Botox-A Injection to Improve Bladder Function in Early Spinal Cord Injury (#H-20344)

Approximately 10,000 spinal cord injuries (SCI) occur each year, most of which occur in males (80%). Many of these patients develop neurogenic bladder dysfunction (NGB) characterized by overactivity of the detrusor muscle, termed detrusor overactivity (DO) or detrusor hyperreflexia (DH). They can also develop detrusor external sphincter dyssynergia (DESD), an abnormal/ uncoordinated response of the sphincter to bladder contraction. A combination of these factors can lead to long-term complications in up to 50% of patients. These complications include hydronephrosis, autonomic dysreflexia, vesicoureteral reflux, nephrolithiasis, sepsis, renal insufficiency or failure and even death. Our basic understanding of the physiology of NGB as well as the introduction of the concept of clean intermittent catheterization (CIC) several decades ago has significantly reduced the death rate due to renal complications in SCI patients. Nevertheless, there continues to be a significant amount of morbidity and risk that these patients experience due to our incomplete understanding of DESD; both its development and subsequent impact on bladder function. We postulate that a primary drive to producing detrusor hypercontractility is the obstruction created by increased tone within the external urethral sphincter (EUS). In addition, we hypothesize that high-pressure obstructive voiding patterns displayed by patients with DESD promote development of bladder wall smooth muscle hypertrophy and fibrosis, loss of bladder compliance, and development of the complications listed above.

Most of our treatment options for neurogenic bladder in the SCI patient population aim to reduce bladder filling pressures and obstructive voiding patterns either by reducing bladder overactivity (i.e. antimuscarinic agents) or by decreasing bladder outlet resistance (i..e. alpha 1-adrenergic receptor antagonists, sphincterotomy, UroLume stent placement, or botulinum toxin injection of external urethral sphincter). However, typically treatments are not initiated until these reflex voiding patterns have already developed. Almost all patients with supraconal lesions, regardless of their neurological level of injury or final voiding patterns, display areflexic bladders during the acute and subacute time period after SCI. This time period can last anywhere from 1 month to 1 year (typically 6-8 weeks) after which spinal reflex voiding develops. Dyssynergic voiding patterns are most common in cervical and thoracic (supraconal) lesions while are flexic voiding patterns predominate in lumbar and sacral conal and infraconal injuries. However, there are many exceptions to this rule, especially in incomplete lesions, and that is why urodynamic testing is an important component in the evaluation of every SCI patient.

Nerve Growth Factor (NGF): Role in Obstructive Uropathy: The processes that lead to reorganization of neural pathways and emergence of hyperactive and dyssynergic voiding are incompletely understood. Possible mechanisms underlying the neural plasticity following SCI could involve alterations in levels of neurotrophic factors within the bladder. Nerve Growth Factor (NGF) is a signaling protein that is thought to play a prominent role in mediating the development of bladder reflex voiding mechanisms in various disorders of bladder dysfunction including neurogenic and non-neurogenic bladder outlet obstruction and chronic bladder inflammation (i.e. interstitial cystitis). Studies have found that by inhibiting NGF's actions through immunization, enhancement of bladder hyperactivity and detrusor sphincter dyssynergia was prevented in SCI rats. Finally, studies in SCI human patients found that bladder hyperactivity as well as bladder NGF tissue levels was significantly reduced by bladder BTX-A treatment.

BOTOX® (Botulinum Toxin Type A) Purified Neurotoxin Complex is a sterile, vacuum-dried purified botulinum toxin type A, produced from fermentation of Hall strain Clostridium botulinum type A grown in a medium containing casein hydrolysate, glucose and yeast extract. It is purified from the culture solution by dialysis and a series of acid precipitations to a complex consisting of the neurotoxin, and several accessory proteins. The complex is dissolved in sterile sodium chloride solution containing Albumin Human and is sterile filtered (0.2 microns) prior to filling and vacuum-drying.

One Unit of BOTOX corresponds to the calculated median intraperitoneal lethal dose (LD50) in mice. The method utilized for performing the assay is specific to Allergan's product, BOTOX®. Due to specific details of this assay such as the vehicle, dilution scheme and laboratory protocols for the various mouse LD50 assays, Units of biological activity of BOTOX cannot be compared to nor converted into Units of any other botulinum toxin or any toxin assessed with any other specific assay method. Therefore, differences in species sensitivities to different botulinum neurotoxin serotypes precludes BOTOX is approximately 20 units/nanogram of neurotoxin protein complex.

Each vial of BOTOX contains 100 Units (U) of Clostridium botulinum type A neurotoxin complex, 0.5 milligrams of Albumin Human, and 0.9 milligrams of sodium chloride in a sterile, vacuum-dried form without a preservative.

Botulinum Toxin (BTX-A) to treat DESD: Botulinum toxin, first isolated by van Ermengem in 1897, is the most potent biological toxin known to man. Through basic and clinical research, clinicians have been able to transform this lethal toxin into a health benefit. BTX-A represents a viable option in the treatment of DESD. When injected, the toxin acts at the neuromuscular junction of the external sphincter to block vesicle transport of acetylcholine; in essence, producing a chemical denervation. The clinical effects begin within 2-3 days and are reversible as terminal nerve sprouting occurs within 3-6 months.

The majority of studies on DESD have examined several outcome measures following BTX-A injection: Change in post-void residual (PVR), change in urethral pressure profile (UPP-static or dynamic), change in bladder pressures during voiding, change in frequency or severity of autonomic dysreflexia (AD), and change in symptoms or satisfaction of the procedure to the patient. Once again, BTX-A treated patients' demonstrated improvements in PVR and UPP similar to their previous study.

However, while most studies of BTX-A for DESD have documented significant reductions in detrusor and urethral pressures as well as PVR, prior research has shown that detrusor leak point pressure (DLPP) is the best prognostic measure for upper tract damage in neurogenic bladder patients. This fundamental concept was corroborated by external sphincterotomy studies demonstrating that failure to achieve a DLPP below 40 cm H2O increases the frequency of upper tract deterioration. This finding underscores the importance that future studies examining the efficacy of BTX treatment for DESD will utilize DLPP as an objective measure of the procedure's success.

Preliminary Data: Effect of BTX-A on Urethral Outlet Resistance by Measuring Changes in Leak Point Pressure. The purpose of these investigations was to evaluate the effects of BTX-A on in vivo urethral resistance by measuring leak point pressure (LPP) with a vertical tilt table and intravesical pressure clamp.

Female SD rats (n=8; 220-250g) were anesthetized with urethane (1.2 g/kg) and injected intraperitoneally with either BTX-A (100u) or saline 18 hours prior to experimentation. LPP was recorded before and after administration of the nicotinic receptor antagonist -bungarotoxin (BGT), and the ganglionic blocker hexamethonium (HEX).

BGT significantly decreased the LPP in control animals by 46% but had no appreciable affect in BTX-A treated animals. In comparison, BTX-A treatment decreased LPP by 47% compared to baseline values in control animals. The ganglionic blocker, HEX, had no appreciable effect on either control or BTX-A treated animals.

BTX-A significantly decreased the basal LPP to the same extent as BGT, confirming it's in vivo potency at the striated neuromuscular junction. However, the fact that HEX had no appreciable effect in either group suggests that sympathetic tone is not a prominent component of outlet resistance in female rats, and may not be a suitable in vivo model to describe the effects of BTX-A on urethral adrenergic pathways. Although originally designed as a method to evaluate stress urinary incontinence in rodents, this method actually measures the intravesical pressure during bladder filling at which urinary leakage occurs, that is, detrusor leak point pressure (DLPP). The marked decrease in DLPP induced by BTX-A in this animal model validates BTX-A's potential effects on DLPP in humans with DESD.

BTX-A Urethral Sphincter Injections in Humans: Sixty eight patients received urethral sphincter injections for bladder outlet obstruction resulting from DESD or pelvic floor spasticity. Patients' mean age was 53 (range 21-71) and the underlying pathophysiology for outlet obstruction included: spinal cord injury (n=9), multiple sclerosis (n=32), stroke (n=4), other (n=8), idiopathic retention/pelvic floor spasticity (n=15). Patients were injected with 100 units of BTX-A into their external urethral sphincters under local or general anesthesia. Postoperatively, significant decreases in maximal detrusor pressures (81cm to 52cm H2O, p<0.05) and post-void residuals (240ml to 88ml, p<0.05) were observed with beneficial effects lasting 3-4 months.

Significance: The significance of these experiments begins with the fact that our proposed intervention occurs during early spinal cord injury (i.e. within 8 weeks) before pathologic bladder reflex pathways have emerged. In addition, our proposed project would be: 1. The largest, prospective randomized trial examining the effects of BTX-A urethral sphincter injection for detrusor external sphincter dyssynergia (DESD) and the first to look at the effect of BTX-A on detrusor leak point pressure (DLPP); 2. The first study to evaluate the role that bladder outlet obstruction by DESD plays in the development of bladder hyperactivity and the development of complications resulting from bladder dysfunction; 3. The first study profiling bladder tissue levels of the signaling protein nerve growth factor (NGF) during early SCI and then again once bladder hyperreflexic patterns develop, and; 4. The first study evaluating the effect of reducing outlet resistance with BTX-A on bladder NGF levels. If our hypotheses prove to be correct, treated patients will display less incontinence, require lower doses of anticholinergic medication, and avoid the complications of DESD listed earlier in this proposal. Although this study as written is of moderate length (i.e. total 5 years), we hope that by finding significant results we will be able to capture a longitudinal history of this population by extending follow-up to a longer duration (i.e. >10 years). In addition, BTX-A treatment could be extended to other neurogenic populations suffering from DESD (i.e. Multiple Sclerosis) as well as other conditions where bladder overactivity appears to be driven by outlet obstruction (i.e. Benign Prostatic Hyperplasia).

Hypotheses:

1. BTX-A injection of the external urethral sphincter significantly decreases detrusor leak point pressure (DLPP).
2. Decreased DLPP during early SCI will markedly reduce bladder tissue nerve growth factor (NGF).
3. Reducing DLPP and bladder NGF during early SCI will diminish complications associated with neurogenic detrusor overactivity (NDO) and outlet obstruction.