Further evidence for the role of free radicals in the limb teratogenicity of L‐NAME

Abstract

These findings support the role of excess reactive oxygen species (ROS) formation in L-NAME-induced limb reduction. We propose that nitric oxide (NO) depletion by L-NAME interferes with vascular integrity, and causes vasoconstriction. Resultant hypoxia stimulates superoxide formation and nitric oxide formation catalyzed by the inducible isoform of nitric oxide synthase. The reduction products of superoxide or the products of its reaction with nitric oxide oxidize or nitrate endothelial components resulting in limb reduction defects.

The Nitric Oxide Synthesis Inhibitor Nω-Nitro-L-Arginine Methyl Ester (L-NAME) Causes Limb Defects in Mouse Fetuses: Protective Effect of Acute Hyperoxia

“…Studies with rats pointed out that the in vivo teratogenicity of L-NAME is confined largely to limbs (3)(4)(5)(6)(7)(8). This was also our evidence in the mouse.…”

“…The L-arginine analog L-NAME, a nonselective inhibitor of NOS, has been shown to be teratogenic when administered to rats (3)(4)(5)(6)(7)(8). Limb reduction defects with associated characteristic areas of macroscopic hemorrhage were the most common phenotypic alterations noted (3)(4)(5)(6)(7)(8).…”

“…Limb reduction defects with associated characteristic areas of macroscopic hemorrhage were the most common phenotypic alterations noted (3)(4)(5)(6)(7)(8). L-NAME is not the only L-arginine analog known to cause dysmelia, as N -nitro-Larginine also induced limb defects (9).…”

“…Notably, disruptions similar to those induced by L-arginine analogs have been noted in knockout mice lacking eNOS (10,11). The current state of knowledge on L-NAME teratogenicity also includes the following facts: 1) the period of fetal vulnerability has an onset relatively late in gestation (3)(4)(5); 2) both oral (3)(4)(5)(6) and parenteral (5) treatments are effective; 3) limb dysmorphology is associated with reduced fetal viability (5); 4) both the teratogenic and fetus lethal effects are dose dependent (5); 5) defects are preceded by hemorrhages that appear in the limbs within hours of treatment (7,8); 6) fetal growth restriction and decrement in placental weight have been observed by some authors (3,4,6), but not by others (5); 7) the compound is teratogenic when instilled in the amnion, suggesting that it exerts its activity within the vasculature of the limb or placenta (7); 8) limb defects were prevented by concurrent administration of L-arginine or the NO donors sodium nitroprusside and S-nitroso-acetyl-penicillamine (4), suggesting that L-NAME initiates teratology via inhibition of NO synthesis; and 9) limb defects were reduced by coadministration of ␣-phenyl-N-tbutylnitrone, a radical spin trap antioxidant, and allopurinol, a xanthine oxidase inhibitor (7,8), suggesting a mechanistic role for radical oxygen species.…”

“…In the present study the relationship between exposure to L-NAME and the induction of limb defects, with respect to stage specificity and dose dependency, was investigated in the mouse. In addition, because hypoxia and/or ischemia have been postulated by several authors as a possible mediator of L-NAME teratogenesis (3,5,7,8), the ability of hyperoxia to prevent L-NAME-induced limb disruption was also investigated.…”