Chronic effects of norharman in rats treated with aniline

Aniline: early indicators of toxicity in male rats and their relevance to spleen carcinogenicity

Early indicators of aniline hydrochloride (AH) toxicity were investigated in male Fisher 344 rats for 1 or 4 weeks at dietary dose levels of 10, 30 or 100 mg/kg body weight (bw)/day (actual intake at least 6, 17 and 57 mg/kg). The doses were based on earlier studies that had shown spleen toxicity and carcinogenicity in male rats at 100 mg/kg/day but not at 10 mg/12/kg/day. In the present study a dose-related formation of haemoglobin adducts and Heinz bodies was found from 10 and 30 mg/kg bw/day, respectively, onwards. Signs of anaemia (decreased red blood cell counts and increased reticulocytes) were recorded from 30 mg/kg onwards. At 100 mg/kg, an overt haemolytic anaemia was associated with increases in serum transferrin concentration and total iron binding capacity in the blood reflecting major perturbations in iron metabolism. At this dose there was an increase in peripheral neutrophil leucocytosis in the blood, indicating an inflammatory process in the spleen. Histopathologic evaluation showed a focal perisplenitis and haemosiderin deposition in sinusoidal Kupffer cells of the liver at 100 mg/kg. These results corroborate the contention that carcinogenic doses of aniline cause early effects on haematological parameters, inflammatory reaction in the spleen and perturbations in iron metabolism as a result of haemolytic anaemia. Accordingly, the carcinogenicity of aniline may be linked to definable threshold-related processes.

Effect of thermal treatment on meat proteins with special reference to heterocyclic aromatic amines (HAAs)

Meat is one of the most imperative protein sources available with respect to its production and consumption. It is the richest source of some valuable nutrients like proteins, essential amino acids, polyunsaturated fatty acids, vitamins, and minerals like iron, zinc, and selenium. Thermal treatment produces conformational changes in protein structure as well as flavor, texture, and appearance, and chemical properties of the ingredients are also changed. Heterocyclic aromatic amines (HAAs), potent mutagens/carcinogens, are formed during the cooking of meat at high temperature. The review paper highlights the effects of various cooking methods, i.e., pan-frying, deep-frying, charcoal grilling, and roasting, on the formation of HAAs. The levels of HAAs produced in cooked meats vary depending upon the cooking method, time of cooking, and the type of meat being cooked. Metabolic behavior of HAAs is very unique, they interfere in the activity of many enzymes, modify the metabolic pathways, and lead to the adduct formation of DNA. The application of black pepper and several other spices during processing may reduce the formation of these (HAAs) mutagenic compounds.

LACK OF COMBINATION HEPATOCARCINOGENICITY OF HARMAN, NORHARMAN AND AMITROLE WHEN GIVEN WITH NaNO2 IN THE RAT

N-nitrosocompounds, which induce cancers in various organs, may be formed endogenously with intake of amino compounds such as secondary amines and sodium nitrite (NaNO(2)) in combination. The present study was performed to investigate whether three amino compounds, 1-methyl-9H-pyrido[3,4-b]indole (harman), 9H-pyrido[3,4-b]indole (norharman) and 2-amino-1,3,4-triazole (amitrole), might be converted in vivo to compounds capable of promoting hepatocarcinogenesis when given with NaNO(2). However, in an 8-week model, no modifying potential was evident in terms of numbers and areas of putative preneoplastic glutathione S-transferase placental form (GST-P)-positive foci in any of the groups receiving paired treatments. These results demonstrate that combinations of harman, norharman and amitrole with NaNO(2) lack promoting effects for liver carcinogenesis in our medium-term bioassay system.

Possibility of the involvement of 9H-pyrido[3,4-b]indole (norharman) in carcinogenesis via inhibition of cytochrome P450-related activities and intercalation to DNA

This study investigated the inhibitory effect of 9H-pyrido[3,4-b]indole (norharman), one of the naturally occurring beta-carbolines, on cytochrome P450 (CYP)-related activities and the relationship between its inhibitory effect, its intercalation to DNA, and its comutagenic effect. Norharman reduced the mutagenicities of heterocyclic amines (HCAs) containing 2-amino-6-methyldipyrido[1,2-a:3',2'-d]imidazole (Glu-P-1), aflatoxin B1, benzo[a]pyrene (BP), and some nitrosamines in the presence of 10 microl liver S9 (20.9 microg protein/ml) from polychlorinated biphenyl-treated rats. Norharman inhibited microsomal CYP-related enzyme activities and CO-binding to the CYP heme (50% inhibitory concentration (IC50), 0.07-6.4 microg/ml). It also inhibited the formation of 3-hydroxyamino-6-methyldipyrido[1,2-a:3',2'-d]imidazole (N-OH-Glu-P-1) and was a noncompetitive-inhibitor of CYP1A-related activities, while it enhanced the direct mutagenicity of N-OH-Glu-P-1 (50% effective concentration, 25.0 microg/ml) and inhibited topo I activity (IC50, 31.0 microg/ml). In the presence of norharman, S9 up to 100 microl incrementally enhanced the mutagenicities of HCAs, BP and dimethylnitrosamine. These data clarified that norharman acts as an inhibitor of the CYP-mediated biotransformation of Glu-P-1 via inhibition of O2-binding to CYP heme, and its inhibition of CYP enzymes occurs at much lower concentration than that for its intercalation to DNA. It is indicated that norharman's inhibitory effect on CYP results in the inhibition of excess metabolism by S9 and this is more likely the mechanism for comutagenic action than the intercalation. Norharman's inhibition of CYP and its enhancement of the N-OH-Glu-P-1 mutagenicity suggest that beta-carbolines modulate chemical carcinogenesis by controlling the xenobiotic metabolism and by intercalating to DNA.

Genotoxic potential of beta-carbolines: a review

The mutagenic and co-mutagenic properties of harman, norharman and of some of their pharmacologically important derivatives are reviewed. These compounds do not behave as true mutagens, but rather interact, directly or indirectly with DNA, leading to various consequences. This unusual behaviour is most probably related to the particular structure of the chemical nucleus common to all beta-carbolines which confers to the different derivatives the property to interact with various macromolecules and enzymatic systems. These interactions are compiled and discussed in this review. The alterations, by beta-carbolines, of some important enzymatic systems, e.g. cytochrome P-450, have been clearly demonstrated, yet many discrepancies and contradictions exist so that an interpretation of the results and the definition of some common mechanism appears premature. Since beta-carbolines are widely distributed in tissues and since they may modify and increase genotoxic and toxic consequences of other compounds, these interactions need to be clarified.

Studies on the mechanism of intestinal passage of the food comutagen harman, in the rabbit

The passage of harman (Ha) across rabbit jejunum and its effects on electrical parameters of the intestinal epithelium were studied in vitro using Ussing chambers. A linear relationship between mucosal to serosal flux (Jm-s) and the concentration of Ha (0.25-2 mM) was found. Ha elicited a dose-related decrease in short-circuit current, but did not affect transmural potential difference. At 2 mM, Ha decreased tissue conductance. Despite changes of electrical parameters, Jm-s of Ha was not modified by metabolic effectors such as glucose, colchicine, 2,4-dinitrophenol and ouabain, indicating that passage was dependent neither on membrane movements nor on cell energy. The transport of Ha was not dependent on Na+, but Ha inhibited in a dose-related manner the cotransport of Na+ and glucose. Luminal sodium taurocholate or beta-lactoglobulin had no appreciable effect on transport of Ha, but ethanol elicited a 45% increase in Ha permeability. These results indicate (1) that substantial amounts of Ha can cross the intestinal epithelium by the transcellular pathway and (2) that the passage of Ha, which appears to be diffusional, is not affected by luminal solutes such as glucose, sodium taurocholate and beta-lactoglobulin, but is markedly enhanced by ethanol.

Enhancing effects of harman and norharman on induction of preneoplastic and neoplastic kidney lesions in rats initiated with N-ethyl-N-hydroxyethylnitrosamine

The modifying potential of two nephrotoxic agents, harman and norharman, on N-ethyl-N-hydroxyethylnitrosamine (EHEN)-induced renal and hepatic carcinogenesis was investigated in male F344/DuCrj rats. Animals were given 0.1% EHEN in their drinking water for the first 2 weeks as an initiator. Subsequently, starting 3 weeks from the commencement, they were fed diet containing these compounds at concentrations of 1000, 500 or 0 ppm until week 26, and then killed for light microscopic examination. The mean numbers of renal tubular cell hyperplasias/cm2 and those of tumors/cm2 in rats given harman and norharman at 1000 ppm after initiation, but not at 500 ppm, were significantly increased as compared to the control values. However, neither compound modified liver carcinogenesis. It is concluded that harman and norharman show enhancing effects on rat kidney carcinogenesis, when ingested at dose levels which cause renal tubular damage.

Dose-dependent renal tubular toxicity of harman and norharman in male F344 rats

The renal toxicity of harman and norharman, administered for 2 or 4 weeks at dietary levels of 1,000, 500, or 0 parts per million (ppm), was investigated in 6-week-old male F344/DuCrj rats. Although rats fed 1,000 ppm harman or norharman, but not the 500 ppm level, demonstrated marked body weight retardation from 1 week to termination, no mortalities occurred. Marked elevation of water consumption was evident in rats given harman or norharman at 1,000 ppm, but not at 500 ppm, together with large increases in urine of low specific gravity. Urinary lysosomal enzymes (N-acetyl-beta-D-glucosaminidase, NAG, and lactate dehydrogenase, LDH) and sugar levels were increased, and the brush border enzymes (gamma-glutamyl transpeptidase, GGT, and alkaline phosphatase, ALP) decreased. Furthermore, serum biochemistry revealed clear elevation of parameters indicating renal toxicity in these rats. Histopathologically, rats fed 1,000 ppm harman or norharman, but not 500 ppm, demonstrated focal toxic renal degenerative/necrotic and regenerative lesions in proximal, distal, and collecting tubules. These changes were associated with a clearly increased labeling index (LI) of the nuclei of renal tubular epithelial cells on immunohistochemical staining for 5-bromo-2'-deoxyuridine (BrdU). Chemical specific crystal formation within tubular lumina was evident in rats fed 1,000 ppm, but not 500 ppm, this being considered the cause of the renal tubular lesions. It was concluded that harman and norharman exert renal toxicity at the dietary level of 1,000 ppm, but not 500 ppm, in male F344 rats.

Lack of hepatotoxicity or promotion of enzyme-altered liver foci development in rats treated with harman or norharman

The modifying effects of harman or norharman on liver carcinogenesis were investigated in male F344/DuCrj rats initially treated with N-nitrosodiethylamine (DEN). Two weeks after a single dose of DEN (200 mg/kg, intraperitoneally), rats were given harman or norharman at dietary levels of 1000 and 200 parts per million (ppm), or sodium phenobarbital (PB) at 500 ppm as a positive control, for 6 wk. At wk 3 following DEN administration, all animals were subjected to partial hepatectomy. Marked retardation of body weight gain was observed in rats treated with harman or norharman at 1000 ppm, but not at 200 ppm. Increased relative kidney but not liver weights were associated with harman or norharman treatment, especially in the higher dose groups. Although no toxicity-related hepatocyte lesions were found, severe renal toxic tubular lesions and regeneration were evident. Neither harman nor norharman significantly increased the numbers or areas of glutathione S-transferase placental form (GST-P) positive foci observed after DEN initiation, in clear contrast to PB. The results thus demonstrated that harman and norharman are nontoxic for the liver and lack modifying potential for liver carcinogenesis in our medium-term bioassay system.

DNA adducts formed by the comutagens harman and norharman in various tissues of mice

Covalent modifications of DNA in various tissues of mice with harman or norharman were analyzed by 32P-postlabeling assay. Administration of 0.1% harman to mice in their diet for 4 weeks resulted in DNA adducts in the liver and kidney. No specific DNA adduct was detected in other tissues, such as the glandular stomach, large intestine and brain. Similar treatment of mice with norharman resulted in DNA adducts in the kidney, glandular stomach and large intestine, but not in the liver or brain. These results suggests the in vivo genotoxicities of harman and norharman.