Peptide mimetic compounds can activate or inhibit cardiac and skeletal ryanodine receptors

AIMS

Our aim was to characterise the actions of novel BIT compounds with structures based on peptides and toxins that bind to significant regulatory sites on ryanodine receptor (RyR) Ca²⁺ release channels. RyRs, located in sarcoplasmic reticulum (SR) Ca²⁺ store membranes of striated muscle, are essential for muscle contraction. Although severe sometimes-deadly myopathies occur when the channels become hyperactive following genetic or acquired changes, specific inhibitors of RyRs are rare.

MAIN METHODS

The effect of BIT compounds was determined by spectrophotometric analysis of Ca²⁺ release from isolated SR vesicles, analysis of single RyR channel activity in artificial lipid bilayers and contraction of intact and skinned skeletal muscle fibres.

KEY FINDINGS

The inhibitory compounds reduced: (a) Ca²⁺ release from SR vesicles with IC50s of 1.1-2.5 μM, competing with activation by parent peptides and toxins; (b) single RyR ion channel activity with IC50s of 0.5-1.5 μM; (c) skinned fibre contraction. In contrast, activating BIT compounds increased Ca²⁺ release with an IC50 of 5.0 μM and channel activity with AC50s of 2 to 12 nM and enhanced skinned fibre contraction. Sub-conductance activity dominated channel activity with both inhibitors and activators. Effects of all compounds on skeletal and cardiac RyRs were similar and reversible. Competition experiments suggest that the BIT compounds bind to the regulatory helical domains of the RyRs that impact on channel gating mechanisms through long-range allosteric interactions.

SIGNIFICANCE

The BIT compounds are strong modulators of RyR activity and provide structural templates for novel research tools and drugs to combat muscle disease.

Changing patient characteristics and survival experience in an Alzheimer's center patient cohort

BACKGROUND

Large and diverse dementia patient cohorts can further a variety of research programs aimed at improving diagnosis, treatment, and meaningful survival in AD.

METHOD

We recruited 1,502 dementia patients between 1989 and 2002, subclassified using standardized criteria and laboratory procedures, and treated according to established guidelines. Baseline clinical and psychometric measures were repeated annually, in person or by use of a multi-modal telephone follow-up program that included many of the measures obtained at in-person visits. We tracked vital status of all subjects at 6-month intervals and offered autopsies to all participants. We assessed for cohort effects in baseline characteristics by 2-year intervals, examined the characteristics and outcomes for those who remained active compared to those who were eventually lost to follow-up, examined survival times for demographic or diagnostic subgroups, and assessed the accuracy of clinical diagnoses versus neuropathology.

RESULTS

The average age at entry, average educational level, and baseline MMSE scores for subjects are increasing over time, and probable AD diagnoses are also increasing. Most (80.6%) subjects have remained active in our Center; those who did not were more likely to have a non-AD diagnosis. Survival averages 5.2 years (CI 4.98--5.37) and is influenced by age and gender, but not by diagnosis of probable versus possible AD. Our diagnostic accuracy is 89.6%, with high sensitivity to the presence of AD (96%).

CONCLUSIONS

In a large and representative clinical cohort, the demographics of AD are changing over time. Careful analyses of those who continue and those who drop out from follow-up suggest that atypical diagnosis, rather than severity or demographic issues accounts for most of the attrition. Clinicians are likely to encounter increasingly older patients with milder disease, and these trends have implications for the design of clinical trials. Survival from the onset of first symptoms, similar for probable and possible AD cases, may be increasing over time.

Frequency of tau mutations in three series of non-Alzheimer's degenerative dementia

Splice-site and missense mutations have been identified in tau associated with frontotemporal dementia with parkinsonism linked to chromosome 17. In this study we assessed the genetic contribution of tau mutations to three patient series with non-Alzheimer's (non-AD) degenerative dementia. The groups included (1) a community-based dementia series from Minnesota, MN; (2) a referral series with clinicopathological tauopathy; and (3) a pathologically confirmed familial frontotemporal dementia series from Manchester, UK. Comparing the three clinical series: in the stringently diagnosed Manchester frontotemporal dementia series, tau mutations were present in 13.6% of cases (three splice-site mutations); in the clinicopathological referral series that used more general inclusion criteria, 3 cases with P301L mutations were observed, which represents a lower mutation frequency of 3.6% (9.4% in familial cases); in contrast, tau mutations were not detected in the Minnesota community-based dementia series, suggesting the occurrence of these mutations in dementia generally is rare (<0.2%). These data identify the prevalence of mutations in three different clinical settings and indicate that this figure is sensitive to the diagnostic criteria used in each patient series.

Use of physician and acute care services by persons with and without Alzheimer's disease: a population-based comparison

OBJECTIVE

To estimate differences in use of acute care services between persons with and without Alzheimer's disease (AD).

STUDY DESIGN

Population-based historical cohort study.

SETTING/SUBJECTS

All Rochester, Minnesota, residents with AD onset between January 1, 1980, and December 31, 1984 (n = 301), plus one age- and sex-matched nondemented control per case, were identified with a retrospective review of community-based medical records.

MEASUREMENTS

Cases and controls were followed in their medical records for number of acute care encounters in the year before January 1 of the index year (year of onset for AD case and their matched control) and in the 4 years following December 31 of the index year. Encounters included clinician visits (office or nursing home), emergency room (ER) visits, hospitalizations (inpatient and outpatient), and inpatient days. Multivariate regression analyses were adjusted for age, sex, pre-index level of illness, and follow-up time.

RESULTS

In the pre-index period, cases and controls were similar with respect to level of illness, number of office visits, ER visits, and hospitalizations. In the year before AD onset, 17 cases (7%) had a clinician visit in the nursing home compared with no controls. In the 4 years after the index year, mean length of follow-up was 3.4 years for both cases and controls. The numbers of ER visits, hospitalizations, and inpatient days were similar for cases and controls. Sixty-four percent of AD cases had a clinician visit in a nursing home versus 1% of controls. Controls experienced more office visits than cases (median = 16 vs 10, P < .001).

CONCLUSIONS

The onset of AD is not associated with greater use of acute care services. However, neither is the high use of nursing home care offset by fewer ER or hospital encounters.

Physiological effects of resistant starches on fecal bulk, short chain fatty acids, blood lipids and glycemic index

OBJECTIVE

To assess the effects on fecal bulking, fecal short chain fatty acid (SCFA) production, blood lipids and glycemic indices of two different forms of resistant starch (RS2 and RS3) from a high-amylose cornstarch.

METHODS

Twenty-four healthy subjects (12 men; 12 women) consumed four supplements taken for 2 weeks in random order separated by 2-week washout periods. The supplements were a low-fiber (control) and supplements providing an additional 30 g dietary fiber as wheat bran (high-fiber control) or the equivalent amount of resistant starch analyzed gravimetrically as dietary fiber from RS2 or RS3. Four-day fecal collections and 12-hour breath gas collections were obtained at the end of each period. Fasting blood was taken at the beginning and end of each period. Glycemic indices of supplements were also assessed.

RESULTS

The wheat bran supplement increased fecal bulk 96+/-14 g/day compared with the low-fiber control (p<0.001) with the mean for both resistant starches also being greater (22+/-8 g/day) than the low-fiber control (p=0.013). On the resistant starch phases, the mean fecal butyrate:SCFA ratio, which has been suggested to have positive implications for colonic health, was significantly above the low-fiber control by 31+/-14% (p=0.035). Resistant starches did not alter serum lipids, urea or breath H2 or CH4. No significant differences in glycemic index were seen between the RS and control supplements.

CONCLUSION

The potential physiological benefits of the resistant starches studied appear to relate to colonic health in terms of effects on fecal bulk and SCFA metabolism.

Rett syndrome: controlled study of an oral opiate antagonist, naltrexone

HYPOTHESIS

The opiate antagonist, naltrexone, will be beneficial in Rett syndrome.

SUBJECTS

Twenty-five individuals fulfilling the criteria for Rett syndrome.

METHOD

Randomized, double-blind, placebo-controlled crossover trial with two treatment periods, 4 months each, and an intervening 1-month washout period. Clinical stage, motor and cognitive development, motor-behavioral analysis, neurophysiological parameters (computerized electroencephalographic analysis, breathing characteristics, quantification of stereotyped hand movements, and sleep characteristics), and cerebrospinal fluid beta-endorphin measurements were evaluated at baseline and at the end of each treatment period.

RESULTS

Only data from the first period of this study were analyzed due to significant sequence effects in the crossover design. This analysis indicated positive effects on certain respiratory characteristics including decreased disorganized breathing during wakefulness. Four (40%) of the individuals receiving naltrexone progressed one or more clinical stages versus none of the individuals receiving placebo. The adjusted (for baseline value and Rett stage) end of treatment psychomotor test age (Bayley Scales) was significantly higher for the placebo group. There was no significant change for the other parameters.

CONCLUSION

Naltrexone may modify some of the respiratory disturbance in Rett syndrome. Declines in motor function and more rapid progression of the disorder suggest a deleterious effect.