High-resolution melt curve analysis: An approach for variant detection in the TPO gene of congenital hypothyroid patients in Bangladesh

TPO (Thyroid Peroxidase) is known to be one of the major genes involved in congenital hypothyroid patients with thyroid dyshormonogenesis. The present study aims to validate high-resolution melting (HRM) curve analysis as a substitute method for Sanger sequencing, focusing on the frequently observed non-synonymous mutations c.1117G>T, c.1193G>C, and c.2173A>C in the TPO gene in patients from Bangladesh. We enrolled 36 confirmed cases of congenital hypothyroid patients with dyshormonogenesis to establish the HRM method. Blood specimens were collected, and DNA was extracted followed by PCR and Sanger sequencing. Among the 36 specimens, 20 were pre-sequenced, and variants were characterized through Sanger sequencing. Following pre-sequencing, the 20 pre-sequenced specimens underwent real-time PCR-HRM curve analysis to determine the proper HRM condition for separating the three variations from the wild-type state into heterozygous and homozygous states. Furthermore, 16 unknown specimens were subjected to HRM analysis to validate the method. This method demonstrated a sensitivity and specificity of 100 percent in accurately discerning wild-type alleles from both homozygous and heterozygous states of c.1117G>T (23/36; 63.8%), c.1193G>C (30/36; 83.3%), and c.2173A>C (23/36; 63.8%) variants frequently encountered among 36 Bangladeshi patients. The HRM data was found to be similar to the sequencing result, thus confirming the validity of the HRM approach for TPO gene variant detection. In conclusion, HRM-based molecular technique targeting variants c.1117G>T, c.1193G>C, and c.2173A>C could be used as a high throughput, rapid, reliable, and cost-effective screening approach for the detection of all common mutations in TPO gene in Bangladeshi patients with dyshormonogenesis.

Investigation of the impact of nonsynonymous mutations on thyroid peroxidase dimer

Congenital hypothyroidism is one of the most common preventable endocrine disorders associated with thyroid dysgenesis or dyshormonogenesis. Thyroid peroxidase (TPO) gene defect is mainly responsible for dyshormonogenesis; a defect in the thyroid hormone biosynthesis pathway. In Bangladesh, there is limited data regarding the genetic etiology of Congenital Hypothyroidism (CH). The present study investigates the impact of the detected mutations (p.Ala373Ser, and p.Thr725Pro) on the TPO dimer protein. We have performed sequential molecular docking of H2O2 and I- ligands with both monomers of TPO dimer to understand the iodination process in thyroid hormone biosynthesis. Understanding homodimer interactions at the atomic level is a critical challenge to elucidate their biological mechanisms of action. The docking results reveal that mutations in the dimer severely disrupt its catalytic interaction with essential ligands. Molecular dynamics simulation has been performed to validate the docking results, thus realizing the consequence of the mutation in the biological system's mimic. The dynamics results expose that mutations destabilize the TPO dimer protein. Finally, principal component analysis exhibits structural and energy profile discrepancies in wild-type and mutant dimers. The findings of this study highlight that the mutations in TPO protein can critically affect the dimer structure and loss of enzymatic activity is persistent. Other factors also might influence the hormone synthesis pathway, which is under investigation.

Molecular investigation of TSHR gene in Bangladeshi congenital hypothyroid patients

The disorder of thyroid gland development or thyroid dysgenesis accounts for 80-85% of congenital hypothyroidism (CH) cases. Mutations in the TSHR gene are mostly associated with thyroid dysgenesis, and prevent or disrupt normal development of the gland. There is limited data available on the genetic spectrum of congenital hypothyroid children in Bangladesh. Thus, an understanding of the molecular aetiology of thyroid dysgenesis is a prerequisite. The aim of the study was to investigate the effect of mutations in the TSHR gene on the small molecule thyrogenic drug-binding site of the protein. We identified two nonsynonymous mutations (p.Ser508Leu, p.Glu727Asp) in the exon 10 of the TSHR gene in 21 patients with dysgenesis by sequencing-based analysis. Later, the TSHR368-764 protein was modeled by the I-TASSER server for wild-type and mutant structures. The model proteins were targeted by thyrogenic drugs, MS437 and MS438 to perceive the effect of mutations. The damaging effect in drug-protein complexes of mutants was explored by molecular docking and molecular dynamics simulations. The binding affinity of wild-type protein was much higher than the mutant cases for both of the drug ligands (MS437 and MS438). Molecular dynamics simulates the dynamic behavior of wild-type and mutant complexes. MS437-TSHR368-764MT2 and MS438-TSHR368-764MT1 showed stable conformations in biological environments. Finally, Principle Component Analysis revealed structural and energy profile discrepancies. TSHR368-764MT1 exhibited much more variations than TSHR368-764WT and TSHR368-764MT2, emphasizing a more damaging pattern in TSHR368-764MT1. This genetic study might be helpful to explore the mutational impact on drug binding sites of TSHR protein which is important for future drug design and selection for the treatment of congenital hypothyroid children with dysgenesis.

Genomic and evolutionary study from SARS-CoV-2 virus isolates from Bangladesh during the early stage of pandemic strongly correlate with European origin and not with China

The goal of this study was to identify the genomic variants and determine molecular epidemiology of SARS-CoV-2 virus during the early pandemic stage in Bangladesh. Viral RNA was extracted, converted to cDNA, and amplified using Ion AmpliSeq™ SARS-CoV-2 Research Panel. 413 unique mutants from 151 viral isolates were identified. 80% of cases belongs to 8 mutants: 241C toT, 1163A toT, 3037C toT, 14408C toT, 23403A toG, 28881G toA, 28,882 G toA, and 28883G toC. Observed dominance of GR clade variants that have strong presence in Europe, suggesting European channel a possible entry route. Among 37 genomic mutants significantly associated with clinical symptoms, 3916CtoT (associated with sore-throat), 14408C to T (associated with cough-protection), 28881G to A, 28882G to A, and 28883G to C (associated with chest pain) were notable. These findings may inform future research platforms for disease management and epidemiological study.

TTN as a candidate gene for distal arthrogryposis type 10 pathogenesis

Background

Arthrogryposis is a medical term used to describe congenital contractures which often affect multiple limbs. Distal arthrogryposis (DA) is one of the major categories of arthrogryposis that primarily affects the distal parts of the body, i.e., the hands and the legs. Although ten different types and several subtypes of DAs have been described, the genes associated with each of these DAs are yet to be characterized. Distal arthrogryposis type 10 (DA10) is a rare genetic disease, which is distinguished from the other arthrogryposis types by plantar flexion contractures resulting in toe-walking during infancy as well as variability in contractures of the hip, hamstring, elbow, wrist and finger joints with no ocular or neurological abnormalities. Symptoms of DA10 indicate impairment specifically in the musculoskeletal system. DA10 is still poorly studied.

Aim

The objective of this study was to identify the candidate gene for DA10 by scrutinizing the protein-protein interaction (PPI) networks using in silico tools.

Results

Among the genes that reside within the previously reported genomic coordinates (human chromosome assembly 38 or GRCh38 coordinates 2:179,700,000–188,500,000) of the causative agent of DA10, only TTN (the gene that codes for the protein Titin or TTN) follows the expression pattern similar to the other known DA associated genes and its expression is predominant in the skeletal and heart muscles. Titin also participates in biological pathways and processes relevant to arthrogryposes. TTN-related known skeletal muscle disorders follow the autosomal-dominant pattern of inheritance, which is a common characteristic of distal arthrogryposes as well.

Conclusion

Based on the findings of the analyses and their correlation with previous reports, TTN appears to be the candidate gene for DA10. Our attempt to discover a potential candidate gene may eventually lead to an understanding of disease mechanism and possible treatment strategies, as well as demonstrate the suitability of PPI in the search for candidate genes.

Supplementary Information

The online version contains supplementary material available at 10.1186/s43141-022-00405-5.

Aspartame, acesulfame K and sucralose- influence on the metabolism of Escherichia coli

Gut microbes play a crucial role in the maintenance of human health. Components in the diet of the host affect their metabolism and diversity. Here, we investigated the influences of three commonly used non-caloric artificial sweeteners-aspartame, acesulfame K and sucralose-on the growth and metabolism of an omnipresent gut microbe Escherichia coli K-12. Methods: Growth of E. coli in the presence of aspartame, acesulfame K and sucralose in media was assessed and the influences of these artificial sweeteners on metabolism were investigated by relative expression analysis of genes encoding the rate limiting steps of important metabolic pathways as well as their global metabolomic profiles. Results: As a whole, E. coli growth was inhibited by aspartame and induced by acesulfame potassium, while the effect of sucralose on growth was less prominent. Although the expressions of multiple key enzymes that regulate important metabolic pathways were significantly altered by all three sweeteners, acesulfame K caused the most notable changes in this regard. In multivariate analysis with the metabolite profiles, the sucralose-treated cells clustered the closest to the untreated cells, while the acesulfame potassium treated cells were the most distant. These sweeteners affect multiple metabolic pathways in E. coli, which include propanoate, phosphonate, phosphinate and fatty acid metabolism, pentose phosphate pathway, and biosynthesis of several amino acids including lysine and the aromatic amino acids. Similar to the gene expression pattern, acesulfame potassium treated E. coli showed the largest deviation in their metabolite profiles compared to the untreated cells.

Non-Caloric Artificial Sweeteners Modulate the Expression of Key Metabolic Genes in the Omnipresent Gut Microbe Escherichia coli

The human gut is inhabited by several hundred different bacterial species. These bacteria are closely associated with our health and well-being. The composition of these diverse commensals is influenced by our dietary intakes. Non-caloric artificial sweeteners (NAS) have gained global popularity, particularly among diabetic patients, due to their perceived health benefits, such as reduction of body weight and maintenance of blood glucose level compared to caloric sugars. Recent studies have reported that these artificial sweeteners can alter the composition of gut microbiota and, thus, affect our normal physiological state. Here, we investigated the effect of aspartame and acesulfame potassium (ace-K), two popular NAS, in a commercial formulation on the growth and metabolic pathways of omnipresent gut commensal Escherichia coliby analyzing the relative expression levels of the key genes, which control over twenty important metabolic pathways. Treatment with NAS preparation (aspartame and ace-K) modulates the growth of E. colias well as inducing the expression of important metabolic genes associated with glucose (pfkA, sucA, aceE, pfkB, lpdA), nucleotide (tmk, adk, tdk, thyA), and fatty acid (fabI) metabolisms, among others. Several of the affected geneswere previously reported to be important for the colonization of the microbes in the gut. These findings may shed light on the mechanism of alteration of gut microbes and their metabolism by NAS.

A Novel Pathogenic β-Thalassemia Mutation Identified at Codon 8 (HBB: c.27delG) in a Bangladeshi Family Acquired De Novo

In Bangladesh, the practice of β-thalassemia (β-thal) carrier screening and prenatal diagnosis (PND) by β-globin gene sequencing has been initiated to prevent the birth of affected children. The study aimed to describe a novel de novo mutation of the β-globin gene and its clinical implication. Out of 100 Bangladeshi β-thal carrier families, one patient with hematological and clinical features associated with β-thal and her parents were included. Molecular characterizations of β-globin gene mutations were performed by direct sequencing. A novel nucleotide deletion mutation at codon 8 in the first exon of the β-globin gene (HBB: c.27delG) was found in a 1-year-old child of the studied family in a heterozygous state along with common Hb E (HBB: c.79G>A). The mutation caused a frameshift to a new stop codon at codon 18 resulting in a β⁰-thal phenotype. The proband exhibited a β-thal intermedia (β-TI)-like genotype, however, showed β-thal major (β-TM)-like complications and was transfusion-dependent. Her mother had a profile consistent with the Hb E trait, while the father had normal hematological indices. Mutation analyses revealed the mother to be heterozygous for Hb E, while the father had a normal genotype. The novel mutation was assumed to be inherited de novo by the paternity test. The study documented a novel pathogenic mutation in the β-globin gene in a Bangladeshi family by β-globin gene sequencing.

Phylogenetic analysis and forensic evaluation among Rakhine, Marma, Hajong, and Manipuri tribes from four culturally defined regions of Bangladesh using 17 Y-chromosomal STRs

We have analyzed haplotypes for 17 Y chromosomal STR loci in Bangladeshi mainstream Bengali population and four largest ethnic groups inhabiting the North-Eastern and Southern region of Bangladesh using AmpFlSTR® Yfiler® PCR amplification systems. A total of 667 haplotypes from Bangladeshi Bangali, 157 from Rakhine, 144 from Marma, 112 from Hajong, and 136 from Manipuri individuals were observed with corresponding discrimination capacity (DC) of 0.973 for Bengali, 0.723 for Rakhine, 0.743 for Marma, 0.794 for Hajong, and 0.720 for Manipuri groups, respectively. In order to investigate genetic relationship and the pattern of paternal contributions of the studied population, a comparison of the studied data with the published data from Y-STR haplotype reference database (YHRD) was conducted based on analysis of molecular variance (AMOVA). Construction of neighbour-joining tree revealed that the Rakhine population lies closer to a clade consisting, Korean and Japanese population. The Hajong population showed close affinity with Riang (Tripura, India) tribe followed by Marma population. On the other hand, Manipuri group is closely related to Thai population followed by Tamil and mainstream Bengali population.

High resolution melting curve analysis enables rapid and reliable detection of G6PD variants in heterozygous females

Background

Like glucose-6-phosphate dehydrogenase (G6PD) deficient hemizygous males and homozygous females, heterozygous females could also manifest hemolytic crisis, neonatal hyperbilirubinemia or kernicterus upon exposure to oxidative stress induced by certain foods such as fava beans, drugs or infections. Although hemizygous males and homozygous females are easily detected by conventional G6PD enzyme assay method, the heterozygous state could be missed by the conventional methods as the mosaic population of both normal and deficient RBCs circulates in the blood. Thus the present study aimed to apply high resolution melting (HRM) curve analysis approach to see whether HRM could be used as a supplemental approach to increase the chance of detection of G6PD heterozygosity.

Results

Sixty-three clinically suspected females were evaluated for G6PD status using both enzyme assay and HRM analysis. Four out of sixty-three participants came out as G6PD deficient by the enzyme assay method, whereas HRM approach could identify nine participants with G6PD variants, one homozygous and eight heterozygous. Although only three out of eight heterozygous samples had G6PD enzyme deficiency, the HRM-based heterozygous G6PD variants detection for the rest of the samples with normal G6PD enzyme activities could have significance because their newborns might fall victim to serious consequences under certain oxidative stress.

Conclusions

In addition to the G6PD enzyme assay, HRM curve analysis could be useful as a supplemental approach for detection of G6PD heterozygosity.

Impaired acylcarnitine profile in transfusion-dependent beta-thalassemia major patients in Bangladesh

Patients with beta-thalassemia major (BTM) suffer from fatigue, poor physical fitness, muscle weakness, lethargy, and cardiac complications which are related to an energy crisis. Carnitine and acylcarnitine derivatives play important roles in fatty acid oxidation, and deregulation of carnitine and acylcarnitine metabolism may lead to an energy crisis. The present study aimed to investigate carnitine and acylcarnitine metabolites to gain an insight into the pathophysiology of BTM. Dried blood spots of 45 patients with BTM and 96 age-matched healthy controls were analyzed for free carnitine and 24 acylcarnitines by using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Although medium chain acylcarnitine levels were similar in the patients with BTM and healthy controls, free carnitine, short chain acylcarnitines, long chain acylcarnitines, and total acylcarnitine levels were significantly lower in patients with BTM than in the healthy controls (P < 0.05). Moreover, an impaired fatty acid oxidation rate was observed in the patients with BTM, as manifested by decreased fatty acid oxidation indicator ratios, namely C2/C0 and (C2 + C3)/C0. Furthermore, an increase in the C0/(C16 + C18) ratio indicated reduced carnitine palmitoyltransferase-1 (CPT-1) activity in the patients with BTM compared with that in the healthy controls. Thus, a low level of free carnitine and acylcarnitines together with impaired CPT-1 activity contribute to energy crisis-related complications in the patients with BTM.

High resolution melting curve analysis targeting the HBB gene mutational hot-spot offers a reliable screening approach for all common as well as most of the rare beta-globin gene mutations in Bangladesh

BACKGROUND

Bangladesh lies in the global thalassemia belt, which has a defined mutational hot-spot in the beta-globin gene. The high carrier frequencies of beta-thalassemia trait and hemoglobin E-trait in Bangladesh necessitate a reliable DNA-based carrier screening approach that could supplement the use of hematological and electrophoretic indices to overcome the barriers of carrier screening. With this view in mind, the study aimed to establish a high resolution melting (HRM) curve-based rapid and reliable mutation screening method targeting the mutational hot-spot of South Asian and Southeast Asian countries that encompasses exon-1 (c.1 - c.92), intron-1 (c.92 + 1 - c.92 + 130) and a portion of exon-2 (c.93 - c.217) of the HBB gene which harbors more than 95% of mutant alleles responsible for beta-thalassemia in Bangladesh.

RESULTS

Our HRM approach could successfully differentiate ten beta-globin gene mutations, namely c.79G > A, c.92 + 5G > C, c.126_129delCTTT, c.27_28insG, c.46delT, c.47G > A, c.92G > C, c.92 + 130G > C, c.126delC and c.135delC in heterozygous states from the wild type alleles, implying the significance of the approach for carrier screening as the first three of these mutations account for ~85% of total mutant alleles in Bangladesh. Moreover, different combinations of compound heterozygous mutations were found to generate melt curves that were distinct from the wild type alleles and from one another. Based on the findings, sixteen reference samples were run in parallel to 41 unknown specimens to perform direct genotyping of the beta-thalassemia specimens using HRM. The HRM-based genotyping of the unknown specimens showed 100% consistency with the sequencing result.

CONCLUSIONS

Targeting the mutational hot-spot, the HRM approach could be successfully applied for screening of beta-thalassemia carriers in Bangladesh as well as in other countries of South Asia and Southeast Asia. The approach could be a useful supplement of hematological and electrophortic indices in order to avoid false positive and false negative results.

Genetic polymorphism studies on 22 autosomal STR loci of the PowerPlex Fusion System in Bangladeshi population

Genetic polymorphism of 22 autosomal STR loci included in PowerPlex® Fusion System (D3S1358, D1S1656, D2S441, D10S1248, D13S317, Penta E, D16S539, D18S51, D2S1338, CSF1PO, Penta D, TH01, vWA, D21S11, D7S820, D5S818, TPOX, D8S1179, D12S391, D19S433, FGA and D22S1045) was studied in 188 unrelated Bangladeshi Bengali individuals. Allele frequencies and forensic efficiency parameters such as, the power of discrimination (PD), observed and expected heterozygosity (Ho & He), polymorphism information content (PIC), probability of match (PM), power of exclusion (PE) and typical paternity index was calculated for the loci. The combined PM and PE for all 22 STR loci were calculated to be 5.29×10^-27 and 0.99999999945 respectively. The dataset indicated the usefulness of these loci in personal identification, parentage testing and complex kinship analysis in Bangladeshi population. A neighbor-joining tree was constructed based on pair-wise Nei's genetic distance by comparing allele frequency data for the 22 loci with six other populations. The analysis showed that Bangladeshi population lies closer to a clade consisting Japan, the Philippines and East Timot populations.

An efficient DNA extraction method from bone and tooth samples by complete demineralization followed by the use of silica-based columns

A highly efficient strategy for recovery of genomic DNA from bone and tooth samples is presented by complete demineralization of the bone pieces or intact tooth with high concentration of EDTA followed by spin column treatment without the need of mechanical grinding or cryogenic method for pulverizing the samples. The DNA yield was between 8 and 12 ng/?l from approximately 1 ?2 g of the starting material. Completed DNA profiles were obtained from of all the bones (52) and tooth (270) samples received from the unidentified victims from a recent building collapse, the Rana Plaza disaster in Dhaka, Bangladesh. DOI: http://dx.doi.org/10.3329/dujbs.v23i2.20089 Dhaka Univ. J. Biol. Sci. 23(2): 101-107, 2014

Allele Frequencies of 10 Autosomal STR Loci from Chakma and Tripura Tribal Populations in Bangladesh

Allele frequencies of ten autosomal STR loci, D3S1358, vWA, D16S539, D2S1338, D8S1179, D21S11, D18S51, D19S433, TH01, and FGA were investigated in Chakma and Tripura tribal populations of Bangladesh. In both the populations, all loci were in Hardy-Weinberg equilibrium except for FGA locus in Chakma and D21S11 in Tripura. All the loci were highly polymorphic in Chakma population with an observed heterozygosity (Ho) of >0.7 and moderately polymorphic in Tripura population (Ho > 0.6). However, both the population showed least polymorphism at TH01 locus (Ho < 0.6). A comparison between Chakma and Tripura population data revealed statistically significant differences in allele frequency distribution for most of the loci. A similar comparison with the mainstream Bengali population using previously published data from this lab also showed significant difference in allele frequency with these two tribal populations.

Haplotype diversity of 17 Y-chromosomal STR loci in the Bangladeshi population

Haplotype and allele frequencies of 17 Y-chromosomal STR loci were determined in 216 unrelated Bangladeshi males. AmpFlSTR Y-filer PCR Amplification kit (Applied Biosystems) was used to type the following Y-STR markers: DYS19, DYS389I, DYS389II, DYS390, DYS391, DYS392, DYS393, DYS385a/b, DYS438, DYS439, DYS437, DYS448, DYS458, DYS456, DYS635, and Y-GATA-H4. A total of 211 haplotypes for the 17 Y-STR markers were detected and, of these, 206 haplotypes were unique. The haplotype diversity was 0.9998, indicating a high potential for differentiating between male individuals in this population. Comparison analysis via Analysis of Molecular Variance (AMOVA) and construction of Neighbor Joining Tree revealed a close association of Bangladeshi population with Indian Gaddi and Southern Indian populations.

Genetic data on 10 autosomal STR loci in the Bangladeshi population

Allele frequencies of 10 autosomal short tandem repeat (STR) loci, D3S1358, vWA, D16S539, D2S1338, D8S1179, D21S11, D18S51, D19S433, TH01 and FGA were determined in 211 unrelated Bangladeshi individual using AmpFLSTR SGM Plus PCR Amplification Kit. Statistical parameters of forensic importance, the power of discrimination (PD), observed and expected heterozygosity values (H), polymorphism information content (PIC), probability of match (PM), power of exclusion (PE) and typical paternity index (TPI) were calculated for the loci. These parameters indicated the usefulness of the loci in paternity testing and personal identification in the Bangladeshi population.

Effect of Tamarindus indica fruits on blood pressure and lipid-profile in human model: an in vivo approach

Fruits of Tamarindus indica were evaluated for their effects on lipid profile, systolic and diastolic blood pressure and body weight in human subjects. Dried and pulverized pulp of T. indica fruits, at a dose of 15 mg/kg body weight, was found to reduce total cholesterol level (p = 0.031) and LDL-cholesterol level (p = 0.004) to a significant extent. Though the fruits exerted no conspicuous effect on body weight and systolic blood pressure, it significantly reduced the diastolic pressure as confirmed by independent sample t-test at 5% significance level.

Association between angiotensin I-converting enzyme gene polymorphism and hypertension in selected individuals of the Bangladeshi population

The genetic factors that contribute to the development of coronary artery disease (CAD) are poorly understood. It is likely that multiple genes that act independently or synergistically contribute to the development of CAD and the outcome. Recently, an insertion/deletion (I/D) polymorphism of the human angiotensin I-converting enzyme (ACE) gene, a major component of the reninangiotensin system (RAS), was identified. The association of the ACE gene D allele with essential hypertension and CAD has been reported in the African-American, Chinese, and Japanese populations. However, other studies have failed to detect such an association. It has been suggested that these inconsistencies may be due to the difference in backgrounds of the population characteristics. In the present study, we investigated the I/D polymorphism of the ACE gene in 103 subjects of both sexes, consisting of 59 normal controls and 44 patients with hypertension. The allele and genotype frequency were significantly different between the hypertensive and control groups (p < 0.01). Among the three ACE I/D variants, the DD genotype was associated with the highest value of the mean systolic blood pressure [SBP] and mean diastolic blood pressure [DBP] (p = < 0.05) in men, but not in women. In the overall population, the mean SBP and DBP was highest in DD subjects, intermediate in I/D subjects, and the least in II subjects

Short-term administration of conjugated linoleic acid reduces liver triglyceride concentration and phosphatidate phosphohydrolase activity in OLETF rats

The present study explored the short-term effects of dietary conjugated-linoleic acid (CLA) on liver lipid metabolism in starved/refed Otsuka Long Evans Tokushima Fatty (OLETF) rats. Male OLETF rats (12 weeks old) were starved for 24 hours, then refed for 48 hours with either a CLA diet [7.5% CLA and 7.5% Safflower oil (SAF)] or a SAF control diet (15% SAF). The results demonstrated a 30% reduction of hepatic triglyceride (TG) concentration in the CLA group when compared to the control group. Liver cholesterol concentration was also 26% lower in the CLA fed rats. The activity of mitochondrial carnitine palmitoyltransferase, the rate-limiting enzyme of fatty acid oxidation, was moderately elevated by 1.2-fold in the livers of the CLA group when compared to the control. In contrast, phosphatidate phosphohydrolase, the rate-limiting enzyme for TG synthesis, was found to be 20% lower in the livers of the CLA-fed rats. Therefore, dietary CLA evidently lowers liver lipid concentrations through a reduced TG synthesis and enhanced fatty acid oxidation in starved/refed OLETF rats.

Carrier-mediated hepatic uptake of peptidic endothelin antagonists in rats

The endothelin antagonist BQ-123, an anionic cyclopentapeptide, is taken up by rat hepatocytes through active transport systems. Here, we have examined the hepatocellular uptake mechanism for several BQ-123 derivatives with anionic charges using isolated rat hepatocytes. BQ-485, a linear peptide, BQ-518, a cyclic peptide, and compound A, a cyclic peptide with a cationic moiety, were taken up by hepatocytes in a concentration-dependent manner. The uptake of BQ-485 was most efficient, whereas compound A showed comparable uptake with BQ-123. The uptake of these peptides was Na(+)- and energy-dependent, suggesting that active transport mechanisms are involved in their uptake into hepatocytes. BQ-485, BQ-518, and compound A can almost completely inhibit both the Na(+)-dependent and -independent uptake of [(3)H]BQ-123, with inhibition constants (K(i)) that are comparable to the Michaelis-Menten constants (K(m)) for their Na(+)-dependent and -independent uptake, respectively. Inhibition by BQ-485 was competitive, and the uptake of BQ-485 can be inhibited by BQ-123, with K(i) values that are comparable with the K(m) values for BQ-123 uptake. The uptake of BQ-123 by COS-7 cells transfected with either Na(+)-dependent taurocholate-cotransporting polypeptide (Ntcp) or Na(+)-independent basolateral organic anion-transporting polypeptide (oatp1) was minimal. Thus, these three peptides share the transporters that also recognize BQ-123 but appear to differ from Ntcp and oatp1.

Primary active transport of peptidic endothelin antagonists by rat hepatic canalicular membrane

The biliary excretion mechanism of three derivatives of BQ-123, an anionic cyclopentapeptide, was examined using isolated canalicular membrane vesicles (CMVs) from Sprague-Dawley rats. The uptake by CMV of BQ-485, a linear peptide, BQ-518, a cyclic peptide, and compound A, a cyclic peptide with a cationic moiety, was stimulated by ATP. An "overshoot" phenomenon and saturation were observed for the ATP-dependent uptake of these three peptides. The Michaelis-Menten constants (Km) for the uptake of BQ-485 and BQ-518 were comparable to the inhibition constants (Ki) for their inhibitory effects on ATP-dependent [3H]BQ-123 uptake. The uptake of BQ-485 showed the highest value and was inhibited by BQ-123 with a Ki that was comparable to the Km for BQ-123 uptake. The ATP-dependent uptake of BQ-123, BQ-485, and BQ-518 was much lower in CMVs from Eisai hyperbilirubinemic rats, a strain having a hereditary defect of the canalicular multispecific organic anion transporter (cMOAT). These results suggest that both BQ-485 and BQ-518 principally share the cMOAT transporter with BQ-123. Compound A almost completely inhibited BQ-123 uptake, although its ATP-dependent uptake was much lower than that of the other three peptides. The ATP-dependent uptake of compound A was not very different in Sprague-Dawley rats and Eisai hyperbilirubinemic rats and was not inhibited by S-(2, 4-dinitrophenyl)-glutathione, a typical substrate for cMOAT. Thus, although compound A inhibits cMOAT-mediated transport, its own transport by cMOAT is minimal and mediated by another transporter. This low degree of primary active transport by cMOAT may be the principal reason for its relatively longer residence in the circulation.

Hepatobiliary transport governs overall elimination of peptidic endothelin antagonists in rats

The overall disposition and hepatobiliary transport of BQ-123, an anionic cyclopentapeptide, and three analogs were examined in rats in vivo. Total body clearance (CLtotal) and biliary excretion clearance (CLbile, p) exhibited 4- to 8-fold differences between the compounds, with those for BQ-485 and compound A having the highest and lowest values, respectively. The CLbile, p values of BQ-485, BQ-123, and BQ-518 were almost equal to the CLtotal, suggesting that hepatobiliary transport is the major elimination pathway for these compounds. Hepatic uptake clearance (CLuptake, vivo) and biliary excretion clearance (CLbile, h/fT), which was defined for the hepatic unbound concentration, were separately determined to examine the hepatic uptake and excretion processes, respectively. Both the CLuptake, vivo and CLbile, h/fT of BQ-485 were higher than those of BQ-123, whereas the corresponding values for BQ-518 were similar to those for BQ-123. The CLuptake, vivo and CLbile, h/fT of compound A were, respectively, approximately two thirds and one half those of BQ-123, suggesting that the lower CLbile, p value is due to the low efficiency of both the uptake and excretion processes. The CLuptake, vivo of these four peptides in vivo was similar to the extrapolated values based on the carrier-mediated transport activity previously assessed in vitro in isolated rat hepatocytes. The primary active transport previously assessed in an in vitro study in canalicular membrane vesicles was also highest for BQ-485 and lowest for compound A, similar to CLbile, h/fT in vivo. Thus, the transporters on both the sinusoidal and canalicular membranes determine the efficiency of the peptide overall elimination from the circulation.