Differential effects of aluminum ion on smooth muscle calpain I and calpain II activities

Calciphylaxis: a report of six cases and review of literature

Calciphylaxis is usually a fatal condition that develops in a few chronic renal failure patients, and it is characterized by calcifications in subcutaneous arteries, infarcts in skin, and the neighboring subcutis. Calciphylaxis, once considered as a rare condition, has been reported to have an annual incidence of 1% and a prevalence of 4% in dialysis patients. We describe our clinical experience in six end-stage renal disease patients on dialysis that presented with calciphylaxis and died due to sepsis, and review the pathogenesis, epidemiology, clinical and histopathologic features, and treatment of calciphylaxis. Physicians should initially consider the possibility of calciphylaxis in case of development of skin lesions in chronic renal failure patients with impaired calcium, phosphorus, and parathyroid hormone levels. The most important cause of mortality in this condition is infection. Therefore, differential diagnosis of these lesions from systemic vasculitis in their early stages and withdrawal of immunosuppressive therapy that increases the tendency to infections are essential.

Calcific uraemic arteriolopathy: an update

PURPOSE OF REVIEW

Calcific uraemic arteriolopathy (CUA) or calciphylaxis is a rare but important cause of morbidity and mortality in patients with chronic kidney disease. The prevalence of CUA is increasing in patients with renal failure, and the condition is also being recognized in nonuraemic patients.

RECENT FINDINGS

There has been increasing understanding of the molecular basis of vascular calcification, in particular on the important role of the uraemic microenvironment in the factors implicated in the differentiation of vascular smooth muscle cells into osteoblasts. New options for treatment of hyperphosphataemia and secondary hyperparathyroidism in patients with chronic kidney disease have become available in the last few years and these have begun to be used in patients with CUA. These include bisphosphonates, newer noncalcium/nonaluminium-containing phosphate binders and case reports of use of cinacalcet. Other treatments for CUA that are not targeted directly at calcium/phosphate homeostasis include hyperbaric oxygen and the antioxidant cation chelator sodium thiosulphate.

SUMMARY

Clinicians managing patients with CUA should consider a combination approach of treating deranged calcium/phosphate with newer therapeutic agents and promoting wound healing with other older modalities such as hyperbaric oxygen and sodium thiosulphate infusions. Randomized controlled trials for treatments in CUA are still lacking.

Pathogenesis of calciphylaxis: Hans Selye to nuclear factor kappa-B

The clinical syndrome of calciphylaxis is characterized by arteriolar medial calcification, thrombotic cutaneous ischemia, necrotic skin ulceration, and a high mortality rate. This review integrates calciphylaxis risk factors with the molecular processes governing osseous and extraosseous mineralization. As the pathogenesis of calciphylaxis is better understood, targeted therapies aimed at disease prevention and reversal will follow.

Calciphylaxis: natural history, risk factor analysis, and outcome

BACKGROUND

Calciphylaxis is characterized by ischemic cutaneous ulceration, high mortality, and ineffective treatment.

METHODS

We conducted a retrospective study of 64 patients with calciphylaxis (including 49 dialysis patients age- and sex-matched to 98 dialysis controls).

RESULTS

The estimated 1-year survival rate of calciphylaxis was 45.8%. Risk factors for calciphylaxis included obesity, liver disease, systemic corticosteroid use, calcium-phosphate product more than 70 mg(2)/dL(2), and serum aluminum greater than 25 ng/mL. Survival rates were similar for 16 patients who received parathyroidectomy and 47 who did not. An estimated 1-year survival rate of 61.6% was observed for 17 patients receiving surgical debridement compared with 27.4% for the 46 who did not (P = .008).

LIMITATIONS

The study was limited by its retrospective design and there was no control group for the 15 nondialysis cases.

CONCLUSIONS

Calciphylaxis is multifactorial and usually fatal. Prevention of calciphylaxis may include correction of risk factors identified in this study. Surgical debridement was associated with improved survival, but parathyroidectomy was not.

Elevation of cerebral proteases after systemic administration of aluminum

The levels of three proteases in the cerebral cortex of rats following a three week exposure to aluminum, were measured. The activity of apopain (CPP32), an interleukin 1beta converting enzyme (ICE)-like cysteine protease specifically associated with apoptosis, was increased following dosing with aluminum. The activity of calcium-activated neutral protease, calpain, was also increased. However, the enzyme activity of trypsin-like serine protease, known to be elevated by oxidative events, was unchanged. Since aluminum is suspected as a possible factor in the pathogenesis of Alzheimer's disease and other neurological diseases, it is speculated that changed levels in proteolytic enzymes may relate to the neurotoxicity of aluminum.

Inhibition of proteolysis enhances aluminum-induced perikaryal neurofilament accumulation but does not enhance tau accumulation

As observed for neurons in situ, phosphorylated neurofilament (NF) epitopes are normally segregated within the axonal cytoskeleton of NB2a/d1 cells. However, accumulations of phosphorylated NFs develop in NB2a/d1 perikarya following exposure to aluminum salts and following inhibition of proteolysis. In the present study, we observed that perikarya of cells exposed to both aluminum and the protease inhibitor C1 (also known as "AllNal") were more intensely labeled by monoclonal antibodies directed against both nonphosphorylated and phosphorylated epitopes than were cells treated with either aluminum or protease inhibitor alone. Since these monoclonal antibodies crossreact with tau, we also immunostained cells treated under these conditions with monoclonal antibodies directed against phosphate-insensitive (5E2) and phosphorylated (PHF-1) epitopes of tau. Aluminum treatment, but not C1 treatment, induced accumulation of total tau isoforms as judged by an increase in 5E2 immunoreactivity. Neither treatment, either separately or in combination, induced an increase in PHF-1 immunoreactivity. These findings suggest that alterations in immunoreactivity with SMI antibodies reflected increases in NF epitopes. This was confirmed by immunoblot analyses. Since proteolysis is apparently instrumental in maintaining the normal distribution patterns of phosphorylated NF epitopes, these findings implicate deficiencies in proteolytic mechanisms in the development of neurofibrillary pathology, and underscore the possibility of a multiple etiology in human neuropathological conditions.

Aluminum interaction with phosphoinositide-associated signal transduction

Concerning molecular and cellular mechanisms of aluminum toxicity, recent studies support the hypothesis that interactions of aluminum ions with elements of signal transduction pathways are apparently primary events in cells. In the case of the phosphoinositide-associated signalling pathway of neuroblastoma cells, guanine nucleotide-binding proteins (G proteins) and a phosphatidylinositol-4,5-diphosphate (PIP2)-specific phospholipase C are probable interaction sites for inhibitory actions of aluminum ions. Following interiorization of aluminum by the cell, metal interactions decrease the accumulation of inositol phosphates, especially that of inositol-1,4,5-triphosphate (IP3), concomitant with derangements of intracellular Ca2+ homeostasis. In the presence of high concentrations of Ca2+, formation of IP3 is also diminished in aluminum-pretreated cells, presumably involving a process not requiring Mg(2+)-dependent G proteins. At higher aluminum doses, metal-induced changes in the lipid milieu of the membrane-bound phospholipase may play a role. These types of primary interactions of aluminum ions with elements of cellular communication channels are probably crucial in the manifestation of the multifacetted aluminum toxicity syndrome. If present as a phosphate-like fluoro-aluminate, a stimulatory role of aluminum ions is displayed in G protein-coupled transmembrane signalling.