Biomedical subjects

M Zhong

Publications and source records attributed to M Zhong.

At least 91 records · Page 5Linked to original sources

PubMed1996

Renal calcitriol synthesis and serum phosphorus in response to dietary phosphorus restriction and anabolic agents.

Calcitriol [1,25-(OH)2D3] synthesis by the renal 25-hydroxyvitamin D3-1alpha-hydroxylase (1alpha-hydroxylase) is induced in rats on a low phosphorus diet, but not in the hypophysectomized (HPX) or diabetic rat. However, the normal response is restored by the administration of growth hormone (GH) or insulin-like growth factor-I (IGF-I), or insulin, respectively. To further characterize this in vivo phenomenon, the acute effects of GH, IGF-I, and insulin were studied in the HPX rat. In the HPX rat the low phosphorus diet alone did not significantly alter serum phosphorus or 1alpha-hydroxylase activity, but treatment with GH resulted in a marked decrease in serum phosphorus that was associated with a fivefold induction of enzyme activity. Time course studies showed that by 6 hours after GH administration, hepatic IGF-I mRNA had increased 10-fold while renal IGF-I mRNA had increased by only 52%. Between 6 and 12 hours, serum phosphorus decreased dramatically and 1alpha-hydroxylase activity increased twofold. Treatment of phosphorus-restricted HPX rats with IGF-I resulted in a decrease in serum phosphorus by 2 hours that preceded a fourfold increase in enzyme activity between 6 and 10 hours. Treatment of phosphorus-restricted HPX rats with insulin produced similar results. This is the first demonstration of hypophosphatemia preceding induction of the 1alpha-hydroxylase after administration of IGF-I or insulin to the HPX rat on a low phosphorus diet. Although these growth factors may have a direct effect on the 1alpha-hydroxylase, these data suggest that the influence of GH, IGF-I, and insulin on transcellular phosphorus flux may have an independent effect on enzyme activity. Furthermore, the much greater induction of hepatic compared with renal IGF-I mRNA in response to GH suggests that systemic, rather than the local, IGF-I may be required for induction of the 1alpha-hydroxylase. This effect may be mediated by either the insulin or the IGF-I receptor.

25-Hydroxyvitamin D3 1-alpha-Hydroxylase↗

PubMed1996

Evaluation of a polymerase chain reaction-based assay for diagnosis of Wuchereria bancrofti infection.

To assess the utility of a polymerase chain reaction (PCR)-based method for diagnosis of Wuchereria bancrofti infection, blood, plasma, and paraffin-embedded tissue samples were tested using a PCR-based assay that detects a W. bancrofti-specific repetitive DNA sequence. The assay was positive in 100 microL of blood from 40 of 42 microfilaria-positive subjects, the 2 subjects with negative assays having microfilarial counts of 1. Samples from 127 uninfected subjects were PCR-negative. The assay was also positive in 7 of 10 daytime samples in regions where infection is nocturnally periodic; PCR amplification from paraffin-embedded sections established the diagnosis of W. bancrofti infection in another 2 cases. A microtiter ELISA plate-based method was developed for rapid evaluation of large numbers of samples. These results suggest that this PCR-based assay will be useful in diagnosis of W. bancrofti infection in a variety of clinical settings.

Adult↗

PubMed1996

Rat calcium-sensing receptor is regulated by vitamin D but not by calcium.

Parathyroid hormone (PTH) secretion is regulated by extracellular calcium acting through a cell surface calcium receptor (CaR). We have examined the potential regulation of the CaR in the parathyroid glands (PTG) and kidney by calcium and 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3]. Rats fed vitamin D-deficient (-D) diets containing 0.02, 0.4, or 2.0% Ca had a wide range of serum ionized Ca (2.5-5.2 mg/dl) and PTH (22-590 pg/ml) concentrations. PTG CaR mRNA did not vary significantly with ionized calcium or PTH, indicating that hypocalcemia and hyperparathyroidism may not alter CaR expression. However, PTG CaR mRNA was 40% lower in the -D rats than in age-matched rats fed a vitamin D-replete (+D) diet (P < 0.002). Repletion of -D rats with 1,25-(OH)2D3 produced a dose-dependent increase in PTG CaR mRNA. Treatment of +D rats with 100 ng of 1,25-(OH)2D3 increased CaR mRNA by 33% (P < 0.05) and 54% (P < 0.002) in the PTG and by 89% (P < 0.02) and 91% (P < 0.02) in the kidney in two independent experiments. PTG CaR peaked at 16 h (150% of control, P < 0.05) after 1,25-(OH)2D3 administration but returned to normal by 24 h. This upregulation of CaR expression by 1,25-(OH)2D3 may be involved in the suppressive effects of vitamin D compounds on PTH secretion.

Animals↗

PubMed1996

Expression of the renal 25-hydroxyvitamin D-24-hydroxylase gene: regulation by dietary phosphate.

1,25-Dihydroxyvitamin D3 [1,25(OH)2D3] plays a key role in phosphate (Pi) homeostasis through its phosphatemic actions on intestine and bone. In turn, dietary Pi restriction increases serum 1,25(OH)2D3 by stimulating its production, but its effect on vitamin D catabolism is less clear. Here we have examined the effects of dietary Pi on the expression of the renal vitamin D-24-hydroxylase (24-OHase), the first enzyme in the catabolic pathway for vitamin D compounds. Rats fed a low Pi (0.02% P) diet showed a fivefold decrease in renal 24-OHase mRNA compared with rats fed a normal Pi (0.67% P) diet. 24-OHase mRNA and 24-OHase activity decreased within 24 h of Pi restriction, reached a minimum by 48 h, and remained low through 14 days. Decreased 24-OHase mRNA was observed with more moderate Pi restriction (0.2% P), but higher Pi (1.2% P) did not increase 24-OHase mRNA over the 0.8% P diet. 24-OHase mRNA correlated well with plasma Pi (r = 0.862, P < 0.001). In conclusion, renal 24-OHase expression is regulated by dietary phosphate at the mRNA level.

Animals↗

PubMed1996

A polymerase chain reaction assay for detection of the parasite Wuchereria bancrofti in human blood samples.

To identify Wuchereria bancrofti DNA sequences that could be used as the basis for a simple and rapid parasite detection assay, a genomic library of W. bancrofti was constructed and screened for highly repeated DNA. The repeat found with the highest copy number was 195 basepairs (bps) long, 77% AT, and 300 copies per haploid genome. This sequence was designated the Ssp I repeat because it has a unique recognition site for that restriction endonuclease in all or most of the repeat copies. The Ssp I repeat DNA family is dispersed, genus-specific, and exists in all of the different geographic isolates of W. bancrofti tested. Based on DNA sequence analysis of this repeat, we have developed an assay to detect very small quantities of W. bancrofti DNA using the polymerase chain reaction (PCR). With this PCR assay, the Ssp I repeat was detected in as little as 1 pg of w. bancrofti genomic DNA (about 1% of the DNA in one microfilaria) added to 100 microliters of human blood. The PCR assay also amplified Ssp I repeat DNA from geographic isolates of W. bancrofti from around the world but not from other species of filariae or from human or mosquito DNA. Microfilaria-positive human blood samples collected in Mauke, Cook Islands were shown to be Ssp I PCR-positive, while microfilaria-negative samples were PCR-negative. The specificity and sensitivity of the Ssp I PCR assay indicates that this approach has significant potential for improved screening of large human populations for active W. bancrofti infection.

Animals↗

PubMed1996

[Identification of vertical transmission of hepatitis B virus from mother to children by direct sequencing a segment of surface gene of hepatitis B virus].

SUBJECTIVE: To explore the reason for the failure to interrupt vertical transmission of hepatitis B virus (HBV) from mother to children in Chinese subjects by vaccination. METHODS: HBV nucleotide sequences isolated from three sets of mother/children pairs were analyzed. HBV DNA from the surface antigen region encoding the amino acids 101 to 160 of hepatitis B surface antigen (HBsAg) was amplified and sequenced from HBsAg positive mother and their children. RESULTS: Nucleotide and deduced amino acid sequences were absolutely identical in the mother and children in family one and two respectively. However, there were five nucleotides different in family one's isolates compared with the family two's isolates. All of them were a subtype. In one child of family three, with coexisted HBsAg and anti-HBs, sequencing result revealed a point mutation which predicted a change from glycine to arginine at residue 145 in the second loop of the determinant. The mother and another child had a glycine at this position. CONCLUSION: This study revealed the vertical transmission linkage of HBV between the mother and children in a molecular level, and also first described a codon 145 immune escape mutant in Chinese vaccinated children.

Adult↗

PubMed1996

[Effect of IL-4 on biological regulation of tumor cell lines].

The effect of IL-4 on biological regulation of tumor cell lines was observed by using human recombinant interleukin-4. The observation included cell proliferation, differentiation, cell surface marker and cytokine secretion. The effect of IL-4 on cell proliferation of nine cell lines was different. It showed 4/9 inhibitory effect, 3/9 enhancing effect and 2/9 no effect. The inhibitory effect of IL-4 on U937 cell proliferation was correlated with cell differentiation. IL-4 enhanced the expression of cell surface markers (including MHC class I, MHC class II and TAA) of some cell lines. Furthermore, IL-4 inhibited the production of IL-2 by MLA144. The preliminary results indicate that the effect of IL-4 on biological regulation of tumor cell lines is benefitial for controlling tumor cell growth and enhancing tumor cell recognition by effector cells. However, the down regulation also could be exerted.

Animals↗

PubMed1996

[Synthesis of adenine derivatives and their activities against herpes virus in vitro].

A series of 9-(N4-substituted acetaldehyde thiosemicarbazone) adenines were synthesized and evaluated for antiherpes virus activity. Compounds 4a-l were prepared by condensation of 9-(acetaldehyde) adenine(6) and the corresponding N4-substituted thiosemicarbazides (10). The antiviral effects of all compounds 4a-l were tested in vitro in primary rabbit kidney cell cultures infected with herpes simplex virus type 1 (HSV-1) and varicella-herpes zoster virus (VZV), and in primary human embryo cell cultures infected with herpes simplex virus type 2 (HSV-2). The results showed that the minimum inhibitory concentrations (MIC) of 4e and 4f for HSV-1 and VZV were 20, 40, 20 and 20 micrograms.ml-1, respectively, and other compounds were 200 micrograms.ml-1. For HSV-2, the MIC of all tested compounds were 300 micrograms.ml-1. We also evaluated the antiherpetic effect of 4e (and 4f) by combination with acyclovir (ACV) in the ratio of 1:1 in vitro. The MIC of the combined compounds were 2 micrograms.ml-1 for 4e and 6 micrograms.ml-1 for 4f, while their minimum cytotoxicities (MCC) in the cell were markedly reduced compared with the individual compounds.

Adenine↗

PubMed1995

Microtubules mediate cellular 25-hydroxyvitamin D3 trafficking and the genomic response to 1,25-dihydroxyvitamin D3 in normal human monocytes.

The genomic actions of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) are mediated by the intracellular vitamin D receptor (VDR). Although immunocytochemistry has shown that disruption of microtubular assembly prevents nuclear access of the sterol-VDR complex, the role of microtubules in the response to 1,25(OH)2D3 has not been studied in viable cells. Our studies examined this interaction in normal human monocytes. Monocytes convert 25(OH)D3 to 1,25(OH)2D3 and to 24-hydroxylated metabolites more polar than 1,25(OH)2D3. Microtubule disruption totally abolished the ability of exogenous 1,25(OH)2D3 to suppress its own synthesis and to induce 24-hydroxylase mRNA and activity, without affecting either total 1,25(OH)2D3 uptake or maximal 1,25(OH)2D3-VDR binding. Thus, intact microtubules are essential for 1,25(OH)2D3-dependent modulation of gene transcription. Interestingly, microtubule disruption also decreased monocyte 1,25(OH)2D3 synthesis, not by decreasing the Vmax of monocyte mitochondrial 1 alpha-hydroxylase but through an increase in the Km for 25(OH)2D3. We examined 25(OH)D3 transport. Microtubule disruption did not affect total cellular 25(OH)D3 uptake but reduced its intracellular trafficking to the mitochondria. Thus, microtubules participate in intracellular 25(OH)D3 transport, and their integrity determines normal 1,25(OH)2D3 synthesis.

Biological Transport↗

PubMed1995

Loss of calcium responsiveness in cultured bovine parathyroid cells is associated with decreased calcium receptor expression.

Suppression of PTH secretion by extracellular calcium is mediated by a plasma membrane calcium receptor (CaR). However, primary cultures of bovine parathyroid cells are known to quickly lose their responsiveness to extracellular calcium. The present study was designed to determine if the loss of calcium responsiveness is due to changes in CaR expression. In primary monolayer cultures of parathyroid cells, calcium-mediated suppression of PTH was still evident after 24 hours in culture but was completely absent after 6 days. This was preceded by a 75% drop in CaR mRNA content within 24 hours. CaR mRNA levels remained low for the 6-day culture. Earlier time points, examined in parathyroid cell suspensions, showed a 70% drop in CaR mRNA by 4 hours after collagenase-dispersion of the glands and an 85% drop after 24 hours. The decreased expression of CaR mRNA was not influenced by altering medium serum, calcium, or 1,25-dihydroxyvitamin D3. Our results indicate that the loss of responsiveness of cultured parathyroid cells to calcium is due to decreased CaR mRNA and, presumably, CaR protein expression.

Animals↗

PubMed1995

Population awareness and control of hypertension and hypercholesterolemia. The Atherosclerosis Risk in Communities study.

BACKGROUND: A national program for hypertension detection and control was implemented in the 1970s, whereas a similar program for control of hypercholesterolemia has been implemented in recent years. We studied the levels of awareness, treatment, and control of these conditions in US population samples during a 3-year period (1987 to 1989). METHODS: The levels of awareness, treatment (by medication), and adequate control of hypertension (systolic blood pressure, > or = 140 mm Hg; diastolic blood pressure, > or = 90 mm Hg; or antihypertensive medication) and hypercholesterolemia (serum cholesterol level, > or = 6.21 mmol/L [> or = 240 mg/dL], or lipid-lowering medication) were studied among participants in the baseline examination of the Atherosclerosis Risk in Communities Study, including 15,739 individuals aged 45 to 64 years. RESULTS: Eighty-four percent of the hypertensive subjects and 42% of the hypercholesterolemic subjects were aware of their conditions. Overall, 50% of the hypertensive subjects and only 4% of the hypercholesterolemic subjects had their conditions both treated and controlled. Rates of hypertension prevalence, awareness, and control remained stable during the 3-year study period. Hypercholesterolemia prevalence decreased from 30% in 1987 to 25% in 1989; its awareness increased from 31% to 50% during the same period. Hypertensive women were more likely than hypertensive men to be aware and treated, whereas hypercholesterolemia awareness was higher in men than in women. Hypertension awareness was highest in black women, but black hypertensive subjects were less likely than whites to be treated and to have their hypertension controlled. Black hypercholesterolemic subjects were less likely to be either aware or treated. CONCLUSIONS: After the recent implementation of the National Cholesterol Education Program, the levels of awareness, treatment, and control of hypercholesterolemia are improving at a high rate, although they are still substantially lower than those for hypertension. Further improvement is necessary, particularly among certain population groups, such as blacks.

Age Distribution↗

PubMed1995

A method for probing the topography and interactions of proteins: footprinting of myoglobin.

We describe a procedure for mapping residues on the surface of a protein molecule to its sequence, using a scheme that is analogous to nucleic acid footprinting. The protein is end labeled radioactively and subjected to limited proteolysis, and the products are analyzed by denaturing polyacrylamide gel electrophoresis and autoradiography. The method is tested with the heme protein myoglobin and applied to mapping the (unknown) surface of the molecule lacking the heme group: apomyoglobin. Sites of protein-protein interaction can be identified, as illustrated by footprinting the association between myoglobin and an anti-myoglobin monoclonal antibody.

Adenosine Triphosphate↗

PubMed1995

The roles of calcium and 1,25-dihydroxyvitamin D3 in the regulation of vitamin D receptor expression by rat parathyroid glands.

Expression of the vitamin D receptor (VDR) in the parathyroid glands is decreased in secondary hyperparathyroidism associated with chronic renal failure by undefined mechanisms. In the present study, we examined the effects of hyperparathyroidism and dietary calcium and 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] on the expression of VDR in rat parathyroid glands. Vitamin D-deficient rats were maintained on diets containing 0.02% Ca (-D, LCD), 0.4% Ca (-D, NCD), or 2.0% Ca (-D, HCD) for 6 weeks. Serum ionized Ca (ICa) in the rats on the three diets ranged from 2.5-5.2 mg/dl. Serum PTH ranged from 22-590 pg/ml and correlated inversely with ICa (r = -0.835; P < 0.001). Rats with the highest ICa had normal PTH values, suggesting that vitamin D deficiency per se does not lead to hyperparathyroidism. VDR messenger RNA (mRNA) levels in the parathyroid glands correlated positively with ICa (r = 0.845; P < 0.001) and negatively with PTH (r = -0.716; P < 0.001). VDR mRNA levels in the rats fed the -D, HCD were 6 times higher than those receiving -D, LCD and the same as those in rats fed a normal (Purina) diet. Thus, prevention of hyperparathyroidism with high dietary calcium prevented the drop in VDR expression. Treatment of the rats on all three diets with 0, 25, or 100 ng 1,25-(OH)2D3, ip, 48 and 12 h before death dose dependently increased ICa and decreased PTH, as expected, and also increased parathyroid gland VDR mRNA. This coordinate regulation of VDR mRNA by calcium and 1,25-(OH)2D3 was also observed in the kidney, but intestinal VDR mRNA was not stimulated by dietary calcium or 1,25-(OH)2D3. Analysis of covariance for parathyroid gland VDR mRNA and ICa for the three doses of 1,25-(OH)2D3 revealed no significant independent effect of 1,25-(OH)2D3 on VDR mRNA, suggesting that the up-regulation of VDR expression by 1,25-(OH)2D3 in the parathyroid glands may be mediated primarily by increasing serum calcium.

Animals↗

PubMed1995

[Myocardial damage after high tension electricity injury in rabbits].

The experiment was designed to study the condition of rabbit myocardium after 10,000-Volt high tension electricity injury by using light and electron microscopes. Early change in myocardium was detected and it took a dynamic development. Also, the enzymogram of myocardium was found to be altered parallel with the pathological alteration, apart from significant changes showed in electrocardiograms. The result of the study demonstrated that organic injury occurred in myocardium after high tension electricity injury.

Animals↗

PubMed1995

[Direct genotyping and antenatal diagnosis of deletional alpha-thalassemia of the southeast Asian type by polymerase chain reaction technique].

OBJECTIVE: To study the gene of deletional alpha-thalassemia of the Southeast Asian type (SEA) and to perform the antenatal diagnosis. METHODS: A new method of polymerase chain reaction technique using three primers bridging the breakpoints was carried out for carrier detection and antenatal diagnosis of deletional alpha-thalassemia of the Southeast Asian type. A DNA fragment of about 630bp in size was amplified in case of--SEA alleles, while a 224 bp fragment was amplified in samples without the deletion. Homozygotes, heterozygotes, and normal subjects could be clearly distinguished with the present method. RESULTS: We used this method in the genotyping and antenatal diagnosis of 10 high risk pregnancies of alpha-thalassemia. 2 homozygotes, 4 heterozygotes, and 4 normal infants were found. CONCLUSION: The present method is simple and rapid in detection of carriers and antenatal diagnosis of the alpha-thalassemia of southeast Asian type.

Base Sequence↗

PubMed1994

Equilibrium analysis of ethidium binding to DNA containing base mismatches and branches.

In the processes of DNA replication, recombination, and repair, duplex DNA can transiently form branched structures, such as Holliday junctions, as well as base pair mismatches and bulges. These stages have altered ligand and protein binding properties from normal double helical DNA. A variety of ligands have been reported to interact more tightly at branches and bulges than to normal duplex sites. The stoichiometry, structural basis, and thermodynamics of this effect have not been determined. We have investigated the binding of the intercalator, ethidium bromide, to several DNA constructs including base mismatches, bulges, and three- and four-arm branched structures, using chemical footprinting, titration calorimetry, and fluorescence lifetime measurements. Two classes of binding sites are detected in three- and four-arm junctions in our high ionic strength conditions: one class is characterized by a small number of ligands (2-4 per DNA), with high binding affinity (K > 10(5)), and the second by a larger number of sites (10-12 per DNA) with lower affinity (K approximately 10(4)). By use of appropriate control experiments, the former appear to be associated with sites at or near the branch point or mismatch, while the latter are consistent with binding to the normal duplex DNA region(s) of the molecule. Titration calorimetry indicates an enthalpy of -10 to -13 kcal/mol for binding of ethidium to a mismatch or three- and four-arm branch point. The tight binding class is associated with a fluorescence lifetime of 12-16 ns, distinct from that of free ethidium (ca. 2 ns) and the longer lifetime observed for ethidium intercalated in duplex DNA (22-26 ns).

Base Composition↗

PubMed1994

Effects of unpaired bases on the conformation and stability of three-arm DNA junctions.

Three-arm DNA junctions, in which three double helices intersect at a branch, have unique structure and reactivity of bases at and near the branch. Their solution conformation is asymmetric in the presence of Mg2+, while bases at the branch are sensitive to single-strand-specific agents. Following the surprising report that unpaired bases at the branch stabilize three-arm junctions, we have investigated the geometry and thermodynamics of three-arm junctions containing pendant T and A bases. The results are consistent with additional structure formation in junctions containing up to four pendant bases at the branch: relative to the tight junction, the thermal stability of junctions with two T's or A's at the branch increases; bases near the branch become less reactive to single-strand-reactive probes; and the enthalpy of formation is more negative. The interaction of ethidium observed at the branch in three-arm junctions is enhanced in junctions with unpaired bases at the branch. The geometry of three-arm junctions is perturbed by the presence of pendant bases, as seen by measuring the electrophoretic mobility of junctions to which long duplex arms are appended pairwise.

Base Composition↗

PubMed1994

Mapping tRNA and 5S RNA tertiary structures by charge dependent Fe(II)-catalyzed cleavage.

Chemical and enzymatic footprinting experiments have made it possible to identify protein binding sites in DNA and RNA, and to localize structural differences within nucleic acids to a resolution of a single base pair. We show here that by combining three reagents, Fe(II).EDTA2-, Fe(II).EDDA and Fe2+, differential maps of sites in RNA that vary in their local conformation and/or charge can be constructed. Comparison of profiles with respect to controls in the absence of a counterion such as Mg2+ allows analysis of sites responsive to tertiary structure. A single site that is labile to metals such as Pb2+ exists in tRNA(Phe) and a number of other tRNA's; this site is hyper-reactive to Fe(II), but not to the other probes. Scission induced by the neutral complex, Fe(II).EDDA, offers the most general measure of surface accessibility, since its distribution about the target molecule is insensitive to charge. Enhanced cleavage by Fe(II) relative to the other agents is detected at several adjacent sites in 5S RNA, consistent with conformational mobility. Protection at a series of positions in the arm formed by loops E and D with helix IV suggests further that at low temperature this arm interacts with loop A and helix I.

Base Composition↗