Alteration of contractile function and calcium ion movements in vascular smooth muscle by gentamicin and other aminoglycoside antibiotics

Gentamicin in Neonates with Hemodynamically Significant Patent Ductus Arteriosus

Background

Gentamicin has been shown to cause vasodilation in preclinical studies. Hemodynamically significant patent ductus arteriosus (hsPDA) is a commonly observed congenital heart disorder in preterm neonates. Concomitant gentamicin theoretically shall delay the closure/result in nonclosure of ductus arteriosus (DA). Similarly, hsPDA can alter the pharmacokinetics of gentamicin and so trough gentamicin concentrations. We carried out the present study to evaluate the association between gentamicin use and closure of hsPDA (treated with acetaminophen) as well as the effect of hsPDA on trough concentrations.

Methods

This study was a prospective, observational study that included 60 neonates diagnosed with hsPDA by echocardiography and 102 neonates without hsPDA. Demographic details, size of DA as per echocardiography at the end of treatment with acetaminophen, gentamicin-dosing regimen, and trough concentrations were collected. Standard definitions were adhered in classifying the gestational age, birth weights, and size of DA. The numerical values are reported in median (range).

Results

Neonates with hsPDA had significantly lower daily doses of gentamicin [4.5 (2.5-10), 7 (3.2-13) mg; P < 0.001] but longer duration of therapy [8 (3-14), 5 (3-7) days; P < 0.001] than those without hsPDA in very preterm neonates. No significant differences were observed in the trough concentrations of gentamicin between the groups. No association was observed between gentamicin use and closure of DA. However, those with successful closure of DA received gentamicin for a longer duration [6 (3-10), 4 (3-14) days; P < 0.05] that was independent of acetaminophen duration and had received higher cumulative doses of gentamicin.

Conclusion

In conclusion, we observed a significantly longer duration of gentamicin therapy in neonates with hsPDA compared to those without hsPDA. No significant differences were observed in the rates of closure of DA with concomitant gentamicin administration and gentamicin trough concentrations.

Low-Frequency (20 kHz) Ultrasonic Modulation of Drug Action

We tested the effect of low-frequency ultrasound (LUS, 20 kHz, 4 W/cm²) on the function of rat mesentery and human pulmonary arteries with wire myography. The vessels were induced to contract with either noradrenaline or physiologic saline solution (PSS) with a high potassium concentration (KPSS) and then incubated with capsaicin (2.1 × 10^-7 M, TRPV1 [transient receptor potential vanilloid 1] activator), dopamine (1 × 10^-4 M, dopamine and α₂-receptor activator), or fenoldopam (dopamine_A1 receptor agonist, 1 × 10^-4 M) with and without glibenclamide (1 μM, KATP [adenosine triphosphate {sensitive potassium channel (ATP)}-sensitive potassium channel] inhibitor and α₂-receptor modulator), and insonated. Vessels were incubated in Ca²⁺-free PSS and induced to contract with added extracellular Ca²⁺ and noradrenaline. Pulmonary arteries were induced to contract with KPSS and dopamine. Then the vessels were insonated. LUS inhibited the influx of external Ca²⁺, inhibited the dopamine-induced vasoconstriction in the KPSS (glibenclamide reversible), reduced the capsaicin-induced vasorelaxation, increased the gentamicin-induced vasorelaxation and increased the dopamine-induced contraction in the KPSS in human pulmonary arteries.

Gentamicin Reduces Calcific Nodule Formation by Aortic Valve Interstitial Cells In Vitro

PURPOSE

Gentamicin is a widely employed antibiotic, but may reduce calcium uptake by eukaryotic cells. This study was conducted to determine whether gentamicin reduces calcification by porcine aortic valvular interstitial cells (pAVICs) grown in 2D culture, which is a common model for calcific aortic valve disease (CAVD).

METHODS AND RESULTS

The presence of gentamicin (up to 0.2 mM) in the medium of pAVICs cultured for 8 days significantly lowered calcification and alkaline phosphatase content in a dose-dependent manner compared to pAVICs cultured without gentamicin. Gentamicin also significantly increased cell proliferation and apoptosis at concentrations of 0.1-0.2 mM. Next, gentamicin was applied to previously calcified pAVIC cultures (grown for 8 days) to determine whether it could stop or reverse the calcification process. Daily application of gentamicin for 8 additional days significantly reduced calcification to below the pre-calcification levels.

CONCLUSIONS

These results confirm that gentamicin should be used cautiously with in vitro studies of calcification, and suggest that gentamicin may have the ability to reverse calcification by pAVICs. Given the nephrotoxicity and ototoxicity of this antibiotic, its clinical potential for the treatment of calcification in heart valves is limited. However, further investigation of the pathways through which gentamicin alters calcium uptake by valvular cells may provide insight into novel therapies for CAVD.

Inadvertent relaxation of the ductus arteriosus by pharmacologic agents that are commonly used in the neonatal period

Premature birth and disruption of the normal maturation process leave the immature ductus arteriosus unable to respond to postnatal cues for closure. Strategies that advocate conservative management of the patent ductus arteriosus (PDA) in premature infants are dependent on identification of the symptomatic PDA and understanding the risk factors that predispose to PDA. Exposure of premature infants to unintended vasodilatory stimuli may be one of the risk factors for PDA that is under recognized. In this article, we summarize the clinical factors that are associated with PDA and review commonly used neonatal drugs for their vasodilatory properties. Data demonstrating relaxation of the ductus arteriosus by gentamicin and other aminoglycoside antibiotics, by cimetidine and other H2 receptor antagonists, and by heparin are provided as examples of neonatal therapies that have unanticipated effects that may promote PDA.

The mechanism by which aminoglycoside antibiotics cause vasodilation of canine cerebral arteries

The effects of aminoglycoside antibiotics were examined in canine cerebral arteries and in cultured cerebrovascular smooth muscle cells stimulated with oxyhemoglobin (OxyHb), a blood constituent which has been implicated in the pathogenesis of cerebrovascular spasm. In cerebral arterial rings precontracted with OxyHb (10 microM), the aminoglycosides caused a concentration-dependent decrease in isometric tension. The EC50s for the relaxation were 0.46+/-0.1 mM (n=6), 0.53+/-0.08 mM (n=12), 1.6+/-0.3 mM (n=7) and 3.9+/-0.5 mM (n=5) for neomycin, gentamicin, streptomycin and kanamycin, respectively. This order of potency corresponds approximately to the number of positive charges in the molecules. The aminoglycosides also inhibited the contractions to prostaglandin F2alpha (1 microM) and depolarizing concentrations of potassium chloride (60 mM). The order of potency was neomycin > gentamicin > streptomycin > kanamycin. The relaxation was maintained in vascular preparations denuded of endothelium. Neomycin (5 mM) abolished the Ca2+-independent contraction to PGF2alpha. In Fura-2-loaded cerebrovascular smooth muscle cells, OxyHb (1 microM) significantly enhanced the concentration of intracellular calcium ([Ca2+]i) by 330%. The administration of neomycin, gentamicin, kanamycin and streptomycin in concentrations corresponding to the EC50 from contractility studies, reduced the effects of OxyHb on [Ca2+]i by about 50% to 221+/-35 nM (n=7), 270+/-31 nM (n=7), 229+/-33 nM (n = 6) and 240+/-6 nM (n = 5), respectively. These results suggests that the effects of the aminoglycosides on the OxyHb-induced contraction and the long-term increase in [Ca2+]i, may arise from several effects, including inhibition of PLC, protection of calcium extrusion mechanisms, and interference with the process of [Ca2+]i accumulation.

Changes in polyurethane calcification due to antibiotics

To develop artificial materials for prolonged use in the vascular system, the complicated process of surface-induced calcification must be better understood. Calcification was examined on porous polyurethane incubated in metastable solutions of calcium phosphate, and the role of certain antibiotics in the medium was evaluated. It seems that certain aminoglycoside antibiotics can modify polyurethane surfaces and, subsequently, their mineralization process. In addition, these antibiotics may alter the calcium transport through polyurethanes. Therefore, it is conceivable that certain antibiotics can, in addition to producing their antibacterial effect, modulate surface calcium binding by changing the calcium mobilization and crystallization. Additional studies are needed to develop applications.

Gentamicin causes the fast depression of action potential and contraction in cultured cardiocytes

The short-term cardiotoxic effects of gentamicin were studied on electrical and mechanical activities in cultures of ventricular confluent cardiocytes of rats. Application of gentamicin to the bath lowered the spontaneous action potential firing rate which was restored when the external calcium was elevated. Fast local application and withdrawal of drugs to non-pacemaker cells allowed effect/dose curves to be made. Such application of 200 nmol gentamicin (approximated concentration: 0.8 x 10(-3)-8.0 x 10(-3) M) lowered the contraction amplitude by 50% and the action potential overshoot by 20% while the action potential duration and maximum diastolic potential remained unchanged. Gentamicin withdrawal was followed by a rapid (half time = 5 s) and complete restoration of contraction. Verapamil, Mn2+, EDTA and La3+ also diminished contraction and overshoot but their effects were reversed 28, 25, 6 and 1.5 times more slowly, respectively. Gentamicin, like La3+, could act extracellularly, probably by competing with calcium ions for some external membrane site.

Gentamicin blockade of slow Ca++ channels in atrial myocardium of guinea pigs

Cardiac dysfunction is occasionally detected in patients undergoing treatment with amino-glycoside antibiotics, however, the mechanism responsible for the negative inotropic effect of these agents has not been identified. In the present investigation electrically driven left atria of guinea pigs were used to study the effects of gentamicin on calcium ion (Ca++)-dependent contractile events in heart muscle isolated from in vivo influences. When atria were first inactivated by excess potassium ion (K+; 22mM) and contractions were then restored by isoproterenol (an experimental model that accentuates the contractile dependence of myocardial fibers on influx of Ca++ through specific "slow channels" of the sarcolemma), the cardiac depressant activity of gentamicin (0.1 mM) was profoundly augmented. Conversely, the negative inotropic effect of tetrodotoxin (23.5 micron) was abolished by the same experimental conditions. Also, gentamicin (1 mM) and La+++ (0.5 mM) markedly decreased the positive inotropic response to increased frequency of stimulation; whereas, D600 (1.05 micron) converted the positive frequency-force relationship to a negative relationship. Present data indicate a direct cardiac depressant action of gentamicin, and suggest that this antibiotic adversely affects either the transport system responsible for Ca++ movement through slow channels of the sarcolemma, the availability of Ca++ for translocation to these sites, or both.

Effects of certain antibiotics on isometric contractions of isolated rat heart muscle

The direct effects of potassium-penicillin-G, kanamycin, streptomycin and chloramphenicol on isometric contraction of isolated rat heart muscle were examined. Potassium-penicillin-G did not depress myocardial contractility but rather increased it. Those increases are not due to penicillin itself but due to a small amount of K+ in potassium-penicillin-G. Kanamycin and streptomycin did show not only direct myocardial depressants effects but concentration-dependent depressions. The depression produced by kanamycin could be restored to normal by adding Ca++ to the bath solution. Chloramphenicol did not show any significant concentration-dependent depression in our studies. We conclude that it is important to be aware of the potential depression of cardiac function by antibiotics, particularly in patients who have diminished cardiac reserve and who are undergoing surgical procedures under anesthesia which may also depress cardiac function.

Contractile function and 45Ca movements in vascular smooth muscle of nonhuman primates: effects of aminoglycoside antibiotics

1. The effects of 7mM neomycin, 10 mM kanamycin and 5 mM gentamicin on vascular smooth muscle contractile responses and 45Ca movements were examined in arterial preparations isolated from nonhuman primates (squirrel monkeys, capuchin monkeys and baboons). 2. Present findings demonstrate that these antibiotics inhibit contractile responses and alter 45Ca movements in monkey blood vessels, and suggest that the manner in which these agents affect vascular smooth muscle from nonhuman primates does not differ qualitatively from their effects in canine and rabbit vascular preparations.

Cardiovascular depressant effects of neomycin and gentamicin in rhesus monkeys

1. The acute cardiovascular effects of neomycin and gentamicin, representative aminoglycoside antibiotics, were examined in surgically-prepared anaesthetized rhesus monkeys. 2. Intravenous administration of 14, 28, and 56 mg/kg of neomycin consistently induced a dose-dependent depression of systemic blood pressure, cardiac output, left ventricular contractile force, maximum dF/dt of left ventricular contraction, and heart rate. Neomycin produced similar cardiovascular depressant effects when heart rate was maintained constant by electrical pacing. 3. Maximum depression of haemodynamic values usually occurred within 2 to 5 min after injection of neomycin; values then gradually returned to control levels within 20 to 30 (14 mg/kg) or 60 to 80 (56 mg/kg) minutes. 4. Injection of CaCl2 (1.35 mEq Ca2+/kg, i.v.) during the peak depressant effect of neomycin produced a rapid and maintained restoration of cardiovascular function to control levels; conversely, noradrenaline (2 mug, i.v.) of isoprenaline (0.5 mug, i.v.) produced only transient reversal of the neomycin effects. 5. Similar evidence of cardiovascular dysfunction was observed with gentamicin. 6. These findings demonstrate the direct cardiovascular depressant effects of aminoglycoside natibiotics in a higher primate species, and suggest that this adverse response is related to an alteration of calcium ion function.

Direct myocardial depressant effects of gentamicin

Effects of gentamicin on myocardial contractile performance were examined in isolated, electrically driven, rat left atria. This aminoglycoside antibiotic produced a maintained and concentration-dependent (0.0156-0.25 mM) depression of myocardial contractile tension that was reversible by replacing the incubation media with gentamicin-free solution. Time to peak tension and total contraction time were not discernibly altered by gentamicin. The negative inotropic response elicited by gentamicin was antagonized in a competivitive-like manner by increasing the calcium ion (Ca2+) concentration of the bathing solution, whereas, the depressant effects of gentamicin were antagonized by norepinephrine in a non-competitive-like manner. Present findings demonstrate a direct negative inotropic effect of gentamicin and suggest that this antibiotic interferes with the participation of Ca2+ in the events leading to mecahnical activity of atrial myocardium.