Molecular Weight Threshold Research Articles

Transfer of exogenous macromolecules from rat stomach wall to blood and lymph is dependent on molecular weight.

Transfer selectivity to the blood and the lymph of exogenous dextrans of various average molecular weight (approximate 4, 10, 18, 39 and 70 kilodaltons (kDa)) after dosing to the subserosal layer of the rat stomach wall was investigated by measuring the fluorescein isothiocyanate labelled dextran concentrations in the lymph of the thoracic duct and the peripheral plasma. The lymph/plasma level ratio of the dextrans rose greatly with the increase in molecular weight (over 10kDa) owing largely to the lower plasma concentration, although the lymph levels of small dextran (4kDa) were not significantly higher than the plasma levels. These results indicate that there is an inverse relation between plasma levels of dextrans and their molecular weight, and also suggest that the molecular weight threshold of transfer selectivity of dextran to the blood and the lymph administered in the rat stomach wall is between 4-10 kDa.

Experimental study and normal individual trial of hemopoietic stem cell mobilizer ds

The munbers of MNC and CFU-GM in peripheral blood began to rise 1 hour after intravenous injection of DS and achieved peak value within 3–5 hours. The toxicity test suggested that the critical drawback of DS for clinical application was hypersensitive reaction rather than LD toxicity. The threshold molecular weight for causing hypersensitive reaction was slightly higher than 10000D. Compared to other kind of mobilizers, such as Cy, Ara—C, DNR, etc., DS may not only be used in patients, but also be used in normal individuals. The safe and effective dose of DS for human being is about 15–20 mg/kg.

Effect of molecular weight (Mw) ofN‐(2‐hydroxypropyl)methacrylamide copolymers on body distribution and rate of excretion after subcutaneous, intraperitoneal, and intravenous administration to rats

A copolymer of N-(2-hydroxypropyl) methacrylamide (HPMA) and N-methacryloyltyrosinamide was prepared and fractionated using Sepharose 4B/6B (1:1) chromatography to produce eight HPMA copolymer fractions of narrow polydispersity and mean molecular weight (Mw) ranging from 12 to 778 kD. These fractions were radioiodinated and injected intravenously, subcutaneously, and intraperitoneally into rats. Their bloodstream-concentration profiles were monitored and rates of excretion assessed. Following intravenous administration the circulating blood volume available to the copolymers was not molecular-weight-dependent. A molecular-weight threshold limiting glomerular filtration was identified at approximately 45 kD, and preparations greater than this threshold were lost from the bloodstream only slowly by extravasation. Molecular weight did not influence the movement of copolymers from the peritoneal compartment to the bloodstream after intraperitoneal injection. The transfer rates observed could be accounted for by bulk phase lymphatic drainage alone, no transcapillary routes being implicated. Following subcutaneous administration the largest HPMA copolymer fraction (Mw = 778 kD, diameter approximately 30 nm) showed increased retention at the site of the injection, approximately 20% of the dose remaining there after 21 days. This could result from physical restriction of movement or from internalization into local phagocytic cells. The smaller copolymer fractions moved readily into the bloodstream whence they were either lost in the urine or they gradually penetrated into other tissues and organs. Long-term (21 days) body distribution of copolymers following both intraperitoneal and subcutaneous administration showed size-dependent accumulation in organs of the reticuloendothelial system.

Selectively reduced biliary excretion of cholyldiglycylhistamine but not of cholytetraglycylhistamine in ethinyl estradioltreated rats: A possible indicator of increased bile canalicular permeability

A series of bile acid derivatives were synthesized, purified and radiolabelled. These were [125I]cholylglycylhistamine [( 125I]CGH), [125I] cholyldiglycylhistamine [( 125I]CG2H), [125I]cholyltriglycylhistamine [( 125I]CG3H), and [125I]cholyltetraglycylhistamine [( 125I]CG4H). These derivatives were rapidly excreted unchanged into the bile of bile-fistula rats. In normal rats the 30-min cumulative excretion following intravenous administration was only 39.0 +/- 0.7% for [125I]CGH but greater than 80% for the three larger compounds. This marked difference in biliary recovery between CGH and the other larger compounds could be due to a threshold biliary permeability, and we postulated that the critical molecular weight threshold for effective biliary retention of such compounds falls between [125I]CGH (MW 683) and [125I]CG2H (MW 740). Increased permeability, involving a shift to a higher molecular weight threshold would then be anticipated to diminish biliary excretion of [125I]CG2H (MW 740) before exerting a major influence on the biliary excretion of [125I]CG4H (MW 854). We previously reported functional and morphological studies which suggest that ethinyl estradiol (EE) may alter the permeability of bile canalicular tight junctions. In this study we have looked for further evidence of a progressive permeability change in EE-induced cholestasis by observing the biliary excretion of CG2H and CG4H in rats. Treatment with EE (5 mg/kg/day) for 3 days (EE3) or with the injection vehicle propylene glycol for 7 days (C7) reduced biliary excretion to a significant extent when compared to 3-day controls (C3) but had no differential effect on the 30-min recoveries from bile of CG2H and CG4H, respectively: C3 (81.2 +/- 1.8% and 81.7 +/- 2.1%, P = CN): C7 (72.3 +/- 3.0% and 73.5 +/- 3.6%, P = NS): EE3 61.8 +/- 2.5% and 61.9 +/- 2.7%, P = NS). However, treatment with EE for 7 days significantly reduced the biliary recovery of CG2H (46.8 +/- 9%) compared to EE3 rats (P less than 0.0025) but there was no significant change of biliary CG4H recovery (61.0 +/- 2.5%, P = NS) compared with EE3 rats. These results are compatible with our hypothesis that EE-induced cholestasis is associated with a change of biliary permeability which, as it progresses, affects successively larger molecules.

Molecular weight dependence of permselectivity to rat small intestinal blood-lymph barrier for exogenous macromolecules absorbed from lumen.

The permselectivity to the small intestinal blood-lymph barrier for the exogenous macromolecules absorbed from the lumen was investigated using in situ rat closed loop experiment. We chose the fluorescein isothiocyanate-labelled dextran (FD) as macromolecule and lipid-surfactant mixed micelles as an absorption promoter. The mean molecular weights of FDs used were 10500, 17500, 39000 and 64200 (abbreviated: FD10 , 20, 40 and 70). The lymph/plasma ratios of FDs concentrations during 5 h post administration were 0.2-1.2 ( FD10 ), 0.4-1.3 ( FD20 ), 1.3-7.2 ( FD40 ) and 2.6-11.9 ( FD70 ), respectively. The FD40 and FD70 levels in the lymph were significantly higher than those in the plasma. The cumulative amounts (% of the absorbed quantity) of FDs in the lymph from the lumen of the small intestine for 5 h after administration were 0.46% ( FD10 ), 0.51% ( FD20 ), 1.17% ( FD40 ) and 1.89% ( FD70 ), respectively. These findings suggest that the threshold molecular weight of FD for the transfer into the lymphatics with higher level compared to the blood concentration from the lumen across the small intestinal blood-lymph barrier exists between 17500 and 39000.

Uptake and Excretion of Chemicals by Aquatic Fauna

Factors influencing the movement of chemicals across biological membranes are: solubility in lipids and in water, chemical stability, ionization, and molecular weight of the chemical. On the part of aquatic fauna, the transport of chemicals is affected by metabolic activity and by the physiological state of the animals. Additional factors include water temperature, hardness or salinity, and presence of other chemicals. The effects of these factors will be discussed and illustrated by examples. The uptake of highly lipid-soluble compounds by fish appears to be determined by their solubility in water, and compounds with extremely low solubility in water are not taken up in spite of their high solubility in lipids. Examples are hexabromo-benzene, highly brominated biphenyls, C24 chlorinated paraffins, and some flame retardants of the Dechlorane series. In addition to solubility in water, there may be a high molecular weight threshold, beyond which compounds are not taken up, and factors based on the chemical structure of the compounds may play a role as well. For example, Dechlorane 604, a tetrabromophenyl norbornene, is accumulated by fish to a much lesser degree than a tribromophenyl norbornene, present as a minor impurity in Dechlorane 604. Chemical and biochemical stability of compounds are additional factors determining the extent of environmental contamination. Examples are the widespread contamination of aquatic biota by two nonachlors, present originally as relatively minor components in technical chlordane, and the contamination by some components of toxaphene. The use of a one compartment model in studies of accumulation and excretion of chemicals by aquatic fauna, and its extension to the determination of lethality curves, will be mentioned.

The metabolism of diethylstilbestrol.

This literature review presents available data on the metabolism of diethylstilbestrol (DES) to shed light on the fate and the mechanism of toxicity of this compound. Biotransformation effects reviewed include conjugation reactions of DES such as glucuronide formation in vivo and in vitro, enterohepatic circulation of DES and its glucuronide, and formation of steroid sulfatases and sulfates; oxidative metabolism of DES (aromatic hydroxylation followed by methylation); and species differences in DES metabolism. Excretion curves for 12 animal species show vast differences; whereas urinary excretion predominates in humans, chimps, rhesus monkeys, and guinea pigs; rats, hamsters, and mice show predominately fecal elimination. The difference among species seems due to capability of biliary excretion. A molecular weight threshold seems to exist, and this may account for the varying remnants of DES housed in different species' organs. Placental transfer is another major problem. Fetuses of many species seem capable of glucurondizing DES. The formation of reactive metabolites (i.e., affinity for estradiol 17-beta receptor attachment and affinity for other proteins bound by estrogen) through oxidative biotransformation suggests that DES metabolites affect hepatic systems and may activate or transform cells to malignancy. Theories of the organotropism of DES carcinogenicity are presented, as well as a discussion of the fate of DES in the environment.

Biliary excretion of cephalosporins in rats: influence of molecular weight.

The biliary excretion of 18 cephalosporin derivatives with varying 3- and 7-substituents was examined in cannulated rats. In spite of the widely differing physical chemical properties imparted by the different structures, the dominant influence on the degree of biliary excretion was the molecular weight of the compound. Above a threshold molecular weight of about 450, biliary excretion increased in a generally progressive way, becoming the principal route of excretion of the higher-molecular-weight derivatives. Examples were found in which the molecular weight influence was modified but not abolished by specific substituents. Biliary excretion varied from less than 5% to greater than 90% of the dose. Interruption of bile flow resulted in an increase in urinary excretion. Biliary excretion may influence the evaluation of new cephalosporins in rodent models. Such influence must be considered when selecting candidate compounds intended for eventual use in humans, where the excretion pattern may be different from that in rodents.

Nonaqueous polystyrene dispersions: Radical dispersion polymerization in the presence of ab block copolymers of polystyrene and poly(dimethyl siloxane)

Well defined AB block copolymers of polystyrene and poly(dimethyl siloxane) have been used as stabilizers in the dispersion polymerisation of styrene in n -alkanes. The dependences of the particle size and particle size distribution on the relative block lengths in the copolymer have been studied. From phase separation studies of polystyrene in n -alkanes, both in the presence and absence of AB block copolymer, the threshold molecular weight for precipitation has been determined. An understanding of the dispersion polymerization kinetics and the broad particle size distribution follows from the relatively high solubility of low molecular weight polystyrene in n -alkanes.

Biliary excretion of cyclohexylphenyl 4-[35S]sulphate in the guinea pig.

The metabolic fate and mode of excretion of cyclohexylphenyl 4-[35S]sulphate were studied in the guinea pig. Up to 54.8% of the dose appeared in the bile, the majority as unchanged ester. Substantial amounts of hydroxylated cyclohexylphenyl 4-[35S]sulphate were also excreted in the bile together with minor amounts of the corresponding glucuronic acid conjugate. When isolated guinea-pig livers were perfused with cyclohexylphenyl 4-[35S]sulphate the biliary components were the same as those in the intact animal, although the relative concentration of the hydroxylated derivative was significantly greater. When the hydroxylated derivative was re-injected into guinea pigs it was excreted almost entirely unchanged in the bile. However, in the rat, it was excreted in the bile as a glucuronic acid conjugate. These findings are discussed in relation to studies carried out in the rat [Hearse, Powell, Olavesen & Dodgson (1969) Biochem. Pharmacol. 18, 181--195] and to differences in enzyme activities in rat and guinea-pig liver. The results are also discussed in terms of the molecular-weight threshold for the excretion of anions in guinea-pig bile.

Molecular weight as a factor in the excretion of monoquaternary ammonium cations in the bile of the rat, rabbit and guinea pig.

1. The excretion in the bile and urine of intraperitoneally injected (14)C-labelled monoquaternary ammonium or pyridinium cations was measured in bile-duct-cannulated rats (ten compounds) and in guinea pigs and rabbits (six compounds). 2. Seven of these, namely N-methylpyridinium, tetraethylammonium, trimethylphenylammonium, diethylmethylphenylammonium, methylphenyldipropylammonium, dibenzyldimethylammonium and tribenzylmethylammonium, were excreted largely unchanged in the bile and urine. 3. 3-Hydroxyphenyltrimethylammonium, 3-bromo-N-methylpyridinium and cetyltrimethylammonium were metabolized to an appreciable extent in the rat. 4. In intact rats intraperitoneally injected trimethylphenylammonium (mol.wt. 136) was excreted mainly in the urine, dibenzyldimethylammonium (mol.wt. 226) was excreted in roughly equal amounts in the urine and faeces, and tribenzylmethylammonium (mol.wt. 302) was excreted mainly in the faeces. The faecal excretion of these compounds corresponded to their biliary excretion in bile-duct-cannulated rats. About 3-4% of tribenzyl[(14)C]methylammonium was eliminated as (14)CO(2). 5. In rats the extent of biliary excretion of four cations with molecular weights in the range 94-164 was less than 10% of the dose, whereas that of five cations with molecular weights 173-302 was greater than 10%. These results and other data from the literature suggested that the molecular weight needed for the biliary excretion of such cations to an extent of 10% or more of the dose was about 200+/-50. Studies with six cations in guinea pigs and rabbits suggest that this value applies also to these species. 6. The results suggest that the threshold molecular weight for the appreciable (>10%) biliary excretion of monoquaternary cations is different from that for anions (Millburn et al., 1967a; Hirom et al., 1972b). With rats, guinea pigs and rabbits, no significant species difference was noted, whereas with anions there is a marked species difference.

Species variations in the threshold molecular-weight factor for the biliary excretion of organic anions.

1. The excretion in the bile and urine after intravenous injection of 16 organic anions having molecular weights between 355 and 752 was studied in female rats, guinea pigs and rabbits. 2. These compounds were mostly excreted unchanged, except for three of them, which were metabolized to a slight extent (<7% of dose). 3. The rat excreted all the compounds extensively (22-90% of dose) in the bile. 4. In guinea pigs four of the compounds with mol.wt. 355-403 were excreted in the bile to the extent of 7-16% of the dose, four with mol.wt. 407-465 to the extent of 25-44% and eight compounds with mol.wt. 479-752 to the extent of 44-100%. 5. In rabbits four compounds with mol.wt. 355-465 were excreted in the bile to the extent of 1-8% of the dose, two compounds with mol.wt. 479 and 495 to the extent of 24 and 22%, and six compounds with mol.wt. 505-752 to the extent of 31-94%. 6. These results, together with those of other investigations from this laboratory, are discussed and the conclusion is reached that there is a threshold molecular weight for appreciable biliary excretion (i.e. more than 10% of dose) of anions, which varies with species: about 325+/-50 for the rat, 400+/-50 for the guinea pig and 475+/-50 for the rabbit. 7. Anions with molecular weights greater than about 500 are extensively excreted in the bile of all three species. 8. That proportion of the dose of these compounds which is not excreted in the bile is excreted in the urine, and in the three species, bile and urine are complementary excretory pathways, urinary excretion being greatest for the compounds of lowest molecular weight and tending to decrease with increasing molecular weight. 9. Some implications of this interspecies variation in the molecular-weight requirement for extensive biliary excretion are discussed.

Determination of hydrodynamic degradation of DNA using flow birefringence techniques

Shear degradation experiments on high molecular weight DNA have for the first time been carried out under uniform velocity gradient conditions. Precursory work on a calf thymus sample (molecular weight 31 x 106) indicates that a rate process is operative and that preferential molecular halving occurs. A gradient of 4 x 104 s-1 produces almost complete halving after shearing for seven minutes. Using an extended chain model for breakage this gradient corresponds to a critical breaking force for the DNA backbone of 1 x 10-4 dynes, which is an order of magnitude smaller than estimated theoretically. Flow birefringence measurements are reported which indicate that such an extended chain model is unrealistic : a loss in molecular anisometry during flow is implied, manifested in a time dependence anomaly of both birefringence and extinction angle. At high gradients, the extinction angle behaviour is further found to be associated with the molecular degradation which occurs. Extensive investigation of the time dependent anomaly, in an attempt to understand changes in DNA conformation during flow, has eliminated some of the possible mechanisms for this behaviour, such as, induced shear-denaturation, protein cross linkage and wall desorption. Quanlitalively, a molecular weight threshold for the time dependent behaviour of between two and five million has been established.