The Ability of Physical Performance Measures to Identify Fall Risk in Older Adults Living With Dementia: A Systematic Review and Meta-Analysis.

OBJECTIVES: To determine whether physical performance measures commonly used in clinical settings can discriminate fallers from nonfallers and predict falls in older adults with dementia. DESIGN: Systematic review and meta-analysis. SETTING AND PARTICIPANTS: Older adults with dementia residing in the community, hospitals, and residential care facilities. METHODS: MEDLINE, Embase, PsycINFO, CINAHL, SPORTDiscus, the Cochrane Library, and the PEDro databases were searched from inception until December 27, 2023 (PROSPERO registration number: CRD42022303670). Retrospective or prospective studies that evaluated the associations between physical performance measures and falls in older adults with dementia were included. A random effects model was used to calculate the standardized mean difference (SMD) and 95% CI for each physical performance measure between fallers and nonfallers. Sensitivity analyses were conducted on the longitudinal studies to determine the ability of physical performance measures to predict future falls. RESULTS: Twenty-eight studies were included in this review (n = 3542). The 5-time chair stand test [SMD = 0.23 (0.01, 0.45)], the Berg Balance Scale [SMD = -0.52 (-0.87, -0.17)], postural sway when standing on the floor [SMD = 0.25 (0.07, 0.43)] and on a foam surface [SMD = 0.45 (0.25, 0.66)], and the Short Physical Performance Battery total score [SMD = -0.46 (-0.66, -0.27)] could discriminate fallers from nonfallers. Sensitivity analyses showed that gait speed could predict future falls in longitudinal cohort studies [SMD = -0.29 (-0.49, -0.08)]. Subgroup analyses showed that gait speed [SMD = -0.21 (-0.38, -0.05)] and the Timed Up and Go test [SMD = 0.54 (0.16, 0.92)] could identify fallers staying in residential care facilities or hospitals. CONCLUSIONS AND IMPLICATIONS: The 5-time chair stand test, the Berg Balance Scale, postural sway when standing on the floor and a foam surface, and the Short Physical Performance Battery can be used to predict falls in older adults with dementia. Gait speed and the Timed Up and Go test can be used to predict falls in institutionalized older adults with dementia. Clinicians are recommended to use these physical performance measures to assess fall risk in older adults with dementia.

Ryanodine receptor mutations in arrhythmias: advances in understanding the mechanisms of channel dysfunction.

The cardiac ryanodine receptor (RyR2) mediates rapid Ca(2+) efflux from intracellular stores to effect myocyte contraction during the process of EC (excitation-contraction) coupling. It is now known that mutations in this channel perturb Ca(2+) release function, leading to triggered arrhythmias that may cause SCD (sudden cardiac death). Resolving the precise molecular mechanisms by which SCD-linked RyR2 dysfunction occurs currently constitutes a burgeoning area of cardiac research. So far, defective channel phosphorylation, accessory protein binding, luminal/cytosolic Ca(2+) sensing, and the disruption of interdomain interactions represent the main candidate mechanisms for explaining aberrant SR (sarcoplasmic reticulum) Ca(2+) release via mutants of RyR2. It appears increasingly unlikely that a single exclusive common mechanism underlies every case of mutant channel dysfunction, and that each of these potential mechanisms may contribute to the resultant phenotype. The present review will consider very recent mechanistic developments in this field, including new observations from mutant RyR2 transgenic mouse models, peptide-probe studies, and the implications of functional and phenotypic heterogeneity of RyR2 mutations and polymorphisms.

Role of ryanodine receptor mutations in cardiac pathology: more questions than answers?

The RyR (ryanodine receptor) mediates rapid Ca2+ efflux from the ER (endoplasmic reticulum) and is responsible for triggering numerous Ca2+-activated physiological processes. The most studied RyR-mediated process is excitation-contraction coupling in striated muscle, where plasma membrane excitation is transmitted to the cell interior and results in Ca2+ efflux that triggers myocyte contraction. Recently, single-residue mutations in the cardiac RyR (RyR2) have been identified in families that exhibit CPVT (catecholaminergic polymorphic ventricular tachycardia), a condition in which physical or emotional stress can trigger severe tachyarrhythmias that can lead to sudden cardiac death. The RyR2 mutations in CPVT are clustered in the N- and C-terminal domains, as well as in a central domain. Further, a critical signalling role for dysfunctional RyR2 has also been implicated in the generation of arrhythmias in the common condition of HF (heart failure). We have prepared cardiac RyR2 plasmids with various CPVT mutations to enable expression and analysis of Ca2+ release mediated by the wild-type and mutated RyR2. These studies suggest that the mutational locus may be important in the mechanism of Ca2+ channel dysfunction. Understanding the causes of aberrant Ca2+ release via RyR2 may assist in the development of effective treatments for the ventricular arrhythmias that often leads to sudden death in HF and in CPVT.

Is fish oil good or bad for heart disease? Two trials with apparently conflicting results.

Two successive randomized trials examined the effect of an increased intake of fatty fish, or the use of fish oil supplements, in reducing mortality in men with heart disease. The Diet and Reinfarction Trial (DART) was conducted in 2033 men who were recovering from acute myocardial infarction (MI). Those who were advised to eat fatty fish (or who opted to take fish oil capsules instead) had a 29% reduction in all-cause mortality over the following two years compared with those not so advised. The effect appeared in the first few months of the trial. The Diet and Angina Randomized Trial (DART 2) involved 3114 men with stable angina. Advice to eat fatty fish did not reduce mortality, and taking fish oil capsules was associated with a higher risk of cardiac and sudden death. The adverse effects of fish or fish oil were restricted to men not taking beta-blockers or dihydropyridine calcium-channel blockers, and were greater in those taking digoxin. Evidence from other sources strongly suggests an anti-arrhythmic action of fish oil, particularly after MI or in the presence of acute ischemia. The apparently conflicting results of the two trials may reflect different actions of n-3 fatty acids in acute and chronic conditions, together with different effects of eating fish and taking fish oil capsules. A mechanism is proposed that could account for these findings.

Strongyloides appendicitis: unusual etiology in two siblings with chronic abdominal pain.

Appendicitis is one of the most common causes of acute surgical disease in children and young adults. Parasites, however, are one of the uncommon etiologies. An 8-year-old girl and her 7-year-old sister presented with more than 2 months of chronic abdominal pain that became worse over a 1-week period before presentation. The 2 sisters presented 1 month apart. Both had similar symptomatology and physical examination findings. At operation, the surgical findings included an inflamed appendix with a cross section of the parasite Strongyloides. Strongyloides appendicitis has occurred almost exclusively in areas endemic to the parasite. Its environment is more common outside the United States but occasionally is seen in the Southeast region and in institutionalized individuals. The presentation of acute exacerbation of chronic abdominal pain coupled with the pathologic finding of Strongyloides in an acutely inflamed appendix, should alert the clinician of other possible cases. This increased index of suspicion will allow more prompt diagnosis and help avoid the morbidity of delayed operation.

Analysis of gap junction assembly using mutated connexins detected in Charcot-Marie-Tooth X-linked disease.

The assembly of gap junction intercellular communication channels was studied by analysis of the molecular basis of the dysfunction of connexin 32 mutations associated with the X-linked form of Charcot-Marie-Tooth disease in which peripheral nervous transmission is impaired. A cell-free translation system showed that six recombinant connexin 32 mutated proteins-four point mutations at the cytoplasmic amino terminus, one at the membrane aspect of the cytoplasmic carboxyl terminus, and a deletion in the intracellular loop-were inserted into microsomal membranes and oligomerised into connexon hemichannels with varying efficiencies. The functionality of the connexons was determined by the ability of HeLa cells expressing the respective connexin cDNAs to transfer Lucifer yellow. The intracellular trafficking properties of the mutated connexins were determined by immunocytochemistry. The results show a relationship between intracellular interruption of connexin trafficking, the efficiency of intercellular communication, and the severity of the disease phenotype. Intracellular retention was explained either by deficiencies in the ability of connexins to oligomerise or by mutational changes at two targeting motifs. The results point to dominance of two specific targeting motifs: one at the amino terminus and one at the membrane aspect of the cytoplasmically located carboxyl tail. An intracellular loop deletion of six amino acids, associated with a mild phenotype, showed partial oligomerisation and low intercellular dye transfer compared with wild-type connexin 32. The results show that modifications in trafficking and assembly of gap junction channels emerge as a major feature of Charcot-Marie-Tooth X-linked disease.

Synthesis and assembly of connexins in vitro into homomeric and heteromeric functional gap junction hemichannels.

The biogenesis of connexins and their assembly into functional gap junction hemichannels (connexons) was studied with the use of a cell-free transcription/translation system. Velocity sedimentation on sucrose gradients showed that a small proportion of connexin (Cx) 26 and Cx32 that were co-translationally translocated into microsomes were oligomers of Cx26 and Cx32. Chemical cross-linking studies showed that these corresponded to hexameric connexons. Reconstitution of connexons synthesized in vitro into liposomes induced permeability properties consistent with the view that open gap junction hemichannels were produced. By using an immunoprecipitation approach, a simultaneous translation of Cx26 and Cx32 incorporated into microsomes resulted in homomeric connexons. However, supplementation of the translation system in vitro with liver Golgi membranes produced heteromeric connexons constructed of Cx32 and Cx26, and also resulted in an increased oligomerization especially of Cx32. All of the connexins analysed were inserted co-translationally into canine pancreatic microsomal membranes. In addition, Cx26 and Cx43, but not Cx32, were also inserted into microsomal membranes post-translationally. Analysis of various connexin constructs in which the cytoplasmic carboxy tails were transposed, the cytoplasmic tail of Cx43 was truncated or a reporter protein, aequorin, was attached to the C-terminus showed that tail length was not the major determinant of the post-translational membrane insertion of connexins.

Trafficking pathways leading to the formation of gap junctions.

This chapter reports the mechanisms resulting in the assembly of gap junction intercellular communication channels. The connexin channel protein subunits are required to oligomerize into hexameric hemichannels (connexons) that may be homoor heteromeric in composition. Pairing of connexons in contacting cells leads to the formation of a gap junction unit. Subcellular fractionation studies using guinea-pig liver showed that oligomerization of connexins was complete on entry into Golgi, and that connexons showed heteromeric properties. The low ratio of connexin26 (Cx26; beta 2) relative to Cx32 (beta 1) in endomembranes compared to the approximately equal ratios found in plasma membranes and gap junctions suggest that Cx26 takes a non-classical route to the plasma membrane. Cultured cells, expressing connexin-aequorin chimeras, also provided evidence that Cx26 takes a more rapid non-classical route to the plasma membrane, because brefeldin A, a drug that disrupts the Golgi, had minimal effects on trafficking of Cx26 to the plasma membrane in contrast to its disruption of Cx32 trafficking. Finally, a cell-free approach for studying synthesis of connexons provided further evidence that Cx26 showed membrane insertion properties compatible with a more direct intracellular route to gap junctions. The presence of dual gap junction assembly pathways can explain many of the differential properties exhibited by connexins in cells.

Intracellular trafficking pathways in the assembly of connexins into gap junctions.

Trafficking pathways underlying the assembly of connexins into gap junctions were examined using living COS-7 cells expressing a range of connexin-aequorin (Cx-Aeq) chimeras. By measuring the chemiluminescence of the aequorin fusion partner, the translocation of oligomerized connexins from intracellular stores to the plasma membrane was shown to occur at different rates that depended on the connexin isoform. Treatment of COS-7 cells expressing Cx32-Aeq and Cx43-Aeq with brefeldin A inhibited the movement of these chimera to the plasma membrane by 84 +/- 4 and 88 +/- 4%, respectively. Nocodazole treatment of the cells expressing Cx32-Aeq and Cx43-Aeq produced 29 +/- 16 and 4 +/- 7% inhibition, respectively. In contrast, the transport of Cx26 to the plasma membrane, studied using a construct (Cx26/43T-Aeq) in which the short cytoplasmic carboxyl-terminal tail of Cx26 was replaced with the extended carboxyl terminus of Cx43, was inhibited 89 +/- 5% by nocodazole and was minimally affected by exposure of cells to brefeldin A (17 +/-11%). The transfer of Lucifer yellow across gap junctions between cells expressing wild-type Cx32, Cx43, and the corresponding Cx32-Aeq and Cx43-Aeq chimeras was reduced by nocodazole treatment and abolished by brefeldin A treatment. However, the extent of dye coupling between cells expressing wild-type Cx26 or the Cx26/43T-Aeq chimeras was not significantly affected by brefeldin A treatment, but after nocodazole treatment, transfer of dye to neighboring cells was greatly reduced. These contrasting effects of brefeldin A and nocodazole on the trafficking properties and intercellular dye transfer are interpreted to suggest that two pathways contribute to the routing of connexins to the gap junction.

Connexin-aequorin chimerae report cytoplasmic calcium environments along trafficking pathways leading to gap junction biogenesis in living COS-7 cells.

The cytoplasmic calcium environments along membrane trafficking pathways leading to gap junction intercellular communication channels at the plasma membrane were studied. Connexins, the constitutive proteins of gap junctions, were fused at their carboxyl terminus to the calcium-sensitive photoprotein aequorin. The cellular location of the chimeric proteins was determined by immunolocalization and subcellular fractionation. The generation of functional gap junctions by the connexin chimerae was monitored by the ability of the cells to exchange small dyes. Although aequorin fused to connexin-26 was nonfunctional, its ability to report Ca2+ and to form functional gap junctions was rescued by replacement of its cytoplasmic carboxyl tail with that of connexin-43. In COS-7 cells expressing these connexin-aequorin chimerae, calcium levels below the plasma membrane were higher (approximately 5 microM) than those in the cytoplasm (approximately 100 nM); gap junctions were able to transfer dyes under these conditions. Cytoplasmic levels of free calcium surrounding the ERGIC/Golgi reported by connexin-43 chimera (approximately 420 nM) were twice those measured by connexin-32 chimera (approximately 200 nM); both chimerae measured calcium levels substantially higher than those reported by a connexin-26 chimera (approximately 130 nM). Dispersion of the ERGIC and Golgi complex by brefeldin A led to a marked reduction in calcium levels. The results show that the various connexin chimerae were located in spatially different subcellular stores and that the ERGIC/Golgi regions of the cell maintain heterogeneous cytoplasmic domains of calcium. The implications of the subplasma-membrane Ca2+ levels on the gating of gap junctions are discussed.

Rapid determination of gap junction formation using HeLa cells microinjected with cDNAs encoding wild-type and chimeric connexins.

A procedure for rapidly determining the functionality of gap junctions constructed of recombinant connexins in communication-deficient HeLa cells is described. Nuclear microinjection of cDNA encoding wild-type connexins (Cx) 26, 32, 43, and a range of connexin-aequorin (Cx-Aeq) chimerase resulted in generation of gap junction intercellular communication channels. Expression of recombinant protein was detected in > 95% of cells 18-72 h following nuclear microinjection, and the functionality of the channels generated was determined according to their ability to transfer the fluorescent dye tracers Lucifer yellow and propidium iodide. The dye transfer results obtained correlated closely with other published studies using stably transfected cells and yet are obtained as rapidly as 18 h following microinjection of cDNA. Expression of a truncated form of Cx43 (Cx43 delta 244) by this new method indicated diminished intercellular transfer of both dyes and supports a channel-gating mechanism that postulates interaction between the carboxyl tail and the intracellular loop.

Assembly of chimeric connexin-aequorin proteins into functional gap junction channels. Reporting intracellular and plasma membrane calcium environments.

Chimeric proteins comprising connexins 26, 32, and 43 and aequorin, a chemiluminescent calcium indicator, were made by fusing the amino terminus of aequorin to the carboxyl terminus of connexins. The retention of function by the chimeric partners was investigated. Connexin 32-aequorin and connexin 43-aequorin retained chemiluminescent activity whereas that of connexin 26-aequorin was negligible. Immunofluorescent staining of COS-7 cells expressing the chimerae showed they were targeted to the plasma membrane. Gap junction intercellular channel formation by the chimerae alone and in combination with wild-type connexins was investigated. Stable HeLa cells expressing connexin 43-aequorin were functional, as demonstrated by Lucifer yellow transfer. Paris of Xenopus oocytes expressing connexin 43-aequorin were electrophysiologically coupled, but those expressing chimeric connexin 26 or 32 showed no detectable levels of coupling. The formation of heteromeric channels constructed of chimeric connexin 32 or connexin 43 and the respective wild-type connexins was inferred from the novel voltage gating properties of the junctional conductance. The results show that the preservation of function by each partner of the chimeric protein is dictated mainly by the nature of the connexin, especially the length of the cytoplasmic carboxyl-terminal domain. The aequorin partner of the connexin 43 chimera reported calcium levels in COS-7 cells in at least two different calcium environments.