Local cooling protects against
TNF-alpha-induced injury by attenuating
inflammation-associated microcirculatory dysfunction and leukocytic response. Mechanisms of protection, however, are not fully understood. We studied whether the metabolites of the HO and NOS pathway, exerting potent vasodilatory,
antioxidant, and anti-apoptotic properties, are involved in tissue cryoprotection. In animals pretreated with
L-NAME or
SnPP-IX, cooling-associated abrogation of
TNF-alpha-induced microcirculatory dysfunction was abolished. Combined
L-NAME/
SnPP-IX pretreatment did not cause greater blunting than seen when each mediator system was inhibited separately. In
SnPP-IX- but not
L-NAME-pretreated animals, transient
hypothermia failed to reduce
TNF-alpha-mediated leukocyte adherence. Vice versa, treatment of
TNF-alpha-exposed animals with either the NO donor
l-arginine or the HO-1 inductor
hemin mimicked cooling-associated tissue protection except for failure of
l-arginine to abrogate the inflammatory leukocyte response. The efficiency of cooling to inhibit
TNF-alpha-induced apoptotic cell death was blunted in
SnPP-IX-,
L-NAME-, and
SnPP-IX/
L-NAME-pretreated animals. Coadministration of
Trolox in
SnPP-IX-treated animals partly attenuated leukocyte adherence and cell apoptosis, implying that the HO pathway metabolite
biliverdin contributes to the salutary effects of cooling. Thus, our study provides evidence that metabolites of the HO and the NOS pathway mediate the cooling-associated protection of inflamed tissue.
Biliverdin rather than CO and NO mediates the anti-inflammatory action, whereas a coordinated function of the gaseous monoxides prevents microcirculatory dysfunction and apoptotic cell death.