Low pH of interstitial fluid around hippocampus of the brain in diabetic OLETF rats

Large-scale animal model study uncovers altered brain pH and lactate levels as a transdiagnostic endophenotype of neuropsychiatric disorders involving cognitive impairment

Increased levels of lactate, an end-product of glycolysis, have been proposed as a potential surrogate marker for metabolic changes during neuronal excitation. These changes in lactate levels can result in decreased brain pH, which has been implicated in patients with various neuropsychiatric disorders. We previously demonstrated that such alterations are commonly observed in five mouse models of schizophrenia, bipolar disorder, and autism, suggesting a shared endophenotype among these disorders rather than mere artifacts due to medications or agonal state. However, there is still limited research on this phenomenon in animal models, leaving its generality across other disease animal models uncertain. Moreover, the association between changes in brain lactate levels and specific behavioral abnormalities remains unclear. To address these gaps, the International Brain pH Project Consortium investigated brain pH and lactate levels in 109 strains/conditions of 2294 animals with genetic and other experimental manipulations relevant to neuropsychiatric disorders. Systematic analysis revealed that decreased brain pH and increased lactate levels were common features observed in multiple models of depression, epilepsy, Alzheimer's disease, and some additional schizophrenia models. While certain autism models also exhibited decreased pH and increased lactate levels, others showed the opposite pattern, potentially reflecting subpopulations within the autism spectrum. Furthermore, utilizing large-scale behavioral test battery, a multivariate cross-validated prediction analysis demonstrated that poor working memory performance was predominantly associated with increased brain lactate levels. Importantly, this association was confirmed in an independent cohort of animal models. Collectively, these findings suggest that altered brain pH and lactate levels, which could be attributed to dysregulated excitation/inhibition balance, may serve as transdiagnostic endophenotypes of debilitating neuropsychiatric disorders characterized by cognitive impairment, irrespective of their beneficial or detrimental nature.

Prediction of subcutaneous drug absorption - do we have reliable data to design a simulated interstitial fluid?

For many years subcutaneous (SC) administration has represented the main route for delivering biopharmaceuticals. However, little information exists about the milieu in the subcutaneous tissue, especially about the properties/composition of the fluid present in this tissue, the interstitial fluid (ISF), which is one of the key elements for the drug release and absorption. Better knowledge on SC ISF composition, properties and dynamics may provide better insight into in vivo drug performance. In addition, a simulated SC ISF, which allows better prediction of in vivo absorption of drugs after subcutaneous administration based on in vitro release experiments, would help to improve formulation design, and reduce the number of animal studies and clinical trials required to obtain marketing authorization. To date, a universal medium for predicting drug solubility/release in the interstitial space does not exist. This review provides an overview of the currently available information on composition and physicochemical properties of SC ISF and critically discusses different isolation techniques in the context of information that could be gained from the isolated fluid. Moreover, it surveys current in vitro release media aiming to mimic SC ISF composition and highlights information gaps that need to be filled for designing a meaningful artificial SC ISF.

The Acidic Microenvironment: Is It a Phenotype of All Cancers? A Focus on Multiple Myeloma and Some Analogies with Diabetes Mellitus

Simple Summary

Multiple myeloma (MM) is a hematological malignancy characterized by an abnormal clone of plasma cells in the bone marrow. Currently, both the disease progression and its therapy are too often followed by a series of complications and the standard treatment for MM is aimed at improving the quality of life and to prolong progression-free survival (PFS), and overall survival (OS) of patients. This review looks at MM therapies from a different sight. It starts from a clear scientific background, suggesting that many malignant tumors have some common phenotype that isolates the tumor from the rest of the body. Between these phenotypes, extracellular acidity exerts a key role and data collected in the last two decades support the use of anti-acidic drugs in the treatment of cancers, including MM. Lastly, as many cancers, MM has some similarities with type II diabetes mellitus (DM) in the mechanism leading to the extracellular acidity, supporting the use of both a wide panel of proton transporters inhibitors and probably also of some anti-DM drugs in the treatment of both MM and DM.

Abstract

Multiple myeloma (MM) is a hematological malignancy with a poor prognosis while with a long and progressive outcome. To date, the therapeutic options are restricted to few drugs, including thalidomide or its derivates and autologous transplantation including stem-cell transplantation. More recently, the use of both proteasome inhibitors and monoclonal antibodies have been included in MM therapy, but the clinical results are still under evaluation. Unfortunately, death rates (within the 5-year overall survival rates) are still very high (45%), with no relevant improvement over the past 10 years. Here, we discuss data supporting a new therapeutic approach against MM, based on a common phenotype of tumor malignancies, which is the acidic microenvironment. Extracellular acidity drastically reduces the efficacy of both anti-tumor drugs and the immune reaction against tumors. Pre-clinical data have shown that anti-acidic drugs, such as proton pump inhibitors (PPIs), have a potent cytotoxic effect against human MM cells, thus supporting their use in the treatment of this malignancy. Here, we discuss also similarities between MM and type II diabetes mellitus (DM) with high risk of developing MM, suggesting that both anti-diabetic drugs and a hypocaloric diet may help in curing MM patients.

Topiramate Decelerates Bicarbonate-Driven Acid-Elimination of Human Neocortical Neurons: Strategic Significance for its Antiepileptic, Antimigraine and Neuroprotective Properties

BACKGROUND

Mammalian central neurons regulate their intracellular pH (pHi) strongly and even slight pHi-fluctuations can influence inter-/intracellular signaling, synaptic plasticity and excitability.

OBJECTIVE

For the first time, we investigated topiramate´s (TPM) influence on pHi-behavior of human central neurons representing a promising target for anticonvulsants and antimigraine drugs.

METHODS

In slice-preparations of tissue resected from the middle temporal gyrus of five adults with intractable temporal lobe epilepsy, BCECF-AM-loaded neocortical pyramidal-cells were investigated by fluorometry. The pHi-regulation was estimated by using the recovery-slope from intracellular acidification after an Ammonium-Prepulse (APP).

RESULTS

Among 17 pyramidal neurons exposed to 50 μM TPM, seven (41.24%) responded with an altered resting-pHi (7.02±0.12), i.e., acidification of 0.01-0.03 pH-units. The more alkaline the neurons, the greater the TPM-related acidifications (r=0.7, p=0.001, n=17). The recovery from APPacidification was significantly slowed under TPM (p<0.001, n=5). Further experiments using nominal bicarbonate-free (n=2) and chloride-free (n=2) conditions pointed to a modulation of the HCO3 -- driven pHi-regulation by TPM, favoring a stimulation of the passive Cl-/HCO3 --antiporter (CBT) - an acid-loader predominantly in more alkaline neurons.

CONCLUSION

TPM modulated the bicarbonate-driven pHi-regulation, just as previously described in adult guinea-pig hippocampal neurons. We discussed the significance of the resulting subtle acidifications for beneficial antiepileptic, antimigraine and neuroprotective effects as well as for unwanted cognitive deficits.

The Effects of Systemic and Local Acidosis on Insulin Resistance and Signaling

Most pathological conditions that cause local or systemic acidosis by overcoming the buffering activities of body fluids overlap with those diseases that are characterized by glucose metabolic disorders, including diabetes mellitus, inflammation, and cancer. This simple observation suggests the existence of a strong relationship between acidosis and insulin metabolism or insulin receptor signaling. In this review, we summarized the current knowledge on the activity of insulin on the induction of acidosis and, vice versa, on the effects of changes of extracellular and intracellular pH on insulin resistance. Insulin influences acidosis by promoting glycolysis. Although with an unclear mechanism, the lowering of pH, in turn, inhibits insulin sensitivity or activity. In addition to ketoacidosis that is frequently associated with diabetes, other important and more complex factors are involved in this delicate feedback mechanism. Among these, in this review we discussed the acid-mediated inhibiting effects on insulin binding affinity to its receptor, on glycolysis, on the recycling of glucose transporters, and on insulin secretion via transforming growth factor β (TGF-β) activity by pancreatic β-cells. Finally, we revised current data available on the mutual interaction between insulin signaling and the activity of ion/proton transporters and pH sensors, and on how acidosis may enhance insulin resistance through the Nuclear Factor kappa B (NF-κB) inflammatory pathway.

Improvement of Diabetes Mellitus Symptoms by Intake of Ninjin'yoeito

Diabetes mellitus is a well-known common disease and one of the most serious social problems in the worldwide. Although various types of drugs are developed, the number of patients suffering from diabetes mellitus is still increasing. Ninjin'yoeito (NYT) is one of formulas used in Japanese traditional herbal medicines for improving various types of metabolic disorders. However, the effect of NYT on diabetes mellitus has not yet been investigated. In the present study, we tried to clarify the action of NYT on the serum glucose level in streptozotocin (STZ)-induced diabetic mice. We found that intake of NYT decreased the serum glucose level and increased insulin sensitivity in STZ-induced diabetic mice. NYT treatment also improved acidification of the interstitial fluid around skeletal muscles found in STZ-induced diabetic mice, while the interstitial fluid acidification has been reported to cause insulin resistance. Furthermore, in the proximal colon of STZ-induced diabetic mice, NYT treatment showed a tendency to increase the expression of sodium-coupled monocarboxylate transporter 1 (SMCT1), which has ability to absorb weak organic acids (pH buffer molecules) resulting in improvement of the interstitial fluid acidification. Based on these observations, the present study suggests that NYT is a useful formula to improve hyperglycemia and insulin resistance via elevation of interstitial fluid pH in diabetes mellitus, which might be caused by increased absorption of pH buffer molecules (SMCT1 substrates, weak organic acids) mediated through possibly elevated SMCT1 expression in the proximal colon.

The Proposal of Molecular Mechanisms of Weak Organic Acids Intake-Induced Improvement of Insulin Resistance in Diabetes Mellitus via Elevation of Interstitial Fluid pH

Blood contains powerful pH-buffering molecules such as hemoglobin (Hb) and albumin, while interstitial fluids have little pH-buffering molecules. Thus, even under metabolic disorder conditions except severe cases, arterial blood pH is kept constant within the normal range (7.35~7.45), but the interstitial fluid pH under metabolic disorder conditions becomes lower than the normal level. Insulin resistance is one of the most important key factors in pathogenesis of diabetes mellitus, nevertheless the molecular mechanism of insulin resistance occurrence is still unclear. Our studies indicate that lowered interstitial fluid pH occurs in diabetes mellitus, causing insulin resistance via reduction of the binding affinity of insulin to its receptor. Therefore, the key point for improvement of insulin resistance occurring in diabetes mellitus is development of methods or techniques elevating the lowered interstitial fluid pH. Intake of weak organic acids is found to improve the insulin resistance by elevating the lowered interstitial fluid pH in diabetes mellitus. One of the molecular mechanisms of the pH elevation is that: (1) the carboxyl group (R-COO⁻) but not H⁺ composing weak organic acids in foods is absorbed into the body, and (2) the absorbed the carboxyl group (R-COO⁻) behaves as a pH buffer material, elevating the interstitial fluid pH. On the other hand, high salt intake has been suggested to cause diabetes mellitus; however, the molecular mechanism is unclear. A possible mechanism of high salt intake-caused diabetes mellitus is proposed from a viewpoint of regulation of the interstitial fluid pH: high salt intake lowers the interstitial fluid pH via high production of H⁺ associated with ATP synthesis required for the Na⁺,K⁺-ATPase to extrude the high leveled intracellular Na⁺ caused by high salt intake. This review article introduces the molecular mechanism causing the lowered interstitial fluid pH and insulin resistance in diabetes mellitus, the improvement of insulin resistance via intake of weak organic acid-containing foods, and a proposal mechanism of high salt intake-caused diabetes mellitus.

Actions of Quercetin, a Polyphenol, on Blood Pressure

Disorder of blood pressure control causes serious diseases in the cardiovascular system. This review focuses on the anti-hypertensive action of quercetin, a flavonoid, which is one of the polyphenols characterized as the compounds containing large multiples of phenol structural units, by varying the values of various blood pressure regulatory factors, such as vascular compliance, peripheral vascular resistance, and total blood volume via anti-inflammatory and anti-oxidant actions. In addition to the anti-inflammatory and anti-oxidant actions of quercetin, we especially describe a novel mechanism of quercetin’s action on the cytosolic Cl⁻ concentration ([Cl⁻]_c) and novel roles of the cytosolic Cl⁻ i.e., (1) quercetin elevates [Cl⁻]_c by activating Na⁺-K⁺-2Cl⁻ cotransporter 1 (NKCC1) in renal epithelial cells contributing to Na⁺ reabsorption via the epithelial Na⁺ channel (ENaC); (2) the quercetin-induced elevation of [Cl⁻]_c in renal epithelial cells diminishes expression of ENaC leading to a decrease in renal Na⁺ reabsorption; and (3) this reduction of ENaC-mediated Na⁺ reabsorption in renal epithelial cells drops volume-dependent elevated blood pressure. In this review, we introduce novel, unique mechanisms of quercetin’s anti-hypertensive action via activation of NKCC1 in detail.

Effect of Brazilian green propolis in patients with type 2 diabetes: A double-blind randomized placebo-controlled study

Propolis contains a variety of chemical compounds, including polyphenols, flavonoids, phenolic aldehydes, amino acids and vitamins, and presents numerous biological and pharmacological properties. The aim of the present study was to evaluate the effect of propolis on blood examination data in patients with type 2 diabetes. In the double-blind, 8-week randomized controlled study, 80 patients with type 2 diabetes were enrolled. Patients were randomly assigned to receive Brazilian green propolis (226.8 mg/day for 8 weeks) (n=41) or the placebo (n=39). The primary endpoint was to detect changes in blood examination data associated with metabolic disorders in patients suffering from diabetes mellitus, including the homeostasis model assessment of insulin resistance (HOMA-IR), uric acid and estimated glomerular filtration rate (eGFR) from baseline to the end of this study. The value of HOMA-IR was not significantly changed by the 8-week administration of propolis or placebo from the baseline data. Values of blood uric acid and eGFR in patients taking the placebo became worse at 8 weeks compared to the baseline, whereas this did not occur in patients consuming Brazilian green propolis. However, HOMA-IR was not improved by propolis intake. A randomized, controlled 8-week trial suggests that Brazilian green propolis (226.8 mg/day) prevents patients with type 2 diabetes from developing worse blood uric acid and eGFR.

Roles of interstitial fluid pH in diabetes mellitus: Glycolysis and mitochondrial function

The pH of body fluids is one the most important key factors regulating various cell function such as enzyme activity and protein-protein interaction via modification of its binding affinity. Therefore, to keep cell function normal, the pH of body fluids is maintained constant by various systems. Insulin resistance is one of the most important, serious factors making the body condition worse in diabetes mellitus. I have recently found that the pH of body (interstitial) fluids is lower in diabetes mellitus than that in non-diabetic control, and that the lowered pH is one of the causes producing insulin resistance. In this review article, I introduce importance of body (interstitial) fluid pH in regulation of body function, evidence on abnormal regulation of body fluid pH in diabetes mellitus, and relationship between the body fluid pH and insulin resistance. Further, this review proposes perspective therapies on the basis of regulation of body fluid pH including propolis (honeybee product) diet.

Significance of propolis administration for homeostasis of CD4(+)CD25(+) immunoregulatory T cells controlling hyperglycemia

In the present study, we examined the effect of ethanolic soluble derivative of propolis (EEP) extract on immunological function in diabetic mouse models with the aim of highlighting the role of regulatory T cell, the change of cell surface molecule, and in vivo productions of IFN-γ. Murine models of diabetes mellitus (DM) were created by injecting normal mice with S961 peptide. Normal BALB/c mice were injected intraperitoneally with peptide S961 300 mg/kg body weight (BW) twice a day for eight days. On day 15, the spleen was isolated; then, cell surface molecules and regulatory T cells were analyzed using flow cytometry. The histopathological changes were monitored in the liver of treated and control mice. Afterward, we tested the ability of propolis as an immunomodulator that initiate normality metabolism and homeostasis. The propolis decreased blood sugar levels and increased the number of naïve T cells expressing CD62L molecule by suppressing the development of effector cells in diabetic mice. However, the propolis stimulated development of effector cells, which was indicated by increasing the number of CD4⁺CD25⁺ T cells in normal mice. Moreover, the propolis increased the production of IFN-γ in normal mice, whereas in mouse models of diabetes mellitus propolis tends to suppress the production of IFN-γ. The histological analysis of the liver shows that at a dose of 50–200 mg/kg BW propolis does not show a toxic effect so that the dose is categorized safe. Therefore, the ethanolic soluble derivative of propolis (EEP) extract warrant for further exploited as an antidiabetic agent that safe for human.

Importance of pH homeostasis in metabolic health and diseases: crucial role of membrane proton transport

Protons dissociated from organic acids in cells are partly buffered. If not, they are transported to the extracellular fluid through the plasma membrane and buffered in circulation or excreted in urine and expiration gas. Several transporters including monocarboxylate transporters and Na(+)/H(+) exchanger play an important role in uptake and output of protons across plasma membranes in cells of metabolic tissues including skeletal muscle and the liver. They also contribute to maintenance of the physiological pH of body fluid. Therefore, impairment of these transporters causes dysfunction of cells, diseases, and a decrease in physical performance associated with abnormal pH. Additionally, it is known that fluid pH in the interstitial space of metabolic tissues is easily changed due to little pH buffering capacitance in interstitial fluids and a reduction in the interstitial fluid pH may mediate the onset of insulin resistance unlike blood containing pH buffers such as Hb (hemoglobin) and albumin. In contrast, habitual exercise and dietary intervention regulate expression/activity of transporters and maintain body fluid pH, which could partly explain the positive effect of healthy lifestyle on disease prognosis.

Lowered extracellular pH is involved in the pathogenesis of skeletal muscle insulin resistance

Insulin resistance in the skeletal muscle is manifested by diminished insulin-stimulated glucose uptake and is a core factor in the pathogenesis of type 2 diabetes mellitus (DM), but the mechanism causing insulin resistance is still unknown. Our recent study has shown that pH of interstitial fluids was lowered in early developmental stage of insulin resistance in OLETF rats, a model of type 2 DM. Therefore, in the present study, we confirmed effects of the extracellular pH on the insulin signaling pathway in a rat skeletal muscle-derived cell line, L6 cell. The phosphorylation level (activation) of the insulin receptor was significantly diminished in low pH media. The phosphorylation level of Akt, which is a downstream target of the insulin signaling pathway, also decreased in low pH media. Moreover, the insulin binding to its receptor was reduced by lowering extracellular pH, while the expression of insulin receptors on the plasma membrane was not affected by the extracellular pH. Finally, insulin-stimulated 2-deoxyglucose uptake in L6 cells was diminished in low pH media. Our present study suggests that lowered extracellular pH conditions may produce the pathogenesis of insulin resistance in skeletal muscle cells.