Biomedical subjects

G Borchard

Publications and source records attributed to G Borchard.

22 records · Page 2Linked to original sources

PubMed1998

Transport of proteolytic enzymes across Caco-2 cell monolayers.

PURPOSE: To investigate the mechanisms by which proteolytic enzymes, such as trypsin, chymotrypsin, papain, and bromelain, are able to cross the intestinal mucosal barrier after oral administration to man. METHODS: Filter-grown Caco-2 cell monolayers were incubated with proteolytic enzymes and then the transepithelial electrical resistance (TEER) and the transport of the paracellular marker fluorescein were monitored. The effects of the enzymes on the cells were investigated by light microscopy and by biochemical assays. Transport of intact proteases across the cells was verified by monitoring the proteolytic activity and MALDI-TOF mass spectroscopic identification of undegraded trypsin. RESULTS: Depending on time, concentration, and side of exposure to Caco-2 cell monolayers, all proteases decreased the TEER and increased the transport of fluorescein. Some morphological and metabolic changes were observed. The effects were reversible, but until 24 hours after removal of the proteases. Under the conditions of this in-vitro model, approximately 10% of the apically applied dose reached the basolateral compartment as biologically active, non-degraded molecules. CONCLUSIONS: Proteolytic enzymes were found to exert considerable effects on the barrier function of Caco-2 monolayers, facilitating the transport of normally non-absorbable compounds. This suggests the also reported, but so far unexplained, systemic absorption of proteolytic enzymes after oral administration in vivo may occur by self-enhanced paracellular transport.

Biological Transport↗

PubMed1996

The role of serum complement on the organ distribution of intravenously administered poly (methyl methacrylate) nanoparticles: effects of pre-coating with plasma and with serum complement.

PURPOSE: The organ distribution of radiolabeled poly (methyl methacrylate) (PMMA) nanoparticles coated with plasma proteins and serum complement in rats was studied in order to determine the effect of serum complement on the particle phagocytosis by the organs of the reticulo-endothelial system (RES). METHODS: PMMA-nanoparticles were coated overnight with plasma proteins or serum complement, and injected into Wistar rats. The body distribution of nanoparticles was measured by means of scintillation counting of organ samples. In addition, proteins adsorbed to the particle surface were inactivated by heat treatment prior to injection, and the particle's distribution was measured as described above. RESULTS: Whereas uncoated nanoparticles (control group) were mainly taken up by the Kupffer cells in the liver, incubation of the particles in plasma for 12 h followed by heat inactivation reduced the particle concentrations in the liver to merely 22% after 30 min. After 120 min, liver concentrations were still lower than the control group, and almost 30% of the administered dose of the heat-inactivated particle group was present in non-RES organs and tissues. Particles with non-inactivated complement were accumulated in the lung at concentrations of 29% after 30 min, which increased to 71% after 120 min, whereas those coated with inactivated complement reached lung concentrations above 70% already after 30 min. CONCLUSIONS: Particles coated with plasma components are able to avoid uptake by the RES, especially after heat inactivation of the plasma components adsorbed. Adsorption and heat inactivation of complement proteins alone, however, does not have the same result as coating with plasma proteins followed by heat inactivation. Therefore, it is concluded that plasma components other than complement proteins take part in the process of RES activation and phagocytosis of injected nanoparticles.

Animals↗

PubMed1995

Mucoadhesive polymers in peroral peptide drug delivery. II. Carbomer and polycarbophil are potent inhibitors of the intestinal proteolytic enzyme trypsin.

PURPOSE: The evaluation of the inhibitory action of two mucoadhesive poly(acrylates), polycarbophil and carbomer, registered by the Food and Drug Administration (FDA), on the intestinal proteolytic enzyme trypsin. METHODS: The effect of the polymers on trypsin activity by measuring the degradation of a trypsin specific substrate. Binding of Ca2+ ions and proteins (125I-BSA) to the poly(acrylates). The influence of the polymers on the secondary trypsin structure by circular dichroism. RESULTS: Trypsin inhibition was found to be time-dependent upon addition of Ca2+ in the degradation experiment. Only when Ca2+ was added within 10 min after trypsin incubation, recovery of the enzyme could be observed. Both polymers showed a strong Ca2+ binding ability. Carbomer, which had a higher inhibitory effect on trypsin activity, also revealed a higher Ca2+ binding affinity than polycarbophil. The amount of Ca2+ depleted out of the trypsin structure and the reduction of enzyme activity were comparable. Immobilization of trypsin by binding to the polymers could not be observed at pH 6.7. Circular dichroism studies suggested that, under depletion of Ca2+ from trypsin, the secondary structure changed its conformation, followed by an increased autodegradation of the enzyme. CONCLUSIONS: The poly(acrylates) investigated may have potential to protect peptides from tryptic degradation and may be used to master the peroral delivery of peptide drugs.

Acrylic Resins↗

PubMed1993

Interaction of serum components with poly(methylmethacrylate) nanoparticles and the resulting body distribution after intravenous injection in rats.

Radiolabelled poly(methylmethacrylate) (PMMA) nanoparticles were coated with rat serum albumin (RSA), serum and inactivated serum, to examine the influence of these blood components on the body distribution of a model colloidal drug carrier. The particles were incubated overnight at 37 degrees C either in a 1% solution of RSA in phosphate buffered saline (PBS) or in serum obtained from the rats. A suspension of nanoparticles in PBS was used as a control. Serum complement inactivation was achieved by storage at 56 degrees C for 30 min. The suspensions were then injected intravenously via the tail vein of Wistar rats. The animals were sacrificed at five different time points (30 min, 2 h, 6 h, 24 h, and 7 d after injection) and two samples of each organ and two blood samples were weighed into scintillation vials. The radioactivity of each sample was then measured in a Beckman scintillation counter. Coating with RSA led to no significant change in the body distribution of the particles, whereas incubation in serum, especially with complement inactivation prior to injection, very significantly reduced the uptake of particles into the organs of the reticuloendothelial system (RES), e.g., liver, spleen, and bone marrow. At the same time, much higher concentrations of nanoparticles were observed in the serum and in non-RES organs and peripheral tissues (kidneys, muscles, and intestine). This effect was most pronounced after 30 min, but was still observable after 7 d.

Animals↗