The oral bioavailability of nitrate from nitrate-rich vegetables in humans.

High dietary nitrate intake may pose a risk to human health. Since up to 80-85% of dietary nitrate intake comes from vegetables, the aim of this study was to determine the absolute bioavailability of nitrate from three nitrate-rich vegetables. In an open, four-way cross-over, single dose study, 12 human subjects underwent the following treatments: (1) intravenous infusion of 500mg sodium nitrate, (2) oral administration of 300g cooked spinach, (3) oral administration of 300g raw lettuce, and (4) oral administration of 300g cooked beetroot. The wash-out period between treatments was at least 6 days. Plasma samples were analysed to assess the nitrate and nitrite concentrations, and pharmacokinetic parameters were calculated. The bioavailability of nitrate was 98+/-12% from cooked spinach, 114+/-14% from raw lettuce and 106+/-15% from cooked beetroot. There was no significant increase in plasma nitrite concentrations. This study shows that nitrate from vegetables, whether cooked or uncooked, is absorbed very effectively, resulting in an absolute nitrate bioavailability of around 100%. Thus, reducing the amount of nitrate in vegetables can be an effective measure to lower the systemic nitrate exposure of the general population. However, other aspects, such as the costs to produce vegetables with a low nitrate content and the possible beneficial effects of nitrate in vegetables, need to be considered when evaluating the usefulness of such a measure.

Potato glycoalkaloids and adverse effects in humans: an ascending dose study.

Glycoalkaloids in potatoes may induce gastro-intestinal and systemic effects, by cell membrane disruption and acetylcholinesterase inhibition, respectively. The present single dose study was designed to evaluate the toxicity and pharmacokinetics of orally administered potato glycoalkaloids (alpha-chaconine and alpha-solanine). It is the first published human volunteer study were pharmacokinetic data were obtained for more than 24 h post-dose. Subjects (2-3 per treatment) received one of the following six treatments: (1-3) solutions with total glycoalkaloid (TGA) doses of 0.30, 0.50 or 0.70 mg/kg body weight (BW), or (4-6) mashed potatoes with TGA doses of 0.95, 1.10 or 1.25 mg/kg BW. The mashed potatoes had a TGA concentration of nearly 200 mg/kg fresh weight (the presently recognised upper limit of safety). None of these treatments induced acute systemic effects. One subject who received the highest dose of TGA (1.25 mg/kg BW) became nauseous and started vomiting about 4 h post-dose, possibly due to local glycoalkaloid toxicity (although the dosis is lower than generally reported in the literature to cause gastro-intestinal disturbances). Most relevant, the clearance of glycoalkaloids usually takes more than 24 h, which implicates that the toxicants may accumulate in case of daily consumption.

Applicability of an in vitro digestion model in assessing the bioaccessibility of mycotoxins from food.

Food is considered a major route of exposure to many contaminants. Only the fraction of the contaminant that is released from the food (bioaccessibility) and is bioavailable can exert toxic effects. Insufficient knowledge on the bioavailability may hamper an accurate risk assessment of ingested contaminants in humans. This paper describes the applicability of an in vitro digestion model allowing for measurement of the bioaccessibility of ingested mycotoxins from food as an indicator of oral bioavailability. Bioaccessibility of aflatoxin B(1) from peanut slurry and ochratoxin A from buckwheat was high, 94% and 100%, respectively, and could be determined reproducibly. With the in vitro digestion model, the bioaccessibilities of aflatoxin B(1) and ochratoxin A in the presence of four different absorption modulators were in five out of six situations in accordance with the in vivo effects in humans and animals. By determining the effect of chlorophyllin on the transport of aflatoxin B(1) across the intestinal Caco-2 cells, also the sixth combination was in agreement with data in humans. Hence, the in vitro digestion model, combined with Caco-2 cells, is a powerful experimental tool, which can aid to a more accurate risk assessment of ingested contaminants.