Comparative effects of dietary fatty acids and triglycerides on lymph lipids in the rat

Drug delivery to the intestinal lymph by oral formulations

Oral drug delivery systems (DDS) targeting lymphocytes in intestinal lymphatic vessels, ducts, and nodes are useful for treating diverse diseases. The intestinal lymph harbors numerous lymphocyte subsets, and DDS containing lipids such as triglycerides and fatty acids can deliver drugs to the lymph through the chylomicron pathway. DDS are efficient, thus allowing the administration of reduced drug doses, which mitigate systemic adverse effects. Here we review orally administered lipid formulations comprising oil solutions, suspensions, micro/nanoemulsions, self-micro/nano emulsifying DDS, liposomes, micelles, solid lipid nanoparticles, and nanostructured lipid carriers for targeting drugs to the lymph. We first describe the structures of lymphatic vessels and lymph nodes and the oral absorption of lipids and drugs into the intestinal lymph. We next summarize the effects of the properties and amounts of lipids and drugs delivered into the lymph and lymphocytes, as well as their effects on drug delivery ratios of lymph to blood. Finally, we describe lymphatic DDS containing saquinavir, tacrolimus, and methotrexate, and their potency that reduce drug concentrations in blood, which are associated with systemic adverse effects.

Lipid Drug Carriers for Cancer Therapeutics: An Insight into Lymphatic Targeting, P-gp, CYP3A4 Modulation and Bioavailability Enhancement

In the treatment of cancer, chemotherapy plays an important role though the efficacy of anti-cancer drug administered orally is limited, due to their poor solubility in physiological medium, inability to cross biological membrane, high Para-glycoprotein (P-gp) mediated drug efflux, and pre-systemic metabolism. These all factors cumulatively reduce drug exposure at the target site leading to multidrug resistance (MDR). Lipid based carriers systems has been explored to overcome solubility and permeability related issues of anti-cancer drugs. The lipid based formulations have also been reported to circumvent the effect of P-gp and CYP3A4. Further long chain triglycerides (LCT) has shown their ability to access Lymphatic route over Medium Chain Triglycerides, as the former has been extensively used for targeting anti-cancer drugs at proliferating cells through lymphatic route. Therefore this review tries to reflect the usefulness of lipid based drug carriers systems (viz. liposome, solid lipid nanoparticle, nano-lipid carriers, self-emulsifying, lipidic pro-drugs) in targeting lymphatic system and overcoming issues related to solubility and permeability of anti-cancer drugs. Moreover, we have also tried to reflect how critically lipid based carriers are important in maximizing therapeutic safety and efficacy of anti-cancer drugs.

Dietary linoleic, alpha-linolenic and oleic acids are oxidized at similar rates in rats fed a diet containing these acids in equal proportions

The objective of this study was to examine whether whole body oxidation rates of dietary linoleic, alpha-linolenic and oleic acids differ when the acids are provided in identical quantities. Male rats were fed for 10 wk a 15% fat (w/w) diet containing equal amounts of linoleic, alpha-linolenic and oleic acids (22.7, 23.0 and 23.2% of total fatty acids, respectively). At week 10, after overnight fasting, rats were intragastrically administered 20 microCi of either [1-14C]-labelled linoleic, alpha-linolenic or oleic acid in a 200-microL bolus of oil containing equal quantities of each fatty acid. The appearance of 14CO2 in expired air was then monitored hourly for 12 h for each animal. A preliminary study had shown that growth and food consumption patterns in animals consuming the oil containing equal quantities of each of the fatty acids paralleled the patterns of animals that were self-selecting among separate diets, each of which contained one of the component oils. The appearance of 14C, expressed as percent dose administered, peaked at 2-3 h post-dose for 14C-labelled linoleic (5.28 +/- 0.37%/h), alpha-linolenic (6.92 +/- 0.51%/h) and oleic (5.98 +/- 0.44%/h) acids. Statistically these values were not significantly different. Cumulative 14CO2 excretion rates over 12 h were also similar for linoleic (27.2 +/- 0.9%), alpha-linolenic (26.8 +/- 1.2%) and oleic (25.9 +/- 1.2%) acids. The results suggest that the rat's capacity to oxidize 18-carbon unsaturated fatty acids is not affected by fatty acid unsaturation when these fatty acids are provided at equal dietary levels.

Absorption, transport and metabolism of vitamin E

Vitamin E includes eight naturally occurring fat-soluble nutrients called tocopherols and dietary intake of vitamin E activity is essential in many species. alpha-Tocopherol has the highest biological activity and the highest molar concentration of lipid soluble antioxidant in man. Deficiency of vitamin E may cause neurological dysfunction, myopathies and diminished erythrocyte life span. alpha-Tocopherol is absorbed via the lymphatic pathway and transported in association with chylomicrons. In plasma alpha-tocopherol is found in all lipoprotein fractions, but mostly associated with apo B-containing lipoproteins in man. In rats approximately 50% of alpha-tocopherol is bound to high density lipoproteins (HDL). After intestinal absorption and transport with chylomicrons alpha-tocopherol is mostly transferred to parenchymal cells of the liver were most of the fat-soluble vitamin is stored. Little vitamin E is stored in the non-parenchymal cells (endothelial, stellate and Kupffer cells). alpha-Tocopherol is secreted in association with very low density lipoprotein (VLDL) from the liver. In the rat about 90% of total body mass of alpha-tocopherol is recovered in the liver, skeletal muscle and adipose tissue. Most alpha-tocopherol is located in the mitochondrial fractions and in the endoplasmic reticulum, whereas little is found in cytosol and peroxisomes. Clinical evidence from heavy drinkers and from experimental work in rats suggests that alcohol may increase oxidation of alpha-tocopherol, causing reduced tissue concentrations of alpha-tocopherol. Increased demand for vitamin E has also been observed in premature babies and patients with malabsorption, but there is little evidence that the well balanced diet of the healthy population would be improved by supplementation with vitamin E.

Transport and distribution of alpha-tocopherol in lymph, serum and liver cells in rats

Rats were cannulated in the major mesenteric lymph duct and given an intraduodenal bolus of unlabeled and alpha-[3H]tocopherol, and [14C]oleic acid in soybean oil. The appearance of alpha-tocopherol in lymph was negligible during the first 2 h and peaked 4-15 h after feeding, whereas no detectable amount was recovered in the portal vein. Intestinal absorption via the lymphatic pathway was 15.4 +/- 8.9% (n = 10) and 45.9 +/- 10.8% (n = 4) for alpha-tocopherol and [14C]oleic acid, respectively. About 99% of alpha-tocopherol in lymph was associated with the chylomicron fraction (d less than 1.006 g/ml). In non-fasting rats, 51% of serum alpha-tocopherol was associated with chylomicrons/VLDL (very-low-density lipoprotein, d less than 1.006 g/ml) and 47% with HDL (high-density lipoprotein, 1.05 less than d less than 1.21 g/ml). Our study revealed that the liver, skeletal muscle and adipose tissue contain approx. 92% of the total mass of alpha-tocopherol measured in ten different organs. Parenchymal and nonparenchymal liver cells contributed to 75% and 25% of the total mass of alpha-tocopherol in the liver, respectively.

The effect of shellfish in the diet upon the plasma lipid levels in humans

In order to document any hypercholesterolemic effects from the ingestion of shellfish, 6 normal men were given two diets containing different shellfish, each preceded by a low cholesterol baseline diet. Diet I contained 449 mg cholesterol per day from lobster, crab, and shrimp. Diet II contained clam, oyster, and scallop and provided 447 mg of sterols of which cholesterol constituted only 40 percent. The other sterols are uniquely characteristic of these shellfish (i.e. brassicasterol, 24-methylene cholesterol, etc.). In a second study, 2 normal men and 1 type II hypercholesterolemic woman were fed the baseline diet and shellfish diet II to provide 623 mg of sterols per day. The plasma cholesterol of the 6 subjects averaged 184 +/- 35 mg/dl during baseline, 192 +/- 35 mg/dl in shellfish diet I (p less than 0.05) and 182 +/- 24 mg/dl during shellfish diet II. In the second study, the plasma cholesterol of the 2 normal men did not change. The cholesterol of the hypercholesterolemic woman increased from 311 mg/dl (baseline) to 352 during the shellfish diet (p less than 0.05). Plasma triglyceride levels remained unchanged. Our data indicated that large quantities of lobster, crab, and shrimp were only mildly hypercholesterolemic in normals, but less so than other cholesterol-containing foods. Clams, oysters, and scallops were not hypercholesterolemic in normal subjects but were in a hypercholesterolemic patient.

Influence of dietary fat saturation on lipid absorption in the rat

Flux (mumole/h) of triglycerides, phospholipids and cholesterol into the thoracic duct lymph was measured in rats receiving a constant intraduodenal infusion of a cholesterol-free oil rich in either polyunsaturated (P/S = 4.8) or saturated (P/S = 0.2) fatty acids. Rats had ad libitum access to a fat-free semi-synthetic diet throughout the experiment. Oils were infused at a rate equivalent to a 10% (w/w) fat-containing diet for at least 18 h prior to collection of lymph; both oils were compared in each animal. Although absorption of the infused oils approximated 100%, triglyceride flux was significantly lower during infusion of the saturated compared to the polyunsaturated oil. Phospholipid and total cholesterol fluxes were not significantly affected by the type of oil, but the percent of lymph total cholesterol which was esterified was slightly but significantly lower during infusion of the unsaturated oil. Using the molar phospholipid/triglyceride ratio as a index of lymph lipoprotein size, it was found that absorption of the oil rich in polyunsaturated fatty acids resulted in an increase in the mean size of lymph lipoproteins. The potential significance of an influence of dietary fat saturation on lymph lipoprotein size and cholesterol esterification for the ultimate metabolic fate of absorptive lipoprotein constituents is discussed.

Initial cholesterol uptake by everted sacs of rat small intestine: kinetic and thermodynamic aspects

The kinetics of initial cholesterol uptake by everted rat proximal and distal small intestinal sacs were evaluated in vitro. The mucosal incubation solution consisted of 0.05 mM cholesterol solubilized in 4.8 mM sodium taurocholate micellar solution at pH 7.4 Experiments were performed at temperatures from 26 to 38 C. The rate of cholesterol uptake followed a linear relationship when plotted against time indicating an apparent zero-order kinetics mechanism for initial uptake. An Arrhenius plot of the results of uptake versus temperature remained linear over the entire range of temperatures studied. The large free energy of activation (20 kcal/mole) suggests that an energy barrier for cholesterol uptake exists at the enterocyte luminal cell membrane and may be an important limiting step in cholesterol uptake. It is proposed that a transient association between cholesterol and a component of the enterocyte luminal cell membrane is formed during initial uptake of cholesterol. The transient association may be an activated complex formed with proteins present at or within the luminal enterocyte cell membrane.

Effect of mixed micellar lipid on the absorption of cholesterol and vitamin D3 into lymph

The absorption of endogenous cholesterol, labeled with tracer doses of cholesterol (14)C or cholesterol-(3)H and of near physiological doses of vitamin D(3)-(3)H was studied in rats with cannulated intestinal lymphatics. The effects of administering mixed micellar solutions of fatty acid, monoglyceride, and bile salt on the absorption of these labeled sterols was determined. It was observed that the specific activity of free cholesterol and the amounts of vitamin D(3) appearing in lymph were significantly increased during the intraduodenal administration of mixed micellar solutions of either linoleic or palmitic acid, in contrast to control rats receiving a micellar solution of taurocholate. These increases were related linearly to the lymph triglyceride level. In addition it was observed that when the linoleic acid solution was administered there was a more marked increase in the ratio of the specific activities of free and esterified cholesterol in lymph than with either the palmitic acid or taurocholate solutions. Additional studies in rats with intact lymphatics showed that the uptake of labeled cholesterol and vitamin D(3) from the intestinal lumen into the wall was similar whether the sterols were administered in taurocholate or in mixed micellar solution. These findings suggest that mixed micellar lipid increased the rate of appearance of labeled free cholesterol and vitamin D(3) in lymph by enhancing their transport out of the intestinal mucosa, rather than by an effect on uptake.

The composition and structure of lymph chylomicrons in dog, rat, and man

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