Transient ischemic attack without self-awareness of symptoms witnessed by bystanders: analysis of the PROMISE-TIA registry.

BACKGROUND AND PURPOSE: A transient ischemic attack (TIA) can occur without self-awareness of symptoms. We aimed to investigate characteristics of patients with a tissue-based diagnosis of TIA but having no self-awareness of their symptoms and whose symptoms were witnessed by bystanders. METHODS: We used data from the multicenter registry of 1414 patients with a clinical diagnosis of TIA. For patients without evidence of ischemic lesions on imaging, clinical characteristics were compared between patients with and without self-awareness of their TIA symptoms. RESULTS: Among 896 patients (559 men, median age of 70 years), 59 (6.6%) were unaware of their TIA symptoms, but had those symptoms witnessed by bystanders. Patients without self-awareness of symptoms were older and more frequently female, and more likely to have previous history of stroke, premorbid disability, and atrial fibrillation, but less likely to have dyslipidemia than those with self-awareness. Patients without self-awareness of symptoms arrive at hospitals earlier than those with self-awareness (P < 0.001). ABCD2 score was higher in patients without self-awareness of symptoms than those with self-awareness (median 5 vs. 4, P = 0.002). Having no self-awareness of symptoms was a significant predictor of ischemic stroke within 1 year after adjustment for sex, ABCD2 score, and onset to arrival time (hazard ratio = 2.44, 95% confidential interval: 1.10-4.83), but was not significant after further adjustment for arterial stenosis or occlusion. CONCLUSIONS: Patients with a TIA but having no self-awareness of their symptoms might have higher risk of subsequent ischemic stroke rather than those with self-awareness, suggesting urgent management is needed even if patients have no self-awareness of symptoms.

Human serum paraoxonase concentration predicts cardiovascular mortality in hemodialysis patients.

AIMS: Human serum paraoxonase (PON1) is associated with high-density lipoprotein, and inhibits oxidative modification of low-density lipoprotein. Therefore, PON1 is supposed to contribute to the prevention of atherosclerosis. We and other investigators have shown that the enzymatic activities and concentrations of PON1 were decreased in maintenance hemodialysis (HD) patients. However, the effect of PON1 status on the long-term outcome of HD patients has not been reported. In this study, we examined the association between baseline PON 1 status and cardiovascular mortality in an observation study of an outpatient HD population. PATIENTS AND METHODS: The relation between baseline cardiovascular risk factors and clinical events was investigated, during 6 years of follow-up, in 81 HD patients (50 males and 31 females) whose enzymatic activities, concentrations and genetic polymorphisms of PON1 had been determined in a previous study. RESULTS: During follow-up for 6 years, we recorded 42 deaths, including 24 fatal cardiovascular events. In univariate analyses, baseline PON1 concentration was associated with not only cardiovascular mortality (p < 0.005), but also all-cause mortality (p < 0.001) during the period of follow-up, as were age, preexisting cardiovascular disease (CVD) and hemoglobin concentration. In a multivariate Cox regression analysis, PON1 concentration retained significant associations with cardiovascular mortality (p < 0.05) and all-cause mortality (p < 0.005) even after correction of known risk factors for CVD or mortality in HD patients. Using Kaplan-Meier survival curves, we assessed the association between low and high concentrations of PON1 divided according to the median value (7.52 U/ml). Significantly increased cardiovascular mortality (log rank 6.125, p = 0.01) and all-cause mortality (log rank 7.113, p < 0.01) were detected in the patients with low PON1 concentrations. CONCLUSIONS: These data suggest that low PON 1 concentration may be an independent predictor of cardiovascular mortality in maintenance HD patients.

Chemosensitivity testing with highly purified fresh human tumour cells with the MTT colorimetric assay.

A major problem associated with the succinate dehydrogenase inhibition (SDI) test using tetrazolium dye (MTT) as a cancer chemosensitivity testing is the contamination of non-malignant cells in the tumour tissues. Highly purified fresh human tumour cells from 44 solid tumours and 24 malignant ascites were used for the MTT assay. The purity of tumour cells was greater than 90% after separation on Ficoll-Hypaque and Percoll discontinuous gradients. The OD570 obtained from tumour cells alone was higher than that from non-malignant cells. The chemosensitivity of tumour cells was distinct from that of non-malignant cells. Moreover, the chemosensitivity of highly purified tumour cells was also distinct from that of non-purified cells just separated from tumour tissues. 31 of the 68 patients had evaluable lesions, and received cancer chemotherapy according to the results of MTT assay using highly purified tumour cells. A clinical response was obtained in 10 of the 31 patients (response rate = 32.3%, 5 complete responses, 5 partial responses).

Significance of angiotensin I-converting enzyme and angiotensin II type 1 receptor gene polymorphisms as risk factors for coronary heart disease.

The D allele of an insertion/deletion (I/D) polymorphism in the angiotensin I-converting enzyme (ACE) gene is associated with a risk of myocardial infarction, and the relative risk associated with the ACE D allele is increased by the C allele of an angiotensin II type 1 receptor (AT1R) gene polymorphism (an A-->C transversion at nucleotide position 1166) [28]. The relation of the ACE and AT1R gene polymorphisms to coronary heart disease and the severity of coronary artery stenosis has now been investigated in 133 patients with myocardial infarction (MI) or angina pectoris who underwent coronary angiography and in 258 control subjects. The frequency of the ACE DD genotype as compared with non-DD was significantly higher in the patients who experienced an MI and in the low-risk patients than that in the controls (P < 0.05). The DD genotype showed a significantly increased risk of MI (odds ratio 1.85). The frequency of the AT1R A/C genotypes did not differ between the patients and the controls. The severity of coronary stenosis in the patients was estimated by the number of affected vessels (> 75% stenosis) and the coronary score of Gensini. Neither the number of affected vessels nor the coronary score differed among the ACE I/D genotypes. However, the number of affected vessels was significantly greater in patients with the AT1R AC genotype than in those with the 4A genotype (1.93 +/- 0.27 vs. 1.27 +/- 0.99; P < 0.05) (CC genotype was not found in the patients). After excluding patients with diabetes mellitus, the coronary score of those with the AC genotype was also significantly higher than in those with the AA genotype (51.7 +/- 34.4 vs. 18.2 +/- 23.3; P < 0.01). These results suggest that the ACE D allele is associated with the occurrence of myocardial infarction, while the AT1R C allele is involved in the development of the coronary artery stenosis.

Clinical significance of quantitative analysis of carcinoembryonic antigen assessed by flow cytometry in fresh human gastric cancer cells.

The expression of carcinoembryonic antigen(CEA) on tumor cells freshly excised from 51 patients with gastric cancer was studied using flow cytometry. The expression of CEA by flow cytometry was more quantitative than that by immunohistochemical staining. There was no relationship between the fluorescence intensity assessed by flow cytometry and serum CEA levels, except for patients with a high titer of serum CEA. The patients with high grade CEA expression on tumor cells by flow cytometry had poor prognoses, compared to patients with low CEA expression in undifferentiated gastric cancer. Thus, it is suggested that the quantitative CEA expression on tumor cells by flow cytometry could be a useful prognostic marker in postoperative gastric cancer patients.

Interleukin-4 inhibits lak and initial phase til activity via interleukin-2 receptor.

In the present study, we analyzed the proliferation and cytotoxic activities of LAK cells and initial phase TILs by stimulation with IL-4. IL-4 obviously inhibited the DNA synthesis of LAK cells and initial phase TILs at the concentration of 250 pg/ml and 25 pg/ml, respectively. Furthermore, IL-4 (25 ng/ml for LAK cells, 25 pg/ml for initial phase TILs) suppressed the cytotoxic activities against K562, KATO-III, and autologous tumor cells. The discrepancy of the concentration between the proliferation and the cytotoxicicity by IL-4 suggested different pathways in terms of the generation of LAK cells. In order to clarify the inhibitory mechanism of IL-4, we measured the expression of IL-2 receptor. IL-2 receptor alpha chain was strongly down-regulated by IL-4. Thus, IL-4 modulates the activation of LAK cells and initial phase TILs via the IL-2 receptor alpha chain.

Enhancement of tumor cell susceptibility to tumor-infiltrating lymphocytes by cisplatin.

Some means of enhancing the susceptibility of tumor cells to tumor-infiltrating lymphocytes (TIL) are required in adoptive immunotherapy. This study was designed to investigate whether or not tumor cell lysis by TIL was enhanced by treatment of the tumor cells with cisplatin, and also to clarify the mechanism of cisplatin's action on tumor cells. Autologous tumor cells and established cancer cell lines, including KATO-III and MKN-28, were used. Cytotoxic activities of TIL, the surface antigens of tumor cells, conjugation of TIL and tumor cells, and the production of TNF alpha from TIL were analyzed. Tumor cells treated with 2 micrograms/ml cisplatin for 12 h in vitro were more susceptible to bulk-cultured TIL and TIL clones. The surface antigens of tumor cells were not altered by the treatment with cisplatin. Cisplatin-treated tumor cells showed a higher binding ratio to TIL than did non-treated tumor cells. The anti-(tumor necrosis factor) (anti-TNF) or anti-TNF receptor antibody blocked the enhancement of cytotoxic activity by cisplatin. Thus, it was clarified that cisplatin enhanced the susceptibility of tumor cells to bulk-cultured TIL and TIL clones. Furthermore, the enhancement of cytotoxic activity by TIL in cisplatin-treated tumor cells was caused by a higher binding ratio to TIL and higher susceptibility to the TNF produced by TIL.

Suppression of plasma cholesteryl ester transfer protein activity in acute hyperinsulinemia and effect of plasma nonesterified fatty acid.

Cholesteryl ester transfer protein (CETP) is a major determinant of the plasma high-density lipoprotein cholesterol (HDL-C) level and plays an important role in the reverse cholesterol transport system. The purpose of this study was to determine the effect of acute hyperinsulinemia on plasma CETP activity in normal subjects and patients with non-insulin-dependent diabetes mellitus (NIDDM). Hyperinsulinemia was achieved using the hyperinsulinemic-euglycemic clamp. CETP activity was determined as the transfer of radiolabeled cholesterol in HDL3 to acceptor lipoprotein. Mean plasma CETP activity during an insulin infusion in both subject groups was significantly decreased compared with the mean basal activity. Suppression of plasma CETP activity in the NIDDM patients was significantly less than in the normal subjects (-4.2% +/- 7.9% v -9.6% +/- 6.4%, P < .02). Regression analysis showed that this suppression was correlated with plasma nonesterified fatty acid (NEFA) levels after the clamp and with the magnitude of the NEFA decrease (r = .318, P < .02 and r = .292, P < .05, respectively). The data suggest that acute hyperinsulinemia reduces plasma CETP activity through a decrease in plasma NEFA.

Serum paraoxonase activity and its relationship to diabetic complications in patients with non-insulin-dependent diabetes mellitus.

Paraoxonase (PON) is an esterase associated with high-density lipoprotein (HDL). Serum PON activity is affected by PON gene polymorphism (L/M, Leu-Met54, and Q/R, Gln-Arg191). We investigated PON activity and polymorphism in 108 patients (53 men and 55 women) with non-insulin-dependent diabetes mellitus (NIDDM) and 161 control subjects (82 men and 79 women) matched to the patients by age and gender. Serum PON activity was determined using paraoxon as a substrate. PON gene polymorphisms were detected by the restriction fragment length polymorphism method after a polymerase chain reaction. The mean PON activity in the patients was significantly lower than in the controls (116+/-55 and 162+/-57 U/L, respectively, P < .001). The distribution of each genotype showed no difference between the patient and control groups, and PON activity increased in the order of the QQ < OR < RR genotype and MM < LM < LL genotype in both groups. However, among each genotype subgroup, the activity was lower in patients than in controls. Forty-one patients with retinopathy had lower PON activity than those without the complication (94+/-36 and 129+/-61 U/L, respectively, P < .002). There was also a significant difference in PON activity between patients with and without overt proteinuria (93+/-38 and 122+/-58 U/L, respectively, P < .05). Logistic analysis showed that serum PON activity was one of the significant factors for retinopathy. These results suggest that decreased PON activity in patients with NIDDM is involved in diabetic vascular complications.

Autologous mixed lymphocyte reaction and postoperative prognosis in patients with gastric carcinoma.

The autologous mixed lymphocyte reaction (AMLR) represents a self recognitive response, which is very important in the immunoregulatory network system. We investigated whether the AMLR activity of patients with gastric carcinoma could reflect the postoperative prognosis to clarify the significance of autoreactivity in anti-tumor immune system in cancer patients. The AMLR activity was suppressed both in the peripheral blood and in the spleen of patients with gastric carcinoma. The patients were divided into two groups; high responder and low responder group. The former consisted of patients whose AMLR activity was extremely suppressed, and the latter of patients whose AMLR activity was mildly suppressed. The survival rate and disease-free survival rate were generally higher in the high responder group than in the low responder group, especially in the spleen. Moreover, none of the patients in the high responder group for the AMLR activity in the spleen died within three years. These results indicated that the AMLR activity could reflect the prognosis of patients who received conventional curative operation. Therefore, it was suggested that the AMLR might be a useful parameter of postoperative prognosis in gastric cancer patients and that autoreactive T cells might play a pivotal role in auto-specific immunological control of tumor growth and metastases.

Cisplatin modulates tumor cell susceptibility to tumor-infiltrating lymphocytes in vivo.

We investigated the in vivo augmentation of susceptibility of tumor cells to tumor-infiltrating lymphocytes (TILs) with cisplatin (CDDP). TILs showed cytotoxicity against autologous and established tumor cells. Pretreatment of tumor cells with CDDP 2 mu g/ml for 12 h enhanced the susceptibility of tumor cells to TILs in vitro. TILs and autologous tumor cells were obtained from malignant ascites of patients, before and after the intraperitoneal administration of CDDP. TILs had higher cytotoxicity against autologous tumor cells of CDDP treated as compared to untreated control tumor cells, providing direct evidence of in vivo immunomodulatory effect of CDDP in cancer patients.

Polysaccharide preparation PSK augments the proliferation and cytotoxicity of tumor-infiltrating lymphocytes in vitro.

We have investigated whether or not polysaccharide preparation PSK directly augments the proliferation and cytotoxicity of tumor-infiltrating lymphocytes (TILs). TILs were separated from 10 patients with gastrointestinal cancer (5 gastric cancers, 3 colon cancers and 2 pancreatic cancers). TILs were cultured with IL-2 and PSK for 7 days. The DNA synthesis of TILs was augmented by incubation with 100 micrograms/ml of PSK, which was similar to serum level with oral administration of PSK in cancer patients. The effect of PSK in DNA synthesis was also found by elimination of non-T cells. Furthermore, we established TIL clones and examined the effect of PSK on TILs clones. The DNA synthesis was augmented by PSK in CD4 positive and CD8 positive TIL clones without non-T cells, suggesting that PSK acts directly on TILs. We examined the cytotoxic activities of TILs by the 4-h and 16-h 51Cr release assay. PSK did not affect the cytotoxic activity of TILs against autologous tumor cells and KATO-III cells in the 4h 51Cr release assay, whereas PSK induced high lysability of TILs against autologous tumor cells in the 16-h 51Cr release assay. We studied the ability of PSK to induce cytokines from TILs using a double chamber plate. The DNA synthesis of tumor cells was more suppressed by the mixed-tumor cell culture supernatants of TILs cultured with PSK, compared to that of TILs cultured without PSK. It is suggesting that PSK induced long term killing activity of TILs by induction of cytotoxic cytokines. Thus, PSK augmented the proliferative response of TILs without interaction of T cells and non-T cells and induced cytotoxic cytokines of TILs.

Ubenimex treatment enhances the susceptibility of gastric cancer cell lines to lymphokine-activated killer cells.

We investigated the direct effects of ubenimex on the modification of gastric carcinoma cell lines' susceptibility to killer cells, and the mechanism of its action. The susceptibility of both MKN-45 cells and KATO-III cells to LAK cells was enhanced by treatment with ubenimex for 48 h (p < 0.05), and the optimal concentration for this effect was 10 micrograms/ml. The susceptibility of ubenimex treated KATO-III cells to CD3+ LAK cells, especially to those also expressing CD8, was enhanced. DNA synthesis of tumor cells was not impaired by treatment with ubenimex at all concentrations tested. The binding rate of LAK cells and ubenimex-treated KATO-III cells was similar to that between LAK cells and untreated KATO-III cells. Moreover, no alterations in the expression of any antigen related to mononuclear cell-binding to tumor cells were induced by ubenimex. Lysis or the inhibition of DNA synthesis of tumor cells by LAK cell supernatant was enhanced by ubenimex. These results suggested that the mechanism responsible for the augmentation of tumor cell susceptibility by ubenimex may be a result of the alteration of their sensitivity to some Iytic factors released by LAK cells. Thus ubenimex shows not only an indirect host-mediated anti-tumor activity but also a direct effect on tumor cells, modifying their susceptibility to killer cells, and this may explain why ubenimex shows beneficial clinical effects as an adjuvant treatment.

In vitro augmentation of cytotoxic activity of peripheral blood lymphocytes and spleen cells of cancer patients by ubenimex.

Ubenimex is used for the immunotherapy of malignant diseases as a biological response modifier (BRM) and shows beneficial effects as an adjuvant treatment. In the present study, the in vitro effects of ubenimex on the cytotoxic activity of peripheral blood lymphocytes (PBL) and spleen cells of cancer patients and the mechanism of killer cell activation were investigated. Cytotoxic activity against K562, KATO-III and autologous tumor cells was augmented by in vitro sensitization with ubenimex (p < 0.05). The optimal concentration of ubenimex for induction of cytotoxic activity was 1 micrograms/ml, similar to serum levels after clinical oral administration. The major population of killer cells activated by ubenimex recognizing K562 was CD16+, and those recognizing KATO-III were mainly CDA+ or CD8(5) cels and CD16+ NK cells, while CDA5 or CD8+T cells comprised the majority of killer cells which showed autologous tumor-killing activity. Augmentation of the cytotoxic activity of mononuclear cells by ubenimex was blocked by both anti-IL-1 beta Ab and anti-IL-2 AB. However, the expression of IL-2 receptor (p55, p75) on effector cells was not altered. Ubenimex augmented not only NK activity but also autologous tumor killing activity of PBL and spleen cells via macrophage activation. These activities of ubenimex may be clinically beneficial as an adjuvant treatment.

Non-T cell disturbance causes the suppression of the autologous mixed lymphocyte reaction in patients with gastric carcinoma.

We investigated the accessory function of non-T cells to autoreactive T cells in autologous mixed lymphocyte reaction (AMLR) and clarified the cause of the suppression of autoreactivity in patients with gastric carcinoma. The response of T cells in the AMLR in gastric cancer patients was significantly suppressed compared with that in controls. In patients in whom the AMLR of the spleen was suppressed more than that of the peripheral blood, the degree of stimulation of non-T cells from the spleen was remarkably suppressed, on the other hand, in patients in whom AMLR of the peripheral blood was suppressed more than the spleen, the degree of stimulation from the peripheral blood was remarkably suppressed. The expression of HLA-DR antigens on non-T cells of gastric cancer patients was lower than that of controls. AMLR was considerably decreased in controls by the treatment non-T cells with anti-HLA-DR MoAb, but not in cancer patients. Treatment of non-T cells from the spleen of gastric cancer patients with IFN-gamma remarkably improved T cell proliferation in the AMLR. IFN-gamma also enhanced the expression of HLA-DR antigens on non-T cells. The disturbance of non-T cells was not biased to a specific population. These disturbances of non-T cells suppressed the AMLR independently of stage status. Therefore, the immunological abnormality of non-T cells manifested by reduced accessory function to autoreactive T cells may cause impaired immunological surveillance against tumors and permit cancer cell growth.

Etoposide enhances the antitumor effects of cisplatin in gastric cancer cells.

We studied the combination effect of cisplatin(CDDP) plus etoposide(VP-16) in an established gastric cancer cell line, KATO-III, and also highly purified fresh human tumor cells obtained from 55 gastric cancer patients, using MTT assay. The synergistic effects of CDDP plus VP-16 were shown by both the fractional product method and median effect plot analysis in KATO-III cells, and by fractional product method in fresh human gastric cancer cells. The combination with CDDP and VP-16 showed the synergistic antitumor effects in not only KATO-III cells, but also fresh human gastric cancer cells. The antitumor effects of CDDP were enhanced by early exposure of VP-16 in KATO-III cells. The combination effects of CDDP and VP-16 were more potent in poorly differentiated gastric cancer, compared with well-differentiated cell types. Thus, it is suggested that the combination of CDDP plus VP-16 is useful in the anticancer chemotherapy of gastric cancer patients.

Neuroprotective effect of immunosuppressant FK506 in transient focal ischemia in rat: therapeutic time window for FK506 in transient focal ischemia.

Tacrolimus (FK506), an immunosuppressant currently used in clinic, is known to have neuroprotective properties. However, effects in focal ischemia are shown only in a endothelin induced middle cerebral artery (MCA) occlusion model or with filament technique at a relatively high dose. We have previously shown that FK506 had significant protective effects at a low dose of 0.3 mg kg(-1) when administered immediately after ischemia. In this study, we explored the therapeutic time window of FK506 at this low dose, in a transient focal ischemia model using filament technique. Male Sprague-Dawley rats were subjected to 2 h MCA occlusion and subsequent reperfusion. They received FK506 or vehicle (0.3 mg kg(-1)) i.v. at 30, 60 or 120 min after induction of ischemia, and were decapitated 24 h after ischemia. FK506 injected at 30 and 60 min significantly reduced cortical infarction volume (FK506 vs. vehicle; 30 min: 95 +/- 33 mm3 vs. 170 +/- 62 mm3, p < 0.05; 60 min: 93 +/- 45 mm3, vs. 168 +/- 35 mm3, p < 0.05, respectively). FK506 was ineffective when given at 120 min after ischemia. FK506 had no effect on edema formation, nor on the infarct volume in striatum. The therapeutic time window for this low dose of FK506 given i.v. is between 60 and 120 min in this model.

Paraoxonase gene polymorphism in Japanese subjects with coronary heart disease.

We investigated the association of paraoxonase (PON) gene polymorphism with both the occurrence of coronary heart disease (CHD) and the severity of coronary artery stenosis in Japanese subjects. PON is a protein associated with plasma HDL. It has been hypothesized an A/B (Gln 192-->Arg) polymorphism of PON may be involved in the pathogenesis of CHD, especially among subjects with non-insulin-dependent diabetes mellitus (NIDDM). The polymorphism was determined in 134 patients with myocardial infarction (MI) or angina pectoris, and in 252 healthy subjects as controls. The frequencies of the AA, AB, and BB genotypes in the patients were 15, 50 and 35%, respectively, and these frequencies did not differ from those in control subjects (14, 49, and 37%). The relative risk of CHD was not found to be associated with these genotypes. These data also were similar among selected subgroups (patients with MIs, those with a low-risk lipoprotein profile for CHD, and those with NIDDM). Neither the number of affected vessels nor Gensini's scores differed among the genotype groups. Our case-control study in Japanese subjects did not show that the PON A/B polymorphism is associated with a risk of CHD.

Lobular form idiopathic glomerulonephritis with massive subendothelial and paramesangial immune deposits, a three-year follow-up case.

We report a patient with unusual glomerulonephritis. A 24-year-old Japanese female was hospitalized in October 1995 because of nephrotic syndrome. Lobular form glomerulonephritis with mesangial proliferation associated with massive wide-spread accumulation of slightly eosinophilic, periodic acid Schiff-positive amorphous materials in the luminal side of the capillary walls and paramesangial area was observed in the renal biopsy specimen. Immunofluorescent study revealed massive strong staining for IgM and C4 along the capillary walls and in the mesangium. Deposits of IgA, IgG, C3 and fibrinogen were also observed. Electron microscopy showed normal thickness of the capillary basement membrane and a large amount of subendothelial and paramesangial electron dense, finely granular deposits without fibrils or tubular structures. There were no clinical or laboratory findings of systemic diseases, such as systemic lupus erythematosus and cryoglobulinemia. Therefore, we believed that this case involved an unusual idiopathic glomerular disease with massive subendothelial and paramesangial immune deposits. Glomerulonephritis in this patient appeared to be resistant to treatment with corticosteroids and that this glomerulopathy may be a progressive disease as shown during the 3-year observation. Furthermore, our patient had idiopathic hyperprolactinemia and subclinical hypothyroidism. However, the relationship between glomerulonephritis and endocrinopathy in our patient is unknown.

Degradation kinetics of L-alanyl-L-glutamine and its derivatives in aqueous solution.

The degradation kinetics of five glutamine dipeptides in aqueous solution, i.e. glycyl-L-glutamine (Gly-Gln), L-alanyl-L-glutamine (Ala-Gln), L-valyl-L-glutamine (Val-Gln), L-leucyl-L-glutamine (Leu-Gln) and L-isoleucyl-L-glutamine (Ile-Gln), were studied. Stability tests were performed using a stability-indicating high-performance liquid chromatographic assay. Two different Ala-Gln degradation routes, i.e. the cleavage of a peptide bond and the deamination of an amide group, were observed. The degradation was adequately described by pseudo-first-order kinetics. The maximum stability of Ala-Gln was obtained at an approximate pH of 6.0. The pH-rate profile described by specific acid-base catalysis and hydrolysis by water molecules agreed with the experimental results. The activation energy of Ala-Gln at pH 6.0 was determined to be 27. 1kcal mol-1, and the shelf-life (90% remaining) at 25 and 40 degrees C was predicted to be 5.3 years and 7.1 months, respectively. The rate constants of the glutamine dipeptides were influenced by the N-terminal amino acid residue and decreased in the order: Gly-Gln, Ala-Gln, Leu-Gln, Val-Gln and Ile-Gln.