Using mitochondrial respiration inhibitors to design a novel model of bipolar disorder-like phenotype with construct, face and predictive validity

Abstract

We mimicked mild mitochondrial-distress robustly reported in bipolar-disorder (BD) by chronic exposure to uniquely low doses of inhibitors of mitochondrial-respiration complexes in vitro and in vivo. Exposure of the neuronal-originating SH-SY5Y cells to very low dose (10 pM) rotenone, a mitochondrial-respiration complex (Co)I inhibitor, for 72 or 96 h did not affect cell viability and reactive oxygen species (ROS) levels. Yet, it induced a dual effect on mitochondrial-respiration: overshooting statistically significant several-fold increase of most oxygen-consumption-rate (OCR) parameters vs. significantly decreased all OCR parameters, respectively. Chronic low doses of 3-nitropropionic acid (3-NP) (CoII inhibitor) did not induce long-lasting changes in the cells’ mitochondria-related parameters. Intraperitoneal administration of 0.75 mg/kg/day rotenone to male mice for 4 or 8 weeks did not affect spontaneous and motor activity, caused behaviors associated with mania and depression following 4 and 8 weeks, respectively, accompanied by relevant changes in mitochondrial basal OCR and in levels of mitochondrial-respiration proteins. Our model is among the very few BD-like animal models exhibiting construct (mild mitochondrial dysfunction), face (decreased/increased immobility time in the forced-swim test, increased/decreased consumption of sweet solution, increased/decreased time spent in the open arms of the elevated plus maze) and predictive (reversal of rotenone-induced behavioral changes by lithium treatment) validity. Our rotenone regime, employing doses that, to the best of our knowledge, have never been used before, differs from those inducing Parkinson’s-like models by not affecting ROS-levels and cell-viability in vitro nor motor activity in vivo.

Do Autophagy Enhancers/ROS Scavengers Alleviate Consequences of Mild Mitochondrial Dysfunction Induced in Neuronal-Derived Cells?

“…з Rot. for 96 h vs. control, p > 0.05-as previously described [23] and confirmed now. A. Rapamycin effects, Two-way ANOVA: Treatment-F 3.16 = 23.8, p = 0.000001; duration-F 1.16 = 89.9, p = 0.000001; TreatmentX-Duration interaction-F 3,16 = 84.9, p = 0.000001; *Fisher's LSD post-hoc test: Rot.…”

“…Neither the autophagy enhancers nor the ROS scavengers as a group demonstrated a consistent effect, suggesting that the mechanisms by which these drugs affect cell viability are not mediated by their autophagy enhancing/ROS scavenging properties. As we reported earlier [23], the predominant effect of 10 pM, rotenone for 72 and 96 h on SH-SY5Y cells was on mitochondrial respiration parameters. We, therefore, now assessed the effect of the autophagy enhancers and the ROS scavengers added for the last 24/48 h of the exposure to rotenone for 72/96 h, respectively, on mitochondrial and nonmitochondrial respiration (OCR parameters) (Figure 2; Table 2).…”

“…As in the case of cell viability, neither the autophagy enhancers nor the ROS scavengers as a group exhibited a consistent effect, supporting the notion that the mechanisms by which these drugs affect ATP levels are also, apparently, not mediated by their autophagy enhancing/ROS scavenging properties. As already recently described by Damri et al [23], among the five mitochondrial respiration complexes, rotenone significantly affected only CoI and CoIV protein levels. Specifically, exposure to rotenone significantly enhanced/decreased CoI activity following 72/96 h, respectively.…”

“…We have recently modeled very mild mitochondrial dysfunction by exposing SH-SY5Y cells to very low rotenone doses in vitro and by chronically injecting (in vivo) mice with very low rotenone doses [23]. In the present study, we examined in the SH-SY5Y cells (in vitro) whether any of the autophagy enhancers trehalose [33], rapamycin [34], and lithium [35], or the ROS scavengers NAC [36] and Mn-Tbap [37], or resveratrol, both an autophagy enhancer and a ROS scavenger [38], reverse the consequences of mild mitochondrial dysfunction.…”

“…Here we recapitulated our recently reported model of mild mitochondrial dysfunction [23] in the human neuron-derived cell line, SH-SY5Y, induced by low rotenone (a mitochondrial complex I inhibitor) concentrations never used before, to examine whether autophagy enhancers or ROS scavengers which are either generally accepted as safe (GRAS) compounds or approved drugs (mood stabilizers) can amend neuronal mild mitochondrial dysfunction. The rationale for using ROS scavengers was that higher rotenone doses, regularly used to model Parkinson's disease (PD) [24], have been reported to raise mitochondrial ROS production, a crucial player in apoptosis [25].…”