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Biomedical subjects

M Hu

Publications and source records attributed to M Hu.

At least 181 records · Page 10Linked to original sources
PubMed1994

Mechanism and kinetics of transcellular transport of a new beta-lactam antibiotic loracarbef across an intestinal epithelial membrane model system (Caco-2).

Various processes involved in the transcellular transport (TT) of loracarbef (LOR) were studied in the Caco-2 cell monolayer, a cell culture model of the small intestinal epithelium. The results provide support for presence of two AP to BL peptide TT pathways in the intestinal epithelial cell monolayer (Caco-2). The H+ gradient-dependent pathway (Km = 0.789 mM, and Jmax = 163 pmol/min per cm2) is relatively "high affinity" and "low capacity" compared to H+ gradient-independent pathway (Km = 8.28 mM, and Jmax = 316 pmol/min per cm2). In addition, TT of LOR in the presence of a H+ gradient was inhibited 77% to 88% (p < 0.05) by 10 mM of cephalexin, enalapril, Gly-Pro and Phe-Pro, while TT of LOR in the absence of a H+ gradient was only inhibited 42% to 48% (p < 0.05) by 10 mM of Gly-Pro and Phe-Pro. Since AP uptake is H+ gradient-dependent and saturable while the BL efflux is mostly nonsaturable and not driven by a H+ gradient, these two transmembrane transport processes must be different, which could be the result of two different peptide carriers. In vivo, these two transport processes must have worked in concert to produce transcellular flux of loracarbef. To explain the differences between kinetic characteristics of AP uptake and TT transport, a cellular pharmacokinetic (PK) model was developed and the results indicate that the PK model appropriately described the kinetics of LOR TT. The use of this PK model may provide an additional advantage to the use of the cell culture model because kinetic parameters at both sides of the intestinal epithelial membrane may be obtained using the same preparation. Taken together, the Caco-2 model system represents an excellent model system for the study of carrier-mediated processes involved in the TT of peptides and peptide-like drugs.

Amino Acid Sequence↗
PubMed1994

Nerve growth factor increases the transcriptional activity of the rat neuronal nicotinic acetylcholine receptor beta 4 subunit promoter in transfected PC12 cells.

Neuronal nicotine acetylcholine receptors play a key role in synaptic transmission in the nervous system. Although complementary DNA clones encoding a family of acetylcholine receptor subunits have been isolated and subsequent anatomical studies indicate differences in the temporal and spatially restricted patterns of expression of each gene, the cellular and molecular mechanisms controlling the expression of these genes are unknown. As part of a long-term goal to elucidate these mechanisms, we have been identifying and characterizing regions of the receptor subunit genes involved in transcriptional regulation. Here, we report the localization of the transcription initiation site of the rat beta 4 subunit gene, demonstrate using transient transfection analysis of PC12 cells that sequences upstream of this site are capable of activating transcription of a heterologous gene, and show that this transcriptional activity is enhanced in PC12 cells by treatment with nerve growth factor.

Amino Acid Isomerases↗
PubMed1994

Mechanisms and kinetics of uptake and efflux of L-methionine in an intestinal epithelial model (Caco-2).

Mechanism and kinetics of uptake and efflux of L-methionine in a human intestinal epithelial model system (Caco-2) were studied to understand the transcellular transport process and to determine its rate-limiting step. The kinetic studies indicated that uptakes from both the apical and basolateral sides were saturable [for apical uptake: Km = 0.96 mmol/L, maximum flux = 673 pmol/(min.cm2); for basolateral uptake: Km = 3.46 mmol/L, maximum flux = 3480 pmol/(min.cm2)], whereas the efflux from these two membranes was apparently linear for intracellular concentrations < 6.5 mmol/L [for apical efflux, the apparent first-order rate constant = 1.01 x 10(-4) cm/min; for basolateral efflux, the rate constant = 1.78 x 10(-4) cm/min]. The results of inhibition studies indicate the apical uptake is partially active and Na(+)-dependent via a combination of amino acid transport systems B0,+ and ASC, which is somewhat different from the less energy- and Na(+)-dependent basolateral uptake. The basolateral uptake is also more dependent on system L and exhibits high counter-exchange capability. Finally, the rate-limiting step in the apical to basolateral transport of methionine is determined to be the basolateral efflux.

Adenocarcinoma↗
PubMed1994

Increased epinephrine and skeletal muscle responses to hypoglycemia in non-insulin-dependent diabetes mellitus.

We evaluated skeletal muscle counterregulation during hypoglycemia in nine subjects with non-insulin-dependent diabetes mellitus (NIDDM) (HbA1c 9.4 +/- 0.5%, nl < 6.2%) compared with six normal controls, matched for age (51 +/- 3 and 49 +/- 5 yr, respectively) and body mass index (27.3 +/- 1.2 and 27.0 +/- 2.1 kg/m2). After 60 min of euglycemia (plasma insulin approximately 140 microU/ml), plasma glucose was lowered to 62 +/- 2 mg/dl by 120 min. Hypoglycemia induced a 2.2-fold greater increase in plasma epinephrine in NIDDM (P < 0.001), while the plasma glucagon response was blunted (P < 0.01). Hepatic glucose output ([3H-3]glucose) suppressed similarly during euglycemia, but during hypoglycemia was greater in NIDDM (P < 0.005). Conversely, glucose uptake during euglycemia was 150% greater in controls (P < 0.01) and remained persistently higher than in NIDDM during hypoglycemia. In NIDDM, plasma FFA concentrations were approximately fivefold greater (P < 0.001), and plasma lactate levels were approximately 40% higher than in controls during hypoglycemia (P < 0.01); the rates of glycolysis from plasma glucose were similar in the two groups despite a 49% lower rate of glucose uptake in NIDDM (3.4 +/- 0.9 vs. 6.9 +/- 1.3 mg/kg per minute, P < 0.001). Muscle glycogen synthase activity fell by 42% with hypoglycemia (P < 0.01) in NIDDM but not in controls. In addition, glycogen phosphorylase was activated by 56% during hypoglycemia in NIDDM only (P < 0.01). Muscle glucose-6-phosphate concentrations rose during hypoglycemia by a twofold greater increment in NIDDM (P < 0.01). Thus, skeletal muscle participates in hypoglycemia counterregulation in NIDDM, directly by decreased removal of plasma glucose and, indirectly, by providing lactate for hepatic gluconeogenesis. Consequently, in addition to inherent insulin resistance in NIDDM, the enhanced plasma epinephrine response during hypoglycemia may partially offset impaired glucagon secretion and counteract the effects of hyperinsulinemia on liver, fat, and skeletal muscle.

Adult↗
PubMed1994

The Caco-2 cell monolayers as an intestinal metabolism model: metabolism of dipeptide Phe-Pro.

The metabolism of Phe-Pro was investigated in Caco-2 cell monolayers, a model of small intestinal epithelium. The results indicate that the majority of Phe-Pro was hydrolyzed during passage from the apical (AP) to basolateral (BL) side. The enzyme responsible for the hydrolysis is prolidase, a cytosolic enzyme. Through kinetic studies of a supernatant enzyme preparation, a Km of 30.4 microM and Vmax of 38.9 nmol/min per mg of protein were obtained. The enzyme catalyzed hydrolysis was inhibited by proline (66%), Zn+ (86%), Cu++ (100%), Fe (100%), PCMB (89%), and captopril (66%), but not by leucine. We also studied the transcellular transport of Phe-Pro by measuring the amount of Phe in the receiver media. In the presence of a proton gradient (AP pH6, BL pH7.4), the appearance rate of Phe in the BL media after Phe-Pro was loaded apically was at least 100 times faster than that in the AP media after Phe-Pro was loaded basolaterally. The former is also higher than the appearance rate of Phe without a transepithelial proton gradient (pH 6-pH 6) or against a proton gradient (pH7.4-pH6). The rate of appearance of Phe in the BL media (pH7.4) after Phe-Pro was loaded on the AP side (pH 6) was decreased by the presence in the AP media of proline (42%), leucine (40%), and captopril (17%), but not by Zn++. In conclusion, the transmembrane uptake of Phe-Pro is dependent on a proton gradient, and the intracellular metabolism of Phe-Pro is complete via hydrolysis by prolidase.

Cell Division↗
PubMed1994

[An epidemiological study on clonorchiasis sinensis in Hubei Province].

An epidemiological study on clonorchiasis sinensis was conducted in 62 counties and cities in Hubei Province during 1987-1991, and clonorchis sinensis was identified in 52 counties and cities. Human population studies showed there were patients with clonorchiasis sinensis in 29 of 31 counties and cities investigated, with infection rates of 0.1%-16.2%. There were five species in two families of freshwater spiral shells as first intermediate host of clonorchis sinensis, 31 species in seven families of freshwater fish (with five species of fish newly discovered) and one species of freshwater shrimp as second intermediate host, and six species as reservoir host. Studies revealed holding small fish in the mouth and eating undercooked roasted fish were two major modes of transmission for clonorchiasis sinensis in the province.

Adolescent↗
PubMed1994

[Factors affecting the visual prognosis after extraction of congenital cataract with IOL implantation].

Multivariated analysis of corrected visual acuities after extraction of congenital cataract with IOL implantation in 24 patients (41 eyes), including 14 children (22 eyes) under 12 years of age, revealed that 6 factors significantly affected the postoperative results, namely, the pattern of lenticular opacity, monocularity, strabismus, nystagmus, after-cataract formation and its time of onset. Therefore, operation as early as possible is recommended for cases with these factors and IOL implantation considered, with discretion, in children for whom other forms of visual aids are not available.

Adolescent↗
PubMed1994

Fusion expression vectors for recombinant gene products processed easily and purified rapidly by affinity chromatography.

A DNA fragment encoding IgG-binding domain B,C (PABC) was separated from protein A gene, cloned into phage M13 and modified by oligo-directed mutagenesis at the hydroxylamine-cleaved site from Asn-Gly to Asn-Ala in domain B and C, respectively. The modified PABCm gene fragment was used to construct one set of fusion expression vectors in different reading frames. Processing sequences such as those recognized by enterkinase, collagenase, thrombin, activated factor X and cleaved by the hydroxylamine, N-chlorosuccinimide etc. can be created in the fusion site. Using the above vectors, fusion proteins such as PABCm-IGF-I, -hGRF, -bGRF and their derivatives were highly expressed in E. coli. The yield of fusion proteins is over 100 mg per liter cultured by analysis of SDS-PAGE. The PABC fusion proteins can be rapidly purified by the affinity chromatography with a IgG-sepharose column.

Base Sequence↗
PubMed1994

[In situ PCR-gene hybridization method for detecting mycobacterium tuberculosis in tissue specimens].

The authors combined the technique of polymerase chain reaction (PCR) with hybridization in situ, and find the method is better, quicker and more sensitive for detecting a trace of bacterial DNA, especially for observing the relation between the lesion and the peripheral tissue, the method is more simple and no radioactive pollution. It seems to be suitable for detection on samples from autopsy, biopsy and smears. We suppose the method might have a prospect for clinical diagnosis.

Base Sequence↗
PubMed1993

Planned sexual behaviour of young Australian visitors to Thailand.

OBJECTIVE: To research the knowledge of AIDS and other sexually transmitted diseases among young Australian tourists to Thailand, and their intended sexual behaviour. DESIGN AND SETTING: A cross-sectional survey by anonymous, self-administered questionnaire, of persons seeking pre-travel medical advice in private clinics in five Australian cities. PARTICIPANTS: 213 consecutive patients travelling to Thailand without a spouse or partner. RESULTS: Only 34% of the sample reported a definite intention not to have sex in Thailand. Regarding choice of potential partners: 24.5% more men than women said they would have sex with a Thai national; 13.7% of men said they would have sex with a "bar girl"; and 21.7% more women than men said they would choose a fellow Australian traveller. Eighty-two per cent of the sample reported that they would use condoms 100% of the time, and there was no significant difference between the number of men and women who expressed this intention. CONCLUSIONS: Although not obviously "sex tourists", many young Australian travellers are likely to have sex while visiting Thailand. These data have important implications for education and prevention programs to control the spread of human immunodeficiency virus (HIV) and other sexually transmitted diseases.

Acquired Immunodeficiency Syndrome↗
PubMed1993

Comparison of uptake characteristics of thymidine and zidovudine in a human intestinal epithelial model system.

The uptake of a natural nucleoside, thymidine (THY), and one of its deoxynucleoside analogues, zidovudine (AZT), was studied in a newly developed intestinal epithelial model system (CaCO-2). The results of the study indicated that the uptake rate of THY was saturable with a Km of 44.6 microM and maximum rate of 1.73 +/- 0.17 pmol/cm2/s. The uptake of AZT, on the other hand, was not saturable. When various naturally occurring nucleosides were used as inhibitors of THY uptake, it was shown that the uptake was inhibited by various pyrimidine nucleosides (e.g., uridine and cytidine), but not by purine nucleosides (e.g., guanosine). Neither group of nucleosides had any effect on the uptake of AZT. Finally, the uptake of THY was also inhibited by the metabolic inhibitor NaCN and a couple of specific nucleoside transporter inhibitors [i.e., dipyridamole and S-(p-nitrobenzyl-6-thioinosine], whereas none of these compounds had a significant effect on the uptake of AZT. The results showed, for the first time, the existence of a nucleoside carrier in the CaCO-2 cell culture model system. Also the results indicated that the uptake of AZT by the CaCO-2 cell monolayers is mainly via a passive diffusion process.

Cells, Cultured↗
PubMed1993

Changes in cell adhesion and cell proliferation are associated with expression of tissue non-specific alkaline phosphatase.

Tissue non-specific alkaline phosphatase is a membrane-bound glycoprotein enzyme which is characterized by its phosphohydrolytic, protein phosphatase, and phosphotransferase activities. This enzyme is distributed virtually in all mammalian tissues, particularly during embryonic development. Its expression is stage-specific and can be demonstrated in the developing embryo as early as the 2-cell stage. It has been suggested that tissue non-specific alkaline phosphatase might play a role in tissue formation. In the study reported here, a gene-transfer approach was employed to investigate possible roles for this enzyme by inserting the cDNA for rat tissue non-specific alkaline phosphatase into CHO and LLC-PK1 cells. Permanently transfected cell-lines expressing varying levels of alkaline phosphatase were established. The data showed that functional enzyme was expressed in the transfected cells. Cell spreading and attachment were enhanced in transfected CHO cells expressing high levels of tissue non-specific alkaline phosphatase but not in the LLC-PK1 cells. Further, in CHO cells, proliferation was shown to be inversely proportional to the level of the tissue non-specific alkaline phosphatase expression. Homotypic cell association was demonstrated in both alkaline phosphatase-positive and alkaline phosphatase-negative cells in both CHO and LLC-PK1 cell-lines. Taken together, these findings suggest that in addition to a role in mineralization of bone, tissue non-specific alkaline phosphatase might also play a role in other cell activities, including those related to differentiation, such as cell-cell or cell-substrate interaction and proliferation.

Alkaline Phosphatase↗
PubMed1993

Mechanism by which hyperglycemia inhibits hepatic glucose production in conscious rats. Implications for the pathophysiology of fasting hyperglycemia in diabetes.

To examine the relationship between the plasma glucose concentration (PG) and the pathways of hepatic glucose production (HGP), five groups of conscious rats were studied after a 6-h fast: (a) control rats (PG = 8.0 +/- 0.2 mM); (b) control rats (PG = 7.9 +/- 0.2 mM) with somatostatin and insulin replaced at the basal level; (c) control rats (PG = 18.1 +/- 0.2 mM) with somatostatin, insulin replaced at the basal level, and glucose infused to acutely raise plasma glucose by 10 mM; (d) control rats (PG = 18.0 +/- 0.2 mM) with somatostatin and glucose infusions to acutely reproduce the metabolic conditions of diabetic rats, i.e., hyperglycemia and moderate hypoinsulinemia; (e) diabetic rats (PG = 18.4 +/- 2.3 mM). All rats received an infusion of [3-3H]glucose and [U-14C]lactate. The ratio between hepatic [14C]UDP-glucose sp act (SA) and 2X [14C]-phosphoenolpyruvate (PEP) SA (the former reflecting glucose-6-phosphate SA) measured the portion of total glucose output derived from PEP-gluconeogenesis. In control rats, HGP was decreased by 58% in hyperglycemic compared to euglycemic conditions (4.5 +/- 0.3 vs. 10.6 +/- 0.2 mg/kg.min; P < 0.01). When evaluated under identical glycemic conditions, HGP was significantly increased in diabetic rats (18.9 +/- 1.4 vs. 6.2 +/- 0.4 mg/kg.min; P < 0.01). In control rats, hyperglycemia increased glucose cycling (by 2.5-fold) and the contribution of gluconeogenesis to HGP (91% vs. 45%), while decreasing that of glycogenolysis (9% vs. 55%). Under identical plasma glucose and insulin concentrations, glucose cycling in diabetic rats was decreased (by 21%) and the percent contribution of gluconeogenesis to HGP (73%) was similar to that of controls (84%). These data indicate that: (a) hyperglycemia causes a marked inhibition of HGP mainly through the suppression of glycogenolysis and the increase in glucokinase flux, with no apparent changes in the fluxes through gluconeogenesis and glucose-6-phosphatase; under similar hyperglycemic hypoinsulinemic conditions: (b) HGP is markedly increased in diabetic rats; however, (c) the contribution of glycogenolysis and gluconeogenesis to HGP is similar to control animals.

Animals↗
PubMed1993

Skeletal muscle glycogenolysis is more sensitive to insulin than is glucose transport/phosphorylation. Relation to the insulin-mediated inhibition of hepatic glucose production.

The effects of minimal increments in plasma insulin concentrations on hepatic glucose production and glucose uptake, skeletal muscle net glycogen synthesis and glycogenolysis, glycogen synthase and phosphorylase activity, glucose-6-phosphate and uridinediphosphoglucose (UDPG) concentrations were examined in 24-h and in 6-h fasted conscious rats. Insulin was infused for 120 min at rates of 1.5, 3, 6, 12, 24, and 108 pmol/kg per min in 24-h fasted rats and at rates of 3, 6, 9, 12, 36, and 108 pmol/kg per min in 6-h fasted rats while endogenous insulin release was inhibited by SRIF infusion and plasma glucose was maintained at the basal level. All rats received an infusion of [3-3H]glucose. The portion of the muscle glucose-6-phosphate (G6P) pool derived from net glycogenolysis was estimated from the ratio of specific activities of muscle UDPG and plasma glucose. Minimal increments in the circulating insulin levels, which did not stimulate glucose uptake, caused: (a) the increase in skeletal muscle glycogen synthase activity and the decrease in the rate of muscle glycogenolysis and in the G6P concentration; (b) the inhibition of hepatic glucose production. Net muscle glycogen synthesis was not stimulated despite submaximal activation of glycogen synthase, and its onset correlated with the rise in muscle G6P levels. Thus, insulin's inhibition of muscle glycogenolysis is the most sensitive insulin action on skeletal muscle and its dose-response characteristics resemble those for the inhibition of hepatic glucose production. These findings indicate that skeletal muscle glycogen synthase may play a major role in carbohydrate homeostasis even under postabsorptive (basal insulin) conditions and support the notion that insulin may exert some of its effects on the liver through an indirect or peripheral mechanism.

Animals↗
PubMed1993

Clinical and experimental studies on shallow needling technique for treating childhood diarrhea.

Treatment of diarrhea in children by shallow needling and by drugs was studied in 3 separate groups for comparison. For Group I, the lateral line II of the forehead was taken, i.e. the upper, middle and lower points of the line staring from Toulinqi (UB 15) vertically downwards to the place 1 cm below the hairline were selected. For Group II, shallow needling was done on body acupoints, the main points selected being Qihai (Ren 6), Shuifen (Ren 9), bilateral Tianshu (St 25), and bilateral Zusanli (St 36); the adjuvant acupoints were Taibai (Sp 3) and Gongsun (Sp 4). The depth of shallow needling was merely puncturing the skin. For Group III the drugs used were Liteling, Berberine, Gentamycin, Ampicillin, and SMZ Co. The results of treatment in Group I and II differed insignificantly, while both were significantly superior to drugs in Group III. Experimental studies also showed that shallow needling enhanced the humoral and cellular immunity and promoted the intestinal peristaltic function.

Acupuncture Therapy↗