PubMed Health⌕ Search

Biomedical subjects

K Seibert

Publications and source records attributed to K Seibert.

At least 55 records · Page 3Linked to original sources
PubMed1995

Mediation of inflammation by cyclooxygenase-2.

Non-steroidal antiinflammatory drugs (NSAIDs) are commonly used for the treatment of inflammation, pain, and fever. Mechanistically, these compounds are believed to act via inhibition of the enzyme cyclooxygenase (COX), which catalyzes the conversion of arachidonic acid to the prostaglandins (PGs). Although commercially available NSAIDS are efficacious antiinflammatory agents, significant side effects limit their use. Recently two forms of COX were identified- a constitutively expressed COX-1 and a cytokine-inducible COX-2. Commercially available NSAIDs like indomethacin inhibit both COX-1 and COX-2 suggesting the hypothesis that toxicities associated with NSAID therapy are due to inhibition of the non-regulated or constitutive form of COX (COX-1) in normal tissues, whereas therapeutic benefit derives from inhibition of the inducible enzyme, COX-2, at the site of inflammation. Therefore, a selective inhibitor of COX-2 may be anti-inflammatory without GI toxicity-providing a significant improvement over currently available NSAIDs.

Animals↗
PubMed1995

Regulation of prostaglandin production by nitric oxide; an in vivo analysis.

1. Endotoxin E. Coli lipopolysaccharide (LPS)-treatment in conscious, restrained rats increased plasma and urinary prostaglandin (PG) and nitric oxide (NO) production. Inducible cyclo-oxygenase (COX-2) and nitric oxide synthase (iNOS) expression accounted for the LPS-induced PG and NO release since the glucocorticoid, dexamethasone inhibited both effects. Thus, LPS (4 mg kg-1) increased the plasma levels of nitrite/nitrate from 14 +/- 1 to 84 +/- 7 microM within 3 h and this rise was inhibited to 35 +/- 1 microM by dexamethasone. Levels of 6-keto PGF1 alpha in the plasma were below the detection limit of the assay (< 0.2 ng ml-1). However, 3 h after the injection of LPS these levels rose to 2.6 +/- 0.2 ng ml-1 and to 0.7 +/- 0.01 ng ml-1 after LPS in rats that received dexamethasone. 2. The induced enzymes were inhibited in vivo with selective COX and NOS inhibitors. Furthermore, NOS inhibitors, that did not affect COX activity in vitro markedly suppressed PG production in the LPS-treated animals. For instance, the LPS-induced increased in plasma nitrite/nitrate and 6-keto PGF1 alpha at 3 h was decreased to 18 +/- 2 microM and 0.5 +/- 0.02 ng ml-1, 23 +/- 1 microM and 0.7 +/- 0.01 ng ml-1, 29 +/- 2 microM and 1 +/- 0.01 ng ml-1 in rats treated with LPS in the presence of the NOS inhibitors NG-monomethyl-L-arginine, NG-nitro arginine methyl ester and aminoguanidine, respectively. 3. The intravenous infusion of the NO donors sodium nitroprusside (SNP) or glyceryl trinitrate (GTN)increased prostaglandin production in normal animals (for instance urinary PGE2 excretion was increased from 96 +/- 10 to 576 +/- 12 pg min-1 and 400 +/- 24 pg min-1 in the presence of GTN or SNP respectively).4. Proteinuria was measured in order to evaluate the roles of NO and PG in renal damage associated with the in vivo injection of LPS. Interestingly, dexamethasone and the NOS inhibitors attenuated proteinuria in the LPS-treated rats. The COX inhibitors had no effect. It therefore appears that NO and not PG contributes to the LPS-induced renal damage; these findings support the potential use of NOS inhibitors in the treatment of renal inflammation.5. This study demonstrates the regulatory contribution of NO on the in vivo production of prostanoids and suggests that in inflammatory diseases that are driven by both NO and the prostaglandins, NOS inhibitors may act to reduce inflammation by the dual inhibition of cytotoxic NO and pro-inflammatory PG.

6-Ketoprostaglandin F1 alpha↗
PubMed1995

Dual inhibition of nitric oxide and prostaglandin production contributes to the antiinflammatory properties of nitric oxide synthase inhibitors.

We have recently put forward the hypothesis that the dual inhibition of proinflammatory nitric oxide (NO) and prostaglandins (PG) may contribute to the antiinflammatory properties of nitric oxide synthase (NOS) inhibitors. This hypothesis was tested in the present study. A rapid inflammatory response characterized by edema, high levels of nitrites (NO2-, a breakdown product of NO), PG, and cellular infiltration into a fluid exudate was induced by the administration of carrageenan into the subcutaneous rat air pouch. The time course of the induction of inducible nitric oxide synthase (iNOS) protein in the pouch tissue was found to coincide with the production of NO2-. Dexamethasone inhibited both iNOS protein expression and NO2- synthesis in the fluid exudate (IC50 = 0.16 mg/kg). Oral administration of N-iminoethyl-L-lysine (L-NIL) or NG-nitro-L-arginine methyl ester (NO2Arg) not only blocked nitrite accumulation in the pouch fluid in a dose-dependent fashion but also attenuated the elevated release of PG. Finally, carrageenan administration produced a time-dependent increase in cellular infiltration into the pouch exudate that was inhibited by dexamethasone and NOS inhibitors. At early times, i.e., 6 h, the cellular infiltrate is composed primarily of neutrophils (98%). Pretreatment with colchicine reduced both neutrophil infiltration and leukotriene B4 accumulation in the air pouch by 98% but did not affect either NO2- or PG levels. In conclusion, the major findings of this paper are that (a) selective inhibitors of iNOS are clearly antiinflammatory agents by inhibiting not only NO but also PG and cellular infiltration and (b) that neutrophils are not responsible for high levels of NO and PG produced.

Amino Acid Oxidoreductases↗
PubMed1994

Pharmacological and biochemical demonstration of the role of cyclooxygenase 2 in inflammation and pain.

Nonsteroidal antiinflammatory drugs (NSAIDs) are widely used for the treatment of inflammatory diseases, but significant side effects such as gastrointestinal erosion and renal damage limit their use. NSAIDs inhibit the enzyme cyclooxygenase (COX), which catalyzes the conversion of arachidonic acid to prostaglandins (PGs) and thromboxane. Two forms of COX have been identified--COX-1, which is constitutively expressed in most tissues and organs, and the inducible enzyme, COX-2, which has been localized primarily to inflammatory cells and tissues. In an animal model of acute inflammation (injection of carrageenan into the footpad), edema was produced that was associated with marked accumulation of COX-2 mRNA and thromboxane. A selective inhibitor of COX-2 (SC-58125) inhibited edema at the inflammatory site and was analgesic but had no effect on PG production in the stomach and did not cause gastric toxicity. These data suggest that selective inhibition of COX-2 may produce superior antiinflammatory drugs with substantial safety advantages over existing NSAIDs.

Abscess↗
PubMed1994

Selective inhibition of inducible cyclooxygenase 2 in vivo is antiinflammatory and nonulcerogenic.

We have examined the role of cyclooxygenase 2 (COX-2) in a model of inflammation in vivo. Carrageenan administration to the subcutaneous rat air pouch induces a rapid inflammatory response characterized by high levels of prostaglandins (PGs) and leukotrienes in the fluid exudate. The time course of the induction of COX-2 mRNA and protein coincided with the production of PGs in the pouch tissue and cellular infiltrate. Carrageenan-induced COX-2 immunoreactivity was localized to macrophages obtained from the fluid exudate as well as to the inner surface layer of cells within the pouch lining. Dexamethasone inhibited both COX-2 expression and PG synthesis in the fluid exudate but failed to inhibit PG synthesis in the stomach. Furthermore, NS-398, a selective COX-2 inhibitor, and indomethacin, a nonselective COX-1/COX-2 inhibitor, blocked proinflammatory PG synthesis in the air pouch. In contrast, only indomethacin blocked gastric PG and, additionally, produced gastric lesions. These results suggest that inhibitors of COX-2 are potent antiinflammatory agents which do not produce the typical side effects (e.g., gastric ulcers) associated with the nonselective, COX-1-directed antiinflammatory drugs.

Amino Acid Sequence↗
PubMed1994

Endogenous nitric oxide enhances prostaglandin production in a model of renal inflammation.

The interaction between nitric oxide (NO) and cyclooxygenase (COX) was studied in a rabbit model of renal inflammation, the ureteral obstructed hydronephrotic kidney (HNK). Ex vivo perfusion of the HNK but not the control kidney (e.g., unobstructed contralateral kidney, CLK), led to a time-dependent release of nitrite (NO2-), a breakdown product of NO. Stimulation of the HNK with bradykinin (BK) evoked a time-dependent increase in prostaglandin E2 (PGE2) production. NG-monomethyl-L-arginine (L-NMMA), which blocks the activity of both constitutive and inducible nitric oxide synthase (cNOS and iNOS), aminoguanidine, a recently described selective iNOS inhibitor, dexamethasone, or cycloheximide abolished the release of NO2- and attenuated the exaggerated BK-induced PGE2 production. This supports the existence of iNOS and COX-2 in the HNK. In the CLK, BK elicited release of both NO2- and PGE2 but this did not augment with time. L-NMMA but not aminoguanidine, dexamethasone, or cycloheximide attenuated NO2- and PGE2 release indicative of the presence of constitutive but not inducible NOS or COX. The current study suggests that the endogenous release of NO from cNOS in the CLK activates a constitutive COX resulting in optimal PGE2 release by BK. In addition, in the HNK, NO release from iNOS activates the induced COX resulting in markedly increased release of proinflammatory prostaglandin. The broader implication of this study is that the cyclooxygenase isozymes are potential receptor targets for nitric oxide.

Amino Acid Oxidoreductases↗
PubMed1994

In vivo glucocorticoids regulate cyclooxygenase-2 but not cyclooxygenase-1 in peritoneal macrophages.

Acute inflammatory stimuli elevate both the production of prostaglandins and the synthesis and activity of prostaglandin synthase/cyclooxygenase enzyme (COX) in murine peritoneal macrophages. Adrenalectomy also elevates prostaglandin production, COX synthesis and COX activity in these cells. We have utilized cDNA probes and antisera specific for the products of the prostaglandin synthase/cyclooxygenase-1 (COX-1) and TIS10/prostaglandin synthase-2/cyclooxygenase-2 (COX-2) genes to demonstrate that adrenalectomy causes elevation of mRNA and protein from the COX-2 gene, but not from the COX-1 gene, in peritoneal macrophages. Dexamethasone replacement suppressed the elevation of COX-2 mRNA message, COX-2 protein and the increased COX enzyme activity observed in adrenalectomized animals. In contrast, both COX-1 message and COX-1 protein levels were unaffected either by adrenalectomy or by dexamethasone administration. Thus, under normal physiological conditions, tonic glucocorticoid inhibition appears to play a major role in the in vivo regulation of the COX-2 gene. These data are consistent with COX-1 being the constitutive, housekeeping enzyme in macrophages in normal physiological conditions and with the enhanced prostaglandin synthesis seen after an inflammatory stimulus resulting from the rapid induction and activity of COX-2.

Adrenalectomy↗
PubMed1994

Role of inducible cyclooxygenase (COX-2) in inflammation.

Nonsteroidal anti-inflammatory drugs (NSAIDs) are potent anti-inflammatory agents that act through the inhibition of the cyclooxygenase (COX) enzyme and the subsequent inhibition of prostaglandins at the site of inflammation. Unfortunately, inhibition of gastrointestinal or renal prostaglandins is associated with mechanism-based toxicities that limit the usefulness of these otherwise potent and efficacious drugs. Recently two forms of the COX enzyme have been identified: COX-1, which is constitutively expressed in many cells and tissues, and COX-2, which is selectively induced by proinflammatory cytokines at the site of inflammation. The discovery of a second COX enzyme led to the hypothesis that toxicity associated with the clinically useful NSAIDs is caused by the inhibition of COX-1, whereas the anti-inflammatory properties were caused by the inhibition of inducible COX-2. In support of this hypothesis, expression of the inducible COX-2 enzyme is selectively blocked by the potent anti-inflammatory drug dexamethasone. Selective inhibition of COX-2 may produce superior anti-inflammatory drugs with substantial safety over existing NSAIDs.

Arachidonic Acid↗
PubMed1994

Regulation of prostaglandin synthesis by glucocorticoids.

Glucocorticoids are very effective anti-inflammatory agents since they affect several of the key mediators responsible for the inflammatory response, including prostaglandins. In particular, under normal physiological conditions, prostaglandin synthesis mediated via the constitutively expressed cyclooxygenase-1 (COX-1) is not affected by endogenously or exogenously administered glucocorticoids. However, within the context of the inflammatory response, phospholipase A2 as well as cyclooxygenase-2 (COX-2) are induced, resulting in an exacerbated production of prostaglandins. The antiinflammatory steroids will reduce inflammation-induced prostaglandin synthesis by inhibiting the expression of these two key enzymes, PLA2 and COX-2.

Cells, Cultured↗
PubMed1993

Nitric oxide activates cyclooxygenase enzymes.

We have evaluated the role of nitric oxide (NO) on the activity of the constitutive and induced forms of cyclooxygenase (COX; COX-1 and COX-2, respectively). Induction of NO synthase (NOS) and COX (COX-2) in the mouse macrophage cell line RAW264.7 by Escherichia coli lipopolysaccharide (1 microgram/ml, 18 h) caused an increase in the release of nitrite (NO2-) and prostaglandin E2 (PGE2), products of NOS and COX, respectively. Production of both NO2- and PGE2 was blocked by the NOS inhibitors NG-monomethyl-L-arginine or aminoguanidine. The effects of NG-monomethyl-L-arginine or aminoguanidine were reversed by coincubation with L-Arg, the precursor for NO synthesis, but not by D-Arg. RAW264.7 cells stimulated for 18 h with lipopolysaccharide in L-Arg-free medium (to reduce NO generation by the endogenous NOS pathway) failed to release NO2- and accumulated at least 4-fold less PGE2 when compared to cells in the presence of L-Arg. PGE2 production elicited by a 15-min arachidonic acid treatment of lipopolysaccharide-induced RAW264.7 cells in L-Arg-deficient medium was decreased 3-fold when compared to the release obtained with cells induced in medium containing L-Arg. To examine the NO activation of the induced form of COX in the absence of an endogenous L-Arg, human fetal fibroblasts were first stimulated for 18 h with interleukin 1 beta. These cells released PGE2 but not NO2-, consistent with the induction of COX but not NOS in the fibroblast. Exogenous NO either as a gaseous solution or released by a NO donor, sodium nitroprusside or glyceryl trinitrate, increased COX activity in the interleukin 1 beta-stimulated fibroblasts by 5-fold; these effects were abolished by coincubation with hemoglobin (10 microM), which binds and inactivates NO, but not by methylene blue, an inhibitor of the soluble guanylate cyclase. Furthermore, sodium nitroprusside (0.25-1 mM) increased arachidonic acid-stimulated PGE2 production by murine recombinant COX-1 and COX-2. These results demonstrate that NO enhances COX activity through a mechanism independent of cGMP and suggest that, in conditions in which both the NOS and COX systems are present, there is an NO-mediated increase in the production of proinflammatory prostaglandins that may result in an exacerbated inflammatory response. The data suggest that NO directly interacts with COX to cause an increase in the enzymatic activity.

Amino Acid Oxidoreductases↗
PubMed1992

Distribution and characterization of cyclooxygenase immunoreactivity in the ovine brain.

Evidence from tissue culture studies suggests that glial cells are the principal source of prostaglandins in the brain. We have used immunohistochemistry, Western blot analysis, and enzyme activity assays to localize cyclooxygenase (COX), the enzyme responsible for the conversion of arachidonic acid to prostaglandins, in situ in the normal ovine brain. We observed very few immunoreactive glial cells. In contrast, an extensive distribution of COX-like immunoreactive (ir) neuronal cell bodies and dendrites and a corresponding pattern of COX enzyme activity were observed. COXir neurons were most abundant in forebrain sites involved in complex, integrative functions and autonomic regulation such as the cerebral cortex, hippocampus, amygdala, bed nucleus of the stria terminalis, substantia innominata, dorsomedial nucleus of the hypothalamus, and tuberomammillary nucleus. Moderate populations were observed in other regions of the central nervous system implicated in sensory afferent processing, including the dorsal column nuclei, spinal trigeminal nucleus, and superior colliculus, and in structures involved in autonomic regulation, such as the nucleus of the solitary tract, parabrachial nucleus, and the periaqueductal gray matter. We did not observe COXir axons or terminal fields, however. Our results suggest that neurons may use prostaglandins as intracellular or perhaps paracrine, but probably not synaptic, mediators in the normal brain.

Acetylcholinesterase↗
PubMed1992

Endogenous glucocorticoids regulate an inducible cyclooxygenase enzyme.

The effect of endogenous glucocorticoids on the expression of the cyclooxygenase enzyme was studied by contrasting cyclooxygenase expression and prostanoid synthesis in adrenalectomized and sham-adrenalectomized mice with or without the concurrent administration of endotoxin. Peritoneal macrophages obtained from adrenalectomized mice showed a 2- to 3-fold induction in cyclooxygenase synthesis and activity when compared to sham controls. Intravenous injection of a sublethal dose of endotoxin (5 micrograms/kg) further stimulated cyclooxygenase synthesis, resulting in a 4-fold increase in prostaglandin production. Similar cyclooxygenase induction can be achieved in macrophages obtained from normal mice but only after high doses of endotoxin (2.5 mg/kg) that are 100% lethal to adrenalectomized mice. Restoration of glucocorticoids in adrenalectomized animals with dexamethasone completely inhibited the elevated cyclooxygenase and protected these animals from endotoxin-induced death. In contrast, no signs of cyclooxygenase induction were observed in the kidneys of the adrenalectomized mice, even when treated with endotoxin. Dexamethasone did not affect the constitutive cyclooxygenase activity and prostaglandin production present in normal and adrenalectomized kidneys. These data indicate the existence of a constitutive cyclooxygenase that is normally present in most cells and tissues and is unaffected by steroids and of an inducible cyclooxygenase that is expressed only in the context of inflammation by proinflammatory cells, like macrophages, and that is under glucocorticoid regulation. Under normal physiological conditions glucocorticoids maintain tonic inhibition of inducible cyclooxygenase expression. Depletion of glucocorticoids or the presence of an inflammatory stimulus such as endotoxin causes rapid induction of this enzyme, resulting in an exacerbated inflammatory response that is often lethal.

6-Ketoprostaglandin F1 alpha↗