BACKGROUND

Dexamethasone (DEX) is demonstrated to have anti-inflammatory properties and known to induce hemodynamic improvement in sepsis and septic shock. L-arginine (L-arg), a semi-essential amino acid, depending on its metabolic pathway, becomes very essential in stress situations such as heatstroke, burns, sepsis, trauma, and wound healing. The aim of this study was to evaluate the synergistic therapeutic effect of DEX and L-arg in rescuing the mice from experimental septic shock induced by bacterial lipopolysaccharide (LPS). The experiments were designed to delineate the molecular mechanisms responsible for the increased therapeutic benefit of the combination therapy (CT) in LPS-induced septic shock.

METHODS

Acute endotoxemia was induced in Swiss male mice by i.p. injection of LPS (18 mg kg(-1)) at 0 h. LPS-treated mice were divided into four groups. The first group (DEX group) received DEX (2 mg kg(-1)) i.p. at +2 h of LPS. The second group (L-arg group) received L-arg i.p. at a dose of 120 mg/kg at +6 h of LPS injection. The third group (CT group) received DEX (2 mg kg(-1)) at +2 h LPS followed by L-arg at +6 h of LPS injection. The fourth group received saline in place of L-arg or DEX (LPS group). A sham group was also included, where normal mice received saline in place of LPS or L-arg or DEX. At +6 h, mice from sham group, LPS group, and DEX group were sacrificed at +24 h. Mice from sham group, DEX group, L-arg group, and CT group were sacrificed to examine various parameters associated with LPS endotoxemia.

RESULTS

The CT with DEX followed by L-arg significantly increased the survival of mice injected with a lethal dose of LPS. Monotherapy with either DEX or L-arg given at the same dose and time did not increase the survival of the mice injected with LPS. DEX administration could significantly reduce the levels of serum TNF-alpha, IL-1beta, IFN-gamma, aspartate aminotransferase (ASAT), alanine aminotransferase (ALAT), and nitrite. DEX also down-regulated the expression of liver-inducible nitric oxide synthase (iNOS), and up-regulated the levels of serum anti-inflammatory cytokines like TGF-beta1 and IL-4, hepatic and splenic arginase, in LPS-injected mice. The enhanced therapeutic effect of CT correlated with reduced pathological symptoms, decreased Th1 cytokines, increased TGF-beta1 and arginase levels compared to the mice administered with either of the monotherapies. The CT group had significantly increased expression of hepatic Hsp 70 and reduced septic shock associated histopathology, in lung and liver, compared to the mice treated with either DEX or L-arg.

CONCLUSIONS

The therapeutic combination therapy with DEX and L-arg, at the appropriate dose, time, and sequence of administration, changed the cytokine profile, in favor of reducing the inflammatory response. The significantly enhanced survival observed in the CT group was accompanied by an increased hepatic Hsp 70, hepatic arginase, splenic arginase, and decreased organ injury. This novel concept of combined therapy could form the basis of an effective therapeutic approach in the treatment of sepsis and septic shock.