Changes in the lipid content of rat lymph after the ingestion of [14C] long-chain fatty acids

Plasma levels, tissue distribution, and excretion of radioactivity after single-dose administration of ((3)H)-oleic acid added to D-004, a lipid extract of the fruit of Roystonea regia, in rats

BACKGROUND

D-004, a lipid extract of the fruit of Roystonea regia, contains a mixture of fatty acids-mainly oleic, lauric, palmitic, and myristic acids, with oleic acid being among the most abundant-that has been found to reduce the risk for prostatic hyperplasia (PH) induced with testosterone (T) in rats. The pharmacokinetic profile of D-004 has not been reported.

OBJECTIVE

The objective of this study in rats was to assess plasma levels, tissue distribution, and excretion of total radioactivity (TR) after single-dose administration of oral D-004 radiolabeled with ((3)H)-oleic acid, as a surrogate for the pharmacokinetics of D-004.

METHODS

This experimental study was conducted at the Pharmacology Department, Center of Natural Products, National Center for Scientific Research, Havana, Cuba. Single doses of suspensions of ((3)H)-oleic acid 0.16 μCi/mg mixed with D-004 400 mg/kg (radioactive dose/animal 7.2 μCi) were given orally to male Wistar rats weighing 150 to 200 g assigned to the treated or control group. Three rats were euthanized at each of the following times: 0.25, 0.5, 1, 1.5, 2, 4, 8, 24, 48, 72, 96, and 144 hours after study drug administration. After administration, the rats euthanized at the last experimental time point were housed individually in metabolism cages. Urine and feces samples were collected daily. At each time point, blood samples were drawn and plasma samples were obtained using centrifugation. After euthanization, tissue samples (liver, lungs, spleen, brain, kidneys, adipose tissue, muscle, stomach, small and large intestines, adrenal glands, heart, testes, prostate, and seminal vesicles) were quickly removed, washed, blotted, and homogenized. Plasma (100 μL), tissue aliquots (100 mg), feces (10 mg), and urine (100μL) were dissolved and TR was measured. Samples were assayed in duplicate. Results were expressed in μgEq of radio-labeled oleic acid per milliliter of plasma or urine or gram of tissue or feces. Plasma, tissue, feces, and urine samples of rats that did not receive ((3)H)-oleic acid were used as controls. Excretion was expressed as the percentage of the radioactivity excreted via each route with respect to the total radioactive dose administered to each rat.

RESULTS

A total of 50 rats were included in the experiment (mean age, 4 weeks; mean weight, 310 g). Absorption was rapid; mean Cmax was 195.56 (31.12) μgEq/mL, and mean Tmax was 2 hours. Thereafter, a biphasic decay of TR was found: a rapid first phase (t1/2α, 1.33 hours), followed by a slower second elimination phase (t1/2β, 36.07 hours). Radioactivity was rapidly and broadly distributed throughout the tissues, with more accumulating in the prostate than elsewhere. In the first 8 hours, accumulation of TR was greatest in the prostate, followed by the liver, small intestine, and plasma. Subsequently, TR increased in the small intestine, while it decreased in the liver and plasma. In contrast, over the periods of 24 and 144 hours after administration, TR increased in the adipose tissue, while it decreased in the other tissues and plasma. During those intervals, TR was greatest in the prostate, followed by adipose tissue. Mean peak radioactivity in the prostate (562.41 μgEq/g) was reached at 4 hours and decreased slowly thereafter. The prostate had the highest values of t1/2β and cumulative AUC compared with the other tissues and plasma. Mean (SD) TR was similar in feces (33.48% [4.90%]) and urine (28.96% [5.32%]), with total excretion being 62.40% (5.90%) of the administered dose.

CONCLUSIONS

In this experimental study, after single-dose administration of oral D-004 radiolabeled with ((3)H)-oleic acid in rats, TR was rapidly and widely distributed across the tissues, with the prostate having the highest accumulation of radioactivity. Excretion of TR was limited, with similar amounts being excreted in feces and urine. The broad distribution of radiolabeled oleic acid and/or its metabolites suggests (SD) pharmacokinetic rationale for the effectiveness of D-004 in reducing the risk for PH induced with T in rats.

Metabolism of Dietary Cetoleic Acid (22:1n‐11) in Mink (Mustela vison) and Gray Seals (Halichoerus grypus) Studied Using Radiolabeled Fatty Acids

Cetoleic acid (22:1n-11) is a good indicator of diet in marine predators and has proven to be an important fatty acid (FA) when using adipose tissue FA composition to study diet in marine mammals and seabirds. Feeding studies have shown that 22:1 isomers are predictably underrepresented in adipose tissue relative to diet, implying that metabolism within the predator strongly influences the relationship between the level of these FAs in diet and adipose tissue. Fully understanding such metabolic processes for individual FAs is important for the quantitative estimation of predator diets. We employed a dual-label radioisotope tracer technique to investigate the potential modification of 22:1n-11 and its recovery in the blubber of gray seals (Halichoerus grypus) and in the adipose tissue and liver of mink (Mustela vison), a smaller model carnivore also accustomed to fish-based diets. In both seals and mink, (3)H radioactivity was found in the chain-shortened products of 22:1n-11, with 18:1 being the dominant product. We also found (3)H radioactivity in saturated FAs. The distribution patterns of (3)H radioactivity across the FAs isolated from seal blubber and mink subcutaneous adipose tissue were comparable, indicating that mink are a good model for the investigation of lipid metabolism in marine carnivores.

Demonstration of the Deposition and Modification of Dietary Fatty Acids in Pinniped Blubber Using Radiolabelled Precursors

Radioisotopes are commonly used to study the in vivo metabolism and deposition of dietary fatty acids in adipose tissue. The application of this approach to pinnipeds is problematic because of their large mass and blubber fat content. We have developed a method where labelled lipids can be fed to seals at financially feasible levels, with the radioactivity in individual fatty acids isolated from blubber detected with standard laboratory equipment. A combination of techniques including argentation thin layer chromatography, high performance liquid chromatography with ultraviolet detection, and independent liquid scintillation counting were employed. Juvenile gray seals (Halichoerus grypus) were fed either 0.5 mCi (3)H-labelled triolein (18:1n-9, n=2) or palmitic acid (16:0, n=2). Blubber samples were taken 12 h later, and the radioactivity in individual fatty acids was determined. Radioactivity was detected in only 18:1 from the animals fed (3)H-labelled triolein, indicating direct deposition without modification. Both animals fed (3)H-labelled palmitic acid showed clear peaks of radioactivity in 16:0; however, there was also significant activity (23%-29%) found in the desaturation product 16:1. Our results demonstrate that this method is sufficiently sensitive to track the deposition of labelled dietary lipids as well as modification products of ingested fatty acids and will be important in the application of fatty acid signatures to study predator diets.