Resistance Invivo Research Articles

Creation of Estrogen Resistance in Vivo by Transgenic Overexpression of the Heterogeneous Nuclear Ribonucleoprotein-Related Estrogen Response Element Binding Protein

Estrogen unresponsiveness among primate species can result from overexpression of a heterogeneous nuclear ribonucleoprotein (hnRNP) that competes with estrogen receptor (ER) for binding to the estrogen-response element (ERE). This hnRNP has been coined the "ERE-binding protein" (ERE-BP). The ERE-BP is a member of the hnRNP C-like subfamily of hnRNPs, traditionally considered to be single-strand RNA binding proteins designed for the stabilization and handling of pre-mRNA. To verify in vivo the dominant-negative actions of the ERE-BP to inhibit ER-ERE-directed transactivation and to avoid the potential for lethality from global overexpression of an hnRNP, we generated transgenic mice that overexpressed ERE-BP in breast tissue under the control of a whey acidic protein gene promoter. Graded overexpression of ERE-BP in transgenic mice was established. Founders were viable and fertile. Female transgenics in all lines gave birth to pups, but their ability to nurse was dependent on the level of ERE-BP expression in breast; high-ERE-BP expressors were unable to lactate. A gradient of impaired breast pheno(histo)type, from near normal to failed ductal development and lactational capacity, correlated with the relative level of transgene expression. ERE-BP, expressed either endogenously as a transgene or after transfection, colocalized with ERalpha in the nucleus of target cells. This work confirms that tissue-targeted overexpression of the ERE-BP can effectively block estrogen-ERalpha-ERE-directed action in vivo.

Chronic endothelin-1 treatment leads to insulin resistance in vivo.

We determined whether chronic endothelin-1 (ET-1) treatment could lead to in vivo insulin resistance. Like insulin, ET-1 acutely stimulated glucose transport in isolated soleus muscle strips of WKY rats. ET-1 pretreatment (1 h) decreased insulin-stimulated glucose transport in muscle strips (-23%). Both ET-1-mediated effects were generated through ET(A) receptors, because a specific ET(A) receptor antagonist (BQ610) blocked these effects of ET-1. Osmotic minipumps were used to treat normal rats with ET-1 for 5 days. Subsequent hyperinsulinemic-euglycemic clamps showed that ET-1 treatment led to an approximately 30% decrease in insulin-stimulated glucose disposal rates in male and female rats. In addition, ex vivo study of soleus muscle strips showed decreased glucose transport into muscle from ET-1-treated animals. With respect to insulin signaling, chronic in vivo ET-1 treatment led to a 30-40% decrease in IRS-I protein content, IRS-I-associated p110(alpha), and AKT activation. In summary, 1) in vitro ET-1 pretreatment leads to decreased insulin-stimulated glucose transport in skeletal muscle strips; 2) chronic ET-1 administration in vivo leads to whole-body insulin resistance, with decreased skeletal muscle glucose transport and impaired insulin signaling; and 3) elevated ET-1 levels may be a cause of insulin resistance in certain pathophysiologic states.

Differential Cellular Distribution of HIV-1 Drug Resistance in Vivo: Evidence for Infection of CD8+ T Cells during HAART

This study presents a detailed analysis of HIV-1 populations isolated from total PBMC, plasma, CD4+ T cells, CD8+ T cells, and monocytes/macrophages in 13 patients receiving HAART. Sequence analysis of the reverse transcriptase and protease genes indicated that viral strains isolated from different blood leukocytes were genetically distinct in each subject. Notably, HIV variants isolated from CD8+ T cells were distantly related to strains derived from other blood cell types, providing evidence for the strain-specific infection of CD8+ T cells in vivo. Compartmentalization of drug resistance mutations in specific blood cell types was observed in approximately 50% of patients. The prevalence of resistance mutations was higher in either CD4+ T cells or monocytes/macrophages in these subjects. However, CD8+ T cells showed markedly lower levels of viral drug resistance in these patients, indicating a lack of viral replication in this compartment. This study is the first to demonstrate the differential distribution of HIV drug resistance in different blood cell types during HAART and provides new insights into the infection of CD8+ T cells in vivo.

TNF-alpha-induced insulin resistance in vivo and its prevention by troglitazone.

Tumor necrosis factor (TNF)-alpha may play a role in the insulin resistance of obesity and NIDDM. Troglitazone is a new orally active hypoglycemic agent that has been shown to ameliorate insulin resistance and hyperinsulinemia in both diabetic animal models and NIDDM subjects. To determine whether this drug could prevent the development of TNF-alpha-induced insulin resistance, glucose turnover was assessed in rats infused with cytokine and pretreated with troglitazone. Normal male Sprague-Dawley rats were fed normal powdered food with or without troglitazone as a food admixture (0.2%). After approximately 10 days, rats were infused with TNF-alpha for 4-5 days, producing a plasma concentration of 632 +/- 30 pg/ml. In vivo insulin action was measured by the euglycemic-hyperinsulinemic clamp technique at a submaximal (24 micromol x kg[-1] x min[-1]) and maximal insulin infusion rate (240 micromol x kg[-1] x min[-1]). TNF-alpha infusion resulted in a pronounced reduction in submaximal insulin-stimulated glucose disposal rate (GDR) (97 +/- 10 vs. 141 +/- 4 micromol x kg[-1] x min[-1], P < 0.05), maximal GDR (175 +/- 8 vs. 267 +/- 6 micromol x kg[-1] x min[-1], P < 0.01), and in insulin receptor-tyrosine kinase activity (IR-TKA) (248 +/- 39 vs. 406 +/- 32 fmol ATP/fmol IR, P < 0.05). It also led to a marked increase in basal insulin (90 +/- 24 vs. 48 +/- 6 micromol/l, P < 0.05) and free fatty acid (FFA) concentration (2.56 +/- 0.76 vs. 0.87 +/- 0.13 mmol/l, P < 0.01). Troglitazone treatment completely prevented the TNF-alpha-induced decline in submaximal GDR (133 +/- 16 vs. 141 +/- 4 micromol x kg[-1] x min[-1], NS) and maximal GDR (271 +/- 19 vs. 267 +/- 6 micromol x kg[-1] x min[-1], NS). The hyperlipidemia was partially corrected by troglitazone (1.53 +/- 0.28 vs. 0.87 +/- 0.13 mmol/l, P < 0.05), while IR-TKA and insulin concentration remained unaffected by the drug. Troglitazone restores insulin action possibly by lowering the FFA concentration of the blood and/or by stimulating glucose uptake at an intracellular point distal to insulin receptor autophosphorylation in muscle. If TNF-alpha plays a role in the development of the obesity/NIDDM syndrome, troglitazone may prove useful in its treatment.

Plasmodium berghei: Implication of Intracellular Glutathione and Its Related Enzyme in Chloroquine Resistance in Vivo

Glutathione (GSH) plays a critical role in the detoxication and the protection of cells against oxidative stress. In the present study we examined the relationship between the intracellular GSH level as well as glutathione S-transferase (GST), glutathione reductase (GR), and glutathione peroxidase (GPx) activities and how they relate to Plasmodium berghei resistance to chloroquine. Resistant strains (CQR30 and CQR60) were selected in vivo from a sensitive strain (NK65). Marked increases in GSH levels and GST activity within resistant parasites were observed, compared to sensitive parasites. On the other hand, GR and GPx activities were similar in sensitive and resistant parasites. Treatment with chloroquine did not influence the intracellular level of GSH, but it was found to significantly decrease GR activity. Intracellular depletion of GSH, by a nontoxic concentration of buthionine sulfoximine (BSO), significantly sensitized the resistant parasites to chloroquine. These results suggest that the P. berghei resistance results from altered GSH and GST levels and activity, respectively, which enable the detoxification of chloroquine in resistant parasites.

Direct and Neurally Mediated Effects of Halothane on Pulmonary Resistance In Vivo

It has been suggested that halothane inhibits contraction of airway smooth muscle in vivo mainly by reducing reflex activity in nerves innervating the muscle with only minimal direct effects on the muscle itself. To examine possible mechanisms of action of halothane at clinically relevant concentrations the authors studied the effect of halothane on increases in pulmonary resistance (RL) produced by either vagus nerve stimulation (VNS, which caused neurally mediated constriction) or the inhalation of nebulized acetylcholine (ACh, which directly stimulated the smooth muscle cell) in nine mongrel dogs. The frequency of bilateral VNS and the dose of nebulized ACh were adjusted to produce approximately equal increases in RL. Halothane reduced the response to both types of stimulation in a dose-dependent fashion. At halothane concentrations greater than or equal to 0.4 MAC, the VNS response was significantly less than the ACh response. When tetrodotoxin was given to block neural activity, the ACh response was unchanged, confirming that neural activation did not contribute significantly to smooth muscle contraction in response to ACh. The authors conclude that in addition to neurally mediated effects, halothane at clinically used concentrations has significant direct effects on airway smooth muscle stimulated by ACh. The relative importance of each factor in vivo should depend on the stimulus that causes contraction of airway smooth muscle.

Induction of Insulin Resistance In Vivo by Amylin and Calcitonin Gene–Related Peptide

During hyperinsulinemic glucose-clamp studies, intravenous infusion of calcitonin gene-related peptide (CGRP) in rats antagonized the ability of insulin to stimulate peripheral glucose disposal by 52% (196 +/- 7.2 vs. 105 +/- 10.5 mumol.kg-1.min-1, P less than 0.05) and to inhibit hepatic glucose output by 54% (P less than 0.01). CGRP also inhibited the in vitro effects of insulin to stimulate hexose uptake in cultured BC3H1 myocytes at all insulin concentrations studied. Amylin is a peptide isolated from amyloid deposits in pancreatic islets of type II (non-insulin-dependent) diabetic subjects, is present in normal beta-cells, and bears a striking homology to CGRP. When synthetic human amylin was infused during clamp studies, it inhibited the ability of insulin to stimulate glucose disposal by 56% (96.9 +/- 9.4 vs. 42.4 +/- 5.0 mumol.kg-1.min-1, P less than 0.05) and to suppress hepatic glucose output by 64%. Therefore, amylin and CGRP can cause insulin resistance in vivo and may be implicated in insulin-resistant states such as type II diabetes mellitus.

TRANSDUCTION OF STAPHYLOCOCCUS AUREUS TO TETRACYCLINE RESISTANCE IN VIVO.

Jarolmen, Howard (Hahnemann Medical College, Philadelphia, Pa.), Amedeo Bondi, and Richard L. Crowell. Transduction of Staphylococcus aureus to tetracycline resistance in vivo. J. Bacteriol. 89:1286-1290. 1965.-Staphylophage 80, propagated on a hospital strain of Staphylococcus aureus 80/81, has been shown to transduce antibiotic resistance markers to a variety of staphylococcal recipient strains in vitro. In an attempt to demonstrate transduction of penicillin and tetracycline resistance in mice, experiments were performed in which mice were injected intravenously with a pathogenic recipient strain, S. aureus N135, and subsequently with transducing phage by the same route. Periodic assays of organs from infected mice revealed that maximal bacterial concentrations were attained in kidneys 6 days after infection, at which time the transducing lysate, containing approximately 5 x 10(10) plaque-forming particles, was introduced. Isolation of tetracycline-resistant transductants from the kidneys of infected animals was facilitated by the therapeutic administration of tetracycline. In contrast, penicillin-resistant transductants, which produced penicillinase, were not found even when penicillin therapy was administered. Results showed that tetracycline-resistant transductants were recovered from as many as 40% of test animals in repeated experiments. Furthermore, in some of these mice the entire staphylococcal population of the kidneys was found to be tetracycline-resistant. Control infected animals which did not receive phage were uniformly negative for tetracycline-resistant staphylococci. The finding that phage levels were low or undetectable at a time when tetracycline-resistant organisms were recovered from test animals provided evidence that transduction had occurred in vivo.