Presentations

Abstract

Introduction: During thermal food processing, as when sugars such as glucose and fructose are heat processed, furan compounds which include HMF are formed. This can be noted in a number of cooking processes: the manufacture of high-fructose corn syrup (HFCS), cooking of fruit sugars as in jams and marmalades, caramelization of sugars, roasting of coffee, and pasteurization and sterilization of milk products. Along with this, HMF is present in foods that have undergone the Maillard reaction which is the browning reaction in baking, frying, and the searing of proteins. As a result of this prominence during heat processing, HMF has been used as a quality indicator in the food industry, signifying overheating or inadequate storage conditions (Lee et al., 2019). For example, HMF content in honey increases with greater storage and heating times, indicating a less fresh product. Moreover, studies reveal several potential effects of HMF, such as an irritant to the eyes, upper respiratory tract, and skin. HMF is a suspected carcinogen, mutagen, diabetogen, hepatotoxin, and nephrotoxin. When comparing soluble protein content in the lenses of cataracts patients, there was a 52% increase in HMF in those lenses derived from diabetic patients versus non-diabetic patients (Rao & Cotlier, 1986). Moreover, in honeybees, varying HMF dosages have shown to lower future brood size and be lethal (Shapla et al., 2018). In a previous experiment in the 832/13 β-cell line, when cultures were shifted from low- (2.5 mM) to high-glucose media (12 mM), we were surprised to see a large increase in intracellular 5-hydroxymethyl-2-furoic acid (Sumiki's acid), a cellular oxidation product of HMF. This caused us to ask the following question: do beta cells exposed to HMF generate Sumiki's Acid, and is this glucose dependent?

Methods: We began our investigation by challenging the rat β-cell line, βG 49/206, with a pulse high-glucose solution spiked with HMF, and assaying HMF and Sumiki's acid at two time points using mass spectrometry. The βG 49/206 cell line shares a close common ancestor with the cells used previously. Trypsinized confluent cultures were seeded onto fresh plates. After adherence, P100 plates were rinsed with phosphate-buffered saline, and then cultured under 10 mL of a low-glucose secretion buffer (2.5 mM) for 60 minutes. Following this, cells were subjected to one of three conditions: 10 mL of low-glucose buffer, 10 mL of high-glucose buffer (12 mM), or 10 mL of high-glucose buffer spiked with HMF (1 mM). Conditioned media and cell lysates were captured at 100 minutes (high-glucose spiked with HMF) and 270 minutes (low-glucose, high-glucose, and high-glucose spiked with HMF). Relative amounts of metabolites were measured by ultrahigh-pressure liquid chromatography / quadrupole, time-of-flight mass spectrometry (UHPLC / QToF MS) on an Agilent 1290 / 6546 system. and by gas chromatography (GC) / MS on an Agilent 8890 / 5977B system. Glucose concentrations were measured on a Beckman UniCel DxC 600 Synchron instrument.

Results: As in our earlier work in the 832/13 insulinoma cell line, the 49/206 β-cell line was able to take up HMF and oxidize it to Sumiki's acid. In cell lysates in the present study, HMF and Sumiki's acid were only observed in plates dosed with HMF. HMF concentrations rose between 100 and 270 minutes, while levels of Sumiki's acid were relatively stable. Compared to high-glucose cultures that received no HMF, at 270 minutes, HMF-treated cells showed a marked increase in adenine (purine), 6-methyluracil (pyrimidine), spermidine (polyamine), components of fetal bovine serum (urea, norepinephrine), taurine, and several amino acids, including lysine, phenylalanine, and tyrosine, perhaps reflecting an acute proteolytic response to the HMF dose. Lactate was increased, and a number of Krebs-cycle intermediates (succinate, fumarate, and malate) were decreased in HMF-dosed cells, suggesting a shift of central fuel metabolism toward glycolysis-but the effect size there was modest.

Conclusion: By deliberately spiking a glucose-secretion buffer with HMF, we confirmed our earlier observation that transgenic rat β-cell lines can absorb HMF and oxidize it to Sumiki's acid. Further work is needed: • Can native rat and human β cells concentrate HMF and oxidize it to Sumiki's acid? If so, what are the pharmacokinetics? If so, is HMF toxic to β cells at physiologically meaningful doses, or does it form adducts with their proteins or DNA? • Is HMF being concentrated in β cells via such transporters as GLUT1 and GLUT2? • If dietary HMF levels in highly processed foods, such as HFCS, are shown to be diabetogenic, could they be reduced by process controls in the food industry?