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Characterization of a Human ALDH2 Mutant that Causes Alcohol Flushing in Non‐east Asians
Author(s) -
Rwere Freeborn,
White Joseph R.,
Chen Che-Hong,
Mochly-Rosen Daria,
Gross Eric R.
Publication year - 2020
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.2020.34.s1.09088
Subject(s) - aldh2 , acetaldehyde , alcohol , aldehyde dehydrogenase , wine , ethanol metabolism , biochemistry , ethanol , chemistry , genetics , medicine , pharmacology , biology , food science , gene
Mitochondrial aldehyde dehydrogenase 2 (ALDH2) is a ~55 kDa protein responsible for the metabolism of the alcohol derived intermediate, acetaldehyde, in addition to a variety of toxic aldehydes including 4‐hydroxynonenal (4HNE) and acrolein. A single nucleotide polymorphism (SNP) of the ALDH2 gene (rs671) is highly prevalent among East Asians with ~540 million people in the world with the ALDH2 genetic variant (ALDH2*2 or E504K) that causes facial flushing and tachycardia after alcohol consumption due inefficient acetaldehyde metabolism. However, anecdotal reports exist of non‐East Asians who flush after alcohol consumption. Therefore, we hypothesize that other dysfunctional human genetic variants exist, besides ALDH2*2, that cause inefficient acetaldehyde metabolism. To address our hypothesis, after receiving IRB approval, we recruited human volunteers with self‐reported alcohol‐induced facial flushing. Volunteers were genotyped in addition to being subjected to an alcohol challenge (0.25g/kg) where levels of acetaldehyde in the breath were quantified by gas mass spectrometry for the 2 hours after an alcohol challenge. In addition, to support these findings, we carried out site‐directed mutagenesis, expressed, and purified an ALDH2 mutant we identified in humans using a nickel affinity column for histidine tagged protein. We measured enzymatic activity of the ADLH2 mutant using wild type ALDH2 and ALDH2*2 as comparators. All data are presented as mean ± SEM. Statistical analysis was performed by ANOVA and Tukey’s post hoc with significance set at P<0.05. We discovered a novel non‐East Asian ALDH2 mutation (R114W) that also causes alcohol‐induced facial flushing and acetaldehyde accumulation. Acetaldehyde levels measured in human breath showed that a human heterozygous for ALDH2 R114W had ~30% more acetaldehyde accumulation compared to homozygote wild‐type ALDH2 human subjects. The heart rate of ALDH2 R114W was not affected by alcohol intake, whereas skin temperature increased after alcohol consumption. To confirm these findings in humans, enzymatic activity of the purified proteins showed that E504K and R114W had 49±3 and 603±11 nmol/min/mg protein, respectively compared to 1209±15 nmol/min/mg protein for wild‐type ALDH2 (n=3, p<0.05). When mixed in the 1:1 ratio with wild‐type enzyme to mimic the heterozygous condition, the activity of E504K and R114W increased to 683±6 and 838±16 nmol/min/mg of pure protein, respectively, but still significantly below the activity of the wild‐type ALDH2. The results presented here demonstrate that a newly found ALDH2 variant, R114W, is also responsible for alcohol‐induced acetaldehyde accumulation and facial flushing. In conclusion, individuals carrying this mutation are more potentially also more susceptible to esophageal cancer similar to those heterozygous for the ALDH2*2 genetic variant. Support or Funding Information NIGMS HL119522 (ERG) and a Stanford ChEM‐H seed grant (ERG, DMR).