Influence of gender on DHA synthesis: the response of rat liver to low dietary α-linolenic acid evidences higher ω3 ∆4-desaturation index in females.

PURPOSE: The conversion rate of α-linolenic acid (ALA) into docosahexaenoic acid (DHA) is determined by dietary and non-dietary factors. Higher capacity of DHA synthesis has been evidenced in females, indicating that sex factors influence the conversion pathway. To evaluate the extent to which sexual dimorphism of DHA synthesis is subordinated to nutritional handling, we measured the ω3 ∆4-desaturation index in male and female rats receiving adequate or inadequate amounts of ALA. The ω3 ∆4-desaturation index was drawn from the DHA to docosapentaenoic acid (ω3DPA) ratio in liver phospholipids. METHODS: Male and female rats born to ω3-deficient dams were fed a supplemented diet supplying low, inadequate, intermediate, or adequate ALA (5, 20, 100, or 300 mg ALA/100 g diet, respectively). Control rats from both gender received the adequate diet from fetal life. RESULTS: Compared with control, low ALA feeding induced the ω3 ∆4-desaturation index to increase by 38 and 70% in the phosphatidylethanolamine fraction of males and females, respectively, and by 67% in phosphatidylcholine in females only. Supplementations with increased doses of ALA progressively smoothed this gender effect. Moreover, the analysis of our data from a previous study shows that ovariectomy decreased, whereas estradiol treatment increased the ω3 index to values comparable with those of diet-matched males and intact females, respectively. CONCLUSION: Females are more prone than males to increase their index of ω3 ∆4-desaturation, especially in response to low supplies in ALA. Estradiol supports the ω3 index, suggesting that this hormone plays a role in the effect of gender on DHA synthesis.

Ovariectomy and 17ß-estradiol alter transcription of lipid metabolism genes and proportions of neo-formed n-3 and n-6 long-chain polyunsaturated fatty acids differently in brain and liver.

Hormonal and nutritional factors regulate the metabolism of long-chain polyunsaturated fatty acids (LC-PUFA). We aimed to determine whether ovarian hormones influence the capacity of rats to synthesize the end-products 22:6n-3 (DHA) and 22:5n-6 (n-6DPA) from their respective dietary precursors (18:3n-3 and 18:2n-6), and can regulate PUFA conversion enzymes gene transcription in brain and/or liver. Females born with a low DHA status were fed from weaning to 8 weeks of age a diet providing both essential precursors, and were concurrently submitted to sham-operated control (SOC) or ovariectomy (OVX) in combination with or without 17ß-estradiol (E2) dosed at 8 or 16 µg/day. Relative to SOC, OVX increased the hepatic Δ9-, Δ6- and Δ5-desaturase transcripts and cognate transcription factors (PPARα, PPARγ, RXRα, RARα), but it did not affect LC-PUFA contents in phospholipids. In comparison with SOC and OVX groups, both E2 doses prevented the increase of transcripts, while paradoxically augmenting DHA and n-6DPA in liver phospholipids. Thus, in the liver of rats undergoing ovariectomy, changes of LC-PUFA synthesizing enzyme transcripts and of LC-PUFA proportions were not correlated. In brain, ovariectomy did not modify the transcripts of lipid metabolism genes, but it decreased DHA (-15%) and n-6DPA (-28%). In comparison with SOC and OVX groups, ovariectomized females treated with E2 preserved their status of both LC-PUFA in brain and had increased transcripts of E2 receptor ß, PPARδ, RARα and LC-PUFA synthesizing enzymes. In conclusion, E2 sustained the transcription of lipid metabolism genes and proportions of neo-formed DHA and n-6DPA differently in brain and liver.

Gender affects liver desaturase expression in a rat model of n-3 fatty acid repletion.

Dietary n-3 polyunsaturated fatty acids (PUFA) are major components of cell membranes and have beneficial effects on human health. Docosahexaenoic acid (DHA; 22:6n-3) is the most biologically important n-3 PUFA and can be synthesized from its dietary essential precursor, alpha-linolenic acid (ALA; 18:3n-3). Gender differences in the efficiency of DHA bioconversion have been reported, but underlying molecular mechanisms are unknown. We compared the capacity for DHA synthesis from ALA and the expression of related enzymes in the liver and cerebral cortex between male and female rats. Wistar rats, born with a low-DHA status, were supplied with a suboptimal amount of ALA from weaning to 8 weeks of age. Fatty acid composition was determined by gas chromatography, the mRNA expression of different genes involved in PUFA metabolism was determined by RT-PCR (low-density array) and the expression of proteins was determined by Western blot analysis. At 8 weeks, DHA content was higher (+20 to +40%) in each phospholipid class of female livers compared to male livers. The "Delta4," Delta5 and Delta6 desaturation indexes were 1.2-3 times higher in females than in males. The mRNA expression of Delta5- and Delta6-desaturase genes was 3.8 and 2.5 times greater, respectively, and the Delta5-desaturase protein was higher in female livers (+50%). No gender difference was observed in the cerebral cortex. We conclude that female rats replete their DHA status more readily than males, probably due to a higher expression of liver desaturases. Our results support the hypothesis on hormonal regulation of PUFA metabolism, which should be taken into account for specific nutritional recommendations.

Differential effects of steroids on the synthesis of polyunsaturated fatty acids by human neuroblastoma cells.

Polyunsaturated fatty acids (PUFA) are crucial for proper functioning of cell membranes, particularly in brain. Biologically important PUFA include docosahexaenoic acid (n-3 series) and arachidonic acid (n-6 series) which can be formed from their respective dietary essential precursors, alpha-linolenic acid (ALA) and linoleic acid (LA). Steroid hormones are thought to modulate PUFA synthesis in humans but whether they regulate PUFA status in brain and/or in neural membranes is unknown. In human neuroblastoma SH-SY5Y cells, we compared the effect of estradiol, testosterone, and progesterone on PUFA synthesis. Cells were incubated with ALA and/or LA 7 microM in combination with estradiol, testosterone, or progesterone at 10 nM without serum. The fatty acid composition was determined by gas chromatography and the mRNA expression of genes involved in PUFA metabolism by real-time RT-PCR. Estradiol affected both the n-3 and the n-6 PUFA conversion, the n-3 PUFA pathway being more sensitive to the estradiol treatment. In ALA-supplemented cells, estradiol increased while testosterone decreased the long-chain n-3 PUFA content (+17% and -15%, respectively) and the mRNA expression of the Delta5-desaturase (+11% and -9%), these two events being strongly correlated. Progesterone did not affect the PUFA composition. The positive effect of estradiol was blocked by the estrogen receptor antagonist ICI-182,780. We conclude that steroids have differential effects on PUFA synthesis and that their mode of action could involve the modulation of the Delta5-desaturase mRNA expression in neuroblastoma cells. These results help our understanding of the regulation of brain PUFA metabolism by steroid hormones.

Estradiol favors the formation of eicosapentaenoic acid (20:5n-3) and n-3 docosapentaenoic acid (22:5n-3) from alpha-linolenic acid (18:3n-3) in SH-SY5Y neuroblastoma cells.

Whether neurosteroids regulate the synthesis of long chain polyunsaturated fatty acids in brain cells is unknown. We examined the influence of 17-beta-estradiol (E2) on the capacity of SH-SY5Y cells supplemented with alpha-linolenic acid (ALA), to produce eicosapentaenoic acid (EPA), docosapentaenoic acid (DPA) and docosahexaenoic acid (DHA). Cells were incubated for 24 or 72 h with ALA added alone or in combination with E2 (ALA + E2). Fatty acids were analyzed by gas chromatography of ethanolamine glycerophospholipids (EtnGpl) and phosphatidylcholine (PtdCho). Incubation for 24 h with ALA alone increased EPA and DPA in EtnGpl, by 330 and 430% compared to controls (P < 0.001) and DHA by only 10% (P < 0.05). Although DHA increased by 30% (P < 0.001) in ALA + E2-treated cells, the difference between the ALA and ALA + E2 treatments were not significant after 24 h (Anova-1, Fisher's test). After 72 h, EPA, DPA and DHA further increased in EtnGpl and PtdCho of cells supplemented with ALA or ALA + E2. Incubation for 72 h with ALA + E2 specifically increased EPA (+34% in EtnGpl, P < 0.001) and DPA (+15%, P < 0.001) compared to ALA alone. Thus, SH-SY5Y cells produced membrane EPA, DPA and DHA from supplemental ALA. The formation of DHA was limited, even in the presence of E2. E2 significantly favored EPA and DPA production in cells grown for 72 h. Enhanced synthesis of ALA-elongation products in neuroblastoma cells treated with E2 supports the hypothesis that neurosteroids could modulate the metabolism of PUFA.