Hit and run, hit and hide or permanent hit: why it is premature to dump Koch's postulates in rheumatic diseases.
Explore the source record for details and available documents.
Antigens, Bacterial↗
SEARCH · PubMed Health
Results for “HITS”
Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Toward the equivalence of the HIT and HIT 25 in community-residing older adults.
In a study by the first author wherein 102 community-residing older adults were administered the Holtzman Inkblot Technique (HIT), data collected were analyzed regarding the equivalence of the HIT and the HIT 25. Although alpha coefficients and split-half correlations were low when single-response-per-card data were analyzed, corrected Spearman-Brown coefficients were more supportive of the use of the HIT 25 with older adults. These data suggest that although a shortened form of the HIT may be useful with aged persons, research exploring the substantive bases for creating a shortened version of the HIT is nevertheless necessary.
Activities of Daily Living↗
Evidence for a one-hit theory in the immune bactericidal reaction and demonstration of a multi-hit response for hemolysis by streptolysin O and Clostridium perfringens theta-toxin.
An analytical method was developed for estimating the number of hits necessary to lyse or kill cells in which various concentrations of the cells are treated with a constant amount of the lytic or killing agent in a constant reaction volume. The reaction may be due to a single-component agent or occur by a sequential chain of reactions due to a multi-component agent, even including side, abortive, or counter-reactions. It was clearly shown by this method that immune bactericidal reactions followed a one-hit theory. It was shown by this method that streptolysin O required four or five hits for hemolysis and Clostridium perfringens theta-toxin required two hits. These results were confirmed by both logarithmic dose-response and survival analyses. It was also shown that streptolysin O and theta-toxin can act complementarily on accumulation of the hits for hemolysis.
Animals↗
A unified theory for the mechanism of the lethal hit by cytotoxic T lymphocytes (CTL) and natural killer (NK) cells as defined by antisera capable of blocking the lethal hit stage of cytotoxicity.
Explore the source record for details and available documents.
Animals↗
Hit and run or permanent hit? Is there evidence for a microbiological cause of rheumatoid arthritis?
Explore the source record for details and available documents.
Arthritis, Rheumatoid↗
Single-hit versus multi-hit concept of hepatocarcinogenesis.
Explore the source record for details and available documents.
2-Acetylaminofluorene↗
Dysregulated release and degradation of insulin during mononuclear cell-induced beta-cell lysis in HIT cells.
Activated human mononuclear cells (MCs) were coincubated for 8 h with HIT cells, a clonal cell line of pancreatic islet beta-cells. Measurements of HIT cell viability and insulin secretion were determined to 1) ascertain whether activated MCs can alter beta-cell viability in the absence of exogenously provided cytokines, 2) examine this response over a range of MC-HIT cell ratios, and 3) identify mechanisms responsible for altered insulin release consequent to MC-induced HIT cell damage. HIT cell viability was markedly decreased by activated MCs during an 8-h coincubation. HIT cell lysis could be attributed to activated natural killer cells, and lysis did not occur in the presence of activated T-lymphocyte clones. Activated MCs caused a marked early increase in insulin release from HIT cells (increase at 2 h: 7.75 +/- 0.16 nM for activated MCs, 2.66 +/- 0.09 nM for control; P less than 0.001). Insulin levels by the 8th h of the coincubation were significantly lower than the 2-h peak (4.33 +/- 0.13 vs. 7.75 +/- 0.16 nM, P less than 0.001). These changes in insulin were dependent on the ratio of activated MCs to HIT cells with the effects clearly evident at an activated MC-HIT cell ratio of greater than or equal to 10:1. Pretreatment of activated MCs and HIT cells with prostaglandin-synthesis inhibitors did not prevent the cytotoxic effects of activated MCs on HIT cells. Somatostatin did not inhibit the early exaggerated insulin release, suggesting that these increased insulin levels represented leakage of insulin from damaged HIT cells rather than functional insulin secretion.(ABSTRACT TRUNCATED AT 250 WORDS)
Arachidonic Acids↗
Multi-hit kinetics of tumor formation, with special reference to experimental liver and human lung carcinogenesis and some gneral conclusions.
On the basis of the multi-hit concept of cancer formation, the relationships between tumor incidence and dose and time of administration of carcinogen have been analyzed. Simple mathematics have been used, since the available data, in our opinion, hardly justify more sophisticated formularization. The exponential relationship between the cumulative tumor incidence and the dose and time of administration of carcinogen can be described as l(d,t) approximately dmtr. With use of Druckrey's formula, dtn=k, it was derived that the exponent of time, r, is equal to m-n, in which m is the power of the dose dependency of tumor formation [l(d) approximately dm measured at a fixed time] and n is the autonomous time factor featured in the former formula. The factor m is interpretable in terms of the number of discrete events (hits) required for tumor formation, whereas the factor n is mainly determined by the rate of proliferation of intermediate cell populations participating in the carcinogenic process. Since r and n can be experimentally determined, the formula allows the calculation of the exponent (m) of the dose dependency of tumor formation. Analysis of malignant liver tumor formation in the rat by continuous administration of diethylnitrosamine yeilded m = 7, from which it was concluded that seven hits were instrumental in the induction of these liver-cell tumors. Analysis of the formation of less malignant liver tumors after one pulse exposure to the same carcinogen suggested that the process was initiated by at most two concomitant hits in a liver cell and brought to completion by three spontaneous events (changes). The view was advanced that tumor formation in general may result from hits inflicted by the carcinogen applied and from "background" hits (i.e., spontaneous changes and/or hits by carcinogenic stimuli from the environment or present endogenously) and that the relative contribution of these two types of hits to the end effect may depend on dose level and potency of the carcinogen under consideration. It was pointed out that the direct measurement of the dose-response relation (l(d) approximately dm) yields only the number of hits contributed by the carcinogen applied anose rate is low or very low, the contribution of background process becomes significant, and these hits contribute to the power of time, r, of the incidence-time relation. Under these conditions, the formula m-n=r becomes (mex + mb)n=r, where mex and mb denote the number of hits scored by extrinsic carcinogen and background processes, respectively. It is argued that the epidemiological data on lung cancer caused by smoking [l(d) approximately d with respect to smoke dose, mex= 1; l(t) approximately t5 with respect to duration of smoking] are not compatible unless at least one additional background hit (mb greater than or equal to 1) is postulated...
Animals↗
Opioids and hibernation. II. Effects of kappa opioid U69593 on induction of hibernation in summer-active ground squirrels by "hibernation induction trigger" (HIT).
A "Hibernation Induction Trigger" (HIT) isolated from plasma of winter-hibernating woodchucks induced hibernation in summer-active ground squirrels (Citellus tridecemlineatus). Effects of kappa opioid U69593 on the HIT-induced hibernation were examined. U69593 alone did not elicit marked behavioral alteration or hibernation in summer-active ground squirrels. U69593, however, antagonized hibernation induced by HIT in summer active ground squirrels. In the guinea pig ileum myenteric plexus-longitudinal muscle preparation, woodchuck HIT depressed the electrically-induced contraction. The depression was, however, neither reversed nor blocked by naloxone even when naloxone was used at high doses. This study demonstrates that kappa opioid, at least in the case of U69593, was unable to induce hibernation in the summer-active ground squirrels. The results also demonstrate that woodchuck HIT, like the bear HIT, did not act directly at opioid receptors. Together with our previous observation that naloxone blocked summer hibernation induced by HIT (Bruce et al., Life Sci.., this issue), it is tempting to suggest that HIT may not mediate its effects through kappa opioid receptors but may do so through other types of opioid receptors such as mu or delta. U69593 may antagonize HIT-induced hibernation as a mu or delta receptor antagonist.
Animals↗
Venetoclax added to dose-adjusted EPOCH-R for newly diagnosed double-hit lymphomas: phase 2 results from ALLIANCE A051701, an open-label, randomised, controlled, phase 2-3 trial.
BACKGROUND: High-grade B-cell lymphoma with rearrangements of MYC and BCL2 and/or BCL6, known as double-hit lymphoma, is a highly aggressive malignancy with poor outcomes after standard chemoimmunotherapy. We aimed to study whether the addition of the BCL2-inhibitor venetoclax to chemoimmunotherapy in patients with double-hit lymphoma resulted in superior efficacy compared with chemotherapy alone. METHODS: ALLIANCE A051701 is an open-label, randomised, controlled, phase 2-3 trial in separate cohorts of patients with double-hit lymphoma and patients with double-expressor lymphoma. In this analysis, we report phase 2 results from the double-hit lymphoma cohort. Patients aged 18-80 years with newly diagnosed double-hit lymphoma and Eastern Cooperative Oncology Group (ECOG) performance status 0-2 were recruited from 41 hospitals and outpatient clinics in the USA. Patients were randomly assigned (1:1) to receive DA-EPOCH-R (dose-adjusted etoposide, prednisone, vincristine, cyclophosphamide, doxorubicin, and rituximab) either alone (DA-EPOCH-R group) or with venetoclax (DA-EPOCH-R plus venetoclax group) using permuted block randomisation schedule. All patients and investigators were aware of group assignment. DA-EPOCH-R was administered on a 21-day schedule for up to six total cycles. Venetoclax was given as 600 mg by mouth daily on days 4-8 of cycle 1 and on days 1-5 of cycles 2-6. The primary endpoint was progression-free survival in the modified intent-to-treat population inclusive of all eligible patients with centrally confirmed double-hit lymphoma. The safety analysis population consisted of all evaluable patients who received at least one dose of protocol treatment. This trial is registered with ClinicalTrials.gov (NCT03984448) and is closed to enrolment. FINDINGS: 36 patients were randomly assigned to the DA-EPOCH-R group and 37 to the DA-EPOCH-R plus venetoclax group between Oct 22, 2019, and Sept 18, 2020. Median age was 65 years (IQR 56-73) and baseline demographic factors were well balanced between groups, with 30 (45%) female and 36 (55%) male patients. Most patients (59 [89%]) were white, two (3%) were Asian, one (2%) was Black or African American, and four (6%) had unknown or unreported ethnicity. The majority of patients had MYC-BCL2 double-hit lymphoma (59 [89%] patients), advanced stage disease (57 [86%] patients), and high-intermediate/high-risk IPI score (42 [64%] patients). Median follow-up was 34·7 months (IQR 30·1-36·8). Median progression-free survival was 28·4 months (95% CI 5·2-not estimable) in the DA-EPOCH-R group (n=30) and 7·7 months (95% CI 4·7-NE) in the DA-EPOCH-R plus venetoclax group (n=36; hazard ratio [HR] 1·13, 95% CI 0·53-2·37; p=0·75). Deaths on treatment occurred in one (3%) patient in the DA-EPOCH-R group (due to dyspnoea; possibly related to treatment) and six (17%) patients in the DA-EPOCH-R plus venetoclax group (four due to sepsis [three at least possible related and one unrelated], two due to cardiac arrest [at least possibly related]), prompting early closure of the double-hit lymphoma cohort. The most common grade 3-4 non-haematological adverse event was febrile neutropenia, occurring in 15 (43%) of 35 patients in the DA-EPOCH-R plus venetoclax group and 11 (37%) of 30 patients in the DA-EPOCH-R group. The median overall survival has not been reached in either group. The 24-month overall survival estimates were 72% (95% CI 52-85) in the DA-EPOCH-R group compared with 52% (95% CI 33-68) in the DA-EPOCH-R plus venetoclax group (HR 2·49, 95% CI 1·03-6·04; p=0·038). INTERPRETATION: The addition of venetoclax to DA-EPOCH-R resulted in excess mortality, prompting early study closure. Robust accrual shows that prospective multicentre trials are feasible in double-hit lymphoma, and the outcomes in the DA-EPOCH-R group serve as a benchmark for future studies. FUNDING: National Cancer Institute of the National Institutes of Health.
Humans↗
The role of cytosolic free Ca2+ and protein kinase C in acetylcholine-induced insulin release in the clonal beta-cell line, HIT-T15.
We examined the contribution of signal-transduction pathways to acetylcholine-induced insulin release in the clonal beta-cell line HIT-T15. To assess the importance of changes in cytosolic free Ca2+ [( Ca2+]i), we studied time courses of the effects of glucose and acetylcholine on [Ca2+]i and insulin release in quin 2-loaded HIT cells. Incubation in the presence of glucose (2 mM) resulted in a sustained increase in [Ca2+]i in HIT cells from 98 +/- 7 nM to 195 +/- 12 nM measured after 9 min, whereas subsequent addition of acetylcholine (50 microM) produced a transient increase in [Ca2+]i which reached a peak after 30 s (at 274 +/- 10 nM), returning to pre-stimulus levels after 3 min. In contrast, incubation of HIT cells with acetylcholine in the presence of glucose produced a sustained increase in insulin release over and above that stimulated by glucose alone; after 10 min acetylcholine had potentiated glucose-stimulated insulin release by an additional increment of 135%. The transient increase in [Ca2+]i induced by acetylcholine was dose-dependent, and was prevented by omission of glucose or extracellular Ca2+ from the incubation medium. It was also inhibited by inclusion of 50 microM-verapamil in the incubation medium (by 87 +/- 3%) or by decreasing the Na+ concentration in the medium (by 73 +/- 6%). To evaluate the role of the protein kinase C pathway, we have pretreated HIT cells with the phorbol ester 12-O-tetradecanoylphorbol acetate (TPA), to deplete the protein kinase C activity, and have compared their secretory activity with that of control cells. Protein kinase C activity was decreased by 73% in HIT cells cultured in the presence of 200 nM-TPA for 22-24 h. TPA pre-treatment also significantly decreased the insulin content of HIT cells, but had no effect on cell number or the increases in [Ca2+]i induced by glucose or acetylcholine. TPA-pre-treated cells responded comparatively less well to secretagogues than did control cells: glucose-stimulated insulin release was decreased by 40%, whereas potentiation by TPA was significantly decreased by 50% in comparison with control cells (P less than 0.05, n = 24). Acetylcholine (50 microM) potentiated glucose-stimulated insulin release by 61% in control cells. This effect was abolished in HIT cells pre-treated with TPA, whereas these cells still retained their normal secretory response to stimulation by forskolin. These data suggest that an early increase in [Ca2+]i may be important for the initial increase in insulin release induced by acetylcholine in HIT cells.(ABSTRACT TRUNCATED AT 400 WORDS)
Acetylcholine↗
Opioids and hibernation. I. Effects of naloxone on bear HIT'S depression of guinea pig ileum contractility and on induction of summer hibernation in the ground squirrel.
Summer hibernation in ground squirrels (Citellus tridecemlineatus) can be induced by intravenous injection of hibernation-induction trigger (HIT) from winter bear plasma or its albumin fraction. In this study, we show that bear HIT depresses electrically-induced contraction of the guinea pig ileum myenteric plexus-longitudinal muscle preparation, and that naloxone, at 100, 1,000, or even 4,000 nM, fails to reverse that effect. In a simultaneous study, four sets of ground squirrels were implanted with osmotic minipumps which delivered solutions at a controlled and continuous rate. Two of the groups had pumps delivering naloxone at 1 mg/kg body weight per hour. The other two groups had saline-filled pumps (controls). One set of squirrels from each of the saline- and naloxone-filled pump groups were then injected intravenously with winter bear plasma. The remaining two groups of squirrels were injected with winter bear albumin fraction. Hibernation frequency was determined by measurements of core temperature (from surgically-implanted radio capsules), respiratory rate, and bouts of activity. Squirrels with saline-filled pumps hibernated four times more frequently than the naloxone groups. To confirm these findings, three squirrels from each naloxone group were reinjected with bear HIT after removal of the pumps. These six squirrels then hibernated over four times their previous frequency. Results suggest that bear HIT is not itself an opioid (since naloxone did not reverse bear HIT's depression of electrically-induced contraction of guinea pig ileum). The fact that bear HIT's effect of inducing summer hibernation in ground squirrels is effectively blocked in vivo by naloxone leads to the speculation that HIT may be either a precursor of endogenous opioids or a potent releaser of them, which, in turn, induce hibernation.
Animals↗
Lactate transport in insulin-secreting beta-cells: contrast between rat islets and HIT-T15 insulinoma cells.
The transport of L- and D-lactate into rat pancreatic islets and HIT-T15 insulinoma cells was studied by measuring uptake of 14C-labelled substrate at room temperature and by following changes in intracellular pH (pHi) in islets and HIT-T15 cells loaded with 2',7'-bis(carboxyethyl)-5'(6')-carboxyfluorescein (BCECF). Uptake of L-lactate into HIT-T15 cells was rapid, reaching equilibrium after 5 min with an apparent Km value of 4.8 mM. Transport was markedly inhibited by alpha-cyano-4-hydroxycinnamate, alpha-fluorocinnamate, quercetin and p-chloromercuribenzenesulphonate (pCMBS), and was enhanced in citrate medium. Uptake of D-lactate was less rapid, apparent equilibrium not being reached within 10 min. In contrast to HIT-T15 cells, rat pancreatic islets showed greatly reduced rates of transport of L- and D-lactate together with a correspondingly lower degree of inhibition by alpha-cyano-4-hydroxycinnamate. The addition of L- or D-lactate to HIT-T15 cells, but not dispersed islet cells, resulted in a marked and rapid intracellular acidification followed by a gradual recovery. In both HIT-T15 cells and isolated islets, the rates of transport of both L- and D-lactate in the presence of alpha-cyano-4-hydroxycinnamate were significantly greater in a depolarising K+ medium compared to the normal Na+ medium. These observations suggest that native rat islet cells have considerably reduced activity of the lactate-/H+ transport system compared to HIT-T15 insulinoma cells. There is evidence in both cell types of an additional electrogenic pathway for lactate which might play a role in coupling lactate efflux to beta-cell depolarisation.
4-Chloromercuribenzenesulfonate↗
Identification of a Bdellovibrio bacteriovorus genetic locus, hit, associated with the host-independent phenotype.
Bdellovibrios invade and grow within the periplasmic space of suitable gram-negative bacteria. Wild-type bdellovibrios are obligately dependent on host cells for growth, but spontaneous host-independent (H-I) mutants that grow axenically on standard rich culture media can be isolated. Such mutants generally retain the ability to grow intraperiplasmically, although the plaques that they produce on lawns of host cells are smaller and more turbid than those produced by wild-type bdellovibrios. Here, we identify the first genetic locus associated with the H-I phenotype: hit (host interaction). We show that three individual H-I mutants suffered mutations at the hit locus and that recombination of wild-type hit sequences into the genomes of the H-I mutants greatly enhanced their plaquing ability. DNA sequence analysis localized the hit mutation in each of the H-I mutants to a 135-bp region of the genome. Mutations at hit may not fully account for the H-I phenotype, however, as recombination of wild-type hit sequences into the genomes of the H-I mutants had little effect on the axenic-growth phenotype of the mutants. Possible explanations for this result and potential roles for the hit locus are discussed.
Amino Acid Sequence↗
Stimulus-response coupling in insulin-secreting HIT cells. Effects of secretagogues on cytosolic Ca2+, diacylglycerol, and protein kinase C activity.
The hamster islet B cell line HIT retains the ability to secret insulin in response to glucose and several receptor agonists. We used HIT cells to study the initial signaling events in glucose or receptor agonist-stimulated insulin secretion. Glucose stimulated insulin release from HIT cells in a dose-dependent manner with a half-maximal effect seen already at 1 mM. Insulin release was also stimulated by carbachol in a glucose-dependent manner. Glucose depolarized the HIT cell membrane potential as assessed with the fluorescent probe bisoxonol and raised intracellular Ca2+ as revealed by fura-2 measurements. Using a Mn2+ fura-2 quenching technique, we could show that the rise in intracellular Ca2+ was due to Ca2+ influx following opening of voltage-gated Ca2+ channels. Glucose is thought to increase the diacylglycerol (DAG) content of insulin-secreting cells. However, although HIT cells respond to glucose in terms of insulin secretion, membrane depolarization, and Ca2+ rise, the hexose was unable to increase the proportion of protein kinase C activity associated with membranes. In contrast, the membrane-associated protein kinase C activity increased in HIT cells exposed to the two receptor agonists carbachol and bombesin. Bombesin was shown to generate DAG with the expected fatty acid composition of activators of phospholipase C. Glucose, in contrast, only caused minor increases in DAG containing myristic and palmitic acid without affecting total DAG mass. The failure to detect stimulation of protein kinase C by glucose could be due to both the limited amount and to the different fatty acid composition of the metabolically generated DAG. The latter was in part supported by experiments performed on protein kinase C partially purified from HIT cells. Indeed, 1,2-dipalmitoylglycerol, presumed to be the main DAG species generated by glucose, was only one-third as active as 1,2-dioleoylglycerol and 1-stearoyl-2-arachidonylglycerol in stimulating the isolated enzyme at physiological Ca2+ concentration. It is therefore unlikely that DAG and protein kinase C play a major role in glucose-stimulated insulin secretion.
Animals↗
Effects of nutrient and non-nutrient stimuli on cytosolic pH in cultured insulinoma (HIT-T15) cells.
Intracellular pH (pHi) was measured in the insulin-secreting HIT-T15 cell line using the pH-sensitive fluorescent dye, 2',7'-bis(carboxyethyl)-5'(6')-carboxyfluorescein (BCECF). It was observed that the addition of a weak acid (e.g., acetate or propionate) caused a rapid decrease in pHi, followed by a slower recovery to the resting pH value. Conversely the addition of N4Cl caused an increase in pHi followed by recovery. The addition of amiloride caused a fall in pHi; however, in this case no recovery to basal pH levels was observed. Subsequent addition of a weak acid caused a further fall in pHi with no recovery. The addition of glucose caused a transient acidification followed by alkalinization. When glucose was added to cells which had been pretreated with amiloride, the initial acidification was not followed by recovery or alkalinization. Addition of glyceraldehyde, alpha-ketoisocaproate, lactate or pyruvate to HIT cells also resulted in intracellular acidification followed by recovery. Similarly, depolarisation of HIT cells by treatment with high K+ or with Ba2+ was associated with a pronounced fall in pHi, followed by a gradual recovery. Insulin secretion from HIT cells was stimulated by glucose, glyceraldehyde, alpha-ketoisocaproate, lactate, pyruvate and KCl, whilst amiloride and weak acids exerted only modest effects in the absence of glucose, but amiloride in particular markedly potentiated glucose-induced insulin release. Thus, HIT cells appear to have an amiloride-sensitive mechanism for the extrusion of protons, probably Na+-H+ exchange. Whilst intracellular acidification appears to potentiate secretory responses to nutrient stimuli, it seems unlikely that the activation of HIT cells by these nutrients occurs as a result of intracellular acidification. The mechanisms by which various nutrient and non-nutrient stimuli might exert distinct effects on pHi are discussed.
Acid-Base Equilibrium↗
Studies of the mechanism of activation of HIT-T15 cells by lactate.
L-Lactate, D-lactate, propionate and acetate (all 20 mM) caused a marked intracellular acidification in HIT-T15 cells loaded with 2'7'-bis(carboxyethyl)-5'(6')-carboxyfluorescein (BCECF), followed by recovery to more alkaline values. The effects of L- and D-lactate, but not propionate or acetate, were inhibited by 5 mM alpha-fluorocinnamate. Both L- and D-lactate caused a marked depolarisation and rise in cytosolic [Ca2+] in HIT cells as assessed by oxonol-V and quin2 fluorescence, respectively. Propionate had similar, though less marked, effects, whereas acetate exerted only a modest influence on membrane potential and cytosolic [Ca2+]. The rate of oxidation of L-lactate by HIT cells greatly exceeded that of D-lactate. alpha-Fluorocinnamate delayed, but did not prevent, the effects of L-lactate on HIT cell membrane potential or cytosolic [Ca2+]. L-lactate diminished the rate of efflux of 86Rb+ from preloaded HIT cells. Inhibition of calcium- and nucleotide-sensitive K+ channels with tetraethylammonium and tolbutamide also reduced the 86Rb+ efflux rate, and prevented any further reduction in response to L-lactate. However, such inhibition of K+ channels did not prevent a further depolarisation and rise in cytosolic [Ca2+] upon the subsequent addition of lactate. It is suggested that the activation of HIT-T15 cells by lactate is not the result of intracellular acidification or increased metabolic flux, and does not require diminished K+ permeability. An alternative mechanism is based upon the possible electrogenic flux of lactate across the plasma membrane.
Acetates↗
Preservation of insulin mRNA levels and insulin secretion in HIT cells by avoidance of chronic exposure to high glucose concentrations.
Glucose toxicity of the pancreatic beta cell is considered to play a secondary role in the pathogenesis of type II diabetes mellitus. To gain insights into possible mechanisms of action of glucose toxicity, we designed studies to assess whether the loss of insulin secretion associated with serial passages of HIT-T15 cells might be caused by chronic exposure to high glucose levels since these cells are routinely cultured in media containing supramaximal stimulatory concentrations of glucose. We found that late passages of HIT cells serially cultured in media containing 11.1 mM glucose lost insulin responsivity and had greatly diminished levels of insulin content and insulin mRNA. In marked contrast, late passages of HIT cells cultured serially in media containing 0.8 mM glucose retained insulin mRNA, insulin content, and insulin responsivity to glucose in static incubations and during perifusion with glucose. No insulin gene mutation or alteration of levels of GLUT-2 were found in late passages of HIT cells cultured with media containing 11.1 mM glucose. These data uniquely indicate that loss of beta cell function in HIT cells passed serially under high glucose conditions is caused by loss of insulin mRNA, insulin content, and insulin secretion and is preventable by culturing HIT cells under low glucose conditions. This strongly suggests potential genetic mechanisms of action for glucose toxicity of beta cells.
Animals↗