Chemical synthesis of nitric oxide in the stomach from dietary nitrate in humans

BACKGROUND/AIMS

It has been suggested that dietary nitrate, after concentration in the saliva and reduction to nitrite by tongue surface bacteria, is chemically reduced to nitric oxide (NO) in the acidic conditions of the stomach. This study aimed to quantify this in humans.

METHODS

Ten healthy fasting volunteers were studied twice, after oral administration of 2 mmol of potassium nitrate or potassium chloride. Plasma, salivary and gastric nitrate, salivary and gastric nitrite, and gastric headspace NO concentrations were measured over six hours.

RESULTS

On the control day the parameters measured varied little from basal values. Gastric nitrate concentration was 105.3 (13) mumol/l (mean (SEM), plasma nitrate concentration was 17.9 (2.4) mumol/l, salivary nitrate concentration 92.6 (31.6) mumol/l, and nitrite concentration 53.9 (22.8) mumol/l. Gastric nitrite concentrations were minimal (< 1 mumol/l). Gastric headspace gas NO concentration was 16.4 (5.8) parts per million (ppm). After nitrate ingestion, gastric nitrate peaked at 20 minutes at 3430 (832) mumol/l, plasma nitrate at 134 (7.2) mumol/l, salivary nitrate at 1516.7 (280.5) mumol/l, and salivary nitrite at 761.5 (187.7) mumol/l after 20-40 minutes. Gastric nitrite concentrations tended to be low, variable, and any rise was non-sustained. Gastric NO concentrations rose considerably from 14.8 (3.1) ppm to 89.4 (28.6) ppm (p < 0.0001) after 60 minutes. All parameters remained increased significantly for the duration of the study.

CONCLUSIONS

A very large and sustained increase in chemically derived gastric NO concentrations after an oral nitrate load was shown, which may be important both in host defence against swallowed pathogens and in gastric physiology.

MR microscopy of the arterial wall in an experimental model of atherosclerosis: preliminary results

PURPOSE

To obtain images of the arterial lumen and wall in a rabbit model of atherosclerosis with use of high-resolution magnetic resonance (MR) imaging to follow morphologic changes during the induction of atherosclerosis and, hence, develop a non-invasive tool to investigate restenosis.

MATERIALS AND METHODS

In vivo microscopic MR images of rabbit aorta were acquired after balloon injury. Measurements of wall and lumen diameter from MR images area were compared with measurements obtained from histologic and angiographic examination.

RESULTS

Injured rabbits exhibited an obvious thickening of the arterial wall, accompanied by an increased wall conspicuity, probably due to increases in T2. Quantitative MR morphometry corresponded well with morphologic measurements based on angiographic and histologic study.

CONCLUSIONS

MR implanted coil technology affords imaging of the arterial lumen and wall, allowing temporal assessment of the morphologic changes due to intimal hyperplasia after balloon dilation and may enable the evaluation of novel techniques to eliminate restenosis.

Nine episodes of CPD-associated peritonitis with vancomycin resistant enterococci

Nine episodes of chronic peritoneal dialysis (CPD)-associated peritonitis with vancomycin resistant enterococci (VRE) were described between November 1993 and February 1996 in our dialysis unit. During the time period, 216 patients were treated for 227 episodes of peritonitis. Of the patients developing peritonitis with VRE the mean age +/- SD was 56.3 +/- 9.7 years. There were 5 females, 4 males, 5 Caucasians and 4 African-Americans. Diabetes mellitus, cardiovascular disease and gastrointestinal disease were present in 7, 8 and 7 of the 9 patients with VRE peritonitis, respectively. Patients were maintained on CPD therapy for an average of 29.9 +/- 19.2 patient months before developing VRE peritonitis. The prior rate of CPD associated peritonitis in the patients developing VRE peritonitis was significantly higher than the rate noted in the CPD patients not developing peritonitis with VRE (1 episode in 6.3 patient months vs. 1 episode in 12.5 patient months, P < 0.05). All 9 patients had used vancomycin in the six months prior to the development of VRE peritonitis and 78% had used a cephalosporin. The antimicrobial therapy used to eradicate peritonitis with VRE varied among the 9 patients with chloramphenicol used in 4 patients. The Tenckhoff catheter was removed in 6 of the 9 patients and was successfully reinserted in one patient. The catheter was not removed in 3 patients and 2 of these patients expired. Five of the 9 patients expired while being treated for VRE, 2 transferred to hemodialysis and 2 continued CPD therapy. VRE peritonitis is a major concern for patients maintained on CPD therapy. Future studies are needed with case controls to determine the significance of prior vancomycin and cephalosporin therapy, fecal VRE carriage and certain demographic data on the acquisition of VRE peritonitis. Furthermore, the optimal therapy and outcome may be better clarified through such a review.

Nitric oxide is generated on the skin surface by reduction of sweat nitrate

Nitric oxide (NO) is known to be synthesized by mammalian cells from L-arginine by a group of NO synthase enzymes. We now show that NO is generated from human skin and propose a different mechanism of production. Whereas enzymatic NO synthesis is inhibited by monomethyl L-arginine, this arginine analog, when infused into the brachial artery at concentrations sufficient to inhibit endothelial NO synthase activity, has little effect on hand skin NO production. Hand skin NO production is increased by topical acidification of the skin surface and greatly increased by the addition of nitrite solutions. We propose that NO generation from skin derives from sweat nitrite (the concentration of which was found to average 3.4 microM in six subjects) due to chemical reduction consequent to the acidic nature of sweat. Sweat contains nitrate in appreciable amounts, and skin commensal bacteria can synthesize nitrate reductase enzyme. Patients on long-term tetracycline antibiotics showed significantly reduced skin NO synthesis, although topical antiseptic and antibiotics had little effect on NO generation in the short-term. We propose that NO generation from skin is dependent on bacterial nitrate reduction to nitrite and subsequent reduction by acidification. We speculate that this has a physiologic role in the inhibition of infection by pathogenic fungi and other susceptible microorganisms and may affect cutaneous T-cell function, keratinocyte differentiation, and skin blood flow.

Antimicrobial effect of acidified nitrite on gut pathogens: importance of dietary nitrate in host defense

Dietary intake of nitrate generates salivary nitrite, which is acidified in the stomach, leading to a number of reactive intermediates of nitrogen, among which are the potentially carcinogenic N-nitrosamines. Acidified nitrite, however, also has antimicrobial activity which coincides with the formation of nitric oxide. The present study examines the antimicrobial effect in vitro of acidified nitrite on Salmonella enteritidis, Salmonella typhimurium, Yersinia enterocolitica, Shigella sonnei, and Escherichia coli O157. First-order regression plots showed a linear inverse relationship of log-transformed proton and nitrite concentrations with MICs and MBCs after 30 min, 2 h, and 24 h of exposure (P < 0.001 for all antibacterial activities). Susceptibility to the acidified nitrate solutions ranked as follows: Y. enterocolitica > S. enteritidis > S. typhimurium = Shigella sonnei > E. coli O157 (P < 0.05). Addition of SCN-, but not that of CI-, increased the antibacterial activity (paired t testing, P < 0.001). Generation of salivary nitrite from dietary nitrate may provide significant protection against gut pathogens in humans.

Chemical generation of nitric oxide in the mouth from the enterosalivary circulation of dietary nitrate

High concentrations of nitrite present in saliva (derived from dietary nitrate) may, upon acidification, generate nitrogen oxides in the stomach in sufficient amounts to provide protection from swallowed pathogens. We now show that, in the rat, reduction of nitrate to nitrite is confined to a specialized area on the posterior surface of the tongue, which is heavily colonized by bacteria, and that nitrate reduction is absent in germ-free rats. We also show that in humans increased salivary nitrite production resulting from nitrate intake enhances oral nitric oxide production. We propose that the salivary generation of nitrite is accomplished by a symbiotic relationship involving nitrate-reducing bacteria on the tongue surface, which is designed to provide host defence against microbial pathogens in the mouth and lower gut. These results provide further evidence for beneficial effects of dietary nitrate.

Depressive symptoms in patients with systemic lupus erythematosus: association with central nervous system lupus and Sjögren's syndrome

OBJECTIVE

To determine if patients with systemic lupus erythematosus (SLE) with depressive symptoms differ in regard to organ involvement and serological activity from other patients with SLE.

METHODS

Disease manifestations were compared between 71 patients with SLE with a history of depressive symptoms and 278 patients without a history of depressive symptoms by univariate analysis and multiple logistic regression.

RESULTS

Both univariate and logistic regression analysis revealed an association of depressive symptoms with neuropsychiatric lupus and secondary Sjögren's syndrome (SS). Patients with neuropsychiatric lupus had an adjusted odds ratio of 3.43 (95% CI 2.55, 4.63; p = 0.00005), and patients with secondary SS had an adjusted odds ratio of 2.97 (95% CI 2.08, 4.25; p = 0.0006) for depressive symptoms. No other organ involvement or serological abnormality was associated with depressed mood.

CONCLUSION

These discrete associations of depressive symptoms with neuropsychiatric lupus and secondary SS suggest that depression does not occur purely as a response to social stresses, and may be a manifestation of autoimmune disease in some patients.

Glycemic response to sucrose-containing mixed meals in diets of children of with insulin-dependent diabetes mellitus

Our pilot study compared the short-term glycemic effects of a traditional "sucrose free" diet (Suc-Free, 2% total calories from sucrose) to a sucrose-containing diet (Suc-Con, 10% total calories from sucrose) in a clinical research center. Both weighed diets were isocaloric and included 50% carbohydrate, 30% fat, and 20% protein in three meals and three snacks; glucose, fructose, and dietary fiber were identical. Sucrose isocalorically replaced complex carbohydrate at each meal and for the afternoon snack. Ten children (7 to 12 years of age; mean total hemoglobin A1 level 8.9 +/- 0.3%) were randomly assigned, in a crossover design, to one of the two orders (Suc-Free followed by Suc-Con or Suc-Con followed by Suc-Free) for consecutive 2-day diet periods; insulin doses remained constant. Preprandial and postprandial blood glucose levels were measured for each meal and snack (18 measurements per day). To account for baseline differences, we calculated the change in blood glucose levels from baseline to 30 minutes and 1 hour for each meal and snack (mean +/- SEM). No differences were detected between diets. Total area under the glucose response curve (levels measured hourly from 8 AM to 9:30 PM in milligrams per deciliter) was not significantly different for the two diets (Suc-Free 3672 +/- 240; Suc-Con 3574 +/- 285; p = 0.74). No difference in 24-hour urinary glucose levels (measured in grams per day) was detected between the two diets (Suc-Free 35.6 +/- 7.5; Suc-Con 34.5 +/- 7.5; p = 0.84). Incidences of hyperglycemia that required supplemental short-acting insulin and of mild hypoglycemia were similar for both diet periods. Thus, in a controlled setting and during a short study period, children with insulin-dependent diabetes mellitus had a similar glycemic response to diets with and without a moderate amount of sucrose.

Reduction in vitro of red cell glutathione reproduces defects of cellular sodium transport seen in oedematous malnutrition

Red cells in oedematous malnutrition (kwashiorkor) have an increased sodium content, 'leakiness' to sodium and enhanced sodium pumping. In non-oedematous malnutrition (marasmus) there is a reduction in the sodium pump activity. The explanation has hitherto been unknown but the glutathione content of red cells is low in kwashiorkor and normal in marasmus. We artificially lowered the glutathione content of normal red cells to values characteristic of mild oedematous malnutrition, using the enzyme inhibitors bischloronitrosourea (BCNU) and buthionine sulfoximine (BSOX). After preincubation, the cells were washed to remove the inhibitors and oxidized glutathione. Cellular content of sodium and potassium, and 86Rb influx were then measured. The reduction in glutathione reproduced the abnormalities of sodium content and flux observed in kwashiorkor. We suggest that oxidant stress in kwashiorkor, by reducing cellular glutathione, may affect cell membrane electrolyte transport. This may act through alterations in membrane sulfhydryl groups. Glutathione depletion may therefore play an important role in the clinical picture and natural history of oedematous malnutrition and may have relevance to other conditions where oxidant stress occurs.

Alteration of extracellular cation concentrations and ratios in culture medium does not affect first cleavage division of hamster zygotes in vitro nor overcome the 'two-cell block'

In vivo fertilized hamster one-cell eggs (embryos) were cultured in a simple medium that was modified to provide a wide range of concentrations and ratios of the four major cation components (sodium, potassium, calcium and magnesium) while maintaining total osmotic pressure at 290 +/- 5 mosm. Embryos were cultured in these media to find the optimum cation concentrations for supporting the first cleavage division in vitro and to determine if physiologically abnormal cation concentrations and/or ratios in standard culture media could account for the 'two-cell block' to development in vitro in this species. Despite using a broad range of ratios for sodium:potassium (from 45:1 to 5:1) and for calcium:magnesium (from 17:1 to 1:1), there were no significant differences in the proportions of fertilized eggs that underwent the first cleavage division (approx. 60-80% across all treatments), and none of the two-cell embryos underwent further cleavage during extended culture. These data demonstrate that the first cleavage division of hamster embryos in vitro is insensitive to extracellular concentrations and ratios of the major cations, and that the non-physiological concentrations and/or ratios of these cations in the culture medium are not the primary reason for the failure of hamster zygotes to develop past the two-cell stage in vitro.