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Biomedical subjects

R H White

Publications and source records attributed to R H White.

At least 55 records · Page 3Linked to original sources

College of American Pathologists Conference XXXI on laboratory monitoring of anticoagulant therapy: laboratory monitoring of oral anticoagulant therapy.

OBJECTIVE: To review the state of the art of laboratory monitoring of oral anticoagulant therapy, as reflected by the medical literature and the consensus opinion of recognized experts in the field, and to make recommendations for improvement in laboratory monitoring of oral anticoagulant therapy. DATA SOURCES: Review of the medical literature, primarily from the last 10 years, and current laboratory practices by a panel of 8 international experts in the field of oral anticoagulant monitoring. DATA EXTRACTION AND SYNTHESIS: After an initial assessment of the literature, key points were identified. Experts were assigned to do an in-depth review of the literature and current practices relevant to each of the key points and to prepare a summary of their findings and recommendations. A draft manuscript was prepared and circulated to every participant in the College of American Pathologists Conference XXXI on Laboratory Monitoring of Anticoagulant Therapy prior to the conference. Each of the key points and associated recommendations was then presented for discussion at the Conference. Recommendations were accepted if a consensus of the 26 experts attending the Conference was reached. The results of the discussion were used to revise the manuscript into its final form. CONCLUSIONS: Consensus was reached on 12 recommendations concerning the laboratory monitoring of oral anticoagulant therapy. Detailed discussion of the rationale for each of these recommendations is found in the text of this article. Discussion of points on which consensus was not reached is also included in the text. It is hoped that widespread adoption of these recommendations will further improve the laboratory monitoring of oral anticoagulant therapy.

Administration, Oral↗

Effect of weight, sex, age, clinical diagnosis, and thromboplastin reagent on steady-state intravenous heparin requirements.

BACKGROUND: There is a significant direct relationship between steady-state intravenous heparin dose requirements and total body weight. Less is known about whether sex, age, clinical diagnosis, and the thromboplastin used to measure the activated partial thromboplastin time (aPTT) affect heparin dose requirements. METHODS: Four cohorts of patients treated with intravenous heparin were gathered from 3 hospitals: 2 cohorts with deep vein thrombosis (DVT) and 2 cohorts with coronary artery disease (CAD). For each clinical diagnosis, half the patients were monitored using one aPTT reagent and the remainder were monitored using a second reagent. Heparin doses and aPTT measurements were recorded, and the dose necessary to achieve an aPTT ratio of 2.0 was calculated using a computer software program. RESULTS: We analyzed the records of 340 patients: 165 with DVT and 175 with CAD. Using analysis of variance, there was a significant difference in the steady-state heparin requirements among patients with DVT compared with patients with CAD (P < .001). For each clinical diagnosis, the use of a different thromboplastin reagent did not affect heparin dose requirements (P > .42). Linear regression modeling disclosed that the steady-state heparin dose for patients with DVT was a function of weight plus an effect modifier involving weight and age, whereas for patients with CAD there was only a weak relationship with weight. CONCLUSIONS: Steady-state heparin dose requirements were significantly different in patients with DVT compared with patients with CAD, suggesting that different dosing nomograms are needed for each condition. For patients with DVT, the accuracy of the initial heparin dose estimate may be improved by considering the patient's age and weight.

Aged↗

Biosynthesis of the peptide bond in the coenzyme N-(7-mercaptoheptanoyl)-L-threonine phosphate.

The biochemical mechanism for the formation of the amide bond in N-(7-mercaptoheptanoyl)-L-threonine phosphate (HS-HTP) has been studied by measuring the incorporation of L-[3-(3)H]threonine into N-(7-mercaptoheptanoyl)-L-threonine (HS-HT) by cell extracts (CE) of Methanosarcina thermophila incubated with different precursors. Synthesis of HS-HT was observed from L-[3-(3)H]threonine and 7-mercaptoheptanoic acid (HS-H) when the incubations were conducted with either crude CE or Sephadex column-purified CE. In the presence of CE, the synthesis of HS-HT was found to be inhibited 66% by preincubation of the extract with ATPase, indicating that ATP was involved in the biosynthesis. In spite of this indication of ATP involvement in the coupling reaction, incubation of the crude CE with L-[3-(3)H]threonine, HS-H, and ATP was found to inhibit the formation of HS-HT. In contrast, the synthesis of HS-HT in the presence of Sephadex column-purified CE was found to be stimulated by the addition of ATP. Incubation of the crude CE with the CoA thioester of 7-mercaptoheptanoic acid (HS-HCoA) or the mixed disulfide formed between coenzyme M and 7-mercaptoheptanoic acid did not stimulate the biosynthesis. The biosynthesis of HS-HT was found to be strongly inhibited by an ethanol extract of the crude CE. This inhibition was found to be attributed to the HS-HTP present in the extract. Stimulation of HS-HT biosynthesis 300-fold was observed when the Sephadex column-purified CE was incubated with L-[3-(3)H]threonine and 7-mercaptoheptanoyl phosphate (HS-H-P). Data indicate that HS-HT is produced by the phosphorylation of HS-H to HS-H-P with ATP, which then reacts with L-threonine to produce HS-HT.

Adenosine Triphosphate↗

Purine biosynthesis in the domain Archaea without folates or modified folates.

The established pathway for the last two steps in purine biosynthesis, the conversion of 5-aminoimidazole-4-carboxamide ribonucleotide (ZMP) to IMP, is known to utilize 10-formyl-tetrahydrofolate as the required C1 donor cofactor. The biosynthetic conversion of ZMP to IMP in three members of the domain Archaea, Methanobacterium thermoautotrophicum deltaH, M. thermoautotrophicum Marburg, and Sulfolobus solfataricus, however, has been demonstrated to occur with only formate and ATP serving as cofactors. Thus, in these archaea, which use methanopterin (MPT) or another modified folate in place of folate as the C1 carrier coenzyme, neither folate nor a modified folate serves as a cofactor for this biosynthetic transformation. It is concluded that archaea, which function with modified folates such as MPT, are able to carry out purine biosynthesis without the involvement of folates or modified folates.

Aminoimidazole Carboxamide↗

D-erythro-neopterin biosynthesis in the methanogenic archaea Methanococcus thermophila and Methanobacterium thermoautotrophicum deltaH.

The steps in the biosynthetic transformation of GTP to 7,8-dihydro-D-erythro-neopterin (H2neopterin), the precursor to the modified folates found in the methanogenic archaea, has been elucidated for the first time in two members of the domain Archaea. In Methanococcus thermophila and Methanobacterium thermoautotrophicum deltaH, it has been demonstrated that H2neopterin 2':3'-cyclic phosphate is an intermediate in this conversion. In addition, the formation of the pterin ring of the H2neopterin 2':3'-cyclic phosphate is catalyzed not by a single enzyme, as is known to occur with GTP cyclohydrolase I in the Eucarya and Bacteria, but rather by two or more enzymes. A 2,4,5-triamino-4(3H)-pyrimidinone-containing molecule, most likely 2,5-diamino-6-ribosylamino-4(3H)-pyrimidinone 5'-triphosphate, has been identified as an intermediate in the formation of the H2neopterin 2':3'-cyclic phosphate. Synthetic H2neopterin 2':3'-cyclic phosphate was found to be readily hydrolyzed by cell extracts of M. thermophila via the H2neopterin 3'-phosphate to H2neopterin, a known precursor to the pterin portion of methanopterin.

Biopterins↗

Purification of the Azotobacter vinelandii nifV-encoded homocitrate synthase.

The nifV gene product (NifV) from Azotobacter vinelandii was recombinantly expressed at high levels in Escherichia coli and purified. NifV is a homodimer that catalyzes the condensation of acetyl coenzyme A (acetyl-CoA) and alpha-ketoglutarate. Although alpha-ketoglutarate supports the highest level of activity, NifV will also catalyze the condensation of acetyl-CoA and certain other keto acids. E. coli cells in which a high level of nifV expression is induced excrete homocitrate into the growth medium.

Azotobacter vinelandii↗

Occurrence and biosynthesis of 5-aminoimidazole-4-carboxamide ribonucleotide and N-(beta-D-ribofuranosyl)formamide 5'-phosphate in Methanobacterium thermoautotrophicum delta(H).

5-Aminoimidazole-4-carboxamide ribonucleotide (ZMP) and N-(beta-D-ribofuranosyl)formamide 5'-phosphate (FAR-P) have been identified as products of the metabolism of ATP and 5-phospho-alpha-D-ribosyl diphosphate by Methanobacterium thermoautotrophicum delta(H), a member of the domain Archaea. Evidence indicates that the first three steps in the pathway to the formation of these compounds are the same as the first three steps of histidine biosynthesis and lead to the generation of pro-phosphoribosyl formimino-5-aminoimidazole-4-carboxamide ribonucleotide (5'-proFAR). The 5'-proFAR then undergoes hydrolysis to ZMP and FAR-P. The reaction was detected by an unexpected high concentration of ZMP in cell extracts of M. thermoautotrophicum delta(H).

Aminoimidazole Carboxamide↗

Purification and properties of serine hydroxymethyltransferase from Sulfolobus solfataricus.

Serine hydroxymethyltransferase (SHMT) catalyzes the reversible cleavage of serine to glycine with the transfer of the one-carbon group to tetrahydrofolate to form 5,10-methylenetetrahydrofolate. No SHMT has been purified from a nonmethanogenic Archaea strain, in part because this group of organisms uses modified folates as the one-carbon acceptor. These modified folates are not readily available for use in assays for SHMT activity. This report describes the purification and characterization of SHMT from the thermophilic organism Sulfolobus solfataricus. The exchange of the alpha-proton of glycine with solvent protons in the absence of the modified folate was used as the activity assay. The purified protein catalyzes the synthesis of serine from glycine and a synthetic derivative of a fragment of the natural modified folate found in S. solfataricus. Replacement of the modified folate with tetrahydrofolate did not support serine synthesis. In addition, this SHMT also catalyzed the cleavage of both allo-threonine and beta-phenylserine in the absence of the modified folate. The cleavage of these two amino acids in the absence of tetrahydrofolate is a property of other characterized SHMTs. The enzyme contains covalently bound pyridoxal phosphate. Sequences of three peptides showed significant similarity with those of peptides of SHMTs from two methanogens.

Archaeal Proteins↗

Three opsin-encoding cDNAS from the compound eye of Manduca sexta.

Three distinct opsin-encoding cDNAs, designated MANOP1, MANOP2 and MANOP3, were isolated from the retina of the sphingid moth Manduca sexta. MANOP1 codes for a protein with 377 amino acid residues. It is similar in sequence to members of a phylogenetic group of long-wavelength-sensitive arthropod photopigments, most closely resembling the opsins of ants, a praying mantis, a locust and the honeybee. MANOP2 and MANOP3 opsins have 377 and 384 residues respectively. They belong to a related group of insect visual pigments that include the ultraviolet-sensitive rhodopsins of flies as well as other insect rhodopsins that are also thought to absorb at short wavelengths. The retina of Manduca sexta contains three rhodopsins, P520, P450 and P357, with absorbance peaks, respectively, at green, blue and ultraviolet wavelengths. There is evidence that MANOP1 encodes the opsin of P520. We suggest that MANOP2 encodes P357 and that MANOP3, representing a class of blue-sensitive insect photopigments, encodes P450.

Amino Acid Sequence↗

Management and prognosis of life-threatening bleeding during warfarin therapy. National Consortium of Anticoagulation Clinics.

BACKGROUND: The incidence of explicity defined life-threatening bleeding during warfarin sodium therapy is largely unknown, as are the prognosis for and treatment of patients who have such bleeding. In addition, the location of the source of the life-threatening bleeding and the risk factors associated with life-threatening bleeding are not well-defined. OBJECTIVES: To determine the incidence of explicitly defined life-threatening bleeding during warfarin therapy, to identify the site of bleeding, to determine the risk factors for life-threatening bleeding, and to determine the risk of subsequent bleeding among patients receiving warfarin therapy. METHODS: A cross-sectional prevalence study was conducted and data were combined with those obtained during prospective observation of a dynamic cohort of patients followed up in 2 university-affiliated and 3 Veterans Administration anticoagulation clinics. RESULTS: For this study, 1999 patients were followed up for 3865 patient-years; 32 patients (11 women, 21 men, mean age of 60 years) met criteria for life-threatening bleeding, an incidence of 0.83 events/100 patient-years (95% confidence interval, 0.54-1.12). The most common indication for warfarin was to prevent thromboembolism because the patient had a mechanical heart valve (17/32 patients, 53%). The gastrointestinal tract was the definite or likely site of bleeding in 21 (66%) of the 32 patients. The prothrombin time ratio was longer than 2.0 or the international normalized ratio was longer than 4.5 in 16 (55%) of the 29 patients in whom a coagulation time was measured. Fourteen (44%) of the 32 patients had a history of peptic ulcer disease or gastrointestinal bleeding. Warfarin was restarted in 26 (81%) of the 32 patients. Twenty-five of 26 patients were followed up for a median of 30 months (range, 5-143 months); 14 (56%) of the 25 patients had a subsequent bleeding event, with 8 (57%) of the 14 having 1 or more additional life-threatening bleeding events (1 fatal) after a median of 11.5 months (range, 0.5-22 months). CONCLUSIONS: We conclude that in this cohort: (1) the incidence of life-threatening bleeding was rare, (2) the gastrointestinal tract was the site of bleeding in two thirds of the patients who experienced life-threatening bleeding, (3) most patients who experienced life-threatening bleeding had multiple risk factors for bleeding, including excessive anticoagulation, and (4) the risk of subsequent bleeding was extremely high among the patients who continued to receive warfarin therapy.

Aged↗

The risk for and severity of bleeding complications in elderly patients treated with warfarin. The National Consortium of Anticoagulation Clinics.

OBJECTIVE: To determine whether increasing age is associated with an increased risk for bleeding during warfarin treatment. DESIGN: Combined retrospective and prospective cohort studies. SETTING: 6 anticoagulation clinics. PATIENTS: 2376 patients receiving warfarin for various indications. MEASUREMENTS: Bleeding events categorized as minor (resulting in no costs or consequences), serious (requiring testing or treatment), life-threatening, or fatal. RESULTS: 812 first bleeding events (4 fatal, 33 life-threatening, 222 serious, and 553 minor) occurred during 3702 patient-years. Age was inversely related to the mean warfarin dose and dose-adjusted prothrombin time ratio. The unadjusted incidence of minor bleeding complications did not vary according to age group: 18.0 per 100 patient-years for patients younger than 50 years of age, 21.5 for patients 50 to 59 years of age, 24.0 for patients 60 to 69 years of age; 23.5 for patients 70 to 79 years of age, and 16.3 for patient 80 years of age and older. The unadjusted incidence of serious bleeding complications also did not vary according to age group: 9.3 per 100 patient-years for patients younger than 50 years of age, 7.1 for patients 50 to 59 years of age, 6.6 for patients 60 to 69 years of age, 5.1 for patients 70 to 79 years of age, and 4.4 for patients 80 years of age and older. The unadjusted incidence of life-threatening or fatal complications combined was significantly higher among the oldest patients: 0.75 per 100 patient-years for patients younger than 50 years of age, 0.97 for patients 50 to 59 years of age, 1.10 for patients 60 to 69 years of age, 0.68 for patients 70 to 79 years of age, and 3.38 for patients 80 years of age and older. Patients 80 years of age and older had a relative risk of 4.5 (95% CI, 1.3 to 15.6) compared with patients younger than 50 years of age. After adjustment for the intensity of anticoagulation therapy and the deviation in the prothrombin time ratio using Cox and Poisson regression, age was not generally associated with the occurrence of bleeding; relative risk estimates ranged from 0.99 to 1.03 per year of age (lower-bound 95% CI, 0.97 to 1.01; upper-bound 95% CI, 1.00 to 1.09). The single exception was life-threatening and fatal complications in patients 80 years of age or older (relative risk, 4.6 [CI, 1.2 to 18.1]). CONCLUSIONS: Age did not appear to be an important determinant of risk for bleeding in patients receiving warfarin, with the possible exception of age 80 years or older. The intensity of anticoagulation therapy and the deviation in the prothrombin time ratio were much stronger predictors of risk for bleeding.

Age Factors↗

Cloning of a potential cytochrome P450 from the archaeon Sulfolobus solfataricus.

Abstract A gene, CYP119, for a potential cytochrome P450 has been isolated and sequenced from the extreme acidothermophilic archaeon Sulfolobus solfataricus. The gene predicts a polypeptide of 368 amino acids containing the consensus heme-binding sequence Phe-Gly-Xaa-Gly-Xaa-His-Xaa-Cys-Xaa-Gly- Xaa3-Ala-Arg-Xaa-Glu. It most closely resembles the cytochrome P450s found in the bacterium Bacillus subtilis, with which it shares 129 identical amino acid residues (35%). This first sequence of a potential archaeal cytochrome P450 represents an important step in tracing the complex evolutionary history of this biologically important enzyme family.

Amino Acid Sequence↗

Biosynthesis of methanopterin.

This paper establishes the pathway for the biosynthesis of methanopterin in Methanosarcina thermophila to proceed by the following series of reactions. First, 5-phospho-alpha-D-ribosyl diphosphate (PRPP) and 4-aminobenzoic acid condense together to produce 4-(beta-D-ribofuranosyl)aminobenzene 5'-phosphate, which then reacts with 6-hydroxymethyl-7,8-H2pterin pyrophosphate to produce 7,8-H2pterin-6-ylmethyl-4-(beta-D-ribofuranosyl)aminobenz ene 5'-phosphate (3'). Compound 3' is then reduced to 7,8-H2pterin-6-ylmethyl-l-(4-aminophenyl)-1-deoxy-D-ribitol 5'-phosphate (4') in a reaction stimulated by the addition of FMN or factor F(420). Dephosphorylation of compound 4' leads to 7,8-H2pterin-6-ylmethyl-1-(4-aminophenyl)-1-deoxy-D-ribitol (5'). Compound 5' then condenses with another molecule of PRPP to form 7,8-H2pterin-6-ylmethyl-1-(4-aminophenyl)-1-deoxy-5-[1-alpha -D- ribofuranosyl 5-phosphate]-D-ribitol (9'). Compound 9', in the presence of ATP, then condenses with (S)-2-hydroxyglutaric acid to form demethylated H2methanopterin, a known precursor to methanopterin. The occurrence of this pathway was confirmed by (a) the chemical and/or biochemical synthesis of most of the proposed intermediates, (b) the detection of these intermediates in cell-free extracts, and (c) by the measurement of their conversion to demethylated methanopterin and/or other intermediates in the pathway.

4-Aminobenzoic Acid↗

Effect of vitamin E on the anticoagulant response to warfarin.

To clarify whether vitamin E enhances the pharmacologic effect of warfarin, we completed a double-blind clinical trial in which 21 subjects taking chronic warfarin therapy were randomized to receive either vitamin E or placebo. None of the subjects who received vitamin E had a significant change in the international normalized ratio, and thus it appears that vitamin E can safely be given to patients who require chronic warfarin therapy.

Anticoagulants↗

Sex differences in sensory and motor branches of the pudendal nerve of the rat.

The morphology of the pudendal nerve was quantified in adult male and female rats. The sensory branch of the pudendal nerve was about three times as large in cross section in males as in females, and the motor branch was about five times as large. Electron microscopy was used to determine the ultrastructural bases of these gross size differences. Differences that were found included greater packing density of both myelinated and unmyelinated axons in females, larger myelinated and unmyelinated axons in males, larger myelin sheaths of sensory axons in males, more numerous myelinated axons in both branches of males, and more numerous unmyelinated axons in the sensory branch of males. There was also some indication that myelinated sensory axons were more likely to branch in the dorsal clitoral nerve of females than in the homologous nerve of males. Morphological differences in the structure of pudendal axons, their associated Schwann cells, and the extracellular matrix as well as differences in sensory and motor axonal number all have potential implications for the sexual differentiation of the central nervous system and behavior.

Animals↗