Laparoscopic cholecystocolostomy: a novel surgical approach for the treatment of progressive familial intrahepatic cholestasis. Ann Surg. 2013;258:1028-1033. [PMID: 23187749 DOI: 10.1097/sla.0b013e31827905eb]

Surgical versus Medical Management of Progressive Familial Intrahepatic Cholestasis-Case Compilation and Review of the Literature

(1) Background: Progressive familial intrahepatic cholestasis (PFIC) is a rare cause of liver failure. Surgical biliary diversion (SBD) and ileal bile salt inhibitors (IBAT) can delay or prevent liver transplantation (LTX). A comparison of the two methodologies in the literature is lacking. The combination has not been investigated. (2) Methods: We performed a literature survey on medical and surgical treatments for PFIC and reviewed the charts of our patients with PFIC of a tertiary hospital. The end points of our analysis were a decrease in serum bile acid (sBA) levels, reduction of pruritus and delay or avoidance of (LTX). (3) Results: We included 17 case series on SBD with more than 5 patients and a total of 536 patients. External or internal SBD, either conventional or minimally invasive, can reduce pruritus and sBA, but not all PFIC types are suitable for SBD. Six publications described the use of two types of IBAT in PFIC with a total of 118 patients. Treatment response was dependent on genetic type and subtype. Patients with PFIC 2 (nt-BSEP) showed the best response to treatment. Four out of eleven PFIC patients underwent SBD at our centre, with two currently receiving IBAT. (4) Conclusions: Limited data on IBAT in selected patients with PFIC show safety and effectiveness, although surgical methods should still be considered as a successful bridging procedure. Further studies to evaluate a possible combination of IBAT and SBD in PFIC are warranted and treatment decision should be discussed in an interdisciplinary board.

Outcomes of internal biliary diversion using cholecystocolostomy for patients with severe Alagille syndrome

Alagille syndrome (AGS) is a disorder that leads to increased serum cholesterol and bile acids, which can result in debilitating xanthomas and pruritus. External biliary drainage and transplantation are effective treatments for AGS. Internal biliary diversion with Roux-en-Y cholecystocolostomy has been described for other biliary conditions, but not AGS. Three patients with severe pruritus due to AGS underwent Roux-en-Y cholecystocolostomy for internal biliary drainage. Retrospective analysis compared preoperative and post-operative lab values and symptom scores (0, none–4, severe). Three patients underwent cholecystocolostomy. All patients had at least three diagnostic criteria for AGS. Mean preoperative pruritus score was 3.33 (range, 2–4) and mean post-operative score was 1. Mean preoperative xanthoma score was 1.33 (range, 0–4) and post-operative score was 1 at 2-month follow-up. Roux-en-Y cholecystocolostomy can be considered for AGS, which is refractory to medical management. This procedure accomplishes internal biliary diversion without significant physiologic derangements.

Biliary diversion in progressive familial intrahepatic cholestasis: a systematic review and meta-analysis

BACKGROUND

Biliary diversion (BD) is indicated in progressive familial intrahepatic cholestasis (PFIC) with refractory pruritus. Three types-partial external biliary drainage (PEBD), partial internal biliary drainage (PIBD), and ileal exclusion (IE) are described, with no consensus about the relative efficacy of these procedures.

METHODS

PubMed, Scopus, and Google Scholar were searched for publications on PFIC and BD. Improvement in pruritus, serum bile acid (BA), and need for liver transplantation (LT) were compared between the various BD procedures.

RESULTS

25 studies [424 children (PEBD-301, PIBD-93, IE-30)] were included. Pruritus resolved in 59.5% [PIBD:72% (95%CI 43-96%), PEBD:57% (95%CI 43-71%) and IE:48% (95%CI 14-82%)] cases. Significant overlap in confidence intervals indicated no significant differences. Absolute decrease in BA (AUROC-0.72) and bilirubin (AUROC-0.69) discriminated responders and non-responders. Eventually, 27% required LT: PIBD 10.7%, PEBD32%, IE 27%. The post-operative BA (AUROC-0.9) and bilirubin (AUROC-0.85) determined need for LT. Complications were commoner in PEBD than PIBD (38% vs 21.8%: p=0.02).

CONCLUSION

59.5% children have pruritus relief after BD and 27% need LT. PIBD has lower complications and LT requirement than PEBD. However, this requires cautious interpretation as the 2 groups differed in PFIC type and follow-up duration.

Partial Biliary Diversion May Promote Long-Term Relief of Pruritus and Native Liver Survival in Children with Cholestatic Liver Diseases

INTRODUCTION

 Rare cholestatic liver diseases may cause debilitating pruritus in children. Partial biliary diversion (PBD) may relieve pruritus and postpone liver transplantation which is the only other alternative when conservative treatment fails. The aim was to report long-term outcome after PBD in a population of 26 million people during a 25-year period.

MATERIALS AND METHODS

 This is an international, multicenter retrospective study reviewing medical journals. Complications were graded according to the Clavien-Dindo classification system.

RESULTS

 Thirty-three patients, 14 males, underwent PBD at a median of 1.5 (0.3-13) years at four Nordic pediatric surgical centers. Progressive familial intrahepatic cholestasis was the most common underlying condition. Initially, all patients got external diversion, either cholecystojejunostomy (25 patients) or button placed in the gallbladder or a jejunal conduit. Early complications occurred in 14 (42%) patients, of which 3 were Clavien-Dindo grade 3. Long-term stoma-related complications were common (55%). Twenty secondary surgeries were performed due to stoma problems such as prolapse, stricture, and bleeding, or conversion to another form of PBD. Thirteen children have undergone liver transplantation, and two are listed for transplantation due to inefficient effect of PBD on pruritus. Serum levels of bile acids in the first week after PBD construction were significantly lower in patients with good relief of pruritus than in those with poor effect (13 [2-192] vs. 148 [5-383] μmol/L; p = 0.02).

CONCLUSION

 PBD may ensure long-term satisfactory effect on intolerable pruritus and native liver survival in children with cholestatic liver disease. However, stoma-related problems and reoperations are common.

Long-term outcome following cholecystocolostomy in 41 patients with progressive familial intrahepatic cholestasis

PURPOSE

Progressive familial intrahepatic cholestasis (PFIC) is a cohort of autosomal recessive syndromes which presents with jaundice, severe pruritus and liver derangement. Without treatments, patients progress to liver failure in early childhood. Biliary diversion strategies have been deployed to interrupt enterohepatic circulation to alleviate symptoms and delay progression to cirrhosis. Cholecystocolostomy has been the diversion method of choice at our institution and we aim to evaluate its long-term outcome.

METHODS

All patients with PFIC who underwent cholecystocolostomy between August 2003 to May 2019 were included. PFIC diagnosed by clinical course, serum liver biochemistry and genotyping excluding other causes of cholestasis. All patients received ursodeoxycholic acid prior to biliary diversion. Those without long-term follow-up were excluded. Long-term follow-up conducted with physical examination, abdominal ultrasonography, liver function tests, contrast enema studies and colonoscopies. Outcome analysis was performed with patients divided into three groups according to their postoperative responses.

RESULTS

58 children underwent cholecystocolostomy, 41 were included in the study. Overall survival rate was 73.2% without a liver transplant. Survival improved to 81.1% in those without cirrhosis. 83.3% of those without a transplant was to no longer need any medication after their cholecystocolostomy. Recurrent cholestasis was seen in those with constipation (n = 8), ascending cholangitis (n = 10), intrahepatic reflux from Y-loop (n = 3) and cystic duct stenosis (n = 4).

CONCLUSION

Cholecystocolostomy is a safe and effective technique for treatment of cholestasis in PFIC patients without cirrhosis. Careful monitoring and proactive management of postoperative constipation and ascending cholangitis is required to prevent stenosis of the cystic duct leading to recurrent cholestasis.

Surgical diversion of enterohepatic circulation in pediatric cholestasis

Progressive familial intrahepatic cholestasis (PFIC) and Alagille syndrome (AS) are conditions caused by either an autosomal recessive or an autosomal dominant genetic defect, and they are both characterized by cholestasis, jaundice, and severe debilitating pruritus refractory to medical management. Before the advent of liver transplantation, most PFIC patients would die from end-stage liver disease in the first decade of life. Although liver transplantation has led to patients' survival, disease recurrence (PFIC-2) and severe extra-hepatic manifestations of the disease (PFIC-1) occurred post transplant. In the late 1980s, Whitington described the use of partial external biliary diversion in PFIC and AS patients as a successful way to improve symptoms and decrease circulating bile acid serum concentrations. Since then, other diversion techniques have been described (ileal exclusion and partial internal biliary diversion). These techniques have the benefit of avoiding a stoma, but equivalent results have not been demonstrated (recurrence of cholestasis after ileal exclusion, limited follow up after internal biliary diversion). Overall, studies have showed that biliary diversions in children with cholestasis are safe procedures with low morbidity and mortality, and that they can reduce inflammation and ongoing liver injury, therefore delaying or avoiding the need for liver transplantation in some patients.

Long-term outcomes after cholecystocolostomy for progressive familial intrahepatic cholestasis

AIM

To evaluate the long-term efficacy of cholecystocolostomy surgery for progressive familial intrahepatic cholestasis (PFIC).

METHODS

From August 2003 to November 2014, 34 clinically diagnosed children, including 11 with familial intrahepatic cholestasis-1 (FIC1), 13 with bile salt export pump (BSEP) disease, five with low γ-glutamyl transpeptidase (GGT) disease (levels <100 U/L), and five with multidrug resistance class III (MDR3) disease with high GGT (>100 U/L), were identified in our center. Data were collected retrospectively from individuals who collectively had 36 surgical operations and two orthotopic liver transplantations (OLT).

RESULTS

Serum total bilirubin (0 = 163.54 ± 106.02, 36 months = 23.38 ± 17.66 μmol/L) and bile acid (0 = 325.83 ± 153.09, 36 months = 48.36 ± 79.71 μmol/L) decreased after cholecystocolostomy in PFIC patients (P < 0.001). All patients experienced decreased severity of pruritus (88.2% vs. 16.1%, P < 0.001) and a greater freedom from growth retardation after cholecystocolostomy (-3.35 vs. -1.03, P < 0.001). Defecation frequency increased in PFIC patients after cholecystocolostomy (P = 0.002). Four patients (three with FIC1 and one with BSEP) experienced recurrence of cholestasis and two underwent reoperation. Two BSEP patients underwent OLT. One patient with BSEP and one patient with MDR3 died due to severe diarrhea and dehydration; one BSEP patient died of intractable constipation.

CONCLUSIONS

This is the first long-term, large-scale analysis of cholecystocolostomy approaches for PFIC. Approaches single and well tolerated, and generally result in improvement of pruritus and cholestasis.

Quality of Life in Patients With Progressive Familial Intrahepatic Cholestasis: No Difference Between Post-liver Transplantation and Post-partial External Biliary Diversion

OBJECTIVES

In patients with progressive familial intrahepatic cholestasis (PFIC), partial external biliary diversion (PEBD), which is associated with a permanent stoma, is recommended as first-line therapy, whereas primary liver transplantation (LTx) is restricted to those with cirrhosis. Our aim was to quantify the health-related quality of life (HRQOL) in patients with PFIC and to evaluate whether there is a difference in their HRQOL depending on the surgical approach.

METHODS

A prospective HRQOL study on a consecutive series of PFIC was conducted using Pediatric Quality of Life Inventory 4.0 child-self and parent-proxy reports. Patients with PFIC after PEBD who still lived with their native livers were compared to those after LTx. Both groups were compared to healthy children.

RESULTS

A total of 32 patients (53% girls) patients with a mean age of 17.7 ± 7.3 years were studied. Twenty-two had undergone LTx at a mean age of 7.8 ± 3.8 years and 10 had undergone PEBD at a mean age of 4.1 ± 3.9 years. At the time of HRQOL assessment, the mean age was 18.9 ± 7.5 years in the LTx group and 15.3 ± 6.5 years in the PEBD group. Child-self and parent-proxy reports showed no significant difference in HRQOL between patients with PFIC after LTx and those after PEBD except for marginal difference in physical functioning/health (P = 0.07). Except for a lower score in patient school functioning of patients after LTx (P = 0.01), HRQOL-results showed no difference from healthy children in any group.

CONCLUSIONS

The HRQOL of patients with PFIC after PEBD was similar to those after LTx. The HRQOL in both groups was also similar to that of healthy children. Thus, our data support the current policy of PEBD as primary surgical treatment for patients with PFIC without cirrhosis.

Progressive familial intrahepatic cholestasis: diagnosis, management, and treatment

Progressive familial intrahepatic cholestasis (PFIC) is a group of autosomal recessive cholestatic liver diseases which are subgrouped according to the genetic defect, clinical presentation, laboratory findings and liver histology. Progressive liver fibrosis, cirrhosis, and end stage liver disease (ESLD) may eventually develop. PFIC was first described in Amish descendants of Jacob Byler, therefore it was originally called Byler disease. But it can be seen anywhere on the globe. This review summarizes the main features of the subtypes of the disease and discusses the current available diagnosis, conservative and surgical therapeutic options.

Surgical outcomes in Alagille syndrome and PFIC: A single institution's 20-year experience

BACKGROUND

Alagille Syndrome (AGS) and Progressive Familial Intrahepatic Cholestasis (PFIC) are rare pediatric biliary disorders that lead to progressive liver disease. This study reviews our experience with the surgical management of these disorders over the last 20years.

METHODS

We retrospectively reviewed the records of children diagnosed with AGS or PFIC from January 1996 to December 2016. Data collected included demographics, surgical intervention (liver transplant or biliary diversion), and complications.

RESULTS

Of 37 patients identified with these disorders, 17 patients (8 AGS,9 PFIC) underwent surgical intervention. Mean postsurgical follow-up was 6.9±4.7years. Liver transplantation was the most common procedure (n=14). Two patients who were initially thought to have biliary atresia underwent hepatoportoenterostomy, but were subsequently shown to have Alagille syndrome. Biliary diversion procedures were performed in 3 patients (external n=1, internal n=2). PFIC patients tended to be older at the time of liver transplant compared to AGS (4.3±3.9years vs. 2.4±1.1years, p=0.25). The AGS patient with external diversion had resolution of symptoms and no complications (follow-up: 12.5years). Both PFIC patients with internal diversion (conduit between gallbladder and transverse colon) had resolution of pruritus and no progression of liver disease (follow-up: 3.8 and 4.5years).

CONCLUSIONS

AGS and PFIC are rare biliary disorders in children which result in pruritus and progressive liver failure. Three patients in this series (8%) benefited from biliary diversion for control of pruritus and have not to date required transplantation for progressive liver disease. 38% underwent transplantation owing to pruritus and severe liver dysfunction.

LEVEL OF EVIDENCE

2b.

Current and future therapies for inherited cholestatic liver diseases

Familial intrahepatic cholestasis (FIC) comprises a group of rare cholestatic liver diseases associated with canalicular transport defects resulting predominantly from mutations in ATP8B1, ABCB11 and ABCB4. Phenotypes range from benign recurrent intrahepatic cholestasis (BRIC), associated with recurrent cholestatic attacks, to progressive FIC (PFIC). Patients often suffer from severe pruritus and eventually progressive cholestasis results in liver failure. Currently, first-line treatment includes ursodeoxycholic acid in patients with ABCB4 deficiency (PFIC3) and partial biliary diversion in patients with ATP8B1 or ABCB11 deficiency (PFIC1 and PFIC2). When treatment fails, liver transplantation is needed which is associated with complications like rejection, post-transplant hepatic steatosis and recurrence of disease. Therefore, the need for more and better therapies for this group of chronic diseases remains. Here, we discuss new symptomatic treatment options like total biliary diversion, pharmacological diversion of bile acids and hepatocyte transplantation. Furthermore, we focus on emerging mutation-targeted therapeutic strategies, providing an outlook for future personalized treatment for inherited cholestatic liver diseases.

Biliary atresia and other cholestatic childhood diseases: Advances and future challenges

Biliary Atresia and other cholestatic childhood diseases are rare conditions affecting the function and/or anatomy along the canalicular-bile duct continuum, characterised by onset of persistent cholestatic jaundice during the neonatal period. Biliary atresia (BA) is the most common among these, but still has an incidence of only 1 in 10-19,000 in Europe and North America. Other diseases such as the genetic conditions, Alagille syndrome (ALGS) and Progressive Familial Intrahepatic Cholestasis (PFIC), are less common. Choledochal malformations are amenable to surgical correction and require a high index of suspicion. The low incidence of such diseases hinder patient-based studies that include large cohorts, while the limited numbers of animal models of disease that recapitulate the spectrum of disease phenotypes hinders both basic research and the development of new treatments. Despite their individual rarity, collectively BA and other cholestatic childhood diseases are the commonest indications for liver transplantation during childhood. Here, we review the recent advances in basic research and clinical progress in these diseases, as well as the research needs. For the various diseases, we formulate current key questions and controversies and identify top priorities to guide future research.

Liver transplantation and the management of progressive familial intrahepatic cholestasis in children

Progressive familial intrahepatic cholestasis (PFIC) is a constellation of inherited disorders that result in the impairment of bile flow through the liver that predominantly affects children. The accumulation of bile results in progressive liver damage, and if left untreated leads to end stage liver disease and death. Patients often present with worsening jaundice and pruritis within the first few years of life. Many of these patients will progress to end stage liver disease and require liver transplantation. The role and timing of liver transplantation still remains debated especially in the management of PFIC1. In those patients who are appropriately selected, liver transplantation offers an excellent survival benefit. Appropriate timing and selection of patients for liver transplantation will be discussed, and the short and long term management of patients post liver transplantation will also be described.

Different techniques for biliary diversion in progressive familial intrahepatic cholestasis

BACKGROUND

Progressive familial intrahepatic cholestasis (PFIC) is a cholestatic liver disease of childhood. Pruritus resulting from increased bile salts in serum might not respond to medical treatment, and internal or external biliary drainage methods have been described. In this study, we aimed to evaluate different internal drainage techniques in patients with PFIC.

PATIENTS AND METHODS

Between 2009 and 2014, seven children (4 male, 3 female, 3months-5years old), (median 2years of age) with PFIC were evaluated. The patients were reviewed according to age, gender, complaints, surgical technique, laboratory findings and outcome. In each two patients, cholecystoileocolonic anastomosis, cholecystojejunocolonic anastomosis and cholecystocolostomy were performed. Cholecysto-appendico-colonic anastomosis was the technique used in one patient.

RESULTS

Jaundice and excessive pruritus were the main complaints. One of the patients with cholecystoileocolonic anastomosis died of comorbid pathologies (cirrhosis, adhesive obstruction and severe sepsis). Temporary rectal bleeding was observed in all the patients postoperatively. Regardless of the surgical technique, pruritus was dramatically decreased in all the patients in the postoperative period.

CONCLUSION

Regardless of the technique, internal biliary diversion methods are beneficial for the relief of pruritus in PFIC patients. Selection of the surgical method might vary depending on the surgeon's preference and the surgical anatomy of the gastrointestinal system of the patient.

Total biliary diversion as a treatment option for patients with progressive familial intrahepatic cholestasis and Alagille syndrome

BACKGROUND

Progressive familial intrahepatic cholestasis (PFIC) with low gamma-glutamyl transpeptidase (GGT) and Alagille syndrome are associated with persistent cholestasis and severe pruritus. Various types of biliary diversion have been used to reduce this pruritus and prevent liver dysfunction. We report our experience concerning the efficacy and safety of total biliary diversion (TBD) as an additional treatment option.

METHODS

TBD was performed in four PFIC patients and one patient with Alagille syndrome, and was accomplished by anastomosing a jejunal segment to the choledochal duct terminating as an end stoma, or by disconnecting the choledochal duct after previous cholecystojejunocutaneostomy.

RESULTS

TBD resulted in a marked improvement of symptoms and biochemical parameters in all PFIC patients. Despite relief of pruritus, cholestasis persisted in the Alagille patient. During 5-15years of follow-up, no clinical signs of fat malabsorption such as diarrhea or weight loss were encountered. However, to maintain adequate levels of fat-soluble vitamins, especially of vitamin K, substantial supplementation was necessary.

CONCLUSIONS

Total biliary diversion can be a useful surgical treatment option for patients with low-GGT PFIC and possibly also Alagille syndrome, when partial biliary diversion is insufficient. It can be performed without inducing clinical signs of fat malabsorption although individualized supplementation of fat-soluble vitamins with careful monitoring is warranted.

Alisol B 23-acetate protects against ANIT-induced hepatotoxity and cholestasis, due to FXR-mediated regulation of transporters and enzymes involved in bile acid homeostasis

Intrahepatic cholestasis is a clinical syndrome with systemic and intrahepatic accumulation of excessive toxic bile acids that ultimately cause hepatobiliary injury. Appropriate regulation of bile acids in hepatocytes is critically important for protection against liver injury. In the present study, we characterized the protective effect of alisol B 23-acetate (AB23A), a natural triterpenoid, on alpha-naphthylisothiocyanate (ANIT)-induced liver injury and intrahepatic cholestasis in mice and further elucidated the mechanisms in vivo and in vitro. AB23A treatment dose-dependently protected against liver injury induced by ANIT through reducing hepatic uptake and increasing efflux of bile acid via down-regulation of hepatic uptake transporters (Ntcp) and up-regulation of efflux transporter (Bsep, Mrp2 and Mdr2) expression. Furthermore, AB23A reduced bile acid synthesis through repressing Cyp7a1 and Cyp8b1, increased bile acid conjugation through inducing Bal, Baat and bile acid metabolism through an induction in gene expression of Sult2a1. We further demonstrate the involvement of farnesoid X receptor (FXR) in the hepatoprotective effect of AB23A. The changes in transporters and enzymes, as well as ameliorative liver histology in AB23A-treated mice were abrogated by FXR antagonist guggulsterone in vivo. In vitro evidences also directly demonstrated the effect of AB23A on FXR activation in a dose-dependent manner using luciferase reporter assay in HepG2 cells. In conclusion, AB23A produces protective effect against ANIT-induced hepatotoxity and cholestasis, due to FXR-mediated regulation of transporters and enzymes.

Outcome of partial internal biliary diversion for intractable pruritus in children with cholestatic liver disease

PURPOSE

Children with cholestatic disorders have undergone liver transplantation for intractable pruritus unresponsive to medical therapy even in the absence of liver failure. Biliary diversion procedures interrupt the entero-hepatic circulation of bile acids allowing them to be excreted in the feces thereby lowering the total bile acid pool. We evaluated the outcome of partial internal biliary diversion (PIBD) in children with intractable pruritus from inherited cholestatic disorders.

METHODS

The records of children who underwent PIBD over a 4-year period were reviewed for etiology of liver disease, demographic data, preoperative and postoperative biochemical profile and improvement of pruritus. Standard statistical methods were used for analysis.

RESULTS

Of the 12 children, 10 had progressive familial intrahepatic cholestasis (PFIC) and 2 had Alagille syndrome (AS). PIBD was done using an isolated jejunal loop as a conduit from gall bladder to mid ascending colon. Median period of follow up was 30 months. Pruritus resolved in nine children with significant reduction of serum bile acids (P < 0.02).

CONCLUSION

To our knowledge, this is the largest reported series of children with PIBD. PIBD is a safe, well-tolerated and effective alternative to liver transplant in children with PFIC and AS who have intractable pruritus in the absence of synthetic liver failure.

Progressive familial intrahepatic cholestasis

Progressive familial intrahepatic cholestasis (PFIC) is a group of rare disorders which are caused by defect in bile secretion and present with intrahepatic cholestasis, usually in infancy and childhood. These are autosomal recessive in inheritance. The estimated incidence is about 1 per 50,000 to 1 per 100,000 births, although exact prevalence is not known. These diseases affect both the genders equally and have been reported from all geographical areas. Based on clinical presentation, laboratory findings, liver histology and genetic defect, these are broadly divided into three types-PFIC type 1, PFIC type 2 and PFIC type 3. The defect is in ATP8B1 gene encoding the FIC1 protein, ABCB 11 gene encoding BSEP protein and ABCB4 gene encoding MDR3 protein in PFIC1, 2 and 3 respectively. The basic defect is impaired bile salt secretion in PFIC1/2 whereas in PFIC3, it is reduced biliary phospholipid secretion. The main clinical presentation is in the form of cholestatic jaundice and pruritus. Serum gamma glutamyl transpeptidase (GGT) is normal in patients with PFIC1/2 while it is raised in patients with PFIC3. Treatment includes nutritional support (adequate calories, supplementation of fat soluble vitamins and medium chain triglycerides) and use of medications to relieve pruritus as initial therapy followed by biliary diversion procedures in selected patients. Ultimately liver transplantation is needed in most patients as they develop progressive liver fibrosis, cirrhosis and end stage liver disease. Due to the high risk of developing liver tumors in PFIC2 patients, monitoring is recommended from infancy. Mutation targeted pharmacotherapy, gene therapy and hepatocyte transplantation are being explored as future therapeutic options.