Cytotoxic triterpenoids from the leaves of Euphorbia pulcherrima.

Two cytotoxic triterpenes have been isolated from Euphorbia pulcherrima. Their structures and stereochemistry have been established from NMR, IR, and EI-mass spectroscopy. The compounds were identified as 9,19-cycloart-23-ene-3 beta,25-diol and, 9,19-cycloart-25-ene-3 beta,24-diol. Cytotoxicity evaluation was performed using Ehrlich ascites tumor cells. While cycloartenol induced no cytotoxic activity against Ehrlich ascites tumor cells, both isolated triterpenes exhibited cell inactivating effects. The IC50 is approximately 7.5 microM, while the IC90 is approximately 13.5 microM for 9,19-cycloart-25-ene-3 beta,24-diol. The 3 beta,25-diol compound is 50% less active.

Endogenous N-nitrosation in man assessed by measurement of apparent total N-nitroso compounds in faeces.

The faecal concentration of substances responding to the chemical test for N-nitroso compounds (apparent total N-nitroso compounds, ATNC) was investigated in human subjects consuming their normal free-choice diet. Concentrations ranged from 40 to 590 micrograms (N-NO)/kg faeces. To ascertain the likely relative contributions of endogenous ATNC formation and preformed, dietary ATNC, the subjects consumed a diet low in nitrate and ATNC for 8 days. At the end of this period, ATNC had decreased substantially with concentrations ranging from below the 40 micrograms (N-NO)/kg detection limit up to 143 micrograms (N-NO)/kg, mean 82 micrograms (N-NO)/kg. On supplementing this diet with 300 mg nitrate/day, faecal ATNC levels increased markedly. On the third day of this regime, values were in the range 73-714 micrograms (N-NO)/kg with a mean of 307 micrograms (N-NO)/kg. The results, together with the known limited occurrence of ATNC in the majority of foodstuffs so far tested, generally non-detectable or less than 100 micrograms (N-NO)/kg, suggest that endogenous formation via species derived from dietary nitrate is likely to be an important source of ATNC in human faeces.

Nitrate and nitrite concentrations in human saliva: variations with salivary flow-rate.

Salivary nitrate concentration has often been used as a measure of human intake of nitrate. However, our findings indicate that this is not a reliable indicator because the nitrate concentration varies with salivary flow-rate and thus depends on the sampling procedure. Parotid or whole saliva was collected from up to six volunteers under carefully controlled conditions. The effects of stimulating saliva production by chewing on silicon tube (mechanical stimulation) or by sucking citric acid from cotton wool (gustatory stimulation) were investigated. Chewing decreased the average nitrate (plus nitrite) concentration in whole saliva by 59% and the nitrate concentration in parotid saliva (which does not contain nitrite) by 53%, relative to unstimulated saliva. Citric acid stimulation decreased the average parotid salivary nitrate concentration by 88%. Stimulation of salivary secretion increased the total salivary nitrate output and the extent of reduction of nitrate to nitrite for most subjects. The unstimulated parotid salivary nitrate concentration was, on average, 2.8 times the nitrate plus nitrite concentration in unstimulated whole saliva.

A possible role of the dietary fibre product, wheat bran, as a nitrite scavenger.

We found that wheat bran acted as a nitrite scavenger under conditions similar to those that exist in the stomach. Wheat flour and cellulose did not act as nitrite scavengers. Wheat bran, at a concentration equivalent to that in the stomach after ingestion of about two pieces of whole-wheat bread, reduces the nitrite concentration from 20 microM to about 10 microM in 60 min at pH 3.5 and 37 degrees C. At pH 2.5 and 1.5, most of the nitrite had disappeared in 10 min. At pH less than or equal to 2.5 the nitrite scavenging effect of bran was as efficient as that of ascorbic acid. Ferulic acid, a component of bran, reacted rapidly with 20 microM-nitrite both at pH 3.5 and 1.5, whereas phenolic lignin model compounds only reacted at pH 1.5.