Biomedical subjects

Kevin A O'Connor

Publications and source records attributed to Kevin A O'Connor.

9 recordsLinked to original sources

PubMed2006

MxA gene expression in juvenile dermatomyositis peripheral blood mononuclear cells: association with muscle involvement.

Juvenile dermatomyositis (JDM), a systemic vasculopathy, is characterized by inflammation of skin and muscle. Muscle biopsies from untreated JDM patients show upregulation of type I interferon (IFN)-inducible genes, including myxovirus resistance protein A (MxA). The present study examines whether MxA mRNA expression in peripheral blood mononuclear cells (PBMC) from JDM patients: (1) is elevated compared to healthy controls, (2) reflects disease activity, and (3) changes with the onset of clinically effective treatment. MxA mRNA expression in JDM PBMC obtained at the initial clinic visit was elevated compared to controls and was positively correlated with Disease Activity Score (DAS) for muscle, but not with DAS for skin, suggesting that damage to skin and muscle in JDM may each have a discrete pathophysiology. During the course of clinically effective treatment, decrease in muscle symptoms was associated with a decrease in PBMC MxA mRNA expression.

Adolescent↗

PubMed2004

Stress-induced sensitization of the hypothalamic-pituitary adrenal axis is associated with alterations of hypothalamic and pituitary gene expression.

We have previously reported that inescapable tail shock (IS) produces persistent changes in hypothalamic-pituitary-adrenal (HPA) axis function. These changes are manifest as an elevation in basal corticosterone (CORT) levels, a sensitization of adrenocorticotropin hormone (ACTH) and CORT responses to subsequent challenge, and a failure of dexamethasone to suppress both the ACTH and CORT responses to a subsequent challenge. The experiments presented here examine IS-induced alterations in the responsiveness of the HPA axis, particularly at the level of the anterior pituitary. The data presented show that adrenalectomy does not abolish the IS-induced sensitization of the HPA axis, suggesting that the sensitization is not solely caused by a defect in glucocorticoid negative feedback. Analysis of gene expression in the anterior pituitary revealed that IS exposure persistently elevated basal levels of proopiomelanocortin (POMC; the precursor to ACTH) mRNA and sensitized the POMC hnRNA and c-fos mRNA response to a subsequent challenge. Analysis of gene expression in the parvocellular division of the paraventricular nucleus of the hypothalamus (pPVN) after IS exposure revealed that basal levels of corticotropin-releasing hormone (CRH) mature mRNA are elevated and the c-fos mRNA response to a subsequent challenge is enhanced. Finally, a blunted in vitro ACTH response to CRH challenge is observed after IS exposure. These data suggest that the ultimate source of the IS-induced sensitization is not the anterior pituitary and implicate an increased drive on the anterior pituitary from the pPVN.

Adrenalectomy↗

PubMed2004

A method for measuring multiple cytokines from small samples.

Commercially available enzyme-linked immunosorbent assay (ELISA) kits are commonly used to assess levels of proinflammatory cytokines in biological samples. Most of these kits require sample volumes of at least 50 microl. Thus, in order to examine multiple cytokines, volumes greater than 100 microl must be collected. However, the volume of many biological samples, especially those collected from the central nervous system (i.e., microdialysates, push-pull perfusions, or cerebrospinal fluid samples), is much less than 100 microl. Therefore, we developed a method for analyzing multiple cytokines from a single, low-volume biological sample, which involves serially assaying the samples on multiple proinflammatory cytokine ELISA kits. In many cases, assaying for one cytokine does not interfere with subsequent assay for another cytokine in the same sample. Moreover, when interference is observed, the interfering factor can be identified and its effect minimized.

Animals↗

PubMed2004

HIV-1 gp120 stimulates proinflammatory cytokine-mediated pain facilitation via activation of nitric oxide synthase-I (nNOS).

It has become clear that spinal cord glia (microglia and astrocytes) importantly contribute to the creation of exaggerated pain responses. One model used to study this is peri-spinal (intrathecal, i.t.) administration of gp120, an envelope protein of HIV-1 known to activate glia. Previous studies demonstrated that i.t. gp120 produces pain facilitation via the release of glial proinflammatory cytokines. The present series of studies tested whether spinal nitric oxide (NO) contributes to i.t. gp120-induced mechanical allodynia and, if so, what effect NO has on spinal proinflammatory cytokines. gp120 stimulation of acutely isolated lumbar dorsal spinal cords released NO as well as proinflammatory cytokines (tumor necrosis factor-alpha, interleukin-1beta (IL1), interleukin-6 (IL6)), thus identifying NO as a candidate mediator of gp120-induced behavioral effects. Behaviorally, identical effects were observed when gp120-induced mechanical allodynia was challenged by i.t. pre-treatment with either a broad-spectrum nitric oxide synthase (NOS) inhibitor (L-NAME) or 7-NINA, a selective inhibitor of NOS type-I (nNOS). Both abolished gp120-induced mechanical allodynia. While the literature pre-dominantly documents that proinflammatory cytokines stimulate the production of NO rather than the reverse, here we show that gp120-induced NO increases proinflammatory cytokine mRNA levels (RT-PCR) and both protein expression and protein release (serial ELISA). Furthermore, gp120 increases mRNA for IL1 converting enzyme and matrix metalloproteinase-9, enzymes responsible for activation and release of proinflammatory cytokines.

Animals↗

PubMed2003

Further characterization of high mobility group box 1 (HMGB1) as a proinflammatory cytokine: central nervous system effects.

High mobility group box 1 (HMGB1), an abundant, highly conserved cellular protein, is widely known as a nuclear DNA-binding protein. HMGB1 has been recently implicated as a proinflammatory cytokine because of its role as a late mediator of endotoxin lethality and ability to stimulate release of proinflammatory cytokines from monocytes. Production of central cytokines is a critical step in the pathway by which endotoxin and peripheral proinflammatory cytokines, including interleukin-1beta (IL-1) and tumor necrosis factor-alpha (TNF), produce sickness behaviors and fever. Intracerebroventricular (ICV) administration of HMGB1 has been shown to increase TNF expression in mouse brain and induce aphagia and taste aversion. Here we show that ICV injections of HMGB1 induce fever and hypothalamic IL-1 in rats. Furthermore, we show that intrathecal administration of HMGB1 produces mechanical allodynia (lowering of the response threshold to calibrated stimuli). Finally, while endotoxin (lipopolysaccharide, LPS) administration elevates IL-1 and TNF mRNA in various brain regions, HMGB1 mRNA is unchanged. It remains possible that HMGB1 protein is released in brain in response to LPS. Nonetheless, these data suggest that HMGB1 may play a role as an endogenous pyrogen and support the concept that HMGB1 has proinflammatory characteristics within the central nervous system.

Animals↗

PubMed2003

Peripheral and central proinflammatory cytokine response to a severe acute stressor.

The role of proinflammatory cytokines in the response to acute stressor exposure has received recent attention. Exposure to a single session of inescapable shock (IS) induces peripheral and central proinflammatory cytokines. Other stressors also increase expression of proinflammatory cytokine mRNA and/or protein in various tissues. However, the induction of central and peripheral proinflammatory cytokines by stressors remains controversial and the pattern of cytokine induction is not consistent across stressors. The present experiments sought to examine the pattern of the proinflammatory cytokine response to a stressor known to cause elevations of IL-1beta protein. mRNA expression for three proinflammatory cytokines, IL-1beta, TNF-alpha and IL-6, and IL-1beta protein was examined after IS. IS increases IL-1beta mRNA and/or protein in a variety of tissues, including hypothalamus, hippocampus, pituitary and spleen. Furthermore, IS concomitantly alters IL-1beta mRNA and protein in hypothalamus and spleen, while the IL-1beta mRNA increase in pituitary lags behind the increase of IL-1beta protein. Interestingly, IL-1beta mRNA is elevated in hippocampus 4 h after IS, but an increase of IL-1beta protein in hippocampus is not detected. Expression of TNF-alpha and IL-6 mRNA do not increase in response to IS. Indeed, TNF-alpha mRNA expression decreases in cortex, pituitary and liver immediately after IS. These findings suggest that alterations of proinflammatory cytokine expression by stressors, and IS in particular, are region- and cytokine-specific.

Animals↗

PubMed2002

Effects of prior stress on LPS-induced cytokine and sickness responses.

It has recently been reported that exposure to inescapable tailshock (IS) enhances the release of proinflammatory cytokines following bacterial challenge. However, it is not known whether the level of potentiation of proinflammatory cytokines is sufficient to exaggerate any of the physiological processes that are regulated by these cytokines. Thus, LPS was administered and fever, activity, hypothalamic-pituitary-adrenal (HPA) responses, and proinflammatory cytokine release were assessed during both the light and dark phases of the light cycle following IS. Exposure to IS resulted in elevated basal core body temperature during the light phase but not the dark phase and decreased activity during the dark phase but not the light phase. IS animals had significantly greater fever, corticosterone, and ACTH responses following LPS during both the light and dark phases, whereas enhanced proinflammatory cytokine responses were only observed during the light phase. These data suggest that enhanced proinflammatory cytokine responses are not necessary to observe enhanced HPA or fever responses.

Adrenocorticotropic Hormone↗

PubMed2002

Prior stressor exposure sensitizes LPS-induced cytokine production.

Exposure to stressors often alters the subsequent responsiveness of many systems. The present study tested whether prior exposure to inescapable tailshock (IS) alters the interleukin (IL)-1beta, tumor necrosis factor (TNF)-alpha, or IL-6 response to an injection of bacterial endotoxin (lipopolysaccharide; LPS). Rats were exposed to IS or remained as home cage controls (HCC); 24 h later animals were injected i.p. with either 10 microg/kg LPS or equilvolume sterile saline. IS significantly increased plasma TNF-alpha, IL-1beta, and pituitary, hypothalamus, hippocampus, cerebellum IL-1beta 1 h, but not 2 h, after LPS, compared to controls. Additional animals were injected with LPS or saline 4, 10, or 21 days after exposure to IS and tail vein blood was collected and assayed for IL-1beta. An enhanced plasma IL-1beta response occurred 4 days after IS, but was gone by 10 days. These results suggest that exposure to IS sensitizes the innate immune response to LPS by resulting in either a larger or a more rapid induction of proinflammatory cytokines.

Animals↗

PubMed2002

Prior stressor exposure primes the HPA axis.

Exposure to stressors often alters the subsequent responsiveness of many systems. The present study tested whether prior exposure to inescapable tailshock (IS) alters the corticosterone (CORT) or adrenocorticotropin hormone (ACTH) response to either an injection of bacterial endotoxin (lipopolysaccharide; LPS) or subsequent placement on a pedestal. Rats were exposed to IS or remained as home cage controls (HCC). 1, 4, 10, or 21 days later animals were injected i.p. with either 10 microg/kg LPS or equivolume sterile saline. Prior IS significantly increased plasma CORT 1 h, but not 2 or 5 h after LPS, compared to controls 1, 4, and 10 days, but not 21 days after IS. Exposure to IS 24 h earlier also significantly increased plasma ACTH 1 h after LPS. Additional animals were placed on a pedestal 24 h after IS, and plasma CORT was measured 15, 30, and 60 min later. IS significantly increased plasma CORT 15 min after pedestal exposure, but not after 30 or 60 min. These results suggest that exposure to IS sensitizes the CORT and ACTH response to subsequent HPA activation.

Adrenocorticotropic Hormone↗