In addition to metabolic differences, the anatomical, physiological, and biochemical differences in the gastrointestinal (GI) tract of the human and common laboratory animals can cause significant variation in drug absorption from the oral route Among the physiological factors, pH, bile, pancreatic juice, and mucus and fluid volume and content can modify dissolution rates, solubility, transit times, and membrane transport of drug molecules The microbial content of the GI tract can significantly affect the reductive metabolism and enterohepatic circulation of drugs and colonic delivery of formulations The transit time of dosage forms can be significantly different between species due to different dimensions and propulsive activities of the GI tract The lipid/protein composition of the enterocyte membrane along the GI tract can alter binding and passive, active, and carrier-mediated transport of drugs The location and number of Peyer's patches can also be important in the absorption of large molecules and particulate matter While small animals, rats, mice, guinea pigs, and rabbits, are most suitable for determining the mechanism of drug absorption and bioavailability values from powder or solution formulations, larger animals, dogs, pigs, and monkeys, are used to assess absorption from formulations The understanding of physiological, anatomical, and biochemical differences between the GI tracts of different animal species can lead to the selection of the correct animal model to mimic the bioavailability of compounds in the human This article reviews the anatomical, physiological, and biochemical differences between the GI tracts of humans and commonly used laboratory animals

https://onlinelibrary.wiley.com/doi/pdf/10.1002/bdd.2510160502

Comparison of the gastrointestinal anatomy, physiology, and biochemistry of humans and commonly used laboratory animals

In addition to metabolic differences, the anatomical, physiological, and biochemical differences in the gastrointestinal (G.I.) tract of the human and common laboratory animals can cause significant variation in drug absorption from the oral route. Among the physiological factors, pH, bile, pancreatic juice, and mucus and fluid volume and content can modify dissolution rates, solubility, transit times, and membrane transport of drug molecules. The microbial content of the G.I. tract can significantly affect the reductive metabolism and enterohepatic circulation of drugs and colonic delivery of formulations. The transit time of dosage forms can be significantly different between species due to different dimensions and propulsive activities of the G.I. tract. The lipid/ protein composition of the enterocyte membrane along the G.I. tract can alter binding and passive, active, and carrier-mediated transport of drugs. The location and number of Peyer’s patches can also be important in the absorption of large molecules and particulate matter. While small animals, rats, mice, guinea pigs, and rabbits, are most suitable for determining the mechanism of drug absorption and bioavailability values from powder or solution formulations, larger animals, dogs, pigs, and monkeys, are used to assess absorption from formulations. The understanding of physiological, anatomical, and biochemical differences between the G.I. tracts of different animal species can lead to the selection of the correct animal model to mimic the bioavailability of compounds in the human. This article reviews the anatomical, physiological, and biochemical differences between the G.I. tracts of humans and commonly used laboratory animals.

Review article comparison of the gastrointestinal anatomy, physiology, and biochemistry of humans and commonly used laboratory animals

https://www.cell.com/cell-chemical-biology/pdf/S1074-5521(00)00025-9.pdf

Selective small molecule inhibitors of glycogen synthase kinase-3 modulate glycogen metabolism and gene transcription.

During the last decade, there have been enormous advances in our knowledge of glycoproteins and the stage has been set for the biotechnological production of many of them for therapeutic use. These advances are reviewed, with special emphasis on the structure and function of the glycoproteins (excluding the proteoglycans). Current methods for structural analysis of glycoproteins are surveyed, as are novel carbohydrate-peptide linking groups, and mono- and oligo-saccharide constituents found in these macromolecules. The possible roles of the carbohydrate units in modulating the physicochemical and biological properties of the parent proteins are discussed, and evidence is presented on their roles as recognition determinants between molecules and cells, or cell and cells. Finally, examples are given of changes that occur in the carbohydrates of soluble and cell-surface glycoproteins during differentiation, growth and malignancy, which further highlight the important role of these substances in health and disease.

Protein glycosylation. Structural and functional aspects.

Endothelial nitric-oxide synthase (eNOS) generates the key signaling molecule nitric oxide in response to intralumenal hormonal and mechanical stimuli We designed studies to determine whether eNOS is localized to plasmalemmal microdomains implicated in signal transduction called caveolae Using immunoblot analysis, eNOS protein was detected in caveolar membrane fractions isolated from endothelial cell plasma membranes by a newly developed detergent-free method; eNOS protein was not found in noneaveolar plasma membrane Similarly, NOS enzymatic activity was 94-fold enriched in caveolar membrane versus whole plasma membrane, whereas it was undetectable in non-caveolar plasma membrane 51-86% of total NOS activity in postnuclear supernatant was recovered in plasma membrane, and 57-100% of activity in plasma membrane was recovered in caveolae Immunoelectron microscopy showed that eNOS heavily decorated endothelial caveolae, whereas coated pits and smooth plasma membrane were devoid of gold particles Furthermore, eNOS was targeted to caveolae in COS-7 cells transfected with wild-type eNOS cDNA Studies with eNOS mutants revealed that both myristoylation and palmitoylation are required to target the enzyme to caveolae and that each acylation process enhances targeting by 10-fold Thus, acylation targets eNOS to plasmalemmal caveolae Localization to this microdomain is likely to optimize eNOS activation and the extracellular release of nitric oxide

Acylation targets endothelial nitric oxide synthase to plasmalemmal caveolae

Microvillus membrane vesicles from pig small intestine Purity and lipid composition

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1016/0014-5793%2874%2980994-4

Isolation of lipid particles from baker's yeast.

To search for caveolar proteins, mice were immunised with rat adipocyte membranes. Hybridoma supernatants were screened for antibodies to proteins on the cytosolic face of caveolae by indirect immunoelectron microscopy of immunogold-labelled adipocyte plasma membrane sheets adsorbed on electron-microscope (EM) grids. One of the hybridoma supernatants (2F11) produced a specific labelling of caveolae which was much more intense than that obtained with caveolin-1 antibodies. In Western blots of sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) separated proteins in crude membrane fractions from different rat tissues, 2F11 labelled a band corresponding to 60 kDa. The intensity of 2F11 labelling was high in adipose tissue and in other tissues varied in parallel to caveolin-1 labelling. In blots of plasma membrane (PM) and light-microsomal (LM) fractions from a homogenate of adipocytes, prior insulin stimulation of the adipocytes translocated GLUT-4 from the LM to the PM fraction, but was without effect on the distribution of the 60-kDa protein labelled by 2F11. Digestion with endoproteinase lys-C produced the same pattern of immunoreactive fragments of the protein in the vesicular PM and LM fractions, indicating similar membrane topology of the 2F11-reactive, 60-kDa protein in vesicles of PM and LM fractions.

A 60-kDa protein abundant in adipocyte caveolae.

Membrane-bound lipid particles from beef heart chemical composition and structure

In this paper, we present the results of an investigation into the catalytic properties of CMP-Neu5Ac hydroxylase (Neu5Ac: N-acetylneuraminic acid) in high-speed supernatants of mouse liver. The enzyme was most active in Hepes/NaOH pH 7.4 and was markedly inhibited by relatively small increases in ionic strength, though the inhibition was abolished by desalting procedures. Several nonionic detergents could activate the hydroxylase to various degrees in a concentration-dependent manner. Ionic detergents and a number of phospholipids were, however, generally inert or inhibitory. The lack of inhibitory influence of a wide range of nucleotides revealed that CMP-Neu5Ac hydroxylase binds its sugar-nucleotide substrate with a high degree of specificity. Thus, even millimolar concentrations of several cytidine nucleotides elicited virtually negligible inhibition, though the reaction product, CMP-Neu5Gc (Neu5Gc: N-glycoloylneuraminic acid), was a weak inhibitor. The results also indicate that the enzyme is not regulated by any nucleotides or sugar-nucleotides. Dilution of high-speed supernatants with buffer gave rise to a decrease in the specific activity of the hydroxylase, implicating the involvement of more than one component in catalysis. Activity could be restored by the addition of a heat extract of the supernatant. The active principle in this extract was found to be a heat-stable protein with a molecular mass of about 17 kDa. Immunochemical studies allowed this protein to be identified as cytochrome b5 and it was shown that this electron carrier is essential for the activity of CMP-Neu5Ac hydroxylase. Inhibition studies using iron ligands and activation by exogenous iron salts suggest the involvement of a non-haem iron cofactor in the catalytic cycle of this hydroxylase. Cytochrome b5 may thus serve as an electron donor for this postulated cofactor.

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1432-1033.1992.tb16925.x

Kirsten Christiansen

Papers

Microvillus membrane vesicles from pig small intestine Purity and lipid composition

Isolation of lipid particles from baker's yeast.

A 60-kDa protein abundant in adipocyte caveolae.

Membrane-bound lipid particles from beef heart chemical composition and structure

Mouse liver cytidine-5'-monophosphate-N-acetylneuraminic acid hydroxylase. Catalytic function and regulation.