Maqsood Siddiqi

The occurrence of preformed N-nitroso compounds in food samples from a high risk area of esophageal cancer in Kashmir, India.

Several commonly used raw foodstuffs from a high risk esophageal cancer region in Kashmir (India) were analysed for the presence of N-nitroso compounds. The food items were selected on the basis of their frequent consumption with particular emphasis on the preserved foods (dried, pickled and smoked) and those which are unique to the region. Nine out of 11 food items were found to contain low concentrations of N-nitrosodimethylamine (NDMA), N-nitrosopyrrolidine (NPYR), N-nitrososarcosine (NSAR), N-nitrosoproline (NPRO) and N-nitrosothaizolidine-4-carboxylic acid (NTCA). The preliminary survey shows a widespread contamination of N-nitroso compounds in raw foodstuffs from Kashmir.

Esophageal cancer in Kashmir--an assessment.

ConclusionKashmir, with its culturally distinct population with uniform and stable dietary habits, provides an interesting field area for studying the relevance of diet in human esophageal carcinogenesis. In the absence of several features of life-style normally associated with increased incidence of the disease, the local food habits appear to be critical factors in the etiology of this cancer in Kashmir. Evidence from our preliminary studies shows a considerable dietary exposure to preformed N-nitroso compounds in the local population. In addition, the potential endogenous formation of N-nitroso compounds, caused by high precursor contents in certain foodstuffs, enhances the relevance of these compounds as possible risk factors for esophageal and other gastrointestinal cancers in this region. The quantitative assessment of total human exposure to N-nitroso compounds and their exact significance to the high cancer incidence in Kashmir requires carefully planned environmental monitoring and prospective epidemiological studies.

N-Nitroso compounds and their precursors in Brassica oleracea

In the present study, Brassica a dried green vegetable from Kashmir, which is a major constituent of the local diet, was analysed for nitrosatable aliphatic amines, N-nitrosamines prior to and after nitrosation) and alkylating activity due to N-nitrosamides following nitrosation. The cooked vegetable contained 11 micrograms/kg nitrosodimethylamine and 21 micrograms/kg nitrosopyrrolidine. Nitrosation under chemical conditions yielded 1200 micrograms/kg N-methylnitrosourea.

Occurrence of volatile N-nitrosamines in dried chillies

Twenty samples of dried chillies, fresh chillies and chilli sauces have been analysed for the presence of volatile N-nitrosamines. Over 75% of both dried whole chillies and chilli powder samples analysed contained N-nitrosodimethylamine and N-nitrosopyrrolidine (NPYR) at concentrations of 0.66-16.5 micrograms/kg and 0.48-6.0 micrograms/kg, respectively. Fresh chillies and chilli sauces were not found to contain volatile N-nitrosamines.

Effect of dietary nitrate on endogenous nitrosation of piperazine in humans.

The effect of dietary nitrate on endogenous nitrosation of a therapeutic dose of piperazine has been described in five human volunteers who acted as their own controls. The urinary excretion of endogenously formed N-nitro-somonopiperazine (MNPz) ranged between 9.2 and 80.1 micrograms/24 h on a normal uncontrolled diet which increased from 25.7 to 163.7 micrograms/24 h when the diet was supplemented with 250 mg nitrate. The corresponding urinary nitrate was 63.0-122.7 mg/24 h and 119.2-322.0 mg/24 h, respectively. The dinitroso derivative of piperazine was detected only in trace amounts and no detectable increase in its excretion was observed during high nitrate exposure. The unchanged piperazine (range 294-784 mg/24 h) in urine showed a decrease under high nitrate regimen (range 185-399 mg/24 h).

Salivary nitrate and nitrite concentrations from a sample population of children and adults in high risk area for esophageal and gastric cancers in Kashmir, India

Salivary nitrate and nitrite levels in a sample population of children and adults from a high risk area of esophageal and gastric cancer in Kashmir are reported. In different age groups mean levels of salivary nitrate/nitrite ranged between 21-36 ppm and 12-17 ppm, respectively.

Caffeine-derived N-nitroso compounds. III: Mutagenicity in S. typhimurium and in vitro induction of DNA single-strand breaks in rat hepatocytes by mononitrosocaffeidine and dinitrosocaffeidine

Mutagenesis in S. typhimurium and in vitro induction of DNA single-strand breaks in primary rat hepatocytes (DNA-SSB) have been investigated for two new N-nitroso compounds, mononitrosocaffeidine (MNC) and dinitrosocaffeidine (DNC). Mononitrosamidocaffeidine (MNAC) and tert.-(butyloxy)carbonyl-mononitrosamidocaffeidine (t-BOC-MNAC), both nitrosated derivatives of caffeidine with nitrosation at methylcarboxamide-N only, were also similarly studied. MNC, an asymmetric nitrosamine, failed to show mutagenicity in any of the tester strains used, and also did not induce DNA-SSB in rat hepatocytes. DNC, having both N-nitrosamide and N-nitrosamine groups in the molecule, showed direct mutagenicity in TA100, TA1535 and TA102. The mutagenic potential of the compound was found to increase on S9 activation. However, it was non-mutagenic in TA98 and TA1537. DNC also exhibited a high potential for inducing alkali-labile DNA-SSB in rat hepatocytes (70-78% C-T value) and was cytotoxic at concentrations over 0.1 mumole/ml. Both MNC and DNC were found to produce formaldehyde on S9 activation. MNAC was not mutagenic directly but showed weak mutagenicity on metabolic activation, whereas t-BOC-MNAC was mutagenic both with and without S9 activation in TA100, TA1535 and TA102. t-BOC-MNAC was more cytotoxic to hepatocytes than MNAC, though both caused DNA-SSB to the same extent (62% C-T value). On the basis of the presented data it is inferred that while DNC is a direct-acting mutagen in TA100, TA1535 and TA102 due to the presence of a reactive N-methylnitrosamido group, its mutagenic potential is greatly enhanced in the presence of S9 possibly due to the synergistic influence of an activated N-methylnitrosamino group in the molecule. Additionally, the study shows a qualitative consistency between Salmonella mutagenicity, genotoxicity in hepatocytes and the reactivity of the methyl group at the nitrosamido-N in nitrosated caffeidine compounds.

Identification of nitrophenols as nitrosation products from capsaicin and red chillies

The in vitro nitrosation of sun-dried red chillies (Capsicum annuum) and of its constituents capsaicin and dihydrocapsaicin was studied. The nitrophenols 4-nitroguaiacol, 4,6-dinitroguaiacol, nitrocapsaicin and nitrodihydrocapsaicin were detected as final products, whereas no formation of nitrosamides was observed though this is expected from the amide precursors capsaicin and dihydrocapsaicin. The nitrosation occurs readily with remarkable yields of nitrophenols even at physiological pH and at nitrite concentrations which are within the range of those found in the human stomach. Due to their toxicity, nitrophenols need to be included in total risk assessment through potential endogenous nitrosation of foodstuffs.

Tobacco-specific N-nitrosamines in tobacco and mainstream smoke of Indian cigarettes

Different brands of Indian cigarettes were analysed, by gas chromatography-thermal energy analysis, for the presence of carcinogenic tobacco-specific N-nitrosamines (TSNA) in both tobacco and mainstream smoke. Preformed TSNA in cigarette tobacco ranged between 68 and 730 ng N-nitrosonornicotine (NNN)/cigarette, between 19 and 174 ng 4-(N-nitrosomethylamino)-1-(3-pyridyl)-1-butanone (NNK)/cigarette and between 98 and 519 ng N-nitrosoanabasine (NAB) together with N-nitrosoanatabine (NAT)/cigarette. The amounts of NNN, NNK and NAB/NAT in mainstream smoke were 11-156, 7-73 and 17-146 ng/cigarette, respectively.