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Biomedical subjects

R J Howard

Publications and source records attributed to R J Howard.

At least 127 records · Page 7Linked to original sources
PubMed1993

Contraceptives, counselling, and pregnancy in women with sickle cell disease.

Sickle cell disease is listed in the manufacturers' data sheets in the United Kingdom as a contraindication to the use of most combined contraceptive pills; the result is confused advice on family planning to a group of women who are at substantial risk from both planned and unplanned pregnancy. A study in north London on the use of contraceptives by women with sickle cell disease indicates that the use of combined oral contraceptives is common. Although medical staff usually advised against pregnancy, such advice was almost always ignored. Over half of the women surveyed had some knowledge about antenatal diagnosis. Family planning advice should be an integral part of the care of women with sickle cell disease. In the absence of specific data to the contrary all methods of contraception may be considered, although with appropriate caution.

Adolescent↗
PubMed1993

Thrombospondin from activated platelets promotes sickle erythrocyte adherence to human microvascular endothelium under physiologic flow: a potential role for platelet activation in sickle cell vaso-occlusion.

Adherence of erythrocytes to vascular endothelium likely contributes to the pathophysiology of episodic vascular occlusion in patients with sickle cell disease (SCD). In addition, coagulation activation has been reported in sickle patients during complications such as pain episodes. To test the hypothesis that platelet activation contributes to sickle erythrocyte binding, we investigated whether factors released from activated sickle platelets promote adherence of sickle erythrocytes to human microvascular endothelial cells (MEC) under flow conditions. Activated sickle platelet supernatant (ASPS) promoted high levels of sickle erythrocyte adherence to MEC (55.4 +/- 3.9 erythrocytes/mm2) but only moderate adherence of normal erythrocytes to MEC (14.1 +/- 0.7 erythrocytes/mm2). When MEC were incubated with an antibody (OKM5) against CD36 (a thrombospondin [TSP] receptor), platelet supernatant mediated sickle erythrocyte adherence was inhibited 86%, suggesting that TSP participated in the adherence. To further define the role of TSP in adherence, additional studies using purified TSP were performed. At a concentration of 0.2 micrograms/mL TSP in serum-free media (SFM), sickle erythrocyte adherence to MEC was 33.9 +/- 2.7 erythrocytes/mm2 and sixfold greater than either sickle erythrocyte adherence in the absence of TSP or normal erythrocyte adherence in the presence of TSP. Doubling the concentration of TSP to 0.4 micrograms/mL proportionally increased adherence of sickle erythrocytes. Incubation of MEC with OKM5 or anti-alpha v monoclonal antibodies inhibited TSP-mediated sickle erythrocyte adherence more than 95%. These data suggest that activated platelet release factors, including alpha-granule TSP, which promote receptor-mediated sickle erythrocyte adherence to microvascular endothelium. Such factors released during in vivo platelet activation could contribute to vaso-occlusive complications by promoting erythrocyte adherence and microvascular occlusion.

Anemia, Sickle Cell↗
PubMed1993

Cloning and characterization of a Plasmodium falciparum gene encoding a novel high-molecular weight host membrane-associated protein, PfEMP3.

The rat monoclonal antibody, mAb 12C11, reacts with numerous proteins from mature asexual stages of Plasmodium falciparum. The largest is 315 kDa and is designated PfEMP3. A lambda gt11 expression library, generated from genomic DNA of Malayan Camp strain parasites, was screened with mAb 12C11. One positive clone, lambda 12.1.3, contained a 1.4-kb fragment in frame with the beta-galactosidase gene of lambda gt11. The deduced 455-amino acid sequence is a novel, highly charged sequence encoding two 15-amino acid repeats at the N-terminus followed by 27 repeats of 13 amino acids. The last 59 C-terminal residues are non-repetitive. Two in-frame stop codons at the 3' end of the DNA suggests that this DNA fragment encodes the C-terminus of the protein. Southern blotting with the cloned fragment identified two copies of this fragment per haploid genome in knob-positive, parasitized erythrocytes (K+PE). Both DNA fragments are absent from K - PE. Northern blotting of trophozoite-stage PE total RNA revealed mRNAs of 10, 4.4 and 2 kb in K+PE, but no hybridization with K - PE. Immune sera were elicited against the lambda 12.1.3 beta-galactosidase fusion protein and peptides generated from the predicted lambda 12.1.3 amino acid sequence. These sera and mAb 12C11 reacted specifically with PfEMP3 in Western blots of mature K+PE but not with K - PE. Rat and mouse sera against the recombinant protein produced an immunofluorescence pattern in fixed mature K+PE almost identical to the pattern produced by a monoclonal antibody against the knob-associated protein, Histidine Rich Protein 1. The same antibodies were immunofluorescence negative with fixed K - PE. Mouse antibodies against the recombinant protein reacted on immunoelectron microscopy with the erythrocyte membrane of K+PE, labeling knobs as well as the membrane between knobs. In contrast, a mAb against Histidine Rich Protein 1 reacted only under the electron dense material of knobs. We conclude that the lambda 12.1.3 clone encodes the C-terminal portion of the 315 kD PfEMP3 antigen and that PfEMP3 may be involved in knob formation or other perturbations of the erythrocyte membrane.

Amino Acid Sequence↗
PubMed1993

Dual natriuretic peptide system in experimental heart failure.

OBJECTIVES: The objectives of this study were 1) to define in an experimental model of heart failure the time course of changes in plasma brain natriuretic peptide concentrations during the development of and recovery from heart failure, and 2) to relate the changes to changes in atrial natriuretic peptide concentration and hemodynamic status. BACKGROUND: Brain natriuretic peptide is a circulating peptide with homology to atrial natriuretic peptide. However, unlike the latter, its changes during heart failure and its relation to cardiac filling pressures have not been studied. METHODS: Eight male mongrel dogs underwent right ventricular pacing at 250 beats/min for 3 weeks until heart failure occurred and were followed up during recovery for 4 weeks after cessation of pacing. RESULTS: Heart failure was characterized by an increase in both left ventricular and end-diastolic pressure (6.6 +/- 4.1 mm Hg at the control measurements to 35.1 +/- 5.9 mm Hg at 3 weeks, p < 0.01) and right atrial pressure (6.7 +/- 1.1 to 11.4 +/- 2.1 mm Hg, p < 0.01). Recovery was accompanied by a return of cardiac filling pressures to control level. The time course of change of arterial plasma brain natriuretic peptide concentration was similar to that of atrial natriuretic peptide. Plasma concentrations of both peptides increased after 1 week of pacing (16 +/- 4 pg/ml at the control measurement to 59 +/- 20 pg/ml at 1 week, p < 0.001 for brain natriuretic peptide and 84 +/- 55 to 856 +/- 295 pg/ml, p < 0.001 for atrial natriuretic peptide). The level of both peptides then stayed level with no further increase at 3 weeks and returned to the control value by 4 weeks of recovery. There was an excellent correlation between plasma concentrations of the two peptides (r = 0.86, p < 0.001) and between the two peptides and cardiac filling pressures. However, compared with atrial natriuretic peptide, plasma brain natriuretic peptide concentration had a smaller percent increase during evolving heart failure and a slower rate of decline at recovery. CONCLUSIONS: Brain and atrial natriuretic peptide constitute a dual natriuretic system and are both responsive to changes in cardiac filling pressures in heart failure. However, brain natriuretic peptide appears to be less responsive than atrial natriuretic peptide.

Analysis of Variance↗
PubMed1993

Surgical hazards posed by marine and freshwater animals in Florida.

Marine and freshwater animals can cause injury to humans by biting, stinging, being poisonous to eat, and causing infections. Biting aquatic animals in Florida include sharks, barracudas, alligators, and moray eels. Devitalized tissue should be débrided, and vascular, neurologic, and tendinous injuries should be repaired. Radiographs should be obtained to examine the injury sit for fractures and retained foreign bodies (teeth). The spines of stingrays and marine catfish can cause soft tissue injury and infection. The spine has a recurved, serrated shape that may cause further injury and break if it is pulled out. The venom may cause local tissue necrosis requiring débridement. Soft tissue infections with marine Vibrio bacteria can occur after eating raw oysters or receiving even minor injuries from marine animals. Thirty-one individuals developed soft tissue infections, 49 developed sepsis, and 23 developed both sepsis and soft tissue infection with marine Vibrio species during a 12-year period. Sixteen patients developed necrotizing soft tissue infections. Treatment is with antibiotics and débridement when necrosis occurs.

Alligators and Crocodiles↗
PubMed1993

Infections caused by halophilic marine Vibrio bacteria.

OBJECTIVE: The authors reviewed patients who developed sepsis or soft tissue infections caused by marine Vibrio bacteria in Florida. SUMMARY BACKGROUND DATA: Marine Vibrio bacteria are the most common bacteria found in seawater. They are concentrated in marine animals that feed by filtration such as oysters and clams. These bacteria can cause gastroenteritis, sepsis, cellulitis leading to necrotizing soft tissue infection after exposure to seawater or consumption of raw seafood. METHODS: The authors received 182 systemic infections that occurred in Florida between January 1, 1979, and December 31, 1991, which were treated by the authors or were reported to the Florida Department of Health and Rehabilitative Services. Patients were divided into two groups depending on whether they presented with primary bacteremia or soft tissue infection. RESULTS: Seventy-one patients had been exposed to these bacteria by eating raw seafood, 94 had direct exposure to seawater, and exposure was uncertain in 27 patients. Vibrio species were cultured from the blood of 103 patients and from wounds or soft tissues of 113. An additional 5 patients had cellulitis but bacteria were not cultured from these sites. In patients in whom it could be determined, 93 had primary soft tissue infections and 82 had primary bacteremia. Twenty-four patients had necrotizing soft tissue infections and required surgical debridement. Three of these 24 patients required amputation. Thirty-seven (20.3%) patients died. Severe liver disease occurred in 54 patients and 25 of these patients died. CONCLUSIONS: Marine Vibrio bacteria can cause sepsis and soft tissue infections, especially in individuals with severe liver disease and other chronic illnesses such as diabetes mellitus. The authors believe all individuals, especially those with systemic illness, should be warned against eating raw seafood.

Adolescent↗
PubMed1993

Relationship of the polymerase chain reaction for cytomegalovirus to the development of hepatitis in liver transplant recipients.

In a pilot study, the polymerase chain reaction was found to be more sensitive than standard viral culture methods for the detection of cytomegalovirus, particularly from blood and tissues. We therefore applied this technique to 71 serially collected liver biopsies from 16 orthotopic liver transplant patients. All patients were CMV-seropositive (n = 15) or seroconverted (n = 1). Seven patients (9 biopsies) had histologically proved CMV hepatitis, and all these biopsies were CMV PCR-positive. Six of these 7 patients had a prior liver biopsy that was CMV PCR-positive, but culture and histology-negative, an average of 13.2 +/- 6.9 days before the histologically positive biopsy. The 7th patient was not biopsied prior to the diagnostic biopsy. Three patients had 7 liver biopsies that were CMV PCR-positive, but histologically negative for CMV hepatitis. Two of these three had CMV infection confirmed by viral culture of blood or liver biopsy. The remaining 6 patients had a total of 26 liver biopsies that were negative for CMV by PCR, culture, and histology. Among liver transplant patients, CMV PCR performed on liver biopsy specimens correctly identified all histologically proven cases of CMV hepatitis. CMV PCR positivity in liver tissue did not correlate with latent infection and preceded the development of CMV hepatitis or other meaningful CMV infection in 8 of 10 patients.

Biopsy↗
PubMed1993

Non-A, non-B hepatitis and elevated serum aminotransferases in renal transplant patients. Correlation with hepatitis C infection.

One hundred renal transplant recipients were studied for antibodies to hepatitis C virus (HCV), and to HCV RNA in serum by reverse transcription+nested polymerase chain reaction (RT-PCR). Presence of antibody to HCV confirmed by recombinant immunoblot assay II was considered evidence of HCV infection, and detection of HCV RNA by RT-PCR was considered evidence for active viremia. On pretransplant sera, 18 patients were RT-PCR positive and an additional 3 had antibody evidence of HCV infection. At 1-year follow-up, all of these patients were RT-PCR positive and an additional 7 patients became RT-PCR positive. Clinical diagnosis of non-A, non-B hepatitis underestimated the prevalence of HCV infection (5/28 cases, 18%). Serum alanine aminotransferase (ALT) elevations were neither sensitive nor specific. An isolated pretransplant ALT elevation predicted a 52% chance of being RT-PCR positive for HCV. An ALT elevation greater than 2 months after transplant predicted a 45% chance of HCV positivity; however, 18% of patients who never had any ALT abnormality were also HCV positive. Sixty-eight patients had an early postoperative rise in ALT, but there was no correlation with HCV status. After an average follow-up of over 4 years, 3/28 HCV-positive patients developed cirrhosis. HCV infection in the renal transplant population is common and underdiagnosed by clinical and biochemical parameters. HCV appears not to cause aggressive liver disease in the early posttransplant period, but longer follow-up is needed to define the natural history of HCV in the renal transplant population.

Adult↗
PubMed1993

An improved microassay for Plasmodium falciparum cytoadherence using stable transformants of Chinese hamster ovary cells expressing CD36 or intercellular adhesion molecule-1.

Stable transformants of Chinese hamster ovary (CHO) cell lines expressing high levels of human CD36 or intercellular adhesion molecule-1 (ICAM-1) have been produced as target cells for cytoadherence of Plasmodium falciparum-infected erythrocytes. An improved adherence microassay has been designed using small sample volumes and allowing convenient and reliable measurements on a large number of samples. The assay can be used both with purified proteins spotted on plastic and with the stably transformed CHO cell lines. The same assay plate can be evaluated either microscopically or by scintillation counting after use of 3H-hypoxanthine-labeled parasites. Using the microassay, functional expression of the transfected receptor molecules on CHO-CD36 and CHO-ICAM was confirmed using parasites with different cytoadherence phenotypes and cytoadherence inhibition experiments with a panel of anti-CD36 antibodies. The use of isolates from The Gambia confirmed the applicability of these assays for laboratory studies of these isolates.

Amino Acid Sequence↗
PubMed1993

Immunochemical characterization and differentiation of two approximately 300-kD erythrocyte membrane-associated proteins of Plasmodium falciparum, PfEMP1 and PfEMP3.

Erythrocyte membrane-associated antigens of Plasmodium falciparum have been of long-standing interest as potential adherence receptors and vaccine candidates. We recently identified in trophozoite-stage infected erythrocytes a novel high molecular weight erythrocyte membrane-associated protein of P. falciparum, PfEMP3, defined by Western blotting with the rat monoclonal antibody 12C11. Genomic clone lambda 12.1.3 and cDNA clone p12.2 contain nucleic acid sequences encoding PfEMP3. Analysis of Malayan Camp strain parasites by sodium dodecyl sulfate-polyacrylamide gel electrophoresis on 5% gels revealed that PfEMP3, defined by Western blot, has the same relative molecular weight (M(r)) as the surface-exposed protein PfEMP1 defined by cell surface iodination. We show here that PfEMP3 is distinct from PfEMP1 by three criteria. First, 125I-labeled PfEMP1 was resolved from PfEMP3 by extended migration on 4% gels. Second, in two strains of P. falciparum in which 125I-PfEMP1 has a different M(r), PfEMP3 had the same M(r). Third, immunization studies were performed with fusion proteins derived from clones lambda 12.1.3 and p12.2. Although one rabbit, Rb 05.75, immunized with the PfEMP3-derived fusion protein beta gal12.1.3, produced a serum that strongly immunoprecipitated PfEMP1 as well as PfEMP3, most sera immunoprecipitated only PfEMP3. Furthermore, immunoprecipitation of PfEMP3 by Rb 05.75 serum was blocked by the glutathione S-transferase 12.1.3 fusion protein, whereas immunoprecipitation of PfEMP1 was unaffected. Therefore, we conclude that PfEMP1 and PfEMP3 are antigenically distinct.

Amino Acid Sequence↗
PubMed1993

Psychological adjustment of liver transplant candidates.

The psychological functioning of 20 adult liver transplant candidates was evaluated. Using standardized assessment instruments, we found few personality disturbances and normal levels of anger. However, clinically significant levels of depression and anxiety were reported for 28% and 37% of the sample, respectively. Moreover, patients whose coping strategies were characterized by avoiding the exigencies of their illness reported more depression, more anxiety, and increased psychopathology. Disease severity was also positively correlated with anxiety and avoidant coping strategies. Implications of these findings for the pre-transplant psychological evaluation are discussed.

Adaptation, Psychological↗
PubMed1993

Left ventricular myocardial blood flow, metabolism, and effects of treatment with enalapril: further insights into the mechanisms of canine experimental pacing-induced heart failure.

Left ventricular myocardial blood flow and metabolic parameters were studied in dogs with severe heart failure induced by rapid ventricular pacing. The impact of early administration of enalapril was also evaluated. Seventeen dogs were randomly assigned in a blinded fashion to receive enalapril at a dose of 10 mg orally per day or a matching placebo commencing 1 week after initiation of pacing. Six dogs underwent sham operations and served as a control for the myocardial blood flow and metabolic studies. In general, there was no significant difference in myocardial blood flow among the control dogs, the placebo-treated, and the enalapril-treated, paced dogs. However, tissue adenosine triphosphate was markedly reduced in both the enalapril-treated, paced dogs (2.43 +/- 0.55 mumol/gm wet weight, mean +/- SD) and the placebo-treated, paced dogs (2.79 +/- 0.39 mumol/gm) compared with the level in control dogs (4.77 +/- 0.88 mumol/gm, both p < 0.01). Tissue glycogen and lactate levels were similar in the three groups. The time to development of severe heart failure tended to be longer in the enalapril-treated dogs (33 +/- 12 days) than in the placebo-treated dogs (24 +/- 10 days, p = 0.07). In pacing-induced heart failure, therefore, an imbalance between energy supply and demand may contribute to the left ventricular dysfunction, myocardial ischemia does not play a major role, and early treatment with enalapril may prolong the time to development of severe heart failure.

Animals↗
PubMed1992

Involvement of CD36 on erythrocytes as a rosetting receptor for Plasmodium falciparum-infected erythrocytes.

Plasmodium falciparum-infected erythrocytes (parasitized red blood cells [PRBCs]) can adhere to uninfected erythrocytes (RBCs) to form rosettes, and adhere to the endothelial cell (EC) surface antigen CD36. These adherence phenomena have previously been considered quite different. We show that anti-CD36 monoclonal antibodies (MoAbs) reverse rosetting of PRBCs from both a culture-adapted line (Malayan Camp [MC] strain) and a natural isolate, GAM425. Three MoAbs that block adherence of PRBCs to ECs or C32 melanoma cells also reversed rosetting by greater than 50% at levels of less than 1 microgram/mL (OKM5, OKM8, and 8A6). Two other MoAbs that react with purified CD36 (1D3 and 1B1), but do not react with the surface of C32 cells, failed to reverse rosetting. When rosettes were disrupted and the RBCs and PRBCs were pretreated separately with antibodies before mixing to allow rosette reformation, only pretreatment of RBCs had an effect. MoAb 8A6 pretreatment of RBCs blocked rosette reformation, while MoAb 1B1 pretreatment did not. Rosetting was also reversed by purified human platelet CD36. In conjunction with evidence that CD36 is expressed on normal human erythrocytes (van Schravendijk et al, Blood 80:2105, 1992), we conclude that this CD36 is able to act as a host receptor for rosetting in the MC strain and some natural isolates of P falciparum.

Animals↗
PubMed1992

Normal human erythrocytes express CD36, an adhesion molecule of monocytes, platelets, and endothelial cells.

We have recently shown that rosetting of Plasmodium falciparum (MC R+ line)-infected erythrocytes (parasitized red blood cells [PRBCs]) with uninfected erythrocytes (RBCs) is blocked by coating of the RBCs with anti-CD36 monoclonal antibodies (MoAbs; Handunnetti et al, Blood 80:2097, 1992). Adult RBCs have previously been considered negative for CD36. However, using fluorescence-activated cell sorter analysis with the anti-CD36 MoAbs 8A6, OKM5, and OKM8, which reverse rosetting, we consistently detect CD36 on the majority of normal adult RBCs. Absorption of the MoAb solutions with CD36-transfected Chinese hamster ovary (CHO-CD36) cells removed the reactivity against both CHO-CD36 cells and RBCs, whereas absorption with CHO cells had no effect. By comparison with staining for glycophorin A, LFA-3, and CR1, the level of expression of CD36 appeared to be low. Nevertheless, normal RBCs were capable of adhering to plastic coated with anti-CD36 MoAbs. RBCs from one African malaria patient were identified as deficient in CD36 and these RBCs did not rosette with the patient's own P falciparum PRBCs, even though these PRBCs were capable of rosetting with RBCs from a normal donor in a CD36-dependent manner. Therefore, the level of expression of CD36 on normal RBCs is sufficient to be important in cell adherence, and may have a biologic role in normal individuals as well as in the pathology of P falciparum malaria.

Animals↗
PubMed1992

CD36 peptides enhance or inhibit CD36-thrombospondin binding. A two-step process of ligand-receptor interaction.

CD36 (glycoprotein IV or IIIB) is an integral plasma membrane protein of wide cellular distribution and functions as a receptor site for thrombospondin (TSP), an adhesive protein important in cell-cell and cell-matrix interactions. OKM5, a monoclonal anti-CD36 antibody, has been reported to block CD36 cell adhesive functions suggesting that the OKM5 epitope on CD36 is functionally important. A panel of 10 synthetic CD36 peptides was made. One peptide, P139-155, specifically inhibited the immunoadsorption of CD36 by OKM5, and P139-155 was directly immunoadsorbed by OKM5, indicating that CD36 sequence 139-155 represents part of the OKM5 epitope. TSP bound to immobilized P139-155 in a dose-dependent and saturable manner. Surprisingly, P139-155 significantly augmented, instead of inhibited, binding of CD36 to TSP. This peptide did not induce platelet aggregation but augmented ADP- and collagen-induced aggregation in platelet-rich plasma. Another CD36 peptide, P93-110, which had no effect on OKM5 immunoadsorption, blocked binding of CD36 to immobilized TSP and partially inhibited collagen-induced platelet aggregation. P93-110 by itself did not bind to TSP; however, in the presence of P139-155, there was a marked enhancement of P93-110 binding to TSP, with a stoichiometry consistent with the trimeric nature of TSP. The data suggest that CD36-TSP interaction is a two-step process; the sequence 139-155 region of CD36 binds first to TSP, triggering a change in TSP to reveal a second site, which binds the 93-110 region of CD36 with high affinity. CD36 peptides can be used as stimulators or inhibitors in cellular adhesive events involving TSP-CD36 interaction. Conformational changes leading to the exposure or activation of high affinity binding sites may occur in both the receptor and the ligand upon cell-cell and cell-matrix adhesion.

Amino Acid Sequence↗