A pilot investigation of poloxamer 407 for the prevention of leptomeningeal adhesions in the rabbit

Clinical Implications of Poloxamer 407 as Packing Material in an Animal Model

BACKGROUND

Endoscopic ear surgery has recently increased, but it is still inconvenient and time-consuming to place packing material in the middle ear with one hand. Poloxamer 407 (P407) is a thermo-reversible gel that can be easily administered with one hand into the middle ear cavity in liquid form. Upon warming to body temperature, the gel form of P407 can support the graft in the target position and is known to prevent postsurgical tissue adhesion.

OBJECTIVES

We aim to investigate the feasibility of P407 as packing material in an animal model. Male Hartley guinea pigs (350 and 400 g) were utilized in this study.

METHOD

The animals were randomly divided into 3 groups according to the packing material: the control group, the P407 group, and the gelatin group. To assess the role of packing material on bacterial colonization, left ears were inoculated with Streptococcus pneumoniae through the tympanic membrane using a 0° endoscope. Five days after inoculation, the middle ear cavity was packed through a transbullar approach using 18% P407 or gelatin in both ears. In the control group, no ear pack was inserted. The tympanic membrane was examined every week using a 0° 1.9-mm endoscope until 6 weeks. Half of the animals in each group were sacrificed 6 weeks after placement of the packing materials.

RESULTS

Compared with the absorbable gelatin sponge, the P407 group showed little inflammation or fibrosis in the tympanic membrane and middle ear mucosa regardless of bacterial inoculation. The gelatin group showed severe otorrhea or perforation until 2 weeks in the right ear (2 of 4) and the left ear (1 of 4). Even though the endoscopic findings were similar between both packing groups at 6 weeks, histological analysis showed persistent packing material, inflammatory cells, and fibrosis in the gelatin group compared to the P407 group.

CONCLUSIONS

This study suggested that P407 is feasible as a packing material to handle with one hand and to prevent adhesion, especially in infected middle ear mucosa. Although there is a lack of data on how well P407 supports grafts, we suggest that P407 could be a candidate for packing material in endoscopic ear surgery.

Effects of a Temperature-Sensitive, Anti-Adhesive Agent on the Reduction of Adhesion in a Rabbit Laminectomy Model

OBJECTIVE

A common cause of failure in laminectomy surgery is when epidural, peridural, or perineural adhesion occurs postoperatively. The purpose of this study is to examine the efficacy of a temperature-sensitive, anti-adhesive agent (TSAA agent), Guardix-SG®, as a mechanical barrier for the prevention or reduction of peridural scar adhesion in a rabbit laminectomy model.

METHODS

Twenty-six mature rabbits were used for this study. Each rabbit underwent two separate laminectomies at lumbar vertebrae L3 and L6, left empty (the control group) and applied 2 mL of the TSAA agent (the experimental group), respectively. Invasive scar formation or inflammation after laminectomy was quantitatively evaluated by measuring the thickness of the dura, the distance from the surface of dura to the scar tissues, the number of inflammatory cells in the scar tissues at the laminectomy site, and the concentration of collagen in histological sections.

RESULTS

At 6 weeks postsurgery, the dura was significantly thinner and the distance from the surface of dura to the scar tissues was greater in the experimental group than in the control group (p=0.04 and p=0.01). The number of inflammatory cells was not significantly different in the two groups (p=0.08), although the mean number of inflammatory cells was relatively lower in the experimental group than in the control group.

CONCLUSION

The current study suggests that the TSAA agent, Guardix-SG®, could be useful as an interpositional physical barrier after laminectomy for the prevention or reduction of adhesion.

Prevention of capsular contracture with Guardix-SG(®) after silicone implant insertion

BACKGROUND

Capsular contracture is the most common side effect of breast implant insertion and the problem that breast surgeons seek to avoid the most. Previous animal studies have proved that an antiadhesive barrier solution (AABS) prevents peri-implant capsule formation. In this study, the authors sought to explore the effect that Guardix-SG(®), an AABS that can encapsulate implants in the form of a gel, can have on capsular contracture.

METHOD

This study used 12 female New Zealand white rabbits weighing 2.5-3 kg. Implants were inserted into the subpanniculus carnosus plane through an incision in the bilateral midback area. Once the implant was inserted, 3 g of Guardix-SG(®) and normal saline were instilled into the left and right sides, respectively. The rabbits were killed 6 months after the procedure. The intracapsular pressure was measured using tonometry with a 38.2-g circular glass piece, and capsular thickness was measured by dyeing the biopsy specimen with hematoxylin and eosin and Masson's trichrome stain. The myofibroblasts were quantitatively analyzed through monoclonal anti-alpha smooth muscle actin antibody immunohistochemistry staining.

RESULTS

The intracapsular pressure in the control group (4.51 ± 0.98 mmHg) was significantly higher (p = 0.002) than in the study group (3.51 ± 0.4 mmHg). The average capsular thickness was significantly greater in the control group (0.33 ± 0.15 mm; p = 0.015). In the analysis, the interrelation between capsular thickness and intracapsular pressure was insignificant in both groups, as was the number of myofibroblasts in both groups (p = 0.582).

CONCLUSION

Through this study, the authors were able to demonstrate that capsular contracture can be suppressed in the rabbit model by instilling Guardix-SG(®) after insertion of cohesive gel implants in the subpanniculus carnosus plane.

LEVEL OF EVIDENCE IV

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The effectiveness of poloxamer 407-based new anti-adhesive material in a laminectomy model in rats

PURPOSE

In the laminectomy model in rats, to verify anti-adhesive effectiveness of the new material, a mixture composed of poloxamer 407, calcium chloride, and xanthorrhizol, we compared it with that of commercially used solution form anti-adhesive agent GUARDIX-SL, Biorane.

MATERIALS AND METHODS

A total of 108 Sprague-Dawley rats (SD rats) were divided equally into three groups: negative control group (NCG), positive control group (PCG), and experimental group (EG). After exposing the dura on L4 level, we closed the wound shortly after hemostasis, after administering the anti-adhesive agent. To evaluate effectiveness, 18 SD rats from each group were killed after 1 week of rearing. Nine were examined by grading of gross adhesion and the other nine, by grading of histological adhesion. The degree of adhesion in the remainder of 18 SD rats in each group was examined with the same method after four weeks of rearing.

RESULTS

Comparing the degree of adhesion after growth for 1 week, the gross and histological adhesion of the EG was lower than that of the NCG. There was no statistical significance in the gross score (P = 0.63), but there was statistical significance in the histological score (P = 0.04). The EG showed similar or improved degrees of adhesion in comparison with the PCG. In comparison after growth for 4 weeks, although gross adhesion of the EG was not significantly lower than the NCG, histological adhesion was remarkably low in the EG (P = 0.01). The EG showed similar or improved degrees of gross and histological adhesion in comparison to that of the PCG. (P = 0.20, 0.07).

CONCLUSION

The new anti-adhesive material showed similar or improved effectiveness with the existing agents for commercial use. This result suggests that the new anti-adhesive material will be a successful candidate as a future product for clinical use.

Safety Assessment of Poloxamers 101, 105, 108, 122, 123, 124, 181, 182, 183, 184, 185, 188, 212, 215, 217, 231, 234, 235, 237, 238, 282, 284, 288, 331, 333, 334, 335, 338, 401, 402, 403, and 407, Poloxamer 105 Benzoate, and Poloxamer 182 Dibenzoate as Used in Cosmetics

Poloxamers are polyoxyethlyene, polyoxypropylene block polymers. The impurities of commercial grade Poloxamer 188, as an example, include low-molecular-weight substances (aldehydes and both formic and acetic acids), as well as 1,4-dioxane and residual ethylene oxide and propylene oxide. Most Poloxamers function in cosmetics as surfactants, emulsifying agents, cleansing agents, and/or solubilizing agents, and are used in 141 cosmetic products at concentrations from 0.005% to 20%. Poloxamers injected intravenously in animals are rapidly excreted in the urine, with some accumulation in lung, liver, brain, and kidney tissue. In humans, the plasma concentration of Poloxamer 188 (given intravenously) reached a maximum at 1 h, then reached a steady state. Poloxamers generally were ineffective in wound healing, but were effective in reducing postsurgical adhesions in several test systems. Poloxamers can cause hypercholesterolemia and hypertriglyceridemia in animals, but overall, they are relatively nontoxic to animals, with LD50 values reported from 5 to 34.6 g/kg. Short-term intravenous doses up to 4 g/kg of Poloxamer 108 produced no change in body weights, but did result in diffuse hepatocellular vacuolization, renal tubular dilation in kidneys, and dose-dependent vacuolization of epithelial cells in the proximal convoluted tubules. A short-term inhalation toxicity study of Poloxamer 101 at 97 mg/m3 identified slight alveolitis after 2 weeks of exposure, which subsided in the 2-week postexposure observation period. A short-term dermal tox-icity study of Poloxamer 184 in rabbits at doses up to 1000 mg/kg produced slight erythema and slight intradermal inflammatory response on histological examination, but no dose-dependent body weight, hematology, blood chemistry, ororgan weight changes. A6-month feeding study in rats and dogs of Poloxamer 188 at exposures up to 5% in the diet produced no adverse effects. Likewise, Poloxamer 331 (tested up to 0.5 g/kg day-1), Poloxamer 235 (tested up to 1.0 g/kg day-1), and Poloxamer 338 (at 0.2 or 1.0 g/kg day-1) produced no adverse effects in dogs. Poloxamer 338 (at 5.0 g/kg day-1) produced slight transient diarrhea in dogs. Poloxamer 188 at levels up to 7.5% in diet given to rats in a 2-year feeding study produced diarrhea at 5% and 7.5% levels, a small decrease in growth at the 7.5% level, but no change in survival. Doses up to 0.5 mg/kg day-1 for 2 years using rats produced yellow discoloration of the serum, high serum alkaline phosphatase activity, and elevated serum glutamicpyruvic transaminase and glutamic-oxalacetic transaminase activities. Poloxamers are minimal ocular irritants, but are not dermal irritants or sensitizers in animals. Data on reproductive and developmental toxicity of Poloxamers were not found. An Ames test did not identify any mutagenic activity of Poloxamer 407, with or without metabolic activation. Several studies have suggested anti-carcinogenic effects of Poloxamers. Poloxamers appear to increase the sensitivity to anticancer drugs of multidrug-resistant cancer cells. In clinical testing, Poloxamer 188 increased the hydration of feces when used in combination with a bulk laxative treatment. Compared to controls, one study of angioplasty patients receiving Poloxamer 188 found a reduced myocardial infarct size and a reduced incidence of reinfarction, with no evidence of toxicity, but two other studies found no effect. Poloxamer 188 given to patients suffering from sickle cell disease had decreased pain and decreased hospitilization, compared to controls. Clinical tests of dermal irritation and sensitization were uniformly negative. The Cosmetic Ingredient Review (CIR) Expert Panel stressed that the cosmetic industry should continue to use the necessary purification procedures to keep the levels below established limits for ethylene oxide, propylene oxide, and 1,4-dioxane. The Panel did note the absence of reproductive and developmental toxicity data, but, based on molecular weight and solubility, there should be little skin penetration and any penetration of the skin should be slow. Also, the available data demonstrate that Poloxamers that are introduced into the body via routes other than dermal exposure have a rapid clearance from the body, suggesting that there would be no risk of reproductive and/or developmental toxicity. Overall, the available data do not suggest any concern about carcinogenesis. Although there are gaps in knowledge about product use, the overall information available on the types of products in which these ingredients are used, and at what concentration, indicates a pattern of use. Based on these safety test data and the information that the manufacturing process can be controlled to limit unwanted impurities, the Panel concluded that these Poloxamers are safe as used.

Primary closure of open myelomeningocele

OBJECT

The purpose of this paper is to describe the technique of closing an open myelomeningocele in the newborn infant.

METHODS

The anatomical rationale behind the closure techniques will be specifically reviewed. Avoidance of complications will be discussed. The management of unusual developmental anatomical abnormalities, such as the management of unusually large skin defects and kyphotic deformities will be discussed. Complications and the postoperative care will be reviewed and specifics regarding postoperative care will be summarized.

CONCLUSIONS

A multidisciplinary team approach is critical to the long-term management of these patients.

Control of staphylococcal adhesion to polymethylmethacrylate and enhancement of susceptibility to antibiotics by poloxamer 407

We studied the antiadhesive effect of Poloxamer 407 (P407), together with modifications in the antimicrobial susceptibility of residual adherent staphylococci. Bacterial adherence was markedly inhibited (77% to more than 99.9%) whether polymethylmethacrylate was exposed to P407 before or during the adherence assay. Furthermore, residual adherent staphylococci appeared to be more susceptible to antibiotic activity, suggesting that combination of P407 with antibiotics could be a promising approach to the prevention of infection of foreign material.

Controlled release of vancomycin from poloxamer 407 gels

The purpose of this study was to investigate Poloxamer 407 25% (w/w) formulations aimed at prolonging the residence time of vancomycin, a time-dependent antibiotic, in a body site with a high infectious risk. Reversible thermal gelation of the formulations permitted their local injection in liquid form and in situ gelation as they warmed to body temperature. Neither the rheological properties of the Poloxamer matrices nor the antibacterial activity of vancomycin was altered by their combination. In vitro, the dispersed form exhibited prolonged release, with a lower diffusion coefficient of vancomycin compared to the solubilized form (4.7x10(-8) vs 2. 1x10(-7) cm(2) s(-1)131 mg l(-1) for the solubilized form), followed by lower but effective antibacterial levels for at least 8 days. Controlled-release profiles, good preservation of vancomycin activity, good tolerability in rats, and ease of administration suggest that Poloxamer 407 may be useful as a vancomycin delivery vehicle for local prophylaxis of infections, especially in prosthetic surgery.

Dural closure with nonpenetrating clips prevents meningoneural adhesions: an experimental study in dogs

OBJECTIVE

Meningospinal and cranial dural adhesions were compared in a canine model, after duraplasty using nonpenetrating clips or penetrating needles and sutures.

METHODS

Fourteen dogs underwent bilateral craniotomies and duraplasties, with implantation of dural prostheses (DuraGuard; Biovascular Corp., Minneapolis, MN), using either 6-0 silk sutures or titanium clips (DuraClose; Surgical Dynamics, Norwalk, CT). Fourteen other dogs underwent L3-L4 laminectomies; three longitudinal dural incisions were closed with 6-0 silk sutures, 6-0 polyglactin 910 (Vicryl) sutures, or clips. Groups of eight dogs (four cranially treated and four spinally treated) were killed 6, 12, 24, and 52 weeks after surgery, and specimens were collected for study after perfusion and fixation (two cranial and two spinal dural reconstructions at 52 wk). Evaluations included assessment of the appearance of approximated dural margins and responses to clips, sutures, and dural prostheses (inflammation, foreign body reaction, fibrosis, and severity of meningospinal/meningocerebral adhesions). Data were evaluated using the Wilcoxon signed-rank and McNemar tests.

RESULTS

Duraplasties with clips displayed significantly less extensive acute and chronic inflammation, foreign body reaction, and meningoneural adhesions than did repairs with needles and sutures.

CONCLUSION

This report is the first long-term experimental study comparing two fundamentally different methods for dural repair in a relevant animal model.

The effect of urokinase in preventing the formation of epidural fibrosis and/or leptomeningeal arachnoiditis

BACKGROUND

Epidural fibrosis and leptomeningeal adhesion formation are among the common causes of failed back surgery syndrome. Urokinase has been commonly used in treating aneurysmal subarachnoid hemorrhage and intracerebral hematoma.

METHODS

In a rat model, the potential of local urokinase in preventing the production of epidural fibrosis due to bleeding was investigated.

RESULTS

A reduction of approximately 48% in leptomeningeal adhesion formation with the use of urokinase was demonstrated. Adhesion score was 2.300 in the control group and 0.700 in the urokinase treated group on day 42 of the postoperative period.

CONCLUSIONS

It can be concluded that urokinase has the important effect of preventing the formation of leptomeningeal adhesion, but many more extensive studies clearly need to be done before such material can be clinically used.