Do polymorphisms in chemosensory genes matter for human ingestive behavior?

Pharmacogenetics of taste: turning bitter pills sweet?

Poor palatability of oral drug formulations used for young children negatively influences medication intake, resulting in suboptimal treatment. Some children are more sensitive to bitter tastes than others. Bitter tasting status is currently assessed by phenotyping with 6-n-propylthiouracil (PROP) as a bitter probe. Recent studies showed that interindividual differences in PROP sensitivity can be largely explained by three SNPs in TAS2R38, encoding a bitter taste receptor. Gustin, involved in the development of taste buds, and the sweet receptor genotype potentially explain remaining parts of PROP sensitivity variability. Other TAS2 receptor bitter receptor genes may also play a role in bitter aversions. Dependent on their genotype, children may have different medication formulation preferences. Taste genetics could improve drug acceptance by enabling better-informed choices on adapting oral formulations to children’s taste preferences. This paper presents an overview of recent findings concerning bitter taste genetics and discusses these in the context of pediatric drug formulation.

Explaining human recreational use of 'pesticides': The neurotoxin regulation model of substance use vs. the hijack model and implications for age and sex differences in drug consumption

Most globally popular drugs are plant neurotoxins or their close chemical analogs. These compounds evolved to deter, not reward or reinforce, consumption. Moreover, they reliably activate virtually all toxin defense mechanisms, and are thus correctly identified by human neurophysiology as toxins. Acute drug toxicity must therefore play a more central role in drug use theory. We accordingly challenge the popular idea that the rewarding and reinforcing properties of drugs "hijack" the brain, and propose instead that the brain evolved to carefully regulate neurotoxin consumption to minimize fitness costs and maximize fitness benefits. This perspective provides a compelling explanation for the dramatic changes in substance use that occur during the transition from childhood to adulthood, and for pervasive sex differences in substance use: because nicotine and many other plant neurotoxins are teratogenic, children, and to a lesser extent women of childbearing age, evolved to avoid ingesting them. However, during the course of human evolution many adolescents and adults reaped net benefits from regulated intake of plant neurotoxins.

Do polymorphisms in the TAS1R1 gene contribute to broader differences in human taste intensity?

The TAS1R genes encode heterodimeric receptors that mediate umami (hTAS1R1 + hTAS1R3) and sweet (hTAS1R2 + hTAS1R3) sensations. The question of interest for this study is if TAS1R1 variation associates with differences in overall taste intensity. We leveraged an existing database of adults (n = 92, primarily European American) to test associations between 2 TAS1R1 single nucleotide polymorphisms (SNPs) (intronic rs17492553, C/T and exonic rs34160967, G/A) and intensity of 4 prototypical tastants (NaCl, sucrose, citric acid, and quinine), applied regionally to fungiform and circumvallate loci, and sampled with the whole mouth. Both SNPs were associated with modest shifts in perceived intensities across all taste qualities. Three genotype groups were represented for the intronic SNP-minor allele homozygotes (TT) averaged 40% lower intensities than did CC homozygotes for all regionally applied tastants, as well as whole-mouth NaCl and citric acid. Similar, but less pronounced, intensity differences were seen for the exonic SNP (GG homozygotes reported greater intensities than did the AA/AG group). Our predominantly European American cohort had a low frequency of AA homozygotes, which may have attenuated the SNP-related differences in perceived intensity. These preliminary findings, if replicated, could add TAS1R1 polymorphisms to the repertoire of genotypic and phenotypic markers of heightened taste sensation.