Mechanistic studies in the simultaneous flow and adsorption of polymer-coated latex particles on intestinal mucus I: Methods and physical model development

The adsorption of particles and concurrent steady-state flow of a dilute suspension from an infinite reservoir over the mucous surface of intestinal strips were quantitatively studied. The micronsize particle systems included negatively charged poly (vinyltoluene) and hydroxylated Dynosphere(R) particles with and without a positively charged polybrene polymer coated layer. The suspensoids were characterized by zeta potential measurements. An in vitro setup and technique likened to a thin falling liquid film system was developed wherein an excised intestinal segment cut lengthwise is spread on a plastic flute and positioned at an incline, and a suspension is allowed to flow down the intestinal strip. The falling liquid film was estimated to be 54 [mu]m in thickness from nonsteady-state flow kinetic experiments. Particle concentrations entering the segment from the dilute suspension reservoir and leaving the intestinal segment were determined with the Coulter counter to quantify the steady-state fraction of particles adsorbed as they relate to intestinal length, flow rate, ionic strength, zeta potential and particle concentration. The flowing liquid film technique was found to be quantitatively sensitive and, consequently, allowed one to focus on the mechanism of the approach of micron-size particles to the mucous surface without the major concern of particle flocculation in the bulk liquid.The logarithm of the fraction of nonadsorbed particles remaining in the liquid film decreased linearly with intestinal length at all flow rates employed. The fraction adsorbed decreased with increasing flow rates on account of the shorter transit times. The steady-state region of the fraction of nonadsorbed particles remaining versus time plots persisted for a relatively long time indicating the existence of a particle concentration gradient along the length of the intestinal strip. The fact that the fraction of particles adsorbed was not affected by particle concentrations ranging from 4.5-14 x 106 particles per ml suggests that there is sufficiently available unoccupied surface area for incoming particles to be adsorbed onto mucus. It has been estimated that no more than 5% of the area of the intestinal strip is occupied by adsorbed particles. Failure to desorb particles from the mucous surface by perfusing the intestinal segment indicates tight binding between the particles and mucus. A physical model was deduced from the experimental results wherein the steady-state fraction of adsorbed particles is related to length of the intestinal strip, flow rate and mass transfer-adsorption coefficient.The mass transfer resistances of negatively charged particles decreased with the addition of sodium chloride and approached the minimum resistance obtained by the positively charged, polybrenecoated latex particles, whose mass transfer resistance was independent of electrolyte concentration. This supports a mechanism involving the diffusion of the negatively charged particles within an electrostatic field of force as the particles approach the negatively charged mucous surface. Passage of particles over the potential energy barrier is required for the successful collision and tight binding with mucus.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26476/1/0000012.pd

Comparative in vitro effects of closantel and selected beta-ketoamide anthelmintics on a gastrointestinal nematode and vertebrate liver cells

PNU-87407 and PrNU-88509, beta-ketoamide anthelmintics that are structurally related to each other and to the salicylanilide anthelmintic closantel, exhibit different anthelmintic spectra and apparent toxicity in mammals, The basis for this differential pharmacology was examined in experiments that measured motility and adenosine triphosphate (ATP) levels in larval and adult stages of the gastrointestinal nematode, Haemonchus contortus, and in a vertebrate liver cell line and mitochondria, PNU-87407 and PNU-88509 both exhibited functional cross-resistance with closantel in larval migration assays using closantel-resistant and -sensitive isolates of H, contortus. Each compound reduced motility and,ATP levels in cultured adult H. contortus in a concentration- and time-dependent manner: however, motility was reduced more rapidly by PNU-88509, and ATP levels were reduced by lower concentrations of closantel than the beta-ketoamides. Tension recordings from segments of adult H, contortus showed that PNU-88509 induces spastic paralysis, while PNU-87407 and closantel induce flaccid paralysis of the somatic musculature. Marked differences in the actions of these compounds were also observed in the mammalian preparations. In Chang liver cells, ATP levels were reduced after 3 h exposures to greater than or equal to 0.25 mu M PNU-87407 1 mu M closantel or 10 mu M PNU-88509, Reductions in ATP caused by PNU-88509 were completely reversible, while the effects of closantel and PNU-87407; were irreversible. PNU-87407, closantel and PNU-88509 uncoupled oxidative phosphorylation in isolated rat liver mitochondria, inhibiting the respiratory control index (with glutamate or succinate as substrate) by 50% at concentrations of 0.14, 0.9 and 7.6 mu M respectively