Gelatin microspheres: Initial clinical experience for the transcatheter arterial embolization

European Journal of Radiology 67 (2008) 536–540

Technical note

Gelatin microspheres: Initial clinical experience for the transcatheter arterial embolization Norihisa Nitta a,∗ , Shinichi Ohta a , Toyohiko Tanaka a , Ryutaro Takazakura a , Yukihiro Nagatani a , Naoaki Kono a , Akinaga Sonoda a , Ayumi Seko a , Akira Furukawa a , Masashi Takahashi a , Kiyoshi Murata a , Yasuhiko Tabata b a

Department of Radiology, Shiga University of Medical Science, Tsukinowa-cho Otsu Shiga 520-2192, Japan b Department of Biomaterials, Institute for Frontier Medical Sciences, Kyoto University, Kyoto, Japan Received 21 May 2007; received in revised form 30 July 2007; accepted 31 July 2007

Abstract Purpose: The purpose of this study is to evaluate the embolization effects of gelatin microspheres (GMSs) when used as an embolic material for transcatheter arterial embolization (TAE) for several organs. Materials and methods: We prepared GMSs that dissolves in 5 days in extravasuclar tissue. GMSs were used in five cases in total, four cases with multiple liver tumors and one case with a pelvic bone tumor. Results: In all five cases, it was possible to treat the targeted tumors by TAE with GMSs. In the contrast-enhanced CT performed 2–4 weeks later, the embolized tumors did not show an enhancement effect. Passage of GMSs in the microcatheter was excellent. Conclusion: GMSs showed sufficient potential to be used as an embolic material. © 2007 Elsevier Ireland Ltd. All rights reserved. Keywords: Embolic material; Gelatine microsphere; Degradable agent; Transcatheter arterial embolization

1. Introduction Transcatheter arterial embolization (TAE) is widely employed due to its efficacy and is used to treat various diseases including tumors, vascular lesions, and hemorrhagic lesions [1–3]. Along with advances in this technique, various embolic materials have been developed and used [4–7]. Among these materials, gelatin sponges are the most popular and are frequently used in Japan because they are easy to handle and inexpensive. Further, other embolic materials such as polyvinyl alcohol and trisacryl gelatin microspheres are not commercially available in Japan [8]. However, since gelatin sponges require manual cutting, the sizes of the fragments are not uniform. Hence, it is impossible to intentionally select the occlusion level of the vessels. Further, although they are believed to degrade in the vessels within a few weeks, the degradation periods of these sponges cannot be strictly controlled [9–11].

In this study, we report on our experiences in five clinical cases in which degradable gelatin microspheres (GMSs) were used (Fig. 1) [12,13]. Two patients with hepatocellular carcinoma (HCC) and two patients with metastatic liver tumors underwent TAE. In these four patients, the tumors were embolized with only GMSs administered from the successfully placed microcatheter, and the retention of both the contrast agent and GMSs within the tumors was confirmed by CT imaging. The last case was a patient with pelvic bone metastasis. The retention of both the contrast agent and GMSs within the tumor was also confirmed by CT imaging. A sufficient embolization effect was achieved in all five cases. These results demonstrate the efficacy of GMSs as an embolization material, suggesting its candidacy for clinical use. 2. Materials and methods 2.1. Preparation of GMSs

∗

Corresponding author. Tel.: +81 77548 2288; fax: +81 77544 0986. E-mail address: [email protected] (N. Nitta).

0720-048X/$ – see front matter © 2007 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.ejrad.2007.07.021

GMSs were prepared according to the modified method of Tabata and Ikada (1989) by glutaraldehyde crosslinking of an

N. Nitta et al. / European Journal of Radiology 67 (2008) 536–540

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three times with double-distilled water by centrifugation and were freeze-dried. The GMSs used in this study were designed to degrade completely within 5 days in the extravascular tissues. The degradation period was confirmed while GMSs were placed in the subcutaneous dorsal neck tissues of rabbits. 2.2. Clinical cases

Fig. 1. Microscopic appearance of gelatin microspheres (GMSs). GMSs are completely spherical in shape within double distilled water.

aqueous gelatin solution dispersed in an oil phase in the absence of a surfactant [14]. In brief, 10 ml of acidic aqueous gelatin solution (10%) that was preheated to 37 ◦ C was added dropwise into 375 ml of olive oil (Wako Pure Chemical Industries Ltd., Osaka, Japan). The mixture was stirred at 400 rpm at 37 ◦ C for 10 min to yield a water-in-oil (w/o) emulsion. The stirring was continued for 30 min at 4 ◦ C, and the microspheres that were formed were washed three times with acetone (Wako Pure Chemical Industries, Ltd., Osaka, Japan) by centrifugation (5000 rpm, 5 min, 4 ◦ C). After air-drying, the microspheres were sized by passing them through sieves with different apertures (50, 100, 200, and 300 ␮m); they were then placed in 2 groups (50–100, 100–200, and 200–300 ␮m) based on the sphere size. The non-crosslinked dry GMSs were dispersed in 5 ml of aqueous glutaraldehyde solution (7.5 mg ml−1 , 25%, NACALAI TESQUE Inc., Kyoto, Japan) at 4 ◦ C for 15 h to facilitate crosslinking. The microspheres were further agitated in 5 ml of 10 mM aqueous glycine solution (NACALAI TESQUE Inc., Kyoto, Japan) at 37 ◦ C for 1 h to block the residual aldehyde groups of the unreacted glutaraldehyde. The resulting microspheres were finally washed

We performed transcatheter arterial embolization (TAE) with GMSs in five patients, including four patients with hepatic arterial embolization and one patient with tumor embolization for pelvic bone metastasis. GMSs of 50–100 ␮m in diameter were used in the two patients with HCC and in the two patient with metastatic liver tumor. GMSs of 200–300 ␮m in diameter were used in the patient with metastatic bone tumor (Table 1). Three patients on which hepatic arterial embolization with GMSs was conducted had multiple tumors. TAE was conducted by selecting only one tumor in each patient. Chemoembolization was conducted for the remaining tumors in each patient. Since influence of small particles 50–100 ␮m in size on normal liver tissue is unknown, TAE was performed with GMS exclusively for the nodules selected in advance. TAE was performed immediately after administering a mixture of GMSs and iopamidol (Iopamiron 370; Nihon Schering Co., Ltd., Osaka, Japan) diluted to 50%. In addition, after absence of shunt vessels was cautiously confirmed by CTA and angiography, TAE with GMS was carried out. In all cases, embolization with GMSs was conducted upon both approval by the ethics committee of our institution and patients’ informed consent. 3. Results TAE was successful in all cases. In the patients with HCC and metastatic liver tumors, in which superselective subsegmental catheterization was achieved, the retention of both GMSs and the contrast agent was demonstrated within the tumors by CT examination (Figs. 2 and 3). In the contrast-enhanced CT performed 2–4 weeks later, the embolized tumors did not show an enhancement effect, suggesting that they were necrotic (Figs. 2 and 3). In the patient with bone metastasis, the embolization was also confirmed by CT examination. The tumor was then confirmed to

Table 1 Detailed information of five patients for whom TAE was conducted Age (years)

Sex

Diameter of used GMS (␮m)

Weight of used GMS (mg)

Case 1

43

F

50–100

50

Case 2

84

M

50–100

50

Case 3

60

M

50–100

30

Case 4

77

M

50–100

60

Case 5

68

M

200–300

200

Embolization branch

A branch(A6) of right hepatic artery A branch(A8) of right hepatic artery A branch (A2) of right hepatic artery A branch (A2) of right hepatic artery Left internal iliac artery

CT findings of the tumor

Complaints

Preoperative

Post TAE

After 2–4 weeks

During embolization

Enhanced

Unenhanced

None

Unenhanced

None

Unenhanced

None

Enhanced

Retention of GMS and contrast agent Retention of GMS and contrast agent Retention of GMS and contrast agent –

Unenhanced

None

Enhanced

–

Unenhanced

None

Enhanced Enhanced

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Fig. 3. A 77-year-old male with metastatic liver tumors (case 4). (a) In CTA, early tumor stain of segment 3 exists (arrow). The embolization by GMSs of 50–100 ␮m in diameter is conducted. (b) Four weeks later, an enhancement CT examination is conducted. Note that the tumor is non-enhanced (arrow).

Fig. 2. An 84-year-old male with multiple HCC (case 2). (a): In CTA, early tumor stain of segment 8 exists (arrow). (b) After embolization by GMSs of 50–100 ␮m in diameter, CT examination is conducted. Intratumoral high density by the retention of GMSs and contrast medium is recognized (arrow). (c) Two weeks later, an enhancement CT examination is conducted. Note that the tumor is non-enhanced (arrow).

be necrotic by the evident lack of enhancement in the contrastenhanced CT performed 2 weeks later (Fig. 4). The fluoroscopic findings at the time of embolization with GMSs suggested that, in contrast to Gelfoam, their uniform size and spherical shape

seemed to ensure the gradual embolization from the peripheral arteries to the proximal arteries. In this study, use of GMS particles 50–100 ␮m was limited to cases in which targeted vessels could be selected, and no critical complications such as severe liver dysfunction and abscess formation occurred. To expand indications of this embolization method in the future, accurate diagnosis on the presence or absence of shunt vessels is a key factor to avoid critical complications. Minor complications such as fever and mild elevation of liver enzymes were observed in patients with TAE for HCC, but were not different from those with TAE using Gelfoam. Passage through the microcatheter was also good, suggesting catheter occlusion may not occur with particle sizes smaller than 300 ␮m. 4. Discussion To date, a number of embolization materials have been developed and clinically utilized. They can be classified into three groups by the duration of embolization effect, that is, short-term, long-term, and permanent. Short-term embolization materials include autologous blood clot and hypertonic glucose as well

N. Nitta et al. / European Journal of Radiology 67 (2008) 536–540

Fig. 4. A 68-year-old male with metastatic bone tumor (case 5). (a) In dynamic CT examination, early tumor stain of pelvic bone exists. Tumor stain is visualized (arrow). (b) Four weeks later, an enhancement CT examination is conducted. Note that tumor is non-enhanced (arrow).

as degradable starch microspheres (SpherexTM ) that dissolve within 30 min [15]. Long-term embolization materials are represented by gelatin sponges such as Gelfoam and Spongel, which dissolve within about 2 weeks. Permanent embolization materials include metallic coil, NBCA, and PVA, which are not degradable. There are also unclassifiable embolization materials such as lipiodol and ethanol. Although these are utilized depending on the case and purpose, hepatic arterial embolization for HCC is usually conducted with gelatin sponge following chemo-lipiodol. Gelatin sponge (Gelfoam) has also been the first choice in TAE for bleeding in areas other than the gastrointestinal tract. This may be because gelatin is easy to obtain, hardly induces foreign body reaction and has neither cytotoxicity nor antigenicity. Gelfoam can also be broken into any size according to the size of the target vessel. As an added advantage, since the thrombus frequently recanalizes 2–3 weeks following arterial administration of Gelfoam, TAE can be repeated. On the other hand, Gelfoam needs to be either cut into small pieces with scissors or broken into small pieces with a grater or by a pumping method, which are cumbersome processes

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[16]. Further, there is a limit as to how small and how uniform the pieces can be cut with scissors. From this standpoint, GMSs have an advantage over gelatin sponge and are possibly a more ideal embolization material. When directly compared to Gelfoam, GMSs have several advantages. Gelfoam is an irregularly shaped sponge, while GMSs are completely spherical and solid and higher in density. The weight of one sheet of 12 cm2 (20 mm × 60 mm) × 7 mm = 8.4 cm3 Gelfoam is 84 mg while the volume of GMSs with the same weight is less than 1 cm3 , though it varies depending on the particle size. Therefore, the weight of embolization material filling the same region is greater with GMSs, which may contribute to the strength of its embolization effect. On the other hand, in terms of dissolution, Gelfoam has a wider area in contact with gelatinase, which may lead to easier recanalization. However, the dissolving time of GMSs can be controlled by reducing the level of cross-linking, and thus, it can be engineered to dissolve faster than Gelfoam. At present, commercialized embolization materials with various particle sizes include IvalonTM , which is made of PVA, EmbosphereTM , which is coated by gelatin, and HepashereTM , which is made of absorbent polymers [17–19]. These are all permanent embolization materials and, thus, cannot control the duration of embolization. On the other hand, there are some materials, such as NBCA, in which the time required for hardening can be manipulated by changing the ratio with lipiodol. However, no material possesses characteristics like that of GMSs in which the dissolving time can be controlled. In this respect, GMS particle size can be designed to be between 10 and 500 ␮m, and their dissolving time can be varied from about 3 days to almost undegradable by changing the level of cross-linkage. [11] Therefore, GMSs can be used for either proximal or peripheral embolization, or both. That is, it can be used for a wide range of purposes and applications, from temporal to permanent embolization. In this study, we used GMSs in four cases with TAE for HCC and metastatic liver tumors, and one case with TAE for metastatic bone tumors. GMSs with the particle size of either 50–100 ␮m or 200–300 ␮m used in this study dissolved within 5 days in the extravascular tissue. We previously confirmed in our pilot study that the dissolving time of GMSs is longer in intravascular tissue than in extravascular tissue, suggesting that GMSs used in this study would take more than 10 days to dissolve intravascularly [12,13]. Regarding the embolization efficiency and solubility of GMSs, Ohta et al. performed embolization of renal arteries using GMSs of three different particle sizes (50–100, 100–200, and 200–300 ␮m) and compared the angiographic and pathological findings. Angiographic findings showed that GMSs of large particle sizes (200–300 ␮m) induced large infarctions and those with small particle sizes (50–100 ␮m) induced infarctions not only in small areas but also in large areas. Pathological examinations revealed that, as a reason why small GMSs induce large infarctions, two or three small GMSs cohere to embolize relatively large vessels like interlobular arteries. Regarding dissolution time, GMSs particle sizes of either 50–100 ␮m or 200–300 ␮m used in this study dissolved within 5 days in the extravascular tissue. Ohta et al. performed pathological investigations 3, 7, and 14 days after emboliza-

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tion of renal arteries using the aforementioned GMSs of three different particle sizes. The results showed no difference in the effectiveness of GMSs regarding the three different particle sizes 3 days after embolization. After 7 days, however, deformity of the GMS particles and formation of mild cleft and cavity were observed in all particle sizes. A reduction of the particle diameter was also observed. After 14 days, a marked reduction of the particle diameter and formation of severe cleft and cavity were found. After 14 days, there were some cases in which no particle was detected. These results suggest that the dissolution time of GMSs is longer in blood vessels than in extravascular tissue. However, the number of GMS particles fell dramatically as time passed and was thought to have dissolved and disappeared. It is necessary to evaluate which sizes of particle should be used for specific kinds of lesions in accumulated cases in the future. In our basic experiment, we made GMSs in six sizes: 50–100,100–200, 200–300, 300–500, 500–700, 700–1000 ␮m. Using these different-sized GMSs, we performed a passage test through different sizes of catheters. The result was that GMSs under 300 ␮m could be passed through 2.1 Fr microcatheters and GMSs under 500 ␮m could be passed through 4 Fr catheters. Minor complications such as fever and mild elevation of liver enzymes were observed in patients with TAE for HCC, but were not different from those with TAE using Gelfoam. As seen in the four patients with HCC and metastatic liver tumors, the localized retention of both contrast agent and GMSs within the tumor was observed when the particle size of 50–100 ␮m was used. The regions were not enhanced in the follow up contrast-enhanced CT, suggesting that there were necrotic regions. Even without combining with anticancer agents, embolization itself can exert a sufficient therapeutic effect if the catheter can reach close enough to the target vessel. However, GMSs alone may not be sufficient to prevent the recurrence from the marginal zone. In this respect, we are also developing new GMSs that involve the slow release of cisplatin, which may become a potential tool for TAE in clinical settings. The results of this study demonstrated that GMSs possess sufficient embolization effects when used as an embolization material. If GMSs having variations in particle size and dissolving time are prepared in the future, our strategy for TAE will be highly configurable and therefore achievable and successful. Although the kinds of slow-release drugs from microspheres are currently limited, combining GMSs with anticancer drugs for slow release would be another potential strategy for anticancer therapy. It may also be applicable as a method for long-term drug administration for chronic diseases. 5. Conclusion GMSs have demonstrated sufficient embolization effects when used as an embolization material and, thus, is suggested to be highly applicable for clinical use.

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