Complement Activation in Dialysis: Effects on Cytokines, Lymphocyte Activation and β2 Microglobulin

Anaphylatoxins generated by complement activation by filter membranes are present in plasma during hemodialysis (HD). In the presence of endotoxins which may contaminate the dialysate, they can trigger monocytes to produce interleukin-1 (IL-1) and tumor necrosis factor (TNF), with detrimental effects for the patients. We have investigated whether or not the use of complement activating (cuprophan) and non- (or less-) activating membranes (polysulfone, polymethylmethacrylate or polyacrylonitrile) per se influences cytokine levels in HD patients. Our results indicate that if a sterile bicarbonate solution is used as dialysate, there are no significant increases in IL-1, TNF, interleukin-2 (IL-2) and soluble IL-2 receptors (sIL-2r) throughout HD, even with cuprophan membranes. Moreover even a prolonged use of this membrane (three months) did not change pre-dialysis levels of cytokines and receptors. Use of complement activating membranes also does not influence β2 microglobulin levels.

Beta 2-microglobulin amyloidosis: role of monocytes/macrophages

PURPOSE OF REVIEW

Macrophage infiltration is a distinctive histological characteristic of beta2-microglobulin amyloidosis. Studies reported during the past years have helped to clarify the role of monocytes/macrophages in the fibrillar precipitation of beta2-microglobulin and in the pathogenesis of osteoarticular pathology.

RECENT FINDINGS

Contrary to the original view, macrophage infiltration is more likely a secondary phenomenon of amyloidosis rather than an initiating event. The observation that macrophages are associated with a later stage of beta2-microglobulin amyloidosis suggests a possible role of these cells in transformation of clinical silent deposits into symptomatic osteoarticular destruction. Accumulating evidence suggests that beta2-microglobulin modified with advanced glycation end products plays a key role in recruitment and activation of macrophages through an advanced glycation end products receptor-mediated pathway, and thus may contribute to the development of local cellular inflammation in beta2-microglobulin amyloidosis.

SUMMARY

Beta 2-microglobulin amyloidosis arthropathies may result from progressive accumulation of advanced glycation end products in long-lived amyloid linked to a heightened cellular response. Antagonism of the interaction between advanced glycation end products and their receptor may be a relevant strategy for cellular inflammation in beta2-microglobulin amyloidosis.

Differentially expressed genes in L6 rat skeletal muscle myoblasts after incubation with inflammatory cytokines

OBJECTIVE

The mechanism underlying exercise intolerance in chronic heart failure is still unclear. An increased concentration of inflammatory cytokines could be detected in the serum of patients with chronic heart failure (CHF) exhibiting a correlation with the severity of the disease. The variety of molecular alterations triggered by these cytokines in the skeletal muscle is almost unknown. The study was designed to analyze the differential gene expression in skeletal muscle myoblasts after stimulation with inflammatory cytokines.

METHODS

L6 rat skeletal muscle myoblasts were incubated for 24 h with a combination of IL-1beta/IFN-gamma and the differential gene expression profile was determined by a PCR-based subtractive hybridization method.

RESULTS

Out of 173 picked clones 141 different sequences could be identified. By comparison with Genebank, the identity of 73 genes (51.7%) could be confirmed, whereas the rest did not show a homology to any known gene. Some of the identified genes are known to be altered in patients with CHF.

CONCLUSION

In summary, the results of this study provide information about changes in gene expression after exposure of skeletal muscle cells to inflammatory cytokines. This information may yield a new gene pool, worthwhile to be analyzed in skeletal muscle of patients with chronic heart failure.

Pathogenesis of beta(2)-microglobulin amyloidosis: role of monocytes/macrophages

beta(2)-microglobulin (beta(2)M) amyloidosis (A beta(2)M) is a serious, often incapacitating complication for patients undergoing long-term hemodialysis. Amyloid deposits composed of beta(2)M fibrils as the major constituent protein are mainly localized in joints and periarticular bone and lead to chronic arthralgias, carpal tunnel syndrome, and eventually destructive arthropathy. Although recent histologic studies have shown the accumulation of monocytes/macrophages around amyloid deposits, the factor(s) causing their infiltration and pathologic involvement have yet to be fully elucidated. Immunohistochemical staining reveals that macrophages in tenosynovial tissues express CD13, CD14, CD33, HLA-DR, and CD68 antigens on their surfaces and express interleukin (IL)-1 beta, tumor necrosis factor (TNF)-alpha, and IL-6. Many of these cells also express LFA-1 (CD11a/CD18), Mac-1 (CD11b/CD18), and VLA-4 (CD49d/CD29) on their surfaces. AGE-modified beta(2)M enhances chemotaxis of monocytes and stimulates macrophages to release bone-resorbing cytokines, such as IL-1 beta, TNF-alpha and IL-6. Via a RAGE-mediated pathway, AGE-modified, but not unmodified beta(2)M, significantly delays constitutive apoptosis of human peripheral blood monocytes. Monocytes survival in an advanced glycation end product (AGE) beta(2)M-containing microenvironment is associated with their phenotypic alteration into macrophage-like cells that generate more reactive oxygen species and elaborate greater quantities of IL-1 beta and TNF-alpha. Thus through regulation of their survival and differentiation, AGE beta(2)M in amyloid deposits may be able to influence the presence and quantity of infiltrated monocytes, and hence their biologic effects.

Histological characteristics of sternoclavicular beta 2-microglobulin amyloidosis and clues for its histogenesis

BACKGROUND

The pathogenesis of beta 2-microglobulin amyloidosis (A beta 2m) has yet to be fully elucidated.

METHODS

We describe the distribution and extent of A beta 2m deposition and macrophagic infiltration in cartilage, capsule, and synovium of sternoclavicular joints obtained postmortem from 54 patients after 3 to 244 (median 46) months of dialysis. Twenty-four nonuremic patients served as a control group. The diagnosis of amyloidosis (A) rested on a positive Congo Red staining (typical birefringence) and that of A beta 2m on positive immunostaining of the A deposits with a monoclonal anti-beta 2m antibody. The size of A deposits was measured.

RESULTS

A beta 2m was detected in 32 (59%), and non-beta 2m amyloid (Anon beta 2m) was detected in an additional 8 (15%) of the 54 dialyzed patients. A beta 2m deposits were present in the cartilage of all A beta 2m (+) patients (100%). They were localized solely in the cartilage in 27% of the cases, either as a thin patchy layer or as a continuous thicker layer (identified as stage I). A beta 2m was additionally present in the capsule and/or synovium without macrophages in 27% of the cases (identified as stage II). The correlation between the size of cartilaginous deposits and dialysis duration (P = 0.02) as well as with the prevalence (P = 0.03) and size of capsular deposits (P = 0.02) suggests that stage II is a later stage of A deposition. Clusters of macrophages were detected around capsular and synovial amyloid deposits in 46% of the cases (identified as stage III). The longer duration of dialysis in those with stage III as well as the relationship between the size of the A beta 2m deposits and the prevalence of macrophagic infiltration suggests that stage III is the last stage of A beta 2m deposition. Marginal bone erosions were observed in 9 out of 12 patients with stage III deposits. Their size was correlated with that of cartilaginous deposits (P = 0.01). Among the 24 control patients, Anon beta 2m was detected in 12 patients (cartilage 100%, capsule 8%, synovium 30%).

CONCLUSIONS

The earliest stage of A beta 2m deposition occurs in the cartilage. A beta 2m subsequently extends to capsule and synovium. These two first stages do not require macrophage infiltration. Macrophages are eventually recruited around larger synovial or capsular deposits in the final stage. Marginal bone erosions develop in this late stage.