Rituximab improves outcomes for persons with lymphoproliferative disorders and is

Cholesterol is eliminated from neurons by oxidization, which generates oxysterols. Cholesterol oxidation is mediated by the enzymes cholesterol 24-hydroxylase (CYP46A1) and cholesterol 27-hydroxylase (CYP27A1). Immunocytochemical studies show that CYP46A1 and CYP27A1 are expressed in neurons and some astrocytes in the normal brain, and CYP27A1 is present in oligodendrocytes. In Alzheimer's disease (AD), CYP46A1 shows prominent expression in astrocytes and around amyloid plaques, whereas CYP27A1 expression decreases in neurons and is not apparent around amyloid plaques but increases in oligodendrocytes. Although previous studies have examined the effects of synthetic oxysterols on the processing of amyloid precursor protein (APP), the actions of the naturally occurring oxysterols have yet to be examined. To understand the role of cholesterol oxidation in AD, we compared the effects of 24(S)-and 27-hydroxycholesterol on the processing of APP and analyzed the cell-specific expression patterns of the two cholesterol hydroxylases in the human brain. Both oxysterols inhibited production of A␤ in neurons, but 24(S)-hydroxycholesterol was ϳ1000-fold more potent than 27-hydroxycholesterol. The IC 50 of 24(S)-hydroxycholesterol for inhibiting A␤ secretion was ϳ1 nM. Both oxysterols induced ABCA1 expression with IC 50 values similar to that for inhibition of A␤ secretion, suggesting the involvement of liver X receptor. Oxysterols also inhibited protein kinase C activity and APP secretion following stimulation of protein kinase C. The selective expression of CYP46A1 around neuritic plaques and the potent inhibition of APP processing in neurons by 24(S)-hydroxycholesterol suggests that CYP46A1 affects the pathophysiology of AD and provides insight into how polymorphisms in the CYP46A1 gene might influence the pathophysiology of this prevalent disease.

The Presenilins are part of the ␥-secretase complex that is involved in the regulated intramembrane proteolysis of amyloid precursor protein and other type I integral membrane proteins. Nicastrin, Pen-2, and Aph1 are the other proteins of this complex. The Presenilins probably contribute the catalytic activity to the protease complex. However, several investigators reported normal A␤-peptide generation in cells expressing Presenilins mutated at the putative catalytic site residue Asp-257, contradicting this hypothesis. Because endogenously expressed wild type Presenilin could contribute to residual ␥-secretase activity in these experiments, we have reinvestigated the problem by expressing mutated Presenilins in a Presenilin-negative cell line. We confirm that Presenilins with mutated Asp residues are catalytically inactive. Unexpectedly, these mutated Presenilins are still partially processed into amino-and carboxyl-terminal fragments by a "Presenilinase"-like activity. They are also able to rescue Pen-2 expression and Nicastrin glycosylation in Presenilin-negative cells and become incorporated into large ϳ440-kDa complexes as assessed by blue native gel electrophoresis. Our study demonstrates that the catalytic activity of Presenilin and its other functions in the generation, stabilization, and transport of the ␥-secretase complex can be separated and extends the concept that Presenilins are multifunctional proteins.

Waldenstrom's macroglobulinemia (WM) is a chronic lymphoproliferative disorder within the spectrum of lymphoplasmacytic lymphoma characterized by proliferation of plasma cells, small lymphocytes, and plasmacytoid lymphocytes. Central nervous system involvement is very rare (Bing-Neel [BN] syndrome). We present the case of a 62-year-old woman previously diagnosed with WM who presented with Bing-Neel syndrome and review the published literature which consists of only case reports. We performed a Medline search using the terms "Waldenstrom's macroglobulinemia and central nervous system" and "Bing-Neel" collecting data on presentation, evaluation, treatment, and outcome and summarizing these findings in the largest pooled series to date. Central nervous system manifestations are localization related. Serum laboratory testing reflects systemic disease. Cerebrospinal fluid analysis may show lymphocytic pleocytosis, elevated protein, and IgM kappa or lambda light chain restriction; cytology results are variable. Imaging is frequently abnormal. Biopsy confirms the diagnosis. Treatment data are limited, but responses are seen with radiation and/or chemotherapy. BN syndrome is a very rare complication of WM that should be considered in patients with neurologic symptoms and a history of WM. Treatment should be initiated as responses do occur that may improve quality of life and extend it when limited or no active systemic disease is present.