In contrast to carbohydrates and proteins, which are detected by specialized taste receptors in the forms of their respective building blocks, sugars, and L-amino acids, the third macronutrient, lipids, has until now not been associated with gustatory receptors. Instead, the recognition of fat stimuli was believed to rely mostly on textural, olfactory, and postingestive cues. During the recent years, however, research done mainly in rodent models revealed an additional gustatory component for the detection of long-chain fatty acids (LCFAs), the main taste-activating component of lipids. Concomitantly, a number of candidate fat taste receptors were proposed to be involved in rodent's gustatory fatty acid perception. Compared with rodent models, much less is known about human fat taste. In order to investigate the ability of the human gustatory system to respond to fat components, we performed sensory experiments with fatty acids of different chain lengths and derivatives thereof. We found that our panelists discriminated a "fatty" and an irritant "scratchy" taste component, with the "fatty" percept restricted to LCFAs. Using functional calcium-imaging experiments with the human orthologs of mouse candidate fat receptors belonging to the G protein-coupled receptor family, we correlated human sensory data with receptor properties characterized in vitro. We demonstrated that the pharmacological activation profile of human GPR40 and GPR120, 2 LCFA-specific receptors associated with gustatory fat perception in rodents, is inconsistent with the "scratchy" sensation of human subjects and more consistent with the percept described as "fatty." Expression analysis of GPR40 and GPR120 in human gustatory tissues revealed that, while the GPR40 gene is not expressed, GPR120 is detected in gustatory and nongustatory epithelia. On a cellular level, we found GPR120 mRNA and protein in taste buds as well as in the surrounding epithelial cells. We conclude that GPR120 may indeed participate in human gustatory fatty acid perception.

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Polybutylcyanoacrylate nanoparticles (PBCA NPs) are candidates for a drug delivery system, which can cross the blood–brain barrier (BBB). Because little is known about their toxicity, we exposed cells to PBCA NPs in vitro and in vivo and monitored their life and death assays. PBCA NPs were fabricated with different surfactants according to the mini-emulsion technique. Viabilities of HeLa and HEK293 cells after NP incubation were quantified by analysing cellular metabolic activity (MTT-test). We then repetitively injected i.v. rhodamine-labelled PBCA NP variations into rats and monitored the survival and morphology of retrogradely labelled neurons by in vivo confocal neuroimaging (ICON) for five weeks. To test for carrier-efficacy and safety, PBCA NPs loaded with Kyotorphin were injected in rats, and a hot plate test was used to quantify analgesic effects. In vitro, we found dose-dependent cell death which was, however, only detectable at very high doses and mainly seen in the cultures incubated with NPs fabricated with the tensids SDS and Tween. However, the in vivo experiments did not show any NP-induced neuronal death, even with particles which were toxic at high dose in vitro, i.e. NPs with Tween and SDS. The increased pain threshold at the hot plate test demonstrated that PBCA NPs are able to cross the BBB and thus comprise a useful tool for drug delivery into the central nervous system (CNS). Our findings showing that different nanoparticle formulations are non-toxic have important implications for the value of NP engineering approaches in medicine.

This article is available online at http://www.jlr.org the fi ve taste qualities, sweet, umami, salty, sour, and bitter ( 2 ). In the past, the existence of additional taste modalities such as fatty ( 3 ), metallic ( 4 ), or a taste for water ( 5 ) has been speculated. In recent years, particular attention has been paid to the potential existence of fat taste and its putative status compared with the other well-accepted taste qualities . Whereas the textural, olfactory, and postingestive recognition of fat constituents have been considered the dominant cues for fat perception in the past, several recent studies, performed mostly in rodents but also in humans, have pointed to a gustatory component in fat perception [for a recent review see ( 6 )]. The use of anosmic ( 7 ) or esophagostomized ( 8 ) rat models in combination with texture-masking buffer compositions indicated an orosensory detection mechanism for long-chain fatty acids, in particular. Moreover, a number of candidate receptors for the oral detection of lipophilic molecules were identifi ed by several independent research groups. These putative fat sensors include potassium channels ( 3 ) and scavenger receptor/fatty acid transporter CD36/FAT ( 9, 10 ), as well as G protein-coupled receptors (GPRs) such as GPR40 ( 11 ) and GPR120 ( 11-13 ). For some of the candidate receptors, knockout mouse models were analyzed and their contribution to orosensory fat perception confi rmed. Mice with a genetic ablation of CD36 exhibit no preference for the polyunsaturated long-chain fatty acid, linoleic acid, in two-bottle preference tests compared with wild-type mice. Moreover, a reduced cephalic phase response upon oral stimulation with oleic, linoleic, and linolenic acid, but not to the saturated long-chain fatty acid, stearic acid, or the medium-chain fatty acid, caprylic acid, suggests pronounced selectivity for particular lipophilic stimuli ( 10 ). Similarly, GPR40 as well as GPR120 knockout mice both show a loss of preference for linoleic acid, and The perception of taste elicited by countless chemicals present in food plays an important role for the survival of organisms. The gustatory system monitors not only the caloric content and the appropriate electrolyte supply, but also the presence of putatively harmful substances in food items ( 1 ). Detection of food constituents within the oral cavity is achieved by taste receptor molecules expressed by sensory cells specifi cally devoted to the detection of one of

The sense of taste plays an important role in the evaluation of the nutrient composition of consumed food. Bitter taste in particular is believed to serve a warning function against the ingestion of poisonous substances. In the past years enormous progress was made in the characterization of bitter taste receptors, including their gene expression patterns, pharmacological features and presumed physiological roles in gustatory as well as in non-gustatory tissues. However, due to a lack in TAS2R-specifc antibodies the localization of receptor proteins within gustatory tissues has never been analyzed. In the present study we have screened a panel of commercially available antisera raised against human bitter taste receptors by immunocytochemical experiments. One of these antisera was found to be highly specific for the human bitter taste receptor TAS2R38. We further demonstrate that this antibody is able to detect heterologously expressed TAS2R38 protein on Western blots. The antiserum is, however, not able to interfere significantly with TAS2R38 function in cell based calcium imaging analyses. Most importantly, we were able to demonstrate the presence of TAS2R38 protein in human gustatory papillae. Using double immunofluorescence we show that TAS2R38-positive cells form a subpopulation of PLCbeta2 expressing cells. On a subcellular level the localization of this bitter taste receptor is neither restricted to the cell surface nor particularly enriched at the level of the microvilli protruding into the pore region of the taste buds, but rather evenly distributed over the entire cell body.