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Biomedical subjects

M D Johnson

Publications and source records attributed to M D Johnson.

At least 91 records · Page 5Linked to original sources
PubMed1996

Cardiovascular hypertrophy and increased vascular contractile responsiveness following repeated cocaine administration in rabbits.

The effects of repeated cocaine administration on contractile responses were studied in adult rabbits. Repeated cocaine exposure caused a significant increase in the maximal response of the aorta to the agonists norepinephrine and serotonin as well as the receptor- independent stimulus KCl when compared to the saline controls. Cocaine exposure caused a significant increase in the wet weights of both heart and aorta. When the contraction was normalized to the wet weight of the aorta there was no difference between rabbits administered cocaine and saline. Acute cocaine administration caused a time-dependent increase in immunoreactivity of the proto-oncogene c-Fos in the aorta. These results show that repeated cocaine administration leads to the development of cardiovascular hypertrophy.

Animals↗
PubMed1996

Distribution of transforming growth factor-beta isoforms in human immunodeficiency virus-1 encephalitis.

The transforming growth factor-beta family of polypeptides includes three related isoforms with pervasive effects on immune system function. In this study, the authors evaluated human brains with human immunodeficiency virus (HIV)-1 encephalitis for transforming growth factor beta (TGFbeta)1, TGFbeta2, and TGFbeta3 immunoreactivity using isoform-specific polyclonal antibodies and avidin-biotin immunohistochemistry. Normal brains and those with progressive multifocal leukoencephalopathy, toxoplasma encephalitis, and cryptococcal meningitis were used as controls. In normal controls, TGFbeta1, TGFbeta2, and TGFbeta3 immunoreactivity were confined to arachnoid cells and blood vessels. In 9 of 10 cases of HIV-1 encephalitis, all three isoforms were also detected in arachnoid cells. In addition, variable, predominantly TGFbeta2 and TGFbeta3 immunoreactivity were also detected in reactive astrocytes and mononuclear cells of white matter lesions. Extensive TGFbeta3 immunoreactivity was also detected in multinucleated giant cells in one case. In a case of cryptococcal meningitis, all three isoforms were detected in arachnoid cells and macrophages. Lesions of progressive multifocal leukoencephalopathy and toxoplasma encephalitis also exhibited TGFbeta1, TGFbeta2, and TGFbeta3 immunostaining in reactive astrocytes. These findings suggest that TGFbeta isoforms are present in HIV-1 encephalitis and may participate in the pathogenesis of this and other inflammatory central nervous system (CNS) lesions associated with acquired immunodeficiency syndrome (AIDS).

AIDS Dementia Complex↗
PubMed1996

Localization of purine metabolizing enzymes in bovine brain microvessel endothelial cells: an enzymatic blood-brain barrier for dideoxynucleosides?

PURPOSE: The specific activities of the purine and pyrimidine metabolizing enzymes, purine nucleoside phosphorylase (PNP), adenosine deaminase (ADA) and cytidine deaminase (CDA) were determined in bovine brain microvessel endothelial cells (BBMECs), whole cerebral tissue and erythrocytes. In addition, the substrate specificities (Km and Vmax) of purified calf spleen PNP for inosine and 2',3'-dideoxyinosine (ddI) and of purified calf intestinal ADA for 2',3'-dideoxyadenosine (ddA), 6-chloro-2',3'-dideoxypurine (6-Cl-ddP), and 2'-beta-fluoro-2', 3'-dideoxyadenosine (F-ddA) have been explored. METHODS: BBMECs were isolated from bovine cerebral cortex by a two step enzymatic dispersion treatment followed by centrifugation over 50% Percoll density gradients. Activities of alkaline phosphatase, gamma-glutamyl transpeptidase, ADA, PNP and CDA were determined in various tissue homogenates (cerebral cortex, BBMECs and erythrocytes). Enzyme kinetic studies were also conducted using commercially available enzymes and several nucleoside analogs of interest. RESULTS: The activities of ADA and PNP were 42-fold and 247-fold higher in the cerebral microvessels than in the cerebral cortex, respectively, while there was no detectable CDA activity in the microvessel fraction and very little overall activity in the cortex. CONCLUSIONS: ADA and PNP may serve as an enzymatic blood-brain barrier for some of the anti-HIV dideoxynucleosides. Simulations of brain availability for ddI, ddA, 6-Cl-ddP, and F-ddA demonstrated that the quantitative significance of enzyme localization may vary dramatically, however, depending on the membrane permeability of the drug and its bioconversion rate constant within the endothelial cell.

Adenosine Deaminase↗
PubMed1996

CGP-48506 increases contractility of ventricular myocytes and myofilaments by effects on actin-myosin reaction.

We measured the effects of the benzodiazocine derivative, CGP-48506 (5-methyl-6-phenyl-1,3,5,6-tetrahydro-3,6-methano-1, 5-benzodiazocine-2,4-dione), on contraction of intact myocytes and permeabilized fibers of rat ventricular muscle. CGP-48506 is unique in that it is able to sensitize cardiac myofilaments to Ca2+, but unlike all other agents in this class, it is not an inhibitor of type III phosphodiesterase. When added to isolated intact myocytes, CGP-48506 significantly increased the amplitude of cell shortening with little or no change in the Ca2+ transient, as determined by the fluorescence ratio of fura 2. The late phase of the relation between fura 2 ratio and cell length was shifted to the left in the presence of CGP-48506. CGP-48506 also induced a relatively small decrease in diastolic length. However, compared with the thiadiazinone EMD-57033, CGP-48506 had a much smaller effect on diastolic length at concentrations in which there was a bigger inotropic effect. When added to solutions bathing detergent-extracted (skinned) fiber bundles, CGP-48506 increased maximum force. CGP-48506 also increased submaximal force and shifted the pGa-force relation to the left. However, compared with EMD-57033, there was less of an effect of CGP-48506 on force at relatively high pCa values. CGP-48506 did not alter Ca2+ binding to myofilament troponin C. CGP-48506 was able to reverse inhibition of contraction induced by butanedione monoxime both in intact cells and in skinned fiber bundles. Our results indicate that CGP-48506, like EMD-57033, is a positive inotropic agent working through a direct effect downstream from troponin C. CGP-48506, however, appears to have a unique mechanism resulting in less effect on diastolic function.

Actin Cytoskeleton↗
PubMed1996

Exposure to mercury alters early activation events in fish leukocytes.

Although fish in natural populations may carry high body burdens of both organic and inorganic mercury, the effects of this divalent metal on such lower vertebrates is poorly understood. In this report, inorganic mercury in the form of mercuric chloride (HgCl2) is shown to produce both high-dose inhibition and low-dose activation of leukocytes in a marine teleost fish, Sciaenops ocellatus. Concentrations of inorganic mercury > or = 10 microM suppressed DNA synthesis and induced rapid influx of radiolabeled calcium, as well as tyrosine phosphorylation of numerous cellular proteins. Lower concentrations (0.1-1 microM) of HgCl2 that activated cell growth also induced a slow sustained rise in intracellular calcium in cells loaded with the calcium indicator dye fura-2, but did not produce detectable tyrosine phosphorylation of leukocyte proteins. These studies support the possibility that subtoxic doses of HgCl2 may inappropriately activate teleost leukocytes, potentially altering the processes that regulate the magnitude and specificity of the fish immune response to environmental pathogens.

Animals↗
PubMed1996

The matrix metalloproteinase inhibitor batimastat (BB-94) retards human breast cancer solid tumor growth but not ascites formation in nude mice.

Matrix metalloproteinases (MMPs) are thought to play a significant role in tumor invasion and metastasis as well as angiogenesis. Batimastat, also known as BB-94, acts as an inhibitor of metalloproteinase activity by binding the zinc ion in the active site of MMPs. In our study, the hormone-independent MDA435/LCC6 human breast cancer cell line was used to seed solid tumors s.c. into the region of the mammary fat pad in athymic nude mice. Mice were treated with 50 mg/kg batimastat i.p. Tumor volume measurements showed a statistically significant decrease in tumor size between batimastat-treated and control animals. In contrast, we also used the same MDA435/LCC6 cell line to propagate a malignant ascites in nude mice, which yielded a very different response to batimastat. Batimastat, in previously published literature, had been shown to prolong the life of mice bearing ovarian ascites tumors. Treatment with batimastat in our ascites model produced no increase in survival or significant suppression of ascites formation. However, treated animals showed dramatic tumor cell consolidation and less dispersed ascites cells compared with control animals. Two potential targets of batimastat, gelatinase A and B (MMP-2 and -9, respectively), were examined in both tumor sites. These metalloproteinases were present in both solid tumor and ascites fluid and in both cases were host derived and not produced by the tumor. We conclude that batimastat may have different effects on tumor progression and growth depending on the site of tumor implantation.

Animals↗
PubMed1995

Metalloproteinase inhibition and erythroid potentiation are independent activities of tissue inhibitor of metalloproteinases-1.

Tissue inhibitor of metalloproteinases-1 (TIMP-1), the major physiological matrix metalloproteinase inhibitor and a potent antimetastatic factor, also stimulates the growth of erythroid progenitors (erythroid-potentiating activity). We analyzed the relationship between the growth factor activity and protease inhibition by preparing purified TIMP-1 "knockout" proteins lacking in vitro antiproteolytic activity. The growth-stimulatory effect of these N-terminal TIMP-1 point mutants, as tested in an in vitro assay using erythroid precursors (erythroid burst-forming units) was equal to that of unmutated TIMP-1. A fully antiproteolytic C-terminal TIMP-1 truncation also stimulated growth in the erythroid burst-forming unit assay. The results indicate that the influence of TIMP-1 on erythroid precursor growth is independent of its ability to inhibit metalloproteinases. TIMP-1 is analogous to proteins that have both proteolytic and growth factor activity, such as plasmin, thrombin, and urokinase. However, TIMP-1 is novel in this regard because it is a metalloproteinase inhibitor. We show that the antiproteolytic and growth factor activities of the TIMP-1 molecule are physically and functionally distinct.

Amino Acid Sequence↗
PubMed1995

Over-expression of tissue inhibitor of matrix metalloproteinases (TIMP1 and TIMP2) suppresses extravasation of pulmonary metastasis of a rat bladder carcinoma.

The balance between matrix metalloproteinases and their inhibitors is a critical factor which affects tumor invasion and metastasis. We have established a rat bladder carcinoma cell line, LMC19, which is tumorigenic, invasive and metastatic to the retroperitoneal lymph nodes and to the lungs in nude mice. LMC19 cells secrete pro-gelatinases A and B as well as tissue inhibitors of matrix metalloproteinase (TIMP1 and TIMP2). We conducted the present study to determine whether or not over-expression of TIMP1 and TIMP2 can affect the metastatic potential of LMC19 cells. We transfected the cells with an expression vector containing TIMP1 or TIMP2 cDNA, isolated several clones over-expressing TIMP1 or TIMP2 and assessed their invasive and metastatic potential by inoculation at an orthotopic site (urinary bladder) in nude mice. Our results show that the transfectants over-expressing TIMP1 and TIMP2 marginally affect primary tumor growth, local invasion or metastasis to the retroperitoneal lymph nodes but significantly inhibit extravascular growth of pulmonary tumor emboli. Our results suggest that the net activity of matrix metalloproteinases of tumor cells may be a critical factor that controls extravasation at this distant metastatic site.

Animals↗
PubMed1995

Serotonin and stress-induced increases in renin secretion are not blocked by sympathectomy/adrenal medullectomy but are blocked by beta antagonists.

The present study examined the role of the sympathetic nervous system as a mediator of the message from the CNS to the kidneys to stimulate the secretion of renin. Two procedures that increase the secretion of renin were tested: administration of the serotonin releaser fenfluramine, which increases renin release without altering blood pressure [53], and subjecting the rats to the 'psychological' stressor of conditioned emotional response (CER) stress. Pretreatment of rats with either the beta antagonist sotalol or the beta 1-selective antagonist atenolol completely prevented the increase in plasma renin activity and concentration caused by fenfluramine (5 mg/kg i.p.) injection. However, chemical sympathectomy with 6-hydroxydopamine (6-OHDA) combined with surgical adrenal medullectomy did not prevent the increase in plasma renin activity and concentration following fenfluramine injection. Since beta-antagonists have been previously shown to prevent the renin response to CER stress, we also tested whether the sympathetic nervous system mediates the renin response to CER stress. Chemical sympathectomy combined with adrenal medullectomy did not prevent the effect of CER stress on renin release. The completeness of the sympathectomy/adrenal medullectomy was verified biochemically by measuring plasma epinephrine and both plasma and renal norepinephrine concentrations. Plasma epinephrine and renal norepinephrine levels were reduced to below 1% of control while plasma norepinephrine was reduced to below 8% of control values. In conclusion, our data support previous reports suggesting that activation of CNS pathways increases the secretion of renin. However, the message from the brain to release renin from the kidneys does not exclusively involve either the sympathetic innervation of the kidneys or adrenal epinephrine. Although beta 1 receptors are involved in mediating this phenomenon, their location or mechanism remains unknown and will be discussed.

Adrenal Medulla↗
PubMed1995

Evaluating contrast-enhancing brain lesions in patients with AIDS by using positron emission tomography.

OBJECTIVE: To determine whether a noninvasive method for evaluating contrast-enhancing brain lesions in patients with the acquired immunodeficiency syndrome (AIDS) can accurately differentiate between lymphoma and nonlymphoma diagnoses. This method is based on Toxoplasma serologic testing and positron emission tomography. DESIGN: Prospective, nonrandomized, criterion-standard clinical study. SETTING: An academic center in the mid-southeastern United States. PATIENTS: 20 patients with AIDS and contrast-enhancing brain lesions. INTERVENTIONS: Positron emission tomographic scanning and Toxoplasma serologic testing. MAIN OUTCOME MEASURE: Diagnoses were confirmed by clinical response, autopsy, or brain biopsy. RESULTS: Eight patients had a confirmed diagnosis of toxoplasmosis, six had lymphoma, four had other diagnoses, and two were not evaluable. Seven of eight patients with toxoplasmosis had positron emission tomographic scans; all of these scans showed hypometabolic lesions consistent with a nonlymphoma diagnosis. The six patients with lymphoma all had hypermetabolic lesions on positron emission tomographic scans. The difference between these two sets of results was statistically significant (P < 0.001, Fisher exact test, two-tailed). The anti-Toxoplasma titer was greater than or equal to 1:4 in all patients with confirmed toxoplasmosis who had serologic testing and in three of six patients with lymphoma. CONCLUSIONS: Evaluating contrast-enhancing brain lesions in patients with AIDS by using Toxoplasma serologic testing and positron emission tomography can accurately guide therapy and obviate the need for most brain biopsies in these patients. A larger, national, multicenter study is needed to confirm our findings and to determine the effect of earlier diagnosis and treatment on morbidity and mortality in patients with AIDS and primary central nervous system lymphoma.

AIDS-Related Opportunistic Infections↗
PubMed1995

Alpha 1-adrenoceptor responsiveness in the aging aorta.

Previous studies from this laboratory have shown that aortic alpha 1-adrenoceptor-mediated responsiveness is altered during maturation and aging. This study examines the possibility that there is a change in the alpha 1-adrenoceptor subtypes in the aorta during maturation and aging. The apparent affinity of norepinephrine, as determined by partial receptor inactivation with the alpha 1-adrenoceptor antagonist phenoxybenzamine, was found to be higher in 1-month-old rats compared to 6- and 24-month-old rats. The alpha 1B-adrenoceptor subtype-selective antagonist chlorethylclonidine was used to examine possible heterogeneity in aortic alpha 1-adrenoceptors. The inhibitory effect of chlorethylclonidine on norepinephrine-stimulated contraction was greater in young animals compared to aged animals. Chlorethylclonidine blocked norepinephrine-stimulated inositol phosphate accumulation in 1-month-old aorta but it produced only partial inhibition in the 6- and 24-month-old aortas. The relatively non-selective alpha 1-adrenoceptor antagonists phenoxybenzamine (0.1 microM) and prazosin (0.1 microM) inhibited inositol phosphate accumulation and contractile responses in all ages. The complete block of alpha 1-adrenoceptor-mediated responses by chlorethylclonidine in younger animals shows that alpha 1-adrenoceptor-mediated responses are mediated by the chlorethylclonidine-sensitive alpha 1-adrenoceptor subtypes. The partial inhibition by chlorethylclonidine of alpha 1-adrenoceptor-mediated responses in 6- and 24-month-old animals indicates an increased role of an alpha 1-adrenoceptor subtype that is relatively insensitive to chlorethylclonidine.

Adrenergic alpha-Antagonists↗
PubMed1995

Effect of age on cardiac norepinephrine release in the female rat.

We previously demonstrated an age-related decline in K(+)-induced norepinephrine (NE) release from cardiac synaptosomes prepared from 6- and 24-month-old male F344 rats. The purpose of the present study was to determine if the age-related decrease in NE release seen in male F344 rats is also present in female F344 rats. K(+)-induced NE release was assessed in cardiac synaptosomes prepared from 6-, 12-, 18-, and 24-month-old male and female F344 rats. NE release was significantly greater in young male rats, compared to old male rats. However, no age-related decrease in NE release was observed in the female rats. In contrast to previous observations in male rats, raising extracellular [Mg2+], an inorganic Ca2+ channel blocker, reduced NE release to the same extent in all female ages. Omega-conotoxin, an organic Ca2+ channel blocker, also decreased NE release to the same extent in all female ages. These studies suggest that in contrast to aging male rats, cardiac adrenergic nerve terminals of aging female rats maintain their capacity to release NE.

Aging↗
PubMed1995

Prenatal cocaine exposure alters norepinephrine release from cardiac adrenergic nerve terminals.

The effect of prenatal cocaine exposure on the development of the cardiac adrenergic nervous system was assessed in neonatal rabbits. Pregnant does received cocaine (4 mg/kg, i.v., bid) or saline during gestational days 8 to 29. Hearts were obtained on postnatal days 10, 20, 30, and 50. Adrenergic nerve function was assessed by measuring 3H-norepinephrine (NE) uptake and 3H-NE release from cardiac synaptosomes. NE uptake increased with postnatal age and was not affected by cocaine exposure. K(+)-induced NE release increased with age, was significantly less in cocaine exposed rabbits compared to saline exposed rabbits at days 10, and 20, but was similar at days 30 and 50. NE release induced by ionomycin, a Ca2+ ionophore, did not change with age, was significantly greater in cocaine exposed rabbits compared to saline exposed rabbits at days 10, 20, and 30, but was similar at day 50. Wet heart weight, heart weight per body weight, and NE content of the hearts were not affected by cocaine exposure. These results suggest that prenatal cocaine exposure delays the development of the mechanisms responsible for Ca2+ influx during K(+)-induced depolarization and increases the neurosecretory response to intracellular Ca2+.

Adrenergic Fibers↗
PubMed1995

Ultrastructure of electrophysiologically-characterized synapses formed by serotonergic raphe neurons in culture.

Recent electrophysiological investigations in this laboratory have shown that cultured mesopontine serotonergic neurons from neonatal rats evoke serotonergic and/or glutamatergic responses in themselves and in non-serotonergic neurons. Serotonergic nerve terminals in vivo are heterogeneous with respect to vesicle type, synaptic structure, and the frequency with which they form conventional synaptic contacts, but the functional correlates of this heterogeneity are unclear. We have therefore examined the ultrastructure of electrophysiologically-characterized synapses formed by cultured serotonergic neurons, and have compared the findings with the ultrastructural characteristics of serotonergic synapses reported in vivo. Dissociated rat serotonergic neurons in microcultures were identified by serotonin immunocytochemistry or by uptake of the autofluorescent serotonin analogue 5,7-dihydroxytryptamine, and were subsequently processed for electron microscopy. Unlabeled axon terminals formed numerous synapses on serotonin-immunoreactive somata and dendrites. Serotonin-immunoreactive axon terminals formed synapses on the somata, dendrites and somatodendritic spine-like appendages of serotonergic and non-serotonergic neurons. In microcultures containing a solitary serotonergic neuron that evoked glutamatergic or serotonergic/glutamatergic autaptic responses, both symmetric and asymmetric synapses were present. In addition to large dense core vesicles, individual neurons contained either microcanaliculi and microvesicles, clear round vesicles, or clear pleiomorphic vesicles. For a given cell, however, the subtypes of vesicles present in each axon terminal were similar. Thus, dissociated serotonergic and non-serotonergic raphe neurons formed functional, morphological synapses in culture. A direct examination of both the synaptic physiology and ultrastructure of single cultured serotonergic neurons indicated that these cells released serotonin and glutamate at synapses that were morphologically similar to synapses formed by serotonergic neurons in vivo. The findings also suggested that individual serotonergic neurons differ with respect to synaptic vesicle morphology, and are capable of simultaneously forming symmetric and asymmetric synapses with target cells.

Animals↗
PubMed1995

Expression of G protein alpha subunits in the aging cardiovascular system.

Alterations in responsiveness to stimulation of G protein-coupled receptors in the cardiovascular system have been noted during aging and may be due to changes in the G proteins. The levels of G protein alpha subunits and their mRNAs were examined in the aorta and heart of adult (6-month-old) and senescent (24-month-old) Fischer 344 rats. Western blot analysis using anti-Gs alpha antiserum revealed 4 bands in the aorta (38, 42, 45, and 52 kD). The 42 kD band decreased significantly in 24-month-old rats, whereas the other bands did not change. Western blots using anti-Go alpha and anti-Gi alpha revealed single bands of 39 kD and 41 kD respectively, which decreased significantly in the aortas from 24-month-old rats. There were no significant changes in the levels of G alpha mRNAs in the aorta during aging. In the heart, anti-Gs alpha antiserum detected 3 bands (42, 45, and 52 kD) which did not change with age. Levels of Gi alpha (41 kD) and Go alpha (39 kD) also did not change with age in the heart. The mRNAs for Gi2 alpha and Gi3 alpha were significantly increased in the heart, but there was no change in Go alpha or Gs alpha mRNAs. Reduced expression of Gi alpha may provide the molecular basis for alterations in receptor responsiveness in the aging vasculature. Altered expression of G protein alpha subunits does not appear to account for age-related alterations in cardiac function.

Aging↗