Occurrence of prostaglandin E3 in human urine as a result of marine oil ingestion: gas chromatographic-mass spectrometric evidence

Maternal fish consumption, mercury levels, and risk of preterm delivery

BACKGROUND

Pregnant women receive mixed messages about fish consumption in pregnancy because unsaturated fatty acids and protein in fish are thought to be beneficial, but contaminants such as methylmercury may pose a hazard.

METHODS

In the Pregnancy Outcomes and Community Health (POUCH) study, women were enrolled in the 15th to 27th week of pregnancy from 52 prenatal clinics in five Michigan communities. At enrollment, information was gathered on amount and category of fish consumed during the current pregnancy, and a hair sample was obtained. A segment of hair closest to the scalp, approximating exposure during pregnancy, was assessed for total mercury levels (70-90% methylmercury) in 1,024 POUCH cohort women.

RESULTS

Mercury levels ranged from 0.01 to 2.50 pg/g (mean = 0.29 microg/g; median = 0.23 microg/g). Total fish consumption and consumption of canned fish, bought fish, and sport-caught fish were positively associated with mercury levels in hair. The greatest fish source for mercury exposure appeared to be canned fish. Compared with women delivering at term, women who delivered before 35 weeks' gestation were more likely to have hair mercury levels at or above the 90th percentile (> or = 0.55 microg/g), even after adjusting for maternal characteristics and fish consumption (adjusted odds ratio = 3.0; 95% confidence interval, 1.3-6.7).

CONCLUSION

This is the first large, community-based study to examine risk of very preterm birth in relation to mercury levels among women with low to moderate exposure. Additional studies are needed to see whether these findings will be replicated in other settings.

Eicosanoids derived from arachidonic and eicosapentaenoic acids inhibit T cell proliferative response

Eicosanoids derived from arachidonic acid (PGE2 and LTB4) have been shown to be involved in the control of mitogen-induced proliferation of lymphocytes but the effects of (n-3) polyunsaturated fatty acids (PUFA)-derived eicosanoids (PGE3 and LTB5) on mitogenic response have not been well described. Supplementation with (n-3) PUFA decreases lymphocyte proliferation in human and animal models. The present study was designed to compare the effect of (n-3)- and (n-6)-derived eicosanoids on mitogenic response. Mouse splenocytes and human peripheral blood mononuclear cells (PBMC) were cultured in the presence or absence of the T cell mitogen Concanavalin A (CON A) with and without the addition of PGE2, LTB4, PGE3 and LTB5 at several concentrations. Lymphocyte proliferation was determined by measuring incorporation of [3H]thymidine into newly synthesized DNA. Both (n-3) and (n-6)-derived eicosanoids inhibited T cell mitogen-induced lymphocyte proliferation in human PBMC and murine splenocytes. The addition of PGE3 and LTB5 decreased Con A-induced mitogenic response in human PBMC more than the same concentration of PGE2 and LTB4 (e.g. -28.7 +/- 4.2% with 10(-9) M PGE3 vs -9.4 +/- 6.3% with 10(-9) M PGE2, P = 0.05 and -95.5 +/- 1.6% with 10(-11) M LTB5 vs -49.2 +/- 3.8% with 10(-11) M LTB4, p < 0.001). A similar trend was observed in murine splenocytes. It is concluded that PGE3 and LTB5 are as potent and at some doses more potent than PGE2 and LTB4 in inhibiting lymphocyte proliferation when added in vitro. These data suggest that eicosanoids derived from (n-3) PUFA may contribute to the (n-3) PUFA-induced suppression of lymphocyte proliferation.

Analysis of the eicosapentaenoic acid (EPA) metabolite delta 17-6-keto-PGF1 alpha in human plasma by GC/SIM using [18O] delta 17-6-keto-PGF1 alpha

A method of the microdetermination of delta 17-6-keto-PGF1 alpha, a hydrolyzed metabolite of PGI3, is described. An authentic delta 17-6-keto-PGF1 alpha (120 mg) was prepared from eicosapentaenoic acid (EPA) incubated with homogenate of bovine aortic intima. [18O]delta 17-6-Keto-PGF1 alpha was synthesized by repeating base-catalyzed hydrolysis of methyl ester derivatives in [18O]water, to obtain an internal standard in gas chromatography/selected ion monitoring (GC/SIM) of delta 17-6-keto-PGF1 alpha. Good linear response over the range of 10 pg-10ng was demonstrated. Chromatographic conditions using a MP-65HT column presented nearly baseline separation of delta 17-6-keto-PGF1 alpha and 6-keto-PGF1 alpha. We were able to detect delta 17-6-keto-PGF1 alpha in the range from 6 to 26 pg/ml of the human plasma. The present method can be applied to the determination of delta 17-6-keto-PGF1 alpha in the human urine and plasma.

Biological activity of prostaglandin E3 with regard to oedema formation in mice

The biological activity of PGE3 with regard to oedema formation in mice was examined. Paw swelling was measured 30 minutes after injection of 10 microliters PGE2 or PGE3 into the plantar region of the hind paw. Doses investigated ranged from 1 ng-10 micrograms. Both PGE2 and PGE3 had substantial oedemogenic activity in this system.

Separation and quantification of PGE3 following derivatization with panacyl bromide by high pressure liquid chromatography with fluorometric detection

Separation of prostaglandin E3 (PGE3) from prostaglandin E2 (PGE2) and prostaglandin E1 (PGE1) was achieved following derivatization with p-(9-anthroyloxy)phenacyl bromide (panacyl bromide). The eicosanoid esters were analysed by reverse phase high pressure liquid chromatography with fluorometric detection (excitation 360nm and emission 470nm). Human, rat and mouse adherent cells were incubated overnight and the culture medium extracted, derivatized and analysed for PG production. PGE2 was detected from biological samples of each species tested. PGE2 synthesis was reduced when cells were incubated overnight with 5 microM eicosapentaenoic acid. PGE3 was not detectable under these experimental conditions. Studies were also undertaken using adherent cells from mice, rats and human subjects given dietary fish oil supplements rich in EPA. PGE3 production by these cells was not detected although the dietary regimens yielded substantial incorporation of EPA into cell membranes and leukocyte LTB5 production was demonstrable.

PGE1 compared to PGE2/PGF2 alpha ratio as a marker for seminal fluid contamination of urine in studies of renal prostaglandin biosynthesis

Occasional and unpredictable seminal plasma leakage (SPL) into the urinary system severely limits the usefulness of primary prostaglandin (PG) excretion rates as markers of renal synthesis in male subjects. Although reports to this effect appeared first some 10 years ago, no specific study has been done to define the magnitude of the problem, while several investigators persisted in the use of primary PG excretion rates, disregarding SPL as a confounding factor. We conducted a systematic study with a group of 5 healthy adult subjects who collected 24-h urine with an average frequency of one collection every other week for a total of 20 weeks. 35% of the urine collected contained seminal plasma. It is imperative to be able to disqualify compromised urine specimens in biological studies. With this objective in mind, we developed a method to identify contaminated samples based on the presence of PGE1. This is a major prostanoid in seminal plasma but is normally absent in 'clear' urine.

Effect of fish oil supplementation on the excretion of the major metabolite of prostaglandin E in healthy male subjects

We investigated the effect of fish oil supplementation on the synthesis of prostaglandin E (PGE) in vivo by measuring the excretion of its catabolite, PGE-M, in 24-hr urine by gas chromatography/mass spectrometry. Forty healthy male volunteers (24-57 years of age) consumed a controlled basal diet providing 40% of energy from fat (P/S ratio about 0.8:1), 130 mg/1000 kcal cholesterol, and a minimum of 22 mg/day of alpha-tocopherol (alpha-T), for three experimental periods lasting a total of 28 weeks. During period 1 (10 weeks) the diet was supplemented with placebo (PO) capsules (15 X 1 g/day) consisting of a blend of fats approaching the fatty acid profile of the basal diet. This was followed by a second 10-week period during which the subjects received 15 X 1 g/day capsules of fish oil concentrate (FOC). During period 3 (8 weeks) they continued the 15 g/day intake of FOC but received an additional 200 mg/day of alpha-T. PO and FOC capsules contained 1 mg alpha-T/g fat as antioxidant. A 14% reduction of PGE-M excretion was observed after 10 weeks of FOC supplementation (period 2), compared to an identical period of placebo supplementation (period 1), P = 0.009. PGE-M excretion during the last week of period 3 was not significantly different from that at the end of period 2. The reduction in PGE synthesis in response to the relatively high marine oil supplementation was large in many subjects participating in this study.

Modification of prostaglandin metabolism in vivo by long-chain omega-3 polyunsaturates

In a pilot study conducted with a healthy male volunteer we determined that short-term dietary supplementation with fish oil markedly suppresses the systemic production of prostaglandin E (P = 0.04). This biochemical effect is observable after an incubation period of several days. The potential consequences of a reduced PGE synthetic rate on renal function, immune system and vascular dynamics, must be considered in the overall evaluation of the safety of fish oil supplements.

Fish oil versus arachis oil food supplementation in relation to pregnancy duration in rats

Throughout pregnancy, Lewis rats were fed standard rat chow supplemented with 15% (w/w) of either MaxEPA fish oil (FO) or arachis oil (AO); a third group was fed standard rat chow only (St) (n = 15, 15, and 16 rats, respectively). Compared to AO-rats, FO-rats had substantially higher levels of n-3 fatty acids and lower levels of n-6 fatty acids in maternal and fetal tissues at delivery. FO-rats had a longer average gestational age than AO-rats (p less than 0.01), primarily due to a high proportion of AO-rats with short gestations. Birthweights of FO-rats were lower than those of AO-rats (p less than 0.05), which may be related to the lower maternal weight gain during pregnancy and the lower food consumption observed in FO-rats (p less than 0.01). Litter size and occurrence of stillborn pups were not significantly different in the groups (p greater than 0.1). The findings are compatible with the hypothesis that gestational age is positively related to a high dietary intake of n-3 fatty acids.

How should we measure n-3 polyunsaturated fatty acids and their metabolites in humans?

Growing interest in nutritional intervention with n-3 polyunsaturated fatty acids demands reliable analyses of these fatty acids and their corresponding eicosanoids in vivo or ex vivo. n-3 polyunsaturated fatty acids are preferably assayed by capillary gas-liquid chromatography after extraction of the lipid classes, their separation by chromatographic methods and conversion of the fatty acids to methylesters. n-3 eicosanoids have to be separated from their arachidonic acid analogues by HPLC or by gas-liquid chromatography and are then quantified by UV-spectroscopy or mass-spectrometry. Structure elucidation has to be performed by chemical reactions and by mass spectrometry. Antibodies for radioimmunoassays against n-3 eicosanoids are not yet available.