Silvia Iannello

Animal and human tissue Na,K-ATPase in obesity and diabetes: A new proposed enzyme regulation.

Background:Na,K-ATPase is a membrane enzyme that energizes the Na-pump, hydrolyzing ATP and wasting energy as heat. It may play a role in thermogenesis, energy balance, and obesity development. Regulation of the enzyme by insulin is controversial. Methods:In animal and human obesity, tissue Na,K-ATPase was assayed by colorimetric measurement of released Pi. Results:Na,K-ATPase of hyperglycemic-hyperinsulinemic ob/ob mice (compared with lean control animals) was reduced in liver (−63%) and in kidney (−47%) (P < 0.001 in both instances). In contrast, in streptozotocin-treated hypoinsulinemic-diabetic Swiss mice, versus untreated animals, we found an increase of liver (+54%, P < 0.01) and kidney (+94%, P < 0.001) Na,K-ATPase. The enzyme was also increased (+99%, P < 0.05) in kidney from ob/ob mice made diabetic-hypoinsulinemic with streptozotocin (versus untreated obese animals). This is contrary to the occurrence of a genetic enzymatic defect and suggests regulation by hyperinsulinemia, present in ob/ob mice. A positive correlation between tissue enzyme activity and glycemia existed in both ob/ob and Swiss mice. In adipose tissue from obese patients (compared with lean subjects), Na,K-ATPase was reduced (−65%, P < 0.001) and negatively correlated with body mass index, oral glucose tolerance test—insulinemic area, and mean blood pressure. In vitro, in human liver tissue, 3 &mgr;g/mL glucagon exerted a statistically inhibitory effect on Na,K-ATPase (−44%). Conclusion:We hypothesize that animal and human obesity is associated with reduction of tissue Na,K-ATPase, linked to hyperinsulinemia, which may repress or inactivate the enzyme, influencing thermogenesis and energy balance.

Rheumatoid Syndrome Associated with Lung Interstitial Disorder in a Dental Technician Exposed to Ceramic Silica Dust. A Case Report and Critical Literature Review

Abstract Exposure to silica minerals is associated with silicosis and autoimmune disorders, especially systemic scleroderma. Evidence of this association has been increasingly reported in the last decade. The aim of this paper is to discuss, on the basis of a literature review, the case of a 28-year-old female dental technician who suffered from episodes of weakness, arthralgia, pain, swelling and stiffness of the fingers, dyspnoea with cough, a positive Waaler–Rose reaction, increased rheumatoid factor and normal ESR. She was a non-smoker. A rheumatoid syndrome with lung interstitial disorder, associated with silica exposure from dental ceramic products, was diagnosed. The patient had the HLA-A2-A31, HLA-B51-B18 and HLA-DR3-DR11 haplotypes, some of which are associated with autoimmune disease susceptibility. A 6-month follow-up, with adequate protection and without treatment, showed disappearance of the symptomatology and negative tests for Waaler–Rose reaction and rheumatoid factor. Exposure to silica should, therefore, be sought in the history of any patient with autoimmune or lupus-like syndrome and pulmonary changes. Symptoms associated with silica dust exposure from dental ceramic products should be recognised as being due potentially to an occupational disease, and dental technicians should be protected as workers at risk.

Animal and human tissue Na,K-ATPase in normal and insulin-resistant states: regulation, behaviour and interpretative hypothesis on NEFA effects.

The sodium(Na)‐ and potassium(K)‐activated adenosine‐triphosphatase (Na,K‐ATPase) is a membrane enzyme that energizes the Na‐pump by hydrolysing adenosine triphosphate and wasting energy as heat, so playing a role in thermogenesis and energy balance. Na,K‐ATPase regulation by insulin is controversial; in tissue of hyperglycemic‐hyperinsulinemic ob/ob mice, we reported a reduction, whereas in streptozotocin‐treated hypoinsulinemic‐diabetic Swiss and ob/ob mice we found an increased activity, which is against a genetic defect and suggests a regulation by hyperinsulinemia. In human adipose tissue from obese patients, Na,K‐ATPase activity was reduced and negatively correlated with body mass index, oral glucose tolerance test‐insulinemic area and blood pressure. We hypothesized that obesity is associated with tissue Na,K‐ATPase reduction, apparently linked to hyperinsulinemia, which may repress or inactivate the enzyme, thus opposing thyroid hormones and influencing thermogenesis and obesity development. Insulin action on Na,K‐ATPase, in vivo, might be mediated by the high level of non‐esterified fatty acids, which are circulating enzyme inhibitors and increase in obesity, diabetes and hypertension. In this paper, we analyse animal and human tissue Na,K‐ATPase, its level, and its regulation and behaviour in some hyperinsulinemic and insulin‐resistant states; moreover, we discuss the link of the enzyme with non‐esterified fatty acids and attempt to interpret and organize in a coherent view the whole body of the exhaustive literature on this complicated topic.

The glucose-6-phosphatase/glucokinase ratio in the liver of obese-diabetic subjects.

The study of G6Pase and GK activities in human liver (needle biopsies) in overnight fasted obese NIDDM patients has shown that, while G6Pase was unchanged, GK was higher (+ 55%, P less than 0.05) than in control subjects. Consequently, the G6Pase/GK ratio (which roughly reflects hepatic glucose production) was significantly reduced (-36%) in the obese diabetic group, due to more GK activity (glucose uptake). This contrasts with the activity in IDDM and nonobese NIDDM patients (where the G6Pase/GK ratio is elevated and normal, respectively) and would suggest that in the obese diabetic subjects, hepatic glucose production is not a major factor contributing to the maintenance of hyperglycemia in the overnight fasting state (leaving peripheral insulin resistance as the major cause of hyperglycemia).

Effects of short-term metformin treatment on insulin sensitivity of blood glucose and free fatty acids

Aim:  Based on the known effect of metformin (MET) in improving insulin sensitivity in type 2 diabetes, with the scope to focus the effects on glycaemic and free fatty acids (FFA) levels, we studied the effects of a short‐term treatment with this drug in obese subjects and obese patients with diabetes or family history of diabetes (FHD). We used a method to allow us to evaluate the possible difference of insulin sensibility with regard to the insulin action on glycaemia and blood FFA, both in the basal state and during oral glucose tolerance test (OGTT).

A Mild Form of Alstrom Disease Associated with Metabolic Syndrome and Very High Fasting Serum Free Fatty Acids: Two Cases Diagnosed in Adult Age

&NA; Alstrom syndrome (ALMS) is a very rare genetic autosomal recessive disease, characterized by early‐onset severe abdominal obesity, impaired glucose tolerance or type 2 diabetes with insulin resistance, acanthosis nigricans, hyperlipidemia, childhood progressive retinal degeneration or retinitis pigmentosa and neurosensory hearing loss or deafness, cardiomyopathy, and other endocrine disorders. Genetic studies locate the ALMS gene on chromosome 2p12–13. The aim of this paper is to describe and discuss two unrelated cases of a mild ALMS form diagnosed after the age of 40 and 60, respectively, in adult fertile female patients. These cases showed several features of the disease plus other alterations characteristic of the classic “metabolic syndrome,” including hypertension, hyperfibrinogenemia, and thrombotic states. Moreover, the patients had very high fasting serum free fatty acid (FFA) levels (2150 and 1919 &mgr;mol/L, respectively), which proved to be sensitive to inhibition by oral glucose tolerance test (OGTT)–induced hyperinsulinemia as well as to caloric restriction. ALMS may have an adverse prognosis and is often underdiagnosed. Its mild form, which allows a long survival, may also be associated with the late complications of the metabolic syndrome, leading to increased vascular risk.

A Large Spontaneous Splenorenal Shunt in a Patient with Liver Cirrhosis and Uncomplicated Portal Hypertension

The aim of this paper is to describe and discuss, on the basis of a thorough review of the literature, the case of a 70-year-old woman with probable cirrhosis secondary to chronic hepatitis B and C, uncomplicated portal hypertension (without ascites, encephalopathy or bleeding varices), splenomegaly and hypersplenism, and an unusual, spontaneous, large splenorenal shunt and recanalization of the umbilical vein. The tortuous and varicose splenorenal shunt was diagnosed by abdominal ultrasound and CT investigations. A duplex Doppler ultrasonography evaluation was performed to study shunt flow direction and velocity. No gastroesophageal varices were identified on endoscopic examination. The clinical relevance of spontaneous splenorenal shunt, often associated with fundic gastric varices, is discussed.

Hypomagnesemia and Smooth Muscle Contractility:Diffuse Esophageal Spasm in anOld Female Patient

The aim of this paper is to describe and discuss, on the basis of the available literature, the case of an old female patient, admitted to our university hospital because of a severe dysphagia for solid foods, in whom laboratory data showed a marked hypomagnesemia. She reported a long history (20 years) of allergic bronchial asthma treated with theophylline. Esophagography evidenced a disorder of esophagus motility with diffuse multiple spasm, reminiscent of the ‘corkscrew esophagus’. A link with the severe hypomagnesemia (Mg 1.1 mEq/l, normal range 1.6–2.1) was suspected, and a therapy with oral pidolate of Mg (1.5 g/twice a day) was started and continued for 4 months. This was associated with a slow progressive normalization of the Mg plasma level and reverted radiographic esophageal findings with disappearance of dysphagia. Mg is an important element for health and disease, and today Mg deficiency in man has become an accepted medical problem which might complicate many diseases. Neuromuscular disorders, as laryngeal spasm, are recognized complications of hypomagnesemia, but until now only 1 case of motor esophageal disorder associated with a low Mg plasma level was briefly reported in the literature, even if dysphagia is generally included in the symptomatological pattern of hypomagnesemia. Our observation of a severe form of esophageal spasm, associated with hypomagnesemia, in an aged female patient underlines the pathophysiological meaning of the plasma Mg level and suggests the need for routine Mg determination in the clinical setting.

Capillaries phosphorylate glucose in a concentration-dependent manner through a glucokinase-like enzyme: A study in the eel

Glucose phosphorylation was studied in a pure capillary preparation obtained from the rete mirabile of the eel swimbladder. In the 3000g supernatant of capillary homogenates, the glucose phosphorylating activity did not reach the maximum at low glucose concentration (1 mmole/liter), as it occurs in most tissues, but increased with the increase in glucose concentration and approached the maximum at very high (300 mmole/liter) glucose levels, with values (mean +/- SEM, n = 10) of 5.85 +/- 0.94 nmole.min-1.mg-1 protein and 19.97 +/- 1.89 at 1 and 300 mmole/liter glucose, respectively. The apparent Km value for glucose was about 50 mmole/liter, i.e., at supraphysiological glucose concentration, like the enzyme glucokinase, typically present in the liver but absent from most other tissues. This new enzyme did not phosphorylate fructose (similar to glucokinase from liver, which is rather specific for glucose) but was not inhibited by N-acetyl-glucosamine (in contrast to hepatic glucokinase). Thus, capillaries phosphorylate glucose in a concentration-dependent manner, which suggests that they are equipped with a glucokinase-like enzyme. This may explain the reported increase in glucose uptake during capillary exposure to high glucose concentrations and would suggest that the hyperglycemia of the diabetic state may be associated with increased glucose utilization, which may play a role in the development of microangiopathy.

A formula for quantifying the effects of substrate cycles (futile cycles) on metabolic regulation. Its application to glucose futile cycle in liver as studied by glucose-6-phosphatase/glucokinase determinations

SummarySubstrate cycles (SC) are formed by a ‘forward pathway’ (FP) and a ‘backward pathway’ (BP), the difference between FP and BP forming the ‘metabolic flux’ (MF) through the route of which the cycle is part. SC modulate regulatory effects, i.e. amplify or reduce the % change in MF compared to the % change in FP and BP, thus affecting the sensitivity to regulatory factors, including hormones. A formula is given to calculate (with an approximation of ± 0.5) the ‘flux response index’ (FRI), i.e. the factor by which the % change in FP plus the % change in BP must be multiplied to obtain the % change in metabolic flux, when FP and BP undergo opposite, nonunidirectional changes (as is often the case in metabolic regulation). The formula is: FRI = [(FP+BP)/(FP-BP)]/2. By this formula we evaluated the hepatic activities of glucose-6-phosphatase and glucokinase (which roughly reflect hepatic glucose production and uptake, respectively), i.e. the two enzymes that catalyze the cycle between glucose-6-phosphate (glucose-6-P) and glucose. Based on data obtained in normal, nonobese diabetic and obese diabetic subjects as well as in normal, streptozotocin-diabetic, and obese diabetic (ob/ob) mice, we found that FRI was reduced in non-obese diabetic humans and animals whereas it was increased in obese-diabetic humans and mice, compared to normal controls. Thus, diabetes without obesitydecreases, and obesity with diabetesincreases, the sensitivity of the glucose-6-P/glucose cycle to regulatory agents.