Search PubMed⌕ Search

Biomedical subjects

G Chen

Publications and source records attributed to G Chen.

At least 613 records · Page 34Linked to original sources
PubMed1996

Antisense oligonucleotides demonstrate a dominant role of c-Ki-RAS proteins in regulating the proliferation of diploid human fibroblasts.

Although members of the RAS protein family (Ha-, Ki-, and N-RAS) are known to play a key role in normal cell proliferation and to be frequently mutated in naturally occurring tumors, it remains unclear which of these proteins functions to regulate growth in normal cells. Gene-specific oligonucleotides (oligos) against c-Ki-RAS (ISIS 6957), c-Ha-RAS (ISIS 2503), and oncogenic Ha-RAS (ISIS 2570) were used to analyze the requirement for individual RAS proteins in the proliferation of diploid human lung fibroblasts (MRC-5), and human bladder carcinoma cell lines with (T24) or without (J-82) a RAS mutation. The oncogenic Ha-RAS oligo substantially inhibited T24 cell proliferation, whereas the c-Ki-RAS and control (ISIS 1966) oligos had little effect. Interestingly, in MRC-5 cells the c-Ki-RAS but not c-Ha-RAS oligo was effective in inhibiting cell proliferation. No inhibition was seen in the J-82 cells with either oligo. In Western analysis, p21 RAS protein was decreased following treatment with the oncogenic Ha-RAS oligo in T24 cells or the c-Ki-RAS oligo in MRC-5 cells, whereas no reductions were observed in J-82 cells with either oligo. The specificity of these oligos was demonstrated in Northern analyses in which both Ha-RAS and Ki-RAS oligo treatment resulted in reduced levels of their respective mRNAs in all three cell lines, whereas the mutant Ha-RAS mRNA in T24 cells was most effectively reduced with the oncogenic Ha-RAS oligo. These results demonstrate that oncogenic Ha-RAS plays an important role in the proliferation of T24 cells, whereas c-Ki-RAS contributes predominantly to the proliferation of normal MRC-5 cells.

Cell Division↗
PubMed1996

Local control in synchronous bilateral Wilms tumor.

PURPOSE: To evaluate the role of radiation therapy (RT), chemotherapy (CT), and surgery in the local control of synchronous bilateral Wilms Tumor (WT). METHODS AND MATERIALS: Between 1962 to 1993, 45 children were treated for bilateral WT; 38 patients with synchronous tumors were reviewed. Initial surgery depended on the era of treatment and included unilateral nephrectomy (N)/partial nephrectomy (PN) and contralateral PN in 6, unilateral N/PN alone in 7, and biopsy only in 25. Chemotherapy (CT) consisted of vincristine, actinomycin-D, and adriamycin in 32 and vincristine/ actinomycin-D in 6. Radiation therapy (RT) was given to 32 patients. Treatment included both kidneys in 20, unilateral kidney plus contralateral renal bed in 9, unilateral kidney in 2, and unilateral renal bed in 1. Follow-up was 16 months to 25 years (median: 6.3 years). RESULTS: Local control (LC) has been maintained in 66 out of 76 sites (87%). For Stage I-II disease with initial N/PN, LC was 10 out of 12 with RT and 11 out of 11 without RT; for Stage III with initial N/PN, LC was 8 out of 9 with RT and 1 out of 1 without RT. Initial CT and RT was followed by delayed N/PN for 20 sites; LC was 15 out of 17 in post induction Stage I-II and 1 out of 3 in postinduction Stage III. In 23 sites undergoing biopsy and chemotherapy, LC was 19 out of 20 with RT and 1 out of 3 without RT. Seven of 23 sites had a complete response (CR) after induction CT, and LC was maintained in four out of four with RT and one out of three without RT. Univariate Cox Regression analysis demonstrated that sites receiving two drugs had a statistically significant increase in loco-regional relapse when compared to sites receiving three drugs (p = 0.004). Major morbidities related to multimodality therapy have included renal failure in one patient and small bowel obstruction requiring lysis of adhesions in two patients. CONCLUSIONS: Local control does not seem to be compromised by renal conservation therapy. Local control is excellent in sites treated with radiation therapy in combination with three drug chemotherapy.

Adolescent↗
PubMed1996

Activation of an interleukin 1 converting enzyme-dependent apoptosis pathway by granzyme B.

Cytotoxic T lymphocytes (CTL) can induce apoptosis through a granzyme B-based killing mechanism. Here we show that in cells undergoing apoptosis by granzyme B, both p45 pro-interleukin 1 beta converting enzyme (ICE) and pro-CPP32 are processed. Using ICE deficient (ICE -/-) mice, embryonic fibroblasts exhibit high levels of resistance to apoptosis by granzyme B or granzyme 3, while B lymphoblasts are granzyme B-resistant, thus identifying an ICE-dependent apoptotic pathway that is activated by CTL granzymes. In contrast, an alternative ICE-independent pathway must also be activated as ICE -/- thymocytes remain susceptible to apoptosis by both granzymes. In ICE -/- B cells or HeLa cells transfected with mutant inactive ICE or Ich-1S that exhibit resistance to granzyme B, CPP32 is processed to p17 and poly(ADP-ribose) polymerase is cleaved indicating that this protease although activated was not associated with an apoptotic nuclear phenotype. Using the peptide inhibitor Ac-DEVD-CHO, apoptosis as well as p45 ICE hydrolysis are suppressed in HeLa cells, suggesting that a CPP32-like protease is upstream of ICE. In contrast, p34cdc2 kinase, which is required for granzyme B-induced apoptosis, remains inactive in ICE -/- B cells indicating it is downstream of ICE. We conclude that granzyme B activates an ICE-dependent cell death pathway in some cell types and requires a CPP32-like Ac-DEVD-CHO inhibitable protease acting upstream to initiate apoptosis.

Animals↗
PubMed1996

Adenovirus E1B 19-kDa death suppressor protein interacts with Bax but not with Bad.

Adenovirus E1B 19-kDa protein (19K) is a member of the Bcl-2 family of suppressors of apoptosis. The suppressors function through heterodimerization with the death promoters, Bax and related proteins, thus establishing a set point within the cell that determines whether or not apoptosis is executed in response to a death signal. Sequence similarities between 19K and Bcl-2 are largely restricted to short Bcl-2 homology (BH) domains that mediate interaction with Bax. The BH1 sequence in 19K is degenerate but nevertheless contains a conserved glycine residue found in all family members that when mutated to alanine in Bcl-2 results in loss of Bcl-2 function and ability to dimerize with Bax (Yin, X.-M., Oltvai, Z. N., and Korsmeyer, S. J. (1994) Nature 369, 321-323). Here, we show that the analogous mutation in BH1 of 19K also abrogates the anti-apoptotic properties of 19K and its ability to interact with Bax, thus establishing the critical importance of this residue within BH1 and the likely similarity of Bcl-2 and 19K function. In distinct contrast to Bcl-2, however, 19K interaction was not detected with Bad, a Bcl-2/Bcl-XL dimerizing protein that can potentially regulate a Bax middle dotBcl-2/Bcl-XL survival set point and reinstate susceptibility to a death signal. Furthermore, the anti-apoptotic function of 19K was not overcome by enforced expression of Bad in transfected cells. This feature of 19K may provide adenovirus with a selective advantage in evading premature induction of apoptosis by the host cell.

Adenovirus E1B Proteins↗
PubMed1996

Neuropeptide Y-mediated long-term depression of excitatory activity in suprachiasmatic nucleus neurons.

A brief exposure to light can shift the phase of mammalian circadian rhythms by 1 hr or more. Neuropeptide Y (NPY) administration to the hypothalamic suprachiasmatic nucleus, the circadian clock in the brain, also causes a phase shift in circadian rhythms. After a phase shift, the neural clock responds differently to light, suggesting that learning has occurred in neural circuits related to clock function. Thus, certain stimuli can produce effects that last for an extended period, but possible mechanisms of this long-term effect have not been previously examined at the cellular level. Here, we report that NPY caused a long-term depression in both electrical activity and intracellular calcium levels of neurons, as studied with whole-cell patch-clamp recording and Fura-2 digital imaging. In contrast to the immediate (1 sec) recovery after relief from glutamate receptor blockade, a brief single application of NPY (100 nM) depressed cytosolic Ca2+ for > 1 hr. The mechanism of this long-term calcium depression, a form of cellular learning, is dependent on the simultaneous release of glutamate and activation of NPY receptors, because both the extended response to NPY and any aftereffect were blocked by coapplication of glutamate receptor antagonists. Postsynaptic actions of NPY, mediated by both Y1- and Y2-like receptors, were short term and recovered rapidly. The primary site of long-term NPY actions may be on presynaptic glutamatergic axons, because the frequency of miniature excitatory postsynaptic currents in the presence of tetrodotoxin was reduced by transient exposure to NPY in both cultures and slices.

Animals↗
PubMed1996

Granzyme B induces apoptosis and cyclin A-associated cyclin-dependent kinase activity in all stages of the cell cycle.

Granzyme B rapidly induces apoptosis in the presence of the pore-forming protein perforin. We have examined the cell cycle restriction of this apoptosis by separating Jurkat cells into fractions representing different stages of the cell cycle by centrifugal elutriation. Cells were susceptible to apoptosis from G1 through to G2/M, with no significant resistance detected at any stage. Similarly, cells arrested at G1/S or G2/M with either hydroxyurea or nocodazole were slightly more sensitive than asynchronously growing cells. Granzyme B induces Cdc2 kinase activity and requires its induction for apoptosis. Cyclin-dependent kinase (CDK) activity is regulated by phosphorylation and association with cyclins that also control subcellular localization of the CDK/cyclin complexes. Cdc2 associates with both cyclin A, which is synthesized at G1 and S, and cyclin B, which is produced later during S and G2 before G2/M transition. We find that the CDK activity induced by granzyme B is associated primarily with cyclin A in both asynchronous and G1/S-arrested cells, while cyclin B-associated kinase activity is minimal. Because cyclin A is also able to associate with Cdk2, a kinase that is important for G1/S transition, we examined the activation of this CDK during granzyme B-induced apoptosis and find that Cdk2 is induced as rapidly as Cdc2. In conclusion, we have identified a lack of cell cycle restriction of granzyme B-induced apoptosis and the rapid activation of both cyclin A/Cdc2 and cyclin A/Cdk2 kinase activity.

Apoptosis↗
PubMed1996

Electrochemical monitoring of bursting exocytotic events from the giant dopamine neuron of Planorbis corneus.

We have discovered a neuronal system that fires bursting exocytotic events. In the giant dopamine neuron of the fresh water snail Planorbis corneus, bursting exocytotic events are evoked following in situ stimulation with elevated potassium. Amperometric detection using carbon fiber microelectrodes, which provides high temporal resolution, has been used to record exocytotic events released from the neuron. Evaluation of the time interval between consecutive exocytotic events (inter-spike interval) recorded from about 80% of the neurons reveals the occurrence of distinct bursting patterns defined by transients having an equal interval among them. Statistical analysis of these bursting exocytotic events shows three distinct distributions of inter-spike intervals with mid points occurring at 5, 22 and 45 ms. This bursting release behavior is not observed from cultured pheochromocytoma cells although they show calcium-dependent exocytosis following in situ stimulation with elevated potassium. Our data appear to indicate that the Planorbis dopamine neuron in vivo is actively involved in specific modes of neural communication and may represent an important phenomenon in understanding single cell activities.

Action Potentials↗
PubMed1996

Granulocyte-macrophage colony-stimulating factor preferentially activates the 94-kD STAT5A and an 80-kD STAT5A isoform in human peripheral blood monocytes.

Granulocyte-macrophage colony-stimulating factor (GM-CSF) induces immediate effects in monocytes by activation of the Janus kinase (JAK2) and STAT transcription factor (STAT5) pathway. Recent studies have identified homologues of STAT5, STAT5A, and STAT5B, as well as lower molecular weight variants of STAT5. To define the activation of the STAT5 homologues and lower molecular weight variant in human monocytes and monocytes differentiated into macrophages by culture in macrophage-CSF (M-CSF), we measured the GM-CSF induced tyrosine phosphorylation of STAT5A, STAT5B, and any lower molecular weight STAT5 isoforms. Freshly isolated monocytes expressed 94-kD STAT5A, 92-kD STAT5B, and an 80-kD STAT5A molecule. Whereas 94-kD STAT5A was clearly tyrosine phosphorylated and bound to the enhancer element, the gamma response region (GRR), of the Fc gamma RI gene, substantially less tyrosine phosphorylated STAT5B bound to the immobilized GRR element. Macrophages lost their ability to express the 80-kD STAT5A protein, but retained their ability to activate STAT5A. STAT5A-STAT5A homodimers and STAT5A-STAT5B heterodimers formed in response to GM-CSF. Therefore, activation of STAT5A predominates compared to STAT5B when assayed by direct immunoprecipitation and by evaluation of bound STATs to immobilized GRR. Selective activation of STAT5 homologues in addition to generation of lower molecular isoforms may provide specificity and control to genes expressed in response to cytokines such as GM-CSF.

Cells, Cultured↗
PubMed1996

Excitatory actions of GABA in developing rat hypothalamic neurones.

1. Gramicidin-perforated patch clamp recording was employed to study GABA-mediated responses in rat hypothalamic neurones (n = 102) with an intracellular Cl- concentration unaltered by the pipette solution. 2. In young cultures after 1-7 days in vitro (DIV), GABA induced depolarizing membrane potentials (+16.5 +/- 1.3 mV) that often surpassed the threshold for the firing of action potentials (-42 +/- 1 mV) and resulted in an increase in neuronal activity. The depolarizing responses to GABA in young cultures were dose dependent. The concentration of GABA necessary to evoke the half-maximal depolarization (EC50) was 2.8 microM. In contrast, GABA induced hyperpolarizing membrane potentials (-12.0 +/- 1.4 mV) and a decrease in neuronal activity in older neurones (20-33 DIV). Both the depolarization and the hyperpolarization induced by GABA were blocked by bicuculline, indicating a mediation by GABAA receptors. 3. The reversal potentials of the GABA-evoked currents were between -40 to -50 mV during the first week of culture, and shifted to below -70 mV after 3 weeks of culture. In parallel, neurones that were dissociated from older animals (postnatal day 5) had a more negative reversal potential for the GABA-evoked currents than cells from younger animals (embryonic day 15), suggesting that the negative shift of the reversal potential occurs both in vitro and in vivo. Our data suggest that the mechanism for GABA-induced depolarization is the depolarized Cl- reversal potential found in young but not older neurones. 4. Consistent with the depolarizing response to exogenous application of GABA, some spontaneous depolarizing postsynaptic potentials in young cultures were insensitive to AP5-CNQX, but were eliminated by bicuculline, indicating that synaptically released GABA mediated excitatory synaptic transmission in early development. 5. By combining a rapid computer-controlled delivery of GABA with subthreshold positive current injections into recorded neurones, we found in young cultures that the GABA-evoked depolarization could directly trigger action potentials, facilitate some depolarizing input to fire action potentials, and shunt other depolarizing input. Whether the GABA-induced depolarization is excitatory or inhibitory would be determined by the reversal potential of the GABA-evoked current, and the temporal relationship between GABA-evoked depolarizations and other excitatory events. 6. We conclude that the reversal potential of the GABA-evoked current shifts negatively from depolarizing to hyperpolarizing in developing hypothalamus. Consequently, GABA neurotransmission may serve both excitatory and inhibitory roles during early development.

Action Potentials↗
PubMed1996

Excitatory actions of GABA after neuronal trauma.

GABA is the dominant inhibitory neurotransmitter in the CNS. By opening Cl- channels, GABA generally hyperpolarizes the membrane potential, decreases neuronal activity, and reduces intracellular Ca2+ of mature neurons. In the present experiment, we show that after neuronal trauma, GABA, both synaptically released and exogenously applied, exerted a novel and opposite effect, depolarizing neurons and increasing intracellular Ca2+. Different types of trauma that were effective included neurite transection, replating, osmotic imbalance, and excess heat. The depolarizing actions of GABA after trauma increased Ca2+ levels up to fourfold in some neurons, occurred in more than half of the severely injured neurons, and was long lasting (>1 week). The mechanism for the reversed action of GABA appears to be a depolarized Cl- reversal potential that results in outward rather than inward movement of Cl-, as revealed by gramicidin-perforated whole-cell patch-clamp recording. The consequent depolarization and resultant activation of the nimodipine sensitive L- and conotoxin-sensitive N-type voltage-activated Ca2+ channel allows extracellular Ca2+ to enter the neuron. The long-lasting capacity to raise Ca2+ may give GABA a greater role during recovery from trauma in modulating gene expression, and directing and enhancing outgrowth of regenerating neurites. On the negative side, by its depolarizing actions, GABA could increase neuronal damage by raising cytosolic Ca2+ levels in injured cells. Furthermore, the excitatory actions of GABA after neuronal injury may contribute to maladaptive signal transmission in affected GABAergic brain circuits.

Animals↗
PubMed1996

Selected Elastic Moduli of Single-Crystal Olivines from Ultrasonic Experiments to Mantle Pressures

Ultrasonic interferometric measurements, developed for polycrystalline samples in a multi-anvil apparatus, were extended to single-crystal samples of San Carlos olivine and forsterite. The elastic moduli, C22 and C55 of San Carlos olivine and C55 of pure forsterite, were measured to about 13 gigapascals. These data on C22 for San Carlos olivine and C55 for forsterite are consistent with earlier measurements and extrapolations. The C55 for San Carlos olivine increases linearly as a function of increasing pressure, unlike the earlier nonlinear behavior observed at high pressure with impulsive stimulated scattering techniques.

Journal Article↗
PubMed1996

Camptothecin post-treatments inhibit the biochemical events linked to the tumor-promoting component of carcinogenesis in mouse epidermis in vivo.

20(S)-Camptothecin (CPT), a topoisomerase I inhibitor specifically toxic toward S-phase cells, was tested topically for its ability to inhibit the biochemical markers of skin tumor promotion. CPT has no or very little inhibitory effect on the covalent binding of an initiating dose of 7,12-dimethylbenz-[a]anthracene (DMBA) to DNA at 24 hr, but CPT post-treatments remarkably inhibit stimulations of DNA synthesis caused by the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) at 16 hr and a carcinogenic dose of DMBA at 7 days. CPT is a much more potent inhibitor if it is applied 10-14 hr after TPA or 4-6 days after DMBA, when DNA synthesis starts being stimulated after the periods of early inhibition caused by TPA and DMBA. When applied 12 hr after the tumor promoter, the ability of 3-3,000 nmol of CPT to inhibit TPA-stimulated DNA synthesis at 16 hr is dose-dependent. A single dose of 500 nmol of CPT inhibits the entire time course for the stimulation of DNA synthesis observed 16-64 hr after TPA. CPT also reduces the various DNA responses to chronic TPA treatments and structurally different non-TPA-type tumor promoters. CPT may indirectly decrease the ornithine decarboxylase-inducing activity of multiple TPA treatments because it can inhibit the stimulation of RNA synthesis by this compound. However, CPT fails to alter TPA-stimulated hydroperoxide production in relation to its inability to inhibit TPA-stimulated protein synthesis. On an equal dose basis, topotecan and 10-hydroxycamptothecin are more and less effective than CPT, respectively, whereas 10,11-methylenedioxycamptothecin is much more potent than its parent compound at inhibiting the DNA response to TPA. A single dose of 400 nmol of CPT has no effect on tumor initiation when applied 4 hr before or 1 hr after a single subcarcinogenic dose of DMBA. In contrast, 400 nmol of CPT chronically applied 1 hr before or 24 hr after each treatment with TPA remarkably inhibits the complete tumor-promoting activity of this agent. CPT post-treatments also inhibit the respective activities of TPA and mezerein in the 1st and 2nd stages of skin tumor promotion.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1996

Molecular cloning and developmental expression of mouse p130, a member of the retinoblastoma gene family.

With sequence homology to the SV40 T antigen-binding domain of the retinoblastoma protein (Rb), p107 and p130 constitute two additional members of the Rb family. To explore the potential function of p130 in mouse development, we cloned the full-length mouse cDNA for p130 and characterized p130 mRNA expression in mice. The deduced mouse p130 protein sequence shares a higher degree of similarity with mouse p107 than with mouse Rb. In adult mice, p130 mRNA is found in all tissues examined. Levels of p130 mRNA vary among different adult tissues, with the highest level in testis. Within testis, p130 mRNA is found predominantly in Leydig cells. Additionally, p130 expression in testis correlates with sexual maturation, suggesting p130 is important for the development of testis and, in particular, Leydig cells. In situ hybridization shows that in post coitus day 12.5 and 14.5 mouse embryos, distribution of p130 mRNA is quite uniform with the exception of a few tissues. Little differences in mRNA levels of either p130 or p107 were found between normal and Rb-deficient embryos, suggesting that p130 and p107 are expressed independently of Rb. Our data are consistent with the hypothesis that p130 and p107 do not compensate for the loss of Rb and support the view that p130 is related to, yet distinct from, the RB gene.

Aging↗
PubMed1996

Bcl-2 and adenovirus E1B 19 kDA protein prevent E1A-induced processing of CPP32 and cleavage of poly(ADP-ribose) polymerase.

The E1A oncoproteins of adenovirus type 5 are potent inducers of apoptotic cell death. To manifest growth promoting and transforming properties, therefore, E1A requires the co-expression of a suppressor of apoptosis. During normal viral infection, this function is provided by the E1B 19 kDa protein. However, the cellular suppressor Bcl-2 can substitute for 19K during infection, and both proteins can effectively cooperate with E1A to facilitate transformation of primary cells in culture. How E1A induces apoptosis and at what point(s) on this pathway Bcl-2 and E1B 19K act are not presently known. Here, we demonstrate that E1A-induced apoptosis is accompanied by specific endo-proteolytic cleavage of poly(ADP-ribose) polymerase (PARP), an event that is linked to the Ced-3/ICE apoptotic pathway in other systems. PARP cleavage was also observed in p53-null cells infected with 19K- virus expressing 13S E1A. In addition to PARP cleavage, expression of E1A caused processing of the zymogen form of CPP32, a Ced-3/ICE protease that cleaves PARP and is required for apoptosis in mammalian cells. These events were prevented when E1A was co-expressed with E1B 19K or BCL-2, which places these suppressors of apoptosis either at or upstream of processing of pro-CPP32.

Adenovirus E1A Proteins↗
PubMed1996

Ability of okadaic acid and other protein phosphatase inhibitors to mimic the stimulatory effects of 12-O-tetradecanoylphorbol-13-acetate on hydroperoxide production in mouse epidermis in vivo.

The non-12-O-tetadecanoylphorbol-13-acetate (TPA)-type tumor promoters, okadaic acid (OA) and calyculin-A (CAL-A), which neither interact with the phorbol ester receptor nor directly activate protein kinase C, mimic the stimulatory effects of and thapsigargin on hydroperoxide (HPx) production in mouse epidermis in vivo. The time course and dose dependency for the stimulation of HPx production by O and TPA are similar. HPx production is maximally stimulated 16 h after two applications of 2 nmol of OA at a 48-h interval. However CAL-A is a stimulator of HPx production about 4 times more potent than OA or TPA. Combinations of TPA and OA or CAL-A have subadditive effects on HPx production. The discrepancies between the abilities of various serine/threonine protein phosphatase (PP) inhibitors to stimulate HPx production suggest that PP inhibition alone is not sufficient for this response. Cycloheximide, Ca2+ antagonists, oxypurinol, diphenyliodonium, nordihydroguaiaretic acid, bromophenacyl bromide, antiinflammatory agents, and antihistamines block or decrease OA-stimulated HPx production. Although most of these inhibitors may have more than one action, their effects suggest that protein synthesis, Ca2+, xanthine oxidase and NADPH oxidase activities, the lipoxygenase pathway of arachidonic acid metabolism, and vascular permeability may be involved in the inflammatory and HPx responses that occur after tumor promoter treatment. The increased HPx-producing activity of the epidermis, therefore, may be a common event resulting from the inflammatory and tumor-promoting actions of diverse TPA- and non-TPA-type agents.

Animals↗
PubMed1996

Detection and identification of microcystins in the drinking water of Haimen City, China.

Cyanobacterial toxins, microcystins, have a potent tumor-promoting activity. We investigated the level of microcystins in drinking water collected from 1992 to 1994 in Haimen City, China, where people who drink pond ditch water usually incurred a high incidence rate of hepatocellular carcinoma compared with those who drink well water. High-performance liquid chromatography, liquid chromatography/mass spectrometry (LC/MS), and protein phosphatase inhibition assay (pp assay) were used to identify and quantify the microcystins. Microcystin LR and [D-Asp3]microcystin LR were detected in 2 of 50 samples at a concentration less than 100 ng/L by LC/MS in 1992. Although no microcystins were found by the chemical method in 1993, 6 of 7 samples except for 3 tap water samples showed an approximate amount of 100 ng/L by using the pp assay in 1994. The obtained results supported the epidemiological results reported by Yu.

Bacterial Toxins↗
PubMed1996

In-vivo activity and enzymatic hydrolysis of novel prostaglandin F2 alpha prodrugs in ocular tissues.

Enzymatic hydrolysis and in-vivo ocular studies were performed on a novel series of prostaglandin F2 alpha (PGF2 alpha) pivaloyl ester prodrugs to assess their therapeutic potential. These novel PGF2 prodrugs were esterified at the 9-, 11-, and 15-OH positions. Their enzymatic hydrolysis rates were compared to PGF2 alpha 1-isopropyl ester in dog, monkey, and human ocular tissues. Intraocular pressure (IOP) studies were performed in monkeys and dogs, and ocular surface hyperemia was monitored in dogs. PGF2 alpha 9-monopivaloyl ester was not enzymatically hydrolysed in dog and human ocular tissues. PGF2 alpha 11- and 15-monopivaloyl esters and PGF2 alpha 11,15-dipivaloyl ester were converted to PGF2 alpha by all ocular tissues at a substantially slower rate than PGF2 alpha l-isopropyl ester. Despite their slow enzymatic hydrolysis rates, the ocular hypotensive activity of PGF2 alpha mono and dipivaloyl esters, where positions 11- and 15- were functionalized, closely approached the activity achieved with PGF2 alpha l-isopropyl ester. The degree of ocular surface hyperemia associated with PGF2 alpha 11-pivaloyl ester and PGF2 alpha 11,15-dipivaloyl ester was less than that associated with equivalent doses of PGF2 alpha l-isopropyl ester. It appears that rapid enzymatic hydrolysis rates are not necessary to obtain efficacious ocular hypotensive PGF2 alpha ester prodrugs. Slow enzymatic hydrolysis rates may assist in reducing the degree of ocular surface hyperemia. A further contributory factor in this regard could be the approximately ten-fold favorable difference in enzymatic hydrolysis rates between iris-ciliary body and conjunctival tissue for these novel pivaloyl esters of PGF2 alpha. These factors appear to translate into an improved therapeutic index for separating ocular hypotensive and ocular surface hyperemic effects.

Animals↗