Dysfunction of Thyroid Hormones Following Acute Coronary Syndrome in a Tertiary Care Hospital in Dhaka City

In cardiovascular homeostasis thyroid hormone plays an important role. We planned to study the changes in thyroid hormone profile in acute coronary syndrome patients admitted in the coronary care unit and compare them between two groups: unstable angina/non-ST elevated Myocardial infarction (UA/NSTEMI) and ST elevated Myocardial infarction (STEMI). This study was a hospital based descriptive cross sectional study which was conducted from 01 March 2018 to 01 February 2019 in Coronary Care Unit of Bangladesh Medical College Hospital and laboratory tests were done in Microbiology Department of Bangladesh Medical College, Dhaka, Bangladesh. Eighty three cases of acute coronary syndromes were taken for the study. Troponin-I was measured as cardiac marker, Electrocardiogram, Complete blood count, blood glucose level, Blood urea, serum creatinine, serum electrolytes, Fasting lipid profile, Thyroid profile, Echocardiography 2D were done. Most of the respondents were distributed in age group 46-60 years where 34(64.15%) male and 19(35.85%) female. Out of 83 Acute Coronary Syndrome (ACS) patients, 27(32.53%) hypertensive, 22(26.50%) diabetic and 16(19.27%) were Chronic kidney disease (CKD). Abnormal lipid profile was present in 30(43.47%) patients. Among total 52 male and 31 female 9(17.30%) male and 6(19.35%) female had abnormal thyroid function. We further elaborated abnormal thyroid function tests in STEMI group and UA/Non STEMI group of ACS patients. We found 10 patients in STEMI group and 5 patients in UA/Non STEMI group with abnormal thyroid function 29.41% and 10.20% respectively which was not statistically significant (p=0.025). This study depicts abnormality in thyroid hormone profile in 18.07% patients of ACS. Abnormal thyroid function increases risk of coronary artery disease. TSH level of ACS patients on hospital admission could be helpful to evaluate further prognosis of the disease.

Low-dose daily folic acid (400 μg) supplementation does not affect regulation of folate transporters found present throughout the terminal ileum and colon of humans: a randomized clinical trial

BACKGROUND

Folic acid supplementation during the periconceptional period reduces the risk of neural tube defects in infants, but concern over chronic folic acid exposure remains. An improved understanding of folate absorption may clarify potential risks. Folate transporters have been characterized in the small intestine, but less so in the colon of healthy, free-living humans. The impact of folic acid fortification or supplementation on regulation of these transporters along the intestinal tract is unknown.

OBJECTIVE

The objective was to characterize expression of folate transporters/receptor (FT/R) and folate hydrolase, glutamate carboxypeptidase II (GCPII), from the terminal ileum and throughout the colon of adults and assess the impact of supplemental folic acid.

METHODS

In this 16-wk open-labeled randomized clinical trial, adults consumed a low folic acid-containing diet, a folate-free multivitamin, and either a 400 μg folic acid supplement or no folic acid supplement. Dietary intakes and blood were assessed at baseline, 8 wk, and 16 wk (time of colonoscopy). Messenger RNA (mRNA) expression and protein expression of FT/R and GCPII were assessed in the terminal ileum, cecum, and ascending and descending colon.

RESULTS

Among 24 randomly assigned subjects, no differences in dietary folate intake or blood folate were observed at baseline. Mean ± SD red blood cell folate at 16 wk was 1765 ± 426 and 911 ± 242 nmol/L in the 400 and 0 μg folic acid group, respectively (P < 0.0001). Reduced folate carrier, proton-coupled folate transporter, and folate-receptor alpha expression were detected in the terminal ileum and colon, as were efflux transporters of breast cancer resistance protein and multidrug resistance protein-3. Other than a higher mRNA expression of FR-alpha and GCPII in the 400 μg supplement group in the ascending colon, no treatment differences were observed (P < 0.02).

CONCLUSIONS

Folate transporters are present throughout the terminal ileum and colon; there is little evidence that a low dose of folic acid supplementation affects colonic absorption. This trial was registered at clinicaltrials.gov as NCT03421483.

PPAR agonists for the treatment of neuroinflammatory diseases

Peroxisome proliferator-activated receptors [PPARs; PPARα, PPARβ/δ (also known as PPARδ), and PPARγ] widely recognized for their important role in glucose/lipid homeostasis, have recently received significant attention due to their additional anti-inflammatory and neuroprotective effects. Several newly developed PPAR agonists have shown high selectivity for specific PPAR isoforms in vitro and in vivo, offering the potential to achieve desired therapeutic outcomes while reducing the risk of adverse effects. In this review, we discuss the latest preclinical and clinical studies of the activation of PPARs by synthetic, natural, and isoform-specific (full, partial, and dual) agonists for the treatment of neuroinflammatory diseases, including HIV-associated neurocognitive disorders (HAND), Alzheimer's disease (AD), Parkinson's disease (PD), multiple sclerosis (MS), and cerebral ischemia.

Psychological Assessment of Health-Care Workers Working during COVID-19 Pandemic Condition in Bangladesh

The study was aimed to assess the psychological aspects and relevant factors of the health-care workers (HCWs) working in COVID 19 pandemic condition in Bangladesh. This online cross-sectional survey was conducted from different tertiary, secondary and primary hospitals in Bangladesh. Eligible 638 HCWs who were directly involved in the caring of confirmed or suspected COVID-19 patients were recruited in this study. The mental health was assessed by the Patient Health Questionnare-9 (PHQ-9), Generalized Anxiety Disorder-7 (GAD-7) and Athens Insomnia Scale (AIS). High frequency of depression 536(84.0%), anxiety 386(60.5%) and insomnia 302(47.3%) was found among the HCWs, which were significantly higher in physicians (p<0.001) than nurses. Moderate to severe depression was significantly higher in female, whereas minimal to mild depression was significant in male HCWs (p=0.014). Symptoms of depression (p<0.001), anxiety (p<0.001) and insomnia (p=0.004) were significantly higher among the HCWs of primary and secondary compared to the tertiary level. The HCWs developed psychological trauma due to family health (45.3%) and contagious disease property (66.6%). After adjusting confounders, multivariable logistic regression analysis showed that physicians and HCWs of secondary hospital had significant symptoms of severe depression (OR=2.95, 95% CI=0.50-17.24; p<0.001), anxiety (OR=2.64, 95% CI=0.80-8.72; p<0.001) and insomnia (OR=2.67, 95% CI=1.23-5.84; p=0.018); whereas female HCWs had more risk of developing symptoms of severe insomnia (OR= 1.84; 95% CI=1.23-2.75; p=0.003). High rate of depression, anxiety and insomnia was found among HCWs working in the COVID-19 pandemic condition in this survey.

Interaction between dolutegravir and folate transporters and receptor in human and rodent placenta

Background

Due to the critical role of folates in neurodevelopment, it is important to understand potential interactions between anti-HIV drugs used during pregnancy, and folate delivery pathways in the placenta. This study investigates the effect of dolutegravir (DTG) exposure on the functional expression of the reduced folate carrier (RFC), proton-coupled folate transporter (PCFT), and folate receptor-α (FRα) in the placenta.

Methods

Human placental cell lines, human placental explants, and a pregnant mouse model treated with clinically relevant concentrations of DTG were used. Gene and protein expression were assessed by qPCR, immunoblot and immunohistochemical assays. Folate transport function was measured by applying radioisotope-based transport assays.

Findings

In placental cells, clinically relevant DTG exposure for 3h or 6h was associated with a modest but significant reduction in the expression of RFC and PCFT both at the mRNA and protein levels, as well as decreased uptake of RFC and PCFT substrates [³H]-methotrexate and [³H]-folic acid, respectively. In pregnant mice, DTG administration was associated with an increase in both placental RFC and PCFT mRNA expression, accompanied by a decrease in placental FRα mRNA under folate-deficient dietary conditions.

Interpretation

These findings demonstrate a potential interaction between DTG and folate transport pathways in the placenta, particularly in vivo, under folate deficient conditions, potentially impacting folate delivery to the foetus in the context of DTG-based ART during pregnancy.

Funding

Funded by Ontario HIV Treatment Network, grant #506657; and Eunice Kennedy Shriver National Institute of Child Health & Human Development of the National Institutes of Health, award #R01HD104553.

Potential pharmacological approaches for the treatment of HIV-1 associated neurocognitive disorders

HIV associated neurocognitive disorders (HAND) are the spectrum of cognitive impairments present in patients infected with human immunodeficiency virus type 1 (HIV-1). The number of patients affected with HAND ranges from 30 to 50% of HIV infected individuals and although the development of combinational antiretroviral therapy (cART) has improved longevity, HAND continues to pose a significant clinical problem as the current standard of care does not alleviate or prevent HAND symptoms. At present, the pathological mechanisms contributing to HAND remain unclear, but evidence suggests that it stems from neuronal injury due to chronic release of neurotoxins, chemokines, viral proteins, and proinflammatory cytokines secreted by HIV-1 activated microglia, macrophages and astrocytes in the central nervous system (CNS). Furthermore, the blood-brain barrier (BBB) not only serves as a route for HIV-1 entry into the brain but also prevents cART therapy from reaching HIV-1 brain reservoirs, and therefore could play an important role in HAND. The goal of this review is to discuss the current data on the epidemiology, pathology and research models of HAND as well as address the potential pharmacological treatment approaches that are being investigated.

Nuclear respiratory factor 1 (NRF-1) upregulates the expression and function of reduced folate carrier (RFC) at the blood-brain barrier

Folates are important for neurodevelopment and cognitive function. Folate transport across biological membranes is mediated by three major pathways: folate receptor alpha (FRα), proton-coupled folate transporter (PCFT), and reduced folate carrier (RFC). Brain folate transport primarily occurs at the choroid plexus through FRα and PCFT; inactivation of these transport systems results in suboptimal folate levels in the cerebrospinal fluid (CSF) causing childhood neurological disorders. Our group has reported that upregulation of RFC at the blood-brain barrier (BBB) through interactions with specific transcription factors, that is, vitamin D receptor (VDR) could increase brain folate delivery. This study investigates the role of nuclear respiratory factor 1 (NRF-1) in the regulation of RFC at the BBB. Activation of NRF-1/PGC-1α signaling through treatment with its specific ligand, pyrroloquinoline quinone (PQQ), significantly induced RFC expression and transport activity in hCMEC/D3 cells. In contrast, transfection with NRF-1 or PGC-1α targeting siRNA downregulated RFC functional expression in the same cell system. Applying chromatin immunoprecipitation (ChIP) assay, we further demonstrated that PQQ treatment increased NRF-1 binding to putative NRF-1 binding sites within the SLC19A1 promoter, which encodes for RFC. Additionally, in vivo treatment of wild type mice with PQQ-induced RFC expression in isolated mouse brain capillaries. Together, these findings demonstrate that NRF-1/PGC-1α activation by PQQ upregulates RFC functional expression at the BBB and could potentially enhance brain folate uptake.

Regulation of Reduced Folate Carrier (RFC) by Vitamin D Receptor at the Blood-Brain Barrier

Folates are essential for brain development and function. Folate transport in mammalian tissues is mediated by three major folate transport systems, i.e., reduced folate carrier (RFC), proton-coupled folate transporter (PCFT), and folate receptor alpha (FRα), known to be regulated by ligand-activated nuclear receptors, such as vitamin D receptor (VDR). Folate uptake at the choroid plexus, which requires the actions of both FRα and PCFT, is critical to cerebral folate delivery. Inactivating FRα or PCFT mutations cause severe cerebral folate deficiency resulting in early childhood neurodegeneration. The objective of this study was to investigate the role of RFC in folate uptake at the level of the blood-brain barrier (BBB) and its potential regulation by VDR. We detected robust expression of RFC in different in vitro BBB model systems, particularly in immortalized cultures of human cerebral microvascular endothelial cells (hCMEC/D3) and isolated mouse brain capillaries. [³H]-methotrexate uptake by hCMEC/D3 cells at pH 7.4 was inhibited by PT523 and pemetrexed, antifolates with high affinity for RFC. We also showed that activation of VDR through calcitriol (1,25-dihydroxyvitamin D₃) exposure up-regulates RFC mRNA and protein expression as well as function in hCMEC/D3 cells and isolated mouse brain capillaries. We further demonstrated that RFC expression could be down-regulated by VDR-targeting siRNA, further confirming the role of VDR in the direct regulation of this folate transporter. Together, these data suggest that augmenting RFC functional expression could constitute a novel strategy for enhancing brain folate delivery for the treatment of neurometabolic disorders caused by loss of FRα or PCFT function.

Antiretroviral drug transporters and metabolic enzymes in human testicular tissue: potential contribution to HIV-1 sanctuary site

OBJECTIVES

The testes are a potential viral sanctuary site for HIV-1 infection. Our study aims to provide insight into the expression and localization of key drug transporters and metabolic enzymes relevant to ART in this tissue compartment.

METHODS

We characterized gene and protein expression of 12 representative drug transporters and two metabolic enzymes in testicular tissue samples obtained from uninfected (n = 8) and virally suppressed HIV-1-infected subjects on ART (n = 5) and quantified antiretroviral drug concentrations in plasma and testicular tissues using LC/MS/MS from HIV-1-infected subjects.

RESULTS

Our data demonstrate that key ABC drug transporters (permeability glycoprotein, multidrug-resistance protein 1, 2 and 4, and breast cancer resistance protein), solute carrier transporters (organic anion transporting polypeptides 1B1 and 2B1, organic anion transporter 1, concentrative nucleoside transporter 1, equilibrative nucleoside transporter 2) and cytochrome P450 metabolic enzymes (CYP3A4 and CYP2D6) previously shown to interact with many commonly used antiretroviral drugs are expressed at the mRNA and protein level in the testes of both subject groups and localize primarily at the blood-testis barrier, with no significant differences between the two groups. Furthermore, we observed that PIs known to be substrates for ATP-binding cassette membrane transporters, displayed variable testicular tissue penetration, with darunavir concentrations falling below therapeutic values. In contrast, the NRTIs emtricitabine, lamivudine and tenofovir displayed favourable tissue penetration, reaching concentrations comparable to plasma levels. We also demonstrated that nuclear receptors, peroxisome proliferator-activated receptors α and γ exhibited higher gene expression in the testicular tissue compared with pregnane X receptor and constitutive androstane receptor, suggesting a potential regulatory pathway governing drug transporter and metabolic enzyme expression in this tissue compartment.

CONCLUSIONS

Our data suggest the testes are a complex pharmacological compartment that can restrict the distribution of certain antiretroviral drugs and potentially contribute to HIV-1 persistence.

In vivo and ex vivo regulation of breast cancer resistant protein (Bcrp) by peroxisome proliferator-activated receptor alpha (Pparα) at the blood-brain barrier

Breast cancer resistance protein (Bcrp/Abcg2) localized at the blood-brain barrier (BBB) limits permeability into the brain of many xenobiotics, including pharmacological agents. Peroxisome proliferator-activated receptor α (Pparα), a ligand-activated transcription factor, primarily involved in lipid metabolism, has been shown to regulate the functional expression of Bcrp in human cerebral microvascular endothelial cells (hCMEC/D3). The aim of this study was to investigate ex vivo and in vivo, the regulation of Bcrp by Pparα in an intact BBB. Ex vivo quantitative real-time PCR and immunoblot analyses showed significant up-regulation of Abcg2/Bcrp mRNA and protein levels in CD-1 mouse brain capillaries incubated with clofibrate, a Pparα ligand. Fluorescence-based transport assays in CD-1 and C57BL/6 brain capillaries showed that exposure to clofibrate significantly increased Bcrp transport activity. This increase was not observed in capillaries isolated from Pparα knockout mice. In vivo, we found: i) significant Bcrp protein up-regulation in clofibrate-dosed CD-1 and C57BL/6 capillary lysates, but no effect in Pparα knockout capillary lysates, and ii) significantly increased Bcrp transport activity in capillaries isolated from clofibrate-treated mice. These results demonstrate an increase in Bcrp functional expression by Pparα in brain capillaries, and suggest that Pparα is another nuclear receptor that can contribute to the regulation of membrane efflux transporters and drug permeability at the BBB. We propose the involvement of the following pathways in clofibrate-mediated induction of the drug transporter Abcg2/Bcrp mRNA, protein expression and function by the nuclear receptor Pparα, in mouse brain capillary endothelial cells. Upon activation with clofibrate (Pparα, ligand), Pparα complex translocates from the cytoplasm into the nucleus and further recruits coactivators and transcription machinery which induce the transcription of Abcg2 gene and ultimately results in upregulation of Bcrp protein expression and function. These findings have significant implications since Bcrp is known to play an important role at the BBB in preventing the permeability of several xenobiotics and drugs into the brain.

Role of anti-inflammatory compounds in human immunodeficiency virus-1 glycoprotein120-mediated brain inflammation

BACKGROUND

Neuroinflammation is a common immune response associated with brain human immunodeficiency virus-1 (HIV-1) infection. Identifying therapeutic compounds that exhibit better brain permeability and can target signaling pathways involved in inflammation may benefit treatment of HIV-associated neurological complications. The objective of this study was to implement an in vivo model of brain inflammation by intracerebroventricular administration of the HIV-1 viral coat protein gp120 in rats and to examine anti-inflammatory properties of HIV adjuvant therapies such as minocycline, chloroquine and simvastatin.

METHODS

Male Wistar rats were administered a single dose of gp120ADA (500 ng) daily for seven consecutive days, intracerebroventricularly, with or without prior intraperitoneal administration of minocycline, chloroquine or simvastatin. Maraviroc, a CCR5 antagonist, was administered intracerebroventricularly prior to gp120 administration for seven days as control. Real-time qPCR was used to assess gene expression of inflammatory markers in the frontal cortex, hippocampus and striatum. Interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) secretion in cerebrospinal fluid (CSF) was measured applying ELISA. Protein expression of mitogen-activated protein kinases (MAPKs) (extracellular signal-related kinase 1/2 (ERK1/2), c-Jun N-terminal kinases (JNKs) and P38 kinases (P38Ks)) was detected using immunoblot analysis. Student's t-test and ANOVA were applied to determine statistical significance.

RESULTS

In gp120ADA-injected rats, mRNA transcripts of interleukin-1β (IL-1β) and inducible nitric oxide synthase (iNOS) were significantly elevated in the frontal cortex, striatum and hippocampus compared to saline or heat-inactivated gp120-injected controls. In CSF, a significant increase in TNF-α and IL-1β was detected. Maraviroc reduced upregulation of these markers suggesting that the interaction of R5-tropic gp120 to CCR5 chemokine receptor is critical for induction of an inflammatory response. Minocycline, chloroquine or simvastatin attenuated upregulation of IL-1β and iNOS transcripts in different brain regions. In CSF, minocycline suppressed TNF-α and IL-1β secretion, whereas chloroquine attenuated IL-1β secretion. In gp120-injected animals, activation of ERK1/2 and JNKs was observed in the hippocampus and ERK1/2 activation was significantly reduced by the anti-inflammatory agents.

CONCLUSIONS

Our data demonstrate that anti-inflammatory compounds can completely or partially reverse gp120-associated brain inflammation through an interaction with MAPK signaling pathways and suggest their potential role in contributing towards the prevention and treatment of HIV-associated neurological complications.

Expression of membrane drug efflux transporters in the sigmoid colon of HIV-infected and uninfected men

The use of antiretroviral therapy (ART) as pre-exposure prophylaxis (PrEP) has gained global attention as a promising HIV prevention strategy in men who have sex with men. Permeability of these agents in the rectal mucosa may be partially regulated by interactions with drug efflux transporters, P-glycoprotein (P-gp), multidrug resistance-associated proteins (MRPs) and/or breast cancer resistance protein (BCRP). The objective of this work was to investigate the expression of drug efflux transporters in recto-sigmoid colon tissues of HIV-infected and uninfected men, and evaluate the association of ART and/or HIV infection with drug transporter expression. MDR1/P-gp, MRPs (1-4) and BCRP mRNA and protein expression were detected in sigmoid colon biopsies of HIV-uninfected individuals. Biopsies from HIV-infected, ART-naïve participants revealed a significant downregulation of P-gp and MRP2 protein levels compared to HIV-uninfected individuals. Biopsies from HIV-infected ART-treated patients showed 1.9-fold higher P-gp protein expression and 1.5-fold higher MRP2 protein expression compared to the ones obtained from the HIV-infected ART-naïve patients. This is a first report demonstrating that HIV infection or ART could alter expression of drug efflux transporters in gut mucosa which in turn could affect the permeability of PrEP antiretroviral agents across this barrier, a highly vulnerable site of HIV transmission.

Regulation of breast cancer resistant protein by peroxisome proliferator-activated receptor α in human brain microvessel endothelial cells

Breast cancer resistance protein (BCRP/ABCG2), an ATP-binding cassette (ABC) membrane-associated drug efflux transporter, is known to localize at the blood-brain barrier (BBB) and can significantly restrict xenobiotic permeability in the brain. The objective of this study is to investigate the regulation of BCRP functional expression by peroxisome proliferator-activated receptor alpha (PPARα), a ligand-activated transcription factor primarily involved in lipid metabolism, in a cerebral microvascular endothelial cell culture system (hCMEC/D3), representative of human BBB. We demonstrate that PPARα-selective ligands (i.e., clofibrate, GW7647) significantly induce BCRP mRNA and protein expression in a time- and concentration-dependent manner, whereas pharmacological inhibitors (i.e., MK886, GW6471) prevent this induction. Using [(3)H]mitoxantrone, an established BCRP substrate, we observe a significant reduction in its cellular accumulation by monolayer cells treated with clofibrate, suggesting increased BCRP efflux activity. In addition, we show a significant decrease in BCRP protein expression and function when PPARα is down-regulated by small interfering RNA. Applying chromatin immunoprecipitation and quantitative real-time polymerase chain reaction, we observe that clofibrate treatment increases PPARα binding to the peroxisome proliferator response element within the ABCG2 gene promoter. This study provides the first evidence of direct BCRP regulation by PPARα in a human in vitro BBB model and suggests new targeting strategies for either improving drug brain bioavailability or increasing neuroprotection.

Involvement of NHERF1 in apical membrane localization of MRP4 in polarized kidney cells

Multidrug resistance protein 4 (MRP4/ABCC4), a member of the ATP-binding cassette protein superfamily, confers resistance to nucleoside and nucleotide analogs as well as camptothecin derivatives. MRP4 also mediates the efflux of certain cyclic nucleotides, eicosanoids, conjugated steroids, and uric acid. Depending on the cell type, MRP4 may localize to either apical or basolateral membranes in polarized cells. The adaptor protein NHERF1 has previously been implicated in MRP4 internalization in non-polarized cells. We have now found that NHERF1 levels are very low in polarized MDCKI cells which express MRP4 on basolateral membranes relative to polarized LLC-PK1 cells which express MRP4 on apical membranes. Furthermore, ectopic expression of FLAG-tagged NHERF1 in MDCKI cells and in MDCKI cells stably expressing eGFP-tagged MRP4 causes endogenous MRP4 and eGFP-MRP4, respectively, to traffic to the apical membranes. These data establish NHERF1 as a major determinant of MRP4 trafficking to apical membranes of mammalian kidney cells.

Cohesin defects lead to premature sister chromatid separation, kinetochore dysfunction, and spindle-assembly checkpoint activation

Scc1/Mcd1 is a component of the cohesin complex that plays an essential role in sister chromatid cohesion in eukaryote cells. Knockout experiments of this gene have been described in budding yeast, fission yeast, and chicken cells, but no study has been reported on human Scc1 thus far. In this study, we found that an N-terminally truncated human Scc1 shows a dominant-negative effect, and we examined the phenotypes of human cells defective in Scc1 function. Scc1 defects led to failure of sister chromatid cohesion in both interphase and mitotic cells. Interestingly, four chromatids derived from two homologues occupied four distinct territories in the nucleus in chromosome painting experiments. In mitotic Scc1-defective cells, chromatids were disjoined with normal condensation, and the spindle-assembly checkpoint was activated. We also found that, although the disjoined kinetochore (half-kinetochore) in Scc1-defective cells contains CENP-A, -B, -C, and -E normally, it apparently does not establish the kinetochore-microtubule association. These results indicate that Scc1 is essential for the association of kinetochores with microtubules.

Human chromatid cohesin component hRad21 is phosphorylated in M phase and associated with metaphase centromeres

Sister chromatids duplicated in S phase are connected with each other during G(2) and M phase until the onset of anaphase. This chromatid cohesion is essential for correct segregation of genetic material to daughter cells. Recently, understanding of the molecular mechanisms governing chromatid cohesion in yeast has been greatly advanced, whereas these processes in mammalian cells remain unclear. We report here biochemical and cytological analyses of human Rad21, a homologue of the yeast cohesin subunit, Scc1p/Mcd1p. hRad21 is a nuclear phosphorylated protein. Its abundance does not change during the cell cycle, and it becomes hyperyphosphorylated in M phase. Most hRad21 is not associated with chromatin when the nuclear envelope breakdown takes place in prophase. However, a detailed analysis of the spread chromosomes indicated that hRad21 remains associated with prometaphase-like chromosomes along their entire lengths. The mitotic chromatin-bound hRad21 becomes dissociated in a highly regulated manner because hRad21 remains specifically at the centromeres but disappears from the arm regions on metaphase-like chromosomes. Interestingly, hRad21 at the metaphase centromeres appears to be present at the inner pairing domain where the two sister chromatids are supposed to be in intimate contact. These results suggest that hRad21 has a critical role in chromatid cohesion in human mitotic cells.