Stereoselective Formation and Metabolism of 20(S)‐Protopanaxadiol Ocotillol Type Epimers in Vivo and in Vitro

(20S,24S)‐epoxy‐dammarane‐3,12,25‐triol (24S‐epimer) and (20S,24R)‐epoxy‐ dammarane‐3,12,25‐triol (24R‐epimer), a pair of ocotillol type epimers, were identified as the main metabolites of 20(S)‐protopanaxadiol (PPD). The aim of this study was to systematically investigate the formation and metabolism of this pair of epimers in vivo and in vitro and to elucidate the isoforms of cytochrome P450 enzymes responsible for the stereoselective metabolism of both epimers. The result showed that 24S‐epimer was a more predominant ingredient in rat plasma after oral administration of PPD with higher area under the curve (AUC) values. Both the enzyme kinetic evaluations of the formation and elimination of 24S‐epimer and 24R‐epimer in rat liver microsomes (RLM) and human liver microsomes (HLM) indicated that 24S‐epimer had a higher formation rate and a lower oxygenation metabolism rate than 24R‐epimer, and the stereoselective differences were more obvious in HLM than in RLM. The chemical inhibition and recombinant human P450 isoforms assay showed that CYP3A4 was the predominant isoform responsible for the further metabolism of 24R‐epimer in HLM. The biliary excretion ratio of the 24S‐epimer glucuronide was more than 28‐fold higher than that of 24R‐epimer glucuronide after intravenous administration to rats, which also indicated 24S‐epimer was more preferential to be metabolized as the glucuronide conjugate than 24R‐epimer. Chirality 27:170–176, 2015. © 2014 Wiley Periodicals, Inc.     

Steady‐State Plasma Concentration of Donepezil Enantiomers and Its Stereoselective Metabolism and Transport In Vitro

The aim of the present study was to elucidate the differences in the plasma concentration of two enantiomers of donepezil in Chinese patients with Alzheimer's disease (AD) and investigate in vitro stereoselective metabolism and transport. Donepezil enantiomers were separated and determined by LC‐MS/MS using D5‐donepezil as an internal standard on a Sepax Chiralomix SB‐5 column. In vitro stereoselective metabolism and transport of donepezil were investigated in human liver microsomes and MDCKII‐MDR1 cell monolayer. Pre‐dose (Css‐min) plasma concentrations were determined in 52 patients. The mean plasma level of (R)‐donepezil was 14.94 ng/ml and that of (S)‐donepezil was 23.37 ng/ml. One patient's plasma concentration of (R)‐donepezil was higher than (S)‐donepezil and the ratio is 1.51. The mean plasma levels of (S)‐donepezil were found to be higher than those of (R)‐donepezil in 51 patients and the ratio of plasma (R)‐ to (S)‐donepezil varies from 0.34 to 0.85. In the in vitro microsomal system, (R)‐donepezil degraded faster than (S)‐donepezil. V_max of (R)‐donepezil was significantly higher than (S)‐donepezil. The P‐gp inhibition experiment shown that the P_app of the two enantiomers was higher than 200 and the efflux ratios were 1.11 and 0.99. The results of the P‐gp inhibition identification experiment showed IC50 values of 35.5 and 20.4 μM, respectively, for the two enantiomers. The results indicate that donepezil exhibits stereoselective hepatic metabolism that may explain the differences in the steady‐state plasma concentrations observed. Neither (R)‐ nor (S)‐donepezil was a P‐gp substance and the two enantiomers are highly permeable through the blood–brain barrier. Chirality 25:498–505, 2013. © 2013 Wiley Periodicals, Inc.     

Separation of Ofloxacin and Its Six Related Substances Enantiomers by Chiral Ligand‐Exchange Chromatography

A chiral ligand‐exchange high‐performance liquid chromatography method was developed for the enantioseparation of ofloxacin and its six related substances termed impurities A, B, C, D, E, and F. The separation was performed on a conventional C₁₈ column. Different organic modifiers, copper salts, amino acids, the ratio of Cu²⁺ to amino acid, pH of aqueous phase, and column temperature were optimized. The optimal mobile phase conditions were methanol‐water systems consisting of 5 mmol/L copper sulfate and 10 mmol/L L‐isoleucine (L‐Ile). Under such conditions, good enantioseparation of ofloxacin and impurities A, C, E, and F could be observed with resolutions (R_S) of 3.54, 1.97, 3.21, 3.50, and 2.12, respectively. On the relationship between the thermodynamic parameters and structures of analytes, the mechanism of chiral recognition was investigated. It was concluded that ofloxacin and impurities A, C, E, and F were all enthalpically driven enantioseparation and that low column temperature was beneficial to enantioseparation. Furthermore, the structure–separation relationship of these analytes is also discussed. Chirality 27:843–849, 2015. © 2015 Wiley Periodicals, Inc.     

Studies of Enantiomeric Degradation of the Triazole Fungicide Hexaconazole in Tomato,Cucumber, and Field Soil by Chiral Liquid Chromatography–Tandem Mass Spectrometry

Chiral pesticide enantiomers often show different bioactivity and toxicity; however, this property is usually ignored when evaluating their environmental and public health risks. Hexaconazole is a chiral fungicide used on a variety of crops for the control of many fungal diseases. This use provides opportunities for the pollution of food and soil. In this study, a sensitive and convenient chiral liquid chromatography coupled with tandem mass spectrometry (LC‐MS/MS) method was developed and validated for measuring hexaconazole enantiomers in tomato, cucumber, and soil. Separation was by a reversed‐phase Chiralcel OD‐RH column, under isocratic conditions using a mixture of acetonitrile‐2 mM ammonium acetate in water (60/40, v/v) as the mobile phase at a flow rate of 0.4 mL/min. Parameters including the matrix effect, linearity, precision, accuracy and stability were undertaken. Then the proposed method was successfully applied to investigate the possible enantioselective degradation of rac‐hexaconazole in plants (tomato and cucumber) and soil under field conditions. The degradation of the two enantiomers of hexaconazole proved to be enantioselective and dependent on the media: The (+)‐enantiomer showed a faster degradation in plants, while the (?)‐enantiomer dissipated faster than the (+)‐form in field soil, resulting in relative enrichment of the opposite enantiomer. The results of this work demonstrate that both the environmental media and environmental conditions influenced the direction and rate of enantioselective degradation of hexaconazole. Chirality 25:160–169, 2013. © 2013 Wiley Periodicals, Inc.     

Separation of Enantiomers by Inclusion Gas Chromatography: On the Influence of Water in the Molecular Complexation of Methyl 2‐Chloropropanoate Enantiomers and the Modified γ‐Cyclodextrin Lipodex‐E

A profound influence of water has previously been detected in the complexation of the enantiomers of methyl 2‐chloropropanoate (MCP) and the chiral selector octakis(3‐O‐butanoyl‐2,6‐di‐O‐pentyl)‐γ‐cyclodextrin (Lipodex‐E) in NMR and sensor experiments. We therefore investigated the retention behavior of MCP enantiomers on Lipodex‐E by gas chromatography (GC) under hydrous conditions. Addition of water to the N₂ carrier gas modestly reduced the retention factors k of the enantiomers, notably for the second eluted enantiomer (S)‐MCP. This resulted in an overall decrease of enantioselectivity ‐Δ_S,R(ΔG) in the presence of water. The effect was fully reversible. Consequently, for a conditioned column in the absence of residual water, the determined thermodynamic data, i.e. Δ_S,R(ΔH) = –12.64 ± 0.08 kJ mol^‐1 and Δ_S,R(ΔS) = –28.18 ± 0.23 J K^‐1 mol^‐1, refer to a true 1:1 complexation process devoid of hydrophobic hydration. Chirality 28:124–131, 2015. © 2015 Wiley Periodicals, Inc.     

Albumin Supplement Affects the Metabolism and Metabolism‐Related Drug–Drug Interaction of Fenoprofen Enantiomers

The influence of albumin towards the metabolism behavior of fenoprofen enantiomers and relevant drug–drug interaction was investigated in the present study. The metabolic behavior of fenoprofen enantiomers was compared in a phase II metabolic incubation system with and without bovine serum albumin (BSA). BSA supplement increased the binding affinity parameter (Km) of (R)‐fenoprofen towards human liver microsomes (HLMs) from 148.3 to 214.4 μM. In contrast, BSA supplement decreased the Km of (S)‐fenoprofen towards HLMs from 218.2 to 123.5 μM. For maximum reaction velocity (Vmax), the addition of BSA increased the Vmax of (R)‐fenoprofen from 1.3 to 1.6 nmol/min/mg protein. In the contrast, BSA supplement decreased the Vmax value from 3.3 to 1.5 nmol/min/mg protein. Andrographolide–fenoprofen interaction was used as an example to investigate the influence of BSA supplement towards fenoprofen‐relevant drug–drug interaction. The addition of 0.2% BSA in the incubation system significantly decreased the inhibition potential of andrographolide towards (R)‐fenoprofen metabolism (P < 0.001). Different from (R)‐fenoprofen, the addition of BSA significantly increased the inhibition potential of andrographolide towards the metabolism of (S)‐fenoprofen. BSA supplement also changed the inhibition kinetic type and parameter of andrographolide towards the metabolism of (S)‐fenoprofen. In conclusion, albumin supplement changes the metabolic behavior of fenoprofen enantiomers and the fenoprofen–andrographolide interaction. Chirality 27:436–440, 2015. © 2015 Wiley Periodicals, Inc.     

Gender‐dimorphic regulation of DJ1 and its interactions with metabolic proteins in streptozotocin‐induced diabetic rats

Regulation of DJ1 is associated with a number of human diseases. To determine the involvement of DJ1 in progression of diabetes in a gender‐dependent manner, we investigated its tissue‐specific expression in streptozotocin (STZ)‐induced diabetic male and female rats in this study. In animal experiments, females showed greater susceptibility towards developing diabetes because of lower insulin secretion and higher blood glucose levels as compared to male diabetic rats upon exposure to STZ. Immunoblotting confirmed sexually dimorphic regulation of DJ1 in various metabolic tissues such as the liver, pancreas and skeletal muscle. Immunofluorescence analysis revealed the location as well as reinforced the gender‐dependent expression of DJ1 in hepatic tissue. Co‐immunoprecipitation assay identified several interacting proteins with DJ1 whose functions were shown to be involved in various metabolic pathways viz. antioxidative and stress defence system, protein and methionine metabolism, nitrogen metabolism, urea metabolism, etc. Using GeneMANIA, a predictive web interface for gene functions, we showed for the first time that DJ1 may regulate T1DM via the JNK1 pathway, suggesting DJ1 interacts with other proteins from various metabolic pathways. We anticipate that the current data will provide insights into the aetiology of T1DM.     

Enhanced rates of herbicide metabolism in low herbicide‐dose selected resistant Lolium rigidum

Lolium rigidum is an obligately cross‐pollinated, genetically diverse species and an economically important herbicide resistance‐prone weed. Our previous work has demonstrated that recurrent selection of initially susceptible L. rigidum populations with low herbicide rates results in rapid herbicide resistance evolution. Here we report on the mechanisms endowing low‐dose‐selected diclofop‐methyl resistance in L. rigidum. Results showed that resistance was not due to target‐site ACCase mutations or overproduction, or differential herbicide leaf uptake and translocation. The in vivo de‐esterification of diclofop‐methyl into phytotoxic diclofop acid was rapid and similar in resistant versus susceptible populations. However, further metabolism of diclofop acid into non‐toxic metabolites was always faster in resistant plants than susceptible plants, resulting in up to 2.6‐fold lower level of diclofop acid in resistant plants. This corresponded well with up to twofold higher level of diclofop acid metabolites in resistant plants. The major polar metabolites of diclofop acid chromatographically resembled those of wheat, a naturally tolerant species. Clearly, recurrent selection at reduced herbicide rates selected for non‐target‐site‐based enhanced rates of herbicide metabolism, likely involving cytochrome P450 monooxygenases.     

Determination of metabolic resistance mechanisms in pyrethroid‐resistant and fipronil‐tolerant brown dog ticks

Rhipicephalus sanguineus (Latreille) (Ixodida: Ixodidae) is a three‐host dog tick found worldwide that is able to complete its' entire lifecycle indoors. Options for the management of R. sanguineus are limited and its' control relies largely on only a few acaricidal active ingredients. Previous studies have confirmed permethrin resistance and fipronil tolerance in R. sanguineus populations, commonly conferred by metabolic detoxification or target site mutations. Herein, five strains of permethrin‐resistant and three strains of fipronil‐tolerant ticks were evaluated for metabolic resistance using synergists to block metabolic enzymes. Synergist studies were completed with triphenyl phosphate (TPP) for esterase inhibition, piperonyl butoxide (PBO) for cytochrome P450 inhibition, and diethyl maleate (DEM) for glutathione‐S‐transferase inhibition. Additionally, increased esterase activity was confirmed using gel electrophoresis. The most important metabolic detoxification mechanism in permethrin‐resistant ticks was increased esterase activity, followed by increased cytochrome P450 activity. The inhibition of metabolic enzymes did not have a marked impact on fipronil‐tolerant tick strains.     

Evaluation of Tetrahydropalmatine Enantiomers on the Activity of Five Cytochrome P450 Isozymes in Rats Using a Liquid Chromatography / Mass Spectrometric Method and a Cocktail Approach

The aim was to evaluate the effects of tetrahydropalmatine (THP) enantiomers on the activity of five cytochrome P450 (CYP450) isozymes in vivo. A liquid chromatography / mass spectrometric (LC‐MS) method was developed for simultaneous determination of five specific probe substrates including metoprolol (2D6), caffeine (1A2), dapsone (3A4), chlorzoxazone (2E1), and tolbutamide (2C9) in rat plasma. Analytes were separated with the mobile phase consisting of 0.1% acetic acid aqueous solution and acetonitrile in a gradient elution. The mass spectrometric detection via selected ion monitoring (SIM) was operated in both positive ion mode (for metoprolol m/z 268, caffeine m/z 195, and dapsone m/z 249) and negative ion mode (for chlorzoxazone m/z 168 and tolbutamide m/z 269) in the same run. Linear correlation was obtained (r² > 0.99) over the concentration range of 0.050–25.0 µg/mL for caffeine and dapsone, 0.025–10.0 µg/mL for metoprolol, 0.050–50.0 µg/mL for chlorzoxazone, and 0.25–100.0 µg/mL for tolbutamide. Intra‐ and interday precision were less than 12.09%. The matrix effect ranged from 87.50% to 109.25% and the absolute recoveries were greater than 70%. The method was successfully applied to evaluate the effect of THP enantiomers on the activity of CYP450 isozymes by a cocktail approach. The pharmacokinetic results of five probe drugs indicated that there were stereoselective differences between the two THP enantiomers, i.e., d‐THP had the potential to inhibit the activities of CYP2D6 and CYP1A2 isozymes, while l‐THP inhibited CYP1A2 isozyme and induced CYP3A4 and CYP2C9 isozymes. Chirality 27:551–556, 2015. © 2015 Wiley Periodicals, Inc.     

The cytochrome P450 2D‐mediated formation of serotonin from 5‐methoxytryptamine in the brain in vivo: a microdialysis study

The cytochrome P450 2D (CYP2D) mediates synthesis of serotonin from 5‐methoxytryptamine (5‐MT), shown in vitro for cDNA‐expressed CYP2D‐isoforms and liver and brain microsomes. We aimed to demonstrate this synthesis in the brain in vivo. We measured serotonin tissue content in brain regions after 5‐MT injection into the raphe nuclei (Model‐A), and its extracellular concentration in rat frontal cortex and striatum using an in vivo microdialysis (Model‐B) in male Wistar rats. Naïve rats served as control animals. 5‐MT injection into the raphe nuclei of PCPA‐(tryptophan hydroxylase inhibitor)‐pretreated rats increased the tissue concentration of serotonin (from 40 to 90% of the control value, respectively, in the striatum), while the CYP2D inhibitor quinine diminished serotonin level in some brain structures of those animals (Model‐A). 5‐MT given locally through a microdialysis probe markedly increased extracellular serotonin concentration in the frontal cortex and striatum (to 800 and 1000% of the basal level, respectively) and changed dopamine concentration (Model‐B). Quinine alone had no effect on serotonin concentration; however, given jointly with 5‐MT, it prevented the 5‐MT‐induced increase in cortical serotonin in naïve rats and in striatal serotonin in PCPA‐treated animals. These results indicate that the CYP2D‐catalyzed alternative pathway of serotonin synthesis from 5‐MT is relevant in the brain in vivo, and set a new target for the action of psychotropics.

     

Functional studies of N‐terminally modified CYP2J2 epoxygenase in model lipid bilayers

CYP2J2 epoxygenase is a membrane bound cytochrome P450 that converts omega‐3 and omega‐6 fatty acids into physiologically active epoxides. In this work, we present a comprehensive comparison of the effects of N‐terminal modifications on the properties of CYP2J2 with respect to the activity of the protein in model lipid bilayers using Nanodiscs. We demonstrate that the complete truncation of the N‐terminus changes the association of this protein with the E.coli membrane but does not disrupt incorporation in the lipid bilayers of Nanodiscs. Notably, the introduction of silent mutations at the N‐terminus was used to express full length CYP2J2 in E. coli while maintaining wild‐type functionality. We further show that lipid bilayers are essential for the productive use of NADPH for ebastine hydroxylation by CYP2J2. Taken together, it was determined that the presence of the N‐terminus is not as critical as the presence of a membrane environment for efficient electron transfer from cytochrome P450 reductase to CYP2J2 for ebastine hydroxylation in Nanodiscs. This suggests that adopting the native‐like conformation of CYP2J2 and cytochrome P450 reductase in lipid bilayers is essential for effective use of reducing equivalents from NADPH for ebastine hydroxylation.     

Metabolic switching of astringent and beneficial triterpenoid saponins in soybean is achieved by a loss‐of‐function mutation in cytochrome P450 72A69

Triterpenoid saponins are major components of secondary metabolites in soybean seeds and are divided into two groups: group A saponins, and 2,3‐dihydro‐2,5‐dihydroxy‐6‐methyl‐4H‐pyran‐4‐one (DDMP) saponins. The aglycone moiety of group A saponins consists of soyasapogenol A (SA), which is an oxidized β‐amyrin product, and the aglycone moiety of the DDMP saponins consists of soyasapogenol B (SB). Group A saponins produce a bitter and astringent aftertaste in soy products, whereas DDMP saponins have known health benefits for humans. We completed map‐based cloning and characterization of the gene Sg‐5, which is responsible for SA biosynthesis. The naturally occurring sg‐5 mutant lacks group A saponins and has a loss‐of‐function mutation (L164*) in Glyma15g39090, which encodes the cytochrome P450 enzyme, CYP72A69. An enzyme assay indicated the hydroxylase activity of recombinant CYP72A69 against SB, which also suggested the production of SA. Additionally, induced Glyma15g39090 mutants (R44* or S348P) lacked group A saponins similar to the sg‐5 mutant, indicating that Glyma15g39090 corresponds to Sg‐5. Endogenous levels of DDMP saponins were higher in the sg‐5 mutant than in the wild‐type lines due to the loss of the enzyme activity that converts SB to SA. Interestingly, the genomes of palaeopolyploid soybean and the closely related common bean carry multiple Sg‐5 paralogs in a genomic region syntenic to the soybean Sg‐5 region. However, SA did not accumulate in common bean samples, suggesting that Sg‐5 activity evolved after gene duplication event(s). Our results demonstrate that metabolic switching of undesirable saponins with beneficial saponins can be achieved in soybean by disabling Sg‐5.     

Stereoselective Degradation of alpha‐Cypermethrin and Its Enantiomers in Rat Liver Microsomes

Alpha‐cypermethrin (α‐CP), [(RS)‐a‐cyano‐3‐phenoxy benzyl (1RS)‐cis‐3‐(2, 2‐dichlorovinyl)‐2, 2‐dimethylcyclopropanecarboxylate], comprises a diastereoisomer pair of cypermethrin, which are (+)‐(1R‐cis‐αS)–CP (insecticidal) and (?)‐(1S‐cis‐αR)–CP (inactive). In this experiment, the stereoselective degradation of α‐CP was investigated in rat liver microsomes by high‐performance liquid chromatography (HPLC) with a cellulose‐tris‐ (3, 5‐dimethylphenylcarbamate)‐based chiral stationary phase. The results revealed that the degradation of (?)‐(1S‐cis‐αR)‐CP was much faster than (+)‐(1R‐cis‐αS)‐CP both in enantiomer monomers and rac‐α‐CP. As for the enzyme kinetic parameters, there were some variances between rac‐α‐CP and the enantiomer monomers. In rac‐α‐CP, the V_max and CL_int of (+)‐(1R‐cis‐αS)–CP (5105.22 ± 326.26 nM/min/mg protein and 189.64 mL/min/mg protein) were about one‐half of those of (?)‐(1S‐cis‐αR)–CP (9308.57 ± 772.24 nM/min/mg protein and 352.19 mL/min/mg protein), while the K_m of the two α‐CP enantiomers were similar. However, in the enantiomer monomers of α‐CP, the V_max and K_m of (+)‐(1R‐cis‐αS) ‐CP were 2‐fold and 5‐fold of (?)‐(1S‐cis‐αR)‐CP, respectively, which showed a significant difference with rac‐α‐CP. The CL_int of (+)‐(1R‐cis‐αS)–CP (140.97 mL/min/mg protein) was still about one‐half of (?)‐(1S‐cis‐αR)–CP (325.72 mL/min/mg protein) in enantiomer monomers. The interaction of enantiomers of α‐CP in rat liver microsomes was researched and the results showed that there were different interactions between the IC₅₀ of (?)‐ to (+)‐(1R‐cis‐αS)‐CP and (+)‐ to (?)‐(1S‐cis‐αR)‐CP(IC_50(?)/(+) / IC_50(+)/(?) = 0.61). Chirality 28:58–64, 2016. © 2015 Wiley Periodicals, Inc.     

Identification of different alkane hydroxylase systems in Rhodococcus ruber strain SP2B,an hexane‐degrading actinomycete

Aims: To investigate the alkane‐hydroxylating system of isolate SP2B, closely related to Rhodococcus ruber DSM 43338^T and uncharacterized so far for its alkane degradation genes. Methods and Results: Although isolate SP2B and reference strain can grow on by‐products from hexane degradation, the type strain R. ruber was unable, unlike SP2B isolate, to use short‐chain alkanes, as assessed by gas chromatography. Using PCR with specific or degenerated primers, inverse PCR and Southern blot, two alkane hydroxylase encoding genes (alkB) were detected in both bacteria, which is in agreement with their alkane range. The first AlkB was related to Rhodococcus AlkB7 enzymes and contains a nonbulky residue at a specific position, suggesting it might be involved in medium‐ and long‐chain alkane oxidation. The second partial alkB gene potentially belongs to alkB5‐type, which was found in bacteria unable to use hexane. Moreover, a partial P450 cytochrome alkane hydroxylase, thought to be responsible for the hexane degradation, was detected only in the isolated strain. Conclusions: Rhodococcus ruber SP2B should prove to be a promising candidate for bioremediation studies of contaminated sites because of its large degradation range of alkanes. Significance and Impact of the Study: This is the first thorough study on R.ruber alkane degradation systems.     

Integrating cell‐free biosyntheses of heme prosthetic group and apoenzyme for the synthesis of functional P450 monooxygenase

Harnessing the isolated protein synthesis machinery, cell‐free protein synthesis reproduces the cellular process of decoding genetic information in artificially controlled environments. More often than not, however, generation of functional proteins requires more than simple translation of genetic sequences. For instance, many of the industrially important enzymes require non‐protein prosthetic groups for biological activity. Herein, we report the complete cell‐free biogenesis of a heme prosthetic group and its integration with concurrent apoenzyme synthesis for the production of functional P450 monooxygenase. Step reactions required for the syntheses of apoenzyme and the prosthetic group have been designed so that these two separate pathways take place in the same reaction mixture, being insulated from each other. Combined pathways for the synthesis of functional P450 monooxygenase were then further integrated with in situ assay reactions to enable real‐time measurement of enzymatic activity during its synthesis. Biotechnol. Bioeng. 2013; 110: 1193–1200. © 2012 Wiley Periodicals, Inc.     

The Relationship between Health‐Related Quality of Life and Weight Loss

Objective: This is a report of health‐related quality of life (HRQOL) changes in obese patients completing at least 1 year of outpatient treatment in a weight reduction program combining phentermine‐fenfluramine and dietary counseling. Research Methods and Procedures: Participants were 141 women (87.6%) and 20 men (12.4%) who had an average body mass index at intake of 41.1 kg/m² (SD = 7.0, range = 29.5 to 67.0 kg/m²) and an average age of 44.9 years (SD = 9.3, range = 23 to 65 years). HRQOL was assessed at intake and at 1‐year follow‐up using the Impact of Weight on Quality of Life (IWQOL)‐Lite questionnaire. The relationship between HRQOL changes and weight loss was examined using Pearson correlations. Clinically meaningful change in HRQOL was defined as a 1.96 SEM reduction in IWQOL‐Lite total score. Results: On average, participants lost 20.2 kg or 17.6% of their weight over the 1‐year period. Of the participants, 15.5% lost <10% of their weight, 24.2% lost 10% to 14.9%, 23.6% lost 15% to 19.9%, and 36.6% lost 20% or more. All five IWQOL‐Lite scales and total score showed statistically significant improvement over the 1‐year period. Changes in IWQOL‐Lite scores from intake to 1 year showed statistically significant correlations with percentage of weight loss for all subscales and total score. Subscale correlations with weight loss ranged from 0.166 (Public Distress) to 0.396 (Physical Function) and was 0.370 for the total score. Forty‐four percent of participants losing <10% met the criterion of clinically meaningful change, compared with 51.3% losing 10% to 14.9%, 55.3% losing 15% to 19.95%, and 76.3% losing >20%. For total score and for three of the five IWQOL‐Lite scales (Physical Function, Self‐Esteem, and Sexual Life), the relationship between weight loss and clinically meaningful change was linear and was significant at p < 0.05. Physical Function and Self‐Esteem were most strongly affected by weight loss. Discussion: HRQOL changes, as measured by an obesity‐specific instrument (IWQOL‐Lite), are strongly related to weight reduction.