Cardiac Mitochondrial Compromise in 1-Yr-Old Erythrocebus patas Monkeys Perinatally- Exposed to Nucleoside Reverse Transcriptase Inhibitors

Hearts from 1-yr-old Erythrocebus patas monkeys were examined after in utero and 6-wk-postbirth exposure to antiretroviral nucleoside reverse transcriptase inhibitors (NRTIs). Protocols were modeled on those given to human immunodeficiency virus (HIV)-1-infected pregnant women. NRTIs were administered daily to the dams for the last 20% or 50% of gestation, and to the infants for 6 wk after birth. Exposures included: no drug (n = 4); Zidovudine, 3'-azido-3'-deoxythymidine (AZT; n = 4); AZT/Lamivudine, (-)-beta-L-2', 3'-Dideoxy-3'-thiacytidine (Epivir, 3TC) (n = 4); AZT/Didanosine (Videx, ddI) (n = 4); and Stavudine (Zerit, d4T)/3TC (n = 4). Echocardiograms and clinical chemistry showed no drug-related changes, but the d4T/3TC-exposed fetuses at 6 and 12 mo had increased white cell counts (p < 0.05). At 1 yr of age, oxidative phosphorylation (OXPHOS) enzyme activities were similar in heart mitochondria from all groups. Mitochondrial pathology, that included clones of damaged mitochondria (p < 0.05), was found in hearts of all 1-yr drug-exposed infants. Levels of mtDNA were elevated (p < 0.05) in hearts of all NRTI-exposed monkeys in the following order: control < d4T/3TC < AZT < AZT/3TC < AZT/ddI. The clinical status of NRTI-exposed infants, as evidenced by behavior, clinical chemistry, OXPHOS activity and echocardiogram, was normal. However, extensive mitochondrial damage with clusters of similar-appearing damaged heart mitochondria observed by electron microscopy, and an increase in mtDNA quantity, that persisted at 1 yr of age, suggest the potential for cardiotoxicity later in life.

Perinatal genotoxicity and carcinogenicity of anti-retroviral nucleoside analog drugs

The current worldwide spread of the human immunodeficiency virus-1 (HIV-1) to the heterosexual population has resulted in approximately 800,000 children born yearly to HIV-1-infected mothers. In the absence of anti-retroviral intervention, about 25% of the approximately 7,000 children born yearly to HIV-1-infected women in the United States are HIV-1 infected. Administration of zidovudine (AZT) prophylaxis during pregnancy reduces the rate of infant HIV-1 infection to approximately 7%, and further reductions are achieved with the addition of lamivudine (3TC) in the clinical formulation Combivir. Whereas clinically this is a remarkable achievement, AZT and 3TC are DNA replication chain terminators known to induce various types of genotoxicity. Studies in rodents have demonstrated AZT-DNA incorporation, HPRT mutagenesis, telomere shortening, and tumorigenicity in organs of fetal mice exposed transplacentally to AZT. In monkeys, both AZT and 3TC become incorporated into the DNA from multiple fetal organs taken at birth after administration of human-equivalent protocols to pregnant dams during gestation, and telomere shortening has been found in monkey fetuses exposed to both drugs. In human infants, AZT-DNA and 3TC-DNA incorporation as well as HPRT and GPA mutagenesis have been documented in cord blood from infants exposed in utero to Combivir. In infants of mice, monkeys, and humans, levels of AZT-DNA incorporation were remarkably similar, and in newborn mice and humans, mutation frequencies were also very similar. Given the risk-benefit ratio, these highly successful drugs will continue to be used for prevention of vertical viral transmission, however evidence of genotoxicity in mouse and monkey models and in the infants themselves would suggest that exposed children should be followed well past adolescence for early detection of potential cancer hazard.

Polycyclic aromatic hydrocarbon-DNA adducts determined by semiquantitative immunohistochemistry in human esophageal biopsies taken in 1985

Esophageal endoscopic biopsy samples were obtained in 1985 in Linxian, China, a region with very high esophageal cancer incidence rates, and where ingested food is known to contain substantial amounts of polycyclic aromatic hydrocarbons (PAHs). In this study, the automated cellular imaging system (ACIS) was used for localization and semi-quantitation of PAH-DNA adducts. Fresh tissue sections were cut from archived paraffin blocks and incubated with an antiserum elicited against DNA modified with 7beta,8alpha-dihydroxy-9alpha,10alpha-epoxy-7,8,9,10-tetrahydro-benzo[a]pyrene (BPDE). Nuclear PAH-DNA adduct staining was observed in four out of five human samples incubated with the anti-BPDE-DNA. By visual inspection, nuclei in the basal layer of the esophageal epithelium had higher levels of PAH-DNA adducts compared to those found in the adjacent superficial squamous layer. Nuclear PAH-DNA staining was absent in serial sections incubated with either normal rabbit serum or BPDE-DNA-antiserum previously absorbed with the immunogen BPDE-DNA. Semi-quantitative evaluation by ACIS revealed that per nucleus values for PAH-DNA adducts in the basal layer of the esophageal epithelium were 5- to 40-fold higher than those in the adjacent superficial squamous layer (P < 0.0001), using a random effects model). This pilot study demonstrates the presence of PAH-DNA adducts in archived paraffin-embedded endoscopic esophageal biopsy samples that are close to 20 years old, and suggests that an appropriate set of archived samples could be used to prospectively correlate PAH-DNA adduct formation with risk of esophageal cancer development.

Mitochondrial damage and DNA depletion in cord blood and umbilical cord from infants exposed in utero to Combivir

OBJECTIVE

Although most uninfected infants born to women infected with HIV-1 show no clinical evidence of mitochondrial compromise, mitochondrial dysfunction has been reported in children born to women receiving zidovudine and/or lamivudine during pregnancy. In this pilot study we examined mitochondrial integrity in HIV-1-uninfected infants born to HIV-1-infected women receiving Combivir during pregnancy.

DESIGN

: Samples of umbilical cord and cord blood were obtained from HIV-1-uninfected infants born to either HIV-1-infected women receiving Combivir therapy during pregnancy (n = 10) or HIV-1-uninfected women (n = 9).

METHODS

Mitochondrial morphological integrity was examined in umbilical cords (n = 16) by electron microscopy and mtDNA quantity was determined in DNA from cord blood (n = 18) and umbilical cord (n = 18) by PCR-chemiluminescence immunoassay detection.

RESULTS

In umbilical cords from six of nine infants born to HIV-1-infected mothers taking Combivir moderate to severe mitochondrial morphological damage was observed (P = 0.011), while none of seven unexposed infants showed similar damage. Compared to unexposed infants, statistically significant mtDNA depletion was observed in umbilical cord (P = 0.006) and cord blood (P = 0.003) from drug-exposed infants.

CONCLUSIONS

A cohort of HIV-1-uninfected Combivir-exposed infants with no clinical symptoms showed morphological and molecular evidence of mitochondrial damage.

DNA adducts in tumour, normal peripheral lung and bronchus, and peripheral blood lymphocytes from smoking and non-smoking lung cancer patients: correlations between tissues and detection by 32P-postlabelling and immunoassay

Smoking is a major risk factor for lung cancer. This comparative study of smoking-related carcinogen-DNA adducts in pulmonary tissues and peripheral blood lymphocytes aims to further explore the primary DNA damaging processes by cigarette smoke in target and surrogate tissues. Samples of tumour and normal peripheral lung tissue, normal bronchial tissue and peripheral blood lymphocytes were obtained from a total of 85 lung cancer patients who underwent lung resection. Bulky DNA adducts were determined by 32P-postlabelling, and polycyclic aromatic hydrocarbon (PAH)-DNA adducts were detected by (+/-)-7beta, 8alpha-dihydroxy-9alpha,10alpha-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene-DNA chemiluminescence immunoassay (BPDE-DNA CIA) in smaller subsets of tissue samples subject to availability of DNA. Bulky DNA adduct levels ranged between 0.3 and 27.8 adducts/10(8) nucleotides (nt) with mean adduct levels between 2.8 and 11.5 adducts/10(8) nt. Mean PAH-DNA adduct levels were 2.6-6.2 adducts/10(8) nt. Significantly higher bulky DNA adduct levels were detected in smokers' lungs as compared with non-smokers' (P < 0.02). PAH-DNA adduct levels appeared higher in the lungs of smokers compared with non-smokers but the difference was not significant. Lung tumour contained on average a 50% lower DNA adduct level compared with normal lung tissue. A statistically significant positive correlation was found between the DNA adduct levels of the corresponding tumour and normal lung tissue samples in both smokers and non-smokers using both methodologies. Bulky DNA adduct levels in normal lung and blood lymphocytes correlated significantly in non-smokers only (r = 0.55, P = 0.023). In lung tumour DNA samples there was a weak correlation between values obtained by 32P-postlabelling and by the BPDE-DNA immunoassay (r = 0.27, P = 0.054). However, with normal lung DNA samples, values obtained by the two assays did not correlate.

Mitochondrial toxicity in fetal Erythrocebus patas monkeys exposed transplacentally to zidovudine plus lamivudine

This study was designed to investigate fetal mitochondrial toxicity in Erythrocebus patas monkeys exposed in utero to zidovudine (AZT) and lamivudine (3TC), and taken at term. Pregnant patas monkeys were given a daily dose of 40 mg AZT (86% of the human daily dose, based on body weight), for the last 10 weeks (50%) of gestation, and a daily dose of 24 mg 3TC (84% of the human daily dose, based on body weight) for the last 4 weeks of gestation. At term, AZT was found to be incorporated into fetal mitochondrial DNA from skeletal muscle, liver, kidney, and placenta. By transmission electron microscopy (EM) drug-exposed fetal cardiac and skeletal muscle cells showed mitochondrial membrane compromise, mitochondrial proliferation, and damaged sarcomeres, while mitochondria in brain cerebrum and cerebellum were morphologically normal. Substantial depletion of oxidative phosphorylation (OXPHOS) Complex I specific activities was observed in heart (87% reduction in mean, p = 0.02) and skeletal muscle (98% reduction in mean, p = 0.002) from drug-exposed fetuses, compared to unexposed fetuses. In addition Complex IV activity was highly depleted (85% reduction in mean, p = 0.004) in skeletal muscle from the drug-exposed fetuses (p = 0.004). Brain cerebrum and cerebellum showed no statistically significant OXPHOS changes with drug exposure. Mitochondrial DNA quantity was substantially depleted (>50%) in heart, skeletal muscle, cerebellum, and cerebrum from drug-exposed fetuses compared to unexposed controls. Overall, the data indicate that significant mitochondrial damage was observed at birth in monkey fetuses exposed in utero to AZT plus 3TC in a human-equivalent dosing protocol.

Formation of tamoxifen-DNA adducts in multiple organs of adult female cynomolgus monkeys dosed with tamoxifen for 30 days

The use of the antiestrogen tamoxifen (TAM) is associated with an increase in endometrial cancer. TAM-induced endometrial carcinogenesis may proceed through a genotoxin-mediated pathway, although the detection of endometrial TAM-DNA adducts in exposed women is still controversial. In this study, a monkey model has been used to investigate the question of TAM-DNA adduct formation in primates. Two methods have been used to determine TAM-DNA adducts: a TAM-DNA chemiluminescence immunoassay (TAM-DNA CIA), using an antiserum that has specificity for (E)-alpha-(deoxyguanosin-N(2)-yl)-tamoxifen (dG-TAM) and (E)-alpha-(deoxyguanosin-N(2)-yl)-N-desmethyltamoxifen (dG-desmethyl-TAM) and electrospray ionization tandem mass spectrometry (ES-MS/MS) coupled with on-line sample preparation and high-performance liquid chromatography (HPLC). Mature (19 year old) cynomolgus monkeys were given either vehicle control (n = 1) or TAM (n = 3) twice daily for a total dose of 2 mg of TAM/kg body weight (bw)/day for 30 days by naso-gastric intubation. Tissues were harvested, and DNA was isolated from uterus, ovary, liver, brain cortex, and kidney. By TAM-DNA CIA, values for uterine TAM-DNA adducts in two monkeys were 0.9 and 1.7 adducts/10(8) nucleotides, whereas values for ovarian TAM-DNA adducts in the same animals were 0.4 and 0.5 adducts/10(8) nucleotides. Liver, brain cortex, and kidney DNA samples from the three exposed monkeys had TAM-DNA levels of 2.1-4.2 adducts/10(8) nucleotides, 0.4-5.0 adducts/10(8) nucleotides, and 0.7-2.1 adducts/10(8) nucleotides, respectively. By HPLC-ES-MS/MS, the levels of TAM-DNA adducts detected in all tissues were comparable with those observed by TAM-DNA CIA. Thus, values for uterine TAM-DNA adducts ranged from 0.5 to 1.4 adducts/10(8) nucleotides, whereas values for ovarian TAM-DNA adducts, measurable in two monkeys, were 0.2 and 0.3 adducts/10(8) nucleotides. Liver DNA contained the highest TAM-DNA adduct levels (7.0-11.1 adducts/10(8) nucleotides), whereas brain cortex DNA contained lower adduct levels (0.6-4.8 adducts/10(8) nucleotides) and the lowest levels were measured in the kidney (0.2-0.4 adducts/10(8) nucleotides). This study indicates that cynomolgus monkeys are capable of metabolizing TAM to genotoxic intermediates that form TAM-DNA adducts in multiple tissues.

Identification of tamoxifen-DNA adducts in monkeys treated with tamoxifen

The risk of developing endometrial cancer is increased in breast cancer patients treated with tamoxifen (TAM) and in healthy women undergoing TAM chemoprevention. We have detected previously TAM-DNA adducts in the endometrium of women receiving TAM (Shibutani et al., Carcinogenesis, 21: 1461-1467, 2000). To investigate the genotoxic damage induced by TAM in the uterus and other tissues of primates, we gave adult female cynomolgus monkeys six times the human-equivalent dose of TAM (2 mg/kg body weight/day) for 30 days. DNA samples were prepared from the uterus, ovary, liver, kidney, and brain cortex of three TAM-exposed monkeys and one control monkey and were analyzed as coded specimens. To identify the TAM-DNA adducts, we established a new high-performance liquid chromatography gradient system for (32)P-postlabeling/high-performance liquid chromatography analysis, which can resolve the trans- and cis-diastereoisomers of alpha-(N(2)-deoxyguanosinyl)TAM (dG-N(2)-TAM), alpha-(N(2)-deoxyguanosinyl)-N-desmethylTAM, and alpha-(N(2)-deoxyguanosinyl)tamoxifen N-oxide. Trans-forms of dG-N(2)-TAM and dG-N(2)-N-desTAM adducts were detected in the livers of all three TAM-fed monkeys at levels of 2.7 adducts/10(8) nucleotides and 1.7 adducts/10(8) nucleotides, respectively. The levels of dG-N(2)-TAM adducts observed in the uterus of one monkey and in the ovaries of two monkeys were approximately 10-fold lower than those observed in the livers. TAM exposure also induced dG-N(2)-TAM adduct in the brain cortex of all three monkeys with a value of 1.5 adducts/10(8) nucleotides. No TAM-DNA adducts were detected in the kidneys or in any tissues obtained from the unexposed monkey. Our results suggest that women receiving TAM may form genotoxic damage in many organs, including the reproductive organs.

The genotoxicity of tamoxifen: extent and consequences, Kona, Hawaii, January 23, 2003

The current recommended adjuvant therapy for oestrogen receptor-positive breast cancer typically includes 20 mg/day tamoxifen (Nolvadex) for 5 years post-operatively. This regimen has been found to reduce the incidence of contralateral breast cancer in breast cancer survivors by 47%, and, when used prophylactically, to reduce new breast cancers in high risk women by 49%. However, epidemiological evidence links tamoxifen therapy to increases in endometrial cancer and thromboembolic events in breast cancer patients. In addition, in tamoxifen-exposed rats dose-related increases in hepatic tamoxifen-DNA adduct formation and liver tumour incidence occur through a classic genotoxic mechanism. In women, endometrial cancers may be the result of genotoxicity, hormonally induced signal transduction and/or other mechanisms. If genotoxicity is relevant to tamoxifen-induced endometrial cancer it may be possible to identify women at risk through detection of tamoxifen-DNA adducts. The aim of this one day conference was to examine the most recent evidence for the occurrence of tamoxifen-induced genotoxicity in women receiving tamoxifen therapy. There were significant experimental differences, as some participants presented evidence for a genotoxic mechanism, while others reported finding insufficient evidence to support a genotoxic mechanism. The discussion was wide ranging and the outcome underscored the need for further investigations, access to more human tissue samples, shared tamoxifen-DNA standards for methodological comparisons and inter-laboratory exchange of human tissue samples.

Long-term mitochondrial toxicity in HIV-uninfected infants born to HIV-infected mothers

Although children born to HIV-infected (HIV+) women receiving antiretroviral therapy during pregnancy show virtually no adverse clinical effects at birth, the antiretroviral nucleoside analog drugs are known to damage nuclear and mitochondrial DNA. In this study, biomarkers of mitochondrial toxicity and genotoxicity have been examined in a well-characterized sample set consisting of infants born to HIV-uninfected (HIV-) mothers (n = 30), and HIV- infants (n = 20) born to HIV-infected (HIV+) mothers who received either no antiretroviral therapy (n = 10) or zidovudine (3'-azido-3'-deoxythymidine [AZT]) during pregnancy (n = 10). DNA from cord blood leukocytes and peripheral blood leukocytes taken at 1 and 2 years of age was examined for loss of mitochondrial DNA (mtDNA) and telomere integrity. Telomere length, a measure of nuclear DNA damage, was the same in all infants at birth and at age 1 year. The quantity of mtDNA was assessed relative to nuclear DNA using a polymerase chain reaction-based chemiluminescence detection (PCR-CID) method that determined mitochondrial D Loop gene copies relative to nuclear 18S RNA gene copies by comparison with a standard curve. MtDNA quantity was expressed as a ratio of gene copy numbers. In infants of uninfected mothers (AZT-/HIV-) at the three time points, the ratios were 442 to 515, whereas in infants of untreated AZT-/HIV+ mothers the ratios were 261 to 297, and in infants of AZT-treated (AZT+/HIV+) mothers the ratios were 146 to 203. At all three time points, differences between the AZT-/HIV- group and the two HIV+ groups were statistically significant (p <.05), and differences between the AZT-/HIV+ and AZT+/HIV+ groups were also statistically significant (p <.05), demonstrating that AZT exposure causes a persistent depletion of mtDNA. The study shows that children of HIV+ mothers are at risk for mitochondrial damage that is further increased in infants of mothers receiving AZT during pregnancy.

Highly sensitive chemiluminescence immunoassay for benzo[a]pyrene-DNA adducts: validation by comparison with other methods, and use in human biomonitoring

A chemiluminescence immunoassay (CIA) utilizing antiserum elicited against DNA modified with (+/-)-7beta, 8alpha-dihydroxy-9alpha,10alpha-epoxy-7,8,9,10-tetrahydrobenzo[a]- pyrene (BPDE) has been developed and validated to study the formation of polycyclic aromatic hydrocarbon (PAH)-DNA adducts in human tissues. Advantages include a low limit of detection for 10b-(deoxyguanosin-N(2)-yl)-7beta,8alpha,9alpha-trihydroxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPdG, approximately 1.5 adducts/10(9) nucleotides using 20 micro g DNA) and a high signal-to-noise ratio (> or =100). The CIA BPDE-DNA standard curve gave 50% inhibition at 0.60 +/- 0.08 fmol BPdG (mean +/- SE, n = 30), which was a 10-fold increase in sensitivity compared with the dissociation-enhanced lanthanide fluoroimmunoassay (DELFIA). Calf thymus DNA modified with [1,3-(3)H]BPDE was assayed by radiolabeling, (32)P-postlabeling, DELFIA and CIA, and all assays gave similar values. Liver DNAs from mice exposed to 0.5 and 1.0 mg [7,8-(3)H]benzo[a]pyrene (BP) were assayed by the same four assays and a dose-response was obtained with all assays. The BPDE-DNA CIA was further validated in MCL-5 cells exposed to 4 micro M BP for 24 h, where nuclear and mitochondrial DNA adduct levels were associated with an increase in DNA tail length measured by the Comet assay. Human peripheral blood cell (buffy coat) DNA samples (n = 43) obtained from 25 individuals who were either colorectal adenocarcinoma patients or controls were assayed by BPDE-DNA CIA. Three samples (7%) were non-detectable, and the remaining 40 samples had values between 0.71 and 2.21 PAH-DNA adducts/10(8) nucleotides. The intra-assay coefficient of variation (CV), for four wells on the same microtiter plate, was 1.85%. Sufficient DNA for two assays, on separate plates, was available for 38 of the 43 samples, and the PAH-DNA adduct values obtained were highly correlated (r(2) = 0.95). Coded duplicate DNA samples from 15 individuals were assayed four times gave an inter-assay CV of 13.8%.

Semiquantitation of polycyclic aromatic hydrocarbon-DNA adducts in human esophagus by immunohistochemistry and the automated cellular imaging system

It has been suggested that ingestion of polycyclic aromatic hydrocarbons (PAHs) may contribute to the high incidence and mortality of esophageal cancer in Linxian, China. To explore this relationship a semiquantitative immunohistochemical staining method was developed for localization of PAH-DNA adducts. Nuclear color intensity (bright field average pink intensity per nucleus for >1000 cells) was measured using the ChromaVision Automated Cellular Imaging System (ACIS). Paraffin-embedded sections of cultured human keratinocytes exposed to increasing concentrations of 7beta,8alpha-dihydroxy-9alpha,10alpha-epoxy-7,8,9,10-tetrahydro-benzo[a]pyrene (BPDE) were incubated with BPDE-DNA antiserum and served as an internal positive control (standard curve). Values for nuclear staining intensity correlated directly with BPDE exposure concentration (r(2) = 0.99) and were reproducible. DNA adduct levels determined by BPDE-DNA chemiluminescence immunoassay in DNA from BPDE-exposed keratinocytes, correlated with BPDE exposure concentrations (r(2) = 0.99), showing that nuclear staining intensity determined by ACIS correlated directly with BPDE-DNA adduct levels determined by chemiluminescence immunoassay. The ACIS methodology was applied to 5 human samples from Linxian, and significantly positive nuclear PAH-DNA adduct staining was observed in this group when compared with esophageal tissue from 4 laboratory-housed monkey controls and 6 samples obtained at autopsy from smokers and nonsmokers in the United States. Nuclear PAH-DNA staining was absent from Linxian samples when serial sections were incubated with normal rabbit serum (negative control) and was significantly reduced on incubation with BPDE-DNA antiserum absorbed previously with the immunogen BPDE-DNA. These results appear to support the hypothesis that high PAH exposure levels may be etiologically associated with the development of esophageal cancer in Linxian.

Transplacental genotoxicity of combined antiretroviral nucleoside analogue therapy in Erythrocebus patas monkeys

Antiretroviral nucleoside analogue drugs are a major constituent of highly active antiretroviral therapy (HAART), the most advanced form of treatment for HIV-1 infection. Currently, HAART combinations that include zidovudine (ZDV) and lamivudine (3TC) are highly effective in preventing HIV-1 vertical transmission; most children are born with no evident adverse clinical effects. However, ZDV is a moderately strong transplacental carcinogen in mice, and potential long-term consequences of fetal exposure to most HAART combinations remain unknown. To model human transplacental ZDV and 3TC exposures, experiments were performed in Erythrocebus patas monkeys given human-equivalent drug exposure protocols. Pregnant monkeys were dosed with either no drug (n = 2), 40.0 mg ZDV/d (about 6 mg/kg body weight/d) for the last 50% (10 weeks) of gestation (n = 3), or with the same regimen of ZDV plus 24.0 mg 3TC/d (about 3.6 mg/kg body weight/d) for the last 20% (4 weeks) of gestation (n = 3). Multiple fetal organs were examined at term for DNA incorporation of ZDV and 3TC using two separate radioimmunoassays (RIAs). Values for ZDV-DNA incorporation were similar in fetuses exposed to ZDV alone and those exposed to ZDV plus 3TC. Values for 3TC-DNA in fetal organs were greater than or equal to values for ZDV-DNA, indicating that the total DNA damage sustained by fetuses exposed to both drugs was at least double that observed in fetuses exposed to ZDV alone. Telomere shortening, determined by Southern blot with a telomeric probe, was observed in most organs of the three animals exposed in utero to ZDV plus 3TC. No telomere shortening was evident in the unexposed fetuses, and occasional telomere shortening was found in fetuses exposed to ZDV alone. Overall, these studies demonstrate that monkey fetuses exposed in utero to the combination ZDV plus 3TC sustain a higher level of drug-DNA incorporation and show evidence of more telomere damage than monkey fetuses exposed to ZDV alone.

Chronic stavudine exposure induces hepatic mitochondrial toxicity in adult Erythrocebus patas monkeys

OBJECTIVES

To understand the mitochondrial mechanisms underlying the lactic acidosis and hepatic steatosis seen in some HIV-1-infected individuals after long-term stavudine (d4T) exposure, we have explored mitochondrial integrity in adult monkeys (Erythrocebus patas) given a daily human equivalent dose of d4T for 78 days.

STUDY DESIGN/METHODS

Three Erythrocebus patas (patas) monkeys were given 3 mg d4T orally twice daily (total 6 mg d4T), or approximately 1.2 mg d4T/kg body weight per day, for 78 days and compared with 3 unexposed animals. Blood taken from controls and from treated monkeys before and after drug exposure was subjected to a complete clinical chemistry profile. Liver and skeletal muscles were examined for oxidative phosphorylation enzyme specific activities, mitochondrial deoxyribonucleic acid (mtDNA) quantity by slot blot, and mtDNA integrity by Southern blot.

RESULTS

Clinical chemistry assays demonstrated few significant differences; however, one d4T-exposed monkey had a serum lactate of 8.1 mmol/L after 78 days of oral d4T ingestion. Specific activities of oxidative phosphorylation Complexes I, II, and IV were significantly altered in both livers and skeletal muscles from the d4T-exposed animals, compared with the controls (p < or = 0.05). Significant depletion of mitochondrial DNA was observed in livers of drug-exposed monkeys, but not in skeletal muscle (p < or = 0.05). Further examination of liver DNA by Southern blot confirmed hepatic mtDNA depletion in drug exposed animals.

CONCLUSIONS

The data suggest that direct examination of the liver may be required to elucidate clinical d4T-induced hepatotoxicity related to mitochondrial damage.

Immunohistochemical localization and semi-quantitation of hepatic tamoxifen-DNA adducts in rats exposed orally to tamoxifen

Administration of tamoxifen (TAM) has been shown to induce hepatocellular carcinogenesis and TAM-DNA adduct formation in rat liver. Here we present TAM-DNA adduct localization and semi-quantitation in hepatic tissue of rats by immunohistochemical staining followed by image analysis. We have also used a quantitative immunoassay to provide a validation for the immunohistochemical values. Rats were fed diets containing 0, 5, 50, 150 or 500 p.p.m. TAM for 45 weeks. Serial sections of paraffin-embedded liver were stained for TAM-DNA adducts using a polyclonal TAM-DNA antiserum. Subsequently, visualization of TAM-DNA adducts was performed by peroxidase-conjugated secondary antibody-mediated signal amplification using biotinyl tyramide followed by streptavidin-alkaline phosphatase and fast red. Semi-quantitation of nuclear color intensity was achieved with an Automated Cellular Imaging System (ACIS), with a detection limit of 1 TAM-DNA adduct per 10(7) nt for these experiments. In parenchymal cells of liver sections from TAM-exposed animals a dose-dependent increase in nuclear staining was observed by ACIS and the TAM-DNA adduct levels determined by ACIS were validated in liver DNA by quantitative chemiluminescence immunoassay (CIA). Comparison of semi-quantitative values determined by ACIS with quantitative values determined by CIA showed a strong correlation (r = 0.924) between the two methods. At 45 weeks of TAM exposure the liver cytoplasm contained placental glutathione S-transferase (GST-p)-positive foci, as indicated by new fuchsin staining. Staining of serial sections revealed a relative lack of TAM-DNA adducts within these enzyme-altered foci. In addition, some GST-p foci contained islands of cells that did not stain for GST-p but were positive for TAM-DNA adduct formation. This study validates the use of ACIS for TAM-DNA adduct formation and demonstrates that steady-state TAM-DNA adduct levels observed in livers of rats chronically fed TAM for several months increase in relation to dose. In addition, unlike the normal surrounding liver, preneoplastic GST-p-positive foci have virtually no TAM-DNA adducts.

Cisplatin exposure induces mitochondrial toxicity in pregnant rats and their fetuses

High levels of cis-diamminedicholorplatinum II (cisplatin)-DNA adducts have previously been observed at term in mitochondrial DNA (mtDNA) from organs of pregnant rats, and from their offspring, after administration of a single injection of cisplatin 15 mg/kg body weight (bw) to the pregnant rat on day 18 of gestation. The consequences of such DNA damage may be clinically relevant as cisplatin is given to pregnant women discovered to have ovarian cancer during pregnancy. In this study, kidneys, livers, and brains of exposed pregnant rats and their offspring were examined for mitochondrial functional integrity. Consistent with previous literature, the most severe toxicity occurred in maternal kidney, where oxidative phosphorylation (OXPHOS) enzyme activities were significantly (approximately 50%) impaired for Complexes II, III, and IV, mtDNA levels in drug-exposed animals were higher than in the unexposed controls, and abnormal mitochondrial morphology was observed by transmission electron microscopy (TEM). In fetal kidneys and livers, cisplatin exposure did not alter mitochondrial morphology or mtDNA quantity, but specific activities of OXPHOS Complexes II and IV were significantly decreased. Fetal brain sustained no discernible mitochondrial toxicity. Therefore, cisplatin-induced mitochondrial toxicity in maternal rat kidney is severe, while damage to mitochondria in fetal kidney and liver, occurring as a result of the transplacental drug exposure, appears to be mild.

Plasma drug levels compared with DNA incorporation of 3'-azido-3'-deoxythymidine (AZT) in adult cynomolgus (Macaca fascicularis) monkeys

Zidovudine (3'-azido-3'-deoxythymidine, AZT), widely used for the therapy of the Human Immunodeficiency Virus-1 (HIV-1), is a nucleoside analog of thymidine that becomes phosphorylated and incorporated into nuclear and mitochondrial DNA. Levels of AZT incorporation into DNA of humans, monkeys, and mice are highly variable and suggest interindividual variability in phosphorylation pathways. In addition, studies in rhesus monkeys (1) have shown a lack of correlation between levels of unbound AZT in plasma and tissue AZT-DNA. However, the correlation between plasma AZT and tissue AZT-DNA has not been previously examined in the same primate. Here we examine the relationship between AZT-DNA incorporation in leukocytes and multiple organs, and levels of the drug circulating in plasma of adult female cynomolgus (Macaca fascicularis) monkeys. Three monkeys were dosed with 40.0 mg of AZT/day for 30 days by naso-gastric intubation. The average daily dose of 9.9 mg of AZT/kg/body wt was similar to the approximately 8.6 mg of AZT/kg/body wt (600 mg/day) given to adult HIV-1-infected patients. In all three monkeys, at the time of sampling, values for AZT concentrations in plasma were similar and values for AZT incorporation into leukocyte DNA (86.1, 100.0, and 114.1 molecules of AZT/10(6) nucleotides) were also similar. AZT-DNA incorporation was detected in liver, uterus, spleen, and kidney from the three AZT-exposed animals, with values for positive samples ranging from 5.8 to 97.4 molecules of AZT/10(6) nucleotides. In brain cortex and lung DNA from AZT-exposed animals, AZT incorporation was undetectable. The data suggest that organ-specific differences in AZT uptake and/or metabolism may contribute to AZT phosphorylation and subsequent drug incorporation into DNA. In addition, AZT-DNA levels in monkey organs were similar to or lower than values observed in peripheral leukocytes of adult AIDS patients.

Zidovudine-didanosine coexposure potentiates DNA incorporation of zidovudine and mutagenesis in human cells

Drug combinations that include nucleoside reverse transcriptase inhibitors (NRTIs) are remarkably effective in preventing maternal-viral transmission of HIV during pregnancy. However, there may be potential long-term risks for children exposed in utero. Examination of the genotoxic and mutagenic effects of two NRTIs, zidovudine [AZT (3'-azido-3'-deoxythymidine)] and didanosine [ddI (2',3'-dideoxyinosine)], in cultured human lymphoblastoid cells revealed multiplicative synergistic enhancement of AZT-DNA incorporation and mutant frequency induction in response to the combined drug exposure, as compared with single-drug exposures. Dose-related increases in DNA incorporation of AZT (as measured by a competitive RIA) and mutagenicity at the HPRT and TK loci (as assessed by cell-cloning assays) were observed in cells exposed in culture to AZT, or equimolar combinations of AZT + ddI, at exposure concentrations ranging from 3 to 30 times the maximum plasma levels found in humans. Because mutagenesis is strongly associated with tumor induction in experimental models, children exposed transplacentally to combinations of NRTIs may be at risk for cancer development later in life.

Incorporation of zidovudine into cord blood DNA of infants and peripheral blood DNA of their HIV-1-positive mothers

The nucleoside analogue 3'-azido-3'-deoxythymidine (AZT) is a weak carcinogen in adult female mice and a moderately strong carcinogen in the offspring of female mice given the drug during gestation. In addition, incorporation of AZT into DNA was observed in multiple organs of transplacentally exposed newborn mice. Here we investigate the incorporation of AZT into peripheral leukocyte DNA of HIV-1-positive adult pregnant women given AZT for variable times during gestation and cord blood of infants exposed to AZT in utero. The length of treatment varied between 10 days and 9 months. High molecular weight DNA was extracted from maternal peripheral blood mononuclear cells (PBMC) and infant cord blood. A specific AZT-DNA radioimmunoassay was used to determine the amount of AZT incorporated into leukocyte DNA. Incorporation of AZT into DNA ranged up to 183.3 and 344.5 molecules of AZT/10(6) nucleotides in the mothers and infants, respectively, and was detected in about 70% of samples. Therefore, AZT-induced mutagenic events are possible in the majority of adults and infants. No correlation was found between level of incorporation and length of AZT treatment, suggesting that the differences observed among the individuals arise from variability in AZT metabolism. These data support previous observations that a high degree of inter-individual variability in AZT phosphorylation occurs in primates.

Fetal patas monkeys sustain mitochondrial toxicity as a result of in utero zidovudine exposure

Mitochondrial toxicity was examined in near-term fetuses of pregnant Erythrocebus patas monkeys given human equivalent doses of 3'-azido-3'deoxythymidine (AZT) during the second half of gestation. Pregnant monkeys were dosed daily with 10 or 40 mg AZT, equivalent to about 21% and 86% of the daily AZT dose (500 mg) given to HIV-1-positive pregnant women to prevent maternal-fetal virus transmission. The fetal tissues examined include heart and skeletal muscle, which have high energy requirements, and placenta, which is less dependent on mitochondrial integrity. Slot blot quantitation of mitochondrial DNA (mtDNA) levels showed dose-dependent depletion in heart, skeletal muscle, and placenta from AZT-exposed fetuses compared to unexposed controls. Furthermore, mtDNA degradation, observed by Southern blot analysis, appeared more extensive in AZT-exposed tissues compared to unexposed controls. Mitochondrial functional integrity, as determined by oxidative phosphorylation (OXPHOS) enzyme assays, was also examined in heart, skeletal muscle, and placenta. All three tissues showed strong dose-related decreases in Complex I. In placenta, dose-related increases for Complexes II and IV and a decrease for Complex III were observed. Dose-related increases for Complexes II and IV observed in heart and skeletal muscle have been reported. The increase in Complex IV (cytochrome c oxidase) activity in heart and skeletal muscle tissue from patas fetuses exposed to 40 mg AZT/day has been confirmed here by histochemical staining. Overall, data demonstrate that mitochondrial toxicity, evidenced by depletion in mtDNA and OXPHOS enzyme abnormalities, is manifested similarly in heart, skeletal muscle, and placenta of AZT-exposed monkey fetuses. It is therefore possible that the placenta, which is a readily accessible tissue, might be an indicator of potential mitochondrial toxicity in human pregnancies involving nucleoside analog drug exposure.

Association between GSTM1*0 and squamous dysplasia of the esophagus in the high risk region of Linxian, China

Individuals with specific phase I and phase II enzyme polymorphisms may be at increased risk for squamous cell carcinoma of the esophagus. However, to our knowledge there has been only one previous report that evaluates a potential role for these polymorphisms in increasing risk for preneoplastic squamous lesions of the esophagus. To explore this further, we examined polymorphisms in CYP1A1, CYP2E1, GSTM1 and GSTT1, both independently and in combination, for potential associations with the risk of biopsy-proven squamous dysplasia of the esophagus in asymptomatic adults from Linxian, a high risk region in China. Cases consisted of 56 individuals from an esophageal cancer screening study with an endoscopic biopsy diagnosis of mild or moderate squamous dysplasia. Each case was matched on age (+/- 1 year) and gender to a control. Controls were defined as screening study participants with an endoscopic biopsy diagnosis of normal mucosa or esophagitis. DNA was extracted from frozen cell samples obtained by cytologic balloon examination and genotyped using standard methods. Individuals who were GSTM1 null (homozygous for GSTM1*0) were found to have a tendency for an increased risk of esophageal squamous dysplasia (odds ratio=2.6, 95% CI, 0.9-7.4). No excess risks were observed for inheritance of other putative at risk genotypes CYP1A1*2B, CYP2E1*6 or GSTT1*0. The risk associated with the inheritance of combined genotypes was not significantly different than the risk estimates from the univariate analysis. These results are consistent with the notion that exposure to environmental carcinogens that are detoxified by GSTM1, such as polycyclic aromatic hydrocarbons, may contribute to the etiology of esophageal cancer in Linxian.