ABSTRACT
The antibiotics known as aminoglycosides are commonly used to treat severe infections caused by Gram-negative bacteria. Unfortunately, they often lead to acute renal failure after their accumulation in the lysosomes of renal cells, where an inhibition of the phospholipid catabolism is observed. The lipopeptidic antibiotic daptomycin has been shown to reduce the nephrotoxicity of aminoglycosides, but the exact mechanism of this protection is still unknown. In the present study, Fourier transform infrared spectroscopy (FTIR) has been used to monitor the hydrolysis of phosphatidylcholine by phospholipase A2 (PLA2) from Naja mocambique mocambique venom in the presence of various aminoglycosides and/or daptomycin. Gentamicin and amikacin inhibited the reaction in its early stage. Kanamycin A, tobramycin, and especially kanamycin B enhanced the initial enzyme activity by reducing the lag time. After the initiation period, the reaction proceeded at a much slower rate in the presence of gentamicin. On the other hand, daptomycin led to dramatic alterations of the hydrolysis profile: the initial latency period was eliminated, and the maximal extent of hydrolysis was reduced. When both daptomycin and any of the aminoglycosides were present, the latency period also disappeared, and the phospholipase activity was higher than with the lipopeptide alone. The most drastic change occurred with gentamicin, which was the most inhibitory aminoglycoside when used alone but worked synergistically with daptomycin to yield the most dramatic activation of PLA2.
Subject(s)
Aminoglycosides/pharmacology , Daptomycin/pharmacology , Elapid Venoms/enzymology , Phospholipases A/metabolism , Animals , Drug Synergism , Gentamicins/pharmacology , Hydrolysis/drug effects , Lipid Bilayers/metabolism , Liposomes/metabolism , Phospholipases A2 , Spectroscopy, Fourier Transform InfraredABSTRACT
1. Sheep hearts have been used to study the effects of beta-adrenoceptor (beta-AR) agonists in order to better understand the effects of common asthma treatment drugs on heart rate, cardiac power output and cardiac pathology. Hearts have been examined both in vivo and in vitro. 2. In whole anaesthetized sheep, isoprenaline, fenoterol and salbutamol induced dose-dependent increases in heart rate. Hypokalaemia in response to salbutamol was accentuated in hypoxia. Many of these hearts showed significant myocardial lesions. Hypoxia alone caused no significant cardiac response. 3. As expected, the beta 1-AR agonist dobutamine caused dose-dependent increases in heart performance (heart rate and cardiac power output). Both responses were blocked by metoprolol and propranolol. The beta 2-AR agonist salbutamol caused dose-dependent increases in heart rate and although cardiac output increased, cardiac power output remained unchanged as a consequence of the fall in peripheral resistance. The heart rate changes were blocked by metoprolol. Importantly, propranolol blocked both the heart rate response and the fall in peripheral resistance. 4. Isolated atrial strips showed a right shift of their dose-response curve to isoprenaline in the presence of the highly selective beta 2-AR antagonist ICI 118,551 at concentrations above 1 x 10(-8) mol/L. 5. We conclude that the sheep heart shows many pharmacological characteristics of the human heart which makes it a good pharmacological model in addition to its being amenable to many common techniques available for humans.
