Endotoxin releases a precursor to vasodilation from large veins in an NF-κB-dependent manner

Effects of NF-kappaB inhibitor on titanium particulate-induced inflammation in a murine model

BACKGROUND

Activation of nuclear factor kappa B (NF-kappaB) signaling in response to implant particulates may be critical in the pathogenesis of implant loosening after joint arthroplasty. The purpose of this study was to investigate the inhibitory effects of pyrrolidine dithiocarbamate (PDTC) in a murine model of inflammation induced by titanium (Ti) particulates.

MATERIALS AND METHODS

Ti particulates were introduced into established air pouches on C57BL/6J mice. Mice were injected intraperitoneally with either high-dose PDTC (100 mg/kg) or low-dose PDTC (50 mg/kg). Mice without drug treatment, as well as mice injected with saline alone were included. Each group consisted of sixteen mice. The membranes and lavage fluid were harvested 2 d or 7 d after injection of particulate suspension for histological and molecular analysis.

RESULTS

Histologic analysis showed that PDTC reduced inflammatory responses in air pouches, that is, thinner membrane and decreased cellular infiltration. In addition, PDTC reduced the release of inflammatory cytokines such as tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) in the lavage fluid or supernatant of homogenates as evaluated by ELISA.

CONCLUSION

These results suggest that PDTC inhibits Ti particulate-induced inflammatory responses in the murine model; thus it represents a promising therapeutic candidate for the prevention and treatment of implant loosening.

Reperfusion injury after hemorrhage: a collective review

OBJECTIVE

To review current knowledge of hemorrhagic shock and reperfusion injury.

SUMMARY BACKGROUND DATA

Patients with hemorrhagic shock require optimal resuscitation and cessation of ongoing bleeding. Often our resuscitative measures, while necessary, cause a wide range of detrimental physiologic effects. Research continues to answer questions regarding measurable endpoints and optimal fluids used in resuscitation. Elucidation and understanding of the complex metabolic pathways involved in reperfusion injury are areas of intense current investigative effort.

METHODS

A literature review was performed using MEDLINE and key words related to experimental and clinical studies concerning shock and reperfusion.

RESULTS

Experimental studies have shown that resuscitation with colloid and crystalloid show no difference in outcomes in critically ill patients. Laboratory studies are showing promising results with immunomodulation of response to injury. However, no clinical trials have shown significance yet.

CONCLUSIONS

It is unlikely that a single treatment modality or "magic bullet" will be able to substantially block such a complex regulated process unless performed before feedback mechanisms known to be in place. Ongoing translational research will inevitably have a major impact on patient care.

Inhibition of NF-KB Does Not Induce C-Jun N-Terminal Kinase-Mediated Apoptosis in Reperfusion Injury

BACKGROUND

The role of C-Jun N-terminal Kinase (c-Jun Kinase) in apoptosis is unclear. It is likely that c-Jun Kinase activation is cell type and stimulus dependent. c-Jun Kinase promotes tumor necrosis factor (TNF)-alpha mediated apoptosis in nuclear factor (NF)-KB deficient cells. Minimal NF-KB expression may be enough to abrogate c-Jun Kinase-mediated apoptosis during reperfusion injury.

STUDY DESIGN

Forty Sprague-Dawley rats underwent hemorrhagic ischemia and reperfusion. Twenty experimental animals were treated with the NF-KB inhibitor herbimycin A, and 20 control animals underwent only hemorrhage and reperfusion. Serum TNF-alpha and c-Jun Kinase levels were measured. Adrenal, kidney, liver, ileum, colon, and skeletal muscle tissues were evaluated for apoptosis by hematoxylin and eosin staining.

RESULTS

TNF-alpha levels were 400 pg/mL (control) and 385 pg/mL (experimental) during ischemia (p=0.46), increased in controls to 450 pg/mL, and decreased in the experimental arm to 175 pg/mL (p=0.028). c-Jun Kinase levels were 1,525 pg/mL (control) and 1,475 pg/mL (experimental) during ischemia (p=0.35) and increased to 5,250 pg/mL (control) and 5,000 pg/mL (experimental) after reperfusion (p=0.26). In control animals, necrosis was seen in kidney, adrenal, and liver specimens. Compared with controls, experimental animals had average tissue hemorrhage scores of less than 1 (p < 0.001), with no necrosis seen in any experimental arm (p<0.001).

CONCLUSIONS

During inhibition of NF-KB, c-Jun Kinase levels remained unchanged. But no increase in cell death or necrosis was seen in tissue samples. Antiapoptotic effects were unchanged with the down-regulation of NF-KB. Minimal expression of NF-KB may be enough to protect against apoptosis in reperfusion injury.

Endotoxin Releases a Substance from the Aorta that Dilates an Isolated Arteriole by Up-Regulating INOS

BACKGROUND

Loss of vascular tone in resistance arterioles has been implicated as the cause of hypotension in septic shock. It is believed that the overproduction of nitric oxide (NO) by the inducible isoform of nitric oxide synthase (iNOS) results in the vasodilatation seen in septic shock. However, we have shown that endotoxin has no effect on vascular tone of an isolated resistance vessel unless the endotoxin flows over a segment of aorta or vena cava upstream in the superfusion line. The aim of this study was to determine if the subsequent vasodilation was due to the release of a direct vasodilator or production of NO in the arteriole and if its source was iNOS by using its selective inhibitor, aminoguanidine.

MATERIALS AND METHODS

First-order rat cremaster arterioles (n = 36) were isolated and cannulated onto micropipettes, superfused with physiological buffer at 34 degrees C, pressurized to 70 mm Hg, and allowed to gain spontaneous tone over 90 min. A segment of abdominal aorta was then placed in series with the arteriole so that the superfusate passed over the aorta and then into the tissue bath containing the isolated arteriole. The vessels were allowed to equilibrate over 60 min. During this interval, the arteriole was exposed to l-NAME (100 mum), aminoguanidine (100 mum), or buffer. The aorta and arteriole were then superfused with endotoxin (Salmonella enteritidis 2.5 mug/ml). Internal diameters of cannulated arterioles were measured and recorded with videomicroscopy and videocalipers at a resolution of +/-1 mum every 15 min for 1 h. Six groups were created with n = 6 for each group: Group 1, endotoxin; Group 2, control; Group 3, l-NAME and endotoxin; Group 4, l-NAME; Group 5, aminoguanidine and endotoxin; and Group 6, aminoguanidine.

RESULTS

After the 60-min equilibration period, there was no significant difference in resting tone among the six groups. At t = 120, the percentage of tone in the control group was 42.7 +/- 0.4% (mean +/- SEM) and this was not changed by treatment with aminoguanidine (42.2 +/- 0.7%). However, exposure to l-NAME alone resulted in vasoconstriction with a gain in tone to 49.5 +/- 1.6% (P > 0.05). Endotoxin alone caused arteriolar tone to fall to 33.5 +/- 1.2% (P < 0.05). Arterioles treated with aminoguanidine did not lose tone (42.6 +/- 1.7%) when exposed to endotoxin and arterioles treated with l-NAME retained their elevated tone (46.0 +/- 2.2%) after treatment with endotoxin.

CONCLUSIONS

This study demonstrates that the aorta exposed to endotoxin releases a substance that vasodilates resistance arterioles through the up-regulation of iNOS. Aminoguanidine prevented the fall in tone following exposure to endotoxin, while use of the nonselective NOS inhibitor, l-NAME, not only blocked the fall due to endotoxin but increased basal tone by blocking the constitutively active eNOS.