Histochemical and immunohistochemical localization of hexokinase isoenzymes in rat kidney

Metabolic derangements in interstitial brain edema with preserved blood flow: selective vulnerability of the hippocampal CA3 region in rat hydrocephalus

Hydrocephalus induces interstitial brain edema, which causes neurological deficits, even if the intracranial pressure is maintained within the normal range, and the cerebral blood flow (CBF) does not decline to an ischemic level. The precise mechanisms underlying such edema-induced neuronal dysfunction remain unclear. In the present study, in an attempt to elucidate the metabolic derangements in brain tissue with interstitial edema, we evaluated the changes in CBF and oxidative/glucose metabolism using a rat model of kaolin-induced hydrocephalus. Hydrocephalus was produced in male Wistar rats by intrathecal injection of 0.1 ml aluminum silicate suspension (200 mg/ml) via the cisterna magna. CBF was determined by 14[C]-iodoantipyrine autoradiography. Oxidative metabolism was evaluated by cytochrome oxidase (CYO) histochemistry, and glucose metabolism by hexokinase (HK) histochemistry. CBF declined with the development of hydrocephalus, but did not reach an ischemic level. The CYO activity was diffusely depressed in both the cortex and hippocampus. The HK activity was preserved at the early stage of hydrocephalus. At the advanced stage, the HK activity was reduced in the hippocampal CA3 region first, and diffusely thereafter. In conclusion, interstitial brain edema impairs oxidative metabolism even at the early stage of hydrocephalus, and shifts the metabolism to anaerobic glycolysis despite a preserved CBF. Impairment of glucose metabolism was first observed in the CA3 region, suggesting that the CA3 is metabolically vulnerable, and CA3 dysfunction may contribute to the memory deficits seen in hydrocephalus.

Tissue-specific differences in 2-fluoro-2-deoxyglucose metabolism beyond FDG-6-P: a 19F NMR spectroscopy study in the rat

2-Fluoro-[(18)F]-2-deoxy-glucose (FDG) is a positron-emitting analogue of glucose used clinically in positron emission tomography (PET) to assess glucose utilization in diseased and healthy tissue. Originally developed to measure local cerebral glucose utilization rates, it has now found applications in tumour diagnosis and in the study of myocardial glucose uptake. Once taken up into the cell, FDG is phosphorylated to FDG-6-phosphate (FDG-6-P) by hexokinase and was originally believed to be trapped as a terminal metabolite. This 'metabolic trapping' of FDG-6-P forms the basis of the analysis of PET data. In this study, we have used (19)F NMR spectroscopy to investigate FDG metabolism following the injection of a bolus of the glucose tracer into the rat (n=6). Ninety minutes after the (19)FDG injection, the brain, heart, liver and kidneys were removed and the (19)FDG metabolites in each were extracted and quantified. We report that significant metabolism of FDG occurs beyond FDG-6-P in all organs examined and that the extent of this metabolism varies from tissue to tissue (degree of metabolism beyond FDG-6-P, expressed as percentage of total organ FDG content, was brain 45 +/- 3%; heart 29 +/- 2%; liver 22+/-3% and kidney 17 +/- 3%, mean +/- SEM n=6). Furthermore, we demonstrate that the relative accumulation of each metabolite was tissue-dependent and reflected the metabolic and regulatory characteristics of each organ. Such inter-tissue differences may have implications for the mathematical modelling of glucose uptake and phosphorylation using FDG as a glucose tracer.

Growth control of C6 glioma in vivo by nerve growth factor

Treatment with nerve growth factor (NGF) causes differentiation of rat C6 glioma cells and strongly inhibits their proliferation in vitro. This suggests that induction of NGF-mediated differentiation may provide a novel therapeutic approach to growth control of glial tumors. We examined the effects of NGF treatment on the growth potential of C6 glioma, which expressed NGF receptor in vivo. C6 glioma cells (1 x 10(6) cells/10 microl) were transplanted into the rat striatum. After 4 days, the animals were given successive injections of 100 ng NGF into the growing tumor at every 4 days (n = 10 rats). Controls were subjected to identical procedures with vehicle which did not contain NGF (n = 10 rats). At 14 days after transplantation, we evaluated the tumor volume, proliferative cell index (PCI) based on the MIB-1 immunoreactivity and enzyme activities related to energy metabolism by enzyme histochemistry. We found that the NGF treatment markedly reduced the tumor volume of the C6 glioma (34.00 +/- 8.47 mm3 to 7.22 +/- 4.92 mm3, p < 0.01). NGF treatment also decreased the PCI (33.34 +/- 9.57% to 3.85 +/- 3.56%, p < 0.01) with a negative correlation with tumor volume (r = 0.972, p < 0.01), and the hexokinase (HK) and glucose-6-phosphate dehydrogenase (G6PDH) activities (p < 0.01 and p < 0.01, respectively) which reflect the demand for nucleic acid synthesis for proliferation through the glycolytic and pentose phosphate pathways. The present results demonstrate for the first time that inhibition of tumor cell proliferation of C6 glioma by NGF occurs in vivo, probably through the NGF-mediated differentiation of C6 glioma cells which has been observed in in vitro studies.

Regulation of mesangial cell hexokinase activity and expression by heparin-binding epidermal growth factor-like growth factor: epidermal growth factors and phorbol esters increase glucose metabolism via a common mechanism involving classic mitogen-activated protein kinase pathway activation and induction of hexokinase II expression

Heparin-binding epidermal growth factor -like growth factor (HB-EGF) expression and hexokinase (HK) activity are increased in various pathologic renal conditions. Although the mitogenic properties of HB-EGF have been well characterized, its effects on glucose (Glc) metabolism have not. We therefore examined the possibility that HB-EGF might regulate HK activity and expression in glomerular mesangial cells, which constitute the principal renal cell type affected by a variety of pathologic conditions. Protein kinase C (PKC)-dependent classic mitogen-activated protein kinase (MAPK) pathway activation has been associated with increased HK activity in this cell type, so we also examined dependence upon these signaling intermediates. HB-EGF (> or =10 nm) increased total HK activity over 50% within 12-24 h, an effect mimicked by other EGF receptor agonists, but not by IGF-1 or elevated Glc. EGF receptor and classic MAPK pathway antagonists prevented this increase, as did general inhibitors of gene transcription and protein synthesis. Both HB-EGF and phorbol esters activated the classic MAPK pathway, albeit via PKC-independent and PKC-dependent mechanisms, respectively. Both stimuli were associated with increased HK activity, selectively increased HKII isoform expression, and increased Glc metabolism via both the glycolytic-tricarboxylic acid cycle route and the pentose phosphate pathway. HB-EGF thus constitutes a novel regulator of mesangial cell HK activity and Glc metabolism. HKII is the principal regulated isoform in these cells, as it is in insulin-sensitive peripheral tissues, such as muscle. However, the uniform requirement for classic MAPK pathway activation distinguishes HKII regulation in mesangial cells from that observed in muscle. These findings suggest a novel mechanism whereby growth factors may couple metabolism to glomerular injury.

Increased hexokinase activity, of either ectopic or endogenous origin, protects renal epithelial cells against acute oxidant-induced cell death

Glucose (Glc) metabolism protects cells against oxidant injury. By virtue of their central position in both Glc uptake and utilization, hexokinases (HKs) are ideally suited to contribute to these effects. Compatible with this hypothesis, endogenous HK activity correlates inversely with injury susceptibility in individual renal cell types. We recently reported that ectopic HK expression mimics the anti-apoptotic effects of growth factors in cultured fibroblasts, but anti-apoptotic roles for HKs have not been examined in other cell types or in a cellular injury model. We therefore evaluated HK overexpression for the ability to mitigate acute oxidant-induced cell death in an established epithelial cell culture injury model. In parallel, we examined salutary heparin-binding epidermal growth factor (EGF)-like growth factor (HB-EGF) treatment for the ability to 1) increase endogenous HK activity and 2) mimic the protective effects of ectopic HK expression. Both HK overexpression and HB-EGF increased Glc-phosphorylating capacity and metabolism, and these changes were associated with markedly reduced susceptibility to acute oxidant-induced apoptosis. The uniform Glc dependence of these effects suggests an important adaptive role for Glc metabolism, and for HK activity in particular, in the promotion of epithelial cell survival. These findings also support the contention that HKs contribute to the protective effects of growth factors.

Ischemia-induced changes in cell element composition and osmolyte contents of outer medulla

The effect of 60 minutes of ischemia and subsequent reflow on cell electrolyte and water homeostasis in the rat renal outer medulla was studied by determining sodium, potassium, chloride and phosphorus concentrations and dry weights in individual tubule cells using electron microprobe analysis. HPLC was employed to measure glycerophosphorylcholine, betaine, inositol and sorbitol, as well as several free amino acids in cortical and outer medullary tissue. Ischemia caused cell sodium and chloride concentrations to rise and cell potassium and phosphorus concentrations and cell dry weights to fall. These changes were most pronounced in the proximal straight tubule (PST) cells, less in thick ascending limb (MAL) and outer medullary collecting duct (OMCD) dark cells and barely noticeable in OMCD light cells. Except for some PST cells these changes were almost completely reversed 60 minutes after reintroducing blood flow. After 24 hours of reperfusion the number of PST cells exhibiting deranged electrolyte homeostasis was greatly increased. The contents of glycerophosphorylcholine, betaine or inositol in the cortex and outer medulla were not affected immediately following ischemia. After 24 hours of reperfusion, the cortical contents of osmolytes were still normal, while outer medullary contents were reduced. Except for low glycine contents, the ischemia-induced changes in amino acid contents were reversed after 24 hours of reflow in the cortex, whereas in the outer medulla aspartate, glycine and taurine contents were diminished. These results indicate increasing manifestation of PST cell injury in the reflow period. The defective re-accumulation of organic osmolytes and free amino acids in the outer medulla during reflow may reflect reduced interstitial tonicities, or may be due to inappropriate cellular uptake, synthesis or/and release.(ABSTRACT TRUNCATED AT 250 WORDS)

Cytochrome oxidase and hexokinase activities in an infusion edema model with preserved blood flow

Despite numerous investigations, the mechanisms underlying the neurological deficits observed in association with interstitial edema remain unclear. A recent study has demonstrated that the cerebral blood flow (CBF) in edematous white matter is unchanged if the blood flow values are corrected for dilution. In contrast, the cerebral glucose metabolism (CMRgl) has been found to be increased. In order to examine the effects of interstitial edema on the oxidative metabolism, we measured the cytochrome oxidase (CYO) activity, a marker of mitochondrial respiration, and the hexokinase (HK) activity, a marker of glycolysis, together with CBF and CMRgl employing the iodoantipyrine and deoxyglucose autoradiography in an infusion edema model in rats. In agreement with the previous study, CBF was not significantly changed in the edematous hemisphere. No significant alterations in CMRgl and HK activity were noted. In contrast, there was a significant decrease in CYO activity in the edematous hemisphere (-17%; p < 0.01), which was correlated to the edema. These findings suggest that interstitial edema causes a decreased mitochondrial respiratory function despite a maintained circulation. This may be explained by postulating a decreased oxygen delivery and/or accumulation of lactate, both of which have been shown to interfere with mitochondrial respiratory function.

A basolateral lactate/H+ co-transporter in Madin-Darby Canine Kidney (MDCK) cells

Monolayers of Madin-Darby Canine Kidney (MDCK) cells grown on permeable filters generated lactate aerobically and accumulated it preferentially in the basolateral compartment, suggesting the presence of a lactate carrier. The mechanism of lactate transport across apical and basolateral membranes was examined by determining intracellular pH (pHi) microspectrofluorimetrically after addition of lactate to the extracellular solutions and by measuring uptake of [14C]lactate. Addition of 20 mM lactate to the apical compartment produced no change in pHi, whereas lactate added to the basolateral compartment rapidly and reversibly lowered pHi. Pyruvate produced similar results. Inhibitors of lactate/H+ co-transporters, alpha-cyano-4-hydroxycinnamate (CnCN) and quercetin, partially inhibited the fall in pHi produced by basolateral lactate. In contrast, the disulphonic stilbene. DIDS (4,4'-di-isothiocyanostilbene-2,2'-disulphonic acid) produced no inhibition at 0.5 mM. Kinetic analysis was performed by applying basolateral lactate at various concentrations and measuring the rate of entry (delta pHi/min) in the presence and absence of CnCN. Lactate flux was shown to occur by both non-ionic diffusion and a alpha-cyano-4-hydroxycinnamate-sensitive component (carrier). The latter has a Km of approximately 7 mM for the lactate anion. Propionate, but not formate, lowered pHi to the same degree as did equimolar lactate, but the propionate effect was not inhibited by CnCN. Influx of [14C]lactate was substantially greater across the basolateral membrane than across the apical membrane and occurred in the absence of Na+. We conclude that MDCK cells grown on permeable filters generate lactate aerobically and transport it across the basolateral membrane by way of a lactate/H+ cotransporter.

Localization of the type III isozyme of hexokinase at the nuclear periphery

The distribution of the type III isozyme of hexokinase (ATP:D-hexose 6-phosphotransferase, EC 2.7.1.1) in rat kidney, liver, spleen, lung, and brain was determined immunohistochemically, using a monoclonal antibody generated against the enzyme purified from rat Novikoff hepatoma. In all tissues, specific cell types exhibited intense staining at the nuclear periphery, as confirmed by analysis using confocal microscopy. Isolated nuclei from kidney or liver were devoid of detectable type III hexokinase, although the enzyme was found in the "soluble" fraction from kidney or liver homogenates; these results suggest that the type III isozyme is associated in a labile manner with the external surface of the nucleus, with this association being disrupted by conventional homogenization and nuclear isolation procedures. The nuclear localization of the type III isozyme contrasts with previously demonstrated association of the type I and II isozymes with mitochondria. The physiological significance of a nuclear localization for the type III isozyme remains unclear. However, it was noted that many of the cells exhibiting prominent nuclear staining for type III hexokinase are endothelial or epithelial cells, suggesting a possible relationship between nuclear type III hexokinase and transport functions which are prominent in such cells.

The use of continuous monitoring and computer-assisted image analysis for the histochemical quantification of hexokinase activity

The effect of endogenous 6-phosphogluconate dehydrogenase (6PGDH) on the histochemical quantification of low-Km hexokinase activity in rat submandibular salivary glands has been investigated using a Seescan Solitaire Plus image analysis system and a modified black and white Newvicon TV camera. Absorbance readings of neutral density filters were close to their known absorbance values. A significant correlation was found between the absorbance of Nitro BT reduction products within sections, with and without the use of a 588 nm interference filter. Furthermore, absorbance readings obtained from 8 microns-thick sections were 1.92 and 2.22 times greater than values obtained from 4 microns-thick sections using 'white' and 588 nm light respectively. The level of background illumination was not critical for absorbance measurements provided it was below the level that saturated the Newvicon camera and was not changed between background and image capture. The greatest variations in absorbance readings on tissue sections were associated with changes in zoom and objective combinations. Our studies indicate that this relatively low cost image analysis system can give reproducible absorbance readings from various structures defined in digitized, captured images of tissue sections. Results from continuous monitoring studies indicated that the high levels of 6PGDH activity in excretory ducts caused a 1.67-fold overestimation of hexokinase activity as assessed by absorbance readings performed throughout a 22-minute reaction period. By contrast, overestimation of hexokinase activity in salivary gland acini only became apparent after 8 min incubation with a 1.4-fold overestimation being seen at 22 min. This difference appears to reflect the relatively low hexokinase and 6PGDH activities present in acini compared with excretory ducts.

The compartmentation of glycolytic and gluconeogenic enzymes in rat kidney and liver and its significance to renal and hepatic metabolism

An indirect immunoperoxidase procedure has been used to demonstrate sites of glycolysis and gluconeogenesis in normal rat kidney and liver. In kidney, the gluconeogenic enzyme fructose 1,6-biphosphatase was restricted to the proximal tubular epithelium, while the glycolytic enzyme hexokinase predominated in more distal segments. Intense staining for the biphosphatase in proximal convoluted tubular brush borders suggests that reabsorbed substrates may be used directly at this site in renal gluconeogenesis. In view of the high phosphofructokinase and pyruvate kinase activities present in collecting ducts, their relatively low hexokinase activities and their relatively pale immunostaining for hexokinase indicate that glycolytic substrates which feed into the pathway subsequent to the initial phosphorylation step, rather than glucose, may be the major energy source for the rat renal papilla. Immunostaining in the liver was consistent with the metabolic zonation of liver parenchyma, in that glucokinase occurred mainly in perivenous regions and fructose 1,6-bisphosphatase in periportal areas. The presence of such metabolic zonation is difficult to reconcile with the widely held view that the majority of hepatic glycogen is derived directly from glucose. A model for hepatic glycogen synthesis is proposed which links the concept of parenchymal zonal heterogeneity with recent biochemical evidence concerning the 'glucose paradox' and with microscopical studies on the dynamics of glycogen deposition after refeeding.

The localization of hexokinase isoenzymes in red and white skeletal muscles of the rat

Maximum assayable hexokinase activities vary with the proportion of red, fast-twitch, oxidative-glycolytic and intermediate, slow-twitch, oxidative fibres in different rat skeletal muscles. The major isoenzymic form, type II hexokinase, is present throughout the intermyofibrillar sarcoplasm in all fibres but a proportion of the total activity appears to be weakly associated with mitochondria. Variations in the histochemical staining intensity between fibre types correlate with their mitochondrial content and seem to be due mainly to differences in mitochondrially-associated hexokinase activity. Changes in the strength of this association may be important in controlling increases in glucose metabolism in response to prolonged increased muscular activity while regulation of the equilibrium between free and loosely-bound forms may be an important control feature in all skeletal muscle. Type I hexokinase is a minor isoenzymic component of skeletal muscle and occurs mainly in blood vessels and nerves in the perimysia and endomysia. The majority of this isoenzyme is tightly bound to mitochondria and is not detectable in homogenates prepared in the absence of Triton X-100.

Histochemical and immunohistochemical localization of hexokinase isoenzymes in normal rat liver

Histochemical and immunohistochemical procedures have been used to examine the localization of three of the four hexokinase isoenzymes present in the liver of fed female Wistar rats. Distinctive distribution patterns were found for hexokinase type I and glucokinase but hexokinase type II was not detectable. Hexokinase type I was identified in sinusoidal cells and in bile duct epithelia, nerves and arteries in the portal triad. Glucokinase, the major isoenzyme, was confined to parenchymal cells where it was present in much higher amounts in perivenous compared with periportal hepatocytes. Staining within these two zones was not homogeneous and each had a mosaic appearance caused by the presence of a few hepatocytes containing little or no glucokinase amongst the majority of darkly stained cells in perivenous areas and a few darkly stained cells amongst the majority of unstained cells in periportal areas. Hence, hepatocytes in situ are a strikingly heterogeneous population of cells. Their metabolic status cannot be controlled simply by the differential supply of oxygen, substrates and hormones to different regions of the liver acini as proposed in the metabolic zonation model. Phenotypic differences may exist between cells within a given metabolic zone which influence their ability to respond to different environmental conditions.

The ubiquitous localization of type I hexokinase in rat peripheral nerves, smooth muscle cells and epithelial cells

An indirect immunoperoxidase technique has been used to determine the localization of type I hexokinase in a wide variety of Carnoy-fixed, paraffin-embedded rat tissues. The results suggest that the widespread tissue distribution of the isoenzyme is due to its ubiquitous localization in the nervous, smooth muscle and epithelial components of each tissue. The majority of the immunostaining was confined to cells with substantial energy requirements which are probably mainly satisfied through the breakdown of glucose. This observation is consistent with the known predominance of type I hexokinase in the central nervous system and with the regulatory role allotted to it in this tissue.