Reiko Inagi

Acute kidney injury (AKI) is characterized by mitochondrial dysfunction and activation of the innate immune system. The cyclic GMP-AMP synthase (cGAS) stimulator of interferon genes (STING) pathway detects cytosolic DNA and induces innate immunity. Here, we investigate the role of mitochondrial damage and subsequent activation of the cGAS-STING pathway using a genetically engineered animal model of cisplatin-induced AKI and cultured tubular cells. Cisplatin induced mtDNA leakage into the cytosol-probably through BCL-2-like protein 4 (BAX) pores in the mitochondrial outer membrane-in tubules, with subsequent activation of the cGAS-STING pathway, thereby triggering inflammation and AKI progression, which is improved in STING-deficient mice. STING knockdown in cultured tubular cells ameliorates inflammatory responses induced by cisplatin. mtDNA depletion and repletion studies support tubular inflammatory responses via the cGAS-STING signal activation by cytosolic mtDNA. Therefore, we conclude that mitochondrial dysfunction and subsequent activation of the mtDNA-cGAS-STING pathway is a critical regulator of kidney injury.

beta 2-Microglobulin (beta 2M) is a major constituent of amyloid fibrils in hemodialysis-associated amyloidosis, a complication of long-term hemodialysis patients. Amyloid fibril proteins were isolated from connective tissues forming carpal tunnels in hemodialysis patients with carpal tunnel syndrome. Two-dimensional polyacrylamide gel electrophoresis and Western blotting demonstrated that most of the beta 2M forming amyloid fibrils exhibited a more acidic pI value than normal beta 2M. This acidic beta 2M was also found in a small fraction of beta 2M in sera and urine from these patients, whereas heterogeneity was not observed in healthy individuals. We purified acidic and normal beta 2M from the urine of long-term hemodialysis patients and compared their physicochemical and immunochemical properties. Acidic beta 2M, but not normal beta 2M, was brown in color and fluoresced, both of which are characteristics of advanced glycation end products (AGEs) of the Maillard reaction. Immunochemical studies showed that acidic beta 2M reacted with anti-AGE antibody and also with an antibody against an Amadori product, an early product of the Maillard reaction, but normal beta 2M did not react with either antibody. Incubating normal beta 2M with glucose in vitro resulted in a shift to a more acidic pI, generation of fluorescence, and immunoreactivity to the anti-AGE antibody. The beta 2M forming amyloid fibrils also reacted with anti-AGE antibody. These data provided evidence that AGE-modified beta 2M is a dominant constituent of the amyloid deposits in hemodialysis-associated amyloidosis.

BACKGROUND: Drug-induced hypersensitivity syndrome is characterized by a severe, potentially fatal, multiorgan hypersensitivity reaction that usually appears after prolonged exposure to certain drugs. Its delayed onset and clinical resemblance to infectious mononucleosis suggest that underlying viral infections may trigger and activate the disease in susceptible individuals receiving these drugs. OBSERVATIONS: A 60-year-old woman developed an itchy, generalized, erythematous, confluent rash on the 39th day of receiving allopurinol therapy. Even after she discontinued treatment with allopurinol, her skin lesions progressed to severe blistering skin eruption. After the patient started oral prednisone therapy, her skin lesions resolved with desquamation. After complete resolution, rechallenge with allopurinol led to the development of an erythematous eruption. Titers of human herpesvirus 6 IgG antibodies dramatically increased with the development of the eruption. The results of a polymerase chain reaction and in situ hybridization indicated the presence of human herpesvirus 6 in the skin lesions, although human herpesvirus 7 DNA was detected only by in situ hybridization. CONCLUSION: Reactivation of human herpesvirus 6, possibly in concert with human herpesvirus 7, can contribute to the development of a severe drug-induced hypersensitivity syndrome.

beta 2-Microglobulin (beta 2M) is a major constituent of amyloid fibrils in hemodialysis-associated amyloidosis (HAA), a complication of long-term hemodialysis. However, the pathological role of beta 2M in HAA remains to be determined. Recently, we demonstrated that beta 2M in the amyloid deposits of HAA is modified with advanced glycation end products (AGEs) of the Maillard reaction. Since AGEs have been implicated in tissue damage associated with diabetic complications and aging, we investigated the possible involvement of AGE-modified beta 2M (AGE-beta 2M) in the pathogenesis of HAA. AGE- and normal-beta 2M were purified from urine of long-term hemodialysis patients. AGE-beta 2M enhanced directed migration (chemotaxis) and random cell migration (chemokinesis) of human monocytes in a dose-dependent manner. However, normal-beta 2M did not enhance any migratory activity. AGE-beta 2M, but not normal-beta 2M, increased the secretion of TNF-alpha and IL-1 beta from macrophages. Similar effects were also induced by in vitro prepared AGE-beta 2M (normal-beta 2M incubated with glucose in vitro for 30 d). When TNF-alpha or IL-1 beta was added to cultured human synovial cells in an amount equivalent to that secreted from macrophages in the presence of AGE-beta 2M, a significant increase in the synthesis of collagenase and morphological changes in cell shape were observed. These findings suggested that AGE-beta 2M, a major component in amyloid deposits, participates in the pathogenesis of HAA as foci where monocyte/macrophage accumulate and initiate an inflammatory response that leads to bone/joint destruction.

The implication of advanced glycation end products (AGE) in the pathogenesis of atherosclerosis and of diabetic and uremic complications has stimulated a search for AGE inhibitors. This study evaluates the AGE inhibitory potential of several well-tolerated hypotensive drugs. Olmesartan, an angiotensin II type 1 receptor (AIIR) antagonist, as well as temocaprilat, an angiotensin-converting enzyme (ACE) inhibitor, unlike nifedipine, a calcium blocker, inhibit in vitro the formation of two AGE, pentosidine and N(epsilon)-carboxymethyllysine (CML), during incubation of nonuremic diabetic, nondiabetic uremic, or diabetic uremic plasma or of BSA fortified with arabinose. This effect is shared by all tested AIIR antagonists and ACE inhibitors. On an equimolar basis, they are more efficient than aminoguanidine or pyridoxamine. Unlike the latter two compounds, they do not trap reactive carbonyl precursors for AGE, but impact on the production of reactive carbonyl precursors for AGE by chelating transition metals and inhibiting various oxidative steps, including carbon-centered and hydroxyl radicals, at both the pre- and post-Amadori steps. Their effect is paralleled by a lowered production of reactive carbonyl precursors. Finally, they do not bind pyridoxal, unlike aminoguanidine. Altogether, this study demonstrates for the first time that widely used hypotensive agents, AIIR antagonists and ACE inhibitors, significantly attenuate AGE production. This study provides a new framework for the assessment of families of AGE-lowering compounds according to their mechanisms of action.