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Biomedical subjects

E Meezan

Publications and source records attributed to E Meezan.

At least 19 recordsLinked to original sources
PubMed2001

Mutual inhibition of the insulin absorption-enhancing properties of dodecylmaltoside and dimethyl-beta-cyclodextrin following nasal administration.

PURPOSE: To determine if a nasal insulin formulation containing two distinct absorption-enhancing agents exhibits an additive or synergistic increase in the rate of systemic insulin absorption. METHODS: The pharmacokinetics and pharmacodynamics of insulin absorption were measured in hyperglycemic anesthetized rats following nasal insulin administration with formulations containing two different types of absorption-promoting agents, dimethyl-beta-cyclodextrin (DMBCD) and dodecylmaltoside (DDM). RESULTS: When either DDM (0.1-0.5%) or DMBCD (1.0-5.0%) was added to the nasal insulin formulation, a significant and rapid increase in plasma insulin levels was observed, with a concomitant decrease in blood glucose concentration. A combined preparation containing 0.25% DDM (0.005 M) and 2.5% DMBCD (0.019M), however, failed to cause an increase in plasma insulin levels or a decrease in blood glucose concentration. Increasing concentrations of DDM added to an insulin formulation with a fixed DMBCD concentration caused a decrease, rather than an increase, in systemic absorption of insulin. CONCLUSIONS: Mixing DMBCD and DDM resulted in mutual inhibition of their ability to enhance systemic absorption of insulin following nasal delivery. The results are consistent with the formation of an inclusion complex between DDM and DMBCD which lacks the ability to enhance nasal insulin absorption.

Absorption↗
PubMed2001

Enhanced bioavailability of calcitonin formulated with alkylglycosides following nasal and ocular administration in rats.

PURPOSE: The purpose of this study was to characterize the effects of alkylglycosides on the bioavailability of calcitonin following nasal and ocular administration. METHODS: A salmon calcitonin specific radioimmunoassay kit was used to measure calcitonin levels in anesthetized rats at various times after nasal or ocular administration of calcitonin formulated with saline or with octylmaltoside, a medium chain length alkylglycoside or tetradecylmaltoside, a long chain alkylglycoside. The extent of calcitonin absorption was determined directly from the plasma calcitonin level-time curve and the bioavailability of calcitonin was determined from the area under the plasma calcium level-time curve. The calcium level was determined using a colorimetric method. RESULTS: When the nasal formulation contained calcitonin plus saline or 0.125% octylmaltoside, little or no calcitonin was absorbed. However, plasma calcitonin levels were increased and plasma calcium levels were decreased when the nasal formulation contained calcitonin plus 0.125% or 0.25% tetradecylmaltoside. Maximal calcitonin levels were observed 7.5-10 min after nasal administration of the formulation. Ocular administration of calcitonin formulated with tetradecylmaltoside also resulted in calcitonin absorption, but less calcitonin absorption was found after ocular administration than after nasal administration. CONCLUSION: The experimental data indicate that tetradecylmaltoside, but not octylmaltoside. can be effectively used to enhance the bioavailability of nasally and ocularly administered calcitonin.

Absorption↗
PubMed1997

Alkylglycosides as artificial primers for glycogen biosynthesis.

Glycogenin is a 37 kDa self-glycosylating protein which has been demonstrated to be the initiating enzyme and primer for glycogen biosynthesis in liver, skeletal muscle and other tissues. We have recently shown that glycogenin will use alkylglucosides and alkylmaltosides as artificial acceptors in glycosyl transfer from UDP-glucose and UDP-xylose in vitro and have suggested that such substrates might be used to promote the synthesis of glycogen in vitro and in vivo. We now report that alkylglycosides can also serve as acceptors for transfer of glucose by glycogen synthase, yielding alkylmaltooligosaccharide products which may potentially be elongated to glycogen. alpha-Glucosides were better substrates than the corresponding beta-glucosides, and alkylmaltosides were preferred over alkylglucosides. The hydrophobicity of the substrates markedly affected their acceptor activity, less hydrophobic substrates being more active. This is in contrast to the behavior of glycogenin, which acted preferentially upon the more hydrophobic substrates tested. Aromatic glycosides were also substrates for glycogen synthase, e.g., naphthyl-alpha-D- and beta-D-glucoside. The substrates were active in vitro both with partially purified rabbit muscle glycogen synthase and in incubations with crude muscle and liver homogenates from rat. In vivo experiments with mice further proved that intraperitoneal administration of alkylglucosides and alkylmaltosides increased the uptake of 14C-glucose in liver. The elevated uptake was due to an increase in both hydrophobic products, isolated by adsorption to Sep-Pak C18 columns, and more hydrophilic material that co-fractionated with glycogen upon treatment of the tissue with alkali and precipitation with ethanol. These results demonstrate the ability of alkylglycosides to serve as artificial primers for glycogen biosynthesis in vivo.

Alkylation↗
PubMed1995

Inhibition of glycogenin-catalyzed glucosyl and xylosyl transfer by cytidine 5'-diphosphate and related compounds.

The self-glucosylation of beef kidney glycogenin was inhibited by the following pyrimidine nucleotides and nucleotide sugars, listed in order of decreasing effectiveness: CDP-glucose, CDP, UDP-xylose, UDP-N-acetylglucosamine, UDP-galactose, UDP, CTP, CDP-choline, UDP-glucuronic acid, beta-S-UDP-glucose, and CMP. In contrast, the purine nucleotide sugars, ADP-glucose and GDP-glucose, were essentially ineffective, as was the pyrimidine nucleoside, cytidine. UDP-Xylose may be utilized by glycogenin as an alternative sugar donor instead of UDP-glucose (Rodén, L., Ananth, S., Campbell, P., Manzella, S., and Meezan, E. (1994) J. Biol. Chem. 269, 11509-11513) and therefore presumably inhibited the glucosyl transfer reaction by being a competitive substrate. Like glucosyl transfer, xylosyl incorporation into glycogenin was also inhibited effectively by CDP. On the other hand, UDP-xylose:proteoglycan core protein xylosyltransferase (EC 2.4.2.26) was not affected by CDP, nor was it inhibited by UDP-glucose. Addition of CDP or UDP-glucose to reaction mixtures containing both enzymes therefore made it possible to assay xylosyltransferase EC 2.4.2.26 reliably without the extensive product characterization that is otherwise necessary. The CDP effect on glycogenin further allowed the development of an improved procedure for the purification of this enzyme, in which specific elution of an affinity matrix (UDP-glucuronic acid-agarose) was carried out with CDP as the eluant.

Animals↗
PubMed1995

Systemic absorption of insulin and glucagon applied topically to the eyes of rats and a diabetic dog.

Nondiabetic rats were anesthetized with xylazine/ketamine to induce hyperglycemia and systemic insulin absorption from eyedrops formulated with dodecylmaltoside was quantitated by both a decrease in serum levels of D-glucose and an increase in immunoreactive insulin levels. When insulin eyedrop administration was delayed until 60 minutes after the administration of eyedrops containing 0.25% dodecylmaltoside, the enhanced systemic absorption of insulin was maintained, suggesting that dodecylmaltoside had an effect directly on the permeability of the nasal sinus epithelium. When glucagon was formulated in eyedrops or nosedrops containing dodecylmaltoside, systemic absorption of glucagon could be measured in the form of an increase in the serum D-glucose concentration following nasal application, but not after ocular application. Eyedrops containing insulin plus 0.125% dodecylmaltoside were administered to a diabetic dog; a dose of 20 units of regular insulin caused a modest decrease in serum D-glucose concentration and a concomitant increase in serum immunoreactive insulin content. These results provide evidence that peptide drugs such as insulin can be formulated in eyedrops with low concentrations of dodecylmaltoside, a mild nonionic surfactant.

Absorption↗
PubMed1995

Dodecyl-beta-D-maltoside as a substrate for glucosyl and xylosyl transfer by glycogenin.

Glycogenin is the core protein of glycogen proteoglycan and is, at the same time, a self-glucosylating enzyme which catalyses early glucosyl transfer steps in the biosynthesis of glycogen. In the course of this process, glycogenin is glucosylated progressively until an oligosaccharide containing 8-11 glucose residues has been formed. Although glycogenin, under physiological conditions, is both enzyme and acceptor in the glucosyl transfer reactions, it is also capable of utilizing p-nitrophenyl-linked malto-oligosaccharides as exogenous acceptors. In view of the potential usefulness of exogenous acceptors in the study of the mechanism of the glycogenin reaction, we have expanded the search for such compounds and report here that several alkyl glucosides and alkyl maltosides may serve as acceptors in glucosyl transfer by beef kidney glycogenin. Dodecyl-beta-D-maltoside (Km approximately 100 microM) was the most effective acceptor among the compounds tested and yielded 30 times as much product as p-nitrophenyl-alpha-maltoside. Substantial product formation was also observed with tetradecyl-beta-D-maltoside and octyl-beta-D-maltoside (39 and 22%, respectively, of the value measured for dodecyl-beta-D-maltoside). It was further demonstrated that dodecyl-beta-D-maltoside served as an acceptor in the transfer of xylose from UDP-xylose, indicating that the exogenous substrate behaved similarly to glycogenin itself in this regard. Dodecyl-beta-D-maltoside has already proven useful in the development of a simple glycogenin assay, and it is further suggested that this and related compounds may be active in vivo and in cell culture as artificial initiators of glycogen synthesis.

Animals↗
PubMed1994

Xylosyl transfer to an endogenous renal acceptor. Characteristics of the reaction and properties of the product.

In the course of a study of UDP-xylose:proteoglycan core protein xylosyltransferase (EC 2.4.2.26), another xylosyltransferase was discovered in the soluble fraction of a rat kidney homogenate. The latter enzyme catalyzed [3H]xylosyl transfer from UDP-[3H]xylose to an endogenous acceptor and yielded a product in which the xylose was bound by an alkali-stable linkage. It was therefore concluded that the acceptor was not the core protein of one of the proteoglycans containing a xylose-->serine linkage, since this linkage is cleaved by alkali. The [3H]xylose-labeled product emerged with the void volume when chromatographed on Sephadex G-50, it was precipitated by trichloroacetic acid, and it had a mobility on sodium dodecyl sulfate-polyacrylamide gel electrophoresis corresponding to a molecular mass of about 32,000 Da. Digestion with trypsin or alpha-amylase degraded the labeled product to small fragments, as determined by gel chromatography, suggesting that it was a glycoprotein related to glycogen. A product of similar characteristics was formed when UDP-[3H]glucose was substituted for UDP-[3H]xylose as the glycosyl donor, and the two nucleotide sugars were mutually competitive in the respective transfer reactions, indicating that they were substrates for the same enzyme. On the basis of these findings, it was tentatively concluded that the xylosyltransferase and its acceptor were the renal form of glycogenin.

Animals↗
PubMed1994

Xylosyl transfer to an endogenous renal acceptor. Purification of the transferase and the acceptor and their identification as glycogenin.

A xylosyltransferase in rat kidney, tentatively identified as glycogenin (Meezan, E., Ananth, S., Manzella, S., Campbell, P., Siegal, S., Pillion, D. J., and Rodén, L. (1994) J. Biol. Chem. 269, 11503-11508), was purified by a procedure in which affinity chromatography on UDP-glucuronic acid-agarose was a particularly useful step. The purified material was nearly homogeneous, as shown by SDS-polyacrylamide gel electrophoresis and silver staining, and had an electrophoretic mobility corresponding to a M(r) of 32,000. The purified enzyme possessed both glucosyl- and xylosyltransferase activity, and incubation with UDP-[3H]xylose or UDP-[3H]glucose yielded a single macromolecular product, which had the same electrophoretic mobility as the major silver-stained component. These results indicate that the kidney transferase was indeed glycogenin and that it was functionally analogous to the larger glycogenin species previously isolated from rabbit muscle. Further examination of the properties of the rat kidney enzyme showed, i.a., that it was inhibited strongly by cytidine 5'-diphosphate. This effect was used to advantage in an alternative purification procedure, which was applied to beef kidney and involved adsorption of the enzyme to UDP-glucuronic acid-agarose and subsequent elution with cytidine 5'-diphosphate. In contrast to glycogenin, glycogen synthase did not catalyze transfer from UDP-xylose, and it is suggested that the incorporation of xylose into glycogen observed by other investigators was due to glycogenin-catalyzed xylosyl transfer and subsequent chain elongation by glycogen synthase.

Animals↗
PubMed1994

A biphasic radiometric assay of glycogenin using the hydrophobic acceptor n-dodecyl-beta-D-maltoside.

Glycogenin is a self-glycosylating protein that catalyzes early glucosyl transfer steps in the biosynthesis of glycogen. In currently used assays of glycogenin activity, the enzyme is incubated with radioactive UDP-glucose, and the labeled reaction product is then isolated by precipitation with trichloroacetic acid. A new assay is reported here which is based on the observation that glycogenin is not only self-glycosylating but may also use exogenous alkyl maltosides as substrates. After incubation of the enzyme with n-dodecyl-beta-D-maltoside and UDP-[3H]glucose, the radioactivity in the resultant n-dodecyl-beta-D-[3H]maltotrioside is determined by any one of the following three procedures, which all rely on the hydrophobic properties conferred on the reaction product by the alkyl aglycone: (i) adsorption of the product to a Sep-Pak C18 cartridge and elution with 70% ethanol; (ii) biphasic liquid scintillation counting in ScintiLene/25% isoamyl alcohol, without isolation of the product, and (iii) precipitation with trichloroacetic acid in the presence of carrier protein. The Sep-Pak C18 procedure has the advantage that it allows essentially quantitative isolation of the reaction product, while, under the conditions chosen, only about 50% of the product is precipitated by trichloroacetic acid. For most applications, however, biphasic liquid scintillation counting is the method of choice, since close to 90% of the labeled product is extracted into the organic phase and can be counted directly without interference from the labeled nucleotide sugar which remains in the aqueous phase.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Efficacy of insulin eyedrops.

Systemic absorption of insulin delivered via eyedrops has been studied in rats made transiently hyperglycemic by anesthesia with xylazine/ketamine. Insulin at a concentration of 2 mg/ml was not absorbed significantly when saline alone was used as the formulation for the eyedrops (0.04 ml). When various emulsant agents were added to the eyedrop formulation, systemic insulin levels were increased and concomitantly, blood D-glucose levels were decreased. Saponin, Brij-78, BL-9 and several alkylglycosides all increased the systemic absorption of insulin following delivery in eyedrops. Not all surfactant agents were effective in promoting systemic insulin absorption from eyedrops, as evidenced by the failure of some non-ionic surfactants to increase insulin absorption. Similar results were obtained when nosedrops containing insulin plus non-ionic surfactants were administered to rats. In conclusion, systemic insulin absorption was greatly accelerated by the addition of certain emulsants to the eyedrop formulation and physiologically important levels of insulin could be delivered systemically following eyedrop administration.

Absorption↗
PubMed1994

Insulin delivery in nosedrops: new formulations containing alkylglycosides.

Insulin was administered to rats via nosedrops in the presence or absence of various alkylglycosides; systemic insulin absorption was measured as a fall in blood D-glucose concentration in animals made hyperglycemic by xylazine/ketamine anesthesia. Nosedrops (0.04 ml) containing alkylglycosides or regular porcine insulin alone were without effect. Nosedrops containing both a small amount of alkylglycoside (0.03-0.50%) and insulin (2 U regular porcine) caused a rapid decrease in blood D-glucose levels and a concomitant increase in serum immunoreactive insulin levels. The maximal hypoglycemic response was observed between 60 and 120 min after delivery of nosedrops. Decylmaltoside was less effective at enhancing systemic insulin absorption than dodecylmaltoside, tridecylmaltoside, or tetradecylmaltoside, whereas octylmaltoside was totally ineffective. Dodecylsucrose, a compound which differs from dodecylmaltoside only in one carbohydrate residue, had a similar effect on blood D-glucose values when it was included in the nosedrop formulation with insulin. Decylsucrose was considerably less potent than dodecylsucrose at enhancing systemic absorption of insulin. Nonylglucoside was effective at promoting insulin absorption from nosedrops only when used at higher doses (0.25-0.50%), whereas heptylglucoside and hexylglucoside were ineffective. These results indicated that nosedrops containing insulin plus an extremely low concentration (0.03%) of an absorption-enhancing agent such as tetradecylmaltoside can be used to lower blood D-glucose values.

Absorption↗
PubMed1994

Alkylglycosides enhance systemic absorption of insulin applied topically to the rat eye.

A series of alkylglycosides with various alkyl chain lengths and carbohydrate residues were tested for their ability to enhance systemic absorption of insulin after topical ocular delivery in anesthetized rats. Several reagents, including tetradecyl-, tridecyl- and dodecylmaltoside and dodecylsucrose, were potent stimulators of insulin absorption when used at concentrations as low as 0.125%. Other alkylglycosides such as decylsucrose, decylmaltoside, nonylglucoside, octylmaltoside, heptylglucoside and hexylglucoside were less potent or ineffective as absorption-enhancing reagents. By comparison, the bile salt sodium glycocholate was effective only when used at concentrations of 0.5% or greater. All of the reagents were effective only when used at concentrations above their critical micelle concentration and the most hydrophobic alkylglycoside reagents were the most efficacious at promoting systemic insulin absorption. The possible utilization of eyedrops containing insulin plus an absorption-enhancing alkylglycoside reagent in humans is discussed.

Absorption↗
PubMed1993

Expression of IGF-II/Man-6-P receptors on rat, rabbit, and human colon epithelial cells.

Previous experiments from this laboratory have established the presence of receptors for insulin and insulin-like growth factor I (IGF-I) on apical membranes prepared from rabbit colon epithelial cells; however, no receptors for multiplication-stimulating activity (MSA), the rat peptide hormone equivalent of human IGF-II, were found in this tissue. In the current studies, radioligand binding assays, covalent cross-linking experiments, and immunoblot analyses using a polyclonal rabbit antiserum that recognizes the IGF-II/mannose 6-phosphate (Man-6-P) receptor, all confirmed the presence of IGF-II/Man-6-P receptors on membranes prepared from rat and human colon epithelial cells. Exposure of rat colon epithelial cell membrane fractions to 5 mM Man-6-P before incubation with 125I-labeled IGF-II increased radioligand binding. Immunoblot analysis indicated that IGF-II/Man-6-P receptors were present in both unfractionated rat colon membranes and fractions enriched with apical membranes. Rabbit and human colon epithelial cells displayed a different pattern of receptor distribution than rat colon epithelial cells, with more insulin receptors but relatively few IGF-II/Man-6-P receptors. Immunohistochemical studies using a rabbit polyclonal antiserum confirmed that IGF-II/Man-6-P receptors were present on both the apical and the basolateral surfaces of colon epithelial cells.

Animals↗
PubMed1992

Insulin signal transduction: the role of protein phosphorylation.

Recent evidence suggests that the mechanism of insulin action depends in part on protein phosphorylation on tyrosine residues. A cascade of phosphorylation/dephosphorylation reactions is proposed to modulate multiple enzymes involved in metabolism, protein synthesis, and cell growth. Direct evidence is presented for the phosphorylation of myelin basic protein and microtubule-associated protein 2 on tyrosine residues by the insulin receptor.

Animals↗
PubMed1992

Altered sulfate transport via anion exchange in CFPAC is corrected by retrovirus-mediated CFTR gene transfer.

PANC-1 (a permanent epithelioid cell line initiated from a pancreatic carcinoma of ductal origin) and CFPAC (a ductal epithelioid cell line established from a cystic fibrosis patient with pancreatic adenocarcinoma) display sulfate transport via carrier-mediated anion exchange as supported by the following lines of evidence: 1) saturation kinetics, 2) inhibition by the anion exchange inhibitor 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), and 3) substrate specificity. The DIDS-sensitive component of sulfate uptake is markedly inhibited by S2O3(2-) and MoO4(2-) but not by HAsO4(2-), H2PO4-, or gluconate-. Competitive inhibition of SO4(2-) uptake by extracellular Cl- (Cl-o) and stimulation of SO4(2-) efflux by Cl-o support the possibility that SO4(2-) transport occurs via a SO4(2-)-Cl- exchange mechanism. Inhibition of sulfate uptake and stimulation of sulfate efflux by extracellular HCO3- indicate that SO4(2-)-HCO3- exchange is an alternative mechanism for sulfate transport in these cells. Further support for SO4(2-) being transported via a typical anion exchanger is the stimulation of its uptake at low extracellular pH and high intracellular pH. Amphotropic viruses have been used by others (M. L. Drumm, H. A. Pope, W. H. Cliff, J. M. Rommens, S. A. Marvin, L.-C. Tsui, F. S. Collins, R. A. Frizzell, and J. M. Wilson. Cell 62: 1227-1233, 1990) to transduce a functional cystic fibrosis transmembrane regulator (CFTR) cDNA into CFPAC, resulting in the PLJ-CFTR clones. Control clones (PLJ) were obtained by exposing CFPAC cells to control virus. In the present study, we report a striking 10-fold increase in the capacity of the DIDS-sensitive component of the sulfate transporter in two PLJ-CFTR clones (which had been shown by others to express corrected Cl- channel activity) compared with CFPAC and two PLJ clones. Our findings indicate that expression of the CFTR gene from a retroviral vector, which confers normal Cl- channel activity in the PLJ-CFTR pancreas epithelial clones, is capable of correcting a second aspect of the cystic fibrosis phenotype, altered sulfate transport via an anion exchange mechanism.

Anions↗