Limits and perspective of oral therapy with statins and aspirin for the prevention of symptomatic cholesterol gallstone disease

The prevalence of gallstones disease in Western countries is 10 - 15%. Gallstones can be one of two types - cholesterol or pigment - with cholesterol gallstones representing nearly the 80% of the total. Cholesterol and pigment gallstones have different predisposing factors: cholesterol gallstones are related to supersaturated bile in cholesterol, whereas black pigment gallstones are related to hyperbilirubinbilia factors (hemolysis, etc.); these are necessary, but not sufficient, factors to produce gallstones in vivo. Gall bladder mucosa factors (gall bladder secretion of mucin, local bile stasis and production of endogenous biliary β-glucuronidase) may coexist with the aforementioned factors and facilitate gallstone nucleation and growth. The gold-standard treatment for symptomatic gallstones is laparoscopic cholecystectomy. Several studies have reported a significant reduction in the onset of symptomatic gallstones disease in patients undergoing chronic therapy with statins, which can reduce bile cholesterol saturation. Aspirin, which has been shown to reduce the local production of gall bladder mucins (mucosal or parietal factors of gallstone formation) in animal experimental models, does not appear to reduce the risk of symptomatic gallstones disease when tested alone. The new horizon of oral therapy for the prevention of symptomatic gallstone disease needs to evaluate the long-term effect of statins and chronic aspirin administration in patients with dyslipidemia and/or atherosclerosis.     

Limits and perspective of oral therapy with statins and aspirin for the prevention of symptomatic cholesterol gallstone disease

The prevalence of gallstones disease in Western countries is 10 – 15%. Gallstones can be one of two types – cholesterol or pigment – with cholesterol gallstones representing nearly the 80% of the total. Cholesterol and pigment gallstones have different predisposing factors: cholesterol gallstones are related to supersaturated bile in cholesterol, whereas black pigment gallstones are related to hyperbilirubinbilia factors (hemolysis, etc.); these are necessary, but not sufficient, factors to produce gallstones in vivo. Gall bladder mucosa factors (gall bladder secretion of mucin, local bile stasis and production of endogenous biliary β-glucuronidase) may coexist with the aforementioned factors and facilitate gallstone nucleation and growth. The gold-standard treatment for symptomatic gallstones is laparoscopic cholecystectomy. Several studies have reported a significant reduction in the onset of symptomatic gallstones disease in patients undergoing chronic therapy with statins, which can reduce bile cholesterol saturation. Aspirin, which has been shown to reduce the local production of gall bladder mucins (mucosal or parietal factors of gallstone formation) in animal experimental models, does not appear to reduce the risk of symptomatic gallstones disease when tested alone. The new horizon of oral therapy for the prevention of symptomatic gallstone disease needs to evaluate the long-term effect of statins and chronic aspirin administration in patients with dyslipidemia and/or atherosclerosis.     

MRP class of human ATP binding cassette (ABC) transporters: historical background and new research directions

1. The adenosine triphosphate (ATP) binding cassette (ABC) transporters form one of the largest protein families encoded in the human genome, and more than 48 genes encoding human ABC transporters have been identified and sequenced. It has been reported that mutations of ABC protein genes are causative in several genetic disorders in humans. 2. Many human ABC transporters are involved in membrane transport of drugs, xenobiotics, endogenous substances or ions, thereby exhibiting a wide spectrum of biological functions. According to the new nomenclature of human ABC transporter genes, the 'ABCC' gene sub-family comprises three classes involving multidrug resistance-associated proteins (MRPs), sulfonylurea receptors (SURs), and a cystic fibrosis transmembrane conductance regulator (CFTR). 3. Molecular cloning studies have identified a total of ten members of the human MRP class including ABCC11, ABCC12, and ABCC13 (pseudo-gene) that have recently been characterized. 4. This review addresses the historical background and discovery of the ATP-driven xenobiotic export pumps (GS-X pumps) encoded by MRP genes, biological functions of ABC transporters belonging to the MRP class, and regulation of gene expression of MRPs by oxidative stress.     

Pharmacogenomics of human ABC transporters: detection of clinically important SNPs by SmartAmp2 method

Genetic polymorphisms and mutations in drug metabolizing enzymes, transporters, receptors, and other drug targets (e.g., toxicity targets) are linked to inter-individual differences in the efficacy and toxicity of many medications as well as risk of genetic diseases. Validation of clinically important genetic polymorphisms and the development of new technologies to rapidly detect clinically important variants are critical issues for advancing personalized medicine. A key requirement for the advancing personalized medicine resides in the ability of rapidly and conveniently testing patients' genetic polymorphisms and/or mutations. We have recently developed a rapid and cost-effective method, named Smart Amplification Process 2 (SmartAmp2), which enables us to detect genetic polymorphisms or mutations in target genes within 30 to 45 min under isothermal conditions without DNA isolation and PCR amplification. Detection of mutations or single nucleotide polymorphisms (SNPs) in human ABC transporter genes is becoming more important, since their functional impairments are reportedly associated with inherited diseases. Thus, certain genetic polymorphisms of ABC transporters are considered important biomarkers for diagnosis of inherited diseases and/or risk of drug-induced adverse reactions. In this review article, we will present the new technology of the SmartAmp2 method and its clinical applications for detection of SNPs in human ABC transporter genes, i.e., ABCC4 and ABCC11.     

MRP class of human ATP binding cassette (ABC) transporters: historical background and new research directions

1.?The adenosine triphosphate (ATP) binding cassette (ABC) transporters form one of the largest protein families encoded in the human genome, and more than 48 genes encoding human ABC transporters have been identified and sequenced. It has been reported that mutations of ABC protein genes are causative in several genetic disorders in humans.

2.?Many human ABC transporters are involved in membrane transport of drugs, xenobiotics, endogenous substances or ions, thereby exhibiting a wide spectrum of biological functions. According to the new nomenclature of human ABC transporter genes, the ‘ABCC’ gene sub-family comprises three classes involving multidrug resistance-associated proteins (MRPs), sulfonylurea receptors (SURs), and a cystic fibrosis transmembrane conductance regulator (CFTR).

3.?Molecular cloning studies have identified a total of ten members of the human MRP class including ABCC11, ABCC12, and ABCC13 (pseudo-gene) that have recently been characterized.

4.?This review addresses the historical background and discovery of the ATP-driven xenobiotic export pumps (GS-X pumps) encoded by MRP genes, biological functions of ABC transporters belonging to the MRP class, and regulation of gene expression of MRPs by oxidative stress.     

Modifier gene studies to identify new therapeutic targets in cystic fibrosis

Since the discovery of the CFTR gene mutations which cause cystic fibrosis (CF) in 1989 the average life expectancy of CF patients has almost doubled and now exceeds 37 years. The advances in molecular diagnostics and medical treatments expanded beyond the CF patient population as some of the newest treatments are also being tested for treatment of complex diseases such as COPD and other inherited disorders. Rapid development of CF therapeutics is important for the cystic fibrosis community and is an excellent example for other nonprofit organizations, disease foundations and pharmaceutical companies alike. Better understanding of disease variability and underlying molecular mechanisms through genetic association studies aimed to identify novel CF modifier genes opens new venues for targeted drug design. Furthermore, these genetic studies allow development of molecular diagnostic tests for patient population stratification and treatment personalization, which is already being done for CF patients with specific mutations in the CFTR gene, as well as implementation of new molecular tests for reliable assessment of disease progression and severity.     

Discovery of the hepatic canalicular and intestinal cholesterol transporters. New targets for treatment of hypercholesterolemia

Arteriosclerosis and cholesterol cholelithiasis are characterized by abnormal regulation of cholesterol trafficking and solubilization, and subsequent development of the arteriosclerotic plaque in the artery walls and gallstone formation in the gallbladder, respectively. Cholesterol metabolism is controlled by many complex polygenetic - environmental interactions that contribute to the regulation of serum lipoprotein cholesterol levels and biliary cholesterol and bile acids secretion, which constitute the only pathway for sterol elimination from the organism. Much of our understanding of cholesterol metabolism has arisen from studies of the pathways controlling cholesterol synthesis and the uptake and degradation of LDL and HDL lipoproteins. Recently, two new members of the ABC transporter family (ABCG5 and ABCG8 heterodimers) have been discovered in the apical pole of the enterocyte and in the canalicular membrane of hepatocytes. Experiments in genetically engineered mice have demonstrated that ABCG5/G8 represent the physiological canalicular transporter of biliary cholesterol and the intestinal secretory mechanism of absorbed dietary plant sterols. Interestingly, mutation of ABCG5 and or ABCG8 genes in man causes sitosterolemia, a rare genetic disease characterized by massive absorption of plant sterols and premature arteriosclerosis. The potential pharmacological manipulation of biliary cholesterol secretion represents another important therapeutic target to treat hypercholesterolemia, if this manipulation is simultaneously accompanied by measures aimed to avoid gallbladder cholesterol crystallization. The best theoretical drug should decrease serum lipoprotein cholesterol levels, increase biliary cholesterol secretion and fecal elimination and favoring at the same time gallbladder emptying to prevent gallstone formation.     

Molecular genetics of human male infertility: from genes to new therapeutic perspectives

Genetic lesions causing human male infertility are manifold. Besides gross chromosomal aneuploidies and rearrangements, microdeletions and single gene defects can interfere with male fertility. Male fertility is not only dependent on genes controlling the male germ line but also on genes of the networks functional for male gonad development and male somatic development, respectively. It is popular to unravel these netweorks with mouse gene knock-out mutants displaying reproductive defects. However, substantial arguments can be given for more functional studies directly on the human genes, because multiple reproductive proteins evolve quickly most likely for adopting to the specific needs of the species class. Prominent examples are mutations of the FSHR gene causing different pathologies in mouse and human and the DAZ gene family not found in the mouse genome but in the human genome with an essential male fertility function. Therefore this review is focussed on a comprehensive overview of human genes known with mutations causing male infertility (AR; AZF gene families; CFTR, DM-1, DNAH gene family, FGFR1, FSHR, INSL3, KAL-1, LGR8- GREAT, LHR, POLG). Then some human genes are described well recognised as functional in spermatogenesis and male fertility although gene specific mutations causing infertility were not yet identified (CREM, CDY1, DAZL1, PHGPx, PRM-1, PRM-2). They are designated as "spermatogenesis phase marker" or "male fertility index" genes, because they are useful tools for diagnosing the patient's spermatogenesis disruption phase and for predicting the presence and quality of his mature sperms. Current therapeutic protocols for human male infertility do usually not cure the specific gene defect but try to bypass it using Artificial Reproductive Technology (ART). Putative imprinting defects in the early embryo probably associated with the used ART protocol and an increase of chromosome abnormalities in the ART offspring now strongly asks for a significant improvement of this outcome requesting urgently more basic research on the genes functioning in the human male germ line and during early human embryogenesis.     

Human leucocyte antigens (HLA) and rheumatic diseases: HLA class ii antigen-associated diseases

The association between genes of the major histocompatibility complex, HLA in man, and disease susceptibility is one of the most intriguing discoveries of modern genetics. These studies are important for understanding the genetic basis, pathogenesis and aetiology of human diseases. With progress in these areas, new and better forms of treatment as well as disease prevention will become possible. In the previous paper, we reviewed the literature on associations between HLA Class I (A,B,C) genes and rheumatic disease. In this article, we will now concentrate on rheumatic disorders associated with genes in the HLA Class II region, including DR, DQ, DP and the transporter associated with antigen processing (TAP) genes. In addition, the role of the pathogenic mechanism(s), which results in an aberrant expression(s) of HLA molecules on the cell surface, in causing disease susceptibility will be examined.     

Expression profiles of 50 xenobiotic transporter genes in humans and pre-clinical species: A resource for investigations into drug disposition

Carrier-mediated transporters play a critical role in xenobiotic disposition and transporter research is complicated by species differences and their selective tissue expression. The purpose of this study was to generate a comprehensive data set of xenobiotic transporter gene expression profiles in humans and the pre-clinical species mouse, rat, beagle dog and cynomolgus monkey. mRNA expression profiles of 50 genes from the ABC, SLC and SLCO transporter superfamilies were examined in 40 human tissues by microarray analyses. Transporter genes that were identified as enriched in the liver or kidney, or that were selected for their known roles in xenobiotic disposition, were then compared in 22 tissues across the five species. Finally, as clinical variability in drug response and adverse reactions may be the result of variability in transporter gene expression, variability in the expression of selected transporter genes in 75 human liver donors were examined and compared with the highly variable drug metabolizing enzyme CYP3A4.     

Expression profiles of 50 xenobiotic transporter genes in humans and pre-clinical species: a resource for investigations into drug disposition

Carrier-mediated transporters play a critical role in xenobiotic disposition and transporter research is complicated by species differences and their selective tissue expression. The purpose of this study was to generate a comprehensive data set of xenobiotic transporter gene expression profiles in humans and the pre-clinical species mouse, rat, beagle dog and cynomolgus monkey. mRNA expression profiles of 50 genes from the ABC, SLC and SLCO transporter superfamilies were examined in 40 human tissues by microarray analyses. Transporter genes that were identified as enriched in the liver or kidney, or that were selected for their known roles in xenobiotic disposition, were then compared in 22 tissues across the five species. Finally, as clinical variability in drug response and adverse reactions may be the result of variability in transporter gene expression, variability in the expression of selected transporter genes in 75 human liver donors were examined and compared with the highly variable drug metabolizing enzyme CYP3A4.     

Disease modifying genes in cystic fibrosis: therapeutic option or one-way road?

Cystic fibrosis (CF) is the most common genetic disease among Caucasians and is caused by mutations in the CF transmembrane conductance regulator (CFTR) gene. CF affects multiple organs but lung disease is the major determinant for morbidity and mortality. Many studies have focussed on the correlation between CFTR genotype and severity of disease. Since patients with identical CFTR mutations often show considerable variability in disease progression, genes other than CFTR are thought to have the potential to modify the course of lung disease in CF patients. Therefore, identification of CF-modifying genes has become the goal of several studies over the last 15 years. Pharmaceutical approaches for CF lung disease have been developed regardless of the underlying genetic defect and in general target symptoms such as airway obstruction and treatment of bacterial infection. Analysing the pathophysiological processes of modifiers may lead to the discovery of pathways involved in CF pathophysiology and possibly to the design of new therapeutics. The purpose of this review is not only to list potential CFTR modifier genes, but also to discuss new therapeutic strategies that could be derived from knowledge of these CF modifiers.     

Lipid lowering drugs and gallstones: a therapeutic option?

Cholelithiasis is a common disease worldwide. The majority of gallstones can occur when the bile is supersaturated with cholesterol. Dyslipidaemia, obesity, insulin resistance are associated with an increased risk for cholesterol gallstone formation as well as with vascular risk. Statins and ezetimibe are used to treat dyslipidaemia and appear to have some effect on bile composition and cholesterol gallstone formation. Statin (e.g. pravastatin, simvastatin, fluvastatin and lovastatin) monotherapy or combined with ursodeoxycholic acid (UDCA) have shown reductions in bile cholesterol saturation, preventing gallstone formation and even dissolving pre-existing stones. However, this effect was not consistently reported in all studies. Statin use has also been associated with a reduced risk for cholecystectomy in 2 large epidemiological studies. Ezetimibe was shown to have a beneficial action against cholelithiasis in animal studies but data in humans - although promising - are very limited. The effect of these drugs on gallstone disease warrants further investigation in large human trials. We also consider the links between cholelithiasis, vascular risk and the use of lipid lowering drugs.     

Genetic and biochemical aspects of drug resistance in malaria parasites

Drug resistance is one of the major factors contributing to the resurgence of malaria, especially resistance to the most affordable drugs such as chloroquine and Fansidar, a combination drug of pyrimethamine and sulfadoxine. Understanding the mechanisms of such resistance and developing new treatments, including new drugs, are urgently needed. Great progress has been made recently in studying the mechanisms of drug action and drug resistance in malaria parasites, particularly in Plasmodium falciparum. These efforts are highlighted by the demonstration of mutations in the parasite dihydrofolate reductase and dihydropteroate synthase genes conferring resistance to pyrimethamine and sulfadoxine, respectively, and by the recent discovery of mutations in the gene coding for a putative transporter, PfCRT, conferring resistance to chloroquine. Mutations in a homologue of a human multiple-drug-resistant gene, pfmdr1, have also been shown to be associated with responses to multiple drugs. However, except in the case of resistance to antifolate drugs, the mechanisms of action and resistance to most drugs currently in use are essentially unknown or are being debated. Additionally, novel mechanisms of resistance exist in different malaria parasites, complicating the process of developing new drugs and treatment strategies. Here we summarise the progress made in drug resistance research in malaria parasites over the past 20 years, emphasising the most recent developments in the genetics of drug resistance.     

The ABCA2 transporter: intracellular roles in trafficking and metabolism of LDL-derived cholesterol and sterol-related compounds

ATP-binding cassette (ABC) transporters comprise a family of critical membrane bound proteins functioning in the translocation of molecules across cellular membranes. Substrates for transport include lipids, cholesterol and pharmacological agents. Mutations in ABC transporter genes cause a variety of human pathologies and elicit drug resistance phenotypes in cancer cells. ABCA2, the second member the A subfamily to be identified, was highly expressed in ovarian carcinoma cells resistant to the anti-cancer agent, estramustine, and more recently, in human vestibular schwannomas. Cells expressing elevated levels of ABCA2 show resistance to variety of compounds, including estradiol, mitoxantrone and a free radical initiator, 2,2'-azobis-(2-amidinopropane). ABCA2 is expressed in a variety of tissues, with greatest abundance in the central nervous system and macrophages. This transporter, along with other proteins that have a high degree of homology to ABCA2, including ABCA1 and ABCA7, are up-regulated in human macrophages during cholesterol import. Recent studies have shown ABCA2 also plays a role in the trafficking of low-density lipoprotein (LDL)-derived free cholesterol and to be coordinately expressed with sterol-responsive genes. A single nucleotide polymorphism in exon 14 of the ABCA2 gene was shown to be linked to early onset Alzheimer disease (AD) in humans, supporting an earlier study showing ABCA2 expression influences levels of APP and beta-amyloid peptide, the primary component of senile plaques. Studies thus far implicate ABCA2 as a sterol transporter, the deregulation of which may affect a cellular phenotype conducive to the pathogenesis of a variety of human diseases including AD, atherosclerosis and cancer.     

Closing in on Genes for Manic-Depressive Illness and Schizophrenia

Advances in the human genetic map, and in genetic analysis of linkage and association in complex inheritance traits, have led to genetic progress in the major psychoses. For chromosome 6 in schizophrenia, and chromosomes 18 and 21 in manic-depressive illness, there are reports of linkage in several independent data sets. These are small effect genes, best detected with affected-relative-pair linkage methods. Association with candidate genes is an alternative strategy to uncovering susceptibility genes for these illnesses, but convincing associations remain to be demonstrated. New clinical and laboratory investigation methods are being developed. Testing every gene in the human genome for association with illness has recently been proposed (Risch and Merikangas 1996). This would require further progress in characterizing the genome and in automated large-scale genotyping. The best type of pedigree sampling for common disease studies, whether for linkage or association, is not yet established. An endophenotype hybrid strategy can combine genetic linkage, association, and pathophysiologic studies. As clinical molecular investigation methods advance, identification of disease susceptibility mutations and delineation of their pathophysiological roles may be expected.     

Molecular pathogenesis of acute myeloid leukemia: a diverse disease with new perspectives

Acute myeloid leukemia (AML) is a very heterogeneous neoplasm of the hematopoietic stem cell. Despite important achievements in the treatment of AML, the long term survival of patients with the disease remains poor. Understanding the pathogenesis of AML better is crucial for finding new treatment approaches. During AML development, hematopoietic precursor cells undergo clonal transformation in a multistep process through acquisition of chromosomal rearrangements and/or different gene mutations. Over recent years, novel gene mutations have been found in patients with AML. These mutations can be divided into two important categories, class I mutations that confer a proliferation advantage and class II mutations that inhibit myeloid differentiation. Screening for some of these mutations is now part of the initial diagnostic workup in newly diagnosed AML patients. Information about the mutation status of specific genes is useful for risk-stratification, minimal residual disease (MRD) monitoring and increasingly also for targeted therapy, especially for patients with cytogenetically normal AML (CN-AML). Besides chromosomal rearrangements and gene mutations, epigenetic regulation of genes — meaning changes in gene expression by mechanisms other than changes in the underlying DNA sequence — also represents an important mechanism of leukemogenesis. This article reviews some of the most common mutations in CN-AML and gives a perspective of the translation of these discoveries from bench to bedside.     

Phenotype Prediction of Non‐Synonymous Single‐Nucleotide Polymorphisms in Human ATP‐Binding Cassette Transporter Genes

Abstract: A large number of non‐synonymous single‐nucleotide polymorphisms (nsSNPs) have been found in human genome, but there is poor knowledge on the relationship between the genotype and phenotype of these nsSNPs. Human ATP‐binding cassette (ABC) transporters are able to transport a number of important substrates including endogenous and exogenous compounds. This study aimed to predict the phenotypical impact of nsSNPs of human ABC transporter genes, and the predicted results were further validated by reported phenotypical data from site‐directed mutagenesis and clinical genetic studies. One thousand and six hundred thirty‐two nsSNPs were found from 49 human ABC transporter genes. Using the PolyPhen and SIFT algorithms, 41.8–53.6% of nsSNPs in ABC transporter genes were predicted to have an impact on protein function. The prediction accuracy was up to 63–85% when compared with known phenotypical data from in vivo and in vitro studies. There was a significant concordance between the prediction results using SIFT and PolyPhen. Of nsSNPs predicted as deleterious, the prediction scores by SIFT and PolyPhen were significantly related to the number of nsSNPs with known phenotypes confirmed by experimental and human studies. The amino acid substitution variants are supposed to be the pathogenetic basis of increased susceptibility to certain diseases with Mendelian or complex inheritance, altered drug resistance and altered drug clearance and response. Predicting the phenotypic consequence of nsSNPs using computational algorithms may provide a better understanding of genetic differences in susceptibility to diseases and drug response. The prediction of nsSNPs in human ABC transporter genes would be useful hints for further genotype–phenotype studies.