Depletion of mitochondrial DNA and enzyme in estrogen-induced hamster kidney tumors: a rodent model of hormonal carcinogenesis

Sensitivity to cadmium of the endangered freshwater pearl mussel Margaritifera margaritifera from the Dronne River (France): experimental exposure

Margaritifera margaritifera is a critically endangered species in Europe. Among the causes explaining its decline, metal pollution had never been deeply studied. Thus, an ecotoxicological investigation was developed on this species which comes from the Dronne River (South-West of France). Cadmium (Cd) exposure of mussels at 2 and 5 μg/L for 7 days was conducted to test their vulnerability to this metal, and also the potential endocrine disruption power of Cd. Morphometric analyses, gonad histological observations, metal bioaccumulation, metallothionein (MTs) production, measures of malondialdehyde (MDA), and finally quantitative relative expression analysis of genes involved in various metabolic functions were performed.The main results showed Cd accumulation increasing in a dose-dependent manner, especially in the gills. The same trend was observed for gene expression relative to oxidative stress. Histological analysis of the gonads highlighted a predominance of hermaphrodite individuals, but after 7 days of exposure to Cd, the percentage of female was largely increased compared with controls, from 17 to 33%. These results demonstrate the endocrine disruption effect of Cd on freshwater pearl mussels.The pearl mussel Margaritifera margaritifera is sensitive to cadmium since the metallothioneins are poorly induced, gene expression reveals oxidative stress, and gonads tend to be feminized.

The complete nucleotide sequence of Chinese hamster (Cricetulus griseus) mitochondrial DNA

Mammalian mitochondria contain their own approximately 16.5 kb circular genome. Mitochondrial DNA (mtDNA) encodes for a subset of the proteins involved in the electron transport chain and depletion or mutation of the sequence is implicated in a number of human disease processes. The recent finding is that mitochondrial damage mediates genotoxicity after exposure to chemical carcinogens has focused attention on the role of mtDNA mutations in the development of cancer. Although the entire genome has been sequenced for a number of mammals, only a small fraction of the mtDNA sequence is available for hamsters. We have obtained here the entire 16,284 bp sequence of the Chinese hamster mitochondrial genome, which will enable detailed analysis of mtDNA mutations caused by exposure to mutagens in hamster-derived cell lines.

Induction of acquired resistance to antiestrogen by reversible mitochondrial DNA depletion in breast cancer cell line

Although the net benefits of tamoxifen in adjuvant breast cancer therapy have been proven, the recurrence of the cancer in an aggressive and hormone independent form has been highly problematic. We previously demonstrated the important role mitochondrial DNA (mtDNA) plays in hormone-independence in prostate cancer. Here, the role of mtDNA in breast cancer progression was investigated. We established hydroxytamoxifen (4-OHT) resistant HTRMCF by growing MCF-7, human breast adenocarcinoma cells, in the presence of 4-OHT. HTRMCF was cross-resistant to 4-OHT and ICI182,780 concurrent with the depletion of mtDNA. To further investigate the role of mtDNA depletion, MCF-7 was depleted of mtDNA by treatment with ethidium bromide. MCF Rho 0 was resistant to both 4-OHT and ICI182,780. Furthermore, cybrid (MCFcyb) prepared by fusion MCF Rho 0 with platelet to transfer mtDNA showed susceptibility to antiestrogen. Surprisingly, after withdrawal of 4-OHT for 8 weeks, HTRMCF and their clones became susceptible to both drugs concurrent with a recovery of mtDNA. Herein, our results substantiated the first evidence that the depletion of mtDNA induced by hormone therapy triggers a shift to acquired resistance to hormone therapy in breast cancer. In addition, we showed that mtDNA depletion can be reversed, rendering the cancer cells susceptible to antiestrogen. The fact that the hormone independent phenotype can be reversed should be a step toward more effective treatments for estrogen-responsive breast cancer.

Reproductive characteristics and risk of kidney cancer: Iowa Women's Health Study

OBJECTIVES

Kidney (renal cell) cancer accounts for approximately 3-4% of all new cases of primary cancer diagnosed in the United States. A relationship between kidney cancer and female reproductive factors has been hypothesized but supporting evidence is inconsistent. Our objectives were to explore the relationship between female reproductive factors and kidney cancer and identify independent risk factors related to female reproductive history and its effects on development of kidney cancer.

METHODS

We measured risk factors for kidney cancer and reproductive characteristics in a group of 37,440 postmenopausal women in Iowa. From 1986 to 2003, 165 cases of incident kidney cancer were identified through a statewide cancer registry.

RESULTS

After adjustment for age and other risk factors, past use of estrogen showed an increased risk of renal cancer (RR 1.56; 95% CI 1.13-2.17) when compared to no use. Women with no live birth (RR 1.91, p=0.02) and women with three to four live births (RR 1.62, p=0.02) also had an increased risk of kidney cancer when compared with women who had one to two live births. There was also a lower risk of kidney cancer with greater lifetime duration of ovulation.

CONCLUSION

Although most reproductive variables were not significantly associated with kidney cancer, our study indicates that a greater exposure to estrogens may increase risk for kidney cancer.

Quantitative analysis of total mitochondrial DNA: competitive polymerase chain reaction versus real-time polymerase chain reaction

An efficient and effective method for quantification of small amounts of nucleic acids contained within a sample specimen would be an important diagnostic tool for determining the content of mitochondrial DNA (mtDNA) in situations where the depletion thereof may be a contributing factor to the exhibited pathology phenotype. This study compares two quantification assays for calculating the total mtDNA molecule number per nanogram of total genomic DNA isolated from human blood, through the amplification of a 613-bp region on the mtDNA molecule. In one case, the mtDNA copy number was calculated by standard competitive polymerase chain reaction (PCR) technique that involves co-amplification of target DNA with various dilutions of a nonhomologous internal competitor that has the same primer binding sites as the target sequence, and subsequent determination of an equivalence point of target and competitor concentrations. In the second method, the calculation of copy number involved extrapolation from the fluorescence versus copy number standard curve generated by real-time PCR using various dilutions of the target amplicon sequence. While the mtDNA copy number was comparable using the two methods (4.92 +/- 1.01 x 10(4) molecules/ng total genomic DNA using competitive PCR vs 4.90 +/- 0.84 x 10(4) molecules/ng total genomic DNA using real-time PCR), both inter- and intraexperimental variance were significantly lower using the real-time PCR analysis. On the basis of reproducibility, assay complexity, and overall efficiency, including the time requirement and number of PCR reactions necessary for the analysis of a single sample, we recommend the real-time PCR quantification method described here, as its versatility and effectiveness will undoubtedly be of great use in various kinds of research related to mitochondrial DNA damage- and depletion-associated disorders.

Mitochondrial DNA 4,977-bp deletion in paired oral cancer and precancerous lesions revealed by laser microdissection and real-time quantitative PCR

Oral cancer is the fourth leading cause of cancer deaths among men in Taiwan and is closely associated with areca quid chewing habits. Recent studies showed that mitochondrial DNA (mtDNA) mutations occur in various tumors, including oral cancers, and that the accumulation of mtDNA deletions could be an important contributor to carcinogenesis. Using laser microdissection, we have analyzed mtDNA deletions by pairwise comparisons in oral cancer, precancerous cells, and their adjacent submucosal stoma tissues in 12 patients with areca quid chewing history. Real-time quantitative polymerase chain reaction (RTQPCR) was performed to detect and quantify mtDNA with the 4,977-bp deletion in the histologically defined specified cell groups. Quantitative analysis of 60 samples by RTQPCR revealed that the average proportions of 4,977-bp deleted mtDNA over total mtDNA were 0.137%, 0.367%, and 0.001% in cancer, precancer cells, and lymphocytes of lymph node biopsies, respectively. Pairwise analysis of the proportion of mtDNA deletion in cancer, precancer, and their stroma tissues revealed a consistent trend among these patients. All of the patients (12/12) presented a higher proportion of mtDNA with 4,977-bp deletion in the lesions than in the lymphocytes, with average increases of 198-fold in cancer and 546-fold in precancer cells. A decrease in the proportion of deleted mtDNA was observed in 8 of 12 patients when the disease progressed from precancer to cancer lesions. Interestingly, 7 of 12 cancer tissues and 8 of 12 precancer lesions exhibited an average of 6.3-fold and 17.4-fold increases in the proportion of 4,977-bp deleted mtDNA in the stromal cells than in the lesion cells, respectively. The observation that the proportion of 4,977-bp deleted mtDNA in all oral lesions was higher than normal and consistently decreased during cancer progression from precancer to primary cancer suggests that accumulation and subsequent cytoplasmic segregation of the mutant mtDNA during cell division may play an important role in oral carcinogenesis. This study also demonstrates that laser microdissection combined with RTQPCR is an efficient and sensitive tool to gain insight into the role that mtDNA mutation may play in carcinogenesis.

History of L-carnitine: implications for renal disease

L-carnitine (LC) plays an essential metabolic role that consists in transferring the long chain fatty acids (LCFAs) through the mitochondrial barrier, thus allowing their energy-yielding oxidation. Other functions of LC are protection of membrane structures, stabilizing a physiologic coenzyme-A (CoA)-sulfate hydrate/acetyl-CoA ratio, and reduction of lactate production. On the other hand, numerous observations have stressed the carnitine ability of influencing, in several ways, the control mechanisms of the vital cell cycle. Much evidence suggests that apoptosis activated by palmitate or stearate addition to cultured cells is correlated with de novo ceramide synthesis. Investigations in vitro strongly support that LC is able to inhibit the death planned, most likely by preventing sphingomyelin breakdown and consequent ceramide synthesis; this effect seems to be specific for acidic sphingomyelinase. The reduction of ceramide generation and the increase in the serum levels of insulin-like growth factor (IGF)-1, could represent 2 important mechanisms underlying the observed antiapoptotic effects of acetyl-LC. Primary carnitine deficiency is an uncommon inherited disorder, related to functional anomalies in a specific organic cation/carnitine transporter (hOCTN2). These conditions have been classified as either systemic or myopathic. Secondary forms also are recognized. These are present in patients with renal tubular disorders, in which excretion of carnitine may be excessive, and in patients on hemodialysis. A lack of carnitine in hemodialysis patients is caused by insufficient carnitine synthesis and particularly by the loss through dialytic membranes, leading, in some patients, to carnitine depletion with a relative increase in esterified forms. Many studies have shown that LC supplementation leads to improvements in several complications seen in uremic patients, including cardiac complications, impaired exercise and functional capacities, muscle symptoms, increased symptomatic intradialytic hypotension, and erythropoietin-resistant anemia, normalizing the reduced carnitine palmitoyl transferase activity in red cells.