Chromosome aberrations induced by pyrolysates of carbohydrates in Chinese hamster V79 cells

Dietary glycation compounds - implications for human health

The term "glycation compounds" comprises a wide range of structurally diverse compounds that are formed endogenously and in food via the Maillard reaction, a chemical reaction between reducing sugars and amino acids. Glycation compounds produced endogenously are considered to contribute to a range of diseases. This has led to the hypothesis that glycation compounds present in food may also cause adverse effects and thus pose a nutritional risk to human health. In this work, the Senate Commission on Food Safety (SKLM) of the German Research Foundation (DFG) summarized data on formation, occurrence, exposure and toxicity of glycation compounds (Part A) and systematically assessed potential associations between dietary intake of defined glycation compounds and disease, including allergy, diabetes, cardiovascular and renal disease, gut/gastrotoxicity, brain/cognitive impairment and cancer (Part B). A systematic search in Pubmed (Medline), Scopus and Web of Science using a combination of keywords defining individual glycation compounds and relevant disease patterns linked to the subject area of food, nutrition and diet retrieved 253 original publications relevant to the research question. Of these, only 192 were found to comply with previously defined quality criteria and were thus considered suitable to assess potential health risks of dietary glycation compounds. For each adverse health effect considered in this assessment, however, only limited numbers of human, animal and in vitro studies were identified. While studies in humans were often limited due to small cohort size, short study duration, and confounders, experimental studies in animals that allow for controlled exposure to individual glycation compounds provided some evidence for impaired glucose tolerance, insulin resistance, cardiovascular effects and renal injury in response to oral exposure to dicarbonyl compounds, albeit at dose levels by far exceeding estimated human exposures. The overall database was generally inconsistent or inconclusive. Based on this systematic review, the SKLM concludes that there is at present no convincing evidence for a causal association between dietary intake of glycation compounds and adverse health effects.

Novel insights into the effects of 5-hydroxymethfurural on genomic instability and phenotypic evolution using a yeast model

5-Hydroxymethfurural (5-HMF) is naturally found in a variety of foods and beverages and represents a main inhibitor in the lignocellulosic hydrolysates used for fermentation. This study investigated the impact of 5-HMF on the genomic stability and phenotypic plasticity of the yeast Saccharomyces cerevisiae. Using next-generation sequencing technology, we examined the genomic alterations of diploid S. cerevisiae isolates that were subcultured on a medium containing 1.2 g/L 5-HMF. We found that in 5-HMF-treated cells, the rates of chromosome aneuploidy, large deletions/duplications, and loss of heterozygosity were elevated compared with that in untreated cells. 5-HMF exposure had a mild impact on the rate of point mutations but altered the mutation spectrum. Contrary to what was observed in untreated cells, more monosomy than trisomy occurred in 5-HMF-treated cells. The aneuploidy mutant with monosomic chromosome IX was more resistant to 5-HMF than the diploid parent strain because of the enhanced activity of alcohol dehydrogenase. Finally, we found that overexpression of ADH6 and ZWF1 effectively stabilized the yeast genome under 5-HMF stress. Our findings not only elucidated the global effect of 5-HMF on the genomic integrity of yeast but also provided novel insights into how chromosomal instability drives the environmental adaptability of eukaryotic cells.IMPORTANCESingle-cell microorganisms are exposed to a range of stressors in both natural and industrial settings. This study investigated the effects of 5-hydroxymethfurural (5-HMF), a major inhibitor found in baked foods and lignocellulosic hydrolysates, on the chromosomal instability of yeast. We examined the mechanisms leading to the distinct patterns of 5-HMF-induced genomic alterations and discovered that chromosomal loss, typically viewed as detrimental to cell growth under most conditions, can contribute to yeast tolerance to 5-HMF. Our results increased the understanding of how specific stressors stimulate genomic plasticity and environmental adaptation in yeast.

The role of endogenous versus exogenous sources in the exposome of putative genotoxins and consequences for risk assessment

The "totality" of the human exposure is conceived to encompass life-associated endogenous and exogenous aggregate exposures. Process-related contaminants (PRCs) are not only formed in foods by heat processing, but also occur endogenously in the organism as physiological components of energy metabolism, potentially also generated by the human microbiome. To arrive at a comprehensive risk assessment, it is necessary to understand the contribution of in vivo background occurrence as compared to the ingestion from exogenous sources. Hence, this review provides an overview of the knowledge on the contribution of endogenous exposure to the overall exposure to putative genotoxic food contaminants, namely ethanol, acetaldehyde, formaldehyde, acrylamide, acrolein, α,β-unsaturated alkenals, glycation compounds, N-nitroso compounds, ethylene oxide, furans, 2- and 3-MCPD, and glycidyl esters. The evidence discussed herein allows to conclude that endogenous formation of some contaminants appears to contribute substantially to the exposome. This is of critical importance for risk assessment in the cases where endogenous exposure is suspected to outweigh the exogenous one (e.g. formaldehyde and acrolein).

Antineoplastic activity of products derived from cellulose-containing materials: levoglucosenone and structurally-related derivatives as new alternatives for breast cancer treatment

Breast cancer is the leading cause of cancer death among women worldwide. For this reason, the development of new therapies is still essential. In this work we have analyzed the antitumor potential of levoglucosenone, a chiral building block derived from the pyrolysis of cellulose-containing materials such as soybean hulls, and three structurally related analogues. Employing human and murine mammary cancer models, we have evaluated the effect of our compounds on cell viability through MTS assay, apoptosis induction by acridine orange/ethidium bromide staining and/or flow cytometry and the loss of mitochondrial potential by tetramethylrhodamine methyl ester staining. Autophagy and senescence induction were also evaluated by Western blot and β-galactosidase activity respectively. Secreted metalloproteases activity was determined by quantitative zymography. Migratory capacity was assessed by wound healing assays while invasive potential was analyzed using Matrigel-coated transwell chambers. In vivo studies were also performed to evaluate subcutaneous tumor growth and experimental lung colonization. All compounds impaired in vitro proliferation with IC₅₀ values in a range of low micromolar. Apoptosis was identified as the main mechanism responsible for the reduction of monolayer cell content induced by the compounds without detecting modulations of autophagy or senescence processes. Two of the four compounds (levoglucosenone and its brominated variant) were able to modulate in vitro events associated with tumor progression, such as migratory potential, invasiveness, and proteases secretion. Furthermore, tumor volume and metastatic spread were significantly reduced in vivo after the treatment these two compounds. Here, we could obtain from soybean hulls, a material with almost no commercial value, a variety of chemical compounds useful for breast cancer treatment.

Validation of the 3D reconstructed human skin Comet assay, an animal-free alternative for following-up positive results from standard in vitro genotoxicity assays

As part of the safety assessment process, all industrial sectors employ genotoxicity test batteries, starting with well-established in vitro assays. However, these batteries have limited predictive capacity for the in vivo situation, which may result in unnecessary follow-up in vivo testing or the loss of promising substances where animal tests are prohibited or not desired. To address this, a project involving regulators, academia and industry was established to develop and validate in vitro human skin-based genotoxicity assays for topically exposed substances, such as cosmetics ingredients. Here, we describe the validation of the 3D reconstructed skin (RS) Comet assay. In this multicenter study, chemicals were applied topically three times to the skin over 48 h. Isolated keratinocytes and fibroblasts were transferred to slides before electrophoresis and the resulting comet formation was recorded as % tail DNA. Before decoding, results of the validation exercise for 32 substances were evaluated by an independent statistician. There was a high predictive capacity of this assay when compared to in vivo outcomes, with a sensitivity of 77 (80)%, a specificity of 88 (97)% and an overall accuracy of 83 (92)%. The numbers reflect the calls of the performing laboratories in the coded phase, whereas those in parenthesis reflect calls according to the agreed evaluation criteria. Intra- and inter-laboratory reproducibility was also very good, with a concordance of 93 and 88%, respectively. These results generated with the Phenion® Full-Thickness skin model demonstrate its suitability for this assay, with reproducibly low background DNA damage and sufficient metabolic capacity to activate pro-mutagens. The validation outcome supports the use of the RS Comet assay to follow up positive results from standard in vitro genotoxicity assays when the expected route of exposure is dermal. Based on the available data, the assay was accepted recently into the OECD test guideline development program.

The Toxicological Aspects of the Heat-Borne Toxicant 5-Hydroxymethylfurfural in Animals: A Review

The incidence of adverse reactions in food is very low, however, some food products contain toxins formed naturally due to their handling, processing and storage conditions. 5-(Hydroxymethyl)-2-furfural (HMF) can be formed by hydrogenation of sugar substances in some of manufactured foodstuffs and honey under elevated temperatures and reduced pH conditions following Maillard reactions. In previous studies, it was found that HMF was responsible for harmful (mutagenic, genotoxic, cytotoxic and enzyme inhibitory) effects on human health. HMF occurs in a wide variety of food products like dried fruit, juice, caramel products, coffee, bakery, malt and vinegar. The formation of HMF is not only an indicator of food storage conditions and quality, but HMF could also be used as an indicator of the potential occurrence of contamination during heat-processing of some food products such as coffee, milk, honey and processed fruits. This review focuses on HMF formation and summarizes the adverse effects of HMF on human health.

Inhibitory Effect of Hydroxymethylfurfural in Viability of BALB/C Mice Splenocytes

Background: This study was designed to discover if hydroxymethylfurfural (HMF) exposure modifies cell proliferation and DNA damage in BALB/c mice splenocytes. Methods: Mitogenesis in T cells and B cells was induced by Concanavalin A (Con A) and lipopolysaccharide (LPS). The colorimetric tetrazolium assay was used to evaluate cell proliferation. DNA damaging consequences were evaluated via measurement of 8-hydroxy-2-deoxyguanosine (8-OHdG) level in BALB/c mice splenocytes. Results: Spleen cells proliferation elicited by ConA, was dramatically suppressed by 25, 50 and 100 mM of HMF. However, there was not any significant difference between various concentrations of HMF. The same result was observed following treatment with LPS and HMF in different concentrations. Eight-OHdG concentration was elevated significantly in HMF treated groups compared with untreated control and mitogens. Conclusion: HMF was found to have immunosuppressing and DNA damaging properties in mM concentrations in mice splenocytes.

5-Hydroxymethylfurfural (HMF) levels in honey and other food products: effects on bees and human health

An organic compound known as 5-hydroxymethylfurfural (HMF) is formed from reducing sugars in honey and various processed foods in acidic environments when they are heated through the Maillard reaction. In addition to processing, storage conditions affect the formation HMF, and HMF has become a suitable indicator of honey quality. HMF is easily absorbed from food through the gastrointestinal tract and, upon being metabolized into different derivatives, is excreted via urine. In addition to exerting detrimental effects (mutagenic, genotoxic, organotoxic and enzyme inhibitory), HMF, which is converted to a non-excretable, genotoxic compound called 5-sulfoxymethylfurfural, is beneficial to human health by providing antioxidative, anti-allergic, anti-inflammatory, anti-hypoxic, anti-sickling, and anti-hyperuricemic effects. Therefore, HMF is a neo-forming contaminant that draws great attention from scientists. This review compiles updated information regarding HMF formation, detection procedures, mitigation strategies and effects of HMF on honey bees and human health.

Effects of honey HMF on enzyme activities and serum biochemical parameters of Wistar rats

Hydroxymethylfurfural (HMF) is a by-product of thermal degradation of glucose and fructose. In this study, the effects of high HMF content of honey on biochemical parameters of rats were investigated. Experiments were conducted with 40 Wistar albino male rats, each weighing 250-350 g and covered a period of 5 weeks. The animals were divided into five groups. The first group was served as control group. HMF was injected subcutaneously at a dose of 200 mg/kg rat b.w. to the animals in group 2. Group 3 was fed with honey that contains 10 mg HMF/kg honey. In group 4 and 5, there were honeys that contain significantly high HMF content due to long storage period (181 mg HMF/kg honey) and heat process (140 mg HMF/kg honey). At the end of the feeding process, biochemical blood parameters of rats were investigated. It was observed that there were no differences among the glucose, triglyceride, HDL cholesterol, uric acid, Na, GGT, and ALP parameters of the groups. On the other hand, significant differences were observed among the cholesterol, LDL, BUN, creatinine, Ca, P, Mg, K, Cl, total bilirubin, LDH, CPK, AST, ALT, total protein, and pseudocholinesterase values of the rats. The highest adverse effects were obtained from group HMF, and it was followed by groups SH (stored honey) and HH (heated honey). It can be concluded that high HMF content of honey may affect the human health adversely; thus, HMF in honey must be controlled by beekeepers.

Cytotoxic effect of levoglucosenone and related derivatives against human hepatocarcinoma cell lines

Levoglucosenone has been used as template for the synthesis of a wide variety of compounds with an impressive structural variability. However, scarce work has been done regarding the generation of new bioactive entities. Here we report the cytotoxic effect of levoglucosenone and some related derivatives against hepatocarcinoma cell lines. Compounds were obtained in only one synthetic step and one of them showed an activity within the range of IC50 values of cisplatin, a frequently administered chemotherapy drug.

The food processing contaminant glyoxal promotes tumour growth in the multiple intestinal neoplasia (Min) mouse model

Glyoxal is formed endogenously and at a higher rate in the case of hyperglycemia. Glyoxal is also a food processing contaminant and has been shown to be mutagenic and genotoxic in vitro. The tumourigenic potential of glyoxal was investigated using the multiple intestinal neoplasia (Min) mouse model, which spontaneously develops intestinal tumours and is susceptible to intestinal carcinogens. C57BL/6J females were mated with Min males. Four days after mating and throughout gestation and lactation, the pregnant dams were exposed to glyoxal through drinking water (0.0125%, 0.025%, 0.05%, 0.1%) or regular tap water. Female and male offspring were housed separately from PND21 and continued with the same treatment. One group were only exposed to 0.1% glyoxal from postnatal day (PND) 21. There was no difference in the number of intestinal tumours between control and treatment groups. However, exposure to 0.1% glyoxal starting in utero and at PND21 caused a significant increase in tumour size in the small intestine for male and female mice in comparison with respective control groups. This study suggests that glyoxal has tumour growth promoting properties in the small intestine in Min mice.

Intestinal carcinogenesis of two food processing contaminants, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine and 5-hydroxymethylfurfural, in transgenic FVB min mice expressing human sulfotransferases

Humans express sulfotransferases (SULTs) of the SULT1A subfamily in many tissues, whilst the single SULT1A gene present in rodents is mainly expressed in liver. The food processing contaminants, 5-hydroxymethylfurfural (HMF) and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), are bioactivated by human SULT1A1 and SULT1A2. FVB multiple intestinal neoplasia (Min) mice, which spontaneously develop tumors and flat aberrant crypt foci (ACF) in intestine, were crossed with transgenic FVB mice expressing human SULT1A1 and 1A2 (hSULT) in several tissues, giving rise to wild-type and Min mice with and without hSULT. One-week-old Min mice with or without hSULT were given HMF (375 or 750 mg/kg bw) or saline by gavage three times a week for 11 wk. In another experiment, the F1 generation received subcutaneous injections of 50 mg/kg bw PhIP or saline 1 wk before birth, and 1, 2, and 3 wk after birth. HMF did not affect the formation of tumors, but may have induced some flat ACF (incidence 15-20%) in Min mice with and without hSULT. No control mouse developed any flat ACF. With the limitation that these putative effects were weak, they were unaffected by hSULT expression. The carcinogenic effect of PhIP increased in the presence of hSULT, with a significant increase in both incidence (31-80%) and number of colonic tumors (0.4-1.3 per animal). Thus, intestinal expression of human SULT1A1 and 1A2 might increase the susceptibility to compounds bioactivated via this pathway implying that humans might be more susceptible than conventional rodent models.

Toxicology and risk assessment of 5-Hydroxymethylfurfural in food

5-Hydroxymethylfurfural (5-HMF) as a product of the Maillard reaction is found in many foods. Estimated intakes range between 4 and 30  mg per person and day, while an intake of up to 350  mg can result from, e.g., beverages made from dried plums. In vitro genotoxicity was positive when the metabolic preconditions for the formation of the reactive metabolite 5-sulphoxymethylfurfural were met. However, so far in vivo genotoxicity was negative. Results obtained in short-term model studies for 5-HMF on the induction of neoplastic changes in the intestinal tract were negative or cannot be reliably interpreted as "carcinogenic". In the only long-term carcinogenicity study in rats and mice no tumours or their precursory stages were induced by 5-HMF aside from liver adenomas in female mice, the relevance of which must be viewed as doubtful. Hence, no relevance for humans concerning carcinogenic and genotoxic effects can be derived. The remaining toxic potential is rather low. Various animal experiments reveal that no adverse effect levels are in the range of 80-100  mg/kg body weight and day. Safety margins are generally sufficient. However, 5-HMF exposure resulting from caramel colours used as food additives should be further evaluated.

Identification, characterization of levoglucosan kinase, and cloning and expression of levoglucosan kinase cDNA from Aspergillus niger CBX-209 in Escherichia coli

The first enzyme responsible for assimilating levoglucosan in Aspergillus niger CBX-209 was corroborated to be levoglucosan kinase that catalyzes the transfer of a phosphate group from ATP to levoglucosan to yield a glucose 6-phosphate in the presence of magnesium ion and ATP by FAB-mass spectrometric method combined with previous observations from HPLC and enzymological experiments. Levoglucosan kinase was purified to apparent homogeneity by using a combination of seven purification steps. SDS-PAGE revealed a single protein band of 56 KDa. It is a monomeric enzyme and maximal enzyme activity was measured at pH 9.3 and 30 degrees C. This kinase is stable below 20 degrees C at a quite broad pHs ranging from 6 to 10 and levoglucosan could protect the enzyme from thermal inactivation. Exclusive substrate specificity for levoglucosan suggested that not only the structure of the intramolecular glucosidic linkage but also the configuration of the pyranose frame would be specific for recognition by levoglucosan kinase. The K(m) values of this enzyme were 71.2mM for levoglucosan and 0.25 mM for ATP, determined by double reciprocal plottings and ADP inhibited on the enzyme activity competitively with a Ki value of 0.20mM. A cDNA library from A. niger was constructed in Escherichia coli DH5alpha. The library was screened for levoglucosan kinase gene on NCE selective medium and three positive recombinants were selected after a five day culture. Detection of activities of levoglucosan kinase in the cell extracts indicated that levoglucosan kinase gene (lgk) was expressed by the recombinant strain of E. coli DH5alpha.

5-Hydroxymethylfurfural: assessment of mutagenicity, DNA-damaging potential and reactivity towards cellular glutathione

5-(hydroxymethyl)-2-furfural (HMF), a common product of the Maillard reaction, occurs in many foods in high concentrations, sometimes exceeding 1 g/kg (in certain dried fruits and caramel products). The toxicological relevance of this exposure has not yet been clarified. Induction of aberrant colonic crypt foci had been reported for HMF, in vitro studies on genotoxicity/mutagenicity have given controversial results. To elucidate the toxic potential of HMF, cytotoxicity (trypan blue exclusion), growth inhibition (SRB assay), mutagenicity (HPRT assay), DNA damage (single-cell gel electrophoresis) and depletion of cellular glutathione were investigated in mammalian cells. Genotoxicity (SOS repair) was monitored in Salmonella typhimurium (umu assay). HMF induced moderate cytotoxicity in V79 cells (LC(50): 115 mM, 1 hr incubation) and in Caco-2 cells (LC(50): 118 mM, 1 hr incubation). Growth inhibition was monitored following 24 hr of incubation (V79, IC(50): 6.4 mM). DNA damage was detectable neither in these cell lines nor in primary rat hepatocytes up to the cytotoxic threshold concentration (75% absolute viability). Likewise, in primary human colon cells, obtained from biopsy material, DNA damage was not measurable. At 120 mM, already exhibiting some reduction in cell viability, HMF was weakly mutagenic at the hprt-locus in V79 cells (mutants/10(6) cells: HMF 120 mM: 16 vs control: 3). Intracelluar glutathione was depleted by HMF (>/=50 mM) in V79 cells, in the human colon adenocarcinoma cell line Caco-2 and in primary rat hepatocytes down to approximately 30% of control (120 mM). Genotoxicity was observed with HMF in the umu assay without external activation (16 mM: 185 rel. umu units, %, P<0.001). The genotoxic potential was not altered by addition of rat liver microsomes. By comparison, the natural flavour constituent (E)-2-hexenal (HEX) was already cytotoxic, mutagenic and depleted glutathione at about 1000-fold lower concentrations. It induced DNA damage in mammalian cells (200-400 microM). These results suggest that HMF does not pose a serious health risk, even though the highest concentrations in specific foods approach the biologically effective concentration range in cell systems.

Sugar, meat, and fat intake, and non-dietary risk factors for colon cancer incidence in Iowa women (United States)

To investigate the relation of dietary intakes of sucrose, meat, and fat, and anthropometric, lifestyle, hormonal, and reproductive factors to colon cancer incidence, data were analyzed from a prospective cohort study of 35,215 Iowa (United States) women, aged 55-69 years and without a history of cancer, who completed mailed dietary and other questionnaires in 1986. Through 1990, 212 incident cases of colon cancer were documented. Proportional hazards regression was used to adjust for age and other risk factors. Risk factors found to be associated significantly with colon cancer included: (i) sucrose-containing foods and beverages other than ice cream/milk; relative risks (RR) across the quintiles = 1.00, 1.73, 1.56, 1.54, and 2.00 (95% confidence intervals [CI] for quintiles two and five exclude 1.0); (ii) sucrose; RR across the quintiles = 1.00, 1.70, 1.81, 1.82, and 1.45 (CI for quintiles two through four exclude 1.0); (iii) height; RR = 1.23 for highest to lowest quintile (P for trend = 0.02); (iv) body mass index; RR = 1.41 for highest to lowest quintile (P for trend = 0.03); and (v) number of livebirths, RR = 1.59 for having had one to two livebirths and 1.80 for having had three or more livebirths compared with having had none (P for trend = 0.04). These data support hypotheses that sucrose intake or being tall or obese increases colon cancer risk; run contrary to the hypothesis that increased parity decreases risk; support previous findings of no association with demographic factors other than age, cigarette smoking, or use of oral contraceptives or estrogen replacement therapy; and raise questions regarding previous associations with meat, fat, protein, and physical activity.

Thiazolidine derivatives as source of free L-cysteine in rat tissue

The present study demonstrates that a variety of thiazolidine-4-(R)-carboxylic acids (TDs) which are the products of reactions of L-cysteine (cys) with carbonyl compounds could serve as a "delivery" system for cys to the cell. Liberation of the amino acid can occur enzymatically as well as non-enzymatically. The two possibilities have been proven by identification of representative compounds. The most specific substrate for mitochondrial enzymatic oxidation was thiazolidine-4-carboxylic acid (CF), the product of the reaction of cys with formaldehyde, and the least metabolized TD was 2-methyl-thiazolidine-4-carboxylic acid (CA), the product of the reaction of cys with acetaldehyde. TDs formed from cys and different sugars were not metabolized at all in mitochondria. N-Formyl-L-cysteine (NFC) the intermediate product of mitochondrial metabolism of CF was ascertained by 1H-NMR spectroscopy whereas N-acetyl-L-cysteine (NAC), the predicted metabolite of CA, was not detected, possibly due to a fast turnover. The further enzymatic hydrolysis of NFC as well as NAC to free cys was demonstrated to take place in the cytoplasm. Non-enzymatic hydrolysis of TDs depended on the chemical nature of the substituents in the thiazolidine (Th) ring. The most stable compound was unsubstituted Th and the least stable were CGlu(D) and CA. Following non-enzymatic ring opening and hydrolysis, CA was converted to methyl-djenkolic acid, which equilibrates with CA. We have identified this new compound by 1H-NMR spectroscopy. TDs may cause both a decrease and an increase in the levels of SH-groups in mitochondria. In the case of the stable CF, which is metabolized only enzymatically, an increase in the levels of SH-groups in mitochondria was observed. This suggests that enzymatic control of the breakdown of TDs prevents overflowing of the cell with thiol groups. The latter seems to be induced by high concentrations of those TDs which are hydrolysed non-enzymatically. This process leads finally to a decrease in free SH-groups by different mechanisms. The findings demonstrate two different mechanisms by which TDs can provide cys to the cells. The biological and pharmacological consequences are discussed.

Diet, aberrant crypt foci and colorectal cancer

We have used the aberrant crypt focus (ACF) assay to test and develop hypotheses linking diet and colon cancer. The hypotheses were suggested by epidemiological studies that identified possible dietary factors associated with colorectal cancer risk. The ACF assay was used to quantitate the effect of the dietary factors on the initiation and growth of these putative precursors of colon cancers in experimental animals. Using this approach we have developed 3 new hypotheses for the role of diet in colorectal cancer. These are (1) a risk associated with 5-hydroxymethyl-2-furaldehyde in caramelized sugar, (2) a risk associated with some factor in thermolyzed casein, and (3) a risk associated with single nutrient boluses of sucrose and fructose. The importance of these hypotheses has still to be tested in long term carcinogenesis experiments, in analytic epidemiology studies and then, perhaps, in intervention trials.