The essential oils component p-cymene induces proton leak through Fo-ATP synthase and uncoupling of mitochondrial respiration

Figures & data

Figure 1 Chemical structure of p-cymene (1-isopropyl-4-methylbenzene).

Figure 2 Effect of p-cymene (PCy) on the respiratory states 2 (A), 3 (B) and 4 (C) of liver mitochondria induced by glutamate/malate. Mitochondrial respiration rates were determined by O₂ consumption using a Clark-type electrode.

Notes: The data represent the means ± SD of 6 independent experiments. *P < 0.05; **P < 0.01; ***P < 0.001 vs control.

Figure 3 Effect of p-cymene (PCy) on respiratory control ratio (RCR) (A) and ADP/O ratio (B).

Notes: Indices were determined as described in Materials and methods and values are expressed as means ± SD of 6 independent experiments. **P < 0.01; ***P < 0.001 vs control.

Figure 4 Effects of p-cymene (PCy) on mitochondrial swelling. The traces, obtained by following the light scattering at 540 nm, are typical of 4 separate experiments with different mitochondrial preparations.

Figure 5 Effect of p-cymene (PCy) on state 2 plus ATP (A) and on state 4 respiration in the presence of oligomycin (st4-olig) (B). State 2 respiration was determined after energization of liver mitochondria with glutamate/malate and state 4 respiration after phosphorylation of ADP. State 4 respiration in the presence of oligomycin (st4-olig) was induced by the addition of ADP and oligomycin after the steady state of oxygen consumption characteristic of state 4 respiration had been reached.

Notes: The data shown represent the means ± SD of 6 independent experiments. *P < 0.05; **P < 0.01 vs control; ⁺P < 0.05; ⁺⁺P < 0.01; ⁺⁺⁺P < 0.001 vs state 4 in the absence of oligomycin (st4).

Table 1 Effects of p-cymene (PCy) on oxidative phosphorylation parameters of rat liver mitochondria

PCy (nmol/mg protein)	Control	25	50	75	100	75+ATP
Δψ (−mV)	223 ± 1.85	219 ± 2.15	216 ± 2.34	202 ± 2.99*	194 ± 1.38**	180 ± 4.87***
Depolarization by ADP (−mV)	32.4 ± 1.93	31.9 ± 1.75	32.1 ± 2.53	28.3 ± 2.10*	23.9 ± 1.34**	15.3 ± 2.89***
Lag phase (min)	1.32 ± 0.07	1.34 ± 0.15	1.42 ± 0.11	2.06 ± 0.15**	2.67 ± 0.35**	∞

Notes: Values are expressed as mean ± SD of 4 independent experiments.

* P < 0.05;

** P < 0.01;

*** P < 0.001 compared with control.

Figure 6 Effect of p-cymene (PCy) on Ca²⁺ fluxes of mitochondria isolated from rat liver. Freshly isolated mitochondria were incubated at 0.25 mg/mL under standard conditions as described in the Materials and Methods section. Standard medium was supplemented with different concentrations of Ca²⁺ 1 minute before mitochondria energization with 5 mM succinate. Cyclosporin A (CsA) (0.85 μM) or p-cymene (25 nmol/mg protein) were added to the reaction medium 3 minutes prior to Ca²⁺ addition. The traces are typical of 6 independent experiments.