Hypoxia increases nitric oxide concentrations that are not completely inhibited by L-NMMA

INTRODUCTION

Recent investigations have demonstrated a wealth of knowledge about the biology of nitric oxide (NO) and the synthases (NOS) that generate it, under both physiologic and pathophysiologic conditions. In this study, we investigated the generation of NO under conditions of hypoxia in the absence of confounding functions such as blood loss or hypovolemia.

METHODS

Rats were subjected to either 30 or 60 min of hypoxia and sacrificed immediately or after 1 or 24 h of recuperation. Splenocyte proliferative ability and NO concentrations were determined in whole splenocytes and purified T-cell populations, with and without the use of 20 mg/kg L-NMMA, a potent NOS inhibitor. RT-PCR was performed to determine the presence or absence of inducible NOS transcription after hypoxia and hypoxia followed by reoxygenation with and without L-NMMA.

RESULTS

Hypoxia followed by reoxygenation stimulated NO production in whole splenocytes, which correlated with a decrease in splenocyte proliferation. T-cell stimulation and NO production were not upregulated under these conditions. Additionally, NO generation occurred following hypoxia, even in the presence of L-NMMA.

CONCLUSION

These results demonstrate that NO production after hypoxia may be due to an alternate, O2-independent pathway. Further investigations into the generation of NO through alternate pathways may identify treatments for hypoxia-related injury.

Allopurinol protects enterocytes from hypoxia-induced apoptosis in vivo

BACKGROUND

Reactive oxygen species can cause apoptosis and may be involved in hypoxic injury to the small bowel. Xanthine oxidase (XO) has been implicated in reactive oxygen species production. We hypothesized that administration of allopurinol would protect rat enterocytes from hypoxia-induced apoptosis.

METHODS

Twenty-four Sprague-Dawley rats (weight, 250-300 g) were subjected to 30 minutes of hypoxia (10% Fio(2)), then killed immediately or allowed to recover for an hour in room air (21% Fio(2)). Intraperitoneal allopurinol (50 mg/kg) or an equivalent amount of 0.9% saline was administered 1 hour before hypoxia. Control rats were exposed to 21% Fio(2) under similar conditions. Proximal jejunum was harvested from all animals in both groups and stained to detect apoptotic cells using terminal deoxynucleotidyl transferase-mediated biotinylated deoxynucleotide end labeling. In addition, sections of proximal jejunum were removed and the mucosal membrane was removed and flash frozen in liquid nitrogen for DNA fragmentation gel.

RESULTS

Intraperitoneal administration of allopurinol significantly reduced the percentage of apoptotic villi in the proximal jejunum compared with those animals receiving saline (11 +/- 7 vs. 25 +/- 12 in the hypoxia no recovery group, 41 +/- 14 vs. 67 +/- 8 in the hypoxia with recovery group, mean +/- SD, Mann-Whitney test, < 0.05). Intestinal XO activity was also significantly reduced in the animals receiving allopurinol compared with those receiving saline (6.8 +/- 3.12 vs. 19.1 +/- 4.56 mU/mL/g wet tissue in the hypoxia no recovery group, 0.86 +/- 0.33 vs. 11.5 +/- 7.13 mU/mL/g wet tissue in the hypoxia with recovery group, mean +/- SD, Mann-Whitney test, < 0.05).

CONCLUSION

Inhibition of XO appears to protect rat enterocytes from hypoxia-induced apoptosis in vivo.

Inhibition of xanthine oxidase does not influence immunosuppression after hemorrhagic shock

BACKGROUND

Resuscitated hemorrhagic shock causes global ischemia reperfusion with generation of toxic oxygen metabolites. We hypothesized that the immunosuppression that follows hemorrhagic shock may be linked to this process.

METHODS

Forty-five male Sprague-Dawley rats (weight, 250-300 g) were bled to a mean arterial pressure of 30 mm Hg for 60 minutes, then were resuscitated with three times the maximum blood loss of lactated Ringer's solution. Immune response was assessed by splenocyte proliferation and interleukin-2 (IL-2) production 72 hours after hemorrhage. Allopurinol (50 mg/kg) was given after hemorrhage and immediately before resuscitation.

RESULTS

Hemorrhagic shock caused significant decreases in splenocyte proliferation (cpm: (157,880 +/- 22,068 (mean +/- SD) vs. 37,787 +/- 15,849) and IL-2 production (1/2 max U/ml: 79.6 +/- 7.9 vs. 48.0 +/- 7.7) (both p < 0.05). Hepatic xanthine oxidase was significantly increased with hemorrhage and resuscitation. Hepatic xanthine oxidase activity after hemorrhage and resuscitation was significantly decreased after treatment with allopurinol (74.2 +/- 41.7 vs. 9.2 +/- 9.40). Allopurinol did not affect splenocyte proliferation (cpm: 21,875 +/- 9,316) or IL-2 production (1/2 max U/ml: 45.0 +/- 7.1).

CONCLUSIONS

These results demonstrate that inhibition of xanthine oxidase by allopurinol after hemorrhagic shock did not affect splenocyte proliferation or IL-2 production. We conclude that the immunosuppression after hemorrhagic shock is not dependent on xanthine oxidase-induced production of toxic oxygen metabolites.

Purification and characterization of the 30,000 dalton native antigen of Mycobacterium tuberculosis and characterization of six monoclonal antibodies reactive with a major epitope of this antigen

The 30,000 dalton native antigen of Mycobacterium tuberculosis is a major constituent of this organism and is secreted into culture medium. We purified this antigen by ammonium sulfate precipitation, ion-exchange chromatography, and reverse-phase high-performance liquid chromatography to yield a single 29 to 30 kd component. The first 20 N-terminal amino acid sequence was determined and found to be identical to that reported for M. bovis alpha-antigen. Immunoelectrophoresis studies demonstrated the purified 30,000 dalton antigen to be immunologically identical with antigen 6 and antigen 85B. The 30,000 dalton native antigen was a potent skin test antigen in sensitized guinea pigs. Six immunoglobulin G1 murine monoclonal antibodies against the 30,000 dalton antigen were generated. By enzyme-linked immunosorbent assay and western immunoblotting, all six monoclonal antibodies reacted with the 30,000 dalton antigen, perhaps with the same epitope. When used with culture filtrates of other mycobacteria, the monoclonal antibodies demonstrated reactivity with M. gordonae and M. kansasii and to a lesser extent with M. avium and M. scrofulaceum.

Characterization of Mycobacterium tuberculosis antigen 5 epitopes by using a panel of 19 monoclonal antibodies

Antigen 5 is a 35,000-dalton protein which has been purified from culture filtrates of Mycobacterium tuberculosis and shown by immunoprecipitation to be restricted in distribution to M. tuberculosis and M. bovis among 14 mycobacterial species studied. We raised 19 antigen 5-reactive monoclonal antibodies and used them to characterize epitopes of this antigen by enzyme-linked immunosorbent assay and immunoabsorbent affinity chromatography. Fifteen monoclonal antibodies, all immunoglobulin M (IgM), cross-reacted in two major patterns with culture filtrates from five species of mycobacteria and with purified mycobacterial arabinomannan and arabinogalactan. All 15 monoclonal antibodies also reacted with M. tuberculosis antigen 6. Immunoabsorbent affinity columns prepared with these antibodies yielded principally arabinomannan and arabinogalactan. Four monoclonal antibodies, three IgG2a and one IgM, reacted by enzyme-linked immunosorbent assay with antigens 5 and 6 exclusively and not with mycobacterial culture filtrates or polysaccharides. All four monoclonal antibodies yielded antigen 5 and small amounts of antigen 6 when used for immunoabsorbent affinity chromatography. We conclude from these studies that antigen 5 has two nonspecific epitopes, possibly carbohydrate in nature, and one apparent species-specific epitope which is shared with antigen 6.