What the acute physician needs to know about Anti-NMDA receptor encephalitis: two case presentations.

These case reports look at two patients with anti-N-methyl-D-aspartate receptor (NMDAr) encephalitis presenting to the same acute medical unit within a month of each other. The following covers the characteristic signs, symptoms and timeline associated with this condition and discusses whether we should be sending CSF for anti-NMDAr antibody testing more readily.

Human monomethylarsonic acid (MMA(V)) reductase is a member of the glutathione-S-transferase superfamily.

The drinking of water containing large amounts of inorganic arsenic is a worldwide major public health problem because of arsenic carcinogenicity. Yet an understanding of the specific mechanism(s) of inorganic arsenic toxicity has been elusive. We have now partially purified the rate-limiting enzyme of inorganic arsenic metabolism, human liver MMA(V) reductase, using ion exchange, molecular exclusion, and hydroxyapatite chromatography. When SDS-beta-mercaptoethanol-PAGE was performed on the most purified fraction, seven protein bands were obtained. Each band was excised from the gel, sequenced by LC-MS/MS and identified according to the SWISS-PROT and TrEMBL Protein Sequence databases. Human liver MMA(V) reductase is 100% identical, over 92% of sequence that we analyzed, with the recently discovered human glutathione-S-transferase Omega class hGSTO 1-1. Recombinant human GSTO1-1 had MMA(V) reductase activity with K(m) and V(max) values comparable to those of human liver MMA(V) reductase. The partially purified human liver MMA(V) reductase had glutathione S-transferase (GST) activity. MMA(V) reductase activity was competitively inhibited by the GST substrate, 1-chloro 2,4-dinitrobenzene and also by the GST inhibitor, deoxycholate. Western blot analysis of the most purified human liver MMA(V) reductase showed one band when probed with hGSTO1-1 antiserum. We propose that MMA(V) reductase and hGSTO 1-1 are identical proteins.

Monomethylarsonic acid reductase and monomethylarsonous acid in hamster tissue.

The formation of monomethylarsonous acid (MMA(III)) by tissue homogenates of brain, bladder, spleen, liver, lung, heart, skin, kidney, or testis of male Golden Syrian hamsters was assessed using [(14)C]monomethylarsonic acid (MMA(V)) as the substrate for MMA(V) reductase. The mean +/- SEM of MMA(V) reductase specific activities (nanomoles of MMA(III) per milligram of protein per hour) were as follows: brain, 91.4 +/- 3.0; bladder, 61.8 +/- 3.7; spleen, 30.2 +/- 5.4; liver, 29.8 +/- 1.4; lung, 21.5 +/- 0.8; heart, 19.4 +/- 1.5; skin, 14.7 +/- 1.6; kidney, 10.6 +/- 0.4; and testis, 9.8 +/- 0.6. The concentrations of MMA(III) in male Golden Syrian hamster livers were determined 15 h after administration of a single intraperitoneal dose of 145 microCi of [(73)As]arsenate (2 mg of As/kg of body weight). Trivalent arsenic species (arsenite, MMA(III), and dimethylarsinous acid, DMA(III)) were extracted from liver homogenates using carbon tetrachloride (CCl(4)) and 20 mM diethylammonium salt of diethyldithiocarbamic acid (DDDC). Pentavalent arsenicals (arsenate, MMA(V), and dimethylarsinic acid, DMA(V)) remained in the aqueous phase. The organic and the aqueous phases then were analyzed by HPLC. Metabolites of inorganic arsenate present in hamster liver after 15 h were observed in the following concentrations (nanograms per gram of liver +/- SEM): MMA(III), 38.5 +/- 2.9; DMA(III), 49.9 +/- 10.2; arsenite, 35.5 +/- 3.0; arsenate, 118.2 +/- 8.7; MMA(V), 31.4 +/- 2.8; and DMA(V), 83.5 +/- 6.7. This first-time identification of MMA(III) and DMA(III) in liver after arsenate exposure indicates that the significance of arsenic species in mammalian tissue needs to be re-examined and re-evaluated with respect to their role in the toxicity and carcinogenicity of inorganic arsenic.

Occurrence of monomethylarsonous acid in urine of humans exposed to inorganic arsenic.

Monomethylarsonous acid (MMA(III)) has been detected for the first time in the urine of some humans exposed to inorganic arsenic in their drinking water. Our experiments have dealt with subjects in Romania who have been exposed to 2.8, 29, 84, or 161 microg of As/L in their drinking water. In the latter two groups, MMA(III) was 11 and 7% of the urinary arsenic while the monomethylarsonic acid (MMA(V)) was 14 and 13%, respectively. Of our 58 subjects, 17% had MMA(III) in their urine. MMA(III) was not found in urine of any members of the group with the lowest level of As exposure. If the lowest-level As exposure group is excluded, 23% of our subjects had MMA(III) in their urine. Our results indicate that (a) future studies concerning urinary arsenic profiles of arsenic-exposed humans must determine MMA(III) concentrations, (b) previous studies of urinary profiles dealing with humans exposed to arsenic need to be re-examined and re-evaluated, and (c) since MMA(III) is more toxic than inorganic arsenite, a re-examination is needed of the two hypotheses which hold that methylation is a detoxication process for inorganic arsenite and that inorganic arsenite is the major cause of the toxicity and carcinogenicity of inorganic arsenic.

DMPS-arsenic challenge test. II. Modulation of arsenic species, including monomethylarsonous acid (MMA(III)), excreted in human urine.

The administration of sodium 2,3-dimercapto-1-propane sulfonate (DMPS) to humans chronically exposed to inorganic arsenic in their drinking water resulted in the increased urinary excretion of arsenic, the appearance and identification of monomethylarsonous acid (MMA(III)) in their urine, and a large decrease in the concentration and percentage of urinary dimethylarsinic acid (DMA). This is the first time that MMA(III) has been detected in the urine. In vitro biochemical experiments were then designed and performed to understand the urinary appearance of MMA(III) and decrease of DMA. The DMPS-MMA(III) complex was not active as a substrate for the MMA(III) methyltransferase. The experimental results support the hypothesis that DMPS competes with endogenous ligands for MMA(III), forming a DMPS-MMA complex that is readily excreted in the urine and points out the need for studying the biochemical toxicology of MMA(III). It should be emphasized that MMA(III) was excreted in the urine only after DMPS administration. The results of these studies raise many questions about the potential central role of MMA(III) in the toxicity of inorganic arsenic and to the potential involvement of MMA(III) in the little-understood etiology of hyperkeratosis, hyperpigmentation, and cancer that can result from chronic inorganic arsenic exposure.

Diversity of inorganic arsenite biotransformation.

Biotransformation of inorganic arsenic in mammals is catalyzed by three serial enzyme activities: arsenate reductase, arsenite methyltransferase, and monomethylarsonate methyltransferase. Our laboratory has purified and characterized these enzymes in order to understand the mechanisms and elucidate the variations of the responses to arsenate/arsenite challenge. Our results indicate a marked deficiency and diversity of these enzyme activities in various animal species.

Enzymatic methylation of arsenic compounds. V. Arsenite methyltransferase activity in tissues of mice.

With the development of a rapid assay for arsenite methyltransferase (Zakharyan et al., 1995), the specific activity of this critical enzyme for arsenite biotransformation was determined by incubating liver, testis, kidney, or lung cytosol of male B6C3F1 mice with sodium arsenite and S-[methyl-3H]adenosyl-L-methionine and measuring the formation of [methyl-3H]monomethylarsonate. The mean arsenite methyltransferase specific activities (U/mg +/- SEM) measured in these organs were liver, 0.40 +/- 0.06; testis, 1.45 +/- 0.08; kidney, 0.70 +/- 0.06; and lung, 0.22 +/- 0.01. Heretofore, the enzymatic methylation of arsenite has been regarded primarily as a hepatic function. The arsenite methyltransferase specific activity of the testis was 3.6 times greater than that of the liver (p < 0.01) and the specific activity of the kidney was 1.8 times greater than that of the liver (p < 0.05). Additionally, when mice were given arsenate in drinking water for 32 or 91 days at concentrations of 25 or 2500 micrograms As/L, the arsenite methyltransferase activities of liver, testis, kidney, and lung cytosol were not significantly increased in animals receiving either dose of arsenic for either 32 or 91 days compared to controls. No evidence for the induction of arsenite methyltransferase was found under these experimental conditions.

Enzymatic methylation of arsenic compounds: IV. In vitro and in vivo deficiency of the methylation of arsenite and monomethylarsonic acid in the guinea pig.

Using an in vitro assay which measures the transfer of a radiolabeled methyl moiety of S-[methyl-3H]adenosylmethionine ([3H]SAM) to arsenite or monomethylarsonate (MMA) to yield [methyl-3H]MMA or [methyl-3H]dimethylarsinate (DMA) respectively, guinea pig liver cytosol was found to be deficient in the enzyme activities which methylate these substrates. Moreover, when guinea pigs were given a single intraperitoneal dose of [73As]arsenate (400 micrograms/kg body weight, 25 microCi/kg body weight), very little or no methylated arsenic species were detected in the urine after cation exchange chromatography. The urine collected 0-12 h after arsenate injection contained 98% inorganic arsenic and less than 1% DMA. No MMA was detected in the 0-12 h urine. Urine collected 12-24 h after injection contained approximately 93% inorganic arsenic, 2% MMA and 3% DMA in five of the six animals studied. However, in the 12-24 h urine of one guinea pig, 17% of the radioactivity was DMA, 80% was inorganic arsenic and 3% was MMA. The guinea pig, like the marmoset and tamarin monkeys and unlike most other animals studied thus far, appears to be deficient as far as the enzyme activities that methylate inorganic arsenite. The results of these experiments suggest that there may be a genetic polymorphism associated with the enzymes that methylate inorganic arsenite.