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Biomedical subjects

L Shen

Publications and source records attributed to L Shen.

At least 145 records · Page 8Linked to original sources
PubMed1998

The equine estrogen metabolite 4-hydroxyequilenin causes DNA single-strand breaks and oxidation of DNA bases in vitro.

Premarin (Wyeth-Ayerst) is the estrogen replacement treatment of choice and continues to be one of the most widely dispensed prescriptions in North America. In addition to endogenous estrogens, Premarin contains unsaturated equine estrogens, including equilenin [1,3,5(10),6,8-estrapentaen-3-ol-17-one]. In previous work, we showed that the equilenin metabolite 4-hydroxyequilenin (4-OHEN) can be autoxidized to 4-OHEN-o-quinone which readily entered into a redox couple with the semiquinone radical catalyzed by NAD(P)H, P450 reductase, or quinone reductase, resulting in generation of reactive oxygen species [Shen, L., Pisha, E., Huang, Z., Pezzuto, J. M., Krol, E., Alam, Z., van Breemen, R. B., and Bolton, J. L. (1997) Carcinogenesis 18, 1093-1101]. As oxidative damage to DNA by reactive oxygen species generated by redox active compounds has been proposed to lead to tumor formation, we investigated whether 4-OHEN could cause DNA damage. We treated lambda phage DNA with 4-OHEN and found that extensive single-strand breaks could be obtained with increasing concentrations of 4-OHEN as well as increasing incubation times. If scavengers of reactive oxygen species are included in the incubations, DNA could be completely protected from 4-OHEN-mediated damage. In contrast, NADH and CuCl2 enhanced the ability of 4-OHEN to cause DNA single-strand breaks presumably due to redox cycling between 4-OHEN and the semiquinone radical generating hydrogen peroxide and ultimately copper peroxide complexes. We also confirmed that 4-OHEN could oxidize DNA bases since hydrolysis of 4-OHEN-treated calf thymus DNA and HPLC separation with electrospray MS detection revealed oxidized deoxynucleosides, including 8-oxodeoxyguanosine and 8-oxodeoxyadenosine. Our data suggest that DNA single-strand breaks and oxidation of DNA bases by 4-OHEN could contribute to the carcinogenic mechanism(s) of equine estrogens.

Animals↗
PubMed1998

Arterial injury by cholesterol oxidation products causes endothelial dysfunction and arterial wall cholesterol accumulation.

Cholesterol oxidation products (ChOx) have been reported to cause acute vascular injury in vivo; however, the pharmacokinetics of ChOx after administration and the mechanisms by which they cause chronic vascular injury are not well understood. To further study the pharmacokinetics and atherogenic properties of ChOx, New Zealand White rabbits were injected intravenously (70 mg per injection, 20 injections per animal) with a ChOx mixture having a composition similar to that found in vivo during a 70-day period. Total ChOx concentrations in plasma peaked almost immediately after a single injection, declined rapidly, and returned to preinjection levels in 2 hours. After multiple injections, the ChOx concentrations rose gradually to levels 2- to 3-fold above baseline levels, increasing mostly in the cholesteryl ester fraction of LDL and VLDL. Rabbit serum and the isolated LDL/VLDL fraction containing elevated ChOx concentrations were cytotoxic to V79 fibroblasts and rabbit aortic endothelial cells. At the time of killing, cholesterol levels in the aortas from ChOx-injected rabbits were significantly elevated despite the fact that plasma cholesterol levels remained in the normal range. In addition, aortas from the ChOx-injected rabbits retained more 125I-labeled horseradish peroxidase, measured 20 minutes after intravenous injection. Transmural concentration profiles across the arterial wall also showed increased horseradish peroxidase accumulation in the inner half of the media from the thoracic aorta in ChOx-injected rabbits. In conclusion, ChOx injection resulted in accumulation of circulating ChOx and induced increased vascular permeability and accumulation of lipids and macromolecules. This study reveals that even under normocholesterolemic conditions, ChOx can cause endothelial dysfunction, increased macromolecular permeability, and increased cholesterol accumulation, parameters believed to be involved in the development of early atherosclerotic lesions.

Animals↗
PubMed1998

Increased angiotensin II type 1 receptor expression in hypercholesterolemic atherosclerosis in rabbits.

Angiotensin II (Ang II) promotes vascular smooth muscle growth and may be involved in the initiation and progression of atherosclerosis. To examine whether Ang II receptor expression in vascular tissues is altered in atherosclerosis, male New Zealand White rabbits were fed a high-cholesterol diet (1% cholesterol + 4% coconut oil mixed with regular chow; hypercholesterolemic group, n=12) or regular chow (control group, n=8) for 10 weeks. At the end of this period, the serum cholesterol level in the rabbits fed the high-cholesterol diet was higher than that in the control group (3616 +/- 144 versus 30 +/- 1 mg/dL, P<0.001). There was no atherosclerosis in the aortas of the control group, whereas 51 +/- 6% of the aorta was covered with atherosclerosis in the hypercholesterolemic group. Total Ang II receptor expression in the atherosclerotic aortic tissues was increased 5-fold in the hypercholesterolemic rabbits (292 +/- 28 versus 51 +/- 32 fmol/mg tissue, mean +/- SE, P<0.001), and the increased Ang II receptor expression was entirely due to enhanced Ang II type 1 (AT1) receptor expression (289 +/- 38 versus 38 +/- 18 fmol/mg, P<0.001), as Ang II type 2 receptor expression was unaltered (7 +/- 5 versus 3 +/- 2 fmol/mg, P=NS). AT1 receptors were localized primarily in the media and to some extent in the intima of the atherosclerotic aorta, as determined by immunohistochemistry with specific monoclonal and polyclonal AT1 receptor antibodies. Increased synthesis of AT1 receptor mRNA in atherosclerotic tissues was confirmed by reverse transcription-polymerase chain reaction. To evaluate the functional significance of increased AT1 receptor expression, the constrictor response of aortic rings to Ang II was examined and found to be markedly enhanced in atherosclerotic aortic rings (P<0.01 versus control aortic rings). The endothelium-dependent relaxation of aortic rings from hypercholesterolemic rabbits was markedly attenuated (P<0.001). This study shows that hypercholesterolemia in rabbits results in atherosclerosis, loss of endothelium-dependent relaxation, and increased Ang II receptor (entirely AT1 receptor) expression in aortic tissues, which may result in altered vasoreactivity.

Acetylcholine↗
PubMed1998

[Follow-up on hepatitis B immunized neonates born to HBsAg positive mothers].

OBJECTIVE: To determine the immune persistence in neonates born to hepatitis B surface antigen (HBsAg) positive mothers with different schedules for HB immunization. METHODS: Two hundred and three neonates born to HBsAg positive mothers were immunized at birth with HB vaccine in different schedules and doses, and followed-up for six years continuously for antibodies against HBs (anti-HBs) and carriage status of HBsAg. RESULTS: Prevalence of anti-HBs in the neonates kept in more than 90% during the six years since immunization, with a peak at the ages of seven to twelve months and decreasing by 48.82% at the ages of one to two years. Their anti-HBs kept relative stable during two to six years of age. Eight children converted to anti-HBs negative for three to five years still kept uninfected. Fourteen children converted to anti-HBs negative reconverted positive again one to two years later. No single chronic carrier with HBsAg was found in them. CONCLUSION: A booster dose of HB vaccine seems unnecessary for children in six to ten years after primary immunization.

Child↗
PubMed1998

[Surgical treatment of excessive hyperplasia symptom of skin keratosis at the limb ends].

OBJECTIVE: We introduce the experience of treating 10 cases with excessive hyperplasia of skin keratosis at the limb end. There were 9 cases of palmar and plantar keratosis and 1 case of epidermodysplasia verruciformis. METHOD: All cases received the operation of lesion excision and skin grafting except 2 cases who received skin flap for defect covering after lesion excision because of deep tissue exposure and postradiation ulcer. RESULT: The operative effects were satisfactory after 8 years of follow-up. No recurrence was found in all cases and all patients resumed normal activity. CONCLUSION: The effect of the skin flap is better than skin graft at the plantar area. Because of lack of fibrous septum in the subcutaneous tissue, the flap, often moving during walking, is liable to trauma and ulceration. The operation area must be well protected.

Adult↗
PubMed1998

[The second phase clinical observation of anti-radiation effect by superoxide dismutase].

Multiple center randomized controlled double blind clinical trait was conducted to evaluate the anti-radiotherapy effect by SOD (produced by Hunan Biochemical Work) in 159 patients. Injection of 4000U SOD immediately after receiving radiotherapy significantly reduced the occurrence rate of skin, oral mucosal, pelvic visceral and systematic adverse reaction, only the reduction of leukopenia did not reach the statistical significant level. No adverse effect of SOD injection was observed. The results suggest that SOD is a safe and effective agent to attenuate the radiotherapy reactions.

Adolescent↗
PubMed1998

[Laparoscopic assisted transvaginal hysterectomy].

OBJECTIVE: To evaluate the indication, technical procedure and the clinical value of laparoscopic assisted trans vaginal hysterectomy (LAVH). METHODS: Ninety-eight patients suffered from various kinds of benign gynecological diseases underwent LAVH from Feb. 1995 to Feb. 1997. The mean age was 52 years (range 38-66), preoperative examination findings were 38 cases of normal uterine size, 60 of uterine enlargement (44 less than 12 week gestational size and 16 larger). Among these patients, 29 cases had a history of lower abdominal laparotomy. RESULTS: 2 out of the 98 cases were switched to laparotomy (2.0%). Mean operation time of LAVH was 106 min (range 60-240 min). The amount of blood loss was approximately 50-150 ml during operation, and the average hospitalization was 6 days. CONCLUSION: Laparoscopic assisted vaginal hysterectomy expands the indication of transvaginal hysterectomy, and avoids laparotomy and lessens injuries, shortens the hospitalization. It is a promising approach of hysterectomy and should be used widely.

Adult↗
PubMed1998

Division of C8 nerve root for treatment of spastic cerebral palsy in the upper limbs: a preliminary report.

OBJECTIVE: To investigate the effect of C8 nerve root division on the treatment of spastic cerebral palsy in the upper limbs. METHODS: Two patients were treated with division of the C8 never root. Supraclavicular incision was made to expose the C5-T1 nerve roots. The intraoperative electromyographic recording technique was used to monitor the responses from the flexor digitorum and flexor carpi ulnaris muscle groups simultaneously. The C5-T1 nerve roots were stimulated and the evoked muscle amplitude potentials (EMAP) were recorded from the muscle groups. The EMAP of the muscle groups obtained during electrical stimulation of the C8 nerve root was the largest, which was used as the basis for C8 nerve root division. RESULTS: Division of the C8 nerve root slightly affected the function of the upper limb, and reduced the muscle tone of the flexor wrist and digitorum. CONCLUSION: Division of the C8 nerve root can reduce the muscle tone of the flexor wrist and digitorum in a short time. The long-term effects need to be followed up further.

Adolescent↗
PubMed1998

The protective effect of procaine blocking on nerve-electrophysiological study during operation.

OBJECTIVE: To clinically evaluate the protective effect of procaine blocking on nerves. METHODS: Electrophysiological examination before and after procaine blocking was conducted on 32 nerves during operation, 18 of which were donor nerves and 14 were injured ones. RESULTS: The latency of somatosensory evoked potentials (SEPs) was lengthened (15.30%) and the amplitude was lowered (18.47) after procaine blocking. Compared with the values before procaine blocking, the differences were significant (P < 0.01 and P < 0.05, respectively). SEP waves disappeared after procaine blocking in some cases (28.13%). CONCLUSION: Latency of SEP is lengthened and amplitude is lowered after procaine blocking. In some cases, SEPs even disappear.

Accessory Nerve↗
PubMed1998

Expression of type-I collagen and matrix metalloproteinase-9 mRNA in bone of castrated adult female rats: effects of estrogen.

OBJECTIVES: To elucidate the molecular changes of bone collagen during the development of postmenopausal osteoporosis and to investigate the molecular effects of estrogen replacement. METHODS: An adult ovariotomy rat model was used. Type-I collagen and matrix metalloproteinase-9 (MMP-9) expressions in bone tissues of rats treated by sham surgery (SH), bilateral ovariotomy (OVX) and OVX with estradiol (OVX-E2) were analysed at mRNA level by using dot blot technique. The distribution of mRNA of these two genes in bone tissues was studied by in situ hybridization. RESULTS: The expression levels of both type-I collagen and MMP-9 in bone tissues of OVX rats were higher than those of SH group, while treated with estradiol, the expression of both genes declined to some degree. In situ hybridization showed that type-I collagen mRNA located in osteoblasts, whereas MMP-9 was mainly expressed in osteoclasts, some lining cells on bone surface, and some mononuclear cells in bone marrow. CONCLUSIONS: The reduction of high bone turnover in osteoporotic bone tissues induced by estrogen replacement may result from alterations in gene expression related to bone formation and bone resorption. These alterations are consistent with the changes observed previously by histomorphometry and biochemical markers of bone metabolism on OVX animals and postmenopausal osteoporosis.

Animals↗
PubMed1998

[Effects of the leaf of Ginkgo biloba L. extract on blood rheology in animals].

OBJECTIVE: To observe the effects of the leaf of Ginkgo biloba extract(GBE) on viscosity and elasticity, coagulation of blood and aggregation of blood platelets. METHOD: The viscosity and elasticity of the whole blood in rats was determined using an in vitro method. The half inhibitory concentration of the drug inhibiting rabbit platelet aggregation was also determined using ADP as an inducer. The blood coagulation in mice was recorded with a coagulation analyser after GBE was administered by vein injection. RESULT: GBE significantly lengthened the recalcium time, lowered the increase ratios of viscosity and elasticity, and reduced the maximum viscosity and elasticity. At doses of 100 and 200 mg/kg administrated by vein injection GBE lengthened the coagulation time, reduced the fibriogenesis and clot retraction ratio significantly in mice. GBE can also inhibit rabbit platelet aggregation induced by ADP and promote the disband of the aggregated platelets. CONCLUSION: GBE is helpful in reducing viscosity and elasticity of the whole blood, slowing blood coagulation and inhibiting platelet aggregation.

Animals↗
PubMed1998

[The measurement of baroreflex sensitivity in stress-induced hypertensive rats by spectral analysis].

Simultaneous spectral analysis of short-term systolic blood pressure variability (SBPV) and heart rate variability (HRV) was applied to determine the change of baroreflex sensitivity (BRS) in Sprague-Dawley (SD) rats. The modulus of the transfer function between fluctuations in systolic pressure and beat-to-beat interval would be an appropriate quantification of BRS. The animal experiment was performed on two groups of rats: normotensive rats and stress-induced hypertensive rats (SIHR). V1-receptor antagonist d(CH2)5Tye(Me) AVP of arginine vasopressin (AVP) was microinjected into intracerebroventricle. The results showed that, in base-line condition before administration, although the BRS in very low frequency band (0-0.035 Cycle/Beat, VLF), low frequency band (0.035-0.12 Cycle/Beat, LF), high frequency band (0.12-0.32 Cycle/Beat, HF) and total BRS(the sum of the three bands) were all decreased, the BRS in VLF(P < 0.05) and LF(P < 0.01) decreased significantly by statistics; and that, to the SIHR, the BRS in VLF was significantly lower after AVP-V1 administration than in base-line condition, while to normotensive rats, the BRS did not change. It indicates that the facilitating effect of AVP on the beroreflex in SIHR is mainly due to V1-receptor in central nerve system. In summary, the transfer function between SBPV and beat-to-beat interval fluctuation could be an index of BRS. This method can be developed for future clinical application.

Animals↗
PubMed1998

Steady-state bioavailability of estradiol from two matrix transdermal delivery systems, Alora and Climara.

OBJECTIVE: The relative bioavailability of estradiol from two matrix transdermal delivery systems, Alora (0.05 mg/day when applied for 3-4 days) and Climara (0.05 mg/day when applied for 7 days), was evaluated in this two-period, randomized crossover study. DESIGN: A total of 27 healthy, postmenopausal women completed this study. Each subject received four successive doses of Alora every 84 h (3.5 days) and two doses of Climara every 168 h (7 days) in a randomized sequence without a washout period. Serial serum samples were collected over a 7-day period during the second week of each treatment. Samples were analyzed for estradiol and estrone using a validated radioimmunoassay method. Pharmacokinetic analyses were conducted using baseline-corrected parameters. RESULTS: Fluctuations in serum estradiol levels were 44% higher for Climara, as indicated by the ratio of Cmax/Cmin. Because the Cmin values for the two regimens were similar, the differences in fluctuation reflected the difference in their Cmax values (49.8 pg/ml for Alora, 67.7 pg/ml for Climara.) The estradiol AUC for Climara was 124% (95% CI 115.6-133.7) of the value for Alora. CONCLUSIONS: Serum estradiol concentrations were maintained at a more constant level during twice-weekly application of Alora than during once-weekly application of Climara. Both regimens were generally well tolerated and no serious skin or other adverse effects were reported by the subjects. However, Alora exhibited better skin tolerability as indicated by a lower incidence of moderate skin erythema. In addition, there was less adhesive transfer to skin at the application site with Alora.

Adhesives↗
PubMed1997

Enhancing the activity of protein C by mutagenesis to improve the membrane-binding site: studies related to proline-10.

Bovine and human protein C show high homology in the amino acids of their GLA domains (amino-terminal 44 residues), despite the about 10-fold higher membrane affinity of the human protein. A proposed membrane contact site and mechanism suggested that this difference was largely due to the presence of proline at position 10 of bovine protein C versus histidine at position 10 of human protein C [McDonald, J.F., Shah, A.M., Schwalbe, R.A., Kisiel, W., Dahlback, B., and Nelsestuen, G.L. (1997) Biochemistry, 36, 5120-5127]. This study examined the impact of replacing proline-10 in bovine protein C with histidine, and the reverse change in human protein C. In both cases, the protein containing proline-10 showed lower membrane affinity, about 10-fold lower for bovine protein C and 5-fold lower for human protein C. As expected, activated human protein C (hAPC) containing proline at position 10 showed 2.4-3.5-fold lower activity than wild type hAPC, depending on the assay used. Most interesting was that bovine APC containing histidine-10 displayed up to 15-fold higher activity than wild type bAPC. This demonstrated the ability to improve both membrane contact and activity by mutation. This general strategy should be applicable to other vitamin K-dependent proteins, providing opportunities to study function as well as to produce proteins that may find use as promoters and inhibitors of blood coagulation in pathological states.

Amino Acid Sequence↗
PubMed1997

The reactivity of o-quinones which do not isomerize to quinone methides correlates with alkylcatechol-induced toxicity in human melanoma cells.

Catechols are widespread in the environment, especially as constituents of edible plants. A number of these catechols may undergo oxidative metabolism to electrophilic o-quinones (3,5-cyclohexadien-1,2-dione) by oxidative enzymes such as cytochrome P450 and peroxidases. Alkylation of cellular nucleophiles by these intermediates and the formation of reactive oxygen species, especially through redox cycling of o-quinones, could contribute to the cytotoxic properties of the parent catechols. In contrast, isomerization of the o-quinones to electrophilic quinone methides (4-methylene-2,5-cyclohexadien-1-one, QM) could cause cellular damage primarily through alkylation. In this investigation, we treated human melanoma cells with two groups of catechols. These cells have high levels of tyrosinase required to oxidize catechols to quinoids. For catechols which are oxidized to o-quinones that cannot isomerize to quinone methides or form unstable quinone methides, plots of the cytotoxicity data (ED50) versus the reactivity of the o-quinones gave an excellent linear correlation; decreasing o-quinone reactivity led to a decrease in the cytotoxic potency of the catechol. In contrast, catechols which are metabolized by the o-quinone/p-quinone methide bioactivation pathway were equally cytotoxic but showed no correlation between the reactivity of the o-quinones and the cytotoxic potency of the catechols. The most likely explanation for this effect is a change in cytotoxic mechanism from o-quinone-mediated inhibition of cell growth to a bioactivation pathway based on both o-quinone and p-QM formation. These results substantiate the conclusion that the involvement of the o-quinone/ QM pathway in catechol toxicity depends on a combination between the rate of enzymatic formation of the o-quinone, the rate of isomerization to the more electrophilic QM, and the chemical reactivity of the quinoids.

Biotransformation↗
PubMed1997

Elongation factor Ts of Chlamydia trachomatis: structure of the gene and properties of the protein.

A putative structural gene cluster containing four open reading frames (ORFs) located downstream of the omp1 gene of Chlamydia trachomatis mouse pneumonitis (MoPn) was cloned and sequenced. A GenBank survey indicated that the identified cluster is similar to the rpsB-tsf-pyrH(smbA)-frr region of Escherichia coli. The second ORF was 846 bp encoding a 282-amino-acid polypeptide with a calculated M(r) 30,824. Alignment of this deduced protein sequence and E. coli elongation factor Ts (EF-Ts, product of tsf) demonstrated 34% identity and an additional 14% similarity. The putative chlamydial tsf gene was expressed in E. coli as a nonfusion protein and as a 6x His-tagged fusion protein. By SDS-PAGE analysis, the molecular weights of the nonfusion recombinant protein and a protein of chlamydial elementary bodies (EBs), which was recognized by monoclonal antibodies derived from the nonfusion recombinant protein, are 34 kDa. The purified recombinant 6x His-tagged fusion protein increased the rate of GDP exchange with both Chlamydia and E. coli elongation factor Tu (EF-Tu). These data show that the second gene of the identified cluster is tsf. Unlike EF-Ts from any other species, its activity was comparable to that of E. coli EF-Ts in exchange reaction with E. coli EF-Tu.

Amino Acid Sequence↗
PubMed1997

Regulation of insulin preRNA splicing by glucose.

Glucose tightly regulates the synthesis and secretion of insulin by beta cells in the pancreatic islets of Langerhans. To investigate whether glucose regulates insulin synthesis at the level of insulin RNA splicing, we developed a method to detect and quantify a small amount of RNA by using the branched DNA (bDNA) signal-amplification technique. This assay is both sensitive and highly specific: mouse insulin II mRNA can be detected from a single beta cell (betaTC3 cells or mouse islets), whereas 1 million non-insulin-producing alpha cells (alphaTC1.6 cells) give no signal. By using intron and exon sequences, oligonucleotide probes were designed to distinguish the various unspliced and partially spliced insulin preRNAs from mature insulin mRNA. Insulin RNA splicing rates were estimated from the rate of disappearance of insulin preRNA signal from beta cells treated with actinomycin D to block transcription. We found that the two introns in mouse insulin II are not spliced with the same efficiency. Intron 2 is spliced out more efficiently than intron 1. As a result, some mRNA retaining intron 1 enters the cytoplasm, making up approximately 2-10% of insulin mRNA in the cell. This partially spliced cytoplasmic mRNA is quite stable, with a half-life similar to the completely spliced form. When islets grown in high glucose are shifted to low glucose medium, the level of insulin preRNA and the rate of splicing fall significantly. We conclude that glucose stimulates insulin gene transcription and insulin preRNA splicing. Previous estimates of insulin transcription rates based on insulin preRNA levels that did not consider the rate of splicing may have underestimated the effect of glucose on insulin gene transcription.

Animals↗