Absorption, Distribution and Excretion
Following intraperitoneal injection of (14)C fluorene, excretion varied among species. Guinea pigs cleared (14)C faster than rats or rabbits; after 12 hours, 53% was excreted in guinea pig urine, compared to 12% and 20% in other species, respectively. After 48 hours, 82% and 6% were excreted in guinea pig urine and feces, respectively, compared to 57% and 16% in rats, and 39% and 1% in rabbits. In rats, the intestinal (14)C concentration was 14% 24 hours after administration and remained unchanged after 24 hours, suggesting that fluorene and/or its metabolites may have undergone enterohepatic circulation to maintain this concentration. However, the slow release of 14C at the injection site provides another explanation. This study investigated the toxicokinetics and bioavailability of 2-methylnaphthalene (2-MN), fluorene, and pyrene after implantation of an indwelling catheter in the dorsal aorta of rainbow trout (Oncorhynchus mykiss). Intra-arterial injection of one of the polycyclic aromatic hydrocarbons (PAHs) (10 mg/kg) into rainbow trout revealed a triphasic decrease in blood concentration over time. The terminal half-lives of 2-MN, fluorene, and pyrene eliminated from the blood were 9.6 hours, 10.5 hours, and 12.8 hours, respectively. The toxicokinetics of PAHs in rainbow trout best conformed to a three-compartment open model, where the central compartment and the deep peripheral compartment represent the blood and adipose tissue, respectively. PAHs are primarily metabolized in trout into water-soluble metabolites and excreted via urine and bile. When trout were exposed to water containing 2-methylnaphthalene, fluorene, or pyrene (0.5 mg/L), these chemicals were detectable in the blood almost immediately. The apparent bioavailability of 2-methylnaphthalene, fluorene, and pyrene in trout was 20%, 36%, and 35%, respectively. In contrast, after intragastric administration of 2-methylnaphthalene, fluorene, or pyrene (50 mg/kg), unmetabolized chemicals were barely detectable or completely undetectable in the blood of trout. These results indicate that polycyclic aromatic hydrocarbons (PAHs) are systemically absorbed by trout via the gill route much faster than via the oral route.
Metabolism/Metabolites
... Fluorene-9-hydroperoxide is considered an intermediate in the hydroxylation of fluorene to fluorene-9-ol.
After incubation of fluorene with rat liver preparations, 1-hydroxyfluorene, 9-hydroxyfluorene, and 9-ketofluorene were detected as metabolites of fluorene.
The metabolic pathway of polycyclic aromatic hydrocarbon (PAH) fluorene and the co-metabolic pathways of PAHs phenanthrene, fluoranthene, anthracene, and dibenzothiophene in Sphingomonas LB126 were investigated. To our knowledge, this is the first study to investigate the co-metabolic degradation of the tricyclic polycyclic aromatic hydrocarbons phenanthrene and anthracene, and the tetracyclic polycyclic aromatic hydrocarbon fluoranthene, using fluorene as a microbial agent. The study shows that the metabolic pathway of fluorene is via the 9-fluorenone pathway to produce phthalic acid and protocatechuic acid. The co-metabolic monohydroxylation of phenanthrene, fluoranthene, and anthracene is similar to that of fluorene. We identified a variety of monohydroxylated, dihydroxylated, and ring-opening products of phenanthrene, fluoranthene, and anthracene. Unlike the metabolism of fluorene, the co-metabolism of these three compounds appears to be a non-specific process. For dibenzothiophene, we identified the metabolites dibenzothiophene-5-oxide and dibenzothiophene-5,5-dioxide; these compounds appear to be products of metabolic dead ends. Since no high concentrations of metabolites were detected in the other substrates except dibenzothiophene, we presume complete degradation, even in the co-metabolic degradation of phenanthrene, fluoranthene, and anthracene.
The Janibacter sp. YY-1 strain of dibenzofurans can degrade fluorene, diphenyl ethers, dibenzodioxins, and carbazole. Metabolites were identified by GC-MS. Angular dioxygenation is the main pathway for the degradation of fluorene, diphenyl ethers, and dibenzodioxins, but not carbazole. The detection of monohydroxy or dihydroxy compounds indicates that lateral dioxygenation occurred in all tested compounds. This bacterium can also catalyze the monooxygenation reaction of fluorene at the C9 position.
For more complete data on the metabolism/metabolites of fluorene (7 metabolites in total), please visit the HSDB record page.
The metabolism of polycyclic aromatic hydrocarbons (PAHs) occurs in all tissues and is generally catalyzed by cytochrome P-450 and its associated enzymes. PAH metabolism produces reactive intermediates, including epoxide intermediates, dihydrodiols, phenols, quinones, and various combinations thereof. Phenols, quinones, and dihydrodiols can all bind to glucuronides and sulfates; quinones can also form glutathione conjugates. (L10)

Toxicity Summary
Identification and Uses: Fluorene forms small, white, flaky crystals; it is fluorescent when impure. Fluorene derivatives have herbicidal and growth regulator activities. It can be used as a chemical intermediate. Fluorene is widely found in incomplete combustion products; it is also present in fossil fuels. Human Exposure and Toxicity: The carcinogenicity of this substance in humans is not yet classified. Animal Studies: A single topical application of 1 mg/10 g of fluorene to neonatal rats significantly induced the activity of aryl hydrocarbon hydroxylase and 7-ethoxycoumarin O-deethylase in the skin and liver. Repeated oral administration of fluorene to adult male rats, regardless of the route of administration, reduced anxiety levels in the lowest doses (1 and 10 mg/kg/day), while motor activity and learning ability remained unchanged. Orally administered rats showed a dose-dependent significant increase in relative liver weight, while this phenomenon was not observed in rats injected intraperitoneally with 100 mg/kg/day. Eighteen female rats were fed a diet containing 0.05% fluorene for 18 months (mean total intake 2553 mg/rat), and the surviving animals were sacrificed at 20.1 months. Reported tumors included one case of uterine carcinosarcoma, one case of uterine fibrosarcoma, one case of granulocytic leukemia, and four cases of pituitary adenoma. In a control group of 18 rats fed a basal diet for an average of 15.5 months, reported tumors included one case of uterine adenocarcinoma, two cases of uterine fibroepithelial polyps, five cases of adrenocortical adenoma, six cases of pituitary adenoma, and one case of inguinal fibroma. Fluorene was not mutagenic to Salmonella typhimurium and did not induce unplanned DNA synthesis in primary rat hepatocyte cultures. Ecotoxicity studies: Static toxicity tests were conducted on fluorene, using subjects including Daphnia magna, chironomus riparius larvae, amphipods (Gammarus pseudolimnaeus), snails (Mudalia potosensis), mayflies (Hexagenia bilineata), bluegill sunfish (Lepomis macrochirus), rainbow trout (Salmo gairdneri), gudgeon (Pimephales promelas), aquatic macrophytes (Chara), and green algae (Selanastrum capricornutum). Daphnia magna was the most sensitive of all tested organisms, with a median effective concentration of 0.43 mg/L over 48 hours. Gudgeon showed the lowest sensitivity to fluorene, with no mortality observed even at concentrations as high as 100 mg/L. Polycyclic aromatic hydrocarbons (PAHs) can bind to blood proteins such as albumin, thereby being transported throughout the body. Many PAHs induce the expression of cytochrome P450 enzymes, particularly CYP1A1, CYP1A2, and CYP1B1, by binding to aryl hydrocarbon receptors or glycine N-methyltransferases. These enzymes metabolize PAHs into toxic intermediates. The active metabolites of PAHs (epoxide intermediates, dihydrodiols, phenols, quinones, and various combinations thereof) covalently bind to DNA and other cellular macromolecules, inducing mutagenicity and carcinogenesis. (L10, L23, A27, A32)

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Interactions
The adrenal cortex has a low physiological cell renewal capacity; even after contralateral adrenalectomy, cell replication remains at only a moderate level. Although the adrenal cortex is not very sensitive to the malignant induction of carcinogens, a cumulative effect of mitotic responses in adrenal cortical cells was observed 48 hours after a single oral administration of multiple tumorigenic xenobiotics. We currently report three different response patterns in rats. First, reserpine selectively stimulates mitosis in the zona fasciculata, accompanied by a decrease in body weight, thymus weight, and liver weight. These are non-specific stress responses, and exogenous adrenocorticotropic hormone (ACTH) can also elicit similar responses. Second, homologues of hepatocyte proliferation and hepatomegaly, such as fluorene (FEN), fluorenone (FON), and 4-benzoyl-FON, as well as the genotoxic 2-acetamidofluorene (2-AAF) and 2,4,7-trinitro-FON, can all induce selective mitotic responses in the zona fasciculata (ZF). These effects occur simultaneously at the lowest effective doses of FEN or FON, but were not observed in the high-dose group (studied with fluorene only). 2-benzyl and 2-benzoyl-substituted derivatives were completely ineffective. Third, a two-zone response was observed only with phenobarbital (PB) or the lowest effective dose of FEN. The preventive effect of low-dose PB on the 2-AAF-induced ZF response suggests a metabolic alteration. We conclude that the rapid mitotic zinc finger response is an endogenously mediated net effect of the interaction of metabolic and various adaptive mechanisms. These adaptive mechanisms have been reported to be activated in a stress-dependent manner and converge in the adrenal glands. Thus, the early mitotic zinc finger response may indirectly reflect the “specific” pro-proliferative properties of exogenous substances. The deposition and oligomerization of amyloid-β peptide (Aβ) play a crucial role in the pathogenesis of Alzheimer's disease (AD). Aβ peptide is produced by the cleavage of the membrane-associated domain of amyloid precursor protein (APP) by β and γ secretases. Multiple pieces of evidence suggest that soluble Aβ oligomers (AβO) are the main neurotoxic substances in the etiology of AD. Recently, we have demonstrated that a class of fluorene molecules can specifically disrupt AβO. To better understand the mechanisms of this destructive ability, we expanded the application of electron paramagnetic resonance (EPR) spectroscopy to site-directed spin labeling of Aβ peptides to investigate the binding of fluorene compounds to the structure and kinetics of AβO and their effects. Furthermore, we synthesized a spin-labeled fluorene (SLF) containing a pyrrololine nitro oxygen radical, which both enhances cellular protection against AβO toxicity and allows for direct observation of the binding of the fluorene-AβO complex. We also evaluated the ability of fluorene compounds to target multiple pathological processes in the neurodegenerative cascade, such as their ability to block AβO toxicity, scavenge free radicals, and reduce intracellular AβO species formation. Fluorenes modified with pyrrololine nitro oxygen radicals may be particularly effective in combating Aβ peptide toxicity because they possess both antioxidant properties and the ability to disrupt the AβO species. /Spin-labeled fluorene/
Previous immunotoxicity studies of complex polycyclic aromatic hydrocarbon (PAH) byproduct mixtures from manufactured gas plants suggested a possible synergistic effect, and therefore this synergistic effect was investigated by measuring the immunosuppressive effect of the recombinant PAH mixture on female B6C3F1 mice. These mice were challenged with either TNP-haptened sheep erythrocytes (SRBCs) (T cell-dependent) or trinitrophenyl lipopolysaccharide (TNP-LPS) (T cell-independent) antigens. The recombinant PAH mixture contained 17 homologues: 2-ring (indene, naphthalene, 1-methylnaphthalene, and 2-methylnaphthalene), 3-ring (acenaphthene, acenaphthene, dibenzofuran, fluorene, phenanthrene, and anthracene), and ≥4-ring (pyrene, fluoranthene, benzo[a]anthene, chrysene, benzo[b]fluoranthene, benzo[k]fluoranthene, and benzo[a]pyrene), similar to mixtures found in manufactured gas plant byproducts. The recombinant mixture, along with the 2-, 3-, and ≥4-ring PAH components, dose-dependently reduced the response of splenic plaque-forming cells (PFCs) to sheep erythrocytes (SRBCs) or TNP-LPS, with ED50 values of 86, 354, 145, and 23 mg/kg, or 163, 439, 637, and 31 mg/kg, for the four treatment groups. The corresponding ED50 values for reducing serum anti-TNP IgM levels by these mixtures were: (TNP haptenized SRBCs, T-cell dependent) 144, 231, 42, and 27 units; (TNP-LPS, T-cell independent) 161, 406, 312, and 69 units. The inhibition of anti-TNP IgM antibody titers was similar to that of PFC antibody titers, suggesting that antigen-specific immunoglobulin titers can serve as a biomarker for PAH exposure. Direct comparison of the immunotoxicity of the recombinant PAH mixture with corresponding doses of ≥4-ring PAHs indicated that the latter was the primary source of the recombinant mixture's activity.

[1]. Biodegradation of fluorene by the newly isolated marine-derived fungus, Mucor irregularis strain bpo1 using response surface methodology. Ecotoxicol Environ Saf. 2021 Jan 15;208:111619.

Fluorene is a white, flake-like molecule that sublimates easily under vacuum and exhibits fluorescence when impure. (NTP, 1992)
Fluorene is an ortho-fused tricyclic hydrocarbon and a major component of fossil fuels and their derivatives. It is both an ortho-fused polycyclic aromatic hydrocarbon and an ortho-fused tricyclic hydrocarbon.
Fluorene has been reported to be found in angelica, corn, and carrots, and relevant data exists.
Fluorene is one of more than 100 polycyclic aromatic hydrocarbons (PAHs). PAHs are chemical substances formed during the incomplete combustion of organic matter (such as fossil fuels). They usually exist as mixtures of two or more compounds. (L10)

C13H10

166.22

166.078

86-73-7

Fluorene-d10;81103-79-9

6853

Off-white to light brown solid powder

1.1±0.1 g/cm3

293.6±10.0 °C at 760 mmHg

111-114 °C(lit.)

133.1±9.7 °C

0.0±0.3 mmHg at 25°C

1.645

4.16

0

0

0

13

165

0

NIHNNTQXNPWCJQ-UHFFFAOYSA-N

InChI=1S/C13H10/c1-3-7-12-10(5-1)9-11-6-2-4-8-13(11)12/h1-8H,9H2

9H-fluorene

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Note: This product requires protection from light (avoid light exposure) during transportation and storage.

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

DMSO: 62.5 mg/mL (376.01 mM)

Note: Listed below are some common formulations that may be used to formulate products with low water solubility (e.g. < 1 mg/mL), you may test these formulations using a minute amount of products to avoid loss of samples.

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Injection Formulation 1: DMSO : Tween 80： Saline = 10 : 5 : 85 (i.e. 100 μL DMSO stock solution → 50 μL Tween 80 → 850 μL Saline)
*Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH ₂ O to obtain a clear solution.
Injection Formulation 2: DMSO : PEG300 ：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL DMSO → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)
Injection Formulation 3: DMSO : Corn oil = 10 : 90 (i.e. 100 μL DMSO → 900 μL Corn oil)
Example: Take the Injection Formulation 3 (DMSO : Corn oil = 10 : 90) as an example, if 1 mL of 2.5 mg/mL working solution is to be prepared, you can take 100 μL 25 mg/mL DMSO stock solution and add to 900 μL corn oil, mix well to obtain a clear or suspension solution (2.5 mg/mL, ready for use in animals).

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Injection Formulation 4: DMSO : 20% SBE-β-CD in saline = 10 : 90 [i.e. 100 μL DMSO → 900 μL (20% SBE-β-CD in saline)]
*Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.
Injection Formulation 5: 2-Hydroxypropyl-β-cyclodextrin : Saline = 50 : 50 (i.e. 500 μL 2-Hydroxypropyl-β-cyclodextrin → 500 μL Saline)
Injection Formulation 6: DMSO : PEG300 : castor oil : Saline = 5 : 10 : 20 : 65 (i.e. 50 μL DMSO → 100 μLPEG300 → 200 μL castor oil → 650 μL Saline)
Injection Formulation 7: Ethanol : Cremophor : Saline = 10： 10 : 80 (i.e. 100 μL Ethanol → 100 μL Cremophor → 800 μL Saline)
Injection Formulation 8: Dissolve in Cremophor/Ethanol (50 : 50), then diluted by Saline
Injection Formulation 9: EtOH : Corn oil = 10 : 90 (i.e. 100 μL EtOH → 900 μL Corn oil)
Injection Formulation 10: EtOH : PEG300：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL EtOH → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)

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Oral Formulation 1: Suspend in 0.5% CMC Na (carboxymethylcellulose sodium)
Oral Formulation 2: Suspend in 0.5% Carboxymethyl cellulose
Example: Take the Oral Formulation 1 (Suspend in 0.5% CMC Na) as an example, if 100 mL of 2.5 mg/mL working solution is to be prepared, you can first prepare 0.5% CMC Na solution by measuring 0.5 g CMC Na and dissolve it in 100 mL ddH2O to obtain a clear solution; then add 250 mg of the product to 100 mL 0.5% CMC Na solution, to make the suspension solution (2.5 mg/mL, ready for use in animals).

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Oral Formulation 3: Dissolved in PEG400
Oral Formulation 4: Suspend in 0.2% Carboxymethyl cellulose
Oral Formulation 5: Dissolve in 0.25% Tween 80 and 0.5% Carboxymethyl cellulose
Oral Formulation 6: Mixing with food powders

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Note: Please be aware that the above formulations are for reference only. InvivoChem strongly recommends customers to read literature methods/protocols carefully before determining which formulation you should use for in vivo studies, as different compounds have different solubility properties and have to be formulated differently.

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