Biomedical subjects

M Chen

Publications and source records attributed to M Chen.

At least 235 records · Page 13Linked to original sources

PubMed2000

Functional role and therapeutic implications of neuronal caspase-1 and -3 in a mouse model of traumatic spinal cord injury.

Evidence indicates that both necrotic and apoptotic cell death contribute to tissue injury and neurological dysfunction following spinal cord injury. Caspases have been implicated as important mediators of apoptosis following acute central nervous system insults. We investigated whether caspase-1 and caspase-3 are involved in spinal cord injury-mediated cell death, and whether caspase inhibition may reduce tissue damage and improve outcome following spinal cord injury. We demonstrate a 17-fold increase in caspase-1 activity in traumatized spinal cord samples when compared with samples from sham-operated mice. Caspase-1 and caspase-3 activation were also detected by western blot following spinal cord injury, which was significantly inhibited by the broad caspase inhibitor N-benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone. By immunofluorescence or in situ fluorogenic substrate assay, caspase-1 and caspase-3 expression were detected in neuronal and non-neuronal cells following spinal cord injury. N-Benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone treated mice, and transgenic mice expressing a caspase-1 dominant negative mutant, demonstrated a significant improvement of motor function and a reduction of lesion size compared with vehicle-treated mice. Our results demonstrate for the first time that both caspase-1 and caspase-3 are activated in neurons following spinal cord injury, and that caspase inhibition reduces post-traumatic lesion size and improves motor performance. Caspase inhibitors may be one of the agents to be used for the treatment of spinal cord injury.

Amino Acid Chloromethyl Ketones↗

PubMed2000

Depression among needle exchange program and methadone maintenance clients.

The objective of this study was to compare the prevalence of major depression in two cohorts of injection drug users, those enrolled in a Rhode Island Methadone Maintenance Treatment Program (MMTP) and those enrolled in a Rhode Island Needle Exchange Program (NEP) using cross-sectional interviews. Symptomatic and duration criteria for major depression in the last 6 months were identified using the Structured Clinical Interview for DSM-III-R (SCID). Among 528 persons interviewed, 54% of those in NEP and 42% of those in MMTP met criteria for major depression. Using multivariate logistic regression, women (odds ratio [OR] 2.5; 95% confidence interval [CI] 1.7-3.7), persons with alcohol use disorders (OR 1.7; 95% CI 1.1-2. 7), and persons without a current partner (OR 1.8; 95% CI 1.2-2.6) were more likely to be depressed controlling for age, race, education and HIV status. Persons enrolled in MMTP were less likely to be depressed (OR 0.6; 95% CI 0.4-0.8) than NEP. Higher rates of depression were found among NEP attendees than among those enrolled in MMTP. Mental health referrals should be part of the growing number of needle exchanges in the United States.

Adult↗

PubMed2000

Understanding the insertion of transporters and other membrane proteins.

Recent studies show that transporters integrate into the lipid bilayer using topogenic sequences present throughout the entire polypeptide chain. These topogenic sequences can act in unpredictable ways with new translocation/stop transfer activities. In addition, a new membrane-insertion pathway has been identified in bacteria with homologs in mitochondria and chloroplasts.

Biological Transport↗

PubMed2000

The biosynthetic gene cluster for the antitumor drug bleomycin from Streptomyces verticillus ATCC15003 supporting functional interactions between nonribosomal peptide synthetases and a polyketide synthase.

BACKGROUND: The structural and catalytic similarities between modular nonribosomal peptide synthetases (NRPSs) and polyketide synthases (PKSs) inspired us to search for a hybrid NRPS-PKS system. The antitumor drug bleomycin (BLM) is a natural hybrid peptide-polyketide metabolite, the biosynthesis of which provides an excellent opportunity to investigate intermodular communication between NRPS and PKS modules. Here, we report the cloning, sequencing, and characterization of the BLM biosynthetic gene cluster from Streptomyces verticillus ATCC15003. RESULTS: A set of 30 genes clustered with the previously characterized blmAB resistance genes were defined by sequencing a 85-kb contiguous region of DNA from S. verticillus ATCC15003. The sequenced gene cluster consists of 10 NRPS genes encoding nine NRPS modules, a PKS gene encoding one PKS module, five sugar biosynthesis genes, as well as genes encoding other biosynthesis, resistance, and regulatory proteins. The substrate specificities of individual NRPS and PKS modules were predicted based on sequence analysis, and the amino acid specificities of two NRPS modules were confirmed biochemically in vitro. The involvement of the cloned genes in BLM biosynthesis was demonstrated by bioconversion of the BLM aglycones into BLMs in Streptomyces lividans expressing a part of the gene cluster. CONCLUSION: The blm gene cluster is characterized by a hybrid NRPS-PKS system, supporting the wisdom of combining individual NRPS and PKS modules for combinatorial biosynthesis. The availability of the blm gene cluster has set the stage for engineering novel BLM analogs by genetic manipulation of genes governing BLM biosynthesis and for investigating the molecular basis for intermodular communication between NRPS and PKS in the biosynthesis of hybrid peptide-polyketide metabolites.

Amino Acid Sequence↗

PubMed2000

Autoantibodies to type VII collagen have heterogeneous subclass and light chain compositions and their complement-activating capacities do not correlate with the inflammatory clinical phenotype.

Epidermolysis bullosa acquisita and bullous systemic lupus erythematosus are blistering skin diseases characterized by IgG autoantibodies that predominantly target the noncollagenous domain 1 of type VII collagen, a skin basement membrane component. The basic immunologic events leading to the blistering processes in these diseases remains unclear. We defined the subclass and light chain compositions of the IgG autoantibodies in 15 patients, in order to gain insight into the blistering mechanism. Immunofluorescence correlated the patients' in vivo-bound and circulating antibasement membrane autoantibodies. Four eukaryotic recombinant proteins, including one full-length and three truncated noncollagenous domain 1 proteins generated by sequential deletion of C-terminal amino acids, were used to perform enzyme-linked immunosorbent assay to detect the patients' anti-type VII collagen autoantibodies. The majority of patients' autoantibodies contained both complement-activating and non-complement-activating IgG subclasses. The presence or absence of complement-activating IgG autoantibody subclasses did not correlate with the inflammatory or noninflammatory clinical phenotype. The majority of tested sera contained both kappa and lambda light chain autoantibodies. All sera that reacted to the full-length noncollagenous domain 1 also reacted to the smallest truncated protein containing the cartilage matrix protein and the first three fibronectinlike repeats. The patients' anti-type VII collagen autoantibodies, likely to be polyclonal in nature, may contribute to the pathogenesis of the blistering process by both complement-dependent inflammatory injury and complement-independent mechanical disruption of the anchoring function of type VII collagen. The N-terminal region of the noncollagenous domain 1 may contain an important antigenic epitope targeted by the IgG autoantibodies.

Autoantibodies↗

PubMed2000

Minocycline inhibits caspase-1 and caspase-3 expression and delays mortality in a transgenic mouse model of Huntington disease.

Huntington disease is an autosomal dominant neurodegenerative disease with no effective treatment. Minocycline is a tetracycline derivative with proven safety. After ischemia, minocycline inhibits caspase-1 and inducible nitric oxide synthetase upregulation, and reduces infarction. As caspase-1 and nitric oxide seem to play a role in Huntington disease, we evaluated the therapeutic efficacy of minocycline in the R6/2 mouse model of Huntington disease. We report that minocycline delays disease progression, inhibits caspase-1 and caspase-3 mRNA upregulation, and decreases inducible nitric oxide synthetase activity. In addition, effective pharmacotherapy in R6/2 mice requires caspase-1 and caspase-3 inhibition. This is the first demonstration of caspase-1 and caspase-3 transcriptional regulation in a Huntington disease model.

Animals↗

PubMed2000

Calcitonin gene-related peptide inhibits lipopolysaccharide-induced interleukin-12 release from mouse peritoneal macrophages, mediated by the cAMP pathway.

Previously we showed that calcitonin gene-related peptide (CGRP), a neuropeptide, inhibited lipopolysaccharide (LPS)-induced tumour necrosis factor-alpha (TNF-alpha) production and increased interleukin (IL)-6 release at low concentrations via activation of the cAMP pathway in mouse peritoneal macrophages (Mphi). In this study we examined whether CGRP could modulate IL-12 release from mouse peritoneal Mphi, and if so, what signal transduction pathway was involved. Mphi were obtained from the peritoneal exudate of male BALB/c mice. The cells were plated on culture dishes at a density of 5 x 105 cells per well and allowed to adhere for 2 hr. After incubation for 24 hr, the Mphi were cultured with 0.1 microg/ml of LPS, alone or together with CGRP (1-1000 nM) for 24 hr. The amount of IL-12 in the cell medium was measured by enzyme-linked immunosorbent assay (ELISA). The results showed that CGRP attenuated LPS-induced IL-12 release in a concentration-dependent manner. Production of IL-12 was decreased from 95.9+/-4.6 to 73.4+/-5.7 pg/ml by 100 nM CGRP. The two cAMP phosphodiesterase (PDE) inhibitors, 3-isobutyl-1-methyl-xanthine (IBMX) and rolipram, significantly potentiated the CGRP response, and the level of IL-12 was further decreased by 28% and 47%, respectively. However, CGRP had no effect on IL-12 production from unstimulated Mphi. The LPS-induced IL-12 release from Mphi could also be reduced by forskolin, an activator of adenylate cyclase, and 8-Br-cAMP, an analogue of cAMP. Using the reverse transcription-polymerase chain reaction (RT-PCR), we found that CGRP also decreased the LPS-induced IL-12 p40 mRNA levels. Furthermore, pretreatment with H89 (0.1 microM or 1 microM), an inhibitor of cAMP-dependent protein kinase, diminished CGRP effects, IL-12 production and gene expression. These data suggest that LPS-induced IL-12 release and gene expression were attenuated by CGRP via an activated cAMP-protein kinase A (PKA) pathway in mouse peritoneal Mphi.

Animals↗

PubMed2000

Mutations in the Arabidopsis VAR2 locus cause leaf variegation due to the loss of a chloroplast FtsH protease.

Variegated plants have green- and white-sectored leaves. Cells in the green sectors contain morphologically normal chloroplasts, whereas cells in the white sectors contain non-pigmented plastids that lack organized lamellar structures. Many variegations are caused by mutations in nuclear genes that affect plastid function, yet in only a few cases have the responsible genes been cloned. We show that mutations in the nuclear VAR2 locus of Arabidopsis cause variegation due to loss of a chloroplast thylakoid membrane protein that bears similarity to the FtsH family of AAA proteins (ATPases associated with diverse cellular activities). Escherichia coli FtsH is a chaperone metalloprotease that functions in a number of diverse membrane-associated events. Although FtsH homologs have been identified in multicellular organisms, their functions and activities are largely unknown; we provide genetic in vivo evidence that VAR2 functions in thylakoid membrane biogenesis. We have isolated four var2 alleles and they have allowed us to define domains of the protein that are required for activity. These include two putative ATP-binding sites. VAR2 protein amounts generally correlate with the severity of the var2 mutant phenotype. One allele lacks detectable VAR2 protein, suggesting that the mechanism of var2 variegation involves the action of a redundant activity in the green sectors. We conclude that redundant activities may be a general mechanism to explain nuclear gene-induced plant variegations.

ATP-Dependent Proteases↗

PubMed2000

Frequency and significance of antibodies to chromatin in autoimmune hepatitis type I.

AIMS AND METHODS: To assess the frequency and clinical significance of antibodies to chromatin (ACA) in autoimmune hepatitis (AIH), 36 Japanese patients with AIH type I were studied for serum reactivity with chromatin by using an ELISA. RESULTS: Antibodies to chromatin were detected in 19 of 36 patients with AIH type I. There was a significantly higher frequency of ACA in patients with AIH type I than in patients with primary biliary cirrhosis, chronic hepatitis C and B (52.8 vs 13.2, 5.4 and 6.7%, respectively; P<0.01). None of the 19 healthy subjects had positive reactions. Sixteen of 19 patients with seropositive sera (44.4%) had reactivities with other nuclear antigens (recombinant nucleoproteins U1RNP-A, U1RNP-70; recombinant ribonucleoprotein complexes SSA/Ro 52K, SSA/Ro 60K; recombinant centromere Cenp-B; dsDNA and histones). Adsorption with double-stranded DNA (dsDNA) and histones could not remove the majority of antichromatin reactivity as 81.9% of the antibody reactivity still remained. In five sera samples from AIH type I patients positive for anti-dsDNA and antihistones, the antibody activities for dsDNA and histones were inhibited after the absorbtion of sera with chromatin. The patterns of antinuclear antibodies (ANA) detected by using indirect immunofluorescence were similar between patients with and without ACA. Patients with ACA had significantly high serum levels of gamma-globulin and immunoglobulin G. The ACA titers dropped significantly after corticosteroid treatment (P< 0.01). CONCLUSIONS: Antibodies to chromatin are frequently present in patients with AIH type I and they are one of the dominant autoantibodies associated with ANA reactivity in AIH type I. Antibodies to chromatin cannot be used to characterize distinct clinical subgroups of AIH type I.

Adrenal Cortex Hormones↗

PubMed2000

Caspase-3 mediated neuronal death after traumatic brain injury in rats.

During programmed cell death, activation of caspase-3 leads to proteolysis of DNA repair proteins, cytoskeletal proteins, and the inhibitor of caspase-activated deoxyribonuclease, culminating in morphologic changes and DNA damage defining apoptosis. The participation of caspase-3 activation in the evolution of neuronal death after traumatic brain injury in rats was examined. Cleavage of pro-caspase-3 in cytosolic cellular fractions and an increase in caspase-3-like enzyme activity were seen in injured brain versus control. Cleavage of the caspase-3 substrates DNA-dependent protein kinase and inhibitor of caspase-activated deoxyribonuclease and co-localization of cytosolic caspase-3 in neurons with evidence of DNA fragmentation were also identified. Intracerebral administration of the caspase-3 inhibitor N-benzyloxycarbonyl-Asp-Glu-Val-Asp-fluoromethyl ketone (480 ng) after trauma reduced caspase-3-like activity and DNA fragmentation in injured brain versus vehicle at 24 h. Treatment with N-benzyloxycarbonyl-Asp-Glu-Val-Asp-fluoromethyl ketone for 72 h (480 ng/day) reduced contusion size and ipsilateral dorsal hippocampal tissue loss at 3 weeks but had no effect on functional outcome versus vehicle. These data demonstrate that caspase-3 activation contributes to brain tissue loss and downstream biochemical events that execute programmed cell death after traumatic brain injury. Caspase inhibition may prove efficacious in the treatment of certain types of brain injury where programmed cell death occurs.

Animals↗

PubMed2000

Clostridium difficile toxin A causes early damage to mitochondria in cultured cells.

BACKGROUND & AIMS: The mechanism by which Clostridium difficile toxin A causes actin depolymerization and cell rounding involves toxin internalization and subsequent monoglucosylation of the Rho family of proteins. This study explored toxin internalization and effects on mitochondrial function before cell rounding. METHODS: Chinese hamster ovary (CHO) cells were exposed to toxin A, and mitochondrial localization was assayed by confocal microscopy. Mitochondrial function was measured by adenosine triphosphate (ATP) concentration, mitochondrial permeability, and leakage of cytochrome c. RESULTS: Confocal microscopy showed toxin A colocalization with the mitochondrial protein GRP 75 at 5 minutes after toxin exposure. Between 5 and 15 minutes, toxin A caused an 80% diminution in cellular ATP levels; cell rounding and Rho glucosylation commenced between 15 and 30 minutes. Toxin A also resulted in reduction of mitochondrial membrane potential and a 2-3-fold increase in reactive oxygen radicals. Preincubation of CHO cells with the antioxidants butylated hydroxyanisole or butylated hydroxytoluene blocked the toxin A-induced increase in oxygen radicals and diminished cell rounding. Western blot analysis of toxin A-exposed isolated mitochondria showed a direct effect of toxin A on leakage of cytochrome c. CONCLUSIONS: The results show that extensive mitochondrial damage occurs within 15 minutes in CHO cells exposed to toxin A. Diminished ATP concentrations and increased oxygen radicals are likely to contribute to cytotoxicity from this bacterial toxin.

Adenosine Triphosphate↗

PubMed2000

Resorbable bioscaffold for esophageal repair in a dog model.

PURPOSE: Porcine-derived, xenogeneic extracellular matrix (ECM) derived from either the small intestinal submucosa (SIS) or urinary bladder submucosa (UBS) was used as a tissue scaffold for esophageal repair in a dog model. METHODS: Patch defects measuring approximately 5 cm in length and encompassing 40% to 50% of the circumference of the esophagus or complete circumferential segmental defects measuring 5 cm in length were created by surgical resection in healthy adult female dogs. The defects were repaired with ECM scaffolds derived from either SIS or UBS. The animals were kept alive for periods ranging from 4 days to 15 months. RESULTS: The xenogeneic scaffolds used for repair of the patch defects were resorbed completely within 30 to 60 days and showed replacement by skeletal muscle, which was oriented appropriately and contiguous with adjacent normal esophageal skeletal muscle, organized collagenous connective tissue, and a complete and intact squamous epithelium. No signs of clinical esophageal dysfunction were seen in any of the animals with the patch defect repair. The xenogeneic scaffolds configured into tubes for repair of the segmental defects all showed stricture within 45 days of surgery. CONCLUSION: These ECMs show promise as a treatment option for esophageal repair, but stricture remains problematic for complete tube grafts.

Animals↗

PubMed2000

Neonatal pulmonary hypoplasia and perinatal mortality in patients with midtrimester rupture of amniotic membranes--a critical analysis.

OBJECTIVE: We sought to critically assess the risk factors for neonatal pulmonary hypoplasia and perinatal death in patients with preterm rupture of the amniotic membranes from 15 to 28 weeks' gestation. STUDY DESIGN: This was a prospective cohort study. The study patients had preterm rupture of the amniotic membranes at 15 to 28 weeks' gestation and were without fetal anomalies, multiple gestation, and oligohydramnios before rupture of the membranes. The amniotic fluid volume index was determined at admission and weekly afterward until delivery. RESULTS: The incidence of pulmonary hypoplasia was 12.9% (21/163). The overall perinatal mortality rate was 54% (88/163). Logistic regression analysis revealed the following: (1) Gestational age at rupture of the membranes, the latency period, and either the initial or the average amniotic fluid index have significant influence on the development of pulmonary hypoplasia; (2) gestational age at rupture of the membranes and latency period are significant factors in predicting perinatal death. CONCLUSIONS: In this large population of patients with rupture of membranes at 15 to 28 weeks' gestation, gestational age at rupture of the membranes, latency period, and amniotic fluid index were important independent predictors of neonatal pulmonary hypoplasia. In addition, gestational age at rupture of the membranes and latency period were important independent determinants of perinatal death. Expectant management of patients with preterm rupture of the amniotic membranes during this gestational age interval was associated with improved perinatal survival, even though it may increase the risk of pulmonary hypoplasia.

Female↗

PubMed2000

Increases in bcl-2 protein in cerebrospinal fluid and evidence for programmed cell death in infants and children after severe traumatic brain injury.

OBJECTIVES: To determine whether bcl-2, a protein that inhibits apoptosis, would be increased in cerebrospinal fluid (CSF) in infants and children after traumatic brain injury (TBI) and to examine the association of bcl-2 concentration with clinical variables. STUDY DESIGN: Bcl-2 was measured in CSF from 23 children (aged 2 months-16 years) with severe TBI and from 19 children without TBI or meningitis (control subjects) by enzyme-linked immunosorbent assay. CSF oligonucleosome concentration was also determined as a marker of DNA degradation. Brain samples from 2 patients undergoing emergent decompressive craniectomies were analyzed for bcl-2 with Western blot and for DNA fragmentation with TUNEL (terminal deoxynucleotidyl-transferase mediated biotin-dUTP nick-end labeling). RESULTS: CSF bcl-2 concentrations were increased in patients with TBI versus control subjects (P =.01). Bcl-2 was increased in patients with TBI who survived versus those who died (P =.02). CSF oligonucleosome concentration tended to be increased after TBI (P =.07) and was not associated with bcl-2. Brain tissue samples showed an increase in bcl-2 in patients with TBI versus adult brain bank control samples and evidence of DNA fragmentation within cells with apoptotic morphology. CONCLUSIONS: Bcl-2 may participate in the regulation of cell death after TBI in infants and children. The increase in bcl-2 seen in patients who survived is consistent with a protective role for this anti-apoptotic protein after TBI.

Adolescent↗

PubMed2000

Changing profile of HIV-1 serotypes in Iceland during 1989-96.

A total of 63 HIV-1 strains collected in Iceland during the years 1989-96 were typed into serotypes A-E using a peptide-based enzyme immunoassay. The majority of the strains were of serotype B (66.6%). 22.2% were untypeable by this method. Until 1993 only serotype B was found, but in 1993 and after that date other serotypes, especially E (7.9%) were detected, indicating the spread of serotypes previously confined to developing countries. This may reflect the increase in the number of Icelanders travelling to distant countries and the increased immigration into Iceland from developing countries.

HIV-1↗

PubMed2000

A nonparametric procedure associated with a clinically meaningful efficacy measure.

Parametric methods such as analysis of (co)variance are commonly used for the analysis of data from clinical trials. They have the advantage of providing an easily interpretable measure of treatment efficacy such as a confidence interval for treatment difference. If there are doubts about the underlying distribution of the response variable, however, a nonparametric approach may be called for. The nonparametric approaches in such settings concentrate on hypothesis testing and are not typically used for providing easily interpretable measures of treatment efficacy. For comparing two treatments, we propose using a nonparametric measure based on the likelihood of observing a better response on one treatment than the other. The bootstrap method is used to construct a confidence interval for the treatment difference.

Journal Article↗

PubMed2000

XPD/ERCC2 polymorphisms and risk of head and neck cancer: a case-control analysis.

DNA repair capacity is central in maintaining normal cellular functions. Variants of several DNA repair genes,including the nucleotide excision repair gene XPD, have been described recently. Because we previously reported that patients with squamous cell carcinoma of the head and neck (SCCHN) had lower DNA repair capacity than healthy controls, we hypothesized that inherited polymorphisms of XPD may contribute to genetic susceptibility to SCCHN, a tobacco-related cancer. To test this hypothesis, we conducted a hospital-based case-control study of 189 SCCHN patients and 496 cancer-free controls who were frequency-matched on age, gender and smoking status. All subjects were non-Hispanic whites. Two XPD polymorphisms (C22541A and A35931C) were typed using the restriction enzymes TfiI and PstI, respectively. Multivariate logistic regression analysis was performed to calculate adjusted odds ratios (ORs) and 95% confidence intervals (CIs). In the controls, the frequencies of the variant 22541A and 35931C alleles were 44.7% and 33.8%, respectively. The frequency of the 22541A homozygous genotype (22541AA) was lower in cases (15.9%) than in controls (20.4%) but was not associated with risk (adjusted OR = 0.90; 95% CI = 0.52-1. 56) for SCCHN. The frequency of the 35931C homozygous genotype (35931CC) was higher in cases (16.4%) than in controls (11.5%) and associated with a borderline increased risk (adjusted OR = 1.55; 95% CI = 0.96-2.52) for SCCHN. The risk was higher in older subjects (OR = 2.22; 95% CI = 1.03-4.80), current smokers (OR = 1.83; 95% CI = 0.79-4.27) and current drinkers (OR = 2.59; 95% CI = 1.25-5.34) in the stratification analysis. These results suggest a gene-environment interaction, but this did not reach statistical significance. The findings are limited due to the relatively small numbers in the subgroups and need to be verified by further investigations.

Adult↗

PubMed2000

Enantiomeric composition of N'-nitrosonornicotine and N'-nitrosoanatabine in tobacco.

The tobacco-specific nitrosamines N'-nitrosonornicotine (NNN) and N'-nitrosoanatabine (NAT) are found in substantial quantities in unburned tobacco. Although this has been documented in many previous studies, no data are available on the enantiomeric composition of these nitrosamines, which both have a chiral center at their 2'-positions. We used chiral stationary phase gas chromatography with nitrosamine-selective detection to determine the enantiomeric composition of NNN and NAT in moist snuff, chewing tobacco, and cigarette tobacco. (S)-NNN comprised 75.0 +/- 8.83% (SD) (n = 12) of total NNN while (S)-NAT comprised 82.6 +/- 1.44% (n = 12) of total NAT. Levels of the (S)-enantiomers of NNN and NAT were generally similar to those of the corresponding secondary amines, nornicotine and anatabine, suggesting a precursor to product relationship. Nitrosation of (S)-nicotine at pH 7.0 produced >99% (S)-NNN. These results suggest that nornicotine is a significant precursor of NNN in tobacco. The results of this study provide new insights into the structures and precursors of tobacco-specific nitrosamines in tobacco products.

Carcinogens↗