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Biomedical subjects

C Kent

Publications and source records attributed to C Kent.

At least 19 recordsLinked to original sources
PubMed1999

Bilateral acute retinal necrosis caused by cytomegalovirus in an immunocompromised patient.

PURPOSE: To report a case of bilateral acute retinal necrosis caused by cytomegalovirus. METHODS: A diagnostic vitrectomy was performed on a patient with non-Hodgkin lymphoma who presented with a bilateral, rapidly progressing necrotizing retinitis and uveitis. RESULTS: Immunohistochemical studies and polymerase chain reaction disclosed cytomegalovirus as the cause of retinitis. The patient was treated with intravitreal and intravenous ganciclovir. CONCLUSIONS: Although rare, cytomegalovirus may lead to an appearance identical to acute retinal necrosis and should be considered among the viral etiologies of this syndrome.

Antibodies, Viral↗
PubMed1998

Efficacy of risk-reduction counseling to prevent human immunodeficiency virus and sexually transmitted diseases: a randomized controlled trial. Project RESPECT Study Group.

CONTEXT: The efficacy of counseling to prevent infection with the human immunodeficiency virus (HIV) and other sexually transmitted diseases (STDs) has not been definitively shown. OBJECTIVE: To compare the effects of 2 interactive HIV/STD counseling interventions with didactic prevention messages typical of current practice. DESIGN: Multicenter randomized controlled trial (Project RESPECT), with participants assigned to 1 of 3 individual face-to-face interventions. SETTING: Five public STD clinics (Baltimore, Md; Denver, Colo; Long Beach, Calif; Newark, NJ; and San Francisco, Calif) between July 1993 and September 1996. PARTICIPANTS: A total of 5758 heterosexual, HIV-negative patients aged 14 years or older who came for STD examinations. INTERVENTIONS: Arm 1 received enhanced counseling, 4 interactive theory-based sessions. Arm 2 received brief counseling, 2 interactive risk-reduction sessions. Arms 3 and 4 each received 2 brief didactic messages typical of current care. Arms 1, 2, and 3 were actively followed up after enrollment with questionnaires at 3, 6, 9, and 12 months and STD tests at 6 and 12 months. An intent-to-treat analysis was used to compare interventions. MAIN OUTCOME MEASURES: Self-reported condom use and new diagnoses of STDs (gonorrhea, chlamydia, syphilis, HIV) defined by laboratory tests. RESULTS: At the 3- and 6-month follow-up visits, self-reported 100% condom use was higher (P<.05) in both the enhanced counseling and brief counseling arms compared with participants in the didactic messages arm. Through the 6-month interval, 30% fewer participants had new STDs in both the enhanced counseling (7.2%; P= .002) and brief counseling (7.3%; P= .005) arms compared with those in the didactic messages arm (10.4%). Through the 12-month study, 20% fewer participants in each counseling intervention had new STDs compared with those in the didactic messages arm (P = .008). Consistently at each of the 5 study sites, STD incidence was lower in the counseling intervention arms than in the didactic messages intervention arm. Reduction of STD was similar for men and women and greater for adolescents and persons with an STD diagnosed at enrollment. CONCLUSIONS: Short counseling interventions using personalized risk reduction plans can increase condom use and prevent new STDs. Effective counseling can be conducted even in busy public clinics.

Adolescent↗
PubMed1998

What about money? Effect of small monetary incentives on enrollment, retention, and motivation to change behaviour in an HIV/STD prevention counselling intervention. The Project RESPECT Study Group.

OBJECTIVES: We studied the effect of small monetary incentives and non-monetary incentives of similar value on enrollment and participation in clinic based HIV/STD prevention counselling. We examined incident STDs to try to assess whether participants offered money may be less motivated to change risky behaviours than those offered other incentives. METHODS: Patients from five US STD clinics were invited to enroll in a multisession risk reduction counselling intervention and, based on their enrollment date, were offered either $15 for each additional session or non-monetary incentives worth $15. The two incentive groups were compared on participants' enrollment, completion of intervention sessions, and new STDs over the 24 months after enrollment. RESULTS: Of 648 patients offered money, 198 (31%) enrolled compared with 160 (23%) of 696 patients offered other incentives (p = 0.002). Enrollees in the two incentive groups had similar baseline characteristics, including condom use. Of the 198 participants offered money, 109 (55%) completed all sessions compared with 59 (37%) of the participants offered other incentives (p < 0.0001). Comparing those offered money with those offered other incentives STD rates were similar after 6, 12, and 24 months. CONCLUSIONS: Small monetary incentives enhanced enrollment and participation compared with other incentives of similar value. Regardless of incentive offered, participants had similar post-enrollment STD rates, suggesting that the type of incentive does not adversely affect motivation to change behaviour. Money may be useful in encouraging high risk individuals to participate in and complete counselling or other public health interventions.

Adult↗
PubMed1997

CTP:phosphocholine cytidylyltransferase.

CTP:phosphocholine cytidylyltransferase (CCT) catalyzes the synthesis of CDP-choline and is regulatory for phosphatidylcholine biosynthesis. This review focuses on recent developments in understanding the catalytic and regulatory mechanisms of this enzyme. Evidence for the nuclear localization of the enzyme is discussed, as well as evidence suggesting cytoplasmic localization. A comparison of the catalytic domains of CCTs from a wide variety of organisms is presented, highlighting a large number of completely conserved residues. Work implying a role for the conserved HXGH sequence in catalysis is described. The membrane-binding domain in rat CCT has been defined, and the role of lipids in activating the enzyme is discussed. The identification of the phosphorylation domain is described, as well as approaches to understand the role of phosphorylation in enzyme activity. Other possible control mechanisms such as enzyme degradation and gene expression are presented.

Amino Acid Sequence↗
PubMed1997

Identification of functional conserved residues of CTP:glycerol-3-phosphate cytidylyltransferase. Role of histidines in the conserved HXGH in catalysis.

The CTP:glycerol-3-phosphate cytidylyltransferase (GCT) of Bacillus subtilis has been shown to be similar in primary structure to the CTP:phosphocholine cytidylyltransferases of several organisms. To identify the residues of this cytidylyltransferase family that function in catalysis, the conserved hydrophilic amino acid residues plus a conserved tryptophan of the GCT were mutated to alanine. The most dramatic losses in activity occurred with H14A and H17A; these histidine residues are part of an HXGH sequence similar to that found in class I aminoacyl-tRNA synthetases. The kcat values for H14A and H17A were decreased by factors of 5 x 10(-5) and 4 x 10(-4), respectively, with no significant change in Km values. Asp-11, which is found near the HXGH sequence in the cytidylyltransferases but not aminoacyl-tRNA synthetases, was also important for activity, with the D11A mutation decreasing activity by a factor of 2 x 10(-3). Several residues found in the sequence RTEGISTT, a signature sequence for this cytidylyltransferase family, as well as other isolated residues were also shown to be important for activity, with kcat values decreasing by factors of 0.14-4 x 10(-4). The Km values of three mutant enzymes, D38A, W74A, and D94A, for both CTP and glycerol-3-phosphate were 6-130-fold higher than that of the wild-type enzyme. Mutant enzymes were analyzed by two-dimensional NMR to determine if the overall structures of the enzymes were intact. One of the mutant enzymes, D66A, was defective in overall structure, but several of the others, including H14A and H17A, were not. These results indicate that His-14 and His-17 play a role in catalysis and suggest that their role is similar to the role of the His residues in the HXGH sequence in class I aminoacyl-tRNA synthetases, i.e. to stabilize a pentacoordinate transition state.

Amino Acid Sequence↗
PubMed1996

Molecular indices of neuronal and glial plasticity in the hippocampal formation in a rodent model of age-induced spatial learning impairment.

Spatial learning ability was quantitated in young and aged Long-Evans rats, and molecular markers were assessed in the striatum and hippocampal formation using immunocytochemical, immunoblotting, and in situ hybridization histochemical procedures. The mRNA for beta-amyloid precursor protein (beta APP), most likely the transcript encoding the 695-amino acid form of this protein, was elevated in pyramidal and granule cells in the hippocampus of aged rats exhibiting poorer spatial learning. In immunoblots of hippocampal protein extracts, however, the level of beta APP-like immunoreactivity was depressed in the more impaired subjects. Similarly, the level in hippocampus of the mRNA for manganese-dependent superoxide dismutase (Mn-SOD), a marker of oxidative stress, was positively correlated with the degree of behavioral impairment, but immunoblotting revealed that Mn-SOD protein was depressed in the aged hippocampus compared with young. The mRNAs for the neuronal form of nitric oxide synthase and for the astrocyte marker glial fibrillary acidic protein (GFAP) were elevated in the hippocampus in correlation with the extent of learning impairment. In the striatum, the levels of mRNA and protein for several candidate genes, including GFAP, were elevated in parallel with the learning index, but these were age effects. Several hippocampal proteins were unchanged (GFAP) or depressed (beta APP and Mn-SOD) in level, despite elevations in corresponding mRNAs. In the aged cohort, hippocampal GFAP mRNA, Mn-SOD mRNA, and beta APP emerged as predictors of behavioral impairment, suggesting the involvement of these hippocampal systems in age-related cognitive impairment.

Aging↗
PubMed1996

Assessment of wall structure and composition of varicose veins with reference to collagen, elastin and smooth muscle content.

OBJECTIVES: To compare collagen, elastin and smooth muscle contents of varicose and control long saphenous veins. DESIGN: Collagen, elastin and muscle were estimated stereologically using random sampling and histological staining. MATERIALS: Varicose vein samples were collected from nine patients (mean age 52 years, range 34-64 years) undergoing vein stripping, sample sites being saphenofemoral junction and knee. Control samples were taken from five patients (mean age 58 years, range 38-76 years) presenting for femoral-popliteal bypass at equivalent levels. METHODS: Veins were fixed, sectioned transversely, and stained with Picric Acid Sirius Red. Analysis of samples was performed using point and intersection counting on vertically projected images. RESULTS: Using two way analysis of variance tests, varicose saphenous veins had significantly larger wall areas (p < 0.01) and higher amounts of collagen (p < 0.01). Collagen content and wall area were significantly larger proximally compared to distally in both control and varicose veins (p < 0.05) with a higher content of smooth muscle and elastin in varicose veins proximally compared to distally (p < 0.05). There was no difference in wall thickness or elastin content between the two groups. CONCLUSIONS: This suggests that varicose veins are a dynamic response to venous hypertension and are not thin walled structures as previously thought.

Adult↗
PubMed1995

Early increase in choline kinase activity upon induction of the H-ras oncogene in mouse fibroblast cell lines.

The effects of expression of the H-ras oncogene on phosphatidylcholine metabolism were examined in C3H10T1/2 and NIH3T3 cells expressing ras constitutively or under the control of inducible promoters. Cell lines expressing ras under the control of the mouse metallothionein promoter and the Escherichia coli lac operator/repressor system and an NIH3T3 cell line stably transfected with the ras oncogene were studied. Phosphocholine levels were elevated in the cells constitutively expressing ras and were increased 4-6 h upon induction in the inducible cell lines. Glycerophosphocholine, which is elevated five- to sixfold in constitutively transfected ras cells, did not increase at early times of induction, suggesting the absence of increased phosphatidylcholine degradation via a phospholipase A. Choline kinase activity increased within 4-6 h upon induction and correlated well with the increase in phosphocholine levels. This increase in phosphocholine levels could be prevented by the addition of hemicholinium-3, a competitive inhibitor of choline kinase. Expression of activated c-raf or v-raf also increased choline kinase activity, suggesting that the induction of choline kinase by ras is downstream of the ras/raf interaction. Long-term and short-term labeling experiments failed to detect evidence for increased phospholipase C activity. These results suggest that the increase in choline kinase activity observed in cells expressing ras is an early, integral part of ras transformation and is the main contributor to increased phosphocholine levels accompanying morphological changes.

3T3 Cells↗
PubMed1995

Identification of an inhibitory domain of CTP:phosphocholine cytidylyltransferase.

The function of the putative amphipathic helices between residues 236 and 314 of CTP:phosphocholine cytidylyltransferase was examined by constructing two truncation mutants; CT314 was missing the entire phosphorylation segment, whereas CT236 was missing both the region with the putative amphipathic helices and the phosphorylation segment. Stable cells lines expressing these truncation mutants in Chinese hamster ovary 58 cells were isolated and characterized. CT314 was predominantly soluble in control cells but became membrane-associated in cells treated with oleate, which also causes translocation of wild-type cytidylyltransferase. CT236 was found to be soluble both in control cells and in cells treated to cause translocation. These results strongly suggest that the membrane-binding site is located within residues 237-314. When assayed for activity in vitro, the mutant forms were catalytically active in the presence of exogenous lipids. CT236, moreover, was as active in the absence of lipids as in their presence, whereas CT314 required lipids for activity. The rate of phosphatidylcholine synthesis in cells expressing CT236 was considerably higher than in wild-type cells, consistent with the enzyme being constitutively active in the cells. These results indicate that residues 237-314 constitute an inhibitory segment; when this segment is removed from the catalytic domain by truncation or by binding to membranes, an inhibitory constraint is removed and cytidylyltransferase is activated.

Animals↗
PubMed1995

Effects of altered phosphorylation sites on the properties of CTP:phosphocholine cytidylyltransferase.

To investigate the role of phosphorylation and dephosphorylation in modulating the activity and location of CTP:phosphocholine cytidylyltransferase, we used site-directed mutagenesis to construct four mutant forms of cytidylyltransferase. These forms were 5SP-->AP, in which five of the seven Ser-Pro sequences were converted to Ala-Pro; 7SP-->AP, in which all of the seven Ser-Pro sequences converted to Ala-Pro; 16S-->A, in which all sixteen Ser residues that can be phosphorylated in wild type cytidylyltransferase were converted to Ala; and 16S-->E, in which all sixteen Ser residues were converted to Glu. The mutant enzymes were expressed in the strain 58 Chinese hamster ovary cell line, which is temperature-sensitive for growth and cytidylyltransferase activity. All mutant enzyme forms were enzymatically as active as the wild type when assayed under optimal conditions. In untreated cells, more of the Ser-->Ala mutants were membrane-associated than in cells expressing wild type enzyme, consistent with the phosphorylation state of the enzyme affecting its affinity for membranes. About half of the 16S-->A mutant remained soluble, however, indicating that dephosphorylation alone does not trigger membrane association. Although the amount of membrane-associated enzyme in the 16S-->A mutant was about 10-fold greater than that of wild type, phosphatidylcholine synthesis was increased by only about 75%, suggesting that membrane association does not necessarily cause full activation. All mutant forms, including the 16S-->E mutant, translocated to the particulate fraction upon oleate treatment, indicating that a high negative charge in the phosphorylation region does not preclude association of cytidylyltransferase with membranes. All mutant enzymes were able to support growth of strain 58 at 40 degrees C, and the rate of phosphatidylcholine synthesis was not greatly altered in the cell lines expressing mutant cytidylyltransferase forms. These results are consistent with a role for phosphorylation in the equilibrium distribution of cytidylyltransferase but suggest that changes in enzyme activity and location are not triggered exclusively by changes in the phosphorylation state.

Amino Acid Sequence↗