Microbial Metabolite; Human Endogenous Metabolite

Palmitic acid (PA) binds to TLR4 through the adaptor protein MD2, and the TLR4 signal that PA produces causes a strong IL-1β response in addition to stimulating dendritic cell activation and maturation. One TLR4/MD-2 ligand is palmitic acid. TLR4 is the mechanism by which it promotes inflammation[1].

Palmitic acid rapidly decreases mouse locomotor activity in a dose-dependent manner through a mechanism that is dependent on fatty acid chain length rather than TLR4, MyD88, IL-1, IL-6, or TNFα. Mice exposed to palmitic acid exhibit anxiety-like behaviors while their amygdala-based serotonin metabolism is elevated[2].

The INS-1 cells are seeded at 4,000 cells/well onto 96-well plates with 10% BSA and then incubated for 24 or 48 hours with either T0901317 (10 μmol/L), palmitic acid (250 μmol/L), a combination of T0901317 and palmitic acid, or PBS (mock control). Following the treatment incubation, 20 microliters of MTT solution (5 milligrams per milliliter of MTT in PBS, pH 7.4) are added to each well, and the mixture is then incubated for four hours at 37°C. After the supernatants are extracted from the wells, 15 μl of DMSO per well is added to dissolve the crystals. A microplate reader is used to measure the optical density at a wavelength of 490 nm.

C57BL/6J mice
0.3, 3, and 30 μmol/mouse
i.p.

Absorption, Distribution and Excretion
Compared to adult monkeys, added 14C-labeled palmitate was more significantly incorporated into the lipid fraction of muscle fibers in fetal and neonatal monkeys. /Palmitrate/ Compared to the control group, genetically obese rats had more 14C-labeled palmitate incorporated into their adipose tissue. Radioactivity was detected in the heart, liver, lungs, spleen, kidneys, muscles, intestines, adrenal glands, blood, lymph, and adipose, mucosal, and dental tissues after administration of radioactive oleic acid, palmitic acid, or stearic acid. Fatty acids derived from adipose tissue storage are either bound to serum albumin or exist in the blood in free form. For more complete data on the absorption, distribution, and excretion of palmitic acids (7 in total), please visit the HSDB records page.

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Metabolism/Metabolites Palmitic acid is rapidly metabolized, primarily through β-oxidation. Besides oxidative decomposition, palmitic acid undergoes various transformations in the liver and intestinal mucosa, producing stearic acid, oleic acid, palmitoleic acid, and myristic acid. In starved rats, ω-oxidation (preceding β-oxidation) may account for 5% to 10% of hepatic palmitic acid metabolism. After palmitic acid is oxidized or converted into other long-chain fatty acids or phospholipids, its carbon skeleton is stored as esterified cholesterol or returned to the plasma depending on the body's nutritional status. Mechanisms of fatty acid uptake in different tissues include passive diffusion, facilitated diffusion, or a combination of both. Fatty acids absorbed by tissues can be stored as triglycerides (98% of which are stored in adipose tissue) or oxidized for energy through catabolic pathways such as β-oxidation and the tricarboxylic acid cycle. /Fatty Acids/
β-oxidation of fatty acids occurs in most vertebrate tissues (except the brain). This process utilizes an enzyme complex for a series of oxidation and hydration reactions, ultimately leading to the cleavage of the acetic acid group to produce acetyl-CoA (CoA). Complete catabolic metabolism of oleic acid requires additional isomerization reactions. Other oxidation pathways exist in the liver (ω-oxidation) and brain (α-oxidation). /Fatty Acids/
The biosynthesis of fatty acids mainly occurs in the liver, adipose tissue, and mammary glands of higher animals, and is derived from acetyl-CoA. A series of reduction and dehydration reactions produce saturated fatty acids with carbon chains up to 16 carbon atoms in length. /Fatty Acids/
Known metabolites of palmitic acid include 15-hydroxyhexadecanoic acid.

Toxicity Summary
Identification and Uses: Palmitic acid is a solid. It is one of the most common fatty acids found in natural fats and oils. It is used as an additive in soaps and cosmetics. It is also used in the manufacture of metal palmitate esters, lubricants, waterproofing agents, and food-grade additives. Human Studies: Palmitic acid is mildly irritating when applied to human skin (total dose of 75 mg over 3 days). Excessive saturated free fatty acids (such as palmitic acid) can induce hepatocellular lipotoxicity, which is associated with the development of non-alcoholic fatty liver disease (NAFLD), also linked to insulin resistance. Growing evidence suggests that elevated levels of free fatty acids, including palmitic acid, are associated with inflammation and oxidative stress, potentially related to endothelial dysfunction characterized by reduced bioavailability of nitric oxide (NO) synthesized by endothelial nitric oxide synthase (eNOS). Studies have found that palmitic acid significantly increases the level of the bioactive neutrophil chemokine IL-8 in fatty liver cells. In human Chang hepatocytes, palmitic acid induces apoptosis accompanied by autophagy through mitochondrial dysfunction and endoplasmic reticulum stress, which are triggered by oxidative stress. Palmitic acid can also stimulate pro-inflammatory responses in human immune cells via Toll-like receptor 4 (TLR4). In a large prospective cohort study, circulating palmitic acid levels were associated with a higher risk of diabetes. However, palmitic acid also plays an important role in early human development. At birth, full-term newborns have 13-15% body fat, of which 45-50% is palmitic acid, mostly derived from endogenous synthesis in the fetus. Palmitic acid is essential for the biosynthesis of pulmonary lecithin, which is closely related to fetal maturation. Radiochromatographic analysis shows that fetal lung incorporates palmitic acid esters at high rates and integrates them into lecithin. Palmitic acid at concentrations up to 100 mg/dL has almost no toxicity to sperm cells. Palmitic acid significantly inhibits granulocyte survival in a time- and dose-dependent manner. Animal studies: Application of formulations containing 2.2% to 74% palmitic acid to the skin of albino rabbits resulted in only mild erythema without edema within 2 to 24 hours. Instillation of commercially available palmitic acid into the eyes of six albino rabbits caused no irritation. Formulations containing 19.4% palmitic acid caused mild to moderate eye irritation in rabbits. One formulation was diluted with corn oil to 75%. Cosmetic formulations containing 2.2% and 4.4% palmitic acid did not cause eye irritation in six albino rabbits. Injection of rats at up to 10 mL/kg of commercially available palmitic acid did not result in death, and no obvious gross lesions were found upon necropsy. Transient clinical symptoms, such as ruffled fur, diarrhea, and mild central nervous system depression, were observed at doses of 4.64 g/kg and 10 mL/kg. Rats fed a diet containing 4.6 g/kg/day of palmitic acid for six consecutive weeks developed hyperlipidemia. Rats fed a diet containing 6% palmitic acid for 16 consecutive weeks developed atherosclerotic lesions. Sixteen mice were injected with 1.0 mg palmitic acid three times a week for a total of 10 injections (total dose 10 mg palmitic acid/mL tricaprylic acid glyceride). Eight mice survived after 12 months, and six mice survived after 18 months. One subcutaneous sarcoma was found after 19 months, two lung tumors were found after 19 months and 22 months respectively, and one breast cancer was found after 22 months. Transient exposure of mouse blastocysts to palmitic acid led to changes in embryonic metabolism and growth, with lasting adverse effects on offspring. Palmitic acid inhibited the growth of rat hepatocytes.

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Interactions
Immunosuppressant cyclosporine A (CsA) treatment can cause serious side effects. Patients taking immunosuppressants after organ transplantation often develop hyperlipidemia and obesity. Elevated free fatty acid levels are associated with the etiology of metabolic syndrome, non-alcoholic fatty liver disease, and steatohepatitis. The contribution of free fatty acids to CsA-induced toxicity remains unclear. This study investigated the effect of palmitic acid on CsA-induced toxicity in HepG2 cells. Treatment with therapeutic doses of cyclosporine A (CsA) alone did not induce detectable cytotoxicity in HepG2 cells. Co-treatment with palmitic acid and CsA resulted in a dose-dependent increase in cytotoxicity, indicating that fatty acids can enhance cellular sensitivity to CsA-induced cytotoxicity. Co-induction of caspase-3/7 activity was also observed, suggesting that apoptosis may be involved in the generation of cytotoxicity. We found that CsA reduced cellular oxygen consumption, and palmitic acid further exacerbated this reduction, suggesting that impaired mitochondrial respiration may be a potential mechanism for enhanced toxicity. Inhibition of c-Jun N-terminal kinase (JNK) attenuated palmitic acid and CsA-induced toxicity, indicating that JNK activation plays an important role in mediating palmitic acid/CsA-induced enhanced toxicity. Our data suggest that elevated levels of free fatty acids (FFA), particularly saturated fatty acids such as palmitic acid, may be a contributing factor to cyclosporine A (CsA) toxicity, and patients with underlying diseases that can lead to elevated FFA levels may be more susceptible to CsA-induced toxicity. Furthermore, dyslipidemia/obesity induced by immunosuppressive therapy may exacerbate CsA-induced toxicity and worsen the prognosis of transplant recipients. Nonalcoholic steatohepatitis (NASH) is an increasingly common cause of chronic liver disease; however, no specific drug therapy has yet been proven effective. This study aimed to establish an experimental cell culture model of NASH based on the two-hit hypothesis, using four fatty acids—palmitic acid (PA), stearic acid (SA), linoleic acid (LA), and oleic acid (OA)—and tumor necrosis factor-α (TNF-α). Saturated fatty acids PA and SA exhibited higher cytotoxicity than unsaturated fatty acids OA and LA. Compared to saturated fatty acids, unsaturated fatty acids were more likely to induce cellular lipid accumulation without producing cytotoxicity. Palmitic acid (PA) enhanced TNF-α-induced cytotoxicity, while unsaturated fatty acids attenuated it. Mechanistic studies showed that, under conditions without oxidative stress (determined by detecting intracellular glutathione and malondialdehyde levels), PA enhanced TNF-α-mediated apoptosis. Furthermore, PA inhibited TNF-α-induced AKT phosphorylation but not c-Jun N-terminal kinase phosphorylation, suggesting that inhibition of TNF-α-activated survival signaling pathways may be the reason for PA's effect on TNF-α-induced cytotoxicity. The in vitro NASH model established in this study can be used to screen for suitable drug candidates for the treatment of NASH. The purpose of this study was to observe the effect of total flavonoids from tartary buckwheat on NO synthesis in palmitic acid-induced EA.hy926 cells. EA.hy926 cells were cultured in vitro and randomly divided into a control group, a palmitic acid-induced insulin resistance group, a total flavonoids group from tartary buckwheat, and a metformin group. The NO content in the supernatant was detected using the nitrate reductase method. The expression levels of eNOS mRNA and protein were detected by RT-PCR and Western blotting, respectively. Compared with the control group, the NO content and eNOS mRNA and protein expression levels in the supernatant of the insulin resistance group were significantly decreased (P<0.05). Compared with the insulin resistance group, the NO content and eNOS mRNA and protein expression in the supernatant of the buckwheat total flavonoid group and the metformin group were significantly increased (P<0.05), but there was no significant difference between the two groups (P>0.05). Buckwheat total flavonoids can effectively promote the expression of eNOS mRNA and protein in endothelial cells stimulated by palmitic acid, thereby promoting NO synthesis. Excessive saturated free fatty acids (such as palmitic acid) can induce hepatocellular lipotoxicity and are closely related to the development of non-alcoholic fatty liver disease (also associated with insulin resistance). Conversely, the monounsaturated fatty acid oleic acid can attenuate the effect of palmitic acid. We evaluated whether palmitic acid is directly related to insulin resistance and lipid apoptosis in mouse and human hepatocytes, and the role of oleic acid in the molecular mechanism mediating these two processes. In human and mouse hepatocytes, lipotoxic concentrations of palmitic acid trigger early activation of endoplasmic reticulum (ER) stress-related kinases, induce expression of the apoptosis transcription factor CHOP, activate caspase 3, and increase the proportion of apoptotic cells. These effects are consistent with decreased activity of the IR/IRS1/Akt insulin signaling pathway. Oleic acid inhibits the toxic effects of palmitic acid on ER stress activation, lipid apoptosis, and insulin resistance. Furthermore, oleic acid also inhibits palmitic acid-induced S6K1 activation. Similar protective effects can be achieved in hepatocytes by inhibiting S6K1 through pharmacological or genetic means. ...
For more complete data on palmitic acid interactions (22 items in total), please visit the HSDB record page.

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Non-human toxicity values
Mice intravenous LD50 57 mg/kg

[1]. PLoS One . 2017 May 2;12(5):e0176793.

[2]. Metabolism . 2014 Sep;63(9):1131-40.

[3]. In Vivo . 2011 Sep-Oct;25(5):711-8.

Hexadecanoic acid (HCA) is a straight-chain, sixteen-carbon saturated long-chain fatty acid. It is an EC 1.1.1.189 (prostaglandin E2 9-reductase) inhibitor and a metabolite in plants, Daphnia magna, and algae. It is a long-chain fatty acid and a straight-chain saturated fatty acid. It is the conjugate acid of hexadecanoic acid. It is a common saturated fatty acid found in fats and waxes, including olive oil, palm oil, and human lipids. Palmitic acid is a metabolite of Escherichia coli (K12 strain, MG1655 strain) or is produced by E. coli. Palmitic acid has been reported in Calodendrum capense, Camellia sinensis, and other organisms with relevant data. Palmitic acid is a saturated long-chain fatty acid with a 16-carbon backbone. Palmitic acid is naturally found in palm oil and palm kernel oil, and also in butter, cheese, milk, and meat. Palmitic acid, also known as hexadecanoic acid, is one of the most common saturated fatty acids found in plants and animals, including olive oil, palm oil, and human lipids. It exists as an ester (glycerol ester) in oils of both plant and animal origin, typically extracted from palm oil, which is widely distributed in plants. Palmitic acid is used to determine water hardness and is also the active ingredient in Levovist™, used for echo enhancement in Doppler ultrasound B-mode imaging and as an ultrasound contrast agent. A common saturated fatty acid found in fats and waxes, including olive oil, palm oil, and human lipids. See also: Fatty acids, C14-18 (note moved to). Mechanism of Action: ... Excessive palmitoylcarnitine production and depletion of L-carnitine reserves leading to energy expenditure, decreased acetylcholine synthesis, and oxidative stress are the main mechanisms by which palmitic acid induces neuronal loss. High palmitic acid exposure is considered a contributing factor to diabetic neuropathy and gastrointestinal dysfunction. ... The first-phase insulin release response of these islets disappears. Free fatty acids slightly increase insulin secretion from normal, fresh pancreatic β-cells. However, prolonged exposure to free fatty acids (FFA) leads to loss of first-phase insulin release and weakens the secretory response of insulin to varying levels of D-glucose stimulation.

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Therapeutic Use
/EXPL THER/ Recent studies have shown that changes in lipid metabolism affect the survival of multiple myeloma (MM) cells. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) is an imaging mass spectrometry technique that can be used to visualize the subcellular distribution of biomolecules, including lipids. Therefore, we applied this method to human clinical specimens to analyze membrane fatty acid composition and identify candidate molecules for MM treatment. We isolated MM cells and normal plasma cells (PCs) from bone marrow aspirates from MM patients and healthy volunteers, respectively, and analyzed these isolated cells using TOF-SIMS. Multiple ions, including fatty acids, were detected, and their ion counts were estimated. In MM cells, the mean intensity of palmitic acid was significantly lower than that in PCs. In cell death assays, palmitic acid dose-dependently reduced the viability of U266 cells in the concentration range of 50–1000 μM. Twenty-four hours after palmitic acid administration, the percentage of apoptotic cells began to increase. Conversely, palmitic acid had no effect on the viability of normal peripheral blood mononuclear cells (PBMCs). These results suggest that palmitic acid is a potential novel therapeutic agent that specifically targets multiple myeloma (MM) cells. Approximately 80% of new HIV-1 infections are transmitted through sexual contact. Currently, there are no clinically approved antimicrobial agents, indicating a clear and urgent therapeutic need. We recently reported that palmitic acid (PA) is a novel, specific HIV-1 fusion and entry inhibitor. Mechanistically, PA inhibits HIV-1 infection by binding to a novel pocket on the CD4 receptor and blocking the efficient binding of gp120 to CD4. Here, we aimed to evaluate the ability of PA to inhibit HIV-1 infection in a human vaginal ex vivo cervical tissue model and determine its effect on the vaginal probiotic flora Lactobacillus (L). Results showed that 100-200 μM PA treatment inhibited up to 50% of HIV-1 infection in cervical tissue, and this treatment was non-toxic to Lactobacillus crispatus and Lactobacillus jensenii in tissue or vaginal flora. In vitro, in a cell-free system independent of in vivo cell-associated CD4 receptors, we measured an inhibition constant (Ki) of approximately 2.53 μM. These results suggest that PA can serve as a model molecule for further preclinical studies to develop safe and effective HIV-1 invading antimicrobial agents. A recent laboratory study showed that a fatty acid derived from algae can reduce the ability of HIV-1 to enter immune system cells. This study was published in the journal AIDS Research and Human Retroviruses. The increasing emergence of drug-resistant HIV-1 strains necessitates new therapeutic agents. Previous studies have shown that naturally derived substances have the potential to inhibit HIV-1 infection. In this laboratory study, researchers evaluated whether palmitic acid (extracted from Sargassum, a seaweed growing along the coasts of Japan and China) could reduce the ability of HIV-1 to enter CD4+ T cells (the primary target cells of HIV-1). Palmitic acid blocked infection by both X4- and R5-tropic viruses, both of which use specific receptors (X4 or R5) to enter cells. Furthermore, the results showed that palmitic acid could protect other cells from HIV-1 infection, reducing X4 infection in primary peripheral blood lymphocytes and R5 infection in primary macrophages (leukocytes). In all cases, the degree of blocking effect depended on the concentration of palmitic acid, and most cells remained active after treatment. The researchers noted that understanding the relationship between palmitic acid and CD4 may help in developing an effective antimicrobial agent for preventing the sexual transmission of HIV. The high mutation rate and frequent sexual transmission of HIV-1 underscore the need to develop novel treatments with broad-spectrum activity against both CXCR4 (X4) and CCR5 (R5)-tropic viruses. We investigated a wide range of natural products and isolated and identified palmitic acid (PA) from Sargassum fusiforme, a small natural bioactive molecule with anti-HIV-1 infection activity. Treatment with 100 μM PA inhibited up to 70% of X4 and R5-independent infection in T cell lines. Treatment with 22 μM PA inhibited up to 95% of X4 infection in primary peripheral blood lymphocytes (PBLs), while 100 μM PA inhibited over 90% of R5 infection in primary macrophages. The infection inhibition was concentration-dependent, and cell viability remained above 80% in all tested treatments, similar to the effect of treatment with the 10⁻⁶ M nucleoside analog 2',3'-dideoxycytidine (ddC). Micromolar concentrations of PA also inhibited cell fusion and specific virus-cell fusion, with inhibition rates up to 62%. PA treatment did not lead to internalization of cell surface CD4 receptors or disruption of lipid rafts, nor did it inhibit intracellular viral replication. PA directly inhibits the formation of the gp120-CD4 complex in a dose-dependent manner. We determined the binding constant K_d of palmitic acid (PA) to the CD4 receptor to be approximately 1.5 ± 0.2 μM using fluorescence spectroscopy, and determined using one-dimensional saturated transfer differential nuclear magnetic resonance (STD-NMR) that the binding epitope of PA to CD4 consists of hydrophobic methyl and methylene groups far from the carboxyl terminus of PA. These groups hinder the efficient binding of gp120 to CD4. These findings reveal a novel class of antiviral compounds that can directly bind to the CD4 receptor, thereby blocking HIV-1 entry and infection. Understanding the structure-affinity relationship (SAR) between PA and CD4 will contribute to the development of PA analogues with stronger efficacy against HIV-1 entry.
Pharmacodynamics
Palmitic acid is the first fatty acid produced during lipogenesis (fatty acid synthesis) and is fundamental to the synthesis of longer-chain fatty acids. Palmitate has a negative feedback effect on acetyl-CoA carboxylase (ACC), which is responsible for converting acetyl-CoA carboxylase (acetyl-ACP) on the ever-growing acyl chain into malonyl-CoA carboxylase (malonyl-ACP), thereby preventing further formation of palmitate.

C16H32O2

256.43

256.24

C, 74.94; H, 12.58; O, 12.48

57-10-3

Palmitic acid sodium;408-35-5;Palmitic acid-13C16 sodium;2483736-17-8;Palmitic acid-d4-1;75736-47-9;Palmitic acid-d31;39756-30-4;Palmitic acid-1-13C;57677-53-9;Palmitic acid-d2;62689-96-7;Palmitic acid-d3;75736-53-7;Palmitic acid-13C16;56599-85-0;Palmitic acid-d4;75736-49-1;Palmitic acid-13C;287100-87-2;Palmitic acid-13C sodium;201612-54-6;Palmitic acid-1,2,3,4-13C4;287100-89-4;Palmitic acid-15,15,16,16,16-d5;285979-77-3;Palmitic acid-13C2;86683-25-2;Palmitic acid-d2-1;62690-28-2;Palmitic acid-d4-2;75736-57-1;Palmitic acid-d17;81462-28-4;Palmitic acid-d2-2;272442-14-5;Palmitic acid-d2-3;83293-32-7;Palmitic acid-d2-4;30719-28-9;Palmitic acid-d;358730-99-1;Palmitic acid-d2-5;1219805-64-7;Palmitic acid-d9;1173022-49-5;Palmitic acid-d5;1219802-61-5;Palmitic acid-9,10-d2;78387-70-9

985

White to off-white solid powder

0.9±0.1 g/cm3

340.6±5.0 °C at 760 mmHg

61-62.5 °C(lit.)

154.1±12.5 °C

0.0±0.8 mmHg at 25°C

1.454

7.15

1

2

14

18

178

0

O([H])C(C([H])([H])C([H])([H])C([H])([H])C([H])([H])C([H])([H])C([H])([H])C([H])([H])C([H])([H])C([H])([H])C([H])([H])C([H])([H])C([H])([H])C([H])([H])C([H])([H])C([H])([H])[H])=O

IPCSVZSSVZVIGE-UHFFFAOYSA-N

InChI=1S/C16H32O2/c1-2-3-4-5-6-7-8-9-10-11-12-13-14-15-16(17)18/h2-15H2,1H3,(H,17,18)

hexadecanoic acid

NSC5030; NSC-5030; NSC 5030; Palmitic acid

2934.99.03.00

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

DMSO: ~51 mg/mL (~198.9 mM)
Ethanol: 12.8~51 mg/mL (~50.0 mM)

Solubility in Formulation 1: 10 mg/mL (39.00 mM) in 15% Cremophor EL + 85% Saline (add these co-solvents sequentially from left to right, and one by one), suspension solution; with sonication.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

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Solubility in Formulation 2: 2.5 mg/mL (9.75 mM) in 10% EtOH + 40% PEG300 + 5% Tween80 + 45% Saline (add these co-solvents sequentially from left to right, and one by one), suspension solution; with ultrasonication.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear EtOH stock solution to 400 μL PEG300 and mix evenly; then add 50 μL Tween-80 to the above solution and mix evenly; then add 450 μL normal saline to adjust the volume to 1 mL.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

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Solubility in Formulation 3: ≥ 2.5 mg/mL (9.75 mM) (saturation unknown) in 10% EtOH + 90% Corn Oil (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear EtOH stock solution to 900 μL of corn oil and mix evenly.

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 (Please use freshly prepared in vivo formulations for optimal results.)