Doi et al.

NIH-PA Author Manuscript

NIH-PA Author Manuscript

NIH-PA Author ManuscriptPage 5induced AKI and multiple organ failure were not determined.24 In the current study, we foundthat a α-MSH analogue AP214 improved sepsis-induced multiple organ failure including AKIand mortality. Moreover, we found that AP214 had a bell-shaped dose-response curve forsepsis-induced AKI. There are several reports that demonstrated biphasic dose-response curvesin the anti-inflammatory influence of α-MSH. Both the large and small doses were ineffectivefor in vivo animal models of ear swelling induced by picryl chloride36, 3738 and crystal-inducedperitonitis, and in vitro cell culture models such as TNF-α production in microglia3940, cyclicAMP production in mast cells and glutathione peroxidase activity in melanocytes andkeratinocytes41. The cause of this phenomenon is unknown, but might be explained in part byreceptor downregulation to avoid excess effects. Equimolar native α-MSH also showed aprotective effect on sepsis-induced AKI, although binding affinity of AP214 for melanocortinreceptors in vitro were higher than native α-MSH. These data suggest that effects of AP214 invivo may not be straightforward and confounded by pharmacokinetic parameters and/orindirect regulatory influences. Further evaluations would be required to clarify the mechanismsof these biphasic responses of AP214 both in physiological and pathological in vivo conditions.Failure to regulate hyperactivation of the inflammatory system plays an important role inpathophysiology of sepsis and blocking inflammatory mediators has been often proposed as atreatment strategy for sepsis. However, many clinical trials with drugs that inhibit specificinflammatory mediators have not been successful. α-MSH has a breadth of anti-inflammatoryactivities and can improve inflammatory disorders through suppressing multiple pathways.Moreover, α-MSH modulates inflammatory responses thorough inhibition of the nucleartranscription factor NF-κB activation, which plays the central role in immune and inflammationsystems.27 In the present study, we demonstrated the inhibition of systemic TNF-α production(Figure 6) and renal and splenic NF-κB activation (Figure 7). AP214 reduced serum TNF-αlevels with a bell-shaped dose-response curve similar to its effects on serum creatinine levels.This indicates that modulation of the exacerbated inflammatory response is beneficial for AKIinduced by lethal CLP. AP214 can be an agonist of several melanocortin receptors (MCR1,

MCR3, MCR4, and MCR5). MCR1 and MCR3 are known to mediate anti-inflammatory

effects and MCR4 regulates hemodynamics in the central nerve system as described above,

whereas MCR5 has been implicated in multiple exocrine functions.42 Further investigation on

the contribution of each melanocortin receptor pathway will be necessary to further understand

the mechanisms of action of α-MSH in sepsis and to minimize unwanted effects from other

melanocortin receptors.

The action of α-MSH is reminiscent of corticosteroids because both of them have multiple anti-

inflammatory effects through several mechanisms including inhibiting NF-κB pathway.43 It

has been recently suggested that ‘physiologic’ but not high doses of corticosteroids might be

beneficial to septic patients.44 Our data indicates that AP214 similarly has a relatively narrow

therapeutic window since 10 μg treatment but not 50 μg showed protective effects in CLP.

Therefore, translation of AP214 to studies in human sepsis will likely require precise evaluation

of the pharmacokinetics and dose responses of AP214 in humans before large-scale clinical

trials can be initiated.

Serum IL-10 levels were increased in our mouse sepsis model and suppressed after AP214

treatment. Although the role of IL-10 as an anti-inflammatory cytokine is apparent in renal

ischemia/reperfusion and cisplatin-induced renal injury,16 the role of IL-10 and its relationship

to α-MSH in sepsis is less clear. IL-10 knockout mice showed higher mortality in CLP than

wild type mice and anti-IL-10 monoclonal antibody treatment worsened the survival after CLP

when injected at 0 or 2 hr before surgery.45, 46 On the other hand, anti-IL-10 monoclonal

antibody treatment was protective when it was injected 10 hr after CLP.46 Therefore, IL-10

appears to have dual effects on sepsis that depends on the timing. The finding that AP214