Takahiko Hirata

Bio: Takahiko Hirata is an academic researcher from Johns Hopkins University. The author has contributed to research in topics: Hyperammonemia & Glutamine. The author has an hindex of 6, co-authored 7 publications receiving 429 citations.

Antiangiogenic Effects of the Quinoline-3-Carboxamide Linomide

Abstract: Linomide ( N -phenylmethyl-1,2-dihydro-4-hydroxyl-1-methyl-2-oxoquinoline-3-carboxamide) has a reproducible in vivo antitumor effect against a series of both androgen responsive and independent Dunning R-3327 rat prostatic cancers. This antitumor effect of linomide is host mediated. One possible mechanism involving the host is that linomide has antiangiogenic activity. An indication that linomide treatment has antiangiogenic activity is the observation that prostatic cancers from linomide treated rats have more focal necrosis than sized matched tumors from untreated rats. To directly test if linomide has antiangiogenic activity, a newly developed Matrigel based quantitative in vivo angiogenic assay was used. These experiments demonstrated that linomide has dose dependent, antiangiogenic activity in vivo in the rat. Additional studies demonstrated that due to its antiangiogenic activity, linomide treatment of rats bearing prostate cancers resulted in a more than 40% decrease in tumor blood flow. Blood flow to a variety of non-tumor bearing organs was not decreased suggesting that linomide selectively inhibits angiogenesis and does not induce loss of established blood vessels. Using as a model the response of human umbilical vein endothelial cells to linomide treatment in a variety of in vitro assays, linomide was demonstrated to have cytostatic but not cytotoxic effect on human umbilical vein endothelial cells at a medium concentration of ≥100 µg/ml. In addition, both endothelial cell chemotactic migration and invasion are steps in angiogenesis inhibited by linomide treatment.

Restoration of cerebrovascular CO2 responsivity by glutamine synthesis inhibition in hyperammonemic rats.

Abstract: Hyperammonemia increases brain glutamine levels, causes astrocytic swelling, and depresses cerebral blood flow (CBF) responsivity to CO2. Methionine sulfoximine (MSO) inhibition of glutamine synthetase activity, known to be enriched in astrocytes, prevents ammonia-induced increases in brain glutamine and water content. We tested the hypothesis that inhibition of glutamine accumulation restores CBF responsivity to CO2 during acute hyperammonemia. Pentobarbital-anesthetized rats treated with either vehicle or MSO (150 mg/kg i.p.) received a 6-hour intravenous infusion of either sodium or ammonium acetate. With subsequent induction of hypercapnia, CBF increased from 113 +/- 14 (mean +/- SEM) to 194 +/- 9 ml/min per 100 g in control rats but was unchanged from 107 +/- 13 to 79 +/- 10 ml/min per 100 g in hyperammonemic rats. Treatment with MSO in hyperammonemic rats restored the CBF response to hypercapnia (from 73 +/- 8 to 141 +/- 14 ml/min per 100 g). With induction of hypocapnia, CBF decreased from 114 +/- 11 to 88 +/- 11 ml/min per 100 g in control rats but increased from 112 +/- 13 to 142 +/- 19 ml/min per 100 g in hyperammonemic rats. Treatment with MSO in hyperammonemic rats did not fully restore the response to hypocapnia but prevented the paradoxical increase in CBF (from 80 +/- 8 to 80 +/- 8 ml/min per 100 g). In control rats, MSO did not affect CO2 responsivity. Treatment with MSO prevented ammonia-induced increases in intracranial pressure. Hyposmotic-induced increases in brain water content and intracranial pressure attenuated the CBF response to hypercapnia but, unlike hyperammonemia, did not attenuate the response to hypocapnia. In contrast to hypercapnia, vasodilation in response to arterial hypotension was intact in hyperammonemic rats. We conclude that the grossly abnormal CBF responsivity to CO2 alterations during hyperammonemia is linked to glutamine accumulation rather than ammonia per se. Cerebral edema secondary to glutamine accumulation may contribute in part to abnormal CBF responses, although other aspects of astrocyte dysfunction are likely to be important.

Impaired Pial Arteriolar Reactivity to Hypercapnia During Hyperammonemia Depends on Glutamine Synthesis

Abstract: Background and Purpose Acute hyperammonemia causes glutamine and water accumulation in astrocytes and loss of the cerebral blood flow response selectively to CO2. We tested whether extraparenchymal pial arterioles not subjected directly to mechanical compression by swollen astrocyte processes also lose hypercapnic reactivity and whether any such loss can be attenuated by inhibiting glutamine synthesis during hyperammonemia. Methods Pentobarbital-anesthetized rats were pretreated intravenously with either saline vehicle, methionine sulfoximine (0.83 mmol/kg), which inhibits glutamine synthetase and potentially γ-glutamylcysteine synthetase, or buthionine sulfoximine (4 mmol/kg), which inhibits γ-glutamylcysteine synthetase. Three hours after pretreatment, cohorts received an intravenous infusion of either sodium or ammonium acetate for 6 hours. Pial arteriolar diameter was measured through a closed cranial window, and blood flow was measured with radiolabeled microspheres during normocapnia and 10 minutes of hypercapnia. Results With sodium acetate infusion, pial arteriolar diameter increased during hypercapnia in groups pretreated with vehicle (23±3% [mean±SE]; n=6), methionine sulfoximine (37±11%; n=5), and buthionine sulfoximine (32±3%; n=5). With ammonium acetate infusion, pial arteriolar diameter increased only in the group pretreated with methionine sulfoximine (31±4%; n=8) but not in those pretreated with vehicle (−2±4%; n=8) or buthionine sulfoximine (4±4%; n=6). Methionine sulfoximine, but not buthionine sulfoximine, also prevented loss of the cerebral blood flow response to hypercapnia, an increase in cortical tissue water content, and an increase in pressure under the cranial window during normocapnia in hyperammonemic rats. In contrast to hypercapnia, hypoxemia increased arteriolar diameter 30±7% (n=5) during ammonium acetate infusion. Conclusions Loss of the blood flow response to hypercapnia during acute hyperammonemia is not due simply to swollen astrocyte processes passively impeding blood flow because extraparenchymal resistance arterioles also lose their reactivity selectively to hypercapnia. Lost reactivity depends on glutamine synthesis rather than on ammonium ions per se and may reflect indirect effects of astrocyte dysfunction associated with glutamine accumulation or possibly effects of glutamine on nitric oxide production.

Preserved hypocapnic pial arteriolar constriction during hyperammonemia by glutamine synthetase inhibition

Abstract: Ammonia intoxication, which results in astrocytic edema and glutamine accumulation, blocks cerebral vasodilation during hypercapnia but not during hypoxia. Ammonia’s effect on blood flow during hyp...

Seminars in Medicine of the Beth Israel Hospital, Boston. Clinical applications of research on angiogenesis.

Abstract: Angiogenesis is fundamental to reproduction, development, and repair. All these processes depend on the tightly regulated growth of blood vessels that can “turn on” and “turn off” within a brief period. When blood vessels grow unabated, angiogenesis becomes pathologic and sustains the progression of many neoplastic and non-neoplastic diseases. The realization that tumor growth requires new blood vessels and the identification of chemical factors that mediate angiogenesis have broadened our understanding of pathologic processes and opened new avenues to the diagnosis and treatment of these diseases. Tumor hypervascularity was initially thought to reflect inflammatory vasodilation of preexisting host vessels, a . . .

KAI1, a metastasis suppressor gene for prostate cancer on human chromosome 11p11.2.

Abstract: A gene from human chromosome 11p112 was isolated and was shown to suppress metastasis when introduced into rat AT61 prostate cancer cells Expression of this gene, designated KAI1, was reduced in human cell lines derived from metastatic prostate tumors KAI1 specifies a protein of 267 amino acids, with four hydrophobic and presumably transmembrane domains and one large extracellular hydrophilic domain with three potential N-glycosylation sites KAI1 is evolutionarily conserved, is expressed in many human tissues, and encodes a member of a structurally distinct family of leukocyte surface glycoproteins Decreased expression of this gene may be involved in the malignant progression of prostate and other cancers

Astrocyte dysfunction in neurological disorders: a molecular perspective

Abstract: Recent work on glial cell physiology has revealed that glial cells, and astrocytes in particular, are much more actively involved in brain information processing than previously thought. This finding has stimulated the view that the active brain should no longer be regarded solely as a network of neuronal contacts, but instead as a circuit of integrated, interactive neurons and glial cells. Consequently, glial cells could also have as yet unexpected roles in the diseased brain. An improved understanding of astrocyte biology and heterogeneity and the involvement of these cells in pathogenesis offers the potential for developing novel strategies to treat neurological disorders.

Combretastatin A-4, an agent that displays potent and selective toxicity toward tumor vasculature

Abstract: Selective induction of vascular damage within tumors represents an emerging approach to cancer treatment Histological studies have shown that several tubulin-binding agents can induce vascular damage within tumors but only at doses approximating the maximum tolerated dose, which has limited their clinical applicability In this study, we show that the combretastatin A-4 prodrug induces vascular shutdown within tumors at doses less than one-tenth of the maximum tolerated dose In vitro studies indicate that a short drug exposure results in profound long-term antiproliferative/cytotoxic effects against proliferating endothelial cells but not cells that are quiescent prior to and during drug exposure Vascular shutdown, within experimental and human breast cancer models in vivo following systemic drug administration, was demonstrated with a reduction in functional vascular volume of 93% at 6 h following drug administration and persisted over the next 12 h, with corresponding histology consistent with hemorrhagic necrosis resulting from vascular damage These actions against tumor vasculature and the broad therapeutic window demonstrate the clinical potential of these drugs and warrant further study to elucidate the mechanisms responsible for the antivascular effects of combretastatin A-4