PURPOSE: alpha-Ketoglutarate (alphaKG), a Krebs cycle intermediate, is extensively used in the kidney as a fuel substrate and as a counter anion for organic acid secretion. It is known to be taken up by the proximal tubule cells via the brush-border as well as basolateral membranes. We explored biochemical characteristics of the brush-border and basolateral alphaKG transport systems in pars convoluta and pars recta of the proximal tubule, respectively. METHODS: Brush-border and basolateral membrane vesicles (BBMV and BLMV) were isolated from rabbit renal outer cortex and outer medulla by Percoll gradient centrifugation. Vesicular uptake of alphaKG was determined by rapid Millipore filtration method using alpha-14[C]KG as a substrate. RESULTS: Both BBMV and BLMV showed a Na-gradient dependent uphill transport of alphaKG. The systems in both membranes were similarly inhibited by Li and activated by Na (Hill coefficient of 1.4). Kinetic analyses indicated that the Na-alphaKG cotransporters in the BBMV had a lower substrate affinity as compared with those in the BLMV. The transport systems in BLMVs showed a similar Km but different Vmax between the outer cortex (Km: 34 uM, Vmax: 3.3 nmol/mg protein/10s) and outer medulla (Km: 37, Vmax: 1.8). On the other hand, the systems in BBMVs were different in both Km and Vmax between the outer cortex (Km: 194, Vmax: 3.3) and outer medulla (Km: 89, Vmax: 1.7). CONCLUSION: The findings suggest that both axial and apical to basolateral heterogeneity of the Na-alphaKG cotransport system in proximal tubules may be due to a physiological adaptation to efficiently utilize alphaKG in the kidney.
Adaptation, Physiological ; Biological Transport, Active ; Centrifugation ; Citric Acid Cycle ; Filtration ; Hand ; Ketoglutaric Acids ; Kidney Tubules ; Kidney* ; Membranes ; Population Characteristics ; Symporters

Quercetin 3-O-glycosides (Q3Gs) are important members of quercetin glycosides with excellent pharmacological activities such as anti-oxidation, anti-inflammation, anti-cancer and anti-virus. Two representatives of Q3Gs, rutin and troxerutin, have been developed into clinical drugs, demonstrating Q3Gs have become one of the important sources of innovative drugs. However, the applications of Q3Gs in food and pharmaceutical industries are hampered by its poor bioavailability. Of the known means, selective acylation modification of Q3Gs through enzymatic catalysis to obtain Q3G esters is one of the effective ways to improve its bioavailability. Herein, the enzyme-mediated acylation of Q3Gs were reviewed in details, focusing on the four tool enzymes (acyltransferases, lipases, proteases and esterases) and the whole-cell mediated biotransformation, as well as the effect of acylations on the biological activities of Q3Gs. Furthermore, the highly efficient synthesis and diversification of acylated site for Q3G esters were also discussed. Taken together, this review provides a new perspective for further structural modifications of Q3Gs towards drug development.
Acylation ; Biological Availability ; Glycosides ; Quercetin ; Rutin

The ionic quantity across the channel of the cell membrane decides the cell in a certain life state. The theory analysis that existed on the bio-effects of the electro-magnetic field (EMF) does not unveil the relationship between the EMF exerted on the cell and the ionic quantity across the cell membrane. Based on the cell construction, the existed theory analysis and the experimental results, an ionic probability wave theory is proposed in this paper to explain the biological window-effects of the electromagnetic wave. The theory regards the membrane channel as the periodic potential barrier and gives the physical view of the ion movement across cell-membrane. The theory revises the relationship between ion's energy in cell channel and the frequency exerted EMF. After the application of the concept of the wave function, the ionic probability across the cell membrane is given by the method of the quantum mechanics. The numerical results analyze the physical factors that influences the ion's movement across the cell membrane. These results show that the theory can explain the phenomenon of the biological window-effects.
Animals ; Biological Transport, Active ; Cell Membrane ; physiology ; radiation effects ; Cell Membrane Permeability ; physiology ; radiation effects ; Computer Simulation ; Electromagnetic Fields ; Ion Channels ; metabolism ; Ions ; metabolism ; Models, Biological

Normally the cornea has a water content varying between 76-78%, a state of relative dehydration maintained through its own metabolism by the active transport of water and ions across its limiting membrane, the epithelium and endothelium. If the metabolism is grossly disturbed or if the effectivity of the limiting membrane is impaired, the living cornea will swell by the absorption of the fluid. Corneal edema are developed due to trauma, inflammation, glaucoma, degeneration, and neuropathic and metabolic conditions. Essential corneal edema are encountered for which no cause can be found, the condition apparantly occuring without other ocular pathology. A 29 years old Korean lady has been found to have bilateral essential edema of the cornea.
Absorption ; Adult ; Biological Transport, Active ; Cornea ; Corneal Edema* ; Dehydration ; Edema ; Endothelium ; Epithelium ; Glaucoma ; Humans ; Inflammation ; Ions ; Membranes ; Metabolism ; Pathology ; Water

The Caco-2 cell model established as a tool for in vitro investigations of intestinal drug transport processes has been widely used because of its growth characteristics, i.e., it forms polarized monolayers in cultures and differentiates into cells with high homology to human intestinal epithelial absorptive cells. Caco-2 cell cultures have provided a major conceptual advance in our understanding of intestinal drug absorption, biotransformation and bioavailability at the cellular level. Caco-2 cells have received considerable attention from the pharmaceutical industry because they have been widely accepted as a potent in vitro model membrane to screen for potential absorption problems in drug discovery programs. However, the Caco-2 monolayers model is still not perfect. The tightness of the monolayers resembles more colonic than small intestinal tissue, resulting in poor permeabilities for hydrophilic compounds traversing the epithelium via the aqueous paracellular pathway. Caco-2 cells have no mucus layer that is a potential barrier to drug absorption and display low expression of cytochrome P450 which are drug metabolizing enzymes. Further refinements of the Caco-2 cell culture model are needed to better predict human intestinal drug transport. To optimize Caco-2 model, the following technics have been used: modifying the condition of the cell culture, using molecular cloning strategies and inducing the expression of relevant enzymes. They are described in this review.
Biological Availability ; Biological Transport ; Caco-2 Cells ; cytology ; Colon ; physiology ; Epithelial Cells ; cytology ; Humans ; Intestinal Absorption ; Models, Biological

Toxicoproteomics integrates the proteomic knowledge into toxicology by enabling protein quantification in biofluids and tissues, thus taking toxicological research to the next level. Post-translational modification (PTM) alters the three-dimensional (3D) structure of proteins by covalently binding small molecules to them and therefore represents a major protein function diversification mechanism. Because of the crucial roles PTM plays in biological systems, the identification of novel PTMs and study of the role of PTMs are gaining much attention in proteomics research. Of the 300 known PTMs, protein acylation, including lysine formylation, acetylation, propionylation, butyrylation, malonylation, succinylation, and crotonylation, regulates the crucial functions of many eukaryotic proteins involved in cellular metabolism, cell cycle, aging, growth, angiogenesis, and cancer. Here, I reviewed recent studies regarding novel types of lysine acylation, their biological functions, and their applicationsin toxicoproteomics research.
Acetylation ; Acylation ; Aging ; Cell Cycle ; Lysine ; Protein Processing, Post-Translational ; Proteins ; Proteomics ; Toxicology

Heavy metals, such as cadmium, copper, lead, chromium and mercury, are important environmental pollutants, particularly in areas with high anthropogenic pressure. Their presence in the atmosphere, soil and water, even in traces can cause serious problems to all organisms, and heavy metal bioaccumulation in the food chain especially can be highly dangerous to human health. Heavy metals enter the human body mainly through two routes namely: inhalation and ingestion, ingestion being the main route of exposure to these elements in human population. Heavy metals intake by human populations through food chain has been reported in many countries. Soil threshold for heavy metal toxicity is an important factor affecting soil environmental capacity of heavy metal and determines heavy metal cumulative loading limits. For soil-plant system, heavy metal toxicity threshold is the highest permissible content in the soil (total or bioavailable concentration) that does not pose any phytotoxic effects or heavy metals in the edible parts of the crops does not exceed food hygiene standards. Factors affecting the thresholds of dietary toxicity of heavy metal in soil-crop system include: soil type which includes soil pH, organic matter content, clay mineral and other soil chemical and biochemical properties; and crop species or cultivars regulated by genetic basis for heavy metal transport and accumulation in plants. In addition, the interactions of soil-plant root-microbes play important roles in regulating heavy metal movement from soil to the edible parts of crops. Agronomic practices such as fertilizer and water managements as well as crop rotation system can affect bioavailability and crop accumulation of heavy metals, thus influencing the thresholds for assessing dietary toxicity of heavy metals in the food chain. This paper reviews the phytotoxic effects and bioaccumulation of heavy metals in vegetables and food crops and assesses soil heavy metal thresholds for potential dietary toxicity.
Biological Availability ; Biological Transport, Active ; Food Contamination ; analysis ; prevention & control ; Humans ; Metals, Heavy ; analysis ; pharmacokinetics ; toxicity ; Plants, Edible ; drug effects ; growth & development ; metabolism ; toxicity ; Soil Pollutants ; analysis ; pharmacokinetics ; toxicity ; Vegetables ; drug effects ; growth & development ; metabolism ; toxicity

The metabolic transformation of the drugs containing carboxylic acid groups can lead to the formation of acyl glucuronide metabolites through catalysis by glucuronosyltransferase, and produce pro-acyl glucuronide intermediate metabolites with electronic activity. Then, protein or DNA adducts appeared after a series of non-enzyme or enzyme reactions. These adducts would change the protein activity and potentially lead to idiosyncratic and genotoxicity. In this paper, we discussed the chemical activity, drug-induced mechanisms, distribution and toxicity resulting from this metabolic activation for these drugs, and stated the status and prospects of research in this field.
Biological Transport, Active ; Biotransformation ; Carboxylic Acids ; metabolism ; toxicity ; DNA Damage ; drug effects ; Drug-Related Side Effects and Adverse Reactions ; Glucuronides ; metabolism ; toxicity ; Glucuronosyltransferase ; metabolism ; Hepatocytes ; metabolism ; Humans ; Pharmaceutical Preparations ; metabolism

OBJECTIVETo study the biotransformation by human intestinal flora, and the absorption and transportation characteristic in a model of human colon adenocarcinoma cell lines (Caco-2 cell) monolayer of d-corydaline (CDL) and tetrahydropalmatine (THP).

METHODCDL or THP was incubated with crude enzymes of human intestinal flora under the anaerobic environment and 37 degrees C conditions to transform CDL or THP. Caco-2 cell monolayer was used as an intestinal epithelial cell model for determination of the permeability of CDL or THP from apical side (AP side) to basolateral side (BL side) or from BL side to AP side. Transportation parameters and permeability coefficients (P(app)) were then calculated, and P(app) values were compared with the reported values for model compounds, propranolol as a well absorbed drug and atenolol as a poor absorbed drug. The concentration of CDL or THP was measured by HPLC coupled with photodiode array detector.

RESULTCDL or THP in the human intestinal flora incubation system did not happen biotransformation. In the Caco-2 cell monolayer model, the P(app) magnitudes of both CDL and THP were 1 x 10(-5) cm x s(-1) in the bi-directional transport, which were identical with propranolol. And their transports were concentration dependent between 0-180 min.

CONCLUSIONBoth CDL and THP may be stable in the human intestinal flora incubation system, and their absorption and transportation in the human Caco-2 cell monolayer model are mainly via passive diffusion mechanism.

Bacteria ; metabolism ; Berberine Alkaloids ; metabolism ; pharmacokinetics ; Biological Transport ; Biotransformation ; Caco-2 Cells ; Corydalis ; chemistry ; Drugs, Chinese Herbal ; metabolism ; pharmacokinetics ; Humans ; Intestinal Absorption ; Intestines ; metabolism ; microbiology ; Models, Biological

OBJECTIVEDehydroandrographolide (DP) from Andrographis paniculata (Burm. F.) Nees is a potential anticancer agent. This study aimed to investigate the oral bioavailability and intestinal disposition of DP to provide useful information for the development of DP as a new candidate anticancer drug.

METHODSThe pharmacokinetics of DP was evaluated in rats, and its intestinal disposition was determined using cultured Caco-2 cells and a single-pass rat intestinal perfusion model.

RESULTSThe oral bioavailability of DP was 11.92% in rats. The apparent permeability coefficient (P(app)) of DP from the basolateral side (B) to the apical side (A) (5.37×10(-5) cm/s) of the Caco-2 model was roughly equal to that from A to B (4.56×10(-5) cm/s), suggesting no involvement of the efflux transporter(s). In the perfusion model, no significant difference was found in the effective permeability (P*(eff)) of DP between the 4 segments of the intestine. No significant metabolism of DP was detected in the intestinal perfusates. The amount of DP found in the bile was only about 0.1% of the absorbed amount. The P*(eff) and bile amounts of DP were not significantly increased by P-glycoprotein (P-gp) inhibitor or breast cancer resistant protein (BCRP) inhibitor (P>0.05).

CONCLUSIONThe bioavailability of DP was 11.92% in rats. DP has good absorption and metabolism stability in the intestine. The efflux transporters such as P-gp and BCRP do not participate in DP transport.

Administration, Oral ; Animals ; Biological Availability ; Biological Transport ; Caco-2 Cells ; Diterpenes ; administration & dosage ; pharmacokinetics ; Humans ; Intestinal Absorption ; Intestines ; drug effects ; metabolism ; Male ; Rats ; Rats, Sprague-Dawley