Enzootic hepatitis A infection in cynomolgus monkeys (Macaca fascicularis).

During a toxicology study in cynomolgus (long-tailed or crab-eating) monkeys (Macaca fascicularis), a randomly distributed incidence of significantly increased hepatic enzyme activity was observed. Premedication hepatic enzyme activity in all monkeys of this study was normal, but increased alanine aminotransferase (ALT) activity was found in 4 of the 24 animals 2 weeks after initiation of the study and in 10 of 24 at 4 weeks. A drug-related effect was considered unlikely initially because the increases were not doserelated, and a 3-year review of 655 cynomolgus monkeys revealed a 15-20% incidence of increased hepatic enzyme activity. Good correlation was subsequently established between increased hepatic enzyme activity, active hepatitis A virus (HAV) infection, and histomorphologic confirmation of hepatitis (chronic periportal inflammation). Follow-up viral serodiagnostic screening of resident macaques revealed an overall incidence of anti-HAV IgG in 80% (155/193) of cynomolgus and in 70% (14/20) of rhesus monkeys. Serial screening demonstrated that several initially negative monkeys became seropositive for anti-HAV IgG, and a few acquired active infection (anti-HAV IgM). Among newly acquired cynomolgus monkeys, 2.5% (2/80) had an acute HAV infection, and 35% (28/80) eventually tested positive for anti-HAV IgG while quarantined in the primate facility. The characterization of an enzootic HAV infection in incoming monkeys posed a significant risk for the primate colony and handlers. Rigorous sanitation, isolation, and quarantine procedures, including personnel training and additional protective clothing for personnel working in the primate colony, reduced tho potential for transmission and arrested the outbreak. Experimenters should be cautious in ascribing toxicity to a test article based solely on increased hepatic enzyme activity associated with chronic periportal inflammation.

Tissue response in dogs to dense hydroxylapatite implantation in the femur.

Six and eight years after the implantation of both granular and solid ceramic hydroxylapatite forms in the femurs of beagle dogs, histologic examination demonstrated that the implants were totally encased in dense mature bone. The endosteal and periosteal surfaces appeared normal, and no resorption of the solid implants was observed. However, at six years, a few granules located at the periosteal surface showed interdigitation of connective tissue stalks, with large multinucleated cells at the interface with the implant. This phenomenon may represent some limited resorptive activity on the surfaces of these few isolated granules. Initially, radiographs showed exaggerated degrees of bone deposition on the endosteal surface under the solid implants (discs), as opposed to a less pronounced endosteal response to the implants of particulate material. In some cases, particularly with the disc implants, cracks were found in the ceramic material six years after implantation. These cracks, on staining, were found to be filled with amorphous material, suggesting an osseous matrix. The results of these long-term studies indicate that such hydroxylapatite implants in bone are highly biocompatible. Bone deposition and maturation on the implant surface resulted in a homogeneous bone/implant interface in which the host tissues appeared to respond to the implant as if it were normal bone.

Subarachnoid administration of iohexol in cynomolgus monkeys.

A non-ionic diagnostic medium, iohexol, was administered by subarachnoid injection to groups of six cynomolgus monkeys and compared with the vehicle, physiologically normal saline, and/or saline of equal osmolality to determine its potential for increasing total protein and leucocyte levels in cerebrospinal fluid. Also investigated was the effect of repeated spinal taps not subsequently followed by the intrathecal injection of test or control articles. In the monkey, unlike man, low-level leucocyte counts were consistently observed following initial withdrawal of spinal fluid. Elevated leucocyte and total protein levels were observed in the present investigations one day to a week after intrathecal injection of radiopaque, vehicle or saline solution. Total protein returned to normal levels earlier than did leucocyte counts. However, repeated needle puncture alone was found to be sufficient to cause an elevation of leucocytes 3 to 4 times the baseline level, while inflammatory effects were observed histologically only when autopsy was performed soon after the final spinal tap.

Evaluation of hydroxylapatite root implants in baboons.

To determine if there is a need for close conformation of a hydroxylapatite implant to the root socket for successful prevention of alveolar ridge resorption after tooth extraction, second premolars and lateral incisors of six mature baboons were extracted bilaterally, and custom-fitted root replicas or half-length, plug-shaped forms of hydroxylapatite were implanted in the fresh sockets. Results showed that precise fit, as achieved by a custom-fitted implant, was not necessary for success. All implants were completely accepted, with evidence of new bone formation continuing for up to six months, the duration of the study. No resorption of the alveolar ridge was observed by gross or microscopic examination.

Long-term study of hydroxylapatite implants in canine alveolar bone.

Routine light and fluorescence microscopic examination of hydroxylapatite root implants showed that, in general, bone formed above the original superior surface of the ceramic implant on the lingual crest. In the 40 experimental specimens recovered, 30% also showed new bone completely covering the implant, proceeding from the buccal to the lingual area. Sixty per cent of the specimens that exhibited complete osseous covering were the more posteriorly placed implants from the fourth premolar and the first molar areas. Thirty-three per cent of the specimens exhibited bone formation at or over the superior buccal margin of the implant.

Comparative nephrotoxicity of hydroxygentamicin and other aminoglycosides in rats.

The nephrotoxicity of hydroxygentamicin and amikacin was examined in young adult Fischer 344 rats. Serum creatinine (SCr) and urea nitrogen (BUN) levels were not significantly affected following sc injection of 80 or 160 mg/kg/day of hydroxygentamicin for 15 days. However, 250 mg/kg of amikacin produced significant increases in both parameters and in kidney/body weight ratios. The ratios were also significantly increased after 80 or 160 mg/kg of hydroxygentamicin, but kidneys of rats receiving amikacin were considerably heavier than those of rats treated with hydroxygentamicin. The antibacterial potency of 250 mg/kg of amikacin is comparable to that of 100 mg/kg of hydroxygentamicin. Additional studies, directly comparing hydroxygentamicin, a mutational biosynthetic, with gentamicin or netilmicin, all at 40, 80, and 160 mg base/kg, and incorporating renal function parameters as well as SCr, BUN, organ weight, tissue concentration, and kidney histopathology, revealed a characteristic pattern typical of aminoglycoside nephrotoxicity in mature adult male rats. In most parameters, values in rats given hydroxygentamicin or netilmicin were normal and comparable to those in controls, but kidney/body weight ratios were significantly increased at high doses. However, kidneys of rats medicated with gentamicin at comparable doses were considerably heavier than those of hydroxygentamicin-treated rats. Significant nephrotoxicity also was seen in rats given low doses of gentamicin or netilmicin. Eosinophilic granulation and vacuolization of renal proximal tubular epithelium, interstitial inflammation, and tubular dilation were observed microscopically with all three drugs in the following descending order of severity: gentamicin greater than netilmicin greater than hydroxygentamicin. The effects on proximal tubular epithelial cells following treatment with amikacin, netilmicin, or hydroxygentamicin correlated reasonably well with renal drug concentrations, but drug concentrations of gentamicin, which produced the most extensive kidney injury, were lower than those of the other three aminoglycosides. Elevated SCr or BUN were indicative of the presence of nephrosis, but early stages of tubular epithelial degeneration were not predicted by increases in BUN or SCr. Although minimal or mild nephrosis was seldom predicted by polyuria, proteinuria, or changes in osmolality, effects observed in renal function parameters usually correlated well with renal histopathology. However, a decrease in osmolality correlated best with enlarged kidneys and changes in renal morphology.

Histologic observation of soft tissue responses to implanted, multifaceted particles and discs of hydroxylapatite.

The effects on soft tissue of short- and long-term implants of ceramic hydroxylapatite (durapatite) are reported. In rats, after one week and one, six, and 12 months of subcutaneous implantation of hydroxylapatite in multifaceted particle and disc form, neither particles nor discs had resulted in any microscopically remarkable inflammation. In beagle dogs, after subcutaneous implantation of hydroxylapatite as multifaceted particles and as discs for seven and 24 days, nine months, and two and six years, no implant migration was observed. Encapsulation of particles and discs of increasing thickness was seen throughout the six years of observation. Except for a few isolated macrophages seen within the connective tissue stroma at seven and 24 days, no evidence of inflammation was found. In tissue sections taken at six months from beagle dogs in which multifaceted particles had been placed subperiosteally beneath the gingiva, dense connective tissue was observed adjacent to and surrounding the individual particles. These results show that hydroxylapatite implanted subcutaneously in rats and dogs produces little or no inflammatory response and is compatible with tissue irrespective of the shape of the implant.

The ototoxicity of hydroxygentamicin, a new aminoglycoside antibiotic, in guinea pigs.

The comparative ototoxicity of hydroxygentamicin (Win 42,122-2), a new aminoglycosidic antibiotic, gentamicin and kanamycin was evaluated in guinea pigs by assessment of the Preyer (pinna) reflex response to pure tone frequencies ranging from 2.5 to 20.0 KHz, and by histologic examination of surface preparations of the organ of Corti. Daily subcutaneous administration of 80.0 mg/kg of gentamicin or 240.0 mg/kg of kanamycin to groups of six guinea pigs for 18 to 45 days resulted in loss of the Preyer reflex in all animals. The Preyer reflex was retained in 5 of 6 guinea pigs given 80.0 mg/kg/day of hydroxygentamicin for 77 days and in 6 of 6 guinea pigs given 160.0 mg/kg/day for the same period. Microscopic examination of cochleas from guinea pigs given gentamicin or kanamycin revealed extensive outer and inner hair cell loss in all animals. Cytocochleograms of 5 of 6 guinea pigs medicated with 160.0 mg/kg of hydroxygentamicin were comparable to those of the controls. In the sixth guinea pig there was a localized lesion involving all three rows of outer hair cells and some inner hair cells in the second turn. The results of this study indicated that hydroxygentamicin may be tolerated better than gentamicin in the guinea pig and therefore warrants further development as a new and less toxic aminoglycosidic antibiotic.

Activity of quinfamide against natural infections of Entamoeba criceti in hamsters: a new potent agent for intestinal amoebiasis.

A novel tetrahydroquinolinyl ester, quinfamide, administered orally in multiple doses for 3 days had an ED50 of 0.25 mg/kg/day (total dose 0.75 mg/kg) for eradicating Entamoeba criceti in hamsters in several tests. It was significantly more active by direct comparison than 3 commercially available amoebicides and at least as active as 2 other esters of the parent compound, 1-(dichloroacety)-1,2,3,4-tetrahydro-6-quinolinol. After administration of a single dose, ED50 calculations for quinfamide averaged 0.9 mg/kg. Quinfamide was considerably more active than the other tetrahydroquinolinols, diloxanide furoate and teclozan, and it was approximately 1.5 times more active than etofamide; a statistical significance between the latter 2 drugs could be demonstrated in one of 4 tests. Administered prophylactically, quinfamide was shown to protect hamsters from re-infection with E. criceti. It also inhibited propagation of E. histolytica in vitro at a concentration of 20 microgram/ml. No adverse effects were noted in rodents after a single dose as high as 10 g/kg. Daily administration to monkeys of doses up to 500 mg/kg for as long as 37 days produced no pharmacological aberrations during or after medication; haematological studies and urine analyses were normal and no gross or microscopical tissue changes attributable to quinfamide were observed. No toxicity was revealed following acute (2 g/kg) and chronic (500 mg/kg/day x 31 days) administration of the drug to dogs and rats, respectively.

Tissue, cellular and subcellular events at a bone-ceramic hydroxylapatite interface.

A new polycrystalline form of hydroxylapatite, durapatite, has been examined as a cortical bone implant in dogs. Utilizing histological and electron optical techniques, it has been found that durapatite does not elicit a foreign body response and that all new bone surrounding the material is normally calcified. Bone was found to strongly adhere to durapatite and preliminary evidence suggests this bonding may be due to direct chemical attachment of bone to the material.