Absorption of Proteins

Absorption of proteins and peptides, which has been reviewed (60), is generally low and somewhat erratic. The judicious use of absorption enhancers may be necessary and can be accomphshed in a very controUed manner in this area. The mouth is routinely exposed to a wide variety of agents of different pH and osmolarity and appears to be more robust than many other epitheha. Exposure to a wide range of pH values produced damage only at the extremes of... 

Amino acids promote the production of proteins, enhance tissue repair and wound healing, and reduce the rate of protein breakdown. Amino acids are used in certain disease states, such as severe kidney and liver disease, as well as in TPN solutions. (See the last section of this chapter for a more detailed discussion of TPN.) TPN may be used in patients with conditions such as impairment of gastrointestinal absorption of protein, in patients with an increased requirement for protein, as seen in those with extensive bums or infections, and in patients with no available oral route for nutritional intake ... 

The nasal tissue is highly vascularized and provides efficient systemic absorption. Compared with oral or subcutaneous administration, nasal administration enhances bioavailability and improves safety and efficacy. Chitosan enhances the absorption of proteins and peptide drugs across nasal and intestinal epithelia. Gogev et al. demonstrated that the soluble formulation of glycol chitosan has potential usefulness as an intranasal adjuvant for recombinant viral vector vaccines in cattle [276]. 

Absorption of proteins in the 230-300 nm range is determined by the aromatic side chains of tyrosine (Xmax = 274 am), tryptophan (Xmax = 280 nm), and phenylalanine (Xmax = 257 nm). Because the difference in the absorption spectra of native and unfolded protein molecules is generally small, difference spectra can... 

Many studies have been carried out regarding the absorption of peptides and proteins after pulmonary drug dehvery. The perspectives of a non-parenteral route of administration for larger proteins led to studies on the pulmonary absorption of proteins of different size. To date, over 30 different proteins have been evaluated with regard to absorption rate and... 

Fat absorption of protein additives has been studied less extensively than water absorption and consequently the available data are meager. Although the mechanism of fat absorption has not been explained, fat absorption is attributed mainly to the physical entrapment of oil (7). Factors affecting the protein-lipid interaction include protein conformation, protein-protein interactions, and the spatial arrangement of the lipid phase resulting from the lipid-lipid interaction. Non-covalent bonds, such as hydrophobic, electrostatic, and hydrogen, are the forces involved in protein-lipid interactions no single molecular force can be attributed to protein-lipid interactions ( ). 

Commercial wines are commonly tested for protein stability. Wine proteins, upon denaturation by heat or cold, may cause cloudiness and unsightly deposits after bottling. In addition, proteins may combine with iron and copper salts to form flocculate material in bottled wines. The reaction and absorption of proteins on bentonite is an effective means of removing protein from wines (109, 110, 111). Therefore, fining wines... 

Ziv, E., O. Lior, and M. Kidron. 1987. Absorption of protein via the intestinal wall. A quantitative model. Biochem Pharmacol 36 1035. 

The experiments described above demonstrate the ability to deliver soluble analytes to bilayer arrays and to evaluate the ability of these species to prevent surface absorption of proteins. Therefore, we have demonstrated methods of creating spatially addressed arrays of aqueous solutions above phospholipid membranes as well as arrays of phospholipid membranes with unique chemistry in each bilayer.13 These two concepts were carried out in separate assays. To be able to control both surface chemistry and aqueous chemistry... 

Barriers to pulmonary absorption of proteins and peptides include respiratory mucus, mucociliary clearance, pulmonary enzymes/proteases, alveolar lining layer, alveolar epithelium, basement membrane, macrophages and other cells [3, 18]. The molecular weight cutoff of tight junctions for alveolar type I cells is 0.6 nm, while endothelial junctions allow the passage of larger molecules (4-6 nm). In order to reach the bloodstream in the endothelial vasculature, proteins and peptides must cross this alveolar epithelium, the capillary endothelium, and the intervening extracellular matrix. 

In contrast to the stomach, where there is a protective pH-gradient from 7 to 1 between Ihc mucosa and the iumen hoe, there is only a slight pH gradient from about 6 (mucosa) to about 7 (lumen). It corresponds to the inner mucosal part of the unstirred water layer. The thickness of this layer is about 20 pm. The pH has no significant influence on the absorption of protein or peptide drugs. 

FIG. 1 Digestion and absorption of proteins in the small intestine. (1) Brush-border peptidases, (2) brush-border amino acid transport systems, (3) brush-border peptide transport systems, (4) cytoplasmic peptidases, (5) basolateral amino acid transport systems, (6) basolateral peptide transport systems. 

Chitosan and its derivatives have been applied to enhance the absorption of proteins (e.g., insulin) and polypeptides (e.g., buserelin). /V-Trimethyl chitosan chloride exhibits opening of the tight junctions of the intranasal and intestinal epithelial cells so that the transport of hydrophilic compounds is increased through the para-cellular transport pathway. The absorption-enhancing effect was concentration dependent and reversible and dependent on the integrity of the intercellular cell contact zone. 

Few pharmacokinetic studies are carried out beyond the range of 28-40 years and, consequently, there are few data on oral bioavailability for extremes of age. Gastric fluid is less acidic in newborns than in adults, which can affect the absorption of ionizable and acid-labile drags. Neonates are also associated with a leaky epithelium, which permits the absorption of proteins and other macromolecules not normally absorbed from the GI tract. Decreased enzymatic activity, including hepatic first-pass metabolism, is associated with the elderly, which may result in an increased oral bioavailabiliy for drags subject to the first-pass effect. 

Infrared spectroscopy is one of the most powerful tools for functional studies of hemoproteins reactive to external hgands with infared absorptions in the triple bond region (1900-2200 cm ) where the background level due to absorptions of proteins and water molecules is quite low as described above. However, recent improvement in the sensitivity and stability of the FTIR apparatus with an MCT detector has enabled infrared spectroscopic examination of the protein moiety also. In fact, one of the most sensitive methods for monitoring the dissociation of a COOH group is infrared spectroscopy. 

Atrophic gastritis will cause decreased secretion of gastric acid before there is any impairment of intrinsic factor secretion. This means that the absorption of crystalline vitamin B12, as used in the Schilling test, is normal but the absorption of protein-bound vitamin B12 from foods will be impaired (Section 10.7.1), and the Schilling test will give a false-negative result. 

Figure 23.1. Digestion and Absorption of Proteins. Protein digestion is primarily a result of the activity of enzymes secreted by the pancreas. Aminopeptidases associated with the intestinal epithelium further digest proteins. The amino...

Rosenzweig, M. Walzer, M. Absorption of protein from the vagina and uterine cervix. Am. J. Obstet. Gynecol. 1943, 45, 286-290. 

Taylor, G. Colthorpe, P. Farr, S.J. Pulmonary absorption of proteins influence of deposition site and competitive elimination processes. In Respiratory Drug Delivery /V Byron, P.R., Dalby, R.N., Farr, S.J., Eds. Interpharm Press, Inc. Buffalo Grove, IL, 1994 25-30. 

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