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Biomedical subjects

C Ng

Publications and source records attributed to C Ng.

At least 19 recordsLinked to original sources
PubMed1997

Cellular changes and induction of apoptosis in human promyelocytic HL-60 cells infected with the agent of human granulocytic ehrlichiosis (HGE).

Human granulocytic ehrlichiosis (HGE) is an emerging and occasionally fatal human infectious disease whose pathogenesis is largely unknown. Goodman et al. (1) recently described the successful cultivation of the HGE infectious agent in human promyelocytic HL-60 leukemic cells. It was reported in the same study that infectivity invariably led to host cell death, although the mechanism by which HGE infection triggers cellular self-destruction is as yet undetermined. In this communication, we show that in vitro passage of HGE pathogen-infected blood elicits a significantly dysfunctional G1-to-S transition. Moreover, we provide evidence that the cytopathic properties of the HGE pathogen are attributed to its ability to induce apoptosis in host HL-60 cells. Determination of specific protein expression changes by Western blot analysis showed that HGE infection resulted in reduced expression of PCNA and pRB, both of which play a role in cell cycling. Moreover, the steady state level of bcl-2, which protects eukaryotic cells against apoptosis, is suppressed by exposure to the HGE agent. These results suggest that this pathogen HGE induces apoptosis in HL-60 cells by a mechanism involving the shut-off of multiple cell cycle and apoptosis regulatory events.

Apoptosis↗
PubMed1997

Adrenal control of erectile function and nitric oxide synthase in the rat penis.

Penile erection is a nitric oxide (NO)-mediated process that has been shown to be androgen dependent in rats. Castration reduces the activity of the penile enzyme involved in NO synthesis, nitric oxide synthase (NOS). To determine whether adrenal androgens and/or corticosteroids contribute to this control, the following groups of Fischer 344 adult male rats (n = 5-7) were studied: 1) intact, 2) castrated, 3) adrenalectomized alone, 4) castrated/adrenalectomized, 5) castrated/adrenalectomized with aldosterone (1.25 mg/kg, s.c.) and hydrocortisone (12 mg/kg, s.c.), 6) castrated/adrenalectomized with dihydrotestosterone (1.2-cm SILASTIC-brand tubing pellet; Dow Corning, Midland, MI), 7) castrated/adrenalectomized with dehydroepiandrosterone (2-cm tubing), 8) castrated/adrenalectomized with aldosterone (1.25 mg/kg, s.c.), and 9) castrated/adrenalectomized with hydrocortisone (12 mg/kg, s.c.). After 1 week, EFS was applied, and the maximal intracavernosal pressure (MIP) and mean arterial pressure (MAP) were recorded. The MIP/MAP ratio in the adrenalectomized group (0.37) was reduced to values found in the castrated group (0.40). The values in both groups were significantly less than those in intact controls (0.75). The most significant reduction in MIP/MAP was seen in the adrenalectomized/castrated group (0.16). Erectile response in animals submitted to adrenalectomy and castration was restored close to intact values with the administration of hydrocortisone and aldosterone (0.63). Similar results were obtained by the administration of either of the substances alone (0.56 and 0.67, respectively). Penile NOS activity assayed by the L-arginine/citrulline conversion was decreased by 55% in the castrated group compared with that in the intact group, but was not further reduced in the adrenalectomized/castrated or adrenalectomized groups. Penile neuronal NOS protein content, estimated by Western blot, was decreased only in the adrenalectomized/castrated animals (35%), and endothelial NOS content was not affected. These data suggest that the rat adrenal gland contributes to the maintenance of the erectile mechanism and may affect neuronal NOS content in the penis in the rat model. The possibility that hypotension may play a role in the erectile dysfunction observed in adrenalectomized rats cannot be discarded.

Adrenal Glands↗
PubMed1997

Effect of long-term passive smoking on erectile function and penile nitric oxide synthase in the rat.

PURPOSE: Given that smoking is a risk factor for erectile dysfunction, this study aimed to determine, in a rat model, whether long-term exposure to cigarette smoke impairs nitric oxide (NO)-dependent erectile function and reduces penile nitric oxide synthase (NOS), and if these changes are accompanied with effects on the systemic blood pressure. MATERIALS AND METHODS: Adult (5 month) and old (20 month) rats were exposed to daily passive smoking for 8 wks. Three days after the conclusion of exposure, half of the animals were submitted to electrical field stimulation (EFS) of the cavernosal nerve and the maximum intracavernosal pressure (MIP) and mean arterial pressure (MAP) were determined and expressed as mm. Hg. On the other half of the animals, NOS activity in the penile cytosol was measured by the arginine/citrulline assay, and neuronal NOS (nNOS) and endothelial NOS (eNOS) contents were estimated by western blot and densitometry. RESULTS: When compared to controls, the smoking rats had a higher MAP in both the adult (115 vs 162) and old (113 vs 140) rats, but surprisingly the MIP also increased, from 78 to 111 (adult rats) and from 59 to 83 (old rats). Smoking reduced penile NOS activity by 73% (adult rats), and 62% (old rats), and nNOS content by 43% and 50%, respectively. In contrast, eNOS was not affected. Nitrite release, in vitro, by cavernosa slices or in rat penile smooth muscle cells (RPSMC) was not inhibited by nicotine or cotinine. CONCLUSION: These results indicate that chronic smoking in the rat leads to age-independent moderate hypertension and considerable decreases in penile NOS activity and nNOS content, that are not reflected in a reduction of the erectile response to EFS or accompanied by a decrease in penile eNOS.

Age Factors↗
PubMed1996

Specific cleavage of recombinant protein tau3 between valine-220 and tyrosine-221 (val-309 and tyr-310 of tau4) by a double-stranded DNA-stimulated protease.

The protein tau was degraded to distinct products by a DNA-stimulated protease isolated from human leukemia HL-60 cell extracts. The enzyme partially purified by sequential chromatography on GTP-agarose, DEAE-cellulose, and TSK 3000 (0.6 X 60 mm) columns eluted as a 300-450 kDa protein which appeared as 60-90 kDa polypeptides on SDS-PAGE. Protease activity was stimulated by synthetic and natural DNAs and was most active at pH 8.5. Human recombinant tau3 was degraded by the DEAE-cellulose-eluted protease to a 26-kDa and several 14- to 16-kDa peptides. Degradation of tau was partially blocked by preincubation with tubulin, suggesting that the DNA-stimulated cleavage of tau occurred at the carboxyl-terminus, at or near the "tubulin-interactive" domains. The 26-kDa fragment was shown by amino acid sequencing to correspond to the N-terminus of tau whereas sequencing of the 16-kDa fragment yielded YKPVDLSKVT. These results show the existence of a DNA-stimulated protease capable of cleaving tau3 between valine-220 and tyrosine-221 (equivalent to valine 309 and tyrosine-310 of tau4).

Amino Acid Sequence↗
PubMed1996

Effects of IFN-beta and 1,25-dihydroxyvitamin D3 on cellular proliferation, induction of 2',5'-oligoadenylate (2-5A) synthetase and changes in immunoreactive pRB/p53 in human prostatic JCA-1 cells.

The combined antimitogenic effects of IFN-beta and 1,25-dihydroxyvitamin D3 (vit. D3) were investigated by treating the androgen-independent JCA-1 cells, established from the primary prostatic tumor site prior to anti-hormonal therapy, with IFN-beta (1000 IU/ml), vit. D3 (100 nM), and both agents. Cell growth, changes in overall RNA and protein contents, and cell cycle regulatory proteins pRB/p53 were determined. After a 24 h exposure, a significant reduction in cell proliferation was observed in all three conditions. IFN-beta, vit D3, and their combination elicited, respectively, a 1.7-, 1.6- and 2.5-fold increase in total RNA and a corresponding 1.4-, 1.2- and 1.7-fold increase in soluble proteins. The IFN-inducible 2-5A synthetase activity was elevated by 15-, 1.4- and 21-fold, respectively. No differences in cell cycle phase distribution were found between control and treated samples. However, a significant change in pRB and p53 expression was observed upon exposure to these agents. A progressive increase in total pRB was observed in untreated JCA-1 cells, with the 48 h culture showing a 1.9-fold increase over the 6 h culture. The ratio of phosphorylated to the nonphosphorylated forms of pRB, however, decreased from 3.00 at 6 h to 1.2 at 48 h. The overall pRB increase as well as the modified:unmodified protein ratio change were both markedly decreased when the cells were treated with IFN-beta, vit. D3, or their combination. With p53, a similar progressive increase was also observed in control cells, which was largely abolished by IFN-beta but only partially blocked by vit. D3. The combination of IFN-beta and vit. D3 gave results similar to samples receiving vit. D3 alone suggesting that the effects of IFN-beta, insofar as p53 modulation is concerned, is distal to the effects of vit. D3.

2',5'-Oligoadenylate Synthetase↗
PubMed1996

Androgen and pituitary control of penile nitric oxide synthase and erectile function in the rat.

Castration of adult male rats reduces by half the penile erectile response to electrical field stimulation (EFS) of the cavernosal nerve, and the activity of penile nitric oxide synthase (NOS). Both changes are prevented by androgen administration. We have now investigated whether other strategies of androgen ablation or competition may act as stronger inhibitors, and, if so, whether the stronger inhibition is due to the depletion of penile NOS content. Rats were castrated or left intact and were treated daily as follows: 1) intact, with the antiandrogen flutamide (25 mg/kg/day, i.p.); 2) castrated, with similar treatment; 3) castrated, with 17 beta-estradiol 3-benzoate (estradiol; via silastic tubing, s.c.). Additional groups of intact rats received injections of a GnRH antagonist (GnRHA, 1.25 mg/kg, s.c.), or were hypophysectomized and left untreated. Controls were untreated intact and castrated animals. After 7 days, rats were subjected to EFS, and the ratios between maximal intracavernosal pressure (MIP) and mean arterial pressure (MAP) were measured. Penile NOS activity and the contents of neuronal NOS (nNOS) and endothelial NOS (eNOS) were determined. Castration reduced the MIP:MAP ratio and penile NOS activity. Androgen receptor blockade with flutamide induced a similar response in intact rats. When flutamide treatment was combined with castration, the erectile response was nearly abolished, but NOS activity was not decreased below the values in castrated rats. Estradiol given to castrated rats and hypophysectomy or GnRHA treatment in intact rats diminished the erectile response below the level in castrated animals. In hypophysectomized rats, penile NOS activity fell below levels in castrated animals. contents of nNOS and eNOS were not significantly reduced by any treatment. These data suggest that penile erection in the rat is completely dependent on androgens, presumably because of their role in the maintenance of penile NOS activity and of other ancillary factors. However, only the complete blockade of residual androgen effects at the tissue level or a total androgen depletion can abolish the erectile response.

Androgen Antagonists↗
PubMed1996

Cavernosal nerve stimulation in the rat reverses castration-induced decrease in penile NOS activity.

Castration in the rat reduces both the erectile response and penile nitric oxide synthase (NOS) activity, and these effects are prevented by androgen administration. In this study we determined that the decrease of penile NOS in the castrated rat is due to NOS enzyme inhibition rather than to a reduction of its content and that this inhibition may be reversed. Adult rats were either castrated or left intact, and, after 1 wk, electrical field stimulation (EFS) was applied to the cavernosal nerve and the penises were excised either at the peak of erection or after detumescence. Penile NOS activity in the non-EFS castrates decreased by 70% as compared with the intact non-EFS-treated controls, but neuronal NOS content remained unaffected despite changes in regional distribution. NOS activity in the castrated penis was restored to normal values by EFS at the peak of stimulation, and then decreased on detumescence. This was in contrast to the intact controls in which EFS did not stimulate penile NOS activity. These data indicate that androgen depletion in the rat reduces penile NOS activity rather than NOS content and that this enzyme inhibition is reversed by cavernosal nerve stimulation.

Animals↗
PubMed1996

Autoregulation of myocardial glycogen concentration during intermittent hypoxia.

During hypoxia, the heart consumes glycogen to generate ATP. Tolerance of repetitive hypoxia logically requires prompt replenishment of glycogen, a process whose regulation is not fully understood. To examine this, we imposed a defined hypoxic stimulus on the rat heart while varying its workload. In intact rats, hypoxia reduced myocardial glycogen approximately 30% and increased both the fraction of glycogen synthase in its physiologically active (GS I) form (from 0.24 +/- 0.06 to 0.82 +/- 0.07; P < 0.005) and glycogen synthesis (from 0.087 +/- 0.011 to 0.375 +/- 0.046 mumol.g-1.min-1; P < 0.005). Reducing cardiac work (with propranolol or heterotopic transplantation) reduced glycogen breakdown, glycogen synthase activation, and glycogen synthesis in parallel, stepwise fashion in intact rats. Correspondingly, hypoxia increased GS I activity in the perfused heart in vitro, but only under conditions where glycogen was consumed. This suggests myocardial glycogen synthase is activated by systemic hypoxia and catalyzes rapid posthypoxic glycogen synthesis. Hypoxic glycogen synthase activation appears to be a proportionate, wholly intrinsic response to local glycogenolysis, operating to preserve myocardial glycogen stores independent of any extracardiac mediator of carbohydrate metabolism.

Animals↗
PubMed1995

Effects of 5 alpha-dihydrotestosterone (DHT) on the transcription of nm23 and c-myc genes in human prostatic LNCaP cells.

Proliferation of the androgen-dependent human prostate LNCaP cells was increased by the androgen DHT. Changes in the steady state level of the nm23 and c-myc mRNA in LNCaP cells, with or without 10 nM DHT, showed the nm23 mRNA to change rapidly, beginning to rise after 2 h and reaching its peak by 4 h of DHT treatment. In contrast, increases in the c-myc gene only became apparent after 4 h of treatment. Maximal increase of nm23 mRNA was observed at 10(-9) M DHT. The basal expression of c-myc and nm23 mRNAs was between 30-70% lower in the LNCaP cells, as compared with the androgen-independent PC-3 and JCA-1 human prostatic human carcinoma cells. Thus nm23 may be classified as a member of the early androgen-responsive genes.

Cell Division↗
PubMed1995

Treatment of hepatitis B surface antigen carriers in the early stage of the infection using recombinant alpha-interferon with steroid priming.

BACKGROUND: Alpha-interferon has been found to inhibit hepatitis B virus (HBV) replication in Chinese patients with chronic HBV infection although a sustained effect was rarely achieved in those with normal pretreatment serum alanine amino transferase (ALT) levels. Prednisolone priming has been found to be beneficial over treatment with interferon alone in these subjects. We studied the effect of steroid pre-treatment followed by recombinant interferon alpha-2a in the treatment of asymptomatic HBV carriers with positive hepatitis Be antigen (HBeAg), hepatitis B viral DNA (HBV-DNA) and minimal changes in liver histology. METHODS: The treatment regimen included a 6-week prednisolone priming, a 2 week rest followed by 14 weeks of three times weekly 9 mega units of interferon alpha-2a injection and 52 weeks of follow-up. There were seven patients in the treatment group and seven controls. RESULTS: The mean age, pre-treatment ALT (normal in all except for one in each of the treatment and control groups), HBV-DNA levels and histological scores were similar in the two groups. Serum HBV-DNA levels fell in six patients during treatment and became undetectable in two of them by the end. During follow-up, serum HBV-DNA returned to pre-treatment levels in all patients. None of the treated patients had HBeAg sero-conversion and none of the controls had spontaneous clearance of HBV-DNA or sero-conversion of HBeAg. No improvement of liver histology was observed in any of the treated patients. There were only mild flu-like side-effects noted and interferon alpha-2a was well tolerated at the doses given among treated patients. CONCLUSION: Prednisolone priming followed by interferon alpha-2a treatment has no beneficial effect on HBV carriers in the early stages of chronic hepatitis B infection.

Adult↗
PubMed1995

The synthetic retinoid N-(4-hydroxyphenyl) retinamide (4-HPR) exerts antiproliferative and apoptosis-inducing effects in the androgen-independent human prostatic JCA-1 cells.

A significant reduction in JCA-1 cell proliferation was observed as a result of treatment with 4-HPR. This was accompanied by the down-regulated expression of the proliferating cell nuclear antigen PCNA, cyclins D and E, and p34cdc2. Unexpectedly, p53 and pRB was also suppressed in response to 4-HPR. A prolonged exposure to 4-HPR (6 days) promoted the appearance of non-adherent cells showing morphological features and DNA fragmentation patterns indicative of apoptosis.

Androgens↗
PubMed1995

Immunogenicity and safety of an inactivated hepatitis A vaccine amongst Singaporeans.

The immunogenicity and reactogenicity of an inactivated hepatitis A virus (HAV) vaccine was studied in healthy Singaporean adult volunteers. One hundred and forty healthy volunteers with normal alanine (ALT) and aspartate (AST) transaminases and no previous exposure to HAV, received three 1 ml doses (720 ELISA units) of an inactivated HAV vaccine (Smithkline Beechams Biologicals) following a 0, 1, 6 months vaccination schedule. All subjects were asked to record and grade the severity of any reactions for three consecutive days after each dose. Serum ALT and AST as well as anti-HAV were measured at 0, 1, 2, 6 and 7 months after the first vaccine dose. Anti-HAV seroconversion occurred when levels rose above 40 mIU/ml. Eighty-five percent of vaccinees seroconverted after the first innoculation and 99% after the second injection. All vaccinees seroconverted after the third dose. Geometric mean anti-HAV titers (GMTs) were, respectively, 119, 391, 4406 mIU/ml one month after each of the three doses. The most common side effect was transient pain and tenderness at the vaccination site. No elevation of ALT or AST levels were noted during the study period. The inactivated hepatitis A vaccine used in this study is safe and highly immunogenic in the local adult population. Two doses one month apart appeared to give adequate protection.

Adult↗
PubMed1994

Cyclooxygenase gene expression in human endometrium and decidua.

The objective of this study was to determine if genes for cyclooxygenase (COX) and 5-lipoxygenase, key enzymes in the synthesis of eicosanoids, are expressed in human endometrium and to determine if the level of expression is affected by decidualization or preeclampsia, a form of pregnancy-induced hypertension. RT-PCR was used to detect mRNA in tissues obtained from various patients. Results demonstrated that COX and 5-lipoxygenase genes are expressed in endometrium and decidua. COX gene expression in endometrium is 2-3-fold greater than in decidua while 5-lipoxygenase gene expression is similar. Neither COX nor 5-lipoxygenase gene expression in decidua is altered by changes resulting from preeclampsia. Thus, genes for key enzymes in the synthesis of eicosanoids are expressed in human endometrium and decidua. Selective down-regulation is evident as decidualization results in a significant reduction in the gene expression of COX, while 5-lipoxygenase gene expression remains unchanged.

Arachidonate 5-Lipoxygenase↗
PubMed1994

An analysis of referral routes and diagnostic accuracy in cases of suspected glaucoma.

Over a nine-month period two hundred and thirteen referrals to the Department of Ophthalmology of the Leicester Royal Infirmary, England, for suspicion of glaucoma were examined by a single ophthalmologist. Ninety-nine percent of referrals resulted from the findings at an optometric visit. Despite this, less than 32% were confirmed as having glaucoma and less than 23% had ocular hypertension. Twenty-nine percent showed no abnormality. Of those with glaucoma 19% showed advanced field loss in their worse eye. The guidelines relating to referral practices as a result of optometric examinations need to be reviewed and agreed upon by ophthalmologists, optometrists and general practitioners.

Adult↗
PubMed1993

Can a divided digital nerve on one side of the finger be left unrepaired?

72 fingers with divided digital nerves on one side alone had their nerves repaired and the sensory recovery assessed at different intervals of up to 2 years. Another 36 fingers with similar digital nerve injuries had their divided nerves left unrepaired and sensory recovery similarly assessed for comparison. In the "repaired" group, the result continued to improve and by 2 years, 90% reached S3+ or above. In the "unrepaired" group, improvement plateaued after 6 months, and at 2 years only 6% reached S3+ or above, although all had regained some protective sensibility.

Adolescent↗