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Biomedical subjects

M A Johnson

Publications and source records attributed to M A Johnson.

At least 145 records · Page 8Linked to original sources
PubMed1998

SCID mice containing muscle with human mitochondrial DNA mutations. An animal model for mitochondrial DNA defects.

Defects of the mitochondrial genome are important causes of disease. Despite major advances in our investigation of patients, there is no effective therapy. Progress in this area is limited by the absence of any animal models in which we can evaluate treatment. To develop such a model we have injected human myoblasts into the tibialis anterior of SCID mice after inducing necrosis. After injection of normal human myoblasts, regenerating fibers expressed human beta-spectrin, confirming they were derived from fusion of human myoblasts. The stability of the muscle fibers was inferred by demonstrating the formation of motor end plates on the regenerating fibers. In addition, we show the presence of human cytochrome c oxidase subunit II, which is encoded by the mitochondrial genome, in the regenerated fibers. After injection of human myoblasts containing either the A8344G or the T8993C heteroplasmic mitochondrial DNA mutations, human beta-spectrin positive fibers were found to contain the mutation at a similar level to the injected myoblasts. These studies highlight the potential value of this model for the study of mitochondrial DNA defects.

Animals↗
PubMed1998

Cytomegalovirus polymerase chain reaction viraemia in patients receiving ganciclovir maintenance therapy for retinitis.

OBJECTIVES: To determine whether recurrence of polymerase chain reaction (PCR) viraemia during maintenance ganciclovir for cytomegalovirus (CMV) retinitis correlates with (i) CMV disease at a new anatomical site, (ii) progression of the presenting retinitis, or (iii) acquisition of genetic changes in gene UL97 associated with resistance to ganciclovir. DESIGN: A previously described cohort of 45 patients presenting with first episode retinitis was followed clinically using ophthalmoscopy and serial tests for PCR viraemia for a median of 7 months. CMV viral load and genetic markers of ganciclovir resistance were measured in PCR-positive samples. METHODS: PCR amplification of the glycoprotein B region of CMV and quantitative competitive PCR assays were employed. Genetic changes in UL97 were identified by sequencing/point mutation assay. RESULTS: PCR viraemia correlated significantly with new episodes of CMV disease (P=0.011) and a trend was seen for the association with progression of retinitis (P=0.07). Amongst the 14 patients PCR-positive during maintenance ganciclovir, 10 (71%) had genetic markers of resistance. None of these patients became PCR-negative in blood after reinduction ganciclovir therapy compared with three out of four without markers of resistance (P=0.022). CONCLUSIONS: CMV PCR viraemia correlated strongly with the development of new episodes of CMV disease. Most patients with progression of retinitis remained PCR-negative in blood, consistent with therapeutic failure due to poor intraocular penetration of ganciclovir. However, the minority who were PCR-positive in blood may have reinfected their eye, and frequently had markers of ganciclovir resistance. The implications of these findings for the management of patients with CMV disease are discussed.

Antiviral Agents↗
PubMed1998

The incidence of AIDS-defining illnesses in 4883 patients with human immunodeficiency virus infection. Royal Free/Chelsea and Westminster Hospitals Collaborative Group.

BACKGROUND: Acquired immunodeficiency syndrome (AIDS)-defining illnesses are known to occur at different levels of immunosuppression, and the incidence of diagnoses may also vary according to the CD4 lymphocyte count strata. Information about the incidence of disease at different levels of immunosuppression would help clinicians monitoring patients and would allow prophylaxis to be targeted at the most appropriate population. METHODS: Between 1982 and July 1995, 4883 patients testing positive for the human immunodeficiency virus were seen at either the Royal Free or Chelsea and Westminster Hospitals in London, England. The incidence of each diagnosis, both overall and stratified by CD4 lymphocyte count, was calculated using a person-years analysis. Patients who had no CD4 lymphocyte counts measured during follow-up were excluded from the analysis. RESULTS: During a median follow-up period of 27.6 months, 3875 AIDS-defining illnesses were reported in 1713 patients. The incidence of AIDS-defining illnesses ranged from 6.22 per 100 person-years of follow-up for Pneumocystis carinii pneumonia (95% confidence interval, 5.74-6.70) to 0.37 for extrapulmonary tuberculosis (95% confidence interval, 0.26-0.48). The incidence of each AIDS-defining illness increased as the CD4 lymphocyte count declined; diagnoses such as cytomegalovirus and Mycobacterium avium-intracellulare complex infection had a low incidence at CD4 lymphocyte counts above 0.05x10(9)/L (50/mm3), while Kaposi sarcoma, P carinii pneumonia, and esophageal candidiasis had a high incidence throughout all CD4 lymphocyte count strata. CONCLUSIONS: This study provides important information about the risk of AIDS-defining illnesses at lower CD4 lymphocyte counts, enabling disease-specific prophylaxis to be targeted at the most appropriate population. In the future, as more prophylactic therapies are developed, this study will provide historical data of the incidence of diseases before specific prophylaxis was introduced.

AIDS-Related Opportunistic Infections↗
PubMed1998

A novel mitochondrial DNA point mutation in the tRNA(Ile) gene: studies in a patient presenting with chronic progressive external ophthalmoplegia and multiple sclerosis.

We report a new mutation, a G to A transition at nucleotide position 4298 within the mitochondrial tRNA(Ile) gene in a patient with chronic progressive external ophthalmoplegia and multiple sclerosis. The mutation, which alters an evolutionary conserved nucleotide within the anticodon stem, was heteroplasmic in skeletal muscle but was not present in the patient's blood. Single fibre PCR analysis revealed significantly higher levels of the G4298A mutation in cytochrome c oxidase (COX) negative fibres than in COX-positive fibres. This mutation represents the seventh pathogenic nucleotide substitution to be found in this gene and as such confirms the tRNA(Ile) gene as a susceptible "hot spot" for mitochondrial DNA point mutations. Of particular interest is that this patient has the clinical features of both multiple sclerosis and a mitochondrial DNA disorder.

Animals↗
PubMed1998

Quantitative differences in the distribution of zidovudine resistance mutations in multiple post-mortem tissues from AIDS patients.

Replication of HIV introduces errors into the genome which are responsible for conferring a growth advantage over wildtype virus when drugs such as zidovudine (ZDV) exert a selective pressure. The molecular basis for HIV-1 resistance to ZDV has been mapped to codons 41, 67, 70, 215 and 219 of the reverse transcriptase gene both in vitro and in clinical samples of blood. This study has investigated the relationship between the quantitative prevalence of ZDV resistance in multiple organs of the same individual. Proviral HIV-1 load was measured by quantitative-competitive PCR in 90 samples from organs of 11 patients dying with AIDS. Nine of these patients had been prescribed zidovudine. The distribution of wildtype and mutant sequences at the positions 41, 67, 70, 215 and 219 of the reverse transcriptase was assessed using a point mutation assay. The results showed that the highest proviral loads were predominately found in lymph node, spleen and lung and there was a significant association between viral load and resistance to ZDV (P=0.008). Inter-organ distribution of wildtype and mutant sequences at codons 41, 67, 70, 215 and 219 was frequently not uniform and in some patients differed markedly between the lymphoreticular system and other organs. These results demonstrate that treatment of HIV-1 infection with zidovudine does not exert uniform selective pressures in multiple organs. These findings have implications for the interpretation of resistance data and design of treatment strategies for HIV, arguing in particular that alterations in therapeutic regimens should consider the likelihood of different resistance patterns being present in multiple sites within the same individual.

Acquired Immunodeficiency Syndrome↗
PubMed1998

Role of mitochondrial DNA mutations in human aging: implications for the central nervous system and muscle.

It has been proposed that one mechanism for nerve and muscle dysfunction with age involves the mitochondria. Mitochondria contain the only DNA outside the nucleus in mammalian cells. Mitochondrial DNA (mtDNA) has a high mutation rate, and low levels of pathogenic mutations have been found in tissues from elderly subjects. However, the role of these mutations in the aging process is uncertain unless a mechanism can be identified that would lead to a biochemical defect. In muscle tissue from normal elderly subjects we show that there are muscle fibers with very low activity of cytochrome c oxidase, suggestive of a mtDNA defect. In these cytochrome c oxidase-deficient fibers we have found very high levels of mutant mtDNA. In addition, different mtDNA mutations are present in different fibers, which explains why there is a low overall incidence of an individual mutation in tissues from elderly subjects. These studies show a direct age-related correlation between a biochemical and genetic defect in normal human tissues and that mtDNA abnormalities are involved in the aging process in human muscle.

Aged↗
PubMed1998

The pharmacokinetics of lamivudine in patients with impaired hepatic function.

OBJECTIVE: This study was designed to evaluate the effect of hepatic impairment on the pharmacokinetics of lamivudine. METHODS: Sixteen patients not infected with hepatitis B virus or human immunodeficiency virus who had hepatic impairment due to liver cirrhosis were assigned to moderately or severely impaired groups by clinical signs/symptoms, 14C-aminopyrine metabolic activity and caffeine clearance and compared with eight healthy controls. Following a 300-mg dose of lamivudine, blood and urine samples were taken for drug assay. RESULTS: Lamivudine was well tolerated in patients with hepatic impairment. There were no statistical differences in overall lamivudine exposure (in terms of AUC or Cmax) or other major pharmacokinetic parameters i.e. CLR, tmax and t1/2, between healthy control subjects and patients with moderate or severe hepatic impairment. CONCLUSIONS: Hepatic impairment does not warrant dose modification of lamivudine based on this single-dose pharmacokinetic study.

Adult↗
PubMed1998

The major late promoter and bipartite leader sequence of fowl adenovirus.

The region of the fowl adenovirus serotype 10 (FAV-10) genome containing the major late promoter (MLP) and leader sequences was determined and appropriate genomic fragments were cloned and sequenced. A TATA box was identified and the location of the putative transcription start site was determined. By using synthetic primers from the transcription start site in conjunction with oligonucleotides from the coding regions of the penton base and hexon genes, cDNA was produced from late mRNA isolated from cell cultures infected with FAV-10 at 24 h post-infection. The resulting cDNA was cloned and sequenced and the leader sequences thus identified. It was found that the FAV-10 MLP utilized only two leader sequences (a bipartite leader). By comparison with human adenoviruses (HAVs) it appeared that the second leader in HAVs was absent from the FAV-10. The second leader sequences of FAV-10 was larger than either the second or third leaders of HAVs, but was 29 basepairs shorter than the combined size of the leader sequences 2 and 3 from HAV-2. To confirm the transcription start site and leader sequences, single stranded cDNA was produced from mRNA using the primers from within the coding sequence for the penton base or hexon. A tail of dGTP's was added and cDNA synthesis was completed using an oligonucleotide from within the hexon or penton base coding sequence and a second poly-dCTP oligonucleotide. Sequencing of the resultant G-tailed DNA confirmed the location of the transcription start site as an adenosine residue 24 basepairs upstream from the 3-prime (3') end of the TATA box. Sequencing 5' of the TATA box failed to reveal any sequence similarity with the human adenovirus upstream stimulatory factor (USF). Various plasmids were constructed which placed the determined sequences of the MLP, leader, and the region upstream of the TATA box linked to the co-acetyl acid transferase (CAT) gene. These expression plasmids in transient expression assays of CAT activity in primary chicken kidney cell culture with or without FAV-10 co-infection were determined. These experiments showed that the cassette containing sequences 5' of the TATA box expressed CAT to a much greater level than cassettes not containing this upstream region and that the presence of virus significantly increased the activity of the promoter following the onset of viral DNA replication. Without the 5' region, cassettes failed to express above background levels. These results suggest that the basic structure of the fowl adenovirus MLP is similar to that of the human adenovirus although it utilizes a bipartite rather than a tripartite leader sequence.

Animals↗
PubMed1998

Muscle pain as a prominent feature of facioscapulohumeral muscular dystrophy (FSHD): four illustrative case reports.

Clinical studies of facioscapulohumeral muscular dystrophy (FSHD) rarely report muscle pain as a significant feature of the condition. We report four adult patients with FSHD in whom muscle pain was a presenting complaint and remains their most disabling symptom. These four patients were investigated using a pain questionnaire and diary. Inflammatory and metabolic causes of muscle pain were sought by muscle biopsy and a range of biochemical investigations. All patients reported between three and seven different pains of varying site and nature. None of the group had more than one painfree day per month and all complained of disturbed sleep. While some pains could potentially be attributed to postural problems, others were clearly myalgic in nature, though most often not specifically exercise-related. These myalgic pains could be particularly difficult to control. Results of metabolic investigations and muscle biopsy revealed no clue to the pathogenesis of these pains and there was no evidence for any exceptional inflammatory response. We believe that pain in FSHD is an under-reported but significant symptom and that further work is necessary to determine its prevalence, understand its cause and provide effective treatment.

Adult↗
PubMed1998

Single dose pharmacokinetics of lamivudine in subjects with impaired renal function and the effect of haemodialysis.

AIMS: The purpose of this study was to investigate the pharmacokinetics of a single oral dose of lamivudine administered to subjects with renal impairment and to determine whether lamivudine was dialysable in subjects with severe renal impairment undergoing haemodialysis. METHODS: Twenty-nine subjects were enrolled, nine with normal renal function (creatinine clearance (CL(CR)) 82-117 ml min(-1)), eight with moderately impaired renal function (CL(CR) 25-49 ml min(-1)), six with severe impairment (CL(CR) 13-19 ml min(-1)) and six with severe impairment who were also receiving haemodialysis. After an overnight fast, nondialysis subjects received a single oral dose of lamivudine. Subjects on haemodialysis were given two doses on separate occasions (intra and interdialysis). Blood was obtained before lamivudine administration and at regular intervals to 48 h post dose. Timed urine collections were performed for subjects able to produce urine. Pharmacokinetic parameters were calculated by using standard non compartmental techniques. RESULTS: Decreasing renal function was associated with reduced lamivudine clearance in a proportional and apparently linear relationship. Lamivudine was well dialysed with an extraction ratio in the order of 50%. However, because lamivudine has a large volume of distribution (approximately 100 1), a haemodialysis session of 4 h did not affect overall exposure to a clinically significant degree in most subjects. CONCLUSIONS: Impaired renal function does require lamivudine dose modification according to the degree of impairment, but no further modification of dose is required for subjects undergoing regular haemodialysis.

Adolescent↗
PubMed1998

Changes to the cytokine microenvironment in the genital tract mucosa of HIV+ women.

As previous studies have indicated that genital tract mucosal T cell function may be impaired in HIV infection, we investigated the T cell cytokine mRNA in the genital tract mucosa of HIV-infected women to determine if there are alterations in the cytokine profile which may explain the T cell impairment. The in situ hybridization technique was used to investigate the T helper-1 (Th1: IL-2, interferon-gamma (IFN-gamma)) and Th2 cytokine (IL-4, IL-5, IL-10) mRNA profile in cervical biopsies from 10 HIV+ and 10 HIV- subjects. Cervical intraepithelial neoplasia (CIN) and genital infection had previously been excluded and the distribution of immunocompetent cells within the cervical mucosa was known for each subject. Non-parametric tests were used to compare the optical density (OD) of cytokine mRNA in the HIV+ and HIV- groups. Comparisons were also made between peripheral CD4 lymphocyte counts, cervical CD4/CD8 T lymphocyte ratios and cytokine mRNA OD in HIV+ subjects. The HIV+ women had significantly higher mRNA OD for the Th2 cytokines IL-4, IL-5 and IL-10 than HIV women. There was also significantly lower IL-2 mRNA OD in the former group. HIV+ women had lower IFN-gamma mRNA than HIV- women, but the difference was not statistically significant. There was no correlation between cytokine mRNA OD and peripheral CD4 count or cervical CD4/CD8 ratio. The predominance of Th2 cytokines, which are immuno-inhibitory, in the cervical mucosa of HIV+ women may underlie the impaired cytotoxic potential observed in the CD8+ T lymphocytes and may contribute to the susceptibility of HIV-infected women to recurrent genital tract infections and cervical neoplasia.

Adult↗
PubMed1998

Rehabilitation outcome of individuals with nontraumatic myelopathy resulting from spinal stenosis.

A study was undertaken of 46 patients (19 cervical and 27 lumbar) admitted to an inpatient rehabilitation unit following surgical decompression for myelopathy or cauda equina syndrome resulting from spinal stenosis (SS). Individuals with SS represented 16 percent of all spinal cord injury (SCI) admissions. When compared to patients with traumatic SCI, patients with SS were significantly (t-test, p < .01) older (mean age 68 versus 39 years), more frequently retired/unemployed (89 percent versus 43 percent), more often married (57 percent versus 36 percent) and less often male (54 percent versus 82 percent) but with similar ethnicity. Significant (p < .01) Functional Independence Measurement (FIM) changes for the SS patients were noted after rehabilitation in the categories of self-care, sphincter control and mobility/locomotion. Additionally, outcome comparisons with a group of traumatic SCI patients who had similar motor function revealed similar lengths of stay, discharge FIM scores and discharge-to-community rates. This study suggests that individuals with weakness secondary to SS represent a significant proportion of individuals with SCI, make significant functional gains following inpatient rehabilitation and can achieve functional outcomes similar to those of traumatic SCI individuals.

Activities of Daily Living↗
PubMed1998

Pharmacokinetics and antiretroviral activity of lamivudine alone or when coadministered with zidovudine in human immunodeficiency virus type 1-infected pregnant women and their offspring.

The safety, pharmacokinetics, and antiretroviral activity of lamivudine alone and in combination with zidovudine was studied in pregnant women infected with human immunodeficiency virus type 1 (HIV-1) and their neonates. Women received the drugs orally from week 38 of pregnancy to 1 week after delivery. Neonate therapy began 12 h after delivery and continued for 1 week. Both treatment regimens were well-tolerated in women and newborns. Lamivudine and zidovudine pharmacokinetics in pregnant women were similar to those in nonpregnant adults. Lamivudine and zidovudine freely crossed the placenta and were secreted in breast milk. Neonatal lamivudine clearance was about half that in pediatric patients; zidovudine clearance was consistent with previous reports. HIV-1 RNA could be quantified in 17 of the 20 women. At the onset of labor/delivery, mean virus load had decreased by approximately 1.5 log10 copies/mL in both treatment cohorts. Although not definitive for HIV-1 infection status, all neonates had HIV-1 RNA levels below the limit of quantification at birth and at ages 1 and 2 weeks.

Administration, Oral↗
PubMed1998

Preliminary findings from a teleultrasound study in Alberta.

BACKGROUND AND OBJECTIVES: Ultrasound practice in Alberta requires direct supervision by an ultrasound-accredited specialist physician (sonologist). This requirement limits access to ultrasound examinations in many rural communities. A prospective study was performed to evaluate the adequacy of teleultrasound service in High Level, Alberta, with remote sonologist supervision from Edmonton, Alberta. METHODS: A total of 146 patients were evaluated in two groups. Group A (72 patients) was evaluated by both an on-site radiologist in High Level and a remote supervising radiologist in Edmonton. Group B (74 patients) was evaluated only by the remote supervising radiologist in Edmonton. The teleultrasound service included digital store-and-forward capabilities using a commercially available teleradiology system, with videoconferencing review for real-time scanning. RESULTS: The teleultrasound service was helpful to the referring physician. It made transfer unnecessary in 42% of patients, and the results of the ultrasound assessment influenced management in 59% of patients. The sonographer on site and the remote radiologists agreed on the quality of the images. The information required for diagnosis was available from the sonographer's study in the majority of cases, with second-look scanning by the on-site radiologist or videoconferencing by the remote radiologist providing a major new diagnosis in only 1% of patients. CONCLUSION: Teleultrasound service to High Level could be provided reliably with remote supervision, comparable to direct on-site supervision.

Alberta↗