Intestinal absorption of dl-alpha-tocopherol from bile salts and polysorbate 80 micellar solutions in rat

Cationic N,N-Dimethylglycine Ester Prodrug of 2R-α-Tocotrienol Promotes Intestinal Absorption via Efficient Self-Micellization with Intrinsic Bile Acid Anion

The intestinal absorption of hydrophobic compounds is severely influenced by their transportation rate through the unstirred water layer in the intestinal lumen. A member of the vitamin E family, α-Tocotrienol (α-T3) has remarkable pharmacological effects, but its intestinal absorption is hampered due to its hydrophobicity. Here, we prepared three ester derivatives of 2R-α-T3, and we selected a suitable prodrug compound using rat plasma and liver microsomes. The micellization profile of the selected compound in the presence of taurocholic acid (TCA) was evaluated. After gastrostomy administration of the prodrug candidate or α-T3 solution containing TCA, AUC values were determined for α-T3 in plasma obtained from bile duct-ligated rats. Among the three types in the efficiency of the reconversion to the parent drug, α-T3 N,N-dimethylglycinate (α-T3DMG) was the best prodrug; α-T3DMG formed mixed micelles via ion pairs with anionic TCA. The solubility of α-T3DMG in n-octanol/water depended on its ratio to TCA. The AUC after α-T3DMG administration to ligated rats was 2-fold higher than that after α-T3 administration, suggesting a smooth interaction with intrinsic bile acids. In conclusion, utilization of the prodrug synthesized using N,N-dimethylglycine ester may be a beneficial approach to promote intestinal absorption of α-T3 via self-micellization with intrinsic bile acid.

Biopharmaceutics classification and intestinal absorption study of apigenin

The aim of the study was to characterize the biopharmaceutics classification system (BCS) category of apigenin (AP) using intrinsic dissolution rate (IDR) and rat intestinal permeability, and to investigate the intestinal absorption mechanism of AP in rats. In the present investigation, equilibrium solubility and intrinsic dissolution rate (IDR) of AP were estimated in phosphate buffers. Effective intestinal permeability (P(eff)) of AP was determined using single-pass intestinal perfusion (SPIP) technique in four segments (duodenum, jejunum, ileum and colon) of rat intestine at three concentrations (10, 50 and 100 μg/ml). The aqueous solubility of AP in tested phosphate buffers was very poor with maximum solubility of 2.16 μg/ml at pH 7.5. The IDR of AP was very low with a value of 0.006 mg/min/cm(2). The minimum and maximum P(eff)s determined by SPIP were 0.198×10(-4) and 0.713×10(-4) cm/s at jejunum and duodenum site, respectively. In addition, the concentration-dependent permeability behavior was observed in the duodenum and jejunum, which suggested that AP was transported by both passive and active carrier-mediated saturable mechanism in these two intestinal segments. However, the observed concentration-independent permeability behavior in ileum and colon indicated primarily passive transport mechanism of absorption of AP in the last two intestinal segments. AP was classified as class II drug of the BCS due to its low solubility and high intestinal permeability. AP could be well absorbed in the whole intestine with the main absorption site at duodenum. The absorption of AP in four intestinal segments exhibited different transport mechanisms.

Enteral infusion of phosphatidylcholine increases the lymphatic absorption of fat, but lowers alpha-tocopherol absorption in rats fed a low zinc diet*

Our previous study has shown that the lymphatic absorption of both fat and alpha-tocopherol (alphaTP) is lowered markedly in rats fed a low zinc diet, with a parallel decrease in lymphatic phospholipid (PL) output. This study was conducted to determine if enteral infusion of phosphatidylcholine (PC) could restore lymphatic absorption of fat and alphaTP in zinc-deficient rats. One group of rats was fed an AIN-93G diet containing 3 mg Zn/kg (low zinc; LZ) and the other was fed the same diet but containing 30 mg Zn/kg (adequate zinc; AZ). Rats were trained to consume two meals daily of equal amounts of food. At 6 wk, each rat with lymph fistula was infused at 3 mL/h with a lipid emulsion containing 3.6 &mgr;mol alphaTP and 565 &mgr;mol [carboxyl-14C]-triolein (14C-OA), with or without 40 &mgr;mol 1,2-dilinoleoyl-PC in 24 mL PBS at pH 6.4. The lymphatic absorptions of fat and alphaTP were determined by measuring 14C-radioactivity and alphaTP appearing in the mesenteric lymph collected hourly for 8 h. When the emulsion devoid of PC was infused, the absorptions of both 14C-OA (41 +/- 4% dose) and alphaTP (431 +/- 55 nmol) in LZ rats were significantly lower than in AZ rats (48 +/- 2% 14C-OA dose and 581 +/- 70 nmol alphaTP). When the emulsion containing PC was infused, the absorption of 14C-OA was restored rapidly to normal in LZ rats, along with a parallel increase in lymphatic PL output. However, PC infusion further lowered the absorption of alphaTP to 311 +/- 20 nmol/8 h in LZ rats and also lowered the absorption of alphaTP in AZ rats (347 +/- 48 nmol/8 h). The results demonstrate that low zinc intake results in impaired intestinal absorption of both alphaTP and fat. The findings also indicate that PC significantly improves the intestinal absorption of fat, but inhibits alphaTP absorption, suggesting that PC affects the intestinal absorption of alphaTP and fat via distinctly different mechanisms.

Intraduodenal infusion of lysophosphatidylcholine restores the intestinal absorption of vitamins A and E in rats fed a low-zinc diet

Our previous work has shown that the lymphatic absorptions of lipids and lipid-soluble vitamins, retinol and alpha-tocopherol (alphaTP), are lowered markedly in rats fed a low-zinc (LZ) diet in parallel with lower lymphatic phospholipid outputs. Phosphatidylcholine (PC), when infused enterally, restored the absorptions of fat and retinol, but further lowered the absorption of alphaTP in rats fed the LZ diet. This study was conducted to determine whether a luminal infusion of lysophosphatidylcholine, a product of PC hydrolysis by pancreatic phospholipase A2 (PLA2), would simultaneously restore the absorptions of retinol and alphaTP in LZ rats. Rats were trained to consume two meals per day and were divided into two groups. One group was fed an AIN-93G diet containing a LZ (3.0 mg Zn/kg), and the other was fed the same diet, but containing adequate zinc (AZ; 30.0 mg Zn/kg) for 6 weeks. Rats with lymph cannula were infused at 3.0 ml/hr for 8 hr with a lipid emulsion containing retinol, alphaTP, and 14C-labeled triolein (14C-oleic acid) with or without 1-oleoyl-2-hydroxy phosphatidylcholine (lysoPC) in 24 ml of PBS (pH 6.5). When the lipid emulsion without lysoPC was infused, the absorptions of retinol and alphaTP were significantly lower in LZ rats (retinol, 13.2+/-1.5 nmol; alphaTP, 430.6+/-66.8 nmol) than in AZ rats (retinol, 18.2+/-1.0 nmol; alphaTP, 543.8+/-58.9 nmol). The lower absorptions of the vitamins in LZ rats occurred in parallel with a significant decrease in 14C-oleic acid absorption. When the emulsion containing lysoPC was infused, however, absorptions of the vitamins (retinol, 18.4+/-3.0 nmol; alphaTP, 777.2+/-92.1 nmol) in LZ rats were restored completely to the control levels (retinol, 20.4+/-2.8 nmol; alphaTP, 756.3+/-136.1 nmol). The results suggest that the luminal hydrolysis of PC to lysoPC by PLA2 may be impaired in LZ rats, resulting in impaired absorption of fat and the fat-soluble vitamins.

Phosphatidylcholine inhibits and lysophosphatidylcholine enhances the lymphatic absorption of alpha-tocopherol in adult rats

This study was conducted to compare the effects of enterally infused phosphatidylcholine (PC) and lysophosphatidylcholine (lysoPC) on the lymphatic absorption of alpha-tocopherol (alphaTP) in male rats. In expt. 1, bile-diverted rats with mesenteric lymph cannulas were infused at 3.0 mL/h for 8 h with a lipid emulsion containing 5.0 micromol alphaTP, 565 micromol 14C-triolein (14C-OA) and 396 micromol Na+-taurocholate with 80 micromol 1,2-dipalmitoyl PC (DPPC) or 1,2-dilinoleoyl PC (DLPC) or without PC (NoPC) in 24 mL phosphate-buffered saline (pH 6.6). In expt. 2, the effects of 1,2-dioleoyl PC (DOPC) and 1-oleoyl-2-hydroxy-PC (lysoPC) on alphaTP and 14C-cholesterol absorption were compared in rats with lymph cannulas. When DPPC or DLPC was infused, the lymphatic absorption of alphaTP was lowered drastically. The cumulative absorptions of alphaTP in rats infused with DPPC and DLPC were 45 and 52%, respectively, of the control values (NoPC). No significant difference was noted between the PC groups. In contrast, the absorption of 14C-OA was increased by 42 to 43% in rats infused with DPPC or DLPC compared with that in NoPC rats. Phospholipid outputs also were significantly higher in DPPC (34.0 +/- 5.5 micromol /8 h) and DLPC (32.4 +/- 2.4 micromol /8 h) rats than in NoPC rats (21.2 +/- 4.2 micromol /8 h). When lysoPC was infused, the absorptions of alphaTP and 14C-cholesterol were increased markedly compared with those for DOPC, with no significant difference in PL output between groups infused with DOPC and lysoPC. These observations provide clear evidence that PC present in a lipid emulsion inhibits alphaTP absorption, whereas it enhances the absorption of fat. The data also demonstrate that lysoPC simultaneously increases the absorption of alphaTP and cholesterol. The findings indicate that luminal PC inhibits the absorption of alphaTP and that hydrolysis of PC is critical to improving the intestinal absorption of the vitamin.