Polyamines, arginine and nitric oxide

Multi-omics reveals the role of MCM2 and hnRNP K phosphorylation in mouse renal aging through genomic instability

The process of aging is characterized by structural degeneration and functional decline, as well as diminished adaptability and resistance. The aging kidney exhibits a variety of structural and functional impairments. In aging mice, thinning and graying of fur were observed, along with a significant increase in kidney indices compared to young mice. Biochemical indicators revealed elevated levels of creatinine, urea nitrogen and serum uric acid, suggesting impaired kidney function. Histological analysis unveiled glomerular enlargement and sclerosis, severe hyaline degeneration, capillary occlusion, lymphocyte infiltration, tubular and glomerular fibrosis, and increased collagen deposition. Observations under electron microscopy showed thickened basement membranes, altered foot processes, and increased mesangium and mesangial matrix. Molecular marker analysis indicated upregulation of aging-related β-galactosidase, p16-INK4A, and the DNA damage marker γH2AX in the kidneys of aged mice. In metabolomics, a total of 62 significantly different metabolites were identified, and 10 pathways were enriched. We propose that citrulline, dopamine, and indoxyl sulfate have the potential to serve as markers of kidney damage related to aging in the future. Phosphoproteomics analysis identified 6656 phosphosites across 1555 proteins, annotated to 62 pathways, and indicated increased phosphorylation at the Ser27 site of Minichromosome maintenance complex component 2 (Mcm2) and decreased at the Ser284 site of heterogeneous nuclear ribonucleoprotein K (hnRNP K), with these modifications being confirmed by western blotting. The phosphorylation changes in these molecules may contribute to aging by affecting genome stability. Eleven common pathways were detected in both omics, including arginine biosynthesis, purine metabolism and biosynthesis of unsaturated fatty acids, etc., which are closely associated with aging and renal insufficiency.

Spermine oxidase is a regulator of macrophage host response to Helicobacter pylori: enhancement of antimicrobial nitric oxide generation by depletion of spermine

The gastric pathogen Helicobacter pylori causes peptic ulcer disease and gastric cancer. We have reported that in H. pylori-activated macrophages, nitric oxide (NO) derived from inducible NO synthase (iNOS) can kill the bacterium, iNOS protein expression is dependent on uptake of its substrate L-arginine (L-Arg), the polyamine spermine can inhibit iNOS translation by inhibiting L-Arg uptake, and inhibition of polyamine synthesis enhances NO-mediated bacterial killing. Because spermine oxidase (SMO), which back-converts spermine to spermidine, is induced in macrophages by H. pylori, we determined its role in iNOS-dependent host defense. SMO shRNA knockdown in RAW 264.7 murine macrophages resulted in a marked decrease in H. pylori-stimulated iNOS protein, but not mRNA expression, and a 90% reduction in NO levels; NO production was also inhibited in primary murine peritoneal macrophages with SMO knockdown. There was an increase in spermine levels after H. pylori stimulation that rapidly decreased, while SMO knockdown caused a greater increase in spermine that was sustained. With SMO knockdown, L-Arg uptake and killing of H. pylori by macrophages was prevented. The overexpression of SMO by transfection of an expression plasmid prevented the H. pylori-stimulated increase in spermine levels, and led to increased L-Arg uptake, iNOS protein expression and NO production, and H. pylori killing. In two human monocytic cell lines, U937 and THP-1, overexpression of SMO caused a significant enhancement of NO production with H. pylori stimulation. By depleting spermine, SMO can abrogate the inhibitory effect of polyamines on innate immune responses to H. pylori by enhancing antimicrobial NO production.

CAT-2 amplifies the agonist-evoked force of airway smooth muscle by enhancing spermine-mediated phosphatidylinositol-(4)-phosphate-5-kinase-gamma activity

We investigated the effect the loss of the CAT-2 gene (CAT-2-/-) has on lung resistance (R(L)) and tracheal isometric tension. The R(L) of CAT-2-/- mice at a maximal dose of acetylcholine (ACh) was decreased by 33.66% (P = 0.05, n = 8) compared with that of C57BL/6 (B6) mice. The isometric tension of tracheal rings from CAT-2-/- mice showed a significant decrease in carbachol (CCh)-induced force generation (33.01%, P < 0.05, n = 8) compared with controls. The isoproterenol- or the sodium nitroprusside-induced relaxation was not affected in tracheal rings from CAT-2-/- mice. The activity of iNOS and arginase in lung tissue lysates of CAT-2-/- mice was indistinguishable from that of B6 mice. Furthermore, the expression of phospholipase-Cbeta (PLC-beta) and phosphatidylinositol-(4)-phosphate-5-kinase-gamma (PIP-5K-gamma) was examined in the lung tissue of CAT-2-/- and B6 mice. The expression of PIP-5K-gamma but not PLC-beta was significantly reduced in CAT-2-/- compared with B6 mice. The reduced airway smooth muscle (ASM) contractility to CCh seen in the CAT-2-/- tracheal rings was completely reversed by pretreating the rings with 100 muM spermine. This increase in the CAT-2-/- tracheal ring contraction upon spermine pretreatment correlated with a recovery of the expression of PIP-5K-gamma. Our data indicates that CAT-2 exerts control over ASM force development through a spermine-dependent pathway that directly correlates with the expression level of PIP-5K-gamma in the lung.

A systematic review of nitric oxide donors and L-arginine in experimental stroke; effects on infarct size and cerebral blood flow

BACKGROUND

Nitric oxide (NO) is a candidate treatment for acute ischaemic stroke, however published studies in experimental stroke have given conflicting results.

METHODS

We performed a systematic review of published controlled studies of L-arginine (the precursor for NO) and NO donors in experimental stroke. Data were analysed using the Cochrane Collaboration Review Manager software. Standardised mean difference (SMD) and 95% confidence intervals (95% CI) were calculated.

RESULTS

Altogether, 25 studies(s) were identified. L-Arginine and NO donors reduced total cerebral infarct volume in permanent (SMD -1.21, 95% CI -1.69 to -0.73, p < 0.01, s = 10) and transient models of ischaemia (SMD -0.78, 95% CI -1.21 to -0.35, p < 0.01, s = 7). Drug administration increased cortical CBF in permanent (SMD +0.86, 95% CI 0.52-1.21, p < 0.01, s = 8) but not transient models (SMD +0.34, 95% CI -0.02 to 0.70, p = 0.07, s = 4).

CONCLUSIONS

Administration of NO in experimental stroke reduces stroke lesion volume in permanent and transient models. This may be mediated, in part, by increased cerebral perfusion in permanent models. These data support clinical trials in stroke patients, although the presence of a narrow therapeutic time window may be a limiting factor.

Arginase and polyamine synthesis are key factors in the regulation of experimental leishmaniasis in vivo

Arginase 1, an enzyme induced by Th2 cytokines, is a hallmark of alternatively activated macrophages and is responsible for the hydrolysis of L-arginine into ornithine, the building block for the production of polyamines. Upregulation of arginase 1 has been observed in a variety of diseases, but the mechanisms by which arginase contributes to pathology are not well understood. We reveal here a unique role for arginase 1 in the pathogenesis of nonhealing leishmaniasis, a prototype Th2 disease, and demonstrate that the activity of this enzyme promotes pathology and uncontrolled growth of Leishmania parasites in vivo. Inhibition of arginase activity during the course of infection has a clear therapeutic effect, as evidenced by markedly reduced pathology and efficient control of parasite replication. Despite the clear amelioration of the disease, this treatment does not alter the Th2 response. To address the underlying mechanisms, the arginase-induced L-arginine catabolism was investigated and the results demonstrate that arginase regulates parasite growth directly by affecting the polyamine synthesis in macrophages.

Counteraction of oxalate induced nitrosative stress by supplementation of l-arginine, a potent antilithic agent

BACKGROUND

Our understanding of nitrosative stress in the process of urolithiasis is far from complete. Earlier studies carried out in our laboratory demonstrate the presence of nitrated THP in stone formers, l-arginine (l-arg) a precursor of nitric oxide (NO), attenuates the endothelial dysfunction caused by reactive nitrogen species. We investigated the role of l-arg in ethylene glycol (EG)-induced urolithic rat model and observed its antilithic and antioxidative properties.

METHODS

Hyperoxaluria was induced using 0.75% EG in drinking water. l-arg [1.25 g/kg body weight] was given orally for a period of 28 days.

RESULTS

EG-treated rats showed significant loss in body weight and increase in the activities of oxalate synthesizing enzymes such as glycollic acid oxidase in liver. Lactate dehydrogenase activity in liver and kidney was increased. The activity of the free radical producing enzyme xanthine oxidase, tissue oxalate and calcium levels were significantly increased in EG-treated rats. Depletion in the antioxidant enzymes, membrane bound ATPases and thiol status was observed in these rats. l-arg co-supplementation to EG-treated rats maintained the activities of the oxalate synthesizing enzymes and free radical producing enzymes with in the normal range. Tissue oxalate and calcium levels were also maintained near normal in l-arg treated hyperoxaluric rats. l-arg, by its cytoprotective effect, maintained the thiol status, thereby preserving the activities of the membrane bound ATPases and preventing proteinuria and subsequent weight loss in EG-treated rats.

CONCLUSION

l-arg feeding prevents the retention of calcium oxalate crystals in hyperoxaluric rats by way of protecting the renal cells from oxidative injury and also by providing a second line of defense through the normalization of the oxalate metabolism. It reduces the risk of stone formation, by curtailing free radicals and hyperoxaluria as both of them have to work in close association to form stones.

L-Arginine increases ischemic injury in wild-type mice but not in iNOS-deficient mice

Delayed administration of the nitric oxide precursor L-arginine increases brain injury in models of focal cerebral ischemia. We tested the hypothesis that L-arginine worsens the damage by acting as a substrate for inducible nitric oxide synthase (iNOS) and increasing the output of this enzyme. iNOS-null mice or wild-type littermates were treated with L-arginine (300 mg/kg; i.p, three times/day) starting 12 h after occlusion of the middle cerebral artery. Infarct volume was determined 96 h after ischemia. We found that L-arginine enlarges infarct volume in wild-type mice (+28+/-5% in neocortex) but not in iNOS-null mice. Thus, the worsening of ischemic damage produced by L-arginine depends on iNOS. The findings support the hypothesis that L-arginine worsens ischemic injury by increasing the catalytic output of iNOS and suggest that administration of L-arginine should be avoided in patients with acute stroke.

Arginine and nitric oxide metabolism in critically ill septic pediatric patients

OBJECTIVE

To investigate whole body, arginine metabolism and nitric oxide synthesis rates in septic, critically ill pediatric patients.

DESIGN

Prospective study.

SETTING

Pediatric intensive care unit at a general hospital.

PATIENTS

Ten consecutive septic patients age 6-16 yrs.

INTERVENTIONS

Septic patients received an 8-hr primed, constant intravenous tracer infusion of L-[guanidino-15N2]arginine, L-[1-13C]leucine, and [13C]urea. A 24-hr urine collection was obtained for determination of [15N]nitrate enrichment (15NO3(-)) and urinary nitrogen. The next day they received an infusion of L-[5-13C]arginine and L-[5-13C-ureido, 5,5, 2H2]citrulline. Blood samples were obtained for determination of plasma isotopic enrichment of the tracers given and of derived [15N]citrulline (nitric oxide synthesis), L-[13C-guanidino 5,5, 2H2]arginine (M+3 arg) (arginine synthesis), and [15N]urea (urea formation). Data are compared with historic controls from studies in healthy young adults.

MEASUREMENTS AND MAIN RESULTS

Plasma arginine fluxes were 67 +/- 21 and 72 +/- 17 micromol x kg(-1) x hr(-1), respectively, for the [15N2 guanidino] and the [13C] arginine labels, which were not different from reported adult values. The rates of arginine oxidation were 22.9 +/- 10.8 micromol x kg(-1) x hr(-1) and were higher than arginine synthesis rates of 9.6 +/- 4.2 micromol x kg(-1) x hr(-1) (p <.01); therefore, these patients were in a negative arginine balance. The rates of nitric oxide synthesis as estimated by the [15N]citrulline method were 1.58 +/- 0.69 micromol x kg(-1) x hr(-1) for septic patients and higher (p <.05) than values of 0.96 +/- 0.1 micromol x kg(-1) x hr(-1) in healthy adults. Septic patients were in a negative protein (leucine) balance of about -1.00 +/- 0.40 g x kg(-1) x day(-1).

CONCLUSIONS

Homeostasis of plasma arginine in septic patients was impaired compared with reported adult values. The rates of arginine oxidation were increased whereas net arginine synthesis was unchanged, leading to a negative arginine balance. The rates of nitric oxide synthesis and the fraction of plasma arginine used for nitric oxide and urea formation were increased. These findings suggest that under condition of sepsis, arginine becomes essential in critically ill children.

Role of nitric oxide in the pathogenesis of chronic pulmonary hypertension

Chronic pulmonary hypertension is a serious complication of a number of chronic lung and heart diseases. In addition to vasoconstriction, its pathogenesis includes injury to the peripheral pulmonary arteries leading to their structural remodeling. Increased pulmonary vascular synthesis of an endogenous vasodilator, nitric oxide (NO), opposes excessive increases of intravascular pressure during acute pulmonary vasoconstriction and chronic pulmonary hypertension, although evidence for reduced NO activity in pulmonary hypertension has also been presented. NO can modulate the degree of vascular injury and subsequent fibroproduction, which both underlie the development of chronic pulmonary hypertension. On one hand, NO can interrupt vascular wall injury by oxygen radicals produced in increased amounts in pulmonary hypertension. NO can also inhibit pulmonary vascular smooth muscle and fibroblast proliferative response to the injury. On the other hand, NO may combine with oxygen radicals to yield peroxynitrite and other related, highly reactive compounds. The oxidants formed in this manner may exert cytotoxic and collagenolytic effects and, therefore, promote the process of reparative vascular remodeling. The balance between the protective and adverse effects of NO is determined by the relative amounts of NO and reactive oxygen species. We speculate that this balance may be shifted toward more severe injury especially during exacerbations of chronic diseases associated with pulmonary hypertension. Targeting these adverse effects of NO-derived radicals on vascular structure represents a potential novel therapeutic approach to pulmonary hypertension in chronic lung diseases.

A mechanism of vasodilatory action of polyamines and acetylpolyamines: possible involvement of their Ca2+ antagonistic properties

Polyamines, a class of low-molecular weight organic polycations, have been shown to produce relaxing effects in vascular smooth muscles, although the mechanism has not been carefully examined. In this study, the mechanism of vascular action of polyamines and their metabolites, acetylpolyamines, was pharmacologically examined in the rabbit isolated thoracic aorta focusing on an endothelium-dependent component of vasodilatation and Ca2+ influx through plasma membrane channels. Both polyamines and acetylpolyamines (except N1-acetylputrescine, which produced no response or very slight contraction) caused concentration-dependent relaxation in preconstricted aortic rings containing an intact endothelium. Aortic rings denuded of endothelium were also responsive to both polyamines and acetylpolyamines. Inhibitors of nitric oxide (reduced haemoglobin and Nomega-nitro-L-arginine methyl ester), vasodilator prostaglandins (indomethacin) and guanylyl cyclase (methylene blue) did not affect the relaxation induced by both polyamines and acetylpolyamines in either endothelium-intact or -denuded aortic rings. Both polyamines and acetylpolyamines inhibited the concentration-dependent contraction for phenylephrine and K+. The Ca2+ agonist Bay K 8644 induced concentration-dependent contraction in segments of rabbit aorta partially depolarized with 15 mM KCl, and both polyamines and acetylpolyamines relaxed the Bay K 8644-induced contraction in a concentration-dependent manner. Interestingly, both polyamines and acetylpolyamines also decreased contractions evoked by the Ca2+ ionophore A23187. The concentration-response curve to exogenous Ca2+ in K+-depolarization medium (K+ = 120 mM) was shifted to the right by both polyamines and acetylpolyamines. The response elicited by Ca2+ was increased by Bay K 8644 (10(-6) M), and this potentiation was also inhibited by both polyamines and acetylpolyamines. The results indicate that both polyamines and acetylpolyamines can induce vasorelaxation of rabbit thoracic aorta by an endothelium-independent mechanism in-vitro and relax vascular smooth muscle by acting at the plasma membrane level, decreasing the influx of Ca2+. Therefore, polyamines and acetylpolyamines may have Ca2+ antagonistic properties which may, in part, be involved in the mechanism of rabbit aortic vascular smooth muscle relaxation.

Production and functional roles of nitric oxide in the proximal tubule

A significant role for nitric oxide (NO) in proximal tubule physiology and pathophysiology has been revealed by a series of in vivo and in vitro studies. Whether the proximal tubule produces NO under basal conditions is still controversial; however, evidence suggests that the proximal tubule is constantly exposed to NO that might include NO from nonproximal tubule sources. When challenged with a variety of stimuli, including hypoxia, the proximal tubule is able to produce large quantities of NO. In vivo studies generally indicate that NO inhibits fluid and sodium reabsorption by the proximal tubule. However, the final effect of NO on proximal tubular reabsorption appears to depend on the concentration of NO and involve interaction with other regulatory mechanisms. NO regulates Na(+)-K(+)-ATPase, Na(+)/H(+) exchangers, and paracellular permeability of proximal tubular cells, which may contribute to its effect on proximal tubular transport. Enhanced production of NO, perhaps depending on macrophage type inducible NO synthase, participates in hypoxic/ischemic proximal tubular injury. In conclusion, NO plays a fundamental role in both physiology and pathophysiology of the proximal tubule.

Arginine, citrulline, and nitric oxide metabolism in end-stage renal disease patients

The kidneys are thought to be a major site of net de novo arginine synthesis, but the quantitative status of arginine metabolism and its substrate precursor relationship to nitric oxide (NO) synthesis in end stage renal disease (ESRD) patients have not been characterized. We have investigated kinetic aspects of whole body arginine metabolism in six patients with ESRD. They received two pre- and two post-hemodialysis intravenous tracer infusion studies with L-[guanidino-(15)N(2)]arginine and L-[(13)C]leucine during the first study, and L-[5-(13)C]arginine and L-[5-(13)C-ureido,5,5, (2)H(2)]citrulline during the second study. Arginine homeostasis in ESRD patients was found to be associated with a lower rate of arginine oxidation, and despite the decrease in renal function, the rate of de novo arginine synthesis appeared to be preserved. Plasma citrulline concentrations and flux were also elevated in these subjects compared with healthy adults. The rate of whole body NO synthesis was increased in the ESRD patients, but apparently not different pre- and post-hemodialysis therapy. The anatomic site(s) responsible for the maintenance of net de novo arginine synthesis and for the elevated NO synthesis and its pathophysiological importance in ESRD remain to be established.

Polyamines in the lung: polyamine uptake and polyamine-linked pathological or toxicological conditions

The natural polyamines putrescine, cadaverine, spermidine, and spermine are found in all cells. These (poly)cations exert interactions with anions, e.g., DNA and RNA. This feature represents their best-known direct physiological role in cellular functions: cell growth, division, and differentiation. The lung and, more specifically, alveolar epithelial cells appear to be endowed with a much higher polyamine uptake system than any other major organ. In the lung, the active accumulation of natural polyamines in the epithelium has been studied in various mammalian species including rat, hamster, rabbit, and human. The kinetic parameters (Michaelis-Menten constant and maximal uptake) of the uptake system are the same order of magnitude regardless of the polyamine or species studied and the in vitro system used. Also, other pulmonary cells accumulate polyamines but never to the same extent as the epithelium. Although different uptake systems exist for putrescine, spermidine, and spermine in the lung, neither the nature of the carrier protein nor the reason for its existence is known. Some pulmonary toxicological and/or pathological conditions have been related to polyamine metabolism and/or polyamine content in the lung. Polyamines possess an important intrinsic toxicity. From in vitro studies with nonpulmonary cells, it has been shown that spermidine and spermine can be metabolized to hydrogen peroxide, ammonium, and acrolein, which can all cause cellular toxicity. In hyperoxia or after ozone exposure, the increased polyamine synthesis and polyamine content of the rat lung is correlated with survival of the animals. Pulmonary hypertension induced by monocrotaline or hypoxia has also been linked to the increased polyamine metabolism and polyamine content of the lung. In a small number of studies, it has been shown that polyamines can contribute to the suppression of immunologic reactions in the lung.

Chronic N(G)-nitro-L-arginine methyl ester-induced hypertension : novel molecular adaptation to systolic load in absence of hypertrophy

BACKGROUND

Chronic N(G)-nitro-L-arginine methyl ester (L-NAME), which inhibits nitric oxide synthesis, causes hypertension and would therefore be expected to induce robust cardiac hypertrophy. However, L-NAME has negative metabolic effects on protein synthesis that suppress the increase in left ventricular (LV) mass in response to sustained pressure overload. In the present study, we used L-NAME-induced hypertension to test the hypothesis that adaptation to pressure overload occurs even when hypertrophy is suppressed.

METHODS AND RESULTS

Male rats received L-NAME (50 mg. kg(-1). d(-1)) or no drug for 6 weeks. Rats with L-NAME-induced hypertension had levels of systolic wall stress similar to those of rats with aortic stenosis (85+/-19 versus 92+/-16 kdyne/cm). Rats with aortic stenosis developed a nearly 2-fold increase in LV mass compared with controls. In contrast, in the L-NAME rats, no increase in LV mass (1. 00+/-0.03 versus 1.04+/-0.04 g) or hypertrophy of isolated myocytes occurred (3586+/-129 versus 3756+/-135 microm(2)) compared with controls. Nevertheless, chronic pressure overload was not accompanied by the development of heart failure. LV systolic performance was maintained by mechanisms of concentric remodeling (decrease of in vivo LV chamber dimension relative to wall thickness) and augmented myocardial calcium-dependent contractile reserve associated with preserved expression of alpha- and beta-myosin heavy chain isoforms and sarcoplasmic reticulum Ca(2+) ATPase (SERCA-2).

CONCLUSIONS

When the expected compensatory hypertrophic response is suppressed during L-NAME-induced hypertension, severe chronic pressure overload is associated with a successful adaptation to maintain systolic performance; this adaptation depends on both LV remodeling and enhanced contractility in response to calcium.

Polyamines. An overview

The polyamines spermine, spermidine, and putrescine are small organic molecules one or more of which are present in all living organisms. Many natural products contain polyamine residues. Polyamines are synthesized by a highly regulated pathway from arginine or ornithine and also can be transported in and out of cells. Polyamines are degraded to a variety of compounds the functions of which are largely unknown. Polyamines influence the transcriptional and translational stages of protein synthesis, stabilize membranes, and, in mammalian systems, modulate neurophysiological functions and may act as intracellular messengers. However, at the molecular level the mode of action of the polyamines is largely unknown.

Induction of intracellular arginase activity does not diminish the capacity of macrophages to produce nitric oxide in vitro

The hypothesis was tested that induction of arginase expression in macrophages (M phi) diminishes nitric oxide (NO) synthesis due to intracellular competition between arginase and inducible nitric oxide synthase (iNOS) for L-arginine (L-arg). Murine M phi cell lines and bone marrow-derived M phi (BMM) were stimulated to express either iNOS or arginase or to co-express these two enzymes. The response pattern obtained was complex but allowed the following conclusions: (i) iNOS and arginase are differentially regulated. (ii) High intracellular arginase levels do not limit the capacity of M phi to synthesize NO even when the L-arg concentration in the culture medium is lowered to physiological levels. (iii) Arginase levels in BMM pre-exposed to either M phi colony-stimulating factor (M-CSF) or granulocyte-M phi colony-stimulating factor (GM-CSF) differ markedly, but iNOS expression and NO synthesis by the two BMM types is similar. (iv) Regulation of iNOS and arginase differs between primary murine bone marrow M phi and murine M phi cell lines. (v) Arginase activity appears to be inhibited during high-output NO synthesis. Taken together, our results show that NO production by M phi is not compromised by conditions that increase intracellular arginase activity.

Involvement of protein kinase A in the induction of arginase in murine bone marrow-derived macrophages

Arginase is induced in bone marrow-derived macrophages by agents that increase the intracellular concentrations of cAMP (Br-cAMP, prostaglandin E2) and, in their presence, the LPS induced NO synthesis is down regulated. Moreover, interleukin 10 which induces arginase in macrophages is able to increase the cAMP-dependent protein kinase A activity. In contrast, suppressors of NOS synthesis like protein kinase C inhibitors and calmodulin antagonists (W7), or NO activators (A23187) have no effect on the induction of arginase by LPS. These results strongly suggest that PKA is involved in the induction of arginase and supports the hypothesis that there is a reciprocal regulation of these two enzymes that drives the macrophages towards opposite functional states.

Aminoguanidine ameliorates and L-arginine worsens brain damage from intraluminal middle cerebral artery occlusion

BACKGROUND AND PURPOSE

We studied whether the inducible nitric oxide synthase (iNOS) inhibitor aminoguanidine reduces focal cerebral ischemic damage in a relatively noninvasive stroke model in which the rat middle cerebral artery (MCA) is occluded using an intravascular filament.

METHODS

In rats anesthetized with halothane, a nylon filament was advanced into the internal carotid artery until its tip occluded the origin of the MCA. The filament was left in place for 2 hours and then withdrawn. Twenty-four hours later, rats received intraperitoneal injections of aminoguanidine (100 mg/kg BID; n = 7), aminoguanidine+L-arginine (300 mg/kg QID; n = 7), L-arginine alone (n = 6), D-arginine alone (n = 6), or vehicle (n = 10). Drugs were administered for 3 consecutive days. Infarct volume was determined by image analysis in thionin-stained brain sections 4 days after ischemia. iNOS mRNA was detected with the use of reverse transcription polymerase chain reaction.

RESULTS

Cerebral ischemia led to iNOS mRNA expression in the affected brain 48 hours after induction of ischemia. Administration of aminoguanidine reduced neocortical infarct volume by 26% (P < .05 versus vehicle, ANOVA and Tukey's test), a reduction that was antagonized by coadministration of L-arginine (P > .05 versus vehicle). Administration of L-arginine alone, but not D-arginine, enlarged the infarct by 29% (P < .05). Aminoguanidine or L-arginine did not influence the increase in water content in the postischemic brain, indicating that the effect on infarct volume is not related to modulation of ischemic edema.

CONCLUSIONS

These results demonstrate that cerebral ischemia is also associated with iNOS expression in a minimally invasive model of transient MCA occlusion and that iNOS inhibition reduces focal ischemic damage. The findings support the hypothesis that nitric oxide produced by iNOS contributes to ischemic brain damage and that inhibition of iNOS may be a valuable tool in the management of cerebral ischemia.