Functional Measurement of CYP2C9 and CYP3A4 Allelic Polymorphism on Sildenafil Metabolism

The effect of gene polymorphism on ticagrelor metabolism: an in vitro study of 22 CYP3A4 variants in Chinese Han population

Background

Ticagrelor is a novel oral antiplatelet agent which can selectively inhibit P2Y12 receptor. Bleeding and dyspnea are common adverse reactions of ticagrelor in clinic. The side effects of ticagrelor are correlated with the plasma concentration of ticagrelor.

Objective

This study aimed to evaluate the catalytic characteristics of 22 CYP3A4 alleles identified in the Chinese Han population on the metabolism of ticagrelor in vitro, focusing on the effect of CYP3A4 polymorphism on ticagrelor metabolism.

Methods

In this study, insect cells were used to express 22 CYP3A4 variants, which were then incubated with 1-50 µM ticagrelor at 37 °C for 30 minutes to obtain the metabolite (AR-C124910XX). AR-C124910XX was detected by UHPLC-MS/MS to calculate the kinetic parameters, including Km, Vmax and CLint.

Results

Compared to the wild-type, most CYP3A4 alleles exhibited significant differences in intrinsic clearance. The intrinsic clearance of CYP3A4*11, *18 and *33 was much higher than that of wild-type; four variants exhibited similar intrinsic clearance values as the wild-type enzyme; The remaining 14 variants showed significantly reduced intrinsic clearance values, ranging from 1.48% to 75.11% of the wild-type; CYP3A4*30 displayed weak or no activity.

Conclusion

This study conducted a comprehensive assessment of the effect of CYP3A4 variants on ticagrelor's metabolism. The results suggested that there is allele-specific activity towards ticagrelor in vitro. These findings can provide some insights and predictions for treatment strategies and risk assessments associated with ticagrelor in clinical practice.

Functional assessment of CYP3A4 and CYP2C19 genetic polymorphisms on the metabolism of clothianidin invitro

Clothianidin, classified as a second-generation neonicotinoid, has achieved extensive application due to its high efficacy against insect pests. This broad-spectrum usage has resulted in its frequent detection in environmental surveys. CYP2C19 and CYP3A4 are crucial for converting clothianidin to desmethyl-clothianidin (dm-clothianidin). The expression of these CYP450s can be significantly influenced by genetic polymorphisms. The objective of our research was to examine the catalytic effects of 27 CYP3A4 variants and 31 CYP2C19 variants on the metabolism of clothianidin within recombinant insect microsomes. These variants were assessed through a well-established incubation procedure. In addition, the concentration of its metabolite dm-clothianidin was quantified by employing an ultra performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS). Lastly, the kinetic parameters of these CYP3A4 and CYP2C19 variants were calculated by applying Michaelis-Menten kinetic analysis to fit the data. The observed changes in enzyme activity were related to the metabolic transformation of clothianidin to dm-clothianidin. In the CYP2C19 metabolic pathway, one variant (CYP2C19.23) showed no notable change in intrinsic clearance (CLint), four variants (CYP2C19.29, .30, .31 and L16F) demonstrated a marked increase in CLint (110.86-183.46 %), and the remaining 25 variants exhibited a considerable decrease in CLint (26.38-89.79 %), with a maximum decrease of 73.62 % (CYP2C19.6). In the CYP3A4 metabolic pathway, 26 variants demonstrated significantly reduced CLint (10.54-52.52 %), with a maximum decrease of 89.46 % (CYP3A4.20). Our results suggested that most variants of CYP3A4 and CYP2C19 significantly altered the enzymatic activities associated with clothianidin metabolism to various degrees. This study provides new insights into assessing the metabolic behavior of pesticides and delivers crucial data that can guide clinical detoxification strategies.

Differential inhibition of sildenafil and macitentan on saxagliptin metabolism

The development of diabetes mellitus (DM) is generally accompanied by erectile dysfunction (ED) and pulmonary arterial hypertension (PAH), which increases the use of combination drug therapy and the risk of drug-drug interactions. Saxagliptin for the treatment of DM, sildenafil for the treatment of ED and PAH, and macitentan for the treatment of PAH are all substrates of CYP3A4, which indicates their potential involvement in drug-drug interactions. Therefore, we investigated potential pharmacokinetic interactions between saxagliptin and sildenafil/macitentan. We investigated this speculation both in vitro and in vivo, and explored the underlying mechanism using in vitro hepatic metabolic models and molecular docking assays. The results showed that sildenafil substantially inhibited the metabolism of saxagliptin by occupying the catalytic site of CYP3A4 in a competitive manner, leading to the alterations in the pharmacokinetic properties of saxagliptin in terms of increased maximum plasma concentration (Cmax), area under the plasma concentration-time curve from time 0 to 24 h (AUC(0-t)), area under the plasma concentration-time curve from time 0 extrapolated to infinite time (AUC(0-∞)), decreased clearance rate (CLz/F), and prolonged terminal half-life (t1/2). In contrast, a slight inhibition was observed in saxagliptin metabolism when concomitantly used with macitentan, as no pharmacokinetic parameters were altered, except for CLz/F. Thus, dosage adjustment of saxagliptin may be required in combination with sildenafil to achieve safe therapeutic plasma concentrations and reduce the risk of potential toxicity, but it is not necessary for co-administration with macitentan.

Functional evaluation of CYP2C19 and CYP3A4 gene polymorphism on ibuprofen metabolism

AIM

Ibuprofen is the most commonly used analgesic. CYP polymorphisms are mainly responsible for the differences in drug metabolism among individuals. Variations in the ability of populations to metabolize ibuprofen can lead to drug exposure events. The aim of this study was to evaluate the effects of CYP2C19 and CYP3A4 polymorphisms on ibuprofen metabolism in a Chinese population.

METHODS

First, 31 CYP2C19 and 12 CYP3A4 microsomal enzymes were identified using an insect expression system. Then, variants were evaluated using a mature incubation system. Moreover, ibuprofen metabolite content was determined via ultra-performance liquid chromatography-tandem mass spectrometry analysis. Finally, kinetic parameters of CYP2C19 and CYP3A4 genotypes were determined via Michaelis-Menten curve fitting.

RESULTS

Most variants exhibited significantly altered intrinsic clearance compared to the wild type. In the CYP2C19 metabolic pathway, seven variants exhibited no significant alterations in intrinsic clearance (CLint), six variants exhibited significantly high CLint (121-291%), and the remaining 15 variants exhibited substantially reduced CLint (1-71%). In the CYP3A4 metabolic pathway, CYP3A4*30 was not detected in the metabolite content due to the absence of activity, and 10 variants exhibited significantly reduced CLint.

CONCLUSION

To the best of our knowledge, this is the first study to assess the kinetic characteristics of 31 CYP2C19 and 12 CYP3A4 genotypes on ibuprofen metabolism. However, further studies are needed on poor metabolizers as they are more susceptible to drug exposure. Our findings suggest that the kinetic characteristics in combination with artificial intelligence to predict the toxicity of ibuprofen and reduce any adverse drug reactions.

Enzymatic activity of 38 CYP2C9 genotypes on ibuprofen

BACKGROUND AND OBJECTIVE

Ibuprofen, a common non-steroidal anti-inflammatory drug, is used clinically for pain relief and antipyretic treatment worldwide. However, regular or long-term use of ibuprofen may lead to a series of adverse reactions, including gastrointestinal bleeding, hypertension and kidney injury. Previous studies have shown that CYP2C9 gene polymorphism plays an important role in the elimination of various drugs, which leads to the variation in drug efficacy. This study aimed to evaluate the effect of 38 CYP2C9 genotypes on ibuprofen metabolism.

METHODS

Thirty-eight recombinant human CYP2C9 microsomal enzymes were obtained using a frugiperda 21 insect expression system according to a previously described method. Assessment of the catalytic function of these variants was completed via a mature incubation system: 5 pmol CYP2C9*1 and 38 CYP2C9 variants recombinant human microsomes, 5 μL cytochrome B5, ibuprofen (5-1000 μM), and Tris-HCl buffer (pH 7.4). The ibuprofen metabolite contents were determined using HPLC analysis. HPLC analysis included a UV detector, Plus-C18 column, and mobile phase [50% acetonitrile and 50% water (containing 0.05% trifluoroacetic acid)]. The kinetic parameters of the CYP2C9 genotypes were obtained by Michaelis-Menten curve fitting.

RESULTS

The intrinsic clearance (CL_int) of eight variants was not significantly different from CYP2C9*1; four CYP2C9 variants (CYP2C9*38, *44, *53 and *59) showed significantly higher CL_int (increase by 35%-230%) than that of the wild-type; the remaining twenty-six variants exhibited significantly reduced CL_int (reduced by 30%-99%) compared to that of the wild-type.

CONCLUSION

This is the first systematic evaluation of the catalytic characteristics of 38 CYP2C9 genotypes involved ibuprofen metabolism. Our results provide a corresponding supplement to studies on CYP2C9 gene polymorphisms and kinetic characteristics of different variants. We need to focus on poor metabolizers (PMs) with severely abnormal metabolic functions, because they are more susceptible to drug exposure.

Cluster headache polygenetic risk and known functional variants of CYP3A4 are not associated with treatment response

BACKGROUND AND PURPOSE

The response to cluster headache treatments has a high interindividual variation. To date, treatment response has only been assessed by a candidate gene approach and no investigations into metabolic pathways have been performed. Our aim was to investigate the association between the polygenetic risk of cluster headache and treatment response to first-line cluster headache treatments as well as known functional variants of CYP3A4 and the response to verapamil. Further, it was aimed to replicate previous single nucleotide polymorphisms found to be associated with treatment response in cluster headache and/or migraine.

METHODS

In, 508 cluster headache patients diagnosed according to the International Classification of Headache Disorders were genotyped and participated in a semi-structured interview to evaluate treatment response. Polygenetic risk scores were calculated by the effect retrieved from a meta-analysis of the latest two genome-wide association studies on cluster headache.

RESULTS

Inferior treatment response to oxygen, triptans and verapamil is associated with chronicity of cluster headache were confirmed but no evidence was found that a response could be predicted by a high genetic risk of cluster headache. Likewise, verapamil response was not associated with functional variants of CYP3A4. No support of the genetic variants previously reported to be associated with treatment response to triptans or verapamil was found.

CONCLUSION

The clinically relevant variation in treatment response for cluster headache was not influenced by genetic factors in the present study.

Chitosan Nanoparticles Alleviated the Adverse Effects of Sildenafil on the Oxidative Stress Markers and Antioxidant Enzyme Activities in Rats

Sildenafil (SF) is widely used for erectile dysfunction and other conditions, though with limitations regarding oral absorption and adverse effects. Despite nanotechnological improvements, the effect of nanocarriers on SF hepatotoxicity has not been documented to date. This study aimed at assessing the impact of chitosan nanoparticles either uncoated (CS NPs) or Tween 80-coated (T-CS NPs) on the effects of SF on oxidative stress markers and antioxidant enzyme activities in rats. Test SF-CS NPs prepared by ionic gelation were uniform positively charged nanospheres (diameter 178-215 nm). SF was administered intraperitoneally to male rats (1.5 mg/kg body weight) in free or nanoencapsulated forms as SF-CS NPs and T-SF-CS NPs for 3 weeks. Free SF significantly suppressed the activity of the antioxidant enzymes glutathione S-transferase (GST), glutathione peroxidase (GPx), glutathione reductase (GR), catalase (CAT), and superoxide dismutase (SOD), as well as the levels of glutathione (GSH) and thiobarbituric acid reactive substances (TBARS) as in an indirect measure of free radicals. Interestingly, SF-CS NPs and T-SF-CS-NPs treatments significantly attenuated the inhibitory effects of SF on the activity of these enzymes whereas, GST activity was inhibited. Moreover, the protein expression of GST was downregulated upon treatment of rats with free SF, SF-CS-NPs, and T-SF CS-NPs. In contrast, the activity and protein expression of GPx was induced by SF-CS NPs and T-SF-CS-NPs treatments. The histopathological study showed that SF induced multiple adverse effects on the rat liver architecture which were markedly suppressed particularly by T-SF-CS NPs. In conclusion, chitosan nanoencapsulation of SF counteracted the adverse effects of SF on the activity of antioxidant enzymes and liver architecture. Findings might have significant implications in improving the safety and efficacy of SF treatment of the widely expanding disease conditions.

Species Difference in the Metabolism of Mulberrin in Vitro and Its Inhibitory Effect on Cytochrome P450 and UDP-Glucuronosyltransferase Enzymes

This study aimed to evaluate the interspecies difference in metabolism of mulberrin and examine the interaction between mulberrin and CYP enzymes or recombinant human uridine 5'-diphosphate (UDP)-glucuronosyltransferase (UGT) enzymes. Liver microsomes from human (HLMs), Beagle dog (DLMs), minipig (PLMs), monkey (MLMs), rabbit (RLMs), rat (RAMs), and mouse (MIMs) were used to investigate metabolic diversity among different species. Additionally, recombinant human supersomes were used to confirm that metabolic enzymes are involved in the biotransformation of mulberrin. We also evaluated the influence of mulberrin on protein expression by Western blot analysis. Mulberrin metabolism showed significant interspecies differences. We found four and two metabolites in phase I and II reaction systems, respectively. In phase I metabolism profiles of mulberrin for HLMs, PLMs and MLMs conformed to the classic Michaelis-Menten kinetics, RAMs and MIMs followed biphasic kinetics; phase II reaction of mulberrin in HLMs, DLMs, PLMs, MLMs, RLMs, RAMs and MIMs followed biphasic kinetics. UGT1A1 were the major CYP isoforms responsible for the metabolism of mulberrin. Mulberrin showed potent inhibitory effects against CYP3A4, CYP2C9, CYP2E1, UGT1A1, UGT1A3 and UGT2B7 with IC₅₀ values of 54.21, 9.93, 39.12, 3.84, 2.01, 16.36 µM, respectively. According to Western blot analysis, mulberrin can upregulate the protein expression of CYP2C19, and downregulate the expression levels of CYP3A5 and CYP2C9 in HepG2 cells as concentration increased. The interspecies comparisons can help find other species with metabolic pathways similar to those in humans for future in vivo studies.

Case Report: Bosentan and Sildenafil Exposure in Human Milk - A Contribution From the ConcePTION Project

Introduction: Quantitative information on disposition of maternal medicines in human milk remains a major knowledge gap. This case report presents the clinical and pharmacokinetic data of a single mother-infant pair exposed to bosentan and sildenafil for the treatment of pulmonary arterial hypertension (PAH) during lactation.

Case presentation: A 43-year old mother was treated with sildenafil (20 mg, 3x/day) and bosentan (125 mg, 2x/day) for PAH. Her 21-months old infant received breastfeeding in combination with adequate complementary foods. Milk samples were collected over 24 h, at day 637 and 651 after delivery. The observed average steady-state concentrations of sildenafil (2.84 μg/L) and bosentan (49.0 μg/L) in human milk were low. The Daily Infant Dosage ingested by the nursing infant through human milk was 0.02 μg/kg/day for sildenafil and 0.29 μg/kg/day for bosentan at day 637, and 0.03 μg/kg/day and 0.60 μg/kg/day at day 651. The Relative Infant Dose calculated for an exclusively breastfed infant with an estimated milk intake of 150 ml/kg/day, was 0.06% for sildenafil and 0.24% for bosentan. General health outcome of the infant, reported by the mother, was uneventful until the sampling days.

Conclusion: Low medicine concentrations were found in human milk expressed 21 months after delivery after maternal intake of 20 mg sildenafil three times daily and 125 mg bosentan twice daily. General health of the nursing infant until sampling was reported as optimal by the mother.

Genomewide Association Study of Simvastatin Pharmacokinetics

We investigated genetic determinants of single-dose simvastatin pharmacokinetics in a prospective study of 170 subjects and a retrospective cohort of 59 healthy volunteers. In a microarray-based genomewide association study with the prospective data, the SLCO1B1 c.521T>C (p.Val174Ala, rs4149056) single nucleotide variation showed the strongest, genomewide significant association with the area under the plasma simvastatin acid concentration-time curve (AUC; P = 6.0 × 10^-10 ). Meta-analysis with the retrospective cohort strengthened the association (P = 1.6 × 10^-17 ). In a stepwise linear regression candidate gene analysis among all 229 participants, SLCO1B1 c.521T>C (P = 1.9 × 10^-13 ) and CYP3A4 c.664T>C (p.Ser222Pro, rs55785340, CYP3A4*2, P = 0.023) were associated with increased simvastatin acid AUC. Moreover, the SLCO1B1 c.463C>A (p.Pro155Thr, rs11045819, P = 7.2 × 10^-6 ) and c.1929A>C (p.Leu643Phe, rs34671512, P = 5.3 × 10^-4 ) variants associated with decreased simvastatin acid AUC. Based on these results and the literature, we classified the volunteers into genotype-predicted OATP1B1 and CYP3A4 phenotype groups. Compared with the normal OATP1B1 function group, simvastatin acid AUC was 273% larger in the poor (90% confidence interval (CI), 137%, 488%; P = 3.1 × 10^-6 ), 40% larger in the decreased (90% CI, 8%, 83%; P = 0.036), and 67% smaller in the highly increased function group (90% CI, 46%, 80%; P = 2.4 × 10^-4 ). Intermediate CYP3A4 metabolizers (i.e., heterozygous carriers of either CYP3A4*2 or CYP3A4*22 (rs35599367)), had 87% (90% CI, 39%, 152%, P = 6.4 × 10^-4 ) larger simvastatin acid AUC than normal metabolizers. These data suggest that in addition to no function SLCO1B1 variants, increased function SLCO1B1 variants and reduced function CYP3A4 variants may affect the pharmacokinetics, efficacy, and safety of simvastatin. Care is warranted if simvastatin is prescribed to patients carrying decreased function SLCO1B1 or CYP3A4 alleles.

Effect of Baicalein on the Pharmacokinetics of Cilostazol and Its Two Metabolites in Rat Plasma Using UPLC-MS/MS Method

This study aimed to explore the effect of baicalein on the pharmacokinetics of cilostazol (CLZ) and its two metabolites 3,4-dehydro cilostazol (3,4-CLZ) and 4'-trans-hydroxy cilostazol (4'-CLZ) in rats using a newly established ultra performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) method. Ticagrelor was used as an internal standard (IS), then cilostazol and its two metabolites were separated by means of a UPLC BEH C18 column (2.1 mm × 50 mm, 1.7 μm) using gradient elution method with 0.4 ml/min of flow rate. Acetonitrile as organic phase and water with 0.1% formic acid as aqueous phase constructed the mobile phase. Selective reaction monitoring (SRM) mode and positive ion mode were preferentially chosen to detect the analytes. Twelve SD rats were divided into two groups (n = 6) when CLZ was administered orally (10 mg/kg) with or without oral baicalein (80 mg/kg). The selectivity, linearity, recovery, accuracy, precision, matrix effect and stability of UPLC-MS/MS assay were satisfied with the standards of United States Food and Drug Administration guidelines. In control group, AUC_0-∞ and C_max of CLZ were 2,169.5 ± 363.1 ng/ml^*h and 258.9 ± 82.6 ng/ml, respectively. The corresponding results were 3,767.6 ± 1,049.8 ng/ml^*h and 308.6 ± 87.9 ng/ml for 3, 4-CLZ, 728.8 ± 189.9 ng/ml^*h and 100.3 ± 51.3 ng/ml for 4'-CLZ, respectively. After combination with baicalein, AUC_0-∞ and C_max of CLZ were 1.48, 1.38 times higher than the controls. Additionally, AUC_0-∞ and C_max were separately decreased by 36.12 and 19.54% for 3,4-CLZ, 13.11 and 44.37% for 4'-CLZ. Baicalein obviously alters the pharmacokinetic parameters of CLZ, 3,4-CLZ and 4'-CLZ in rats. These results suggested that there was a potential drug-drug interaction between baicalein and CLZ. Therefore, it must raise the awareness when concomitant use of CLZ with baicalein, the dosage regimen of CLZ should be taken into consideration, if this result is confirmed in clinical studies.

Changes in CYP3A4 Enzyme Expression and Biochemical Markers Under Acute Hypoxia Affect the Pharmacokinetics of Sildenafil

To investigate the effects of pathological, physiological, biochemical and metabolic enzymes CYP3A4 on the pharmacokinetics of sildenafil under acute hypoxia, rats were randomly divided into the plain group (50 m above sea level), acute plateau group 1 (2300 m above sea level), and acute plateau group 2 (4300 m above sea level), and blood samples and liver tissues were collected. Our results showed that the blood gas, physiological and biochemical indexes of rats changed under acute hypoxia, and the protein expression of CYP3A4 enzyme decreased. The process of absorption, distribution, metabolism and excretion of sildenafil in rats has changed. Compared with the P group, the area under the drug-time curve and the average resident in the H2 group increased to 213.32 and 72.34%, respectively. The half-life and peak concentration increased by 44.27 and 133.67%, respectively. The clearance rate and apparent distribution volume decreased to 69.13 and 46.75%, respectively. There were no statistical differences in the pharmacokinetic parameters between the P group and the H1 group. In conclusion, the pharmacokinetic changes of sildenafil have a multi-factor regulation mechanism, and changes in blood gas, pathology, and biochemical indicators and metabolic enzymes affect the absorption, distribution, excretion, and metabolism of sildenafil, respectively. This study provides experimental evidence and new ideas for the rational use of sildenafil under acute hypoxic conditions.

Enzymatic activity on valsartan of 38 CYP2C9 variants from the Chinese population

BACKGROUND AND OBJECTIVE

Valsartan is widely used for the treatment of moderate hypertension. However, previous studies have found that efficacy of the valsartan depends on the dose and intake. Cytochrome P450 (CYP) 2C9 metabolizes ∼15% of the clinical drugs. Genetic polymorphisms of CYP2C9 markedly affect the safety and effectiveness of many drugs, which might lead to adverse reactions and therapeutic failure. Twenty-four novel CYP2C9 variants (*36-*60) had been previously discovered via gene sequencing in the Han population. Our study aims to evaluate the impact of 38 CYP2C9 variants from the Chinese population on valsartan metabolism compared with CYP2C9*1 in vitro.

METHODS

Wild-type CYP2C9*1 and other CYP2C9 variants were expressed in Spodoptera frugiperda 21 insect cells. Incubations were performed at 37 °C with 20-2000 μM substrate for 30 min. The metabolite 4-OH valsartan was determined via UPLC-MS/MS.

RESULTS

Among the 38 CYP2C9 variants, the enzymatic activities of most variants were significantly altered compared with the wild-type. Three variants (CYP2C9*27, *40 and *49) exhibited increased intrinsic clearance values (134-153% relative clearance). However, 12 variants (CYP *8, *13, *16, *19, *33, *36, *42, *43, *45, *52, *54, *58) caused >90% decreases in the relative clearance of valsartan compared to CYP2C9*1.

CONCLUSIONS

Our research provides systematic data for evaluating the effects of CYP2C9 variants on valsartan metabolism in the Chinese population. These results will expand our understanding of the impact of CYP2C9 genetic polymorphisms on valsartan metabolism and will contribute to precision medicine.

Pharmacokinetic profile of sildenafil citrate in healthy Middle Eastern Males: Comparison with other ethnicities

AIM

1) To investigate the pharmacokinetic profile of sildenafil citrate in Middle Eastern males and, 2) To highlight the impact of ethnicity on its pharmacokinetics parameters through comparing Middle Eastern data to the data estimated from different ethnic groups.

METHOD

The study was conducted on 24 Middle Eastern healthy male volunteers. Pharmacokinetic data including Cmax, Tmax, t1/2, AUC0-t, AUC0-∞ were estimated from blood samples collected at several time points within 24 h post-administration of a single 100-mg tablet of sildenafil citrate (Viagra®). Pharmacokinetic data of sildenafil generic 100-mg tablet (product B) was determined in the volunteers using the same analytical method. Pharmacokinetic data of other studies published on different ethnicities were obtained and compared to our Viagra®-related data.

RESULTS

Analysis of Middle Eastern data (mean ± SD) revealed Cmax = 398.9 ± 107.7 ng/ml; Tmax = 1.84 ± 0.22 h; t1/2 = 2.66 ± 0.97 h; AUC0-24 = 1475 ± 515.3 ng.h/ml; AUC0-∞ = 1556 ± 567.58 ng.h/ml. There was no significant difference between Viagra® and product B, confirming the bioequivalence of the two preparation as well as the reliability of utilized analytical method. Data comparisons between Middle Eastern and other ethnicities indicated that Iranian, Mexican, and Thai would potentially have twice the effect observed in Arabs and Caucasians, considering the same prescribed drug formulation and dose.

CONCLUSION

There is a considerable difference in the pharmacokinetic profile of sildenafil citrate between Middle Eastern and other ethnic groups. Ethnicity may predispose individuals to unwanted prolonged activity of sildenafil and adverse events. Thus, it should be taken in consideration by clinicians when recommending sildenafil dose.

Effect of Genetic Variation in CYP450 on Gonadal Impairment in a European Cohort of Female Childhood Cancer Survivors, Based on a Candidate Gene Approach: Results from the PanCareLIFE Study

BACKGROUND

Female childhood cancer survivors (CCSs) carry a risk of therapy-related gonadal dysfunction. Alkylating agents (AA) are well-established risk factors, yet inter-individual variability in ovarian function is observed. Polymorphisms in CYP450 enzymes may explain this variability in AA-induced ovarian damage. We aimed to evaluate associations between previously identified genetic polymorphisms in CYP450 enzymes and AA-related ovarian function among adult CCSs.

METHODS

Anti-Müllerian hormone (AMH) levels served as a proxy for ovarian function in a discovery cohort of adult female CCSs, from the pan-European PanCareLIFE cohort (n = 743; age (years): median 25.8, interquartile range (IQR) 22.1-30.6). Using two additive genetic models in linear and logistic regression, nine genetic variants in three CYP450 enzymes were analyzed in relation to cyclophosphamide equivalent dose (CED) score and their impact on AMH levels. The main model evaluated the effect of the variant on AMH and the interaction model evaluated the modifying effect of the variant on the impact of CED score on log-transformed AMH levels. Results were validated, and meta-analysis performed, using the USA-based St. Jude Lifetime Cohort (n = 391; age (years): median 31.3, IQR 26.6-37.4).

RESULTS

CYP3A4*3 was significantly associated with AMH levels in the discovery and replication cohort. Meta-analysis revealed a significant main deleterious effect (Beta (95% CI): -0.706 (-1.11--0.298), p-value = 7 × 10-4) of CYP3A4*3 (rs4986910) on log-transformed AMH levels. CYP2B6*2 (rs8192709) showed a significant protective interaction effect (Beta (95% CI): 0.527 (0.126-0.928), p-value = 0.01) on log-transformed AMH levels in CCSs receiving more than 8000 mg/m2 CED.

CONCLUSIONS

Female CCSs CYP3A4*3 carriers had significantly lower AMH levels, and CYP2B6*2 may have a protective effect on AMH levels. Identification of risk-contributing variants may improve individualized counselling regarding the treatment-related risk of infertility and fertility preservation options.

Changes in the Pharmacokinetics and Pharmacodynamics of Sildenafil in Cigarette and Cannabis Smokers

Sildenafil citrate, a widely-used oral therapy for erectile dysfunction, is a cytochrome P3A4 (CYP3A4) enzyme substrate. Studies have reported that this substrate has an inhibitory effect on CYP3A4 enzymes in long-term cigarette and cannabis smokers, which predominantly mediate the hepatic elimination of sildenafil. Cigarette and/or cannabis smoking could therefore alter the exposure of sildenafil. The aim of this study was to examine the effect of smoking cigarettes and/or cannabis on the pharmacokinetics, pharmacodynamics, safety and tolerability of sildenafil. Thirty-six healthy human subjects were equally divided into three groups: non-smokers, cigarette smokers and cannabis smokers. Each group was administered a single dose of sildenafil (50 mg tablets). The primary outcome measures included the maximum concentration of sildenafil in plasma (C_max), the elimination half-life (t1/2) and the area under the plasma concentration time curve from zero to time (AUC_0-t). The pharmacodynamics were assessed by the International Index of Erectile Function (IIEF-5). The exposure of sildenafil (AUC_0-t) showed a statistically significant increase in cigarette smokers (1156 ± 542 ng·h/mL) of 61% (p < 0.05) while in cannabis smokers (967 ± 262 ng·h/mL), a non-significant increase in AUC_0-t of 35% (p > 0.05) was observed relative to non-smokers (717 ± 311 ng·h/mL). Moreover, the C_max of sildenafil increased by 63% (p < 0.05) and 22% (p > 0.05) in cigarette smokers and cannabis smokers, respectively. Cigarette smoking increases the exposure of sildenafil to a statistically significant level with no effect on its pharmacodynamics, safety and tolerability.

Visual Side Effects Linked to Sildenafil Consumption: An Update

Phosphodiesterase type 5 (PDE5) inhibitors such as Viagra^® (sildenafil citrate) have demonstrated efficacy in the treatment of erectile dysfunction (ED) by inducing cyclic guanosine monophosphate (cGMP) elevation followed by vasodilation and increased blood flow. It also exerts minor inhibitory action against PDE6, which is present exclusively in rod and cone photoreceptors. The effects of sildenafil on the visual system have been investigated in a wide variety of clinical and preclinical studies due to the fact that a high dose of sildenafil may cause mild and transient visual symptoms in some patients. A literature review was performed using PubMed, Cochrane Library and Clinical Trials databases from 1990 up to 2020, focusing on the pathophysiology of visual disorders induced by sildenafil. The aim of this review was not only to gather and summarize the information available on sildenafil clinical trials (CTs), but also to spot subpopulations with increased risk of developing undesirable visual side effects. This PDE inhibitor has been associated with transient and reversible ocular side effects, including changes in color vision and light perception, blurred vision, photophobia, conjunctival hyperemia and keratitis, and alterations in the electroretinogram (ERG). Sildenafil may induce a reversible increase in intraocular pressure (IOP) and a few case reports suggest it is involved in the development of nonarteritic ischemic optic neuropathy (NAION). Reversible idiopathic serous macular detachment, central serous retinopathy and ERG disturbances have been related to the significant impact of sildenafil on retinal perfusion. So far, sildenafil does not seem to cause permanent toxic effects on chorioretinal tissue and photoreceptors as long as the therapeutic dose is not exceeded and is taken under a physician’s direction to treat a medical condition. However, the recreational use of sildenafil can lead to harmful side effects, including vision changes.