Affective and metabolic effects of 2,4-dinitrophenol in ovariectomised rats fed a high-fat diet

Introduction and aims: Postmenopausal oestrogen deprivation and high-fat diet exposure may affect mood and cognition through metabolic vulnerability, mitochondrial dysfunction and altered neurotrophic signalling [1]. Mild mitochondrial uncoupling may thus represent an experimental intervention target for neurobehavioural disturbances related to metabolic stress [2]. This study aimed to evaluate the effects of 2,4-dinitrophenol (DNP) on affective-like behaviour, cognitive performance, homeostasis model assessment of insulin resistance (HOMA-IR), leptin, brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) in ovariectomised rats fed a high-fat diet.

Methods

Female Wistar Albino rats were allocated to seven groups (n=10/group): sham + standard diet (Sham+SD), sham + high-fat diet (Sham+HFD), ovariectomy + SD (OVX+SD), OVX+HFD, OVX+HFD + vehicle (Veh), OVX+HFD + DNP 1 mg/kg (DNP1) and OVX+HFD + DNP 5 mg/kg (DNP5). Following sham surgery or ovariectomy, animals received SD or HFD for eight weeks. DNP was administered intraperitoneally at 1 or 5 mg/kg/day for four weeks. Locomotor activity, anxiety-like behaviour, depressive-like behaviour and recognition memory were assessed using the open field test (OFT), elevated plus maze (EPM), forced swim test (FST) and novel object recognition test (NOR). HOMA-IR was calculated; serum leptin, BDNF and NGF were measured. Data are presented as mean±SEM. The non-injected and injected groups were analysed separately. Kruskal–Wallis tests followed by Dunn’s post hoc multiple-comparison tests were used for multi-group comparisons, and Mann–Whitney U tests for two-group comparisons.

Results

In the EPM, Sham+HFD rats spent more time in the open arms than Sham+SD and OVX+SD rats (75.0±8.7 vs 50.2±28.4 and 28.3±8.9 s, p<0.05). DNP5 increased open-arm time compared with Veh (49.6±7.7 vs 19.0±3.5 s, p<0.05). In the FST, OVX+HFD rats showed longer immobility than Sham+SD and Sham+HFD rats (152.4±18.2 vs 25.8±5.7 and 49.9±10.9 s, p<0.05), whereas DNP1 reduced immobility compared with Veh (53.7±10.4 vs 169.8±11.6 s, p<0.001). OVX and/or HFD did not significantly alter OFT or NOR outcomes. HOMA-IR was higher in Sham+HFD than in Sham+SD rats (2.5±0.3 vs 1.2±0.2, p<0.05). Serum leptin was higher in Sham+HFD and OVX+HFD groups than in the corresponding SD groups (Sham+HFD: 0.29±0.03; OVX+HFD: 0.31±0.07; Sham+SD: 0.11±0.01; OVX+SD: 0.10±0.01 ng/mL, p<0.05). Serum BDNF was lower in OVX+HFD than in Sham+SD and OVX+SD groups (314.4±31.9 vs 465.8±29.3 and 496.3±40.3 pg/mL, p<0.05), while NGF did not differ significantly. DNP1 reduced HOMA-IR compared with Veh (0.9±0.1 vs 2.5±0.7, p<0.05), but DNP did not significantly alter serum leptin, BDNF or NGF levels.

Conclusions

Ovariectomy and a high-fat diet synergistically drive metabolic dysregulation and depressive-like behaviours, accompanied by altered peripheral neuroadipokine profiles. DNP showed dose-differential effects on depressive-like and anxiety-like behaviours in ovariectomised rats fed a high-fat diet, with low-dose DNP additionally improving HOMA-IR. The reduction in HOMA-IR with DNP1 suggests that behavioural effects may occur alongside improved metabolic sensitivity. These findings provide preclinical support for mild mitochondrial uncoupling as a translationally relevant approach to metabolic–affective dysfunction in menopausal models. The unexpected increase in open-arm time in Sham+HFD rats warrants further investigation.

References

1. . Yao, J., Brinton, R.D., 2012. Estrogen regulation of mitochondrial bioenergetics: implications for prevention of Alzheimer’s disease. Adv. Pharmacol. 64, 327-371.
2. . Geisler, J.G., Marosi, K., Halpern, J., Mattson, M.P., 2017. DNP, mitochondrial uncoupling, and neuroprotection: A little dab’ll do ya. Alzheimers Dement. 13 (5), 582–591.