Defluorination as the key trait to gauge the biodegradability of fluorinated pollutants in environmental microbial communities.

Research on microbial defluorination is largely centred on controlled experiments using axenic or well defined microbial inocula. These approaches serve a relevant purpose in the field, offering fundamental biochemical and mechanistic insights on the intricacies of biological defluorination. However, they fail to account for the effective contribution of environmental microbial communities in the recycling of fluoroorganic pollutants, a highly relevant perspective from an environmental risk assessment standpoint, while also missing an important outlook on how community-wide dynamics can leverage the breakdown of C─F bonds in these recalcitrant compounds. With that in mind, this chapter provides experimental and methodological insights on the study of microbial defluorination in wild environmental communities, using this critical catabolic step as the de facto endpoint to evolve, select and cultivate microorganisms with improved defluorination performances.

Fluorine materials scavenge excess carbon dioxide and promote Escherichia coli growth.

Fluorinated solvents have been used as oxygen carriers in closed microbial cultures to sustain aerobic conditions. However, the growth-promoting effects of fluorinated solvents remain unclear. Therefore, this study aimed to elucidate the mechanism by which fluorinated solvents promote microbial growth and to explore alternative materials that can be easily isolated after culture. Escherichia coli and HFE-7200, a fluorinated solvent, were used to explore factors other than oxygen released by fluorinated solvents that promote microbial growth. E. coli growth was promoted in gas-permeable cultures, and HFE-7200 alleviated medium acidification. Gas chromatography confirmed that HFE-7200 functioned as a scavenger of carbon dioxide produced by E. coli metabolism. Because fluorinated solvents can dissolve various gases, they could scavenge metabolically produced toxic gases from microbial cultures. Furthermore, using polytetrafluoroethylene, a solid fluorine material, results in enhanced bacterial growth. Such solid materials can be easily isolated and reused for microbial culture, suggesting their potential as valuable technologies in food production and biotechnology.

Low dosage fluorine ameliorates the bioaccumulation, hepatorenal dysfunction and oxidative stress, and gut microbiota perturbation of cadmium in rats.

Many "hot spot" geographic areas around the world with soils and crops co-polluted with cadmium (Cd) and fluorine (F), two of the most representative pollutants in the environment. However, it still exists argumentative on the dose-effect relationship between F and Cd so far. To explore this, a rat model was established to evaluate the effects of F on Cd-mediated bioaccumulation, hepatorenal dysfunction and oxidative stress, and the disorder of intestinal microbiota as well. 30 healthy rats were randomly assigned to Control group (C group), Cd 1 mg/kg (Cd group), Cd 1 mg/kg and F 15 mg/kg (L group), Cd 1 mg/kg and F 45 mg/kg (M group), and Cd 1 mg/kg and F 75 mg/kg (H group) for 12 weeks by gavage. Our results showed that Cd exposure could accumulate in organs, cause hepatorenal function damage and oxidative stress, and disorder of gut microflora. However, different dosages of F showed various effects on Cd-induced damages in liver, kidney, and intestine, and only the low supplement of F showed a consistent trend. After low supplement of F, Cd levels were declined by 31.29% for liver, 18.31% for kidney, and 2.89% for colon, respectively. The serum aspartate aminotransferase (AST), blood urea nitrogen (BUN), creatinine (Cr), and N-acetyl-ß-glucosaminidase (NAG) were significantly reduced (p < 0.01); The activity of superoxide dismutase (SOD) was elevated and mRNA expression level of NAD(P)H quinone oxidoreductase 1 (NQO1) was decreased in the liver and kidney (p < 0.05). Moreover, low F dosage up-regulated the abundance of Lactobacillus from 15.56% to 28.73% and the 6.23% of F/B ratio was declined to 3.70%. Collectively, this highlights that low dosage of F might be a potential strategy to ameliorate the hazardous effects by Cd-exposed in the environment.

Multi-fluorine labeled indanone derivatives as potential MRI imaging probes for ß-Amyloid plaques.

In order to realize the early diagnosis of Alzheimer's disease (AD), we designed and synthesized a series of multi-fluorine labeled indanone derivatives based on indanone which could target ß-amyloid (Aß). Through the in vitro staining experiment and affinity experiment, we selected 7d out, and then evaluated it through other in vivo and in vitro experiments. The staining of AD human brain adjacent sections revealed that compound 7d could bind to Aß plaques with high affinity. In the in vitro binding assay, 7d showed a balanced affinity with Aß1-40 (Kd = 367 ± 13) and Aß1-42 (Kd = 384 ± 56). Also, 7d exhibited a low toxicity (LD50 > 50 mg/kg) and an excellent ability to pass through the blood-brain barrier (Log p = 3.87). The biodistribution experiment in mice showed that 7d reached the highest brain uptake after 1 h of tail vein injection and cleared after 24 h. A low concentration of 7d (1.875 mg/ml) showed a strong imaging ability (19F-weighted mode), and the imaging capability increased with the increasing of concentration. All the results showed that 7d could provide a feasible solution for the early diagnosis of AD under non-radioactive condition.

Fluorine labelling of therapeutic human tolerogenic dendritic cells for 19F-magnetic resonance imaging.

Tolerogenic dendritic cell (tolDC) therapies aim to restore self-tolerance in patients suffering from autoimmune diseases. Phase 1 clinical trials with tolDC have shown the feasibility and safety of this approach, but have also highlighted a lack of understanding of their distribution in vivo. Fluorine-19 magnetic resonance imaging (19F-MRI) promises an attractive cell tracking method because it allows for detection of 19F-labelled cells in a non-invasive and longitudinal manner. Here, we tested the suitability of nanoparticles containing 19F (19F-NP) for labelling of therapeutic human tolDC for detection by 19F-MRI. We found that tolDC readily endocytosed 19F-NP with acceptable effects on cell viability and yield. The MRI signal-to-noise ratios obtained are more than sufficient for detection of the administered tolDC dose (10 million cells) at the injection site in vivo, depending on the tissue depth and the rate of cell dispersal. Importantly, 19F-NP labelling did not revert tolDC into immunogenic DC, as confirmed by their low expression of typical mature DC surface markers (CD83, CD86), low secretion of pro-inflammatory IL-12p70, and low capacity to induce IFN-γ in allogeneic CD4+ T cells. In addition, the capacity of tolDC to secrete anti-inflammatory IL-10 was not diminished by 19F-NP labelling. We conclude that 19F-NP is a suitable imaging agent for tolDC. With currently available technologies, this imaging approach does not yet approach the sensitivity required to detect small numbers of migrating cells, but could have important utility for determining the accuracy of injecting tolDC into the desired target tissue and their efflux rate.

Aromatic Ring Fluorination Patterns Modulate Inhibitory Potency of Fluorophenylhydroxamates Complexed with Histone Deacetylase 6.

Bavarostat (EKZ-001) is a selective inhibitor of histone deacetylase 6 (HDAC6) that contains a meta-fluorophenylhydroxamate Zn2+-binding group. The recently determined crystal structure of its complex with HDAC6 from Danio rerio (zebrafish) revealed that the meta-fluoro substituent binds exclusively in an aromatic crevice defined by F583 and F643 rather than being oriented out toward solvent. To explore the binding of inhibitor C-F groups in this fluorophilic crevice, we now report a series of 10 simple fluorophenylhydroxamates bearing one or more fluorine atoms with different substitution patterns. Inhibitory potencies against human and zebrafish HDAC6 range widely from 121 to >30,000 nM. The best inhibitory potency is measured for meta-difluorophenylhydroxamate (5) with IC50 = 121 nM against human HDAC6; the worst inhibitory potencies are measured for ortho-fluorophenylhydroxamate (1) as well as fluorophenylhydroxamates 4, 7, 9, and 10, although there are some variations in activity trends against human and zebrafish HDAC6. These studies show that aromatic ring fluorination at the meta position(s) does not improve inhibitory activity against human HDAC6 relative to the nonfluorinated parent compound phenylhydroxamate (IC50 = 120 nM), but meta-fluorination does not seriously compromise inhibitory activity either. Crystal structures of selected zebrafish HDAC6-fluorophenylhydroxamate complexes reveal that the fluoroaromatic ring is uniformly accommodated in the F583-F643 aromatic crevice, so ring fluorination does not perturb the inhibitor binding conformation. However, hydroxamate-Zn2+ coordination is bidentate for some inhibitors and monodentate for others. These studies will inform design strategies underlying the design of 18F-labeled HDAC6 inhibitors intended for positron emission tomography.

Structural basis for product specificities of MLL family methyltransferases.

Human mixed-lineage leukemia (MLL) family methyltransferases methylate histone H3 lysine 4 to different methylation states (me1/me2/me3) with distinct functional outputs, but the mechanism underlying the different product specificities of MLL proteins remains unclear. Here, we develop methodologies to quantitatively measure the methylation rate difference between mono-, di-, and tri-methylation steps and demonstrate that MLL proteins possess distinct product specificities in the context of the minimum MLL-RBBP5-ASH2L complex. Comparative structural analyses of MLL complexes by X-ray crystal structures, fluorine-19 nuclear magnetic resonance, and molecular dynamics simulations reveal that the dynamics of two conserved tyrosine residues at the "F/Y (phenylalanine/tyrosine) switch" positions fine-tune the product specificity. The variation in the intramolecular interaction between SET-N and SET-C affects the F/Y switch dynamics, thus determining the product specificities of MLL proteins. These results indicate a modified F/Y switch rule applicable for most SET domain methyltransferases and implicate the functional divergence of MLL proteins.

Synthesis of [18F] fluorine-labeled K-2 derivatives as radiotracers for AMPA receptors.

INTRODUCTION: AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor) receptors play a central role in neurotransmission and neuronal function. A positron emission tomography (PET) tracer for AMPA receptors, [11C]K-2, was recently developed by us to visualize AMPA receptors in the living human brain. [11C]K-2 is a derivative of 4-[2-(phenylsulphonylamino)ethylthio]-2,6-difuluoro-phenoxyacetamide (PEPA), and is labeled with the radioactive isotope 11C, which has a short half-life. PET drugs are usually labeled with 18F because of its long half-life. Therefore, we screened and identified potential 18F-labeled PET drugs for AMPA receptors (AMPA-PET drugs), which could provide an image equivalent to that of [11C]K-2. METHODS: Derivatives of K-2 labeled with 18F were synthesized and administered to rats and PET imaging was performed. The transferability of each compound to the brain and its correlation with the PET image of [11C]K-2 were evaluated from the obtained PET images. Furthermore, the specific binding ability of promising compounds to the AMPA receptor was evaluated by the PET imaging of rats, which we specifically knocked down the expression of AMPA by the lentivirus-mediated introduction of short hairpin RNA (shRNA) targeted to subunits of the AMPA receptor (GluA1-A3). The specific binding ability was also evaluated through electrophysiological experiments with acute brain slices. RESULTS: Some of the synthesized 18F-labeled candidate compounds showed a distribution similar to that of K-2, with reasonable transferability to the brain. In addition, from the evaluation of the specific binding ability to the AMPA receptor, a promising structure of an 18F-labeled AMPA PET drug was identified. This study also revealed that the alkylation of the sulfonamide group of PEPA enhances brain transferability.

Estrogen deficiency aggravates fluorine ion-induced renal fibrosis via the TGF-ß1/Smad signaling pathway in rats.

To investigate the role and molecular mechanism of estrogen deficiency in fluorine ion (F-)-induced renal fibrosis, the models of F- exposure in ovary removed rats were established by drinking water with different doses of F- (0, 25, 50 and 100 mg/L) for 90 days. Results of H&E staining and BrdU labeled experiment showed that F- induced renal pathomorphological damage and inhibited cell proliferation. Further, Masson staining showed that F- induced renal glomerular and tubulointerstitial fibrosis. Meanwhile, renal fibrosis was confirmed by detecting the expression levels of collagen I, collagen III, collagen IV and fibronectin using immunofluorescence. In the state of estrogen deficiency, F--induced renal damage and fibrosis were aggravated. Moreover, the molecular mechanism of F--induced renal fibrosis was evaluated, and the results showed that F- induced TGF-ß1/Smad signaling pathway further dysregulation after ovariectomy, which manifested as the further up-regulated expression of TGF-ß1, Smad2, p-Smad2, Smad3 and p-Smad3, and further down-regulated of Smad7. Accompanied by renal damage and renal fibrosis, renal function was also disturbed, especially in ovariectomized rats. This study indicated that estrogen deficiency aggravated F--induced renal fibrosis via the TGF-ß1/Smad signaling pathway, leading to more serious renal dysfunction.

In Vivo Evaluation of 6 Analogs of 11C-ER176 as Candidate 18F-Labeled Radioligands for 18-kDa Translocator Protein.

Because of its excellent ratio of specific to nondisplaceable uptake, the radioligand 11C-ER176 can successfully image 18-kDa translocator protein (TSPO), a biomarker of inflammation, in the human brain and accurately quantify target density in homozygous low-affinity binders. Our laboratory sought to develop an 18F-labeled TSPO PET radioligand based on ER176 with the potential for broader distribution. This study used generic 11C labeling and in vivo performance in the monkey brain to select the most promising among 6 fluorine-containing analogs of ER176 for subsequent labeling with longer-lived 18F. Methods: Six fluorine-containing analogs of ER176-3 fluoro and 3 trifluoromethyl isomers-were synthesized and labeled by 11C methylation at the secondary amide group of the respective N-desmethyl precursor. PET imaging of the monkey brain was performed at baseline and after blockade by N-butan-2-yl-1-(2-chlorophenyl)-N-methylisoquinoline-3-carboxamide (PK11195). Uptake was quantified using radiometabolite-corrected arterial input function. The 6 candidate radioligands were ranked for performance on the basis of 2 in vivo criteria: the ratio of specific to nondisplaceable uptake (i.e., nondisplaceable binding potential [BPND]) and the time stability of total distribution volume (VT), an indirect measure of lack of radiometabolite accumulation in the brain. Results: Total TSPO binding was quantified as VT corrected for plasma free fraction (VT/fP) using Logan graphical analysis for all 6 radioligands. VT/fP was generally high at baseline (222 ± 178 mL·cm-3) and decreased by 70%-90% after preblocking with PK11195. BPND calculated using the Lassen plot was 9.6 ± 3.8; the o-fluoro radioligand exhibited the highest BPND (12.1), followed by the m-trifluoromethyl (11.7) and m-fluoro (8.1) radioligands. For all 6 radioligands, VT reached 90% of the terminal 120-min values by 70 min and remained relatively stable thereafter, with excellent identifiability (SEs < 5%), suggesting that no significant radiometabolites accumulated in the brain. Conclusion: All 6 radioligands had good BPND and good time stability of VT Among them, the o-fluoro, m-trifluoromethyl, and m-fluoro compounds were the 3 best candidates for development as radioligands with an 18F label.

Effects of different selenium sources on duodenum and jejunum tight junction network and growth performance of broilers in a model of fluorine-induced chronic oxidative stress.

The protective effects and underlying molecular mechanisms of sodium selenite (SS) and selenomethionine (SM) against chronic oxidative stress-induced duodenum and jejunum tight junction (TJ) network disturbance and growth inhibition of broilers were investigated in the current experiment. At the age of 1 d, 720 Lingnan Yellow broiler chicks were allocated to 4 experimental diets (with 6 replicates per diet and 30 birds per replicate) and offered either a control diet (fluorine [F] 23 mg/kg, control [CoN] group) or test diets (800 mg/kg F, high F [HF] group; 800 mg/kg F+0.15 mg selenium [Se]/kg as SS [SS group] or SM [SM group]) for 56 d. The results showed that HF group could induce chronic oxidative stress and subsequently increased (P < 0.05) proinflammatory cytokines levels of duodenum and jejunum in comparison with the CoN group. Increased proinflammatory cytokines levels of HF group promoted myosin light chain kinase (MLCK) transcription, thus leading to a decrease (P < 0.05) in TJ proteins expression of duodenum and jejunum when compared with the CoN group. A reduction of TJ proteins expression destroyed the TJ structures in the HF group, which in turn increased intestinal mucosal permeability of duodenum and jejunum and ultimately induced growth inhibition of broilers. Dietary Se supplementation could ameliorate HF-induced duodenum and jejunum TJ network impairment and growth retardation of broilers, potentially by increasing (P < 0.05) the glutathione peroxidase and thioredoxin reductase activities, reducing (P < 0.05) the reactive oxygen species and malondialdehyde levels, regulating the secretion of proinflammatory cytokines, and mediating the transcription level of MLCK in the duodenum and jejunum. Additionally, our data also suggested that the protective effects of SM were superior to those of SS. This study will provide a theoretical basis for developing SM into an efficient protective agent for intestinal mucosal barrier in poultry.

Why Is the Biodegradation of Polyfluorinated Compounds So Rare?

Thousands of heavily fluorinated chemicals are found in the environment, impact human and ecosystem health, and are relatively resistant to biological and chemical degradation. Their persistence in the environment is due to the inability of most microorganisms to biodegrade them. Only a very few examples of polyfluorinated compound biodegradation are known, and the reported rates are very low. This has been mostly attributed to the low chemical reactivity of the C-F bond. This Perspective goes beyond that explanation to highlight microbiological reasons why polyfluorinated compounds resist metabolism. The evolutionary and physiological impediments must be appreciated to better find, study, and harness microbes that degrade polyfluorinated compounds.

The Effects of Calcium, Magnesium, Phosphorus, Fluoride, and Lead on Bone Tissue.

Bones are metabolically active organs. Their reconstruction is crucial for the proper functioning of the skeletal system during bone growth and remodeling, fracture healing, and maintaining calcium-phosphorus homeostasis. The bone metabolism and tissue properties are influenced by trace elements that may act either indirectly through the regulation of macromineral metabolism, or directly by affecting osteoblast and osteoclast proliferation or activity, or through becoming part of the bone mineral matrix. This study analyzes the skeletal impact of macroelements (calcium, magnesium, phosphorus), microelements (fluorine), and heavy metals (lead), and discusses the concentration of each of these elements in the various bone tissues.

Phenotyping placental oxygenation in Lgals1 deficient mice using 19F MRI.

Placental hypoperfusion and hypoxia are key drivers in complications during fetal development such as fetal growth restriction and preeclampsia. In order to study the mechanisms of disease in mouse models, the development of quantitative biomarkers of placental hypoxia is a prerequisite. The goal of this exploratory study was to establish a technique to noninvasively characterize placental partial pressure of oxygen (PO2) in vivo in the Lgals1 (lectin, galactoside-binding, soluble, 1) deficient mouse model of preeclampsia using fluorine magnetic resonance imaging. We hypothesized a decrease in placental oxygenation in knockout mice. Wildtype and knockout animals received fluorescently labeled perfluoro-5-crown-15-ether nanoemulsion i.v. on day E14-15 during pregnancy. Placental PO2 was assessed via calibrated 19F MRI saturation recovery T1 mapping. A gas challenge with varying levels of oxygen in breathing air (30%, 60% and 100% O2) was used to validate that changes in oxygenation can be detected in freely breathing, anesthetized animals. At the end of the experiment, fluorophore-coupled lectin was injected i.v. to label the vasculature for histology. Differences in PO2 between breathing conditions and genotype were statistically analyzed with linear mixed-effects modeling. As expected, a significant increase in PO2 with increasing oxygen in breathing air was found. PO2 in Lgals1 knockout animals was decreased but this effect was only present at 30% oxygen in breathing air, not at 60% and 100%. Histological examinations showed crossing of the perfluorocarbon nanoemulsion to the fetal blood pool but the dominating contribution of 19F MR signal is estimated at > 70% from maternal plasma based on volume fraction measurements of previous studies. These results show for the first time that 19F MRI can characterize oxygenation in mouse models of placental malfunction.

In vivo detection of teriflunomide-derived fluorine signal during neuroinflammation using fluorine MR spectroscopy.

Background: Magnetic resonance imaging (MRI) is indispensable for diagnosing neurological conditions such as multiple sclerosis (MS). MRI also supports decisions regarding the choice of disease-modifying drugs (DMDs). Determining in vivo tissue concentrations of DMDs has the potential to become an essential clinical tool for therapeutic drug monitoring (TDM). The aim here was to examine the feasibility of fluorine-19 (19F) MR methods to detect the fluorinated DMD teriflunomide (TF) during normal and pathological conditions. Methods: We used 19F MR spectroscopy to detect TF in the experimental autoimmune encephalomyelitis (EAE) mouse model of multiple sclerosis (MS) in vivo. Prior to the in vivo investigations we characterized the MR properties of TF in vitro. We studied the impact of pH and protein binding as well as MR contrast agents. Results: We could detect TF in vivo and could follow the 19F MR signal over different time points of disease. We quantified TF concentrations in different tissues using HPLC/MS and showed a significant correlation between ex vivo TF levels in serum and the ex vivo19F MR signal. Conclusion: This study demonstrates the feasibility of 19F MR methods to detect TF during neuroinflammation in vivo. It also highlights the need for further technological developments in this field. The ultimate goal is to add 19F MR protocols to conventional 1H MRI protocols in clinical practice to guide therapy decisions.

A fluoride-responsive genetic circuit enables in vivo biofluorination in engineered Pseudomonas putida.

Fluorine is a key element in the synthesis of molecules broadly used in medicine, agriculture and materials. Addition of fluorine to organic structures represents a unique strategy for tuning molecular properties, yet this atom is rarely found in Nature and approaches to integrate fluorometabolites into the biochemistry of living cells are scarce. In this work, synthetic gene circuits for organofluorine biosynthesis are implemented in the platform bacterium Pseudomonas putida. By harnessing fluoride-responsive riboswitches and the orthogonal T7 RNA polymerase, biochemical reactions needed for in vivo biofluorination are wired to the presence of fluoride (i.e. circumventing the need of feeding expensive additives). Biosynthesis of fluoronucleotides and fluorosugars in engineered P. putida is demonstrated with mineral fluoride both as only fluorine source (i.e. substrate of the pathway) and as inducer of the synthetic circuit. This approach expands the chemical landscape of cell factories by providing alternative biosynthetic strategies towards fluorinated building-blocks.

Surface-enhanced Raman scattering sensing platform for detecting amyloid-ß peptide interaction with an aggregation inhibitor.

Soluble, small amyloid-ß oligomers (AßO) are recognized as significant contributors to the pathology of Alzheimer's disease (AD). Although drugs for treating AD symptoms have been approved, no therapy targeting amyloid-ß (Aß) capable of modifying the course of the disease is available. In an effort to develop a label-free method for screening new anti-AD therapeutic agents, we show the use of a surface-enhanced Raman scattering (SERS) active substrate for detecting the interactions between Aß peptides and spin-labeled fluorine (SLF), a peptide aggregation inhibitor. Changes in the peak positions and intensity ratios of two spectral peaks near 1600cm-1 and 2900cm-1 can be used to monitor the molecular interactions between SLF and Aß. This study demonstrates the potential of SERS spectroscopy for rapidly screening and identifying new anti-Aß therapeutic agents.

One-Step, Rapid, 18F-19F Isotopic Exchange Radiolabeling of Difluoro-dioxaborinins: Substituent Effect on Stability and In Vivo Applications.

The ß-diketone moiety is commonly present in many anticancer drugs, antibiotics, and natural products. We describe a general method for radiolabeling ß-diketone-bearing molecules with fluoride-18. Radiolabeling was carried out via 18F-19F isotopic exchange on nonradioactive difluoro-dioxaborinins, which were generated by minimally modifying the ß-diketone as a difluoroborate. Radiochemistry was one-step, rapid (<10 min), and high-yielding (>80%) and proceeded at room temperature to accommodate the half-life of F-18 (t1/2 = 110 min). High molar activities (7.4 Ci/µmol) were achieved with relatively low starting activities (16.4 mCi). It was found that substituents affected both the solvolytic stability and fluorescence properties of difluoro-dioxaborinins. An F-18 radiolabeled difluoro-dioxaborinin probe that was simultaneously fluorescent showed sufficient stability for in vivo positron emission tomography (PET)/fluorescence imaging in mice, rabbits, and patients. These findings will guide the design of probes with specific PET/fluorescence properties; the development of new PET/fluorescence dual-modality reporters; and accurate in vivo tracking of ß-diketone molecules.

Carbon-fluorine bond cleavage mediated by metalloenzymes.

Fluorochemicals are a widely distributed class of compounds and have been utilized across a wide range of industries for decades. Given the environmental toxicity and adverse health threats of some fluorochemicals, the development of new methods for their decomposition is significant to public health. However, the carbon-fluorine (C-F) bond is among the most chemically robust bonds; consequently, the degradation of fluorinated hydrocarbons is exceptionally difficult. Here, metalloenzymes that catalyze the cleavage of this chemically challenging bond are reviewed. These enzymes include histidine-ligated heme-dependent dehaloperoxidase and tyrosine hydroxylase, thiolate-ligated heme-dependent cytochrome P450, and four nonheme oxygenases, namely, tetrahydrobiopterin-dependent aromatic amino acid hydroxylase, 2-oxoglutarate-dependent hydroxylase, Rieske dioxygenase, and thiol dioxygenase. While much of the literature regarding the aforementioned enzymes highlights their ability to catalyze C-H bond activation and functionalization, in many cases, the C-F bond cleavage has been shown to occur on fluorinated substrates. A copper-dependent laccase-mediated system representing an unnatural radical defluorination approach is also described. Detailed discussions on the structure-function relationships and catalytic mechanisms provide insights into biocatalytic defluorination, which may inspire drug design considerations and environmental remediation of halogenated contaminants.