2,4,6-Trichloroanisole is a potent suppressor of olfactory signal transduction

Abstract

We investigated the sensitivity of single olfactory receptor cells to 2,4,6-trichloroanisole (TCA), a compound known for causing cork taint in wines. Such off-flavors have been thought to originate from unpleasant odor qualities evoked by contaminants. However, we here show that TCA attenuates olfactory transduction by suppressing cyclic nucleotide-gated channels, without evoking odorant responses. Surprisingly, suppression was observed even at extremely low (i.e., attomolar) TCA concentrations. The high sensitivity to TCA was associated with temporal integration of the suppression effect. We confirmed that potent suppression by TCA and similar compounds was correlated with their lipophilicity, as quantified by the partition coefficient at octanol/water boundary (pH 7.4), suggesting that channel suppression is mediated by a partitioning of TCA into the lipid bilayer of plasma membranes. The rank order of suppression matched human recognition of offflavors: TCA equivalent to 2,4,6-tribromoanisole, which is much greater than 2,4,6-trichlorophenol. Furthermore, TCA was detected in a wide variety of foods and beverages surveyed for odor losses. Our findings demonstrate a potential molecular mechanism for the reduction of flavor.olfactory masking | ion channel | patch-clamp T hroughout culinary history, consumers have been disturbed by naturally generated off-flavor substances that can greatly reduce the palatability of foods and beverages. Because off-flavors appear at very low concentrations of contaminants, chemical identification of responsible compounds has been limited. One of the most potent off-flavor compounds identified to date is 2,4,6-trichloroanisole (TCA), known specifically for inducing a cork taint in wines (1). In general, off-flavor compounds have been thought to induce unpleasant exogenous smells (2-9), and would therefore be expected to excite specific olfactory receptors (10) transducing malodors. However, we found that TCA did not generate excitatory responses in single olfactory receptor cells (ORCs), but potently suppressed cyclic nucleotide-gated (CNG) channels in these cells. Because CNG channels play a key role in olfactory transduction, suppression of these channels suggests a reduction of endogenous odors, rather than an addition of exogenous odors. Surprisingly, TCA exerted a much more potent suppressive effect on CNG channels (100-1,000-fold) than other known olfactory masking agents that have been widely used in perfumery. It was also more potent than a well-known CNG channel blocker, L-cis-diltiazem. We could account for such high suppressive potency in terms of temporal integration and slow recovery from suppression by TCA. The order of potency of CNG suppression by TCA analogues or precursors was identical to that of the human detection of the corresponding off-flavors, i.e., TCA equivalent to 2,4,6-tribromoanisole(TBA), which is much greater than 2,4,6-trichlorophenol (TCP; precursor of TCA), suggesting that cork taint is related to TCA suppression of CNG channels. We further confi...

Antagonism in olfactory receptor neurons and its implications for the perception of odor mixtures

“…The model above (and detailed in the Methods) reproduces qualitative features of odorant suppression observed in experiments [22] (Fig. 4A) and shows a good fit with available experimental data [46] on masking agents ( Fig. 4B).…”

“…Specifically, the list of psychophysical effects relevant here is as follows (see [16,[23][24][25]46]). 1) Inhibition and synergy: The former is the strong reduction of perceived intensities when two odorants are mixed, usually at high concentrations ; synergy is occasionally observed, namely at low concentrations.…”

Biosensor-Based Approaches for Detecting Ochratoxin A and 2,4,6-Trichloroanisole in Beverages

“…Even so, they are responsible, as off-flavor compounds, for the so-called "cork taint", a moldy olfactory effect that is acutely associated with inferior beverage quality and possible carcinogenicity after long-term exposure [50][51][52]. The olfactory properties of TCA have been experimentally ascribed, at least in part, to the suppression of cyclic nucleotide-gated (CNG) channels in olfactory receptor cells (ORCs), leading to the reduced perception of odors [53]. More analytically, the membrane current of single ORCs, enzymatically derived from the olfactory epithelium of the newt (Cynops pyrrhogaster), was measured using a whole-cell patch-clamp set up and after loading cells with caged cAMP or Ca 2+ with or w/o the addition of TCA.…”

“…They emphasized on the potential of the method as an outstanding tool for the express, sensitive and low-cost on-site screening of the cork material, even though not yet suitable for the derivation of quantitative results. Beyond membrane-engineered cells with designed selectivity, cellular biorecognition elements having a natural response against haloanisols (e.g., cells expressing olfactory receptors [53]) could also be used as part of an improved bioelectric recognition biosensor for TCA determination. That said, the broader use of cell-based biosensors faces additional challenges, for instance cell handling and storage, which could render problematic their use in automated screening system.…”

Taints, Off‐flavors, and Mycotoxins

“…The major cause is the potent and earthy/musty/ moldy-smelling 2,4,6-trichloroanisole (TCA , Table 18.1). In addition to having an undesirable aroma, TCA can inhibit olfactory signal transduction, thereby interfering with the perception of other odorants [14]. The requirements for formation of TCA are:…”