Engineering a stable and selective peptide blocker of the Kv1.3 channel in T lymphocytes

Kv1.3 potassium channels maintain the membrane potential of effector memory (T(EM)) T cells that are important mediators of multiple sclerosis, type 1 diabetes mellitus, and rheumatoid arthritis. The polypeptide ShK-170 (ShK-L5), containing an N-terminal phosphotyrosine extension of the Stichodactyla helianthus ShK toxin, is a potent and selective blocker of these channels. However, a stability study of ShK-170 showed minor pH-related hydrolysis and oxidation byproducts that were exacerbated by increasing temperatures. We therefore engineered a series of analogs to minimize the formation of these byproducts. The analog with the greatest stability, ShK-192, contains a nonhydrolyzable phosphotyrosine surrogate, a methionine isostere, and a C-terminal amide. ShK-192 shows the same overall fold as ShK, and there is no evidence of any interaction between the N-terminal adduct and the rest of the peptide. The docking configuration of ShK-192 in Kv1.3 shows the N-terminal para-phosphonophenylalanine group lying at the junction of two channel monomers to form a salt bridge with Lys(411) of the channel. ShK-192 blocks Kv1.3 with an IC(50) of 140 pM and exhibits greater than 100-fold selectivity over closely related channels. After a single subcutaneous injection of 100 microg/kg, approximately 100 to 200 pM concentrations of active peptide is detectable in the blood of Lewis rats 24, 48, and 72 h after the injection. ShK-192 effectively inhibits the proliferation of T(EM) cells and suppresses delayed type hypersensitivity when administered at 10 or 100 microg/kg by subcutaneous injection once daily. ShK-192 has potential as a therapeutic for autoimmune diseases mediated by T(EM) cells.

Canaux ioniques et démyélinisation : les fondements d’un traitement de l’encéphalomyélite autoimmune expérimentale (EAE) par des bloqueurs des canaux potassium

Voltage-gated potassium channels (Kv channels) are ion channels, openings of which provide an outward flow of potassium ions repolarising the cell. In neurons, Kv channels play a crucial role in action potential repolarisation and in shaping neuronal excitability. In non-excitable cells, such as T lymphocytes, Kv channels and calcium-activated K+ channels (KCa channels) determine the driving force for Ca2+ entry. During T cell activation the calcium entry depolarises the cell and increases the cytosolic calcium concentration, which in return activates Kv and KCa channels. K+ channel opening repolarises the cell and drives the membrane potential to a negative voltage. The roles of Kv channels in nervous and immune systems have been investigated here by means of a rat experimental autoimmune disease of the central nervous system, the experimental autoimmune encephalomyelitis (EAE). EAE is characterised clinically by paralysis, and pathologically by inflammatory cell infiltrations into the brain and the spinal cord. Among the inflammatory cells, T lymphocytes play a major role. Hence, EAE can be adoptively transferred into syngenic animals by the injection of T cells reactive to myelin antigens. During adoptive-EAE, somato-sensory evoked potentials recorded along the spinal tracts decrease in amplitude and axonal propagation is disrupted. We have analysed the consequences of Kv channels blockade by peptidyl toxins on central nerve conduction, on T cell activation and on the time course of EAE. In rat optic nerves, Kv channels have been identified up from postnatal day 1. Their blockade by kaliotoxin (a scorpion toxin) or by dendrotoxin-I (a snake toxin) enlarges the compound action potentials, demonstrating the participation of Kv channels to spike repolarisation. This effect disappears at adult age due to the sequestration of Kv channels under the myelin, in the paranodal regions. During acute demyelination by lysophosphatidyl-choline, the surface area of compound action potential decreased probably because conduction block occurred. Demyelination unmasked Kv channels, which are again accessible to toxins. Their blockade by dendrotoxin-I or kaliotoxin favoured a slow delayed conduction suggesting that those Kv channel blockers exert a neurological benefit during demyelinating diseases. In a T-cell line reactive to myelin basic protein antigen, which is used to adoptively transfer experimental autoimmune encephalomyelitis, Kv1.3 channels are constitutively expressed. Their blockade leads to a pronounced reduction of the T cell proliferative response, cytokine production and Ca2+ influx. In the rat, blockade of Kv1.3 inhibits the delayed type hypersensitivity response to myelin basic protein prevents and treats adoptive experimental autoimmune encephalomyelitis. Blockade of Kv channels alone or in combination with KCa channels improves the symptoms of the disease. These results demonstrate that K+ channel blockers displaying high selectivity are potent immunosuppressive agents with beneficial symptomatic effects in experimental autoimmune encephalomyelitis.

Selective blockade of T lymphocyte K(+) channels ameliorates experimental autoimmune encephalomyelitis, a model for multiple sclerosis

Adoptive transfer experimental autoimmune encephalomyelitis (AT-EAE), a disease resembling multiple sclerosis, is induced in rats by myelin basic protein (MBP)-activated CD4(+) T lymphocytes. By patch-clamp analysis, encephalitogenic rat T cells stimulated repeatedly in vitro expressed a unique channel phenotype ("chronically activated") with large numbers of Kv1.3 voltage-gated channels (approximately 1500 per cell) and small numbers of IKCa1 Ca(2+)-activated K(+) channels (approximately 50-120 per cell). In contrast, resting T cells displayed 0-10 Kv1.3 and 10-20 IKCa1 channels per cell ("quiescent" phenotype), whereas T cells stimulated once or twice expressed approximately 200 Kv1.3 and approximately 350 IKCa1 channels per cell ("acutely activated" phenotype). Consistent with their channel phenotype, [(3)H]thymidine incorporation by MBP-stimulated chronically activated T cells was suppressed by the peptide ShK, a blocker of Kv1.3 and IKCa1, and by an analog (ShK-Dap(22)) engineered to be highly specific for Kv1.3, but not by a selective IKCa1 blocker (TRAM-34). The combination of ShK-Dap(22) and TRAM-34 enhanced the suppression of MBP-stimulated T cell proliferation. Based on these in vitro results, we assessed the efficacy of K(+) channel blockers in AT-EAE. Specific and simultaneous blockade of the T cell channels by ShK or by a combination of ShK-Dap(22) plus TRAM-34 prevented lethal AT-EAE. Blockade of Kv1.3 alone with ShK-Dap(22), but not of IKCa1 with TRAM-34, was also effective. When administered after the onset of symptoms, ShK or the combination of ShK-Dap(22) plus TRAM-34 greatly ameliorated the clinical course of both moderate and severe AT-EAE. We conclude that selective targeting of Kv1.3, alone or with IKCa1, may provide an effective new mode of therapy for multiple sclerosis.

Early joint erosions and serum levels of matrix metalloproteinase 1, matrix metalloproteinase 3, and tissue inhibitor of metalloproteinases 1 in rheumatoid arthritis

OBJECTIVE

To further evaluate the roles of matrix metalloproteinase 1 (MMP-1), MMP-3, and tissue inhibitor of metalloproteinases 1 (TIMP-1) in the pathogenesis of joint inflammation and articular erosions in early inflammatory arthritis.

METHODS

Untreated patients with joint symptoms for <2 years were evaluated at presentation and followed up prospectively for 18 months. Swollen joint count and serum levels of C-reactive protein (CRP) were determined every 6 months. Serum levels of MMP-1, MMP-3, and TIMP-1 were measured by double-antibody sandwich enzyme-linked immunosorbent assay at the same time intervals. The number of joint erosions in serial radiographs of the hands and feet was also recorded. Analysis of synovial fluid levels of MMPs and TIMP-1 at presentation was completed in some patients.

RESULTS

Of 175 patients evaluated at baseline, 85 had rheumatoid arthritis (RA), 39 had seronegative spondylarthropathy, 38 had undifferentiated arthritis, and 13 had self-limiting arthritis. Of 164 patients with available radiographs of the hands and feet at presentation, 33 (20.1%) had joint erosions. Baseline levels of MMP-1, MMP-3, and TIMP-1 were significantly higher (P = 0.0001, P = 0.013, and P = 0.0001, respectively) and ratios of TIMP-1:MMP-1 and TIMP-1:MMP-3 were significantly lower (P = 0.0001 and P = 0.013, respectively) in RA versus non-RA patients. In RA patients, serum levels of CRP correlated with MMP-3 and TIMP-1 levels, but not with MMP-1 levels. The number of erosions at presentation correlated with baseline levels of both MMP-1 and MMP-3, but not with levels of TIMP-1. One hundred one patients were followed up for the next 18 months. The number of patients with erosions and the number of erosions per patient increased significantly during this period. Area under the curve (AUC) measurements of MMP-1 and TIMP-1 levels, but not of MMP-3 levels, yielded significantly higher values in RA than in non-RA patients. In RA patients, only the AUC level of MMP-3 correlated with the AUC CRP level (r = 0.67, P = 0.0001), while only the AUC level of MMP-1 correlated with the number of new joint erosions (r = 0.28, P = 0.034).

CONCLUSION

These data suggest an uncoupling of the pathophysiologic mechanisms associated with joint inflammation and articular erosion. Treatments that inhibit the production and activity of MMP-1 may preferentially limit the formation of new joint erosions and improve the long-term functional outcome of some patients with inflammatory arthritis.

Serum TIMP-1, TIMP-2, and MMP-1 in patients with systemic sclerosis, primary Raynaud's phenomenon, and in normal controls

BACKGROUND

Excess tissue matrix accumulates in systemic sclerosis (SSc), accounting for both visceral and dermal fibrosis. It is suggested that decreased serum levels of matrix metalloproteinases (MMPs) or increased levels of tissue inhibitors of matrix metalloproteinases (TIMPs) may account for this matrix accumulation.

OBJECTIVE

To measure serum levels of tissue inhibitors of metalloproteinases, TIMP-1, TIMP-2, and collagenase-1 (MMP-1), in patients with diffuse cutaneous systemic sclerosis (dcSSc), limited cutaneous systemic sclerosis (lcSSc), primary Raynaud's phenomenon (RP), and in normal controls.

METHODS

Serum samples from patients with dcSSc (n=83), lcSSc (n=87), RP (n=80), and normal controls (n=98) were analysed using enzyme linked immunosorbent assays (ELISAs) for total TIMP-1, TIMP-2, and MMP-1. Results from each assay were analysed by the Kruskal-Wallis test. Dunn's multiple comparison post-test was then applied between groups.

RESULTS

TIMP-1 levels were significantly raised in dcSSc and lcSSc groups compared with the RP group and normal controls (p<0.01 to p<0.001). In the dcSSc group, TIMP-1 levels were significantly higher in early disease (<2 years) than in late stage disease (>4 years) (p<0.05). This was not found for the lcSSc group. Serum TIMP-2 and MMP-1 levels in dcSSc and lcSSc did not differ significantly from those in normal controls. Increased levels of TIMPs were not convincingly associated with organ disease. No assay result correlated with autoantibody status (anti-topoisomerase 1 (anti-Scl-70), anticentromere antibody, or anti-RNA polymerase). No significant differences in serum TIMP-1, TIMP-2, or MMP-1 levels were shown in the RP group compared with normal controls.

CONCLUSIONS

Raised TIMP-1 levels in the SSc groups support the hypothesis that matrix accumulation occurs in SSc at least in part owing to decreased degradation. Moreover, the variation in TIMP-1 levels between the early and late disease stages of dcSSc seems to reflect the early progressive course of dermal fibrosis seen clinically. The expected reduction in serum MMP-1 levels in the SSc groups was not found. This suggests that tissue matrix accumulation is due to increased inhibitors rather than to decreased MMPs.

Selective blocking of voltage-gated K+ channels improves experimental autoimmune encephalomyelitis and inhibits T cell activation

Kaliotoxin (KTX), a blocker of voltage-gated potassium channels (Kv), is highly selective for Kv1.1 and Kv1.3. First, Kv1.3 is expressed by T lymphocytes. Blockers of Kv1.3 inhibit T lymphocyte activation. Second, Kv1.1 is found in paranodal regions of axons in the central nervous system. Kv blockers improve the impaired neuronal conduction of demyelinated axons in vitro and potentiate the synaptic transmission. Therefore, we investigated the therapeutic properties of KTX via its immunosuppressive and symptomatic neurological effects, using experimental autoimmune encephalomyelitis (EAE), an animal model for multiple sclerosis. The T line cells used to induce adoptive EAE were myelin basic protein (MBP)-specific, constitutively contained mRNA for Kv1.3. and expressed Kv1.3. These channels were shown to be blocked by KTX. Activation is a crucial step for MBP T cells to become encephalitogenic. The addition of KTX during Ag-T cell activation led to a great reduction in the MBP T cell proliferative response, in the production of IL-2 and TNF, and in Ca(2+) influx. Furthermore, the addition of KTX during T cell activation in vitro led a decreased encephalitogenicity of MBP T cells. Moreover, KTX injected into Lewis rats impaired T cell function such as the delayed-type hypersensitivity. Lastly, the administration of this blocker of neuronal and lymphocyte channels to Lewis rats improved the symptoms of EAE. We conclude that KTX is a potent immunosuppressive agent with beneficial effects on the neurological symptoms of EAE.

Immunolocalisation of vascular endothelial growth factor (VEGF) in human neonatal growth plate cartilage

Angiogenesis is essential for the replacement of cartilage by bone during growth and repair. In order to obtain a better understanding of the mechanisms regulating vascular invasion at sites of endochondral ossification we have investigated the expression of the endothelial cell-specific mitogen, vascular endothelial growth factor (VEGF), by chondrocytes in human neonatal growth plates. VEGF was absent from chondrocytes in the resting zone and only weakly expressed by occasional chondrocytes in the proliferating region. In the hypertrophic zone the number of chondrocytes stained and the intensity of staining for VEGF increased with chondrocyte hypertrophy, maximum expression of VEGF being observed in chondrocytes in the lower hypertrophic and mineralised regions of the cartilage. These observations provide the first demonstration of the presence of VEGF in situ in developing human bone and are consistent with in vitro observations demonstrating the upregulation of proangiogenic growth factor production with increasing chondrocyte hypertrophy. The presence of numerous small blood vessels and vascular structures in the subchondral region where VEGF expression was maximal indicates that VEGF produced by hypertrophic chondrocytes may play a key role in the regulation of vascular invasion of the growth plate.

Plasma morphine levels produced by continuous infusion in children

Blood samples were taken from six children aged between 10 months and 15 years, at intervals over a period of 40 hours while they were receiving continuous morphine infusions. The plasma morphine values obtained showed similar and consistent levels 15-30 minutes after starting the infusions.