Direct effects of diphenylhydantoin (phenytoin) on the ion-transporting ATPases of cultured osteoblast-like cells

The effect of phenytoin on parathyroid hormone stimulated cAMP activity in cultured murine osteoblasts

Cells were isolated by sequential collagenase digestion from the parietal segments of one day old mice (Swiss albino BNL strain) and characterized for osteoblast parameters by alkaline phosphatase histochemistry and bovine parathyroid hormone (bPTH-(1-34] induced cAMP activity (protein binding assay). Phenytoin (DPH) reduced PTH stimulated cAMP activity nearly 3-fold in the presence and nearly 1.5-fold in the absence of added calcium. In the absence of PTH, DPH exerted no significant effect. Bay-K-8644, a calcium channel activator, appeared to approximate the PTH stimulation of cAMP activity, even in the presence of DPH. This study demonstrates that DPH has a direct effect on PTH stimulated cAMP activity in cultured murine osteoblasts.

The effects of phenytoin on calcium uptake in osteoblastic cells

The effects of phenytoin (diphenylhydantoin, DPH) on calcium uptake in osteoblastic cells were studied to elucidate the potential mechanism of action of this antiepileptic drug on bone metabolism. Preincubation of the human osteoblastic osteosarcomal cell line, SaOS-2, and normal rat osteoblastic cells with DPH decreased basal calcium uptake. This inhibition occurred at DPH doses from 0.1 to 50 micrograms/ml. Parathyroid hormone (PTH) and prostaglandin E2 (PGE2) increased calcium uptake in the SaOS-2 cell line. Following preincubation with DPH, calcium uptake in cells treated with PTH or PGE2 did not exceed control levels. However, significant increases in the PTH- or PGE2-treated + DPH-pretreated cells compared to DPH pretreatment alone were still observed. These studies indicate that DPH induces decreases in osteoblastic calcium influx and they add further information on the possible mode of action of this drug on bone.

Effect of prolonged anticonvulsant medication in epileptic patients: serum lipids, vitamins B6, B12, and folic acid, proteins, and fine structure of liver

Twenty-seven epileptic patients, most from low socioeconomic groups and aged 15-54 years, were studied for effects of prolonged anticonvulsant medication. They had received the usual doses of phenobarbitone and diphenylhydantoin (PHT) regularly for 3-32 years, with control of seizures, and had not taken any B-vitamins in the year before investigation. Besides reduced serum and cerebrospinal fluid (CSF) folate levels, significantly increased levels of total vitamin B6 in CSF and serum and of vitamin B12 in serum were found in patients as compared with normal healthy subjects. The bone marrow was normoblastic, and significant elevation of serum triglycerides and/or cholesterol was observed in patients. The total protein level was only slightly reduced as compared with that of controls, but there was significant increase in beta-lipoprotein fraction on gel electrophoresis. Plasma proteins concerned with vitamins and lipid transport showed no remarkable change, and no abnormal protein was detected. Although there was no clinical hepatic involvement, liver biopsy performed in 9 of 27 patients revealed fine structural changes in hepatocytes suggestive of varying degrees of drug-induced changes. A ramifying network of short, smooth, endoplasmic cisternae with depleted rough endoplasmic reticulum (RER), distended sinusoids with Kupffer cells, dark shrunken hepatocytes with reduced mitochondria, and increased lipofuscin were observed. This suggested an adaptive response of the liver, a reversible change, possibly related to the increased serum lipids in the same patients.

Effect of phenytoin on rat bone resorption in vitro

Effects of phenytoin (DPH) on parathyroid hormone (PTH)- and 1,25-dihydroxyvitamin D3(1,25DHCC)-mediated bone resorption in bone organ culture were evaluated: it markedly inhibited the actions of both. However, PTH tended to overcome the initial effects of DPH, whereas bone resorption due to 1,25DHCC remained depressed as if DPH treatment had continued. Thus DPH-induced bone abnormalities may involve a greater direct effect on 1,25DHCC regulation of bone homeostasis than on PTH.