CES1 Metabolizing enzyme

Carboxylesterase 1 (CES1) is the most common enzyme in the liver (approx. 1 % of liver proteins). CES1 causes 80 to 95 % of hydrolysis in the liver. It is also found to a lesser extent in the lungs and brain.
In addition to its important role in the degradation of xenobiotic compounds, CES1 appears to be involved in endogenous metabolic functions, e.g. in relation to:¹

• Cholesterol esters
• Triglycerides
• bioactive lipids

Methylphenidate is primarily metabolized by carboxylesterase 1A1 (CES1) in the liver to ritalinic acid (aphenyl-2-piperidine acetic acid).² The earlier assumption that MPH is metabolized by hepatic lysozyme enzymes is outdated.³
CES1 mainly breaks down L-MPH and less d-MPH. Therefore, more d-MPH (dexmethylphenidate) remains in the plasma. Most MPH preparations contain a racemic mixture of d- and L-MPH, whereby only d-MPH is pharmacologically active.⁴ 60 to 80 % of the MPH taken is excreted in the urine as ritalinic acid.⁵

• aromatic hydroxylation to p-hydroxy-methylphenidate (p-hydroxy-MPH)⁴ proportion between 1.5 and 12 % of the degradation.
• microsomal oxidation to form 6-oxo-methylphenidate (6-oxo-MPH; inactive metabolite)⁴ Up to 2.5 % of MPH.
• unchanged excretion of MPH is indicated from below 1 %⁵ to with urine: 2 %, in feces: 3 %⁴

The activity of CES1 is highly variable. What contributes to this variability was still largely unknown in 2018.⁶
There are large individual differences in the response to many drugs that are metabolized by CES1.¹ The expression and activity of CES1 varies greatly in humans. Therefore, significant individual differences in CES1-based pharmacokinetics and pharmacodynamics may exist. The bioavailability of MPH in children varies between 11% and 53%⁷

A higher CES1 plasma concentration correlated with a reduced d-methylphenidate plasma level. In one study, the CES1 plasma protein level could explain about 50 % of the variability of the d-methylphenidate plasma level. It is possible that an individualized dosing strategy based on the measurement of CES1 could considerably facilitate the dosing of d-methylphenidate.⁸

Factors that influence degradation by CES1 are non-genetic or genetic in nature:⁹

• 1. Non-genetic factors that influence CES1 metabolism
• 2. Genetic influences that affect CES1 metabolism
  • 2.1. CES1 haplotypes, hybrid genes
  • 2.2. CES1 gene variants influence CES1 activity
  • 2.3. POR gene variants do not influence CES1 metabolization
• 3. CES1 substrates / CES1 inhibitors / CES1 inducers
  • 3.1. CES1 substrates
  • 3.2. CES1 inhibitors
  • 3.3. CES1 inducers

1. Non-genetic factors that influence CES1 metabolism¶

• State of development
• Gender
• Interactions between drugs (see substrates, inhibitors, inducers)

2. Genetic influences that affect CES1 metabolism¶

The degree of CES1 expression is related to the degree of methylation of the CpG islands (CGIs) of the CES1 promoter. Melatonin reduces the degree of methylation of the CES1 promoter by promoting the expression of sirtuin 1 (SIRT1), which mediates the deacetylation of DNA methyltransferase 1 (DNMT1).¹⁰

2.1. CES1 haplotypes, hybrid genes¶

Two haplotypes of CES1 are known:¹⁴⁶

• the first haplotype (“wild type”) is a hybrid gene from
  • CES1P1
    • CES1P1 (CES1A3) is an inactive, truncated pseudogene. It is located in the vicinity of CES1 on chromosome 16. CES1P1 appears to have arisen through gene replacement.
  • CES1A1 (prototype of CES1)
• the second haplotype is a hybrid gene from
  • CES1A1
  • CES1A2 (a CES1-like variant)
    • A computational modeling study found significantly reduced MPH degradation and approximately 70% higher d-MPH plasma exposure in two CES1A2 copies compared to the wild-type genotype¹¹
    • A CES1A2 copy resulted in approx. 22% higher MPH levels¹¹
    • CES1A2 showed increased degradation in relation to irinotecan¹²
    • A clinical trial with oseltamivir found no effect of the CES1 diplotype on degradation¹³
    • A study of 99 children on MPH found:¹⁴
      • the MPH dose amounted to an overall average of 0.79 mg/kg/day.
      • the mean MPH dose by haplotype was
        • CES1A2/CES1A2: 0.92 mg/kg for
        • CES1A2/CES1P1: 0.81 mg/kg
        • CES1P1/CES1P1: 0.78 mg/kg

Therefore, some people carry two almost identical CES1 copies on the same chromosome.¹
Four CES1 copies had the lowest MPH degradation and the MPH AUC was about 1.5 times higher than in the control group¹⁵
With two or three CES1 copies, MPH degradation was only slightly reduced¹⁵

Hybrid gene variants are:

• CES1P1 with CES1
  • higher transcriptional activity than CES1P1
• CES1A2 (another hybrid gene variant from CES1 and CES1P1)
  • has 2% of the transcription efficiency of CES1
• CES1A1b
• CES1A1c (CES1VAR)
  • has no noticeable effect on the metabolism of medication⁶

2.2. CES1 gene variants influence CES1 activity¶

CES1 gene variants with functional effects are rare. The main factors influencing the metabolism of CES1 appear to depend on other influences⁶

To date, almost 200 variants have been found in the CES1 / CES1P1 gene region.¹

• genetic polymorphisms
  • Single nucleotide polymorphisms (SNPs)
    • Over 2500 single nucleotide polymorphisms (SNPs) have been identified in the CES1 gene (NCBI dbSNP). Some SNPs, such as G143E, D269fs, E220G and L40T, are detrimental to the enzymatic activity of the gene and could alter CES1-mediated drug metabolism. However, these variants account for only a small fraction of CES1 variability, leaving the majority unexplained.¹⁶
    • G143E (rs71647871)
      • Frequency; 3.7 % for Caucasians¹⁷
      • G143E carriers required less MPH,^{6 18} in one study it was 28% less¹⁹ where up to 2.5 times the d-MPH AUC was observed with the same dose of MPH.¹⁵ and one third of MPH metabolization²⁰
      • Subjects who were heterozygous for the CES1 variant G143E (p.Gly143Glu of rs71647871)
        • metabolized MPH significantly slower¹¹, about half as fast as non-carriers²¹
          • male G143E carriers who consume alcohol are likely to have a higher risk of MPH overexposure
        • p.Gly143Glu (rs71647871) appears to significantly impair the metabolism of:¹
          • Methylphenidate
          • Trandolapril
          • Oseltamivir
      • A computational modeling study found rs71647871 to be a highly significant covariate in determining interindividual differences in MPH metabolism. rs71647871 GA resulted in a 2.4-fold increase in plasma d-MPH exposure. rs71647871 may be a risk factor for adverse MPH effects¹¹
    • rs115629050 TG (p.Ala270Ser)
      • An in-silico simulation showed a significantly reduced MPH degradation with an approximately 68% higher d-MPH plasma exposure compared to the wild-type genotype. For rs115629050 TG, scores were equal to or greater than those of rs71647871 GA in 6 of 9 models¹¹
      • rs115629050 reduces CES1²²
      • In vitro, rs115629050 TG showed no effect on drug metabolism with respect to angiotensin²³
    • E220G (c.662A>G, rs200707504) is reported to be associated with reduced CES1 activity²⁴
    • c.428G>A (p.Gly143Glu, rs121912777) is reported to be associated with reduced CES1 activity²⁴
    • c.780delT (p.Asp260fs, rs71647872) is reported to be associated with reduced CES1 activity²⁴
    • c56G>T (rs3826190) is reported to be associated with reduced CES1 activity²⁴
    • c.808G>T (rs115629050) is reported to be associated with reduced CES1 activity²⁴
    • rs114119971 may be associated with reduced CES1 activity:¹⁴
      • the overall average MPH dose in the 2 (out of 99) people with ADHD was 0.42 mg/kg/day compared to those without SNV of 0.88 mg/kg/day
    • S75N (rs2307240)
      • appears to increase the activity of CES1 in relation to clopidogrel²⁵
      • does not appear to affect the activity of CES1 in relation to methylphenidate in children²⁶
    • rs3815589
      • does not appear to affect the activity of CES1 in relation to methylphenidate in children²⁷
    • rs2287194
      • does not appear to affect the activity of CES1 in relation to methylphenidate in children²⁸
    • rs2244613
      • does not appear to affect the activity of CES1 in relation to methylphenidate in children²⁹
      • correlated significantly with sadness as a side effect of immediate release MPH in A/A subjects
      • rs2244613-G showed an increased side effect risk of MPH with comorbid ASA³⁰
    • rs2002577
      • does not appear to affect the activity of CES1 in relation to methylphenidate in children³¹
      • tended to correlate with sadness as a side effect of immediate release MPH in G/G carriers
    • rs2307244
      • does not appear to affect the activity of CES1 in relation to methylphenidate in children³²
    • rs12443580
      • does not appear to affect the activity of CES1 in relation to methylphenidate in children³³
    • the 75 T/G and 75 G/G polymorphisms appear to be associated with greater loss of appetite with MPH intake compared to the T/T variant.³⁴
    • different CES1A2 promoter haplotypes are associated with increased CES1 expression:¹
      • 47C,
      • 46T
      • 41G
      • 40
      • 37C
      • 34G
      • 32T
• rs2307235-A
  • increased risk of side effects of MPH with comorbid ASA³⁰
• rs8192950-T
  • increased risk of side effects of MPH with comorbid ASA³⁰
• rs2302722-C
  • reduced risk of side effects of MPH with comorbid ASA³⁰
  • Copy number variants⁴
    • The different CES1 variants exist in several haplotypes and diplotypes. Individuals can carry more than two active copies of CES1 (i.e. two CES1 copies and one CES1A2 copy for a copy number of three or two CES1 copies and two CES1A2 copies for a copy number of four).
      • Individuals can carry more than two active copies of CES1
    • Contrary to the expectation that a higher copy number should be associated with increased degradation, one study found reduced degradation:
      • Carriers of 4 CES1 copies had 45% (P = 0.011) and 61% (P = 0.028) higher d-MPH levels (AUC) than control subjects or carriers of 3 CES1 copies.

Stevens et al have compiled studies that dealt with the influence of gene variants on the effect of MPH:⁴

2.3. POR gene variants do not influence CES1 metabolization¶

In contrast to CYP 450 enzymes, the efficacy of CES1 is not influenced by gene variants of the POR gene (cytochrome P450 oxidoreductase, NADPH P450 oxidoreductase, CPR).

3. CES1 substrates / CES1 inhibitors / CES1 inducers¶

This list - like all information from ADxS.org - is not intended for personal therapeutic use. Even though we endeavor to collect all information, the list is nevertheless incomplete. Errors cannot be ruled out. Please ask your doctor or pharmacist.

The lower the IC50, the higher the therapeutic potency of an active ingredient.
The smaller Ki is, the greater the binding affinity and the lower the amount of drug required to inhibit the activity of the enzyme.
If Ki is much greater than the maximum drug concentration to which a patient is exposed during typical administration, it is unlikely that the drug will inhibit the activity of the enzyme.³⁵
The inhibition constant Ki is the inhibitor concentration at which half of the enzymes are inhibited.
Ki indicates the binding affinity, IC50 rather indicates the functional strength of the inhibitor for a drug. Ki takes the IC50 into account in its calculation.
Non-competitive enzyme inhibition: Ki approximately equal to IC50
Competitive / uncompetitive inhibition: Ki is approx. 1/2 of IC50

3.1. CES1 substrates¶

CES1 is crucial for the degradation of various active ingredients.⁹

• 11-Deoxyalisol A (triterpenoid)

• 2-oxo-clopidogrel (anticoagulant)³⁶

• 25-O-Ethylalisol A (triterpenoid)
• Alismanol B (triterpenoid)
• Alismanol D (triterpenoid)
• Alismanol F (triterpenoid)

• Amphetamines (CNS active ingredient)²²
  • METH
  • Although predominantly through CYP2D6
• Benzapril (ACE inhibitor, angiotensin receptor neprilysin inhibitor, ARNI)³⁶
• Capecitabine (cancer drug)
• Cholesterol (Endogenous compound
• Ciclesonide (immunosuppressive agent, adrenal glucocorticoid)³⁶

• Cilazapril (angiotensin receptor neprilysin inhibitor, ARNI)³⁶

• Clopidogrel (anticoagulant)³⁷
• Dabigatran exilate (anticoagulant)³⁷

• Delapril (angiotensin receptor neprilysin inhibitor, ARNI)³⁶* Clofibrate (antihyperlipidemic)³⁶

• Dimethyl fumarate (MS agent)
• Enalapril (ACE inhibitor, angiotensin receptor neprilysin inhibitor, ARNI)³⁶
• Fenofibrate (antihyperlipidemic)³⁶
• Fatty acid ethyl ester (endogenous compound)

• Fosinopril (angiotensin receptor neprilysin inhibitor, ARNI)³⁶

• Flumazenil (CNS active ingredient)
• Heroin (CNS active ingredient)
• Imidapril (ACE inhibitor, angiotensin receptor neprilysin inhibitor, ARNI)³⁷³⁶
• Irinotecan (cancer drug)
• Cocaine(CNS active ingredient)
• Lovastatin (antihyperlipidemic)³⁶
• Meperidine (CNS active ingredient)
• Methylphenidate (CNS active ingredient)

• Moxeipril (angiotensin receptor neprilysin inhibitor, ARNI)³⁶

• Mycophenolate mofetil (immunosuppressive agent)
• Nintedanib (cancer drug)³⁶
• Oseltamivir (antiviral agent)³⁷
• Oxybutynin (anticholinergic; used for urinary incontinence, among other things; antispasmodic)³⁶
• Para-nitrophenyl valerate (pesticide)

• Perindopril³⁶

• Quinapril (ACE inhibitor, angiotensin receptor neprilysin inhibitor, ARNI)³⁶
• Ramipril (ACE inhibitor, angiotensin receptor neprilysin inhibitor, ARNI)³⁶
• Rufinamide (CNS active ingredient)
• Sacubitril (angiotensin receptor neprilysin inhibitor, ARNI; antihypertensive agent)³⁶
• Sarin (chemical warfare agent)
• Simvastatin (antihyperlipidemic)³⁶
• Sofosbuvir (antiviral agent)
• Soman (chemical warfare agent)
• Tabun (chemical warfare agent)
• Telotristat ethyl (tryptophan hydroxylase inhibitor)³⁶
• Telotristat etiprate (cancer drug)

• Temocapril (angiotensin receptor neprilysin inhibitor, ARNI)³⁶

• Tenofoviralafenamide (antiviral agent)
• Trandolapril (ACE inhibitor, angiotensin receptor neprilysin inhibitor, ARNI)³⁶
• Trans-permethrin (pesticide)
• Travoprost (prostaglandin analog)³⁶

3.2. CES1 inhibitors¶

These active ingredients inhibit the degradation of MPH by CES1 and should therefore not be combined with MPH if possible. We hypothesize, however, that such a combination could be helpful for super-rapid metabolizers, with particularly close medical monitoring at the same time.

• 11-Deoxo-glycyrrhetinic acid (IC50: 10.5 µM) (triterpenoid)
• 1,12-Epoxy-5E,8E,14E- Eicosatrienoic acid (IC50: 27 µM) (Vegetable fatty acid)
• 15-Deoxy-12,14-prostaglandin J2 (IC50: 12 µM) (Vegetable fatty acid)
• 22(R)-hydroxycholesterol (unsaturated fatty acid, weak)³⁸³⁸
• 24(S)-hydroxycholesterol (unsaturated fatty acid, weak)³⁸
• 24(S),25-epoxycholesterol (IC50=8.1 μM) (unsaturated fatty acid, moderate)³⁸
• 25-hydroxycholesterol (unsaturated fatty acid, weak)³⁸
• 27-Hydroxycholesterol (27-HC) (IC50=33 nM, Kiapp=10 nM) (unsaturated fatty acid, partially non-competitive inhibitor)³⁸
  • impaired intracellular CES1 activity after treatment of intact THP1 cells
• 3-O-(-carboxypropionyl)-11-deoxo-glycyrrhetinic acid 30-ethyl ester (IC50: 20.4 µM) (triterpenoid)
• 4,15-Epoxy-5E,8E,11E-eicosatrienoic acid (IC50: 38 µM) (vegetable fatty acid)
• 7-ketocholesterol (unsaturated fatty acid, weak)³⁸
• Alcohol (strong) ³⁹⁷
  • If alcohol and MPH are taken at the same time:³⁹
    • increases the MPH concentration in humans
    • alcohol inhibits CES1-mediated MPH degradation by catalyzing MPH to ethylphenidate⁷⁴⁰
      • more l-ethylphenidate (pharmacologically ineffective) appears to be produced than d-ethylphenidate⁴¹
      • Ethylphenidate appears to be toxic
      • Ethylphenidate correlates with significantly higher d-MPH plasma levels and increased euphoric effects⁷
      • Ethylphenidate binds similarly strongly to DAT, but less strongly to NET than MPH⁴¹
• Arachidonic acid (strong) (IC50: 2 µM; Ki: 1.7 µM) (vegetable fatty acid)³⁸
  • strongest fatty acid inhibitor of recombinant CES1
  • acted through a non-competitive mechanism (Kiapp=1.7 μM)
• Aripiprazole (strong) (IC50: 5.7 µM)⁴²⁷
• Asiatic acid (triterpenoid), (Ki: 0.64 µM) (strong)³⁶
• Bavachinin (Ki: 0.5 µM) (strong) (vegetable, phenol)³⁶
• Bakuchiol (vegetable)³⁶
• Benzoic acid-4-O–D-(6-galloyl)-glucopyranoside (vegetable, phenol)³⁶
• Brevifolin (herbal)³⁶
• Cannabidiol (cannabinoid), (Ki: 0.974 µM) (strong)³⁶⁴³
  • nevertheless, CBD (cannabidiol) increased the MPH level and -AUC only insignificantly⁴⁴
• Cannabinol (cannabinoid), (Ki: 0.263 µM) (strong)³⁶
• Celastrol (triterpenoid), (Ki: 4.43 µM) (strong)³⁶
• Cholesterol (unsaturated fatty acid, low)³⁸
• Corilagina (vegetable)³⁶
• Coryfolin (strong) (Ki: 1.9 µM) (vegetable, phenol)³⁶
• Corylin (strong) (Ki: 0.7 µM) (vegetable, phenol)³⁶
• Corylifol A (vegetable, phenol)³⁶
• Coryfolinin (Ki: 9.4 µM) (vegetable, phenol)³⁶
• Desmethoxyyangonine (Ki = 25.2 μM)⁴⁵
• Dihydrocavaine (Ki = 105.3 μM)⁴⁵
• Dihydromethysticin (Ki = 68.2 μM)⁴⁵
• Dihydrotanshinone (strong) (Ki: 0.39 µM) (Tanshinone)
• Ellagic acid 4-O-D-glucopyranoside (vegetable, phenol)³⁶
• Euphorbic acid (triterpenoid)
• Euphorbin A (triterpenoid)
• Euphorbin B (triterpenoid)
• Euphorbin C (triterpenoid)
• Fatty acids inhibit CES1³⁸
  • especially unsaturated fatty acids
• Fluoxetine (strong) (IC50: 6.1 µM)⁴²⁷
• Gallic acid-4-O–D-(6-O-galloyl)-glucopyranoside (vegetable, phenol)³⁶
• Gallic acid 3-O-D-(6-O-galloyl)-glucopyranoside (vegetable, phenol, phenol)³⁶
• Gambogic acid³⁶
• Glycyrrhetinic acid (triterpenoid), (Ki: 13 µM) (strong)³⁶
• Isobavachalkon (vegetable, phenol)³⁶
• Kaempferol (flavonoid), (Ki: 62 µM)³⁶
• Kavain (Ki = 81.6 μM)⁴⁵
• Cryptotanshinone (tanshinone), (Ki: 0.54 µM) (very strong)³⁶
• Kuwanon G (vegetable, phenol)³⁶
• Linoleic acid (strong)(IC50: 9 µM) (Vegetable fatty acid)
• Linolenic acid (IC50: 19 µM) (vegetable fatty acid)
• Luteolin (flavonoid), (Ki: 5.34 µM) (strong)³⁶
• Methysticin (Ki = 35.2 μM) (Kavalactone)⁴⁵
• Miltirone (strong) (Ki: 0.39 µM) (Tanshinon)
• Myristic acid (strong) (IC50: 9 µM) (Vegetable fatty acid)
• Myristoleic acid (IC50: 12 µM) (vegetable fatty acid)
• Naringenin (flavonoid), (Ki: 30 µM)³⁶
• Neobavaisoflavones (strong) (Ki: 5.3 µM) (vegetable, phenol)³⁶
• Oleic acid (strong) (IC50: 7 µM) (Vegetable fatty acid)
• Oheno (vegetable, phenol)³⁶
• Oleanolic acid (triterpenoid), (Ki: 0.28 µM) (strong)³⁶
• Oxysterol³⁸
  • Cholesterol metabolite; also inhibits CES1
• Pachymic acid (triterpenoid), (Ki: 21.7 µM)³⁶
• Paeoveitol B (vegetable, phenol)³⁶
• Palmitic acid (IC50: 25 µM) (vegetable fatty acid)
• Palmitoleic acid (strong) (IC50: 7 µM) (Vegetable fatty acid)
• Perphenazine (strong) (IC50: 13.9 µM)⁴²⁷
• Pyrone-2-O–D-(6-galloyl)-glucopyranoside (vegetable, phenol)³⁶
• Pyrone-2-O–D-(2,6-digalloyl)-glucopyranoside (vegetable, phenol)³⁶
• Pryomeconic acid-3-O–D-glucopyranoside-6-(O-4-hydroxybenzoate) (vegetable, phenol)³⁶
• Quercetin (flavonoid), (Ki: 33.4 µM)³⁶
• Resveratrol³⁶
• Sanggenon C (vegetable, phenol)³⁶
• Sanggenon D (vegetable, phenol)³⁶
• Scopoletin-7-O–D-(6-galloyl)-glucopyranoside (vegetable)³⁶
• Sulforaphane³⁶
• Tanshinon I (Tanshinon), (Ki: 26.3 µM)³⁶
• Tanshinone IIA (Tanshinone), (Ki: 6.89 µM) (strong)³⁶
• Tanshinone IIA sulfonate (Ki: 100 µM) (Tanshinone)
• Δ⁹-Tetrahydrocannabinol (cannabinoid), (Ki: 0.541 µM) (very strong)³⁶⁴³
• Thioridazine (strong) (IC50: 7.0 µM)⁴²⁷
• Ursolic acid (triterpenoid), (Ki: 0.24 µM) (strong)³⁶
• Compound 12 (triterpenoid)
• Compound 13 (triterpenoid)
• Yangonin (Ki = 24.9 μM)⁴⁵

3.3. CES1 inducers¶

A combination of methylphenidate and inducers causes a significant decrease in MPH in the blood.

• Carmabazine is said to be an inducer of CES1.⁴²
  - Glucose (sugar)⁴⁶
• Phenobarbital (possible)⁴²
• Phenytoin (possible)⁴²
• Rifampin (possible)⁴²
• Sulforaphane compounds (antioxidant)³⁶ Sulforaphane (4-methylsulfinylbutylisothiocyanate; 1-isothiocyanato-4-methylsulfinylbutane) is a dietary and herbal phytochemical that occurs in plants as a biologically inactive precursor
  • Sulforaphane is a strong CES1 inducer⁴⁷
    - Trinitrobenzene sulfonate (strong)
  • Skin sensitizers, such as those used to test cosmetic products, can increase CES1 up to 20-fold⁴⁸
    - Cinnamaldehyde (strong)
  • Skin sensitizers, such as those used to test cosmetic products, can increase CES1 up to 20-fold.⁴⁸