SEARCH · PubMed Health
Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Explore the source record for details and available documents.
Phytol, a branched-chain fatty alcohol, is the naturally occurring precursor of phytanic and pristanic acid, branched-chain fatty acids that are both ligands for the nuclear hormone receptor peroxisome proliferator-activated receptor alpha (PPARalpha). To investigate the metabolism of phytol and the role of PPARalpha in its regulation, wild-type and PPARalpha knockout (PPARalpha-/-) mice were fed a phytol-enriched diet or, for comparison, a diet enriched with Wy-14,643, a synthetic PPARalpha agonist. After the phytol-enriched diet, phytol could only be detected in small intestine, the site of uptake, and liver. Upon longer duration of the diet, the level of the (E)-isomer of phytol increased significantly in the liver of PPARalpha-/- mice compared with wild-type mice. Activity measurements of the enzymes involved in phytol metabolism showed that treatment with a PPARalpha agonist resulted in a PPARalpha-dependent induction of at least two steps of the phytol degradation pathway in liver. Furthermore, the enzymes involved showed a higher activity toward the (E)-isomer than the (Z)-isomer of their respective substrates, indicating a stereospecificity toward the metabolism of (E)-phytol. In conclusion, the results described here show that the conversion of phytol to phytanic acid is regulated via PPARalpha and is specific for the breakdown of (E)-phytol.
Chlorophyll is the most abundant photosynthetic pigment in higher plants. During senescence, chlorophyll is hydrolyzed, resulting in the release of free phytol and chlorophyllide. Although the degradation of chlorophyllide has been studied in depth, the metabolic fate of phytol in plants is less clear. Here, we provide evidence that phytol can be incorporated into chlorophyll, tocopherol, and lipid esters by Arabidopsis seedlings. Phytol is phosphorylated to phytyl-phosphate and phytyl-diphosphate by two successive kinase activities associated with chloroplast envelope membranes of Arabidopsis. Although phytol kinase is CTP-dependent, the second kinase reaction, phytyl-phosphate kinase, shows broader specificity for CTP, GTP, UTP, and ATP. Therefore, in addition to de novo synthesis from geranylgeranyl-diphosphate, phosphorylation of free phytol represents an alternative route for phytyl-diphosphate production as the precursor for chloroplast prenyl lipid synthesis. Lipid esters are produced after feeding phytol to Arabidopsis seedlings, and they also accumulate in large amounts in leaves during senescence. The predominant phytyl ester that accumulates during senescence is hexadecatrienoic acid phytyl ester. Fatty acid phytyl ester synthesis by protein extracts of Arabidopsis is stimulated in the presence of phytol- and acyl-CoA esters. Thus, Arabidopsis contains a distinct enzymatic machinery for redirecting free phytol released from chlorophyll degradation into chloroplast lipid metabolism.
Phytol is a branched, long-chain aliphatic alcohol which has various biological effects. In this study, we examined phytol as a tumor promoter in a mouse skin initiation-promotion model, and compared its promotion activity with that of 12-O-tetradecanoyl phorbol-13-acetate (TPA). Female ICR mice, 7 weeks of age, were initiated with 100 microg of 7,12-dimethylbenz(a)anthracene, and were then topically promoted twice a week for 16 weeks with 100 mg of phytol or with 2.5 microg of TPA. In this model 95% of animals treated with phytol developed skin tumors within 16 weeks. The average number of lesions per mouse treated with phytol was significantly lower than that in mice treated with TPA, and this significant difference continued up to 16 weeks after the end of promotion treatment. Characterization of hyperplasia 48 h after topical application of agents showed that epidermal thickness and vertical thickness following topical application of phytol were significantly increased compared with vehicle controls, but were significantly smaller than in animals treated with TPA. Ornithine decarboxylase (ODC) activity following topical application of phytol was increased in a dose-dependent manner and showed a weak, delayed induction (which was maximal 11-12 h after treatment) as compared with the case of TPA. The specific binding of [3H]phorbol-12,13-dibutyrate (PDBU) by JB6 cells was not inhibited by phytol at concentrations up to 1 mM. These results indicate that phytol has a weak tumor promoter activity compared to TPA and is a non-TPA-type tumor promoter in this model of mouse skin carcinogenesis.
The metabolism of uniformly-labeled (14)C-phytol, (14)C-phytenic acid, and (14)C-phytanic acid was studied in the rat. Conversion of both phytol and phytenic acid to phytanic acid was demonstrated. Tracer doses of phytol-U-(14)C given orally were well absorbed (30-66%), and approximately 30% of the absorbed dose was converted to (14)CO(2) in 18 hr. After intravenous injection, 20% appeared in (14)CO(2) in 4 hr. Phytanic acid-U-(14)C given intravenously was oxidized at a comparable rate (22-37% in 4 hr) and was as rapidly oxidized as palmitic acid-1-(14)C (21% in 4 hr). Metabolism of these substrates was also studied in rats previously maintained on a diet containing 5% phytol by weight, which causes accumulation of phytanic acid, phytenic acid, and, to a lesser extent, phytol in blood and tissues. Despite the large body pools of preformed, unlabeled substrate in these animals, the fraction of an administered dose of phytol-U-(14)C or phytanic acid-U-(14)C converted to (14)CO(2) was not significantly diminished. These studies indicate that the rat has an appreciable capacity to degrade the highly branched carbon skeleton of phytol and its derivatives. Twenty-four hours after administration of phytol-U-(14)C, the lipid radioactivity remaining in the body was widely distributed among the tissues, highest concentrations being found in liver and adipose tissue. Four hours after intravenous administration of phytanic acid-U-(14)C, all of the major lipid classes in the liver contained radioactivity, most in triglycerides and phospholipids and least in cholesterol esters and lower glycerides. There was no demonstrable incorporation of mevalonate-2-(14)C or acetate-1-(14)C into liver phytanic acid when they were given intravenously to a rat previously fed phytol. Endogenous biosynthesis, if it occurs at all, must be extremely limited.
The effects of dietary phytol and the type of dietary fat on hepatic fatty acid oxidation were examined in male ICR mice. Mice were fed diets containing 0 or 5 g/kg phytol and 100 g/kg palm, safflower, or fish oil for 21 d. Among the groups fed phytol-free diets, the activities and mRNA abundance of various enzymes involved in fatty acid oxidation were greater in mice fed fish oil than in those fed palm or safflower oil. Dietary phytol profoundly increased the activities and mRNA abundance of hepatic fatty acid oxidation enzymes in mice fed palm oil. However, safflower and fish oils, especially the latter, greatly attenuated the phytol-dependent increase in hepatic fatty acid oxidation. The hepatic concentration of phytanic acid, a metabolite of phytol that is the ligand and activator of retinoid X receptors and peroxisome proliferator-activated receptors, was higher in mice fed fish oil than safflower or palm oil, and in those administered safflower oil than palm oil. The hepatic mRNA abundance of sterol carrier protein-2, a lipid-binding protein involved in phytol metabolism, was inversely correlated with the hepatic concentration of phytanic acid. We demonstrated that polyunsaturated fats attenuate the enhancing effect of dietary phytol on hepatic fatty acid oxidation. Dietary fat-dependent changes in the hepatic phytanic acid concentration cannot account for this phenomenon.
Previous studies in our laboratory showed a synergistic interaction of synthetic ligands selective for the retinoid receptors RAR and RXR in regard to teratogenic effects produced in mice (M. M. Elmazar et al., 2001, TOXICOL: Appl. Pharmacol. 170, 2-9). In the present study the influence of phytol and phytanic acid (a RXR-selective ligand) on the teratogenicity of retinol and the RAR-selective ligand all-trans-retinoic acid was investigated by coadministration experiments on day 8.25 of gestation in NMRI mice. Phytol and phytanic acid, noneffective when administered alone, did not potentiate the teratogenicity induced by retinol or all-trans-retinoic acid. On the contrary, phytol and phytanic acid greatly reduced retinol-induced teratogenic effects (ear anotia, tail defects, exencephaly). The effect of phytol on all-trans-retinoic acid teratogenesis was limited (only resorptions and tail defects were reduced). Pharmacokinetic studies in nonpregnant animals revealed that phytol coadministration with retinol reduced plasma levels of retinol and retinyl esters, and drastically reduced the levels of the teratogenic retinol metabolite, all-trans-retinoic acid. Phytanic acid also reduced the oxidative metabolism and teratogenic effects of retinol. These results indicate that phytol and phytanic acid did not synergize with retinol and all-trans-retinoic acid in our mouse teratogenesis model. Instead, phytol and phytanic acid effectively blocked the teratogenic effects of retinol by drastically reducing the metabolic production of all-trans-retinoic acid. Phytol and phytanic acid may be useful for the prevention of vitamin A teratogenicity.
Microbial degradation of phytol is often proposed to be the primary source of the acyclic isoprenoid acids observed in sediments, yet only a limited number of these acids have been found in bacterial cultures grown on phytol. This study reports detailed capillary gas chromatography and gas chromatography-mass spectrometry analyses of the products resulting from growth of marine bacteria on phytol as the sole carbon source. We examined two strains of bacteria which were able to oxidize phytol to phytenic acid but were unable to further degrade phytol. The third isolate studied converted phytol to a mixture of five saturated isoprenoid acids. The C(17) isoprenoid acid produced was of particular interest, since its genesis from phytol would have involved several unusual intermediates. It is suggested that this acid is produced by bacterial metabolism of the C(18) isoprenoid ketone (produced from phytol abiologically under oxic conditions) and that its abundance is thus a sensitive indicator of sedimentary depositional conditions.
Feeding of phytol in large doses (2-5% by weight in the diet) led to accumulation of phytanic acid in the mouse, rat, rabbit, and chinchilla, the degree of accumulation depending upon the level of dietary intake. The relative concentration of phytanic acid, expressed as a percentage of the total fatty acids, was as high as 20-60% in liver and 30-40% in serum. Phytenic acid, which may be an intermediate in the conversion of phytol to phytanic acid, also accumulated. When phytol was withdrawn from the diet, tissue and serum concentrations of phytanic acid fell rapidly, which indicates the ability of the normal animal to metabolize phytanic acid readily. At high dosages in the diet, phytol inhibited growth and caused death within 1-4 weeks. In the mouse, dietary phytanic acid and dietary phytol fed in equivalent amounts were of comparable toxicity. Accumulation of tissue phytanic acid occurred more rapidly when phytanic acid was fed than when phytol was fed in equal amounts. In none of the animals fed either phytol or phytanic acid were there any signs of neurological defects. Histologic examination of rats fed phytol showed some fat accumulation, glycogen depletion, and karyokinesis in the liver. There were no pathologic changes in the retina or in the peripheral and central nervous system such as those described in Refsum's disease.
The crude methanol extract of the Kenyan shrub Leucas volkensii Gürke (Labiatae) displayed in a radiorespirometric bioassay antimycobacterial activity against Mycobacterium tuberculosis. Bioassay-guided fractionation of the crude extract led to the identification of (E)-phytol as the principal active component with a minimum inhibitory concentration (MIC) of 2 micrograms/ml, a value also observed for (3R,S,7R,11R)-phytanol, (Z)-phytol, and a commercially available 2:1 mixture of (E)- and (Z)-phytol. The derivatives (E)-phytol acetate, a mixture of the (2S,3S)- and (2R,3R)-isomers of (E)-phytol epoxide and (3R,S,7R,11R)-phytanic acid displayed lower activities with MICs of 8, 16, and > 128 micrograms/ml, respectively. Geraniol and farnesol, displayed MICs of 64 and 8 micrograms/ml, respectively. The activities of (E)-phytol, (Z)-phytol and (3R,S,7R,11R)-phytanol were found to be in the same range as ethambutol, a clinically useful drug with an MIC in the range 0.95-3.8 micrograms/ml.
BACKGROUND: Vaccine efficacy depends significantly on the use of appropriate adjuvant(s) in the formulation. Phytol, a dietary diterpene alcohol, is similar in structure to naturally occurring isoprenoid adjuvants; but little is known of its adjuvanticity. In this report, we describe the relative safety and efficacy of phytol and its hydrogenated derivative PHIS-01 compared to commercial adjuvants. METHODS: We tested adjuvant properties using a formulation consisting of either a hapten, phthalate-conjugated to a protein, keyhole limpet hemocyanin (KLH), or ovalbumin (OVA) emulsified with the test adjuvants in mice without any surfactant. Humoral immunity was assessed in terms of titer, specificity, and isotypic profiles. The effect on cell-mediated immunity was studied by assaying the induction of either OVA- or B-lymphoma-specific cytotoxic T-lymphocyte (CTL) activity. RESULTS AND DISCUSSION: The phytol compounds, particularly PHIS-01, elicit increased titers of all major IgG subclasses, especially IgG2a. Unlike commercial adjuvants, both phytol compounds are capable of inducing specific cytotoxic effector T cell responses specific to both OVA and B-lymphoma tested. Phytols as adjuvants are also distinctive in that they provoke no adverse anti-DNA autoimmune response. Intraperitoneally administered phytol is comparable to complete Freund's adjuvant in toxicity in doses over 40 ug/mouse, but PHIS-01 has no such toxicity. CONCLUSION: These results and our ongoing studies on antibacterial immunity show that phytol and PHIS-01 are novel and effective adjuvants with little toxicity.
A ferriprotoporphyrin, hemin (Fe(3+)), modified with 3,7,11,15-tetramethyl-2-hexadecen-1-ol, phytol, was adsorbed in nano-spaces of about 4 nm in diameter in mesoporous silica (FSM; folded-sheet mesoporous material) forming a phytol-modified hemin (Fe(3+))-FSM nano-conjugate. The properties and the structure of the conjugate were studied by UV-visible light absorption, IR absorption spectroscopy, and a nitrogen adsorption isotherm. Although the hemin without phytol could not be adsorbed to the mesoporous silica, modification with phytol imparted preferential adsorption properties. The conjugate was not only stable but also had a peroxidase-like activity in a 0.1% hydrogen peroxide solution, while free hemin in the solution was easily destroyed. The hemin (Fe(3+)) in the FSM was reduced to heme (Fe(2+)) by hydrazine. The phytol-modified heme (Fe(2+))-FSM conjugate formed an O(2)-heme complex with a superoxide type structure, resembling oxyhemoglobin or oxymyoglobin, which has not been previously observed for free heme in solution. The addition of carbon monoxide or nitrogen monoxide to the phytol-modified heme (Fe(2+))-FSM conjugate caused the formation of CO- or NO-heme complex in the nano-spaces of the FSM. These properties are attributed not only to the Fe-complex but also to the cooperative functions of the heme with mesoporous silica, resembling properties of a natural heme-protein conjugate; hemoglobin or peroxidase. These results are an elegant example of biomimetic nano-technology.
The enzymatic conversion of phytol to phytanic acid was investigated in rat liver postnuclear and other subcellular fractions using [1-3H]phytol as the substrate. The assay method involved incubation of the substrate with appropriate cofactors and the enzyme source, followed by subjecting the mixture to Folch partition and measuring the radioactivity in the upper layer. The phytol-phytanate conversion activity was present in mitochondrial and microsomal fractions. Cytosol had no activity. In mitochondrial fraction, investigation of cofactor requirements indicated that only NAD was required for activity. Other pyridine nucleotides supported the activity to a lesser extent when compared with NAD. FAD at 1 mM concentration did not support the activity. Bovine serum albumin (0.4 mg/ml) stimulated the activity. The reaction did not require molecular oxygen. From substrate kinetic studies, an apparent Km of 14.3 and 11.1 microM was calculated for phytol in mitochondrial and microsomal fractions, respectively. The amount of tritiated water produced from incubation increased linearly up to 7-8 min. The activity was linear with the amount of mitochondrial and microsomal protein up to 200 and 40 micrograms, respectively. Among the various rat tissue homogenates tested, liver had the highest activity. Spleen and kidney had 8-9% of the activity of liver. Brain possessed negligible activity. Both ethanol and pyrazole had no inhibitory effect on phytol-phytanate conversion. This observation and the absence of activity in cytosol suggests that alcohol dehydrogenase may not be involved in phytol-phytanate conversion.
Phytol is a branched chain fatty alcohol, which is abundantly present in nature as part of the chlorophyll molecule. In its free form, phytol is metabolized to phytanic acid, which accumulates in patients suffering from a variety of peroxisomal disorders, including Refsum disease. The breakdown of phytol to phytanic acid takes place in three steps, in which first, the alcohol is converted to the aldehyde, second the aldehyde is converted to phytenic acid, and finally the double bond is reduced to yield phytanic acid. By culturing fibroblasts in the presence of phytol, increases in the levels of phytenic and phytanic acid were detected. Interestingly, fibroblasts derived from patients affected by Sjögren Larsson syndrome (SLS), known to be deficient in microsomal fatty aldehyde dehydrogenase (FALDH) were found to be deficient in this. In addition, fibroblast homogenates of these patients, incubated with phytol in the presence of NAD+ did not produce any phytenic acid. This indicates that FALDH is involved in the breakdown of phytol.
BACKGROUND: Adjuvants are known to significantly enhance vaccine efficacy. However, commercial adjuvants often have limited use because of toxicity in humans. The objective of this study was to determine the comparative effectiveness of a diterpene alcohol, phytol and its hydrogenated derivative PHIS-01, relative to incomplete Freund's adjuvant (IFA), a commonly used adjuvant in augmenting protective immunity in mice against E. coli and S. aureus, and in terms of inflammatory cytokines. METHODS: Vaccines, consisting of heat-attenuated E. coli or S. aureus and either of the two phytol-based adjuvants or IFA, were tested in female BALB/c mice. The vaccines were administered intraperitoneally at 10-day intervals. The efficacy of the phytol and PHIS-01, as compared to IFA, was assessed by ELISA in terms of anti-bacterial antibody and inflammatory cytokines. We also examined the ability of the vaccines to induce specific protective immunity by challenging mice with different doses of live bacteria. RESULTS AND DISCUSSION: IFA, phytol, and PHIS-01 were equally efficient in evoking anti-E. coli antibody response and in providing protective immunity against live E. coli challenges. In contrast, the antibody response to S. aureus was significant when PHIS-01 was used as the adjuvant. However, in terms of the ability to induce protective immunity, phytol was most effective against S. aureus. Moreover, during challenges with live E. coli and S. aureus immune mice produced much less IL-6, the mediators of fatal septic shock syndromes. CONCLUSION: Our results show that vaccine formulations containing phytol and PHIS-01 as adjuvants confer a robust and protective immunity against both Gram-negative and Gram-positive bacteria without inducing adverse inflammatory cytokine due to IL-6.
This study was made to determine the extent of absorption of chlorophyll phytol from the intestine of man, and the importance of chlorophyll as a source of the phytanic acid that accumulates in Refsum's disease. Uniformly (14)C-labeled pheophytin a (the Mg-free derivative of chlorophyll a) was fed to normal human subjects and to patients with Refsum's disease. Feces were collected and analyzed. In all subjects, 90-95% of the administered radioactivity was recovered in the feces, still largely in the form of pheophytin a. The phytol radioactivity recovered in the feces averaged about 95% of that in the administered material, which indicates that there had been little absorption of the phytol moiety. Similarly, after 250 g of cooked spinach had been fed to a normal subject, almost the entire phytol content was found in the feces. Less than 5% of the ingested spinach phytol was accounted for in the thoracic duct lymph of another subject. It was concluded that not more than about 5% of the ingested chlorophyll phytol is absorbed by man, whether normal or afflicted with Refsum's disease. On this basis we conclude that the major portion of the phytanic acid that accumulates in Refsum's disease could not be derived from dietary chlorophyll.
The fate of ingested chlorophyll-particularly of the phytol portion of the molecule-was studied. Uniformly (14)C-labeled pheophytin a (the Mg-free derivative of chlorophyll a) was prepared from an extract of tobacco leaves grown in (14)CO(2), and was administered by stomach tube to rats in which the thoracic duct had been cannulated. Only about 2% of the administered radioactivity was absorbed in 24 hr, largely into the thoracic duct lymph. Moreover, only a fraction of this lymph radioactivity was derived from phytol (i.e., was found in phytol, phytenic acid, or phytanic acid). The results indicated that not more than 1-2% of chlorophyll phytol is available for absorption by the rat. Similarly, after the administration of whole spinach or spinach extract (not labeled) to rats, only about 1% of the total phytol content was absorbed into the intestinal lymph. Nearly all of the administered phytol was found in the feces and the contents of the colon, and was still largely in the form of pheophytin. The study also indicated that little of the nonphytol portion of the chlorophyll molecule is absorbed.
The peroxisome proliferator-activated receptor (PPAR) is one of the indispensable transcription factors for regulating lipid metabolism in various tissues. In our screening for natural compounds that activate PPAR using luciferase assays, a branched-carbon-chain alcohol (a component of chlorophylls), phytol, has been identified as a PPARalpha-specific activator. Phytol induced the increase in PPARalpha-dependent luciferase activity and the degree of in vitro binding of a coactivator, SRC-1, to GST-PPARalpha. Moreover, the addition of phytol upregulated the expression of PPARalpha-target genes at both mRNA and protein levels in PPARalpha-expressing HepG2 hepatocytes. These findings indicate that phytol is functional as a PPARalpha ligand and that it stimulates the expression of PPARalpha-target genes in intact cells. Because PPARalpha activation enhances circulating lipid clearance, phytol may be important in managing abnormalities in lipid metabolism.