAc-alpha-1-P. There was no evidence for the release of disaccharides or of fucitol. A rabbit antiserum and monoclonal antibodies prepared against proteinase-1 recognize GlcNAc-alpha-1-P residues in immunoblots and are specifically competed by UDP-GlcNAc or GlcNAc-alpha-1-P. Use of other monoclonal antibodies showed the presence of mannose-6-sulfate on N-linked sugar chains, and alpha-fucose residues on the protein. Thus, proteinase-1 has at least two types of modifications: Glc NAc-alpha-1-P-Ser, which we call phosphoglycosylation, and N-linked oligosaccharides. This is the first purified lysosomal enzyme in Dictyostelium that does not contain Man-6-P residues. The GlcNAc-alpha-1-P-specific antibodies also recognize a group of developmentally regulated proteins, especially enriched in vegetative cells. Some of them are also lysosomal cysteine proteinases, and all bind to the GlcNAc-alpha-1-P-specific monoclonal antibody but not to the mammalian CI-Man-6-P receptor. Conversely, lysosomal enzymes that have Man-6-P do not bind to the GlcNAc-alpha-1-P-specific antibody. An exception to this is beta-N-acetylglucosaminidase, where 15% of the activity binds to this antibody. Thus, there appear to be two sets of lysosomal enzymes with distinct post-translational modifications.

Isolation and characterization of a sialo-glycopeptide from buffalo colostrum

A sialoglycopeptide was isolated from buffalo colostrum in pure form by chromatography on Sephadex G-25 and QAE-Sephadex A-25. This was found to be homogeneous by cellulose acetate membrane electrophoresis and reverse phase HPLC. It consisted of fucose, galactose, mannose, N-acetyl glucosamine and N-acetyl neuraminic acid in the ratio 1:2:3:4:1, and aspartic acid, serine, threonine, proline and glutamic acid were the major amino acids. Glycine was identified as the N-terminal amino acid residue. The structure elucidation of the carbohydrate moiety was carried out by methylation analysis, mass spectrometry. 1H-NMR spectroscopy and the probable structure was revealed to be that of a complex biantennary type.

Identification of a novel glycosaminoglycan core-like molecule. II. Alpha-GalNAc-capped xylosides can be made by many cell types

The accompanying article (Manzi, A., Salimath, P. V., Spiro, R. C., Keifer, P. A., and Freeze, H. H. (1995) J. Biol. Chem. 270, 9154-9163) reported the complete structure of a novel molecule made by human melanoma cells incubated with 1 mM 4-methylumbelliferyl-beta Xyl (Xyl beta MU). The product resembles a common pentasaccharide core region found in chondroitin/dermatan sulfate glycosaminoglycans, except that a terminal alpha-Gal-NAc residue is found in a location normally occupied by beta-GalNAc in these chains or alpha-GlcNAc in heparan sulfate chains. In this paper we show that several other human cancer cell lines and Chinese hamster ovary cells also make alpha-GalNAc-capped xylosides. The [6-3H]galactose-labeled Xyl beta MU product binds to immobilized alpha-GalNAc-specific lectin from Helix pomatia and the binding is competed by GalNAc, but not by Glc. Binding to the lectin is destroyed by digestion with alpha-N-acetylgalactosaminidase, but not beta-hexosaminidase. The nature of the aglycone influences the amount and relative proportion of this material made, with p-nitrophenyl-beta-xyloside being a better promoter of alpha-GalNAc-terminated product than Xyl beta MU. This novel oligosaccharide accounts for 45-65% of xyloside-based products made by both human melanoma and Chinese hamster ovary cells when they are incubated with 30 microM Xyl beta MU, but at 1 mM both the total amount and the proportion decreases to only 5-10%. In both cell lines this product is replaced by a corresponding amount of Sia alpha 2,3Gal beta 4Xyl beta MU. Preferential synthesis of the alpha-GalNAc-capped material at very low xyloside concentration argues that it is a normal biosynthetic product and not an experimental artifact. This pentasaccharide may be a previously unrecognized intermediate in glycosaminoglycan chain biosynthesis. Since this alpha-GalNAc residue occurs at a position that determines whether chondroitin or heparan chains are added to the acceptor, it may influence the timing, type, and extent of further chain elongation.

Identification of a novel glycosaminoglycan core-like molecule. I. 500 MHz 1H NMR analysis using a nano-NMR probe indicates the presence of a terminal alpha-GalNAc residue capping 4-methylumbelliferyl-beta-D-xylosides

beta-Xylosides compete with endogenous proteoglycan core proteins and act as alternate acceptors for synthesizing protein-free glycosaminoglycan chains. Their assembly on these alternate acceptors utilizes the same glycosyltransferases that make the protein-bound chains. Most studies using alternate acceptors focus on the production of sulfated glycosaminoglycan chains that are thought to be the major products. However, we previously showed that labeling melanoma cells with [6-3H]galactose in the presence of 4-methylumbelliferyl (MU) or p-nitrophenyl (pNP) beta-xylosides led to the synthesis of mostly di- to tetrasaccharide products including incomplete core structures. We have solved the structure of one of the previously unidentified products as, GalNAc alpha(1,4)GlcA beta(1,3)Gal beta(1,3)Gal beta(1,4)Xyl beta MU, based on compositional analysis by high performance liquid chromatography, fast atom bombardment, electrospray mass spectrometry, and one-dimensional and two-dimensional 1H NMR spectroscopy. The novel aspect of this molecule is the presence of a terminal alpha-Gal-NAc residue at a position that is normally occupied by beta-GalNAc in chondroitin/dermatan sulfate or by alpha-Glc-NAc in heparin or heparan sulfate chains. An alpha-GalNAc residue at this critical location may prevent further chain extension or influence the type of chain subsequently added to the common tetrasaccharide core.

Carbohydrates of pigeon milk and their changes in the first week of secretion

The carbohydrate content of pigeon crop secretion called pigeon milk (PM) was in the range of 0.9-1.5%. Sugars of trichloroacetic acid soluble (TCA-S) fraction increased by 67% between day-1 and day-5 of secretion while those of TCA- insoluble (TCA-P) fraction remained fairly constant. Sialic acids constituted 5-9% of carbohydrates. The proportion of lipid- and protein-bound sialic acids was 51% and 31% respectively; the former increased from 41% to 68% between day-1 and day-5 whereas the latter decreased from 45% to 21% during the corresponding period. Some of the sugars of PM were fucose (40%), glucosamine (31%), galactose (12%), mannose (9%) and glucose (8%). The free sugars whose content was very low (0.05%) included fucose, mannose, glucose and some unidentified oligosaccharides. The proportion of lipid- and protein-bound sugars was 31% and 63% respectively; the former decreased by 7% from day-1 to day-5 while the latter increased by 11% during the same period. Gel chromatography of PM confirmed the presence of sialic acids and glucosamine; the latter existed both in free and bound form. The nature of changes in the carbohydrate composition of PM in the first week of secretion was more quantitative than qualitative.

The structure of the polysaccharide moiety of Rhodopseudomonas sphaeroides ATCC 17023 lipopolysaccharide

The chemical structure of the polysaccharide moiety of the lipopolysaccharide Rhodopseudomonas sphaeroides ATCC 17023 was established. Mild acetic acid hydrolysis of isolated lipopolysaccharide, followed by preparative high-voltage paper electrophoresis afforded three oligosaccharides. They were characterized by chemical and physicochemical studies to be: GlcA(alpha 1----4)dOclA8P, Thr(6') GlcA(alpha 1----4)GlcA and GlcA(alpha 1----4)dOclA, where GlcA is D-glucuronic acid and dOc1A is 3-deoxy-D-manno-octulosonic acid. Carboxyl-reduction of the lipopolysaccharide followed by acid hydrolysis gave a trisaccharide: GlcA(alpha 1----4)Glc(alpha 1----4)Glc, showing the presence of three residues of glucuronic acids in the O-specific chain and indicating that only two of them are reducible by NaBH4. The linkage between the polysaccharide and lipid A was shown to be through a single 1,4-linked residue of dOc1A attached by a 2,6'-linkage to the lipid A moiety.

Unusual lipid A types in phototrophic bacteria and related species

Photosynthetic bacteria of the Rhodospirillaceae family (sulfur-free purple bacteria) possess lipopolysaccharides (LPS) that deviate markedly from the Salmonella lipopolysaccharides in the chemical makeup of the lipid A component and in their biologic properties. LPS of Rhodopseudomonas gelatinosa is highly toxic and pyrogenic, while that of Rhodospirillum tenue shows cryptic toxicity. Two LPS types are completely non-toxic. The Rhodopseudomonas sphaeroides lipid A has the same backbone as that of Salmonella, but a part of the amide-linked fatty acids has the unusual 3-oxo structure (3-oxo-14:0). The lipid A's of Rhodopseudomonas viridis and Rhodopseudomonas palustris have 2,3-diamino-2,3-dideoxy-D-glucose as the backbone sugar. This is the first demonstration of this sugar in nature. In recent studies using 16S rRNA sequencing, the nonphotosynthetic Nitrobacter strains were shown to be phylogenetically closely related to R. palustris. The R. palustris lipid A type has been identified in three Nitrobacter species, including Nitrobacter winogradskyi, the type strain. The data demonstrate the taxonomic significance of lipid A constituents and structures.

Structural studies on the non-toxic lipid A from Rhodopseudomonas sphaeroides ATCC 17023

The lipid A isolated from Rhodopseudomonas sphaeroides ATCC 17023 has been investigated. A sequence of analyses indicated beta-D-glucosaminyl-1,6-D-glucosamine as the sugar backbone carrying phosphate groups at C-1 of the reducing glucosamine and C-4 of the non-reducing glucosamine. Both 3-(7-tetradecenoyl)oxytetradecanoic and 3-oxotetradecanoic acid are linked to the NH2 groups. Two residues of 3-hydroxydecanoic acid are linked to hydroxy groups at C-3 of both reducing and non-reducing glucosamine, and the hydroxy group of 3-hydroxydecanoic acid is free. In free lipid A, the hydroxy group at C-4 of the reducing glucosamine and at C-6 of the non-reducing glucosamine are unsubstituted. The latter probably arises from a 3-deoxy-D-manno-octulosonate linkage. The structural similarities and dissimilarities existing between lipid A of R. sphaeroides, which is non-toxic, and lipid A types such as those from Salmonella, which are toxic, are discussed.

Nontoxic lipopolysaccharide from Rhodopseudomonas sphaeroides ATCC 17023

Chemical analysis of the lipopolysaccharide from Rhodopseudomonas sphaeroides ATCC 17023, isolated by the phenol-chloroform-petroleum ether method, revealed the presence of glucuronic acid, 2-keto-3-deoxyoctonate, threonine, and phosphorus in the polysaccharide moiety. The lipid A component contained glucosamine, glucosamine phosphate, amide-bound 3-oxotetradecanoic acid and 3-hydroxytetradecanoic acid, and ester-bound 3-hydroxydecanoic acid and 7-tetradecenoic acid. Structural similarity of the lipid A from R. sphaeroides ATCC 17023 to enterobacterial lipid A is indicated by the existence of a serological cross-reaction occurring between the lipid A from R. sphaeroides ATCC 17023 and that from Salmonella minnesota R595. The lipopolysaccharide and lipid A of R. sphaeroides, however, were found to be neither toxic in mice nor pyrogenic in rabbits.