Mitochondrial permeability transition pore component cyclophilin D distinguishes nigrostriatal dopaminergic death paradigms in the MPTP mouse model of Parkinson's disease

AIMS

Mitochondrial damage due to Ca(2+) overload-induced opening of permeability transition pores (PTP) is believed to play a role in selective degeneration of nigrostriatal dopaminergic neurons in Parkinson's disease (PD). Genetic ablation of mitochondrial matrix protein cyclophilin D (CYPD) has been shown to increase Ca(2+) threshold of PTP in vitro and to prevent cell death in several in vivo disease models. We investigated the role of CYPD in a mouse model of MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine)-induced PD.

RESULTS

We demonstrate that in vitro, brain mitochondria isolated from CYPD knockout mice were less sensitive to MPP+ (1-methyl-4-phenyl-pyridinium ion)-induced membrane depolarization, and free radical generation compared to wild-type mice. CYPD knockout mitochondria isolated from ventral midbrain of mice treated with MPTP in vivo exhibited less damage as judged from respiratory chain Complex I activity, State 3 respiration rate, and respiratory control index than wild-type mice, whereas assessment of apoptotic markers showed no differences between the two genotypes. However, CYPD knockout mice were significantly resistant only to an acute regimen of MPTP neurotoxicity in contrast to the subacute and chronic MPTP paradigms.

INNOVATION

Inactivation of CYPD is beneficial in preserving mitochondrial functions only in an acute insult model of MPTP-induced dopaminergic neurotoxicity.

CONCLUSION

Our results suggest that CYPD deficiency distinguishes the modes of dopaminergic neurodegeneration in various regimens of MPTP-neurotoxicity.

Promethazine protects against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine neurotoxicity

Promethazine (PMZ) is an FDA-approved antihistaminergic drug that was identified as a potentially neuroprotective compound in the NINDS screening program. PMZ accumulates in brain mitochondria in vivo and inhibits Ca2+-induced mitochondrial permeability transition pore (PTP) in rat liver mitochondria in vitro. We hypothesized that PMZ may have a protective effect in a mitochondrial toxin model of Parkinson's disease (PD). Mice treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) sustained a significant loss of dopaminergic neurons within the SNpc that was strongly attenuated by PMZ treatment. However, neither striatal MPP+ concentrations nor MPTP-induced inhibition of mitochondrial complex I were affected by PMZ treatment. In isolated mouse brain mitochondria, PMZ partially prevented and reversed MPP+-induced depolarization of membrane potential and inhibited the Ca2+-induced PTP in brain mitochondria. The sum of data indicates that PMZ is a strong neuroprotective agent capable of protecting dopaminergic neurons against MPTP toxicity in vivo.

Mitochondrial alpha-ketoglutarate dehydrogenase complex generates reactive oxygen species

Mitochondria-produced reactive oxygen species (ROS) are thought to contribute to cell death caused by a multitude of pathological conditions. The molecular sites of mitochondrial ROS production are not well established but are generally thought to be located in complex I and complex III of the electron transport chain. We measured H(2)O(2) production, respiration, and NADPH reduction level in rat brain mitochondria oxidizing a variety of respiratory substrates. Under conditions of maximum respiration induced with either ADP or carbonyl cyanide p-trifluoromethoxyphenylhydrazone,alpha-ketoglutarate supported the highest rate of H(2)O(2) production. In the absence of ADP or in the presence of rotenone, H(2)O(2) production rates correlated with the reduction level of mitochondrial NADPH with various substrates, with the exception of alpha-ketoglutarate. Isolated mitochondrial alpha-ketoglutarate dehydrogenase (KGDHC) and pyruvate dehydrogenase (PDHC) complexes produced superoxide and H(2)O(2). NAD(+) inhibited ROS production by the isolated enzymes and by permeabilized mitochondria. We also measured H(2)O(2) production by brain mitochondria isolated from heterozygous knock-out mice deficient in dihydrolipoyl dehydrogenase (Dld). Although this enzyme is a part of both KGDHC and PDHC, there was greater impairment of KGDHC activity in Dld-deficient mitochondria. These mitochondria also produced significantly less H(2)O(2) than mitochondria isolated from their littermate wild-type mice. The data strongly indicate that KGDHC is a primary site of ROS production in normally functioning mitochondria.

NAD- and NADP-dependent 11 beta-hydroxysteroid dehydrogenase isoforms in guinea pig kidney with gossypol inhibition

AIM

To study the mechanism of gossypol-induced hypokalemia.

METHODS

The 11 beta-hydroxysteroid dehydrogenase (11 beta-OHSD) protein was prepared from guinea pig kidney. The activity of 11 beta-OHSD with NAD or NADP as the coenzyme was measured by HPLC in both control and gossypol treatment.

RESULTS

The Vmax and K(m) were 0.64 mmol.h-1/g protein and 0.07 mumol (cortisol) for NAD-dependent 11 beta-OHSD, 1.75 mmol.h-1/g protein and 0.21 mumol (cortisol) for NADP-dependent 11 beta-OHSD, respectively when 80 micrograms of enzyme protein was used. The inhibitory effects of gossypol on these two 11 beta-OHSD isoforms were different. The IC50 (95% confidence limits) were 50.2 (48.3-52.0) mumol of gossypol for NAD-dependent 11 beta-OHSD and 1143 (1098-1188) mumol of gossypol for NADP-dependent 11 beta-OHSD. The Ki was gossypol 96 mmol.L-1 for the former and 340 mmol.L-1 for the latter.

CONCLUSION

The NAD-dependent 11 beta-OHSD is a more critical physiologic mechanism than NADP-dependent 11 beta-OHSD for hypokalemia caused by gossypol.

Grapefruit juice and its flavonoids inhibit 11 beta-hydroxysteroid dehydrogenase

INTRODUCTION

The enzyme 11 beta-hydroxysteroid dehydrogenase (11 beta-OHSD) oxidizes cortisol to inactive cortisone. Its congenital absence or inhibition by licorice increases cortisol levels at the mineralocorticoid receptor, causing mineralocorticoid effects. We tested the hypothesis that flavonoids found in grapefruit juice inhibit this enzyme in vitro and that grapefruit juice itself inhibits it in vivo.

METHODS

Microsomes from guinea pig kidney cortex were incubated with cortisol and nicotinamide adenine dinucleotide (NAD) or nicotinamide adenine dinucleotide phosphate (NADP) and different flavonoids and the oxidation to cortisone measured with use of HPLC analysis. In addition, healthy human volunteers drank grapefruit juice, and the ratio of cortisone to cortisol in their urine was measured by HPLC and used as an index of endogenous enzyme activity.

RESULTS

Both forms of 11 beta-OHSD requiring either NAD or NADP were inhibited in a concentration-dependent manner by the flavonoids in grapefruit juice. Normal men who drank grapefruit juice had a fall in their urinary cortisone/cortisol ratio, suggesting in vivo inhibition of the enzyme.

CONCLUSION

Dietary flavonoids can inhibit this enzyme and, at high doses, may cause an apparent mineralocorticoid effect.

Cortisol metabolism in hypertensive patients who do and do not develop hypokalemia from diuretics

Deficiency of 11 beta-hydroxysteroid dehydrogenase causes hypertension and hypokalemia. To test whether hypertensive patients who develop hypokalemia when treated with diuretics have low levels of activity of this enzyme as a metabolic predisposition to the development of hypokalemia, we measured urinary cortisone, cortisol, tetrahydrocortisol, tetrahydrocortisone, and creatinine in 42 hypertensive patients who either did or did not become hypokalemic on hydrochlorothiazide. The mean ratios of cortisone to cortisol, tetrahydrocortisone to tetrahydrocortisol, tetrahydrocortisol to cortisol, and cortisol to creatinine did not differ between the two groups. We conclude that hypertensives who develop hypokalemia on diuretics do not have low activity of this enzyme. They also do not appear to have low ring A reduction or higher cortisol secretion rates compared with hypertensives who do not develop hypokalemia. We failed to find a metabolic predisposition to the development of hypokalemia by diuretic treatment.

Lipophilic beta-blockers inhibit rat skeletal muscle mitochondrial respiration

Propranolol, metoprolol, acebutolol, nadolol and atenolol were incubated with isolated rat skeletal muscle mitochondria at 30 degrees C, and the rate of oxygen consumption was measured with an oxygen microelectrode. The potency of these drugs to inhibit state III respiration was correlated with lipid solubility as measured by the octanol/water partition coefficient. The most lipid-soluble beta-blocker, propranolol, had an ED50 of 0.6 mmol/l. The most water-soluble one, atenolol, showed no inhibition at concentrations up to 16 mmol/l. Inhibition of respiratory control ratio, state IV respiration and ADP/O ratio occurred at 2 mmol/l for propranolol, 16 mmol/l for metoprolol and was not consistently observed for the other beta-blockers at the concentrations tested. The inhibition of state III respiration of skeletal muscle mitochondria by lipid-soluble beta-blockers may be one of the causes of the fatigue observed in some patients receiving these drugs.

A nonradioactive iothalamate method for measuring glomerular filtration rate and its use to study the renal handling of cibenzoline

A high-pressure liquid chromatographic method was developed to measure nonradioactive iothalamate in serum and urine for use in estimating glomerular filtration rate (GFR). This method was used to study the renal handling of cibenzoline, an experimental antiarrhythmic drug. The mean cibenzoline clearance was 3.5 +/- 2.5 (SD) times the glomerular filtration rate. The clearance of non-protein-bound cibenzoline was seven times GFR, indicating excretion by the renal tubular secretory pathway for organic bases. This drug, at the doses used, did not lower creatinine clearance, indicating that the effect of basic drugs competing with creatinine for the base secretory pathway appears to be dose and drug dependent.