The relationship between Na+ and the active transport of arbutin in the small intestine

Determination of arbutin in vitro and in vivo by LC-MS/MS: Pre-clinical evaluation of natural product arbutin for its early medicinal properties

ETHNOPHARMACOLOGICAL RELEVANCE

Arbutin is a naturally occurring glucoside extracted from plants, known for its antioxidant and tyrosinase inhibiting properties. It is widely used in cosmetic and pharmaceutical industries. With in-depth study of arbutin, its application in disease treatment is expanding, presenting promising development prospects. However, reports on the metabolic stability, plasma protein binding rate, and pharmacokinetic properties of arbutin are scarce.

AIM OF THE STUDY

The aim of this study is to enrich the data of metabolic stability and pharmacokinetics of arbutin through the early pre-clinical evaluation, thereby providing some experimental basis for advancing arbutin into clinical research.

MATERIALS AND METHODS

We developed an efficient and rapid liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay for determining arbutin in plasma. We investigated the metabolic and pharmacokinetic properties of arbutin through in vitro metabolism assay, cytochrome enzymes P450 (CYP450) inhibition studies, plasma protein binding rate analysis, Caco-2 cell permeability tests, and rat pharmacokinetics to understand its in vivo performance.

RESULTS

In vitro studies show that arbutin is stable, albeit with some species differences. It exhibits low plasma protein binding (35.35 ± 11.03% ∼ 40.25 ± 2.47%), low lipophilicity, low permeability, short half-life (0.42 ± 0.30 h) and high oral bioavailability (65 ± 11.6%). Arbutin is primarily found in the liver and kidneys and is eliminated in the urine. It does not significantly inhibit CYP450 up to 10 μM, suggesting a low potential for drug interactions. Futhermore, preliminary toxicological experiments indicate arbutin's safety, supporting its potential as a therapeutic agent.

CONCLUSION

This study provides a comprehensive analysis the drug metabolism and pharmacokinetics (DMPK) of arbutin, enriching our understanding of its metabolism stability and pharmacokinetics properties, It establishes a foundation for further structural optimization, pharmacological studies, and the clinical development of arbutin.

Urinary excretion and metabolism of arbutin after oral administration of Arctostaphylos uvae ursi extract as film-coated tablets and aqueous solution in healthy humans

Bearberry leaves and preparations made from them are traditionally used for urinary tract infections. The urinary excretion of arbutin metabolites was examined in a randomized crossover design in 16 healthy volunteers after the application of a single oral dose of bearberry leaves dry extract (BLDE). There were two groups of application using either film-coated tablets (FCT) or aqueous solution (AS). The urine sample analysis was performed by a validated HPLC coolarray method (hydroquinone) and a validated capillary electrophoresis method (hydroquinone-glucuronide, hydroquinone-sulfate). The total amounts of hydroquinone equivalents excreted in the urine from BLDE were similar in both groups. With FCT, 64.8% of the arbutin dose administered was excreted; with AS, 66.7% was excreted (p = 0.61). The maximum mean urinary concentration of hydroquinone equivalents was a little higher and peaked earlier in the AS group versus the FCT group, although this did not reach statistical significance (Cur max = 1.6893 micromol/ml vs. 1.1250 micromol/ml, p = 0.13; tmax (t midpoint) = 3.60 h vs. 4.40 h, p = 0.38). The relative bioavailability of FCT compared to AS was 103.3% for total hydroquinone equivalents. There was substantial intersubject variability. No significant differences between the two groups were found in the metabolite patterns detected (hydroquinone, hydroquinone-glucuronide, and hydroquinone-sulfate).

Disaccharide uptake by brush-border membrane vesicles lacking the corresponding hydrolases

Intestinal disaccharide uptake was studied with isolated brush-border membrane vesicles lacking the corresponding hydrolase. Either 15-day-old chick intestine, lacking both trehalase and lactase, or newborn pig intestine, lacking sucrase, was used. Both animal species yielded osmotically active vesicles capable of D-glucose/Na+ cotransport with a positive overshoot test. Vesicles from either origin gave quantitatively similar results in regard to both initial uptake rates and relative vesicle volumes. The nontransported analogs D-mannitol and L-glucose were used as diffusion markers. When tested with the appropriate disaccharidase-lacking vesicles, lactose, trehalose and sucrose exhibited uptake rates indistinguishable from those of D-mannitol and L-glucose. These uptakes were unaffected by the presence or absence of Na+, phlorizin and Tris. Chromatographic analysis confirmed the lack of hydrolysis of each disaccharide after prolonged incubation. The inescapable conclusion seems to be that intact disaccharides are not transported through the brush-border membrane, their uptake occurring through simple diffusion.

Influence of ionic strength on rectal absorption of gentamicin sulfate in the presence and absence of sodium salicylate

The rectal absorption of gentamicin sulfate in rats, both in the presence and absence of sodium salicylate, was facilitated by the use of high ionic strength aqueous formulations. The relative order of effectiveness in promoting gentamicin absorption was sodium dihydrogen phosphate congruent to sodium chloride much greater than potassium chloride, indicating a preferential effect of sodium ions. The increased gentamicin bioavailability in response to sodium salicylate adjuvant activity appeared to be independent of and additive to the increased gentamicin absorption due to high ionic strength conditions. The inability of sorbitol to increase gentamicin bioavailability above control levels indicated that elevated osmotic pressure was not a major determinant of rectal gentamicin absorption.

Sugar transport by intestine. Escape of galactose from preloaded mucosa of hamster jejunum

Everted hamster jejunum was loaded with D-galactose and then escape into an initially galactose-free mucosal solution was followed. Mucosal anaerobiosis greatly increased the rate of escape, an effect which might have been caused by inhibiting reuptake from the unstirred layer and/or by augmenting the ease of unidirectional efflux across the brush border membrane. The former effect was expected because of our previous results from influx studies, and the main object here was to find out if the ease of efflux is affected by anaerobiosis. With phlorizin present in the mucosal solution during escape, information about unidirectional efflux was obtainable. We estimated that 10(-4) M phlorizin inhibited the ease of efflux via the phlorizin-sensitive pathway by about 65%. Apparently the reason why mucosal phlorizin accelerates escape of sugar from loaded mucosa, an effect which has been reported previously by others, is that it inhibits unidirectional efflux less effectively than it inhibits reuptake from the unstirred layer. Residual efflux via the phlorizin-sensitive pathway was markedly increased by mucosal anaerobiosis. This increase did not require an elevation of intracellular Na+ concentration. These results, together with those of our previous study, show that mucosal anaerobiosis abolishes uphill transport of galactose across the brush border of hamster jejunum by inhibiting unidirectional influx and by increasing the ease of unidirectional efflux. Neither of these effects requires a rise in intracellular Na+ concentration.

Accumulation of iron in the rabbit erythroid cell as affected by ouabain, sodium and potassium ions, and temperature

Reticulocytosis was induced in rabbits with phenylhydrazine. The accumulation of a small part of (59)Fe in blood cells of these animals was inhibited by ouabain and related to changes in extracellular sodium and potassium concentrations. Sodium increases movement from the cell surface into the cell, whereas potassium and ouabain decrease this movement. (59)Fe movement was found to be temperature-dependent. Thus, the Na-K ATPase system appears to be important in the movement of iron from the cell membrane (stroma) to the cell interior, but influences only a small part of the total iron transport.

Active sugar transport by the small intestine. The effects of sugars, amino acids, hexosamines, sulfhydryl-reacting compounds, and cations on the preferential binding of D-glucose to tris-disrupted brush borders

Tris-disrupted and intact brush border membrane preparations from mucosa of hamster jejunum were capable of preferentially binding actively transported D-glucose in a similar manner. Density gradient centrifugation of the Tris-disrupted brush borders indicated that D-glucose was bound to a fraction containing the cores or inner material of the microvilli. The properties of this binding were examined with the Tris-disrupted brush border preparation. Actively transported sugars competitively inhibited preferential D-glucose binding, whereas no effect was observed with nonactively transported sugars. Neither actively nor nonactively transported amino acids affected D-glucose binding. D-Glucosamine, which is not actively transported, was inhibitory to preferential D-glucose binding as well as to the active transport of D-glucose by everted sacs of hamster jejunum. No inhibitory effect was observed with the same concentration of D-galactosamine. Preferential D-glucose binding was also inhibited by sulfhydryl-reacting compounds, Ca(2+), and Li(+) ions. On the other hand, Mg(2+) was shown to be stimulatory and Na(+), NH(4) (+), and K(+) had no effect on this phenomenon. The results of these experiments suggest that preferential D-glucose binding to brush borders is related to the initial step in active sugar transport by the small intestine.

Transport of glucose and galactose in kidney-cortex cells

1. The aerobic transport of d-glucose and d-galactose in rabbit kidney tissue at 25 degrees was studied. 2. In slices forming glucose from added substrates an accumulation of glucose against its concentration gradient was found. The apparent ratio of intracellular ([S](i)) and extracellular ([S](o)) glucose concentrations was increased by 0.4mm-phlorrhizin and 0.3mm-ouabain. 3. Slices and isolated renal tubules actively accumulated glucose from the saline; the apparent [S](i)/[S](o) fell below 1.0 only at [S](o) higher than 0.5mm. 4. The rate of glucose oxidation by slices was characterized by the following parameters: K(m) 1.16mm; V(max.) 4.5mumoles/g. wet wt./hr. 5. The active accumulation of glucose from the saline was decreased by 0.1mm-2,4-dinitrophenol, 0.4mm-phlorrhizin and by the absence of external Na(+). 6. The kinetic parameters of galactose entry into the cells were: K(m) 1.5mm; V(max) 10mumoles/g. wet wt./hr. 7. The efflux kinetics from slices indicated two intracellular compartments for d-galactose. The galactose efflux was greatly diminished at 0 degrees , was inhibited by 0.4mm-phlorrhizin, but was insensitive to ouabain. 8. The following mechanism of glucose and galactose transport in renal tubular cells is suggested: (a) at the tubular membrane, these sugars are actively transported into the cells by a metabolically- and Na(+)-dependent phlorrhizin-sensitive mechanism; (b) at the basal cell membrane, these sugars are transported in accordance with their concentration gradient by a phlorrhizin-sensitive Na(+)-independent facilitated diffusion. The steady-state intracellular sugar concentration is determined by the kinetic parameters of active entry, passive outflow and intracellular utilization.

Transport of monosaccharides in kidney-cortex cells

1. The aerobic accumulation of various monosaccharides in slices of rabbit kidney cortex at 25 degrees was studied. 2. d-Fructose and alpha-methyl d-glucoside were readily accumulated against their concentration gradient by a phlorrhizin-sensitive Na(+)-dependent active transport. In the absence of external Na(+) the maximal rate of alpha-methyl glucoside transport was decreased tenfold, the K(m) of entry into the cells (8.2mm) not being affected. Phlorrhizin and d-galactose inhibited the entry of alpha-methyl glucoside also in the absence of external Na(+). 3. d-Xylose, 6-deoxy-d-glucose and 6-deoxy-d-galactose were poorly accumulated ([S](i)/[S](o) ratios slightly above 1.0); this transport was inhibited by phlorrhizin and by the absence of Na(+). 4. 3-O-Methyl-d-glucose, d-arabinose and l-arabinose were not actively transported, [S](i)/[S](o) ratios never exceeding 1.0. 5. 2-Deoxy-d-glucose and 2-deoxy-d-galactose were readily accumulated against a high concentration gradient, this transport being Na(+)-independent and only slightly sensitive to phlorrhizin. External Na(+) was not required for an inhibitory action of phlorrhizin and d-galactose on the entry of 2-deoxy-d-galactose into the cells. 6. Interference for entry into the cells between the following saccharides was found: d-galactose inhibited alpha-methyl d-glucoside transport; d-xylose entry was inhibited by d-glucose; d-galactose transport was inhibited by d-xylose; a mutual interference between d-galactose and its 2-deoxy analogue was found. 7. It is concluded that d-glucose, d-galactose, alpha-methyl d-glucoside, d-xylose and possibly also some other monosaccharides share a common active transport system. 8. The specificity of the Na(+)-dependent phlorrhizin-sensitive active transport system for monosaccharides in kidney-cortex cells differs from that in intestinal epithelial cells.

Transport of sugars and amino acids in the intestine: evidence for a common carrier

D-Galactose, L-arginine, and their respective actively transported analogs are partially competitive inhibitors of the active transport of neutral amino acids in the small intestine of hamsters. Since the aforesaid classes of compounds are all transported by similar, sodium-ion-dependent mechanisms and elicit countertransport of each other, all may share a common, polyfunctional carrier in which a series of separate binding sites, namely, one each for sugars, neutral amino acids, basic amino acids, and Na(+) are joined together, as in a mosaic.