Microscopic study of ultrasound-mediated microbubble destruction
effects on vascular smooth muscle cells
Bo Zhang1*
, Yi-Rong Hou1
, Tian Chen1
, Bing Hu2
1
Department of Ultrasound Medicine, East Hospital, School of Medicine, Tongji University, Shanghai 200120, China
2
Department of Ultrasound, 6th People’s Hospital Affiliated to Shanghai Jiaotong University, Shanghai, China
Contents lists available at ScienceDirect
Asian Pacific Journal of Tropical Medicine
journal homepage:www.elsevier.com/locate/apjtm
ARTICLE INFO ABSTRACT
Article history:
Received15 January 2015
Received in revised form 20 February 2015
Accepted 15 March 2015
Available online 20 April 2015
Keywords:
Atomic force acoustic microscopy
Vascular smooth muscle cell
Ultrasound
Microbubble
*Corresponding author: Bo Zhang, M.D., Chief Physician, Department of
Ultrasound Medicine, East Hospital, School of Medicine, Tongji University, Shanghai
200120, China.
Tel: 86-15800620806
E-mail: zhangbodongfang@qq.com
Foundation project: It is supported by Shanghai Pudong New Area Health Plan
Committee Of Academic Leaders Project (NO. PWRd2013-02), National Natural
Fund (NO. 81401428).
1. Introduction
Coronary heart disease and cerebral vascular stenosis caused by
cardiovascular and cerebrovascular stenosis has become one of
the main life-threatening diseases in human health and safety[1,2].
At present, vascular stenosis treatments are divided into three
categories: drug treatment, surgical operation, interventional therapy.
Among these methods, interventional therapy is a new treatment
that has minimum trauma effects and performs well. Percutaneous
transluminal angioplasty (PTA) is a common approach for relieving
stenosis, and improving cardiac and cerebral blood supply; but this
approach has a recurrence rate of 30%-50%[3]. Research revealed
that excessive proliferation and migration of smooth muscle cells
were the main causes, which leads to restenosis[4]. Effectively
preventing vascular restenosis after PTA operation has been a
big problem that needs to be solved during cardiovascular and
cerebrovascular disease PTA treatments. So far, there are mainly
Objective: To observe vascular smooth muscle cell morphological changes induced by
ultrasound combined with microbubbles by Atomic Force Acoustic Microscopy (AFAM).
Methods: A7r5 rat aortic smooth muscle cells were divided into groups: control group (without
ultrasonic irradiation, no micro bubbles) and US+MB group (45 kHz, 0.4 W/cm2
ultrasound
irradiate for 20 seconds with a SonoVue™ concentration of [(56-140)暳105
/mL]. Cell micromorphological
changes (such as topographic and acoustic prognosis) were detected, before and
after ultrasound destruction by AFAM. Results: In cell morphology, smooth muscle cells were
spread o and connected to each another by fibers. At the center of the cell, the nuclear area had
a rough surface and was significantly elevated from its surroundings. The cytoskeletal structure
of the reticular nucleus and cytoplasm in the morphology of A7r5 cells (20毺m×20毺m) were
clear before microbubble intervention. After acoustic exciting, the cell structure details of
the acoustic image were improved with better resolution, showing the elasticity of different
tissues. In the acoustic image, the nucleus was harder, more flexible and uneven compared
with the cytoplasm. Many strong various-sized echo particles were stuck on the rough nuclear
membrane’s substrate surface. The nuclear membrane did not have a continuous smooth
surface; there were many obstructions (pores). After ultrasound-intervention was combined
with microbubbles, the dark areas of the A7r5 cell images was increased in various sizes and
degrees. The dark areas showed the depth or low altitudes of the lower regions, suggesting
regional depressions. However, the location and scope of the acoustic image dark areas were
not similar to those found in the topographic images. Therefore, it was likely that the dark
areas, both from the topographic and acoustic images, were sound-holes. In addition, some
cell nuclei become round in different degrees after irradiation. Conclusions: Atomic force
microscopy and acoustic excitation method can noninvasively and completely display a cell’s
structure, connections and elastic properties at a nano scale in just several minutes. The dark
areas, both from the topographic and acoustic images, may be sound-holes; therefore, it would
be helpful if these sound-holes were found. These findings provide a relationship between cell
apoptosis after ultrasound and microbubble ultrasound irradiation, and the sound-hole effect.
IF: 0.926
326 Bo Zhang et al./Asian Pacific Journal of Tropical Medicine (2015)325-329
four methods used for reducing restenosis; but the effects are not
ideal[3]. Among those methods, anticoagulants does not achieve high
local drug concentrations surrounding the stent. Radiation can easily
cause hemal brittleness, increasing the rate of cancer. At present,
gene therapy is still not a safe, effective and stable method for
enabling the objective gene to express in the target organs. The longterm
efficacy of drug-eluting stents has not yet been determined;
however, the risk of inducing thrombosis has already been proven[4].
Therefore, there is an urgent clinical need for establishing a method
that has a long-term efficacy and can conveniently, safely, and
efficiently inhibit intimal hyperplasia; as well as preventive methods
for vascular restenosis.
In recent years, it has been found that ultrasonic irradiation can
inhibit proliferation and promote vascular smooth muscle cell
apoptosis[5]. This method can be used for treating vascular restenosis,
which promises positive results in clinical practice. However, the
efficiency of inhibiting cells’ proliferation is rather low. Study of
Zhang et al revealed that cell apoptosis is only around 3%[6] after
ultrasonic irradiation. Consequently, researchers are studying the
effect of the combination of ultrasonic irradiation and microbubbles.
And it turned out that the combination method performed better
than using ultrasonic irradiation purely, which could led 20% cells’
apoptosis after s ultrasonic irradiation for 24 hour[7]. What’s more,
with the same irradiation frequency and intensity, different types of
microbubbles can have a direct impact on ultrasonic intervention,
which may be associated with the number of microbubbles, the
expansion size at a certain frequency and radiation intensity, and the
jets and shock waves that occurs when a bubble bursts. Atomic force
acoustic microscopy (AFAM) has been developed to observe the
morphology and internal information of a cell. AFAM can produce
high-resolution images by atomic force microscopy (AFM) and
provide a non-destructive imaging method by acoustic microscopy.
These features can help observe atomic force micrographs and
acoustic microscopy in situ, simultaneously. AFAM can obtain the
internal information of cells through acoustic waves at a nanometerlevel
resolution. Once the ultrafine images and elastic coefficients
of the same internal and surface areas are acquired, a 3D image of
the sample can be easily obtained. The elasticity information of cells
can also be observed by AFAM, which has become a powerful tool
for observing cell morphology. The research aims to observe the
morphological changes of vascular smooth muscle cells (A7r5 cells)
after ultrasound, and microbubble ultrasound irradiation by AFAM.
We hope to explain the effects of microbubbles on single vascular
smooth muscle cells and to explore the mechanisms of vascular
smooth muscle cell apoptosis. Providing experimental basis and
reference would be helpful in exploring the most suitable frequency
and microbubble dose for further studies.
2. Materials and methods
2.1. Cell preparation method and cell samples
A7r5 rat aortic smooth muscle cells were purchased from the cell
bank of the Chinese Academy of Sciences. Cells were cultured
with a high glucose DMEM medium, containing 10% fetal bovine
serum and 1% penicillin and streptomycin, in a cultivating box with
5% CO2 at 37 曟. A borosilicate glass was used as a cell adhesion
substrate. To make the polylysine adhere on the glass coverslips, the
coverslips were immersed and soaked in ethanol for 15 minutes, and
100 毺g/mL of polylysine diluted with PBS solution 0.25 mL was
dribbled on the coverslips; after preparation, the coverslips kept at 4
曟 overnight. On the next day, the excess polylysine was absorbed
and the coverslips were washed with sterile water, twice[5]. Then,
the coverslips were air-dried and irradiated in ultraviolet light for 15
minutes[5].
The coverslips were placed in a 6-well culture plate, placed in 1
伊106
/mL cells 1 mL, then the cells were cultured according to the
above conditions. It was removed when 70%-80% of the coverslip
was covered with cells.
2.2. Experimental equipment
Instruments used for the experiment included: carbon dioxide
incubator (BPH-9042, Shanghai Yiheng Scientific Instrument Co.
Ltd.); HiRox7700 optical microscope (for observing cells in 6-well
culture plate); ultrasonic transducer connected to an ultrasonic
generator (model: dm-40; Acoustic Laboratory of Shanghai
Academy of Sciences, China), the output power was monitored by a
digital power analyzer (model: ppa2500; N4L); needle hydrophone
(model: SPRH -S -1000; SEA) connected to a digital display
(model: TDS 1024B Tech); Atomic force acoustic microscopy was
used for monitoring ultrasound (AFAM, SPM by Veeco DI, Santa
Barbara, CA, USA production). Two AFAM modes, contact mode
and vibration mode were used.
2.3. Analysis method
The cells were divided into 2 groups: control group (treated without
ultrasonic irradiation, no microbubbles) and US+MB group [45 kHz,
0.4 W/cm2
by ultrasound-mediated microbubble destruction for 20
seconds with microbubble concentration: (56-140)伊105
microbubbles
per milliliter]. The coverslips that were covered with cells were
placed into c