Cyclophilin D knockout significantly prevents HCC development in a streptozotocin-induced mouse model of diabetes-linked NASH.

A family of Peptidyl-prolyl isomerases (PPIases), called Cyclophilins, localize to numerous intracellular and extracellular locations where they contribute to a variety of essential functions. We previously reported that non-immunosuppressive pan-cyclophilin inhibitor drugs like reconfilstat (CRV431) or NV556 decreased multiple aspects of non-alcoholic fatty liver disease (NAFLD) in mice under two different non-alcoholic steatohepatitis (NASH) mouse models. Both CRV431 and NV556 inhibit several cyclophilin isoforms, among which cyclophilin D (CypD) has not been previously investigated in this context. It is unknown whether it is necessary to simultaneously inhibit multiple cyclophilin family members to achieve therapeutic benefits or if loss-of-function of one is sufficient. Furthermore, narrowing down the isoform most responsible for a particular aspect of NAFLD/NASH, such as hepatocellular carcinoma (HCC), would allow for more precise future therapies. Features of human diabetes-linked NAFLD/NASH can be reliably replicated in mice by administering a single high dose of streptozotocin to disrupt pancreatic beta cells, in conjunction with a high sugar, high fat, high cholesterol western diet over the course of 30 weeks. Here we show that while both wild-type (WT) and Ppif-/- CypD KO mice develop multipe severe NASH disease features under this model, the formation of HCC nodules was significantly blunted only in the CypD KO mice. Furthermore, of differentially expressed transcripts in a qPCR panel of select HCC-related genes, nearly all were downregulated in the CypD KO background. Cyclophilin inhibition is a promising and novel avenue of treatment for diet-induced NAFLD/NASH. This study highlights the impact of CypD loss-of-function on the development of HCC, one of the most severe disease outcomes.

Mice lacking cyclophilin B, but not cyclophilin A, are protected from the development of NASH in a diet and chemical-induced model.

Cyclophilins are a diverse family of peptidyl-prolyl isomerases (PPIases) of importance in a variety of essential cellular functions. We previously reported that the pan-cyclophilin inhibitor drug reconfilstat (CRV431) decreased disease in mice under the western-diet and carbon tetrachloride (CCl4) non-alcoholic steatohepatitis (NASH) model. CRV431 inhibits several cyclophilin isoforms, among which cyclophilin A (CypA) and B (CypB) are the most abundant. It is not known whether simultaneous inhibition of multiple cyclophilin family members is necessary for the observed therapeutic effects or if loss-of-function of one is sufficient. Identifying the responsible isoform(s) would enable future fine-tuning of drug treatments. Features of human liver fibrosis and complete NASH can be reliably replicated in mice by administration of intraperitoneal CCl4 alone or CCl4 in conjunction with high sugar, high cholesterol western diet, respectively. Here we show that while wild-type (WT) and Ppia-/- CypA KO mice develop severe NASH disease features under these models, Ppib-/- CypB KO mice do not, as measured by analysis of picrosirius red and hematoxylin & eosin-stained liver sections and TNFα immuno-stained liver sections. Cyclophilin inhibition is a promising and novel avenue of treatment for diet-induced NASH. In this study, mice without CypB, but not mice without CypA, were significantly protected from the development of the characteristic features of NASH. These data suggest that CypB is necessary for NASH disease progression. Further investigation is necessary to determine whether the specific role of CypB in the endoplasmic reticulum secretory pathway is of significance to its effect on NASH development.

The Cyclophilin Inhibitor Rencofilstat Decreases HCV-Induced Hepatocellular Carcinoma Independently of Its Antiviral Activity.

There is an urgent need for the identification of new drugs that inhibit HCV-induced hepatocellular carcinoma (HCC). Our work demonstrates that cyclophilin inhibitors (CypIs) represent such new drugs. We demonstrate that the nonimmunosuppressive cyclosporine A (CsA) analog (CsAa) rencofilstat possesses dual therapeutic activities for the treatment of HCV infection and HCV-induced HCC. Specifically, we show that the HCV infection of humanized mice results in the progressive development of HCC. This is true for the four genotypes tested (1 to 4). Remarkably, we demonstrate that rencofilstat inhibits the development of HCV-induced HCC in mice even when added 16 weeks after infection when HCC is well established. Importantly, we show that rencofilstat drastically reduces HCC progression independently of its anti-HCV activity. Indeed, the CypI rencofilstat inhibits HCC, while other anti-HCV agents such as NS5A (NS5Ai) and NS5B (NS5Bi) fail to reduce HCC. In conclusion, this study shows for the first time that the CypI rencofilstat represents a potent therapeutic agent for the treatment of HCV-induced HCC.

The Cyclophilin Inhibitor Rencofilstat Decreases HCV-induced Hepatocellular Carcinoma Independently of Its Antiviral Activity.

There is an urgent need for the identification of new drugs that inhibit HCV-induced hepatocellular carcinoma (HCC). Our work demonstrates that cyclophilin inhibitors (CypI) represent such new drugs. We demonstrated that the non-immunosuppressive cyclosporine A (CsA) analog (CsAa) rencofilstat possesses dual therapeutic activities for the treatment of HCV infection and HCV-induced HCC. Specifically, we showed that HCV infection of humanized mice results in the progressive development of HCC. This was true for four genotypes tested (1 to 4). Remarkably, we demonstrated that rencofilstat inhibits the development of HCV-induced HCC in mice even when added 16 weeks post-infection when HCC is well established. Importantly, we showed that rencofilstat drastically reduces HCC progression independently of its anti-HCV activity. Indeed, the CypI rencofilstat inhibits HCC while other anti-HCV agents such as NS5A (NS5Ai) and NS5B (NS5Bi) fail to reduce HCC. In conclusion, this study shows for the first time that the CypI rencofilstat represents a potent therapeutic agent for the treatment of HCV-induced HCC.

Effect of a High-Fat Meal on Single-Dose Rencofilstat (CRV431) Oral Bioavailability in Healthy Human Subjects.

Rencofilstat (RCF) is a novel cyclophilin inhibitor under development for the treatment of nonalcoholic steatohepatitis and hepatocellular carcinoma. This phase 1, randomized, open-label study in healthy participants assessed the relative bioavailability of a single dose of RCF 225-mg soft gelatin capsules in both fasted and high-fat conditions. Forty-four participants were enrolled to either the fasted (n = 24) or the high-fat fed (n = 20) arm. Noncompartmental pharmacokinetics were evaluated following a single 225-mg oral dose. Administration of RCF with a high-fat meal led to increases in maximum concentration, area under the concentration-time curve (AUC) from time 0 to 24 hours, and AUC from time 0 to infinity fed-to-fasted geometric mean ratios of 102.2%, 114.5%, and 132.9%, respectively. All AUC geometric mean ratios were outside of the 80% to 125% range, suggesting that a high-fat meal can increase the extent of RCF exposure. Time to maximum concentration increased from 1.5 to 1.8 hours in the fasted and high-fat groups, respectively, suggesting slightly delayed absorption. High fat intake may delay gastric emptying while increasing the absorption and bioavailability of RCF. No treatment-emergent adverse events were observed in the fasted group, and 1 treatment-emergent adverse event occurred in the high-fat meal group. The differences in observed whole-blood concentrations are unlikely to have clinically relevant effects given the wide therapeutic index of RCF demonstrated in previous phase 1 studies.

Rencofilstat, a cyclophilin inhibitor: A phase 2a, multicenter, single-blind, placebo-controlled study in F2/F3 NASH.

Rencofilstat (RCF) demonstrated antifibrotic effects in preclinical models and was safe and well tolerated in Phase 1 studies. The aim of this Phase 2a study was safety, tolerability, pharmacokinetics, and exploration of efficacy biomarkers in subjects with nonalcoholic steatohepatitis (NASH). This Phase 2a, multicenter, single-blind, placebo-controlled study randomized 49 presumed F2/F3 subjects to RCF 75 mg once daily (QD), RCF 225 mg QD, or placebo for 28 days. Primary safety and tolerability endpoints were explored using descriptive statistics with post hoc analyses comparing active to placebo groups. Pharmacokinetics were evaluated using population pharmacokinetics methods. Efficacy was explored using biomarkers, transcriptomics, and lipidomics. RCF was safe and well tolerated, with no safety signals identified. The most frequently reported treatment-emergent adverse events were constipation, diarrhea, back pain, dizziness, and headache. No clinically significant changes in laboratory parameters were observed, and RCF pharmacokinetics were unchanged in subjects with NASH. Alanine transaminase (ALT) reduction was greater in active subjects than in placebo groups. Nonparametric analysis suggested that ALT reductions were statistically different in the 225-mg cohort compared with matching placebo: -16.3 ± 25.5% versus -0.7 ± 13.4%, respectively. ProC3 and C6M reduction was statistically significant in groups having baseline ProC3 > 15.0 ng/ml. RCF was safe and well tolerated after 28 days in subjects with presumed F2/F3 NASH. Presence of NASH did not alter its pharmacokinetics. Reductions in ALT, ProC3, and C6M suggest direct antifibrotic effects with longer treatment duration. Reductions in key collagen genes support a mechanism of action via suppression and/or regression of collagen deposition. Conclusion: These results support advancement of rencofilstat into a larger and longer Phase 2b study.

The combination of the NS5A and cyclophilin inhibitors results in an additive anti-HCV inhibition in humanized mice without development of resistance.

We and others previously reported that the direct-acting agents (DAA) NS5A inhibitors (NS5Ai) and the host-targeting agents cyclophilin inhibitors (CypIs) inhibit HCV replication in vitro. In this study, we investigated whether the combination of NS5Ai and CypI offers a potent anti-HCV effect in vivo. A single administration of NS5Ai or CypI alone to HCV-infected humanized-mice inhibits HCV replication. The combination of NS5Ai with CypI suppresses HCV (GT1a, GT2a, GT3a and GT4a) replication in an additive manner. NS5Ai/CypI combinations provide a statistically more profound anti-HCV inhibition for GT2a and GT3a than GT1a and GT4a, leading to a fastest and deepest inhibition of GT2a and GT3a replications. Combining CypI with NS5Ai prevents the viral rebound normally observed in mice treated with NS5Ai alone. Results were confirmed in mice implanted with human hepatocytes from different donors. Therefore, the combination of NS5Ai with CypI may serve as a regimen for the treatment of HCV patients with specific genotypes and disorder conditions, which diminish sustain viral response levels to DAA, such as GT3a infection, cirrhosis, and DAA resistance associated with the selection of resistance-associated substitutions present at baseline or are acquired during treatment.

Differential Effects of Voclosporin and Tacrolimus on Insulin Secretion From Human Islets.

The incidence of new onset diabetes after transplant (NODAT) has increased over the past decade, likely due to calcineurin inhibitor-based immunosuppressants, including tacrolimus (TAC) and cyclosporin. Voclosporin (VCS), a next-generation calcineurin inhibitor, is reported to cause fewer incidences of NODAT but the reason is unclear. While calcineurin signaling plays important roles in pancreatic ß-cell survival, proliferation, and function, its effects on human ß-cells remain understudied. In particular, we do not understand why some calcineurin inhibitors have more profound effects on the incidence of NODAT. We compared the effects of TAC and VCS on the dynamics of insulin secretory function, programmed cell death rate, and the transcriptomic profile of human islets. We studied 2 clinically relevant doses of TAC (10 ng/mL, 30 ng/mL) and VCS (20 ng/mL, 60 ng/mL), meant to approximate the clinical trough and peak concentrations. TAC, but not VCS, caused a significant impairment of 15 mM glucose-stimulated and 30 mM KCl-stimulated insulin secretion. This points to molecular defects in the distal stages of exocytosis after voltage-gated Ca2+ entry. No significant effects on islet cell survival or total insulin content were identified. RNA sequencing showed that TAC significantly decreased the expression of 17 genes, including direct and indirect regulators of exocytosis (SYT16, TBC1D30, PCK1, SMOC1, SYT5, PDK4, and CREM), whereas VCS has less broad, and milder, effects on gene expression. Clinically relevant doses of TAC, but not VCS, directly inhibit insulin secretion from human islets, likely via transcriptional control of exocytosis machinery.

Structurally distinct cyclosporin and sanglifehrin analogs CRV431 and NV556 suppress established HCV infection in humanized-liver mice.

We previously reported that the non-immunosuppressive cyclophilin inhibitors (CypIs)-cyclosporin A analog CRV431 and sanglifehrin analog NV556-efficiently inhibit HCV replication in vitro. In this study, we asked whether they can also reduce HCV replication in vivo. We found that a single oral administration of CRV431 and NV556 to HCV-infected humanized-liver mice drastically reduced HCV blood levels. The antiviral effect was observed when CRV431 or NV556 were each individually administered with HCV, 3, 6 weeks or even 3 months post-infection when viral replication is robust. These results were confirmed in chimeric mice implanted with human hepatocytes isolated from three distinct donors. Remarkably, no viral rebound was observed 5 months after a single dose administration of 50 mg/kg of CRV431 or NV556 four weeks post-HCV infection, indicating the possibility of suppression of an established viral infection. Since we recently demonstrated that both CRV431 and NV556 also inhibit the development of liver fibrosis and hepatocellular carcinoma in nonviral-induced non-alcoholic steatohepatitis mouse models, our present data suggest that the two entirely structurally different CypIs-CRV431 and NV556-derived from unrelated natural products, represent attractive partners to current direct-acting agent (DAA) regimens for the treatment of hepatitis C and liver diseases.

Cyclophilin inhibition as a potential treatment for nonalcoholic steatohepatitis (NASH).

Introduction: Cyclophilins are a family of diverse regulatory enzymes that have been studied for over 30 years; they participate in many pathophysiological processes. Genetic deletion or pharmacologic inhibition of cyclophilins has shown therapeutic effects in a wide spectrum of disease models, including liver disorders, and hence may be beneficial in treating nonalcoholic steatohepatitis (NASH).Areas Covered: This articles briefly describes cyclophilin isomerases and the main classes of cyclophilin antagonists; it then summarizes data showing cyclophilin participation in the major pathophysiological activities that occur in NASH.Expert Opinion: Optimization of therapeutic outcomes in the treatment of NASH may be best realized by targeting multiple pathologic pathways, especially when treating advanced stages of the disease. A preferred approach for achieving this goal is to use compounds such as cyclophilin inhibitors that simultaneously target multiple disease processes. The pleiotropic benefits of this drug class derive from the extraordinary functionality of prolyl isomerization as a regulatory mechanism and its evolutionary diversification into many biochemical pathways. Nonimmunosuppressive analogs of cyclosporine A are the most thoroughly characterized cyclophilin inhibitors and show significant potential to attenuate several of the major pathophysiological events in NASH - mitochondrial dysfunction, cellular injury and death, inflammation, and in particular, fibrosis.

A Pan-Cyclophilin Inhibitor, CRV431, Decreases Fibrosis and Tumor Development in Chronic Liver Disease Models.

Previous studies show that cyclophilins contribute to many pathologic processes, and cyclophilin inhibitors demonstrate therapeutic activities in many experimental models. However, no drug with cyclophilin inhibition as the primary mode of action has advanced completely through clinical development to market. In this study, we present findings on the cyclophilin inhibitor, CRV431, that highlight its potential as a drug candidate for chronic liver diseases. CRV431 was found to potently inhibit all cyclophilin isoforms tested-A, B, D, and G. Inhibitory constant or IC50 values ranged from 1 to 7 nM, which was up to 13 times more potent than the parent compound, cyclosporine A (CsA), from which CRV431 was derived. Other CRV431 advantages over CsA as a nontransplant drug candidate were significantly diminished immunosuppressive activity, less drug transporter inhibition, and reduced cytotoxicity potential. Oral dosing to mice and rats led to good blood exposures and a 5- to 15-fold accumulation of CRV431 in liver compared with blood concentrations across a wide range of CRV431 dosing levels. Most importantly, CRV431 decreased liver fibrosis in a 6-week carbon tetrachloride model and in a mouse model of nonalcoholic steatohepatitis (NASH). Additionally, CRV431 administration during a late, oncogenic stage of the NASH disease model resulted in a 50% reduction in the number and size of liver tumors. These findings are consistent with CRV431 targeting fibrosis and cancer through multiple, cyclophilin-mediated mechanisms and support the development of CRV431 as a safe and effective drug candidate for liver diseases. SIGNIFICANCE STATEMENT: Cyclophilin inhibitors have demonstrated therapeutic activities in many disease models, but no drug candidates have yet advanced completely through development to market. In this study, CRV431 is shown to potently inhibit multiple cyclophilin isoforms, possess several optimized pharmacological properties, and decrease liver fibrosis and tumors in mouse models of chronic liver disease, which highlights its potential to be the first approved drug primarily targeting cyclophilin isomerases.

The cyclophilin inhibitor CRV431 inhibits liver HBV DNA and HBsAg in transgenic mice.

Hepatitis B virus (HBV) infection is a major health burden worldwide with 240 million chronically infected individuals. Nucleos(t)ide analogs and interferons are the current standards of care due to their suppression of HBV replication, but the treatments rarely eradicate HBV from individuals. Similar to current treatments for human immunodeficiency virus type-1 (HIV-1) and hepatitis C virus (HCV) patients, improved HBV therapies will require the combination of multiple drugs which target distinct steps of the HBV life cycle. In this study, we tested the potential of a cyclophilin inhibitor, CRV431, to affect HBV replication in transgenic mice. We found that oral treatment with CRV431 (50 mg/kg/day) for a period of 16 days significantly reduced liver HBV DNA levels and moderately decreased serum HBsAg levels. We observed an additive inhibitory effect on liver HBV DNA levels in mice treated with a combination of low doses of CRV431 (10 mg/kg/day) and the nucleotide prodrug, tenofovir exalidex (TXL), (5 mg/kg/day). No toxicity was observed in CRV431-treated mice. Although it is well known that CRV431 neutralizes the peptidyl-prolyl isomerase activity of cyclophilins, its anti-HBV mechanism(s) of action remains unknown. Nevertheless, this study provides the first demonstration of a beneficial effect of a cyclophilin inhibitor in vivo in an HBV transgenic mouse model. Altogether our data reveal the potential of CRV431 to be part of improved new therapies for HBV patients.

Development, Characterization, and Pharmacokinetic Evaluation of a CRV431 Loaded Self-Microemulsifying Drug Delivery System.

PURPOSE: The objective of this study was to develop a self-microemulsifying drug delivery system (SMEDDS) formulation for the oral delivery of CRV431, a non-immunosuppressive analogue of cyclosporine A. Relative to cyclosporine A, CRV431 is poorly soluble in lipid solvents and thusly presents a challenge for the development of a formulation of sufficient oral bioavailability for clinical use. METHODS: The solubility of CRV431, a cyclosporine derivative, was determined in a range of commonly used surfactants, oils and co-solvents. A pseudo-ternary phase diagram was constructed from the most soluble excipients and prototype formulations, SERIES 1 and SERIES 2 were developed. The pharmacokinetics, following single oral doses of 1 and 3 mg/kg of CRV431 SMEDDS, was studied in healthy human volunteers using liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS). RESULTS: The maximum drug load for the SERIES 1 formulations was less than 40 mg/ml. Manipulation of the excipient ratios allowed for the development of SERIES 2 formulations, which had higher drug loading capacity and stability for CRV431 compared to SERIES 1. Further improvements allowed for the development of an optimized SMEDDS formulation containing up to 90 mg/ml CRV431 and which generated a microemulsion mean particle size of 25 nm when dispersed into aqueous media. The pharmacokinetics of the optimized CRV431 SMEDDS displayed excellent total body exposure and dose-proportional effects in humans, and high drug levels in the liver of rats. CONCLUSIONS: The developed SMEDDS formulation should allow for effective clinical development of CRV431, targeted to the treatment of liver diseases including hepatitis B (HBV), fibrosis, and hepatocellular carcinoma.

In Vitro Phase I Metabolism of CRV431, a Novel Oral Drug Candidate for Chronic Hepatitis B.

The cytochrome P450-mediated Phase I in vitro metabolism of CRV431 was studied using selective chemical inhibition and recombinant human enzymes. Additionally, the metabolic profile of CRV431 in human, rat, and monkey liver microsomes was investigated. Liver microsomes were incubated for 0-80 min with CRV431, and the metabolite profile was assessed by electrospray ionization liquid chromatography mass spectrometry (ESI-LCMS). CRV431 was extensively metabolized through oxidation to produce various hydroxylated and demethylated species. Species identified included monohydroxylated CRV431 (two distinct products), dihydroxylated CRV431, demethylated CRV431 (two distinct products), demethylated and hydroxylated CRV431 (two distinct products), didemethylated and hydroxylated CRV431, and didemethylated and dihydroxylated CRV431. The magnitude of metabolism was greatest in monkey, followed by human, followed by rat. Importantly, all of the species identified in human microsomes were correspondingly identified in monkey and/or rat microsomes. Human liver microsome studies using selective chemical inhibition, as well as studies using recombinant human cytochrome P450 enzymes, revealed that the major enzymes involved are cytochromes P450 3A4 and 3A5. Enzymes 1A2, 2B6, 2C8, 2C9, 2C19, and 2D6 are not involved in the in vitro metabolism of CRV431. This information will be useful for the further development of CRV431 both preclinically and clinically.

The Novel Cyclophilin Inhibitor CPI-431-32 Concurrently Blocks HCV and HIV-1 Infections via a Similar Mechanism of Action.

HCV-related liver disease is the main cause of morbidity and mortality of HCV/HIV-1 co-infected patients. Despite the recent advent of anti-HCV direct acting antivirals (DAAs), the treatment of HCV/HIV-1 co-infected patients remains a challenge, as these patients are refractory to most therapies and develop liver fibrosis, cirrhosis and liver cancer more often than HCV mono-infected patients. Until the present study, there was no suitable in vitro assay to test the inhibitory activity of drugs on HCV/HIV-1 co-infection. Here we developed a novel in vitro "co-infection" model where HCV and HIV-1 concurrently replicate in their respective main host target cells--human hepatocytes and CD4+ T-lymphocytes. Using this co-culture model, we demonstrate that cyclophilin inhibitors (CypI), including a novel cyclosporin A (CsA) analog, CPI-431-32, simultaneously inhibits replication of both HCV and HIV-1 when added pre- and post-infection. In contrast, the HIV-1 protease inhibitor nelfinavir or the HCV NS5A inhibitor daclatasvir only blocks the replication of a single virus in the "co-infection" system. CPI-431-32 efficiently inhibits HCV and HIV-1 variants, which are normally resistant to DAAs. CPI-431-32 is slightly, but consistently more efficacious than the most advanced clinically tested CypI--alisporivir (ALV)--at interrupting an established HCV/HIV-1 co-infection. The superior antiviral efficacy of CPI-431-32 over ALV correlates with its higher potency inhibition of cyclophilin A (CypA) isomerase activity and at preventing HCV NS5A-CypA and HIV-1 capsid-CypA interactions known to be vital for replication of the respective viruses. Moreover, we obtained evidence that CPI-431-32 prevents the cloaking of both the HIV-1 and HCV genomes from cellular sensors. Based on these results, CPI-431-32 has the potential, as a single agent or in combination with DAAs, to inhibit both HCV and HIV-1 infections.

CD8+ T cells directed against a viral peptide contribute to loss of motor function by disrupting axonal transport in a viral model of fulminant demyelination.

Demyelination, a pathological hallmark of multiple sclerosis, may be a necessary but not a sufficient condition for motor dysfunction associated with this disease. We favor a neurodegenerative model of multiple sclerosis and suggest that demyelination creates a permissive environment wherein the denuded axon becomes susceptible to immune-mediated injury. Unfortunately, the cellular effectors responsible for eliciting such axonal injury are currently unknown. Based on previous observations implicating cytotoxic T cells in this injury, we assessed motor function, axon dropout, and axon injury following peptide depletion of the immunodominant CD8+ antiviral T cell response in the IFNgamma receptor-deficient mouse model of acute demyelination. We found that the targeted removal of this population of cytotoxic effector cells prior to infection with the Theiler's murine encephalomyelitis virus caused a substantial preservation of motor function at 45 days postinfection that was associated with preservation of retrograde axonal transport in a subpopulation of surviving axons within the spinal cord. We conclude that cytotoxic T cells may be responsible for the initiation of axon injury following demyelination.

Neutralization of chemokines RANTES and MIG increases virus antigen expression and spinal cord pathology during Theiler's virus infection.

The role of chemokines during some viral infections is unpredictable because the inflammatory response regulated by these molecules can have two, contrasting effects-viral immunity and immunopathologic injury to host tissues. Using Theiler's virus infection of SJL mice as a model of this type of disease, we have investigated the roles of two chemokines-regulated on activation, normal T cell-expressed and secreted (RANTES) chemokine and monokine induced by IFN-gamma (MIG)-by treating mice with antisera that block lymphocyte migration. Control, infected mice showed virus persistence, mild inflammation and a small degree of demyelination in the white matter of the spinal cord at 6 weeks post-infection. Treatment of mice with RANTES antiserum starting at 2 weeks post-infection increased both viral antigen expression and the severity of inflammatory demyelination at 6 weeks post-infection. MIG antiserum increased the spread of virus and the proportion of spinal cord white matter with demyelination. Overall, viral antigen levels correlated strongly with the extent of pathology. At the RNA level, high virus expression was associated with low IL-2 and high IL-10 levels, and RANTES antiserum decreased the IL-2/IL-10 ratio. Our results suggest that RANTES and MIG participate in an immune response that attempts to restrict viral expression while limiting immunopathology and that anti-chemokine treatment poses the risk of exacerbating both conditions in the long term.

Genetically dominant spinal cord repair in a murine model of chronic progressive multiple sclerosis.

For reasons that are not well understood, central nervous system repair in multiple sclerosis is often minimal. We present evidence, in a murine model of chronic progressive multiple sclerosis, that genetic factors can substantially influence remyelination, axonal integrity, and neurologic function. Four inbred mouse strains, SJL, B10.D1-H2(q), FVB, and SWR, developed extensive inflammatory demyelination by 3 months after infection with Theiler's murine encephalomyelitis virus. Demyelination continued lifelong in SJL and B10.D1-H2(q) mice, accompanied by axonal injury, minimal remyelination, and progressive motor dysfunction. In contrast, FVB and SWR mice showed less axonal injury, progressive remyelination, and stabilization of motor function. Genetic dominance of the reparative traits was demonstrated by crossing remyelinating strains (FVB and SWR) with nonremyelinating strains (SJL and B10.D1-H2(q)). All F1 mice developed a phenotype identical to FVB and SWR, showing extensive remyelination, partial preservation of axons, and preserved motor function. Analyses of viral RNA and antigen, immune cell infiltration, and antiviral antibody titers did not predict the phenotypic differences between strains. These results highlight the significant extent to which hereditary factors can control disease course and demonstrate that the switch from a pathogenic to a reparative phenotype can occur even after prolonged inflammatory demyelination.

Mutant huntingtin impairs axonal trafficking in mammalian neurons in vivo and in vitro.

Recent data in invertebrates demonstrated that huntingtin (htt) is essential for fast axonal trafficking. Here, we provide direct and functional evidence that htt is involved in fast axonal trafficking in mammals. Moreover, expression of full-length mutant htt (mhtt) impairs vesicular and mitochondrial trafficking in mammalian neurons in vitro and in whole animals in vivo. Particularly, mitochondria become progressively immobilized and stop more frequently in neurons from transgenic animals. These defects occurred early in development prior to the onset of measurable neurological or mitochondrial abnormalities. Consistent with a progressive loss of function, wild-type htt, trafficking motors, and mitochondrial components were selectively sequestered by mhtt in human Huntington's disease-affected brain. Data provide a model for how loss of htt function causes toxicity; mhtt-mediated aggregation sequesters htt and components of trafficking machinery leading to loss of mitochondrial motility and eventual mitochondrial dysfunction.