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Biomedical subjects

D J Graham

Publications and source records attributed to D J Graham.

At least 37 records · Page 2Linked to original sources
PubMed1995

Hepatic hemorrhage and the HELLP syndrome: a surgeon's perspective.

Hypertension-induced hepatic disease is a common cause of abdominal pain and liver function test abnormalities in the pregnant patient. Liver hemorrhage and rupture, in turn, are the most unusual and serious complications of preeclamptic/eclamptic or HELLP (Hemolysis Elevated Liver enzymes and Low Platelet count) associated disease. Should a liver hematoma be documented, management must be aggressive, with treatment of hypertension, correction of any coagulopathy, and prompt delivery of the child. Rupture remains a surgical emergency with control of bleeding based on trauma principles. Postoperative care is difficult, with a propensity toward multiple system organ failure. With an aggressive multidisciplinary approach to the management of these patients, mortality rates have been decreased by fifty per cent. Subsequent pregnancies appear to carry no increased risk of liver rupture over the general population but should be followed carefully by a high-risk obstetrician.

Adult↗
PubMed1994

Human immunodeficiency virus type 1 protease inhibitors: evaluation of resistance engendered by amino acid substitutions in the enzyme's substrate binding site.

The human immunodeficiency virus type 1 (HIV-1) protease is a homodimeric aspartyl endopeptidase that is required for virus replication. A number of specific, active-site inhibitors for this enzyme have been described. Many of the inhibitors exhibit significant differences in activity against the HIV-1 and HIV type 2 (HIV-2) enzymes. An initial study was conducted to ascertain the HIV-1 protease's potential to lose sensitivity to several test inhibitors while retaining full enzymatic activity. The substrate binding sites of the HIV-1 and HIV-2 enzymes are almost fully conserved, except for four amino acid residues at positions 32, 47, 76, and 82. Accordingly, recombinant mutant type 1 proteases were constructed that contained the cognate type 2 residue at each of these four positions. The substitution at position 32 resulted in a significant adverse effect on inhibitor potency. However, this substitution also mediated a noted increase in the Km of the substrate. Individual substitutions at the remaining three positions, as well as a combination of all four substitutions, had very little effect on enzyme activity or inhibitor susceptibility. Hence, the four studied active site residues are insufficient to be responsible for differences in inhibitor sensitivity between the HIV-1 and HIV-2 proteases and are unlikely to contribute to the generation of inhibitor-resistant mutant HIV-1 protease.

Amino Acids↗
PubMed1994

Purification and characterization of HIV-1 reverse transcriptase having a 1:1 ratio of p66 and p51 subunits.

Wild-type and several mutant forms of recombinant human immunodeficiency virus type-1 reverse transcriptase were overexpressed as either the p66 or the p51 subunit in a protease-deficient strain of Escherichia coli. Immediately prior to cell lysis, p51 cell paste was mixed with cell paste containing the corresponding overexpressed p66 subunit in a ratio resulting in an excess of the smaller subunit with respect to the larger. During the subsequent chromatography steps stable heterodimer p66/p51 was purified to homogeneity. This protein was characterized by amino acid analysis, denaturing sodium dodecyl sulfate-polyacrylamide gel electrophoresis, analytical gel filtration HPLC, laser desorption mass spectroscopy, and isoelectric focusing. In addition, we were able to obtain crystals of the purified enzyme complexed with a quinazolinone class nonnucleoside inhibitor that diffracted to 3.2 A resolution. A potential application of this expression/purification methodology is the ability to alter specific amino acids residues, by site-directed-mutagenesis, of only one subunit of the RT-dimer.

Base Sequence↗
PubMed1994

Temafloxacin syndrome: review of 95 cases.

Four months after its approval in the United States, temafloxacin was withdrawn from the market worldwide because of frequent reports of serious hemolysis with or without other organ system dysfunction. We describe this "temafloxacin syndrome" on the basis of a review of 95 spontaneous reports of hemolysis sent to the Food and Drug Administration. Patients typically presented with fever, chills, and jaundice a mean of 6.4 days after starting therapy. A moderate degree of hemolysis was reflected by the mean drop in hemoglobin level (by 42 g/L) and by the mean lowest concentration of hemoglobin (97 g/L). New-onset renal dysfunction was noted in 54 cases (57%), and dialysis was required in 34 cases (63%). Coagulopathy was noted in 33 cases (35%), and 48 cases (51%) met the criteria for hepatic dysfunction. Four patients developed central nervous system complications, and two patients died. Prior quinolone use was more common among patients who developed hemolysis after only one dose as opposed to two or more doses (P < .001). These data suggest that temafloxacin causes immune hemolytic anemia, most likely secondary to immune complex formation.

Adult↗
PubMed1994

Susceptibilities of human immunodeficiency virus type 1 enzyme and viral variants expressing multiple resistance-engendering amino acid substitutions to reserve transcriptase inhibitors.

To evaluate the potential that multiply resistant human immunodeficiency virus type 1 variants may arise during combination nucleoside and nonnucleoside reverse transcriptase inhibitor therapy, we constructed a series of mutant reverse transcriptase enzymes and viruses that coexpressed various combinations of resistance-associated amino acid substitutions. Substitutions at residues 100 (Leu-->Ile) and 181 (Tyr-->Cys), which mediate resistance to the nonnucleosides, suppressed resistance to 3'-azido-3'-deoxythymidine (AZT) when coexpressed with AZT-specific substitutions. However, a number of viral variants that exhibited significantly reduced susceptibilities to both classes of inhibitors were constructed.

Drug Resistance, Microbial↗
PubMed1993

Inhibition of HIV-1 reverse transcriptase by pyridinone derivatives. Potency, binding characteristics, and effect of template sequence.

The inhibition of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase by pyridinone compounds has been investigated using as templates synthetic RNA with sequences based on the HIV-1 genome sequence. In reactions catalyzed by the enzyme that incorporated more than one nucleotide per primer, inhibition by a representative pyridinone inhibitor, 3-[2-(1,3-benzoxazol-2-yl)ethyl]-5-ethyl-6-methyl-pyridin-2(1H)one (L-696,229), was noncompetitive against deoxynucleotide triphosphate. For reactions that incorporated one deoxynucleotide per primer, IC50 values ranged from 20 to 200 nM, depending on the position of incorporation of the incoming deoxynucleotide base on the template. Inhibition of synthesis on a set of four templates differing only at the template base complementary to the incoming nucleotide had similar IC50 values. These results demonstrate that inhibitory potency is dependent on the primary structure of the template and that inhibitory potency is largely independent of the identity of the incoming nucleotide base. The inhibition of HIV-1 reverse transcription by L-696,229 also displayed slow-binding characteristics. The slow-binding aspect was exploited to gauge the interaction between inhibitor and enzyme. By titrating the reduction in the extent of the burst of synthesis observed in a reaction incorporating dideoxythymidine monophosphate into poly(rA)-oligo(dT)18, the apparent equilibrium constant for dissociation of the reverse transcriptase-L-696,229 complex was estimated to be 400 nM.

Antiviral Agents↗
PubMed1993

Application of a system analysis approach to population pharmacokinetics and pharmacodynamics of nicardipine hydrochloride in healthy males.

Nicardipine hydrochloride, a dihydropyridine calcium channel blocker, possesses antihypertensive and arterial vasodilator properties. A system analysis approach, which makes fewer structural assumptions than compartmental methods, is presented for determining the pharmacokinetics and pharmacodynamics of nicardipine hydrochloride in healthy males following a discontinuous infusion at four dose levels. The results indicate that the average total body clearance of nicardipine is 0.920 L/h/kg and the volume of distribution is 0.275 L/kg. Nicardipine hydrochloride has a mean residence time in the body of 1.27 h, of which 0.324 h were spent in the systemic circulation and the remainder in the periphery. The determined pharmacokinetic model was linked to a pharmacodynamic model that allowed the change in the mean arterial blood pressure and heart rate to be described and predicted. A population pharmacokinetic-pharmacodynamic model was derived and the predictive power of the proposed model was assessed with a cross-validation technique that employs a relative predictive quotient for comparing the predictions to the fitted model. The results indicate that the proposed model describes the pharmacodynamics of nicardipine in healthy males and has good predictive ability when tested with a cross-validation procedure.

Adult↗
PubMed1993

Colonoscopy for intermittent rectal bleeding: impact on patient management.

Rectal bleeding is a frequent presenting symptom of a number of benign anorectal disorders. However, it may also be a warning sign of more significant gastrointestinal pathology. For this reason, full colonic evaluation has been recommended in patients with intermittent bright red rectal bleeding. The purpose of this study is to evaluate the utility of colonoscopy in this setting. Data were prospectively collected on 125 colonoscopies performed on the surgical service at the Cleveland Wade Park Veterans Administration Medical Center during a two year period. During this period 33 patients underwent colonoscopy for the evaluation of intermittent bright red rectal bleeding. Fourteen patients had abnormal rectal exams, including hemorrhoids in 9, mass lesions in 3, prolapse in 1, and fistula in ano in 1. Colonoscopy was normal in only 7 (21%) of the 33 patients examined. Findings in the remaining 26 included 31 polyps in 14 patients, cancer in 3, AVM in 1, diverticula in 9, hemorrhoids in 4, and other benign lesions in 5. Positive findings on rectal examination had no relationship to findings at endoscopy, with abnormal findings in 52% of patients with normal rectal exams and in 27% of patients with abnormal rectal exams (P = 0.187, NS). Findings at colonoscopy resulted in a change in management in 16 (48%) of patients examined. In patients with intermittent rectal bleeding, the entire colon should be evaluated regardless of findings on rectal examination, as a significant number of patients will have concomitant findings. Colonoscopy is an excellent method for colonic evaluation in this setting.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Functional analysis of HIV-1 reverse transcriptase amino acids involved in resistance to multiple nonnucleoside inhibitors.

Several novel, structurally distinct classes of specific human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) nonnucleoside inhibitors have been described recently. These include the pyridinone derivatives L-697,639, L-697,661, and L-696,229 as well as BI-RG-587 and the tetrahydroimidazo[4,5,1-j,k]-benzodiazepin-2(1H)-one and -thione compounds. Previous studies have implicated involvement of the RT amino acid residues at positions 103, 181, and 188 in the activity of the compounds. Accordingly, HIV-1 RT mutants containing a series of amino acid substitutions at these positions were constructed. The relative resistance of purified mutant enzymes to each of the inhibitors was assessed. This analysis established the functional equivalence of the three inhibitor classes and provided evidence for the interaction of the 103 site with the 181/188 region. Amino acid substitutions at these positions were also found to influence RT sensitivity to inhibition by phosphonoformate, thereby suggesting a close association between this pyrophosphate analog's binding site in RT and the binding site of the nonnucleoside inhibitors. In addition, aromatic stacking of the amino acid side groups at residues 181 and 188 was suggested to be required for inhibitor activity.

Amino Acid Sequence↗
PubMed1992

Domains 1 and 2 of ICAM-1 are sufficient to bind human rhinoviruses.

The intercellular adhesion molecule-1 (ICAM-1) receptor was expressed in primary chicken embryo cells using a retroviral vector and shown to specifically bind major group human rhinoviruses (HRVs). A truncated, membrane-bound ICAM-1 protein containing N-terminal domains 1, 2, and 3 retained the ability to bind virus whereas proteins containing domains 1 and 2 or domain 1 were not expressed under these conditions. Soluble forms of ICAM-1 proteins were expressed to circumvent the reduced expression levels of shorter ICAM-1 truncations. Full-length and truncated ICAM-1 molecules containing only domains 1 and 2 were capable of neutralizing HRV binding to cells. Soluble receptors containing only domain 1 could not be recovered. Mutants of ICAM-1 lacking carbohydrate attachment sites were constructed and shown to have no effect on the ability of ICAM-1 to bind HRVs. In addition, ICAM-1 proteins expressed in the presence of tunicamycin also retained their virus binding capability. These data suggest that the N-terminal two domains of ICAM-1 are sufficient for virus interaction and that carbohydrates do not play a major role in virus binding.

Animals↗
PubMed1992

Network interference and number-fact retrieval: evidence from children's alphaplication.

The origins of several phenomena of number-fact retrieval were investigated by having children in Grades 3 and 4 memorize alphaplication facts (arithmetic-like memory items composed of letters instead of numbers). Alphaplication performance paralleled memory for arithmetic facts in several important respects: Results showed (a) a large performance advantage for tie (e.g., E, E = j) over nontie problems (E, I = p), (b) that most errors involved answers from the correct alpha-table, (c) that response times and error rates were strongly correlated across problems, (d) that the correct answers to poorly learned problems tended to be the most common error responses, and (e) that performance was lower for problems introduced later in the learning sequence. Taken together, these findings support a network-interference approach (Campbell & Graham, 1985) to memory for arithmetic facts.

Attention↗
PubMed1992

Identification of the human immunodeficiency virus reverse transcriptase residues that contribute to the activity of diverse nonnucleoside inhibitors.

The reverse transcriptase (RT) of human immunodeficiency virus type 1 (HIV-1) is potently inhibited by a structurally diverse group of nonnucleoside compounds. These include pyridinone derivatives, tetrahydroimadazo[4,5,1-j,k][1,4]-benzodiazepin-2(1H)-one and -thione, and BI-RG-587 (nevirapine). The compounds act noncompetitively, by an unknown mechanism, with respect to template-primer and nucleotide substrates. Despite a high degree of similarity between the HIV-1 and HIV-2 RTs, the HIV-2 enzyme is totally insensitive to these inhibitors. Using a novel method for joining DNA sequences, we have exploited this difference between the two enzymes to identify the regions of the RT that contribute to the compounds' inhibitory activities. The relative in vitro sensitivities of HIV-1/HIV-2 chimeric and site-specific mutant enzymes were determined. Sensitivity to inhibition was largely, though not exclusively, dependent upon the RT region defined by amino acid residues 176 to 190, with specific contributions by residues 181 and 188. The region defined by residues 101 to 106 was found to functionally interact with the domain from 155 to 217. In addition, the functional equivalence of the three inhibitor groups was shown.

Antiviral Agents↗
PubMed1992

The metabolism of imiloxan hydrochloride in healthy male volunteers.

1. The metabolism of imiloxan hydrochloride [(+-)-2-(1-ethyl-2-imidazoyl)methyl-1,4-benzodioxane hydrochloride], an alpha 2-adrenoceptor antagonist, was studied in four male volunteers given a 500 mg oral dose containing 0.48 MBq of the 14C-labelled material. Compound-related radioactivity was rapidly excreted chiefly in the urine within 24 h of dosing. 2. Metabolites derived by initial oxidation on either or both the benzodioxane and imidazoyl moieties followed by glucuronic acid and sulphate conjugation, and an N-glucuronide of imiloxan were tentatively identified in urine. 3. The major urinary metabolites, comprising some 37-41% of the dose, appeared to be +-2-(1-ethyl-2-imidazoyl)methyl-1,4-benzodioxane-6/7-sulphonic acid (19% of dose), [+-2-(1-ethyl-2-imidazoyl)methyl-1,4-benzodioxane- 6/7-ylium D-glucopyranoside]uronate (10-14% of dose), and a glucuronide conjugate of +-2-(1-ethyl-2-imidazoyl-4/5-hydroxy)methyl-1,4-benzodioxane (8% of dose).

Adrenergic alpha-Antagonists↗
PubMed1992

Chemical peritonitis following the intraperitoneal administration of vancomycin.

The Food and Drug Administration has received 51 reports of cases in the United States in which chemical peritonitis was associated with the intraperitoneal administration of sterile vancomycin hydrochloride, USP intravenous. The clinical presentation of the cases ranged from mild (cloudy dialysate alone) to more severe (severe abdominal pain and fever). The temporal circumstances suggest that intraperitoneal vancomycin may be associated with chemical peritonitis. A positive rechallenge was reported in 9 cases. The underlying mechanism responsible for this adverse reaction has not yet been identified.

Adverse Drug Reaction Reporting Systems↗
PubMed1991

Oxygen radicals alter LDL permeability and uptake by an endothelial-smooth muscle cell bilayer.

There is evidence to suggest that the deposition of lipid within the arterial wall, which is characteristic of atherosclerosis, involves a break in the integrity of the endothelial barrier. Oxidative modification of low density lipoproteins by reactive oxygen species may enhance this process. In this study, an aortic endothelial (EC) smooth muscle cell (SMC) bilayer was briefly exposed to a free-radical generating system to determine the effect of superoxides on lipid permeability and uptake. 125I-LDL (10 micrograms/ml) was added to the EC medium at various time intervals (3, 24, and 48 hr and 9 days). The amount of lipid reaching the subendothelial space was measured. Measurements of EC and SMC binding and uptake of LDL were also obtained and compared with those of untreated cells. The results demonstrate a significant increase in the permeability of the treated EC layer to LDL (P less than 10(-6)), which was sustained over time. Superoxide exposure led to a limited initial increase in EC binding and uptake of LDL, which later returned to control values. In contrast, SMC uptake of LDL was significantly (P less than 10(-3)) and persistently increased over control values and disproportionately increased over cellular binding. Such results suggest that superoxides can increase LDL permeability of the EC barrier. Because this was not associated with a comparable increase in EC binding and uptake, it is unlikely to be due to changes in receptor-mediated, transcellular transport.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗