Cortically evoked motor action potential in spinal cord injury research

Somatosensory evoked potentials (SEPs) have been used extensively in the neurophysiological assessment of spinal cord integrity. However, SEPs mainly reflect the function of the dorsal column. In an effort to find a reliable method of assessing the integrity of the motor tracts for experimental purposes, we studied cortically evoked motor action potentials (CEMAPs). Twenty white rats used were anesthetized with ketamine, and extradural cortical stimulation was carried out through a parasagittal craniectomy posterior to the coronal suture. A single stimulus of 325 mV for a duration of 0.1 to 0.5 ms was used to obtain a motor action potential from the contralateral lower extremity. Complete transsection of the spinal cord abolished the CEMAP. A progressive increase in pressure applied to the spinal cord with a progressive increase in duration produced loss of the CEMAP. The selective motor tract study made possible by cortical stimulation makes this a good technique for studying the motor tracts in experimental work.

Brainstem auditory evoked potentials in chronic renal failure and maintenance hemodialysis

Brainstem auditory evoked potentials (BAEPs) were recorded in 36 chronic uremic patients maintained on hemodialysis and in 10 normal controls. Both absolute response latencies and central transmission times were affected. There were transitory increases in interpeak latencies of I-II and III-V that were reversed by dialysis. A permanent increase in wave III-V interpeak latency was not reversed by dialysis. Wave II-III interpeak latency was unaffected.

The use of colonoscopy in the treatment of colonic volvulus: three cases and review of the literature

Four to 10% of cases of large bowel obstruction are caused by volvulus. Nonoperative therapy is the preferred initial treatment of patients with colonic volvulus who do not have signs of bowel strangulation because of the high mortality associated with emergency surgery. We report our experience with three cases and review the literature on the use of the colonoscope to treat colonic volvulus.

Organ specificity in the microsomal activation and toxicity of N-nitrosomethylbenzylamine in various species

The microsomal metabolism of the rat esophageal carcinogen N-nitrosomethylbenzylamine (NMBZA) at the methylene carbon atom to yield benzaldehyde was studied in various organs of a number of species to determine the role of metabolic activation in the carcinogenicity or toxicity of the nitrosamine. In the Sprague-Dawley rat, NMBZA was metabolized by microsomes from liver, lung, and esophageal mucosa. In the F344 rat and rabbit, metabolic activity was present in both liver and esophageal mucosa, the only tissues studied in these species. In contrast, in the Syrian hamster and BALB/cByJ mouse, NMBZA debenzylation was undetectable in the esophagus but occurred at relatively high rates in liver, lung, and kidney. The forestomach mucosa exhibited undetectable levels of activity in the Sprague-Dawley rat and BALB/cByJ mouse, although in the hamster, it was present at a very low level. Administration of a dose of NMBZA acutely toxic to the rat (18 mg/kg i.p.) resulted in significant cellular damage only to the rat esophageal mucosa, no other tissues examined in the rat, hamster, or mouse being affected. These observations, together with the available data on carcinogenicity of the nitrosamine in the rat and rabbit, suggest that in the esophagus, at least, metabolic activation of NMBZA is necessary to elicit its toxic and/or carcinogenic effect. However, NMBZA is also metabolized at a high rate in the liver of all species but is not toxic or carcinogenic in this tissue, suggesting that other factors besides metabolic activation must be involved in the resistance of hepatocytes to the effects of the nitrosamine. Microsomes prepared from human esophageal mucosa from six patients metabolized NMBZA at rates that were either undetectable or approximately 70 times lower than in the Sprague-Dawley rat.

Liposome-encapsulated amphotericin B for treatment of disseminated candidiasis in neutropenic mice

The relative efficacies of free amphotericin B (Amp B) and liposome-encapsulated Amp B (L-AmpB) in the treatment of established Candida albicans infection in mice rendered neutropenic with cyclophosphamide were studied. AmpB was entrapped in multilamellar liposomes composed of dimyristoyl phosphatidylcholine and dimyristoyl phosphatidylglycerol in a molar ratio of 7:3. Infected mice treated with single doses of 3 mg L-AmpB/kg of body weight had an increased survival time compared with those injected with either single (dose, 0.8 mg/kg) or multiple doses (dose, 0.8 mg/kg daily for five days) of free AmpB. When treatment was delayed beyond three days postinfection, neither single nor multiple doses of free AmpB resulted in increased survival, whereas treatment with single-dose L-AmpB (dose, 4 mg/kg) showed efficacy when delayed as much as four days postinfection. Five days postinfection only higher doses (dose, 5.6 mg-11.2 mg/kg) of L-AmpB improved survival time and the renal impairment present in the infected animals. These data provided a rational basis for using high-dose L-AmpB to treat fungal diseases in humans, particularly in neutropenic patients.

Acute renal failure following poisonous snakebite

This study describes acute renal failure (ARF) following snakebite in humans and the effects of viperide venoms on the renal structure and function in subhuman primates. ARF developed in 45 of 157 patients with a history of snakebite admitted to the hospitals of the Postgraduate Medical Institute, Chandigarh, India. They were studied clinically, hematologically, and in 35 cases, for renal histopathology. All 45 were treated with antibiotics, and 8 received anti-snake venom. Ten cases had bilateral renal cortical necrosis (BRCN), eight of whom died; less severe acute tubular lesions (ATL) occurred in 23 patients, four of whom died (P less than .001). Sepsis was significantly more common with BRCN than ATL (P less than .05). No statistical difference was found between these groups in bleeding incidence, disseminated intravascular coagulation (DIC), hemolysis, or hypotension. Monkeys given lethal doses of viperide venom developed hypotensive shock, DIC, and hemolysis, with significantly reduced serum complement, and died within 24 hours. However, no renal functional changes or lesions were found. Monkeys given sublethal doses of viperide venom showed a significant increase in serum creatinine levels after 48 hours, and renal lesions were observed in a majority of animals. In conclusion, ARF in snakebite victims appears to be multifactorial in origin. Although hypotension, hemolysis, and DIC are likely to be important pathogenetic factors, a direct cytotoxic effect of the venom on the kidney in producing ARF cannot be excluded.

Induction and suppression of N-nitrosomethylbenzylamine activation by microsomes from rat liver and esophagus

Male Sprague-Dawley rats were pretreated with various chemicals to determine their effects on the microsomal activation of the esophageal carcinogen N-nitrosomethylbenzylamine [( NMBzA ) CAS: 937-40-6; N-methyl-N- nitrosobenzylamine ] in the rat esophagus and, for comparative purposes, in the rat liver. When rats were pretreated with NMBzA , little change in hepatic NMBzA - debenzylase activity was observed. In contrast, NMBzA metabolism in the esophagus was significantly (60-65%) reduced. Similarly, pretreatment of rats with disulfiram [CAS: 97-77-8; bis( diethylthiocarbamoyl )disulfide] caused a 40% decrease in esophageal metabolism, but it had no significant effect in the liver. Pretreatments with the methylenedioxybenzenes safrole [CAS: 94-59-7; 4-allyl-1,2-(methylenedioxy)benzene], isosafrole [CAS: 120-58-1; 1,2-(methylenedioxy)-4-propenylbenzene], and dihydrosafrole (CAS: 94-58-6; 1,2-(methylenedioxy)-4- propylbenzene ) caused a marked induction (twofold to fivefold) of the hepatic metabolism of NMBzA , but again esophageal metabolism was suppressed. The results indicate that esophageal metabolism of NMBzA is either unchanged or suppressed by the various chemical pretreatments, but hepatic metabolism of the nitrosamine is induced by the methylenedioxybenzenes .

Liposomal amphotericin B is toxic to fungal cells but not to mammalian cells

Amphotericin B is an efficacious but extremely toxic anti fungal drug. Recently it has been shown that the incorporation of Amphotericin B in multilamellar liposomes results in a marked reduction in drug toxicity in mice with no loss of anti fungal potency. Until now, the mechanistic basis of the enhanced therapeutic index of liposomal Amphotericin B has been unclear. In this report, however, we show that the in vivo effects can be mimicked in vitro where free but not liposomal Amphotericin B causes lysis of erythrocytes while both free and liposomal drug kill fungal cells. These results suggest that the markedly improved therapeutic index of liposomal Amphotericin B is largely due to a fundamental alteration in the ability of the drug to interact with mammalian cell membranes rather than to alterations in pharmacokinetics or drug distribution.

In vitro antifungal activities of amphotericin B and liposome-encapsulated amphotericin B

The in vitro activities of liposome-encapsulated amphotericin B and free amphotericin B against Candida albicans 336 were comparable. Amphotericin B concentrations 12-fold and greater than 50-fold higher were required to kill the same organism when cholesterol and ergosterol were incorporated into the liposomes. The addition of cholesterol to liposomes caused a significant increase in the minimal fungicidal concentration of amphotericin B in 7 of 19 other yeast strains tested, whereas ergosterol caused an increase in 18 of the 19 strains.

Prophylaxis of Candida albicans infection in neutropenic mice with liposome-encapsulated amphotericin B

The efficacy of liposome-encapsulated amphotericin B in the prophylaxis of disseminated Candida albicans infections in neutropenic mice was studied. The administration of liposome-encapsulated amphotericin B was associated with protection against infection with C. albicans when used at doses of greater than or equal to 2 mg of amphotericin B per kg of body weight. Neither empty liposomes nor free amphotericin B showed prophylactic efficacy.

Altered tissue distribution of amphotericin B by liposomal encapsulation: comparison of normal mice to mice infected with Candida albicans

Recently, it has been observed that encapsulation of Amphotericin B (Amp-B) into multilamellar vesicles (liposomes) decreases the toxicity associated with the administration of Amp-B, while maintaining its antifungal efficacy. In this study, the tissue concentrations of Amp-B in normal mice and in mice infected with Candida albicans were examined. Amp-B concentrations in various tissues were quantitated by high-performance liquid chromatography. Liposomal encapsulation improved the delivery of Amp-B to the liver, spleen, lung, and kidney in both normal and infected mice. Furthermore, after injection of the encapsulated drug, Amp-B was demonstrable in brain tissue of infected animals at potentially therapeutic concentrations. None was demonstrable in the brains of normal animals or animals injected with free Amp-B. The results suggest that capillary endothelial damage and phagocytic cell uptake may contribute to an enhanced liposome delivery of Amp-B to those organs most frequently infected with fungi.

Clinical pharmacology of 99mTc-labeled liposomes in patients with cancer

The pharmacokinetics, organ distribution, and 24-hr urinary excretion of negatively charged 99mTc-labeled multilamellar liposomes, composed of dimyristoylphosphatidylcholine and dimyristoylphosphatidylglycerol in a 7:3 molar ratio, were studied in seven patients with cancer. The radiolabeled liposomes were administered i.v. in three doses: 150 mg/sq m of body surface area; 300 mg/sq m; and 450 mg/sq m of lipid. The dose of 99mTc was 4.8 to 7.6 mCi per patient. The plasma disappearance curve was biphasic (half-life alpha = 5.53 min, half-life beta = 289 min), suggesting a two-compartmental model of distribution. The calculated volume of distribution indicated considerable tissue retention of liposomes. This was confirmed by body imaging. Twenty-four hr after injection, liposomes were localized in organs rich in reticuloendothelial cells, i.e., liver [44.5 +/- 9.1% (S.E.)], spleen [25.5 +/- 7.7%], lung [14.5 +/- 4.9%], and bone marrow. Although the hepatic uptake accounted for more than 40% of the total uptake, the spleen retained liposomes at a higher density. Cumulative urinary excretion of radioactivity was 13.4 +/- 1.5% over 24 hr. Liposome administration was safe and devoid of any adverse side effects. The results provide a basis for the use of liposomes as potential target-specific and safe drug carriers in the treatment of pathological conditions that involve organs rich in reticuloendothelial cells.

Disseminated Mycobacterium chelonei infection following cadaveric renal transplantation: favorable response to cefoxitin

This article describes a case of disseminated Mycobacterium chelonei infection in a renal transplant recipient. This patient, who underwent thoracic duct drainage prior to cadaveric renal transplantation, developed M chelonei bacteremia and numerous subcutaneous nodules a few weeks after transplantation. The M chelonei initially responded to amikacin and tetracycline. Because of side effects and bacterial resistance, however, these drugs had to be discontinued. Subsequent treatment with cefoxitin led to reduction in size of subcutaneous nodules, but control of the infection was not achieved until an intravascular nidus of infection at the anastomotic site of an arteriovenous fistula was removed.

Treatment and prophylaxis of disseminated infection due to Candida albicans in mice with liposome-encapsulated amphotericin B

The toxicology of liposome-encapsulated amphotericin B in mice and its efficacy in the treatment and prophylaxis of systemic candidiasis in these animals were studied. The toxicology studies indicated that the maximal tolerated dose of free amphotericin B was 0.8 mg/kg of body weight and the 50% lethal dose (LD50) was reached at 1.2 mg/kg, while neither the maximal tolerated dose nor the LD50 for the liposomal amphotericin B was reached at a dose of 12 mg/kg. No abnormalities in blood chemistry or histology were observed in the animals injected with encapsulated amphotericin B, while the administration of free amphotericin B was associated with nephrocalcinosis and renal parenchymal edema. The encapsulated drug was as effective as the free drug when used in similar concentrations, while the animals treated with higher concentrations of liposomal amphotericin B (4 mg/kg) had a longer survival time. Thus, an improved therapeutic index resulted by encapsulating amphotericin B in liposomes.