Identification of genes mediating branched chain fatty acid elongation

Quantifying acyl-chain diversity in isobaric compound lipids containing monomethyl branched-chain fatty acids

Compound lipids comprise a diverse group of metabolites present in living systems, and metabolic- and environmentally-driven structural distinctions across this family is increasingly linked to biological function. However, methods for deconvoluting these often isobaric lipid species are lacking or require specialized instrumentation. Notably, acyl-chain diversity within cells may be influenced by nutritional states, metabolic dysregulation, or genetic alterations. Therefore, a reliable, validated method of quantifying structurally similar even-, odd-, and branched-chain acyl groups within intact compound lipids will be invaluable for gaining molecular insights into their biological functions. Here we demonstrate the chromatographic resolution of isobaric lipids containing distinct combinations of straight-chain and branched-chain acyl groups via ultra-high-pressure liquid chromatography (UHPLC)-mass spectrometry (MS) using a C30 liquid chromatography column. Using metabolically-engineered adipocytes lacking branched-keto acid dehydrogenase A (Bckdha), we validate this approach through a combination of fatty acid supplementation and metabolic tracing using monomethyl branched-chain fatty acids and valine. We observe resolution of numerous isobaric triacylglycerols and other compound lipids, demonstrating the resolving utility of this method. This approach strengthens our ability to quantify and characterize the inherent diversity of acyl chains across the lipidome.

Dietary sources of branched-chain fatty acids and their biosynthesis, distribution, and nutritional properties

Branched-chain fatty acids (BCFAs) consist of a wide variety of fatty acids with alkyl branching of methyl group. The most common BCFAs are the types with one methyl group (mmBCFA) on the penultimate carbon (iBCFA) or the antepenultimate carbon (aiBCFA). Long-chain mmBCFAs are widely existing in animal fats, milks and are mostly derived from bacteria in the diet or animal digestive system. Recent studies show that BCFAs benefit human intestinal health and immune homeostasis, but the connection between their content, distribution in the human and their nutritional functions are not well established. In this paper, we reviewed BCFAs from various dietary sources focused on their molecular species. The BCFAs biosynthesis in bacteria, Caenorhabditis elegans, mammals and their distribution in human tissues are summarized. This paper also discusses the nutritional properties of BCFAs including influences on intestinal health, immunoregulatory effects, anti-carcinoma, and anti-obesity activities, by highlighting the most recent research progress.

Branched-Long-Chain Monomethyl Fatty Acids: Are They Hidden Gems?

Branched-long-chain monomethyl fatty acids (BLCFA) are consumed daily in significant amounts by humans in all stages of life. BLCFA are absorbed and metabolized in human intestinal epithelial cells and are not only oxidized for energy. Thus far, BLCFA have been revealed to possess versatile beneficial bioactivities, including cytotoxicity to cancer cells, anti-inflammation, lipid-lowering, reducing the risk of metabolic disorders, maintaining normal β cell function and insulin sensitivity, regulation of development, and mitigating cerebral ischemia/reperfusion injury. However, compared to other well-studied dietary fatty acids like eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), BLCFA has received disproportionate attention despite their potential importance. Here we outlined the major food sources, estimated intake, absorption, and metabolism in human cells, and bioactive properties of BLCFA with a focus on the bioactive mechanisms to advocate for an increased commitment to BLCFA investigations. Humans were estimated to absorb 6-5000 mg of dietary BLCFA daily from fetus to adult. Notably, iso-15:0 inhibited the growth of prostate cancer, liver cancer and T-cell non-Hodgkin lymphomas in rodent models at the effective doses of 35-105 mg/kg/day, 70 mg/kg/day, and 70 mg/kg/day, respectively. Feeding formula prepared with 20% w/w BLCFA mixture to neonatal rats with enterocolitis mitigated the intestine inflammation. Iso-15:0 at doses of 10, 40, and 80 mg/kg relieved brain ischemia/reperfusion injury in rats. In the future, it is crucial to conduct research to establish the epidemiology of BLCFA intake and their impacts on health outcomes in humans as well as to fully uncover the underlying mechanisms for their bioactivities.

Monomethyl branched-chain fatty acids: Health effects and biological mechanisms

Branched-chain fatty acids (BCFA) are a group of lipids that are widely present in various organisms; they take part in numerous biochemical processes and affect multiple signaling pathways. However, BCFA are not well explored in terms of their effects on human health. Recently, they have been gaining interest, especially in relation to various human diseases. This review describes the occurrence of BCFA, their dietary sources, their potential health effects, and the current state of knowledge concerning their mechanism(s) of action. Many studies have been conducted so far in cellular and animal models, which reveal potent anti-cancer, lipid lowering, anti-inflammatory and neuroprotective actions. Research in humans is scarce. Therefore, further studies on animals and humans should be performed to confirm and expand these findings, and improve our understanding of the potential relevance of BCFA to human health and disease.

Downregulation of Elovl5 promotes breast cancer metastasis through a lipid-droplet accumulation-mediated induction of TGF-β receptors

Metastatic breast cancer cannot be cured, and alteration of fatty acid metabolism contributes to tumor progression and metastasis. Here, we were interested in the elongation of very long-chain fatty acids protein 5 (Elovl5) in breast cancer. We observed that breast cancer tumors had a lower expression of Elovl5 than normal breast tissues. Furthermore, low expression of Elovl5 is associated with a worse prognosis in ER⁺ breast cancer patients. In accordance with this finding, decrease of Elovl5 expression was more pronounced in ER⁺ breast tumors from patients with metastases in lymph nodes. Although downregulation of Elovl5 expression limited breast cancer cell proliferation and cancer progression, suppression of Elovl5 promoted EMT, cell invasion and lung metastases in murine breast cancer models. The loss of Elovl5 expression induced upregulation of TGF-β receptors mediated by a lipid-droplet accumulation-dependent Smad2 acetylation. As expected, inhibition of TGF-β receptors restored proliferation and dampened invasion in low Elovl5 expressing cancer cells. Interestingly, the abolition of lipid-droplet formation by inhibition of diacylglycerol acyltransferase activity reversed induction of TGF-β receptors, cell invasion, and lung metastasis triggered by Elovl5 knockdown. Altogether, we showed that Elovl5 is involved in metastasis through lipid droplets-regulated TGF-β receptor expression and is a predictive biomarker of metastatic ER⁺ breast cancer.

Identification of High and Low Branched-Chain Fatty Acid-Producing Phenotypes in Holstein Cows following High-Forage and Low-Forage Diets in a Crossover Designed Trial

BACKGROUND

Branched-chain fatty acids (BCFAs) are rumen-derived fatty acids comprising ∼2% of bovine-milk fatty acids. BCFAs possess anti-inflammatory properties and enriching the BCFA content of bovine milk may provide human health benefits.

OBJECTIVE

We determined whether forage content impacts the BCFA content of milk from Holstein cows and identified fatty acid phenotypes in high vs. low BCFA-containing milks.

METHODS

Holstein cows (n = 62), fed for 67 d in a crossover design, consumed a diet with high forage and low concentrate (HF:C) and a diet with low forage and high concentrate (LF:C). Milk samples were collected at the end of each treatment period and fatty acid content determined. Paired t-tests, 1-factor ANOVA, sparse partial least-squares discriminant analysis (sPLSDA), and Pearson's correlation analysis were used to analyze the data.

RESULTS

The total milk fatty acid concentration for cows fed the HF:C diet was greater than that of cows fed the LF:C diet (4.2 ± 0.7 g/100 mL vs. 3.9 ± 0.9 g/100 mL). sPLSDA demonstrated separation of the dietary treatments, with BCFAs and odd-chain fatty acids as primary determinants. Total BCFA content in milk fat was elevated by HF:C intake compared with LF:C intake (1.80 vs. 1.68%). Quintile separation of high vs. low BCFA milks resulted in 4 groups: HF:C /low BCFAs, HF:C /high BCFAs; LF:C /low BCFAs, and LF:C /high BCFAs. Milks from the high BCFA quintiles had lower palmitic acid content (29.6% vs. 34.4%) but higher oleic acid content than milks from the low BCFA quintiles (19.7% vs. 17.0%). Some cows were identified as high BCFA producers or low BCFA producers regardless of diet.

CONCLUSIONS

BCFA content of milk is diet-sensitive but variation in responses exists. The potential to produce milk with high BCFA content and lower SFA content needs further study.

Newborn infant skin gene expression: Remarkable differences versus adults

At birth, human infants are poised to survive in harsh, hostile conditions. An understanding of the state of newborn skin development and maturation is key to the maintenance of health, optimum response to injury, healing and disease. The observational study collected full-thickness newborn skin samples from 27 infants at surgery and compared them to skin samples from 43 adult sites protected from ultraviolet radiation exposure, as the standard for stable, mature skin. Transcriptomics profiling and gene set enrichment analysis were performed. Statistical analysis established over 25,000 differentially regulated probe sets, representing 10,647 distinct genes, in infant skin compared to adult skin. Gene set enrichment analysis showed a significant increase in 143 biological processes (adjusted p < 0.01) in infant skin, versus adult skin samples, including extracellular matrix (ECM) organization, cell adhesion, collagen fibril organization and fatty acid metabolic process. ECM organization and ECM structure organization were the biological processes in infant skin with the lowest adjusted P-value. Genes involving epidermal development, immune function, cell differentiation, and hair cycle were overexpressed in adults, representing 101 significantly enriched biological processes (adjusted p < 0.01). The processes with the highest significant difference were skin and epidermal development, e.g., keratinocyte differentiation, keratinization and cornification intermediate filament cytoskeleton organization and hair cycle. Enriched Gene Ontology (GO) biological processes also involved immune function, including antigen processing and presentation. When compared to ultraviolet radiation-protected adult skin, our results provide essential insight into infant skin and its ability to support the newborn's preparedness to survive and flourish, despite the infant's new environment laden with microbes, high oxygen tension and potential irritants. This fundamental knowledge is expected to guide strategies to protect and preserve the features of unperturbed, young skin.

Very Long-Chain Branched-Chain Fatty Acids in Chia Seeds: Implications for Human Use

Dairy and fermented foods are common sources of dietary branched-chain fatty acids (BCFA) of chain lengths C13-C18 serving a putative prebiotic role and a component of human integument. Few studies have reported on nonfermented plant-derived BCFA in human diets or cosmetics. A three-ion monitoring method was adapted to confirm branch position of ultratrace (<0.01%, w/w) BCFA. We identified chia as a new source of BCFA with C15-C35 chain lengths. Surprisingly, even-numbered very long-chain BCFA (VLC BCFA), anteiso-22:0, anteiso-24:0, and anteiso-26:0 were unequivocally identified in natural products for the first time. Plant-derived BCFA are predominantly anteiso, in contrast with similar iso and anteiso levels in ruminant and fermented foods. Chia seeds contain 0.4% BCFA, w/w of total fatty acids, or 32 mg BCFA in a food serving, surpassing other plant oils. Topical administration of chia seed oil containing VLC BCFA may have a role in skin and hair functionality.

Production of branched-chain very-long-chain fatty acids by fatty acid elongases and their tissue distribution in mammals

Although most mammalian fatty acids (FAs) are straight-chain, there also exist branched-chain FAs such as iso- and anteiso-FAs, especially in the meibomian glands. Meibum lipids, which are secreted from the meibomian glands and are important for dry eye prevention, contain abundant branched-chain lipids, such as cholesteryl esters and wax esters with chain-lengths of ≥C21 (very-long-chain; VLC). However, the exact tissue distribution of branched-chain lipids or the enzymes involved in the production of branched-chain VLCFAs has remained poorly understood. Here, we revealed that FA elongases ELOVL1, ELOVL3, and ELOVL7, of the seven mammalian ELOVL isozymes, elongated saturated branched-chain acyl-CoAs. ELOVL3 was highly active toward iso-C17:0 and anteiso-C17:0 acyl-CoAs and elongated them up to iso-C23:0 and anteiso-C25:0 acyl-CoAs, respectively. ELOVL1 elongated both iso- and anteiso-C23:0 acyl-CoAs to C25:0 acyl-CoAs. By establishing a liquid chromatography-tandem mass spectrometry method capable of separating branched- and straight-chain lipids, we showed that essentially all of the cholesteryl esters and 88% of the wax esters in the mouse meibomian glands are branched. In Elovl1 mutant mice, the levels of ≥C24:0 branched-chain cholesteryl esters and ≥C25:0 branched-chain wax esters were decreased, indicating that ELOVL1 indeed elongates branched-chain VLC acyl-CoAs in vivo. In addition, substantial amounts of ceramides containing branched-chain FAs were present in the skin, meibomian glands, and liver. Our findings provide new insights into the molecular mechanisms that create FA and lipid diversity.

Gas Chromatography Chemical Ionization Mass Spectrometry and Tandem Mass Spectrometry for Identification and Straightforward Quantification of Branched Chain Fatty Acids in Foods

Fatty acid analysis of food lipids containing branched chain fatty acids (BCFAs) are complex because of unavoidable gas chromatography (GC) co-elution. We demonstrate a method for convenient quantitative GC coupled to novel solvent-mediated chemical ionization (CI) mass spectrometry (MS) that enables resolution of co-eluting peaks by mass. The relevant masses yield uniform responses for C_14-20 normal fatty acids and BCFAs, eliminating the need for rare purified BCFA standards essential for unpredictable responses, as for electron ionization (EI). CI-tandem mass spectrometry analysis of MH⁺ yields fragments characteristic of the branch position. Application of the measurement to BCFAs in salami samples demonstrates consistent results for the novel method and EI-MS. A higher proportion of C_17-18 BCFAs was found in beef compared to milkfat, possibly indicative of fatty acid elongation, endogenous in the beef animal. This method enables straightforward structure elucidation and quantification of food BCFAs and similar chain length normal fatty acids without purified standards.

Fatty acid desaturase 2 (FADS2) but not FADS1 desaturates branched chain and odd chain saturated fatty acids

Branched chain fatty acids (BCFA) and linear chain/normal odd chain fatty acids (n-OCFA) are major fatty acids in human skin lipids, especially sebaceous gland (SG) wax esters. Skin lipids contain variable amounts of monounsaturated BCFA and n-OCFA, in some reports exceeding over 20% of total fatty acids. Fatty acid desaturase 2 (FADS2) codes for a multifunctional enzyme that catalyzes Δ4-, Δ6- and Δ8-desaturation towards ten unsaturated fatty acids but only one saturate, palmitic acid, converting it to 16:1n-10; FADS2 is not active towards 14:0 or 18:0. Here we test the hypothesis that FADS2 also operates on BCFA and n-OCFA. MCF-7 cancer cells stably expressing FADS1 or FADS2 along with empty vector control cells were incubated with anteiso-15:0, iso-16:0, iso-17:0, anteiso-17:0, iso-18:0, or n-17:0. BCFA were Δ6-desaturated by FADS2 as follows: iso-16:0 → iso-6Z-16:1, iso-17:0 → iso-6Z-17:1, anteiso-17:0 → anteiso-6Z-17:1 and iso-18:0 → iso-6Z-18:1. anteiso-15:0 was not desaturated in either FADS1 or FADS2 cells. n-17:0 was converted to both n-6Z-17:1 by FADS2 Δ6-desaturation and n-9Z-17:1 by SCD Δ9-desaturation. We thus establish novel FADS2-coded enzymatic activity towards BCFA and n-OCFA, expanding the number of known FADS2 saturated fatty acid substrates from one to six. Because of the importance of FADS2 in human skin, our results imply that dysfunction in activity of sebaceous FADS2 may play a role in skin abnormalities associated with skin lipids.

Iso- but Not Anteiso-Branched Chain Fatty Acids Exert Growth-Inhibiting and Apoptosis-Inducing Effects in MCF-7 Cells

The present study compared the growth-inhibitory effects of four common branched chain fatty acids (BCFAs) found in beef and dairy fats including iso 15:0, anteiso 15:0, iso 17:0, and anteiso 17:0. MCF-7 human breast cancer cells were exposed for 72 h to media containing increasing doses (50 to -400 μM) of the four BCFA. Cell viability was not affected by any of the BCFA treatments at doses less than 200 μM. Culturing cells with 200 μM of iso-15:0 or iso-17:0 reduced cell viability by 27 ± 2.8 and 43 ± 8.3% at 24 h, 35 ± 4.6 and 49 ± 9.1% at 48 h, and 44 ± 6.8 and 57 ± 8.8% at 72 h posttreatment. In contrast, culturing cells with 200 μM of anteiso-15:0 or anteiso-17:0 did not affect cell viability for any durations tested. The incorporation of iso 15:0 and iso 17:0 into cells (19.1 ± 1.3 and 21.2 ± 1.4 μmol/mg protein, respectively) was greater (P < 0.01) than that of anteiso 15:0 and anteiso 17:0 (11.8 ± 0.7 and 13.8 ± 0.8 μmol/mg protein, respectively). Iso-15:0 and iso-17:0 downregulated (P < 0.01) the expression of antiapoptotic Bcl-2 (0.71 ± 0.6-fold and 0.64 ± 0.09-fold, respectively) and upregulated (P < 0.01) the expression of proapoptotic Bax (1.72 ± 0.14-fold and 2.15 ± 0.24-fold, respectively) compared to the control, whereas their corresponding anteiso isomers did not affect the expression of any apoptosis-related genes. Our findings suggest that the branching structure influences anticarcinogenic effects of BCFAs, with iso being more potent than anteiso.